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Revision 1.382 by root, Thu Sep 1 23:46:26 2011 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - the DBI of event loop programming
4		4
5	Event, Coro, Glib, Tk - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, Qt,
		6	FLTK and POE are various supported event loops/environments.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# if you prefer function calls, look at the AE manpage for
		13	# an alternative API.
		14
		15	# file handle or descriptor readable
11	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {	16	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12	my ($poll_got) = @_;	17
		18	# one-shot or repeating timers
		19	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		20	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
		21
		22	print AnyEvent->now; # prints current event loop time
		23	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		24
		25	# POSIX signal
		26	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		27
		28	# child process exit
		29	my $w = AnyEvent->child (pid => $pid, cb => sub {
		30	my ($pid, $status) = @_;
13	...	31	...
14	});	32	});
15		33
16	* only one io watcher per $fh and $poll type is allowed (i.e. on a socket	34	# called when event loop idle (if applicable)
17	you can have one r + one w or one rw watcher, not any more (limitation by	35	my $w = AnyEvent->idle (cb => sub { ... });
18	Tk).
19		36
20	* the C<$poll_got> passed to the handler needs to be checked by looking	37	my $w = AnyEvent->condvar; # stores whether a condition was flagged
21	for single characters (e.g. with a regex), as it can contain more event	38	$w->send; # wake up current and all future recv's
22	types than were requested (e.g. a 'w' watcher might generate 'rw' events,	39	$w->recv; # enters "main loop" till $condvar gets ->send
23	limitation by Glib).	40	# use a condvar in callback mode:
		41	$w->cb (sub { $_[0]->recv });
24		42
25	* AnyEvent will keep filehandles alive, so as long as the watcher exists,	43	=head1 INTRODUCTION/TUTORIAL
26	the filehandle exists.
27		44
		45	This manpage is mainly a reference manual. If you are interested
		46	in a tutorial or some gentle introduction, have a look at the
		47	L<AnyEvent::Intro> manpage.
		48
		49	=head1 SUPPORT
		50
		51	An FAQ document is available as L<AnyEvent::FAQ>.
		52
		53	There also is a mailinglist for discussing all things AnyEvent, and an IRC
		54	channel, too.
		55
		56	See the AnyEvent project page at the B<Schmorpforge Ta-Sa Software
		57	Repository>, at L<http://anyevent.schmorp.de>, for more info.
		58
		59	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		60
		61	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		62	nowadays. So what is different about AnyEvent?
		63
		64	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		65	policy> and AnyEvent is I<small and efficient>.
		66
		67	First and foremost, I<AnyEvent is not an event model> itself, it only
		68	interfaces to whatever event model the main program happens to use, in a
		69	pragmatic way. For event models and certain classes of immortals alike,
		70	the statement "there can only be one" is a bitter reality: In general,
		71	only one event loop can be active at the same time in a process. AnyEvent
		72	cannot change this, but it can hide the differences between those event
		73	loops.
		74
		75	The goal of AnyEvent is to offer module authors the ability to do event
		76	programming (waiting for I/O or timer events) without subscribing to a
		77	religion, a way of living, and most importantly: without forcing your
		78	module users into the same thing by forcing them to use the same event
		79	model you use.
		80
		81	For modules like POE or IO::Async (which is a total misnomer as it is
		82	actually doing all I/O I<synchronously>...), using them in your module is
		83	like joining a cult: After you join, you are dependent on them and you
		84	cannot use anything else, as they are simply incompatible to everything
		85	that isn't them. What's worse, all the potential users of your
		86	module are I<also> forced to use the same event loop you use.
		87
		88	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		89	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		90	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
		91	uses one of those, every user of your module has to use it, too. But if
		92	your module uses AnyEvent, it works transparently with all event models it
		93	supports (including stuff like IO::Async, as long as those use one of the
		94	supported event loops. It is easy to add new event loops to AnyEvent, too,
		95	so it is future-proof).
		96
		97	In addition to being free of having to use I<the one and only true event
		98	model>, AnyEvent also is free of bloat and policy: with POE or similar
		99	modules, you get an enormous amount of code and strict rules you have to
		100	follow. AnyEvent, on the other hand, is lean and to the point, by only
		101	offering the functionality that is necessary, in as thin as a wrapper as
		102	technically possible.
		103
		104	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		105	of useful functionality, such as an asynchronous DNS resolver, 100%
		106	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		107	such as Windows) and lots of real-world knowledge and workarounds for
		108	platform bugs and differences.
		109
		110	Now, if you I<do want> lots of policy (this can arguably be somewhat
		111	useful) and you want to force your users to use the one and only event
		112	model, you should I<not> use this module.
		113
		114	=head1 DESCRIPTION
		115
		116	L<AnyEvent> provides a uniform interface to various event loops. This
		117	allows module authors to use event loop functionality without forcing
		118	module users to use a specific event loop implementation (since more
		119	than one event loop cannot coexist peacefully).
		120
		121	The interface itself is vaguely similar, but not identical to the L<Event>
		122	module.
		123
		124	During the first call of any watcher-creation method, the module tries
		125	to detect the currently loaded event loop by probing whether one of the
		126	following modules is already loaded: L<EV>, L<AnyEvent::Loop>,
		127	L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>. The first one
		128	found is used. If none are detected, the module tries to load the first
		129	four modules in the order given; but note that if L<EV> is not
		130	available, the pure-perl L<AnyEvent::Loop> should always work, so
		131	the other two are not normally tried.
		132
		133	Because AnyEvent first checks for modules that are already loaded, loading
		134	an event model explicitly before first using AnyEvent will likely make
		135	that model the default. For example:
		136
		137	use Tk;
		138	use AnyEvent;
		139
		140	# .. AnyEvent will likely default to Tk
		141
		142	The I<likely> means that, if any module loads another event model and
		143	starts using it, all bets are off - this case should be very rare though,
		144	as very few modules hardcode event loops without announcing this very
		145	loudly.
		146
		147	The pure-perl implementation of AnyEvent is called C<AnyEvent::Loop>. Like
		148	other event modules you can load it explicitly and enjoy the high
		149	availability of that event loop :)
		150
		151	=head1 WATCHERS
		152
		153	AnyEvent has the central concept of a I<watcher>, which is an object that
		154	stores relevant data for each kind of event you are waiting for, such as
		155	the callback to call, the file handle to watch, etc.
		156
		157	These watchers are normal Perl objects with normal Perl lifetime. After
		158	creating a watcher it will immediately "watch" for events and invoke the
		159	callback when the event occurs (of course, only when the event model
		160	is in control).
		161
		162	Note that B<callbacks must not permanently change global variables>
		163	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		164	callbacks must not C<die> >>. The former is good programming practice in
		165	Perl and the latter stems from the fact that exception handling differs
		166	widely between event loops.
		167
		168	To disable a watcher you have to destroy it (e.g. by setting the
		169	variable you store it in to C<undef> or otherwise deleting all references
		170	to it).
		171
		172	All watchers are created by calling a method on the C<AnyEvent> class.
		173
		174	Many watchers either are used with "recursion" (repeating timers for
		175	example), or need to refer to their watcher object in other ways.
		176
		177	One way to achieve that is this pattern:
		178
		179	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		180	# you can use $w here, for example to undef it
		181	undef $w;
		182	});
		183
		184	Note that C<my $w; $w => combination. This is necessary because in Perl,
		185	my variables are only visible after the statement in which they are
		186	declared.
		187
		188	=head2 I/O WATCHERS
		189
		190	$w = AnyEvent->io (
		191	fh => <filehandle_or_fileno>,
		192	poll => <"r" or "w">,
		193	cb => <callback>,
		194	);
		195
		196	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		197	with the following mandatory key-value pairs as arguments:
		198
		199	C<fh> is the Perl I<file handle> (or a naked file descriptor) to watch
		200	for events (AnyEvent might or might not keep a reference to this file
		201	handle). Note that only file handles pointing to things for which
		202	non-blocking operation makes sense are allowed. This includes sockets,
		203	most character devices, pipes, fifos and so on, but not for example files
		204	or block devices.
		205
		206	C<poll> must be a string that is either C<r> or C<w>, which creates a
		207	watcher waiting for "r"eadable or "w"ritable events, respectively.
		208
		209	C<cb> is the callback to invoke each time the file handle becomes ready.
		210
		211	Although the callback might get passed parameters, their value and
		212	presence is undefined and you cannot rely on them. Portable AnyEvent
		213	callbacks cannot use arguments passed to I/O watcher callbacks.
		214
		215	The I/O watcher might use the underlying file descriptor or a copy of it.
		216	You must not close a file handle as long as any watcher is active on the
		217	underlying file descriptor.
		218
		219	Some event loops issue spurious readiness notifications, so you should
		220	always use non-blocking calls when reading/writing from/to your file
		221	handles.
		222
		223	Example: wait for readability of STDIN, then read a line and disable the
		224	watcher.
		225
		226	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		227	chomp (my $input = <STDIN>);
		228	warn "read: $input\n";
		229	undef $w;
		230	});
		231
		232	=head2 TIME WATCHERS
		233
		234	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		235
		236	$w = AnyEvent->timer (
		237	after => <fractional_seconds>,
		238	interval => <fractional_seconds>,
		239	cb => <callback>,
		240	);
		241
		242	You can create a time watcher by calling the C<< AnyEvent->timer >>
		243	method with the following mandatory arguments:
		244
		245	C<after> specifies after how many seconds (fractional values are
		246	supported) the callback should be invoked. C<cb> is the callback to invoke
		247	in that case.
		248
		249	Although the callback might get passed parameters, their value and
		250	presence is undefined and you cannot rely on them. Portable AnyEvent
		251	callbacks cannot use arguments passed to time watcher callbacks.
		252
		253	The callback will normally be invoked only once. If you specify another
		254	parameter, C<interval>, as a strictly positive number (> 0), then the
		255	callback will be invoked regularly at that interval (in fractional
		256	seconds) after the first invocation. If C<interval> is specified with a
		257	false value, then it is treated as if it were not specified at all.
		258
		259	The callback will be rescheduled before invoking the callback, but no
		260	attempt is made to avoid timer drift in most backends, so the interval is
		261	only approximate.
		262
		263	Example: fire an event after 7.7 seconds.
		264
28	my $w = AnyEvent->timer (after => $seconds, cb => sub {	265	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		266	warn "timeout\n";
		267	});
		268
		269	# to cancel the timer:
		270	undef $w;
		271
		272	Example 2: fire an event after 0.5 seconds, then roughly every second.
		273
		274	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		275	warn "timeout\n";
		276	};
		277
		278	=head3 TIMING ISSUES
		279
		280	There are two ways to handle timers: based on real time (relative, "fire
		281	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		282	o'clock").
		283
		284	While most event loops expect timers to specified in a relative way, they
		285	use absolute time internally. This makes a difference when your clock
		286	"jumps", for example, when ntp decides to set your clock backwards from
		287	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		288	fire "after a second" might actually take six years to finally fire.
