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Revision 1.7 by root, Fri Dec 30 01:28:31 2005 UTC vs.
Revision 1.149 by root, Sat May 31 01:41:22 2008 UTC

1	=head1 NAME	1	=head1 => NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	Event, Coro, Glib, Tk - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
11	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
12	my ($poll_got) = @_;
13	...	12	...
14	});	13	});
15
16	* only one io watcher per $fh and $poll type is allowed (i.e. on a socket
17	you can have one r + one w or one rw watcher, not any more (limitation by
18	Tk).
19
20	* the C<$poll_got> passed to the handler needs to be checked by looking
21	for single characters (e.g. with a regex), as it can contain more event
22	types than were requested (e.g. a 'w' watcher might generate 'rw' events,
23	limitation by Glib).
24
25	* AnyEvent will keep filehandles alive, so as long as the watcher exists,
26	the filehandle exists.
27		14
28	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
29	...	16	...
30	});	17	});
31		18
32	* io and time watchers get canceled whenever $w is destroyed, so keep a copy	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
33		20	$w->send; # wake up current and all future recv's
34	* timers can only be used once and must be recreated for repeated
35	operation (limitation by Glib and Tk).
36
37	my $w = AnyEvent->condvar; # kind of main loop replacement
38	$w->wait; # enters main loop till $condvar gets ->broadcast	21	$w->recv; # enters "main loop" till $condvar gets ->send
39	$w->broadcast; # wake up current and all future wait's
40		22
41	* condvars are used to give blocking behaviour when neccessary. Create	23	=head1 INTRODUCTION/TUTORIAL
42	a condvar for any "request" or "event" your module might create, C<<	24
43	->broadcast >> it when the event happens and provide a function that calls	25	This manpage is mainly a reference manual. If you are interested
44	C<< ->wait >> for it. See the examples below.	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.
45		82
46	=head1 DESCRIPTION	83	=head1 DESCRIPTION
47		84
48	L<AnyEvent> provides an identical interface to multiple event loops. This	85	L<AnyEvent> provides an identical interface to multiple event loops. This
49	allows module authors to utilizy an event loop without forcing module	86	allows module authors to utilise an event loop without forcing module
50	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
51	peacefully at any one time).	88	peacefully at any one time).
52		89
53	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>
54	module.	91	module.
55		92
56	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
57	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
58	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	95	following modules is already loaded: L<EV>,
59	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>,
60	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
61	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":
62		245
63	=over 4	246	=over 4
64		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::HTTPD>
		758
		759	Provides a simple web application server framework.
		760
		761	=item L<AnyEvent::FastPing>
		762
		763	The fastest ping in the west.
		764
		765	=item L<Net::IRC3>
		766
		767	AnyEvent based IRC client module family.
		768
		769	=item L<Net::XMPP2>
		770
		771	AnyEvent based XMPP (Jabber protocol) module family.
		772
		773	=item L<Net::FCP>
		774
		775	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		776	of AnyEvent.
		777
		778	=item L<Event::ExecFlow>
		779
		780	High level API for event-based execution flow control.
		781
		782	=item L<Coro>
		783
		784	Has special support for AnyEvent via L<Coro::AnyEvent>.
		785
		786	=item L<AnyEvent::AIO>, L<IO::AIO>
		787
		788	Truly asynchronous I/O, should be in the toolbox of every event
		789	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		790	together.
		791
		792	=item L<AnyEvent::BDB>, L<BDB>
		793
		794	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		795	IO::AIO and AnyEvent together.
