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Revision 1.373 by root, Thu Aug 25 03:08:48 2011 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - ???	3	AnyEvent - the DBI of event loop programming
		4
		5	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, Qt,
		6	FLTK and POE are various supported event loops/environments.
4		7
5	=head1 SYNOPSIS	8	=head1 SYNOPSIS
6		9
		10	use AnyEvent;
		11
		12	# if you prefer function calls, look at the AE manpage for
		13	# an alternative API.
		14
		15	# file handle or descriptor readable
		16	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		17
		18	# one-shot or repeating timers
		19	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		20	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
		21
		22	print AnyEvent->now; # prints current event loop time
		23	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		24
		25	# POSIX signal
		26	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		27
		28	# child process exit
		29	my $w = AnyEvent->child (pid => $pid, cb => sub {
		30	my ($pid, $status) = @_;
		31	...
		32	});
		33
		34	# called when event loop idle (if applicable)
		35	my $w = AnyEvent->idle (cb => sub { ... });
		36
		37	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		38	$w->send; # wake up current and all future recv's
		39	$w->recv; # enters "main loop" till $condvar gets ->send
		40	# use a condvar in callback mode:
		41	$w->cb (sub { $_[0]->recv });
		42
		43	=head1 INTRODUCTION/TUTORIAL
		44
		45	This manpage is mainly a reference manual. If you are interested
		46	in a tutorial or some gentle introduction, have a look at the
		47	L<AnyEvent::Intro> manpage.
		48
		49	=head1 SUPPORT
		50
		51	An FAQ document is available as L<AnyEvent::FAQ>.
		52
		53	There also is a mailinglist for discussing all things AnyEvent, and an IRC
		54	channel, too.
		55
		56	See the AnyEvent project page at the B<Schmorpforge Ta-Sa Software
		57	Repository>, at L<http://anyevent.schmorp.de>, for more info.
		58
		59	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		60
		61	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		62	nowadays. So what is different about AnyEvent?
		63
		64	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		65	policy> and AnyEvent is I<small and efficient>.
		66
		67	First and foremost, I<AnyEvent is not an event model> itself, it only
		68	interfaces to whatever event model the main program happens to use, in a
		69	pragmatic way. For event models and certain classes of immortals alike,
		70	the statement "there can only be one" is a bitter reality: In general,
		71	only one event loop can be active at the same time in a process. AnyEvent
		72	cannot change this, but it can hide the differences between those event
		73	loops.
		74
		75	The goal of AnyEvent is to offer module authors the ability to do event
		76	programming (waiting for I/O or timer events) without subscribing to a
		77	religion, a way of living, and most importantly: without forcing your
		78	module users into the same thing by forcing them to use the same event
		79	model you use.
		80
		81	For modules like POE or IO::Async (which is a total misnomer as it is
		82	actually doing all I/O I<synchronously>...), using them in your module is
		83	like joining a cult: After you join, you are dependent on them and you
		84	cannot use anything else, as they are simply incompatible to everything
		85	that isn't them. What's worse, all the potential users of your
		86	module are I<also> forced to use the same event loop you use.
		87
		88	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		89	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		90	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
		91	uses one of those, every user of your module has to use it, too. But if
		92	your module uses AnyEvent, it works transparently with all event models it
		93	supports (including stuff like IO::Async, as long as those use one of the
		94	supported event loops. It is easy to add new event loops to AnyEvent, too,
		95	so it is future-proof).
		96
		97	In addition to being free of having to use I<the one and only true event
		98	model>, AnyEvent also is free of bloat and policy: with POE or similar
		99	modules, you get an enormous amount of code and strict rules you have to
		100	follow. AnyEvent, on the other hand, is lean and to the point, by only
		101	offering the functionality that is necessary, in as thin as a wrapper as
		102	technically possible.
		103
		104	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		105	of useful functionality, such as an asynchronous DNS resolver, 100%
		106	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		107	such as Windows) and lots of real-world knowledge and workarounds for
		108	platform bugs and differences.
		109
		110	Now, if you I<do want> lots of policy (this can arguably be somewhat
		111	useful) and you want to force your users to use the one and only event
		112	model, you should I<not> use this module.
		113
7	=head1 DESCRIPTION	114	=head1 DESCRIPTION
8		115
		116	L<AnyEvent> provides a uniform interface to various event loops. This
		117	allows module authors to use event loop functionality without forcing
		118	module users to use a specific event loop implementation (since more
		119	than one event loop cannot coexist peacefully).
		120
		121	The interface itself is vaguely similar, but not identical to the L<Event>
		122	module.
		123
		124	During the first call of any watcher-creation method, the module tries
		125	to detect the currently loaded event loop by probing whether one of the
		126	following modules is already loaded: L<EV>, L<AnyEvent::Loop>,
		127	L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>. The first one
		128	found is used. If none are detected, the module tries to load the first
		129	four modules in the order given; but note that if L<EV> is not
		130	available, the pure-perl L<AnyEvent::Loop> should always work, so
		131	the other two are not normally tried.
		132
		133	Because AnyEvent first checks for modules that are already loaded, loading
		134	an event model explicitly before first using AnyEvent will likely make
		135	that model the default. For example:
		136
		137	use Tk;
		138	use AnyEvent;
		139
		140	# .. AnyEvent will likely default to Tk
		141
		142	The I<likely> means that, if any module loads another event model and
		143	starts using it, all bets are off - this case should be very rare though,
		144	as very few modules hardcode event loops without announcing this very
		145	loudly.
		146
		147	The pure-perl implementation of AnyEvent is called C<AnyEvent::Loop>. Like
		148	other event modules you can load it explicitly and enjoy the high
		149	availability of that event loop :)
		150
		151	=head1 WATCHERS
		152
		153	AnyEvent has the central concept of a I<watcher>, which is an object that
		154	stores relevant data for each kind of event you are waiting for, such as
		155	the callback to call, the file handle to watch, etc.
		156
		157	These watchers are normal Perl objects with normal Perl lifetime. After
		158	creating a watcher it will immediately "watch" for events and invoke the
		159	callback when the event occurs (of course, only when the event model
		160	is in control).
		161
		162	Note that B<callbacks must not permanently change global variables>
		163	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		164	callbacks must not C<die> >>. The former is good programming practice in
		165	Perl and the latter stems from the fact that exception handling differs
		166	widely between event loops.
		167
		168	To disable a watcher you have to destroy it (e.g. by setting the
		169	variable you store it in to C<undef> or otherwise deleting all references
		170	to it).
		171
		172	All watchers are created by calling a method on the C<AnyEvent> class.
		173
		174	Many watchers either are used with "recursion" (repeating timers for
		175	example), or need to refer to their watcher object in other ways.
		176
		177	One way to achieve that is this pattern:
		178
		179	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		180	# you can use $w here, for example to undef it
		181	undef $w;
		182	});
		183
		184	Note that C<my $w; $w => combination. This is necessary because in Perl,
		185	my variables are only visible after the statement in which they are
		186	declared.
		187
		188	=head2 I/O WATCHERS
		189
		190	$w = AnyEvent->io (
		191	fh => <filehandle_or_fileno>,
		192	poll => <"r" or "w">,
		193	cb => <callback>,
		194	);
		195
		196	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		197	with the following mandatory key-value pairs as arguments:
		198
		199	C<fh> is the Perl I<file handle> (or a naked file descriptor) to watch
		200	for events (AnyEvent might or might not keep a reference to this file
		201	handle). Note that only file handles pointing to things for which
		202	non-blocking operation makes sense are allowed. This includes sockets,
		203	most character devices, pipes, fifos and so on, but not for example files
		204	or block devices.
		205
		206	C<poll> must be a string that is either C<r> or C<w>, which creates a
		207	watcher waiting for "r"eadable or "w"ritable events, respectively.
		208
		209	C<cb> is the callback to invoke each time the file handle becomes ready.
		210
		211	Although the callback might get passed parameters, their value and
		212	presence is undefined and you cannot rely on them. Portable AnyEvent
		213	callbacks cannot use arguments passed to I/O watcher callbacks.
		214
		215	The I/O watcher might use the underlying file descriptor or a copy of it.
		216	You must not close a file handle as long as any watcher is active on the
		217	underlying file descriptor.
		218
		219	Some event loops issue spurious readiness notifications, so you should
		220	always use non-blocking calls when reading/writing from/to your file
		221	handles.
		222
		223	Example: wait for readability of STDIN, then read a line and disable the
		224	watcher.
		225
		226	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		227	chomp (my $input = <STDIN>);
		228	warn "read: $input\n";
		229	undef $w;
		230	});
		231
		232	=head2 TIME WATCHERS
		233
		234	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		235
		236	$w = AnyEvent->timer (
		237	after => <fractional_seconds>,
		238	interval => <fractional_seconds>,
		239	cb => <callback>,
		240	);
		241
		242	You can create a time watcher by calling the C<< AnyEvent->timer >>
		243	method with the following mandatory arguments:
		244
		245	C<after> specifies after how many seconds (fractional values are
		246	supported) the callback should be invoked. C<cb> is the callback to invoke
		247	in that case.
		248
		249	Although the callback might get passed parameters, their value and
		250	presence is undefined and you cannot rely on them. Portable AnyEvent
		251	callbacks cannot use arguments passed to time watcher callbacks.
		252
		253	The callback will normally be invoked only once. If you specify another
		254	parameter, C<interval>, as a strictly positive number (> 0), then the
		255	callback will be invoked regularly at that interval (in fractional
		256	seconds) after the first invocation. If C<interval> is specified with a
		257	false value, then it is treated as if it were not specified at all.
		258
		259	The callback will be rescheduled before invoking the callback, but no
		260	attempt is made to avoid timer drift in most backends, so the interval is
		261	only approximate.
		262
		263	Example: fire an event after 7.7 seconds.
		264
		265	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		266	warn "timeout\n";
		267	});
		268
		269	# to cancel the timer:
		270	undef $w;
		271
		272	Example 2: fire an event after 0.5 seconds, then roughly every second.
		273
		274	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		275	warn "timeout\n";
		276	};
		277
		278	=head3 TIMING ISSUES
		279
		280	There are two ways to handle timers: based on real time (relative, "fire
		281	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		282	o'clock").
		283
		284	While most event loops expect timers to specified in a relative way, they
		285	use absolute time internally. This makes a difference when your clock
		286	"jumps", for example, when ntp decides to set your clock backwards from
		287	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		288	fire "after a second" might actually take six years to finally fire.
		289
		290	AnyEvent cannot compensate for this. The only event loop that is conscious
		291	of these issues is L<EV>, which offers both relative (ev_timer, based
		292	on true relative time) and absolute (ev_periodic, based on wallclock time)
		293	timers.
		294
		295	AnyEvent always prefers relative timers, if available, matching the
		296	AnyEvent API.
		297
		298	AnyEvent has two additional methods that return the "current time":
		299
9	=over 4	300	=over 4
10		301
		302	=item AnyEvent->time
		303
		304	This returns the "current wallclock time" as a fractional number of
		305	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		306	return, and the result is guaranteed to be compatible with those).
		307
		308	It progresses independently of any event loop processing, i.e. each call
		309	will check the system clock, which usually gets updated frequently.
		310
		311	=item AnyEvent->now
		312
		313	This also returns the "current wallclock time", but unlike C<time>, above,
		314	this value might change only once per event loop iteration, depending on
		315	the event loop (most return the same time as C<time>, above). This is the
		316	time that AnyEvent's timers get scheduled against.
		317
		318	I<In almost all cases (in all cases if you don't care), this is the
		319	function to call when you want to know the current time.>
		320
		321	This function is also often faster then C<< AnyEvent->time >>, and
		322	thus the preferred method if you want some timestamp (for example,
		323	L<AnyEvent::Handle> uses this to update its activity timeouts).
		324
		325	The rest of this section is only of relevance if you try to be very exact
		326	with your timing; you can skip it without a bad conscience.
		327
		328	For a practical example of when these times differ, consider L<Event::Lib>
		329	and L<EV> and the following set-up:
		330
		331	The event loop is running and has just invoked one of your callbacks at
		332	time=500 (assume no other callbacks delay processing). In your callback,
		333	you wait a second by executing C<sleep 1> (blocking the process for a
		334	second) and then (at time=501) you create a relative timer that fires
		335	after three seconds.
		336
		337	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		338	both return C<501>, because that is the current time, and the timer will
		339	be scheduled to fire at time=504 (C<501> + C<3>).
		340
		341	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		342	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		343	last event processing phase started. With L<EV>, your timer gets scheduled
		344	to run at time=503 (C<500> + C<3>).
		345
		346	In one sense, L<Event::Lib> is more exact, as it uses the current time
		347	regardless of any delays introduced by event processing. However, most
		348	callbacks do not expect large delays in processing, so this causes a
		349	higher drift (and a lot more system calls to get the current time).
