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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
…		…
103	Libev is very configurable. In this manual the default (and most common)	117	Libev is very configurable. In this manual the default (and most common)
104	configuration will be described, which supports multiple event loops. For	118	configuration will be described, which supports multiple event loops. For
105	more info about various configuration options please have a look at	119	more info about various configuration options please have a look at
106	B<EMBED> section in this manual. If libev was configured without support	120	B<EMBED> section in this manual. If libev was configured without support
107	for multiple event loops, then all functions taking an initial argument of	121	for multiple event loops, then all functions taking an initial argument of
108	name C<loop> (which is always of type C<struct ev_loop *>) will not have	122	name C<loop> (which is always of type C<ev_loop *>) will not have
109	this argument.	123	this argument.
110		124
111	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
112		126
113	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
114	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
115	the beginning of 1970, details are complicated, don't ask). This type is	129	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	130	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	131	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	132	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	133	component C<stamp> might indicate, it is also used for time differences
120	throughout libev.	134	throughout libev.
121		135
122	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
123		137
…		…
214	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	228	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
215	recommended ones.	229	recommended ones.
216		230
217	See the description of C<ev_embed> watchers for more info.	231	See the description of C<ev_embed> watchers for more info.
218		232
219	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	233	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
220		234
221	Sets the allocation function to use (the prototype is similar - the	235	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	236	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	237	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	238	when memory needs to be allocated (C<size != 0>), the library might abort
…		…
250	}	264	}
251		265
252	...	266	...
253	ev_set_allocator (persistent_realloc);	267	ev_set_allocator (persistent_realloc);
254		268
255	=item ev_set_syserr_cb (void (*cb)(const char *msg));	269	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
256		270
257	Set the callback function to call on a retryable system call error (such	271	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	272	as failed select, poll, epoll_wait). The message is a printable string
259	indicating the system call or subsystem causing the problem. If this	273	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	274	callback is set, then libev will expect it to remedy the situation, no
…		…
276		290
277	=back	291	=back
278		292
279	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	293	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
280		294
281	An event loop is described by a C<struct ev_loop *>. The library knows two	295	An event loop is described by a C<struct ev_loop *> (the C<struct>
282	types of such loops, the I<default> loop, which supports signals and child	296	is I<not> optional in this case, as there is also an C<ev_loop>
283	events, and dynamically created loops which do not.	297	I<function>).
		298
		299	The library knows two types of such loops, the I<default> loop, which
		300	supports signals and child events, and dynamically created loops which do
		301	not.
284		302
285	=over 4	303	=over 4
286		304
287	=item struct ev_loop *ev_default_loop (unsigned int flags)	305	=item struct ev_loop *ev_default_loop (unsigned int flags)
288		306
…		…
294	If you don't know what event loop to use, use the one returned from this	312	If you don't know what event loop to use, use the one returned from this
295	function.	313	function.
296		314
297	Note that this function is I<not> thread-safe, so if you want to use it	315	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,	316	from multiple threads, you have to lock (note also that this is unlikely,
299	as loops cannot bes hared easily between threads anyway).	317	as loops cannot be shared easily between threads anyway).
300		318
301	The default loop is the only loop that can handle C<ev_signal> and	319	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	320	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	321	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	322	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
…		…
344	flag.	362	flag.
345		363
346	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>	364	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
347	environment variable.	365	environment variable.
348		366
		367	=item C<EVFLAG_NOINOTIFY>
		368
		369	When this flag is specified, then libev will not attempt to use the
		370	I<inotify> API for it's C<ev_stat> watchers. Apart from debugging and
		371	testing, this flag can be useful to conserve inotify file descriptors, as
		372	otherwise each loop using C<ev_stat> watchers consumes one inotify handle.
		373
		374	=item C<EVFLAG_NOSIGNALFD>
		375
		376	When this flag is specified, then libev will not attempt to use the
		377	I<signalfd> API for it's C<ev_signal> (and C<ev_child>) watchers. This is
		378	probably only useful to work around any bugs in libev. Consequently, this
		379	flag might go away once the signalfd functionality is considered stable,
		380	so it's useful mostly in environment variables and not in program code.
		381
349	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	382	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
350		383
351	This is your standard select(2) backend. Not I<completely> standard, as	384	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,	385	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	386	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	392	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	393	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	394	a look at C<ev_set_io_collect_interval ()> to increase the amount of
362	readiness notifications you get per iteration.	395	readiness notifications you get per iteration.
363		396
		397	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		398	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		399	C<exceptfds> set on that platform).
		400
364	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	401	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
365		402
366	And this is your standard poll(2) backend. It's more complicated	403	And this is your standard poll(2) backend. It's more complicated
367	than select, but handles sparse fds better and has no artificial	404	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	405	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,	406	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	407	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
371	performance tips.	408	performance tips.
372		409
		410	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		411	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
		412
373	=item C<EVBACKEND_EPOLL> (value 4, Linux)	413	=item C<EVBACKEND_EPOLL> (value 4, Linux)
374		414
375	For few fds, this backend is a bit little slower than poll and select,	415	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	416	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),	417	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	418	epoll scales either O(1) or O(active_fds).
379	of shortcomings, such as silently dropping events in some hard-to-detect	419
380	cases and requiring a system call per fd change, no fork support and bad	420	The epoll mechanism deserves honorable mention as the most misdesigned
381	support for dup.	421	of the more advanced event mechanisms: mere annoyances include silently
		422	dropping file descriptors, requiring a system call per change per file
		423	descriptor (and unnecessary guessing of parameters), problems with dup and
		424	so on. The biggest issue is fork races, however - if a program forks then
		425	I<both> parent and child process have to recreate the epoll set, which can
		426	take considerable time (one syscall per file descriptor) and is of course
		427	hard to detect.
		428
		429	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		430	of course I<doesn't>, and epoll just loves to report events for totally
		431	I<different> file descriptors (even already closed ones, so one cannot
		432	even remove them from the set) than registered in the set (especially
		433	on SMP systems). Libev tries to counter these spurious notifications by
		434	employing an additional generation counter and comparing that against the
		435	events to filter out spurious ones, recreating the set when required.
382		436
383	While stopping, setting and starting an I/O watcher in the same iteration	437	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	438	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	439	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	440	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
387	very well if you register events for both fds.	441	file descriptors might not work very well if you register events for both
388		442	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		443
393	Best performance from this backend is achieved by not unregistering all	444	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.	445	watchers for a file descriptor until it has been closed, if possible,
395	keep at least one watcher active per fd at all times.	446	i.e. keep at least one watcher active per fd at all times. Stopping and
		447	starting a watcher (without re-setting it) also usually doesn't cause
		448	extra overhead. A fork can both result in spurious notifications as well
		449	as in libev having to destroy and recreate the epoll object, which can
		450	take considerable time and thus should be avoided.
		451
		452	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		453	faster than epoll for maybe up to a hundred file descriptors, depending on
		454	the usage. So sad.
396		455
397	While nominally embeddable in other event loops, this feature is broken in	456	While nominally embeddable in other event loops, this feature is broken in
398	all kernel versions tested so far.	457	all kernel versions tested so far.
		458
		459	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		460	C<EVBACKEND_POLL>.
399		461
400	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	462	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
401		463
402	Kqueue deserves special mention, as at the time of this writing, it	464	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	465	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	466	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"	467	it's completely useless). Unlike epoll, however, whose brokenness
		468	is by design, these kqueue bugs can (and eventually will) be fixed
		469	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	470	"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)	471	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
408	system like NetBSD.	472	system like NetBSD.
409		473
410	You still can embed kqueue into a normal poll or select backend and use it	474	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	475	only for sockets (after having made sure that sockets work with kqueue on
…		…
413		477
414	It scales in the same way as the epoll backend, but the interface to the	478	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	479	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	480	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	481	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	482	two event changes per incident. Support for C<fork ()> is very bad (but
419	drops fds silently in similarly hard-to-detect cases.	483	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		484	cases
420		485
421	This backend usually performs well under most conditions.	486	This backend usually performs well under most conditions.
422		487
423	While nominally embeddable in other event loops, this doesn't work	488	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	489	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	490	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	491	(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	492	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
428	sockets.	493	also broken on OS X)) and, did I mention it, using it only for sockets.
		494
		495	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		496	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		497	C<NOTE_EOF>.
429		498
430	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	499	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
431		500
432	This is not implemented yet (and might never be, unless you send me an	501	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	502	implementation). According to reports, C</dev/poll> only supports sockets
…		…
446	While this backend scales well, it requires one system call per active	515	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	516	file descriptor per loop iteration. For small and medium numbers of file
448	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend	517	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
449	might perform better.	518	might perform better.
450		519
451	On the positive side, ignoring the spurious readiness notifications, this	520	On the positive side, with the exception of the spurious readiness
452	backend actually performed to specification in all tests and is fully	521	notifications, this backend actually performed fully to specification
453	embeddable, which is a rare feat among the OS-specific backends.	522	in all tests and is fully embeddable, which is a rare feat among the
		523	OS-specific backends (I vastly prefer correctness over speed hacks).
		524
		525	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		526	C<EVBACKEND_POLL>.
454		527
455	=item C<EVBACKEND_ALL>	528	=item C<EVBACKEND_ALL>
456		529
457	Try all backends (even potentially broken ones that wouldn't be tried	530	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	531	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
…		…
460		533
461	It is definitely not recommended to use this flag.	534	It is definitely not recommended to use this flag.
462		535
463	=back	536	=back
464		537
465	If one or more of these are or'ed into the flags value, then only these	538	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	539	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.	540	here). If none are specified, all backends in C<ev_recommended_backends
		541	()> will be tried.
468		542
469	The most typical usage is like this:	543	Example: This is the most typical usage.
470		544
471	if (!ev_default_loop (0))	545	if (!ev_default_loop (0))
472	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	546	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
473		547
474	Restrict libev to the select and poll backends, and do not allow	548	Example: Restrict libev to the select and poll backends, and do not allow
475	environment settings to be taken into account:	549	environment settings to be taken into account:
476		550
477	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	551	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
478		552
479	Use whatever libev has to offer, but make sure that kqueue is used if	553	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	554	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):	555	private event loop and only if you know the OS supports your types of
		556	fds):
482		557
483	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	558	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
484		559
485	=item struct ev_loop *ev_loop_new (unsigned int flags)	560	=item struct ev_loop *ev_loop_new (unsigned int flags)
486		561
…		…
507	responsibility to either stop all watchers cleanly yourself I<before>	582	responsibility to either stop all watchers cleanly yourself I<before>
508	calling this function, or cope with the fact afterwards (which is usually	583	calling this function, or cope with the fact afterwards (which is usually
509	the easiest thing, you can just ignore the watchers and/or C<free ()> them	584	the easiest thing, you can just ignore the watchers and/or C<free ()> them
510	for example).	585	for example).
511		586
512	Note that certain global state, such as signal state, will not be freed by	587	Note that certain global state, such as signal state (and installed signal
513	this function, and related watchers (such as signal and child watchers)	588	handlers), will not be freed by this function, and related watchers (such
514	would need to be stopped manually.	589	as signal and child watchers) would need to be stopped manually.
515		590
516	In general it is not advisable to call this function except in the	591	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	592	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	593	pipe fds. If you need dynamically allocated loops it is better to use
519	C<ev_loop_new> and C<ev_loop_destroy>).	594	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
544		619
545	=item ev_loop_fork (loop)	620	=item ev_loop_fork (loop)
546		621
547	Like C<ev_default_fork>, but acts on an event loop created by	622	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	623	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.	624	after fork that you want to re-use in the child, and how you do this is
		625	entirely your own problem.
550		626
551	=item int ev_is_default_loop (loop)	627	=item int ev_is_default_loop (loop)
552		628
553	Returns true when the given loop actually is the default loop, false otherwise.	629	Returns true when the given loop is, in fact, the default loop, and false
		630	otherwise.
554		631
555	=item unsigned int ev_loop_count (loop)	632	=item unsigned int ev_loop_count (loop)
556		633
557	Returns the count of loop iterations for the loop, which is identical to	634	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	635	the number of times libev did poll for new events. It starts at C<0> and
559	happily wraps around with enough iterations.	636	happily wraps around with enough iterations.
560		637
561	This value can sometimes be useful as a generation counter of sorts (it	638	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	639	"ticks" the number of loop iterations), as it roughly corresponds with
563	C<ev_prepare> and C<ev_check> calls.	640	C<ev_prepare> and C<ev_check> calls.
		641
		642	=item unsigned int ev_loop_depth (loop)
		643
		644	Returns the number of times C<ev_loop> was entered minus the number of
		645	times C<ev_loop> was exited, in other words, the recursion depth.
		646
		647	Outside C<ev_loop>, this number is zero. In a callback, this number is
		648	C<1>, unless C<ev_loop> was invoked recursively (or from another thread),
		649	in which case it is higher.
		650
		651	Leaving C<ev_loop> abnormally (setjmp/longjmp, cancelling the thread
		652	etc.), doesn't count as exit.
564		653
565	=item unsigned int ev_backend (loop)	654	=item unsigned int ev_backend (loop)
566		655
567	Returns one of the C<EVBACKEND_*> flags indicating the event backend in	656	Returns one of the C<EVBACKEND_*> flags indicating the event backend in
568	use.	657	use.
…		…
573	received events and started processing them. This timestamp does not	662	received events and started processing them. This timestamp does not
574	change as long as callbacks are being processed, and this is also the base	663	change as long as callbacks are being processed, and this is also the base
575	time used for relative timers. You can treat it as the timestamp of the	664	time used for relative timers. You can treat it as the timestamp of the
576	event occurring (or more correctly, libev finding out about it).	665	event occurring (or more correctly, libev finding out about it).
577		666
		667	=item ev_now_update (loop)
		668
		669	Establishes the current time by querying the kernel, updating the time
		670	returned by C<ev_now ()> in the progress. This is a costly operation and
		671	is usually done automatically within C<ev_loop ()>.
		672
		673	This function is rarely useful, but when some event callback runs for a
		674	very long time without entering the event loop, updating libev's idea of
		675	the current time is a good idea.
		676
		677	See also L<The special problem of time updates> in the C<ev_timer> section.
		678
		679	=item ev_suspend (loop)
		680
		681	=item ev_resume (loop)
		682
		683	These two functions suspend and resume a loop, for use when the loop is
		684	not used for a while and timeouts should not be processed.
		685
		686	A typical use case would be an interactive program such as a game: When
		687	the user presses C<^Z> to suspend the game and resumes it an hour later it
		688	would be best to handle timeouts as if no time had actually passed while
		689	the program was suspended. This can be achieved by calling C<ev_suspend>
		690	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		691	C<ev_resume> directly afterwards to resume timer processing.
		692
		693	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		694	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		695	will be rescheduled (that is, they will lose any events that would have
		696	occured while suspended).
		697
		698	After calling C<ev_suspend> you B<must not> call I<any> function on the
		699	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		700	without a previous call to C<ev_suspend>.
		701
		702	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		703	event loop time (see C<ev_now_update>).
		704
578	=item ev_loop (loop, int flags)	705	=item ev_loop (loop, int flags)
579		706
580	Finally, this is it, the event handler. This function usually is called	707	Finally, this is it, the event handler. This function usually is called
581	after you initialised all your watchers and you want to start handling	708	after you initialised all your watchers and you want to start handling
582	events.	709	events.
…		…
584	If the flags argument is specified as C<0>, it will not return until	711	If the flags argument is specified as C<0>, it will not return until
585	either no event watchers are active anymore or C<ev_unloop> was called.	712	either no event watchers are active anymore or C<ev_unloop> was called.
586		713
587	Please note that an explicit C<ev_unloop> is usually better than	714	Please note that an explicit C<ev_unloop> is usually better than
588	relying on all watchers to be stopped when deciding when a program has	715	relying on all watchers to be stopped when deciding when a program has
589	finished (especially in interactive programs), but having a program that	716	finished (especially in interactive programs), but having a program
590	automatically loops as long as it has to and no longer by virtue of	717	that automatically loops as long as it has to and no longer by virtue
591	relying on its watchers stopping correctly is a thing of beauty.	718	of relying on its watchers stopping correctly, that is truly a thing of
		719	beauty.
592		720
593	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	721	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
594	those events and any outstanding ones, but will not block your process in	722	those events and any already outstanding ones, but will not block your
595	case there are no events and will return after one iteration of the loop.	723	process in case there are no events and will return after one iteration of
		724	the loop.
596		725
597	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	726	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
598	necessary) and will handle those and any outstanding ones. It will block	727	necessary) and will handle those and any already outstanding ones. It
599	your process until at least one new event arrives, and will return after	728	will block your process until at least one new event arrives (which could
600	one iteration of the loop. This is useful if you are waiting for some	729	be an event internal to libev itself, so there is no guarantee that a
601	external event in conjunction with something not expressible using other	730	user-registered callback will be called), and will return after one
		731	iteration of the loop.
		732
		733	This is useful if you are waiting for some external event in conjunction
		734	with something not expressible using other libev watchers (i.e. "roll your
602	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	735	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
603	usually a better approach for this kind of thing.	736	usually a better approach for this kind of thing.
604		737
605	Here are the gory details of what C<ev_loop> does:	738	Here are the gory details of what C<ev_loop> does:
606		739
607	- Before the first iteration, call any pending watchers.	740	- Before the first iteration, call any pending watchers.
…		…
617	any active watchers at all will result in not sleeping).	750	any active watchers at all will result in not sleeping).
618	- Sleep if the I/O and timer collect interval say so.	751	- Sleep if the I/O and timer collect interval say so.
619	- Block the process, waiting for any events.	752	- Block the process, waiting for any events.
620	- Queue all outstanding I/O (fd) events.	753	- Queue all outstanding I/O (fd) events.
621	- Update the "event loop time" (ev_now ()), and do time jump adjustments.	754	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
622	- Queue all outstanding timers.	755	- Queue all expired timers.
623	- Queue all outstanding periodics.	756	- Queue all expired periodics.
624	- Unless any events are pending now, queue all idle watchers.	757	- Unless any events are pending now, queue all idle watchers.
625	- Queue all check watchers.	758	- Queue all check watchers.
626	- Call all queued watchers in reverse order (i.e. check watchers first).	759	- Call all queued watchers in reverse order (i.e. check watchers first).
627	Signals and child watchers are implemented as I/O watchers, and will	760	Signals and child watchers are implemented as I/O watchers, and will
628	be handled here by queueing them when their watcher gets executed.	761	be handled here by queueing them when their watcher gets executed.
…		…
645	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	778	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
646	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	779	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
647		780
648	This "unloop state" will be cleared when entering C<ev_loop> again.	781	This "unloop state" will be cleared when entering C<ev_loop> again.
649		782
		783	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		784
650	=item ev_ref (loop)	785	=item ev_ref (loop)
651		786
652	=item ev_unref (loop)	787	=item ev_unref (loop)
653		788
654	Ref/unref can be used to add or remove a reference count on the event	789	Ref/unref can be used to add or remove a reference count on the event
655	loop: Every watcher keeps one reference, and as long as the reference	790	loop: Every watcher keeps one reference, and as long as the reference
656	count is nonzero, C<ev_loop> will not return on its own. If you have	791	count is nonzero, C<ev_loop> will not return on its own.
		792
657	a watcher you never unregister that should not keep C<ev_loop> from	793	If you have a watcher you never unregister that should not keep C<ev_loop>
658	returning, ev_unref() after starting, and ev_ref() before stopping it. For	794	from returning, call ev_unref() after starting, and ev_ref() before
		795	stopping it.
		796
659	example, libev itself uses this for its internal signal pipe: It is not	797	As an example, libev itself uses this for its internal signal pipe: It
660	visible to the libev user and should not keep C<ev_loop> from exiting if	798	is not visible to the libev user and should not keep C<ev_loop> from
661	no event watchers registered by it are active. It is also an excellent	799	exiting if no event watchers registered by it are active. It is also an
662	way to do this for generic recurring timers or from within third-party	800	excellent way to do this for generic recurring timers or from within
663	libraries. Just remember to I<unref after start> and I<ref before stop>	801	third-party libraries. Just remember to I<unref after start> and I<ref
664	(but only if the watcher wasn't active before, or was active before,	802	before stop> (but only if the watcher wasn't active before, or was active
665	respectively).	803	before, respectively. Note also that libev might stop watchers itself
		804	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		805	in the callback).
666		806
667	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	807	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
668	running when nothing else is active.	808	running when nothing else is active.
669		809
670	struct ev_signal exitsig;	810	ev_signal exitsig;
671	ev_signal_init (&exitsig, sig_cb, SIGINT);	811	ev_signal_init (&exitsig, sig_cb, SIGINT);
672	ev_signal_start (loop, &exitsig);	812	ev_signal_start (loop, &exitsig);
673	evf_unref (loop);	813	evf_unref (loop);
674		814
675	Example: For some weird reason, unregister the above signal handler again.	815	Example: For some weird reason, unregister the above signal handler again.
