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Revision 1.210 by root, Wed May 13 15:19:43 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	# file descriptor readable
11	my $w = AnyEvent->timer (fh => ..., poll => "[rw]+", cb => sub {	12	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12	my ($poll_got) = @_;	13
		14	# one-shot or repeating timers
		15	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		16	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		17
		18	print AnyEvent->now; # prints current event loop time
		19	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		20
		21	# POSIX signal
		22	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		23
		24	# child process exit
		25	my $w = AnyEvent->child (pid => $pid, cb => sub {
		26	my ($pid, $status) = @_;
13	...	27	...
14	});	28	});
15	my $w = AnyEvent->io (after => $seconds, cb => sub {
16	...
17	});
18		29
19	# watchers get canceled whenever $w is destroyed	30	# called when event loop idle (if applicable)
20	# only one watcher per $fh and $poll type is allowed	31	my $w = AnyEvent->idle (cb => sub { ... });
21	# (i.e. on a socket you cna have one r + one w or one rw
22	# watcher, not any more.
23	# timers can only be used once
24		32
25	my $w = AnyEvent->condvar; # kind of main loop replacement	33	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	# can only be used once	34	$w->send; # wake up current and all future recv's
27	$w->wait; # enters main loop till $condvar gets ->send	35	$w->recv; # enters "main loop" till $condvar gets ->send
28	$w->broadcast; # wake up waiting and future wait's	36	# use a condvar in callback mode:
		37	$w->cb (sub { $_[0]->recv });
		38
		39	=head1 INTRODUCTION/TUTORIAL
		40
		41	This manpage is mainly a reference manual. If you are interested
		42	in a tutorial or some gentle introduction, have a look at the
		43	L<AnyEvent::Intro> manpage.
		44
		45	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		46
		47	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		48	nowadays. So what is different about AnyEvent?
		49
		50	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		51	policy> and AnyEvent is I<small and efficient>.
		52
		53	First and foremost, I<AnyEvent is not an event model> itself, it only
		54	interfaces to whatever event model the main program happens to use, in a
		55	pragmatic way. For event models and certain classes of immortals alike,
		56	the statement "there can only be one" is a bitter reality: In general,
		57	only one event loop can be active at the same time in a process. AnyEvent
		58	cannot change this, but it can hide the differences between those event
		59	loops.
		60
		61	The goal of AnyEvent is to offer module authors the ability to do event
		62	programming (waiting for I/O or timer events) without subscribing to a
		63	religion, a way of living, and most importantly: without forcing your
		64	module users into the same thing by forcing them to use the same event
		65	model you use.
		66
		67	For modules like POE or IO::Async (which is a total misnomer as it is
		68	actually doing all I/O I<synchronously>...), using them in your module is
		69	like joining a cult: After you joined, you are dependent on them and you
		70	cannot use anything else, as they are simply incompatible to everything
		71	that isn't them. What's worse, all the potential users of your
		72	module are I<also> forced to use the same event loop you use.
		73
		74	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		75	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		76	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		77	your module uses one of those, every user of your module has to use it,
		78	too. But if your module uses AnyEvent, it works transparently with all
		79	event models it supports (including stuff like IO::Async, as long as those
		80	use one of the supported event loops. It is trivial to add new event loops
		81	to AnyEvent, too, so it is future-proof).
		82
		83	In addition to being free of having to use I<the one and only true event
		84	model>, AnyEvent also is free of bloat and policy: with POE or similar
		85	modules, you get an enormous amount of code and strict rules you have to
		86	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		87	offering the functionality that is necessary, in as thin as a wrapper as
		88	technically possible.
		89
		90	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		91	of useful functionality, such as an asynchronous DNS resolver, 100%
		92	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		93	such as Windows) and lots of real-world knowledge and workarounds for
		94	platform bugs and differences.
		95
		96	Now, if you I<do want> lots of policy (this can arguably be somewhat
		97	useful) and you want to force your users to use the one and only event
		98	model, you should I<not> use this module.
29		99
30	=head1 DESCRIPTION	100	=head1 DESCRIPTION
31		101
32	L<AnyEvent> provides an identical interface to multiple event loops. This	102	L<AnyEvent> provides an identical interface to multiple event loops. This
33	allows module authors to utilizy an event loop without forcing module	103	allows module authors to utilise an event loop without forcing module
34	users to use the same event loop (as only a single event loop can coexist	104	users to use the same event loop (as only a single event loop can coexist
35	peacefully at any one time).	105	peacefully at any one time).
36		106
37	The interface itself is vaguely similar but not identical to the Event	107	The interface itself is vaguely similar, but not identical to the L<Event>
38	module.	108	module.
39		109
40	On the first call of any method, the module tries to detect the currently	110	During the first call of any watcher-creation method, the module tries
41	loaded event loop by probing wether any of the following modules is	111	to detect the currently loaded event loop by probing whether one of the
42	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	112	following modules is already loaded: L<EV>,
43	used. If none is found, the module tries to load these modules in the	113	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
44	order given. The first one that could be successfully loaded will be	114	L<POE>. The first one found is used. If none are found, the module tries
45	used. If still none could be found, it will issue an error.	115	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		116	adaptor should always succeed) in the order given. The first one that can
		117	be successfully loaded will be used. If, after this, still none could be
		118	found, AnyEvent will fall back to a pure-perl event loop, which is not
		119	very efficient, but should work everywhere.
		120
		121	Because AnyEvent first checks for modules that are already loaded, loading
		122	an event model explicitly before first using AnyEvent will likely make
		123	that model the default. For example:
		124
		125	use Tk;
		126	use AnyEvent;
		127
		128	# .. AnyEvent will likely default to Tk
		129
		130	The I<likely> means that, if any module loads another event model and
		131	starts using it, all bets are off. Maybe you should tell their authors to
		132	use AnyEvent so their modules work together with others seamlessly...
		133
		134	The pure-perl implementation of AnyEvent is called
		135	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		136	explicitly and enjoy the high availability of that event loop :)
		137
		138	=head1 WATCHERS
		139
		140	AnyEvent has the central concept of a I<watcher>, which is an object that
		141	stores relevant data for each kind of event you are waiting for, such as
		142	the callback to call, the file handle to watch, etc.
		143
		144	These watchers are normal Perl objects with normal Perl lifetime. After
		145	creating a watcher it will immediately "watch" for events and invoke the
		146	callback when the event occurs (of course, only when the event model
		147	is in control).
		148
		149	Note that B<callbacks must not permanently change global variables>
		150	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		151	callbacks must not C<die> >>. The former is good programming practise in
		152	Perl and the latter stems from the fact that exception handling differs
		153	widely between event loops.
		154
		155	To disable the watcher you have to destroy it (e.g. by setting the
		156	variable you store it in to C<undef> or otherwise deleting all references
		157	to it).
		158
		159	All watchers are created by calling a method on the C<AnyEvent> class.
		160
		161	Many watchers either are used with "recursion" (repeating timers for
		162	example), or need to refer to their watcher object in other ways.
		163
		164	An any way to achieve that is this pattern:
		165
		166	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		167	# you can use $w here, for example to undef it
		168	undef $w;
		169	});
		170
		171	Note that C<my $w; $w => combination. This is necessary because in Perl,
		172	my variables are only visible after the statement in which they are
		173	declared.
		174
		175	=head2 I/O WATCHERS
		176
		177	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		178	with the following mandatory key-value pairs as arguments:
		179
		180	C<fh> is the Perl I<file handle> (I<not> file descriptor) to watch
		181	for events (AnyEvent might or might not keep a reference to this file
		182	handle). Note that only file handles pointing to things for which
		183	non-blocking operation makes sense are allowed. This includes sockets,
		184	most character devices, pipes, fifos and so on, but not for example files
		185	or block devices.
		186
		187	C<poll> must be a string that is either C<r> or C<w>, which creates a
		188	watcher waiting for "r"eadable or "w"ritable events, respectively.
		189
		190	C<cb> is the callback to invoke each time the file handle becomes ready.
		191
		192	Although the callback might get passed parameters, their value and
		193	presence is undefined and you cannot rely on them. Portable AnyEvent
		194	callbacks cannot use arguments passed to I/O watcher callbacks.
		195
		196	The I/O watcher might use the underlying file descriptor or a copy of it.
		197	You must not close a file handle as long as any watcher is active on the
		198	underlying file descriptor.
		199
		200	Some event loops issue spurious readyness notifications, so you should
		201	always use non-blocking calls when reading/writing from/to your file
		202	handles.