		796
		797	=item L<IO::Lambda>
		798
		799	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		800
		801	=back
		802
65	=cut	803	=cut
66		804
67	package AnyEvent;	805	package AnyEvent;
68		806
69	no warnings;	807	no warnings;
70	use strict 'vars';	808	use strict;
		809
71	use Carp;	810	use Carp;
72		811
73	our $VERSION = '0.4';	812	our $VERSION = 4.11;
74	our $MODEL;	813	our $MODEL;
75		814
76	our $AUTOLOAD;	815	our $AUTOLOAD;
77	our @ISA;	816	our @ISA;
78		817
		818	our @REGISTRY;
		819
		820	our $WIN32;
		821
		822	BEGIN {
		823	my $win32 = ! ! ($^O =~ /mswin32/i);
		824	eval "sub WIN32(){ $win32 }";
		825	}
		826
79	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	827	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
80		828
		829	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		830
		831	{
		832	my $idx;
		833	$PROTOCOL{$_} = ++$idx
		834	for reverse split /\s*,\s*/,
		835	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		836	}
		837
81	my @models = (	838	my @models = (
82	[Coro => Coro::Event::],	839	[EV:: => AnyEvent::Impl::EV::],
83	[Event => Event::],	840	[Event:: => AnyEvent::Impl::Event::],
84	[Glib => Glib::],	841	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
85	[Tk => Tk::],	842	# everything below here will not be autoprobed
		843	# as the pureperl backend should work everywhere
		844	# and is usually faster
		845	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		846	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		847	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		848	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		849	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		850	[Wx:: => AnyEvent::Impl::POE::],
		851	[Prima:: => AnyEvent::Impl::POE::],
86	);	852	);
87		853
88	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	854	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
89		855
90	sub AUTOLOAD {	856	our @post_detect;
91	$AUTOLOAD =~ s/.*://;
92		857
93	$method{$AUTOLOAD}	858	sub post_detect(&) {
94	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	859	my ($cb) = @_;
95		860
		861	if ($MODEL) {
		862	$cb->();
		863
		864	1
		865	} else {
		866	push @post_detect, $cb;
		867
		868	defined wantarray
		869	? bless \$cb, "AnyEvent::Util::PostDetect"
		870	: ()
		871	}
		872	}
		873
		874	sub AnyEvent::Util::PostDetect::DESTROY {
		875	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		876	}
		877
		878	sub detect() {
96	unless ($MODEL) {	879	unless ($MODEL) {
97	# check for already loaded models	880	no strict 'refs';
98	for (@models) {	881	local $SIG{__DIE__};
99	my ($model, $package) = @$_;	882
100	if (${"$package\::VERSION"} > 0) {	883	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
101	eval "require AnyEvent::Impl::$model";	884	my $model = "AnyEvent::Impl::$1";
102	warn "AnyEvent: found model '$model', using it.\n" if $MODEL && $verbose > 1;	885	if (eval "require $model") {
103	last if $MODEL;	886	$MODEL = $model;
		887	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		888	} else {
		889	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
104	}	890	}
105	}	891	}
106		892
		893	# check for already loaded models
107	unless ($MODEL) {	894	unless ($MODEL) {
108	# try to load a model
109
110	for (@models) {	895	for (@REGISTRY, @models) {
111	my ($model, $package) = @$_;	896	my ($package, $model) = @$_;
112	eval "require AnyEvent::Impl::$model";	897	if (${"$package\::VERSION"} > 0) {
		898	if (eval "require $model") {
		899	$MODEL = $model;
113	warn "AnyEvent: autprobed and loaded model '$model', using it.\n" if $MODEL && $verbose > 1;	900	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
114	last if $MODEL;	901	last;
		902	}
		903	}
115	}	904	}
116		905
		906	unless ($MODEL) {
		907	# try to load a model
		908
		909	for (@REGISTRY, @models) {
		910	my ($package, $model) = @$_;
		911	if (eval "require $package"
		912	and ${"$package\::VERSION"} > 0
		913	and eval "require $model") {
		914	$MODEL = $model;
		915	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		916	last;
		917	}
		918	}
		919
117	$MODEL	920	$MODEL
118	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	921	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		922	}
119	}	923	}
		924
		925	unshift @ISA, $MODEL;
		926	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		927
		928	(shift @post_detect)->() while @post_detect;
120	}	929	}
121		930
122	@ISA = $MODEL;	931	$MODEL
