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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
…		…
380	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
381		399
382	For few fds, this backend is a bit little slower than poll and select,	400	For few fds, this backend is a bit little slower than poll and select,
383	but it scales phenomenally better. While poll and select usually scale	401	but it scales phenomenally better. While poll and select usually scale
384	like O(total_fds) where n is the total number of fds (or the highest fd),	402	like O(total_fds) where n is the total number of fds (or the highest fd),
385	epoll scales either O(1) or O(active_fds). The epoll design has a number	403	epoll scales either O(1) or O(active_fds).
386	of shortcomings, such as silently dropping events in some hard-to-detect	404
387	cases and requiring a system call per fd change, no fork support and bad	405	The epoll mechanism deserves honorable mention as the most misdesigned
388	support for dup.	406	of the more advanced event mechanisms: mere annoyances include silently
		407	dropping file descriptors, requiring a system call per change per file
		408	descriptor (and unnecessary guessing of parameters), problems with dup and
		409	so on. The biggest issue is fork races, however - if a program forks then
		410	I<both> parent and child process have to recreate the epoll set, which can
		411	take considerable time (one syscall per file descriptor) and is of course
		412	hard to detect.
		413
		414	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		415	of course I<doesn't>, and epoll just loves to report events for totally
		416	I<different> file descriptors (even already closed ones, so one cannot
		417	even remove them from the set) than registered in the set (especially
		418	on SMP systems). Libev tries to counter these spurious notifications by
		419	employing an additional generation counter and comparing that against the
		420	events to filter out spurious ones, recreating the set when required.
389		421
390	While stopping, setting and starting an I/O watcher in the same iteration	422	While stopping, setting and starting an I/O watcher in the same iteration
391	will result in some caching, there is still a system call per such incident	423	will result in some caching, there is still a system call per such
392	(because the fd could point to a different file description now), so its	424	incident (because the same I<file descriptor> could point to a different
393	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	425	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
394	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
395		427	file descriptors.
396	Please note that epoll sometimes generates spurious notifications, so you
397	need to use non-blocking I/O or other means to avoid blocking when no data
398	(or space) is available.
399		428
400	Best performance from this backend is achieved by not unregistering all	429	Best performance from this backend is achieved by not unregistering all
401	watchers for a file descriptor until it has been closed, if possible,	430	watchers for a file descriptor until it has been closed, if possible,
402	i.e. keep at least one watcher active per fd at all times. Stopping and	431	i.e. keep at least one watcher active per fd at all times. Stopping and
403	starting a watcher (without re-setting it) also usually doesn't cause	432	starting a watcher (without re-setting it) also usually doesn't cause
404	extra overhead.	433	extra overhead. A fork can both result in spurious notifications as well
		434	as in libev having to destroy and recreate the epoll object, which can
		435	take considerable time and thus should be avoided.
		436
		437	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		438	faster than epoll for maybe up to a hundred file descriptors, depending on
		439	the usage. So sad.
405		440
406	While nominally embeddable in other event loops, this feature is broken in	441	While nominally embeddable in other event loops, this feature is broken in
407	all kernel versions tested so far.	442	all kernel versions tested so far.
408		443
409	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	444	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
410	C<EVBACKEND_POLL>.	445	C<EVBACKEND_POLL>.
411		446
412	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
413		448
414	Kqueue deserves special mention, as at the time of this writing, it was	449	Kqueue deserves special mention, as at the time of this writing, it
415	broken on all BSDs except NetBSD (usually it doesn't work reliably with	450	was broken on all BSDs except NetBSD (usually it doesn't work reliably
416	anything but sockets and pipes, except on Darwin, where of course it's	451	with anything but sockets and pipes, except on Darwin, where of course
417	completely useless). For this reason it's not being "auto-detected" unless	452	it's completely useless). Unlike epoll, however, whose brokenness
418	you explicitly specify it in the flags (i.e. using C<EVBACKEND_KQUEUE>) or	453	is by design, these kqueue bugs can (and eventually will) be fixed
419	libev was compiled on a known-to-be-good (-enough) system like NetBSD.	454	without API changes to existing programs. For this reason it's not being
		455	"auto-detected" unless you explicitly specify it in the flags (i.e. using
		456	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
		457	system like NetBSD.
420		458
421	You still can embed kqueue into a normal poll or select backend and use it	459	You still can embed kqueue into a normal poll or select backend and use it
422	only for sockets (after having made sure that sockets work with kqueue on	460	only for sockets (after having made sure that sockets work with kqueue on
423	the target platform). See C<ev_embed> watchers for more info.	461	the target platform). See C<ev_embed> watchers for more info.
424		462
425	It scales in the same way as the epoll backend, but the interface to the	463	It scales in the same way as the epoll backend, but the interface to the
426	kernel is more efficient (which says nothing about its actual speed, of	464	kernel is more efficient (which says nothing about its actual speed, of
427	course). While stopping, setting and starting an I/O watcher does never	465	course). While stopping, setting and starting an I/O watcher does never
428	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to	466	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
429	two event changes per incident. Support for C<fork ()> is very bad and it	467	two event changes per incident. Support for C<fork ()> is very bad (but
430	drops fds silently in similarly hard-to-detect cases.	468	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		469	cases
431		470
432	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
433		472
434	While nominally embeddable in other event loops, this doesn't work	473	While nominally embeddable in other event loops, this doesn't work
435	everywhere, so you might need to test for this. And since it is broken	474	everywhere, so you might need to test for this. And since it is broken
436	almost everywhere, you should only use it when you have a lot of sockets	475	almost everywhere, you should only use it when you have a lot of sockets
437	(for which it usually works), by embedding it into another event loop	476	(for which it usually works), by embedding it into another event loop
438	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and, did I mention it,	477	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
439	using it only for sockets.	478	also broken on OS X)) and, did I mention it, using it only for sockets.
440		479
441	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with	480	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
442	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with	481	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
443	C<NOTE_EOF>.	482	C<NOTE_EOF>.
444		483
…		…
464	might perform better.	503	might perform better.
465		504
466	On the positive side, with the exception of the spurious readiness	505	On the positive side, with the exception of the spurious readiness
467	notifications, this backend actually performed fully to specification	506	notifications, this backend actually performed fully to specification
468	in all tests and is fully embeddable, which is a rare feat among the	507	in all tests and is fully embeddable, which is a rare feat among the
469	OS-specific backends.	508	OS-specific backends (I vastly prefer correctness over speed hacks).
470		509
471	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as	510	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
472	C<EVBACKEND_POLL>.	511	C<EVBACKEND_POLL>.
473		512
474	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
…		…
527	responsibility to either stop all watchers cleanly yourself I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
528	calling this function, or cope with the fact afterwards (which is usually	567	calling this function, or cope with the fact afterwards (which is usually
529	the easiest thing, you can just ignore the watchers and/or C<free ()> them	568	the easiest thing, you can just ignore the watchers and/or C<free ()> them
530	for example).	569	for example).
531		570
532	Note that certain global state, such as signal state, will not be freed by	571	Note that certain global state, such as signal state (and installed signal
533	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
534	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
535		574
536	In general it is not advisable to call this function except in the	575	In general it is not advisable to call this function except in the
537	rare occasion where you really need to free e.g. the signal handling	576	rare occasion where you really need to free e.g. the signal handling
538	pipe fds. If you need dynamically allocated loops it is better to use	577	pipe fds. If you need dynamically allocated loops it is better to use
539	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
605		644
606	This function is rarely useful, but when some event callback runs for a	645	This function is rarely useful, but when some event callback runs for a
607	very long time without entering the event loop, updating libev's idea of	646	very long time without entering the event loop, updating libev's idea of
608	the current time is a good idea.	647	the current time is a good idea.
609		648
610	See also "The special problem of time updates" in the C<ev_timer> section.	649	See also L<The special problem of time updates> in the C<ev_timer> section.
		650
		651	=item ev_suspend (loop)
		652
		653	=item ev_resume (loop)
		654
		655	These two functions suspend and resume a loop, for use when the loop is
		656	not used for a while and timeouts should not be processed.
		657
		658	A typical use case would be an interactive program such as a game: When
		659	the user presses C<^Z> to suspend the game and resumes it an hour later it
		660	would be best to handle timeouts as if no time had actually passed while
		661	the program was suspended. This can be achieved by calling C<ev_suspend>
		662	in your C<SIGTSTP> handler, sending yourself a C<SIGSTOP> and calling
		663	C<ev_resume> directly afterwards to resume timer processing.
		664
		665	Effectively, all C<ev_timer> watchers will be delayed by the time spend
		666	between C<ev_suspend> and C<ev_resume>, and all C<ev_periodic> watchers
		667	will be rescheduled (that is, they will lose any events that would have
		668	occured while suspended).
		669
		670	After calling C<ev_suspend> you B<must not> call I<any> function on the
		671	given loop other than C<ev_resume>, and you B<must not> call C<ev_resume>
		672	without a previous call to C<ev_suspend>.
		673
		674	Calling C<ev_suspend>/C<ev_resume> has the side effect of updating the
		675	event loop time (see C<ev_now_update>).
611		676
612	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
613		678
614	Finally, this is it, the event handler. This function usually is called	679	Finally, this is it, the event handler. This function usually is called
615	after you initialised all your watchers and you want to start handling	680	after you initialised all your watchers and you want to start handling
…		…
631	the loop.	696	the loop.
632		697
633	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	698	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
634	necessary) and will handle those and any already outstanding ones. It	699	necessary) and will handle those and any already outstanding ones. It
635	will block your process until at least one new event arrives (which could	700	will block your process until at least one new event arrives (which could
636	be an event internal to libev itself, so there is no guarentee that a	701	be an event internal to libev itself, so there is no guarantee that a
637	user-registered callback will be called), and will return after one	702	user-registered callback will be called), and will return after one
638	iteration of the loop.	703	iteration of the loop.
639		704
640	This is useful if you are waiting for some external event in conjunction	705	This is useful if you are waiting for some external event in conjunction
641	with something not expressible using other libev watchers (i.e. "roll your	706	with something not expressible using other libev watchers (i.e. "roll your
…		…
685	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	750	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
686	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	751	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
687		752
688	This "unloop state" will be cleared when entering C<ev_loop> again.	753	This "unloop state" will be cleared when entering C<ev_loop> again.
689		754
		755	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		756
690	=item ev_ref (loop)	757	=item ev_ref (loop)
691		758
692	=item ev_unref (loop)	759	=item ev_unref (loop)
693		760
694	Ref/unref can be used to add or remove a reference count on the event	761	Ref/unref can be used to add or remove a reference count on the event
…		…
697		764
698	If you have a watcher you never unregister that should not keep C<ev_loop>	765	If you have a watcher you never unregister that should not keep C<ev_loop>
699	from returning, call ev_unref() after starting, and ev_ref() before	766	from returning, call ev_unref() after starting, and ev_ref() before
700	stopping it.	767	stopping it.
701		768
702	As an example, libev itself uses this for its internal signal pipe: It is	769	As an example, libev itself uses this for its internal signal pipe: It
703	not visible to the libev user and should not keep C<ev_loop> from exiting	770	is not visible to the libev user and should not keep C<ev_loop> from
704	if no event watchers registered by it are active. It is also an excellent	771	exiting if no event watchers registered by it are active. It is also an
705	way to do this for generic recurring timers or from within third-party	772	excellent way to do this for generic recurring timers or from within
706	libraries. Just remember to I<unref after start> and I<ref before stop>	773	third-party libraries. Just remember to I<unref after start> and I<ref
707	(but only if the watcher wasn't active before, or was active before,	774	before stop> (but only if the watcher wasn't active before, or was active
708	respectively).	775	before, respectively. Note also that libev might stop watchers itself
		776	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		777	in the callback).
709		778
710	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	779	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
711	running when nothing else is active.	780	running when nothing else is active.
712		781
713	struct ev_signal exitsig;	782	ev_signal exitsig;
714	ev_signal_init (&exitsig, sig_cb, SIGINT);	783	ev_signal_init (&exitsig, sig_cb, SIGINT);
715	ev_signal_start (loop, &exitsig);	784	ev_signal_start (loop, &exitsig);
716	evf_unref (loop);	785	evf_unref (loop);
717		786
718	Example: For some weird reason, unregister the above signal handler again.	787	Example: For some weird reason, unregister the above signal handler again.
…		…
766	they fire on, say, one-second boundaries only.	835	they fire on, say, one-second boundaries only.
767		836
768	=item ev_loop_verify (loop)	837	=item ev_loop_verify (loop)
769		838
770	This function only does something when C<EV_VERIFY> support has been	839	This function only does something when C<EV_VERIFY> support has been
771	compiled in. which is the default for non-minimal builds. It tries to go	840	compiled in, which is the default for non-minimal builds. It tries to go
772	through all internal structures and checks them for validity. If anything	841	through all internal structures and checks them for validity. If anything
773	is found to be inconsistent, it will print an error message to standard	842	is found to be inconsistent, it will print an error message to standard
774	error and call C<abort ()>.	843	error and call C<abort ()>.
775		844
776	This can be used to catch bugs inside libev itself: under normal	845	This can be used to catch bugs inside libev itself: under normal
…		…
780	=back	849	=back
781		850
782		851
783	=head1 ANATOMY OF A WATCHER	852	=head1 ANATOMY OF A WATCHER
784		853
		854	In the following description, uppercase C<TYPE> in names stands for the
		855	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		856	watchers and C<ev_io_start> for I/O watchers.
		857
785	A watcher is a structure that you create and register to record your	858	A watcher is a structure that you create and register to record your
786	interest in some event. For instance, if you want to wait for STDIN to	859	interest in some event. For instance, if you want to wait for STDIN to
787	become readable, you would create an C<ev_io> watcher for that:	860	become readable, you would create an C<ev_io> watcher for that:
788		861
789	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	862	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
790	{	863	{
791	ev_io_stop (w);	864	ev_io_stop (w);
792	ev_unloop (loop, EVUNLOOP_ALL);	865	ev_unloop (loop, EVUNLOOP_ALL);
793	}	866	}
794		867
795	struct ev_loop *loop = ev_default_loop (0);	868	struct ev_loop *loop = ev_default_loop (0);
		869
796	struct ev_io stdin_watcher;	870	ev_io stdin_watcher;
		871
797	ev_init (&stdin_watcher, my_cb);	872	ev_init (&stdin_watcher, my_cb);
798	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	873	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
799	ev_io_start (loop, &stdin_watcher);	874	ev_io_start (loop, &stdin_watcher);
		875
800	ev_loop (loop, 0);	876	ev_loop (loop, 0);
801		877
802	As you can see, you are responsible for allocating the memory for your	878	As you can see, you are responsible for allocating the memory for your
803	watcher structures (and it is usually a bad idea to do this on the stack,	879	watcher structures (and it is I<usually> a bad idea to do this on the
804	although this can sometimes be quite valid).	880	stack).