…		…
689	Setting these to a higher value (the C<interval> I<must> be >= C<0>)	829	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
690	allows libev to delay invocation of I/O and timer/periodic callbacks	830	allows libev to delay invocation of I/O and timer/periodic callbacks
691	to increase efficiency of loop iterations (or to increase power-saving	831	to increase efficiency of loop iterations (or to increase power-saving
692	opportunities).	832	opportunities).
693		833
694	The background is that sometimes your program runs just fast enough to	834	The idea is that sometimes your program runs just fast enough to handle
695	handle one (or very few) event(s) per loop iteration. While this makes	835	one (or very few) event(s) per loop iteration. While this makes the
696	the program responsive, it also wastes a lot of CPU time to poll for new	836	program responsive, it also wastes a lot of CPU time to poll for new
697	events, especially with backends like C<select ()> which have a high	837	events, especially with backends like C<select ()> which have a high
698	overhead for the actual polling but can deliver many events at once.	838	overhead for the actual polling but can deliver many events at once.
699		839
700	By setting a higher I<io collect interval> you allow libev to spend more	840	By setting a higher I<io collect interval> you allow libev to spend more
701	time collecting I/O events, so you can handle more events per iteration,	841	time collecting I/O events, so you can handle more events per iteration,
702	at the cost of increasing latency. Timeouts (both C<ev_periodic> and	842	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
703	C<ev_timer>) will be not affected. Setting this to a non-null value will	843	C<ev_timer>) will be not affected. Setting this to a non-null value will
704	introduce an additional C<ev_sleep ()> call into most loop iterations.	844	introduce an additional C<ev_sleep ()> call into most loop iterations. The
		845	sleep time ensures that libev will not poll for I/O events more often then
		846	once per this interval, on average.
705		847
706	Likewise, by setting a higher I<timeout collect interval> you allow libev	848	Likewise, by setting a higher I<timeout collect interval> you allow libev
707	to spend more time collecting timeouts, at the expense of increased	849	to spend more time collecting timeouts, at the expense of increased
708	latency (the watcher callback will be called later). C<ev_io> watchers	850	latency/jitter/inexactness (the watcher callback will be called
709	will not be affected. Setting this to a non-null value will not introduce	851	later). C<ev_io> watchers will not be affected. Setting this to a non-null
710	any overhead in libev.	852	value will not introduce any overhead in libev.
711		853
712	Many (busy) programs can usually benefit by setting the I/O collect	854	Many (busy) programs can usually benefit by setting the I/O collect
713	interval to a value near C<0.1> or so, which is often enough for	855	interval to a value near C<0.1> or so, which is often enough for
714	interactive servers (of course not for games), likewise for timeouts. It	856	interactive servers (of course not for games), likewise for timeouts. It
715	usually doesn't make much sense to set it to a lower value than C<0.01>,	857	usually doesn't make much sense to set it to a lower value than C<0.01>,
716	as this approaches the timing granularity of most systems.	858	as this approaches the timing granularity of most systems. Note that if
		859	you do transactions with the outside world and you can't increase the
		860	parallelity, then this setting will limit your transaction rate (if you
		861	need to poll once per transaction and the I/O collect interval is 0.01,
		862	then you can't do more than 100 transations per second).
717		863
718	Setting the I<timeout collect interval> can improve the opportunity for	864	Setting the I<timeout collect interval> can improve the opportunity for
719	saving power, as the program will "bundle" timer callback invocations that	865	saving power, as the program will "bundle" timer callback invocations that
720	are "near" in time together, by delaying some, thus reducing the number of	866	are "near" in time together, by delaying some, thus reducing the number of
721	times the process sleeps and wakes up again. Another useful technique to	867	times the process sleeps and wakes up again. Another useful technique to
722	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure	868	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
723	they fire on, say, one-second boundaries only.	869	they fire on, say, one-second boundaries only.
724		870
		871	Example: we only need 0.1s timeout granularity, and we wish not to poll
		872	more often than 100 times per second:
		873
		874	ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
		875	ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
		876
		877	=item ev_invoke_pending (loop)
		878
		879	This call will simply invoke all pending watchers while resetting their
		880	pending state. Normally, C<ev_loop> does this automatically when required,
		881	but when overriding the invoke callback this call comes handy.
		882
		883	=item int ev_pending_count (loop)
		884
		885	Returns the number of pending watchers - zero indicates that no watchers
		886	are pending.
		887
		888	=item ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))
		889
		890	This overrides the invoke pending functionality of the loop: Instead of
		891	invoking all pending watchers when there are any, C<ev_loop> will call
		892	this callback instead. This is useful, for example, when you want to
		893	invoke the actual watchers inside another context (another thread etc.).
		894
		895	If you want to reset the callback, use C<ev_invoke_pending> as new
		896	callback.
		897
		898	=item ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))
		899
		900	Sometimes you want to share the same loop between multiple threads. This
		901	can be done relatively simply by putting mutex_lock/unlock calls around
		902	each call to a libev function.
		903
		904	However, C<ev_loop> can run an indefinite time, so it is not feasible to
		905	wait for it to return. One way around this is to wake up the loop via
		906	C<ev_unloop> and C<av_async_send>, another way is to set these I<release>
		907	and I<acquire> callbacks on the loop.
		908
		909	When set, then C<release> will be called just before the thread is
		910	suspended waiting for new events, and C<acquire> is called just
		911	afterwards.
		912
		913	Ideally, C<release> will just call your mutex_unlock function, and
		914	C<acquire> will just call the mutex_lock function again.
		915
		916	While event loop modifications are allowed between invocations of
		917	C<release> and C<acquire> (that's their only purpose after all), no
		918	modifications done will affect the event loop, i.e. adding watchers will
		919	have no effect on the set of file descriptors being watched, or the time
		920	waited. USe an C<ev_async> watcher to wake up C<ev_loop> when you want it
		921	to take note of any changes you made.
		922
		923	In theory, threads executing C<ev_loop> will be async-cancel safe between
		924	invocations of C<release> and C<acquire>.
		925
		926	See also the locking example in the C<THREADS> section later in this
		927	document.
		928
		929	=item ev_set_userdata (loop, void *data)
		930
		931	=item ev_userdata (loop)
		932
		933	Set and retrieve a single C<void *> associated with a loop. When
		934	C<ev_set_userdata> has never been called, then C<ev_userdata> returns
		935	C<0.>
		936
		937	These two functions can be used to associate arbitrary data with a loop,
		938	and are intended solely for the C<invoke_pending_cb>, C<release> and
		939	C<acquire> callbacks described above, but of course can be (ab-)used for
		940	any other purpose as well.
		941
725	=item ev_loop_verify (loop)	942	=item ev_loop_verify (loop)
726		943
727	This function only does something when C<EV_VERIFY> support has been	944	This function only does something when C<EV_VERIFY> support has been
728	compiled in. It tries to go through all internal structures and checks	945	compiled in, which is the default for non-minimal builds. It tries to go
729	them for validity. If anything is found to be inconsistent, it will print	946	through all internal structures and checks them for validity. If anything
730	an error message to standard error and call C<abort ()>.	947	is found to be inconsistent, it will print an error message to standard
		948	error and call C<abort ()>.
731		949
732	This can be used to catch bugs inside libev itself: under normal	950	This can be used to catch bugs inside libev itself: under normal
733	circumstances, this function will never abort as of course libev keeps its	951	circumstances, this function will never abort as of course libev keeps its
734	data structures consistent.	952	data structures consistent.
735		953
736	=back	954	=back
737		955
738		956
739	=head1 ANATOMY OF A WATCHER	957	=head1 ANATOMY OF A WATCHER
740		958
		959	In the following description, uppercase C<TYPE> in names stands for the
		960	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		961	watchers and C<ev_io_start> for I/O watchers.
		962
741	A watcher is a structure that you create and register to record your	963	A watcher is a structure that you create and register to record your
742	interest in some event. For instance, if you want to wait for STDIN to	964	interest in some event. For instance, if you want to wait for STDIN to
743	become readable, you would create an C<ev_io> watcher for that:	965	become readable, you would create an C<ev_io> watcher for that:
744		966
745	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	967	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
746	{	968	{
747	ev_io_stop (w);	969	ev_io_stop (w);
748	ev_unloop (loop, EVUNLOOP_ALL);	970	ev_unloop (loop, EVUNLOOP_ALL);
749	}	971	}
750		972
751	struct ev_loop *loop = ev_default_loop (0);	973	struct ev_loop *loop = ev_default_loop (0);
		974
752	struct ev_io stdin_watcher;	975	ev_io stdin_watcher;
		976
753	ev_init (&stdin_watcher, my_cb);	977	ev_init (&stdin_watcher, my_cb);
754	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	978	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
755	ev_io_start (loop, &stdin_watcher);	979	ev_io_start (loop, &stdin_watcher);
		980
756	ev_loop (loop, 0);	981	ev_loop (loop, 0);
757		982
758	As you can see, you are responsible for allocating the memory for your	983	As you can see, you are responsible for allocating the memory for your
759	watcher structures (and it is usually a bad idea to do this on the stack,	984	watcher structures (and it is I<usually> a bad idea to do this on the
760	although this can sometimes be quite valid).	985	stack).
		986
		987	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		988	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
761		989
762	Each watcher structure must be initialised by a call to C<ev_init	990	Each watcher structure must be initialised by a call to C<ev_init
763	(watcher *, callback)>, which expects a callback to be provided. This	991	(watcher *, callback)>, which expects a callback to be provided. This
764	callback gets invoked each time the event occurs (or, in the case of I/O	992	callback gets invoked each time the event occurs (or, in the case of I/O
765	watchers, each time the event loop detects that the file descriptor given	993	watchers, each time the event loop detects that the file descriptor given
766	is readable and/or writable).	994	is readable and/or writable).
767		995
768	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	996	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
769	with arguments specific to this watcher type. There is also a macro	997	macro to configure it, with arguments specific to the watcher type. There
770	to combine initialisation and setting in one call: C<< ev_<type>_init	998	is also a macro to combine initialisation and setting in one call: C<<
771	(watcher *, callback, ...) >>.	999	ev_TYPE_init (watcher *, callback, ...) >>.
772		1000
773	To make the watcher actually watch out for events, you have to start it	1001	To make the watcher actually watch out for events, you have to start it
774	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	1002	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
775	*) >>), and you can stop watching for events at any time by calling the	1003	*) >>), and you can stop watching for events at any time by calling the
776	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	1004	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
777		1005
778	As long as your watcher is active (has been started but not stopped) you	1006	As long as your watcher is active (has been started but not stopped) you
779	must not touch the values stored in it. Most specifically you must never	1007	must not touch the values stored in it. Most specifically you must never
780	reinitialise it or call its C<set> macro.	1008	reinitialise it or call its C<ev_TYPE_set> macro.
781		1009
782	Each and every callback receives the event loop pointer as first, the	1010	Each and every callback receives the event loop pointer as first, the
783	registered watcher structure as second, and a bitset of received events as	1011	registered watcher structure as second, and a bitset of received events as
784	third argument.	1012	third argument.
785		1013
…		…
843		1071
844	=item C<EV_ASYNC>	1072	=item C<EV_ASYNC>
845		1073
846	The given async watcher has been asynchronously notified (see C<ev_async>).	1074	The given async watcher has been asynchronously notified (see C<ev_async>).
847		1075
		1076	=item C<EV_CUSTOM>
		1077
		1078	Not ever sent (or otherwise used) by libev itself, but can be freely used
		1079	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		1080
848	=item C<EV_ERROR>	1081	=item C<EV_ERROR>
849		1082
850	An unspecified error has occurred, the watcher has been stopped. This might	1083	An unspecified error has occurred, the watcher has been stopped. This might
851	happen because the watcher could not be properly started because libev	1084	happen because the watcher could not be properly started because libev
852	ran out of memory, a file descriptor was found to be closed or any other	1085	ran out of memory, a file descriptor was found to be closed or any other
		1086	problem. Libev considers these application bugs.
		1087
853	problem. You best act on it by reporting the problem and somehow coping	1088	You best act on it by reporting the problem and somehow coping with the
854	with the watcher being stopped.	1089	watcher being stopped. Note that well-written programs should not receive
		1090	an error ever, so when your watcher receives it, this usually indicates a
		1091	bug in your program.
855		1092
856	Libev will usually signal a few "dummy" events together with an error,	1093	Libev will usually signal a few "dummy" events together with an error, for
857	for example it might indicate that a fd is readable or writable, and if	1094	example it might indicate that a fd is readable or writable, and if your
858	your callbacks is well-written it can just attempt the operation and cope	1095	callbacks is well-written it can just attempt the operation and cope with
859	with the error from read() or write(). This will not work in multi-threaded	1096	the error from read() or write(). This will not work in multi-threaded
860	programs, though, so beware.	1097	programs, though, as the fd could already be closed and reused for another
		1098	thing, so beware.
861		1099
862	=back	1100	=back
863		1101
864	=head2 GENERIC WATCHER FUNCTIONS	1102	=head2 GENERIC WATCHER FUNCTIONS
865
866	In the following description, C<TYPE> stands for the watcher type,
867	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
868		1103
869	=over 4	1104	=over 4
870		1105
871	=item C<ev_init> (ev_TYPE *watcher, callback)	1106	=item C<ev_init> (ev_TYPE *watcher, callback)
872		1107
…		…
878	which rolls both calls into one.	1113	which rolls both calls into one.
879		1114
880	You can reinitialise a watcher at any time as long as it has been stopped	1115	You can reinitialise a watcher at any time as long as it has been stopped
881	(or never started) and there are no pending events outstanding.	1116	(or never started) and there are no pending events outstanding.
882		1117
883	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1118	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
884	int revents)>.	1119	int revents)>.
		1120
		1121	Example: Initialise an C<ev_io> watcher in two steps.
		1122
		1123	ev_io w;
		1124	ev_init (&w, my_cb);
		1125	ev_io_set (&w, STDIN_FILENO, EV_READ);
885		1126
886	=item C<ev_TYPE_set> (ev_TYPE *, [args])	1127	=item C<ev_TYPE_set> (ev_TYPE *, [args])
887		1128
888	This macro initialises the type-specific parts of a watcher. You need to	1129	This macro initialises the type-specific parts of a watcher. You need to
889	call C<ev_init> at least once before you call this macro, but you can	1130	call C<ev_init> at least once before you call this macro, but you can
…		…
892	difference to the C<ev_init> macro).	1133	difference to the C<ev_init> macro).
893		1134
894	Although some watcher types do not have type-specific arguments	1135	Although some watcher types do not have type-specific arguments
895	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	1136	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
896		1137
		1138	See C<ev_init>, above, for an example.
		1139
897	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	1140	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
898		1141
899	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	1142	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
900	calls into a single call. This is the most convenient method to initialise	1143	calls into a single call. This is the most convenient method to initialise
901	a watcher. The same limitations apply, of course.	1144	a watcher. The same limitations apply, of course.
902		1145
		1146	Example: Initialise and set an C<ev_io> watcher in one step.
		1147
		1148	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
		1149
903	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1150	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
904		1151
905	Starts (activates) the given watcher. Only active watchers will receive	1152	Starts (activates) the given watcher. Only active watchers will receive
906	events. If the watcher is already active nothing will happen.	1153	events. If the watcher is already active nothing will happen.
907		1154
		1155	Example: Start the C<ev_io> watcher that is being abused as example in this
		1156	whole section.
		1157
		1158	ev_io_start (EV_DEFAULT_UC, &w);
		1159
908	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1160	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
909		1161
910	Stops the given watcher again (if active) and clears the pending	1162	Stops the given watcher if active, and clears the pending status (whether
		1163	the watcher was active or not).
		1164
911	status. It is possible that stopped watchers are pending (for example,	1165	It is possible that stopped watchers are pending - for example,
912	non-repeating timers are being stopped when they become pending), but	1166	non-repeating timers are being stopped when they become pending - but
913	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1167	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
914	you want to free or reuse the memory used by the watcher it is therefore a	1168	pending. If you want to free or reuse the memory used by the watcher it is
915	good idea to always call its C<ev_TYPE_stop> function.	1169	therefore a good idea to always call its C<ev_TYPE_stop> function.
916		1170
917	=item bool ev_is_active (ev_TYPE *watcher)	1171	=item bool ev_is_active (ev_TYPE *watcher)
918		1172
919	Returns a true value iff the watcher is active (i.e. it has been started	1173	Returns a true value iff the watcher is active (i.e. it has been started
920	and not yet been stopped). As long as a watcher is active you must not modify	1174	and not yet been stopped). As long as a watcher is active you must not modify
…		…
946	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1200	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
947	(default: C<-2>). Pending watchers with higher priority will be invoked	1201	(default: C<-2>). Pending watchers with higher priority will be invoked
948	before watchers with lower priority, but priority will not keep watchers	1202	before watchers with lower priority, but priority will not keep watchers
949	from being executed (except for C<ev_idle> watchers).	1203	from being executed (except for C<ev_idle> watchers).
950		1204
951	This means that priorities are I<only> used for ordering callback
952	invocation after new events have been received. This is useful, for
953	example, to reduce latency after idling, or more often, to bind two
954	watchers on the same event and make sure one is called first.
955
956	If you need to suppress invocation when higher priority events are pending	1205	If you need to suppress invocation when higher priority events are pending
957	you need to look at C<ev_idle> watchers, which provide this functionality.	1206	you need to look at C<ev_idle> watchers, which provide this functionality.
958		1207
959	You I<must not> change the priority of a watcher as long as it is active or	1208	You I<must not> change the priority of a watcher as long as it is active or
960	pending.	1209	pending.
961		1210
		1211	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1212	fine, as long as you do not mind that the priority value you query might
		1213	or might not have been clamped to the valid range.
		1214
962	The default priority used by watchers when no priority has been set is	1215	The default priority used by watchers when no priority has been set is
963	always C<0>, which is supposed to not be too high and not be too low :).	1216	always C<0>, which is supposed to not be too high and not be too low :).
964		1217
965	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1218	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
966	fine, as long as you do not mind that the priority value you query might	1219	priorities.
967	or might not have been adjusted to be within valid range.
968		1220
969	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1221	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
970		1222
971	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1223	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
972	C<loop> nor C<revents> need to be valid as long as the watcher callback	1224	C<loop> nor C<revents> need to be valid as long as the watcher callback
973	can deal with that fact.	1225	can deal with that fact, as both are simply passed through to the
		1226	callback.
974		1227
975	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1228	=item int ev_clear_pending (loop, ev_TYPE *watcher)
976		1229
977	If the watcher is pending, this function returns clears its pending status	1230	If the watcher is pending, this function clears its pending status and
978	and returns its C<revents> bitset (as if its callback was invoked). If the	1231	returns its C<revents> bitset (as if its callback was invoked). If the
979	watcher isn't pending it does nothing and returns C<0>.	1232	watcher isn't pending it does nothing and returns C<0>.
980		1233
		1234	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1235	callback to be invoked, which can be accomplished with this function.
		1236
981	=back	1237	=back
982		1238
983		1239
984	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1240	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
985		1241
986	Each watcher has, by default, a member C<void *data> that you can change	1242	Each watcher has, by default, a member C<void *data> that you can change
987	and read at any time, libev will completely ignore it. This can be used	1243	and read at any time: libev will completely ignore it. This can be used
988	to associate arbitrary data with your watcher. If you need more data and	1244	to associate arbitrary data with your watcher. If you need more data and
989	don't want to allocate memory and store a pointer to it in that data	1245	don't want to allocate memory and store a pointer to it in that data
990	member, you can also "subclass" the watcher type and provide your own	1246	member, you can also "subclass" the watcher type and provide your own
991	data:	1247	data:
992		1248
993	struct my_io	1249	struct my_io
994	{	1250	{
995	struct ev_io io;	1251	ev_io io;
996	int otherfd;	1252	int otherfd;
997	void *somedata;	1253	void *somedata;
998	struct whatever *mostinteresting;	1254	struct whatever *mostinteresting;
999	}	1255	};
		1256
		1257	...
		1258	struct my_io w;
		1259	ev_io_init (&w.io, my_cb, fd, EV_READ);
1000		1260
1001	And since your callback will be called with a pointer to the watcher, you	1261	And since your callback will be called with a pointer to the watcher, you
1002	can cast it back to your own type:	1262	can cast it back to your own type:
1003		1263
1004	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1264	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1005	{	1265	{
1006	struct my_io *w = (struct my_io *)w_;	1266	struct my_io *w = (struct my_io *)w_;
1007	...	1267	...
1008	}	1268	}
1009		1269
1010	More interesting and less C-conformant ways of casting your callback type	1270	More interesting and less C-conformant ways of casting your callback type
1011	instead have been omitted.	1271	instead have been omitted.
