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Revision 1.163 by root, Fri Jul 4 12:25:44 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->timer (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	});
		14
15	my $w = AnyEvent->io (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	# watchers get canceled whenever $w is destroyed	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
20	# only one watcher per $fh and $poll type is allowed	20	$w->send; # wake up current and all future recv's
21	# (i.e. on a socket you cna have one r + one w or one rw
22	# watcher, not any more.
23	# timers can only be used once
24
25	my $w = AnyEvent->condvar; # kind of main loop replacement
26	# can only be used once
27	$w->wait; # enters main loop till $condvar gets ->send	21	$w->recv; # enters "main loop" till $condvar gets ->send
28	$w->broadcast; # wake up waiting and future wait's	22
		23	=head1 INTRODUCTION/TUTORIAL
		24
		25	This manpage is mainly a reference manual. If you are interested
		26	in a tutorial or some gentle introduction, have a look at the
		27	L<AnyEvent::Intro> manpage.
		28
		29	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		30
		31	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		32	nowadays. So what is different about AnyEvent?
		33
		34	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		35	policy> and AnyEvent is I<small and efficient>.
		36
		37	First and foremost, I<AnyEvent is not an event model> itself, it only
		38	interfaces to whatever event model the main program happens to use in a
		39	pragmatic way. For event models and certain classes of immortals alike,
		40	the statement "there can only be one" is a bitter reality: In general,
		41	only one event loop can be active at the same time in a process. AnyEvent
		42	helps hiding the differences between those event loops.
		43
		44	The goal of AnyEvent is to offer module authors the ability to do event
		45	programming (waiting for I/O or timer events) without subscribing to a
		46	religion, a way of living, and most importantly: without forcing your
		47	module users into the same thing by forcing them to use the same event
		48	model you use.
		49
		50	For modules like POE or IO::Async (which is a total misnomer as it is
		51	actually doing all I/O I<synchronously>...), using them in your module is
		52	like joining a cult: After you joined, you are dependent on them and you
		53	cannot use anything else, as it is simply incompatible to everything that
		54	isn't itself. What's worse, all the potential users of your module are
		55	I<also> forced to use the same event loop you use.
		56
		57	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		58	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		59	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		60	your module uses one of those, every user of your module has to use it,
		61	too. But if your module uses AnyEvent, it works transparently with all
		62	event models it supports (including stuff like POE and IO::Async, as long
		63	as those use one of the supported event loops. It is trivial to add new
		64	event loops to AnyEvent, too, so it is future-proof).
		65
		66	In addition to being free of having to use I<the one and only true event
		67	model>, AnyEvent also is free of bloat and policy: with POE or similar
		68	modules, you get an enormous amount of code and strict rules you have to
		69	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		70	offering the functionality that is necessary, in as thin as a wrapper as
		71	technically possible.
		72
		73	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		74	of useful functionality, such as an asynchronous DNS resolver, 100%
		75	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		76	such as Windows) and lots of real-world knowledge and workarounds for
		77	platform bugs and differences.
		78
		79	Now, if you I<do want> lots of policy (this can arguably be somewhat
		80	useful) and you want to force your users to use the one and only event
		81	model, you should I<not> use this module.
29		82
30	=head1 DESCRIPTION	83	=head1 DESCRIPTION
31		84
32	L<AnyEvent> provides an identical interface to multiple event loops. This	85	L<AnyEvent> provides an identical interface to multiple event loops. This
33	allows module authors to utilizy an event loop without forcing module	86	allows module authors to utilise an event loop without forcing module
34	users to use the same event loop (as only a single event loop can coexist	87	users to use the same event loop (as only a single event loop can coexist
35	peacefully at any one time).	88	peacefully at any one time).
36		89
37	The interface itself is vaguely similar but not identical to the Event	90	The interface itself is vaguely similar, but not identical to the L<Event>
38	module.	91	module.
39		92
40	On the first call of any method, the module tries to detect the currently	93	During the first call of any watcher-creation method, the module tries
41	loaded event loop by probing wether any of the following modules is	94	to detect the currently loaded event loop by probing whether one of the
42	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	95	following modules is already loaded: L<EV>,
43	used. If none is found, the module tries to load these modules in the	96	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
44	order given. The first one that could be successfully loaded will be	97	L<POE>. The first one found is used. If none are found, the module tries
45	used. If still none could be found, it will issue an error.	98	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		99	adaptor should always succeed) in the order given. The first one that can
		100	be successfully loaded will be used. If, after this, still none could be
		101	found, AnyEvent will fall back to a pure-perl event loop, which is not
		102	very efficient, but should work everywhere.
		103
		104	Because AnyEvent first checks for modules that are already loaded, loading
		105	an event model explicitly before first using AnyEvent will likely make
		106	that model the default. For example:
		107
		108	use Tk;
		109	use AnyEvent;
		110
		111	# .. AnyEvent will likely default to Tk
		112
		113	The I<likely> means that, if any module loads another event model and
		114	starts using it, all bets are off. Maybe you should tell their authors to
		115	use AnyEvent so their modules work together with others seamlessly...
		116
		117	The pure-perl implementation of AnyEvent is called
		118	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		119	explicitly and enjoy the high availability of that event loop :)
		120
		121	=head1 WATCHERS
		122
		123	AnyEvent has the central concept of a I<watcher>, which is an object that
		124	stores relevant data for each kind of event you are waiting for, such as
		125	the callback to call, the file handle to watch, etc.
		126
		127	These watchers are normal Perl objects with normal Perl lifetime. After
		128	creating a watcher it will immediately "watch" for events and invoke the
		129	callback when the event occurs (of course, only when the event model
		130	is in control).
		131
		132	To disable the watcher you have to destroy it (e.g. by setting the
		133	variable you store it in to C<undef> or otherwise deleting all references
		134	to it).
		135
		136	All watchers are created by calling a method on the C<AnyEvent> class.
		137
		138	Many watchers either are used with "recursion" (repeating timers for
		139	example), or need to refer to their watcher object in other ways.
		140
		141	An any way to achieve that is this pattern:
		142
		143	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		144	# you can use $w here, for example to undef it
		145	undef $w;
		146	});
		147
		148	Note that C<my $w; $w => combination. This is necessary because in Perl,
		149	my variables are only visible after the statement in which they are
		150	declared.
		151
		152	=head2 I/O WATCHERS
		153
		154	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		155	with the following mandatory key-value pairs as arguments:
		156
		157	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
		158	for events. C<poll> must be a string that is either C<r> or C<w>,
		159	which creates a watcher waiting for "r"eadable or "w"ritable events,
		160	respectively. C<cb> is the callback to invoke each time the file handle
		161	becomes ready.
		162
		163	Although the callback might get passed parameters, their value and
		164	presence is undefined and you cannot rely on them. Portable AnyEvent
		165	callbacks cannot use arguments passed to I/O watcher callbacks.
		166
		167	The I/O watcher might use the underlying file descriptor or a copy of it.
		168	You must not close a file handle as long as any watcher is active on the
		169	underlying file descriptor.
		170
		171	Some event loops issue spurious readyness notifications, so you should
		172	always use non-blocking calls when reading/writing from/to your file
		173	handles.