		932	}
		933
		934	sub AUTOLOAD {
		935	(my $func = $AUTOLOAD) =~ s/.*://;
		936
		937	$method{$func}
		938	or croak "$func: not a valid method for AnyEvent objects";
		939
		940	detect unless $MODEL;
123		941
124	my $class = shift;	942	my $class = shift;
125	$class->$AUTOLOAD (@_);	943	$class->$func (@_);
126	}	944	}
		945
		946	package AnyEvent::Base;
		947
		948	# default implementation for now and time
		949
		950	use Time::HiRes ();
		951
		952	sub time { Time::HiRes::time }
		953	sub now { Time::HiRes::time }
		954
		955	# default implementation for ->condvar
		956
		957	sub condvar {
		958	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		959	}
		960
		961	# default implementation for ->signal
		962
		963	our %SIG_CB;
		964
		965	sub signal {
		966	my (undef, %arg) = @_;
		967
		968	my $signal = uc $arg{signal}
		969	or Carp::croak "required option 'signal' is missing";
		970
		971	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		972	$SIG{$signal} ||= sub {
		973	$_->() for values %{ $SIG_CB{$signal} || {} };
		974	};
		975
		976	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		977	}
		978
		979	sub AnyEvent::Base::Signal::DESTROY {
		980	my ($signal, $cb) = @{$_[0]};
		981
		982	delete $SIG_CB{$signal}{$cb};
		983
		984	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		985	}
		986
		987	# default implementation for ->child
		988
		989	our %PID_CB;
		990	our $CHLD_W;
		991	our $CHLD_DELAY_W;
		992	our $PID_IDLE;
		993	our $WNOHANG;
		994
		995	sub _child_wait {
		996	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		997	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		998	(values %{ $PID_CB{0} || {} });
		999	}
		1000
		1001	undef $PID_IDLE;
		1002	}
		1003
		1004	sub _sigchld {
		1005	# make sure we deliver these changes "synchronous" with the event loop.
		1006	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		1007	undef $CHLD_DELAY_W;
		1008	&_child_wait;
		1009	});
		1010	}
		1011
		1012	sub child {
		1013	my (undef, %arg) = @_;
		1014
		1015	defined (my $pid = $arg{pid} + 0)
		1016	or Carp::croak "required option 'pid' is missing";
		1017
		1018	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1019
		1020	unless ($WNOHANG) {
		1021	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1022	}
		1023
		1024	unless ($CHLD_W) {
		1025	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1026	# child could be a zombie already, so make at least one round
		1027	&_sigchld;
		1028	}
		1029
		1030	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		1031	}
		1032
		1033	sub AnyEvent::Base::Child::DESTROY {
		1034	my ($pid, $cb) = @{$_[0]};
		1035
		1036	delete $PID_CB{$pid}{$cb};
		1037	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1038
		1039	undef $CHLD_W unless keys %PID_CB;
		1040	}
		1041
		1042	package AnyEvent::CondVar;
		1043
		1044	our @ISA = AnyEvent::CondVar::Base::;
		1045
		1046	package AnyEvent::CondVar::Base;
		1047
		1048	use overload
		1049	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1050	fallback => 1;
		1051
		1052	sub _send {
		1053	# nop
		1054	}
		1055
		1056	sub send {
		1057	my $cv = shift;
		1058	$cv->{_ae_sent} = [@_];
		1059	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1060	$cv->_send;
		1061	}
		1062
		1063	sub croak {
		1064	$_[0]{_ae_croak} = $_[1];
		1065	$_[0]->send;
		1066	}
		1067
		1068	sub ready {
		1069	$_[0]{_ae_sent}
		1070	}
		1071
		1072	sub _wait {
		1073	AnyEvent->one_event while !$_[0]{_ae_sent};
		1074	}
		1075
		1076	sub recv {
		1077	$_[0]->_wait;
		1078
		1079	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1080	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1081	}
		1082
		1083	sub cb {
		1084	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1085	$_[0]{_ae_cb}
		1086	}
		1087
		1088	sub begin {
		1089	++$_[0]{_ae_counter};
		1090	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1091	}
		1092
		1093	sub end {
		1094	return if --$_[0]{_ae_counter};
		1095	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1096	}
		1097
		1098	# undocumented/compatibility with pre-3.4
		1099	*broadcast = \&send;
		1100	*wait = \&_wait;
		1101
		1102	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1103
		1104	This is an advanced topic that you do not normally need to use AnyEvent in
		1105	a module. This section is only of use to event loop authors who want to
		1106	provide AnyEvent compatibility.
