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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.76 by root, Fri Apr 25 08:41:38 2008 UTC vs.
Revision 1.105 by root, Thu May 1 12:35:54 2008 UTC

…		…
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		70
71
72	=head1 DESCRIPTION	71	=head1 DESCRIPTION
73		72
74	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
76	users to use the same event loop (as only a single event loop can coexist	75	users to use the same event loop (as only a single event loop can coexist
…		…
80	module.	79	module.
81		80
82	During the first call of any watcher-creation method, the module tries	81	During the first call of any watcher-creation method, the module tries
83	to detect the currently loaded event loop by probing whether one of the	82	to detect the currently loaded event loop by probing whether one of the
84	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,	83	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
85	L<Event>, L<Glib>, L<Tk>, L<AnyEvent::Impl::Perl>, L<Event::Lib>, L<Qt>,	84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	L<POE>. The first one found is used. If none are found, the module tries	85	L<POE>. The first one found is used. If none are found, the module tries
87	to load these modules (excluding Event::Lib, Qt and POE as the pure perl	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
88	adaptor should always succeed) in the order given. The first one that can	87	adaptor should always succeed) in the order given. The first one that can
89	be successfully loaded will be used. If, after this, still none could be	88	be successfully loaded will be used. If, after this, still none could be
90	found, AnyEvent will fall back to a pure-perl event loop, which is not	89	found, AnyEvent will fall back to a pure-perl event loop, which is not
91	very efficient, but should work everywhere.	90	very efficient, but should work everywhere.
92		91
…		…
136		135
137	Note that C<my $w; $w => combination. This is necessary because in Perl,	136	Note that C<my $w; $w => combination. This is necessary because in Perl,
138	my variables are only visible after the statement in which they are	137	my variables are only visible after the statement in which they are
139	declared.	138	declared.
140		139
141	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
142		141
143	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
144	with the following mandatory key-value pairs as arguments:	143	with the following mandatory key-value pairs as arguments:
145		144
146	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
147	events. C<poll> must be a string that is either C<r> or C<w>, which	146	for events. C<poll> must be a string that is either C<r> or C<w>,
148	creates a watcher waiting for "r"eadable or "w"ritable events,	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
149	respectively. C<cb> is the callback to invoke each time the file handle	148	respectively. C<cb> is the callback to invoke each time the file handle
150	becomes ready.	149	becomes ready.
151		150
152	As long as the I/O watcher exists it will keep the file descriptor or a	151	Although the callback might get passed parameters, their value and
153	copy of it alive/open.	152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
154		154
		155	The I/O watcher might use the underlying file descriptor or a copy of it.
155	It is not allowed to close a file handle as long as any watcher is active	156	You must not close a file handle as long as any watcher is active on the
156	on the underlying file descriptor.	157	underlying file descriptor.
157		158
158	Some event loops issue spurious readyness notifications, so you should	159	Some event loops issue spurious readyness notifications, so you should
159	always use non-blocking calls when reading/writing from/to your file	160	always use non-blocking calls when reading/writing from/to your file
160	handles.	161	handles.
161		162
…		…
172		173
173	You can create a time watcher by calling the C<< AnyEvent->timer >>	174	You can create a time watcher by calling the C<< AnyEvent->timer >>
174	method with the following mandatory arguments:	175	method with the following mandatory arguments:
175		176
176	C<after> specifies after how many seconds (fractional values are	177	C<after> specifies after how many seconds (fractional values are
177	supported) should the timer activate. C<cb> the callback to invoke in that	178	supported) the callback should be invoked. C<cb> is the callback to invoke
178	case.	179	in that case.
		180
		181	Although the callback might get passed parameters, their value and
		182	presence is undefined and you cannot rely on them. Portable AnyEvent
		183	callbacks cannot use arguments passed to time watcher callbacks.
179		184
180	The timer callback will be invoked at most once: if you want a repeating	185	The timer callback will be invoked at most once: if you want a repeating
181	timer you have to create a new watcher (this is a limitation by both Tk	186	timer you have to create a new watcher (this is a limitation by both Tk
182	and Glib).	187	and Glib).
183		188
…		…
228		233
229	You can watch for signals using a signal watcher, C<signal> is the signal	234	You can watch for signals using a signal watcher, C<signal> is the signal
230	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
231	be invoked whenever a signal occurs.	236	be invoked whenever a signal occurs.
