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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.60 by root, Fri Apr 25 01:05:26 2008 UTC vs.
Revision 1.125 by root, Fri May 23 23:37:13 2008 UTC

…		…
1	=head1 NAME	1	=head1 => NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
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->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	21	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # 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?
…		…
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
…		…
78		77
79	The interface itself is vaguely similar, but not identical to the L<Event>	78	The interface itself is vaguely similar, but not identical to the L<Event>
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	82	to detect the currently loaded event loop by probing whether one of the
84	the following modules is already loaded: L<Coro::EV>, L<Coro::Event>,	83	following modules is already loaded: L<EV>,
85	L<EV>, L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>. The first one	84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	found is used. If none are found, the module tries to load these modules	85	L<POE>. The first one found is used. If none are found, the module tries
87	(excluding Event::Lib and Qt) in the order given. The first one that can	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		87	adaptor should always succeed) in the order given. The first one that can
88	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
89	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
90	very efficient, but should work everywhere.	90	very efficient, but should work everywhere.
91		91
92	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
…		…
135		135
136	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,
137	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
138	declared.	138	declared.
139		139
140	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
141		141
142	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
143	with the following mandatory key-value pairs as arguments:	143	with the following mandatory key-value pairs as arguments:
144		144
145	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
146	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>,
147	creates a watcher waiting for "r"eadable or "w"ritable events,	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
148	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
149	becomes ready.	149	becomes ready.
150		150
151	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
152	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.
153		154
		155	The I/O watcher might use the underlying file descriptor or a copy of it.
154	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
155	on the underlying file descriptor.	157	underlying file descriptor.
156		158
157	Some event loops issue spurious readyness notifications, so you should	159	Some event loops issue spurious readyness notifications, so you should
158	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
159	handles.	161	handles.
160		162
…		…
171		173
172	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 >>
173	method with the following mandatory arguments:	175	method with the following mandatory arguments:
174		176
175	C<after> specifies after how many seconds (fractional values are	177	C<after> specifies after how many seconds (fractional values are
176	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
177	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.
178		184
179	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
180	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
181	and Glib).	187	and Glib).
182		188
…		…
227		233
228	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
229	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
230	be invoked whenever a signal occurs.	236	be invoked whenever a signal occurs.
231		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
232	Multiple signal occurances can be clumped together into one callback	242	Multiple signal occurances can be clumped together into one callback
233	invocation, and callback invocation will be synchronous. synchronous means	243	invocation, and callback invocation will be synchronous. synchronous means
234	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,
235	but it is guarenteed not to interrupt any other callbacks.	245	but it is guarenteed not to interrupt any other callbacks.
236		246
…		…
250		260
251	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
252	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
253	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
254	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
255	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.
256		267
257	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	my $pid = fork or exit 5;
258		285
259	my $w = AnyEvent->child (	286	my $w = AnyEvent->child (
260	pid => 1333,	287	pid => $pid,
261	cb => sub {	288	cb => sub {
262	my ($pid, $status) = @_;	289	my ($pid, $status) = @_;
263	warn "pid $pid exited with status $status";	290	warn "pid $pid exited with status $status";
		291	$done->send;
264	},	292	},
265	);	293	);
266		294
		295	# do something else, then wait for process exit
		296	$done->recv;
		297
267	=head2 CONDITION VARIABLES	298	=head2 CONDITION VARIABLES
268		299
		300	If you are familiar with some event loops you will know that all of them
		301	require you to run some blocking "loop", "run" or similar function that
		302	will actively watch for new events and call your callbacks.
		303
		304	AnyEvent is different, it expects somebody else to run the event loop and
		305	will only block when necessary (usually when told by the user).
		306
		307	The instrument to do that is called a "condition variable", so called
		308	because they represent a condition that must become true.
		309
269	Condition variables can be created by calling the C<< AnyEvent->condvar >>	310	Condition variables can be created by calling the C<< AnyEvent->condvar
270	method without any arguments.	311	>> method, usually without arguments. The only argument pair allowed is
		312	C<cb>, which specifies a callback to be called when the condition variable
		313	becomes true.
271		314
272	A condition variable waits for a condition - precisely that the C<<	315	After creation, the conditon variable is "false" until it becomes "true"
273	->broadcast >> method has been called.	316	by calling the C<send> method.
274		317
275	They are very useful to signal that a condition has been fulfilled, for	318	Condition variables are similar to callbacks, except that you can
		319	optionally wait for them. They can also be called merge points - points
		320	in time where multiple outstandign events have been processed. And yet
		321	another way to call them is transations - each condition variable can be
		322	used to represent a transaction, which finishes at some point and delivers
		323	a result.
		324
		325	Condition variables are very useful to signal that something has finished,
276	example, if you write a module that does asynchronous http requests,	326	for example, if you write a module that does asynchronous http requests,
277	then a condition variable would be the ideal candidate to signal the	327	then a condition variable would be the ideal candidate to signal the
278	availability of results.	328	availability of results. The user can either act when the callback is
		329	called or can synchronously C<< ->recv >> for the results.
