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Revision 1.180 by root, Sat Sep 6 07:00:45 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) = @_;	12
		13	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		14	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		15
		16	print AnyEvent->now; # prints current event loop time
		17	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		18
		19	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		20
		21	my $w = AnyEvent->child (pid => $pid, cb => sub {
		22	my ($pid, $status) = @_;
13	...	23	...
14	});	24	});
15	my $w = AnyEvent->io (after => $seconds, cb => sub {
16	...
17	});
18		25
19	# watchers get canceled whenever $w is destroyed	26	my $w = AnyEvent->condvar; # stores whether a condition was flagged
20	# only one watcher per $fh and $poll type is allowed	27	$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	28	$w->recv; # enters "main loop" till $condvar gets ->send
28	$w->broadcast; # wake up waiting and future wait's	29	# use a condvar in callback mode:
		30	$w->cb (sub { $_[0]->recv });
		31
		32	=head1 INTRODUCTION/TUTORIAL
		33
		34	This manpage is mainly a reference manual. If you are interested
		35	in a tutorial or some gentle introduction, have a look at the
		36	L<AnyEvent::Intro> manpage.
		37
		38	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		39
		40	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		41	nowadays. So what is different about AnyEvent?
		42
		43	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		44	policy> and AnyEvent is I<small and efficient>.
		45
		46	First and foremost, I<AnyEvent is not an event model> itself, it only
		47	interfaces to whatever event model the main program happens to use, in a
		48	pragmatic way. For event models and certain classes of immortals alike,
		49	the statement "there can only be one" is a bitter reality: In general,
		50	only one event loop can be active at the same time in a process. AnyEvent
		51	cannot change this, but it can hide the differences between those event
		52	loops.
		53
		54	The goal of AnyEvent is to offer module authors the ability to do event
		55	programming (waiting for I/O or timer events) without subscribing to a
		56	religion, a way of living, and most importantly: without forcing your
		57	module users into the same thing by forcing them to use the same event
		58	model you use.
		59
		60	For modules like POE or IO::Async (which is a total misnomer as it is
		61	actually doing all I/O I<synchronously>...), using them in your module is
		62	like joining a cult: After you joined, you are dependent on them and you
		63	cannot use anything else, as they are simply incompatible to everything
		64	that isn't them. What's worse, all the potential users of your
		65	module are I<also> forced to use the same event loop you use.
		66
		67	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		68	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		69	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		70	your module uses one of those, every user of your module has to use it,
		71	too. But if your module uses AnyEvent, it works transparently with all
		72	event models it supports (including stuff like IO::Async, as long as those
		73	use one of the supported event loops. It is trivial to add new event loops
		74	to AnyEvent, too, so it is future-proof).
		75
		76	In addition to being free of having to use I<the one and only true event
		77	model>, AnyEvent also is free of bloat and policy: with POE or similar
		78	modules, you get an enormous amount of code and strict rules you have to
		79	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		80	offering the functionality that is necessary, in as thin as a wrapper as
		81	technically possible.
		82
		83	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		84	of useful functionality, such as an asynchronous DNS resolver, 100%
		85	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		86	such as Windows) and lots of real-world knowledge and workarounds for
		87	platform bugs and differences.
		88
		89	Now, if you I<do want> lots of policy (this can arguably be somewhat
		90	useful) and you want to force your users to use the one and only event
		91	model, you should I<not> use this module.
29		92
30	=head1 DESCRIPTION	93	=head1 DESCRIPTION
31		94
32	L<AnyEvent> provides an identical interface to multiple event loops. This	95	L<AnyEvent> provides an identical interface to multiple event loops. This
33	allows module authors to utilizy an event loop without forcing module	96	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	97	users to use the same event loop (as only a single event loop can coexist
35	peacefully at any one time).	98	peacefully at any one time).
36		99
37	The interface itself is vaguely similar but not identical to the Event	100	The interface itself is vaguely similar, but not identical to the L<Event>
38	module.	101	module.
39		102
40	On the first call of any method, the module tries to detect the currently	103	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	104	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	105	following modules is already loaded: L<EV>,
43	used. If none is found, the module tries to load these modules in the	106	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	107	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.	108	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		109	adaptor should always succeed) in the order given. The first one that can
		110	be successfully loaded will be used. If, after this, still none could be
		111	found, AnyEvent will fall back to a pure-perl event loop, which is not
		112	very efficient, but should work everywhere.
		113
		114	Because AnyEvent first checks for modules that are already loaded, loading
		115	an event model explicitly before first using AnyEvent will likely make
		116	that model the default. For example:
		117
		118	use Tk;
		119	use AnyEvent;
		120
		121	# .. AnyEvent will likely default to Tk
		122
		123	The I<likely> means that, if any module loads another event model and
		124	starts using it, all bets are off. Maybe you should tell their authors to
		125	use AnyEvent so their modules work together with others seamlessly...
		126
		127	The pure-perl implementation of AnyEvent is called
		128	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		129	explicitly and enjoy the high availability of that event loop :)
		130
		131	=head1 WATCHERS
		132
		133	AnyEvent has the central concept of a I<watcher>, which is an object that
		134	stores relevant data for each kind of event you are waiting for, such as
		135	the callback to call, the file handle to watch, etc.
		136
		137	These watchers are normal Perl objects with normal Perl lifetime. After
		138	creating a watcher it will immediately "watch" for events and invoke the
		139	callback when the event occurs (of course, only when the event model
		140	is in control).
		141
		142	To disable the watcher you have to destroy it (e.g. by setting the
		143	variable you store it in to C<undef> or otherwise deleting all references
		144	to it).
		145
		146	All watchers are created by calling a method on the C<AnyEvent> class.
		147
		148	Many watchers either are used with "recursion" (repeating timers for
		149	example), or need to refer to their watcher object in other ways.
		150
		151	An any way to achieve that is this pattern:
		152
		153	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		154	# you can use $w here, for example to undef it
		155	undef $w;
		156	});
		157
		158	Note that C<my $w; $w => combination. This is necessary because in Perl,
		159	my variables are only visible after the statement in which they are
		160	declared.
		161
		162	=head2 I/O WATCHERS
		163
		164	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		165	with the following mandatory key-value pairs as arguments:
		166
		167	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for events
		168	(AnyEvent might or might not keep a reference to this file handle). C<poll>
		169	must be a string that is either C<r> or C<w>, which creates a watcher
		170	waiting for "r"eadable or "w"ritable events, respectively. C<cb> is the
		171	callback to invoke each time the file handle becomes ready.
		172
		173	Although the callback might get passed parameters, their value and
		174	presence is undefined and you cannot rely on them. Portable AnyEvent
		175	callbacks cannot use arguments passed to I/O watcher callbacks.
		176
		177	The I/O watcher might use the underlying file descriptor or a copy of it.
		178	You must not close a file handle as long as any watcher is active on the
		179	underlying file descriptor.
		180
		181	Some event loops issue spurious readyness notifications, so you should
		182	always use non-blocking calls when reading/writing from/to your file
		183	handles.
		184
		185	Example: wait for readability of STDIN, then read a line and disable the
		186	watcher.
		187
		188	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		189	chomp (my $input = <STDIN>);
		190	warn "read: $input\n";
		191	undef $w;
		192	});
		193
		194	=head2 TIME WATCHERS
		195
		196	You can create a time watcher by calling the C<< AnyEvent->timer >>
		197	method with the following mandatory arguments:
		198
		199	C<after> specifies after how many seconds (fractional values are
		200	supported) the callback should be invoked. C<cb> is the callback to invoke
		201	in that case.
		202
		203	Although the callback might get passed parameters, their value and
		204	presence is undefined and you cannot rely on them. Portable AnyEvent
		205	callbacks cannot use arguments passed to time watcher callbacks.
