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Revision 1.200 by root, Wed Apr 1 14:02:27 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	26	my $w = AnyEvent->condvar; # stores whether a condition was flagged
17	(i.e. on a socket you can have one r + one w or one rw	27	$w->send; # wake up current and all future recv's
18	watcher, not any more.
19
20	- AnyEvent will keep filehandles alive, so as long as the watcher exists,
21	the filehandle exists.
22
23	my $w = AnyEvent->timer (after => $seconds, cb => sub {
24	...
25	});
26
27	- io and time watchers get canceled whenever $w is destroyed, so keep a copy
28
29	- timers can only be used once and must be recreated for repeated operation
30
31	my $w = AnyEvent->condvar; # kind of main loop replacement
32	$w->wait; # enters main loop till $condvar gets ->broadcast	28	$w->recv; # enters "main loop" till $condvar gets ->send
33	$w->broadcast; # wake up current and all future wait's	29	# use a condvar in callback mode:
		30	$w->cb (sub { $_[0]->recv });
34		31
35	- condvars are used to give blocking behaviour when neccessary. Create	32	=head1 INTRODUCTION/TUTORIAL
36	a condvar for any "request" or "event" your module might create, C<<	33
37	->broadcast >> it when the event happens and provide a function that calls	34	This manpage is mainly a reference manual. If you are interested
38	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.
39		92
40	=head1 DESCRIPTION	93	=head1 DESCRIPTION
41		94
42	L<AnyEvent> provides an identical interface to multiple event loops. This	95	L<AnyEvent> provides an identical interface to multiple event loops. This
43	allows module authors to utilizy an event loop without forcing module	96	allows module authors to utilise an event loop without forcing module
44	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
45	peacefully at any one time).	98	peacefully at any one time).
46		99
47	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>
48	module.	101	module.
49		102
50	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
51	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
52	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	105	following modules is already loaded: L<EV>,
53	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>,
54	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
55	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> is the Perl I<file handle> (I<not> file descriptor) to watch
		174	for events (AnyEvent might or might not keep a reference to this file
		175	handle). Note that only file handles pointing to things for which
		176	non-blocking operation makes sense are allowed. This includes sockets,
		177	most character devices, pipes, fifos and so on, but not for example files
		178	or block devices.
		179
		180	C<poll> must be a string that is either C<r> or C<w>, which creates a
		181	watcher waiting for "r"eadable or "w"ritable events, respectively.
		182
		183	C<cb> is the callback to invoke each time the file handle becomes ready.
		184
		185	Although the callback might get passed parameters, their value and
		186	presence is undefined and you cannot rely on them. Portable AnyEvent
		187	callbacks cannot use arguments passed to I/O watcher callbacks.
		188
		189	The I/O watcher might use the underlying file descriptor or a copy of it.
		190	You must not close a file handle as long as any watcher is active on the
		191	underlying file descriptor.
		192
		193	Some event loops issue spurious readyness notifications, so you should
		194	always use non-blocking calls when reading/writing from/to your file
		195	handles.
		196
		197	Example: wait for readability of STDIN, then read a line and disable the
		198	watcher.
		199
		200	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		201	chomp (my $input = <STDIN>);
		202	warn "read: $input\n";
		203	undef $w;
		204	});
		205
		206	=head2 TIME WATCHERS
		207
		208	You can create a time watcher by calling the C<< AnyEvent->timer >>
		209	method with the following mandatory arguments:
		210
		211	C<after> specifies after how many seconds (fractional values are
		212	supported) the callback should be invoked. C<cb> is the callback to invoke
		213	in that case.
		214
		215	Although the callback might get passed parameters, their value and
		216	presence is undefined and you cannot rely on them. Portable AnyEvent
		217	callbacks cannot use arguments passed to time watcher callbacks.
		218
		219	The callback will normally be invoked once only. If you specify another
		220	parameter, C<interval>, as a strictly positive number (> 0), then the
		221	callback will be invoked regularly at that interval (in fractional
		222	seconds) after the first invocation. If C<interval> is specified with a
		223	false value, then it is treated as if it were missing.
		224
		225	The callback will be rescheduled before invoking the callback, but no
		226	attempt is done to avoid timer drift in most backends, so the interval is
		227	only approximate.
		228
		229	Example: fire an event after 7.7 seconds.
		230
		231	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		232	warn "timeout\n";
		233	});
		234
		235	# to cancel the timer:
		236	undef $w;
		237
		238	Example 2: fire an event after 0.5 seconds, then roughly every second.
		239
		240	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		241	warn "timeout\n";
		242	};
		243
		244	=head3 TIMING ISSUES
		245
		246	There are two ways to handle timers: based on real time (relative, "fire
		247	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		248	o'clock").
		249
		250	While most event loops expect timers to specified in a relative way, they
		251	use absolute time internally. This makes a difference when your clock
		252	"jumps", for example, when ntp decides to set your clock backwards from
		253	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		254	fire "after" a second might actually take six years to finally fire.
		255
		256	AnyEvent cannot compensate for this. The only event loop that is conscious
		257	about these issues is L<EV>, which offers both relative (ev_timer, based
		258	on true relative time) and absolute (ev_periodic, based on wallclock time)
		259	timers.
		260
		261	AnyEvent always prefers relative timers, if available, matching the
		262	AnyEvent API.
		263
		264	AnyEvent has two additional methods that return the "current time":
56		265
57	=over 4	266	=over 4
58		267
		268	=item AnyEvent->time
		269
		270	This returns the "current wallclock time" as a fractional number of
		271	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		272	return, and the result is guaranteed to be compatible with those).
		273
		274	It progresses independently of any event loop processing, i.e. each call
		275	will check the system clock, which usually gets updated frequently.
		276
		277	=item AnyEvent->now
		278
		279	This also returns the "current wallclock time", but unlike C<time>, above,
		280	this value might change only once per event loop iteration, depending on
		281	the event loop (most return the same time as C<time>, above). This is the
		282	time that AnyEvent's timers get scheduled against.
		283
		284	I<In almost all cases (in all cases if you don't care), this is the
		285	function to call when you want to know the current time.>
		286
		287	This function is also often faster then C<< AnyEvent->time >>, and
		288	thus the preferred method if you want some timestamp (for example,
		289	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		290
		291	The rest of this section is only of relevance if you try to be very exact
		292	with your timing, you can skip it without bad conscience.
		293
		294	For a practical example of when these times differ, consider L<Event::Lib>
		295	and L<EV> and the following set-up:
		296
		297	The event loop is running and has just invoked one of your callback at
		298	time=500 (assume no other callbacks delay processing). In your callback,
		299	you wait a second by executing C<sleep 1> (blocking the process for a
		300	second) and then (at time=501) you create a relative timer that fires
		301	after three seconds.
		302
		303	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		304	both return C<501>, because that is the current time, and the timer will
		305	be scheduled to fire at time=504 (C<501> + C<3>).
		306
		307	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		308	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		309	last event processing phase started. With L<EV>, your timer gets scheduled
		310	to run at time=503 (C<500> + C<3>).
		311
		312	In one sense, L<Event::Lib> is more exact, as it uses the current time
		313	regardless of any delays introduced by event processing. However, most
		314	callbacks do not expect large delays in processing, so this causes a
		315	higher drift (and a lot more system calls to get the current time).
		316
		317	In another sense, L<EV> is more exact, as your timer will be scheduled at
		318	the same time, regardless of how long event processing actually took.
