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1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - ???	3	AnyEvent - provide framework for multiple event loops
		4
		5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
4		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
		9	use AnyEvent;
		10
		11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... });
		12
		13	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		14	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		15
		16	print AnyEvent->now; # prints current event loop time
		17	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		18
		19	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		20
		21	my $w = AnyEvent->child (pid => $pid, cb => sub {
		22	my ($pid, $status) = @_;
		23	...
		24	});
		25
		26	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		27	$w->send; # wake up current and all future recv's
		28	$w->recv; # enters "main loop" till $condvar gets ->send
		29	# use a condvar in callback mode:
		30	$w->cb (sub { $_[0]->recv });
		31
		32	=head1 INTRODUCTION/TUTORIAL
		33
		34	This manpage is mainly a reference manual. If you are interested
		35	in a tutorial or some gentle introduction, have a look at the
		36	L<AnyEvent::Intro> manpage.
		37
		38	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		39
		40	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		41	nowadays. So what is different about AnyEvent?
		42
		43	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		44	policy> and AnyEvent is I<small and efficient>.
		45
		46	First and foremost, I<AnyEvent is not an event model> itself, it only
		47	interfaces to whatever event model the main program happens to use, in a
		48	pragmatic way. For event models and certain classes of immortals alike,
		49	the statement "there can only be one" is a bitter reality: In general,
		50	only one event loop can be active at the same time in a process. AnyEvent
		51	cannot change this, but it can hide the differences between those event
		52	loops.
		53
		54	The goal of AnyEvent is to offer module authors the ability to do event
		55	programming (waiting for I/O or timer events) without subscribing to a
		56	religion, a way of living, and most importantly: without forcing your
		57	module users into the same thing by forcing them to use the same event
		58	model you use.
		59
		60	For modules like POE or IO::Async (which is a total misnomer as it is
		61	actually doing all I/O I<synchronously>...), using them in your module is
		62	like joining a cult: After you joined, you are dependent on them and you
		63	cannot use anything else, as they are simply incompatible to everything
		64	that isn't them. What's worse, all the potential users of your
		65	module are I<also> forced to use the same event loop you use.
		66
		67	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		68	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		69	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		70	your module uses one of those, every user of your module has to use it,
		71	too. But if your module uses AnyEvent, it works transparently with all
		72	event models it supports (including stuff like IO::Async, as long as those
		73	use one of the supported event loops. It is trivial to add new event loops
		74	to AnyEvent, too, so it is future-proof).
		75
		76	In addition to being free of having to use I<the one and only true event
		77	model>, AnyEvent also is free of bloat and policy: with POE or similar
		78	modules, you get an enormous amount of code and strict rules you have to
		79	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		80	offering the functionality that is necessary, in as thin as a wrapper as
		81	technically possible.
		82
		83	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		84	of useful functionality, such as an asynchronous DNS resolver, 100%
		85	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		86	such as Windows) and lots of real-world knowledge and workarounds for
		87	platform bugs and differences.
		88
		89	Now, if you I<do want> lots of policy (this can arguably be somewhat
		90	useful) and you want to force your users to use the one and only event
		91	model, you should I<not> use this module.
		92
7	=head1 DESCRIPTION	93	=head1 DESCRIPTION
8		94
		95	L<AnyEvent> provides an identical interface to multiple event loops. This
		96	allows module authors to utilise an event loop without forcing module
		97	users to use the same event loop (as only a single event loop can coexist
		98	peacefully at any one time).
		99
		100	The interface itself is vaguely similar, but not identical to the L<Event>
		101	module.
		102
		103	During the first call of any watcher-creation method, the module tries
		104	to detect the currently loaded event loop by probing whether one of the
		105	following modules is already loaded: L<EV>,
		106	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
		107	L<POE>. The first one found is used. If none are found, the module tries
		108	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		109	adaptor should always succeed) in the order given. The first one that can
		110	be successfully loaded will be used. If, after this, still none could be
		111	found, AnyEvent will fall back to a pure-perl event loop, which is not
		112	very efficient, but should work everywhere.
		113
		114	Because AnyEvent first checks for modules that are already loaded, loading
		115	an event model explicitly before first using AnyEvent will likely make
		116	that model the default. For example:
		117
		118	use Tk;
		119	use AnyEvent;
		120
		121	# .. AnyEvent will likely default to Tk
		122
		123	The I<likely> means that, if any module loads another event model and
		124	starts using it, all bets are off. Maybe you should tell their authors to
		125	use AnyEvent so their modules work together with others seamlessly...
		126
		127	The pure-perl implementation of AnyEvent is called
		128	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		129	explicitly and enjoy the high availability of that event loop :)
		130
		131	=head1 WATCHERS
		132
		133	AnyEvent has the central concept of a I<watcher>, which is an object that
		134	stores relevant data for each kind of event you are waiting for, such as
		135	the callback to call, the file handle to watch, etc.
		136
		137	These watchers are normal Perl objects with normal Perl lifetime. After
		138	creating a watcher it will immediately "watch" for events and invoke the
		139	callback when the event occurs (of course, only when the event model
		140	is in control).
		141
		142	To disable the watcher you have to destroy it (e.g. by setting the
		143	variable you store it in to C<undef> or otherwise deleting all references
		144	to it).
		145
		146	All watchers are created by calling a method on the C<AnyEvent> class.
		147
		148	Many watchers either are used with "recursion" (repeating timers for
		149	example), or need to refer to their watcher object in other ways.
		150
		151	An any way to achieve that is this pattern:
		152
		153	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		154	# you can use $w here, for example to undef it
		155	undef $w;
		156	});
		157
		158	Note that C<my $w; $w => combination. This is necessary because in Perl,
		159	my variables are only visible after the statement in which they are
		160	declared.
		161
		162	=head2 I/O WATCHERS
		163
		164	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		165	with the following mandatory key-value pairs as arguments:
		166
		167	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for events
		168	(AnyEvent might or might not keep a reference to this file handle). C<poll>
		169	must be a string that is either C<r> or C<w>, which creates a watcher
		170	waiting for "r"eadable or "w"ritable events, respectively. C<cb> is the
		171	callback to invoke each time the file handle becomes ready.
		172
		173	Although the callback might get passed parameters, their value and
		174	presence is undefined and you cannot rely on them. Portable AnyEvent
		175	callbacks cannot use arguments passed to I/O watcher callbacks.
		176
		177	The I/O watcher might use the underlying file descriptor or a copy of it.
		178	You must not close a file handle as long as any watcher is active on the
		179	underlying file descriptor.
		180
		181	Some event loops issue spurious readyness notifications, so you should
		182	always use non-blocking calls when reading/writing from/to your file
		183	handles.
		184
		185	Example: wait for readability of STDIN, then read a line and disable the
		186	watcher.
		187
		188	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		189	chomp (my $input = <STDIN>);
		190	warn "read: $input\n";
		191	undef $w;
		192	});
		193
		194	=head2 TIME WATCHERS
		195
		196	You can create a time watcher by calling the C<< AnyEvent->timer >>
		197	method with the following mandatory arguments:
		198
		199	C<after> specifies after how many seconds (fractional values are
		200	supported) the callback should be invoked. C<cb> is the callback to invoke
		201	in that case.
		202
		203	Although the callback might get passed parameters, their value and
		204	presence is undefined and you cannot rely on them. Portable AnyEvent
		205	callbacks cannot use arguments passed to time watcher callbacks.
		206
		207	The callback will normally be invoked once only. If you specify another
		208	parameter, C<interval>, as a strictly positive number (> 0), then the
		209	callback will be invoked regularly at that interval (in fractional
		210	seconds) after the first invocation. If C<interval> is specified with a
		211	false value, then it is treated as if it were missing.