279		330
280	You can also use condition variables to block your main program until	331	You can also use them to simulate traditional event loops - for example,
281	an event occurs - for example, you could C<< ->wait >> in your main	332	you can block your main program until an event occurs - for example, you
282	program until the user clicks the Quit button in your app, which would C<<	333	could C<< ->recv >> in your main program until the user clicks the Quit
283	->broadcast >> the "quit" event.	334	button of your app, which would C<< ->send >> the "quit" event.
284		335
285	Note that condition variables recurse into the event loop - if you have	336	Note that condition variables recurse into the event loop - if you have
286	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	337	two pieces of code that call C<< ->recv >> in a round-robbin fashion, you
287	lose. Therefore, condition variables are good to export to your caller, but	338	lose. Therefore, condition variables are good to export to your caller, but
288	you should avoid making a blocking wait yourself, at least in callbacks,	339	you should avoid making a blocking wait yourself, at least in callbacks,
289	as this asks for trouble.	340	as this asks for trouble.
290		341
291	This object has two methods:	342	Condition variables are represented by hash refs in perl, and the keys
		343	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		344	easy (it is often useful to build your own transaction class on top of
		345	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		346	it's C<new> method in your own C<new> method.
		347
		348	There are two "sides" to a condition variable - the "producer side" which
		349	eventually calls C<< -> send >>, and the "consumer side", which waits
		350	for the send to occur.
		351
		352	Example:
		353
		354	# wait till the result is ready
		355	my $result_ready = AnyEvent->condvar;
		356
		357	# do something such as adding a timer
		358	# or socket watcher the calls $result_ready->send
		359	# when the "result" is ready.
		360	# in this case, we simply use a timer:
		361	my $w = AnyEvent->timer (
		362	after => 1,
		363	cb => sub { $result_ready->send },
		364	);
		365
		366	# this "blocks" (while handling events) till the callback
		367	# calls send
		368	$result_ready->recv;
		369
		370	=head3 METHODS FOR PRODUCERS
		371
		372	These methods should only be used by the producing side, i.e. the
		373	code/module that eventually sends the signal. Note that it is also
		374	the producer side which creates the condvar in most cases, but it isn't
		375	uncommon for the consumer to create it as well.
292		376
293	=over 4	377	=over 4
294		378
		379	=item $cv->send (...)
		380
		381	Flag the condition as ready - a running C<< ->recv >> and all further
		382	calls to C<recv> will (eventually) return after this method has been
		383	called. If nobody is waiting the send will be remembered.
		384
		385	If a callback has been set on the condition variable, it is called
		386	immediately from within send.
		387
		388	Any arguments passed to the C<send> call will be returned by all
		389	future C<< ->recv >> calls.
		390
		391	=item $cv->croak ($error)
		392
		393	Similar to send, but causes all call's to C<< ->recv >> to invoke
		394	C<Carp::croak> with the given error message/object/scalar.
		395
		396	This can be used to signal any errors to the condition variable
		397	user/consumer.
		398
		399	=item $cv->begin ([group callback])
		400
295	=item $cv->wait	401	=item $cv->end
296		402
297	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	403	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		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
		459	=item $cv->recv
		460
		461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
298	called on c<$cv>, while servicing other watchers normally.	462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
299		464
300	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
301	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.
302		473
303	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
304	(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
305	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
306	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
307	condition variables with some kind of request results and supporting	478	condition variables with some kind of request results and supporting
308	callbacks so the caller knows that getting the result will not block,	479	callbacks so the caller knows that getting the result will not block,
309	while still suppporting blocking waits if the caller so desires).	480	while still suppporting blocking waits if the caller so desires).
310		481
311	Another reason I<never> to C<< ->wait >> in a module is that you cannot	482	Another reason I<never> to C<< ->recv >> in a module is that you cannot
312	sensibly have two C<< ->wait >>'s in parallel, as that would require	483	sensibly have two C<< ->recv >>'s in parallel, as that would require
313	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
314	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	485	can supply.
315	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
316	from different coroutines, however).
317		486
318	=item $cv->broadcast	487	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		488	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		489	versions and also integrates coroutines into AnyEvent, making blocking
		490	C<< ->recv >> calls perfectly safe as long as they are done from another
		491	coroutine (one that doesn't run the event loop).
319		492
320	Flag the condition as ready - a running C<< ->wait >> and all further	493	You can ensure that C<< -recv >> never blocks by setting a callback and
321	calls to C<wait> will (eventually) return after this method has been	494	only calling C<< ->recv >> from within that callback (or at a later
322	called. If nobody is waiting the broadcast will be remembered..	495	time). This will work even when the event loop does not support blocking
		496	waits otherwise.
		497
		498	=item $bool = $cv->ready
		499
		500	Returns true when the condition is "true", i.e. whether C<send> or
		501	C<croak> have been called.
		502
		503	=item $cb = $cv->cb ([new callback])
		504
		505	This is a mutator function that returns the callback set and optionally
		506	replaces it before doing so.
