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Revision 1.5 by root, Sun Dec 4 09:44:32 2005 UTC vs.
Revision 1.109 by root, Sat May 10 00:45:18 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	Event, Coro, Glib, Tk - 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
11	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
12	my ($poll_got) = @_;
13	...	12	...
14	});	13	});
15
16	- only one io watcher per $fh and $poll type is allowed
17	(i.e. on a socket you can have one r + one w or one rw
18	watcher, not any more.
19
20	- AnyEvent will keep filehandles alive, so as long as the watcher exists,
21	the filehandle exists.
22		14
23	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
24	...	16	...
25	});	17	});
26		18
27	- io and time watchers get canceled whenever $w is destroyed, so keep a copy	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
28
29	- timers can only be used once and must be recreated for repeated operation
30
31	my $w = AnyEvent->condvar; # kind of main loop replacement
32	$w->wait; # enters main loop till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->send
33	$w->broadcast; # wake up current and all future wait's	21	$w->send; # wake up current and all future wait's
34		22
35	- condvars are used to give blocking behaviour when neccessary. Create	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
36	a condvar for any "request" or "event" your module might create, C<<	24
37	->broadcast >> it when the event happens and provide a function that calls	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
38	C<< ->wait >> for it. See the examples below.	26	nowadays. So what is different about AnyEvent?
		27
		28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		29	policy> and AnyEvent is I<small and efficient>.
		30
		31	First and foremost, I<AnyEvent is not an event model> itself, it only
		32	interfaces to whatever event model the main program happens to use in a
		33	pragmatic way. For event models and certain classes of immortals alike,
		34	the statement "there can only be one" is a bitter reality: In general,
		35	only one event loop can be active at the same time in a process. AnyEvent
		36	helps hiding the differences between those event loops.
		37
		38	The goal of AnyEvent is to offer module authors the ability to do event
		39	programming (waiting for I/O or timer events) without subscribing to a
		40	religion, a way of living, and most importantly: without forcing your
		41	module users into the same thing by forcing them to use the same event
		42	model you use.
		43
		44	For modules like POE or IO::Async (which is a total misnomer as it is
		45	actually doing all I/O I<synchronously>...), using them in your module is
		46	like joining a cult: After you joined, you are dependent on them and you
		47	cannot use anything else, as it is simply incompatible to everything that
		48	isn't itself. What's worse, all the potential users of your module are
		49	I<also> forced to use the same event loop you use.
		50
		51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if
		54	your module uses one of those, every user of your module has to use it,
		55	too. But if your module uses AnyEvent, it works transparently with all
		56	event models it supports (including stuff like POE and IO::Async, as long
		57	as those use one of the supported event loops. It is trivial to add new
		58	event loops to AnyEvent, too, so it is future-proof).
		59
		60	In addition to being free of having to use I<the one and only true event
		61	model>, AnyEvent also is free of bloat and policy: with POE or similar
		62	modules, you get an enourmous amount of code and strict rules you have to
		63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		64	offering the functionality that is necessary, in as thin as a wrapper as
		65	technically possible.
		66
		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
		69	model, you should I<not> use this module.
39		70
40	=head1 DESCRIPTION	71	=head1 DESCRIPTION
41		72
42	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
43	allows module authors to utilizy an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
44	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
45	peacefully at any one time).	76	peacefully at any one time).
46		77
47	The interface itself is vaguely similar but not identical to the Event	78	The interface itself is vaguely similar, but not identical to the L<Event>
48	module.	79	module.
49		80
50	On the first call of any method, the module tries to detect the currently	81	During the first call of any watcher-creation method, the module tries
51	loaded event loop by probing wether any of the following modules is	82	to detect the currently loaded event loop by probing whether one of the
52	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
53	used. If none is found, the module tries to load these modules in the	84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
54	order given. The first one that could be successfully loaded will be	85	L<POE>. The first one found is used. If none are found, the module tries
55	used. If still none could be found, it will issue an error.	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
		89	found, AnyEvent will fall back to a pure-perl event loop, which is not
		90	very efficient, but should work everywhere.
		91
		92	Because AnyEvent first checks for modules that are already loaded, loading
		93	an event model explicitly before first using AnyEvent will likely make
		94	that model the default. For example:
		95
		96	use Tk;
		97	use AnyEvent;
		98
		99	# .. AnyEvent will likely default to Tk
		100
		101	The I<likely> means that, if any module loads another event model and
		102	starts using it, all bets are off. Maybe you should tell their authors to
		103	use AnyEvent so their modules work together with others seamlessly...
		104
		105	The pure-perl implementation of AnyEvent is called
		106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		107	explicitly.
		108
		109	=head1 WATCHERS
		110
		111	AnyEvent has the central concept of a I<watcher>, which is an object that
		112	stores relevant data for each kind of event you are waiting for, such as
		113	the callback to call, the filehandle to watch, etc.
		114
		115	These watchers are normal Perl objects with normal Perl lifetime. After
		116	creating a watcher it will immediately "watch" for events and invoke the
		117	callback when the event occurs (of course, only when the event model
		118	is in control).
		119
		120	To disable the watcher you have to destroy it (e.g. by setting the
		121	variable you store it in to C<undef> or otherwise deleting all references
		122	to it).
