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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 and POE are various supported
		6	event loops.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# file descriptor readable
11	my $w = AnyEvent->timer (fh => ..., poll => "[rw]+", cb => sub {	13	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12	my ($poll_got) = @_;	14
		15	# one-shot or repeating timers
		16	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		17	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		18
		19	print AnyEvent->now; # prints current event loop time
		20	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		21
		22	# POSIX signal
		23	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		24
		25	# child process exit
		26	my $w = AnyEvent->child (pid => $pid, cb => sub {
		27	my ($pid, $status) = @_;
13	...	28	...
14	});	29	});
15	my $w = AnyEvent->io (after => $seconds, cb => sub {
16	...
17	});
18		30
19	# watchers get canceled whenever $w is destroyed	31	# called when event loop idle (if applicable)
20	# only one watcher per $fh and $poll type is allowed	32	my $w = AnyEvent->idle (cb => sub { ... });
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		33
25	my $w = AnyEvent->condvar; # kind of main loop replacement	34	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	# can only be used once	35	$w->send; # wake up current and all future recv's
27	$w->wait; # enters main loop till $condvar gets ->send	36	$w->recv; # enters "main loop" till $condvar gets ->send
28	$w->broadcast; # wake up waiting and future wait's	37	# use a condvar in callback mode:
		38	$w->cb (sub { $_[0]->recv });
		39
		40	=head1 INTRODUCTION/TUTORIAL
		41
		42	This manpage is mainly a reference manual. If you are interested
		43	in a tutorial or some gentle introduction, have a look at the
		44	L<AnyEvent::Intro> manpage.
		45
		46	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		47
		48	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		49	nowadays. So what is different about AnyEvent?
		50
		51	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		52	policy> and AnyEvent is I<small and efficient>.
		53
		54	First and foremost, I<AnyEvent is not an event model> itself, it only
		55	interfaces to whatever event model the main program happens to use, in a
		56	pragmatic way. For event models and certain classes of immortals alike,
		57	the statement "there can only be one" is a bitter reality: In general,
		58	only one event loop can be active at the same time in a process. AnyEvent
		59	cannot change this, but it can hide the differences between those event
		60	loops.
		61
		62	The goal of AnyEvent is to offer module authors the ability to do event
		63	programming (waiting for I/O or timer events) without subscribing to a
		64	religion, a way of living, and most importantly: without forcing your
		65	module users into the same thing by forcing them to use the same event
		66	model you use.
		67
		68	For modules like POE or IO::Async (which is a total misnomer as it is
		69	actually doing all I/O I<synchronously>...), using them in your module is
		70	like joining a cult: After you joined, you are dependent on them and you
		71	cannot use anything else, as they are simply incompatible to everything
		72	that isn't them. What's worse, all the potential users of your
		73	module are I<also> forced to use the same event loop you use.
		74
		75	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		76	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		77	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		78	your module uses one of those, every user of your module has to use it,
		79	too. But if your module uses AnyEvent, it works transparently with all
		80	event models it supports (including stuff like IO::Async, as long as those
		81	use one of the supported event loops. It is trivial to add new event loops
		82	to AnyEvent, too, so it is future-proof).
		83
		84	In addition to being free of having to use I<the one and only true event
		85	model>, AnyEvent also is free of bloat and policy: with POE or similar
		86	modules, you get an enormous amount of code and strict rules you have to
		87	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		88	offering the functionality that is necessary, in as thin as a wrapper as
		89	technically possible.
		90
		91	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		92	of useful functionality, such as an asynchronous DNS resolver, 100%
		93	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		94	such as Windows) and lots of real-world knowledge and workarounds for
		95	platform bugs and differences.
		96
		97	Now, if you I<do want> lots of policy (this can arguably be somewhat
		98	useful) and you want to force your users to use the one and only event
		99	model, you should I<not> use this module.
29		100
30	=head1 DESCRIPTION	101	=head1 DESCRIPTION
31		102
32	L<AnyEvent> provides an identical interface to multiple event loops. This	103	L<AnyEvent> provides an identical interface to multiple event loops. This
33	allows module authors to utilizy an event loop without forcing module	104	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	105	users to use the same event loop (as only a single event loop can coexist
35	peacefully at any one time).	106	peacefully at any one time).
36		107
37	The interface itself is vaguely similar but not identical to the Event	108	The interface itself is vaguely similar, but not identical to the L<Event>
38	module.	109	module.
39		110
40	On the first call of any method, the module tries to detect the currently	111	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	112	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	113	following modules is already loaded: L<EV>,
43	used. If none is found, the module tries to load these modules in the	114	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	115	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.	116	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		117	adaptor should always succeed) in the order given. The first one that can
		118	be successfully loaded will be used. If, after this, still none could be
		119	found, AnyEvent will fall back to a pure-perl event loop, which is not
		120	very efficient, but should work everywhere.
		121
		122	Because AnyEvent first checks for modules that are already loaded, loading
		123	an event model explicitly before first using AnyEvent will likely make
		124	that model the default. For example:
		125
		126	use Tk;
		127	use AnyEvent;
		128
		129	# .. AnyEvent will likely default to Tk
		130
		131	The I<likely> means that, if any module loads another event model and
		132	starts using it, all bets are off. Maybe you should tell their authors to
		133	use AnyEvent so their modules work together with others seamlessly...
		134
		135	The pure-perl implementation of AnyEvent is called
		136	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		137	explicitly and enjoy the high availability of that event loop :)
		138
		139	=head1 WATCHERS
		140
		141	AnyEvent has the central concept of a I<watcher>, which is an object that
		142	stores relevant data for each kind of event you are waiting for, such as
		143	the callback to call, the file handle to watch, etc.
		144
		145	These watchers are normal Perl objects with normal Perl lifetime. After
		146	creating a watcher it will immediately "watch" for events and invoke the
		147	callback when the event occurs (of course, only when the event model
		148	is in control).
		149
		150	Note that B<callbacks must not permanently change global variables>
		151	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		152	callbacks must not C<die> >>. The former is good programming practise in
		153	Perl and the latter stems from the fact that exception handling differs
		154	widely between event loops.
		155
		156	To disable the watcher you have to destroy it (e.g. by setting the
		157	variable you store it in to C<undef> or otherwise deleting all references
		158	to it).
		159
		160	All watchers are created by calling a method on the C<AnyEvent> class.
		161
		162	Many watchers either are used with "recursion" (repeating timers for
		163	example), or need to refer to their watcher object in other ways.
		164
		165	An any way to achieve that is this pattern:
		166
		167	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		168	# you can use $w here, for example to undef it
		169	undef $w;
		170	});
		171
		172	Note that C<my $w; $w => combination. This is necessary because in Perl,
		173	my variables are only visible after the statement in which they are
		174	declared.
		175
		176	=head2 I/O WATCHERS
		177
		178	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		179	with the following mandatory key-value pairs as arguments:
		180
		181	C<fh> is the Perl I<file handle> (or a naked file descriptor) to watch
		182	for events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example files
		186	or block devices.
		187
		188	C<poll> must be a string that is either C<r> or C<w>, which creates a
		189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
		191	C<cb> is the callback to invoke each time the file handle becomes ready.
		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 I/O watcher callbacks.
		196
		197	The I/O watcher might use the underlying file descriptor or a copy of it.
		198	You must not close a file handle as long as any watcher is active on the
		199	underlying file descriptor.
		200
		201	Some event loops issue spurious readyness notifications, so you should
		202	always use non-blocking calls when reading/writing from/to your file
		203	handles.
		204
		205	Example: wait for readability of STDIN, then read a line and disable the
		206	watcher.
		207
		208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		209	chomp (my $input = <STDIN>);
		210	warn "read: $input\n";
		211	undef $w;
		212	});
		213
		214	=head2 TIME WATCHERS
		215
		216	You can create a time watcher by calling the C<< AnyEvent->timer >>
		217	method with the following mandatory arguments:
		218
		219	C<after> specifies after how many seconds (fractional values are
		220	supported) the callback should be invoked. C<cb> is the callback to invoke
		221	in that case.
		222
		223	Although the callback might get passed parameters, their value and
		224	presence is undefined and you cannot rely on them. Portable AnyEvent
		225	callbacks cannot use arguments passed to time watcher callbacks.
		226
		227	The callback will normally be invoked once only. If you specify another
		228	parameter, C<interval>, as a strictly positive number (> 0), then the
		229	callback will be invoked regularly at that interval (in fractional
		230	seconds) after the first invocation. If C<interval> is specified with a
		231	false value, then it is treated as if it were missing.
		232
		233	The callback will be rescheduled before invoking the callback, but no
		234	attempt is done to avoid timer drift in most backends, so the interval is
		235	only approximate.
		236
		237	Example: fire an event after 7.7 seconds.
		238
		239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		240	warn "timeout\n";
		241	});
		242
		243	# to cancel the timer:
		244	undef $w;
		245
		246	Example 2: fire an event after 0.5 seconds, then roughly every second.
		247
		248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		249	warn "timeout\n";
		250	};
		251
		252	=head3 TIMING ISSUES
		253
		254	There are two ways to handle timers: based on real time (relative, "fire
		255	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		256	o'clock").
		257
		258	While most event loops expect timers to specified in a relative way, they
		259	use absolute time internally. This makes a difference when your clock
		260	"jumps", for example, when ntp decides to set your clock backwards from
		261	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		262	fire "after" a second might actually take six years to finally fire.
		263
		264	AnyEvent cannot compensate for this. The only event loop that is conscious
		265	about these issues is L<EV>, which offers both relative (ev_timer, based
		266	on true relative time) and absolute (ev_periodic, based on wallclock time)
		267	timers.
		268
		269	AnyEvent always prefers relative timers, if available, matching the
		270	AnyEvent API.
		271
		272	AnyEvent has two additional methods that return the "current time":
46		273
47	=over 4	274	=over 4
48		275
		276	=item AnyEvent->time
		277
		278	This returns the "current wallclock time" as a fractional number of
		279	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		280	return, and the result is guaranteed to be compatible with those).
		281
		282	It progresses independently of any event loop processing, i.e. each call
		283	will check the system clock, which usually gets updated frequently.