		507
		508	The callback will be called when the condition becomes "true", i.e. when
		509	C<send> or C<croak> are called. Calling C<recv> inside the callback
		510	or at any later time is guaranteed not to block.
323		511
324	=back	512	=back
325
326	Example:
327
328	# wait till the result is ready
329	my $result_ready = AnyEvent->condvar;
330
331	# do something such as adding a timer
332	# or socket watcher the calls $result_ready->broadcast
333	# when the "result" is ready.
334	# in this case, we simply use a timer:
335	my $w = AnyEvent->timer (
336	after => 1,
337	cb => sub { $result_ready->broadcast },
338	);
339
340	# this "blocks" (while handling events) till the watcher
341	# calls broadcast
342	$result_ready->wait;
343		513
344	=head1 GLOBAL VARIABLES AND FUNCTIONS	514	=head1 GLOBAL VARIABLES AND FUNCTIONS
345		515
346	=over 4	516	=over 4
347		517
…		…
353	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	523	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
354	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	524	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
355		525
356	The known classes so far are:	526	The known classes so far are:
357		527
358	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
359	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
360	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	528	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
361	AnyEvent::Impl::Event based on Event, second best choice.	529	AnyEvent::Impl::Event based on Event, second best choice.
		530	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
362	AnyEvent::Impl::Glib based on Glib, third-best choice.	531	AnyEvent::Impl::Glib based on Glib, third-best choice.
363	AnyEvent::Impl::Tk based on Tk, very bad choice.	532	AnyEvent::Impl::Tk based on Tk, very bad choice.
364	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
365	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	533	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
366	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	534	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		535	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		536
		537	There is no support for WxWidgets, as WxWidgets has no support for
		538	watching file handles. However, you can use WxWidgets through the
		539	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		540	second, which was considered to be too horrible to even consider for
		541	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		542	it's adaptor.
		543
		544	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		545	autodetecting them.
367		546
368	=item AnyEvent::detect	547	=item AnyEvent::detect
369		548
370	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	549	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
371	if necessary. You should only call this function right before you would	550	if necessary. You should only call this function right before you would
372	have created an AnyEvent watcher anyway, that is, as late as possible at	551	have created an AnyEvent watcher anyway, that is, as late as possible at
373	runtime.	552	runtime.
374		553
		554	=item $guard = AnyEvent::post_detect { BLOCK }
		555
		556	Arranges for the code block to be executed as soon as the event model is
		557	autodetected (or immediately if this has already happened).
		558
		559	If called in scalar or list context, then it creates and returns an object
		560	that automatically removes the callback again when it is destroyed. See
		561	L<Coro::BDB> for a case where this is useful.
		562
		563	=item @AnyEvent::post_detect
		564
		565	If there are any code references in this array (you can C<push> to it
		566	before or after loading AnyEvent), then they will called directly after
		567	the event loop has been chosen.
		568
		569	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		570	if it contains a true value then the event loop has already been detected,
		571	and the array will be ignored.
		572
		573	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		574
375	=back	575	=back
376		576
377	=head1 WHAT TO DO IN A MODULE	577	=head1 WHAT TO DO IN A MODULE
378		578
379	As a module author, you should C<use AnyEvent> and call AnyEvent methods	579	As a module author, you should C<use AnyEvent> and call AnyEvent methods
…		…
382	Be careful when you create watchers in the module body - AnyEvent will	582	Be careful when you create watchers in the module body - AnyEvent will
383	decide which event module to use as soon as the first method is called, so	583	decide which event module to use as soon as the first method is called, so
384	by calling AnyEvent in your module body you force the user of your module	584	by calling AnyEvent in your module body you force the user of your module
385	to load the event module first.	585	to load the event module first.
386		586
387	Never call C<< ->wait >> on a condition variable unless you I<know> that	587	Never call C<< ->recv >> on a condition variable unless you I<know> that
388	the C<< ->broadcast >> method has been called on it already. This is	588	the C<< ->send >> method has been called on it already. This is
389	because it will stall the whole program, and the whole point of using	589	because it will stall the whole program, and the whole point of using
390	events is to stay interactive.	590	events is to stay interactive.
391		591
392	It is fine, however, to call C<< ->wait >> when the user of your module	592	It is fine, however, to call C<< ->recv >> when the user of your module
393	requests it (i.e. if you create a http request object ad have a method	593	requests it (i.e. if you create a http request object ad have a method
394	called C<results> that returns the results, it should call C<< ->wait >>	594	called C<results> that returns the results, it should call C<< ->recv >>
395	freely, as the user of your module knows what she is doing. always).	595	freely, as the user of your module knows what she is doing. always).