		289
		290	AnyEvent cannot compensate for this. The only event loop that is conscious
		291	of these issues is L<EV>, which offers both relative (ev_timer, based
		292	on true relative time) and absolute (ev_periodic, based on wallclock time)
		293	timers.
		294
		295	AnyEvent always prefers relative timers, if available, matching the
		296	AnyEvent API.
		297
		298	AnyEvent has two additional methods that return the "current time":
		299
		300	=over 4
		301
		302	=item AnyEvent->time
		303
		304	This returns the "current wallclock time" as a fractional number of
		305	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		306	return, and the result is guaranteed to be compatible with those).
		307
		308	It progresses independently of any event loop processing, i.e. each call
		309	will check the system clock, which usually gets updated frequently.
		310
		311	=item AnyEvent->now
		312
		313	This also returns the "current wallclock time", but unlike C<time>, above,
		314	this value might change only once per event loop iteration, depending on
		315	the event loop (most return the same time as C<time>, above). This is the
		316	time that AnyEvent's timers get scheduled against.
		317
		318	I<In almost all cases (in all cases if you don't care), this is the
		319	function to call when you want to know the current time.>
		320
		321	This function is also often faster then C<< AnyEvent->time >>, and
		322	thus the preferred method if you want some timestamp (for example,
		323	L<AnyEvent::Handle> uses this to update its activity timeouts).
		324
		325	The rest of this section is only of relevance if you try to be very exact
		326	with your timing; you can skip it without a bad conscience.
		327
		328	For a practical example of when these times differ, consider L<Event::Lib>
		329	and L<EV> and the following set-up:
		330
		331	The event loop is running and has just invoked one of your callbacks at
		332	time=500 (assume no other callbacks delay processing). In your callback,
		333	you wait a second by executing C<sleep 1> (blocking the process for a
		334	second) and then (at time=501) you create a relative timer that fires
		335	after three seconds.
		336
		337	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		338	both return C<501>, because that is the current time, and the timer will
		339	be scheduled to fire at time=504 (C<501> + C<3>).
		340
		341	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		342	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		343	last event processing phase started. With L<EV>, your timer gets scheduled
		344	to run at time=503 (C<500> + C<3>).
		345
		346	In one sense, L<Event::Lib> is more exact, as it uses the current time
		347	regardless of any delays introduced by event processing. However, most
		348	callbacks do not expect large delays in processing, so this causes a
		349	higher drift (and a lot more system calls to get the current time).
		350
		351	In another sense, L<EV> is more exact, as your timer will be scheduled at
		352	the same time, regardless of how long event processing actually took.
		353
		354	In either case, if you care (and in most cases, you don't), then you
		355	can get whatever behaviour you want with any event loop, by taking the
		356	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		357	account.
		358
		359	=item AnyEvent->now_update
		360
		361	Some event loops (such as L<EV> or L<AnyEvent::Loop>) cache the current
		362	time for each loop iteration (see the discussion of L<< AnyEvent->now >>,
		363	above).
		364
		365	When a callback runs for a long time (or when the process sleeps), then
		366	this "current" time will differ substantially from the real time, which
		367	might affect timers and time-outs.
		368
		369	When this is the case, you can call this method, which will update the
		370	event loop's idea of "current time".
		371
		372	A typical example would be a script in a web server (e.g. C<mod_perl>) -
		373	when mod_perl executes the script, then the event loop will have the wrong
		374	idea about the "current time" (being potentially far in the past, when the
		375	script ran the last time). In that case you should arrange a call to C<<
		376	AnyEvent->now_update >> each time the web server process wakes up again
		377	(e.g. at the start of your script, or in a handler).
		378
		379	Note that updating the time I<might> cause some events to be handled.
		380
		381	=back
		382
		383	=head2 SIGNAL WATCHERS
		384
		385	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		386
		387	You can watch for signals using a signal watcher, C<signal> is the signal
		388	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
		389	callback to be invoked whenever a signal occurs.
		390
		391	Although the callback might get passed parameters, their value and
		392	presence is undefined and you cannot rely on them. Portable AnyEvent
		393	callbacks cannot use arguments passed to signal watcher callbacks.
		394
		395	Multiple signal occurrences can be clumped together into one callback
		396	invocation, and callback invocation will be synchronous. Synchronous means
		397	that it might take a while until the signal gets handled by the process,
		398	but it is guaranteed not to interrupt any other callbacks.
		399
		400	The main advantage of using these watchers is that you can share a signal
		401	between multiple watchers, and AnyEvent will ensure that signals will not
		402	interrupt your program at bad times.
		403
		404	This watcher might use C<%SIG> (depending on the event loop used),
		405	so programs overwriting those signals directly will likely not work
		406	correctly.
		407
		408	Example: exit on SIGINT
		409
		410	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		411
		412	=head3 Restart Behaviour
		413
		414	While restart behaviour is up to the event loop implementation, most will
		415	not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
		416	pure perl implementation).
		417
		418	=head3 Safe/Unsafe Signals
		419
		420	Perl signals can be either "safe" (synchronous to opcode handling) or
		421	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		422	latter might corrupt your memory.
		423
		424	AnyEvent signal handlers are, in addition, synchronous to the event loop,
		425	i.e. they will not interrupt your running perl program but will only be
		426	called as part of the normal event handling (just like timer, I/O etc.
		427	callbacks, too).
		428
		429	=head3 Signal Races, Delays and Workarounds
		430
		431	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		432	callbacks to signals in a generic way, which is a pity, as you cannot
		433	do race-free signal handling in perl, requiring C libraries for
		434	this. AnyEvent will try to do its best, which means in some cases,
		435	signals will be delayed. The maximum time a signal might be delayed is
		436	specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10 seconds). This
		437	variable can be changed only before the first signal watcher is created,
		438	and should be left alone otherwise. This variable determines how often
		439	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		440	will cause fewer spurious wake-ups, which is better for power and CPU
		441	saving.
		442
		443	All these problems can be avoided by installing the optional
		444	L<Async::Interrupt> module, which works with most event loops. It will not
		445	work with inherently broken event loops such as L<Event> or L<Event::Lib>
		446	(and not with L<POE> currently, as POE does its own workaround with
		447	one-second latency). For those, you just have to suffer the delays.
		448
		449	=head2 CHILD PROCESS WATCHERS
		450
		451	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		452
		453	You can also watch for a child process exit and catch its exit status.
		454
		455	The child process is specified by the C<pid> argument (on some backends,
		456	using C<0> watches for any child process exit, on others this will
		457	croak). The watcher will be triggered only when the child process has
		458	finished and an exit status is available, not on any trace events
		459	(stopped/continued).
		460
		461	The callback will be called with the pid and exit status (as returned by
		462	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		463	callback arguments.
		464
		465	This watcher type works by installing a signal handler for C<SIGCHLD>,
		466	and since it cannot be shared, nothing else should use SIGCHLD or reap
		467	random child processes (waiting for specific child processes, e.g. inside
		468	C<system>, is just fine).
		469
		470	There is a slight catch to child watchers, however: you usually start them
		471	I<after> the child process was created, and this means the process could
		472	have exited already (and no SIGCHLD will be sent anymore).
		473
		474	Not all event models handle this correctly (neither POE nor IO::Async do,
		475	see their AnyEvent::Impl manpages for details), but even for event models
		476	that I<do> handle this correctly, they usually need to be loaded before
		477	the process exits (i.e. before you fork in the first place). AnyEvent's
		478	pure perl event loop handles all cases correctly regardless of when you
		479	start the watcher.
		480
		481	This means you cannot create a child watcher as the very first
		482	thing in an AnyEvent program, you I<have> to create at least one
		483	watcher before you C<fork> the child (alternatively, you can call
		484	C<AnyEvent::detect>).
		485
		486	As most event loops do not support waiting for child events, they will be
		487	emulated by AnyEvent in most cases, in which case the latency and race
		488	problems mentioned in the description of signal watchers apply.
		489
		490	Example: fork a process and wait for it
		491
		492	my $done = AnyEvent->condvar;
		493
		494	my $pid = fork or exit 5;
		495
		496	my $w = AnyEvent->child (
		497	pid => $pid,
		498	cb => sub {
		499	my ($pid, $status) = @_;
		500	warn "pid $pid exited with status $status";
		501	$done->send;
		502	},
		503	);
		504
		505	# do something else, then wait for process exit
		506	$done->recv;
		507
		508	=head2 IDLE WATCHERS
		509
		510	$w = AnyEvent->idle (cb => <callback>);
		511
		512	This will repeatedly invoke the callback after the process becomes idle,
		513	until either the watcher is destroyed or new events have been detected.
		514
		515	Idle watchers are useful when there is a need to do something, but it
		516	is not so important (or wise) to do it instantly. The callback will be
		517	invoked only when there is "nothing better to do", which is usually
		518	defined as "all outstanding events have been handled and no new events
		519	have been detected". That means that idle watchers ideally get invoked
		520	when the event loop has just polled for new events but none have been
		521	detected. Instead of blocking to wait for more events, the idle watchers
		522	will be invoked.
		523
		524	Unfortunately, most event loops do not really support idle watchers (only
		525	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		526	will simply call the callback "from time to time".
		527
		528	Example: read lines from STDIN, but only process them when the
		529	program is otherwise idle:
		530
		531	my @lines; # read data
		532	my $idle_w;
		533	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		534	push @lines, scalar <STDIN>;
		535
		536	# start an idle watcher, if not already done
		537	$idle_w ||= AnyEvent->idle (cb => sub {
		538	# handle only one line, when there are lines left
		539	if (my $line = shift @lines) {
		540	print "handled when idle: $line";
		541	} else {
		542	# otherwise disable the idle watcher again
		543	undef $idle_w;
		544	}
		545	});
		546	});
		547
		548	=head2 CONDITION VARIABLES
		549
		550	$cv = AnyEvent->condvar;
		551
		552	$cv->send (<list>);
		553	my @res = $cv->recv;
		554
		555	If you are familiar with some event loops you will know that all of them
		556	require you to run some blocking "loop", "run" or similar function that
		557	will actively watch for new events and call your callbacks.
		558
		559	AnyEvent is slightly different: it expects somebody else to run the event
		560	loop and will only block when necessary (usually when told by the user).
		561
		562	The tool to do that is called a "condition variable", so called because
		563	they represent a condition that must become true.
		564
		565	Now is probably a good time to look at the examples further below.
		566
		567	Condition variables can be created by calling the C<< AnyEvent->condvar
		568	>> method, usually without arguments. The only argument pair allowed is
		569	C<cb>, which specifies a callback to be called when the condition variable
		570	becomes true, with the condition variable as the first argument (but not
		571	the results).
		572
		573	After creation, the condition variable is "false" until it becomes "true"
		574	by calling the C<send> method (or calling the condition variable as if it
		575	were a callback, read about the caveats in the description for the C<<
		576	->send >> method).
