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Revision 1.354 by root, Thu Aug 11 21:26:39 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 utilizy 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	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1238	}
		1239
83	my @models = (	1240	my @models = (
84	[Coro::Event:: => AnyEvent::Impl::Coro::],	1241	[EV:: => AnyEvent::Impl::EV:: , 1],
		1242	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
		1243	# everything below here will not (normally) be autoprobed
		1244	# as the pure perl backend should work everywhere
		1245	# and is usually faster
85	[Event:: => AnyEvent::Impl::Event::],	1246	[Event:: => AnyEvent::Impl::Event::, 1],
		1247	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1248	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1249	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1250	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1251	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1252	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1253	[Wx:: => AnyEvent::Impl::POE::],
86	[Glib:: => AnyEvent::Impl::Glib::],	1254	[Prima:: => AnyEvent::Impl::POE::],
		1255	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::],
		1256	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
87	[Tk:: => AnyEvent::Impl::Tk::],	1257	[FLTK:: => AnyEvent::Impl::FLTK::],
88	);	1258	);
89		1259
90	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	1260	our %method = map +($_ => 1),
		1261	qw(io timer time now now_update signal child idle condvar DESTROY);
91		1262
92	sub AUTOLOAD {	1263	our @post_detect;
93	$AUTOLOAD =~ s/.*://;
94		1264
95	$method{$AUTOLOAD}	1265	sub post_detect(&) {
96	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	1266	my ($cb) = @_;
97		1267
		1268	push @post_detect, $cb;
		1269
		1270	defined wantarray
		1271	? bless \$cb, "AnyEvent::Util::postdetect"
		1272	: ()
		1273	}
		1274
		1275	sub AnyEvent::Util::postdetect::DESTROY {
		1276	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1277	}
		1278
		1279	sub detect() {
		1280	# free some memory
		1281	*detect = sub () { $MODEL };
		1282
		1283	local $!; # for good measure
		1284	local $SIG{__DIE__};
		1285
		1286	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		1287	my $model = "AnyEvent::Impl::$1";
		1288	if (eval "require $model") {
		1289	$MODEL = $model;
		1290	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1291	} else {
		1292	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
		1293	}
		1294	}
		1295
		1296	# check for already loaded models
98	unless ($MODEL) {	1297	unless ($MODEL) {
99	# check for already loaded models
100	for (@REGISTRY, @models) {	1298	for (@REGISTRY, @models) {
101	my ($package, $model) = @$_;	1299	my ($package, $model) = @$_;
102	if (${"$package\::VERSION"} > 0) {	1300	if (${"$package\::VERSION"} > 0) {
103	if (eval "require $model") {	1301	if (eval "require $model") {
104	$MODEL = $model;	1302	$MODEL = $model;
105	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1303	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
106	last;	1304	last;
107	}	1305	}
108	}	1306	}
109	}	1307	}
110		1308
111	unless ($MODEL) {	1309	unless ($MODEL) {
112	# try to load a model	1310	# try to autoload a model
113
114	for (@REGISTRY, @models) {	1311	for (@REGISTRY, @models) {
115	my ($package, $model) = @$_;	1312	my ($package, $model, $autoload) = @$_;
		1313	if (
		1314	$autoload
		1315	and eval "require $package"
		1316	and ${"$package\::VERSION"} > 0
116	if (eval "require $model") {	1317	and eval "require $model"
		1318	) {
117	$MODEL = $model;	1319	$MODEL = $model;
118	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	1320	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
119	last;	1321	last;
120	}	1322	}
121	}	1323	}
122		1324
123	$MODEL	1325	$MODEL
124	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1326	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?\n";
125	}	1327	}
126	}	1328	}
127		1329
128	@ISA = $MODEL;	1330	@models = (); # free probe data
		1331
		1332	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1333	unshift @ISA, $MODEL;
		1334
		1335	# now nuke some methods that are overridden by the backend.
		1336	# SUPER is not allowed.
		1337	for (qw(time signal child idle)) {
		1338	undef &{"AnyEvent::Base::$_"}
		1339	if defined &{"$MODEL\::$_"};
		1340	}
		1341
		1342	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1343	eval { require AnyEvent::Strict };
		1344	warn "AnyEvent: cannot load AnyEvent::Strict: $@"
		1345	if $@ && $VERBOSE;
		1346	}
		1347
		1348	(shift @post_detect)->() while @post_detect;
		1349
		1350	*post_detect = sub(&) {
		1351	shift->();
		1352
		1353	undef
		1354	};
		1355
		1356	$MODEL
		1357	}
		1358
		1359	sub AUTOLOAD {
		1360	(my $func = $AUTOLOAD) =~ s/.*://;
		1361
		1362	$method{$func}
		1363	or Carp::croak "$func: not a valid AnyEvent class method";
		1364
		1365	detect;
129		1366
130	my $class = shift;	1367	my $class = shift;
131	$class->$AUTOLOAD (@_);	1368	$class->$func (@_);
132	}	1369	}
		1370
		1371	our $POSTPONE_W;
		1372	our @POSTPONE;
		1373
		1374	sub _postpone_exec {
		1375	undef $POSTPONE_W;
		1376	(pop @POSTPONE)->()
		1377	while @POSTPONE;
		1378	}
		1379
		1380	sub postpone(&) {
		1381	push @POSTPONE, shift;
		1382
		1383	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1384
		1385	()
		1386	}
		1387
		1388	# utility function to dup a filehandle. this is used by many backends
		1389	# to support binding more than one watcher per filehandle (they usually
		1390	# allow only one watcher per fd, so we dup it to get a different one).
		1391	sub _dupfh($$;$$) {
		1392	my ($poll, $fh, $r, $w) = @_;
		1393
		1394	# cygwin requires the fh mode to be matching, unix doesn't
		1395	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1396
		1397	open my $fh2, $mode, $fh
		1398	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1399
		1400	# we assume CLOEXEC is already set by perl in all important cases
		1401
		1402	($fh2, $rw)
		1403	}
		1404
		1405	=head1 SIMPLIFIED AE API
		1406
		1407	Starting with version 5.0, AnyEvent officially supports a second, much
		1408	simpler, API that is designed to reduce the calling, typing and memory
		1409	overhead by using function call syntax and a fixed number of parameters.