		206
		207	The callback will normally be invoked once only. If you specify another
		208	parameter, C<interval>, as a strictly positive number (> 0), then the
		209	callback will be invoked regularly at that interval (in fractional
		210	seconds) after the first invocation. If C<interval> is specified with a
		211	false value, then it is treated as if it were missing.
		212
		213	The callback will be rescheduled before invoking the callback, but no
		214	attempt is done to avoid timer drift in most backends, so the interval is
		215	only approximate.
		216
		217	Example: fire an event after 7.7 seconds.
		218
		219	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		220	warn "timeout\n";
		221	});
		222
		223	# to cancel the timer:
		224	undef $w;
		225
		226	Example 2: fire an event after 0.5 seconds, then roughly every second.
		227
		228	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		229	warn "timeout\n";
		230	};
		231
		232	=head3 TIMING ISSUES
		233
		234	There are two ways to handle timers: based on real time (relative, "fire
		235	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		236	o'clock").
		237
		238	While most event loops expect timers to specified in a relative way, they
		239	use absolute time internally. This makes a difference when your clock
		240	"jumps", for example, when ntp decides to set your clock backwards from
		241	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		242	fire "after" a second might actually take six years to finally fire.
		243
		244	AnyEvent cannot compensate for this. The only event loop that is conscious
		245	about these issues is L<EV>, which offers both relative (ev_timer, based
		246	on true relative time) and absolute (ev_periodic, based on wallclock time)
		247	timers.
		248
		249	AnyEvent always prefers relative timers, if available, matching the
		250	AnyEvent API.
		251
		252	AnyEvent has two additional methods that return the "current time":
46		253
47	=over 4	254	=over 4
48		255
		256	=item AnyEvent->time
		257
		258	This returns the "current wallclock time" as a fractional number of
		259	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		260	return, and the result is guaranteed to be compatible with those).
		261
		262	It progresses independently of any event loop processing, i.e. each call
		263	will check the system clock, which usually gets updated frequently.
		264
		265	=item AnyEvent->now
		266
		267	This also returns the "current wallclock time", but unlike C<time>, above,
		268	this value might change only once per event loop iteration, depending on
		269	the event loop (most return the same time as C<time>, above). This is the
		270	time that AnyEvent's timers get scheduled against.
		271
		272	I<In almost all cases (in all cases if you don't care), this is the
		273	function to call when you want to know the current time.>
		274
		275	This function is also often faster then C<< AnyEvent->time >>, and
		276	thus the preferred method if you want some timestamp (for example,
		277	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		278
		279	The rest of this section is only of relevance if you try to be very exact
		280	with your timing, you can skip it without bad conscience.
		281
		282	For a practical example of when these times differ, consider L<Event::Lib>
		283	and L<EV> and the following set-up:
		284
		285	The event loop is running and has just invoked one of your callback at
		286	time=500 (assume no other callbacks delay processing). In your callback,
		287	you wait a second by executing C<sleep 1> (blocking the process for a
		288	second) and then (at time=501) you create a relative timer that fires
		289	after three seconds.
		290
		291	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		292	both return C<501>, because that is the current time, and the timer will
		293	be scheduled to fire at time=504 (C<501> + C<3>).
		294
		295	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		296	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		297	last event processing phase started. With L<EV>, your timer gets scheduled
		298	to run at time=503 (C<500> + C<3>).
		299
		300	In one sense, L<Event::Lib> is more exact, as it uses the current time
		301	regardless of any delays introduced by event processing. However, most
		302	callbacks do not expect large delays in processing, so this causes a
		303	higher drift (and a lot more system calls to get the current time).
		304
		305	In another sense, L<EV> is more exact, as your timer will be scheduled at
		306	the same time, regardless of how long event processing actually took.
		307
		308	In either case, if you care (and in most cases, you don't), then you
		309	can get whatever behaviour you want with any event loop, by taking the
		310	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		311	account.
		312
		313	=back
		314
		315	=head2 SIGNAL WATCHERS
		316
		317	You can watch for signals using a signal watcher, C<signal> is the signal
		318	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		319	callback to be invoked whenever a signal occurs.
		320
		321	Although the callback might get passed parameters, their value and
		322	presence is undefined and you cannot rely on them. Portable AnyEvent
		323	callbacks cannot use arguments passed to signal watcher callbacks.
		324
		325	Multiple signal occurrences can be clumped together into one callback
		326	invocation, and callback invocation will be synchronous. Synchronous means
		327	that it might take a while until the signal gets handled by the process,
		328	but it is guaranteed not to interrupt any other callbacks.
		329
		330	The main advantage of using these watchers is that you can share a signal
		331	between multiple watchers.
		332
		333	This watcher might use C<%SIG>, so programs overwriting those signals
		334	directly will likely not work correctly.
		335
		336	Example: exit on SIGINT
		337
		338	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		339
		340	=head2 CHILD PROCESS WATCHERS
		341
		342	You can also watch on a child process exit and catch its exit status.
		343
		344	The child process is specified by the C<pid> argument (if set to C<0>, it
		345	watches for any child process exit). The watcher will trigger as often
		346	as status change for the child are received. This works by installing a
		347	signal handler for C<SIGCHLD>. The callback will be called with the pid
		348	and exit status (as returned by waitpid), so unlike other watcher types,
		349	you I<can> rely on child watcher callback arguments.
		350
		351	There is a slight catch to child watchers, however: you usually start them
		352	I<after> the child process was created, and this means the process could
		353	have exited already (and no SIGCHLD will be sent anymore).
		354
		355	Not all event models handle this correctly (POE doesn't), but even for
		356	event models that I<do> handle this correctly, they usually need to be
		357	loaded before the process exits (i.e. before you fork in the first place).
		358
		359	This means you cannot create a child watcher as the very first thing in an
		360	AnyEvent program, you I<have> to create at least one watcher before you
		361	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		362
		363	Example: fork a process and wait for it
		364
		365	my $done = AnyEvent->condvar;
		366
		367	my $pid = fork or exit 5;
		368
		369	my $w = AnyEvent->child (
		370	pid => $pid,
		371	cb => sub {
		372	my ($pid, $status) = @_;
		373	warn "pid $pid exited with status $status";
		374	$done->send;
		375	},
		376	);
		377
		378	# do something else, then wait for process exit
		379	$done->recv;
		380
		381	=head2 CONDITION VARIABLES
		382
		383	If you are familiar with some event loops you will know that all of them
		384	require you to run some blocking "loop", "run" or similar function that
		385	will actively watch for new events and call your callbacks.
		386
		387	AnyEvent is different, it expects somebody else to run the event loop and
		388	will only block when necessary (usually when told by the user).
		389
		390	The instrument to do that is called a "condition variable", so called
		391	because they represent a condition that must become true.
		392
		393	Condition variables can be created by calling the C<< AnyEvent->condvar
		394	>> method, usually without arguments. The only argument pair allowed is
		395
		396	C<cb>, which specifies a callback to be called when the condition variable
		397	becomes true, with the condition variable as the first argument (but not
		398	the results).
		399
		400	After creation, the condition variable is "false" until it becomes "true"
		401	by calling the C<send> method (or calling the condition variable as if it
		402	were a callback, read about the caveats in the description for the C<<
		403	->send >> method).
		404
		405	Condition variables are similar to callbacks, except that you can
		406	optionally wait for them. They can also be called merge points - points
		407	in time where multiple outstanding events have been processed. And yet
		408	another way to call them is transactions - each condition variable can be
		409	used to represent a transaction, which finishes at some point and delivers
		410	a result.
		411
		412	Condition variables are very useful to signal that something has finished,
		413	for example, if you write a module that does asynchronous http requests,
		414	then a condition variable would be the ideal candidate to signal the
		415	availability of results. The user can either act when the callback is
		416	called or can synchronously C<< ->recv >> for the results.