		881
		882	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		883	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
805		884
806	Each watcher structure must be initialised by a call to C<ev_init	885	Each watcher structure must be initialised by a call to C<ev_init
807	(watcher *, callback)>, which expects a callback to be provided. This	886	(watcher *, callback)>, which expects a callback to be provided. This
808	callback gets invoked each time the event occurs (or, in the case of I/O	887	callback gets invoked each time the event occurs (or, in the case of I/O
809	watchers, each time the event loop detects that the file descriptor given	888	watchers, each time the event loop detects that the file descriptor given
810	is readable and/or writable).	889	is readable and/or writable).
811		890
812	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	891	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
813	with arguments specific to this watcher type. There is also a macro	892	macro to configure it, with arguments specific to the watcher type. There
814	to combine initialisation and setting in one call: C<< ev_<type>_init	893	is also a macro to combine initialisation and setting in one call: C<<
815	(watcher *, callback, ...) >>.	894	ev_TYPE_init (watcher *, callback, ...) >>.
816		895
817	To make the watcher actually watch out for events, you have to start it	896	To make the watcher actually watch out for events, you have to start it
818	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	897	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
819	*) >>), and you can stop watching for events at any time by calling the	898	*) >>), and you can stop watching for events at any time by calling the
820	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	899	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
821		900
822	As long as your watcher is active (has been started but not stopped) you	901	As long as your watcher is active (has been started but not stopped) you
823	must not touch the values stored in it. Most specifically you must never	902	must not touch the values stored in it. Most specifically you must never
824	reinitialise it or call its C<set> macro.	903	reinitialise it or call its C<ev_TYPE_set> macro.
825		904
826	Each and every callback receives the event loop pointer as first, the	905	Each and every callback receives the event loop pointer as first, the
827	registered watcher structure as second, and a bitset of received events as	906	registered watcher structure as second, and a bitset of received events as
828	third argument.	907	third argument.
829		908
…		…
887		966
888	=item C<EV_ASYNC>	967	=item C<EV_ASYNC>
889		968
890	The given async watcher has been asynchronously notified (see C<ev_async>).	969	The given async watcher has been asynchronously notified (see C<ev_async>).
891		970
		971	=item C<EV_CUSTOM>
		972
		973	Not ever sent (or otherwise used) by libev itself, but can be freely used
		974	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		975
892	=item C<EV_ERROR>	976	=item C<EV_ERROR>
893		977
894	An unspecified error has occurred, the watcher has been stopped. This might	978	An unspecified error has occurred, the watcher has been stopped. This might
895	happen because the watcher could not be properly started because libev	979	happen because the watcher could not be properly started because libev
896	ran out of memory, a file descriptor was found to be closed or any other	980	ran out of memory, a file descriptor was found to be closed or any other
		981	problem. Libev considers these application bugs.
		982
897	problem. You best act on it by reporting the problem and somehow coping	983	You best act on it by reporting the problem and somehow coping with the
898	with the watcher being stopped.	984	watcher being stopped. Note that well-written programs should not receive
		985	an error ever, so when your watcher receives it, this usually indicates a
		986	bug in your program.
899		987
900	Libev will usually signal a few "dummy" events together with an error, for	988	Libev will usually signal a few "dummy" events together with an error, for
901	example it might indicate that a fd is readable or writable, and if your	989	example it might indicate that a fd is readable or writable, and if your
902	callbacks is well-written it can just attempt the operation and cope with	990	callbacks is well-written it can just attempt the operation and cope with
903	the error from read() or write(). This will not work in multi-threaded	991	the error from read() or write(). This will not work in multi-threaded
…		…
906		994
907	=back	995	=back
908		996
909	=head2 GENERIC WATCHER FUNCTIONS	997	=head2 GENERIC WATCHER FUNCTIONS
910		998
911	In the following description, C<TYPE> stands for the watcher type,
912	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
913
914	=over 4	999	=over 4
915		1000
916	=item C<ev_init> (ev_TYPE *watcher, callback)	1001	=item C<ev_init> (ev_TYPE *watcher, callback)
917		1002
918	This macro initialises the generic portion of a watcher. The contents	1003	This macro initialises the generic portion of a watcher. The contents
…		…
923	which rolls both calls into one.	1008	which rolls both calls into one.
924		1009
925	You can reinitialise a watcher at any time as long as it has been stopped	1010	You can reinitialise a watcher at any time as long as it has been stopped
926	(or never started) and there are no pending events outstanding.	1011	(or never started) and there are no pending events outstanding.
927		1012
928	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	1013	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
929	int revents)>.	1014	int revents)>.
930		1015
931	Example: Initialise an C<ev_io> watcher in two steps.	1016	Example: Initialise an C<ev_io> watcher in two steps.
932		1017
933	ev_io w;	1018	ev_io w;
…		…
967		1052
968	ev_io_start (EV_DEFAULT_UC, &w);	1053	ev_io_start (EV_DEFAULT_UC, &w);
969		1054
970	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1055	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
971		1056
972	Stops the given watcher again (if active) and clears the pending	1057	Stops the given watcher if active, and clears the pending status (whether
		1058	the watcher was active or not).
		1059
973	status. It is possible that stopped watchers are pending (for example,	1060	It is possible that stopped watchers are pending - for example,
974	non-repeating timers are being stopped when they become pending), but	1061	non-repeating timers are being stopped when they become pending - but
975	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1062	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
976	you want to free or reuse the memory used by the watcher it is therefore a	1063	pending. If you want to free or reuse the memory used by the watcher it is
977	good idea to always call its C<ev_TYPE_stop> function.	1064	therefore a good idea to always call its C<ev_TYPE_stop> function.
978		1065
979	=item bool ev_is_active (ev_TYPE *watcher)	1066	=item bool ev_is_active (ev_TYPE *watcher)
980		1067
981	Returns a true value iff the watcher is active (i.e. it has been started	1068	Returns a true value iff the watcher is active (i.e. it has been started
982	and not yet been stopped). As long as a watcher is active you must not modify	1069	and not yet been stopped). As long as a watcher is active you must not modify
…		…
1008	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>	1095	integer between C<EV_MAXPRI> (default: C<2>) and C<EV_MINPRI>
1009	(default: C<-2>). Pending watchers with higher priority will be invoked	1096	(default: C<-2>). Pending watchers with higher priority will be invoked
1010	before watchers with lower priority, but priority will not keep watchers	1097	before watchers with lower priority, but priority will not keep watchers
1011	from being executed (except for C<ev_idle> watchers).	1098	from being executed (except for C<ev_idle> watchers).
1012		1099
1013	This means that priorities are I<only> used for ordering callback
1014	invocation after new events have been received. This is useful, for
1015	example, to reduce latency after idling, or more often, to bind two
1016	watchers on the same event and make sure one is called first.
1017
1018	If you need to suppress invocation when higher priority events are pending	1100	If you need to suppress invocation when higher priority events are pending
1019	you need to look at C<ev_idle> watchers, which provide this functionality.	1101	you need to look at C<ev_idle> watchers, which provide this functionality.
1020		1102
1021	You I<must not> change the priority of a watcher as long as it is active or	1103	You I<must not> change the priority of a watcher as long as it is active or
1022	pending.	1104	pending.
1023		1105
		1106	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
		1107	fine, as long as you do not mind that the priority value you query might
		1108	or might not have been clamped to the valid range.
		1109
1024	The default priority used by watchers when no priority has been set is	1110	The default priority used by watchers when no priority has been set is
1025	always C<0>, which is supposed to not be too high and not be too low :).	1111	always C<0>, which is supposed to not be too high and not be too low :).
1026		1112
1027	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1113	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1028	fine, as long as you do not mind that the priority value you query might	1114	priorities.
1029	or might not have been adjusted to be within valid range.
1030		1115
1031	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1116	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1032		1117
1033	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1118	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
1034	C<loop> nor C<revents> need to be valid as long as the watcher callback	1119	C<loop> nor C<revents> need to be valid as long as the watcher callback
…		…
1056	member, you can also "subclass" the watcher type and provide your own	1141	member, you can also "subclass" the watcher type and provide your own
1057	data:	1142	data:
1058		1143
1059	struct my_io	1144	struct my_io
1060	{	1145	{
1061	struct ev_io io;	1146	ev_io io;
1062	int otherfd;	1147	int otherfd;
1063	void *somedata;	1148	void *somedata;
1064	struct whatever *mostinteresting;	1149	struct whatever *mostinteresting;
1065	};	1150	};
1066		1151
…		…
1069	ev_io_init (&w.io, my_cb, fd, EV_READ);	1154	ev_io_init (&w.io, my_cb, fd, EV_READ);
1070		1155
1071	And since your callback will be called with a pointer to the watcher, you	1156	And since your callback will be called with a pointer to the watcher, you
1072	can cast it back to your own type:	1157	can cast it back to your own type:
1073		1158
1074	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1159	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
1075	{	1160	{
1076	struct my_io *w = (struct my_io *)w_;	1161	struct my_io *w = (struct my_io *)w_;
1077	...	1162	...
1078	}	1163	}
1079		1164
…		…
1097	programmers):	1182	programmers):
1098		1183
1099	#include <stddef.h>	1184	#include <stddef.h>
1100		1185
1101	static void	1186	static void
1102	t1_cb (EV_P_ struct ev_timer *w, int revents)	1187	t1_cb (EV_P_ ev_timer *w, int revents)
1103	{	1188	{
1104	struct my_biggy big = (struct my_biggy *	1189	struct my_biggy big = (struct my_biggy *
1105	(((char *)w) - offsetof (struct my_biggy, t1));	1190	(((char *)w) - offsetof (struct my_biggy, t1));
1106	}	1191	}
1107		1192
1108	static void	1193	static void
1109	t2_cb (EV_P_ struct ev_timer *w, int revents)	1194	t2_cb (EV_P_ ev_timer *w, int revents)
1110	{	1195	{
1111	struct my_biggy big = (struct my_biggy *	1196	struct my_biggy big = (struct my_biggy *
1112	(((char *)w) - offsetof (struct my_biggy, t2));	1197	(((char *)w) - offsetof (struct my_biggy, t2));
1113	}	1198	}
		1199
		1200	=head2 WATCHER PRIORITY MODELS
		1201
		1202	Many event loops support I<watcher priorities>, which are usually small
		1203	integers that influence the ordering of event callback invocation
		1204	between watchers in some way, all else being equal.
		1205
		1206	In libev, Watcher priorities can be set using C<ev_set_priority>. See its
		1207	description for the more technical details such as the actual priority
		1208	range.
		1209
		1210	There are two common ways how these these priorities are being interpreted
		1211	by event loops:
		1212
		1213	In the more common lock-out model, higher priorities "lock out" invocation
		1214	of lower priority watchers, which means as long as higher priority
		1215	watchers receive events, lower priority watchers are not being invoked.
		1216
		1217	The less common only-for-ordering model uses priorities solely to order
		1218	callback invocation within a single event loop iteration: Higher priority
		1219	watchers are invoked before lower priority ones, but they all get invoked
		1220	before polling for new events.
		1221
		1222	Libev uses the second (only-for-ordering) model for all its watchers
		1223	except for idle watchers (which use the lock-out model).
		1224
		1225	The rationale behind this is that implementing the lock-out model for
		1226	watchers is not well supported by most kernel interfaces, and most event
		1227	libraries will just poll for the same events again and again as long as
		1228	their callbacks have not been executed, which is very inefficient in the
		1229	common case of one high-priority watcher locking out a mass of lower
		1230	priority ones.
		1231
		1232	Static (ordering) priorities are most useful when you have two or more
		1233	watchers handling the same resource: a typical usage example is having an
		1234	C<ev_io> watcher to receive data, and an associated C<ev_timer> to handle
		1235	timeouts. Under load, data might be received while the program handles
		1236	other jobs, but since timers normally get invoked first, the timeout
		1237	handler will be executed before checking for data. In that case, giving
		1238	the timer a lower priority than the I/O watcher ensures that I/O will be
		1239	handled first even under adverse conditions (which is usually, but not
		1240	always, what you want).
		1241
		1242	Since idle watchers use the "lock-out" model, meaning that idle watchers
		1243	will only be executed when no same or higher priority watchers have
		1244	received events, they can be used to implement the "lock-out" model when
		1245	required.
		1246
		1247	For example, to emulate how many other event libraries handle priorities,
		1248	you can associate an C<ev_idle> watcher to each such watcher, and in
		1249	the normal watcher callback, you just start the idle watcher. The real
		1250	processing is done in the idle watcher callback. This causes libev to
		1251	continously poll and process kernel event data for the watcher, but when
		1252	the lock-out case is known to be rare (which in turn is rare :), this is
		1253	workable.
		1254
		1255	Usually, however, the lock-out model implemented that way will perform
		1256	miserably under the type of load it was designed to handle. In that case,
		1257	it might be preferable to stop the real watcher before starting the
		1258	idle watcher, so the kernel will not have to process the event in case
		1259	the actual processing will be delayed for considerable time.
		1260
		1261	Here is an example of an I/O watcher that should run at a strictly lower
		1262	priority than the default, and which should only process data when no
		1263	other events are pending:
		1264
		1265	ev_idle idle; // actual processing watcher
		1266	ev_io io; // actual event watcher
		1267
		1268	static void
		1269	io_cb (EV_P_ ev_io *w, int revents)
		1270	{
		1271	// stop the I/O watcher, we received the event, but
		1272	// are not yet ready to handle it.
		1273	ev_io_stop (EV_A_ w);
		1274
		1275	// start the idle watcher to ahndle the actual event.
		1276	// it will not be executed as long as other watchers
		1277	// with the default priority are receiving events.
		1278	ev_idle_start (EV_A_ &idle);
		1279	}
		1280
		1281	static void
		1282	idle-cb (EV_P_ ev_idle *w, int revents)
		1283	{
		1284	// actual processing
		1285	read (STDIN_FILENO, ...);
		1286
		1287	// have to start the I/O watcher again, as
		1288	// we have handled the event
		1289	ev_io_start (EV_P_ &io);
		1290	}
		1291
		1292	// initialisation
		1293	ev_idle_init (&idle, idle_cb);
		1294	ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
		1295	ev_io_start (EV_DEFAULT_ &io);
		1296
		1297	In the "real" world, it might also be beneficial to start a timer, so that
		1298	low-priority connections can not be locked out forever under load. This
		1299	enables your program to keep a lower latency for important connections
		1300	during short periods of high load, while not completely locking out less
		1301	important ones.