1012		1272
1013	Another common scenario is having some data structure with multiple	1273	Another common scenario is to use some data structure with multiple
1014	watchers:	1274	embedded watchers:
1015		1275
1016	struct my_biggy	1276	struct my_biggy
1017	{	1277	{
1018	int some_data;	1278	int some_data;
1019	ev_timer t1;	1279	ev_timer t1;
1020	ev_timer t2;	1280	ev_timer t2;
1021	}	1281	}
1022		1282
1023	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1283	In this case getting the pointer to C<my_biggy> is a bit more
1024	you need to use C<offsetof>:	1284	complicated: Either you store the address of your C<my_biggy> struct
		1285	in the C<data> member of the watcher (for woozies), or you need to use
		1286	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1287	programmers):
1025		1288
1026	#include <stddef.h>	1289	#include <stddef.h>
1027		1290
1028	static void	1291	static void
1029	t1_cb (EV_P_ struct ev_timer *w, int revents)	1292	t1_cb (EV_P_ ev_timer *w, int revents)
1030	{	1293	{
1031	struct my_biggy big = (struct my_biggy *	1294	struct my_biggy big = (struct my_biggy *)
1032	(((char *)w) - offsetof (struct my_biggy, t1));	1295	(((char *)w) - offsetof (struct my_biggy, t1));
1033	}	1296	}
1034		1297
1035	static void	1298	static void
1036	t2_cb (EV_P_ struct ev_timer *w, int revents)	1299	t2_cb (EV_P_ ev_timer *w, int revents)
1037	{	1300	{
1038	struct my_biggy big = (struct my_biggy *	1301	struct my_biggy big = (struct my_biggy *)
1039	(((char *)w) - offsetof (struct my_biggy, t2));	1302	(((char *)w) - offsetof (struct my_biggy, t2));
1040	}	1303	}
		1304
		1305	=head2 WATCHER PRIORITY MODELS
		1306
		1307	Many event loops support I<watcher priorities>, which are usually small
		1308	integers that influence the ordering of event callback invocation
		1309	between watchers in some way, all else being equal.
		1310
		1311	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1312	description for the more technical details such as the actual priority
		1313	range.
		1314
		1315	There are two common ways how these these priorities are being interpreted
		1316	by event loops:
		1317
		1318	In the more common lock-out model, higher priorities "lock out" invocation
		1319	of lower priority watchers, which means as long as higher priority
		1320	watchers receive events, lower priority watchers are not being invoked.
		1321
		1322	The less common only-for-ordering model uses priorities solely to order
		1323	callback invocation within a single event loop iteration: Higher priority
		1324	watchers are invoked before lower priority ones, but they all get invoked
		1325	before polling for new events.
		1326
		1327	Libev uses the second (only-for-ordering) model for all its watchers
		1328	except for idle watchers (which use the lock-out model).
		1329
		1330	The rationale behind this is that implementing the lock-out model for
		1331	watchers is not well supported by most kernel interfaces, and most event
		1332	libraries will just poll for the same events again and again as long as
		1333	their callbacks have not been executed, which is very inefficient in the
		1334	common case of one high-priority watcher locking out a mass of lower
		1335	priority ones.
		1336
		1337	Static (ordering) priorities are most useful when you have two or more
		1338	watchers handling the same resource: a typical usage example is having an
		1339	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1340	timeouts. Under load, data might be received while the program handles
		1341	other jobs, but since timers normally get invoked first, the timeout
		1342	handler will be executed before checking for data. In that case, giving
		1343	the timer a lower priority than the I/O watcher ensures that I/O will be
		1344	handled first even under adverse conditions (which is usually, but not
		1345	always, what you want).
		1346
		1347	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1348	will only be executed when no same or higher priority watchers have
		1349	received events, they can be used to implement the "lock-out" model when
		1350	required.
		1351
		1352	For example, to emulate how many other event libraries handle priorities,
		1353	you can associate an C<ev_idle> watcher to each such watcher, and in
		1354	the normal watcher callback, you just start the idle watcher. The real
		1355	processing is done in the idle watcher callback. This causes libev to
		1356	continously poll and process kernel event data for the watcher, but when
		1357	the lock-out case is known to be rare (which in turn is rare :), this is
		1358	workable.
		1359
		1360	Usually, however, the lock-out model implemented that way will perform
		1361	miserably under the type of load it was designed to handle. In that case,
		1362	it might be preferable to stop the real watcher before starting the
		1363	idle watcher, so the kernel will not have to process the event in case
		1364	the actual processing will be delayed for considerable time.
		1365
		1366	Here is an example of an I/O watcher that should run at a strictly lower
		1367	priority than the default, and which should only process data when no
		1368	other events are pending:
		1369
		1370	ev_idle idle; // actual processing watcher
		1371	ev_io io; // actual event watcher
		1372
		1373	static void
		1374	io_cb (EV_P_ ev_io *w, int revents)
		1375	{
		1376	// stop the I/O watcher, we received the event, but
		1377	// are not yet ready to handle it.
		1378	ev_io_stop (EV_A_ w);
		1379
		1380	// start the idle watcher to ahndle the actual event.
		1381	// it will not be executed as long as other watchers
		1382	// with the default priority are receiving events.
		1383	ev_idle_start (EV_A_ &idle);
		1384	}
		1385
		1386	static void
		1387	idle_cb (EV_P_ ev_idle *w, int revents)
		1388	{
		1389	// actual processing
		1390	read (STDIN_FILENO, ...);
		1391
		1392	// have to start the I/O watcher again, as
		1393	// we have handled the event
		1394	ev_io_start (EV_P_ &io);
		1395	}
		1396
		1397	// initialisation
		1398	ev_idle_init (&idle, idle_cb);
		1399	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1400	ev_io_start (EV_DEFAULT_ &io);
		1401
		1402	In the "real" world, it might also be beneficial to start a timer, so that
		1403	low-priority connections can not be locked out forever under load. This
		1404	enables your program to keep a lower latency for important connections
		1405	during short periods of high load, while not completely locking out less
		1406	important ones.
1041		1407
1042		1408
1043	=head1 WATCHER TYPES	1409	=head1 WATCHER TYPES
1044		1410
1045	This section describes each watcher in detail, but will not repeat	1411	This section describes each watcher in detail, but will not repeat
…		…
1069	In general you can register as many read and/or write event watchers per	1435	In general you can register as many read and/or write event watchers per
1070	fd as you want (as long as you don't confuse yourself). Setting all file	1436	fd as you want (as long as you don't confuse yourself). Setting all file
1071	descriptors to non-blocking mode is also usually a good idea (but not	1437	descriptors to non-blocking mode is also usually a good idea (but not
1072	required if you know what you are doing).	1438	required if you know what you are doing).
1073		1439
1074	If you must do this, then force the use of a known-to-be-good backend	1440	If you cannot use non-blocking mode, then force the use of a
1075	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and	1441	known-to-be-good backend (at the time of this writing, this includes only
1076	C<EVBACKEND_POLL>).	1442	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1443	descriptors for which non-blocking operation makes no sense (such as
		1444	files) - libev doesn't guarentee any specific behaviour in that case.
1077		1445
1078	Another thing you have to watch out for is that it is quite easy to	1446	Another thing you have to watch out for is that it is quite easy to
1079	receive "spurious" readiness notifications, that is your callback might	1447	receive "spurious" readiness notifications, that is your callback might
1080	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1448	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1081	because there is no data. Not only are some backends known to create a	1449	because there is no data. Not only are some backends known to create a
1082	lot of those (for example Solaris ports), it is very easy to get into	1450	lot of those (for example Solaris ports), it is very easy to get into
1083	this situation even with a relatively standard program structure. Thus	1451	this situation even with a relatively standard program structure. Thus
1084	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1452	it is best to always use non-blocking I/O: An extra C<read>(2) returning
1085	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1453	C<EAGAIN> is far preferable to a program hanging until some data arrives.
1086		1454
1087	If you cannot run the fd in non-blocking mode (for example you should not	1455	If you cannot run the fd in non-blocking mode (for example you should
1088	play around with an Xlib connection), then you have to separately re-test	1456	not play around with an Xlib connection), then you have to separately
1089	whether a file descriptor is really ready with a known-to-be good interface	1457	re-test whether a file descriptor is really ready with a known-to-be good
1090	such as poll (fortunately in our Xlib example, Xlib already does this on	1458	interface such as poll (fortunately in our Xlib example, Xlib already
1091	its own, so its quite safe to use).	1459	does this on its own, so its quite safe to use). Some people additionally
		1460	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1461	indefinitely.
		1462
		1463	But really, best use non-blocking mode.
1092		1464
1093	=head3 The special problem of disappearing file descriptors	1465	=head3 The special problem of disappearing file descriptors
1094		1466
1095	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1467	Some backends (e.g. kqueue, epoll) need to be told about closing a file
1096	descriptor (either by calling C<close> explicitly or by any other means,	1468	descriptor (either due to calling C<close> explicitly or any other means,
1097	such as C<dup>). The reason is that you register interest in some file	1469	such as C<dup2>). The reason is that you register interest in some file
1098	descriptor, but when it goes away, the operating system will silently drop	1470	descriptor, but when it goes away, the operating system will silently drop
1099	this interest. If another file descriptor with the same number then is	1471	this interest. If another file descriptor with the same number then is
1100	registered with libev, there is no efficient way to see that this is, in	1472	registered with libev, there is no efficient way to see that this is, in
1101	fact, a different file descriptor.	1473	fact, a different file descriptor.
1102		1474
…		…
1133	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1505	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
1134	C<EVBACKEND_POLL>.	1506	C<EVBACKEND_POLL>.
1135		1507
1136	=head3 The special problem of SIGPIPE	1508	=head3 The special problem of SIGPIPE
1137		1509
1138	While not really specific to libev, it is easy to forget about SIGPIPE:	1510	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
1139	when reading from a pipe whose other end has been closed, your program	1511	when writing to a pipe whose other end has been closed, your program gets
1140	gets send a SIGPIPE, which, by default, aborts your program. For most	1512	sent a SIGPIPE, which, by default, aborts your program. For most programs
1141	programs this is sensible behaviour, for daemons, this is usually	1513	this is sensible behaviour, for daemons, this is usually undesirable.
1142	undesirable.
1143		1514
1144	So when you encounter spurious, unexplained daemon exits, make sure you	1515	So when you encounter spurious, unexplained daemon exits, make sure you
1145	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon	1516	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
1146	somewhere, as that would have given you a big clue).	1517	somewhere, as that would have given you a big clue).
1147		1518
…		…
1153	=item ev_io_init (ev_io *, callback, int fd, int events)	1524	=item ev_io_init (ev_io *, callback, int fd, int events)
1154		1525
1155	=item ev_io_set (ev_io *, int fd, int events)	1526	=item ev_io_set (ev_io *, int fd, int events)
1156		1527
1157	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1528	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
1158	receive events for and events is either C<EV_READ>, C<EV_WRITE> or	1529	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
1159	C<EV_READ | EV_WRITE> to receive the given events.	1530	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
1160		1531
1161	=item int fd [read-only]	1532	=item int fd [read-only]
1162		1533
1163	The file descriptor being watched.	1534	The file descriptor being watched.
1164		1535
…		…
1173	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1544	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1174	readable, but only once. Since it is likely line-buffered, you could	1545	readable, but only once. Since it is likely line-buffered, you could
1175	attempt to read a whole line in the callback.	1546	attempt to read a whole line in the callback.
1176		1547
1177	static void	1548	static void
1178	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1549	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1179	{	1550	{
1180	ev_io_stop (loop, w);	1551	ev_io_stop (loop, w);
1181	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1552	.. read from stdin here (or from w->fd) and handle any I/O errors
1182	}	1553	}
1183		1554
1184	...	1555	...
1185	struct ev_loop *loop = ev_default_init (0);	1556	struct ev_loop *loop = ev_default_init (0);
1186	struct ev_io stdin_readable;	1557	ev_io stdin_readable;
1187	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1558	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1188	ev_io_start (loop, &stdin_readable);	1559	ev_io_start (loop, &stdin_readable);
1189	ev_loop (loop, 0);	1560	ev_loop (loop, 0);
1190		1561
1191		1562
…		…
1194	Timer watchers are simple relative timers that generate an event after a	1565	Timer watchers are simple relative timers that generate an event after a
1195	given time, and optionally repeating in regular intervals after that.	1566	given time, and optionally repeating in regular intervals after that.
1196		1567
1197	The timers are based on real time, that is, if you register an event that	1568	The timers are based on real time, that is, if you register an event that
1198	times out after an hour and you reset your system clock to January last	1569	times out after an hour and you reset your system clock to January last
1199	year, it will still time out after (roughly) and hour. "Roughly" because	1570	year, it will still time out after (roughly) one hour. "Roughly" because
1200	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1571	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1201	monotonic clock option helps a lot here).	1572	monotonic clock option helps a lot here).
		1573
		1574	The callback is guaranteed to be invoked only I<after> its timeout has
		1575	passed (not I<at>, so on systems with very low-resolution clocks this
		1576	might introduce a small delay). If multiple timers become ready during the
		1577	same loop iteration then the ones with earlier time-out values are invoked
		1578	before ones of the same priority with later time-out values (but this is
		1579	no longer true when a callback calls C<ev_loop> recursively).
		1580
		1581	=head3 Be smart about timeouts
		1582
		1583	Many real-world problems involve some kind of timeout, usually for error
		1584	recovery. A typical example is an HTTP request - if the other side hangs,
		1585	you want to raise some error after a while.
		1586
		1587	What follows are some ways to handle this problem, from obvious and
		1588	inefficient to smart and efficient.
		1589
		1590	In the following, a 60 second activity timeout is assumed - a timeout that
		1591	gets reset to 60 seconds each time there is activity (e.g. each time some
		1592	data or other life sign was received).
		1593
		1594	=over 4
		1595
		1596	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1597
		1598	This is the most obvious, but not the most simple way: In the beginning,
		1599	start the watcher:
		1600
		1601	ev_timer_init (timer, callback, 60., 0.);
		1602	ev_timer_start (loop, timer);
		1603
		1604	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1605	and start it again:
		1606
		1607	ev_timer_stop (loop, timer);
		1608	ev_timer_set (timer, 60., 0.);
		1609	ev_timer_start (loop, timer);
		1610
		1611	This is relatively simple to implement, but means that each time there is
		1612	some activity, libev will first have to remove the timer from its internal
		1613	data structure and then add it again. Libev tries to be fast, but it's
		1614	still not a constant-time operation.
		1615
		1616	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1617
		1618	This is the easiest way, and involves using C<ev_timer_again> instead of
		1619	C<ev_timer_start>.
		1620
		1621	To implement this, configure an C<ev_timer> with a C<repeat> value
		1622	of C<60> and then call C<ev_timer_again> at start and each time you
		1623	successfully read or write some data. If you go into an idle state where
		1624	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1625	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1626
		1627	That means you can ignore both the C<ev_timer_start> function and the
		1628	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1629	member and C<ev_timer_again>.
		1630
		1631	At start:
		1632
		1633	ev_init (timer, callback);
		1634	timer->repeat = 60.;
		1635	ev_timer_again (loop, timer);
		1636
		1637	Each time there is some activity:
		1638
		1639	ev_timer_again (loop, timer);
		1640
		1641	It is even possible to change the time-out on the fly, regardless of
		1642	whether the watcher is active or not:
		1643
		1644	timer->repeat = 30.;
		1645	ev_timer_again (loop, timer);
		1646
		1647	This is slightly more efficient then stopping/starting the timer each time
		1648	you want to modify its timeout value, as libev does not have to completely
		1649	remove and re-insert the timer from/into its internal data structure.
		1650
		1651	It is, however, even simpler than the "obvious" way to do it.
		1652
		1653	=item 3. Let the timer time out, but then re-arm it as required.
		1654
		1655	This method is more tricky, but usually most efficient: Most timeouts are
		1656	relatively long compared to the intervals between other activity - in
		1657	our example, within 60 seconds, there are usually many I/O events with
		1658	associated activity resets.
		1659
		1660	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1661	but remember the time of last activity, and check for a real timeout only
		1662	within the callback:
		1663
		1664	ev_tstamp last_activity; // time of last activity
		1665
		1666	static void
		1667	callback (EV_P_ ev_timer *w, int revents)
		1668	{
		1669	ev_tstamp now = ev_now (EV_A);
		1670	ev_tstamp timeout = last_activity + 60.;
		1671
		1672	// if last_activity + 60. is older than now, we did time out
		1673	if (timeout < now)
		1674	{
		1675	// timeout occured, take action
		1676	}
		1677	else
		1678	{
		1679	// callback was invoked, but there was some activity, re-arm
		1680	// the watcher to fire in last_activity + 60, which is
		1681	// guaranteed to be in the future, so "again" is positive:
		1682	w->repeat = timeout - now;
		1683	ev_timer_again (EV_A_ w);
		1684	}
		1685	}
		1686
		1687	To summarise the callback: first calculate the real timeout (defined
		1688	as "60 seconds after the last activity"), then check if that time has
		1689	been reached, which means something I<did>, in fact, time out. Otherwise
		1690	the callback was invoked too early (C<timeout> is in the future), so
		1691	re-schedule the timer to fire at that future time, to see if maybe we have
		1692	a timeout then.
		1693
		1694	Note how C<ev_timer_again> is used, taking advantage of the
		1695	C<ev_timer_again> optimisation when the timer is already running.
		1696
		1697	This scheme causes more callback invocations (about one every 60 seconds
		1698	minus half the average time between activity), but virtually no calls to
		1699	libev to change the timeout.
		1700
		1701	To start the timer, simply initialise the watcher and set C<last_activity>
		1702	to the current time (meaning we just have some activity :), then call the
		1703	callback, which will "do the right thing" and start the timer:
		1704
		1705	ev_init (timer, callback);
		1706	last_activity = ev_now (loop);
		1707	callback (loop, timer, EV_TIMEOUT);
		1708
		1709	And when there is some activity, simply store the current time in
		1710	C<last_activity>, no libev calls at all:
		1711
		1712	last_actiivty = ev_now (loop);
		1713
		1714	This technique is slightly more complex, but in most cases where the
		1715	time-out is unlikely to be triggered, much more efficient.
		1716
		1717	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1718	callback :) - just change the timeout and invoke the callback, which will
		1719	fix things for you.
		1720
		1721	=item 4. Wee, just use a double-linked list for your timeouts.
		1722
		1723	If there is not one request, but many thousands (millions...), all
		1724	employing some kind of timeout with the same timeout value, then one can
		1725	do even better:
		1726
		1727	When starting the timeout, calculate the timeout value and put the timeout
		1728	at the I<end> of the list.
		1729
		1730	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1731	the list is expected to fire (for example, using the technique #3).
		1732
		1733	When there is some activity, remove the timer from the list, recalculate
		1734	the timeout, append it to the end of the list again, and make sure to
		1735	update the C<ev_timer> if it was taken from the beginning of the list.
		1736
		1737	This way, one can manage an unlimited number of timeouts in O(1) time for
		1738	starting, stopping and updating the timers, at the expense of a major
		1739	complication, and having to use a constant timeout. The constant timeout
		1740	ensures that the list stays sorted.
		1741
		1742	=back
		1743
		1744	So which method the best?
		1745
		1746	Method #2 is a simple no-brain-required solution that is adequate in most
		1747	situations. Method #3 requires a bit more thinking, but handles many cases
		1748	better, and isn't very complicated either. In most case, choosing either
		1749	one is fine, with #3 being better in typical situations.
		1750
		1751	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1752	rather complicated, but extremely efficient, something that really pays
		1753	off after the first million or so of active timers, i.e. it's usually
		1754	overkill :)
		1755
		1756	=head3 The special problem of time updates
		1757
		1758	Establishing the current time is a costly operation (it usually takes at
		1759	least two system calls): EV therefore updates its idea of the current
		1760	time only before and after C<ev_loop> collects new events, which causes a
		1761	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1762	lots of events in one iteration.
1202		1763
1203	The relative timeouts are calculated relative to the C<ev_now ()>	1764	The relative timeouts are calculated relative to the C<ev_now ()>
1204	time. This is usually the right thing as this timestamp refers to the time	1765	time. This is usually the right thing as this timestamp refers to the time
1205	of the event triggering whatever timeout you are modifying/starting. If	1766	of the event triggering whatever timeout you are modifying/starting. If
1206	you suspect event processing to be delayed and you I<need> to base the timeout	1767	you suspect event processing to be delayed and you I<need> to base the
1207	on the current time, use something like this to adjust for this:	1768	timeout on the current time, use something like this to adjust for this:
1208		1769
1209	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1770	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1210		1771
1211	The callback is guaranteed to be invoked only after its timeout has passed,	1772	If the event loop is suspended for a long time, you can also force an
1212	but if multiple timers become ready during the same loop iteration then	1773	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1213	order of execution is undefined.	1774	()>.
		1775
		1776	=head3 The special problems of suspended animation
		1777
		1778	When you leave the server world it is quite customary to hit machines that
		1779	can suspend/hibernate - what happens to the clocks during such a suspend?
