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Revision 1.13 by root, Thu Jul 20 08:26:00 2006 UTC vs.
Revision 1.355 by root, Fri Aug 12 00:53:29 2011 UTC

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->io (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	});
15		33
16	* only one io watcher per $fh and $poll type is allowed (i.e. on a socket	34	# called when event loop idle (if applicable)
17	you can have one r + one w or one rw watcher, not any more (limitation by	35	my $w = AnyEvent->idle (cb => sub { ... });
18	Tk).
19		36
20	* the C<$poll_got> passed to the handler needs to be checked by looking	37	my $w = AnyEvent->condvar; # stores whether a condition was flagged
21	for single characters (e.g. with a regex), as it can contain more event	38	$w->send; # wake up current and all future recv's
22	types than were requested (e.g. a 'w' watcher might generate 'rw' events,	39	$w->recv; # enters "main loop" till $condvar gets ->send
23	limitation by Glib).	40	# use a condvar in callback mode:
		41	$w->cb (sub { $_[0]->recv });
24		42
25	* AnyEvent will keep filehandles alive, so as long as the watcher exists,	43	=head1 INTRODUCTION/TUTORIAL
26	the filehandle exists.
27		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
28	my $w = AnyEvent->timer (after => $seconds, cb => sub {	265	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		266	warn "timeout\n";
		267	});
		268
		269	# to cancel the timer:
		270	undef $w;
		271
		272	Example 2: fire an event after 0.5 seconds, then roughly every second.
		273
		274	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		275	warn "timeout\n";
		276	};
		277
		278	=head3 TIMING ISSUES
		279
		280	There are two ways to handle timers: based on real time (relative, "fire
		281	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		282	o'clock").
		283
		284	While most event loops expect timers to specified in a relative way, they
		285	use absolute time internally. This makes a difference when your clock
		286	"jumps", for example, when ntp decides to set your clock backwards from
		287	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		288	fire "after a second" might actually take six years to finally fire.
		289
		290	AnyEvent cannot compensate for this. The only event loop that is conscious
		291	of these issues is L<EV>, which offers both relative (ev_timer, based
		292	on true relative time) and absolute (ev_periodic, based on wallclock time)
		293	timers.
		294
		295	AnyEvent always prefers relative timers, if available, matching the
		296	AnyEvent API.
		297
		298	AnyEvent has two additional methods that return the "current time":
		299
		300	=over 4
		301
		302	=item AnyEvent->time
		303
		304	This returns the "current wallclock time" as a fractional number of
		305	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		306	return, and the result is guaranteed to be compatible with those).
		307
		308	It progresses independently of any event loop processing, i.e. each call
		309	will check the system clock, which usually gets updated frequently.
		310
		311	=item AnyEvent->now
		312
		313	This also returns the "current wallclock time", but unlike C<time>, above,
		314	this value might change only once per event loop iteration, depending on
		315	the event loop (most return the same time as C<time>, above). This is the
		316	time that AnyEvent's timers get scheduled against.
		317
		318	I<In almost all cases (in all cases if you don't care), this is the
		319	function to call when you want to know the current time.>
		320
		321	This function is also often faster then C<< AnyEvent->time >>, and
		322	thus the preferred method if you want some timestamp (for example,
		323	L<AnyEvent::Handle> uses this to update its activity timeouts).
		324
		325	The rest of this section is only of relevance if you try to be very exact
		326	with your timing; you can skip it without a bad conscience.
		327
		328	For a practical example of when these times differ, consider L<Event::Lib>
		329	and L<EV> and the following set-up:
		330
		331	The event loop is running and has just invoked one of your callbacks at
		332	time=500 (assume no other callbacks delay processing). In your callback,
		333	you wait a second by executing C<sleep 1> (blocking the process for a
		334	second) and then (at time=501) you create a relative timer that fires
		335	after three seconds.
		336
		337	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		338	both return C<501>, because that is the current time, and the timer will
		339	be scheduled to fire at time=504 (C<501> + C<3>).
		340
		341	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		342	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		343	last event processing phase started. With L<EV>, your timer gets scheduled
		344	to run at time=503 (C<500> + C<3>).
		345
		346	In one sense, L<Event::Lib> is more exact, as it uses the current time
		347	regardless of any delays introduced by event processing. However, most
		348	callbacks do not expect large delays in processing, so this causes a
		349	higher drift (and a lot more system calls to get the current time).
		350
		351	In another sense, L<EV> is more exact, as your timer will be scheduled at
		352	the same time, regardless of how long event processing actually took.
		353
		354	In either case, if you care (and in most cases, you don't), then you
		355	can get whatever behaviour you want with any event loop, by taking the
		356	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		357	account.
		358
		359	=item AnyEvent->now_update
		360
		361	Some event loops (such as L<EV> or L<AnyEvent::Loop>) cache the current
		362	time for each loop iteration (see the discussion of L<< AnyEvent->now >>,
		363	above).
		364
		365	When a callback runs for a long time (or when the process sleeps), then
		366	this "current" time will differ substantially from the real time, which
		367	might affect timers and time-outs.
		368
		369	When this is the case, you can call this method, which will update the
		370	event loop's idea of "current time".
		371
		372	A typical example would be a script in a web server (e.g. C<mod_perl>) -
		373	when mod_perl executes the script, then the event loop will have the wrong
		374	idea about the "current time" (being potentially far in the past, when the
		375	script ran the last time). In that case you should arrange a call to C<<
		376	AnyEvent->now_update >> each time the web server process wakes up again
		377	(e.g. at the start of your script, or in a handler).
		378
		379	Note that updating the time I<might> cause some events to be handled.
		380
		381	=back
		382
		383	=head2 SIGNAL WATCHERS
		384
		385	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		386
		387	You can watch for signals using a signal watcher, C<signal> is the signal
		388	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		389	callback to be invoked whenever a signal occurs.
		390
		391	Although the callback might get passed parameters, their value and
		392	presence is undefined and you cannot rely on them. Portable AnyEvent
		393	callbacks cannot use arguments passed to signal watcher callbacks.
		394
		395	Multiple signal occurrences can be clumped together into one callback
		396	invocation, and callback invocation will be synchronous. Synchronous means
		397	that it might take a while until the signal gets handled by the process,
		398	but it is guaranteed not to interrupt any other callbacks.
		399
		400	The main advantage of using these watchers is that you can share a signal
		401	between multiple watchers, and AnyEvent will ensure that signals will not
		402	interrupt your program at bad times.
		403
		404	This watcher might use C<%SIG> (depending on the event loop used),
		405	so programs overwriting those signals directly will likely not work
		406	correctly.
		407
		408	Example: exit on SIGINT
		409
		410	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		411
		412	=head3 Restart Behaviour
		413
		414	While restart behaviour is up to the event loop implementation, most will
		415	not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
		416	pure perl implementation).
		417
		418	=head3 Safe/Unsafe Signals
		419
		420	Perl signals can be either "safe" (synchronous to opcode handling) or
		421	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		422	latter might corrupt your memory.
		423
		424	AnyEvent signal handlers are, in addition, synchronous to the event loop,
		425	i.e. they will not interrupt your running perl program but will only be
		426	called as part of the normal event handling (just like timer, I/O etc.
		427	callbacks, too).
		428
		429	=head3 Signal Races, Delays and Workarounds
		430
		431	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		432	callbacks to signals in a generic way, which is a pity, as you cannot
		433	do race-free signal handling in perl, requiring C libraries for
		434	this. AnyEvent will try to do its best, which means in some cases,
		435	signals will be delayed. The maximum time a signal might be delayed is
		436	specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10 seconds). This
		437	variable can be changed only before the first signal watcher is created,
		438	and should be left alone otherwise. This variable determines how often
		439	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		440	will cause fewer spurious wake-ups, which is better for power and CPU
		441	saving.
		442
		443	All these problems can be avoided by installing the optional
		444	L<Async::Interrupt> module, which works with most event loops. It will not
		445	work with inherently broken event loops such as L<Event> or L<Event::Lib>
		446	(and not with L<POE> currently, as POE does its own workaround with
		447	one-second latency). For those, you just have to suffer the delays.
		448
		449	=head2 CHILD PROCESS WATCHERS
		450
		451	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		452
		453	You can also watch for a child process exit and catch its exit status.
		454
		455	The child process is specified by the C<pid> argument (on some backends,
		456	using C<0> watches for any child process exit, on others this will
		457	croak). The watcher will be triggered only when the child process has
		458	finished and an exit status is available, not on any trace events
		459	(stopped/continued).
		460
		461	The callback will be called with the pid and exit status (as returned by
		462	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		463	callback arguments.
		464
		465	This watcher type works by installing a signal handler for C<SIGCHLD>,
		466	and since it cannot be shared, nothing else should use SIGCHLD or reap
		467	random child processes (waiting for specific child processes, e.g. inside
		468	C<system>, is just fine).
		469
		470	There is a slight catch to child watchers, however: you usually start them
		471	I<after> the child process was created, and this means the process could
		472	have exited already (and no SIGCHLD will be sent anymore).
		473
		474	Not all event models handle this correctly (neither POE nor IO::Async do,
		475	see their AnyEvent::Impl manpages for details), but even for event models
		476	that I<do> handle this correctly, they usually need to be loaded before
		477	the process exits (i.e. before you fork in the first place). AnyEvent's
		478	pure perl event loop handles all cases correctly regardless of when you
		479	start the watcher.
		480
		481	This means you cannot create a child watcher as the very first
		482	thing in an AnyEvent program, you I<have> to create at least one
		483	watcher before you C<fork> the child (alternatively, you can call
		484	C<AnyEvent::detect>).
		485
		486	As most event loops do not support waiting for child events, they will be
		487	emulated by AnyEvent in most cases, in which case the latency and race
		488	problems mentioned in the description of signal watchers apply.
		489
		490	Example: fork a process and wait for it
		491
		492	my $done = AnyEvent->condvar;
		493
		494	my $pid = fork or exit 5;
		495
		496	my $w = AnyEvent->child (
		497	pid => $pid,
		498	cb => sub {
		499	my ($pid, $status) = @_;
		500	warn "pid $pid exited with status $status";
		501	$done->send;
		502	},
		503	);
		504
		505	# do something else, then wait for process exit
		506	$done->recv;
		507
		508	=head2 IDLE WATCHERS
		509
		510	$w = AnyEvent->idle (cb => <callback>);
		511
		512	This will repeatedly invoke the callback after the process becomes idle,
		513	until either the watcher is destroyed or new events have been detected.
		514
		515	Idle watchers are useful when there is a need to do something, but it
		516	is not so important (or wise) to do it instantly. The callback will be
		517	invoked only when there is "nothing better to do", which is usually
		518	defined as "all outstanding events have been handled and no new events
		519	have been detected". That means that idle watchers ideally get invoked
		520	when the event loop has just polled for new events but none have been
		521	detected. Instead of blocking to wait for more events, the idle watchers
		522	will be invoked.