		417
		418	You can also use them to simulate traditional event loops - for example,
		419	you can block your main program until an event occurs - for example, you
		420	could C<< ->recv >> in your main program until the user clicks the Quit
		421	button of your app, which would C<< ->send >> the "quit" event.
		422
		423	Note that condition variables recurse into the event loop - if you have
		424	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		425	lose. Therefore, condition variables are good to export to your caller, but
		426	you should avoid making a blocking wait yourself, at least in callbacks,
		427	as this asks for trouble.
		428
		429	Condition variables are represented by hash refs in perl, and the keys
		430	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		431	easy (it is often useful to build your own transaction class on top of
		432	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		433	it's C<new> method in your own C<new> method.
		434
		435	There are two "sides" to a condition variable - the "producer side" which
		436	eventually calls C<< -> send >>, and the "consumer side", which waits
		437	for the send to occur.
		438
		439	Example: wait for a timer.
		440
		441	# wait till the result is ready
		442	my $result_ready = AnyEvent->condvar;
		443
		444	# do something such as adding a timer
		445	# or socket watcher the calls $result_ready->send
		446	# when the "result" is ready.
		447	# in this case, we simply use a timer:
		448	my $w = AnyEvent->timer (
		449	after => 1,
		450	cb => sub { $result_ready->send },
		451	);
		452
		453	# this "blocks" (while handling events) till the callback
		454	# calls send
		455	$result_ready->recv;
		456
		457	Example: wait for a timer, but take advantage of the fact that
		458	condition variables are also code references.
		459
		460	my $done = AnyEvent->condvar;
		461	my $delay = AnyEvent->timer (after => 5, cb => $done);
		462	$done->recv;
		463
		464	Example: Imagine an API that returns a condvar and doesn't support
		465	callbacks. This is how you make a synchronous call, for example from
		466	the main program:
		467
		468	use AnyEvent::CouchDB;
		469
		470	...
		471
		472	my @info = $couchdb->info->recv;
		473
		474	And this is how you would just ste a callback to be called whenever the
		475	results are available:
		476
		477	$couchdb->info->cb (sub {
		478	my @info = $_[0]->recv;
		479	});
		480
		481	=head3 METHODS FOR PRODUCERS
		482
		483	These methods should only be used by the producing side, i.e. the
		484	code/module that eventually sends the signal. Note that it is also
		485	the producer side which creates the condvar in most cases, but it isn't
		486	uncommon for the consumer to create it as well.
		487
		488	=over 4
		489
		490	=item $cv->send (...)
		491
		492	Flag the condition as ready - a running C<< ->recv >> and all further
		493	calls to C<recv> will (eventually) return after this method has been
		494	called. If nobody is waiting the send will be remembered.
		495
		496	If a callback has been set on the condition variable, it is called
		497	immediately from within send.
		498
		499	Any arguments passed to the C<send> call will be returned by all
		500	future C<< ->recv >> calls.
		501
		502	Condition variables are overloaded so one can call them directly
		503	(as a code reference). Calling them directly is the same as calling
		504	C<send>. Note, however, that many C-based event loops do not handle
		505	overloading, so as tempting as it may be, passing a condition variable
		506	instead of a callback does not work. Both the pure perl and EV loops
		507	support overloading, however, as well as all functions that use perl to
		508	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		509	example).
		510
		511	=item $cv->croak ($error)
		512
		513	Similar to send, but causes all call's to C<< ->recv >> to invoke
		514	C<Carp::croak> with the given error message/object/scalar.
		515
		516	This can be used to signal any errors to the condition variable
		517	user/consumer.
		518
		519	=item $cv->begin ([group callback])
		520
		521	=item $cv->end
		522
		523	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		524
		525	These two methods can be used to combine many transactions/events into
		526	one. For example, a function that pings many hosts in parallel might want
		527	to use a condition variable for the whole process.
		528
		529	Every call to C<< ->begin >> will increment a counter, and every call to
		530	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		531	>>, the (last) callback passed to C<begin> will be executed. That callback
		532	is I<supposed> to call C<< ->send >>, but that is not required. If no
		533	callback was set, C<send> will be called without any arguments.
		534
		535	Let's clarify this with the ping example:
		536
		537	my $cv = AnyEvent->condvar;
		538
		539	my %result;
		540	$cv->begin (sub { $cv->send (\%result) });
		541
		542	for my $host (@list_of_hosts) {
		543	$cv->begin;
		544	ping_host_then_call_callback $host, sub {
		545	$result{$host} = ...;
		546	$cv->end;
		547	};
		548	}
		549
		550	$cv->end;
		551
		552	This code fragment supposedly pings a number of hosts and calls
		553	C<send> after results for all then have have been gathered - in any
		554	order. To achieve this, the code issues a call to C<begin> when it starts
		555	each ping request and calls C<end> when it has received some result for
		556	it. Since C<begin> and C<end> only maintain a counter, the order in which
		557	results arrive is not relevant.
		558
		559	There is an additional bracketing call to C<begin> and C<end> outside the
		560	loop, which serves two important purposes: first, it sets the callback
		561	to be called once the counter reaches C<0>, and second, it ensures that
		562	C<send> is called even when C<no> hosts are being pinged (the loop
		563	doesn't execute once).
		564
		565	This is the general pattern when you "fan out" into multiple subrequests:
		566	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		567	is called at least once, and then, for each subrequest you start, call
		568	C<begin> and for each subrequest you finish, call C<end>.
		569
		570	=back
		571
		572	=head3 METHODS FOR CONSUMERS
		573
		574	These methods should only be used by the consuming side, i.e. the
		575	code awaits the condition.
		576
		577	=over 4
		578
		579	=item $cv->recv
		580
		581	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		582	>> methods have been called on c<$cv>, while servicing other watchers
		583	normally.
		584
		585	You can only wait once on a condition - additional calls are valid but
		586	will return immediately.
		587
		588	If an error condition has been set by calling C<< ->croak >>, then this
		589	function will call C<croak>.
		590
		591	In list context, all parameters passed to C<send> will be returned,
		592	in scalar context only the first one will be returned.
		593
		594	Not all event models support a blocking wait - some die in that case
		595	(programs might want to do that to stay interactive), so I<if you are
		596	using this from a module, never require a blocking wait>, but let the
		597	caller decide whether the call will block or not (for example, by coupling
		598	condition variables with some kind of request results and supporting
		599	callbacks so the caller knows that getting the result will not block,
		600	while still supporting blocking waits if the caller so desires).
		601
		602	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		603	sensibly have two C<< ->recv >>'s in parallel, as that would require
		604	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		605	can supply.
		606
		607	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		608	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		609	versions and also integrates coroutines into AnyEvent, making blocking
		610	C<< ->recv >> calls perfectly safe as long as they are done from another
		611	coroutine (one that doesn't run the event loop).
		612
		613	You can ensure that C<< -recv >> never blocks by setting a callback and
		614	only calling C<< ->recv >> from within that callback (or at a later
		615	time). This will work even when the event loop does not support blocking
		616	waits otherwise.
		617
		618	=item $bool = $cv->ready
		619
		620	Returns true when the condition is "true", i.e. whether C<send> or
		621	C<croak> have been called.
		622
		623	=item $cb = $cv->cb ($cb->($cv))
		624
		625	This is a mutator function that returns the callback set and optionally
		626	replaces it before doing so.
		627
		628	The callback will be called when the condition becomes "true", i.e. when
		629	C<send> or C<croak> are called, with the only argument being the condition
		630	variable itself. Calling C<recv> inside the callback or at any later time
		631	is guaranteed not to block.