		212
		213	The callback will be rescheduled before invoking the callback, but no
		214	attempt is done to avoid timer drift in most backends, so the interval is
		215	only approximate.
		216
		217	Example: fire an event after 7.7 seconds.
		218
		219	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		220	warn "timeout\n";
		221	});
		222
		223	# to cancel the timer:
		224	undef $w;
		225
		226	Example 2: fire an event after 0.5 seconds, then roughly every second.
		227
		228	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		229	warn "timeout\n";
		230	};
		231
		232	=head3 TIMING ISSUES
		233
		234	There are two ways to handle timers: based on real time (relative, "fire
		235	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		236	o'clock").
		237
		238	While most event loops expect timers to specified in a relative way, they
		239	use absolute time internally. This makes a difference when your clock
		240	"jumps", for example, when ntp decides to set your clock backwards from
		241	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		242	fire "after" a second might actually take six years to finally fire.
		243
		244	AnyEvent cannot compensate for this. The only event loop that is conscious
		245	about these issues is L<EV>, which offers both relative (ev_timer, based
		246	on true relative time) and absolute (ev_periodic, based on wallclock time)
		247	timers.
		248
		249	AnyEvent always prefers relative timers, if available, matching the
		250	AnyEvent API.
		251
		252	AnyEvent has two additional methods that return the "current time":
		253
9	=over 4	254	=over 4
10		255
		256	=item AnyEvent->time
		257
		258	This returns the "current wallclock time" as a fractional number of
		259	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		260	return, and the result is guaranteed to be compatible with those).
		261
		262	It progresses independently of any event loop processing, i.e. each call
		263	will check the system clock, which usually gets updated frequently.
		264
		265	=item AnyEvent->now
		266
		267	This also returns the "current wallclock time", but unlike C<time>, above,
		268	this value might change only once per event loop iteration, depending on
		269	the event loop (most return the same time as C<time>, above). This is the
		270	time that AnyEvent's timers get scheduled against.
		271
		272	I<In almost all cases (in all cases if you don't care), this is the
		273	function to call when you want to know the current time.>
		274
		275	This function is also often faster then C<< AnyEvent->time >>, and
		276	thus the preferred method if you want some timestamp (for example,
		277	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		278
		279	The rest of this section is only of relevance if you try to be very exact
		280	with your timing, you can skip it without bad conscience.
		281
		282	For a practical example of when these times differ, consider L<Event::Lib>
		283	and L<EV> and the following set-up:
		284
		285	The event loop is running and has just invoked one of your callback at
		286	time=500 (assume no other callbacks delay processing). In your callback,
		287	you wait a second by executing C<sleep 1> (blocking the process for a
		288	second) and then (at time=501) you create a relative timer that fires
		289	after three seconds.
		290
		291	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		292	both return C<501>, because that is the current time, and the timer will
		293	be scheduled to fire at time=504 (C<501> + C<3>).
		294
		295	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		296	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		297	last event processing phase started. With L<EV>, your timer gets scheduled
		298	to run at time=503 (C<500> + C<3>).
		299
		300	In one sense, L<Event::Lib> is more exact, as it uses the current time
		301	regardless of any delays introduced by event processing. However, most
		302	callbacks do not expect large delays in processing, so this causes a
		303	higher drift (and a lot more system calls to get the current time).
		304
		305	In another sense, L<EV> is more exact, as your timer will be scheduled at
		306	the same time, regardless of how long event processing actually took.
		307
		308	In either case, if you care (and in most cases, you don't), then you
		309	can get whatever behaviour you want with any event loop, by taking the
		310	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		311	account.
		312
		313	=back
		314
		315	=head2 SIGNAL WATCHERS
		316
		317	You can watch for signals using a signal watcher, C<signal> is the signal
		318	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		319	callback to be invoked whenever a signal occurs.
		320
		321	Although the callback might get passed parameters, their value and
		322	presence is undefined and you cannot rely on them. Portable AnyEvent
		323	callbacks cannot use arguments passed to signal watcher callbacks.
		324
		325	Multiple signal occurrences can be clumped together into one callback
		326	invocation, and callback invocation will be synchronous. Synchronous means
		327	that it might take a while until the signal gets handled by the process,
		328	but it is guaranteed not to interrupt any other callbacks.
		329
		330	The main advantage of using these watchers is that you can share a signal
		331	between multiple watchers.
		332
		333	This watcher might use C<%SIG>, so programs overwriting those signals
		334	directly will likely not work correctly.
		335
		336	Example: exit on SIGINT
		337
		338	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		339
		340	=head2 CHILD PROCESS WATCHERS
		341
		342	You can also watch on a child process exit and catch its exit status.
		343
		344	The child process is specified by the C<pid> argument (if set to C<0>, it
		345	watches for any child process exit). The watcher will triggered only when
		346	the child process has finished and an exit status is available, not on
		347	any trace events (stopped/continued).
		348
		349	The callback will be called with the pid and exit status (as returned by
		350	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		351	callback arguments.
		352
		353	This watcher type works by installing a signal handler for C<SIGCHLD>,
		354	and since it cannot be shared, nothing else should use SIGCHLD or reap
		355	random child processes (waiting for specific child processes, e.g. inside
		356	C<system>, is just fine).
		357
		358	There is a slight catch to child watchers, however: you usually start them
		359	I<after> the child process was created, and this means the process could
		360	have exited already (and no SIGCHLD will be sent anymore).
		361
		362	Not all event models handle this correctly (POE doesn't), but even for
		363	event models that I<do> handle this correctly, they usually need to be
		364	loaded before the process exits (i.e. before you fork in the first place).
		365
		366	This means you cannot create a child watcher as the very first thing in an
		367	AnyEvent program, you I<have> to create at least one watcher before you
		368	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		369
		370	Example: fork a process and wait for it
		371
		372	my $done = AnyEvent->condvar;
		373
		374	my $pid = fork or exit 5;
		375
		376	my $w = AnyEvent->child (
		377	pid => $pid,
		378	cb => sub {
		379	my ($pid, $status) = @_;
		380	warn "pid $pid exited with status $status";
		381	$done->send;
		382	},
		383	);
		384
		385	# do something else, then wait for process exit
		386	$done->recv;
		387
		388	=head2 CONDITION VARIABLES
		389
		390	If you are familiar with some event loops you will know that all of them
		391	require you to run some blocking "loop", "run" or similar function that
		392	will actively watch for new events and call your callbacks.
		393
		394	AnyEvent is different, it expects somebody else to run the event loop and
		395	will only block when necessary (usually when told by the user).
		396
		397	The instrument to do that is called a "condition variable", so called
		398	because they represent a condition that must become true.
		399
		400	Condition variables can be created by calling the C<< AnyEvent->condvar
		401	>> method, usually without arguments. The only argument pair allowed is
		402
		403	C<cb>, which specifies a callback to be called when the condition variable
		404	becomes true, with the condition variable as the first argument (but not
		405	the results).
		406
		407	After creation, the condition variable is "false" until it becomes "true"
		408	by calling the C<send> method (or calling the condition variable as if it
		409	were a callback, read about the caveats in the description for the C<<
		410	->send >> method).
		411
		412	Condition variables are similar to callbacks, except that you can
		413	optionally wait for them. They can also be called merge points - points
		414	in time where multiple outstanding events have been processed. And yet
		415	another way to call them is transactions - each condition variable can be
		416	used to represent a transaction, which finishes at some point and delivers
		417	a result.