		523
		524	Unfortunately, most event loops do not really support idle watchers (only
		525	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		526	will simply call the callback "from time to time".
		527
		528	Example: read lines from STDIN, but only process them when the
		529	program is otherwise idle:
		530
		531	my @lines; # read data
		532	my $idle_w;
		533	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		534	push @lines, scalar <STDIN>;
		535
		536	# start an idle watcher, if not already done
		537	$idle_w ||= AnyEvent->idle (cb => sub {
		538	# handle only one line, when there are lines left
		539	if (my $line = shift @lines) {
		540	print "handled when idle: $line";
		541	} else {
		542	# otherwise disable the idle watcher again
		543	undef $idle_w;
		544	}
		545	});
		546	});
		547
		548	=head2 CONDITION VARIABLES
		549
		550	$cv = AnyEvent->condvar;
		551
		552	$cv->send (<list>);
		553	my @res = $cv->recv;
		554
		555	If you are familiar with some event loops you will know that all of them
		556	require you to run some blocking "loop", "run" or similar function that
		557	will actively watch for new events and call your callbacks.
		558
		559	AnyEvent is slightly different: it expects somebody else to run the event
		560	loop and will only block when necessary (usually when told by the user).
		561
		562	The tool to do that is called a "condition variable", so called because
		563	they represent a condition that must become true.
		564
		565	Now is probably a good time to look at the examples further below.
		566
		567	Condition variables can be created by calling the C<< AnyEvent->condvar
		568	>> method, usually without arguments. The only argument pair allowed is
		569	C<cb>, which specifies a callback to be called when the condition variable
		570	becomes true, with the condition variable as the first argument (but not
		571	the results).
		572
		573	After creation, the condition variable is "false" until it becomes "true"
		574	by calling the C<send> method (or calling the condition variable as if it
		575	were a callback, read about the caveats in the description for the C<<
		576	->send >> method).
		577
		578	Since condition variables are the most complex part of the AnyEvent API, here are
		579	some different mental models of what they are - pick the ones you can connect to:
		580
		581	=over 4
		582
		583	=item * Condition variables are like callbacks - you can call them (and pass them instead
		584	of callbacks). Unlike callbacks however, you can also wait for them to be called.
		585
		586	=item * Condition variables are signals - one side can emit or send them,
		587	the other side can wait for them, or install a handler that is called when
		588	the signal fires.
		589
		590	=item * Condition variables are like "Merge Points" - points in your program
		591	where you merge multiple independent results/control flows into one.
		592
		593	=item * Condition variables represent a transaction - functions that start
		594	some kind of transaction can return them, leaving the caller the choice
		595	between waiting in a blocking fashion, or setting a callback.
		596
		597	=item * Condition variables represent future values, or promises to deliver
		598	some result, long before the result is available.
		599
		600	=back
		601
		602	Condition variables are very useful to signal that something has finished,
		603	for example, if you write a module that does asynchronous http requests,
		604	then a condition variable would be the ideal candidate to signal the
		605	availability of results. The user can either act when the callback is
		606	called or can synchronously C<< ->recv >> for the results.
		607
		608	You can also use them to simulate traditional event loops - for example,
		609	you can block your main program until an event occurs - for example, you
		610	could C<< ->recv >> in your main program until the user clicks the Quit
		611	button of your app, which would C<< ->send >> the "quit" event.
		612
		613	Note that condition variables recurse into the event loop - if you have
		614	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		615	lose. Therefore, condition variables are good to export to your caller, but
		616	you should avoid making a blocking wait yourself, at least in callbacks,
		617	as this asks for trouble.
		618
		619	Condition variables are represented by hash refs in perl, and the keys
		620	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		621	easy (it is often useful to build your own transaction class on top of
		622	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		623	its C<new> method in your own C<new> method.
		624
		625	There are two "sides" to a condition variable - the "producer side" which
		626	eventually calls C<< -> send >>, and the "consumer side", which waits
		627	for the send to occur.
		628
		629	Example: wait for a timer.
		630
		631	# condition: "wait till the timer is fired"
		632	my $timer_fired = AnyEvent->condvar;
		633
		634	# create the timer - we could wait for, say
		635	# a handle becomign ready, or even an
		636	# AnyEvent::HTTP request to finish, but
		637	# in this case, we simply use a timer:
		638	my $w = AnyEvent->timer (
		639	after => 1,
		640	cb => sub { $timer_fired->send },
		641	);
		642
		643	# this "blocks" (while handling events) till the callback
		644	# calls ->send
		645	$timer_fired->recv;
		646
		647	Example: wait for a timer, but take advantage of the fact that condition
		648	variables are also callable directly.
		649
		650	my $done = AnyEvent->condvar;
		651	my $delay = AnyEvent->timer (after => 5, cb => $done);
		652	$done->recv;
		653
		654	Example: Imagine an API that returns a condvar and doesn't support
		655	callbacks. This is how you make a synchronous call, for example from
		656	the main program:
		657
		658	use AnyEvent::CouchDB;
		659
		660	...
		661
		662	my @info = $couchdb->info->recv;
		663
		664	And this is how you would just set a callback to be called whenever the
		665	results are available:
		666
		667	$couchdb->info->cb (sub {
		668	my @info = $_[0]->recv;
		669	});
		670
		671	=head3 METHODS FOR PRODUCERS
		672
		673	These methods should only be used by the producing side, i.e. the
		674	code/module that eventually sends the signal. Note that it is also
		675	the producer side which creates the condvar in most cases, but it isn't
		676	uncommon for the consumer to create it as well.
		677
		678	=over 4
		679
		680	=item $cv->send (...)
		681
		682	Flag the condition as ready - a running C<< ->recv >> and all further
		683	calls to C<recv> will (eventually) return after this method has been
		684	called. If nobody is waiting the send will be remembered.
		685
		686	If a callback has been set on the condition variable, it is called
		687	immediately from within send.
		688
		689	Any arguments passed to the C<send> call will be returned by all
		690	future C<< ->recv >> calls.
		691
		692	Condition variables are overloaded so one can call them directly (as if
		693	they were a code reference). Calling them directly is the same as calling
		694	C<send>.
		695
		696	=item $cv->croak ($error)
		697
		698	Similar to send, but causes all calls to C<< ->recv >> to invoke
		699	C<Carp::croak> with the given error message/object/scalar.
		700
		701	This can be used to signal any errors to the condition variable
		702	user/consumer. Doing it this way instead of calling C<croak> directly
		703	delays the error detection, but has the overwhelming advantage that it
		704	diagnoses the error at the place where the result is expected, and not
		705	deep in some event callback with no connection to the actual code causing
		706	the problem.
		707
		708	=item $cv->begin ([group callback])
		709
		710	=item $cv->end
		711
		712	These two methods can be used to combine many transactions/events into
		713	one. For example, a function that pings many hosts in parallel might want
		714	to use a condition variable for the whole process.
		715
		716	Every call to C<< ->begin >> will increment a counter, and every call to
		717	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		718	>>, the (last) callback passed to C<begin> will be executed, passing the
		719	condvar as first argument. That callback is I<supposed> to call C<< ->send
		720	>>, but that is not required. If no group callback was set, C<send> will
		721	be called without any arguments.
		722
		723	You can think of C<< $cv->send >> giving you an OR condition (one call
		724	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		725	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		726
		727	Let's start with a simple example: you have two I/O watchers (for example,
		728	STDOUT and STDERR for a program), and you want to wait for both streams to
		729	close before activating a condvar:
		730
		731	my $cv = AnyEvent->condvar;
		732
		733	$cv->begin; # first watcher
		734	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		735	defined sysread $fh1, my $buf, 4096
		736	or $cv->end;
		737	});
		738
		739	$cv->begin; # second watcher
		740	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		741	defined sysread $fh2, my $buf, 4096
		742	or $cv->end;
		743	});
		744
		745	$cv->recv;
		746
		747	This works because for every event source (EOF on file handle), there is
		748	one call to C<begin>, so the condvar waits for all calls to C<end> before
		749	sending.
		750
		751	The ping example mentioned above is slightly more complicated, as the
		752	there are results to be passwd back, and the number of tasks that are
		753	begun can potentially be zero:
		754
		755	my $cv = AnyEvent->condvar;
		756
		757	my %result;
		758	$cv->begin (sub { shift->send (\%result) });
		759
		760	for my $host (@list_of_hosts) {
		761	$cv->begin;
		762	ping_host_then_call_callback $host, sub {
		763	$result{$host} = ...;
		764	$cv->end;
		765	};
		766	}
		767
		768	$cv->end;
		769
		770	This code fragment supposedly pings a number of hosts and calls
		771	C<send> after results for all then have have been gathered - in any
		772	order. To achieve this, the code issues a call to C<begin> when it starts
		773	each ping request and calls C<end> when it has received some result for
		774	it. Since C<begin> and C<end> only maintain a counter, the order in which
		775	results arrive is not relevant.
		776
		777	There is an additional bracketing call to C<begin> and C<end> outside the
		778	loop, which serves two important purposes: first, it sets the callback
		779	to be called once the counter reaches C<0>, and second, it ensures that
		780	C<send> is called even when C<no> hosts are being pinged (the loop
		781	doesn't execute once).
		782
		783	This is the general pattern when you "fan out" into multiple (but
		784	potentially zero) subrequests: use an outer C<begin>/C<end> pair to set
		785	the callback and ensure C<end> is called at least once, and then, for each
		786	subrequest you start, call C<begin> and for each subrequest you finish,
		787	call C<end>.
		788
		789	=back
		790
		791	=head3 METHODS FOR CONSUMERS
		792
		793	These methods should only be used by the consuming side, i.e. the
		794	code awaits the condition.
		795
		796	=over 4
		797
		798	=item $cv->recv
		799
		800	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		801	>> methods have been called on C<$cv>, while servicing other watchers
		802	normally.
		803
		804	You can only wait once on a condition - additional calls are valid but
		805	will return immediately.
		806
		807	If an error condition has been set by calling C<< ->croak >>, then this
		808	function will call C<croak>.
		809
		810	In list context, all parameters passed to C<send> will be returned,
		811	in scalar context only the first one will be returned.
		812
		813	Note that doing a blocking wait in a callback is not supported by any
		814	event loop, that is, recursive invocation of a blocking C<< ->recv
		815	>> is not allowed, and the C<recv> call will C<croak> if such a
		816	condition is detected. This condition can be slightly loosened by using
		817	L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
		818	any thread that doesn't run the event loop itself.
		819
		820	Not all event models support a blocking wait - some die in that case
		821	(programs might want to do that to stay interactive), so I<if you are
		822	using this from a module, never require a blocking wait>. Instead, let the
		823	caller decide whether the call will block or not (for example, by coupling
		824	condition variables with some kind of request results and supporting
		825	callbacks so the caller knows that getting the result will not block,
		826	while still supporting blocking waits if the caller so desires).