1114		1302
1115		1303
1116	=head1 WATCHER TYPES	1304	=head1 WATCHER TYPES
1117		1305
1118	This section describes each watcher in detail, but will not repeat	1306	This section describes each watcher in detail, but will not repeat
…		…
1249	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1437	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1250	readable, but only once. Since it is likely line-buffered, you could	1438	readable, but only once. Since it is likely line-buffered, you could
1251	attempt to read a whole line in the callback.	1439	attempt to read a whole line in the callback.
1252		1440
1253	static void	1441	static void
1254	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1442	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1255	{	1443	{
1256	ev_io_stop (loop, w);	1444	ev_io_stop (loop, w);
1257	.. read from stdin here (or from w->fd) and handle any I/O errors	1445	.. read from stdin here (or from w->fd) and handle any I/O errors
1258	}	1446	}
1259		1447
1260	...	1448	...
1261	struct ev_loop *loop = ev_default_init (0);	1449	struct ev_loop *loop = ev_default_init (0);
1262	struct ev_io stdin_readable;	1450	ev_io stdin_readable;
1263	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1451	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1264	ev_io_start (loop, &stdin_readable);	1452	ev_io_start (loop, &stdin_readable);
1265	ev_loop (loop, 0);	1453	ev_loop (loop, 0);
1266		1454
1267		1455
…		…
1275	year, it will still time out after (roughly) one hour. "Roughly" because	1463	year, it will still time out after (roughly) one hour. "Roughly" because
1276	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1464	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1277	monotonic clock option helps a lot here).	1465	monotonic clock option helps a lot here).
1278		1466
1279	The callback is guaranteed to be invoked only I<after> its timeout has	1467	The callback is guaranteed to be invoked only I<after> its timeout has
1280	passed, but if multiple timers become ready during the same loop iteration	1468	passed. If multiple timers become ready during the same loop iteration
1281	then order of execution is undefined.	1469	then the ones with earlier time-out values are invoked before ones with
		1470	later time-out values (but this is no longer true when a callback calls
		1471	C<ev_loop> recursively).
		1472
		1473	=head3 Be smart about timeouts
		1474
		1475	Many real-world problems involve some kind of timeout, usually for error
		1476	recovery. A typical example is an HTTP request - if the other side hangs,
		1477	you want to raise some error after a while.
		1478
		1479	What follows are some ways to handle this problem, from obvious and
		1480	inefficient to smart and efficient.
		1481
		1482	In the following, a 60 second activity timeout is assumed - a timeout that
		1483	gets reset to 60 seconds each time there is activity (e.g. each time some
		1484	data or other life sign was received).
		1485
		1486	=over 4
		1487
		1488	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1489
		1490	This is the most obvious, but not the most simple way: In the beginning,
		1491	start the watcher:
		1492
		1493	ev_timer_init (timer, callback, 60., 0.);
		1494	ev_timer_start (loop, timer);
		1495
		1496	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1497	and start it again:
		1498
		1499	ev_timer_stop (loop, timer);
		1500	ev_timer_set (timer, 60., 0.);
		1501	ev_timer_start (loop, timer);
		1502
		1503	This is relatively simple to implement, but means that each time there is
		1504	some activity, libev will first have to remove the timer from its internal
		1505	data structure and then add it again. Libev tries to be fast, but it's
		1506	still not a constant-time operation.
		1507
		1508	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1509
		1510	This is the easiest way, and involves using C<ev_timer_again> instead of
		1511	C<ev_timer_start>.
		1512
		1513	To implement this, configure an C<ev_timer> with a C<repeat> value
		1514	of C<60> and then call C<ev_timer_again> at start and each time you
		1515	successfully read or write some data. If you go into an idle state where
		1516	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1517	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1518
		1519	That means you can ignore both the C<ev_timer_start> function and the
		1520	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1521	member and C<ev_timer_again>.
		1522
		1523	At start:
		1524
		1525	ev_timer_init (timer, callback);
		1526	timer->repeat = 60.;
		1527	ev_timer_again (loop, timer);
		1528
		1529	Each time there is some activity:
		1530
		1531	ev_timer_again (loop, timer);
		1532
		1533	It is even possible to change the time-out on the fly, regardless of
		1534	whether the watcher is active or not:
		1535
		1536	timer->repeat = 30.;
		1537	ev_timer_again (loop, timer);
		1538
		1539	This is slightly more efficient then stopping/starting the timer each time
		1540	you want to modify its timeout value, as libev does not have to completely
		1541	remove and re-insert the timer from/into its internal data structure.
		1542
		1543	It is, however, even simpler than the "obvious" way to do it.
		1544
		1545	=item 3. Let the timer time out, but then re-arm it as required.
		1546
		1547	This method is more tricky, but usually most efficient: Most timeouts are
		1548	relatively long compared to the intervals between other activity - in
		1549	our example, within 60 seconds, there are usually many I/O events with
		1550	associated activity resets.
		1551
		1552	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1553	but remember the time of last activity, and check for a real timeout only
		1554	within the callback:
		1555
		1556	ev_tstamp last_activity; // time of last activity
		1557
		1558	static void
		1559	callback (EV_P_ ev_timer *w, int revents)
		1560	{
		1561	ev_tstamp now = ev_now (EV_A);
		1562	ev_tstamp timeout = last_activity + 60.;
		1563
		1564	// if last_activity + 60. is older than now, we did time out
		1565	if (timeout < now)
		1566	{
		1567	// timeout occured, take action
		1568	}
		1569	else
		1570	{
		1571	// callback was invoked, but there was some activity, re-arm
		1572	// the watcher to fire in last_activity + 60, which is
		1573	// guaranteed to be in the future, so "again" is positive:
		1574	w->repeat = timeout - now;
		1575	ev_timer_again (EV_A_ w);
		1576	}
		1577	}
		1578
		1579	To summarise the callback: first calculate the real timeout (defined
		1580	as "60 seconds after the last activity"), then check if that time has
		1581	been reached, which means something I<did>, in fact, time out. Otherwise
		1582	the callback was invoked too early (C<timeout> is in the future), so
		1583	re-schedule the timer to fire at that future time, to see if maybe we have
		1584	a timeout then.
		1585
		1586	Note how C<ev_timer_again> is used, taking advantage of the
		1587	C<ev_timer_again> optimisation when the timer is already running.
		1588
		1589	This scheme causes more callback invocations (about one every 60 seconds
		1590	minus half the average time between activity), but virtually no calls to
		1591	libev to change the timeout.
		1592
		1593	To start the timer, simply initialise the watcher and set C<last_activity>
		1594	to the current time (meaning we just have some activity :), then call the
		1595	callback, which will "do the right thing" and start the timer:
		1596
		1597	ev_timer_init (timer, callback);
		1598	last_activity = ev_now (loop);
		1599	callback (loop, timer, EV_TIMEOUT);
		1600
		1601	And when there is some activity, simply store the current time in
		1602	C<last_activity>, no libev calls at all:
		1603
		1604	last_actiivty = ev_now (loop);
		1605
		1606	This technique is slightly more complex, but in most cases where the
		1607	time-out is unlikely to be triggered, much more efficient.
		1608
		1609	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1610	callback :) - just change the timeout and invoke the callback, which will
		1611	fix things for you.
		1612
		1613	=item 4. Wee, just use a double-linked list for your timeouts.
		1614
		1615	If there is not one request, but many thousands (millions...), all
		1616	employing some kind of timeout with the same timeout value, then one can
		1617	do even better:
		1618
		1619	When starting the timeout, calculate the timeout value and put the timeout
		1620	at the I<end> of the list.
		1621
		1622	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1623	the list is expected to fire (for example, using the technique #3).
		1624
		1625	When there is some activity, remove the timer from the list, recalculate
		1626	the timeout, append it to the end of the list again, and make sure to
		1627	update the C<ev_timer> if it was taken from the beginning of the list.
		1628
		1629	This way, one can manage an unlimited number of timeouts in O(1) time for
		1630	starting, stopping and updating the timers, at the expense of a major
		1631	complication, and having to use a constant timeout. The constant timeout
		1632	ensures that the list stays sorted.
		1633
		1634	=back
		1635
		1636	So which method the best?
		1637
		1638	Method #2 is a simple no-brain-required solution that is adequate in most
		1639	situations. Method #3 requires a bit more thinking, but handles many cases
		1640	better, and isn't very complicated either. In most case, choosing either
		1641	one is fine, with #3 being better in typical situations.
		1642
		1643	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1644	rather complicated, but extremely efficient, something that really pays
		1645	off after the first million or so of active timers, i.e. it's usually
		1646	overkill :)
1282		1647
1283	=head3 The special problem of time updates	1648	=head3 The special problem of time updates
1284		1649
1285	Establishing the current time is a costly operation (it usually takes at	1650	Establishing the current time is a costly operation (it usually takes at
1286	least two system calls): EV therefore updates its idea of the current	1651	least two system calls): EV therefore updates its idea of the current
…		…
1330	If the timer is started but non-repeating, stop it (as if it timed out).	1695	If the timer is started but non-repeating, stop it (as if it timed out).
1331		1696
1332	If the timer is repeating, either start it if necessary (with the	1697	If the timer is repeating, either start it if necessary (with the
1333	C<repeat> value), or reset the running timer to the C<repeat> value.	1698	C<repeat> value), or reset the running timer to the C<repeat> value.
1334		1699
1335	This sounds a bit complicated, but here is a useful and typical	1700	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1336	example: Imagine you have a TCP connection and you want a so-called idle	1701	usage example.
1337	timeout, that is, you want to be called when there have been, say, 60
1338	seconds of inactivity on the socket. The easiest way to do this is to
1339	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1340	C<ev_timer_again> each time you successfully read or write some data. If
1341	you go into an idle state where you do not expect data to travel on the
1342	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1343	automatically restart it if need be.
1344
1345	That means you can ignore the C<after> value and C<ev_timer_start>
1346	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1347
1348	ev_timer_init (timer, callback, 0., 5.);
1349	ev_timer_again (loop, timer);
1350	...
1351	timer->again = 17.;
1352	ev_timer_again (loop, timer);
1353	...
1354	timer->again = 10.;
1355	ev_timer_again (loop, timer);
1356
1357	This is more slightly efficient then stopping/starting the timer each time
1358	you want to modify its timeout value.
1359
1360	Note, however, that it is often even more efficient to remember the
1361	time of the last activity and let the timer time-out naturally. In the
1362	callback, you then check whether the time-out is real, or, if there was
1363	some activity, you reschedule the watcher to time-out in "last_activity +
1364	timeout - ev_now ()" seconds.
1365		1702
1366	=item ev_tstamp repeat [read-write]	1703	=item ev_tstamp repeat [read-write]
1367		1704
1368	The current C<repeat> value. Will be used each time the watcher times out	1705	The current C<repeat> value. Will be used each time the watcher times out
1369	or C<ev_timer_again> is called, and determines the next timeout (if any),	1706	or C<ev_timer_again> is called, and determines the next timeout (if any),
…		…
1374	=head3 Examples	1711	=head3 Examples
1375		1712
1376	Example: Create a timer that fires after 60 seconds.	1713	Example: Create a timer that fires after 60 seconds.
1377		1714
1378	static void	1715	static void
1379	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1716	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1380	{	1717	{
1381	.. one minute over, w is actually stopped right here	1718	.. one minute over, w is actually stopped right here
1382	}	1719	}
1383		1720
1384	struct ev_timer mytimer;	1721	ev_timer mytimer;
1385	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1722	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1386	ev_timer_start (loop, &mytimer);	1723	ev_timer_start (loop, &mytimer);
1387		1724
1388	Example: Create a timeout timer that times out after 10 seconds of	1725	Example: Create a timeout timer that times out after 10 seconds of
1389	inactivity.	1726	inactivity.
1390		1727
1391	static void	1728	static void
1392	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1729	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1393	{	1730	{
1394	.. ten seconds without any activity	1731	.. ten seconds without any activity
1395	}	1732	}
1396		1733
1397	struct ev_timer mytimer;	1734	ev_timer mytimer;
1398	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1735	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1399	ev_timer_again (&mytimer); /* start timer */	1736	ev_timer_again (&mytimer); /* start timer */
1400	ev_loop (loop, 0);	1737	ev_loop (loop, 0);
1401		1738
1402	// and in some piece of code that gets executed on any "activity":	1739	// and in some piece of code that gets executed on any "activity":
…		…
1407	=head2 C<ev_periodic> - to cron or not to cron?	1744	=head2 C<ev_periodic> - to cron or not to cron?
1408		1745
1409	Periodic watchers are also timers of a kind, but they are very versatile	1746	Periodic watchers are also timers of a kind, but they are very versatile
1410	(and unfortunately a bit complex).	1747	(and unfortunately a bit complex).
1411		1748
1412	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1749	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1413	but on wall clock time (absolute time). You can tell a periodic watcher	1750	relative time, the physical time that passes) but on wall clock time
1414	to trigger after some specific point in time. For example, if you tell a	1751	(absolute time, the thing you can read on your calender or clock). The
1415	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1752	difference is that wall clock time can run faster or slower than real
1416	+ 10.>, that is, an absolute time not a delay) and then reset your system	1753	time, and time jumps are not uncommon (e.g. when you adjust your
1417	clock to January of the previous year, then it will take more than year	1754	wrist-watch).
1418	to trigger the event (unlike an C<ev_timer>, which would still trigger
1419	roughly 10 seconds later as it uses a relative timeout).
1420		1755
		1756	You can tell a periodic watcher to trigger after some specific point
		1757	in time: for example, if you tell a periodic watcher to trigger "in 10
		1758	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1759	not a delay) and then reset your system clock to January of the previous
		1760	year, then it will take a year or more to trigger the event (unlike an
		1761	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1762	it, as it uses a relative timeout).
		1763
1421	C<ev_periodic>s can also be used to implement vastly more complex timers,	1764	C<ev_periodic> watchers can also be used to implement vastly more complex
1422	such as triggering an event on each "midnight, local time", or other	1765	timers, such as triggering an event on each "midnight, local time", or
1423	complicated rules.	1766	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1767	those cannot react to time jumps.
1424		1768
1425	As with timers, the callback is guaranteed to be invoked only when the	1769	As with timers, the callback is guaranteed to be invoked only when the
1426	time (C<at>) has passed, but if multiple periodic timers become ready	1770	point in time where it is supposed to trigger has passed. If multiple
1427	during the same loop iteration, then order of execution is undefined.	1771	timers become ready during the same loop iteration then the ones with
		1772	earlier time-out values are invoked before ones with later time-out values
		1773	(but this is no longer true when a callback calls C<ev_loop> recursively).