232		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
233	Multiple signal occurances can be clumped together into one callback	242	Multiple signal occurances can be clumped together into one callback
234	invocation, and callback invocation will be synchronous. synchronous means	243	invocation, and callback invocation will be synchronous. synchronous means
235	that it might take a while until the signal gets handled by the process,	244	that it might take a while until the signal gets handled by the process,
236	but it is guarenteed not to interrupt any other callbacks.	245	but it is guarenteed not to interrupt any other callbacks.
237		246
…		…
251		260
252	The child process is specified by the C<pid> argument (if set to C<0>, it	261	The child process is specified by the C<pid> argument (if set to C<0>, it
253	watches for any child process exit). The watcher will trigger as often	262	watches for any child process exit). The watcher will trigger as often
254	as status change for the child are received. This works by installing a	263	as status change for the child are received. This works by installing a
255	signal handler for C<SIGCHLD>. The callback will be called with the pid	264	signal handler for C<SIGCHLD>. The callback will be called with the pid
256	and exit status (as returned by waitpid).	265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
257		267
258	Example: wait for pid 1333	268	There is a slight catch to child watchers, however: you usually start them
		269	I<after> the child process was created, and this means the process could
		270	have exited already (and no SIGCHLD will be sent anymore).
		271
		272	Not all event models handle this correctly (POE doesn't), but even for
		273	event models that I<do> handle this correctly, they usually need to be
		274	loaded before the process exits (i.e. before you fork in the first place).
		275
		276	This means you cannot create a child watcher as the very first thing in an
		277	AnyEvent program, you I<have> to create at least one watcher before you
		278	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		279
		280	Example: fork a process and wait for it
		281
		282	my $done = AnyEvent->condvar;
		283
		284	AnyEvent::detect; # force event module to be initialised
		285
		286	my $pid = fork or exit 5;
259		287
260	my $w = AnyEvent->child (	288	my $w = AnyEvent->child (
261	pid => 1333,	289	pid => $pid,
262	cb => sub {	290	cb => sub {
263	my ($pid, $status) = @_;	291	my ($pid, $status) = @_;
264	warn "pid $pid exited with status $status";	292	warn "pid $pid exited with status $status";
		293	$done->broadcast;
265	},	294	},
266	);	295	);
267		296
		297	# do something else, then wait for process exit
		298	$done->wait;
		299
268	=head2 CONDITION VARIABLES	300	=head2 CONDITION VARIABLES
269		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
270	Condition variables can be created by calling the C<< AnyEvent->condvar >>	312	Condition variables can be created by calling the C<< AnyEvent->condvar
271	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.
272		316
273	A condition variable waits for a condition - precisely that the C<<	317	After creation, the conditon variable is "false" until it becomes "true"
274	->broadcast >> method has been called.	318	by calling the C<broadcast> method.
275		319
276	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,
277	example, if you write a module that does asynchronous http requests,	328	for example, if you write a module that does asynchronous http requests,
278	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
279	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.
280		332
281	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,
282	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
283	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
284	->broadcast >> the "quit" event.	336	button of your app, which would C<< ->broadcast >> the "quit" event.
285		337
286	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
287	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
288	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
289	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,
290	as this asks for trouble.	342	as this asks for trouble.
291		343
292	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.
293		349
294	=over 4	350	There are two "sides" to a condition variable - the "producer side" which
295		351	eventually calls C<< -> broadcast >>, and the "consumer side", which waits
296	=item $cv->wait	352	for the broadcast to occur.
297
298	Wait (blocking if necessary) until the C<< ->broadcast >> method has been
299	called on c<$cv>, while servicing other watchers normally.
300
301	You can only wait once on a condition - additional calls will return
302	immediately.
303
304	Not all event models support a blocking wait - some die in that case
305	(programs might want to do that to stay interactive), so I<if you are
306	using this from a module, never require a blocking wait>, but let the
307	caller decide whether the call will block or not (for example, by coupling
308	condition variables with some kind of request results and supporting
309	callbacks so the caller knows that getting the result will not block,
310	while still suppporting blocking waits if the caller so desires).
311
312	Another reason I<never> to C<< ->wait >> in a module is that you cannot
313	sensibly have two C<< ->wait >>'s in parallel, as that would require
314	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
315	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
316	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
317	from different coroutines, however).
318
319	=item $cv->broadcast
320
321	Flag the condition as ready - a running C<< ->wait >> and all further
322	calls to C<wait> will (eventually) return after this method has been
323	called. If nobody is waiting the broadcast will be remembered..