		203
		204	Example: wait for readability of STDIN, then read a line and disable the
		205	watcher.
		206
		207	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		208	chomp (my $input = <STDIN>);
		209	warn "read: $input\n";
		210	undef $w;
		211	});
		212
		213	=head2 TIME WATCHERS
		214
		215	You can create a time watcher by calling the C<< AnyEvent->timer >>
		216	method with the following mandatory arguments:
		217
		218	C<after> specifies after how many seconds (fractional values are
		219	supported) the callback should be invoked. C<cb> is the callback to invoke
		220	in that case.
		221
		222	Although the callback might get passed parameters, their value and
		223	presence is undefined and you cannot rely on them. Portable AnyEvent
		224	callbacks cannot use arguments passed to time watcher callbacks.
		225
		226	The callback will normally be invoked once only. If you specify another
		227	parameter, C<interval>, as a strictly positive number (> 0), then the
		228	callback will be invoked regularly at that interval (in fractional
		229	seconds) after the first invocation. If C<interval> is specified with a
		230	false value, then it is treated as if it were missing.
		231
		232	The callback will be rescheduled before invoking the callback, but no
		233	attempt is done to avoid timer drift in most backends, so the interval is
		234	only approximate.
		235
		236	Example: fire an event after 7.7 seconds.
		237
		238	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		239	warn "timeout\n";
		240	});
		241
		242	# to cancel the timer:
		243	undef $w;
		244
		245	Example 2: fire an event after 0.5 seconds, then roughly every second.
		246
		247	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		248	warn "timeout\n";
		249	};
		250
		251	=head3 TIMING ISSUES
		252
		253	There are two ways to handle timers: based on real time (relative, "fire
		254	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		255	o'clock").
		256
		257	While most event loops expect timers to specified in a relative way, they
		258	use absolute time internally. This makes a difference when your clock
		259	"jumps", for example, when ntp decides to set your clock backwards from
		260	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		261	fire "after" a second might actually take six years to finally fire.
		262
		263	AnyEvent cannot compensate for this. The only event loop that is conscious
		264	about these issues is L<EV>, which offers both relative (ev_timer, based
		265	on true relative time) and absolute (ev_periodic, based on wallclock time)
		266	timers.
		267
		268	AnyEvent always prefers relative timers, if available, matching the
		269	AnyEvent API.
		270
		271	AnyEvent has two additional methods that return the "current time":
46		272
47	=over 4	273	=over 4
48		274
		275	=item AnyEvent->time
		276
		277	This returns the "current wallclock time" as a fractional number of
		278	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		279	return, and the result is guaranteed to be compatible with those).
		280
		281	It progresses independently of any event loop processing, i.e. each call
		282	will check the system clock, which usually gets updated frequently.
		283
		284	=item AnyEvent->now
		285
		286	This also returns the "current wallclock time", but unlike C<time>, above,
		287	this value might change only once per event loop iteration, depending on
		288	the event loop (most return the same time as C<time>, above). This is the
		289	time that AnyEvent's timers get scheduled against.
		290
		291	I<In almost all cases (in all cases if you don't care), this is the
		292	function to call when you want to know the current time.>
		293
		294	This function is also often faster then C<< AnyEvent->time >>, and
		295	thus the preferred method if you want some timestamp (for example,
		296	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		297
		298	The rest of this section is only of relevance if you try to be very exact
		299	with your timing, you can skip it without bad conscience.
		300
		301	For a practical example of when these times differ, consider L<Event::Lib>
		302	and L<EV> and the following set-up:
		303
		304	The event loop is running and has just invoked one of your callback at
		305	time=500 (assume no other callbacks delay processing). In your callback,
		306	you wait a second by executing C<sleep 1> (blocking the process for a
		307	second) and then (at time=501) you create a relative timer that fires
		308	after three seconds.
		309
		310	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		311	both return C<501>, because that is the current time, and the timer will
		312	be scheduled to fire at time=504 (C<501> + C<3>).
		313
		314	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		315	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		316	last event processing phase started. With L<EV>, your timer gets scheduled
		317	to run at time=503 (C<500> + C<3>).
		318
		319	In one sense, L<Event::Lib> is more exact, as it uses the current time
		320	regardless of any delays introduced by event processing. However, most
		321	callbacks do not expect large delays in processing, so this causes a
		322	higher drift (and a lot more system calls to get the current time).
		323
		324	In another sense, L<EV> is more exact, as your timer will be scheduled at
		325	the same time, regardless of how long event processing actually took.
		326
		327	In either case, if you care (and in most cases, you don't), then you
		328	can get whatever behaviour you want with any event loop, by taking the
		329	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		330	account.
		331
		332	=item AnyEvent->now_update
		333
		334	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		335	the current time for each loop iteration (see the discussion of L<<
		336	AnyEvent->now >>, above).
		337
		338	When a callback runs for a long time (or when the process sleeps), then
		339	this "current" time will differ substantially from the real time, which
		340	might affect timers and time-outs.
		341
		342	When this is the case, you can call this method, which will update the
		343	event loop's idea of "current time".
		344
		345	Note that updating the time I<might> cause some events to be handled.
		346
		347	=back
		348
		349	=head2 SIGNAL WATCHERS
		350
		351	You can watch for signals using a signal watcher, C<signal> is the signal
		352	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		353	callback to be invoked whenever a signal occurs.
		354
		355	Although the callback might get passed parameters, their value and
		356	presence is undefined and you cannot rely on them. Portable AnyEvent
		357	callbacks cannot use arguments passed to signal watcher callbacks.
		358
		359	Multiple signal occurrences can be clumped together into one callback
		360	invocation, and callback invocation will be synchronous. Synchronous means
		361	that it might take a while until the signal gets handled by the process,
		362	but it is guaranteed not to interrupt any other callbacks.
		363
		364	The main advantage of using these watchers is that you can share a signal
		365	between multiple watchers.
		366
		367	This watcher might use C<%SIG>, so programs overwriting those signals
		368	directly will likely not work correctly.
		369
		370	Example: exit on SIGINT
		371
		372	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		373
		374	=head2 CHILD PROCESS WATCHERS
		375
		376	You can also watch on a child process exit and catch its exit status.
		377
		378	The child process is specified by the C<pid> argument (if set to C<0>, it
		379	watches for any child process exit). The watcher will triggered only when
		380	the child process has finished and an exit status is available, not on
		381	any trace events (stopped/continued).
		382
		383	The callback will be called with the pid and exit status (as returned by
		384	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		385	callback arguments.
		386
		387	This watcher type works by installing a signal handler for C<SIGCHLD>,
		388	and since it cannot be shared, nothing else should use SIGCHLD or reap
		389	random child processes (waiting for specific child processes, e.g. inside
		390	C<system>, is just fine).
		391
		392	There is a slight catch to child watchers, however: you usually start them
		393	I<after> the child process was created, and this means the process could
		394	have exited already (and no SIGCHLD will be sent anymore).
		395
		396	Not all event models handle this correctly (POE doesn't), but even for
		397	event models that I<do> handle this correctly, they usually need to be
		398	loaded before the process exits (i.e. before you fork in the first place).
		399
		400	This means you cannot create a child watcher as the very first thing in an
		401	AnyEvent program, you I<have> to create at least one watcher before you
		402	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		403
		404	Example: fork a process and wait for it
		405
		406	my $done = AnyEvent->condvar;
		407
		408	my $pid = fork or exit 5;
		409
		410	my $w = AnyEvent->child (
		411	pid => $pid,
		412	cb => sub {
		413	my ($pid, $status) = @_;
		414	warn "pid $pid exited with status $status";
		415	$done->send;
		416	},
		417	);
		418
		419	# do something else, then wait for process exit
		420	$done->recv;
		421
		422	=head2 IDLE WATCHERS
		423
		424	Sometimes there is a need to do something, but it is not so important
		425	to do it instantly, but only when there is nothing better to do. This
		426	"nothing better to do" is usually defined to be "no other events need
		427	attention by the event loop".
		428
		429	Idle watchers ideally get invoked when the event loop has nothing
		430	better to do, just before it would block the process to wait for new
		431	events. Instead of blocking, the idle watcher is invoked.
		432
		433	Most event loops unfortunately do not really support idle watchers (only
		434	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		435	will simply call the callback "from time to time".