		174
		175	Example:
		176
		177	# wait for readability of STDIN, then read a line and disable the watcher
		178	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		179	chomp (my $input = <STDIN>);
		180	warn "read: $input\n";
		181	undef $w;
		182	});
		183
		184	=head2 TIME WATCHERS
		185
		186	You can create a time watcher by calling the C<< AnyEvent->timer >>
		187	method with the following mandatory arguments:
		188
		189	C<after> specifies after how many seconds (fractional values are
		190	supported) the callback should be invoked. C<cb> is the callback to invoke
		191	in that case.
		192
		193	Although the callback might get passed parameters, their value and
		194	presence is undefined and you cannot rely on them. Portable AnyEvent
		195	callbacks cannot use arguments passed to time watcher callbacks.
		196
		197	The timer callback will be invoked at most once: if you want a repeating
		198	timer you have to create a new watcher (this is a limitation by both Tk
		199	and Glib).
		200
		201	Example:
		202
		203	# fire an event after 7.7 seconds
		204	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		205	warn "timeout\n";
		206	});
		207
		208	# to cancel the timer:
		209	undef $w;
		210
		211	Example 2:
		212
		213	# fire an event after 0.5 seconds, then roughly every second
		214	my $w;
		215
		216	my $cb = sub {
		217	# cancel the old timer while creating a new one
		218	$w = AnyEvent->timer (after => 1, cb => $cb);
		219	};
		220
		221	# start the "loop" by creating the first watcher
		222	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		223
		224	=head3 TIMING ISSUES
		225
		226	There are two ways to handle timers: based on real time (relative, "fire
		227	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		228	o'clock").
		229
		230	While most event loops expect timers to specified in a relative way, they
		231	use absolute time internally. This makes a difference when your clock
		232	"jumps", for example, when ntp decides to set your clock backwards from
		233	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		234	fire "after" a second might actually take six years to finally fire.
		235
		236	AnyEvent cannot compensate for this. The only event loop that is conscious
		237	about these issues is L<EV>, which offers both relative (ev_timer, based
		238	on true relative time) and absolute (ev_periodic, based on wallclock time)
		239	timers.
		240
		241	AnyEvent always prefers relative timers, if available, matching the
		242	AnyEvent API.
		243
		244	AnyEvent has two additional methods that return the "current time":
46		245
47	=over 4	246	=over 4
48		247
		248	=item AnyEvent->time
		249
		250	This returns the "current wallclock time" as a fractional number of
		251	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		252	return, and the result is guaranteed to be compatible with those).
		253
		254	It progresses independently of any event loop processing, i.e. each call
		255	will check the system clock, which usually gets updated frequently.
		256
		257	=item AnyEvent->now
		258
		259	This also returns the "current wallclock time", but unlike C<time>, above,
		260	this value might change only once per event loop iteration, depending on
		261	the event loop (most return the same time as C<time>, above). This is the
		262	time that AnyEvent's timers get scheduled against.
		263
		264	I<In almost all cases (in all cases if you don't care), this is the
		265	function to call when you want to know the current time.>
		266
		267	This function is also often faster then C<< AnyEvent->time >>, and
		268	thus the preferred method if you want some timestamp (for example,
		269	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		270
		271	The rest of this section is only of relevance if you try to be very exact
		272	with your timing, you can skip it without bad conscience.
		273
		274	For a practical example of when these times differ, consider L<Event::Lib>
		275	and L<EV> and the following set-up:
		276
		277	The event loop is running and has just invoked one of your callback at
		278	time=500 (assume no other callbacks delay processing). In your callback,
		279	you wait a second by executing C<sleep 1> (blocking the process for a
		280	second) and then (at time=501) you create a relative timer that fires
		281	after three seconds.
		282
		283	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		284	both return C<501>, because that is the current time, and the timer will
		285	be scheduled to fire at time=504 (C<501> + C<3>).
		286
		287	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		288	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		289	last event processing phase started. With L<EV>, your timer gets scheduled
		290	to run at time=503 (C<500> + C<3>).
		291
		292	In one sense, L<Event::Lib> is more exact, as it uses the current time
		293	regardless of any delays introduced by event processing. However, most
		294	callbacks do not expect large delays in processing, so this causes a
		295	higher drift (and a lot more system calls to get the current time).
		296
		297	In another sense, L<EV> is more exact, as your timer will be scheduled at
		298	the same time, regardless of how long event processing actually took.
		299
		300	In either case, if you care (and in most cases, you don't), then you
		301	can get whatever behaviour you want with any event loop, by taking the
		302	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		303	account.
		304
		305	=back
		306
		307	=head2 SIGNAL WATCHERS
		308
		309	You can watch for signals using a signal watcher, C<signal> is the signal
		310	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		311	be invoked whenever a signal occurs.
		312
		313	Although the callback might get passed parameters, their value and
		314	presence is undefined and you cannot rely on them. Portable AnyEvent
		315	callbacks cannot use arguments passed to signal watcher callbacks.
		316
		317	Multiple signal occurrences can be clumped together into one callback
		318	invocation, and callback invocation will be synchronous. Synchronous means
		319	that it might take a while until the signal gets handled by the process,
		320	but it is guaranteed not to interrupt any other callbacks.
		321
		322	The main advantage of using these watchers is that you can share a signal
		323	between multiple watchers.
		324
		325	This watcher might use C<%SIG>, so programs overwriting those signals
		326	directly will likely not work correctly.
		327
		328	Example: exit on SIGINT
		329
		330	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		331
		332	=head2 CHILD PROCESS WATCHERS
		333
		334	You can also watch on a child process exit and catch its exit status.
		335
		336	The child process is specified by the C<pid> argument (if set to C<0>, it
		337	watches for any child process exit). The watcher will trigger as often
		338	as status change for the child are received. This works by installing a
		339	signal handler for C<SIGCHLD>. The callback will be called with the pid
		340	and exit status (as returned by waitpid), so unlike other watcher types,
		341	you I<can> rely on child watcher callback arguments.
		342
		343	There is a slight catch to child watchers, however: you usually start them
		344	I<after> the child process was created, and this means the process could
		345	have exited already (and no SIGCHLD will be sent anymore).
		346
		347	Not all event models handle this correctly (POE doesn't), but even for
		348	event models that I<do> handle this correctly, they usually need to be
		349	loaded before the process exits (i.e. before you fork in the first place).
		350
		351	This means you cannot create a child watcher as the very first thing in an
		352	AnyEvent program, you I<have> to create at least one watcher before you
		353	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		354
		355	Example: fork a process and wait for it
		356
		357	my $done = AnyEvent->condvar;
		358
		359	my $pid = fork or exit 5;
		360
		361	my $w = AnyEvent->child (
		362	pid => $pid,
		363	cb => sub {
		364	my ($pid, $status) = @_;
		365	warn "pid $pid exited with status $status";
		366	$done->send;
		367	},
		368	);
		369
		370	# do something else, then wait for process exit
		371	$done->recv;
		372
		373	=head2 CONDITION VARIABLES
		374
		375	If you are familiar with some event loops you will know that all of them
		376	require you to run some blocking "loop", "run" or similar function that
		377	will actively watch for new events and call your callbacks.
		378
		379	AnyEvent is different, it expects somebody else to run the event loop and
		380	will only block when necessary (usually when told by the user).
		381
		382	The instrument to do that is called a "condition variable", so called
		383	because they represent a condition that must become true.
		384
		385	Condition variables can be created by calling the C<< AnyEvent->condvar
		386	>> method, usually without arguments. The only argument pair allowed is
		387	C<cb>, which specifies a callback to be called when the condition variable
		388	becomes true.
