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Revision 1.13 by root, Thu Jul 20 08:26:00 2006 UTC vs.
Revision 1.341 by root, Sun Dec 5 11:41:45 2010 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 + IO::Async? No go. Tk + Event? No go. Again: if
		91	your module uses one of those, every user of your module has to use it,
		92	too. But if your module uses AnyEvent, it works transparently with all
		93	event models it supports (including stuff like IO::Async, as long as those
		94	use one of the supported event loops. It is easy to add new event loops
		95	to AnyEvent, too, 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::Impl::Perl>,
		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::Impl::Perl> 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
		148	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		149	explicitly and enjoy the high 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
28	my $w = AnyEvent->timer (after => $seconds, cb => sub {	179	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
29	...	180	# you can use $w here, for example to undef it
		181	undef $w;
30	});	182	});
31		183
32	* io and time watchers get canceled whenever $w is destroyed, so keep a copy	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.
33		187
34	* timers can only be used once and must be recreated for repeated	188	=head2 I/O WATCHERS
35	operation (limitation by Glib and Tk).
36		189
37	my $w = AnyEvent->condvar; # kind of main loop replacement	190	$w = AnyEvent->io (
38	$w->wait; # enters main loop till $condvar gets ->broadcast	191	fh => <filehandle_or_fileno>,
39	$w->broadcast; # wake up current and all future wait's	192	poll => <"r" or "w">,
		193	cb => <callback>,
		194	);
40		195
41	* condvars are used to give blocking behaviour when neccessary. Create	196	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
42	a condvar for any "request" or "event" your module might create, C<<	197	with the following mandatory key-value pairs as arguments:
43	->broadcast >> it when the event happens and provide a function that calls
44	C<< ->wait >> for it. See the examples below.
45		198
46	=head1 DESCRIPTION	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.
47		205
48	L<AnyEvent> provides an identical interface to multiple event loops. This	206	C<poll> must be a string that is either C<r> or C<w>, which creates a
49	allows module authors to utilise an event loop without forcing module	207	watcher waiting for "r"eadable or "w"ritable events, respectively.
50	users to use the same event loop (as only a single event loop can coexist
51	peacefully at any one time).
52		208
53	The interface itself is vaguely similar but not identical to the Event	209	C<cb> is the callback to invoke each time the file handle becomes ready.
54	module.
55		210
56	On the first call of any method, the module tries to detect the currently	211	Although the callback might get passed parameters, their value and
57	loaded event loop by probing wether any of the following modules is	212	presence is undefined and you cannot rely on them. Portable AnyEvent
58	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	213	callbacks cannot use arguments passed to I/O watcher callbacks.
59	used. If none is found, the module tries to load these modules in the	214
60	order given. The first one that could be successfully loaded will be	215	The I/O watcher might use the underlying file descriptor or a copy of it.
61	used. If still none could be found, it will issue an error.	216	You must not close a file handle as long as any watcher is active on the
		217	underlying file descriptor.
		218
		219	Some event loops issue spurious readiness notifications, so you should
		220	always use non-blocking calls when reading/writing from/to your file
		221	handles.
		222
		223	Example: wait for readability of STDIN, then read a line and disable the
		224	watcher.
		225
		226	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		227	chomp (my $input = <STDIN>);
		228	warn "read: $input\n";
		229	undef $w;
		230	});
		231
		232	=head2 TIME WATCHERS
		233
		234	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		235
		236	$w = AnyEvent->timer (
		237	after => <fractional_seconds>,
		238	interval => <fractional_seconds>,
		239	cb => <callback>,
		240	);
		241
		242	You can create a time watcher by calling the C<< AnyEvent->timer >>
		243	method with the following mandatory arguments:
		244
		245	C<after> specifies after how many seconds (fractional values are
		246	supported) the callback should be invoked. C<cb> is the callback to invoke
		247	in that case.
		248
		249	Although the callback might get passed parameters, their value and
		250	presence is undefined and you cannot rely on them. Portable AnyEvent
		251	callbacks cannot use arguments passed to time watcher callbacks.
		252
		253	The callback will normally be invoked only once. If you specify another
		254	parameter, C<interval>, as a strictly positive number (> 0), then the
		255	callback will be invoked regularly at that interval (in fractional
		256	seconds) after the first invocation. If C<interval> is specified with a
		257	false value, then it is treated as if it were not specified at all.
		258
		259	The callback will be rescheduled before invoking the callback, but no
		260	attempt is made to avoid timer drift in most backends, so the interval is
		261	only approximate.
		262
		263	Example: fire an event after 7.7 seconds.
		264
		265	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		266	warn "timeout\n";
		267	});
		268
		269	# to cancel the timer:
		270	undef $w;
		271
		272	Example 2: fire an event after 0.5 seconds, then roughly every second.
		273
		274	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		275	warn "timeout\n";
		276	};
		277
		278	=head3 TIMING ISSUES
		279
		280	There are two ways to handle timers: based on real time (relative, "fire
		281	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		282	o'clock").
		283
		284	While most event loops expect timers to specified in a relative way, they
		285	use absolute time internally. This makes a difference when your clock
		286	"jumps", for example, when ntp decides to set your clock backwards from
		287	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		288	fire "after a second" might actually take six years to finally fire.
		289
		290	AnyEvent cannot compensate for this. The only event loop that is conscious
		291	of these issues is L<EV>, which offers both relative (ev_timer, based
		292	on true relative time) and absolute (ev_periodic, based on wallclock time)
		293	timers.
		294
		295	AnyEvent always prefers relative timers, if available, matching the
		296	AnyEvent API.
		297
		298	AnyEvent has two additional methods that return the "current time":
62		299
63	=over 4	300	=over 4
64		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::Impl::Perl>) cache
		362	the current time for each loop iteration (see the discussion of L<<
		363	AnyEvent->now >>, 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 the latency and race problems
		488	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 implementation, 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
		882	=item Backends with special needs.
		883
		884	Qt requires the Qt::Application to be instantiated first, but will
		885	otherwise be picked up automatically. As long as the main program
		886	instantiates the application before any AnyEvent watchers are created,
		887	everything should just work.
		888
		889	AnyEvent::Impl::Qt based on Qt.
		890
		891	Support for IO::Async can only be partial, as it is too broken and
		892	architecturally limited to even support the AnyEvent API. It also
		893	is the only event loop that needs the loop to be set explicitly, so
		894	it can only be used by a main program knowing about AnyEvent. See
		895	L<AnyEvent::Impl::IOAsync> for the gory details.
		896
		897	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		898
		899	=item Event loops that are indirectly supported via other backends.
		900
		901	Some event loops can be supported via other modules:
		902
		903	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		904
		905	B<WxWidgets> has no support for watching file handles. However, you can
		906	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		907	polls 20 times per second, which was considered to be too horrible to even
		908	consider for AnyEvent.
		909
		910	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		911	backend, so it can be supported through POE.
		912
		913	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		914	load L<POE> when detecting them, in the hope that POE will pick them up,
		915	in which case everything will be automatic.
		916
		917	=back
		918
		919	=head1 GLOBAL VARIABLES AND FUNCTIONS
		920
		921	These are not normally required to use AnyEvent, but can be useful to
		922	write AnyEvent extension modules.
		923
		924	=over 4
		925
		926	=item $AnyEvent::MODEL
		927
		928	Contains C<undef> until the first watcher is being created, before the
		929	backend has been autodetected.
		930
		931	Afterwards it contains the event model that is being used, which is the
		932	name of the Perl class implementing the model. This class is usually one
		933	of the C<AnyEvent::Impl::xxx> modules, but can be any other class in the
		934	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
		935	will be C<urxvt::anyevent>).
		936
		937	=item AnyEvent::detect
		938
		939	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		940	if necessary. You should only call this function right before you would
		941	have created an AnyEvent watcher anyway, that is, as late as possible at
		942	runtime, and not e.g. during initialisation of your module.
		943
		944	If you need to do some initialisation before AnyEvent watchers are
		945	created, use C<post_detect>.
		946
		947	=item $guard = AnyEvent::post_detect { BLOCK }
		948
		949	Arranges for the code block to be executed as soon as the event model is
		950	autodetected (or immediately if that has already happened).
		951
		952	The block will be executed I<after> the actual backend has been detected
		953	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		954	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		955	other initialisations - see the sources of L<AnyEvent::Strict> or
		956	L<AnyEvent::AIO> to see how this is used.
		957
		958	The most common usage is to create some global watchers, without forcing
		959	event module detection too early, for example, L<AnyEvent::AIO> creates
		960	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		961	avoid autodetecting the event module at load time.
