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Revision 1.12 by root, Thu Jul 20 01:39:40 2006 UTC vs.
Revision 1.198 by root, Thu Mar 26 20:17:44 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	Event, Coro, Glib, Tk - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
11	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... });
12	my ($poll_got) = @_;	12
		13	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		14	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		15
		16	print AnyEvent->now; # prints current event loop time
		17	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		18
		19	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		20
		21	my $w = AnyEvent->child (pid => $pid, cb => sub {
		22	my ($pid, $status) = @_;
13	...	23	...
14	});	24	});
15		25
16	* only one io watcher per $fh and $poll type is allowed (i.e. on a socket	26	my $w = AnyEvent->condvar; # stores whether a condition was flagged
17	you can have one r + one w or one rw watcher, not any more (limitation by	27	$w->send; # wake up current and all future recv's
18	Tk).
19
20	* the C<$poll_got> passed to the handler needs to be checked by looking
21	for single characters (e.g. with a regex), as it can contain more event
22	types than were requested (e.g. a 'w' watcher might generate 'rw' events,
23	limitation by Glib).
24
25	* AnyEvent will keep filehandles alive, so as long as the watcher exists,
26	the filehandle exists.
27
28	my $w = AnyEvent->timer (after => $seconds, cb => sub {
29	...
30	});
31
32	* io and time watchers get canceled whenever $w is destroyed, so keep a copy
33
34	* timers can only be used once and must be recreated for repeated
35	operation (limitation by Glib and Tk).
36
37	my $w = AnyEvent->condvar; # kind of main loop replacement
38	$w->wait; # enters main loop till $condvar gets ->broadcast	28	$w->recv; # enters "main loop" till $condvar gets ->send
39	$w->broadcast; # wake up current and all future wait's	29	# use a condvar in callback mode:
		30	$w->cb (sub { $_[0]->recv });
40		31
41	* condvars are used to give blocking behaviour when neccessary. Create	32	=head1 INTRODUCTION/TUTORIAL
42	a condvar for any "request" or "event" your module might create, C<<	33
43	->broadcast >> it when the event happens and provide a function that calls	34	This manpage is mainly a reference manual. If you are interested
44	C<< ->wait >> for it. See the examples below.	35	in a tutorial or some gentle introduction, have a look at the
		36	L<AnyEvent::Intro> manpage.
		37
		38	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		39
		40	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		41	nowadays. So what is different about AnyEvent?
		42
		43	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		44	policy> and AnyEvent is I<small and efficient>.
		45
		46	First and foremost, I<AnyEvent is not an event model> itself, it only
		47	interfaces to whatever event model the main program happens to use, in a
		48	pragmatic way. For event models and certain classes of immortals alike,
		49	the statement "there can only be one" is a bitter reality: In general,
		50	only one event loop can be active at the same time in a process. AnyEvent
		51	cannot change this, but it can hide the differences between those event
		52	loops.
		53
		54	The goal of AnyEvent is to offer module authors the ability to do event
		55	programming (waiting for I/O or timer events) without subscribing to a
		56	religion, a way of living, and most importantly: without forcing your
		57	module users into the same thing by forcing them to use the same event
		58	model you use.
		59
		60	For modules like POE or IO::Async (which is a total misnomer as it is
		61	actually doing all I/O I<synchronously>...), using them in your module is
		62	like joining a cult: After you joined, you are dependent on them and you
		63	cannot use anything else, as they are simply incompatible to everything
		64	that isn't them. What's worse, all the potential users of your
		65	module are I<also> forced to use the same event loop you use.
		66
		67	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		68	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		69	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		70	your module uses one of those, every user of your module has to use it,
		71	too. But if your module uses AnyEvent, it works transparently with all
		72	event models it supports (including stuff like IO::Async, as long as those
		73	use one of the supported event loops. It is trivial to add new event loops
		74	to AnyEvent, too, so it is future-proof).
		75
		76	In addition to being free of having to use I<the one and only true event
		77	model>, AnyEvent also is free of bloat and policy: with POE or similar
		78	modules, you get an enormous amount of code and strict rules you have to
		79	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		80	offering the functionality that is necessary, in as thin as a wrapper as
		81	technically possible.
		82
		83	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		84	of useful functionality, such as an asynchronous DNS resolver, 100%
		85	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		86	such as Windows) and lots of real-world knowledge and workarounds for
		87	platform bugs and differences.
		88
		89	Now, if you I<do want> lots of policy (this can arguably be somewhat
		90	useful) and you want to force your users to use the one and only event
		91	model, you should I<not> use this module.
45		92
46	=head1 DESCRIPTION	93	=head1 DESCRIPTION
47		94
48	L<AnyEvent> provides an identical interface to multiple event loops. This	95	L<AnyEvent> provides an identical interface to multiple event loops. This
49	allows module authors to utilizy an event loop without forcing module	96	allows module authors to utilise an event loop without forcing module
50	users to use the same event loop (as only a single event loop can coexist	97	users to use the same event loop (as only a single event loop can coexist
51	peacefully at any one time).	98	peacefully at any one time).
52		99
53	The interface itself is vaguely similar but not identical to the Event	100	The interface itself is vaguely similar, but not identical to the L<Event>
54	module.	101	module.
55		102
56	On the first call of any method, the module tries to detect the currently	103	During the first call of any watcher-creation method, the module tries
57	loaded event loop by probing wether any of the following modules is	104	to detect the currently loaded event loop by probing whether one of the
58	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	105	following modules is already loaded: L<EV>,
59	used. If none is found, the module tries to load these modules in the	106	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
60	order given. The first one that could be successfully loaded will be	107	L<POE>. The first one found is used. If none are found, the module tries
61	used. If still none could be found, it will issue an error.	108	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		109	adaptor should always succeed) in the order given. The first one that can
		110	be successfully loaded will be used. If, after this, still none could be
		111	found, AnyEvent will fall back to a pure-perl event loop, which is not
		112	very efficient, but should work everywhere.
		113
		114	Because AnyEvent first checks for modules that are already loaded, loading
		115	an event model explicitly before first using AnyEvent will likely make
		116	that model the default. For example:
		117
		118	use Tk;
		119	use AnyEvent;
		120
		121	# .. AnyEvent will likely default to Tk
		122
		123	The I<likely> means that, if any module loads another event model and
		124	starts using it, all bets are off. Maybe you should tell their authors to
		125	use AnyEvent so their modules work together with others seamlessly...
		126
		127	The pure-perl implementation of AnyEvent is called
		128	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		129	explicitly and enjoy the high availability of that event loop :)
		130
		131	=head1 WATCHERS
		132
		133	AnyEvent has the central concept of a I<watcher>, which is an object that
		134	stores relevant data for each kind of event you are waiting for, such as
		135	the callback to call, the file handle to watch, etc.
		136
		137	These watchers are normal Perl objects with normal Perl lifetime. After
		138	creating a watcher it will immediately "watch" for events and invoke the
		139	callback when the event occurs (of course, only when the event model
		140	is in control).
		141
		142	Note that B<callbacks must not permanently change global variables>
		143	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		144	callbacks must not C<die> >>. The former is good programming practise in
		145	Perl and the latter stems from the fact that exception handling differs
		146	widely between event loops.
		147
		148	To disable the watcher you have to destroy it (e.g. by setting the
		149	variable you store it in to C<undef> or otherwise deleting all references
		150	to it).
		151
		152	All watchers are created by calling a method on the C<AnyEvent> class.
		153
		154	Many watchers either are used with "recursion" (repeating timers for
		155	example), or need to refer to their watcher object in other ways.
		156
		157	An any way to achieve that is this pattern:
		158
		159	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		160	# you can use $w here, for example to undef it
		161	undef $w;
		162	});
		163
		164	Note that C<my $w; $w => combination. This is necessary because in Perl,
		165	my variables are only visible after the statement in which they are
		166	declared.
		167
		168	=head2 I/O WATCHERS
		169
		170	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		171	with the following mandatory key-value pairs as arguments:
		172
		173	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for events
		174	(AnyEvent might or might not keep a reference to this file handle). C<poll>
		175	must be a string that is either C<r> or C<w>, which creates a watcher
		176	waiting for "r"eadable or "w"ritable events, respectively. C<cb> is the
		177	callback to invoke each time the file handle becomes ready.