1428		1774
1429	=head3 Watcher-Specific Functions and Data Members	1775	=head3 Watcher-Specific Functions and Data Members
1430		1776
1431	=over 4	1777	=over 4
1432		1778
1433	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1779	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1434		1780
1435	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1781	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1436		1782
1437	Lots of arguments, lets sort it out... There are basically three modes of	1783	Lots of arguments, let's sort it out... There are basically three modes of
1438	operation, and we will explain them from simplest to most complex:	1784	operation, and we will explain them from simplest to most complex:
1439		1785
1440	=over 4	1786	=over 4
1441		1787
1442	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1788	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1443		1789
1444	In this configuration the watcher triggers an event after the wall clock	1790	In this configuration the watcher triggers an event after the wall clock
1445	time C<at> has passed. It will not repeat and will not adjust when a time	1791	time C<offset> has passed. It will not repeat and will not adjust when a
1446	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1792	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1447	only run when the system clock reaches or surpasses this time.	1793	will be stopped and invoked when the system clock reaches or surpasses
		1794	this point in time.
1448		1795
1449	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1796	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1450		1797
1451	In this mode the watcher will always be scheduled to time out at the next	1798	In this mode the watcher will always be scheduled to time out at the next
1452	C<at + N * interval> time (for some integer N, which can also be negative)	1799	C<offset + N * interval> time (for some integer N, which can also be
1453	and then repeat, regardless of any time jumps.	1800	negative) and then repeat, regardless of any time jumps. The C<offset>
		1801	argument is merely an offset into the C<interval> periods.
1454		1802
1455	This can be used to create timers that do not drift with respect to the	1803	This can be used to create timers that do not drift with respect to the
1456	system clock, for example, here is a C<ev_periodic> that triggers each	1804	system clock, for example, here is an C<ev_periodic> that triggers each
1457	hour, on the hour:	1805	hour, on the hour (with respect to UTC):
1458		1806
1459	ev_periodic_set (&periodic, 0., 3600., 0);	1807	ev_periodic_set (&periodic, 0., 3600., 0);
1460		1808
1461	This doesn't mean there will always be 3600 seconds in between triggers,	1809	This doesn't mean there will always be 3600 seconds in between triggers,
1462	but only that the callback will be called when the system time shows a	1810	but only that the callback will be called when the system time shows a
1463	full hour (UTC), or more correctly, when the system time is evenly divisible	1811	full hour (UTC), or more correctly, when the system time is evenly divisible
1464	by 3600.	1812	by 3600.
1465		1813
1466	Another way to think about it (for the mathematically inclined) is that	1814	Another way to think about it (for the mathematically inclined) is that
1467	C<ev_periodic> will try to run the callback in this mode at the next possible	1815	C<ev_periodic> will try to run the callback in this mode at the next possible
1468	time where C<time = at (mod interval)>, regardless of any time jumps.	1816	time where C<time = offset (mod interval)>, regardless of any time jumps.
1469		1817
1470	For numerical stability it is preferable that the C<at> value is near	1818	For numerical stability it is preferable that the C<offset> value is near
1471	C<ev_now ()> (the current time), but there is no range requirement for	1819	C<ev_now ()> (the current time), but there is no range requirement for
1472	this value, and in fact is often specified as zero.	1820	this value, and in fact is often specified as zero.
1473		1821
1474	Note also that there is an upper limit to how often a timer can fire (CPU	1822	Note also that there is an upper limit to how often a timer can fire (CPU
1475	speed for example), so if C<interval> is very small then timing stability	1823	speed for example), so if C<interval> is very small then timing stability
1476	will of course deteriorate. Libev itself tries to be exact to be about one	1824	will of course deteriorate. Libev itself tries to be exact to be about one
1477	millisecond (if the OS supports it and the machine is fast enough).	1825	millisecond (if the OS supports it and the machine is fast enough).
1478		1826
1479	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1827	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1480		1828
1481	In this mode the values for C<interval> and C<at> are both being	1829	In this mode the values for C<interval> and C<offset> are both being
1482	ignored. Instead, each time the periodic watcher gets scheduled, the	1830	ignored. Instead, each time the periodic watcher gets scheduled, the
1483	reschedule callback will be called with the watcher as first, and the	1831	reschedule callback will be called with the watcher as first, and the
1484	current time as second argument.	1832	current time as second argument.
1485		1833
1486	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1834	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1487	ever, or make ANY event loop modifications whatsoever>.	1835	or make ANY other event loop modifications whatsoever, unless explicitly
		1836	allowed by documentation here>.
1488		1837
1489	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1838	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1490	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1839	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1491	only event loop modification you are allowed to do).	1840	only event loop modification you are allowed to do).
1492		1841
1493	The callback prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic	1842	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1494	*w, ev_tstamp now)>, e.g.:	1843	*w, ev_tstamp now)>, e.g.:
1495		1844
		1845	static ev_tstamp
1496	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1846	my_rescheduler (ev_periodic *w, ev_tstamp now)
1497	{	1847	{
1498	return now + 60.;	1848	return now + 60.;
1499	}	1849	}
1500		1850
1501	It must return the next time to trigger, based on the passed time value	1851	It must return the next time to trigger, based on the passed time value
…		…
1521	a different time than the last time it was called (e.g. in a crond like	1871	a different time than the last time it was called (e.g. in a crond like
1522	program when the crontabs have changed).	1872	program when the crontabs have changed).
1523		1873
1524	=item ev_tstamp ev_periodic_at (ev_periodic *)	1874	=item ev_tstamp ev_periodic_at (ev_periodic *)
1525		1875
1526	When active, returns the absolute time that the watcher is supposed to	1876	When active, returns the absolute time that the watcher is supposed
1527	trigger next.	1877	to trigger next. This is not the same as the C<offset> argument to
		1878	C<ev_periodic_set>, but indeed works even in interval and manual
		1879	rescheduling modes.
1528		1880
1529	=item ev_tstamp offset [read-write]	1881	=item ev_tstamp offset [read-write]
1530		1882
1531	When repeating, this contains the offset value, otherwise this is the	1883	When repeating, this contains the offset value, otherwise this is the
1532	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1884	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1885	although libev might modify this value for better numerical stability).
1533		1886
1534	Can be modified any time, but changes only take effect when the periodic	1887	Can be modified any time, but changes only take effect when the periodic
1535	timer fires or C<ev_periodic_again> is being called.	1888	timer fires or C<ev_periodic_again> is being called.
1536		1889
1537	=item ev_tstamp interval [read-write]	1890	=item ev_tstamp interval [read-write]
1538		1891
1539	The current interval value. Can be modified any time, but changes only	1892	The current interval value. Can be modified any time, but changes only
1540	take effect when the periodic timer fires or C<ev_periodic_again> is being	1893	take effect when the periodic timer fires or C<ev_periodic_again> is being
1541	called.	1894	called.
1542		1895
1543	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1896	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1544		1897
1545	The current reschedule callback, or C<0>, if this functionality is	1898	The current reschedule callback, or C<0>, if this functionality is
1546	switched off. Can be changed any time, but changes only take effect when	1899	switched off. Can be changed any time, but changes only take effect when
1547	the periodic timer fires or C<ev_periodic_again> is being called.	1900	the periodic timer fires or C<ev_periodic_again> is being called.
1548		1901
…		…
1553	Example: Call a callback every hour, or, more precisely, whenever the	1906	Example: Call a callback every hour, or, more precisely, whenever the
1554	system time is divisible by 3600. The callback invocation times have	1907	system time is divisible by 3600. The callback invocation times have
1555	potentially a lot of jitter, but good long-term stability.	1908	potentially a lot of jitter, but good long-term stability.
1556		1909
1557	static void	1910	static void
1558	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1911	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1559	{	1912	{
1560	... its now a full hour (UTC, or TAI or whatever your clock follows)	1913	... its now a full hour (UTC, or TAI or whatever your clock follows)
1561	}	1914	}
1562		1915
1563	struct ev_periodic hourly_tick;	1916	ev_periodic hourly_tick;
1564	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1917	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1565	ev_periodic_start (loop, &hourly_tick);	1918	ev_periodic_start (loop, &hourly_tick);
1566		1919
1567	Example: The same as above, but use a reschedule callback to do it:	1920	Example: The same as above, but use a reschedule callback to do it:
1568		1921
1569	#include <math.h>	1922	#include <math.h>
1570		1923
1571	static ev_tstamp	1924	static ev_tstamp
1572	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1925	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1573	{	1926	{
1574	return now + (3600. - fmod (now, 3600.));	1927	return now + (3600. - fmod (now, 3600.));
1575	}	1928	}
1576		1929
1577	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1930	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1578		1931
1579	Example: Call a callback every hour, starting now:	1932	Example: Call a callback every hour, starting now:
1580		1933
1581	struct ev_periodic hourly_tick;	1934	ev_periodic hourly_tick;
1582	ev_periodic_init (&hourly_tick, clock_cb,	1935	ev_periodic_init (&hourly_tick, clock_cb,
1583	fmod (ev_now (loop), 3600.), 3600., 0);	1936	fmod (ev_now (loop), 3600.), 3600., 0);
1584	ev_periodic_start (loop, &hourly_tick);	1937	ev_periodic_start (loop, &hourly_tick);
1585		1938
1586		1939
…		…
1625		1978
1626	=back	1979	=back
1627		1980
1628	=head3 Examples	1981	=head3 Examples
1629		1982
1630	Example: Try to exit cleanly on SIGINT and SIGTERM.	1983	Example: Try to exit cleanly on SIGINT.
1631		1984
1632	static void	1985	static void
1633	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1986	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
1634	{	1987	{
1635	ev_unloop (loop, EVUNLOOP_ALL);	1988	ev_unloop (loop, EVUNLOOP_ALL);
1636	}	1989	}
1637		1990
1638	struct ev_signal signal_watcher;	1991	ev_signal signal_watcher;
1639	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1992	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1640	ev_signal_start (loop, &sigint_cb);	1993	ev_signal_start (loop, &signal_watcher);
1641		1994
1642		1995
1643	=head2 C<ev_child> - watch out for process status changes	1996	=head2 C<ev_child> - watch out for process status changes
1644		1997
1645	Child watchers trigger when your process receives a SIGCHLD in response to	1998	Child watchers trigger when your process receives a SIGCHLD in response to
…		…
1718	its completion.	2071	its completion.
1719		2072
1720	ev_child cw;	2073	ev_child cw;
1721		2074
1722	static void	2075	static void
1723	child_cb (EV_P_ struct ev_child *w, int revents)	2076	child_cb (EV_P_ ev_child *w, int revents)
1724	{	2077	{
1725	ev_child_stop (EV_A_ w);	2078	ev_child_stop (EV_A_ w);
1726	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);	2079	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1727	}	2080	}
1728		2081
…		…
1743		2096
1744		2097
1745	=head2 C<ev_stat> - did the file attributes just change?	2098	=head2 C<ev_stat> - did the file attributes just change?
1746		2099
1747	This watches a file system path for attribute changes. That is, it calls	2100	This watches a file system path for attribute changes. That is, it calls
1748	C<stat> regularly (or when the OS says it changed) and sees if it changed	2101	C<stat> on that path in regular intervals (or when the OS says it changed)
1749	compared to the last time, invoking the callback if it did.	2102	and sees if it changed compared to the last time, invoking the callback if
		2103	it did.
1750		2104
1751	The path does not need to exist: changing from "path exists" to "path does	2105	The path does not need to exist: changing from "path exists" to "path does
1752	not exist" is a status change like any other. The condition "path does	2106	not exist" is a status change like any other. The condition "path does not
1753	not exist" is signified by the C<st_nlink> field being zero (which is	2107	exist" (or more correctly "path cannot be stat'ed") is signified by the
1754	otherwise always forced to be at least one) and all the other fields of	2108	C<st_nlink> field being zero (which is otherwise always forced to be at
1755	the stat buffer having unspecified contents.	2109	least one) and all the other fields of the stat buffer having unspecified
		2110	contents.
1756		2111
1757	The path I<should> be absolute and I<must not> end in a slash. If it is	2112	The path I<must not> end in a slash or contain special components such as
		2113	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1758	relative and your working directory changes, the behaviour is undefined.	2114	your working directory changes, then the behaviour is undefined.
1759		2115
1760	Since there is no standard kernel interface to do this, the portable	2116	Since there is no portable change notification interface available, the
1761	implementation simply calls C<stat (2)> regularly on the path to see if	2117	portable implementation simply calls C<stat(2)> regularly on the path
1762	it changed somehow. You can specify a recommended polling interval for	2118	to see if it changed somehow. You can specify a recommended polling
1763	this case. If you specify a polling interval of C<0> (highly recommended!)	2119	interval for this case. If you specify a polling interval of C<0> (highly
1764	then a I<suitable, unspecified default> value will be used (which	2120	recommended!) then a I<suitable, unspecified default> value will be used
1765	you can expect to be around five seconds, although this might change	2121	(which you can expect to be around five seconds, although this might
1766	dynamically). Libev will also impose a minimum interval which is currently	2122	change dynamically). Libev will also impose a minimum interval which is
1767	around C<0.1>, but thats usually overkill.	2123	currently around C<0.1>, but that's usually overkill.
1768		2124
1769	This watcher type is not meant for massive numbers of stat watchers,	2125	This watcher type is not meant for massive numbers of stat watchers,
1770	as even with OS-supported change notifications, this can be	2126	as even with OS-supported change notifications, this can be
1771	resource-intensive.	2127	resource-intensive.
1772		2128
1773	At the time of this writing, the only OS-specific interface implemented	2129	At the time of this writing, the only OS-specific interface implemented
1774	is the Linux inotify interface (implementing kqueue support is left as	2130	is the Linux inotify interface (implementing kqueue support is left as an
1775	an exercise for the reader. Note, however, that the author sees no way	2131	exercise for the reader. Note, however, that the author sees no way of
1776	of implementing C<ev_stat> semantics with kqueue).	2132	implementing C<ev_stat> semantics with kqueue, except as a hint).
1777		2133
1778	=head3 ABI Issues (Largefile Support)	2134	=head3 ABI Issues (Largefile Support)
1779		2135
1780	Libev by default (unless the user overrides this) uses the default	2136	Libev by default (unless the user overrides this) uses the default
1781	compilation environment, which means that on systems with large file	2137	compilation environment, which means that on systems with large file
1782	support disabled by default, you get the 32 bit version of the stat	2138	support disabled by default, you get the 32 bit version of the stat
1783	structure. When using the library from programs that change the ABI to	2139	structure. When using the library from programs that change the ABI to
1784	use 64 bit file offsets the programs will fail. In that case you have to	2140	use 64 bit file offsets the programs will fail. In that case you have to
1785	compile libev with the same flags to get binary compatibility. This is	2141	compile libev with the same flags to get binary compatibility. This is
1786	obviously the case with any flags that change the ABI, but the problem is	2142	obviously the case with any flags that change the ABI, but the problem is
1787	most noticeably disabled with ev_stat and large file support.	2143	most noticeably displayed with ev_stat and large file support.