		418
		419	Condition variables are very useful to signal that something has finished,
		420	for example, if you write a module that does asynchronous http requests,
		421	then a condition variable would be the ideal candidate to signal the
		422	availability of results. The user can either act when the callback is
		423	called or can synchronously C<< ->recv >> for the results.
		424
		425	You can also use them to simulate traditional event loops - for example,
		426	you can block your main program until an event occurs - for example, you
		427	could C<< ->recv >> in your main program until the user clicks the Quit
		428	button of your app, which would C<< ->send >> the "quit" event.
		429
		430	Note that condition variables recurse into the event loop - if you have
		431	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		432	lose. Therefore, condition variables are good to export to your caller, but
		433	you should avoid making a blocking wait yourself, at least in callbacks,
		434	as this asks for trouble.
		435
		436	Condition variables are represented by hash refs in perl, and the keys
		437	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		438	easy (it is often useful to build your own transaction class on top of
		439	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		440	it's C<new> method in your own C<new> method.
		441
		442	There are two "sides" to a condition variable - the "producer side" which
		443	eventually calls C<< -> send >>, and the "consumer side", which waits
		444	for the send to occur.
		445
		446	Example: wait for a timer.
		447
		448	# wait till the result is ready
		449	my $result_ready = AnyEvent->condvar;
		450
		451	# do something such as adding a timer
		452	# or socket watcher the calls $result_ready->send
		453	# when the "result" is ready.
		454	# in this case, we simply use a timer:
		455	my $w = AnyEvent->timer (
		456	after => 1,
		457	cb => sub { $result_ready->send },
		458	);
		459
		460	# this "blocks" (while handling events) till the callback
		461	# calls send
		462	$result_ready->recv;
		463
		464	Example: wait for a timer, but take advantage of the fact that
		465	condition variables are also code references.
		466
		467	my $done = AnyEvent->condvar;
		468	my $delay = AnyEvent->timer (after => 5, cb => $done);
		469	$done->recv;
		470
		471	Example: Imagine an API that returns a condvar and doesn't support
		472	callbacks. This is how you make a synchronous call, for example from
		473	the main program:
		474
		475	use AnyEvent::CouchDB;
		476
		477	...
		478
		479	my @info = $couchdb->info->recv;
		480
		481	And this is how you would just ste a callback to be called whenever the
		482	results are available:
		483
		484	$couchdb->info->cb (sub {
		485	my @info = $_[0]->recv;
		486	});
		487
		488	=head3 METHODS FOR PRODUCERS
		489
		490	These methods should only be used by the producing side, i.e. the
		491	code/module that eventually sends the signal. Note that it is also
		492	the producer side which creates the condvar in most cases, but it isn't
		493	uncommon for the consumer to create it as well.
		494
		495	=over 4
		496
		497	=item $cv->send (...)
		498
		499	Flag the condition as ready - a running C<< ->recv >> and all further
		500	calls to C<recv> will (eventually) return after this method has been
		501	called. If nobody is waiting the send will be remembered.
		502
		503	If a callback has been set on the condition variable, it is called
		504	immediately from within send.
		505
		506	Any arguments passed to the C<send> call will be returned by all
		507	future C<< ->recv >> calls.
		508
		509	Condition variables are overloaded so one can call them directly
		510	(as a code reference). Calling them directly is the same as calling
		511	C<send>. Note, however, that many C-based event loops do not handle
		512	overloading, so as tempting as it may be, passing a condition variable
		513	instead of a callback does not work. Both the pure perl and EV loops
		514	support overloading, however, as well as all functions that use perl to
		515	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		516	example).
		517
		518	=item $cv->croak ($error)
		519
		520	Similar to send, but causes all call's to C<< ->recv >> to invoke
		521	C<Carp::croak> with the given error message/object/scalar.
		522
		523	This can be used to signal any errors to the condition variable
		524	user/consumer.
		525
		526	=item $cv->begin ([group callback])
		527
		528	=item $cv->end
		529
		530	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		531
		532	These two methods can be used to combine many transactions/events into
		533	one. For example, a function that pings many hosts in parallel might want
		534	to use a condition variable for the whole process.
		535
		536	Every call to C<< ->begin >> will increment a counter, and every call to
		537	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		538	>>, the (last) callback passed to C<begin> will be executed. That callback
		539	is I<supposed> to call C<< ->send >>, but that is not required. If no
		540	callback was set, C<send> will be called without any arguments.
		541
		542	Let's clarify this with the ping example:
		543
		544	my $cv = AnyEvent->condvar;
		545
		546	my %result;
		547	$cv->begin (sub { $cv->send (\%result) });
		548
		549	for my $host (@list_of_hosts) {
		550	$cv->begin;
		551	ping_host_then_call_callback $host, sub {
		552	$result{$host} = ...;
		553	$cv->end;
		554	};
		555	}
		556
		557	$cv->end;
		558
		559	This code fragment supposedly pings a number of hosts and calls
		560	C<send> after results for all then have have been gathered - in any
		561	order. To achieve this, the code issues a call to C<begin> when it starts
		562	each ping request and calls C<end> when it has received some result for
		563	it. Since C<begin> and C<end> only maintain a counter, the order in which
		564	results arrive is not relevant.
		565
		566	There is an additional bracketing call to C<begin> and C<end> outside the
		567	loop, which serves two important purposes: first, it sets the callback
		568	to be called once the counter reaches C<0>, and second, it ensures that
		569	C<send> is called even when C<no> hosts are being pinged (the loop
		570	doesn't execute once).
		571
		572	This is the general pattern when you "fan out" into multiple subrequests:
		573	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		574	is called at least once, and then, for each subrequest you start, call
		575	C<begin> and for each subrequest you finish, call C<end>.
		576
		577	=back
		578
		579	=head3 METHODS FOR CONSUMERS
		580
		581	These methods should only be used by the consuming side, i.e. the
		582	code awaits the condition.
		583
		584	=over 4
		585
		586	=item $cv->recv
		587
		588	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		589	>> methods have been called on c<$cv>, while servicing other watchers
		590	normally.
		591
		592	You can only wait once on a condition - additional calls are valid but
		593	will return immediately.
		594
		595	If an error condition has been set by calling C<< ->croak >>, then this
		596	function will call C<croak>.
		597
		598	In list context, all parameters passed to C<send> will be returned,
		599	in scalar context only the first one will be returned.
		600
		601	Not all event models support a blocking wait - some die in that case
		602	(programs might want to do that to stay interactive), so I<if you are
		603	using this from a module, never require a blocking wait>, but let the
		604	caller decide whether the call will block or not (for example, by coupling
		605	condition variables with some kind of request results and supporting
		606	callbacks so the caller knows that getting the result will not block,
		607	while still supporting blocking waits if the caller so desires).
		608
		609	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		610	sensibly have two C<< ->recv >>'s in parallel, as that would require
		611	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		612	can supply.
		613
		614	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		615	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		616	versions and also integrates coroutines into AnyEvent, making blocking
		617	C<< ->recv >> calls perfectly safe as long as they are done from another
		618	coroutine (one that doesn't run the event loop).
		619
		620	You can ensure that C<< -recv >> never blocks by setting a callback and
		621	only calling C<< ->recv >> from within that callback (or at a later
		622	time). This will work even when the event loop does not support blocking
		623	waits otherwise.
		624
		625	=item $bool = $cv->ready
		626
		627	Returns true when the condition is "true", i.e. whether C<send> or
		628	C<croak> have been called.
		629
		630	=item $cb = $cv->cb ($cb->($cv))
		631
		632	This is a mutator function that returns the callback set and optionally
		633	replaces it before doing so.