		1780
		1781	Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
		1782	all processes, while the clocks (C<times>, C<CLOCK_MONOTONIC>) continue
		1783	to run until the system is suspended, but they will not advance while the
		1784	system is suspended. That means, on resume, it will be as if the program
		1785	was frozen for a few seconds, but the suspend time will not be counted
		1786	towards C<ev_timer> when a monotonic clock source is used. The real time
		1787	clock advanced as expected, but if it is used as sole clocksource, then a
		1788	long suspend would be detected as a time jump by libev, and timers would
		1789	be adjusted accordingly.
		1790
		1791	I would not be surprised to see different behaviour in different between
		1792	operating systems, OS versions or even different hardware.
		1793
		1794	The other form of suspend (job control, or sending a SIGSTOP) will see a
		1795	time jump in the monotonic clocks and the realtime clock. If the program
		1796	is suspended for a very long time, and monotonic clock sources are in use,
		1797	then you can expect C<ev_timer>s to expire as the full suspension time
		1798	will be counted towards the timers. When no monotonic clock source is in
		1799	use, then libev will again assume a timejump and adjust accordingly.
		1800
		1801	It might be beneficial for this latter case to call C<ev_suspend>
		1802	and C<ev_resume> in code that handles C<SIGTSTP>, to at least get
		1803	deterministic behaviour in this case (you can do nothing against
		1804	C<SIGSTOP>).
1214		1805
1215	=head3 Watcher-Specific Functions and Data Members	1806	=head3 Watcher-Specific Functions and Data Members
1216		1807
1217	=over 4	1808	=over 4
1218		1809
…		…
1242	If the timer is started but non-repeating, stop it (as if it timed out).	1833	If the timer is started but non-repeating, stop it (as if it timed out).
1243		1834
1244	If the timer is repeating, either start it if necessary (with the	1835	If the timer is repeating, either start it if necessary (with the
1245	C<repeat> value), or reset the running timer to the C<repeat> value.	1836	C<repeat> value), or reset the running timer to the C<repeat> value.
1246		1837
1247	This sounds a bit complicated, but here is a useful and typical	1838	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1248	example: Imagine you have a TCP connection and you want a so-called idle	1839	usage example.
1249	timeout, that is, you want to be called when there have been, say, 60
1250	seconds of inactivity on the socket. The easiest way to do this is to
1251	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1252	C<ev_timer_again> each time you successfully read or write some data. If
1253	you go into an idle state where you do not expect data to travel on the
1254	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1255	automatically restart it if need be.
1256		1840
1257	That means you can ignore the C<after> value and C<ev_timer_start>	1841	=item ev_timer_remaining (loop, ev_timer *)
1258	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1259		1842
1260	ev_timer_init (timer, callback, 0., 5.);	1843	Returns the remaining time until a timer fires. If the timer is active,
1261	ev_timer_again (loop, timer);	1844	then this time is relative to the current event loop time, otherwise it's
1262	...	1845	the timeout value currently configured.
1263	timer->again = 17.;
1264	ev_timer_again (loop, timer);
1265	...
1266	timer->again = 10.;
1267	ev_timer_again (loop, timer);
1268		1846
1269	This is more slightly efficient then stopping/starting the timer each time	1847	That is, after an C<ev_timer_set (w, 5, 7)>, C<ev_timer_remaining> returns
1270	you want to modify its timeout value.	1848	C<5>. When the timer is started and one second passes, C<ev_timer_remain>
		1849	will return C<4>. When the timer expires and is restarted, it will return
		1850	roughly C<7> (likely slightly less as callback invocation takes some time,
		1851	too), and so on.
1271		1852
1272	=item ev_tstamp repeat [read-write]	1853	=item ev_tstamp repeat [read-write]
1273		1854
1274	The current C<repeat> value. Will be used each time the watcher times out	1855	The current C<repeat> value. Will be used each time the watcher times out
1275	or C<ev_timer_again> is called and determines the next timeout (if any),	1856	or C<ev_timer_again> is called, and determines the next timeout (if any),
1276	which is also when any modifications are taken into account.	1857	which is also when any modifications are taken into account.
1277		1858
1278	=back	1859	=back
1279		1860
1280	=head3 Examples	1861	=head3 Examples
1281		1862
1282	Example: Create a timer that fires after 60 seconds.	1863	Example: Create a timer that fires after 60 seconds.
1283		1864
1284	static void	1865	static void
1285	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1866	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1286	{	1867	{
1287	.. one minute over, w is actually stopped right here	1868	.. one minute over, w is actually stopped right here
1288	}	1869	}
1289		1870
1290	struct ev_timer mytimer;	1871	ev_timer mytimer;
1291	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1872	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1292	ev_timer_start (loop, &mytimer);	1873	ev_timer_start (loop, &mytimer);
1293		1874
1294	Example: Create a timeout timer that times out after 10 seconds of	1875	Example: Create a timeout timer that times out after 10 seconds of
1295	inactivity.	1876	inactivity.
1296		1877
1297	static void	1878	static void
1298	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1879	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1299	{	1880	{
1300	.. ten seconds without any activity	1881	.. ten seconds without any activity
1301	}	1882	}
1302		1883
1303	struct ev_timer mytimer;	1884	ev_timer mytimer;
1304	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1885	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1305	ev_timer_again (&mytimer); /* start timer */	1886	ev_timer_again (&mytimer); /* start timer */
1306	ev_loop (loop, 0);	1887	ev_loop (loop, 0);
1307		1888
1308	// and in some piece of code that gets executed on any "activity":	1889	// and in some piece of code that gets executed on any "activity":
…		…
1313	=head2 C<ev_periodic> - to cron or not to cron?	1894	=head2 C<ev_periodic> - to cron or not to cron?
1314		1895
1315	Periodic watchers are also timers of a kind, but they are very versatile	1896	Periodic watchers are also timers of a kind, but they are very versatile
1316	(and unfortunately a bit complex).	1897	(and unfortunately a bit complex).
1317		1898
1318	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1899	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1319	but on wall clock time (absolute time). You can tell a periodic watcher	1900	relative time, the physical time that passes) but on wall clock time
1320	to trigger after some specific point in time. For example, if you tell a	1901	(absolute time, the thing you can read on your calender or clock). The
1321	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1902	difference is that wall clock time can run faster or slower than real
1322	+ 10.>, that is, an absolute time not a delay) and then reset your system	1903	time, and time jumps are not uncommon (e.g. when you adjust your
1323	clock to January of the previous year, then it will take more than year	1904	wrist-watch).
1324	to trigger the event (unlike an C<ev_timer>, which would still trigger
1325	roughly 10 seconds later as it uses a relative timeout).
1326		1905
		1906	You can tell a periodic watcher to trigger after some specific point
		1907	in time: for example, if you tell a periodic watcher to trigger "in 10
		1908	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1909	not a delay) and then reset your system clock to January of the previous
		1910	year, then it will take a year or more to trigger the event (unlike an
		1911	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1912	it, as it uses a relative timeout).
		1913
1327	C<ev_periodic>s can also be used to implement vastly more complex timers,	1914	C<ev_periodic> watchers can also be used to implement vastly more complex
1328	such as triggering an event on each "midnight, local time", or other	1915	timers, such as triggering an event on each "midnight, local time", or
1329	complicated, rules.	1916	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1917	those cannot react to time jumps.
1330		1918
1331	As with timers, the callback is guaranteed to be invoked only when the	1919	As with timers, the callback is guaranteed to be invoked only when the
1332	time (C<at>) has passed, but if multiple periodic timers become ready	1920	point in time where it is supposed to trigger has passed. If multiple
1333	during the same loop iteration then order of execution is undefined.	1921	timers become ready during the same loop iteration then the ones with
		1922	earlier time-out values are invoked before ones with later time-out values
		1923	(but this is no longer true when a callback calls C<ev_loop> recursively).
1334		1924
1335	=head3 Watcher-Specific Functions and Data Members	1925	=head3 Watcher-Specific Functions and Data Members
1336		1926
1337	=over 4	1927	=over 4
1338		1928
1339	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1929	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1340		1930
1341	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1931	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1342		1932
1343	Lots of arguments, lets sort it out... There are basically three modes of	1933	Lots of arguments, let's sort it out... There are basically three modes of
1344	operation, and we will explain them from simplest to complex:	1934	operation, and we will explain them from simplest to most complex:
1345		1935
1346	=over 4	1936	=over 4
1347		1937
1348	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1938	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1349		1939
1350	In this configuration the watcher triggers an event after the wall clock	1940	In this configuration the watcher triggers an event after the wall clock
1351	time C<at> has passed and doesn't repeat. It will not adjust when a time	1941	time C<offset> has passed. It will not repeat and will not adjust when a
1352	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1942	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1353	run when the system time reaches or surpasses this time.	1943	will be stopped and invoked when the system clock reaches or surpasses
		1944	this point in time.
1354		1945
1355	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1946	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1356		1947
1357	In this mode the watcher will always be scheduled to time out at the next	1948	In this mode the watcher will always be scheduled to time out at the next
1358	C<at + N * interval> time (for some integer N, which can also be negative)	1949	C<offset + N * interval> time (for some integer N, which can also be
1359	and then repeat, regardless of any time jumps.	1950	negative) and then repeat, regardless of any time jumps. The C<offset>
		1951	argument is merely an offset into the C<interval> periods.
1360		1952
1361	This can be used to create timers that do not drift with respect to system	1953	This can be used to create timers that do not drift with respect to the
1362	time, for example, here is a C<ev_periodic> that triggers each hour, on	1954	system clock, for example, here is an C<ev_periodic> that triggers each
1363	the hour:	1955	hour, on the hour (with respect to UTC):
1364		1956
1365	ev_periodic_set (&periodic, 0., 3600., 0);	1957	ev_periodic_set (&periodic, 0., 3600., 0);
1366		1958
1367	This doesn't mean there will always be 3600 seconds in between triggers,	1959	This doesn't mean there will always be 3600 seconds in between triggers,
1368	but only that the callback will be called when the system time shows a	1960	but only that the callback will be called when the system time shows a
1369	full hour (UTC), or more correctly, when the system time is evenly divisible	1961	full hour (UTC), or more correctly, when the system time is evenly divisible
1370	by 3600.	1962	by 3600.
1371		1963
1372	Another way to think about it (for the mathematically inclined) is that	1964	Another way to think about it (for the mathematically inclined) is that
1373	C<ev_periodic> will try to run the callback in this mode at the next possible	1965	C<ev_periodic> will try to run the callback in this mode at the next possible
1374	time where C<time = at (mod interval)>, regardless of any time jumps.	1966	time where C<time = offset (mod interval)>, regardless of any time jumps.
1375		1967
1376	For numerical stability it is preferable that the C<at> value is near	1968	For numerical stability it is preferable that the C<offset> value is near
1377	C<ev_now ()> (the current time), but there is no range requirement for	1969	C<ev_now ()> (the current time), but there is no range requirement for
1378	this value, and in fact is often specified as zero.	1970	this value, and in fact is often specified as zero.
1379		1971
1380	Note also that there is an upper limit to how often a timer can fire (CPU	1972	Note also that there is an upper limit to how often a timer can fire (CPU
1381	speed for example), so if C<interval> is very small then timing stability	1973	speed for example), so if C<interval> is very small then timing stability
1382	will of course deteriorate. Libev itself tries to be exact to be about one	1974	will of course deteriorate. Libev itself tries to be exact to be about one
1383	millisecond (if the OS supports it and the machine is fast enough).	1975	millisecond (if the OS supports it and the machine is fast enough).
1384		1976
1385	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1977	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1386		1978
1387	In this mode the values for C<interval> and C<at> are both being	1979	In this mode the values for C<interval> and C<offset> are both being
1388	ignored. Instead, each time the periodic watcher gets scheduled, the	1980	ignored. Instead, each time the periodic watcher gets scheduled, the
1389	reschedule callback will be called with the watcher as first, and the	1981	reschedule callback will be called with the watcher as first, and the
1390	current time as second argument.	1982	current time as second argument.
1391		1983
1392	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1984	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1393	ever, or make ANY event loop modifications whatsoever>.	1985	or make ANY other event loop modifications whatsoever, unless explicitly
		1986	allowed by documentation here>.
1394		1987
1395	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1988	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1396	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1989	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1397	only event loop modification you are allowed to do).	1990	only event loop modification you are allowed to do).
1398		1991
1399	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1992	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1400	*w, ev_tstamp now)>, e.g.:	1993	*w, ev_tstamp now)>, e.g.:
1401		1994
		1995	static ev_tstamp
1402	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1996	my_rescheduler (ev_periodic *w, ev_tstamp now)
1403	{	1997	{
1404	return now + 60.;	1998	return now + 60.;
1405	}	1999	}
1406		2000
1407	It must return the next time to trigger, based on the passed time value	2001	It must return the next time to trigger, based on the passed time value
…		…
1427	a different time than the last time it was called (e.g. in a crond like	2021	a different time than the last time it was called (e.g. in a crond like
1428	program when the crontabs have changed).	2022	program when the crontabs have changed).
1429		2023
1430	=item ev_tstamp ev_periodic_at (ev_periodic *)	2024	=item ev_tstamp ev_periodic_at (ev_periodic *)
1431		2025
1432	When active, returns the absolute time that the watcher is supposed to	2026	When active, returns the absolute time that the watcher is supposed
1433	trigger next.	2027	to trigger next. This is not the same as the C<offset> argument to
		2028	C<ev_periodic_set>, but indeed works even in interval and manual
		2029	rescheduling modes.
1434		2030
1435	=item ev_tstamp offset [read-write]	2031	=item ev_tstamp offset [read-write]
1436		2032
1437	When repeating, this contains the offset value, otherwise this is the	2033	When repeating, this contains the offset value, otherwise this is the
1438	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	2034	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		2035	although libev might modify this value for better numerical stability).
1439		2036
1440	Can be modified any time, but changes only take effect when the periodic	2037	Can be modified any time, but changes only take effect when the periodic
1441	timer fires or C<ev_periodic_again> is being called.	2038	timer fires or C<ev_periodic_again> is being called.
1442		2039
1443	=item ev_tstamp interval [read-write]	2040	=item ev_tstamp interval [read-write]
1444		2041
1445	The current interval value. Can be modified any time, but changes only	2042	The current interval value. Can be modified any time, but changes only
1446	take effect when the periodic timer fires or C<ev_periodic_again> is being	2043	take effect when the periodic timer fires or C<ev_periodic_again> is being
1447	called.	2044	called.
1448		2045
1449	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	2046	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1450		2047
1451	The current reschedule callback, or C<0>, if this functionality is	2048	The current reschedule callback, or C<0>, if this functionality is
1452	switched off. Can be changed any time, but changes only take effect when	2049	switched off. Can be changed any time, but changes only take effect when
1453	the periodic timer fires or C<ev_periodic_again> is being called.	2050	the periodic timer fires or C<ev_periodic_again> is being called.
1454		2051
1455	=back	2052	=back
1456		2053
1457	=head3 Examples	2054	=head3 Examples
1458		2055
1459	Example: Call a callback every hour, or, more precisely, whenever the	2056	Example: Call a callback every hour, or, more precisely, whenever the
1460	system clock is divisible by 3600. The callback invocation times have	2057	system time is divisible by 3600. The callback invocation times have
1461	potentially a lot of jitter, but good long-term stability.	2058	potentially a lot of jitter, but good long-term stability.
1462		2059
1463	static void	2060	static void
1464	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	2061	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1465	{	2062	{
1466	... its now a full hour (UTC, or TAI or whatever your clock follows)	2063	... its now a full hour (UTC, or TAI or whatever your clock follows)
1467	}	2064	}
1468		2065
1469	struct ev_periodic hourly_tick;	2066	ev_periodic hourly_tick;
1470	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	2067	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1471	ev_periodic_start (loop, &hourly_tick);	2068	ev_periodic_start (loop, &hourly_tick);
1472		2069
1473	Example: The same as above, but use a reschedule callback to do it:	2070	Example: The same as above, but use a reschedule callback to do it:
1474		2071
1475	#include <math.h>	2072	#include <math.h>
1476		2073
1477	static ev_tstamp	2074	static ev_tstamp
1478	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	2075	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1479	{	2076	{
1480	return fmod (now, 3600.) + 3600.;	2077	return now + (3600. - fmod (now, 3600.));
1481	}	2078	}
1482		2079
1483	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	2080	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1484		2081
1485	Example: Call a callback every hour, starting now:	2082	Example: Call a callback every hour, starting now:
1486		2083
1487	struct ev_periodic hourly_tick;	2084	ev_periodic hourly_tick;
1488	ev_periodic_init (&hourly_tick, clock_cb,	2085	ev_periodic_init (&hourly_tick, clock_cb,
1489	fmod (ev_now (loop), 3600.), 3600., 0);	2086	fmod (ev_now (loop), 3600.), 3600., 0);
1490	ev_periodic_start (loop, &hourly_tick);	2087	ev_periodic_start (loop, &hourly_tick);
1491		2088
1492		2089
…		…
1495	Signal watchers will trigger an event when the process receives a specific	2092	Signal watchers will trigger an event when the process receives a specific
1496	signal one or more times. Even though signals are very asynchronous, libev	2093	signal one or more times. Even though signals are very asynchronous, libev
1497	will try it's best to deliver signals synchronously, i.e. as part of the	2094	will try it's best to deliver signals synchronously, i.e. as part of the
1498	normal event processing, like any other event.	2095	normal event processing, like any other event.
1499		2096
		2097	If you want signals to be delivered truly asynchronously, just use
		2098	C<sigaction> as you would do without libev and forget about sharing
		2099	the signal. You can even use C<ev_async> from a signal handler to
		2100	synchronously wake up an event loop.
		2101
1500	You can configure as many watchers as you like per signal. Only when the	2102	You can configure as many watchers as you like for the same signal, but
		2103	only within the same loop, i.e. you can watch for C<SIGINT> in your
		2104	default loop and for C<SIGIO> in another loop, but you cannot watch for
		2105	C<SIGINT> in both the default loop and another loop at the same time. At
		2106	the moment, C<SIGCHLD> is permanently tied to the default loop.
		2107
1501	first watcher gets started will libev actually register a signal watcher	2108	When the first watcher gets started will libev actually register something
1502	with the kernel (thus it coexists with your own signal handlers as long	2109	with the kernel (thus it coexists with your own signal handlers as long as
1503	as you don't register any with libev). Similarly, when the last signal	2110	you don't register any with libev for the same signal).
1504	watcher for a signal is stopped libev will reset the signal handler to	2111
1505	SIG_DFL (regardless of what it was set to before).	2112	Both the signal mask state (C<sigprocmask>) and the signal handler state
		2113	(C<sigaction>) are unspecified after starting a signal watcher (and after
		2114	sotpping it again), that is, libev might or might not block the signal,
		2115	and might or might not set or restore the installed signal handler.
1506		2116
1507	If possible and supported, libev will install its handlers with	2117	If possible and supported, libev will install its handlers with
1508	C<SA_RESTART> behaviour enabled, so system calls should not be unduly	2118	C<SA_RESTART> (or equivalent) behaviour enabled, so system calls should
1509	interrupted. If you have a problem with system calls getting interrupted by	2119	not be unduly interrupted. If you have a problem with system calls getting
1510	signals you can block all signals in an C<ev_check> watcher and unblock	2120	interrupted by signals you can block all signals in an C<ev_check> watcher
1511	them in an C<ev_prepare> watcher.	2121	and unblock them in an C<ev_prepare> watcher.
1512		2122
1513	=head3 Watcher-Specific Functions and Data Members	2123	=head3 Watcher-Specific Functions and Data Members
1514		2124
1515	=over 4	2125	=over 4
1516		2126
…		…
1527		2137
1528	=back	2138	=back
1529		2139
1530	=head3 Examples	2140	=head3 Examples
1531		2141
1532	Example: Try to exit cleanly on SIGINT and SIGTERM.	2142	Example: Try to exit cleanly on SIGINT.
1533		2143
1534	static void	2144	static void
1535	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	2145	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1536	{	2146	{
1537	ev_unloop (loop, EVUNLOOP_ALL);	2147	ev_unloop (loop, EVUNLOOP_ALL);
1538	}	2148	}
1539		2149
1540	struct ev_signal signal_watcher;	2150	ev_signal signal_watcher;
1541	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	2151	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1542	ev_signal_start (loop, &sigint_cb);	2152	ev_signal_start (loop, &signal_watcher);
1543		2153
1544		2154
1545	=head2 C<ev_child> - watch out for process status changes	2155	=head2 C<ev_child> - watch out for process status changes
1546		2156
1547	Child watchers trigger when your process receives a SIGCHLD in response to	2157	Child watchers trigger when your process receives a SIGCHLD in response to
1548	some child status changes (most typically when a child of yours dies). It	2158	some child status changes (most typically when a child of yours dies or
1549	is permissible to install a child watcher I<after> the child has been	2159	exits). It is permissible to install a child watcher I<after> the child
1550	forked (which implies it might have already exited), as long as the event	2160	has been forked (which implies it might have already exited), as long
1551	loop isn't entered (or is continued from a watcher).	2161	as the event loop isn't entered (or is continued from a watcher), i.e.,
		2162	forking and then immediately registering a watcher for the child is fine,
		2163	but forking and registering a watcher a few event loop iterations later or
		2164	in the next callback invocation is not.