		436
		437	Example: read lines from STDIN, but only process them when the
		438	program is otherwise idle:
		439
		440	my @lines; # read data
		441	my $idle_w;
		442	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		443	push @lines, scalar <STDIN>;
		444
		445	# start an idle watcher, if not already done
		446	$idle_w ||= AnyEvent->idle (cb => sub {
		447	# handle only one line, when there are lines left
		448	if (my $line = shift @lines) {
		449	print "handled when idle: $line";
		450	} else {
		451	# otherwise disable the idle watcher again
		452	undef $idle_w;
		453	}
		454	});
		455	});
		456
		457	=head2 CONDITION VARIABLES
		458
		459	If you are familiar with some event loops you will know that all of them
		460	require you to run some blocking "loop", "run" or similar function that
		461	will actively watch for new events and call your callbacks.
		462
		463	AnyEvent is different, it expects somebody else to run the event loop and
		464	will only block when necessary (usually when told by the user).
		465
		466	The instrument to do that is called a "condition variable", so called
		467	because they represent a condition that must become true.
		468
		469	Condition variables can be created by calling the C<< AnyEvent->condvar
		470	>> method, usually without arguments. The only argument pair allowed is
		471
		472	C<cb>, which specifies a callback to be called when the condition variable
		473	becomes true, with the condition variable as the first argument (but not
		474	the results).
		475
		476	After creation, the condition variable is "false" until it becomes "true"
		477	by calling the C<send> method (or calling the condition variable as if it
		478	were a callback, read about the caveats in the description for the C<<
		479	->send >> method).
		480
		481	Condition variables are similar to callbacks, except that you can
		482	optionally wait for them. They can also be called merge points - points
		483	in time where multiple outstanding events have been processed. And yet
		484	another way to call them is transactions - each condition variable can be
		485	used to represent a transaction, which finishes at some point and delivers
		486	a result.
		487
		488	Condition variables are very useful to signal that something has finished,
		489	for example, if you write a module that does asynchronous http requests,
		490	then a condition variable would be the ideal candidate to signal the
		491	availability of results. The user can either act when the callback is
		492	called or can synchronously C<< ->recv >> for the results.
		493
		494	You can also use them to simulate traditional event loops - for example,
		495	you can block your main program until an event occurs - for example, you
		496	could C<< ->recv >> in your main program until the user clicks the Quit
		497	button of your app, which would C<< ->send >> the "quit" event.
		498
		499	Note that condition variables recurse into the event loop - if you have
		500	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		501	lose. Therefore, condition variables are good to export to your caller, but
		502	you should avoid making a blocking wait yourself, at least in callbacks,
		503	as this asks for trouble.
		504
		505	Condition variables are represented by hash refs in perl, and the keys
		506	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		507	easy (it is often useful to build your own transaction class on top of
		508	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		509	it's C<new> method in your own C<new> method.
		510
		511	There are two "sides" to a condition variable - the "producer side" which
		512	eventually calls C<< -> send >>, and the "consumer side", which waits
		513	for the send to occur.
		514
		515	Example: wait for a timer.
		516
		517	# wait till the result is ready
		518	my $result_ready = AnyEvent->condvar;
		519
		520	# do something such as adding a timer
		521	# or socket watcher the calls $result_ready->send
		522	# when the "result" is ready.
		523	# in this case, we simply use a timer:
		524	my $w = AnyEvent->timer (
		525	after => 1,
		526	cb => sub { $result_ready->send },
		527	);
		528
		529	# this "blocks" (while handling events) till the callback
		530	# calls send
		531	$result_ready->recv;
		532
		533	Example: wait for a timer, but take advantage of the fact that
		534	condition variables are also code references.
		535
		536	my $done = AnyEvent->condvar;
		537	my $delay = AnyEvent->timer (after => 5, cb => $done);
		538	$done->recv;
		539
		540	Example: Imagine an API that returns a condvar and doesn't support
		541	callbacks. This is how you make a synchronous call, for example from
		542	the main program:
		543
		544	use AnyEvent::CouchDB;
		545
		546	...
		547
		548	my @info = $couchdb->info->recv;
		549
		550	And this is how you would just ste a callback to be called whenever the
		551	results are available:
		552
		553	$couchdb->info->cb (sub {
		554	my @info = $_[0]->recv;
		555	});
		556
		557	=head3 METHODS FOR PRODUCERS
		558
		559	These methods should only be used by the producing side, i.e. the
		560	code/module that eventually sends the signal. Note that it is also
		561	the producer side which creates the condvar in most cases, but it isn't
		562	uncommon for the consumer to create it as well.
		563
		564	=over 4
		565
		566	=item $cv->send (...)
		567
		568	Flag the condition as ready - a running C<< ->recv >> and all further
		569	calls to C<recv> will (eventually) return after this method has been
		570	called. If nobody is waiting the send will be remembered.
		571
		572	If a callback has been set on the condition variable, it is called
		573	immediately from within send.
		574
		575	Any arguments passed to the C<send> call will be returned by all
		576	future C<< ->recv >> calls.
		577
		578	Condition variables are overloaded so one can call them directly
		579	(as a code reference). Calling them directly is the same as calling
		580	C<send>. Note, however, that many C-based event loops do not handle
		581	overloading, so as tempting as it may be, passing a condition variable
		582	instead of a callback does not work. Both the pure perl and EV loops
		583	support overloading, however, as well as all functions that use perl to
		584	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		585	example).
		586
		587	=item $cv->croak ($error)
		588
		589	Similar to send, but causes all call's to C<< ->recv >> to invoke
		590	C<Carp::croak> with the given error message/object/scalar.
		591
		592	This can be used to signal any errors to the condition variable
		593	user/consumer.
		594
		595	=item $cv->begin ([group callback])
		596
		597	=item $cv->end
		598
		599	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		600
		601	These two methods can be used to combine many transactions/events into
		602	one. For example, a function that pings many hosts in parallel might want
		603	to use a condition variable for the whole process.
		604
		605	Every call to C<< ->begin >> will increment a counter, and every call to
		606	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		607	>>, the (last) callback passed to C<begin> will be executed. That callback
		608	is I<supposed> to call C<< ->send >>, but that is not required. If no
		609	callback was set, C<send> will be called without any arguments.
		610
		611	Let's clarify this with the ping example:
		612
		613	my $cv = AnyEvent->condvar;
		614
		615	my %result;
		616	$cv->begin (sub { $cv->send (\%result) });
		617
		618	for my $host (@list_of_hosts) {
		619	$cv->begin;
		620	ping_host_then_call_callback $host, sub {
		621	$result{$host} = ...;
		622	$cv->end;
		623	};
		624	}
		625
		626	$cv->end;
		627
		628	This code fragment supposedly pings a number of hosts and calls
		629	C<send> after results for all then have have been gathered - in any
		630	order. To achieve this, the code issues a call to C<begin> when it starts
		631	each ping request and calls C<end> when it has received some result for
		632	it. Since C<begin> and C<end> only maintain a counter, the order in which
		633	results arrive is not relevant.
		634
		635	There is an additional bracketing call to C<begin> and C<end> outside the
		636	loop, which serves two important purposes: first, it sets the callback
		637	to be called once the counter reaches C<0>, and second, it ensures that
		638	C<send> is called even when C<no> hosts are being pinged (the loop
		639	doesn't execute once).
		640
		641	This is the general pattern when you "fan out" into multiple subrequests:
		642	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		643	is called at least once, and then, for each subrequest you start, call
		644	C<begin> and for each subrequest you finish, call C<end>.
		645
		646	=back
		647
		648	=head3 METHODS FOR CONSUMERS
		649
		650	These methods should only be used by the consuming side, i.e. the
		651	code awaits the condition.
		652
		653	=over 4
		654
		655	=item $cv->recv
		656
		657	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		658	>> methods have been called on c<$cv>, while servicing other watchers
		659	normally.
		660
		661	You can only wait once on a condition - additional calls are valid but
		662	will return immediately.
		663
		664	If an error condition has been set by calling C<< ->croak >>, then this
		665	function will call C<croak>.
		666
		667	In list context, all parameters passed to C<send> will be returned,
		668	in scalar context only the first one will be returned.
		669
		670	Not all event models support a blocking wait - some die in that case
		671	(programs might want to do that to stay interactive), so I<if you are
		672	using this from a module, never require a blocking wait>, but let the
		673	caller decide whether the call will block or not (for example, by coupling
		674	condition variables with some kind of request results and supporting
		675	callbacks so the caller knows that getting the result will not block,
		676	while still supporting blocking waits if the caller so desires).
		677
		678	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		679	sensibly have two C<< ->recv >>'s in parallel, as that would require
		680	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		681	can supply.