		319
		320	In either case, if you care (and in most cases, you don't), then you
		321	can get whatever behaviour you want with any event loop, by taking the
		322	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		323	account.
		324
		325	=back
		326
		327	=head2 SIGNAL WATCHERS
		328
		329	You can watch for signals using a signal watcher, C<signal> is the signal
		330	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		331	callback to be invoked whenever a signal occurs.
		332
		333	Although the callback might get passed parameters, their value and
		334	presence is undefined and you cannot rely on them. Portable AnyEvent
		335	callbacks cannot use arguments passed to signal watcher callbacks.
		336
		337	Multiple signal occurrences can be clumped together into one callback
		338	invocation, and callback invocation will be synchronous. Synchronous means
		339	that it might take a while until the signal gets handled by the process,
		340	but it is guaranteed not to interrupt any other callbacks.
		341
		342	The main advantage of using these watchers is that you can share a signal
		343	between multiple watchers.
		344
		345	This watcher might use C<%SIG>, so programs overwriting those signals
		346	directly will likely not work correctly.
		347
		348	Example: exit on SIGINT
		349
		350	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		351
		352	=head2 CHILD PROCESS WATCHERS
		353
		354	You can also watch on a child process exit and catch its exit status.
		355
		356	The child process is specified by the C<pid> argument (if set to C<0>, it
		357	watches for any child process exit). The watcher will triggered only when
		358	the child process has finished and an exit status is available, not on
		359	any trace events (stopped/continued).
		360
		361	The callback will be called with the pid and exit status (as returned by
		362	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		363	callback arguments.
		364
		365	This watcher type works by installing a signal handler for C<SIGCHLD>,
		366	and since it cannot be shared, nothing else should use SIGCHLD or reap
		367	random child processes (waiting for specific child processes, e.g. inside
		368	C<system>, is just fine).
		369
		370	There is a slight catch to child watchers, however: you usually start them
		371	I<after> the child process was created, and this means the process could
		372	have exited already (and no SIGCHLD will be sent anymore).
		373
		374	Not all event models handle this correctly (POE doesn't), but even for
		375	event models that I<do> handle this correctly, they usually need to be
		376	loaded before the process exits (i.e. before you fork in the first place).
		377
		378	This means you cannot create a child watcher as the very first thing in an
		379	AnyEvent program, you I<have> to create at least one watcher before you
		380	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		381
		382	Example: fork a process and wait for it
		383
		384	my $done = AnyEvent->condvar;
		385
		386	my $pid = fork or exit 5;
		387
		388	my $w = AnyEvent->child (
		389	pid => $pid,
		390	cb => sub {
		391	my ($pid, $status) = @_;
		392	warn "pid $pid exited with status $status";
		393	$done->send;
		394	},
		395	);
		396
		397	# do something else, then wait for process exit
		398	$done->recv;
		399
		400	=head2 CONDITION VARIABLES
		401
		402	If you are familiar with some event loops you will know that all of them
		403	require you to run some blocking "loop", "run" or similar function that
		404	will actively watch for new events and call your callbacks.
		405
		406	AnyEvent is different, it expects somebody else to run the event loop and
		407	will only block when necessary (usually when told by the user).
		408
		409	The instrument to do that is called a "condition variable", so called
		410	because they represent a condition that must become true.
		411
		412	Condition variables can be created by calling the C<< AnyEvent->condvar
		413	>> method, usually without arguments. The only argument pair allowed is
		414
		415	C<cb>, which specifies a callback to be called when the condition variable
		416	becomes true, with the condition variable as the first argument (but not
		417	the results).
		418
		419	After creation, the condition variable is "false" until it becomes "true"
		420	by calling the C<send> method (or calling the condition variable as if it
		421	were a callback, read about the caveats in the description for the C<<
		422	->send >> method).
		423
		424	Condition variables are similar to callbacks, except that you can
		425	optionally wait for them. They can also be called merge points - points
		426	in time where multiple outstanding events have been processed. And yet
		427	another way to call them is transactions - each condition variable can be
		428	used to represent a transaction, which finishes at some point and delivers
		429	a result.
		430
		431	Condition variables are very useful to signal that something has finished,
		432	for example, if you write a module that does asynchronous http requests,
		433	then a condition variable would be the ideal candidate to signal the
		434	availability of results. The user can either act when the callback is
		435	called or can synchronously C<< ->recv >> for the results.
		436
		437	You can also use them to simulate traditional event loops - for example,
		438	you can block your main program until an event occurs - for example, you
		439	could C<< ->recv >> in your main program until the user clicks the Quit
		440	button of your app, which would C<< ->send >> the "quit" event.
		441
		442	Note that condition variables recurse into the event loop - if you have
		443	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		444	lose. Therefore, condition variables are good to export to your caller, but
		445	you should avoid making a blocking wait yourself, at least in callbacks,
		446	as this asks for trouble.
		447
		448	Condition variables are represented by hash refs in perl, and the keys
		449	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		450	easy (it is often useful to build your own transaction class on top of
		451	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		452	it's C<new> method in your own C<new> method.
		453
		454	There are two "sides" to a condition variable - the "producer side" which
		455	eventually calls C<< -> send >>, and the "consumer side", which waits
		456	for the send to occur.
		457
		458	Example: wait for a timer.
		459
		460	# wait till the result is ready
		461	my $result_ready = AnyEvent->condvar;
		462
		463	# do something such as adding a timer
		464	# or socket watcher the calls $result_ready->send
		465	# when the "result" is ready.
		466	# in this case, we simply use a timer:
		467	my $w = AnyEvent->timer (
		468	after => 1,
		469	cb => sub { $result_ready->send },
		470	);
		471
		472	# this "blocks" (while handling events) till the callback
		473	# calls send
		474	$result_ready->recv;
		475
		476	Example: wait for a timer, but take advantage of the fact that
		477	condition variables are also code references.
		478
		479	my $done = AnyEvent->condvar;
		480	my $delay = AnyEvent->timer (after => 5, cb => $done);
		481	$done->recv;
		482
		483	Example: Imagine an API that returns a condvar and doesn't support
		484	callbacks. This is how you make a synchronous call, for example from
		485	the main program:
		486
		487	use AnyEvent::CouchDB;
		488
		489	...
		490
		491	my @info = $couchdb->info->recv;
		492
		493	And this is how you would just ste a callback to be called whenever the
		494	results are available:
		495
		496	$couchdb->info->cb (sub {
		497	my @info = $_[0]->recv;
		498	});
		499
		500	=head3 METHODS FOR PRODUCERS
		501
		502	These methods should only be used by the producing side, i.e. the
		503	code/module that eventually sends the signal. Note that it is also
		504	the producer side which creates the condvar in most cases, but it isn't
		505	uncommon for the consumer to create it as well.
		506
		507	=over 4
		508
		509	=item $cv->send (...)
		510
		511	Flag the condition as ready - a running C<< ->recv >> and all further
		512	calls to C<recv> will (eventually) return after this method has been
		513	called. If nobody is waiting the send will be remembered.
		514
		515	If a callback has been set on the condition variable, it is called
		516	immediately from within send.
		517
		518	Any arguments passed to the C<send> call will be returned by all
		519	future C<< ->recv >> calls.
		520
		521	Condition variables are overloaded so one can call them directly
		522	(as a code reference). Calling them directly is the same as calling
		523	C<send>. Note, however, that many C-based event loops do not handle
		524	overloading, so as tempting as it may be, passing a condition variable
		525	instead of a callback does not work. Both the pure perl and EV loops
		526	support overloading, however, as well as all functions that use perl to
		527	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		528	example).
