[ViewVC] Diff of: cvs/libev/ev.pod

Comparing libev/ev.pod (file contents):
Revision 1.202 by root, Fri Oct 24 08:30:01 2008 UTC vs.
Revision 1.240 by root, Sat Apr 25 14:12:48 2009 UTC

…		…
8		8
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
		14	#include <stdio.h> // for puts
13		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;
…		…
41		43
42	int	44	int
43	main (void)	45	main (void)
44	{	46	{
45	// use the default event loop unless you have special needs	47	// use the default event loop unless you have special needs
46	ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
47		49
48	// initialise an io watcher, then start it	50	// initialise an io watcher, then start it
49	// this one will watch for stdin to become readable	51	// this one will watch for stdin to become readable
50	ev_io_init (&stdin_watcher, stdin_cb, /STDIN_FILENO/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /STDIN_FILENO/ 0, EV_READ);
51	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
…		…
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
…		…
108	name C<loop> (which is always of type C<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
…		…
298	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
299	function.	313	function.
300		314
301	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
302	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,
303	as loops cannot bes hared easily between threads anyway).	317	as loops cannot be shared easily between threads anyway).
304		318
305	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
306	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
307	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
308	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
…		…
384	=item C<EVBACKEND_EPOLL> (value 4, Linux)	398	=item C<EVBACKEND_EPOLL> (value 4, Linux)
385		399
386	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,
387	but it scales phenomenally better. While poll and select usually scale	401	but it scales phenomenally better. While poll and select usually scale
388	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),
389	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).
390	of shortcomings, such as silently dropping events in some hard-to-detect	404
391	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
392	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.
393		421
394	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
395	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
396	(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
397	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
398	very well if you register events for both fds.	426	file descriptors might not work very well if you register events for both
399		427	file descriptors.
400	Please note that epoll sometimes generates spurious notifications, so you
401	need to use non-blocking I/O or other means to avoid blocking when no data
402	(or space) is available.
403		428
404	Best performance from this backend is achieved by not unregistering all	429	Best performance from this backend is achieved by not unregistering all
405	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,
406	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
407	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
408	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.
409		440
410	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
411	all kernel versions tested so far.	442	all kernel versions tested so far.
412		443
413	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
414	C<EVBACKEND_POLL>.	445	C<EVBACKEND_POLL>.
415		446
416	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	447	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
417		448
418	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
419	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
420	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
421	completely useless). For this reason it's not being "auto-detected" unless	452	it's completely useless). Unlike epoll, however, whose brokenness
422	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
423	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.
424		458
425	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
426	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
427	the target platform). See C<ev_embed> watchers for more info.	461	the target platform). See C<ev_embed> watchers for more info.
428		462
429	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
430	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
431	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
432	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
433	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
434	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
435		470
436	This backend usually performs well under most conditions.	471	This backend usually performs well under most conditions.
437		472
438	While nominally embeddable in other event loops, this doesn't work	473	While nominally embeddable in other event loops, this doesn't work
439	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
440	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
441	(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
442	(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
443	using it only for sockets.	478	also broken on OS X)) and, did I mention it, using it only for sockets.
444		479
445	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
446	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
447	C<NOTE_EOF>.	482	C<NOTE_EOF>.
448		483
…		…
468	might perform better.	503	might perform better.
469		504
470	On the positive side, with the exception of the spurious readiness	505	On the positive side, with the exception of the spurious readiness
471	notifications, this backend actually performed fully to specification	506	notifications, this backend actually performed fully to specification
472	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
473	OS-specific backends.	508	OS-specific backends (I vastly prefer correctness over speed hacks).
474		509
475	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
476	C<EVBACKEND_POLL>.	511	C<EVBACKEND_POLL>.
477		512
478	=item C<EVBACKEND_ALL>	513	=item C<EVBACKEND_ALL>
…		…
531	responsibility to either stop all watchers cleanly yourself I<before>	566	responsibility to either stop all watchers cleanly yourself I<before>
532	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
533	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
534	for example).	569	for example).
535		570
536	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
537	this function, and related watchers (such as signal and child watchers)	572	handlers), will not be freed by this function, and related watchers (such
538	would need to be stopped manually.	573	as signal and child watchers) would need to be stopped manually.
539		574
540	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
541	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
542	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
543	C<ev_loop_new> and C<ev_loop_destroy>).	578	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
609		644
610	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
611	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
612	the current time is a good idea.	647	the current time is a good idea.
613		648
614	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>).
615		676
616	=item ev_loop (loop, int flags)	677	=item ev_loop (loop, int flags)
617		678
618	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
619	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
…		…
635	the loop.	696	the loop.
636		697
637	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
638	necessary) and will handle those and any already outstanding ones. It	699	necessary) and will handle those and any already outstanding ones. It
639	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
640	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
641	user-registered callback will be called), and will return after one	702	user-registered callback will be called), and will return after one
642	iteration of the loop.	703	iteration of the loop.
643		704
644	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
645	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
…		…
703		764
704	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>
705	from returning, call ev_unref() after starting, and ev_ref() before	766	from returning, call ev_unref() after starting, and ev_ref() before
706	stopping it.	767	stopping it.
707		768
708	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
709	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
710	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
711	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
712	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
713	(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
714	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).
715		778
716	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>
717	running when nothing else is active.	780	running when nothing else is active.
718		781
719	ev_signal exitsig;	782	ev_signal exitsig;
…		…
903		966
904	=item C<EV_ASYNC>	967	=item C<EV_ASYNC>
905		968
906	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>).
907		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
908	=item C<EV_ERROR>	976	=item C<EV_ERROR>
909		977
910	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
911	happen because the watcher could not be properly started because libev	979	happen because the watcher could not be properly started because libev
912	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
…		…
1027	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>
1028	(default: C<-2>). Pending watchers with higher priority will be invoked	1096	(default: C<-2>). Pending watchers with higher priority will be invoked
1029	before watchers with lower priority, but priority will not keep watchers	1097	before watchers with lower priority, but priority will not keep watchers
1030	from being executed (except for C<ev_idle> watchers).	1098	from being executed (except for C<ev_idle> watchers).
1031		1099
1032	This means that priorities are I<only> used for ordering callback
1033	invocation after new events have been received. This is useful, for
1034	example, to reduce latency after idling, or more often, to bind two
1035	watchers on the same event and make sure one is called first.
