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1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - the DBI of event loop programming
4		4
5	Event, Coro, Glib, Tk - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, Qt,
		6	FLTK and POE are various supported event loops/environments.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# if you prefer function calls, look at the AE manpage for
		13	# an alternative API.
		14
		15	# file handle or descriptor readable
11	my $w = AnyEvent->timer (fh => ..., poll => "[rw]+", cb => sub {	16	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12	my ($poll_got) = @_;	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) = @_;
13	...	31	...
14	});	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
		114	=head1 DESCRIPTION
		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
15	my $w = AnyEvent->io (after => $seconds, cb => sub {	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
		300	=over 4
		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<$level>.
		1057
		1058	If L<AnyEvent::Log> is not loaded then this function makes a simple test
		1059	to see whether the message will be logged. If the test succeeds it will
		1060	load AnyEvent::Log and call C<AnyEvent::Log::log> - consequently, look at
		1061	the L<AnyEvent::Log> documentation for details.
		1062
		1063	If the test fails it will simply return. Right now this happens when a
		1064	numerical loglevel is used and it is larger than the level specified via
		1065	C<$ENV{PERL_ANYEVENT_VERBOSE}>.
		1066
		1067	If you want to sprinkle loads of logging calls around your code, consider
		1068	creating a logger callback with the C<AnyEvent::Log::logger> function,
		1069	which can reduce typing, codesize and can reduce the logging overhead
		1070	enourmously.
		1071
		1072	=back
		1073
		1074	=head1 WHAT TO DO IN A MODULE
		1075
		1076	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		1077	freely, but you should not load a specific event module or rely on it.
		1078
		1079	Be careful when you create watchers in the module body - AnyEvent will
		1080	decide which event module to use as soon as the first method is called, so
		1081	by calling AnyEvent in your module body you force the user of your module
		1082	to load the event module first.
		1083
		1084	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1085	the C<< ->send >> method has been called on it already. This is
		1086	because it will stall the whole program, and the whole point of using
		1087	events is to stay interactive.
		1088
		1089	It is fine, however, to call C<< ->recv >> when the user of your module
		1090	requests it (i.e. if you create a http request object ad have a method
		1091	called C<results> that returns the results, it may call C<< ->recv >>
		1092	freely, as the user of your module knows what she is doing. Always).
		1093
		1094	=head1 WHAT TO DO IN THE MAIN PROGRAM
		1095
		1096	There will always be a single main program - the only place that should
		1097	dictate which event model to use.
		1098
		1099	If the program is not event-based, it need not do anything special, even
		1100	when it depends on a module that uses an AnyEvent. If the program itself
		1101	uses AnyEvent, but does not care which event loop is used, all it needs
		1102	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1103	available loop implementation.
		1104
		1105	If the main program relies on a specific event model - for example, in
		1106	Gtk2 programs you have to rely on the Glib module - you should load the
		1107	event module before loading AnyEvent or any module that uses it: generally
		1108	speaking, you should load it as early as possible. The reason is that
		1109	modules might create watchers when they are loaded, and AnyEvent will
		1110	decide on the event model to use as soon as it creates watchers, and it
		1111	might choose the wrong one unless you load the correct one yourself.
		1112
		1113	You can chose to use a pure-perl implementation by loading the
		1114	C<AnyEvent::Loop> module, which gives you similar behaviour
		1115	everywhere, but letting AnyEvent chose the model is generally better.
		1116
		1117	=head2 MAINLOOP EMULATION
		1118
		1119	Sometimes (often for short test scripts, or even standalone programs who
		1120	only want to use AnyEvent), you do not want to run a specific event loop.
		1121
		1122	In that case, you can use a condition variable like this:
		1123
		1124	AnyEvent->condvar->recv;
		1125
		1126	This has the effect of entering the event loop and looping forever.
		1127
		1128	Note that usually your program has some exit condition, in which case
		1129	it is better to use the "traditional" approach of storing a condition
		1130	variable somewhere, waiting for it, and sending it when the program should
		1131	exit cleanly.
		1132
		1133
		1134	=head1 OTHER MODULES
		1135
		1136	The following is a non-exhaustive list of additional modules that use
		1137	AnyEvent as a client and can therefore be mixed easily with other
		1138	AnyEvent modules and other event loops in the same program. Some of the
		1139	modules come as part of AnyEvent, the others are available via CPAN (see
		1140	L<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for
		1141	a longer non-exhaustive list), and the list is heavily biased towards
		1142	modules of the AnyEvent author himself :)
		1143
		1144	=over 4
		1145
		1146	=item L<AnyEvent::Util>
		1147
		1148	Contains various utility functions that replace often-used blocking
		1149	functions such as C<inet_aton> with event/callback-based versions.
		1150
		1151	=item L<AnyEvent::Socket>
		1152
		1153	Provides various utility functions for (internet protocol) sockets,
		1154	addresses and name resolution. Also functions to create non-blocking tcp
		1155	connections or tcp servers, with IPv6 and SRV record support and more.
		1156
		1157	=item L<AnyEvent::Handle>
		1158
		1159	Provide read and write buffers, manages watchers for reads and writes,
		1160	supports raw and formatted I/O, I/O queued and fully transparent and
		1161	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1162
		1163	=item L<AnyEvent::DNS>
		1164
		1165	Provides rich asynchronous DNS resolver capabilities.
		1166
		1167	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1168
		1169	Implement event-based interfaces to the protocols of the same name (for
		1170	the curious, IGS is the International Go Server and FCP is the Freenet
		1171	Client Protocol).
		1172
		1173	=item L<AnyEvent::AIO>
		1174
		1175	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1176	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1177	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1178	file I/O, and much more.
		1179
		1180	=item L<AnyEvent::Filesys::Notify>
		1181
		1182	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1183	path changes (e.g. "watch this directory for new files", "watch this
		1184	file for changes"). The L<AnyEvent::Filesys::Notify> module promises to
		1185	do just that in a portbale fashion, supporting inotify on GNU/Linux and
		1186	some weird, without doubt broken, stuff on OS X to monitor files. It can
		1187	fall back to blocking scans at regular intervals transparently on other
		1188	platforms, so it's about as portable as it gets.
		1189
		1190	(I haven't used it myself, but I haven't heard anybody complaining about
		1191	it yet).
		1192
		1193	=item L<AnyEvent::DBI>
		1194
		1195	Executes L<DBI> requests asynchronously in a proxy process for you,
		1196	notifying you in an event-based way when the operation is finished.
		1197
		1198	=item L<AnyEvent::HTTPD>
		1199
		1200	A simple embedded webserver.
		1201
		1202	=item L<AnyEvent::FastPing>
		1203
		1204	The fastest ping in the west.
		1205
		1206	=item L<Coro>
		1207
		1208	Has special support for AnyEvent via L<Coro::AnyEvent>, which allows you
		1209	to simply invert the flow control - don't call us, we will call you:
		1210
		1211	async {
		1212	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
		1213	print "5 seconds later!\n";
		1214
		1215	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1216	my $line = <STDIN>; # works for ttys
		1217
		1218	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1219	my ($body, $hdr) = Coro::rouse_wait;
		1220	};
		1221
		1222	=back
		1223
		1224	=cut
		1225
		1226	package AnyEvent;
		1227
		1228	# basically a tuned-down version of common::sense
		1229	sub common_sense {
		1230	# from common:.sense 3.4
		1231	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
		1232	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1233	$^H |= 0x00000600;
		1234	}
		1235
		1236	BEGIN { AnyEvent::common_sense }
		1237
		1238	use Carp ();
		1239
		1240	our $VERSION = '6.02';
		1241	our $MODEL;
		1242
		1243	our @ISA;
		1244
		1245	our @REGISTRY;
		1246
		1247	our $VERBOSE;
		1248
		1249	BEGIN {
		1250	require "AnyEvent/constants.pl";
		1251
		1252	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1253
		1254	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1255	if ${^TAINT};
		1256
		1257	$ENV{"PERL_ANYEVENT_$_"} = $ENV{"AE_$_"}
		1258	for grep s/^AE_// && !exists $ENV{"PERL_ANYEVENT_$_"}, keys %ENV;
		1259
		1260	@ENV{grep /^PERL_ANYEVENT_/, keys %ENV} = ()
		1261	if ${^TAINT};
		1262
		1263	$VERBOSE = length $ENV{PERL_ANYEVENT_VERBOSE} ? $ENV{PERL_ANYEVENT_VERBOSE}*1 : 3;
		1264	}
		1265
		1266	our $MAX_SIGNAL_LATENCY = 10;
		1267
		1268	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1269
		1270	{
		1271	my $idx;
		1272	$PROTOCOL{$_} = ++$idx
		1273	for reverse split /\s*,\s*/,
		1274	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1275	}
		1276
		1277	our @post_detect;
		1278
		1279	sub post_detect(&) {
		1280	my ($cb) = @_;
		1281
		1282	push @post_detect, $cb;
		1283
		1284	defined wantarray
		1285	? bless \$cb, "AnyEvent::Util::postdetect"
		1286	: ()
		1287	}
		1288
		1289	sub AnyEvent::Util::postdetect::DESTROY {
		1290	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1291	}
		1292
		1293	our $POSTPONE_W;
		1294	our @POSTPONE;
		1295
		1296	sub _postpone_exec {
		1297	undef $POSTPONE_W;
		1298
		1299	&{ shift @POSTPONE }
		1300	while @POSTPONE;
		1301	}
		1302
		1303	sub postpone(&) {
		1304	push @POSTPONE, shift;
		1305
		1306	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1307
		1308	()
		1309	}
		1310
		1311	sub log($$;@) {
		1312	# only load the big bloated module when we actually are about to log something
		1313	if ($_[0] <= $VERBOSE) { # also catches non-numeric levels(!)