		827
		828	You can ensure that C<< ->recv >> never blocks by setting a callback and
		829	only calling C<< ->recv >> from within that callback (or at a later
		830	time). This will work even when the event loop does not support blocking
		831	waits otherwise.
		832
		833	=item $bool = $cv->ready
		834
		835	Returns true when the condition is "true", i.e. whether C<send> or
		836	C<croak> have been called.
		837
		838	=item $cb = $cv->cb ($cb->($cv))
		839
		840	This is a mutator function that returns the callback set and optionally
		841	replaces it before doing so.
		842
		843	The callback will be called when the condition becomes "true", i.e. when
		844	C<send> or C<croak> are called, with the only argument being the
		845	condition variable itself. If the condition is already true, the
		846	callback is called immediately when it is set. Calling C<recv> inside
		847	the callback or at any later time is guaranteed not to block.
		848
		849	=back
		850
		851	=head1 SUPPORTED EVENT LOOPS/BACKENDS
		852
		853	The available backend classes are (every class has its own manpage):
		854
		855	=over 4
		856
		857	=item Backends that are autoprobed when no other event loop can be found.
		858
		859	EV is the preferred backend when no other event loop seems to be in
		860	use. If EV is not installed, then AnyEvent will fall back to its own
		861	pure-perl implementation, which is available everywhere as it comes with
		862	AnyEvent itself.
		863
		864	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		865	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		866
		867	=item Backends that are transparently being picked up when they are used.
		868
		869	These will be used if they are already loaded when the first watcher
		870	is created, in which case it is assumed that the application is using
		871	them. This means that AnyEvent will automatically pick the right backend
		872	when the main program loads an event module before anything starts to
		873	create watchers. Nothing special needs to be done by the main program.
		874
		875	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		876	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		877	AnyEvent::Impl::Tk based on Tk, very broken.
		878	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		879	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		880	AnyEvent::Impl::Irssi used when running within irssi.
		881	AnyEvent::Impl::IOAsync based on IO::Async.
		882	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		883	AnyEvent::Impl::FLTK based on FLTK.
		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	If you need to do some initialisation before AnyEvent watchers are
		940	created, use C<post_detect>.
		941
		942	=item $guard = AnyEvent::post_detect { BLOCK }
		943
		944	Arranges for the code block to be executed as soon as the event model is
		945	autodetected (or immediately if that has already happened).
		946
		947	The block will be executed I<after> the actual backend has been detected
		948	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		949	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		950	other initialisations - see the sources of L<AnyEvent::Strict> or
		951	L<AnyEvent::AIO> to see how this is used.
		952
		953	The most common usage is to create some global watchers, without forcing
		954	event module detection too early, for example, L<AnyEvent::AIO> creates
		955	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		956	avoid autodetecting the event module at load time.
		957
		958	If called in scalar or list context, then it creates and returns an object
		959	that automatically removes the callback again when it is destroyed (or
		960	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		961	a case where this is useful.
		962
		963	Example: Create a watcher for the IO::AIO module and store it in
		964	C<$WATCHER>, but do so only do so after the event loop is initialised.
		965
		966	our WATCHER;
		967
		968	my $guard = AnyEvent::post_detect {
		969	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		970	};
		971
		972	# the ||= is important in case post_detect immediately runs the block,
		973	# as to not clobber the newly-created watcher. assigning both watcher and
		974	# post_detect guard to the same variable has the advantage of users being
		975	# able to just C<undef $WATCHER> if the watcher causes them grief.
		976
		977	$WATCHER ||= $guard;
		978
		979	=item @AnyEvent::post_detect
		980
		981	If there are any code references in this array (you can C<push> to it
		982	before or after loading AnyEvent), then they will be called directly
		983	after the event loop has been chosen.
		984
		985	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		986	if it is defined then the event loop has already been detected, and the
		987	array will be ignored.
		988
		989	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		990	it, as it takes care of these details.
		991
		992	This variable is mainly useful for modules that can do something useful
		993	when AnyEvent is used and thus want to know when it is initialised, but do
		994	not need to even load it by default. This array provides the means to hook
		995	into AnyEvent passively, without loading it.
		996
		997	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		998	together, you could put this into Coro (this is the actual code used by
		999	Coro to accomplish this):
		1000
		1001	if (defined $AnyEvent::MODEL) {
		1002	# AnyEvent already initialised, so load Coro::AnyEvent
		1003	require Coro::AnyEvent;
		1004	} else {
		1005	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		1006	# as soon as it is
		1007	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		1008	}
		1009
		1010	=item AnyEvent::postpone { BLOCK }
		1011
		1012	Arranges for the block to be executed as soon as possible, but not before
		1013	the call itself returns. In practise, the block will be executed just
		1014	before the event loop polls for new events, or shortly afterwards.
		1015
		1016	This function never returns anything (to make the C<return postpone { ...
		1017	}> idiom more useful.
		1018
		1019	To understand the usefulness of this function, consider a function that
		1020	asynchronously does something for you and returns some transaction
		1021	object or guard to let you cancel the operation. For example,
		1022	C<AnyEvent::Socket::tcp_connect>:
		1023
		1024	# start a conenction attempt unless one is active
		1025	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		1026	delete $self->{connect_guard};
29	...	1027	...
30	});	1028	};
31		1029
32	* io and time watchers get canceled whenever $w is destroyed, so keep a copy	1030	Imagine that this function could instantly call the callback, for
		1031	example, because it detects an obvious error such as a negative port
		1032	number. Invoking the callback before the function returns causes problems
		1033	however: the callback will be called and will try to delete the guard
		1034	object. But since the function hasn't returned yet, there is nothing to
		1035	delete. When the function eventually returns it will assign the guard
		1036	object to C<< $self->{connect_guard} >>, where it will likely never be
		1037	deleted, so the program thinks it is still trying to connect.
33		1038
34	* timers can only be used once and must be recreated for repeated	1039	This is where C<AnyEvent::postpone> should be used. Instead of calling the
35	operation (limitation by Glib and Tk).	1040	callback directly on error:
36		1041
37	my $w = AnyEvent->condvar; # kind of main loop replacement	1042	$cb->(undef), return # signal error to callback, BAD!
38	$w->wait; # enters main loop till $condvar gets ->broadcast	1043	if $some_error_condition;
39	$w->broadcast; # wake up current and all future wait's
40		1044
41	* condvars are used to give blocking behaviour when neccessary. Create	1045	It should use C<postpone>:
42	a condvar for any "request" or "event" your module might create, C<<
43	->broadcast >> it when the event happens and provide a function that calls
44	C<< ->wait >> for it. See the examples below.
45		1046
46	=head1 DESCRIPTION	1047	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1048	if $some_error_condition;
47		1049
48	L<AnyEvent> provides an identical interface to multiple event loops. This	1050	=back
49	allows module authors to utilise an event loop without forcing module
50	users to use the same event loop (as only a single event loop can coexist
51	peacefully at any one time).
52		1051
53	The interface itself is vaguely similar but not identical to the Event	1052	=head1 WHAT TO DO IN A MODULE
54	module.
55		1053
56	On the first call of any method, the module tries to detect the currently	1054	As a module author, you should C<use AnyEvent> and call AnyEvent methods
57	loaded event loop by probing wether any of the following modules is	1055	freely, but you should not load a specific event module or rely on it.
58	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	1056
59	used. If none is found, the module tries to load these modules in the	1057	Be careful when you create watchers in the module body - AnyEvent will
60	order given. The first one that could be successfully loaded will be	1058	decide which event module to use as soon as the first method is called, so
61	used. If still none could be found, it will issue an error.	1059	by calling AnyEvent in your module body you force the user of your module
		1060	to load the event module first.
		1061
		1062	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1063	the C<< ->send >> method has been called on it already. This is
		1064	because it will stall the whole program, and the whole point of using
		1065	events is to stay interactive.
		1066
		1067	It is fine, however, to call C<< ->recv >> when the user of your module
		1068	requests it (i.e. if you create a http request object ad have a method
		1069	called C<results> that returns the results, it may call C<< ->recv >>
		1070	freely, as the user of your module knows what she is doing. Always).
		1071
		1072	=head1 WHAT TO DO IN THE MAIN PROGRAM
		1073
		1074	There will always be a single main program - the only place that should
		1075	dictate which event model to use.
		1076
		1077	If the program is not event-based, it need not do anything special, even
		1078	when it depends on a module that uses an AnyEvent. If the program itself
		1079	uses AnyEvent, but does not care which event loop is used, all it needs
		1080	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1081	available loop implementation.
		1082
		1083	If the main program relies on a specific event model - for example, in
		1084	Gtk2 programs you have to rely on the Glib module - you should load the
		1085	event module before loading AnyEvent or any module that uses it: generally
		1086	speaking, you should load it as early as possible. The reason is that
		1087	modules might create watchers when they are loaded, and AnyEvent will
		1088	decide on the event model to use as soon as it creates watchers, and it
		1089	might choose the wrong one unless you load the correct one yourself.
		1090
		1091	You can chose to use a pure-perl implementation by loading the
		1092	C<AnyEvent::Loop> module, which gives you similar behaviour
		1093	everywhere, but letting AnyEvent chose the model is generally better.
		1094
		1095	=head2 MAINLOOP EMULATION
		1096
		1097	Sometimes (often for short test scripts, or even standalone programs who
		1098	only want to use AnyEvent), you do not want to run a specific event loop.
		1099
		1100	In that case, you can use a condition variable like this:
		1101
		1102	AnyEvent->condvar->recv;
		1103
		1104	This has the effect of entering the event loop and looping forever.
		1105
		1106	Note that usually your program has some exit condition, in which case
		1107	it is better to use the "traditional" approach of storing a condition
		1108	variable somewhere, waiting for it, and sending it when the program should
		1109	exit cleanly.
		1110
		1111
		1112	=head1 OTHER MODULES
		1113
		1114	The following is a non-exhaustive list of additional modules that use
		1115	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		1116	modules and other event loops in the same program. Some of the modules
		1117	come as part of AnyEvent, the others are available via CPAN.
62		1118
63	=over 4	1119	=over 4
64		1120
		1121	=item L<AnyEvent::Util>
		1122
		1123	Contains various utility functions that replace often-used blocking
		1124	functions such as C<inet_aton> with event/callback-based versions.
		1125
		1126	=item L<AnyEvent::Socket>
		1127
		1128	Provides various utility functions for (internet protocol) sockets,
		1129	addresses and name resolution. Also functions to create non-blocking tcp
		1130	connections or tcp servers, with IPv6 and SRV record support and more.