		634
		635	The callback will be called when the condition becomes "true", i.e. when
		636	C<send> or C<croak> are called, with the only argument being the condition
		637	variable itself. Calling C<recv> inside the callback or at any later time
		638	is guaranteed not to block.
		639
		640	=back
		641
		642	=head1 GLOBAL VARIABLES AND FUNCTIONS
		643
		644	=over 4
		645
		646	=item $AnyEvent::MODEL
		647
		648	Contains C<undef> until the first watcher is being created. Then it
		649	contains the event model that is being used, which is the name of the
		650	Perl class implementing the model. This class is usually one of the
		651	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		652	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		653
		654	The known classes so far are:
		655
		656	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		657	AnyEvent::Impl::Event based on Event, second best choice.
		658	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		659	AnyEvent::Impl::Glib based on Glib, third-best choice.
		660	AnyEvent::Impl::Tk based on Tk, very bad choice.
		661	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		662	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		663	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		664
		665	There is no support for WxWidgets, as WxWidgets has no support for
		666	watching file handles. However, you can use WxWidgets through the
		667	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		668	second, which was considered to be too horrible to even consider for
		669	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		670	it's adaptor.
		671
		672	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		673	autodetecting them.
		674
		675	=item AnyEvent::detect
		676
		677	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		678	if necessary. You should only call this function right before you would
		679	have created an AnyEvent watcher anyway, that is, as late as possible at
		680	runtime.
		681
		682	=item $guard = AnyEvent::post_detect { BLOCK }
		683
		684	Arranges for the code block to be executed as soon as the event model is
		685	autodetected (or immediately if this has already happened).
		686
		687	If called in scalar or list context, then it creates and returns an object
		688	that automatically removes the callback again when it is destroyed. See
		689	L<Coro::BDB> for a case where this is useful.
		690
		691	=item @AnyEvent::post_detect
		692
		693	If there are any code references in this array (you can C<push> to it
		694	before or after loading AnyEvent), then they will called directly after
		695	the event loop has been chosen.
		696
		697	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		698	if it contains a true value then the event loop has already been detected,
		699	and the array will be ignored.
		700
		701	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		702
		703	=back
		704
		705	=head1 WHAT TO DO IN A MODULE
		706
		707	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		708	freely, but you should not load a specific event module or rely on it.
		709
		710	Be careful when you create watchers in the module body - AnyEvent will
		711	decide which event module to use as soon as the first method is called, so
		712	by calling AnyEvent in your module body you force the user of your module
		713	to load the event module first.
		714
		715	Never call C<< ->recv >> on a condition variable unless you I<know> that
		716	the C<< ->send >> method has been called on it already. This is
		717	because it will stall the whole program, and the whole point of using
		718	events is to stay interactive.
		719
		720	It is fine, however, to call C<< ->recv >> when the user of your module
		721	requests it (i.e. if you create a http request object ad have a method
		722	called C<results> that returns the results, it should call C<< ->recv >>
		723	freely, as the user of your module knows what she is doing. always).
		724
		725	=head1 WHAT TO DO IN THE MAIN PROGRAM
		726
		727	There will always be a single main program - the only place that should
		728	dictate which event model to use.
		729
		730	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		731	do anything special (it does not need to be event-based) and let AnyEvent
		732	decide which implementation to chose if some module relies on it.
		733
		734	If the main program relies on a specific event model - for example, in
		735	Gtk2 programs you have to rely on the Glib module - you should load the
		736	event module before loading AnyEvent or any module that uses it: generally
		737	speaking, you should load it as early as possible. The reason is that
		738	modules might create watchers when they are loaded, and AnyEvent will
		739	decide on the event model to use as soon as it creates watchers, and it
		740	might chose the wrong one unless you load the correct one yourself.
		741
		742	You can chose to use a pure-perl implementation by loading the
		743	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		744	everywhere, but letting AnyEvent chose the model is generally better.
		745
		746	=head2 MAINLOOP EMULATION
		747
		748	Sometimes (often for short test scripts, or even standalone programs who
		749	only want to use AnyEvent), you do not want to run a specific event loop.
		750
		751	In that case, you can use a condition variable like this:
		752
		753	AnyEvent->condvar->recv;
		754
		755	This has the effect of entering the event loop and looping forever.
		756
		757	Note that usually your program has some exit condition, in which case
		758	it is better to use the "traditional" approach of storing a condition
		759	variable somewhere, waiting for it, and sending it when the program should
		760	exit cleanly.
		761
		762
		763	=head1 OTHER MODULES
		764
		765	The following is a non-exhaustive list of additional modules that use
		766	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		767	in the same program. Some of the modules come with AnyEvent, some are
		768	available via CPAN.
		769
		770	=over 4
		771
		772	=item L<AnyEvent::Util>
		773
		774	Contains various utility functions that replace often-used but blocking
		775	functions such as C<inet_aton> by event-/callback-based versions.
		776
		777	=item L<AnyEvent::Socket>
		778
		779	Provides various utility functions for (internet protocol) sockets,
		780	addresses and name resolution. Also functions to create non-blocking tcp
		781	connections or tcp servers, with IPv6 and SRV record support and more.
		782
		783	=item L<AnyEvent::Handle>
		784
		785	Provide read and write buffers, manages watchers for reads and writes,
		786	supports raw and formatted I/O, I/O queued and fully transparent and
		787	non-blocking SSL/TLS.
		788
		789	=item L<AnyEvent::DNS>
		790
		791	Provides rich asynchronous DNS resolver capabilities.
		792
		793	=item L<AnyEvent::HTTP>
		794
		795	A simple-to-use HTTP library that is capable of making a lot of concurrent
		796	HTTP requests.
		797
		798	=item L<AnyEvent::HTTPD>
		799
		800	Provides a simple web application server framework.
		801
		802	=item L<AnyEvent::FastPing>
		803
		804	The fastest ping in the west.
		805
		806	=item L<AnyEvent::DBI>
		807
		808	Executes L<DBI> requests asynchronously in a proxy process.
		809
		810	=item L<AnyEvent::AIO>
		811
		812	Truly asynchronous I/O, should be in the toolbox of every event
		813	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		814	together.
		815
		816	=item L<AnyEvent::BDB>
		817
		818	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		819	L<BDB> and AnyEvent together.
		820
		821	=item L<AnyEvent::GPSD>
		822
		823	A non-blocking interface to gpsd, a daemon delivering GPS information.
		824
		825	=item L<AnyEvent::IGS>
		826
		827	A non-blocking interface to the Internet Go Server protocol (used by
		828	L<App::IGS>).
		829
		830	=item L<Net::IRC3>
		831
		832	AnyEvent based IRC client module family.
		833
		834	=item L<Net::XMPP2>
		835
		836	AnyEvent based XMPP (Jabber protocol) module family.
		837
		838	=item L<Net::FCP>
		839
		840	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		841	of AnyEvent.