1036
1037	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
1038	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.
1039		1102
1040	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
1041	pending.	1104	pending.
1042
1043	The default priority used by watchers when no priority has been set is
1044	always C<0>, which is supposed to not be too high and not be too low :).
1045		1105
1046	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1106	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
1047	fine, as long as you do not mind that the priority value you query might	1107	fine, as long as you do not mind that the priority value you query might
1048	or might not have been clamped to the valid range.	1108	or might not have been clamped to the valid range.
		1109
		1110	The default priority used by watchers when no priority has been set is
		1111	always C<0>, which is supposed to not be too high and not be too low :).
		1112
		1113	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
		1114	priorities.
1049		1115
1050	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1116	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1051		1117
1052	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
1053	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
…		…
1128	t2_cb (EV_P_ ev_timer *w, int revents)	1194	t2_cb (EV_P_ ev_timer *w, int revents)
1129	{	1195	{
1130	struct my_biggy big = (struct my_biggy *	1196	struct my_biggy big = (struct my_biggy *
1131	(((char *)w) - offsetof (struct my_biggy, t2));	1197	(((char *)w) - offsetof (struct my_biggy, t2));
1132	}	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.
1133		1302
1134		1303
1135	=head1 WATCHER TYPES	1304	=head1 WATCHER TYPES
1136		1305
1137	This section describes each watcher in detail, but will not repeat	1306	This section describes each watcher in detail, but will not repeat
…		…
1163	descriptors to non-blocking mode is also usually a good idea (but not	1332	descriptors to non-blocking mode is also usually a good idea (but not
1164	required if you know what you are doing).	1333	required if you know what you are doing).
1165		1334
1166	If you cannot use non-blocking mode, then force the use of a	1335	If you cannot use non-blocking mode, then force the use of a
1167	known-to-be-good backend (at the time of this writing, this includes only	1336	known-to-be-good backend (at the time of this writing, this includes only
1168	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).	1337	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>). The same applies to file
		1338	descriptors for which non-blocking operation makes no sense (such as
		1339	files) - libev doesn't guarentee any specific behaviour in that case.
1169		1340
1170	Another thing you have to watch out for is that it is quite easy to	1341	Another thing you have to watch out for is that it is quite easy to
1171	receive "spurious" readiness notifications, that is your callback might	1342	receive "spurious" readiness notifications, that is your callback might
1172	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1343	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
1173	because there is no data. Not only are some backends known to create a	1344	because there is no data. Not only are some backends known to create a
…		…
1294	year, it will still time out after (roughly) one hour. "Roughly" because	1465	year, it will still time out after (roughly) one hour. "Roughly" because
1295	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1466	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1296	monotonic clock option helps a lot here).	1467	monotonic clock option helps a lot here).
1297		1468
1298	The callback is guaranteed to be invoked only I<after> its timeout has	1469	The callback is guaranteed to be invoked only I<after> its timeout has
1299	passed, but if multiple timers become ready during the same loop iteration	1470	passed (not I<at>, so on systems with very low-resolution clocks this
1300	then order of execution is undefined.	1471	might introduce a small delay). If multiple timers become ready during the
		1472	same loop iteration then the ones with earlier time-out values are invoked
		1473	before ones with later time-out values (but this is no longer true when a
		1474	callback calls C<ev_loop> recursively).
1301		1475
1302	=head3 Be smart about timeouts	1476	=head3 Be smart about timeouts
1303		1477
1304	Many real-world problems involve some kind of timeout, usually for error	1478	Many real-world problems involve some kind of timeout, usually for error
1305	recovery. A typical example is an HTTP request - if the other side hangs,	1479	recovery. A typical example is an HTTP request - if the other side hangs,
…		…
1398	else	1572	else
1399	{	1573	{
1400	// callback was invoked, but there was some activity, re-arm	1574	// callback was invoked, but there was some activity, re-arm
1401	// the watcher to fire in last_activity + 60, which is	1575	// the watcher to fire in last_activity + 60, which is
1402	// guaranteed to be in the future, so "again" is positive:	1576	// guaranteed to be in the future, so "again" is positive:
1403	w->again = timeout - now;	1577	w->repeat = timeout - now;
1404	ev_timer_again (EV_A_ w);	1578	ev_timer_again (EV_A_ w);
1405	}	1579	}
1406	}	1580	}
1407		1581
1408	To summarise the callback: first calculate the real timeout (defined	1582	To summarise the callback: first calculate the real timeout (defined
…		…
1524	If the timer is started but non-repeating, stop it (as if it timed out).	1698	If the timer is started but non-repeating, stop it (as if it timed out).
1525		1699
1526	If the timer is repeating, either start it if necessary (with the	1700	If the timer is repeating, either start it if necessary (with the
1527	C<repeat> value), or reset the running timer to the C<repeat> value.	1701	C<repeat> value), or reset the running timer to the C<repeat> value.
1528		1702
1529	This sounds a bit complicated, see "Be smart about timeouts", above, for a	1703	This sounds a bit complicated, see L<Be smart about timeouts>, above, for a
1530	usage example.	1704	usage example.
1531		1705
1532	=item ev_tstamp repeat [read-write]	1706	=item ev_tstamp repeat [read-write]
1533		1707
1534	The current C<repeat> value. Will be used each time the watcher times out	1708	The current C<repeat> value. Will be used each time the watcher times out
…		…
1573	=head2 C<ev_periodic> - to cron or not to cron?	1747	=head2 C<ev_periodic> - to cron or not to cron?
1574		1748
1575	Periodic watchers are also timers of a kind, but they are very versatile	1749	Periodic watchers are also timers of a kind, but they are very versatile
1576	(and unfortunately a bit complex).	1750	(and unfortunately a bit complex).
1577		1751
1578	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1752	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1579	but on wall clock time (absolute time). You can tell a periodic watcher	1753	relative time, the physical time that passes) but on wall clock time
1580	to trigger after some specific point in time. For example, if you tell a	1754	(absolute time, the thing you can read on your calender or clock). The
1581	periodic watcher to trigger in 10 seconds (by specifying e.g. C<ev_now ()	1755	difference is that wall clock time can run faster or slower than real
1582	+ 10.>, that is, an absolute time not a delay) and then reset your system	1756	time, and time jumps are not uncommon (e.g. when you adjust your
1583	clock to January of the previous year, then it will take more than year	1757	wrist-watch).
