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…		…
9	=head2 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
11	// a single header file is required	11	// a single header file is required
12	#include <ev.h>	12	#include <ev.h>
13		13
		14	#include <stdio.h> // for puts
		15
14	// every watcher type has its own typedef'd struct	16	// every watcher type has its own typedef'd struct
15	// with the name ev_<type>	17	// with the name ev_TYPE
16	ev_io stdin_watcher;	18	ev_io stdin_watcher;
17	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
18		20
19	// all watcher callbacks have a similar signature	21	// all watcher callbacks have a similar signature
20	// this callback is called when data is readable on stdin	22	// this callback is called when data is readable on stdin
21	static void	23	static void
22	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
23	{	25	{
24	puts ("stdin ready");	26	puts ("stdin ready");
25	// for one-shot events, one must manually stop the watcher	27	// for one-shot events, one must manually stop the watcher
26	// with its corresponding stop function.	28	// with its corresponding stop function.
27	ev_io_stop (EV_A_ w);	29	ev_io_stop (EV_A_ w);
…		…
30	ev_unloop (EV_A_ EVUNLOOP_ALL);	32	ev_unloop (EV_A_ EVUNLOOP_ALL);
31	}	33	}
32		34
33	// another callback, this time for a time-out	35	// another callback, this time for a time-out
34	static void	36	static void
35	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
36	{	38	{
37	puts ("timeout");	39	puts ("timeout");
38	// this causes the innermost ev_loop to stop iterating	40	// this causes the innermost ev_loop to stop iterating
39	ev_unloop (EV_A_ EVUNLOOP_ONE);	41	ev_unloop (EV_A_ EVUNLOOP_ONE);
40	}	42	}
…		…
60		62
61	// unloop was called, so exit	63	// unloop was called, so exit
62	return 0;	64	return 0;
63	}	65	}
64		66
65	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
66		70
67	The newest version of this document is also available as an html-formatted	71	The newest version of this document is also available as an html-formatted
68	web page you might find easier to navigate when reading it for the first	72	web page you might find easier to navigate when reading it for the first
69	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.	73	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
		74
		75	While this document tries to be as complete as possible in documenting
		76	libev, its usage and the rationale behind its design, it is not a tutorial
		77	on event-based programming, nor will it introduce event-based programming
		78	with libev.
		79
		80	Familarity with event based programming techniques in general is assumed
		81	throughout this document.
		82
		83	=head1 ABOUT LIBEV
70		84
71	Libev is an event loop: you register interest in certain events (such as a	85	Libev is an event loop: you register interest in certain events (such as a
72	file descriptor being readable or a timeout occurring), and it will manage	86	file descriptor being readable or a timeout occurring), and it will manage
73	these event sources and provide your program with events.	87	these event sources and provide your program with events.
74		88
…		…
84	=head2 FEATURES	98	=head2 FEATURES
85		99
86	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	100	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
87	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	101	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
88	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	102	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
89	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	103	(for C<ev_stat>), Linux eventfd/signalfd (for faster and cleaner
90	with customised rescheduling (C<ev_periodic>), synchronous signals	104	inter-thread wakeup (C<ev_async>)/signal handling (C<ev_signal>)) relative
91	(C<ev_signal>), process status change events (C<ev_child>), and event	105	timers (C<ev_timer>), absolute timers with customised rescheduling
92	watchers dealing with the event loop mechanism itself (C<ev_idle>,	106	(C<ev_periodic>), synchronous signals (C<ev_signal>), process status
93	C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as	107	change events (C<ev_child>), and event watchers dealing with the event
94	file watchers (C<ev_stat>) and even limited support for fork events	108	loop mechanism itself (C<ev_idle>, C<ev_embed>, C<ev_prepare> and
95	(C<ev_fork>).	109	C<ev_check> watchers) as well as file watchers (C<ev_stat>) and even
		110	limited support for fork events (C<ev_fork>).
96		111
97	It also is quite fast (see this	112	It also is quite fast (see this
98	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	113	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
99	for example).	114	for example).
100		115
…		…
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	123	name C<loop> (which is always of type C<struct ev_loop *>) will not have
109	this argument.	124	this argument.
110		125
111	=head2 TIME REPRESENTATION	126	=head2 TIME REPRESENTATION
112		127
113	Libev represents time as a single floating point number, representing the	128	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	129	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	130	near the beginning of 1970, details are complicated, don't ask). This
116	called C<ev_tstamp>, which is what you should use too. It usually aliases	131	type is called C<ev_tstamp>, which is what you should use too. It usually
117	to the C<double> type in C, and when you need to do any calculations on	132	aliases to the C<double> type in C. When you need to do any calculations
118	it, you should treat it as some floating point value. Unlike the name	133	on it, you should treat it as some floating point value. Unlike the name
119	component C<stamp> might indicate, it is also used for time differences	134	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	135	throughout libev.
121		136
122	=head1 ERROR HANDLING	137	=head1 ERROR HANDLING
123		138
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	229	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	230	recommended ones.
216		231
217	See the description of C<ev_embed> watchers for more info.	232	See the description of C<ev_embed> watchers for more info.
218		233
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	234	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		235
221	Sets the allocation function to use (the prototype is similar - the	236	Sets the allocation function to use (the prototype is similar - the
222	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is	237	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
223	used to allocate and free memory (no surprises here). If it returns zero	238	used to allocate and free memory (no surprises here). If it returns zero
224	when memory needs to be allocated (C<size != 0>), the library might abort	239	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	265	}
251		266
252	...	267	...
253	ev_set_allocator (persistent_realloc);	268	ev_set_allocator (persistent_realloc);
254		269
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	270	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		271
257	Set the callback function to call on a retryable system call error (such	272	Set the callback function to call on a retryable system call error (such
258	as failed select, poll, epoll_wait). The message is a printable string	273	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	274	indicating the system call or subsystem causing the problem. If this
260	callback is set, then libev will expect it to remedy the situation, no	275	callback is set, then libev will expect it to remedy the situation, no
…		…
276		291
277	=back	292	=back
278		293
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	294	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		295
281	An event loop is described by a C<struct ev_loop *>. The library knows two	296	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	297	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	298	I<function>).
		299
		300	The library knows two types of such loops, the I<default> loop, which
		301	supports signals and child events, and dynamically created loops which do
		302	not.
284		303
285	=over 4	304	=over 4
286		305
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	306	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		307
…		…
294	If you don't know what event loop to use, use the one returned from this	313	If you don't know what event loop to use, use the one returned from this
295	function.	314	function.
296		315
297	Note that this function is I<not> thread-safe, so if you want to use it	316	Note that this function is I<not> thread-safe, so if you want to use it
298	from multiple threads, you have to lock (note also that this is unlikely,	317	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	318	as loops cannot be shared easily between threads anyway).
300		319
301	The default loop is the only loop that can handle C<ev_signal> and	320	The default loop is the only loop that can handle C<ev_signal> and
302	C<ev_child> watchers, and to do this, it always registers a handler	321	C<ev_child> watchers, and to do this, it always registers a handler
303	for C<SIGCHLD>. If this is a problem for your application you can either	322	for C<SIGCHLD>. If this is a problem for your application you can either
304	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you	323	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
344	flag.	363	flag.
345		364
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	365	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	366	environment variable.
348		367
		368	=item C<EVFLAG_NOINOTIFY>
		369
		370	When this flag is specified, then libev will not attempt to use the
		371	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		372	testing, this flag can be useful to conserve inotify file descriptors, as
		373	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		374
		375	=item C<EVFLAG_SIGNALFD>
		376
		377	When this flag is specified, then libev will attempt to use the
		378	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This API
		379	delivers signals synchronously, which makes it both faster and might make
		380	it possible to get the queued signal data. It can also simplify signal
		381	handling with threads, as long as you properly block signals in your
		382	threads that are not interested in handling them.
		383
		384	Signalfd will not be used by default as this changes your signal mask, and
		385	there are a lot of shoddy libraries and programs (glib's threadpool for
		386	example) that can't properly initialise their signal masks.
		387
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	388	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		389
351	This is your standard select(2) backend. Not I<completely> standard, as	390	This is your standard select(2) backend. Not I<completely> standard, as
352	libev tries to roll its own fd_set with no limits on the number of fds,	391	libev tries to roll its own fd_set with no limits on the number of fds,
353	but if that fails, expect a fairly low limit on the number of fds when	392	but if that fails, expect a fairly low limit on the number of fds when
…		…
359	writing a server, you should C<accept ()> in a loop to accept as many	398	writing a server, you should C<accept ()> in a loop to accept as many
360	connections as possible during one iteration. You might also want to have	399	connections as possible during one iteration. You might also want to have
361	a look at C<ev_set_io_collect_interval ()> to increase the amount of	400	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	401	readiness notifications you get per iteration.
363		402
		403	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		404	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		405	C<exceptfds> set on that platform).
		406
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	407	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		408
366	And this is your standard poll(2) backend. It's more complicated	409	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	410	than select, but handles sparse fds better and has no artificial
368	limit on the number of fds you can use (except it will slow down	411	limit on the number of fds you can use (except it will slow down
369	considerably with a lot of inactive fds). It scales similarly to select,	412	considerably with a lot of inactive fds). It scales similarly to select,
370	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for	413	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	414	performance tips.
372		415
		416	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		417	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		418
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	419	=item C<EVBACKEND_EPOLL> (value 4, Linux)
		420
		421	Use the linux-specific epoll(7) interface (for both pre- and post-2.6.9
		422	kernels).
374		423
375	For few fds, this backend is a bit little slower than poll and select,	424	For few fds, this backend is a bit little slower than poll and select,
376	but it scales phenomenally better. While poll and select usually scale	425	but it scales phenomenally better. While poll and select usually scale
377	like O(total_fds) where n is the total number of fds (or the highest fd),	426	like O(total_fds) where n is the total number of fds (or the highest fd),
378	epoll scales either O(1) or O(active_fds). The epoll design has a number	427	epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	428
380	cases and requiring a system call per fd change, no fork support and bad	429	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	430	of the more advanced event mechanisms: mere annoyances include silently
		431	dropping file descriptors, requiring a system call per change per file
		432	descriptor (and unnecessary guessing of parameters), problems with dup and
		433	so on. The biggest issue is fork races, however - if a program forks then
		434	I<both> parent and child process have to recreate the epoll set, which can
		435	take considerable time (one syscall per file descriptor) and is of course
		436	hard to detect.
		437
		438	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		439	of course I<doesn't>, and epoll just loves to report events for totally
		440	I<different> file descriptors (even already closed ones, so one cannot
		441	even remove them from the set) than registered in the set (especially
		442	on SMP systems). Libev tries to counter these spurious notifications by
		443	employing an additional generation counter and comparing that against the
		444	events to filter out spurious ones, recreating the set when required.
382		445
383	While stopping, setting and starting an I/O watcher in the same iteration	446	While stopping, setting and starting an I/O watcher in the same iteration
384	will result in some caching, there is still a system call per such incident	447	will result in some caching, there is still a system call per such
385	(because the fd could point to a different file description now), so its	448	incident (because the same I<file descriptor> could point to a different
386	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	449	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	450	file descriptors might not work very well if you register events for both
388		451	file descriptors.
389	Please note that epoll sometimes generates spurious notifications, so you
390	need to use non-blocking I/O or other means to avoid blocking when no data
391	(or space) is available.
392		452
393	Best performance from this backend is achieved by not unregistering all	453	Best performance from this backend is achieved by not unregistering all
394	watchers for a file descriptor until it has been closed, if possible, i.e.	454	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	455	i.e. keep at least one watcher active per fd at all times. Stopping and
		456	starting a watcher (without re-setting it) also usually doesn't cause
		457	extra overhead. A fork can both result in spurious notifications as well
		458	as in libev having to destroy and recreate the epoll object, which can
		459	take considerable time and thus should be avoided.
		460
		461	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		462	faster than epoll for maybe up to a hundred file descriptors, depending on
		463	the usage. So sad.
396		464
397	While nominally embeddable in other event loops, this feature is broken in	465	While nominally embeddable in other event loops, this feature is broken in
398	all kernel versions tested so far.	466	all kernel versions tested so far.
		467
		468	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		469	C<EVBACKEND_POLL>.
399		470
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	471	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		472
402	Kqueue deserves special mention, as at the time of this writing, it	473	Kqueue deserves special mention, as at the time of this writing, it
403	was broken on all BSDs except NetBSD (usually it doesn't work reliably	474	was broken on all BSDs except NetBSD (usually it doesn't work reliably
404	with anything but sockets and pipes, except on Darwin, where of course	475	with anything but sockets and pipes, except on Darwin, where of course
405	it's completely useless). For this reason it's not being "auto-detected"	476	it's completely useless). Unlike epoll, however, whose brokenness
		477	is by design, these kqueue bugs can (and eventually will) be fixed
		478	without API changes to existing programs. For this reason it's not being
406	unless you explicitly specify it explicitly in the flags (i.e. using	479	"auto-detected" unless you explicitly specify it in the flags (i.e. using
407	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	480	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	481	system like NetBSD.
409		482
410	You still can embed kqueue into a normal poll or select backend and use it	483	You still can embed kqueue into a normal poll or select backend and use it
411	only for sockets (after having made sure that sockets work with kqueue on	484	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		486
414	It scales in the same way as the epoll backend, but the interface to the	487	It scales in the same way as the epoll backend, but the interface to the
415	kernel is more efficient (which says nothing about its actual speed, of	488	kernel is more efficient (which says nothing about its actual speed, of
416	course). While stopping, setting and starting an I/O watcher does never	489	course). While stopping, setting and starting an I/O watcher does never
417	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	490	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
418	two event changes per incident, support for C<fork ()> is very bad and it	491	two event changes per incident. Support for C<fork ()> is very bad (but
419	drops fds silently in similarly hard-to-detect cases.	492	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		493	cases
420		494
421	This backend usually performs well under most conditions.	495	This backend usually performs well under most conditions.
422		496
423	While nominally embeddable in other event loops, this doesn't work	497	While nominally embeddable in other event loops, this doesn't work
424	everywhere, so you might need to test for this. And since it is broken	498	everywhere, so you might need to test for this. And since it is broken
425	almost everywhere, you should only use it when you have a lot of sockets	499	almost everywhere, you should only use it when you have a lot of sockets
426	(for which it usually works), by embedding it into another event loop	500	(for which it usually works), by embedding it into another event loop
427	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for	501	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	502	also broken on OS X)) and, did I mention it, using it only for sockets.
		503
		504	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		505	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		506	C<NOTE_EOF>.
429		507
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	508	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		509
432	This is not implemented yet (and might never be, unless you send me an	510	This is not implemented yet (and might never be, unless you send me an
433	implementation). According to reports, C</dev/poll> only supports sockets	511	implementation). According to reports, C</dev/poll> only supports sockets
…		…
446	While this backend scales well, it requires one system call per active	524	While this backend scales well, it requires one system call per active
447	file descriptor per loop iteration. For small and medium numbers of file	525	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	526	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	527	might perform better.
450		528
451	On the positive side, ignoring the spurious readiness notifications, this	529	On the positive side, with the exception of the spurious readiness
452	backend actually performed to specification in all tests and is fully	530	notifications, this backend actually performed fully to specification
453	embeddable, which is a rare feat among the OS-specific backends.	531	in all tests and is fully embeddable, which is a rare feat among the
		532	OS-specific backends (I vastly prefer correctness over speed hacks).
		533
		534	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		535	C<EVBACKEND_POLL>.
454		536
455	=item C<EVBACKEND_ALL>	537	=item C<EVBACKEND_ALL>
456		538
457	Try all backends (even potentially broken ones that wouldn't be tried	539	Try all backends (even potentially broken ones that wouldn't be tried
458	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	540	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
460		542
461	It is definitely not recommended to use this flag.	543	It is definitely not recommended to use this flag.
462		544
463	=back	545	=back
464		546
465	If one or more of these are or'ed into the flags value, then only these	547	If one or more of the backend flags are or'ed into the flags value,
466	backends will be tried (in the reverse order as listed here). If none are	548	then only these backends will be tried (in the reverse order as listed
467	specified, all backends in C<ev_recommended_backends ()> will be tried.	549	here). If none are specified, all backends in C<ev_recommended_backends
		550	()> will be tried.
468		551
469	The most typical usage is like this:	552	Example: This is the most typical usage.
470		553
471	if (!ev_default_loop (0))	554	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	555	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473		556
474	Restrict libev to the select and poll backends, and do not allow	557	Example: Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:	558	environment settings to be taken into account:
476		559
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	560	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478		561
479	Use whatever libev has to offer, but make sure that kqueue is used if	562	Example: Use whatever libev has to offer, but make sure that kqueue is
480	available (warning, breaks stuff, best use only with your own private	563	used if available (warning, breaks stuff, best use only with your own
481	event loop and only if you know the OS supports your types of fds):	564	private event loop and only if you know the OS supports your types of
		565	fds):
482		566
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	567	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484		568
485	=item struct ev_loop *ev_loop_new (unsigned int flags)	569	=item struct ev_loop *ev_loop_new (unsigned int flags)
486		570
487	Similar to C<ev_default_loop>, but always creates a new event loop that is	571	Similar to C<ev_default_loop>, but always creates a new event loop that is
488	always distinct from the default loop. Unlike the default loop, it cannot	572	always distinct from the default loop.
489	handle signal and child watchers, and attempts to do so will be greeted by
490	undefined behaviour (or a failed assertion if assertions are enabled).
491		573
492	Note that this function I<is> thread-safe, and the recommended way to use	574	Note that this function I<is> thread-safe, and one common way to use
493	libev with threads is indeed to create one loop per thread, and using the	575	libev with threads is indeed to create one loop per thread, and using the
494	default loop in the "main" or "initial" thread.	576	default loop in the "main" or "initial" thread.
495		577
496	Example: Try to create a event loop that uses epoll and nothing else.	578	Example: Try to create a event loop that uses epoll and nothing else.
497		579
…		…
499	if (!epoller)	581	if (!epoller)
500	fatal ("no epoll found here, maybe it hides under your chair");	582	fatal ("no epoll found here, maybe it hides under your chair");
501		583
502	=item ev_default_destroy ()	584	=item ev_default_destroy ()
503		585
504	Destroys the default loop again (frees all memory and kernel state	586	Destroys the default loop (frees all memory and kernel state etc.). None
505	etc.). None of the active event watchers will be stopped in the normal	587	of the active event watchers will be stopped in the normal sense, so
506	sense, so e.g. C<ev_is_active> might still return true. It is your	588	e.g. C<ev_is_active> might still return true. It is your responsibility to
507	responsibility to either stop all watchers cleanly yourself I<before>	589	either stop all watchers cleanly yourself I<before> calling this function,
508	calling this function, or cope with the fact afterwards (which is usually	590	or cope with the fact afterwards (which is usually the easiest thing, you
509	the easiest thing, you can just ignore the watchers and/or C<free ()> them	591	can just ignore the watchers and/or C<free ()> them for example).
510	for example).
511		592
512	Note that certain global state, such as signal state, will not be freed by	593	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	594	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	595	as signal and child watchers) would need to be stopped manually.
515		596
516	In general it is not advisable to call this function except in the	597	In general it is not advisable to call this function except in the
517	rare occasion where you really need to free e.g. the signal handling	598	rare occasion where you really need to free e.g. the signal handling
518	pipe fds. If you need dynamically allocated loops it is better to use	599	pipe fds. If you need dynamically allocated loops it is better to use
519	C<ev_loop_new> and C<ev_loop_destroy>).	600	C<ev_loop_new> and C<ev_loop_destroy>.
520		601
521	=item ev_loop_destroy (loop)	602	=item ev_loop_destroy (loop)
522		603
523	Like C<ev_default_destroy>, but destroys an event loop created by an	604	Like C<ev_default_destroy>, but destroys an event loop created by an
524	earlier call to C<ev_loop_new>.	605	earlier call to C<ev_loop_new>.
…		…
544		625
545	=item ev_loop_fork (loop)	626	=item ev_loop_fork (loop)
546		627
547	Like C<ev_default_fork>, but acts on an event loop created by	628	Like C<ev_default_fork>, but acts on an event loop created by
548	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	629	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
549	after fork, and how you do this is entirely your own problem.	630	after fork that you want to re-use in the child, and how you do this is
		631	entirely your own problem.
550		632
551	=item int ev_is_default_loop (loop)	633	=item int ev_is_default_loop (loop)
552		634
553	Returns true when the given loop actually is the default loop, false otherwise.	635	Returns true when the given loop is, in fact, the default loop, and false
		636	otherwise.
554		637
555	=item unsigned int ev_loop_count (loop)	638	=item unsigned int ev_loop_count (loop)
556		639
557	Returns the count of loop iterations for the loop, which is identical to	640	Returns the count of loop iterations for the loop, which is identical to
558	the number of times libev did poll for new events. It starts at C<0> and	641	the number of times libev did poll for new events. It starts at C<0> and
559	happily wraps around with enough iterations.	642	happily wraps around with enough iterations.
560		643
561	This value can sometimes be useful as a generation counter of sorts (it	644	This value can sometimes be useful as a generation counter of sorts (it
562	"ticks" the number of loop iterations), as it roughly corresponds with	645	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	646	C<ev_prepare> and C<ev_check> calls.
		647
		648	=item unsigned int ev_loop_depth (loop)
		649
		650	Returns the number of times C<ev_loop> was entered minus the number of
		651	times C<ev_loop> was exited, in other words, the recursion depth.
		652
		653	Outside C<ev_loop>, this number is zero. In a callback, this number is
		654	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		655	in which case it is higher.
		656
		657	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		658	etc.), doesn't count as exit.
564		659
565	=item unsigned int ev_backend (loop)	660	=item unsigned int ev_backend (loop)
566		661
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	662	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	663	use.
…		…
583		678
584	This function is rarely useful, but when some event callback runs for a	679	This function is rarely useful, but when some event callback runs for a
585	very long time without entering the event loop, updating libev's idea of	680	very long time without entering the event loop, updating libev's idea of
586	the current time is a good idea.	681	the current time is a good idea.
587		682
588	See also "The special problem of time updates" in the C<ev_timer> section.	683	See also L<The special problem of time updates> in the C<ev_timer> section.
		684
		685	=item ev_suspend (loop)
		686
		687	=item ev_resume (loop)
		688
		689	These two functions suspend and resume a loop, for use when the loop is
		690	not used for a while and timeouts should not be processed.
		691
		692	A typical use case would be an interactive program such as a game: When
		693	the user presses C<^Z> to suspend the game and resumes it an hour later it
		694	would be best to handle timeouts as if no time had actually passed while
		695	the program was suspended. This can be achieved by calling C<ev_suspend>
		696	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		697	C<ev_resume> directly afterwards to resume timer processing.
		698
		699	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		700	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		701	will be rescheduled (that is, they will lose any events that would have
		702	occured while suspended).
		703
		704	After calling C<ev_suspend> you B<must not> call I<any> function on the
		705	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		706	without a previous call to C<ev_suspend>.
		707
		708	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		709	event loop time (see C<ev_now_update>).
589		710
590	=item ev_loop (loop, int flags)	711	=item ev_loop (loop, int flags)
591		712
592	Finally, this is it, the event handler. This function usually is called	713	Finally, this is it, the event handler. This function usually is called
593	after you initialised all your watchers and you want to start handling	714	after you have initialised all your watchers and you want to start
594	events.	715	handling events.
595		716
596	If the flags argument is specified as C<0>, it will not return until	717	If the flags argument is specified as C<0>, it will not return until
597	either no event watchers are active anymore or C<ev_unloop> was called.	718	either no event watchers are active anymore or C<ev_unloop> was called.
