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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 and POE are various supported
		6	event loops.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# file descriptor readable
11	my $w = AnyEvent->timer (fh => ..., poll => "[rw]+", cb => sub {	13	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12	my ($poll_got) = @_;	14
		15	# one-shot or repeating timers
		16	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		17	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		18
		19	print AnyEvent->now; # prints current event loop time
		20	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		21
		22	# POSIX signal
		23	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		24
		25	# child process exit
		26	my $w = AnyEvent->child (pid => $pid, cb => sub {
		27	my ($pid, $status) = @_;
13	...	28	...
14	});	29	});
15	my $w = AnyEvent->io (after => $seconds, cb => sub {
16	...
17	});
18		30
19	# watchers get canceled whenever $w is destroyed	31	# called when event loop idle (if applicable)
20	# only one watcher per $fh and $poll type is allowed	32	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		33
25	my $w = AnyEvent->condvar; # kind of main loop replacement	34	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	# can only be used once	35	$w->send; # wake up current and all future recv's
27	$w->wait; # enters main loop till $condvar gets ->send	36	$w->recv; # enters "main loop" till $condvar gets ->send
28	$w->broadcast; # wake up waiting and future wait's	37	# use a condvar in callback mode:
		38	$w->cb (sub { $_[0]->recv });
		39
		40	=head1 INTRODUCTION/TUTORIAL
		41
		42	This manpage is mainly a reference manual. If you are interested
		43	in a tutorial or some gentle introduction, have a look at the
		44	L<AnyEvent::Intro> manpage.
		45
		46	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		47
		48	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		49	nowadays. So what is different about AnyEvent?
		50
		51	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		52	policy> and AnyEvent is I<small and efficient>.
		53
		54	First and foremost, I<AnyEvent is not an event model> itself, it only
		55	interfaces to whatever event model the main program happens to use, in a
		56	pragmatic way. For event models and certain classes of immortals alike,
		57	the statement "there can only be one" is a bitter reality: In general,
		58	only one event loop can be active at the same time in a process. AnyEvent
		59	cannot change this, but it can hide the differences between those event
		60	loops.
		61
		62	The goal of AnyEvent is to offer module authors the ability to do event
		63	programming (waiting for I/O or timer events) without subscribing to a
		64	religion, a way of living, and most importantly: without forcing your
		65	module users into the same thing by forcing them to use the same event
		66	model you use.
		67
		68	For modules like POE or IO::Async (which is a total misnomer as it is
		69	actually doing all I/O I<synchronously>...), using them in your module is
		70	like joining a cult: After you joined, you are dependent on them and you
		71	cannot use anything else, as they are simply incompatible to everything
		72	that isn't them. What's worse, all the potential users of your
		73	module are I<also> forced to use the same event loop you use.
		74
		75	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		76	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		77	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		78	your module uses one of those, every user of your module has to use it,
		79	too. But if your module uses AnyEvent, it works transparently with all
		80	event models it supports (including stuff like IO::Async, as long as those
		81	use one of the supported event loops. It is trivial to add new event loops
		82	to AnyEvent, too, so it is future-proof).
		83
		84	In addition to being free of having to use I<the one and only true event
		85	model>, AnyEvent also is free of bloat and policy: with POE or similar
		86	modules, you get an enormous amount of code and strict rules you have to
		87	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		88	offering the functionality that is necessary, in as thin as a wrapper as
		89	technically possible.
		90
		91	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		92	of useful functionality, such as an asynchronous DNS resolver, 100%
		93	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		94	such as Windows) and lots of real-world knowledge and workarounds for
		95	platform bugs and differences.
		96
		97	Now, if you I<do want> lots of policy (this can arguably be somewhat
		98	useful) and you want to force your users to use the one and only event
		99	model, you should I<not> use this module.
29		100
30	=head1 DESCRIPTION	101	=head1 DESCRIPTION
31		102
32	L<AnyEvent> provides an identical interface to multiple event loops. This	103	L<AnyEvent> provides an identical interface to multiple event loops. This
33	allows module authors to utilizy an event loop without forcing module	104	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	105	users to use the same event loop (as only a single event loop can coexist
35	peacefully at any one time).	106	peacefully at any one time).
36		107
37	The interface itself is vaguely similar but not identical to the Event	108	The interface itself is vaguely similar, but not identical to the L<Event>
38	module.	109	module.
39		110
40	On the first call of any method, the module tries to detect the currently	111	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	112	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	113	following modules is already loaded: L<EV>,
43	used. If none is found, the module tries to load these modules in the	114	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	115	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.	116	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		117	adaptor should always succeed) in the order given. The first one that can
		118	be successfully loaded will be used. If, after this, still none could be
		119	found, AnyEvent will fall back to a pure-perl event loop, which is not
		120	very efficient, but should work everywhere.
		121
		122	Because AnyEvent first checks for modules that are already loaded, loading
		123	an event model explicitly before first using AnyEvent will likely make
		124	that model the default. For example:
		125
		126	use Tk;
		127	use AnyEvent;
		128
		129	# .. AnyEvent will likely default to Tk
		130
		131	The I<likely> means that, if any module loads another event model and
		132	starts using it, all bets are off. Maybe you should tell their authors to
		133	use AnyEvent so their modules work together with others seamlessly...
		134
		135	The pure-perl implementation of AnyEvent is called
		136	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		137	explicitly and enjoy the high availability of that event loop :)
		138
		139	=head1 WATCHERS
		140
		141	AnyEvent has the central concept of a I<watcher>, which is an object that
		142	stores relevant data for each kind of event you are waiting for, such as
		143	the callback to call, the file handle to watch, etc.
		144
		145	These watchers are normal Perl objects with normal Perl lifetime. After
		146	creating a watcher it will immediately "watch" for events and invoke the
		147	callback when the event occurs (of course, only when the event model
		148	is in control).
		149
		150	Note that B<callbacks must not permanently change global variables>
		151	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		152	callbacks must not C<die> >>. The former is good programming practise in
		153	Perl and the latter stems from the fact that exception handling differs
		154	widely between event loops.
		155
		156	To disable the watcher you have to destroy it (e.g. by setting the
		157	variable you store it in to C<undef> or otherwise deleting all references
		158	to it).
		159
		160	All watchers are created by calling a method on the C<AnyEvent> class.
		161
		162	Many watchers either are used with "recursion" (repeating timers for
		163	example), or need to refer to their watcher object in other ways.
		164
		165	An any way to achieve that is this pattern:
		166
		167	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		168	# you can use $w here, for example to undef it
		169	undef $w;
		170	});
		171
		172	Note that C<my $w; $w => combination. This is necessary because in Perl,
		173	my variables are only visible after the statement in which they are
		174	declared.
		175
		176	=head2 I/O WATCHERS
		177
		178	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		179	with the following mandatory key-value pairs as arguments:
		180
		181	C<fh> is the Perl I<file handle> (I<not> file descriptor) to watch
		182	for events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example files
		186	or block devices.
		187
		188	C<poll> must be a string that is either C<r> or C<w>, which creates a
		189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
		191	C<cb> is the callback to invoke each time the file handle becomes ready.
		192
		193	Although the callback might get passed parameters, their value and
		194	presence is undefined and you cannot rely on them. Portable AnyEvent
		195	callbacks cannot use arguments passed to I/O watcher callbacks.
		196
		197	The I/O watcher might use the underlying file descriptor or a copy of it.
		198	You must not close a file handle as long as any watcher is active on the
		199	underlying file descriptor.
		200
		201	Some event loops issue spurious readyness notifications, so you should
		202	always use non-blocking calls when reading/writing from/to your file
		203	handles.
		204
		205	Example: wait for readability of STDIN, then read a line and disable the
		206	watcher.
		207
		208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		209	chomp (my $input = <STDIN>);
		210	warn "read: $input\n";
		211	undef $w;
		212	});
		213
		214	=head2 TIME WATCHERS
		215
		216	You can create a time watcher by calling the C<< AnyEvent->timer >>
		217	method with the following mandatory arguments:
		218
		219	C<after> specifies after how many seconds (fractional values are
		220	supported) the callback should be invoked. C<cb> is the callback to invoke
		221	in that case.
		222
		223	Although the callback might get passed parameters, their value and
		224	presence is undefined and you cannot rely on them. Portable AnyEvent
		225	callbacks cannot use arguments passed to time watcher callbacks.