		389
		390	After creation, the condition variable is "false" until it becomes "true"
		391	by calling the C<send> method (or calling the condition variable as if it
		392	were a callback, read about the caveats in the description for the C<<
		393	->send >> method).
		394
		395	Condition variables are similar to callbacks, except that you can
		396	optionally wait for them. They can also be called merge points - points
		397	in time where multiple outstanding events have been processed. And yet
		398	another way to call them is transactions - each condition variable can be
		399	used to represent a transaction, which finishes at some point and delivers
		400	a result.
		401
		402	Condition variables are very useful to signal that something has finished,
		403	for example, if you write a module that does asynchronous http requests,
		404	then a condition variable would be the ideal candidate to signal the
		405	availability of results. The user can either act when the callback is
		406	called or can synchronously C<< ->recv >> for the results.
		407
		408	You can also use them to simulate traditional event loops - for example,
		409	you can block your main program until an event occurs - for example, you
		410	could C<< ->recv >> in your main program until the user clicks the Quit
		411	button of your app, which would C<< ->send >> the "quit" event.
		412
		413	Note that condition variables recurse into the event loop - if you have
		414	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		415	lose. Therefore, condition variables are good to export to your caller, but
		416	you should avoid making a blocking wait yourself, at least in callbacks,
		417	as this asks for trouble.
		418
		419	Condition variables are represented by hash refs in perl, and the keys
		420	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		421	easy (it is often useful to build your own transaction class on top of
		422	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		423	it's C<new> method in your own C<new> method.
		424
		425	There are two "sides" to a condition variable - the "producer side" which
		426	eventually calls C<< -> send >>, and the "consumer side", which waits
		427	for the send to occur.
		428
		429	Example: wait for a timer.
		430
		431	# wait till the result is ready
		432	my $result_ready = AnyEvent->condvar;
		433
		434	# do something such as adding a timer
		435	# or socket watcher the calls $result_ready->send
		436	# when the "result" is ready.
		437	# in this case, we simply use a timer:
		438	my $w = AnyEvent->timer (
		439	after => 1,
		440	cb => sub { $result_ready->send },
		441	);
		442
		443	# this "blocks" (while handling events) till the callback
		444	# calls send
		445	$result_ready->recv;
		446
		447	Example: wait for a timer, but take advantage of the fact that
		448	condition variables are also code references.
		449
		450	my $done = AnyEvent->condvar;
		451	my $delay = AnyEvent->timer (after => 5, cb => $done);
		452	$done->recv;
		453
		454	=head3 METHODS FOR PRODUCERS
		455
		456	These methods should only be used by the producing side, i.e. the
		457	code/module that eventually sends the signal. Note that it is also
		458	the producer side which creates the condvar in most cases, but it isn't
		459	uncommon for the consumer to create it as well.
		460
		461	=over 4
		462
		463	=item $cv->send (...)
		464
		465	Flag the condition as ready - a running C<< ->recv >> and all further
		466	calls to C<recv> will (eventually) return after this method has been
		467	called. If nobody is waiting the send will be remembered.
		468
		469	If a callback has been set on the condition variable, it is called
		470	immediately from within send.
		471
		472	Any arguments passed to the C<send> call will be returned by all
		473	future C<< ->recv >> calls.
		474
		475	Condition variables are overloaded so one can call them directly
		476	(as a code reference). Calling them directly is the same as calling
		477	C<send>. Note, however, that many C-based event loops do not handle
		478	overloading, so as tempting as it may be, passing a condition variable
		479	instead of a callback does not work. Both the pure perl and EV loops
		480	support overloading, however, as well as all functions that use perl to
		481	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		482	example).
		483
		484	=item $cv->croak ($error)
		485
		486	Similar to send, but causes all call's to C<< ->recv >> to invoke
		487	C<Carp::croak> with the given error message/object/scalar.
		488
		489	This can be used to signal any errors to the condition variable
		490	user/consumer.
		491
		492	=item $cv->begin ([group callback])
		493
		494	=item $cv->end
		495
		496	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		497
		498	These two methods can be used to combine many transactions/events into
		499	one. For example, a function that pings many hosts in parallel might want
		500	to use a condition variable for the whole process.
		501
		502	Every call to C<< ->begin >> will increment a counter, and every call to
		503	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		504	>>, the (last) callback passed to C<begin> will be executed. That callback
		505	is I<supposed> to call C<< ->send >>, but that is not required. If no
		506	callback was set, C<send> will be called without any arguments.
		507
		508	Let's clarify this with the ping example:
		509
		510	my $cv = AnyEvent->condvar;
		511
		512	my %result;
		513	$cv->begin (sub { $cv->send (\%result) });
		514
		515	for my $host (@list_of_hosts) {
		516	$cv->begin;
		517	ping_host_then_call_callback $host, sub {
		518	$result{$host} = ...;
		519	$cv->end;
		520	};
		521	}
		522
		523	$cv->end;
		524
		525	This code fragment supposedly pings a number of hosts and calls
		526	C<send> after results for all then have have been gathered - in any
		527	order. To achieve this, the code issues a call to C<begin> when it starts
		528	each ping request and calls C<end> when it has received some result for
		529	it. Since C<begin> and C<end> only maintain a counter, the order in which
		530	results arrive is not relevant.
		531
		532	There is an additional bracketing call to C<begin> and C<end> outside the
		533	loop, which serves two important purposes: first, it sets the callback
		534	to be called once the counter reaches C<0>, and second, it ensures that
		535	C<send> is called even when C<no> hosts are being pinged (the loop
		536	doesn't execute once).
		537
		538	This is the general pattern when you "fan out" into multiple subrequests:
		539	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		540	is called at least once, and then, for each subrequest you start, call
		541	C<begin> and for each subrequest you finish, call C<end>.
		542
		543	=back
		544
		545	=head3 METHODS FOR CONSUMERS
		546
		547	These methods should only be used by the consuming side, i.e. the
		548	code awaits the condition.
		549
		550	=over 4
		551
		552	=item $cv->recv
		553
		554	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		555	>> methods have been called on c<$cv>, while servicing other watchers
		556	normally.
		557
		558	You can only wait once on a condition - additional calls are valid but
		559	will return immediately.
		560
		561	If an error condition has been set by calling C<< ->croak >>, then this
		562	function will call C<croak>.
		563
		564	In list context, all parameters passed to C<send> will be returned,
		565	in scalar context only the first one will be returned.
		566
		567	Not all event models support a blocking wait - some die in that case
		568	(programs might want to do that to stay interactive), so I<if you are
		569	using this from a module, never require a blocking wait>, but let the
		570	caller decide whether the call will block or not (for example, by coupling
		571	condition variables with some kind of request results and supporting
		572	callbacks so the caller knows that getting the result will not block,
		573	while still supporting blocking waits if the caller so desires).
		574
		575	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		576	sensibly have two C<< ->recv >>'s in parallel, as that would require
		577	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		578	can supply.
		579
		580	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		581	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		582	versions and also integrates coroutines into AnyEvent, making blocking
		583	C<< ->recv >> calls perfectly safe as long as they are done from another
		584	coroutine (one that doesn't run the event loop).
		585
		586	You can ensure that C<< -recv >> never blocks by setting a callback and
		587	only calling C<< ->recv >> from within that callback (or at a later
		588	time). This will work even when the event loop does not support blocking
		589	waits otherwise.