		284
		285	=item AnyEvent->now
		286
		287	This also returns the "current wallclock time", but unlike C<time>, above,
		288	this value might change only once per event loop iteration, depending on
		289	the event loop (most return the same time as C<time>, above). This is the
		290	time that AnyEvent's timers get scheduled against.
		291
		292	I<In almost all cases (in all cases if you don't care), this is the
		293	function to call when you want to know the current time.>
		294
		295	This function is also often faster then C<< AnyEvent->time >>, and
		296	thus the preferred method if you want some timestamp (for example,
		297	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		298
		299	The rest of this section is only of relevance if you try to be very exact
		300	with your timing, you can skip it without bad conscience.
		301
		302	For a practical example of when these times differ, consider L<Event::Lib>
		303	and L<EV> and the following set-up:
		304
		305	The event loop is running and has just invoked one of your callback at
		306	time=500 (assume no other callbacks delay processing). In your callback,
		307	you wait a second by executing C<sleep 1> (blocking the process for a
		308	second) and then (at time=501) you create a relative timer that fires
		309	after three seconds.
		310
		311	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		312	both return C<501>, because that is the current time, and the timer will
		313	be scheduled to fire at time=504 (C<501> + C<3>).
		314
		315	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		316	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		317	last event processing phase started. With L<EV>, your timer gets scheduled
		318	to run at time=503 (C<500> + C<3>).
		319
		320	In one sense, L<Event::Lib> is more exact, as it uses the current time
		321	regardless of any delays introduced by event processing. However, most
		322	callbacks do not expect large delays in processing, so this causes a
		323	higher drift (and a lot more system calls to get the current time).
		324
		325	In another sense, L<EV> is more exact, as your timer will be scheduled at
		326	the same time, regardless of how long event processing actually took.
		327
		328	In either case, if you care (and in most cases, you don't), then you
		329	can get whatever behaviour you want with any event loop, by taking the
		330	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		331	account.
		332
		333	=item AnyEvent->now_update
		334
		335	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		336	the current time for each loop iteration (see the discussion of L<<
		337	AnyEvent->now >>, above).
		338
		339	When a callback runs for a long time (or when the process sleeps), then
		340	this "current" time will differ substantially from the real time, which
		341	might affect timers and time-outs.
		342
		343	When this is the case, you can call this method, which will update the
		344	event loop's idea of "current time".
		345
		346	Note that updating the time I<might> cause some events to be handled.
		347
		348	=back
		349
		350	=head2 SIGNAL WATCHERS
		351
		352	You can watch for signals using a signal watcher, C<signal> is the signal
		353	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		354	callback to be invoked whenever a signal occurs.
		355
		356	Although the callback might get passed parameters, their value and
		357	presence is undefined and you cannot rely on them. Portable AnyEvent
		358	callbacks cannot use arguments passed to signal watcher callbacks.
		359
		360	Multiple signal occurrences can be clumped together into one callback
		361	invocation, and callback invocation will be synchronous. Synchronous means
		362	that it might take a while until the signal gets handled by the process,
		363	but it is guaranteed not to interrupt any other callbacks.
		364
		365	The main advantage of using these watchers is that you can share a signal
		366	between multiple watchers, and AnyEvent will ensure that signals will not
		367	interrupt your program at bad times.
		368
		369	This watcher might use C<%SIG> (depending on the event loop used),
		370	so programs overwriting those signals directly will likely not work
		371	correctly.
		372
		373	Also note that many event loops (e.g. Glib, Tk, Qt, IO::Async) do not
		374	support attaching callbacks to signals, which is a pity, as you cannot do
		375	race-free signal handling in perl. AnyEvent will try to do it's best, but
		376	in some cases, signals will be delayed. The maximum time a signal might
		377	be delayed is specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10
		378	seconds). This variable can be changed only before the first signal
		379	watcher is created, and should be left alone otherwise. Higher values
		380	will cause fewer spurious wake-ups, which is better for power and CPU
		381	saving. All these problems can be avoided by installing the optional
		382	L<Async::Interrupt> module.
		383
		384	Example: exit on SIGINT
		385
		386	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		387
		388	=head2 CHILD PROCESS WATCHERS
		389
		390	You can also watch on a child process exit and catch its exit status.
		391
		392	The child process is specified by the C<pid> argument (if set to C<0>, it
		393	watches for any child process exit). The watcher will triggered only when
		394	the child process has finished and an exit status is available, not on
		395	any trace events (stopped/continued).
		396
		397	The callback will be called with the pid and exit status (as returned by
		398	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		399	callback arguments.
		400
		401	This watcher type works by installing a signal handler for C<SIGCHLD>,
		402	and since it cannot be shared, nothing else should use SIGCHLD or reap
		403	random child processes (waiting for specific child processes, e.g. inside
		404	C<system>, is just fine).
		405
		406	There is a slight catch to child watchers, however: you usually start them
		407	I<after> the child process was created, and this means the process could
		408	have exited already (and no SIGCHLD will be sent anymore).
		409
		410	Not all event models handle this correctly (neither POE nor IO::Async do,
		411	see their AnyEvent::Impl manpages for details), but even for event models
		412	that I<do> handle this correctly, they usually need to be loaded before
		413	the process exits (i.e. before you fork in the first place). AnyEvent's
		414	pure perl event loop handles all cases correctly regardless of when you
		415	start the watcher.
		416
		417	This means you cannot create a child watcher as the very first
		418	thing in an AnyEvent program, you I<have> to create at least one
		419	watcher before you C<fork> the child (alternatively, you can call
		420	C<AnyEvent::detect>).
		421
		422	As most event loops do not support waiting for child events, they will be
		423	emulated by AnyEvent in most cases, in which the latency and race problems
		424	mentioned in the description of signal watchers apply.
		425
		426	Example: fork a process and wait for it
		427
		428	my $done = AnyEvent->condvar;
		429
		430	my $pid = fork or exit 5;
		431
		432	my $w = AnyEvent->child (
		433	pid => $pid,
		434	cb => sub {
		435	my ($pid, $status) = @_;
		436	warn "pid $pid exited with status $status";
		437	$done->send;
		438	},
		439	);
		440
		441	# do something else, then wait for process exit
		442	$done->recv;
		443
		444	=head2 IDLE WATCHERS
		445
		446	Sometimes there is a need to do something, but it is not so important
		447	to do it instantly, but only when there is nothing better to do. This
		448	"nothing better to do" is usually defined to be "no other events need
		449	attention by the event loop".
		450
		451	Idle watchers ideally get invoked when the event loop has nothing
		452	better to do, just before it would block the process to wait for new
		453	events. Instead of blocking, the idle watcher is invoked.
		454
		455	Most event loops unfortunately do not really support idle watchers (only
		456	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		457	will simply call the callback "from time to time".
		458
		459	Example: read lines from STDIN, but only process them when the
		460	program is otherwise idle:
		461
		462	my @lines; # read data
		463	my $idle_w;
		464	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		465	push @lines, scalar <STDIN>;
		466
		467	# start an idle watcher, if not already done
		468	$idle_w ||= AnyEvent->idle (cb => sub {
		469	# handle only one line, when there are lines left
		470	if (my $line = shift @lines) {
		471	print "handled when idle: $line";
		472	} else {
		473	# otherwise disable the idle watcher again
		474	undef $idle_w;
		475	}
		476	});
		477	});
		478
		479	=head2 CONDITION VARIABLES
		480
		481	If you are familiar with some event loops you will know that all of them
		482	require you to run some blocking "loop", "run" or similar function that
		483	will actively watch for new events and call your callbacks.
		484
		485	AnyEvent is slightly different: it expects somebody else to run the event
		486	loop and will only block when necessary (usually when told by the user).
		487
		488	The instrument to do that is called a "condition variable", so called
		489	because they represent a condition that must become true.
		490
		491	Now is probably a good time to look at the examples further below.
		492
		493	Condition variables can be created by calling the C<< AnyEvent->condvar
		494	>> method, usually without arguments. The only argument pair allowed is
		495	C<cb>, which specifies a callback to be called when the condition variable
		496	becomes true, with the condition variable as the first argument (but not
		497	the results).
		498
		499	After creation, the condition variable is "false" until it becomes "true"
		500	by calling the C<send> method (or calling the condition variable as if it
		501	were a callback, read about the caveats in the description for the C<<
		502	->send >> method).
		503
		504	Condition variables are similar to callbacks, except that you can
		505	optionally wait for them. They can also be called merge points - points
		506	in time where multiple outstanding events have been processed. And yet
		507	another way to call them is transactions - each condition variable can be
		508	used to represent a transaction, which finishes at some point and delivers
		509	a result.
		510
		511	Condition variables are very useful to signal that something has finished,
		512	for example, if you write a module that does asynchronous http requests,
		513	then a condition variable would be the ideal candidate to signal the
		514	availability of results. The user can either act when the callback is
		515	called or can synchronously C<< ->recv >> for the results.
		516
		517	You can also use them to simulate traditional event loops - for example,
		518	you can block your main program until an event occurs - for example, you
		519	could C<< ->recv >> in your main program until the user clicks the Quit
		520	button of your app, which would C<< ->send >> the "quit" event.
		521
		522	Note that condition variables recurse into the event loop - if you have
		523	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		524	lose. Therefore, condition variables are good to export to your caller, but
		525	you should avoid making a blocking wait yourself, at least in callbacks,
		526	as this asks for trouble.
		527
		528	Condition variables are represented by hash refs in perl, and the keys
		529	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		530	easy (it is often useful to build your own transaction class on top of
		531	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		532	it's C<new> method in your own C<new> method.
		533
		534	There are two "sides" to a condition variable - the "producer side" which
		535	eventually calls C<< -> send >>, and the "consumer side", which waits
		536	for the send to occur.
		537
		538	Example: wait for a timer.
		539
		540	# wait till the result is ready
		541	my $result_ready = AnyEvent->condvar;
		542
		543	# do something such as adding a timer
		544	# or socket watcher the calls $result_ready->send
		545	# when the "result" is ready.