		1410
		1411	See the L<AE> manpage for details.
		1412
		1413	=cut
		1414
		1415	package AE;
		1416
		1417	our $VERSION = $AnyEvent::VERSION;
		1418
		1419	# fall back to the main API by default - backends and AnyEvent::Base
		1420	# implementations can overwrite these.
		1421
		1422	sub io($$$) {
		1423	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1424	}
		1425
		1426	sub timer($$$) {
		1427	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1428	}
		1429
		1430	sub signal($$) {
		1431	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1432	}
		1433
		1434	sub child($$) {
		1435	AnyEvent->child (pid => $_[0], cb => $_[1])
		1436	}
		1437
		1438	sub idle($) {
		1439	AnyEvent->idle (cb => $_[0])
		1440	}
		1441
		1442	sub cv(;&) {
		1443	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1444	}
		1445
		1446	sub now() {
		1447	AnyEvent->now
		1448	}
		1449
		1450	sub now_update() {
		1451	AnyEvent->now_update
		1452	}
		1453
		1454	sub time() {
		1455	AnyEvent->time
		1456	}
		1457
		1458	*postpone = \&AnyEvent::postpone;
		1459
		1460	package AnyEvent::Base;
		1461
		1462	# default implementations for many methods
		1463
		1464	sub time {
		1465	eval q{ # poor man's autoloading {}
		1466	# probe for availability of Time::HiRes
		1467	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1468	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1469	*AE::time = \&Time::HiRes::time;
		1470	# if (eval "use POSIX (); (POSIX::times())...
		1471	} else {
		1472	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1473	*AE::time = sub (){ time }; # epic fail
		1474	}
		1475
		1476	*time = sub { AE::time }; # different prototypes
		1477	};
		1478	die if $@;
		1479
		1480	&time
		1481	}
		1482
		1483	*now = \&time;
		1484
		1485	sub now_update { }
		1486
		1487	sub _poll {
		1488	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1489	}
		1490
		1491	# default implementation for ->condvar
		1492	# in fact, the default should not be overwritten
		1493
		1494	sub condvar {
		1495	eval q{ # poor man's autoloading {}
		1496	*condvar = sub {
		1497	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1498	};
		1499
		1500	*AE::cv = sub (;&) {
		1501	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1502	};
		1503	};
		1504	die if $@;
		1505
		1506	&condvar
		1507	}
		1508
		1509	# default implementation for ->signal
		1510
		1511	our $HAVE_ASYNC_INTERRUPT;
		1512
		1513	sub _have_async_interrupt() {
		1514	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1515	&& eval "use Async::Interrupt 1.02 (); 1")
		1516	unless defined $HAVE_ASYNC_INTERRUPT;
		1517
		1518	$HAVE_ASYNC_INTERRUPT
		1519	}
		1520
		1521	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1522	our (%SIG_ASY, %SIG_ASY_W);
		1523	our ($SIG_COUNT, $SIG_TW);
		1524
		1525	# install a dummy wakeup watcher to reduce signal catching latency
		1526	# used by Impls
		1527	sub _sig_add() {
		1528	unless ($SIG_COUNT++) {
		1529	# try to align timer on a full-second boundary, if possible
		1530	my $NOW = AE::now;
		1531
		1532	$SIG_TW = AE::timer
		1533	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1534	$MAX_SIGNAL_LATENCY,
		1535	sub { } # just for the PERL_ASYNC_CHECK
		1536	;
		1537	}
		1538	}
		1539
		1540	sub _sig_del {
		1541	undef $SIG_TW
		1542	unless --$SIG_COUNT;
		1543	}
		1544
		1545	our $_sig_name_init; $_sig_name_init = sub {
		1546	eval q{ # poor man's autoloading {}
		1547	undef $_sig_name_init;
		1548
		1549	if (_have_async_interrupt) {
		1550	*sig2num = \&Async::Interrupt::sig2num;
		1551	*sig2name = \&Async::Interrupt::sig2name;
		1552	} else {
		1553	require Config;
		1554
		1555	my %signame2num;
		1556	@signame2num{ split ' ', $Config::Config{sig_name} }
		1557	= split ' ', $Config::Config{sig_num};
		1558
		1559	my @signum2name;
		1560	@signum2name[values %signame2num] = keys %signame2num;
		1561
		1562	*sig2num = sub($) {
		1563	$_[0] > 0 ? shift : $signame2num{+shift}
		1564	};
		1565	*sig2name = sub ($) {
		1566	$_[0] > 0 ? $signum2name[+shift] : shift
		1567	};
		1568	}
		1569	};
		1570	die if $@;
		1571	};
		1572
		1573	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1574	sub sig2name($) { &$_sig_name_init; &sig2name }
		1575
		1576	sub signal {
		1577	eval q{ # poor man's autoloading {}
		1578	# probe for availability of Async::Interrupt
		1579	if (_have_async_interrupt) {
		1580	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1581
		1582	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1583	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1584
		1585	} else {
		1586	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1587
		1588	if (AnyEvent::WIN32) {
		1589	require AnyEvent::Util;
		1590
		1591	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1592	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1593	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1594	} else {
		1595	pipe $SIGPIPE_R, $SIGPIPE_W;
		1596	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1597	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1598
		1599	# not strictly required, as $^F is normally 2, but let's make sure...
		1600	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1601	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1602	}
		1603
		1604	$SIGPIPE_R
		1605	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1606
		1607	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1608	}
		1609
		1610	*signal = $HAVE_ASYNC_INTERRUPT
		1611	? sub {
		1612	my (undef, %arg) = @_;
		1613
		1614	# async::interrupt
		1615	my $signal = sig2num $arg{signal};
		1616	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1617
		1618	$SIG_ASY{$signal} ||= new Async::Interrupt
		1619	cb => sub { undef $SIG_EV{$signal} },
		1620	signal => $signal,
		1621	pipe => [$SIGPIPE_R->filenos],
		1622	pipe_autodrain => 0,
		1623	;
		1624
		1625	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1626	}
		1627	: sub {
		1628	my (undef, %arg) = @_;
		1629
		1630	# pure perl
		1631	my $signal = sig2name $arg{signal};
		1632	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1633
		1634	$SIG{$signal} ||= sub {
		1635	local $!;
		1636	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1637	undef $SIG_EV{$signal};
		1638	};
		1639
		1640	# can't do signal processing without introducing races in pure perl,
		1641	# so limit the signal latency.
