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Revision 1.378 by root, Fri Aug 26 18:08:07 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::FLTK 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	If L<AnyEvent::Log> is not loaded then this function makes a simple test
		1059	to see whether the message will be logged. If the test succeeds it will
		1060	load AnyEvent::Log and call C<AnyEvent::Log::log> - consequently, look at
		1061	the L<AnyEvent::Log> documentation for details.
		1062
		1063	If the test fails it will simply return.
		1064
		1065	If you want to sprinkle loads of logging calls around your code, consider
		1066	creating a logger callback with the C<AnyEvent::Log::logger> function,
		1067	which can reduce typing, codesize and can reduce the logging overhead
		1068	enourmously.
		1069
		1070	=back
		1071
		1072	=head1 WHAT TO DO IN A MODULE
		1073
		1074	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		1075	freely, but you should not load a specific event module or rely on it.
		1076
		1077	Be careful when you create watchers in the module body - AnyEvent will
		1078	decide which event module to use as soon as the first method is called, so
		1079	by calling AnyEvent in your module body you force the user of your module
		1080	to load the event module first.
		1081
		1082	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1083	the C<< ->send >> method has been called on it already. This is
		1084	because it will stall the whole program, and the whole point of using
		1085	events is to stay interactive.
		1086
		1087	It is fine, however, to call C<< ->recv >> when the user of your module
		1088	requests it (i.e. if you create a http request object ad have a method
		1089	called C<results> that returns the results, it may call C<< ->recv >>
		1090	freely, as the user of your module knows what she is doing. Always).
		1091
		1092	=head1 WHAT TO DO IN THE MAIN PROGRAM
		1093
		1094	There will always be a single main program - the only place that should
		1095	dictate which event model to use.
		1096
		1097	If the program is not event-based, it need not do anything special, even
		1098	when it depends on a module that uses an AnyEvent. If the program itself
		1099	uses AnyEvent, but does not care which event loop is used, all it needs
		1100	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1101	available loop implementation.
		1102
		1103	If the main program relies on a specific event model - for example, in
		1104	Gtk2 programs you have to rely on the Glib module - you should load the
		1105	event module before loading AnyEvent or any module that uses it: generally
		1106	speaking, you should load it as early as possible. The reason is that
		1107	modules might create watchers when they are loaded, and AnyEvent will
		1108	decide on the event model to use as soon as it creates watchers, and it
		1109	might choose the wrong one unless you load the correct one yourself.
		1110
		1111	You can chose to use a pure-perl implementation by loading the
		1112	C<AnyEvent::Loop> module, which gives you similar behaviour
		1113	everywhere, but letting AnyEvent chose the model is generally better.
		1114
		1115	=head2 MAINLOOP EMULATION
		1116
		1117	Sometimes (often for short test scripts, or even standalone programs who
		1118	only want to use AnyEvent), you do not want to run a specific event loop.
		1119
		1120	In that case, you can use a condition variable like this:
		1121
		1122	AnyEvent->condvar->recv;
		1123
		1124	This has the effect of entering the event loop and looping forever.
		1125
		1126	Note that usually your program has some exit condition, in which case
		1127	it is better to use the "traditional" approach of storing a condition
		1128	variable somewhere, waiting for it, and sending it when the program should
		1129	exit cleanly.
		1130
		1131
		1132	=head1 OTHER MODULES
		1133
		1134	The following is a non-exhaustive list of additional modules that use
		1135	AnyEvent as a client and can therefore be mixed easily with other
		1136	AnyEvent modules and other event loops in the same program. Some of the
		1137	modules come as part of AnyEvent, the others are available via CPAN (see
		1138	L<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for
		1139	a longer non-exhaustive list), and the list is heavily biased towards
		1140	modules of the AnyEvent author himself :)
		1141
		1142	=over 4
		1143
		1144	=item L<AnyEvent::Util>
		1145
		1146	Contains various utility functions that replace often-used blocking
		1147	functions such as C<inet_aton> with event/callback-based versions.
		1148
		1149	=item L<AnyEvent::Socket>
		1150
		1151	Provides various utility functions for (internet protocol) sockets,
		1152	addresses and name resolution. Also functions to create non-blocking tcp
		1153	connections or tcp servers, with IPv6 and SRV record support and more.
		1154
		1155	=item L<AnyEvent::Handle>
		1156
		1157	Provide read and write buffers, manages watchers for reads and writes,
		1158	supports raw and formatted I/O, I/O queued and fully transparent and
		1159	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1160
		1161	=item L<AnyEvent::DNS>
		1162
		1163	Provides rich asynchronous DNS resolver capabilities.
		1164
		1165	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1166
		1167	Implement event-based interfaces to the protocols of the same name (for
		1168	the curious, IGS is the International Go Server and FCP is the Freenet
		1169	Client Protocol).
		1170
		1171	=item L<AnyEvent::AIO>
		1172
		1173	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1174	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1175	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1176	file I/O, and much more.
		1177
		1178	=item L<AnyEvent::Filesys::Notify>
		1179
		1180	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1181	path changes (e.g. "watch this directory for new files", "watch this
		1182	file for changes"). The L<AnyEvent::Filesys::Notify> module promises to
		1183	do just that in a portbale fashion, supporting inotify on GNU/Linux and
		1184	some weird, without doubt broken, stuff on OS X to monitor files. It can
		1185	fall back to blocking scans at regular intervals transparently on other
		1186	platforms, so it's about as portable as it gets.
		1187
		1188	(I haven't used it myself, but I haven't heard anybody complaining about
		1189	it yet).
		1190
		1191	=item L<AnyEvent::DBI>
		1192
		1193	Executes L<DBI> requests asynchronously in a proxy process for you,
		1194	notifying you in an event-based way when the operation is finished.
		1195
		1196	=item L<AnyEvent::HTTPD>
		1197
		1198	A simple embedded webserver.
		1199
		1200	=item L<AnyEvent::FastPing>
		1201
		1202	The fastest ping in the west.
		1203
		1204	=item L<Coro>
		1205
		1206	Has special support for AnyEvent via L<Coro::AnyEvent>, which allows you
		1207	to simply invert the flow control - don't call us, we will call you:
		1208
		1209	async {
		1210	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
		1211	print "5 seconds later!\n";
		1212
		1213	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1214	my $line = <STDIN>; # works for ttys
		1215
		1216	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1217	my ($body, $hdr) = Coro::rouse_wait;
		1218	};
		1219
		1220	=back
		1221
11	=cut	1222	=cut
12		1223
13	package AnyEvent;	1224	package AnyEvent;
14		1225
		1226	# basically a tuned-down version of common::sense
		1227	sub common_sense {
		1228	# from common:.sense 3.4
		1229	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
		1230	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1231	$^H |= 0x00000600;
		1232	}
		1233
		1234	BEGIN { AnyEvent::common_sense }
		1235
15	use Carp;	1236	use Carp ();
16		1237
17	$VERSION = 0.1;	1238	our $VERSION = '6.01';
		1239	our $MODEL;
18		1240
19	no warnings;	1241	our @ISA;
20		1242
		1243	our @REGISTRY;
		1244
		1245	our $VERBOSE;
		1246
		1247	BEGIN {
		1248	require "AnyEvent/constants.pl";
		1249
		1250	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1251
		1252	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1253	if ${^TAINT};
		1254
		1255	$ENV{"PERL_ANYEVENT_$_"} = $ENV{"AE_$_"}
		1256	for grep s/^AE_// && !exists $ENV{"PERL_ANYEVENT_$_"}, keys %ENV;
		1257
		1258	@ENV{grep /^PERL_ANYEVENT_/, keys %ENV} = ()
		1259	if ${^TAINT};
		1260
		1261	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1262	}
		1263
		1264	our $MAX_SIGNAL_LATENCY = 10;
		1265
		1266	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1267
		1268	{
		1269	my $idx;
		1270	$PROTOCOL{$_} = ++$idx
		1271	for reverse split /\s*,\s*/,
		1272	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1273	}
		1274
		1275	our @post_detect;
		1276
		1277	sub post_detect(&) {
		1278	my ($cb) = @_;
		1279
		1280	push @post_detect, $cb;
		1281
		1282	defined wantarray
		1283	? bless \$cb, "AnyEvent::Util::postdetect"
		1284	: ()
		1285	}
		1286
		1287	sub AnyEvent::Util::postdetect::DESTROY {
		1288	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1289	}
		1290
		1291	our $POSTPONE_W;
		1292	our @POSTPONE;
		1293
		1294	sub _postpone_exec {
		1295	undef $POSTPONE_W;
		1296
		1297	&{ shift @POSTPONE }
		1298	while @POSTPONE;
		1299	}
		1300
		1301	sub postpone(&) {
		1302	push @POSTPONE, shift;
		1303
		1304	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1305
		1306	()
		1307	}
		1308
		1309	sub log($$;@) {
		1310	# only load the big bloated module when we actually are about to log something
		1311	if ($_[0] <= $VERBOSE) { # also catches non-numeric levels(!)