		1314	require AnyEvent::Log;
		1315	# AnyEvent::Log overwrites this function
		1316	goto &log;
		1317	}
		1318
		1319	0 # not logged
		1320	}
		1321
		1322	if (length $ENV{PERL_ANYEVENT_LOG}) {
		1323	require AnyEvent::Log; # AnyEvent::Log does the thing for us
		1324	}
		1325
		1326	our @models = (
		1327	[EV:: => AnyEvent::Impl::EV:: , 1],
		1328	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
		1329	# everything below here will not (normally) be autoprobed
		1330	# as the pure perl backend should work everywhere
		1331	# and is usually faster
		1332	[Event:: => AnyEvent::Impl::Event::, 1],
		1333	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1334	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1335	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1336	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1337	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1338	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1339	[Wx:: => AnyEvent::Impl::POE::],
		1340	[Prima:: => AnyEvent::Impl::POE::],
		1341	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1342	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
		1343	[FLTK:: => AnyEvent::Impl::FLTK::],
		1344	);
		1345
		1346	our @isa_hook;
		1347
		1348	sub _isa_set {
		1349	my @pkg = ("AnyEvent", (map $_->[0], grep defined, @isa_hook), $MODEL);
		1350
		1351	@{"$pkg[$_-1]::ISA"} = $pkg[$_]
		1352	for 1 .. $#pkg;
		1353
		1354	grep $_ && $_->[1], @isa_hook
		1355	and AE::_reset ();
		1356	}
		1357
		1358	# used for hooking AnyEvent::Strict and AnyEvent::Debug::Wrap into the class hierarchy
		1359	sub _isa_hook($$;$) {
		1360	my ($i, $pkg, $reset_ae) = @_;
		1361
		1362	$isa_hook[$i] = $pkg ? [$pkg, $reset_ae] : undef;
		1363
		1364	_isa_set;
		1365	}
		1366
		1367	# all autoloaded methods reserve the complete glob, not just the method slot.
		1368	# due to bugs in perls method cache implementation.
		1369	our @methods = qw(io timer time now now_update signal child idle condvar);
		1370
		1371	sub detect() {
		1372	return $MODEL if $MODEL; # some programs keep references to detect
		1373
		1374	local $!; # for good measure
		1375	local $SIG{__DIE__}; # we use eval
		1376
		1377	# free some memory
		1378	*detect = sub () { $MODEL };
		1379	# undef &func doesn't correctly update the method cache. grmbl.
		1380	# so we delete the whole glob. grmbl.
		1381	# otoh, perl doesn't let me undef an active usb, but it lets me free
		1382	# a glob with an active sub. hrm. i hope it works, but perl is
		1383	# usually buggy in this department. sigh.
		1384	delete @{"AnyEvent::"}{@methods};
		1385	undef @methods;
		1386
		1387	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1388	my $model = $1;
		1389	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1390	if (eval "require $model") {
		1391	AnyEvent::log 7 => "loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.";
		1392	$MODEL = $model;
		1393	} else {
		1394	AnyEvent::log 5 => "unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@";
		1395	}
		1396	}
		1397
		1398	# check for already loaded models
		1399	unless ($MODEL) {
		1400	for (@REGISTRY, @models) {
		1401	my ($package, $model) = @$_;
		1402	if (${"$package\::VERSION"} > 0) {
		1403	if (eval "require $model") {
		1404	AnyEvent::log 7 => "autodetected model '$model', using it.";
		1405	$MODEL = $model;
		1406	last;
		1407	}
		1408	}
		1409	}
		1410
		1411	unless ($MODEL) {
		1412	# try to autoload a model
		1413	for (@REGISTRY, @models) {
		1414	my ($package, $model, $autoload) = @$_;
		1415	if (
		1416	$autoload
		1417	and eval "require $package"
		1418	and ${"$package\::VERSION"} > 0
		1419	and eval "require $model"
		1420	) {
		1421	AnyEvent::log 7 => "autoloaded model '$model', using it.";
		1422	$MODEL = $model;
		1423	last;
		1424	}
		1425	}
		1426
		1427	$MODEL
		1428	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?";
		1429	}
		1430	}
		1431
		1432	# free memory only needed for probing
		1433	undef @models;
		1434	undef @REGISTRY;
		1435
		1436	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1437
		1438	# now nuke some methods that are overridden by the backend.
		1439	# SUPER usage is not allowed in these.
		1440	for (qw(time signal child idle)) {
		1441	undef &{"AnyEvent::Base::$_"}
		1442	if defined &{"$MODEL\::$_"};
		1443	}
		1444
		1445	_isa_set;
		1446
		1447	# we're officially open!
		1448
		1449	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1450	require AnyEvent::Strict;
		1451	}
		1452
		1453	if ($ENV{PERL_ANYEVENT_DEBUG_WRAP}) {
		1454	require AnyEvent::Debug;
		1455	AnyEvent::Debug::wrap ($ENV{PERL_ANYEVENT_DEBUG_WRAP});
		1456	}
		1457
		1458	if (length $ENV{PERL_ANYEVENT_DEBUG_SHELL}) {
		1459	require AnyEvent::Socket;
		1460	require AnyEvent::Debug;
		1461
		1462	my $shell = $ENV{PERL_ANYEVENT_DEBUG_SHELL};
		1463	$shell =~ s/\$\$/$$/g;
		1464
		1465	my ($host, $service) = AnyEvent::Socket::parse_hostport ($shell);
		1466	$AnyEvent::Debug::SHELL = AnyEvent::Debug::shell ($host, $service);
		1467	}
		1468
		1469	# now the anyevent environment is set up as the user told us to, so
		1470	# call the actual user code - post detects
		1471
		1472	(shift @post_detect)->() while @post_detect;
		1473	undef @post_detect;
		1474
		1475	*post_detect = sub(&) {
		1476	shift->();
		1477
		1478	undef
		1479	};
		1480
		1481	$MODEL
		1482	}
		1483
		1484	for my $name (@methods) {
		1485	*$name = sub {
		1486	detect;
		1487	# we use goto because
		1488	# a) it makes the thunk more transparent
		1489	# b) it allows us to delete the thunk later
		1490	goto &{ UNIVERSAL::can AnyEvent => "SUPER::$name" }
		1491	};
		1492	}
		1493
		1494	# utility function to dup a filehandle. this is used by many backends
		1495	# to support binding more than one watcher per filehandle (they usually
		1496	# allow only one watcher per fd, so we dup it to get a different one).
		1497	sub _dupfh($$;$$) {
		1498	my ($poll, $fh, $r, $w) = @_;
		1499
		1500	# cygwin requires the fh mode to be matching, unix doesn't
		1501	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1502
		1503	open my $fh2, $mode, $fh
		1504	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1505
		1506	# we assume CLOEXEC is already set by perl in all important cases
		1507
		1508	($fh2, $rw)
		1509	}
		1510
		1511	=head1 SIMPLIFIED AE API
		1512
		1513	Starting with version 5.0, AnyEvent officially supports a second, much
		1514	simpler, API that is designed to reduce the calling, typing and memory
		1515	overhead by using function call syntax and a fixed number of parameters.
		1516
		1517	See the L<AE> manpage for details.
		1518
		1519	=cut
		1520
		1521	package AE;
		1522
		1523	our $VERSION = $AnyEvent::VERSION;
		1524
		1525	sub _reset() {
		1526	eval q{
		1527	# fall back to the main API by default - backends and AnyEvent::Base
		1528	# implementations can overwrite these.