		1642	_sig_add;
		1643
		1644	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1645	}
		1646	;
		1647
		1648	*AnyEvent::Base::signal::DESTROY = sub {
		1649	my ($signal, $cb) = @{$_[0]};
		1650
		1651	_sig_del;
		1652
		1653	delete $SIG_CB{$signal}{$cb};
		1654
		1655	$HAVE_ASYNC_INTERRUPT
		1656	? delete $SIG_ASY{$signal}
		1657	: # delete doesn't work with older perls - they then
		1658	# print weird messages, or just unconditionally exit
		1659	# instead of getting the default action.
		1660	undef $SIG{$signal}
		1661	unless keys %{ $SIG_CB{$signal} };
		1662	};
		1663
		1664	*_signal_exec = sub {
		1665	$HAVE_ASYNC_INTERRUPT
		1666	? $SIGPIPE_R->drain
		1667	: sysread $SIGPIPE_R, (my $dummy), 9;
		1668
		1669	while (%SIG_EV) {
		1670	for (keys %SIG_EV) {
		1671	delete $SIG_EV{$_};
		1672	$_->() for values %{ $SIG_CB{$_} || {} };
		1673	}
		1674	}
		1675	};
		1676	};
		1677	die if $@;
		1678
		1679	&signal
		1680	}
		1681
		1682	# default implementation for ->child
		1683
		1684	our %PID_CB;
		1685	our $CHLD_W;
		1686	our $CHLD_DELAY_W;
		1687
		1688	# used by many Impl's
		1689	sub _emit_childstatus($$) {
		1690	my (undef, $rpid, $rstatus) = @_;
		1691
		1692	$_->($rpid, $rstatus)
		1693	for values %{ $PID_CB{$rpid} || {} },
		1694	values %{ $PID_CB{0} || {} };
		1695	}
		1696
		1697	sub child {
		1698	eval q{ # poor man's autoloading {}
		1699	*_sigchld = sub {
		1700	my $pid;
		1701
		1702	AnyEvent->_emit_childstatus ($pid, $?)
		1703	while ($pid = waitpid -1, WNOHANG) > 0;
		1704	};
		1705
		1706	*child = sub {
		1707	my (undef, %arg) = @_;
		1708
		1709	my $pid = $arg{pid};
		1710	my $cb = $arg{cb};
		1711
		1712	$PID_CB{$pid}{$cb+0} = $cb;
		1713
		1714	unless ($CHLD_W) {
		1715	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1716	# child could be a zombie already, so make at least one round
		1717	&_sigchld;
		1718	}
		1719
		1720	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1721	};
		1722
		1723	*AnyEvent::Base::child::DESTROY = sub {
		1724	my ($pid, $icb) = @{$_[0]};
		1725
		1726	delete $PID_CB{$pid}{$icb};
		1727	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1728
		1729	undef $CHLD_W unless keys %PID_CB;
		1730	};
		1731	};
		1732	die if $@;
		1733
		1734	&child
		1735	}
		1736
		1737	# idle emulation is done by simply using a timer, regardless
		1738	# of whether the process is idle or not, and not letting
		1739	# the callback use more than 50% of the time.
		1740	sub idle {
		1741	eval q{ # poor man's autoloading {}
		1742	*idle = sub {
		1743	my (undef, %arg) = @_;
		1744
		1745	my ($cb, $w, $rcb) = $arg{cb};
		1746
		1747	$rcb = sub {
		1748	if ($cb) {
		1749	$w = _time;
		1750	&$cb;
		1751	$w = _time - $w;
		1752
		1753	# never use more then 50% of the time for the idle watcher,
		1754	# within some limits
		1755	$w = 0.0001 if $w < 0.0001;
		1756	$w = 5 if $w > 5;
		1757
		1758	$w = AE::timer $w, 0, $rcb;
		1759	} else {
		1760	# clean up...
		1761	undef $w;
		1762	undef $rcb;
		1763	}
		1764	};
		1765
		1766	$w = AE::timer 0.05, 0, $rcb;
		1767
		1768	bless \\$cb, "AnyEvent::Base::idle"
		1769	};
		1770
		1771	*AnyEvent::Base::idle::DESTROY = sub {
		1772	undef $${$_[0]};
		1773	};
		1774	};
		1775	die if $@;
		1776
		1777	&idle
		1778	}
		1779
		1780	package AnyEvent::CondVar;
		1781
		1782	our @ISA = AnyEvent::CondVar::Base::;
		1783
		1784	# only to be used for subclassing
		1785	sub new {
		1786	my $class = shift;
		1787	bless AnyEvent->condvar (@_), $class
		1788	}
		1789
		1790	package AnyEvent::CondVar::Base;
		1791
		1792	#use overload
		1793	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1794	# fallback => 1;
		1795
		1796	# save 300+ kilobytes by dirtily hardcoding overloading
		1797	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1798	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1799	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1800	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1801
		1802	our $WAITING;
		1803
		1804	sub _send {
		1805	# nop
		1806	}
		1807
		1808	sub _wait {
		1809	AnyEvent->_poll until $_[0]{_ae_sent};
		1810	}
		1811
		1812	sub send {
		1813	my $cv = shift;
		1814	$cv->{_ae_sent} = [@_];
		1815	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1816	$cv->_send;
		1817	}
		1818
		1819	sub croak {
		1820	$_[0]{_ae_croak} = $_[1];
		1821	$_[0]->send;
		1822	}
		1823
		1824	sub ready {
		1825	$_[0]{_ae_sent}
		1826	}
		1827
		1828	sub recv {
		1829	unless ($_[0]{_ae_sent}) {
		1830	$WAITING
		1831	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1832
		1833	local $WAITING = 1;
		1834	$_[0]->_wait;
		1835	}
		1836
		1837	$_[0]{_ae_croak}
		1838	and Carp::croak $_[0]{_ae_croak};
		1839
		1840	wantarray
		1841	? @{ $_[0]{_ae_sent} }
		1842	: $_[0]{_ae_sent}[0]
		1843	}
		1844
		1845	sub cb {
		1846	my $cv = shift;
		1847
		1848	@_
		1849	and $cv->{_ae_cb} = shift
		1850	and $cv->{_ae_sent}
		1851	and (delete $cv->{_ae_cb})->($cv);
		1852
		1853	$cv->{_ae_cb}
		1854	}
		1855
		1856	sub begin {
		1857	++$_[0]{_ae_counter};
		1858	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1859	}
		1860
		1861	sub end {
		1862	return if --$_[0]{_ae_counter};
		1863	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1864	}
		1865
		1866	# undocumented/compatibility with pre-3.4
		1867	*broadcast = \&send;
		1868	*wait = \&recv;
		1869
		1870	=head1 ERROR AND EXCEPTION HANDLING
		1871
		1872	In general, AnyEvent does not do any error handling - it relies on the
		1873	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1874	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1875	checking of all AnyEvent methods, however, which is highly useful during
		1876	development.