		590
		591	=item $bool = $cv->ready
		592
		593	Returns true when the condition is "true", i.e. whether C<send> or
		594	C<croak> have been called.
		595
		596	=item $cb = $cv->cb ([new callback])
		597
		598	This is a mutator function that returns the callback set and optionally
		599	replaces it before doing so.
		600
		601	The callback will be called when the condition becomes "true", i.e. when
		602	C<send> or C<croak> are called, with the only argument being the condition
		603	variable itself. Calling C<recv> inside the callback or at any later time
		604	is guaranteed not to block.
		605
		606	=back
		607
		608	=head1 GLOBAL VARIABLES AND FUNCTIONS
		609
		610	=over 4
		611
		612	=item $AnyEvent::MODEL
		613
		614	Contains C<undef> until the first watcher is being created. Then it
		615	contains the event model that is being used, which is the name of the
		616	Perl class implementing the model. This class is usually one of the
		617	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		618	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		619
		620	The known classes so far are:
		621
		622	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		623	AnyEvent::Impl::Event based on Event, second best choice.
		624	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		625	AnyEvent::Impl::Glib based on Glib, third-best choice.
		626	AnyEvent::Impl::Tk based on Tk, very bad choice.
		627	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		628	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		629	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		630
		631	There is no support for WxWidgets, as WxWidgets has no support for
		632	watching file handles. However, you can use WxWidgets through the
		633	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		634	second, which was considered to be too horrible to even consider for
		635	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		636	it's adaptor.
		637
		638	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		639	autodetecting them.
		640
		641	=item AnyEvent::detect
		642
		643	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		644	if necessary. You should only call this function right before you would
		645	have created an AnyEvent watcher anyway, that is, as late as possible at
		646	runtime.
		647
		648	=item $guard = AnyEvent::post_detect { BLOCK }
		649
		650	Arranges for the code block to be executed as soon as the event model is
		651	autodetected (or immediately if this has already happened).
		652
		653	If called in scalar or list context, then it creates and returns an object
		654	that automatically removes the callback again when it is destroyed. See
		655	L<Coro::BDB> for a case where this is useful.
		656
		657	=item @AnyEvent::post_detect
		658
		659	If there are any code references in this array (you can C<push> to it
		660	before or after loading AnyEvent), then they will called directly after
		661	the event loop has been chosen.
		662
		663	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		664	if it contains a true value then the event loop has already been detected,
		665	and the array will be ignored.
		666
		667	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		668
		669	=back
		670
		671	=head1 WHAT TO DO IN A MODULE
		672
		673	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		674	freely, but you should not load a specific event module or rely on it.
		675
		676	Be careful when you create watchers in the module body - AnyEvent will
		677	decide which event module to use as soon as the first method is called, so
		678	by calling AnyEvent in your module body you force the user of your module
		679	to load the event module first.
		680
		681	Never call C<< ->recv >> on a condition variable unless you I<know> that
		682	the C<< ->send >> method has been called on it already. This is
		683	because it will stall the whole program, and the whole point of using
		684	events is to stay interactive.
		685
		686	It is fine, however, to call C<< ->recv >> when the user of your module
		687	requests it (i.e. if you create a http request object ad have a method
		688	called C<results> that returns the results, it should call C<< ->recv >>
		689	freely, as the user of your module knows what she is doing. always).
		690
		691	=head1 WHAT TO DO IN THE MAIN PROGRAM
		692
		693	There will always be a single main program - the only place that should
		694	dictate which event model to use.
		695
		696	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		697	do anything special (it does not need to be event-based) and let AnyEvent
		698	decide which implementation to chose if some module relies on it.
		699
		700	If the main program relies on a specific event model - for example, in
		701	Gtk2 programs you have to rely on the Glib module - you should load the
		702	event module before loading AnyEvent or any module that uses it: generally
		703	speaking, you should load it as early as possible. The reason is that
		704	modules might create watchers when they are loaded, and AnyEvent will
		705	decide on the event model to use as soon as it creates watchers, and it
		706	might chose the wrong one unless you load the correct one yourself.
		707
		708	You can chose to use a pure-perl implementation by loading the
		709	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		710	everywhere, but letting AnyEvent chose the model is generally better.
		711
		712	=head2 MAINLOOP EMULATION
		713
		714	Sometimes (often for short test scripts, or even standalone programs who
		715	only want to use AnyEvent), you do not want to run a specific event loop.
		716
		717	In that case, you can use a condition variable like this:
		718
		719	AnyEvent->condvar->recv;
		720
		721	This has the effect of entering the event loop and looping forever.
		722
		723	Note that usually your program has some exit condition, in which case
		724	it is better to use the "traditional" approach of storing a condition
		725	variable somewhere, waiting for it, and sending it when the program should
		726	exit cleanly.
		727
		728
		729	=head1 OTHER MODULES
		730
		731	The following is a non-exhaustive list of additional modules that use
		732	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		733	in the same program. Some of the modules come with AnyEvent, some are
		734	available via CPAN.
		735
		736	=over 4
		737
		738	=item L<AnyEvent::Util>
		739
		740	Contains various utility functions that replace often-used but blocking
		741	functions such as C<inet_aton> by event-/callback-based versions.
		742
		743	=item L<AnyEvent::Handle>
		744
		745	Provide read and write buffers and manages watchers for reads and writes.
		746
		747	=item L<AnyEvent::Socket>
		748
		749	Provides various utility functions for (internet protocol) sockets,
		750	addresses and name resolution. Also functions to create non-blocking tcp
		751	connections or tcp servers, with IPv6 and SRV record support and more.
		752
		753	=item L<AnyEvent::DNS>
		754
		755	Provides rich asynchronous DNS resolver capabilities.
		756
		757	=item L<AnyEvent::HTTP>
		758
		759	A simple-to-use HTTP library that is capable of making a lot of concurrent
		760	HTTP requests.
		761
		762	=item L<AnyEvent::HTTPD>
		763
		764	Provides a simple web application server framework.
		765
		766	=item L<AnyEvent::FastPing>
		767
		768	The fastest ping in the west.
		769
		770	=item L<AnyEvent::DBI>
		771
		772	Executes DBI requests asynchronously in a proxy process.
		773
		774	=item L<Net::IRC3>
		775
		776	AnyEvent based IRC client module family.
		777
		778	=item L<Net::XMPP2>
		779
		780	AnyEvent based XMPP (Jabber protocol) module family.
		781
		782	=item L<Net::FCP>
		783
		784	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		785	of AnyEvent.
		786
		787	=item L<Event::ExecFlow>
		788
		789	High level API for event-based execution flow control.
		790
		791	=item L<Coro>
		792
		793	Has special support for AnyEvent via L<Coro::AnyEvent>.
		794
		795	=item L<AnyEvent::AIO>, L<IO::AIO>
		796
		797	Truly asynchronous I/O, should be in the toolbox of every event
		798	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		799	together.
		800
		801	=item L<AnyEvent::BDB>, L<BDB>
		802
		803	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		804	IO::AIO and AnyEvent together.