		1312	require AnyEvent::Log;
		1313	# AnyEvent::Log overwrites this function
		1314	goto &log;
		1315	}
		1316
		1317	0 # not logged
		1318	}
		1319
		1320	if (length $ENV{PERL_ANYEVENT_LOG}) {
		1321	require AnyEvent::Log; # AnyEvent::Log does the thing for us
		1322	}
		1323
21	my @models = (	1324	our @models = (
22	[Coro => Coro::Event::],	1325	[EV:: => AnyEvent::Impl::EV:: , 1],
23	[Event => Event::],	1326	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
24	[Glib => Glib::],	1327	# everything below here will not (normally) be autoprobed
25	[Tk => Tk::],	1328	# as the pure perl backend should work everywhere
		1329	# and is usually faster
		1330	[Event:: => AnyEvent::Impl::Event::, 1],
		1331	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1332	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1333	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1334	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1335	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1336	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1337	[Wx:: => AnyEvent::Impl::POE::],
		1338	[Prima:: => AnyEvent::Impl::POE::],
		1339	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1340	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
		1341	[FLTK:: => AnyEvent::Impl::FLTK::],
26	);	1342	);
27		1343
28	sub AUTOLOAD {	1344	our @isa_hook;
29	$AUTOLOAD =~ s/.*://;
30		1345
31	for (@models) {	1346	sub _isa_set {
32	my ($model, $package) = @$_;	1347	my @pkg = ("AnyEvent", (map $_->[0], grep defined, @isa_hook), $MODEL);
33	if (defined ${"$package\::VERSION"}) {	1348
34	$EVENT = "AnyEvent::Impl::$model";	1349	@{"$pkg[$_-1]::ISA"} = $pkg[$_]
35	eval "require $EVENT"; die if $@;	1350	for 1 .. $#pkg;
36	goto &{"$EVENT\::$AUTOLOAD"};	1351
		1352	grep $_ && $_->[1], @isa_hook
		1353	and AE::_reset ();
		1354	}
		1355
		1356	# used for hooking AnyEvent::Strict and AnyEvent::Debug::Wrap into the class hierarchy
		1357	sub _isa_hook($$;$) {
		1358	my ($i, $pkg, $reset_ae) = @_;
		1359
		1360	$isa_hook[$i] = $pkg ? [$pkg, $reset_ae] : undef;
		1361
		1362	_isa_set;
		1363	}
		1364
		1365	# all autoloaded methods reserve the complete glob, not just the method slot.
		1366	# due to bugs in perls method cache implementation.
		1367	our @methods = qw(io timer time now now_update signal child idle condvar);
		1368
		1369	sub detect() {
		1370	return $MODEL if $MODEL; # some programs keep references to detect
		1371
		1372	local $!; # for good measure
		1373	local $SIG{__DIE__}; # we use eval
		1374
		1375	# free some memory
		1376	*detect = sub () { $MODEL };
		1377	# undef &func doesn't correctly update the method cache. grmbl.
		1378	# so we delete the whole glob. grmbl.
		1379	# otoh, perl doesn't let me undef an active usb, but it lets me free
		1380	# a glob with an active sub. hrm. i hope it works, but perl is
		1381	# usually buggy in this department. sigh.
		1382	delete @{"AnyEvent::"}{@methods};
		1383	undef @methods;
		1384
		1385	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1386	my $model = $1;
		1387	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1388	if (eval "require $model") {
		1389	AnyEvent::log 7 => "loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.";
		1390	$MODEL = $model;
		1391	} else {
		1392	AnyEvent::log 5 => "unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@";
37	}	1393	}
38	}	1394	}
39		1395
40	for (@models) {	1396	# check for already loaded models
41	my ($model, $package) = @$_;	1397	unless ($MODEL) {
42	$EVENT = "AnyEvent::Impl::$model";	1398	for (@REGISTRY, @models) {
		1399	my ($package, $model) = @$_;
		1400	if (${"$package\::VERSION"} > 0) {
43	if (eval "require $EVENT") {	1401	if (eval "require $model") {
44	goto &{"$EVENT\::$AUTOLOAD"};	1402	AnyEvent::log 7 => "autodetected model '$model', using it.";
		1403	$MODEL = $model;
		1404	last;
		1405	}
		1406	}
		1407	}
		1408
		1409	unless ($MODEL) {
		1410	# try to autoload a model
		1411	for (@REGISTRY, @models) {
		1412	my ($package, $model, $autoload) = @$_;
		1413	if (
		1414	$autoload
		1415	and eval "require $package"
		1416	and ${"$package\::VERSION"} > 0
		1417	and eval "require $model"
		1418	) {
		1419	AnyEvent::log 7 => "autoloaded model '$model', using it.";
		1420	$MODEL = $model;
		1421	last;
		1422	}
		1423	}
		1424
		1425	$MODEL
		1426	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?";
45	}	1427	}
46	}	1428	}
47		1429
48	die "No event module selected for AnyEvent and autodetect failed. Install any of these: Coro, Event, Glib or Tk.";	1430	# free memory only needed for probing
49	}	1431	undef @models;
		1432	undef @REGISTRY;
50		1433
51	1;	1434	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
52		1435
		1436	# now nuke some methods that are overridden by the backend.
		1437	# SUPER usage is not allowed in these.
		1438	for (qw(time signal child idle)) {
		1439	undef &{"AnyEvent::Base::$_"}
		1440	if defined &{"$MODEL\::$_"};
		1441	}
		1442
		1443	_isa_set;
		1444
		1445	# we're officially open!
		1446
		1447	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1448	require AnyEvent::Strict;
		1449	}
		1450
		1451	if ($ENV{PERL_ANYEVENT_DEBUG_WRAP}) {
		1452	require AnyEvent::Debug;
		1453	AnyEvent::Debug::wrap ($ENV{PERL_ANYEVENT_DEBUG_WRAP});
		1454	}
		1455
		1456	if (length $ENV{PERL_ANYEVENT_DEBUG_SHELL}) {
		1457	require AnyEvent::Socket;
		1458	require AnyEvent::Debug;
		1459
		1460	my $shell = $ENV{PERL_ANYEVENT_DEBUG_SHELL};
		1461	$shell =~ s/\$\$/$$/g;
		1462
		1463	my ($host, $service) = AnyEvent::Socket::parse_hostport ($shell);
		1464	$AnyEvent::Debug::SHELL = AnyEvent::Debug::shell ($host, $service);
		1465	}
		1466
		1467	# now the anyevent environment is set up as the user told us to, so
		1468	# call the actual user code - post detects
		1469
		1470	(shift @post_detect)->() while @post_detect;
		1471	undef @post_detect;
		1472
		1473	*post_detect = sub(&) {
		1474	shift->();
		1475
		1476	undef
		1477	};
		1478
		1479	$MODEL
		1480	}
		1481
		1482	for my $name (@methods) {
		1483	*$name = sub {
		1484	detect;
		1485	# we use goto because
		1486	# a) it makes the thunk more transparent
		1487	# b) it allows us to delete the thunk later
		1488	goto &{ UNIVERSAL::can AnyEvent => "SUPER::$name" }
		1489	};
		1490	}
		1491
		1492	# utility function to dup a filehandle. this is used by many backends
		1493	# to support binding more than one watcher per filehandle (they usually
		1494	# allow only one watcher per fd, so we dup it to get a different one).
