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Revision 1.37 by root, Fri Nov 23 10:42:00 2007 UTC vs.
Revision 1.226 by root, Mon Jul 6 23:32:49 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	Event, Coro, Glib, Tk, Perl - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
		6	event loops.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# file descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	13	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		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) = @_;
12	...	28	...
13	});	29	});
14		30
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	31	# called when event loop idle (if applicable)
16	...	32	my $w = AnyEvent->idle (cb => sub { ... });
17	});
18		33
19	my $w = AnyEvent->condvar; # stores wether a condition was flagged	34	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		35	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	36	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	37	# use a condvar in callback mode:
		38	$w->cb (sub { $_[0]->recv });
		39
		40	=head1 INTRODUCTION/TUTORIAL
		41
		42	This manpage is mainly a reference manual. If you are interested
		43	in a tutorial or some gentle introduction, have a look at the
		44	L<AnyEvent::Intro> manpage.
		45
		46	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		47
		48	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		49	nowadays. So what is different about AnyEvent?
		50
		51	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		52	policy> and AnyEvent is I<small and efficient>.
		53
		54	First and foremost, I<AnyEvent is not an event model> itself, it only
		55	interfaces to whatever event model the main program happens to use, in a
		56	pragmatic way. For event models and certain classes of immortals alike,
		57	the statement "there can only be one" is a bitter reality: In general,
		58	only one event loop can be active at the same time in a process. AnyEvent
		59	cannot change this, but it can hide the differences between those event
		60	loops.
		61
		62	The goal of AnyEvent is to offer module authors the ability to do event
		63	programming (waiting for I/O or timer events) without subscribing to a
		64	religion, a way of living, and most importantly: without forcing your
		65	module users into the same thing by forcing them to use the same event
		66	model you use.
		67
		68	For modules like POE or IO::Async (which is a total misnomer as it is
		69	actually doing all I/O I<synchronously>...), using them in your module is
		70	like joining a cult: After you joined, you are dependent on them and you
		71	cannot use anything else, as they are simply incompatible to everything
		72	that isn't them. What's worse, all the potential users of your
		73	module are I<also> forced to use the same event loop you use.
		74
		75	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		76	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		77	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		78	your module uses one of those, every user of your module has to use it,
		79	too. But if your module uses AnyEvent, it works transparently with all
		80	event models it supports (including stuff like IO::Async, as long as those
		81	use one of the supported event loops. It is trivial to add new event loops
		82	to AnyEvent, too, so it is future-proof).
		83
		84	In addition to being free of having to use I<the one and only true event
		85	model>, AnyEvent also is free of bloat and policy: with POE or similar
		86	modules, you get an enormous amount of code and strict rules you have to
		87	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		88	offering the functionality that is necessary, in as thin as a wrapper as
		89	technically possible.
		90
		91	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		92	of useful functionality, such as an asynchronous DNS resolver, 100%
		93	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		94	such as Windows) and lots of real-world knowledge and workarounds for
		95	platform bugs and differences.
		96
		97	Now, if you I<do want> lots of policy (this can arguably be somewhat
		98	useful) and you want to force your users to use the one and only event
		99	model, you should I<not> use this module.
22		100
23	=head1 DESCRIPTION	101	=head1 DESCRIPTION
24		102
25	L<AnyEvent> provides an identical interface to multiple event loops. This	103	L<AnyEvent> provides an identical interface to multiple event loops. This
26	allows module authors to utilise an event loop without forcing module	104	allows module authors to utilise an event loop without forcing module
27	users to use the same event loop (as only a single event loop can coexist	105	users to use the same event loop (as only a single event loop can coexist
28	peacefully at any one time).	106	peacefully at any one time).
29		107
30	The interface itself is vaguely similar but not identical to the Event	108	The interface itself is vaguely similar, but not identical to the L<Event>
31	module.	109	module.
32		110
33	On the first call of any method, the module tries to detect the currently	111	During the first call of any watcher-creation method, the module tries
34	loaded event loop by probing wether any of the following modules is	112	to detect the currently loaded event loop by probing whether one of the
35	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	113	following modules is already loaded: L<EV>,
36	used. If none is found, the module tries to load these modules in the	114	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
37	order given. The first one that could be successfully loaded will be	115	L<POE>. The first one found is used. If none are found, the module tries
38	used. If still none could be found, AnyEvent will fall back to a pure-perl	116	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
39	event loop, which is also not very efficient.	117	adaptor should always succeed) in the order given. The first one that can
		118	be successfully loaded will be used. If, after this, still none could be
		119	found, AnyEvent will fall back to a pure-perl event loop, which is not
		120	very efficient, but should work everywhere.
40		121
41	Because AnyEvent first checks for modules that are already loaded, loading	122	Because AnyEvent first checks for modules that are already loaded, loading
42	an Event model explicitly before first using AnyEvent will likely make	123	an event model explicitly before first using AnyEvent will likely make
43	that model the default. For example:	124	that model the default. For example:
44		125
45	use Tk;	126	use Tk;
46	use AnyEvent;	127	use AnyEvent;
47		128
48	# .. AnyEvent will likely default to Tk	129	# .. AnyEvent will likely default to Tk
49		130
		131	The I<likely> means that, if any module loads another event model and
		132	starts using it, all bets are off. Maybe you should tell their authors to
		133	use AnyEvent so their modules work together with others seamlessly...
		134
50	The pure-perl implementation of AnyEvent is called	135	The pure-perl implementation of AnyEvent is called
51	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	136	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
52	explicitly.	137	explicitly and enjoy the high availability of that event loop :)
53		138
54	=head1 WATCHERS	139	=head1 WATCHERS
55		140
56	AnyEvent has the central concept of a I<watcher>, which is an object that	141	AnyEvent has the central concept of a I<watcher>, which is an object that
57	stores relevant data for each kind of event you are waiting for, such as	142	stores relevant data for each kind of event you are waiting for, such as
58	the callback to call, the filehandle to watch, etc.	143	the callback to call, the file handle to watch, etc.
59		144
60	These watchers are normal Perl objects with normal Perl lifetime. After	145	These watchers are normal Perl objects with normal Perl lifetime. After
61	creating a watcher it will immediately "watch" for events and invoke	146	creating a watcher it will immediately "watch" for events and invoke the
		147	callback when the event occurs (of course, only when the event model
		148	is in control).
		149
		150	Note that B<callbacks must not permanently change global variables>
		151	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		152	callbacks must not C<die> >>. The former is good programming practise in
		153	Perl and the latter stems from the fact that exception handling differs
		154	widely between event loops.
		155
62	the callback. To disable the watcher you have to destroy it (e.g. by	156	To disable the watcher you have to destroy it (e.g. by setting the
63	setting the variable that stores it to C<undef> or otherwise deleting all	157	variable you store it in to C<undef> or otherwise deleting all references
64	references to it).	158	to it).
65		159
66	All watchers are created by calling a method on the C<AnyEvent> class.	160	All watchers are created by calling a method on the C<AnyEvent> class.
67		161
		162	Many watchers either are used with "recursion" (repeating timers for
		163	example), or need to refer to their watcher object in other ways.
		164
		165	An any way to achieve that is this pattern:
		166
		167	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		168	# you can use $w here, for example to undef it
		169	undef $w;
		170	});
		171
		172	Note that C<my $w; $w => combination. This is necessary because in Perl,
		173	my variables are only visible after the statement in which they are
		174	declared.
		175
68	=head2 IO WATCHERS	176	=head2 I/O WATCHERS
69		177
70	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	178	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
71	the following mandatory arguments:	179	with the following mandatory key-value pairs as arguments:
72		180
73	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	181	C<fh> is the Perl I<file handle> (I<not> file descriptor) to watch
		182	for events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example files
		186	or block devices.
		187
74	events. C<poll> must be a string that is either C<r> or C<w>, that creates	188	C<poll> must be a string that is either C<r> or C<w>, which creates a
75	a watcher waiting for "r"eadable or "w"ritable events. C<cb> the callback	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
76	to invoke everytime the filehandle becomes ready.
77		190
78	Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on	191	C<cb> is the callback to invoke each time the file handle becomes ready.
79	a socket you can have one r + one w, not any more (limitation comes from
80	Tk - if you are sure you are not using Tk this limitation is gone).
81		192
82	Filehandles will be kept alive, so as long as the watcher exists, the	193	Although the callback might get passed parameters, their value and
83	filehandle exists, too.	194	presence is undefined and you cannot rely on them. Portable AnyEvent
		195	callbacks cannot use arguments passed to I/O watcher callbacks.
84		196
85	Example:	197	The I/O watcher might use the underlying file descriptor or a copy of it.
		198	You must not close a file handle as long as any watcher is active on the
		199	underlying file descriptor.
86		200
		201	Some event loops issue spurious readyness notifications, so you should
		202	always use non-blocking calls when reading/writing from/to your file
		203	handles.
		204
87	# wait for readability of STDIN, then read a line and disable the watcher	205	Example: wait for readability of STDIN, then read a line and disable the
		206	watcher.
		207
88	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
89	chomp (my $input = <STDIN>);	209	chomp (my $input = <STDIN>);
90	warn "read: $input\n";	210	warn "read: $input\n";
91	undef $w;	211	undef $w;
92	});	212	});
…		…
94	=head2 TIME WATCHERS	214	=head2 TIME WATCHERS
95		215
96	You can create a time watcher by calling the C<< AnyEvent->timer >>	216	You can create a time watcher by calling the C<< AnyEvent->timer >>
97	method with the following mandatory arguments:	217	method with the following mandatory arguments:
98		218
99	C<after> after how many seconds (fractions are supported) should the timer	219	C<after> specifies after how many seconds (fractional values are
100	activate. C<cb> the callback to invoke.	220	supported) the callback should be invoked. C<cb> is the callback to invoke
		221	in that case.
101		222
102	The timer callback will be invoked at most once: if you want a repeating	223	Although the callback might get passed parameters, their value and
103	timer you have to create a new watcher (this is a limitation by both Tk	224	presence is undefined and you cannot rely on them. Portable AnyEvent
104	and Glib).	225	callbacks cannot use arguments passed to time watcher callbacks.