		577
		578	Since condition variables are the most complex part of the AnyEvent API, here are
		579	some different mental models of what they are - pick the ones you can connect to:
		580
		581	=over 4
		582
		583	=item * Condition variables are like callbacks - you can call them (and pass them instead
		584	of callbacks). Unlike callbacks however, you can also wait for them to be called.
		585
		586	=item * Condition variables are signals - one side can emit or send them,
		587	the other side can wait for them, or install a handler that is called when
		588	the signal fires.
		589
		590	=item * Condition variables are like "Merge Points" - points in your program
		591	where you merge multiple independent results/control flows into one.
		592
		593	=item * Condition variables represent a transaction - functions that start
		594	some kind of transaction can return them, leaving the caller the choice
		595	between waiting in a blocking fashion, or setting a callback.
		596
		597	=item * Condition variables represent future values, or promises to deliver
		598	some result, long before the result is available.
		599
		600	=back
		601
		602	Condition variables are very useful to signal that something has finished,
		603	for example, if you write a module that does asynchronous http requests,
		604	then a condition variable would be the ideal candidate to signal the
		605	availability of results. The user can either act when the callback is
		606	called or can synchronously C<< ->recv >> for the results.
		607
		608	You can also use them to simulate traditional event loops - for example,
		609	you can block your main program until an event occurs - for example, you
		610	could C<< ->recv >> in your main program until the user clicks the Quit
		611	button of your app, which would C<< ->send >> the "quit" event.
		612
		613	Note that condition variables recurse into the event loop - if you have
		614	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		615	lose. Therefore, condition variables are good to export to your caller, but
		616	you should avoid making a blocking wait yourself, at least in callbacks,
		617	as this asks for trouble.
		618
		619	Condition variables are represented by hash refs in perl, and the keys
		620	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		621	easy (it is often useful to build your own transaction class on top of
		622	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		623	its C<new> method in your own C<new> method.
		624
		625	There are two "sides" to a condition variable - the "producer side" which
		626	eventually calls C<< -> send >>, and the "consumer side", which waits
		627	for the send to occur.
		628
		629	Example: wait for a timer.
		630
		631	# condition: "wait till the timer is fired"
		632	my $timer_fired = AnyEvent->condvar;
		633
		634	# create the timer - we could wait for, say
		635	# a handle becomign ready, or even an
		636	# AnyEvent::HTTP request to finish, but
		637	# in this case, we simply use a timer:
		638	my $w = AnyEvent->timer (
		639	after => 1,
		640	cb => sub { $timer_fired->send },
		641	);
		642
		643	# this "blocks" (while handling events) till the callback
		644	# calls ->send
		645	$timer_fired->recv;
		646
		647	Example: wait for a timer, but take advantage of the fact that condition
		648	variables are also callable directly.
		649
		650	my $done = AnyEvent->condvar;
		651	my $delay = AnyEvent->timer (after => 5, cb => $done);
		652	$done->recv;
		653
		654	Example: Imagine an API that returns a condvar and doesn't support
		655	callbacks. This is how you make a synchronous call, for example from
		656	the main program:
		657
		658	use AnyEvent::CouchDB;
		659
		660	...
		661
		662	my @info = $couchdb->info->recv;
		663
		664	And this is how you would just set a callback to be called whenever the
		665	results are available:
		666
		667	$couchdb->info->cb (sub {
		668	my @info = $_[0]->recv;
		669	});
		670
		671	=head3 METHODS FOR PRODUCERS
		672
		673	These methods should only be used by the producing side, i.e. the
		674	code/module that eventually sends the signal. Note that it is also
		675	the producer side which creates the condvar in most cases, but it isn't
		676	uncommon for the consumer to create it as well.
		677
		678	=over 4
		679
		680	=item $cv->send (...)
		681
		682	Flag the condition as ready - a running C<< ->recv >> and all further
		683	calls to C<recv> will (eventually) return after this method has been
		684	called. If nobody is waiting the send will be remembered.
		685
		686	If a callback has been set on the condition variable, it is called
		687	immediately from within send.
		688
		689	Any arguments passed to the C<send> call will be returned by all
		690	future C<< ->recv >> calls.
		691
		692	Condition variables are overloaded so one can call them directly (as if
		693	they were a code reference). Calling them directly is the same as calling
		694	C<send>.
		695
		696	=item $cv->croak ($error)
		697
		698	Similar to send, but causes all calls to C<< ->recv >> to invoke
		699	C<Carp::croak> with the given error message/object/scalar.
		700
		701	This can be used to signal any errors to the condition variable
		702	user/consumer. Doing it this way instead of calling C<croak> directly
		703	delays the error detection, but has the overwhelming advantage that it
		704	diagnoses the error at the place where the result is expected, and not
		705	deep in some event callback with no connection to the actual code causing
		706	the problem.
		707
		708	=item $cv->begin ([group callback])
		709
		710	=item $cv->end
		711
		712	These two methods can be used to combine many transactions/events into
		713	one. For example, a function that pings many hosts in parallel might want
		714	to use a condition variable for the whole process.
		715
		716	Every call to C<< ->begin >> will increment a counter, and every call to
		717	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		718	>>, the (last) callback passed to C<begin> will be executed, passing the
		719	condvar as first argument. That callback is I<supposed> to call C<< ->send
		720	>>, but that is not required. If no group callback was set, C<send> will
		721	be called without any arguments.
		722
		723	You can think of C<< $cv->send >> giving you an OR condition (one call
		724	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		725	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		726
		727	Let's start with a simple example: you have two I/O watchers (for example,
		728	STDOUT and STDERR for a program), and you want to wait for both streams to
		729	close before activating a condvar:
		730
		731	my $cv = AnyEvent->condvar;
		732
		733	$cv->begin; # first watcher
		734	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		735	defined sysread $fh1, my $buf, 4096
		736	or $cv->end;
		737	});
		738
		739	$cv->begin; # second watcher
		740	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		741	defined sysread $fh2, my $buf, 4096
		742	or $cv->end;
		743	});
		744
		745	$cv->recv;
		746
		747	This works because for every event source (EOF on file handle), there is
		748	one call to C<begin>, so the condvar waits for all calls to C<end> before
		749	sending.
		750
		751	The ping example mentioned above is slightly more complicated, as the
		752	there are results to be passwd back, and the number of tasks that are
		753	begun can potentially be zero:
		754
		755	my $cv = AnyEvent->condvar;
		756
		757	my %result;
		758	$cv->begin (sub { shift->send (\%result) });
		759
		760	for my $host (@list_of_hosts) {
		761	$cv->begin;
		762	ping_host_then_call_callback $host, sub {
		763	$result{$host} = ...;
		764	$cv->end;
		765	};
		766	}
		767
		768	$cv->end;
		769
		770	This code fragment supposedly pings a number of hosts and calls
		771	C<send> after results for all then have have been gathered - in any
		772	order. To achieve this, the code issues a call to C<begin> when it starts
		773	each ping request and calls C<end> when it has received some result for
		774	it. Since C<begin> and C<end> only maintain a counter, the order in which
		775	results arrive is not relevant.
		776
		777	There is an additional bracketing call to C<begin> and C<end> outside the
		778	loop, which serves two important purposes: first, it sets the callback
		779	to be called once the counter reaches C<0>, and second, it ensures that
		780	C<send> is called even when C<no> hosts are being pinged (the loop
		781	doesn't execute once).
		782
		783	This is the general pattern when you "fan out" into multiple (but
		784	potentially zero) subrequests: use an outer C<begin>/C<end> pair to set
		785	the callback and ensure C<end> is called at least once, and then, for each
		786	subrequest you start, call C<begin> and for each subrequest you finish,
		787	call C<end>.
		788
		789	=back
		790
		791	=head3 METHODS FOR CONSUMERS
		792
		793	These methods should only be used by the consuming side, i.e. the
		794	code awaits the condition.
		795
		796	=over 4
		797
		798	=item $cv->recv
		799
		800	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		801	>> methods have been called on C<$cv>, while servicing other watchers
		802	normally.
		803
		804	You can only wait once on a condition - additional calls are valid but
		805	will return immediately.
		806
		807	If an error condition has been set by calling C<< ->croak >>, then this
		808	function will call C<croak>.
		809
		810	In list context, all parameters passed to C<send> will be returned,
		811	in scalar context only the first one will be returned.
		812
		813	Note that doing a blocking wait in a callback is not supported by any
		814	event loop, that is, recursive invocation of a blocking C<< ->recv
		815	>> is not allowed, and the C<recv> call will C<croak> if such a
		816	condition is detected. This condition can be slightly loosened by using
		817	L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
		818	any thread that doesn't run the event loop itself.
		819
		820	Not all event models support a blocking wait - some die in that case
		821	(programs might want to do that to stay interactive), so I<if you are
		822	using this from a module, never require a blocking wait>. Instead, let the
		823	caller decide whether the call will block or not (for example, by coupling
		824	condition variables with some kind of request results and supporting
		825	callbacks so the caller knows that getting the result will not block,
		826	while still supporting blocking waits if the caller so desires).
		827
		828	You can ensure that C<< ->recv >> never blocks by setting a callback and
		829	only calling C<< ->recv >> from within that callback (or at a later
		830	time). This will work even when the event loop does not support blocking
		831	waits otherwise.
		832
		833	=item $bool = $cv->ready
		834
		835	Returns true when the condition is "true", i.e. whether C<send> or
		836	C<croak> have been called.
		837
		838	=item $cb = $cv->cb ($cb->($cv))
		839
		840	This is a mutator function that returns the callback set and optionally
		841	replaces it before doing so.
		842
		843	The callback will be called when the condition becomes "true", i.e. when
		844	C<send> or C<croak> are called, with the only argument being the
		845	condition variable itself. If the condition is already true, the
		846	callback is called immediately when it is set. Calling C<recv> inside
		847	the callback or at any later time is guaranteed not to block.
		848
		849	=back
		850
		851	=head1 SUPPORTED EVENT LOOPS/BACKENDS
		852
		853	The available backend classes are (every class has its own manpage):
		854
		855	=over 4
		856
		857	=item Backends that are autoprobed when no other event loop can be found.
		858
		859	EV is the preferred backend when no other event loop seems to be in
		860	use. If EV is not installed, then AnyEvent will fall back to its own
		861	pure-perl implementation, which is available everywhere as it comes with
		862	AnyEvent itself.
		863
		864	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		865	AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
		866
		867	=item Backends that are transparently being picked up when they are used.
		868
		869	These will be used if they are already loaded when the first watcher
		870	is created, in which case it is assumed that the application is using
		871	them. This means that AnyEvent will automatically pick the right backend
		872	when the main program loads an event module before anything starts to
		873	create watchers. Nothing special needs to be done by the main program.
		874
		875	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		876	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		877	AnyEvent::Impl::Tk based on Tk, very broken.
		878	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		879	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		880	AnyEvent::Impl::Irssi used when running within irssi.
		881	AnyEvent::Impl::IOAsync based on IO::Async.
		882	AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
		883	AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
		884
		885	=item Backends with special needs.