		1495	sub _dupfh($$;$$) {
		1496	my ($poll, $fh, $r, $w) = @_;
		1497
		1498	# cygwin requires the fh mode to be matching, unix doesn't
		1499	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1500
		1501	open my $fh2, $mode, $fh
		1502	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1503
		1504	# we assume CLOEXEC is already set by perl in all important cases
		1505
		1506	($fh2, $rw)
		1507	}
		1508
		1509	=head1 SIMPLIFIED AE API
		1510
		1511	Starting with version 5.0, AnyEvent officially supports a second, much
		1512	simpler, API that is designed to reduce the calling, typing and memory
		1513	overhead by using function call syntax and a fixed number of parameters.
		1514
		1515	See the L<AE> manpage for details.
		1516
		1517	=cut
		1518
		1519	package AE;
		1520
		1521	our $VERSION = $AnyEvent::VERSION;
		1522
		1523	sub _reset() {
		1524	eval q{
		1525	# fall back to the main API by default - backends and AnyEvent::Base
		1526	# implementations can overwrite these.
		1527
		1528	sub io($$$) {
		1529	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1530	}
		1531
		1532	sub timer($$$) {
		1533	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1534	}
		1535
		1536	sub signal($$) {
		1537	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1538	}
		1539
		1540	sub child($$) {
		1541	AnyEvent->child (pid => $_[0], cb => $_[1])
		1542	}
		1543
		1544	sub idle($) {
		1545	AnyEvent->idle (cb => $_[0]);
		1546	}
		1547
		1548	sub cv(;&) {
		1549	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1550	}
		1551
		1552	sub now() {
		1553	AnyEvent->now
		1554	}
		1555
		1556	sub now_update() {
		1557	AnyEvent->now_update
		1558	}
		1559
		1560	sub time() {
		1561	AnyEvent->time
		1562	}
		1563
		1564	*postpone = \&AnyEvent::postpone;
		1565	*log = \&AnyEvent::log;
		1566	};
		1567	die if $@;
		1568	}
		1569
		1570	BEGIN { _reset }
		1571
		1572	package AnyEvent::Base;
		1573
		1574	# default implementations for many methods
		1575
		1576	sub time {
		1577	eval q{ # poor man's autoloading {}
		1578	# probe for availability of Time::HiRes
		1579	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1580	*time = sub { Time::HiRes::time () };
		1581	*AE::time = \& Time::HiRes::time ;
		1582	*now = \&time;
		1583	AnyEvent::log 8 => "AnyEvent: using Time::HiRes for sub-second timing accuracy.";
		1584	# if (eval "use POSIX (); (POSIX::times())...
		1585	} else {
		1586	*time = sub { CORE::time };
		1587	*AE::time = sub (){ CORE::time };
		1588	*now = \&time;
		1589	AnyEvent::log 3 => "using built-in time(), WARNING, no sub-second resolution!";
		1590	}
		1591	};
		1592	die if $@;
		1593
		1594	&time
		1595	}
		1596
		1597	*now = \&time;
		1598	sub now_update { }
		1599
		1600	sub _poll {
		1601	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1602	}
		1603
		1604	# default implementation for ->condvar
		1605	# in fact, the default should not be overwritten
		1606
		1607	sub condvar {
		1608	eval q{ # poor man's autoloading {}
		1609	*condvar = sub {
		1610	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1611	};
		1612
		1613	*AE::cv = sub (;&) {
		1614	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1615	};
		1616	};
		1617	die if $@;
		1618
		1619	&condvar
		1620	}
		1621
		1622	# default implementation for ->signal
		1623
		1624	our $HAVE_ASYNC_INTERRUPT;
		1625
		1626	sub _have_async_interrupt() {
		1627	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1628	&& eval "use Async::Interrupt 1.02 (); 1")
		1629	unless defined $HAVE_ASYNC_INTERRUPT;
		1630
		1631	$HAVE_ASYNC_INTERRUPT
		1632	}
		1633
		1634	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1635	our (%SIG_ASY, %SIG_ASY_W);
		1636	our ($SIG_COUNT, $SIG_TW);
		1637
		1638	# install a dummy wakeup watcher to reduce signal catching latency
		1639	# used by Impls
		1640	sub _sig_add() {
		1641	unless ($SIG_COUNT++) {
		1642	# try to align timer on a full-second boundary, if possible
		1643	my $NOW = AE::now;
		1644
		1645	$SIG_TW = AE::timer
		1646	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1647	$MAX_SIGNAL_LATENCY,
		1648	sub { } # just for the PERL_ASYNC_CHECK
		1649	;
		1650	}
		1651	}
		1652
		1653	sub _sig_del {
		1654	undef $SIG_TW
		1655	unless --$SIG_COUNT;
		1656	}
		1657
		1658	our $_sig_name_init; $_sig_name_init = sub {
		1659	eval q{ # poor man's autoloading {}
		1660	undef $_sig_name_init;
		1661
		1662	if (_have_async_interrupt) {
		1663	*sig2num = \&Async::Interrupt::sig2num;
		1664	*sig2name = \&Async::Interrupt::sig2name;
		1665	} else {
		1666	require Config;
		1667
		1668	my %signame2num;
		1669	@signame2num{ split ' ', $Config::Config{sig_name} }
		1670	= split ' ', $Config::Config{sig_num};
		1671
		1672	my @signum2name;
		1673	@signum2name[values %signame2num] = keys %signame2num;
		1674
		1675	*sig2num = sub($) {
		1676	$_[0] > 0 ? shift : $signame2num{+shift}
		1677	};
		1678	*sig2name = sub ($) {
		1679	$_[0] > 0 ? $signum2name[+shift] : shift
		1680	};
		1681	}
		1682	};
		1683	die if $@;
		1684	};
		1685
		1686	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1687	sub sig2name($) { &$_sig_name_init; &sig2name }
		1688
		1689	sub signal {
		1690	eval q{ # poor man's autoloading {}
		1691	# probe for availability of Async::Interrupt
		1692	if (_have_async_interrupt) {
		1693	AnyEvent::log 8 => "using Async::Interrupt for race-free signal handling.";
		1694
		1695	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1696	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1697
		1698	} else {
		1699	AnyEvent::log 8 => "using emulated perl signal handling with latency timer.";
		1700
		1701	if (AnyEvent::WIN32) {
		1702	require AnyEvent::Util;
		1703
		1704	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1705	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1706	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1707	} else {
		1708	pipe $SIGPIPE_R, $SIGPIPE_W;
		1709	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1710	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1711
		1712	# not strictly required, as $^F is normally 2, but let's make sure...
		1713	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1714	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1715	}
		1716
		1717	$SIGPIPE_R
		1718	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1719
		1720	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1721	}
		1722
		1723	*signal = $HAVE_ASYNC_INTERRUPT
		1724	? sub {
		1725	my (undef, %arg) = @_;
		1726
		1727	# async::interrupt
		1728	my $signal = sig2num $arg{signal};
		1729	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1730
		1731	$SIG_ASY{$signal} ||= new Async::Interrupt
		1732	cb => sub { undef $SIG_EV{$signal} },
		1733	signal => $signal,
		1734	pipe => [$SIGPIPE_R->filenos],
		1735	pipe_autodrain => 0,
		1736	;
		1737
		1738	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1739	}
		1740	: sub {
		1741	my (undef, %arg) = @_;
		1742
		1743	# pure perl
		1744	my $signal = sig2name $arg{signal};
		1745	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1746
		1747	$SIG{$signal} ||= sub {
		1748	local $!;
		1749	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1750	undef $SIG_EV{$signal};
		1751	};
		1752
		1753	# can't do signal processing without introducing races in pure perl,
		1754	# so limit the signal latency.
		1755	_sig_add;
		1756
		1757	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1758	}
		1759	;
		1760
		1761	*AnyEvent::Base::signal::DESTROY = sub {
		1762	my ($signal, $cb) = @{$_[0]};
		1763
		1764	_sig_del;
		1765
		1766	delete $SIG_CB{$signal}{$cb};
		1767
		1768	$HAVE_ASYNC_INTERRUPT
		1769	? delete $SIG_ASY{$signal}
		1770	: # delete doesn't work with older perls - they then
		1771	# print weird messages, or just unconditionally exit
		1772	# instead of getting the default action.