		1877
		1878	As for exception handling (i.e. runtime errors and exceptions thrown while
		1879	executing a callback), this is not only highly event-loop specific, but
		1880	also not in any way wrapped by this module, as this is the job of the main
		1881	program.
		1882
		1883	The pure perl event loop simply re-throws the exception (usually
		1884	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1885	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1886	so on.
		1887
		1888	=head1 ENVIRONMENT VARIABLES
		1889
		1890	The following environment variables are used by this module or its
		1891	submodules.
		1892
		1893	Note that AnyEvent will remove I<all> environment variables starting with
		1894	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1895	enabled.
		1896
		1897	=over 4
		1898
		1899	=item C<PERL_ANYEVENT_VERBOSE>
		1900
		1901	By default, AnyEvent will be completely silent except in fatal
		1902	conditions. You can set this environment variable to make AnyEvent more
		1903	talkative.
		1904
		1905	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1906	conditions, such as not being able to load the event model specified by
		1907	C<PERL_ANYEVENT_MODEL>.
		1908
		1909	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1910	model it chooses.
		1911
		1912	When set to C<8> or higher, then AnyEvent will report extra information on
		1913	which optional modules it loads and how it implements certain features.
		1914
		1915	=item C<PERL_ANYEVENT_STRICT>
		1916
		1917	AnyEvent does not do much argument checking by default, as thorough
		1918	argument checking is very costly. Setting this variable to a true value
		1919	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1920	check the arguments passed to most method calls. If it finds any problems,
		1921	it will croak.
		1922
		1923	In other words, enables "strict" mode.
		1924
		1925	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		1926	>>, it is definitely recommended to keep it off in production. Keeping
		1927	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1928	can be very useful, however.
		1929
		1930	=item C<PERL_ANYEVENT_MODEL>
		1931
		1932	This can be used to specify the event model to be used by AnyEvent, before
		1933	auto detection and -probing kicks in. It must be a string consisting
		1934	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1935	and the resulting module name is loaded and if the load was successful,
		1936	used as event model. If it fails to load AnyEvent will proceed with
		1937	auto detection and -probing.
		1938
		1939	This functionality might change in future versions.
		1940
		1941	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		1942	could start your program like this:
		1943
		1944	PERL_ANYEVENT_MODEL=Perl perl ...
		1945
		1946	=item C<PERL_ANYEVENT_PROTOCOLS>
		1947
		1948	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1949	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1950	of auto probing).
		1951
		1952	Must be set to a comma-separated list of protocols or address families,
		1953	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1954	used, and preference will be given to protocols mentioned earlier in the
		1955	list.
		1956
		1957	This variable can effectively be used for denial-of-service attacks
		1958	against local programs (e.g. when setuid), although the impact is likely
		1959	small, as the program has to handle conenction and other failures anyways.
		1960
		1961	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1962	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1963	- only support IPv4, never try to resolve or contact IPv6
		1964	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1965	IPv6, but prefer IPv6 over IPv4.
		1966
		1967	=item C<PERL_ANYEVENT_EDNS0>
		1968
		1969	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1970	for DNS. This extension is generally useful to reduce DNS traffic, but
		1971	some (broken) firewalls drop such DNS packets, which is why it is off by
		1972	default.
		1973
		1974	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1975	EDNS0 in its DNS requests.
		1976
		1977	=item C<PERL_ANYEVENT_MAX_FORKS>
		1978
		1979	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1980	will create in parallel.
		1981
		1982	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1983
		1984	The default value for the C<max_outstanding> parameter for the default DNS
		1985	resolver - this is the maximum number of parallel DNS requests that are
		1986	sent to the DNS server.
		1987
		1988	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1989
		1990	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1991	configuration) in the default resolver. When set to the empty string, no
		1992	default config will be used.
		1993
		1994	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1995
		1996	When neither C<ca_file> nor C<ca_path> was specified during
		1997	L<AnyEvent::TLS> context creation, and either of these environment
		1998	variables exist, they will be used to specify CA certificate locations
		1999	instead of a system-dependent default.
		2000
		2001	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2002
		2003	When these are set to C<1>, then the respective modules are not
		2004	loaded. Mostly good for testing AnyEvent itself.
133		2005
134	=back	2006	=back
135		2007
136	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	2008	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		2009
		2010	This is an advanced topic that you do not normally need to use AnyEvent in
		2011	a module. This section is only of use to event loop authors who want to
		2012	provide AnyEvent compatibility.
137		2013
138	If you need to support another event library which isn't directly	2014	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	2015	supported by AnyEvent, you can supply your own interface to it by
140	pushing, before the first watch gets created, the package name of	2016	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	2017	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	2018	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
143	AnyEvent.	2019	AnyEvent, so it is reasonably cheap.
144		2020
145	Example:	2021	Example:
146		2022
147	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	2023	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
148		2024
149	This tells AnyEvent to (literally) use the C<urxvt::anyevent::> module	2025	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
150	when it finds the C<urxvt> module is loaded. When AnyEvent is loaded and	2026	package/class when it finds the C<urxvt> package/module is already loaded.
151	requested to find a suitable event model, it will first check for the
152	urxvt module.
153		2027
		2028	When AnyEvent is loaded and asked to find a suitable event model, it
		2029	will first check for the presence of urxvt by trying to C<use> the
		2030	C<urxvt::anyevent> module.
		2031
		2032	The class should provide implementations for all watcher types. See
		2033	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		2034	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		2035	see the sources.
		2036
		2037	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2038	provide suitable (hopefully) replacements.