		805
		806	=item L<IO::Lambda>
		807
		808	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		809
		810	=back
		811
49	=cut	812	=cut
50		813
51	package AnyEvent;	814	package AnyEvent;
52		815
53	no warnings;	816	no warnings;
54	use strict 'vars';	817	use strict;
		818
55	use Carp;	819	use Carp;
56		820
57	our $VERSION = 0.2;	821	our $VERSION = 4.161;
58	our $MODEL;	822	our $MODEL;
59		823
60	our $AUTOLOAD;	824	our $AUTOLOAD;
61	our @ISA;	825	our @ISA;
62		826
		827	our @REGISTRY;
		828
		829	our $WIN32;
		830
		831	BEGIN {
		832	my $win32 = ! ! ($^O =~ /mswin32/i);
		833	eval "sub WIN32(){ $win32 }";
		834	}
		835
		836	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		837
		838	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		839
		840	{
		841	my $idx;
		842	$PROTOCOL{$_} = ++$idx
		843	for reverse split /\s*,\s*/,
		844	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		845	}
		846
63	my @models = (	847	my @models = (
64	[Coro => Coro::Event::],	848	[EV:: => AnyEvent::Impl::EV::],
65	[Event => Event::],	849	[Event:: => AnyEvent::Impl::Event::],
66	[Glib => Glib::],	850	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
67	[Tk => Tk::],	851	# everything below here will not be autoprobed
		852	# as the pureperl backend should work everywhere
		853	# and is usually faster
		854	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		855	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		856	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		857	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		858	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		859	[Wx:: => AnyEvent::Impl::POE::],
		860	[Prima:: => AnyEvent::Impl::POE::],
68	);	861	);
69		862
70	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	863	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
71		864
72	sub AUTOLOAD {	865	our @post_detect;
73	$AUTOLOAD =~ s/.*://;
74		866
75	$method{$AUTOLOAD}	867	sub post_detect(&) {
76	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	868	my ($cb) = @_;
77		869
		870	if ($MODEL) {
		871	$cb->();
		872
		873	1
		874	} else {
		875	push @post_detect, $cb;
		876
		877	defined wantarray
		878	? bless \$cb, "AnyEvent::Util::PostDetect"
		879	: ()
		880	}
		881	}
		882
		883	sub AnyEvent::Util::PostDetect::DESTROY {
		884	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		885	}
		886
		887	sub detect() {
78	unless ($MODEL) {	888	unless ($MODEL) {
79	# check for already loaded models	889	no strict 'refs';
80	for (@models) {	890	local $SIG{__DIE__};
81	my ($model, $package) = @$_;	891
82	if (scalar keys %{ *{"$package\::"} }) {	892	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
83	eval "require AnyEvent::Impl::$model";	893	my $model = "AnyEvent::Impl::$1";
84	last if $MODEL;	894	if (eval "require $model") {
		895	$MODEL = $model;
		896	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		897	} else {
		898	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
85	}	899	}
86	}	900	}
87		901
		902	# check for already loaded models
88	unless ($MODEL) {	903	unless ($MODEL) {
89	# try to load a model
90
91	for (@models) {	904	for (@REGISTRY, @models) {
92	my ($model, $package) = @$_;	905	my ($package, $model) = @$_;
93	eval "require AnyEvent::Impl::$model";	906	if (${"$package\::VERSION"} > 0) {
94	last if $MODEL;	907	if (eval "require $model") {
		908	$MODEL = $model;
		909	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		910	last;
		911	}
		912	}
95	}	913	}
96		914
		915	unless ($MODEL) {
		916	# try to load a model
		917
		918	for (@REGISTRY, @models) {
		919	my ($package, $model) = @$_;
		920	if (eval "require $package"
		921	and ${"$package\::VERSION"} > 0
		922	and eval "require $model") {
		923	$MODEL = $model;
		924	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		925	last;
		926	}
		927	}
		928
97	$MODEL	929	$MODEL
98	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	930	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		931	}
99	}	932	}
		933
		934	unshift @ISA, $MODEL;
		935	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		936
		937	(shift @post_detect)->() while @post_detect;
100	}	938	}
101		939
102	@ISA = $MODEL;	940	$MODEL
		941	}
		942
		943	sub AUTOLOAD {
		944	(my $func = $AUTOLOAD) =~ s/.*://;
		945
		946	$method{$func}
		947	or croak "$func: not a valid method for AnyEvent objects";
		948
		949	detect unless $MODEL;
103		950
104	my $class = shift;	951	my $class = shift;
105	$class->$AUTOLOAD (@_);	952	$class->$func (@_);
106	}	953	}
		954
		955	package AnyEvent::Base;
		956
		957	# default implementation for now and time
		958
		959	use Time::HiRes ();
		960
		961	sub time { Time::HiRes::time }
		962	sub now { Time::HiRes::time }
		963
		964	# default implementation for ->condvar
		965
		966	sub condvar {
		967	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		968	}
		969
		970	# default implementation for ->signal
		971
		972	our %SIG_CB;
		973
		974	sub signal {
		975	my (undef, %arg) = @_;
		976
		977	my $signal = uc $arg{signal}
		978	or Carp::croak "required option 'signal' is missing";
		979
		980	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		981	$SIG{$signal} ||= sub {
		982	$_->() for values %{ $SIG_CB{$signal} || {} };
		983	};
		984
		985	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		986	}
		987
		988	sub AnyEvent::Base::Signal::DESTROY {
		989	my ($signal, $cb) = @{$_[0]};
		990
		991	delete $SIG_CB{$signal}{$cb};
		992
		993	delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
		994	}
		995
		996	# default implementation for ->child
		997
		998	our %PID_CB;
		999	our $CHLD_W;
		1000	our $CHLD_DELAY_W;
		1001	our $PID_IDLE;
		1002	our $WNOHANG;
		1003
		1004	sub _child_wait {
		1005	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1006	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		1007	(values %{ $PID_CB{0} || {} });
		1008	}
		1009
		1010	undef $PID_IDLE;
		1011	}
		1012
		1013	sub _sigchld {
		1014	# make sure we deliver these changes "synchronous" with the event loop.
		1015	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		1016	undef $CHLD_DELAY_W;
		1017	&_child_wait;
		1018	});
		1019	}
		1020
		1021	sub child {
		1022	my (undef, %arg) = @_;
		1023
		1024	defined (my $pid = $arg{pid} + 0)
		1025	or Carp::croak "required option 'pid' is missing";
		1026
		1027	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1028
		1029	unless ($WNOHANG) {
		1030	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1031	}
		1032
		1033	unless ($CHLD_W) {
		1034	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1035	# child could be a zombie already, so make at least one round
		1036	&_sigchld;
		1037	}
		1038
		1039	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		1040	}
		1041
		1042	sub AnyEvent::Base::Child::DESTROY {
		1043	my ($pid, $cb) = @{$_[0]};
		1044
		1045	delete $PID_CB{$pid}{$cb};
		1046	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1047
		1048	undef $CHLD_W unless keys %PID_CB;
		1049	}
		1050
		1051	package AnyEvent::CondVar;
		1052
		1053	our @ISA = AnyEvent::CondVar::Base::;
		1054
		1055	package AnyEvent::CondVar::Base;
		1056
		1057	use overload
		1058	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1059	fallback => 1;
		1060
		1061	sub _send {
		1062	# nop
		1063	}
		1064
		1065	sub send {
		1066	my $cv = shift;
		1067	$cv->{_ae_sent} = [@_];
		1068	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1069	$cv->_send;
		1070	}
		1071
		1072	sub croak {
		1073	$_[0]{_ae_croak} = $_[1];
		1074	$_[0]->send;
		1075	}
		1076
		1077	sub ready {
		1078	$_[0]{_ae_sent}
		1079	}
		1080
		1081	sub _wait {
		1082	AnyEvent->one_event while !$_[0]{_ae_sent};
		1083	}
		1084
		1085	sub recv {
		1086	$_[0]->_wait;
		1087
		1088	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1089	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1090	}
		1091
		1092	sub cb {
		1093	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1094	$_[0]{_ae_cb}
		1095	}
		1096
		1097	sub begin {
		1098	++$_[0]{_ae_counter};
		1099	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1100	}
		1101
		1102	sub end {
		1103	return if --$_[0]{_ae_counter};
		1104	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1105	}
		1106
		1107	# undocumented/compatibility with pre-3.4
		1108	*broadcast = \&send;
		1109	*wait = \&_wait;
		1110
		1111	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1112
		1113	This is an advanced topic that you do not normally need to use AnyEvent in
		1114	a module. This section is only of use to event loop authors who want to
		1115	provide AnyEvent compatibility.