598		719
599	Please note that an explicit C<ev_unloop> is usually better than	720	Please note that an explicit C<ev_unloop> is usually better than
600	relying on all watchers to be stopped when deciding when a program has	721	relying on all watchers to be stopped when deciding when a program has
601	finished (especially in interactive programs), but having a program that	722	finished (especially in interactive programs), but having a program
602	automatically loops as long as it has to and no longer by virtue of	723	that automatically loops as long as it has to and no longer by virtue
603	relying on its watchers stopping correctly is a thing of beauty.	724	of relying on its watchers stopping correctly, that is truly a thing of
		725	beauty.
604		726
605	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	727	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
606	those events and any outstanding ones, but will not block your process in	728	those events and any already outstanding ones, but will not block your
607	case there are no events and will return after one iteration of the loop.	729	process in case there are no events and will return after one iteration of
		730	the loop.
608		731
609	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	732	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
610	necessary) and will handle those and any outstanding ones. It will block	733	necessary) and will handle those and any already outstanding ones. It
611	your process until at least one new event arrives, and will return after	734	will block your process until at least one new event arrives (which could
612	one iteration of the loop. This is useful if you are waiting for some	735	be an event internal to libev itself, so there is no guarantee that a
613	external event in conjunction with something not expressible using other	736	user-registered callback will be called), and will return after one
		737	iteration of the loop.
		738
		739	This is useful if you are waiting for some external event in conjunction
		740	with something not expressible using other libev watchers (i.e. "roll your
614	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	741	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
615	usually a better approach for this kind of thing.	742	usually a better approach for this kind of thing.
616		743
617	Here are the gory details of what C<ev_loop> does:	744	Here are the gory details of what C<ev_loop> does:
618		745
619	- Before the first iteration, call any pending watchers.	746	- Before the first iteration, call any pending watchers.
…		…
629	any active watchers at all will result in not sleeping).	756	any active watchers at all will result in not sleeping).
630	- Sleep if the I/O and timer collect interval say so.	757	- Sleep if the I/O and timer collect interval say so.
631	- Block the process, waiting for any events.	758	- Block the process, waiting for any events.
632	- Queue all outstanding I/O (fd) events.	759	- Queue all outstanding I/O (fd) events.
633	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	760	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
634	- Queue all outstanding timers.	761	- Queue all expired timers.
635	- Queue all outstanding periodics.	762	- Queue all expired periodics.
636	- Unless any events are pending now, queue all idle watchers.	763	- Unless any events are pending now, queue all idle watchers.
637	- Queue all check watchers.	764	- Queue all check watchers.
638	- Call all queued watchers in reverse order (i.e. check watchers first).	765	- Call all queued watchers in reverse order (i.e. check watchers first).
639	Signals and child watchers are implemented as I/O watchers, and will	766	Signals and child watchers are implemented as I/O watchers, and will
640	be handled here by queueing them when their watcher gets executed.	767	be handled here by queueing them when their watcher gets executed.
…		…
657	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	784	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
658	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	785	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
659		786
660	This "unloop state" will be cleared when entering C<ev_loop> again.	787	This "unloop state" will be cleared when entering C<ev_loop> again.
661		788
		789	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		790
662	=item ev_ref (loop)	791	=item ev_ref (loop)
663		792
664	=item ev_unref (loop)	793	=item ev_unref (loop)
665		794
666	Ref/unref can be used to add or remove a reference count on the event	795	Ref/unref can be used to add or remove a reference count on the event
667	loop: Every watcher keeps one reference, and as long as the reference	796	loop: Every watcher keeps one reference, and as long as the reference
668	count is nonzero, C<ev_loop> will not return on its own. If you have	797	count is nonzero, C<ev_loop> will not return on its own.
669	a watcher you never unregister that should not keep C<ev_loop> from	798
670	returning, ev_unref() after starting, and ev_ref() before stopping it. For	799	This is useful when you have a watcher that you never intend to
		800	unregister, but that nevertheless should not keep C<ev_loop> from
		801	returning. In such a case, call C<ev_unref> after starting, and C<ev_ref>
		802	before stopping it.
		803
671	example, libev itself uses this for its internal signal pipe: It is not	804	As an example, libev itself uses this for its internal signal pipe: It
672	visible to the libev user and should not keep C<ev_loop> from exiting if	805	is not visible to the libev user and should not keep C<ev_loop> from
673	no event watchers registered by it are active. It is also an excellent	806	exiting if no event watchers registered by it are active. It is also an
674	way to do this for generic recurring timers or from within third-party	807	excellent way to do this for generic recurring timers or from within
675	libraries. Just remember to I<unref after start> and I<ref before stop>	808	third-party libraries. Just remember to I<unref after start> and I<ref
676	(but only if the watcher wasn't active before, or was active before,	809	before stop> (but only if the watcher wasn't active before, or was active
677	respectively).	810	before, respectively. Note also that libev might stop watchers itself
		811	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		812	in the callback).
678		813
679	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	814	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
680	running when nothing else is active.	815	running when nothing else is active.
681		816
682	struct ev_signal exitsig;	817	ev_signal exitsig;
683	ev_signal_init (&exitsig, sig_cb, SIGINT);	818	ev_signal_init (&exitsig, sig_cb, SIGINT);
684	ev_signal_start (loop, &exitsig);	819	ev_signal_start (loop, &exitsig);
685	evf_unref (loop);	820	evf_unref (loop);
686		821
687	Example: For some weird reason, unregister the above signal handler again.	822	Example: For some weird reason, unregister the above signal handler again.
…		…
701	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	836	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
702	allows libev to delay invocation of I/O and timer/periodic callbacks	837	allows libev to delay invocation of I/O and timer/periodic callbacks
703	to increase efficiency of loop iterations (or to increase power-saving	838	to increase efficiency of loop iterations (or to increase power-saving
704	opportunities).	839	opportunities).
705		840
706	The background is that sometimes your program runs just fast enough to	841	The idea is that sometimes your program runs just fast enough to handle
707	handle one (or very few) event(s) per loop iteration. While this makes	842	one (or very few) event(s) per loop iteration. While this makes the
708	the program responsive, it also wastes a lot of CPU time to poll for new	843	program responsive, it also wastes a lot of CPU time to poll for new
709	events, especially with backends like C<select ()> which have a high	844	events, especially with backends like C<select ()> which have a high
710	overhead for the actual polling but can deliver many events at once.	845	overhead for the actual polling but can deliver many events at once.
711		846
712	By setting a higher I<io collect interval> you allow libev to spend more	847	By setting a higher I<io collect interval> you allow libev to spend more
713	time collecting I/O events, so you can handle more events per iteration,	848	time collecting I/O events, so you can handle more events per iteration,
714	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	849	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
715	C<ev_timer>) will be not affected. Setting this to a non-null value will	850	C<ev_timer>) will be not affected. Setting this to a non-null value will
716	introduce an additional C<ev_sleep ()> call into most loop iterations.	851	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		852	sleep time ensures that libev will not poll for I/O events more often then
		853	once per this interval, on average.
717		854
718	Likewise, by setting a higher I<timeout collect interval> you allow libev	855	Likewise, by setting a higher I<timeout collect interval> you allow libev
719	to spend more time collecting timeouts, at the expense of increased	856	to spend more time collecting timeouts, at the expense of increased
720	latency (the watcher callback will be called later). C<ev_io> watchers	857	latency/jitter/inexactness (the watcher callback will be called
721	will not be affected. Setting this to a non-null value will not introduce	858	later). C<ev_io> watchers will not be affected. Setting this to a non-null
722	any overhead in libev.	859	value will not introduce any overhead in libev.
723		860
724	Many (busy) programs can usually benefit by setting the I/O collect	861	Many (busy) programs can usually benefit by setting the I/O collect
725	interval to a value near C<0.1> or so, which is often enough for	862	interval to a value near C<0.1> or so, which is often enough for
726	interactive servers (of course not for games), likewise for timeouts. It	863	interactive servers (of course not for games), likewise for timeouts. It
727	usually doesn't make much sense to set it to a lower value than C<0.01>,	864	usually doesn't make much sense to set it to a lower value than C<0.01>,
728	as this approaches the timing granularity of most systems.	865	as this approaches the timing granularity of most systems. Note that if
		866	you do transactions with the outside world and you can't increase the
		867	parallelity, then this setting will limit your transaction rate (if you
		868	need to poll once per transaction and the I/O collect interval is 0.01,
		869	then you can't do more than 100 transations per second).
729		870
730	Setting the I<timeout collect interval> can improve the opportunity for	871	Setting the I<timeout collect interval> can improve the opportunity for
731	saving power, as the program will "bundle" timer callback invocations that	872	saving power, as the program will "bundle" timer callback invocations that
732	are "near" in time together, by delaying some, thus reducing the number of	873	are "near" in time together, by delaying some, thus reducing the number of
733	times the process sleeps and wakes up again. Another useful technique to	874	times the process sleeps and wakes up again. Another useful technique to
734	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	875	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
735	they fire on, say, one-second boundaries only.	876	they fire on, say, one-second boundaries only.
736		877
		878	Example: we only need 0.1s timeout granularity, and we wish not to poll
		879	more often than 100 times per second:
		880
		881	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		882	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		883
		884	=item ev_invoke_pending (loop)
		885
		886	This call will simply invoke all pending watchers while resetting their
		887	pending state. Normally, C<ev_loop> does this automatically when required,
		888	but when overriding the invoke callback this call comes handy.
		889
		890	=item int ev_pending_count (loop)
		891
		892	Returns the number of pending watchers - zero indicates that no watchers
		893	are pending.
		894
		895	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		896
		897	This overrides the invoke pending functionality of the loop: Instead of
		898	invoking all pending watchers when there are any, C<ev_loop> will call
		899	this callback instead. This is useful, for example, when you want to
		900	invoke the actual watchers inside another context (another thread etc.).
		901
		902	If you want to reset the callback, use C<ev_invoke_pending> as new
		903	callback.
		904
		905	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		906
		907	Sometimes you want to share the same loop between multiple threads. This
		908	can be done relatively simply by putting mutex_lock/unlock calls around
		909	each call to a libev function.
		910
		911	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		912	wait for it to return. One way around this is to wake up the loop via
		913	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		914	and I<acquire> callbacks on the loop.
		915
		916	When set, then C<release> will be called just before the thread is
		917	suspended waiting for new events, and C<acquire> is called just
		918	afterwards.
		919
		920	Ideally, C<release> will just call your mutex_unlock function, and
		921	C<acquire> will just call the mutex_lock function again.
		922
		923	While event loop modifications are allowed between invocations of
		924	C<release> and C<acquire> (that's their only purpose after all), no
		925	modifications done will affect the event loop, i.e. adding watchers will
		926	have no effect on the set of file descriptors being watched, or the time
		927	waited. Use an C<ev_async> watcher to wake up C<ev_loop> when you want it
		928	to take note of any changes you made.
		929
		930	In theory, threads executing C<ev_loop> will be async-cancel safe between
		931	invocations of C<release> and C<acquire>.
		932
		933	See also the locking example in the C<THREADS> section later in this
		934	document.
		935
		936	=item ev_set_userdata (loop, void *data)
		937
		938	=item ev_userdata (loop)
		939
		940	Set and retrieve a single C<void *> associated with a loop. When
		941	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		942	C<0.>
		943
		944	These two functions can be used to associate arbitrary data with a loop,
		945	and are intended solely for the C<invoke_pending_cb>, C<release> and
		946	C<acquire> callbacks described above, but of course can be (ab-)used for
		947	any other purpose as well.
		948
737	=item ev_loop_verify (loop)	949	=item ev_loop_verify (loop)
738		950
739	This function only does something when C<EV_VERIFY> support has been	951	This function only does something when C<EV_VERIFY> support has been
740	compiled in. It tries to go through all internal structures and checks	952	compiled in, which is the default for non-minimal builds. It tries to go
741	them for validity. If anything is found to be inconsistent, it will print	953	through all internal structures and checks them for validity. If anything
742	an error message to standard error and call C<abort ()>.	954	is found to be inconsistent, it will print an error message to standard
		955	error and call C<abort ()>.
743		956
744	This can be used to catch bugs inside libev itself: under normal	957	This can be used to catch bugs inside libev itself: under normal
745	circumstances, this function will never abort as of course libev keeps its	958	circumstances, this function will never abort as of course libev keeps its
746	data structures consistent.	959	data structures consistent.
747		960
748	=back	961	=back
749		962
750		963
751	=head1 ANATOMY OF A WATCHER	964	=head1 ANATOMY OF A WATCHER
752		965
		966	In the following description, uppercase C<TYPE> in names stands for the
		967	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		968	watchers and C<ev_io_start> for I/O watchers.
		969
753	A watcher is a structure that you create and register to record your	970	A watcher is a structure that you create and register to record your
754	interest in some event. For instance, if you want to wait for STDIN to	971	interest in some event. For instance, if you want to wait for STDIN to
755	become readable, you would create an C<ev_io> watcher for that:	972	become readable, you would create an C<ev_io> watcher for that:
756		973
757	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	974	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
758	{	975	{
759	ev_io_stop (w);	976	ev_io_stop (w);
760	ev_unloop (loop, EVUNLOOP_ALL);	977	ev_unloop (loop, EVUNLOOP_ALL);
761	}	978	}
762		979
763	struct ev_loop *loop = ev_default_loop (0);	980	struct ev_loop *loop = ev_default_loop (0);
		981
764	struct ev_io stdin_watcher;	982	ev_io stdin_watcher;
		983
765	ev_init (&stdin_watcher, my_cb);	984	ev_init (&stdin_watcher, my_cb);
766	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	985	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
767	ev_io_start (loop, &stdin_watcher);	986	ev_io_start (loop, &stdin_watcher);
		987
768	ev_loop (loop, 0);	988	ev_loop (loop, 0);
769		989
770	As you can see, you are responsible for allocating the memory for your	990	As you can see, you are responsible for allocating the memory for your
771	watcher structures (and it is usually a bad idea to do this on the stack,	991	watcher structures (and it is I<usually> a bad idea to do this on the
772	although this can sometimes be quite valid).	992	stack).
		993
		994	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		995	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
773		996
774	Each watcher structure must be initialised by a call to C<ev_init	997	Each watcher structure must be initialised by a call to C<ev_init
775	(watcher *, callback)>, which expects a callback to be provided. This	998	(watcher *, callback)>, which expects a callback to be provided. This
776	callback gets invoked each time the event occurs (or, in the case of I/O	999	callback gets invoked each time the event occurs (or, in the case of I/O
777	watchers, each time the event loop detects that the file descriptor given	1000	watchers, each time the event loop detects that the file descriptor given
778	is readable and/or writable).	1001	is readable and/or writable).
779		1002
780	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	1003	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
781	with arguments specific to this watcher type. There is also a macro	1004	macro to configure it, with arguments specific to the watcher type. There
782	to combine initialisation and setting in one call: C<< ev_<type>_init	1005	is also a macro to combine initialisation and setting in one call: C<<
783	(watcher *, callback, ...) >>.	1006	ev_TYPE_init (watcher *, callback, ...) >>.
784		1007
785	To make the watcher actually watch out for events, you have to start it	1008	To make the watcher actually watch out for events, you have to start it
786	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1009	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
787	*) >>), and you can stop watching for events at any time by calling the	1010	*) >>), and you can stop watching for events at any time by calling the
788	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1011	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
789		1012
790	As long as your watcher is active (has been started but not stopped) you	1013	As long as your watcher is active (has been started but not stopped) you
791	must not touch the values stored in it. Most specifically you must never	1014	must not touch the values stored in it. Most specifically you must never
792	reinitialise it or call its C<set> macro.	1015	reinitialise it or call its C<ev_TYPE_set> macro.
793		1016
794	Each and every callback receives the event loop pointer as first, the	1017	Each and every callback receives the event loop pointer as first, the
795	registered watcher structure as second, and a bitset of received events as	1018	registered watcher structure as second, and a bitset of received events as
796	third argument.	1019	third argument.
797		1020
…		…
806	=item C<EV_WRITE>	1029	=item C<EV_WRITE>
807		1030
808	The file descriptor in the C<ev_io> watcher has become readable and/or	1031	The file descriptor in the C<ev_io> watcher has become readable and/or
809	writable.	1032	writable.
810		1033
811	=item C<EV_TIMEOUT>	1034	=item C<EV_TIMER>
812		1035
813	The C<ev_timer> watcher has timed out.	1036	The C<ev_timer> watcher has timed out.
814		1037
815	=item C<EV_PERIODIC>	1038	=item C<EV_PERIODIC>
816		1039
…		…
855		1078
856	=item C<EV_ASYNC>	1079	=item C<EV_ASYNC>
857		1080
858	The given async watcher has been asynchronously notified (see C<ev_async>).	1081	The given async watcher has been asynchronously notified (see C<ev_async>).
859		1082
		1083	=item C<EV_CUSTOM>
		1084
		1085	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1086	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1087
860	=item C<EV_ERROR>	1088	=item C<EV_ERROR>
861		1089
862	An unspecified error has occurred, the watcher has been stopped. This might	1090	An unspecified error has occurred, the watcher has been stopped. This might
863	happen because the watcher could not be properly started because libev	1091	happen because the watcher could not be properly started because libev
864	ran out of memory, a file descriptor was found to be closed or any other	1092	ran out of memory, a file descriptor was found to be closed or any other
		1093	problem. Libev considers these application bugs.
		1094
865	problem. You best act on it by reporting the problem and somehow coping	1095	You best act on it by reporting the problem and somehow coping with the
866	with the watcher being stopped.	1096	watcher being stopped. Note that well-written programs should not receive
		1097	an error ever, so when your watcher receives it, this usually indicates a
		1098	bug in your program.
867		1099
868	Libev will usually signal a few "dummy" events together with an error,	1100	Libev will usually signal a few "dummy" events together with an error, for
869	for example it might indicate that a fd is readable or writable, and if	1101	example it might indicate that a fd is readable or writable, and if your
870	your callbacks is well-written it can just attempt the operation and cope	1102	callbacks is well-written it can just attempt the operation and cope with
871	with the error from read() or write(). This will not work in multi-threaded	1103	the error from read() or write(). This will not work in multi-threaded
872	programs, though, so beware.	1104	programs, though, as the fd could already be closed and reused for another
		1105	thing, so beware.
873		1106
874	=back	1107	=back
875		1108
876	=head2 GENERIC WATCHER FUNCTIONS	1109	=head2 GENERIC WATCHER FUNCTIONS
877
878	In the following description, C<TYPE> stands for the watcher type,
879	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
880		1110
881	=over 4	1111	=over 4
882		1112
883	=item C<ev_init> (ev_TYPE *watcher, callback)	1113	=item C<ev_init> (ev_TYPE *watcher, callback)
884		1114
…		…
890	which rolls both calls into one.	1120	which rolls both calls into one.
891		1121
892	You can reinitialise a watcher at any time as long as it has been stopped	1122	You can reinitialise a watcher at any time as long as it has been stopped
893	(or never started) and there are no pending events outstanding.	1123	(or never started) and there are no pending events outstanding.
894		1124
895	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1125	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
896	int revents)>.	1126	int revents)>.
897		1127
		1128	Example: Initialise an C<ev_io> watcher in two steps.
		1129
		1130	ev_io w;
		1131	ev_init (&w, my_cb);
		1132	ev_io_set (&w, STDIN_FILENO, EV_READ);
		1133
898	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1134	=item C<ev_TYPE_set> (ev_TYPE *watcher, [args])
899		1135
900	This macro initialises the type-specific parts of a watcher. You need to	1136	This macro initialises the type-specific parts of a watcher. You need to
901	call C<ev_init> at least once before you call this macro, but you can	1137	call C<ev_init> at least once before you call this macro, but you can
902	call C<ev_TYPE_set> any number of times. You must not, however, call this	1138	call C<ev_TYPE_set> any number of times. You must not, however, call this
903	macro on a watcher that is active (it can be pending, however, which is a	1139	macro on a watcher that is active (it can be pending, however, which is a
904	difference to the C<ev_init> macro).	1140	difference to the C<ev_init> macro).
905		1141
906	Although some watcher types do not have type-specific arguments	1142	Although some watcher types do not have type-specific arguments
907	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1143	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
908		1144
		1145	See C<ev_init>, above, for an example.
		1146
909	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1147	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
910		1148
911	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1149	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
912	calls into a single call. This is the most convenient method to initialise	1150	calls into a single call. This is the most convenient method to initialise
913	a watcher. The same limitations apply, of course.	1151	a watcher. The same limitations apply, of course.
914		1152
		1153	Example: Initialise and set an C<ev_io> watcher in one step.
		1154
		1155	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1156
915	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1157	=item C<ev_TYPE_start> (loop, ev_TYPE *watcher)
916		1158
917	Starts (activates) the given watcher. Only active watchers will receive	1159	Starts (activates) the given watcher. Only active watchers will receive
918	events. If the watcher is already active nothing will happen.	1160	events. If the watcher is already active nothing will happen.
919		1161
		1162	Example: Start the C<ev_io> watcher that is being abused as example in this
		1163	whole section.
		1164
		1165	ev_io_start (EV_DEFAULT_UC, &w);
		1166
920	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1167	=item C<ev_TYPE_stop> (loop, ev_TYPE *watcher)
921		1168
922	Stops the given watcher again (if active) and clears the pending	1169	Stops the given watcher if active, and clears the pending status (whether
		1170	the watcher was active or not).
		1171
923	status. It is possible that stopped watchers are pending (for example,	1172	It is possible that stopped watchers are pending - for example,
924	non-repeating timers are being stopped when they become pending), but	1173	non-repeating timers are being stopped when they become pending - but
925	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1174	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
926	you want to free or reuse the memory used by the watcher it is therefore a	1175	pending. If you want to free or reuse the memory used by the watcher it is
927	good idea to always call its C<ev_TYPE_stop> function.	1176	therefore a good idea to always call its C<ev_TYPE_stop> function.
928		1177
929	=item bool ev_is_active (ev_TYPE *watcher)	1178	=item bool ev_is_active (ev_TYPE *watcher)
930		1179
931	Returns a true value iff the watcher is active (i.e. it has been started	1180	Returns a true value iff the watcher is active (i.e. it has been started
932	and not yet been stopped). As long as a watcher is active you must not modify	1181	and not yet been stopped). As long as a watcher is active you must not modify
…		…
948	=item ev_cb_set (ev_TYPE *watcher, callback)	1197	=item ev_cb_set (ev_TYPE *watcher, callback)
949		1198
950	Change the callback. You can change the callback at virtually any time	1199	Change the callback. You can change the callback at virtually any time
951	(modulo threads).	1200	(modulo threads).
952		1201
953	=item ev_set_priority (ev_TYPE *watcher, priority)	1202	=item ev_set_priority (ev_TYPE *watcher, int priority)
954		1203
955	=item int ev_priority (ev_TYPE *watcher)	1204	=item int ev_priority (ev_TYPE *watcher)
956		1205
957	Set and query the priority of the watcher. The priority is a small	1206	Set and query the priority of the watcher. The priority is a small
958	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1207	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
959	(default: C<-2>). Pending watchers with higher priority will be invoked	1208	(default: C<-2>). Pending watchers with higher priority will be invoked
960	before watchers with lower priority, but priority will not keep watchers	1209	before watchers with lower priority, but priority will not keep watchers
961	from being executed (except for C<ev_idle> watchers).	1210	from being executed (except for C<ev_idle> watchers).
962		1211
963	This means that priorities are I<only> used for ordering callback
964	invocation after new events have been received. This is useful, for
965	example, to reduce latency after idling, or more often, to bind two
966	watchers on the same event and make sure one is called first.
967
968	If you need to suppress invocation when higher priority events are pending	1212	If you need to suppress invocation when higher priority events are pending
969	you need to look at C<ev_idle> watchers, which provide this functionality.	1213	you need to look at C<ev_idle> watchers, which provide this functionality.