		2039
154	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt) uses	2040	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
155	the above line exactly. An interface isn't included in AnyEvent	2041	terminal emulator uses the above line as-is. An interface isn't included
156	because it doesn't make sense outside the embedded interpreter inside	2042	in AnyEvent because it doesn't make sense outside the embedded interpreter
157	I<rxvt-unicode>, and it is updated and maintained as part of the	2043	inside I<rxvt-unicode>, and it is updated and maintained as part of the
158	I<rxvt-unicode> distribution.	2044	I<rxvt-unicode> distribution.
159		2045
160	=head1 ENVIRONMENT VARIABLES	2046	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		2047	condition variables: code blocking while waiting for a condition will
		2048	C<die>. This still works with most modules/usages, and blocking calls must
		2049	not be done in an interactive application, so it makes sense.
161		2050
162	The following environment variables are used by this module:
163
164	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
165	model gets used.
166
167	=head1 EXAMPLE	2051	=head1 EXAMPLE PROGRAM
168		2052
169	The following program uses an io watcher to read data from stdin, a timer	2053	The following program uses an I/O watcher to read data from STDIN, a timer
170	to display a message once per second, and a condvar to exit the program	2054	to display a message once per second, and a condition variable to quit the
171	when the user enters quit:	2055	program when the user enters quit:
172		2056
173	use AnyEvent;	2057	use AnyEvent;
174		2058
175	my $cv = AnyEvent->condvar;	2059	my $cv = AnyEvent->condvar;
176		2060
177	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	2061	my $io_watcher = AnyEvent->io (
		2062	fh => \*STDIN,
		2063	poll => 'r',
		2064	cb => sub {
178	warn "io event <$_[0]>\n"; # will always output <r>	2065	warn "io event <$_[0]>\n"; # will always output <r>
179	chomp (my $input = <STDIN>); # read a line	2066	chomp (my $input = <STDIN>); # read a line
180	warn "read: $input\n"; # output what has been read	2067	warn "read: $input\n"; # output what has been read
181	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	2068	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2069	},
		2070	);
		2071
		2072	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2073	warn "timeout\n"; # print 'timeout' at most every second
182	});	2074	});
183		2075
184	my $time_watcher; # can only be used once
185
186	sub new_timer {
187	$timer = AnyEvent->timer (after => 1, cb => sub {
188	warn "timeout\n"; # print 'timeout' about every second
189	&new_timer; # and restart the time
190	});
191	}
192
193	new_timer; # create first timer
194
195	$cv->wait; # wait until user enters /^q/i	2076	$cv->recv; # wait until user enters /^q/i
196		2077
197	=head1 REAL-WORLD EXAMPLE	2078	=head1 REAL-WORLD EXAMPLE
198		2079
199	Consider the L<Net::FCP> module. It features (among others) the following	2080	Consider the L<Net::FCP> module. It features (among others) the following
200	API calls, which are to freenet what HTTP GET requests are to http:	2081	API calls, which are to freenet what HTTP GET requests are to http:
…		…
250	syswrite $txn->{fh}, $txn->{request}	2131	syswrite $txn->{fh}, $txn->{request}
251	or die "connection or write error";	2132	or die "connection or write error";
252	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	2133	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
253		2134
254	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	2135	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
255	result and signals any possible waiters that the request ahs finished:	2136	result and signals any possible waiters that the request has finished:
256		2137
257	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	2138	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
258		2139
259	if (end-of-file or data complete) {	2140	if (end-of-file or data complete) {
260	$txn->{result} = $txn->{buf};	2141	$txn->{result} = $txn->{buf};
261	$txn->{finished}->broadcast;	2142	$txn->{finished}->send;
262	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	2143	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
263	}	2144	}
264		2145
265	The C<result> method, finally, just waits for the finished signal (if the	2146	The C<result> method, finally, just waits for the finished signal (if the
266	request was already finished, it doesn't wait, of course, and returns the	2147	request was already finished, it doesn't wait, of course, and returns the
267	data:	2148	data:
268		2149
269	$txn->{finished}->wait;	2150	$txn->{finished}->recv;
270	return $txn->{result};	2151	return $txn->{result};
271		2152
272	The actual code goes further and collects all errors (C<die>s, exceptions)	2153	The actual code goes further and collects all errors (C<die>s, exceptions)
273	that occured during request processing. The C<result> method detects	2154	that occurred during request processing. The C<result> method detects
274	wether an exception as thrown (it is stored inside the $txn object)	2155	whether an exception as thrown (it is stored inside the $txn object)
275	and just throws the exception, which means connection errors and other	2156	and just throws the exception, which means connection errors and other
276	problems get reported tot he code that tries to use the result, not in a	2157	problems get reported to the code that tries to use the result, not in a
277	random callback.	2158	random callback.
278		2159
279	All of this enables the following usage styles:	2160	All of this enables the following usage styles:
280		2161
281	1. Blocking:	2162	1. Blocking:
282		2163
283	my $data = $fcp->client_get ($url);	2164	my $data = $fcp->client_get ($url);
284		2165
285	2. Blocking, but parallelizing:	2166	2. Blocking, but running in parallel:
286		2167
287	my @datas = map $_->result,	2168	my @datas = map $_->result,
288	map $fcp->txn_client_get ($_),	2169	map $fcp->txn_client_get ($_),
289	@urls;	2170	@urls;
290		2171
291	Both blocking examples work without the module user having to know	2172	Both blocking examples work without the module user having to know
292	anything about events.	2173	anything about events.
293		2174
294	3a. Event-based in a main program, using any support Event module:	2175	3a. Event-based in a main program, using any supported event module:
295		2176
296	use Event;	2177	use EV;
297		2178
298	$fcp->txn_client_get ($url)->cb (sub {	2179	$fcp->txn_client_get ($url)->cb (sub {
299	my $txn = shift;	2180	my $txn = shift;
300	my $data = $txn->result;	2181	my $data = $txn->result;
301	...	2182	...
302	});	2183	});
303		2184
304	Event::loop;	2185	EV::loop;
305		2186
306	3b. The module user could use AnyEvent, too:	2187	3b. The module user could use AnyEvent, too:
307		2188
308	use AnyEvent;	2189	use AnyEvent;
309		2190
310	my $quit = AnyEvent->condvar;	2191	my $quit = AnyEvent->condvar;
311		2192
312	$fcp->txn_client_get ($url)->cb (sub {	2193	$fcp->txn_client_get ($url)->cb (sub {
313	...	2194	...
314	$quit->broadcast;	2195	$quit->send;
315	});	2196	});
316		2197
317	$quit->wait;	2198	$quit->recv;
		2199
		2200
		2201	=head1 BENCHMARKS
		2202
		2203	To give you an idea of the performance and overheads that AnyEvent adds
		2204	over the event loops themselves and to give you an impression of the speed
		2205	of various event loops I prepared some benchmarks.