1584	to trigger the event (unlike an C<ev_timer>, which would still trigger
1585	roughly 10 seconds later as it uses a relative timeout).
1586		1758
		1759	You can tell a periodic watcher to trigger after some specific point
		1760	in time: for example, if you tell a periodic watcher to trigger "in 10
		1761	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1762	not a delay) and then reset your system clock to January of the previous
		1763	year, then it will take a year or more to trigger the event (unlike an
		1764	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1765	it, as it uses a relative timeout).
		1766
1587	C<ev_periodic>s can also be used to implement vastly more complex timers,	1767	C<ev_periodic> watchers can also be used to implement vastly more complex
1588	such as triggering an event on each "midnight, local time", or other	1768	timers, such as triggering an event on each "midnight, local time", or
1589	complicated rules.	1769	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1770	those cannot react to time jumps.
1590		1771
1591	As with timers, the callback is guaranteed to be invoked only when the	1772	As with timers, the callback is guaranteed to be invoked only when the
1592	time (C<at>) has passed, but if multiple periodic timers become ready	1773	point in time where it is supposed to trigger has passed. If multiple
1593	during the same loop iteration, then order of execution is undefined.	1774	timers become ready during the same loop iteration then the ones with
		1775	earlier time-out values are invoked before ones with later time-out values
		1776	(but this is no longer true when a callback calls C<ev_loop> recursively).
1594		1777
1595	=head3 Watcher-Specific Functions and Data Members	1778	=head3 Watcher-Specific Functions and Data Members
1596		1779
1597	=over 4	1780	=over 4
1598		1781
1599	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1782	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1600		1783
1601	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1784	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1602		1785
1603	Lots of arguments, lets sort it out... There are basically three modes of	1786	Lots of arguments, let's sort it out... There are basically three modes of
1604	operation, and we will explain them from simplest to most complex:	1787	operation, and we will explain them from simplest to most complex:
1605		1788
1606	=over 4	1789	=over 4
1607		1790
1608	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1791	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1609		1792
1610	In this configuration the watcher triggers an event after the wall clock	1793	In this configuration the watcher triggers an event after the wall clock
1611	time C<at> has passed. It will not repeat and will not adjust when a time	1794	time C<offset> has passed. It will not repeat and will not adjust when a
1612	jump occurs, that is, if it is to be run at January 1st 2011 then it will	1795	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1613	only run when the system clock reaches or surpasses this time.	1796	will be stopped and invoked when the system clock reaches or surpasses
		1797	this point in time.
1614		1798
1615	=item * repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1799	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1616		1800
1617	In this mode the watcher will always be scheduled to time out at the next	1801	In this mode the watcher will always be scheduled to time out at the next
1618	C<at + N * interval> time (for some integer N, which can also be negative)	1802	C<offset + N * interval> time (for some integer N, which can also be
1619	and then repeat, regardless of any time jumps.	1803	negative) and then repeat, regardless of any time jumps. The C<offset>
		1804	argument is merely an offset into the C<interval> periods.
1620		1805
1621	This can be used to create timers that do not drift with respect to the	1806	This can be used to create timers that do not drift with respect to the
1622	system clock, for example, here is a C<ev_periodic> that triggers each	1807	system clock, for example, here is an C<ev_periodic> that triggers each
1623	hour, on the hour:	1808	hour, on the hour (with respect to UTC):
1624		1809
1625	ev_periodic_set (&periodic, 0., 3600., 0);	1810	ev_periodic_set (&periodic, 0., 3600., 0);
1626		1811
1627	This doesn't mean there will always be 3600 seconds in between triggers,	1812	This doesn't mean there will always be 3600 seconds in between triggers,
1628	but only that the callback will be called when the system time shows a	1813	but only that the callback will be called when the system time shows a
1629	full hour (UTC), or more correctly, when the system time is evenly divisible	1814	full hour (UTC), or more correctly, when the system time is evenly divisible
1630	by 3600.	1815	by 3600.
1631		1816
1632	Another way to think about it (for the mathematically inclined) is that	1817	Another way to think about it (for the mathematically inclined) is that
1633	C<ev_periodic> will try to run the callback in this mode at the next possible	1818	C<ev_periodic> will try to run the callback in this mode at the next possible
1634	time where C<time = at (mod interval)>, regardless of any time jumps.	1819	time where C<time = offset (mod interval)>, regardless of any time jumps.
1635		1820
1636	For numerical stability it is preferable that the C<at> value is near	1821	For numerical stability it is preferable that the C<offset> value is near
1637	C<ev_now ()> (the current time), but there is no range requirement for	1822	C<ev_now ()> (the current time), but there is no range requirement for
1638	this value, and in fact is often specified as zero.	1823	this value, and in fact is often specified as zero.
1639		1824
1640	Note also that there is an upper limit to how often a timer can fire (CPU	1825	Note also that there is an upper limit to how often a timer can fire (CPU
1641	speed for example), so if C<interval> is very small then timing stability	1826	speed for example), so if C<interval> is very small then timing stability
1642	will of course deteriorate. Libev itself tries to be exact to be about one	1827	will of course deteriorate. Libev itself tries to be exact to be about one
1643	millisecond (if the OS supports it and the machine is fast enough).	1828	millisecond (if the OS supports it and the machine is fast enough).
1644		1829
1645	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1830	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1646		1831
1647	In this mode the values for C<interval> and C<at> are both being	1832	In this mode the values for C<interval> and C<offset> are both being
1648	ignored. Instead, each time the periodic watcher gets scheduled, the	1833	ignored. Instead, each time the periodic watcher gets scheduled, the
1649	reschedule callback will be called with the watcher as first, and the	1834	reschedule callback will be called with the watcher as first, and the
1650	current time as second argument.	1835	current time as second argument.
1651		1836
1652	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1837	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1653	ever, or make ANY event loop modifications whatsoever>.	1838	or make ANY other event loop modifications whatsoever, unless explicitly
		1839	allowed by documentation here>.
1654		1840
1655	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop	1841	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
1656	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the	1842	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
1657	only event loop modification you are allowed to do).	1843	only event loop modification you are allowed to do).
