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Revision 1.10 by root, Fri Jan 13 13:16:15 2006 UTC vs.
Revision 1.275 by root, Sun Aug 9 00:24:35 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - the DBI of event loop programming
4		4
5	Event, Coro, Glib, Tk - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, Qt
		6	and POE are various supported event loops/environments.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# file descriptor readable
11	my $w = AnyEvent->io (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		30
16	* only one io watcher per $fh and $poll type is allowed (i.e. on a socket	31	# called when event loop idle (if applicable)
17	you can have one r + one w or one rw watcher, not any more (limitation by	32	my $w = AnyEvent->idle (cb => sub { ... });
18	Tk).
19		33
20	* the C<$poll_got> passed to the handler needs to be checked by looking	34	my $w = AnyEvent->condvar; # stores whether a condition was flagged
21	for single characters (e.g. with a regex), as it can contain more event	35	$w->send; # wake up current and all future recv's
22	types than were requested (e.g. a 'w' watcher might generate 'rw' events,
23	limitation by Glib).
24
25	* AnyEvent will keep filehandles alive, so as long as the watcher exists,
26	the filehandle exists.
27
28	my $w = AnyEvent->timer (after => $seconds, cb => sub {
29	...
30	});
31
32	* io and time watchers get canceled whenever $w is destroyed, so keep a copy
33
34	* timers can only be used once and must be recreated for repeated
35	operation (limitation by Glib and Tk).
36
37	my $w = AnyEvent->condvar; # kind of main loop replacement
38	$w->wait; # enters main loop till $condvar gets ->broadcast	36	$w->recv; # enters "main loop" till $condvar gets ->send
39	$w->broadcast; # wake up current and all future wait's	37	# use a condvar in callback mode:
		38	$w->cb (sub { $_[0]->recv });
40		39
41	* condvars are used to give blocking behaviour when neccessary. Create	40	=head1 INTRODUCTION/TUTORIAL
42	a condvar for any "request" or "event" your module might create, C<<	41
43	->broadcast >> it when the event happens and provide a function that calls	42	This manpage is mainly a reference manual. If you are interested
44	C<< ->wait >> for it. See the examples below.	43	in a tutorial or some gentle introduction, have a look at the
		44	L<AnyEvent::Intro> manpage.
		45
		46	=head1 SUPPORT
		47
		48	There is a mailinglist for discussing all things AnyEvent, and an IRC
		49	channel, too.
		50
		51	See the AnyEvent project page at the B<Schmorpforge Ta-Sa Software
		52	Repository>, at L<http://anyevent.schmorp.de>, for more info.
		53
		54	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		55
		56	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		57	nowadays. So what is different about AnyEvent?
		58
		59	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		60	policy> and AnyEvent is I<small and efficient>.
		61
		62	First and foremost, I<AnyEvent is not an event model> itself, it only
		63	interfaces to whatever event model the main program happens to use, in a
		64	pragmatic way. For event models and certain classes of immortals alike,
		65	the statement "there can only be one" is a bitter reality: In general,
		66	only one event loop can be active at the same time in a process. AnyEvent
		67	cannot change this, but it can hide the differences between those event
		68	loops.
		69
		70	The goal of AnyEvent is to offer module authors the ability to do event
		71	programming (waiting for I/O or timer events) without subscribing to a
		72	religion, a way of living, and most importantly: without forcing your
		73	module users into the same thing by forcing them to use the same event
		74	model you use.
		75
		76	For modules like POE or IO::Async (which is a total misnomer as it is
		77	actually doing all I/O I<synchronously>...), using them in your module is
		78	like joining a cult: After you joined, you are dependent on them and you
		79	cannot use anything else, as they are simply incompatible to everything
		80	that isn't them. What's worse, all the potential users of your
		81	module are I<also> forced to use the same event loop you use.
		82
		83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		84	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		85	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		86	your module uses one of those, every user of your module has to use it,
		87	too. But if your module uses AnyEvent, it works transparently with all
		88	event models it supports (including stuff like IO::Async, as long as those
		89	use one of the supported event loops. It is trivial to add new event loops
		90	to AnyEvent, too, so it is future-proof).
		91
		92	In addition to being free of having to use I<the one and only true event
		93	model>, AnyEvent also is free of bloat and policy: with POE or similar
		94	modules, you get an enormous amount of code and strict rules you have to
		95	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		96	offering the functionality that is necessary, in as thin as a wrapper as
		97	technically possible.
		98
		99	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		100	of useful functionality, such as an asynchronous DNS resolver, 100%
		101	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		102	such as Windows) and lots of real-world knowledge and workarounds for
		103	platform bugs and differences.
		104
		105	Now, if you I<do want> lots of policy (this can arguably be somewhat
		106	useful) and you want to force your users to use the one and only event
		107	model, you should I<not> use this module.
45		108
46	=head1 DESCRIPTION	109	=head1 DESCRIPTION
47		110
48	L<AnyEvent> provides an identical interface to multiple event loops. This	111	L<AnyEvent> provides an identical interface to multiple event loops. This
49	allows module authors to utilizy an event loop without forcing module	112	allows module authors to utilise an event loop without forcing module
50	users to use the same event loop (as only a single event loop can coexist	113	users to use the same event loop (as only a single event loop can coexist
51	peacefully at any one time).	114	peacefully at any one time).
52		115
53	The interface itself is vaguely similar but not identical to the Event	116	The interface itself is vaguely similar, but not identical to the L<Event>
54	module.	117	module.
55		118
56	On the first call of any method, the module tries to detect the currently	119	During the first call of any watcher-creation method, the module tries
57	loaded event loop by probing wether any of the following modules is	120	to detect the currently loaded event loop by probing whether one of the
58	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	121	following modules is already loaded: L<EV>,
59	used. If none is found, the module tries to load these modules in the	122	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
60	order given. The first one that could be successfully loaded will be	123	L<POE>. The first one found is used. If none are found, the module tries
61	used. If still none could be found, it will issue an error.	124	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		125	adaptor should always succeed) in the order given. The first one that can
		126	be successfully loaded will be used. If, after this, still none could be
		127	found, AnyEvent will fall back to a pure-perl event loop, which is not
		128	very efficient, but should work everywhere.
		129
		130	Because AnyEvent first checks for modules that are already loaded, loading
		131	an event model explicitly before first using AnyEvent will likely make
		132	that model the default. For example:
		133
		134	use Tk;
		135	use AnyEvent;
		136
		137	# .. AnyEvent will likely default to Tk
		138
		139	The I<likely> means that, if any module loads another event model and
		140	starts using it, all bets are off. Maybe you should tell their authors to
		141	use AnyEvent so their modules work together with others seamlessly...
		142
		143	The pure-perl implementation of AnyEvent is called
		144	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		145	explicitly and enjoy the high availability of that event loop :)
		146
		147	=head1 WATCHERS
		148
		149	AnyEvent has the central concept of a I<watcher>, which is an object that
		150	stores relevant data for each kind of event you are waiting for, such as
		151	the callback to call, the file handle to watch, etc.
		152
		153	These watchers are normal Perl objects with normal Perl lifetime. After
		154	creating a watcher it will immediately "watch" for events and invoke the
		155	callback when the event occurs (of course, only when the event model
		156	is in control).
		157
		158	Note that B<callbacks must not permanently change global variables>
		159	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		160	callbacks must not C<die> >>. The former is good programming practise in
		161	Perl and the latter stems from the fact that exception handling differs
		162	widely between event loops.
		163
		164	To disable the watcher you have to destroy it (e.g. by setting the
		165	variable you store it in to C<undef> or otherwise deleting all references
		166	to it).
		167
		168	All watchers are created by calling a method on the C<AnyEvent> class.
		169
		170	Many watchers either are used with "recursion" (repeating timers for
		171	example), or need to refer to their watcher object in other ways.
		172
		173	An any way to achieve that is this pattern:
		174
		175	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		176	# you can use $w here, for example to undef it
		177	undef $w;
		178	});
		179
		180	Note that C<my $w; $w => combination. This is necessary because in Perl,
		181	my variables are only visible after the statement in which they are
		182	declared.
		183
		184	=head2 I/O WATCHERS
		185
		186	$w = AnyEvent->io (
		187	fh => <filehandle_or_fileno>,
		188	poll => <"r" or "w">,
		189	cb => <callback>,
		190	);
		191
		192	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		193	with the following mandatory key-value pairs as arguments:
		194
		195	C<fh> is the Perl I<file handle> (or a naked file descriptor) to watch
		196	for events (AnyEvent might or might not keep a reference to this file
		197	handle). Note that only file handles pointing to things for which
		198	non-blocking operation makes sense are allowed. This includes sockets,
		199	most character devices, pipes, fifos and so on, but not for example files
		200	or block devices.
		201
		202	C<poll> must be a string that is either C<r> or C<w>, which creates a
		203	watcher waiting for "r"eadable or "w"ritable events, respectively.
		204
		205	C<cb> is the callback to invoke each time the file handle becomes ready.
		206
		207	Although the callback might get passed parameters, their value and
		208	presence is undefined and you cannot rely on them. Portable AnyEvent
		209	callbacks cannot use arguments passed to I/O watcher callbacks.
		210
		211	The I/O watcher might use the underlying file descriptor or a copy of it.
		212	You must not close a file handle as long as any watcher is active on the
		213	underlying file descriptor.
		214
		215	Some event loops issue spurious readyness notifications, so you should
		216	always use non-blocking calls when reading/writing from/to your file
		217	handles.
		218
		219	Example: wait for readability of STDIN, then read a line and disable the
		220	watcher.
		221
		222	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		223	chomp (my $input = <STDIN>);
		224	warn "read: $input\n";
		225	undef $w;
		226	});
		227
		228	=head2 TIME WATCHERS
		229
		230	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		231
		232	$w = AnyEvent->timer (
		233	after => <fractional_seconds>,
		234	interval => <fractional_seconds>,
		235	cb => <callback>,
		236	);
		237
		238	You can create a time watcher by calling the C<< AnyEvent->timer >>
		239	method with the following mandatory arguments:
		240
		241	C<after> specifies after how many seconds (fractional values are
		242	supported) the callback should be invoked. C<cb> is the callback to invoke
		243	in that case.
		244
		245	Although the callback might get passed parameters, their value and
		246	presence is undefined and you cannot rely on them. Portable AnyEvent
		247	callbacks cannot use arguments passed to time watcher callbacks.
		248
		249	The callback will normally be invoked once only. If you specify another
		250	parameter, C<interval>, as a strictly positive number (> 0), then the
		251	callback will be invoked regularly at that interval (in fractional
		252	seconds) after the first invocation. If C<interval> is specified with a
		253	false value, then it is treated as if it were missing.
		254
		255	The callback will be rescheduled before invoking the callback, but no
		256	attempt is done to avoid timer drift in most backends, so the interval is
		257	only approximate.
		258
		259	Example: fire an event after 7.7 seconds.
		260
		261	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		262	warn "timeout\n";
		263	});
		264
		265	# to cancel the timer:
		266	undef $w;
		267
		268	Example 2: fire an event after 0.5 seconds, then roughly every second.
		269
		270	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		271	warn "timeout\n";
		272	};
		273
		274	=head3 TIMING ISSUES
		275
		276	There are two ways to handle timers: based on real time (relative, "fire
		277	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		278	o'clock").