324
325	=back
326		353
327	Example:	354	Example:
328		355
329	# wait till the result is ready	356	# wait till the result is ready
330	my $result_ready = AnyEvent->condvar;	357	my $result_ready = AnyEvent->condvar;
…		…
336	my $w = AnyEvent->timer (	363	my $w = AnyEvent->timer (
337	after => 1,	364	after => 1,
338	cb => sub { $result_ready->broadcast },	365	cb => sub { $result_ready->broadcast },
339	);	366	);
340		367
341	# this "blocks" (while handling events) till the watcher	368	# this "blocks" (while handling events) till the callback
342	# calls broadcast	369	# calls broadcast
343	$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
344		493
345	=head1 GLOBAL VARIABLES AND FUNCTIONS	494	=head1 GLOBAL VARIABLES AND FUNCTIONS
346		495
347	=over 4	496	=over 4
348		497
…		…
358		507
359	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	508	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	509	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361	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).
362	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.
363	AnyEvent::Impl::Glib based on Glib, third-best choice.	513	AnyEvent::Impl::Glib based on Glib, third-best choice.
364	AnyEvent::Impl::Tk based on Tk, very bad choice.	514	AnyEvent::Impl::Tk based on Tk, very bad choice.
365	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
366	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).
367	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	516	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368	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.
369		518
370	There is no support for WxWidgets, as WxWidgets has no support for	519	There is no support for WxWidgets, as WxWidgets has no support for
…		…
425		574
426	You can chose to use a rather inefficient pure-perl implementation by	575	You can chose to use a rather inefficient pure-perl implementation by
427	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	576	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
428	behaviour everywhere, but letting AnyEvent chose is generally better.	577	behaviour everywhere, but letting AnyEvent chose is generally better.
429		578
		579	=head1 OTHER MODULES
		580
		581	The following is a non-exhaustive list of additional modules that use
		582	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		583	in the same program. Some of the modules come with AnyEvent, some are
		584	available via CPAN.
		585
		586	=over 4
		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
		610	=item L<AnyEvent::FastPing>
		611
		612	The fastest ping in the west.
		613
		614	=item L<Net::IRC3>
		615
		616	AnyEvent based IRC client module family.
		617
		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.
		648
		649	=back
		650
430	=cut	651	=cut
431		652
432	package AnyEvent;	653	package AnyEvent;
433		654
434	no warnings;	655	no warnings;
…		…
449	my @models = (	670	my @models = (
450	[Coro::EV:: => AnyEvent::Impl::CoroEV::],	671	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
451	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],	672	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
452	[EV:: => AnyEvent::Impl::EV::],	673	[EV:: => AnyEvent::Impl::EV::],
453	[Event:: => AnyEvent::Impl::Event::],	674	[Event:: => AnyEvent::Impl::Event::],
454	[Glib:: => AnyEvent::Impl::Glib::],
455	[Tk:: => AnyEvent::Impl::Tk::],	675	[Tk:: => AnyEvent::Impl::Tk::],
456	[Wx:: => AnyEvent::Impl::POE::],	676	[Wx:: => AnyEvent::Impl::POE::],
457	[Prima:: => AnyEvent::Impl::POE::],	677	[Prima:: => AnyEvent::Impl::POE::],
458	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	678	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
459	# 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::],
460	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy	681	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
461	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program	682	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
462	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza	683	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
463	);	684	);
464		685
…		…
706		927
707	=back	928	=back
708		929
709	=head1 EXAMPLE PROGRAM	930	=head1 EXAMPLE PROGRAM
710		931
711	The following program uses an IO watcher to read data from STDIN, a timer	932	The following program uses an I/O watcher to read data from STDIN, a timer
712	to display a message once per second, and a condition variable to quit the	933	to display a message once per second, and a condition variable to quit the
713	program when the user enters quit:	934	program when the user enters quit:
714		935
715	use AnyEvent;	936	use AnyEvent;
716		937
…		…
861	});	1082	});
862		1083
863	$quit->wait;	1084	$quit->wait;
864		1085
865		1086
866	=head1 BENCHMARK	1087	=head1 BENCHMARKS
867		1088
868	To give you an idea of the performance and overheads that AnyEvent adds	1089	To give you an idea of the performance and overheads that AnyEvent adds
869	over the event loops themselves (and to give you an impression of the	1090	over the event loops themselves and to give you an impression of the speed
870	speed of various event loops), here is a benchmark of various supported	1091	of various event loops I prepared some benchmarks.