		886
		887	Qt requires the Qt::Application to be instantiated first, but will
		888	otherwise be picked up automatically. As long as the main program
		889	instantiates the application before any AnyEvent watchers are created,
		890	everything should just work.
		891
		892	AnyEvent::Impl::Qt based on Qt.
		893
		894	=item Event loops that are indirectly supported via other backends.
		895
		896	Some event loops can be supported via other modules:
		897
		898	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		899
		900	B<WxWidgets> has no support for watching file handles. However, you can
		901	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		902	polls 20 times per second, which was considered to be too horrible to even
		903	consider for AnyEvent.
		904
		905	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		906	backend, so it can be supported through POE.
		907
		908	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		909	load L<POE> when detecting them, in the hope that POE will pick them up,
		910	in which case everything will be automatic.
		911
		912	=back
		913
		914	=head1 GLOBAL VARIABLES AND FUNCTIONS
		915
		916	These are not normally required to use AnyEvent, but can be useful to
		917	write AnyEvent extension modules.
		918
		919	=over 4
		920
		921	=item $AnyEvent::MODEL
		922
		923	Contains C<undef> until the first watcher is being created, before the
		924	backend has been autodetected.
		925
		926	Afterwards it contains the event model that is being used, which is the
		927	name of the Perl class implementing the model. This class is usually one
		928	of the C<AnyEvent::Impl::xxx> modules, but can be any other class in the
		929	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
		930	will be C<urxvt::anyevent>).
		931
		932	=item AnyEvent::detect
		933
		934	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		935	if necessary. You should only call this function right before you would
		936	have created an AnyEvent watcher anyway, that is, as late as possible at
		937	runtime, and not e.g. during initialisation of your module.
		938
		939	The effect of calling this function is as if a watcher had been created
		940	(specifically, actions that happen "when the first watcher is created"
		941	happen when calling detetc as well).
		942
		943	If you need to do some initialisation before AnyEvent watchers are
		944	created, use C<post_detect>.
		945
		946	=item $guard = AnyEvent::post_detect { BLOCK }
		947
		948	Arranges for the code block to be executed as soon as the event model is
		949	autodetected (or immediately if that has already happened).
		950
		951	The block will be executed I<after> the actual backend has been detected
		952	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		953	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		954	other initialisations - see the sources of L<AnyEvent::Strict> or
		955	L<AnyEvent::AIO> to see how this is used.
		956
		957	The most common usage is to create some global watchers, without forcing
		958	event module detection too early, for example, L<AnyEvent::AIO> creates
		959	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		960	avoid autodetecting the event module at load time.
		961
		962	If called in scalar or list context, then it creates and returns an object
		963	that automatically removes the callback again when it is destroyed (or
		964	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		965	a case where this is useful.
		966
		967	Example: Create a watcher for the IO::AIO module and store it in
		968	C<$WATCHER>, but do so only do so after the event loop is initialised.
		969
		970	our WATCHER;
		971
		972	my $guard = AnyEvent::post_detect {
		973	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		974	};
		975
		976	# the ||= is important in case post_detect immediately runs the block,
		977	# as to not clobber the newly-created watcher. assigning both watcher and
		978	# post_detect guard to the same variable has the advantage of users being
		979	# able to just C<undef $WATCHER> if the watcher causes them grief.
		980
		981	$WATCHER ||= $guard;
		982
		983	=item @AnyEvent::post_detect
		984
		985	If there are any code references in this array (you can C<push> to it
		986	before or after loading AnyEvent), then they will be called directly
		987	after the event loop has been chosen.
		988
		989	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		990	if it is defined then the event loop has already been detected, and the
		991	array will be ignored.
		992
		993	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		994	it, as it takes care of these details.
		995
		996	This variable is mainly useful for modules that can do something useful
		997	when AnyEvent is used and thus want to know when it is initialised, but do
		998	not need to even load it by default. This array provides the means to hook
		999	into AnyEvent passively, without loading it.
		1000
		1001	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		1002	together, you could put this into Coro (this is the actual code used by
		1003	Coro to accomplish this):
		1004
		1005	if (defined $AnyEvent::MODEL) {
		1006	# AnyEvent already initialised, so load Coro::AnyEvent
		1007	require Coro::AnyEvent;
		1008	} else {
		1009	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		1010	# as soon as it is
		1011	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		1012	}
		1013
		1014	=item AnyEvent::postpone { BLOCK }
		1015
		1016	Arranges for the block to be executed as soon as possible, but not before
		1017	the call itself returns. In practise, the block will be executed just
		1018	before the event loop polls for new events, or shortly afterwards.
		1019
		1020	This function never returns anything (to make the C<return postpone { ...
		1021	}> idiom more useful.
		1022
		1023	To understand the usefulness of this function, consider a function that
		1024	asynchronously does something for you and returns some transaction
		1025	object or guard to let you cancel the operation. For example,
		1026	C<AnyEvent::Socket::tcp_connect>:
		1027
		1028	# start a conenction attempt unless one is active
		1029	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		1030	delete $self->{connect_guard};
29	...	1031	...
30	});	1032	};
31		1033
32	* io and time watchers get canceled whenever $w is destroyed, so keep a copy	1034	Imagine that this function could instantly call the callback, for
		1035	example, because it detects an obvious error such as a negative port
		1036	number. Invoking the callback before the function returns causes problems
		1037	however: the callback will be called and will try to delete the guard
		1038	object. But since the function hasn't returned yet, there is nothing to
		1039	delete. When the function eventually returns it will assign the guard
		1040	object to C<< $self->{connect_guard} >>, where it will likely never be
		1041	deleted, so the program thinks it is still trying to connect.
33		1042
34	* timers can only be used once and must be recreated for repeated	1043	This is where C<AnyEvent::postpone> should be used. Instead of calling the
35	operation (limitation by Glib and Tk).	1044	callback directly on error:
36		1045
37	my $w = AnyEvent->condvar; # kind of main loop replacement	1046	$cb->(undef), return # signal error to callback, BAD!
38	$w->wait; # enters main loop till $condvar gets ->broadcast	1047	if $some_error_condition;
39	$w->broadcast; # wake up current and all future wait's
40		1048
41	* condvars are used to give blocking behaviour when neccessary. Create	1049	It should use C<postpone>:
42	a condvar for any "request" or "event" your module might create, C<<
43	->broadcast >> it when the event happens and provide a function that calls
44	C<< ->wait >> for it. See the examples below.
45		1050
46	=head1 DESCRIPTION	1051	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1052	if $some_error_condition;
47		1053
48	L<AnyEvent> provides an identical interface to multiple event loops. This	1054	=item AnyEvent::log $level, $msg[, @args]
49	allows module authors to utilizy an event loop without forcing module
50	users to use the same event loop (as only a single event loop can coexist
51	peacefully at any one time).
52		1055
53	The interface itself is vaguely similar but not identical to the Event	1056	Log the given C<$msg> at the given C<$level>.
54	module.
55		1057
56	On the first call of any method, the module tries to detect the currently	1058	If L<AnyEvent::Log> is not loaded then this function makes a simple test
57	loaded event loop by probing wether any of the following modules is	1059	to see whether the message will be logged. If the test succeeds it will
58	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	1060	load AnyEvent::Log and call C<AnyEvent::Log::log> - consequently, look at
59	used. If none is found, the module tries to load these modules in the	1061	the L<AnyEvent::Log> documentation for details.
60	order given. The first one that could be successfully loaded will be	1062
61	used. If still none could be found, it will issue an error.	1063	If the test fails it will simply return. Right now this happens when a
		1064	numerical loglevel is used and it is larger than the level specified via
		1065	C<$ENV{PERL_ANYEVENT_VERBOSE}>.
		1066
		1067	If you want to sprinkle loads of logging calls around your code, consider
		1068	creating a logger callback with the C<AnyEvent::Log::logger> function,
		1069	which can reduce typing, codesize and can reduce the logging overhead
		1070	enourmously.
		1071
		1072	=back
		1073
		1074	=head1 WHAT TO DO IN A MODULE
		1075
		1076	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		1077	freely, but you should not load a specific event module or rely on it.
		1078
		1079	Be careful when you create watchers in the module body - AnyEvent will
		1080	decide which event module to use as soon as the first method is called, so
		1081	by calling AnyEvent in your module body you force the user of your module
		1082	to load the event module first.
		1083
		1084	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1085	the C<< ->send >> method has been called on it already. This is
		1086	because it will stall the whole program, and the whole point of using
		1087	events is to stay interactive.
		1088
		1089	It is fine, however, to call C<< ->recv >> when the user of your module
		1090	requests it (i.e. if you create a http request object ad have a method
		1091	called C<results> that returns the results, it may call C<< ->recv >>
		1092	freely, as the user of your module knows what she is doing. Always).
		1093
		1094	=head1 WHAT TO DO IN THE MAIN PROGRAM
		1095
		1096	There will always be a single main program - the only place that should
		1097	dictate which event model to use.
		1098
		1099	If the program is not event-based, it need not do anything special, even
		1100	when it depends on a module that uses an AnyEvent. If the program itself
		1101	uses AnyEvent, but does not care which event loop is used, all it needs
		1102	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1103	available loop implementation.
		1104
		1105	If the main program relies on a specific event model - for example, in
		1106	Gtk2 programs you have to rely on the Glib module - you should load the
		1107	event module before loading AnyEvent or any module that uses it: generally
		1108	speaking, you should load it as early as possible. The reason is that
		1109	modules might create watchers when they are loaded, and AnyEvent will
		1110	decide on the event model to use as soon as it creates watchers, and it
		1111	might choose the wrong one unless you load the correct one yourself.
		1112
		1113	You can chose to use a pure-perl implementation by loading the
		1114	C<AnyEvent::Loop> module, which gives you similar behaviour
		1115	everywhere, but letting AnyEvent chose the model is generally better.
		1116
		1117	=head2 MAINLOOP EMULATION
		1118
		1119	Sometimes (often for short test scripts, or even standalone programs who
		1120	only want to use AnyEvent), you do not want to run a specific event loop.
		1121
		1122	In that case, you can use a condition variable like this:
		1123
		1124	AnyEvent->condvar->recv;
		1125
		1126	This has the effect of entering the event loop and looping forever.
		1127
		1128	Note that usually your program has some exit condition, in which case
		1129	it is better to use the "traditional" approach of storing a condition
		1130	variable somewhere, waiting for it, and sending it when the program should
		1131	exit cleanly.
		1132
		1133
		1134	=head1 OTHER MODULES
		1135
		1136	The following is a non-exhaustive list of additional modules that use
		1137	AnyEvent as a client and can therefore be mixed easily with other
		1138	AnyEvent modules and other event loops in the same program. Some of the
		1139	modules come as part of AnyEvent, the others are available via CPAN (see
		1140	L<http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for
		1141	a longer non-exhaustive list), and the list is heavily biased towards
		1142	modules of the AnyEvent author himself :)
62		1143
63	=over 4	1144	=over 4
64		1145
		1146	=item L<AnyEvent::Util>
		1147
		1148	Contains various utility functions that replace often-used blocking
		1149	functions such as C<inet_aton> with event/callback-based versions.