		350
		351	In another sense, L<EV> is more exact, as your timer will be scheduled at
		352	the same time, regardless of how long event processing actually took.
		353
		354	In either case, if you care (and in most cases, you don't), then you
		355	can get whatever behaviour you want with any event loop, by taking the
		356	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		357	account.
		358
		359	=item AnyEvent->now_update
		360
		361	Some event loops (such as L<EV> or L<AnyEvent::Loop>) cache the current
		362	time for each loop iteration (see the discussion of L<< AnyEvent->now >>,
		363	above).
		364
		365	When a callback runs for a long time (or when the process sleeps), then
		366	this "current" time will differ substantially from the real time, which
		367	might affect timers and time-outs.
		368
		369	When this is the case, you can call this method, which will update the
		370	event loop's idea of "current time".
		371
		372	A typical example would be a script in a web server (e.g. C<mod_perl>) -
		373	when mod_perl executes the script, then the event loop will have the wrong
		374	idea about the "current time" (being potentially far in the past, when the
		375	script ran the last time). In that case you should arrange a call to C<<
		376	AnyEvent->now_update >> each time the web server process wakes up again
		377	(e.g. at the start of your script, or in a handler).
		378
		379	Note that updating the time I<might> cause some events to be handled.
		380
		381	=back
		382
		383	=head2 SIGNAL WATCHERS
		384
		385	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		386
		387	You can watch for signals using a signal watcher, C<signal> is the signal
		388	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		389	callback to be invoked whenever a signal occurs.
		390
		391	Although the callback might get passed parameters, their value and
		392	presence is undefined and you cannot rely on them. Portable AnyEvent
		393	callbacks cannot use arguments passed to signal watcher callbacks.
		394
		395	Multiple signal occurrences can be clumped together into one callback
		396	invocation, and callback invocation will be synchronous. Synchronous means
		397	that it might take a while until the signal gets handled by the process,
		398	but it is guaranteed not to interrupt any other callbacks.
		399
		400	The main advantage of using these watchers is that you can share a signal
		401	between multiple watchers, and AnyEvent will ensure that signals will not
		402	interrupt your program at bad times.
		403
		404	This watcher might use C<%SIG> (depending on the event loop used),
		405	so programs overwriting those signals directly will likely not work
		406	correctly.
		407
		408	Example: exit on SIGINT
		409
		410	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		411
		412	=head3 Restart Behaviour
		413
		414	While restart behaviour is up to the event loop implementation, most will
		415	not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
		416	pure perl implementation).
		417
		418	=head3 Safe/Unsafe Signals
		419
		420	Perl signals can be either "safe" (synchronous to opcode handling) or
		421	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		422	latter might corrupt your memory.
		423
		424	AnyEvent signal handlers are, in addition, synchronous to the event loop,
		425	i.e. they will not interrupt your running perl program but will only be
		426	called as part of the normal event handling (just like timer, I/O etc.
		427	callbacks, too).
		428
		429	=head3 Signal Races, Delays and Workarounds
		430
		431	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		432	callbacks to signals in a generic way, which is a pity, as you cannot
		433	do race-free signal handling in perl, requiring C libraries for
		434	this. AnyEvent will try to do its best, which means in some cases,
		435	signals will be delayed. The maximum time a signal might be delayed is
		436	specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10 seconds). This
		437	variable can be changed only before the first signal watcher is created,
		438	and should be left alone otherwise. This variable determines how often
		439	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		440	will cause fewer spurious wake-ups, which is better for power and CPU
		441	saving.
		442
		443	All these problems can be avoided by installing the optional
		444	L<Async::Interrupt> module, which works with most event loops. It will not
		445	work with inherently broken event loops such as L<Event> or L<Event::Lib>
		446	(and not with L<POE> currently, as POE does its own workaround with
		447	one-second latency). For those, you just have to suffer the delays.
		448
		449	=head2 CHILD PROCESS WATCHERS
		450
		451	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		452
		453	You can also watch for a child process exit and catch its exit status.
		454
		455	The child process is specified by the C<pid> argument (on some backends,
		456	using C<0> watches for any child process exit, on others this will
		457	croak). The watcher will be triggered only when the child process has
		458	finished and an exit status is available, not on any trace events
		459	(stopped/continued).
		460
		461	The callback will be called with the pid and exit status (as returned by
		462	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		463	callback arguments.
		464
		465	This watcher type works by installing a signal handler for C<SIGCHLD>,
		466	and since it cannot be shared, nothing else should use SIGCHLD or reap
		467	random child processes (waiting for specific child processes, e.g. inside
		468	C<system>, is just fine).
		469
		470	There is a slight catch to child watchers, however: you usually start them
		471	I<after> the child process was created, and this means the process could
		472	have exited already (and no SIGCHLD will be sent anymore).
		473
		474	Not all event models handle this correctly (neither POE nor IO::Async do,
		475	see their AnyEvent::Impl manpages for details), but even for event models
		476	that I<do> handle this correctly, they usually need to be loaded before
		477	the process exits (i.e. before you fork in the first place). AnyEvent's
		478	pure perl event loop handles all cases correctly regardless of when you
		479	start the watcher.
		480
		481	This means you cannot create a child watcher as the very first
		482	thing in an AnyEvent program, you I<have> to create at least one
		483	watcher before you C<fork> the child (alternatively, you can call
		484	C<AnyEvent::detect>).
		485
		486	As most event loops do not support waiting for child events, they will be
		487	emulated by AnyEvent in most cases, in which case the latency and race
		488	problems mentioned in the description of signal watchers apply.
		489
		490	Example: fork a process and wait for it
		491
		492	my $done = AnyEvent->condvar;
		493
		494	my $pid = fork or exit 5;
		495
		496	my $w = AnyEvent->child (
		497	pid => $pid,
		498	cb => sub {
		499	my ($pid, $status) = @_;
		500	warn "pid $pid exited with status $status";
		501	$done->send;
		502	},
		503	);
		504
		505	# do something else, then wait for process exit
		506	$done->recv;
		507
		508	=head2 IDLE WATCHERS
		509
		510	$w = AnyEvent->idle (cb => <callback>);
		511
		512	This will repeatedly invoke the callback after the process becomes idle,
		513	until either the watcher is destroyed or new events have been detected.
		514
		515	Idle watchers are useful when there is a need to do something, but it
		516	is not so important (or wise) to do it instantly. The callback will be
		517	invoked only when there is "nothing better to do", which is usually
		518	defined as "all outstanding events have been handled and no new events
		519	have been detected". That means that idle watchers ideally get invoked
		520	when the event loop has just polled for new events but none have been
		521	detected. Instead of blocking to wait for more events, the idle watchers
		522	will be invoked.
		523
		524	Unfortunately, most event loops do not really support idle watchers (only
		525	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		526	will simply call the callback "from time to time".
		527
		528	Example: read lines from STDIN, but only process them when the
		529	program is otherwise idle:
		530
		531	my @lines; # read data
		532	my $idle_w;
		533	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		534	push @lines, scalar <STDIN>;
		535
		536	# start an idle watcher, if not already done
		537	$idle_w ||= AnyEvent->idle (cb => sub {
		538	# handle only one line, when there are lines left
		539	if (my $line = shift @lines) {
		540	print "handled when idle: $line";
		541	} else {
		542	# otherwise disable the idle watcher again
		543	undef $idle_w;
		544	}
		545	});
		546	});
		547
		548	=head2 CONDITION VARIABLES
		549
		550	$cv = AnyEvent->condvar;
		551
		552	$cv->send (<list>);
		553	my @res = $cv->recv;
		554
		555	If you are familiar with some event loops you will know that all of them
		556	require you to run some blocking "loop", "run" or similar function that
		557	will actively watch for new events and call your callbacks.
		558
		559	AnyEvent is slightly different: it expects somebody else to run the event
		560	loop and will only block when necessary (usually when told by the user).
		561
		562	The tool to do that is called a "condition variable", so called because
		563	they represent a condition that must become true.
		564
		565	Now is probably a good time to look at the examples further below.
		566
		567	Condition variables can be created by calling the C<< AnyEvent->condvar
		568	>> method, usually without arguments. The only argument pair allowed is
		569	C<cb>, which specifies a callback to be called when the condition variable
		570	becomes true, with the condition variable as the first argument (but not
		571	the results).
		572
		573	After creation, the condition variable is "false" until it becomes "true"
		574	by calling the C<send> method (or calling the condition variable as if it
		575	were a callback, read about the caveats in the description for the C<<
		576	->send >> method).
		577
		578	Since condition variables are the most complex part of the AnyEvent API, here are
		579	some different mental models of what they are - pick the ones you can connect to:
		580
		581	=over 4
		582
		583	=item * Condition variables are like callbacks - you can call them (and pass them instead
		584	of callbacks). Unlike callbacks however, you can also wait for them to be called.
		585
		586	=item * Condition variables are signals - one side can emit or send them,
		587	the other side can wait for them, or install a handler that is called when
		588	the signal fires.
		589
		590	=item * Condition variables are like "Merge Points" - points in your program
		591	where you merge multiple independent results/control flows into one.
		592
		593	=item * Condition variables represent a transaction - functions that start
		594	some kind of transaction can return them, leaving the caller the choice
		595	between waiting in a blocking fashion, or setting a callback.
		596
		597	=item * Condition variables represent future values, or promises to deliver
		598	some result, long before the result is available.
		599
		600	=back
		601
		602	Condition variables are very useful to signal that something has finished,
		603	for example, if you write a module that does asynchronous http requests,
		604	then a condition variable would be the ideal candidate to signal the
		605	availability of results. The user can either act when the callback is
		606	called or can synchronously C<< ->recv >> for the results.
		607
		608	You can also use them to simulate traditional event loops - for example,
		609	you can block your main program until an event occurs - for example, you
		610	could C<< ->recv >> in your main program until the user clicks the Quit
		611	button of your app, which would C<< ->send >> the "quit" event.
		612
		613	Note that condition variables recurse into the event loop - if you have
		614	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		615	lose. Therefore, condition variables are good to export to your caller, but
		616	you should avoid making a blocking wait yourself, at least in callbacks,
		617	as this asks for trouble.
		618
		619	Condition variables are represented by hash refs in perl, and the keys
		620	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		621	easy (it is often useful to build your own transaction class on top of
		622	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		623	its C<new> method in your own C<new> method.
		624
		625	There are two "sides" to a condition variable - the "producer side" which
		626	eventually calls C<< -> send >>, and the "consumer side", which waits
		627	for the send to occur.
		628
		629	Example: wait for a timer.
		630
		631	# condition: "wait till the timer is fired"
		632	my $timer_fired = AnyEvent->condvar;
		633
		634	# create the timer - we could wait for, say
		635	# a handle becomign ready, or even an
		636	# AnyEvent::HTTP request to finish, but
		637	# in this case, we simply use a timer:
		638	my $w = AnyEvent->timer (
		639	after => 1,
		640	cb => sub { $timer_fired->send },
		641	);
		642
		643	# this "blocks" (while handling events) till the callback
		644	# calls ->send
		645	$timer_fired->recv;
		646
		647	Example: wait for a timer, but take advantage of the fact that condition
		648	variables are also callable directly.
		649
		650	my $done = AnyEvent->condvar;
		651	my $delay = AnyEvent->timer (after => 5, cb => $done);
		652	$done->recv;
		653
		654	Example: Imagine an API that returns a condvar and doesn't support
		655	callbacks. This is how you make a synchronous call, for example from
		656	the main program:
		657
		658	use AnyEvent::CouchDB;
		659
		660	...
		661
		662	my @info = $couchdb->info->recv;
		663
		664	And this is how you would just set a callback to be called whenever the
		665	results are available:
		666
		667	$couchdb->info->cb (sub {
		668	my @info = $_[0]->recv;
		669	});
		670
		671	=head3 METHODS FOR PRODUCERS
		672
		673	These methods should only be used by the producing side, i.e. the
		674	code/module that eventually sends the signal. Note that it is also
		675	the producer side which creates the condvar in most cases, but it isn't
		676	uncommon for the consumer to create it as well.
		677
		678	=over 4
		679
		680	=item $cv->send (...)
		681
		682	Flag the condition as ready - a running C<< ->recv >> and all further
		683	calls to C<recv> will (eventually) return after this method has been
		684	called. If nobody is waiting the send will be remembered.
		685
		686	If a callback has been set on the condition variable, it is called
		687	immediately from within send.
		688
		689	Any arguments passed to the C<send> call will be returned by all
		690	future C<< ->recv >> calls.
		691
		692	Condition variables are overloaded so one can call them directly (as if
		693	they were a code reference). Calling them directly is the same as calling
		694	C<send>.
		695
		696	=item $cv->croak ($error)
		697
		698	Similar to send, but causes all calls to C<< ->recv >> to invoke
		699	C<Carp::croak> with the given error message/object/scalar.
		700
		701	This can be used to signal any errors to the condition variable
		702	user/consumer. Doing it this way instead of calling C<croak> directly
		703	delays the error detection, but has the overwhelming advantage that it
		704	diagnoses the error at the place where the result is expected, and not
		705	deep in some event callback with no connection to the actual code causing
		706	the problem.