		1107
		1108	If you need to support another event library which isn't directly
		1109	supported by AnyEvent, you can supply your own interface to it by
		1110	pushing, before the first watcher gets created, the package name of
		1111	the event module and the package name of the interface to use onto
		1112	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1113	AnyEvent, so it is reasonably cheap.
		1114
		1115	Example:
		1116
		1117	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1118
		1119	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1120	package/class when it finds the C<urxvt> package/module is already loaded.
		1121
		1122	When AnyEvent is loaded and asked to find a suitable event model, it
		1123	will first check for the presence of urxvt by trying to C<use> the
		1124	C<urxvt::anyevent> module.
		1125
		1126	The class should provide implementations for all watcher types. See
		1127	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1128	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1129	see the sources.
		1130
		1131	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1132	provide suitable (hopefully) replacements.
		1133
		1134	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1135	terminal emulator uses the above line as-is. An interface isn't included
		1136	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1137	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1138	I<rxvt-unicode> distribution.
		1139
		1140	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1141	condition variables: code blocking while waiting for a condition will
		1142	C<die>. This still works with most modules/usages, and blocking calls must
		1143	not be done in an interactive application, so it makes sense.
		1144
		1145	=head1 ENVIRONMENT VARIABLES
		1146
		1147	The following environment variables are used by this module:
		1148
		1149	=over 4
		1150
		1151	=item C<PERL_ANYEVENT_VERBOSE>
		1152
		1153	By default, AnyEvent will be completely silent except in fatal
		1154	conditions. You can set this environment variable to make AnyEvent more
		1155	talkative.
		1156
		1157	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1158	conditions, such as not being able to load the event model specified by
		1159	C<PERL_ANYEVENT_MODEL>.
		1160
		1161	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1162	model it chooses.
		1163
		1164	=item C<PERL_ANYEVENT_MODEL>
		1165
		1166	This can be used to specify the event model to be used by AnyEvent, before
		1167	auto detection and -probing kicks in. It must be a string consisting
		1168	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1169	and the resulting module name is loaded and if the load was successful,
		1170	used as event model. If it fails to load AnyEvent will proceed with
		1171	auto detection and -probing.
		1172
		1173	This functionality might change in future versions.
		1174
		1175	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1176	could start your program like this:
		1177
		1178	PERL_ANYEVENT_MODEL=Perl perl ...
		1179
		1180	=item C<PERL_ANYEVENT_PROTOCOLS>
		1181
		1182	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1183	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1184	of auto probing).
		1185
		1186	Must be set to a comma-separated list of protocols or address families,
		1187	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1188	used, and preference will be given to protocols mentioned earlier in the
		1189	list.
		1190
		1191	This variable can effectively be used for denial-of-service attacks
		1192	against local programs (e.g. when setuid), although the impact is likely
		1193	small, as the program has to handle connection errors already-
		1194
		1195	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1196	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1197	- only support IPv4, never try to resolve or contact IPv6
		1198	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1199	IPv6, but prefer IPv6 over IPv4.
		1200
		1201	=item C<PERL_ANYEVENT_EDNS0>
		1202
		1203	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1204	for DNS. This extension is generally useful to reduce DNS traffic, but
		1205	some (broken) firewalls drop such DNS packets, which is why it is off by
		1206	default.
		1207
		1208	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1209	EDNS0 in its DNS requests.
		1210
		1211	=item C<PERL_ANYEVENT_MAX_FORKS>
		1212
		1213	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1214	will create in parallel.
127		1215
128	=back	1216	=back
129		1217
130	=head1 ENVIRONMENT VARIABLES
131
132	The following environment variables are used by this module:
133
134	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
135	model gets used.