		1529
		1530	sub io($$$) {
		1531	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1532	}
		1533
		1534	sub timer($$$) {
		1535	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1536	}
		1537
		1538	sub signal($$) {
		1539	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1540	}
		1541
		1542	sub child($$) {
		1543	AnyEvent->child (pid => $_[0], cb => $_[1])
		1544	}
		1545
		1546	sub idle($) {
		1547	AnyEvent->idle (cb => $_[0]);
		1548	}
		1549
		1550	sub cv(;&) {
		1551	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1552	}
		1553
		1554	sub now() {
		1555	AnyEvent->now
		1556	}
		1557
		1558	sub now_update() {
		1559	AnyEvent->now_update
		1560	}
		1561
		1562	sub time() {
		1563	AnyEvent->time
		1564	}
		1565
		1566	*postpone = \&AnyEvent::postpone;
		1567	*log = \&AnyEvent::log;
		1568	};
		1569	die if $@;
		1570	}
		1571
		1572	BEGIN { _reset }
		1573
		1574	package AnyEvent::Base;
		1575
		1576	# default implementations for many methods
		1577
		1578	sub time {
		1579	eval q{ # poor man's autoloading {}
		1580	# probe for availability of Time::HiRes
		1581	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1582	*time = sub { Time::HiRes::time () };
		1583	*AE::time = \& Time::HiRes::time ;
		1584	*now = \&time;
		1585	AnyEvent::log 8 => "AnyEvent: using Time::HiRes for sub-second timing accuracy.";
		1586	# if (eval "use POSIX (); (POSIX::times())...
		1587	} else {
		1588	*time = sub { CORE::time };
		1589	*AE::time = sub (){ CORE::time };
		1590	*now = \&time;
		1591	AnyEvent::log 3 => "using built-in time(), WARNING, no sub-second resolution!";
		1592	}
		1593	};
		1594	die if $@;
		1595
		1596	&time
		1597	}
		1598
		1599	*now = \&time;
		1600	sub now_update { }
		1601
		1602	sub _poll {
		1603	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1604	}
		1605
		1606	# default implementation for ->condvar
		1607	# in fact, the default should not be overwritten
		1608
		1609	sub condvar {
		1610	eval q{ # poor man's autoloading {}
		1611	*condvar = sub {
		1612	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1613	};
		1614
		1615	*AE::cv = sub (;&) {
		1616	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1617	};
		1618	};
		1619	die if $@;
		1620
		1621	&condvar
		1622	}
		1623
		1624	# default implementation for ->signal
		1625
		1626	our $HAVE_ASYNC_INTERRUPT;
		1627
		1628	sub _have_async_interrupt() {
		1629	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1630	&& eval "use Async::Interrupt 1.02 (); 1")
		1631	unless defined $HAVE_ASYNC_INTERRUPT;
		1632
		1633	$HAVE_ASYNC_INTERRUPT
		1634	}
		1635
		1636	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1637	our (%SIG_ASY, %SIG_ASY_W);
		1638	our ($SIG_COUNT, $SIG_TW);
		1639
		1640	# install a dummy wakeup watcher to reduce signal catching latency
		1641	# used by Impls
		1642	sub _sig_add() {
		1643	unless ($SIG_COUNT++) {
		1644	# try to align timer on a full-second boundary, if possible
		1645	my $NOW = AE::now;
		1646
		1647	$SIG_TW = AE::timer
		1648	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1649	$MAX_SIGNAL_LATENCY,
		1650	sub { } # just for the PERL_ASYNC_CHECK
		1651	;
		1652	}
		1653	}
		1654
		1655	sub _sig_del {
		1656	undef $SIG_TW
		1657	unless --$SIG_COUNT;
		1658	}
		1659
		1660	our $_sig_name_init; $_sig_name_init = sub {
		1661	eval q{ # poor man's autoloading {}
		1662	undef $_sig_name_init;
		1663
		1664	if (_have_async_interrupt) {
		1665	*sig2num = \&Async::Interrupt::sig2num;
		1666	*sig2name = \&Async::Interrupt::sig2name;
		1667	} else {
		1668	require Config;
		1669
		1670	my %signame2num;
		1671	@signame2num{ split ' ', $Config::Config{sig_name} }
		1672	= split ' ', $Config::Config{sig_num};
		1673
		1674	my @signum2name;
		1675	@signum2name[values %signame2num] = keys %signame2num;
		1676
		1677	*sig2num = sub($) {
		1678	$_[0] > 0 ? shift : $signame2num{+shift}
		1679	};
		1680	*sig2name = sub ($) {
		1681	$_[0] > 0 ? $signum2name[+shift] : shift
		1682	};
		1683	}
		1684	};
		1685	die if $@;
		1686	};
		1687
		1688	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1689	sub sig2name($) { &$_sig_name_init; &sig2name }
		1690
		1691	sub signal {
		1692	eval q{ # poor man's autoloading {}
		1693	# probe for availability of Async::Interrupt
		1694	if (_have_async_interrupt) {
		1695	AnyEvent::log 8 => "using Async::Interrupt for race-free signal handling.";
		1696
		1697	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1698	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1699
		1700	} else {
		1701	AnyEvent::log 8 => "using emulated perl signal handling with latency timer.";
		1702
		1703	if (AnyEvent::WIN32) {
		1704	require AnyEvent::Util;
		1705
		1706	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1707	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1708	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1709	} else {
		1710	pipe $SIGPIPE_R, $SIGPIPE_W;
		1711	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1712	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1713
		1714	# not strictly required, as $^F is normally 2, but let's make sure...
		1715	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1716	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1717	}
		1718
		1719	$SIGPIPE_R
		1720	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1721
		1722	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1723	}
		1724
		1725	*signal = $HAVE_ASYNC_INTERRUPT
		1726	? sub {
		1727	my (undef, %arg) = @_;
		1728
		1729	# async::interrupt
		1730	my $signal = sig2num $arg{signal};
		1731	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1732
		1733	$SIG_ASY{$signal} ||= new Async::Interrupt
		1734	cb => sub { undef $SIG_EV{$signal} },
		1735	signal => $signal,
		1736	pipe => [$SIGPIPE_R->filenos],
		1737	pipe_autodrain => 0,
		1738	;
		1739
		1740	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1741	}
		1742	: sub {
		1743	my (undef, %arg) = @_;
		1744
		1745	# pure perl
		1746	my $signal = sig2name $arg{signal};
		1747	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1748
		1749	$SIG{$signal} ||= sub {
		1750	local $!;
		1751	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1752	undef $SIG_EV{$signal};
		1753	};
		1754
		1755	# can't do signal processing without introducing races in pure perl,
		1756	# so limit the signal latency.
		1757	_sig_add;
		1758
		1759	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1760	}
		1761	;
		1762
		1763	*AnyEvent::Base::signal::DESTROY = sub {
		1764	my ($signal, $cb) = @{$_[0]};
		1765
		1766	_sig_del;
		1767
		1768	delete $SIG_CB{$signal}{$cb};
		1769
		1770	$HAVE_ASYNC_INTERRUPT
		1771	? delete $SIG_ASY{$signal}
		1772	: # delete doesn't work with older perls - they then
		1773	# print weird messages, or just unconditionally exit
		1774	# instead of getting the default action.
		1775	undef $SIG{$signal}
		1776	unless keys %{ $SIG_CB{$signal} };
		1777	};
		1778
		1779	*_signal_exec = sub {
		1780	$HAVE_ASYNC_INTERRUPT
		1781	? $SIGPIPE_R->drain
		1782	: sysread $SIGPIPE_R, (my $dummy), 9;
		1783
		1784	while (%SIG_EV) {
		1785	for (keys %SIG_EV) {
		1786	delete $SIG_EV{$_};
		1787	&$_ for values %{ $SIG_CB{$_} || {} };
		1788	}
		1789	}
		1790	};
		1791	};
		1792	die if $@;
		1793
		1794	&signal
		1795	}
		1796
		1797	# default implementation for ->child
		1798
		1799	our %PID_CB;
		1800	our $CHLD_W;
		1801	our $CHLD_DELAY_W;
		1802
		1803	# used by many Impl's
		1804	sub _emit_childstatus($$) {
		1805	my (undef, $rpid, $rstatus) = @_;
		1806
		1807	$_->($rpid, $rstatus)
		1808	for values %{ $PID_CB{$rpid} || {} },
		1809	values %{ $PID_CB{0} || {} };
		1810	}
		1811
		1812	sub child {
		1813	eval q{ # poor man's autoloading {}
		1814	*_sigchld = sub {
		1815	my $pid;
		1816
		1817	AnyEvent->_emit_childstatus ($pid, $?)
		1818	while ($pid = waitpid -1, WNOHANG) > 0;
		1819	};
		1820
		1821	*child = sub {
		1822	my (undef, %arg) = @_;
		1823
		1824	my $pid = $arg{pid};
		1825	my $cb = $arg{cb};
		1826
		1827	$PID_CB{$pid}{$cb+0} = $cb;
		1828
		1829	unless ($CHLD_W) {
		1830	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1831	# child could be a zombie already, so make at least one round
		1832	&_sigchld;
		1833	}
		1834
		1835	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1836	};
		1837
		1838	*AnyEvent::Base::child::DESTROY = sub {
		1839	my ($pid, $icb) = @{$_[0]};
		1840
		1841	delete $PID_CB{$pid}{$icb};
		1842	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1843
		1844	undef $CHLD_W unless keys %PID_CB;
		1845	};
		1846	};
		1847	die if $@;
		1848
		1849	&child
		1850	}
		1851
		1852	# idle emulation is done by simply using a timer, regardless
		1853	# of whether the process is idle or not, and not letting
		1854	# the callback use more than 50% of the time.