		632
		633	=back
		634
		635	=head1 GLOBAL VARIABLES AND FUNCTIONS
		636
		637	=over 4
		638
		639	=item $AnyEvent::MODEL
		640
		641	Contains C<undef> until the first watcher is being created. Then it
		642	contains the event model that is being used, which is the name of the
		643	Perl class implementing the model. This class is usually one of the
		644	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		645	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		646
		647	The known classes so far are:
		648
		649	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		650	AnyEvent::Impl::Event based on Event, second best choice.
		651	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		652	AnyEvent::Impl::Glib based on Glib, third-best choice.
		653	AnyEvent::Impl::Tk based on Tk, very bad choice.
		654	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		655	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		656	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		657
		658	There is no support for WxWidgets, as WxWidgets has no support for
		659	watching file handles. However, you can use WxWidgets through the
		660	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		661	second, which was considered to be too horrible to even consider for
		662	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		663	it's adaptor.
		664
		665	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		666	autodetecting them.
		667
		668	=item AnyEvent::detect
		669
		670	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		671	if necessary. You should only call this function right before you would
		672	have created an AnyEvent watcher anyway, that is, as late as possible at
		673	runtime.
		674
		675	=item $guard = AnyEvent::post_detect { BLOCK }
		676
		677	Arranges for the code block to be executed as soon as the event model is
		678	autodetected (or immediately if this has already happened).
		679
		680	If called in scalar or list context, then it creates and returns an object
		681	that automatically removes the callback again when it is destroyed. See
		682	L<Coro::BDB> for a case where this is useful.
		683
		684	=item @AnyEvent::post_detect
		685
		686	If there are any code references in this array (you can C<push> to it
		687	before or after loading AnyEvent), then they will called directly after
		688	the event loop has been chosen.
		689
		690	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		691	if it contains a true value then the event loop has already been detected,
		692	and the array will be ignored.
		693
		694	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		695
		696	=back
		697
		698	=head1 WHAT TO DO IN A MODULE
		699
		700	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		701	freely, but you should not load a specific event module or rely on it.
		702
		703	Be careful when you create watchers in the module body - AnyEvent will
		704	decide which event module to use as soon as the first method is called, so
		705	by calling AnyEvent in your module body you force the user of your module
		706	to load the event module first.
		707
		708	Never call C<< ->recv >> on a condition variable unless you I<know> that
		709	the C<< ->send >> method has been called on it already. This is
		710	because it will stall the whole program, and the whole point of using
		711	events is to stay interactive.
		712
		713	It is fine, however, to call C<< ->recv >> when the user of your module
		714	requests it (i.e. if you create a http request object ad have a method
		715	called C<results> that returns the results, it should call C<< ->recv >>
		716	freely, as the user of your module knows what she is doing. always).
		717
		718	=head1 WHAT TO DO IN THE MAIN PROGRAM
		719
		720	There will always be a single main program - the only place that should
		721	dictate which event model to use.
		722
		723	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		724	do anything special (it does not need to be event-based) and let AnyEvent
		725	decide which implementation to chose if some module relies on it.
		726
		727	If the main program relies on a specific event model - for example, in
		728	Gtk2 programs you have to rely on the Glib module - you should load the
		729	event module before loading AnyEvent or any module that uses it: generally
		730	speaking, you should load it as early as possible. The reason is that
		731	modules might create watchers when they are loaded, and AnyEvent will
		732	decide on the event model to use as soon as it creates watchers, and it
		733	might chose the wrong one unless you load the correct one yourself.
		734
		735	You can chose to use a pure-perl implementation by loading the
		736	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		737	everywhere, but letting AnyEvent chose the model is generally better.
		738
		739	=head2 MAINLOOP EMULATION
		740
		741	Sometimes (often for short test scripts, or even standalone programs who
		742	only want to use AnyEvent), you do not want to run a specific event loop.
		743
		744	In that case, you can use a condition variable like this:
		745
		746	AnyEvent->condvar->recv;
		747
		748	This has the effect of entering the event loop and looping forever.
		749
		750	Note that usually your program has some exit condition, in which case
		751	it is better to use the "traditional" approach of storing a condition
		752	variable somewhere, waiting for it, and sending it when the program should
		753	exit cleanly.
		754
		755
		756	=head1 OTHER MODULES
		757
		758	The following is a non-exhaustive list of additional modules that use
		759	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		760	in the same program. Some of the modules come with AnyEvent, some are
		761	available via CPAN.
		762
		763	=over 4
		764
		765	=item L<AnyEvent::Util>
		766
		767	Contains various utility functions that replace often-used but blocking
		768	functions such as C<inet_aton> by event-/callback-based versions.
		769
		770	=item L<AnyEvent::Socket>
		771
		772	Provides various utility functions for (internet protocol) sockets,
		773	addresses and name resolution. Also functions to create non-blocking tcp
		774	connections or tcp servers, with IPv6 and SRV record support and more.
		775
		776	=item L<AnyEvent::Handle>
		777
		778	Provide read and write buffers, manages watchers for reads and writes,
		779	supports raw and formatted I/O, I/O queued and fully transparent and
		780	non-blocking SSL/TLS.
		781
		782	=item L<AnyEvent::DNS>
		783
		784	Provides rich asynchronous DNS resolver capabilities.
		785
		786	=item L<AnyEvent::HTTP>
		787
		788	A simple-to-use HTTP library that is capable of making a lot of concurrent
		789	HTTP requests.
		790
		791	=item L<AnyEvent::HTTPD>
		792
		793	Provides a simple web application server framework.
		794
		795	=item L<AnyEvent::FastPing>
		796
		797	The fastest ping in the west.
		798
		799	=item L<AnyEvent::DBI>
		800
		801	Executes L<DBI> requests asynchronously in a proxy process.
		802
		803	=item L<AnyEvent::AIO>
		804
		805	Truly asynchronous I/O, should be in the toolbox of every event
		806	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		807	together.
		808
		809	=item L<AnyEvent::BDB>
		810
		811	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		812	L<BDB> and AnyEvent together.
		813
		814	=item L<AnyEvent::GPSD>
		815
		816	A non-blocking interface to gpsd, a daemon delivering GPS information.
		817
		818	=item L<AnyEvent::IGS>
		819
		820	A non-blocking interface to the Internet Go Server protocol (used by
		821	L<App::IGS>).
		822
		823	=item L<Net::IRC3>
		824
		825	AnyEvent based IRC client module family.
		826
		827	=item L<Net::XMPP2>
		828
		829	AnyEvent based XMPP (Jabber protocol) module family.
		830
		831	=item L<Net::FCP>
		832
		833	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		834	of AnyEvent.