		962
		963	If called in scalar or list context, then it creates and returns an object
		964	that automatically removes the callback again when it is destroyed (or
		965	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		966	a case where this is useful.
		967
		968	Example: Create a watcher for the IO::AIO module and store it in
		969	C<$WATCHER>, but do so only do so after the event loop is initialised.
		970
		971	our WATCHER;
		972
		973	my $guard = AnyEvent::post_detect {
		974	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		975	};
		976
		977	# the ||= is important in case post_detect immediately runs the block,
		978	# as to not clobber the newly-created watcher. assigning both watcher and
		979	# post_detect guard to the same variable has the advantage of users being
		980	# able to just C<undef $WATCHER> if the watcher causes them grief.
		981
		982	$WATCHER ||= $guard;
		983
		984	=item @AnyEvent::post_detect
		985
		986	If there are any code references in this array (you can C<push> to it
		987	before or after loading AnyEvent), then they will be called directly
		988	after the event loop has been chosen.
		989
		990	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		991	if it is defined then the event loop has already been detected, and the
		992	array will be ignored.
		993
		994	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		995	it, as it takes care of these details.
		996
		997	This variable is mainly useful for modules that can do something useful
		998	when AnyEvent is used and thus want to know when it is initialised, but do
		999	not need to even load it by default. This array provides the means to hook
		1000	into AnyEvent passively, without loading it.
		1001
		1002	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		1003	together, you could put this into Coro (this is the actual code used by
		1004	Coro to accomplish this):
		1005
		1006	if (defined $AnyEvent::MODEL) {
		1007	# AnyEvent already initialised, so load Coro::AnyEvent
		1008	require Coro::AnyEvent;
		1009	} else {
		1010	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		1011	# as soon as it is
		1012	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		1013	}
		1014
		1015	=back
		1016
		1017	=head1 WHAT TO DO IN A MODULE
		1018
		1019	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		1020	freely, but you should not load a specific event module or rely on it.
		1021
		1022	Be careful when you create watchers in the module body - AnyEvent will
		1023	decide which event module to use as soon as the first method is called, so
		1024	by calling AnyEvent in your module body you force the user of your module
		1025	to load the event module first.
		1026
		1027	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1028	the C<< ->send >> method has been called on it already. This is
		1029	because it will stall the whole program, and the whole point of using
		1030	events is to stay interactive.
		1031
		1032	It is fine, however, to call C<< ->recv >> when the user of your module
		1033	requests it (i.e. if you create a http request object ad have a method
		1034	called C<results> that returns the results, it may call C<< ->recv >>
		1035	freely, as the user of your module knows what she is doing. Always).
		1036
		1037	=head1 WHAT TO DO IN THE MAIN PROGRAM
		1038
		1039	There will always be a single main program - the only place that should
		1040	dictate which event model to use.
		1041
		1042	If the program is not event-based, it need not do anything special, even
		1043	when it depends on a module that uses an AnyEvent. If the program itself
		1044	uses AnyEvent, but does not care which event loop is used, all it needs
		1045	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1046	available loop implementation.
		1047
		1048	If the main program relies on a specific event model - for example, in
		1049	Gtk2 programs you have to rely on the Glib module - you should load the
		1050	event module before loading AnyEvent or any module that uses it: generally
		1051	speaking, you should load it as early as possible. The reason is that
		1052	modules might create watchers when they are loaded, and AnyEvent will
		1053	decide on the event model to use as soon as it creates watchers, and it
		1054	might choose the wrong one unless you load the correct one yourself.
		1055
		1056	You can chose to use a pure-perl implementation by loading the
		1057	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		1058	everywhere, but letting AnyEvent chose the model is generally better.
		1059
		1060	=head2 MAINLOOP EMULATION
		1061
		1062	Sometimes (often for short test scripts, or even standalone programs who
		1063	only want to use AnyEvent), you do not want to run a specific event loop.
		1064
		1065	In that case, you can use a condition variable like this:
		1066
		1067	AnyEvent->condvar->recv;
		1068
		1069	This has the effect of entering the event loop and looping forever.
		1070
		1071	Note that usually your program has some exit condition, in which case
		1072	it is better to use the "traditional" approach of storing a condition
		1073	variable somewhere, waiting for it, and sending it when the program should
		1074	exit cleanly.
		1075
		1076
		1077	=head1 OTHER MODULES
		1078
		1079	The following is a non-exhaustive list of additional modules that use
		1080	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		1081	modules and other event loops in the same program. Some of the modules
		1082	come as part of AnyEvent, the others are available via CPAN.
		1083
		1084	=over 4
		1085
		1086	=item L<AnyEvent::Util>
		1087
		1088	Contains various utility functions that replace often-used blocking
		1089	functions such as C<inet_aton> with event/callback-based versions.
		1090
		1091	=item L<AnyEvent::Socket>
		1092
		1093	Provides various utility functions for (internet protocol) sockets,
		1094	addresses and name resolution. Also functions to create non-blocking tcp
		1095	connections or tcp servers, with IPv6 and SRV record support and more.
		1096
		1097	=item L<AnyEvent::Handle>
		1098
		1099	Provide read and write buffers, manages watchers for reads and writes,
		1100	supports raw and formatted I/O, I/O queued and fully transparent and
		1101	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1102
		1103	=item L<AnyEvent::DNS>
		1104
		1105	Provides rich asynchronous DNS resolver capabilities.
		1106
		1107	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1108
		1109	Implement event-based interfaces to the protocols of the same name (for
		1110	the curious, IGS is the International Go Server and FCP is the Freenet
		1111	Client Protocol).
		1112
		1113	=item L<AnyEvent::Handle::UDP>
		1114
		1115	Here be danger!
		1116
		1117	As Pauli would put it, "Not only is it not right, it's not even wrong!" -
		1118	there are so many things wrong with AnyEvent::Handle::UDP, most notably
		1119	its use of a stream-based API with a protocol that isn't streamable, that
		1120	the only way to improve it is to delete it.
		1121
		1122	It features data corruption (but typically only under load) and general
		1123	confusion. On top, the author is not only clueless about UDP but also
		1124	fact-resistant - some gems of his understanding: "connect doesn't work
		1125	with UDP", "UDP packets are not IP packets", "UDP only has datagrams, not
		1126	packets", "I don't need to implement proper error checking as UDP doesn't
		1127	support error checking" and so on - he doesn't even understand what's
		1128	wrong with his module when it is explained to him.
		1129
		1130	=item L<AnyEvent::DBI>
		1131
		1132	Executes L<DBI> requests asynchronously in a proxy process for you,
		1133	notifying you in an event-based way when the operation is finished.
		1134
		1135	=item L<AnyEvent::AIO>
		1136
		1137	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1138	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1139	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1140	file I/O, and much more.
		1141
		1142	=item L<AnyEvent::HTTPD>
		1143
		1144	A simple embedded webserver.
		1145
		1146	=item L<AnyEvent::FastPing>
		1147
		1148	The fastest ping in the west.
		1149
		1150	=item L<Coro>
		1151
		1152	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1153
		1154	=back
		1155
65	=cut	1156	=cut
66		1157
67	package AnyEvent;	1158	package AnyEvent;
68		1159
69	no warnings;	1160	# basically a tuned-down version of common::sense
70	use strict 'vars';	1161	sub common_sense {
		1162	# from common:.sense 3.3
		1163	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf3\x0f\xc0\xf0\xfc\x33\x00";
		1164	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1165	$^H |= 0x00000600;
		1166	}
		1167
		1168	BEGIN { AnyEvent::common_sense }
		1169
71	use Carp;	1170	use Carp ();
72		1171
73	our $VERSION = '1.02';	1172	our $VERSION = '5.29';
74	our $MODEL;	1173	our $MODEL;
75		1174
76	our $AUTOLOAD;	1175	our $AUTOLOAD;
77	our @ISA;	1176	our @ISA;
78		1177
79	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
80
81	our @REGISTRY;	1178	our @REGISTRY;
82		1179
		1180	our $VERBOSE;
		1181
		1182	BEGIN {
		1183	require "AnyEvent/constants.pl";
		1184
		1185	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1186
		1187	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1188	if ${^TAINT};
		1189
		1190	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1191
		1192	}
		1193
		1194	our $MAX_SIGNAL_LATENCY = 10;
		1195
		1196	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1197
		1198	{
		1199	my $idx;
		1200	$PROTOCOL{$_} = ++$idx
		1201	for reverse split /\s*,\s*/,
		1202	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1203	}
		1204
83	my @models = (	1205	my @models = (
84	[Coro::Event:: => AnyEvent::Impl::Coro::],	1206	[EV:: => AnyEvent::Impl::EV:: , 1],
		1207	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl:: , 1],
		1208	# everything below here will not (normally) be autoprobed
		1209	# as the pureperl backend should work everywhere
		1210	# and is usually faster
85	[Event:: => AnyEvent::Impl::Event::],	1211	[Event:: => AnyEvent::Impl::Event::, 1],
86	[Glib:: => AnyEvent::Impl::Glib::],	1212	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1213	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1214	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1215	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1216	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1217	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
87	[Tk:: => AnyEvent::Impl::Tk::],	1218	[Wx:: => AnyEvent::Impl::POE::],
		1219	[Prima:: => AnyEvent::Impl::POE::],
		1220	# IO::Async is just too broken - we would need workarounds for its
		1221	# byzantine signal and broken child handling, among others.