		682
		683	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		684	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		685	versions and also integrates coroutines into AnyEvent, making blocking
		686	C<< ->recv >> calls perfectly safe as long as they are done from another
		687	coroutine (one that doesn't run the event loop).
		688
		689	You can ensure that C<< -recv >> never blocks by setting a callback and
		690	only calling C<< ->recv >> from within that callback (or at a later
		691	time). This will work even when the event loop does not support blocking
		692	waits otherwise.
		693
		694	=item $bool = $cv->ready
		695
		696	Returns true when the condition is "true", i.e. whether C<send> or
		697	C<croak> have been called.
		698
		699	=item $cb = $cv->cb ($cb->($cv))
		700
		701	This is a mutator function that returns the callback set and optionally
		702	replaces it before doing so.
		703
		704	The callback will be called when the condition becomes "true", i.e. when
		705	C<send> or C<croak> are called, with the only argument being the condition
		706	variable itself. Calling C<recv> inside the callback or at any later time
		707	is guaranteed not to block.
		708
		709	=back
		710
		711	=head1 GLOBAL VARIABLES AND FUNCTIONS
		712
		713	=over 4
		714
		715	=item $AnyEvent::MODEL
		716
		717	Contains C<undef> until the first watcher is being created. Then it
		718	contains the event model that is being used, which is the name of the
		719	Perl class implementing the model. This class is usually one of the
		720	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		721	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		722
		723	The known classes so far are:
		724
		725	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		726	AnyEvent::Impl::Event based on Event, second best choice.
		727	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		728	AnyEvent::Impl::Glib based on Glib, third-best choice.
		729	AnyEvent::Impl::Tk based on Tk, very bad choice.
		730	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		731	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		732	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		733
		734	There is no support for WxWidgets, as WxWidgets has no support for
		735	watching file handles. However, you can use WxWidgets through the
		736	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		737	second, which was considered to be too horrible to even consider for
		738	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		739	it's adaptor.
		740
		741	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		742	autodetecting them.
		743
		744	=item AnyEvent::detect
		745
		746	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		747	if necessary. You should only call this function right before you would
		748	have created an AnyEvent watcher anyway, that is, as late as possible at
		749	runtime.
		750
		751	=item $guard = AnyEvent::post_detect { BLOCK }
		752
		753	Arranges for the code block to be executed as soon as the event model is
		754	autodetected (or immediately if this has already happened).
		755
		756	If called in scalar or list context, then it creates and returns an object
		757	that automatically removes the callback again when it is destroyed. See
		758	L<Coro::BDB> for a case where this is useful.
		759
		760	=item @AnyEvent::post_detect
		761
		762	If there are any code references in this array (you can C<push> to it
		763	before or after loading AnyEvent), then they will called directly after
		764	the event loop has been chosen.
		765
		766	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		767	if it contains a true value then the event loop has already been detected,
		768	and the array will be ignored.
		769
		770	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		771
		772	=back
		773
		774	=head1 WHAT TO DO IN A MODULE
		775
		776	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		777	freely, but you should not load a specific event module or rely on it.
		778
		779	Be careful when you create watchers in the module body - AnyEvent will
		780	decide which event module to use as soon as the first method is called, so
		781	by calling AnyEvent in your module body you force the user of your module
		782	to load the event module first.
		783
		784	Never call C<< ->recv >> on a condition variable unless you I<know> that
		785	the C<< ->send >> method has been called on it already. This is
		786	because it will stall the whole program, and the whole point of using
		787	events is to stay interactive.
		788
		789	It is fine, however, to call C<< ->recv >> when the user of your module
		790	requests it (i.e. if you create a http request object ad have a method
		791	called C<results> that returns the results, it should call C<< ->recv >>
		792	freely, as the user of your module knows what she is doing. always).
		793
		794	=head1 WHAT TO DO IN THE MAIN PROGRAM
		795
		796	There will always be a single main program - the only place that should
		797	dictate which event model to use.
		798
		799	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		800	do anything special (it does not need to be event-based) and let AnyEvent
		801	decide which implementation to chose if some module relies on it.
		802
		803	If the main program relies on a specific event model - for example, in
		804	Gtk2 programs you have to rely on the Glib module - you should load the
		805	event module before loading AnyEvent or any module that uses it: generally
		806	speaking, you should load it as early as possible. The reason is that
		807	modules might create watchers when they are loaded, and AnyEvent will
		808	decide on the event model to use as soon as it creates watchers, and it
		809	might chose the wrong one unless you load the correct one yourself.
		810
		811	You can chose to use a pure-perl implementation by loading the
		812	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		813	everywhere, but letting AnyEvent chose the model is generally better.
		814
		815	=head2 MAINLOOP EMULATION
		816
		817	Sometimes (often for short test scripts, or even standalone programs who
		818	only want to use AnyEvent), you do not want to run a specific event loop.
		819
		820	In that case, you can use a condition variable like this:
		821
		822	AnyEvent->condvar->recv;
		823
		824	This has the effect of entering the event loop and looping forever.
		825
		826	Note that usually your program has some exit condition, in which case
		827	it is better to use the "traditional" approach of storing a condition
		828	variable somewhere, waiting for it, and sending it when the program should
		829	exit cleanly.
		830
		831
		832	=head1 OTHER MODULES
		833
		834	The following is a non-exhaustive list of additional modules that use
		835	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		836	in the same program. Some of the modules come with AnyEvent, some are
		837	available via CPAN.
		838
		839	=over 4
		840
		841	=item L<AnyEvent::Util>
		842
		843	Contains various utility functions that replace often-used but blocking
		844	functions such as C<inet_aton> by event-/callback-based versions.
		845
		846	=item L<AnyEvent::Socket>
		847
		848	Provides various utility functions for (internet protocol) sockets,
		849	addresses and name resolution. Also functions to create non-blocking tcp
		850	connections or tcp servers, with IPv6 and SRV record support and more.
		851
		852	=item L<AnyEvent::Handle>
		853
		854	Provide read and write buffers, manages watchers for reads and writes,
		855	supports raw and formatted I/O, I/O queued and fully transparent and
		856	non-blocking SSL/TLS.
		857
		858	=item L<AnyEvent::DNS>
		859
		860	Provides rich asynchronous DNS resolver capabilities.
		861
		862	=item L<AnyEvent::HTTP>
		863
		864	A simple-to-use HTTP library that is capable of making a lot of concurrent
		865	HTTP requests.
		866
		867	=item L<AnyEvent::HTTPD>
		868
		869	Provides a simple web application server framework.
		870
		871	=item L<AnyEvent::FastPing>
		872
		873	The fastest ping in the west.
		874
		875	=item L<AnyEvent::DBI>
		876
		877	Executes L<DBI> requests asynchronously in a proxy process.
		878
		879	=item L<AnyEvent::AIO>
		880
		881	Truly asynchronous I/O, should be in the toolbox of every event
		882	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		883	together.
		884
		885	=item L<AnyEvent::BDB>
		886
		887	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		888	L<BDB> and AnyEvent together.
		889
		890	=item L<AnyEvent::GPSD>
		891
		892	A non-blocking interface to gpsd, a daemon delivering GPS information.
		893
		894	=item L<AnyEvent::IGS>
		895
		896	A non-blocking interface to the Internet Go Server protocol (used by
		897	L<App::IGS>).
		898
		899	=item L<AnyEvent::IRC>
		900
		901	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		902
		903	=item L<Net::XMPP2>
		904
		905	AnyEvent based XMPP (Jabber protocol) module family.
		906
		907	=item L<Net::FCP>
		908
		909	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		910	of AnyEvent.