		835
		836	=item L<Event::ExecFlow>
		837
		838	High level API for event-based execution flow control.
		839
		840	=item L<Coro>
		841
		842	Has special support for AnyEvent via L<Coro::AnyEvent>.
		843
		844	=item L<IO::Lambda>
		845
		846	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		847
		848	=back
		849
49	=cut	850	=cut
50		851
51	package AnyEvent;	852	package AnyEvent;
52		853
53	no warnings;	854	no warnings;
54	use strict 'vars';	855	use strict qw(vars subs);
		856
55	use Carp;	857	use Carp;
56		858
57	our $VERSION = 0.2;	859	our $VERSION = 4.233;
58	our $MODEL;	860	our $MODEL;
59		861
60	our $AUTOLOAD;	862	our $AUTOLOAD;
61	our @ISA;	863	our @ISA;
62		864
		865	our @REGISTRY;
		866
		867	our $WIN32;
		868
		869	BEGIN {
		870	my $win32 = ! ! ($^O =~ /mswin32/i);
		871	eval "sub WIN32(){ $win32 }";
		872	}
		873
		874	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		875
		876	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		877
		878	{
		879	my $idx;
		880	$PROTOCOL{$_} = ++$idx
		881	for reverse split /\s*,\s*/,
		882	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		883	}
		884
63	my @models = (	885	my @models = (
64	[Coro => Coro::Event::],	886	[EV:: => AnyEvent::Impl::EV::],
65	[Event => Event::],	887	[Event:: => AnyEvent::Impl::Event::],
66	[Glib => Glib::],	888	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
67	[Tk => Tk::],	889	# everything below here will not be autoprobed
		890	# as the pureperl backend should work everywhere
		891	# and is usually faster
		892	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		893	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		894	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		895	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		896	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		897	[Wx:: => AnyEvent::Impl::POE::],
		898	[Prima:: => AnyEvent::Impl::POE::],
68	);	899	);
69		900
70	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	901	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
71		902
72	sub AUTOLOAD {	903	our @post_detect;
73	$AUTOLOAD =~ s/.*://;
74		904
75	$method{$AUTOLOAD}	905	sub post_detect(&) {
76	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	906	my ($cb) = @_;
77		907
		908	if ($MODEL) {
		909	$cb->();
		910
		911	1
		912	} else {
		913	push @post_detect, $cb;
		914
		915	defined wantarray
		916	? bless \$cb, "AnyEvent::Util::PostDetect"
		917	: ()
		918	}
		919	}
		920
		921	sub AnyEvent::Util::PostDetect::DESTROY {
		922	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		923	}
		924
		925	sub detect() {
78	unless ($MODEL) {	926	unless ($MODEL) {
79	# check for already loaded models	927	no strict 'refs';
80	for (@models) {	928	local $SIG{__DIE__};
81	my ($model, $package) = @$_;
82	if (scalar keys %{ *{"$package\::"} }) {
83	eval "require AnyEvent::Impl::$model"
84	or die;
85		929
86	last if $MODEL;	930	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		931	my $model = "AnyEvent::Impl::$1";
		932	if (eval "require $model") {
		933	$MODEL = $model;
		934	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		935	} else {
		936	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
87	}	937	}
88	}	938	}
89		939
		940	# check for already loaded models
90	unless ($MODEL) {	941	unless ($MODEL) {
91	# try to load a model
92
93	for (@models) {	942	for (@REGISTRY, @models) {
94	my ($model, $package) = @$_;	943	my ($package, $model) = @$_;
95	eval "require AnyEvent::Impl::$model"	944	if (${"$package\::VERSION"} > 0) {
		945	if (eval "require $model") {
		946	$MODEL = $model;
		947	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		948	last;
96	or die;	949	}
97		950	}
98	last if $MODEL;
99	}	951	}
100		952
		953	unless ($MODEL) {
		954	# try to load a model
		955
		956	for (@REGISTRY, @models) {
		957	my ($package, $model) = @$_;
		958	if (eval "require $package"
		959	and ${"$package\::VERSION"} > 0
		960	and eval "require $model") {
		961	$MODEL = $model;
		962	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		963	last;
		964	}
		965	}
		966
101	$MODEL	967	$MODEL
102	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	968	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		969	}
103	}	970	}
		971
		972	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		973
		974	unshift @ISA, $MODEL;
		975
		976	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		977
		978	(shift @post_detect)->() while @post_detect;
104	}	979	}
105		980
106	@ISA = $MODEL;	981	$MODEL
		982	}
		983
		984	sub AUTOLOAD {
		985	(my $func = $AUTOLOAD) =~ s/.*://;
		986
		987	$method{$func}
		988	or croak "$func: not a valid method for AnyEvent objects";
		989
		990	detect unless $MODEL;
107		991
108	my $class = shift;	992	my $class = shift;
109	$class->$AUTOLOAD (@_);	993	$class->$func (@_);
110	}	994	}
		995
		996	# utility function to dup a filehandle. this is used by many backends
		997	# to support binding more than one watcher per filehandle (they usually
		998	# allow only one watcher per fd, so we dup it to get a different one).
		999	sub _dupfh($$$$) {
		1000	my ($poll, $fh, $r, $w) = @_;
		1001
		1002	require Fcntl;
		1003
		1004	# cygwin requires the fh mode to be matching, unix doesn't
		1005	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1006	: $poll eq "w" ? ($w, ">")
		1007	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1008
		1009	open my $fh2, "$mode&" . fileno $fh
		1010	or die "cannot dup() filehandle: $!";
		1011
		1012	# we assume CLOEXEC is already set by perl in all important cases
		1013
		1014	($fh2, $rw)
		1015	}
		1016
		1017	package AnyEvent::Base;
		1018
		1019	# default implementation for now and time
		1020
		1021	BEGIN {
		1022	if (eval "use Time::HiRes (); time (); 1") {
		1023	*_time = \&Time::HiRes::time;
		1024	# if (eval "use POSIX (); (POSIX::times())...
		1025	} else {
		1026	*_time = \&CORE::time; # epic fail
		1027	}
		1028	}
		1029
		1030	sub time { _time }
		1031	sub now { _time }
		1032
		1033	# default implementation for ->condvar
		1034
		1035	sub condvar {
		1036	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		1037	}
		1038
		1039	# default implementation for ->signal
		1040
		1041	our %SIG_CB;
		1042
		1043	sub signal {
		1044	my (undef, %arg) = @_;
		1045
		1046	my $signal = uc $arg{signal}
		1047	or Carp::croak "required option 'signal' is missing";
		1048
		1049	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1050	$SIG{$signal} ||= sub {
		1051	$_->() for values %{ $SIG_CB{$signal} || {} };
		1052	};
		1053
		1054	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		1055	}
		1056
		1057	sub AnyEvent::Base::Signal::DESTROY {
		1058	my ($signal, $cb) = @{$_[0]};
		1059
		1060	delete $SIG_CB{$signal}{$cb};
		1061
		1062	delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
		1063	}
		1064
		1065	# default implementation for ->child
		1066
		1067	our %PID_CB;
		1068	our $CHLD_W;
		1069	our $CHLD_DELAY_W;
		1070	our $PID_IDLE;
		1071	our $WNOHANG;
		1072
		1073	sub _child_wait {
		1074	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1075	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		1076	(values %{ $PID_CB{0} || {} });
		1077	}
		1078
		1079	undef $PID_IDLE;
		1080	}
		1081
		1082	sub _sigchld {
		1083	# make sure we deliver these changes "synchronous" with the event loop.
		1084	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		1085	undef $CHLD_DELAY_W;
		1086	&_child_wait;
		1087	});
		1088	}
		1089
		1090	sub child {
		1091	my (undef, %arg) = @_;
		1092
		1093	defined (my $pid = $arg{pid} + 0)
		1094	or Carp::croak "required option 'pid' is missing";
		1095
		1096	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1097
		1098	unless ($WNOHANG) {
		1099	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1100	}
		1101
		1102	unless ($CHLD_W) {
		1103	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1104	# child could be a zombie already, so make at least one round
		1105	&_sigchld;
		1106	}
		1107
		1108	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		1109	}
		1110
		1111	sub AnyEvent::Base::Child::DESTROY {
		1112	my ($pid, $cb) = @{$_[0]};
		1113
		1114	delete $PID_CB{$pid}{$cb};
		1115	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1116
		1117	undef $CHLD_W unless keys %PID_CB;
		1118	}
		1119
		1120	package AnyEvent::CondVar;
		1121
		1122	our @ISA = AnyEvent::CondVar::Base::;
		1123
		1124	package AnyEvent::CondVar::Base;
		1125
		1126	use overload
		1127	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1128	fallback => 1;
		1129
		1130	sub _send {
		1131	# nop
		1132	}
		1133
		1134	sub send {
		1135	my $cv = shift;
		1136	$cv->{_ae_sent} = [@_];
		1137	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1138	$cv->_send;
		1139	}
		1140
		1141	sub croak {
		1142	$_[0]{_ae_croak} = $_[1];
		1143	$_[0]->send;
		1144	}
		1145
		1146	sub ready {
		1147	$_[0]{_ae_sent}
		1148	}
		1149
		1150	sub _wait {
		1151	AnyEvent->one_event while !$_[0]{_ae_sent};
		1152	}
		1153
		1154	sub recv {
		1155	$_[0]->_wait;
		1156
		1157	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1158	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1159	}
		1160
		1161	sub cb {
		1162	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1163	$_[0]{_ae_cb}
		1164	}
		1165
		1166	sub begin {
		1167	++$_[0]{_ae_counter};
		1168	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1169	}
		1170
		1171	sub end {
		1172	return if --$_[0]{_ae_counter};
		1173	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1174	}
		1175
		1176	# undocumented/compatibility with pre-3.4
		1177	*broadcast = \&send;
		1178	*wait = \&_wait;
		1179
		1180	=head1 ERROR AND EXCEPTION HANDLING
		1181
		1182	In general, AnyEvent does not do any error handling - it relies on the
		1183	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1184	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1185	checking of all AnyEvent methods, however, which is highly useful during
		1186	development.