		178
		179	Although the callback might get passed parameters, their value and
		180	presence is undefined and you cannot rely on them. Portable AnyEvent
		181	callbacks cannot use arguments passed to I/O watcher callbacks.
		182
		183	The I/O watcher might use the underlying file descriptor or a copy of it.
		184	You must not close a file handle as long as any watcher is active on the
		185	underlying file descriptor.
		186
		187	Some event loops issue spurious readyness notifications, so you should
		188	always use non-blocking calls when reading/writing from/to your file
		189	handles.
		190
		191	Example: wait for readability of STDIN, then read a line and disable the
		192	watcher.
		193
		194	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		195	chomp (my $input = <STDIN>);
		196	warn "read: $input\n";
		197	undef $w;
		198	});
		199
		200	=head2 TIME WATCHERS
		201
		202	You can create a time watcher by calling the C<< AnyEvent->timer >>
		203	method with the following mandatory arguments:
		204
		205	C<after> specifies after how many seconds (fractional values are
		206	supported) the callback should be invoked. C<cb> is the callback to invoke
		207	in that case.
		208
		209	Although the callback might get passed parameters, their value and
		210	presence is undefined and you cannot rely on them. Portable AnyEvent
		211	callbacks cannot use arguments passed to time watcher callbacks.
		212
		213	The callback will normally be invoked once only. If you specify another
		214	parameter, C<interval>, as a strictly positive number (> 0), then the
		215	callback will be invoked regularly at that interval (in fractional
		216	seconds) after the first invocation. If C<interval> is specified with a
		217	false value, then it is treated as if it were missing.
		218
		219	The callback will be rescheduled before invoking the callback, but no
		220	attempt is done to avoid timer drift in most backends, so the interval is
		221	only approximate.
		222
		223	Example: fire an event after 7.7 seconds.
		224
		225	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		226	warn "timeout\n";
		227	});
		228
		229	# to cancel the timer:
		230	undef $w;
		231
		232	Example 2: fire an event after 0.5 seconds, then roughly every second.
		233
		234	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		235	warn "timeout\n";
		236	};
		237
		238	=head3 TIMING ISSUES
		239
		240	There are two ways to handle timers: based on real time (relative, "fire
		241	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		242	o'clock").
		243
		244	While most event loops expect timers to specified in a relative way, they
		245	use absolute time internally. This makes a difference when your clock
		246	"jumps", for example, when ntp decides to set your clock backwards from
		247	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		248	fire "after" a second might actually take six years to finally fire.
		249
		250	AnyEvent cannot compensate for this. The only event loop that is conscious
		251	about these issues is L<EV>, which offers both relative (ev_timer, based
		252	on true relative time) and absolute (ev_periodic, based on wallclock time)
		253	timers.
		254
		255	AnyEvent always prefers relative timers, if available, matching the
		256	AnyEvent API.
		257
		258	AnyEvent has two additional methods that return the "current time":
62		259
63	=over 4	260	=over 4
64		261
		262	=item AnyEvent->time
		263
		264	This returns the "current wallclock time" as a fractional number of
		265	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		266	return, and the result is guaranteed to be compatible with those).
		267
		268	It progresses independently of any event loop processing, i.e. each call
		269	will check the system clock, which usually gets updated frequently.
		270
		271	=item AnyEvent->now
		272
		273	This also returns the "current wallclock time", but unlike C<time>, above,
		274	this value might change only once per event loop iteration, depending on
		275	the event loop (most return the same time as C<time>, above). This is the
		276	time that AnyEvent's timers get scheduled against.
		277
		278	I<In almost all cases (in all cases if you don't care), this is the
		279	function to call when you want to know the current time.>
		280
		281	This function is also often faster then C<< AnyEvent->time >>, and
		282	thus the preferred method if you want some timestamp (for example,
		283	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		284
		285	The rest of this section is only of relevance if you try to be very exact
		286	with your timing, you can skip it without bad conscience.
		287
		288	For a practical example of when these times differ, consider L<Event::Lib>
		289	and L<EV> and the following set-up:
		290
		291	The event loop is running and has just invoked one of your callback at
		292	time=500 (assume no other callbacks delay processing). In your callback,
		293	you wait a second by executing C<sleep 1> (blocking the process for a
		294	second) and then (at time=501) you create a relative timer that fires
		295	after three seconds.
		296
		297	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		298	both return C<501>, because that is the current time, and the timer will
		299	be scheduled to fire at time=504 (C<501> + C<3>).
		300
		301	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		302	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		303	last event processing phase started. With L<EV>, your timer gets scheduled
		304	to run at time=503 (C<500> + C<3>).
		305
		306	In one sense, L<Event::Lib> is more exact, as it uses the current time
		307	regardless of any delays introduced by event processing. However, most
		308	callbacks do not expect large delays in processing, so this causes a
		309	higher drift (and a lot more system calls to get the current time).
		310
		311	In another sense, L<EV> is more exact, as your timer will be scheduled at
		312	the same time, regardless of how long event processing actually took.
		313
		314	In either case, if you care (and in most cases, you don't), then you
		315	can get whatever behaviour you want with any event loop, by taking the
		316	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		317	account.
		318
		319	=back
		320
		321	=head2 SIGNAL WATCHERS
		322
		323	You can watch for signals using a signal watcher, C<signal> is the signal
		324	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		325	callback to be invoked whenever a signal occurs.
		326
		327	Although the callback might get passed parameters, their value and
		328	presence is undefined and you cannot rely on them. Portable AnyEvent
		329	callbacks cannot use arguments passed to signal watcher callbacks.
		330
		331	Multiple signal occurrences can be clumped together into one callback
		332	invocation, and callback invocation will be synchronous. Synchronous means
		333	that it might take a while until the signal gets handled by the process,
		334	but it is guaranteed not to interrupt any other callbacks.
		335
		336	The main advantage of using these watchers is that you can share a signal
		337	between multiple watchers.
		338
		339	This watcher might use C<%SIG>, so programs overwriting those signals
		340	directly will likely not work correctly.
		341
		342	Example: exit on SIGINT
		343
		344	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		345
		346	=head2 CHILD PROCESS WATCHERS
		347
		348	You can also watch on a child process exit and catch its exit status.
		349
		350	The child process is specified by the C<pid> argument (if set to C<0>, it
		351	watches for any child process exit). The watcher will triggered only when
		352	the child process has finished and an exit status is available, not on
		353	any trace events (stopped/continued).
		354
		355	The callback will be called with the pid and exit status (as returned by
		356	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		357	callback arguments.
		358
		359	This watcher type works by installing a signal handler for C<SIGCHLD>,
		360	and since it cannot be shared, nothing else should use SIGCHLD or reap
		361	random child processes (waiting for specific child processes, e.g. inside
		362	C<system>, is just fine).
		363
		364	There is a slight catch to child watchers, however: you usually start them
		365	I<after> the child process was created, and this means the process could
		366	have exited already (and no SIGCHLD will be sent anymore).
		367
		368	Not all event models handle this correctly (POE doesn't), but even for
		369	event models that I<do> handle this correctly, they usually need to be
		370	loaded before the process exits (i.e. before you fork in the first place).
		371
		372	This means you cannot create a child watcher as the very first thing in an
		373	AnyEvent program, you I<have> to create at least one watcher before you
		374	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		375
		376	Example: fork a process and wait for it
		377
		378	my $done = AnyEvent->condvar;
		379
		380	my $pid = fork or exit 5;
		381
		382	my $w = AnyEvent->child (
		383	pid => $pid,
		384	cb => sub {
		385	my ($pid, $status) = @_;
		386	warn "pid $pid exited with status $status";
		387	$done->send;
		388	},
		389	);
		390
		391	# do something else, then wait for process exit
		392	$done->recv;
		393
		394	=head2 CONDITION VARIABLES
		395
		396	If you are familiar with some event loops you will know that all of them
		397	require you to run some blocking "loop", "run" or similar function that
		398	will actively watch for new events and call your callbacks.
		399
		400	AnyEvent is different, it expects somebody else to run the event loop and
		401	will only block when necessary (usually when told by the user).
		402
		403	The instrument to do that is called a "condition variable", so called
		404	because they represent a condition that must become true.