		279
		280	While most event loops expect timers to specified in a relative way, they
		281	use absolute time internally. This makes a difference when your clock
		282	"jumps", for example, when ntp decides to set your clock backwards from
		283	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		284	fire "after" a second might actually take six years to finally fire.
		285
		286	AnyEvent cannot compensate for this. The only event loop that is conscious
		287	about these issues is L<EV>, which offers both relative (ev_timer, based
		288	on true relative time) and absolute (ev_periodic, based on wallclock time)
		289	timers.
		290
		291	AnyEvent always prefers relative timers, if available, matching the
		292	AnyEvent API.
		293
		294	AnyEvent has two additional methods that return the "current time":
62		295
63	=over 4	296	=over 4
64		297
		298	=item AnyEvent->time
		299
		300	This returns the "current wallclock time" as a fractional number of
		301	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		302	return, and the result is guaranteed to be compatible with those).
		303
		304	It progresses independently of any event loop processing, i.e. each call
		305	will check the system clock, which usually gets updated frequently.
		306
		307	=item AnyEvent->now
		308
		309	This also returns the "current wallclock time", but unlike C<time>, above,
		310	this value might change only once per event loop iteration, depending on
		311	the event loop (most return the same time as C<time>, above). This is the
		312	time that AnyEvent's timers get scheduled against.
		313
		314	I<In almost all cases (in all cases if you don't care), this is the
		315	function to call when you want to know the current time.>
		316
		317	This function is also often faster then C<< AnyEvent->time >>, and
		318	thus the preferred method if you want some timestamp (for example,
		319	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		320
		321	The rest of this section is only of relevance if you try to be very exact
		322	with your timing, you can skip it without bad conscience.
		323
		324	For a practical example of when these times differ, consider L<Event::Lib>
		325	and L<EV> and the following set-up:
		326
		327	The event loop is running and has just invoked one of your callback at
		328	time=500 (assume no other callbacks delay processing). In your callback,
		329	you wait a second by executing C<sleep 1> (blocking the process for a
		330	second) and then (at time=501) you create a relative timer that fires
		331	after three seconds.
		332
		333	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		334	both return C<501>, because that is the current time, and the timer will
		335	be scheduled to fire at time=504 (C<501> + C<3>).
		336
		337	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		338	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		339	last event processing phase started. With L<EV>, your timer gets scheduled
		340	to run at time=503 (C<500> + C<3>).
		341
		342	In one sense, L<Event::Lib> is more exact, as it uses the current time
		343	regardless of any delays introduced by event processing. However, most
		344	callbacks do not expect large delays in processing, so this causes a
		345	higher drift (and a lot more system calls to get the current time).
		346
		347	In another sense, L<EV> is more exact, as your timer will be scheduled at
		348	the same time, regardless of how long event processing actually took.
		349
		350	In either case, if you care (and in most cases, you don't), then you
		351	can get whatever behaviour you want with any event loop, by taking the
		352	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		353	account.
		354
		355	=item AnyEvent->now_update
		356
		357	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		358	the current time for each loop iteration (see the discussion of L<<
		359	AnyEvent->now >>, above).
		360
		361	When a callback runs for a long time (or when the process sleeps), then
		362	this "current" time will differ substantially from the real time, which
		363	might affect timers and time-outs.
		364
		365	When this is the case, you can call this method, which will update the
		366	event loop's idea of "current time".
		367
		368	Note that updating the time I<might> cause some events to be handled.
		369
		370	=back
		371
		372	=head2 SIGNAL WATCHERS
		373
		374	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		375
		376	You can watch for signals using a signal watcher, C<signal> is the signal
		377	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		378	callback to be invoked whenever a signal occurs.
		379
		380	Although the callback might get passed parameters, their value and
		381	presence is undefined and you cannot rely on them. Portable AnyEvent
		382	callbacks cannot use arguments passed to signal watcher callbacks.
		383
		384	Multiple signal occurrences can be clumped together into one callback
		385	invocation, and callback invocation will be synchronous. Synchronous means
		386	that it might take a while until the signal gets handled by the process,
		387	but it is guaranteed not to interrupt any other callbacks.
		388
		389	The main advantage of using these watchers is that you can share a signal
		390	between multiple watchers, and AnyEvent will ensure that signals will not
		391	interrupt your program at bad times.
		392
		393	This watcher might use C<%SIG> (depending on the event loop used),
		394	so programs overwriting those signals directly will likely not work
		395	correctly.
		396
		397	Example: exit on SIGINT
		398
		399	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		400
		401	=head3 Signal Races, Delays and Workarounds
		402
		403	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		404	callbacks to signals in a generic way, which is a pity, as you cannot
		405	do race-free signal handling in perl, requiring C libraries for
		406	this. AnyEvent will try to do it's best, which means in some cases,
		407	signals will be delayed. The maximum time a signal might be delayed is
		408	specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10 seconds). This
		409	variable can be changed only before the first signal watcher is created,
		410	and should be left alone otherwise. This variable determines how often
		411	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		412	will cause fewer spurious wake-ups, which is better for power and CPU
		413	saving.
		414
		415	All these problems can be avoided by installing the optional
		416	L<Async::Interrupt> module, which works with most event loops. It will not
		417	work with inherently broken event loops such as L<Event> or L<Event::Lib>
		418	(and not with L<POE> currently, as POE does it's own workaround with
		419	one-second latency). For those, you just have to suffer the delays.
		420
		421	=head2 CHILD PROCESS WATCHERS
		422
		423	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		424
		425	You can also watch on a child process exit and catch its exit status.
		426
		427	The child process is specified by the C<pid> argument (one some backends,
		428	using C<0> watches for any child process exit, on others this will
		429	croak). The watcher will be triggered only when the child process has
		430	finished and an exit status is available, not on any trace events
		431	(stopped/continued).
		432
		433	The callback will be called with the pid and exit status (as returned by
		434	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		435	callback arguments.
		436
		437	This watcher type works by installing a signal handler for C<SIGCHLD>,
		438	and since it cannot be shared, nothing else should use SIGCHLD or reap
		439	random child processes (waiting for specific child processes, e.g. inside
		440	C<system>, is just fine).
		441
		442	There is a slight catch to child watchers, however: you usually start them
		443	I<after> the child process was created, and this means the process could
		444	have exited already (and no SIGCHLD will be sent anymore).
		445
		446	Not all event models handle this correctly (neither POE nor IO::Async do,
		447	see their AnyEvent::Impl manpages for details), but even for event models
		448	that I<do> handle this correctly, they usually need to be loaded before
		449	the process exits (i.e. before you fork in the first place). AnyEvent's
		450	pure perl event loop handles all cases correctly regardless of when you
		451	start the watcher.
		452
		453	This means you cannot create a child watcher as the very first
		454	thing in an AnyEvent program, you I<have> to create at least one
		455	watcher before you C<fork> the child (alternatively, you can call
		456	C<AnyEvent::detect>).
		457
		458	As most event loops do not support waiting for child events, they will be
		459	emulated by AnyEvent in most cases, in which the latency and race problems
		460	mentioned in the description of signal watchers apply.
		461
		462	Example: fork a process and wait for it
		463
		464	my $done = AnyEvent->condvar;
		465
		466	my $pid = fork or exit 5;
		467
		468	my $w = AnyEvent->child (
		469	pid => $pid,
		470	cb => sub {
		471	my ($pid, $status) = @_;
		472	warn "pid $pid exited with status $status";
		473	$done->send;
		474	},
		475	);
		476
		477	# do something else, then wait for process exit
		478	$done->recv;
		479
		480	=head2 IDLE WATCHERS
		481
		482	$w = AnyEvent->idle (cb => <callback>);
		483
		484	Sometimes there is a need to do something, but it is not so important
		485	to do it instantly, but only when there is nothing better to do. This
		486	"nothing better to do" is usually defined to be "no other events need
		487	attention by the event loop".
		488
		489	Idle watchers ideally get invoked when the event loop has nothing
		490	better to do, just before it would block the process to wait for new
		491	events. Instead of blocking, the idle watcher is invoked.
		492
		493	Most event loops unfortunately do not really support idle watchers (only
		494	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		495	will simply call the callback "from time to time".
		496
		497	Example: read lines from STDIN, but only process them when the
		498	program is otherwise idle:
		499
		500	my @lines; # read data
		501	my $idle_w;
		502	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		503	push @lines, scalar <STDIN>;
		504
		505	# start an idle watcher, if not already done
		506	$idle_w ||= AnyEvent->idle (cb => sub {
		507	# handle only one line, when there are lines left
		508	if (my $line = shift @lines) {
		509	print "handled when idle: $line";
		510	} else {
		511	# otherwise disable the idle watcher again
		512	undef $idle_w;
		513	}
		514	});
		515	});
		516
		517	=head2 CONDITION VARIABLES
		518
		519	$cv = AnyEvent->condvar;
		520
		521	$cv->send (<list>);
		522	my @res = $cv->recv;
		523
		524	If you are familiar with some event loops you will know that all of them
		525	require you to run some blocking "loop", "run" or similar function that
		526	will actively watch for new events and call your callbacks.
		527
		528	AnyEvent is slightly different: it expects somebody else to run the event
		529	loop and will only block when necessary (usually when told by the user).
		530
		531	The instrument to do that is called a "condition variable", so called
		532	because they represent a condition that must become true.
		533
		534	Now is probably a good time to look at the examples further below.
		535
		536	Condition variables can be created by calling the C<< AnyEvent->condvar
		537	>> method, usually without arguments. The only argument pair allowed is
		538	C<cb>, which specifies a callback to be called when the condition variable
		539	becomes true, with the condition variable as the first argument (but not
		540	the results).
		541
		542	After creation, the condition variable is "false" until it becomes "true"
		543	by calling the C<send> method (or calling the condition variable as if it
		544	were a callback, read about the caveats in the description for the C<<
		545	->send >> method).
		546
		547	Condition variables are similar to callbacks, except that you can
		548	optionally wait for them. They can also be called merge points - points
		549	in time where multiple outstanding events have been processed. And yet
		550	another way to call them is transactions - each condition variable can be
		551	used to represent a transaction, which finishes at some point and delivers
		552	a result. And yet some people know them as "futures" - a promise to
		553	compute/deliver something that you can wait for.
		554
		555	Condition variables are very useful to signal that something has finished,
		556	for example, if you write a module that does asynchronous http requests,
		557	then a condition variable would be the ideal candidate to signal the
		558	availability of results. The user can either act when the callback is
		559	called or can synchronously C<< ->recv >> for the results.
		560
		561	You can also use them to simulate traditional event loops - for example,
		562	you can block your main program until an event occurs - for example, you
		563	could C<< ->recv >> in your main program until the user clicks the Quit
		564	button of your app, which would C<< ->send >> the "quit" event.
		565
		566	Note that condition variables recurse into the event loop - if you have
		567	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		568	lose. Therefore, condition variables are good to export to your caller, but
		569	you should avoid making a blocking wait yourself, at least in callbacks,
		570	as this asks for trouble.
		571
		572	Condition variables are represented by hash refs in perl, and the keys
		573	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		574	easy (it is often useful to build your own transaction class on top of
		575	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		576	it's C<new> method in your own C<new> method.