1658		1844
…		…
1688	a different time than the last time it was called (e.g. in a crond like	1874	a different time than the last time it was called (e.g. in a crond like
1689	program when the crontabs have changed).	1875	program when the crontabs have changed).
1690		1876
1691	=item ev_tstamp ev_periodic_at (ev_periodic *)	1877	=item ev_tstamp ev_periodic_at (ev_periodic *)
1692		1878
1693	When active, returns the absolute time that the watcher is supposed to	1879	When active, returns the absolute time that the watcher is supposed
1694	trigger next.	1880	to trigger next. This is not the same as the C<offset> argument to
		1881	C<ev_periodic_set>, but indeed works even in interval and manual
		1882	rescheduling modes.
1695		1883
1696	=item ev_tstamp offset [read-write]	1884	=item ev_tstamp offset [read-write]
1697		1885
1698	When repeating, this contains the offset value, otherwise this is the	1886	When repeating, this contains the offset value, otherwise this is the
1699	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1887	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1888	although libev might modify this value for better numerical stability).
1700		1889
1701	Can be modified any time, but changes only take effect when the periodic	1890	Can be modified any time, but changes only take effect when the periodic
1702	timer fires or C<ev_periodic_again> is being called.	1891	timer fires or C<ev_periodic_again> is being called.
1703		1892
1704	=item ev_tstamp interval [read-write]	1893	=item ev_tstamp interval [read-write]
…		…
1910		2099
1911		2100
1912	=head2 C<ev_stat> - did the file attributes just change?	2101	=head2 C<ev_stat> - did the file attributes just change?
1913		2102
1914	This watches a file system path for attribute changes. That is, it calls	2103	This watches a file system path for attribute changes. That is, it calls
1915	C<stat> regularly (or when the OS says it changed) and sees if it changed	2104	C<stat> on that path in regular intervals (or when the OS says it changed)
1916	compared to the last time, invoking the callback if it did.	2105	and sees if it changed compared to the last time, invoking the callback if
		2106	it did.
1917		2107
1918	The path does not need to exist: changing from "path exists" to "path does	2108	The path does not need to exist: changing from "path exists" to "path does
1919	not exist" is a status change like any other. The condition "path does	2109	not exist" is a status change like any other. The condition "path does not
1920	not exist" is signified by the C<st_nlink> field being zero (which is	2110	exist" (or more correctly "path cannot be stat'ed") is signified by the
1921	otherwise always forced to be at least one) and all the other fields of	2111	C<st_nlink> field being zero (which is otherwise always forced to be at
1922	the stat buffer having unspecified contents.	2112	least one) and all the other fields of the stat buffer having unspecified
		2113	contents.
1923		2114
1924	The path I<should> be absolute and I<must not> end in a slash. If it is	2115	The path I<must not> end in a slash or contain special components such as
		2116	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1925	relative and your working directory changes, the behaviour is undefined.	2117	your working directory changes, then the behaviour is undefined.
1926		2118
1927	Since there is no standard kernel interface to do this, the portable	2119	Since there is no portable change notification interface available, the
1928	implementation simply calls C<stat (2)> regularly on the path to see if	2120	portable implementation simply calls C<stat(2)> regularly on the path
1929	it changed somehow. You can specify a recommended polling interval for	2121	to see if it changed somehow. You can specify a recommended polling
1930	this case. If you specify a polling interval of C<0> (highly recommended!)	2122	interval for this case. If you specify a polling interval of C<0> (highly
1931	then a I<suitable, unspecified default> value will be used (which	2123	recommended!) then a I<suitable, unspecified default> value will be used
1932	you can expect to be around five seconds, although this might change	2124	(which you can expect to be around five seconds, although this might
1933	dynamically). Libev will also impose a minimum interval which is currently	2125	change dynamically). Libev will also impose a minimum interval which is
1934	around C<0.1>, but thats usually overkill.	2126	currently around C<0.1>, but that's usually overkill.
1935		2127
1936	This watcher type is not meant for massive numbers of stat watchers,	2128	This watcher type is not meant for massive numbers of stat watchers,
1937	as even with OS-supported change notifications, this can be	2129	as even with OS-supported change notifications, this can be
1938	resource-intensive.	2130	resource-intensive.
1939		2131
1940	At the time of this writing, the only OS-specific interface implemented	2132	At the time of this writing, the only OS-specific interface implemented
1941	is the Linux inotify interface (implementing kqueue support is left as	2133	is the Linux inotify interface (implementing kqueue support is left as an
1942	an exercise for the reader. Note, however, that the author sees no way	2134	exercise for the reader. Note, however, that the author sees no way of
1943	of implementing C<ev_stat> semantics with kqueue).	2135	implementing C<ev_stat> semantics with kqueue, except as a hint).
1944		2136
1945	=head3 ABI Issues (Largefile Support)	2137	=head3 ABI Issues (Largefile Support)
1946		2138
1947	Libev by default (unless the user overrides this) uses the default	2139	Libev by default (unless the user overrides this) uses the default
1948	compilation environment, which means that on systems with large file	2140	compilation environment, which means that on systems with large file
1949	support disabled by default, you get the 32 bit version of the stat	2141	support disabled by default, you get the 32 bit version of the stat
1950	structure. When using the library from programs that change the ABI to	2142	structure. When using the library from programs that change the ABI to
1951	use 64 bit file offsets the programs will fail. In that case you have to	2143	use 64 bit file offsets the programs will fail. In that case you have to
1952	compile libev with the same flags to get binary compatibility. This is	2144	compile libev with the same flags to get binary compatibility. This is
1953	obviously the case with any flags that change the ABI, but the problem is	2145	obviously the case with any flags that change the ABI, but the problem is
1954	most noticeably disabled with ev_stat and large file support.	2146	most noticeably displayed with ev_stat and large file support.
1955		2147
1956	The solution for this is to lobby your distribution maker to make large	2148	The solution for this is to lobby your distribution maker to make large
1957	file interfaces available by default (as e.g. FreeBSD does) and not	2149	file interfaces available by default (as e.g. FreeBSD does) and not
1958	optional. Libev cannot simply switch on large file support because it has	2150	optional. Libev cannot simply switch on large file support because it has
1959	to exchange stat structures with application programs compiled using the	2151	to exchange stat structures with application programs compiled using the
1960	default compilation environment.	2152	default compilation environment.