		1187
		1188	As for exception handling (i.e. runtime errors and exceptions thrown while
		1189	executing a callback), this is not only highly event-loop specific, but
		1190	also not in any way wrapped by this module, as this is the job of the main
		1191	program.
		1192
		1193	The pure perl event loop simply re-throws the exception (usually
		1194	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1195	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1196	so on.
		1197
		1198	=head1 ENVIRONMENT VARIABLES
		1199
		1200	The following environment variables are used by this module or its
		1201	submodules:
		1202
		1203	=over 4
		1204
		1205	=item C<PERL_ANYEVENT_VERBOSE>
		1206
		1207	By default, AnyEvent will be completely silent except in fatal
		1208	conditions. You can set this environment variable to make AnyEvent more
		1209	talkative.
		1210
		1211	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1212	conditions, such as not being able to load the event model specified by
		1213	C<PERL_ANYEVENT_MODEL>.
		1214
		1215	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1216	model it chooses.
		1217
		1218	=item C<PERL_ANYEVENT_STRICT>
		1219
		1220	AnyEvent does not do much argument checking by default, as thorough
		1221	argument checking is very costly. Setting this variable to a true value
		1222	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1223	check the arguments passed to most method calls. If it finds any problems
		1224	it will croak.
		1225
		1226	In other words, enables "strict" mode.
		1227
		1228	Unlike C<use strict>, it is definitely recommended ot keep it off in
		1229	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1230	developing programs can be very useful, however.
		1231
		1232	=item C<PERL_ANYEVENT_MODEL>
		1233
		1234	This can be used to specify the event model to be used by AnyEvent, before
		1235	auto detection and -probing kicks in. It must be a string consisting
		1236	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1237	and the resulting module name is loaded and if the load was successful,
		1238	used as event model. If it fails to load AnyEvent will proceed with
		1239	auto detection and -probing.
		1240
		1241	This functionality might change in future versions.
		1242
		1243	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1244	could start your program like this:
		1245
		1246	PERL_ANYEVENT_MODEL=Perl perl ...
		1247
		1248	=item C<PERL_ANYEVENT_PROTOCOLS>
		1249
		1250	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1251	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1252	of auto probing).
		1253
		1254	Must be set to a comma-separated list of protocols or address families,
		1255	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1256	used, and preference will be given to protocols mentioned earlier in the
		1257	list.
		1258
		1259	This variable can effectively be used for denial-of-service attacks
		1260	against local programs (e.g. when setuid), although the impact is likely
		1261	small, as the program has to handle connection errors already-
		1262
		1263	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1264	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1265	- only support IPv4, never try to resolve or contact IPv6
		1266	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1267	IPv6, but prefer IPv6 over IPv4.
		1268
		1269	=item C<PERL_ANYEVENT_EDNS0>
		1270
		1271	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1272	for DNS. This extension is generally useful to reduce DNS traffic, but
		1273	some (broken) firewalls drop such DNS packets, which is why it is off by
		1274	default.
		1275
		1276	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1277	EDNS0 in its DNS requests.
		1278
		1279	=item C<PERL_ANYEVENT_MAX_FORKS>
		1280
		1281	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1282	will create in parallel.
111		1283
112	=back	1284	=back
113		1285
		1286	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1287
		1288	This is an advanced topic that you do not normally need to use AnyEvent in
		1289	a module. This section is only of use to event loop authors who want to
		1290	provide AnyEvent compatibility.
		1291
		1292	If you need to support another event library which isn't directly
		1293	supported by AnyEvent, you can supply your own interface to it by
		1294	pushing, before the first watcher gets created, the package name of
		1295	the event module and the package name of the interface to use onto
		1296	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1297	AnyEvent, so it is reasonably cheap.
		1298
		1299	Example:
		1300
		1301	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1302
		1303	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1304	package/class when it finds the C<urxvt> package/module is already loaded.
		1305
		1306	When AnyEvent is loaded and asked to find a suitable event model, it
		1307	will first check for the presence of urxvt by trying to C<use> the
		1308	C<urxvt::anyevent> module.
		1309
		1310	The class should provide implementations for all watcher types. See
		1311	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1312	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1313	see the sources.
		1314
		1315	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1316	provide suitable (hopefully) replacements.
		1317
		1318	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1319	terminal emulator uses the above line as-is. An interface isn't included
		1320	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1321	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1322	I<rxvt-unicode> distribution.
		1323
		1324	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1325	condition variables: code blocking while waiting for a condition will
		1326	C<die>. This still works with most modules/usages, and blocking calls must
		1327	not be done in an interactive application, so it makes sense.
		1328
114	=head1 EXAMPLE	1329	=head1 EXAMPLE PROGRAM
115		1330
116	The following program uses an io watcher to read data from stdin, a timer	1331	The following program uses an I/O watcher to read data from STDIN, a timer
117	to display a message once per second, and a condvar to exit the program	1332	to display a message once per second, and a condition variable to quit the
118	when the user enters quit:	1333	program when the user enters quit:
119		1334
120	use AnyEvent;	1335	use AnyEvent;
121		1336
122	my $cv = AnyEvent->condvar;	1337	my $cv = AnyEvent->condvar;
123		1338
124	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1339	my $io_watcher = AnyEvent->io (
		1340	fh => \*STDIN,
		1341	poll => 'r',
		1342	cb => sub {
125	warn "io event <$_[0]>\n"; # will always output <r>	1343	warn "io event <$_[0]>\n"; # will always output <r>
126	chomp (my $input = <STDIN>); # read a line	1344	chomp (my $input = <STDIN>); # read a line
127	warn "read: $input\n"; # output what has been read	1345	warn "read: $input\n"; # output what has been read
128	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1346	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1347	},
129	});	1348	);
130		1349
131	my $time_watcher; # can only be used once	1350	my $time_watcher; # can only be used once
132		1351
133	sub new_timer {	1352	sub new_timer {
134	$timer = AnyEvent->timer (after => 1, cb => sub {	1353	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
137	});	1356	});
138	}	1357	}
139		1358
140	new_timer; # create first timer	1359	new_timer; # create first timer
141		1360
142	$cv->wait; # wait until user enters /^q/i	1361	$cv->recv; # wait until user enters /^q/i
		1362
		1363	=head1 REAL-WORLD EXAMPLE
		1364
		1365	Consider the L<Net::FCP> module. It features (among others) the following
		1366	API calls, which are to freenet what HTTP GET requests are to http:
		1367
		1368	my $data = $fcp->client_get ($url); # blocks
		1369
		1370	my $transaction = $fcp->txn_client_get ($url); # does not block
		1371	$transaction->cb ( sub { ... } ); # set optional result callback
		1372	my $data = $transaction->result; # possibly blocks
		1373
		1374	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		1375	given URL and waits till the data has arrived. It is defined to be:
		1376
		1377	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		1378
		1379	And in fact is automatically generated. This is the blocking API of
		1380	L<Net::FCP>, and it works as simple as in any other, similar, module.
		1381
		1382	More complicated is C<txn_client_get>: It only creates a transaction
		1383	(completion, result, ...) object and initiates the transaction.
