[ViewVC] Diff of: cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.100 by elmex, Sun Apr 27 19:15:43 2008 UTC vs.
Revision 1.105 by root, Thu May 1 12:35:54 2008 UTC

…		…
65	technically possible.	65	technically possible.
66		66
67	Of course, if you want lots of policy (this can arguably be somewhat	67	Of course, if you want lots of policy (this can arguably be somewhat
68	useful) and you want to force your users to use the one and only event	68	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	69	model, you should I<not> use this module.
70
71	#TODO#
72
73	Net::IRC3
74	AnyEvent::HTTPD
75	AnyEvent::DNS
76	IO::AnyEvent
77	Net::FPing
78	Net::XMPP2
79	Coro
80
81	AnyEvent::IRC
82	AnyEvent::HTTPD
83	AnyEvent::DNS
84	AnyEvent::Handle
85	AnyEvent::Socket
86	AnyEvent::FPing
87	AnyEvent::XMPP
88	AnyEvent::SNMP
89	Coro
90		70
91	=head1 DESCRIPTION	71	=head1 DESCRIPTION
92		72
93	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
94	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
…		…
317	# do something else, then wait for process exit	297	# do something else, then wait for process exit
318	$done->wait;	298	$done->wait;
319		299
320	=head2 CONDITION VARIABLES	300	=head2 CONDITION VARIABLES
321		301
		302	If you are familiar with some event loops you will know that all of them
		303	require you to run some blocking "loop", "run" or similar function that
		304	will actively watch for new events and call your callbacks.
		305
		306	AnyEvent is different, it expects somebody else to run the event loop and
		307	will only block when necessary (usually when told by the user).
		308
		309	The instrument to do that is called a "condition variable", so called
		310	because they represent a condition that must become true.
		311
322	Condition variables can be created by calling the C<< AnyEvent->condvar >>	312	Condition variables can be created by calling the C<< AnyEvent->condvar
323	method without any arguments.	313	>> method, usually without arguments. The only argument pair allowed is
		314	C<cb>, which specifies a callback to be called when the condition variable
		315	becomes true.
324		316
325	A condition variable waits for a condition - precisely that the C<<	317	After creation, the conditon variable is "false" until it becomes "true"
326	->broadcast >> method has been called.	318	by calling the C<broadcast> method.
327		319
328	They are very useful to signal that a condition has been fulfilled, for	320	Condition variables are similar to callbacks, except that you can
		321	optionally wait for them. They can also be called merge points - points
		322	in time where multiple outstandign events have been processed. And yet
		323	another way to call them is transations - each condition variable can be
		324	used to represent a transaction, which finishes at some point and delivers
		325	a result.
		326
		327	Condition variables are very useful to signal that something has finished,
329	example, if you write a module that does asynchronous http requests,	328	for example, if you write a module that does asynchronous http requests,
330	then a condition variable would be the ideal candidate to signal the	329	then a condition variable would be the ideal candidate to signal the
331	availability of results.	330	availability of results. The user can either act when the callback is
		331	called or can synchronously C<< ->wait >> for the results.
332		332
333	You can also use condition variables to block your main program until	333	You can also use them to simulate traditional event loops - for example,
334	an event occurs - for example, you could C<< ->wait >> in your main	334	you can block your main program until an event occurs - for example, you
335	program until the user clicks the Quit button in your app, which would C<<	335	could C<< ->wait >> in your main program until the user clicks the Quit
336	->broadcast >> the "quit" event.	336	button of your app, which would C<< ->broadcast >> the "quit" event.
337		337
338	Note that condition variables recurse into the event loop - if you have	338	Note that condition variables recurse into the event loop - if you have
339	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	339	two pieces of code that call C<< ->wait >> in a round-robbin fashion, you
340	lose. Therefore, condition variables are good to export to your caller, but	340	lose. Therefore, condition variables are good to export to your caller, but
341	you should avoid making a blocking wait yourself, at least in callbacks,	341	you should avoid making a blocking wait yourself, at least in callbacks,
342	as this asks for trouble.	342	as this asks for trouble.