1961		2153
1962	=head3 Inotify and Kqueue	2154	=head3 Inotify and Kqueue
1963		2155
1964	When C<inotify (7)> support has been compiled into libev (generally	2156	When C<inotify (7)> support has been compiled into libev and present at
1965	only available with Linux 2.6.25 or above due to bugs in earlier	2157	runtime, it will be used to speed up change detection where possible. The
1966	implementations) and present at runtime, it will be used to speed up	2158	inotify descriptor will be created lazily when the first C<ev_stat>
1967	change detection where possible. The inotify descriptor will be created	2159	watcher is being started.
1968	lazily when the first C<ev_stat> watcher is being started.
1969		2160
1970	Inotify presence does not change the semantics of C<ev_stat> watchers	2161	Inotify presence does not change the semantics of C<ev_stat> watchers
1971	except that changes might be detected earlier, and in some cases, to avoid	2162	except that changes might be detected earlier, and in some cases, to avoid
1972	making regular C<stat> calls. Even in the presence of inotify support	2163	making regular C<stat> calls. Even in the presence of inotify support
1973	there are many cases where libev has to resort to regular C<stat> polling,	2164	there are many cases where libev has to resort to regular C<stat> polling,
1974	but as long as the path exists, libev usually gets away without polling.	2165	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2166	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2167	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2168	xfs are fully working) libev usually gets away without polling.
1975		2169
1976	There is no support for kqueue, as apparently it cannot be used to	2170	There is no support for kqueue, as apparently it cannot be used to
1977	implement this functionality, due to the requirement of having a file	2171	implement this functionality, due to the requirement of having a file
1978	descriptor open on the object at all times, and detecting renames, unlinks	2172	descriptor open on the object at all times, and detecting renames, unlinks
1979	etc. is difficult.	2173	etc. is difficult.
1980		2174
		2175	=head3 C<stat ()> is a synchronous operation
		2176
		2177	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2178	the process. The exception are C<ev_stat> watchers - those call C<stat
		2179	()>, which is a synchronous operation.
		2180
		2181	For local paths, this usually doesn't matter: unless the system is very
		2182	busy or the intervals between stat's are large, a stat call will be fast,
		2183	as the path data is usually in memory already (except when starting the
		2184	watcher).
		2185
		2186	For networked file systems, calling C<stat ()> can block an indefinite
		2187	time due to network issues, and even under good conditions, a stat call
		2188	often takes multiple milliseconds.
		2189
		2190	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2191	paths, although this is fully supported by libev.
		2192
1981	=head3 The special problem of stat time resolution	2193	=head3 The special problem of stat time resolution
1982		2194
1983	The C<stat ()> system call only supports full-second resolution portably, and	2195	The C<stat ()> system call only supports full-second resolution portably,
1984	even on systems where the resolution is higher, most file systems still	2196	and even on systems where the resolution is higher, most file systems
1985	only support whole seconds.	2197	still only support whole seconds.
1986		2198
1987	That means that, if the time is the only thing that changes, you can	2199	That means that, if the time is the only thing that changes, you can
1988	easily miss updates: on the first update, C<ev_stat> detects a change and	2200	easily miss updates: on the first update, C<ev_stat> detects a change and
1989	calls your callback, which does something. When there is another update	2201	calls your callback, which does something. When there is another update
1990	within the same second, C<ev_stat> will be unable to detect unless the	2202	within the same second, C<ev_stat> will be unable to detect unless the
…		…
2133		2345
2134	=head3 Watcher-Specific Functions and Data Members	2346	=head3 Watcher-Specific Functions and Data Members
2135		2347
2136	=over 4	2348	=over 4
2137		2349
2138	=item ev_idle_init (ev_signal *, callback)	2350	=item ev_idle_init (ev_idle *, callback)
2139		2351
2140	Initialises and configures the idle watcher - it has no parameters of any	2352	Initialises and configures the idle watcher - it has no parameters of any
2141	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2353	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
2142	believe me.	2354	believe me.
2143		2355
…		…
2382	some fds have to be watched and handled very quickly (with low latency),	2594	some fds have to be watched and handled very quickly (with low latency),
2383	and even priorities and idle watchers might have too much overhead. In	2595	and even priorities and idle watchers might have too much overhead. In
2384	this case you would put all the high priority stuff in one loop and all	2596	this case you would put all the high priority stuff in one loop and all
2385	the rest in a second one, and embed the second one in the first.	2597	the rest in a second one, and embed the second one in the first.
2386		2598
2387	As long as the watcher is active, the callback will be invoked every time	2599	As long as the watcher is active, the callback will be invoked every
2388	there might be events pending in the embedded loop. The callback must then	2600	time there might be events pending in the embedded loop. The callback
2389	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2601	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
2390	their callbacks (you could also start an idle watcher to give the embedded	2602	sweep and invoke their callbacks (the callback doesn't need to invoke the
2391	loop strictly lower priority for example). You can also set the callback	2603	C<ev_embed_sweep> function directly, it could also start an idle watcher
2392	to C<0>, in which case the embed watcher will automatically execute the	2604	to give the embedded loop strictly lower priority for example).
2393	embedded loop sweep.
2394		2605
2395	As long as the watcher is started it will automatically handle events. The	2606	You can also set the callback to C<0>, in which case the embed watcher
2396	callback will be invoked whenever some events have been handled. You can	2607	will automatically execute the embedded loop sweep whenever necessary.
2397	set the callback to C<0> to avoid having to specify one if you are not
2398	interested in that.
2399		2608
2400	Also, there have not currently been made special provisions for forking:	2609	Fork detection will be handled transparently while the C<ev_embed> watcher
2401	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2610	is active, i.e., the embedded loop will automatically be forked when the
2402	but you will also have to stop and restart any C<ev_embed> watchers	2611	embedding loop forks. In other cases, the user is responsible for calling
2403	yourself - but you can use a fork watcher to handle this automatically,	2612	C<ev_loop_fork> on the embedded loop.
2404	and future versions of libev might do just that.
2405		2613
2406	Unfortunately, not all backends are embeddable: only the ones returned by	2614	Unfortunately, not all backends are embeddable: only the ones returned by
2407	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2615	C<ev_embeddable_backends> are, which, unfortunately, does not include any
2408	portable one.	2616	portable one.