136
137	=head1 EXAMPLE	1218	=head1 EXAMPLE PROGRAM
138		1219
139	The following program uses an io watcher to read data from stdin, a timer	1220	The following program uses an I/O watcher to read data from STDIN, a timer
140	to display a message once per second, and a condvar to exit the program	1221	to display a message once per second, and a condition variable to quit the
141	when the user enters quit:	1222	program when the user enters quit:
142		1223
143	use AnyEvent;	1224	use AnyEvent;
144		1225
145	my $cv = AnyEvent->condvar;	1226	my $cv = AnyEvent->condvar;
146		1227
147	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1228	my $io_watcher = AnyEvent->io (
		1229	fh => \*STDIN,
		1230	poll => 'r',
		1231	cb => sub {
148	warn "io event <$_[0]>\n"; # will always output <r>	1232	warn "io event <$_[0]>\n"; # will always output <r>
149	chomp (my $input = <STDIN>); # read a line	1233	chomp (my $input = <STDIN>); # read a line
150	warn "read: $input\n"; # output what has been read	1234	warn "read: $input\n"; # output what has been read
151	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1235	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1236	},
152	});	1237	);
153		1238
154	my $time_watcher; # can only be used once	1239	my $time_watcher; # can only be used once
155		1240
156	sub new_timer {	1241	sub new_timer {
157	$timer = AnyEvent->timer (after => 1, cb => sub {	1242	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
160	});	1245	});
161	}	1246	}
162		1247
163	new_timer; # create first timer	1248	new_timer; # create first timer
164		1249
165	$cv->wait; # wait until user enters /^q/i	1250	$cv->recv; # wait until user enters /^q/i
166		1251
167	=head1 REAL-WORLD EXAMPLE	1252	=head1 REAL-WORLD EXAMPLE
168		1253
169	Consider the L<Net::FCP> module. It features (among others) the following	1254	Consider the L<Net::FCP> module. It features (among others) the following
170	API calls, which are to freenet what HTTP GET requests are to http:	1255	API calls, which are to freenet what HTTP GET requests are to http:
…		…
220	syswrite $txn->{fh}, $txn->{request}	1305	syswrite $txn->{fh}, $txn->{request}
221	or die "connection or write error";	1306	or die "connection or write error";
222	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1307	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
223		1308
224	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1309	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
225	result and signals any possible waiters that the request ahs finished:	1310	result and signals any possible waiters that the request has finished:
226		1311
227	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1312	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
228		1313
229	if (end-of-file or data complete) {	1314	if (end-of-file or data complete) {
230	$txn->{result} = $txn->{buf};	1315	$txn->{result} = $txn->{buf};
231	$txn->{finished}->broadcast;	1316	$txn->{finished}->send;
232	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1317	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
233	}	1318	}
234		1319
235	The C<result> method, finally, just waits for the finished signal (if the	1320	The C<result> method, finally, just waits for the finished signal (if the
236	request was already finished, it doesn't wait, of course, and returns the	1321	request was already finished, it doesn't wait, of course, and returns the
237	data:	1322	data:
238		1323
239	$txn->{finished}->wait;	1324	$txn->{finished}->recv;
240	return $txn->{result};	1325	return $txn->{result};
241		1326
242	The actual code goes further and collects all errors (C<die>s, exceptions)	1327	The actual code goes further and collects all errors (C<die>s, exceptions)
243	that occured during request processing. The C<result> method detects	1328	that occurred during request processing. The C<result> method detects
244	wether an exception as thrown (it is stored inside the $txn object)	1329	whether an exception as thrown (it is stored inside the $txn object)
245	and just throws the exception, which means connection errors and other	1330	and just throws the exception, which means connection errors and other
246	problems get reported tot he code that tries to use the result, not in a	1331	problems get reported tot he code that tries to use the result, not in a
247	random callback.	1332	random callback.
248		1333
249	All of this enables the following usage styles:	1334	All of this enables the following usage styles:
250		1335
251	1. Blocking:	1336	1. Blocking:
252		1337
253	my $data = $fcp->client_get ($url);	1338	my $data = $fcp->client_get ($url);
254		1339
255	2. Blocking, but parallelizing:	1340	2. Blocking, but running in parallel:
256		1341
257	my @datas = map $_->result,	1342	my @datas = map $_->result,
258	map $fcp->txn_client_get ($_),	1343	map $fcp->txn_client_get ($_),
259	@urls;	1344	@urls;
260		1345
261	Both blocking examples work without the module user having to know	1346	Both blocking examples work without the module user having to know
262	anything about events.	1347	anything about events.
263		1348
264	3a. Event-based in a main program, using any support Event module:	1349	3a. Event-based in a main program, using any supported event module:
265		1350
266	use Event;	1351	use EV;
267		1352
268	$fcp->txn_client_get ($url)->cb (sub {	1353	$fcp->txn_client_get ($url)->cb (sub {
269	my $txn = shift;	1354	my $txn = shift;
270	my $data = $txn->result;	1355	my $data = $txn->result;
271	...	1356	...
