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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	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::FLTK2 based on FLTK (fltk 2 binding).
		884
		885	=item Backends with special needs.
		886
		887	Qt requires the Qt::Application to be instantiated first, but will
		888	otherwise be picked up automatically. As long as the main program
		889	instantiates the application before any AnyEvent watchers are created,
		890	everything should just work.
		891
		892	AnyEvent::Impl::Qt based on Qt.
		893
		894	=item Event loops that are indirectly supported via other backends.
		895
		896	Some event loops can be supported via other modules:
		897
		898	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		899
		900	B<WxWidgets> has no support for watching file handles. However, you can
		901	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		902	polls 20 times per second, which was considered to be too horrible to even
		903	consider for AnyEvent.
		904
		905	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		906	backend, so it can be supported through POE.
		907
		908	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		909	load L<POE> when detecting them, in the hope that POE will pick them up,
		910	in which case everything will be automatic.
		911
		912	=back
		913
		914	=head1 GLOBAL VARIABLES AND FUNCTIONS
		915
		916	These are not normally required to use AnyEvent, but can be useful to
		917	write AnyEvent extension modules.
		918
		919	=over 4
		920
		921	=item $AnyEvent::MODEL
		922
		923	Contains C<undef> until the first watcher is being created, before the
		924	backend has been autodetected.
		925
		926	Afterwards it contains the event model that is being used, which is the
		927	name of the Perl class implementing the model. This class is usually one
		928	of the C<AnyEvent::Impl::xxx> modules, but can be any other class in the
		929	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
		930	will be C<urxvt::anyevent>).
		931
		932	=item AnyEvent::detect
		933
		934	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		935	if necessary. You should only call this function right before you would
		936	have created an AnyEvent watcher anyway, that is, as late as possible at
		937	runtime, and not e.g. during initialisation of your module.
		938
		939	The effect of calling this function is as if a watcher had been created
		940	(specifically, actions that happen "when the first watcher is created"
		941	happen when calling detetc as well).
		942
		943	If you need to do some initialisation before AnyEvent watchers are
		944	created, use C<post_detect>.
		945
		946	=item $guard = AnyEvent::post_detect { BLOCK }
		947
		948	Arranges for the code block to be executed as soon as the event model is
		949	autodetected (or immediately if that has already happened).
		950
		951	The block will be executed I<after> the actual backend has been detected
		952	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		953	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		954	other initialisations - see the sources of L<AnyEvent::Strict> or
		955	L<AnyEvent::AIO> to see how this is used.
		956
		957	The most common usage is to create some global watchers, without forcing
		958	event module detection too early, for example, L<AnyEvent::AIO> creates
		959	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		960	avoid autodetecting the event module at load time.
		961
		962	If called in scalar or list context, then it creates and returns an object
		963	that automatically removes the callback again when it is destroyed (or
		964	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		965	a case where this is useful.
		966
		967	Example: Create a watcher for the IO::AIO module and store it in
		968	C<$WATCHER>, but do so only do so after the event loop is initialised.
		969
		970	our WATCHER;
		971
		972	my $guard = AnyEvent::post_detect {
		973	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		974	};
		975
		976	# the ||= is important in case post_detect immediately runs the block,
		977	# as to not clobber the newly-created watcher. assigning both watcher and
		978	# post_detect guard to the same variable has the advantage of users being
		979	# able to just C<undef $WATCHER> if the watcher causes them grief.
		980
		981	$WATCHER ||= $guard;
		982
		983	=item @AnyEvent::post_detect
		984
		985	If there are any code references in this array (you can C<push> to it
		986	before or after loading AnyEvent), then they will be called directly
		987	after the event loop has been chosen.
		988
		989	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		990	if it is defined then the event loop has already been detected, and the
		991	array will be ignored.
		992
		993	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		994	it, as it takes care of these details.
		995
		996	This variable is mainly useful for modules that can do something useful
		997	when AnyEvent is used and thus want to know when it is initialised, but do
		998	not need to even load it by default. This array provides the means to hook
		999	into AnyEvent passively, without loading it.
		1000
		1001	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		1002	together, you could put this into Coro (this is the actual code used by
		1003	Coro to accomplish this):
		1004
		1005	if (defined $AnyEvent::MODEL) {
		1006	# AnyEvent already initialised, so load Coro::AnyEvent
		1007	require Coro::AnyEvent;
		1008	} else {
		1009	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		1010	# as soon as it is
		1011	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		1012	}
		1013
		1014	=item AnyEvent::postpone { BLOCK }
		1015
		1016	Arranges for the block to be executed as soon as possible, but not before
		1017	the call itself returns. In practise, the block will be executed just
		1018	before the event loop polls for new events, or shortly afterwards.
		1019
		1020	This function never returns anything (to make the C<return postpone { ...
		1021	}> idiom more useful.
		1022
		1023	To understand the usefulness of this function, consider a function that
		1024	asynchronously does something for you and returns some transaction
		1025	object or guard to let you cancel the operation. For example,
		1026	C<AnyEvent::Socket::tcp_connect>:
		1027
		1028	# start a conenction attempt unless one is active
		1029	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		1030	delete $self->{connect_guard};
		1031	...
		1032	};
		1033
		1034	Imagine that this function could instantly call the callback, for
		1035	example, because it detects an obvious error such as a negative port
		1036	number. Invoking the callback before the function returns causes problems
		1037	however: the callback will be called and will try to delete the guard
		1038	object. But since the function hasn't returned yet, there is nothing to
		1039	delete. When the function eventually returns it will assign the guard
		1040	object to C<< $self->{connect_guard} >>, where it will likely never be
		1041	deleted, so the program thinks it is still trying to connect.
		1042
		1043	This is where C<AnyEvent::postpone> should be used. Instead of calling the
		1044	callback directly on error:
		1045
		1046	$cb->(undef), return # signal error to callback, BAD!
		1047	if $some_error_condition;
		1048
		1049	It should use C<postpone>:
		1050
		1051	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1052	if $some_error_condition;
		1053
		1054	=back
		1055
		1056	=head1 WHAT TO DO IN A MODULE
		1057
		1058	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		1059	freely, but you should not load a specific event module or rely on it.
		1060
		1061	Be careful when you create watchers in the module body - AnyEvent will
		1062	decide which event module to use as soon as the first method is called, so
		1063	by calling AnyEvent in your module body you force the user of your module
		1064	to load the event module first.
		1065
		1066	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1067	the C<< ->send >> method has been called on it already. This is
		1068	because it will stall the whole program, and the whole point of using
		1069	events is to stay interactive.
		1070
		1071	It is fine, however, to call C<< ->recv >> when the user of your module
		1072	requests it (i.e. if you create a http request object ad have a method
		1073	called C<results> that returns the results, it may call C<< ->recv >>
		1074	freely, as the user of your module knows what she is doing. Always).
		1075
		1076	=head1 WHAT TO DO IN THE MAIN PROGRAM
		1077
		1078	There will always be a single main program - the only place that should
		1079	dictate which event model to use.
		1080
		1081	If the program is not event-based, it need not do anything special, even
		1082	when it depends on a module that uses an AnyEvent. If the program itself
		1083	uses AnyEvent, but does not care which event loop is used, all it needs
		1084	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1085	available loop implementation.
		1086
		1087	If the main program relies on a specific event model - for example, in
		1088	Gtk2 programs you have to rely on the Glib module - you should load the
		1089	event module before loading AnyEvent or any module that uses it: generally
		1090	speaking, you should load it as early as possible. The reason is that
		1091	modules might create watchers when they are loaded, and AnyEvent will
		1092	decide on the event model to use as soon as it creates watchers, and it
		1093	might choose the wrong one unless you load the correct one yourself.
		1094
		1095	You can chose to use a pure-perl implementation by loading the
		1096	C<AnyEvent::Loop> module, which gives you similar behaviour
		1097	everywhere, but letting AnyEvent chose the model is generally better.
		1098
		1099	=head2 MAINLOOP EMULATION
		1100
		1101	Sometimes (often for short test scripts, or even standalone programs who
		1102	only want to use AnyEvent), you do not want to run a specific event loop.