		842
		843	=item L<Event::ExecFlow>
		844
		845	High level API for event-based execution flow control.
		846
		847	=item L<Coro>
		848
		849	Has special support for AnyEvent via L<Coro::AnyEvent>.
		850
		851	=item L<IO::Lambda>
		852
		853	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		854
		855	=back
		856
11	=cut	857	=cut
12		858
13	package AnyEvent;	859	package AnyEvent;
14		860
		861	no warnings;
		862	use strict qw(vars subs);
		863
15	use Carp;	864	use Carp;
16		865
17	$VERSION = 0.1;	866	our $VERSION = 4.234;
		867	our $MODEL;
18		868
19	no warnings;	869	our $AUTOLOAD;
		870	our @ISA;
		871
		872	our @REGISTRY;
		873
		874	our $WIN32;
		875
		876	BEGIN {
		877	my $win32 = ! ! ($^O =~ /mswin32/i);
		878	eval "sub WIN32(){ $win32 }";
		879	}
		880
		881	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		882
		883	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		884
		885	{
		886	my $idx;
		887	$PROTOCOL{$_} = ++$idx
		888	for reverse split /\s*,\s*/,
		889	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		890	}
20		891
21	my @models = (	892	my @models = (
22	[Coro => Coro::Event::],	893	[EV:: => AnyEvent::Impl::EV::],
23	[Event => Event::],	894	[Event:: => AnyEvent::Impl::Event::],
24	[Glib => Glib::],	895	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
25	[Tk => Tk::],	896	# everything below here will not be autoprobed
		897	# as the pureperl backend should work everywhere
		898	# and is usually faster
		899	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		900	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		901	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		902	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		903	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		904	[Wx:: => AnyEvent::Impl::POE::],
		905	[Prima:: => AnyEvent::Impl::POE::],
26	);	906	);
27		907
		908	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
		909
		910	our @post_detect;
		911
		912	sub post_detect(&) {
		913	my ($cb) = @_;
		914
		915	if ($MODEL) {
		916	$cb->();
		917
		918	1
		919	} else {
		920	push @post_detect, $cb;
		921
		922	defined wantarray
		923	? bless \$cb, "AnyEvent::Util::PostDetect"
		924	: ()
		925	}
		926	}
		927
		928	sub AnyEvent::Util::PostDetect::DESTROY {
		929	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		930	}
		931
		932	sub detect() {
		933	unless ($MODEL) {
		934	no strict 'refs';
		935	local $SIG{__DIE__};
		936
		937	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		938	my $model = "AnyEvent::Impl::$1";
		939	if (eval "require $model") {
		940	$MODEL = $model;
		941	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		942	} else {
		943	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		944	}
		945	}
		946
		947	# check for already loaded models
		948	unless ($MODEL) {
		949	for (@REGISTRY, @models) {
		950	my ($package, $model) = @$_;
		951	if (${"$package\::VERSION"} > 0) {
		952	if (eval "require $model") {
		953	$MODEL = $model;
		954	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		955	last;
		956	}
		957	}
		958	}
		959
		960	unless ($MODEL) {
		961	# try to load a model
		962
		963	for (@REGISTRY, @models) {
		964	my ($package, $model) = @$_;
		965	if (eval "require $package"
		966	and ${"$package\::VERSION"} > 0
		967	and eval "require $model") {
		968	$MODEL = $model;
		969	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		970	last;
		971	}
		972	}
		973
		974	$MODEL
		975	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		976	}
		977	}
		978
		979	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		980
		981	unshift @ISA, $MODEL;
		982
		983	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		984
		985	(shift @post_detect)->() while @post_detect;
		986	}
		987
		988	$MODEL
		989	}
		990
28	sub AUTOLOAD {	991	sub AUTOLOAD {
29	$AUTOLOAD =~ s/.*://;	992	(my $func = $AUTOLOAD) =~ s/.*://;
30		993
31	for (@models) {	994	$method{$func}
32	my ($model, $package) = @$_;	995	or croak "$func: not a valid method for AnyEvent objects";
33	if (defined ${"$package\::VERSION"}) {	996
34	$EVENT = "AnyEvent::Impl::$model";	997	detect unless $MODEL;
35	eval "require $EVENT"; die if $@;	998
36	goto &{"$EVENT\::$AUTOLOAD"};	999	my $class = shift;
37	}	1000	$class->$func (@_);
		1001	}
		1002
		1003	# utility function to dup a filehandle. this is used by many backends
		1004	# to support binding more than one watcher per filehandle (they usually
		1005	# allow only one watcher per fd, so we dup it to get a different one).
		1006	sub _dupfh($$$$) {
		1007	my ($poll, $fh, $r, $w) = @_;
		1008
		1009	require Fcntl;
		1010
		1011	# cygwin requires the fh mode to be matching, unix doesn't
		1012	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1013	: $poll eq "w" ? ($w, ">")
		1014	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1015
		1016	open my $fh2, "$mode&" . fileno $fh
		1017	or die "cannot dup() filehandle: $!";
		1018
		1019	# we assume CLOEXEC is already set by perl in all important cases
		1020
		1021	($fh2, $rw)
		1022	}
		1023
		1024	package AnyEvent::Base;
		1025
		1026	# default implementation for now and time
		1027
		1028	BEGIN {
		1029	if (eval "use Time::HiRes (); time (); 1") {
		1030	*_time = \&Time::HiRes::time;
		1031	# if (eval "use POSIX (); (POSIX::times())...
		1032	} else {
		1033	*_time = sub { time }; # epic fail
38	}	1034	}
		1035	}
39		1036
40	for (@models) {	1037	sub time { _time }
41	my ($model, $package) = @$_;	1038	sub now { _time }
42	$EVENT = "AnyEvent::Impl::$model";	1039
43	if (eval "require $EVENT") {	1040	# default implementation for ->condvar
44	goto &{"$EVENT\::$AUTOLOAD"};	1041
45	}	1042	sub condvar {
		1043	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		1044	}
		1045
		1046	# default implementation for ->signal
		1047
		1048	our %SIG_CB;
		1049
		1050	sub signal {
		1051	my (undef, %arg) = @_;
		1052
		1053	my $signal = uc $arg{signal}
		1054	or Carp::croak "required option 'signal' is missing";
		1055
		1056	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1057	$SIG{$signal} ||= sub {
		1058	$_->() for values %{ $SIG_CB{$signal} || {} };
		1059	};
		1060
		1061	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		1062	}
		1063
		1064	sub AnyEvent::Base::Signal::DESTROY {
		1065	my ($signal, $cb) = @{$_[0]};
		1066
		1067	delete $SIG_CB{$signal}{$cb};
		1068
		1069	delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
		1070	}
		1071
		1072	# default implementation for ->child
		1073
		1074	our %PID_CB;
		1075	our $CHLD_W;
		1076	our $CHLD_DELAY_W;
		1077	our $PID_IDLE;
		1078	our $WNOHANG;
		1079
		1080	sub _child_wait {
		1081	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1082	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		1083	(values %{ $PID_CB{0} || {} });
46	}	1084	}
47		1085
48	die "No event module selected for AnyEvent and autodetect failed. Install any of these: Coro, Event, Glib or Tk.";	1086	undef $PID_IDLE;
49	}	1087	}
50		1088
51	1;	1089	sub _sigchld {
		1090	# make sure we deliver these changes "synchronous" with the event loop.