		1116
		1117	If you need to support another event library which isn't directly
		1118	supported by AnyEvent, you can supply your own interface to it by
		1119	pushing, before the first watcher gets created, the package name of
		1120	the event module and the package name of the interface to use onto
		1121	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1122	AnyEvent, so it is reasonably cheap.
		1123
		1124	Example:
		1125
		1126	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1127
		1128	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1129	package/class when it finds the C<urxvt> package/module is already loaded.
		1130
		1131	When AnyEvent is loaded and asked to find a suitable event model, it
		1132	will first check for the presence of urxvt by trying to C<use> the
		1133	C<urxvt::anyevent> module.
		1134
		1135	The class should provide implementations for all watcher types. See
		1136	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1137	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1138	see the sources.
		1139
		1140	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1141	provide suitable (hopefully) replacements.
		1142
		1143	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1144	terminal emulator uses the above line as-is. An interface isn't included
		1145	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1146	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1147	I<rxvt-unicode> distribution.
		1148
		1149	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1150	condition variables: code blocking while waiting for a condition will
		1151	C<die>. This still works with most modules/usages, and blocking calls must
		1152	not be done in an interactive application, so it makes sense.
		1153
		1154	=head1 ENVIRONMENT VARIABLES
		1155
		1156	The following environment variables are used by this module:
		1157
		1158	=over 4
		1159
		1160	=item C<PERL_ANYEVENT_VERBOSE>
		1161
		1162	By default, AnyEvent will be completely silent except in fatal
		1163	conditions. You can set this environment variable to make AnyEvent more
		1164	talkative.
		1165
		1166	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1167	conditions, such as not being able to load the event model specified by
		1168	C<PERL_ANYEVENT_MODEL>.
		1169
		1170	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1171	model it chooses.
		1172
		1173	=item C<PERL_ANYEVENT_MODEL>
		1174
		1175	This can be used to specify the event model to be used by AnyEvent, before
		1176	auto detection and -probing kicks in. It must be a string consisting
		1177	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1178	and the resulting module name is loaded and if the load was successful,
		1179	used as event model. If it fails to load AnyEvent will proceed with
		1180	auto detection and -probing.
		1181
		1182	This functionality might change in future versions.
		1183
		1184	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1185	could start your program like this:
		1186
		1187	PERL_ANYEVENT_MODEL=Perl perl ...
		1188
		1189	=item C<PERL_ANYEVENT_PROTOCOLS>
		1190
		1191	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1192	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1193	of auto probing).
		1194
		1195	Must be set to a comma-separated list of protocols or address families,
		1196	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1197	used, and preference will be given to protocols mentioned earlier in the
		1198	list.
		1199
		1200	This variable can effectively be used for denial-of-service attacks
		1201	against local programs (e.g. when setuid), although the impact is likely
		1202	small, as the program has to handle connection errors already-
		1203
		1204	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1205	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1206	- only support IPv4, never try to resolve or contact IPv6
		1207	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1208	IPv6, but prefer IPv6 over IPv4.
		1209
		1210	=item C<PERL_ANYEVENT_EDNS0>
		1211
		1212	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1213	for DNS. This extension is generally useful to reduce DNS traffic, but
		1214	some (broken) firewalls drop such DNS packets, which is why it is off by
		1215	default.
		1216
		1217	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1218	EDNS0 in its DNS requests.
		1219
		1220	=item C<PERL_ANYEVENT_MAX_FORKS>
		1221
		1222	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1223	will create in parallel.
107		1224
108	=back	1225	=back
109		1226
110	=head1 EXAMPLE	1227	=head1 EXAMPLE PROGRAM
111		1228
112	The following program uses an io watcher to read data from stdin, a timer	1229	The following program uses an I/O watcher to read data from STDIN, a timer
113	to display a message once per second, and a condvar to exit the program	1230	to display a message once per second, and a condition variable to quit the
114	when the user enters quit:	1231	program when the user enters quit:
115		1232
116	use AnyEvent;	1233	use AnyEvent;
117		1234
118	my $cv = AnyEvent->condvar;	1235	my $cv = AnyEvent->condvar;
119		1236
120	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1237	my $io_watcher = AnyEvent->io (
		1238	fh => \*STDIN,
		1239	poll => 'r',
		1240	cb => sub {
121	warn "io event <$_[0]>\n"; # will always output <r>	1241	warn "io event <$_[0]>\n"; # will always output <r>
122	chomp (my $input = <STDIN>); # read a line	1242	chomp (my $input = <STDIN>); # read a line
123	warn "read: $input\n"; # output what has been read	1243	warn "read: $input\n"; # output what has been read
124	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1244	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1245	},
125	});	1246	);
126		1247
127	my $time_watcher; # can only be used once	1248	my $time_watcher; # can only be used once
128		1249
129	sub new_timer {	1250	sub new_timer {
130	$timer = AnyEvent->timer (after => 1, cb => sub {	1251	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
133	});	1254	});
134	}	1255	}
135		1256
136	new_timer; # create first timer	1257	new_timer; # create first timer
137		1258
138	$cv->wait; # wait until user enters /^q/i	1259	$cv->recv; # wait until user enters /^q/i
		1260
		1261	=head1 REAL-WORLD EXAMPLE
		1262
		1263	Consider the L<Net::FCP> module. It features (among others) the following
		1264	API calls, which are to freenet what HTTP GET requests are to http:
		1265
		1266	my $data = $fcp->client_get ($url); # blocks
		1267
		1268	my $transaction = $fcp->txn_client_get ($url); # does not block
		1269	$transaction->cb ( sub { ... } ); # set optional result callback
		1270	my $data = $transaction->result; # possibly blocks
		1271
		1272	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		1273	given URL and waits till the data has arrived. It is defined to be:
		1274
		1275	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		1276
		1277	And in fact is automatically generated. This is the blocking API of
		1278	L<Net::FCP>, and it works as simple as in any other, similar, module.
		1279
		1280	More complicated is C<txn_client_get>: It only creates a transaction
		1281	(completion, result, ...) object and initiates the transaction.
		1282
		1283	my $txn = bless { }, Net::FCP::Txn::;
		1284
		1285	It also creates a condition variable that is used to signal the completion
		1286	of the request:
		1287
		1288	$txn->{finished} = AnyAvent->condvar;
		1289
		1290	It then creates a socket in non-blocking mode.
		1291
		1292	socket $txn->{fh}, ...;
		1293	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		1294	connect $txn->{fh}, ...