272	});	1357	});
273		1358
274	Event::loop;	1359	EV::loop;
275		1360
276	3b. The module user could use AnyEvent, too:	1361	3b. The module user could use AnyEvent, too:
277		1362
278	use AnyEvent;	1363	use AnyEvent;
279		1364
280	my $quit = AnyEvent->condvar;	1365	my $quit = AnyEvent->condvar;
281		1366
282	$fcp->txn_client_get ($url)->cb (sub {	1367	$fcp->txn_client_get ($url)->cb (sub {
283	...	1368	...
284	$quit->broadcast;	1369	$quit->send;
285	});	1370	});
286		1371
287	$quit->wait;	1372	$quit->recv;
		1373
		1374
		1375	=head1 BENCHMARKS
		1376
		1377	To give you an idea of the performance and overheads that AnyEvent adds
		1378	over the event loops themselves and to give you an impression of the speed
		1379	of various event loops I prepared some benchmarks.
		1380
		1381	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1382
		1383	Here is a benchmark of various supported event models used natively and
		1384	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1385	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1386	which it is), lets them fire exactly once and destroys them again.
		1387
		1388	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1389	distribution.
		1390
		1391	=head3 Explanation of the columns
		1392
		1393	I<watcher> is the number of event watchers created/destroyed. Since
		1394	different event models feature vastly different performances, each event
		1395	loop was given a number of watchers so that overall runtime is acceptable
		1396	and similar between tested event loop (and keep them from crashing): Glib
		1397	would probably take thousands of years if asked to process the same number
		1398	of watchers as EV in this benchmark.
		1399
		1400	I<bytes> is the number of bytes (as measured by the resident set size,
		1401	RSS) consumed by each watcher. This method of measuring captures both C
		1402	and Perl-based overheads.
		1403
		1404	I<create> is the time, in microseconds (millionths of seconds), that it
		1405	takes to create a single watcher. The callback is a closure shared between
		1406	all watchers, to avoid adding memory overhead. That means closure creation
		1407	and memory usage is not included in the figures.
		1408
		1409	I<invoke> is the time, in microseconds, used to invoke a simple
		1410	callback. The callback simply counts down a Perl variable and after it was
		1411	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1412	signal the end of this phase.
		1413
		1414	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1415	watcher.
		1416
		1417	=head3 Results
		1418
		1419	name watchers bytes create invoke destroy comment
		1420	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1421	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1422	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1423	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1424	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1425	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1426	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1427	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1428	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1429	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1430
		1431	=head3 Discussion
		1432
		1433	The benchmark does I<not> measure scalability of the event loop very
		1434	well. For example, a select-based event loop (such as the pure perl one)
		1435	can never compete with an event loop that uses epoll when the number of
		1436	file descriptors grows high. In this benchmark, all events become ready at
		1437	the same time, so select/poll-based implementations get an unnatural speed
		1438	boost.
		1439
		1440	Also, note that the number of watchers usually has a nonlinear effect on
		1441	overall speed, that is, creating twice as many watchers doesn't take twice
		1442	the time - usually it takes longer. This puts event loops tested with a
		1443	higher number of watchers at a disadvantage.
		1444
		1445	To put the range of results into perspective, consider that on the
		1446	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1447	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1448	cycles with POE.
		1449
		1450	C<EV> is the sole leader regarding speed and memory use, which are both
		1451	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1452	far less memory than any other event loop and is still faster than Event
		1453	natively.
		1454
		1455	The pure perl implementation is hit in a few sweet spots (both the
		1456	constant timeout and the use of a single fd hit optimisations in the perl
		1457	interpreter and the backend itself). Nevertheless this shows that it
		1458	adds very little overhead in itself. Like any select-based backend its
		1459	performance becomes really bad with lots of file descriptors (and few of
		1460	them active), of course, but this was not subject of this benchmark.
		1461
		1462	The C<Event> module has a relatively high setup and callback invocation
		1463	cost, but overall scores in on the third place.