		1103
		1104	In that case, you can use a condition variable like this:
		1105
		1106	AnyEvent->condvar->recv;
		1107
		1108	This has the effect of entering the event loop and looping forever.
		1109
		1110	Note that usually your program has some exit condition, in which case
		1111	it is better to use the "traditional" approach of storing a condition
		1112	variable somewhere, waiting for it, and sending it when the program should
		1113	exit cleanly.
		1114
		1115
		1116	=head1 OTHER MODULES
		1117
		1118	The following is a non-exhaustive list of additional modules that use
		1119	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		1120	modules and other event loops in the same program. Some of the modules
		1121	come as part of AnyEvent, the others are available via CPAN.
		1122
		1123	=over 4
		1124
		1125	=item L<AnyEvent::Util>
		1126
		1127	Contains various utility functions that replace often-used blocking
		1128	functions such as C<inet_aton> with event/callback-based versions.
		1129
		1130	=item L<AnyEvent::Socket>
		1131
		1132	Provides various utility functions for (internet protocol) sockets,
		1133	addresses and name resolution. Also functions to create non-blocking tcp
		1134	connections or tcp servers, with IPv6 and SRV record support and more.
		1135
		1136	=item L<AnyEvent::Handle>
		1137
		1138	Provide read and write buffers, manages watchers for reads and writes,
		1139	supports raw and formatted I/O, I/O queued and fully transparent and
		1140	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1141
		1142	=item L<AnyEvent::DNS>
		1143
		1144	Provides rich asynchronous DNS resolver capabilities.
		1145
		1146	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1147
		1148	Implement event-based interfaces to the protocols of the same name (for
		1149	the curious, IGS is the International Go Server and FCP is the Freenet
		1150	Client Protocol).
		1151
		1152	=item L<AnyEvent::Handle::UDP>
		1153
		1154	Here be danger!
		1155
		1156	As Pauli would put it, "Not only is it not right, it's not even wrong!" -
		1157	there are so many things wrong with AnyEvent::Handle::UDP, most notably
		1158	its use of a stream-based API with a protocol that isn't streamable, that
		1159	the only way to improve it is to delete it.
		1160
		1161	It features data corruption (but typically only under load) and general
		1162	confusion. On top, the author is not only clueless about UDP but also
		1163	fact-resistant - some gems of his understanding: "connect doesn't work
		1164	with UDP", "UDP packets are not IP packets", "UDP only has datagrams, not
		1165	packets", "I don't need to implement proper error checking as UDP doesn't
		1166	support error checking" and so on - he doesn't even understand what's
		1167	wrong with his module when it is explained to him.
		1168
		1169	=item L<AnyEvent::DBI>
		1170
		1171	Executes L<DBI> requests asynchronously in a proxy process for you,
		1172	notifying you in an event-based way when the operation is finished.
		1173
		1174	=item L<AnyEvent::AIO>
		1175
		1176	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1177	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1178	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1179	file I/O, and much more.
		1180
		1181	=item L<AnyEvent::HTTPD>
		1182
		1183	A simple embedded webserver.
		1184
		1185	=item L<AnyEvent::FastPing>
		1186
		1187	The fastest ping in the west.
		1188
		1189	=item L<Coro>
		1190
		1191	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1192
		1193	=back
		1194
		1195	=cut
		1196
		1197	package AnyEvent;
		1198
		1199	# basically a tuned-down version of common::sense
		1200	sub common_sense {
		1201	# from common:.sense 3.4
		1202	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
		1203	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1204	$^H |= 0x00000600;
		1205	}
		1206
		1207	BEGIN { AnyEvent::common_sense }
		1208
		1209	use Carp ();
		1210
		1211	our $VERSION = '5.34';
		1212	our $MODEL;
		1213
		1214	our @ISA;
		1215
		1216	our @REGISTRY;
		1217
		1218	our $VERBOSE;
		1219
		1220	BEGIN {
		1221	require "AnyEvent/constants.pl";
		1222
		1223	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1224
		1225	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1226	if ${^TAINT};
		1227
		1228	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1229
		1230	}
		1231
		1232	our $MAX_SIGNAL_LATENCY = 10;
		1233
		1234	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1235
		1236	{
		1237	my $idx;
		1238	$PROTOCOL{$_} = ++$idx
		1239	for reverse split /\s*,\s*/,
		1240	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1241	}
		1242
		1243	our @post_detect;
		1244
		1245	sub post_detect(&) {
		1246	my ($cb) = @_;
		1247
		1248	push @post_detect, $cb;
		1249
		1250	defined wantarray
		1251	? bless \$cb, "AnyEvent::Util::postdetect"
		1252	: ()
		1253	}
		1254
		1255	sub AnyEvent::Util::postdetect::DESTROY {
		1256	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1257	}
		1258
		1259	our $POSTPONE_W;
		1260	our @POSTPONE;
		1261
		1262	sub _postpone_exec {
		1263	undef $POSTPONE_W;
		1264
		1265	&{ shift @POSTPONE }
		1266	while @POSTPONE;
		1267	}
		1268
		1269	sub postpone(&) {
		1270	push @POSTPONE, shift;
		1271
		1272	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1273
		1274	()
		1275	}
		1276
		1277	our @models = (
		1278	[EV:: => AnyEvent::Impl::EV:: , 1],
		1279	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
		1280	# everything below here will not (normally) be autoprobed
		1281	# as the pure perl backend should work everywhere
		1282	# and is usually faster
		1283	[Event:: => AnyEvent::Impl::Event::, 1],
		1284	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1285	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1286	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1287	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1288	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1289	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1290	[Wx:: => AnyEvent::Impl::POE::],
		1291	[Prima:: => AnyEvent::Impl::POE::],
		1292	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1293	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
		1294	[FLTK:: => AnyEvent::Impl::FLTK2::],
		1295	);
		1296
		1297	# all autoloaded methods reserve the complete glob, not just the method slot.
		1298	# due to bugs in perls method cache implementation.
		1299	our @methods = qw(io timer time now now_update signal child idle condvar);
		1300
		1301	sub detect() {
		1302	local $!; # for good measure
		1303	local $SIG{__DIE__}; # we use eval
		1304
		1305	# free some memory
		1306	*detect = sub () { $MODEL };
		1307	# undef &func doesn't correctly update the method cache. grmbl.
		1308	# so we delete the whole glob. grmbl.
		1309	# otoh, perl doesn't let me undef an active usb, but it lets me free
		1310	# a glob with an active sub. hrm. i hope it works, but perl is
		1311	# usually buggy in this department. sigh.
		1312	delete @{"AnyEvent::"}{@methods};
		1313	undef @methods;
		1314
		1315	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1316	my $model = $1;
		1317	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1318	if (eval "require $model") {
		1319	$MODEL = $model;
		1320	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1321	} else {
		1322	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
		1323	}
		1324	}
		1325
		1326	# check for already loaded models
		1327	unless ($MODEL) {
		1328	for (@REGISTRY, @models) {
		1329	my ($package, $model) = @$_;
		1330	if (${"$package\::VERSION"} > 0) {
		1331	if (eval "require $model") {
		1332	$MODEL = $model;
		1333	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
		1334	last;
		1335	}
		1336	}
		1337	}
		1338
		1339	unless ($MODEL) {
		1340	# try to autoload a model
		1341	for (@REGISTRY, @models) {
		1342	my ($package, $model, $autoload) = @$_;
		1343	if (
		1344	$autoload
		1345	and eval "require $package"
		1346	and ${"$package\::VERSION"} > 0
		1347	and eval "require $model"
		1348	) {
		1349	$MODEL = $model;
		1350	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
		1351	last;
		1352	}
		1353	}
		1354
		1355	$MODEL
		1356	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?\n";
		1357	}
		1358	}
		1359
		1360	# free memory only needed for probing
		1361	undef @models;
		1362	undef @REGISTRY;
		1363
		1364	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1365	unshift @ISA, $MODEL;
		1366
		1367	# now nuke some methods that are overridden by the backend.
		1368	# SUPER usage is not allowed in these.