		546	# in this case, we simply use a timer:
		547	my $w = AnyEvent->timer (
		548	after => 1,
		549	cb => sub { $result_ready->send },
		550	);
		551
		552	# this "blocks" (while handling events) till the callback
		553	# calls -<send
		554	$result_ready->recv;
		555
		556	Example: wait for a timer, but take advantage of the fact that condition
		557	variables are also callable directly.
		558
		559	my $done = AnyEvent->condvar;
		560	my $delay = AnyEvent->timer (after => 5, cb => $done);
		561	$done->recv;
		562
		563	Example: Imagine an API that returns a condvar and doesn't support
		564	callbacks. This is how you make a synchronous call, for example from
		565	the main program:
		566
		567	use AnyEvent::CouchDB;
		568
		569	...
		570
		571	my @info = $couchdb->info->recv;
		572
		573	And this is how you would just set a callback to be called whenever the
		574	results are available:
		575
		576	$couchdb->info->cb (sub {
		577	my @info = $_[0]->recv;
		578	});
		579
		580	=head3 METHODS FOR PRODUCERS
		581
		582	These methods should only be used by the producing side, i.e. the
		583	code/module that eventually sends the signal. Note that it is also
		584	the producer side which creates the condvar in most cases, but it isn't
		585	uncommon for the consumer to create it as well.
		586
		587	=over 4
		588
		589	=item $cv->send (...)
		590
		591	Flag the condition as ready - a running C<< ->recv >> and all further
		592	calls to C<recv> will (eventually) return after this method has been
		593	called. If nobody is waiting the send will be remembered.
		594
		595	If a callback has been set on the condition variable, it is called
		596	immediately from within send.
		597
		598	Any arguments passed to the C<send> call will be returned by all
		599	future C<< ->recv >> calls.
		600
		601	Condition variables are overloaded so one can call them directly (as if
		602	they were a code reference). Calling them directly is the same as calling
		603	C<send>.
		604
		605	=item $cv->croak ($error)
		606
		607	Similar to send, but causes all call's to C<< ->recv >> to invoke
		608	C<Carp::croak> with the given error message/object/scalar.
		609
		610	This can be used to signal any errors to the condition variable
		611	user/consumer. Doing it this way instead of calling C<croak> directly
		612	delays the error detetcion, but has the overwhelmign advantage that it
		613	diagnoses the error at the place where the result is expected, and not
		614	deep in some event clalback without connection to the actual code causing
		615	the problem.
		616
		617	=item $cv->begin ([group callback])
		618
		619	=item $cv->end
		620
		621	These two methods can be used to combine many transactions/events into
		622	one. For example, a function that pings many hosts in parallel might want
		623	to use a condition variable for the whole process.
		624
		625	Every call to C<< ->begin >> will increment a counter, and every call to
		626	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		627	>>, the (last) callback passed to C<begin> will be executed. That callback
		628	is I<supposed> to call C<< ->send >>, but that is not required. If no
		629	callback was set, C<send> will be called without any arguments.
		630
		631	You can think of C<< $cv->send >> giving you an OR condition (one call
		632	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		633	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		634
		635	Let's start with a simple example: you have two I/O watchers (for example,
		636	STDOUT and STDERR for a program), and you want to wait for both streams to
		637	close before activating a condvar:
		638
		639	my $cv = AnyEvent->condvar;
		640
		641	$cv->begin; # first watcher
		642	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		643	defined sysread $fh1, my $buf, 4096
		644	or $cv->end;
		645	});
		646
		647	$cv->begin; # second watcher
		648	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		649	defined sysread $fh2, my $buf, 4096
		650	or $cv->end;
		651	});
		652
		653	$cv->recv;
		654
		655	This works because for every event source (EOF on file handle), there is
		656	one call to C<begin>, so the condvar waits for all calls to C<end> before
		657	sending.
		658
		659	The ping example mentioned above is slightly more complicated, as the
		660	there are results to be passwd back, and the number of tasks that are
		661	begung can potentially be zero:
		662
		663	my $cv = AnyEvent->condvar;
		664
		665	my %result;
		666	$cv->begin (sub { $cv->send (\%result) });
		667
		668	for my $host (@list_of_hosts) {
		669	$cv->begin;
		670	ping_host_then_call_callback $host, sub {
		671	$result{$host} = ...;
		672	$cv->end;
		673	};
		674	}
		675
		676	$cv->end;
		677
		678	This code fragment supposedly pings a number of hosts and calls
		679	C<send> after results for all then have have been gathered - in any
		680	order. To achieve this, the code issues a call to C<begin> when it starts
		681	each ping request and calls C<end> when it has received some result for
		682	it. Since C<begin> and C<end> only maintain a counter, the order in which
		683	results arrive is not relevant.
		684
		685	There is an additional bracketing call to C<begin> and C<end> outside the
		686	loop, which serves two important purposes: first, it sets the callback
		687	to be called once the counter reaches C<0>, and second, it ensures that
		688	C<send> is called even when C<no> hosts are being pinged (the loop
		689	doesn't execute once).
		690
		691	This is the general pattern when you "fan out" into multiple (but
		692	potentially none) subrequests: use an outer C<begin>/C<end> pair to set
		693	the callback and ensure C<end> is called at least once, and then, for each
		694	subrequest you start, call C<begin> and for each subrequest you finish,
		695	call C<end>.
		696
		697	=back
		698
		699	=head3 METHODS FOR CONSUMERS
		700
		701	These methods should only be used by the consuming side, i.e. the
		702	code awaits the condition.
		703
		704	=over 4
		705
		706	=item $cv->recv
		707
		708	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		709	>> methods have been called on c<$cv>, while servicing other watchers
		710	normally.
		711
		712	You can only wait once on a condition - additional calls are valid but
		713	will return immediately.
		714
		715	If an error condition has been set by calling C<< ->croak >>, then this
		716	function will call C<croak>.
		717
		718	In list context, all parameters passed to C<send> will be returned,
		719	in scalar context only the first one will be returned.
		720
		721	Note that doing a blocking wait in a callback is not supported by any
		722	event loop, that is, recursive invocation of a blocking C<< ->recv
		723	>> is not allowed, and the C<recv> call will C<croak> if such a
		724	condition is detected. This condition can be slightly loosened by using
		725	L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
		726	any thread that doesn't run the event loop itself.
		727
		728	Not all event models support a blocking wait - some die in that case
		729	(programs might want to do that to stay interactive), so I<if you are
		730	using this from a module, never require a blocking wait>. Instead, let the
		731	caller decide whether the call will block or not (for example, by coupling
		732	condition variables with some kind of request results and supporting
		733	callbacks so the caller knows that getting the result will not block,
		734	while still supporting blocking waits if the caller so desires).
		735
		736	You can ensure that C<< -recv >> never blocks by setting a callback and
		737	only calling C<< ->recv >> from within that callback (or at a later
		738	time). This will work even when the event loop does not support blocking
		739	waits otherwise.
		740
		741	=item $bool = $cv->ready
		742
		743	Returns true when the condition is "true", i.e. whether C<send> or
		744	C<croak> have been called.
		745
		746	=item $cb = $cv->cb ($cb->($cv))
		747
		748	This is a mutator function that returns the callback set and optionally
		749	replaces it before doing so.
		750
		751	The callback will be called when the condition becomes "true", i.e. when
		752	C<send> or C<croak> are called, with the only argument being the condition
		753	variable itself. Calling C<recv> inside the callback or at any later time
		754	is guaranteed not to block.
		755
		756	=back
		757
		758	=head1 SUPPORTED EVENT LOOPS/BACKENDS
		759
		760	The available backend classes are (every class has its own manpage):
		761
		762	=over 4
		763
		764	=item Backends that are autoprobed when no other event loop can be found.
		765
		766	EV is the preferred backend when no other event loop seems to be in
		767	use. If EV is not installed, then AnyEvent will try Event, and, failing
		768	that, will fall back to its own pure-perl implementation, which is
		769	available everywhere as it comes with AnyEvent itself.
		770
		771	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		772	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		773	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		774
		775	=item Backends that are transparently being picked up when they are used.
		776
		777	These will be used when they are currently loaded when the first watcher
		778	is created, in which case it is assumed that the application is using
		779	them. This means that AnyEvent will automatically pick the right backend
		780	when the main program loads an event module before anything starts to
		781	create watchers. Nothing special needs to be done by the main program.
		782
		783	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		784	AnyEvent::Impl::Tk based on Tk, very broken.
		785	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		786	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		787
		788	=item Backends with special needs.
		789
		790	Qt requires the Qt::Application to be instantiated first, but will
		791	otherwise be picked up automatically. As long as the main program
		792	instantiates the application before any AnyEvent watchers are created,
		793	everything should just work.
		794
		795	AnyEvent::Impl::Qt based on Qt.
		796
		797	Support for IO::Async can only be partial, as it is too broken and
		798	architecturally limited to even support the AnyEvent API. It also
		799	is the only event loop that needs the loop to be set explicitly, so
		800	it can only be used by a main program knowing about AnyEvent. See
		801	L<AnyEvent::Impl::Async> for the gory details.
		802
		803	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		804
		805	=item Event loops that are indirectly supported via other backends.
		806
		807	Some event loops can be supported via other modules:
		808
		809	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		810
		811	B<WxWidgets> has no support for watching file handles. However, you can
		812	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		813	polls 20 times per second, which was considered to be too horrible to even
		814	consider for AnyEvent.
		815
		816	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		817	backend, so it can be supported through POE.
		818
		819	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		820	load L<POE> when detecting them, in the hope that POE will pick them up,
		821	in which case everything will be automatic.
		822
		823	=back
		824
		825	=head1 GLOBAL VARIABLES AND FUNCTIONS
		826
		827	These are not normally required to use AnyEvent, but can be useful to
		828	write AnyEvent extension modules.
		829
		830	=over 4
		831
		832	=item $AnyEvent::MODEL
		833
		834	Contains C<undef> until the first watcher is being created, before the
		835	backend has been autodetected.
		836
		837	Afterwards it contains the event model that is being used, which is the
		838	name of the Perl class implementing the model. This class is usually one
		839	of the C<AnyEvent::Impl:xxx> modules, but can be any other class in the
		840	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
		841	will be C<urxvt::anyevent>).