		1773	undef $SIG{$signal}
		1774	unless keys %{ $SIG_CB{$signal} };
		1775	};
		1776
		1777	*_signal_exec = sub {
		1778	$HAVE_ASYNC_INTERRUPT
		1779	? $SIGPIPE_R->drain
		1780	: sysread $SIGPIPE_R, (my $dummy), 9;
		1781
		1782	while (%SIG_EV) {
		1783	for (keys %SIG_EV) {
		1784	delete $SIG_EV{$_};
		1785	&$_ for values %{ $SIG_CB{$_} || {} };
		1786	}
		1787	}
		1788	};
		1789	};
		1790	die if $@;
		1791
		1792	&signal
		1793	}
		1794
		1795	# default implementation for ->child
		1796
		1797	our %PID_CB;
		1798	our $CHLD_W;
		1799	our $CHLD_DELAY_W;
		1800
		1801	# used by many Impl's
		1802	sub _emit_childstatus($$) {
		1803	my (undef, $rpid, $rstatus) = @_;
		1804
		1805	$_->($rpid, $rstatus)
		1806	for values %{ $PID_CB{$rpid} || {} },
		1807	values %{ $PID_CB{0} || {} };
		1808	}
		1809
		1810	sub child {
		1811	eval q{ # poor man's autoloading {}
		1812	*_sigchld = sub {
		1813	my $pid;
		1814
		1815	AnyEvent->_emit_childstatus ($pid, $?)
		1816	while ($pid = waitpid -1, WNOHANG) > 0;
		1817	};
		1818
		1819	*child = sub {
		1820	my (undef, %arg) = @_;
		1821
		1822	my $pid = $arg{pid};
		1823	my $cb = $arg{cb};
		1824
		1825	$PID_CB{$pid}{$cb+0} = $cb;
		1826
		1827	unless ($CHLD_W) {
		1828	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1829	# child could be a zombie already, so make at least one round
		1830	&_sigchld;
		1831	}
		1832
		1833	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1834	};
		1835
		1836	*AnyEvent::Base::child::DESTROY = sub {
		1837	my ($pid, $icb) = @{$_[0]};
		1838
		1839	delete $PID_CB{$pid}{$icb};
		1840	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1841
		1842	undef $CHLD_W unless keys %PID_CB;
		1843	};
		1844	};
		1845	die if $@;
		1846
		1847	&child
		1848	}
		1849
		1850	# idle emulation is done by simply using a timer, regardless
		1851	# of whether the process is idle or not, and not letting
		1852	# the callback use more than 50% of the time.
		1853	sub idle {
		1854	eval q{ # poor man's autoloading {}
		1855	*idle = sub {
		1856	my (undef, %arg) = @_;
		1857
		1858	my ($cb, $w, $rcb) = $arg{cb};
		1859
		1860	$rcb = sub {
		1861	if ($cb) {
		1862	$w = AE::time;
		1863	&$cb;
		1864	$w = AE::time - $w;
		1865
		1866	# never use more then 50% of the time for the idle watcher,
		1867	# within some limits
		1868	$w = 0.0001 if $w < 0.0001;
		1869	$w = 5 if $w > 5;
		1870
		1871	$w = AE::timer $w, 0, $rcb;
		1872	} else {
		1873	# clean up...
		1874	undef $w;
		1875	undef $rcb;
		1876	}
		1877	};
		1878
		1879	$w = AE::timer 0.05, 0, $rcb;
		1880
		1881	bless \\$cb, "AnyEvent::Base::idle"
		1882	};
		1883
		1884	*AnyEvent::Base::idle::DESTROY = sub {
		1885	undef $${$_[0]};
		1886	};
		1887	};
		1888	die if $@;
		1889
		1890	&idle
		1891	}
		1892
		1893	package AnyEvent::CondVar;
		1894
		1895	our @ISA = AnyEvent::CondVar::Base::;
		1896
		1897	# only to be used for subclassing
		1898	sub new {
		1899	my $class = shift;
		1900	bless AnyEvent->condvar (@_), $class
		1901	}
		1902
		1903	package AnyEvent::CondVar::Base;
		1904
		1905	#use overload
		1906	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1907	# fallback => 1;
		1908
		1909	# save 300+ kilobytes by dirtily hardcoding overloading
		1910	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1911	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1912	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1913	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1914
		1915	our $WAITING;
		1916
		1917	sub _send {
		1918	# nop
		1919	}
		1920
		1921	sub _wait {
		1922	AnyEvent->_poll until $_[0]{_ae_sent};
		1923	}
		1924
		1925	sub send {
		1926	my $cv = shift;
		1927	$cv->{_ae_sent} = [@_];
		1928	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1929	$cv->_send;
		1930	}
		1931
		1932	sub croak {
		1933	$_[0]{_ae_croak} = $_[1];
		1934	$_[0]->send;
		1935	}
		1936
		1937	sub ready {
		1938	$_[0]{_ae_sent}
		1939	}
		1940
		1941	sub recv {
		1942	unless ($_[0]{_ae_sent}) {
		1943	$WAITING
		1944	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1945
		1946	local $WAITING = 1;
		1947	$_[0]->_wait;
		1948	}
		1949
		1950	$_[0]{_ae_croak}
		1951	and Carp::croak $_[0]{_ae_croak};
		1952
		1953	wantarray
		1954	? @{ $_[0]{_ae_sent} }
		1955	: $_[0]{_ae_sent}[0]
		1956	}
		1957
		1958	sub cb {
		1959	my $cv = shift;
		1960
		1961	@_
		1962	and $cv->{_ae_cb} = shift
		1963	and $cv->{_ae_sent}
		1964	and (delete $cv->{_ae_cb})->($cv);
		1965
		1966	$cv->{_ae_cb}
		1967	}
		1968
		1969	sub begin {
		1970	++$_[0]{_ae_counter};
		1971	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1972	}
		1973
		1974	sub end {
		1975	return if --$_[0]{_ae_counter};
		1976	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1977	}
		1978
		1979	# undocumented/compatibility with pre-3.4
		1980	*broadcast = \&send;
		1981	*wait = \&recv;
		1982
		1983	=head1 ERROR AND EXCEPTION HANDLING
		1984
		1985	In general, AnyEvent does not do any error handling - it relies on the
		1986	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1987	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1988	checking of all AnyEvent methods, however, which is highly useful during
		1989	development.
		1990
		1991	As for exception handling (i.e. runtime errors and exceptions thrown while
		1992	executing a callback), this is not only highly event-loop specific, but
		1993	also not in any way wrapped by this module, as this is the job of the main
		1994	program.
		1995
		1996	The pure perl event loop simply re-throws the exception (usually
		1997	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1998	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1999	so on.
		2000
		2001	=head1 ENVIRONMENT VARIABLES
		2002
		2003	AnyEvent supports a number of environment variables that tune the
		2004	runtime behaviour. They are usually evaluated when AnyEvent is
		2005	loaded, initialised, or a submodule that uses them is loaded. Many of
		2006	them also cause AnyEvent to load additional modules - for example,
		2007	C<PERL_ANYEVENT_DEBUG_WRAP> causes the L<AnyEvent::Debug> module to be
		2008	loaded.
		2009
		2010	All the environment variables documented here start with
		2011	C<PERL_ANYEVENT_>, which is what AnyEvent considers its own
		2012	namespace. Other modules are encouraged (but by no means required) to use
		2013	C<PERL_ANYEVENT_SUBMODULE> if they have registered the AnyEvent::Submodule
		2014	namespace on CPAN, for any submodule. For example, L<AnyEvent::HTTP> could
		2015	be expected to use C<PERL_ANYEVENT_HTTP_PROXY> (it should not access env
		2016	variables starting with C<AE_>, see below).
		2017
		2018	All variables can also be set via the C<AE_> prefix, that is, instead
		2019	of setting C<PERL_ANYEVENT_VERBOSE> you can also set C<AE_VERBOSE>. In
		2020	case there is a clash btween anyevent and another program that uses
		2021	C<AE_something> you can set the corresponding C<PERL_ANYEVENT_something>
		2022	variable to the empty string, as those variables take precedence.