396		596
397	=head1 WHAT TO DO IN THE MAIN PROGRAM	597	=head1 WHAT TO DO IN THE MAIN PROGRAM
398		598
399	There will always be a single main program - the only place that should	599	There will always be a single main program - the only place that should
…		…
413		613
414	You can chose to use a rather inefficient pure-perl implementation by	614	You can chose to use a rather inefficient pure-perl implementation by
415	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	615	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
416	behaviour everywhere, but letting AnyEvent chose is generally better.	616	behaviour everywhere, but letting AnyEvent chose is generally better.
417		617
		618	=head1 OTHER MODULES
		619
		620	The following is a non-exhaustive list of additional modules that use
		621	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		622	in the same program. Some of the modules come with AnyEvent, some are
		623	available via CPAN.
		624
		625	=over 4
		626
		627	=item L<AnyEvent::Util>
		628
		629	Contains various utility functions that replace often-used but blocking
		630	functions such as C<inet_aton> by event-/callback-based versions.
		631
		632	=item L<AnyEvent::Handle>
		633
		634	Provide read and write buffers and manages watchers for reads and writes.
		635
		636	=item L<AnyEvent::Socket>
		637
		638	Provides various utility functions for (internet protocol) sockets,
		639	addresses and name resolution. Also functions to create non-blocking tcp
		640	connections or tcp servers, with IPv6 and SRV record support and more.
		641
		642	=item L<AnyEvent::HTTPD>
		643
		644	Provides a simple web application server framework.
		645
		646	=item L<AnyEvent::DNS>
		647
		648	Provides rich asynchronous DNS resolver capabilities.
		649
		650	=item L<AnyEvent::FastPing>
		651
		652	The fastest ping in the west.
		653
		654	=item L<Net::IRC3>
		655
		656	AnyEvent based IRC client module family.
		657
		658	=item L<Net::XMPP2>
		659
		660	AnyEvent based XMPP (Jabber protocol) module family.
		661
		662	=item L<Net::FCP>
		663
		664	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		665	of AnyEvent.
		666
		667	=item L<Event::ExecFlow>
		668
		669	High level API for event-based execution flow control.
		670
		671	=item L<Coro>
		672
		673	Has special support for AnyEvent via L<Coro::AnyEvent>.
		674
		675	=item L<AnyEvent::AIO>, L<IO::AIO>
		676
		677	Truly asynchronous I/O, should be in the toolbox of every event
		678	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		679	together.
		680
		681	=item L<AnyEvent::BDB>, L<BDB>
		682
		683	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		684	IO::AIO and AnyEvent together.
		685
		686	=item L<IO::Lambda>
		687
		688	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		689
		690	=back
		691
418	=cut	692	=cut
419		693
420	package AnyEvent;	694	package AnyEvent;
421		695
422	no warnings;	696	no warnings;
423	use strict;	697	use strict;
424		698
425	use Carp;	699	use Carp;
426		700
427	our $VERSION = '3.2';	701	our $VERSION = '3.6';
428	our $MODEL;	702	our $MODEL;
429		703
430	our $AUTOLOAD;	704	our $AUTOLOAD;
431	our @ISA;	705	our @ISA;
432		706
433	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	707	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
434		708
435	our @REGISTRY;	709	our @REGISTRY;
436		710
437	my @models = (	711	my @models = (
438	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
439	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
440	[EV:: => AnyEvent::Impl::EV::],	712	[EV:: => AnyEvent::Impl::EV::],
441	[Event:: => AnyEvent::Impl::Event::],	713	[Event:: => AnyEvent::Impl::Event::],
		714	[Tk:: => AnyEvent::Impl::Tk::],
		715	[Wx:: => AnyEvent::Impl::POE::],
		716	[Prima:: => AnyEvent::Impl::POE::],
		717	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		718	# everything below here will not be autoprobed as the pureperl backend should work everywhere
442	[Glib:: => AnyEvent::Impl::Glib::],	719	[Glib:: => AnyEvent::Impl::Glib::],
443	[Tk:: => AnyEvent::Impl::Tk::],	720	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
444	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	721	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		722	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
445	);	723	);
446	my @models_detect = (
447	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
448	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
449	);
450		724
451	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);	725	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		726
		727	our @post_detect;
		728
		729	sub post_detect(&) {
		730	my ($cb) = @_;
		731
		732	if ($MODEL) {
		733	$cb->();
		734
		735	1
		736	} else {
		737	push @post_detect, $cb;
		738
		739	defined wantarray
		740	? bless \$cb, "AnyEvent::Util::PostDetect"
		741	: ()
		742	}
		743	}
		744
		745	sub AnyEvent::Util::PostDetect::DESTROY {
		746	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		747	}