		842
		843	=item AnyEvent::detect
		844
		845	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		846	if necessary. You should only call this function right before you would
		847	have created an AnyEvent watcher anyway, that is, as late as possible at
		848	runtime, and not e.g. while initialising of your module.
		849
		850	If you need to do some initialisation before AnyEvent watchers are
		851	created, use C<post_detect>.
		852
		853	=item $guard = AnyEvent::post_detect { BLOCK }
		854
		855	Arranges for the code block to be executed as soon as the event model is
		856	autodetected (or immediately if this has already happened).
		857
		858	The block will be executed I<after> the actual backend has been detected
		859	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		860	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		861	other initialisations - see the sources of L<AnyEvent::Strict> or
		862	L<AnyEvent::AIO> to see how this is used.
		863
		864	The most common usage is to create some global watchers, without forcing
		865	event module detection too early, for example, L<AnyEvent::AIO> creates
		866	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		867	avoid autodetecting the event module at load time.
		868
		869	If called in scalar or list context, then it creates and returns an object
		870	that automatically removes the callback again when it is destroyed. See
		871	L<Coro::BDB> for a case where this is useful.
		872
		873	=item @AnyEvent::post_detect
		874
		875	If there are any code references in this array (you can C<push> to it
		876	before or after loading AnyEvent), then they will called directly after
		877	the event loop has been chosen.
		878
		879	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		880	if it is defined then the event loop has already been detected, and the
		881	array will be ignored.
		882
		883	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		884	it,as it takes care of these details.
		885
		886	This variable is mainly useful for modules that can do something useful
		887	when AnyEvent is used and thus want to know when it is initialised, but do
		888	not need to even load it by default. This array provides the means to hook
		889	into AnyEvent passively, without loading it.
		890
		891	=back
		892
		893	=head1 WHAT TO DO IN A MODULE
		894
		895	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		896	freely, but you should not load a specific event module or rely on it.
		897
		898	Be careful when you create watchers in the module body - AnyEvent will
		899	decide which event module to use as soon as the first method is called, so
		900	by calling AnyEvent in your module body you force the user of your module
		901	to load the event module first.
		902
		903	Never call C<< ->recv >> on a condition variable unless you I<know> that
		904	the C<< ->send >> method has been called on it already. This is
		905	because it will stall the whole program, and the whole point of using
		906	events is to stay interactive.
		907
		908	It is fine, however, to call C<< ->recv >> when the user of your module
		909	requests it (i.e. if you create a http request object ad have a method
		910	called C<results> that returns the results, it should call C<< ->recv >>
		911	freely, as the user of your module knows what she is doing. always).
		912
		913	=head1 WHAT TO DO IN THE MAIN PROGRAM
		914
		915	There will always be a single main program - the only place that should
		916	dictate which event model to use.
		917
		918	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		919	do anything special (it does not need to be event-based) and let AnyEvent
		920	decide which implementation to chose if some module relies on it.
		921
		922	If the main program relies on a specific event model - for example, in
		923	Gtk2 programs you have to rely on the Glib module - you should load the
		924	event module before loading AnyEvent or any module that uses it: generally
		925	speaking, you should load it as early as possible. The reason is that
		926	modules might create watchers when they are loaded, and AnyEvent will
		927	decide on the event model to use as soon as it creates watchers, and it
		928	might chose the wrong one unless you load the correct one yourself.
		929
		930	You can chose to use a pure-perl implementation by loading the
		931	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		932	everywhere, but letting AnyEvent chose the model is generally better.
		933
		934	=head2 MAINLOOP EMULATION
		935
		936	Sometimes (often for short test scripts, or even standalone programs who
		937	only want to use AnyEvent), you do not want to run a specific event loop.
		938
		939	In that case, you can use a condition variable like this:
		940
		941	AnyEvent->condvar->recv;
		942
		943	This has the effect of entering the event loop and looping forever.
		944
		945	Note that usually your program has some exit condition, in which case
		946	it is better to use the "traditional" approach of storing a condition
		947	variable somewhere, waiting for it, and sending it when the program should
		948	exit cleanly.
		949
		950
		951	=head1 OTHER MODULES
		952
		953	The following is a non-exhaustive list of additional modules that use
		954	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		955	modules and other event loops in the same program. Some of the modules
		956	come with AnyEvent, most are available via CPAN.
		957
		958	=over 4
		959
		960	=item L<AnyEvent::Util>
		961
		962	Contains various utility functions that replace often-used but blocking
		963	functions such as C<inet_aton> by event-/callback-based versions.
		964
		965	=item L<AnyEvent::Socket>
		966
		967	Provides various utility functions for (internet protocol) sockets,
		968	addresses and name resolution. Also functions to create non-blocking tcp
		969	connections or tcp servers, with IPv6 and SRV record support and more.
		970
		971	=item L<AnyEvent::Handle>
		972
		973	Provide read and write buffers, manages watchers for reads and writes,
		974	supports raw and formatted I/O, I/O queued and fully transparent and
		975	non-blocking SSL/TLS (via L<AnyEvent::TLS>.
		976
		977	=item L<AnyEvent::DNS>
		978
		979	Provides rich asynchronous DNS resolver capabilities.
		980
		981	=item L<AnyEvent::HTTP>
		982
		983	A simple-to-use HTTP library that is capable of making a lot of concurrent
		984	HTTP requests.
		985
		986	=item L<AnyEvent::HTTPD>
		987
		988	Provides a simple web application server framework.
		989
		990	=item L<AnyEvent::FastPing>
		991
		992	The fastest ping in the west.
		993
		994	=item L<AnyEvent::DBI>
		995
		996	Executes L<DBI> requests asynchronously in a proxy process.
		997
		998	=item L<AnyEvent::AIO>
		999
		1000	Truly asynchronous I/O, should be in the toolbox of every event
		1001	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		1002	together.
		1003
		1004	=item L<AnyEvent::BDB>
		1005
		1006	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		1007	L<BDB> and AnyEvent together.
		1008
		1009	=item L<AnyEvent::GPSD>
		1010
		1011	A non-blocking interface to gpsd, a daemon delivering GPS information.
		1012
		1013	=item L<AnyEvent::IRC>
		1014
		1015	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		1016
		1017	=item L<AnyEvent::XMPP>
		1018
		1019	AnyEvent based XMPP (Jabber protocol) module family (replacing the older
		1020	Net::XMPP2>.
		1021
		1022	=item L<AnyEvent::IGS>
		1023
		1024	A non-blocking interface to the Internet Go Server protocol (used by
		1025	L<App::IGS>).
		1026
		1027	=item L<Net::FCP>
		1028
		1029	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		1030	of AnyEvent.
		1031
		1032	=item L<Event::ExecFlow>
		1033
		1034	High level API for event-based execution flow control.
		1035
		1036	=item L<Coro>
		1037
		1038	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1039
		1040	=back
		1041
49	=cut	1042	=cut
50		1043
51	package AnyEvent;	1044	package AnyEvent;
52		1045
53	no warnings;	1046	no warnings;
54	use strict 'vars';	1047	use strict qw(vars subs);
		1048
55	use Carp;	1049	use Carp ();
56		1050
57	our $VERSION = 0.2;	1051	our $VERSION = 4.83;
58	our $MODEL;	1052	our $MODEL;
59		1053
60	our $AUTOLOAD;	1054	our $AUTOLOAD;
61	our @ISA;	1055	our @ISA;
62		1056
		1057	our @REGISTRY;
		1058
		1059	our $WIN32;
		1060
		1061	our $VERBOSE;
		1062
		1063	BEGIN {
		1064	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		1065	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		1066
		1067	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1068	if ${^TAINT};
		1069
		1070	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1071
		1072	}
		1073
		1074	our $MAX_SIGNAL_LATENCY = 10;
		1075
		1076	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1077
		1078	{
		1079	my $idx;
		1080	$PROTOCOL{$_} = ++$idx
		1081	for reverse split /\s*,\s*/,
		1082	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1083	}
		1084
63	my @models = (	1085	my @models = (
64	[Coro => Coro::Event::],	1086	[EV:: => AnyEvent::Impl::EV::],
65	[Event => Event::],	1087	[Event:: => AnyEvent::Impl::Event::],
66	[Glib => Glib::],	1088	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
67	[Tk => Tk::],	1089	# everything below here will not be autoprobed
		1090	# as the pureperl backend should work everywhere
		1091	# and is usually faster
		1092	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		1093	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1094	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1095	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1096	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1097	[Wx:: => AnyEvent::Impl::POE::],
		1098	[Prima:: => AnyEvent::Impl::POE::],
		1099	# IO::Async is just too broken - we would need workarounds for its
		1100	# byzantine signal and broken child handling, among others.
		1101	# IO::Async is rather hard to detect, as it doesn't have any
		1102	# obvious default class.