		1222	# IO::Async is rather hard to detect, as it doesn't have any
		1223	# obvious default class.
		1224	[IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1225	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1226	[IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1227	[AnyEvent::Impl::IOAsync:: => AnyEvent::Impl::IOAsync::], # requires special main program
88	);	1228	);
89		1229
90	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	1230	our %method = map +($_ => 1),
		1231	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
91		1232
92	sub AUTOLOAD {	1233	our @post_detect;
93	$AUTOLOAD =~ s/.*://;
94		1234
95	$method{$AUTOLOAD}	1235	sub post_detect(&) {
96	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	1236	my ($cb) = @_;
97		1237
		1238	push @post_detect, $cb;
		1239
		1240	defined wantarray
		1241	? bless \$cb, "AnyEvent::Util::postdetect"
		1242	: ()
		1243	}
		1244
		1245	sub AnyEvent::Util::postdetect::DESTROY {
		1246	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1247	}
		1248
		1249	sub detect() {
		1250	# free some memory
		1251	*detect = sub () { $MODEL };
		1252
		1253	local $!; # for good measure
		1254	local $SIG{__DIE__};
		1255
		1256	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		1257	my $model = "AnyEvent::Impl::$1";
		1258	if (eval "require $model") {
		1259	$MODEL = $model;
		1260	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1261	} else {
		1262	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
		1263	}
		1264	}
		1265
		1266	# check for already loaded models
98	unless ($MODEL) {	1267	unless ($MODEL) {
99	# check for already loaded models
100	for (@REGISTRY, @models) {	1268	for (@REGISTRY, @models) {
101	my ($package, $model) = @$_;	1269	my ($package, $model) = @$_;
102	if (${"$package\::VERSION"} > 0) {	1270	if (${"$package\::VERSION"} > 0) {
103	if (eval "require $model") {	1271	if (eval "require $model") {
104	$MODEL = $model;	1272	$MODEL = $model;
105	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1273	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
106	last;	1274	last;
107	}	1275	}
108	}	1276	}
109	}	1277	}
110		1278
111	unless ($MODEL) {	1279	unless ($MODEL) {
112	# try to load a model	1280	# try to autoload a model
113
114	for (@REGISTRY, @models) {	1281	for (@REGISTRY, @models) {
115	my ($package, $model) = @$_;	1282	my ($package, $model, $autoload) = @$_;
		1283	if (
		1284	$autoload
		1285	and eval "require $package"
		1286	and ${"$package\::VERSION"} > 0
116	if (eval "require $model") {	1287	and eval "require $model"
		1288	) {
117	$MODEL = $model;	1289	$MODEL = $model;
118	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	1290	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
119	last;	1291	last;
120	}	1292	}
121	}	1293	}
122		1294
123	$MODEL	1295	$MODEL
124	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1296	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?\n";
125	}	1297	}
126	}	1298	}
127		1299
128	@ISA = $MODEL;	1300	@models = (); # free probe data
		1301
		1302	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1303	unshift @ISA, $MODEL;
		1304
		1305	# now nuke some methods that are overridden by the backend.
		1306	# SUPER is not allowed.
		1307	for (qw(time signal child idle)) {
		1308	undef &{"AnyEvent::Base::$_"}
		1309	if defined &{"$MODEL\::$_"};
		1310	}
		1311
		1312	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1313	eval { require AnyEvent::Strict };
		1314	warn "AnyEvent: cannot load AnyEvent::Strict: $@"
		1315	if $@ && $VERBOSE;
		1316	}
		1317
		1318	(shift @post_detect)->() while @post_detect;
		1319
		1320	*post_detect = sub(&) {
		1321	shift->();
		1322
		1323	undef
		1324	};
		1325
		1326	$MODEL
		1327	}
		1328
		1329	sub AUTOLOAD {
		1330	(my $func = $AUTOLOAD) =~ s/.*://;
		1331
		1332	$method{$func}
		1333	or Carp::croak "$func: not a valid AnyEvent class method";
		1334
		1335	detect;
129		1336
130	my $class = shift;	1337	my $class = shift;
131	$class->$AUTOLOAD (@_);	1338	$class->$func (@_);
132	}	1339	}
		1340
		1341	# utility function to dup a filehandle. this is used by many backends
		1342	# to support binding more than one watcher per filehandle (they usually
		1343	# allow only one watcher per fd, so we dup it to get a different one).
		1344	sub _dupfh($$;$$) {
		1345	my ($poll, $fh, $r, $w) = @_;
		1346
		1347	# cygwin requires the fh mode to be matching, unix doesn't
		1348	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1349
		1350	open my $fh2, $mode, $fh
		1351	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1352
		1353	# we assume CLOEXEC is already set by perl in all important cases
		1354
		1355	($fh2, $rw)
		1356	}
		1357
		1358	=head1 SIMPLIFIED AE API
		1359
		1360	Starting with version 5.0, AnyEvent officially supports a second, much
		1361	simpler, API that is designed to reduce the calling, typing and memory
		1362	overhead by using function call syntax and a fixed number of parameters.
		1363
		1364	See the L<AE> manpage for details.
		1365
		1366	=cut
		1367
		1368	package AE;
		1369
		1370	our $VERSION = $AnyEvent::VERSION;
		1371
		1372	# fall back to the main API by default - backends and AnyEvent::Base
		1373	# implementations can overwrite these.
		1374
		1375	sub io($$$) {
		1376	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1377	}
		1378
		1379	sub timer($$$) {
		1380	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1381	}
		1382
		1383	sub signal($$) {
		1384	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1385	}
		1386
		1387	sub child($$) {
		1388	AnyEvent->child (pid => $_[0], cb => $_[1])
		1389	}
		1390
		1391	sub idle($) {
		1392	AnyEvent->idle (cb => $_[0])
		1393	}
		1394
		1395	sub cv(;&) {
		1396	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1397	}
		1398
		1399	sub now() {
		1400	AnyEvent->now
		1401	}
		1402
		1403	sub now_update() {
		1404	AnyEvent->now_update
		1405	}
		1406
		1407	sub time() {
		1408	AnyEvent->time
		1409	}
		1410
		1411	package AnyEvent::Base;
		1412
		1413	# default implementations for many methods
		1414
		1415	sub time {
		1416	eval q{ # poor man's autoloading {}
		1417	# probe for availability of Time::HiRes
		1418	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1419	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1420	*AE::time = \&Time::HiRes::time;
		1421	# if (eval "use POSIX (); (POSIX::times())...