		529
		530	=item $cv->croak ($error)
		531
		532	Similar to send, but causes all call's to C<< ->recv >> to invoke
		533	C<Carp::croak> with the given error message/object/scalar.
		534
		535	This can be used to signal any errors to the condition variable
		536	user/consumer.
		537
		538	=item $cv->begin ([group callback])
		539
		540	=item $cv->end
		541
		542	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		543
		544	These two methods can be used to combine many transactions/events into
		545	one. For example, a function that pings many hosts in parallel might want
		546	to use a condition variable for the whole process.
		547
		548	Every call to C<< ->begin >> will increment a counter, and every call to
		549	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		550	>>, the (last) callback passed to C<begin> will be executed. That callback
		551	is I<supposed> to call C<< ->send >>, but that is not required. If no
		552	callback was set, C<send> will be called without any arguments.
		553
		554	Let's clarify this with the ping example:
		555
		556	my $cv = AnyEvent->condvar;
		557
		558	my %result;
		559	$cv->begin (sub { $cv->send (\%result) });
		560
		561	for my $host (@list_of_hosts) {
		562	$cv->begin;
		563	ping_host_then_call_callback $host, sub {
		564	$result{$host} = ...;
		565	$cv->end;
		566	};
		567	}
		568
		569	$cv->end;
		570
		571	This code fragment supposedly pings a number of hosts and calls
		572	C<send> after results for all then have have been gathered - in any
		573	order. To achieve this, the code issues a call to C<begin> when it starts
		574	each ping request and calls C<end> when it has received some result for
		575	it. Since C<begin> and C<end> only maintain a counter, the order in which
		576	results arrive is not relevant.
		577
		578	There is an additional bracketing call to C<begin> and C<end> outside the
		579	loop, which serves two important purposes: first, it sets the callback
		580	to be called once the counter reaches C<0>, and second, it ensures that
		581	C<send> is called even when C<no> hosts are being pinged (the loop
		582	doesn't execute once).
		583
		584	This is the general pattern when you "fan out" into multiple subrequests:
		585	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		586	is called at least once, and then, for each subrequest you start, call
		587	C<begin> and for each subrequest you finish, call C<end>.
		588
		589	=back
		590
		591	=head3 METHODS FOR CONSUMERS
		592
		593	These methods should only be used by the consuming side, i.e. the
		594	code awaits the condition.
		595
		596	=over 4
		597
		598	=item $cv->recv
		599
		600	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		601	>> methods have been called on c<$cv>, while servicing other watchers
		602	normally.
		603
		604	You can only wait once on a condition - additional calls are valid but
		605	will return immediately.
		606
		607	If an error condition has been set by calling C<< ->croak >>, then this
		608	function will call C<croak>.
		609
		610	In list context, all parameters passed to C<send> will be returned,
		611	in scalar context only the first one will be returned.
		612
		613	Not all event models support a blocking wait - some die in that case
		614	(programs might want to do that to stay interactive), so I<if you are
		615	using this from a module, never require a blocking wait>, but let the
		616	caller decide whether the call will block or not (for example, by coupling
		617	condition variables with some kind of request results and supporting
		618	callbacks so the caller knows that getting the result will not block,
		619	while still supporting blocking waits if the caller so desires).
		620
		621	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		622	sensibly have two C<< ->recv >>'s in parallel, as that would require
		623	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		624	can supply.
		625
		626	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		627	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		628	versions and also integrates coroutines into AnyEvent, making blocking
		629	C<< ->recv >> calls perfectly safe as long as they are done from another
		630	coroutine (one that doesn't run the event loop).
		631
		632	You can ensure that C<< -recv >> never blocks by setting a callback and
		633	only calling C<< ->recv >> from within that callback (or at a later
		634	time). This will work even when the event loop does not support blocking
		635	waits otherwise.
		636
		637	=item $bool = $cv->ready
		638
		639	Returns true when the condition is "true", i.e. whether C<send> or
		640	C<croak> have been called.
		641
		642	=item $cb = $cv->cb ($cb->($cv))
		643
		644	This is a mutator function that returns the callback set and optionally
		645	replaces it before doing so.
		646
		647	The callback will be called when the condition becomes "true", i.e. when
		648	C<send> or C<croak> are called, with the only argument being the condition
		649	variable itself. Calling C<recv> inside the callback or at any later time
		650	is guaranteed not to block.
		651
		652	=back
		653
		654	=head1 GLOBAL VARIABLES AND FUNCTIONS
		655
		656	=over 4
		657
		658	=item $AnyEvent::MODEL
		659
		660	Contains C<undef> until the first watcher is being created. Then it
		661	contains the event model that is being used, which is the name of the
		662	Perl class implementing the model. This class is usually one of the
		663	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		664	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		665
		666	The known classes so far are:
		667
		668	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		669	AnyEvent::Impl::Event based on Event, second best choice.
		670	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		671	AnyEvent::Impl::Glib based on Glib, third-best choice.
		672	AnyEvent::Impl::Tk based on Tk, very bad choice.
		673	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		674	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		675	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		676
		677	There is no support for WxWidgets, as WxWidgets has no support for
		678	watching file handles. However, you can use WxWidgets through the
		679	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		680	second, which was considered to be too horrible to even consider for
		681	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		682	it's adaptor.
		683
		684	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		685	autodetecting them.
		686
		687	=item AnyEvent::detect
		688
		689	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		690	if necessary. You should only call this function right before you would
		691	have created an AnyEvent watcher anyway, that is, as late as possible at
		692	runtime.
		693
		694	=item $guard = AnyEvent::post_detect { BLOCK }
		695
		696	Arranges for the code block to be executed as soon as the event model is
		697	autodetected (or immediately if this has already happened).
		698
		699	If called in scalar or list context, then it creates and returns an object
		700	that automatically removes the callback again when it is destroyed. See
		701	L<Coro::BDB> for a case where this is useful.
		702
		703	=item @AnyEvent::post_detect
		704
		705	If there are any code references in this array (you can C<push> to it
		706	before or after loading AnyEvent), then they will called directly after
		707	the event loop has been chosen.
		708
		709	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		710	if it contains a true value then the event loop has already been detected,
		711	and the array will be ignored.
		712
		713	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		714
		715	=back
		716
		717	=head1 WHAT TO DO IN A MODULE
		718
		719	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		720	freely, but you should not load a specific event module or rely on it.
		721
		722	Be careful when you create watchers in the module body - AnyEvent will
		723	decide which event module to use as soon as the first method is called, so
		724	by calling AnyEvent in your module body you force the user of your module
		725	to load the event module first.
		726
		727	Never call C<< ->recv >> on a condition variable unless you I<know> that
		728	the C<< ->send >> method has been called on it already. This is
		729	because it will stall the whole program, and the whole point of using
		730	events is to stay interactive.
		731
		732	It is fine, however, to call C<< ->recv >> when the user of your module
		733	requests it (i.e. if you create a http request object ad have a method
		734	called C<results> that returns the results, it should call C<< ->recv >>
		735	freely, as the user of your module knows what she is doing. always).
		736
		737	=head1 WHAT TO DO IN THE MAIN PROGRAM
		738
		739	There will always be a single main program - the only place that should
		740	dictate which event model to use.
		741
		742	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		743	do anything special (it does not need to be event-based) and let AnyEvent
		744	decide which implementation to chose if some module relies on it.