		2206
		2207	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2208
		2209	Here is a benchmark of various supported event models used natively and
		2210	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2211	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2212	which it is), lets them fire exactly once and destroys them again.
		2213
		2214	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2215	distribution. It uses the L<AE> interface, which makes a real difference
		2216	for the EV and Perl backends only.
		2217
		2218	=head3 Explanation of the columns
		2219
		2220	I<watcher> is the number of event watchers created/destroyed. Since
		2221	different event models feature vastly different performances, each event
		2222	loop was given a number of watchers so that overall runtime is acceptable
		2223	and similar between tested event loop (and keep them from crashing): Glib
		2224	would probably take thousands of years if asked to process the same number
		2225	of watchers as EV in this benchmark.
		2226
		2227	I<bytes> is the number of bytes (as measured by the resident set size,
		2228	RSS) consumed by each watcher. This method of measuring captures both C
		2229	and Perl-based overheads.
		2230
		2231	I<create> is the time, in microseconds (millionths of seconds), that it
		2232	takes to create a single watcher. The callback is a closure shared between
		2233	all watchers, to avoid adding memory overhead. That means closure creation
		2234	and memory usage is not included in the figures.
		2235
		2236	I<invoke> is the time, in microseconds, used to invoke a simple
		2237	callback. The callback simply counts down a Perl variable and after it was
		2238	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2239	signal the end of this phase.
		2240
		2241	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2242	watcher.
		2243
		2244	=head3 Results
		2245
		2246	name watchers bytes create invoke destroy comment
		2247	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2248	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2249	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2250	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2251	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2252	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2253	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2254	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2255	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2256	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2257	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2258	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2259
		2260	=head3 Discussion
		2261
		2262	The benchmark does I<not> measure scalability of the event loop very
		2263	well. For example, a select-based event loop (such as the pure perl one)
		2264	can never compete with an event loop that uses epoll when the number of
		2265	file descriptors grows high. In this benchmark, all events become ready at
		2266	the same time, so select/poll-based implementations get an unnatural speed
		2267	boost.
		2268
		2269	Also, note that the number of watchers usually has a nonlinear effect on
		2270	overall speed, that is, creating twice as many watchers doesn't take twice
		2271	the time - usually it takes longer. This puts event loops tested with a
		2272	higher number of watchers at a disadvantage.
		2273
		2274	To put the range of results into perspective, consider that on the
		2275	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2276	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2277	cycles with POE.
		2278
		2279	C<EV> is the sole leader regarding speed and memory use, which are both
		2280	maximal/minimal, respectively. When using the L<AE> API there is zero
		2281	overhead (when going through the AnyEvent API create is about 5-6 times
		2282	slower, with other times being equal, so still uses far less memory than
		2283	any other event loop and is still faster than Event natively).
		2284
		2285	The pure perl implementation is hit in a few sweet spots (both the
		2286	constant timeout and the use of a single fd hit optimisations in the perl
		2287	interpreter and the backend itself). Nevertheless this shows that it
		2288	adds very little overhead in itself. Like any select-based backend its
		2289	performance becomes really bad with lots of file descriptors (and few of
		2290	them active), of course, but this was not subject of this benchmark.
		2291
		2292	The C<Event> module has a relatively high setup and callback invocation
		2293	cost, but overall scores in on the third place.
		2294
		2295	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2296	when using its pure perl backend.
		2297
		2298	C<Glib>'s memory usage is quite a bit higher, but it features a
		2299	faster callback invocation and overall ends up in the same class as
		2300	C<Event>. However, Glib scales extremely badly, doubling the number of
		2301	watchers increases the processing time by more than a factor of four,
		2302	making it completely unusable when using larger numbers of watchers
		2303	(note that only a single file descriptor was used in the benchmark, so
		2304	inefficiencies of C<poll> do not account for this).
		2305
		2306	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2307	more than 2000 watchers is a big setback, however, as correctness takes
		2308	precedence over speed. Nevertheless, its performance is surprising, as the
		2309	file descriptor is dup()ed for each watcher. This shows that the dup()
		2310	employed by some adaptors is not a big performance issue (it does incur a
		2311	hidden memory cost inside the kernel which is not reflected in the figures
		2312	above).
		2313
		2314	C<POE>, regardless of underlying event loop (whether using its pure perl
		2315	select-based backend or the Event module, the POE-EV backend couldn't
		2316	be tested because it wasn't working) shows abysmal performance and
		2317	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2318	as EV watchers, and 10 times as much memory as Event (the high memory
		2319	requirements are caused by requiring a session for each watcher). Watcher
		2320	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2321	implementation.
		2322
		2323	The design of the POE adaptor class in AnyEvent can not really account
		2324	for the performance issues, though, as session creation overhead is
		2325	small compared to execution of the state machine, which is coded pretty
		2326	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2327	using multiple sessions is not a good approach, especially regarding
		2328	memory usage, even the author of POE could not come up with a faster
		2329	design).
		2330
		2331	=head3 Summary
		2332
		2333	=over 4
		2334
		2335	=item * Using EV through AnyEvent is faster than any other event loop
		2336	(even when used without AnyEvent), but most event loops have acceptable
		2337	performance with or without AnyEvent.
		2338
		2339	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2340	the actual event loop, only with extremely fast event loops such as EV
		2341	adds AnyEvent significant overhead.
		2342
		2343	=item * You should avoid POE like the plague if you want performance or
		2344	reasonable memory usage.
		2345
		2346	=back
		2347
		2348	=head2 BENCHMARKING THE LARGE SERVER CASE
		2349
		2350	This benchmark actually benchmarks the event loop itself. It works by
		2351	creating a number of "servers": each server consists of a socket pair, a
		2352	timeout watcher that gets reset on activity (but never fires), and an I/O
		2353	watcher waiting for input on one side of the socket. Each time the socket
		2354	watcher reads a byte it will write that byte to a random other "server".
		2355
		2356	The effect is that there will be a lot of I/O watchers, only part of which
		2357	are active at any one point (so there is a constant number of active
		2358	fds for each loop iteration, but which fds these are is random). The
		2359	timeout is reset each time something is read because that reflects how
		2360	most timeouts work (and puts extra pressure on the event loops).
		2361
		2362	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2363	(1%) are active. This mirrors the activity of large servers with many
		2364	connections, most of which are idle at any one point in time.