		577
		578	There are two "sides" to a condition variable - the "producer side" which
		579	eventually calls C<< -> send >>, and the "consumer side", which waits
		580	for the send to occur.
		581
		582	Example: wait for a timer.
		583
		584	# wait till the result is ready
		585	my $result_ready = AnyEvent->condvar;
		586
		587	# do something such as adding a timer
		588	# or socket watcher the calls $result_ready->send
		589	# when the "result" is ready.
		590	# in this case, we simply use a timer:
		591	my $w = AnyEvent->timer (
		592	after => 1,
		593	cb => sub { $result_ready->send },
		594	);
		595
		596	# this "blocks" (while handling events) till the callback
		597	# calls -<send
		598	$result_ready->recv;
		599
		600	Example: wait for a timer, but take advantage of the fact that condition
		601	variables are also callable directly.
		602
		603	my $done = AnyEvent->condvar;
		604	my $delay = AnyEvent->timer (after => 5, cb => $done);
		605	$done->recv;
		606
		607	Example: Imagine an API that returns a condvar and doesn't support
		608	callbacks. This is how you make a synchronous call, for example from
		609	the main program:
		610
		611	use AnyEvent::CouchDB;
		612
		613	...
		614
		615	my @info = $couchdb->info->recv;
		616
		617	And this is how you would just set a callback to be called whenever the
		618	results are available:
		619
		620	$couchdb->info->cb (sub {
		621	my @info = $_[0]->recv;
		622	});
		623
		624	=head3 METHODS FOR PRODUCERS
		625
		626	These methods should only be used by the producing side, i.e. the
		627	code/module that eventually sends the signal. Note that it is also
		628	the producer side which creates the condvar in most cases, but it isn't
		629	uncommon for the consumer to create it as well.
		630
		631	=over 4
		632
		633	=item $cv->send (...)
		634
		635	Flag the condition as ready - a running C<< ->recv >> and all further
		636	calls to C<recv> will (eventually) return after this method has been
		637	called. If nobody is waiting the send will be remembered.
		638
		639	If a callback has been set on the condition variable, it is called
		640	immediately from within send.
		641
		642	Any arguments passed to the C<send> call will be returned by all
		643	future C<< ->recv >> calls.
		644
		645	Condition variables are overloaded so one can call them directly (as if
		646	they were a code reference). Calling them directly is the same as calling
		647	C<send>.
		648
		649	=item $cv->croak ($error)
		650
		651	Similar to send, but causes all call's to C<< ->recv >> to invoke
		652	C<Carp::croak> with the given error message/object/scalar.
		653
		654	This can be used to signal any errors to the condition variable
		655	user/consumer. Doing it this way instead of calling C<croak> directly
		656	delays the error detetcion, but has the overwhelmign advantage that it
		657	diagnoses the error at the place where the result is expected, and not
		658	deep in some event clalback without connection to the actual code causing
		659	the problem.
		660
		661	=item $cv->begin ([group callback])
		662
		663	=item $cv->end
		664
		665	These two methods can be used to combine many transactions/events into
		666	one. For example, a function that pings many hosts in parallel might want
		667	to use a condition variable for the whole process.
		668
		669	Every call to C<< ->begin >> will increment a counter, and every call to
		670	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		671	>>, the (last) callback passed to C<begin> will be executed. That callback
		672	is I<supposed> to call C<< ->send >>, but that is not required. If no
		673	callback was set, C<send> will be called without any arguments.
		674
		675	You can think of C<< $cv->send >> giving you an OR condition (one call
		676	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		677	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		678
		679	Let's start with a simple example: you have two I/O watchers (for example,
		680	STDOUT and STDERR for a program), and you want to wait for both streams to
		681	close before activating a condvar:
		682
		683	my $cv = AnyEvent->condvar;
		684
		685	$cv->begin; # first watcher
		686	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		687	defined sysread $fh1, my $buf, 4096
		688	or $cv->end;
		689	});
		690
		691	$cv->begin; # second watcher
		692	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		693	defined sysread $fh2, my $buf, 4096
		694	or $cv->end;
		695	});
		696
		697	$cv->recv;
		698
		699	This works because for every event source (EOF on file handle), there is
		700	one call to C<begin>, so the condvar waits for all calls to C<end> before
		701	sending.
		702
		703	The ping example mentioned above is slightly more complicated, as the
		704	there are results to be passwd back, and the number of tasks that are
		705	begung can potentially be zero:
		706
		707	my $cv = AnyEvent->condvar;
		708
		709	my %result;
		710	$cv->begin (sub { $cv->send (\%result) });
		711
		712	for my $host (@list_of_hosts) {
		713	$cv->begin;
		714	ping_host_then_call_callback $host, sub {
		715	$result{$host} = ...;
		716	$cv->end;
		717	};
		718	}
		719
		720	$cv->end;
		721
		722	This code fragment supposedly pings a number of hosts and calls
		723	C<send> after results for all then have have been gathered - in any
		724	order. To achieve this, the code issues a call to C<begin> when it starts
		725	each ping request and calls C<end> when it has received some result for
		726	it. Since C<begin> and C<end> only maintain a counter, the order in which
		727	results arrive is not relevant.
		728
		729	There is an additional bracketing call to C<begin> and C<end> outside the
		730	loop, which serves two important purposes: first, it sets the callback
		731	to be called once the counter reaches C<0>, and second, it ensures that
		732	C<send> is called even when C<no> hosts are being pinged (the loop
		733	doesn't execute once).
		734
		735	This is the general pattern when you "fan out" into multiple (but
		736	potentially none) subrequests: use an outer C<begin>/C<end> pair to set
		737	the callback and ensure C<end> is called at least once, and then, for each
		738	subrequest you start, call C<begin> and for each subrequest you finish,
		739	call C<end>.
		740
		741	=back
		742
		743	=head3 METHODS FOR CONSUMERS
		744
		745	These methods should only be used by the consuming side, i.e. the
		746	code awaits the condition.
		747
		748	=over 4
		749
		750	=item $cv->recv
		751
		752	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		753	>> methods have been called on c<$cv>, while servicing other watchers
		754	normally.
		755
		756	You can only wait once on a condition - additional calls are valid but
		757	will return immediately.
		758
		759	If an error condition has been set by calling C<< ->croak >>, then this
		760	function will call C<croak>.
		761
		762	In list context, all parameters passed to C<send> will be returned,
		763	in scalar context only the first one will be returned.
		764
		765	Note that doing a blocking wait in a callback is not supported by any
		766	event loop, that is, recursive invocation of a blocking C<< ->recv
		767	>> is not allowed, and the C<recv> call will C<croak> if such a
		768	condition is detected. This condition can be slightly loosened by using
		769	L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
		770	any thread that doesn't run the event loop itself.
		771
		772	Not all event models support a blocking wait - some die in that case
		773	(programs might want to do that to stay interactive), so I<if you are
		774	using this from a module, never require a blocking wait>. Instead, let the
		775	caller decide whether the call will block or not (for example, by coupling
		776	condition variables with some kind of request results and supporting
		777	callbacks so the caller knows that getting the result will not block,
		778	while still supporting blocking waits if the caller so desires).
		779
		780	You can ensure that C<< -recv >> never blocks by setting a callback and
		781	only calling C<< ->recv >> from within that callback (or at a later
		782	time). This will work even when the event loop does not support blocking
		783	waits otherwise.
		784
		785	=item $bool = $cv->ready
		786
		787	Returns true when the condition is "true", i.e. whether C<send> or
		788	C<croak> have been called.
		789
		790	=item $cb = $cv->cb ($cb->($cv))
		791
		792	This is a mutator function that returns the callback set and optionally
		793	replaces it before doing so.
		794
		795	The callback will be called when the condition becomes (or already was)
		796	"true", i.e. when C<send> or C<croak> are called (or were called), with
		797	the only argument being the condition variable itself. Calling C<recv>
		798	inside the callback or at any later time is guaranteed not to block.
		799
		800	=back
		801
		802	=head1 SUPPORTED EVENT LOOPS/BACKENDS
		803
		804	The available backend classes are (every class has its own manpage):
		805
		806	=over 4
		807
		808	=item Backends that are autoprobed when no other event loop can be found.
		809
		810	EV is the preferred backend when no other event loop seems to be in
		811	use. If EV is not installed, then AnyEvent will try Event, and, failing
		812	that, will fall back to its own pure-perl implementation, which is
		813	available everywhere as it comes with AnyEvent itself.
		814
		815	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		816	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		817	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		818
		819	=item Backends that are transparently being picked up when they are used.
		820
		821	These will be used when they are currently loaded when the first watcher
		822	is created, in which case it is assumed that the application is using
		823	them. This means that AnyEvent will automatically pick the right backend
		824	when the main program loads an event module before anything starts to
		825	create watchers. Nothing special needs to be done by the main program.
		826
		827	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		828	AnyEvent::Impl::Tk based on Tk, very broken.
		829	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		830	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		831	AnyEvent::Impl::Irssi used when running within irssi.
		832
		833	=item Backends with special needs.
		834
		835	Qt requires the Qt::Application to be instantiated first, but will
		836	otherwise be picked up automatically. As long as the main program
		837	instantiates the application before any AnyEvent watchers are created,
		838	everything should just work.
		839
		840	AnyEvent::Impl::Qt based on Qt.
		841
		842	Support for IO::Async can only be partial, as it is too broken and
		843	architecturally limited to even support the AnyEvent API. It also
		844	is the only event loop that needs the loop to be set explicitly, so
		845	it can only be used by a main program knowing about AnyEvent. See
		846	L<AnyEvent::Impl::Async> for the gory details.
		847
		848	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		849
		850	=item Event loops that are indirectly supported via other backends.
		851
		852	Some event loops can be supported via other modules:
		853
		854	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		855
		856	B<WxWidgets> has no support for watching file handles. However, you can
		857	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		858	polls 20 times per second, which was considered to be too horrible to even
		859	consider for AnyEvent.
		860
		861	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		862	backend, so it can be supported through POE.
		863
		864	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		865	load L<POE> when detecting them, in the hope that POE will pick them up,
		866	in which case everything will be automatic.
		867
		868	=back
		869
		870	=head1 GLOBAL VARIABLES AND FUNCTIONS
		871
		872	These are not normally required to use AnyEvent, but can be useful to
		873	write AnyEvent extension modules.
		874
		875	=over 4
		876
		877	=item $AnyEvent::MODEL
		878
		879	Contains C<undef> until the first watcher is being created, before the
		880	backend has been autodetected.
		881
		882	Afterwards it contains the event model that is being used, which is the
		883	name of the Perl class implementing the model. This class is usually one
		884	of the C<AnyEvent::Impl:xxx> modules, but can be any other class in the
		885	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
		886	will be C<urxvt::anyevent>).
		887
		888	=item AnyEvent::detect
		889
		890	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		891	if necessary. You should only call this function right before you would
		892	have created an AnyEvent watcher anyway, that is, as late as possible at
		893	runtime, and not e.g. while initialising of your module.
		894
		895	If you need to do some initialisation before AnyEvent watchers are
		896	created, use C<post_detect>.