		1855	sub idle {
		1856	eval q{ # poor man's autoloading {}
		1857	*idle = sub {
		1858	my (undef, %arg) = @_;
		1859
		1860	my ($cb, $w, $rcb) = $arg{cb};
		1861
		1862	$rcb = sub {
		1863	if ($cb) {
		1864	$w = AE::time;
		1865	&$cb;
		1866	$w = AE::time - $w;
		1867
		1868	# never use more then 50% of the time for the idle watcher,
		1869	# within some limits
		1870	$w = 0.0001 if $w < 0.0001;
		1871	$w = 5 if $w > 5;
		1872
		1873	$w = AE::timer $w, 0, $rcb;
		1874	} else {
		1875	# clean up...
		1876	undef $w;
		1877	undef $rcb;
		1878	}
		1879	};
		1880
		1881	$w = AE::timer 0.05, 0, $rcb;
		1882
		1883	bless \\$cb, "AnyEvent::Base::idle"
		1884	};
		1885
		1886	*AnyEvent::Base::idle::DESTROY = sub {
		1887	undef $${$_[0]};
		1888	};
		1889	};
		1890	die if $@;
		1891
		1892	&idle
		1893	}
		1894
		1895	package AnyEvent::CondVar;
		1896
		1897	our @ISA = AnyEvent::CondVar::Base::;
		1898
		1899	# only to be used for subclassing
		1900	sub new {
		1901	my $class = shift;
		1902	bless AnyEvent->condvar (@_), $class
		1903	}
		1904
		1905	package AnyEvent::CondVar::Base;
		1906
		1907	#use overload
		1908	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1909	# fallback => 1;
		1910
		1911	# save 300+ kilobytes by dirtily hardcoding overloading
		1912	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1913	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1914	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1915	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1916
		1917	our $WAITING;
		1918
		1919	sub _send {
		1920	# nop
		1921	}
		1922
		1923	sub _wait {
		1924	AnyEvent->_poll until $_[0]{_ae_sent};
		1925	}
		1926
		1927	sub send {
		1928	my $cv = shift;
		1929	$cv->{_ae_sent} = [@_];
		1930	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1931	$cv->_send;
		1932	}
		1933
		1934	sub croak {
		1935	$_[0]{_ae_croak} = $_[1];
		1936	$_[0]->send;
		1937	}
		1938
		1939	sub ready {
		1940	$_[0]{_ae_sent}
		1941	}
		1942
		1943	sub recv {
		1944	unless ($_[0]{_ae_sent}) {
		1945	$WAITING
		1946	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1947
		1948	local $WAITING = 1;
		1949	$_[0]->_wait;
		1950	}
		1951
		1952	$_[0]{_ae_croak}
		1953	and Carp::croak $_[0]{_ae_croak};
		1954
		1955	wantarray
		1956	? @{ $_[0]{_ae_sent} }
		1957	: $_[0]{_ae_sent}[0]
		1958	}
		1959
		1960	sub cb {
		1961	my $cv = shift;
		1962
		1963	@_
		1964	and $cv->{_ae_cb} = shift
		1965	and $cv->{_ae_sent}
		1966	and (delete $cv->{_ae_cb})->($cv);
		1967
		1968	$cv->{_ae_cb}
		1969	}
		1970
		1971	sub begin {
		1972	++$_[0]{_ae_counter};
		1973	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1974	}
		1975
		1976	sub end {
		1977	return if --$_[0]{_ae_counter};
		1978	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1979	}
		1980
		1981	# undocumented/compatibility with pre-3.4
		1982	*broadcast = \&send;
		1983	*wait = \&recv;
		1984
		1985	=head1 ERROR AND EXCEPTION HANDLING
		1986
		1987	In general, AnyEvent does not do any error handling - it relies on the
		1988	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1989	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1990	checking of all AnyEvent methods, however, which is highly useful during
		1991	development.
		1992
		1993	As for exception handling (i.e. runtime errors and exceptions thrown while
		1994	executing a callback), this is not only highly event-loop specific, but
		1995	also not in any way wrapped by this module, as this is the job of the main
		1996	program.
		1997
		1998	The pure perl event loop simply re-throws the exception (usually
		1999	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		2000	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		2001	so on.
		2002
		2003	=head1 ENVIRONMENT VARIABLES
		2004
		2005	AnyEvent supports a number of environment variables that tune the
		2006	runtime behaviour. They are usually evaluated when AnyEvent is
		2007	loaded, initialised, or a submodule that uses them is loaded. Many of
		2008	them also cause AnyEvent to load additional modules - for example,
		2009	C<PERL_ANYEVENT_DEBUG_WRAP> causes the L<AnyEvent::Debug> module to be
		2010	loaded.
		2011
		2012	All the environment variables documented here start with
		2013	C<PERL_ANYEVENT_>, which is what AnyEvent considers its own
		2014	namespace. Other modules are encouraged (but by no means required) to use
		2015	C<PERL_ANYEVENT_SUBMODULE> if they have registered the AnyEvent::Submodule
		2016	namespace on CPAN, for any submodule. For example, L<AnyEvent::HTTP> could
		2017	be expected to use C<PERL_ANYEVENT_HTTP_PROXY> (it should not access env
		2018	variables starting with C<AE_>, see below).
		2019
		2020	All variables can also be set via the C<AE_> prefix, that is, instead
		2021	of setting C<PERL_ANYEVENT_VERBOSE> you can also set C<AE_VERBOSE>. In
		2022	case there is a clash btween anyevent and another program that uses
		2023	C<AE_something> you can set the corresponding C<PERL_ANYEVENT_something>
		2024	variable to the empty string, as those variables take precedence.
		2025
		2026	When AnyEvent is first loaded, it copies all C<AE_xxx> env variables
		2027	to their C<PERL_ANYEVENT_xxx> counterpart unless that variable already
		2028	exists. If taint mode is on, then AnyEvent will remove I<all> environment
		2029	variables starting with C<PERL_ANYEVENT_> from C<%ENV> (or replace them
		2030	with C<undef> or the empty string, if the corresaponding C<AE_> variable
		2031	is set).
		2032
		2033	The exact algorithm is currently:
		2034
		2035	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		2036	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		2037	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		2038
		2039	This ensures that child processes will not see the C<AE_> variables.
		2040
		2041	The following environment variables are currently known to AnyEvent:
		2042
		2043	=over 4
		2044
		2045	=item C<PERL_ANYEVENT_VERBOSE>
		2046
		2047	By default, AnyEvent will only log messages with loglevel C<3>
		2048	(C<critical>) or higher (see L<AnyEvent::Log>). You can set this
		2049	environment variable to a numerical loglevel to make AnyEvent more (or
		2050	less) talkative.
		2051
		2052	If you want to do more than just set the global logging level
		2053	you should have a look at C<PERL_ANYEVENT_LOG>, which allows much more
		2054	complex specifications.
		2055
		2056	When set to C<0> (C<off>), then no messages whatsoever will be logged with
		2057	the default logging settings.
		2058
		2059	When set to C<5> or higher (C<warn>), causes AnyEvent to warn about
		2060	unexpected conditions, such as not being able to load the event model
		2061	specified by C<PERL_ANYEVENT_MODEL>, or a guard callback throwing an
		2062	exception - this is the minimum recommended level.
		2063
		2064	When set to C<7> or higher (info), cause AnyEvent to report which event model it
		2065	chooses.
		2066
		2067	When set to C<8> or higher (debug), then AnyEvent will report extra information on
		2068	which optional modules it loads and how it implements certain features.