		911
		912	=item L<Event::ExecFlow>
		913
		914	High level API for event-based execution flow control.
		915
		916	=item L<Coro>
		917
		918	Has special support for AnyEvent via L<Coro::AnyEvent>.
		919
		920	=item L<IO::Lambda>
		921
		922	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		923
		924	=back
		925
49	=cut	926	=cut
50		927
51	package AnyEvent;	928	package AnyEvent;
52		929
53	no warnings;	930	no warnings;
54	use strict 'vars';	931	use strict qw(vars subs);
		932
55	use Carp;	933	use Carp;
56		934
57	our $VERSION = 0.1;	935	our $VERSION = 4.41;
58	our $MODEL;	936	our $MODEL;
59		937
60	our $AUTOLOAD;	938	our $AUTOLOAD;
61	our @ISA;	939	our @ISA;
62		940
		941	our @REGISTRY;
		942
		943	our $WIN32;
		944
		945	BEGIN {
		946	my $win32 = ! ! ($^O =~ /mswin32/i);
		947	eval "sub WIN32(){ $win32 }";
		948	}
		949
		950	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		951
		952	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		953
		954	{
		955	my $idx;
		956	$PROTOCOL{$_} = ++$idx
		957	for reverse split /\s*,\s*/,
		958	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		959	}
		960
63	my @models = (	961	my @models = (
64	[Coro => Coro::Event::],	962	[EV:: => AnyEvent::Impl::EV::],
65	[Event => Event::],	963	[Event:: => AnyEvent::Impl::Event::],
66	[Glib => Glib::],	964	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
67	[Tk => Tk::],	965	# everything below here will not be autoprobed
		966	# as the pureperl backend should work everywhere
		967	# and is usually faster
		968	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		969	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		970	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		971	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		972	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		973	[Wx:: => AnyEvent::Impl::POE::],
		974	[Prima:: => AnyEvent::Impl::POE::],
68	);	975	);
69		976
70	sub AUTOLOAD {	977	our %method = map +($_ => 1),
71	$AUTOLOAD =~ s/.*://;	978	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
72		979
		980	our @post_detect;
		981
		982	sub post_detect(&) {
		983	my ($cb) = @_;
		984
		985	if ($MODEL) {
		986	$cb->();
		987
		988	1
		989	} else {
		990	push @post_detect, $cb;
		991
		992	defined wantarray
		993	? bless \$cb, "AnyEvent::Util::postdetect"
		994	: ()
		995	}
		996	}
		997
		998	sub AnyEvent::Util::postdetect::DESTROY {
		999	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1000	}
		1001
		1002	sub detect() {
73	unless ($MODEL) {	1003	unless ($MODEL) {
74	# check for already loaded models	1004	no strict 'refs';
75	for (@models) {	1005	local $SIG{__DIE__};
76	my ($model, $package) = @$_;
77	if (scalar keys %{ *{"$package\::"} }) {
78	eval "require AnyEvent::Impl::$model"
79	or die;
80		1006
81	last if $MODEL;	1007	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		1008	my $model = "AnyEvent::Impl::$1";
		1009	if (eval "require $model") {
		1010	$MODEL = $model;
		1011	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		1012	} else {
		1013	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
82	}	1014	}
83	}	1015	}
84		1016
		1017	# check for already loaded models
85	unless ($MODEL) {	1018	unless ($MODEL) {
86	# try to load a model
87
88	for (@models) {	1019	for (@REGISTRY, @models) {
89	my ($model, $package) = @$_;	1020	my ($package, $model) = @$_;
90	eval "require AnyEvent::Impl::$model"	1021	if (${"$package\::VERSION"} > 0) {
		1022	if (eval "require $model") {
		1023	$MODEL = $model;
		1024	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		1025	last;
91	or die;	1026	}
92		1027	}
93	last if $MODEL;
94	}	1028	}
95		1029
		1030	unless ($MODEL) {
		1031	# try to load a model
		1032
		1033	for (@REGISTRY, @models) {
		1034	my ($package, $model) = @$_;
		1035	if (eval "require $package"
		1036	and ${"$package\::VERSION"} > 0
		1037	and eval "require $model") {
		1038	$MODEL = $model;
		1039	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		1040	last;
		1041	}
		1042	}
		1043
96	$MODEL	1044	$MODEL
97	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1045	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
		1046	}
		1047	}
		1048
		1049	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1050
		1051	unshift @ISA, $MODEL;
		1052
		1053	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1054
		1055	(shift @post_detect)->() while @post_detect;
		1056	}
		1057
		1058	$MODEL
		1059	}
		1060
		1061	sub AUTOLOAD {
		1062	(my $func = $AUTOLOAD) =~ s/.*://;
		1063
		1064	$method{$func}
		1065	or croak "$func: not a valid method for AnyEvent objects";
		1066
		1067	detect unless $MODEL;
		1068
		1069	my $class = shift;
		1070	$class->$func (@_);
		1071	}
		1072
		1073	# utility function to dup a filehandle. this is used by many backends
		1074	# to support binding more than one watcher per filehandle (they usually
		1075	# allow only one watcher per fd, so we dup it to get a different one).
		1076	sub _dupfh($$$$) {
		1077	my ($poll, $fh, $r, $w) = @_;
		1078
		1079	# cygwin requires the fh mode to be matching, unix doesn't
		1080	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1081	: $poll eq "w" ? ($w, ">")
		1082	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1083
		1084	open my $fh2, "$mode&" . fileno $fh
		1085	or die "cannot dup() filehandle: $!,";
		1086
		1087	# we assume CLOEXEC is already set by perl in all important cases
		1088
		1089	($fh2, $rw)
		1090	}
		1091
		1092	package AnyEvent::Base;
		1093
		1094	# default implementations for many methods
		1095
		1096	BEGIN {
		1097	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1098	*_time = \&Time::HiRes::time;
		1099	# if (eval "use POSIX (); (POSIX::times())...
		1100	} else {
		1101	*_time = sub { time }; # epic fail
		1102	}
		1103	}
		1104
		1105	sub time { _time }
		1106	sub now { _time }
		1107	sub now_update { }
		1108
		1109	# default implementation for ->condvar
		1110
		1111	sub condvar {
		1112	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1113	}
		1114
		1115	# default implementation for ->signal
		1116
		1117	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1118
		1119	sub _signal_exec {
		1120	sysread $SIGPIPE_R, my $dummy, 4;
		1121
		1122	while (%SIG_EV) {
		1123	for (keys %SIG_EV) {
		1124	delete $SIG_EV{$_};
		1125	$_->() for values %{ $SIG_CB{$_} || {} };
98	}	1126	}
99	}	1127	}
		1128	}
100		1129
101	@ISA = $MODEL;	1130	sub signal {
		1131	my (undef, %arg) = @_;
102		1132
		1133	unless ($SIGPIPE_R) {
		1134	require Fcntl;
		1135
		1136	if (AnyEvent::WIN32) {
		1137	require AnyEvent::Util;
		1138
		1139	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1140	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1141	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1142	} else {
		1143	pipe $SIGPIPE_R, $SIGPIPE_W;
		1144	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1145	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1146	}
		1147
		1148	$SIGPIPE_R
		1149	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1150
		1151	# not strictly required, as $^F is normally 2, but let's make sure...
		1152	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1153	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1154
		1155	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1156	}
		1157
		1158	my $signal = uc $arg{signal}
		1159	or Carp::croak "required option 'signal' is missing";
		1160
		1161	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1162	$SIG{$signal} ||= sub {
		1163	local $!;
		1164	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1165	undef $SIG_EV{$signal};
		1166	};
		1167
		1168	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1169	}
		1170
		1171	sub AnyEvent::Base::signal::DESTROY {
		1172	my ($signal, $cb) = @{$_[0]};
		1173
		1174	delete $SIG_CB{$signal}{$cb};
		1175
		1176	# delete doesn't work with older perls - they then
		1177	# print weird messages, or just unconditionally exit
		1178	# instead of getting the default action.
		1179	undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
		1180	}
		1181
		1182	# default implementation for ->child
		1183
		1184	our %PID_CB;
		1185	our $CHLD_W;
		1186	our $CHLD_DELAY_W;
		1187	our $WNOHANG;
		1188
		1189	sub _sigchld {
		1190	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1191	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		1192	(values %{ $PID_CB{0} || {} });
		1193	}
		1194	}
		1195
		1196	sub child {
		1197	my (undef, %arg) = @_;
		1198
		1199	defined (my $pid = $arg{pid} + 0)
		1200	or Carp::croak "required option 'pid' is missing";
		1201
		1202	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1203
		1204	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1205
		1206	unless ($CHLD_W) {
		1207	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1208	# child could be a zombie already, so make at least one round
		1209	&_sigchld;
		1210	}
		1211
		1212	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
		1213	}
		1214
		1215	sub AnyEvent::Base::child::DESTROY {
		1216	my ($pid, $cb) = @{$_[0]};
		1217
		1218	delete $PID_CB{$pid}{$cb};
		1219	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1220
		1221	undef $CHLD_W unless keys %PID_CB;
		1222	}
		1223
		1224	# idle emulation is done by simply using a timer, regardless
		1225	# of whether the process is idle or not, and not letting
		1226	# the callback use more than 50% of the time.