		1131
		1132	=item L<AnyEvent::Handle>
		1133
		1134	Provide read and write buffers, manages watchers for reads and writes,
		1135	supports raw and formatted I/O, I/O queued and fully transparent and
		1136	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1137
		1138	=item L<AnyEvent::DNS>
		1139
		1140	Provides rich asynchronous DNS resolver capabilities.
		1141
		1142	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1143
		1144	Implement event-based interfaces to the protocols of the same name (for
		1145	the curious, IGS is the International Go Server and FCP is the Freenet
		1146	Client Protocol).
		1147
		1148	=item L<AnyEvent::Handle::UDP>
		1149
		1150	Here be danger!
		1151
		1152	As Pauli would put it, "Not only is it not right, it's not even wrong!" -
		1153	there are so many things wrong with AnyEvent::Handle::UDP, most notably
		1154	its use of a stream-based API with a protocol that isn't streamable, that
		1155	the only way to improve it is to delete it.
		1156
		1157	It features data corruption (but typically only under load) and general
		1158	confusion. On top, the author is not only clueless about UDP but also
		1159	fact-resistant - some gems of his understanding: "connect doesn't work
		1160	with UDP", "UDP packets are not IP packets", "UDP only has datagrams, not
		1161	packets", "I don't need to implement proper error checking as UDP doesn't
		1162	support error checking" and so on - he doesn't even understand what's
		1163	wrong with his module when it is explained to him.
		1164
		1165	=item L<AnyEvent::DBI>
		1166
		1167	Executes L<DBI> requests asynchronously in a proxy process for you,
		1168	notifying you in an event-based way when the operation is finished.
		1169
		1170	=item L<AnyEvent::AIO>
		1171
		1172	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1173	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1174	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1175	file I/O, and much more.
		1176
		1177	=item L<AnyEvent::HTTPD>
		1178
		1179	A simple embedded webserver.
		1180
		1181	=item L<AnyEvent::FastPing>
		1182
		1183	The fastest ping in the west.
		1184
		1185	=item L<Coro>
		1186
		1187	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1188
		1189	=back
		1190
65	=cut	1191	=cut
66		1192
67	package AnyEvent;	1193	package AnyEvent;
68		1194
69	no warnings;	1195	# basically a tuned-down version of common::sense
70	use strict 'vars';	1196	sub common_sense {
		1197	# from common:.sense 3.4
		1198	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
		1199	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1200	$^H |= 0x00000600;
		1201	}
		1202
		1203	BEGIN { AnyEvent::common_sense }
		1204
71	use Carp;	1205	use Carp ();
72		1206
73	our $VERSION = '1.02';	1207	our $VERSION = '5.34';
74	our $MODEL;	1208	our $MODEL;
75		1209
76	our $AUTOLOAD;	1210	our $AUTOLOAD;
77	our @ISA;	1211	our @ISA;
78		1212
79	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
80
81	our @REGISTRY;	1213	our @REGISTRY;
82		1214
		1215	our $VERBOSE;
		1216
		1217	BEGIN {
		1218	require "AnyEvent/constants.pl";
		1219
		1220	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1221
		1222	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1223	if ${^TAINT};
		1224
		1225	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1226
		1227	}
		1228
		1229	our $MAX_SIGNAL_LATENCY = 10;
		1230
		1231	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1232
		1233	{
		1234	my $idx;
		1235	$PROTOCOL{$_} = ++$idx
		1236	for reverse split /\s*,\s*/,
		1237	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1238	}
		1239
		1240	our @post_detect;
		1241
		1242	sub post_detect(&) {
		1243	my ($cb) = @_;
		1244
		1245	push @post_detect, $cb;
		1246
		1247	defined wantarray
		1248	? bless \$cb, "AnyEvent::Util::postdetect"
		1249	: ()
		1250	}
		1251
		1252	sub AnyEvent::Util::postdetect::DESTROY {
		1253	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1254	}
		1255
		1256	our $POSTPONE_W;
		1257	our @POSTPONE;
		1258
		1259	sub _postpone_exec {
		1260	undef $POSTPONE_W;
		1261
		1262	&{ shift @POSTPONE }
		1263	while @POSTPONE;
		1264	}
		1265
		1266	sub postpone(&) {
		1267	push @POSTPONE, shift;
		1268
		1269	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1270
		1271	()
		1272	}
		1273
83	my @models = (	1274	our @models = (
84	[Coro::Event:: => AnyEvent::Impl::Coro::],	1275	[EV:: => AnyEvent::Impl::EV:: , 1],
		1276	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
		1277	# everything below here will not (normally) be autoprobed
		1278	# as the pure perl backend should work everywhere
		1279	# and is usually faster
85	[Event:: => AnyEvent::Impl::Event::],	1280	[Event:: => AnyEvent::Impl::Event::, 1],
		1281	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1282	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1283	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1284	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1285	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1286	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1287	[Wx:: => AnyEvent::Impl::POE::],
86	[Glib:: => AnyEvent::Impl::Glib::],	1288	[Prima:: => AnyEvent::Impl::POE::],
		1289	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1290	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
87	[Tk:: => AnyEvent::Impl::Tk::],	1291	[FLTK:: => AnyEvent::Impl::FLTK::],
88	);	1292	);
89		1293
90	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	1294	our %method = map +($_ => 1),
		1295	qw(io timer time now now_update signal child idle condvar DESTROY);
91		1296
92	sub AUTOLOAD {	1297	sub detect() {
93	$AUTOLOAD =~ s/.*://;	1298	# free some memory
		1299	*detect = sub () { $MODEL };
94		1300
95	$method{$AUTOLOAD}	1301	local $!; # for good measure
96	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	1302	local $SIG{__DIE__};
97		1303
		1304	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1305	my $model = $1;
		1306	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1307	if (eval "require $model") {
		1308	$MODEL = $model;
		1309	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1310	} else {
		1311	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
		1312	}
		1313	}
		1314
		1315	# check for already loaded models
98	unless ($MODEL) {	1316	unless ($MODEL) {
99	# check for already loaded models
100	for (@REGISTRY, @models) {	1317	for (@REGISTRY, @models) {
101	my ($package, $model) = @$_;	1318	my ($package, $model) = @$_;
102	if (${"$package\::VERSION"} > 0) {	1319	if (${"$package\::VERSION"} > 0) {
103	if (eval "require $model") {	1320	if (eval "require $model") {
104	$MODEL = $model;	1321	$MODEL = $model;
105	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1322	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
106	last;	1323	last;
107	}	1324	}
108	}	1325	}
109	}	1326	}
110		1327
111	unless ($MODEL) {	1328	unless ($MODEL) {
112	# try to load a model	1329	# try to autoload a model
113
114	for (@REGISTRY, @models) {	1330	for (@REGISTRY, @models) {
115	my ($package, $model) = @$_;	1331	my ($package, $model, $autoload) = @$_;
		1332	if (
		1333	$autoload
		1334	and eval "require $package"
		1335	and ${"$package\::VERSION"} > 0
116	if (eval "require $model") {	1336	and eval "require $model"
		1337	) {
117	$MODEL = $model;	1338	$MODEL = $model;
118	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	1339	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
119	last;	1340	last;
120	}	1341	}
121	}	1342	}
122		1343
123	$MODEL	1344	$MODEL
124	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1345	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?\n";
125	}	1346	}
126	}	1347	}
127		1348
128	@ISA = $MODEL;	1349	# free memory only needed for probing
		1350	undef @models;
		1351	undef @REGISTRY;
		1352
		1353	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1354	unshift @ISA, $MODEL;
		1355
		1356	# now nuke some methods that are overridden by the backend.
		1357	# SUPER usage is not allowed in these.
		1358	for (qw(time signal child idle)) {
		1359	undef &{"AnyEvent::Base::$_"}
		1360	if defined &{"$MODEL\::$_"};
		1361	}
		1362
		1363	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1364	eval { require AnyEvent::Strict };
		1365	warn "AnyEvent: cannot load AnyEvent::Strict: $@"
		1366	if $@ && $VERBOSE;
		1367	}
		1368
		1369	(shift @post_detect)->() while @post_detect;
		1370	undef @post_detect;
		1371
		1372	*post_detect = sub(&) {
		1373	shift->();
		1374
		1375	undef
		1376	};
		1377
		1378	# recover a few more bytes
		1379	postpone {
		1380	undef &AUTOLOAD;
		1381	};
		1382
		1383	$MODEL
		1384	}
		1385
		1386	our %method = map +($_ => 1),
		1387	qw(io timer time now now_update signal child idle condvar DESTROY);
		1388
		1389	sub AUTOLOAD {
		1390	(my $func = $AUTOLOAD) =~ s/.*://;
		1391
		1392	$method{$func}
		1393	or Carp::croak "$func: not a valid AnyEvent class method";
		1394
		1395	# free some memory
		1396	undef %method;
		1397
		1398	detect;
129		1399
130	my $class = shift;	1400	my $class = shift;
131	$class->$AUTOLOAD (@_);	1401	$class->$func (@_);
132	}	1402	}
		1403
		1404	# utility function to dup a filehandle. this is used by many backends
		1405	# to support binding more than one watcher per filehandle (they usually
		1406	# allow only one watcher per fd, so we dup it to get a different one).
		1407	sub _dupfh($$;$$) {
		1408	my ($poll, $fh, $r, $w) = @_;
		1409
		1410	# cygwin requires the fh mode to be matching, unix doesn't
		1411	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1412
		1413	open my $fh2, $mode, $fh
		1414	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1415
		1416	# we assume CLOEXEC is already set by perl in all important cases
		1417
		1418	($fh2, $rw)
		1419	}
		1420
		1421	=head1 SIMPLIFIED AE API
		1422
		1423	Starting with version 5.0, AnyEvent officially supports a second, much
		1424	simpler, API that is designed to reduce the calling, typing and memory
		1425	overhead by using function call syntax and a fixed number of parameters.
		1426
		1427	See the L<AE> manpage for details.
		1428
		1429	=cut
		1430
		1431	package AE;
		1432
		1433	our $VERSION = $AnyEvent::VERSION;
		1434
		1435
		1436	sub _reset() {
		1437	eval q{
		1438	# fall back to the main API by default - backends and AnyEvent::Base
		1439	# implementations can overwrite these.
		1440
		1441	sub io($$$) {
		1442	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1443	}
		1444
		1445	sub timer($$$) {
		1446	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1447	}
		1448
		1449	sub signal($$) {
		1450	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1451	}
		1452
		1453	sub child($$) {
		1454	AnyEvent->child (pid => $_[0], cb => $_[1])
		1455	}
		1456
		1457	sub idle($) {
		1458	AnyEvent->idle (cb => $_[0])
		1459	}
		1460
		1461	sub cv(;&) {
		1462	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1463	}
		1464
		1465	sub now() {
		1466	AnyEvent->now
		1467	}
		1468
		1469	sub now_update() {
		1470	AnyEvent->now_update
		1471	}
		1472
		1473	sub time() {
		1474	AnyEvent->time
		1475	}
		1476
		1477	*postpone = \&AnyEvent::postpone;
		1478	};
		1479	die if $@;
		1480	}
		1481
		1482	BEGIN { _reset }
		1483
		1484	package AnyEvent::Base;
		1485
		1486	# default implementations for many methods
		1487
		1488	sub time {
		1489	eval q{ # poor man's autoloading {}
		1490	# probe for availability of Time::HiRes
		1491	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1492	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1493	*AE::time = \&Time::HiRes::time;
		1494	# if (eval "use POSIX (); (POSIX::times())...