		707
		708	=item $cv->begin ([group callback])
		709
		710	=item $cv->end
		711
		712	These two methods can be used to combine many transactions/events into
		713	one. For example, a function that pings many hosts in parallel might want
		714	to use a condition variable for the whole process.
		715
		716	Every call to C<< ->begin >> will increment a counter, and every call to
		717	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		718	>>, the (last) callback passed to C<begin> will be executed, passing the
		719	condvar as first argument. That callback is I<supposed> to call C<< ->send
		720	>>, but that is not required. If no group callback was set, C<send> will
		721	be called without any arguments.
		722
		723	You can think of C<< $cv->send >> giving you an OR condition (one call
		724	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		725	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		726
		727	Let's start with a simple example: you have two I/O watchers (for example,
		728	STDOUT and STDERR for a program), and you want to wait for both streams to
		729	close before activating a condvar:
		730
		731	my $cv = AnyEvent->condvar;
		732
		733	$cv->begin; # first watcher
		734	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		735	defined sysread $fh1, my $buf, 4096
		736	or $cv->end;
		737	});
		738
		739	$cv->begin; # second watcher
		740	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		741	defined sysread $fh2, my $buf, 4096
		742	or $cv->end;
		743	});
		744
		745	$cv->recv;
		746
		747	This works because for every event source (EOF on file handle), there is
		748	one call to C<begin>, so the condvar waits for all calls to C<end> before
		749	sending.
		750
		751	The ping example mentioned above is slightly more complicated, as the
		752	there are results to be passwd back, and the number of tasks that are
		753	begun can potentially be zero:
		754
		755	my $cv = AnyEvent->condvar;
		756
		757	my %result;
		758	$cv->begin (sub { shift->send (\%result) });
		759
		760	for my $host (@list_of_hosts) {
		761	$cv->begin;
		762	ping_host_then_call_callback $host, sub {
		763	$result{$host} = ...;
		764	$cv->end;
		765	};
		766	}
		767
		768	$cv->end;
		769
		770	This code fragment supposedly pings a number of hosts and calls
		771	C<send> after results for all then have have been gathered - in any
		772	order. To achieve this, the code issues a call to C<begin> when it starts
		773	each ping request and calls C<end> when it has received some result for
		774	it. Since C<begin> and C<end> only maintain a counter, the order in which
		775	results arrive is not relevant.
		776
		777	There is an additional bracketing call to C<begin> and C<end> outside the
		778	loop, which serves two important purposes: first, it sets the callback
		779	to be called once the counter reaches C<0>, and second, it ensures that
		780	C<send> is called even when C<no> hosts are being pinged (the loop
		781	doesn't execute once).
		782
		783	This is the general pattern when you "fan out" into multiple (but
		784	potentially zero) subrequests: use an outer C<begin>/C<end> pair to set
		785	the callback and ensure C<end> is called at least once, and then, for each
		786	subrequest you start, call C<begin> and for each subrequest you finish,
		787	call C<end>.
		788
		789	=back
		790
		791	=head3 METHODS FOR CONSUMERS
		792
		793	These methods should only be used by the consuming side, i.e. the
		794	code awaits the condition.
		795
		796	=over 4
		797
		798	=item $cv->recv
		799
		800	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		801	>> methods have been called on C<$cv>, while servicing other watchers
		802	normally.
		803
		804	You can only wait once on a condition - additional calls are valid but
		805	will return immediately.
		806
		807	If an error condition has been set by calling C<< ->croak >>, then this
		808	function will call C<croak>.
		809
		810	In list context, all parameters passed to C<send> will be returned,
		811	in scalar context only the first one will be returned.
		812
		813	Note that doing a blocking wait in a callback is not supported by any
		814	event loop, that is, recursive invocation of a blocking C<< ->recv
		815	>> is not allowed, and the C<recv> call will C<croak> if such a
		816	condition is detected. This condition can be slightly loosened by using
		817	L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
		818	any thread that doesn't run the event loop itself.
		819
		820	Not all event models support a blocking wait - some die in that case
		821	(programs might want to do that to stay interactive), so I<if you are
		822	using this from a module, never require a blocking wait>. Instead, let the
		823	caller decide whether the call will block or not (for example, by coupling
		824	condition variables with some kind of request results and supporting
		825	callbacks so the caller knows that getting the result will not block,
		826	while still supporting blocking waits if the caller so desires).
		827
		828	You can ensure that C<< ->recv >> never blocks by setting a callback and
		829	only calling C<< ->recv >> from within that callback (or at a later
		830	time). This will work even when the event loop does not support blocking
		831	waits otherwise.
		832
		833	=item $bool = $cv->ready
		834
		835	Returns true when the condition is "true", i.e. whether C<send> or
		836	C<croak> have been called.
		837
		838	=item $cb = $cv->cb ($cb->($cv))
		839
		840	This is a mutator function that returns the callback set and optionally
		841	replaces it before doing so.
		842
		843	The callback will be called when the condition becomes "true", i.e. when
		844	C<send> or C<croak> are called, with the only argument being the
		845	condition variable itself. If the condition is already true, the
		846	callback is called immediately when it is set. Calling C<recv> inside
		847	the callback or at any later time is guaranteed not to block.
		848
		849	=back
		850
		851	=head1 SUPPORTED EVENT LOOPS/BACKENDS
		852
		853	The available backend classes are (every class has its own manpage):
		854
		855	=over 4
		856
		857	=item Backends that are autoprobed when no other event loop can be found.
		858
		859	EV is the preferred backend when no other event loop seems to be in
		860	use. If EV is not installed, then AnyEvent will fall back to its own
		861	pure-perl implementation, which is available everywhere as it comes with
		862	AnyEvent itself.
		863
		864	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		865	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		866
		867	=item Backends that are transparently being picked up when they are used.
		868
		869	These will be used if they are already loaded when the first watcher
		870	is created, in which case it is assumed that the application is using
		871	them. This means that AnyEvent will automatically pick the right backend
		872	when the main program loads an event module before anything starts to
		873	create watchers. Nothing special needs to be done by the main program.
		874
		875	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		876	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		877	AnyEvent::Impl::Tk based on Tk, very broken.
		878	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		879	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		880	AnyEvent::Impl::Irssi used when running within irssi.
		881	AnyEvent::Impl::IOAsync based on IO::Async.
		882	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		883	AnyEvent::Impl::FLTK2 based on FLTK (fltk 2 binding).
		884
		885	=item Backends with special needs.
		886
		887	Qt requires the Qt::Application to be instantiated first, but will
		888	otherwise be picked up automatically. As long as the main program
		889	instantiates the application before any AnyEvent watchers are created,
		890	everything should just work.
		891
		892	AnyEvent::Impl::Qt based on Qt.
		893
		894	=item Event loops that are indirectly supported via other backends.
		895
		896	Some event loops can be supported via other modules:
		897
		898	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		899
		900	B<WxWidgets> has no support for watching file handles. However, you can
		901	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		902	polls 20 times per second, which was considered to be too horrible to even
		903	consider for AnyEvent.
		904
		905	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		906	backend, so it can be supported through POE.
		907
		908	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		909	load L<POE> when detecting them, in the hope that POE will pick them up,
		910	in which case everything will be automatic.
		911
		912	=back
		913
		914	=head1 GLOBAL VARIABLES AND FUNCTIONS
		915
		916	These are not normally required to use AnyEvent, but can be useful to
		917	write AnyEvent extension modules.
		918
		919	=over 4
		920
		921	=item $AnyEvent::MODEL
		922
		923	Contains C<undef> until the first watcher is being created, before the
		924	backend has been autodetected.
		925
		926	Afterwards it contains the event model that is being used, which is the
		927	name of the Perl class implementing the model. This class is usually one
		928	of the C<AnyEvent::Impl::xxx> modules, but can be any other class in the
		929	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
		930	will be C<urxvt::anyevent>).
		931
		932	=item AnyEvent::detect
		933
		934	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		935	if necessary. You should only call this function right before you would
		936	have created an AnyEvent watcher anyway, that is, as late as possible at
		937	runtime, and not e.g. during initialisation of your module.
		938
		939	The effect of calling this function is as if a watcher had been created
		940	(specifically, actions that happen "when the first watcher is created"
		941	happen when calling detetc as well).
		942
		943	If you need to do some initialisation before AnyEvent watchers are
		944	created, use C<post_detect>.
		945
		946	=item $guard = AnyEvent::post_detect { BLOCK }
		947
		948	Arranges for the code block to be executed as soon as the event model is
		949	autodetected (or immediately if that has already happened).
		950
		951	The block will be executed I<after> the actual backend has been detected
		952	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		953	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		954	other initialisations - see the sources of L<AnyEvent::Strict> or
		955	L<AnyEvent::AIO> to see how this is used.
		956
		957	The most common usage is to create some global watchers, without forcing
		958	event module detection too early, for example, L<AnyEvent::AIO> creates
		959	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		960	avoid autodetecting the event module at load time.
		961
		962	If called in scalar or list context, then it creates and returns an object
		963	that automatically removes the callback again when it is destroyed (or
		964	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		965	a case where this is useful.
		966
		967	Example: Create a watcher for the IO::AIO module and store it in
		968	C<$WATCHER>, but do so only do so after the event loop is initialised.
		969
		970	our WATCHER;
		971
		972	my $guard = AnyEvent::post_detect {
		973	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		974	};
		975
		976	# the ||= is important in case post_detect immediately runs the block,
		977	# as to not clobber the newly-created watcher. assigning both watcher and
		978	# post_detect guard to the same variable has the advantage of users being
		979	# able to just C<undef $WATCHER> if the watcher causes them grief.
		980
		981	$WATCHER ||= $guard;
		982
		983	=item @AnyEvent::post_detect
		984
		985	If there are any code references in this array (you can C<push> to it
		986	before or after loading AnyEvent), then they will be called directly
		987	after the event loop has been chosen.
		988
		989	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		990	if it is defined then the event loop has already been detected, and the
		991	array will be ignored.
		992
		993	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		994	it, as it takes care of these details.
		995
		996	This variable is mainly useful for modules that can do something useful
		997	when AnyEvent is used and thus want to know when it is initialised, but do
		998	not need to even load it by default. This array provides the means to hook
		999	into AnyEvent passively, without loading it.
		1000
		1001	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		1002	together, you could put this into Coro (this is the actual code used by
		1003	Coro to accomplish this):
		1004
		1005	if (defined $AnyEvent::MODEL) {
		1006	# AnyEvent already initialised, so load Coro::AnyEvent
		1007	require Coro::AnyEvent;
		1008	} else {
		1009	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		1010	# as soon as it is
		1011	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		1012	}
		1013
		1014	=item AnyEvent::postpone { BLOCK }
		1015
		1016	Arranges for the block to be executed as soon as possible, but not before
		1017	the call itself returns. In practise, the block will be executed just
		1018	before the event loop polls for new events, or shortly afterwards.
		1019
		1020	This function never returns anything (to make the C<return postpone { ...
		1021	}> idiom more useful.
		1022
		1023	To understand the usefulness of this function, consider a function that
		1024	asynchronously does something for you and returns some transaction
		1025	object or guard to let you cancel the operation. For example,
		1026	C<AnyEvent::Socket::tcp_connect>:
		1027
		1028	# start a conenction attempt unless one is active
		1029	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		1030	delete $self->{connect_guard};
		1031	...
		1032	};
		1033
		1034	Imagine that this function could instantly call the callback, for
		1035	example, because it detects an obvious error such as a negative port
		1036	number. Invoking the callback before the function returns causes problems
		1037	however: the callback will be called and will try to delete the guard
		1038	object. But since the function hasn't returned yet, there is nothing to
		1039	delete. When the function eventually returns it will assign the guard
		1040	object to C<< $self->{connect_guard} >>, where it will likely never be
		1041	deleted, so the program thinks it is still trying to connect.
		1042
		1043	This is where C<AnyEvent::postpone> should be used. Instead of calling the
		1044	callback directly on error:
		1045
		1046	$cb->(undef), return # signal error to callback, BAD!
		1047	if $some_error_condition;
		1048
		1049	It should use C<postpone>:
		1050
		1051	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1052	if $some_error_condition;
		1053
		1054	=item AnyEvent::log $level, $msg[, @args]
		1055
		1056	Log the given C<$msg> at the given C<$level>.
		1057
		1058	Loads AnyEvent::Log on first use and calls C<AnyEvent::Log::log> -
		1059	consequently, look at the L<AnyEvent::Log> documentation for details.