		2023
		2024	When AnyEvent is first loaded, it copies all C<AE_xxx> env variables
		2025	to their C<PERL_ANYEVENT_xxx> counterpart unless that variable already
		2026	exists. If taint mode is on, then AnyEvent will remove I<all> environment
		2027	variables starting with C<PERL_ANYEVENT_> from C<%ENV> (or replace them
		2028	with C<undef> or the empty string, if the corresaponding C<AE_> variable
		2029	is set).
		2030
		2031	The exact algorithm is currently:
		2032
		2033	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		2034	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		2035	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		2036
		2037	This ensures that child processes will not see the C<AE_> variables.
		2038
		2039	The following environment variables are currently known to AnyEvent:
		2040
		2041	=over 4
		2042
		2043	=item C<PERL_ANYEVENT_VERBOSE>
		2044
		2045	By default, AnyEvent will be completely silent except in fatal
		2046	conditions. You can set this environment variable to make AnyEvent more
		2047	talkative. If you want to do more than just set the global logging level
		2048	you should have a look at C<PERL_ANYEVENT_LOG>, which allows much more
		2049	complex specifications.
		2050
		2051	When set to C<5> or higher (warn), causes AnyEvent to warn about unexpected
		2052	conditions, such as not being able to load the event model specified by
		2053	C<PERL_ANYEVENT_MODEL>, or a guard callback throwing an exception - this
		2054	is the minimum recommended level.
		2055
		2056	When set to C<7> or higher (info), cause AnyEvent to report which event model it
		2057	chooses.
		2058
		2059	When set to C<8> or higher (debug), then AnyEvent will report extra information on
		2060	which optional modules it loads and how it implements certain features.
		2061
		2062	=item C<PERL_ANYEVENT_LOG>
		2063
		2064	Accepts rather complex logging specifications. For example, you could log
		2065	all C<debug> messages of some module to stderr, warnings and above to
		2066	stderr, and errors and above to syslog, with:
		2067
		2068	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		2069
		2070	For the rather extensive details, see L<AnyEvent::Log>.
		2071
		2072	This variable is evaluated when AnyEvent (or L<AnyEvent::Log>) is loaded,
		2073	so will take effect even before AnyEvent has initialised itself.
		2074
		2075	Note that specifying this environment variable causes the L<AnyEvent::Log>
		2076	module to be loaded, while C<PERL_ANYEVENT_VERBOSE> does not, so only
		2077	using the latter saves a few hundred kB of memory until the first message
		2078	is being logged.
		2079
		2080	=item C<PERL_ANYEVENT_STRICT>
		2081
		2082	AnyEvent does not do much argument checking by default, as thorough
		2083	argument checking is very costly. Setting this variable to a true value
		2084	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		2085	check the arguments passed to most method calls. If it finds any problems,
		2086	it will croak.
		2087
		2088	In other words, enables "strict" mode.
		2089
		2090	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		2091	>>, it is definitely recommended to keep it off in production. Keeping
		2092	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		2093	can be very useful, however.
		2094
		2095	=item C<PERL_ANYEVENT_DEBUG_SHELL>
		2096
		2097	If this env variable is set, then its contents will be interpreted by
		2098	C<AnyEvent::Socket::parse_hostport> (after replacing every occurance of
		2099	C<$$> by the process pid) and an C<AnyEvent::Debug::shell> is bound on
		2100	that port. The shell object is saved in C<$AnyEvent::Debug::SHELL>.
		2101
		2102	This happens when the first watcher is created.
		2103
		2104	For example, to bind a debug shell on a unix domain socket in
		2105	F<< /tmp/debug<pid>.sock >>, you could use this:
		2106
		2107	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		2108
		2109	Note that creating sockets in F</tmp> is very unsafe on multiuser
		2110	systems.
		2111
		2112	=item C<PERL_ANYEVENT_DEBUG_WRAP>
		2113
		2114	Can be set to C<0>, C<1> or C<2> and enables wrapping of all watchers for
		2115	debugging purposes. See C<AnyEvent::Debug::wrap> for details.
		2116
		2117	=item C<PERL_ANYEVENT_MODEL>
		2118
		2119	This can be used to specify the event model to be used by AnyEvent, before
		2120	auto detection and -probing kicks in.
		2121
		2122	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		2123	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		2124	resulting module name is loaded and - if the load was successful - used as
		2125	event model backend. If it fails to load then AnyEvent will proceed with
		2126	auto detection and -probing.
		2127
		2128	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		2129	nothing gets prepended and the module name is used as-is (hint: C<::> at
		2130	the end of a string designates a module name and quotes it appropriately).
		2131
		2132	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		2133	could start your program like this:
		2134
		2135	PERL_ANYEVENT_MODEL=Perl perl ...
		2136
		2137	=item C<PERL_ANYEVENT_PROTOCOLS>
		2138
		2139	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		2140	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		2141	of auto probing).
		2142
		2143	Must be set to a comma-separated list of protocols or address families,
		2144	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		2145	used, and preference will be given to protocols mentioned earlier in the
		2146	list.
		2147
		2148	This variable can effectively be used for denial-of-service attacks
		2149	against local programs (e.g. when setuid), although the impact is likely
		2150	small, as the program has to handle conenction and other failures anyways.
		2151
		2152	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		2153	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		2154	- only support IPv4, never try to resolve or contact IPv6
		2155	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		2156	IPv6, but prefer IPv6 over IPv4.
		2157
		2158	=item C<PERL_ANYEVENT_HOSTS>
		2159
		2160	This variable, if specified, overrides the F</etc/hosts> file used by
		2161	L<AnyEvent::Socket>C<::resolve_sockaddr>, i.e. hosts aliases will be read
		2162	from that file instead.
		2163
		2164	=item C<PERL_ANYEVENT_EDNS0>
		2165
		2166	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension for
		2167	DNS. This extension is generally useful to reduce DNS traffic, especially
		2168	when DNSSEC is involved, but some (broken) firewalls drop such DNS
		2169	packets, which is why it is off by default.
		2170
		2171	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2172	EDNS0 in its DNS requests.
		2173
		2174	=item C<PERL_ANYEVENT_MAX_FORKS>
		2175
		2176	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2177	will create in parallel.
		2178
		2179	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2180
		2181	The default value for the C<max_outstanding> parameter for the default DNS
		2182	resolver - this is the maximum number of parallel DNS requests that are
		2183	sent to the DNS server.
		2184
		2185	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2186
		2187	The absolute path to a F<resolv.conf>-style file to use instead of
		2188	F</etc/resolv.conf> (or the OS-specific configuration) in the default
		2189	resolver, or the empty string to select the default configuration.
		2190
		2191	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2192
		2193	When neither C<ca_file> nor C<ca_path> was specified during
		2194	L<AnyEvent::TLS> context creation, and either of these environment
		2195	variables are nonempty, they will be used to specify CA certificate
		2196	locations instead of a system-dependent default.
		2197
		2198	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2199
		2200	When these are set to C<1>, then the respective modules are not
		2201	loaded. Mostly good for testing AnyEvent itself.
		2202
		2203	=back
		2204
		2205	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		2206
		2207	This is an advanced topic that you do not normally need to use AnyEvent in
		2208	a module. This section is only of use to event loop authors who want to
		2209	provide AnyEvent compatibility.
		2210
		2211	If you need to support another event library which isn't directly
		2212	supported by AnyEvent, you can supply your own interface to it by
		2213	pushing, before the first watcher gets created, the package name of
		2214	the event module and the package name of the interface to use onto
		2215	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		2216	AnyEvent, so it is reasonably cheap.
		2217
		2218	Example:
		2219
		2220	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		2221
		2222	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		2223	package/class when it finds the C<urxvt> package/module is already loaded.
		2224
		2225	When AnyEvent is loaded and asked to find a suitable event model, it
		2226	will first check for the presence of urxvt by trying to C<use> the
		2227	C<urxvt::anyevent> module.
		2228
		2229	The class should provide implementations for all watcher types. See
		2230	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		2231	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		2232	see the sources.
		2233
		2234	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2235	provide suitable (hopefully) replacements.
		2236
		2237	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		2238	terminal emulator uses the above line as-is. An interface isn't included
		2239	in AnyEvent because it doesn't make sense outside the embedded interpreter
		2240	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		2241	I<rxvt-unicode> distribution.