		405
		406	Condition variables can be created by calling the C<< AnyEvent->condvar
		407	>> method, usually without arguments. The only argument pair allowed is
		408
		409	C<cb>, which specifies a callback to be called when the condition variable
		410	becomes true, with the condition variable as the first argument (but not
		411	the results).
		412
		413	After creation, the condition variable is "false" until it becomes "true"
		414	by calling the C<send> method (or calling the condition variable as if it
		415	were a callback, read about the caveats in the description for the C<<
		416	->send >> method).
		417
		418	Condition variables are similar to callbacks, except that you can
		419	optionally wait for them. They can also be called merge points - points
		420	in time where multiple outstanding events have been processed. And yet
		421	another way to call them is transactions - each condition variable can be
		422	used to represent a transaction, which finishes at some point and delivers
		423	a result.
		424
		425	Condition variables are very useful to signal that something has finished,
		426	for example, if you write a module that does asynchronous http requests,
		427	then a condition variable would be the ideal candidate to signal the
		428	availability of results. The user can either act when the callback is
		429	called or can synchronously C<< ->recv >> for the results.
		430
		431	You can also use them to simulate traditional event loops - for example,
		432	you can block your main program until an event occurs - for example, you
		433	could C<< ->recv >> in your main program until the user clicks the Quit
		434	button of your app, which would C<< ->send >> the "quit" event.
		435
		436	Note that condition variables recurse into the event loop - if you have
		437	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		438	lose. Therefore, condition variables are good to export to your caller, but
		439	you should avoid making a blocking wait yourself, at least in callbacks,
		440	as this asks for trouble.
		441
		442	Condition variables are represented by hash refs in perl, and the keys
		443	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		444	easy (it is often useful to build your own transaction class on top of
		445	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		446	it's C<new> method in your own C<new> method.
		447
		448	There are two "sides" to a condition variable - the "producer side" which
		449	eventually calls C<< -> send >>, and the "consumer side", which waits
		450	for the send to occur.
		451
		452	Example: wait for a timer.
		453
		454	# wait till the result is ready
		455	my $result_ready = AnyEvent->condvar;
		456
		457	# do something such as adding a timer
		458	# or socket watcher the calls $result_ready->send
		459	# when the "result" is ready.
		460	# in this case, we simply use a timer:
		461	my $w = AnyEvent->timer (
		462	after => 1,
		463	cb => sub { $result_ready->send },
		464	);
		465
		466	# this "blocks" (while handling events) till the callback
		467	# calls send
		468	$result_ready->recv;
		469
		470	Example: wait for a timer, but take advantage of the fact that
		471	condition variables are also code references.
		472
		473	my $done = AnyEvent->condvar;
		474	my $delay = AnyEvent->timer (after => 5, cb => $done);
		475	$done->recv;
		476
		477	Example: Imagine an API that returns a condvar and doesn't support
		478	callbacks. This is how you make a synchronous call, for example from
		479	the main program:
		480
		481	use AnyEvent::CouchDB;
		482
		483	...
		484
		485	my @info = $couchdb->info->recv;
		486
		487	And this is how you would just ste a callback to be called whenever the
		488	results are available:
		489
		490	$couchdb->info->cb (sub {
		491	my @info = $_[0]->recv;
		492	});
		493
		494	=head3 METHODS FOR PRODUCERS
		495
		496	These methods should only be used by the producing side, i.e. the
		497	code/module that eventually sends the signal. Note that it is also
		498	the producer side which creates the condvar in most cases, but it isn't
		499	uncommon for the consumer to create it as well.
		500
		501	=over 4
		502
		503	=item $cv->send (...)
		504
		505	Flag the condition as ready - a running C<< ->recv >> and all further
		506	calls to C<recv> will (eventually) return after this method has been
		507	called. If nobody is waiting the send will be remembered.
		508
		509	If a callback has been set on the condition variable, it is called
		510	immediately from within send.
		511
		512	Any arguments passed to the C<send> call will be returned by all
		513	future C<< ->recv >> calls.
		514
		515	Condition variables are overloaded so one can call them directly
		516	(as a code reference). Calling them directly is the same as calling
		517	C<send>. Note, however, that many C-based event loops do not handle
		518	overloading, so as tempting as it may be, passing a condition variable
		519	instead of a callback does not work. Both the pure perl and EV loops
		520	support overloading, however, as well as all functions that use perl to
		521	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		522	example).
		523
		524	=item $cv->croak ($error)
		525
		526	Similar to send, but causes all call's to C<< ->recv >> to invoke
		527	C<Carp::croak> with the given error message/object/scalar.
		528
		529	This can be used to signal any errors to the condition variable
		530	user/consumer.
		531
		532	=item $cv->begin ([group callback])
		533
		534	=item $cv->end
		535
		536	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		537
		538	These two methods can be used to combine many transactions/events into
		539	one. For example, a function that pings many hosts in parallel might want
		540	to use a condition variable for the whole process.
		541
		542	Every call to C<< ->begin >> will increment a counter, and every call to
		543	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		544	>>, the (last) callback passed to C<begin> will be executed. That callback
		545	is I<supposed> to call C<< ->send >>, but that is not required. If no
		546	callback was set, C<send> will be called without any arguments.
		547
		548	Let's clarify this with the ping example:
		549
		550	my $cv = AnyEvent->condvar;
		551
		552	my %result;
		553	$cv->begin (sub { $cv->send (\%result) });
		554
		555	for my $host (@list_of_hosts) {
		556	$cv->begin;
		557	ping_host_then_call_callback $host, sub {
		558	$result{$host} = ...;
		559	$cv->end;
		560	};
		561	}
		562
		563	$cv->end;
		564
		565	This code fragment supposedly pings a number of hosts and calls
		566	C<send> after results for all then have have been gathered - in any
		567	order. To achieve this, the code issues a call to C<begin> when it starts
		568	each ping request and calls C<end> when it has received some result for
		569	it. Since C<begin> and C<end> only maintain a counter, the order in which
		570	results arrive is not relevant.
		571
		572	There is an additional bracketing call to C<begin> and C<end> outside the
		573	loop, which serves two important purposes: first, it sets the callback
		574	to be called once the counter reaches C<0>, and second, it ensures that
		575	C<send> is called even when C<no> hosts are being pinged (the loop
		576	doesn't execute once).
		577
		578	This is the general pattern when you "fan out" into multiple subrequests:
		579	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		580	is called at least once, and then, for each subrequest you start, call
		581	C<begin> and for each subrequest you finish, call C<end>.
		582
		583	=back
		584
		585	=head3 METHODS FOR CONSUMERS
		586
		587	These methods should only be used by the consuming side, i.e. the
		588	code awaits the condition.
		589
		590	=over 4
		591
		592	=item $cv->recv
		593
		594	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		595	>> methods have been called on c<$cv>, while servicing other watchers
		596	normally.
		597
		598	You can only wait once on a condition - additional calls are valid but
		599	will return immediately.
		600
		601	If an error condition has been set by calling C<< ->croak >>, then this
		602	function will call C<croak>.
		603
		604	In list context, all parameters passed to C<send> will be returned,
		605	in scalar context only the first one will be returned.
		606
		607	Not all event models support a blocking wait - some die in that case
		608	(programs might want to do that to stay interactive), so I<if you are
		609	using this from a module, never require a blocking wait>, but let the
		610	caller decide whether the call will block or not (for example, by coupling
		611	condition variables with some kind of request results and supporting
		612	callbacks so the caller knows that getting the result will not block,
		613	while still supporting blocking waits if the caller so desires).
		614
		615	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		616	sensibly have two C<< ->recv >>'s in parallel, as that would require
		617	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		618	can supply.
		619
		620	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		621	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		622	versions and also integrates coroutines into AnyEvent, making blocking
		623	C<< ->recv >> calls perfectly safe as long as they are done from another
		624	coroutine (one that doesn't run the event loop).
		625
		626	You can ensure that C<< -recv >> never blocks by setting a callback and
		627	only calling C<< ->recv >> from within that callback (or at a later
		628	time). This will work even when the event loop does not support blocking
		629	waits otherwise.