		897
		898	=item $guard = AnyEvent::post_detect { BLOCK }
		899
		900	Arranges for the code block to be executed as soon as the event model is
		901	autodetected (or immediately if this has already happened).
		902
		903	The block will be executed I<after> the actual backend has been detected
		904	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		905	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		906	other initialisations - see the sources of L<AnyEvent::Strict> or
		907	L<AnyEvent::AIO> to see how this is used.
		908
		909	The most common usage is to create some global watchers, without forcing
		910	event module detection too early, for example, L<AnyEvent::AIO> creates
		911	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		912	avoid autodetecting the event module at load time.
		913
		914	If called in scalar or list context, then it creates and returns an object
		915	that automatically removes the callback again when it is destroyed (or
		916	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		917	a case where this is useful.
		918
		919	Example: Create a watcher for the IO::AIO module and store it in
		920	C<$WATCHER>. Only do so after the event loop is initialised, though.
		921
		922	our WATCHER;
		923
		924	my $guard = AnyEvent::post_detect {
		925	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		926	};
		927
		928	# the ||= is important in case post_detect immediately runs the block,
		929	# as to not clobber the newly-created watcher. assigning both watcher and
		930	# post_detect guard to the same variable has the advantage of users being
		931	# able to just C<undef $WATCHER> if the watcher causes them grief.
		932
		933	$WATCHER ||= $guard;
		934
		935	=item @AnyEvent::post_detect
		936
		937	If there are any code references in this array (you can C<push> to it
		938	before or after loading AnyEvent), then they will called directly after
		939	the event loop has been chosen.
		940
		941	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		942	if it is defined then the event loop has already been detected, and the
		943	array will be ignored.
		944
		945	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		946	it,as it takes care of these details.
		947
		948	This variable is mainly useful for modules that can do something useful
		949	when AnyEvent is used and thus want to know when it is initialised, but do
		950	not need to even load it by default. This array provides the means to hook
		951	into AnyEvent passively, without loading it.
		952
		953	=back
		954
		955	=head1 WHAT TO DO IN A MODULE
		956
		957	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		958	freely, but you should not load a specific event module or rely on it.
		959
		960	Be careful when you create watchers in the module body - AnyEvent will
		961	decide which event module to use as soon as the first method is called, so
		962	by calling AnyEvent in your module body you force the user of your module
		963	to load the event module first.
		964
		965	Never call C<< ->recv >> on a condition variable unless you I<know> that
		966	the C<< ->send >> method has been called on it already. This is
		967	because it will stall the whole program, and the whole point of using
		968	events is to stay interactive.
		969
		970	It is fine, however, to call C<< ->recv >> when the user of your module
		971	requests it (i.e. if you create a http request object ad have a method
		972	called C<results> that returns the results, it should call C<< ->recv >>
		973	freely, as the user of your module knows what she is doing. always).
		974
		975	=head1 WHAT TO DO IN THE MAIN PROGRAM
		976
		977	There will always be a single main program - the only place that should
		978	dictate which event model to use.
		979
		980	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		981	do anything special (it does not need to be event-based) and let AnyEvent
		982	decide which implementation to chose if some module relies on it.
		983
		984	If the main program relies on a specific event model - for example, in
		985	Gtk2 programs you have to rely on the Glib module - you should load the
		986	event module before loading AnyEvent or any module that uses it: generally
		987	speaking, you should load it as early as possible. The reason is that
		988	modules might create watchers when they are loaded, and AnyEvent will
		989	decide on the event model to use as soon as it creates watchers, and it
		990	might chose the wrong one unless you load the correct one yourself.
		991
		992	You can chose to use a pure-perl implementation by loading the
		993	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		994	everywhere, but letting AnyEvent chose the model is generally better.
		995
		996	=head2 MAINLOOP EMULATION
		997
		998	Sometimes (often for short test scripts, or even standalone programs who
		999	only want to use AnyEvent), you do not want to run a specific event loop.
		1000
		1001	In that case, you can use a condition variable like this:
		1002
		1003	AnyEvent->condvar->recv;
		1004
		1005	This has the effect of entering the event loop and looping forever.
		1006
		1007	Note that usually your program has some exit condition, in which case
		1008	it is better to use the "traditional" approach of storing a condition
		1009	variable somewhere, waiting for it, and sending it when the program should
		1010	exit cleanly.
		1011
		1012
		1013	=head1 OTHER MODULES
		1014
		1015	The following is a non-exhaustive list of additional modules that use
		1016	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		1017	modules and other event loops in the same program. Some of the modules
		1018	come with AnyEvent, most are available via CPAN.
		1019
		1020	=over 4
		1021
		1022	=item L<AnyEvent::Util>
		1023
		1024	Contains various utility functions that replace often-used but blocking
		1025	functions such as C<inet_aton> by event-/callback-based versions.
		1026
		1027	=item L<AnyEvent::Socket>
		1028
		1029	Provides various utility functions for (internet protocol) sockets,
		1030	addresses and name resolution. Also functions to create non-blocking tcp
		1031	connections or tcp servers, with IPv6 and SRV record support and more.
		1032
		1033	=item L<AnyEvent::Handle>
		1034
		1035	Provide read and write buffers, manages watchers for reads and writes,
		1036	supports raw and formatted I/O, I/O queued and fully transparent and
		1037	non-blocking SSL/TLS (via L<AnyEvent::TLS>.
		1038
		1039	=item L<AnyEvent::DNS>
		1040
		1041	Provides rich asynchronous DNS resolver capabilities.
		1042
		1043	=item L<AnyEvent::HTTP>
		1044
		1045	A simple-to-use HTTP library that is capable of making a lot of concurrent
		1046	HTTP requests.
		1047
		1048	=item L<AnyEvent::HTTPD>
		1049
		1050	Provides a simple web application server framework.
		1051
		1052	=item L<AnyEvent::FastPing>
		1053
		1054	The fastest ping in the west.
		1055
		1056	=item L<AnyEvent::DBI>
		1057
		1058	Executes L<DBI> requests asynchronously in a proxy process.
		1059
		1060	=item L<AnyEvent::AIO>
		1061
		1062	Truly asynchronous I/O, should be in the toolbox of every event
		1063	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		1064	together.
		1065
		1066	=item L<AnyEvent::BDB>
		1067
		1068	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		1069	L<BDB> and AnyEvent together.
		1070
		1071	=item L<AnyEvent::GPSD>
		1072
		1073	A non-blocking interface to gpsd, a daemon delivering GPS information.
		1074
		1075	=item L<AnyEvent::IRC>
		1076
		1077	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		1078
		1079	=item L<AnyEvent::XMPP>
		1080
		1081	AnyEvent based XMPP (Jabber protocol) module family (replacing the older
		1082	Net::XMPP2>.
		1083
		1084	=item L<AnyEvent::IGS>
		1085
		1086	A non-blocking interface to the Internet Go Server protocol (used by
		1087	L<App::IGS>).
		1088
		1089	=item L<Net::FCP>
		1090
		1091	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		1092	of AnyEvent.
		1093
		1094	=item L<Event::ExecFlow>
		1095
		1096	High level API for event-based execution flow control.
		1097
		1098	=item L<Coro>
		1099
		1100	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1101
		1102	=back
		1103
65	=cut	1104	=cut
66		1105
67	package AnyEvent;	1106	package AnyEvent;
68		1107
		1108	# basically a tuned-down version of common::sense
		1109	sub common_sense {
69	no warnings;	1110	# no warnings
70	use strict 'vars';	1111	${^WARNING_BITS} ^= ${^WARNING_BITS};
		1112	# use strict vars subs
		1113	$^H |= 0x00000600;
		1114	}
		1115
		1116	BEGIN { AnyEvent::common_sense }
		1117
71	use Carp;	1118	use Carp ();
72		1119
73	our $VERSION = '1.02';	1120	our $VERSION = 4.92;
74	our $MODEL;	1121	our $MODEL;
75		1122
76	our $AUTOLOAD;	1123	our $AUTOLOAD;
77	our @ISA;	1124	our @ISA;
78		1125
79	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
80
81	our @REGISTRY;	1126	our @REGISTRY;
82		1127
		1128	our $WIN32;
		1129
		1130	our $VERBOSE;
		1131
		1132	BEGIN {
		1133	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		1134	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		1135
		1136	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1137	if ${^TAINT};
		1138
		1139	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1140
		1141	}
		1142
		1143	our $MAX_SIGNAL_LATENCY = 10;
		1144
		1145	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1146
		1147	{
		1148	my $idx;
		1149	$PROTOCOL{$_} = ++$idx
		1150	for reverse split /\s*,\s*/,
		1151	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1152	}
		1153
83	my @models = (	1154	my @models = (
84	[Coro::Event:: => AnyEvent::Impl::Coro::],	1155	[EV:: => AnyEvent::Impl::EV:: , 1],
85	[Event:: => AnyEvent::Impl::Event::],	1156	[Event:: => AnyEvent::Impl::Event::, 1],
86	[Glib:: => AnyEvent::Impl::Glib::],	1157	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl:: , 1],
		1158	# everything below here will not (normally) be autoprobed
		1159	# as the pureperl backend should work everywhere
		1160	# and is usually faster
		1161	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1162	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1163	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1164	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1165	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1166	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
87	[Tk:: => AnyEvent::Impl::Tk::],	1167	[Wx:: => AnyEvent::Impl::POE::],
		1168	[Prima:: => AnyEvent::Impl::POE::],
		1169	# IO::Async is just too broken - we would need workarounds for its
		1170	# byzantine signal and broken child handling, among others.
		1171	# IO::Async is rather hard to detect, as it doesn't have any
		1172	# obvious default class.