1788		2144
1789	The solution for this is to lobby your distribution maker to make large	2145	The solution for this is to lobby your distribution maker to make large
1790	file interfaces available by default (as e.g. FreeBSD does) and not	2146	file interfaces available by default (as e.g. FreeBSD does) and not
1791	optional. Libev cannot simply switch on large file support because it has	2147	optional. Libev cannot simply switch on large file support because it has
1792	to exchange stat structures with application programs compiled using the	2148	to exchange stat structures with application programs compiled using the
1793	default compilation environment.	2149	default compilation environment.
1794		2150
1795	=head3 Inotify and Kqueue	2151	=head3 Inotify and Kqueue
1796		2152
1797	When C<inotify (7)> support has been compiled into libev (generally only	2153	When C<inotify (7)> support has been compiled into libev and present at
1798	available with Linux) and present at runtime, it will be used to speed up	2154	runtime, it will be used to speed up change detection where possible. The
1799	change detection where possible. The inotify descriptor will be created lazily	2155	inotify descriptor will be created lazily when the first C<ev_stat>
1800	when the first C<ev_stat> watcher is being started.	2156	watcher is being started.
1801		2157
1802	Inotify presence does not change the semantics of C<ev_stat> watchers	2158	Inotify presence does not change the semantics of C<ev_stat> watchers
1803	except that changes might be detected earlier, and in some cases, to avoid	2159	except that changes might be detected earlier, and in some cases, to avoid
1804	making regular C<stat> calls. Even in the presence of inotify support	2160	making regular C<stat> calls. Even in the presence of inotify support
1805	there are many cases where libev has to resort to regular C<stat> polling,	2161	there are many cases where libev has to resort to regular C<stat> polling,
1806	but as long as the path exists, libev usually gets away without polling.	2162	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2163	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2164	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2165	xfs are fully working) libev usually gets away without polling.
1807		2166
1808	There is no support for kqueue, as apparently it cannot be used to	2167	There is no support for kqueue, as apparently it cannot be used to
1809	implement this functionality, due to the requirement of having a file	2168	implement this functionality, due to the requirement of having a file
1810	descriptor open on the object at all times, and detecting renames, unlinks	2169	descriptor open on the object at all times, and detecting renames, unlinks
1811	etc. is difficult.	2170	etc. is difficult.
1812		2171
		2172	=head3 C<stat ()> is a synchronous operation
		2173
		2174	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2175	the process. The exception are C<ev_stat> watchers - those call C<stat
		2176	()>, which is a synchronous operation.
		2177
		2178	For local paths, this usually doesn't matter: unless the system is very
		2179	busy or the intervals between stat's are large, a stat call will be fast,
		2180	as the path data is usually in memory already (except when starting the
		2181	watcher).
		2182
		2183	For networked file systems, calling C<stat ()> can block an indefinite
		2184	time due to network issues, and even under good conditions, a stat call
		2185	often takes multiple milliseconds.
		2186
		2187	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2188	paths, although this is fully supported by libev.
		2189
1813	=head3 The special problem of stat time resolution	2190	=head3 The special problem of stat time resolution
1814		2191
1815	The C<stat ()> system call only supports full-second resolution portably, and	2192	The C<stat ()> system call only supports full-second resolution portably,
1816	even on systems where the resolution is higher, most file systems still	2193	and even on systems where the resolution is higher, most file systems
1817	only support whole seconds.	2194	still only support whole seconds.
1818		2195
1819	That means that, if the time is the only thing that changes, you can	2196	That means that, if the time is the only thing that changes, you can
1820	easily miss updates: on the first update, C<ev_stat> detects a change and	2197	easily miss updates: on the first update, C<ev_stat> detects a change and
1821	calls your callback, which does something. When there is another update	2198	calls your callback, which does something. When there is another update
1822	within the same second, C<ev_stat> will be unable to detect unless the	2199	within the same second, C<ev_stat> will be unable to detect unless the
…		…
1965		2342
1966	=head3 Watcher-Specific Functions and Data Members	2343	=head3 Watcher-Specific Functions and Data Members
1967		2344
1968	=over 4	2345	=over 4
1969		2346
1970	=item ev_idle_init (ev_signal *, callback)	2347	=item ev_idle_init (ev_idle *, callback)
1971		2348
1972	Initialises and configures the idle watcher - it has no parameters of any	2349	Initialises and configures the idle watcher - it has no parameters of any
1973	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2350	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1974	believe me.	2351	believe me.
1975		2352
…		…
1979		2356
1980	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2357	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1981	callback, free it. Also, use no error checking, as usual.	2358	callback, free it. Also, use no error checking, as usual.
1982		2359
1983	static void	2360	static void
1984	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2361	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1985	{	2362	{
1986	free (w);	2363	free (w);
1987	// now do something you wanted to do when the program has	2364	// now do something you wanted to do when the program has
1988	// no longer anything immediate to do.	2365	// no longer anything immediate to do.
1989	}	2366	}
1990		2367
1991	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2368	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1992	ev_idle_init (idle_watcher, idle_cb);	2369	ev_idle_init (idle_watcher, idle_cb);
1993	ev_idle_start (loop, idle_cb);	2370	ev_idle_start (loop, idle_cb);
1994		2371
1995		2372
1996	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2373	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
…		…
2077		2454
2078	static ev_io iow [nfd];	2455	static ev_io iow [nfd];
2079	static ev_timer tw;	2456	static ev_timer tw;
2080		2457
2081	static void	2458	static void
2082	io_cb (ev_loop *loop, ev_io *w, int revents)	2459	io_cb (struct ev_loop *loop, ev_io *w, int revents)
2083	{	2460	{
2084	}	2461	}
2085		2462
2086	// create io watchers for each fd and a timer before blocking	2463	// create io watchers for each fd and a timer before blocking
2087	static void	2464	static void
2088	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2465	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2089	{	2466	{
2090	int timeout = 3600000;	2467	int timeout = 3600000;
2091	struct pollfd fds [nfd];	2468	struct pollfd fds [nfd];
2092	// actual code will need to loop here and realloc etc.	2469	// actual code will need to loop here and realloc etc.
2093	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2470	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
…		…
2108	}	2485	}
2109	}	2486	}
2110		2487
2111	// stop all watchers after blocking	2488	// stop all watchers after blocking
2112	static void	2489	static void
2113	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2490	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2114	{	2491	{
2115	ev_timer_stop (loop, &tw);	2492	ev_timer_stop (loop, &tw);
2116		2493
2117	for (int i = 0; i < nfd; ++i)	2494	for (int i = 0; i < nfd; ++i)
2118	{	2495	{
…		…
2214	some fds have to be watched and handled very quickly (with low latency),	2591	some fds have to be watched and handled very quickly (with low latency),
2215	and even priorities and idle watchers might have too much overhead. In	2592	and even priorities and idle watchers might have too much overhead. In
2216	this case you would put all the high priority stuff in one loop and all	2593	this case you would put all the high priority stuff in one loop and all
2217	the rest in a second one, and embed the second one in the first.	2594	the rest in a second one, and embed the second one in the first.
2218		2595
2219	As long as the watcher is active, the callback will be invoked every time	2596	As long as the watcher is active, the callback will be invoked every
2220	there might be events pending in the embedded loop. The callback must then	2597	time there might be events pending in the embedded loop. The callback
2221	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2598	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2222	their callbacks (you could also start an idle watcher to give the embedded	2599	sweep and invoke their callbacks (the callback doesn't need to invoke the
2223	loop strictly lower priority for example). You can also set the callback	2600	C<ev_embed_sweep> function directly, it could also start an idle watcher
2224	to C<0>, in which case the embed watcher will automatically execute the	2601	to give the embedded loop strictly lower priority for example).
2225	embedded loop sweep.
2226		2602
2227	As long as the watcher is started it will automatically handle events. The	2603	You can also set the callback to C<0>, in which case the embed watcher
2228	callback will be invoked whenever some events have been handled. You can	2604	will automatically execute the embedded loop sweep whenever necessary.
2229	set the callback to C<0> to avoid having to specify one if you are not
2230	interested in that.
2231		2605
2232	Also, there have not currently been made special provisions for forking:	2606	Fork detection will be handled transparently while the C<ev_embed> watcher
2233	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2607	is active, i.e., the embedded loop will automatically be forked when the
2234	but you will also have to stop and restart any C<ev_embed> watchers	2608	embedding loop forks. In other cases, the user is responsible for calling
2235	yourself - but you can use a fork watcher to handle this automatically,	2609	C<ev_loop_fork> on the embedded loop.
2236	and future versions of libev might do just that.
2237		2610
2238	Unfortunately, not all backends are embeddable, only the ones returned by	2611	Unfortunately, not all backends are embeddable: only the ones returned by
2239	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2612	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2240	portable one.	2613	portable one.
2241		2614
2242	So when you want to use this feature you will always have to be prepared	2615	So when you want to use this feature you will always have to be prepared
2243	that you cannot get an embeddable loop. The recommended way to get around	2616	that you cannot get an embeddable loop. The recommended way to get around
2244	this is to have a separate variables for your embeddable loop, try to	2617	this is to have a separate variables for your embeddable loop, try to
2245	create it, and if that fails, use the normal loop for everything.	2618	create it, and if that fails, use the normal loop for everything.
		2619
		2620	=head3 C<ev_embed> and fork
		2621
		2622	While the C<ev_embed> watcher is running, forks in the embedding loop will
		2623	automatically be applied to the embedded loop as well, so no special
		2624	fork handling is required in that case. When the watcher is not running,
		2625	however, it is still the task of the libev user to call C<ev_loop_fork ()>
		2626	as applicable.
2246		2627
2247	=head3 Watcher-Specific Functions and Data Members	2628	=head3 Watcher-Specific Functions and Data Members
2248		2629
2249	=over 4	2630	=over 4
2250		2631
…		…
2278	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be	2659	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
2279	used).	2660	used).
2280		2661
2281	struct ev_loop *loop_hi = ev_default_init (0);	2662	struct ev_loop *loop_hi = ev_default_init (0);
2282	struct ev_loop *loop_lo = 0;	2663	struct ev_loop *loop_lo = 0;
2283	struct ev_embed embed;	2664	ev_embed embed;
2284		2665
2285	// see if there is a chance of getting one that works	2666	// see if there is a chance of getting one that works
2286	// (remember that a flags value of 0 means autodetection)	2667	// (remember that a flags value of 0 means autodetection)
2287	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()	2668	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2288	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())	2669	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
…		…
2302	kqueue implementation). Store the kqueue/socket-only event loop in	2683	kqueue implementation). Store the kqueue/socket-only event loop in
2303	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).	2684	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
2304		2685
2305	struct ev_loop *loop = ev_default_init (0);	2686	struct ev_loop *loop = ev_default_init (0);
2306	struct ev_loop *loop_socket = 0;	2687	struct ev_loop *loop_socket = 0;
2307	struct ev_embed embed;	2688	ev_embed embed;
2308		2689
2309	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)	2690	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2310	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))	2691	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2311	{	2692	{
2312	ev_embed_init (&embed, 0, loop_socket);	2693	ev_embed_init (&embed, 0, loop_socket);
…		…
2327	event loop blocks next and before C<ev_check> watchers are being called,	2708	event loop blocks next and before C<ev_check> watchers are being called,
2328	and only in the child after the fork. If whoever good citizen calling	2709	and only in the child after the fork. If whoever good citizen calling
2329	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2710	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2330	handlers will be invoked, too, of course.	2711	handlers will be invoked, too, of course.
2331		2712
		2713	=head3 The special problem of life after fork - how is it possible?
		2714
		2715	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2716	up/change the process environment, followed by a call to C<exec()>. This
		2717	sequence should be handled by libev without any problems.
		2718
		2719	This changes when the application actually wants to do event handling
		2720	in the child, or both parent in child, in effect "continuing" after the
		2721	fork.
		2722
		2723	The default mode of operation (for libev, with application help to detect
		2724	forks) is to duplicate all the state in the child, as would be expected
		2725	when I<either> the parent I<or> the child process continues.
		2726
		2727	When both processes want to continue using libev, then this is usually the
		2728	wrong result. In that case, usually one process (typically the parent) is
		2729	supposed to continue with all watchers in place as before, while the other
		2730	process typically wants to start fresh, i.e. without any active watchers.
		2731
		2732	The cleanest and most efficient way to achieve that with libev is to
		2733	simply create a new event loop, which of course will be "empty", and
		2734	use that for new watchers. This has the advantage of not touching more
		2735	memory than necessary, and thus avoiding the copy-on-write, and the
		2736	disadvantage of having to use multiple event loops (which do not support
		2737	signal watchers).
		2738
		2739	When this is not possible, or you want to use the default loop for
		2740	other reasons, then in the process that wants to start "fresh", call
		2741	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2742	the default loop will "orphan" (not stop) all registered watchers, so you
		2743	have to be careful not to execute code that modifies those watchers. Note
		2744	also that in that case, you have to re-register any signal watchers.
		2745
2332	=head3 Watcher-Specific Functions and Data Members	2746	=head3 Watcher-Specific Functions and Data Members
2333		2747
2334	=over 4	2748	=over 4
2335		2749
2336	=item ev_fork_init (ev_signal *, callback)	2750	=item ev_fork_init (ev_signal *, callback)
…		…
2368	is that the author does not know of a simple (or any) algorithm for a	2782	is that the author does not know of a simple (or any) algorithm for a
2369	multiple-writer-single-reader queue that works in all cases and doesn't	2783	multiple-writer-single-reader queue that works in all cases and doesn't
2370	need elaborate support such as pthreads.	2784	need elaborate support such as pthreads.