		1060
		1061	If you want to sprinkle loads of logging calls around your code, consider
		1062	creating a logger callback with the C<AnyEvent::Log::logger> function.
		1063
		1064	=back
		1065
		1066	=head1 WHAT TO DO IN A MODULE
		1067
		1068	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		1069	freely, but you should not load a specific event module or rely on it.
		1070
		1071	Be careful when you create watchers in the module body - AnyEvent will
		1072	decide which event module to use as soon as the first method is called, so
		1073	by calling AnyEvent in your module body you force the user of your module
		1074	to load the event module first.
		1075
		1076	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1077	the C<< ->send >> method has been called on it already. This is
		1078	because it will stall the whole program, and the whole point of using
		1079	events is to stay interactive.
		1080
		1081	It is fine, however, to call C<< ->recv >> when the user of your module
		1082	requests it (i.e. if you create a http request object ad have a method
		1083	called C<results> that returns the results, it may call C<< ->recv >>
		1084	freely, as the user of your module knows what she is doing. Always).
		1085
		1086	=head1 WHAT TO DO IN THE MAIN PROGRAM
		1087
		1088	There will always be a single main program - the only place that should
		1089	dictate which event model to use.
		1090
		1091	If the program is not event-based, it need not do anything special, even
		1092	when it depends on a module that uses an AnyEvent. If the program itself
		1093	uses AnyEvent, but does not care which event loop is used, all it needs
		1094	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1095	available loop implementation.
		1096
		1097	If the main program relies on a specific event model - for example, in
		1098	Gtk2 programs you have to rely on the Glib module - you should load the
		1099	event module before loading AnyEvent or any module that uses it: generally
		1100	speaking, you should load it as early as possible. The reason is that
		1101	modules might create watchers when they are loaded, and AnyEvent will
		1102	decide on the event model to use as soon as it creates watchers, and it
		1103	might choose the wrong one unless you load the correct one yourself.
		1104
		1105	You can chose to use a pure-perl implementation by loading the
		1106	C<AnyEvent::Loop> module, which gives you similar behaviour
		1107	everywhere, but letting AnyEvent chose the model is generally better.
		1108
		1109	=head2 MAINLOOP EMULATION
		1110
		1111	Sometimes (often for short test scripts, or even standalone programs who
		1112	only want to use AnyEvent), you do not want to run a specific event loop.
		1113
		1114	In that case, you can use a condition variable like this:
		1115
		1116	AnyEvent->condvar->recv;
		1117
		1118	This has the effect of entering the event loop and looping forever.
		1119
		1120	Note that usually your program has some exit condition, in which case
		1121	it is better to use the "traditional" approach of storing a condition
		1122	variable somewhere, waiting for it, and sending it when the program should
		1123	exit cleanly.
		1124
		1125
		1126	=head1 OTHER MODULES
		1127
		1128	The following is a non-exhaustive list of additional modules that use
		1129	AnyEvent as a client and can therefore be mixed easily with other
		1130	AnyEvent modules and other event loops in the same program. Some of the
		1131	modules come as part of AnyEvent, the others are available via CPAN (see
		1132	L<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for
		1133	a longer non-exhaustive list), and the list is heavily biased towards
		1134	modules of the AnyEvent author himself :)
		1135
		1136	=over 4
		1137
		1138	=item L<AnyEvent::Util>
		1139
		1140	Contains various utility functions that replace often-used blocking
		1141	functions such as C<inet_aton> with event/callback-based versions.
		1142
		1143	=item L<AnyEvent::Socket>
		1144
		1145	Provides various utility functions for (internet protocol) sockets,
		1146	addresses and name resolution. Also functions to create non-blocking tcp
		1147	connections or tcp servers, with IPv6 and SRV record support and more.
		1148
		1149	=item L<AnyEvent::Handle>
		1150
		1151	Provide read and write buffers, manages watchers for reads and writes,
		1152	supports raw and formatted I/O, I/O queued and fully transparent and
		1153	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1154
		1155	=item L<AnyEvent::DNS>
		1156
		1157	Provides rich asynchronous DNS resolver capabilities.
		1158
		1159	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1160
		1161	Implement event-based interfaces to the protocols of the same name (for
		1162	the curious, IGS is the International Go Server and FCP is the Freenet
		1163	Client Protocol).
		1164
		1165	=item L<AnyEvent::Handle::UDP>
		1166
		1167	Here be danger!
		1168
		1169	As Pauli would put it, "Not only is it not right, it's not even wrong!" -
		1170	there are so many things wrong with AnyEvent::Handle::UDP, most notably
		1171	its use of a stream-based API with a protocol that isn't streamable, that
		1172	the only way to improve it is to delete it.
		1173
		1174	It features data corruption (but typically only under load) and general
		1175	confusion. On top, the author is not only clueless about UDP but also
		1176	fact-resistant - some gems of his understanding: "connect doesn't work
		1177	with UDP", "UDP packets are not IP packets", "UDP only has datagrams, not
		1178	packets", "I don't need to implement proper error checking as UDP doesn't
		1179	support error checking" and so on - he doesn't even understand what's
		1180	wrong with his module when it is explained to him.
		1181
		1182	=item L<AnyEvent::DBI>
		1183
		1184	Executes L<DBI> requests asynchronously in a proxy process for you,
		1185	notifying you in an event-based way when the operation is finished.
		1186
		1187	=item L<AnyEvent::AIO>
		1188
		1189	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1190	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1191	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1192	file I/O, and much more.
		1193
		1194	=item L<AnyEvent::HTTPD>
		1195
		1196	A simple embedded webserver.
		1197
		1198	=item L<AnyEvent::FastPing>
		1199
		1200	The fastest ping in the west.
		1201
		1202	=item L<Coro>
		1203
		1204	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1205
		1206	=back
		1207
11	=cut	1208	=cut
12		1209
13	package AnyEvent;	1210	package AnyEvent;
14		1211
		1212	# basically a tuned-down version of common::sense
		1213	sub common_sense {
		1214	# from common:.sense 3.4
		1215	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
		1216	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1217	$^H |= 0x00000600;
		1218	}
		1219
		1220	BEGIN { AnyEvent::common_sense }
		1221
15	use Carp;	1222	use Carp ();
16		1223
17	$VERSION = 0.1;	1224	our $VERSION = '6.01';
		1225	our $MODEL;
18		1226
19	no warnings;	1227	our @ISA;
20		1228
		1229	our @REGISTRY;
		1230
		1231	our $VERBOSE;
		1232
		1233	BEGIN {
		1234	require "AnyEvent/constants.pl";
		1235
		1236	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1237
		1238	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1239	if ${^TAINT};
		1240
		1241	$ENV{"PERL_ANYEVENT_$_"} = $ENV{"AE_$_"}
		1242	for grep s/^AE_// && !exists $ENV{"PERL_ANYEVENT_$_"}, keys %ENV;
		1243
		1244	@ENV{grep /^PERL_ANYEVENT_/, keys %ENV} = ()
		1245	if ${^TAINT};
		1246
		1247	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1248	}
		1249
		1250	our $MAX_SIGNAL_LATENCY = 10;
		1251
		1252	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1253
		1254	{
		1255	my $idx;
		1256	$PROTOCOL{$_} = ++$idx
		1257	for reverse split /\s*,\s*/,
		1258	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1259	}
		1260
		1261	our @post_detect;
		1262
		1263	sub post_detect(&) {
		1264	my ($cb) = @_;
		1265
		1266	push @post_detect, $cb;
		1267
		1268	defined wantarray
		1269	? bless \$cb, "AnyEvent::Util::postdetect"
		1270	: ()
		1271	}
		1272
		1273	sub AnyEvent::Util::postdetect::DESTROY {
		1274	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1275	}
		1276
		1277	our $POSTPONE_W;
		1278	our @POSTPONE;
		1279
		1280	sub _postpone_exec {
		1281	undef $POSTPONE_W;
		1282
		1283	&{ shift @POSTPONE }
		1284	while @POSTPONE;
		1285	}
		1286
		1287	sub postpone(&) {
		1288	push @POSTPONE, shift;
		1289
		1290	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1291
		1292	()
		1293	}
		1294
		1295	sub log($$;@) {
		1296	# only load the bug bloated module when we actually are about to log something
		1297	if ($_[0] <= $VERBOSE) {
		1298	require AnyEvent::Log;
		1299	# AnyEvent::Log overwrites this function
		1300	goto &log;
		1301	}
		1302	}
		1303
		1304	if (length $ENV{PERL_ANYEVENT_LOG}) {
		1305	require AnyEvent::Log; # AnyEvent::Log does the thing for us
		1306	}
		1307
21	my @models = (	1308	our @models = (
22	[Coro => Coro::Event::],	1309	[EV:: => AnyEvent::Impl::EV:: , 1],
23	[Event => Event::],	1310	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
24	[Glib => Glib::],	1311	# everything below here will not (normally) be autoprobed
25	[Tk => Tk::],	1312	# as the pure perl backend should work everywhere
		1313	# and is usually faster
		1314	[Event:: => AnyEvent::Impl::Event::, 1],
		1315	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1316	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1317	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1318	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1319	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1320	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1321	[Wx:: => AnyEvent::Impl::POE::],
		1322	[Prima:: => AnyEvent::Impl::POE::],
		1323	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1324	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
		1325	[FLTK:: => AnyEvent::Impl::FLTK2::],
26	);	1326	);
27		1327
28	sub AUTOLOAD {	1328	our @isa_hook;
29	$AUTOLOAD =~ s/.*://;
30		1329
31	for (@models) {	1330	sub _isa_set {
32	my ($model, $package) = @$_;	1331	my @pkg = ("AnyEvent", (map $_->[0], grep defined, @isa_hook), $MODEL);
33	if (defined ${"$package\::VERSION"}) {	1332
34	$EVENT = "AnyEvent::Impl::$model";	1333	@{"$pkg[$_-1]::ISA"} = $pkg[$_]
35	eval "require $EVENT"; die if $@;	1334	for 1 .. $#pkg;
36	goto &{"$EVENT\::$AUTOLOAD"};	1335
		1336	grep $_ && $_->[1], @isa_hook
		1337	and AE::_reset ();
		1338	}
		1339
		1340	# used for hooking AnyEvent::Strict and AnyEvent::Debug::Wrap into the class hierarchy
		1341	sub _isa_hook($$;$) {
		1342	my ($i, $pkg, $reset_ae) = @_;
		1343
		1344	$isa_hook[$i] = $pkg ? [$pkg, $reset_ae] : undef;
		1345
		1346	_isa_set;
		1347	}
		1348
		1349	# all autoloaded methods reserve the complete glob, not just the method slot.
		1350	# due to bugs in perls method cache implementation.
		1351	our @methods = qw(io timer time now now_update signal child idle condvar);
		1352
		1353	sub detect() {
		1354	return $MODEL if $MODEL; # some programs keep references to detect
		1355
		1356	local $!; # for good measure
		1357	local $SIG{__DIE__}; # we use eval
		1358
		1359	# free some memory
		1360	*detect = sub () { $MODEL };
		1361	# undef &func doesn't correctly update the method cache. grmbl.
		1362	# so we delete the whole glob. grmbl.
		1363	# otoh, perl doesn't let me undef an active usb, but it lets me free
		1364	# a glob with an active sub. hrm. i hope it works, but perl is
		1365	# usually buggy in this department. sigh.
		1366	delete @{"AnyEvent::"}{@methods};
		1367	undef @methods;
		1368
		1369	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1370	my $model = $1;
		1371	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1372	if (eval "require $model") {
		1373	AnyEvent::log 7 => "loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.";
		1374	$MODEL = $model;
		1375	} else {
		1376	AnyEvent::log warn => "unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@";
37	}	1377	}
38	}	1378	}
39		1379
40	for (@models) {	1380	# check for already loaded models
41	my ($model, $package) = @$_;	1381	unless ($MODEL) {
42	$EVENT = "AnyEvent::Impl::$model";	1382	for (@REGISTRY, @models) {
		1383	my ($package, $model) = @$_;
		1384	if (${"$package\::VERSION"} > 0) {
43	if (eval "require $EVENT") {	1385	if (eval "require $model") {
44	goto &{"$EVENT\::$AUTOLOAD"};	1386	AnyEvent::log 7 => "autodetected model '$model', using it.";
		1387	$MODEL = $model;
		1388	last;
		1389	}
		1390	}
		1391	}
		1392
		1393	unless ($MODEL) {
		1394	# try to autoload a model
		1395	for (@REGISTRY, @models) {
		1396	my ($package, $model, $autoload) = @$_;
		1397	if (
		1398	$autoload
		1399	and eval "require $package"
		1400	and ${"$package\::VERSION"} > 0
		1401	and eval "require $model"
		1402	) {
		1403	AnyEvent::log 7 => "autoloaded model '$model', using it.";
		1404	$MODEL = $model;
		1405	last;
		1406	}
		1407	}
		1408
		1409	$MODEL
		1410	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?";
45	}	1411	}
46	}	1412	}
47		1413
48	die "No event module selected for AnyEvent and autodetect failed. Install any of these: Coro, Event, Glib or Tk.";	1414	# free memory only needed for probing
49	}	1415	undef @models;
		1416	undef @REGISTRY;
50		1417
51	1;	1418	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
52		1419
		1420	# now nuke some methods that are overridden by the backend.