		1173	# [0, IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1174	# [0, IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1175	# [0, IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
88	);	1176	);
89		1177
90	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	1178	our %method = map +($_ => 1),
		1179	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
91		1180
92	sub AUTOLOAD {	1181	our @post_detect;
93	$AUTOLOAD =~ s/.*://;
94		1182
95	$method{$AUTOLOAD}	1183	sub post_detect(&) {
96	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	1184	my ($cb) = @_;
97		1185
		1186	if ($MODEL) {
		1187	$cb->();
		1188
		1189	undef
		1190	} else {
		1191	push @post_detect, $cb;
		1192
		1193	defined wantarray
		1194	? bless \$cb, "AnyEvent::Util::postdetect"
		1195	: ()
		1196	}
		1197	}
		1198
		1199	sub AnyEvent::Util::postdetect::DESTROY {
		1200	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1201	}
		1202
		1203	sub detect() {
98	unless ($MODEL) {	1204	unless ($MODEL) {
		1205	local $SIG{__DIE__};
		1206
		1207	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		1208	my $model = "AnyEvent::Impl::$1";
		1209	if (eval "require $model") {
		1210	$MODEL = $model;
		1211	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1212	} else {
		1213	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
		1214	}
		1215	}
		1216
99	# check for already loaded models	1217	# check for already loaded models
		1218	unless ($MODEL) {
100	for (@REGISTRY, @models) {	1219	for (@REGISTRY, @models) {
101	my ($package, $model) = @$_;	1220	my ($package, $model) = @$_;
102	if (${"$package\::VERSION"} > 0) {	1221	if (${"$package\::VERSION"} > 0) {
103	if (eval "require $model") {	1222	if (eval "require $model") {
104	$MODEL = $model;	1223	$MODEL = $model;
105	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1224	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
106	last;	1225	last;
		1226	}
107	}	1227	}
108	}	1228	}
		1229
		1230	unless ($MODEL) {
		1231	# try to autoload a model
		1232	for (@REGISTRY, @models) {
		1233	my ($package, $model, $autoload) = @$_;
		1234	if (
		1235	$autoload
		1236	and eval "require $package"
		1237	and ${"$package\::VERSION"} > 0
		1238	and eval "require $model"
		1239	) {
		1240	$MODEL = $model;
		1241	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
		1242	last;
		1243	}
		1244	}
		1245
		1246	$MODEL
		1247	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
		1248	}
109	}	1249	}
110		1250
111	unless ($MODEL) {	1251	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
112	# try to load a model
113		1252
114	for (@REGISTRY, @models) {	1253	unshift @ISA, $MODEL;
115	my ($package, $model) = @$_;
116	if (eval "require $model") {
117	$MODEL = $model;
118	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
119	last;
120	}
121	}
122		1254
		1255	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1256
		1257	(shift @post_detect)->() while @post_detect;
		1258	}
		1259
123	$MODEL	1260	$MODEL
124	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1261	}
		1262
		1263	sub AUTOLOAD {
		1264	(my $func = $AUTOLOAD) =~ s/.*://;
		1265
		1266	$method{$func}
		1267	or Carp::croak "$func: not a valid method for AnyEvent objects";
		1268
		1269	detect unless $MODEL;
		1270
		1271	my $class = shift;
		1272	$class->$func (@_);
		1273	}
		1274
		1275	# utility function to dup a filehandle. this is used by many backends
		1276	# to support binding more than one watcher per filehandle (they usually
		1277	# allow only one watcher per fd, so we dup it to get a different one).
		1278	sub _dupfh($$;$$) {
		1279	my ($poll, $fh, $r, $w) = @_;
		1280
		1281	# cygwin requires the fh mode to be matching, unix doesn't
		1282	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1283
		1284	open my $fh2, $mode, $fh
		1285	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1286
		1287	# we assume CLOEXEC is already set by perl in all important cases
		1288
		1289	($fh2, $rw)
		1290	}
		1291
		1292	#############################################################################
		1293	# "new" API, currently only emulation of it
		1294	#############################################################################
		1295
		1296	package AE;
		1297
		1298	our $VERSION = $AnyEvent::VERSION;
		1299
		1300	sub io($$$) {
		1301	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1302	}
		1303
		1304	sub timer($$$) {
		1305	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2]);
		1306	}
		1307
		1308	sub signal($$) {
		1309	AnyEvent->signal (signal => $_[0], cb => $_[1]);
		1310	}
		1311
		1312	sub child($$) {
		1313	AnyEvent->child (pid => $_[0], cb => $_[1]);
		1314	}
		1315
		1316	sub idle($) {
		1317	AnyEvent->idle (cb => $_[0]);
		1318	}
		1319
		1320	sub cv(;&) {
		1321	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1322	}
		1323
		1324	sub now() {
		1325	AnyEvent->now
		1326	}
		1327
		1328	sub now_update() {
		1329	AnyEvent->now_update
		1330	}
		1331
		1332	sub time() {
		1333	AnyEvent->time
		1334	}
		1335
		1336	package AnyEvent::Base;
		1337
		1338	# default implementations for many methods
		1339
		1340	sub _time {
		1341	# probe for availability of Time::HiRes
		1342	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1343	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1344	*_time = \&Time::HiRes::time;
		1345	# if (eval "use POSIX (); (POSIX::times())...
		1346	} else {
		1347	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1348	*_time = sub { time }; # epic fail
		1349	}
		1350
		1351	&_time
		1352	}
		1353
		1354	sub time { _time }
		1355	sub now { _time }
		1356	sub now_update { }
		1357
		1358	# default implementation for ->condvar
		1359
		1360	sub condvar {
		1361	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1362	}
		1363
		1364	# default implementation for ->signal
		1365
		1366	our $HAVE_ASYNC_INTERRUPT;
		1367
		1368	sub _have_async_interrupt() {
		1369	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1370	&& eval "use Async::Interrupt 1.0 (); 1")
		1371	unless defined $HAVE_ASYNC_INTERRUPT;
		1372
		1373	$HAVE_ASYNC_INTERRUPT
		1374	}
		1375
		1376	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1377	our (%SIG_ASY, %SIG_ASY_W);
		1378	our ($SIG_COUNT, $SIG_TW);
		1379
		1380	sub _signal_exec {
		1381	$HAVE_ASYNC_INTERRUPT
		1382	? $SIGPIPE_R->drain
		1383	: sysread $SIGPIPE_R, my $dummy, 9;
		1384
		1385	while (%SIG_EV) {
		1386	for (keys %SIG_EV) {
		1387	delete $SIG_EV{$_};
		1388	$_->() for values %{ $SIG_CB{$_} || {} };
125	}	1389	}
126	}	1390	}
		1391	}
127		1392
128	@ISA = $MODEL;	1393	# install a dummy wakeup watcher to reduce signal catching latency
		1394	sub _sig_add() {
		1395	unless ($SIG_COUNT++) {
		1396	# try to align timer on a full-second boundary, if possible
		1397	my $NOW = AE::now;
129		1398
		1399	$SIG_TW = AE::timer
		1400	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1401	$MAX_SIGNAL_LATENCY,
		1402	sub { } # just for the PERL_ASYNC_CHECK
		1403	;
		1404	}
		1405	}
		1406
		1407	sub _sig_del {
		1408	undef $SIG_TW
		1409	unless --$SIG_COUNT;
		1410	}
		1411
		1412	our $_sig_name_init; $_sig_name_init = sub {
		1413	eval q{ # poor man's autoloading
		1414	undef $_sig_name_init;
		1415
		1416	if (_have_async_interrupt) {
		1417	*sig2num = \&Async::Interrupt::sig2num;
		1418	*sig2name = \&Async::Interrupt::sig2name;
		1419	} else {
		1420	require Config;
		1421
		1422	my %signame2num;
		1423	@signame2num{ split ' ', $Config::Config{sig_name} }
		1424	= split ' ', $Config::Config{sig_num};
		1425
		1426	my @signum2name;
		1427	@signum2name[values %signame2num] = keys %signame2num;
		1428
		1429	*sig2num = sub($) {
		1430	$_[0] > 0 ? shift : $signame2num{+shift}
		1431	};
		1432	*sig2name = sub ($) {
		1433	$_[0] > 0 ? $signum2name[+shift] : shift
		1434	};
		1435	}
		1436	};
		1437	die if $@;
		1438	};
		1439
		1440	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1441	sub sig2name($) { &$_sig_name_init; &sig2name }
		1442
		1443	sub signal {
		1444	eval q{ # poor man's autoloading {}
		1445	# probe for availability of Async::Interrupt
		1446	if (_have_async_interrupt) {
		1447	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1448
		1449	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1450	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1451
		1452	} else {
		1453	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1454
		1455	require Fcntl;
		1456
		1457	if (AnyEvent::WIN32) {
		1458	require AnyEvent::Util;
		1459
		1460	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1461	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1462	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1463	} else {
		1464	pipe $SIGPIPE_R, $SIGPIPE_W;
		1465	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1466	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1467
		1468	# not strictly required, as $^F is normally 2, but let's make sure...
		1469	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1470	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1471	}
		1472
		1473	$SIGPIPE_R
		1474	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1475
		1476	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1477	}
		1478
		1479	*signal = sub {
		1480	my (undef, %arg) = @_;
		1481
		1482	my $signal = uc $arg{signal}
		1483	or Carp::croak "required option 'signal' is missing";
		1484
		1485	if ($HAVE_ASYNC_INTERRUPT) {
		1486	# async::interrupt
		1487
		1488	$signal = sig2num $signal;
		1489	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1490
		1491	$SIG_ASY{$signal} ||= new Async::Interrupt
		1492	cb => sub { undef $SIG_EV{$signal} },
		1493	signal => $signal,
		1494	pipe => [$SIGPIPE_R->filenos],
		1495	pipe_autodrain => 0,
		1496	;
		1497
		1498	} else {
		1499	# pure perl
		1500
		1501	# AE::Util has been loaded in signal
		1502	$signal = sig2name $signal;
		1503	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1504
		1505	$SIG{$signal} ||= sub {
		1506	local $!;
		1507	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1508	undef $SIG_EV{$signal};
		1509	};
		1510
		1511	# can't do signal processing without introducing races in pure perl,
		1512	# so limit the signal latency.
		1513	_sig_add;
		1514	}
		1515
		1516	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1517	};
		1518
		1519	*AnyEvent::Base::signal::DESTROY = sub {
		1520	my ($signal, $cb) = @{$_[0]};
		1521
		1522	_sig_del;
		1523
		1524	delete $SIG_CB{$signal}{$cb};
		1525
		1526	$HAVE_ASYNC_INTERRUPT
		1527	? delete $SIG_ASY{$signal}
		1528	: # delete doesn't work with older perls - they then
		1529	# print weird messages, or just unconditionally exit
		1530	# instead of getting the default action.
		1531	undef $SIG{$signal}
		1532	unless keys %{ $SIG_CB{$signal} };
		1533	};
		1534	};
		1535	die if $@;
		1536	&signal
		1537	}
		1538
		1539	# default implementation for ->child
		1540
		1541	our %PID_CB;
		1542	our $CHLD_W;
		1543	our $CHLD_DELAY_W;
		1544	our $WNOHANG;
		1545
		1546	sub _emit_childstatus($$) {
		1547	my (undef, $rpid, $rstatus) = @_;
		1548
		1549	$_->($rpid, $rstatus)
		1550	for values %{ $PID_CB{$rpid} || {} },
		1551	values %{ $PID_CB{0} || {} };
		1552	}
		1553
		1554	sub _sigchld {
		1555	my $pid;
		1556
		1557	AnyEvent->_emit_childstatus ($pid, $?)
		1558	while ($pid = waitpid -1, $WNOHANG) > 0;
		1559	}
		1560
		1561	sub child {
		1562	my (undef, %arg) = @_;
		1563
		1564	defined (my $pid = $arg{pid} + 0)
		1565	or Carp::croak "required option 'pid' is missing";
		1566
		1567	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		1568
		1569	# WNOHANG is almost cetrainly 1 everywhere
		1570	$WNOHANG ||= $^O =~ /^(?:openbsd|netbsd|linux|freebsd|cygwin|MSWin32)$/
		1571	? 1
		1572	: eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
		1573
		1574	unless ($CHLD_W) {
		1575	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1576	# child could be a zombie already, so make at least one round
		1577	&_sigchld;
		1578	}
		1579
		1580	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
		1581	}
		1582
		1583	sub AnyEvent::Base::child::DESTROY {
		1584	my ($pid, $cb) = @{$_[0]};
		1585
		1586	delete $PID_CB{$pid}{$cb};
		1587	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1588
		1589	undef $CHLD_W unless keys %PID_CB;
		1590	}
		1591
		1592	# idle emulation is done by simply using a timer, regardless
		1593	# of whether the process is idle or not, and not letting
		1594	# the callback use more than 50% of the time.
