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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.102 by root, Sun Apr 27 21:16:26 2008 UTC vs.
Revision 1.107 by root, Tue May 6 12:15:50 2008 UTC

…		…
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	my $w = AnyEvent->condvar; # stores whether a condition was flagged	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	21	$w->send; # wake up current and all future wait's
22		22
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		24
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	26	nowadays. So what is different about AnyEvent?
…		…
288	my $w = AnyEvent->child (	288	my $w = AnyEvent->child (
289	pid => $pid,	289	pid => $pid,
290	cb => sub {	290	cb => sub {
291	my ($pid, $status) = @_;	291	my ($pid, $status) = @_;
292	warn "pid $pid exited with status $status";	292	warn "pid $pid exited with status $status";
293	$done->broadcast;	293	$done->send;
294	},	294	},
295	);	295	);
296		296
297	# do something else, then wait for process exit	297	# do something else, then wait for process exit
298	$done->wait;	298	$done->wait;
299		299
300	=head2 CONDITION VARIABLES	300	=head2 CONDITION VARIABLES
301		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
302	Condition variables can be created by calling the C<< AnyEvent->condvar >>	312	Condition variables can be created by calling the C<< AnyEvent->condvar
303	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.
304		316
305	A condition variable waits for a condition - precisely that the C<<	317	After creation, the conditon variable is "false" until it becomes "true"
306	->broadcast >> method has been called.	318	by calling the C<send> method.
307		319
308	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,
309	example, if you write a module that does asynchronous http requests,	328	for example, if you write a module that does asynchronous http requests,
310	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
311	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.
312		332
313	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,
314	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
315	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
316	->broadcast >> the "quit" event.	336	button of your app, which would C<< ->send >> the "quit" event.
317		337
318	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
319	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
320	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
321	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,
322	as this asks for trouble.	342	as this asks for trouble.
323		343
324	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.
		349
		350	There are two "sides" to a condition variable - the "producer side" which
		351	eventually calls C<< -> send >>, and the "consumer side", which waits
		352	for the send to occur.
		353
		354	Example:
		355
		356	# wait till the result is ready
		357	my $result_ready = AnyEvent->condvar;
		358
		359	# do something such as adding a timer
		360	# or socket watcher the calls $result_ready->send
		361	# when the "result" is ready.
		362	# in this case, we simply use a timer:
		363	my $w = AnyEvent->timer (
		364	after => 1,
		365	cb => sub { $result_ready->send },
		366	);
		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls send
		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 sends 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.
325		378
326	=over 4	379	=over 4
327		380
		381	=item $cv->send (...)
		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 send will be remembered.
		386
		387	If a callback has been set on the condition variable, it is called
		388	immediately from within send.
		389
		390	Any arguments passed to the C<send> call will be returned by all
		391	future C<< ->wait >> calls.
		392
		393	=item $cv->croak ($error)
		394
		395	Similar to send, 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<< ->send >>, but that is not required. If no
		413	callback was set, C<send> 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->send (\%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<send> 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	C<send> 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	=over 4
		458
328	=item $cv->wait	459	=item $cv->wait
329		460
330	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
331	called on c<$cv>, while servicing other watchers normally.	462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
332		464
333	You can only wait once on a condition - additional calls will return	465	You can only wait once on a condition - additional calls are valid but
334	immediately.	466	will return immediately.
		467
		468	If an error condition has been set by calling C<< ->croak >>, then this
		469	function will call C<croak>.
		470
		471	In list context, all parameters passed to C<send> will be returned,
		472	in scalar context only the first one will be returned.
335		473
336	Not all event models support a blocking wait - some die in that case	474	Not all event models support a blocking wait - some die in that case
337	(programs might want to do that to stay interactive), so I<if you are	475	(programs might want to do that to stay interactive), so I<if you are
338	using this from a module, never require a blocking wait>, but let the	476	using this from a module, never require a blocking wait>, but let the
339	caller decide whether the call will block or not (for example, by coupling	477	caller decide whether the call will block or not (for example, by coupling
…		…
346	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
347	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	485	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
348	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s	486	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
349	from different coroutines, however).	487	from different coroutines, however).
350		488
351	=item $cv->broadcast	489	You can ensure that C<< -wait >> never blocks by setting a callback and
		490	only calling C<< ->wait >> from within that callback (or at a later
		491	time). This will work even when the event loop does not support blocking
		492	waits otherwise.