		2242
		2243	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		2244	condition variables: code blocking while waiting for a condition will
		2245	C<die>. This still works with most modules/usages, and blocking calls must
		2246	not be done in an interactive application, so it makes sense.
		2247
		2248	=head1 EXAMPLE PROGRAM
		2249
		2250	The following program uses an I/O watcher to read data from STDIN, a timer
		2251	to display a message once per second, and a condition variable to quit the
		2252	program when the user enters quit:
		2253
		2254	use AnyEvent;
		2255
		2256	my $cv = AnyEvent->condvar;
		2257
		2258	my $io_watcher = AnyEvent->io (
		2259	fh => \*STDIN,
		2260	poll => 'r',
		2261	cb => sub {
		2262	warn "io event <$_[0]>\n"; # will always output <r>
		2263	chomp (my $input = <STDIN>); # read a line
		2264	warn "read: $input\n"; # output what has been read
		2265	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2266	},
		2267	);
		2268
		2269	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2270	warn "timeout\n"; # print 'timeout' at most every second
		2271	});
		2272
		2273	$cv->recv; # wait until user enters /^q/i
		2274
		2275	=head1 REAL-WORLD EXAMPLE
		2276
		2277	Consider the L<Net::FCP> module. It features (among others) the following
		2278	API calls, which are to freenet what HTTP GET requests are to http:
		2279
		2280	my $data = $fcp->client_get ($url); # blocks
		2281
		2282	my $transaction = $fcp->txn_client_get ($url); # does not block
		2283	$transaction->cb ( sub { ... } ); # set optional result callback
		2284	my $data = $transaction->result; # possibly blocks
		2285
		2286	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		2287	given URL and waits till the data has arrived. It is defined to be:
		2288
		2289	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		2290
		2291	And in fact is automatically generated. This is the blocking API of
		2292	L<Net::FCP>, and it works as simple as in any other, similar, module.
		2293
		2294	More complicated is C<txn_client_get>: It only creates a transaction
		2295	(completion, result, ...) object and initiates the transaction.
		2296
		2297	my $txn = bless { }, Net::FCP::Txn::;
		2298
		2299	It also creates a condition variable that is used to signal the completion
		2300	of the request:
		2301
		2302	$txn->{finished} = AnyAvent->condvar;
		2303
		2304	It then creates a socket in non-blocking mode.
		2305
		2306	socket $txn->{fh}, ...;
		2307	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		2308	connect $txn->{fh}, ...
		2309	and !$!{EWOULDBLOCK}
		2310	and !$!{EINPROGRESS}
		2311	and Carp::croak "unable to connect: $!\n";
		2312
		2313	Then it creates a write-watcher which gets called whenever an error occurs
		2314	or the connection succeeds:
		2315
		2316	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		2317
		2318	And returns this transaction object. The C<fh_ready_w> callback gets
		2319	called as soon as the event loop detects that the socket is ready for
		2320	writing.
		2321
		2322	The C<fh_ready_w> method makes the socket blocking again, writes the
		2323	request data and replaces the watcher by a read watcher (waiting for reply
		2324	data). The actual code is more complicated, but that doesn't matter for
		2325	this example:
		2326
		2327	fcntl $txn->{fh}, F_SETFL, 0;
		2328	syswrite $txn->{fh}, $txn->{request}
		2329	or die "connection or write error";
		2330	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		2331
		2332	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		2333	result and signals any possible waiters that the request has finished:
		2334
		2335	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		2336
		2337	if (end-of-file or data complete) {
		2338	$txn->{result} = $txn->{buf};
		2339	$txn->{finished}->send;
		2340	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		2341	}
		2342
		2343	The C<result> method, finally, just waits for the finished signal (if the
		2344	request was already finished, it doesn't wait, of course, and returns the
		2345	data:
		2346
		2347	$txn->{finished}->recv;
		2348	return $txn->{result};
		2349
		2350	The actual code goes further and collects all errors (C<die>s, exceptions)
		2351	that occurred during request processing. The C<result> method detects
		2352	whether an exception as thrown (it is stored inside the $txn object)
		2353	and just throws the exception, which means connection errors and other
		2354	problems get reported to the code that tries to use the result, not in a
		2355	random callback.
		2356
		2357	All of this enables the following usage styles:
		2358
		2359	1. Blocking:
		2360
		2361	my $data = $fcp->client_get ($url);
		2362
		2363	2. Blocking, but running in parallel:
		2364
		2365	my @datas = map $_->result,
		2366	map $fcp->txn_client_get ($_),
		2367	@urls;
		2368
		2369	Both blocking examples work without the module user having to know
		2370	anything about events.
		2371
		2372	3a. Event-based in a main program, using any supported event module:
		2373
		2374	use EV;
		2375
		2376	$fcp->txn_client_get ($url)->cb (sub {
		2377	my $txn = shift;
		2378	my $data = $txn->result;
		2379	...
		2380	});
		2381
		2382	EV::loop;
		2383
		2384	3b. The module user could use AnyEvent, too:
		2385
		2386	use AnyEvent;
		2387
		2388	my $quit = AnyEvent->condvar;
		2389
		2390	$fcp->txn_client_get ($url)->cb (sub {
		2391	...
		2392	$quit->send;
		2393	});
		2394
		2395	$quit->recv;
		2396
		2397
		2398	=head1 BENCHMARKS
		2399
		2400	To give you an idea of the performance and overheads that AnyEvent adds
		2401	over the event loops themselves and to give you an impression of the speed
		2402	of various event loops I prepared some benchmarks.
		2403
		2404	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2405
		2406	Here is a benchmark of various supported event models used natively and
		2407	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2408	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2409	which it is), lets them fire exactly once and destroys them again.
		2410
		2411	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2412	distribution. It uses the L<AE> interface, which makes a real difference
		2413	for the EV and Perl backends only.
		2414
		2415	=head3 Explanation of the columns
		2416
		2417	I<watcher> is the number of event watchers created/destroyed. Since
		2418	different event models feature vastly different performances, each event
		2419	loop was given a number of watchers so that overall runtime is acceptable
		2420	and similar between tested event loop (and keep them from crashing): Glib
		2421	would probably take thousands of years if asked to process the same number
		2422	of watchers as EV in this benchmark.
		2423
		2424	I<bytes> is the number of bytes (as measured by the resident set size,
		2425	RSS) consumed by each watcher. This method of measuring captures both C
		2426	and Perl-based overheads.
		2427
		2428	I<create> is the time, in microseconds (millionths of seconds), that it
		2429	takes to create a single watcher. The callback is a closure shared between
		2430	all watchers, to avoid adding memory overhead. That means closure creation
		2431	and memory usage is not included in the figures.
		2432
		2433	I<invoke> is the time, in microseconds, used to invoke a simple
		2434	callback. The callback simply counts down a Perl variable and after it was
		2435	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2436	signal the end of this phase.
		2437
		2438	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2439	watcher.
		2440
		2441	=head3 Results
		2442
		2443	name watchers bytes create invoke destroy comment
		2444	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2445	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2446	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2447	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2448	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2449	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2450	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2451	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2452	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2453	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2454	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2455	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2456
		2457	=head3 Discussion
		2458
		2459	The benchmark does I<not> measure scalability of the event loop very
		2460	well. For example, a select-based event loop (such as the pure perl one)
		2461	can never compete with an event loop that uses epoll when the number of
		2462	file descriptors grows high. In this benchmark, all events become ready at
		2463	the same time, so select/poll-based implementations get an unnatural speed
		2464	boost.
		2465
		2466	Also, note that the number of watchers usually has a nonlinear effect on
		2467	overall speed, that is, creating twice as many watchers doesn't take twice
		2468	the time - usually it takes longer. This puts event loops tested with a
		2469	higher number of watchers at a disadvantage.
		2470
		2471	To put the range of results into perspective, consider that on the
		2472	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2473	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2474	cycles with POE.
		2475
		2476	C<EV> is the sole leader regarding speed and memory use, which are both
		2477	maximal/minimal, respectively. When using the L<AE> API there is zero
		2478	overhead (when going through the AnyEvent API create is about 5-6 times
		2479	slower, with other times being equal, so still uses far less memory than
		2480	any other event loop and is still faster than Event natively).