		630
		631	=item $bool = $cv->ready
		632
		633	Returns true when the condition is "true", i.e. whether C<send> or
		634	C<croak> have been called.
		635
		636	=item $cb = $cv->cb ($cb->($cv))
		637
		638	This is a mutator function that returns the callback set and optionally
		639	replaces it before doing so.
		640
		641	The callback will be called when the condition becomes "true", i.e. when
		642	C<send> or C<croak> are called, with the only argument being the condition
		643	variable itself. Calling C<recv> inside the callback or at any later time
		644	is guaranteed not to block.
		645
		646	=back
		647
		648	=head1 GLOBAL VARIABLES AND FUNCTIONS
		649
		650	=over 4
		651
		652	=item $AnyEvent::MODEL
		653
		654	Contains C<undef> until the first watcher is being created. Then it
		655	contains the event model that is being used, which is the name of the
		656	Perl class implementing the model. This class is usually one of the
		657	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		658	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		659
		660	The known classes so far are:
		661
		662	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		663	AnyEvent::Impl::Event based on Event, second best choice.
		664	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		665	AnyEvent::Impl::Glib based on Glib, third-best choice.
		666	AnyEvent::Impl::Tk based on Tk, very bad choice.
		667	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		668	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		669	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		670
		671	There is no support for WxWidgets, as WxWidgets has no support for
		672	watching file handles. However, you can use WxWidgets through the
		673	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		674	second, which was considered to be too horrible to even consider for
		675	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		676	it's adaptor.
		677
		678	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		679	autodetecting them.
		680
		681	=item AnyEvent::detect
		682
		683	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		684	if necessary. You should only call this function right before you would
		685	have created an AnyEvent watcher anyway, that is, as late as possible at
		686	runtime.
		687
		688	=item $guard = AnyEvent::post_detect { BLOCK }
		689
		690	Arranges for the code block to be executed as soon as the event model is
		691	autodetected (or immediately if this has already happened).
		692
		693	If called in scalar or list context, then it creates and returns an object
		694	that automatically removes the callback again when it is destroyed. See
		695	L<Coro::BDB> for a case where this is useful.
		696
		697	=item @AnyEvent::post_detect
		698
		699	If there are any code references in this array (you can C<push> to it
		700	before or after loading AnyEvent), then they will called directly after
		701	the event loop has been chosen.
		702
		703	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		704	if it contains a true value then the event loop has already been detected,
		705	and the array will be ignored.
		706
		707	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		708
		709	=back
		710
		711	=head1 WHAT TO DO IN A MODULE
		712
		713	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		714	freely, but you should not load a specific event module or rely on it.
		715
		716	Be careful when you create watchers in the module body - AnyEvent will
		717	decide which event module to use as soon as the first method is called, so
		718	by calling AnyEvent in your module body you force the user of your module
		719	to load the event module first.
		720
		721	Never call C<< ->recv >> on a condition variable unless you I<know> that
		722	the C<< ->send >> method has been called on it already. This is
		723	because it will stall the whole program, and the whole point of using
		724	events is to stay interactive.
		725
		726	It is fine, however, to call C<< ->recv >> when the user of your module
		727	requests it (i.e. if you create a http request object ad have a method
		728	called C<results> that returns the results, it should call C<< ->recv >>
		729	freely, as the user of your module knows what she is doing. always).
		730
		731	=head1 WHAT TO DO IN THE MAIN PROGRAM
		732
		733	There will always be a single main program - the only place that should
		734	dictate which event model to use.
		735
		736	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		737	do anything special (it does not need to be event-based) and let AnyEvent
		738	decide which implementation to chose if some module relies on it.
		739
		740	If the main program relies on a specific event model - for example, in
		741	Gtk2 programs you have to rely on the Glib module - you should load the
		742	event module before loading AnyEvent or any module that uses it: generally
		743	speaking, you should load it as early as possible. The reason is that
		744	modules might create watchers when they are loaded, and AnyEvent will
		745	decide on the event model to use as soon as it creates watchers, and it
		746	might chose the wrong one unless you load the correct one yourself.
		747
		748	You can chose to use a pure-perl implementation by loading the
		749	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		750	everywhere, but letting AnyEvent chose the model is generally better.
		751
		752	=head2 MAINLOOP EMULATION
		753
		754	Sometimes (often for short test scripts, or even standalone programs who
		755	only want to use AnyEvent), you do not want to run a specific event loop.
		756
		757	In that case, you can use a condition variable like this:
		758
		759	AnyEvent->condvar->recv;
		760
		761	This has the effect of entering the event loop and looping forever.
		762
		763	Note that usually your program has some exit condition, in which case
		764	it is better to use the "traditional" approach of storing a condition
		765	variable somewhere, waiting for it, and sending it when the program should
		766	exit cleanly.
		767
		768
		769	=head1 OTHER MODULES
		770
		771	The following is a non-exhaustive list of additional modules that use
		772	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		773	in the same program. Some of the modules come with AnyEvent, some are
		774	available via CPAN.
		775
		776	=over 4
		777
		778	=item L<AnyEvent::Util>
		779
		780	Contains various utility functions that replace often-used but blocking
		781	functions such as C<inet_aton> by event-/callback-based versions.
		782
		783	=item L<AnyEvent::Socket>
		784
		785	Provides various utility functions for (internet protocol) sockets,
		786	addresses and name resolution. Also functions to create non-blocking tcp
		787	connections or tcp servers, with IPv6 and SRV record support and more.
		788
		789	=item L<AnyEvent::Handle>
		790
		791	Provide read and write buffers, manages watchers for reads and writes,
		792	supports raw and formatted I/O, I/O queued and fully transparent and
		793	non-blocking SSL/TLS.
		794
		795	=item L<AnyEvent::DNS>
		796
		797	Provides rich asynchronous DNS resolver capabilities.
		798
		799	=item L<AnyEvent::HTTP>
		800
		801	A simple-to-use HTTP library that is capable of making a lot of concurrent
		802	HTTP requests.
		803
		804	=item L<AnyEvent::HTTPD>
		805
		806	Provides a simple web application server framework.
		807
		808	=item L<AnyEvent::FastPing>
		809
		810	The fastest ping in the west.
		811
		812	=item L<AnyEvent::DBI>
		813
		814	Executes L<DBI> requests asynchronously in a proxy process.
		815
		816	=item L<AnyEvent::AIO>
		817
		818	Truly asynchronous I/O, should be in the toolbox of every event
		819	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		820	together.
		821
		822	=item L<AnyEvent::BDB>
		823
		824	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		825	L<BDB> and AnyEvent together.
		826
		827	=item L<AnyEvent::GPSD>
		828
		829	A non-blocking interface to gpsd, a daemon delivering GPS information.
		830
		831	=item L<AnyEvent::IGS>
		832
		833	A non-blocking interface to the Internet Go Server protocol (used by
		834	L<App::IGS>).
		835
		836	=item L<AnyEvent::IRC>
		837
		838	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		839
		840	=item L<Net::XMPP2>
		841
		842	AnyEvent based XMPP (Jabber protocol) module family.
		843
		844	=item L<Net::FCP>
		845
		846	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		847	of AnyEvent.