		123
		124	All watchers are created by calling a method on the C<AnyEvent> class.
		125
		126	Many watchers either are used with "recursion" (repeating timers for
		127	example), or need to refer to their watcher object in other ways.
		128
		129	An any way to achieve that is this pattern:
		130
		131	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		132	# you can use $w here, for example to undef it
		133	undef $w;
		134	});
		135
		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
		138	declared.
		139
		140	=head2 I/O WATCHERS
		141
		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:
		144
		145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
		146	for events. C<poll> must be a string that is either C<r> or C<w>,
		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
		149	becomes ready.
		150
		151	Although the callback might get passed parameters, their value and
		152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
		154
		155	The I/O watcher might use the underlying file descriptor or a copy of it.
		156	You must not close a file handle as long as any watcher is active on the
		157	underlying file descriptor.
		158
		159	Some event loops issue spurious readyness notifications, so you should
		160	always use non-blocking calls when reading/writing from/to your file
		161	handles.
		162
		163	Example:
		164
		165	# wait for readability of STDIN, then read a line and disable the watcher
		166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		167	chomp (my $input = <STDIN>);
		168	warn "read: $input\n";
		169	undef $w;
		170	});
		171
		172	=head2 TIME WATCHERS
		173
		174	You can create a time watcher by calling the C<< AnyEvent->timer >>
		175	method with the following mandatory arguments:
		176
		177	C<after> specifies after how many seconds (fractional values are
		178	supported) the callback should be invoked. C<cb> is the callback to invoke
		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.
		184
		185	The timer callback will be invoked at most once: if you want a repeating
		186	timer you have to create a new watcher (this is a limitation by both Tk
		187	and Glib).
		188
		189	Example:
		190
		191	# fire an event after 7.7 seconds
		192	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		193	warn "timeout\n";
		194	});
		195
		196	# to cancel the timer:
		197	undef $w;
		198
		199	Example 2:
		200
		201	# fire an event after 0.5 seconds, then roughly every second
		202	my $w;
		203
		204	my $cb = sub {
		205	# cancel the old timer while creating a new one
		206	$w = AnyEvent->timer (after => 1, cb => $cb);
		207	};
		208
		209	# start the "loop" by creating the first watcher
		210	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		211
		212	=head3 TIMING ISSUES
		213
		214	There are two ways to handle timers: based on real time (relative, "fire
		215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		216	o'clock").
		217
		218	While most event loops expect timers to specified in a relative way, they
		219	use absolute time internally. This makes a difference when your clock
		220	"jumps", for example, when ntp decides to set your clock backwards from
		221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		222	fire "after" a second might actually take six years to finally fire.
		223
		224	AnyEvent cannot compensate for this. The only event loop that is conscious
		225	about these issues is L<EV>, which offers both relative (ev_timer, based
		226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
		228
		229	AnyEvent always prefers relative timers, if available, matching the
		230	AnyEvent API.
		231
		232	=head2 SIGNAL WATCHERS
		233
		234	You can watch for signals using a signal watcher, C<signal> is the signal
		235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		236	be invoked whenever a signal occurs.
		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
		242	Multiple signal occurances can be clumped together into one callback
		243	invocation, and callback invocation will be synchronous. synchronous means
		244	that it might take a while until the signal gets handled by the process,
		245	but it is guarenteed not to interrupt any other callbacks.
		246
		247	The main advantage of using these watchers is that you can share a signal
		248	between multiple watchers.
		249
		250	This watcher might use C<%SIG>, so programs overwriting those signals
		251	directly will likely not work correctly.
		252
		253	Example: exit on SIGINT
		254
		255	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		256
		257	=head2 CHILD PROCESS WATCHERS
		258
		259	You can also watch on a child process exit and catch its exit status.
		260
		261	The child process is specified by the C<pid> argument (if set to C<0>, it
		262	watches for any child process exit). The watcher will trigger as often
		263	as status change for the child are received. This works by installing a
		264	signal handler for C<SIGCHLD>. The callback will be called with the pid
		265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
		267
		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;
		287
		288	my $w = AnyEvent->child (
		289	pid => $pid,
		290	cb => sub {
		291	my ($pid, $status) = @_;
		292	warn "pid $pid exited with status $status";
		293	$done->send;
		294	},
		295	);
		296
		297	# do something else, then wait for process exit
		298	$done->wait;
		299
		300	=head2 CONDITION VARIABLES
		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
		312	Condition variables can be created by calling the C<< AnyEvent->condvar
		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.
		316
		317	After creation, the conditon variable is "false" until it becomes "true"
		318	by calling the C<send> method.
		319
		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,
		328	for example, if you write a module that does asynchronous http requests,
		329	then a condition variable would be the ideal candidate to signal the
		330	availability of results. The user can either act when the callback is
		331	called or can synchronously C<< ->wait >> for the results.
		332
		333	You can also use them to simulate traditional event loops - for example,
		334	you can block your main program until an event occurs - for example, you
		335	could C<< ->wait >> in your main program until the user clicks the Quit
		336	button of your app, which would C<< ->send >> the "quit" event.
		337
		338	Note that condition variables recurse into the event loop - if you have
		339	two pieces of code that call C<< ->wait >> in a round-robbin fashion, you
		340	lose. Therefore, condition variables are good to export to your caller, but
		341	you should avoid making a blocking wait yourself, at least in callbacks,
		342	as this asks for trouble.
		343
		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.