		2481
		2482	The pure perl implementation is hit in a few sweet spots (both the
		2483	constant timeout and the use of a single fd hit optimisations in the perl
		2484	interpreter and the backend itself). Nevertheless this shows that it
		2485	adds very little overhead in itself. Like any select-based backend its
		2486	performance becomes really bad with lots of file descriptors (and few of
		2487	them active), of course, but this was not subject of this benchmark.
		2488
		2489	The C<Event> module has a relatively high setup and callback invocation
		2490	cost, but overall scores in on the third place.
		2491
		2492	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2493	when using its pure perl backend.
		2494
		2495	C<Glib>'s memory usage is quite a bit higher, but it features a
		2496	faster callback invocation and overall ends up in the same class as
		2497	C<Event>. However, Glib scales extremely badly, doubling the number of
		2498	watchers increases the processing time by more than a factor of four,
		2499	making it completely unusable when using larger numbers of watchers
		2500	(note that only a single file descriptor was used in the benchmark, so
		2501	inefficiencies of C<poll> do not account for this).
		2502
		2503	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2504	more than 2000 watchers is a big setback, however, as correctness takes
		2505	precedence over speed. Nevertheless, its performance is surprising, as the
		2506	file descriptor is dup()ed for each watcher. This shows that the dup()
		2507	employed by some adaptors is not a big performance issue (it does incur a
		2508	hidden memory cost inside the kernel which is not reflected in the figures
		2509	above).
		2510
		2511	C<POE>, regardless of underlying event loop (whether using its pure perl
		2512	select-based backend or the Event module, the POE-EV backend couldn't
		2513	be tested because it wasn't working) shows abysmal performance and
		2514	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2515	as EV watchers, and 10 times as much memory as Event (the high memory
		2516	requirements are caused by requiring a session for each watcher). Watcher
		2517	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2518	implementation.
		2519
		2520	The design of the POE adaptor class in AnyEvent can not really account
		2521	for the performance issues, though, as session creation overhead is
		2522	small compared to execution of the state machine, which is coded pretty
		2523	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2524	using multiple sessions is not a good approach, especially regarding
		2525	memory usage, even the author of POE could not come up with a faster
		2526	design).
		2527
		2528	=head3 Summary
		2529
		2530	=over 4
		2531
		2532	=item * Using EV through AnyEvent is faster than any other event loop
		2533	(even when used without AnyEvent), but most event loops have acceptable
		2534	performance with or without AnyEvent.
		2535
		2536	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2537	the actual event loop, only with extremely fast event loops such as EV
		2538	does AnyEvent add significant overhead.
		2539
		2540	=item * You should avoid POE like the plague if you want performance or
		2541	reasonable memory usage.
		2542
		2543	=back
		2544
		2545	=head2 BENCHMARKING THE LARGE SERVER CASE
		2546
		2547	This benchmark actually benchmarks the event loop itself. It works by
		2548	creating a number of "servers": each server consists of a socket pair, a
		2549	timeout watcher that gets reset on activity (but never fires), and an I/O
		2550	watcher waiting for input on one side of the socket. Each time the socket
		2551	watcher reads a byte it will write that byte to a random other "server".
		2552
		2553	The effect is that there will be a lot of I/O watchers, only part of which
		2554	are active at any one point (so there is a constant number of active
		2555	fds for each loop iteration, but which fds these are is random). The
		2556	timeout is reset each time something is read because that reflects how
		2557	most timeouts work (and puts extra pressure on the event loops).
		2558
		2559	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2560	(1%) are active. This mirrors the activity of large servers with many
		2561	connections, most of which are idle at any one point in time.
		2562
		2563	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2564	distribution. It uses the L<AE> interface, which makes a real difference
		2565	for the EV and Perl backends only.
		2566
		2567	=head3 Explanation of the columns
		2568
		2569	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2570	each server has a read and write socket end).
		2571
		2572	I<create> is the time it takes to create a socket pair (which is
		2573	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2574
		2575	I<request>, the most important value, is the time it takes to handle a
		2576	single "request", that is, reading the token from the pipe and forwarding
		2577	it to another server. This includes deleting the old timeout and creating
		2578	a new one that moves the timeout into the future.
		2579
		2580	=head3 Results
		2581
		2582	name sockets create request
		2583	EV 20000 62.66 7.99
		2584	Perl 20000 68.32 32.64
		2585	IOAsync 20000 174.06 101.15 epoll
		2586	IOAsync 20000 174.67 610.84 poll
		2587	Event 20000 202.69 242.91
		2588	Glib 20000 557.01 1689.52
		2589	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2590
		2591	=head3 Discussion
		2592
		2593	This benchmark I<does> measure scalability and overall performance of the
		2594	particular event loop.
		2595
		2596	EV is again fastest. Since it is using epoll on my system, the setup time
		2597	is relatively high, though.
		2598
		2599	Perl surprisingly comes second. It is much faster than the C-based event
		2600	loops Event and Glib.
		2601
		2602	IO::Async performs very well when using its epoll backend, and still quite
		2603	good compared to Glib when using its pure perl backend.
		2604
		2605	Event suffers from high setup time as well (look at its code and you will
		2606	understand why). Callback invocation also has a high overhead compared to
		2607	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2608	uses select or poll in basically all documented configurations.
		2609
		2610	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2611	clearly fails to perform with many filehandles or in busy servers.
		2612
		2613	POE is still completely out of the picture, taking over 1000 times as long
		2614	as EV, and over 100 times as long as the Perl implementation, even though
		2615	it uses a C-based event loop in this case.
		2616
		2617	=head3 Summary
		2618
		2619	=over 4
		2620
		2621	=item * The pure perl implementation performs extremely well.
		2622
		2623	=item * Avoid Glib or POE in large projects where performance matters.
		2624
		2625	=back
		2626
		2627	=head2 BENCHMARKING SMALL SERVERS
		2628
		2629	While event loops should scale (and select-based ones do not...) even to
		2630	large servers, most programs we (or I :) actually write have only a few
		2631	I/O watchers.
		2632
		2633	In this benchmark, I use the same benchmark program as in the large server
		2634	case, but it uses only eight "servers", of which three are active at any
		2635	one time. This should reflect performance for a small server relatively
		2636	well.
		2637
		2638	The columns are identical to the previous table.
		2639
		2640	=head3 Results
		2641
		2642	name sockets create request
		2643	EV 16 20.00 6.54
		2644	Perl 16 25.75 12.62
		2645	Event 16 81.27 35.86
		2646	Glib 16 32.63 15.48
		2647	POE 16 261.87 276.28 uses POE::Loop::Event
		2648
		2649	=head3 Discussion
		2650
		2651	The benchmark tries to test the performance of a typical small
		2652	server. While knowing how various event loops perform is interesting, keep
		2653	in mind that their overhead in this case is usually not as important, due
		2654	to the small absolute number of watchers (that is, you need efficiency and
		2655	speed most when you have lots of watchers, not when you only have a few of
		2656	them).
		2657
		2658	EV is again fastest.
		2659
		2660	Perl again comes second. It is noticeably faster than the C-based event
		2661	loops Event and Glib, although the difference is too small to really
		2662	matter.
		2663
		2664	POE also performs much better in this case, but is is still far behind the
		2665	others.
		2666
		2667	=head3 Summary
		2668
		2669	=over 4
		2670
		2671	=item * C-based event loops perform very well with small number of
		2672	watchers, as the management overhead dominates.
		2673
		2674	=back
		2675
		2676	=head2 THE IO::Lambda BENCHMARK
		2677
		2678	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2679	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2680	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2681	shouldn't come as a surprise to anybody). As such, the benchmark is
		2682	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2683	very optimal. But how would AnyEvent compare when used without the extra
		2684	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2685
		2686	The benchmark itself creates an echo-server, and then, for 500 times,
		2687	connects to the echo server, sends a line, waits for the reply, and then
		2688	creates the next connection. This is a rather bad benchmark, as it doesn't
		2689	test the efficiency of the framework or much non-blocking I/O, but it is a
		2690	benchmark nevertheless.