		1595	sub idle {
		1596	my (undef, %arg) = @_;
		1597
		1598	my ($cb, $w, $rcb) = $arg{cb};
		1599
		1600	$rcb = sub {
		1601	if ($cb) {
		1602	$w = _time;
		1603	&$cb;
		1604	$w = _time - $w;
		1605
		1606	# never use more then 50% of the time for the idle watcher,
		1607	# within some limits
		1608	$w = 0.0001 if $w < 0.0001;
		1609	$w = 5 if $w > 5;
		1610
		1611	$w = AE::timer $w, 0, $rcb;
		1612	} else {
		1613	# clean up...
		1614	undef $w;
		1615	undef $rcb;
		1616	}
		1617	};
		1618
		1619	$w = AE::timer 0.05, 0, $rcb;
		1620
		1621	bless \\$cb, "AnyEvent::Base::idle"
		1622	}
		1623
		1624	sub AnyEvent::Base::idle::DESTROY {
		1625	undef $${$_[0]};
		1626	}
		1627
		1628	package AnyEvent::CondVar;
		1629
		1630	our @ISA = AnyEvent::CondVar::Base::;
		1631
		1632	package AnyEvent::CondVar::Base;
		1633
		1634	#use overload
		1635	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1636	# fallback => 1;
		1637
		1638	# save 300+ kilobytes by dirtily hardcoding overloading
		1639	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1640	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1641	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1642	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1643
		1644	our $WAITING;
		1645
		1646	sub _send {
		1647	# nop
		1648	}
		1649
		1650	sub send {
130	my $class = shift;	1651	my $cv = shift;
131	$class->$AUTOLOAD (@_);	1652	$cv->{_ae_sent} = [@_];
		1653	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1654	$cv->_send;
132	}	1655	}
		1656
		1657	sub croak {
		1658	$_[0]{_ae_croak} = $_[1];
		1659	$_[0]->send;
		1660	}
		1661
		1662	sub ready {
		1663	$_[0]{_ae_sent}
		1664	}
		1665
		1666	sub _wait {
		1667	$WAITING
		1668	and !$_[0]{_ae_sent}
		1669	and Carp::croak "AnyEvent::CondVar: recursive blocking wait detected";
		1670
		1671	local $WAITING = 1;
		1672	AnyEvent->one_event while !$_[0]{_ae_sent};
		1673	}
		1674
		1675	sub recv {
		1676	$_[0]->_wait;
		1677
		1678	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1679	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1680	}
		1681
		1682	sub cb {
		1683	my $cv = shift;
		1684
		1685	@_
		1686	and $cv->{_ae_cb} = shift
		1687	and $cv->{_ae_sent}
		1688	and (delete $cv->{_ae_cb})->($cv);
		1689
		1690	$cv->{_ae_cb}
		1691	}
		1692
		1693	sub begin {
		1694	++$_[0]{_ae_counter};
		1695	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1696	}
		1697
		1698	sub end {
		1699	return if --$_[0]{_ae_counter};
		1700	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1701	}
		1702
		1703	# undocumented/compatibility with pre-3.4
		1704	*broadcast = \&send;
		1705	*wait = \&_wait;
		1706
		1707	=head1 ERROR AND EXCEPTION HANDLING
		1708
		1709	In general, AnyEvent does not do any error handling - it relies on the
		1710	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1711	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1712	checking of all AnyEvent methods, however, which is highly useful during
		1713	development.
		1714
		1715	As for exception handling (i.e. runtime errors and exceptions thrown while
		1716	executing a callback), this is not only highly event-loop specific, but
		1717	also not in any way wrapped by this module, as this is the job of the main
		1718	program.
		1719
		1720	The pure perl event loop simply re-throws the exception (usually
		1721	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1722	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1723	so on.
		1724
		1725	=head1 ENVIRONMENT VARIABLES
		1726
		1727	The following environment variables are used by this module or its
		1728	submodules.
		1729
		1730	Note that AnyEvent will remove I<all> environment variables starting with
		1731	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1732	enabled.
		1733
		1734	=over 4
		1735
		1736	=item C<PERL_ANYEVENT_VERBOSE>
		1737
		1738	By default, AnyEvent will be completely silent except in fatal
		1739	conditions. You can set this environment variable to make AnyEvent more
		1740	talkative.
		1741
		1742	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1743	conditions, such as not being able to load the event model specified by
		1744	C<PERL_ANYEVENT_MODEL>.
		1745
		1746	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1747	model it chooses.
		1748
		1749	When set to C<8> or higher, then AnyEvent will report extra information on
		1750	which optional modules it loads and how it implements certain features.
		1751
		1752	=item C<PERL_ANYEVENT_STRICT>
		1753
		1754	AnyEvent does not do much argument checking by default, as thorough
		1755	argument checking is very costly. Setting this variable to a true value
		1756	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1757	check the arguments passed to most method calls. If it finds any problems,
		1758	it will croak.
		1759
		1760	In other words, enables "strict" mode.
		1761
		1762	Unlike C<use strict> (or it's modern cousin, C<< use L<common::sense>
		1763	>>, it is definitely recommended to keep it off in production. Keeping
		1764	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1765	can be very useful, however.
		1766
		1767	=item C<PERL_ANYEVENT_MODEL>
		1768
		1769	This can be used to specify the event model to be used by AnyEvent, before
		1770	auto detection and -probing kicks in. It must be a string consisting
		1771	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1772	and the resulting module name is loaded and if the load was successful,
		1773	used as event model. If it fails to load AnyEvent will proceed with
		1774	auto detection and -probing.
		1775
		1776	This functionality might change in future versions.
		1777
		1778	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1779	could start your program like this:
		1780
		1781	PERL_ANYEVENT_MODEL=Perl perl ...
		1782
		1783	=item C<PERL_ANYEVENT_PROTOCOLS>
		1784
		1785	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1786	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1787	of auto probing).
		1788
		1789	Must be set to a comma-separated list of protocols or address families,
		1790	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1791	used, and preference will be given to protocols mentioned earlier in the
		1792	list.
		1793
		1794	This variable can effectively be used for denial-of-service attacks
		1795	against local programs (e.g. when setuid), although the impact is likely
		1796	small, as the program has to handle conenction and other failures anyways.
		1797
		1798	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1799	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1800	- only support IPv4, never try to resolve or contact IPv6
		1801	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1802	IPv6, but prefer IPv6 over IPv4.
		1803
		1804	=item C<PERL_ANYEVENT_EDNS0>
		1805
		1806	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1807	for DNS. This extension is generally useful to reduce DNS traffic, but
		1808	some (broken) firewalls drop such DNS packets, which is why it is off by
		1809	default.
		1810
		1811	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1812	EDNS0 in its DNS requests.
		1813
		1814	=item C<PERL_ANYEVENT_MAX_FORKS>
		1815
		1816	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1817	will create in parallel.
		1818
		1819	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1820
		1821	The default value for the C<max_outstanding> parameter for the default DNS
		1822	resolver - this is the maximum number of parallel DNS requests that are
		1823	sent to the DNS server.
		1824
		1825	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1826
		1827	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1828	configuration) in the default resolver. When set to the empty string, no
		1829	default config will be used.
		1830
		1831	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1832
		1833	When neither C<ca_file> nor C<ca_path> was specified during
		1834	L<AnyEvent::TLS> context creation, and either of these environment
		1835	variables exist, they will be used to specify CA certificate locations
		1836	instead of a system-dependent default.
		1837
		1838	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		1839
		1840	When these are set to C<1>, then the respective modules are not
		1841	loaded. Mostly good for testing AnyEvent itself.
133		1842
134	=back	1843	=back
135		1844
136	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1845	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1846
		1847	This is an advanced topic that you do not normally need to use AnyEvent in
		1848	a module. This section is only of use to event loop authors who want to
		1849	provide AnyEvent compatibility.
137		1850
138	If you need to support another event library which isn't directly	1851	If you need to support another event library which isn't directly
139	supported by AnyEvent, you can supply your own interface to it by	1852	supported by AnyEvent, you can supply your own interface to it by
140	pushing, before the first watch gets created, the package name of	1853	pushing, before the first watcher gets created, the package name of
141	the event module and the package name of the interface to use onto	1854	the event module and the package name of the interface to use onto
142	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	1855	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
143	AnyEvent.	1856	AnyEvent, so it is reasonably cheap.
144		1857
145	Example:	1858	Example:
146		1859
147	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1860	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
148		1861
149	This tells AnyEvent to (literally) use the C<urxvt::anyevent::> module	1862	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
150	when it finds the C<urxvt> module is loaded. When AnyEvent is loaded and	1863	package/class when it finds the C<urxvt> package/module is already loaded.
151	requested to find a suitable event model, it will first check for the
152	urxvt module.
153		1864
		1865	When AnyEvent is loaded and asked to find a suitable event model, it
		1866	will first check for the presence of urxvt by trying to C<use> the
		1867	C<urxvt::anyevent> module.
		1868
		1869	The class should provide implementations for all watcher types. See
		1870	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1871	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1872	see the sources.
		1873
		1874	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1875	provide suitable (hopefully) replacements.
		1876
154	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt) uses	1877	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
155	the above line exactly. An interface isn't included in AnyEvent	1878	terminal emulator uses the above line as-is. An interface isn't included
156	because it doesn't make sense outside the embedded interpreter inside	1879	in AnyEvent because it doesn't make sense outside the embedded interpreter
157	I<rxvt-unicode>, and it is updated and maintained as part of the	1880	inside I<rxvt-unicode>, and it is updated and maintained as part of the
158	I<rxvt-unicode> distribution.	1881	I<rxvt-unicode> distribution.
159		1882
160	=head1 ENVIRONMENT VARIABLES	1883	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1884	condition variables: code blocking while waiting for a condition will
		1885	C<die>. This still works with most modules/usages, and blocking calls must
		1886	not be done in an interactive application, so it makes sense.
161		1887
162	The following environment variables are used by this module:
163
164	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
165	model gets used.