		848
		849	=item L<Event::ExecFlow>
		850
		851	High level API for event-based execution flow control.
		852
		853	=item L<Coro>
		854
		855	Has special support for AnyEvent via L<Coro::AnyEvent>.
		856
		857	=item L<IO::Lambda>
		858
		859	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		860
		861	=back
		862
65	=cut	863	=cut
66		864
67	package AnyEvent;	865	package AnyEvent;
68		866
69	no warnings;	867	no warnings;
70	use strict 'vars';	868	use strict qw(vars subs);
		869
71	use Carp;	870	use Carp;
72		871
73	our $VERSION = '1.02';	872	our $VERSION = 4.341;
74	our $MODEL;	873	our $MODEL;
75		874
76	our $AUTOLOAD;	875	our $AUTOLOAD;
77	our @ISA;	876	our @ISA;
78		877
		878	our @REGISTRY;
		879
		880	our $WIN32;
		881
		882	BEGIN {
		883	my $win32 = ! ! ($^O =~ /mswin32/i);
		884	eval "sub WIN32(){ $win32 }";
		885	}
		886
79	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	887	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
80		888
81	our @REGISTRY;	889	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		890
		891	{
		892	my $idx;
		893	$PROTOCOL{$_} = ++$idx
		894	for reverse split /\s*,\s*/,
		895	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		896	}
82		897
83	my @models = (	898	my @models = (
84	[Coro::Event:: => AnyEvent::Impl::Coro::],	899	[EV:: => AnyEvent::Impl::EV::],
85	[Event:: => AnyEvent::Impl::Event::],	900	[Event:: => AnyEvent::Impl::Event::],
86	[Glib:: => AnyEvent::Impl::Glib::],	901	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		902	# everything below here will not be autoprobed
		903	# as the pureperl backend should work everywhere
		904	# and is usually faster
		905	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		906	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		907	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		908	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		909	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
87	[Tk:: => AnyEvent::Impl::Tk::],	910	[Wx:: => AnyEvent::Impl::POE::],
		911	[Prima:: => AnyEvent::Impl::POE::],
88	);	912	);
89		913
90	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	914	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
91		915
92	sub AUTOLOAD {	916	our @post_detect;
93	$AUTOLOAD =~ s/.*://;
94		917
95	$method{$AUTOLOAD}	918	sub post_detect(&) {
96	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	919	my ($cb) = @_;
97		920
		921	if ($MODEL) {
		922	$cb->();
		923
		924	1
		925	} else {
		926	push @post_detect, $cb;
		927
		928	defined wantarray
		929	? bless \$cb, "AnyEvent::Util::PostDetect"
		930	: ()
		931	}
		932	}
		933
		934	sub AnyEvent::Util::PostDetect::DESTROY {
		935	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		936	}
		937
		938	sub detect() {
98	unless ($MODEL) {	939	unless ($MODEL) {
		940	no strict 'refs';
		941	local $SIG{__DIE__};
		942
		943	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		944	my $model = "AnyEvent::Impl::$1";
		945	if (eval "require $model") {
		946	$MODEL = $model;
		947	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		948	} else {
		949	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		950	}
		951	}
		952
99	# check for already loaded models	953	# check for already loaded models
		954	unless ($MODEL) {
100	for (@REGISTRY, @models) {	955	for (@REGISTRY, @models) {
101	my ($package, $model) = @$_;	956	my ($package, $model) = @$_;
102	if (${"$package\::VERSION"} > 0) {	957	if (${"$package\::VERSION"} > 0) {
103	if (eval "require $model") {	958	if (eval "require $model") {
104	$MODEL = $model;	959	$MODEL = $model;
105	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	960	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
106	last;	961	last;
		962	}
107	}	963	}
108	}	964	}
		965
		966	unless ($MODEL) {
		967	# try to load a model
		968
		969	for (@REGISTRY, @models) {
		970	my ($package, $model) = @$_;
		971	if (eval "require $package"
		972	and ${"$package\::VERSION"} > 0
		973	and eval "require $model") {
		974	$MODEL = $model;
		975	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		976	last;
		977	}
		978	}
		979
		980	$MODEL
		981	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		982	}
109	}	983	}
110		984
111	unless ($MODEL) {	985	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
112	# try to load a model
113		986
114	for (@REGISTRY, @models) {	987	unshift @ISA, $MODEL;
115	my ($package, $model) = @$_;
116	if (eval "require $model") {
117	$MODEL = $model;
118	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
119	last;
120	}
121	}
122		988
		989	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		990
		991	(shift @post_detect)->() while @post_detect;
		992	}
		993
123	$MODEL	994	$MODEL
124	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	995	}
		996
		997	sub AUTOLOAD {
		998	(my $func = $AUTOLOAD) =~ s/.*://;
		999
		1000	$method{$func}
		1001	or croak "$func: not a valid method for AnyEvent objects";
		1002
		1003	detect unless $MODEL;
		1004
		1005	my $class = shift;
		1006	$class->$func (@_);
		1007	}
		1008
		1009	# utility function to dup a filehandle. this is used by many backends
		1010	# to support binding more than one watcher per filehandle (they usually
		1011	# allow only one watcher per fd, so we dup it to get a different one).
		1012	sub _dupfh($$$$) {
		1013	my ($poll, $fh, $r, $w) = @_;
		1014
		1015	# cygwin requires the fh mode to be matching, unix doesn't
		1016	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1017	: $poll eq "w" ? ($w, ">")
		1018	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1019
		1020	open my $fh2, "$mode&" . fileno $fh
		1021	or die "cannot dup() filehandle: $!";
		1022
		1023	# we assume CLOEXEC is already set by perl in all important cases
		1024
		1025	($fh2, $rw)
		1026	}
		1027
		1028	package AnyEvent::Base;
		1029
		1030	# default implementation for now and time
		1031
		1032	BEGIN {
		1033	if (eval "use Time::HiRes (); time (); 1") {
		1034	*_time = \&Time::HiRes::time;
		1035	# if (eval "use POSIX (); (POSIX::times())...
		1036	} else {
		1037	*_time = sub { time }; # epic fail
		1038	}
		1039	}
		1040
		1041	sub time { _time }
		1042	sub now { _time }
		1043
		1044	# default implementation for ->condvar
		1045
		1046	sub condvar {
		1047	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		1048	}
		1049
		1050	# default implementation for ->signal
		1051
		1052	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1053
		1054	sub _signal_exec {
		1055	sysread $SIGPIPE_R, my $dummy, 4;
		1056
		1057	while (%SIG_EV) {
		1058	for (keys %SIG_EV) {
		1059	delete $SIG_EV{$_};
		1060	$_->() for values %{ $SIG_CB{$_} || {} };
125	}	1061	}
126	}	1062	}
		1063	}
127		1064
128	@ISA = $MODEL;	1065	sub signal {
		1066	my (undef, %arg) = @_;
129		1067
		1068	unless ($SIGPIPE_R) {
		1069	if (AnyEvent::WIN32) {
		1070	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1071	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1072	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1073	} else {
		1074	pipe $SIGPIPE_R, $SIGPIPE_W;
		1075	require Fcntl;
		1076	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1077	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1078	}
		1079
		1080	$SIGPIPE_R
		1081	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1082
		1083	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1084	}
		1085
		1086	my $signal = uc $arg{signal}
		1087	or Carp::croak "required option 'signal' is missing";
		1088
		1089	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1090	$SIG{$signal} ||= sub {
		1091	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1092	undef $SIG_EV{$signal};
		1093	};
		1094
		1095	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		1096	}
		1097
		1098	sub AnyEvent::Base::Signal::DESTROY {
		1099	my ($signal, $cb) = @{$_[0]};
		1100
		1101	delete $SIG_CB{$signal}{$cb};
		1102
		1103	delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
		1104	}
		1105
		1106	# default implementation for ->child
		1107
		1108	our %PID_CB;
		1109	our $CHLD_W;
		1110	our $CHLD_DELAY_W;
		1111	our $PID_IDLE;
		1112	our $WNOHANG;
		1113
		1114	sub _child_wait {
		1115	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1116	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		1117	(values %{ $PID_CB{0} || {} });
		1118	}
		1119
		1120	undef $PID_IDLE;
		1121	}
		1122
		1123	sub _sigchld {
		1124	# make sure we deliver these changes "synchronous" with the event loop.