970		1214
971	You I<must not> change the priority of a watcher as long as it is active or	1215	You I<must not> change the priority of a watcher as long as it is active or
972	pending.	1216	pending.
973		1217
		1218	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1219	fine, as long as you do not mind that the priority value you query might
		1220	or might not have been clamped to the valid range.
		1221
974	The default priority used by watchers when no priority has been set is	1222	The default priority used by watchers when no priority has been set is
975	always C<0>, which is supposed to not be too high and not be too low :).	1223	always C<0>, which is supposed to not be too high and not be too low :).
976		1224
977	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1225	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
978	fine, as long as you do not mind that the priority value you query might	1226	priorities.
979	or might not have been adjusted to be within valid range.
980		1227
981	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1228	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
982		1229
983	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1230	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
984	C<loop> nor C<revents> need to be valid as long as the watcher callback	1231	C<loop> nor C<revents> need to be valid as long as the watcher callback
985	can deal with that fact.	1232	can deal with that fact, as both are simply passed through to the
		1233	callback.
986		1234
987	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1235	=item int ev_clear_pending (loop, ev_TYPE *watcher)
988		1236
989	If the watcher is pending, this function returns clears its pending status	1237	If the watcher is pending, this function clears its pending status and
990	and returns its C<revents> bitset (as if its callback was invoked). If the	1238	returns its C<revents> bitset (as if its callback was invoked). If the
991	watcher isn't pending it does nothing and returns C<0>.	1239	watcher isn't pending it does nothing and returns C<0>.
992		1240
		1241	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1242	callback to be invoked, which can be accomplished with this function.
		1243
		1244	=item ev_feed_event (loop, ev_TYPE *watcher, int revents)
		1245
		1246	Feeds the given event set into the event loop, as if the specified event
		1247	had happened for the specified watcher (which must be a pointer to an
		1248	initialised but not necessarily started event watcher). Obviously you must
		1249	not free the watcher as long as it has pending events.
		1250
		1251	Stopping the watcher, letting libev invoke it, or calling
		1252	C<ev_clear_pending> will clear the pending event, even if the watcher was
		1253	not started in the first place.
		1254
		1255	See also C<ev_feed_fd_event> and C<ev_feed_signal_event> for related
		1256	functions that do not need a watcher.
		1257
993	=back	1258	=back
994		1259
995		1260
996	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1261	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
997		1262
998	Each watcher has, by default, a member C<void *data> that you can change	1263	Each watcher has, by default, a member C<void *data> that you can change
999	and read at any time, libev will completely ignore it. This can be used	1264	and read at any time: libev will completely ignore it. This can be used
1000	to associate arbitrary data with your watcher. If you need more data and	1265	to associate arbitrary data with your watcher. If you need more data and
1001	don't want to allocate memory and store a pointer to it in that data	1266	don't want to allocate memory and store a pointer to it in that data
1002	member, you can also "subclass" the watcher type and provide your own	1267	member, you can also "subclass" the watcher type and provide your own
1003	data:	1268	data:
1004		1269
1005	struct my_io	1270	struct my_io
1006	{	1271	{
1007	struct ev_io io;	1272	ev_io io;
1008	int otherfd;	1273	int otherfd;
1009	void *somedata;	1274	void *somedata;
1010	struct whatever *mostinteresting;	1275	struct whatever *mostinteresting;
1011	};	1276	};
1012		1277
…		…
1015	ev_io_init (&w.io, my_cb, fd, EV_READ);	1280	ev_io_init (&w.io, my_cb, fd, EV_READ);
1016		1281
1017	And since your callback will be called with a pointer to the watcher, you	1282	And since your callback will be called with a pointer to the watcher, you
1018	can cast it back to your own type:	1283	can cast it back to your own type:
1019		1284
1020	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1285	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1021	{	1286	{
1022	struct my_io *w = (struct my_io *)w_;	1287	struct my_io *w = (struct my_io *)w_;
1023	...	1288	...
1024	}	1289	}
1025		1290
…		…
1036	ev_timer t2;	1301	ev_timer t2;
1037	}	1302	}
1038		1303
1039	In this case getting the pointer to C<my_biggy> is a bit more	1304	In this case getting the pointer to C<my_biggy> is a bit more
1040	complicated: Either you store the address of your C<my_biggy> struct	1305	complicated: Either you store the address of your C<my_biggy> struct
1041	in the C<data> member of the watcher, or you need to use some pointer	1306	in the C<data> member of the watcher (for woozies), or you need to use
1042	arithmetic using C<offsetof> inside your watchers:	1307	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1308	programmers):
1043		1309
1044	#include <stddef.h>	1310	#include <stddef.h>
1045		1311
1046	static void	1312	static void
1047	t1_cb (EV_P_ struct ev_timer *w, int revents)	1313	t1_cb (EV_P_ ev_timer *w, int revents)
1048	{	1314	{
1049	struct my_biggy big = (struct my_biggy *	1315	struct my_biggy big = (struct my_biggy *)
1050	(((char *)w) - offsetof (struct my_biggy, t1));	1316	(((char *)w) - offsetof (struct my_biggy, t1));
1051	}	1317	}
1052		1318
1053	static void	1319	static void
1054	t2_cb (EV_P_ struct ev_timer *w, int revents)	1320	t2_cb (EV_P_ ev_timer *w, int revents)
1055	{	1321	{
1056	struct my_biggy big = (struct my_biggy *	1322	struct my_biggy big = (struct my_biggy *)
1057	(((char *)w) - offsetof (struct my_biggy, t2));	1323	(((char *)w) - offsetof (struct my_biggy, t2));
1058	}	1324	}
		1325
		1326	=head2 WATCHER PRIORITY MODELS
		1327
		1328	Many event loops support I<watcher priorities>, which are usually small
		1329	integers that influence the ordering of event callback invocation
		1330	between watchers in some way, all else being equal.
		1331
		1332	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1333	description for the more technical details such as the actual priority
		1334	range.
		1335
		1336	There are two common ways how these these priorities are being interpreted
		1337	by event loops:
		1338
		1339	In the more common lock-out model, higher priorities "lock out" invocation
		1340	of lower priority watchers, which means as long as higher priority
		1341	watchers receive events, lower priority watchers are not being invoked.
		1342
		1343	The less common only-for-ordering model uses priorities solely to order
		1344	callback invocation within a single event loop iteration: Higher priority
		1345	watchers are invoked before lower priority ones, but they all get invoked
		1346	before polling for new events.
		1347
		1348	Libev uses the second (only-for-ordering) model for all its watchers
		1349	except for idle watchers (which use the lock-out model).
		1350
		1351	The rationale behind this is that implementing the lock-out model for
		1352	watchers is not well supported by most kernel interfaces, and most event
		1353	libraries will just poll for the same events again and again as long as
		1354	their callbacks have not been executed, which is very inefficient in the
		1355	common case of one high-priority watcher locking out a mass of lower
		1356	priority ones.
		1357
		1358	Static (ordering) priorities are most useful when you have two or more
		1359	watchers handling the same resource: a typical usage example is having an
		1360	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1361	timeouts. Under load, data might be received while the program handles
		1362	other jobs, but since timers normally get invoked first, the timeout
		1363	handler will be executed before checking for data. In that case, giving
		1364	the timer a lower priority than the I/O watcher ensures that I/O will be
		1365	handled first even under adverse conditions (which is usually, but not
		1366	always, what you want).
		1367
		1368	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1369	will only be executed when no same or higher priority watchers have
		1370	received events, they can be used to implement the "lock-out" model when
		1371	required.
		1372
		1373	For example, to emulate how many other event libraries handle priorities,
		1374	you can associate an C<ev_idle> watcher to each such watcher, and in
		1375	the normal watcher callback, you just start the idle watcher. The real
		1376	processing is done in the idle watcher callback. This causes libev to
		1377	continously poll and process kernel event data for the watcher, but when
		1378	the lock-out case is known to be rare (which in turn is rare :), this is
		1379	workable.
		1380
		1381	Usually, however, the lock-out model implemented that way will perform
		1382	miserably under the type of load it was designed to handle. In that case,
		1383	it might be preferable to stop the real watcher before starting the
		1384	idle watcher, so the kernel will not have to process the event in case
		1385	the actual processing will be delayed for considerable time.
		1386
		1387	Here is an example of an I/O watcher that should run at a strictly lower
		1388	priority than the default, and which should only process data when no
		1389	other events are pending:
		1390
		1391	ev_idle idle; // actual processing watcher
		1392	ev_io io; // actual event watcher
		1393
		1394	static void
		1395	io_cb (EV_P_ ev_io *w, int revents)
		1396	{
		1397	// stop the I/O watcher, we received the event, but
		1398	// are not yet ready to handle it.
		1399	ev_io_stop (EV_A_ w);
		1400
		1401	// start the idle watcher to ahndle the actual event.
		1402	// it will not be executed as long as other watchers
		1403	// with the default priority are receiving events.
		1404	ev_idle_start (EV_A_ &idle);
		1405	}
		1406
		1407	static void
		1408	idle_cb (EV_P_ ev_idle *w, int revents)
		1409	{
		1410	// actual processing
		1411	read (STDIN_FILENO, ...);
		1412
		1413	// have to start the I/O watcher again, as
		1414	// we have handled the event
		1415	ev_io_start (EV_P_ &io);
		1416	}
		1417
		1418	// initialisation
		1419	ev_idle_init (&idle, idle_cb);
		1420	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1421	ev_io_start (EV_DEFAULT_ &io);
		1422
		1423	In the "real" world, it might also be beneficial to start a timer, so that
		1424	low-priority connections can not be locked out forever under load. This
		1425	enables your program to keep a lower latency for important connections
		1426	during short periods of high load, while not completely locking out less
		1427	important ones.
1059		1428
1060		1429
1061	=head1 WATCHER TYPES	1430	=head1 WATCHER TYPES
1062		1431
1063	This section describes each watcher in detail, but will not repeat	1432	This section describes each watcher in detail, but will not repeat
…		…
1087	In general you can register as many read and/or write event watchers per	1456	In general you can register as many read and/or write event watchers per
1088	fd as you want (as long as you don't confuse yourself). Setting all file	1457	fd as you want (as long as you don't confuse yourself). Setting all file
1089	descriptors to non-blocking mode is also usually a good idea (but not	1458	descriptors to non-blocking mode is also usually a good idea (but not
1090	required if you know what you are doing).	1459	required if you know what you are doing).
1091		1460
1092	If you must do this, then force the use of a known-to-be-good backend	1461	If you cannot use non-blocking mode, then force the use of a
1093	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1462	known-to-be-good backend (at the time of this writing, this includes only
1094	C<EVBACKEND_POLL>).	1463	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1464	descriptors for which non-blocking operation makes no sense (such as
		1465	files) - libev doesn't guarentee any specific behaviour in that case.
1095		1466
1096	Another thing you have to watch out for is that it is quite easy to	1467	Another thing you have to watch out for is that it is quite easy to
1097	receive "spurious" readiness notifications, that is your callback might	1468	receive "spurious" readiness notifications, that is your callback might
1098	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1469	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1099	because there is no data. Not only are some backends known to create a	1470	because there is no data. Not only are some backends known to create a
1100	lot of those (for example Solaris ports), it is very easy to get into	1471	lot of those (for example Solaris ports), it is very easy to get into
1101	this situation even with a relatively standard program structure. Thus	1472	this situation even with a relatively standard program structure. Thus
1102	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1473	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1103	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1474	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1104		1475
1105	If you cannot run the fd in non-blocking mode (for example you should not	1476	If you cannot run the fd in non-blocking mode (for example you should
1106	play around with an Xlib connection), then you have to separately re-test	1477	not play around with an Xlib connection), then you have to separately
1107	whether a file descriptor is really ready with a known-to-be good interface	1478	re-test whether a file descriptor is really ready with a known-to-be good
1108	such as poll (fortunately in our Xlib example, Xlib already does this on	1479	interface such as poll (fortunately in our Xlib example, Xlib already
1109	its own, so its quite safe to use).	1480	does this on its own, so its quite safe to use). Some people additionally
		1481	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1482	indefinitely.
		1483
		1484	But really, best use non-blocking mode.
1110		1485
1111	=head3 The special problem of disappearing file descriptors	1486	=head3 The special problem of disappearing file descriptors
1112		1487
1113	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1488	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1114	descriptor (either by calling C<close> explicitly or by any other means,	1489	descriptor (either due to calling C<close> explicitly or any other means,
1115	such as C<dup>). The reason is that you register interest in some file	1490	such as C<dup2>). The reason is that you register interest in some file
1116	descriptor, but when it goes away, the operating system will silently drop	1491	descriptor, but when it goes away, the operating system will silently drop
1117	this interest. If another file descriptor with the same number then is	1492	this interest. If another file descriptor with the same number then is
1118	registered with libev, there is no efficient way to see that this is, in	1493	registered with libev, there is no efficient way to see that this is, in
1119	fact, a different file descriptor.	1494	fact, a different file descriptor.
1120		1495
…		…
1151	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1526	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1152	C<EVBACKEND_POLL>.	1527	C<EVBACKEND_POLL>.
1153		1528
1154	=head3 The special problem of SIGPIPE	1529	=head3 The special problem of SIGPIPE
1155		1530
1156	While not really specific to libev, it is easy to forget about SIGPIPE:	1531	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1157	when writing to a pipe whose other end has been closed, your program gets	1532	when writing to a pipe whose other end has been closed, your program gets
1158	send a SIGPIPE, which, by default, aborts your program. For most programs	1533	sent a SIGPIPE, which, by default, aborts your program. For most programs
1159	this is sensible behaviour, for daemons, this is usually undesirable.	1534	this is sensible behaviour, for daemons, this is usually undesirable.
1160		1535
1161	So when you encounter spurious, unexplained daemon exits, make sure you	1536	So when you encounter spurious, unexplained daemon exits, make sure you
1162	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1537	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1163	somewhere, as that would have given you a big clue).	1538	somewhere, as that would have given you a big clue).
1164		1539
		1540	=head3 The special problem of accept()ing when you can't
		1541
		1542	Many implementations of the POSIX C<accept> function (for example,
		1543	found in port-2004 Linux) have the peculiar behaviour of not removing a
		1544	connection from the pending queue in all error cases.
		1545
		1546	For example, larger servers often run out of file descriptors (because
		1547	of resource limits), causing C<accept> to fail with C<ENFILE> but not
		1548	rejecting the connection, leading to libev signalling readiness on
		1549	the next iteration again (the connection still exists after all), and
		1550	typically causing the program to loop at 100% CPU usage.
		1551
		1552	Unfortunately, the set of errors that cause this issue differs between
		1553	operating systems, there is usually little the app can do to remedy the
		1554	situation, and no known thread-safe method of removing the connection to
		1555	cope with overload is known (to me).
		1556
		1557	One of the easiest ways to handle this situation is to just ignore it
		1558	- when the program encounters an overload, it will just loop until the
		1559	situation is over. While this is a form of busy waiting, no OS offers an
		1560	event-based way to handle this situation, so it's the best one can do.
		1561
		1562	A better way to handle the situation is to log any errors other than
		1563	C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such
		1564	messages, and continue as usual, which at least gives the user an idea of
		1565	what could be wrong ("raise the ulimit!"). For extra points one could stop
		1566	the C<ev_io> watcher on the listening fd "for a while", which reduces CPU
		1567	usage.
		1568
		1569	If your program is single-threaded, then you could also keep a dummy file
		1570	descriptor for overload situations (e.g. by opening F</dev/null>), and
		1571	when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>,
		1572	close that fd, and create a new dummy fd. This will gracefully refuse
		1573	clients under typical overload conditions.
		1574
		1575	The last way to handle it is to simply log the error and C<exit>, as
		1576	is often done with C<malloc> failures, but this results in an easy
		1577	opportunity for a DoS attack.
1165		1578
1166	=head3 Watcher-Specific Functions	1579	=head3 Watcher-Specific Functions
1167		1580
1168	=over 4	1581	=over 4
1169		1582
1170	=item ev_io_init (ev_io *, callback, int fd, int events)	1583	=item ev_io_init (ev_io *, callback, int fd, int events)
1171		1584
1172	=item ev_io_set (ev_io *, int fd, int events)	1585	=item ev_io_set (ev_io *, int fd, int events)
1173		1586
1174	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1587	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1175	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1588	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1176	C<EV_READ | EV_WRITE> to receive the given events.	1589	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1177		1590
1178	=item int fd [read-only]	1591	=item int fd [read-only]
1179		1592
1180	The file descriptor being watched.	1593	The file descriptor being watched.
1181		1594
…		…
1190	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1603	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1191	readable, but only once. Since it is likely line-buffered, you could	1604	readable, but only once. Since it is likely line-buffered, you could
1192	attempt to read a whole line in the callback.	1605	attempt to read a whole line in the callback.
1193		1606
1194	static void	1607	static void
1195	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1608	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1196	{	1609	{
1197	ev_io_stop (loop, w);	1610	ev_io_stop (loop, w);
1198	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1611	.. read from stdin here (or from w->fd) and handle any I/O errors
1199	}	1612	}
1200		1613
1201	...	1614	...
1202	struct ev_loop *loop = ev_default_init (0);	1615	struct ev_loop *loop = ev_default_init (0);
1203	struct ev_io stdin_readable;	1616	ev_io stdin_readable;
1204	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1617	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1205	ev_io_start (loop, &stdin_readable);	1618	ev_io_start (loop, &stdin_readable);
1206	ev_loop (loop, 0);	1619	ev_loop (loop, 0);
1207		1620
1208		1621
…		…
1211	Timer watchers are simple relative timers that generate an event after a	1624	Timer watchers are simple relative timers that generate an event after a
1212	given time, and optionally repeating in regular intervals after that.	1625	given time, and optionally repeating in regular intervals after that.
1213		1626
1214	The timers are based on real time, that is, if you register an event that	1627	The timers are based on real time, that is, if you register an event that
1215	times out after an hour and you reset your system clock to January last	1628	times out after an hour and you reset your system clock to January last
1216	year, it will still time out after (roughly) and hour. "Roughly" because	1629	year, it will still time out after (roughly) one hour. "Roughly" because
1217	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1630	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1218	monotonic clock option helps a lot here).	1631	monotonic clock option helps a lot here).
1219		1632
1220	The callback is guaranteed to be invoked only after its timeout has passed,	1633	The callback is guaranteed to be invoked only I<after> its timeout has
1221	but if multiple timers become ready during the same loop iteration then	1634	passed (not I<at>, so on systems with very low-resolution clocks this
1222	order of execution is undefined.	1635	might introduce a small delay). If multiple timers become ready during the
		1636	same loop iteration then the ones with earlier time-out values are invoked
		1637	before ones of the same priority with later time-out values (but this is
		1638	no longer true when a callback calls C<ev_loop> recursively).
		1639
		1640	=head3 Be smart about timeouts
		1641
		1642	Many real-world problems involve some kind of timeout, usually for error
		1643	recovery. A typical example is an HTTP request - if the other side hangs,
		1644	you want to raise some error after a while.
		1645
		1646	What follows are some ways to handle this problem, from obvious and
		1647	inefficient to smart and efficient.
		1648
		1649	In the following, a 60 second activity timeout is assumed - a timeout that
		1650	gets reset to 60 seconds each time there is activity (e.g. each time some
		1651	data or other life sign was received).
		1652
		1653	=over 4
		1654
		1655	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1656
		1657	This is the most obvious, but not the most simple way: In the beginning,
		1658	start the watcher:
		1659
		1660	ev_timer_init (timer, callback, 60., 0.);
		1661	ev_timer_start (loop, timer);
		1662
		1663	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1664	and start it again:
		1665
		1666	ev_timer_stop (loop, timer);
		1667	ev_timer_set (timer, 60., 0.);
		1668	ev_timer_start (loop, timer);
		1669
		1670	This is relatively simple to implement, but means that each time there is
		1671	some activity, libev will first have to remove the timer from its internal
		1672	data structure and then add it again. Libev tries to be fast, but it's
		1673	still not a constant-time operation.
		1674
		1675	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1676
		1677	This is the easiest way, and involves using C<ev_timer_again> instead of
		1678	C<ev_timer_start>.
		1679
		1680	To implement this, configure an C<ev_timer> with a C<repeat> value
		1681	of C<60> and then call C<ev_timer_again> at start and each time you
		1682	successfully read or write some data. If you go into an idle state where
		1683	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1684	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1685
		1686	That means you can ignore both the C<ev_timer_start> function and the
		1687	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1688	member and C<ev_timer_again>.
		1689
		1690	At start:
		1691
		1692	ev_init (timer, callback);
		1693	timer->repeat = 60.;
		1694	ev_timer_again (loop, timer);
		1695
		1696	Each time there is some activity:
		1697
		1698	ev_timer_again (loop, timer);
		1699
		1700	It is even possible to change the time-out on the fly, regardless of
		1701	whether the watcher is active or not:
		1702
		1703	timer->repeat = 30.;
		1704	ev_timer_again (loop, timer);
		1705
		1706	This is slightly more efficient then stopping/starting the timer each time
		1707	you want to modify its timeout value, as libev does not have to completely
		1708	remove and re-insert the timer from/into its internal data structure.
		1709
		1710	It is, however, even simpler than the "obvious" way to do it.
		1711
		1712	=item 3. Let the timer time out, but then re-arm it as required.
		1713
		1714	This method is more tricky, but usually most efficient: Most timeouts are
		1715	relatively long compared to the intervals between other activity - in
		1716	our example, within 60 seconds, there are usually many I/O events with
		1717	associated activity resets.
		1718
		1719	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1720	but remember the time of last activity, and check for a real timeout only
		1721	within the callback:
		1722
		1723	ev_tstamp last_activity; // time of last activity
		1724
		1725	static void
		1726	callback (EV_P_ ev_timer *w, int revents)
		1727	{
		1728	ev_tstamp now = ev_now (EV_A);
		1729	ev_tstamp timeout = last_activity + 60.;
		1730
		1731	// if last_activity + 60. is older than now, we did time out
		1732	if (timeout < now)
		1733	{
		1734	// timeout occured, take action
		1735	}
		1736	else
		1737	{
		1738	// callback was invoked, but there was some activity, re-arm
		1739	// the watcher to fire in last_activity + 60, which is
		1740	// guaranteed to be in the future, so "again" is positive:
		1741	w->repeat = timeout - now;
		1742	ev_timer_again (EV_A_ w);
		1743	}
		1744	}
		1745
		1746	To summarise the callback: first calculate the real timeout (defined
		1747	as "60 seconds after the last activity"), then check if that time has
		1748	been reached, which means something I<did>, in fact, time out. Otherwise
		1749	the callback was invoked too early (C<timeout> is in the future), so
		1750	re-schedule the timer to fire at that future time, to see if maybe we have
		1751	a timeout then.
		1752
		1753	Note how C<ev_timer_again> is used, taking advantage of the
		1754	C<ev_timer_again> optimisation when the timer is already running.
		1755
		1756	This scheme causes more callback invocations (about one every 60 seconds
		1757	minus half the average time between activity), but virtually no calls to
		1758	libev to change the timeout.
		1759
		1760	To start the timer, simply initialise the watcher and set C<last_activity>
		1761	to the current time (meaning we just have some activity :), then call the
		1762	callback, which will "do the right thing" and start the timer:
		1763
		1764	ev_init (timer, callback);
		1765	last_activity = ev_now (loop);
		1766	callback (loop, timer, EV_TIMER);
		1767
		1768	And when there is some activity, simply store the current time in
		1769	C<last_activity>, no libev calls at all:
		1770
		1771	last_actiivty = ev_now (loop);
		1772
		1773	This technique is slightly more complex, but in most cases where the
		1774	time-out is unlikely to be triggered, much more efficient.