352		493
353	Flag the condition as ready - a running C<< ->wait >> and all further	494	=item $bool = $cv->ready
354	calls to C<wait> will (eventually) return after this method has been	495
355	called. If nobody is waiting the broadcast will be remembered..	496	Returns true when the condition is "true", i.e. whether C<send> or
		497	C<croak> have been called.
		498
		499	=item $cb = $cv->cb ([new callback])
		500
		501	This is a mutator function that returns the callback set and optionally
		502	replaces it before doing so.
		503
		504	The callback will be called when the condition becomes "true", i.e. when
		505	C<send> or C<croak> are called. Calling C<wait> inside the callback
		506	or at any later time is guaranteed not to block.
356		507
357	=back	508	=back
358
359	Example:
360
361	# wait till the result is ready
362	my $result_ready = AnyEvent->condvar;
363
364	# do something such as adding a timer
365	# or socket watcher the calls $result_ready->broadcast
366	# when the "result" is ready.
367	# in this case, we simply use a timer:
368	my $w = AnyEvent->timer (
369	after => 1,
370	cb => sub { $result_ready->broadcast },
371	);
372
373	# this "blocks" (while handling events) till the watcher
374	# calls broadcast
375	$result_ready->wait;
376		509
377	=head1 GLOBAL VARIABLES AND FUNCTIONS	510	=head1 GLOBAL VARIABLES AND FUNCTIONS
378		511
379	=over 4	512	=over 4
380		513
…		…
390		523
391	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	524	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
392	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	525	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
393	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	526	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
394	AnyEvent::Impl::Event based on Event, second best choice.	527	AnyEvent::Impl::Event based on Event, second best choice.
		528	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
395	AnyEvent::Impl::Glib based on Glib, third-best choice.	529	AnyEvent::Impl::Glib based on Glib, third-best choice.
396	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
397	AnyEvent::Impl::Tk based on Tk, very bad choice.	530	AnyEvent::Impl::Tk based on Tk, very bad choice.
398	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	531	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
399	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	532	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
400	AnyEvent::Impl::POE based on POE, not generic enough for full support.	533	AnyEvent::Impl::POE based on POE, not generic enough for full support.
401		534
…		…
427	decide which event module to use as soon as the first method is called, so	560	decide which event module to use as soon as the first method is called, so
428	by calling AnyEvent in your module body you force the user of your module	561	by calling AnyEvent in your module body you force the user of your module
429	to load the event module first.	562	to load the event module first.
430		563
431	Never call C<< ->wait >> on a condition variable unless you I<know> that	564	Never call C<< ->wait >> on a condition variable unless you I<know> that
432	the C<< ->broadcast >> method has been called on it already. This is	565	the C<< ->send >> method has been called on it already. This is
433	because it will stall the whole program, and the whole point of using	566	because it will stall the whole program, and the whole point of using
434	events is to stay interactive.	567	events is to stay interactive.
435		568
436	It is fine, however, to call C<< ->wait >> when the user of your module	569	It is fine, however, to call C<< ->wait >> when the user of your module
437	requests it (i.e. if you create a http request object ad have a method	570	requests it (i.e. if you create a http request object ad have a method
…		…
553	my @models = (	686	my @models = (
554	[Coro::EV:: => AnyEvent::Impl::CoroEV::],	687	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
555	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],	688	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
556	[EV:: => AnyEvent::Impl::EV::],	689	[EV:: => AnyEvent::Impl::EV::],
557	[Event:: => AnyEvent::Impl::Event::],	690	[Event:: => AnyEvent::Impl::Event::],
558	[Glib:: => AnyEvent::Impl::Glib::],
559	[Tk:: => AnyEvent::Impl::Tk::],	691	[Tk:: => AnyEvent::Impl::Tk::],
560	[Wx:: => AnyEvent::Impl::POE::],	692	[Wx:: => AnyEvent::Impl::POE::],
561	[Prima:: => AnyEvent::Impl::POE::],	693	[Prima:: => AnyEvent::Impl::POE::],
562	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	694	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
563	# everything below here will not be autoprobed as the pureperl backend should work everywhere	695	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		696	[Glib:: => AnyEvent::Impl::Glib::],
564	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy	697	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
565	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program	698	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
566	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza	699	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
567	);	700	);
568		701
569	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);	702	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
570		703
571	sub detect() {	704	sub detect() {
572	unless ($MODEL) {	705	unless ($MODEL) {
573	no strict 'refs';	706	no strict 'refs';
574		707
…		…
1071	file descriptor is dup()ed for each watcher. This shows that the dup()	1204	file descriptor is dup()ed for each watcher. This shows that the dup()
1072	employed by some adaptors is not a big performance issue (it does incur a	1205	employed by some adaptors is not a big performance issue (it does incur a
1073	hidden memory cost inside the kernel which is not reflected in the figures	1206	hidden memory cost inside the kernel which is not reflected in the figures
1074	above).	1207	above).
