[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 1.106 by root, Thu May 1 13:45:22 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?
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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
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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->send;
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<send> 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<< ->send >> 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.
		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.
293		378
294	=over 4	379	=over 4
295		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
296	=item $cv->wait	459	=item $cv->wait
297		460
298	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
299	called on c<$cv>, while servicing other watchers normally.	462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
300		464
301	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
302	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.
303		473
304	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
305	(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
306	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
307	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
…		…
314	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
315	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	485	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
316	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s	486	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
317	from different coroutines, however).	487	from different coroutines, however).
318		488
319	=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.
320		493
321	Flag the condition as ready - a running C<< ->wait >> and all further	494	=item $bool = $cv->ready
322	calls to C<wait> will (eventually) return after this method has been	495
323	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.
324		507
325	=back	508	=back
326
327	Example:
328
329	# wait till the result is ready
330	my $result_ready = AnyEvent->condvar;
331
332	# do something such as adding a timer
333	# or socket watcher the calls $result_ready->broadcast
334	# when the "result" is ready.
335	# in this case, we simply use a timer:
336	my $w = AnyEvent->timer (
337	after => 1,
338	cb => sub { $result_ready->broadcast },
339	);
340
341	# this "blocks" (while handling events) till the watcher
342	# calls broadcast
343	$result_ready->wait;
344		509
345	=head1 GLOBAL VARIABLES AND FUNCTIONS	510	=head1 GLOBAL VARIABLES AND FUNCTIONS
346		511
347	=over 4	512	=over 4
348		513
…		…
358		523
359	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.	524	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.	525	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361	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).
362	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.
363	AnyEvent::Impl::Glib based on Glib, third-best choice.	529	AnyEvent::Impl::Glib based on Glib, third-best choice.
364	AnyEvent::Impl::Tk based on Tk, very bad choice.	530	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).	531	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
367	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	532	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368	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.
369		534
370	There is no support for WxWidgets, as WxWidgets has no support for	535	There is no support for WxWidgets, as WxWidgets has no support for
…		…
395	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
396	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
397	to load the event module first.	562	to load the event module first.
398		563
399	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
400	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
401	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
402	events is to stay interactive.	567	events is to stay interactive.
403		568
404	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
405	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
…		…
425		590
426	You can chose to use a rather inefficient pure-perl implementation by	591	You can chose to use a rather inefficient pure-perl implementation by
427	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	592	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
428	behaviour everywhere, but letting AnyEvent chose is generally better.	593	behaviour everywhere, but letting AnyEvent chose is generally better.
429		594
		595	=head1 OTHER MODULES
		596
		597	The following is a non-exhaustive list of additional modules that use
		598	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		599	in the same program. Some of the modules come with AnyEvent, some are
		600	available via CPAN.
		601
		602	=over 4
		603
		604	=item L<AnyEvent::Util>
		605
		606	Contains various utility functions that replace often-used but blocking
		607	functions such as C<inet_aton> by event-/callback-based versions.
		608
		609	=item L<AnyEvent::Handle>
		610
		611	Provide read and write buffers and manages watchers for reads and writes.
		612
		613	=item L<AnyEvent::Socket>
		614
		615	Provides a means to do non-blocking connects, accepts etc.
		616
		617	=item L<AnyEvent::HTTPD>
		618
		619	Provides a simple web application server framework.
		620
		621	=item L<AnyEvent::DNS>
		622
		623	Provides asynchronous DNS resolver capabilities, beyond what
		624	L<AnyEvent::Util> offers.
		625
		626	=item L<AnyEvent::FastPing>
		627
		628	The fastest ping in the west.
		629
		630	=item L<Net::IRC3>
		631
		632	AnyEvent based IRC client module family.
		633
		634	=item L<Net::XMPP2>
		635
		636	AnyEvent based XMPP (Jabber protocol) module family.
		637
		638	=item L<Net::FCP>
		639
		640	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		641	of AnyEvent.
		642
		643	=item L<Event::ExecFlow>
		644
		645	High level API for event-based execution flow control.
		646
		647	=item L<Coro>
		648
		649	Has special support for AnyEvent.
		650
		651	=item L<IO::Lambda>
		652
		653	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		654
		655	=item L<IO::AIO>
		656
		657	Truly asynchronous I/O, should be in the toolbox of every event
		658	programmer. Can be trivially made to use AnyEvent.