2371		2785
2372	That means that if you want to queue data, you have to provide your own	2786	That means that if you want to queue data, you have to provide your own
2373	queue. But at least I can tell you would implement locking around your	2787	queue. But at least I can tell you how to implement locking around your
2374	queue:	2788	queue:
2375		2789
2376	=over 4	2790	=over 4
2377		2791
2378	=item queueing from a signal handler context	2792	=item queueing from a signal handler context
2379		2793
2380	To implement race-free queueing, you simply add to the queue in the signal	2794	To implement race-free queueing, you simply add to the queue in the signal
2381	handler but you block the signal handler in the watcher callback. Here is an example that does that for	2795	handler but you block the signal handler in the watcher callback. Here is
2382	some fictitious SIGUSR1 handler:	2796	an example that does that for some fictitious SIGUSR1 handler:
2383		2797
2384	static ev_async mysig;	2798	static ev_async mysig;
2385		2799
2386	static void	2800	static void
2387	sigusr1_handler (void)	2801	sigusr1_handler (void)
…		…
2453	=over 4	2867	=over 4
2454		2868
2455	=item ev_async_init (ev_async *, callback)	2869	=item ev_async_init (ev_async *, callback)
2456		2870
2457	Initialises and configures the async watcher - it has no parameters of any	2871	Initialises and configures the async watcher - it has no parameters of any
2458	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2872	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2459	believe me.	2873	trust me.
2460		2874
2461	=item ev_async_send (loop, ev_async *)	2875	=item ev_async_send (loop, ev_async *)
2462		2876
2463	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2877	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2464	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	2878	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2465	C<ev_feed_event>, this call is safe to do in other threads, signal or	2879	C<ev_feed_event>, this call is safe to do from other threads, signal or
2466	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	2880	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2467	section below on what exactly this means).	2881	section below on what exactly this means).
2468		2882
		2883	Note that, as with other watchers in libev, multiple events might get
		2884	compressed into a single callback invocation (another way to look at this
		2885	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2886	reset when the event loop detects that).
		2887
2469	This call incurs the overhead of a system call only once per loop iteration,	2888	This call incurs the overhead of a system call only once per event loop
2470	so while the overhead might be noticeable, it doesn't apply to repeated	2889	iteration, so while the overhead might be noticeable, it doesn't apply to
2471	calls to C<ev_async_send>.	2890	repeated calls to C<ev_async_send> for the same event loop.
2472		2891
2473	=item bool = ev_async_pending (ev_async *)	2892	=item bool = ev_async_pending (ev_async *)
2474		2893
2475	Returns a non-zero value when C<ev_async_send> has been called on the	2894	Returns a non-zero value when C<ev_async_send> has been called on the
2476	watcher but the event has not yet been processed (or even noted) by the	2895	watcher but the event has not yet been processed (or even noted) by the
…		…
2479	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	2898	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2480	the loop iterates next and checks for the watcher to have become active,	2899	the loop iterates next and checks for the watcher to have become active,
2481	it will reset the flag again. C<ev_async_pending> can be used to very	2900	it will reset the flag again. C<ev_async_pending> can be used to very
2482	quickly check whether invoking the loop might be a good idea.	2901	quickly check whether invoking the loop might be a good idea.
2483		2902
2484	Not that this does I<not> check whether the watcher itself is pending, only	2903	Not that this does I<not> check whether the watcher itself is pending,
2485	whether it has been requested to make this watcher pending.	2904	only whether it has been requested to make this watcher pending: there
		2905	is a time window between the event loop checking and resetting the async
		2906	notification, and the callback being invoked.
2486		2907
2487	=back	2908	=back
2488		2909
2489		2910
2490	=head1 OTHER FUNCTIONS	2911	=head1 OTHER FUNCTIONS
…		…
2494	=over 4	2915	=over 4
2495		2916
2496	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2917	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
2497		2918
2498	This function combines a simple timer and an I/O watcher, calls your	2919	This function combines a simple timer and an I/O watcher, calls your
2499	callback on whichever event happens first and automatically stop both	2920	callback on whichever event happens first and automatically stops both
2500	watchers. This is useful if you want to wait for a single event on an fd	2921	watchers. This is useful if you want to wait for a single event on an fd
2501	or timeout without having to allocate/configure/start/stop/free one or	2922	or timeout without having to allocate/configure/start/stop/free one or
2502	more watchers yourself.	2923	more watchers yourself.
2503		2924
2504	If C<fd> is less than 0, then no I/O watcher will be started and events	2925	If C<fd> is less than 0, then no I/O watcher will be started and the
2505	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2926	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
2506	C<events> set will be created and started.	2927	the given C<fd> and C<events> set will be created and started.
2507		2928
2508	If C<timeout> is less than 0, then no timeout watcher will be	2929	If C<timeout> is less than 0, then no timeout watcher will be
2509	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2930	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
2510	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2931	repeat = 0) will be started. C<0> is a valid timeout.
2511	dubious value.
2512		2932
2513	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2933	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
2514	passed an C<revents> set like normal event callbacks (a combination of	2934	passed an C<revents> set like normal event callbacks (a combination of
2515	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2935	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
2516	value passed to C<ev_once>:	2936	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2937	a timeout and an io event at the same time - you probably should give io
		2938	events precedence.
		2939
		2940	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
2517		2941
2518	static void stdin_ready (int revents, void *arg)	2942	static void stdin_ready (int revents, void *arg)
2519	{	2943	{
		2944	if (revents & EV_READ)
		2945	/* stdin might have data for us, joy! */;
2520	if (revents & EV_TIMEOUT)	2946	else if (revents & EV_TIMEOUT)
2521	/* doh, nothing entered */;	2947	/* doh, nothing entered */;
2522	else if (revents & EV_READ)
2523	/* stdin might have data for us, joy! */;
2524	}	2948	}
2525		2949
2526	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2950	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
2527		2951
2528	=item ev_feed_event (ev_loop *, watcher *, int revents)	2952	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
2529		2953
2530	Feeds the given event set into the event loop, as if the specified event	2954	Feeds the given event set into the event loop, as if the specified event
2531	had happened for the specified watcher (which must be a pointer to an	2955	had happened for the specified watcher (which must be a pointer to an
2532	initialised but not necessarily started event watcher).	2956	initialised but not necessarily started event watcher).
2533		2957
2534	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2958	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
2535		2959
2536	Feed an event on the given fd, as if a file descriptor backend detected	2960	Feed an event on the given fd, as if a file descriptor backend detected
2537	the given events it.	2961	the given events it.
2538		2962
2539	=item ev_feed_signal_event (ev_loop *loop, int signum)	2963	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
2540		2964
2541	Feed an event as if the given signal occurred (C<loop> must be the default	2965	Feed an event as if the given signal occurred (C<loop> must be the default
2542	loop!).	2966	loop!).
2543		2967
2544	=back	2968	=back
…		…
2666		3090
2667	myclass obj;	3091	myclass obj;
2668	ev::io iow;	3092	ev::io iow;
2669	iow.set <myclass, &myclass::io_cb> (&obj);	3093	iow.set <myclass, &myclass::io_cb> (&obj);
2670		3094
		3095	=item w->set (object *)
		3096
		3097	This is an B<experimental> feature that might go away in a future version.
		3098
		3099	This is a variation of a method callback - leaving out the method to call
		3100	will default the method to C<operator ()>, which makes it possible to use
		3101	functor objects without having to manually specify the C<operator ()> all
		3102	the time. Incidentally, you can then also leave out the template argument
		3103	list.
		3104
		3105	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3106	int revents)>.
		3107
		3108	See the method-C<set> above for more details.
		3109
		3110	Example: use a functor object as callback.
		3111
		3112	struct myfunctor
		3113	{
		3114	void operator() (ev::io &w, int revents)
		3115	{
		3116	...
		3117	}
		3118	}
		3119
		3120	myfunctor f;
		3121
		3122	ev::io w;
		3123	w.set (&f);
		3124
2671	=item w->set<function> (void *data = 0)	3125	=item w->set<function> (void *data = 0)
2672		3126
2673	Also sets a callback, but uses a static method or plain function as	3127	Also sets a callback, but uses a static method or plain function as
2674	callback. The optional C<data> argument will be stored in the watcher's	3128	callback. The optional C<data> argument will be stored in the watcher's
2675	C<data> member and is free for you to use.	3129	C<data> member and is free for you to use.
2676		3130
2677	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	3131	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2678		3132
2679	See the method-C<set> above for more details.	3133	See the method-C<set> above for more details.
2680		3134
2681	Example:	3135	Example: Use a plain function as callback.
2682		3136
2683	static void io_cb (ev::io &w, int revents) { }	3137	static void io_cb (ev::io &w, int revents) { }
2684	iow.set <io_cb> ();	3138	iow.set <io_cb> ();
2685		3139
2686	=item w->set (struct ev_loop *)	3140	=item w->set (struct ev_loop *)
…		…
2724	Example: Define a class with an IO and idle watcher, start one of them in	3178	Example: Define a class with an IO and idle watcher, start one of them in
2725	the constructor.	3179	the constructor.
2726		3180
2727	class myclass	3181	class myclass
2728	{	3182	{
2729	ev::io io; void io_cb (ev::io &w, int revents);	3183	ev::io io ; void io_cb (ev::io &w, int revents);
2730	ev:idle idle void idle_cb (ev::idle &w, int revents);	3184	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2731		3185
2732	myclass (int fd)	3186	myclass (int fd)
2733	{	3187	{
2734	io .set <myclass, &myclass::io_cb > (this);	3188	io .set <myclass, &myclass::io_cb > (this);
2735	idle.set <myclass, &myclass::idle_cb> (this);	3189	idle.set <myclass, &myclass::idle_cb> (this);
…		…
2751	=item Perl	3205	=item Perl
2752		3206
2753	The EV module implements the full libev API and is actually used to test	3207	The EV module implements the full libev API and is actually used to test
2754	libev. EV is developed together with libev. Apart from the EV core module,	3208	libev. EV is developed together with libev. Apart from the EV core module,
2755	there are additional modules that implement libev-compatible interfaces	3209	there are additional modules that implement libev-compatible interfaces
2756	to C<libadns> (C<EV::ADNS>), C<Net::SNMP> (C<Net::SNMP::EV>) and the	3210	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
2757	C<libglib> event core (C<Glib::EV> and C<EV::Glib>).	3211	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3212	and C<EV::Glib>).
2758		3213
2759	It can be found and installed via CPAN, its homepage is at	3214	It can be found and installed via CPAN, its homepage is at
2760	L<http://software.schmorp.de/pkg/EV>.	3215	L<http://software.schmorp.de/pkg/EV>.
2761		3216
2762	=item Python	3217	=item Python
2763		3218
2764	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3219	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2765	seems to be quite complete and well-documented. Note, however, that the	3220	seems to be quite complete and well-documented.
2766	patch they require for libev is outright dangerous as it breaks the ABI
2767	for everybody else, and therefore, should never be applied in an installed
2768	libev (if python requires an incompatible ABI then it needs to embed
2769	libev).
2770		3221
2771	=item Ruby	3222	=item Ruby
2772		3223
2773	Tony Arcieri has written a ruby extension that offers access to a subset	3224	Tony Arcieri has written a ruby extension that offers access to a subset
2774	of the libev API and adds file handle abstractions, asynchronous DNS and	3225	of the libev API and adds file handle abstractions, asynchronous DNS and
2775	more on top of it. It can be found via gem servers. Its homepage is at	3226	more on top of it. It can be found via gem servers. Its homepage is at
2776	L<http://rev.rubyforge.org/>.	3227	L<http://rev.rubyforge.org/>.
2777		3228
		3229	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3230	makes rev work even on mingw.
		3231
		3232	=item Haskell
		3233
		3234	A haskell binding to libev is available at
		3235	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3236
2778	=item D	3237	=item D
2779		3238
2780	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3239	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2781	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3240	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3241
		3242	=item Ocaml
		3243
		3244	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3245	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
2782		3246
2783	=back	3247	=back
2784		3248
2785		3249
2786	=head1 MACRO MAGIC	3250	=head1 MACRO MAGIC
…		…
2887		3351
2888	#define EV_STANDALONE 1	3352	#define EV_STANDALONE 1
2889	#include "ev.h"	3353	#include "ev.h"
2890		3354
2891	Both header files and implementation files can be compiled with a C++	3355	Both header files and implementation files can be compiled with a C++
2892	compiler (at least, thats a stated goal, and breakage will be treated	3356	compiler (at least, that's a stated goal, and breakage will be treated
2893	as a bug).	3357	as a bug).
2894		3358
2895	You need the following files in your source tree, or in a directory	3359	You need the following files in your source tree, or in a directory
2896	in your include path (e.g. in libev/ when using -Ilibev):	3360	in your include path (e.g. in libev/ when using -Ilibev):
2897		3361
…		…
2941		3405
2942	=head2 PREPROCESSOR SYMBOLS/MACROS	3406	=head2 PREPROCESSOR SYMBOLS/MACROS
2943		3407
2944	Libev can be configured via a variety of preprocessor symbols you have to	3408	Libev can be configured via a variety of preprocessor symbols you have to
2945	define before including any of its files. The default in the absence of	3409	define before including any of its files. The default in the absence of
2946	autoconf is noted for every option.	3410	autoconf is documented for every option.
2947		3411
2948	=over 4	3412	=over 4
2949		3413
2950	=item EV_STANDALONE	3414	=item EV_STANDALONE
2951		3415
…		…
2953	keeps libev from including F<config.h>, and it also defines dummy	3417	keeps libev from including F<config.h>, and it also defines dummy
2954	implementations for some libevent functions (such as logging, which is not	3418	implementations for some libevent functions (such as logging, which is not
2955	supported). It will also not define any of the structs usually found in	3419	supported). It will also not define any of the structs usually found in
2956	F<event.h> that are not directly supported by the libev core alone.	3420	F<event.h> that are not directly supported by the libev core alone.
2957		3421
		3422	In stanbdalone mode, libev will still try to automatically deduce the
		3423	configuration, but has to be more conservative.
		3424
2958	=item EV_USE_MONOTONIC	3425	=item EV_USE_MONOTONIC
2959		3426
2960	If defined to be C<1>, libev will try to detect the availability of the	3427	If defined to be C<1>, libev will try to detect the availability of the
2961	monotonic clock option at both compile time and runtime. Otherwise no use	3428	monotonic clock option at both compile time and runtime. Otherwise no
2962	of the monotonic clock option will be attempted. If you enable this, you	3429	use of the monotonic clock option will be attempted. If you enable this,
2963	usually have to link against librt or something similar. Enabling it when	3430	you usually have to link against librt or something similar. Enabling it
2964	the functionality isn't available is safe, though, although you have	3431	when the functionality isn't available is safe, though, although you have
2965	to make sure you link against any libraries where the C<clock_gettime>	3432	to make sure you link against any libraries where the C<clock_gettime>
2966	function is hiding in (often F<-lrt>).	3433	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2967		3434
2968	=item EV_USE_REALTIME	3435	=item EV_USE_REALTIME
2969		3436
2970	If defined to be C<1>, libev will try to detect the availability of the	3437	If defined to be C<1>, libev will try to detect the availability of the
2971	real-time clock option at compile time (and assume its availability at	3438	real-time clock option at compile time (and assume its availability
2972	runtime if successful). Otherwise no use of the real-time clock option will	3439	at runtime if successful). Otherwise no use of the real-time clock
2973	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3440	option will be attempted. This effectively replaces C<gettimeofday>
2974	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3441	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2975	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3442	correctness. See the note about libraries in the description of
		3443	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3444	C<EV_USE_CLOCK_SYSCALL>.