452		748
453	sub detect() {	749	sub detect() {
454	unless ($MODEL) {	750	unless ($MODEL) {
455	no strict 'refs';	751	no strict 'refs';
456		752
…		…
464	}	760	}
465	}	761	}
466		762
467	# check for already loaded models	763	# check for already loaded models
468	unless ($MODEL) {	764	unless ($MODEL) {
469	for (@REGISTRY, @models, @models_detect) {	765	for (@REGISTRY, @models) {
470	my ($package, $model) = @$_;	766	my ($package, $model) = @$_;
471	if (${"$package\::VERSION"} > 0) {	767	if (${"$package\::VERSION"} > 0) {
472	if (eval "require $model") {	768	if (eval "require $model") {
473	$MODEL = $model;	769	$MODEL = $model;
474	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;	770	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
…		…
490	last;	786	last;
491	}	787	}
492	}	788	}
493		789
494	$MODEL	790	$MODEL
495	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";	791	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
496	}	792	}
497	}	793	}
498		794
499	unshift @ISA, $MODEL;	795	unshift @ISA, $MODEL;
500	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	796	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		797
		798	(shift @post_detect)->() while @post_detect;
501	}	799	}
502		800
503	$MODEL	801	$MODEL
504	}	802	}
505		803
…		…
515	$class->$func (@_);	813	$class->$func (@_);
516	}	814	}
517		815
518	package AnyEvent::Base;	816	package AnyEvent::Base;
519		817
520	# default implementation for ->condvar, ->wait, ->broadcast	818	# default implementation for ->condvar
521		819
522	sub condvar {	820	sub condvar {
523	bless \my $flag, "AnyEvent::Base::CondVar"	821	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
524	}
525
526	sub AnyEvent::Base::CondVar::broadcast {
527	${$_[0]}++;
528	}
529
530	sub AnyEvent::Base::CondVar::wait {
531	AnyEvent->one_event while !${$_[0]};
532	}	822	}
533		823
534	# default implementation for ->signal	824	# default implementation for ->signal
535		825
536	our %SIG_CB;	826	our %SIG_CB;
…		…
610	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	900	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
611		901
612	undef $CHLD_W unless keys %PID_CB;	902	undef $CHLD_W unless keys %PID_CB;
613	}	903	}
614		904
		905	package AnyEvent::CondVar;
		906
		907	our @ISA = AnyEvent::CondVar::Base::;
		908
		909	package AnyEvent::CondVar::Base;
		910
		911	sub _send {
		912	# nop
		913	}
		914
		915	sub send {
		916	my $cv = shift;
		917	$cv->{_ae_sent} = [@_];
		918	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		919	$cv->_send;
		920	}
		921
		922	sub croak {
		923	$_[0]{_ae_croak} = $_[1];
		924	$_[0]->send;
		925	}
		926
		927	sub ready {
		928	$_[0]{_ae_sent}
		929	}
		930
		931	sub _wait {
		932	AnyEvent->one_event while !$_[0]{_ae_sent};
		933	}
		934
		935	sub recv {
		936	$_[0]->_wait;
		937
		938	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		939	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		940	}
		941
		942	sub cb {
		943	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		944	$_[0]{_ae_cb}
		945	}
		946
		947	sub begin {
		948	++$_[0]{_ae_counter};
		949	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		950	}
		951
		952	sub end {
		953	return if --$_[0]{_ae_counter};
		954	&{ $_[0]{_ae_end_cb} \|\| sub { $_[0]->send } };
		955	}
		956
		957	# undocumented/compatibility with pre-3.4
		958	*broadcast = \&send;
		959	*wait = \&_wait;
		960
615	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	961	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
616		962
617	This is an advanced topic that you do not normally need to use AnyEvent in	963	This is an advanced topic that you do not normally need to use AnyEvent in
618	a module. This section is only of use to event loop authors who want to	964	a module. This section is only of use to event loop authors who want to
619	provide AnyEvent compatibility.	965	provide AnyEvent compatibility.
…		…
688	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you	1034	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
689	could start your program like this:	1035	could start your program like this:
690		1036
691	PERL_ANYEVENT_MODEL=Perl perl ...	1037	PERL_ANYEVENT_MODEL=Perl perl ...
692		1038
		1039	=item C<PERL_ANYEVENT_PROTOCOLS>
		1040
		1041	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1042	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1043	of autoprobing).
		1044
		1045	Must be set to a comma-separated list of protocols or address families,
		1046	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1047	used, and preference will be given to protocols mentioned earlier in the
		1048	list.
		1049
		1050	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1051	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1052	- only support IPv4, never try to resolve or contact IPv6
		1053	addressses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1054	IPv6, but prefer IPv6 over IPv4.