		745
		746	If the main program relies on a specific event model - for example, in
		747	Gtk2 programs you have to rely on the Glib module - you should load the
		748	event module before loading AnyEvent or any module that uses it: generally
		749	speaking, you should load it as early as possible. The reason is that
		750	modules might create watchers when they are loaded, and AnyEvent will
		751	decide on the event model to use as soon as it creates watchers, and it
		752	might chose the wrong one unless you load the correct one yourself.
		753
		754	You can chose to use a pure-perl implementation by loading the
		755	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		756	everywhere, but letting AnyEvent chose the model is generally better.
		757
		758	=head2 MAINLOOP EMULATION
		759
		760	Sometimes (often for short test scripts, or even standalone programs who
		761	only want to use AnyEvent), you do not want to run a specific event loop.
		762
		763	In that case, you can use a condition variable like this:
		764
		765	AnyEvent->condvar->recv;
		766
		767	This has the effect of entering the event loop and looping forever.
		768
		769	Note that usually your program has some exit condition, in which case
		770	it is better to use the "traditional" approach of storing a condition
		771	variable somewhere, waiting for it, and sending it when the program should
		772	exit cleanly.
		773
		774
		775	=head1 OTHER MODULES
		776
		777	The following is a non-exhaustive list of additional modules that use
		778	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		779	in the same program. Some of the modules come with AnyEvent, some are
		780	available via CPAN.
		781
		782	=over 4
		783
		784	=item L<AnyEvent::Util>
		785
		786	Contains various utility functions that replace often-used but blocking
		787	functions such as C<inet_aton> by event-/callback-based versions.
		788
		789	=item L<AnyEvent::Socket>
		790
		791	Provides various utility functions for (internet protocol) sockets,
		792	addresses and name resolution. Also functions to create non-blocking tcp
		793	connections or tcp servers, with IPv6 and SRV record support and more.
		794
		795	=item L<AnyEvent::Handle>
		796
		797	Provide read and write buffers, manages watchers for reads and writes,
		798	supports raw and formatted I/O, I/O queued and fully transparent and
		799	non-blocking SSL/TLS.
		800
		801	=item L<AnyEvent::DNS>
		802
		803	Provides rich asynchronous DNS resolver capabilities.
		804
		805	=item L<AnyEvent::HTTP>
		806
		807	A simple-to-use HTTP library that is capable of making a lot of concurrent
		808	HTTP requests.
		809
		810	=item L<AnyEvent::HTTPD>
		811
		812	Provides a simple web application server framework.
		813
		814	=item L<AnyEvent::FastPing>
		815
		816	The fastest ping in the west.
		817
		818	=item L<AnyEvent::DBI>
		819
		820	Executes L<DBI> requests asynchronously in a proxy process.
		821
		822	=item L<AnyEvent::AIO>
		823
		824	Truly asynchronous I/O, should be in the toolbox of every event
		825	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		826	together.
		827
		828	=item L<AnyEvent::BDB>
		829
		830	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		831	L<BDB> and AnyEvent together.
		832
		833	=item L<AnyEvent::GPSD>
		834
		835	A non-blocking interface to gpsd, a daemon delivering GPS information.
		836
		837	=item L<AnyEvent::IGS>
		838
		839	A non-blocking interface to the Internet Go Server protocol (used by
		840	L<App::IGS>).
		841
		842	=item L<AnyEvent::IRC>
		843
		844	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		845
		846	=item L<Net::XMPP2>
		847
		848	AnyEvent based XMPP (Jabber protocol) module family.
		849
		850	=item L<Net::FCP>
		851
		852	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		853	of AnyEvent.
		854
		855	=item L<Event::ExecFlow>
		856
		857	High level API for event-based execution flow control.
		858
		859	=item L<Coro>
		860
		861	Has special support for AnyEvent via L<Coro::AnyEvent>.
		862
		863	=item L<IO::Lambda>
		864
		865	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		866
		867	=back
		868
59	=cut	869	=cut
60		870
61	package AnyEvent;	871	package AnyEvent;
62		872
63	no warnings;	873	no warnings;
64	use strict 'vars';	874	use strict qw(vars subs);
		875
65	use Carp;	876	use Carp;
66		877
67	our $VERSION = 0.3;	878	our $VERSION = 4.35;
68	our $MODEL;	879	our $MODEL;
69		880
70	our $AUTOLOAD;	881	our $AUTOLOAD;
71	our @ISA;	882	our @ISA;
72		883
		884	our @REGISTRY;
		885
		886	our $WIN32;
		887
		888	BEGIN {
		889	my $win32 = ! ! ($^O =~ /mswin32/i);
		890	eval "sub WIN32(){ $win32 }";
		891	}
		892
		893	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		894
		895	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		896
		897	{
		898	my $idx;
		899	$PROTOCOL{$_} = ++$idx
		900	for reverse split /\s*,\s*/,
		901	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		902	}
		903
73	my @models = (	904	my @models = (
74	[Coro => Coro::Event::],	905	[EV:: => AnyEvent::Impl::EV::],
75	[Event => Event::],	906	[Event:: => AnyEvent::Impl::Event::],
76	[Glib => Glib::],	907	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
77	[Tk => Tk::],	908	# everything below here will not be autoprobed
		909	# as the pureperl backend should work everywhere
		910	# and is usually faster
		911	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		912	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		913	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		914	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		915	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		916	[Wx:: => AnyEvent::Impl::POE::],
		917	[Prima:: => AnyEvent::Impl::POE::],
78	);	918	);
79		919
80	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	920	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
81		921
82	sub AUTOLOAD {	922	our @post_detect;
83	$AUTOLOAD =~ s/.*://;
84		923
85	$method{$AUTOLOAD}	924	sub post_detect(&) {
86	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	925	my ($cb) = @_;
87		926
		927	if ($MODEL) {
		928	$cb->();
		929
		930	1
		931	} else {
		932	push @post_detect, $cb;
		933
		934	defined wantarray
		935	? bless \$cb, "AnyEvent::Util::PostDetect"
		936	: ()
		937	}
		938	}
		939
		940	sub AnyEvent::Util::PostDetect::DESTROY {
		941	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		942	}
		943
		944	sub detect() {
88	unless ($MODEL) {	945	unless ($MODEL) {
89	# check for already loaded models	946	no strict 'refs';
90	for (@models) {	947	local $SIG{__DIE__};
91	my ($model, $package) = @$_;	948
92	if (scalar keys %{ *{"$package\::"} }) {	949	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
93	eval "require AnyEvent::Impl::$model";	950	my $model = "AnyEvent::Impl::$1";
94	last if $MODEL;	951	if (eval "require $model") {
		952	$MODEL = $model;
		953	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		954	} else {
		955	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
95	}	956	}
96	}	957	}
97		958
		959	# check for already loaded models
98	unless ($MODEL) {	960	unless ($MODEL) {
99	# try to load a model
100
101	for (@models) {	961	for (@REGISTRY, @models) {
102	my ($model, $package) = @$_;	962	my ($package, $model) = @$_;
103	eval "require AnyEvent::Impl::$model";	963	if (${"$package\::VERSION"} > 0) {
104	last if $MODEL;	964	if (eval "require $model") {
		965	$MODEL = $model;
		966	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		967	last;
		968	}
		969	}
105	}	970	}
106		971
		972	unless ($MODEL) {
		973	# try to load a model
		974
		975	for (@REGISTRY, @models) {
		976	my ($package, $model) = @$_;
		977	if (eval "require $package"
		978	and ${"$package\::VERSION"} > 0
		979	and eval "require $model") {
		980	$MODEL = $model;
		981	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		982	last;
		983	}
		984	}
		985
107	$MODEL	986	$MODEL
108	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	987	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		988	}
		989	}
		990
		991	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		992
		993	unshift @ISA, $MODEL;
		994
		995	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		996
		997	(shift @post_detect)->() while @post_detect;
		998	}
		999
		1000	$MODEL
		1001	}
		1002
		1003	sub AUTOLOAD {
		1004	(my $func = $AUTOLOAD) =~ s/.*://;
		1005
		1006	$method{$func}
		1007	or croak "$func: not a valid method for AnyEvent objects";
		1008
		1009	detect unless $MODEL;
		1010
		1011	my $class = shift;
		1012	$class->$func (@_);
		1013	}
		1014
		1015	# utility function to dup a filehandle. this is used by many backends
		1016	# to support binding more than one watcher per filehandle (they usually
		1017	# allow only one watcher per fd, so we dup it to get a different one).