		1464
		1465	C<Glib>'s memory usage is quite a bit higher, but it features a
		1466	faster callback invocation and overall ends up in the same class as
		1467	C<Event>. However, Glib scales extremely badly, doubling the number of
		1468	watchers increases the processing time by more than a factor of four,
		1469	making it completely unusable when using larger numbers of watchers
		1470	(note that only a single file descriptor was used in the benchmark, so
		1471	inefficiencies of C<poll> do not account for this).
		1472
		1473	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1474	more than 2000 watchers is a big setback, however, as correctness takes
		1475	precedence over speed. Nevertheless, its performance is surprising, as the
		1476	file descriptor is dup()ed for each watcher. This shows that the dup()
		1477	employed by some adaptors is not a big performance issue (it does incur a
		1478	hidden memory cost inside the kernel which is not reflected in the figures
		1479	above).
		1480
		1481	C<POE>, regardless of underlying event loop (whether using its pure perl
		1482	select-based backend or the Event module, the POE-EV backend couldn't
		1483	be tested because it wasn't working) shows abysmal performance and
		1484	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1485	as EV watchers, and 10 times as much memory as Event (the high memory
		1486	requirements are caused by requiring a session for each watcher). Watcher
		1487	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1488	implementation.
		1489
		1490	The design of the POE adaptor class in AnyEvent can not really account
		1491	for the performance issues, though, as session creation overhead is
		1492	small compared to execution of the state machine, which is coded pretty
		1493	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1494	using multiple sessions is not a good approach, especially regarding
		1495	memory usage, even the author of POE could not come up with a faster
		1496	design).
		1497
		1498	=head3 Summary
		1499
		1500	=over 4
		1501
		1502	=item * Using EV through AnyEvent is faster than any other event loop
		1503	(even when used without AnyEvent), but most event loops have acceptable
		1504	performance with or without AnyEvent.
		1505
		1506	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1507	the actual event loop, only with extremely fast event loops such as EV
		1508	adds AnyEvent significant overhead.
		1509
		1510	=item * You should avoid POE like the plague if you want performance or
		1511	reasonable memory usage.
		1512
		1513	=back
		1514
		1515	=head2 BENCHMARKING THE LARGE SERVER CASE
		1516
		1517	This benchmark actually benchmarks the event loop itself. It works by
		1518	creating a number of "servers": each server consists of a socket pair, a
		1519	timeout watcher that gets reset on activity (but never fires), and an I/O
		1520	watcher waiting for input on one side of the socket. Each time the socket
		1521	watcher reads a byte it will write that byte to a random other "server".
		1522
		1523	The effect is that there will be a lot of I/O watchers, only part of which
		1524	are active at any one point (so there is a constant number of active
		1525	fds for each loop iteration, but which fds these are is random). The
		1526	timeout is reset each time something is read because that reflects how
		1527	most timeouts work (and puts extra pressure on the event loops).
		1528
		1529	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1530	(1%) are active. This mirrors the activity of large servers with many
		1531	connections, most of which are idle at any one point in time.
		1532
		1533	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1534	distribution.
		1535
		1536	=head3 Explanation of the columns
		1537
		1538	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1539	each server has a read and write socket end).
		1540
		1541	I<create> is the time it takes to create a socket pair (which is
		1542	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1543
		1544	I<request>, the most important value, is the time it takes to handle a
		1545	single "request", that is, reading the token from the pipe and forwarding
		1546	it to another server. This includes deleting the old timeout and creating
		1547	a new one that moves the timeout into the future.
		1548
		1549	=head3 Results
		1550
		1551	name sockets create request
		1552	EV 20000 69.01 11.16
		1553	Perl 20000 73.32 35.87
		1554	Event 20000 212.62 257.32
		1555	Glib 20000 651.16 1896.30
		1556	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1557
		1558	=head3 Discussion
		1559
		1560	This benchmark I<does> measure scalability and overall performance of the
		1561	particular event loop.
		1562
		1563	EV is again fastest. Since it is using epoll on my system, the setup time
		1564	is relatively high, though.
		1565
		1566	Perl surprisingly comes second. It is much faster than the C-based event
		1567	loops Event and Glib.