		1775
		1776	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1777	callback :) - just change the timeout and invoke the callback, which will
		1778	fix things for you.
		1779
		1780	=item 4. Wee, just use a double-linked list for your timeouts.
		1781
		1782	If there is not one request, but many thousands (millions...), all
		1783	employing some kind of timeout with the same timeout value, then one can
		1784	do even better:
		1785
		1786	When starting the timeout, calculate the timeout value and put the timeout
		1787	at the I<end> of the list.
		1788
		1789	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1790	the list is expected to fire (for example, using the technique #3).
		1791
		1792	When there is some activity, remove the timer from the list, recalculate
		1793	the timeout, append it to the end of the list again, and make sure to
		1794	update the C<ev_timer> if it was taken from the beginning of the list.
		1795
		1796	This way, one can manage an unlimited number of timeouts in O(1) time for
		1797	starting, stopping and updating the timers, at the expense of a major
		1798	complication, and having to use a constant timeout. The constant timeout
		1799	ensures that the list stays sorted.
		1800
		1801	=back
		1802
		1803	So which method the best?
		1804
		1805	Method #2 is a simple no-brain-required solution that is adequate in most
		1806	situations. Method #3 requires a bit more thinking, but handles many cases
		1807	better, and isn't very complicated either. In most case, choosing either
		1808	one is fine, with #3 being better in typical situations.
		1809
		1810	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1811	rather complicated, but extremely efficient, something that really pays
		1812	off after the first million or so of active timers, i.e. it's usually
		1813	overkill :)
1223		1814
1224	=head3 The special problem of time updates	1815	=head3 The special problem of time updates
1225		1816
1226	Establishing the current time is a costly operation (it usually takes at	1817	Establishing the current time is a costly operation (it usually takes at
1227	least two system calls): EV therefore updates its idea of the current	1818	least two system calls): EV therefore updates its idea of the current
1228	time only before and after C<ev_loop> polls for new events, which causes	1819	time only before and after C<ev_loop> collects new events, which causes a
1229	a growing difference between C<ev_now ()> and C<ev_time ()> when handling	1820	growing difference between C<ev_now ()> and C<ev_time ()> when handling
1230	lots of events.	1821	lots of events in one iteration.
1231		1822
1232	The relative timeouts are calculated relative to the C<ev_now ()>	1823	The relative timeouts are calculated relative to the C<ev_now ()>
1233	time. This is usually the right thing as this timestamp refers to the time	1824	time. This is usually the right thing as this timestamp refers to the time
1234	of the event triggering whatever timeout you are modifying/starting. If	1825	of the event triggering whatever timeout you are modifying/starting. If
1235	you suspect event processing to be delayed and you I<need> to base the	1826	you suspect event processing to be delayed and you I<need> to base the
…		…
1239		1830
1240	If the event loop is suspended for a long time, you can also force an	1831	If the event loop is suspended for a long time, you can also force an
1241	update of the time returned by C<ev_now ()> by calling C<ev_now_update	1832	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1242	()>.	1833	()>.
1243		1834
		1835	=head3 The special problems of suspended animation
		1836
		1837	When you leave the server world it is quite customary to hit machines that
		1838	can suspend/hibernate - what happens to the clocks during such a suspend?
		1839
		1840	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1841	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1842	to run until the system is suspended, but they will not advance while the
		1843	system is suspended. That means, on resume, it will be as if the program
		1844	was frozen for a few seconds, but the suspend time will not be counted
		1845	towards C<ev_timer> when a monotonic clock source is used. The real time
		1846	clock advanced as expected, but if it is used as sole clocksource, then a
		1847	long suspend would be detected as a time jump by libev, and timers would
		1848	be adjusted accordingly.
		1849
		1850	I would not be surprised to see different behaviour in different between
		1851	operating systems, OS versions or even different hardware.
		1852
		1853	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1854	time jump in the monotonic clocks and the realtime clock. If the program
		1855	is suspended for a very long time, and monotonic clock sources are in use,
		1856	then you can expect C<ev_timer>s to expire as the full suspension time
		1857	will be counted towards the timers. When no monotonic clock source is in
		1858	use, then libev will again assume a timejump and adjust accordingly.
		1859
		1860	It might be beneficial for this latter case to call C<ev_suspend>
		1861	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1862	deterministic behaviour in this case (you can do nothing against
		1863	C<SIGSTOP>).
		1864
1244	=head3 Watcher-Specific Functions and Data Members	1865	=head3 Watcher-Specific Functions and Data Members
1245		1866
1246	=over 4	1867	=over 4
1247		1868
1248	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1869	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
…		…
1271	If the timer is started but non-repeating, stop it (as if it timed out).	1892	If the timer is started but non-repeating, stop it (as if it timed out).
1272		1893
1273	If the timer is repeating, either start it if necessary (with the	1894	If the timer is repeating, either start it if necessary (with the
1274	C<repeat> value), or reset the running timer to the C<repeat> value.	1895	C<repeat> value), or reset the running timer to the C<repeat> value.
1275		1896
1276	This sounds a bit complicated, but here is a useful and typical	1897	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1277	example: Imagine you have a TCP connection and you want a so-called idle	1898	usage example.
1278	timeout, that is, you want to be called when there have been, say, 60
1279	seconds of inactivity on the socket. The easiest way to do this is to
1280	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1281	C<ev_timer_again> each time you successfully read or write some data. If
1282	you go into an idle state where you do not expect data to travel on the
1283	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1284	automatically restart it if need be.
1285		1899
1286	That means you can ignore the C<after> value and C<ev_timer_start>	1900	=item ev_tstamp ev_timer_remaining (loop, ev_timer *)
1287	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1288		1901
1289	ev_timer_init (timer, callback, 0., 5.);	1902	Returns the remaining time until a timer fires. If the timer is active,
1290	ev_timer_again (loop, timer);	1903	then this time is relative to the current event loop time, otherwise it's
1291	...	1904	the timeout value currently configured.
1292	timer->again = 17.;
1293	ev_timer_again (loop, timer);
1294	...
1295	timer->again = 10.;
1296	ev_timer_again (loop, timer);
1297		1905
1298	This is more slightly efficient then stopping/starting the timer each time	1906	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1299	you want to modify its timeout value.	1907	C<5>. When the timer is started and one second passes, C<ev_timer_remaining>
		1908	will return C<4>. When the timer expires and is restarted, it will return
		1909	roughly C<7> (likely slightly less as callback invocation takes some time,
		1910	too), and so on.
1300		1911
1301	=item ev_tstamp repeat [read-write]	1912	=item ev_tstamp repeat [read-write]
1302		1913
1303	The current C<repeat> value. Will be used each time the watcher times out	1914	The current C<repeat> value. Will be used each time the watcher times out
1304	or C<ev_timer_again> is called and determines the next timeout (if any),	1915	or C<ev_timer_again> is called, and determines the next timeout (if any),
1305	which is also when any modifications are taken into account.	1916	which is also when any modifications are taken into account.
1306		1917
1307	=back	1918	=back
1308		1919
1309	=head3 Examples	1920	=head3 Examples
1310		1921
1311	Example: Create a timer that fires after 60 seconds.	1922	Example: Create a timer that fires after 60 seconds.
1312		1923
1313	static void	1924	static void
1314	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1925	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1315	{	1926	{
1316	.. one minute over, w is actually stopped right here	1927	.. one minute over, w is actually stopped right here
1317	}	1928	}
1318		1929
1319	struct ev_timer mytimer;	1930	ev_timer mytimer;
1320	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1931	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1321	ev_timer_start (loop, &mytimer);	1932	ev_timer_start (loop, &mytimer);
1322		1933
1323	Example: Create a timeout timer that times out after 10 seconds of	1934	Example: Create a timeout timer that times out after 10 seconds of
1324	inactivity.	1935	inactivity.
1325		1936
1326	static void	1937	static void
1327	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1938	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1328	{	1939	{
1329	.. ten seconds without any activity	1940	.. ten seconds without any activity
1330	}	1941	}
1331		1942
1332	struct ev_timer mytimer;	1943	ev_timer mytimer;
1333	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1944	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1334	ev_timer_again (&mytimer); /* start timer */	1945	ev_timer_again (&mytimer); /* start timer */
1335	ev_loop (loop, 0);	1946	ev_loop (loop, 0);
1336		1947
1337	// and in some piece of code that gets executed on any "activity":	1948	// and in some piece of code that gets executed on any "activity":
…		…
1342	=head2 C<ev_periodic> - to cron or not to cron?	1953	=head2 C<ev_periodic> - to cron or not to cron?
1343		1954
1344	Periodic watchers are also timers of a kind, but they are very versatile	1955	Periodic watchers are also timers of a kind, but they are very versatile
1345	(and unfortunately a bit complex).	1956	(and unfortunately a bit complex).
1346		1957
1347	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1958	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1348	but on wall clock time (absolute time). You can tell a periodic watcher	1959	relative time, the physical time that passes) but on wall clock time
1349	to trigger after some specific point in time. For example, if you tell a	1960	(absolute time, the thing you can read on your calender or clock). The
1350	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1961	difference is that wall clock time can run faster or slower than real
1351	+ 10.>, that is, an absolute time not a delay) and then reset your system	1962	time, and time jumps are not uncommon (e.g. when you adjust your
1352	clock to January of the previous year, then it will take more than year	1963	wrist-watch).
1353	to trigger the event (unlike an C<ev_timer>, which would still trigger
1354	roughly 10 seconds later as it uses a relative timeout).
1355		1964
		1965	You can tell a periodic watcher to trigger after some specific point
		1966	in time: for example, if you tell a periodic watcher to trigger "in 10
		1967	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1968	not a delay) and then reset your system clock to January of the previous
		1969	year, then it will take a year or more to trigger the event (unlike an
		1970	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1971	it, as it uses a relative timeout).
		1972
1356	C<ev_periodic>s can also be used to implement vastly more complex timers,	1973	C<ev_periodic> watchers can also be used to implement vastly more complex
1357	such as triggering an event on each "midnight, local time", or other	1974	timers, such as triggering an event on each "midnight, local time", or
1358	complicated, rules.	1975	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1976	those cannot react to time jumps.
1359		1977
1360	As with timers, the callback is guaranteed to be invoked only when the	1978	As with timers, the callback is guaranteed to be invoked only when the
1361	time (C<at>) has passed, but if multiple periodic timers become ready	1979	point in time where it is supposed to trigger has passed. If multiple
1362	during the same loop iteration then order of execution is undefined.	1980	timers become ready during the same loop iteration then the ones with
		1981	earlier time-out values are invoked before ones with later time-out values
		1982	(but this is no longer true when a callback calls C<ev_loop> recursively).
1363		1983
1364	=head3 Watcher-Specific Functions and Data Members	1984	=head3 Watcher-Specific Functions and Data Members
1365		1985
1366	=over 4	1986	=over 4
1367		1987
1368	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1988	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1369		1989
1370	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1990	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1371		1991
1372	Lots of arguments, lets sort it out... There are basically three modes of	1992	Lots of arguments, let's sort it out... There are basically three modes of
1373	operation, and we will explain them from simplest to complex:	1993	operation, and we will explain them from simplest to most complex:
1374		1994
1375	=over 4	1995	=over 4
1376		1996
1377	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1997	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1378		1998
1379	In this configuration the watcher triggers an event after the wall clock	1999	In this configuration the watcher triggers an event after the wall clock
1380	time C<at> has passed and doesn't repeat. It will not adjust when a time	2000	time C<offset> has passed. It will not repeat and will not adjust when a
1381	jump occurs, that is, if it is to be run at January 1st 2011 then it will	2001	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1382	run when the system time reaches or surpasses this time.	2002	will be stopped and invoked when the system clock reaches or surpasses
		2003	this point in time.
1383		2004
1384	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	2005	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1385		2006
1386	In this mode the watcher will always be scheduled to time out at the next	2007	In this mode the watcher will always be scheduled to time out at the next
1387	C<at + N * interval> time (for some integer N, which can also be negative)	2008	C<offset + N * interval> time (for some integer N, which can also be
1388	and then repeat, regardless of any time jumps.	2009	negative) and then repeat, regardless of any time jumps. The C<offset>
		2010	argument is merely an offset into the C<interval> periods.
1389		2011
1390	This can be used to create timers that do not drift with respect to system	2012	This can be used to create timers that do not drift with respect to the
1391	time, for example, here is a C<ev_periodic> that triggers each hour, on	2013	system clock, for example, here is an C<ev_periodic> that triggers each
1392	the hour:	2014	hour, on the hour (with respect to UTC):
1393		2015
1394	ev_periodic_set (&periodic, 0., 3600., 0);	2016	ev_periodic_set (&periodic, 0., 3600., 0);
1395		2017
1396	This doesn't mean there will always be 3600 seconds in between triggers,	2018	This doesn't mean there will always be 3600 seconds in between triggers,
1397	but only that the callback will be called when the system time shows a	2019	but only that the callback will be called when the system time shows a
1398	full hour (UTC), or more correctly, when the system time is evenly divisible	2020	full hour (UTC), or more correctly, when the system time is evenly divisible
1399	by 3600.	2021	by 3600.
1400		2022
1401	Another way to think about it (for the mathematically inclined) is that	2023	Another way to think about it (for the mathematically inclined) is that
1402	C<ev_periodic> will try to run the callback in this mode at the next possible	2024	C<ev_periodic> will try to run the callback in this mode at the next possible
1403	time where C<time = at (mod interval)>, regardless of any time jumps.	2025	time where C<time = offset (mod interval)>, regardless of any time jumps.
1404		2026
1405	For numerical stability it is preferable that the C<at> value is near	2027	For numerical stability it is preferable that the C<offset> value is near
1406	C<ev_now ()> (the current time), but there is no range requirement for	2028	C<ev_now ()> (the current time), but there is no range requirement for
1407	this value, and in fact is often specified as zero.	2029	this value, and in fact is often specified as zero.
1408		2030
1409	Note also that there is an upper limit to how often a timer can fire (CPU	2031	Note also that there is an upper limit to how often a timer can fire (CPU
1410	speed for example), so if C<interval> is very small then timing stability	2032	speed for example), so if C<interval> is very small then timing stability
1411	will of course deteriorate. Libev itself tries to be exact to be about one	2033	will of course deteriorate. Libev itself tries to be exact to be about one
1412	millisecond (if the OS supports it and the machine is fast enough).	2034	millisecond (if the OS supports it and the machine is fast enough).
1413		2035
1414	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	2036	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1415		2037
1416	In this mode the values for C<interval> and C<at> are both being	2038	In this mode the values for C<interval> and C<offset> are both being
1417	ignored. Instead, each time the periodic watcher gets scheduled, the	2039	ignored. Instead, each time the periodic watcher gets scheduled, the
1418	reschedule callback will be called with the watcher as first, and the	2040	reschedule callback will be called with the watcher as first, and the
1419	current time as second argument.	2041	current time as second argument.
1420		2042
1421	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	2043	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1422	ever, or make ANY event loop modifications whatsoever>.	2044	or make ANY other event loop modifications whatsoever, unless explicitly
		2045	allowed by documentation here>.
1423		2046
1424	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	2047	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1425	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	2048	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1426	only event loop modification you are allowed to do).	2049	only event loop modification you are allowed to do).
1427		2050
1428	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	2051	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1429	*w, ev_tstamp now)>, e.g.:	2052	*w, ev_tstamp now)>, e.g.:
1430		2053
		2054	static ev_tstamp
1431	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	2055	my_rescheduler (ev_periodic *w, ev_tstamp now)
1432	{	2056	{
1433	return now + 60.;	2057	return now + 60.;
1434	}	2058	}
1435		2059
1436	It must return the next time to trigger, based on the passed time value	2060	It must return the next time to trigger, based on the passed time value
…		…
1456	a different time than the last time it was called (e.g. in a crond like	2080	a different time than the last time it was called (e.g. in a crond like
1457	program when the crontabs have changed).	2081	program when the crontabs have changed).
1458		2082
1459	=item ev_tstamp ev_periodic_at (ev_periodic *)	2083	=item ev_tstamp ev_periodic_at (ev_periodic *)
1460		2084
1461	When active, returns the absolute time that the watcher is supposed to	2085	When active, returns the absolute time that the watcher is supposed
1462	trigger next.	2086	to trigger next. This is not the same as the C<offset> argument to
		2087	C<ev_periodic_set>, but indeed works even in interval and manual
		2088	rescheduling modes.
1463		2089
1464	=item ev_tstamp offset [read-write]	2090	=item ev_tstamp offset [read-write]
1465		2091
1466	When repeating, this contains the offset value, otherwise this is the	2092	When repeating, this contains the offset value, otherwise this is the
1467	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2093	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2094	although libev might modify this value for better numerical stability).
1468		2095
1469	Can be modified any time, but changes only take effect when the periodic	2096	Can be modified any time, but changes only take effect when the periodic
1470	timer fires or C<ev_periodic_again> is being called.	2097	timer fires or C<ev_periodic_again> is being called.
1471		2098
1472	=item ev_tstamp interval [read-write]	2099	=item ev_tstamp interval [read-write]
1473		2100
1474	The current interval value. Can be modified any time, but changes only	2101	The current interval value. Can be modified any time, but changes only
1475	take effect when the periodic timer fires or C<ev_periodic_again> is being	2102	take effect when the periodic timer fires or C<ev_periodic_again> is being
1476	called.	2103	called.
1477		2104
1478	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2105	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1479		2106
1480	The current reschedule callback, or C<0>, if this functionality is	2107	The current reschedule callback, or C<0>, if this functionality is
1481	switched off. Can be changed any time, but changes only take effect when	2108	switched off. Can be changed any time, but changes only take effect when
1482	the periodic timer fires or C<ev_periodic_again> is being called.	2109	the periodic timer fires or C<ev_periodic_again> is being called.
1483		2110
1484	=back	2111	=back
1485		2112
1486	=head3 Examples	2113	=head3 Examples
1487		2114
1488	Example: Call a callback every hour, or, more precisely, whenever the	2115	Example: Call a callback every hour, or, more precisely, whenever the
1489	system clock is divisible by 3600. The callback invocation times have	2116	system time is divisible by 3600. The callback invocation times have
1490	potentially a lot of jitter, but good long-term stability.	2117	potentially a lot of jitter, but good long-term stability.
1491		2118
1492	static void	2119	static void
1493	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2120	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1494	{	2121	{
1495	... its now a full hour (UTC, or TAI or whatever your clock follows)	2122	... its now a full hour (UTC, or TAI or whatever your clock follows)
1496	}	2123	}
1497		2124
1498	struct ev_periodic hourly_tick;	2125	ev_periodic hourly_tick;
1499	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2126	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1500	ev_periodic_start (loop, &hourly_tick);	2127	ev_periodic_start (loop, &hourly_tick);
1501		2128
1502	Example: The same as above, but use a reschedule callback to do it:	2129	Example: The same as above, but use a reschedule callback to do it:
1503		2130
1504	#include <math.h>	2131	#include <math.h>
1505		2132
1506	static ev_tstamp	2133	static ev_tstamp
1507	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2134	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1508	{	2135	{
1509	return fmod (now, 3600.) + 3600.;	2136	return now + (3600. - fmod (now, 3600.));
1510	}	2137	}
1511		2138
1512	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2139	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1513		2140
1514	Example: Call a callback every hour, starting now:	2141	Example: Call a callback every hour, starting now:
1515		2142
1516	struct ev_periodic hourly_tick;	2143	ev_periodic hourly_tick;
1517	ev_periodic_init (&hourly_tick, clock_cb,	2144	ev_periodic_init (&hourly_tick, clock_cb,
1518	fmod (ev_now (loop), 3600.), 3600., 0);	2145	fmod (ev_now (loop), 3600.), 3600., 0);
1519	ev_periodic_start (loop, &hourly_tick);	2146	ev_periodic_start (loop, &hourly_tick);
1520		2147
1521		2148
…		…
1524	Signal watchers will trigger an event when the process receives a specific	2151	Signal watchers will trigger an event when the process receives a specific
1525	signal one or more times. Even though signals are very asynchronous, libev	2152	signal one or more times. Even though signals are very asynchronous, libev
1526	will try it's best to deliver signals synchronously, i.e. as part of the	2153	will try it's best to deliver signals synchronously, i.e. as part of the
1527	normal event processing, like any other event.	2154	normal event processing, like any other event.
1528		2155
		2156	If you want signals to be delivered truly asynchronously, just use
		2157	C<sigaction> as you would do without libev and forget about sharing
		2158	the signal. You can even use C<ev_async> from a signal handler to
		2159	synchronously wake up an event loop.
		2160
1529	You can configure as many watchers as you like per signal. Only when the	2161	You can configure as many watchers as you like for the same signal, but
		2162	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2163	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2164	C<SIGINT> in both the default loop and another loop at the same time. At
		2165	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2166
1530	first watcher gets started will libev actually register a signal watcher	2167	When the first watcher gets started will libev actually register something
1531	with the kernel (thus it coexists with your own signal handlers as long	2168	with the kernel (thus it coexists with your own signal handlers as long as
1532	as you don't register any with libev). Similarly, when the last signal	2169	you don't register any with libev for the same signal).
1533	watcher for a signal is stopped libev will reset the signal handler to
1534	SIG_DFL (regardless of what it was set to before).
1535		2170
1536	If possible and supported, libev will install its handlers with	2171	If possible and supported, libev will install its handlers with
1537	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2172	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1538	interrupted. If you have a problem with system calls getting interrupted by	2173	not be unduly interrupted. If you have a problem with system calls getting
1539	signals you can block all signals in an C<ev_check> watcher and unblock	2174	interrupted by signals you can block all signals in an C<ev_check> watcher
1540	them in an C<ev_prepare> watcher.	2175	and unblock them in an C<ev_prepare> watcher.
		2176
		2177	=head3 The special problem of inheritance over fork/execve/pthread_create
		2178
		2179	Both the signal mask (C<sigprocmask>) and the signal disposition
		2180	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2181	stopping it again), that is, libev might or might not block the signal,
		2182	and might or might not set or restore the installed signal handler.
		2183
		2184	While this does not matter for the signal disposition (libev never
		2185	sets signals to C<SIG_IGN>, so handlers will be reset to C<SIG_DFL> on
		2186	C<execve>), this matters for the signal mask: many programs do not expect
		2187	certain signals to be blocked.
		2188
		2189	This means that before calling C<exec> (from the child) you should reset
		2190	the signal mask to whatever "default" you expect (all clear is a good
		2191	choice usually).
		2192
		2193	The simplest way to ensure that the signal mask is reset in the child is
		2194	to install a fork handler with C<pthread_atfork> that resets it. That will
		2195	catch fork calls done by libraries (such as the libc) as well.
		2196
		2197	In current versions of libev, the signal will not be blocked indefinitely
		2198	unless you use the C<signalfd> API (C<EV_SIGNALFD>). While this reduces
		2199	the window of opportunity for problems, it will not go away, as libev
		2200	I<has> to modify the signal mask, at least temporarily.
		2201
		2202	So I can't stress this enough: I<If you do not reset your signal mask when
		2203	you expect it to be empty, you have a race condition in your code>. This
		2204	is not a libev-specific thing, this is true for most event libraries.