56		378
57	=over 4	379	=over 4
58		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
		459	=item $cv->wait
		460
		461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
		464
		465	You can only wait once on a condition - additional calls are valid but
		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.
		473
		474	Not all event models support a blocking wait - some die in that case
		475	(programs might want to do that to stay interactive), so I<if you are
		476	using this from a module, never require a blocking wait>, but let the
		477	caller decide whether the call will block or not (for example, by coupling
		478	condition variables with some kind of request results and supporting
		479	callbacks so the caller knows that getting the result will not block,
		480	while still suppporting blocking waits if the caller so desires).
		481
		482	Another reason I<never> to C<< ->wait >> in a module is that you cannot
		483	sensibly have two C<< ->wait >>'s in parallel, as that would require
		484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		485	can supply.
		486
		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<< ->wait >> calls perfectly safe as long as they are done from another
		491	coroutine (one that doesn't run the event loop).
		492
		493	You can ensure that C<< -wait >> never blocks by setting a callback and
		494	only calling C<< ->wait >> from within that callback (or at a later
		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<wait> inside the callback
		510	or at any later time is guaranteed not to block.
		511
		512	=back
		513
		514	=head1 GLOBAL VARIABLES AND FUNCTIONS
		515
		516	=over 4
		517
		518	=item $AnyEvent::MODEL
		519
		520	Contains C<undef> until the first watcher is being created. Then it
		521	contains the event model that is being used, which is the name of the
		522	Perl class implementing the model. This class is usually one of the
		523	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		524	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		525
		526	The known classes so far are:
		527
		528	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		529	AnyEvent::Impl::Event based on Event, second best choice.
		530	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		531	AnyEvent::Impl::Glib based on Glib, third-best choice.
		532	AnyEvent::Impl::Tk based on Tk, very bad choice.
		533	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		534	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		535	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		536
		537	There is no support for WxWidgets, as WxWidgets has no support for
		538	watching file handles. However, you can use WxWidgets through the
		539	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		540	second, which was considered to be too horrible to even consider for
		541	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		542	it's adaptor.
		543
		544	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		545	autodetecting them.
		546
		547	=item AnyEvent::detect
		548
		549	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		550	if necessary. You should only call this function right before you would
		551	have created an AnyEvent watcher anyway, that is, as late as possible at
		552	runtime.
		553
		554	=item AnyEvent::on_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	=item @AnyEvent::on_detect
		560
		561	If there are any code references in this array (you can C<push> to it
		562	before or after loading AnyEvent), then they will called directly after
		563	the event loop has been chosen.
		564
		565	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		566	if it contains a true value then the event loop has already been detected,
		567	and the array will be ignored.
		568
		569	Best use C<AnyEvent::on_detect { BLOCK }> instead.
		570
		571	=back
		572
		573	=head1 WHAT TO DO IN A MODULE
		574
		575	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		576	freely, but you should not load a specific event module or rely on it.
		577
		578	Be careful when you create watchers in the module body - AnyEvent will
		579	decide which event module to use as soon as the first method is called, so
		580	by calling AnyEvent in your module body you force the user of your module
		581	to load the event module first.
		582
		583	Never call C<< ->wait >> on a condition variable unless you I<know> that
		584	the C<< ->send >> method has been called on it already. This is
		585	because it will stall the whole program, and the whole point of using
		586	events is to stay interactive.
		587
		588	It is fine, however, to call C<< ->wait >> when the user of your module
		589	requests it (i.e. if you create a http request object ad have a method
		590	called C<results> that returns the results, it should call C<< ->wait >>
		591	freely, as the user of your module knows what she is doing. always).
		592
		593	=head1 WHAT TO DO IN THE MAIN PROGRAM
		594
		595	There will always be a single main program - the only place that should
		596	dictate which event model to use.
		597
		598	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		599	do anything special (it does not need to be event-based) and let AnyEvent
		600	decide which implementation to chose if some module relies on it.
		601
		602	If the main program relies on a specific event model. For example, in
		603	Gtk2 programs you have to rely on the Glib module. You should load the
		604	event module before loading AnyEvent or any module that uses it: generally
		605	speaking, you should load it as early as possible. The reason is that
		606	modules might create watchers when they are loaded, and AnyEvent will
		607	decide on the event model to use as soon as it creates watchers, and it
		608	might chose the wrong one unless you load the correct one yourself.
		609
		610	You can chose to use a rather inefficient pure-perl implementation by
		611	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
		612	behaviour everywhere, but letting AnyEvent chose is generally better.
		613
		614	=head1 OTHER MODULES
		615
		616	The following is a non-exhaustive list of additional modules that use
		617	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		618	in the same program. Some of the modules come with AnyEvent, some are
		619	available via CPAN.
		620
		621	=over 4
		622
		623	=item L<AnyEvent::Util>
		624
		625	Contains various utility functions that replace often-used but blocking
		626	functions such as C<inet_aton> by event-/callback-based versions.