		1150
		1151	=item L<AnyEvent::Socket>
		1152
		1153	Provides various utility functions for (internet protocol) sockets,
		1154	addresses and name resolution. Also functions to create non-blocking tcp
		1155	connections or tcp servers, with IPv6 and SRV record support and more.
		1156
		1157	=item L<AnyEvent::Handle>
		1158
		1159	Provide read and write buffers, manages watchers for reads and writes,
		1160	supports raw and formatted I/O, I/O queued and fully transparent and
		1161	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1162
		1163	=item L<AnyEvent::DNS>
		1164
		1165	Provides rich asynchronous DNS resolver capabilities.
		1166
		1167	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1168
		1169	Implement event-based interfaces to the protocols of the same name (for
		1170	the curious, IGS is the International Go Server and FCP is the Freenet
		1171	Client Protocol).
		1172
		1173	=item L<AnyEvent::AIO>
		1174
		1175	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1176	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1177	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1178	file I/O, and much more.
		1179
		1180	=item L<AnyEvent::Filesys::Notify>
		1181
		1182	AnyEvent is good for non-blocking stuff, but it can't detect file or
		1183	path changes (e.g. "watch this directory for new files", "watch this
		1184	file for changes"). The L<AnyEvent::Filesys::Notify> module promises to
		1185	do just that in a portbale fashion, supporting inotify on GNU/Linux and
		1186	some weird, without doubt broken, stuff on OS X to monitor files. It can
		1187	fall back to blocking scans at regular intervals transparently on other
		1188	platforms, so it's about as portable as it gets.
		1189
		1190	(I haven't used it myself, but I haven't heard anybody complaining about
		1191	it yet).
		1192
		1193	=item L<AnyEvent::DBI>
		1194
		1195	Executes L<DBI> requests asynchronously in a proxy process for you,
		1196	notifying you in an event-based way when the operation is finished.
		1197
		1198	=item L<AnyEvent::HTTPD>
		1199
		1200	A simple embedded webserver.
		1201
		1202	=item L<AnyEvent::FastPing>
		1203
		1204	The fastest ping in the west.
		1205
		1206	=item L<Coro>
		1207
		1208	Has special support for AnyEvent via L<Coro::AnyEvent>, which allows you
		1209	to simply invert the flow control - don't call us, we will call you:
		1210
		1211	async {
		1212	Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
		1213	print "5 seconds later!\n";
		1214
		1215	Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
		1216	my $line = <STDIN>; # works for ttys
		1217
		1218	AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
		1219	my ($body, $hdr) = Coro::rouse_wait;
		1220	};
		1221
		1222	=back
		1223
65	=cut	1224	=cut
66		1225
67	package AnyEvent;	1226	package AnyEvent;
68		1227
69	no warnings;	1228	# basically a tuned-down version of common::sense
70	use strict 'vars';	1229	sub common_sense {
		1230	# from common:.sense 3.4
		1231	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
		1232	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1233	$^H |= 0x00000600;
		1234	}
		1235
		1236	BEGIN { AnyEvent::common_sense }
		1237
71	use Carp;	1238	use Carp ();
72		1239
73	our $VERSION = '0.4';	1240	our $VERSION = '6.02';
74	our $MODEL;	1241	our $MODEL;
75
76	our $AUTOLOAD;
77	our @ISA;	1242	our @ISA;
		1243	our @REGISTRY;
		1244	our $VERBOSE;
		1245	our $MAX_SIGNAL_LATENCY = 10;
		1246	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
78		1247
79	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	1248	BEGIN {
		1249	require "AnyEvent/constants.pl";
80		1250
		1251	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1252
		1253	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1254	if ${^TAINT};
		1255
		1256	$ENV{"PERL_ANYEVENT_$_"} = $ENV{"AE_$_"}
		1257	for grep s/^AE_// && !exists $ENV{"PERL_ANYEVENT_$_"}, keys %ENV;
		1258
		1259	@ENV{grep /^PERL_ANYEVENT_/, keys %ENV} = ()
		1260	if ${^TAINT};
		1261
		1262	# $ENV{PERL_ANYEVENT_xxx} now valid
		1263
		1264	$VERBOSE = length $ENV{PERL_ANYEVENT_VERBOSE} ? $ENV{PERL_ANYEVENT_VERBOSE}*1 : 3;
		1265
		1266	my $idx;
		1267	$PROTOCOL{$_} = ++$idx
		1268	for reverse split /\s*,\s*/,
		1269	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1270	}
		1271
		1272	our @post_detect;
		1273
		1274	sub post_detect(&) {
		1275	my ($cb) = @_;
		1276
		1277	push @post_detect, $cb;
		1278
		1279	defined wantarray
		1280	? bless \$cb, "AnyEvent::Util::postdetect"
		1281	: ()
		1282	}
		1283
		1284	sub AnyEvent::Util::postdetect::DESTROY {
		1285	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1286	}
		1287
		1288	our $POSTPONE_W;
		1289	our @POSTPONE;
		1290
		1291	sub _postpone_exec {
		1292	undef $POSTPONE_W;
		1293
		1294	&{ shift @POSTPONE }
		1295	while @POSTPONE;
		1296	}
		1297
		1298	sub postpone(&) {
		1299	push @POSTPONE, shift;
		1300
		1301	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1302
		1303	()
		1304	}
		1305
		1306	sub log($$;@) {
		1307	# only load the big bloated module when we actually are about to log something
		1308	if ($_[0] <= $VERBOSE) { # also catches non-numeric levels(!)
		1309	require AnyEvent::Log;
		1310	# AnyEvent::Log overwrites this function
		1311	goto &log;
		1312	}
		1313
		1314	0 # not logged
		1315	}
		1316
		1317	if (length $ENV{PERL_ANYEVENT_LOG}) {
		1318	require AnyEvent::Log; # AnyEvent::Log does the thing for us
		1319	}
		1320
81	my @models = (	1321	our @models = (
82	[Coro => Coro::Event::],	1322	[EV:: => AnyEvent::Impl::EV:: , 1],
83	[Event => Event::],	1323	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
84	[Glib => Glib::],	1324	# everything below here will not (normally) be autoprobed
85	[Tk => Tk::],	1325	# as the pure perl backend should work everywhere
		1326	# and is usually faster
		1327	[Event:: => AnyEvent::Impl::Event::, 1],
		1328	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1329	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1330	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1331	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1332	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1333	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1334	[Wx:: => AnyEvent::Impl::POE::],
		1335	[Prima:: => AnyEvent::Impl::POE::],
		1336	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1337	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
		1338	[FLTK:: => AnyEvent::Impl::FLTK::],
86	);	1339	);
87		1340
88	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	1341	our @isa_hook;
89		1342
90	sub AUTOLOAD {	1343	sub _isa_set {
91	$AUTOLOAD =~ s/.*://;	1344	my @pkg = ("AnyEvent", (map $_->[0], grep defined, @isa_hook), $MODEL);
92		1345
93	$method{$AUTOLOAD}	1346	@{"$pkg[$_-1]::ISA"} = $pkg[$_]
94	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	1347	for 1 .. $#pkg;
95		1348
		1349	grep $_ && $_->[1], @isa_hook
		1350	and AE::_reset ();
		1351	}
		1352
		1353	# used for hooking AnyEvent::Strict and AnyEvent::Debug::Wrap into the class hierarchy
		1354	sub _isa_hook($$;$) {
		1355	my ($i, $pkg, $reset_ae) = @_;
		1356
		1357	$isa_hook[$i] = $pkg ? [$pkg, $reset_ae] : undef;
		1358
		1359	_isa_set;
		1360	}
		1361
		1362	# all autoloaded methods reserve the complete glob, not just the method slot.
		1363	# due to bugs in perls method cache implementation.
		1364	our @methods = qw(io timer time now now_update signal child idle condvar);
		1365
		1366	sub detect() {
		1367	return $MODEL if $MODEL; # some programs keep references to detect
		1368
		1369	local $!; # for good measure
		1370	local $SIG{__DIE__}; # we use eval
		1371
		1372	# free some memory
		1373	*detect = sub () { $MODEL };
		1374	# undef &func doesn't correctly update the method cache. grmbl.
		1375	# so we delete the whole glob. grmbl.
		1376	# otoh, perl doesn't let me undef an active usb, but it lets me free
		1377	# a glob with an active sub. hrm. i hope it works, but perl is
		1378	# usually buggy in this department. sigh.
		1379	delete @{"AnyEvent::"}{@methods};
		1380	undef @methods;
		1381
		1382	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1383	my $model = $1;
		1384	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1385	if (eval "require $model") {
		1386	AnyEvent::log 7 => "loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.";
		1387	$MODEL = $model;
		1388	} else {
		1389	AnyEvent::log 5 => "unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@";
		1390	}
		1391	}
		1392
		1393	# check for already loaded models
96	unless ($MODEL) {	1394	unless ($MODEL) {
97	# check for already loaded models
98	for (@models) {	1395	for (@REGISTRY, @models) {
99	my ($model, $package) = @$_;	1396	my ($package, $model) = @$_;
100	if (${"$package\::VERSION"} > 0) {	1397	if (${"$package\::VERSION"} > 0) {
101	eval "require AnyEvent::Impl::$model";	1398	if (eval "require $model") {
102	warn "AnyEvent: found model '$model', using it.\n" if $MODEL && $verbose > 1;	1399	AnyEvent::log 7 => "autodetected model '$model', using it.";
103	last if $MODEL;	1400	$MODEL = $model;
		1401	last;
		1402	}
104	}	1403	}
105	}	1404	}
106		1405
107	unless ($MODEL) {	1406	unless ($MODEL) {
108	# try to load a model	1407	# try to autoload a model
109
110	for (@models) {	1408	for (@REGISTRY, @models) {
111	my ($model, $package) = @$_;	1409	my ($package, $model, $autoload) = @$_;
112	eval "require AnyEvent::Impl::$model";	1410	if (
113	warn "AnyEvent: autprobed and loaded model '$model', using it.\n" if $MODEL && $verbose > 1;	1411	$autoload
114	last if $MODEL;	1412	and eval "require $package"
		1413	and ${"$package\::VERSION"} > 0
		1414	and eval "require $model"
		1415	) {
		1416	AnyEvent::log 7 => "autoloaded model '$model', using it.";
		1417	$MODEL = $model;
		1418	last;
		1419	}
115	}	1420	}
116		1421
117	$MODEL	1422	$MODEL
118	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	1423	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?";
119	}	1424	}
120	}	1425	}
121		1426
122	@ISA = $MODEL;	1427	# free memory only needed for probing
		1428	undef @models;
		1429	undef @REGISTRY;
123		1430
		1431	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1432
		1433	# now nuke some methods that are overridden by the backend.
		1434	# SUPER usage is not allowed in these.