		1422	} else {
		1423	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1424	*AE::time = sub (){ time }; # epic fail
		1425	}
		1426
		1427	*time = sub { AE::time }; # different prototypes
		1428	};
		1429	die if $@;
		1430
		1431	&time
		1432	}
		1433
		1434	*now = \&time;
		1435
		1436	sub now_update { }
		1437
		1438	# default implementation for ->condvar
		1439
		1440	sub condvar {
		1441	eval q{ # poor man's autoloading {}
		1442	*condvar = sub {
		1443	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1444	};
		1445
		1446	*AE::cv = sub (;&) {
		1447	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1448	};
		1449	};
		1450	die if $@;
		1451
		1452	&condvar
		1453	}
		1454
		1455	# default implementation for ->signal
		1456
		1457	our $HAVE_ASYNC_INTERRUPT;
		1458
		1459	sub _have_async_interrupt() {
		1460	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1461	&& eval "use Async::Interrupt 1.02 (); 1")
		1462	unless defined $HAVE_ASYNC_INTERRUPT;
		1463
		1464	$HAVE_ASYNC_INTERRUPT
		1465	}
		1466
		1467	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1468	our (%SIG_ASY, %SIG_ASY_W);
		1469	our ($SIG_COUNT, $SIG_TW);
		1470
		1471	# install a dummy wakeup watcher to reduce signal catching latency
		1472	# used by Impls
		1473	sub _sig_add() {
		1474	unless ($SIG_COUNT++) {
		1475	# try to align timer on a full-second boundary, if possible
		1476	my $NOW = AE::now;
		1477
		1478	$SIG_TW = AE::timer
		1479	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1480	$MAX_SIGNAL_LATENCY,
		1481	sub { } # just for the PERL_ASYNC_CHECK
		1482	;
		1483	}
		1484	}
		1485
		1486	sub _sig_del {
		1487	undef $SIG_TW
		1488	unless --$SIG_COUNT;
		1489	}
		1490
		1491	our $_sig_name_init; $_sig_name_init = sub {
		1492	eval q{ # poor man's autoloading {}
		1493	undef $_sig_name_init;
		1494
		1495	if (_have_async_interrupt) {
		1496	*sig2num = \&Async::Interrupt::sig2num;
		1497	*sig2name = \&Async::Interrupt::sig2name;
		1498	} else {
		1499	require Config;
		1500
		1501	my %signame2num;
		1502	@signame2num{ split ' ', $Config::Config{sig_name} }
		1503	= split ' ', $Config::Config{sig_num};
		1504
		1505	my @signum2name;
		1506	@signum2name[values %signame2num] = keys %signame2num;
		1507
		1508	*sig2num = sub($) {
		1509	$_[0] > 0 ? shift : $signame2num{+shift}
		1510	};
		1511	*sig2name = sub ($) {
		1512	$_[0] > 0 ? $signum2name[+shift] : shift
		1513	};
		1514	}
		1515	};
		1516	die if $@;
		1517	};
		1518
		1519	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1520	sub sig2name($) { &$_sig_name_init; &sig2name }
		1521
		1522	sub signal {
		1523	eval q{ # poor man's autoloading {}
		1524	# probe for availability of Async::Interrupt
		1525	if (_have_async_interrupt) {
		1526	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1527
		1528	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1529	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1530
		1531	} else {
		1532	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1533
		1534	if (AnyEvent::WIN32) {
		1535	require AnyEvent::Util;
		1536
		1537	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1538	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1539	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1540	} else {
		1541	pipe $SIGPIPE_R, $SIGPIPE_W;
		1542	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1543	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1544
		1545	# not strictly required, as $^F is normally 2, but let's make sure...
		1546	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1547	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1548	}
		1549
		1550	$SIGPIPE_R
		1551	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1552
		1553	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1554	}
		1555
		1556	*signal = $HAVE_ASYNC_INTERRUPT
		1557	? sub {
		1558	my (undef, %arg) = @_;
		1559
		1560	# async::interrupt
		1561	my $signal = sig2num $arg{signal};
		1562	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1563
		1564	$SIG_ASY{$signal} ||= new Async::Interrupt
		1565	cb => sub { undef $SIG_EV{$signal} },
		1566	signal => $signal,
		1567	pipe => [$SIGPIPE_R->filenos],
		1568	pipe_autodrain => 0,
		1569	;
		1570
		1571	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1572	}
		1573	: sub {
		1574	my (undef, %arg) = @_;
		1575
		1576	# pure perl
		1577	my $signal = sig2name $arg{signal};
		1578	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1579
		1580	$SIG{$signal} ||= sub {
		1581	local $!;
		1582	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1583	undef $SIG_EV{$signal};
		1584	};
		1585
		1586	# can't do signal processing without introducing races in pure perl,
		1587	# so limit the signal latency.
		1588	_sig_add;
		1589
		1590	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1591	}
		1592	;
		1593
		1594	*AnyEvent::Base::signal::DESTROY = sub {
		1595	my ($signal, $cb) = @{$_[0]};
		1596
		1597	_sig_del;
		1598
		1599	delete $SIG_CB{$signal}{$cb};
		1600
		1601	$HAVE_ASYNC_INTERRUPT
		1602	? delete $SIG_ASY{$signal}
		1603	: # delete doesn't work with older perls - they then
		1604	# print weird messages, or just unconditionally exit
		1605	# instead of getting the default action.
		1606	undef $SIG{$signal}
		1607	unless keys %{ $SIG_CB{$signal} };
		1608	};
		1609
		1610	*_signal_exec = sub {
		1611	$HAVE_ASYNC_INTERRUPT
		1612	? $SIGPIPE_R->drain
		1613	: sysread $SIGPIPE_R, (my $dummy), 9;
		1614
		1615	while (%SIG_EV) {
		1616	for (keys %SIG_EV) {
		1617	delete $SIG_EV{$_};
		1618	$_->() for values %{ $SIG_CB{$_} || {} };
		1619	}
		1620	}
		1621	};
		1622	};
		1623	die if $@;
		1624
		1625	&signal
		1626	}
		1627
		1628	# default implementation for ->child
		1629
		1630	our %PID_CB;
		1631	our $CHLD_W;
		1632	our $CHLD_DELAY_W;
		1633
		1634	# used by many Impl's
		1635	sub _emit_childstatus($$) {
		1636	my (undef, $rpid, $rstatus) = @_;
		1637
		1638	$_->($rpid, $rstatus)
		1639	for values %{ $PID_CB{$rpid} || {} },
		1640	values %{ $PID_CB{0} || {} };
		1641	}
		1642
		1643	sub child {
		1644	eval q{ # poor man's autoloading {}
		1645	*_sigchld = sub {
		1646	my $pid;
		1647
		1648	AnyEvent->_emit_childstatus ($pid, $?)
		1649	while ($pid = waitpid -1, WNOHANG) > 0;
		1650	};
		1651
		1652	*child = sub {
		1653	my (undef, %arg) = @_;
		1654
		1655	defined (my $pid = $arg{pid} + 0)
		1656	or Carp::croak "required option 'pid' is missing";
		1657
		1658	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1659
		1660	unless ($CHLD_W) {
		1661	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1662	# child could be a zombie already, so make at least one round
		1663	&_sigchld;
		1664	}
		1665
		1666	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
		1667	};
		1668
		1669	*AnyEvent::Base::child::DESTROY = sub {
		1670	my ($pid, $cb) = @{$_[0]};
		1671
		1672	delete $PID_CB{$pid}{$cb};
		1673	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1674
		1675	undef $CHLD_W unless keys %PID_CB;
		1676	};
		1677	};
		1678	die if $@;
		1679
		1680	&child
		1681	}
		1682
		1683	# idle emulation is done by simply using a timer, regardless
		1684	# of whether the process is idle or not, and not letting
		1685	# the callback use more than 50% of the time.
		1686	sub idle {
		1687	eval q{ # poor man's autoloading {}
		1688	*idle = sub {
		1689	my (undef, %arg) = @_;
		1690
		1691	my ($cb, $w, $rcb) = $arg{cb};
		1692
		1693	$rcb = sub {
		1694	if ($cb) {
		1695	$w = _time;
		1696	&$cb;
		1697	$w = _time - $w;
		1698
		1699	# never use more then 50% of the time for the idle watcher,
		1700	# within some limits
		1701	$w = 0.0001 if $w < 0.0001;
		1702	$w = 5 if $w > 5;
		1703
		1704	$w = AE::timer $w, 0, $rcb;
		1705	} else {
		1706	# clean up...