		2691
		2692	name runtime
		2693	Lambda/select 0.330 sec
		2694	+ optimized 0.122 sec
		2695	Lambda/AnyEvent 0.327 sec
		2696	+ optimized 0.138 sec
		2697	Raw sockets/select 0.077 sec
		2698	POE/select, components 0.662 sec
		2699	POE/select, raw sockets 0.226 sec
		2700	POE/select, optimized 0.404 sec
		2701
		2702	AnyEvent/select/nb 0.085 sec
		2703	AnyEvent/EV/nb 0.068 sec
		2704	+state machine 0.134 sec
		2705
		2706	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2707	benchmarks actually make blocking connects and use 100% blocking I/O,
		2708	defeating the purpose of an event-based solution. All of the newly
		2709	written AnyEvent benchmarks use 100% non-blocking connects (using
		2710	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2711	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2712	generally require a lot more bookkeeping and event handling than blocking
		2713	connects (which involve a single syscall only).
		2714
		2715	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2716	offers similar expressive power as POE and IO::Lambda, using conventional
		2717	Perl syntax. This means that both the echo server and the client are 100%
		2718	non-blocking, further placing it at a disadvantage.
		2719
		2720	As you can see, the AnyEvent + EV combination even beats the
		2721	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2722	backend easily beats IO::Lambda and POE.
		2723
		2724	And even the 100% non-blocking version written using the high-level (and
		2725	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2726	higher level ("unoptimised") abstractions by a large margin, even though
		2727	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2728
		2729	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2730	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2731	part of the IO::Lambda distribution and were used without any changes.
		2732
		2733
		2734	=head1 SIGNALS
		2735
		2736	AnyEvent currently installs handlers for these signals:
		2737
		2738	=over 4
		2739
		2740	=item SIGCHLD
		2741
		2742	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2743	emulation for event loops that do not support them natively. Also, some
		2744	event loops install a similar handler.
		2745
		2746	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2747	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2748
		2749	=item SIGPIPE
		2750
		2751	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2752	when AnyEvent gets loaded.
		2753
		2754	The rationale for this is that AnyEvent users usually do not really depend
		2755	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2756	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2757	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2758	some random socket.
		2759
		2760	The rationale for installing a no-op handler as opposed to ignoring it is
		2761	that this way, the handler will be restored to defaults on exec.
		2762
		2763	Feel free to install your own handler, or reset it to defaults.
		2764
		2765	=back
		2766
		2767	=cut
		2768
		2769	undef $SIG{CHLD}
		2770	if $SIG{CHLD} eq 'IGNORE';
		2771
		2772	$SIG{PIPE} = sub { }
		2773	unless defined $SIG{PIPE};
		2774
		2775	=head1 RECOMMENDED/OPTIONAL MODULES
		2776
		2777	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2778	its built-in modules) are required to use it.
		2779
		2780	That does not mean that AnyEvent won't take advantage of some additional
		2781	modules if they are installed.
		2782
		2783	This section explains which additional modules will be used, and how they
		2784	affect AnyEvent's operation.
		2785
		2786	=over 4
		2787
		2788	=item L<Async::Interrupt>
		2789
		2790	This slightly arcane module is used to implement fast signal handling: To
		2791	my knowledge, there is no way to do completely race-free and quick
		2792	signal handling in pure perl. To ensure that signals still get
		2793	delivered, AnyEvent will start an interval timer to wake up perl (and
		2794	catch the signals) with some delay (default is 10 seconds, look for
		2795	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2796
		2797	If this module is available, then it will be used to implement signal
		2798	catching, which means that signals will not be delayed, and the event loop
		2799	will not be interrupted regularly, which is more efficient (and good for
		2800	battery life on laptops).
		2801
		2802	This affects not just the pure-perl event loop, but also other event loops
		2803	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2804
		2805	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2806	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2807	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2808	does nothing for those backends.
		2809
		2810	=item L<EV>
		2811
		2812	This module isn't really "optional", as it is simply one of the backend
		2813	event loops that AnyEvent can use. However, it is simply the best event
		2814	loop available in terms of features, speed and stability: It supports
		2815	the AnyEvent API optimally, implements all the watcher types in XS, does
		2816	automatic timer adjustments even when no monotonic clock is available,
		2817	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2818	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2819	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2820
		2821	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2822	then this module will do nothing for you.
		2823
		2824	=item L<Guard>
		2825
		2826	The guard module, when used, will be used to implement
		2827	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2828	lot less memory), but otherwise doesn't affect guard operation much. It is
		2829	purely used for performance.
		2830
		2831	=item L<JSON> and L<JSON::XS>
		2832
		2833	One of these modules is required when you want to read or write JSON data
		2834	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2835	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2836
		2837	=item L<Net::SSLeay>
		2838
		2839	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2840	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2841	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2842
		2843	=item L<Time::HiRes>
		2844
		2845	This module is part of perl since release 5.008. It will be used when the
		2846	chosen event library does not come with a timing source of its own. The
		2847	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2848	try to use a monotonic clock for timing stability.
		2849
		2850	=back
		2851
		2852
		2853	=head1 FORK
		2854
		2855	Most event libraries are not fork-safe. The ones who are usually are
		2856	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2857	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2858	are usually badly thought-out hacks that are incompatible with fork in
		2859	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2860	continue event-processing in both parent and child (or both, if you know
		2861	what you are doing).
		2862
		2863	This means that, in general, you cannot fork and do event processing in
		2864	the child if the event library was initialised before the fork (which
		2865	usually happens when the first AnyEvent watcher is created, or the library
		2866	is loaded).
		2867
		2868	If you have to fork, you must either do so I<before> creating your first
		2869	watcher OR you must not use AnyEvent at all in the child OR you must do
		2870	something completely out of the scope of AnyEvent.
		2871
		2872	The problem of doing event processing in the parent I<and> the child
		2873	is much more complicated: even for backends that I<are> fork-aware or
		2874	fork-safe, their behaviour is not usually what you want: fork clones all
		2875	watchers, that means all timers, I/O watchers etc. are active in both
		2876	parent and child, which is almost never what you want. USing C<exec>
		2877	to start worker children from some kind of manage rprocess is usually
		2878	preferred, because it is much easier and cleaner, at the expense of having
		2879	to have another binary.
		2880
		2881
		2882	=head1 SECURITY CONSIDERATIONS
		2883
		2884	AnyEvent can be forced to load any event model via
		2885	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2886	execute arbitrary code or directly gain access, it can easily be used to
		2887	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2888	will not be active when the program uses a different event model than
		2889	specified in the variable.
		2890
		2891	You can make AnyEvent completely ignore this variable by deleting it
		2892	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2893
		2894	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2895
		2896	use AnyEvent;
		2897
		2898	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2899	be used to probe what backend is used and gain other information (which is
		2900	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2901	$ENV{PERL_ANYEVENT_STRICT}.
		2902
		2903	Note that AnyEvent will remove I<all> environment variables starting with
		2904	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2905	enabled.
		2906
		2907
		2908	=head1 BUGS
		2909
		2910	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2911	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2912	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2913	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2914	pronounced).
		2915
		2916
		2917	=head1 SEE ALSO
		2918
		2919	Tutorial/Introduction: L<AnyEvent::Intro>.
		2920
		2921	FAQ: L<AnyEvent::FAQ>.
		2922
		2923	Utility functions: L<AnyEvent::Util> (misc. grab-bag), L<AnyEvent::Log>
		2924	(simply logging).
		2925
		2926	Development/Debugging: L<AnyEvent::Strict> (stricter checking),
		2927	L<AnyEvent::Debug> (interactive shell, watcher tracing).
		2928
		2929	Supported event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>,
		2930	L<Glib::EV>, L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>,
		2931	L<Qt>, L<POE>, L<FLTK>.
		2932
		2933	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2934	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2935	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2936	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>,
		2937	L<AnyEvent::Impl::FLTK>.
		2938
		2939	Non-blocking handles, pipes, stream sockets, TCP clients and
		2940	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2941
		2942	Asynchronous DNS: L<AnyEvent::DNS>.
		2943
		2944	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2945
		2946	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2947	L<AnyEvent::HTTP>.
		2948
		2949
		2950	=head1 AUTHOR
		2951
		2952	Marc Lehmann <schmorp@schmorp.de>
		2953	http://home.schmorp.de/
		2954
		2955	=cut
		2956
		2957	1
		2958

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