1541		2205
1542	=head3 Watcher-Specific Functions and Data Members	2206	=head3 Watcher-Specific Functions and Data Members
1543		2207
1544	=over 4	2208	=over 4
1545		2209
…		…
1556		2220
1557	=back	2221	=back
1558		2222
1559	=head3 Examples	2223	=head3 Examples
1560		2224
1561	Example: Try to exit cleanly on SIGINT and SIGTERM.	2225	Example: Try to exit cleanly on SIGINT.
1562		2226
1563	static void	2227	static void
1564	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2228	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1565	{	2229	{
1566	ev_unloop (loop, EVUNLOOP_ALL);	2230	ev_unloop (loop, EVUNLOOP_ALL);
1567	}	2231	}
1568		2232
1569	struct ev_signal signal_watcher;	2233	ev_signal signal_watcher;
1570	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2234	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1571	ev_signal_start (loop, &sigint_cb);	2235	ev_signal_start (loop, &signal_watcher);
1572		2236
1573		2237
1574	=head2 C<ev_child> - watch out for process status changes	2238	=head2 C<ev_child> - watch out for process status changes
1575		2239
1576	Child watchers trigger when your process receives a SIGCHLD in response to	2240	Child watchers trigger when your process receives a SIGCHLD in response to
1577	some child status changes (most typically when a child of yours dies). It	2241	some child status changes (most typically when a child of yours dies or
1578	is permissible to install a child watcher I<after> the child has been	2242	exits). It is permissible to install a child watcher I<after> the child
1579	forked (which implies it might have already exited), as long as the event	2243	has been forked (which implies it might have already exited), as long
1580	loop isn't entered (or is continued from a watcher).	2244	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2245	forking and then immediately registering a watcher for the child is fine,
		2246	but forking and registering a watcher a few event loop iterations later or
		2247	in the next callback invocation is not.
1581		2248
1582	Only the default event loop is capable of handling signals, and therefore	2249	Only the default event loop is capable of handling signals, and therefore
1583	you can only register child watchers in the default event loop.	2250	you can only register child watchers in the default event loop.
1584		2251
		2252	Due to some design glitches inside libev, child watchers will always be
		2253	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2254	libev)
		2255
1585	=head3 Process Interaction	2256	=head3 Process Interaction
1586		2257
1587	Libev grabs C<SIGCHLD> as soon as the default event loop is	2258	Libev grabs C<SIGCHLD> as soon as the default event loop is
1588	initialised. This is necessary to guarantee proper behaviour even if	2259	initialised. This is necessary to guarantee proper behaviour even if the
1589	the first child watcher is started after the child exits. The occurrence	2260	first child watcher is started after the child exits. The occurrence
1590	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2261	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1591	synchronously as part of the event loop processing. Libev always reaps all	2262	synchronously as part of the event loop processing. Libev always reaps all
1592	children, even ones not watched.	2263	children, even ones not watched.
1593		2264
1594	=head3 Overriding the Built-In Processing	2265	=head3 Overriding the Built-In Processing
…		…
1604	=head3 Stopping the Child Watcher	2275	=head3 Stopping the Child Watcher
1605		2276
1606	Currently, the child watcher never gets stopped, even when the	2277	Currently, the child watcher never gets stopped, even when the
1607	child terminates, so normally one needs to stop the watcher in the	2278	child terminates, so normally one needs to stop the watcher in the
1608	callback. Future versions of libev might stop the watcher automatically	2279	callback. Future versions of libev might stop the watcher automatically
1609	when a child exit is detected.	2280	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2281	problem).
1610		2282
1611	=head3 Watcher-Specific Functions and Data Members	2283	=head3 Watcher-Specific Functions and Data Members
1612		2284
1613	=over 4	2285	=over 4
1614		2286
…		…
1646	its completion.	2318	its completion.
1647		2319
1648	ev_child cw;	2320	ev_child cw;
1649		2321
1650	static void	2322	static void
1651	child_cb (EV_P_ struct ev_child *w, int revents)	2323	child_cb (EV_P_ ev_child *w, int revents)
1652	{	2324	{
1653	ev_child_stop (EV_A_ w);	2325	ev_child_stop (EV_A_ w);
1654	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2326	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1655	}	2327	}
1656		2328
…		…
1671		2343
1672		2344
1673	=head2 C<ev_stat> - did the file attributes just change?	2345	=head2 C<ev_stat> - did the file attributes just change?
1674		2346
1675	This watches a file system path for attribute changes. That is, it calls	2347	This watches a file system path for attribute changes. That is, it calls
1676	C<stat> regularly (or when the OS says it changed) and sees if it changed	2348	C<stat> on that path in regular intervals (or when the OS says it changed)
1677	compared to the last time, invoking the callback if it did.	2349	and sees if it changed compared to the last time, invoking the callback if
		2350	it did.
1678		2351
1679	The path does not need to exist: changing from "path exists" to "path does	2352	The path does not need to exist: changing from "path exists" to "path does
1680	not exist" is a status change like any other. The condition "path does	2353	not exist" is a status change like any other. The condition "path does not
1681	not exist" is signified by the C<st_nlink> field being zero (which is	2354	exist" (or more correctly "path cannot be stat'ed") is signified by the
1682	otherwise always forced to be at least one) and all the other fields of	2355	C<st_nlink> field being zero (which is otherwise always forced to be at
1683	the stat buffer having unspecified contents.	2356	least one) and all the other fields of the stat buffer having unspecified
		2357	contents.
1684		2358
1685	The path I<should> be absolute and I<must not> end in a slash. If it is	2359	The path I<must not> end in a slash or contain special components such as
		2360	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1686	relative and your working directory changes, the behaviour is undefined.	2361	your working directory changes, then the behaviour is undefined.
1687		2362
1688	Since there is no standard to do this, the portable implementation simply	2363	Since there is no portable change notification interface available, the
1689	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2364	portable implementation simply calls C<stat(2)> regularly on the path
1690	can specify a recommended polling interval for this case. If you specify	2365	to see if it changed somehow. You can specify a recommended polling
1691	a polling interval of C<0> (highly recommended!) then a I<suitable,	2366	interval for this case. If you specify a polling interval of C<0> (highly
1692	unspecified default> value will be used (which you can expect to be around	2367	recommended!) then a I<suitable, unspecified default> value will be used
1693	five seconds, although this might change dynamically). Libev will also	2368	(which you can expect to be around five seconds, although this might
1694	impose a minimum interval which is currently around C<0.1>, but thats	2369	change dynamically). Libev will also impose a minimum interval which is
1695	usually overkill.	2370	currently around C<0.1>, but that's usually overkill.
1696		2371
1697	This watcher type is not meant for massive numbers of stat watchers,	2372	This watcher type is not meant for massive numbers of stat watchers,
1698	as even with OS-supported change notifications, this can be	2373	as even with OS-supported change notifications, this can be
1699	resource-intensive.	2374	resource-intensive.
1700		2375
1701	At the time of this writing, only the Linux inotify interface is	2376	At the time of this writing, the only OS-specific interface implemented
1702	implemented (implementing kqueue support is left as an exercise for the	2377	is the Linux inotify interface (implementing kqueue support is left as an
1703	reader, note, however, that the author sees no way of implementing ev_stat	2378	exercise for the reader. Note, however, that the author sees no way of
1704	semantics with kqueue). Inotify will be used to give hints only and should	2379	implementing C<ev_stat> semantics with kqueue, except as a hint).
1705	not change the semantics of C<ev_stat> watchers, which means that libev
1706	sometimes needs to fall back to regular polling again even with inotify,
1707	but changes are usually detected immediately, and if the file exists there
1708	will be no polling.
1709		2380
1710	=head3 ABI Issues (Largefile Support)	2381	=head3 ABI Issues (Largefile Support)
1711		2382
1712	Libev by default (unless the user overrides this) uses the default	2383	Libev by default (unless the user overrides this) uses the default
1713	compilation environment, which means that on systems with large file	2384	compilation environment, which means that on systems with large file
1714	support disabled by default, you get the 32 bit version of the stat	2385	support disabled by default, you get the 32 bit version of the stat
1715	structure. When using the library from programs that change the ABI to	2386	structure. When using the library from programs that change the ABI to
1716	use 64 bit file offsets the programs will fail. In that case you have to	2387	use 64 bit file offsets the programs will fail. In that case you have to
1717	compile libev with the same flags to get binary compatibility. This is	2388	compile libev with the same flags to get binary compatibility. This is
1718	obviously the case with any flags that change the ABI, but the problem is	2389	obviously the case with any flags that change the ABI, but the problem is
1719	most noticeably disabled with ev_stat and large file support.	2390	most noticeably displayed with ev_stat and large file support.
1720		2391
1721	The solution for this is to lobby your distribution maker to make large	2392	The solution for this is to lobby your distribution maker to make large
1722	file interfaces available by default (as e.g. FreeBSD does) and not	2393	file interfaces available by default (as e.g. FreeBSD does) and not
1723	optional. Libev cannot simply switch on large file support because it has	2394	optional. Libev cannot simply switch on large file support because it has
1724	to exchange stat structures with application programs compiled using the	2395	to exchange stat structures with application programs compiled using the
1725	default compilation environment.	2396	default compilation environment.
1726		2397
1727	=head3 Inotify	2398	=head3 Inotify and Kqueue
1728		2399
1729	When C<inotify (7)> support has been compiled into libev (generally only	2400	When C<inotify (7)> support has been compiled into libev and present at
1730	available on Linux) and present at runtime, it will be used to speed up	2401	runtime, it will be used to speed up change detection where possible. The
1731	change detection where possible. The inotify descriptor will be created lazily	2402	inotify descriptor will be created lazily when the first C<ev_stat>
1732	when the first C<ev_stat> watcher is being started.	2403	watcher is being started.
1733		2404
1734	Inotify presence does not change the semantics of C<ev_stat> watchers	2405	Inotify presence does not change the semantics of C<ev_stat> watchers
1735	except that changes might be detected earlier, and in some cases, to avoid	2406	except that changes might be detected earlier, and in some cases, to avoid
1736	making regular C<stat> calls. Even in the presence of inotify support	2407	making regular C<stat> calls. Even in the presence of inotify support
1737	there are many cases where libev has to resort to regular C<stat> polling.	2408	there are many cases where libev has to resort to regular C<stat> polling,
		2409	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2410	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2411	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2412	xfs are fully working) libev usually gets away without polling.
1738		2413
1739	(There is no support for kqueue, as apparently it cannot be used to	2414	There is no support for kqueue, as apparently it cannot be used to
1740	implement this functionality, due to the requirement of having a file	2415	implement this functionality, due to the requirement of having a file
1741	descriptor open on the object at all times).	2416	descriptor open on the object at all times, and detecting renames, unlinks
		2417	etc. is difficult.
		2418
		2419	=head3 C<stat ()> is a synchronous operation
		2420
		2421	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2422	the process. The exception are C<ev_stat> watchers - those call C<stat
		2423	()>, which is a synchronous operation.
		2424
		2425	For local paths, this usually doesn't matter: unless the system is very
		2426	busy or the intervals between stat's are large, a stat call will be fast,
		2427	as the path data is usually in memory already (except when starting the
		2428	watcher).
		2429
		2430	For networked file systems, calling C<stat ()> can block an indefinite
		2431	time due to network issues, and even under good conditions, a stat call
		2432	often takes multiple milliseconds.
		2433
		2434	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2435	paths, although this is fully supported by libev.
1742		2436
1743	=head3 The special problem of stat time resolution	2437	=head3 The special problem of stat time resolution
1744		2438
1745	The C<stat ()> system call only supports full-second resolution portably, and	2439	The C<stat ()> system call only supports full-second resolution portably,
1746	even on systems where the resolution is higher, many file systems still	2440	and even on systems where the resolution is higher, most file systems
1747	only support whole seconds.	2441	still only support whole seconds.
1748		2442
1749	That means that, if the time is the only thing that changes, you can	2443	That means that, if the time is the only thing that changes, you can
1750	easily miss updates: on the first update, C<ev_stat> detects a change and	2444	easily miss updates: on the first update, C<ev_stat> detects a change and
1751	calls your callback, which does something. When there is another update	2445	calls your callback, which does something. When there is another update
1752	within the same second, C<ev_stat> will be unable to detect it as the stat	2446	within the same second, C<ev_stat> will be unable to detect unless the
1753	data does not change.	2447	stat data does change in other ways (e.g. file size).
1754		2448
1755	The solution to this is to delay acting on a change for slightly more	2449	The solution to this is to delay acting on a change for slightly more
1756	than a second (or till slightly after the next full second boundary), using	2450	than a second (or till slightly after the next full second boundary), using
1757	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2451	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1758	ev_timer_again (loop, w)>).	2452	ev_timer_again (loop, w)>).
…		…
1778	C<path>. The C<interval> is a hint on how quickly a change is expected to	2472	C<path>. The C<interval> is a hint on how quickly a change is expected to
1779	be detected and should normally be specified as C<0> to let libev choose	2473	be detected and should normally be specified as C<0> to let libev choose
1780	a suitable value. The memory pointed to by C<path> must point to the same	2474	a suitable value. The memory pointed to by C<path> must point to the same
1781	path for as long as the watcher is active.	2475	path for as long as the watcher is active.
1782		2476
1783	The callback will receive C<EV_STAT> when a change was detected, relative	2477	The callback will receive an C<EV_STAT> event when a change was detected,
1784	to the attributes at the time the watcher was started (or the last change	2478	relative to the attributes at the time the watcher was started (or the
1785	was detected).	2479	last change was detected).
1786		2480
1787	=item ev_stat_stat (loop, ev_stat *)	2481	=item ev_stat_stat (loop, ev_stat *)
1788		2482
1789	Updates the stat buffer immediately with new values. If you change the	2483	Updates the stat buffer immediately with new values. If you change the
1790	watched path in your callback, you could call this function to avoid	2484	watched path in your callback, you could call this function to avoid
…		…
1873		2567
1874		2568
1875	=head2 C<ev_idle> - when you've got nothing better to do...	2569	=head2 C<ev_idle> - when you've got nothing better to do...
1876		2570
1877	Idle watchers trigger events when no other events of the same or higher	2571	Idle watchers trigger events when no other events of the same or higher
1878	priority are pending (prepare, check and other idle watchers do not	2572	priority are pending (prepare, check and other idle watchers do not count
1879	count).	2573	as receiving "events").
1880		2574
1881	That is, as long as your process is busy handling sockets or timeouts	2575	That is, as long as your process is busy handling sockets or timeouts
1882	(or even signals, imagine) of the same or higher priority it will not be	2576	(or even signals, imagine) of the same or higher priority it will not be
1883	triggered. But when your process is idle (or only lower-priority watchers	2577	triggered. But when your process is idle (or only lower-priority watchers
1884	are pending), the idle watchers are being called once per event loop	2578	are pending), the idle watchers are being called once per event loop
…		…
1895		2589
1896	=head3 Watcher-Specific Functions and Data Members	2590	=head3 Watcher-Specific Functions and Data Members
1897		2591
1898	=over 4	2592	=over 4
1899		2593
1900	=item ev_idle_init (ev_signal *, callback)	2594	=item ev_idle_init (ev_idle *, callback)
1901		2595
1902	Initialises and configures the idle watcher - it has no parameters of any	2596	Initialises and configures the idle watcher - it has no parameters of any
1903	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2597	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1904	believe me.	2598	believe me.
1905		2599
…		…
1909		2603
1910	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2604	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1911	callback, free it. Also, use no error checking, as usual.	2605	callback, free it. Also, use no error checking, as usual.
1912		2606
1913	static void	2607	static void
1914	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2608	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1915	{	2609	{
1916	free (w);	2610	free (w);
1917	// now do something you wanted to do when the program has	2611	// now do something you wanted to do when the program has
1918	// no longer anything immediate to do.	2612	// no longer anything immediate to do.
1919	}	2613	}
1920		2614
1921	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2615	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1922	ev_idle_init (idle_watcher, idle_cb);	2616	ev_idle_init (idle_watcher, idle_cb);
1923	ev_idle_start (loop, idle_cb);	2617	ev_idle_start (loop, idle_watcher);
1924		2618
1925		2619
1926	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2620	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1927		2621
1928	Prepare and check watchers are usually (but not always) used in tandem:	2622	Prepare and check watchers are usually (but not always) used in pairs:
1929	prepare watchers get invoked before the process blocks and check watchers	2623	prepare watchers get invoked before the process blocks and check watchers
1930	afterwards.	2624	afterwards.
1931		2625
1932	You I<must not> call C<ev_loop> or similar functions that enter	2626	You I<must not> call C<ev_loop> or similar functions that enter
1933	the current event loop from either C<ev_prepare> or C<ev_check>	2627	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1936	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2630	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1937	C<ev_check> so if you have one watcher of each kind they will always be	2631	C<ev_check> so if you have one watcher of each kind they will always be
1938	called in pairs bracketing the blocking call.	2632	called in pairs bracketing the blocking call.
1939		2633
1940	Their main purpose is to integrate other event mechanisms into libev and	2634	Their main purpose is to integrate other event mechanisms into libev and
1941	their use is somewhat advanced. This could be used, for example, to track	2635	their use is somewhat advanced. They could be used, for example, to track
1942	variable changes, implement your own watchers, integrate net-snmp or a	2636	variable changes, implement your own watchers, integrate net-snmp or a
1943	coroutine library and lots more. They are also occasionally useful if	2637	coroutine library and lots more. They are also occasionally useful if
1944	you cache some data and want to flush it before blocking (for example,	2638	you cache some data and want to flush it before blocking (for example,
1945	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2639	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1946	watcher).	2640	watcher).
1947		2641
1948	This is done by examining in each prepare call which file descriptors need	2642	This is done by examining in each prepare call which file descriptors
1949	to be watched by the other library, registering C<ev_io> watchers for	2643	need to be watched by the other library, registering C<ev_io> watchers
1950	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2644	for them and starting an C<ev_timer> watcher for any timeouts (many
1951	provide just this functionality). Then, in the check watcher you check for	2645	libraries provide exactly this functionality). Then, in the check watcher,
1952	any events that occurred (by checking the pending status of all watchers	2646	you check for any events that occurred (by checking the pending status
1953	and stopping them) and call back into the library. The I/O and timer	2647	of all watchers and stopping them) and call back into the library. The
1954	callbacks will never actually be called (but must be valid nevertheless,	2648	I/O and timer callbacks will never actually be called (but must be valid
1955	because you never know, you know?).	2649	nevertheless, because you never know, you know?).
1956		2650
1957	As another example, the Perl Coro module uses these hooks to integrate	2651	As another example, the Perl Coro module uses these hooks to integrate
1958	coroutines into libev programs, by yielding to other active coroutines	2652	coroutines into libev programs, by yielding to other active coroutines
1959	during each prepare and only letting the process block if no coroutines	2653	during each prepare and only letting the process block if no coroutines
1960	are ready to run (it's actually more complicated: it only runs coroutines	2654	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1963	loop from blocking if lower-priority coroutines are active, thus mapping	2657	loop from blocking if lower-priority coroutines are active, thus mapping
1964	low-priority coroutines to idle/background tasks).	2658	low-priority coroutines to idle/background tasks).
1965		2659
1966	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2660	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1967	priority, to ensure that they are being run before any other watchers	2661	priority, to ensure that they are being run before any other watchers
		2662	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2663
1968	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2664	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1969	too) should not activate ("feed") events into libev. While libev fully	2665	activate ("feed") events into libev. While libev fully supports this, they
1970	supports this, they might get executed before other C<ev_check> watchers	2666	might get executed before other C<ev_check> watchers did their job. As
1971	did their job. As C<ev_check> watchers are often used to embed other	2667	C<ev_check> watchers are often used to embed other (non-libev) event
1972	(non-libev) event loops those other event loops might be in an unusable	2668	loops those other event loops might be in an unusable state until their
1973	state until their C<ev_check> watcher ran (always remind yourself to	2669	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1974	coexist peacefully with others).	2670	others).
1975		2671
1976	=head3 Watcher-Specific Functions and Data Members	2672	=head3 Watcher-Specific Functions and Data Members
1977		2673
1978	=over 4	2674	=over 4
1979		2675
…		…
1981		2677
1982	=item ev_check_init (ev_check *, callback)	2678	=item ev_check_init (ev_check *, callback)
1983		2679
1984	Initialises and configures the prepare or check watcher - they have no	2680	Initialises and configures the prepare or check watcher - they have no
1985	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2681	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1986	macros, but using them is utterly, utterly and completely pointless.	2682	macros, but using them is utterly, utterly, utterly and completely
		2683	pointless.
1987		2684
1988	=back	2685	=back
1989		2686
1990	=head3 Examples	2687	=head3 Examples
1991		2688
…		…
2004		2701
2005	static ev_io iow [nfd];	2702	static ev_io iow [nfd];
2006	static ev_timer tw;	2703	static ev_timer tw;
2007		2704
2008	static void	2705	static void
2009	io_cb (ev_loop *loop, ev_io *w, int revents)	2706	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2010	{	2707	{
2011	}	2708	}
2012		2709
2013	// create io watchers for each fd and a timer before blocking	2710	// create io watchers for each fd and a timer before blocking
2014	static void	2711	static void
2015	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2712	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2016	{	2713	{
2017	int timeout = 3600000;	2714	int timeout = 3600000;
2018	struct pollfd fds [nfd];	2715	struct pollfd fds [nfd];
2019	// actual code will need to loop here and realloc etc.	2716	// actual code will need to loop here and realloc etc.
2020	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2717	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2021		2718
2022	/* the callback is illegal, but won't be called as we stop during check */	2719	/* the callback is illegal, but won't be called as we stop during check */
2023	ev_timer_init (&tw, 0, timeout * 1e-3);	2720	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
2024	ev_timer_start (loop, &tw);	2721	ev_timer_start (loop, &tw);
2025		2722
2026	// create one ev_io per pollfd	2723	// create one ev_io per pollfd
2027	for (int i = 0; i < nfd; ++i)	2724	for (int i = 0; i < nfd; ++i)
2028	{	2725	{
…		…
2035	}	2732	}
2036	}	2733	}
2037		2734
2038	// stop all watchers after blocking	2735	// stop all watchers after blocking
2039	static void	2736	static void
2040	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2737	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2041	{	2738	{
2042	ev_timer_stop (loop, &tw);	2739	ev_timer_stop (loop, &tw);
2043		2740
2044	for (int i = 0; i < nfd; ++i)	2741	for (int i = 0; i < nfd; ++i)
2045	{	2742	{
…		…
2084	}	2781	}
2085		2782
2086	// do not ever call adns_afterpoll	2783	// do not ever call adns_afterpoll
2087		2784
2088	Method 4: Do not use a prepare or check watcher because the module you	2785	Method 4: Do not use a prepare or check watcher because the module you
2089	want to embed is too inflexible to support it. Instead, you can override	2786	want to embed is not flexible enough to support it. Instead, you can
2090	their poll function. The drawback with this solution is that the main	2787	override their poll function. The drawback with this solution is that the
2091	loop is now no longer controllable by EV. The C<Glib::EV> module does	2788	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2092	this.	2789	this approach, effectively embedding EV as a client into the horrible
		2790	libglib event loop.
2093		2791
2094	static gint	2792	static gint
2095	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2793	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2096	{	2794	{
2097	int got_events = 0;	2795	int got_events = 0;
…		…
2128	prioritise I/O.	2826	prioritise I/O.
2129		2827
2130	As an example for a bug workaround, the kqueue backend might only support	2828	As an example for a bug workaround, the kqueue backend might only support
2131	sockets on some platform, so it is unusable as generic backend, but you	2829	sockets on some platform, so it is unusable as generic backend, but you
2132	still want to make use of it because you have many sockets and it scales	2830	still want to make use of it because you have many sockets and it scales
2133	so nicely. In this case, you would create a kqueue-based loop and embed it	2831	so nicely. In this case, you would create a kqueue-based loop and embed
2134	into your default loop (which might use e.g. poll). Overall operation will	2832	it into your default loop (which might use e.g. poll). Overall operation
2135	be a bit slower because first libev has to poll and then call kevent, but	2833	will be a bit slower because first libev has to call C<poll> and then
2136	at least you can use both at what they are best.	2834	C<kevent>, but at least you can use both mechanisms for what they are
		2835	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2137		2836
2138	As for prioritising I/O: rarely you have the case where some fds have	2837	As for prioritising I/O: under rare circumstances you have the case where
2139	to be watched and handled very quickly (with low latency), and even	2838	some fds have to be watched and handled very quickly (with low latency),
2140	priorities and idle watchers might have too much overhead. In this case	2839	and even priorities and idle watchers might have too much overhead. In
2141	you would put all the high priority stuff in one loop and all the rest in	2840	this case you would put all the high priority stuff in one loop and all
2142	a second one, and embed the second one in the first.	2841	the rest in a second one, and embed the second one in the first.