		627
		628	=item L<AnyEvent::Handle>
		629
		630	Provide read and write buffers and manages watchers for reads and writes.
		631
		632	=item L<AnyEvent::Socket>
		633
		634	Provides a means to do non-blocking connects, accepts etc.
		635
		636	=item L<AnyEvent::HTTPD>
		637
		638	Provides a simple web application server framework.
		639
		640	=item L<AnyEvent::DNS>
		641
		642	Provides asynchronous DNS resolver capabilities, beyond what
		643	L<AnyEvent::Util> offers.
		644
		645	=item L<AnyEvent::FastPing>
		646
		647	The fastest ping in the west.
		648
		649	=item L<Net::IRC3>
		650
		651	AnyEvent based IRC client module family.
		652
		653	=item L<Net::XMPP2>
		654
		655	AnyEvent based XMPP (Jabber protocol) module family.
		656
		657	=item L<Net::FCP>
		658
		659	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		660	of AnyEvent.
		661
		662	=item L<Event::ExecFlow>
		663
		664	High level API for event-based execution flow control.
		665
		666	=item L<Coro>
		667
		668	Has special support for AnyEvent via L<Coro::AnyEvent>.
		669
		670	=item L<IO::Lambda>
		671
		672	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		673
		674	=item L<IO::AIO>
		675
		676	Truly asynchronous I/O, should be in the toolbox of every event
		677	programmer. Can be trivially made to use AnyEvent.
		678
		679	=item L<BDB>
		680
		681	Truly asynchronous Berkeley DB access. Can be trivially made to use
		682	AnyEvent.
		683
		684	=back
		685
59	=cut	686	=cut
60		687
61	package AnyEvent;	688	package AnyEvent;
62		689
63	no warnings;	690	no warnings;
64	use strict 'vars';	691	use strict;
		692
65	use Carp;	693	use Carp;
66		694
67	our $VERSION = 0.3;	695	our $VERSION = '3.4';
68	our $MODEL;	696	our $MODEL;
69		697
70	our $AUTOLOAD;	698	our $AUTOLOAD;
71	our @ISA;	699	our @ISA;
72		700
		701	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		702
		703	our @REGISTRY;
		704
73	my @models = (	705	my @models = (
74	[Coro => Coro::Event::],	706	[EV:: => AnyEvent::Impl::EV::],
75	[Event => Event::],	707	[Event:: => AnyEvent::Impl::Event::],
76	[Glib => Glib::],	708	[Tk:: => AnyEvent::Impl::Tk::],
77	[Tk => Tk::],	709	[Wx:: => AnyEvent::Impl::POE::],
		710	[Prima:: => AnyEvent::Impl::POE::],
		711	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		712	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		713	[Glib:: => AnyEvent::Impl::Glib::],
		714	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		715	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		716	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
78	);	717	);
79		718
80	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	719	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
81		720
82	sub AUTOLOAD {	721	our @on_detect;
83	$AUTOLOAD =~ s/.*://;
84		722
85	$method{$AUTOLOAD}	723	sub on_detect(&) {
86	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	724	if ($MODEL) {
		725	$_[0]->();
		726	} else {
		727	push @on_detect, $_[0];
		728	}
		729	}
87		730
		731	sub detect() {
88	unless ($MODEL) {	732	unless ($MODEL) {
89	# check for already loaded models	733	no strict 'refs';
90	for (@models) {	734
91	my ($model, $package) = @$_;	735	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
92	if (scalar keys %{ *{"$package\::"} }) {	736	my $model = "AnyEvent::Impl::$1";
93	eval "require AnyEvent::Impl::$model";	737	if (eval "require $model") {
94	last if $MODEL;	738	$MODEL = $model;
		739	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		740	} else {
		741	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
95	}	742	}
96	}	743	}
97		744
		745	# check for already loaded models
98	unless ($MODEL) {	746	unless ($MODEL) {
99	# try to load a model
100
101	for (@models) {	747	for (@REGISTRY, @models) {
102	my ($model, $package) = @$_;	748	my ($package, $model) = @$_;
103	eval "require AnyEvent::Impl::$model";	749	if (${"$package\::VERSION"} > 0) {
104	last if $MODEL;	750	if (eval "require $model") {
		751	$MODEL = $model;
		752	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		753	last;
		754	}
		755	}
105	}	756	}
106		757
		758	unless ($MODEL) {
		759	# try to load a model
		760
		761	for (@REGISTRY, @models) {
		762	my ($package, $model) = @$_;
		763	if (eval "require $package"
		764	and ${"$package\::VERSION"} > 0
		765	and eval "require $model") {
		766	$MODEL = $model;
		767	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		768	last;
		769	}
		770	}
		771
107	$MODEL	772	$MODEL
108	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	773	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		774	}
109	}	775	}
		776
		777	unshift @ISA, $MODEL;
		778	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		779
		780	(shift @on_detect)->() while @on_detect;
110	}	781	}
111		782
112	@ISA = $MODEL;	783	$MODEL
		784	}
		785
		786	sub AUTOLOAD {
		787	(my $func = $AUTOLOAD) =~ s/.*://;
		788
		789	$method{$func}
		790	or croak "$func: not a valid method for AnyEvent objects";
		791
		792	detect unless $MODEL;
113		793
114	my $class = shift;	794	my $class = shift;
115	$class->$AUTOLOAD (@_);	795	$class->$func (@_);
116	}	796	}
117		797
		798	package AnyEvent::Base;
		799
		800	# default implementation for ->condvar, ->wait, ->broadcast
		801
		802	sub condvar {
		803	bless \my $flag, "AnyEvent::Base::CondVar"
		804	}
		805
		806	sub AnyEvent::Base::CondVar::broadcast {
		807	${$_[0]}++;
		808	}
		809
		810	sub AnyEvent::Base::CondVar::wait {
		811	AnyEvent->one_event while !${$_[0]};
		812	}
		813
		814	# default implementation for ->signal
		815
		816	our %SIG_CB;
		817
		818	sub signal {
		819	my (undef, %arg) = @_;
		820
		821	my $signal = uc $arg{signal}
		822	or Carp::croak "required option 'signal' is missing";
		823
		824	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		825	$SIG{$signal} ||= sub {
		826	$_->() for values %{ $SIG_CB{$signal} || {} };
		827	};
		828
		829	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		830	}
		831
		832	sub AnyEvent::Base::Signal::DESTROY {
		833	my ($signal, $cb) = @{$_[0]};
		834
		835	delete $SIG_CB{$signal}{$cb};
		836
		837	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		838	}
		839
		840	# default implementation for ->child
		841
		842	our %PID_CB;
		843	our $CHLD_W;
		844	our $CHLD_DELAY_W;
		845	our $PID_IDLE;
		846	our $WNOHANG;
		847
		848	sub _child_wait {
		849	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		850	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		851	(values %{ $PID_CB{0} || {} });
		852	}
		853
		854	undef $PID_IDLE;
		855	}
		856
		857	sub _sigchld {
		858	# make sure we deliver these changes "synchronous" with the event loop.