166
167	=head1 EXAMPLE	1888	=head1 EXAMPLE PROGRAM
168		1889
169	The following program uses an io watcher to read data from stdin, a timer	1890	The following program uses an I/O watcher to read data from STDIN, a timer
170	to display a message once per second, and a condvar to exit the program	1891	to display a message once per second, and a condition variable to quit the
171	when the user enters quit:	1892	program when the user enters quit:
172		1893
173	use AnyEvent;	1894	use AnyEvent;
174		1895
175	my $cv = AnyEvent->condvar;	1896	my $cv = AnyEvent->condvar;
176		1897
177	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1898	my $io_watcher = AnyEvent->io (
		1899	fh => \*STDIN,
		1900	poll => 'r',
		1901	cb => sub {
178	warn "io event <$_[0]>\n"; # will always output <r>	1902	warn "io event <$_[0]>\n"; # will always output <r>
179	chomp (my $input = <STDIN>); # read a line	1903	chomp (my $input = <STDIN>); # read a line
180	warn "read: $input\n"; # output what has been read	1904	warn "read: $input\n"; # output what has been read
181	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1905	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1906	},
182	});	1907	);
183		1908
184	my $time_watcher; # can only be used once	1909	my $time_watcher; # can only be used once
185		1910
186	sub new_timer {	1911	sub new_timer {
187	$timer = AnyEvent->timer (after => 1, cb => sub {	1912	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
190	});	1915	});
191	}	1916	}
192		1917
193	new_timer; # create first timer	1918	new_timer; # create first timer
194		1919
195	$cv->wait; # wait until user enters /^q/i	1920	$cv->recv; # wait until user enters /^q/i
196		1921
197	=head1 REAL-WORLD EXAMPLE	1922	=head1 REAL-WORLD EXAMPLE
198		1923
199	Consider the L<Net::FCP> module. It features (among others) the following	1924	Consider the L<Net::FCP> module. It features (among others) the following
200	API calls, which are to freenet what HTTP GET requests are to http:	1925	API calls, which are to freenet what HTTP GET requests are to http:
…		…
250	syswrite $txn->{fh}, $txn->{request}	1975	syswrite $txn->{fh}, $txn->{request}
251	or die "connection or write error";	1976	or die "connection or write error";
252	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1977	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
253		1978
254	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1979	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
255	result and signals any possible waiters that the request ahs finished:	1980	result and signals any possible waiters that the request has finished:
256		1981
257	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1982	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
258		1983
259	if (end-of-file or data complete) {	1984	if (end-of-file or data complete) {
260	$txn->{result} = $txn->{buf};	1985	$txn->{result} = $txn->{buf};
261	$txn->{finished}->broadcast;	1986	$txn->{finished}->send;
262	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1987	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
263	}	1988	}
264		1989
265	The C<result> method, finally, just waits for the finished signal (if the	1990	The C<result> method, finally, just waits for the finished signal (if the
266	request was already finished, it doesn't wait, of course, and returns the	1991	request was already finished, it doesn't wait, of course, and returns the
267	data:	1992	data:
268		1993
269	$txn->{finished}->wait;	1994	$txn->{finished}->recv;
270	return $txn->{result};	1995	return $txn->{result};
271		1996
272	The actual code goes further and collects all errors (C<die>s, exceptions)	1997	The actual code goes further and collects all errors (C<die>s, exceptions)
273	that occured during request processing. The C<result> method detects	1998	that occurred during request processing. The C<result> method detects
274	wether an exception as thrown (it is stored inside the $txn object)	1999	whether an exception as thrown (it is stored inside the $txn object)
275	and just throws the exception, which means connection errors and other	2000	and just throws the exception, which means connection errors and other
276	problems get reported tot he code that tries to use the result, not in a	2001	problems get reported tot he code that tries to use the result, not in a
277	random callback.	2002	random callback.
278		2003
279	All of this enables the following usage styles:	2004	All of this enables the following usage styles:
280		2005
281	1. Blocking:	2006	1. Blocking:
282		2007
283	my $data = $fcp->client_get ($url);	2008	my $data = $fcp->client_get ($url);
284		2009
285	2. Blocking, but parallelizing:	2010	2. Blocking, but running in parallel:
286		2011
287	my @datas = map $_->result,	2012	my @datas = map $_->result,
288	map $fcp->txn_client_get ($_),	2013	map $fcp->txn_client_get ($_),
289	@urls;	2014	@urls;
290		2015
291	Both blocking examples work without the module user having to know	2016	Both blocking examples work without the module user having to know
292	anything about events.	2017	anything about events.
293		2018
294	3a. Event-based in a main program, using any support Event module:	2019	3a. Event-based in a main program, using any supported event module:
295		2020
296	use Event;	2021	use EV;
297		2022
298	$fcp->txn_client_get ($url)->cb (sub {	2023	$fcp->txn_client_get ($url)->cb (sub {
299	my $txn = shift;	2024	my $txn = shift;
300	my $data = $txn->result;	2025	my $data = $txn->result;
301	...	2026	...
302	});	2027	});
303		2028
304	Event::loop;	2029	EV::loop;
305		2030
306	3b. The module user could use AnyEvent, too:	2031	3b. The module user could use AnyEvent, too:
307		2032
308	use AnyEvent;	2033	use AnyEvent;
309		2034
310	my $quit = AnyEvent->condvar;	2035	my $quit = AnyEvent->condvar;
311		2036
312	$fcp->txn_client_get ($url)->cb (sub {	2037	$fcp->txn_client_get ($url)->cb (sub {
313	...	2038	...
314	$quit->broadcast;	2039	$quit->send;
315	});	2040	});
316		2041
317	$quit->wait;	2042	$quit->recv;
		2043
		2044
		2045	=head1 BENCHMARKS
		2046
		2047	To give you an idea of the performance and overheads that AnyEvent adds
		2048	over the event loops themselves and to give you an impression of the speed
		2049	of various event loops I prepared some benchmarks.
		2050
		2051	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2052
		2053	Here is a benchmark of various supported event models used natively and
		2054	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2055	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2056	which it is), lets them fire exactly once and destroys them again.
		2057
		2058	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2059	distribution.
		2060
		2061	=head3 Explanation of the columns
		2062
		2063	I<watcher> is the number of event watchers created/destroyed. Since
		2064	different event models feature vastly different performances, each event
		2065	loop was given a number of watchers so that overall runtime is acceptable
		2066	and similar between tested event loop (and keep them from crashing): Glib
		2067	would probably take thousands of years if asked to process the same number
		2068	of watchers as EV in this benchmark.
		2069
		2070	I<bytes> is the number of bytes (as measured by the resident set size,
		2071	RSS) consumed by each watcher. This method of measuring captures both C
		2072	and Perl-based overheads.
		2073
		2074	I<create> is the time, in microseconds (millionths of seconds), that it
		2075	takes to create a single watcher. The callback is a closure shared between
		2076	all watchers, to avoid adding memory overhead. That means closure creation
		2077	and memory usage is not included in the figures.
		2078
		2079	I<invoke> is the time, in microseconds, used to invoke a simple
		2080	callback. The callback simply counts down a Perl variable and after it was
		2081	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2082	signal the end of this phase.
		2083
		2084	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2085	watcher.
		2086
		2087	=head3 Results
		2088
		2089	name watchers bytes create invoke destroy comment
		2090	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		2091	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		2092	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		2093	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		2094	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		2095	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		2096	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		2097	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
		2098	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		2099	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		2100	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		2101	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		2102
		2103	=head3 Discussion
		2104
		2105	The benchmark does I<not> measure scalability of the event loop very
		2106	well. For example, a select-based event loop (such as the pure perl one)
		2107	can never compete with an event loop that uses epoll when the number of
		2108	file descriptors grows high. In this benchmark, all events become ready at
		2109	the same time, so select/poll-based implementations get an unnatural speed
		2110	boost.
		2111
		2112	Also, note that the number of watchers usually has a nonlinear effect on
		2113	overall speed, that is, creating twice as many watchers doesn't take twice
		2114	the time - usually it takes longer. This puts event loops tested with a
		2115	higher number of watchers at a disadvantage.
		2116
		2117	To put the range of results into perspective, consider that on the
		2118	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2119	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2120	cycles with POE.
		2121
		2122	C<EV> is the sole leader regarding speed and memory use, which are both
		2123	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		2124	far less memory than any other event loop and is still faster than Event
		2125	natively.
		2126
		2127	The pure perl implementation is hit in a few sweet spots (both the
		2128	constant timeout and the use of a single fd hit optimisations in the perl
		2129	interpreter and the backend itself). Nevertheless this shows that it
		2130	adds very little overhead in itself. Like any select-based backend its
		2131	performance becomes really bad with lots of file descriptors (and few of
		2132	them active), of course, but this was not subject of this benchmark.
		2133
		2134	The C<Event> module has a relatively high setup and callback invocation
		2135	cost, but overall scores in on the third place.
		2136
		2137	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2138	when using its pure perl backend.
		2139
		2140	C<Glib>'s memory usage is quite a bit higher, but it features a
		2141	faster callback invocation and overall ends up in the same class as
		2142	C<Event>. However, Glib scales extremely badly, doubling the number of
		2143	watchers increases the processing time by more than a factor of four,
		2144	making it completely unusable when using larger numbers of watchers
		2145	(note that only a single file descriptor was used in the benchmark, so
		2146	inefficiencies of C<poll> do not account for this).
		2147
		2148	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2149	more than 2000 watchers is a big setback, however, as correctness takes
		2150	precedence over speed. Nevertheless, its performance is surprising, as the
		2151	file descriptor is dup()ed for each watcher. This shows that the dup()
		2152	employed by some adaptors is not a big performance issue (it does incur a
		2153	hidden memory cost inside the kernel which is not reflected in the figures
		2154	above).
		2155
		2156	C<POE>, regardless of underlying event loop (whether using its pure perl
		2157	select-based backend or the Event module, the POE-EV backend couldn't
		2158	be tested because it wasn't working) shows abysmal performance and
		2159	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2160	as EV watchers, and 10 times as much memory as Event (the high memory
		2161	requirements are caused by requiring a session for each watcher). Watcher
		2162	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2163	implementation.
		2164
		2165	The design of the POE adaptor class in AnyEvent can not really account
		2166	for the performance issues, though, as session creation overhead is
		2167	small compared to execution of the state machine, which is coded pretty
		2168	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2169	using multiple sessions is not a good approach, especially regarding
		2170	memory usage, even the author of POE could not come up with a faster
		2171	design).
		2172
		2173	=head3 Summary
		2174
		2175	=over 4
		2176
		2177	=item * Using EV through AnyEvent is faster than any other event loop
		2178	(even when used without AnyEvent), but most event loops have acceptable
		2179	performance with or without AnyEvent.
		2180
		2181	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2182	the actual event loop, only with extremely fast event loops such as EV
		2183	adds AnyEvent significant overhead.
		2184
		2185	=item * You should avoid POE like the plague if you want performance or
		2186	reasonable memory usage.
		2187
		2188	=back
		2189
		2190	=head2 BENCHMARKING THE LARGE SERVER CASE
		2191
		2192	This benchmark actually benchmarks the event loop itself. It works by
		2193	creating a number of "servers": each server consists of a socket pair, a
		2194	timeout watcher that gets reset on activity (but never fires), and an I/O
		2195	watcher waiting for input on one side of the socket. Each time the socket
		2196	watcher reads a byte it will write that byte to a random other "server".
		2197
		2198	The effect is that there will be a lot of I/O watchers, only part of which
		2199	are active at any one point (so there is a constant number of active
		2200	fds for each loop iteration, but which fds these are is random). The
		2201	timeout is reset each time something is read because that reflects how
		2202	most timeouts work (and puts extra pressure on the event loops).
		2203
		2204	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2205	(1%) are active. This mirrors the activity of large servers with many
		2206	connections, most of which are idle at any one point in time.
		2207
		2208	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2209	distribution.
		2210
		2211	=head3 Explanation of the columns
		2212
		2213	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2214	each server has a read and write socket end).
		2215
		2216	I<create> is the time it takes to create a socket pair (which is
		2217	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2218
		2219	I<request>, the most important value, is the time it takes to handle a
		2220	single "request", that is, reading the token from the pipe and forwarding
		2221	it to another server. This includes deleting the old timeout and creating
		2222	a new one that moves the timeout into the future.