		1369	for (qw(time signal child idle)) {
		1370	undef &{"AnyEvent::Base::$_"}
		1371	if defined &{"$MODEL\::$_"};
		1372	}
		1373
		1374	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1375	require AnyEvent::Strict;
		1376	}
		1377
		1378	if ($ENV{PERL_ANYEVENT_DEBUG_WRAP}) {
		1379	require AnyEvent::Debug;
		1380	AnyEvent::Debug::wrap ($ENV{PERL_ANYEVENT_DEBUG_WRAP});
		1381	}
		1382
		1383	if (exists $ENV{PERL_ANYEVENT_DEBUG_SHELL}) {
		1384	require AnyEvent::Socket;
		1385	require AnyEvent::Debug;
		1386
		1387	my $shell = $ENV{PERL_ANYEVENT_DEBUG_SHELL};
		1388	$shell =~ s/\$\$/$$/g;
		1389
		1390	my ($host, $service) = AnyEvent::Socket::parse_hostport ($shell);
		1391	$AnyEvent::Debug::SHELL = AnyEvent::Debug::shell ($host, $service);
		1392	}
		1393
		1394	(shift @post_detect)->() while @post_detect;
		1395	undef @post_detect;
		1396
		1397	*post_detect = sub(&) {
		1398	shift->();
		1399
		1400	undef
		1401	};
		1402
		1403	$MODEL
		1404	}
		1405
		1406	for my $name (@methods) {
		1407	*$name = sub {
		1408	detect;
		1409	# we use goto because
		1410	# a) it makes the thunk more transparent
		1411	# b) it allows us to delete the thunk later
		1412	goto &{ UNIVERSAL::can AnyEvent => "SUPER::$name" }
		1413	};
		1414	}
		1415
		1416	# utility function to dup a filehandle. this is used by many backends
		1417	# to support binding more than one watcher per filehandle (they usually
		1418	# allow only one watcher per fd, so we dup it to get a different one).
		1419	sub _dupfh($$;$$) {
		1420	my ($poll, $fh, $r, $w) = @_;
		1421
		1422	# cygwin requires the fh mode to be matching, unix doesn't
		1423	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1424
		1425	open my $fh2, $mode, $fh
		1426	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1427
		1428	# we assume CLOEXEC is already set by perl in all important cases
		1429
		1430	($fh2, $rw)
		1431	}
		1432
		1433	=head1 SIMPLIFIED AE API
		1434
		1435	Starting with version 5.0, AnyEvent officially supports a second, much
		1436	simpler, API that is designed to reduce the calling, typing and memory
		1437	overhead by using function call syntax and a fixed number of parameters.
		1438
		1439	See the L<AE> manpage for details.
		1440
		1441	=cut
		1442
		1443	package AE;
		1444
		1445	our $VERSION = $AnyEvent::VERSION;
		1446
		1447	sub _reset() {
		1448	eval q{
		1449	# fall back to the main API by default - backends and AnyEvent::Base
		1450	# implementations can overwrite these.
		1451
		1452	sub io($$$) {
		1453	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1454	}
		1455
		1456	sub timer($$$) {
		1457	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1458	}
		1459
		1460	sub signal($$) {
		1461	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1462	}
		1463
		1464	sub child($$) {
		1465	AnyEvent->child (pid => $_[0], cb => $_[1])
		1466	}
		1467
		1468	sub idle($) {
		1469	AnyEvent->idle (cb => $_[0]);
		1470	}
		1471
		1472	sub cv(;&) {
		1473	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1474	}
		1475
		1476	sub now() {
		1477	AnyEvent->now
		1478	}
		1479
		1480	sub now_update() {
		1481	AnyEvent->now_update
		1482	}
		1483
		1484	sub time() {
		1485	AnyEvent->time
		1486	}
		1487
		1488	*postpone = \&AnyEvent::postpone;
		1489	};
		1490	die if $@;
		1491	}
		1492
		1493	BEGIN { _reset }
		1494
		1495	package AnyEvent::Base;
		1496
		1497	# default implementations for many methods
		1498
		1499	sub time {
		1500	eval q{ # poor man's autoloading {}
		1501	# probe for availability of Time::HiRes
		1502	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1503	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1504	*AE::time = \&Time::HiRes::time;
		1505	# if (eval "use POSIX (); (POSIX::times())...
		1506	} else {
		1507	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1508	*AE::time = sub (){ time }; # epic fail
		1509	}
		1510
		1511	*time = sub { AE::time }; # different prototypes
		1512	};
		1513	die if $@;
		1514
		1515	&time
		1516	}
		1517
		1518	*now = \&time;
		1519
		1520	sub now_update { }
		1521
		1522	sub _poll {
		1523	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1524	}
		1525
		1526	# default implementation for ->condvar
		1527	# in fact, the default should not be overwritten
		1528
		1529	sub condvar {
		1530	eval q{ # poor man's autoloading {}
		1531	*condvar = sub {
		1532	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1533	};
		1534
		1535	*AE::cv = sub (;&) {
		1536	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1537	};
		1538	};
		1539	die if $@;
		1540
		1541	&condvar
		1542	}
		1543
		1544	# default implementation for ->signal
		1545
		1546	our $HAVE_ASYNC_INTERRUPT;
		1547
		1548	sub _have_async_interrupt() {
		1549	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1550	&& eval "use Async::Interrupt 1.02 (); 1")
		1551	unless defined $HAVE_ASYNC_INTERRUPT;
		1552
		1553	$HAVE_ASYNC_INTERRUPT
		1554	}
		1555
		1556	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1557	our (%SIG_ASY, %SIG_ASY_W);
		1558	our ($SIG_COUNT, $SIG_TW);
		1559
		1560	# install a dummy wakeup watcher to reduce signal catching latency
		1561	# used by Impls
		1562	sub _sig_add() {
		1563	unless ($SIG_COUNT++) {
		1564	# try to align timer on a full-second boundary, if possible
		1565	my $NOW = AE::now;
		1566
		1567	$SIG_TW = AE::timer
		1568	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1569	$MAX_SIGNAL_LATENCY,
		1570	sub { } # just for the PERL_ASYNC_CHECK
		1571	;
		1572	}
		1573	}
		1574
		1575	sub _sig_del {
		1576	undef $SIG_TW
		1577	unless --$SIG_COUNT;
		1578	}
		1579
		1580	our $_sig_name_init; $_sig_name_init = sub {
		1581	eval q{ # poor man's autoloading {}
		1582	undef $_sig_name_init;
		1583
		1584	if (_have_async_interrupt) {
		1585	*sig2num = \&Async::Interrupt::sig2num;
		1586	*sig2name = \&Async::Interrupt::sig2name;
		1587	} else {
		1588	require Config;
		1589
		1590	my %signame2num;
		1591	@signame2num{ split ' ', $Config::Config{sig_name} }
		1592	= split ' ', $Config::Config{sig_num};
		1593
		1594	my @signum2name;
		1595	@signum2name[values %signame2num] = keys %signame2num;
		1596
		1597	*sig2num = sub($) {
		1598	$_[0] > 0 ? shift : $signame2num{+shift}
		1599	};
		1600	*sig2name = sub ($) {
		1601	$_[0] > 0 ? $signum2name[+shift] : shift
		1602	};
		1603	}
		1604	};
		1605	die if $@;
		1606	};
		1607
		1608	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1609	sub sig2name($) { &$_sig_name_init; &sig2name }
		1610
		1611	sub signal {
		1612	eval q{ # poor man's autoloading {}
		1613	# probe for availability of Async::Interrupt
		1614	if (_have_async_interrupt) {
		1615	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1616
		1617	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1618	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1619
		1620	} else {
		1621	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1622
		1623	if (AnyEvent::WIN32) {
		1624	require AnyEvent::Util;
		1625
		1626	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1627	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1628	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1629	} else {
		1630	pipe $SIGPIPE_R, $SIGPIPE_W;
		1631	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1632	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1633
		1634	# not strictly required, as $^F is normally 2, but let's make sure...