105		226
106	Example:	227	The callback will normally be invoked once only. If you specify another
		228	parameter, C<interval>, as a strictly positive number (> 0), then the
		229	callback will be invoked regularly at that interval (in fractional
		230	seconds) after the first invocation. If C<interval> is specified with a
		231	false value, then it is treated as if it were missing.
107		232
		233	The callback will be rescheduled before invoking the callback, but no
		234	attempt is done to avoid timer drift in most backends, so the interval is
		235	only approximate.
		236
108	# fire an event after 7.7 seconds	237	Example: fire an event after 7.7 seconds.
		238
109	my $w = AnyEvent->timer (after => 7.7, cb => sub {	239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
110	warn "timeout\n";	240	warn "timeout\n";
111	});	241	});
112		242
113	# to cancel the timer:	243	# to cancel the timer:
114	undef $w;	244	undef $w;
115		245
116	=head2 CONDITION WATCHERS	246	Example 2: fire an event after 0.5 seconds, then roughly every second.
117		247
118	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
119	method without any arguments.	249	warn "timeout\n";
		250	};
120		251
121	A condition watcher watches for a condition - precisely that the C<<	252	=head3 TIMING ISSUES
122	->broadcast >> method has been called.
123		253
124	The watcher has only two methods:	254	There are two ways to handle timers: based on real time (relative, "fire
		255	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		256	o'clock").
		257
		258	While most event loops expect timers to specified in a relative way, they
		259	use absolute time internally. This makes a difference when your clock
		260	"jumps", for example, when ntp decides to set your clock backwards from
		261	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		262	fire "after" a second might actually take six years to finally fire.
		263
		264	AnyEvent cannot compensate for this. The only event loop that is conscious
		265	about these issues is L<EV>, which offers both relative (ev_timer, based
		266	on true relative time) and absolute (ev_periodic, based on wallclock time)
		267	timers.
		268
		269	AnyEvent always prefers relative timers, if available, matching the
		270	AnyEvent API.
		271
		272	AnyEvent has two additional methods that return the "current time":
125		273
126	=over 4	274	=over 4
127		275
128	=item $cv->wait	276	=item AnyEvent->time
129		277
130	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	278	This returns the "current wallclock time" as a fractional number of
131	called on c<$cv>, while servicing other watchers normally.	279	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		280	return, and the result is guaranteed to be compatible with those).
132		281
133	Not all event models support a blocking wait - some die in that case, so	282	It progresses independently of any event loop processing, i.e. each call
134	if you are using this from a module, never require a blocking wait, but	283	will check the system clock, which usually gets updated frequently.
135	let the caller decide wether the call will block or not (for example,
136	by coupling condition variables with some kind of request results and
137	supporting callbacks so the caller knows that getting the result will not
138	block, while still suppporting blockign waits if the caller so desires).
139		284
140	You can only wait once on a condition - additional calls will return	285	=item AnyEvent->now
141	immediately.
142		286
143	=item $cv->broadcast	287	This also returns the "current wallclock time", but unlike C<time>, above,
		288	this value might change only once per event loop iteration, depending on
		289	the event loop (most return the same time as C<time>, above). This is the
		290	time that AnyEvent's timers get scheduled against.
144		291
145	Flag the condition as ready - a running C<< ->wait >> and all further	292	I<In almost all cases (in all cases if you don't care), this is the
146	calls to C<wait> will return after this method has been called. If nobody	293	function to call when you want to know the current time.>
147	is waiting the broadcast will be remembered..
148		294
149	Example:	295	This function is also often faster then C<< AnyEvent->time >>, and
		296	thus the preferred method if you want some timestamp (for example,
		297	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		298
		299	The rest of this section is only of relevance if you try to be very exact
		300	with your timing, you can skip it without bad conscience.
		301
		302	For a practical example of when these times differ, consider L<Event::Lib>
		303	and L<EV> and the following set-up:
		304
		305	The event loop is running and has just invoked one of your callback at
		306	time=500 (assume no other callbacks delay processing). In your callback,
		307	you wait a second by executing C<sleep 1> (blocking the process for a
		308	second) and then (at time=501) you create a relative timer that fires
		309	after three seconds.
		310
		311	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		312	both return C<501>, because that is the current time, and the timer will
		313	be scheduled to fire at time=504 (C<501> + C<3>).
		314
		315	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		316	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		317	last event processing phase started. With L<EV>, your timer gets scheduled
		318	to run at time=503 (C<500> + C<3>).
		319
		320	In one sense, L<Event::Lib> is more exact, as it uses the current time
		321	regardless of any delays introduced by event processing. However, most
		322	callbacks do not expect large delays in processing, so this causes a
		323	higher drift (and a lot more system calls to get the current time).
		324
		325	In another sense, L<EV> is more exact, as your timer will be scheduled at
		326	the same time, regardless of how long event processing actually took.
		327
		328	In either case, if you care (and in most cases, you don't), then you
		329	can get whatever behaviour you want with any event loop, by taking the
		330	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		331	account.
		332
		333	=item AnyEvent->now_update
		334
		335	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		336	the current time for each loop iteration (see the discussion of L<<
		337	AnyEvent->now >>, above).
		338
		339	When a callback runs for a long time (or when the process sleeps), then
		340	this "current" time will differ substantially from the real time, which
		341	might affect timers and time-outs.
		342
		343	When this is the case, you can call this method, which will update the
		344	event loop's idea of "current time".
		345
		346	Note that updating the time I<might> cause some events to be handled.
		347
		348	=back
		349
		350	=head2 SIGNAL WATCHERS
		351
		352	You can watch for signals using a signal watcher, C<signal> is the signal
		353	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		354	callback to be invoked whenever a signal occurs.
		355
		356	Although the callback might get passed parameters, their value and
		357	presence is undefined and you cannot rely on them. Portable AnyEvent
		358	callbacks cannot use arguments passed to signal watcher callbacks.
		359
		360	Multiple signal occurrences can be clumped together into one callback
		361	invocation, and callback invocation will be synchronous. Synchronous means
		362	that it might take a while until the signal gets handled by the process,
		363	but it is guaranteed not to interrupt any other callbacks.
		364
		365	The main advantage of using these watchers is that you can share a signal
		366	between multiple watchers.
		367
		368	This watcher might use C<%SIG>, so programs overwriting those signals
		369	directly will likely not work correctly.
		370
		371	Example: exit on SIGINT
		372
		373	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		374
		375	=head2 CHILD PROCESS WATCHERS
		376
		377	You can also watch on a child process exit and catch its exit status.
		378
		379	The child process is specified by the C<pid> argument (if set to C<0>, it
		380	watches for any child process exit). The watcher will triggered only when
		381	the child process has finished and an exit status is available, not on
		382	any trace events (stopped/continued).
		383
		384	The callback will be called with the pid and exit status (as returned by
		385	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		386	callback arguments.
		387
		388	This watcher type works by installing a signal handler for C<SIGCHLD>,
		389	and since it cannot be shared, nothing else should use SIGCHLD or reap
		390	random child processes (waiting for specific child processes, e.g. inside
		391	C<system>, is just fine).
		392
		393	There is a slight catch to child watchers, however: you usually start them
		394	I<after> the child process was created, and this means the process could
		395	have exited already (and no SIGCHLD will be sent anymore).
		396
		397	Not all event models handle this correctly (neither POE nor IO::Async do,
		398	see their AnyEvent::Impl manpages for details), but even for event models
		399	that I<do> handle this correctly, they usually need to be loaded before
		400	the process exits (i.e. before you fork in the first place). AnyEvent's
		401	pure perl event loop handles all cases correctly regardless of when you
		402	start the watcher.
		403
		404	This means you cannot create a child watcher as the very first
		405	thing in an AnyEvent program, you I<have> to create at least one
		406	watcher before you C<fork> the child (alternatively, you can call
		407	C<AnyEvent::detect>).
		408
		409	Example: fork a process and wait for it
		410
		411	my $done = AnyEvent->condvar;
		412
		413	my $pid = fork or exit 5;
		414
		415	my $w = AnyEvent->child (
		416	pid => $pid,
		417	cb => sub {
		418	my ($pid, $status) = @_;
		419	warn "pid $pid exited with status $status";
		420	$done->send;
		421	},
		422	);
		423
		424	# do something else, then wait for process exit
		425	$done->recv;
		426
		427	=head2 IDLE WATCHERS
		428
		429	Sometimes there is a need to do something, but it is not so important
		430	to do it instantly, but only when there is nothing better to do. This
		431	"nothing better to do" is usually defined to be "no other events need
		432	attention by the event loop".
		433
		434	Idle watchers ideally get invoked when the event loop has nothing
		435	better to do, just before it would block the process to wait for new
		436	events. Instead of blocking, the idle watcher is invoked.
		437
		438	Most event loops unfortunately do not really support idle watchers (only
		439	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		440	will simply call the callback "from time to time".
		441
		442	Example: read lines from STDIN, but only process them when the
		443	program is otherwise idle:
		444
		445	my @lines; # read data
		446	my $idle_w;
		447	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		448	push @lines, scalar <STDIN>;
		449
		450	# start an idle watcher, if not already done
		451	$idle_w ||= AnyEvent->idle (cb => sub {
		452	# handle only one line, when there are lines left
		453	if (my $line = shift @lines) {
		454	print "handled when idle: $line";
		455	} else {
		456	# otherwise disable the idle watcher again
		457	undef $idle_w;
		458	}
		459	});
		460	});
		461
		462	=head2 CONDITION VARIABLES
		463
		464	If you are familiar with some event loops you will know that all of them
		465	require you to run some blocking "loop", "run" or similar function that
		466	will actively watch for new events and call your callbacks.
		467
		468	AnyEvent is different, it expects somebody else to run the event loop and
		469	will only block when necessary (usually when told by the user).
		470
		471	The instrument to do that is called a "condition variable", so called
		472	because they represent a condition that must become true.
		473
		474	Condition variables can be created by calling the C<< AnyEvent->condvar
		475	>> method, usually without arguments. The only argument pair allowed is
		476
		477	C<cb>, which specifies a callback to be called when the condition variable
		478	becomes true, with the condition variable as the first argument (but not
		479	the results).