		2223
		2224	=head3 Results
		2225
		2226	name sockets create request
		2227	EV 20000 69.01 11.16
		2228	Perl 20000 73.32 35.87
		2229	IOAsync 20000 157.00 98.14 epoll
		2230	IOAsync 20000 159.31 616.06 poll
		2231	Event 20000 212.62 257.32
		2232	Glib 20000 651.16 1896.30
		2233	POE 20000 349.67 12317.24 uses POE::Loop::Event
		2234
		2235	=head3 Discussion
		2236
		2237	This benchmark I<does> measure scalability and overall performance of the
		2238	particular event loop.
		2239
		2240	EV is again fastest. Since it is using epoll on my system, the setup time
		2241	is relatively high, though.
		2242
		2243	Perl surprisingly comes second. It is much faster than the C-based event
		2244	loops Event and Glib.
		2245
		2246	IO::Async performs very well when using its epoll backend, and still quite
		2247	good compared to Glib when using its pure perl backend.
		2248
		2249	Event suffers from high setup time as well (look at its code and you will
		2250	understand why). Callback invocation also has a high overhead compared to
		2251	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2252	uses select or poll in basically all documented configurations.
		2253
		2254	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2255	clearly fails to perform with many filehandles or in busy servers.
		2256
		2257	POE is still completely out of the picture, taking over 1000 times as long
		2258	as EV, and over 100 times as long as the Perl implementation, even though
		2259	it uses a C-based event loop in this case.
		2260
		2261	=head3 Summary
		2262
		2263	=over 4
		2264
		2265	=item * The pure perl implementation performs extremely well.
		2266
		2267	=item * Avoid Glib or POE in large projects where performance matters.
		2268
		2269	=back
		2270
		2271	=head2 BENCHMARKING SMALL SERVERS
		2272
		2273	While event loops should scale (and select-based ones do not...) even to
		2274	large servers, most programs we (or I :) actually write have only a few
		2275	I/O watchers.
		2276
		2277	In this benchmark, I use the same benchmark program as in the large server
		2278	case, but it uses only eight "servers", of which three are active at any
		2279	one time. This should reflect performance for a small server relatively
		2280	well.
		2281
		2282	The columns are identical to the previous table.
		2283
		2284	=head3 Results
		2285
		2286	name sockets create request
		2287	EV 16 20.00 6.54
		2288	Perl 16 25.75 12.62
		2289	Event 16 81.27 35.86
		2290	Glib 16 32.63 15.48
		2291	POE 16 261.87 276.28 uses POE::Loop::Event
		2292
		2293	=head3 Discussion
		2294
		2295	The benchmark tries to test the performance of a typical small
		2296	server. While knowing how various event loops perform is interesting, keep
		2297	in mind that their overhead in this case is usually not as important, due
		2298	to the small absolute number of watchers (that is, you need efficiency and
		2299	speed most when you have lots of watchers, not when you only have a few of
		2300	them).
		2301
		2302	EV is again fastest.
		2303
		2304	Perl again comes second. It is noticeably faster than the C-based event
		2305	loops Event and Glib, although the difference is too small to really
		2306	matter.
		2307
		2308	POE also performs much better in this case, but is is still far behind the
		2309	others.
		2310
		2311	=head3 Summary
		2312
		2313	=over 4
		2314
		2315	=item * C-based event loops perform very well with small number of
		2316	watchers, as the management overhead dominates.
		2317
		2318	=back
		2319
		2320	=head2 THE IO::Lambda BENCHMARK
		2321
		2322	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2323	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2324	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2325	shouldn't come as a surprise to anybody). As such, the benchmark is
		2326	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2327	very optimal. But how would AnyEvent compare when used without the extra
		2328	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2329
		2330	The benchmark itself creates an echo-server, and then, for 500 times,
		2331	connects to the echo server, sends a line, waits for the reply, and then
		2332	creates the next connection. This is a rather bad benchmark, as it doesn't
		2333	test the efficiency of the framework or much non-blocking I/O, but it is a
		2334	benchmark nevertheless.
		2335
		2336	name runtime
		2337	Lambda/select 0.330 sec
		2338	+ optimized 0.122 sec
		2339	Lambda/AnyEvent 0.327 sec
		2340	+ optimized 0.138 sec
		2341	Raw sockets/select 0.077 sec
		2342	POE/select, components 0.662 sec
		2343	POE/select, raw sockets 0.226 sec
		2344	POE/select, optimized 0.404 sec
		2345
		2346	AnyEvent/select/nb 0.085 sec
		2347	AnyEvent/EV/nb 0.068 sec
		2348	+state machine 0.134 sec
		2349
		2350	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2351	benchmarks actually make blocking connects and use 100% blocking I/O,
		2352	defeating the purpose of an event-based solution. All of the newly
		2353	written AnyEvent benchmarks use 100% non-blocking connects (using
		2354	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2355	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2356	generally require a lot more bookkeeping and event handling than blocking
		2357	connects (which involve a single syscall only).
		2358
		2359	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2360	offers similar expressive power as POE and IO::Lambda, using conventional
		2361	Perl syntax. This means that both the echo server and the client are 100%
		2362	non-blocking, further placing it at a disadvantage.
		2363
		2364	As you can see, the AnyEvent + EV combination even beats the
		2365	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2366	backend easily beats IO::Lambda and POE.
		2367
		2368	And even the 100% non-blocking version written using the high-level (and
		2369	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
		2370	large margin, even though it does all of DNS, tcp-connect and socket I/O
		2371	in a non-blocking way.
		2372
		2373	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2374	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2375	part of the IO::lambda distribution and were used without any changes.
		2376
		2377
		2378	=head1 SIGNALS
		2379
		2380	AnyEvent currently installs handlers for these signals:
		2381
		2382	=over 4
		2383
		2384	=item SIGCHLD
		2385
		2386	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2387	emulation for event loops that do not support them natively. Also, some
		2388	event loops install a similar handler.
		2389
		2390	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2391	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2392
		2393	=item SIGPIPE
		2394
		2395	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2396	when AnyEvent gets loaded.
		2397
		2398	The rationale for this is that AnyEvent users usually do not really depend
		2399	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2400	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2401	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2402	some random socket.
		2403
		2404	The rationale for installing a no-op handler as opposed to ignoring it is
		2405	that this way, the handler will be restored to defaults on exec.
		2406
		2407	Feel free to install your own handler, or reset it to defaults.
		2408
		2409	=back
		2410
		2411	=cut
		2412
		2413	undef $SIG{CHLD}
		2414	if $SIG{CHLD} eq 'IGNORE';
		2415
		2416	$SIG{PIPE} = sub { }
		2417	unless defined $SIG{PIPE};
		2418
		2419	=head1 RECOMMENDED/OPTIONAL MODULES
		2420
		2421	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2422	it's built-in modules) are required to use it.
		2423
		2424	That does not mean that AnyEvent won't take advantage of some additional
		2425	modules if they are installed.
		2426
		2427	This section epxlains which additional modules will be used, and how they
		2428	affect AnyEvent's operetion.
		2429
		2430	=over 4
		2431
		2432	=item L<Async::Interrupt>
		2433
		2434	This slightly arcane module is used to implement fast signal handling: To
		2435	my knowledge, there is no way to do completely race-free and quick
		2436	signal handling in pure perl. To ensure that signals still get
		2437	delivered, AnyEvent will start an interval timer to wake up perl (and
		2438	catch the signals) with some delay (default is 10 seconds, look for
		2439	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2440
		2441	If this module is available, then it will be used to implement signal
		2442	catching, which means that signals will not be delayed, and the event loop
		2443	will not be interrupted regularly, which is more efficient (And good for
		2444	battery life on laptops).
		2445
		2446	This affects not just the pure-perl event loop, but also other event loops
		2447	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2448
		2449	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2450	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2451	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2452	does nothing for those backends.
		2453
		2454	=item L<EV>
		2455
		2456	This module isn't really "optional", as it is simply one of the backend
		2457	event loops that AnyEvent can use. However, it is simply the best event
		2458	loop available in terms of features, speed and stability: It supports
		2459	the AnyEvent API optimally, implements all the watcher types in XS, does
		2460	automatic timer adjustments even when no monotonic clock is available,
		2461	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2462	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2463	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2464
		2465	=item L<Guard>
		2466
		2467	The guard module, when used, will be used to implement
		2468	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2469	lot less memory), but otherwise doesn't affect guard operation much. It is
		2470	purely used for performance.
		2471
		2472	=item L<JSON> and L<JSON::XS>
		2473
		2474	This module is required when you want to read or write JSON data via
		2475	L<AnyEvent::Handle>. It is also written in pure-perl, but can take
		2476	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2477
		2478	In fact, L<AnyEvent::Handle> will use L<JSON::XS> by default if it is
		2479	installed.
		2480
		2481	=item L<Net::SSLeay>
		2482
		2483	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2484	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2485	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2486
		2487	=item L<Time::HiRes>
		2488
		2489	This module is part of perl since release 5.008. It will be used when the
		2490	chosen event library does not come with a timing source on it's own. The
		2491	pure-perl event loop (L<AnyEvent::Impl::Perl>) will additionally use it to
		2492	try to use a monotonic clock for timing stability.
		2493
		2494	=back
		2495
		2496
		2497	=head1 FORK
		2498
		2499	Most event libraries are not fork-safe. The ones who are usually are
		2500	because they rely on inefficient but fork-safe C<select> or C<poll>
		2501	calls. Only L<EV> is fully fork-aware.
		2502
		2503	If you have to fork, you must either do so I<before> creating your first
		2504	watcher OR you must not use AnyEvent at all in the child OR you must do
		2505	something completely out of the scope of AnyEvent.
		2506
		2507
		2508	=head1 SECURITY CONSIDERATIONS
		2509
		2510	AnyEvent can be forced to load any event model via
		2511	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2512	execute arbitrary code or directly gain access, it can easily be used to
		2513	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2514	will not be active when the program uses a different event model than
		2515	specified in the variable.
		2516
		2517	You can make AnyEvent completely ignore this variable by deleting it
		2518	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2519
		2520	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2521
		2522	use AnyEvent;
		2523
		2524	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2525	be used to probe what backend is used and gain other information (which is
		2526	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2527	$ENV{PERL_ANYEVENT_STRICT}.
		2528
		2529	Note that AnyEvent will remove I<all> environment variables starting with
		2530	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2531	enabled.
		2532
		2533
		2534	=head1 BUGS
		2535
		2536	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2537	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2538	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2539	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2540	pronounced).
		2541
318		2542
319	=head1 SEE ALSO	2543	=head1 SEE ALSO
320		2544
321	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	2545	Utility functions: L<AnyEvent::Util>.
322		2546
323	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	2547	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		2548	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
324		2549
325	Nontrivial usage example: L<Net::FCP>.	2550	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2551	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2552	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2553	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
326		2554
327	=head1	2555	Non-blocking file handles, sockets, TCP clients and
		2556	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2557
		2558	Asynchronous DNS: L<AnyEvent::DNS>.
		2559
		2560	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>,
		2561	L<Coro::Event>,
		2562
		2563	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::XMPP>,
		2564	L<AnyEvent::HTTP>.
		2565
		2566
		2567	=head1 AUTHOR
		2568
		2569	Marc Lehmann <schmorp@schmorp.de>
		2570	http://home.schmorp.de/
328		2571
329	=cut	2572	=cut
330		2573
331	1	2574	1
332		2575

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