		1384
		1385	my $txn = bless { }, Net::FCP::Txn::;
		1386
		1387	It also creates a condition variable that is used to signal the completion
		1388	of the request:
		1389
		1390	$txn->{finished} = AnyAvent->condvar;
		1391
		1392	It then creates a socket in non-blocking mode.
		1393
		1394	socket $txn->{fh}, ...;
		1395	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		1396	connect $txn->{fh}, ...
		1397	and !$!{EWOULDBLOCK}
		1398	and !$!{EINPROGRESS}
		1399	and Carp::croak "unable to connect: $!\n";
		1400
		1401	Then it creates a write-watcher which gets called whenever an error occurs
		1402	or the connection succeeds:
		1403
		1404	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		1405
		1406	And returns this transaction object. The C<fh_ready_w> callback gets
		1407	called as soon as the event loop detects that the socket is ready for
		1408	writing.
		1409
		1410	The C<fh_ready_w> method makes the socket blocking again, writes the
		1411	request data and replaces the watcher by a read watcher (waiting for reply
		1412	data). The actual code is more complicated, but that doesn't matter for
		1413	this example:
		1414
		1415	fcntl $txn->{fh}, F_SETFL, 0;
		1416	syswrite $txn->{fh}, $txn->{request}
		1417	or die "connection or write error";
		1418	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		1419
		1420	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		1421	result and signals any possible waiters that the request has finished:
		1422
		1423	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		1424
		1425	if (end-of-file or data complete) {
		1426	$txn->{result} = $txn->{buf};
		1427	$txn->{finished}->send;
		1428	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		1429	}
		1430
		1431	The C<result> method, finally, just waits for the finished signal (if the
		1432	request was already finished, it doesn't wait, of course, and returns the
		1433	data:
		1434
		1435	$txn->{finished}->recv;
		1436	return $txn->{result};
		1437
		1438	The actual code goes further and collects all errors (C<die>s, exceptions)
		1439	that occurred during request processing. The C<result> method detects
		1440	whether an exception as thrown (it is stored inside the $txn object)
		1441	and just throws the exception, which means connection errors and other
		1442	problems get reported tot he code that tries to use the result, not in a
		1443	random callback.
		1444
		1445	All of this enables the following usage styles:
		1446
		1447	1. Blocking:
		1448
		1449	my $data = $fcp->client_get ($url);
		1450
		1451	2. Blocking, but running in parallel:
		1452
		1453	my @datas = map $_->result,
		1454	map $fcp->txn_client_get ($_),
		1455	@urls;
		1456
		1457	Both blocking examples work without the module user having to know
		1458	anything about events.
		1459
		1460	3a. Event-based in a main program, using any supported event module:
		1461
		1462	use EV;
		1463
		1464	$fcp->txn_client_get ($url)->cb (sub {
		1465	my $txn = shift;
		1466	my $data = $txn->result;
		1467	...
		1468	});
		1469
		1470	EV::loop;
		1471
		1472	3b. The module user could use AnyEvent, too:
		1473
		1474	use AnyEvent;
		1475
		1476	my $quit = AnyEvent->condvar;
		1477
		1478	$fcp->txn_client_get ($url)->cb (sub {
		1479	...
		1480	$quit->send;
		1481	});
		1482
		1483	$quit->recv;
		1484
		1485
		1486	=head1 BENCHMARKS
		1487
		1488	To give you an idea of the performance and overheads that AnyEvent adds
		1489	over the event loops themselves and to give you an impression of the speed
		1490	of various event loops I prepared some benchmarks.
		1491
		1492	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1493
		1494	Here is a benchmark of various supported event models used natively and
		1495	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1496	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1497	which it is), lets them fire exactly once and destroys them again.
		1498
		1499	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1500	distribution.
		1501
		1502	=head3 Explanation of the columns
		1503
		1504	I<watcher> is the number of event watchers created/destroyed. Since
		1505	different event models feature vastly different performances, each event
		1506	loop was given a number of watchers so that overall runtime is acceptable
		1507	and similar between tested event loop (and keep them from crashing): Glib
		1508	would probably take thousands of years if asked to process the same number
		1509	of watchers as EV in this benchmark.
		1510
		1511	I<bytes> is the number of bytes (as measured by the resident set size,
		1512	RSS) consumed by each watcher. This method of measuring captures both C
		1513	and Perl-based overheads.
		1514
		1515	I<create> is the time, in microseconds (millionths of seconds), that it
		1516	takes to create a single watcher. The callback is a closure shared between
		1517	all watchers, to avoid adding memory overhead. That means closure creation
		1518	and memory usage is not included in the figures.
		1519
		1520	I<invoke> is the time, in microseconds, used to invoke a simple
		1521	callback. The callback simply counts down a Perl variable and after it was
		1522	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1523	signal the end of this phase.
		1524
		1525	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1526	watcher.
		1527
		1528	=head3 Results
		1529
		1530	name watchers bytes create invoke destroy comment
		1531	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1532	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1533	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1534	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1535	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1536	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1537	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1538	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1539	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1540	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1541
		1542	=head3 Discussion
		1543
		1544	The benchmark does I<not> measure scalability of the event loop very
		1545	well. For example, a select-based event loop (such as the pure perl one)
		1546	can never compete with an event loop that uses epoll when the number of
		1547	file descriptors grows high. In this benchmark, all events become ready at
		1548	the same time, so select/poll-based implementations get an unnatural speed
		1549	boost.
		1550
		1551	Also, note that the number of watchers usually has a nonlinear effect on
		1552	overall speed, that is, creating twice as many watchers doesn't take twice
		1553	the time - usually it takes longer. This puts event loops tested with a
		1554	higher number of watchers at a disadvantage.
		1555
		1556	To put the range of results into perspective, consider that on the
		1557	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1558	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1559	cycles with POE.
		1560
		1561	C<EV> is the sole leader regarding speed and memory use, which are both
		1562	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1563	far less memory than any other event loop and is still faster than Event
		1564	natively.
		1565
		1566	The pure perl implementation is hit in a few sweet spots (both the
		1567	constant timeout and the use of a single fd hit optimisations in the perl
		1568	interpreter and the backend itself). Nevertheless this shows that it
		1569	adds very little overhead in itself. Like any select-based backend its
		1570	performance becomes really bad with lots of file descriptors (and few of
		1571	them active), of course, but this was not subject of this benchmark.
		1572
		1573	The C<Event> module has a relatively high setup and callback invocation
		1574	cost, but overall scores in on the third place.
		1575
		1576	C<Glib>'s memory usage is quite a bit higher, but it features a
		1577	faster callback invocation and overall ends up in the same class as
		1578	C<Event>. However, Glib scales extremely badly, doubling the number of
		1579	watchers increases the processing time by more than a factor of four,
		1580	making it completely unusable when using larger numbers of watchers
		1581	(note that only a single file descriptor was used in the benchmark, so
		1582	inefficiencies of C<poll> do not account for this).
		1583
		1584	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1585	more than 2000 watchers is a big setback, however, as correctness takes
		1586	precedence over speed. Nevertheless, its performance is surprising, as the
		1587	file descriptor is dup()ed for each watcher. This shows that the dup()
		1588	employed by some adaptors is not a big performance issue (it does incur a
		1589	hidden memory cost inside the kernel which is not reflected in the figures
		1590	above).