		2069
		2070	=item C<PERL_ANYEVENT_LOG>
		2071
		2072	Accepts rather complex logging specifications. For example, you could log
		2073	all C<debug> messages of some module to stderr, warnings and above to
		2074	stderr, and errors and above to syslog, with:
		2075
		2076	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		2077
		2078	For the rather extensive details, see L<AnyEvent::Log>.
		2079
		2080	This variable is evaluated when AnyEvent (or L<AnyEvent::Log>) is loaded,
		2081	so will take effect even before AnyEvent has initialised itself.
		2082
		2083	Note that specifying this environment variable causes the L<AnyEvent::Log>
		2084	module to be loaded, while C<PERL_ANYEVENT_VERBOSE> does not, so only
		2085	using the latter saves a few hundred kB of memory until the first message
		2086	is being logged.
		2087
		2088	=item C<PERL_ANYEVENT_STRICT>
		2089
		2090	AnyEvent does not do much argument checking by default, as thorough
		2091	argument checking is very costly. Setting this variable to a true value
		2092	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		2093	check the arguments passed to most method calls. If it finds any problems,
		2094	it will croak.
		2095
		2096	In other words, enables "strict" mode.
		2097
		2098	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		2099	>>, it is definitely recommended to keep it off in production. Keeping
		2100	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		2101	can be very useful, however.
		2102
		2103	=item C<PERL_ANYEVENT_DEBUG_SHELL>
		2104
		2105	If this env variable is set, then its contents will be interpreted by
		2106	C<AnyEvent::Socket::parse_hostport> (after replacing every occurance of
		2107	C<$$> by the process pid) and an C<AnyEvent::Debug::shell> is bound on
		2108	that port. The shell object is saved in C<$AnyEvent::Debug::SHELL>.
		2109
		2110	This happens when the first watcher is created.
		2111
		2112	For example, to bind a debug shell on a unix domain socket in
		2113	F<< /tmp/debug<pid>.sock >>, you could use this:
		2114
		2115	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		2116
		2117	Note that creating sockets in F</tmp> is very unsafe on multiuser
		2118	systems.
		2119
		2120	=item C<PERL_ANYEVENT_DEBUG_WRAP>
		2121
		2122	Can be set to C<0>, C<1> or C<2> and enables wrapping of all watchers for
		2123	debugging purposes. See C<AnyEvent::Debug::wrap> for details.
		2124
		2125	=item C<PERL_ANYEVENT_MODEL>
		2126
		2127	This can be used to specify the event model to be used by AnyEvent, before
		2128	auto detection and -probing kicks in.
		2129
		2130	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		2131	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		2132	resulting module name is loaded and - if the load was successful - used as
		2133	event model backend. If it fails to load then AnyEvent will proceed with
		2134	auto detection and -probing.
		2135
		2136	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		2137	nothing gets prepended and the module name is used as-is (hint: C<::> at
		2138	the end of a string designates a module name and quotes it appropriately).
		2139
		2140	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		2141	could start your program like this:
		2142
		2143	PERL_ANYEVENT_MODEL=Perl perl ...
		2144
		2145	=item C<PERL_ANYEVENT_PROTOCOLS>
		2146
		2147	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		2148	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		2149	of auto probing).
		2150
		2151	Must be set to a comma-separated list of protocols or address families,
		2152	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		2153	used, and preference will be given to protocols mentioned earlier in the
		2154	list.
		2155
		2156	This variable can effectively be used for denial-of-service attacks
		2157	against local programs (e.g. when setuid), although the impact is likely
		2158	small, as the program has to handle conenction and other failures anyways.
		2159
		2160	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		2161	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		2162	- only support IPv4, never try to resolve or contact IPv6
		2163	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		2164	IPv6, but prefer IPv6 over IPv4.
		2165
		2166	=item C<PERL_ANYEVENT_HOSTS>
		2167
		2168	This variable, if specified, overrides the F</etc/hosts> file used by
		2169	L<AnyEvent::Socket>C<::resolve_sockaddr>, i.e. hosts aliases will be read
		2170	from that file instead.
		2171
		2172	=item C<PERL_ANYEVENT_EDNS0>
		2173
		2174	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension for
		2175	DNS. This extension is generally useful to reduce DNS traffic, especially
		2176	when DNSSEC is involved, but some (broken) firewalls drop such DNS
		2177	packets, which is why it is off by default.
		2178
		2179	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2180	EDNS0 in its DNS requests.
		2181
		2182	=item C<PERL_ANYEVENT_MAX_FORKS>
		2183
		2184	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2185	will create in parallel.
		2186
		2187	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2188
		2189	The default value for the C<max_outstanding> parameter for the default DNS
		2190	resolver - this is the maximum number of parallel DNS requests that are
		2191	sent to the DNS server.
		2192
		2193	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2194
		2195	The absolute path to a F<resolv.conf>-style file to use instead of
		2196	F</etc/resolv.conf> (or the OS-specific configuration) in the default
		2197	resolver, or the empty string to select the default configuration.
		2198
		2199	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2200
		2201	When neither C<ca_file> nor C<ca_path> was specified during
		2202	L<AnyEvent::TLS> context creation, and either of these environment
		2203	variables are nonempty, they will be used to specify CA certificate
		2204	locations instead of a system-dependent default.
		2205
		2206	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2207
		2208	When these are set to C<1>, then the respective modules are not
		2209	loaded. Mostly good for testing AnyEvent itself.
		2210
		2211	=back
		2212
		2213	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		2214
		2215	This is an advanced topic that you do not normally need to use AnyEvent in
		2216	a module. This section is only of use to event loop authors who want to
		2217	provide AnyEvent compatibility.
		2218
		2219	If you need to support another event library which isn't directly
		2220	supported by AnyEvent, you can supply your own interface to it by
		2221	pushing, before the first watcher gets created, the package name of
		2222	the event module and the package name of the interface to use onto
		2223	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		2224	AnyEvent, so it is reasonably cheap.
		2225
		2226	Example:
		2227
		2228	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		2229
		2230	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		2231	package/class when it finds the C<urxvt> package/module is already loaded.
		2232
		2233	When AnyEvent is loaded and asked to find a suitable event model, it
		2234	will first check for the presence of urxvt by trying to C<use> the
		2235	C<urxvt::anyevent> module.
		2236
		2237	The class should provide implementations for all watcher types. See
		2238	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		2239	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		2240	see the sources.
		2241
		2242	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2243	provide suitable (hopefully) replacements.
		2244
		2245	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		2246	terminal emulator uses the above line as-is. An interface isn't included
		2247	in AnyEvent because it doesn't make sense outside the embedded interpreter
		2248	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		2249	I<rxvt-unicode> distribution.
		2250
		2251	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		2252	condition variables: code blocking while waiting for a condition will
		2253	C<die>. This still works with most modules/usages, and blocking calls must
		2254	not be done in an interactive application, so it makes sense.
		2255
		2256	=head1 EXAMPLE PROGRAM
		2257
		2258	The following program uses an I/O watcher to read data from STDIN, a timer
		2259	to display a message once per second, and a condition variable to quit the
		2260	program when the user enters quit:
		2261
		2262	use AnyEvent;
		2263
		2264	my $cv = AnyEvent->condvar;
		2265
		2266	my $io_watcher = AnyEvent->io (
		2267	fh => \*STDIN,
		2268	poll => 'r',
		2269	cb => sub {
		2270	warn "io event <$_[0]>\n"; # will always output <r>
		2271	chomp (my $input = <STDIN>); # read a line
		2272	warn "read: $input\n"; # output what has been read
		2273	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2274	},
		2275	);
		2276
		2277	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2278	warn "timeout\n"; # print 'timeout' at most every second
		2279	});
		2280
		2281	$cv->recv; # wait until user enters /^q/i
		2282
		2283	=head1 REAL-WORLD EXAMPLE
		2284
		2285	Consider the L<Net::FCP> module. It features (among others) the following
		2286	API calls, which are to freenet what HTTP GET requests are to http:
		2287
		2288	my $data = $fcp->client_get ($url); # blocks
		2289
		2290	my $transaction = $fcp->txn_client_get ($url); # does not block
		2291	$transaction->cb ( sub { ... } ); # set optional result callback
		2292	my $data = $transaction->result; # possibly blocks
		2293
		2294	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		2295	given URL and waits till the data has arrived. It is defined to be:
		2296
		2297	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		2298
		2299	And in fact is automatically generated. This is the blocking API of
		2300	L<Net::FCP>, and it works as simple as in any other, similar, module.
		2301
		2302	More complicated is C<txn_client_get>: It only creates a transaction
		2303	(completion, result, ...) object and initiates the transaction.