		480
		481	After creation, the condition variable is "false" until it becomes "true"
		482	by calling the C<send> method (or calling the condition variable as if it
		483	were a callback, read about the caveats in the description for the C<<
		484	->send >> method).
		485
		486	Condition variables are similar to callbacks, except that you can
		487	optionally wait for them. They can also be called merge points - points
		488	in time where multiple outstanding events have been processed. And yet
		489	another way to call them is transactions - each condition variable can be
		490	used to represent a transaction, which finishes at some point and delivers
		491	a result.
		492
		493	Condition variables are very useful to signal that something has finished,
		494	for example, if you write a module that does asynchronous http requests,
		495	then a condition variable would be the ideal candidate to signal the
		496	availability of results. The user can either act when the callback is
		497	called or can synchronously C<< ->recv >> for the results.
		498
		499	You can also use them to simulate traditional event loops - for example,
		500	you can block your main program until an event occurs - for example, you
		501	could C<< ->recv >> in your main program until the user clicks the Quit
		502	button of your app, which would C<< ->send >> the "quit" event.
		503
		504	Note that condition variables recurse into the event loop - if you have
		505	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		506	lose. Therefore, condition variables are good to export to your caller, but
		507	you should avoid making a blocking wait yourself, at least in callbacks,
		508	as this asks for trouble.
		509
		510	Condition variables are represented by hash refs in perl, and the keys
		511	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		512	easy (it is often useful to build your own transaction class on top of
		513	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		514	it's C<new> method in your own C<new> method.
		515
		516	There are two "sides" to a condition variable - the "producer side" which
		517	eventually calls C<< -> send >>, and the "consumer side", which waits
		518	for the send to occur.
		519
		520	Example: wait for a timer.
150		521
151	# wait till the result is ready	522	# wait till the result is ready
152	my $result_ready = AnyEvent->condvar;	523	my $result_ready = AnyEvent->condvar;
153		524
154	# do something such as adding a timer	525	# do something such as adding a timer
155	# or socket watcher the calls $result_ready->broadcast	526	# or socket watcher the calls $result_ready->send
156	# when the "result" is ready.	527	# when the "result" is ready.
		528	# in this case, we simply use a timer:
		529	my $w = AnyEvent->timer (
		530	after => 1,
		531	cb => sub { $result_ready->send },
		532	);
157		533
		534	# this "blocks" (while handling events) till the callback
		535	# calls send
158	$result_ready->wait;	536	$result_ready->recv;
		537
		538	Example: wait for a timer, but take advantage of the fact that
		539	condition variables are also code references.
		540
		541	my $done = AnyEvent->condvar;
		542	my $delay = AnyEvent->timer (after => 5, cb => $done);
		543	$done->recv;
		544
		545	Example: Imagine an API that returns a condvar and doesn't support
		546	callbacks. This is how you make a synchronous call, for example from
		547	the main program:
		548
		549	use AnyEvent::CouchDB;
		550
		551	...
		552
		553	my @info = $couchdb->info->recv;
		554
		555	And this is how you would just ste a callback to be called whenever the
		556	results are available:
		557
		558	$couchdb->info->cb (sub {
		559	my @info = $_[0]->recv;
		560	});
		561
		562	=head3 METHODS FOR PRODUCERS
		563
		564	These methods should only be used by the producing side, i.e. the
		565	code/module that eventually sends the signal. Note that it is also
		566	the producer side which creates the condvar in most cases, but it isn't
		567	uncommon for the consumer to create it as well.
		568
		569	=over 4
		570
		571	=item $cv->send (...)
		572
		573	Flag the condition as ready - a running C<< ->recv >> and all further
		574	calls to C<recv> will (eventually) return after this method has been
		575	called. If nobody is waiting the send will be remembered.
		576
		577	If a callback has been set on the condition variable, it is called
		578	immediately from within send.
		579
		580	Any arguments passed to the C<send> call will be returned by all
		581	future C<< ->recv >> calls.
		582
		583	Condition variables are overloaded so one can call them directly
		584	(as a code reference). Calling them directly is the same as calling
		585	C<send>. Note, however, that many C-based event loops do not handle
		586	overloading, so as tempting as it may be, passing a condition variable
		587	instead of a callback does not work. Both the pure perl and EV loops
		588	support overloading, however, as well as all functions that use perl to
		589	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		590	example).
		591
		592	=item $cv->croak ($error)
		593
		594	Similar to send, but causes all call's to C<< ->recv >> to invoke
		595	C<Carp::croak> with the given error message/object/scalar.
		596
		597	This can be used to signal any errors to the condition variable
		598	user/consumer.
		599
		600	=item $cv->begin ([group callback])
		601
		602	=item $cv->end
		603
		604	These two methods can be used to combine many transactions/events into
		605	one. For example, a function that pings many hosts in parallel might want
		606	to use a condition variable for the whole process.
		607
		608	Every call to C<< ->begin >> will increment a counter, and every call to
		609	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		610	>>, the (last) callback passed to C<begin> will be executed. That callback
		611	is I<supposed> to call C<< ->send >>, but that is not required. If no
		612	callback was set, C<send> will be called without any arguments.
		613
		614	You can think of C<< $cv->send >> giving you an OR condition (one call
		615	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		616	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		617
		618	Let's start with a simple example: you have two I/O watchers (for example,
		619	STDOUT and STDERR for a program), and you want to wait for both streams to
		620	close before activating a condvar:
		621
		622	my $cv = AnyEvent->condvar;
		623
		624	$cv->begin; # first watcher
		625	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		626	defined sysread $fh1, my $buf, 4096
		627	or $cv->end;
		628	});
		629
		630	$cv->begin; # second watcher
		631	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		632	defined sysread $fh2, my $buf, 4096
		633	or $cv->end;
		634	});
		635
		636	$cv->recv;
		637
		638	This works because for every event source (EOF on file handle), there is
		639	one call to C<begin>, so the condvar waits for all calls to C<end> before
		640	sending.
		641
		642	The ping example mentioned above is slightly more complicated, as the
		643	there are results to be passwd back, and the number of tasks that are
		644	begung can potentially be zero:
		645
		646	my $cv = AnyEvent->condvar;
		647
		648	my %result;
		649	$cv->begin (sub { $cv->send (\%result) });
		650
		651	for my $host (@list_of_hosts) {
		652	$cv->begin;
		653	ping_host_then_call_callback $host, sub {
		654	$result{$host} = ...;
		655	$cv->end;
		656	};
		657	}
		658
		659	$cv->end;
		660
		661	This code fragment supposedly pings a number of hosts and calls
		662	C<send> after results for all then have have been gathered - in any
		663	order. To achieve this, the code issues a call to C<begin> when it starts
		664	each ping request and calls C<end> when it has received some result for
		665	it. Since C<begin> and C<end> only maintain a counter, the order in which
		666	results arrive is not relevant.
		667
		668	There is an additional bracketing call to C<begin> and C<end> outside the
		669	loop, which serves two important purposes: first, it sets the callback
		670	to be called once the counter reaches C<0>, and second, it ensures that
		671	C<send> is called even when C<no> hosts are being pinged (the loop
		672	doesn't execute once).
		673
		674	This is the general pattern when you "fan out" into multiple (but
		675	potentially none) subrequests: use an outer C<begin>/C<end> pair to set
		676	the callback and ensure C<end> is called at least once, and then, for each
		677	subrequest you start, call C<begin> and for each subrequest you finish,
		678	call C<end>.
159		679
160	=back	680	=back
161		681
162	=head2 SIGNAL WATCHERS	682	=head3 METHODS FOR CONSUMERS
163		683
164	You can listen for signals using a signal watcher, C<signal> is the signal	684	These methods should only be used by the consuming side, i.e. the
165	I<name> without any C<SIG> prefix. Multiple signals events can be clumped	685	code awaits the condition.
166	together into one callback invocation, and callback invocation might or
167	might not be asynchronous.
168		686
169	These watchers might use C<%SIG>, so programs overwriting those signals	687	=over 4
170	directly will likely not work correctly.
171		688
172	Example: exit on SIGINT	689	=item $cv->recv
173		690
174	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	691	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		692	>> methods have been called on c<$cv>, while servicing other watchers
		693	normally.
175		694
176	=head2 CHILD PROCESS WATCHERS	695	You can only wait once on a condition - additional calls are valid but
		696	will return immediately.
177		697
178	You can also listen for the status of a child process specified by the	698	If an error condition has been set by calling C<< ->croak >>, then this
179	C<pid> argument (or any child if the pid argument is 0). The watcher will	699	function will call C<croak>.
180	trigger as often as status change for the child are received. This works
181	by installing a signal handler for C<SIGCHLD>. The callback will be called with
182	the pid and exit status (as returned by waitpid).
183		700
184	Example: wait for pid 1333	701	In list context, all parameters passed to C<send> will be returned,
		702	in scalar context only the first one will be returned.
185		703
186	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });	704	Not all event models support a blocking wait - some die in that case
		705	(programs might want to do that to stay interactive), so I<if you are
		706	using this from a module, never require a blocking wait>, but let the
		707	caller decide whether the call will block or not (for example, by coupling
		708	condition variables with some kind of request results and supporting
		709	callbacks so the caller knows that getting the result will not block,
		710	while still supporting blocking waits if the caller so desires).
187		711
188	=head1 GLOBALS	712	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		713	sensibly have two C<< ->recv >>'s in parallel, as that would require
		714	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		715	can supply.
		716
		717	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		718	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		719	versions and also integrates coroutines into AnyEvent, making blocking
		720	C<< ->recv >> calls perfectly safe as long as they are done from another
		721	coroutine (one that doesn't run the event loop).
		722
		723	You can ensure that C<< -recv >> never blocks by setting a callback and
		724	only calling C<< ->recv >> from within that callback (or at a later
		725	time). This will work even when the event loop does not support blocking
		726	waits otherwise.
		727
		728	=item $bool = $cv->ready
		729
		730	Returns true when the condition is "true", i.e. whether C<send> or
		731	C<croak> have been called.
		732
		733	=item $cb = $cv->cb ($cb->($cv))
		734
		735	This is a mutator function that returns the callback set and optionally
		736	replaces it before doing so.