		2365
		2366	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2367	distribution. It uses the L<AE> interface, which makes a real difference
		2368	for the EV and Perl backends only.
		2369
		2370	=head3 Explanation of the columns
		2371
		2372	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2373	each server has a read and write socket end).
		2374
		2375	I<create> is the time it takes to create a socket pair (which is
		2376	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2377
		2378	I<request>, the most important value, is the time it takes to handle a
		2379	single "request", that is, reading the token from the pipe and forwarding
		2380	it to another server. This includes deleting the old timeout and creating
		2381	a new one that moves the timeout into the future.
		2382
		2383	=head3 Results
		2384
		2385	name sockets create request
		2386	EV 20000 62.66 7.99
		2387	Perl 20000 68.32 32.64
		2388	IOAsync 20000 174.06 101.15 epoll
		2389	IOAsync 20000 174.67 610.84 poll
		2390	Event 20000 202.69 242.91
		2391	Glib 20000 557.01 1689.52
		2392	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2393
		2394	=head3 Discussion
		2395
		2396	This benchmark I<does> measure scalability and overall performance of the
		2397	particular event loop.
		2398
		2399	EV is again fastest. Since it is using epoll on my system, the setup time
		2400	is relatively high, though.
		2401
		2402	Perl surprisingly comes second. It is much faster than the C-based event
		2403	loops Event and Glib.
		2404
		2405	IO::Async performs very well when using its epoll backend, and still quite
		2406	good compared to Glib when using its pure perl backend.
		2407
		2408	Event suffers from high setup time as well (look at its code and you will
		2409	understand why). Callback invocation also has a high overhead compared to
		2410	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2411	uses select or poll in basically all documented configurations.
		2412
		2413	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2414	clearly fails to perform with many filehandles or in busy servers.
		2415
		2416	POE is still completely out of the picture, taking over 1000 times as long
		2417	as EV, and over 100 times as long as the Perl implementation, even though
		2418	it uses a C-based event loop in this case.
		2419
		2420	=head3 Summary
		2421
		2422	=over 4
		2423
		2424	=item * The pure perl implementation performs extremely well.
		2425
		2426	=item * Avoid Glib or POE in large projects where performance matters.
		2427
		2428	=back
		2429
		2430	=head2 BENCHMARKING SMALL SERVERS
		2431
		2432	While event loops should scale (and select-based ones do not...) even to
		2433	large servers, most programs we (or I :) actually write have only a few
		2434	I/O watchers.
		2435
		2436	In this benchmark, I use the same benchmark program as in the large server
		2437	case, but it uses only eight "servers", of which three are active at any
		2438	one time. This should reflect performance for a small server relatively
		2439	well.
		2440
		2441	The columns are identical to the previous table.
		2442
		2443	=head3 Results
		2444
		2445	name sockets create request
		2446	EV 16 20.00 6.54
		2447	Perl 16 25.75 12.62
		2448	Event 16 81.27 35.86
		2449	Glib 16 32.63 15.48
		2450	POE 16 261.87 276.28 uses POE::Loop::Event
		2451
		2452	=head3 Discussion
		2453
		2454	The benchmark tries to test the performance of a typical small
		2455	server. While knowing how various event loops perform is interesting, keep
		2456	in mind that their overhead in this case is usually not as important, due
		2457	to the small absolute number of watchers (that is, you need efficiency and
		2458	speed most when you have lots of watchers, not when you only have a few of
		2459	them).
		2460
		2461	EV is again fastest.
		2462
		2463	Perl again comes second. It is noticeably faster than the C-based event
		2464	loops Event and Glib, although the difference is too small to really
		2465	matter.
		2466
		2467	POE also performs much better in this case, but is is still far behind the
		2468	others.
		2469
		2470	=head3 Summary
		2471
		2472	=over 4
		2473
		2474	=item * C-based event loops perform very well with small number of
		2475	watchers, as the management overhead dominates.
		2476
		2477	=back
		2478
		2479	=head2 THE IO::Lambda BENCHMARK
		2480
		2481	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2482	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2483	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2484	shouldn't come as a surprise to anybody). As such, the benchmark is
		2485	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2486	very optimal. But how would AnyEvent compare when used without the extra
		2487	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2488
		2489	The benchmark itself creates an echo-server, and then, for 500 times,
		2490	connects to the echo server, sends a line, waits for the reply, and then
		2491	creates the next connection. This is a rather bad benchmark, as it doesn't
		2492	test the efficiency of the framework or much non-blocking I/O, but it is a
		2493	benchmark nevertheless.
		2494
		2495	name runtime
		2496	Lambda/select 0.330 sec
		2497	+ optimized 0.122 sec
		2498	Lambda/AnyEvent 0.327 sec
		2499	+ optimized 0.138 sec
		2500	Raw sockets/select 0.077 sec
		2501	POE/select, components 0.662 sec
		2502	POE/select, raw sockets 0.226 sec
		2503	POE/select, optimized 0.404 sec
		2504
		2505	AnyEvent/select/nb 0.085 sec
		2506	AnyEvent/EV/nb 0.068 sec
		2507	+state machine 0.134 sec
		2508
		2509	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2510	benchmarks actually make blocking connects and use 100% blocking I/O,
		2511	defeating the purpose of an event-based solution. All of the newly
		2512	written AnyEvent benchmarks use 100% non-blocking connects (using
		2513	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2514	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2515	generally require a lot more bookkeeping and event handling than blocking
		2516	connects (which involve a single syscall only).
		2517
		2518	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2519	offers similar expressive power as POE and IO::Lambda, using conventional
		2520	Perl syntax. This means that both the echo server and the client are 100%
		2521	non-blocking, further placing it at a disadvantage.
		2522
		2523	As you can see, the AnyEvent + EV combination even beats the
		2524	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2525	backend easily beats IO::Lambda and POE.
		2526
		2527	And even the 100% non-blocking version written using the high-level (and
		2528	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2529	higher level ("unoptimised") abstractions by a large margin, even though
		2530	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2531
		2532	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2533	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2534	part of the IO::Lambda distribution and were used without any changes.
		2535
		2536
		2537	=head1 SIGNALS
		2538
		2539	AnyEvent currently installs handlers for these signals:
		2540
		2541	=over 4
		2542
		2543	=item SIGCHLD
		2544
		2545	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2546	emulation for event loops that do not support them natively. Also, some
		2547	event loops install a similar handler.