343		343
344	This object has two methods:	344	Condition variables are represented by hash refs in perl, and the keys
		345	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		346	easy (it is often useful to build your own transaction class on top of
		347	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		348	it's C<new> method in your own C<new> method.
345		349
346	=over 4	350	There are two "sides" to a condition variable - the "producer side" which
347		351	eventually calls C<< -> broadcast >>, and the "consumer side", which waits
348	=item $cv->wait	352	for the broadcast to occur.
349
350	Wait (blocking if necessary) until the C<< ->broadcast >> method has been
351	called on c<$cv>, while servicing other watchers normally.
352
353	You can only wait once on a condition - additional calls will return
354	immediately.
355
356	Not all event models support a blocking wait - some die in that case
357	(programs might want to do that to stay interactive), so I<if you are
358	using this from a module, never require a blocking wait>, but let the
359	caller decide whether the call will block or not (for example, by coupling
360	condition variables with some kind of request results and supporting
361	callbacks so the caller knows that getting the result will not block,
362	while still suppporting blocking waits if the caller so desires).
363
364	Another reason I<never> to C<< ->wait >> in a module is that you cannot
365	sensibly have two C<< ->wait >>'s in parallel, as that would require
366	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
367	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
368	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
369	from different coroutines, however).
370
371	=item $cv->broadcast
372
373	Flag the condition as ready - a running C<< ->wait >> and all further
374	calls to C<wait> will (eventually) return after this method has been
375	called. If nobody is waiting the broadcast will be remembered..
376
377	=back
378		353
379	Example:	354	Example:
380		355
381	# wait till the result is ready	356	# wait till the result is ready
382	my $result_ready = AnyEvent->condvar;	357	my $result_ready = AnyEvent->condvar;
…		…
388	my $w = AnyEvent->timer (	363	my $w = AnyEvent->timer (
389	after => 1,	364	after => 1,
390	cb => sub { $result_ready->broadcast },	365	cb => sub { $result_ready->broadcast },
391	);	366	);
392		367
393	# this "blocks" (while handling events) till the watcher	368	# this "blocks" (while handling events) till the callback
394	# calls broadcast	369	# calls broadcast
395	$result_ready->wait;	370	$result_ready->wait;
		371
		372	=head3 METHODS FOR PRODUCERS
		373
		374	These methods should only be used by the producing side, i.e. the
		375	code/module that eventually broadcasts the signal. Note that it is also
		376	the producer side which creates the condvar in most cases, but it isn't
		377	uncommon for the consumer to create it as well.
		378
		379	=over 4
		380
		381	=item $cv->broadcast (...)
		382
		383	Flag the condition as ready - a running C<< ->wait >> and all further
		384	calls to C<wait> will (eventually) return after this method has been
		385	called. If nobody is waiting the broadcast will be remembered.
		386
		387	If a callback has been set on the condition variable, it is called
		388	immediately from within broadcast.
		389
		390	Any arguments passed to the C<broadcast> call will be returned by all
		391	future C<< ->wait >> calls.
		392
		393	=item $cv->croak ($error)
		394
		395	Similar to broadcast, but causes all call's wait C<< ->wait >> to invoke
		396	C<Carp::croak> with the given error message/object/scalar.
		397
		398	This can be used to signal any errors to the condition variable
		399	user/consumer.
		400
		401	=item $cv->begin ([group callback])
		402
		403	=item $cv->end
		404
		405	These two methods can be used to combine many transactions/events into
		406	one. For example, a function that pings many hosts in parallel might want
		407	to use a condition variable for the whole process.
		408
		409	Every call to C<< ->begin >> will increment a counter, and every call to
		410	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		411	>>, the (last) callback passed to C<begin> will be executed. That callback
		412	is I<supposed> to call C<< ->broadcast >>, but that is not required. If no
		413	callback was set, C<broadcast> will be called without any arguments.