		3445
		3446	=item EV_USE_CLOCK_SYSCALL
		3447
		3448	If defined to be C<1>, libev will try to use a direct syscall instead
		3449	of calling the system-provided C<clock_gettime> function. This option
		3450	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3451	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3452	programs needlessly. Using a direct syscall is slightly slower (in
		3453	theory), because no optimised vdso implementation can be used, but avoids
		3454	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3455	higher, as it simplifies linking (no need for C<-lrt>).
2976		3456
2977	=item EV_USE_NANOSLEEP	3457	=item EV_USE_NANOSLEEP
2978		3458
2979	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3459	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
2980	and will use it for delays. Otherwise it will use C<select ()>.	3460	and will use it for delays. Otherwise it will use C<select ()>.
…		…
2996		3476
2997	=item EV_SELECT_USE_FD_SET	3477	=item EV_SELECT_USE_FD_SET
2998		3478
2999	If defined to C<1>, then the select backend will use the system C<fd_set>	3479	If defined to C<1>, then the select backend will use the system C<fd_set>
3000	structure. This is useful if libev doesn't compile due to a missing	3480	structure. This is useful if libev doesn't compile due to a missing
3001	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3481	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3002	exotic systems. This usually limits the range of file descriptors to some	3482	on exotic systems. This usually limits the range of file descriptors to
3003	low limit such as 1024 or might have other limitations (winsocket only	3483	some low limit such as 1024 or might have other limitations (winsocket
3004	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3484	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3005	influence the size of the C<fd_set> used.	3485	configures the maximum size of the C<fd_set>.
3006		3486
3007	=item EV_SELECT_IS_WINSOCKET	3487	=item EV_SELECT_IS_WINSOCKET
3008		3488
3009	When defined to C<1>, the select backend will assume that	3489	When defined to C<1>, the select backend will assume that
3010	select/socket/connect etc. don't understand file descriptors but	3490	select/socket/connect etc. don't understand file descriptors but
…		…
3121	When doing priority-based operations, libev usually has to linearly search	3601	When doing priority-based operations, libev usually has to linearly search
3122	all the priorities, so having many of them (hundreds) uses a lot of space	3602	all the priorities, so having many of them (hundreds) uses a lot of space
3123	and time, so using the defaults of five priorities (-2 .. +2) is usually	3603	and time, so using the defaults of five priorities (-2 .. +2) is usually
3124	fine.	3604	fine.
3125		3605
3126	If your embedding application does not need any priorities, defining these both to	3606	If your embedding application does not need any priorities, defining these
3127	C<0> will save some memory and CPU.	3607	both to C<0> will save some memory and CPU.
3128		3608
3129	=item EV_PERIODIC_ENABLE	3609	=item EV_PERIODIC_ENABLE
3130		3610
3131	If undefined or defined to be C<1>, then periodic timers are supported. If	3611	If undefined or defined to be C<1>, then periodic timers are supported. If
3132	defined to be C<0>, then they are not. Disabling them saves a few kB of	3612	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
3139	code.	3619	code.
3140		3620
3141	=item EV_EMBED_ENABLE	3621	=item EV_EMBED_ENABLE
3142		3622
3143	If undefined or defined to be C<1>, then embed watchers are supported. If	3623	If undefined or defined to be C<1>, then embed watchers are supported. If
3144	defined to be C<0>, then they are not.	3624	defined to be C<0>, then they are not. Embed watchers rely on most other
		3625	watcher types, which therefore must not be disabled.
3145		3626
3146	=item EV_STAT_ENABLE	3627	=item EV_STAT_ENABLE
3147		3628
3148	If undefined or defined to be C<1>, then stat watchers are supported. If	3629	If undefined or defined to be C<1>, then stat watchers are supported. If
3149	defined to be C<0>, then they are not.	3630	defined to be C<0>, then they are not.
…		…
3181	two).	3662	two).
3182		3663
3183	=item EV_USE_4HEAP	3664	=item EV_USE_4HEAP
3184		3665
3185	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3666	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3186	timer and periodics heap, libev uses a 4-heap when this symbol is defined	3667	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
3187	to C<1>. The 4-heap uses more complicated (longer) code but has	3668	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
3188	noticeably faster performance with many (thousands) of watchers.	3669	faster performance with many (thousands) of watchers.
3189		3670
3190	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3671	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3191	(disabled).	3672	(disabled).
3192		3673
3193	=item EV_HEAP_CACHE_AT	3674	=item EV_HEAP_CACHE_AT
3194		3675
3195	Heaps are not very cache-efficient. To improve the cache-efficiency of the	3676	Heaps are not very cache-efficient. To improve the cache-efficiency of the
3196	timer and periodics heap, libev can cache the timestamp (I<at>) within	3677	timer and periodics heaps, libev can cache the timestamp (I<at>) within
3197	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),	3678	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
3198	which uses 8-12 bytes more per watcher and a few hundred bytes more code,	3679	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
3199	but avoids random read accesses on heap changes. This improves performance	3680	but avoids random read accesses on heap changes. This improves performance
3200	noticeably with with many (hundreds) of watchers.	3681	noticeably with many (hundreds) of watchers.
3201		3682
3202	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>	3683	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
3203	(disabled).	3684	(disabled).
3204		3685
3205	=item EV_VERIFY	3686	=item EV_VERIFY
…		…
3211	called once per loop, which can slow down libev. If set to C<3>, then the	3692	called once per loop, which can slow down libev. If set to C<3>, then the
3212	verification code will be called very frequently, which will slow down	3693	verification code will be called very frequently, which will slow down
3213	libev considerably.	3694	libev considerably.
3214		3695
3215	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be	3696	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
3216	C<0.>	3697	C<0>.
3217		3698
3218	=item EV_COMMON	3699	=item EV_COMMON
3219		3700
3220	By default, all watchers have a C<void *data> member. By redefining	3701	By default, all watchers have a C<void *data> member. By redefining
3221	this macro to a something else you can include more and other types of	3702	this macro to a something else you can include more and other types of
…		…
3238	and the way callbacks are invoked and set. Must expand to a struct member	3719	and the way callbacks are invoked and set. Must expand to a struct member
3239	definition and a statement, respectively. See the F<ev.h> header file for	3720	definition and a statement, respectively. See the F<ev.h> header file for
3240	their default definitions. One possible use for overriding these is to	3721	their default definitions. One possible use for overriding these is to
3241	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3722	avoid the C<struct ev_loop *> as first argument in all cases, or to use
3242	method calls instead of plain function calls in C++.	3723	method calls instead of plain function calls in C++.
		3724
		3725	=back
3243		3726
3244	=head2 EXPORTED API SYMBOLS	3727	=head2 EXPORTED API SYMBOLS
3245		3728
3246	If you need to re-export the API (e.g. via a DLL) and you need a list of	3729	If you need to re-export the API (e.g. via a DLL) and you need a list of
3247	exported symbols, you can use the provided F<Symbol.*> files which list	3730	exported symbols, you can use the provided F<Symbol.*> files which list
…		…
3294	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3777	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
3295		3778
3296	#include "ev_cpp.h"	3779	#include "ev_cpp.h"
3297	#include "ev.c"	3780	#include "ev.c"
3298		3781
		3782	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
3299		3783
3300	=head1 THREADS AND COROUTINES	3784	=head2 THREADS AND COROUTINES
3301		3785
3302	=head2 THREADS	3786	=head3 THREADS
3303		3787
3304	Libev itself is thread-safe (unless the opposite is specifically	3788	All libev functions are reentrant and thread-safe unless explicitly
3305	documented for a function), but it uses no locking itself. This means that	3789	documented otherwise, but libev implements no locking itself. This means
3306	you can use as many loops as you want in parallel, as long as only one	3790	that you can use as many loops as you want in parallel, as long as there
3307	thread ever calls into one libev function with the same loop parameter:	3791	are no concurrent calls into any libev function with the same loop
		3792	parameter (C<ev_default_*> calls have an implicit default loop parameter,
3308	libev guarentees that different event loops share no data structures that	3793	of course): libev guarantees that different event loops share no data
3309	need locking.	3794	structures that need any locking.
3310		3795
3311	Or to put it differently: calls with different loop parameters can be done	3796	Or to put it differently: calls with different loop parameters can be done
3312	concurrently from multiple threads, calls with the same loop parameter	3797	concurrently from multiple threads, calls with the same loop parameter
3313	must be done serially (but can be done from different threads, as long as	3798	must be done serially (but can be done from different threads, as long as
3314	only one thread ever is inside a call at any point in time, e.g. by using	3799	only one thread ever is inside a call at any point in time, e.g. by using
3315	a mutex per loop).	3800	a mutex per loop).
3316		3801
3317	Specifically to support threads (and signal handlers), libev implements	3802	Specifically to support threads (and signal handlers), libev implements
3318	so-called C<ev_async> watchers, which allow some limited form of	3803	so-called C<ev_async> watchers, which allow some limited form of
3319	concurrency on the same event loop.	3804	concurrency on the same event loop, namely waking it up "from the
		3805	outside".
3320		3806
3321	If you want to know which design (one loop, locking, or multiple loops	3807	If you want to know which design (one loop, locking, or multiple loops
3322	without or something else still) is best for your problem, then I cannot	3808	without or something else still) is best for your problem, then I cannot
3323	help you. I can give some generic advice however:	3809	help you, but here is some generic advice:
3324		3810
3325	=over 4	3811	=over 4
3326		3812
3327	=item * most applications have a main thread: use the default libev loop	3813	=item * most applications have a main thread: use the default libev loop
3328	in that thread, or create a separate thread running only the default loop.	3814	in that thread, or create a separate thread running only the default loop.
…		…
3352	default loop and triggering an C<ev_async> watcher from the default loop	3838	default loop and triggering an C<ev_async> watcher from the default loop
3353	watcher callback into the event loop interested in the signal.	3839	watcher callback into the event loop interested in the signal.
3354		3840
3355	=back	3841	=back
3356		3842
3357	=head2 COROUTINES	3843	=head3 COROUTINES
3358		3844
3359	Libev is much more accommodating to coroutines ("cooperative threads"):	3845	Libev is very accommodating to coroutines ("cooperative threads"):
3360	libev fully supports nesting calls to it's functions from different	3846	libev fully supports nesting calls to its functions from different
3361	coroutines (e.g. you can call C<ev_loop> on the same loop from two	3847	coroutines (e.g. you can call C<ev_loop> on the same loop from two
3362	different coroutines and switch freely between both coroutines running the	3848	different coroutines, and switch freely between both coroutines running the
3363	loop, as long as you don't confuse yourself). The only exception is that	3849	loop, as long as you don't confuse yourself). The only exception is that
3364	you must not do this from C<ev_periodic> reschedule callbacks.	3850	you must not do this from C<ev_periodic> reschedule callbacks.
3365		3851
3366	Care has been taken to ensure that libev does not keep local state inside	3852	Care has been taken to ensure that libev does not keep local state inside
3367	C<ev_loop>, and other calls do not usually allow coroutine switches.	3853	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3854	they do not call any callbacks.
3368		3855
		3856	=head2 COMPILER WARNINGS
3369		3857
3370	=head1 COMPLEXITIES	3858	Depending on your compiler and compiler settings, you might get no or a
		3859	lot of warnings when compiling libev code. Some people are apparently
		3860	scared by this.
3371		3861
3372	In this section the complexities of (many of) the algorithms used inside	3862	However, these are unavoidable for many reasons. For one, each compiler
3373	libev will be explained. For complexity discussions about backends see the	3863	has different warnings, and each user has different tastes regarding
3374	documentation for C<ev_default_init>.	3864	warning options. "Warn-free" code therefore cannot be a goal except when
		3865	targeting a specific compiler and compiler-version.
3375		3866
3376	All of the following are about amortised time: If an array needs to be	3867	Another reason is that some compiler warnings require elaborate
3377	extended, libev needs to realloc and move the whole array, but this	3868	workarounds, or other changes to the code that make it less clear and less
3378	happens asymptotically never with higher number of elements, so O(1) might	3869	maintainable.
3379	mean it might do a lengthy realloc operation in rare cases, but on average
3380	it is much faster and asymptotically approaches constant time.
3381		3870
3382	=over 4	3871	And of course, some compiler warnings are just plain stupid, or simply
		3872	wrong (because they don't actually warn about the condition their message
		3873	seems to warn about). For example, certain older gcc versions had some
		3874	warnings that resulted an extreme number of false positives. These have
		3875	been fixed, but some people still insist on making code warn-free with
		3876	such buggy versions.
3383		3877
3384	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3878	While libev is written to generate as few warnings as possible,
		3879	"warn-free" code is not a goal, and it is recommended not to build libev
		3880	with any compiler warnings enabled unless you are prepared to cope with
		3881	them (e.g. by ignoring them). Remember that warnings are just that:
		3882	warnings, not errors, or proof of bugs.
3385		3883
3386	This means that, when you have a watcher that triggers in one hour and
3387	there are 100 watchers that would trigger before that then inserting will
3388	have to skip roughly seven (C<ld 100>) of these watchers.
3389		3884
3390	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)	3885	=head2 VALGRIND
3391		3886
3392	That means that changing a timer costs less than removing/adding them	3887	Valgrind has a special section here because it is a popular tool that is
3393	as only the relative motion in the event queue has to be paid for.	3888	highly useful. Unfortunately, valgrind reports are very hard to interpret.
3394		3889
3395	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)	3890	If you think you found a bug (memory leak, uninitialised data access etc.)
		3891	in libev, then check twice: If valgrind reports something like:
3396		3892
3397	These just add the watcher into an array or at the head of a list.	3893	==2274== definitely lost: 0 bytes in 0 blocks.
		3894	==2274== possibly lost: 0 bytes in 0 blocks.
		3895	==2274== still reachable: 256 bytes in 1 blocks.
3398		3896
3399	=item Stopping check/prepare/idle/fork/async watchers: O(1)	3897	Then there is no memory leak, just as memory accounted to global variables
		3898	is not a memleak - the memory is still being referenced, and didn't leak.
3400		3899
3401	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3900	Similarly, under some circumstances, valgrind might report kernel bugs
		3901	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3902	although an acceptable workaround has been found here), or it might be
		3903	confused.