2409		2617
…		…
2503	event loop blocks next and before C<ev_check> watchers are being called,	2711	event loop blocks next and before C<ev_check> watchers are being called,
2504	and only in the child after the fork. If whoever good citizen calling	2712	and only in the child after the fork. If whoever good citizen calling
2505	C<ev_default_fork> cheats and calls it in the wrong process, the fork	2713	C<ev_default_fork> cheats and calls it in the wrong process, the fork
2506	handlers will be invoked, too, of course.	2714	handlers will be invoked, too, of course.
2507		2715
		2716	=head3 The special problem of life after fork - how is it possible?
		2717
		2718	Most uses of C<fork()> consist of forking, then some simple calls to ste
		2719	up/change the process environment, followed by a call to C<exec()>. This
		2720	sequence should be handled by libev without any problems.
		2721
		2722	This changes when the application actually wants to do event handling
		2723	in the child, or both parent in child, in effect "continuing" after the
		2724	fork.
		2725
		2726	The default mode of operation (for libev, with application help to detect
		2727	forks) is to duplicate all the state in the child, as would be expected
		2728	when I<either> the parent I<or> the child process continues.
		2729
		2730	When both processes want to continue using libev, then this is usually the
		2731	wrong result. In that case, usually one process (typically the parent) is
		2732	supposed to continue with all watchers in place as before, while the other
		2733	process typically wants to start fresh, i.e. without any active watchers.
		2734
		2735	The cleanest and most efficient way to achieve that with libev is to
		2736	simply create a new event loop, which of course will be "empty", and
		2737	use that for new watchers. This has the advantage of not touching more
		2738	memory than necessary, and thus avoiding the copy-on-write, and the
		2739	disadvantage of having to use multiple event loops (which do not support
		2740	signal watchers).
		2741
		2742	When this is not possible, or you want to use the default loop for
		2743	other reasons, then in the process that wants to start "fresh", call
		2744	C<ev_default_destroy ()> followed by C<ev_default_loop (...)>. Destroying
		2745	the default loop will "orphan" (not stop) all registered watchers, so you
		2746	have to be careful not to execute code that modifies those watchers. Note
		2747	also that in that case, you have to re-register any signal watchers.
		2748
2508	=head3 Watcher-Specific Functions and Data Members	2749	=head3 Watcher-Specific Functions and Data Members
2509		2750
2510	=over 4	2751	=over 4
2511		2752
2512	=item ev_fork_init (ev_signal *, callback)	2753	=item ev_fork_init (ev_signal *, callback)
…		…
2629	=over 4	2870	=over 4
2630		2871
2631	=item ev_async_init (ev_async *, callback)	2872	=item ev_async_init (ev_async *, callback)
2632		2873
2633	Initialises and configures the async watcher - it has no parameters of any	2874	Initialises and configures the async watcher - it has no parameters of any
2634	kind. There is a C<ev_asynd_set> macro, but using it is utterly pointless,	2875	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
2635	trust me.	2876	trust me.
2636		2877
2637	=item ev_async_send (loop, ev_async *)	2878	=item ev_async_send (loop, ev_async *)
2638		2879
2639	Sends/signals/activates the given C<ev_async> watcher, that is, feeds	2880	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
2640	an C<EV_ASYNC> event on the watcher into the event loop. Unlike	2881	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
2641	C<ev_feed_event>, this call is safe to do from other threads, signal or	2882	C<ev_feed_event>, this call is safe to do from other threads, signal or
2642	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding	2883	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
2643	section below on what exactly this means).	2884	section below on what exactly this means).
2644		2885
		2886	Note that, as with other watchers in libev, multiple events might get
		2887	compressed into a single callback invocation (another way to look at this
		2888	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2889	reset when the event loop detects that).
		2890
2645	This call incurs the overhead of a system call only once per loop iteration,	2891	This call incurs the overhead of a system call only once per event loop
2646	so while the overhead might be noticeable, it doesn't apply to repeated	2892	iteration, so while the overhead might be noticeable, it doesn't apply to
2647	calls to C<ev_async_send>.	2893	repeated calls to C<ev_async_send> for the same event loop.
2648		2894
2649	=item bool = ev_async_pending (ev_async *)	2895	=item bool = ev_async_pending (ev_async *)
2650		2896
2651	Returns a non-zero value when C<ev_async_send> has been called on the	2897	Returns a non-zero value when C<ev_async_send> has been called on the
2652	watcher but the event has not yet been processed (or even noted) by the	2898	watcher but the event has not yet been processed (or even noted) by the
…		…
2655	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When	2901	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
2656	the loop iterates next and checks for the watcher to have become active,	2902	the loop iterates next and checks for the watcher to have become active,
2657	it will reset the flag again. C<ev_async_pending> can be used to very	2903	it will reset the flag again. C<ev_async_pending> can be used to very
2658	quickly check whether invoking the loop might be a good idea.	2904	quickly check whether invoking the loop might be a good idea.
2659		2905
2660	Not that this does I<not> check whether the watcher itself is pending, only	2906	Not that this does I<not> check whether the watcher itself is pending,
2661	whether it has been requested to make this watcher pending.	2907	only whether it has been requested to make this watcher pending: there
		2908	is a time window between the event loop checking and resetting the async
		2909	notification, and the callback being invoked.
2662		2910
2663	=back	2911	=back
2664		2912
2665		2913
2666	=head1 OTHER FUNCTIONS	2914	=head1 OTHER FUNCTIONS
…		…
2845		3093
2846	myclass obj;	3094	myclass obj;
2847	ev::io iow;	3095	ev::io iow;
2848	iow.set <myclass, &myclass::io_cb> (&obj);	3096	iow.set <myclass, &myclass::io_cb> (&obj);
2849		3097
		3098	=item w->set (object *)
		3099
		3100	This is an B<experimental> feature that might go away in a future version.
		3101
		3102	This is a variation of a method callback - leaving out the method to call
		3103	will default the method to C<operator ()>, which makes it possible to use
		3104	functor objects without having to manually specify the C<operator ()> all
		3105	the time. Incidentally, you can then also leave out the template argument
		3106	list.
		3107
		3108	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		3109	int revents)>.
		3110
		3111	See the method-C<set> above for more details.
		3112
		3113	Example: use a functor object as callback.
		3114
		3115	struct myfunctor
		3116	{
		3117	void operator() (ev::io &w, int revents)
		3118	{
		3119	...