		1055
693	=back	1056	=back
694		1057
695	=head1 EXAMPLE PROGRAM	1058	=head1 EXAMPLE PROGRAM
696		1059
697	The following program uses an IO watcher to read data from STDIN, a timer	1060	The following program uses an I/O watcher to read data from STDIN, a timer
698	to display a message once per second, and a condition variable to quit the	1061	to display a message once per second, and a condition variable to quit the
699	program when the user enters quit:	1062	program when the user enters quit:
700		1063
701	use AnyEvent;	1064	use AnyEvent;
702		1065
…		…
707	poll => 'r',	1070	poll => 'r',
708	cb => sub {	1071	cb => sub {
709	warn "io event <$_[0]>\n"; # will always output <r>	1072	warn "io event <$_[0]>\n"; # will always output <r>
710	chomp (my $input = <STDIN>); # read a line	1073	chomp (my $input = <STDIN>); # read a line
711	warn "read: $input\n"; # output what has been read	1074	warn "read: $input\n"; # output what has been read
712	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1075	$cv->send if $input =~ /^q/i; # quit program if /^q/i
713	},	1076	},
714	);	1077	);
715		1078
716	my $time_watcher; # can only be used once	1079	my $time_watcher; # can only be used once
717		1080
…		…
722	});	1085	});
723	}	1086	}
724		1087
725	new_timer; # create first timer	1088	new_timer; # create first timer
726		1089
727	$cv->wait; # wait until user enters /^q/i	1090	$cv->recv; # wait until user enters /^q/i
728		1091
729	=head1 REAL-WORLD EXAMPLE	1092	=head1 REAL-WORLD EXAMPLE
730		1093
731	Consider the L<Net::FCP> module. It features (among others) the following	1094	Consider the L<Net::FCP> module. It features (among others) the following
732	API calls, which are to freenet what HTTP GET requests are to http:	1095	API calls, which are to freenet what HTTP GET requests are to http:
…		…
788		1151
789	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1152	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
790		1153
791	if (end-of-file or data complete) {	1154	if (end-of-file or data complete) {
792	$txn->{result} = $txn->{buf};	1155	$txn->{result} = $txn->{buf};
793	$txn->{finished}->broadcast;	1156	$txn->{finished}->send;
794	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1157	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
795	}	1158	}
796		1159
797	The C<result> method, finally, just waits for the finished signal (if the	1160	The C<result> method, finally, just waits for the finished signal (if the
798	request was already finished, it doesn't wait, of course, and returns the	1161	request was already finished, it doesn't wait, of course, and returns the
799	data:	1162	data:
800		1163
801	$txn->{finished}->wait;	1164	$txn->{finished}->recv;
802	return $txn->{result};	1165	return $txn->{result};
803		1166
804	The actual code goes further and collects all errors (C<die>s, exceptions)	1167	The actual code goes further and collects all errors (C<die>s, exceptions)
805	that occured during request processing. The C<result> method detects	1168	that occured during request processing. The C<result> method detects
806	whether an exception as thrown (it is stored inside the $txn object)	1169	whether an exception as thrown (it is stored inside the $txn object)
…		…
841		1204
842	my $quit = AnyEvent->condvar;	1205	my $quit = AnyEvent->condvar;
843		1206
844	$fcp->txn_client_get ($url)->cb (sub {	1207	$fcp->txn_client_get ($url)->cb (sub {
845	...	1208	...
846	$quit->broadcast;	1209	$quit->send;
847	});	1210	});
848		1211
849	$quit->wait;	1212	$quit->recv;
		1213
		1214
		1215	=head1 BENCHMARKS
		1216
		1217	To give you an idea of the performance and overheads that AnyEvent adds
		1218	over the event loops themselves and to give you an impression of the speed
		1219	of various event loops I prepared some benchmarks.
		1220
		1221	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1222
		1223	Here is a benchmark of various supported event models used natively and
		1224	through anyevent. The benchmark creates a lot of timers (with a zero
		1225	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1226	which it is), lets them fire exactly once and destroys them again.
		1227
		1228	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1229	distribution.
		1230
		1231	=head3 Explanation of the columns
		1232
		1233	I<watcher> is the number of event watchers created/destroyed. Since
		1234	different event models feature vastly different performances, each event
		1235	loop was given a number of watchers so that overall runtime is acceptable
		1236	and similar between tested event loop (and keep them from crashing): Glib
		1237	would probably take thousands of years if asked to process the same number
		1238	of watchers as EV in this benchmark.
		1239
		1240	I<bytes> is the number of bytes (as measured by the resident set size,
		1241	RSS) consumed by each watcher. This method of measuring captures both C
		1242	and Perl-based overheads.
		1243
		1244	I<create> is the time, in microseconds (millionths of seconds), that it
		1245	takes to create a single watcher. The callback is a closure shared between
		1246	all watchers, to avoid adding memory overhead. That means closure creation
		1247	and memory usage is not included in the figures.
		1248
		1249	I<invoke> is the time, in microseconds, used to invoke a simple
		1250	callback. The callback simply counts down a Perl variable and after it was
		1251	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1252	signal the end of this phase.
		1253
		1254	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1255	watcher.
		1256
		1257	=head3 Results
		1258
		1259	name watchers bytes create invoke destroy comment
		1260	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1261	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1262	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1263	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1264	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1265	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1266	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1267	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1268	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1269	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1270
		1271	=head3 Discussion
		1272
		1273	The benchmark does I<not> measure scalability of the event loop very
		1274	well. For example, a select-based event loop (such as the pure perl one)
		1275	can never compete with an event loop that uses epoll when the number of
		1276	file descriptors grows high. In this benchmark, all events become ready at
		1277	the same time, so select/poll-based implementations get an unnatural speed
		1278	boost.