		1125	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		1126	undef $CHLD_DELAY_W;
		1127	&_child_wait;
		1128	});
		1129	}
		1130
		1131	sub child {
		1132	my (undef, %arg) = @_;
		1133
		1134	defined (my $pid = $arg{pid} + 0)
		1135	or Carp::croak "required option 'pid' is missing";
		1136
		1137	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1138
		1139	unless ($WNOHANG) {
		1140	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1141	}
		1142
		1143	unless ($CHLD_W) {
		1144	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1145	# child could be a zombie already, so make at least one round
		1146	&_sigchld;
		1147	}
		1148
		1149	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		1150	}
		1151
		1152	sub AnyEvent::Base::Child::DESTROY {
		1153	my ($pid, $cb) = @{$_[0]};
		1154
		1155	delete $PID_CB{$pid}{$cb};
		1156	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1157
		1158	undef $CHLD_W unless keys %PID_CB;
		1159	}
		1160
		1161	package AnyEvent::CondVar;
		1162
		1163	our @ISA = AnyEvent::CondVar::Base::;
		1164
		1165	package AnyEvent::CondVar::Base;
		1166
		1167	use overload
		1168	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1169	fallback => 1;
		1170
		1171	sub _send {
		1172	# nop
		1173	}
		1174
		1175	sub send {
130	my $class = shift;	1176	my $cv = shift;
131	$class->$AUTOLOAD (@_);	1177	$cv->{_ae_sent} = [@_];
		1178	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1179	$cv->_send;
132	}	1180	}
		1181
		1182	sub croak {
		1183	$_[0]{_ae_croak} = $_[1];
		1184	$_[0]->send;
		1185	}
		1186
		1187	sub ready {
		1188	$_[0]{_ae_sent}
		1189	}
		1190
		1191	sub _wait {
		1192	AnyEvent->one_event while !$_[0]{_ae_sent};
		1193	}
		1194
		1195	sub recv {
		1196	$_[0]->_wait;
		1197
		1198	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1199	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1200	}
		1201
		1202	sub cb {
		1203	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1204	$_[0]{_ae_cb}
		1205	}
		1206
		1207	sub begin {
		1208	++$_[0]{_ae_counter};
		1209	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1210	}
		1211
		1212	sub end {
		1213	return if --$_[0]{_ae_counter};
		1214	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1215	}
		1216
		1217	# undocumented/compatibility with pre-3.4
		1218	*broadcast = \&send;
		1219	*wait = \&_wait;
		1220
		1221	=head1 ERROR AND EXCEPTION HANDLING
		1222
		1223	In general, AnyEvent does not do any error handling - it relies on the
		1224	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1225	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1226	checking of all AnyEvent methods, however, which is highly useful during
		1227	development.
		1228
		1229	As for exception handling (i.e. runtime errors and exceptions thrown while
		1230	executing a callback), this is not only highly event-loop specific, but
		1231	also not in any way wrapped by this module, as this is the job of the main
		1232	program.
		1233
		1234	The pure perl event loop simply re-throws the exception (usually
		1235	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1236	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1237	so on.
		1238
		1239	=head1 ENVIRONMENT VARIABLES
		1240
		1241	The following environment variables are used by this module or its
		1242	submodules:
		1243
		1244	=over 4
		1245
		1246	=item C<PERL_ANYEVENT_VERBOSE>
		1247
		1248	By default, AnyEvent will be completely silent except in fatal
		1249	conditions. You can set this environment variable to make AnyEvent more
		1250	talkative.
		1251
		1252	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1253	conditions, such as not being able to load the event model specified by
		1254	C<PERL_ANYEVENT_MODEL>.
		1255
		1256	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1257	model it chooses.
		1258
		1259	=item C<PERL_ANYEVENT_STRICT>
		1260
		1261	AnyEvent does not do much argument checking by default, as thorough
		1262	argument checking is very costly. Setting this variable to a true value
		1263	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1264	check the arguments passed to most method calls. If it finds any problems
		1265	it will croak.
		1266
		1267	In other words, enables "strict" mode.
		1268
		1269	Unlike C<use strict>, it is definitely recommended ot keep it off in
		1270	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1271	developing programs can be very useful, however.
		1272
		1273	=item C<PERL_ANYEVENT_MODEL>
		1274
		1275	This can be used to specify the event model to be used by AnyEvent, before
		1276	auto detection and -probing kicks in. It must be a string consisting
		1277	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1278	and the resulting module name is loaded and if the load was successful,
		1279	used as event model. If it fails to load AnyEvent will proceed with
		1280	auto detection and -probing.
		1281
		1282	This functionality might change in future versions.
		1283
		1284	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1285	could start your program like this:
		1286
		1287	PERL_ANYEVENT_MODEL=Perl perl ...
		1288
		1289	=item C<PERL_ANYEVENT_PROTOCOLS>
		1290
		1291	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1292	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1293	of auto probing).
		1294
		1295	Must be set to a comma-separated list of protocols or address families,
		1296	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1297	used, and preference will be given to protocols mentioned earlier in the
		1298	list.
		1299
		1300	This variable can effectively be used for denial-of-service attacks
		1301	against local programs (e.g. when setuid), although the impact is likely
		1302	small, as the program has to handle conenction and other failures anyways.
		1303
		1304	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1305	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1306	- only support IPv4, never try to resolve or contact IPv6
		1307	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1308	IPv6, but prefer IPv6 over IPv4.
		1309
		1310	=item C<PERL_ANYEVENT_EDNS0>
		1311
		1312	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1313	for DNS. This extension is generally useful to reduce DNS traffic, but
		1314	some (broken) firewalls drop such DNS packets, which is why it is off by
		1315	default.
		1316
		1317	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1318	EDNS0 in its DNS requests.
		1319
		1320	=item C<PERL_ANYEVENT_MAX_FORKS>
		1321
		1322	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1323	will create in parallel.
133		1324
134	=back	1325	=back
135		1326
136	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1327	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1328
		1329	This is an advanced topic that you do not normally need to use AnyEvent in
		1330	a module. This section is only of use to event loop authors who want to
		1331	provide AnyEvent compatibility.
137		1332
138	If you need to support another event library which isn't directly	1333	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	1334	supported by AnyEvent, you can supply your own interface to it by
140	pushing, before the first watcher gets created, the package name of	1335	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	1336	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	1337	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
143	AnyEvent.	1338	AnyEvent, so it is reasonably cheap.
144		1339
145	Example:	1340	Example:
146		1341
147	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1342	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
148		1343
149	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1344	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
150	package/class when it finds the C<urxvt> package/module is loaded. When	1345	package/class when it finds the C<urxvt> package/module is already loaded.
		1346
151	AnyEvent is loaded and asked to find a suitable event model, it will	1347	When AnyEvent is loaded and asked to find a suitable event model, it
152	first check for the presence of urxvt.	1348	will first check for the presence of urxvt by trying to C<use> the
		1349	C<urxvt::anyevent> module.
153		1350
154	The class should prove implementations for all watcher types (see	1351	The class should provide implementations for all watcher types. See
155	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1352	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	1353	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
157	AnyEvent::Impl::Glib> to see the sources).	1354	see the sources.
158		1355
		1356	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1357	provide suitable (hopefully) replacements.
		1358
159	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1359	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	1360	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	1361	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	1362	inside I<rxvt-unicode>, and it is updated and maintained as part of the
163	I<rxvt-unicode> distribution.	1363	I<rxvt-unicode> distribution.
164		1364
165	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1365	I<rxvt-unicode> also cheats a bit by not providing blocking access to
166	condition variables: code blocking while waiting for a condition will	1366	condition variables: code blocking while waiting for a condition will
167	C<die>. This still works with most modules/usages, and blocking calls must	1367	C<die>. This still works with most modules/usages, and blocking calls must
168	not be in an interactive appliation, so it makes sense.	1368	not be done in an interactive application, so it makes sense.