1552		2165
1553	Only the default event loop is capable of handling signals, and therefore	2166	Only the default event loop is capable of handling signals, and therefore
1554	you can only register child watchers in the default event loop.	2167	you can only register child watchers in the default event loop.
1555		2168
		2169	Due to some design glitches inside libev, child watchers will always be
		2170	handled at maximum priority (their priority is set to C<EV_MAXPRI> by
		2171	libev)
		2172
1556	=head3 Process Interaction	2173	=head3 Process Interaction
1557		2174
1558	Libev grabs C<SIGCHLD> as soon as the default event loop is	2175	Libev grabs C<SIGCHLD> as soon as the default event loop is
1559	initialised. This is necessary to guarantee proper behaviour even if	2176	initialised. This is necessary to guarantee proper behaviour even if the
1560	the first child watcher is started after the child exits. The occurrence	2177	first child watcher is started after the child exits. The occurrence
1561	of C<SIGCHLD> is recorded asynchronously, but child reaping is done	2178	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
1562	synchronously as part of the event loop processing. Libev always reaps all	2179	synchronously as part of the event loop processing. Libev always reaps all
1563	children, even ones not watched.	2180	children, even ones not watched.
1564		2181
1565	=head3 Overriding the Built-In Processing	2182	=head3 Overriding the Built-In Processing
…		…
1575	=head3 Stopping the Child Watcher	2192	=head3 Stopping the Child Watcher
1576		2193
1577	Currently, the child watcher never gets stopped, even when the	2194	Currently, the child watcher never gets stopped, even when the
1578	child terminates, so normally one needs to stop the watcher in the	2195	child terminates, so normally one needs to stop the watcher in the
1579	callback. Future versions of libev might stop the watcher automatically	2196	callback. Future versions of libev might stop the watcher automatically
1580	when a child exit is detected.	2197	when a child exit is detected (calling C<ev_child_stop> twice is not a
		2198	problem).
1581		2199
1582	=head3 Watcher-Specific Functions and Data Members	2200	=head3 Watcher-Specific Functions and Data Members
1583		2201
1584	=over 4	2202	=over 4
1585		2203
…		…
1617	its completion.	2235	its completion.
1618		2236
1619	ev_child cw;	2237	ev_child cw;
1620		2238
1621	static void	2239	static void
1622	child_cb (EV_P_ struct ev_child *w, int revents)	2240	child_cb (EV_P_ ev_child *w, int revents)
1623	{	2241	{
1624	ev_child_stop (EV_A_ w);	2242	ev_child_stop (EV_A_ w);
1625	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2243	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1626	}	2244	}
1627		2245
…		…
1642		2260
1643		2261
1644	=head2 C<ev_stat> - did the file attributes just change?	2262	=head2 C<ev_stat> - did the file attributes just change?
1645		2263
1646	This watches a file system path for attribute changes. That is, it calls	2264	This watches a file system path for attribute changes. That is, it calls
1647	C<stat> regularly (or when the OS says it changed) and sees if it changed	2265	C<stat> on that path in regular intervals (or when the OS says it changed)
1648	compared to the last time, invoking the callback if it did.	2266	and sees if it changed compared to the last time, invoking the callback if
		2267	it did.
1649		2268
1650	The path does not need to exist: changing from "path exists" to "path does	2269	The path does not need to exist: changing from "path exists" to "path does
1651	not exist" is a status change like any other. The condition "path does	2270	not exist" is a status change like any other. The condition "path does not
1652	not exist" is signified by the C<st_nlink> field being zero (which is	2271	exist" (or more correctly "path cannot be stat'ed") is signified by the
1653	otherwise always forced to be at least one) and all the other fields of	2272	C<st_nlink> field being zero (which is otherwise always forced to be at
1654	the stat buffer having unspecified contents.	2273	least one) and all the other fields of the stat buffer having unspecified
		2274	contents.
1655		2275
1656	The path I<should> be absolute and I<must not> end in a slash. If it is	2276	The path I<must not> end in a slash or contain special components such as
		2277	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1657	relative and your working directory changes, the behaviour is undefined.	2278	your working directory changes, then the behaviour is undefined.
1658		2279
1659	Since there is no standard to do this, the portable implementation simply	2280	Since there is no portable change notification interface available, the
1660	calls C<stat (2)> regularly on the path to see if it changed somehow. You	2281	portable implementation simply calls C<stat(2)> regularly on the path
1661	can specify a recommended polling interval for this case. If you specify	2282	to see if it changed somehow. You can specify a recommended polling
1662	a polling interval of C<0> (highly recommended!) then a I<suitable,	2283	interval for this case. If you specify a polling interval of C<0> (highly
1663	unspecified default> value will be used (which you can expect to be around	2284	recommended!) then a I<suitable, unspecified default> value will be used
1664	five seconds, although this might change dynamically). Libev will also	2285	(which you can expect to be around five seconds, although this might
1665	impose a minimum interval which is currently around C<0.1>, but thats	2286	change dynamically). Libev will also impose a minimum interval which is
1666	usually overkill.	2287	currently around C<0.1>, but that's usually overkill.
1667		2288
1668	This watcher type is not meant for massive numbers of stat watchers,	2289	This watcher type is not meant for massive numbers of stat watchers,
1669	as even with OS-supported change notifications, this can be	2290	as even with OS-supported change notifications, this can be
1670	resource-intensive.	2291	resource-intensive.
1671		2292
1672	At the time of this writing, only the Linux inotify interface is	2293	At the time of this writing, the only OS-specific interface implemented
1673	implemented (implementing kqueue support is left as an exercise for the	2294	is the Linux inotify interface (implementing kqueue support is left as an
1674	reader, note, however, that the author sees no way of implementing ev_stat	2295	exercise for the reader. Note, however, that the author sees no way of
1675	semantics with kqueue). Inotify will be used to give hints only and should	2296	implementing C<ev_stat> semantics with kqueue, except as a hint).
1676	not change the semantics of C<ev_stat> watchers, which means that libev
1677	sometimes needs to fall back to regular polling again even with inotify,
1678	but changes are usually detected immediately, and if the file exists there
1679	will be no polling.
1680		2297
1681	=head3 ABI Issues (Largefile Support)	2298	=head3 ABI Issues (Largefile Support)
1682		2299
1683	Libev by default (unless the user overrides this) uses the default	2300	Libev by default (unless the user overrides this) uses the default
1684	compilation environment, which means that on systems with large file	2301	compilation environment, which means that on systems with large file
1685	support disabled by default, you get the 32 bit version of the stat	2302	support disabled by default, you get the 32 bit version of the stat
1686	structure. When using the library from programs that change the ABI to	2303	structure. When using the library from programs that change the ABI to
1687	use 64 bit file offsets the programs will fail. In that case you have to	2304	use 64 bit file offsets the programs will fail. In that case you have to
1688	compile libev with the same flags to get binary compatibility. This is	2305	compile libev with the same flags to get binary compatibility. This is
1689	obviously the case with any flags that change the ABI, but the problem is	2306	obviously the case with any flags that change the ABI, but the problem is
1690	most noticeably disabled with ev_stat and large file support.	2307	most noticeably displayed with ev_stat and large file support.
1691		2308
1692	The solution for this is to lobby your distribution maker to make large	2309	The solution for this is to lobby your distribution maker to make large
1693	file interfaces available by default (as e.g. FreeBSD does) and not	2310	file interfaces available by default (as e.g. FreeBSD does) and not
1694	optional. Libev cannot simply switch on large file support because it has	2311	optional. Libev cannot simply switch on large file support because it has
1695	to exchange stat structures with application programs compiled using the	2312	to exchange stat structures with application programs compiled using the
1696	default compilation environment.	2313	default compilation environment.
1697		2314
1698	=head3 Inotify	2315	=head3 Inotify and Kqueue
1699		2316
1700	When C<inotify (7)> support has been compiled into libev (generally only	2317	When C<inotify (7)> support has been compiled into libev and present at
1701	available on Linux) and present at runtime, it will be used to speed up	2318	runtime, it will be used to speed up change detection where possible. The
1702	change detection where possible. The inotify descriptor will be created lazily	2319	inotify descriptor will be created lazily when the first C<ev_stat>
1703	when the first C<ev_stat> watcher is being started.	2320	watcher is being started.
1704		2321
1705	Inotify presence does not change the semantics of C<ev_stat> watchers	2322	Inotify presence does not change the semantics of C<ev_stat> watchers
1706	except that changes might be detected earlier, and in some cases, to avoid	2323	except that changes might be detected earlier, and in some cases, to avoid
1707	making regular C<stat> calls. Even in the presence of inotify support	2324	making regular C<stat> calls. Even in the presence of inotify support
1708	there are many cases where libev has to resort to regular C<stat> polling.	2325	there are many cases where libev has to resort to regular C<stat> polling,
		2326	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2327	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2328	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2329	xfs are fully working) libev usually gets away without polling.
1709		2330
1710	(There is no support for kqueue, as apparently it cannot be used to	2331	There is no support for kqueue, as apparently it cannot be used to
1711	implement this functionality, due to the requirement of having a file	2332	implement this functionality, due to the requirement of having a file
1712	descriptor open on the object at all times).	2333	descriptor open on the object at all times, and detecting renames, unlinks
		2334	etc. is difficult.
		2335
		2336	=head3 C<stat ()> is a synchronous operation
		2337
		2338	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2339	the process. The exception are C<ev_stat> watchers - those call C<stat
		2340	()>, which is a synchronous operation.
		2341
		2342	For local paths, this usually doesn't matter: unless the system is very
		2343	busy or the intervals between stat's are large, a stat call will be fast,
		2344	as the path data is usually in memory already (except when starting the
		2345	watcher).
		2346
		2347	For networked file systems, calling C<stat ()> can block an indefinite
		2348	time due to network issues, and even under good conditions, a stat call
		2349	often takes multiple milliseconds.
		2350
		2351	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2352	paths, although this is fully supported by libev.
1713		2353
1714	=head3 The special problem of stat time resolution	2354	=head3 The special problem of stat time resolution
1715		2355
1716	The C<stat ()> system call only supports full-second resolution portably, and	2356	The C<stat ()> system call only supports full-second resolution portably,
1717	even on systems where the resolution is higher, many file systems still	2357	and even on systems where the resolution is higher, most file systems
1718	only support whole seconds.	2358	still only support whole seconds.
1719		2359
1720	That means that, if the time is the only thing that changes, you can	2360	That means that, if the time is the only thing that changes, you can
1721	easily miss updates: on the first update, C<ev_stat> detects a change and	2361	easily miss updates: on the first update, C<ev_stat> detects a change and
1722	calls your callback, which does something. When there is another update	2362	calls your callback, which does something. When there is another update
1723	within the same second, C<ev_stat> will be unable to detect it as the stat	2363	within the same second, C<ev_stat> will be unable to detect unless the
1724	data does not change.	2364	stat data does change in other ways (e.g. file size).
1725		2365
1726	The solution to this is to delay acting on a change for slightly more	2366	The solution to this is to delay acting on a change for slightly more
1727	than a second (or till slightly after the next full second boundary), using	2367	than a second (or till slightly after the next full second boundary), using
1728	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);	2368	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
1729	ev_timer_again (loop, w)>).	2369	ev_timer_again (loop, w)>).
…		…
1749	C<path>. The C<interval> is a hint on how quickly a change is expected to	2389	C<path>. The C<interval> is a hint on how quickly a change is expected to
1750	be detected and should normally be specified as C<0> to let libev choose	2390	be detected and should normally be specified as C<0> to let libev choose
1751	a suitable value. The memory pointed to by C<path> must point to the same	2391	a suitable value. The memory pointed to by C<path> must point to the same
1752	path for as long as the watcher is active.	2392	path for as long as the watcher is active.
1753		2393
1754	The callback will receive C<EV_STAT> when a change was detected, relative	2394	The callback will receive an C<EV_STAT> event when a change was detected,
1755	to the attributes at the time the watcher was started (or the last change	2395	relative to the attributes at the time the watcher was started (or the
1756	was detected).	2396	last change was detected).
1757		2397
1758	=item ev_stat_stat (loop, ev_stat *)	2398	=item ev_stat_stat (loop, ev_stat *)
1759		2399
1760	Updates the stat buffer immediately with new values. If you change the	2400	Updates the stat buffer immediately with new values. If you change the
1761	watched path in your callback, you could call this function to avoid	2401	watched path in your callback, you could call this function to avoid
…		…
1844		2484
1845		2485
1846	=head2 C<ev_idle> - when you've got nothing better to do...	2486	=head2 C<ev_idle> - when you've got nothing better to do...
1847		2487
1848	Idle watchers trigger events when no other events of the same or higher	2488	Idle watchers trigger events when no other events of the same or higher
1849	priority are pending (prepare, check and other idle watchers do not	2489	priority are pending (prepare, check and other idle watchers do not count
1850	count).	2490	as receiving "events").
1851		2491
1852	That is, as long as your process is busy handling sockets or timeouts	2492	That is, as long as your process is busy handling sockets or timeouts
1853	(or even signals, imagine) of the same or higher priority it will not be	2493	(or even signals, imagine) of the same or higher priority it will not be
1854	triggered. But when your process is idle (or only lower-priority watchers	2494	triggered. But when your process is idle (or only lower-priority watchers
1855	are pending), the idle watchers are being called once per event loop	2495	are pending), the idle watchers are being called once per event loop
…		…
1866		2506
1867	=head3 Watcher-Specific Functions and Data Members	2507	=head3 Watcher-Specific Functions and Data Members
1868		2508
1869	=over 4	2509	=over 4
1870		2510
1871	=item ev_idle_init (ev_signal *, callback)	2511	=item ev_idle_init (ev_idle *, callback)
1872		2512
1873	Initialises and configures the idle watcher - it has no parameters of any	2513	Initialises and configures the idle watcher - it has no parameters of any
1874	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2514	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1875	believe me.	2515	believe me.
1876		2516
…		…
1880		2520
1881	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2521	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1882	callback, free it. Also, use no error checking, as usual.	2522	callback, free it. Also, use no error checking, as usual.
1883		2523
1884	static void	2524	static void
1885	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2525	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1886	{	2526	{
1887	free (w);	2527	free (w);
1888	// now do something you wanted to do when the program has	2528	// now do something you wanted to do when the program has
1889	// no longer anything immediate to do.	2529	// no longer anything immediate to do.
1890	}	2530	}
1891		2531
1892	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2532	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1893	ev_idle_init (idle_watcher, idle_cb);	2533	ev_idle_init (idle_watcher, idle_cb);
1894	ev_idle_start (loop, idle_cb);	2534	ev_idle_start (loop, idle_watcher);
1895		2535
1896		2536
1897	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2537	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1898		2538
1899	Prepare and check watchers are usually (but not always) used in tandem:	2539	Prepare and check watchers are usually (but not always) used in pairs:
1900	prepare watchers get invoked before the process blocks and check watchers	2540	prepare watchers get invoked before the process blocks and check watchers
1901	afterwards.	2541	afterwards.
1902		2542
1903	You I<must not> call C<ev_loop> or similar functions that enter	2543	You I<must not> call C<ev_loop> or similar functions that enter
1904	the current event loop from either C<ev_prepare> or C<ev_check>	2544	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1907	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2547	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1908	C<ev_check> so if you have one watcher of each kind they will always be	2548	C<ev_check> so if you have one watcher of each kind they will always be
1909	called in pairs bracketing the blocking call.	2549	called in pairs bracketing the blocking call.
1910		2550
1911	Their main purpose is to integrate other event mechanisms into libev and	2551	Their main purpose is to integrate other event mechanisms into libev and
1912	their use is somewhat advanced. This could be used, for example, to track	2552	their use is somewhat advanced. They could be used, for example, to track
1913	variable changes, implement your own watchers, integrate net-snmp or a	2553	variable changes, implement your own watchers, integrate net-snmp or a
1914	coroutine library and lots more. They are also occasionally useful if	2554	coroutine library and lots more. They are also occasionally useful if
1915	you cache some data and want to flush it before blocking (for example,	2555	you cache some data and want to flush it before blocking (for example,
1916	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2556	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1917	watcher).	2557	watcher).
1918		2558
1919	This is done by examining in each prepare call which file descriptors need	2559	This is done by examining in each prepare call which file descriptors
1920	to be watched by the other library, registering C<ev_io> watchers for	2560	need to be watched by the other library, registering C<ev_io> watchers
1921	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2561	for them and starting an C<ev_timer> watcher for any timeouts (many
1922	provide just this functionality). Then, in the check watcher you check for	2562	libraries provide exactly this functionality). Then, in the check watcher,
1923	any events that occurred (by checking the pending status of all watchers	2563	you check for any events that occurred (by checking the pending status
1924	and stopping them) and call back into the library. The I/O and timer	2564	of all watchers and stopping them) and call back into the library. The
1925	callbacks will never actually be called (but must be valid nevertheless,	2565	I/O and timer callbacks will never actually be called (but must be valid
1926	because you never know, you know?).	2566	nevertheless, because you never know, you know?).
1927		2567
1928	As another example, the Perl Coro module uses these hooks to integrate	2568	As another example, the Perl Coro module uses these hooks to integrate
1929	coroutines into libev programs, by yielding to other active coroutines	2569	coroutines into libev programs, by yielding to other active coroutines
1930	during each prepare and only letting the process block if no coroutines	2570	during each prepare and only letting the process block if no coroutines
1931	are ready to run (it's actually more complicated: it only runs coroutines	2571	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1934	loop from blocking if lower-priority coroutines are active, thus mapping	2574	loop from blocking if lower-priority coroutines are active, thus mapping
1935	low-priority coroutines to idle/background tasks).	2575	low-priority coroutines to idle/background tasks).
1936		2576
1937	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2577	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1938	priority, to ensure that they are being run before any other watchers	2578	priority, to ensure that they are being run before any other watchers
		2579	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2580
1939	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2581	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1940	too) should not activate ("feed") events into libev. While libev fully	2582	activate ("feed") events into libev. While libev fully supports this, they
1941	supports this, they might get executed before other C<ev_check> watchers	2583	might get executed before other C<ev_check> watchers did their job. As
1942	did their job. As C<ev_check> watchers are often used to embed other	2584	C<ev_check> watchers are often used to embed other (non-libev) event
1943	(non-libev) event loops those other event loops might be in an unusable	2585	loops those other event loops might be in an unusable state until their
1944	state until their C<ev_check> watcher ran (always remind yourself to	2586	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1945	coexist peacefully with others).	2587	others).
1946		2588
1947	=head3 Watcher-Specific Functions and Data Members	2589	=head3 Watcher-Specific Functions and Data Members
1948		2590
1949	=over 4	2591	=over 4
1950		2592
…		…
1952		2594
1953	=item ev_check_init (ev_check *, callback)	2595	=item ev_check_init (ev_check *, callback)
1954		2596
1955	Initialises and configures the prepare or check watcher - they have no	2597	Initialises and configures the prepare or check watcher - they have no
1956	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2598	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1957	macros, but using them is utterly, utterly and completely pointless.	2599	macros, but using them is utterly, utterly, utterly and completely
		2600	pointless.
1958		2601
1959	=back	2602	=back
1960		2603
1961	=head3 Examples	2604	=head3 Examples
1962		2605
…		…
1975		2618
1976	static ev_io iow [nfd];	2619	static ev_io iow [nfd];
1977	static ev_timer tw;	2620	static ev_timer tw;
1978		2621
1979	static void	2622	static void
1980	io_cb (ev_loop *loop, ev_io *w, int revents)	2623	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1981	{	2624	{
1982	}	2625	}
1983		2626
1984	// create io watchers for each fd and a timer before blocking	2627	// create io watchers for each fd and a timer before blocking
1985	static void	2628	static void
1986	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2629	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1987	{	2630	{
1988	int timeout = 3600000;	2631	int timeout = 3600000;
1989	struct pollfd fds [nfd];	2632	struct pollfd fds [nfd];
1990	// actual code will need to loop here and realloc etc.	2633	// actual code will need to loop here and realloc etc.