		1103	# [IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1104	# [IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1105	# [IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
68	);	1106	);
69		1107
70	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	1108	our %method = map +($_ => 1),
		1109	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
71		1110
72	sub AUTOLOAD {	1111	our @post_detect;
73	$AUTOLOAD =~ s/.*://;
74		1112
75	$method{$AUTOLOAD}	1113	sub post_detect(&) {
76	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	1114	my ($cb) = @_;
77		1115
		1116	if ($MODEL) {
		1117	$cb->();
		1118
		1119	1
		1120	} else {
		1121	push @post_detect, $cb;
		1122
		1123	defined wantarray
		1124	? bless \$cb, "AnyEvent::Util::postdetect"
		1125	: ()
		1126	}
		1127	}
		1128
		1129	sub AnyEvent::Util::postdetect::DESTROY {
		1130	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1131	}
		1132
		1133	sub detect() {
78	unless ($MODEL) {	1134	unless ($MODEL) {
79	# check for already loaded models	1135	no strict 'refs';
80	for (@models) {	1136	local $SIG{__DIE__};
81	my ($model, $package) = @$_;	1137
82	if (scalar keys %{ *{"$package\::"} }) {	1138	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
83	eval "require AnyEvent::Impl::$model";	1139	my $model = "AnyEvent::Impl::$1";
84	last if $MODEL;	1140	if (eval "require $model") {
		1141	$MODEL = $model;
		1142	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1143	} else {
		1144	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
85	}	1145	}
86	}	1146	}
87		1147
		1148	# check for already loaded models
88	unless ($MODEL) {	1149	unless ($MODEL) {
89	# try to load a model
90
91	for (@models) {	1150	for (@REGISTRY, @models) {
92	my ($model, $package) = @$_;	1151	my ($package, $model) = @$_;
93	eval "require AnyEvent::Impl::$model";	1152	if (${"$package\::VERSION"} > 0) {
94	last if $MODEL;	1153	if (eval "require $model") {
		1154	$MODEL = $model;
		1155	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
		1156	last;
		1157	}
		1158	}
95	}	1159	}
96		1160
		1161	unless ($MODEL) {
		1162	# try to load a model
		1163
		1164	for (@REGISTRY, @models) {
		1165	my ($package, $model) = @$_;
		1166	if (eval "require $package"
		1167	and ${"$package\::VERSION"} > 0
		1168	and eval "require $model") {
		1169	$MODEL = $model;
		1170	warn "AnyEvent: autoprobed model '$model', using it.\n" if $VERBOSE >= 2;
		1171	last;
		1172	}
		1173	}
		1174
97	$MODEL	1175	$MODEL
98	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1176	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
		1177	}
		1178	}
		1179
		1180	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1181
		1182	unshift @ISA, $MODEL;
		1183
		1184	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1185
		1186	(shift @post_detect)->() while @post_detect;
		1187	}
		1188
		1189	$MODEL
		1190	}
		1191
		1192	sub AUTOLOAD {
		1193	(my $func = $AUTOLOAD) =~ s/.*://;
		1194
		1195	$method{$func}
		1196	or Carp::croak "$func: not a valid method for AnyEvent objects";
		1197
		1198	detect unless $MODEL;
		1199
		1200	my $class = shift;
		1201	$class->$func (@_);
		1202	}
		1203
		1204	# utility function to dup a filehandle. this is used by many backends
		1205	# to support binding more than one watcher per filehandle (they usually
		1206	# allow only one watcher per fd, so we dup it to get a different one).
		1207	sub _dupfh($$;$$) {
		1208	my ($poll, $fh, $r, $w) = @_;
		1209
		1210	# cygwin requires the fh mode to be matching, unix doesn't
		1211	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1212
		1213	open my $fh2, $mode, $fh
		1214	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1215
		1216	# we assume CLOEXEC is already set by perl in all important cases
		1217
		1218	($fh2, $rw)
		1219	}
		1220
		1221	package AnyEvent::Base;
		1222
		1223	# default implementations for many methods
		1224
		1225	sub _time {
		1226	# probe for availability of Time::HiRes
		1227	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1228	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1229	*_time = \&Time::HiRes::time;
		1230	# if (eval "use POSIX (); (POSIX::times())...
		1231	} else {
		1232	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1233	*_time = sub { time }; # epic fail
		1234	}
		1235
		1236	&_time
		1237	}
		1238
		1239	sub time { _time }
		1240	sub now { _time }
		1241	sub now_update { }
		1242
		1243	# default implementation for ->condvar
		1244
		1245	sub condvar {
		1246	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1247	}
		1248
		1249	# default implementation for ->signal
		1250
		1251	our $HAVE_ASYNC_INTERRUPT;
		1252	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1253	our (%SIG_ASY, %SIG_ASY_W);
		1254	our ($SIG_COUNT, $SIG_TW);
		1255
		1256	sub _signal_exec {
		1257	$HAVE_ASYNC_INTERRUPT
		1258	? $SIGPIPE_R->drain
		1259	: sysread $SIGPIPE_R, my $dummy, 9;
		1260
		1261	while (%SIG_EV) {
		1262	for (keys %SIG_EV) {
		1263	delete $SIG_EV{$_};
		1264	$_->() for values %{ $SIG_CB{$_} || {} };
99	}	1265	}
100	}	1266	}
		1267	}
101		1268
102	@ISA = $MODEL;	1269	sub _signal {
		1270	my (undef, %arg) = @_;
103		1271
		1272	my $signal = uc $arg{signal}
		1273	or Carp::croak "required option 'signal' is missing";
		1274
		1275	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1276
		1277	if ($HAVE_ASYNC_INTERRUPT) {
		1278	# async::interrupt
		1279
		1280	$SIG_ASY{$signal} ||= do {
		1281	my $asy = new Async::Interrupt
		1282	cb => sub { undef $SIG_EV{$signal} },
		1283	signal => $signal,
		1284	pipe => [$SIGPIPE_R->filenos],
		1285	;
		1286	$asy->pipe_autodrain (0);
		1287
		1288	$asy
		1289	};
		1290
		1291	} else {
		1292	# pure perl
		1293
		1294	$SIG{$signal} ||= sub {
		1295	local $!;
		1296	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1297	undef $SIG_EV{$signal};
		1298	};
		1299
		1300	# can't do signal processing without introducing races in pure perl,
		1301	# so limit the signal latency.
		1302	++$SIG_COUNT;
		1303	$SIG_TW ||= AnyEvent->timer (
		1304	after => $MAX_SIGNAL_LATENCY,
		1305	interval => $MAX_SIGNAL_LATENCY,
		1306	cb => sub { }, # just for the PERL_ASYNC_CHECK
		1307	);
		1308	}
		1309
		1310	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1311	}
		1312
		1313	sub signal {
		1314	# probe for availability of Async::Interrupt
		1315	if (!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT} && eval "use Async::Interrupt 0.6 (); 1") {
		1316	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1317
		1318	$HAVE_ASYNC_INTERRUPT = 1;
		1319	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1320	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R->fileno, poll => "r", cb => \&_signal_exec);
		1321
		1322	} else {
		1323	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1324
		1325	require Fcntl;
		1326
		1327	if (AnyEvent::WIN32) {
		1328	require AnyEvent::Util;
		1329
		1330	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1331	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1332	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1333	} else {
		1334	pipe $SIGPIPE_R, $SIGPIPE_W;
		1335	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1336	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1337
		1338	# not strictly required, as $^F is normally 2, but let's make sure...
		1339	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1340	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1341	}
		1342
		1343	$SIGPIPE_R
		1344	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1345
		1346	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1347	}
		1348
		1349	*signal = \&_signal;
		1350	&signal
		1351	}
		1352
		1353	sub AnyEvent::Base::signal::DESTROY {
		1354	my ($signal, $cb) = @{$_[0]};
		1355
		1356	undef $SIG_TW
		1357	unless --$SIG_COUNT;
		1358
		1359	delete $SIG_CB{$signal}{$cb};
		1360
		1361	# delete doesn't work with older perls - they then
		1362	# print weird messages, or just unconditionally exit
		1363	# instead of getting the default action.
		1364	undef $SIG{$signal}
		1365	unless keys %{ $SIG_CB{$signal} };
		1366	}
		1367
		1368	# default implementation for ->child
		1369
		1370	our %PID_CB;
		1371	our $CHLD_W;
		1372	our $CHLD_DELAY_W;
		1373	our $WNOHANG;
		1374
		1375	sub _sigchld {
		1376	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1377	$_->($pid, $?)
		1378	for values %{ $PID_CB{$pid} || {} },
		1379	values %{ $PID_CB{0} || {} };
		1380	}
		1381	}
		1382
		1383	sub child {
		1384	my (undef, %arg) = @_;
		1385
		1386	defined (my $pid = $arg{pid} + 0)
		1387	or Carp::croak "required option 'pid' is missing";
		1388
		1389	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1390
		1391	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1392
		1393	unless ($CHLD_W) {
		1394	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1395	# child could be a zombie already, so make at least one round
		1396	&_sigchld;
		1397	}
		1398
		1399	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
		1400	}
		1401
		1402	sub AnyEvent::Base::child::DESTROY {
		1403	my ($pid, $cb) = @{$_[0]};
		1404
		1405	delete $PID_CB{$pid}{$cb};
		1406	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1407
		1408	undef $CHLD_W unless keys %PID_CB;
		1409	}
		1410
		1411	# idle emulation is done by simply using a timer, regardless
		1412	# of whether the process is idle or not, and not letting
		1413	# the callback use more than 50% of the time.
		1414	sub idle {
		1415	my (undef, %arg) = @_;
		1416
		1417	my ($cb, $w, $rcb) = $arg{cb};
		1418
		1419	$rcb = sub {
		1420	if ($cb) {
		1421	$w = _time;
		1422	&$cb;
		1423	$w = _time - $w;
		1424
		1425	# never use more then 50% of the time for the idle watcher,
		1426	# within some limits
		1427	$w = 0.0001 if $w < 0.0001;
		1428	$w = 5 if $w > 5;
		1429
		1430	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1431	} else {
		1432	# clean up...
		1433	undef $w;
		1434	undef $rcb;
		1435	}
		1436	};
		1437
		1438	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1439
		1440	bless \\$cb, "AnyEvent::Base::idle"
		1441	}
		1442
		1443	sub AnyEvent::Base::idle::DESTROY {
		1444	undef $${$_[0]};
		1445	}
		1446
		1447	package AnyEvent::CondVar;
		1448
		1449	our @ISA = AnyEvent::CondVar::Base::;
		1450
		1451	package AnyEvent::CondVar::Base;
		1452
		1453	use overload
		1454	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1455	fallback => 1;
		1456
		1457	our $WAITING;
		1458
		1459	sub _send {
		1460	# nop
		1461	}
		1462
		1463	sub send {
104	my $class = shift;	1464	my $cv = shift;
105	$class->$AUTOLOAD (@_);	1465	$cv->{_ae_sent} = [@_];
		1466	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1467	$cv->_send;
106	}	1468	}
		1469
		1470	sub croak {
		1471	$_[0]{_ae_croak} = $_[1];
		1472	$_[0]->send;
		1473	}
		1474
		1475	sub ready {
		1476	$_[0]{_ae_sent}
		1477	}
		1478
		1479	sub _wait {
		1480	$WAITING
		1481	and !$_[0]{_ae_sent}
		1482	and Carp::croak "AnyEvent::CondVar: recursive blocking wait detected";
		1483
		1484	local $WAITING = 1;
		1485	AnyEvent->one_event while !$_[0]{_ae_sent};
		1486	}
		1487
		1488	sub recv {
		1489	$_[0]->_wait;
		1490
		1491	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1492	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1493	}
		1494
		1495	sub cb {
		1496	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1497	$_[0]{_ae_cb}
		1498	}
		1499
		1500	sub begin {
		1501	++$_[0]{_ae_counter};
		1502	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1503	}
		1504
		1505	sub end {
		1506	return if --$_[0]{_ae_counter};
		1507	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1508	}
		1509
		1510	# undocumented/compatibility with pre-3.4
		1511	*broadcast = \&send;
		1512	*wait = \&_wait;
		1513
		1514	=head1 ERROR AND EXCEPTION HANDLING
		1515
		1516	In general, AnyEvent does not do any error handling - it relies on the
		1517	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1518	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1519	checking of all AnyEvent methods, however, which is highly useful during
		1520	development.