871	event models natively and with anyevent. The benchmark creates a lot of	1092
872	timers (with a zero timeout) and io watchers (watching STDOUT, a pty, to	1093	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1094
		1095	Here is a benchmark of various supported event models used natively and
		1096	through anyevent. The benchmark creates a lot of timers (with a zero
		1097	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
873	become writable, which it is), lets them fire exactly once and destroys	1098	which it is), lets them fire exactly once and destroys them again.
874	them again.
875		1099
		1100	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1101	distribution.
		1102
876	=head2 Explanation of the columns	1103	=head3 Explanation of the columns
877		1104
878	I<watcher> is the number of event watchers created/destroyed. Since	1105	I<watcher> is the number of event watchers created/destroyed. Since
879	different event models feature vastly different performances, each event	1106	different event models feature vastly different performances, each event
880	loop was given a number of watchers so that overall runtime is acceptable	1107	loop was given a number of watchers so that overall runtime is acceptable
881	and similar between tested event loop (and keep them from crashing): Glib	1108	and similar between tested event loop (and keep them from crashing): Glib
…		…
897	signal the end of this phase.	1124	signal the end of this phase.
898		1125
899	I<destroy> is the time, in microseconds, that it takes to destroy a single	1126	I<destroy> is the time, in microseconds, that it takes to destroy a single
900	watcher.	1127	watcher.
901		1128
902	=head2 Results	1129	=head3 Results
903		1130
904	name watchers bytes create invoke destroy comment	1131	name watchers bytes create invoke destroy comment
905	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1132	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
906	EV/Any 100000 610 3.52 0.91 0.75 EV + AnyEvent watchers	1133	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
907	CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal	1134	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
908	Perl/Any 100000 513 4.91 0.92 1.15 pure perl implementation	1135	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
909	Event/Event 16000 523 28.05 21.38 0.86 Event native interface	1136	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
910	Event/Any 16000 943 34.43 20.48 1.39 Event + AnyEvent watchers	1137	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
911	Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour	1138	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
912	Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers	1139	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
913	POE/Event 2000 6644 108.15 768.19 14.33 via POE::Loop::Event	1140	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
914	POE/Select 2000 6343 94.69 807.65 562.69 via POE::Loop::Select	1141	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
915		1142
916	=head2 Discussion	1143	=head3 Discussion
917		1144
918	The benchmark does I<not> measure scalability of the event loop very	1145	The benchmark does I<not> measure scalability of the event loop very
919	well. For example, a select-based event loop (such as the pure perl one)	1146	well. For example, a select-based event loop (such as the pure perl one)
920	can never compete with an event loop that uses epoll when the number of	1147	can never compete with an event loop that uses epoll when the number of
921	file descriptors grows high. In this benchmark, only a single filehandle	1148	file descriptors grows high. In this benchmark, all events become ready at
922	is used (although some of the AnyEvent adaptors dup() its file descriptor	1149	the same time, so select/poll-based implementations get an unnatural speed
923	to worka round bugs).	1150	boost.
		1151
		1152	Also, note that the number of watchers usually has a nonlinear effect on
		1153	overall speed, that is, creating twice as many watchers doesn't take twice
		1154	the time - usually it takes longer. This puts event loops tested with a
		1155	higher number of watchers at a disadvantage.
		1156
		1157	To put the range of results into perspective, consider that on the
		1158	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1159	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1160	cycles with POE.
924		1161
925	C<EV> is the sole leader regarding speed and memory use, which are both	1162	C<EV> is the sole leader regarding speed and memory use, which are both
926	maximal/minimal, respectively. Even when going through AnyEvent, there are	1163	maximal/minimal, respectively. Even when going through AnyEvent, it uses
927	only two event loops that use slightly less memory (the C<Event> module	1164	far less memory than any other event loop and is still faster than Event
928	natively and the pure perl backend), and no faster event models, not even	1165	natively.