		1707	undef $w;
		1708	undef $rcb;
		1709	}
		1710	};
		1711
		1712	$w = AE::timer 0.05, 0, $rcb;
		1713
		1714	bless \\$cb, "AnyEvent::Base::idle"
		1715	};
		1716
		1717	*AnyEvent::Base::idle::DESTROY = sub {
		1718	undef $${$_[0]};
		1719	};
		1720	};
		1721	die if $@;
		1722
		1723	&idle
		1724	}
		1725
		1726	package AnyEvent::CondVar;
		1727
		1728	our @ISA = AnyEvent::CondVar::Base::;
		1729
		1730	# only to be used for subclassing
		1731	sub new {
		1732	my $class = shift;
		1733	bless AnyEvent->condvar (@_), $class
		1734	}
		1735
		1736	package AnyEvent::CondVar::Base;
		1737
		1738	#use overload
		1739	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1740	# fallback => 1;
		1741
		1742	# save 300+ kilobytes by dirtily hardcoding overloading
		1743	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1744	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1745	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1746	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1747
		1748	our $WAITING;
		1749
		1750	sub _send {
		1751	# nop
		1752	}
		1753
		1754	sub send {
		1755	my $cv = shift;
		1756	$cv->{_ae_sent} = [@_];
		1757	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1758	$cv->_send;
		1759	}
		1760
		1761	sub croak {
		1762	$_[0]{_ae_croak} = $_[1];
		1763	$_[0]->send;
		1764	}
		1765
		1766	sub ready {
		1767	$_[0]{_ae_sent}
		1768	}
		1769
		1770	sub _wait {
		1771	$WAITING
		1772	and !$_[0]{_ae_sent}
		1773	and Carp::croak "AnyEvent::CondVar: recursive blocking wait detected";
		1774
		1775	local $WAITING = 1;
		1776	AnyEvent->one_event while !$_[0]{_ae_sent};
		1777	}
		1778
		1779	sub recv {
		1780	$_[0]->_wait;
		1781
		1782	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1783	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1784	}
		1785
		1786	sub cb {
		1787	my $cv = shift;
		1788
		1789	@_
		1790	and $cv->{_ae_cb} = shift
		1791	and $cv->{_ae_sent}
		1792	and (delete $cv->{_ae_cb})->($cv);
		1793
		1794	$cv->{_ae_cb}
		1795	}
		1796
		1797	sub begin {
		1798	++$_[0]{_ae_counter};
		1799	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1800	}
		1801
		1802	sub end {
		1803	return if --$_[0]{_ae_counter};
		1804	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1805	}
		1806
		1807	# undocumented/compatibility with pre-3.4
		1808	*broadcast = \&send;
		1809	*wait = \&_wait;
		1810
		1811	=head1 ERROR AND EXCEPTION HANDLING
		1812
		1813	In general, AnyEvent does not do any error handling - it relies on the
		1814	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1815	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1816	checking of all AnyEvent methods, however, which is highly useful during
		1817	development.
		1818
		1819	As for exception handling (i.e. runtime errors and exceptions thrown while
		1820	executing a callback), this is not only highly event-loop specific, but
		1821	also not in any way wrapped by this module, as this is the job of the main
		1822	program.
		1823
		1824	The pure perl event loop simply re-throws the exception (usually
		1825	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1826	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1827	so on.
		1828
		1829	=head1 ENVIRONMENT VARIABLES
		1830
		1831	The following environment variables are used by this module or its
		1832	submodules.
		1833
		1834	Note that AnyEvent will remove I<all> environment variables starting with
		1835	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1836	enabled.
		1837
		1838	=over 4
		1839
		1840	=item C<PERL_ANYEVENT_VERBOSE>
		1841
		1842	By default, AnyEvent will be completely silent except in fatal
		1843	conditions. You can set this environment variable to make AnyEvent more
		1844	talkative.
		1845
		1846	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1847	conditions, such as not being able to load the event model specified by
		1848	C<PERL_ANYEVENT_MODEL>.
		1849
		1850	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1851	model it chooses.
		1852
		1853	When set to C<8> or higher, then AnyEvent will report extra information on
		1854	which optional modules it loads and how it implements certain features.
		1855
		1856	=item C<PERL_ANYEVENT_STRICT>
		1857
		1858	AnyEvent does not do much argument checking by default, as thorough
		1859	argument checking is very costly. Setting this variable to a true value
		1860	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1861	check the arguments passed to most method calls. If it finds any problems,
		1862	it will croak.
		1863
		1864	In other words, enables "strict" mode.
		1865
		1866	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		1867	>>, it is definitely recommended to keep it off in production. Keeping
		1868	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1869	can be very useful, however.
		1870
		1871	=item C<PERL_ANYEVENT_MODEL>
		1872
		1873	This can be used to specify the event model to be used by AnyEvent, before
		1874	auto detection and -probing kicks in. It must be a string consisting
		1875	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1876	and the resulting module name is loaded and if the load was successful,
		1877	used as event model. If it fails to load AnyEvent will proceed with
		1878	auto detection and -probing.
		1879
		1880	This functionality might change in future versions.
		1881
		1882	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1883	could start your program like this:
		1884
		1885	PERL_ANYEVENT_MODEL=Perl perl ...
		1886
		1887	=item C<PERL_ANYEVENT_PROTOCOLS>
		1888
		1889	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1890	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1891	of auto probing).
		1892
		1893	Must be set to a comma-separated list of protocols or address families,
		1894	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1895	used, and preference will be given to protocols mentioned earlier in the
		1896	list.
		1897
		1898	This variable can effectively be used for denial-of-service attacks
		1899	against local programs (e.g. when setuid), although the impact is likely
		1900	small, as the program has to handle conenction and other failures anyways.
		1901
		1902	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1903	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1904	- only support IPv4, never try to resolve or contact IPv6
		1905	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1906	IPv6, but prefer IPv6 over IPv4.
		1907
		1908	=item C<PERL_ANYEVENT_EDNS0>
		1909
		1910	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1911	for DNS. This extension is generally useful to reduce DNS traffic, but
		1912	some (broken) firewalls drop such DNS packets, which is why it is off by
		1913	default.
		1914
		1915	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1916	EDNS0 in its DNS requests.
		1917
		1918	=item C<PERL_ANYEVENT_MAX_FORKS>
		1919
		1920	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1921	will create in parallel.
		1922
		1923	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1924
		1925	The default value for the C<max_outstanding> parameter for the default DNS
		1926	resolver - this is the maximum number of parallel DNS requests that are
		1927	sent to the DNS server.
		1928
		1929	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1930
		1931	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1932	configuration) in the default resolver. When set to the empty string, no
		1933	default config will be used.
		1934
		1935	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1936
		1937	When neither C<ca_file> nor C<ca_path> was specified during
		1938	L<AnyEvent::TLS> context creation, and either of these environment
		1939	variables exist, they will be used to specify CA certificate locations
		1940	instead of a system-dependent default.
		1941
		1942	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		1943
		1944	When these are set to C<1>, then the respective modules are not
		1945	loaded. Mostly good for testing AnyEvent itself.
133		1946
134	=back	1947	=back
135		1948
136	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1949	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1950
		1951	This is an advanced topic that you do not normally need to use AnyEvent in
		1952	a module. This section is only of use to event loop authors who want to
		1953	provide AnyEvent compatibility.
137		1954
138	If you need to support another event library which isn't directly	1955	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	1956	supported by AnyEvent, you can supply your own interface to it by
140	pushing, before the first watcher gets created, the package name of	1957	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	1958	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	1959	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
143	AnyEvent.	1960	AnyEvent, so it is reasonably cheap.
144		1961
145	Example:	1962	Example:
146		1963
147	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1964	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
148		1965
149	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1966	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
150	package/class when it finds the C<urxvt> package/module is loaded. When	1967	package/class when it finds the C<urxvt> package/module is already loaded.
		1968
151	AnyEvent is loaded and asked to find a suitable event model, it will	1969	When AnyEvent is loaded and asked to find a suitable event model, it
152	first check for the presence of urxvt.	1970	will first check for the presence of urxvt by trying to C<use> the
		1971	C<urxvt::anyevent> module.
153		1972
154	The class should prove implementations for all watcher types (see	1973	The class should provide implementations for all watcher types. See
155	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1974	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
156	(Source code) and so on for actual examples, use C<perldoc -m	1975	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
157	AnyEvent::Impl::Glib> to see the sources).	1976	see the sources.
158		1977
		1978	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1979	provide suitable (hopefully) replacements.
		1980
159	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1981	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
160	uses the above line as-is. An interface isn't included in AnyEvent	1982	terminal emulator uses the above line as-is. An interface isn't included
161	because it doesn't make sense outside the embedded interpreter inside	1983	in AnyEvent because it doesn't make sense outside the embedded interpreter
162	I<rxvt-unicode>, and it is updated and maintained as part of the	1984	inside I<rxvt-unicode>, and it is updated and maintained as part of the
163	I<rxvt-unicode> distribution.	1985	I<rxvt-unicode> distribution.
164		1986
165	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1987	I<rxvt-unicode> also cheats a bit by not providing blocking access to
166	condition variables: code blocking while waiting for a condition will	1988	condition variables: code blocking while waiting for a condition will
167	C<die>. This still works with most modules/usages, and blocking calls must	1989	C<die>. This still works with most modules/usages, and blocking calls must
168	not be in an interactive appliation, so it makes sense.	1990	not be done in an interactive application, so it makes sense.