		2304
		2305	my $txn = bless { }, Net::FCP::Txn::;
		2306
		2307	It also creates a condition variable that is used to signal the completion
		2308	of the request:
		2309
		2310	$txn->{finished} = AnyAvent->condvar;
		2311
		2312	It then creates a socket in non-blocking mode.
		2313
		2314	socket $txn->{fh}, ...;
		2315	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		2316	connect $txn->{fh}, ...
		2317	and !$!{EWOULDBLOCK}
		2318	and !$!{EINPROGRESS}
		2319	and Carp::croak "unable to connect: $!\n";
		2320
		2321	Then it creates a write-watcher which gets called whenever an error occurs
		2322	or the connection succeeds:
		2323
		2324	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		2325
		2326	And returns this transaction object. The C<fh_ready_w> callback gets
		2327	called as soon as the event loop detects that the socket is ready for
		2328	writing.
		2329
		2330	The C<fh_ready_w> method makes the socket blocking again, writes the
		2331	request data and replaces the watcher by a read watcher (waiting for reply
		2332	data). The actual code is more complicated, but that doesn't matter for
		2333	this example:
		2334
		2335	fcntl $txn->{fh}, F_SETFL, 0;
		2336	syswrite $txn->{fh}, $txn->{request}
		2337	or die "connection or write error";
		2338	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		2339
		2340	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		2341	result and signals any possible waiters that the request has finished:
		2342
		2343	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		2344
		2345	if (end-of-file or data complete) {
		2346	$txn->{result} = $txn->{buf};
		2347	$txn->{finished}->send;
		2348	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		2349	}
		2350
		2351	The C<result> method, finally, just waits for the finished signal (if the
		2352	request was already finished, it doesn't wait, of course, and returns the
		2353	data:
		2354
		2355	$txn->{finished}->recv;
		2356	return $txn->{result};
		2357
		2358	The actual code goes further and collects all errors (C<die>s, exceptions)
		2359	that occurred during request processing. The C<result> method detects
		2360	whether an exception as thrown (it is stored inside the $txn object)
		2361	and just throws the exception, which means connection errors and other
		2362	problems get reported to the code that tries to use the result, not in a
		2363	random callback.
		2364
		2365	All of this enables the following usage styles:
		2366
		2367	1. Blocking:
		2368
		2369	my $data = $fcp->client_get ($url);
		2370
		2371	2. Blocking, but running in parallel:
		2372
		2373	my @datas = map $_->result,
		2374	map $fcp->txn_client_get ($_),
		2375	@urls;
		2376
		2377	Both blocking examples work without the module user having to know
		2378	anything about events.
		2379
		2380	3a. Event-based in a main program, using any supported event module:
		2381
		2382	use EV;
		2383
		2384	$fcp->txn_client_get ($url)->cb (sub {
		2385	my $txn = shift;
		2386	my $data = $txn->result;
16	...	2387	...
17	});	2388	});
18		2389
19	# watchers get canceled whenever $w is destroyed	2390	EV::loop;
20	# only one watcher per $fh and $poll type is allowed
21	# (i.e. on a socket you cna have one r + one w or one rw
22	# watcher, not any more.
23	# timers can only be used once
24		2391
25	my $w = AnyEvent->condvar; # kind of main loop replacement	2392	3b. The module user could use AnyEvent, too:
26	# can only be used once
27	$w->wait; # enters main loop till $condvar gets ->send
28	$w->broadcast; # wake up waiting and future wait's
29		2393
30	=head1 DESCRIPTION	2394	use AnyEvent;
31		2395
32	L<AnyEvent> provides an identical interface to multiple event loops. This	2396	my $quit = AnyEvent->condvar;
33	allows module authors to utilizy an event loop without forcing module
34	users to use the same event loop (as only a single event loop can coexist
35	peacefully at any one time).
36		2397
37	The interface itself is vaguely similar but not identical to the Event	2398	$fcp->txn_client_get ($url)->cb (sub {
38	module.	2399	...
		2400	$quit->send;
		2401	});
39		2402
40	On the first call of any method, the module tries to detect the currently	2403	$quit->recv;
41	loaded event loop by probing wether any of the following modules is	2404
42	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	2405
43	used. If none is found, the module tries to load these modules in the	2406	=head1 BENCHMARKS
44	order given. The first one that could be successfully loaded will be	2407
45	used. If still none could be found, it will issue an error.	2408	To give you an idea of the performance and overheads that AnyEvent adds
		2409	over the event loops themselves and to give you an impression of the speed
		2410	of various event loops I prepared some benchmarks.
		2411
		2412	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2413
		2414	Here is a benchmark of various supported event models used natively and
		2415	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2416	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2417	which it is), lets them fire exactly once and destroys them again.
		2418
		2419	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2420	distribution. It uses the L<AE> interface, which makes a real difference
		2421	for the EV and Perl backends only.
		2422
		2423	=head3 Explanation of the columns
		2424
		2425	I<watcher> is the number of event watchers created/destroyed. Since
		2426	different event models feature vastly different performances, each event
		2427	loop was given a number of watchers so that overall runtime is acceptable
		2428	and similar between tested event loop (and keep them from crashing): Glib
		2429	would probably take thousands of years if asked to process the same number
		2430	of watchers as EV in this benchmark.
		2431
		2432	I<bytes> is the number of bytes (as measured by the resident set size,
		2433	RSS) consumed by each watcher. This method of measuring captures both C
		2434	and Perl-based overheads.
		2435
		2436	I<create> is the time, in microseconds (millionths of seconds), that it
		2437	takes to create a single watcher. The callback is a closure shared between
		2438	all watchers, to avoid adding memory overhead. That means closure creation
		2439	and memory usage is not included in the figures.
		2440
		2441	I<invoke> is the time, in microseconds, used to invoke a simple
		2442	callback. The callback simply counts down a Perl variable and after it was
		2443	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2444	signal the end of this phase.
		2445
		2446	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2447	watcher.
		2448
		2449	=head3 Results
		2450
		2451	name watchers bytes create invoke destroy comment
		2452	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2453	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2454	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2455	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2456	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2457	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2458	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2459	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2460	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2461	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2462	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2463	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2464
		2465	=head3 Discussion
		2466
		2467	The benchmark does I<not> measure scalability of the event loop very
		2468	well. For example, a select-based event loop (such as the pure perl one)
		2469	can never compete with an event loop that uses epoll when the number of
		2470	file descriptors grows high. In this benchmark, all events become ready at
		2471	the same time, so select/poll-based implementations get an unnatural speed
		2472	boost.
		2473
		2474	Also, note that the number of watchers usually has a nonlinear effect on
		2475	overall speed, that is, creating twice as many watchers doesn't take twice
		2476	the time - usually it takes longer. This puts event loops tested with a
		2477	higher number of watchers at a disadvantage.
		2478
		2479	To put the range of results into perspective, consider that on the
		2480	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2481	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2482	cycles with POE.
		2483
		2484	C<EV> is the sole leader regarding speed and memory use, which are both
		2485	maximal/minimal, respectively. When using the L<AE> API there is zero
		2486	overhead (when going through the AnyEvent API create is about 5-6 times
		2487	slower, with other times being equal, so still uses far less memory than
		2488	any other event loop and is still faster than Event natively).
		2489
		2490	The pure perl implementation is hit in a few sweet spots (both the
		2491	constant timeout and the use of a single fd hit optimisations in the perl
		2492	interpreter and the backend itself). Nevertheless this shows that it
		2493	adds very little overhead in itself. Like any select-based backend its
		2494	performance becomes really bad with lots of file descriptors (and few of
		2495	them active), of course, but this was not subject of this benchmark.
		2496
		2497	The C<Event> module has a relatively high setup and callback invocation
		2498	cost, but overall scores in on the third place.
		2499
		2500	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2501	when using its pure perl backend.
		2502
		2503	C<Glib>'s memory usage is quite a bit higher, but it features a
		2504	faster callback invocation and overall ends up in the same class as
		2505	C<Event>. However, Glib scales extremely badly, doubling the number of
		2506	watchers increases the processing time by more than a factor of four,
		2507	making it completely unusable when using larger numbers of watchers
		2508	(note that only a single file descriptor was used in the benchmark, so
		2509	inefficiencies of C<poll> do not account for this).
		2510
		2511	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2512	more than 2000 watchers is a big setback, however, as correctness takes
		2513	precedence over speed. Nevertheless, its performance is surprising, as the
		2514	file descriptor is dup()ed for each watcher. This shows that the dup()
		2515	employed by some adaptors is not a big performance issue (it does incur a
		2516	hidden memory cost inside the kernel which is not reflected in the figures
		2517	above).