		659
		660	=item L<BDB>
		661
		662	Truly asynchronous Berkeley DB access. Can be trivially made to use
		663	AnyEvent.
		664
		665	=back
		666
430	=cut	667	=cut
431		668
432	package AnyEvent;	669	package AnyEvent;
433		670
434	no warnings;	671	no warnings;
…		…
449	my @models = (	686	my @models = (
450	[Coro::EV:: => AnyEvent::Impl::CoroEV::],	687	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
451	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],	688	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
452	[EV:: => AnyEvent::Impl::EV::],	689	[EV:: => AnyEvent::Impl::EV::],
453	[Event:: => AnyEvent::Impl::Event::],	690	[Event:: => AnyEvent::Impl::Event::],
454	[Glib:: => AnyEvent::Impl::Glib::],
455	[Tk:: => AnyEvent::Impl::Tk::],	691	[Tk:: => AnyEvent::Impl::Tk::],
456	[Wx:: => AnyEvent::Impl::POE::],	692	[Wx:: => AnyEvent::Impl::POE::],
457	[Prima:: => AnyEvent::Impl::POE::],	693	[Prima:: => AnyEvent::Impl::POE::],
458	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	694	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
459	# 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::],
460	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy	697	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
461	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program	698	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
462	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza	699	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
463	);	700	);
464		701
465	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);	702	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
466		703
467	sub detect() {	704	sub detect() {
468	unless ($MODEL) {	705	unless ($MODEL) {
469	no strict 'refs';	706	no strict 'refs';
470		707
…		…
706		943
707	=back	944	=back
708		945
709	=head1 EXAMPLE PROGRAM	946	=head1 EXAMPLE PROGRAM
710		947
711	The following program uses an IO watcher to read data from STDIN, a timer	948	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	949	to display a message once per second, and a condition variable to quit the
713	program when the user enters quit:	950	program when the user enters quit:
714		951
715	use AnyEvent;	952	use AnyEvent;
716		953
…		…
861	});	1098	});
862		1099
863	$quit->wait;	1100	$quit->wait;
864		1101
865		1102
866	=head1 BENCHMARK	1103	=head1 BENCHMARKS
867		1104
868	To give you an idea of the performance and overheads that AnyEvent adds	1105	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	1106	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	1107	of various event loops I prepared some benchmarks.
871	event models natively and with anyevent. The benchmark creates a lot of	1108
872	timers (with a zero timeout) and io watchers (watching STDOUT, a pty, to	1109	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1110
		1111	Here is a benchmark of various supported event models used natively and
		1112	through anyevent. The benchmark creates a lot of timers (with a zero
		1113	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	1114	which it is), lets them fire exactly once and destroys them again.
874	them again.
875		1115
		1116	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1117	distribution.
		1118
876	=head2 Explanation of the columns	1119	=head3 Explanation of the columns
877		1120
878	I<watcher> is the number of event watchers created/destroyed. Since	1121	I<watcher> is the number of event watchers created/destroyed. Since
879	different event models feature vastly different performances, each event	1122	different event models feature vastly different performances, each event
880	loop was given a number of watchers so that overall runtime is acceptable	1123	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	1124	and similar between tested event loop (and keep them from crashing): Glib
…		…
897	signal the end of this phase.	1140	signal the end of this phase.
898		1141
899	I<destroy> is the time, in microseconds, that it takes to destroy a single	1142	I<destroy> is the time, in microseconds, that it takes to destroy a single
900	watcher.	1143	watcher.
901		1144
902	=head2 Results	1145	=head3 Results
903		1146
904	name watchers bytes create invoke destroy comment	1147	name watchers bytes create invoke destroy comment
905	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1148	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	1149	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	1150	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	1151	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	1152	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	1153	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	1154	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	1155	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	1156	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	1157	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
915		1158
916	=head2 Discussion	1159	=head3 Discussion
917		1160
918	The benchmark does I<not> measure scalability of the event loop very	1161	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)	1162	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	1163	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	1164	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	1165	the same time, so select/poll-based implementations get an unnatural speed
923	to worka round bugs).	1166	boost.
