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

Comparing libev/ev.pod (file contents):
Revision 1.233 by root, Thu Apr 16 07:32:51 2009 UTC vs.
Revision 1.240 by root, Sat Apr 25 14:12:48 2009 UTC

…		…
62		62
63	// unloop was called, so exit	63	// unloop was called, so exit
64	return 0;	64	return 0;
65	}	65	}
66		66
67	=head1 DESCRIPTION	67	=head1 ABOUT THIS DOCUMENT
		68
		69	This document documents the libev software package.
68		70
69	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
70	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
71	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
72		84
73	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
74	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
75	these event sources and provide your program with events.	87	these event sources and provide your program with events.
76		88
…		…
110	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
111	this argument.	123	this argument.
112		124
113	=head2 TIME REPRESENTATION	125	=head2 TIME REPRESENTATION
114		126
115	Libev represents time as a single floating point number, representing the	127	Libev represents time as a single floating point number, representing
116	(fractional) number of seconds since the (POSIX) epoch (somewhere near	128	the (fractional) number of seconds since the (POSIX) epoch (somewhere
117	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
118	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
119	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
120	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
121	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
122	throughout libev.	134	throughout libev.
123		135
124	=head1 ERROR HANDLING	136	=head1 ERROR HANDLING
125		137
…		…
632		644
633	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
634	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
635	the current time is a good idea.	647	the current time is a good idea.
636		648
637	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.
638		650
639	=item ev_suspend (loop)	651	=item ev_suspend (loop)
640		652
641	=item ev_resume (loop)	653	=item ev_resume (loop)
642		654
…		…
1096	or might not have been clamped to the valid range.	1108	or might not have been clamped to the valid range.
1097		1109
1098	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
1099	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 :).
1100		1112
1101	See L<WATCHER PRIORITIES>, below, for a more thorough treatment of	1113	See L<WATCHER PRIORITY MODELS>, below, for a more thorough treatment of
1102	priorities.	1114	priorities.
1103		1115
1104	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1116	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
1105		1117
1106	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
…		…
1320	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
1321	required if you know what you are doing).	1333	required if you know what you are doing).
1322		1334
1323	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
1324	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
1325	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.
1326		1340
1327	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
1328	receive "spurious" readiness notifications, that is your callback might	1342	receive "spurious" readiness notifications, that is your callback might
1329	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
1330	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
…		…
1451	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
1452	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1466	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1453	monotonic clock option helps a lot here).	1467	monotonic clock option helps a lot here).
1454		1468
1455	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
1456	passed. If multiple timers become ready during the same loop iteration	1470	passed (not I<at>, so on systems with very low-resolution clocks this
1457	then the ones with earlier time-out values are invoked before ones with	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
1458	later time-out values (but this is no longer true when a callback calls	1473	before ones with later time-out values (but this is no longer true when a
1459	C<ev_loop> recursively).	1474	callback calls C<ev_loop> recursively).
1460		1475
1461	=head3 Be smart about timeouts	1476	=head3 Be smart about timeouts
1462		1477
1463	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
1464	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,
…		…
2696	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,
2697	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
2698	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
2699	handlers will be invoked, too, of course.	2714	handlers will be invoked, too, of course.
2700		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
2701	=head3 Watcher-Specific Functions and Data Members	2749	=head3 Watcher-Specific Functions and Data Members
2702		2750
2703	=over 4	2751	=over 4
2704		2752
2705	=item ev_fork_init (ev_signal *, callback)	2753	=item ev_fork_init (ev_signal *, callback)
…		…
4094	involves iterating over all running async watchers or all signal numbers.	4142	involves iterating over all running async watchers or all signal numbers.
4095		4143
4096	=back	4144	=back
4097		4145
4098		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
4099	=head1 AUTHOR	4223	=head1 AUTHOR
4100		4224
4101	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.	4225	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
4102		4226

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Comparing libev/ev.pod (file contents): Revision 1.233 by root, Thu Apr 16 07:32:51 2009 UTC vs. Revision 1.240 by root, Sat Apr 25 14:12:48 2009 UTC

Diff Legend

Comparing libev/ev.pod (file contents):
Revision 1.233 by root, Thu Apr 16 07:32:51 2009 UTC vs.
Revision 1.240 by root, Sat Apr 25 14:12:48 2009 UTC