		226
		227	The callback will normally be invoked once only. If you specify another
		228	parameter, C<interval>, as a strictly positive number (> 0), then the
		229	callback will be invoked regularly at that interval (in fractional
		230	seconds) after the first invocation. If C<interval> is specified with a
		231	false value, then it is treated as if it were missing.
		232
		233	The callback will be rescheduled before invoking the callback, but no
		234	attempt is done to avoid timer drift in most backends, so the interval is
		235	only approximate.
		236
		237	Example: fire an event after 7.7 seconds.
		238
		239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		240	warn "timeout\n";
		241	});
		242
		243	# to cancel the timer:
		244	undef $w;
		245
		246	Example 2: fire an event after 0.5 seconds, then roughly every second.
		247
		248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		249	warn "timeout\n";
		250	};
		251
		252	=head3 TIMING ISSUES
		253
		254	There are two ways to handle timers: based on real time (relative, "fire
		255	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		256	o'clock").
		257
		258	While most event loops expect timers to specified in a relative way, they
		259	use absolute time internally. This makes a difference when your clock
		260	"jumps", for example, when ntp decides to set your clock backwards from
		261	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		262	fire "after" a second might actually take six years to finally fire.
		263
		264	AnyEvent cannot compensate for this. The only event loop that is conscious
		265	about these issues is L<EV>, which offers both relative (ev_timer, based
		266	on true relative time) and absolute (ev_periodic, based on wallclock time)
		267	timers.
		268
		269	AnyEvent always prefers relative timers, if available, matching the
		270	AnyEvent API.
		271
		272	AnyEvent has two additional methods that return the "current time":
46		273
47	=over 4	274	=over 4
48		275
		276	=item AnyEvent->time
		277
		278	This returns the "current wallclock time" as a fractional number of
		279	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		280	return, and the result is guaranteed to be compatible with those).
		281
		282	It progresses independently of any event loop processing, i.e. each call
		283	will check the system clock, which usually gets updated frequently.
		284
		285	=item AnyEvent->now
		286
		287	This also returns the "current wallclock time", but unlike C<time>, above,
		288	this value might change only once per event loop iteration, depending on
		289	the event loop (most return the same time as C<time>, above). This is the
		290	time that AnyEvent's timers get scheduled against.
		291
		292	I<In almost all cases (in all cases if you don't care), this is the
		293	function to call when you want to know the current time.>
		294
		295	This function is also often faster then C<< AnyEvent->time >>, and
		296	thus the preferred method if you want some timestamp (for example,
		297	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		298
		299	The rest of this section is only of relevance if you try to be very exact
		300	with your timing, you can skip it without bad conscience.
		301
		302	For a practical example of when these times differ, consider L<Event::Lib>
		303	and L<EV> and the following set-up:
		304
		305	The event loop is running and has just invoked one of your callback at
		306	time=500 (assume no other callbacks delay processing). In your callback,
		307	you wait a second by executing C<sleep 1> (blocking the process for a
		308	second) and then (at time=501) you create a relative timer that fires
		309	after three seconds.
		310
		311	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		312	both return C<501>, because that is the current time, and the timer will
		313	be scheduled to fire at time=504 (C<501> + C<3>).
		314
		315	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		316	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		317	last event processing phase started. With L<EV>, your timer gets scheduled
		318	to run at time=503 (C<500> + C<3>).
		319
		320	In one sense, L<Event::Lib> is more exact, as it uses the current time
		321	regardless of any delays introduced by event processing. However, most
		322	callbacks do not expect large delays in processing, so this causes a
		323	higher drift (and a lot more system calls to get the current time).
		324
		325	In another sense, L<EV> is more exact, as your timer will be scheduled at
		326	the same time, regardless of how long event processing actually took.
		327
		328	In either case, if you care (and in most cases, you don't), then you
		329	can get whatever behaviour you want with any event loop, by taking the
		330	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		331	account.
		332
		333	=item AnyEvent->now_update
		334
		335	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		336	the current time for each loop iteration (see the discussion of L<<
		337	AnyEvent->now >>, above).
		338
		339	When a callback runs for a long time (or when the process sleeps), then
		340	this "current" time will differ substantially from the real time, which
		341	might affect timers and time-outs.
		342
		343	When this is the case, you can call this method, which will update the
		344	event loop's idea of "current time".
		345
		346	Note that updating the time I<might> cause some events to be handled.
		347
		348	=back
		349
		350	=head2 SIGNAL WATCHERS
		351
		352	You can watch for signals using a signal watcher, C<signal> is the signal
		353	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		354	callback to be invoked whenever a signal occurs.
		355
		356	Although the callback might get passed parameters, their value and
		357	presence is undefined and you cannot rely on them. Portable AnyEvent
		358	callbacks cannot use arguments passed to signal watcher callbacks.
		359
		360	Multiple signal occurrences can be clumped together into one callback
		361	invocation, and callback invocation will be synchronous. Synchronous means
		362	that it might take a while until the signal gets handled by the process,
		363	but it is guaranteed not to interrupt any other callbacks.
		364
		365	The main advantage of using these watchers is that you can share a signal
		366	between multiple watchers.
		367
		368	This watcher might use C<%SIG>, so programs overwriting those signals
		369	directly will likely not work correctly.
		370
		371	Example: exit on SIGINT
		372
		373	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		374
		375	=head2 CHILD PROCESS WATCHERS
		376
		377	You can also watch on a child process exit and catch its exit status.
		378
		379	The child process is specified by the C<pid> argument (if set to C<0>, it
		380	watches for any child process exit). The watcher will triggered only when
		381	the child process has finished and an exit status is available, not on
		382	any trace events (stopped/continued).
		383
		384	The callback will be called with the pid and exit status (as returned by
		385	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		386	callback arguments.
		387
		388	This watcher type works by installing a signal handler for C<SIGCHLD>,
		389	and since it cannot be shared, nothing else should use SIGCHLD or reap
		390	random child processes (waiting for specific child processes, e.g. inside
		391	C<system>, is just fine).
		392
		393	There is a slight catch to child watchers, however: you usually start them
		394	I<after> the child process was created, and this means the process could
		395	have exited already (and no SIGCHLD will be sent anymore).
		396
		397	Not all event models handle this correctly (POE doesn't), but even for
		398	event models that I<do> handle this correctly, they usually need to be
		399	loaded before the process exits (i.e. before you fork in the first place).
		400
		401	This means you cannot create a child watcher as the very first thing in an
		402	AnyEvent program, you I<have> to create at least one watcher before you
		403	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		404
		405	Example: fork a process and wait for it
		406
		407	my $done = AnyEvent->condvar;
		408
		409	my $pid = fork or exit 5;
		410
		411	my $w = AnyEvent->child (
		412	pid => $pid,
		413	cb => sub {
		414	my ($pid, $status) = @_;
		415	warn "pid $pid exited with status $status";
		416	$done->send;
		417	},
		418	);
		419
		420	# do something else, then wait for process exit
		421	$done->recv;
		422
		423	=head2 IDLE WATCHERS
		424
		425	Sometimes there is a need to do something, but it is not so important
		426	to do it instantly, but only when there is nothing better to do. This
		427	"nothing better to do" is usually defined to be "no other events need
		428	attention by the event loop".
		429
		430	Idle watchers ideally get invoked when the event loop has nothing
		431	better to do, just before it would block the process to wait for new
		432	events. Instead of blocking, the idle watcher is invoked.
		433
		434	Most event loops unfortunately do not really support idle watchers (only
		435	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		436	will simply call the callback "from time to time".
		437
		438	Example: read lines from STDIN, but only process them when the
		439	program is otherwise idle:
		440
		441	my @lines; # read data
		442	my $idle_w;
		443	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		444	push @lines, scalar <STDIN>;
		445
		446	# start an idle watcher, if not already done
		447	$idle_w ||= AnyEvent->idle (cb => sub {
		448	# handle only one line, when there are lines left
		449	if (my $line = shift @lines) {
		450	print "handled when idle: $line";
		451	} else {
		452	# otherwise disable the idle watcher again
		453	undef $idle_w;
		454	}
		455	});
		456	});
		457
		458	=head2 CONDITION VARIABLES
		459
		460	If you are familiar with some event loops you will know that all of them
		461	require you to run some blocking "loop", "run" or similar function that
		462	will actively watch for new events and call your callbacks.
		463
		464	AnyEvent is different, it expects somebody else to run the event loop and
		465	will only block when necessary (usually when told by the user).