		1091	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		1092	undef $CHLD_DELAY_W;
		1093	&_child_wait;
		1094	});
		1095	}
52		1096
		1097	sub child {
		1098	my (undef, %arg) = @_;
		1099
		1100	defined (my $pid = $arg{pid} + 0)
		1101	or Carp::croak "required option 'pid' is missing";
		1102
		1103	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1104
		1105	unless ($WNOHANG) {
		1106	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1107	}
		1108
		1109	unless ($CHLD_W) {
		1110	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1111	# child could be a zombie already, so make at least one round
		1112	&_sigchld;
		1113	}
		1114
		1115	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		1116	}
		1117
		1118	sub AnyEvent::Base::Child::DESTROY {
		1119	my ($pid, $cb) = @{$_[0]};
		1120
		1121	delete $PID_CB{$pid}{$cb};
		1122	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1123
		1124	undef $CHLD_W unless keys %PID_CB;
		1125	}
		1126
		1127	package AnyEvent::CondVar;
		1128
		1129	our @ISA = AnyEvent::CondVar::Base::;
		1130
		1131	package AnyEvent::CondVar::Base;
		1132
		1133	use overload
		1134	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1135	fallback => 1;
		1136
		1137	sub _send {
		1138	# nop
		1139	}
		1140
		1141	sub send {
		1142	my $cv = shift;
		1143	$cv->{_ae_sent} = [@_];
		1144	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1145	$cv->_send;
		1146	}
		1147
		1148	sub croak {
		1149	$_[0]{_ae_croak} = $_[1];
		1150	$_[0]->send;
		1151	}
		1152
		1153	sub ready {
		1154	$_[0]{_ae_sent}
		1155	}
		1156
		1157	sub _wait {
		1158	AnyEvent->one_event while !$_[0]{_ae_sent};
		1159	}
		1160
		1161	sub recv {
		1162	$_[0]->_wait;
		1163
		1164	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1165	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1166	}
		1167
		1168	sub cb {
		1169	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1170	$_[0]{_ae_cb}
		1171	}
		1172
		1173	sub begin {
		1174	++$_[0]{_ae_counter};
		1175	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1176	}
		1177
		1178	sub end {
		1179	return if --$_[0]{_ae_counter};
		1180	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1181	}
		1182
		1183	# undocumented/compatibility with pre-3.4
		1184	*broadcast = \&send;
		1185	*wait = \&_wait;
		1186
		1187	=head1 ERROR AND EXCEPTION HANDLING
		1188
		1189	In general, AnyEvent does not do any error handling - it relies on the
		1190	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1191	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1192	checking of all AnyEvent methods, however, which is highly useful during
		1193	development.
		1194
		1195	As for exception handling (i.e. runtime errors and exceptions thrown while
		1196	executing a callback), this is not only highly event-loop specific, but
		1197	also not in any way wrapped by this module, as this is the job of the main
		1198	program.
		1199
		1200	The pure perl event loop simply re-throws the exception (usually
		1201	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1202	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1203	so on.
		1204
		1205	=head1 ENVIRONMENT VARIABLES
		1206
		1207	The following environment variables are used by this module or its
		1208	submodules:
		1209
		1210	=over 4
		1211
		1212	=item C<PERL_ANYEVENT_VERBOSE>
		1213
		1214	By default, AnyEvent will be completely silent except in fatal
		1215	conditions. You can set this environment variable to make AnyEvent more
		1216	talkative.
		1217
		1218	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1219	conditions, such as not being able to load the event model specified by
		1220	C<PERL_ANYEVENT_MODEL>.
		1221
		1222	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1223	model it chooses.
		1224
		1225	=item C<PERL_ANYEVENT_STRICT>
		1226
		1227	AnyEvent does not do much argument checking by default, as thorough
		1228	argument checking is very costly. Setting this variable to a true value
		1229	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1230	check the arguments passed to most method calls. If it finds any problems
		1231	it will croak.
		1232
		1233	In other words, enables "strict" mode.
		1234
		1235	Unlike C<use strict>, it is definitely recommended ot keep it off in
		1236	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1237	developing programs can be very useful, however.
		1238
		1239	=item C<PERL_ANYEVENT_MODEL>
		1240
		1241	This can be used to specify the event model to be used by AnyEvent, before
		1242	auto detection and -probing kicks in. It must be a string consisting
		1243	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1244	and the resulting module name is loaded and if the load was successful,
		1245	used as event model. If it fails to load AnyEvent will proceed with
		1246	auto detection and -probing.
		1247
		1248	This functionality might change in future versions.
		1249
		1250	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1251	could start your program like this:
		1252
		1253	PERL_ANYEVENT_MODEL=Perl perl ...
		1254
		1255	=item C<PERL_ANYEVENT_PROTOCOLS>
		1256
		1257	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1258	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1259	of auto probing).
		1260
		1261	Must be set to a comma-separated list of protocols or address families,
		1262	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1263	used, and preference will be given to protocols mentioned earlier in the
		1264	list.
		1265
		1266	This variable can effectively be used for denial-of-service attacks
		1267	against local programs (e.g. when setuid), although the impact is likely
		1268	small, as the program has to handle connection errors already-
		1269
		1270	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1271	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1272	- only support IPv4, never try to resolve or contact IPv6
		1273	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1274	IPv6, but prefer IPv6 over IPv4.
		1275
		1276	=item C<PERL_ANYEVENT_EDNS0>
		1277
		1278	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1279	for DNS. This extension is generally useful to reduce DNS traffic, but
		1280	some (broken) firewalls drop such DNS packets, which is why it is off by
		1281	default.
		1282
		1283	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1284	EDNS0 in its DNS requests.
		1285
		1286	=item C<PERL_ANYEVENT_MAX_FORKS>
		1287
		1288	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1289	will create in parallel.
		1290
		1291	=back
		1292
		1293	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1294
		1295	This is an advanced topic that you do not normally need to use AnyEvent in
		1296	a module. This section is only of use to event loop authors who want to
		1297	provide AnyEvent compatibility.
		1298
		1299	If you need to support another event library which isn't directly
		1300	supported by AnyEvent, you can supply your own interface to it by
		1301	pushing, before the first watcher gets created, the package name of
		1302	the event module and the package name of the interface to use onto
		1303	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1304	AnyEvent, so it is reasonably cheap.
		1305
		1306	Example:
		1307
		1308	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1309
		1310	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1311	package/class when it finds the C<urxvt> package/module is already loaded.
		1312
		1313	When AnyEvent is loaded and asked to find a suitable event model, it
		1314	will first check for the presence of urxvt by trying to C<use> the
		1315	C<urxvt::anyevent> module.
		1316
		1317	The class should provide implementations for all watcher types. See
		1318	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1319	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1320	see the sources.
		1321
		1322	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1323	provide suitable (hopefully) replacements.
		1324
		1325	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1326	terminal emulator uses the above line as-is. An interface isn't included
		1327	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1328	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1329	I<rxvt-unicode> distribution.
		1330
		1331	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1332	condition variables: code blocking while waiting for a condition will
		1333	C<die>. This still works with most modules/usages, and blocking calls must
		1334	not be done in an interactive application, so it makes sense.
		1335
		1336	=head1 EXAMPLE PROGRAM
		1337
		1338	The following program uses an I/O watcher to read data from STDIN, a timer
		1339	to display a message once per second, and a condition variable to quit the
		1340	program when the user enters quit:
		1341
		1342	use AnyEvent;
		1343
		1344	my $cv = AnyEvent->condvar;
		1345
		1346	my $io_watcher = AnyEvent->io (
		1347	fh => \*STDIN,
		1348	poll => 'r',
		1349	cb => sub {
		1350	warn "io event <$_[0]>\n"; # will always output <r>
		1351	chomp (my $input = <STDIN>); # read a line
		1352	warn "read: $input\n"; # output what has been read
		1353	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1354	},
		1355	);
		1356
		1357	my $time_watcher; # can only be used once
		1358
		1359	sub new_timer {
		1360	$timer = AnyEvent->timer (after => 1, cb => sub {
		1361	warn "timeout\n"; # print 'timeout' about every second
		1362	&new_timer; # and restart the time
		1363	});
		1364	}
		1365
		1366	new_timer; # create first timer
		1367
		1368	$cv->recv; # wait until user enters /^q/i
		1369
		1370	=head1 REAL-WORLD EXAMPLE
		1371
		1372	Consider the L<Net::FCP> module. It features (among others) the following
		1373	API calls, which are to freenet what HTTP GET requests are to http:
		1374
		1375	my $data = $fcp->client_get ($url); # blocks
		1376
		1377	my $transaction = $fcp->txn_client_get ($url); # does not block
		1378	$transaction->cb ( sub { ... } ); # set optional result callback
		1379	my $data = $transaction->result; # possibly blocks
		1380
		1381	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		1382	given URL and waits till the data has arrived. It is defined to be:
		1383
		1384	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		1385
		1386	And in fact is automatically generated. This is the blocking API of
		1387	L<Net::FCP>, and it works as simple as in any other, similar, module.
		1388
		1389	More complicated is C<txn_client_get>: It only creates a transaction
		1390	(completion, result, ...) object and initiates the transaction.