169		1991
170	=head1 ENVIRONMENT VARIABLES
171
172	The following environment variables are used by this module:
173
174	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
175	model gets used.
176
177	=head1 EXAMPLE	1992	=head1 EXAMPLE PROGRAM
178		1993
179	The following program uses an io watcher to read data from stdin, a timer	1994	The following program uses an I/O watcher to read data from STDIN, a timer
180	to display a message once per second, and a condvar to exit the program	1995	to display a message once per second, and a condition variable to quit the
181	when the user enters quit:	1996	program when the user enters quit:
182		1997
183	use AnyEvent;	1998	use AnyEvent;
184		1999
185	my $cv = AnyEvent->condvar;	2000	my $cv = AnyEvent->condvar;
186		2001
187	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	2002	my $io_watcher = AnyEvent->io (
		2003	fh => \*STDIN,
		2004	poll => 'r',
		2005	cb => sub {
188	warn "io event <$_[0]>\n"; # will always output <r>	2006	warn "io event <$_[0]>\n"; # will always output <r>
189	chomp (my $input = <STDIN>); # read a line	2007	chomp (my $input = <STDIN>); # read a line
190	warn "read: $input\n"; # output what has been read	2008	warn "read: $input\n"; # output what has been read
191	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	2009	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2010	},
		2011	);
		2012
		2013	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2014	warn "timeout\n"; # print 'timeout' at most every second
192	});	2015	});
193		2016
194	my $time_watcher; # can only be used once
195
196	sub new_timer {
197	$timer = AnyEvent->timer (after => 1, cb => sub {
198	warn "timeout\n"; # print 'timeout' about every second
199	&new_timer; # and restart the time
200	});
201	}
202
203	new_timer; # create first timer
204
205	$cv->wait; # wait until user enters /^q/i	2017	$cv->recv; # wait until user enters /^q/i
206		2018
207	=head1 REAL-WORLD EXAMPLE	2019	=head1 REAL-WORLD EXAMPLE
208		2020
209	Consider the L<Net::FCP> module. It features (among others) the following	2021	Consider the L<Net::FCP> module. It features (among others) the following
210	API calls, which are to freenet what HTTP GET requests are to http:	2022	API calls, which are to freenet what HTTP GET requests are to http:
…		…
260	syswrite $txn->{fh}, $txn->{request}	2072	syswrite $txn->{fh}, $txn->{request}
261	or die "connection or write error";	2073	or die "connection or write error";
262	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	2074	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
263		2075
264	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	2076	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
265	result and signals any possible waiters that the request ahs finished:	2077	result and signals any possible waiters that the request has finished:
266		2078
267	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	2079	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
268		2080
269	if (end-of-file or data complete) {	2081	if (end-of-file or data complete) {
270	$txn->{result} = $txn->{buf};	2082	$txn->{result} = $txn->{buf};
271	$txn->{finished}->broadcast;	2083	$txn->{finished}->send;
272	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	2084	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
273	}	2085	}
274		2086
275	The C<result> method, finally, just waits for the finished signal (if the	2087	The C<result> method, finally, just waits for the finished signal (if the
276	request was already finished, it doesn't wait, of course, and returns the	2088	request was already finished, it doesn't wait, of course, and returns the
277	data:	2089	data:
278		2090
279	$txn->{finished}->wait;	2091	$txn->{finished}->recv;
280	return $txn->{result};	2092	return $txn->{result};
281		2093
282	The actual code goes further and collects all errors (C<die>s, exceptions)	2094	The actual code goes further and collects all errors (C<die>s, exceptions)
283	that occured during request processing. The C<result> method detects	2095	that occurred during request processing. The C<result> method detects
284	wether an exception as thrown (it is stored inside the $txn object)	2096	whether an exception as thrown (it is stored inside the $txn object)
285	and just throws the exception, which means connection errors and other	2097	and just throws the exception, which means connection errors and other
286	problems get reported tot he code that tries to use the result, not in a	2098	problems get reported to the code that tries to use the result, not in a
287	random callback.	2099	random callback.
288		2100
289	All of this enables the following usage styles:	2101	All of this enables the following usage styles:
290		2102
291	1. Blocking:	2103	1. Blocking:
292		2104
293	my $data = $fcp->client_get ($url);	2105	my $data = $fcp->client_get ($url);
294		2106
295	2. Blocking, but parallelizing:	2107	2. Blocking, but running in parallel:
296		2108
297	my @datas = map $_->result,	2109	my @datas = map $_->result,
298	map $fcp->txn_client_get ($_),	2110	map $fcp->txn_client_get ($_),
299	@urls;	2111	@urls;
300		2112
301	Both blocking examples work without the module user having to know	2113	Both blocking examples work without the module user having to know
302	anything about events.	2114	anything about events.
303		2115
304	3a. Event-based in a main program, using any support Event module:	2116	3a. Event-based in a main program, using any supported event module:
305		2117
306	use Event;	2118	use EV;
307		2119
308	$fcp->txn_client_get ($url)->cb (sub {	2120	$fcp->txn_client_get ($url)->cb (sub {
309	my $txn = shift;	2121	my $txn = shift;
310	my $data = $txn->result;	2122	my $data = $txn->result;
311	...	2123	...
312	});	2124	});
313		2125
314	Event::loop;	2126	EV::loop;
315		2127
316	3b. The module user could use AnyEvent, too:	2128	3b. The module user could use AnyEvent, too:
317		2129
318	use AnyEvent;	2130	use AnyEvent;
319		2131
320	my $quit = AnyEvent->condvar;	2132	my $quit = AnyEvent->condvar;
321		2133
322	$fcp->txn_client_get ($url)->cb (sub {	2134	$fcp->txn_client_get ($url)->cb (sub {
323	...	2135	...
324	$quit->broadcast;	2136	$quit->send;
325	});	2137	});
326		2138
327	$quit->wait;	2139	$quit->recv;
		2140
		2141
		2142	=head1 BENCHMARKS
		2143
		2144	To give you an idea of the performance and overheads that AnyEvent adds
		2145	over the event loops themselves and to give you an impression of the speed
		2146	of various event loops I prepared some benchmarks.
		2147
		2148	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2149
		2150	Here is a benchmark of various supported event models used natively and
		2151	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2152	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2153	which it is), lets them fire exactly once and destroys them again.
		2154
		2155	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2156	distribution. It uses the L<AE> interface, which makes a real difference
		2157	for the EV and Perl backends only.
		2158
		2159	=head3 Explanation of the columns
		2160
		2161	I<watcher> is the number of event watchers created/destroyed. Since
		2162	different event models feature vastly different performances, each event
		2163	loop was given a number of watchers so that overall runtime is acceptable
		2164	and similar between tested event loop (and keep them from crashing): Glib
		2165	would probably take thousands of years if asked to process the same number
		2166	of watchers as EV in this benchmark.
		2167
		2168	I<bytes> is the number of bytes (as measured by the resident set size,
		2169	RSS) consumed by each watcher. This method of measuring captures both C
		2170	and Perl-based overheads.
		2171
		2172	I<create> is the time, in microseconds (millionths of seconds), that it
		2173	takes to create a single watcher. The callback is a closure shared between
		2174	all watchers, to avoid adding memory overhead. That means closure creation
		2175	and memory usage is not included in the figures.
		2176
		2177	I<invoke> is the time, in microseconds, used to invoke a simple
		2178	callback. The callback simply counts down a Perl variable and after it was
		2179	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2180	signal the end of this phase.
		2181
		2182	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2183	watcher.
		2184
		2185	=head3 Results
		2186
		2187	name watchers bytes create invoke destroy comment
		2188	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2189	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2190	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2191	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2192	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2193	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2194	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2195	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2196	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2197	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2198	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2199	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2200
		2201	=head3 Discussion
		2202
		2203	The benchmark does I<not> measure scalability of the event loop very
		2204	well. For example, a select-based event loop (such as the pure perl one)
		2205	can never compete with an event loop that uses epoll when the number of
		2206	file descriptors grows high. In this benchmark, all events become ready at
		2207	the same time, so select/poll-based implementations get an unnatural speed
		2208	boost.