		1521
		1522	As for exception handling (i.e. runtime errors and exceptions thrown while
		1523	executing a callback), this is not only highly event-loop specific, but
		1524	also not in any way wrapped by this module, as this is the job of the main
		1525	program.
		1526
		1527	The pure perl event loop simply re-throws the exception (usually
		1528	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1529	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1530	so on.
		1531
		1532	=head1 ENVIRONMENT VARIABLES
		1533
		1534	The following environment variables are used by this module or its
		1535	submodules.
		1536
		1537	Note that AnyEvent will remove I<all> environment variables starting with
		1538	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1539	enabled.
		1540
		1541	=over 4
		1542
		1543	=item C<PERL_ANYEVENT_VERBOSE>
		1544
		1545	By default, AnyEvent will be completely silent except in fatal
		1546	conditions. You can set this environment variable to make AnyEvent more
		1547	talkative.
		1548
		1549	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1550	conditions, such as not being able to load the event model specified by
		1551	C<PERL_ANYEVENT_MODEL>.
		1552
		1553	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1554	model it chooses.
		1555
		1556	=item C<PERL_ANYEVENT_STRICT>
		1557
		1558	AnyEvent does not do much argument checking by default, as thorough
		1559	argument checking is very costly. Setting this variable to a true value
		1560	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1561	check the arguments passed to most method calls. If it finds any problems,
		1562	it will croak.
		1563
		1564	In other words, enables "strict" mode.
		1565
		1566	Unlike C<use strict>, it is definitely recommended to keep it off in
		1567	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1568	developing programs can be very useful, however.
		1569
		1570	=item C<PERL_ANYEVENT_MODEL>
		1571
		1572	This can be used to specify the event model to be used by AnyEvent, before
		1573	auto detection and -probing kicks in. It must be a string consisting
		1574	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1575	and the resulting module name is loaded and if the load was successful,
		1576	used as event model. If it fails to load AnyEvent will proceed with
		1577	auto detection and -probing.
		1578
		1579	This functionality might change in future versions.
		1580
		1581	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1582	could start your program like this:
		1583
		1584	PERL_ANYEVENT_MODEL=Perl perl ...
		1585
		1586	=item C<PERL_ANYEVENT_PROTOCOLS>
		1587
		1588	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1589	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1590	of auto probing).
		1591
		1592	Must be set to a comma-separated list of protocols or address families,
		1593	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1594	used, and preference will be given to protocols mentioned earlier in the
		1595	list.
		1596
		1597	This variable can effectively be used for denial-of-service attacks
		1598	against local programs (e.g. when setuid), although the impact is likely
		1599	small, as the program has to handle conenction and other failures anyways.
		1600
		1601	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1602	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1603	- only support IPv4, never try to resolve or contact IPv6
		1604	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1605	IPv6, but prefer IPv6 over IPv4.
		1606
		1607	=item C<PERL_ANYEVENT_EDNS0>
		1608
		1609	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1610	for DNS. This extension is generally useful to reduce DNS traffic, but
		1611	some (broken) firewalls drop such DNS packets, which is why it is off by
		1612	default.
		1613
		1614	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1615	EDNS0 in its DNS requests.
		1616
		1617	=item C<PERL_ANYEVENT_MAX_FORKS>
		1618
		1619	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1620	will create in parallel.
		1621
		1622	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1623
		1624	The default value for the C<max_outstanding> parameter for the default DNS
		1625	resolver - this is the maximum number of parallel DNS requests that are
		1626	sent to the DNS server.
		1627
		1628	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1629
		1630	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1631	configuration) in the default resolver. When set to the empty string, no
		1632	default config will be used.
		1633
		1634	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1635
		1636	When neither C<ca_file> nor C<ca_path> was specified during
		1637	L<AnyEvent::TLS> context creation, and either of these environment
		1638	variables exist, they will be used to specify CA certificate locations
		1639	instead of a system-dependent default.
107		1640
108	=back	1641	=back
109		1642
		1643	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1644
		1645	This is an advanced topic that you do not normally need to use AnyEvent in
		1646	a module. This section is only of use to event loop authors who want to
		1647	provide AnyEvent compatibility.
		1648
		1649	If you need to support another event library which isn't directly
		1650	supported by AnyEvent, you can supply your own interface to it by
		1651	pushing, before the first watcher gets created, the package name of
		1652	the event module and the package name of the interface to use onto
		1653	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1654	AnyEvent, so it is reasonably cheap.
		1655
		1656	Example:
		1657
		1658	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1659
		1660	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1661	package/class when it finds the C<urxvt> package/module is already loaded.
		1662
		1663	When AnyEvent is loaded and asked to find a suitable event model, it
		1664	will first check for the presence of urxvt by trying to C<use> the
		1665	C<urxvt::anyevent> module.
		1666
		1667	The class should provide implementations for all watcher types. See
		1668	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1669	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1670	see the sources.
		1671
		1672	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1673	provide suitable (hopefully) replacements.
		1674
		1675	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1676	terminal emulator uses the above line as-is. An interface isn't included
		1677	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1678	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1679	I<rxvt-unicode> distribution.
		1680
		1681	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1682	condition variables: code blocking while waiting for a condition will
		1683	C<die>. This still works with most modules/usages, and blocking calls must
		1684	not be done in an interactive application, so it makes sense.
		1685
110	=head1 EXAMPLE	1686	=head1 EXAMPLE PROGRAM
111		1687
112	The following program uses an io watcher to read data from stdin, a timer	1688	The following program uses an I/O watcher to read data from STDIN, a timer
113	to display a message once per second, and a condvar to exit the program	1689	to display a message once per second, and a condition variable to quit the
114	when the user enters quit:	1690	program when the user enters quit:
115		1691
116	use AnyEvent;	1692	use AnyEvent;
117		1693
118	my $cv = AnyEvent->condvar;	1694	my $cv = AnyEvent->condvar;
119		1695
120	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1696	my $io_watcher = AnyEvent->io (
		1697	fh => \*STDIN,
		1698	poll => 'r',
		1699	cb => sub {
121	warn "io event <$_[0]>\n"; # will always output <r>	1700	warn "io event <$_[0]>\n"; # will always output <r>
122	chomp (my $input = <STDIN>); # read a line	1701	chomp (my $input = <STDIN>); # read a line
123	warn "read: $input\n"; # output what has been read	1702	warn "read: $input\n"; # output what has been read
124	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1703	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1704	},
125	});	1705	);
126		1706
127	my $time_watcher; # can only be used once	1707	my $time_watcher; # can only be used once
128		1708
129	sub new_timer {	1709	sub new_timer {
130	$timer = AnyEvent->timer (after => 1, cb => sub {	1710	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
133	});	1713	});
134	}	1714	}
135		1715
136	new_timer; # create first timer	1716	new_timer; # create first timer
137		1717
138	$cv->wait; # wait until user enters /^q/i	1718	$cv->recv; # wait until user enters /^q/i
		1719
		1720	=head1 REAL-WORLD EXAMPLE
		1721
		1722	Consider the L<Net::FCP> module. It features (among others) the following
		1723	API calls, which are to freenet what HTTP GET requests are to http:
		1724
		1725	my $data = $fcp->client_get ($url); # blocks
		1726
		1727	my $transaction = $fcp->txn_client_get ($url); # does not block
		1728	$transaction->cb ( sub { ... } ); # set optional result callback
		1729	my $data = $transaction->result; # possibly blocks
		1730
		1731	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		1732	given URL and waits till the data has arrived. It is defined to be:
		1733
		1734	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		1735
		1736	And in fact is automatically generated. This is the blocking API of
		1737	L<Net::FCP>, and it works as simple as in any other, similar, module.
		1738
		1739	More complicated is C<txn_client_get>: It only creates a transaction
		1740	(completion, result, ...) object and initiates the transaction.
		1741
		1742	my $txn = bless { }, Net::FCP::Txn::;
		1743
		1744	It also creates a condition variable that is used to signal the completion
		1745	of the request:
		1746
		1747	$txn->{finished} = AnyAvent->condvar;
		1748
		1749	It then creates a socket in non-blocking mode.
		1750
		1751	socket $txn->{fh}, ...;
		1752	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		1753	connect $txn->{fh}, ...
		1754	and !$!{EWOULDBLOCK}
		1755	and !$!{EINPROGRESS}
		1756	and Carp::croak "unable to connect: $!\n";
		1757
		1758	Then it creates a write-watcher which gets called whenever an error occurs
		1759	or the connection succeeds:
		1760
		1761	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		1762
		1763	And returns this transaction object. The C<fh_ready_w> callback gets
		1764	called as soon as the event loop detects that the socket is ready for
		1765	writing.