		1227	sub idle {
		1228	my (undef, %arg) = @_;
		1229
		1230	my ($cb, $w, $rcb) = $arg{cb};
		1231
		1232	$rcb = sub {
		1233	if ($cb) {
		1234	$w = _time;
		1235	&$cb;
		1236	$w = _time - $w;
		1237
		1238	# never use more then 50% of the time for the idle watcher,
		1239	# within some limits
		1240	$w = 0.0001 if $w < 0.0001;
		1241	$w = 5 if $w > 5;
		1242
		1243	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1244	} else {
		1245	# clean up...
		1246	undef $w;
		1247	undef $rcb;
		1248	}
		1249	};
		1250
		1251	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1252
		1253	bless \\$cb, "AnyEvent::Base::idle"
		1254	}
		1255
		1256	sub AnyEvent::Base::idle::DESTROY {
		1257	undef $${$_[0]};
		1258	}
		1259
		1260	package AnyEvent::CondVar;
		1261
		1262	our @ISA = AnyEvent::CondVar::Base::;
		1263
		1264	package AnyEvent::CondVar::Base;
		1265
		1266	use overload
		1267	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1268	fallback => 1;
		1269
		1270	sub _send {
		1271	# nop
		1272	}
		1273
		1274	sub send {
103	my $class = shift;	1275	my $cv = shift;
104	$class->$AUTOLOAD (@_);	1276	$cv->{_ae_sent} = [@_];
		1277	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1278	$cv->_send;
105	}	1279	}
		1280
		1281	sub croak {
		1282	$_[0]{_ae_croak} = $_[1];
		1283	$_[0]->send;
		1284	}
		1285
		1286	sub ready {
		1287	$_[0]{_ae_sent}
		1288	}
		1289
		1290	sub _wait {
		1291	AnyEvent->one_event while !$_[0]{_ae_sent};
		1292	}
		1293
		1294	sub recv {
		1295	$_[0]->_wait;
		1296
		1297	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1298	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1299	}
		1300
		1301	sub cb {
		1302	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1303	$_[0]{_ae_cb}
		1304	}
		1305
		1306	sub begin {
		1307	++$_[0]{_ae_counter};
		1308	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1309	}
		1310
		1311	sub end {
		1312	return if --$_[0]{_ae_counter};
		1313	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1314	}
		1315
		1316	# undocumented/compatibility with pre-3.4
		1317	*broadcast = \&send;
		1318	*wait = \&_wait;
		1319
		1320	=head1 ERROR AND EXCEPTION HANDLING
		1321
		1322	In general, AnyEvent does not do any error handling - it relies on the
		1323	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1324	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1325	checking of all AnyEvent methods, however, which is highly useful during
		1326	development.
		1327
		1328	As for exception handling (i.e. runtime errors and exceptions thrown while
		1329	executing a callback), this is not only highly event-loop specific, but
		1330	also not in any way wrapped by this module, as this is the job of the main
		1331	program.
		1332
		1333	The pure perl event loop simply re-throws the exception (usually
		1334	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1335	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1336	so on.
		1337
		1338	=head1 ENVIRONMENT VARIABLES
		1339
		1340	The following environment variables are used by this module or its
		1341	submodules:
		1342
		1343	=over 4
		1344
		1345	=item C<PERL_ANYEVENT_VERBOSE>
		1346
		1347	By default, AnyEvent will be completely silent except in fatal
		1348	conditions. You can set this environment variable to make AnyEvent more
		1349	talkative.
		1350
		1351	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1352	conditions, such as not being able to load the event model specified by
		1353	C<PERL_ANYEVENT_MODEL>.
		1354
		1355	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1356	model it chooses.
		1357
		1358	=item C<PERL_ANYEVENT_STRICT>
		1359
		1360	AnyEvent does not do much argument checking by default, as thorough
		1361	argument checking is very costly. Setting this variable to a true value
		1362	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1363	check the arguments passed to most method calls. If it finds any problems
		1364	it will croak.
		1365
		1366	In other words, enables "strict" mode.
		1367
		1368	Unlike C<use strict>, it is definitely recommended ot keep it off in
		1369	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1370	developing programs can be very useful, however.
		1371
		1372	=item C<PERL_ANYEVENT_MODEL>
		1373
		1374	This can be used to specify the event model to be used by AnyEvent, before
		1375	auto detection and -probing kicks in. It must be a string consisting
		1376	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1377	and the resulting module name is loaded and if the load was successful,
		1378	used as event model. If it fails to load AnyEvent will proceed with
		1379	auto detection and -probing.
		1380
		1381	This functionality might change in future versions.
		1382
		1383	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1384	could start your program like this:
		1385
		1386	PERL_ANYEVENT_MODEL=Perl perl ...
		1387
		1388	=item C<PERL_ANYEVENT_PROTOCOLS>
		1389
		1390	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1391	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1392	of auto probing).
		1393
		1394	Must be set to a comma-separated list of protocols or address families,
		1395	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1396	used, and preference will be given to protocols mentioned earlier in the
		1397	list.
		1398
		1399	This variable can effectively be used for denial-of-service attacks
		1400	against local programs (e.g. when setuid), although the impact is likely
		1401	small, as the program has to handle conenction and other failures anyways.
		1402
		1403	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1404	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1405	- only support IPv4, never try to resolve or contact IPv6
		1406	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1407	IPv6, but prefer IPv6 over IPv4.
		1408
		1409	=item C<PERL_ANYEVENT_EDNS0>
		1410
		1411	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1412	for DNS. This extension is generally useful to reduce DNS traffic, but
		1413	some (broken) firewalls drop such DNS packets, which is why it is off by
		1414	default.
		1415
		1416	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1417	EDNS0 in its DNS requests.
		1418
		1419	=item C<PERL_ANYEVENT_MAX_FORKS>
		1420
		1421	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1422	will create in parallel.
106		1423
107	=back	1424	=back
108		1425
		1426	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1427
		1428	This is an advanced topic that you do not normally need to use AnyEvent in
		1429	a module. This section is only of use to event loop authors who want to
		1430	provide AnyEvent compatibility.
		1431
		1432	If you need to support another event library which isn't directly
		1433	supported by AnyEvent, you can supply your own interface to it by
		1434	pushing, before the first watcher gets created, the package name of
		1435	the event module and the package name of the interface to use onto
		1436	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1437	AnyEvent, so it is reasonably cheap.
		1438
		1439	Example:
		1440
		1441	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1442
		1443	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1444	package/class when it finds the C<urxvt> package/module is already loaded.
		1445
		1446	When AnyEvent is loaded and asked to find a suitable event model, it
		1447	will first check for the presence of urxvt by trying to C<use> the
		1448	C<urxvt::anyevent> module.
		1449
		1450	The class should provide implementations for all watcher types. See
		1451	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1452	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1453	see the sources.
		1454
		1455	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1456	provide suitable (hopefully) replacements.
		1457
		1458	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1459	terminal emulator uses the above line as-is. An interface isn't included
		1460	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1461	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1462	I<rxvt-unicode> distribution.
		1463
		1464	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1465	condition variables: code blocking while waiting for a condition will
		1466	C<die>. This still works with most modules/usages, and blocking calls must
		1467	not be done in an interactive application, so it makes sense.
		1468
109	=head1 EXAMPLE	1469	=head1 EXAMPLE PROGRAM
110		1470
111	The following program uses an io watcher to read data from stdin, a timer	1471	The following program uses an I/O watcher to read data from STDIN, a timer
112	to display a message once per second, and a condvar to exit the program	1472	to display a message once per second, and a condition variable to quit the
113	when the user enters quit:	1473	program when the user enters quit:
114		1474
115	use AnyEvent;	1475	use AnyEvent;
116		1476
117	my $cv = AnyEvent->condvar;	1477	my $cv = AnyEvent->condvar;
118		1478
119	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1479	my $io_watcher = AnyEvent->io (
		1480	fh => \*STDIN,
		1481	poll => 'r',
		1482	cb => sub {
120	warn "io event <$_[0]>\n"; # will always output <r>	1483	warn "io event <$_[0]>\n"; # will always output <r>
121	chomp (my $input = <STDIN>); # read a line	1484	chomp (my $input = <STDIN>); # read a line
122	warn "read: $input\n"; # output what has been read	1485	warn "read: $input\n"; # output what has been read
123	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1486	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1487	},
124	});	1488	);
125		1489
126	my $time_watcher; # can only be used once	1490	my $time_watcher; # can only be used once
127		1491
128	sub new_timer {	1492	sub new_timer {
129	$timer = AnyEvent->timer (after => 1, cb => sub {	1493	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
132	});	1496	});
133	}	1497	}
134		1498
135	new_timer; # create first timer	1499	new_timer; # create first timer
136		1500
137	$cv->wait; # wait until user enters /^q/i	1501	$cv->recv; # wait until user enters /^q/i
		1502
		1503	=head1 REAL-WORLD EXAMPLE
		1504
		1505	Consider the L<Net::FCP> module. It features (among others) the following
		1506	API calls, which are to freenet what HTTP GET requests are to http:
		1507
		1508	my $data = $fcp->client_get ($url); # blocks
		1509
		1510	my $transaction = $fcp->txn_client_get ($url); # does not block
		1511	$transaction->cb ( sub { ... } ); # set optional result callback
		1512	my $data = $transaction->result; # possibly blocks
		1513
		1514	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		1515	given URL and waits till the data has arrived. It is defined to be:
		1516
		1517	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		1518
		1519	And in fact is automatically generated. This is the blocking API of
		1520	L<Net::FCP>, and it works as simple as in any other, similar, module.
		1521
		1522	More complicated is C<txn_client_get>: It only creates a transaction
		1523	(completion, result, ...) object and initiates the transaction.