		1167
		1168	Also, note that the number of watchers usually has a nonlinear effect on
		1169	overall speed, that is, creating twice as many watchers doesn't take twice
		1170	the time - usually it takes longer. This puts event loops tested with a
		1171	higher number of watchers at a disadvantage.
		1172
		1173	To put the range of results into perspective, consider that on the
		1174	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1175	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1176	cycles with POE.
924		1177
925	C<EV> is the sole leader regarding speed and memory use, which are both	1178	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	1179	maximal/minimal, respectively. Even when going through AnyEvent, it uses
927	only two event loops that use slightly less memory (the C<Event> module	1180	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	1181	natively.
929	C<Event> natively.
930		1182
931	The pure perl implementation is hit in a few sweet spots (both the	1183	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	1184	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	1185	interpreter and the backend itself). Nevertheless this shows that it
934	adds very little overhead in itself. Like any select-based backend its	1186	adds very little overhead in itself. Like any select-based backend its
935	performance becomes really bad with lots of file descriptors, of course,	1187	performance becomes really bad with lots of file descriptors (and few of
936	but this was not subject of this benchmark.	1188	them active), of course, but this was not subject of this benchmark.
937		1189
938	The C<Event> module has a relatively high setup and callback invocation cost,	1190	The C<Event> module has a relatively high setup and callback invocation
939	but overall scores on the third place.	1191	cost, but overall scores in on the third place.
940		1192
941	C<Glib>'s memory usage is quite a bit bit higher, but it features a	1193	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	1194	faster callback invocation and overall ends up in the same class as
943	C<Event>. However, Glib scales extremely badly, doubling the number of	1195	C<Event>. However, Glib scales extremely badly, doubling the number of
944	watchers increases the processing time by more than a factor of four,	1196	watchers increases the processing time by more than a factor of four,
945	making it completely unusable when using larger numbers of watchers	1197	making it completely unusable when using larger numbers of watchers
946	(note that only a single file descriptor was used in the benchmark, so	1198	(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	1201	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	1202	more than 2000 watchers is a big setback, however, as correctness takes
951	precedence over speed. Nevertheless, its performance is surprising, as the	1203	precedence over speed. Nevertheless, its performance is surprising, as the
952	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()
953	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
954	hidden memory cost inside the kernel, though, that is not reflected in the	1206	hidden memory cost inside the kernel which is not reflected in the figures
955	figures above).	1207	above).
956		1208
957	C<POE>, regardless of underlying event loop (wether using its pure perl	1209	C<POE>, regardless of underlying event loop (whether using its pure perl
958	select-based backend or the Event module) shows abysmal performance and	1210	select-based backend or the Event module, the POE-EV backend couldn't
		1211	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,	1212	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	1213	as EV watchers, and 10 times as much memory as Event (the high memory
		1214	requirements are caused by requiring a session for each watcher). Watcher
961	invocation is almost 700 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
962	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
963	really account for this, as session creation overhead is small compared	1219	for the performance issues, though, as session creation overhead is
964	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
965	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).
966		1225
967	=head2 Summary	1226	=head3 Summary
968		1227
		1228	=over 4
		1229
969	Using EV through AnyEvent is faster than any other event loop, but most	1230	=item * Using EV through AnyEvent is faster than any other event loop
970	event loops have acceptable performance with or without AnyEvent.	1231	(even when used without AnyEvent), but most event loops have acceptable
		1232	performance with or without AnyEvent.
971		1233
972	The overhead AnyEvent adds is usually much smaller than the overhead of	1234	=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	1235	the actual event loop, only with extremely fast event loops such as EV
974	adds AnyEvent significant overhead.	1236	adds AnyEvent significant overhead.
975		1237
976	And you should simply avoid POE like the plague if you want performance or	1238	=item * You should avoid POE like the plague if you want performance or
977	reasonable memory usage.	1239	reasonable memory usage.
978		1240
		1241	=back
		1242
		1243	=head2 BENCHMARKING THE LARGE SERVER CASE
		1244
		1245	This benchmark atcually benchmarks the event loop itself. It works by
		1246	creating a number of "servers": each server consists of a socketpair, a
		1247	timeout watcher that gets reset on activity (but never fires), and an I/O
		1248	watcher waiting for input on one side of the socket. Each time the socket
		1249	watcher reads a byte it will write that byte to a random other "server".