		1766
		1767	The C<fh_ready_w> method makes the socket blocking again, writes the
		1768	request data and replaces the watcher by a read watcher (waiting for reply
		1769	data). The actual code is more complicated, but that doesn't matter for
		1770	this example:
		1771
		1772	fcntl $txn->{fh}, F_SETFL, 0;
		1773	syswrite $txn->{fh}, $txn->{request}
		1774	or die "connection or write error";
		1775	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		1776
		1777	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		1778	result and signals any possible waiters that the request has finished:
		1779
		1780	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		1781
		1782	if (end-of-file or data complete) {
		1783	$txn->{result} = $txn->{buf};
		1784	$txn->{finished}->send;
		1785	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		1786	}
		1787
		1788	The C<result> method, finally, just waits for the finished signal (if the
		1789	request was already finished, it doesn't wait, of course, and returns the
		1790	data:
		1791
		1792	$txn->{finished}->recv;
		1793	return $txn->{result};
		1794
		1795	The actual code goes further and collects all errors (C<die>s, exceptions)
		1796	that occurred during request processing. The C<result> method detects
		1797	whether an exception as thrown (it is stored inside the $txn object)
		1798	and just throws the exception, which means connection errors and other
		1799	problems get reported tot he code that tries to use the result, not in a
		1800	random callback.
		1801
		1802	All of this enables the following usage styles:
		1803
		1804	1. Blocking:
		1805
		1806	my $data = $fcp->client_get ($url);
		1807
		1808	2. Blocking, but running in parallel:
		1809
		1810	my @datas = map $_->result,
		1811	map $fcp->txn_client_get ($_),
		1812	@urls;
		1813
		1814	Both blocking examples work without the module user having to know
		1815	anything about events.
		1816
		1817	3a. Event-based in a main program, using any supported event module:
		1818
		1819	use EV;
		1820
		1821	$fcp->txn_client_get ($url)->cb (sub {
		1822	my $txn = shift;
		1823	my $data = $txn->result;
		1824	...
		1825	});
		1826
		1827	EV::loop;
		1828
		1829	3b. The module user could use AnyEvent, too:
		1830
		1831	use AnyEvent;
		1832
		1833	my $quit = AnyEvent->condvar;
		1834
		1835	$fcp->txn_client_get ($url)->cb (sub {
		1836	...
		1837	$quit->send;
		1838	});
		1839
		1840	$quit->recv;
		1841
		1842
		1843	=head1 BENCHMARKS
		1844
		1845	To give you an idea of the performance and overheads that AnyEvent adds
		1846	over the event loops themselves and to give you an impression of the speed
		1847	of various event loops I prepared some benchmarks.
		1848
		1849	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1850
		1851	Here is a benchmark of various supported event models used natively and
		1852	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1853	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1854	which it is), lets them fire exactly once and destroys them again.
		1855
		1856	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1857	distribution.
		1858
		1859	=head3 Explanation of the columns
		1860
		1861	I<watcher> is the number of event watchers created/destroyed. Since
		1862	different event models feature vastly different performances, each event
		1863	loop was given a number of watchers so that overall runtime is acceptable
		1864	and similar between tested event loop (and keep them from crashing): Glib
		1865	would probably take thousands of years if asked to process the same number
		1866	of watchers as EV in this benchmark.
		1867
		1868	I<bytes> is the number of bytes (as measured by the resident set size,
		1869	RSS) consumed by each watcher. This method of measuring captures both C
		1870	and Perl-based overheads.
		1871
		1872	I<create> is the time, in microseconds (millionths of seconds), that it
		1873	takes to create a single watcher. The callback is a closure shared between
		1874	all watchers, to avoid adding memory overhead. That means closure creation
		1875	and memory usage is not included in the figures.
		1876
		1877	I<invoke> is the time, in microseconds, used to invoke a simple
		1878	callback. The callback simply counts down a Perl variable and after it was
		1879	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1880	signal the end of this phase.
		1881
		1882	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1883	watcher.
		1884
		1885	=head3 Results
		1886
		1887	name watchers bytes create invoke destroy comment
		1888	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1889	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1890	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1891	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1892	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1893	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1894	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1895	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
		1896	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1897	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1898	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1899	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1900
		1901	=head3 Discussion
		1902
		1903	The benchmark does I<not> measure scalability of the event loop very
		1904	well. For example, a select-based event loop (such as the pure perl one)
		1905	can never compete with an event loop that uses epoll when the number of
		1906	file descriptors grows high. In this benchmark, all events become ready at
		1907	the same time, so select/poll-based implementations get an unnatural speed
		1908	boost.
		1909
		1910	Also, note that the number of watchers usually has a nonlinear effect on
		1911	overall speed, that is, creating twice as many watchers doesn't take twice
		1912	the time - usually it takes longer. This puts event loops tested with a
		1913	higher number of watchers at a disadvantage.
		1914
		1915	To put the range of results into perspective, consider that on the
		1916	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1917	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1918	cycles with POE.
		1919
		1920	C<EV> is the sole leader regarding speed and memory use, which are both
		1921	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1922	far less memory than any other event loop and is still faster than Event
		1923	natively.
		1924
		1925	The pure perl implementation is hit in a few sweet spots (both the
		1926	constant timeout and the use of a single fd hit optimisations in the perl
		1927	interpreter and the backend itself). Nevertheless this shows that it
		1928	adds very little overhead in itself. Like any select-based backend its
		1929	performance becomes really bad with lots of file descriptors (and few of
		1930	them active), of course, but this was not subject of this benchmark.
		1931
		1932	The C<Event> module has a relatively high setup and callback invocation
		1933	cost, but overall scores in on the third place.
		1934
		1935	C<IO::Async> performs admirably well, about on par with C<Event>, even
		1936	when using its pure perl backend.
		1937
		1938	C<Glib>'s memory usage is quite a bit higher, but it features a
		1939	faster callback invocation and overall ends up in the same class as
		1940	C<Event>. However, Glib scales extremely badly, doubling the number of
		1941	watchers increases the processing time by more than a factor of four,
		1942	making it completely unusable when using larger numbers of watchers
		1943	(note that only a single file descriptor was used in the benchmark, so
		1944	inefficiencies of C<poll> do not account for this).
		1945
		1946	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1947	more than 2000 watchers is a big setback, however, as correctness takes
		1948	precedence over speed. Nevertheless, its performance is surprising, as the
		1949	file descriptor is dup()ed for each watcher. This shows that the dup()
		1950	employed by some adaptors is not a big performance issue (it does incur a
		1951	hidden memory cost inside the kernel which is not reflected in the figures
		1952	above).
		1953
		1954	C<POE>, regardless of underlying event loop (whether using its pure perl
		1955	select-based backend or the Event module, the POE-EV backend couldn't
		1956	be tested because it wasn't working) shows abysmal performance and
		1957	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1958	as EV watchers, and 10 times as much memory as Event (the high memory
		1959	requirements are caused by requiring a session for each watcher). Watcher
		1960	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1961	implementation.
		1962
		1963	The design of the POE adaptor class in AnyEvent can not really account
		1964	for the performance issues, though, as session creation overhead is
		1965	small compared to execution of the state machine, which is coded pretty
		1966	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1967	using multiple sessions is not a good approach, especially regarding
		1968	memory usage, even the author of POE could not come up with a faster
		1969	design).
		1970
		1971	=head3 Summary
		1972
		1973	=over 4
		1974
		1975	=item * Using EV through AnyEvent is faster than any other event loop
		1976	(even when used without AnyEvent), but most event loops have acceptable
		1977	performance with or without AnyEvent.
		1978
		1979	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1980	the actual event loop, only with extremely fast event loops such as EV
		1981	adds AnyEvent significant overhead.
		1982
		1983	=item * You should avoid POE like the plague if you want performance or
		1984	reasonable memory usage.
		1985
		1986	=back
		1987
		1988	=head2 BENCHMARKING THE LARGE SERVER CASE
		1989
		1990	This benchmark actually benchmarks the event loop itself. It works by
		1991	creating a number of "servers": each server consists of a socket pair, a
		1992	timeout watcher that gets reset on activity (but never fires), and an I/O
		1993	watcher waiting for input on one side of the socket. Each time the socket
		1994	watcher reads a byte it will write that byte to a random other "server".
		1995
		1996	The effect is that there will be a lot of I/O watchers, only part of which
		1997	are active at any one point (so there is a constant number of active
		1998	fds for each loop iteration, but which fds these are is random). The
		1999	timeout is reset each time something is read because that reflects how
		2000	most timeouts work (and puts extra pressure on the event loops).
		2001
		2002	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2003	(1%) are active. This mirrors the activity of large servers with many
		2004	connections, most of which are idle at any one point in time.
		2005
		2006	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2007	distribution.
		2008
		2009	=head3 Explanation of the columns
		2010
		2011	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2012	each server has a read and write socket end).
		2013
		2014	I<create> is the time it takes to create a socket pair (which is
		2015	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2016
		2017	I<request>, the most important value, is the time it takes to handle a
		2018	single "request", that is, reading the token from the pipe and forwarding
		2019	it to another server. This includes deleting the old timeout and creating
		2020	a new one that moves the timeout into the future.
		2021
		2022	=head3 Results
		2023
		2024	name sockets create request
		2025	EV 20000 69.01 11.16
		2026	Perl 20000 73.32 35.87
		2027	IOAsync 20000 157.00 98.14 epoll
		2028	IOAsync 20000 159.31 616.06 poll
		2029	Event 20000 212.62 257.32
		2030	Glib 20000 651.16 1896.30
		2031	POE 20000 349.67 12317.24 uses POE::Loop::Event
		2032
		2033	=head3 Discussion
		2034
		2035	This benchmark I<does> measure scalability and overall performance of the
		2036	particular event loop.
		2037
		2038	EV is again fastest. Since it is using epoll on my system, the setup time
		2039	is relatively high, though.
		2040
		2041	Perl surprisingly comes second. It is much faster than the C-based event
		2042	loops Event and Glib.
		2043
		2044	IO::Async performs very well when using its epoll backend, and still quite
		2045	good compared to Glib when using its pure perl backend.
		2046
		2047	Event suffers from high setup time as well (look at its code and you will
		2048	understand why). Callback invocation also has a high overhead compared to
		2049	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2050	uses select or poll in basically all documented configurations.
		2051
		2052	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2053	clearly fails to perform with many filehandles or in busy servers.
		2054
		2055	POE is still completely out of the picture, taking over 1000 times as long
		2056	as EV, and over 100 times as long as the Perl implementation, even though
		2057	it uses a C-based event loop in this case.