		1495	} else {
		1496	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1497	*AE::time = sub (){ time }; # epic fail
		1498	}
		1499
		1500	*time = sub { AE::time }; # different prototypes
		1501	};
		1502	die if $@;
		1503
		1504	&time
		1505	}
		1506
		1507	*now = \&time;
		1508
		1509	sub now_update { }
		1510
		1511	sub _poll {
		1512	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1513	}
		1514
		1515	# default implementation for ->condvar
		1516	# in fact, the default should not be overwritten
		1517
		1518	sub condvar {
		1519	eval q{ # poor man's autoloading {}
		1520	*condvar = sub {
		1521	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1522	};
		1523
		1524	*AE::cv = sub (;&) {
		1525	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1526	};
		1527	};
		1528	die if $@;
		1529
		1530	&condvar
		1531	}
		1532
		1533	# default implementation for ->signal
		1534
		1535	our $HAVE_ASYNC_INTERRUPT;
		1536
		1537	sub _have_async_interrupt() {
		1538	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1539	&& eval "use Async::Interrupt 1.02 (); 1")
		1540	unless defined $HAVE_ASYNC_INTERRUPT;
		1541
		1542	$HAVE_ASYNC_INTERRUPT
		1543	}
		1544
		1545	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1546	our (%SIG_ASY, %SIG_ASY_W);
		1547	our ($SIG_COUNT, $SIG_TW);
		1548
		1549	# install a dummy wakeup watcher to reduce signal catching latency
		1550	# used by Impls
		1551	sub _sig_add() {
		1552	unless ($SIG_COUNT++) {
		1553	# try to align timer on a full-second boundary, if possible
		1554	my $NOW = AE::now;
		1555
		1556	$SIG_TW = AE::timer
		1557	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1558	$MAX_SIGNAL_LATENCY,
		1559	sub { } # just for the PERL_ASYNC_CHECK
		1560	;
		1561	}
		1562	}
		1563
		1564	sub _sig_del {
		1565	undef $SIG_TW
		1566	unless --$SIG_COUNT;
		1567	}
		1568
		1569	our $_sig_name_init; $_sig_name_init = sub {
		1570	eval q{ # poor man's autoloading {}
		1571	undef $_sig_name_init;
		1572
		1573	if (_have_async_interrupt) {
		1574	*sig2num = \&Async::Interrupt::sig2num;
		1575	*sig2name = \&Async::Interrupt::sig2name;
		1576	} else {
		1577	require Config;
		1578
		1579	my %signame2num;
		1580	@signame2num{ split ' ', $Config::Config{sig_name} }
		1581	= split ' ', $Config::Config{sig_num};
		1582
		1583	my @signum2name;
		1584	@signum2name[values %signame2num] = keys %signame2num;
		1585
		1586	*sig2num = sub($) {
		1587	$_[0] > 0 ? shift : $signame2num{+shift}
		1588	};
		1589	*sig2name = sub ($) {
		1590	$_[0] > 0 ? $signum2name[+shift] : shift
		1591	};
		1592	}
		1593	};
		1594	die if $@;
		1595	};
		1596
		1597	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1598	sub sig2name($) { &$_sig_name_init; &sig2name }
		1599
		1600	sub signal {
		1601	eval q{ # poor man's autoloading {}
		1602	# probe for availability of Async::Interrupt
		1603	if (_have_async_interrupt) {
		1604	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1605
		1606	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1607	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1608
		1609	} else {
		1610	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1611
		1612	if (AnyEvent::WIN32) {
		1613	require AnyEvent::Util;
		1614
		1615	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1616	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1617	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1618	} else {
		1619	pipe $SIGPIPE_R, $SIGPIPE_W;
		1620	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1621	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1622
		1623	# not strictly required, as $^F is normally 2, but let's make sure...
		1624	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1625	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1626	}
		1627
		1628	$SIGPIPE_R
		1629	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1630
		1631	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1632	}
		1633
		1634	*signal = $HAVE_ASYNC_INTERRUPT
		1635	? sub {
		1636	my (undef, %arg) = @_;
		1637
		1638	# async::interrupt
		1639	my $signal = sig2num $arg{signal};
		1640	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1641
		1642	$SIG_ASY{$signal} ||= new Async::Interrupt
		1643	cb => sub { undef $SIG_EV{$signal} },
		1644	signal => $signal,
		1645	pipe => [$SIGPIPE_R->filenos],
		1646	pipe_autodrain => 0,
		1647	;
		1648
		1649	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1650	}
		1651	: sub {
		1652	my (undef, %arg) = @_;
		1653
		1654	# pure perl
		1655	my $signal = sig2name $arg{signal};
		1656	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1657
		1658	$SIG{$signal} ||= sub {
		1659	local $!;
		1660	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1661	undef $SIG_EV{$signal};
		1662	};
		1663
		1664	# can't do signal processing without introducing races in pure perl,
		1665	# so limit the signal latency.
		1666	_sig_add;
		1667
		1668	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1669	}
		1670	;
		1671
		1672	*AnyEvent::Base::signal::DESTROY = sub {
		1673	my ($signal, $cb) = @{$_[0]};
		1674
		1675	_sig_del;
		1676
		1677	delete $SIG_CB{$signal}{$cb};
		1678
		1679	$HAVE_ASYNC_INTERRUPT
		1680	? delete $SIG_ASY{$signal}
		1681	: # delete doesn't work with older perls - they then
		1682	# print weird messages, or just unconditionally exit
		1683	# instead of getting the default action.
		1684	undef $SIG{$signal}
		1685	unless keys %{ $SIG_CB{$signal} };
		1686	};
		1687
		1688	*_signal_exec = sub {
		1689	$HAVE_ASYNC_INTERRUPT
		1690	? $SIGPIPE_R->drain
		1691	: sysread $SIGPIPE_R, (my $dummy), 9;
		1692
		1693	while (%SIG_EV) {
		1694	for (keys %SIG_EV) {
		1695	delete $SIG_EV{$_};
		1696	&$_ for values %{ $SIG_CB{$_} || {} };
		1697	}
		1698	}
		1699	};
		1700	};
		1701	die if $@;
		1702
		1703	&signal
		1704	}
		1705
		1706	# default implementation for ->child
		1707
		1708	our %PID_CB;
		1709	our $CHLD_W;
		1710	our $CHLD_DELAY_W;
		1711
		1712	# used by many Impl's
		1713	sub _emit_childstatus($$) {
		1714	my (undef, $rpid, $rstatus) = @_;
		1715
		1716	$_->($rpid, $rstatus)
		1717	for values %{ $PID_CB{$rpid} || {} },
		1718	values %{ $PID_CB{0} || {} };
		1719	}
		1720
		1721	sub child {
		1722	eval q{ # poor man's autoloading {}
		1723	*_sigchld = sub {
		1724	my $pid;
		1725
		1726	AnyEvent->_emit_childstatus ($pid, $?)
		1727	while ($pid = waitpid -1, WNOHANG) > 0;
		1728	};
		1729
		1730	*child = sub {
		1731	my (undef, %arg) = @_;
		1732
		1733	my $pid = $arg{pid};
		1734	my $cb = $arg{cb};
		1735
		1736	$PID_CB{$pid}{$cb+0} = $cb;
		1737
		1738	unless ($CHLD_W) {
		1739	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1740	# child could be a zombie already, so make at least one round
		1741	&_sigchld;
		1742	}
		1743
		1744	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1745	};
		1746
		1747	*AnyEvent::Base::child::DESTROY = sub {
		1748	my ($pid, $icb) = @{$_[0]};
		1749
		1750	delete $PID_CB{$pid}{$icb};
		1751	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1752
		1753	undef $CHLD_W unless keys %PID_CB;
		1754	};
		1755	};
		1756	die if $@;
		1757
		1758	&child
		1759	}
		1760
		1761	# idle emulation is done by simply using a timer, regardless
		1762	# of whether the process is idle or not, and not letting
		1763	# the callback use more than 50% of the time.
		1764	sub idle {
		1765	eval q{ # poor man's autoloading {}
		1766	*idle = sub {
		1767	my (undef, %arg) = @_;
		1768
		1769	my ($cb, $w, $rcb) = $arg{cb};
		1770
		1771	$rcb = sub {
		1772	if ($cb) {
		1773	$w = _time;
		1774	&$cb;
		1775	$w = _time - $w;
		1776
		1777	# never use more then 50% of the time for the idle watcher,
		1778	# within some limits
		1779	$w = 0.0001 if $w < 0.0001;
		1780	$w = 5 if $w > 5;
		1781
		1782	$w = AE::timer $w, 0, $rcb;
		1783	} else {
		1784	# clean up...
		1785	undef $w;
		1786	undef $rcb;
		1787	}
		1788	};
		1789
		1790	$w = AE::timer 0.05, 0, $rcb;
		1791
		1792	bless \\$cb, "AnyEvent::Base::idle"
		1793	};
		1794
		1795	*AnyEvent::Base::idle::DESTROY = sub {
		1796	undef $${$_[0]};
		1797	};
		1798	};
		1799	die if $@;
		1800
		1801	&idle
		1802	}
		1803
		1804	package AnyEvent::CondVar;
		1805
		1806	our @ISA = AnyEvent::CondVar::Base::;
		1807
		1808	# only to be used for subclassing
		1809	sub new {
		1810	my $class = shift;
		1811	bless AnyEvent->condvar (@_), $class
		1812	}
		1813
		1814	package AnyEvent::CondVar::Base;
		1815
		1816	#use overload
		1817	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1818	# fallback => 1;
		1819
		1820	# save 300+ kilobytes by dirtily hardcoding overloading
		1821	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1822	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1823	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1824	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1825
		1826	our $WAITING;
		1827
		1828	sub _send {
		1829	# nop
		1830	}
		1831
		1832	sub _wait {
		1833	AnyEvent->_poll until $_[0]{_ae_sent};
		1834	}
		1835
		1836	sub send {
		1837	my $cv = shift;
		1838	$cv->{_ae_sent} = [@_];
		1839	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1840	$cv->_send;
		1841	}
		1842
		1843	sub croak {
		1844	$_[0]{_ae_croak} = $_[1];
		1845	$_[0]->send;
		1846	}
		1847
		1848	sub ready {
		1849	$_[0]{_ae_sent}
		1850	}
		1851
		1852	sub recv {
		1853	unless ($_[0]{_ae_sent}) {
		1854	$WAITING
		1855	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1856
		1857	local $WAITING = 1;
		1858	$_[0]->_wait;
		1859	}
		1860
		1861	$_[0]{_ae_croak}
		1862	and Carp::croak $_[0]{_ae_croak};
		1863
		1864	wantarray
		1865	? @{ $_[0]{_ae_sent} }
		1866	: $_[0]{_ae_sent}[0]
		1867	}
		1868
		1869	sub cb {
		1870	my $cv = shift;
		1871
		1872	@_
		1873	and $cv->{_ae_cb} = shift
		1874	and $cv->{_ae_sent}
		1875	and (delete $cv->{_ae_cb})->($cv);
		1876
		1877	$cv->{_ae_cb}
		1878	}
		1879
		1880	sub begin {
		1881	++$_[0]{_ae_counter};
		1882	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1883	}
		1884
		1885	sub end {
		1886	return if --$_[0]{_ae_counter};
		1887	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1888	}
		1889
		1890	# undocumented/compatibility with pre-3.4
		1891	*broadcast = \&send;
		1892	*wait = \&recv;
		1893
		1894	=head1 ERROR AND EXCEPTION HANDLING
		1895
		1896	In general, AnyEvent does not do any error handling - it relies on the
		1897	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1898	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1899	checking of all AnyEvent methods, however, which is highly useful during
		1900	development.