169		1369
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	1370	=head1 EXAMPLE PROGRAM
178		1371
179	The following program uses an io watcher to read data from stdin, a timer	1372	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	1373	to display a message once per second, and a condition variable to quit the
181	when the user enters quit:	1374	program when the user enters quit:
182		1375
183	use AnyEvent;	1376	use AnyEvent;
184		1377
185	my $cv = AnyEvent->condvar;	1378	my $cv = AnyEvent->condvar;
186		1379
187	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1380	my $io_watcher = AnyEvent->io (
		1381	fh => \*STDIN,
		1382	poll => 'r',
		1383	cb => sub {
188	warn "io event <$_[0]>\n"; # will always output <r>	1384	warn "io event <$_[0]>\n"; # will always output <r>
189	chomp (my $input = <STDIN>); # read a line	1385	chomp (my $input = <STDIN>); # read a line
190	warn "read: $input\n"; # output what has been read	1386	warn "read: $input\n"; # output what has been read
191	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1387	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1388	},
192	});	1389	);
193		1390
194	my $time_watcher; # can only be used once	1391	my $time_watcher; # can only be used once
195		1392
196	sub new_timer {	1393	sub new_timer {
197	$timer = AnyEvent->timer (after => 1, cb => sub {	1394	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
200	});	1397	});
201	}	1398	}
202		1399
203	new_timer; # create first timer	1400	new_timer; # create first timer
204		1401
205	$cv->wait; # wait until user enters /^q/i	1402	$cv->recv; # wait until user enters /^q/i
206		1403
207	=head1 REAL-WORLD EXAMPLE	1404	=head1 REAL-WORLD EXAMPLE
208		1405
209	Consider the L<Net::FCP> module. It features (among others) the following	1406	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:	1407	API calls, which are to freenet what HTTP GET requests are to http:
…		…
260	syswrite $txn->{fh}, $txn->{request}	1457	syswrite $txn->{fh}, $txn->{request}
261	or die "connection or write error";	1458	or die "connection or write error";
262	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1459	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
263		1460
264	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1461	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:	1462	result and signals any possible waiters that the request has finished:
266		1463
267	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1464	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
268		1465
269	if (end-of-file or data complete) {	1466	if (end-of-file or data complete) {
270	$txn->{result} = $txn->{buf};	1467	$txn->{result} = $txn->{buf};
271	$txn->{finished}->broadcast;	1468	$txn->{finished}->send;
272	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1469	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
273	}	1470	}
274		1471
275	The C<result> method, finally, just waits for the finished signal (if the	1472	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	1473	request was already finished, it doesn't wait, of course, and returns the
277	data:	1474	data:
278		1475
279	$txn->{finished}->wait;	1476	$txn->{finished}->recv;
280	return $txn->{result};	1477	return $txn->{result};
281		1478
282	The actual code goes further and collects all errors (C<die>s, exceptions)	1479	The actual code goes further and collects all errors (C<die>s, exceptions)
283	that occured during request processing. The C<result> method detects	1480	that occurred during request processing. The C<result> method detects
284	wether an exception as thrown (it is stored inside the $txn object)	1481	whether an exception as thrown (it is stored inside the $txn object)
285	and just throws the exception, which means connection errors and other	1482	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	1483	problems get reported tot he code that tries to use the result, not in a
287	random callback.	1484	random callback.
288		1485
289	All of this enables the following usage styles:	1486	All of this enables the following usage styles:
290		1487
291	1. Blocking:	1488	1. Blocking:
292		1489
293	my $data = $fcp->client_get ($url);	1490	my $data = $fcp->client_get ($url);
294		1491
295	2. Blocking, but parallelizing:	1492	2. Blocking, but running in parallel:
296		1493
297	my @datas = map $_->result,	1494	my @datas = map $_->result,
298	map $fcp->txn_client_get ($_),	1495	map $fcp->txn_client_get ($_),
299	@urls;	1496	@urls;
300		1497
301	Both blocking examples work without the module user having to know	1498	Both blocking examples work without the module user having to know
302	anything about events.	1499	anything about events.
303		1500
304	3a. Event-based in a main program, using any support Event module:	1501	3a. Event-based in a main program, using any supported event module:
305		1502
306	use Event;	1503	use EV;
307		1504
308	$fcp->txn_client_get ($url)->cb (sub {	1505	$fcp->txn_client_get ($url)->cb (sub {
309	my $txn = shift;	1506	my $txn = shift;
310	my $data = $txn->result;	1507	my $data = $txn->result;
311	...	1508	...
312	});	1509	});
313		1510
314	Event::loop;	1511	EV::loop;
315		1512
316	3b. The module user could use AnyEvent, too:	1513	3b. The module user could use AnyEvent, too:
317		1514
318	use AnyEvent;	1515	use AnyEvent;
319		1516
320	my $quit = AnyEvent->condvar;	1517	my $quit = AnyEvent->condvar;
321		1518
322	$fcp->txn_client_get ($url)->cb (sub {	1519	$fcp->txn_client_get ($url)->cb (sub {
323	...	1520	...
324	$quit->broadcast;	1521	$quit->send;
325	});	1522	});
326		1523
327	$quit->wait;	1524	$quit->recv;
		1525
		1526
		1527	=head1 BENCHMARKS
		1528
		1529	To give you an idea of the performance and overheads that AnyEvent adds
		1530	over the event loops themselves and to give you an impression of the speed
		1531	of various event loops I prepared some benchmarks.
		1532
		1533	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1534
		1535	Here is a benchmark of various supported event models used natively and
		1536	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1537	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1538	which it is), lets them fire exactly once and destroys them again.
		1539
		1540	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1541	distribution.
		1542
		1543	=head3 Explanation of the columns
		1544
		1545	I<watcher> is the number of event watchers created/destroyed. Since
		1546	different event models feature vastly different performances, each event
		1547	loop was given a number of watchers so that overall runtime is acceptable
		1548	and similar between tested event loop (and keep them from crashing): Glib
		1549	would probably take thousands of years if asked to process the same number
		1550	of watchers as EV in this benchmark.
		1551
		1552	I<bytes> is the number of bytes (as measured by the resident set size,
		1553	RSS) consumed by each watcher. This method of measuring captures both C
		1554	and Perl-based overheads.
		1555
		1556	I<create> is the time, in microseconds (millionths of seconds), that it
		1557	takes to create a single watcher. The callback is a closure shared between
		1558	all watchers, to avoid adding memory overhead. That means closure creation
		1559	and memory usage is not included in the figures.
		1560
		1561	I<invoke> is the time, in microseconds, used to invoke a simple
		1562	callback. The callback simply counts down a Perl variable and after it was
		1563	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1564	signal the end of this phase.
		1565
		1566	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1567	watcher.
		1568
		1569	=head3 Results
		1570
		1571	name watchers bytes create invoke destroy comment
		1572	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1573	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1574	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1575	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1576	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1577	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1578	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1579	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1580	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1581	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1582
		1583	=head3 Discussion
		1584
		1585	The benchmark does I<not> measure scalability of the event loop very
		1586	well. For example, a select-based event loop (such as the pure perl one)
		1587	can never compete with an event loop that uses epoll when the number of
		1588	file descriptors grows high. In this benchmark, all events become ready at
		1589	the same time, so select/poll-based implementations get an unnatural speed
		1590	boost.
		1591
		1592	Also, note that the number of watchers usually has a nonlinear effect on
		1593	overall speed, that is, creating twice as many watchers doesn't take twice
		1594	the time - usually it takes longer. This puts event loops tested with a
		1595	higher number of watchers at a disadvantage.
		1596
		1597	To put the range of results into perspective, consider that on the
		1598	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1599	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1600	cycles with POE.
		1601
		1602	C<EV> is the sole leader regarding speed and memory use, which are both
		1603	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1604	far less memory than any other event loop and is still faster than Event
		1605	natively.
		1606
		1607	The pure perl implementation is hit in a few sweet spots (both the
		1608	constant timeout and the use of a single fd hit optimisations in the perl
		1609	interpreter and the backend itself). Nevertheless this shows that it
		1610	adds very little overhead in itself. Like any select-based backend its
		1611	performance becomes really bad with lots of file descriptors (and few of
		1612	them active), of course, but this was not subject of this benchmark.
		1613
		1614	The C<Event> module has a relatively high setup and callback invocation
		1615	cost, but overall scores in on the third place.
		1616
		1617	C<Glib>'s memory usage is quite a bit higher, but it features a
		1618	faster callback invocation and overall ends up in the same class as
		1619	C<Event>. However, Glib scales extremely badly, doubling the number of
		1620	watchers increases the processing time by more than a factor of four,
		1621	making it completely unusable when using larger numbers of watchers
		1622	(note that only a single file descriptor was used in the benchmark, so
		1623	inefficiencies of C<poll> do not account for this).
		1624
		1625	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1626	more than 2000 watchers is a big setback, however, as correctness takes
		1627	precedence over speed. Nevertheless, its performance is surprising, as the
		1628	file descriptor is dup()ed for each watcher. This shows that the dup()
		1629	employed by some adaptors is not a big performance issue (it does incur a
		1630	hidden memory cost inside the kernel which is not reflected in the figures
		1631	above).
		1632
		1633	C<POE>, regardless of underlying event loop (whether using its pure perl
		1634	select-based backend or the Event module, the POE-EV backend couldn't
		1635	be tested because it wasn't working) shows abysmal performance and
		1636	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1637	as EV watchers, and 10 times as much memory as Event (the high memory
		1638	requirements are caused by requiring a session for each watcher). Watcher
		1639	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1640	implementation.