2143		2842
2144	As long as the watcher is active, the callback will be invoked every time	2843	As long as the watcher is active, the callback will be invoked every
2145	there might be events pending in the embedded loop. The callback must then	2844	time there might be events pending in the embedded loop. The callback
2146	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2845	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2147	their callbacks (you could also start an idle watcher to give the embedded	2846	sweep and invoke their callbacks (the callback doesn't need to invoke the
2148	loop strictly lower priority for example). You can also set the callback	2847	C<ev_embed_sweep> function directly, it could also start an idle watcher
2149	to C<0>, in which case the embed watcher will automatically execute the	2848	to give the embedded loop strictly lower priority for example).
2150	embedded loop sweep.
2151		2849
2152	As long as the watcher is started it will automatically handle events. The	2850	You can also set the callback to C<0>, in which case the embed watcher
2153	callback will be invoked whenever some events have been handled. You can	2851	will automatically execute the embedded loop sweep whenever necessary.
2154	set the callback to C<0> to avoid having to specify one if you are not
2155	interested in that.
2156		2852
2157	Also, there have not currently been made special provisions for forking:	2853	Fork detection will be handled transparently while the C<ev_embed> watcher
2158	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2854	is active, i.e., the embedded loop will automatically be forked when the
2159	but you will also have to stop and restart any C<ev_embed> watchers	2855	embedding loop forks. In other cases, the user is responsible for calling
2160	yourself.	2856	C<ev_loop_fork> on the embedded loop.
2161		2857
2162	Unfortunately, not all backends are embeddable, only the ones returned by	2858	Unfortunately, not all backends are embeddable: only the ones returned by
2163	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2859	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2164	portable one.	2860	portable one.
2165		2861
2166	So when you want to use this feature you will always have to be prepared	2862	So when you want to use this feature you will always have to be prepared
2167	that you cannot get an embeddable loop. The recommended way to get around	2863	that you cannot get an embeddable loop. The recommended way to get around
2168	this is to have a separate variables for your embeddable loop, try to	2864	this is to have a separate variables for your embeddable loop, try to
2169	create it, and if that fails, use the normal loop for everything.	2865	create it, and if that fails, use the normal loop for everything.
		2866
		2867	=head3 C<ev_embed> and fork
		2868
		2869	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2870	automatically be applied to the embedded loop as well, so no special
		2871	fork handling is required in that case. When the watcher is not running,
		2872	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2873	as applicable.
2170		2874
2171	=head3 Watcher-Specific Functions and Data Members	2875	=head3 Watcher-Specific Functions and Data Members
2172		2876
2173	=over 4	2877	=over 4
2174		2878
…		…
2202	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2906	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2203	used).	2907	used).
2204		2908
2205	struct ev_loop *loop_hi = ev_default_init (0);	2909	struct ev_loop *loop_hi = ev_default_init (0);
2206	struct ev_loop *loop_lo = 0;	2910	struct ev_loop *loop_lo = 0;
2207	struct ev_embed embed;	2911	ev_embed embed;
2208		2912
2209	// see if there is a chance of getting one that works	2913	// see if there is a chance of getting one that works
2210	// (remember that a flags value of 0 means autodetection)	2914	// (remember that a flags value of 0 means autodetection)
2211	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2915	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2212	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2916	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2226	kqueue implementation). Store the kqueue/socket-only event loop in	2930	kqueue implementation). Store the kqueue/socket-only event loop in
2227	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2931	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2228		2932
2229	struct ev_loop *loop = ev_default_init (0);	2933	struct ev_loop *loop = ev_default_init (0);
2230	struct ev_loop *loop_socket = 0;	2934	struct ev_loop *loop_socket = 0;
2231	struct ev_embed embed;	2935	ev_embed embed;
2232		2936
2233	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2937	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2234	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2938	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2235	{	2939	{
2236	ev_embed_init (&embed, 0, loop_socket);	2940	ev_embed_init (&embed, 0, loop_socket);
…		…
2251	event loop blocks next and before C<ev_check> watchers are being called,	2955	event loop blocks next and before C<ev_check> watchers are being called,
2252	and only in the child after the fork. If whoever good citizen calling	2956	and only in the child after the fork. If whoever good citizen calling
2253	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2957	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2254	handlers will be invoked, too, of course.	2958	handlers will be invoked, too, of course.
2255		2959
		2960	=head3 The special problem of life after fork - how is it possible?
		2961
		2962	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2963	up/change the process environment, followed by a call to C<exec()>. This
		2964	sequence should be handled by libev without any problems.
		2965
		2966	This changes when the application actually wants to do event handling
		2967	in the child, or both parent in child, in effect "continuing" after the
		2968	fork.
		2969
		2970	The default mode of operation (for libev, with application help to detect
		2971	forks) is to duplicate all the state in the child, as would be expected
		2972	when I<either> the parent I<or> the child process continues.
		2973
		2974	When both processes want to continue using libev, then this is usually the
		2975	wrong result. In that case, usually one process (typically the parent) is
		2976	supposed to continue with all watchers in place as before, while the other
		2977	process typically wants to start fresh, i.e. without any active watchers.
		2978
		2979	The cleanest and most efficient way to achieve that with libev is to
		2980	simply create a new event loop, which of course will be "empty", and
		2981	use that for new watchers. This has the advantage of not touching more
		2982	memory than necessary, and thus avoiding the copy-on-write, and the
		2983	disadvantage of having to use multiple event loops (which do not support
		2984	signal watchers).
		2985
		2986	When this is not possible, or you want to use the default loop for
		2987	other reasons, then in the process that wants to start "fresh", call
		2988	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2989	the default loop will "orphan" (not stop) all registered watchers, so you
		2990	have to be careful not to execute code that modifies those watchers. Note
		2991	also that in that case, you have to re-register any signal watchers.
		2992
2256	=head3 Watcher-Specific Functions and Data Members	2993	=head3 Watcher-Specific Functions and Data Members
2257		2994
2258	=over 4	2995	=over 4
2259		2996
2260	=item ev_fork_init (ev_signal *, callback)	2997	=item ev_fork_init (ev_signal *, callback)
…		…
2289	=head3 Queueing	3026	=head3 Queueing
2290		3027
2291	C<ev_async> does not support queueing of data in any way. The reason	3028	C<ev_async> does not support queueing of data in any way. The reason
2292	is that the author does not know of a simple (or any) algorithm for a	3029	is that the author does not know of a simple (or any) algorithm for a
2293	multiple-writer-single-reader queue that works in all cases and doesn't	3030	multiple-writer-single-reader queue that works in all cases and doesn't
2294	need elaborate support such as pthreads.	3031	need elaborate support such as pthreads or unportable memory access
		3032	semantics.
2295		3033
2296	That means that if you want to queue data, you have to provide your own	3034	That means that if you want to queue data, you have to provide your own
2297	queue. But at least I can tell you would implement locking around your	3035	queue. But at least I can tell you how to implement locking around your
2298	queue:	3036	queue:
2299		3037
2300	=over 4	3038	=over 4
2301		3039
2302	=item queueing from a signal handler context	3040	=item queueing from a signal handler context
2303		3041
2304	To implement race-free queueing, you simply add to the queue in the signal	3042	To implement race-free queueing, you simply add to the queue in the signal
2305	handler but you block the signal handler in the watcher callback. Here is an example that does that for	3043	handler but you block the signal handler in the watcher callback. Here is
2306	some fictitious SIGUSR1 handler:	3044	an example that does that for some fictitious SIGUSR1 handler:
2307		3045
2308	static ev_async mysig;	3046	static ev_async mysig;
2309		3047
2310	static void	3048	static void
2311	sigusr1_handler (void)	3049	sigusr1_handler (void)
…		…
2377	=over 4	3115	=over 4
2378		3116
2379	=item ev_async_init (ev_async *, callback)	3117	=item ev_async_init (ev_async *, callback)
2380		3118
2381	Initialises and configures the async watcher - it has no parameters of any	3119	Initialises and configures the async watcher - it has no parameters of any
2382	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3120	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2383	believe me.	3121	trust me.
2384		3122
2385	=item ev_async_send (loop, ev_async *)	3123	=item ev_async_send (loop, ev_async *)
2386		3124
2387	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3125	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2388	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3126	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2389	C<ev_feed_event>, this call is safe to do in other threads, signal or	3127	C<ev_feed_event>, this call is safe to do from other threads, signal or
2390	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3128	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2391	section below on what exactly this means).	3129	section below on what exactly this means).
2392		3130
		3131	Note that, as with other watchers in libev, multiple events might get
		3132	compressed into a single callback invocation (another way to look at this
		3133	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3134	reset when the event loop detects that).
		3135
2393	This call incurs the overhead of a system call only once per loop iteration,	3136	This call incurs the overhead of a system call only once per event loop
2394	so while the overhead might be noticeable, it doesn't apply to repeated	3137	iteration, so while the overhead might be noticeable, it doesn't apply to
2395	calls to C<ev_async_send>.	3138	repeated calls to C<ev_async_send> for the same event loop.
2396		3139
2397	=item bool = ev_async_pending (ev_async *)	3140	=item bool = ev_async_pending (ev_async *)
2398		3141
2399	Returns a non-zero value when C<ev_async_send> has been called on the	3142	Returns a non-zero value when C<ev_async_send> has been called on the
2400	watcher but the event has not yet been processed (or even noted) by the	3143	watcher but the event has not yet been processed (or even noted) by the
…		…
2403	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3146	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2404	the loop iterates next and checks for the watcher to have become active,	3147	the loop iterates next and checks for the watcher to have become active,
2405	it will reset the flag again. C<ev_async_pending> can be used to very	3148	it will reset the flag again. C<ev_async_pending> can be used to very
2406	quickly check whether invoking the loop might be a good idea.	3149	quickly check whether invoking the loop might be a good idea.
2407		3150
2408	Not that this does I<not> check whether the watcher itself is pending, only	3151	Not that this does I<not> check whether the watcher itself is pending,
2409	whether it has been requested to make this watcher pending.	3152	only whether it has been requested to make this watcher pending: there
		3153	is a time window between the event loop checking and resetting the async
		3154	notification, and the callback being invoked.
2410		3155
2411	=back	3156	=back
2412		3157
2413		3158
2414	=head1 OTHER FUNCTIONS	3159	=head1 OTHER FUNCTIONS
…		…
2418	=over 4	3163	=over 4
2419		3164
2420	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3165	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2421		3166
2422	This function combines a simple timer and an I/O watcher, calls your	3167	This function combines a simple timer and an I/O watcher, calls your
2423	callback on whichever event happens first and automatically stop both	3168	callback on whichever event happens first and automatically stops both
2424	watchers. This is useful if you want to wait for a single event on an fd	3169	watchers. This is useful if you want to wait for a single event on an fd
2425	or timeout without having to allocate/configure/start/stop/free one or	3170	or timeout without having to allocate/configure/start/stop/free one or
2426	more watchers yourself.	3171	more watchers yourself.
2427		3172
2428	If C<fd> is less than 0, then no I/O watcher will be started and events	3173	If C<fd> is less than 0, then no I/O watcher will be started and the
2429	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3174	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2430	C<events> set will be created and started.	3175	the given C<fd> and C<events> set will be created and started.
2431		3176
2432	If C<timeout> is less than 0, then no timeout watcher will be	3177	If C<timeout> is less than 0, then no timeout watcher will be
2433	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3178	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2434	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3179	repeat = 0) will be started. C<0> is a valid timeout.
2435	dubious value.
2436		3180
2437	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3181	The callback has the type C<void (*cb)(int revents, void *arg)> and is
2438	passed an C<revents> set like normal event callbacks (a combination of	3182	passed an C<revents> set like normal event callbacks (a combination of
2439	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3183	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMER>) and the C<arg>
2440	value passed to C<ev_once>:	3184	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3185	a timeout and an io event at the same time - you probably should give io
		3186	events precedence.
		3187
		3188	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2441		3189
2442	static void stdin_ready (int revents, void *arg)	3190	static void stdin_ready (int revents, void *arg)
2443	{	3191	{
		3192	if (revents & EV_READ)
		3193	/* stdin might have data for us, joy! */;
2444	if (revents & EV_TIMEOUT)	3194	else if (revents & EV_TIMER)
2445	/* doh, nothing entered */;	3195	/* doh, nothing entered */;
2446	else if (revents & EV_READ)
2447	/* stdin might have data for us, joy! */;
2448	}	3196	}
2449		3197
2450	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3198	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2451		3199
2452	=item ev_feed_event (ev_loop *, watcher *, int revents)
2453
2454	Feeds the given event set into the event loop, as if the specified event
2455	had happened for the specified watcher (which must be a pointer to an
2456	initialised but not necessarily started event watcher).
2457
2458	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3200	=item ev_feed_fd_event (loop, int fd, int revents)
2459		3201
2460	Feed an event on the given fd, as if a file descriptor backend detected	3202	Feed an event on the given fd, as if a file descriptor backend detected
2461	the given events it.	3203	the given events it.
2462		3204
2463	=item ev_feed_signal_event (ev_loop *loop, int signum)	3205	=item ev_feed_signal_event (loop, int signum)
2464		3206
2465	Feed an event as if the given signal occurred (C<loop> must be the default	3207	Feed an event as if the given signal occurred (C<loop> must be the default
2466	loop!).	3208	loop!).
2467		3209
2468	=back	3210	=back
…		…
2548		3290
2549	=over 4	3291	=over 4
2550		3292
2551	=item ev::TYPE::TYPE ()	3293	=item ev::TYPE::TYPE ()
2552		3294
2553	=item ev::TYPE::TYPE (struct ev_loop *)	3295	=item ev::TYPE::TYPE (loop)
2554		3296
2555	=item ev::TYPE::~TYPE	3297	=item ev::TYPE::~TYPE
2556		3298
2557	The constructor (optionally) takes an event loop to associate the watcher	3299	The constructor (optionally) takes an event loop to associate the watcher
2558	with. If it is omitted, it will use C<EV_DEFAULT>.	3300	with. If it is omitted, it will use C<EV_DEFAULT>.
…		…
2590		3332
2591	myclass obj;	3333	myclass obj;
2592	ev::io iow;	3334	ev::io iow;
2593	iow.set <myclass, &myclass::io_cb> (&obj);	3335	iow.set <myclass, &myclass::io_cb> (&obj);
2594		3336
		3337	=item w->set (object *)
		3338
		3339	This is an B<experimental> feature that might go away in a future version.
		3340
		3341	This is a variation of a method callback - leaving out the method to call
		3342	will default the method to C<operator ()>, which makes it possible to use
		3343	functor objects without having to manually specify the C<operator ()> all
		3344	the time. Incidentally, you can then also leave out the template argument
		3345	list.
		3346
		3347	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3348	int revents)>.
		3349
		3350	See the method-C<set> above for more details.
		3351
		3352	Example: use a functor object as callback.
		3353
		3354	struct myfunctor
		3355	{
		3356	void operator() (ev::io &w, int revents)
		3357	{
		3358	...
		3359	}
		3360	}
		3361
		3362	myfunctor f;
		3363
		3364	ev::io w;
		3365	w.set (&f);
		3366
2595	=item w->set<function> (void *data = 0)	3367	=item w->set<function> (void *data = 0)
2596		3368
2597	Also sets a callback, but uses a static method or plain function as	3369	Also sets a callback, but uses a static method or plain function as
2598	callback. The optional C<data> argument will be stored in the watcher's	3370	callback. The optional C<data> argument will be stored in the watcher's
2599	C<data> member and is free for you to use.	3371	C<data> member and is free for you to use.
2600		3372
2601	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3373	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2602		3374
2603	See the method-C<set> above for more details.	3375	See the method-C<set> above for more details.
2604		3376
2605	Example:	3377	Example: Use a plain function as callback.
2606		3378
2607	static void io_cb (ev::io &w, int revents) { }	3379	static void io_cb (ev::io &w, int revents) { }
2608	iow.set <io_cb> ();	3380	iow.set <io_cb> ();
2609		3381
2610	=item w->set (struct ev_loop *)	3382	=item w->set (loop)
2611		3383
2612	Associates a different C<struct ev_loop> with this watcher. You can only	3384	Associates a different C<struct ev_loop> with this watcher. You can only
2613	do this when the watcher is inactive (and not pending either).	3385	do this when the watcher is inactive (and not pending either).
2614		3386
2615	=item w->set ([arguments])	3387	=item w->set ([arguments])
…		…
2648	Example: Define a class with an IO and idle watcher, start one of them in	3420	Example: Define a class with an IO and idle watcher, start one of them in
2649	the constructor.	3421	the constructor.
2650		3422
2651	class myclass	3423	class myclass
2652	{	3424	{
2653	ev::io io; void io_cb (ev::io &w, int revents);	3425	ev::io io ; void io_cb (ev::io &w, int revents);
2654	ev:idle idle void idle_cb (ev::idle &w, int revents);	3426	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2655		3427
2656	myclass (int fd)	3428	myclass (int fd)
2657	{	3429	{
2658	io .set <myclass, &myclass::io_cb > (this);	3430	io .set <myclass, &myclass::io_cb > (this);
2659	idle.set <myclass, &myclass::idle_cb> (this);	3431	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2675	=item Perl	3447	=item Perl
2676		3448
2677	The EV module implements the full libev API and is actually used to test	3449	The EV module implements the full libev API and is actually used to test
2678	libev. EV is developed together with libev. Apart from the EV core module,	3450	libev. EV is developed together with libev. Apart from the EV core module,
2679	there are additional modules that implement libev-compatible interfaces	3451	there are additional modules that implement libev-compatible interfaces
2680	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3452	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2681	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3453	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3454	and C<EV::Glib>).
2682		3455
2683	It can be found and installed via CPAN, its homepage is at	3456	It can be found and installed via CPAN, its homepage is at
2684	L<http://software.schmorp.de/pkg/EV>.	3457	L<http://software.schmorp.de/pkg/EV>.
2685		3458
2686	=item Python	3459	=item Python
2687		3460
2688	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3461	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2689	seems to be quite complete and well-documented. Note, however, that the	3462	seems to be quite complete and well-documented.
2690	patch they require for libev is outright dangerous as it breaks the ABI
2691	for everybody else, and therefore, should never be applied in an installed
2692	libev (if python requires an incompatible ABI then it needs to embed
2693	libev).
2694		3463
2695	=item Ruby	3464	=item Ruby
2696		3465
2697	Tony Arcieri has written a ruby extension that offers access to a subset	3466	Tony Arcieri has written a ruby extension that offers access to a subset
2698	of the libev API and adds file handle abstractions, asynchronous DNS and	3467	of the libev API and adds file handle abstractions, asynchronous DNS and
2699	more on top of it. It can be found via gem servers. Its homepage is at	3468	more on top of it. It can be found via gem servers. Its homepage is at
2700	L<http://rev.rubyforge.org/>.	3469	L<http://rev.rubyforge.org/>.
2701		3470
		3471	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3472	makes rev work even on mingw.
		3473
		3474	=item Haskell
		3475
		3476	A haskell binding to libev is available at
		3477	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3478
2702	=item D	3479	=item D
2703		3480
2704	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3481	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2705	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3482	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3483
		3484	=item Ocaml
		3485
		3486	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3487	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3488
		3489	=item Lua
		3490
		3491	Brian Maher has written a partial interface to libev for lua (at the
		3492	time of this writing, only C<ev_io> and C<ev_timer>), to be found at
		3493	L<http://github.com/brimworks/lua-ev>.
2706		3494
2707	=back	3495	=back
2708		3496
2709		3497
2710	=head1 MACRO MAGIC	3498	=head1 MACRO MAGIC
…		…
2811		3599
2812	#define EV_STANDALONE 1	3600	#define EV_STANDALONE 1
2813	#include "ev.h"	3601	#include "ev.h"
2814		3602
2815	Both header files and implementation files can be compiled with a C++	3603	Both header files and implementation files can be compiled with a C++
2816	compiler (at least, thats a stated goal, and breakage will be treated	3604	compiler (at least, that's a stated goal, and breakage will be treated
2817	as a bug).	3605	as a bug).
2818		3606
2819	You need the following files in your source tree, or in a directory	3607	You need the following files in your source tree, or in a directory
2820	in your include path (e.g. in libev/ when using -Ilibev):	3608	in your include path (e.g. in libev/ when using -Ilibev):
2821		3609
…		…
2864	libev.m4	3652	libev.m4
2865		3653
2866	=head2 PREPROCESSOR SYMBOLS/MACROS	3654	=head2 PREPROCESSOR SYMBOLS/MACROS
2867		3655
2868	Libev can be configured via a variety of preprocessor symbols you have to	3656	Libev can be configured via a variety of preprocessor symbols you have to
2869	define before including any of its files. The default in the absence of	3657	define before including (or compiling) any of its files. The default in
2870	autoconf is noted for every option.	3658	the absence of autoconf is documented for every option.
		3659
		3660	Symbols marked with "(h)" do not change the ABI, and can have different
		3661	values when compiling libev vs. including F<ev.h>, so it is permissible
		3662	to redefine them before including F<ev.h> without breakign compatibility
		3663	to a compiled library. All other symbols change the ABI, which means all
		3664	users of libev and the libev code itself must be compiled with compatible
		3665	settings.
2871		3666
2872	=over 4	3667	=over 4
2873		3668
2874	=item EV_STANDALONE	3669	=item EV_STANDALONE (h)
2875		3670
2876	Must always be C<1> if you do not use autoconf configuration, which	3671	Must always be C<1> if you do not use autoconf configuration, which
2877	keeps libev from including F<config.h>, and it also defines dummy	3672	keeps libev from including F<config.h>, and it also defines dummy
2878	implementations for some libevent functions (such as logging, which is not	3673	implementations for some libevent functions (such as logging, which is not
2879	supported). It will also not define any of the structs usually found in	3674	supported). It will also not define any of the structs usually found in
2880	F<event.h> that are not directly supported by the libev core alone.	3675	F<event.h> that are not directly supported by the libev core alone.
2881		3676
		3677	In standalone mode, libev will still try to automatically deduce the
		3678	configuration, but has to be more conservative.
		3679
2882	=item EV_USE_MONOTONIC	3680	=item EV_USE_MONOTONIC
2883		3681
2884	If defined to be C<1>, libev will try to detect the availability of the	3682	If defined to be C<1>, libev will try to detect the availability of the
2885	monotonic clock option at both compile time and runtime. Otherwise no use	3683	monotonic clock option at both compile time and runtime. Otherwise no
2886	of the monotonic clock option will be attempted. If you enable this, you	3684	use of the monotonic clock option will be attempted. If you enable this,
2887	usually have to link against librt or something similar. Enabling it when	3685	you usually have to link against librt or something similar. Enabling it
2888	the functionality isn't available is safe, though, although you have	3686	when the functionality isn't available is safe, though, although you have
2889	to make sure you link against any libraries where the C<clock_gettime>	3687	to make sure you link against any libraries where the C<clock_gettime>
2890	function is hiding in (often F<-lrt>).	3688	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2891		3689
2892	=item EV_USE_REALTIME	3690	=item EV_USE_REALTIME
2893		3691
2894	If defined to be C<1>, libev will try to detect the availability of the	3692	If defined to be C<1>, libev will try to detect the availability of the
2895	real-time clock option at compile time (and assume its availability at	3693	real-time clock option at compile time (and assume its availability
2896	runtime if successful). Otherwise no use of the real-time clock option will	3694	at runtime if successful). Otherwise no use of the real-time clock
2897	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3695	option will be attempted. This effectively replaces C<gettimeofday>
2898	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3696	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2899	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3697	correctness. See the note about libraries in the description of
		3698	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3699	C<EV_USE_CLOCK_SYSCALL>.