3402		3904
3403	These watchers are stored in lists then need to be walked to find the	3905	Keep in mind that valgrind is a very good tool, but only a tool. Don't
3404	correct watcher to remove. The lists are usually short (you don't usually	3906	make it into some kind of religion.
3405	have many watchers waiting for the same fd or signal).
3406		3907
3407	=item Finding the next timer in each loop iteration: O(1)	3908	If you are unsure about something, feel free to contact the mailing list
		3909	with the full valgrind report and an explanation on why you think this
		3910	is a bug in libev (best check the archives, too :). However, don't be
		3911	annoyed when you get a brisk "this is no bug" answer and take the chance
		3912	of learning how to interpret valgrind properly.
3408		3913
3409	By virtue of using a binary or 4-heap, the next timer is always found at a	3914	If you need, for some reason, empty reports from valgrind for your project
3410	fixed position in the storage array.	3915	I suggest using suppression lists.
3411		3916
3412	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
3413		3917
3414	A change means an I/O watcher gets started or stopped, which requires	3918	=head1 PORTABILITY NOTES
3415	libev to recalculate its status (and possibly tell the kernel, depending
3416	on backend and whether C<ev_io_set> was used).
3417		3919
3418	=item Activating one watcher (putting it into the pending state): O(1)
3419
3420	=item Priority handling: O(number_of_priorities)
3421
3422	Priorities are implemented by allocating some space for each
3423	priority. When doing priority-based operations, libev usually has to
3424	linearly search all the priorities, but starting/stopping and activating
3425	watchers becomes O(1) w.r.t. priority handling.
3426
3427	=item Sending an ev_async: O(1)
3428
3429	=item Processing ev_async_send: O(number_of_async_watchers)
3430
3431	=item Processing signals: O(max_signal_number)
3432
3433	Sending involves a system call I<iff> there were no other C<ev_async_send>
3434	calls in the current loop iteration. Checking for async and signal events
3435	involves iterating over all running async watchers or all signal numbers.
3436
3437	=back
3438
3439
3440	=head1 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS	3920	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
3441		3921
3442	Win32 doesn't support any of the standards (e.g. POSIX) that libev	3922	Win32 doesn't support any of the standards (e.g. POSIX) that libev
3443	requires, and its I/O model is fundamentally incompatible with the POSIX	3923	requires, and its I/O model is fundamentally incompatible with the POSIX
3444	model. Libev still offers limited functionality on this platform in	3924	model. Libev still offers limited functionality on this platform in
3445	the form of the C<EVBACKEND_SELECT> backend, and only supports socket	3925	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
…		…
3456		3936
3457	Not a libev limitation but worth mentioning: windows apparently doesn't	3937	Not a libev limitation but worth mentioning: windows apparently doesn't
3458	accept large writes: instead of resulting in a partial write, windows will	3938	accept large writes: instead of resulting in a partial write, windows will
3459	either accept everything or return C<ENOBUFS> if the buffer is too large,	3939	either accept everything or return C<ENOBUFS> if the buffer is too large,
3460	so make sure you only write small amounts into your sockets (less than a	3940	so make sure you only write small amounts into your sockets (less than a
3461	megabyte seems safe, but thsi apparently depends on the amount of memory	3941	megabyte seems safe, but this apparently depends on the amount of memory
3462	available).	3942	available).
3463		3943
3464	Due to the many, low, and arbitrary limits on the win32 platform and	3944	Due to the many, low, and arbitrary limits on the win32 platform and
3465	the abysmal performance of winsockets, using a large number of sockets	3945	the abysmal performance of winsockets, using a large number of sockets
3466	is not recommended (and not reasonable). If your program needs to use	3946	is not recommended (and not reasonable). If your program needs to use
…		…
3477	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */	3957	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3478		3958
3479	#include "ev.h"	3959	#include "ev.h"
3480		3960
3481	And compile the following F<evwrap.c> file into your project (make sure	3961	And compile the following F<evwrap.c> file into your project (make sure
3482	you do I<not> compile the F<ev.c> or any other embedded soruce files!):	3962	you do I<not> compile the F<ev.c> or any other embedded source files!):
3483		3963
3484	#include "evwrap.h"	3964	#include "evwrap.h"
3485	#include "ev.c"	3965	#include "ev.c"
3486		3966
3487	=over 4	3967	=over 4
…		…
3532	wrap all I/O functions and provide your own fd management, but the cost of	4012	wrap all I/O functions and provide your own fd management, but the cost of
3533	calling select (O(n²)) will likely make this unworkable.	4013	calling select (O(n²)) will likely make this unworkable.
3534		4014
3535	=back	4015	=back
3536		4016
3537
3538	=head1 PORTABILITY REQUIREMENTS	4017	=head2 PORTABILITY REQUIREMENTS
3539		4018
3540	In addition to a working ISO-C implementation, libev relies on a few	4019	In addition to a working ISO-C implementation and of course the
3541	additional extensions:	4020	backend-specific APIs, libev relies on a few additional extensions:
3542		4021
3543	=over 4	4022	=over 4
3544		4023
3545	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible	4024	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
3546	calling conventions regardless of C<ev_watcher_type *>.	4025	calling conventions regardless of C<ev_watcher_type *>.
…		…
3552	calls them using an C<ev_watcher *> internally.	4031	calls them using an C<ev_watcher *> internally.
3553		4032
3554	=item C<sig_atomic_t volatile> must be thread-atomic as well	4033	=item C<sig_atomic_t volatile> must be thread-atomic as well
3555		4034
3556	The type C<sig_atomic_t volatile> (or whatever is defined as	4035	The type C<sig_atomic_t volatile> (or whatever is defined as
3557	C<EV_ATOMIC_T>) must be atomic w.r.t. accesses from different	4036	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
3558	threads. This is not part of the specification for C<sig_atomic_t>, but is	4037	threads. This is not part of the specification for C<sig_atomic_t>, but is
3559	believed to be sufficiently portable.	4038	believed to be sufficiently portable.
3560		4039
3561	=item C<sigprocmask> must work in a threaded environment	4040	=item C<sigprocmask> must work in a threaded environment
3562		4041
…		…
3571	except the initial one, and run the default loop in the initial thread as	4050	except the initial one, and run the default loop in the initial thread as
3572	well.	4051	well.
3573		4052
3574	=item C<long> must be large enough for common memory allocation sizes	4053	=item C<long> must be large enough for common memory allocation sizes
3575		4054
3576	To improve portability and simplify using libev, libev uses C<long>	4055	To improve portability and simplify its API, libev uses C<long> internally
3577	internally instead of C<size_t> when allocating its data structures. On	4056	instead of C<size_t> when allocating its data structures. On non-POSIX
3578	non-POSIX systems (Microsoft...) this might be unexpectedly low, but	4057	systems (Microsoft...) this might be unexpectedly low, but is still at
3579	is still at least 31 bits everywhere, which is enough for hundreds of	4058	least 31 bits everywhere, which is enough for hundreds of millions of
3580	millions of watchers.	4059	watchers.
3581		4060
3582	=item C<double> must hold a time value in seconds with enough accuracy	4061	=item C<double> must hold a time value in seconds with enough accuracy
3583		4062
3584	The type C<double> is used to represent timestamps. It is required to	4063	The type C<double> is used to represent timestamps. It is required to
3585	have at least 51 bits of mantissa (and 9 bits of exponent), which is good	4064	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
…		…
3589	=back	4068	=back
3590		4069
3591	If you know of other additional requirements drop me a note.	4070	If you know of other additional requirements drop me a note.
3592		4071
3593		4072
3594	=head1 COMPILER WARNINGS	4073	=head1 ALGORITHMIC COMPLEXITIES
3595		4074
3596	Depending on your compiler and compiler settings, you might get no or a	4075	In this section the complexities of (many of) the algorithms used inside
3597	lot of warnings when compiling libev code. Some people are apparently	4076	libev will be documented. For complexity discussions about backends see
3598	scared by this.	4077	the documentation for C<ev_default_init>.
3599		4078
3600	However, these are unavoidable for many reasons. For one, each compiler	4079	All of the following are about amortised time: If an array needs to be
3601	has different warnings, and each user has different tastes regarding	4080	extended, libev needs to realloc and move the whole array, but this
3602	warning options. "Warn-free" code therefore cannot be a goal except when	4081	happens asymptotically rarer with higher number of elements, so O(1) might
3603	targeting a specific compiler and compiler-version.	4082	mean that libev does a lengthy realloc operation in rare cases, but on
		4083	average it is much faster and asymptotically approaches constant time.
3604		4084
3605	Another reason is that some compiler warnings require elaborate	4085	=over 4
3606	workarounds, or other changes to the code that make it less clear and less
3607	maintainable.
3608		4086
3609	And of course, some compiler warnings are just plain stupid, or simply	4087	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
3610	wrong (because they don't actually warn about the condition their message
3611	seems to warn about).
3612		4088
3613	While libev is written to generate as few warnings as possible,	4089	This means that, when you have a watcher that triggers in one hour and
3614	"warn-free" code is not a goal, and it is recommended not to build libev	4090	there are 100 watchers that would trigger before that, then inserting will
3615	with any compiler warnings enabled unless you are prepared to cope with	4091	have to skip roughly seven (C<ld 100>) of these watchers.
3616	them (e.g. by ignoring them). Remember that warnings are just that:
3617	warnings, not errors, or proof of bugs.
3618		4092
		4093	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
3619		4094
3620	=head1 VALGRIND	4095	That means that changing a timer costs less than removing/adding them,
		4096	as only the relative motion in the event queue has to be paid for.
3621		4097
3622	Valgrind has a special section here because it is a popular tool that is	4098	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
3623	highly useful, but valgrind reports are very hard to interpret.
3624		4099
3625	If you think you found a bug (memory leak, uninitialised data access etc.)	4100	These just add the watcher into an array or at the head of a list.
3626	in libev, then check twice: If valgrind reports something like:
3627		4101
3628	==2274== definitely lost: 0 bytes in 0 blocks.	4102	=item Stopping check/prepare/idle/fork/async watchers: O(1)
3629	==2274== possibly lost: 0 bytes in 0 blocks.
3630	==2274== still reachable: 256 bytes in 1 blocks.
3631		4103
3632	Then there is no memory leak. Similarly, under some circumstances,	4104	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
3633	valgrind might report kernel bugs as if it were a bug in libev, or it
3634	might be confused (it is a very good tool, but only a tool).
3635		4105
3636	If you are unsure about something, feel free to contact the mailing list	4106	These watchers are stored in lists, so they need to be walked to find the
3637	with the full valgrind report and an explanation on why you think this is	4107	correct watcher to remove. The lists are usually short (you don't usually
3638	a bug in libev. However, don't be annoyed when you get a brisk "this is	4108	have many watchers waiting for the same fd or signal: one is typical, two
3639	no bug" answer and take the chance of learning how to interpret valgrind	4109	is rare).
3640	properly.
3641		4110
3642	If you need, for some reason, empty reports from valgrind for your project	4111	=item Finding the next timer in each loop iteration: O(1)
3643	I suggest using suppression lists.
3644		4112
		4113	By virtue of using a binary or 4-heap, the next timer is always found at a
		4114	fixed position in the storage array.
		4115
		4116	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
		4117
		4118	A change means an I/O watcher gets started or stopped, which requires
		4119	libev to recalculate its status (and possibly tell the kernel, depending
		4120	on backend and whether C<ev_io_set> was used).
		4121
		4122	=item Activating one watcher (putting it into the pending state): O(1)
		4123
		4124	=item Priority handling: O(number_of_priorities)
		4125
		4126	Priorities are implemented by allocating some space for each
		4127	priority. When doing priority-based operations, libev usually has to
		4128	linearly search all the priorities, but starting/stopping and activating
		4129	watchers becomes O(1) with respect to priority handling.
		4130
		4131	=item Sending an ev_async: O(1)
		4132
		4133	=item Processing ev_async_send: O(number_of_async_watchers)
		4134
		4135	=item Processing signals: O(max_signal_number)
		4136
		4137	Sending involves a system call I<iff> there were no other C<ev_async_send>
		4138	calls in the current loop iteration. Checking for async and signal events
		4139	involves iterating over all running async watchers or all signal numbers.
		4140
		4141	=back
		4142
		4143
		4144	=head1 GLOSSARY
		4145
		4146	=over 4
		4147
		4148	=item active
		4149
		4150	A watcher is active as long as it has been started (has been attached to
		4151	an event loop) but not yet stopped (disassociated from the event loop).
		4152
		4153	=item application
		4154
		4155	In this document, an application is whatever is using libev.
		4156
		4157	=item callback
		4158
		4159	The address of a function that is called when some event has been
		4160	detected. Callbacks are being passed the event loop, the watcher that
		4161	received the event, and the actual event bitset.
		4162
		4163	=item callback invocation
		4164
		4165	The act of calling the callback associated with a watcher.
		4166
		4167	=item event
		4168
		4169	A change of state of some external event, such as data now being available
		4170	for reading on a file descriptor, time having passed or simply not having
		4171	any other events happening anymore.
		4172
		4173	In libev, events are represented as single bits (such as C<EV_READ> or
		4174	C<EV_TIMEOUT>).
		4175
		4176	=item event library
		4177
		4178	A software package implementing an event model and loop.
		4179
		4180	=item event loop
		4181
		4182	An entity that handles and processes external events and converts them
		4183	into callback invocations.
		4184
		4185	=item event model
		4186
		4187	The model used to describe how an event loop handles and processes
		4188	watchers and events.
		4189
		4190	=item pending
		4191
		4192	A watcher is pending as soon as the corresponding event has been detected,
		4193	and stops being pending as soon as the watcher will be invoked or its
		4194	pending status is explicitly cleared by the application.
		4195
		4196	A watcher can be pending, but not active. Stopping a watcher also clears
		4197	its pending status.
		4198
		4199	=item real time
		4200
		4201	The physical time that is observed. It is apparently strictly monotonic :)
		4202
		4203	=item wall-clock time
		4204
		4205	The time and date as shown on clocks. Unlike real time, it can actually
		4206	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4207	clock.
		4208
		4209	=item watcher
		4210
		4211	A data structure that describes interest in certain events. Watchers need
		4212	to be started (attached to an event loop) before they can receive events.
		4213
		4214	=item watcher invocation
		4215
		4216	The act of calling the callback associated with a watcher.
		4217
		4218	=back
3645		4219
3646	=head1 AUTHOR	4220	=head1 AUTHOR
3647		4221
3648	Marc Lehmann <libev@schmorp.de>.	4222	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3649		4223

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