		1391
		1392	my $txn = bless { }, Net::FCP::Txn::;
		1393
		1394	It also creates a condition variable that is used to signal the completion
		1395	of the request:
		1396
		1397	$txn->{finished} = AnyAvent->condvar;
		1398
		1399	It then creates a socket in non-blocking mode.
		1400
		1401	socket $txn->{fh}, ...;
		1402	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		1403	connect $txn->{fh}, ...
		1404	and !$!{EWOULDBLOCK}
		1405	and !$!{EINPROGRESS}
		1406	and Carp::croak "unable to connect: $!\n";
		1407
		1408	Then it creates a write-watcher which gets called whenever an error occurs
		1409	or the connection succeeds:
		1410
		1411	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		1412
		1413	And returns this transaction object. The C<fh_ready_w> callback gets
		1414	called as soon as the event loop detects that the socket is ready for
		1415	writing.
		1416
		1417	The C<fh_ready_w> method makes the socket blocking again, writes the
		1418	request data and replaces the watcher by a read watcher (waiting for reply
		1419	data). The actual code is more complicated, but that doesn't matter for
		1420	this example:
		1421
		1422	fcntl $txn->{fh}, F_SETFL, 0;
		1423	syswrite $txn->{fh}, $txn->{request}
		1424	or die "connection or write error";
		1425	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		1426
		1427	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		1428	result and signals any possible waiters that the request has finished:
		1429
		1430	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		1431
		1432	if (end-of-file or data complete) {
		1433	$txn->{result} = $txn->{buf};
		1434	$txn->{finished}->send;
		1435	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		1436	}
		1437
		1438	The C<result> method, finally, just waits for the finished signal (if the
		1439	request was already finished, it doesn't wait, of course, and returns the
		1440	data:
		1441
		1442	$txn->{finished}->recv;
		1443	return $txn->{result};
		1444
		1445	The actual code goes further and collects all errors (C<die>s, exceptions)
		1446	that occurred during request processing. The C<result> method detects
		1447	whether an exception as thrown (it is stored inside the $txn object)
		1448	and just throws the exception, which means connection errors and other
		1449	problems get reported tot he code that tries to use the result, not in a
		1450	random callback.
		1451
		1452	All of this enables the following usage styles:
		1453
		1454	1. Blocking:
		1455
		1456	my $data = $fcp->client_get ($url);
		1457
		1458	2. Blocking, but running in parallel:
		1459
		1460	my @datas = map $_->result,
		1461	map $fcp->txn_client_get ($_),
		1462	@urls;
		1463
		1464	Both blocking examples work without the module user having to know
		1465	anything about events.
		1466
		1467	3a. Event-based in a main program, using any supported event module:
		1468
		1469	use EV;
		1470
		1471	$fcp->txn_client_get ($url)->cb (sub {
		1472	my $txn = shift;
		1473	my $data = $txn->result;
		1474	...
		1475	});
		1476
		1477	EV::loop;
		1478
		1479	3b. The module user could use AnyEvent, too:
		1480
		1481	use AnyEvent;
		1482
		1483	my $quit = AnyEvent->condvar;
		1484
		1485	$fcp->txn_client_get ($url)->cb (sub {
		1486	...
		1487	$quit->send;
		1488	});
		1489
		1490	$quit->recv;
		1491
		1492
		1493	=head1 BENCHMARKS
		1494
		1495	To give you an idea of the performance and overheads that AnyEvent adds
		1496	over the event loops themselves and to give you an impression of the speed
		1497	of various event loops I prepared some benchmarks.
		1498
		1499	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1500
		1501	Here is a benchmark of various supported event models used natively and
		1502	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1503	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1504	which it is), lets them fire exactly once and destroys them again.
		1505
		1506	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1507	distribution.
		1508
		1509	=head3 Explanation of the columns
		1510
		1511	I<watcher> is the number of event watchers created/destroyed. Since
		1512	different event models feature vastly different performances, each event
		1513	loop was given a number of watchers so that overall runtime is acceptable
		1514	and similar between tested event loop (and keep them from crashing): Glib
		1515	would probably take thousands of years if asked to process the same number
		1516	of watchers as EV in this benchmark.
		1517
		1518	I<bytes> is the number of bytes (as measured by the resident set size,
		1519	RSS) consumed by each watcher. This method of measuring captures both C
		1520	and Perl-based overheads.
		1521
		1522	I<create> is the time, in microseconds (millionths of seconds), that it
		1523	takes to create a single watcher. The callback is a closure shared between
		1524	all watchers, to avoid adding memory overhead. That means closure creation
		1525	and memory usage is not included in the figures.
		1526
		1527	I<invoke> is the time, in microseconds, used to invoke a simple
		1528	callback. The callback simply counts down a Perl variable and after it was
		1529	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1530	signal the end of this phase.
		1531
		1532	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1533	watcher.
		1534
		1535	=head3 Results
		1536
		1537	name watchers bytes create invoke destroy comment
		1538	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1539	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1540	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1541	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1542	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1543	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1544	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1545	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1546	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1547	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1548
		1549	=head3 Discussion
		1550
		1551	The benchmark does I<not> measure scalability of the event loop very
		1552	well. For example, a select-based event loop (such as the pure perl one)
		1553	can never compete with an event loop that uses epoll when the number of
		1554	file descriptors grows high. In this benchmark, all events become ready at
		1555	the same time, so select/poll-based implementations get an unnatural speed
		1556	boost.
		1557
		1558	Also, note that the number of watchers usually has a nonlinear effect on
		1559	overall speed, that is, creating twice as many watchers doesn't take twice
		1560	the time - usually it takes longer. This puts event loops tested with a
		1561	higher number of watchers at a disadvantage.
		1562
		1563	To put the range of results into perspective, consider that on the
		1564	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1565	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1566	cycles with POE.
		1567
		1568	C<EV> is the sole leader regarding speed and memory use, which are both
		1569	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1570	far less memory than any other event loop and is still faster than Event
		1571	natively.
		1572
		1573	The pure perl implementation is hit in a few sweet spots (both the
		1574	constant timeout and the use of a single fd hit optimisations in the perl
		1575	interpreter and the backend itself). Nevertheless this shows that it
		1576	adds very little overhead in itself. Like any select-based backend its
		1577	performance becomes really bad with lots of file descriptors (and few of
		1578	them active), of course, but this was not subject of this benchmark.
		1579
		1580	The C<Event> module has a relatively high setup and callback invocation
		1581	cost, but overall scores in on the third place.
		1582
		1583	C<Glib>'s memory usage is quite a bit higher, but it features a
		1584	faster callback invocation and overall ends up in the same class as
		1585	C<Event>. However, Glib scales extremely badly, doubling the number of
		1586	watchers increases the processing time by more than a factor of four,
		1587	making it completely unusable when using larger numbers of watchers
		1588	(note that only a single file descriptor was used in the benchmark, so
		1589	inefficiencies of C<poll> do not account for this).
		1590
		1591	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1592	more than 2000 watchers is a big setback, however, as correctness takes
		1593	precedence over speed. Nevertheless, its performance is surprising, as the
		1594	file descriptor is dup()ed for each watcher. This shows that the dup()
		1595	employed by some adaptors is not a big performance issue (it does incur a
		1596	hidden memory cost inside the kernel which is not reflected in the figures
		1597	above).