		3700
		3701	=item EV_USE_CLOCK_SYSCALL
		3702
		3703	If defined to be C<1>, libev will try to use a direct syscall instead
		3704	of calling the system-provided C<clock_gettime> function. This option
		3705	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3706	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3707	programs needlessly. Using a direct syscall is slightly slower (in
		3708	theory), because no optimised vdso implementation can be used, but avoids
		3709	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3710	higher, as it simplifies linking (no need for C<-lrt>).
2900		3711
2901	=item EV_USE_NANOSLEEP	3712	=item EV_USE_NANOSLEEP
2902		3713
2903	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3714	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2904	and will use it for delays. Otherwise it will use C<select ()>.	3715	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2920		3731
2921	=item EV_SELECT_USE_FD_SET	3732	=item EV_SELECT_USE_FD_SET
2922		3733
2923	If defined to C<1>, then the select backend will use the system C<fd_set>	3734	If defined to C<1>, then the select backend will use the system C<fd_set>
2924	structure. This is useful if libev doesn't compile due to a missing	3735	structure. This is useful if libev doesn't compile due to a missing
2925	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3736	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2926	exotic systems. This usually limits the range of file descriptors to some	3737	on exotic systems. This usually limits the range of file descriptors to
2927	low limit such as 1024 or might have other limitations (winsocket only	3738	some low limit such as 1024 or might have other limitations (winsocket
2928	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3739	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2929	influence the size of the C<fd_set> used.	3740	configures the maximum size of the C<fd_set>.
2930		3741
2931	=item EV_SELECT_IS_WINSOCKET	3742	=item EV_SELECT_IS_WINSOCKET
2932		3743
2933	When defined to C<1>, the select backend will assume that	3744	When defined to C<1>, the select backend will assume that
2934	select/socket/connect etc. don't understand file descriptors but	3745	select/socket/connect etc. don't understand file descriptors but
…		…
2936	be used is the winsock select). This means that it will call	3747	be used is the winsock select). This means that it will call
2937	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3748	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2938	it is assumed that all these functions actually work on fds, even	3749	it is assumed that all these functions actually work on fds, even
2939	on win32. Should not be defined on non-win32 platforms.	3750	on win32. Should not be defined on non-win32 platforms.
2940		3751
2941	=item EV_FD_TO_WIN32_HANDLE	3752	=item EV_FD_TO_WIN32_HANDLE(fd)
2942		3753
2943	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map	3754	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
2944	file descriptors to socket handles. When not defining this symbol (the	3755	file descriptors to socket handles. When not defining this symbol (the
2945	default), then libev will call C<_get_osfhandle>, which is usually	3756	default), then libev will call C<_get_osfhandle>, which is usually
2946	correct. In some cases, programs use their own file descriptor management,	3757	correct. In some cases, programs use their own file descriptor management,
2947	in which case they can provide this function to map fds to socket handles.	3758	in which case they can provide this function to map fds to socket handles.
		3759
		3760	=item EV_WIN32_HANDLE_TO_FD(handle)
		3761
		3762	If C<EV_SELECT_IS_WINSOCKET> then libev maps handles to file descriptors
		3763	using the standard C<_open_osfhandle> function. For programs implementing
		3764	their own fd to handle mapping, overwriting this function makes it easier
		3765	to do so. This can be done by defining this macro to an appropriate value.
		3766
		3767	=item EV_WIN32_CLOSE_FD(fd)
		3768
		3769	If programs implement their own fd to handle mapping on win32, then this
		3770	macro can be used to override the C<close> function, useful to unregister
		3771	file descriptors again. Note that the replacement function has to close
		3772	the underlying OS handle.
2948		3773
2949	=item EV_USE_POLL	3774	=item EV_USE_POLL
2950		3775
2951	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3776	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2952	backend. Otherwise it will be enabled on non-win32 platforms. It	3777	backend. Otherwise it will be enabled on non-win32 platforms. It
…		…
2999	as well as for signal and thread safety in C<ev_async> watchers.	3824	as well as for signal and thread safety in C<ev_async> watchers.
3000		3825
3001	In the absence of this define, libev will use C<sig_atomic_t volatile>	3826	In the absence of this define, libev will use C<sig_atomic_t volatile>
3002	(from F<signal.h>), which is usually good enough on most platforms.	3827	(from F<signal.h>), which is usually good enough on most platforms.
3003		3828
3004	=item EV_H	3829	=item EV_H (h)
3005		3830
3006	The name of the F<ev.h> header file used to include it. The default if	3831	The name of the F<ev.h> header file used to include it. The default if
3007	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be	3832	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
3008	used to virtually rename the F<ev.h> header file in case of conflicts.	3833	used to virtually rename the F<ev.h> header file in case of conflicts.
3009		3834
3010	=item EV_CONFIG_H	3835	=item EV_CONFIG_H (h)
3011		3836
3012	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3837	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
3013	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3838	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
3014	C<EV_H>, above.	3839	C<EV_H>, above.
3015		3840
3016	=item EV_EVENT_H	3841	=item EV_EVENT_H (h)
3017		3842
3018	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3843	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
3019	of how the F<event.h> header can be found, the default is C<"event.h">.	3844	of how the F<event.h> header can be found, the default is C<"event.h">.
3020		3845
3021	=item EV_PROTOTYPES	3846	=item EV_PROTOTYPES (h)
3022		3847
3023	If defined to be C<0>, then F<ev.h> will not define any function	3848	If defined to be C<0>, then F<ev.h> will not define any function
3024	prototypes, but still define all the structs and other symbols. This is	3849	prototypes, but still define all the structs and other symbols. This is
3025	occasionally useful if you want to provide your own wrapper functions	3850	occasionally useful if you want to provide your own wrapper functions
3026	around libev functions.	3851	around libev functions.
…		…
3045	When doing priority-based operations, libev usually has to linearly search	3870	When doing priority-based operations, libev usually has to linearly search
3046	all the priorities, so having many of them (hundreds) uses a lot of space	3871	all the priorities, so having many of them (hundreds) uses a lot of space
3047	and time, so using the defaults of five priorities (-2 .. +2) is usually	3872	and time, so using the defaults of five priorities (-2 .. +2) is usually
3048	fine.	3873	fine.
3049		3874
3050	If your embedding application does not need any priorities, defining these both to	3875	If your embedding application does not need any priorities, defining these
3051	C<0> will save some memory and CPU.	3876	both to C<0> will save some memory and CPU.
3052		3877
3053	=item EV_PERIODIC_ENABLE	3878	=item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE,
		3879	EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE,
		3880	EV_ASYNC_ENABLE, EV_CHILD_ENABLE.
3054		3881
3055	If undefined or defined to be C<1>, then periodic timers are supported. If	3882	If undefined or defined to be C<1> (and the platform supports it), then
3056	defined to be C<0>, then they are not. Disabling them saves a few kB of	3883	the respective watcher type is supported. If defined to be C<0>, then it
3057	code.	3884	is not. Disabling watcher types mainly saves codesize.
3058		3885
3059	=item EV_IDLE_ENABLE	3886	=item EV_FEATURES
3060
3061	If undefined or defined to be C<1>, then idle watchers are supported. If
3062	defined to be C<0>, then they are not. Disabling them saves a few kB of
3063	code.
3064
3065	=item EV_EMBED_ENABLE
3066
3067	If undefined or defined to be C<1>, then embed watchers are supported. If
3068	defined to be C<0>, then they are not.
3069
3070	=item EV_STAT_ENABLE
3071
3072	If undefined or defined to be C<1>, then stat watchers are supported. If
3073	defined to be C<0>, then they are not.
3074
3075	=item EV_FORK_ENABLE
3076
3077	If undefined or defined to be C<1>, then fork watchers are supported. If
3078	defined to be C<0>, then they are not.
3079
3080	=item EV_ASYNC_ENABLE
3081
3082	If undefined or defined to be C<1>, then async watchers are supported. If
3083	defined to be C<0>, then they are not.
3084
3085	=item EV_MINIMAL
3086		3887
3087	If you need to shave off some kilobytes of code at the expense of some	3888	If you need to shave off some kilobytes of code at the expense of some
3088	speed, define this symbol to C<1>. Currently this is used to override some	3889	speed (but with the full API), you can define this symbol to request
3089	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3890	certain subsets of functionality. The default is to enable all features
3090	much smaller 2-heap for timer management over the default 4-heap.	3891	that can be enabled on the platform.
		3892
		3893	A typical way to use this symbol is to define it to C<0> (or to a bitset
		3894	with some broad features you want) and then selectively re-enable
		3895	additional parts you want, for example if you want everything minimal,
		3896	but multiple event loop support, async and child watchers and the poll
		3897	backend, use this:
		3898
		3899	#define EV_FEATURES 0
		3900	#define EV_MULTIPLICITY 1
		3901	#define EV_USE_POLL 1
		3902	#define EV_CHILD_ENABLE 1
		3903	#define EV_ASYNC_ENABLE 1
		3904
		3905	The actual value is a bitset, it can be a combination of the following
		3906	values:
		3907
		3908	=over 4
		3909
		3910	=item C<1> - faster/larger code
		3911
		3912	Use larger code to speed up some operations.
		3913
		3914	Currently this is used to override some inlining decisions (enlarging the roughly
		3915	30% code size on amd64.
		3916
		3917	When optimising for size, use of compiler flags such as C<-Os> with
		3918	gcc recommended, as well as C<-DNDEBUG>, as libev contains a number of
		3919	assertions.
		3920
		3921	=item C<2> - faster/larger data structures
		3922
		3923	Replaces the small 2-heap for timer management by a faster 4-heap, larger
		3924	hash table sizes and so on. This will usually further increase codesize
		3925	and can additionally have an effect on the size of data structures at
		3926	runtime.
		3927
		3928	=item C<4> - full API configuration
		3929
		3930	This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and
		3931	enables multiplicity (C<EV_MULTIPLICITY>=1).
		3932
		3933	=item C<8> - full API
		3934
		3935	This enables a lot of the "lesser used" API functions. See C<ev.h> for
		3936	details on which parts of the API are still available without this
		3937	feature, and do not complain if this subset changes over time.
		3938
		3939	=item C<16> - enable all optional watcher types
		3940
		3941	Enables all optional watcher types. If you want to selectively enable
		3942	only some watcher types other than I/O and timers (e.g. prepare,
		3943	embed, async, child...) you can enable them manually by defining
		3944	C<EV_watchertype_ENABLE> to C<1> instead.
		3945
		3946	=item C<32> - enable all backends
		3947
		3948	This enables all backends - without this feature, you need to enable at
		3949	least one backend manually (C<EV_USE_SELECT> is a good choice).
		3950
		3951	=item C<64> - enable OS-specific "helper" APIs
		3952
		3953	Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
		3954	default.
		3955
		3956	=back
		3957
		3958	Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0>
		3959	reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
		3960	code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
		3961	watchers, timers and monotonic clock support.
		3962
		3963	With an intelligent-enough linker (gcc+binutils are intelligent enough
		3964	when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by
		3965	your program might be left out as well - a binary starting a timer and an
		3966	I/O watcher then might come out at only 5Kb.
		3967
		3968	=item EV_AVOID_STDIO
		3969
		3970	If this is set to C<1> at compiletime, then libev will avoid using stdio
		3971	functions (printf, scanf, perror etc.). This will increase the codesize
		3972	somewhat, but if your program doesn't otherwise depend on stdio and your
		3973	libc allows it, this avoids linking in the stdio library which is quite
		3974	big.
		3975
		3976	Note that error messages might become less precise when this option is
		3977	enabled.
		3978
		3979	=item EV_NSIG
		3980
		3981	The highest supported signal number, +1 (or, the number of
		3982	signals): Normally, libev tries to deduce the maximum number of signals
		3983	automatically, but sometimes this fails, in which case it can be
		3984	specified. Also, using a lower number than detected (C<32> should be
		3985	good for about any system in existance) can save some memory, as libev
		3986	statically allocates some 12-24 bytes per signal number.
3091		3987
3092	=item EV_PID_HASHSIZE	3988	=item EV_PID_HASHSIZE
3093		3989
3094	C<ev_child> watchers use a small hash table to distribute workload by	3990	C<ev_child> watchers use a small hash table to distribute workload by
3095	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3991	pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled),
3096	than enough. If you need to manage thousands of children you might want to	3992	usually more than enough. If you need to manage thousands of children you
3097	increase this value (I<must> be a power of two).	3993	might want to increase this value (I<must> be a power of two).
3098		3994
3099	=item EV_INOTIFY_HASHSIZE	3995	=item EV_INOTIFY_HASHSIZE
3100		3996
3101	C<ev_stat> watchers use a small hash table to distribute workload by	3997	C<ev_stat> watchers use a small hash table to distribute workload by
3102	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3998	inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES>
3103	usually more than enough. If you need to manage thousands of C<ev_stat>	3999	disabled), usually more than enough. If you need to manage thousands of
3104	watchers you might want to increase this value (I<must> be a power of	4000	C<ev_stat> watchers you might want to increase this value (I<must> be a
3105	two).	4001	power of two).
3106		4002
3107	=item EV_USE_4HEAP	4003	=item EV_USE_4HEAP
3108		4004
3109	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4005	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3110	timer and periodics heap, libev uses a 4-heap when this symbol is defined	4006	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3111	to C<1>. The 4-heap uses more complicated (longer) code but has	4007	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3112	noticeably faster performance with many (thousands) of watchers.	4008	faster performance with many (thousands) of watchers.
3113		4009
3114	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4010	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3115	(disabled).	4011	will be C<0>.
3116		4012
3117	=item EV_HEAP_CACHE_AT	4013	=item EV_HEAP_CACHE_AT
3118		4014
3119	Heaps are not very cache-efficient. To improve the cache-efficiency of the	4015	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3120	timer and periodics heap, libev can cache the timestamp (I<at>) within	4016	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3121	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	4017	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3122	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	4018	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3123	but avoids random read accesses on heap changes. This improves performance	4019	but avoids random read accesses on heap changes. This improves performance
3124	noticeably with with many (hundreds) of watchers.	4020	noticeably with many (hundreds) of watchers.
3125		4021
3126	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	4022	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3127	(disabled).	4023	will be C<0>.
3128		4024
3129	=item EV_VERIFY	4025	=item EV_VERIFY
3130		4026
3131	Controls how much internal verification (see C<ev_loop_verify ()>) will	4027	Controls how much internal verification (see C<ev_loop_verify ()>) will
3132	be done: If set to C<0>, no internal verification code will be compiled	4028	be done: If set to C<0>, no internal verification code will be compiled
…		…
3134	called. If set to C<2>, then the internal verification code will be	4030	called. If set to C<2>, then the internal verification code will be
3135	called once per loop, which can slow down libev. If set to C<3>, then the	4031	called once per loop, which can slow down libev. If set to C<3>, then the
3136	verification code will be called very frequently, which will slow down	4032	verification code will be called very frequently, which will slow down
3137	libev considerably.	4033	libev considerably.
3138		4034
3139	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	4035	The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it
3140	C<0.>	4036	will be C<0>.
3141		4037
3142	=item EV_COMMON	4038	=item EV_COMMON
3143		4039
3144	By default, all watchers have a C<void *data> member. By redefining	4040	By default, all watchers have a C<void *data> member. By redefining
3145	this macro to a something else you can include more and other types of	4041	this macro to a something else you can include more and other types of
…		…
3162	and the way callbacks are invoked and set. Must expand to a struct member	4058	and the way callbacks are invoked and set. Must expand to a struct member
3163	definition and a statement, respectively. See the F<ev.h> header file for	4059	definition and a statement, respectively. See the F<ev.h> header file for
3164	their default definitions. One possible use for overriding these is to	4060	their default definitions. One possible use for overriding these is to
3165	avoid the C<struct ev_loop *> as first argument in all cases, or to use	4061	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3166	method calls instead of plain function calls in C++.	4062	method calls instead of plain function calls in C++.
		4063
		4064	=back
3167		4065
3168	=head2 EXPORTED API SYMBOLS	4066	=head2 EXPORTED API SYMBOLS
3169		4067
3170	If you need to re-export the API (e.g. via a DLL) and you need a list of	4068	If you need to re-export the API (e.g. via a DLL) and you need a list of
3171	exported symbols, you can use the provided F<Symbol.*> files which list	4069	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3201	file.	4099	file.
3202		4100
3203	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	4101	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
3204	that everybody includes and which overrides some configure choices:	4102	that everybody includes and which overrides some configure choices:
3205		4103
3206	#define EV_MINIMAL 1	4104	#define EV_FEATURES 8
3207	#define EV_USE_POLL 0	4105	#define EV_USE_SELECT 1
3208	#define EV_MULTIPLICITY 0
3209	#define EV_PERIODIC_ENABLE 0	4106	#define EV_PREPARE_ENABLE 1
		4107	#define EV_IDLE_ENABLE 1
3210	#define EV_STAT_ENABLE 0	4108	#define EV_SIGNAL_ENABLE 1
3211	#define EV_FORK_ENABLE 0	4109	#define EV_CHILD_ENABLE 1
		4110	#define EV_USE_STDEXCEPT 0
3212	#define EV_CONFIG_H <config.h>	4111	#define EV_CONFIG_H <config.h>
3213	#define EV_MINPRI 0
3214	#define EV_MAXPRI 0
3215		4112
3216	#include "ev++.h"	4113	#include "ev++.h"
3217		4114
3218	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	4115	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3219		4116
3220	#include "ev_cpp.h"	4117	#include "ev_cpp.h"
3221	#include "ev.c"	4118	#include "ev.c"
3222		4119
		4120	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3223		4121
3224	=head1 THREADS AND COROUTINES	4122	=head2 THREADS AND COROUTINES
3225		4123
3226	=head2 THREADS	4124	=head3 THREADS
3227		4125
3228	Libev itself is completely thread-safe, but it uses no locking. This	4126	All libev functions are reentrant and thread-safe unless explicitly
		4127	documented otherwise, but libev implements no locking itself. This means
3229	means that you can use as many loops as you want in parallel, as long as	4128	that you can use as many loops as you want in parallel, as long as there
3230	only one thread ever calls into one libev function with the same loop	4129	are no concurrent calls into any libev function with the same loop
3231	parameter.	4130	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		4131	of course): libev guarantees that different event loops share no data
		4132	structures that need any locking.
3232		4133
3233	Or put differently: calls with different loop parameters can be done in	4134	Or to put it differently: calls with different loop parameters can be done
3234	parallel from multiple threads, calls with the same loop parameter must be	4135	concurrently from multiple threads, calls with the same loop parameter
3235	done serially (but can be done from different threads, as long as only one	4136	must be done serially (but can be done from different threads, as long as
3236	thread ever is inside a call at any point in time, e.g. by using a mutex	4137	only one thread ever is inside a call at any point in time, e.g. by using
3237	per loop).	4138	a mutex per loop).
		4139
		4140	Specifically to support threads (and signal handlers), libev implements
		4141	so-called C<ev_async> watchers, which allow some limited form of
		4142	concurrency on the same event loop, namely waking it up "from the
		4143	outside".
3238		4144
3239	If you want to know which design (one loop, locking, or multiple loops	4145	If you want to know which design (one loop, locking, or multiple loops
3240	without or something else still) is best for your problem, then I cannot	4146	without or something else still) is best for your problem, then I cannot
3241	help you. I can give some generic advice however:	4147	help you, but here is some generic advice:
3242		4148
3243	=over 4	4149	=over 4
3244		4150
3245	=item * most applications have a main thread: use the default libev loop	4151	=item * most applications have a main thread: use the default libev loop
3246	in that thread, or create a separate thread running only the default loop.	4152	in that thread, or create a separate thread running only the default loop.
…		…
3258		4164
3259	Choosing a model is hard - look around, learn, know that usually you can do	4165	Choosing a model is hard - look around, learn, know that usually you can do
3260	better than you currently do :-)	4166	better than you currently do :-)
3261		4167
3262	=item * often you need to talk to some other thread which blocks in the	4168	=item * often you need to talk to some other thread which blocks in the
		4169	event loop.
		4170
3263	event loop - C<ev_async> watchers can be used to wake them up from other	4171	C<ev_async> watchers can be used to wake them up from other threads safely
3264	threads safely (or from signal contexts...).	4172	(or from signal contexts...).
		4173
		4174	An example use would be to communicate signals or other events that only
		4175	work in the default loop by registering the signal watcher with the
		4176	default loop and triggering an C<ev_async> watcher from the default loop
		4177	watcher callback into the event loop interested in the signal.
3265		4178
3266	=back	4179	=back
3267		4180
		4181	=head4 THREAD LOCKING EXAMPLE
		4182
		4183	Here is a fictitious example of how to run an event loop in a different
		4184	thread than where callbacks are being invoked and watchers are
		4185	created/added/removed.
		4186
		4187	For a real-world example, see the C<EV::Loop::Async> perl module,
		4188	which uses exactly this technique (which is suited for many high-level
		4189	languages).
		4190
		4191	The example uses a pthread mutex to protect the loop data, a condition
		4192	variable to wait for callback invocations, an async watcher to notify the
		4193	event loop thread and an unspecified mechanism to wake up the main thread.
		4194
		4195	First, you need to associate some data with the event loop:
		4196
		4197	typedef struct {
		4198	mutex_t lock; /* global loop lock */
		4199	ev_async async_w;
		4200	thread_t tid;
		4201	cond_t invoke_cv;
		4202	} userdata;
		4203
		4204	void prepare_loop (EV_P)
		4205	{
		4206	// for simplicity, we use a static userdata struct.
		4207	static userdata u;
		4208
		4209	ev_async_init (&u->async_w, async_cb);
		4210	ev_async_start (EV_A_ &u->async_w);
		4211
		4212	pthread_mutex_init (&u->lock, 0);
		4213	pthread_cond_init (&u->invoke_cv, 0);
		4214
		4215	// now associate this with the loop
		4216	ev_set_userdata (EV_A_ u);
		4217	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4218	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4219
		4220	// then create the thread running ev_loop
		4221	pthread_create (&u->tid, 0, l_run, EV_A);
		4222	}
		4223
		4224	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4225	solely to wake up the event loop so it takes notice of any new watchers
		4226	that might have been added:
		4227
		4228	static void
		4229	async_cb (EV_P_ ev_async *w, int revents)
		4230	{
		4231	// just used for the side effects
		4232	}
		4233
		4234	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4235	protecting the loop data, respectively.