		1421	# SUPER usage is not allowed in these.
		1422	for (qw(time signal child idle)) {
		1423	undef &{"AnyEvent::Base::$_"}
		1424	if defined &{"$MODEL\::$_"};
		1425	}
		1426
		1427	_isa_set;
		1428
		1429	# we're officially open!
		1430
		1431	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1432	require AnyEvent::Strict;
		1433	}
		1434
		1435	if ($ENV{PERL_ANYEVENT_DEBUG_WRAP}) {
		1436	require AnyEvent::Debug;
		1437	AnyEvent::Debug::wrap ($ENV{PERL_ANYEVENT_DEBUG_WRAP});
		1438	}
		1439
		1440	if (length $ENV{PERL_ANYEVENT_DEBUG_SHELL}) {
		1441	require AnyEvent::Socket;
		1442	require AnyEvent::Debug;
		1443
		1444	my $shell = $ENV{PERL_ANYEVENT_DEBUG_SHELL};
		1445	$shell =~ s/\$\$/$$/g;
		1446
		1447	my ($host, $service) = AnyEvent::Socket::parse_hostport ($shell);
		1448	$AnyEvent::Debug::SHELL = AnyEvent::Debug::shell ($host, $service);
		1449	}
		1450
		1451	# now the anyevent environment is set up as the user told us to, so
		1452	# call the actual user code - post detects
		1453
		1454	(shift @post_detect)->() while @post_detect;
		1455	undef @post_detect;
		1456
		1457	*post_detect = sub(&) {
		1458	shift->();
		1459
		1460	undef
		1461	};
		1462
		1463	$MODEL
		1464	}
		1465
		1466	for my $name (@methods) {
		1467	*$name = sub {
		1468	detect;
		1469	# we use goto because
		1470	# a) it makes the thunk more transparent
		1471	# b) it allows us to delete the thunk later
		1472	goto &{ UNIVERSAL::can AnyEvent => "SUPER::$name" }
		1473	};
		1474	}
		1475
		1476	# utility function to dup a filehandle. this is used by many backends
		1477	# to support binding more than one watcher per filehandle (they usually
		1478	# allow only one watcher per fd, so we dup it to get a different one).
		1479	sub _dupfh($$;$$) {
		1480	my ($poll, $fh, $r, $w) = @_;
		1481
		1482	# cygwin requires the fh mode to be matching, unix doesn't
		1483	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1484
		1485	open my $fh2, $mode, $fh
		1486	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1487
		1488	# we assume CLOEXEC is already set by perl in all important cases
		1489
		1490	($fh2, $rw)
		1491	}
		1492
		1493	=head1 SIMPLIFIED AE API
		1494
		1495	Starting with version 5.0, AnyEvent officially supports a second, much
		1496	simpler, API that is designed to reduce the calling, typing and memory
		1497	overhead by using function call syntax and a fixed number of parameters.
		1498
		1499	See the L<AE> manpage for details.
		1500
		1501	=cut
		1502
		1503	package AE;
		1504
		1505	our $VERSION = $AnyEvent::VERSION;
		1506
		1507	sub _reset() {
		1508	eval q{
		1509	# fall back to the main API by default - backends and AnyEvent::Base
		1510	# implementations can overwrite these.
		1511
		1512	sub io($$$) {
		1513	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1514	}
		1515
		1516	sub timer($$$) {
		1517	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1518	}
		1519
		1520	sub signal($$) {
		1521	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1522	}
		1523
		1524	sub child($$) {
		1525	AnyEvent->child (pid => $_[0], cb => $_[1])
		1526	}
		1527
		1528	sub idle($) {
		1529	AnyEvent->idle (cb => $_[0]);
		1530	}
		1531
		1532	sub cv(;&) {
		1533	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1534	}
		1535
		1536	sub now() {
		1537	AnyEvent->now
		1538	}
		1539
		1540	sub now_update() {
		1541	AnyEvent->now_update
		1542	}
		1543
		1544	sub time() {
		1545	AnyEvent->time
		1546	}
		1547
		1548	*postpone = \&AnyEvent::postpone;
		1549	*log = \&AnyEvent::log;
		1550	};
		1551	die if $@;
		1552	}
		1553
		1554	BEGIN { _reset }
		1555
		1556	package AnyEvent::Base;
		1557
		1558	# default implementations for many methods
		1559
		1560	sub time {
		1561	eval q{ # poor man's autoloading {}
		1562	# probe for availability of Time::HiRes
		1563	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1564	AnyEvent::log 8 => "AnyEvent: using Time::HiRes for sub-second timing accuracy."
		1565	if $AnyEvent::VERBOSE >= 8;
		1566	*time = sub { Time::HiRes::time () };
		1567	*AE::time = \& Time::HiRes::time ;
		1568	# if (eval "use POSIX (); (POSIX::times())...
		1569	} else {
		1570	AnyEvent::log critical => "using built-in time(), WARNING, no sub-second resolution!";
		1571	*time = sub { CORE::time };
		1572	*AE::time = sub (){ CORE::time };
		1573	}
		1574
		1575	*now = \&time;
		1576	};
		1577	die if $@;
		1578
		1579	&time
		1580	}
		1581
		1582	*now = \&time;
		1583	sub now_update { }
		1584
		1585	sub _poll {
		1586	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1587	}
		1588
		1589	# default implementation for ->condvar
		1590	# in fact, the default should not be overwritten
		1591
		1592	sub condvar {
		1593	eval q{ # poor man's autoloading {}
		1594	*condvar = sub {
		1595	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1596	};
		1597
		1598	*AE::cv = sub (;&) {
		1599	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1600	};
		1601	};
		1602	die if $@;
		1603
		1604	&condvar
		1605	}
		1606
		1607	# default implementation for ->signal
		1608
		1609	our $HAVE_ASYNC_INTERRUPT;
		1610
		1611	sub _have_async_interrupt() {
		1612	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1613	&& eval "use Async::Interrupt 1.02 (); 1")
		1614	unless defined $HAVE_ASYNC_INTERRUPT;
		1615
		1616	$HAVE_ASYNC_INTERRUPT
		1617	}
		1618
		1619	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1620	our (%SIG_ASY, %SIG_ASY_W);
		1621	our ($SIG_COUNT, $SIG_TW);
		1622
		1623	# install a dummy wakeup watcher to reduce signal catching latency
		1624	# used by Impls
		1625	sub _sig_add() {
		1626	unless ($SIG_COUNT++) {
		1627	# try to align timer on a full-second boundary, if possible
		1628	my $NOW = AE::now;
		1629
		1630	$SIG_TW = AE::timer
		1631	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1632	$MAX_SIGNAL_LATENCY,
		1633	sub { } # just for the PERL_ASYNC_CHECK
		1634	;
		1635	}
		1636	}
		1637
		1638	sub _sig_del {
		1639	undef $SIG_TW
		1640	unless --$SIG_COUNT;
		1641	}
		1642
		1643	our $_sig_name_init; $_sig_name_init = sub {
		1644	eval q{ # poor man's autoloading {}
		1645	undef $_sig_name_init;
		1646
		1647	if (_have_async_interrupt) {
		1648	*sig2num = \&Async::Interrupt::sig2num;
		1649	*sig2name = \&Async::Interrupt::sig2name;
		1650	} else {
		1651	require Config;
		1652
		1653	my %signame2num;
		1654	@signame2num{ split ' ', $Config::Config{sig_name} }
		1655	= split ' ', $Config::Config{sig_num};
		1656
		1657	my @signum2name;
		1658	@signum2name[values %signame2num] = keys %signame2num;
		1659
		1660	*sig2num = sub($) {
		1661	$_[0] > 0 ? shift : $signame2num{+shift}
		1662	};
		1663	*sig2name = sub ($) {
		1664	$_[0] > 0 ? $signum2name[+shift] : shift
		1665	};
		1666	}
		1667	};
		1668	die if $@;
		1669	};
		1670
		1671	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1672	sub sig2name($) { &$_sig_name_init; &sig2name }
		1673
		1674	sub signal {
		1675	eval q{ # poor man's autoloading {}
		1676	# probe for availability of Async::Interrupt
		1677	if (_have_async_interrupt) {
		1678	AnyEvent::log 8 => "using Async::Interrupt for race-free signal handling."
		1679	if $AnyEvent::VERBOSE >= 8;
		1680
		1681	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1682	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1683
		1684	} else {
		1685	AnyEvent::log 8 => "using emulated perl signal handling with latency timer."
		1686	if $AnyEvent::VERBOSE >= 8;
		1687
		1688	if (AnyEvent::WIN32) {
		1689	require AnyEvent::Util;
		1690
		1691	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1692	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1693	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1694	} else {
		1695	pipe $SIGPIPE_R, $SIGPIPE_W;
		1696	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1697	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1698
		1699	# not strictly required, as $^F is normally 2, but let's make sure...
		1700	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1701	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1702	}
		1703
		1704	$SIGPIPE_R
		1705	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1706
		1707	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1708	}
		1709
		1710	*signal = $HAVE_ASYNC_INTERRUPT
		1711	? sub {
		1712	my (undef, %arg) = @_;
		1713
		1714	# async::interrupt
		1715	my $signal = sig2num $arg{signal};
		1716	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1717
		1718	$SIG_ASY{$signal} ||= new Async::Interrupt
		1719	cb => sub { undef $SIG_EV{$signal} },
		1720	signal => $signal,
		1721	pipe => [$SIGPIPE_R->filenos],
		1722	pipe_autodrain => 0,
		1723	;
		1724
		1725	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1726	}
		1727	: sub {
		1728	my (undef, %arg) = @_;
		1729
		1730	# pure perl
		1731	my $signal = sig2name $arg{signal};
		1732	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1733
		1734	$SIG{$signal} ||= sub {
		1735	local $!;
		1736	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1737	undef $SIG_EV{$signal};
		1738	};
		1739
		1740	# can't do signal processing without introducing races in pure perl,
		1741	# so limit the signal latency.
		1742	_sig_add;
		1743
		1744	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1745	}
		1746	;
		1747
		1748	*AnyEvent::Base::signal::DESTROY = sub {
		1749	my ($signal, $cb) = @{$_[0]};
		1750
		1751	_sig_del;
		1752
		1753	delete $SIG_CB{$signal}{$cb};
		1754
		1755	$HAVE_ASYNC_INTERRUPT
		1756	? delete $SIG_ASY{$signal}
		1757	: # delete doesn't work with older perls - they then
		1758	# print weird messages, or just unconditionally exit
		1759	# instead of getting the default action.
		1760	undef $SIG{$signal}
		1761	unless keys %{ $SIG_CB{$signal} };
		1762	};
		1763
		1764	*_signal_exec = sub {
		1765	$HAVE_ASYNC_INTERRUPT
		1766	? $SIGPIPE_R->drain
		1767	: sysread $SIGPIPE_R, (my $dummy), 9;
		1768
		1769	while (%SIG_EV) {
		1770	for (keys %SIG_EV) {
		1771	delete $SIG_EV{$_};
		1772	&$_ for values %{ $SIG_CB{$_} || {} };
		1773	}
		1774	}
		1775	};
		1776	};
		1777	die if $@;
		1778
		1779	&signal
		1780	}
		1781
		1782	# default implementation for ->child
		1783
		1784	our %PID_CB;
		1785	our $CHLD_W;
		1786	our $CHLD_DELAY_W;
		1787
		1788	# used by many Impl's
		1789	sub _emit_childstatus($$) {
		1790	my (undef, $rpid, $rstatus) = @_;
		1791
		1792	$_->($rpid, $rstatus)
		1793	for values %{ $PID_CB{$rpid} || {} },
		1794	values %{ $PID_CB{0} || {} };
		1795	}
		1796
		1797	sub child {
		1798	eval q{ # poor man's autoloading {}
		1799	*_sigchld = sub {
		1800	my $pid;
		1801
		1802	AnyEvent->_emit_childstatus ($pid, $?)
		1803	while ($pid = waitpid -1, WNOHANG) > 0;
		1804	};
		1805
		1806	*child = sub {
		1807	my (undef, %arg) = @_;
		1808
		1809	my $pid = $arg{pid};
		1810	my $cb = $arg{cb};
		1811
		1812	$PID_CB{$pid}{$cb+0} = $cb;
		1813
		1814	unless ($CHLD_W) {
		1815	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1816	# child could be a zombie already, so make at least one round
		1817	&_sigchld;
		1818	}
		1819
		1820	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1821	};
		1822
		1823	*AnyEvent::Base::child::DESTROY = sub {
		1824	my ($pid, $icb) = @{$_[0]};
		1825
		1826	delete $PID_CB{$pid}{$icb};
		1827	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1828
		1829	undef $CHLD_W unless keys %PID_CB;
		1830	};
		1831	};
		1832	die if $@;
		1833
		1834	&child
		1835	}
		1836
		1837	# idle emulation is done by simply using a timer, regardless
		1838	# of whether the process is idle or not, and not letting
		1839	# the callback use more than 50% of the time.