		859	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		860	undef $CHLD_DELAY_W;
		861	&_child_wait;
		862	});
		863	}
		864
		865	sub child {
		866	my (undef, %arg) = @_;
		867
		868	defined (my $pid = $arg{pid} + 0)
		869	or Carp::croak "required option 'pid' is missing";
		870
		871	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		872
		873	unless ($WNOHANG) {
		874	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		875	}
		876
		877	unless ($CHLD_W) {
		878	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		879	# child could be a zombie already, so make at least one round
		880	&_sigchld;
		881	}
		882
		883	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		884	}
		885
		886	sub AnyEvent::Base::Child::DESTROY {
		887	my ($pid, $cb) = @{$_[0]};
		888
		889	delete $PID_CB{$pid}{$cb};
		890	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		891
		892	undef $CHLD_W unless keys %PID_CB;
		893	}
		894
		895	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		896
		897	This is an advanced topic that you do not normally need to use AnyEvent in
		898	a module. This section is only of use to event loop authors who want to
		899	provide AnyEvent compatibility.
		900
		901	If you need to support another event library which isn't directly
		902	supported by AnyEvent, you can supply your own interface to it by
		903	pushing, before the first watcher gets created, the package name of
		904	the event module and the package name of the interface to use onto
		905	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		906	AnyEvent, so it is reasonably cheap.
		907
		908	Example:
		909
		910	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		911
		912	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		913	package/class when it finds the C<urxvt> package/module is already loaded.
		914
		915	When AnyEvent is loaded and asked to find a suitable event model, it
		916	will first check for the presence of urxvt by trying to C<use> the
		917	C<urxvt::anyevent> module.
		918
		919	The class should provide implementations for all watcher types. See
		920	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		921	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		922	see the sources.
		923
		924	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		925	provide suitable (hopefully) replacements.
		926
		927	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		928	terminal emulator uses the above line as-is. An interface isn't included
		929	in AnyEvent because it doesn't make sense outside the embedded interpreter
		930	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		931	I<rxvt-unicode> distribution.
		932
		933	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		934	condition variables: code blocking while waiting for a condition will
		935	C<die>. This still works with most modules/usages, and blocking calls must
		936	not be done in an interactive application, so it makes sense.
		937
		938	=head1 ENVIRONMENT VARIABLES
		939
		940	The following environment variables are used by this module:
		941
		942	=over 4
		943
		944	=item C<PERL_ANYEVENT_VERBOSE>
		945
		946	By default, AnyEvent will be completely silent except in fatal
		947	conditions. You can set this environment variable to make AnyEvent more
		948	talkative.
		949
		950	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		951	conditions, such as not being able to load the event model specified by
		952	C<PERL_ANYEVENT_MODEL>.
		953
		954	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		955	model it chooses.
		956
		957	=item C<PERL_ANYEVENT_MODEL>
		958
		959	This can be used to specify the event model to be used by AnyEvent, before
		960	autodetection and -probing kicks in. It must be a string consisting
		961	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		962	and the resulting module name is loaded and if the load was successful,
		963	used as event model. If it fails to load AnyEvent will proceed with
		964	autodetection and -probing.
		965
		966	This functionality might change in future versions.
		967
		968	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		969	could start your program like this:
		970
		971	PERL_ANYEVENT_MODEL=Perl perl ...
		972
118	=back	973	=back
119		974
120	=head1 EXAMPLE	975	=head1 EXAMPLE PROGRAM
121		976
122	The following program uses an io watcher to read data from stdin, a timer	977	The following program uses an I/O watcher to read data from STDIN, a timer
123	to display a message once per second, and a condvar to exit the program	978	to display a message once per second, and a condition variable to quit the
124	when the user enters quit:	979	program when the user enters quit:
125		980
126	use AnyEvent;	981	use AnyEvent;
127		982
128	my $cv = AnyEvent->condvar;	983	my $cv = AnyEvent->condvar;
129		984
130	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	985	my $io_watcher = AnyEvent->io (
		986	fh => \*STDIN,
		987	poll => 'r',
		988	cb => sub {
131	warn "io event <$_[0]>\n"; # will always output <r>	989	warn "io event <$_[0]>\n"; # will always output <r>
132	chomp (my $input = <STDIN>); # read a line	990	chomp (my $input = <STDIN>); # read a line
133	warn "read: $input\n"; # output what has been read	991	warn "read: $input\n"; # output what has been read
134	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	992	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		993	},
135	});	994	);
136		995
137	my $time_watcher; # can only be used once	996	my $time_watcher; # can only be used once
138		997
139	sub new_timer {	998	sub new_timer {
140	$timer = AnyEvent->timer (after => 1, cb => sub {	999	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
183	connect $txn->{fh}, ...	1042	connect $txn->{fh}, ...