		4236
		4237	static void
		4238	l_release (EV_P)
		4239	{
		4240	userdata *u = ev_userdata (EV_A);
		4241	pthread_mutex_unlock (&u->lock);
		4242	}
		4243
		4244	static void
		4245	l_acquire (EV_P)
		4246	{
		4247	userdata *u = ev_userdata (EV_A);
		4248	pthread_mutex_lock (&u->lock);
		4249	}
		4250
		4251	The event loop thread first acquires the mutex, and then jumps straight
		4252	into C<ev_loop>:
		4253
		4254	void *
		4255	l_run (void *thr_arg)
		4256	{
		4257	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4258
		4259	l_acquire (EV_A);
		4260	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4261	ev_loop (EV_A_ 0);
		4262	l_release (EV_A);
		4263
		4264	return 0;
		4265	}
		4266
		4267	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4268	signal the main thread via some unspecified mechanism (signals? pipe
		4269	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4270	have been called (in a while loop because a) spurious wakeups are possible
		4271	and b) skipping inter-thread-communication when there are no pending
		4272	watchers is very beneficial):
		4273
		4274	static void
		4275	l_invoke (EV_P)
		4276	{
		4277	userdata *u = ev_userdata (EV_A);
		4278
		4279	while (ev_pending_count (EV_A))
		4280	{
		4281	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4282	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4283	}
		4284	}
		4285
		4286	Now, whenever the main thread gets told to invoke pending watchers, it
		4287	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4288	thread to continue:
		4289
		4290	static void
		4291	real_invoke_pending (EV_P)
		4292	{
		4293	userdata *u = ev_userdata (EV_A);
		4294
		4295	pthread_mutex_lock (&u->lock);
		4296	ev_invoke_pending (EV_A);
		4297	pthread_cond_signal (&u->invoke_cv);
		4298	pthread_mutex_unlock (&u->lock);
		4299	}
		4300
		4301	Whenever you want to start/stop a watcher or do other modifications to an
		4302	event loop, you will now have to lock:
		4303
		4304	ev_timer timeout_watcher;
		4305	userdata *u = ev_userdata (EV_A);
		4306
		4307	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4308
		4309	pthread_mutex_lock (&u->lock);
		4310	ev_timer_start (EV_A_ &timeout_watcher);
		4311	ev_async_send (EV_A_ &u->async_w);
		4312	pthread_mutex_unlock (&u->lock);
		4313
		4314	Note that sending the C<ev_async> watcher is required because otherwise
		4315	an event loop currently blocking in the kernel will have no knowledge
		4316	about the newly added timer. By waking up the loop it will pick up any new
		4317	watchers in the next event loop iteration.
		4318
3268	=head2 COROUTINES	4319	=head3 COROUTINES
3269		4320
3270	Libev is much more accommodating to coroutines ("cooperative threads"):	4321	Libev is very accommodating to coroutines ("cooperative threads"):
3271	libev fully supports nesting calls to it's functions from different	4322	libev fully supports nesting calls to its functions from different
3272	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4323	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3273	different coroutines and switch freely between both coroutines running the	4324	different coroutines, and switch freely between both coroutines running
3274	loop, as long as you don't confuse yourself). The only exception is that	4325	the loop, as long as you don't confuse yourself). The only exception is
3275	you must not do this from C<ev_periodic> reschedule callbacks.	4326	that you must not do this from C<ev_periodic> reschedule callbacks.
3276		4327
3277	Care has been invested into making sure that libev does not keep local	4328	Care has been taken to ensure that libev does not keep local state inside
3278	state inside C<ev_loop>, and other calls do not usually allow coroutine	4329	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3279	switches.	4330	they do not call any callbacks.
3280		4331
		4332	=head2 COMPILER WARNINGS
3281		4333
3282	=head1 COMPLEXITIES	4334	Depending on your compiler and compiler settings, you might get no or a
		4335	lot of warnings when compiling libev code. Some people are apparently
		4336	scared by this.
3283		4337
3284	In this section the complexities of (many of) the algorithms used inside	4338	However, these are unavoidable for many reasons. For one, each compiler
3285	libev will be explained. For complexity discussions about backends see the	4339	has different warnings, and each user has different tastes regarding
3286	documentation for C<ev_default_init>.	4340	warning options. "Warn-free" code therefore cannot be a goal except when
		4341	targeting a specific compiler and compiler-version.
3287		4342
3288	All of the following are about amortised time: If an array needs to be	4343	Another reason is that some compiler warnings require elaborate
3289	extended, libev needs to realloc and move the whole array, but this	4344	workarounds, or other changes to the code that make it less clear and less
3290	happens asymptotically never with higher number of elements, so O(1) might	4345	maintainable.
3291	mean it might do a lengthy realloc operation in rare cases, but on average
3292	it is much faster and asymptotically approaches constant time.
3293		4346
3294	=over 4	4347	And of course, some compiler warnings are just plain stupid, or simply
		4348	wrong (because they don't actually warn about the condition their message
		4349	seems to warn about). For example, certain older gcc versions had some
		4350	warnings that resulted an extreme number of false positives. These have
		4351	been fixed, but some people still insist on making code warn-free with
		4352	such buggy versions.
3295		4353
3296	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4354	While libev is written to generate as few warnings as possible,
		4355	"warn-free" code is not a goal, and it is recommended not to build libev
		4356	with any compiler warnings enabled unless you are prepared to cope with
		4357	them (e.g. by ignoring them). Remember that warnings are just that:
		4358	warnings, not errors, or proof of bugs.
3297		4359
3298	This means that, when you have a watcher that triggers in one hour and
3299	there are 100 watchers that would trigger before that then inserting will
3300	have to skip roughly seven (C<ld 100>) of these watchers.
3301		4360
3302	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4361	=head2 VALGRIND
3303		4362
3304	That means that changing a timer costs less than removing/adding them	4363	Valgrind has a special section here because it is a popular tool that is
3305	as only the relative motion in the event queue has to be paid for.	4364	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3306		4365
3307	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4366	If you think you found a bug (memory leak, uninitialised data access etc.)
		4367	in libev, then check twice: If valgrind reports something like:
3308		4368
3309	These just add the watcher into an array or at the head of a list.	4369	==2274== definitely lost: 0 bytes in 0 blocks.
		4370	==2274== possibly lost: 0 bytes in 0 blocks.
		4371	==2274== still reachable: 256 bytes in 1 blocks.
3310		4372
3311	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4373	Then there is no memory leak, just as memory accounted to global variables
		4374	is not a memleak - the memory is still being referenced, and didn't leak.
3312		4375
3313	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4376	Similarly, under some circumstances, valgrind might report kernel bugs
		4377	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4378	although an acceptable workaround has been found here), or it might be
		4379	confused.
3314		4380
3315	These watchers are stored in lists then need to be walked to find the	4381	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3316	correct watcher to remove. The lists are usually short (you don't usually	4382	make it into some kind of religion.
3317	have many watchers waiting for the same fd or signal).
3318		4383
3319	=item Finding the next timer in each loop iteration: O(1)	4384	If you are unsure about something, feel free to contact the mailing list
		4385	with the full valgrind report and an explanation on why you think this
		4386	is a bug in libev (best check the archives, too :). However, don't be
		4387	annoyed when you get a brisk "this is no bug" answer and take the chance
		4388	of learning how to interpret valgrind properly.
3320		4389
3321	By virtue of using a binary or 4-heap, the next timer is always found at a	4390	If you need, for some reason, empty reports from valgrind for your project
3322	fixed position in the storage array.	4391	I suggest using suppression lists.
3323		4392
3324	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3325		4393
3326	A change means an I/O watcher gets started or stopped, which requires	4394	=head1 PORTABILITY NOTES
3327	libev to recalculate its status (and possibly tell the kernel, depending
3328	on backend and whether C<ev_io_set> was used).
3329		4395
3330	=item Activating one watcher (putting it into the pending state): O(1)
3331
3332	=item Priority handling: O(number_of_priorities)
3333
3334	Priorities are implemented by allocating some space for each
3335	priority. When doing priority-based operations, libev usually has to
3336	linearly search all the priorities, but starting/stopping and activating
3337	watchers becomes O(1) w.r.t. priority handling.
3338
3339	=item Sending an ev_async: O(1)
3340
3341	=item Processing ev_async_send: O(number_of_async_watchers)
3342
3343	=item Processing signals: O(max_signal_number)
3344
3345	Sending involves a system call I<iff> there were no other C<ev_async_send>
3346	calls in the current loop iteration. Checking for async and signal events
3347	involves iterating over all running async watchers or all signal numbers.
3348
3349	=back
3350
3351
3352	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4396	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3353		4397
3354	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4398	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3355	requires, and its I/O model is fundamentally incompatible with the POSIX	4399	requires, and its I/O model is fundamentally incompatible with the POSIX
3356	model. Libev still offers limited functionality on this platform in	4400	model. Libev still offers limited functionality on this platform in
3357	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4401	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3364	way (note also that glib is the slowest event library known to man).	4408	way (note also that glib is the slowest event library known to man).
3365		4409
3366	There is no supported compilation method available on windows except	4410	There is no supported compilation method available on windows except
3367	embedding it into other applications.	4411	embedding it into other applications.
3368		4412
		4413	Sensible signal handling is officially unsupported by Microsoft - libev
		4414	tries its best, but under most conditions, signals will simply not work.
		4415
3369	Not a libev limitation but worth mentioning: windows apparently doesn't	4416	Not a libev limitation but worth mentioning: windows apparently doesn't
3370	accept large writes: instead of resulting in a partial write, windows will	4417	accept large writes: instead of resulting in a partial write, windows will
3371	either accept everything or return C<ENOBUFS> if the buffer is too large,	4418	either accept everything or return C<ENOBUFS> if the buffer is too large,
3372	so make sure you only write small amounts into your sockets (less than a	4419	so make sure you only write small amounts into your sockets (less than a
3373	megabyte seems safe, but thsi apparently depends on the amount of memory	4420	megabyte seems safe, but this apparently depends on the amount of memory
3374	available).	4421	available).
3375		4422
3376	Due to the many, low, and arbitrary limits on the win32 platform and	4423	Due to the many, low, and arbitrary limits on the win32 platform and
3377	the abysmal performance of winsockets, using a large number of sockets	4424	the abysmal performance of winsockets, using a large number of sockets
3378	is not recommended (and not reasonable). If your program needs to use	4425	is not recommended (and not reasonable). If your program needs to use
3379	more than a hundred or so sockets, then likely it needs to use a totally	4426	more than a hundred or so sockets, then likely it needs to use a totally
3380	different implementation for windows, as libev offers the POSIX readiness	4427	different implementation for windows, as libev offers the POSIX readiness
3381	notification model, which cannot be implemented efficiently on windows	4428	notification model, which cannot be implemented efficiently on windows
3382	(Microsoft monopoly games).	4429	(due to Microsoft monopoly games).
3383		4430
3384	A typical way to use libev under windows is to embed it (see the embedding	4431	A typical way to use libev under windows is to embed it (see the embedding
3385	section for details) and use the following F<evwrap.h> header file instead	4432	section for details) and use the following F<evwrap.h> header file instead
3386	of F<ev.h>:	4433	of F<ev.h>:
3387		4434
…		…
3389	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4436	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3390		4437
3391	#include "ev.h"	4438	#include "ev.h"
3392		4439
3393	And compile the following F<evwrap.c> file into your project (make sure	4440	And compile the following F<evwrap.c> file into your project (make sure
3394	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4441	you do I<not> compile the F<ev.c> or any other embedded source files!):
3395		4442
3396	#include "evwrap.h"	4443	#include "evwrap.h"
3397	#include "ev.c"	4444	#include "ev.c"
3398		4445
3399	=over 4	4446	=over 4
…		…
3423		4470
3424	Early versions of winsocket's select only supported waiting for a maximum	4471	Early versions of winsocket's select only supported waiting for a maximum
3425	of C<64> handles (probably owning to the fact that all windows kernels	4472	of C<64> handles (probably owning to the fact that all windows kernels
3426	can only wait for C<64> things at the same time internally; Microsoft	4473	can only wait for C<64> things at the same time internally; Microsoft
3427	recommends spawning a chain of threads and wait for 63 handles and the	4474	recommends spawning a chain of threads and wait for 63 handles and the
3428	previous thread in each. Great).	4475	previous thread in each. Sounds great!).
3429		4476
3430	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4477	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3431	to some high number (e.g. C<2048>) before compiling the winsocket select	4478	to some high number (e.g. C<2048>) before compiling the winsocket select
3432	call (which might be in libev or elsewhere, for example, perl does its own	4479	call (which might be in libev or elsewhere, for example, perl and many
3433	select emulation on windows).	4480	other interpreters do their own select emulation on windows).
3434		4481
3435	Another limit is the number of file descriptors in the Microsoft runtime	4482	Another limit is the number of file descriptors in the Microsoft runtime
3436	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4483	libraries, which by default is C<64> (there must be a hidden I<64>
3437	or something like this inside Microsoft). You can increase this by calling	4484	fetish or something like this inside Microsoft). You can increase this
3438	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4485	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3439	arbitrary limit), but is broken in many versions of the Microsoft runtime	4486	(another arbitrary limit), but is broken in many versions of the Microsoft
3440	libraries.
3441
3442	This might get you to about C<512> or C<2048> sockets (depending on	4487	runtime libraries. This might get you to about C<512> or C<2048> sockets
3443	windows version and/or the phase of the moon). To get more, you need to	4488	(depending on windows version and/or the phase of the moon). To get more,
3444	wrap all I/O functions and provide your own fd management, but the cost of	4489	you need to wrap all I/O functions and provide your own fd management, but
3445	calling select (O(n²)) will likely make this unworkable.	4490	the cost of calling select (O(n²)) will likely make this unworkable.
3446		4491
3447	=back	4492	=back
3448		4493
3449
3450	=head1 PORTABILITY REQUIREMENTS	4494	=head2 PORTABILITY REQUIREMENTS
3451		4495
3452	In addition to a working ISO-C implementation, libev relies on a few	4496	In addition to a working ISO-C implementation and of course the
3453	additional extensions:	4497	backend-specific APIs, libev relies on a few additional extensions:
3454		4498
3455	=over 4	4499	=over 4
3456		4500
3457	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4501	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3458	calling conventions regardless of C<ev_watcher_type *>.	4502	calling conventions regardless of C<ev_watcher_type *>.
…		…
3464	calls them using an C<ev_watcher *> internally.	4508	calls them using an C<ev_watcher *> internally.
3465		4509
3466	=item C<sig_atomic_t volatile> must be thread-atomic as well	4510	=item C<sig_atomic_t volatile> must be thread-atomic as well
3467		4511
3468	The type C<sig_atomic_t volatile> (or whatever is defined as	4512	The type C<sig_atomic_t volatile> (or whatever is defined as
3469	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4513	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3470	threads. This is not part of the specification for C<sig_atomic_t>, but is	4514	threads. This is not part of the specification for C<sig_atomic_t>, but is
3471	believed to be sufficiently portable.	4515	believed to be sufficiently portable.
3472		4516
3473	=item C<sigprocmask> must work in a threaded environment	4517	=item C<sigprocmask> must work in a threaded environment
3474		4518
…		…
3483	except the initial one, and run the default loop in the initial thread as	4527	except the initial one, and run the default loop in the initial thread as
3484	well.	4528	well.
3485		4529
3486	=item C<long> must be large enough for common memory allocation sizes	4530	=item C<long> must be large enough for common memory allocation sizes
3487		4531
3488	To improve portability and simplify using libev, libev uses C<long>	4532	To improve portability and simplify its API, libev uses C<long> internally
3489	internally instead of C<size_t> when allocating its data structures. On	4533	instead of C<size_t> when allocating its data structures. On non-POSIX
3490	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4534	systems (Microsoft...) this might be unexpectedly low, but is still at
3491	is still at least 31 bits everywhere, which is enough for hundreds of	4535	least 31 bits everywhere, which is enough for hundreds of millions of
3492	millions of watchers.	4536	watchers.
3493		4537
3494	=item C<double> must hold a time value in seconds with enough accuracy	4538	=item C<double> must hold a time value in seconds with enough accuracy
3495		4539
3496	The type C<double> is used to represent timestamps. It is required to	4540	The type C<double> is used to represent timestamps. It is required to
3497	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4541	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3498	enough for at least into the year 4000. This requirement is fulfilled by	4542	enough for at least into the year 4000. This requirement is fulfilled by
3499	implementations implementing IEEE 754 (basically all existing ones).	4543	implementations implementing IEEE 754, which is basically all existing
		4544	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4545	2200.
3500		4546
3501	=back	4547	=back
3502		4548
3503	If you know of other additional requirements drop me a note.	4549	If you know of other additional requirements drop me a note.
3504		4550
3505		4551
3506	=head1 COMPILER WARNINGS	4552	=head1 ALGORITHMIC COMPLEXITIES
3507		4553
3508	Depending on your compiler and compiler settings, you might get no or a	4554	In this section the complexities of (many of) the algorithms used inside
3509	lot of warnings when compiling libev code. Some people are apparently	4555	libev will be documented. For complexity discussions about backends see
3510	scared by this.	4556	the documentation for C<ev_default_init>.
3511		4557
3512	However, these are unavoidable for many reasons. For one, each compiler	4558	All of the following are about amortised time: If an array needs to be
3513	has different warnings, and each user has different tastes regarding	4559	extended, libev needs to realloc and move the whole array, but this
3514	warning options. "Warn-free" code therefore cannot be a goal except when	4560	happens asymptotically rarer with higher number of elements, so O(1) might
3515	targeting a specific compiler and compiler-version.	4561	mean that libev does a lengthy realloc operation in rare cases, but on
		4562	average it is much faster and asymptotically approaches constant time.
3516		4563
3517	Another reason is that some compiler warnings require elaborate	4564	=over 4
3518	workarounds, or other changes to the code that make it less clear and less
3519	maintainable.
3520		4565
3521	And of course, some compiler warnings are just plain stupid, or simply	4566	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3522	wrong (because they don't actually warn about the condition their message
3523	seems to warn about).
3524		4567
3525	While libev is written to generate as few warnings as possible,	4568	This means that, when you have a watcher that triggers in one hour and
3526	"warn-free" code is not a goal, and it is recommended not to build libev	4569	there are 100 watchers that would trigger before that, then inserting will
3527	with any compiler warnings enabled unless you are prepared to cope with	4570	have to skip roughly seven (C<ld 100>) of these watchers.
3528	them (e.g. by ignoring them). Remember that warnings are just that:
3529	warnings, not errors, or proof of bugs.
3530		4571
		4572	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3531		4573
3532	=head1 VALGRIND	4574	That means that changing a timer costs less than removing/adding them,
		4575	as only the relative motion in the event queue has to be paid for.
3533		4576
3534	Valgrind has a special section here because it is a popular tool that is	4577	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3535	highly useful, but valgrind reports are very hard to interpret.
3536		4578
3537	If you think you found a bug (memory leak, uninitialised data access etc.)	4579	These just add the watcher into an array or at the head of a list.
3538	in libev, then check twice: If valgrind reports something like:
3539		4580
3540	==2274== definitely lost: 0 bytes in 0 blocks.	4581	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3541	==2274== possibly lost: 0 bytes in 0 blocks.
3542	==2274== still reachable: 256 bytes in 1 blocks.
3543		4582
3544	Then there is no memory leak. Similarly, under some circumstances,	4583	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3545	valgrind might report kernel bugs as if it were a bug in libev, or it
3546	might be confused (it is a very good tool, but only a tool).
3547		4584
3548	If you are unsure about something, feel free to contact the mailing list	4585	These watchers are stored in lists, so they need to be walked to find the
3549	with the full valgrind report and an explanation on why you think this is	4586	correct watcher to remove. The lists are usually short (you don't usually
3550	a bug in libev. However, don't be annoyed when you get a brisk "this is	4587	have many watchers waiting for the same fd or signal: one is typical, two
3551	no bug" answer and take the chance of learning how to interpret valgrind	4588	is rare).
3552	properly.
3553		4589
3554	If you need, for some reason, empty reports from valgrind for your project	4590	=item Finding the next timer in each loop iteration: O(1)
3555	I suggest using suppression lists.
3556		4591
		4592	By virtue of using a binary or 4-heap, the next timer is always found at a
		4593	fixed position in the storage array.
		4594
		4595	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4596
		4597	A change means an I/O watcher gets started or stopped, which requires
		4598	libev to recalculate its status (and possibly tell the kernel, depending
		4599	on backend and whether C<ev_io_set> was used).
		4600
		4601	=item Activating one watcher (putting it into the pending state): O(1)
		4602
		4603	=item Priority handling: O(number_of_priorities)
		4604
		4605	Priorities are implemented by allocating some space for each
		4606	priority. When doing priority-based operations, libev usually has to
		4607	linearly search all the priorities, but starting/stopping and activating
		4608	watchers becomes O(1) with respect to priority handling.
		4609
		4610	=item Sending an ev_async: O(1)
		4611
		4612	=item Processing ev_async_send: O(number_of_async_watchers)
		4613
		4614	=item Processing signals: O(max_signal_number)
		4615
		4616	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4617	calls in the current loop iteration. Checking for async and signal events
		4618	involves iterating over all running async watchers or all signal numbers.
		4619
		4620	=back
		4621
		4622
		4623	=head1 PORTING FROM 3.X TO 4.X
		4624
		4625	The major version 4 introduced some minor incompatible changes to the API.
		4626
		4627	=over 4
		4628
		4629	=item C<EV_TIMEOUT> replaced by C<EV_TIMER> in C<revents>
		4630
		4631	This is a simple rename - all other watcher types use their name
		4632	as revents flag, and now C<ev_timer> does, too.
		4633
		4634	Both C<EV_TIMER> and C<EV_TIMEOUT> symbols were present in 3.x versions
		4635	and continue to be present for the forseeable future, so this is mostly a
		4636	documentation change.
		4637
		4638	=item C<EV_MINIMAL> mechanism replaced by C<EV_FEATURES>
		4639
		4640	The preprocessor symbol C<EV_MINIMAL> has been replaced by a different
		4641	mechanism, C<EV_FEATURES>. Programs using C<EV_MINIMAL> usually compile
		4642	and work, but the library code will of course be larger.
		4643
		4644	=back
		4645
		4646
		4647	=head1 GLOSSARY
		4648
		4649	=over 4
		4650
		4651	=item active
		4652
		4653	A watcher is active as long as it has been started (has been attached to
		4654	an event loop) but not yet stopped (disassociated from the event loop).
		4655
		4656	=item application
		4657
		4658	In this document, an application is whatever is using libev.
		4659
		4660	=item callback
		4661
		4662	The address of a function that is called when some event has been
		4663	detected. Callbacks are being passed the event loop, the watcher that
		4664	received the event, and the actual event bitset.
		4665
		4666	=item callback invocation
		4667
		4668	The act of calling the callback associated with a watcher.
		4669
		4670	=item event
		4671
		4672	A change of state of some external event, such as data now being available
		4673	for reading on a file descriptor, time having passed or simply not having
		4674	any other events happening anymore.
		4675
		4676	In libev, events are represented as single bits (such as C<EV_READ> or
		4677	C<EV_TIMER>).
		4678
		4679	=item event library
		4680
		4681	A software package implementing an event model and loop.
		4682
		4683	=item event loop
		4684
		4685	An entity that handles and processes external events and converts them
		4686	into callback invocations.
		4687
		4688	=item event model
		4689
		4690	The model used to describe how an event loop handles and processes
		4691	watchers and events.
		4692
		4693	=item pending
		4694
		4695	A watcher is pending as soon as the corresponding event has been detected,
		4696	and stops being pending as soon as the watcher will be invoked or its
		4697	pending status is explicitly cleared by the application.
		4698
		4699	A watcher can be pending, but not active. Stopping a watcher also clears
		4700	its pending status.
		4701
		4702	=item real time
		4703
		4704	The physical time that is observed. It is apparently strictly monotonic :)
		4705
		4706	=item wall-clock time
		4707
		4708	The time and date as shown on clocks. Unlike real time, it can actually
		4709	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4710	clock.
		4711
		4712	=item watcher
		4713
		4714	A data structure that describes interest in certain events. Watchers need
		4715	to be started (attached to an event loop) before they can receive events.
		4716
		4717	=item watcher invocation
		4718
		4719	The act of calling the callback associated with a watcher.
		4720
		4721	=back
3557		4722
3558	=head1 AUTHOR	4723	=head1 AUTHOR
3559		4724
3560	Marc Lehmann <libev@schmorp.de>.	4725	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3561		4726

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