		1295	and !$!{EWOULDBLOCK}
		1296	and !$!{EINPROGRESS}
		1297	and Carp::croak "unable to connect: $!\n";
		1298
		1299	Then it creates a write-watcher which gets called whenever an error occurs
		1300	or the connection succeeds:
		1301
		1302	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		1303
		1304	And returns this transaction object. The C<fh_ready_w> callback gets
		1305	called as soon as the event loop detects that the socket is ready for
		1306	writing.
		1307
		1308	The C<fh_ready_w> method makes the socket blocking again, writes the
		1309	request data and replaces the watcher by a read watcher (waiting for reply
		1310	data). The actual code is more complicated, but that doesn't matter for
		1311	this example:
		1312
		1313	fcntl $txn->{fh}, F_SETFL, 0;
		1314	syswrite $txn->{fh}, $txn->{request}
		1315	or die "connection or write error";
		1316	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		1317
		1318	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		1319	result and signals any possible waiters that the request has finished:
		1320
		1321	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		1322
		1323	if (end-of-file or data complete) {
		1324	$txn->{result} = $txn->{buf};
		1325	$txn->{finished}->send;
		1326	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		1327	}
		1328
		1329	The C<result> method, finally, just waits for the finished signal (if the
		1330	request was already finished, it doesn't wait, of course, and returns the
		1331	data:
		1332
		1333	$txn->{finished}->recv;
		1334	return $txn->{result};
		1335
		1336	The actual code goes further and collects all errors (C<die>s, exceptions)
		1337	that occurred during request processing. The C<result> method detects
		1338	whether an exception as thrown (it is stored inside the $txn object)
		1339	and just throws the exception, which means connection errors and other
		1340	problems get reported tot he code that tries to use the result, not in a
		1341	random callback.
		1342
		1343	All of this enables the following usage styles:
		1344
		1345	1. Blocking:
		1346
		1347	my $data = $fcp->client_get ($url);
		1348
		1349	2. Blocking, but running in parallel:
		1350
		1351	my @datas = map $_->result,
		1352	map $fcp->txn_client_get ($_),
		1353	@urls;
		1354
		1355	Both blocking examples work without the module user having to know
		1356	anything about events.
		1357
		1358	3a. Event-based in a main program, using any supported event module:
		1359
		1360	use EV;
		1361
		1362	$fcp->txn_client_get ($url)->cb (sub {
		1363	my $txn = shift;
		1364	my $data = $txn->result;
		1365	...
		1366	});
		1367
		1368	EV::loop;
		1369
		1370	3b. The module user could use AnyEvent, too:
		1371
		1372	use AnyEvent;
		1373
		1374	my $quit = AnyEvent->condvar;
		1375
		1376	$fcp->txn_client_get ($url)->cb (sub {
		1377	...
		1378	$quit->send;
		1379	});
		1380
		1381	$quit->recv;
		1382
		1383
		1384	=head1 BENCHMARKS
		1385
		1386	To give you an idea of the performance and overheads that AnyEvent adds
		1387	over the event loops themselves and to give you an impression of the speed
		1388	of various event loops I prepared some benchmarks.
		1389
		1390	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1391
		1392	Here is a benchmark of various supported event models used natively and
		1393	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1394	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1395	which it is), lets them fire exactly once and destroys them again.
		1396
		1397	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1398	distribution.
		1399
		1400	=head3 Explanation of the columns
		1401
		1402	I<watcher> is the number of event watchers created/destroyed. Since
		1403	different event models feature vastly different performances, each event
		1404	loop was given a number of watchers so that overall runtime is acceptable
		1405	and similar between tested event loop (and keep them from crashing): Glib
		1406	would probably take thousands of years if asked to process the same number
		1407	of watchers as EV in this benchmark.
		1408
		1409	I<bytes> is the number of bytes (as measured by the resident set size,
		1410	RSS) consumed by each watcher. This method of measuring captures both C
		1411	and Perl-based overheads.
		1412
		1413	I<create> is the time, in microseconds (millionths of seconds), that it
		1414	takes to create a single watcher. The callback is a closure shared between
		1415	all watchers, to avoid adding memory overhead. That means closure creation
		1416	and memory usage is not included in the figures.
		1417
		1418	I<invoke> is the time, in microseconds, used to invoke a simple
		1419	callback. The callback simply counts down a Perl variable and after it was
		1420	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1421	signal the end of this phase.
		1422
		1423	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1424	watcher.
		1425
		1426	=head3 Results
		1427
		1428	name watchers bytes create invoke destroy comment
		1429	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1430	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1431	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1432	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1433	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1434	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1435	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1436	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1437	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1438	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1439
		1440	=head3 Discussion
		1441
		1442	The benchmark does I<not> measure scalability of the event loop very
		1443	well. For example, a select-based event loop (such as the pure perl one)
		1444	can never compete with an event loop that uses epoll when the number of
		1445	file descriptors grows high. In this benchmark, all events become ready at
		1446	the same time, so select/poll-based implementations get an unnatural speed
		1447	boost.
		1448
		1449	Also, note that the number of watchers usually has a nonlinear effect on
		1450	overall speed, that is, creating twice as many watchers doesn't take twice
		1451	the time - usually it takes longer. This puts event loops tested with a
		1452	higher number of watchers at a disadvantage.
		1453
		1454	To put the range of results into perspective, consider that on the
		1455	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1456	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1457	cycles with POE.
		1458
		1459	C<EV> is the sole leader regarding speed and memory use, which are both
		1460	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1461	far less memory than any other event loop and is still faster than Event
		1462	natively.
		1463
		1464	The pure perl implementation is hit in a few sweet spots (both the
		1465	constant timeout and the use of a single fd hit optimisations in the perl
		1466	interpreter and the backend itself). Nevertheless this shows that it
		1467	adds very little overhead in itself. Like any select-based backend its
		1468	performance becomes really bad with lots of file descriptors (and few of
		1469	them active), of course, but this was not subject of this benchmark.
		1470
		1471	The C<Event> module has a relatively high setup and callback invocation
		1472	cost, but overall scores in on the third place.
		1473
		1474	C<Glib>'s memory usage is quite a bit higher, but it features a
		1475	faster callback invocation and overall ends up in the same class as
		1476	C<Event>. However, Glib scales extremely badly, doubling the number of
		1477	watchers increases the processing time by more than a factor of four,
		1478	making it completely unusable when using larger numbers of watchers
		1479	(note that only a single file descriptor was used in the benchmark, so
		1480	inefficiencies of C<poll> do not account for this).
		1481
		1482	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1483	more than 2000 watchers is a big setback, however, as correctness takes
		1484	precedence over speed. Nevertheless, its performance is surprising, as the
		1485	file descriptor is dup()ed for each watcher. This shows that the dup()
		1486	employed by some adaptors is not a big performance issue (it does incur a
		1487	hidden memory cost inside the kernel which is not reflected in the figures
		1488	above).
		1489
		1490	C<POE>, regardless of underlying event loop (whether using its pure perl
		1491	select-based backend or the Event module, the POE-EV backend couldn't
		1492	be tested because it wasn't working) shows abysmal performance and
		1493	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1494	as EV watchers, and 10 times as much memory as Event (the high memory
		1495	requirements are caused by requiring a session for each watcher). Watcher
		1496	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1497	implementation.