		1901
		1902	As for exception handling (i.e. runtime errors and exceptions thrown while
		1903	executing a callback), this is not only highly event-loop specific, but
		1904	also not in any way wrapped by this module, as this is the job of the main
		1905	program.
		1906
		1907	The pure perl event loop simply re-throws the exception (usually
		1908	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1909	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1910	so on.
		1911
		1912	=head1 ENVIRONMENT VARIABLES
		1913
		1914	The following environment variables are used by this module or its
		1915	submodules.
		1916
		1917	Note that AnyEvent will remove I<all> environment variables starting with
		1918	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1919	enabled.
		1920
		1921	=over 4
		1922
		1923	=item C<PERL_ANYEVENT_VERBOSE>
		1924
		1925	By default, AnyEvent will be completely silent except in fatal
		1926	conditions. You can set this environment variable to make AnyEvent more
		1927	talkative.
		1928
		1929	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1930	conditions, such as not being able to load the event model specified by
		1931	C<PERL_ANYEVENT_MODEL>.
		1932
		1933	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1934	model it chooses.
		1935
		1936	When set to C<8> or higher, then AnyEvent will report extra information on
		1937	which optional modules it loads and how it implements certain features.
		1938
		1939	=item C<PERL_ANYEVENT_STRICT>
		1940
		1941	AnyEvent does not do much argument checking by default, as thorough
		1942	argument checking is very costly. Setting this variable to a true value
		1943	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1944	check the arguments passed to most method calls. If it finds any problems,
		1945	it will croak.
		1946
		1947	In other words, enables "strict" mode.
		1948
		1949	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		1950	>>, it is definitely recommended to keep it off in production. Keeping
		1951	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1952	can be very useful, however.
		1953
		1954	=item C<PERL_ANYEVENT_MODEL>
		1955
		1956	This can be used to specify the event model to be used by AnyEvent, before
		1957	auto detection and -probing kicks in.
		1958
		1959	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		1960	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		1961	resulting module name is loaded and - if the load was successful - used as
		1962	event model backend. If it fails to load then AnyEvent will proceed with
		1963	auto detection and -probing.
		1964
		1965	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		1966	nothing gets prepended and the module name is used as-is (hint: C<::> at
		1967	the end of a string designates a module name and quotes it appropriately).
		1968
		1969	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		1970	could start your program like this:
		1971
		1972	PERL_ANYEVENT_MODEL=Perl perl ...
		1973
		1974	=item C<PERL_ANYEVENT_PROTOCOLS>
		1975
		1976	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1977	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1978	of auto probing).
		1979
		1980	Must be set to a comma-separated list of protocols or address families,
		1981	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1982	used, and preference will be given to protocols mentioned earlier in the
		1983	list.
		1984
		1985	This variable can effectively be used for denial-of-service attacks
		1986	against local programs (e.g. when setuid), although the impact is likely
		1987	small, as the program has to handle conenction and other failures anyways.
		1988
		1989	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1990	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1991	- only support IPv4, never try to resolve or contact IPv6
		1992	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1993	IPv6, but prefer IPv6 over IPv4.
		1994
		1995	=item C<PERL_ANYEVENT_EDNS0>
		1996
		1997	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1998	for DNS. This extension is generally useful to reduce DNS traffic, but
		1999	some (broken) firewalls drop such DNS packets, which is why it is off by
		2000	default.
		2001
		2002	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2003	EDNS0 in its DNS requests.
		2004
		2005	=item C<PERL_ANYEVENT_MAX_FORKS>
		2006
		2007	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2008	will create in parallel.
		2009
		2010	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2011
		2012	The default value for the C<max_outstanding> parameter for the default DNS
		2013	resolver - this is the maximum number of parallel DNS requests that are
		2014	sent to the DNS server.
		2015
		2016	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2017
		2018	The file to use instead of F</etc/resolv.conf> (or OS-specific
		2019	configuration) in the default resolver. When set to the empty string, no
		2020	default config will be used.
		2021
		2022	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2023
		2024	When neither C<ca_file> nor C<ca_path> was specified during
		2025	L<AnyEvent::TLS> context creation, and either of these environment
		2026	variables exist, they will be used to specify CA certificate locations
		2027	instead of a system-dependent default.
		2028
		2029	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2030
		2031	When these are set to C<1>, then the respective modules are not
		2032	loaded. Mostly good for testing AnyEvent itself.
133		2033
134	=back	2034	=back
135		2035
136	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	2036	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		2037
		2038	This is an advanced topic that you do not normally need to use AnyEvent in
		2039	a module. This section is only of use to event loop authors who want to
		2040	provide AnyEvent compatibility.
137		2041
138	If you need to support another event library which isn't directly	2042	If you need to support another event library which isn't directly
139	supported by AnyEvent, you can supply your own interface to it by	2043	supported by AnyEvent, you can supply your own interface to it by
140	pushing, before the first watcher gets created, the package name of	2044	pushing, before the first watcher gets created, the package name of
141	the event module and the package name of the interface to use onto	2045	the event module and the package name of the interface to use onto
142	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	2046	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
143	AnyEvent.	2047	AnyEvent, so it is reasonably cheap.
144		2048
145	Example:	2049	Example:
146		2050
147	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	2051	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
148		2052
149	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	2053	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
150	package/class when it finds the C<urxvt> package/module is loaded. When	2054	package/class when it finds the C<urxvt> package/module is already loaded.
		2055
151	AnyEvent is loaded and asked to find a suitable event model, it will	2056	When AnyEvent is loaded and asked to find a suitable event model, it
152	first check for the presence of urxvt.	2057	will first check for the presence of urxvt by trying to C<use> the
		2058	C<urxvt::anyevent> module.
153		2059
154	The class should prove implementations for all watcher types (see	2060	The class should provide implementations for all watcher types. See
155	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	2061	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
156	(Source code) and so on for actual examples, use C<perldoc -m	2062	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
157	AnyEvent::Impl::Glib> to see the sources).	2063	see the sources.
158		2064
		2065	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2066	provide suitable (hopefully) replacements.
		2067
159	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	2068	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
160	uses the above line as-is. An interface isn't included in AnyEvent	2069	terminal emulator uses the above line as-is. An interface isn't included
161	because it doesn't make sense outside the embedded interpreter inside	2070	in AnyEvent because it doesn't make sense outside the embedded interpreter
162	I<rxvt-unicode>, and it is updated and maintained as part of the	2071	inside I<rxvt-unicode>, and it is updated and maintained as part of the
163	I<rxvt-unicode> distribution.	2072	I<rxvt-unicode> distribution.
164		2073
165	I<rxvt-unicode> also cheats a bit by not providing blocking access to	2074	I<rxvt-unicode> also cheats a bit by not providing blocking access to
166	condition variables: code blocking while waiting for a condition will	2075	condition variables: code blocking while waiting for a condition will
167	C<die>. This still works with most modules/usages, and blocking calls must	2076	C<die>. This still works with most modules/usages, and blocking calls must
168	not be in an interactive appliation, so it makes sense.	2077	not be done in an interactive application, so it makes sense.
169		2078
170	=head1 ENVIRONMENT VARIABLES
171
172	The following environment variables are used by this module:
173
174	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
175	model gets used.
176
177	=head1 EXAMPLE	2079	=head1 EXAMPLE PROGRAM
178		2080
179	The following program uses an io watcher to read data from stdin, a timer	2081	The following program uses an I/O watcher to read data from STDIN, a timer
180	to display a message once per second, and a condvar to exit the program	2082	to display a message once per second, and a condition variable to quit the
181	when the user enters quit:	2083	program when the user enters quit:
182		2084
183	use AnyEvent;	2085	use AnyEvent;
184		2086
185	my $cv = AnyEvent->condvar;	2087	my $cv = AnyEvent->condvar;
186		2088
187	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	2089	my $io_watcher = AnyEvent->io (
		2090	fh => \*STDIN,
		2091	poll => 'r',
		2092	cb => sub {
188	warn "io event <$_[0]>\n"; # will always output <r>	2093	warn "io event <$_[0]>\n"; # will always output <r>
189	chomp (my $input = <STDIN>); # read a line	2094	chomp (my $input = <STDIN>); # read a line
190	warn "read: $input\n"; # output what has been read	2095	warn "read: $input\n"; # output what has been read
191	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	2096	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2097	},
		2098	);
		2099
		2100	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2101	warn "timeout\n"; # print 'timeout' at most every second
192	});	2102	});
193		2103
194	my $time_watcher; # can only be used once
195
196	sub new_timer {
197	$timer = AnyEvent->timer (after => 1, cb => sub {
198	warn "timeout\n"; # print 'timeout' about every second
199	&new_timer; # and restart the time
200	});
201	}
202
203	new_timer; # create first timer
204
205	$cv->wait; # wait until user enters /^q/i	2104	$cv->recv; # wait until user enters /^q/i
206		2105
207	=head1 REAL-WORLD EXAMPLE	2106	=head1 REAL-WORLD EXAMPLE
208		2107
209	Consider the L<Net::FCP> module. It features (among others) the following	2108	Consider the L<Net::FCP> module. It features (among others) the following
210	API calls, which are to freenet what HTTP GET requests are to http:	2109	API calls, which are to freenet what HTTP GET requests are to http:
…		…
260	syswrite $txn->{fh}, $txn->{request}	2159	syswrite $txn->{fh}, $txn->{request}
261	or die "connection or write error";	2160	or die "connection or write error";
262	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	2161	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
263		2162
264	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	2163	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
265	result and signals any possible waiters that the request ahs finished:	2164	result and signals any possible waiters that the request has finished:
266		2165
267	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	2166	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
268		2167
269	if (end-of-file or data complete) {	2168	if (end-of-file or data complete) {
270	$txn->{result} = $txn->{buf};	2169	$txn->{result} = $txn->{buf};
271	$txn->{finished}->broadcast;	2170	$txn->{finished}->send;
272	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	2171	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
273	}	2172	}
274		2173
275	The C<result> method, finally, just waits for the finished signal (if the	2174	The C<result> method, finally, just waits for the finished signal (if the
276	request was already finished, it doesn't wait, of course, and returns the	2175	request was already finished, it doesn't wait, of course, and returns the
277	data:	2176	data:
278		2177
279	$txn->{finished}->wait;	2178	$txn->{finished}->recv;
280	return $txn->{result};	2179	return $txn->{result};
281		2180
282	The actual code goes further and collects all errors (C<die>s, exceptions)	2181	The actual code goes further and collects all errors (C<die>s, exceptions)
283	that occured during request processing. The C<result> method detects	2182	that occurred during request processing. The C<result> method detects
284	wether an exception as thrown (it is stored inside the $txn object)	2183	whether an exception as thrown (it is stored inside the $txn object)
285	and just throws the exception, which means connection errors and other	2184	and just throws the exception, which means connection errors and other
286	problems get reported tot he code that tries to use the result, not in a	2185	problems get reported to the code that tries to use the result, not in a
287	random callback.	2186	random callback.