		1598
		1599	C<POE>, regardless of underlying event loop (whether using its pure perl
		1600	select-based backend or the Event module, the POE-EV backend couldn't
		1601	be tested because it wasn't working) shows abysmal performance and
		1602	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1603	as EV watchers, and 10 times as much memory as Event (the high memory
		1604	requirements are caused by requiring a session for each watcher). Watcher
		1605	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1606	implementation.
		1607
		1608	The design of the POE adaptor class in AnyEvent can not really account
		1609	for the performance issues, though, as session creation overhead is
		1610	small compared to execution of the state machine, which is coded pretty
		1611	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1612	using multiple sessions is not a good approach, especially regarding
		1613	memory usage, even the author of POE could not come up with a faster
		1614	design).
		1615
		1616	=head3 Summary
		1617
		1618	=over 4
		1619
		1620	=item * Using EV through AnyEvent is faster than any other event loop
		1621	(even when used without AnyEvent), but most event loops have acceptable
		1622	performance with or without AnyEvent.
		1623
		1624	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1625	the actual event loop, only with extremely fast event loops such as EV
		1626	adds AnyEvent significant overhead.
		1627
		1628	=item * You should avoid POE like the plague if you want performance or
		1629	reasonable memory usage.
		1630
		1631	=back
		1632
		1633	=head2 BENCHMARKING THE LARGE SERVER CASE
		1634
		1635	This benchmark actually benchmarks the event loop itself. It works by
		1636	creating a number of "servers": each server consists of a socket pair, a
		1637	timeout watcher that gets reset on activity (but never fires), and an I/O
		1638	watcher waiting for input on one side of the socket. Each time the socket
		1639	watcher reads a byte it will write that byte to a random other "server".
		1640
		1641	The effect is that there will be a lot of I/O watchers, only part of which
		1642	are active at any one point (so there is a constant number of active
		1643	fds for each loop iteration, but which fds these are is random). The
		1644	timeout is reset each time something is read because that reflects how
		1645	most timeouts work (and puts extra pressure on the event loops).
		1646
		1647	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1648	(1%) are active. This mirrors the activity of large servers with many
		1649	connections, most of which are idle at any one point in time.
		1650
		1651	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1652	distribution.
		1653
		1654	=head3 Explanation of the columns
		1655
		1656	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1657	each server has a read and write socket end).
		1658
		1659	I<create> is the time it takes to create a socket pair (which is
		1660	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1661
		1662	I<request>, the most important value, is the time it takes to handle a
		1663	single "request", that is, reading the token from the pipe and forwarding
		1664	it to another server. This includes deleting the old timeout and creating
		1665	a new one that moves the timeout into the future.
		1666
		1667	=head3 Results
		1668
		1669	name sockets create request
		1670	EV 20000 69.01 11.16
		1671	Perl 20000 73.32 35.87
		1672	Event 20000 212.62 257.32
		1673	Glib 20000 651.16 1896.30
		1674	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1675
		1676	=head3 Discussion
		1677
		1678	This benchmark I<does> measure scalability and overall performance of the
		1679	particular event loop.
		1680
		1681	EV is again fastest. Since it is using epoll on my system, the setup time
		1682	is relatively high, though.
		1683
		1684	Perl surprisingly comes second. It is much faster than the C-based event
		1685	loops Event and Glib.
		1686
		1687	Event suffers from high setup time as well (look at its code and you will
		1688	understand why). Callback invocation also has a high overhead compared to
		1689	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1690	uses select or poll in basically all documented configurations.
		1691
		1692	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1693	clearly fails to perform with many filehandles or in busy servers.
		1694
		1695	POE is still completely out of the picture, taking over 1000 times as long
		1696	as EV, and over 100 times as long as the Perl implementation, even though
		1697	it uses a C-based event loop in this case.
		1698
		1699	=head3 Summary
		1700
		1701	=over 4
		1702
		1703	=item * The pure perl implementation performs extremely well.
		1704
		1705	=item * Avoid Glib or POE in large projects where performance matters.
		1706
		1707	=back
		1708
		1709	=head2 BENCHMARKING SMALL SERVERS
		1710
		1711	While event loops should scale (and select-based ones do not...) even to
		1712	large servers, most programs we (or I :) actually write have only a few
		1713	I/O watchers.
		1714
		1715	In this benchmark, I use the same benchmark program as in the large server
		1716	case, but it uses only eight "servers", of which three are active at any
		1717	one time. This should reflect performance for a small server relatively
		1718	well.
		1719
		1720	The columns are identical to the previous table.
		1721
		1722	=head3 Results
		1723
		1724	name sockets create request
		1725	EV 16 20.00 6.54
		1726	Perl 16 25.75 12.62
		1727	Event 16 81.27 35.86
		1728	Glib 16 32.63 15.48
		1729	POE 16 261.87 276.28 uses POE::Loop::Event
		1730
		1731	=head3 Discussion
		1732
		1733	The benchmark tries to test the performance of a typical small
		1734	server. While knowing how various event loops perform is interesting, keep
		1735	in mind that their overhead in this case is usually not as important, due
		1736	to the small absolute number of watchers (that is, you need efficiency and
		1737	speed most when you have lots of watchers, not when you only have a few of
		1738	them).
		1739
		1740	EV is again fastest.
		1741
		1742	Perl again comes second. It is noticeably faster than the C-based event
		1743	loops Event and Glib, although the difference is too small to really
		1744	matter.
		1745
		1746	POE also performs much better in this case, but is is still far behind the
		1747	others.
		1748
		1749	=head3 Summary
		1750
		1751	=over 4
		1752
		1753	=item * C-based event loops perform very well with small number of
		1754	watchers, as the management overhead dominates.
		1755
		1756	=back
		1757
		1758
		1759	=head1 FORK
		1760
		1761	Most event libraries are not fork-safe. The ones who are usually are
		1762	because they rely on inefficient but fork-safe C<select> or C<poll>
		1763	calls. Only L<EV> is fully fork-aware.
		1764
		1765	If you have to fork, you must either do so I<before> creating your first
		1766	watcher OR you must not use AnyEvent at all in the child.
		1767
		1768
		1769	=head1 SECURITY CONSIDERATIONS
		1770
		1771	AnyEvent can be forced to load any event model via
		1772	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1773	execute arbitrary code or directly gain access, it can easily be used to
		1774	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1775	will not be active when the program uses a different event model than
		1776	specified in the variable.
		1777
		1778	You can make AnyEvent completely ignore this variable by deleting it
		1779	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1780
		1781	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1782
		1783	use AnyEvent;
		1784
		1785	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1786	be used to probe what backend is used and gain other information (which is
		1787	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1788	$ENV{PERL_ANYEGENT_STRICT}.
		1789
		1790
		1791	=head1 BUGS
		1792
		1793	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1794	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1795	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1796	mamleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1797	pronounced).
		1798
		1799
		1800	=head1 SEE ALSO
		1801
		1802	Utility functions: L<AnyEvent::Util>.
		1803
		1804	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1805	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1806
		1807	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1809	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1810	L<AnyEvent::Impl::POE>.
		1811
		1812	Non-blocking file handles, sockets, TCP clients and
		1813	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1814
		1815	Asynchronous DNS: L<AnyEvent::DNS>.
		1816
		1817	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1818
		1819	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1820
		1821
		1822	=head1 AUTHOR
		1823
		1824	Marc Lehmann <schmorp@schmorp.de>
		1825	http://home.schmorp.de/
		1826
		1827	=cut
		1828
		1829	1
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