		3120	}
		3121	}
		3122
		3123	myfunctor f;
		3124
		3125	ev::io w;
		3126	w.set (&f);
		3127
2850	=item w->set<function> (void *data = 0)	3128	=item w->set<function> (void *data = 0)
2851		3129
2852	Also sets a callback, but uses a static method or plain function as	3130	Also sets a callback, but uses a static method or plain function as
2853	callback. The optional C<data> argument will be stored in the watcher's	3131	callback. The optional C<data> argument will be stored in the watcher's
2854	C<data> member and is free for you to use.	3132	C<data> member and is free for you to use.
…		…
2940	L<http://software.schmorp.de/pkg/EV>.	3218	L<http://software.schmorp.de/pkg/EV>.
2941		3219
2942	=item Python	3220	=item Python
2943		3221
2944	Python bindings can be found at L<http://code.google.com/p/pyev/>. It	3222	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
2945	seems to be quite complete and well-documented. Note, however, that the	3223	seems to be quite complete and well-documented.
2946	patch they require for libev is outright dangerous as it breaks the ABI
2947	for everybody else, and therefore, should never be applied in an installed
2948	libev (if python requires an incompatible ABI then it needs to embed
2949	libev).
2950		3224
2951	=item Ruby	3225	=item Ruby
2952		3226
2953	Tony Arcieri has written a ruby extension that offers access to a subset	3227	Tony Arcieri has written a ruby extension that offers access to a subset
2954	of the libev API and adds file handle abstractions, asynchronous DNS and	3228	of the libev API and adds file handle abstractions, asynchronous DNS and
2955	more on top of it. It can be found via gem servers. Its homepage is at	3229	more on top of it. It can be found via gem servers. Its homepage is at
2956	L<http://rev.rubyforge.org/>.	3230	L<http://rev.rubyforge.org/>.
		3231
		3232	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3233	makes rev work even on mingw.
		3234
		3235	=item Haskell
		3236
		3237	A haskell binding to libev is available at
		3238	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
2957		3239
2958	=item D	3240	=item D
2959		3241
2960	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to	3242	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
2961	be found at L<http://proj.llucax.com.ar/wiki/evd>.	3243	be found at L<http://proj.llucax.com.ar/wiki/evd>.
…		…
3072		3354
3073	#define EV_STANDALONE 1	3355	#define EV_STANDALONE 1
3074	#include "ev.h"	3356	#include "ev.h"
3075		3357
3076	Both header files and implementation files can be compiled with a C++	3358	Both header files and implementation files can be compiled with a C++
3077	compiler (at least, thats a stated goal, and breakage will be treated	3359	compiler (at least, that's a stated goal, and breakage will be treated
3078	as a bug).	3360	as a bug).
3079		3361
3080	You need the following files in your source tree, or in a directory	3362	You need the following files in your source tree, or in a directory
3081	in your include path (e.g. in libev/ when using -Ilibev):	3363	in your include path (e.g. in libev/ when using -Ilibev):
3082		3364
…		…
3138	keeps libev from including F<config.h>, and it also defines dummy	3420	keeps libev from including F<config.h>, and it also defines dummy
3139	implementations for some libevent functions (such as logging, which is not	3421	implementations for some libevent functions (such as logging, which is not
3140	supported). It will also not define any of the structs usually found in	3422	supported). It will also not define any of the structs usually found in
3141	F<event.h> that are not directly supported by the libev core alone.	3423	F<event.h> that are not directly supported by the libev core alone.
3142		3424
		3425	In stanbdalone mode, libev will still try to automatically deduce the
		3426	configuration, but has to be more conservative.
		3427
3143	=item EV_USE_MONOTONIC	3428	=item EV_USE_MONOTONIC
3144		3429
3145	If defined to be C<1>, libev will try to detect the availability of the	3430	If defined to be C<1>, libev will try to detect the availability of the
3146	monotonic clock option at both compile time and runtime. Otherwise no use	3431	monotonic clock option at both compile time and runtime. Otherwise no
3147	of the monotonic clock option will be attempted. If you enable this, you	3432	use of the monotonic clock option will be attempted. If you enable this,
3148	usually have to link against librt or something similar. Enabling it when	3433	you usually have to link against librt or something similar. Enabling it
3149	the functionality isn't available is safe, though, although you have	3434	when the functionality isn't available is safe, though, although you have
3150	to make sure you link against any libraries where the C<clock_gettime>	3435	to make sure you link against any libraries where the C<clock_gettime>
3151	function is hiding in (often F<-lrt>).	3436	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
3152		3437
3153	=item EV_USE_REALTIME	3438	=item EV_USE_REALTIME
3154		3439
3155	If defined to be C<1>, libev will try to detect the availability of the	3440	If defined to be C<1>, libev will try to detect the availability of the
3156	real-time clock option at compile time (and assume its availability at	3441	real-time clock option at compile time (and assume its availability
3157	runtime if successful). Otherwise no use of the real-time clock option will	3442	at runtime if successful). Otherwise no use of the real-time clock
3158	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3443	option will be attempted. This effectively replaces C<gettimeofday>
3159	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3444	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
3160	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3445	correctness. See the note about libraries in the description of
		3446	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3447	C<EV_USE_CLOCK_SYSCALL>.
		3448
		3449	=item EV_USE_CLOCK_SYSCALL
		3450
		3451	If defined to be C<1>, libev will try to use a direct syscall instead
		3452	of calling the system-provided C<clock_gettime> function. This option
		3453	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3454	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3455	programs needlessly. Using a direct syscall is slightly slower (in
		3456	theory), because no optimised vdso implementation can be used, but avoids
		3457	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3458	higher, as it simplifies linking (no need for C<-lrt>).
3161		3459
3162	=item EV_USE_NANOSLEEP	3460	=item EV_USE_NANOSLEEP
3163		3461
3164	If defined to be C<1>, libev will assume that C<nanosleep ()> is available	3462	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
3165	and will use it for delays. Otherwise it will use C<select ()>.	3463	and will use it for delays. Otherwise it will use C<select ()>.