		414
		415	Let's clarify this with the ping example:
		416
		417	my $cv = AnyEvent->condvar;
		418
		419	my %result;
		420	$cv->begin (sub { $cv->broadcast (\%result) });
		421
		422	for my $host (@list_of_hosts) {
		423	$cv->begin;
		424	ping_host_then_call_callback $host, sub {
		425	$result{$host} = ...;
		426	$cv->end;
		427	};
		428	}
		429
		430	$cv->end;
		431
		432	This code fragment supposedly pings a number of hosts and calls
		433	C<broadcast> after results for all then have have been gathered - in any
		434	order. To achieve this, the code issues a call to C<begin> when it starts
		435	each ping request and calls C<end> when it has received some result for
		436	it. Since C<begin> and C<end> only maintain a counter, the order in which
		437	results arrive is not relevant.
		438
		439	There is an additional bracketing call to C<begin> and C<end> outside the
		440	loop, which serves two important purposes: first, it sets the callback
		441	to be called once the counter reaches C<0>, and second, it ensures that
		442	broadcast is called even when C<no> hosts are being pinged (the loop
		443	doesn't execute once).
		444
		445	This is the general pattern when you "fan out" into multiple subrequests:
		446	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		447	is called at least once, and then, for each subrequest you start, call
		448	C<begin> and for eahc subrequest you finish, call C<end>.
		449
		450	=back
		451
		452	=head3 METHODS FOR CONSUMERS
		453
		454	These methods should only be used by the consuming side, i.e. the
		455	code awaits the condition.
		456
		457	=item $cv->wait
		458
		459	Wait (blocking if necessary) until the C<< ->broadcast >> or C<< ->croak
		460	>> methods have been called on c<$cv>, while servicing other watchers
		461	normally.
		462
		463	You can only wait once on a condition - additional calls are valid but
		464	will return immediately.
		465
		466	If an error condition has been set by calling C<< ->croak >>, then this
		467	function will call C<croak>.
		468
		469	In list context, all parameters passed to C<broadcast> will be returned,
		470	in scalar context only the first one will be returned.
		471
		472	Not all event models support a blocking wait - some die in that case
		473	(programs might want to do that to stay interactive), so I<if you are
		474	using this from a module, never require a blocking wait>, but let the
		475	caller decide whether the call will block or not (for example, by coupling
		476	condition variables with some kind of request results and supporting
		477	callbacks so the caller knows that getting the result will not block,
		478	while still suppporting blocking waits if the caller so desires).
		479
		480	Another reason I<never> to C<< ->wait >> in a module is that you cannot
		481	sensibly have two C<< ->wait >>'s in parallel, as that would require
		482	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		483	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
		484	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
		485	from different coroutines, however).
		486
		487	You can ensure that C<< -wait >> never blocks by setting a callback and
		488	only calling C<< ->wait >> from within that callback (or at a later
		489	time). This will work even when the event loop does not support blocking
		490	waits otherwise.
		491
		492	=back
396		493
397	=head1 GLOBAL VARIABLES AND FUNCTIONS	494	=head1 GLOBAL VARIABLES AND FUNCTIONS
398		495
399	=over 4	496	=over 4
400		497
…		…
410		507
411	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	508	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
412	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	509	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
413	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	510	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
414	AnyEvent::Impl::Event based on Event, second best choice.	511	AnyEvent::Impl::Event based on Event, second best choice.
		512	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
415	AnyEvent::Impl::Glib based on Glib, third-best choice.	513	AnyEvent::Impl::Glib based on Glib, third-best choice.
416	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
417	AnyEvent::Impl::Tk based on Tk, very bad choice.	514	AnyEvent::Impl::Tk based on Tk, very bad choice.
418	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	515	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
419	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	516	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
420	AnyEvent::Impl::POE based on POE, not generic enough for full support.	517	AnyEvent::Impl::POE based on POE, not generic enough for full support.
421		518
…		…
479	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	576	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
480	behaviour everywhere, but letting AnyEvent chose is generally better.	577	behaviour everywhere, but letting AnyEvent chose is generally better.