		1435	for (qw(time signal child idle)) {
		1436	undef &{"AnyEvent::Base::$_"}
		1437	if defined &{"$MODEL\::$_"};
		1438	}
		1439
		1440	_isa_set;
		1441
		1442	# we're officially open!
		1443
		1444	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1445	require AnyEvent::Strict;
		1446	}
		1447
		1448	if ($ENV{PERL_ANYEVENT_DEBUG_WRAP}) {
		1449	require AnyEvent::Debug;
		1450	AnyEvent::Debug::wrap ($ENV{PERL_ANYEVENT_DEBUG_WRAP});
		1451	}
		1452
		1453	if (length $ENV{PERL_ANYEVENT_DEBUG_SHELL}) {
		1454	require AnyEvent::Socket;
		1455	require AnyEvent::Debug;
		1456
		1457	my $shell = $ENV{PERL_ANYEVENT_DEBUG_SHELL};
		1458	$shell =~ s/\$\$/$$/g;
		1459
		1460	my ($host, $service) = AnyEvent::Socket::parse_hostport ($shell);
		1461	$AnyEvent::Debug::SHELL = AnyEvent::Debug::shell ($host, $service);
		1462	}
		1463
		1464	# now the anyevent environment is set up as the user told us to, so
		1465	# call the actual user code - post detects
		1466
		1467	(shift @post_detect)->() while @post_detect;
		1468	undef @post_detect;
		1469
		1470	*post_detect = sub(&) {
		1471	shift->();
		1472
		1473	undef
		1474	};
		1475
		1476	$MODEL
		1477	}
		1478
		1479	for my $name (@methods) {
		1480	*$name = sub {
		1481	detect;
		1482	# we use goto because
		1483	# a) it makes the thunk more transparent
		1484	# b) it allows us to delete the thunk later
		1485	goto &{ UNIVERSAL::can AnyEvent => "SUPER::$name" }
		1486	};
		1487	}
		1488
		1489	# utility function to dup a filehandle. this is used by many backends
		1490	# to support binding more than one watcher per filehandle (they usually
		1491	# allow only one watcher per fd, so we dup it to get a different one).
		1492	sub _dupfh($$;$$) {
		1493	my ($poll, $fh, $r, $w) = @_;
		1494
		1495	# cygwin requires the fh mode to be matching, unix doesn't
		1496	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1497
		1498	open my $fh2, $mode, $fh
		1499	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1500
		1501	# we assume CLOEXEC is already set by perl in all important cases
		1502
		1503	($fh2, $rw)
		1504	}
		1505
		1506	=head1 SIMPLIFIED AE API
		1507
		1508	Starting with version 5.0, AnyEvent officially supports a second, much
		1509	simpler, API that is designed to reduce the calling, typing and memory
		1510	overhead by using function call syntax and a fixed number of parameters.
		1511
		1512	See the L<AE> manpage for details.
		1513
		1514	=cut
		1515
		1516	package AE;
		1517
		1518	our $VERSION = $AnyEvent::VERSION;
		1519
		1520	sub _reset() {
		1521	eval q{
		1522	# fall back to the main API by default - backends and AnyEvent::Base
		1523	# implementations can overwrite these.
		1524
		1525	sub io($$$) {
		1526	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1527	}
		1528
		1529	sub timer($$$) {
		1530	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1531	}
		1532
		1533	sub signal($$) {
		1534	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1535	}
		1536
		1537	sub child($$) {
		1538	AnyEvent->child (pid => $_[0], cb => $_[1])
		1539	}
		1540
		1541	sub idle($) {
		1542	AnyEvent->idle (cb => $_[0]);
		1543	}
		1544
		1545	sub cv(;&) {
		1546	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1547	}
		1548
		1549	sub now() {
		1550	AnyEvent->now
		1551	}
		1552
		1553	sub now_update() {
		1554	AnyEvent->now_update
		1555	}
		1556
		1557	sub time() {
		1558	AnyEvent->time
		1559	}
		1560
		1561	*postpone = \&AnyEvent::postpone;
		1562	*log = \&AnyEvent::log;
		1563	};
		1564	die if $@;
		1565	}
		1566
		1567	BEGIN { _reset }
		1568
		1569	package AnyEvent::Base;
		1570
		1571	# default implementations for many methods
		1572
		1573	sub time {
		1574	eval q{ # poor man's autoloading {}
		1575	# probe for availability of Time::HiRes
		1576	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1577	*time = sub { Time::HiRes::time () };
		1578	*AE::time = \& Time::HiRes::time ;
		1579	*now = \&time;
		1580	AnyEvent::log 8 => "AnyEvent: using Time::HiRes for sub-second timing accuracy.";
		1581	# if (eval "use POSIX (); (POSIX::times())...
		1582	} else {
		1583	*time = sub { CORE::time };
		1584	*AE::time = sub (){ CORE::time };
		1585	*now = \&time;
		1586	AnyEvent::log 3 => "using built-in time(), WARNING, no sub-second resolution!";
		1587	}
		1588	};
		1589	die if $@;
		1590
		1591	&time
		1592	}
		1593
		1594	*now = \&time;
		1595	sub now_update { }
		1596
		1597	sub _poll {
		1598	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1599	}
		1600
		1601	# default implementation for ->condvar
		1602	# in fact, the default should not be overwritten
		1603
		1604	sub condvar {
		1605	eval q{ # poor man's autoloading {}
		1606	*condvar = sub {
		1607	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1608	};
		1609
		1610	*AE::cv = sub (;&) {
		1611	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
		1612	};
		1613	};
		1614	die if $@;
		1615
		1616	&condvar
		1617	}
		1618
		1619	# default implementation for ->signal
		1620
		1621	our $HAVE_ASYNC_INTERRUPT;
		1622
		1623	sub _have_async_interrupt() {
		1624	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1625	&& eval "use Async::Interrupt 1.02 (); 1")
		1626	unless defined $HAVE_ASYNC_INTERRUPT;
		1627
		1628	$HAVE_ASYNC_INTERRUPT
		1629	}
		1630
		1631	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1632	our (%SIG_ASY, %SIG_ASY_W);
		1633	our ($SIG_COUNT, $SIG_TW);
		1634
		1635	# install a dummy wakeup watcher to reduce signal catching latency
		1636	# used by Impls
		1637	sub _sig_add() {
		1638	unless ($SIG_COUNT++) {
		1639	# try to align timer on a full-second boundary, if possible
		1640	my $NOW = AE::now;
		1641
		1642	$SIG_TW = AE::timer
		1643	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1644	$MAX_SIGNAL_LATENCY,
		1645	sub { } # just for the PERL_ASYNC_CHECK
		1646	;
		1647	}
		1648	}
		1649
		1650	sub _sig_del {
		1651	undef $SIG_TW
		1652	unless --$SIG_COUNT;
		1653	}
		1654
		1655	our $_sig_name_init; $_sig_name_init = sub {
		1656	eval q{ # poor man's autoloading {}
		1657	undef $_sig_name_init;
		1658
		1659	if (_have_async_interrupt) {
		1660	*sig2num = \&Async::Interrupt::sig2num;
		1661	*sig2name = \&Async::Interrupt::sig2name;
		1662	} else {
		1663	require Config;
		1664
		1665	my %signame2num;
		1666	@signame2num{ split ' ', $Config::Config{sig_name} }
		1667	= split ' ', $Config::Config{sig_num};
		1668
		1669	my @signum2name;
		1670	@signum2name[values %signame2num] = keys %signame2num;
		1671
		1672	*sig2num = sub($) {
		1673	$_[0] > 0 ? shift : $signame2num{+shift}
		1674	};
		1675	*sig2name = sub ($) {
		1676	$_[0] > 0 ? $signum2name[+shift] : shift
		1677	};
		1678	}
		1679	};
		1680	die if $@;
		1681	};
		1682
		1683	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1684	sub sig2name($) { &$_sig_name_init; &sig2name }
		1685
		1686	sub signal {
		1687	eval q{ # poor man's autoloading {}
		1688	# probe for availability of Async::Interrupt
		1689	if (_have_async_interrupt) {
		1690	AnyEvent::log 8 => "using Async::Interrupt for race-free signal handling.";
		1691
		1692	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1693	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1694
		1695	} else {
		1696	AnyEvent::log 8 => "using emulated perl signal handling with latency timer.";
		1697
		1698	if (AnyEvent::WIN32) {
		1699	require AnyEvent::Util;
		1700
		1701	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1702	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1703	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1704	} else {
		1705	pipe $SIGPIPE_R, $SIGPIPE_W;
		1706	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1707	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1708
		1709	# not strictly required, as $^F is normally 2, but let's make sure...
		1710	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1711	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1712	}
		1713
		1714	$SIGPIPE_R
		1715	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1716
		1717	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1718	}
		1719
		1720	*signal = $HAVE_ASYNC_INTERRUPT
		1721	? sub {
		1722	my (undef, %arg) = @_;
		1723
		1724	# async::interrupt
		1725	my $signal = sig2num $arg{signal};
		1726	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1727
		1728	$SIG_ASY{$signal} ||= new Async::Interrupt
		1729	cb => sub { undef $SIG_EV{$signal} },
		1730	signal => $signal,
		1731	pipe => [$SIGPIPE_R->filenos],
		1732	pipe_autodrain => 0,
		1733	;
		1734
		1735	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1736	}
		1737	: sub {
		1738	my (undef, %arg) = @_;
		1739
		1740	# pure perl
		1741	my $signal = sig2name $arg{signal};
		1742	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1743
		1744	$SIG{$signal} ||= sub {
		1745	local $!;
		1746	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1747	undef $SIG_EV{$signal};
		1748	};
		1749
		1750	# can't do signal processing without introducing races in pure perl,
		1751	# so limit the signal latency.
		1752	_sig_add;
		1753
		1754	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1755	}
		1756	;
		1757
		1758	*AnyEvent::Base::signal::DESTROY = sub {
		1759	my ($signal, $cb) = @{$_[0]};
		1760
		1761	_sig_del;
		1762
		1763	delete $SIG_CB{$signal}{$cb};
		1764
		1765	$HAVE_ASYNC_INTERRUPT
		1766	? delete $SIG_ASY{$signal}
		1767	: # delete doesn't work with older perls - they then
		1768	# print weird messages, or just unconditionally exit
		1769	# instead of getting the default action.