		1840	sub idle {
		1841	eval q{ # poor man's autoloading {}
		1842	*idle = sub {
		1843	my (undef, %arg) = @_;
		1844
		1845	my ($cb, $w, $rcb) = $arg{cb};
		1846
		1847	$rcb = sub {
		1848	if ($cb) {
		1849	$w = AE::time;
		1850	&$cb;
		1851	$w = AE::time - $w;
		1852
		1853	# never use more then 50% of the time for the idle watcher,
		1854	# within some limits
		1855	$w = 0.0001 if $w < 0.0001;
		1856	$w = 5 if $w > 5;
		1857
		1858	$w = AE::timer $w, 0, $rcb;
		1859	} else {
		1860	# clean up...
		1861	undef $w;
		1862	undef $rcb;
		1863	}
		1864	};
		1865
		1866	$w = AE::timer 0.05, 0, $rcb;
		1867
		1868	bless \\$cb, "AnyEvent::Base::idle"
		1869	};
		1870
		1871	*AnyEvent::Base::idle::DESTROY = sub {
		1872	undef $${$_[0]};
		1873	};
		1874	};
		1875	die if $@;
		1876
		1877	&idle
		1878	}
		1879
		1880	package AnyEvent::CondVar;
		1881
		1882	our @ISA = AnyEvent::CondVar::Base::;
		1883
		1884	# only to be used for subclassing
		1885	sub new {
		1886	my $class = shift;
		1887	bless AnyEvent->condvar (@_), $class
		1888	}
		1889
		1890	package AnyEvent::CondVar::Base;
		1891
		1892	#use overload
		1893	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1894	# fallback => 1;
		1895
		1896	# save 300+ kilobytes by dirtily hardcoding overloading
		1897	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1898	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1899	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1900	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1901
		1902	our $WAITING;
		1903
		1904	sub _send {
		1905	# nop
		1906	}
		1907
		1908	sub _wait {
		1909	AnyEvent->_poll until $_[0]{_ae_sent};
		1910	}
		1911
		1912	sub send {
		1913	my $cv = shift;
		1914	$cv->{_ae_sent} = [@_];
		1915	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1916	$cv->_send;
		1917	}
		1918
		1919	sub croak {
		1920	$_[0]{_ae_croak} = $_[1];
		1921	$_[0]->send;
		1922	}
		1923
		1924	sub ready {
		1925	$_[0]{_ae_sent}
		1926	}
		1927
		1928	sub recv {
		1929	unless ($_[0]{_ae_sent}) {
		1930	$WAITING
		1931	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1932
		1933	local $WAITING = 1;
		1934	$_[0]->_wait;
		1935	}
		1936
		1937	$_[0]{_ae_croak}
		1938	and Carp::croak $_[0]{_ae_croak};
		1939
		1940	wantarray
		1941	? @{ $_[0]{_ae_sent} }
		1942	: $_[0]{_ae_sent}[0]
		1943	}
		1944
		1945	sub cb {
		1946	my $cv = shift;
		1947
		1948	@_
		1949	and $cv->{_ae_cb} = shift
		1950	and $cv->{_ae_sent}
		1951	and (delete $cv->{_ae_cb})->($cv);
		1952
		1953	$cv->{_ae_cb}
		1954	}
		1955
		1956	sub begin {
		1957	++$_[0]{_ae_counter};
		1958	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1959	}
		1960
		1961	sub end {
		1962	return if --$_[0]{_ae_counter};
		1963	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1964	}
		1965
		1966	# undocumented/compatibility with pre-3.4
		1967	*broadcast = \&send;
		1968	*wait = \&recv;
		1969
		1970	=head1 ERROR AND EXCEPTION HANDLING
		1971
		1972	In general, AnyEvent does not do any error handling - it relies on the
		1973	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1974	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1975	checking of all AnyEvent methods, however, which is highly useful during
		1976	development.
		1977
		1978	As for exception handling (i.e. runtime errors and exceptions thrown while
		1979	executing a callback), this is not only highly event-loop specific, but
		1980	also not in any way wrapped by this module, as this is the job of the main
		1981	program.
		1982
		1983	The pure perl event loop simply re-throws the exception (usually
		1984	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1985	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1986	so on.
		1987
		1988	=head1 ENVIRONMENT VARIABLES
		1989
		1990	AnyEvent supports a number of environment variables that tune the
		1991	runtime behaviour. They are usually evaluated when AnyEvent is
		1992	loaded, initialised, or a submodule that uses them is loaded. Many of
		1993	them also cause AnyEvent to load additional modules - for example,
		1994	C<PERL_ANYEVENT_DEBUG_WRAP> causes the L<AnyEvent::Debug> module to be
		1995	loaded.
		1996
		1997	All the environment variables documented here start with
		1998	C<PERL_ANYEVENT_>, which is what AnyEvent considers its own
		1999	namespace. Other modules are encouraged (but by no means required) to use
		2000	C<PERL_ANYEVENT_SUBMODULE> if they have registered the AnyEvent::Submodule
		2001	namespace on CPAN, for any submodule. For example, L<AnyEvent::HTTP> could
		2002	be expected to use C<PERL_ANYEVENT_HTTP_PROXY> (it should not access env
		2003	variables starting with C<AE_>, see below).
		2004
		2005	All variables can also be set via the C<AE_> prefix, that is, instead
		2006	of setting C<PERL_ANYEVENT_VERBOSE> you can also set C<AE_VERBOSE>. In
		2007	case there is a clash btween anyevent and another program that uses
		2008	C<AE_something> you can set the corresponding C<PERL_ANYEVENT_something>
		2009	variable to the empty string, as those variables take precedence.
		2010
		2011	When AnyEvent is first loaded, it copies all C<AE_xxx> env variables
		2012	to their C<PERL_ANYEVENT_xxx> counterpart unless that variable already
		2013	exists. If taint mode is on, then AnyEvent will remove I<all> environment
		2014	variables starting with C<PERL_ANYEVENT_> from C<%ENV> (or replace them
		2015	with C<undef> or the empty string, if the corresaponding C<AE_> variable
		2016	is set).
		2017
		2018	The exact algorithm is currently:
		2019
		2020	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		2021	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		2022	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		2023
		2024	This ensures that child processes will not see the C<AE_> variables.
		2025
		2026	The following environment variables are currently known to AnyEvent:
		2027
		2028	=over 4
		2029
		2030	=item C<PERL_ANYEVENT_VERBOSE>
		2031
		2032	By default, AnyEvent will be completely silent except in fatal
		2033	conditions. You can set this environment variable to make AnyEvent more
		2034	talkative. If you want to do more than just set the global logging level
		2035	you should have a look at C<PERL_ANYEVENT_LOG>, which allows much more
		2036	complex specifications.
		2037
		2038	When set to C<5> or higher, causes AnyEvent to warn about unexpected
		2039	conditions, such as not being able to load the event model specified by
		2040	C<PERL_ANYEVENT_MODEL>.
		2041
		2042	When set to C<7> or higher, cause AnyEvent to report to STDERR which event
		2043	model it chooses.
		2044
		2045	When set to C<8> or higher, then AnyEvent will report extra information on
		2046	which optional modules it loads and how it implements certain features.
		2047
		2048	=item C<PERL_ANYEVENT_LOG>
		2049
		2050	Accepts rather complex logging specifications. For example, you could log
		2051	all C<debug> messages of some module to stderr, warnings and above to
		2052	stderr, and errors and above to syslog, with:
		2053
		2054	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		2055
		2056	For the rather extensive details, see L<AnyEvent::Log>.
		2057
		2058	Note that specifying this environment variable causes the L<AnyEvent::Log>
		2059	module to be loaded, while C<PERL_ANYEVENT_VERBOSE> does not, so only
		2060	using the latter saves a few hundred kB of memory until the first message
		2061	is being logged.
		2062
		2063	=item C<PERL_ANYEVENT_STRICT>
		2064
		2065	AnyEvent does not do much argument checking by default, as thorough
		2066	argument checking is very costly. Setting this variable to a true value
		2067	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		2068	check the arguments passed to most method calls. If it finds any problems,
		2069	it will croak.
		2070
		2071	In other words, enables "strict" mode.
		2072
		2073	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		2074	>>, it is definitely recommended to keep it off in production. Keeping
		2075	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		2076	can be very useful, however.
		2077
		2078	=item C<PERL_ANYEVENT_DEBUG_SHELL>
		2079
		2080	If this env variable is set, then its contents will be interpreted by
		2081	C<AnyEvent::Socket::parse_hostport> (after replacing every occurance of
		2082	C<$$> by the process pid) and an C<AnyEvent::Debug::shell> is bound on
		2083	that port. The shell object is saved in C<$AnyEvent::Debug::SHELL>.
		2084
		2085	This takes place when the first watcher is created.
		2086
		2087	For example, to bind a debug shell on a unix domain socket in
		2088	F<< /tmp/debug<pid>.sock >>, you could use this:
		2089
		2090	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		2091
		2092	Note that creating sockets in F</tmp> is very unsafe on multiuser
		2093	systems.
		2094
		2095	=item C<PERL_ANYEVENT_DEBUG_WRAP>
		2096
		2097	Can be set to C<0>, C<1> or C<2> and enables wrapping of all watchers for
		2098	debugging purposes. See C<AnyEvent::Debug::wrap> for details.
		2099
		2100	=item C<PERL_ANYEVENT_MODEL>
		2101
		2102	This can be used to specify the event model to be used by AnyEvent, before
		2103	auto detection and -probing kicks in.
		2104
		2105	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		2106	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		2107	resulting module name is loaded and - if the load was successful - used as
		2108	event model backend. If it fails to load then AnyEvent will proceed with
		2109	auto detection and -probing.
		2110
		2111	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		2112	nothing gets prepended and the module name is used as-is (hint: C<::> at
		2113	the end of a string designates a module name and quotes it appropriately).
		2114
		2115	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		2116	could start your program like this:
		2117
		2118	PERL_ANYEVENT_MODEL=Perl perl ...
		2119
		2120	=item C<PERL_ANYEVENT_PROTOCOLS>
		2121
		2122	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		2123	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		2124	of auto probing).
		2125
		2126	Must be set to a comma-separated list of protocols or address families,
		2127	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		2128	used, and preference will be given to protocols mentioned earlier in the
		2129	list.
		2130
		2131	This variable can effectively be used for denial-of-service attacks
		2132	against local programs (e.g. when setuid), although the impact is likely
		2133	small, as the program has to handle conenction and other failures anyways.
		2134
		2135	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		2136	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		2137	- only support IPv4, never try to resolve or contact IPv6
		2138	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		2139	IPv6, but prefer IPv6 over IPv4.
		2140
		2141	=item C<PERL_ANYEVENT_HOSTS>
		2142
		2143	This variable, if specified, overrides the F</etc/hosts> file used by
		2144	L<AnyEvent::Socket>C<::resolve_sockaddr>, i.e. hosts aliases will be read
		2145	from that file instead.
		2146
		2147	=item C<PERL_ANYEVENT_EDNS0>
		2148
		2149	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension for
		2150	DNS. This extension is generally useful to reduce DNS traffic, especially
		2151	when DNSSEC is involved, but some (broken) firewalls drop such DNS
		2152	packets, which is why it is off by default.
		2153
		2154	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2155	EDNS0 in its DNS requests.
		2156
		2157	=item C<PERL_ANYEVENT_MAX_FORKS>
		2158
		2159	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2160	will create in parallel.
		2161
		2162	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2163
		2164	The default value for the C<max_outstanding> parameter for the default DNS
		2165	resolver - this is the maximum number of parallel DNS requests that are
		2166	sent to the DNS server.
		2167
		2168	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2169
		2170	The absolute path to a F<resolv.conf>-style file to use instead of
		2171	F</etc/resolv.conf> (or the OS-specific configuration) in the default
		2172	resolver, or the empty string to select the default configuration.
		2173
		2174	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2175
		2176	When neither C<ca_file> nor C<ca_path> was specified during
		2177	L<AnyEvent::TLS> context creation, and either of these environment
		2178	variables are nonempty, they will be used to specify CA certificate
		2179	locations instead of a system-dependent default.
		2180
		2181	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2182
		2183	When these are set to C<1>, then the respective modules are not
		2184	loaded. Mostly good for testing AnyEvent itself.