		1279
		1280	Also, note that the number of watchers usually has a nonlinear effect on
		1281	overall speed, that is, creating twice as many watchers doesn't take twice
		1282	the time - usually it takes longer. This puts event loops tested with a
		1283	higher number of watchers at a disadvantage.
		1284
		1285	To put the range of results into perspective, consider that on the
		1286	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1287	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1288	cycles with POE.
		1289
		1290	C<EV> is the sole leader regarding speed and memory use, which are both
		1291	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1292	far less memory than any other event loop and is still faster than Event
		1293	natively.
		1294
		1295	The pure perl implementation is hit in a few sweet spots (both the
		1296	constant timeout and the use of a single fd hit optimisations in the perl
		1297	interpreter and the backend itself). Nevertheless this shows that it
		1298	adds very little overhead in itself. Like any select-based backend its
		1299	performance becomes really bad with lots of file descriptors (and few of
		1300	them active), of course, but this was not subject of this benchmark.
		1301
		1302	The C<Event> module has a relatively high setup and callback invocation
		1303	cost, but overall scores in on the third place.
		1304
		1305	C<Glib>'s memory usage is quite a bit higher, but it features a
		1306	faster callback invocation and overall ends up in the same class as
		1307	C<Event>. However, Glib scales extremely badly, doubling the number of
		1308	watchers increases the processing time by more than a factor of four,
		1309	making it completely unusable when using larger numbers of watchers
		1310	(note that only a single file descriptor was used in the benchmark, so
		1311	inefficiencies of C<poll> do not account for this).
		1312
		1313	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1314	more than 2000 watchers is a big setback, however, as correctness takes
		1315	precedence over speed. Nevertheless, its performance is surprising, as the
		1316	file descriptor is dup()ed for each watcher. This shows that the dup()
		1317	employed by some adaptors is not a big performance issue (it does incur a
		1318	hidden memory cost inside the kernel which is not reflected in the figures
		1319	above).
		1320
		1321	C<POE>, regardless of underlying event loop (whether using its pure perl
		1322	select-based backend or the Event module, the POE-EV backend couldn't
		1323	be tested because it wasn't working) shows abysmal performance and
		1324	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1325	as EV watchers, and 10 times as much memory as Event (the high memory
		1326	requirements are caused by requiring a session for each watcher). Watcher
		1327	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1328	implementation.
		1329
		1330	The design of the POE adaptor class in AnyEvent can not really account
		1331	for the performance issues, though, as session creation overhead is
		1332	small compared to execution of the state machine, which is coded pretty
		1333	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1334	using multiple sessions is not a good approach, especially regarding
		1335	memory usage, even the author of POE could not come up with a faster
		1336	design).
		1337
		1338	=head3 Summary
		1339
		1340	=over 4
		1341
		1342	=item * Using EV through AnyEvent is faster than any other event loop
		1343	(even when used without AnyEvent), but most event loops have acceptable
		1344	performance with or without AnyEvent.
		1345
		1346	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1347	the actual event loop, only with extremely fast event loops such as EV
		1348	adds AnyEvent significant overhead.
		1349
		1350	=item * You should avoid POE like the plague if you want performance or
		1351	reasonable memory usage.
		1352
		1353	=back
		1354
		1355	=head2 BENCHMARKING THE LARGE SERVER CASE
		1356
		1357	This benchmark atcually benchmarks the event loop itself. It works by
		1358	creating a number of "servers": each server consists of a socketpair, a
		1359	timeout watcher that gets reset on activity (but never fires), and an I/O
		1360	watcher waiting for input on one side of the socket. Each time the socket
		1361	watcher reads a byte it will write that byte to a random other "server".
		1362
		1363	The effect is that there will be a lot of I/O watchers, only part of which
		1364	are active at any one point (so there is a constant number of active
		1365	fds for each loop iterstaion, but which fds these are is random). The
		1366	timeout is reset each time something is read because that reflects how
		1367	most timeouts work (and puts extra pressure on the event loops).
		1368
		1369	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1370	(1%) are active. This mirrors the activity of large servers with many
		1371	connections, most of which are idle at any one point in time.
		1372
		1373	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1374	distribution.
		1375
		1376	=head3 Explanation of the columns
		1377
		1378	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1379	each server has a read and write socket end).
		1380
		1381	I<create> is the time it takes to create a socketpair (which is
		1382	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1383
		1384	I<request>, the most important value, is the time it takes to handle a
		1385	single "request", that is, reading the token from the pipe and forwarding
		1386	it to another server. This includes deleting the old timeout and creating
		1387	a new one that moves the timeout into the future.
		1388
		1389	=head3 Results
		1390
		1391	name sockets create request
		1392	EV 20000 69.01 11.16
		1393	Perl 20000 73.32 35.87
		1394	Event 20000 212.62 257.32
		1395	Glib 20000 651.16 1896.30
		1396	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1397
		1398	=head3 Discussion
		1399
		1400	This benchmark I<does> measure scalability and overall performance of the
		1401	particular event loop.