		2518
		2519	C<POE>, regardless of underlying event loop (whether using its pure perl
		2520	select-based backend or the Event module, the POE-EV backend couldn't
		2521	be tested because it wasn't working) shows abysmal performance and
		2522	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2523	as EV watchers, and 10 times as much memory as Event (the high memory
		2524	requirements are caused by requiring a session for each watcher). Watcher
		2525	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2526	implementation.
		2527
		2528	The design of the POE adaptor class in AnyEvent can not really account
		2529	for the performance issues, though, as session creation overhead is
		2530	small compared to execution of the state machine, which is coded pretty
		2531	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2532	using multiple sessions is not a good approach, especially regarding
		2533	memory usage, even the author of POE could not come up with a faster
		2534	design).
		2535
		2536	=head3 Summary
46		2537
47	=over 4	2538	=over 4
48		2539
		2540	=item * Using EV through AnyEvent is faster than any other event loop
		2541	(even when used without AnyEvent), but most event loops have acceptable
		2542	performance with or without AnyEvent.
		2543
		2544	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2545	the actual event loop, only with extremely fast event loops such as EV
		2546	does AnyEvent add significant overhead.
		2547
		2548	=item * You should avoid POE like the plague if you want performance or
		2549	reasonable memory usage.
		2550
		2551	=back
		2552
		2553	=head2 BENCHMARKING THE LARGE SERVER CASE
		2554
		2555	This benchmark actually benchmarks the event loop itself. It works by
		2556	creating a number of "servers": each server consists of a socket pair, a
		2557	timeout watcher that gets reset on activity (but never fires), and an I/O
		2558	watcher waiting for input on one side of the socket. Each time the socket
		2559	watcher reads a byte it will write that byte to a random other "server".
		2560
		2561	The effect is that there will be a lot of I/O watchers, only part of which
		2562	are active at any one point (so there is a constant number of active
		2563	fds for each loop iteration, but which fds these are is random). The
		2564	timeout is reset each time something is read because that reflects how
		2565	most timeouts work (and puts extra pressure on the event loops).
		2566
		2567	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2568	(1%) are active. This mirrors the activity of large servers with many
		2569	connections, most of which are idle at any one point in time.
		2570
		2571	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2572	distribution. It uses the L<AE> interface, which makes a real difference
		2573	for the EV and Perl backends only.
		2574
		2575	=head3 Explanation of the columns
		2576
		2577	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2578	each server has a read and write socket end).
		2579
		2580	I<create> is the time it takes to create a socket pair (which is
		2581	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2582
		2583	I<request>, the most important value, is the time it takes to handle a
		2584	single "request", that is, reading the token from the pipe and forwarding
		2585	it to another server. This includes deleting the old timeout and creating
		2586	a new one that moves the timeout into the future.
		2587
		2588	=head3 Results
		2589
		2590	name sockets create request
		2591	EV 20000 62.66 7.99
		2592	Perl 20000 68.32 32.64
		2593	IOAsync 20000 174.06 101.15 epoll
		2594	IOAsync 20000 174.67 610.84 poll
		2595	Event 20000 202.69 242.91
		2596	Glib 20000 557.01 1689.52
		2597	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2598
		2599	=head3 Discussion
		2600
		2601	This benchmark I<does> measure scalability and overall performance of the
		2602	particular event loop.
		2603
		2604	EV is again fastest. Since it is using epoll on my system, the setup time
		2605	is relatively high, though.
		2606
		2607	Perl surprisingly comes second. It is much faster than the C-based event
		2608	loops Event and Glib.
		2609
		2610	IO::Async performs very well when using its epoll backend, and still quite
		2611	good compared to Glib when using its pure perl backend.
		2612
		2613	Event suffers from high setup time as well (look at its code and you will
		2614	understand why). Callback invocation also has a high overhead compared to
		2615	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2616	uses select or poll in basically all documented configurations.
		2617
		2618	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2619	clearly fails to perform with many filehandles or in busy servers.
		2620
		2621	POE is still completely out of the picture, taking over 1000 times as long
		2622	as EV, and over 100 times as long as the Perl implementation, even though
		2623	it uses a C-based event loop in this case.
		2624
		2625	=head3 Summary
		2626
		2627	=over 4
		2628
		2629	=item * The pure perl implementation performs extremely well.
		2630
		2631	=item * Avoid Glib or POE in large projects where performance matters.
		2632
		2633	=back
		2634
		2635	=head2 BENCHMARKING SMALL SERVERS
		2636
		2637	While event loops should scale (and select-based ones do not...) even to
		2638	large servers, most programs we (or I :) actually write have only a few
		2639	I/O watchers.
		2640
		2641	In this benchmark, I use the same benchmark program as in the large server
		2642	case, but it uses only eight "servers", of which three are active at any
		2643	one time. This should reflect performance for a small server relatively
		2644	well.
		2645
		2646	The columns are identical to the previous table.
		2647
		2648	=head3 Results
		2649
		2650	name sockets create request
		2651	EV 16 20.00 6.54
		2652	Perl 16 25.75 12.62
		2653	Event 16 81.27 35.86
		2654	Glib 16 32.63 15.48
		2655	POE 16 261.87 276.28 uses POE::Loop::Event
		2656
		2657	=head3 Discussion
		2658
		2659	The benchmark tries to test the performance of a typical small
		2660	server. While knowing how various event loops perform is interesting, keep
		2661	in mind that their overhead in this case is usually not as important, due
		2662	to the small absolute number of watchers (that is, you need efficiency and
		2663	speed most when you have lots of watchers, not when you only have a few of
		2664	them).
		2665
		2666	EV is again fastest.
		2667
		2668	Perl again comes second. It is noticeably faster than the C-based event
		2669	loops Event and Glib, although the difference is too small to really
		2670	matter.
		2671
		2672	POE also performs much better in this case, but is is still far behind the
		2673	others.
		2674
		2675	=head3 Summary
		2676
		2677	=over 4
		2678
		2679	=item * C-based event loops perform very well with small number of
		2680	watchers, as the management overhead dominates.
		2681
		2682	=back
		2683
		2684	=head2 THE IO::Lambda BENCHMARK
		2685
		2686	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2687	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2688	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2689	shouldn't come as a surprise to anybody). As such, the benchmark is
		2690	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2691	very optimal. But how would AnyEvent compare when used without the extra
		2692	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2693
		2694	The benchmark itself creates an echo-server, and then, for 500 times,
		2695	connects to the echo server, sends a line, waits for the reply, and then
		2696	creates the next connection. This is a rather bad benchmark, as it doesn't
		2697	test the efficiency of the framework or much non-blocking I/O, but it is a
		2698	benchmark nevertheless.
		2699
		2700	name runtime
		2701	Lambda/select 0.330 sec
		2702	+ optimized 0.122 sec
		2703	Lambda/AnyEvent 0.327 sec
		2704	+ optimized 0.138 sec
		2705	Raw sockets/select 0.077 sec
		2706	POE/select, components 0.662 sec
		2707	POE/select, raw sockets 0.226 sec
		2708	POE/select, optimized 0.404 sec
		2709
		2710	AnyEvent/select/nb 0.085 sec
		2711	AnyEvent/EV/nb 0.068 sec
		2712	+state machine 0.134 sec
		2713
		2714	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2715	benchmarks actually make blocking connects and use 100% blocking I/O,
		2716	defeating the purpose of an event-based solution. All of the newly
		2717	written AnyEvent benchmarks use 100% non-blocking connects (using
		2718	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2719	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2720	generally require a lot more bookkeeping and event handling than blocking
		2721	connects (which involve a single syscall only).
		2722
		2723	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2724	offers similar expressive power as POE and IO::Lambda, using conventional
		2725	Perl syntax. This means that both the echo server and the client are 100%
		2726	non-blocking, further placing it at a disadvantage.
		2727
		2728	As you can see, the AnyEvent + EV combination even beats the
		2729	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2730	backend easily beats IO::Lambda and POE.
		2731
		2732	And even the 100% non-blocking version written using the high-level (and
		2733	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2734	higher level ("unoptimised") abstractions by a large margin, even though
		2735	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2736
		2737	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2738	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2739	part of the IO::Lambda distribution and were used without any changes.
		2740
		2741
		2742	=head1 SIGNALS
		2743
		2744	AnyEvent currently installs handlers for these signals:
		2745
		2746	=over 4
		2747
		2748	=item SIGCHLD
		2749
		2750	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2751	emulation for event loops that do not support them natively. Also, some
		2752	event loops install a similar handler.
		2753
		2754	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2755	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2756
		2757	=item SIGPIPE
		2758
		2759	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2760	when AnyEvent gets loaded.
		2761
		2762	The rationale for this is that AnyEvent users usually do not really depend
		2763	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2764	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2765	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2766	some random socket.