		1250
		1251	The effect is that there will be a lot of I/O watchers, only part of which
		1252	are active at any one point (so there is a constant number of active
		1253	fds for each loop iterstaion, but which fds these are is random). The
		1254	timeout is reset each time something is read because that reflects how
		1255	most timeouts work (and puts extra pressure on the event loops).
		1256
		1257	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1258	(1%) are active. This mirrors the activity of large servers with many
		1259	connections, most of which are idle at any one point in time.
		1260
		1261	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1262	distribution.
		1263
		1264	=head3 Explanation of the columns
		1265
		1266	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1267	each server has a read and write socket end).
		1268
		1269	I<create> is the time it takes to create a socketpair (which is
		1270	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1271
		1272	I<request>, the most important value, is the time it takes to handle a
		1273	single "request", that is, reading the token from the pipe and forwarding
		1274	it to another server. This includes deleting the old timeout and creating
		1275	a new one that moves the timeout into the future.
		1276
		1277	=head3 Results
		1278
		1279	name sockets create request
		1280	EV 20000 69.01 11.16
		1281	Perl 20000 73.32 35.87
		1282	Event 20000 212.62 257.32
		1283	Glib 20000 651.16 1896.30
		1284	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1285
		1286	=head3 Discussion
		1287
		1288	This benchmark I<does> measure scalability and overall performance of the
		1289	particular event loop.
		1290
		1291	EV is again fastest. Since it is using epoll on my system, the setup time
		1292	is relatively high, though.
		1293
		1294	Perl surprisingly comes second. It is much faster than the C-based event
		1295	loops Event and Glib.
		1296
		1297	Event suffers from high setup time as well (look at its code and you will
		1298	understand why). Callback invocation also has a high overhead compared to
		1299	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1300	uses select or poll in basically all documented configurations.
		1301
		1302	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1303	clearly fails to perform with many filehandles or in busy servers.
		1304
		1305	POE is still completely out of the picture, taking over 1000 times as long
		1306	as EV, and over 100 times as long as the Perl implementation, even though
		1307	it uses a C-based event loop in this case.
		1308
		1309	=head3 Summary
		1310
		1311	=over 4
		1312
		1313	=item * The pure perl implementation performs extremely well.
		1314
		1315	=item * Avoid Glib or POE in large projects where performance matters.
		1316
		1317	=back
		1318
		1319	=head2 BENCHMARKING SMALL SERVERS
		1320
		1321	While event loops should scale (and select-based ones do not...) even to
		1322	large servers, most programs we (or I :) actually write have only a few
		1323	I/O watchers.
		1324
		1325	In this benchmark, I use the same benchmark program as in the large server
		1326	case, but it uses only eight "servers", of which three are active at any
		1327	one time. This should reflect performance for a small server relatively
		1328	well.
		1329
		1330	The columns are identical to the previous table.
		1331
		1332	=head3 Results
		1333
		1334	name sockets create request
		1335	EV 16 20.00 6.54
		1336	Perl 16 25.75 12.62
		1337	Event 16 81.27 35.86
		1338	Glib 16 32.63 15.48
		1339	POE 16 261.87 276.28 uses POE::Loop::Event
		1340
		1341	=head3 Discussion
		1342
		1343	The benchmark tries to test the performance of a typical small
		1344	server. While knowing how various event loops perform is interesting, keep
		1345	in mind that their overhead in this case is usually not as important, due
		1346	to the small absolute number of watchers (that is, you need efficiency and
		1347	speed most when you have lots of watchers, not when you only have a few of
		1348	them).
		1349
		1350	EV is again fastest.
		1351
		1352	Perl again comes second. It is noticably faster than the C-based event
		1353	loops Event and Glib, although the difference is too small to really
		1354	matter.
		1355
		1356	POE also performs much better in this case, but is is still far behind the
		1357	others.
		1358
		1359	=head3 Summary
		1360
		1361	=over 4
		1362
		1363	=item * C-based event loops perform very well with small number of
		1364	watchers, as the management overhead dominates.
		1365
		1366	=back
		1367
979		1368
980	=head1 FORK	1369	=head1 FORK
981		1370
982	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
983	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.
984		1374
985	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
986	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.
987		1377
988		1378

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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 1.106 by root, Thu May 1 13:45:22 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 1.106 by root, Thu May 1 13:45:22 2008 UTC