		737
		738	The callback will be called when the condition becomes "true", i.e. when
		739	C<send> or C<croak> are called, with the only argument being the condition
		740	variable itself. Calling C<recv> inside the callback or at any later time
		741	is guaranteed not to block.
		742
		743	=back
		744
		745	=head1 GLOBAL VARIABLES AND FUNCTIONS
189		746
190	=over 4	747	=over 4
191		748
192	=item $AnyEvent::MODEL	749	=item $AnyEvent::MODEL
193		750
…		…
197	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	754	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
198	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	755	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
199		756
200	The known classes so far are:	757	The known classes so far are:
201		758
202	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
203	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	759	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
204	AnyEvent::Impl::Coro based on Coro::Event, second best choice.
205	AnyEvent::Impl::Event based on Event, also second best choice :)	760	AnyEvent::Impl::Event based on Event, second best choice.
		761	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
206	AnyEvent::Impl::Glib based on Glib, second-best choice.	762	AnyEvent::Impl::Glib based on Glib, third-best choice.
207	AnyEvent::Impl::Tk based on Tk, very bad choice.	763	AnyEvent::Impl::Tk based on Tk, very bad choice.
208	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	764	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		765	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		766	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		767
		768	# warning, support for IO::Async is only partial, as it is too broken
		769	# and limited toe ven support the AnyEvent API. See AnyEvent::Impl::Async.
		770	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed (see its docs).
		771
		772	There is no support for WxWidgets, as WxWidgets has no support for
		773	watching file handles. However, you can use WxWidgets through the
		774	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		775	second, which was considered to be too horrible to even consider for
		776	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		777	it's adaptor.
		778
		779	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		780	autodetecting them.
209		781
210	=item AnyEvent::detect	782	=item AnyEvent::detect
211		783
212	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	784	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
213	necessary. You should only call this function right before you would have	785	if necessary. You should only call this function right before you would
214	created an AnyEvent watcher anyway, that is, very late at runtime.	786	have created an AnyEvent watcher anyway, that is, as late as possible at
		787	runtime.
		788
		789	=item $guard = AnyEvent::post_detect { BLOCK }
		790
		791	Arranges for the code block to be executed as soon as the event model is
		792	autodetected (or immediately if this has already happened).
		793
		794	If called in scalar or list context, then it creates and returns an object
		795	that automatically removes the callback again when it is destroyed. See
		796	L<Coro::BDB> for a case where this is useful.
		797
		798	=item @AnyEvent::post_detect
		799
		800	If there are any code references in this array (you can C<push> to it
		801	before or after loading AnyEvent), then they will called directly after
		802	the event loop has been chosen.
		803
		804	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		805	if it contains a true value then the event loop has already been detected,
		806	and the array will be ignored.
		807
		808	Best use C<AnyEvent::post_detect { BLOCK }> instead.
215		809
216	=back	810	=back
217		811
218	=head1 WHAT TO DO IN A MODULE	812	=head1 WHAT TO DO IN A MODULE
219		813
220	As a module author, you should "use AnyEvent" and call AnyEvent methods	814	As a module author, you should C<use AnyEvent> and call AnyEvent methods
221	freely, but you should not load a specific event module or rely on it.	815	freely, but you should not load a specific event module or rely on it.
222		816
223	Be careful when you create watchers in the module body - Anyevent will	817	Be careful when you create watchers in the module body - AnyEvent will
224	decide which event module to use as soon as the first method is called, so	818	decide which event module to use as soon as the first method is called, so
225	by calling AnyEvent in your module body you force the user of your module	819	by calling AnyEvent in your module body you force the user of your module
226	to load the event module first.	820	to load the event module first.
227		821
		822	Never call C<< ->recv >> on a condition variable unless you I<know> that
		823	the C<< ->send >> method has been called on it already. This is
		824	because it will stall the whole program, and the whole point of using
		825	events is to stay interactive.
		826
		827	It is fine, however, to call C<< ->recv >> when the user of your module
		828	requests it (i.e. if you create a http request object ad have a method
		829	called C<results> that returns the results, it should call C<< ->recv >>
		830	freely, as the user of your module knows what she is doing. always).
		831
228	=head1 WHAT TO DO IN THE MAIN PROGRAM	832	=head1 WHAT TO DO IN THE MAIN PROGRAM
229		833
230	There will always be a single main program - the only place that should	834	There will always be a single main program - the only place that should
231	dictate which event model to use.	835	dictate which event model to use.
232		836
233	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	837	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
234	do anything special and let AnyEvent decide which implementation to chose.	838	do anything special (it does not need to be event-based) and let AnyEvent
		839	decide which implementation to chose if some module relies on it.
235		840
236	If the main program relies on a specific event model (for example, in Gtk2	841	If the main program relies on a specific event model - for example, in
237	programs you have to rely on either Glib or Glib::Event), you should load	842	Gtk2 programs you have to rely on the Glib module - you should load the
238	it before loading AnyEvent or any module that uses it, generally, as early	843	event module before loading AnyEvent or any module that uses it: generally
239	as possible. The reason is that modules might create watchers when they	844	speaking, you should load it as early as possible. The reason is that
240	are loaded, and AnyEvent will decide on the event model to use as soon as	845	modules might create watchers when they are loaded, and AnyEvent will
241	it creates watchers, and it might chose the wrong one unless you load the	846	decide on the event model to use as soon as it creates watchers, and it
242	correct one yourself.	847	might chose the wrong one unless you load the correct one yourself.
243		848
244	You can chose to use a rather inefficient pure-perl implementation by	849	You can chose to use a pure-perl implementation by loading the
245	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	850	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
246	generally better.	851	everywhere, but letting AnyEvent chose the model is generally better.
		852
		853	=head2 MAINLOOP EMULATION
		854
		855	Sometimes (often for short test scripts, or even standalone programs who
		856	only want to use AnyEvent), you do not want to run a specific event loop.
		857
		858	In that case, you can use a condition variable like this:
		859
		860	AnyEvent->condvar->recv;
		861
		862	This has the effect of entering the event loop and looping forever.
		863
		864	Note that usually your program has some exit condition, in which case
		865	it is better to use the "traditional" approach of storing a condition
		866	variable somewhere, waiting for it, and sending it when the program should
		867	exit cleanly.
		868
		869
		870	=head1 OTHER MODULES
		871
		872	The following is a non-exhaustive list of additional modules that use
		873	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		874	in the same program. Some of the modules come with AnyEvent, some are
		875	available via CPAN.
		876
		877	=over 4
		878
		879	=item L<AnyEvent::Util>
		880
		881	Contains various utility functions that replace often-used but blocking
		882	functions such as C<inet_aton> by event-/callback-based versions.
		883
		884	=item L<AnyEvent::Socket>
		885
		886	Provides various utility functions for (internet protocol) sockets,
		887	addresses and name resolution. Also functions to create non-blocking tcp
		888	connections or tcp servers, with IPv6 and SRV record support and more.
		889
		890	=item L<AnyEvent::Handle>
		891
		892	Provide read and write buffers, manages watchers for reads and writes,
		893	supports raw and formatted I/O, I/O queued and fully transparent and
		894	non-blocking SSL/TLS.
		895
		896	=item L<AnyEvent::DNS>
		897
		898	Provides rich asynchronous DNS resolver capabilities.
		899
		900	=item L<AnyEvent::HTTP>
		901
		902	A simple-to-use HTTP library that is capable of making a lot of concurrent
		903	HTTP requests.
		904
		905	=item L<AnyEvent::HTTPD>
		906
		907	Provides a simple web application server framework.
		908
		909	=item L<AnyEvent::FastPing>
		910
		911	The fastest ping in the west.
		912
		913	=item L<AnyEvent::DBI>
		914
		915	Executes L<DBI> requests asynchronously in a proxy process.
		916
		917	=item L<AnyEvent::AIO>
		918
		919	Truly asynchronous I/O, should be in the toolbox of every event
		920	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		921	together.
		922
		923	=item L<AnyEvent::BDB>
		924
		925	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		926	L<BDB> and AnyEvent together.
		927
		928	=item L<AnyEvent::GPSD>
		929
		930	A non-blocking interface to gpsd, a daemon delivering GPS information.
		931
		932	=item L<AnyEvent::IGS>
		933
		934	A non-blocking interface to the Internet Go Server protocol (used by
		935	L<App::IGS>).
		936
		937	=item L<AnyEvent::IRC>
		938
		939	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		940
		941	=item L<Net::XMPP2>
		942
		943	AnyEvent based XMPP (Jabber protocol) module family.
		944
		945	=item L<Net::FCP>
		946
		947	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		948	of AnyEvent.
		949
		950	=item L<Event::ExecFlow>
		951
		952	High level API for event-based execution flow control.
		953
		954	=item L<Coro>
		955
		956	Has special support for AnyEvent via L<Coro::AnyEvent>.
		957
		958	=item L<IO::Lambda>
		959
		960	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		961
		962	=back
247		963
248	=cut	964	=cut
249		965
250	package AnyEvent;	966	package AnyEvent;
251		967
252	no warnings;	968	no warnings;
253	use strict;	969	use strict qw(vars subs);
254		970
255	use Carp;	971	use Carp;
256		972
257	our $VERSION = '2.7';	973	our $VERSION = 4.8;
258	our $MODEL;	974	our $MODEL;
259		975
260	our $AUTOLOAD;	976	our $AUTOLOAD;
261	our @ISA;	977	our @ISA;
262		978
		979	our @REGISTRY;
		980
		981	our $WIN32;
		982
		983	BEGIN {
		984	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		985	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		986
		987	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		988	if ${^TAINT};
		989	}
		990
263	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	991	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
264		992
265	our @REGISTRY;	993	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		994
		995	{
		996	my $idx;
		997	$PROTOCOL{$_} = ++$idx
		998	for reverse split /\s*,\s*/,
		999	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1000	}
266		1001
267	my @models = (	1002	my @models = (
268	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
269	[EV:: => AnyEvent::Impl::EV::],	1003	[EV:: => AnyEvent::Impl::EV::],
270	[Coro::Event:: => AnyEvent::Impl::Coro::],
271	[Event:: => AnyEvent::Impl::Event::],	1004	[Event:: => AnyEvent::Impl::Event::],
272	[Glib:: => AnyEvent::Impl::Glib::],
273	[Tk:: => AnyEvent::Impl::Tk::],
274	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	1005	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		1006	# everything below here will not be autoprobed
		1007	# as the pureperl backend should work everywhere
		1008	# and is usually faster
		1009	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1010	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		1011	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1012	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1013	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1014	[Wx:: => AnyEvent::Impl::POE::],
		1015	[Prima:: => AnyEvent::Impl::POE::],
		1016	# IO::Async is just too broken - we would need workaorunds for its
		1017	# byzantine signal and broken child handling, among others.