		466
		467	The instrument to do that is called a "condition variable", so called
		468	because they represent a condition that must become true.
		469
		470	Condition variables can be created by calling the C<< AnyEvent->condvar
		471	>> method, usually without arguments. The only argument pair allowed is
		472
		473	C<cb>, which specifies a callback to be called when the condition variable
		474	becomes true, with the condition variable as the first argument (but not
		475	the results).
		476
		477	After creation, the condition variable is "false" until it becomes "true"
		478	by calling the C<send> method (or calling the condition variable as if it
		479	were a callback, read about the caveats in the description for the C<<
		480	->send >> method).
		481
		482	Condition variables are similar to callbacks, except that you can
		483	optionally wait for them. They can also be called merge points - points
		484	in time where multiple outstanding events have been processed. And yet
		485	another way to call them is transactions - each condition variable can be
		486	used to represent a transaction, which finishes at some point and delivers
		487	a result.
		488
		489	Condition variables are very useful to signal that something has finished,
		490	for example, if you write a module that does asynchronous http requests,
		491	then a condition variable would be the ideal candidate to signal the
		492	availability of results. The user can either act when the callback is
		493	called or can synchronously C<< ->recv >> for the results.
		494
		495	You can also use them to simulate traditional event loops - for example,
		496	you can block your main program until an event occurs - for example, you
		497	could C<< ->recv >> in your main program until the user clicks the Quit
		498	button of your app, which would C<< ->send >> the "quit" event.
		499
		500	Note that condition variables recurse into the event loop - if you have
		501	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		502	lose. Therefore, condition variables are good to export to your caller, but
		503	you should avoid making a blocking wait yourself, at least in callbacks,
		504	as this asks for trouble.
		505
		506	Condition variables are represented by hash refs in perl, and the keys
		507	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		508	easy (it is often useful to build your own transaction class on top of
		509	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		510	it's C<new> method in your own C<new> method.
		511
		512	There are two "sides" to a condition variable - the "producer side" which
		513	eventually calls C<< -> send >>, and the "consumer side", which waits
		514	for the send to occur.
		515
		516	Example: wait for a timer.
		517
		518	# wait till the result is ready
		519	my $result_ready = AnyEvent->condvar;
		520
		521	# do something such as adding a timer
		522	# or socket watcher the calls $result_ready->send
		523	# when the "result" is ready.
		524	# in this case, we simply use a timer:
		525	my $w = AnyEvent->timer (
		526	after => 1,
		527	cb => sub { $result_ready->send },
		528	);
		529
		530	# this "blocks" (while handling events) till the callback
		531	# calls send
		532	$result_ready->recv;
		533
		534	Example: wait for a timer, but take advantage of the fact that
		535	condition variables are also code references.
		536
		537	my $done = AnyEvent->condvar;
		538	my $delay = AnyEvent->timer (after => 5, cb => $done);
		539	$done->recv;
		540
		541	Example: Imagine an API that returns a condvar and doesn't support
		542	callbacks. This is how you make a synchronous call, for example from
		543	the main program:
		544
		545	use AnyEvent::CouchDB;
		546
		547	...
		548
		549	my @info = $couchdb->info->recv;
		550
		551	And this is how you would just ste a callback to be called whenever the
		552	results are available:
		553
		554	$couchdb->info->cb (sub {
		555	my @info = $_[0]->recv;
		556	});
		557
		558	=head3 METHODS FOR PRODUCERS
		559
		560	These methods should only be used by the producing side, i.e. the
		561	code/module that eventually sends the signal. Note that it is also
		562	the producer side which creates the condvar in most cases, but it isn't
		563	uncommon for the consumer to create it as well.
		564
		565	=over 4
		566
		567	=item $cv->send (...)
		568
		569	Flag the condition as ready - a running C<< ->recv >> and all further
		570	calls to C<recv> will (eventually) return after this method has been
		571	called. If nobody is waiting the send will be remembered.
		572
		573	If a callback has been set on the condition variable, it is called
		574	immediately from within send.
		575
		576	Any arguments passed to the C<send> call will be returned by all
		577	future C<< ->recv >> calls.
		578
		579	Condition variables are overloaded so one can call them directly
		580	(as a code reference). Calling them directly is the same as calling
		581	C<send>. Note, however, that many C-based event loops do not handle
		582	overloading, so as tempting as it may be, passing a condition variable
		583	instead of a callback does not work. Both the pure perl and EV loops
		584	support overloading, however, as well as all functions that use perl to
		585	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		586	example).
		587
		588	=item $cv->croak ($error)
		589
		590	Similar to send, but causes all call's to C<< ->recv >> to invoke
		591	C<Carp::croak> with the given error message/object/scalar.
		592
		593	This can be used to signal any errors to the condition variable
		594	user/consumer.
		595
		596	=item $cv->begin ([group callback])
		597
		598	=item $cv->end
		599
		600	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		601
		602	These two methods can be used to combine many transactions/events into
		603	one. For example, a function that pings many hosts in parallel might want
		604	to use a condition variable for the whole process.
		605
		606	Every call to C<< ->begin >> will increment a counter, and every call to
		607	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		608	>>, the (last) callback passed to C<begin> will be executed. That callback
		609	is I<supposed> to call C<< ->send >>, but that is not required. If no
		610	callback was set, C<send> will be called without any arguments.
		611
		612	Let's clarify this with the ping example:
		613
		614	my $cv = AnyEvent->condvar;
		615
		616	my %result;
		617	$cv->begin (sub { $cv->send (\%result) });
		618
		619	for my $host (@list_of_hosts) {
		620	$cv->begin;
		621	ping_host_then_call_callback $host, sub {
		622	$result{$host} = ...;
		623	$cv->end;
		624	};
		625	}
		626
		627	$cv->end;
		628
		629	This code fragment supposedly pings a number of hosts and calls
		630	C<send> after results for all then have have been gathered - in any
		631	order. To achieve this, the code issues a call to C<begin> when it starts
		632	each ping request and calls C<end> when it has received some result for
		633	it. Since C<begin> and C<end> only maintain a counter, the order in which
		634	results arrive is not relevant.
		635
		636	There is an additional bracketing call to C<begin> and C<end> outside the
		637	loop, which serves two important purposes: first, it sets the callback
		638	to be called once the counter reaches C<0>, and second, it ensures that
		639	C<send> is called even when C<no> hosts are being pinged (the loop
		640	doesn't execute once).
		641
		642	This is the general pattern when you "fan out" into multiple subrequests:
		643	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		644	is called at least once, and then, for each subrequest you start, call
		645	C<begin> and for each subrequest you finish, call C<end>.
		646
		647	=back
		648
		649	=head3 METHODS FOR CONSUMERS
		650
		651	These methods should only be used by the consuming side, i.e. the
		652	code awaits the condition.
		653
		654	=over 4
		655
		656	=item $cv->recv
		657
		658	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		659	>> methods have been called on c<$cv>, while servicing other watchers
		660	normally.
		661
		662	You can only wait once on a condition - additional calls are valid but
		663	will return immediately.
		664
		665	If an error condition has been set by calling C<< ->croak >>, then this
		666	function will call C<croak>.
		667
		668	In list context, all parameters passed to C<send> will be returned,
		669	in scalar context only the first one will be returned.
		670
		671	Not all event models support a blocking wait - some die in that case
		672	(programs might want to do that to stay interactive), so I<if you are
		673	using this from a module, never require a blocking wait>, but let the
		674	caller decide whether the call will block or not (for example, by coupling
		675	condition variables with some kind of request results and supporting
		676	callbacks so the caller knows that getting the result will not block,
		677	while still supporting blocking waits if the caller so desires).
		678
		679	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		680	sensibly have two C<< ->recv >>'s in parallel, as that would require
		681	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		682	can supply.
		683
		684	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		685	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		686	versions and also integrates coroutines into AnyEvent, making blocking
		687	C<< ->recv >> calls perfectly safe as long as they are done from another
		688	coroutine (one that doesn't run the event loop).
		689
		690	You can ensure that C<< -recv >> never blocks by setting a callback and
		691	only calling C<< ->recv >> from within that callback (or at a later
		692	time). This will work even when the event loop does not support blocking
		693	waits otherwise.
		694
		695	=item $bool = $cv->ready
		696
		697	Returns true when the condition is "true", i.e. whether C<send> or
		698	C<croak> have been called.
		699
		700	=item $cb = $cv->cb ($cb->($cv))
		701
		702	This is a mutator function that returns the callback set and optionally
		703	replaces it before doing so.