184	and !$!{EWOULDBLOCK}	1043	and !$!{EWOULDBLOCK}
185	and !$!{EINPROGRESS}	1044	and !$!{EINPROGRESS}
186	and Carp::croak "unable to connect: $!\n";	1045	and Carp::croak "unable to connect: $!\n";
187		1046
188	Then it creates a write-watcher which gets called wehnever an error occurs	1047	Then it creates a write-watcher which gets called whenever an error occurs
189	or the connection succeeds:	1048	or the connection succeeds:
190		1049
191	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });	1050	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
192		1051
193	And returns this transaction object. The C<fh_ready_w> callback gets	1052	And returns this transaction object. The C<fh_ready_w> callback gets
…		…
210	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1069	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
211		1070
212	if (end-of-file or data complete) {	1071	if (end-of-file or data complete) {
213	$txn->{result} = $txn->{buf};	1072	$txn->{result} = $txn->{buf};
214	$txn->{finished}->broadcast;	1073	$txn->{finished}->broadcast;
		1074	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
215	}	1075	}
216		1076
217	The C<result> method, finally, just waits for the finished signal (if the	1077	The C<result> method, finally, just waits for the finished signal (if the
218	request was already finished, it doesn't wait, of course, and returns the	1078	request was already finished, it doesn't wait, of course, and returns the
219	data:	1079	data:
220		1080
221	$txn->{finished}->wait;	1081	$txn->{finished}->wait;
222	return $txn->{buf};	1082	return $txn->{result};
223		1083
224	The actual code goes further and collects all errors (C<die>s, exceptions)	1084	The actual code goes further and collects all errors (C<die>s, exceptions)
225	that occured during request processing. The C<result> method detects	1085	that occured during request processing. The C<result> method detects
226	wether an exception as thrown (it is stored inside the $txn object)	1086	whether an exception as thrown (it is stored inside the $txn object)
227	and just throws the exception, which means connection errors and other	1087	and just throws the exception, which means connection errors and other
228	problems get reported tot he code that tries to use the result, not in a	1088	problems get reported tot he code that tries to use the result, not in a
229	random callback.	1089	random callback.
230		1090
231	All of this enables the following usage styles:	1091	All of this enables the following usage styles:
232		1092
233	1. Blocking:	1093	1. Blocking:
234		1094
235	my $data = $fcp->client_get ($url);	1095	my $data = $fcp->client_get ($url);
236		1096
237	2. Blocking, but parallelizing:	1097	2. Blocking, but running in parallel:
238		1098
239	my @datas = map $_->result,	1099	my @datas = map $_->result,
240	map $fcp->txn_client_get ($_),	1100	map $fcp->txn_client_get ($_),
241	@urls;	1101	@urls;
242		1102
243	Both blocking examples work without the module user having to know	1103	Both blocking examples work without the module user having to know
244	anything about events.	1104	anything about events.
245		1105
246	3a. Event-based in a main program, using any support Event module:	1106	3a. Event-based in a main program, using any supported event module:
247		1107
248	use Event;	1108	use EV;
249		1109
250	$fcp->txn_client_get ($url)->cb (sub {	1110	$fcp->txn_client_get ($url)->cb (sub {
251	my $txn = shift;	1111	my $txn = shift;
252	my $data = $txn->result;	1112	my $data = $txn->result;
253	...	1113	...
254	});	1114	});
255		1115
256	Event::loop;	1116	EV::loop;
257		1117
258	3b. The module user could use AnyEvent, too:	1118	3b. The module user could use AnyEvent, too:
259		1119
260	use AnyEvent;	1120	use AnyEvent;
261		1121
…		…
266	$quit->broadcast;	1126	$quit->broadcast;
267	});	1127	});
268		1128
269	$quit->wait;	1129	$quit->wait;
270		1130
		1131
		1132	=head1 BENCHMARKS
		1133
		1134	To give you an idea of the performance and overheads that AnyEvent adds
		1135	over the event loops themselves and to give you an impression of the speed
		1136	of various event loops I prepared some benchmarks.
		1137
		1138	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1139
		1140	Here is a benchmark of various supported event models used natively and
		1141	through anyevent. The benchmark creates a lot of timers (with a zero
		1142	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1143	which it is), lets them fire exactly once and destroys them again.
		1144
		1145	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1146	distribution.
		1147
		1148	=head3 Explanation of the columns
		1149
		1150	I<watcher> is the number of event watchers created/destroyed. Since
		1151	different event models feature vastly different performances, each event
		1152	loop was given a number of watchers so that overall runtime is acceptable
		1153	and similar between tested event loop (and keep them from crashing): Glib
		1154	would probably take thousands of years if asked to process the same number
		1155	of watchers as EV in this benchmark.