		2209
		2210	Also, note that the number of watchers usually has a nonlinear effect on
		2211	overall speed, that is, creating twice as many watchers doesn't take twice
		2212	the time - usually it takes longer. This puts event loops tested with a
		2213	higher number of watchers at a disadvantage.
		2214
		2215	To put the range of results into perspective, consider that on the
		2216	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2217	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2218	cycles with POE.
		2219
		2220	C<EV> is the sole leader regarding speed and memory use, which are both
		2221	maximal/minimal, respectively. When using the L<AE> API there is zero
		2222	overhead (when going through the AnyEvent API create is about 5-6 times
		2223	slower, with other times being equal, so still uses far less memory than
		2224	any other event loop and is still faster than Event natively).
		2225
		2226	The pure perl implementation is hit in a few sweet spots (both the
		2227	constant timeout and the use of a single fd hit optimisations in the perl
		2228	interpreter and the backend itself). Nevertheless this shows that it
		2229	adds very little overhead in itself. Like any select-based backend its
		2230	performance becomes really bad with lots of file descriptors (and few of
		2231	them active), of course, but this was not subject of this benchmark.
		2232
		2233	The C<Event> module has a relatively high setup and callback invocation
		2234	cost, but overall scores in on the third place.
		2235
		2236	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2237	when using its pure perl backend.
		2238
		2239	C<Glib>'s memory usage is quite a bit higher, but it features a
		2240	faster callback invocation and overall ends up in the same class as
		2241	C<Event>. However, Glib scales extremely badly, doubling the number of
		2242	watchers increases the processing time by more than a factor of four,
		2243	making it completely unusable when using larger numbers of watchers
		2244	(note that only a single file descriptor was used in the benchmark, so
		2245	inefficiencies of C<poll> do not account for this).
		2246
		2247	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2248	more than 2000 watchers is a big setback, however, as correctness takes
		2249	precedence over speed. Nevertheless, its performance is surprising, as the
		2250	file descriptor is dup()ed for each watcher. This shows that the dup()
		2251	employed by some adaptors is not a big performance issue (it does incur a
		2252	hidden memory cost inside the kernel which is not reflected in the figures
		2253	above).
		2254
		2255	C<POE>, regardless of underlying event loop (whether using its pure perl
		2256	select-based backend or the Event module, the POE-EV backend couldn't
		2257	be tested because it wasn't working) shows abysmal performance and
		2258	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2259	as EV watchers, and 10 times as much memory as Event (the high memory
		2260	requirements are caused by requiring a session for each watcher). Watcher
		2261	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2262	implementation.
		2263
		2264	The design of the POE adaptor class in AnyEvent can not really account
		2265	for the performance issues, though, as session creation overhead is
		2266	small compared to execution of the state machine, which is coded pretty
		2267	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2268	using multiple sessions is not a good approach, especially regarding
		2269	memory usage, even the author of POE could not come up with a faster
		2270	design).
		2271
		2272	=head3 Summary
		2273
		2274	=over 4
		2275
		2276	=item * Using EV through AnyEvent is faster than any other event loop
		2277	(even when used without AnyEvent), but most event loops have acceptable
		2278	performance with or without AnyEvent.
		2279
		2280	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2281	the actual event loop, only with extremely fast event loops such as EV
		2282	adds AnyEvent significant overhead.
		2283
		2284	=item * You should avoid POE like the plague if you want performance or
		2285	reasonable memory usage.
		2286
		2287	=back
		2288
		2289	=head2 BENCHMARKING THE LARGE SERVER CASE
		2290
		2291	This benchmark actually benchmarks the event loop itself. It works by
		2292	creating a number of "servers": each server consists of a socket pair, a
		2293	timeout watcher that gets reset on activity (but never fires), and an I/O
		2294	watcher waiting for input on one side of the socket. Each time the socket
		2295	watcher reads a byte it will write that byte to a random other "server".
		2296
		2297	The effect is that there will be a lot of I/O watchers, only part of which
		2298	are active at any one point (so there is a constant number of active
		2299	fds for each loop iteration, but which fds these are is random). The
		2300	timeout is reset each time something is read because that reflects how
		2301	most timeouts work (and puts extra pressure on the event loops).
		2302
		2303	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2304	(1%) are active. This mirrors the activity of large servers with many
		2305	connections, most of which are idle at any one point in time.
		2306
		2307	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2308	distribution. It uses the L<AE> interface, which makes a real difference
		2309	for the EV and Perl backends only.
		2310
		2311	=head3 Explanation of the columns
		2312
		2313	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2314	each server has a read and write socket end).
		2315
		2316	I<create> is the time it takes to create a socket pair (which is
		2317	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2318
		2319	I<request>, the most important value, is the time it takes to handle a
		2320	single "request", that is, reading the token from the pipe and forwarding
		2321	it to another server. This includes deleting the old timeout and creating
		2322	a new one that moves the timeout into the future.
		2323
		2324	=head3 Results
		2325
		2326	name sockets create request
		2327	EV 20000 62.66 7.99
		2328	Perl 20000 68.32 32.64
		2329	IOAsync 20000 174.06 101.15 epoll
		2330	IOAsync 20000 174.67 610.84 poll
		2331	Event 20000 202.69 242.91
		2332	Glib 20000 557.01 1689.52
		2333	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2334
		2335	=head3 Discussion
		2336
		2337	This benchmark I<does> measure scalability and overall performance of the
		2338	particular event loop.
		2339
		2340	EV is again fastest. Since it is using epoll on my system, the setup time
		2341	is relatively high, though.
		2342
		2343	Perl surprisingly comes second. It is much faster than the C-based event
		2344	loops Event and Glib.
		2345
		2346	IO::Async performs very well when using its epoll backend, and still quite
		2347	good compared to Glib when using its pure perl backend.
		2348
		2349	Event suffers from high setup time as well (look at its code and you will
		2350	understand why). Callback invocation also has a high overhead compared to
		2351	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2352	uses select or poll in basically all documented configurations.
		2353
		2354	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2355	clearly fails to perform with many filehandles or in busy servers.
		2356
		2357	POE is still completely out of the picture, taking over 1000 times as long
		2358	as EV, and over 100 times as long as the Perl implementation, even though
		2359	it uses a C-based event loop in this case.
		2360
		2361	=head3 Summary
		2362
		2363	=over 4
		2364
		2365	=item * The pure perl implementation performs extremely well.
		2366
		2367	=item * Avoid Glib or POE in large projects where performance matters.
		2368
		2369	=back
		2370
		2371	=head2 BENCHMARKING SMALL SERVERS
		2372
		2373	While event loops should scale (and select-based ones do not...) even to
		2374	large servers, most programs we (or I :) actually write have only a few
		2375	I/O watchers.
		2376
		2377	In this benchmark, I use the same benchmark program as in the large server
		2378	case, but it uses only eight "servers", of which three are active at any
		2379	one time. This should reflect performance for a small server relatively
		2380	well.
		2381
		2382	The columns are identical to the previous table.
		2383
		2384	=head3 Results
		2385
		2386	name sockets create request
		2387	EV 16 20.00 6.54
		2388	Perl 16 25.75 12.62
		2389	Event 16 81.27 35.86
		2390	Glib 16 32.63 15.48
		2391	POE 16 261.87 276.28 uses POE::Loop::Event
		2392
		2393	=head3 Discussion
		2394
		2395	The benchmark tries to test the performance of a typical small
		2396	server. While knowing how various event loops perform is interesting, keep
		2397	in mind that their overhead in this case is usually not as important, due
		2398	to the small absolute number of watchers (that is, you need efficiency and
		2399	speed most when you have lots of watchers, not when you only have a few of
		2400	them).
		2401
		2402	EV is again fastest.
		2403
		2404	Perl again comes second. It is noticeably faster than the C-based event
		2405	loops Event and Glib, although the difference is too small to really
		2406	matter.
		2407
		2408	POE also performs much better in this case, but is is still far behind the
		2409	others.
		2410
		2411	=head3 Summary
		2412
		2413	=over 4
		2414
		2415	=item * C-based event loops perform very well with small number of
		2416	watchers, as the management overhead dominates.
		2417
		2418	=back
		2419
		2420	=head2 THE IO::Lambda BENCHMARK
		2421
		2422	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2423	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2424	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2425	shouldn't come as a surprise to anybody). As such, the benchmark is
		2426	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2427	very optimal. But how would AnyEvent compare when used without the extra
		2428	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2429
		2430	The benchmark itself creates an echo-server, and then, for 500 times,
		2431	connects to the echo server, sends a line, waits for the reply, and then
		2432	creates the next connection. This is a rather bad benchmark, as it doesn't
		2433	test the efficiency of the framework or much non-blocking I/O, but it is a
		2434	benchmark nevertheless.