		1635	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1636	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1637	}
		1638
		1639	$SIGPIPE_R
		1640	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1641
		1642	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1643	}
		1644
		1645	*signal = $HAVE_ASYNC_INTERRUPT
		1646	? sub {
		1647	my (undef, %arg) = @_;
		1648
		1649	# async::interrupt
		1650	my $signal = sig2num $arg{signal};
		1651	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1652
		1653	$SIG_ASY{$signal} ||= new Async::Interrupt
		1654	cb => sub { undef $SIG_EV{$signal} },
		1655	signal => $signal,
		1656	pipe => [$SIGPIPE_R->filenos],
		1657	pipe_autodrain => 0,
		1658	;
		1659
		1660	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1661	}
		1662	: sub {
		1663	my (undef, %arg) = @_;
		1664
		1665	# pure perl
		1666	my $signal = sig2name $arg{signal};
		1667	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1668
		1669	$SIG{$signal} ||= sub {
		1670	local $!;
		1671	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1672	undef $SIG_EV{$signal};
		1673	};
		1674
		1675	# can't do signal processing without introducing races in pure perl,
		1676	# so limit the signal latency.
		1677	_sig_add;
		1678
		1679	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1680	}
		1681	;
		1682
		1683	*AnyEvent::Base::signal::DESTROY = sub {
		1684	my ($signal, $cb) = @{$_[0]};
		1685
		1686	_sig_del;
		1687
		1688	delete $SIG_CB{$signal}{$cb};
		1689
		1690	$HAVE_ASYNC_INTERRUPT
		1691	? delete $SIG_ASY{$signal}
		1692	: # delete doesn't work with older perls - they then
		1693	# print weird messages, or just unconditionally exit
		1694	# instead of getting the default action.
		1695	undef $SIG{$signal}
		1696	unless keys %{ $SIG_CB{$signal} };
		1697	};
		1698
		1699	*_signal_exec = sub {
		1700	$HAVE_ASYNC_INTERRUPT
		1701	? $SIGPIPE_R->drain
		1702	: sysread $SIGPIPE_R, (my $dummy), 9;
		1703
		1704	while (%SIG_EV) {
		1705	for (keys %SIG_EV) {
		1706	delete $SIG_EV{$_};
		1707	&$_ for values %{ $SIG_CB{$_} || {} };
		1708	}
		1709	}
		1710	};
		1711	};
		1712	die if $@;
		1713
		1714	&signal
		1715	}
		1716
		1717	# default implementation for ->child
		1718
		1719	our %PID_CB;
		1720	our $CHLD_W;
		1721	our $CHLD_DELAY_W;
		1722
		1723	# used by many Impl's
		1724	sub _emit_childstatus($$) {
		1725	my (undef, $rpid, $rstatus) = @_;
		1726
		1727	$_->($rpid, $rstatus)
		1728	for values %{ $PID_CB{$rpid} || {} },
		1729	values %{ $PID_CB{0} || {} };
		1730	}
		1731
		1732	sub child {
		1733	eval q{ # poor man's autoloading {}
		1734	*_sigchld = sub {
		1735	my $pid;
		1736
		1737	AnyEvent->_emit_childstatus ($pid, $?)
		1738	while ($pid = waitpid -1, WNOHANG) > 0;
		1739	};
		1740
		1741	*child = sub {
		1742	my (undef, %arg) = @_;
		1743
		1744	my $pid = $arg{pid};
		1745	my $cb = $arg{cb};
		1746
		1747	$PID_CB{$pid}{$cb+0} = $cb;
		1748
		1749	unless ($CHLD_W) {
		1750	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1751	# child could be a zombie already, so make at least one round
		1752	&_sigchld;
		1753	}
		1754
		1755	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1756	};
		1757
		1758	*AnyEvent::Base::child::DESTROY = sub {
		1759	my ($pid, $icb) = @{$_[0]};
		1760
		1761	delete $PID_CB{$pid}{$icb};
		1762	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1763
		1764	undef $CHLD_W unless keys %PID_CB;
		1765	};
		1766	};
		1767	die if $@;
		1768
		1769	&child
		1770	}
		1771
		1772	# idle emulation is done by simply using a timer, regardless
		1773	# of whether the process is idle or not, and not letting
		1774	# the callback use more than 50% of the time.
		1775	sub idle {
		1776	eval q{ # poor man's autoloading {}
		1777	*idle = sub {
		1778	my (undef, %arg) = @_;
		1779
		1780	my ($cb, $w, $rcb) = $arg{cb};
		1781
		1782	$rcb = sub {
		1783	if ($cb) {
		1784	$w = AE::time;
		1785	&$cb;
		1786	$w = AE::time - $w;
		1787
		1788	# never use more then 50% of the time for the idle watcher,
		1789	# within some limits
		1790	$w = 0.0001 if $w < 0.0001;
		1791	$w = 5 if $w > 5;
		1792
		1793	$w = AE::timer $w, 0, $rcb;
		1794	} else {
		1795	# clean up...
		1796	undef $w;
		1797	undef $rcb;
		1798	}
		1799	};
		1800
		1801	$w = AE::timer 0.05, 0, $rcb;
		1802
		1803	bless \\$cb, "AnyEvent::Base::idle"
		1804	};
		1805
		1806	*AnyEvent::Base::idle::DESTROY = sub {
		1807	undef $${$_[0]};
		1808	};
		1809	};
		1810	die if $@;
		1811
		1812	&idle
		1813	}
		1814
		1815	package AnyEvent::CondVar;
		1816
		1817	our @ISA = AnyEvent::CondVar::Base::;
		1818
		1819	# only to be used for subclassing
		1820	sub new {
		1821	my $class = shift;
		1822	bless AnyEvent->condvar (@_), $class
		1823	}
		1824
		1825	package AnyEvent::CondVar::Base;
		1826
		1827	#use overload
		1828	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1829	# fallback => 1;
		1830
		1831	# save 300+ kilobytes by dirtily hardcoding overloading
		1832	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1833	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1834	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1835	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1836
		1837	our $WAITING;
		1838
		1839	sub _send {
		1840	# nop
		1841	}
		1842
		1843	sub _wait {
		1844	AnyEvent->_poll until $_[0]{_ae_sent};
		1845	}
		1846
		1847	sub send {
		1848	my $cv = shift;
		1849	$cv->{_ae_sent} = [@_];
		1850	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1851	$cv->_send;
		1852	}
		1853
		1854	sub croak {
		1855	$_[0]{_ae_croak} = $_[1];
		1856	$_[0]->send;
		1857	}
		1858
		1859	sub ready {
		1860	$_[0]{_ae_sent}
		1861	}
		1862
		1863	sub recv {
		1864	unless ($_[0]{_ae_sent}) {
		1865	$WAITING
		1866	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1867
		1868	local $WAITING = 1;
		1869	$_[0]->_wait;
		1870	}
		1871
		1872	$_[0]{_ae_croak}
		1873	and Carp::croak $_[0]{_ae_croak};
		1874
		1875	wantarray
		1876	? @{ $_[0]{_ae_sent} }
		1877	: $_[0]{_ae_sent}[0]
		1878	}
		1879
		1880	sub cb {
		1881	my $cv = shift;
		1882
		1883	@_
		1884	and $cv->{_ae_cb} = shift
		1885	and $cv->{_ae_sent}
		1886	and (delete $cv->{_ae_cb})->($cv);
		1887
		1888	$cv->{_ae_cb}
		1889	}
		1890
		1891	sub begin {
		1892	++$_[0]{_ae_counter};
		1893	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1894	}
		1895
		1896	sub end {
		1897	return if --$_[0]{_ae_counter};
		1898	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1899	}
		1900
		1901	# undocumented/compatibility with pre-3.4
		1902	*broadcast = \&send;
		1903	*wait = \&recv;
		1904
		1905	=head1 ERROR AND EXCEPTION HANDLING
		1906
		1907	In general, AnyEvent does not do any error handling - it relies on the
		1908	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1909	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1910	checking of all AnyEvent methods, however, which is highly useful during
		1911	development.
		1912
		1913	As for exception handling (i.e. runtime errors and exceptions thrown while
		1914	executing a callback), this is not only highly event-loop specific, but
		1915	also not in any way wrapped by this module, as this is the job of the main
		1916	program.
		1917
		1918	The pure perl event loop simply re-throws the exception (usually
		1919	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1920	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1921	so on.
		1922
		1923	=head1 ENVIRONMENT VARIABLES
		1924
		1925	The following environment variables are used by this module or its
		1926	submodules.
		1927
		1928	Note that AnyEvent will remove I<all> environment variables starting with
		1929	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1930	enabled.