481		578
482	=head1 OTHER MODULES	579	=head1 OTHER MODULES
483		580
484	L<AnyEvent> itself comes with useful utility modules:	581	The following is a non-exhaustive list of additional modules that use
485		582	AnyEvent and can therefore be mixed easily with other AnyEvent modules
486	To make it easier to do non-blocking IO the modules L<AnyEvent::Handle>	583	in the same program. Some of the modules come with AnyEvent, some are
487	and L<AnyEvent::Socket> are provided. L<AnyEvent::Handle> provides	584	available via CPAN.
488	read and write buffers and manages watchers for reads and writes.
489	L<AnyEvent::Socket> provides means to do non-blocking connects.
490
491	Aside from those there are these modules that support AnyEvent (and use it
492	for non-blocking IO):
493		585
494	=over 4	586	=over 4
495		587
		588	=item L<AnyEvent::Util>
		589
		590	Contains various utility functions that replace often-used but blocking
		591	functions such as C<inet_aton> by event-/callback-based versions.
		592
		593	=item L<AnyEvent::Handle>
		594
		595	Provide read and write buffers and manages watchers for reads and writes.
		596
		597	=item L<AnyEvent::Socket>
		598
		599	Provides a means to do non-blocking connects, accepts etc.
		600
		601	=item L<AnyEvent::HTTPD>
		602
		603	Provides a simple web application server framework.
		604
		605	=item L<AnyEvent::DNS>
		606
		607	Provides asynchronous DNS resolver capabilities, beyond what
		608	L<AnyEvent::Util> offers.
		609
496	=item L<AnyEvent::FastPing>	610	=item L<AnyEvent::FastPing>
497		611
		612	The fastest ping in the west.
		613
498	=item L<Net::IRC3>	614	=item L<Net::IRC3>
499		615
		616	AnyEvent based IRC client module family.
		617
500	=item L<Net::XMPP2>	618	=item L<Net::XMPP2>
		619
		620	AnyEvent based XMPP (Jabber protocol) module family.
		621
		622	=item L<Net::FCP>
		623
		624	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		625	of AnyEvent.
		626
		627	=item L<Event::ExecFlow>
		628
		629	High level API for event-based execution flow control.
		630
		631	=item L<Coro>
		632
		633	Has special support for AnyEvent.
		634
		635	=item L<IO::Lambda>
		636
		637	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		638
		639	=item L<IO::AIO>
		640
		641	Truly asynchronous I/O, should be in the toolbox of every event
		642	programmer. Can be trivially made to use AnyEvent.
		643
		644	=item L<BDB>
		645
		646	Truly asynchronous Berkeley DB access. Can be trivially made to use
		647	AnyEvent.
501		648
502	=back	649	=back
503		650
504	=cut	651	=cut
505		652
…		…
523	my @models = (	670	my @models = (
524	[Coro::EV:: => AnyEvent::Impl::CoroEV::],	671	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
525	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],	672	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
526	[EV:: => AnyEvent::Impl::EV::],	673	[EV:: => AnyEvent::Impl::EV::],
527	[Event:: => AnyEvent::Impl::Event::],	674	[Event:: => AnyEvent::Impl::Event::],
528	[Glib:: => AnyEvent::Impl::Glib::],
529	[Tk:: => AnyEvent::Impl::Tk::],	675	[Tk:: => AnyEvent::Impl::Tk::],
530	[Wx:: => AnyEvent::Impl::POE::],	676	[Wx:: => AnyEvent::Impl::POE::],
531	[Prima:: => AnyEvent::Impl::POE::],	677	[Prima:: => AnyEvent::Impl::POE::],
532	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	678	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
533	# everything below here will not be autoprobed as the pureperl backend should work everywhere	679	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		680	[Glib:: => AnyEvent::Impl::Glib::],
534	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy	681	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
535	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program	682	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
536	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza	683	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
537	);	684	);
538		685
…		…
1041	file descriptor is dup()ed for each watcher. This shows that the dup()	1188	file descriptor is dup()ed for each watcher. This shows that the dup()
1042	employed by some adaptors is not a big performance issue (it does incur a	1189	employed by some adaptors is not a big performance issue (it does incur a
1043	hidden memory cost inside the kernel which is not reflected in the figures	1190	hidden memory cost inside the kernel which is not reflected in the figures
1044	above).	1191	above).