		2185
		2186	=back
		2187
		2188	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		2189
		2190	This is an advanced topic that you do not normally need to use AnyEvent in
		2191	a module. This section is only of use to event loop authors who want to
		2192	provide AnyEvent compatibility.
		2193
		2194	If you need to support another event library which isn't directly
		2195	supported by AnyEvent, you can supply your own interface to it by
		2196	pushing, before the first watcher gets created, the package name of
		2197	the event module and the package name of the interface to use onto
		2198	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		2199	AnyEvent, so it is reasonably cheap.
		2200
		2201	Example:
		2202
		2203	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		2204
		2205	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		2206	package/class when it finds the C<urxvt> package/module is already loaded.
		2207
		2208	When AnyEvent is loaded and asked to find a suitable event model, it
		2209	will first check for the presence of urxvt by trying to C<use> the
		2210	C<urxvt::anyevent> module.
		2211
		2212	The class should provide implementations for all watcher types. See
		2213	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		2214	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		2215	see the sources.
		2216
		2217	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2218	provide suitable (hopefully) replacements.
		2219
		2220	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		2221	terminal emulator uses the above line as-is. An interface isn't included
		2222	in AnyEvent because it doesn't make sense outside the embedded interpreter
		2223	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		2224	I<rxvt-unicode> distribution.
		2225
		2226	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		2227	condition variables: code blocking while waiting for a condition will
		2228	C<die>. This still works with most modules/usages, and blocking calls must
		2229	not be done in an interactive application, so it makes sense.
		2230
		2231	=head1 EXAMPLE PROGRAM
		2232
		2233	The following program uses an I/O watcher to read data from STDIN, a timer
		2234	to display a message once per second, and a condition variable to quit the
		2235	program when the user enters quit:
		2236
		2237	use AnyEvent;
		2238
		2239	my $cv = AnyEvent->condvar;
		2240
		2241	my $io_watcher = AnyEvent->io (
		2242	fh => \*STDIN,
		2243	poll => 'r',
		2244	cb => sub {
		2245	warn "io event <$_[0]>\n"; # will always output <r>
		2246	chomp (my $input = <STDIN>); # read a line
		2247	warn "read: $input\n"; # output what has been read
		2248	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2249	},
		2250	);
		2251
		2252	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2253	warn "timeout\n"; # print 'timeout' at most every second
		2254	});
		2255
		2256	$cv->recv; # wait until user enters /^q/i
		2257
		2258	=head1 REAL-WORLD EXAMPLE
		2259
		2260	Consider the L<Net::FCP> module. It features (among others) the following
		2261	API calls, which are to freenet what HTTP GET requests are to http:
		2262
		2263	my $data = $fcp->client_get ($url); # blocks
		2264
		2265	my $transaction = $fcp->txn_client_get ($url); # does not block
		2266	$transaction->cb ( sub { ... } ); # set optional result callback
		2267	my $data = $transaction->result; # possibly blocks
		2268
		2269	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		2270	given URL and waits till the data has arrived. It is defined to be:
		2271
		2272	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		2273
		2274	And in fact is automatically generated. This is the blocking API of
		2275	L<Net::FCP>, and it works as simple as in any other, similar, module.
		2276
		2277	More complicated is C<txn_client_get>: It only creates a transaction
		2278	(completion, result, ...) object and initiates the transaction.
		2279
		2280	my $txn = bless { }, Net::FCP::Txn::;
		2281
		2282	It also creates a condition variable that is used to signal the completion
		2283	of the request:
		2284
		2285	$txn->{finished} = AnyAvent->condvar;
		2286
		2287	It then creates a socket in non-blocking mode.
		2288
		2289	socket $txn->{fh}, ...;
		2290	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		2291	connect $txn->{fh}, ...
		2292	and !$!{EWOULDBLOCK}
		2293	and !$!{EINPROGRESS}
		2294	and Carp::croak "unable to connect: $!\n";
		2295
		2296	Then it creates a write-watcher which gets called whenever an error occurs
		2297	or the connection succeeds:
		2298
		2299	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		2300
		2301	And returns this transaction object. The C<fh_ready_w> callback gets
		2302	called as soon as the event loop detects that the socket is ready for
		2303	writing.
		2304
		2305	The C<fh_ready_w> method makes the socket blocking again, writes the
		2306	request data and replaces the watcher by a read watcher (waiting for reply
		2307	data). The actual code is more complicated, but that doesn't matter for
		2308	this example:
		2309
		2310	fcntl $txn->{fh}, F_SETFL, 0;
		2311	syswrite $txn->{fh}, $txn->{request}
		2312	or die "connection or write error";
		2313	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		2314
		2315	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		2316	result and signals any possible waiters that the request has finished:
		2317
		2318	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		2319
		2320	if (end-of-file or data complete) {
		2321	$txn->{result} = $txn->{buf};
		2322	$txn->{finished}->send;
		2323	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		2324	}
		2325
		2326	The C<result> method, finally, just waits for the finished signal (if the
		2327	request was already finished, it doesn't wait, of course, and returns the
		2328	data:
		2329
		2330	$txn->{finished}->recv;
		2331	return $txn->{result};
		2332
		2333	The actual code goes further and collects all errors (C<die>s, exceptions)
		2334	that occurred during request processing. The C<result> method detects
		2335	whether an exception as thrown (it is stored inside the $txn object)
		2336	and just throws the exception, which means connection errors and other
		2337	problems get reported to the code that tries to use the result, not in a
		2338	random callback.
		2339
		2340	All of this enables the following usage styles:
		2341
		2342	1. Blocking:
		2343
		2344	my $data = $fcp->client_get ($url);
		2345
		2346	2. Blocking, but running in parallel:
		2347
		2348	my @datas = map $_->result,
		2349	map $fcp->txn_client_get ($_),
		2350	@urls;
		2351
		2352	Both blocking examples work without the module user having to know
		2353	anything about events.
		2354
		2355	3a. Event-based in a main program, using any supported event module:
		2356
		2357	use EV;
		2358
		2359	$fcp->txn_client_get ($url)->cb (sub {
		2360	my $txn = shift;
		2361	my $data = $txn->result;
		2362	...
		2363	});
		2364
		2365	EV::loop;
		2366
		2367	3b. The module user could use AnyEvent, too:
		2368
		2369	use AnyEvent;
		2370
		2371	my $quit = AnyEvent->condvar;
		2372
		2373	$fcp->txn_client_get ($url)->cb (sub {
		2374	...
		2375	$quit->send;
		2376	});
		2377
		2378	$quit->recv;
		2379
		2380
		2381	=head1 BENCHMARKS
		2382
		2383	To give you an idea of the performance and overheads that AnyEvent adds
		2384	over the event loops themselves and to give you an impression of the speed
		2385	of various event loops I prepared some benchmarks.
		2386
		2387	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2388
		2389	Here is a benchmark of various supported event models used natively and
		2390	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2391	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2392	which it is), lets them fire exactly once and destroys them again.
		2393
		2394	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2395	distribution. It uses the L<AE> interface, which makes a real difference
		2396	for the EV and Perl backends only.
		2397
		2398	=head3 Explanation of the columns
		2399
		2400	I<watcher> is the number of event watchers created/destroyed. Since
		2401	different event models feature vastly different performances, each event
		2402	loop was given a number of watchers so that overall runtime is acceptable
		2403	and similar between tested event loop (and keep them from crashing): Glib
		2404	would probably take thousands of years if asked to process the same number
		2405	of watchers as EV in this benchmark.
		2406
		2407	I<bytes> is the number of bytes (as measured by the resident set size,
		2408	RSS) consumed by each watcher. This method of measuring captures both C
		2409	and Perl-based overheads.
		2410
		2411	I<create> is the time, in microseconds (millionths of seconds), that it
		2412	takes to create a single watcher. The callback is a closure shared between
		2413	all watchers, to avoid adding memory overhead. That means closure creation
		2414	and memory usage is not included in the figures.
		2415
		2416	I<invoke> is the time, in microseconds, used to invoke a simple
		2417	callback. The callback simply counts down a Perl variable and after it was
		2418	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2419	signal the end of this phase.
		2420
		2421	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2422	watcher.
		2423
		2424	=head3 Results
		2425
		2426	name watchers bytes create invoke destroy comment
		2427	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2428	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2429	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2430	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2431	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2432	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2433	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2434	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2435	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2436	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2437	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2438	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2439
		2440	=head3 Discussion
		2441
		2442	The benchmark does I<not> measure scalability of the event loop very
		2443	well. For example, a select-based event loop (such as the pure perl one)
		2444	can never compete with an event loop that uses epoll when the number of
		2445	file descriptors grows high. In this benchmark, all events become ready at
		2446	the same time, so select/poll-based implementations get an unnatural speed
		2447	boost.
		2448
		2449	Also, note that the number of watchers usually has a nonlinear effect on
		2450	overall speed, that is, creating twice as many watchers doesn't take twice
		2451	the time - usually it takes longer. This puts event loops tested with a
		2452	higher number of watchers at a disadvantage.
		2453
		2454	To put the range of results into perspective, consider that on the
		2455	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2456	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2457	cycles with POE.
		2458
		2459	C<EV> is the sole leader regarding speed and memory use, which are both
		2460	maximal/minimal, respectively. When using the L<AE> API there is zero
		2461	overhead (when going through the AnyEvent API create is about 5-6 times
		2462	slower, with other times being equal, so still uses far less memory than
		2463	any other event loop and is still faster than Event natively).
		2464
		2465	The pure perl implementation is hit in a few sweet spots (both the
		2466	constant timeout and the use of a single fd hit optimisations in the perl
		2467	interpreter and the backend itself). Nevertheless this shows that it
		2468	adds very little overhead in itself. Like any select-based backend its
		2469	performance becomes really bad with lots of file descriptors (and few of
		2470	them active), of course, but this was not subject of this benchmark.
		2471
		2472	The C<Event> module has a relatively high setup and callback invocation
		2473	cost, but overall scores in on the third place.
		2474
		2475	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2476	when using its pure perl backend.
		2477
		2478	C<Glib>'s memory usage is quite a bit higher, but it features a
		2479	faster callback invocation and overall ends up in the same class as
		2480	C<Event>. However, Glib scales extremely badly, doubling the number of
		2481	watchers increases the processing time by more than a factor of four,
		2482	making it completely unusable when using larger numbers of watchers
		2483	(note that only a single file descriptor was used in the benchmark, so
		2484	inefficiencies of C<poll> do not account for this).
		2485
		2486	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2487	more than 2000 watchers is a big setback, however, as correctness takes
		2488	precedence over speed. Nevertheless, its performance is surprising, as the
		2489	file descriptor is dup()ed for each watcher. This shows that the dup()
		2490	employed by some adaptors is not a big performance issue (it does incur a
		2491	hidden memory cost inside the kernel which is not reflected in the figures
		2492	above).
		2493
		2494	C<POE>, regardless of underlying event loop (whether using its pure perl
		2495	select-based backend or the Event module, the POE-EV backend couldn't
		2496	be tested because it wasn't working) shows abysmal performance and
		2497	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2498	as EV watchers, and 10 times as much memory as Event (the high memory
		2499	requirements are caused by requiring a session for each watcher). Watcher
		2500	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2501	implementation.
		2502
		2503	The design of the POE adaptor class in AnyEvent can not really account
		2504	for the performance issues, though, as session creation overhead is
		2505	small compared to execution of the state machine, which is coded pretty
		2506	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2507	using multiple sessions is not a good approach, especially regarding
		2508	memory usage, even the author of POE could not come up with a faster
		2509	design).
		2510
		2511	=head3 Summary
		2512
		2513	=over 4
		2514
		2515	=item * Using EV through AnyEvent is faster than any other event loop
		2516	(even when used without AnyEvent), but most event loops have acceptable
		2517	performance with or without AnyEvent.
		2518
		2519	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2520	the actual event loop, only with extremely fast event loops such as EV
		2521	does AnyEvent add significant overhead.
		2522
		2523	=item * You should avoid POE like the plague if you want performance or
		2524	reasonable memory usage.
		2525
		2526	=back
		2527
		2528	=head2 BENCHMARKING THE LARGE SERVER CASE
		2529
		2530	This benchmark actually benchmarks the event loop itself. It works by
		2531	creating a number of "servers": each server consists of a socket pair, a
		2532	timeout watcher that gets reset on activity (but never fires), and an I/O
		2533	watcher waiting for input on one side of the socket. Each time the socket
		2534	watcher reads a byte it will write that byte to a random other "server".
		2535
		2536	The effect is that there will be a lot of I/O watchers, only part of which
		2537	are active at any one point (so there is a constant number of active
		2538	fds for each loop iteration, but which fds these are is random). The
		2539	timeout is reset each time something is read because that reflects how
		2540	most timeouts work (and puts extra pressure on the event loops).