288		2187
289	All of this enables the following usage styles:	2188	All of this enables the following usage styles:
290		2189
291	1. Blocking:	2190	1. Blocking:
292		2191
293	my $data = $fcp->client_get ($url);	2192	my $data = $fcp->client_get ($url);
294		2193
295	2. Blocking, but parallelizing:	2194	2. Blocking, but running in parallel:
296		2195
297	my @datas = map $_->result,	2196	my @datas = map $_->result,
298	map $fcp->txn_client_get ($_),	2197	map $fcp->txn_client_get ($_),
299	@urls;	2198	@urls;
300		2199
301	Both blocking examples work without the module user having to know	2200	Both blocking examples work without the module user having to know
302	anything about events.	2201	anything about events.
303		2202
304	3a. Event-based in a main program, using any support Event module:	2203	3a. Event-based in a main program, using any supported event module:
305		2204
306	use Event;	2205	use EV;
307		2206
308	$fcp->txn_client_get ($url)->cb (sub {	2207	$fcp->txn_client_get ($url)->cb (sub {
309	my $txn = shift;	2208	my $txn = shift;
310	my $data = $txn->result;	2209	my $data = $txn->result;
311	...	2210	...
312	});	2211	});
313		2212
314	Event::loop;	2213	EV::loop;
315		2214
316	3b. The module user could use AnyEvent, too:	2215	3b. The module user could use AnyEvent, too:
317		2216
318	use AnyEvent;	2217	use AnyEvent;
319		2218
320	my $quit = AnyEvent->condvar;	2219	my $quit = AnyEvent->condvar;
321		2220
322	$fcp->txn_client_get ($url)->cb (sub {	2221	$fcp->txn_client_get ($url)->cb (sub {
323	...	2222	...
324	$quit->broadcast;	2223	$quit->send;
325	});	2224	});
326		2225
327	$quit->wait;	2226	$quit->recv;
		2227
		2228
		2229	=head1 BENCHMARKS
		2230
		2231	To give you an idea of the performance and overheads that AnyEvent adds
		2232	over the event loops themselves and to give you an impression of the speed
		2233	of various event loops I prepared some benchmarks.
		2234
		2235	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2236
		2237	Here is a benchmark of various supported event models used natively and
		2238	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2239	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2240	which it is), lets them fire exactly once and destroys them again.
		2241
		2242	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2243	distribution. It uses the L<AE> interface, which makes a real difference
		2244	for the EV and Perl backends only.
		2245
		2246	=head3 Explanation of the columns
		2247
		2248	I<watcher> is the number of event watchers created/destroyed. Since
		2249	different event models feature vastly different performances, each event
		2250	loop was given a number of watchers so that overall runtime is acceptable
		2251	and similar between tested event loop (and keep them from crashing): Glib
		2252	would probably take thousands of years if asked to process the same number
		2253	of watchers as EV in this benchmark.
		2254
		2255	I<bytes> is the number of bytes (as measured by the resident set size,
		2256	RSS) consumed by each watcher. This method of measuring captures both C
		2257	and Perl-based overheads.
		2258
		2259	I<create> is the time, in microseconds (millionths of seconds), that it
		2260	takes to create a single watcher. The callback is a closure shared between
		2261	all watchers, to avoid adding memory overhead. That means closure creation
		2262	and memory usage is not included in the figures.
		2263
		2264	I<invoke> is the time, in microseconds, used to invoke a simple
		2265	callback. The callback simply counts down a Perl variable and after it was
		2266	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2267	signal the end of this phase.
		2268
		2269	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2270	watcher.
		2271
		2272	=head3 Results
		2273
		2274	name watchers bytes create invoke destroy comment
		2275	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2276	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2277	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2278	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2279	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2280	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2281	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2282	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2283	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2284	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2285	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2286	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2287
		2288	=head3 Discussion
		2289
		2290	The benchmark does I<not> measure scalability of the event loop very
		2291	well. For example, a select-based event loop (such as the pure perl one)
		2292	can never compete with an event loop that uses epoll when the number of
		2293	file descriptors grows high. In this benchmark, all events become ready at
		2294	the same time, so select/poll-based implementations get an unnatural speed
		2295	boost.
		2296
		2297	Also, note that the number of watchers usually has a nonlinear effect on
		2298	overall speed, that is, creating twice as many watchers doesn't take twice
		2299	the time - usually it takes longer. This puts event loops tested with a
		2300	higher number of watchers at a disadvantage.
		2301
		2302	To put the range of results into perspective, consider that on the
		2303	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2304	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2305	cycles with POE.
		2306
		2307	C<EV> is the sole leader regarding speed and memory use, which are both
		2308	maximal/minimal, respectively. When using the L<AE> API there is zero
		2309	overhead (when going through the AnyEvent API create is about 5-6 times
		2310	slower, with other times being equal, so still uses far less memory than
		2311	any other event loop and is still faster than Event natively).
		2312
		2313	The pure perl implementation is hit in a few sweet spots (both the
		2314	constant timeout and the use of a single fd hit optimisations in the perl
		2315	interpreter and the backend itself). Nevertheless this shows that it
		2316	adds very little overhead in itself. Like any select-based backend its
		2317	performance becomes really bad with lots of file descriptors (and few of
		2318	them active), of course, but this was not subject of this benchmark.
		2319
		2320	The C<Event> module has a relatively high setup and callback invocation
		2321	cost, but overall scores in on the third place.
		2322
		2323	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2324	when using its pure perl backend.
		2325
		2326	C<Glib>'s memory usage is quite a bit higher, but it features a
		2327	faster callback invocation and overall ends up in the same class as
		2328	C<Event>. However, Glib scales extremely badly, doubling the number of
		2329	watchers increases the processing time by more than a factor of four,
		2330	making it completely unusable when using larger numbers of watchers
		2331	(note that only a single file descriptor was used in the benchmark, so
		2332	inefficiencies of C<poll> do not account for this).
		2333
		2334	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2335	more than 2000 watchers is a big setback, however, as correctness takes
		2336	precedence over speed. Nevertheless, its performance is surprising, as the
		2337	file descriptor is dup()ed for each watcher. This shows that the dup()
		2338	employed by some adaptors is not a big performance issue (it does incur a
		2339	hidden memory cost inside the kernel which is not reflected in the figures
		2340	above).
		2341
		2342	C<POE>, regardless of underlying event loop (whether using its pure perl
		2343	select-based backend or the Event module, the POE-EV backend couldn't
		2344	be tested because it wasn't working) shows abysmal performance and
		2345	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2346	as EV watchers, and 10 times as much memory as Event (the high memory
		2347	requirements are caused by requiring a session for each watcher). Watcher
		2348	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2349	implementation.
		2350
		2351	The design of the POE adaptor class in AnyEvent can not really account
		2352	for the performance issues, though, as session creation overhead is
		2353	small compared to execution of the state machine, which is coded pretty
		2354	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2355	using multiple sessions is not a good approach, especially regarding
		2356	memory usage, even the author of POE could not come up with a faster
		2357	design).
		2358
		2359	=head3 Summary
		2360
		2361	=over 4
		2362
		2363	=item * Using EV through AnyEvent is faster than any other event loop
		2364	(even when used without AnyEvent), but most event loops have acceptable
		2365	performance with or without AnyEvent.
		2366
		2367	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2368	the actual event loop, only with extremely fast event loops such as EV
		2369	adds AnyEvent significant overhead.
		2370
		2371	=item * You should avoid POE like the plague if you want performance or
		2372	reasonable memory usage.
		2373
		2374	=back
		2375
		2376	=head2 BENCHMARKING THE LARGE SERVER CASE
		2377
		2378	This benchmark actually benchmarks the event loop itself. It works by
		2379	creating a number of "servers": each server consists of a socket pair, a
		2380	timeout watcher that gets reset on activity (but never fires), and an I/O
		2381	watcher waiting for input on one side of the socket. Each time the socket
		2382	watcher reads a byte it will write that byte to a random other "server".
		2383
		2384	The effect is that there will be a lot of I/O watchers, only part of which
		2385	are active at any one point (so there is a constant number of active
		2386	fds for each loop iteration, but which fds these are is random). The
		2387	timeout is reset each time something is read because that reflects how
		2388	most timeouts work (and puts extra pressure on the event loops).
		2389
		2390	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2391	(1%) are active. This mirrors the activity of large servers with many
		2392	connections, most of which are idle at any one point in time.
		2393
		2394	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2395	distribution. It uses the L<AE> interface, which makes a real difference
		2396	for the EV and Perl backends only.
		2397
		2398	=head3 Explanation of the columns
		2399
		2400	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2401	each server has a read and write socket end).
		2402
		2403	I<create> is the time it takes to create a socket pair (which is
		2404	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2405
		2406	I<request>, the most important value, is the time it takes to handle a
		2407	single "request", that is, reading the token from the pipe and forwarding
		2408	it to another server. This includes deleting the old timeout and creating
		2409	a new one that moves the timeout into the future.
		2410
		2411	=head3 Results
		2412
		2413	name sockets create request
		2414	EV 20000 62.66 7.99
		2415	Perl 20000 68.32 32.64
		2416	IOAsync 20000 174.06 101.15 epoll
		2417	IOAsync 20000 174.67 610.84 poll
		2418	Event 20000 202.69 242.91
		2419	Glib 20000 557.01 1689.52
		2420	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2421
		2422	=head3 Discussion
		2423
		2424	This benchmark I<does> measure scalability and overall performance of the
		2425	particular event loop.
		2426
		2427	EV is again fastest. Since it is using epoll on my system, the setup time
		2428	is relatively high, though.
		2429
		2430	Perl surprisingly comes second. It is much faster than the C-based event
		2431	loops Event and Glib.
		2432
		2433	IO::Async performs very well when using its epoll backend, and still quite
		2434	good compared to Glib when using its pure perl backend.
		2435
		2436	Event suffers from high setup time as well (look at its code and you will
		2437	understand why). Callback invocation also has a high overhead compared to
		2438	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2439	uses select or poll in basically all documented configurations.