		1018	sub _dupfh($$$$) {
		1019	my ($poll, $fh, $r, $w) = @_;
		1020
		1021	# cygwin requires the fh mode to be matching, unix doesn't
		1022	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1023	: $poll eq "w" ? ($w, ">")
		1024	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1025
		1026	open my $fh2, "$mode&" . fileno $fh
		1027	or die "cannot dup() filehandle: $!";
		1028
		1029	# we assume CLOEXEC is already set by perl in all important cases
		1030
		1031	($fh2, $rw)
		1032	}
		1033
		1034	package AnyEvent::Base;
		1035
		1036	# default implementation for now and time
		1037
		1038	BEGIN {
		1039	if (eval "use Time::HiRes (); time (); 1") {
		1040	*_time = \&Time::HiRes::time;
		1041	# if (eval "use POSIX (); (POSIX::times())...
		1042	} else {
		1043	*_time = sub { time }; # epic fail
		1044	}
		1045	}
		1046
		1047	sub time { _time }
		1048	sub now { _time }
		1049
		1050	# default implementation for ->condvar
		1051
		1052	sub condvar {
		1053	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		1054	}
		1055
		1056	# default implementation for ->signal
		1057
		1058	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1059
		1060	sub _signal_exec {
		1061	sysread $SIGPIPE_R, my $dummy, 4;
		1062
		1063	while (%SIG_EV) {
		1064	for (keys %SIG_EV) {
		1065	delete $SIG_EV{$_};
		1066	$_->() for values %{ $SIG_CB{$_} || {} };
109	}	1067	}
110	}	1068	}
		1069	}
111		1070
112	@ISA = $MODEL;	1071	sub signal {
		1072	my (undef, %arg) = @_;
113		1073
		1074	unless ($SIGPIPE_R) {
		1075	require Fcntl;
		1076
		1077	if (AnyEvent::WIN32) {
		1078	require AnyEvent::Util;
		1079
		1080	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1081	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1082	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1083	} else {
		1084	pipe $SIGPIPE_R, $SIGPIPE_W;
		1085	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1086	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1087	}
		1088
		1089	$SIGPIPE_R
		1090	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1091
		1092	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1093	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1094
		1095	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1096	}
		1097
		1098	my $signal = uc $arg{signal}
		1099	or Carp::croak "required option 'signal' is missing";
		1100
		1101	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1102	$SIG{$signal} ||= sub {
		1103	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1104	undef $SIG_EV{$signal};
		1105	};
		1106
		1107	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		1108	}
		1109
		1110	sub AnyEvent::Base::Signal::DESTROY {
		1111	my ($signal, $cb) = @{$_[0]};
		1112
		1113	delete $SIG_CB{$signal}{$cb};
		1114
		1115	delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
		1116	}
		1117
		1118	# default implementation for ->child
		1119
		1120	our %PID_CB;
		1121	our $CHLD_W;
		1122	our $CHLD_DELAY_W;
		1123	our $PID_IDLE;
		1124	our $WNOHANG;
		1125
		1126	sub _child_wait {
		1127	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1128	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		1129	(values %{ $PID_CB{0} || {} });
		1130	}
		1131
		1132	undef $PID_IDLE;
		1133	}
		1134
		1135	sub _sigchld {
		1136	# make sure we deliver these changes "synchronous" with the event loop.
		1137	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		1138	undef $CHLD_DELAY_W;
		1139	&_child_wait;
		1140	});
		1141	}
		1142
		1143	sub child {
		1144	my (undef, %arg) = @_;
		1145
		1146	defined (my $pid = $arg{pid} + 0)
		1147	or Carp::croak "required option 'pid' is missing";
		1148
		1149	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1150
		1151	unless ($WNOHANG) {
		1152	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1153	}
		1154
		1155	unless ($CHLD_W) {
		1156	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1157	# child could be a zombie already, so make at least one round
		1158	&_sigchld;
		1159	}
		1160
		1161	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		1162	}
		1163
		1164	sub AnyEvent::Base::Child::DESTROY {
		1165	my ($pid, $cb) = @{$_[0]};
		1166
		1167	delete $PID_CB{$pid}{$cb};
		1168	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1169
		1170	undef $CHLD_W unless keys %PID_CB;
		1171	}
		1172
		1173	package AnyEvent::CondVar;
		1174
		1175	our @ISA = AnyEvent::CondVar::Base::;
		1176
		1177	package AnyEvent::CondVar::Base;
		1178
		1179	use overload
		1180	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1181	fallback => 1;
		1182
		1183	sub _send {
		1184	# nop
		1185	}
		1186
		1187	sub send {
114	my $class = shift;	1188	my $cv = shift;
115	$class->$AUTOLOAD (@_);	1189	$cv->{_ae_sent} = [@_];
		1190	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1191	$cv->_send;
116	}	1192	}
		1193
		1194	sub croak {
		1195	$_[0]{_ae_croak} = $_[1];
		1196	$_[0]->send;
		1197	}
		1198
		1199	sub ready {
		1200	$_[0]{_ae_sent}
		1201	}
		1202
		1203	sub _wait {
		1204	AnyEvent->one_event while !$_[0]{_ae_sent};
		1205	}
		1206
		1207	sub recv {
		1208	$_[0]->_wait;
		1209
		1210	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1211	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1212	}
		1213
		1214	sub cb {
		1215	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1216	$_[0]{_ae_cb}
		1217	}
		1218
		1219	sub begin {
		1220	++$_[0]{_ae_counter};
		1221	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1222	}
		1223
		1224	sub end {
		1225	return if --$_[0]{_ae_counter};
		1226	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1227	}
		1228
		1229	# undocumented/compatibility with pre-3.4
		1230	*broadcast = \&send;
		1231	*wait = \&_wait;
		1232
		1233	=head1 ERROR AND EXCEPTION HANDLING
		1234
		1235	In general, AnyEvent does not do any error handling - it relies on the
		1236	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1237	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1238	checking of all AnyEvent methods, however, which is highly useful during
		1239	development.
		1240
		1241	As for exception handling (i.e. runtime errors and exceptions thrown while
		1242	executing a callback), this is not only highly event-loop specific, but
		1243	also not in any way wrapped by this module, as this is the job of the main
		1244	program.
		1245
		1246	The pure perl event loop simply re-throws the exception (usually
		1247	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1248	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1249	so on.