		2767
		2768	The rationale for installing a no-op handler as opposed to ignoring it is
		2769	that this way, the handler will be restored to defaults on exec.
		2770
		2771	Feel free to install your own handler, or reset it to defaults.
		2772
		2773	=back
		2774
49	=cut	2775	=cut
50		2776
51	package AnyEvent;	2777	undef $SIG{CHLD}
		2778	if $SIG{CHLD} eq 'IGNORE';
52		2779
53	no warnings;	2780	$SIG{PIPE} = sub { }
54	use strict 'vars';	2781	unless defined $SIG{PIPE};
55	use Carp;
56		2782
57	our $VERSION = 0.2;	2783	=head1 RECOMMENDED/OPTIONAL MODULES
58	our $MODEL;
59		2784
60	our $AUTOLOAD;	2785	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
61	our @ISA;	2786	its built-in modules) are required to use it.
62		2787
63	my @models = (	2788	That does not mean that AnyEvent won't take advantage of some additional
64	[Coro => Coro::Event::],	2789	modules if they are installed.
65	[Event => Event::],
66	[Glib => Glib::],
67	[Tk => Tk::],
68	);
69		2790
70	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	2791	This section explains which additional modules will be used, and how they
		2792	affect AnyEvent's operation.
71		2793
72	sub AUTOLOAD {	2794	=over 4
73	$AUTOLOAD =~ s/.*://;
74		2795
75	$method{$AUTOLOAD}	2796	=item L<Async::Interrupt>
76	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";
77		2797
78	unless ($MODEL) {	2798	This slightly arcane module is used to implement fast signal handling: To
79	# check for already loaded models	2799	my knowledge, there is no way to do completely race-free and quick
80	for (@models) {	2800	signal handling in pure perl. To ensure that signals still get
81	my ($model, $package) = @$_;	2801	delivered, AnyEvent will start an interval timer to wake up perl (and
82	if (scalar keys %{ *{"$package\::"} }) {	2802	catch the signals) with some delay (default is 10 seconds, look for
83	eval "require AnyEvent::Impl::$model";	2803	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
84	last if $MODEL;
85	}
86	}
87		2804
88	unless ($MODEL) {	2805	If this module is available, then it will be used to implement signal
89	# try to load a model	2806	catching, which means that signals will not be delayed, and the event loop
		2807	will not be interrupted regularly, which is more efficient (and good for
		2808	battery life on laptops).
90		2809
91	for (@models) {	2810	This affects not just the pure-perl event loop, but also other event loops
92	my ($model, $package) = @$_;	2811	that have no signal handling on their own (e.g. Glib, Tk, Qt).
93	eval "require AnyEvent::Impl::$model";
94	last if $MODEL;
95	}
96		2812
97	$MODEL	2813	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
98	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	2814	and either employ their own workarounds (POE) or use AnyEvent's workaround
99	}	2815	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
100	}	2816	does nothing for those backends.
101		2817
102	@ISA = $MODEL;	2818	=item L<EV>
103		2819
104	my $class = shift;	2820	This module isn't really "optional", as it is simply one of the backend
105	$class->$AUTOLOAD (@_);	2821	event loops that AnyEvent can use. However, it is simply the best event
106	}	2822	loop available in terms of features, speed and stability: It supports
		2823	the AnyEvent API optimally, implements all the watcher types in XS, does
		2824	automatic timer adjustments even when no monotonic clock is available,
		2825	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2826	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2827	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2828
		2829	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2830	then this module will do nothing for you.
		2831
		2832	=item L<Guard>
		2833
		2834	The guard module, when used, will be used to implement
		2835	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2836	lot less memory), but otherwise doesn't affect guard operation much. It is
		2837	purely used for performance.
		2838
		2839	=item L<JSON> and L<JSON::XS>
		2840
		2841	One of these modules is required when you want to read or write JSON data
		2842	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2843	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2844
		2845	=item L<Net::SSLeay>
		2846
		2847	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2848	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2849	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2850
		2851	=item L<Time::HiRes>
		2852
		2853	This module is part of perl since release 5.008. It will be used when the
		2854	chosen event library does not come with a timing source of its own. The
		2855	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2856	try to use a monotonic clock for timing stability.
107		2857
108	=back	2858	=back
109		2859
110	=head1 EXAMPLE
111		2860
112	The following program uses an io watcher to read data from stdin, a timer	2861	=head1 FORK
113	to display a message once per second, and a condvar to exit the program
114	when the user enters quit:
115		2862
		2863	Most event libraries are not fork-safe. The ones who are usually are
		2864	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2865	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2866	are usually badly thought-out hacks that are incompatible with fork in
		2867	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2868	continue event-processing in both parent and child (or both, if you know
		2869	what you are doing).
		2870
		2871	This means that, in general, you cannot fork and do event processing in
		2872	the child if the event library was initialised before the fork (which
		2873	usually happens when the first AnyEvent watcher is created, or the library
		2874	is loaded).
		2875
		2876	If you have to fork, you must either do so I<before> creating your first
		2877	watcher OR you must not use AnyEvent at all in the child OR you must do
		2878	something completely out of the scope of AnyEvent.
		2879
		2880	The problem of doing event processing in the parent I<and> the child
		2881	is much more complicated: even for backends that I<are> fork-aware or
		2882	fork-safe, their behaviour is not usually what you want: fork clones all
		2883	watchers, that means all timers, I/O watchers etc. are active in both
		2884	parent and child, which is almost never what you want. USing C<exec>
		2885	to start worker children from some kind of manage rprocess is usually
		2886	preferred, because it is much easier and cleaner, at the expense of having
		2887	to have another binary.
		2888
		2889
		2890	=head1 SECURITY CONSIDERATIONS
		2891
		2892	AnyEvent can be forced to load any event model via
		2893	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2894	execute arbitrary code or directly gain access, it can easily be used to
		2895	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2896	will not be active when the program uses a different event model than
		2897	specified in the variable.
		2898
		2899	You can make AnyEvent completely ignore this variable by deleting it
		2900	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2901
		2902	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2903
116	use AnyEvent;	2904	use AnyEvent;
117		2905
118	my $cv = AnyEvent->condvar;	2906	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2907	be used to probe what backend is used and gain other information (which is
		2908	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2909	$ENV{PERL_ANYEVENT_STRICT}.
119		2910
120	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	2911	Note that AnyEvent will remove I<all> environment variables starting with
121	warn "io event <$_[0]>\n"; # will always output <r>	2912	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
122	chomp (my $input = <STDIN>); # read a line	2913	enabled.
123	warn "read: $input\n"; # output what has been read
124	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
125	});
126		2914
127	my $time_watcher; # can only be used once
128		2915
129	sub new_timer {	2916	=head1 BUGS
130	$timer = AnyEvent->timer (after => 1, cb => sub {
131	warn "timeout\n"; # print 'timeout' about every second
132	&new_timer; # and restart the time
133	});
134	}
135		2917
136	new_timer; # create first timer	2918	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2919	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2920	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2921	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2922	pronounced).
137		2923
138	$cv->wait; # wait until user enters /^q/i
139		2924
140	=head1 SEE ALSO	2925	=head1 SEE ALSO
141		2926
142	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	2927	Tutorial/Introduction: L<AnyEvent::Intro>.
143	L<AnyEvent::Impl::Coro>,	2928
144	L<AnyEvent::Impl::Event>,	2929	FAQ: L<AnyEvent::FAQ>.
145	L<AnyEvent::Impl::Glib>,	2930
		2931	Utility functions: L<AnyEvent::Util> (misc. grab-bag), L<AnyEvent::Log>
		2932	(simply logging).
		2933
		2934	Development/Debugging: L<AnyEvent::Strict> (stricter checking),
		2935	L<AnyEvent::Debug> (interactive shell, watcher tracing).
		2936
		2937	Supported event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>,
		2938	L<Glib::EV>, L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>,
		2939	L<Qt>, L<POE>, L<FLTK>.
		2940
		2941	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2942	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2943	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2944	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>,
146	L<AnyEvent::Impl::Tk>.	2945	L<AnyEvent::Impl::FLTK>.
147		2946
148	=head1	2947	Non-blocking handles, pipes, stream sockets, TCP clients and
		2948	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2949
		2950	Asynchronous DNS: L<AnyEvent::DNS>.
		2951
		2952	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2953
		2954	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2955	L<AnyEvent::HTTP>.
		2956
		2957
		2958	=head1 AUTHOR
		2959
		2960	Marc Lehmann <schmorp@schmorp.de>
		2961	http://home.schmorp.de/
149		2962
150	=cut	2963	=cut
151		2964
152	1	2965	1
153		2966

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