		1770	undef $SIG{$signal}
		1771	unless keys %{ $SIG_CB{$signal} };
		1772	};
		1773
		1774	*_signal_exec = sub {
		1775	$HAVE_ASYNC_INTERRUPT
		1776	? $SIGPIPE_R->drain
		1777	: sysread $SIGPIPE_R, (my $dummy), 9;
		1778
		1779	while (%SIG_EV) {
		1780	for (keys %SIG_EV) {
		1781	delete $SIG_EV{$_};
		1782	&$_ for values %{ $SIG_CB{$_} || {} };
		1783	}
		1784	}
		1785	};
		1786	};
		1787	die if $@;
		1788
		1789	&signal
		1790	}
		1791
		1792	# default implementation for ->child
		1793
		1794	our %PID_CB;
		1795	our $CHLD_W;
		1796	our $CHLD_DELAY_W;
		1797
		1798	# used by many Impl's
		1799	sub _emit_childstatus($$) {
		1800	my (undef, $rpid, $rstatus) = @_;
		1801
		1802	$_->($rpid, $rstatus)
		1803	for values %{ $PID_CB{$rpid} || {} },
		1804	values %{ $PID_CB{0} || {} };
		1805	}
		1806
		1807	sub child {
		1808	eval q{ # poor man's autoloading {}
		1809	*_sigchld = sub {
		1810	my $pid;
		1811
		1812	AnyEvent->_emit_childstatus ($pid, $?)
		1813	while ($pid = waitpid -1, WNOHANG) > 0;
		1814	};
		1815
		1816	*child = sub {
		1817	my (undef, %arg) = @_;
		1818
		1819	my $pid = $arg{pid};
		1820	my $cb = $arg{cb};
		1821
		1822	$PID_CB{$pid}{$cb+0} = $cb;
		1823
		1824	unless ($CHLD_W) {
		1825	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1826	# child could be a zombie already, so make at least one round
		1827	&_sigchld;
		1828	}
		1829
		1830	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1831	};
		1832
		1833	*AnyEvent::Base::child::DESTROY = sub {
		1834	my ($pid, $icb) = @{$_[0]};
		1835
		1836	delete $PID_CB{$pid}{$icb};
		1837	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1838
		1839	undef $CHLD_W unless keys %PID_CB;
		1840	};
		1841	};
		1842	die if $@;
		1843
		1844	&child
		1845	}
		1846
		1847	# idle emulation is done by simply using a timer, regardless
		1848	# of whether the process is idle or not, and not letting
		1849	# the callback use more than 50% of the time.
		1850	sub idle {
		1851	eval q{ # poor man's autoloading {}
		1852	*idle = sub {
		1853	my (undef, %arg) = @_;
		1854
		1855	my ($cb, $w, $rcb) = $arg{cb};
		1856
		1857	$rcb = sub {
		1858	if ($cb) {
		1859	$w = AE::time;
		1860	&$cb;
		1861	$w = AE::time - $w;
		1862
		1863	# never use more then 50% of the time for the idle watcher,
		1864	# within some limits
		1865	$w = 0.0001 if $w < 0.0001;
		1866	$w = 5 if $w > 5;
		1867
		1868	$w = AE::timer $w, 0, $rcb;
		1869	} else {
		1870	# clean up...
		1871	undef $w;
		1872	undef $rcb;
		1873	}
		1874	};
		1875
		1876	$w = AE::timer 0.05, 0, $rcb;
		1877
		1878	bless \\$cb, "AnyEvent::Base::idle"
		1879	};
		1880
		1881	*AnyEvent::Base::idle::DESTROY = sub {
		1882	undef $${$_[0]};
		1883	};
		1884	};
		1885	die if $@;
		1886
		1887	&idle
		1888	}
		1889
		1890	package AnyEvent::CondVar;
		1891
		1892	our @ISA = AnyEvent::CondVar::Base::;
		1893
		1894	# only to be used for subclassing
		1895	sub new {
124	my $class = shift;	1896	my $class = shift;
125	$class->$AUTOLOAD (@_);	1897	bless AnyEvent->condvar (@_), $class
126	}	1898	}
		1899
		1900	package AnyEvent::CondVar::Base;
		1901
		1902	#use overload
		1903	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1904	# fallback => 1;
		1905
		1906	# save 300+ kilobytes by dirtily hardcoding overloading
		1907	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1908	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1909	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1910	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1911
		1912	our $WAITING;
		1913
		1914	sub _send {
		1915	# nop
		1916	}
		1917
		1918	sub _wait {
		1919	AnyEvent->_poll until $_[0]{_ae_sent};
		1920	}
		1921
		1922	sub send {
		1923	my $cv = shift;
		1924	$cv->{_ae_sent} = [@_];
		1925	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1926	$cv->_send;
		1927	}
		1928
		1929	sub croak {
		1930	$_[0]{_ae_croak} = $_[1];
		1931	$_[0]->send;
		1932	}
		1933
		1934	sub ready {
		1935	$_[0]{_ae_sent}
		1936	}
		1937
		1938	sub recv {
		1939	unless ($_[0]{_ae_sent}) {
		1940	$WAITING
		1941	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1942
		1943	local $WAITING = 1;
		1944	$_[0]->_wait;
		1945	}
		1946
		1947	$_[0]{_ae_croak}
		1948	and Carp::croak $_[0]{_ae_croak};
		1949
		1950	wantarray
		1951	? @{ $_[0]{_ae_sent} }
		1952	: $_[0]{_ae_sent}[0]
		1953	}
		1954
		1955	sub cb {
		1956	my $cv = shift;
		1957
		1958	@_
		1959	and $cv->{_ae_cb} = shift
		1960	and $cv->{_ae_sent}
		1961	and (delete $cv->{_ae_cb})->($cv);
		1962
		1963	$cv->{_ae_cb}
		1964	}
		1965
		1966	sub begin {
		1967	++$_[0]{_ae_counter};
		1968	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1969	}
		1970
		1971	sub end {
		1972	return if --$_[0]{_ae_counter};
		1973	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1974	}
		1975
		1976	# undocumented/compatibility with pre-3.4
		1977	*broadcast = \&send;
		1978	*wait = \&recv;
		1979
		1980	=head1 ERROR AND EXCEPTION HANDLING
		1981
		1982	In general, AnyEvent does not do any error handling - it relies on the
		1983	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1984	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1985	checking of all AnyEvent methods, however, which is highly useful during
		1986	development.
		1987
		1988	As for exception handling (i.e. runtime errors and exceptions thrown while
		1989	executing a callback), this is not only highly event-loop specific, but
		1990	also not in any way wrapped by this module, as this is the job of the main
		1991	program.
		1992
		1993	The pure perl event loop simply re-throws the exception (usually
		1994	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1995	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1996	so on.
		1997
		1998	=head1 ENVIRONMENT VARIABLES
		1999
		2000	AnyEvent supports a number of environment variables that tune the
		2001	runtime behaviour. They are usually evaluated when AnyEvent is
		2002	loaded, initialised, or a submodule that uses them is loaded. Many of
		2003	them also cause AnyEvent to load additional modules - for example,
		2004	C<PERL_ANYEVENT_DEBUG_WRAP> causes the L<AnyEvent::Debug> module to be
		2005	loaded.
		2006
		2007	All the environment variables documented here start with
		2008	C<PERL_ANYEVENT_>, which is what AnyEvent considers its own
		2009	namespace. Other modules are encouraged (but by no means required) to use
		2010	C<PERL_ANYEVENT_SUBMODULE> if they have registered the AnyEvent::Submodule
		2011	namespace on CPAN, for any submodule. For example, L<AnyEvent::HTTP> could
		2012	be expected to use C<PERL_ANYEVENT_HTTP_PROXY> (it should not access env
		2013	variables starting with C<AE_>, see below).
		2014
		2015	All variables can also be set via the C<AE_> prefix, that is, instead
		2016	of setting C<PERL_ANYEVENT_VERBOSE> you can also set C<AE_VERBOSE>. In
		2017	case there is a clash btween anyevent and another program that uses
		2018	C<AE_something> you can set the corresponding C<PERL_ANYEVENT_something>
		2019	variable to the empty string, as those variables take precedence.
		2020
		2021	When AnyEvent is first loaded, it copies all C<AE_xxx> env variables
		2022	to their C<PERL_ANYEVENT_xxx> counterpart unless that variable already
		2023	exists. If taint mode is on, then AnyEvent will remove I<all> environment
		2024	variables starting with C<PERL_ANYEVENT_> from C<%ENV> (or replace them
		2025	with C<undef> or the empty string, if the corresaponding C<AE_> variable
		2026	is set).
		2027
		2028	The exact algorithm is currently:
		2029
		2030	1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
		2031	2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
		2032	3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
		2033
		2034	This ensures that child processes will not see the C<AE_> variables.
		2035
		2036	The following environment variables are currently known to AnyEvent:
		2037
		2038	=over 4
		2039
		2040	=item C<PERL_ANYEVENT_VERBOSE>
		2041
		2042	By default, AnyEvent will only log messages with loglevel C<3>
		2043	(C<critical>) or higher (see L<AnyEvent::Log>). You can set this
		2044	environment variable to a numerical loglevel to make AnyEvent more (or
		2045	less) talkative.
		2046
		2047	If you want to do more than just set the global logging level
		2048	you should have a look at C<PERL_ANYEVENT_LOG>, which allows much more
		2049	complex specifications.
		2050
		2051	When set to C<0> (C<off>), then no messages whatsoever will be logged with
		2052	the default logging settings.
		2053
		2054	When set to C<5> or higher (C<warn>), causes AnyEvent to warn about
		2055	unexpected conditions, such as not being able to load the event model
		2056	specified by C<PERL_ANYEVENT_MODEL>, or a guard callback throwing an
		2057	exception - this is the minimum recommended level.
		2058
		2059	When set to C<7> or higher (info), cause AnyEvent to report which event model it
		2060	chooses.
		2061
		2062	When set to C<8> or higher (debug), then AnyEvent will report extra information on
		2063	which optional modules it loads and how it implements certain features.
		2064
		2065	=item C<PERL_ANYEVENT_LOG>
		2066
		2067	Accepts rather complex logging specifications. For example, you could log
		2068	all C<debug> messages of some module to stderr, warnings and above to
		2069	stderr, and errors and above to syslog, with:
		2070
		2071	PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
		2072
		2073	For the rather extensive details, see L<AnyEvent::Log>.
		2074
		2075	This variable is evaluated when AnyEvent (or L<AnyEvent::Log>) is loaded,
		2076	so will take effect even before AnyEvent has initialised itself.
		2077
		2078	Note that specifying this environment variable causes the L<AnyEvent::Log>
		2079	module to be loaded, while C<PERL_ANYEVENT_VERBOSE> does not, so only
		2080	using the latter saves a few hundred kB of memory until the first message
		2081	is being logged.
		2082
		2083	=item C<PERL_ANYEVENT_STRICT>
		2084
		2085	AnyEvent does not do much argument checking by default, as thorough
		2086	argument checking is very costly. Setting this variable to a true value
		2087	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		2088	check the arguments passed to most method calls. If it finds any problems,
		2089	it will croak.
		2090
		2091	In other words, enables "strict" mode.
		2092
		2093	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		2094	>>, it is definitely recommended to keep it off in production. Keeping
		2095	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		2096	can be very useful, however.
		2097
		2098	=item C<PERL_ANYEVENT_DEBUG_SHELL>
		2099
		2100	If this env variable is set, then its contents will be interpreted by
		2101	C<AnyEvent::Socket::parse_hostport> (after replacing every occurance of
		2102	C<$$> by the process pid) and an C<AnyEvent::Debug::shell> is bound on
		2103	that port. The shell object is saved in C<$AnyEvent::Debug::SHELL>.