1045		1192
1046	C<POE>, regardless of underlying event loop (whether using its pure	1193	C<POE>, regardless of underlying event loop (whether using its pure perl
1047	perl select-based backend or the Event module, the POE-EV backend	1194	select-based backend or the Event module, the POE-EV backend couldn't
1048	couldn't be tested because it wasn't working) shows abysmal performance	1195	be tested because it wasn't working) shows abysmal performance and
1049	and memory usage: Watchers use almost 30 times as much memory as	1196	memory usage with AnyEvent: Watchers use almost 30 times as much memory
1050	EV watchers, and 10 times as much memory as Event (the high memory	1197	as EV watchers, and 10 times as much memory as Event (the high memory
1051	requirements are caused by requiring a session for each watcher). Watcher	1198	requirements are caused by requiring a session for each watcher). Watcher
1052	invocation speed is almost 900 times slower than with AnyEvent's pure perl	1199	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1200	implementation.
		1201
1053	implementation. The design of the POE adaptor class in AnyEvent can not	1202	The design of the POE adaptor class in AnyEvent can not really account
1054	really account for this, as session creation overhead is small compared	1203	for the performance issues, though, as session creation overhead is
1055	to execution of the state machine, which is coded pretty optimally within	1204	small compared to execution of the state machine, which is coded pretty
1056	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.	1205	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1206	using multiple sessions is not a good approach, especially regarding
		1207	memory usage, even the author of POE could not come up with a faster
		1208	design).
1057		1209
1058	=head3 Summary	1210	=head3 Summary
1059		1211
1060	=over 4	1212	=over 4
1061		1213
…		…
1140		1292
1141	=head3 Summary	1293	=head3 Summary
1142		1294
1143	=over 4	1295	=over 4
1144		1296
1145	=item * The pure perl implementation performs extremely well, considering	1297	=item * The pure perl implementation performs extremely well.
1146	that it uses select.
1147		1298
1148	=item * Avoid Glib or POE in large projects where performance matters.	1299	=item * Avoid Glib or POE in large projects where performance matters.
1149		1300
1150	=back	1301	=back
1151		1302
…		…
1180	speed most when you have lots of watchers, not when you only have a few of	1331	speed most when you have lots of watchers, not when you only have a few of
1181	them).	1332	them).
1182		1333
1183	EV is again fastest.	1334	EV is again fastest.
1184		1335
1185	The C-based event loops Event and Glib come in second this time, as the	1336	Perl again comes second. It is noticably faster than the C-based event
1186	overhead of running an iteration is much smaller in C than in Perl (little	1337	loops Event and Glib, although the difference is too small to really
1187	code to execute in the inner loop, and perl's function calling overhead is	1338	matter.
1188	high, and updating all the data structures is costly).
1189
1190	The pure perl event loop is much slower, but still competitive.
1191		1339
1192	POE also performs much better in this case, but is is still far behind the	1340	POE also performs much better in this case, but is is still far behind the
1193	others.	1341	others.
1194		1342
1195	=head3 Summary	1343	=head3 Summary
…		…
1203		1351
1204		1352
1205	=head1 FORK	1353	=head1 FORK
1206		1354
1207	Most event libraries are not fork-safe. The ones who are usually are	1355	Most event libraries are not fork-safe. The ones who are usually are
1208	because they are so inefficient. Only L<EV> is fully fork-aware.	1356	because they rely on inefficient but fork-safe C<select> or C<poll>
		1357	calls. Only L<EV> is fully fork-aware.
1209		1358
1210	If you have to fork, you must either do so I<before> creating your first	1359	If you have to fork, you must either do so I<before> creating your first
1211	watcher OR you must not use AnyEvent at all in the child.	1360	watcher OR you must not use AnyEvent at all in the child.
1212		1361
1213		1362

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.100 by elmex, Sun Apr 27 19:15:43 2008 UTC vs. Revision 1.105 by root, Thu May 1 12:35:54 2008 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.100 by elmex, Sun Apr 27 19:15:43 2008 UTC vs.
Revision 1.105 by root, Thu May 1 12:35:54 2008 UTC