		1931
		1932	=over 4
		1933
		1934	=item C<PERL_ANYEVENT_VERBOSE>
		1935
		1936	By default, AnyEvent will be completely silent except in fatal
		1937	conditions. You can set this environment variable to make AnyEvent more
		1938	talkative.
		1939
		1940	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1941	conditions, such as not being able to load the event model specified by
		1942	C<PERL_ANYEVENT_MODEL>.
		1943
		1944	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1945	model it chooses.
		1946
		1947	When set to C<8> or higher, then AnyEvent will report extra information on
		1948	which optional modules it loads and how it implements certain features.
		1949
		1950	=item C<PERL_ANYEVENT_STRICT>
		1951
		1952	AnyEvent does not do much argument checking by default, as thorough
		1953	argument checking is very costly. Setting this variable to a true value
		1954	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1955	check the arguments passed to most method calls. If it finds any problems,
		1956	it will croak.
		1957
		1958	In other words, enables "strict" mode.
		1959
		1960	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		1961	>>, it is definitely recommended to keep it off in production. Keeping
		1962	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1963	can be very useful, however.
		1964
		1965	=item C<PERL_ANYEVENT_DEBUG_SHELL>
		1966
		1967	If this env variable is set, then its contents will be interpreted by
		1968	C<AnyEvent::Socket::parse_hostport> (after replacing every occurance of
		1969	C<$$> by the process pid) and an C<AnyEvent::Debug::shell> is bound on
		1970	that port. The shell object is saved in C<$AnyEvent::Debug::SHELL>.
		1971
		1972	This takes place when the first watcher is created.
		1973
		1974	For example, to bind a debug shell on a unix domain socket in
		1975	F<< /tmp/debug<pid>.sock >>, you could use this:
		1976
		1977	PERL_ANYEVENT_DEBUG_SHELL=unix/:/tmp/debug\$\$.sock perlprog
		1978
		1979	Note that creating sockets in F</tmp> is very unsafe on multiuser
		1980	systems.
		1981
		1982	=item C<PERL_ANYEVENT_DEBUG_WRAP>
		1983
		1984	Can be set to C<0>, C<1> or C<2> and enables wrapping of all watchers for
		1985	debugging purposes. See C<AnyEvent::Debug::wrap> for details.
		1986
		1987	=item C<PERL_ANYEVENT_MODEL>
		1988
		1989	This can be used to specify the event model to be used by AnyEvent, before
		1990	auto detection and -probing kicks in.
		1991
		1992	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		1993	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		1994	resulting module name is loaded and - if the load was successful - used as
		1995	event model backend. If it fails to load then AnyEvent will proceed with
		1996	auto detection and -probing.
		1997
		1998	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		1999	nothing gets prepended and the module name is used as-is (hint: C<::> at
		2000	the end of a string designates a module name and quotes it appropriately).
		2001
		2002	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		2003	could start your program like this:
		2004
		2005	PERL_ANYEVENT_MODEL=Perl perl ...
		2006
		2007	=item C<PERL_ANYEVENT_PROTOCOLS>
		2008
		2009	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		2010	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		2011	of auto probing).
		2012
		2013	Must be set to a comma-separated list of protocols or address families,
		2014	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		2015	used, and preference will be given to protocols mentioned earlier in the
		2016	list.
		2017
		2018	This variable can effectively be used for denial-of-service attacks
		2019	against local programs (e.g. when setuid), although the impact is likely
		2020	small, as the program has to handle conenction and other failures anyways.
		2021
		2022	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		2023	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		2024	- only support IPv4, never try to resolve or contact IPv6
		2025	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		2026	IPv6, but prefer IPv6 over IPv4.
		2027
		2028	=item C<PERL_ANYEVENT_EDNS0>
		2029
		2030	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		2031	for DNS. This extension is generally useful to reduce DNS traffic, but
		2032	some (broken) firewalls drop such DNS packets, which is why it is off by
		2033	default.
		2034
		2035	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2036	EDNS0 in its DNS requests.
		2037
		2038	=item C<PERL_ANYEVENT_MAX_FORKS>
		2039
		2040	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2041	will create in parallel.
		2042
		2043	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2044
		2045	The default value for the C<max_outstanding> parameter for the default DNS
		2046	resolver - this is the maximum number of parallel DNS requests that are
		2047	sent to the DNS server.
		2048
		2049	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2050
		2051	The file to use instead of F</etc/resolv.conf> (or OS-specific
		2052	configuration) in the default resolver. When set to the empty string, no
		2053	default config will be used.
		2054
		2055	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2056
		2057	When neither C<ca_file> nor C<ca_path> was specified during
		2058	L<AnyEvent::TLS> context creation, and either of these environment
		2059	variables exist, they will be used to specify CA certificate locations
		2060	instead of a system-dependent default.
		2061
		2062	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2063
		2064	When these are set to C<1>, then the respective modules are not
		2065	loaded. Mostly good for testing AnyEvent itself.
		2066
		2067	=back
		2068
		2069	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		2070
		2071	This is an advanced topic that you do not normally need to use AnyEvent in
		2072	a module. This section is only of use to event loop authors who want to
		2073	provide AnyEvent compatibility.
		2074
		2075	If you need to support another event library which isn't directly
		2076	supported by AnyEvent, you can supply your own interface to it by
		2077	pushing, before the first watcher gets created, the package name of
		2078	the event module and the package name of the interface to use onto
		2079	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		2080	AnyEvent, so it is reasonably cheap.
		2081
		2082	Example:
		2083
		2084	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		2085
		2086	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		2087	package/class when it finds the C<urxvt> package/module is already loaded.
		2088
		2089	When AnyEvent is loaded and asked to find a suitable event model, it
		2090	will first check for the presence of urxvt by trying to C<use> the
		2091	C<urxvt::anyevent> module.
		2092
		2093	The class should provide implementations for all watcher types. See
		2094	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		2095	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		2096	see the sources.
		2097
		2098	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2099	provide suitable (hopefully) replacements.
		2100
		2101	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		2102	terminal emulator uses the above line as-is. An interface isn't included
		2103	in AnyEvent because it doesn't make sense outside the embedded interpreter
		2104	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		2105	I<rxvt-unicode> distribution.
		2106
		2107	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		2108	condition variables: code blocking while waiting for a condition will
		2109	C<die>. This still works with most modules/usages, and blocking calls must
		2110	not be done in an interactive application, so it makes sense.
		2111
		2112	=head1 EXAMPLE PROGRAM
		2113
		2114	The following program uses an I/O watcher to read data from STDIN, a timer
		2115	to display a message once per second, and a condition variable to quit the
		2116	program when the user enters quit:
		2117
		2118	use AnyEvent;
		2119
		2120	my $cv = AnyEvent->condvar;
		2121
		2122	my $io_watcher = AnyEvent->io (
		2123	fh => \*STDIN,
		2124	poll => 'r',
		2125	cb => sub {
		2126	warn "io event <$_[0]>\n"; # will always output <r>
		2127	chomp (my $input = <STDIN>); # read a line
		2128	warn "read: $input\n"; # output what has been read
		2129	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2130	},
		2131	);
		2132
		2133	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2134	warn "timeout\n"; # print 'timeout' at most every second
		2135	});
		2136
		2137	$cv->recv; # wait until user enters /^q/i
		2138
		2139	=head1 REAL-WORLD EXAMPLE
		2140
		2141	Consider the L<Net::FCP> module. It features (among others) the following
		2142	API calls, which are to freenet what HTTP GET requests are to http:
		2143
		2144	my $data = $fcp->client_get ($url); # blocks
		2145
		2146	my $transaction = $fcp->txn_client_get ($url); # does not block
		2147	$transaction->cb ( sub { ... } ); # set optional result callback
		2148	my $data = $transaction->result; # possibly blocks
		2149
		2150	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		2151	given URL and waits till the data has arrived. It is defined to be:
		2152
		2153	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		2154
		2155	And in fact is automatically generated. This is the blocking API of
		2156	L<Net::FCP>, and it works as simple as in any other, similar, module.
		2157
		2158	More complicated is C<txn_client_get>: It only creates a transaction
		2159	(completion, result, ...) object and initiates the transaction.