1991	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2634	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1992		2635
1993	/* the callback is illegal, but won't be called as we stop during check */	2636	/* the callback is illegal, but won't be called as we stop during check */
1994	ev_timer_init (&tw, 0, timeout * 1e-3);	2637	ev_timer_init (&tw, 0, timeout * 1e-3, 0.);
1995	ev_timer_start (loop, &tw);	2638	ev_timer_start (loop, &tw);
1996		2639
1997	// create one ev_io per pollfd	2640	// create one ev_io per pollfd
1998	for (int i = 0; i < nfd; ++i)	2641	for (int i = 0; i < nfd; ++i)
1999	{	2642	{
…		…
2006	}	2649	}
2007	}	2650	}
2008		2651
2009	// stop all watchers after blocking	2652	// stop all watchers after blocking
2010	static void	2653	static void
2011	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2654	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2012	{	2655	{
2013	ev_timer_stop (loop, &tw);	2656	ev_timer_stop (loop, &tw);
2014		2657
2015	for (int i = 0; i < nfd; ++i)	2658	for (int i = 0; i < nfd; ++i)
2016	{	2659	{
…		…
2055	}	2698	}
2056		2699
2057	// do not ever call adns_afterpoll	2700	// do not ever call adns_afterpoll
2058		2701
2059	Method 4: Do not use a prepare or check watcher because the module you	2702	Method 4: Do not use a prepare or check watcher because the module you
2060	want to embed is too inflexible to support it. Instead, you can override	2703	want to embed is not flexible enough to support it. Instead, you can
2061	their poll function. The drawback with this solution is that the main	2704	override their poll function. The drawback with this solution is that the
2062	loop is now no longer controllable by EV. The C<Glib::EV> module does	2705	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
2063	this.	2706	this approach, effectively embedding EV as a client into the horrible
		2707	libglib event loop.
2064		2708
2065	static gint	2709	static gint
2066	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2710	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2067	{	2711	{
2068	int got_events = 0;	2712	int got_events = 0;
…		…
2099	prioritise I/O.	2743	prioritise I/O.
2100		2744
2101	As an example for a bug workaround, the kqueue backend might only support	2745	As an example for a bug workaround, the kqueue backend might only support
2102	sockets on some platform, so it is unusable as generic backend, but you	2746	sockets on some platform, so it is unusable as generic backend, but you
2103	still want to make use of it because you have many sockets and it scales	2747	still want to make use of it because you have many sockets and it scales
2104	so nicely. In this case, you would create a kqueue-based loop and embed it	2748	so nicely. In this case, you would create a kqueue-based loop and embed
2105	into your default loop (which might use e.g. poll). Overall operation will	2749	it into your default loop (which might use e.g. poll). Overall operation
2106	be a bit slower because first libev has to poll and then call kevent, but	2750	will be a bit slower because first libev has to call C<poll> and then
2107	at least you can use both at what they are best.	2751	C<kevent>, but at least you can use both mechanisms for what they are
		2752	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
2108		2753
2109	As for prioritising I/O: rarely you have the case where some fds have	2754	As for prioritising I/O: under rare circumstances you have the case where
2110	to be watched and handled very quickly (with low latency), and even	2755	some fds have to be watched and handled very quickly (with low latency),
2111	priorities and idle watchers might have too much overhead. In this case	2756	and even priorities and idle watchers might have too much overhead. In
2112	you would put all the high priority stuff in one loop and all the rest in	2757	this case you would put all the high priority stuff in one loop and all
2113	a second one, and embed the second one in the first.	2758	the rest in a second one, and embed the second one in the first.
2114		2759
2115	As long as the watcher is active, the callback will be invoked every time	2760	As long as the watcher is active, the callback will be invoked every
2116	there might be events pending in the embedded loop. The callback must then	2761	time there might be events pending in the embedded loop. The callback
2117	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2762	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2118	their callbacks (you could also start an idle watcher to give the embedded	2763	sweep and invoke their callbacks (the callback doesn't need to invoke the
2119	loop strictly lower priority for example). You can also set the callback	2764	C<ev_embed_sweep> function directly, it could also start an idle watcher
2120	to C<0>, in which case the embed watcher will automatically execute the	2765	to give the embedded loop strictly lower priority for example).
2121	embedded loop sweep.
2122		2766
2123	As long as the watcher is started it will automatically handle events. The	2767	You can also set the callback to C<0>, in which case the embed watcher
2124	callback will be invoked whenever some events have been handled. You can	2768	will automatically execute the embedded loop sweep whenever necessary.
2125	set the callback to C<0> to avoid having to specify one if you are not
2126	interested in that.
2127		2769
2128	Also, there have not currently been made special provisions for forking:	2770	Fork detection will be handled transparently while the C<ev_embed> watcher
2129	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2771	is active, i.e., the embedded loop will automatically be forked when the
2130	but you will also have to stop and restart any C<ev_embed> watchers	2772	embedding loop forks. In other cases, the user is responsible for calling
2131	yourself.	2773	C<ev_loop_fork> on the embedded loop.
2132		2774
2133	Unfortunately, not all backends are embeddable, only the ones returned by	2775	Unfortunately, not all backends are embeddable: only the ones returned by
2134	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2776	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2135	portable one.	2777	portable one.
2136		2778
2137	So when you want to use this feature you will always have to be prepared	2779	So when you want to use this feature you will always have to be prepared
2138	that you cannot get an embeddable loop. The recommended way to get around	2780	that you cannot get an embeddable loop. The recommended way to get around
2139	this is to have a separate variables for your embeddable loop, try to	2781	this is to have a separate variables for your embeddable loop, try to
2140	create it, and if that fails, use the normal loop for everything.	2782	create it, and if that fails, use the normal loop for everything.
		2783
		2784	=head3 C<ev_embed> and fork
		2785
		2786	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2787	automatically be applied to the embedded loop as well, so no special
		2788	fork handling is required in that case. When the watcher is not running,
		2789	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2790	as applicable.
2141		2791
2142	=head3 Watcher-Specific Functions and Data Members	2792	=head3 Watcher-Specific Functions and Data Members
2143		2793
2144	=over 4	2794	=over 4
2145		2795
…		…
2173	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2823	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2174	used).	2824	used).
2175		2825
2176	struct ev_loop *loop_hi = ev_default_init (0);	2826	struct ev_loop *loop_hi = ev_default_init (0);
2177	struct ev_loop *loop_lo = 0;	2827	struct ev_loop *loop_lo = 0;
2178	struct ev_embed embed;	2828	ev_embed embed;
2179		2829
2180	// see if there is a chance of getting one that works	2830	// see if there is a chance of getting one that works
2181	// (remember that a flags value of 0 means autodetection)	2831	// (remember that a flags value of 0 means autodetection)
2182	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2832	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2183	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2833	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2197	kqueue implementation). Store the kqueue/socket-only event loop in	2847	kqueue implementation). Store the kqueue/socket-only event loop in
2198	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2848	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2199		2849
2200	struct ev_loop *loop = ev_default_init (0);	2850	struct ev_loop *loop = ev_default_init (0);
2201	struct ev_loop *loop_socket = 0;	2851	struct ev_loop *loop_socket = 0;
2202	struct ev_embed embed;	2852	ev_embed embed;
2203		2853
2204	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2854	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2205	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2855	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2206	{	2856	{
2207	ev_embed_init (&embed, 0, loop_socket);	2857	ev_embed_init (&embed, 0, loop_socket);
…		…
2222	event loop blocks next and before C<ev_check> watchers are being called,	2872	event loop blocks next and before C<ev_check> watchers are being called,
2223	and only in the child after the fork. If whoever good citizen calling	2873	and only in the child after the fork. If whoever good citizen calling
2224	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2874	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2225	handlers will be invoked, too, of course.	2875	handlers will be invoked, too, of course.
2226		2876
		2877	=head3 The special problem of life after fork - how is it possible?
		2878
		2879	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2880	up/change the process environment, followed by a call to C<exec()>. This
		2881	sequence should be handled by libev without any problems.
		2882
		2883	This changes when the application actually wants to do event handling
		2884	in the child, or both parent in child, in effect "continuing" after the
		2885	fork.
		2886
		2887	The default mode of operation (for libev, with application help to detect
		2888	forks) is to duplicate all the state in the child, as would be expected
		2889	when I<either> the parent I<or> the child process continues.
		2890
		2891	When both processes want to continue using libev, then this is usually the
		2892	wrong result. In that case, usually one process (typically the parent) is
		2893	supposed to continue with all watchers in place as before, while the other
		2894	process typically wants to start fresh, i.e. without any active watchers.
		2895
		2896	The cleanest and most efficient way to achieve that with libev is to
		2897	simply create a new event loop, which of course will be "empty", and
		2898	use that for new watchers. This has the advantage of not touching more
		2899	memory than necessary, and thus avoiding the copy-on-write, and the
		2900	disadvantage of having to use multiple event loops (which do not support
		2901	signal watchers).
		2902
		2903	When this is not possible, or you want to use the default loop for
		2904	other reasons, then in the process that wants to start "fresh", call
		2905	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2906	the default loop will "orphan" (not stop) all registered watchers, so you
		2907	have to be careful not to execute code that modifies those watchers. Note
		2908	also that in that case, you have to re-register any signal watchers.
		2909
2227	=head3 Watcher-Specific Functions and Data Members	2910	=head3 Watcher-Specific Functions and Data Members
2228		2911
2229	=over 4	2912	=over 4
2230		2913
2231	=item ev_fork_init (ev_signal *, callback)	2914	=item ev_fork_init (ev_signal *, callback)
…		…
2263	is that the author does not know of a simple (or any) algorithm for a	2946	is that the author does not know of a simple (or any) algorithm for a
2264	multiple-writer-single-reader queue that works in all cases and doesn't	2947	multiple-writer-single-reader queue that works in all cases and doesn't
2265	need elaborate support such as pthreads.	2948	need elaborate support such as pthreads.
2266		2949
2267	That means that if you want to queue data, you have to provide your own	2950	That means that if you want to queue data, you have to provide your own
2268	queue. But at least I can tell you would implement locking around your	2951	queue. But at least I can tell you how to implement locking around your
2269	queue:	2952	queue:
2270		2953
2271	=over 4	2954	=over 4
2272		2955
2273	=item queueing from a signal handler context	2956	=item queueing from a signal handler context
2274		2957
2275	To implement race-free queueing, you simply add to the queue in the signal	2958	To implement race-free queueing, you simply add to the queue in the signal
2276	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2959	handler but you block the signal handler in the watcher callback. Here is
2277	some fictitious SIGUSR1 handler:	2960	an example that does that for some fictitious SIGUSR1 handler:
2278		2961
2279	static ev_async mysig;	2962	static ev_async mysig;
2280		2963
2281	static void	2964	static void
2282	sigusr1_handler (void)	2965	sigusr1_handler (void)
…		…
2348	=over 4	3031	=over 4
2349		3032
2350	=item ev_async_init (ev_async *, callback)	3033	=item ev_async_init (ev_async *, callback)
2351		3034
2352	Initialises and configures the async watcher - it has no parameters of any	3035	Initialises and configures the async watcher - it has no parameters of any
2353	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	3036	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2354	believe me.	3037	trust me.
2355		3038
2356	=item ev_async_send (loop, ev_async *)	3039	=item ev_async_send (loop, ev_async *)
2357		3040
2358	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	3041	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2359	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	3042	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2360	C<ev_feed_event>, this call is safe to do in other threads, signal or	3043	C<ev_feed_event>, this call is safe to do from other threads, signal or
2361	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	3044	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2362	section below on what exactly this means).	3045	section below on what exactly this means).
2363		3046
		3047	Note that, as with other watchers in libev, multiple events might get
		3048	compressed into a single callback invocation (another way to look at this
		3049	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		3050	reset when the event loop detects that).
		3051
2364	This call incurs the overhead of a system call only once per loop iteration,	3052	This call incurs the overhead of a system call only once per event loop
2365	so while the overhead might be noticeable, it doesn't apply to repeated	3053	iteration, so while the overhead might be noticeable, it doesn't apply to
2366	calls to C<ev_async_send>.	3054	repeated calls to C<ev_async_send> for the same event loop.
2367		3055
2368	=item bool = ev_async_pending (ev_async *)	3056	=item bool = ev_async_pending (ev_async *)
2369		3057
2370	Returns a non-zero value when C<ev_async_send> has been called on the	3058	Returns a non-zero value when C<ev_async_send> has been called on the
2371	watcher but the event has not yet been processed (or even noted) by the	3059	watcher but the event has not yet been processed (or even noted) by the
…		…
2374	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	3062	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2375	the loop iterates next and checks for the watcher to have become active,	3063	the loop iterates next and checks for the watcher to have become active,
2376	it will reset the flag again. C<ev_async_pending> can be used to very	3064	it will reset the flag again. C<ev_async_pending> can be used to very
2377	quickly check whether invoking the loop might be a good idea.	3065	quickly check whether invoking the loop might be a good idea.
2378		3066
2379	Not that this does I<not> check whether the watcher itself is pending, only	3067	Not that this does I<not> check whether the watcher itself is pending,
2380	whether it has been requested to make this watcher pending.	3068	only whether it has been requested to make this watcher pending: there
		3069	is a time window between the event loop checking and resetting the async
		3070	notification, and the callback being invoked.
2381		3071
2382	=back	3072	=back
2383		3073
2384		3074
2385	=head1 OTHER FUNCTIONS	3075	=head1 OTHER FUNCTIONS
…		…
2389	=over 4	3079	=over 4
2390		3080
2391	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	3081	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2392		3082
2393	This function combines a simple timer and an I/O watcher, calls your	3083	This function combines a simple timer and an I/O watcher, calls your
2394	callback on whichever event happens first and automatically stop both	3084	callback on whichever event happens first and automatically stops both
2395	watchers. This is useful if you want to wait for a single event on an fd	3085	watchers. This is useful if you want to wait for a single event on an fd
2396	or timeout without having to allocate/configure/start/stop/free one or	3086	or timeout without having to allocate/configure/start/stop/free one or
2397	more watchers yourself.	3087	more watchers yourself.
2398		3088
2399	If C<fd> is less than 0, then no I/O watcher will be started and events	3089	If C<fd> is less than 0, then no I/O watcher will be started and the
2400	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	3090	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2401	C<events> set will be created and started.	3091	the given C<fd> and C<events> set will be created and started.
2402		3092
2403	If C<timeout> is less than 0, then no timeout watcher will be	3093	If C<timeout> is less than 0, then no timeout watcher will be
2404	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	3094	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2405	repeat = 0) will be started. While C<0> is a valid timeout, it is of	3095	repeat = 0) will be started. C<0> is a valid timeout.
2406	dubious value.
2407		3096
2408	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	3097	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2409	passed an C<revents> set like normal event callbacks (a combination of	3098	passed an C<revents> set like normal event callbacks (a combination of
2410	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	3099	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2411	value passed to C<ev_once>:	3100	value passed to C<ev_once>. Note that it is possible to receive I<both>
		3101	a timeout and an io event at the same time - you probably should give io
		3102	events precedence.
		3103
		3104	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2412		3105
2413	static void stdin_ready (int revents, void *arg)	3106	static void stdin_ready (int revents, void *arg)
2414	{	3107	{
		3108	if (revents & EV_READ)
		3109	/* stdin might have data for us, joy! */;
2415	if (revents & EV_TIMEOUT)	3110	else if (revents & EV_TIMEOUT)
2416	/* doh, nothing entered */;	3111	/* doh, nothing entered */;
2417	else if (revents & EV_READ)
2418	/* stdin might have data for us, joy! */;
2419	}	3112	}
2420		3113
2421	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	3114	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2422		3115
2423	=item ev_feed_event (ev_loop *, watcher *, int revents)	3116	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2424		3117
2425	Feeds the given event set into the event loop, as if the specified event	3118	Feeds the given event set into the event loop, as if the specified event
2426	had happened for the specified watcher (which must be a pointer to an	3119	had happened for the specified watcher (which must be a pointer to an
2427	initialised but not necessarily started event watcher).	3120	initialised but not necessarily started event watcher).
2428		3121
2429	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	3122	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2430		3123
2431	Feed an event on the given fd, as if a file descriptor backend detected	3124	Feed an event on the given fd, as if a file descriptor backend detected
2432	the given events it.	3125	the given events it.
2433		3126
2434	=item ev_feed_signal_event (ev_loop *loop, int signum)	3127	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2435		3128
2436	Feed an event as if the given signal occurred (C<loop> must be the default	3129	Feed an event as if the given signal occurred (C<loop> must be the default
2437	loop!).	3130	loop!).
2438		3131
2439	=back	3132	=back
…		…
2561		3254
2562	myclass obj;	3255	myclass obj;
2563	ev::io iow;	3256	ev::io iow;
2564	iow.set <myclass, &myclass::io_cb> (&obj);	3257	iow.set <myclass, &myclass::io_cb> (&obj);
2565		3258
		3259	=item w->set (object *)
		3260
		3261	This is an B<experimental> feature that might go away in a future version.
		3262
		3263	This is a variation of a method callback - leaving out the method to call
		3264	will default the method to C<operator ()>, which makes it possible to use
		3265	functor objects without having to manually specify the C<operator ()> all
		3266	the time. Incidentally, you can then also leave out the template argument
		3267	list.
		3268
		3269	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3270	int revents)>.
		3271
		3272	See the method-C<set> above for more details.
		3273
		3274	Example: use a functor object as callback.
		3275
		3276	struct myfunctor
		3277	{
		3278	void operator() (ev::io &w, int revents)
		3279	{
		3280	...
		3281	}
		3282	}
		3283
		3284	myfunctor f;
		3285
		3286	ev::io w;
		3287	w.set (&f);
		3288
2566	=item w->set<function> (void *data = 0)	3289	=item w->set<function> (void *data = 0)
2567		3290
2568	Also sets a callback, but uses a static method or plain function as	3291	Also sets a callback, but uses a static method or plain function as
2569	callback. The optional C<data> argument will be stored in the watcher's	3292	callback. The optional C<data> argument will be stored in the watcher's
2570	C<data> member and is free for you to use.	3293	C<data> member and is free for you to use.
2571		3294
2572	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3295	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2573		3296
2574	See the method-C<set> above for more details.	3297	See the method-C<set> above for more details.
2575		3298
2576	Example:	3299	Example: Use a plain function as callback.
2577		3300
2578	static void io_cb (ev::io &w, int revents) { }	3301	static void io_cb (ev::io &w, int revents) { }
2579	iow.set <io_cb> ();	3302	iow.set <io_cb> ();
2580		3303
2581	=item w->set (struct ev_loop *)	3304	=item w->set (struct ev_loop *)
…		…
2619	Example: Define a class with an IO and idle watcher, start one of them in	3342	Example: Define a class with an IO and idle watcher, start one of them in
2620	the constructor.	3343	the constructor.
2621		3344
2622	class myclass	3345	class myclass
2623	{	3346	{
2624	ev::io io; void io_cb (ev::io &w, int revents);	3347	ev::io io ; void io_cb (ev::io &w, int revents);
2625	ev:idle idle void idle_cb (ev::idle &w, int revents);	3348	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2626		3349
2627	myclass (int fd)	3350	myclass (int fd)
2628	{	3351	{
2629	io .set <myclass, &myclass::io_cb > (this);	3352	io .set <myclass, &myclass::io_cb > (this);
2630	idle.set <myclass, &myclass::idle_cb> (this);	3353	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2646	=item Perl	3369	=item Perl
2647		3370
2648	The EV module implements the full libev API and is actually used to test	3371	The EV module implements the full libev API and is actually used to test
2649	libev. EV is developed together with libev. Apart from the EV core module,	3372	libev. EV is developed together with libev. Apart from the EV core module,
2650	there are additional modules that implement libev-compatible interfaces	3373	there are additional modules that implement libev-compatible interfaces
2651	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3374	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2652	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3375	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3376	and C<EV::Glib>).
2653		3377
2654	It can be found and installed via CPAN, its homepage is at	3378	It can be found and installed via CPAN, its homepage is at
2655	L<http://software.schmorp.de/pkg/EV>.	3379	L<http://software.schmorp.de/pkg/EV>.
2656		3380
2657	=item Python	3381	=item Python
2658		3382
2659	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3383	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2660	seems to be quite complete and well-documented. Note, however, that the	3384	seems to be quite complete and well-documented.
2661	patch they require for libev is outright dangerous as it breaks the ABI
2662	for everybody else, and therefore, should never be applied in an installed
2663	libev (if python requires an incompatible ABI then it needs to embed
2664	libev).
2665		3385
2666	=item Ruby	3386	=item Ruby
2667		3387
2668	Tony Arcieri has written a ruby extension that offers access to a subset	3388	Tony Arcieri has written a ruby extension that offers access to a subset
2669	of the libev API and adds file handle abstractions, asynchronous DNS and	3389	of the libev API and adds file handle abstractions, asynchronous DNS and
2670	more on top of it. It can be found via gem servers. Its homepage is at	3390	more on top of it. It can be found via gem servers. Its homepage is at
2671	L<http://rev.rubyforge.org/>.	3391	L<http://rev.rubyforge.org/>.
2672		3392
		3393	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3394	makes rev work even on mingw.