		2548
		2549	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2550	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2551
		2552	=item SIGPIPE
		2553
		2554	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2555	when AnyEvent gets loaded.
		2556
		2557	The rationale for this is that AnyEvent users usually do not really depend
		2558	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2559	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2560	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2561	some random socket.
		2562
		2563	The rationale for installing a no-op handler as opposed to ignoring it is
		2564	that this way, the handler will be restored to defaults on exec.
		2565
		2566	Feel free to install your own handler, or reset it to defaults.
		2567
		2568	=back
		2569
		2570	=cut
		2571
		2572	undef $SIG{CHLD}
		2573	if $SIG{CHLD} eq 'IGNORE';
		2574
		2575	$SIG{PIPE} = sub { }
		2576	unless defined $SIG{PIPE};
		2577
		2578	=head1 RECOMMENDED/OPTIONAL MODULES
		2579
		2580	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2581	its built-in modules) are required to use it.
		2582
		2583	That does not mean that AnyEvent won't take advantage of some additional
		2584	modules if they are installed.
		2585
		2586	This section explains which additional modules will be used, and how they
		2587	affect AnyEvent's operation.
		2588
		2589	=over 4
		2590
		2591	=item L<Async::Interrupt>
		2592
		2593	This slightly arcane module is used to implement fast signal handling: To
		2594	my knowledge, there is no way to do completely race-free and quick
		2595	signal handling in pure perl. To ensure that signals still get
		2596	delivered, AnyEvent will start an interval timer to wake up perl (and
		2597	catch the signals) with some delay (default is 10 seconds, look for
		2598	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2599
		2600	If this module is available, then it will be used to implement signal
		2601	catching, which means that signals will not be delayed, and the event loop
		2602	will not be interrupted regularly, which is more efficient (and good for
		2603	battery life on laptops).
		2604
		2605	This affects not just the pure-perl event loop, but also other event loops
		2606	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2607
		2608	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2609	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2610	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2611	does nothing for those backends.
		2612
		2613	=item L<EV>
		2614
		2615	This module isn't really "optional", as it is simply one of the backend
		2616	event loops that AnyEvent can use. However, it is simply the best event
		2617	loop available in terms of features, speed and stability: It supports
		2618	the AnyEvent API optimally, implements all the watcher types in XS, does
		2619	automatic timer adjustments even when no monotonic clock is available,
		2620	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2621	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2622	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2623
		2624	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2625	then this module will do nothing for you.
		2626
		2627	=item L<Guard>
		2628
		2629	The guard module, when used, will be used to implement
		2630	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2631	lot less memory), but otherwise doesn't affect guard operation much. It is
		2632	purely used for performance.
		2633
		2634	=item L<JSON> and L<JSON::XS>
		2635
		2636	One of these modules is required when you want to read or write JSON data
		2637	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2638	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2639
		2640	=item L<Net::SSLeay>
		2641
		2642	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2643	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2644	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2645
		2646	=item L<Time::HiRes>
		2647
		2648	This module is part of perl since release 5.008. It will be used when the
		2649	chosen event library does not come with a timing source of its own. The
		2650	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2651	try to use a monotonic clock for timing stability.
		2652
		2653	=back
		2654
		2655
		2656	=head1 FORK
		2657
		2658	Most event libraries are not fork-safe. The ones who are usually are
		2659	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2660	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2661	are usually badly thought-out hacks that are incompatible with fork in
		2662	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2663	continue event-processing in both parent and child (or both, if you know
		2664	what you are doing).
		2665
		2666	This means that, in general, you cannot fork and do event processing in
		2667	the child if the event library was initialised before the fork (which
		2668	usually happens when the first AnyEvent watcher is created, or the library
		2669	is loaded).
		2670
		2671	If you have to fork, you must either do so I<before> creating your first
		2672	watcher OR you must not use AnyEvent at all in the child OR you must do
		2673	something completely out of the scope of AnyEvent.
		2674
		2675	The problem of doing event processing in the parent I<and> the child
		2676	is much more complicated: even for backends that I<are> fork-aware or
		2677	fork-safe, their behaviour is not usually what you want: fork clones all
		2678	watchers, that means all timers, I/O watchers etc. are active in both
		2679	parent and child, which is almost never what you want. USing C<exec>
		2680	to start worker children from some kind of manage rprocess is usually
		2681	preferred, because it is much easier and cleaner, at the expense of having
		2682	to have another binary.
		2683
		2684
		2685	=head1 SECURITY CONSIDERATIONS
		2686
		2687	AnyEvent can be forced to load any event model via
		2688	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2689	execute arbitrary code or directly gain access, it can easily be used to
		2690	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2691	will not be active when the program uses a different event model than
		2692	specified in the variable.
		2693
		2694	You can make AnyEvent completely ignore this variable by deleting it
		2695	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2696
		2697	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2698
		2699	use AnyEvent;
		2700
		2701	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2702	be used to probe what backend is used and gain other information (which is
		2703	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2704	$ENV{PERL_ANYEVENT_STRICT}.
		2705
		2706	Note that AnyEvent will remove I<all> environment variables starting with
		2707	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2708	enabled.
		2709
		2710
		2711	=head1 BUGS
		2712
		2713	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2714	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2715	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2716	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2717	pronounced).
		2718
318		2719
319	=head1 SEE ALSO	2720	=head1 SEE ALSO
320		2721
321	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	2722	Tutorial/Introduction: L<AnyEvent::Intro>.
322		2723
323	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	2724	FAQ: L<AnyEvent::FAQ>.
324		2725
325	Nontrivial usage example: L<Net::FCP>.	2726	Utility functions: L<AnyEvent::Util>.
326		2727
327	=head1	2728	Event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>, L<Glib::EV>,
		2729	L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		2730
		2731	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2732	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2733	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2734	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
		2735
		2736	Non-blocking file handles, sockets, TCP clients and
		2737	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2738
		2739	Asynchronous DNS: L<AnyEvent::DNS>.
		2740
		2741	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2742
		2743	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2744	L<AnyEvent::HTTP>.
		2745
		2746
		2747	=head1 AUTHOR
		2748
		2749	Marc Lehmann <schmorp@schmorp.de>
		2750	http://home.schmorp.de/
328		2751
329	=cut	2752	=cut
330		2753
331	1	2754	1
332		2755

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