		704
		705	The callback will be called when the condition becomes "true", i.e. when
		706	C<send> or C<croak> are called, with the only argument being the condition
		707	variable itself. Calling C<recv> inside the callback or at any later time
		708	is guaranteed not to block.
		709
		710	=back
		711
		712	=head1 GLOBAL VARIABLES AND FUNCTIONS
		713
		714	=over 4
		715
		716	=item $AnyEvent::MODEL
		717
		718	Contains C<undef> until the first watcher is being created. Then it
		719	contains the event model that is being used, which is the name of the
		720	Perl class implementing the model. This class is usually one of the
		721	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		722	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		723
		724	The known classes so far are:
		725
		726	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		727	AnyEvent::Impl::Event based on Event, second best choice.
		728	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		729	AnyEvent::Impl::Glib based on Glib, third-best choice.
		730	AnyEvent::Impl::Tk based on Tk, very bad choice.
		731	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		732	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		733	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		734
		735	There is no support for WxWidgets, as WxWidgets has no support for
		736	watching file handles. However, you can use WxWidgets through the
		737	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		738	second, which was considered to be too horrible to even consider for
		739	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		740	it's adaptor.
		741
		742	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		743	autodetecting them.
		744
		745	=item AnyEvent::detect
		746
		747	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		748	if necessary. You should only call this function right before you would
		749	have created an AnyEvent watcher anyway, that is, as late as possible at
		750	runtime.
		751
		752	=item $guard = AnyEvent::post_detect { BLOCK }
		753
		754	Arranges for the code block to be executed as soon as the event model is
		755	autodetected (or immediately if this has already happened).
		756
		757	If called in scalar or list context, then it creates and returns an object
		758	that automatically removes the callback again when it is destroyed. See
		759	L<Coro::BDB> for a case where this is useful.
		760
		761	=item @AnyEvent::post_detect
		762
		763	If there are any code references in this array (you can C<push> to it
		764	before or after loading AnyEvent), then they will called directly after
		765	the event loop has been chosen.
		766
		767	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		768	if it contains a true value then the event loop has already been detected,
		769	and the array will be ignored.
		770
		771	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		772
		773	=back
		774
		775	=head1 WHAT TO DO IN A MODULE
		776
		777	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		778	freely, but you should not load a specific event module or rely on it.
		779
		780	Be careful when you create watchers in the module body - AnyEvent will
		781	decide which event module to use as soon as the first method is called, so
		782	by calling AnyEvent in your module body you force the user of your module
		783	to load the event module first.
		784
		785	Never call C<< ->recv >> on a condition variable unless you I<know> that
		786	the C<< ->send >> method has been called on it already. This is
		787	because it will stall the whole program, and the whole point of using
		788	events is to stay interactive.
		789
		790	It is fine, however, to call C<< ->recv >> when the user of your module
		791	requests it (i.e. if you create a http request object ad have a method
		792	called C<results> that returns the results, it should call C<< ->recv >>
		793	freely, as the user of your module knows what she is doing. always).
		794
		795	=head1 WHAT TO DO IN THE MAIN PROGRAM
		796
		797	There will always be a single main program - the only place that should
		798	dictate which event model to use.
		799
		800	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		801	do anything special (it does not need to be event-based) and let AnyEvent
		802	decide which implementation to chose if some module relies on it.
		803
		804	If the main program relies on a specific event model - for example, in
		805	Gtk2 programs you have to rely on the Glib module - you should load the
		806	event module before loading AnyEvent or any module that uses it: generally
		807	speaking, you should load it as early as possible. The reason is that
		808	modules might create watchers when they are loaded, and AnyEvent will
		809	decide on the event model to use as soon as it creates watchers, and it
		810	might chose the wrong one unless you load the correct one yourself.
		811
		812	You can chose to use a pure-perl implementation by loading the
		813	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		814	everywhere, but letting AnyEvent chose the model is generally better.
		815
		816	=head2 MAINLOOP EMULATION
		817
		818	Sometimes (often for short test scripts, or even standalone programs who
		819	only want to use AnyEvent), you do not want to run a specific event loop.
		820
		821	In that case, you can use a condition variable like this:
		822
		823	AnyEvent->condvar->recv;
		824
		825	This has the effect of entering the event loop and looping forever.
		826
		827	Note that usually your program has some exit condition, in which case
		828	it is better to use the "traditional" approach of storing a condition
		829	variable somewhere, waiting for it, and sending it when the program should
		830	exit cleanly.
		831
		832
		833	=head1 OTHER MODULES
		834
		835	The following is a non-exhaustive list of additional modules that use
		836	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		837	in the same program. Some of the modules come with AnyEvent, some are
		838	available via CPAN.
		839
		840	=over 4
		841
		842	=item L<AnyEvent::Util>
		843
		844	Contains various utility functions that replace often-used but blocking
		845	functions such as C<inet_aton> by event-/callback-based versions.
		846
		847	=item L<AnyEvent::Socket>
		848
		849	Provides various utility functions for (internet protocol) sockets,
		850	addresses and name resolution. Also functions to create non-blocking tcp
		851	connections or tcp servers, with IPv6 and SRV record support and more.
		852
		853	=item L<AnyEvent::Handle>
		854
		855	Provide read and write buffers, manages watchers for reads and writes,
		856	supports raw and formatted I/O, I/O queued and fully transparent and
		857	non-blocking SSL/TLS.
		858
		859	=item L<AnyEvent::DNS>
		860
		861	Provides rich asynchronous DNS resolver capabilities.
		862
		863	=item L<AnyEvent::HTTP>
		864
		865	A simple-to-use HTTP library that is capable of making a lot of concurrent
		866	HTTP requests.
		867
		868	=item L<AnyEvent::HTTPD>
		869
		870	Provides a simple web application server framework.
		871
		872	=item L<AnyEvent::FastPing>
		873
		874	The fastest ping in the west.
		875
		876	=item L<AnyEvent::DBI>
		877
		878	Executes L<DBI> requests asynchronously in a proxy process.
		879
		880	=item L<AnyEvent::AIO>
		881
		882	Truly asynchronous I/O, should be in the toolbox of every event
		883	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		884	together.
		885
		886	=item L<AnyEvent::BDB>
		887
		888	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		889	L<BDB> and AnyEvent together.
		890
		891	=item L<AnyEvent::GPSD>
		892
		893	A non-blocking interface to gpsd, a daemon delivering GPS information.
		894
		895	=item L<AnyEvent::IGS>
		896
		897	A non-blocking interface to the Internet Go Server protocol (used by
		898	L<App::IGS>).
		899
		900	=item L<AnyEvent::IRC>
		901
		902	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		903
		904	=item L<Net::XMPP2>
		905
		906	AnyEvent based XMPP (Jabber protocol) module family.
		907
		908	=item L<Net::FCP>
		909
		910	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		911	of AnyEvent.