		1250
		1251	=head1 ENVIRONMENT VARIABLES
		1252
		1253	The following environment variables are used by this module or its
		1254	submodules:
		1255
		1256	=over 4
		1257
		1258	=item C<PERL_ANYEVENT_VERBOSE>
		1259
		1260	By default, AnyEvent will be completely silent except in fatal
		1261	conditions. You can set this environment variable to make AnyEvent more
		1262	talkative.
		1263
		1264	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1265	conditions, such as not being able to load the event model specified by
		1266	C<PERL_ANYEVENT_MODEL>.
		1267
		1268	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1269	model it chooses.
		1270
		1271	=item C<PERL_ANYEVENT_STRICT>
		1272
		1273	AnyEvent does not do much argument checking by default, as thorough
		1274	argument checking is very costly. Setting this variable to a true value
		1275	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1276	check the arguments passed to most method calls. If it finds any problems
		1277	it will croak.
		1278
		1279	In other words, enables "strict" mode.
		1280
		1281	Unlike C<use strict>, it is definitely recommended ot keep it off in
		1282	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1283	developing programs can be very useful, however.
		1284
		1285	=item C<PERL_ANYEVENT_MODEL>
		1286
		1287	This can be used to specify the event model to be used by AnyEvent, before
		1288	auto detection and -probing kicks in. It must be a string consisting
		1289	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1290	and the resulting module name is loaded and if the load was successful,
		1291	used as event model. If it fails to load AnyEvent will proceed with
		1292	auto detection and -probing.
		1293
		1294	This functionality might change in future versions.
		1295
		1296	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1297	could start your program like this:
		1298
		1299	PERL_ANYEVENT_MODEL=Perl perl ...
		1300
		1301	=item C<PERL_ANYEVENT_PROTOCOLS>
		1302
		1303	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1304	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1305	of auto probing).
		1306
		1307	Must be set to a comma-separated list of protocols or address families,
		1308	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1309	used, and preference will be given to protocols mentioned earlier in the
		1310	list.
		1311
		1312	This variable can effectively be used for denial-of-service attacks
		1313	against local programs (e.g. when setuid), although the impact is likely
		1314	small, as the program has to handle conenction and other failures anyways.
		1315
		1316	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1317	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1318	- only support IPv4, never try to resolve or contact IPv6
		1319	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1320	IPv6, but prefer IPv6 over IPv4.
		1321
		1322	=item C<PERL_ANYEVENT_EDNS0>
		1323
		1324	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1325	for DNS. This extension is generally useful to reduce DNS traffic, but
		1326	some (broken) firewalls drop such DNS packets, which is why it is off by
		1327	default.
		1328
		1329	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1330	EDNS0 in its DNS requests.
		1331
		1332	=item C<PERL_ANYEVENT_MAX_FORKS>
		1333
		1334	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1335	will create in parallel.
117		1336
118	=back	1337	=back
119		1338
		1339	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1340
		1341	This is an advanced topic that you do not normally need to use AnyEvent in
		1342	a module. This section is only of use to event loop authors who want to
		1343	provide AnyEvent compatibility.
		1344
		1345	If you need to support another event library which isn't directly
		1346	supported by AnyEvent, you can supply your own interface to it by
		1347	pushing, before the first watcher gets created, the package name of
		1348	the event module and the package name of the interface to use onto
		1349	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1350	AnyEvent, so it is reasonably cheap.
		1351
		1352	Example:
		1353
		1354	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1355
		1356	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1357	package/class when it finds the C<urxvt> package/module is already loaded.
		1358
		1359	When AnyEvent is loaded and asked to find a suitable event model, it
		1360	will first check for the presence of urxvt by trying to C<use> the
		1361	C<urxvt::anyevent> module.
		1362
		1363	The class should provide implementations for all watcher types. See
		1364	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1365	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1366	see the sources.
		1367
		1368	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1369	provide suitable (hopefully) replacements.
		1370
		1371	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1372	terminal emulator uses the above line as-is. An interface isn't included
		1373	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1374	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1375	I<rxvt-unicode> distribution.
		1376
		1377	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1378	condition variables: code blocking while waiting for a condition will
		1379	C<die>. This still works with most modules/usages, and blocking calls must
		1380	not be done in an interactive application, so it makes sense.
		1381
120	=head1 EXAMPLE	1382	=head1 EXAMPLE PROGRAM
121		1383
122	The following program uses an io watcher to read data from stdin, a timer	1384	The following program uses an I/O watcher to read data from STDIN, a timer
123	to display a message once per second, and a condvar to exit the program	1385	to display a message once per second, and a condition variable to quit the
124	when the user enters quit:	1386	program when the user enters quit:
125		1387
126	use AnyEvent;	1388	use AnyEvent;
127		1389
128	my $cv = AnyEvent->condvar;	1390	my $cv = AnyEvent->condvar;
129		1391
130	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1392	my $io_watcher = AnyEvent->io (
		1393	fh => \*STDIN,
		1394	poll => 'r',
		1395	cb => sub {
131	warn "io event <$_[0]>\n"; # will always output <r>	1396	warn "io event <$_[0]>\n"; # will always output <r>
132	chomp (my $input = <STDIN>); # read a line	1397	chomp (my $input = <STDIN>); # read a line
133	warn "read: $input\n"; # output what has been read	1398	warn "read: $input\n"; # output what has been read
134	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1399	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1400	},
135	});	1401	);
136		1402
137	my $time_watcher; # can only be used once	1403	my $time_watcher; # can only be used once
138		1404
139	sub new_timer {	1405	sub new_timer {
140	$timer = AnyEvent->timer (after => 1, cb => sub {	1406	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
143	});	1409	});
144	}	1410	}
145		1411
146	new_timer; # create first timer	1412	new_timer; # create first timer
147		1413
148	$cv->wait; # wait until user enters /^q/i	1414	$cv->recv; # wait until user enters /^q/i
149		1415
150	=head1 REAL-WORLD EXAMPLE	1416	=head1 REAL-WORLD EXAMPLE
151		1417
152	Consider the L<Net::FCP> module. It features (among others) the following	1418	Consider the L<Net::FCP> module. It features (among others) the following
153	API calls, which are to freenet what HTTP GET requests are to http:	1419	API calls, which are to freenet what HTTP GET requests are to http:
…		…
203	syswrite $txn->{fh}, $txn->{request}	1469	syswrite $txn->{fh}, $txn->{request}
204	or die "connection or write error";	1470	or die "connection or write error";
205	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1471	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
206		1472
207	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1473	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
208	result and signals any possible waiters that the request ahs finished:	1474	result and signals any possible waiters that the request has finished:
209		1475
210	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1476	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
211		1477
212	if (end-of-file or data complete) {	1478	if (end-of-file or data complete) {
213	$txn->{result} = $txn->{buf};	1479	$txn->{result} = $txn->{buf};
214	$txn->{finished}->broadcast;	1480	$txn->{finished}->send;
215	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1481	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
216	}	1482	}
217		1483
218	The C<result> method, finally, just waits for the finished signal (if the	1484	The C<result> method, finally, just waits for the finished signal (if the
219	request was already finished, it doesn't wait, of course, and returns the	1485	request was already finished, it doesn't wait, of course, and returns the
220	data:	1486	data:
221		1487
222	$txn->{finished}->wait;	1488	$txn->{finished}->recv;
223	return $txn->{result};	1489	return $txn->{result};
224		1490
225	The actual code goes further and collects all errors (C<die>s, exceptions)	1491	The actual code goes further and collects all errors (C<die>s, exceptions)
226	that occured during request processing. The C<result> method detects	1492	that occurred during request processing. The C<result> method detects
227	wether an exception as thrown (it is stored inside the $txn object)	1493	whether an exception as thrown (it is stored inside the $txn object)
228	and just throws the exception, which means connection errors and other	1494	and just throws the exception, which means connection errors and other
229	problems get reported tot he code that tries to use the result, not in a	1495	problems get reported tot he code that tries to use the result, not in a
230	random callback.	1496	random callback.