		2058
		2059	=head3 Summary
		2060
		2061	=over 4
		2062
		2063	=item * The pure perl implementation performs extremely well.
		2064
		2065	=item * Avoid Glib or POE in large projects where performance matters.
		2066
		2067	=back
		2068
		2069	=head2 BENCHMARKING SMALL SERVERS
		2070
		2071	While event loops should scale (and select-based ones do not...) even to
		2072	large servers, most programs we (or I :) actually write have only a few
		2073	I/O watchers.
		2074
		2075	In this benchmark, I use the same benchmark program as in the large server
		2076	case, but it uses only eight "servers", of which three are active at any
		2077	one time. This should reflect performance for a small server relatively
		2078	well.
		2079
		2080	The columns are identical to the previous table.
		2081
		2082	=head3 Results
		2083
		2084	name sockets create request
		2085	EV 16 20.00 6.54
		2086	Perl 16 25.75 12.62
		2087	Event 16 81.27 35.86
		2088	Glib 16 32.63 15.48
		2089	POE 16 261.87 276.28 uses POE::Loop::Event
		2090
		2091	=head3 Discussion
		2092
		2093	The benchmark tries to test the performance of a typical small
		2094	server. While knowing how various event loops perform is interesting, keep
		2095	in mind that their overhead in this case is usually not as important, due
		2096	to the small absolute number of watchers (that is, you need efficiency and
		2097	speed most when you have lots of watchers, not when you only have a few of
		2098	them).
		2099
		2100	EV is again fastest.
		2101
		2102	Perl again comes second. It is noticeably faster than the C-based event
		2103	loops Event and Glib, although the difference is too small to really
		2104	matter.
		2105
		2106	POE also performs much better in this case, but is is still far behind the
		2107	others.
		2108
		2109	=head3 Summary
		2110
		2111	=over 4
		2112
		2113	=item * C-based event loops perform very well with small number of
		2114	watchers, as the management overhead dominates.
		2115
		2116	=back
		2117
		2118	=head2 THE IO::Lambda BENCHMARK
		2119
		2120	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2121	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2122	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2123	shouldn't come as a surprise to anybody). As such, the benchmark is
		2124	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2125	very optimal. But how would AnyEvent compare when used without the extra
		2126	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2127
		2128	The benchmark itself creates an echo-server, and then, for 500 times,
		2129	connects to the echo server, sends a line, waits for the reply, and then
		2130	creates the next connection. This is a rather bad benchmark, as it doesn't
		2131	test the efficiency of the framework or much non-blocking I/O, but it is a
		2132	benchmark nevertheless.
		2133
		2134	name runtime
		2135	Lambda/select 0.330 sec
		2136	+ optimized 0.122 sec
		2137	Lambda/AnyEvent 0.327 sec
		2138	+ optimized 0.138 sec
		2139	Raw sockets/select 0.077 sec
		2140	POE/select, components 0.662 sec
		2141	POE/select, raw sockets 0.226 sec
		2142	POE/select, optimized 0.404 sec
		2143
		2144	AnyEvent/select/nb 0.085 sec
		2145	AnyEvent/EV/nb 0.068 sec
		2146	+state machine 0.134 sec
		2147
		2148	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2149	benchmarks actually make blocking connects and use 100% blocking I/O,
		2150	defeating the purpose of an event-based solution. All of the newly
		2151	written AnyEvent benchmarks use 100% non-blocking connects (using
		2152	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2153	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2154	generally require a lot more bookkeeping and event handling than blocking
		2155	connects (which involve a single syscall only).
		2156
		2157	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2158	offers similar expressive power as POE and IO::Lambda, using conventional
		2159	Perl syntax. This means that both the echo server and the client are 100%
		2160	non-blocking, further placing it at a disadvantage.
		2161
		2162	As you can see, the AnyEvent + EV combination even beats the
		2163	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2164	backend easily beats IO::Lambda and POE.
		2165
		2166	And even the 100% non-blocking version written using the high-level (and
		2167	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
		2168	large margin, even though it does all of DNS, tcp-connect and socket I/O
		2169	in a non-blocking way.
		2170
		2171	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2172	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2173	part of the IO::lambda distribution and were used without any changes.
		2174
		2175
		2176	=head1 SIGNALS
		2177
		2178	AnyEvent currently installs handlers for these signals:
		2179
		2180	=over 4
		2181
		2182	=item SIGCHLD
		2183
		2184	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2185	emulation for event loops that do not support them natively. Also, some
		2186	event loops install a similar handler.
		2187
		2188	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2189	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2190
		2191	=item SIGPIPE
		2192
		2193	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2194	when AnyEvent gets loaded.
		2195
		2196	The rationale for this is that AnyEvent users usually do not really depend
		2197	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2198	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2199	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2200	some random socket.
		2201
		2202	The rationale for installing a no-op handler as opposed to ignoring it is
		2203	that this way, the handler will be restored to defaults on exec.
		2204
		2205	Feel free to install your own handler, or reset it to defaults.
		2206
		2207	=back
		2208
		2209	=cut
		2210
		2211	undef $SIG{CHLD}
		2212	if $SIG{CHLD} eq 'IGNORE';
		2213
		2214	$SIG{PIPE} = sub { }
		2215	unless defined $SIG{PIPE};
		2216
		2217	=head1 RECOMMENDED/OPTIONAL MODULES
		2218
		2219	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2220	it's built-in modules) are required to use it.
		2221
		2222	That does not mean that AnyEvent won't take advantage of some additional
		2223	modules if they are installed.
		2224
		2225	This section epxlains which additional modules will be used, and how they
		2226	affect AnyEvent's operetion.
		2227
		2228	=over 4
		2229
		2230	=item L<Async::Interrupt>
		2231
		2232	This slightly arcane module is used to implement fast signal handling: To
		2233	my knowledge, there is no way to do completely race-free and quick
		2234	signal handling in pure perl. To ensure that signals still get
		2235	delivered, AnyEvent will start an interval timer to wake up perl (and
		2236	catch the signals) with soemd elay (default is 10 seconds, look for
		2237	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2238
		2239	If this module is available, then it will be used to implement signal
		2240	catching, which means that signals will not be delayed, and the event loop
		2241	will not be interrupted regularly, which is more efficient (And good for
		2242	battery life on laptops).
		2243
		2244	This affects not just the pure-perl event loop, but also other event loops
		2245	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2246
		2247	=item L<EV>
		2248
		2249	This module isn't really "optional", as it is simply one of the backend
		2250	event loops that AnyEvent can use. However, it is simply the best event
		2251	loop available in terms of features, speed and stability: It supports
		2252	the AnyEvent API optimally, implements all the watcher types in XS, does
		2253	automatic timer adjustments even when no monotonic clock is available,
		2254	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2255	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2256	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2257
		2258	=item L<Guard>
		2259
		2260	The guard module, when used, will be used to implement
		2261	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2262	lot less memory), but otherwise doesn't affect guard operation much. It is
		2263	purely used for performance.
		2264
		2265	=item L<JSON> and L<JSON::XS>
		2266
		2267	This module is required when you want to read or write JSON data via
		2268	L<AnyEvent::Handle>. It is also written in pure-perl, but can take
		2269	advantage of the ulta-high-speed L<JSON::XS> module when it is installed.
		2270
		2271	In fact, L<AnyEvent::Handle> will use L<JSON::XS> by default if it is
		2272	installed.
		2273
		2274	=item L<Net::SSLeay>
		2275
		2276	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2277	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2278	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2279
		2280	=item L<Time::HiRes>
		2281
		2282	This module is part of perl since release 5.008. It will be used when the
		2283	chosen event library does not come with a timing source on it's own. The
		2284	pure-perl event loop (L<AnyEvent::Impl::Perl>) will additionally use it to
		2285	try to use a monotonic clock for timing stability.
		2286
		2287	=back
		2288
		2289
		2290	=head1 FORK
		2291
		2292	Most event libraries are not fork-safe. The ones who are usually are
		2293	because they rely on inefficient but fork-safe C<select> or C<poll>
		2294	calls. Only L<EV> is fully fork-aware.
		2295
		2296	If you have to fork, you must either do so I<before> creating your first
		2297	watcher OR you must not use AnyEvent at all in the child OR you must do
		2298	something completely out of the scope of AnyEvent.
		2299
		2300
		2301	=head1 SECURITY CONSIDERATIONS
		2302
		2303	AnyEvent can be forced to load any event model via
		2304	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2305	execute arbitrary code or directly gain access, it can easily be used to
		2306	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2307	will not be active when the program uses a different event model than
		2308	specified in the variable.
		2309
		2310	You can make AnyEvent completely ignore this variable by deleting it
		2311	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2312
		2313	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2314
		2315	use AnyEvent;
		2316
		2317	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2318	be used to probe what backend is used and gain other information (which is
		2319	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2320	$ENV{PERL_ANYEVENT_STRICT}.
		2321
		2322	Note that AnyEvent will remove I<all> environment variables starting with
		2323	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2324	enabled.
		2325
		2326
		2327	=head1 BUGS
		2328
		2329	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2330	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2331	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2332	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2333	pronounced).
		2334
139		2335
140	=head1 SEE ALSO	2336	=head1 SEE ALSO
141		2337
142	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	2338	Utility functions: L<AnyEvent::Util>.
143	L<AnyEvent::Impl::Coro>,	2339
144	L<AnyEvent::Impl::Event>,	2340	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
145	L<AnyEvent::Impl::Glib>,	2341	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		2342
		2343	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2344	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2345	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2346	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>.
		2347
		2348	Non-blocking file handles, sockets, TCP clients and
		2349	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2350
		2351	Asynchronous DNS: L<AnyEvent::DNS>.
		2352
		2353	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>,
		2354	L<Coro::Event>,
		2355
		2356	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::XMPP>,
146	L<AnyEvent::Impl::Tk>.	2357	L<AnyEvent::HTTP>.
147		2358
148	=head1	2359
		2360	=head1 AUTHOR
		2361
		2362	Marc Lehmann <schmorp@schmorp.de>
		2363	http://home.schmorp.de/
149		2364
150	=cut	2365	=cut
151		2366
152	1	2367	1
153		2368

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