		2160
		2161	my $txn = bless { }, Net::FCP::Txn::;
		2162
		2163	It also creates a condition variable that is used to signal the completion
		2164	of the request:
		2165
		2166	$txn->{finished} = AnyAvent->condvar;
		2167
		2168	It then creates a socket in non-blocking mode.
		2169
		2170	socket $txn->{fh}, ...;
		2171	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		2172	connect $txn->{fh}, ...
		2173	and !$!{EWOULDBLOCK}
		2174	and !$!{EINPROGRESS}
		2175	and Carp::croak "unable to connect: $!\n";
		2176
		2177	Then it creates a write-watcher which gets called whenever an error occurs
		2178	or the connection succeeds:
		2179
		2180	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		2181
		2182	And returns this transaction object. The C<fh_ready_w> callback gets
		2183	called as soon as the event loop detects that the socket is ready for
		2184	writing.
		2185
		2186	The C<fh_ready_w> method makes the socket blocking again, writes the
		2187	request data and replaces the watcher by a read watcher (waiting for reply
		2188	data). The actual code is more complicated, but that doesn't matter for
		2189	this example:
		2190
		2191	fcntl $txn->{fh}, F_SETFL, 0;
		2192	syswrite $txn->{fh}, $txn->{request}
		2193	or die "connection or write error";
		2194	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		2195
		2196	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		2197	result and signals any possible waiters that the request has finished:
		2198
		2199	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		2200
		2201	if (end-of-file or data complete) {
		2202	$txn->{result} = $txn->{buf};
		2203	$txn->{finished}->send;
		2204	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		2205	}
		2206
		2207	The C<result> method, finally, just waits for the finished signal (if the
		2208	request was already finished, it doesn't wait, of course, and returns the
		2209	data:
		2210
		2211	$txn->{finished}->recv;
		2212	return $txn->{result};
		2213
		2214	The actual code goes further and collects all errors (C<die>s, exceptions)
		2215	that occurred during request processing. The C<result> method detects
		2216	whether an exception as thrown (it is stored inside the $txn object)
		2217	and just throws the exception, which means connection errors and other
		2218	problems get reported to the code that tries to use the result, not in a
		2219	random callback.
		2220
		2221	All of this enables the following usage styles:
		2222
		2223	1. Blocking:
		2224
		2225	my $data = $fcp->client_get ($url);
		2226
		2227	2. Blocking, but running in parallel:
		2228
		2229	my @datas = map $_->result,
		2230	map $fcp->txn_client_get ($_),
		2231	@urls;
		2232
		2233	Both blocking examples work without the module user having to know
		2234	anything about events.
		2235
		2236	3a. Event-based in a main program, using any supported event module:
		2237
		2238	use EV;
		2239
		2240	$fcp->txn_client_get ($url)->cb (sub {
		2241	my $txn = shift;
		2242	my $data = $txn->result;
16	...	2243	...
17	});	2244	});
18		2245
19	# watchers get canceled whenever $w is destroyed	2246	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		2247
25	my $w = AnyEvent->condvar; # kind of main loop replacement	2248	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		2249
30	=head1 DESCRIPTION	2250	use AnyEvent;
31		2251
32	L<AnyEvent> provides an identical interface to multiple event loops. This	2252	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		2253
37	The interface itself is vaguely similar but not identical to the Event	2254	$fcp->txn_client_get ($url)->cb (sub {
38	module.	2255	...
		2256	$quit->send;
		2257	});
39		2258
40	On the first call of any method, the module tries to detect the currently	2259	$quit->recv;
41	loaded event loop by probing wether any of the following modules is	2260
42	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	2261
43	used. If none is found, the module tries to load these modules in the	2262	=head1 BENCHMARKS
44	order given. The first one that could be successfully loaded will be	2263
45	used. If still none could be found, it will issue an error.	2264	To give you an idea of the performance and overheads that AnyEvent adds
		2265	over the event loops themselves and to give you an impression of the speed
		2266	of various event loops I prepared some benchmarks.
		2267
		2268	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2269
		2270	Here is a benchmark of various supported event models used natively and
		2271	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2272	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2273	which it is), lets them fire exactly once and destroys them again.
		2274
		2275	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2276	distribution. It uses the L<AE> interface, which makes a real difference
		2277	for the EV and Perl backends only.
		2278
		2279	=head3 Explanation of the columns
		2280
		2281	I<watcher> is the number of event watchers created/destroyed. Since
		2282	different event models feature vastly different performances, each event
		2283	loop was given a number of watchers so that overall runtime is acceptable
		2284	and similar between tested event loop (and keep them from crashing): Glib
		2285	would probably take thousands of years if asked to process the same number
		2286	of watchers as EV in this benchmark.
		2287
		2288	I<bytes> is the number of bytes (as measured by the resident set size,
		2289	RSS) consumed by each watcher. This method of measuring captures both C
		2290	and Perl-based overheads.
		2291
		2292	I<create> is the time, in microseconds (millionths of seconds), that it
		2293	takes to create a single watcher. The callback is a closure shared between
		2294	all watchers, to avoid adding memory overhead. That means closure creation
		2295	and memory usage is not included in the figures.
		2296
		2297	I<invoke> is the time, in microseconds, used to invoke a simple
		2298	callback. The callback simply counts down a Perl variable and after it was
		2299	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2300	signal the end of this phase.
		2301
		2302	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2303	watcher.
		2304
		2305	=head3 Results
		2306
		2307	name watchers bytes create invoke destroy comment
		2308	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2309	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2310	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2311	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2312	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2313	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2314	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2315	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2316	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2317	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2318	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2319	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2320
		2321	=head3 Discussion
		2322
		2323	The benchmark does I<not> measure scalability of the event loop very
		2324	well. For example, a select-based event loop (such as the pure perl one)
		2325	can never compete with an event loop that uses epoll when the number of
		2326	file descriptors grows high. In this benchmark, all events become ready at
		2327	the same time, so select/poll-based implementations get an unnatural speed
		2328	boost.
		2329
		2330	Also, note that the number of watchers usually has a nonlinear effect on
		2331	overall speed, that is, creating twice as many watchers doesn't take twice
		2332	the time - usually it takes longer. This puts event loops tested with a
		2333	higher number of watchers at a disadvantage.
		2334
		2335	To put the range of results into perspective, consider that on the
		2336	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2337	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2338	cycles with POE.
		2339
		2340	C<EV> is the sole leader regarding speed and memory use, which are both
		2341	maximal/minimal, respectively. When using the L<AE> API there is zero
		2342	overhead (when going through the AnyEvent API create is about 5-6 times
		2343	slower, with other times being equal, so still uses far less memory than
		2344	any other event loop and is still faster than Event natively).
		2345
		2346	The pure perl implementation is hit in a few sweet spots (both the
		2347	constant timeout and the use of a single fd hit optimisations in the perl
		2348	interpreter and the backend itself). Nevertheless this shows that it
		2349	adds very little overhead in itself. Like any select-based backend its
		2350	performance becomes really bad with lots of file descriptors (and few of
		2351	them active), of course, but this was not subject of this benchmark.
		2352
		2353	The C<Event> module has a relatively high setup and callback invocation
		2354	cost, but overall scores in on the third place.
		2355
		2356	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2357	when using its pure perl backend.
		2358
		2359	C<Glib>'s memory usage is quite a bit higher, but it features a
		2360	faster callback invocation and overall ends up in the same class as
		2361	C<Event>. However, Glib scales extremely badly, doubling the number of
		2362	watchers increases the processing time by more than a factor of four,
		2363	making it completely unusable when using larger numbers of watchers
		2364	(note that only a single file descriptor was used in the benchmark, so
		2365	inefficiencies of C<poll> do not account for this).
		2366
		2367	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2368	more than 2000 watchers is a big setback, however, as correctness takes
		2369	precedence over speed. Nevertheless, its performance is surprising, as the
		2370	file descriptor is dup()ed for each watcher. This shows that the dup()
		2371	employed by some adaptors is not a big performance issue (it does incur a
		2372	hidden memory cost inside the kernel which is not reflected in the figures
		2373	above).