		2440
		2441	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2442	clearly fails to perform with many filehandles or in busy servers.
		2443
		2444	POE is still completely out of the picture, taking over 1000 times as long
		2445	as EV, and over 100 times as long as the Perl implementation, even though
		2446	it uses a C-based event loop in this case.
		2447
		2448	=head3 Summary
		2449
		2450	=over 4
		2451
		2452	=item * The pure perl implementation performs extremely well.
		2453
		2454	=item * Avoid Glib or POE in large projects where performance matters.
		2455
		2456	=back
		2457
		2458	=head2 BENCHMARKING SMALL SERVERS
		2459
		2460	While event loops should scale (and select-based ones do not...) even to
		2461	large servers, most programs we (or I :) actually write have only a few
		2462	I/O watchers.
		2463
		2464	In this benchmark, I use the same benchmark program as in the large server
		2465	case, but it uses only eight "servers", of which three are active at any
		2466	one time. This should reflect performance for a small server relatively
		2467	well.
		2468
		2469	The columns are identical to the previous table.
		2470
		2471	=head3 Results
		2472
		2473	name sockets create request
		2474	EV 16 20.00 6.54
		2475	Perl 16 25.75 12.62
		2476	Event 16 81.27 35.86
		2477	Glib 16 32.63 15.48
		2478	POE 16 261.87 276.28 uses POE::Loop::Event
		2479
		2480	=head3 Discussion
		2481
		2482	The benchmark tries to test the performance of a typical small
		2483	server. While knowing how various event loops perform is interesting, keep
		2484	in mind that their overhead in this case is usually not as important, due
		2485	to the small absolute number of watchers (that is, you need efficiency and
		2486	speed most when you have lots of watchers, not when you only have a few of
		2487	them).
		2488
		2489	EV is again fastest.
		2490
		2491	Perl again comes second. It is noticeably faster than the C-based event
		2492	loops Event and Glib, although the difference is too small to really
		2493	matter.
		2494
		2495	POE also performs much better in this case, but is is still far behind the
		2496	others.
		2497
		2498	=head3 Summary
		2499
		2500	=over 4
		2501
		2502	=item * C-based event loops perform very well with small number of
		2503	watchers, as the management overhead dominates.
		2504
		2505	=back
		2506
		2507	=head2 THE IO::Lambda BENCHMARK
		2508
		2509	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2510	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2511	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2512	shouldn't come as a surprise to anybody). As such, the benchmark is
		2513	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2514	very optimal. But how would AnyEvent compare when used without the extra
		2515	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2516
		2517	The benchmark itself creates an echo-server, and then, for 500 times,
		2518	connects to the echo server, sends a line, waits for the reply, and then
		2519	creates the next connection. This is a rather bad benchmark, as it doesn't
		2520	test the efficiency of the framework or much non-blocking I/O, but it is a
		2521	benchmark nevertheless.
		2522
		2523	name runtime
		2524	Lambda/select 0.330 sec
		2525	+ optimized 0.122 sec
		2526	Lambda/AnyEvent 0.327 sec
		2527	+ optimized 0.138 sec
		2528	Raw sockets/select 0.077 sec
		2529	POE/select, components 0.662 sec
		2530	POE/select, raw sockets 0.226 sec
		2531	POE/select, optimized 0.404 sec
		2532
		2533	AnyEvent/select/nb 0.085 sec
		2534	AnyEvent/EV/nb 0.068 sec
		2535	+state machine 0.134 sec
		2536
		2537	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2538	benchmarks actually make blocking connects and use 100% blocking I/O,
		2539	defeating the purpose of an event-based solution. All of the newly
		2540	written AnyEvent benchmarks use 100% non-blocking connects (using
		2541	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2542	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2543	generally require a lot more bookkeeping and event handling than blocking
		2544	connects (which involve a single syscall only).
		2545
		2546	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2547	offers similar expressive power as POE and IO::Lambda, using conventional
		2548	Perl syntax. This means that both the echo server and the client are 100%
		2549	non-blocking, further placing it at a disadvantage.
		2550
		2551	As you can see, the AnyEvent + EV combination even beats the
		2552	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2553	backend easily beats IO::Lambda and POE.
		2554
		2555	And even the 100% non-blocking version written using the high-level (and
		2556	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2557	higher level ("unoptimised") abstractions by a large margin, even though
		2558	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2559
		2560	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2561	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2562	part of the IO::Lambda distribution and were used without any changes.
		2563
		2564
		2565	=head1 SIGNALS
		2566
		2567	AnyEvent currently installs handlers for these signals:
		2568
		2569	=over 4
		2570
		2571	=item SIGCHLD
		2572
		2573	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2574	emulation for event loops that do not support them natively. Also, some
		2575	event loops install a similar handler.
		2576
		2577	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2578	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2579
		2580	=item SIGPIPE
		2581
		2582	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2583	when AnyEvent gets loaded.
		2584
		2585	The rationale for this is that AnyEvent users usually do not really depend
		2586	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2587	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2588	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2589	some random socket.
		2590
		2591	The rationale for installing a no-op handler as opposed to ignoring it is
		2592	that this way, the handler will be restored to defaults on exec.
		2593
		2594	Feel free to install your own handler, or reset it to defaults.
		2595
		2596	=back
		2597
		2598	=cut
		2599
		2600	undef $SIG{CHLD}
		2601	if $SIG{CHLD} eq 'IGNORE';
		2602
		2603	$SIG{PIPE} = sub { }
		2604	unless defined $SIG{PIPE};
		2605
		2606	=head1 RECOMMENDED/OPTIONAL MODULES
		2607
		2608	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2609	its built-in modules) are required to use it.
		2610
		2611	That does not mean that AnyEvent won't take advantage of some additional
		2612	modules if they are installed.
		2613
		2614	This section explains which additional modules will be used, and how they
		2615	affect AnyEvent's operation.
		2616
		2617	=over 4
		2618
		2619	=item L<Async::Interrupt>
		2620
		2621	This slightly arcane module is used to implement fast signal handling: To
		2622	my knowledge, there is no way to do completely race-free and quick
		2623	signal handling in pure perl. To ensure that signals still get
		2624	delivered, AnyEvent will start an interval timer to wake up perl (and
		2625	catch the signals) with some delay (default is 10 seconds, look for
		2626	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2627
		2628	If this module is available, then it will be used to implement signal
		2629	catching, which means that signals will not be delayed, and the event loop
		2630	will not be interrupted regularly, which is more efficient (and good for
		2631	battery life on laptops).
		2632
		2633	This affects not just the pure-perl event loop, but also other event loops
		2634	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2635
		2636	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2637	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2638	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2639	does nothing for those backends.
		2640
		2641	=item L<EV>
		2642
		2643	This module isn't really "optional", as it is simply one of the backend
		2644	event loops that AnyEvent can use. However, it is simply the best event
		2645	loop available in terms of features, speed and stability: It supports
		2646	the AnyEvent API optimally, implements all the watcher types in XS, does
		2647	automatic timer adjustments even when no monotonic clock is available,
		2648	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2649	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2650	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2651
		2652	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2653	then this module will do nothing for you.
		2654
		2655	=item L<Guard>
		2656
		2657	The guard module, when used, will be used to implement
		2658	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2659	lot less memory), but otherwise doesn't affect guard operation much. It is
		2660	purely used for performance.
		2661
		2662	=item L<JSON> and L<JSON::XS>
		2663
		2664	One of these modules is required when you want to read or write JSON data
		2665	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2666	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2667
		2668	=item L<Net::SSLeay>
		2669
		2670	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2671	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2672	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2673
		2674	=item L<Time::HiRes>
		2675
		2676	This module is part of perl since release 5.008. It will be used when the
		2677	chosen event library does not come with a timing source of its own. The
		2678	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2679	try to use a monotonic clock for timing stability.
		2680
		2681	=back
		2682
		2683
		2684	=head1 FORK
		2685
		2686	Most event libraries are not fork-safe. The ones who are usually are
		2687	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2688	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2689	are usually badly thought-out hacks that are incompatible with fork in
		2690	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2691	continue event-processing in both parent and child (or both, if you know
		2692	what you are doing).
		2693
		2694	This means that, in general, you cannot fork and do event processing in
		2695	the child if the event library was initialised before the fork (which
		2696	usually happens when the first AnyEvent watcher is created, or the library
		2697	is loaded).
		2698
		2699	If you have to fork, you must either do so I<before> creating your first
		2700	watcher OR you must not use AnyEvent at all in the child OR you must do
		2701	something completely out of the scope of AnyEvent.
		2702
		2703	The problem of doing event processing in the parent I<and> the child
		2704	is much more complicated: even for backends that I<are> fork-aware or
		2705	fork-safe, their behaviour is not usually what you want: fork clones all
		2706	watchers, that means all timers, I/O watchers etc. are active in both
		2707	parent and child, which is almost never what you want. USing C<exec>
		2708	to start worker children from some kind of manage rprocess is usually
		2709	preferred, because it is much easier and cleaner, at the expense of having
		2710	to have another binary.
		2711
		2712
		2713	=head1 SECURITY CONSIDERATIONS
		2714
		2715	AnyEvent can be forced to load any event model via
		2716	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2717	execute arbitrary code or directly gain access, it can easily be used to
		2718	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2719	will not be active when the program uses a different event model than
		2720	specified in the variable.
		2721
		2722	You can make AnyEvent completely ignore this variable by deleting it
		2723	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2724
		2725	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2726
		2727	use AnyEvent;
		2728
		2729	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2730	be used to probe what backend is used and gain other information (which is
		2731	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2732	$ENV{PERL_ANYEVENT_STRICT}.
		2733
		2734	Note that AnyEvent will remove I<all> environment variables starting with
		2735	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2736	enabled.
		2737
		2738
		2739	=head1 BUGS
		2740
		2741	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2742	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2743	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2744	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2745	pronounced).
		2746
328		2747
329	=head1 SEE ALSO	2748	=head1 SEE ALSO
330		2749
331	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	2750	Tutorial/Introduction: L<AnyEvent::Intro>.
332		2751
333	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	2752	FAQ: L<AnyEvent::FAQ>.
334		2753
335	Nontrivial usage example: L<Net::FCP>.	2754	Utility functions: L<AnyEvent::Util>.
336		2755
337	=head1	2756	Event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>, L<Glib::EV>,
		2757	L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		2758
		2759	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2760	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2761	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2762	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
		2763
		2764	Non-blocking file handles, sockets, TCP clients and
		2765	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2766
		2767	Asynchronous DNS: L<AnyEvent::DNS>.
		2768
		2769	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2770
		2771	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2772	L<AnyEvent::HTTP>.
		2773
		2774
		2775	=head1 AUTHOR
		2776
		2777	Marc Lehmann <schmorp@schmorp.de>
		2778	http://home.schmorp.de/
338		2779
339	=cut	2780	=cut
340		2781
341	1	2782	1
342		2783

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