929	C<Event> natively.
930		1166
931	The pure perl implementation is hit in a few sweet spots (both the	1167	The pure perl implementation is hit in a few sweet spots (both the
932	zero timeout and the use of a single fd hit optimisations in the perl	1168	constant timeout and the use of a single fd hit optimisations in the perl
933	interpreter and the backend itself). Nevertheless tis shows that it	1169	interpreter and the backend itself). Nevertheless this shows that it
934	adds very little overhead in itself. Like any select-based backend its	1170	adds very little overhead in itself. Like any select-based backend its
935	performance becomes really bad with lots of file descriptors, of course,	1171	performance becomes really bad with lots of file descriptors (and few of
936	but this was not subject of this benchmark.	1172	them active), of course, but this was not subject of this benchmark.
937		1173
938	The C<Event> module has a relatively high setup and callback invocation cost,	1174	The C<Event> module has a relatively high setup and callback invocation
939	but overall scores on the third place.	1175	cost, but overall scores in on the third place.
940		1176
941	C<Glib>'s memory usage is quite a bit bit higher, but it features a	1177	C<Glib>'s memory usage is quite a bit higher, but it features a
942	faster callback invocation and overall ends up in the same class as	1178	faster callback invocation and overall ends up in the same class as
943	C<Event>. However, Glib scales extremely badly, doubling the number of	1179	C<Event>. However, Glib scales extremely badly, doubling the number of
944	watchers increases the processing time by more than a factor of four,	1180	watchers increases the processing time by more than a factor of four,
945	making it completely unusable when using larger numbers of watchers	1181	making it completely unusable when using larger numbers of watchers
946	(note that only a single file descriptor was used in the benchmark, so	1182	(note that only a single file descriptor was used in the benchmark, so
…		…
949	The C<Tk> adaptor works relatively well. The fact that it crashes with	1185	The C<Tk> adaptor works relatively well. The fact that it crashes with
950	more than 2000 watchers is a big setback, however, as correctness takes	1186	more than 2000 watchers is a big setback, however, as correctness takes
951	precedence over speed. Nevertheless, its performance is surprising, as the	1187	precedence over speed. Nevertheless, its performance is surprising, as the
952	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()
953	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
954	hidden memory cost inside the kernel, though, that is not reflected in the	1190	hidden memory cost inside the kernel which is not reflected in the figures
955	figures above).	1191	above).
956		1192
957	C<POE>, regardless of underlying event loop (wether using its pure perl	1193	C<POE>, regardless of underlying event loop (whether using its pure perl
958	select-based backend or the Event module) shows abysmal performance and	1194	select-based backend or the Event module, the POE-EV backend couldn't
		1195	be tested because it wasn't working) shows abysmal performance and
959	memory usage: Watchers use almost 30 times as much memory as EV watchers,	1196	memory usage with AnyEvent: Watchers use almost 30 times as much memory
960	and 10 times as much memory as both Event or EV via AnyEvent. Watcher	1197	as EV watchers, and 10 times as much memory as Event (the high memory
		1198	requirements are caused by requiring a session for each watcher). Watcher
961	invocation is almost 700 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
962	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
963	really account for this, as session creation overhead is small compared	1203	for the performance issues, though, as session creation overhead is
964	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
965	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).
966		1209
967	=head2 Summary	1210	=head3 Summary
968		1211
		1212	=over 4
		1213
969	Using EV through AnyEvent is faster than any other event loop, but most	1214	=item * Using EV through AnyEvent is faster than any other event loop
970	event loops have acceptable performance with or without AnyEvent.	1215	(even when used without AnyEvent), but most event loops have acceptable
		1216	performance with or without AnyEvent.
971		1217
972	The overhead AnyEvent adds is usually much smaller than the overhead of	1218	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
973	the actual event loop, only with extremely fast event loops such as the EV	1219	the actual event loop, only with extremely fast event loops such as EV
974	adds AnyEvent significant overhead.	1220	adds AnyEvent significant overhead.
975		1221
976	And you should simply avoid POE like the plague if you want performance or	1222	=item * You should avoid POE like the plague if you want performance or
977	reasonable memory usage.	1223	reasonable memory usage.
978		1224
		1225	=back
		1226
		1227	=head2 BENCHMARKING THE LARGE SERVER CASE
		1228
		1229	This benchmark atcually benchmarks the event loop itself. It works by
		1230	creating a number of "servers": each server consists of a socketpair, a
		1231	timeout watcher that gets reset on activity (but never fires), and an I/O
		1232	watcher waiting for input on one side of the socket. Each time the socket
		1233	watcher reads a byte it will write that byte to a random other "server".