		1156
		1157	I<bytes> is the number of bytes (as measured by the resident set size,
		1158	RSS) consumed by each watcher. This method of measuring captures both C
		1159	and Perl-based overheads.
		1160
		1161	I<create> is the time, in microseconds (millionths of seconds), that it
		1162	takes to create a single watcher. The callback is a closure shared between
		1163	all watchers, to avoid adding memory overhead. That means closure creation
		1164	and memory usage is not included in the figures.
		1165
		1166	I<invoke> is the time, in microseconds, used to invoke a simple
		1167	callback. The callback simply counts down a Perl variable and after it was
		1168	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1169	signal the end of this phase.
		1170
		1171	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1172	watcher.
		1173
		1174	=head3 Results
		1175
		1176	name watchers bytes create invoke destroy comment
		1177	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1178	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1179	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1180	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1181	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1182	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1183	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1184	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1185	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1186	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1187
		1188	=head3 Discussion
		1189
		1190	The benchmark does I<not> measure scalability of the event loop very
		1191	well. For example, a select-based event loop (such as the pure perl one)
		1192	can never compete with an event loop that uses epoll when the number of
		1193	file descriptors grows high. In this benchmark, all events become ready at
		1194	the same time, so select/poll-based implementations get an unnatural speed
		1195	boost.
		1196
		1197	Also, note that the number of watchers usually has a nonlinear effect on
		1198	overall speed, that is, creating twice as many watchers doesn't take twice
		1199	the time - usually it takes longer. This puts event loops tested with a
		1200	higher number of watchers at a disadvantage.
		1201
		1202	To put the range of results into perspective, consider that on the
		1203	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1204	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1205	cycles with POE.
		1206
		1207	C<EV> is the sole leader regarding speed and memory use, which are both
		1208	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1209	far less memory than any other event loop and is still faster than Event
		1210	natively.
		1211
		1212	The pure perl implementation is hit in a few sweet spots (both the
		1213	constant timeout and the use of a single fd hit optimisations in the perl
		1214	interpreter and the backend itself). Nevertheless this shows that it
		1215	adds very little overhead in itself. Like any select-based backend its
		1216	performance becomes really bad with lots of file descriptors (and few of
		1217	them active), of course, but this was not subject of this benchmark.
		1218
		1219	The C<Event> module has a relatively high setup and callback invocation
		1220	cost, but overall scores in on the third place.
		1221
		1222	C<Glib>'s memory usage is quite a bit higher, but it features a
		1223	faster callback invocation and overall ends up in the same class as
		1224	C<Event>. However, Glib scales extremely badly, doubling the number of
		1225	watchers increases the processing time by more than a factor of four,
		1226	making it completely unusable when using larger numbers of watchers
		1227	(note that only a single file descriptor was used in the benchmark, so
		1228	inefficiencies of C<poll> do not account for this).
		1229
		1230	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1231	more than 2000 watchers is a big setback, however, as correctness takes
		1232	precedence over speed. Nevertheless, its performance is surprising, as the
		1233	file descriptor is dup()ed for each watcher. This shows that the dup()
		1234	employed by some adaptors is not a big performance issue (it does incur a
		1235	hidden memory cost inside the kernel which is not reflected in the figures
		1236	above).
		1237
		1238	C<POE>, regardless of underlying event loop (whether using its pure perl
		1239	select-based backend or the Event module, the POE-EV backend couldn't
		1240	be tested because it wasn't working) shows abysmal performance and
		1241	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1242	as EV watchers, and 10 times as much memory as Event (the high memory
		1243	requirements are caused by requiring a session for each watcher). Watcher
		1244	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1245	implementation.
		1246
		1247	The design of the POE adaptor class in AnyEvent can not really account
		1248	for the performance issues, though, as session creation overhead is
		1249	small compared to execution of the state machine, which is coded pretty
		1250	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1251	using multiple sessions is not a good approach, especially regarding
		1252	memory usage, even the author of POE could not come up with a faster
		1253	design).
		1254
		1255	=head3 Summary
		1256
		1257	=over 4
		1258
		1259	=item * Using EV through AnyEvent is faster than any other event loop
		1260	(even when used without AnyEvent), but most event loops have acceptable
		1261	performance with or without AnyEvent.
		1262
		1263	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1264	the actual event loop, only with extremely fast event loops such as EV
		1265	adds AnyEvent significant overhead.
		1266
		1267	=item * You should avoid POE like the plague if you want performance or
		1268	reasonable memory usage.
		1269
		1270	=back
		1271
		1272	=head2 BENCHMARKING THE LARGE SERVER CASE
		1273
		1274	This benchmark atcually benchmarks the event loop itself. It works by
		1275	creating a number of "servers": each server consists of a socketpair, a
		1276	timeout watcher that gets reset on activity (but never fires), and an I/O
		1277	watcher waiting for input on one side of the socket. Each time the socket
		1278	watcher reads a byte it will write that byte to a random other "server".
		1279
		1280	The effect is that there will be a lot of I/O watchers, only part of which
		1281	are active at any one point (so there is a constant number of active
		1282	fds for each loop iterstaion, but which fds these are is random). The
		1283	timeout is reset each time something is read because that reflects how
		1284	most timeouts work (and puts extra pressure on the event loops).