		1568
		1569	Event suffers from high setup time as well (look at its code and you will
		1570	understand why). Callback invocation also has a high overhead compared to
		1571	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1572	uses select or poll in basically all documented configurations.
		1573
		1574	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1575	clearly fails to perform with many filehandles or in busy servers.
		1576
		1577	POE is still completely out of the picture, taking over 1000 times as long
		1578	as EV, and over 100 times as long as the Perl implementation, even though
		1579	it uses a C-based event loop in this case.
		1580
		1581	=head3 Summary
		1582
		1583	=over 4
		1584
		1585	=item * The pure perl implementation performs extremely well.
		1586
		1587	=item * Avoid Glib or POE in large projects where performance matters.
		1588
		1589	=back
		1590
		1591	=head2 BENCHMARKING SMALL SERVERS
		1592
		1593	While event loops should scale (and select-based ones do not...) even to
		1594	large servers, most programs we (or I :) actually write have only a few
		1595	I/O watchers.
		1596
		1597	In this benchmark, I use the same benchmark program as in the large server
		1598	case, but it uses only eight "servers", of which three are active at any
		1599	one time. This should reflect performance for a small server relatively
		1600	well.
		1601
		1602	The columns are identical to the previous table.
		1603
		1604	=head3 Results
		1605
		1606	name sockets create request
		1607	EV 16 20.00 6.54
		1608	Perl 16 25.75 12.62
		1609	Event 16 81.27 35.86
		1610	Glib 16 32.63 15.48
		1611	POE 16 261.87 276.28 uses POE::Loop::Event
		1612
		1613	=head3 Discussion
		1614
		1615	The benchmark tries to test the performance of a typical small
		1616	server. While knowing how various event loops perform is interesting, keep
		1617	in mind that their overhead in this case is usually not as important, due
		1618	to the small absolute number of watchers (that is, you need efficiency and
		1619	speed most when you have lots of watchers, not when you only have a few of
		1620	them).
		1621
		1622	EV is again fastest.
		1623
		1624	Perl again comes second. It is noticeably faster than the C-based event
		1625	loops Event and Glib, although the difference is too small to really
		1626	matter.
		1627
		1628	POE also performs much better in this case, but is is still far behind the
		1629	others.
		1630
		1631	=head3 Summary
		1632
		1633	=over 4
		1634
		1635	=item * C-based event loops perform very well with small number of
		1636	watchers, as the management overhead dominates.
		1637
		1638	=back
		1639
		1640
		1641	=head1 FORK
		1642
		1643	Most event libraries are not fork-safe. The ones who are usually are
		1644	because they rely on inefficient but fork-safe C<select> or C<poll>
		1645	calls. Only L<EV> is fully fork-aware.
		1646
		1647	If you have to fork, you must either do so I<before> creating your first
		1648	watcher OR you must not use AnyEvent at all in the child.
		1649
		1650
		1651	=head1 SECURITY CONSIDERATIONS
		1652
		1653	AnyEvent can be forced to load any event model via
		1654	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1655	execute arbitrary code or directly gain access, it can easily be used to
		1656	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1657	will not be active when the program uses a different event model than
		1658	specified in the variable.
		1659
		1660	You can make AnyEvent completely ignore this variable by deleting it
		1661	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1662
		1663	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1664
		1665	use AnyEvent;
		1666
		1667	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1668	be used to probe what backend is used and gain other information (which is
		1669	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1670
288		1671
289	=head1 SEE ALSO	1672	=head1 SEE ALSO
290		1673
291	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1674	Utility functions: L<AnyEvent::Util>.
292		1675
293	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1676	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1677	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
294		1678
295	Nontrivial usage example: L<Net::FCP>.	1679	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1680	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1681	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1682	L<AnyEvent::Impl::POE>.
296		1683
297	=head1	1684	Non-blocking file handles, sockets, TCP clients and
		1685	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1686
		1687	Asynchronous DNS: L<AnyEvent::DNS>.
		1688
		1689	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1690
		1691	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1692
		1693
		1694	=head1 AUTHOR
		1695
		1696	Marc Lehmann <schmorp@schmorp.de>
		1697	http://home.schmorp.de/
298		1698
299	=cut	1699	=cut
300		1700
301	1	1701	1
302		1702

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