1075		1208
1076	C<POE>, regardless of underlying event loop (whether using its pure	1209	C<POE>, regardless of underlying event loop (whether using its pure perl
1077	perl select-based backend or the Event module, the POE-EV backend	1210	select-based backend or the Event module, the POE-EV backend couldn't
1078	couldn't be tested because it wasn't working) shows abysmal performance	1211	be tested because it wasn't working) shows abysmal performance and
1079	and memory usage: Watchers use almost 30 times as much memory as	1212	memory usage with AnyEvent: Watchers use almost 30 times as much memory
1080	EV watchers, and 10 times as much memory as Event (the high memory	1213	as EV watchers, and 10 times as much memory as Event (the high memory
1081	requirements are caused by requiring a session for each watcher). Watcher	1214	requirements are caused by requiring a session for each watcher). Watcher
1082	invocation speed is almost 900 times slower than with AnyEvent's pure perl	1215	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1216	implementation.
		1217
1083	implementation. The design of the POE adaptor class in AnyEvent can not	1218	The design of the POE adaptor class in AnyEvent can not really account
1084	really account for this, as session creation overhead is small compared	1219	for the performance issues, though, as session creation overhead is
1085	to execution of the state machine, which is coded pretty optimally within	1220	small compared to execution of the state machine, which is coded pretty
1086	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.	1221	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1222	using multiple sessions is not a good approach, especially regarding
		1223	memory usage, even the author of POE could not come up with a faster
		1224	design).
1087		1225
1088	=head3 Summary	1226	=head3 Summary
1089		1227
1090	=over 4	1228	=over 4
1091		1229
…		…
1170		1308
1171	=head3 Summary	1309	=head3 Summary
1172		1310
1173	=over 4	1311	=over 4
1174		1312
1175	=item * The pure perl implementation performs extremely well, considering	1313	=item * The pure perl implementation performs extremely well.
1176	that it uses select.
1177		1314
1178	=item * Avoid Glib or POE in large projects where performance matters.	1315	=item * Avoid Glib or POE in large projects where performance matters.
1179		1316
1180	=back	1317	=back
1181		1318
…		…
1230		1367
1231		1368
1232	=head1 FORK	1369	=head1 FORK
1233		1370
1234	Most event libraries are not fork-safe. The ones who are usually are	1371	Most event libraries are not fork-safe. The ones who are usually are
1235	because they are so inefficient. Only L<EV> is fully fork-aware.	1372	because they rely on inefficient but fork-safe C<select> or C<poll>
		1373	calls. Only L<EV> is fully fork-aware.
1236		1374
1237	If you have to fork, you must either do so I<before> creating your first	1375	If you have to fork, you must either do so I<before> creating your first
1238	watcher OR you must not use AnyEvent at all in the child.	1376	watcher OR you must not use AnyEvent at all in the child.
1239		1377
1240		1378
…		…
1252		1390
1253	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1391	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1254		1392
1255	use AnyEvent;	1393	use AnyEvent;
1256		1394
		1395	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1396	be used to probe what backend is used and gain other information (which is
		1397	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1398
1257		1399
1258	=head1 SEE ALSO	1400	=head1 SEE ALSO
1259		1401
1260	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1402	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
1261	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,	1403	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,

Diff Legend

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

Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.102 by root, Sun Apr 27 21:16:26 2008 UTC vs. Revision 1.107 by root, Tue May 6 12:15:50 2008 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.102 by root, Sun Apr 27 21:16:26 2008 UTC vs.
Revision 1.107 by root, Tue May 6 12:15:50 2008 UTC