		1018	# IO::Async is rather hard to detect, as it doesn't have any
		1019	# obvious default class.
		1020	# [IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1021	# [IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1022	# [IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
275	);	1023	);
276		1024
277	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	1025	our %method = map +($_ => 1),
		1026	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
		1027
		1028	our @post_detect;
		1029
		1030	sub post_detect(&) {
		1031	my ($cb) = @_;
		1032
		1033	if ($MODEL) {
		1034	$cb->();
		1035
		1036	1
		1037	} else {
		1038	push @post_detect, $cb;
		1039
		1040	defined wantarray
		1041	? bless \$cb, "AnyEvent::Util::postdetect"
		1042	: ()
		1043	}
		1044	}
		1045
		1046	sub AnyEvent::Util::postdetect::DESTROY {
		1047	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1048	}
278		1049
279	sub detect() {	1050	sub detect() {
280	unless ($MODEL) {	1051	unless ($MODEL) {
281	no strict 'refs';	1052	no strict 'refs';
		1053	local $SIG{__DIE__};
		1054
		1055	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		1056	my $model = "AnyEvent::Impl::$1";
		1057	if (eval "require $model") {
		1058	$MODEL = $model;
		1059	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		1060	} else {
		1061	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		1062	}
		1063	}
282		1064
283	# check for already loaded models	1065	# check for already loaded models
		1066	unless ($MODEL) {
284	for (@REGISTRY, @models) {	1067	for (@REGISTRY, @models) {
285	my ($package, $model) = @$_;	1068	my ($package, $model) = @$_;
286	if (${"$package\::VERSION"} > 0) {	1069	if (${"$package\::VERSION"} > 0) {
287	if (eval "require $model") {	1070	if (eval "require $model") {
288	$MODEL = $model;	1071	$MODEL = $model;
289	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1072	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
290	last;	1073	last;
		1074	}
291	}	1075	}
292	}	1076	}
		1077
		1078	unless ($MODEL) {
		1079	# try to load a model
		1080
		1081	for (@REGISTRY, @models) {
		1082	my ($package, $model) = @$_;
		1083	if (eval "require $package"
		1084	and ${"$package\::VERSION"} > 0
		1085	and eval "require $model") {
		1086	$MODEL = $model;
		1087	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		1088	last;
		1089	}
		1090	}
		1091
		1092	$MODEL
		1093	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
		1094	}
293	}	1095	}
294		1096
295	unless ($MODEL) {	1097	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
296	# try to load a model
297
298	for (@REGISTRY, @models) {
299	my ($package, $model) = @$_;
300	if (eval "require $package"
301	and ${"$package\::VERSION"} > 0
302	and eval "require $model") {
303	$MODEL = $model;
304	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
305	last;
306	}
307	}
308
309	$MODEL
310	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk.";
311	}
312		1098
313	unshift @ISA, $MODEL;	1099	unshift @ISA, $MODEL;
314	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	1100
		1101	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1102
		1103	(shift @post_detect)->() while @post_detect;
315	}	1104	}
316		1105
317	$MODEL	1106	$MODEL
318	}	1107	}
319		1108
…		…
327		1116
328	my $class = shift;	1117	my $class = shift;
329	$class->$func (@_);	1118	$class->$func (@_);
330	}	1119	}
331		1120
		1121	# utility function to dup a filehandle. this is used by many backends
		1122	# to support binding more than one watcher per filehandle (they usually
		1123	# allow only one watcher per fd, so we dup it to get a different one).
		1124	sub _dupfh($$;$$) {
		1125	my ($poll, $fh, $r, $w) = @_;
		1126
		1127	# cygwin requires the fh mode to be matching, unix doesn't
		1128	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1129	: $poll eq "w" ? ($w, ">")
		1130	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1131
		1132	open my $fh2, "$mode&" . fileno $fh
		1133	or die "cannot dup() filehandle: $!,";
		1134
		1135	# we assume CLOEXEC is already set by perl in all important cases
		1136
		1137	($fh2, $rw)
		1138	}
		1139
332	package AnyEvent::Base;	1140	package AnyEvent::Base;
333		1141
		1142	# default implementations for many methods
		1143
		1144	BEGIN {
		1145	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1146	*_time = \&Time::HiRes::time;
		1147	# if (eval "use POSIX (); (POSIX::times())...
		1148	} else {
		1149	*_time = sub { time }; # epic fail
		1150	}
		1151	}
		1152
		1153	sub time { _time }
		1154	sub now { _time }
		1155	sub now_update { }
		1156
334	# default implementation for ->condvar, ->wait, ->broadcast	1157	# default implementation for ->condvar
335		1158
336	sub condvar {	1159	sub condvar {
337	bless \my $flag, "AnyEvent::Base::CondVar"	1160	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
338	}
339
340	sub AnyEvent::Base::CondVar::broadcast {
341	${$_[0]}++;
342	}
343
344	sub AnyEvent::Base::CondVar::wait {
345	AnyEvent->one_event while !${$_[0]};
346	}	1161	}
347		1162
348	# default implementation for ->signal	1163	# default implementation for ->signal
349		1164
350	our %SIG_CB;	1165	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1166
		1167	sub _signal_exec {
		1168	sysread $SIGPIPE_R, my $dummy, 4;
		1169
		1170	while (%SIG_EV) {
		1171	for (keys %SIG_EV) {
		1172	delete $SIG_EV{$_};
		1173	$_->() for values %{ $SIG_CB{$_} || {} };
		1174	}
		1175	}
		1176	}
351		1177
352	sub signal {	1178	sub signal {
353	my (undef, %arg) = @_;	1179	my (undef, %arg) = @_;
354		1180
		1181	unless ($SIGPIPE_R) {
		1182	require Fcntl;
		1183
		1184	if (AnyEvent::WIN32) {
		1185	require AnyEvent::Util;
		1186
		1187	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1188	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1189	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1190	} else {
		1191	pipe $SIGPIPE_R, $SIGPIPE_W;
		1192	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1193	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1194
		1195	# not strictly required, as $^F is normally 2, but let's make sure...
		1196	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1197	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1198	}
		1199
		1200	$SIGPIPE_R
		1201	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1202
		1203	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1204	}
		1205
355	my $signal = uc $arg{signal}	1206	my $signal = uc $arg{signal}
356	or Carp::croak "required option 'signal' is missing";	1207	or Carp::croak "required option 'signal' is missing";
357		1208
358	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1209	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
359	$SIG{$signal} ||= sub {	1210	$SIG{$signal} ||= sub {
360	$_->() for values %{ $SIG_CB{$signal} || {} };	1211	local $!;
		1212	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1213	undef $SIG_EV{$signal};
361	};	1214	};
362		1215
363	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1216	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
364	}	1217	}
365		1218
366	sub AnyEvent::Base::Signal::DESTROY {	1219	sub AnyEvent::Base::signal::DESTROY {
367	my ($signal, $cb) = @{$_[0]};	1220	my ($signal, $cb) = @{$_[0]};
368		1221
369	delete $SIG_CB{$signal}{$cb};	1222	delete $SIG_CB{$signal}{$cb};
370		1223
		1224	# delete doesn't work with older perls - they then
		1225	# print weird messages, or just unconditionally exit
		1226	# instead of getting the default action.
371	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1227	undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
372	}	1228	}
373		1229
374	# default implementation for ->child	1230	# default implementation for ->child
375		1231
376	our %PID_CB;	1232	our %PID_CB;
377	our $CHLD_W;	1233	our $CHLD_W;
378	our $CHLD_DELAY_W;	1234	our $CHLD_DELAY_W;
379	our $PID_IDLE;
380	our $WNOHANG;	1235	our $WNOHANG;
381		1236
382	sub _child_wait {	1237	sub _sigchld {
383	while (0 <= (my $pid = waitpid -1, $WNOHANG)) {	1238	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
384	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1239	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
385	(values %{ $PID_CB{0} || {} });	1240	(values %{ $PID_CB{0} || {} });
386	}	1241	}
387
388	undef $PID_IDLE;
389	}
390
391	sub _sigchld {
392	# make sure we deliver these changes "synchronous" with the event loop.
393	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
394	undef $CHLD_DELAY_W;
395	&_child_wait;
396	});
397	}	1242	}
398		1243
399	sub child {	1244	sub child {
400	my (undef, %arg) = @_;	1245	my (undef, %arg) = @_;
401		1246
402	defined (my $pid = $arg{pid} + 0)	1247	defined (my $pid = $arg{pid} + 0)
403	or Carp::croak "required option 'pid' is missing";	1248	or Carp::croak "required option 'pid' is missing";
404		1249
405	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1250	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
406		1251
407	unless ($WNOHANG) {
408	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1252	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
409	}
410		1253
411	unless ($CHLD_W) {	1254	unless ($CHLD_W) {
412	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1255	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
413	# child could be a zombie already, so make at least one round	1256	# child could be a zombie already, so make at least one round
414	&_sigchld;	1257	&_sigchld;
415	}	1258	}
416		1259
417	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1260	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
418	}	1261	}
419		1262
420	sub AnyEvent::Base::Child::DESTROY {	1263	sub AnyEvent::Base::child::DESTROY {
421	my ($pid, $cb) = @{$_[0]};	1264	my ($pid, $cb) = @{$_[0]};
422		1265
423	delete $PID_CB{$pid}{$cb};	1266	delete $PID_CB{$pid}{$cb};
424	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1267	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
425		1268
426	undef $CHLD_W unless keys %PID_CB;	1269	undef $CHLD_W unless keys %PID_CB;
427	}	1270	}
428		1271
		1272	# idle emulation is done by simply using a timer, regardless
		1273	# of whether the process is idle or not, and not letting
		1274	# the callback use more than 50% of the time.