		912
		913	=item L<Event::ExecFlow>
		914
		915	High level API for event-based execution flow control.
		916
		917	=item L<Coro>
		918
		919	Has special support for AnyEvent via L<Coro::AnyEvent>.
		920
		921	=item L<IO::Lambda>
		922
		923	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		924
		925	=back
		926
49	=cut	927	=cut
50		928
51	package AnyEvent;	929	package AnyEvent;
52		930
53	no warnings;	931	no warnings;
54	use strict 'vars';	932	use strict qw(vars subs);
		933
55	use Carp;	934	use Carp;
56		935
57	our $VERSION = 0.2;	936	our $VERSION = 4.411;
58	our $MODEL;	937	our $MODEL;
59		938
60	our $AUTOLOAD;	939	our $AUTOLOAD;
61	our @ISA;	940	our @ISA;
62		941
		942	our @REGISTRY;
		943
		944	our $WIN32;
		945
		946	BEGIN {
		947	my $win32 = ! ! ($^O =~ /mswin32/i);
		948	eval "sub WIN32(){ $win32 }";
		949	}
		950
		951	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		952
		953	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		954
		955	{
		956	my $idx;
		957	$PROTOCOL{$_} = ++$idx
		958	for reverse split /\s*,\s*/,
		959	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		960	}
		961
63	my @models = (	962	my @models = (
64	[Coro => Coro::Event::],	963	[EV:: => AnyEvent::Impl::EV::],
65	[Event => Event::],	964	[Event:: => AnyEvent::Impl::Event::],
66	[Glib => Glib::],	965	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
67	[Tk => Tk::],	966	# everything below here will not be autoprobed
		967	# as the pureperl backend should work everywhere
		968	# and is usually faster
		969	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		970	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		971	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		972	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		973	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		974	[Wx:: => AnyEvent::Impl::POE::],
		975	[Prima:: => AnyEvent::Impl::POE::],
68	);	976	);
69		977
70	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	978	our %method = map +($_ => 1),
		979	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
71		980
72	sub AUTOLOAD {	981	our @post_detect;
73	$AUTOLOAD =~ s/.*://;
74		982
75	$method{$AUTOLOAD}	983	sub post_detect(&) {
76	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	984	my ($cb) = @_;
77		985
		986	if ($MODEL) {
		987	$cb->();
		988
		989	1
		990	} else {
		991	push @post_detect, $cb;
		992
		993	defined wantarray
		994	? bless \$cb, "AnyEvent::Util::postdetect"
		995	: ()
		996	}
		997	}
		998
		999	sub AnyEvent::Util::postdetect::DESTROY {
		1000	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1001	}
		1002
		1003	sub detect() {
78	unless ($MODEL) {	1004	unless ($MODEL) {
79	# check for already loaded models	1005	no strict 'refs';
80	for (@models) {	1006	local $SIG{__DIE__};
81	my ($model, $package) = @$_;	1007
82	if (scalar keys %{ *{"$package\::"} }) {	1008	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
83	eval "require AnyEvent::Impl::$model";	1009	my $model = "AnyEvent::Impl::$1";
84	last if $MODEL;	1010	if (eval "require $model") {
		1011	$MODEL = $model;
		1012	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		1013	} else {
		1014	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
85	}	1015	}
86	}	1016	}
87		1017
		1018	# check for already loaded models
88	unless ($MODEL) {	1019	unless ($MODEL) {
89	# try to load a model
90
91	for (@models) {	1020	for (@REGISTRY, @models) {
92	my ($model, $package) = @$_;	1021	my ($package, $model) = @$_;
93	eval "require AnyEvent::Impl::$model";	1022	if (${"$package\::VERSION"} > 0) {
94	last if $MODEL;	1023	if (eval "require $model") {
		1024	$MODEL = $model;
		1025	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		1026	last;
		1027	}
		1028	}
95	}	1029	}
96		1030
		1031	unless ($MODEL) {
		1032	# try to load a model
		1033
		1034	for (@REGISTRY, @models) {
		1035	my ($package, $model) = @$_;
		1036	if (eval "require $package"
		1037	and ${"$package\::VERSION"} > 0
		1038	and eval "require $model") {
		1039	$MODEL = $model;
		1040	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		1041	last;
		1042	}
		1043	}
		1044
97	$MODEL	1045	$MODEL
98	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1046	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
		1047	}
		1048	}
		1049
		1050	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1051
		1052	unshift @ISA, $MODEL;
		1053
		1054	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1055
		1056	(shift @post_detect)->() while @post_detect;
		1057	}
		1058
		1059	$MODEL
		1060	}
		1061
		1062	sub AUTOLOAD {
		1063	(my $func = $AUTOLOAD) =~ s/.*://;
		1064
		1065	$method{$func}
		1066	or croak "$func: not a valid method for AnyEvent objects";
		1067
		1068	detect unless $MODEL;
		1069
		1070	my $class = shift;
		1071	$class->$func (@_);
		1072	}
		1073
		1074	# utility function to dup a filehandle. this is used by many backends
		1075	# to support binding more than one watcher per filehandle (they usually
		1076	# allow only one watcher per fd, so we dup it to get a different one).
		1077	sub _dupfh($$$$) {
		1078	my ($poll, $fh, $r, $w) = @_;
		1079
		1080	# cygwin requires the fh mode to be matching, unix doesn't
		1081	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1082	: $poll eq "w" ? ($w, ">")
		1083	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1084
		1085	open my $fh2, "$mode&" . fileno $fh
		1086	or die "cannot dup() filehandle: $!,";
		1087
		1088	# we assume CLOEXEC is already set by perl in all important cases
		1089
		1090	($fh2, $rw)
		1091	}
		1092
		1093	package AnyEvent::Base;
		1094
		1095	# default implementations for many methods
		1096
		1097	BEGIN {
		1098	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1099	*_time = \&Time::HiRes::time;
		1100	# if (eval "use POSIX (); (POSIX::times())...
		1101	} else {
		1102	*_time = sub { time }; # epic fail
		1103	}
		1104	}
		1105
		1106	sub time { _time }
		1107	sub now { _time }
		1108	sub now_update { }
		1109
		1110	# default implementation for ->condvar
		1111
		1112	sub condvar {
		1113	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1114	}
		1115
		1116	# default implementation for ->signal
		1117
		1118	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1119
		1120	sub _signal_exec {
		1121	sysread $SIGPIPE_R, my $dummy, 4;
		1122
		1123	while (%SIG_EV) {
		1124	for (keys %SIG_EV) {
		1125	delete $SIG_EV{$_};
		1126	$_->() for values %{ $SIG_CB{$_} || {} };
99	}	1127	}
100	}	1128	}
		1129	}
101		1130
102	@ISA = $MODEL;	1131	sub signal {
		1132	my (undef, %arg) = @_;
103		1133
		1134	unless ($SIGPIPE_R) {
		1135	require Fcntl;
		1136
		1137	if (AnyEvent::WIN32) {
		1138	require AnyEvent::Util;
		1139
		1140	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1141	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1142	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1143	} else {
		1144	pipe $SIGPIPE_R, $SIGPIPE_W;
		1145	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1146	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1147
		1148	# not strictly required, as $^F is normally 2, but let's make sure...
		1149	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1150	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1151	}
		1152
		1153	$SIGPIPE_R
		1154	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1155
		1156	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1157	}
		1158
		1159	my $signal = uc $arg{signal}
		1160	or Carp::croak "required option 'signal' is missing";
		1161
		1162	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1163	$SIG{$signal} ||= sub {
		1164	local $!;
		1165	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1166	undef $SIG_EV{$signal};
		1167	};
		1168
		1169	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1170	}
		1171
		1172	sub AnyEvent::Base::signal::DESTROY {
		1173	my ($signal, $cb) = @{$_[0]};
		1174
		1175	delete $SIG_CB{$signal}{$cb};
		1176
		1177	# delete doesn't work with older perls - they then
		1178	# print weird messages, or just unconditionally exit
		1179	# instead of getting the default action.
		1180	undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
		1181	}
		1182
		1183	# default implementation for ->child
		1184
		1185	our %PID_CB;
		1186	our $CHLD_W;
		1187	our $CHLD_DELAY_W;
		1188	our $WNOHANG;
		1189
		1190	sub _sigchld {
		1191	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1192	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		1193	(values %{ $PID_CB{0} || {} });
		1194	}
		1195	}
		1196
		1197	sub child {
		1198	my (undef, %arg) = @_;
		1199
		1200	defined (my $pid = $arg{pid} + 0)
		1201	or Carp::croak "required option 'pid' is missing";
		1202
		1203	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1204
		1205	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1206
		1207	unless ($CHLD_W) {
		1208	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1209	# child could be a zombie already, so make at least one round
		1210	&_sigchld;
		1211	}
		1212
		1213	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
		1214	}
		1215
		1216	sub AnyEvent::Base::child::DESTROY {
		1217	my ($pid, $cb) = @{$_[0]};
		1218
		1219	delete $PID_CB{$pid}{$cb};
		1220	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1221
		1222	undef $CHLD_W unless keys %PID_CB;
		1223	}
		1224
		1225	# idle emulation is done by simply using a timer, regardless
		1226	# of whether the process is idle or not, and not letting
		1227	# the callback use more than 50% of the time.
		1228	sub idle {
		1229	my (undef, %arg) = @_;
		1230
		1231	my ($cb, $w, $rcb) = $arg{cb};
		1232
		1233	$rcb = sub {
		1234	if ($cb) {
		1235	$w = _time;
		1236	&$cb;
		1237	$w = _time - $w;
		1238
		1239	# never use more then 50% of the time for the idle watcher,
		1240	# within some limits
		1241	$w = 0.0001 if $w < 0.0001;
		1242	$w = 5 if $w > 5;
		1243
		1244	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1245	} else {
		1246	# clean up...