		1524
		1525	my $txn = bless { }, Net::FCP::Txn::;
		1526
		1527	It also creates a condition variable that is used to signal the completion
		1528	of the request:
		1529
		1530	$txn->{finished} = AnyAvent->condvar;
		1531
		1532	It then creates a socket in non-blocking mode.
		1533
		1534	socket $txn->{fh}, ...;
		1535	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		1536	connect $txn->{fh}, ...
		1537	and !$!{EWOULDBLOCK}
		1538	and !$!{EINPROGRESS}
		1539	and Carp::croak "unable to connect: $!\n";
		1540
		1541	Then it creates a write-watcher which gets called whenever an error occurs
		1542	or the connection succeeds:
		1543
		1544	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		1545
		1546	And returns this transaction object. The C<fh_ready_w> callback gets
		1547	called as soon as the event loop detects that the socket is ready for
		1548	writing.
		1549
		1550	The C<fh_ready_w> method makes the socket blocking again, writes the
		1551	request data and replaces the watcher by a read watcher (waiting for reply
		1552	data). The actual code is more complicated, but that doesn't matter for
		1553	this example:
		1554
		1555	fcntl $txn->{fh}, F_SETFL, 0;
		1556	syswrite $txn->{fh}, $txn->{request}
		1557	or die "connection or write error";
		1558	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		1559
		1560	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		1561	result and signals any possible waiters that the request has finished:
		1562
		1563	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		1564
		1565	if (end-of-file or data complete) {
		1566	$txn->{result} = $txn->{buf};
		1567	$txn->{finished}->send;
		1568	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		1569	}
		1570
		1571	The C<result> method, finally, just waits for the finished signal (if the
		1572	request was already finished, it doesn't wait, of course, and returns the
		1573	data:
		1574
		1575	$txn->{finished}->recv;
		1576	return $txn->{result};
		1577
		1578	The actual code goes further and collects all errors (C<die>s, exceptions)
		1579	that occurred during request processing. The C<result> method detects
		1580	whether an exception as thrown (it is stored inside the $txn object)
		1581	and just throws the exception, which means connection errors and other
		1582	problems get reported tot he code that tries to use the result, not in a
		1583	random callback.
		1584
		1585	All of this enables the following usage styles:
		1586
		1587	1. Blocking:
		1588
		1589	my $data = $fcp->client_get ($url);
		1590
		1591	2. Blocking, but running in parallel:
		1592
		1593	my @datas = map $_->result,
		1594	map $fcp->txn_client_get ($_),
		1595	@urls;
		1596
		1597	Both blocking examples work without the module user having to know
		1598	anything about events.
		1599
		1600	3a. Event-based in a main program, using any supported event module:
		1601
		1602	use EV;
		1603
		1604	$fcp->txn_client_get ($url)->cb (sub {
		1605	my $txn = shift;
		1606	my $data = $txn->result;
		1607	...
		1608	});
		1609
		1610	EV::loop;
		1611
		1612	3b. The module user could use AnyEvent, too:
		1613
		1614	use AnyEvent;
		1615
		1616	my $quit = AnyEvent->condvar;
		1617
		1618	$fcp->txn_client_get ($url)->cb (sub {
		1619	...
		1620	$quit->send;
		1621	});
		1622
		1623	$quit->recv;
		1624
		1625
		1626	=head1 BENCHMARKS
		1627
		1628	To give you an idea of the performance and overheads that AnyEvent adds
		1629	over the event loops themselves and to give you an impression of the speed
		1630	of various event loops I prepared some benchmarks.
		1631
		1632	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1633
		1634	Here is a benchmark of various supported event models used natively and
		1635	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1636	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1637	which it is), lets them fire exactly once and destroys them again.
		1638
		1639	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1640	distribution.
		1641
		1642	=head3 Explanation of the columns
		1643
		1644	I<watcher> is the number of event watchers created/destroyed. Since
		1645	different event models feature vastly different performances, each event
		1646	loop was given a number of watchers so that overall runtime is acceptable
		1647	and similar between tested event loop (and keep them from crashing): Glib
		1648	would probably take thousands of years if asked to process the same number
		1649	of watchers as EV in this benchmark.
		1650
		1651	I<bytes> is the number of bytes (as measured by the resident set size,
		1652	RSS) consumed by each watcher. This method of measuring captures both C
		1653	and Perl-based overheads.
		1654
		1655	I<create> is the time, in microseconds (millionths of seconds), that it
		1656	takes to create a single watcher. The callback is a closure shared between
		1657	all watchers, to avoid adding memory overhead. That means closure creation
		1658	and memory usage is not included in the figures.
		1659
		1660	I<invoke> is the time, in microseconds, used to invoke a simple
		1661	callback. The callback simply counts down a Perl variable and after it was
		1662	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1663	signal the end of this phase.
		1664
		1665	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1666	watcher.
		1667
		1668	=head3 Results
		1669
		1670	name watchers bytes create invoke destroy comment
		1671	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1672	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1673	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1674	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1675	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1676	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1677	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1678	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1679	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1680	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1681
		1682	=head3 Discussion
		1683
		1684	The benchmark does I<not> measure scalability of the event loop very
		1685	well. For example, a select-based event loop (such as the pure perl one)
		1686	can never compete with an event loop that uses epoll when the number of
		1687	file descriptors grows high. In this benchmark, all events become ready at
		1688	the same time, so select/poll-based implementations get an unnatural speed
		1689	boost.
		1690
		1691	Also, note that the number of watchers usually has a nonlinear effect on
		1692	overall speed, that is, creating twice as many watchers doesn't take twice
		1693	the time - usually it takes longer. This puts event loops tested with a
		1694	higher number of watchers at a disadvantage.
		1695
		1696	To put the range of results into perspective, consider that on the
		1697	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1698	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1699	cycles with POE.
		1700
		1701	C<EV> is the sole leader regarding speed and memory use, which are both
		1702	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1703	far less memory than any other event loop and is still faster than Event
		1704	natively.
		1705
		1706	The pure perl implementation is hit in a few sweet spots (both the
		1707	constant timeout and the use of a single fd hit optimisations in the perl
		1708	interpreter and the backend itself). Nevertheless this shows that it
		1709	adds very little overhead in itself. Like any select-based backend its
		1710	performance becomes really bad with lots of file descriptors (and few of
		1711	them active), of course, but this was not subject of this benchmark.
		1712
		1713	The C<Event> module has a relatively high setup and callback invocation
		1714	cost, but overall scores in on the third place.
		1715
		1716	C<Glib>'s memory usage is quite a bit higher, but it features a
		1717	faster callback invocation and overall ends up in the same class as
		1718	C<Event>. However, Glib scales extremely badly, doubling the number of
		1719	watchers increases the processing time by more than a factor of four,
		1720	making it completely unusable when using larger numbers of watchers
		1721	(note that only a single file descriptor was used in the benchmark, so
		1722	inefficiencies of C<poll> do not account for this).
		1723
		1724	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1725	more than 2000 watchers is a big setback, however, as correctness takes
		1726	precedence over speed. Nevertheless, its performance is surprising, as the
		1727	file descriptor is dup()ed for each watcher. This shows that the dup()
		1728	employed by some adaptors is not a big performance issue (it does incur a
		1729	hidden memory cost inside the kernel which is not reflected in the figures
		1730	above).
		1731
		1732	C<POE>, regardless of underlying event loop (whether using its pure perl
		1733	select-based backend or the Event module, the POE-EV backend couldn't
		1734	be tested because it wasn't working) shows abysmal performance and
		1735	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1736	as EV watchers, and 10 times as much memory as Event (the high memory
		1737	requirements are caused by requiring a session for each watcher). Watcher
		1738	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1739	implementation.