		1591
		1592	C<POE>, regardless of underlying event loop (whether using its pure perl
		1593	select-based backend or the Event module, the POE-EV backend couldn't
		1594	be tested because it wasn't working) shows abysmal performance and
		1595	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1596	as EV watchers, and 10 times as much memory as Event (the high memory
		1597	requirements are caused by requiring a session for each watcher). Watcher
		1598	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1599	implementation.
		1600
		1601	The design of the POE adaptor class in AnyEvent can not really account
		1602	for the performance issues, though, as session creation overhead is
		1603	small compared to execution of the state machine, which is coded pretty
		1604	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1605	using multiple sessions is not a good approach, especially regarding
		1606	memory usage, even the author of POE could not come up with a faster
		1607	design).
		1608
		1609	=head3 Summary
		1610
		1611	=over 4
		1612
		1613	=item * Using EV through AnyEvent is faster than any other event loop
		1614	(even when used without AnyEvent), but most event loops have acceptable
		1615	performance with or without AnyEvent.
		1616
		1617	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1618	the actual event loop, only with extremely fast event loops such as EV
		1619	adds AnyEvent significant overhead.
		1620
		1621	=item * You should avoid POE like the plague if you want performance or
		1622	reasonable memory usage.
		1623
		1624	=back
		1625
		1626	=head2 BENCHMARKING THE LARGE SERVER CASE
		1627
		1628	This benchmark actually benchmarks the event loop itself. It works by
		1629	creating a number of "servers": each server consists of a socket pair, a
		1630	timeout watcher that gets reset on activity (but never fires), and an I/O
		1631	watcher waiting for input on one side of the socket. Each time the socket
		1632	watcher reads a byte it will write that byte to a random other "server".
		1633
		1634	The effect is that there will be a lot of I/O watchers, only part of which
		1635	are active at any one point (so there is a constant number of active
		1636	fds for each loop iteration, but which fds these are is random). The
		1637	timeout is reset each time something is read because that reflects how
		1638	most timeouts work (and puts extra pressure on the event loops).
		1639
		1640	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1641	(1%) are active. This mirrors the activity of large servers with many
		1642	connections, most of which are idle at any one point in time.
		1643
		1644	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1645	distribution.
		1646
		1647	=head3 Explanation of the columns
		1648
		1649	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1650	each server has a read and write socket end).
		1651
		1652	I<create> is the time it takes to create a socket pair (which is
		1653	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1654
		1655	I<request>, the most important value, is the time it takes to handle a
		1656	single "request", that is, reading the token from the pipe and forwarding
		1657	it to another server. This includes deleting the old timeout and creating
		1658	a new one that moves the timeout into the future.
		1659
		1660	=head3 Results
		1661
		1662	name sockets create request
		1663	EV 20000 69.01 11.16
		1664	Perl 20000 73.32 35.87
		1665	Event 20000 212.62 257.32
		1666	Glib 20000 651.16 1896.30
		1667	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1668
		1669	=head3 Discussion
		1670
		1671	This benchmark I<does> measure scalability and overall performance of the
		1672	particular event loop.
		1673
		1674	EV is again fastest. Since it is using epoll on my system, the setup time
		1675	is relatively high, though.
		1676
		1677	Perl surprisingly comes second. It is much faster than the C-based event
		1678	loops Event and Glib.
		1679
		1680	Event suffers from high setup time as well (look at its code and you will
		1681	understand why). Callback invocation also has a high overhead compared to
		1682	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1683	uses select or poll in basically all documented configurations.
		1684
		1685	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1686	clearly fails to perform with many filehandles or in busy servers.
		1687
		1688	POE is still completely out of the picture, taking over 1000 times as long
		1689	as EV, and over 100 times as long as the Perl implementation, even though
		1690	it uses a C-based event loop in this case.
		1691
		1692	=head3 Summary
		1693
		1694	=over 4
		1695
		1696	=item * The pure perl implementation performs extremely well.
		1697
		1698	=item * Avoid Glib or POE in large projects where performance matters.
		1699
		1700	=back
		1701
		1702	=head2 BENCHMARKING SMALL SERVERS
		1703
		1704	While event loops should scale (and select-based ones do not...) even to
		1705	large servers, most programs we (or I :) actually write have only a few
		1706	I/O watchers.
		1707
		1708	In this benchmark, I use the same benchmark program as in the large server
		1709	case, but it uses only eight "servers", of which three are active at any
		1710	one time. This should reflect performance for a small server relatively
		1711	well.
		1712
		1713	The columns are identical to the previous table.
		1714
		1715	=head3 Results
		1716
		1717	name sockets create request
		1718	EV 16 20.00 6.54
		1719	Perl 16 25.75 12.62
		1720	Event 16 81.27 35.86
		1721	Glib 16 32.63 15.48
		1722	POE 16 261.87 276.28 uses POE::Loop::Event
		1723
		1724	=head3 Discussion
		1725
		1726	The benchmark tries to test the performance of a typical small
		1727	server. While knowing how various event loops perform is interesting, keep
		1728	in mind that their overhead in this case is usually not as important, due
		1729	to the small absolute number of watchers (that is, you need efficiency and
		1730	speed most when you have lots of watchers, not when you only have a few of
		1731	them).
		1732
		1733	EV is again fastest.
		1734
		1735	Perl again comes second. It is noticeably faster than the C-based event
		1736	loops Event and Glib, although the difference is too small to really
		1737	matter.
		1738
		1739	POE also performs much better in this case, but is is still far behind the
		1740	others.
		1741
		1742	=head3 Summary
		1743
		1744	=over 4
		1745
		1746	=item * C-based event loops perform very well with small number of
		1747	watchers, as the management overhead dominates.
		1748
		1749	=back
		1750
		1751
		1752	=head1 FORK
		1753
		1754	Most event libraries are not fork-safe. The ones who are usually are
		1755	because they rely on inefficient but fork-safe C<select> or C<poll>
		1756	calls. Only L<EV> is fully fork-aware.
		1757
		1758	If you have to fork, you must either do so I<before> creating your first
		1759	watcher OR you must not use AnyEvent at all in the child.
		1760
		1761
		1762	=head1 SECURITY CONSIDERATIONS
		1763
		1764	AnyEvent can be forced to load any event model via
		1765	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1766	execute arbitrary code or directly gain access, it can easily be used to
		1767	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1768	will not be active when the program uses a different event model than
		1769	specified in the variable.
		1770
		1771	You can make AnyEvent completely ignore this variable by deleting it
		1772	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1773
		1774	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1775
		1776	use AnyEvent;
		1777
		1778	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1779	be used to probe what backend is used and gain other information (which is
		1780	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1781	$ENV{PERL_ANYEGENT_STRICT}.
		1782
		1783
		1784	=head1 BUGS
		1785
		1786	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1787	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1788	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1789	mamleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1790	pronounced).
		1791
143		1792
144	=head1 SEE ALSO	1793	=head1 SEE ALSO
145		1794
146	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	1795	Utility functions: L<AnyEvent::Util>.
147	L<AnyEvent::Impl::Coro>,	1796
148	L<AnyEvent::Impl::Event>,	1797	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
149	L<AnyEvent::Impl::Glib>,	1798	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1799
		1800	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1801	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1802	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
150	L<AnyEvent::Impl::Tk>.	1803	L<AnyEvent::Impl::POE>.
151		1804
152	=head1	1805	Non-blocking file handles, sockets, TCP clients and
		1806	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1807
		1808	Asynchronous DNS: L<AnyEvent::DNS>.
		1809
		1810	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1811
		1812	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1813
		1814
		1815	=head1 AUTHOR
		1816
		1817	Marc Lehmann <schmorp@schmorp.de>
		1818	http://home.schmorp.de/
153		1819
154	=cut	1820	=cut
155		1821
156	1	1822	1
157		1823

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