		1275	sub idle {
		1276	my (undef, %arg) = @_;
		1277
		1278	my ($cb, $w, $rcb) = $arg{cb};
		1279
		1280	$rcb = sub {
		1281	if ($cb) {
		1282	$w = _time;
		1283	&$cb;
		1284	$w = _time - $w;
		1285
		1286	# never use more then 50% of the time for the idle watcher,
		1287	# within some limits
		1288	$w = 0.0001 if $w < 0.0001;
		1289	$w = 5 if $w > 5;
		1290
		1291	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1292	} else {
		1293	# clean up...
		1294	undef $w;
		1295	undef $rcb;
		1296	}
		1297	};
		1298
		1299	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1300
		1301	bless \\$cb, "AnyEvent::Base::idle"
		1302	}
		1303
		1304	sub AnyEvent::Base::idle::DESTROY {
		1305	undef $${$_[0]};
		1306	}
		1307
		1308	package AnyEvent::CondVar;
		1309
		1310	our @ISA = AnyEvent::CondVar::Base::;
		1311
		1312	package AnyEvent::CondVar::Base;
		1313
		1314	use overload
		1315	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1316	fallback => 1;
		1317
		1318	sub _send {
		1319	# nop
		1320	}
		1321
		1322	sub send {
		1323	my $cv = shift;
		1324	$cv->{_ae_sent} = [@_];
		1325	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1326	$cv->_send;
		1327	}
		1328
		1329	sub croak {
		1330	$_[0]{_ae_croak} = $_[1];
		1331	$_[0]->send;
		1332	}
		1333
		1334	sub ready {
		1335	$_[0]{_ae_sent}
		1336	}
		1337
		1338	sub _wait {
		1339	AnyEvent->one_event while !$_[0]{_ae_sent};
		1340	}
		1341
		1342	sub recv {
		1343	$_[0]->_wait;
		1344
		1345	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1346	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1347	}
		1348
		1349	sub cb {
		1350	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1351	$_[0]{_ae_cb}
		1352	}
		1353
		1354	sub begin {
		1355	++$_[0]{_ae_counter};
		1356	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1357	}
		1358
		1359	sub end {
		1360	return if --$_[0]{_ae_counter};
		1361	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1362	}
		1363
		1364	# undocumented/compatibility with pre-3.4
		1365	*broadcast = \&send;
		1366	*wait = \&_wait;
		1367
		1368	=head1 ERROR AND EXCEPTION HANDLING
		1369
		1370	In general, AnyEvent does not do any error handling - it relies on the
		1371	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1372	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1373	checking of all AnyEvent methods, however, which is highly useful during
		1374	development.
		1375
		1376	As for exception handling (i.e. runtime errors and exceptions thrown while
		1377	executing a callback), this is not only highly event-loop specific, but
		1378	also not in any way wrapped by this module, as this is the job of the main
		1379	program.
		1380
		1381	The pure perl event loop simply re-throws the exception (usually
		1382	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1383	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1384	so on.
		1385
		1386	=head1 ENVIRONMENT VARIABLES
		1387
		1388	The following environment variables are used by this module or its
		1389	submodules.
		1390
		1391	Note that AnyEvent will remove I<all> environment variables starting with
		1392	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1393	enabled.
		1394
		1395	=over 4
		1396
		1397	=item C<PERL_ANYEVENT_VERBOSE>
		1398
		1399	By default, AnyEvent will be completely silent except in fatal
		1400	conditions. You can set this environment variable to make AnyEvent more
		1401	talkative.
		1402
		1403	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1404	conditions, such as not being able to load the event model specified by
		1405	C<PERL_ANYEVENT_MODEL>.
		1406
		1407	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1408	model it chooses.
		1409
		1410	=item C<PERL_ANYEVENT_STRICT>
		1411
		1412	AnyEvent does not do much argument checking by default, as thorough
		1413	argument checking is very costly. Setting this variable to a true value
		1414	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1415	check the arguments passed to most method calls. If it finds any problems,
		1416	it will croak.
		1417
		1418	In other words, enables "strict" mode.
		1419
		1420	Unlike C<use strict>, it is definitely recommended to keep it off in
		1421	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1422	developing programs can be very useful, however.
		1423
		1424	=item C<PERL_ANYEVENT_MODEL>
		1425
		1426	This can be used to specify the event model to be used by AnyEvent, before
		1427	auto detection and -probing kicks in. It must be a string consisting
		1428	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1429	and the resulting module name is loaded and if the load was successful,
		1430	used as event model. If it fails to load AnyEvent will proceed with
		1431	auto detection and -probing.
		1432
		1433	This functionality might change in future versions.
		1434
		1435	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1436	could start your program like this:
		1437
		1438	PERL_ANYEVENT_MODEL=Perl perl ...
		1439
		1440	=item C<PERL_ANYEVENT_PROTOCOLS>
		1441
		1442	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1443	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1444	of auto probing).
		1445
		1446	Must be set to a comma-separated list of protocols or address families,
		1447	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1448	used, and preference will be given to protocols mentioned earlier in the
		1449	list.
		1450
		1451	This variable can effectively be used for denial-of-service attacks
		1452	against local programs (e.g. when setuid), although the impact is likely
		1453	small, as the program has to handle conenction and other failures anyways.
		1454
		1455	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1456	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1457	- only support IPv4, never try to resolve or contact IPv6
		1458	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1459	IPv6, but prefer IPv6 over IPv4.
		1460
		1461	=item C<PERL_ANYEVENT_EDNS0>
		1462
		1463	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1464	for DNS. This extension is generally useful to reduce DNS traffic, but
		1465	some (broken) firewalls drop such DNS packets, which is why it is off by
		1466	default.
		1467
		1468	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1469	EDNS0 in its DNS requests.
		1470
		1471	=item C<PERL_ANYEVENT_MAX_FORKS>
		1472
		1473	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1474	will create in parallel.
		1475
		1476	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1477
		1478	The default value for the C<max_outstanding> parameter for the default DNS
		1479	resolver - this is the maximum number of parallel DNS requests that are
		1480	sent to the DNS server.
		1481
		1482	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1483
		1484	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1485	configuration) in the default resolver. When set to the empty string, no
		1486	default config will be used.
		1487
		1488	=back
		1489
429	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1490	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1491
		1492	This is an advanced topic that you do not normally need to use AnyEvent in
		1493	a module. This section is only of use to event loop authors who want to
		1494	provide AnyEvent compatibility.
430		1495
431	If you need to support another event library which isn't directly	1496	If you need to support another event library which isn't directly
432	supported by AnyEvent, you can supply your own interface to it by	1497	supported by AnyEvent, you can supply your own interface to it by
433	pushing, before the first watcher gets created, the package name of	1498	pushing, before the first watcher gets created, the package name of
434	the event module and the package name of the interface to use onto	1499	the event module and the package name of the interface to use onto
435	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	1500	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
436	AnyEvent.	1501	AnyEvent, so it is reasonably cheap.
437		1502
438	Example:	1503	Example:
439		1504
440	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1505	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
441		1506
442	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1507	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
443	package/class when it finds the C<urxvt> package/module is loaded. When	1508	package/class when it finds the C<urxvt> package/module is already loaded.
		1509
444	AnyEvent is loaded and asked to find a suitable event model, it will	1510	When AnyEvent is loaded and asked to find a suitable event model, it
445	first check for the presence of urxvt.	1511	will first check for the presence of urxvt by trying to C<use> the
		1512	C<urxvt::anyevent> module.
446		1513
447	The class should provide implementations for all watcher types (see	1514	The class should provide implementations for all watcher types. See
448	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1515	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
449	(Source code) and so on for actual examples, use C<perldoc -m	1516	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
450	AnyEvent::Impl::Glib> to see the sources).	1517	see the sources.
451		1518
		1519	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1520	provide suitable (hopefully) replacements.
		1521
452	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1522	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
453	uses the above line as-is. An interface isn't included in AnyEvent	1523	terminal emulator uses the above line as-is. An interface isn't included
454	because it doesn't make sense outside the embedded interpreter inside	1524	in AnyEvent because it doesn't make sense outside the embedded interpreter
455	I<rxvt-unicode>, and it is updated and maintained as part of the	1525	inside I<rxvt-unicode>, and it is updated and maintained as part of the
456	I<rxvt-unicode> distribution.	1526	I<rxvt-unicode> distribution.
457		1527
458	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1528	I<rxvt-unicode> also cheats a bit by not providing blocking access to
459	condition variables: code blocking while waiting for a condition will	1529	condition variables: code blocking while waiting for a condition will
460	C<die>. This still works with most modules/usages, and blocking calls must	1530	C<die>. This still works with most modules/usages, and blocking calls must
461	not be in an interactive application, so it makes sense.	1531	not be done in an interactive application, so it makes sense.
462		1532
463	=head1 ENVIRONMENT VARIABLES
464
465	The following environment variables are used by this module:
466
467	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
468	model gets used.