231		1497
232	All of this enables the following usage styles:	1498	All of this enables the following usage styles:
233		1499
234	1. Blocking:	1500	1. Blocking:
235		1501
236	my $data = $fcp->client_get ($url);	1502	my $data = $fcp->client_get ($url);
237		1503
238	2. Blocking, but parallelizing:	1504	2. Blocking, but running in parallel:
239		1505
240	my @datas = map $_->result,	1506	my @datas = map $_->result,
241	map $fcp->txn_client_get ($_),	1507	map $fcp->txn_client_get ($_),
242	@urls;	1508	@urls;
243		1509
244	Both blocking examples work without the module user having to know	1510	Both blocking examples work without the module user having to know
245	anything about events.	1511	anything about events.
246		1512
247	3a. Event-based in a main program, using any support Event module:	1513	3a. Event-based in a main program, using any supported event module:
248		1514
249	use Event;	1515	use EV;
250		1516
251	$fcp->txn_client_get ($url)->cb (sub {	1517	$fcp->txn_client_get ($url)->cb (sub {
252	my $txn = shift;	1518	my $txn = shift;
253	my $data = $txn->result;	1519	my $data = $txn->result;
254	...	1520	...
255	});	1521	});
256		1522
257	Event::loop;	1523	EV::loop;
258		1524
259	3b. The module user could use AnyEvent, too:	1525	3b. The module user could use AnyEvent, too:
260		1526
261	use AnyEvent;	1527	use AnyEvent;
262		1528
263	my $quit = AnyEvent->condvar;	1529	my $quit = AnyEvent->condvar;
264		1530
265	$fcp->txn_client_get ($url)->cb (sub {	1531	$fcp->txn_client_get ($url)->cb (sub {
266	...	1532	...
267	$quit->broadcast;	1533	$quit->send;
268	});	1534	});
269		1535
270	$quit->wait;	1536	$quit->recv;
		1537
		1538
		1539	=head1 BENCHMARKS
		1540
		1541	To give you an idea of the performance and overheads that AnyEvent adds
		1542	over the event loops themselves and to give you an impression of the speed
		1543	of various event loops I prepared some benchmarks.
		1544
		1545	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1546
		1547	Here is a benchmark of various supported event models used natively and
		1548	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1549	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1550	which it is), lets them fire exactly once and destroys them again.
		1551
		1552	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1553	distribution.
		1554
		1555	=head3 Explanation of the columns
		1556
		1557	I<watcher> is the number of event watchers created/destroyed. Since
		1558	different event models feature vastly different performances, each event
		1559	loop was given a number of watchers so that overall runtime is acceptable
		1560	and similar between tested event loop (and keep them from crashing): Glib
		1561	would probably take thousands of years if asked to process the same number
		1562	of watchers as EV in this benchmark.
		1563
		1564	I<bytes> is the number of bytes (as measured by the resident set size,
		1565	RSS) consumed by each watcher. This method of measuring captures both C
		1566	and Perl-based overheads.
		1567
		1568	I<create> is the time, in microseconds (millionths of seconds), that it
		1569	takes to create a single watcher. The callback is a closure shared between
		1570	all watchers, to avoid adding memory overhead. That means closure creation
		1571	and memory usage is not included in the figures.
		1572
		1573	I<invoke> is the time, in microseconds, used to invoke a simple
		1574	callback. The callback simply counts down a Perl variable and after it was
		1575	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1576	signal the end of this phase.
		1577
		1578	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1579	watcher.
		1580
		1581	=head3 Results
		1582
		1583	name watchers bytes create invoke destroy comment
		1584	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1585	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1586	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1587	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1588	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1589	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1590	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1591	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1592	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1593	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1594
		1595	=head3 Discussion
		1596
		1597	The benchmark does I<not> measure scalability of the event loop very
		1598	well. For example, a select-based event loop (such as the pure perl one)
		1599	can never compete with an event loop that uses epoll when the number of
		1600	file descriptors grows high. In this benchmark, all events become ready at
		1601	the same time, so select/poll-based implementations get an unnatural speed
		1602	boost.
		1603
		1604	Also, note that the number of watchers usually has a nonlinear effect on
		1605	overall speed, that is, creating twice as many watchers doesn't take twice
		1606	the time - usually it takes longer. This puts event loops tested with a
		1607	higher number of watchers at a disadvantage.
		1608
		1609	To put the range of results into perspective, consider that on the
		1610	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1611	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1612	cycles with POE.
		1613
		1614	C<EV> is the sole leader regarding speed and memory use, which are both
		1615	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1616	far less memory than any other event loop and is still faster than Event
		1617	natively.
		1618
		1619	The pure perl implementation is hit in a few sweet spots (both the
		1620	constant timeout and the use of a single fd hit optimisations in the perl
		1621	interpreter and the backend itself). Nevertheless this shows that it
		1622	adds very little overhead in itself. Like any select-based backend its
		1623	performance becomes really bad with lots of file descriptors (and few of
		1624	them active), of course, but this was not subject of this benchmark.
		1625
		1626	The C<Event> module has a relatively high setup and callback invocation
		1627	cost, but overall scores in on the third place.
		1628
		1629	C<Glib>'s memory usage is quite a bit higher, but it features a
		1630	faster callback invocation and overall ends up in the same class as
		1631	C<Event>. However, Glib scales extremely badly, doubling the number of
		1632	watchers increases the processing time by more than a factor of four,
		1633	making it completely unusable when using larger numbers of watchers
		1634	(note that only a single file descriptor was used in the benchmark, so
		1635	inefficiencies of C<poll> do not account for this).
		1636
		1637	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1638	more than 2000 watchers is a big setback, however, as correctness takes
		1639	precedence over speed. Nevertheless, its performance is surprising, as the
		1640	file descriptor is dup()ed for each watcher. This shows that the dup()
		1641	employed by some adaptors is not a big performance issue (it does incur a
		1642	hidden memory cost inside the kernel which is not reflected in the figures
		1643	above).
		1644
		1645	C<POE>, regardless of underlying event loop (whether using its pure perl
		1646	select-based backend or the Event module, the POE-EV backend couldn't
		1647	be tested because it wasn't working) shows abysmal performance and
		1648	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1649	as EV watchers, and 10 times as much memory as Event (the high memory
		1650	requirements are caused by requiring a session for each watcher). Watcher
		1651	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1652	implementation.
		1653
		1654	The design of the POE adaptor class in AnyEvent can not really account
		1655	for the performance issues, though, as session creation overhead is
		1656	small compared to execution of the state machine, which is coded pretty
		1657	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1658	using multiple sessions is not a good approach, especially regarding
		1659	memory usage, even the author of POE could not come up with a faster
		1660	design).
		1661
		1662	=head3 Summary
		1663
		1664	=over 4
		1665
		1666	=item * Using EV through AnyEvent is faster than any other event loop
		1667	(even when used without AnyEvent), but most event loops have acceptable
		1668	performance with or without AnyEvent.
		1669
		1670	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1671	the actual event loop, only with extremely fast event loops such as EV
		1672	adds AnyEvent significant overhead.