		3395
		3396	=item Haskell
		3397
		3398	A haskell binding to libev is available at
		3399	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3400
2673	=item D	3401	=item D
2674		3402
2675	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3403	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2676	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3404	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3405
		3406	=item Ocaml
		3407
		3408	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3409	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2677		3410
2678	=back	3411	=back
2679		3412
2680		3413
2681	=head1 MACRO MAGIC	3414	=head1 MACRO MAGIC
…		…
2782		3515
2783	#define EV_STANDALONE 1	3516	#define EV_STANDALONE 1
2784	#include "ev.h"	3517	#include "ev.h"
2785		3518
2786	Both header files and implementation files can be compiled with a C++	3519	Both header files and implementation files can be compiled with a C++
2787	compiler (at least, thats a stated goal, and breakage will be treated	3520	compiler (at least, that's a stated goal, and breakage will be treated
2788	as a bug).	3521	as a bug).
2789		3522
2790	You need the following files in your source tree, or in a directory	3523	You need the following files in your source tree, or in a directory
2791	in your include path (e.g. in libev/ when using -Ilibev):	3524	in your include path (e.g. in libev/ when using -Ilibev):
2792		3525
…		…
2836		3569
2837	=head2 PREPROCESSOR SYMBOLS/MACROS	3570	=head2 PREPROCESSOR SYMBOLS/MACROS
2838		3571
2839	Libev can be configured via a variety of preprocessor symbols you have to	3572	Libev can be configured via a variety of preprocessor symbols you have to
2840	define before including any of its files. The default in the absence of	3573	define before including any of its files. The default in the absence of
2841	autoconf is noted for every option.	3574	autoconf is documented for every option.
2842		3575
2843	=over 4	3576	=over 4
2844		3577
2845	=item EV_STANDALONE	3578	=item EV_STANDALONE
2846		3579
…		…
2848	keeps libev from including F<config.h>, and it also defines dummy	3581	keeps libev from including F<config.h>, and it also defines dummy
2849	implementations for some libevent functions (such as logging, which is not	3582	implementations for some libevent functions (such as logging, which is not
2850	supported). It will also not define any of the structs usually found in	3583	supported). It will also not define any of the structs usually found in
2851	F<event.h> that are not directly supported by the libev core alone.	3584	F<event.h> that are not directly supported by the libev core alone.
2852		3585
		3586	In stanbdalone mode, libev will still try to automatically deduce the
		3587	configuration, but has to be more conservative.
		3588
2853	=item EV_USE_MONOTONIC	3589	=item EV_USE_MONOTONIC
2854		3590
2855	If defined to be C<1>, libev will try to detect the availability of the	3591	If defined to be C<1>, libev will try to detect the availability of the
2856	monotonic clock option at both compile time and runtime. Otherwise no use	3592	monotonic clock option at both compile time and runtime. Otherwise no
2857	of the monotonic clock option will be attempted. If you enable this, you	3593	use of the monotonic clock option will be attempted. If you enable this,
2858	usually have to link against librt or something similar. Enabling it when	3594	you usually have to link against librt or something similar. Enabling it
2859	the functionality isn't available is safe, though, although you have	3595	when the functionality isn't available is safe, though, although you have
2860	to make sure you link against any libraries where the C<clock_gettime>	3596	to make sure you link against any libraries where the C<clock_gettime>
2861	function is hiding in (often F<-lrt>).	3597	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2862		3598
2863	=item EV_USE_REALTIME	3599	=item EV_USE_REALTIME
2864		3600
2865	If defined to be C<1>, libev will try to detect the availability of the	3601	If defined to be C<1>, libev will try to detect the availability of the
2866	real-time clock option at compile time (and assume its availability at	3602	real-time clock option at compile time (and assume its availability
2867	runtime if successful). Otherwise no use of the real-time clock option will	3603	at runtime if successful). Otherwise no use of the real-time clock
2868	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3604	option will be attempted. This effectively replaces C<gettimeofday>
2869	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3605	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2870	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3606	correctness. See the note about libraries in the description of
		3607	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3608	C<EV_USE_CLOCK_SYSCALL>.
		3609
		3610	=item EV_USE_CLOCK_SYSCALL
		3611
		3612	If defined to be C<1>, libev will try to use a direct syscall instead
		3613	of calling the system-provided C<clock_gettime> function. This option
		3614	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3615	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3616	programs needlessly. Using a direct syscall is slightly slower (in
		3617	theory), because no optimised vdso implementation can be used, but avoids
		3618	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3619	higher, as it simplifies linking (no need for C<-lrt>).
2871		3620
2872	=item EV_USE_NANOSLEEP	3621	=item EV_USE_NANOSLEEP
2873		3622
2874	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3623	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2875	and will use it for delays. Otherwise it will use C<select ()>.	3624	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2891		3640
2892	=item EV_SELECT_USE_FD_SET	3641	=item EV_SELECT_USE_FD_SET
2893		3642
2894	If defined to C<1>, then the select backend will use the system C<fd_set>	3643	If defined to C<1>, then the select backend will use the system C<fd_set>
2895	structure. This is useful if libev doesn't compile due to a missing	3644	structure. This is useful if libev doesn't compile due to a missing
2896	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3645	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2897	exotic systems. This usually limits the range of file descriptors to some	3646	on exotic systems. This usually limits the range of file descriptors to
2898	low limit such as 1024 or might have other limitations (winsocket only	3647	some low limit such as 1024 or might have other limitations (winsocket
2899	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3648	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2900	influence the size of the C<fd_set> used.	3649	configures the maximum size of the C<fd_set>.
2901		3650
2902	=item EV_SELECT_IS_WINSOCKET	3651	=item EV_SELECT_IS_WINSOCKET
2903		3652
2904	When defined to C<1>, the select backend will assume that	3653	When defined to C<1>, the select backend will assume that
2905	select/socket/connect etc. don't understand file descriptors but	3654	select/socket/connect etc. don't understand file descriptors but
…		…
3016	When doing priority-based operations, libev usually has to linearly search	3765	When doing priority-based operations, libev usually has to linearly search
3017	all the priorities, so having many of them (hundreds) uses a lot of space	3766	all the priorities, so having many of them (hundreds) uses a lot of space
3018	and time, so using the defaults of five priorities (-2 .. +2) is usually	3767	and time, so using the defaults of five priorities (-2 .. +2) is usually
3019	fine.	3768	fine.
3020		3769
3021	If your embedding application does not need any priorities, defining these both to	3770	If your embedding application does not need any priorities, defining these
3022	C<0> will save some memory and CPU.	3771	both to C<0> will save some memory and CPU.
3023		3772
3024	=item EV_PERIODIC_ENABLE	3773	=item EV_PERIODIC_ENABLE
3025		3774
3026	If undefined or defined to be C<1>, then periodic timers are supported. If	3775	If undefined or defined to be C<1>, then periodic timers are supported. If
3027	defined to be C<0>, then they are not. Disabling them saves a few kB of	3776	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
3034	code.	3783	code.
3035		3784
3036	=item EV_EMBED_ENABLE	3785	=item EV_EMBED_ENABLE
3037		3786
3038	If undefined or defined to be C<1>, then embed watchers are supported. If	3787	If undefined or defined to be C<1>, then embed watchers are supported. If
3039	defined to be C<0>, then they are not.	3788	defined to be C<0>, then they are not. Embed watchers rely on most other
		3789	watcher types, which therefore must not be disabled.
3040		3790
3041	=item EV_STAT_ENABLE	3791	=item EV_STAT_ENABLE
3042		3792
3043	If undefined or defined to be C<1>, then stat watchers are supported. If	3793	If undefined or defined to be C<1>, then stat watchers are supported. If
3044	defined to be C<0>, then they are not.	3794	defined to be C<0>, then they are not.
…		…
3054	defined to be C<0>, then they are not.	3804	defined to be C<0>, then they are not.
3055		3805
3056	=item EV_MINIMAL	3806	=item EV_MINIMAL
3057		3807
3058	If you need to shave off some kilobytes of code at the expense of some	3808	If you need to shave off some kilobytes of code at the expense of some
3059	speed, define this symbol to C<1>. Currently this is used to override some	3809	speed (but with the full API), define this symbol to C<1>. Currently this
3060	inlining decisions, saves roughly 30% code size on amd64. It also selects a	3810	is used to override some inlining decisions, saves roughly 30% code size
3061	much smaller 2-heap for timer management over the default 4-heap.	3811	on amd64. It also selects a much smaller 2-heap for timer management over
		3812	the default 4-heap.
		3813
		3814	You can save even more by disabling watcher types you do not need
		3815	and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert>
		3816	(C<-DNDEBUG>) will usually reduce code size a lot.
		3817
		3818	Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to
		3819	provide a bare-bones event library. See C<ev.h> for details on what parts
		3820	of the API are still available, and do not complain if this subset changes
		3821	over time.
		3822
		3823	=item EV_NSIG
		3824
		3825	The highest supported signal number, +1 (or, the number of
		3826	signals): Normally, libev tries to deduce the maximum number of signals
		3827	automatically, but sometimes this fails, in which case it can be
		3828	specified. Also, using a lower number than detected (C<32> should be
		3829	good for about any system in existance) can save some memory, as libev
		3830	statically allocates some 12-24 bytes per signal number.
3062		3831
3063	=item EV_PID_HASHSIZE	3832	=item EV_PID_HASHSIZE
3064		3833
3065	C<ev_child> watchers use a small hash table to distribute workload by	3834	C<ev_child> watchers use a small hash table to distribute workload by
3066	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3835	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
…		…
3076	two).	3845	two).
3077		3846
3078	=item EV_USE_4HEAP	3847	=item EV_USE_4HEAP
3079		3848
3080	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3849	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3081	timer and periodics heap, libev uses a 4-heap when this symbol is defined	3850	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3082	to C<1>. The 4-heap uses more complicated (longer) code but has	3851	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3083	noticeably faster performance with many (thousands) of watchers.	3852	faster performance with many (thousands) of watchers.
3084		3853
3085	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3854	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3086	(disabled).	3855	(disabled).
3087		3856
3088	=item EV_HEAP_CACHE_AT	3857	=item EV_HEAP_CACHE_AT
3089		3858
3090	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3859	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3091	timer and periodics heap, libev can cache the timestamp (I<at>) within	3860	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3092	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	3861	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3093	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	3862	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3094	but avoids random read accesses on heap changes. This improves performance	3863	but avoids random read accesses on heap changes. This improves performance
3095	noticeably with with many (hundreds) of watchers.	3864	noticeably with many (hundreds) of watchers.
3096		3865
3097	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3866	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3098	(disabled).	3867	(disabled).
3099		3868
3100	=item EV_VERIFY	3869	=item EV_VERIFY
…		…
3106	called once per loop, which can slow down libev. If set to C<3>, then the	3875	called once per loop, which can slow down libev. If set to C<3>, then the
3107	verification code will be called very frequently, which will slow down	3876	verification code will be called very frequently, which will slow down
3108	libev considerably.	3877	libev considerably.
3109		3878
3110	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	3879	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
3111	C<0.>	3880	C<0>.
3112		3881
3113	=item EV_COMMON	3882	=item EV_COMMON
3114		3883
3115	By default, all watchers have a C<void *data> member. By redefining	3884	By default, all watchers have a C<void *data> member. By redefining
3116	this macro to a something else you can include more and other types of	3885	this macro to a something else you can include more and other types of
…		…
3133	and the way callbacks are invoked and set. Must expand to a struct member	3902	and the way callbacks are invoked and set. Must expand to a struct member
3134	definition and a statement, respectively. See the F<ev.h> header file for	3903	definition and a statement, respectively. See the F<ev.h> header file for
3135	their default definitions. One possible use for overriding these is to	3904	their default definitions. One possible use for overriding these is to
3136	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3905	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3137	method calls instead of plain function calls in C++.	3906	method calls instead of plain function calls in C++.
		3907
		3908	=back
3138		3909
3139	=head2 EXPORTED API SYMBOLS	3910	=head2 EXPORTED API SYMBOLS
3140		3911
3141	If you need to re-export the API (e.g. via a DLL) and you need a list of	3912	If you need to re-export the API (e.g. via a DLL) and you need a list of
3142	exported symbols, you can use the provided F<Symbol.*> files which list	3913	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3189	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3960	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3190		3961
3191	#include "ev_cpp.h"	3962	#include "ev_cpp.h"
3192	#include "ev.c"	3963	#include "ev.c"
3193		3964
		3965	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3194		3966
3195	=head1 THREADS AND COROUTINES	3967	=head2 THREADS AND COROUTINES
3196		3968
3197	=head2 THREADS	3969	=head3 THREADS
3198		3970
3199	Libev itself is completely thread-safe, but it uses no locking. This	3971	All libev functions are reentrant and thread-safe unless explicitly
		3972	documented otherwise, but libev implements no locking itself. This means
3200	means that you can use as many loops as you want in parallel, as long as	3973	that you can use as many loops as you want in parallel, as long as there
3201	only one thread ever calls into one libev function with the same loop	3974	are no concurrent calls into any libev function with the same loop
3202	parameter.	3975	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3976	of course): libev guarantees that different event loops share no data
		3977	structures that need any locking.
3203		3978
3204	Or put differently: calls with different loop parameters can be done in	3979	Or to put it differently: calls with different loop parameters can be done
3205	parallel from multiple threads, calls with the same loop parameter must be	3980	concurrently from multiple threads, calls with the same loop parameter
3206	done serially (but can be done from different threads, as long as only one	3981	must be done serially (but can be done from different threads, as long as
3207	thread ever is inside a call at any point in time, e.g. by using a mutex	3982	only one thread ever is inside a call at any point in time, e.g. by using
3208	per loop).	3983	a mutex per loop).
		3984
		3985	Specifically to support threads (and signal handlers), libev implements
		3986	so-called C<ev_async> watchers, which allow some limited form of
		3987	concurrency on the same event loop, namely waking it up "from the
		3988	outside".
3209		3989
3210	If you want to know which design (one loop, locking, or multiple loops	3990	If you want to know which design (one loop, locking, or multiple loops
3211	without or something else still) is best for your problem, then I cannot	3991	without or something else still) is best for your problem, then I cannot
3212	help you. I can give some generic advice however:	3992	help you, but here is some generic advice:
3213		3993
3214	=over 4	3994	=over 4
3215		3995
3216	=item * most applications have a main thread: use the default libev loop	3996	=item * most applications have a main thread: use the default libev loop
3217	in that thread, or create a separate thread running only the default loop.	3997	in that thread, or create a separate thread running only the default loop.
…		…
3229		4009
3230	Choosing a model is hard - look around, learn, know that usually you can do	4010	Choosing a model is hard - look around, learn, know that usually you can do
3231	better than you currently do :-)	4011	better than you currently do :-)
3232		4012
3233	=item * often you need to talk to some other thread which blocks in the	4013	=item * often you need to talk to some other thread which blocks in the
		4014	event loop.
		4015
3234	event loop - C<ev_async> watchers can be used to wake them up from other	4016	C<ev_async> watchers can be used to wake them up from other threads safely
3235	threads safely (or from signal contexts...).	4017	(or from signal contexts...).
		4018
		4019	An example use would be to communicate signals or other events that only
		4020	work in the default loop by registering the signal watcher with the
		4021	default loop and triggering an C<ev_async> watcher from the default loop
		4022	watcher callback into the event loop interested in the signal.
3236		4023
3237	=back	4024	=back
3238		4025
		4026	=head4 THREAD LOCKING EXAMPLE
		4027
		4028	Here is a fictitious example of how to run an event loop in a different
		4029	thread than where callbacks are being invoked and watchers are
		4030	created/added/removed.
		4031
		4032	For a real-world example, see the C<EV::Loop::Async> perl module,
		4033	which uses exactly this technique (which is suited for many high-level
		4034	languages).
		4035
		4036	The example uses a pthread mutex to protect the loop data, a condition
		4037	variable to wait for callback invocations, an async watcher to notify the
		4038	event loop thread and an unspecified mechanism to wake up the main thread.
		4039
		4040	First, you need to associate some data with the event loop:
		4041
		4042	typedef struct {
		4043	mutex_t lock; /* global loop lock */
		4044	ev_async async_w;
		4045	thread_t tid;
		4046	cond_t invoke_cv;
		4047	} userdata;
		4048
		4049	void prepare_loop (EV_P)
		4050	{
		4051	// for simplicity, we use a static userdata struct.
		4052	static userdata u;
		4053
		4054	ev_async_init (&u->async_w, async_cb);
		4055	ev_async_start (EV_A_ &u->async_w);
		4056
		4057	pthread_mutex_init (&u->lock, 0);
		4058	pthread_cond_init (&u->invoke_cv, 0);
		4059
		4060	// now associate this with the loop
		4061	ev_set_userdata (EV_A_ u);
		4062	ev_set_invoke_pending_cb (EV_A_ l_invoke);
		4063	ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
		4064
		4065	// then create the thread running ev_loop
		4066	pthread_create (&u->tid, 0, l_run, EV_A);
		4067	}
		4068
		4069	The callback for the C<ev_async> watcher does nothing: the watcher is used
		4070	solely to wake up the event loop so it takes notice of any new watchers
		4071	that might have been added:
		4072
		4073	static void
		4074	async_cb (EV_P_ ev_async *w, int revents)
		4075	{
		4076	// just used for the side effects
		4077	}
		4078
		4079	The C<l_release> and C<l_acquire> callbacks simply unlock/lock the mutex
		4080	protecting the loop data, respectively.
		4081
		4082	static void
		4083	l_release (EV_P)
		4084	{
		4085	userdata *u = ev_userdata (EV_A);
		4086	pthread_mutex_unlock (&u->lock);
		4087	}
		4088
		4089	static void
		4090	l_acquire (EV_P)
		4091	{
		4092	userdata *u = ev_userdata (EV_A);
		4093	pthread_mutex_lock (&u->lock);
		4094	}
		4095
		4096	The event loop thread first acquires the mutex, and then jumps straight
		4097	into C<ev_loop>:
		4098
		4099	void *
		4100	l_run (void *thr_arg)
		4101	{
		4102	struct ev_loop *loop = (struct ev_loop *)thr_arg;
		4103
		4104	l_acquire (EV_A);
		4105	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
		4106	ev_loop (EV_A_ 0);
		4107	l_release (EV_A);
		4108
		4109	return 0;
		4110	}
		4111
		4112	Instead of invoking all pending watchers, the C<l_invoke> callback will
		4113	signal the main thread via some unspecified mechanism (signals? pipe
		4114	writes? C<Async::Interrupt>?) and then waits until all pending watchers
		4115	have been called (in a while loop because a) spurious wakeups are possible
		4116	and b) skipping inter-thread-communication when there are no pending
		4117	watchers is very beneficial):
		4118
		4119	static void
		4120	l_invoke (EV_P)
		4121	{
		4122	userdata *u = ev_userdata (EV_A);
		4123
		4124	while (ev_pending_count (EV_A))
		4125	{
		4126	wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
		4127	pthread_cond_wait (&u->invoke_cv, &u->lock);
		4128	}
		4129	}
		4130
		4131	Now, whenever the main thread gets told to invoke pending watchers, it
		4132	will grab the lock, call C<ev_invoke_pending> and then signal the loop
		4133	thread to continue:
		4134
		4135	static void
		4136	real_invoke_pending (EV_P)
		4137	{
		4138	userdata *u = ev_userdata (EV_A);
		4139
		4140	pthread_mutex_lock (&u->lock);
		4141	ev_invoke_pending (EV_A);
		4142	pthread_cond_signal (&u->invoke_cv);
		4143	pthread_mutex_unlock (&u->lock);
		4144	}
		4145
		4146	Whenever you want to start/stop a watcher or do other modifications to an
		4147	event loop, you will now have to lock:
		4148
		4149	ev_timer timeout_watcher;
		4150	userdata *u = ev_userdata (EV_A);
		4151
		4152	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
		4153
		4154	pthread_mutex_lock (&u->lock);
		4155	ev_timer_start (EV_A_ &timeout_watcher);
		4156	ev_async_send (EV_A_ &u->async_w);
		4157	pthread_mutex_unlock (&u->lock);
		4158
		4159	Note that sending the C<ev_async> watcher is required because otherwise
		4160	an event loop currently blocking in the kernel will have no knowledge
		4161	about the newly added timer. By waking up the loop it will pick up any new
		4162	watchers in the next event loop iteration.
		4163
3239	=head2 COROUTINES	4164	=head3 COROUTINES
3240		4165
3241	Libev is much more accommodating to coroutines ("cooperative threads"):	4166	Libev is very accommodating to coroutines ("cooperative threads"):
3242	libev fully supports nesting calls to it's functions from different	4167	libev fully supports nesting calls to its functions from different
3243	coroutines (e.g. you can call C<ev_loop> on the same loop from two	4168	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3244	different coroutines and switch freely between both coroutines running the	4169	different coroutines, and switch freely between both coroutines running
3245	loop, as long as you don't confuse yourself). The only exception is that	4170	the loop, as long as you don't confuse yourself). The only exception is
3246	you must not do this from C<ev_periodic> reschedule callbacks.	4171	that you must not do this from C<ev_periodic> reschedule callbacks.