469
470	=head1 EXAMPLE	1533	=head1 EXAMPLE PROGRAM
471		1534
472	The following program uses an io watcher to read data from stdin, a timer	1535	The following program uses an I/O watcher to read data from STDIN, a timer
473	to display a message once per second, and a condvar to exit the program	1536	to display a message once per second, and a condition variable to quit the
474	when the user enters quit:	1537	program when the user enters quit:
475		1538
476	use AnyEvent;	1539	use AnyEvent;
477		1540
478	my $cv = AnyEvent->condvar;	1541	my $cv = AnyEvent->condvar;
479		1542
480	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1543	my $io_watcher = AnyEvent->io (
		1544	fh => \*STDIN,
		1545	poll => 'r',
		1546	cb => sub {
481	warn "io event <$_[0]>\n"; # will always output <r>	1547	warn "io event <$_[0]>\n"; # will always output <r>
482	chomp (my $input = <STDIN>); # read a line	1548	chomp (my $input = <STDIN>); # read a line
483	warn "read: $input\n"; # output what has been read	1549	warn "read: $input\n"; # output what has been read
484	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1550	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1551	},
485	});	1552	);
486		1553
487	my $time_watcher; # can only be used once	1554	my $time_watcher; # can only be used once
488		1555
489	sub new_timer {	1556	sub new_timer {
490	$timer = AnyEvent->timer (after => 1, cb => sub {	1557	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
493	});	1560	});
494	}	1561	}
495		1562
496	new_timer; # create first timer	1563	new_timer; # create first timer
497		1564
498	$cv->wait; # wait until user enters /^q/i	1565	$cv->recv; # wait until user enters /^q/i
499		1566
500	=head1 REAL-WORLD EXAMPLE	1567	=head1 REAL-WORLD EXAMPLE
501		1568
502	Consider the L<Net::FCP> module. It features (among others) the following	1569	Consider the L<Net::FCP> module. It features (among others) the following
503	API calls, which are to freenet what HTTP GET requests are to http:	1570	API calls, which are to freenet what HTTP GET requests are to http:
…		…
553	syswrite $txn->{fh}, $txn->{request}	1620	syswrite $txn->{fh}, $txn->{request}
554	or die "connection or write error";	1621	or die "connection or write error";
555	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1622	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
556		1623
557	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1624	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
558	result and signals any possible waiters that the request ahs finished:	1625	result and signals any possible waiters that the request has finished:
559		1626
560	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1627	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
561		1628
562	if (end-of-file or data complete) {	1629	if (end-of-file or data complete) {
563	$txn->{result} = $txn->{buf};	1630	$txn->{result} = $txn->{buf};
564	$txn->{finished}->broadcast;	1631	$txn->{finished}->send;
565	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1632	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
566	}	1633	}
567		1634
568	The C<result> method, finally, just waits for the finished signal (if the	1635	The C<result> method, finally, just waits for the finished signal (if the
569	request was already finished, it doesn't wait, of course, and returns the	1636	request was already finished, it doesn't wait, of course, and returns the
570	data:	1637	data:
571		1638
572	$txn->{finished}->wait;	1639	$txn->{finished}->recv;
573	return $txn->{result};	1640	return $txn->{result};
574		1641
575	The actual code goes further and collects all errors (C<die>s, exceptions)	1642	The actual code goes further and collects all errors (C<die>s, exceptions)
576	that occured during request processing. The C<result> method detects	1643	that occurred during request processing. The C<result> method detects
577	wether an exception as thrown (it is stored inside the $txn object)	1644	whether an exception as thrown (it is stored inside the $txn object)
578	and just throws the exception, which means connection errors and other	1645	and just throws the exception, which means connection errors and other
579	problems get reported tot he code that tries to use the result, not in a	1646	problems get reported tot he code that tries to use the result, not in a
580	random callback.	1647	random callback.
581		1648
582	All of this enables the following usage styles:	1649	All of this enables the following usage styles:
583		1650
584	1. Blocking:	1651	1. Blocking:
585		1652
586	my $data = $fcp->client_get ($url);	1653	my $data = $fcp->client_get ($url);
587		1654
588	2. Blocking, but parallelizing:	1655	2. Blocking, but running in parallel:
589		1656
590	my @datas = map $_->result,	1657	my @datas = map $_->result,
591	map $fcp->txn_client_get ($_),	1658	map $fcp->txn_client_get ($_),
592	@urls;	1659	@urls;
593		1660
594	Both blocking examples work without the module user having to know	1661	Both blocking examples work without the module user having to know
595	anything about events.	1662	anything about events.
596		1663
597	3a. Event-based in a main program, using any support Event module:	1664	3a. Event-based in a main program, using any supported event module:
598		1665
599	use Event;	1666	use EV;
600		1667
601	$fcp->txn_client_get ($url)->cb (sub {	1668	$fcp->txn_client_get ($url)->cb (sub {
602	my $txn = shift;	1669	my $txn = shift;
603	my $data = $txn->result;	1670	my $data = $txn->result;
604	...	1671	...
605	});	1672	});
606		1673
607	Event::loop;	1674	EV::loop;
608		1675
609	3b. The module user could use AnyEvent, too:	1676	3b. The module user could use AnyEvent, too:
610		1677
611	use AnyEvent;	1678	use AnyEvent;
612		1679
613	my $quit = AnyEvent->condvar;	1680	my $quit = AnyEvent->condvar;
614		1681
615	$fcp->txn_client_get ($url)->cb (sub {	1682	$fcp->txn_client_get ($url)->cb (sub {
616	...	1683	...
617	$quit->broadcast;	1684	$quit->send;
618	});	1685	});
619		1686
620	$quit->wait;	1687	$quit->recv;
		1688
		1689
		1690	=head1 BENCHMARKS
		1691
		1692	To give you an idea of the performance and overheads that AnyEvent adds
		1693	over the event loops themselves and to give you an impression of the speed
		1694	of various event loops I prepared some benchmarks.
		1695
		1696	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1697
		1698	Here is a benchmark of various supported event models used natively and
		1699	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1700	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1701	which it is), lets them fire exactly once and destroys them again.
		1702
		1703	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1704	distribution.
		1705
		1706	=head3 Explanation of the columns
		1707
		1708	I<watcher> is the number of event watchers created/destroyed. Since
		1709	different event models feature vastly different performances, each event
		1710	loop was given a number of watchers so that overall runtime is acceptable
		1711	and similar between tested event loop (and keep them from crashing): Glib
		1712	would probably take thousands of years if asked to process the same number
		1713	of watchers as EV in this benchmark.
		1714
		1715	I<bytes> is the number of bytes (as measured by the resident set size,
		1716	RSS) consumed by each watcher. This method of measuring captures both C
		1717	and Perl-based overheads.
		1718
		1719	I<create> is the time, in microseconds (millionths of seconds), that it
		1720	takes to create a single watcher. The callback is a closure shared between
		1721	all watchers, to avoid adding memory overhead. That means closure creation
		1722	and memory usage is not included in the figures.
		1723
		1724	I<invoke> is the time, in microseconds, used to invoke a simple
		1725	callback. The callback simply counts down a Perl variable and after it was
		1726	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1727	signal the end of this phase.
		1728
		1729	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1730	watcher.
		1731
		1732	=head3 Results
		1733
		1734	name watchers bytes create invoke destroy comment
		1735	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1736	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1737	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1738	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1739	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1740	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1741	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1742	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
		1743	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1744	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1745	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1746	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1747
		1748	=head3 Discussion
		1749
		1750	The benchmark does I<not> measure scalability of the event loop very
		1751	well. For example, a select-based event loop (such as the pure perl one)
		1752	can never compete with an event loop that uses epoll when the number of
		1753	file descriptors grows high. In this benchmark, all events become ready at
		1754	the same time, so select/poll-based implementations get an unnatural speed
		1755	boost.
		1756
		1757	Also, note that the number of watchers usually has a nonlinear effect on
		1758	overall speed, that is, creating twice as many watchers doesn't take twice
		1759	the time - usually it takes longer. This puts event loops tested with a
		1760	higher number of watchers at a disadvantage.
		1761
		1762	To put the range of results into perspective, consider that on the
		1763	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1764	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1765	cycles with POE.
		1766
		1767	C<EV> is the sole leader regarding speed and memory use, which are both
		1768	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1769	far less memory than any other event loop and is still faster than Event
		1770	natively.
		1771
		1772	The pure perl implementation is hit in a few sweet spots (both the
		1773	constant timeout and the use of a single fd hit optimisations in the perl
		1774	interpreter and the backend itself). Nevertheless this shows that it
		1775	adds very little overhead in itself. Like any select-based backend its
		1776	performance becomes really bad with lots of file descriptors (and few of
		1777	them active), of course, but this was not subject of this benchmark.
		1778
		1779	The C<Event> module has a relatively high setup and callback invocation
		1780	cost, but overall scores in on the third place.
		1781
		1782	C<IO::Async> performs admirably well, about on par with C<Event>, even
		1783	when using its pure perl backend.
		1784
		1785	C<Glib>'s memory usage is quite a bit higher, but it features a
		1786	faster callback invocation and overall ends up in the same class as
		1787	C<Event>. However, Glib scales extremely badly, doubling the number of
		1788	watchers increases the processing time by more than a factor of four,
		1789	making it completely unusable when using larger numbers of watchers
		1790	(note that only a single file descriptor was used in the benchmark, so
		1791	inefficiencies of C<poll> do not account for this).
		1792
		1793	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1794	more than 2000 watchers is a big setback, however, as correctness takes
		1795	precedence over speed. Nevertheless, its performance is surprising, as the
		1796	file descriptor is dup()ed for each watcher. This shows that the dup()
		1797	employed by some adaptors is not a big performance issue (it does incur a
		1798	hidden memory cost inside the kernel which is not reflected in the figures
		1799	above).
		1800
		1801	C<POE>, regardless of underlying event loop (whether using its pure perl
		1802	select-based backend or the Event module, the POE-EV backend couldn't
		1803	be tested because it wasn't working) shows abysmal performance and
		1804	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1805	as EV watchers, and 10 times as much memory as Event (the high memory
		1806	requirements are caused by requiring a session for each watcher). Watcher
		1807	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1808	implementation.
		1809
		1810	The design of the POE adaptor class in AnyEvent can not really account
		1811	for the performance issues, though, as session creation overhead is
		1812	small compared to execution of the state machine, which is coded pretty
		1813	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1814	using multiple sessions is not a good approach, especially regarding
		1815	memory usage, even the author of POE could not come up with a faster
		1816	design).
		1817
		1818	=head3 Summary
		1819
		1820	=over 4
		1821
		1822	=item * Using EV through AnyEvent is faster than any other event loop
		1823	(even when used without AnyEvent), but most event loops have acceptable
		1824	performance with or without AnyEvent.
		1825
		1826	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1827	the actual event loop, only with extremely fast event loops such as EV
		1828	adds AnyEvent significant overhead.
		1829
		1830	=item * You should avoid POE like the plague if you want performance or
		1831	reasonable memory usage.