		1673
		1674	=item * You should avoid POE like the plague if you want performance or
		1675	reasonable memory usage.
		1676
		1677	=back
		1678
		1679	=head2 BENCHMARKING THE LARGE SERVER CASE
		1680
		1681	This benchmark actually benchmarks the event loop itself. It works by
		1682	creating a number of "servers": each server consists of a socket pair, a
		1683	timeout watcher that gets reset on activity (but never fires), and an I/O
		1684	watcher waiting for input on one side of the socket. Each time the socket
		1685	watcher reads a byte it will write that byte to a random other "server".
		1686
		1687	The effect is that there will be a lot of I/O watchers, only part of which
		1688	are active at any one point (so there is a constant number of active
		1689	fds for each loop iteration, but which fds these are is random). The
		1690	timeout is reset each time something is read because that reflects how
		1691	most timeouts work (and puts extra pressure on the event loops).
		1692
		1693	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1694	(1%) are active. This mirrors the activity of large servers with many
		1695	connections, most of which are idle at any one point in time.
		1696
		1697	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1698	distribution.
		1699
		1700	=head3 Explanation of the columns
		1701
		1702	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1703	each server has a read and write socket end).
		1704
		1705	I<create> is the time it takes to create a socket pair (which is
		1706	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1707
		1708	I<request>, the most important value, is the time it takes to handle a
		1709	single "request", that is, reading the token from the pipe and forwarding
		1710	it to another server. This includes deleting the old timeout and creating
		1711	a new one that moves the timeout into the future.
		1712
		1713	=head3 Results
		1714
		1715	name sockets create request
		1716	EV 20000 69.01 11.16
		1717	Perl 20000 73.32 35.87
		1718	Event 20000 212.62 257.32
		1719	Glib 20000 651.16 1896.30
		1720	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1721
		1722	=head3 Discussion
		1723
		1724	This benchmark I<does> measure scalability and overall performance of the
		1725	particular event loop.
		1726
		1727	EV is again fastest. Since it is using epoll on my system, the setup time
		1728	is relatively high, though.
		1729
		1730	Perl surprisingly comes second. It is much faster than the C-based event
		1731	loops Event and Glib.
		1732
		1733	Event suffers from high setup time as well (look at its code and you will
		1734	understand why). Callback invocation also has a high overhead compared to
		1735	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1736	uses select or poll in basically all documented configurations.
		1737
		1738	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1739	clearly fails to perform with many filehandles or in busy servers.
		1740
		1741	POE is still completely out of the picture, taking over 1000 times as long
		1742	as EV, and over 100 times as long as the Perl implementation, even though
		1743	it uses a C-based event loop in this case.
		1744
		1745	=head3 Summary
		1746
		1747	=over 4
		1748
		1749	=item * The pure perl implementation performs extremely well.
		1750
		1751	=item * Avoid Glib or POE in large projects where performance matters.
		1752
		1753	=back
		1754
		1755	=head2 BENCHMARKING SMALL SERVERS
		1756
		1757	While event loops should scale (and select-based ones do not...) even to
		1758	large servers, most programs we (or I :) actually write have only a few
		1759	I/O watchers.
		1760
		1761	In this benchmark, I use the same benchmark program as in the large server
		1762	case, but it uses only eight "servers", of which three are active at any
		1763	one time. This should reflect performance for a small server relatively
		1764	well.
		1765
		1766	The columns are identical to the previous table.
		1767
		1768	=head3 Results
		1769
		1770	name sockets create request
		1771	EV 16 20.00 6.54
		1772	Perl 16 25.75 12.62
		1773	Event 16 81.27 35.86
		1774	Glib 16 32.63 15.48
		1775	POE 16 261.87 276.28 uses POE::Loop::Event
		1776
		1777	=head3 Discussion
		1778
		1779	The benchmark tries to test the performance of a typical small
		1780	server. While knowing how various event loops perform is interesting, keep
		1781	in mind that their overhead in this case is usually not as important, due
		1782	to the small absolute number of watchers (that is, you need efficiency and
		1783	speed most when you have lots of watchers, not when you only have a few of
		1784	them).
		1785
		1786	EV is again fastest.
		1787
		1788	Perl again comes second. It is noticeably faster than the C-based event
		1789	loops Event and Glib, although the difference is too small to really
		1790	matter.
		1791
		1792	POE also performs much better in this case, but is is still far behind the
		1793	others.
		1794
		1795	=head3 Summary
		1796
		1797	=over 4
		1798
		1799	=item * C-based event loops perform very well with small number of
		1800	watchers, as the management overhead dominates.
		1801
		1802	=back
		1803
		1804
		1805	=head1 SIGNALS
		1806
		1807	AnyEvent currently installs handlers for these signals:
		1808
		1809	=over 4
		1810
		1811	=item SIGCHLD
		1812
		1813	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		1814	emulation for event loops that do not support them natively. Also, some
		1815	event loops install a similar handler.
		1816
		1817	=item SIGPIPE
		1818
		1819	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		1820	when AnyEvent gets loaded.
		1821
		1822	The rationale for this is that AnyEvent users usually do not really depend
		1823	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		1824	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		1825	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		1826	some random socket.
		1827
		1828	The rationale for installing a no-op handler as opposed to ignoring it is
		1829	that this way, the handler will be restored to defaults on exec.
		1830
		1831	Feel free to install your own handler, or reset it to defaults.
		1832
		1833	=back
		1834
		1835	=cut
		1836
		1837	$SIG{PIPE} = sub { }
		1838	unless defined $SIG{PIPE};
		1839
		1840
		1841	=head1 FORK
		1842
		1843	Most event libraries are not fork-safe. The ones who are usually are
		1844	because they rely on inefficient but fork-safe C<select> or C<poll>
		1845	calls. Only L<EV> is fully fork-aware.
		1846
		1847	If you have to fork, you must either do so I<before> creating your first
		1848	watcher OR you must not use AnyEvent at all in the child.
		1849
		1850
		1851	=head1 SECURITY CONSIDERATIONS
		1852
		1853	AnyEvent can be forced to load any event model via
		1854	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1855	execute arbitrary code or directly gain access, it can easily be used to
		1856	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1857	will not be active when the program uses a different event model than
		1858	specified in the variable.
		1859
		1860	You can make AnyEvent completely ignore this variable by deleting it
		1861	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1862
		1863	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1864
		1865	use AnyEvent;
		1866
		1867	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1868	be used to probe what backend is used and gain other information (which is
		1869	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1870	$ENV{PERL_ANYEGENT_STRICT}.
		1871
		1872
		1873	=head1 BUGS
		1874
		1875	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1876	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1877	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1878	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1879	pronounced).
		1880
271		1881
272	=head1 SEE ALSO	1882	=head1 SEE ALSO
273		1883
274	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1884	Utility functions: L<AnyEvent::Util>.
275		1885
276	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1886	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1887	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
277		1888
278	Nontrivial usage example: L<Net::FCP>.	1889	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1890	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1891	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1892	L<AnyEvent::Impl::POE>.
279		1893
280	=head1	1894	Non-blocking file handles, sockets, TCP clients and
		1895	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1896
		1897	Asynchronous DNS: L<AnyEvent::DNS>.
		1898
		1899	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1900
		1901	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1902
		1903
		1904	=head1 AUTHOR
		1905
		1906	Marc Lehmann <schmorp@schmorp.de>
		1907	http://home.schmorp.de/
281		1908
282	=cut	1909	=cut
283		1910
284	1	1911	1
285		1912

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