		1402
		1403	EV is again fastest. Since it is using epoll on my system, the setup time
		1404	is relatively high, though.
		1405
		1406	Perl surprisingly comes second. It is much faster than the C-based event
		1407	loops Event and Glib.
		1408
		1409	Event suffers from high setup time as well (look at its code and you will
		1410	understand why). Callback invocation also has a high overhead compared to
		1411	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1412	uses select or poll in basically all documented configurations.
		1413
		1414	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1415	clearly fails to perform with many filehandles or in busy servers.
		1416
		1417	POE is still completely out of the picture, taking over 1000 times as long
		1418	as EV, and over 100 times as long as the Perl implementation, even though
		1419	it uses a C-based event loop in this case.
		1420
		1421	=head3 Summary
		1422
		1423	=over 4
		1424
		1425	=item * The pure perl implementation performs extremely well.
		1426
		1427	=item * Avoid Glib or POE in large projects where performance matters.
		1428
		1429	=back
		1430
		1431	=head2 BENCHMARKING SMALL SERVERS
		1432
		1433	While event loops should scale (and select-based ones do not...) even to
		1434	large servers, most programs we (or I :) actually write have only a few
		1435	I/O watchers.
		1436
		1437	In this benchmark, I use the same benchmark program as in the large server
		1438	case, but it uses only eight "servers", of which three are active at any
		1439	one time. This should reflect performance for a small server relatively
		1440	well.
		1441
		1442	The columns are identical to the previous table.
		1443
		1444	=head3 Results
		1445
		1446	name sockets create request
		1447	EV 16 20.00 6.54
		1448	Perl 16 25.75 12.62
		1449	Event 16 81.27 35.86
		1450	Glib 16 32.63 15.48
		1451	POE 16 261.87 276.28 uses POE::Loop::Event
		1452
		1453	=head3 Discussion
		1454
		1455	The benchmark tries to test the performance of a typical small
		1456	server. While knowing how various event loops perform is interesting, keep
		1457	in mind that their overhead in this case is usually not as important, due
		1458	to the small absolute number of watchers (that is, you need efficiency and
		1459	speed most when you have lots of watchers, not when you only have a few of
		1460	them).
		1461
		1462	EV is again fastest.
		1463
		1464	Perl again comes second. It is noticably faster than the C-based event
		1465	loops Event and Glib, although the difference is too small to really
		1466	matter.
		1467
		1468	POE also performs much better in this case, but is is still far behind the
		1469	others.
		1470
		1471	=head3 Summary
		1472
		1473	=over 4
		1474
		1475	=item * C-based event loops perform very well with small number of
		1476	watchers, as the management overhead dominates.
		1477
		1478	=back
		1479
850		1480
851	=head1 FORK	1481	=head1 FORK
852		1482
853	Most event libraries are not fork-safe. The ones who are usually are	1483	Most event libraries are not fork-safe. The ones who are usually are
854	because they are so inefficient. Only L<EV> is fully fork-aware.	1484	because they rely on inefficient but fork-safe C<select> or C<poll>
		1485	calls. Only L<EV> is fully fork-aware.
855		1486
856	If you have to fork, you must either do so I<before> creating your first	1487	If you have to fork, you must either do so I<before> creating your first
857	watcher OR you must not use AnyEvent at all in the child.	1488	watcher OR you must not use AnyEvent at all in the child.
		1489
858		1490
859	=head1 SECURITY CONSIDERATIONS	1491	=head1 SECURITY CONSIDERATIONS
860		1492
861	AnyEvent can be forced to load any event model via	1493	AnyEvent can be forced to load any event model via
862	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to	1494	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
…		…
870		1502
871	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1503	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
872		1504
873	use AnyEvent;	1505	use AnyEvent;
874		1506
		1507	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1508	be used to probe what backend is used and gain other information (which is
		1509	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1510
		1511
875	=head1 SEE ALSO	1512	=head1 SEE ALSO
876		1513
877	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1514	Utility functions: L<AnyEvent::Util>.
878	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
879	L<Event::Lib>, L<Qt>.
880		1515
881	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1516	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
882	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,	1517	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
883	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,	1518
		1519	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1520	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1521	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
884	L<AnyEvent::Impl::Qt>.	1522	L<AnyEvent::Impl::POE>.
885		1523
		1524	Non-blocking file handles, sockets, TCP clients and
		1525	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1526
		1527	Asynchronous DNS: L<AnyEvent::DNS>.
		1528
		1529	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1530
886	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1531	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1532
887		1533
888	=head1 AUTHOR	1534	=head1 AUTHOR
889		1535
890	Marc Lehmann <schmorp@schmorp.de>	1536	Marc Lehmann <schmorp@schmorp.de>
891	http://home.schmorp.de/	1537	http://home.schmorp.de/

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Revision 1.125 by root, Fri May 23 23:37:13 2008 UTC