		1832
		1833	=back
		1834
		1835	=head2 BENCHMARKING THE LARGE SERVER CASE
		1836
		1837	This benchmark actually benchmarks the event loop itself. It works by
		1838	creating a number of "servers": each server consists of a socket pair, a
		1839	timeout watcher that gets reset on activity (but never fires), and an I/O
		1840	watcher waiting for input on one side of the socket. Each time the socket
		1841	watcher reads a byte it will write that byte to a random other "server".
		1842
		1843	The effect is that there will be a lot of I/O watchers, only part of which
		1844	are active at any one point (so there is a constant number of active
		1845	fds for each loop iteration, but which fds these are is random). The
		1846	timeout is reset each time something is read because that reflects how
		1847	most timeouts work (and puts extra pressure on the event loops).
		1848
		1849	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1850	(1%) are active. This mirrors the activity of large servers with many
		1851	connections, most of which are idle at any one point in time.
		1852
		1853	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1854	distribution.
		1855
		1856	=head3 Explanation of the columns
		1857
		1858	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1859	each server has a read and write socket end).
		1860
		1861	I<create> is the time it takes to create a socket pair (which is
		1862	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1863
		1864	I<request>, the most important value, is the time it takes to handle a
		1865	single "request", that is, reading the token from the pipe and forwarding
		1866	it to another server. This includes deleting the old timeout and creating
		1867	a new one that moves the timeout into the future.
		1868
		1869	=head3 Results
		1870
		1871	name sockets create request
		1872	EV 20000 69.01 11.16
		1873	Perl 20000 73.32 35.87
		1874	IOAsync 20000 157.00 98.14 epoll
		1875	IOAsync 20000 159.31 616.06 poll
		1876	Event 20000 212.62 257.32
		1877	Glib 20000 651.16 1896.30
		1878	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1879
		1880	=head3 Discussion
		1881
		1882	This benchmark I<does> measure scalability and overall performance of the
		1883	particular event loop.
		1884
		1885	EV is again fastest. Since it is using epoll on my system, the setup time
		1886	is relatively high, though.
		1887
		1888	Perl surprisingly comes second. It is much faster than the C-based event
		1889	loops Event and Glib.
		1890
		1891	IO::Async performs very well when using its epoll backend, and still quite
		1892	good compared to Glib when using its pure perl backend.
		1893
		1894	Event suffers from high setup time as well (look at its code and you will
		1895	understand why). Callback invocation also has a high overhead compared to
		1896	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1897	uses select or poll in basically all documented configurations.
		1898
		1899	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1900	clearly fails to perform with many filehandles or in busy servers.
		1901
		1902	POE is still completely out of the picture, taking over 1000 times as long
		1903	as EV, and over 100 times as long as the Perl implementation, even though
		1904	it uses a C-based event loop in this case.
		1905
		1906	=head3 Summary
		1907
		1908	=over 4
		1909
		1910	=item * The pure perl implementation performs extremely well.
		1911
		1912	=item * Avoid Glib or POE in large projects where performance matters.
		1913
		1914	=back
		1915
		1916	=head2 BENCHMARKING SMALL SERVERS
		1917
		1918	While event loops should scale (and select-based ones do not...) even to
		1919	large servers, most programs we (or I :) actually write have only a few
		1920	I/O watchers.
		1921
		1922	In this benchmark, I use the same benchmark program as in the large server
		1923	case, but it uses only eight "servers", of which three are active at any
		1924	one time. This should reflect performance for a small server relatively
		1925	well.
		1926
		1927	The columns are identical to the previous table.
		1928
		1929	=head3 Results
		1930
		1931	name sockets create request
		1932	EV 16 20.00 6.54
		1933	Perl 16 25.75 12.62
		1934	Event 16 81.27 35.86
		1935	Glib 16 32.63 15.48
		1936	POE 16 261.87 276.28 uses POE::Loop::Event
		1937
		1938	=head3 Discussion
		1939
		1940	The benchmark tries to test the performance of a typical small
		1941	server. While knowing how various event loops perform is interesting, keep
		1942	in mind that their overhead in this case is usually not as important, due
		1943	to the small absolute number of watchers (that is, you need efficiency and
		1944	speed most when you have lots of watchers, not when you only have a few of
		1945	them).
		1946
		1947	EV is again fastest.
		1948
		1949	Perl again comes second. It is noticeably faster than the C-based event
		1950	loops Event and Glib, although the difference is too small to really
		1951	matter.
		1952
		1953	POE also performs much better in this case, but is is still far behind the
		1954	others.
		1955
		1956	=head3 Summary
		1957
		1958	=over 4
		1959
		1960	=item * C-based event loops perform very well with small number of
		1961	watchers, as the management overhead dominates.
		1962
		1963	=back
		1964
		1965	=head2 THE IO::Lambda BENCHMARK
		1966
		1967	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1968	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		1969	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		1970	shouldn't come as a surprise to anybody). As such, the benchmark is
		1971	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		1972	very optimal. But how would AnyEvent compare when used without the extra
		1973	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		1974
		1975	The benchmark itself creates an echo-server, and then, for 500 times,
		1976	connects to the echo server, sends a line, waits for the reply, and then
		1977	creates the next connection. This is a rather bad benchmark, as it doesn't
		1978	test the efficiency of the framework or much non-blocking I/O, but it is a
		1979	benchmark nevertheless.
		1980
		1981	name runtime
		1982	Lambda/select 0.330 sec
		1983	+ optimized 0.122 sec
		1984	Lambda/AnyEvent 0.327 sec
		1985	+ optimized 0.138 sec
		1986	Raw sockets/select 0.077 sec
		1987	POE/select, components 0.662 sec
		1988	POE/select, raw sockets 0.226 sec
		1989	POE/select, optimized 0.404 sec
		1990
		1991	AnyEvent/select/nb 0.085 sec
		1992	AnyEvent/EV/nb 0.068 sec
		1993	+state machine 0.134 sec
		1994
		1995	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1996	benchmarks actually make blocking connects and use 100% blocking I/O,
		1997	defeating the purpose of an event-based solution. All of the newly
		1998	written AnyEvent benchmarks use 100% non-blocking connects (using
		1999	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2000	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2001	generally require a lot more bookkeeping and event handling than blocking
		2002	connects (which involve a single syscall only).
		2003
		2004	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2005	offers similar expressive power as POE and IO::Lambda, using conventional
		2006	Perl syntax. This means that both the echo server and the client are 100%
		2007	non-blocking, further placing it at a disadvantage.
		2008
		2009	As you can see, the AnyEvent + EV combination even beats the
		2010	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2011	backend easily beats IO::Lambda and POE.
		2012
		2013	And even the 100% non-blocking version written using the high-level (and
		2014	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
		2015	large margin, even though it does all of DNS, tcp-connect and socket I/O
		2016	in a non-blocking way.
		2017
		2018	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2019	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2020	part of the IO::lambda distribution and were used without any changes.
		2021
		2022
		2023	=head1 SIGNALS
		2024
		2025	AnyEvent currently installs handlers for these signals:
		2026
		2027	=over 4
		2028
		2029	=item SIGCHLD
		2030
		2031	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2032	emulation for event loops that do not support them natively. Also, some
		2033	event loops install a similar handler.
		2034
		2035	If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent will
		2036	reset it to default, to avoid losing child exit statuses.
		2037
		2038	=item SIGPIPE
		2039
		2040	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2041	when AnyEvent gets loaded.
		2042
		2043	The rationale for this is that AnyEvent users usually do not really depend
		2044	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2045	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2046	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2047	some random socket.
		2048
		2049	The rationale for installing a no-op handler as opposed to ignoring it is
		2050	that this way, the handler will be restored to defaults on exec.
		2051
		2052	Feel free to install your own handler, or reset it to defaults.
		2053
		2054	=back
		2055
		2056	=cut
		2057
		2058	undef $SIG{CHLD}
		2059	if $SIG{CHLD} eq 'IGNORE';
		2060
		2061	$SIG{PIPE} = sub { }
		2062	unless defined $SIG{PIPE};
		2063
		2064	=head1 FORK
		2065
		2066	Most event libraries are not fork-safe. The ones who are usually are
		2067	because they rely on inefficient but fork-safe C<select> or C<poll>
		2068	calls. Only L<EV> is fully fork-aware.
		2069
		2070	If you have to fork, you must either do so I<before> creating your first
		2071	watcher OR you must not use AnyEvent at all in the child.
		2072
		2073
		2074	=head1 SECURITY CONSIDERATIONS
		2075
		2076	AnyEvent can be forced to load any event model via
		2077	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2078	execute arbitrary code or directly gain access, it can easily be used to
		2079	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2080	will not be active when the program uses a different event model than
		2081	specified in the variable.
		2082
		2083	You can make AnyEvent completely ignore this variable by deleting it
		2084	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2085
		2086	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2087
		2088	use AnyEvent;
		2089
		2090	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2091	be used to probe what backend is used and gain other information (which is
		2092	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2093	$ENV{PERL_ANYEVENT_STRICT}.
		2094
		2095	Note that AnyEvent will remove I<all> environment variables starting with
		2096	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2097	enabled.
		2098
		2099
		2100	=head1 BUGS
		2101
		2102	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2103	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2104	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2105	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2106	pronounced).
		2107
621		2108
622	=head1 SEE ALSO	2109	=head1 SEE ALSO
623		2110
624	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	2111	Utility functions: L<AnyEvent::Util>.
625		2112
626	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	2113	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		2114	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
627		2115
628	Nontrivial usage example: L<Net::FCP>.	2116	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2117	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2118	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2119	L<AnyEvent::Impl::POE>.
629		2120
630	=head1	2121	Non-blocking file handles, sockets, TCP clients and
		2122	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		2123
		2124	Asynchronous DNS: L<AnyEvent::DNS>.
		2125
		2126	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		2127
		2128	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		2129
		2130
		2131	=head1 AUTHOR
		2132
		2133	Marc Lehmann <schmorp@schmorp.de>
		2134	http://home.schmorp.de/
631		2135
632	=cut	2136	=cut
633		2137
634	1	2138	1
635		2139

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