		1641
		1642	The design of the POE adaptor class in AnyEvent can not really account
		1643	for the performance issues, though, as session creation overhead is
		1644	small compared to execution of the state machine, which is coded pretty
		1645	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1646	using multiple sessions is not a good approach, especially regarding
		1647	memory usage, even the author of POE could not come up with a faster
		1648	design).
		1649
		1650	=head3 Summary
		1651
		1652	=over 4
		1653
		1654	=item * Using EV through AnyEvent is faster than any other event loop
		1655	(even when used without AnyEvent), but most event loops have acceptable
		1656	performance with or without AnyEvent.
		1657
		1658	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1659	the actual event loop, only with extremely fast event loops such as EV
		1660	adds AnyEvent significant overhead.
		1661
		1662	=item * You should avoid POE like the plague if you want performance or
		1663	reasonable memory usage.
		1664
		1665	=back
		1666
		1667	=head2 BENCHMARKING THE LARGE SERVER CASE
		1668
		1669	This benchmark actually benchmarks the event loop itself. It works by
		1670	creating a number of "servers": each server consists of a socket pair, a
		1671	timeout watcher that gets reset on activity (but never fires), and an I/O
		1672	watcher waiting for input on one side of the socket. Each time the socket
		1673	watcher reads a byte it will write that byte to a random other "server".
		1674
		1675	The effect is that there will be a lot of I/O watchers, only part of which
		1676	are active at any one point (so there is a constant number of active
		1677	fds for each loop iteration, but which fds these are is random). The
		1678	timeout is reset each time something is read because that reflects how
		1679	most timeouts work (and puts extra pressure on the event loops).
		1680
		1681	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1682	(1%) are active. This mirrors the activity of large servers with many
		1683	connections, most of which are idle at any one point in time.
		1684
		1685	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1686	distribution.
		1687
		1688	=head3 Explanation of the columns
		1689
		1690	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1691	each server has a read and write socket end).
		1692
		1693	I<create> is the time it takes to create a socket pair (which is
		1694	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1695
		1696	I<request>, the most important value, is the time it takes to handle a
		1697	single "request", that is, reading the token from the pipe and forwarding
		1698	it to another server. This includes deleting the old timeout and creating
		1699	a new one that moves the timeout into the future.
		1700
		1701	=head3 Results
		1702
		1703	name sockets create request
		1704	EV 20000 69.01 11.16
		1705	Perl 20000 73.32 35.87
		1706	Event 20000 212.62 257.32
		1707	Glib 20000 651.16 1896.30
		1708	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1709
		1710	=head3 Discussion
		1711
		1712	This benchmark I<does> measure scalability and overall performance of the
		1713	particular event loop.
		1714
		1715	EV is again fastest. Since it is using epoll on my system, the setup time
		1716	is relatively high, though.
		1717
		1718	Perl surprisingly comes second. It is much faster than the C-based event
		1719	loops Event and Glib.
		1720
		1721	Event suffers from high setup time as well (look at its code and you will
		1722	understand why). Callback invocation also has a high overhead compared to
		1723	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1724	uses select or poll in basically all documented configurations.
		1725
		1726	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1727	clearly fails to perform with many filehandles or in busy servers.
		1728
		1729	POE is still completely out of the picture, taking over 1000 times as long
		1730	as EV, and over 100 times as long as the Perl implementation, even though
		1731	it uses a C-based event loop in this case.
		1732
		1733	=head3 Summary
		1734
		1735	=over 4
		1736
		1737	=item * The pure perl implementation performs extremely well.
		1738
		1739	=item * Avoid Glib or POE in large projects where performance matters.
		1740
		1741	=back
		1742
		1743	=head2 BENCHMARKING SMALL SERVERS
		1744
		1745	While event loops should scale (and select-based ones do not...) even to
		1746	large servers, most programs we (or I :) actually write have only a few
		1747	I/O watchers.
		1748
		1749	In this benchmark, I use the same benchmark program as in the large server
		1750	case, but it uses only eight "servers", of which three are active at any
		1751	one time. This should reflect performance for a small server relatively
		1752	well.
		1753
		1754	The columns are identical to the previous table.
		1755
		1756	=head3 Results
		1757
		1758	name sockets create request
		1759	EV 16 20.00 6.54
		1760	Perl 16 25.75 12.62
		1761	Event 16 81.27 35.86
		1762	Glib 16 32.63 15.48
		1763	POE 16 261.87 276.28 uses POE::Loop::Event
		1764
		1765	=head3 Discussion
		1766
		1767	The benchmark tries to test the performance of a typical small
		1768	server. While knowing how various event loops perform is interesting, keep
		1769	in mind that their overhead in this case is usually not as important, due
		1770	to the small absolute number of watchers (that is, you need efficiency and
		1771	speed most when you have lots of watchers, not when you only have a few of
		1772	them).
		1773
		1774	EV is again fastest.
		1775
		1776	Perl again comes second. It is noticeably faster than the C-based event
		1777	loops Event and Glib, although the difference is too small to really
		1778	matter.
		1779
		1780	POE also performs much better in this case, but is is still far behind the
		1781	others.
		1782
		1783	=head3 Summary
		1784
		1785	=over 4
		1786
		1787	=item * C-based event loops perform very well with small number of
		1788	watchers, as the management overhead dominates.
		1789
		1790	=back
		1791
		1792
		1793	=head1 SIGNALS
		1794
		1795	AnyEvent currently installs handlers for these signals:
		1796
		1797	=over 4
		1798
		1799	=item SIGCHLD
		1800
		1801	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		1802	emulation for event loops that do not support them natively. Also, some
		1803	event loops install a similar handler.
		1804
		1805	=item SIGPIPE
		1806
		1807	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		1808	when AnyEvent gets loaded.
		1809
		1810	The rationale for this is that AnyEvent users usually do not really depend
		1811	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		1812	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		1813	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		1814	some random socket.
		1815
		1816	The rationale for installing a no-op handler as opposed to ignoring it is
		1817	that this way, the handler will be restored to defaults on exec.
		1818
		1819	Feel free to install your own handler, or reset it to defaults.
		1820
		1821	=back
		1822
		1823	=cut
		1824
		1825	$SIG{PIPE} = sub { }
		1826	unless defined $SIG{PIPE};
		1827
		1828
		1829	=head1 FORK
		1830
		1831	Most event libraries are not fork-safe. The ones who are usually are
		1832	because they rely on inefficient but fork-safe C<select> or C<poll>
		1833	calls. Only L<EV> is fully fork-aware.
		1834
		1835	If you have to fork, you must either do so I<before> creating your first
		1836	watcher OR you must not use AnyEvent at all in the child.
		1837
		1838
		1839	=head1 SECURITY CONSIDERATIONS
		1840
		1841	AnyEvent can be forced to load any event model via
		1842	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1843	execute arbitrary code or directly gain access, it can easily be used to
		1844	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1845	will not be active when the program uses a different event model than
		1846	specified in the variable.
		1847
		1848	You can make AnyEvent completely ignore this variable by deleting it
		1849	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1850
		1851	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1852
		1853	use AnyEvent;
		1854
		1855	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1856	be used to probe what backend is used and gain other information (which is
		1857	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1858	$ENV{PERL_ANYEGENT_STRICT}.
		1859
		1860
		1861	=head1 BUGS
		1862
		1863	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1864	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1865	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1866	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1867	pronounced).
		1868
328		1869
329	=head1 SEE ALSO	1870	=head1 SEE ALSO
330		1871
331	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1872	Utility functions: L<AnyEvent::Util>.
332		1873
333	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1874	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1875	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
334		1876
335	Nontrivial usage example: L<Net::FCP>.	1877	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1878	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1879	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1880	L<AnyEvent::Impl::POE>.
336		1881
337	=head1	1882	Non-blocking file handles, sockets, TCP clients and
		1883	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1884
		1885	Asynchronous DNS: L<AnyEvent::DNS>.
		1886
		1887	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1888
		1889	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1890
		1891
		1892	=head1 AUTHOR
		1893
		1894	Marc Lehmann <schmorp@schmorp.de>
		1895	http://home.schmorp.de/
338		1896
339	=cut	1897	=cut
340		1898
341	1	1899	1
342		1900

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