		1247	undef $w;
		1248	undef $rcb;
		1249	}
		1250	};
		1251
		1252	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1253
		1254	bless \\$cb, "AnyEvent::Base::idle"
		1255	}
		1256
		1257	sub AnyEvent::Base::idle::DESTROY {
		1258	undef $${$_[0]};
		1259	}
		1260
		1261	package AnyEvent::CondVar;
		1262
		1263	our @ISA = AnyEvent::CondVar::Base::;
		1264
		1265	package AnyEvent::CondVar::Base;
		1266
		1267	use overload
		1268	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1269	fallback => 1;
		1270
		1271	sub _send {
		1272	# nop
		1273	}
		1274
		1275	sub send {
104	my $class = shift;	1276	my $cv = shift;
105	$class->$AUTOLOAD (@_);	1277	$cv->{_ae_sent} = [@_];
		1278	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1279	$cv->_send;
106	}	1280	}
		1281
		1282	sub croak {
		1283	$_[0]{_ae_croak} = $_[1];
		1284	$_[0]->send;
		1285	}
		1286
		1287	sub ready {
		1288	$_[0]{_ae_sent}
		1289	}
		1290
		1291	sub _wait {
		1292	AnyEvent->one_event while !$_[0]{_ae_sent};
		1293	}
		1294
		1295	sub recv {
		1296	$_[0]->_wait;
		1297
		1298	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1299	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1300	}
		1301
		1302	sub cb {
		1303	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1304	$_[0]{_ae_cb}
		1305	}
		1306
		1307	sub begin {
		1308	++$_[0]{_ae_counter};
		1309	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1310	}
		1311
		1312	sub end {
		1313	return if --$_[0]{_ae_counter};
		1314	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1315	}
		1316
		1317	# undocumented/compatibility with pre-3.4
		1318	*broadcast = \&send;
		1319	*wait = \&_wait;
		1320
		1321	=head1 ERROR AND EXCEPTION HANDLING
		1322
		1323	In general, AnyEvent does not do any error handling - it relies on the
		1324	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1325	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1326	checking of all AnyEvent methods, however, which is highly useful during
		1327	development.
		1328
		1329	As for exception handling (i.e. runtime errors and exceptions thrown while
		1330	executing a callback), this is not only highly event-loop specific, but
		1331	also not in any way wrapped by this module, as this is the job of the main
		1332	program.
		1333
		1334	The pure perl event loop simply re-throws the exception (usually
		1335	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1336	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1337	so on.
		1338
		1339	=head1 ENVIRONMENT VARIABLES
		1340
		1341	The following environment variables are used by this module or its
		1342	submodules:
		1343
		1344	=over 4
		1345
		1346	=item C<PERL_ANYEVENT_VERBOSE>
		1347
		1348	By default, AnyEvent will be completely silent except in fatal
		1349	conditions. You can set this environment variable to make AnyEvent more
		1350	talkative.
		1351
		1352	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1353	conditions, such as not being able to load the event model specified by
		1354	C<PERL_ANYEVENT_MODEL>.
		1355
		1356	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1357	model it chooses.
		1358
		1359	=item C<PERL_ANYEVENT_STRICT>
		1360
		1361	AnyEvent does not do much argument checking by default, as thorough
		1362	argument checking is very costly. Setting this variable to a true value
		1363	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1364	check the arguments passed to most method calls. If it finds any problems
		1365	it will croak.
		1366
		1367	In other words, enables "strict" mode.
		1368
		1369	Unlike C<use strict>, it is definitely recommended ot keep it off in
		1370	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1371	developing programs can be very useful, however.
		1372
		1373	=item C<PERL_ANYEVENT_MODEL>
		1374
		1375	This can be used to specify the event model to be used by AnyEvent, before
		1376	auto detection and -probing kicks in. It must be a string consisting
		1377	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1378	and the resulting module name is loaded and if the load was successful,
		1379	used as event model. If it fails to load AnyEvent will proceed with
		1380	auto detection and -probing.
		1381
		1382	This functionality might change in future versions.
		1383
		1384	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1385	could start your program like this:
		1386
		1387	PERL_ANYEVENT_MODEL=Perl perl ...
		1388
		1389	=item C<PERL_ANYEVENT_PROTOCOLS>
		1390
		1391	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1392	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1393	of auto probing).
		1394
		1395	Must be set to a comma-separated list of protocols or address families,
		1396	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1397	used, and preference will be given to protocols mentioned earlier in the
		1398	list.
		1399
		1400	This variable can effectively be used for denial-of-service attacks
		1401	against local programs (e.g. when setuid), although the impact is likely
		1402	small, as the program has to handle conenction and other failures anyways.
		1403
		1404	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1405	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1406	- only support IPv4, never try to resolve or contact IPv6
		1407	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1408	IPv6, but prefer IPv6 over IPv4.
		1409
		1410	=item C<PERL_ANYEVENT_EDNS0>
		1411
		1412	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1413	for DNS. This extension is generally useful to reduce DNS traffic, but
		1414	some (broken) firewalls drop such DNS packets, which is why it is off by
		1415	default.
		1416
		1417	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1418	EDNS0 in its DNS requests.
		1419
		1420	=item C<PERL_ANYEVENT_MAX_FORKS>
		1421
		1422	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1423	will create in parallel.
107		1424
108	=back	1425	=back
109		1426
		1427	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1428
		1429	This is an advanced topic that you do not normally need to use AnyEvent in
		1430	a module. This section is only of use to event loop authors who want to
		1431	provide AnyEvent compatibility.
		1432
		1433	If you need to support another event library which isn't directly
		1434	supported by AnyEvent, you can supply your own interface to it by
		1435	pushing, before the first watcher gets created, the package name of
		1436	the event module and the package name of the interface to use onto
		1437	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1438	AnyEvent, so it is reasonably cheap.
		1439
		1440	Example:
		1441
		1442	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1443
		1444	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1445	package/class when it finds the C<urxvt> package/module is already loaded.
		1446
		1447	When AnyEvent is loaded and asked to find a suitable event model, it
		1448	will first check for the presence of urxvt by trying to C<use> the
		1449	C<urxvt::anyevent> module.
		1450
		1451	The class should provide implementations for all watcher types. See
		1452	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1453	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1454	see the sources.
		1455
		1456	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1457	provide suitable (hopefully) replacements.
		1458
		1459	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1460	terminal emulator uses the above line as-is. An interface isn't included
		1461	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1462	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1463	I<rxvt-unicode> distribution.
		1464
		1465	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1466	condition variables: code blocking while waiting for a condition will
		1467	C<die>. This still works with most modules/usages, and blocking calls must
		1468	not be done in an interactive application, so it makes sense.
		1469
110	=head1 EXAMPLE	1470	=head1 EXAMPLE PROGRAM
111		1471
112	The following program uses an io watcher to read data from stdin, a timer	1472	The following program uses an I/O watcher to read data from STDIN, a timer
113	to display a message once per second, and a condvar to exit the program	1473	to display a message once per second, and a condition variable to quit the
114	when the user enters quit:	1474	program when the user enters quit:
115		1475
116	use AnyEvent;	1476	use AnyEvent;
117		1477
118	my $cv = AnyEvent->condvar;	1478	my $cv = AnyEvent->condvar;
119		1479
120	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1480	my $io_watcher = AnyEvent->io (
		1481	fh => \*STDIN,
		1482	poll => 'r',
		1483	cb => sub {
121	warn "io event <$_[0]>\n"; # will always output <r>	1484	warn "io event <$_[0]>\n"; # will always output <r>
122	chomp (my $input = <STDIN>); # read a line	1485	chomp (my $input = <STDIN>); # read a line
123	warn "read: $input\n"; # output what has been read	1486	warn "read: $input\n"; # output what has been read
124	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1487	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1488	},
125	});	1489	);
126		1490
127	my $time_watcher; # can only be used once	1491	my $time_watcher; # can only be used once
128		1492
129	sub new_timer {	1493	sub new_timer {
130	$timer = AnyEvent->timer (after => 1, cb => sub {	1494	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
133	});	1497	});
134	}	1498	}
135		1499
136	new_timer; # create first timer	1500	new_timer; # create first timer
137		1501
138	$cv->wait; # wait until user enters /^q/i	1502	$cv->recv; # wait until user enters /^q/i
		1503
		1504	=head1 REAL-WORLD EXAMPLE
		1505
		1506	Consider the L<Net::FCP> module. It features (among others) the following
		1507	API calls, which are to freenet what HTTP GET requests are to http:
		1508
		1509	my $data = $fcp->client_get ($url); # blocks
		1510
		1511	my $transaction = $fcp->txn_client_get ($url); # does not block
		1512	$transaction->cb ( sub { ... } ); # set optional result callback
		1513	my $data = $transaction->result; # possibly blocks
		1514
		1515	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		1516	given URL and waits till the data has arrived. It is defined to be:
		1517
		1518	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		1519
		1520	And in fact is automatically generated. This is the blocking API of
		1521	L<Net::FCP>, and it works as simple as in any other, similar, module.
		1522
		1523	More complicated is C<txn_client_get>: It only creates a transaction
		1524	(completion, result, ...) object and initiates the transaction.