		1740
		1741	The design of the POE adaptor class in AnyEvent can not really account
		1742	for the performance issues, though, as session creation overhead is
		1743	small compared to execution of the state machine, which is coded pretty
		1744	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1745	using multiple sessions is not a good approach, especially regarding
		1746	memory usage, even the author of POE could not come up with a faster
		1747	design).
		1748
		1749	=head3 Summary
		1750
		1751	=over 4
		1752
		1753	=item * Using EV through AnyEvent is faster than any other event loop
		1754	(even when used without AnyEvent), but most event loops have acceptable
		1755	performance with or without AnyEvent.
		1756
		1757	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1758	the actual event loop, only with extremely fast event loops such as EV
		1759	adds AnyEvent significant overhead.
		1760
		1761	=item * You should avoid POE like the plague if you want performance or
		1762	reasonable memory usage.
		1763
		1764	=back
		1765
		1766	=head2 BENCHMARKING THE LARGE SERVER CASE
		1767
		1768	This benchmark actually benchmarks the event loop itself. It works by
		1769	creating a number of "servers": each server consists of a socket pair, a
		1770	timeout watcher that gets reset on activity (but never fires), and an I/O
		1771	watcher waiting for input on one side of the socket. Each time the socket
		1772	watcher reads a byte it will write that byte to a random other "server".
		1773
		1774	The effect is that there will be a lot of I/O watchers, only part of which
		1775	are active at any one point (so there is a constant number of active
		1776	fds for each loop iteration, but which fds these are is random). The
		1777	timeout is reset each time something is read because that reflects how
		1778	most timeouts work (and puts extra pressure on the event loops).
		1779
		1780	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1781	(1%) are active. This mirrors the activity of large servers with many
		1782	connections, most of which are idle at any one point in time.
		1783
		1784	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1785	distribution.
		1786
		1787	=head3 Explanation of the columns
		1788
		1789	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1790	each server has a read and write socket end).
		1791
		1792	I<create> is the time it takes to create a socket pair (which is
		1793	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1794
		1795	I<request>, the most important value, is the time it takes to handle a
		1796	single "request", that is, reading the token from the pipe and forwarding
		1797	it to another server. This includes deleting the old timeout and creating
		1798	a new one that moves the timeout into the future.
		1799
		1800	=head3 Results
		1801
		1802	name sockets create request
		1803	EV 20000 69.01 11.16
		1804	Perl 20000 73.32 35.87
		1805	Event 20000 212.62 257.32
		1806	Glib 20000 651.16 1896.30
		1807	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1808
		1809	=head3 Discussion
		1810
		1811	This benchmark I<does> measure scalability and overall performance of the
		1812	particular event loop.
		1813
		1814	EV is again fastest. Since it is using epoll on my system, the setup time
		1815	is relatively high, though.
		1816
		1817	Perl surprisingly comes second. It is much faster than the C-based event
		1818	loops Event and Glib.
		1819
		1820	Event suffers from high setup time as well (look at its code and you will
		1821	understand why). Callback invocation also has a high overhead compared to
		1822	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1823	uses select or poll in basically all documented configurations.
		1824
		1825	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1826	clearly fails to perform with many filehandles or in busy servers.
		1827
		1828	POE is still completely out of the picture, taking over 1000 times as long
		1829	as EV, and over 100 times as long as the Perl implementation, even though
		1830	it uses a C-based event loop in this case.
		1831
		1832	=head3 Summary
		1833
		1834	=over 4
		1835
		1836	=item * The pure perl implementation performs extremely well.
		1837
		1838	=item * Avoid Glib or POE in large projects where performance matters.
		1839
		1840	=back
		1841
		1842	=head2 BENCHMARKING SMALL SERVERS
		1843
		1844	While event loops should scale (and select-based ones do not...) even to
		1845	large servers, most programs we (or I :) actually write have only a few
		1846	I/O watchers.
		1847
		1848	In this benchmark, I use the same benchmark program as in the large server
		1849	case, but it uses only eight "servers", of which three are active at any
		1850	one time. This should reflect performance for a small server relatively
		1851	well.
		1852
		1853	The columns are identical to the previous table.
		1854
		1855	=head3 Results
		1856
		1857	name sockets create request
		1858	EV 16 20.00 6.54
		1859	Perl 16 25.75 12.62
		1860	Event 16 81.27 35.86
		1861	Glib 16 32.63 15.48
		1862	POE 16 261.87 276.28 uses POE::Loop::Event
		1863
		1864	=head3 Discussion
		1865
		1866	The benchmark tries to test the performance of a typical small
		1867	server. While knowing how various event loops perform is interesting, keep
		1868	in mind that their overhead in this case is usually not as important, due
		1869	to the small absolute number of watchers (that is, you need efficiency and
		1870	speed most when you have lots of watchers, not when you only have a few of
		1871	them).
		1872
		1873	EV is again fastest.
		1874
		1875	Perl again comes second. It is noticeably faster than the C-based event
		1876	loops Event and Glib, although the difference is too small to really
		1877	matter.
		1878
		1879	POE also performs much better in this case, but is is still far behind the
		1880	others.
		1881
		1882	=head3 Summary
		1883
		1884	=over 4
		1885
		1886	=item * C-based event loops perform very well with small number of
		1887	watchers, as the management overhead dominates.
		1888
		1889	=back
		1890
		1891
		1892	=head1 SIGNALS
		1893
		1894	AnyEvent currently installs handlers for these signals:
		1895
		1896	=over 4
		1897
		1898	=item SIGCHLD
		1899
		1900	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		1901	emulation for event loops that do not support them natively. Also, some
		1902	event loops install a similar handler.
		1903
		1904	=item SIGPIPE
		1905
		1906	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		1907	when AnyEvent gets loaded.
		1908
		1909	The rationale for this is that AnyEvent users usually do not really depend
		1910	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		1911	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		1912	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		1913	some random socket.
		1914
		1915	The rationale for installing a no-op handler as opposed to ignoring it is
		1916	that this way, the handler will be restored to defaults on exec.
		1917
		1918	Feel free to install your own handler, or reset it to defaults.
		1919
		1920	=back
		1921
		1922	=cut
		1923
		1924	$SIG{PIPE} = sub { }
		1925	unless defined $SIG{PIPE};
		1926
		1927
		1928	=head1 FORK
		1929
		1930	Most event libraries are not fork-safe. The ones who are usually are
		1931	because they rely on inefficient but fork-safe C<select> or C<poll>
		1932	calls. Only L<EV> is fully fork-aware.
		1933
		1934	If you have to fork, you must either do so I<before> creating your first
		1935	watcher OR you must not use AnyEvent at all in the child.
		1936
		1937
		1938	=head1 SECURITY CONSIDERATIONS
		1939
		1940	AnyEvent can be forced to load any event model via
		1941	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1942	execute arbitrary code or directly gain access, it can easily be used to
		1943	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1944	will not be active when the program uses a different event model than
		1945	specified in the variable.
		1946
		1947	You can make AnyEvent completely ignore this variable by deleting it
		1948	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1949
		1950	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1951
		1952	use AnyEvent;
		1953
		1954	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1955	be used to probe what backend is used and gain other information (which is
		1956	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1957	$ENV{PERL_ANYEGENT_STRICT}.
		1958
		1959
		1960	=head1 BUGS
		1961
		1962	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1963	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1964	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1965	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1966	pronounced).
		1967
138		1968
139	=head1 SEE ALSO	1969	=head1 SEE ALSO
140		1970
141	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	1971	Utility functions: L<AnyEvent::Util>.
142	L<AnyEvent::Impl::Coro>,	1972
143	L<AnyEvent::Impl::Event>,	1973	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
144	L<AnyEvent::Impl::Glib>,	1974	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1975
		1976	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1977	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1978	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
145	L<AnyEvent::Impl::Tk>.	1979	L<AnyEvent::Impl::POE>.
146		1980
147	=head1	1981	Non-blocking file handles, sockets, TCP clients and
		1982	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1983
		1984	Asynchronous DNS: L<AnyEvent::DNS>.
		1985
		1986	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1987
		1988	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1989
		1990
		1991	=head1 AUTHOR
		1992
		1993	Marc Lehmann <schmorp@schmorp.de>
		1994	http://home.schmorp.de/
148		1995
149	=cut	1996	=cut
150		1997
151	1	1998	1
152		1999

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