3247		4172
3248	Care has been invested into making sure that libev does not keep local	4173	Care has been taken to ensure that libev does not keep local state inside
3249	state inside C<ev_loop>, and other calls do not usually allow coroutine	4174	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3250	switches.	4175	they do not call any callbacks.
3251		4176
		4177	=head2 COMPILER WARNINGS
3252		4178
3253	=head1 COMPLEXITIES	4179	Depending on your compiler and compiler settings, you might get no or a
		4180	lot of warnings when compiling libev code. Some people are apparently
		4181	scared by this.
3254		4182
3255	In this section the complexities of (many of) the algorithms used inside	4183	However, these are unavoidable for many reasons. For one, each compiler
3256	libev will be explained. For complexity discussions about backends see the	4184	has different warnings, and each user has different tastes regarding
3257	documentation for C<ev_default_init>.	4185	warning options. "Warn-free" code therefore cannot be a goal except when
		4186	targeting a specific compiler and compiler-version.
3258		4187
3259	All of the following are about amortised time: If an array needs to be	4188	Another reason is that some compiler warnings require elaborate
3260	extended, libev needs to realloc and move the whole array, but this	4189	workarounds, or other changes to the code that make it less clear and less
3261	happens asymptotically never with higher number of elements, so O(1) might	4190	maintainable.
3262	mean it might do a lengthy realloc operation in rare cases, but on average
3263	it is much faster and asymptotically approaches constant time.
3264		4191
3265	=over 4	4192	And of course, some compiler warnings are just plain stupid, or simply
		4193	wrong (because they don't actually warn about the condition their message
		4194	seems to warn about). For example, certain older gcc versions had some
		4195	warnings that resulted an extreme number of false positives. These have
		4196	been fixed, but some people still insist on making code warn-free with
		4197	such buggy versions.
3266		4198
3267	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	4199	While libev is written to generate as few warnings as possible,
		4200	"warn-free" code is not a goal, and it is recommended not to build libev
		4201	with any compiler warnings enabled unless you are prepared to cope with
		4202	them (e.g. by ignoring them). Remember that warnings are just that:
		4203	warnings, not errors, or proof of bugs.
3268		4204
3269	This means that, when you have a watcher that triggers in one hour and
3270	there are 100 watchers that would trigger before that then inserting will
3271	have to skip roughly seven (C<ld 100>) of these watchers.
3272		4205
3273	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	4206	=head2 VALGRIND
3274		4207
3275	That means that changing a timer costs less than removing/adding them	4208	Valgrind has a special section here because it is a popular tool that is
3276	as only the relative motion in the event queue has to be paid for.	4209	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3277		4210
3278	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	4211	If you think you found a bug (memory leak, uninitialised data access etc.)
		4212	in libev, then check twice: If valgrind reports something like:
3279		4213
3280	These just add the watcher into an array or at the head of a list.	4214	==2274== definitely lost: 0 bytes in 0 blocks.
		4215	==2274== possibly lost: 0 bytes in 0 blocks.
		4216	==2274== still reachable: 256 bytes in 1 blocks.
3281		4217
3282	=item Stopping check/prepare/idle/fork/async watchers: O(1)	4218	Then there is no memory leak, just as memory accounted to global variables
		4219	is not a memleak - the memory is still being referenced, and didn't leak.
3283		4220
3284	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	4221	Similarly, under some circumstances, valgrind might report kernel bugs
		4222	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		4223	although an acceptable workaround has been found here), or it might be
		4224	confused.
3285		4225
3286	These watchers are stored in lists then need to be walked to find the	4226	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3287	correct watcher to remove. The lists are usually short (you don't usually	4227	make it into some kind of religion.
3288	have many watchers waiting for the same fd or signal).
3289		4228
3290	=item Finding the next timer in each loop iteration: O(1)	4229	If you are unsure about something, feel free to contact the mailing list
		4230	with the full valgrind report and an explanation on why you think this
		4231	is a bug in libev (best check the archives, too :). However, don't be
		4232	annoyed when you get a brisk "this is no bug" answer and take the chance
		4233	of learning how to interpret valgrind properly.
3291		4234
3292	By virtue of using a binary or 4-heap, the next timer is always found at a	4235	If you need, for some reason, empty reports from valgrind for your project
3293	fixed position in the storage array.	4236	I suggest using suppression lists.
3294		4237
3295	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3296		4238
3297	A change means an I/O watcher gets started or stopped, which requires	4239	=head1 PORTABILITY NOTES
3298	libev to recalculate its status (and possibly tell the kernel, depending
3299	on backend and whether C<ev_io_set> was used).
3300		4240
3301	=item Activating one watcher (putting it into the pending state): O(1)
3302
3303	=item Priority handling: O(number_of_priorities)
3304
3305	Priorities are implemented by allocating some space for each
3306	priority. When doing priority-based operations, libev usually has to
3307	linearly search all the priorities, but starting/stopping and activating
3308	watchers becomes O(1) w.r.t. priority handling.
3309
3310	=item Sending an ev_async: O(1)
3311
3312	=item Processing ev_async_send: O(number_of_async_watchers)
3313
3314	=item Processing signals: O(max_signal_number)
3315
3316	Sending involves a system call I<iff> there were no other C<ev_async_send>
3317	calls in the current loop iteration. Checking for async and signal events
3318	involves iterating over all running async watchers or all signal numbers.
3319
3320	=back
3321
3322
3323	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	4241	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3324		4242
3325	Win32 doesn't support any of the standards (e.g. POSIX) that libev	4243	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3326	requires, and its I/O model is fundamentally incompatible with the POSIX	4244	requires, and its I/O model is fundamentally incompatible with the POSIX
3327	model. Libev still offers limited functionality on this platform in	4245	model. Libev still offers limited functionality on this platform in
3328	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	4246	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3335	way (note also that glib is the slowest event library known to man).	4253	way (note also that glib is the slowest event library known to man).
3336		4254
3337	There is no supported compilation method available on windows except	4255	There is no supported compilation method available on windows except
3338	embedding it into other applications.	4256	embedding it into other applications.
3339		4257
		4258	Sensible signal handling is officially unsupported by Microsoft - libev
		4259	tries its best, but under most conditions, signals will simply not work.
		4260
3340	Not a libev limitation but worth mentioning: windows apparently doesn't	4261	Not a libev limitation but worth mentioning: windows apparently doesn't
3341	accept large writes: instead of resulting in a partial write, windows will	4262	accept large writes: instead of resulting in a partial write, windows will
3342	either accept everything or return C<ENOBUFS> if the buffer is too large,	4263	either accept everything or return C<ENOBUFS> if the buffer is too large,
3343	so make sure you only write small amounts into your sockets (less than a	4264	so make sure you only write small amounts into your sockets (less than a
3344	megabyte seems safe, but thsi apparently depends on the amount of memory	4265	megabyte seems safe, but this apparently depends on the amount of memory
3345	available).	4266	available).
3346		4267
3347	Due to the many, low, and arbitrary limits on the win32 platform and	4268	Due to the many, low, and arbitrary limits on the win32 platform and
3348	the abysmal performance of winsockets, using a large number of sockets	4269	the abysmal performance of winsockets, using a large number of sockets
3349	is not recommended (and not reasonable). If your program needs to use	4270	is not recommended (and not reasonable). If your program needs to use
3350	more than a hundred or so sockets, then likely it needs to use a totally	4271	more than a hundred or so sockets, then likely it needs to use a totally
3351	different implementation for windows, as libev offers the POSIX readiness	4272	different implementation for windows, as libev offers the POSIX readiness
3352	notification model, which cannot be implemented efficiently on windows	4273	notification model, which cannot be implemented efficiently on windows
3353	(Microsoft monopoly games).	4274	(due to Microsoft monopoly games).
3354		4275
3355	A typical way to use libev under windows is to embed it (see the embedding	4276	A typical way to use libev under windows is to embed it (see the embedding
3356	section for details) and use the following F<evwrap.h> header file instead	4277	section for details) and use the following F<evwrap.h> header file instead
3357	of F<ev.h>:	4278	of F<ev.h>:
3358		4279
…		…
3360	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	4281	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3361		4282
3362	#include "ev.h"	4283	#include "ev.h"
3363		4284
3364	And compile the following F<evwrap.c> file into your project (make sure	4285	And compile the following F<evwrap.c> file into your project (make sure
3365	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	4286	you do I<not> compile the F<ev.c> or any other embedded source files!):
3366		4287
3367	#include "evwrap.h"	4288	#include "evwrap.h"
3368	#include "ev.c"	4289	#include "ev.c"
3369		4290
3370	=over 4	4291	=over 4
…		…
3394		4315
3395	Early versions of winsocket's select only supported waiting for a maximum	4316	Early versions of winsocket's select only supported waiting for a maximum
3396	of C<64> handles (probably owning to the fact that all windows kernels	4317	of C<64> handles (probably owning to the fact that all windows kernels
3397	can only wait for C<64> things at the same time internally; Microsoft	4318	can only wait for C<64> things at the same time internally; Microsoft
3398	recommends spawning a chain of threads and wait for 63 handles and the	4319	recommends spawning a chain of threads and wait for 63 handles and the
3399	previous thread in each. Great).	4320	previous thread in each. Sounds great!).
3400		4321
3401	Newer versions support more handles, but you need to define C<FD_SETSIZE>	4322	Newer versions support more handles, but you need to define C<FD_SETSIZE>
3402	to some high number (e.g. C<2048>) before compiling the winsocket select	4323	to some high number (e.g. C<2048>) before compiling the winsocket select
3403	call (which might be in libev or elsewhere, for example, perl does its own	4324	call (which might be in libev or elsewhere, for example, perl and many
3404	select emulation on windows).	4325	other interpreters do their own select emulation on windows).
3405		4326
3406	Another limit is the number of file descriptors in the Microsoft runtime	4327	Another limit is the number of file descriptors in the Microsoft runtime
3407	libraries, which by default is C<64> (there must be a hidden I<64> fetish	4328	libraries, which by default is C<64> (there must be a hidden I<64>
3408	or something like this inside Microsoft). You can increase this by calling	4329	fetish or something like this inside Microsoft). You can increase this
3409	C<_setmaxstdio>, which can increase this limit to C<2048> (another	4330	by calling C<_setmaxstdio>, which can increase this limit to C<2048>
3410	arbitrary limit), but is broken in many versions of the Microsoft runtime	4331	(another arbitrary limit), but is broken in many versions of the Microsoft
3411	libraries.
3412
3413	This might get you to about C<512> or C<2048> sockets (depending on	4332	runtime libraries. This might get you to about C<512> or C<2048> sockets
3414	windows version and/or the phase of the moon). To get more, you need to	4333	(depending on windows version and/or the phase of the moon). To get more,
3415	wrap all I/O functions and provide your own fd management, but the cost of	4334	you need to wrap all I/O functions and provide your own fd management, but
3416	calling select (O(n²)) will likely make this unworkable.	4335	the cost of calling select (O(n²)) will likely make this unworkable.
3417		4336
3418	=back	4337	=back
3419		4338
3420
3421	=head1 PORTABILITY REQUIREMENTS	4339	=head2 PORTABILITY REQUIREMENTS
3422		4340
3423	In addition to a working ISO-C implementation, libev relies on a few	4341	In addition to a working ISO-C implementation and of course the
3424	additional extensions:	4342	backend-specific APIs, libev relies on a few additional extensions:
3425		4343
3426	=over 4	4344	=over 4
3427		4345
3428	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4346	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3429	calling conventions regardless of C<ev_watcher_type *>.	4347	calling conventions regardless of C<ev_watcher_type *>.
…		…
3435	calls them using an C<ev_watcher *> internally.	4353	calls them using an C<ev_watcher *> internally.
3436		4354
3437	=item C<sig_atomic_t volatile> must be thread-atomic as well	4355	=item C<sig_atomic_t volatile> must be thread-atomic as well
3438		4356
3439	The type C<sig_atomic_t volatile> (or whatever is defined as	4357	The type C<sig_atomic_t volatile> (or whatever is defined as
3440	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4358	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3441	threads. This is not part of the specification for C<sig_atomic_t>, but is	4359	threads. This is not part of the specification for C<sig_atomic_t>, but is
3442	believed to be sufficiently portable.	4360	believed to be sufficiently portable.
3443		4361
3444	=item C<sigprocmask> must work in a threaded environment	4362	=item C<sigprocmask> must work in a threaded environment
3445		4363
…		…
3454	except the initial one, and run the default loop in the initial thread as	4372	except the initial one, and run the default loop in the initial thread as
3455	well.	4373	well.
3456		4374
3457	=item C<long> must be large enough for common memory allocation sizes	4375	=item C<long> must be large enough for common memory allocation sizes
3458		4376
3459	To improve portability and simplify using libev, libev uses C<long>	4377	To improve portability and simplify its API, libev uses C<long> internally
3460	internally instead of C<size_t> when allocating its data structures. On	4378	instead of C<size_t> when allocating its data structures. On non-POSIX
3461	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4379	systems (Microsoft...) this might be unexpectedly low, but is still at
3462	is still at least 31 bits everywhere, which is enough for hundreds of	4380	least 31 bits everywhere, which is enough for hundreds of millions of
3463	millions of watchers.	4381	watchers.
3464		4382
3465	=item C<double> must hold a time value in seconds with enough accuracy	4383	=item C<double> must hold a time value in seconds with enough accuracy
3466		4384
3467	The type C<double> is used to represent timestamps. It is required to	4385	The type C<double> is used to represent timestamps. It is required to
3468	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4386	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3469	enough for at least into the year 4000. This requirement is fulfilled by	4387	enough for at least into the year 4000. This requirement is fulfilled by
3470	implementations implementing IEEE 754 (basically all existing ones).	4388	implementations implementing IEEE 754, which is basically all existing
		4389	ones. With IEEE 754 doubles, you get microsecond accuracy until at least
		4390	2200.
3471		4391
3472	=back	4392	=back
3473		4393
3474	If you know of other additional requirements drop me a note.	4394	If you know of other additional requirements drop me a note.
3475		4395
3476		4396
3477	=head1 COMPILER WARNINGS	4397	=head1 ALGORITHMIC COMPLEXITIES
3478		4398
3479	Depending on your compiler and compiler settings, you might get no or a	4399	In this section the complexities of (many of) the algorithms used inside
3480	lot of warnings when compiling libev code. Some people are apparently	4400	libev will be documented. For complexity discussions about backends see
3481	scared by this.	4401	the documentation for C<ev_default_init>.
3482		4402
3483	However, these are unavoidable for many reasons. For one, each compiler	4403	All of the following are about amortised time: If an array needs to be
3484	has different warnings, and each user has different tastes regarding	4404	extended, libev needs to realloc and move the whole array, but this
3485	warning options. "Warn-free" code therefore cannot be a goal except when	4405	happens asymptotically rarer with higher number of elements, so O(1) might
3486	targeting a specific compiler and compiler-version.	4406	mean that libev does a lengthy realloc operation in rare cases, but on
		4407	average it is much faster and asymptotically approaches constant time.
3487		4408
3488	Another reason is that some compiler warnings require elaborate	4409	=over 4
3489	workarounds, or other changes to the code that make it less clear and less
3490	maintainable.
3491		4410
3492	And of course, some compiler warnings are just plain stupid, or simply	4411	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3493	wrong (because they don't actually warn about the condition their message
3494	seems to warn about).
3495		4412
3496	While libev is written to generate as few warnings as possible,	4413	This means that, when you have a watcher that triggers in one hour and
3497	"warn-free" code is not a goal, and it is recommended not to build libev	4414	there are 100 watchers that would trigger before that, then inserting will
3498	with any compiler warnings enabled unless you are prepared to cope with	4415	have to skip roughly seven (C<ld 100>) of these watchers.
3499	them (e.g. by ignoring them). Remember that warnings are just that:
3500	warnings, not errors, or proof of bugs.
3501		4416
		4417	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3502		4418
3503	=head1 VALGRIND	4419	That means that changing a timer costs less than removing/adding them,
		4420	as only the relative motion in the event queue has to be paid for.
3504		4421
3505	Valgrind has a special section here because it is a popular tool that is	4422	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3506	highly useful, but valgrind reports are very hard to interpret.
3507		4423
3508	If you think you found a bug (memory leak, uninitialised data access etc.)	4424	These just add the watcher into an array or at the head of a list.
3509	in libev, then check twice: If valgrind reports something like:
3510		4425
3511	==2274== definitely lost: 0 bytes in 0 blocks.	4426	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3512	==2274== possibly lost: 0 bytes in 0 blocks.
3513	==2274== still reachable: 256 bytes in 1 blocks.
3514		4427
3515	Then there is no memory leak. Similarly, under some circumstances,	4428	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3516	valgrind might report kernel bugs as if it were a bug in libev, or it
3517	might be confused (it is a very good tool, but only a tool).
3518		4429
3519	If you are unsure about something, feel free to contact the mailing list	4430	These watchers are stored in lists, so they need to be walked to find the
3520	with the full valgrind report and an explanation on why you think this is	4431	correct watcher to remove. The lists are usually short (you don't usually
3521	a bug in libev. However, don't be annoyed when you get a brisk "this is	4432	have many watchers waiting for the same fd or signal: one is typical, two
3522	no bug" answer and take the chance of learning how to interpret valgrind	4433	is rare).
3523	properly.
3524		4434
3525	If you need, for some reason, empty reports from valgrind for your project	4435	=item Finding the next timer in each loop iteration: O(1)
3526	I suggest using suppression lists.
3527		4436
		4437	By virtue of using a binary or 4-heap, the next timer is always found at a
		4438	fixed position in the storage array.
		4439
		4440	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4441
		4442	A change means an I/O watcher gets started or stopped, which requires
		4443	libev to recalculate its status (and possibly tell the kernel, depending
		4444	on backend and whether C<ev_io_set> was used).
		4445
		4446	=item Activating one watcher (putting it into the pending state): O(1)
		4447
		4448	=item Priority handling: O(number_of_priorities)
		4449
		4450	Priorities are implemented by allocating some space for each
		4451	priority. When doing priority-based operations, libev usually has to
		4452	linearly search all the priorities, but starting/stopping and activating
		4453	watchers becomes O(1) with respect to priority handling.
		4454
		4455	=item Sending an ev_async: O(1)
		4456
		4457	=item Processing ev_async_send: O(number_of_async_watchers)
		4458
		4459	=item Processing signals: O(max_signal_number)
		4460
		4461	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4462	calls in the current loop iteration. Checking for async and signal events
		4463	involves iterating over all running async watchers or all signal numbers.
		4464
		4465	=back
		4466
		4467
		4468	=head1 GLOSSARY
		4469
		4470	=over 4
		4471
		4472	=item active
		4473
		4474	A watcher is active as long as it has been started (has been attached to
		4475	an event loop) but not yet stopped (disassociated from the event loop).
		4476
		4477	=item application
		4478
		4479	In this document, an application is whatever is using libev.
		4480
		4481	=item callback
		4482
		4483	The address of a function that is called when some event has been
		4484	detected. Callbacks are being passed the event loop, the watcher that
		4485	received the event, and the actual event bitset.
		4486
		4487	=item callback invocation
		4488
		4489	The act of calling the callback associated with a watcher.
		4490
		4491	=item event
		4492
		4493	A change of state of some external event, such as data now being available
		4494	for reading on a file descriptor, time having passed or simply not having
		4495	any other events happening anymore.
		4496
		4497	In libev, events are represented as single bits (such as C<EV_READ> or
		4498	C<EV_TIMEOUT>).
		4499
		4500	=item event library
		4501
		4502	A software package implementing an event model and loop.
		4503
		4504	=item event loop
		4505
		4506	An entity that handles and processes external events and converts them
		4507	into callback invocations.
		4508
		4509	=item event model
		4510
		4511	The model used to describe how an event loop handles and processes
		4512	watchers and events.
		4513
		4514	=item pending
		4515
		4516	A watcher is pending as soon as the corresponding event has been detected,
		4517	and stops being pending as soon as the watcher will be invoked or its
		4518	pending status is explicitly cleared by the application.
		4519
		4520	A watcher can be pending, but not active. Stopping a watcher also clears
		4521	its pending status.
		4522
		4523	=item real time
		4524
		4525	The physical time that is observed. It is apparently strictly monotonic :)
		4526
		4527	=item wall-clock time
		4528
		4529	The time and date as shown on clocks. Unlike real time, it can actually
		4530	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4531	clock.
		4532
		4533	=item watcher
		4534
		4535	A data structure that describes interest in certain events. Watchers need
		4536	to be started (attached to an event loop) before they can receive events.
		4537
		4538	=item watcher invocation
		4539
		4540	The act of calling the callback associated with a watcher.
		4541
		4542	=back
3528		4543
3529	=head1 AUTHOR	4544	=head1 AUTHOR
3530		4545
3531	Marc Lehmann <libev@schmorp.de>.	4546	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3532		4547

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