		2374
		2375	C<POE>, regardless of underlying event loop (whether using its pure perl
		2376	select-based backend or the Event module, the POE-EV backend couldn't
		2377	be tested because it wasn't working) shows abysmal performance and
		2378	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2379	as EV watchers, and 10 times as much memory as Event (the high memory
		2380	requirements are caused by requiring a session for each watcher). Watcher
		2381	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2382	implementation.
		2383
		2384	The design of the POE adaptor class in AnyEvent can not really account
		2385	for the performance issues, though, as session creation overhead is
		2386	small compared to execution of the state machine, which is coded pretty
		2387	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2388	using multiple sessions is not a good approach, especially regarding
		2389	memory usage, even the author of POE could not come up with a faster
		2390	design).
		2391
		2392	=head3 Summary
46		2393
47	=over 4	2394	=over 4
48		2395
		2396	=item * Using EV through AnyEvent is faster than any other event loop
		2397	(even when used without AnyEvent), but most event loops have acceptable
		2398	performance with or without AnyEvent.
		2399
		2400	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2401	the actual event loop, only with extremely fast event loops such as EV
		2402	adds AnyEvent significant overhead.
		2403
		2404	=item * You should avoid POE like the plague if you want performance or
		2405	reasonable memory usage.
		2406
		2407	=back
		2408
		2409	=head2 BENCHMARKING THE LARGE SERVER CASE
		2410
		2411	This benchmark actually benchmarks the event loop itself. It works by
		2412	creating a number of "servers": each server consists of a socket pair, a
		2413	timeout watcher that gets reset on activity (but never fires), and an I/O
		2414	watcher waiting for input on one side of the socket. Each time the socket
		2415	watcher reads a byte it will write that byte to a random other "server".
		2416
		2417	The effect is that there will be a lot of I/O watchers, only part of which
		2418	are active at any one point (so there is a constant number of active
		2419	fds for each loop iteration, but which fds these are is random). The
		2420	timeout is reset each time something is read because that reflects how
		2421	most timeouts work (and puts extra pressure on the event loops).
		2422
		2423	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2424	(1%) are active. This mirrors the activity of large servers with many
		2425	connections, most of which are idle at any one point in time.
		2426
		2427	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2428	distribution. It uses the L<AE> interface, which makes a real difference
		2429	for the EV and Perl backends only.
		2430
		2431	=head3 Explanation of the columns
		2432
		2433	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2434	each server has a read and write socket end).
		2435
		2436	I<create> is the time it takes to create a socket pair (which is
		2437	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2438
		2439	I<request>, the most important value, is the time it takes to handle a
		2440	single "request", that is, reading the token from the pipe and forwarding
		2441	it to another server. This includes deleting the old timeout and creating
		2442	a new one that moves the timeout into the future.
		2443
		2444	=head3 Results
		2445
		2446	name sockets create request
		2447	EV 20000 62.66 7.99
		2448	Perl 20000 68.32 32.64
		2449	IOAsync 20000 174.06 101.15 epoll
		2450	IOAsync 20000 174.67 610.84 poll
		2451	Event 20000 202.69 242.91
		2452	Glib 20000 557.01 1689.52
		2453	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2454
		2455	=head3 Discussion
		2456
		2457	This benchmark I<does> measure scalability and overall performance of the
		2458	particular event loop.
		2459
		2460	EV is again fastest. Since it is using epoll on my system, the setup time
		2461	is relatively high, though.
		2462
		2463	Perl surprisingly comes second. It is much faster than the C-based event
		2464	loops Event and Glib.
		2465
		2466	IO::Async performs very well when using its epoll backend, and still quite
		2467	good compared to Glib when using its pure perl backend.
		2468
		2469	Event suffers from high setup time as well (look at its code and you will
		2470	understand why). Callback invocation also has a high overhead compared to
		2471	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2472	uses select or poll in basically all documented configurations.
		2473
		2474	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2475	clearly fails to perform with many filehandles or in busy servers.
		2476
		2477	POE is still completely out of the picture, taking over 1000 times as long
		2478	as EV, and over 100 times as long as the Perl implementation, even though
		2479	it uses a C-based event loop in this case.
		2480
		2481	=head3 Summary
		2482
		2483	=over 4
		2484
		2485	=item * The pure perl implementation performs extremely well.
		2486
		2487	=item * Avoid Glib or POE in large projects where performance matters.
		2488
		2489	=back
		2490
		2491	=head2 BENCHMARKING SMALL SERVERS
		2492
		2493	While event loops should scale (and select-based ones do not...) even to
		2494	large servers, most programs we (or I :) actually write have only a few
		2495	I/O watchers.
		2496
		2497	In this benchmark, I use the same benchmark program as in the large server
		2498	case, but it uses only eight "servers", of which three are active at any
		2499	one time. This should reflect performance for a small server relatively
		2500	well.
		2501
		2502	The columns are identical to the previous table.
		2503
		2504	=head3 Results
		2505
		2506	name sockets create request
		2507	EV 16 20.00 6.54
		2508	Perl 16 25.75 12.62
		2509	Event 16 81.27 35.86
		2510	Glib 16 32.63 15.48
		2511	POE 16 261.87 276.28 uses POE::Loop::Event
		2512
		2513	=head3 Discussion
		2514
		2515	The benchmark tries to test the performance of a typical small
		2516	server. While knowing how various event loops perform is interesting, keep
		2517	in mind that their overhead in this case is usually not as important, due
		2518	to the small absolute number of watchers (that is, you need efficiency and
		2519	speed most when you have lots of watchers, not when you only have a few of
		2520	them).
		2521
		2522	EV is again fastest.
		2523
		2524	Perl again comes second. It is noticeably faster than the C-based event
		2525	loops Event and Glib, although the difference is too small to really
		2526	matter.
		2527
		2528	POE also performs much better in this case, but is is still far behind the
		2529	others.
		2530
		2531	=head3 Summary
		2532
		2533	=over 4
		2534
		2535	=item * C-based event loops perform very well with small number of
		2536	watchers, as the management overhead dominates.
		2537
		2538	=back
		2539
		2540	=head2 THE IO::Lambda BENCHMARK
		2541
		2542	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2543	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2544	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2545	shouldn't come as a surprise to anybody). As such, the benchmark is
		2546	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2547	very optimal. But how would AnyEvent compare when used without the extra
		2548	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2549
		2550	The benchmark itself creates an echo-server, and then, for 500 times,
		2551	connects to the echo server, sends a line, waits for the reply, and then
		2552	creates the next connection. This is a rather bad benchmark, as it doesn't
		2553	test the efficiency of the framework or much non-blocking I/O, but it is a
		2554	benchmark nevertheless.
		2555
		2556	name runtime
		2557	Lambda/select 0.330 sec
		2558	+ optimized 0.122 sec
		2559	Lambda/AnyEvent 0.327 sec
		2560	+ optimized 0.138 sec
		2561	Raw sockets/select 0.077 sec
		2562	POE/select, components 0.662 sec
		2563	POE/select, raw sockets 0.226 sec
		2564	POE/select, optimized 0.404 sec
		2565
		2566	AnyEvent/select/nb 0.085 sec
		2567	AnyEvent/EV/nb 0.068 sec
		2568	+state machine 0.134 sec
		2569
		2570	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2571	benchmarks actually make blocking connects and use 100% blocking I/O,
		2572	defeating the purpose of an event-based solution. All of the newly
		2573	written AnyEvent benchmarks use 100% non-blocking connects (using
		2574	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2575	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2576	generally require a lot more bookkeeping and event handling than blocking
		2577	connects (which involve a single syscall only).
		2578
		2579	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2580	offers similar expressive power as POE and IO::Lambda, using conventional
		2581	Perl syntax. This means that both the echo server and the client are 100%
		2582	non-blocking, further placing it at a disadvantage.
		2583
		2584	As you can see, the AnyEvent + EV combination even beats the
		2585	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2586	backend easily beats IO::Lambda and POE.
		2587
		2588	And even the 100% non-blocking version written using the high-level (and
		2589	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2590	higher level ("unoptimised") abstractions by a large margin, even though
		2591	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2592
		2593	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2594	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2595	part of the IO::Lambda distribution and were used without any changes.
		2596
		2597
		2598	=head1 SIGNALS
		2599
		2600	AnyEvent currently installs handlers for these signals:
		2601
		2602	=over 4
		2603
		2604	=item SIGCHLD
		2605
		2606	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2607	emulation for event loops that do not support them natively. Also, some
		2608	event loops install a similar handler.