		1525
		1526	my $txn = bless { }, Net::FCP::Txn::;
		1527
		1528	It also creates a condition variable that is used to signal the completion
		1529	of the request:
		1530
		1531	$txn->{finished} = AnyAvent->condvar;
		1532
		1533	It then creates a socket in non-blocking mode.
		1534
		1535	socket $txn->{fh}, ...;
		1536	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		1537	connect $txn->{fh}, ...
		1538	and !$!{EWOULDBLOCK}
		1539	and !$!{EINPROGRESS}
		1540	and Carp::croak "unable to connect: $!\n";
		1541
		1542	Then it creates a write-watcher which gets called whenever an error occurs
		1543	or the connection succeeds:
		1544
		1545	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		1546
		1547	And returns this transaction object. The C<fh_ready_w> callback gets
		1548	called as soon as the event loop detects that the socket is ready for
		1549	writing.
		1550
		1551	The C<fh_ready_w> method makes the socket blocking again, writes the
		1552	request data and replaces the watcher by a read watcher (waiting for reply
		1553	data). The actual code is more complicated, but that doesn't matter for
		1554	this example:
		1555
		1556	fcntl $txn->{fh}, F_SETFL, 0;
		1557	syswrite $txn->{fh}, $txn->{request}
		1558	or die "connection or write error";
		1559	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		1560
		1561	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		1562	result and signals any possible waiters that the request has finished:
		1563
		1564	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		1565
		1566	if (end-of-file or data complete) {
		1567	$txn->{result} = $txn->{buf};
		1568	$txn->{finished}->send;
		1569	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		1570	}
		1571
		1572	The C<result> method, finally, just waits for the finished signal (if the
		1573	request was already finished, it doesn't wait, of course, and returns the
		1574	data:
		1575
		1576	$txn->{finished}->recv;
		1577	return $txn->{result};
		1578
		1579	The actual code goes further and collects all errors (C<die>s, exceptions)
		1580	that occurred during request processing. The C<result> method detects
		1581	whether an exception as thrown (it is stored inside the $txn object)
		1582	and just throws the exception, which means connection errors and other
		1583	problems get reported tot he code that tries to use the result, not in a
		1584	random callback.
		1585
		1586	All of this enables the following usage styles:
		1587
		1588	1. Blocking:
		1589
		1590	my $data = $fcp->client_get ($url);
		1591
		1592	2. Blocking, but running in parallel:
		1593
		1594	my @datas = map $_->result,
		1595	map $fcp->txn_client_get ($_),
		1596	@urls;
		1597
		1598	Both blocking examples work without the module user having to know
		1599	anything about events.
		1600
		1601	3a. Event-based in a main program, using any supported event module:
		1602
		1603	use EV;
		1604
		1605	$fcp->txn_client_get ($url)->cb (sub {
		1606	my $txn = shift;
		1607	my $data = $txn->result;
		1608	...
		1609	});
		1610
		1611	EV::loop;
		1612
		1613	3b. The module user could use AnyEvent, too:
		1614
		1615	use AnyEvent;
		1616
		1617	my $quit = AnyEvent->condvar;
		1618
		1619	$fcp->txn_client_get ($url)->cb (sub {
		1620	...
		1621	$quit->send;
		1622	});
		1623
		1624	$quit->recv;
		1625
		1626
		1627	=head1 BENCHMARKS
		1628
		1629	To give you an idea of the performance and overheads that AnyEvent adds
		1630	over the event loops themselves and to give you an impression of the speed
		1631	of various event loops I prepared some benchmarks.
		1632
		1633	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1634
		1635	Here is a benchmark of various supported event models used natively and
		1636	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1637	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1638	which it is), lets them fire exactly once and destroys them again.
		1639
		1640	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1641	distribution.
		1642
		1643	=head3 Explanation of the columns
		1644
		1645	I<watcher> is the number of event watchers created/destroyed. Since
		1646	different event models feature vastly different performances, each event
		1647	loop was given a number of watchers so that overall runtime is acceptable
		1648	and similar between tested event loop (and keep them from crashing): Glib
		1649	would probably take thousands of years if asked to process the same number
		1650	of watchers as EV in this benchmark.
		1651
		1652	I<bytes> is the number of bytes (as measured by the resident set size,
		1653	RSS) consumed by each watcher. This method of measuring captures both C
		1654	and Perl-based overheads.
		1655
		1656	I<create> is the time, in microseconds (millionths of seconds), that it
		1657	takes to create a single watcher. The callback is a closure shared between
		1658	all watchers, to avoid adding memory overhead. That means closure creation
		1659	and memory usage is not included in the figures.
		1660
		1661	I<invoke> is the time, in microseconds, used to invoke a simple
		1662	callback. The callback simply counts down a Perl variable and after it was
		1663	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1664	signal the end of this phase.
		1665
		1666	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1667	watcher.
		1668
		1669	=head3 Results
		1670
		1671	name watchers bytes create invoke destroy comment
		1672	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1673	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1674	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1675	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1676	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1677	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1678	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1679	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1680	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1681	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1682
		1683	=head3 Discussion
		1684
		1685	The benchmark does I<not> measure scalability of the event loop very
		1686	well. For example, a select-based event loop (such as the pure perl one)
		1687	can never compete with an event loop that uses epoll when the number of
		1688	file descriptors grows high. In this benchmark, all events become ready at
		1689	the same time, so select/poll-based implementations get an unnatural speed
		1690	boost.
		1691
		1692	Also, note that the number of watchers usually has a nonlinear effect on
		1693	overall speed, that is, creating twice as many watchers doesn't take twice
		1694	the time - usually it takes longer. This puts event loops tested with a
		1695	higher number of watchers at a disadvantage.
		1696
		1697	To put the range of results into perspective, consider that on the
		1698	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1699	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1700	cycles with POE.
		1701
		1702	C<EV> is the sole leader regarding speed and memory use, which are both
		1703	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1704	far less memory than any other event loop and is still faster than Event
		1705	natively.
		1706
		1707	The pure perl implementation is hit in a few sweet spots (both the
		1708	constant timeout and the use of a single fd hit optimisations in the perl
		1709	interpreter and the backend itself). Nevertheless this shows that it
		1710	adds very little overhead in itself. Like any select-based backend its
		1711	performance becomes really bad with lots of file descriptors (and few of
		1712	them active), of course, but this was not subject of this benchmark.
		1713
		1714	The C<Event> module has a relatively high setup and callback invocation
		1715	cost, but overall scores in on the third place.
		1716
		1717	C<Glib>'s memory usage is quite a bit higher, but it features a
		1718	faster callback invocation and overall ends up in the same class as
		1719	C<Event>. However, Glib scales extremely badly, doubling the number of
		1720	watchers increases the processing time by more than a factor of four,
		1721	making it completely unusable when using larger numbers of watchers
		1722	(note that only a single file descriptor was used in the benchmark, so
		1723	inefficiencies of C<poll> do not account for this).
		1724
		1725	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1726	more than 2000 watchers is a big setback, however, as correctness takes
		1727	precedence over speed. Nevertheless, its performance is surprising, as the
		1728	file descriptor is dup()ed for each watcher. This shows that the dup()
		1729	employed by some adaptors is not a big performance issue (it does incur a
		1730	hidden memory cost inside the kernel which is not reflected in the figures
		1731	above).
		1732
		1733	C<POE>, regardless of underlying event loop (whether using its pure perl
		1734	select-based backend or the Event module, the POE-EV backend couldn't
		1735	be tested because it wasn't working) shows abysmal performance and
		1736	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1737	as EV watchers, and 10 times as much memory as Event (the high memory
		1738	requirements are caused by requiring a session for each watcher). Watcher
		1739	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1740	implementation.