		1234
		1235	The effect is that there will be a lot of I/O watchers, only part of which
		1236	are active at any one point (so there is a constant number of active
		1237	fds for each loop iterstaion, but which fds these are is random). The
		1238	timeout is reset each time something is read because that reflects how
		1239	most timeouts work (and puts extra pressure on the event loops).
		1240
		1241	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1242	(1%) are active. This mirrors the activity of large servers with many
		1243	connections, most of which are idle at any one point in time.
		1244
		1245	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1246	distribution.
		1247
		1248	=head3 Explanation of the columns
		1249
		1250	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1251	each server has a read and write socket end).
		1252
		1253	I<create> is the time it takes to create a socketpair (which is
		1254	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1255
		1256	I<request>, the most important value, is the time it takes to handle a
		1257	single "request", that is, reading the token from the pipe and forwarding
		1258	it to another server. This includes deleting the old timeout and creating
		1259	a new one that moves the timeout into the future.
		1260
		1261	=head3 Results
		1262
		1263	name sockets create request
		1264	EV 20000 69.01 11.16
		1265	Perl 20000 73.32 35.87
		1266	Event 20000 212.62 257.32
		1267	Glib 20000 651.16 1896.30
		1268	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1269
		1270	=head3 Discussion
		1271
		1272	This benchmark I<does> measure scalability and overall performance of the
		1273	particular event loop.
		1274
		1275	EV is again fastest. Since it is using epoll on my system, the setup time
		1276	is relatively high, though.
		1277
		1278	Perl surprisingly comes second. It is much faster than the C-based event
		1279	loops Event and Glib.
		1280
		1281	Event suffers from high setup time as well (look at its code and you will
		1282	understand why). Callback invocation also has a high overhead compared to
		1283	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1284	uses select or poll in basically all documented configurations.
		1285
		1286	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1287	clearly fails to perform with many filehandles or in busy servers.
		1288
		1289	POE is still completely out of the picture, taking over 1000 times as long
		1290	as EV, and over 100 times as long as the Perl implementation, even though
		1291	it uses a C-based event loop in this case.
		1292
		1293	=head3 Summary
		1294
		1295	=over 4
		1296
		1297	=item * The pure perl implementation performs extremely well.
		1298
		1299	=item * Avoid Glib or POE in large projects where performance matters.
		1300
		1301	=back
		1302
		1303	=head2 BENCHMARKING SMALL SERVERS
		1304
		1305	While event loops should scale (and select-based ones do not...) even to
		1306	large servers, most programs we (or I :) actually write have only a few
		1307	I/O watchers.
		1308
		1309	In this benchmark, I use the same benchmark program as in the large server
		1310	case, but it uses only eight "servers", of which three are active at any
		1311	one time. This should reflect performance for a small server relatively
		1312	well.
		1313
		1314	The columns are identical to the previous table.
		1315
		1316	=head3 Results
		1317
		1318	name sockets create request
		1319	EV 16 20.00 6.54
		1320	Perl 16 25.75 12.62
		1321	Event 16 81.27 35.86
		1322	Glib 16 32.63 15.48
		1323	POE 16 261.87 276.28 uses POE::Loop::Event
		1324
		1325	=head3 Discussion
		1326
		1327	The benchmark tries to test the performance of a typical small
		1328	server. While knowing how various event loops perform is interesting, keep
		1329	in mind that their overhead in this case is usually not as important, due
		1330	to the small absolute number of watchers (that is, you need efficiency and
		1331	speed most when you have lots of watchers, not when you only have a few of
		1332	them).
		1333
		1334	EV is again fastest.
		1335
		1336	Perl again comes second. It is noticably faster than the C-based event
		1337	loops Event and Glib, although the difference is too small to really
		1338	matter.
		1339
		1340	POE also performs much better in this case, but is is still far behind the
		1341	others.
		1342
		1343	=head3 Summary
		1344
		1345	=over 4
		1346
		1347	=item * C-based event loops perform very well with small number of
		1348	watchers, as the management overhead dominates.
		1349
		1350	=back
		1351
979		1352
980	=head1 FORK	1353	=head1 FORK
981		1354
982	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
983	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.
984		1358
985	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
986	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.
987		1361
988		1362

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.76 by root, Fri Apr 25 08:41:38 2008 UTC vs. Revision 1.105 by root, Thu May 1 12:35:54 2008 UTC

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.76 by root, Fri Apr 25 08:41:38 2008 UTC vs.
Revision 1.105 by root, Thu May 1 12:35:54 2008 UTC