		2609
		2610	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2611	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2612
		2613	=item SIGPIPE
		2614
		2615	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2616	when AnyEvent gets loaded.
		2617
		2618	The rationale for this is that AnyEvent users usually do not really depend
		2619	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2620	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2621	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2622	some random socket.
		2623
		2624	The rationale for installing a no-op handler as opposed to ignoring it is
		2625	that this way, the handler will be restored to defaults on exec.
		2626
		2627	Feel free to install your own handler, or reset it to defaults.
		2628
		2629	=back
		2630
49	=cut	2631	=cut
50		2632
51	package AnyEvent;	2633	undef $SIG{CHLD}
		2634	if $SIG{CHLD} eq 'IGNORE';
52		2635
53	no warnings;	2636	$SIG{PIPE} = sub { }
54	use strict 'vars';	2637	unless defined $SIG{PIPE};
55	use Carp;
56		2638
57	our $VERSION = 0.2;	2639	=head1 RECOMMENDED/OPTIONAL MODULES
58	our $MODEL;
59		2640
60	our $AUTOLOAD;	2641	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
61	our @ISA;	2642	its built-in modules) are required to use it.
62		2643
63	my @models = (	2644	That does not mean that AnyEvent won't take advantage of some additional
64	[Coro => Coro::Event::],	2645	modules if they are installed.
65	[Event => Event::],
66	[Glib => Glib::],
67	[Tk => Tk::],
68	);
69		2646
70	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	2647	This section explains which additional modules will be used, and how they
		2648	affect AnyEvent's operation.
71		2649
72	sub AUTOLOAD {	2650	=over 4
73	$AUTOLOAD =~ s/.*://;
74		2651
75	$method{$AUTOLOAD}	2652	=item L<Async::Interrupt>
76	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";
77		2653
78	unless ($MODEL) {	2654	This slightly arcane module is used to implement fast signal handling: To
79	# check for already loaded models	2655	my knowledge, there is no way to do completely race-free and quick
80	for (@models) {	2656	signal handling in pure perl. To ensure that signals still get
81	my ($model, $package) = @$_;	2657	delivered, AnyEvent will start an interval timer to wake up perl (and
82	if (scalar keys %{ *{"$package\::"} }) {	2658	catch the signals) with some delay (default is 10 seconds, look for
83	eval "require AnyEvent::Impl::$model";	2659	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
84	last if $MODEL;
85	}
86	}
87		2660
88	unless ($MODEL) {	2661	If this module is available, then it will be used to implement signal
89	# try to load a model	2662	catching, which means that signals will not be delayed, and the event loop
		2663	will not be interrupted regularly, which is more efficient (and good for
		2664	battery life on laptops).
90		2665
91	for (@models) {	2666	This affects not just the pure-perl event loop, but also other event loops
92	my ($model, $package) = @$_;	2667	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		2668
97	$MODEL	2669	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
98	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	2670	and either employ their own workarounds (POE) or use AnyEvent's workaround
99	}	2671	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
100	}	2672	does nothing for those backends.
101		2673
102	@ISA = $MODEL;	2674	=item L<EV>
103		2675
104	my $class = shift;	2676	This module isn't really "optional", as it is simply one of the backend
105	$class->$AUTOLOAD (@_);	2677	event loops that AnyEvent can use. However, it is simply the best event
106	}	2678	loop available in terms of features, speed and stability: It supports
		2679	the AnyEvent API optimally, implements all the watcher types in XS, does
		2680	automatic timer adjustments even when no monotonic clock is available,
		2681	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2682	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2683	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2684
		2685	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2686	then this module will do nothing for you.
		2687
		2688	=item L<Guard>
		2689
		2690	The guard module, when used, will be used to implement
		2691	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2692	lot less memory), but otherwise doesn't affect guard operation much. It is
		2693	purely used for performance.
		2694
		2695	=item L<JSON> and L<JSON::XS>
		2696
		2697	One of these modules is required when you want to read or write JSON data
		2698	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2699	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2700
		2701	=item L<Net::SSLeay>
		2702
		2703	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2704	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2705	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2706
		2707	=item L<Time::HiRes>
		2708
		2709	This module is part of perl since release 5.008. It will be used when the
		2710	chosen event library does not come with a timing source of its own. The
		2711	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2712	try to use a monotonic clock for timing stability.
107		2713
108	=back	2714	=back
109		2715
110	=head1 EXAMPLE
111		2716
112	The following program uses an io watcher to read data from stdin, a timer	2717	=head1 FORK
113	to display a message once per second, and a condvar to exit the program
114	when the user enters quit:
115		2718
		2719	Most event libraries are not fork-safe. The ones who are usually are
		2720	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2721	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2722	are usually badly thought-out hacks that are incompatible with fork in
		2723	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2724	continue event-processing in both parent and child (or both, if you know
		2725	what you are doing).
		2726
		2727	This means that, in general, you cannot fork and do event processing in
		2728	the child if the event library was initialised before the fork (which
		2729	usually happens when the first AnyEvent watcher is created, or the library
		2730	is loaded).
		2731
		2732	If you have to fork, you must either do so I<before> creating your first
		2733	watcher OR you must not use AnyEvent at all in the child OR you must do
		2734	something completely out of the scope of AnyEvent.
		2735
		2736	The problem of doing event processing in the parent I<and> the child
		2737	is much more complicated: even for backends that I<are> fork-aware or
		2738	fork-safe, their behaviour is not usually what you want: fork clones all
		2739	watchers, that means all timers, I/O watchers etc. are active in both
		2740	parent and child, which is almost never what you want. USing C<exec>
		2741	to start worker children from some kind of manage rprocess is usually
		2742	preferred, because it is much easier and cleaner, at the expense of having
		2743	to have another binary.
		2744
		2745
		2746	=head1 SECURITY CONSIDERATIONS
		2747
		2748	AnyEvent can be forced to load any event model via
		2749	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2750	execute arbitrary code or directly gain access, it can easily be used to
		2751	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2752	will not be active when the program uses a different event model than
		2753	specified in the variable.
		2754
		2755	You can make AnyEvent completely ignore this variable by deleting it
		2756	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2757
		2758	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2759
116	use AnyEvent;	2760	use AnyEvent;
117		2761
118	my $cv = AnyEvent->condvar;	2762	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2763	be used to probe what backend is used and gain other information (which is
		2764	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2765	$ENV{PERL_ANYEVENT_STRICT}.
119		2766
120	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	2767	Note that AnyEvent will remove I<all> environment variables starting with
121	warn "io event <$_[0]>\n"; # will always output <r>	2768	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
122	chomp (my $input = <STDIN>); # read a line	2769	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		2770
127	my $time_watcher; # can only be used once
128		2771
129	sub new_timer {	2772	=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		2773
136	new_timer; # create first timer	2774	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2775	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2776	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2777	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2778	pronounced).
137		2779
138	$cv->wait; # wait until user enters /^q/i
139		2780
140	=head1 SEE ALSO	2781	=head1 SEE ALSO
141		2782
142	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	2783	Tutorial/Introduction: L<AnyEvent::Intro>.
143	L<AnyEvent::Impl::Coro>,	2784
144	L<AnyEvent::Impl::Event>,	2785	FAQ: L<AnyEvent::FAQ>.
145	L<AnyEvent::Impl::Glib>,	2786
		2787	Utility functions: L<AnyEvent::Util>.
		2788
		2789	Event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>, L<Glib::EV>,
		2790	L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		2791
		2792	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2793	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2794	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2795	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
		2796
		2797	Non-blocking file handles, sockets, TCP clients and
		2798	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2799
		2800	Asynchronous DNS: L<AnyEvent::DNS>.
		2801
		2802	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2803
		2804	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
146	L<AnyEvent::Impl::Tk>.	2805	L<AnyEvent::HTTP>.
147		2806
148	=head1	2807
		2808	=head1 AUTHOR
		2809
		2810	Marc Lehmann <schmorp@schmorp.de>
		2811	http://home.schmorp.de/
149		2812
150	=cut	2813	=cut
151		2814
152	1	2815	1
153		2816

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