		1285
		1286	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1287	(1%) are active. This mirrors the activity of large servers with many
		1288	connections, most of which are idle at any one point in time.
		1289
		1290	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1291	distribution.
		1292
		1293	=head3 Explanation of the columns
		1294
		1295	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1296	each server has a read and write socket end).
		1297
		1298	I<create> is the time it takes to create a socketpair (which is
		1299	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1300
		1301	I<request>, the most important value, is the time it takes to handle a
		1302	single "request", that is, reading the token from the pipe and forwarding
		1303	it to another server. This includes deleting the old timeout and creating
		1304	a new one that moves the timeout into the future.
		1305
		1306	=head3 Results
		1307
		1308	name sockets create request
		1309	EV 20000 69.01 11.16
		1310	Perl 20000 73.32 35.87
		1311	Event 20000 212.62 257.32
		1312	Glib 20000 651.16 1896.30
		1313	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1314
		1315	=head3 Discussion
		1316
		1317	This benchmark I<does> measure scalability and overall performance of the
		1318	particular event loop.
		1319
		1320	EV is again fastest. Since it is using epoll on my system, the setup time
		1321	is relatively high, though.
		1322
		1323	Perl surprisingly comes second. It is much faster than the C-based event
		1324	loops Event and Glib.
		1325
		1326	Event suffers from high setup time as well (look at its code and you will
		1327	understand why). Callback invocation also has a high overhead compared to
		1328	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1329	uses select or poll in basically all documented configurations.
		1330
		1331	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1332	clearly fails to perform with many filehandles or in busy servers.
		1333
		1334	POE is still completely out of the picture, taking over 1000 times as long
		1335	as EV, and over 100 times as long as the Perl implementation, even though
		1336	it uses a C-based event loop in this case.
		1337
		1338	=head3 Summary
		1339
		1340	=over 4
		1341
		1342	=item * The pure perl implementation performs extremely well.
		1343
		1344	=item * Avoid Glib or POE in large projects where performance matters.
		1345
		1346	=back
		1347
		1348	=head2 BENCHMARKING SMALL SERVERS
		1349
		1350	While event loops should scale (and select-based ones do not...) even to
		1351	large servers, most programs we (or I :) actually write have only a few
		1352	I/O watchers.
		1353
		1354	In this benchmark, I use the same benchmark program as in the large server
		1355	case, but it uses only eight "servers", of which three are active at any
		1356	one time. This should reflect performance for a small server relatively
		1357	well.
		1358
		1359	The columns are identical to the previous table.
		1360
		1361	=head3 Results
		1362
		1363	name sockets create request
		1364	EV 16 20.00 6.54
		1365	Perl 16 25.75 12.62
		1366	Event 16 81.27 35.86
		1367	Glib 16 32.63 15.48
		1368	POE 16 261.87 276.28 uses POE::Loop::Event
		1369
		1370	=head3 Discussion
		1371
		1372	The benchmark tries to test the performance of a typical small
		1373	server. While knowing how various event loops perform is interesting, keep
		1374	in mind that their overhead in this case is usually not as important, due
		1375	to the small absolute number of watchers (that is, you need efficiency and
		1376	speed most when you have lots of watchers, not when you only have a few of
		1377	them).
		1378
		1379	EV is again fastest.
		1380
		1381	Perl again comes second. It is noticably faster than the C-based event
		1382	loops Event and Glib, although the difference is too small to really
		1383	matter.
		1384
		1385	POE also performs much better in this case, but is is still far behind the
		1386	others.
		1387
		1388	=head3 Summary
		1389
		1390	=over 4
		1391
		1392	=item * C-based event loops perform very well with small number of
		1393	watchers, as the management overhead dominates.
		1394
		1395	=back
		1396
		1397
		1398	=head1 FORK
		1399
		1400	Most event libraries are not fork-safe. The ones who are usually are
		1401	because they rely on inefficient but fork-safe C<select> or C<poll>
		1402	calls. Only L<EV> is fully fork-aware.
		1403
		1404	If you have to fork, you must either do so I<before> creating your first
		1405	watcher OR you must not use AnyEvent at all in the child.
		1406
		1407
		1408	=head1 SECURITY CONSIDERATIONS
		1409
		1410	AnyEvent can be forced to load any event model via
		1411	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1412	execute arbitrary code or directly gain access, it can easily be used to
		1413	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1414	will not be active when the program uses a different event model than
		1415	specified in the variable.
		1416
		1417	You can make AnyEvent completely ignore this variable by deleting it
		1418	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1419
		1420	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1421
		1422	use AnyEvent;
		1423
		1424	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1425	be used to probe what backend is used and gain other information (which is
		1426	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1427
		1428
271	=head1 SEE ALSO	1429	=head1 SEE ALSO
272		1430
273	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1431	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1432	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
274		1433
275	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1434	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1435	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1436	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1437	L<AnyEvent::Impl::POE>.
276		1438
		1439	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1440
277	Nontrivial usage example: L<Net::FCP>.	1441	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
278		1442
279	=head1	1443
		1444	=head1 AUTHOR
		1445
		1446	Marc Lehmann <schmorp@schmorp.de>
		1447	http://home.schmorp.de/
280		1448
281	=cut	1449	=cut
282		1450
283	1	1451	1
284		1452

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