		2435
		2436	name runtime
		2437	Lambda/select 0.330 sec
		2438	+ optimized 0.122 sec
		2439	Lambda/AnyEvent 0.327 sec
		2440	+ optimized 0.138 sec
		2441	Raw sockets/select 0.077 sec
		2442	POE/select, components 0.662 sec
		2443	POE/select, raw sockets 0.226 sec
		2444	POE/select, optimized 0.404 sec
		2445
		2446	AnyEvent/select/nb 0.085 sec
		2447	AnyEvent/EV/nb 0.068 sec
		2448	+state machine 0.134 sec
		2449
		2450	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2451	benchmarks actually make blocking connects and use 100% blocking I/O,
		2452	defeating the purpose of an event-based solution. All of the newly
		2453	written AnyEvent benchmarks use 100% non-blocking connects (using
		2454	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2455	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2456	generally require a lot more bookkeeping and event handling than blocking
		2457	connects (which involve a single syscall only).
		2458
		2459	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2460	offers similar expressive power as POE and IO::Lambda, using conventional
		2461	Perl syntax. This means that both the echo server and the client are 100%
		2462	non-blocking, further placing it at a disadvantage.
		2463
		2464	As you can see, the AnyEvent + EV combination even beats the
		2465	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2466	backend easily beats IO::Lambda and POE.
		2467
		2468	And even the 100% non-blocking version written using the high-level (and
		2469	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2470	higher level ("unoptimised") abstractions by a large margin, even though
		2471	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2472
		2473	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2474	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2475	part of the IO::Lambda distribution and were used without any changes.
		2476
		2477
		2478	=head1 SIGNALS
		2479
		2480	AnyEvent currently installs handlers for these signals:
		2481
		2482	=over 4
		2483
		2484	=item SIGCHLD
		2485
		2486	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2487	emulation for event loops that do not support them natively. Also, some
		2488	event loops install a similar handler.
		2489
		2490	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2491	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2492
		2493	=item SIGPIPE
		2494
		2495	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2496	when AnyEvent gets loaded.
		2497
		2498	The rationale for this is that AnyEvent users usually do not really depend
		2499	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2500	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2501	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2502	some random socket.
		2503
		2504	The rationale for installing a no-op handler as opposed to ignoring it is
		2505	that this way, the handler will be restored to defaults on exec.
		2506
		2507	Feel free to install your own handler, or reset it to defaults.
		2508
		2509	=back
		2510
		2511	=cut
		2512
		2513	undef $SIG{CHLD}
		2514	if $SIG{CHLD} eq 'IGNORE';
		2515
		2516	$SIG{PIPE} = sub { }
		2517	unless defined $SIG{PIPE};
		2518
		2519	=head1 RECOMMENDED/OPTIONAL MODULES
		2520
		2521	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2522	its built-in modules) are required to use it.
		2523
		2524	That does not mean that AnyEvent won't take advantage of some additional
		2525	modules if they are installed.
		2526
		2527	This section explains which additional modules will be used, and how they
		2528	affect AnyEvent's operation.
		2529
		2530	=over 4
		2531
		2532	=item L<Async::Interrupt>
		2533
		2534	This slightly arcane module is used to implement fast signal handling: To
		2535	my knowledge, there is no way to do completely race-free and quick
		2536	signal handling in pure perl. To ensure that signals still get
		2537	delivered, AnyEvent will start an interval timer to wake up perl (and
		2538	catch the signals) with some delay (default is 10 seconds, look for
		2539	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2540
		2541	If this module is available, then it will be used to implement signal
		2542	catching, which means that signals will not be delayed, and the event loop
		2543	will not be interrupted regularly, which is more efficient (and good for
		2544	battery life on laptops).
		2545
		2546	This affects not just the pure-perl event loop, but also other event loops
		2547	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2548
		2549	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2550	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2551	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2552	does nothing for those backends.
		2553
		2554	=item L<EV>
		2555
		2556	This module isn't really "optional", as it is simply one of the backend
		2557	event loops that AnyEvent can use. However, it is simply the best event
		2558	loop available in terms of features, speed and stability: It supports
		2559	the AnyEvent API optimally, implements all the watcher types in XS, does
		2560	automatic timer adjustments even when no monotonic clock is available,
		2561	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2562	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2563	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2564
		2565	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2566	then this module will do nothing for you.
		2567
		2568	=item L<Guard>
		2569
		2570	The guard module, when used, will be used to implement
		2571	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2572	lot less memory), but otherwise doesn't affect guard operation much. It is
		2573	purely used for performance.
		2574
		2575	=item L<JSON> and L<JSON::XS>
		2576
		2577	One of these modules is required when you want to read or write JSON data
		2578	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2579	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2580
		2581	=item L<Net::SSLeay>
		2582
		2583	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2584	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2585	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2586
		2587	=item L<Time::HiRes>
		2588
		2589	This module is part of perl since release 5.008. It will be used when the
		2590	chosen event library does not come with a timing source of its own. The
		2591	pure-perl event loop (L<AnyEvent::Impl::Perl>) will additionally use it to
		2592	try to use a monotonic clock for timing stability.
		2593
		2594	=back
		2595
		2596
		2597	=head1 FORK
		2598
		2599	Most event libraries are not fork-safe. The ones who are usually are
		2600	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2601	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2602	are usually badly thought-out hacks that are incompatible with fork in
		2603	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2604	continue event-processing in both parent and child (or both, if you know
		2605	what you are doing).
		2606
		2607	This means that, in general, you cannot fork and do event processing in
		2608	the child if the event library was initialised before the fork (which
		2609	usually happens when the first AnyEvent watcher is created, or the library
		2610	is loaded).
		2611
		2612	If you have to fork, you must either do so I<before> creating your first
		2613	watcher OR you must not use AnyEvent at all in the child OR you must do
		2614	something completely out of the scope of AnyEvent.
		2615
		2616	The problem of doing event processing in the parent I<and> the child
		2617	is much more complicated: even for backends that I<are> fork-aware or
		2618	fork-safe, their behaviour is not usually what you want: fork clones all
		2619	watchers, that means all timers, I/O watchers etc. are active in both
		2620	parent and child, which is almost never what you want. USing C<exec>
		2621	to start worker children from some kind of manage rprocess is usually
		2622	preferred, because it is much easier and cleaner, at the expense of having
		2623	to have another binary.
		2624
		2625
		2626	=head1 SECURITY CONSIDERATIONS
		2627
		2628	AnyEvent can be forced to load any event model via
		2629	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2630	execute arbitrary code or directly gain access, it can easily be used to
		2631	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2632	will not be active when the program uses a different event model than
		2633	specified in the variable.
		2634
		2635	You can make AnyEvent completely ignore this variable by deleting it
		2636	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2637
		2638	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2639
		2640	use AnyEvent;
		2641
		2642	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2643	be used to probe what backend is used and gain other information (which is
		2644	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2645	$ENV{PERL_ANYEVENT_STRICT}.
		2646
		2647	Note that AnyEvent will remove I<all> environment variables starting with
		2648	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2649	enabled.
		2650
		2651
		2652	=head1 BUGS
		2653
		2654	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2655	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2656	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2657	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2658	pronounced).
		2659
328		2660
329	=head1 SEE ALSO	2661	=head1 SEE ALSO
330		2662
331	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	2663	Tutorial/Introduction: L<AnyEvent::Intro>.
332		2664
333	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	2665	FAQ: L<AnyEvent::FAQ>.
334		2666
335	Nontrivial usage example: L<Net::FCP>.	2667	Utility functions: L<AnyEvent::Util>.
336		2668
337	=head1	2669	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		2670	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		2671
		2672	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2673	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2674	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2675	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
		2676
		2677	Non-blocking file handles, sockets, TCP clients and
		2678	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2679
		2680	Asynchronous DNS: L<AnyEvent::DNS>.
		2681
		2682	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2683
		2684	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2685	L<AnyEvent::HTTP>.
		2686
		2687
		2688	=head1 AUTHOR
		2689
		2690	Marc Lehmann <schmorp@schmorp.de>
		2691	http://home.schmorp.de/
338		2692
339	=cut	2693	=cut
340		2694
341	1	2695	1
342		2696

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