		1741
		1742	The design of the POE adaptor class in AnyEvent can not really account
		1743	for the performance issues, though, as session creation overhead is
		1744	small compared to execution of the state machine, which is coded pretty
		1745	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1746	using multiple sessions is not a good approach, especially regarding
		1747	memory usage, even the author of POE could not come up with a faster
		1748	design).
		1749
		1750	=head3 Summary
		1751
		1752	=over 4
		1753
		1754	=item * Using EV through AnyEvent is faster than any other event loop
		1755	(even when used without AnyEvent), but most event loops have acceptable
		1756	performance with or without AnyEvent.
		1757
		1758	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1759	the actual event loop, only with extremely fast event loops such as EV
		1760	adds AnyEvent significant overhead.
		1761
		1762	=item * You should avoid POE like the plague if you want performance or
		1763	reasonable memory usage.
		1764
		1765	=back
		1766
		1767	=head2 BENCHMARKING THE LARGE SERVER CASE
		1768
		1769	This benchmark actually benchmarks the event loop itself. It works by
		1770	creating a number of "servers": each server consists of a socket pair, a
		1771	timeout watcher that gets reset on activity (but never fires), and an I/O
		1772	watcher waiting for input on one side of the socket. Each time the socket
		1773	watcher reads a byte it will write that byte to a random other "server".
		1774
		1775	The effect is that there will be a lot of I/O watchers, only part of which
		1776	are active at any one point (so there is a constant number of active
		1777	fds for each loop iteration, but which fds these are is random). The
		1778	timeout is reset each time something is read because that reflects how
		1779	most timeouts work (and puts extra pressure on the event loops).
		1780
		1781	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1782	(1%) are active. This mirrors the activity of large servers with many
		1783	connections, most of which are idle at any one point in time.
		1784
		1785	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1786	distribution.
		1787
		1788	=head3 Explanation of the columns
		1789
		1790	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1791	each server has a read and write socket end).
		1792
		1793	I<create> is the time it takes to create a socket pair (which is
		1794	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1795
		1796	I<request>, the most important value, is the time it takes to handle a
		1797	single "request", that is, reading the token from the pipe and forwarding
		1798	it to another server. This includes deleting the old timeout and creating
		1799	a new one that moves the timeout into the future.
		1800
		1801	=head3 Results
		1802
		1803	name sockets create request
		1804	EV 20000 69.01 11.16
		1805	Perl 20000 73.32 35.87
		1806	Event 20000 212.62 257.32
		1807	Glib 20000 651.16 1896.30
		1808	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1809
		1810	=head3 Discussion
		1811
		1812	This benchmark I<does> measure scalability and overall performance of the
		1813	particular event loop.
		1814
		1815	EV is again fastest. Since it is using epoll on my system, the setup time
		1816	is relatively high, though.
		1817
		1818	Perl surprisingly comes second. It is much faster than the C-based event
		1819	loops Event and Glib.
		1820
		1821	Event suffers from high setup time as well (look at its code and you will
		1822	understand why). Callback invocation also has a high overhead compared to
		1823	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1824	uses select or poll in basically all documented configurations.
		1825
		1826	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1827	clearly fails to perform with many filehandles or in busy servers.
		1828
		1829	POE is still completely out of the picture, taking over 1000 times as long
		1830	as EV, and over 100 times as long as the Perl implementation, even though
		1831	it uses a C-based event loop in this case.
		1832
		1833	=head3 Summary
		1834
		1835	=over 4
		1836
		1837	=item * The pure perl implementation performs extremely well.
		1838
		1839	=item * Avoid Glib or POE in large projects where performance matters.
		1840
		1841	=back
		1842
		1843	=head2 BENCHMARKING SMALL SERVERS
		1844
		1845	While event loops should scale (and select-based ones do not...) even to
		1846	large servers, most programs we (or I :) actually write have only a few
		1847	I/O watchers.
		1848
		1849	In this benchmark, I use the same benchmark program as in the large server
		1850	case, but it uses only eight "servers", of which three are active at any
		1851	one time. This should reflect performance for a small server relatively
		1852	well.
		1853
		1854	The columns are identical to the previous table.
		1855
		1856	=head3 Results
		1857
		1858	name sockets create request
		1859	EV 16 20.00 6.54
		1860	Perl 16 25.75 12.62
		1861	Event 16 81.27 35.86
		1862	Glib 16 32.63 15.48
		1863	POE 16 261.87 276.28 uses POE::Loop::Event
		1864
		1865	=head3 Discussion
		1866
		1867	The benchmark tries to test the performance of a typical small
		1868	server. While knowing how various event loops perform is interesting, keep
		1869	in mind that their overhead in this case is usually not as important, due
		1870	to the small absolute number of watchers (that is, you need efficiency and
		1871	speed most when you have lots of watchers, not when you only have a few of
		1872	them).
		1873
		1874	EV is again fastest.
		1875
		1876	Perl again comes second. It is noticeably faster than the C-based event
		1877	loops Event and Glib, although the difference is too small to really
		1878	matter.
		1879
		1880	POE also performs much better in this case, but is is still far behind the
		1881	others.
		1882
		1883	=head3 Summary
		1884
		1885	=over 4
		1886
		1887	=item * C-based event loops perform very well with small number of
		1888	watchers, as the management overhead dominates.
		1889
		1890	=back
		1891
		1892
		1893	=head1 SIGNALS
		1894
		1895	AnyEvent currently installs handlers for these signals:
		1896
		1897	=over 4
		1898
		1899	=item SIGCHLD
		1900
		1901	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		1902	emulation for event loops that do not support them natively. Also, some
		1903	event loops install a similar handler.
		1904
		1905	=item SIGPIPE
		1906
		1907	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		1908	when AnyEvent gets loaded.
		1909
		1910	The rationale for this is that AnyEvent users usually do not really depend
		1911	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		1912	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		1913	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		1914	some random socket.
		1915
		1916	The rationale for installing a no-op handler as opposed to ignoring it is
		1917	that this way, the handler will be restored to defaults on exec.
		1918
		1919	Feel free to install your own handler, or reset it to defaults.
		1920
		1921	=back
		1922
		1923	=cut
		1924
		1925	$SIG{PIPE} = sub { }
		1926	unless defined $SIG{PIPE};
		1927
		1928
		1929	=head1 FORK
		1930
		1931	Most event libraries are not fork-safe. The ones who are usually are
		1932	because they rely on inefficient but fork-safe C<select> or C<poll>
		1933	calls. Only L<EV> is fully fork-aware.
		1934
		1935	If you have to fork, you must either do so I<before> creating your first
		1936	watcher OR you must not use AnyEvent at all in the child.
		1937
		1938
		1939	=head1 SECURITY CONSIDERATIONS
		1940
		1941	AnyEvent can be forced to load any event model via
		1942	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1943	execute arbitrary code or directly gain access, it can easily be used to
		1944	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1945	will not be active when the program uses a different event model than
		1946	specified in the variable.
		1947
		1948	You can make AnyEvent completely ignore this variable by deleting it
		1949	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1950
		1951	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1952
		1953	use AnyEvent;
		1954
		1955	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1956	be used to probe what backend is used and gain other information (which is
		1957	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1958	$ENV{PERL_ANYEGENT_STRICT}.
		1959
		1960
		1961	=head1 BUGS
		1962
		1963	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1964	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1965	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1966	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1967	pronounced).
		1968
139		1969
140	=head1 SEE ALSO	1970	=head1 SEE ALSO
141		1971
142	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	1972	Utility functions: L<AnyEvent::Util>.
143	L<AnyEvent::Impl::Coro>,	1973
144	L<AnyEvent::Impl::Event>,	1974	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
145	L<AnyEvent::Impl::Glib>,	1975	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1976
		1977	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1978	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1979	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
146	L<AnyEvent::Impl::Tk>.	1980	L<AnyEvent::Impl::POE>.
147		1981
148	=head1	1982	Non-blocking file handles, sockets, TCP clients and
		1983	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1984
		1985	Asynchronous DNS: L<AnyEvent::DNS>.
		1986
		1987	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1988
		1989	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1990
		1991
		1992	=head1 AUTHOR
		1993
		1994	Marc Lehmann <schmorp@schmorp.de>
		1995	http://home.schmorp.de/
149		1996
150	=cut	1997	=cut
151		1998
152	1	1999	1
153		2000

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