…		…
3181		3479
3182	=item EV_SELECT_USE_FD_SET	3480	=item EV_SELECT_USE_FD_SET
3183		3481
3184	If defined to C<1>, then the select backend will use the system C<fd_set>	3482	If defined to C<1>, then the select backend will use the system C<fd_set>
3185	structure. This is useful if libev doesn't compile due to a missing	3483	structure. This is useful if libev doesn't compile due to a missing
3186	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout on	3484	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
3187	exotic systems. This usually limits the range of file descriptors to some	3485	on exotic systems. This usually limits the range of file descriptors to
3188	low limit such as 1024 or might have other limitations (winsocket only	3486	some low limit such as 1024 or might have other limitations (winsocket
3189	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3487	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
3190	influence the size of the C<fd_set> used.	3488	configures the maximum size of the C<fd_set>.
3191		3489
3192	=item EV_SELECT_IS_WINSOCKET	3490	=item EV_SELECT_IS_WINSOCKET
3193		3491
3194	When defined to C<1>, the select backend will assume that	3492	When defined to C<1>, the select backend will assume that
3195	select/socket/connect etc. don't understand file descriptors but	3493	select/socket/connect etc. don't understand file descriptors but
…		…
3554	loop, as long as you don't confuse yourself). The only exception is that	3852	loop, as long as you don't confuse yourself). The only exception is that
3555	you must not do this from C<ev_periodic> reschedule callbacks.	3853	you must not do this from C<ev_periodic> reschedule callbacks.
3556		3854
3557	Care has been taken to ensure that libev does not keep local state inside	3855	Care has been taken to ensure that libev does not keep local state inside
3558	C<ev_loop>, and other calls do not usually allow for coroutine switches as	3856	C<ev_loop>, and other calls do not usually allow for coroutine switches as
3559	they do not clal any callbacks.	3857	they do not call any callbacks.
3560		3858
3561	=head2 COMPILER WARNINGS	3859	=head2 COMPILER WARNINGS
3562		3860
3563	Depending on your compiler and compiler settings, you might get no or a	3861	Depending on your compiler and compiler settings, you might get no or a
3564	lot of warnings when compiling libev code. Some people are apparently	3862	lot of warnings when compiling libev code. Some people are apparently
…		…
3598	==2274== definitely lost: 0 bytes in 0 blocks.	3896	==2274== definitely lost: 0 bytes in 0 blocks.
3599	==2274== possibly lost: 0 bytes in 0 blocks.	3897	==2274== possibly lost: 0 bytes in 0 blocks.
3600	==2274== still reachable: 256 bytes in 1 blocks.	3898	==2274== still reachable: 256 bytes in 1 blocks.
3601		3899
3602	Then there is no memory leak, just as memory accounted to global variables	3900	Then there is no memory leak, just as memory accounted to global variables
3603	is not a memleak - the memory is still being refernced, and didn't leak.	3901	is not a memleak - the memory is still being referenced, and didn't leak.
3604		3902
3605	Similarly, under some circumstances, valgrind might report kernel bugs	3903	Similarly, under some circumstances, valgrind might report kernel bugs
3606	as if it were a bug in libev (e.g. in realloc or in the poll backend,	3904	as if it were a bug in libev (e.g. in realloc or in the poll backend,
3607	although an acceptable workaround has been found here), or it might be	3905	although an acceptable workaround has been found here), or it might be
3608	confused.	3906	confused.
…		…
3844	involves iterating over all running async watchers or all signal numbers.	4142	involves iterating over all running async watchers or all signal numbers.
3845		4143
3846	=back	4144	=back
3847		4145
3848		4146
		4147	=head1 GLOSSARY
		4148
		4149	=over 4
		4150
		4151	=item active
		4152
		4153	A watcher is active as long as it has been started (has been attached to
		4154	an event loop) but not yet stopped (disassociated from the event loop).
		4155
		4156	=item application
		4157
		4158	In this document, an application is whatever is using libev.
		4159
		4160	=item callback
		4161
		4162	The address of a function that is called when some event has been
		4163	detected. Callbacks are being passed the event loop, the watcher that
		4164	received the event, and the actual event bitset.
		4165
		4166	=item callback invocation
		4167
		4168	The act of calling the callback associated with a watcher.
		4169
		4170	=item event
		4171
		4172	A change of state of some external event, such as data now being available
		4173	for reading on a file descriptor, time having passed or simply not having
		4174	any other events happening anymore.
		4175
		4176	In libev, events are represented as single bits (such as C<EV_READ> or
		4177	C<EV_TIMEOUT>).
		4178
		4179	=item event library
		4180
		4181	A software package implementing an event model and loop.
		4182
		4183	=item event loop
		4184
		4185	An entity that handles and processes external events and converts them
		4186	into callback invocations.
		4187
		4188	=item event model
		4189
		4190	The model used to describe how an event loop handles and processes
		4191	watchers and events.
		4192
		4193	=item pending
		4194
		4195	A watcher is pending as soon as the corresponding event has been detected,
		4196	and stops being pending as soon as the watcher will be invoked or its
		4197	pending status is explicitly cleared by the application.
		4198
		4199	A watcher can be pending, but not active. Stopping a watcher also clears
		4200	its pending status.
		4201
		4202	=item real time
		4203
		4204	The physical time that is observed. It is apparently strictly monotonic :)
		4205
		4206	=item wall-clock time
		4207
		4208	The time and date as shown on clocks. Unlike real time, it can actually
		4209	be wrong and jump forwards and backwards, e.g. when the you adjust your
		4210	clock.
		4211
		4212	=item watcher
		4213
		4214	A data structure that describes interest in certain events. Watchers need
		4215	to be started (attached to an event loop) before they can receive events.
		4216
		4217	=item watcher invocation
		4218
		4219	The act of calling the callback associated with a watcher.
		4220
		4221	=back
		4222
3849	=head1 AUTHOR	4223	=head1 AUTHOR
3850		4224
3851	Marc Lehmann <libev@schmorp.de>.	4225	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
3852		4226

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Comparing libev/ev.pod (file contents): Revision 1.202 by root, Fri Oct 24 08:30:01 2008 UTC vs. Revision 1.240 by root, Sat Apr 25 14:12:48 2009 UTC

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Comparing libev/ev.pod (file contents):
Revision 1.202 by root, Fri Oct 24 08:30:01 2008 UTC vs.
Revision 1.240 by root, Sat Apr 25 14:12:48 2009 UTC