		2541
		2542	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2543	(1%) are active. This mirrors the activity of large servers with many
		2544	connections, most of which are idle at any one point in time.
		2545
		2546	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2547	distribution. It uses the L<AE> interface, which makes a real difference
		2548	for the EV and Perl backends only.
		2549
		2550	=head3 Explanation of the columns
		2551
		2552	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2553	each server has a read and write socket end).
		2554
		2555	I<create> is the time it takes to create a socket pair (which is
		2556	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2557
		2558	I<request>, the most important value, is the time it takes to handle a
		2559	single "request", that is, reading the token from the pipe and forwarding
		2560	it to another server. This includes deleting the old timeout and creating
		2561	a new one that moves the timeout into the future.
		2562
		2563	=head3 Results
		2564
		2565	name sockets create request
		2566	EV 20000 62.66 7.99
		2567	Perl 20000 68.32 32.64
		2568	IOAsync 20000 174.06 101.15 epoll
		2569	IOAsync 20000 174.67 610.84 poll
		2570	Event 20000 202.69 242.91
		2571	Glib 20000 557.01 1689.52
		2572	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2573
		2574	=head3 Discussion
		2575
		2576	This benchmark I<does> measure scalability and overall performance of the
		2577	particular event loop.
		2578
		2579	EV is again fastest. Since it is using epoll on my system, the setup time
		2580	is relatively high, though.
		2581
		2582	Perl surprisingly comes second. It is much faster than the C-based event
		2583	loops Event and Glib.
		2584
		2585	IO::Async performs very well when using its epoll backend, and still quite
		2586	good compared to Glib when using its pure perl backend.
		2587
		2588	Event suffers from high setup time as well (look at its code and you will
		2589	understand why). Callback invocation also has a high overhead compared to
		2590	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2591	uses select or poll in basically all documented configurations.
		2592
		2593	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2594	clearly fails to perform with many filehandles or in busy servers.
		2595
		2596	POE is still completely out of the picture, taking over 1000 times as long
		2597	as EV, and over 100 times as long as the Perl implementation, even though
		2598	it uses a C-based event loop in this case.
		2599
		2600	=head3 Summary
		2601
		2602	=over 4
		2603
		2604	=item * The pure perl implementation performs extremely well.
		2605
		2606	=item * Avoid Glib or POE in large projects where performance matters.
		2607
		2608	=back
		2609
		2610	=head2 BENCHMARKING SMALL SERVERS
		2611
		2612	While event loops should scale (and select-based ones do not...) even to
		2613	large servers, most programs we (or I :) actually write have only a few
		2614	I/O watchers.
		2615
		2616	In this benchmark, I use the same benchmark program as in the large server
		2617	case, but it uses only eight "servers", of which three are active at any
		2618	one time. This should reflect performance for a small server relatively
		2619	well.
		2620
		2621	The columns are identical to the previous table.
		2622
		2623	=head3 Results
		2624
		2625	name sockets create request
		2626	EV 16 20.00 6.54
		2627	Perl 16 25.75 12.62
		2628	Event 16 81.27 35.86
		2629	Glib 16 32.63 15.48
		2630	POE 16 261.87 276.28 uses POE::Loop::Event
		2631
		2632	=head3 Discussion
		2633
		2634	The benchmark tries to test the performance of a typical small
		2635	server. While knowing how various event loops perform is interesting, keep
		2636	in mind that their overhead in this case is usually not as important, due
		2637	to the small absolute number of watchers (that is, you need efficiency and
		2638	speed most when you have lots of watchers, not when you only have a few of
		2639	them).
		2640
		2641	EV is again fastest.
		2642
		2643	Perl again comes second. It is noticeably faster than the C-based event
		2644	loops Event and Glib, although the difference is too small to really
		2645	matter.
		2646
		2647	POE also performs much better in this case, but is is still far behind the
		2648	others.
		2649
		2650	=head3 Summary
		2651
		2652	=over 4
		2653
		2654	=item * C-based event loops perform very well with small number of
		2655	watchers, as the management overhead dominates.
		2656
		2657	=back
		2658
		2659	=head2 THE IO::Lambda BENCHMARK
		2660
		2661	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2662	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2663	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2664	shouldn't come as a surprise to anybody). As such, the benchmark is
		2665	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2666	very optimal. But how would AnyEvent compare when used without the extra
		2667	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2668
		2669	The benchmark itself creates an echo-server, and then, for 500 times,
		2670	connects to the echo server, sends a line, waits for the reply, and then
		2671	creates the next connection. This is a rather bad benchmark, as it doesn't
		2672	test the efficiency of the framework or much non-blocking I/O, but it is a
		2673	benchmark nevertheless.
		2674
		2675	name runtime
		2676	Lambda/select 0.330 sec
		2677	+ optimized 0.122 sec
		2678	Lambda/AnyEvent 0.327 sec
		2679	+ optimized 0.138 sec
		2680	Raw sockets/select 0.077 sec
		2681	POE/select, components 0.662 sec
		2682	POE/select, raw sockets 0.226 sec
		2683	POE/select, optimized 0.404 sec
		2684
		2685	AnyEvent/select/nb 0.085 sec
		2686	AnyEvent/EV/nb 0.068 sec
		2687	+state machine 0.134 sec
		2688
		2689	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2690	benchmarks actually make blocking connects and use 100% blocking I/O,
		2691	defeating the purpose of an event-based solution. All of the newly
		2692	written AnyEvent benchmarks use 100% non-blocking connects (using
		2693	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2694	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2695	generally require a lot more bookkeeping and event handling than blocking
		2696	connects (which involve a single syscall only).
		2697
		2698	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2699	offers similar expressive power as POE and IO::Lambda, using conventional
		2700	Perl syntax. This means that both the echo server and the client are 100%
		2701	non-blocking, further placing it at a disadvantage.
		2702
		2703	As you can see, the AnyEvent + EV combination even beats the
		2704	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2705	backend easily beats IO::Lambda and POE.
		2706
		2707	And even the 100% non-blocking version written using the high-level (and
		2708	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2709	higher level ("unoptimised") abstractions by a large margin, even though
		2710	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2711
		2712	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2713	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2714	part of the IO::Lambda distribution and were used without any changes.
		2715
		2716
		2717	=head1 SIGNALS
		2718
		2719	AnyEvent currently installs handlers for these signals:
		2720
		2721	=over 4
		2722
		2723	=item SIGCHLD
		2724
		2725	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2726	emulation for event loops that do not support them natively. Also, some
		2727	event loops install a similar handler.
		2728
		2729	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2730	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2731
		2732	=item SIGPIPE
		2733
		2734	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2735	when AnyEvent gets loaded.
		2736
		2737	The rationale for this is that AnyEvent users usually do not really depend
		2738	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2739	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2740	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2741	some random socket.
		2742
		2743	The rationale for installing a no-op handler as opposed to ignoring it is
		2744	that this way, the handler will be restored to defaults on exec.
		2745
		2746	Feel free to install your own handler, or reset it to defaults.
		2747
		2748	=back
		2749
		2750	=cut
		2751
		2752	undef $SIG{CHLD}
		2753	if $SIG{CHLD} eq 'IGNORE';
		2754
		2755	$SIG{PIPE} = sub { }
		2756	unless defined $SIG{PIPE};
		2757
		2758	=head1 RECOMMENDED/OPTIONAL MODULES
		2759
		2760	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2761	its built-in modules) are required to use it.
		2762
		2763	That does not mean that AnyEvent won't take advantage of some additional
		2764	modules if they are installed.
		2765
		2766	This section explains which additional modules will be used, and how they
		2767	affect AnyEvent's operation.
		2768
		2769	=over 4
		2770
		2771	=item L<Async::Interrupt>
		2772
		2773	This slightly arcane module is used to implement fast signal handling: To
		2774	my knowledge, there is no way to do completely race-free and quick
		2775	signal handling in pure perl. To ensure that signals still get
		2776	delivered, AnyEvent will start an interval timer to wake up perl (and
		2777	catch the signals) with some delay (default is 10 seconds, look for
		2778	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2779
		2780	If this module is available, then it will be used to implement signal
		2781	catching, which means that signals will not be delayed, and the event loop
		2782	will not be interrupted regularly, which is more efficient (and good for
		2783	battery life on laptops).
		2784
		2785	This affects not just the pure-perl event loop, but also other event loops
		2786	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2787
		2788	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2789	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2790	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2791	does nothing for those backends.
		2792
		2793	=item L<EV>
		2794
		2795	This module isn't really "optional", as it is simply one of the backend
		2796	event loops that AnyEvent can use. However, it is simply the best event
		2797	loop available in terms of features, speed and stability: It supports
		2798	the AnyEvent API optimally, implements all the watcher types in XS, does
		2799	automatic timer adjustments even when no monotonic clock is available,
		2800	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2801	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2802	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2803
		2804	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2805	then this module will do nothing for you.
		2806
		2807	=item L<Guard>
		2808
		2809	The guard module, when used, will be used to implement
		2810	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2811	lot less memory), but otherwise doesn't affect guard operation much. It is
		2812	purely used for performance.
		2813
		2814	=item L<JSON> and L<JSON::XS>
		2815
		2816	One of these modules is required when you want to read or write JSON data
		2817	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2818	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2819
		2820	=item L<Net::SSLeay>
		2821
		2822	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2823	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2824	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2825
		2826	=item L<Time::HiRes>
		2827
		2828	This module is part of perl since release 5.008. It will be used when the
		2829	chosen event library does not come with a timing source of its own. The
		2830	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2831	try to use a monotonic clock for timing stability.
		2832
		2833	=back
		2834
		2835
		2836	=head1 FORK
		2837
		2838	Most event libraries are not fork-safe. The ones who are usually are
		2839	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2840	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2841	are usually badly thought-out hacks that are incompatible with fork in
		2842	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2843	continue event-processing in both parent and child (or both, if you know
		2844	what you are doing).
		2845
		2846	This means that, in general, you cannot fork and do event processing in
		2847	the child if the event library was initialised before the fork (which
		2848	usually happens when the first AnyEvent watcher is created, or the library
		2849	is loaded).
		2850
		2851	If you have to fork, you must either do so I<before> creating your first
		2852	watcher OR you must not use AnyEvent at all in the child OR you must do
		2853	something completely out of the scope of AnyEvent.
		2854
		2855	The problem of doing event processing in the parent I<and> the child
		2856	is much more complicated: even for backends that I<are> fork-aware or
		2857	fork-safe, their behaviour is not usually what you want: fork clones all
		2858	watchers, that means all timers, I/O watchers etc. are active in both
		2859	parent and child, which is almost never what you want. USing C<exec>
		2860	to start worker children from some kind of manage rprocess is usually
		2861	preferred, because it is much easier and cleaner, at the expense of having
		2862	to have another binary.
		2863
		2864
		2865	=head1 SECURITY CONSIDERATIONS
		2866
		2867	AnyEvent can be forced to load any event model via
		2868	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2869	execute arbitrary code or directly gain access, it can easily be used to
		2870	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2871	will not be active when the program uses a different event model than
		2872	specified in the variable.
		2873
		2874	You can make AnyEvent completely ignore this variable by deleting it
		2875	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2876
		2877	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2878
		2879	use AnyEvent;
		2880
		2881	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2882	be used to probe what backend is used and gain other information (which is
		2883	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2884	$ENV{PERL_ANYEVENT_STRICT}.
		2885
		2886	Note that AnyEvent will remove I<all> environment variables starting with
		2887	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2888	enabled.
		2889
		2890
		2891	=head1 BUGS
		2892
		2893	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2894	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2895	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2896	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2897	pronounced).
		2898
		2899
		2900	=head1 SEE ALSO
		2901
		2902	Tutorial/Introduction: L<AnyEvent::Intro>.
		2903
		2904	FAQ: L<AnyEvent::FAQ>.
		2905
		2906	Utility functions: L<AnyEvent::Util> (misc. grab-bag), L<AnyEvent::Log>
		2907	(simply logging).
		2908
		2909	Development/Debugging: L<AnyEvent::Strict> (stricter checking),
		2910	L<AnyEvent::Debug> (interactive shell, watcher tracing).
		2911
		2912	Supported event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>,
		2913	L<Glib::EV>, L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>,
		2914	L<Qt>, L<POE>, L<FLTK>.
		2915
		2916	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2917	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2918	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2919	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>,
		2920	L<AnyEvent::Impl::FLTK>.
		2921
		2922	Non-blocking handles, pipes, stream sockets, TCP clients and
		2923	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2924
		2925	Asynchronous DNS: L<AnyEvent::DNS>.
		2926
		2927	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2928
		2929	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2930	L<AnyEvent::HTTP>.
		2931
		2932
		2933	=head1 AUTHOR
		2934
		2935	Marc Lehmann <schmorp@schmorp.de>
		2936	http://home.schmorp.de/
		2937
		2938	=cut
		2939
		2940	1
		2941

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