		1498
		1499	The design of the POE adaptor class in AnyEvent can not really account
		1500	for the performance issues, though, as session creation overhead is
		1501	small compared to execution of the state machine, which is coded pretty
		1502	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1503	using multiple sessions is not a good approach, especially regarding
		1504	memory usage, even the author of POE could not come up with a faster
		1505	design).
		1506
		1507	=head3 Summary
		1508
		1509	=over 4
		1510
		1511	=item * Using EV through AnyEvent is faster than any other event loop
		1512	(even when used without AnyEvent), but most event loops have acceptable
		1513	performance with or without AnyEvent.
		1514
		1515	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1516	the actual event loop, only with extremely fast event loops such as EV
		1517	adds AnyEvent significant overhead.
		1518
		1519	=item * You should avoid POE like the plague if you want performance or
		1520	reasonable memory usage.
		1521
		1522	=back
		1523
		1524	=head2 BENCHMARKING THE LARGE SERVER CASE
		1525
		1526	This benchmark actually benchmarks the event loop itself. It works by
		1527	creating a number of "servers": each server consists of a socket pair, a
		1528	timeout watcher that gets reset on activity (but never fires), and an I/O
		1529	watcher waiting for input on one side of the socket. Each time the socket
		1530	watcher reads a byte it will write that byte to a random other "server".
		1531
		1532	The effect is that there will be a lot of I/O watchers, only part of which
		1533	are active at any one point (so there is a constant number of active
		1534	fds for each loop iteration, but which fds these are is random). The
		1535	timeout is reset each time something is read because that reflects how
		1536	most timeouts work (and puts extra pressure on the event loops).
		1537
		1538	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1539	(1%) are active. This mirrors the activity of large servers with many
		1540	connections, most of which are idle at any one point in time.
		1541
		1542	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1543	distribution.
		1544
		1545	=head3 Explanation of the columns
		1546
		1547	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1548	each server has a read and write socket end).
		1549
		1550	I<create> is the time it takes to create a socket pair (which is
		1551	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1552
		1553	I<request>, the most important value, is the time it takes to handle a
		1554	single "request", that is, reading the token from the pipe and forwarding
		1555	it to another server. This includes deleting the old timeout and creating
		1556	a new one that moves the timeout into the future.
		1557
		1558	=head3 Results
		1559
		1560	name sockets create request
		1561	EV 20000 69.01 11.16
		1562	Perl 20000 73.32 35.87
		1563	Event 20000 212.62 257.32
		1564	Glib 20000 651.16 1896.30
		1565	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1566
		1567	=head3 Discussion
		1568
		1569	This benchmark I<does> measure scalability and overall performance of the
		1570	particular event loop.
		1571
		1572	EV is again fastest. Since it is using epoll on my system, the setup time
		1573	is relatively high, though.
		1574
		1575	Perl surprisingly comes second. It is much faster than the C-based event
		1576	loops Event and Glib.
		1577
		1578	Event suffers from high setup time as well (look at its code and you will
		1579	understand why). Callback invocation also has a high overhead compared to
		1580	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1581	uses select or poll in basically all documented configurations.
		1582
		1583	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1584	clearly fails to perform with many filehandles or in busy servers.
		1585
		1586	POE is still completely out of the picture, taking over 1000 times as long
		1587	as EV, and over 100 times as long as the Perl implementation, even though
		1588	it uses a C-based event loop in this case.
		1589
		1590	=head3 Summary
		1591
		1592	=over 4
		1593
		1594	=item * The pure perl implementation performs extremely well.
		1595
		1596	=item * Avoid Glib or POE in large projects where performance matters.
		1597
		1598	=back
		1599
		1600	=head2 BENCHMARKING SMALL SERVERS
		1601
		1602	While event loops should scale (and select-based ones do not...) even to
		1603	large servers, most programs we (or I :) actually write have only a few
		1604	I/O watchers.
		1605
		1606	In this benchmark, I use the same benchmark program as in the large server
		1607	case, but it uses only eight "servers", of which three are active at any
		1608	one time. This should reflect performance for a small server relatively
		1609	well.
		1610
		1611	The columns are identical to the previous table.
		1612
		1613	=head3 Results
		1614
		1615	name sockets create request
		1616	EV 16 20.00 6.54
		1617	Perl 16 25.75 12.62
		1618	Event 16 81.27 35.86
		1619	Glib 16 32.63 15.48
		1620	POE 16 261.87 276.28 uses POE::Loop::Event
		1621
		1622	=head3 Discussion
		1623
		1624	The benchmark tries to test the performance of a typical small
		1625	server. While knowing how various event loops perform is interesting, keep
		1626	in mind that their overhead in this case is usually not as important, due
		1627	to the small absolute number of watchers (that is, you need efficiency and
		1628	speed most when you have lots of watchers, not when you only have a few of
		1629	them).
		1630
		1631	EV is again fastest.
		1632
		1633	Perl again comes second. It is noticeably faster than the C-based event
		1634	loops Event and Glib, although the difference is too small to really
		1635	matter.
		1636
		1637	POE also performs much better in this case, but is is still far behind the
		1638	others.
		1639
		1640	=head3 Summary
		1641
		1642	=over 4
		1643
		1644	=item * C-based event loops perform very well with small number of
		1645	watchers, as the management overhead dominates.
		1646
		1647	=back
		1648
		1649
		1650	=head1 FORK
		1651
		1652	Most event libraries are not fork-safe. The ones who are usually are
		1653	because they rely on inefficient but fork-safe C<select> or C<poll>
		1654	calls. Only L<EV> is fully fork-aware.
		1655
		1656	If you have to fork, you must either do so I<before> creating your first
		1657	watcher OR you must not use AnyEvent at all in the child.
		1658
		1659
		1660	=head1 SECURITY CONSIDERATIONS
		1661
		1662	AnyEvent can be forced to load any event model via
		1663	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1664	execute arbitrary code or directly gain access, it can easily be used to
		1665	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1666	will not be active when the program uses a different event model than
		1667	specified in the variable.
		1668
		1669	You can make AnyEvent completely ignore this variable by deleting it
		1670	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1671
		1672	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1673
		1674	use AnyEvent;
		1675
		1676	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1677	be used to probe what backend is used and gain other information (which is
		1678	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1679
		1680
		1681	=head1 BUGS
		1682
		1683	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1684	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1685	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1686	mamleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1687	pronounced).
		1688
139		1689
140	=head1 SEE ALSO	1690	=head1 SEE ALSO
141		1691
142	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	1692	Utility functions: L<AnyEvent::Util>.
143	L<AnyEvent::Impl::Coro>,	1693
144	L<AnyEvent::Impl::Event>,	1694	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
145	L<AnyEvent::Impl::Glib>,	1695	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1696
		1697	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1698	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1699	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
146	L<AnyEvent::Impl::Tk>.	1700	L<AnyEvent::Impl::POE>.
147		1701
148	=head1	1702	Non-blocking file handles, sockets, TCP clients and
		1703	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1704
		1705	Asynchronous DNS: L<AnyEvent::DNS>.
		1706
		1707	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1708
		1709	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1710
		1711
		1712	=head1 AUTHOR
		1713
		1714	Marc Lehmann <schmorp@schmorp.de>
		1715	http://home.schmorp.de/
149		1716
150	=cut	1717	=cut
151		1718
152	1	1719	1
153		1720

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