		2104
		2105	This happens when the first watcher is created.
		2106
		2107	For example, to bind a debug shell on a unix domain socket in
		2108	F<< /tmp/debug<pid>.sock >>, you could use this:
		2109
		2110	PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
		2111
		2112	Note that creating sockets in F</tmp> is very unsafe on multiuser
		2113	systems.
		2114
		2115	=item C<PERL_ANYEVENT_DEBUG_WRAP>
		2116
		2117	Can be set to C<0>, C<1> or C<2> and enables wrapping of all watchers for
		2118	debugging purposes. See C<AnyEvent::Debug::wrap> for details.
		2119
		2120	=item C<PERL_ANYEVENT_MODEL>
		2121
		2122	This can be used to specify the event model to be used by AnyEvent, before
		2123	auto detection and -probing kicks in.
		2124
		2125	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		2126	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		2127	resulting module name is loaded and - if the load was successful - used as
		2128	event model backend. If it fails to load then AnyEvent will proceed with
		2129	auto detection and -probing.
		2130
		2131	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		2132	nothing gets prepended and the module name is used as-is (hint: C<::> at
		2133	the end of a string designates a module name and quotes it appropriately).
		2134
		2135	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		2136	could start your program like this:
		2137
		2138	PERL_ANYEVENT_MODEL=Perl perl ...
		2139
		2140	=item C<PERL_ANYEVENT_PROTOCOLS>
		2141
		2142	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		2143	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		2144	of auto probing).
		2145
		2146	Must be set to a comma-separated list of protocols or address families,
		2147	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		2148	used, and preference will be given to protocols mentioned earlier in the
		2149	list.
		2150
		2151	This variable can effectively be used for denial-of-service attacks
		2152	against local programs (e.g. when setuid), although the impact is likely
		2153	small, as the program has to handle conenction and other failures anyways.
		2154
		2155	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		2156	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		2157	- only support IPv4, never try to resolve or contact IPv6
		2158	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		2159	IPv6, but prefer IPv6 over IPv4.
		2160
		2161	=item C<PERL_ANYEVENT_HOSTS>
		2162
		2163	This variable, if specified, overrides the F</etc/hosts> file used by
		2164	L<AnyEvent::Socket>C<::resolve_sockaddr>, i.e. hosts aliases will be read
		2165	from that file instead.
		2166
		2167	=item C<PERL_ANYEVENT_EDNS0>
		2168
		2169	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension for
		2170	DNS. This extension is generally useful to reduce DNS traffic, especially
		2171	when DNSSEC is involved, but some (broken) firewalls drop such DNS
		2172	packets, which is why it is off by default.
		2173
		2174	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2175	EDNS0 in its DNS requests.
		2176
		2177	=item C<PERL_ANYEVENT_MAX_FORKS>
		2178
		2179	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2180	will create in parallel.
		2181
		2182	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2183
		2184	The default value for the C<max_outstanding> parameter for the default DNS
		2185	resolver - this is the maximum number of parallel DNS requests that are
		2186	sent to the DNS server.
		2187
		2188	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2189
		2190	The absolute path to a F<resolv.conf>-style file to use instead of
		2191	F</etc/resolv.conf> (or the OS-specific configuration) in the default
		2192	resolver, or the empty string to select the default configuration.
		2193
		2194	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2195
		2196	When neither C<ca_file> nor C<ca_path> was specified during
		2197	L<AnyEvent::TLS> context creation, and either of these environment
		2198	variables are nonempty, they will be used to specify CA certificate
		2199	locations instead of a system-dependent default.
		2200
		2201	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2202
		2203	When these are set to C<1>, then the respective modules are not
		2204	loaded. Mostly good for testing AnyEvent itself.
127		2205
128	=back	2206	=back
129		2207
130	=head1 ENVIRONMENT VARIABLES	2208	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
131		2209
132	The following environment variables are used by this module:	2210	This is an advanced topic that you do not normally need to use AnyEvent in
		2211	a module. This section is only of use to event loop authors who want to
		2212	provide AnyEvent compatibility.
133		2213
134	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	2214	If you need to support another event library which isn't directly
135	model gets used.	2215	supported by AnyEvent, you can supply your own interface to it by
		2216	pushing, before the first watcher gets created, the package name of
		2217	the event module and the package name of the interface to use onto
		2218	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		2219	AnyEvent, so it is reasonably cheap.
136		2220
		2221	Example:
		2222
		2223	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		2224
		2225	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		2226	package/class when it finds the C<urxvt> package/module is already loaded.
		2227
		2228	When AnyEvent is loaded and asked to find a suitable event model, it
		2229	will first check for the presence of urxvt by trying to C<use> the
		2230	C<urxvt::anyevent> module.
		2231
		2232	The class should provide implementations for all watcher types. See
		2233	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		2234	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		2235	see the sources.
		2236
		2237	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2238	provide suitable (hopefully) replacements.
		2239
		2240	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		2241	terminal emulator uses the above line as-is. An interface isn't included
		2242	in AnyEvent because it doesn't make sense outside the embedded interpreter
		2243	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		2244	I<rxvt-unicode> distribution.
		2245
		2246	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		2247	condition variables: code blocking while waiting for a condition will
		2248	C<die>. This still works with most modules/usages, and blocking calls must
		2249	not be done in an interactive application, so it makes sense.
		2250
137	=head1 EXAMPLE	2251	=head1 EXAMPLE PROGRAM
138		2252
139	The following program uses an io watcher to read data from stdin, a timer	2253	The following program uses an I/O watcher to read data from STDIN, a timer
140	to display a message once per second, and a condvar to exit the program	2254	to display a message once per second, and a condition variable to quit the
141	when the user enters quit:	2255	program when the user enters quit:
142		2256
143	use AnyEvent;	2257	use AnyEvent;
144		2258
145	my $cv = AnyEvent->condvar;	2259	my $cv = AnyEvent->condvar;
146		2260
147	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	2261	my $io_watcher = AnyEvent->io (
		2262	fh => \*STDIN,
		2263	poll => 'r',
		2264	cb => sub {
148	warn "io event <$_[0]>\n"; # will always output <r>	2265	warn "io event <$_[0]>\n"; # will always output <r>
149	chomp (my $input = <STDIN>); # read a line	2266	chomp (my $input = <STDIN>); # read a line
150	warn "read: $input\n"; # output what has been read	2267	warn "read: $input\n"; # output what has been read
151	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	2268	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2269	},
		2270	);
		2271
		2272	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2273	warn "timeout\n"; # print 'timeout' at most every second
152	});	2274	});
153		2275
154	my $time_watcher; # can only be used once
155
156	sub new_timer {
157	$timer = AnyEvent->timer (after => 1, cb => sub {
158	warn "timeout\n"; # print 'timeout' about every second
159	&new_timer; # and restart the time
160	});
161	}
162
163	new_timer; # create first timer
164
165	$cv->wait; # wait until user enters /^q/i	2276	$cv->recv; # wait until user enters /^q/i
166		2277
167	=head1 REAL-WORLD EXAMPLE	2278	=head1 REAL-WORLD EXAMPLE
168		2279
169	Consider the L<Net::FCP> module. It features (among others) the following	2280	Consider the L<Net::FCP> module. It features (among others) the following
170	API calls, which are to freenet what HTTP GET requests are to http:	2281	API calls, which are to freenet what HTTP GET requests are to http:
…		…
220	syswrite $txn->{fh}, $txn->{request}	2331	syswrite $txn->{fh}, $txn->{request}
221	or die "connection or write error";	2332	or die "connection or write error";
222	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	2333	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
223		2334
224	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	2335	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
225	result and signals any possible waiters that the request ahs finished:	2336	result and signals any possible waiters that the request has finished:
226		2337
227	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	2338	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
228		2339
229	if (end-of-file or data complete) {	2340	if (end-of-file or data complete) {
230	$txn->{result} = $txn->{buf};	2341	$txn->{result} = $txn->{buf};
231	$txn->{finished}->broadcast;	2342	$txn->{finished}->send;
232	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	2343	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
233	}	2344	}
234		2345
235	The C<result> method, finally, just waits for the finished signal (if the	2346	The C<result> method, finally, just waits for the finished signal (if the
236	request was already finished, it doesn't wait, of course, and returns the	2347	request was already finished, it doesn't wait, of course, and returns the
237	data:	2348	data:
238		2349
239	$txn->{finished}->wait;	2350	$txn->{finished}->recv;
240	return $txn->{result};	2351	return $txn->{result};
241		2352
242	The actual code goes further and collects all errors (C<die>s, exceptions)	2353	The actual code goes further and collects all errors (C<die>s, exceptions)
243	that occured during request processing. The C<result> method detects	2354	that occurred during request processing. The C<result> method detects
244	wether an exception as thrown (it is stored inside the $txn object)	2355	whether an exception as thrown (it is stored inside the $txn object)
245	and just throws the exception, which means connection errors and other	2356	and just throws the exception, which means connection errors and other
246	problems get reported tot he code that tries to use the result, not in a	2357	problems get reported to the code that tries to use the result, not in a
247	random callback.	2358	random callback.
248		2359
249	All of this enables the following usage styles:	2360	All of this enables the following usage styles:
250		2361
251	1. Blocking:	2362	1. Blocking:
252		2363
253	my $data = $fcp->client_get ($url);	2364	my $data = $fcp->client_get ($url);
254		2365
255	2. Blocking, but parallelizing:	2366	2. Blocking, but running in parallel:
256		2367
257	my @datas = map $_->result,	2368	my @datas = map $_->result,
258	map $fcp->txn_client_get ($_),	2369	map $fcp->txn_client_get ($_),
259	@urls;	2370	@urls;
260		2371
261	Both blocking examples work without the module user having to know	2372	Both blocking examples work without the module user having to know
262	anything about events.	2373	anything about events.
263		2374
264	3a. Event-based in a main program, using any support Event module:	2375	3a. Event-based in a main program, using any supported event module:
265		2376
266	use Event;	2377	use EV;
267		2378
268	$fcp->txn_client_get ($url)->cb (sub {	2379	$fcp->txn_client_get ($url)->cb (sub {
269	my $txn = shift;	2380	my $txn = shift;
270	my $data = $txn->result;	2381	my $data = $txn->result;
271	...	2382	...
272	});	2383	});
273		2384
274	Event::loop;	2385	EV::loop;
275		2386
276	3b. The module user could use AnyEvent, too:	2387	3b. The module user could use AnyEvent, too:
277		2388
278	use AnyEvent;	2389	use AnyEvent;
279		2390
280	my $quit = AnyEvent->condvar;	2391	my $quit = AnyEvent->condvar;
281		2392
282	$fcp->txn_client_get ($url)->cb (sub {	2393	$fcp->txn_client_get ($url)->cb (sub {
283	...	2394	...
284	$quit->broadcast;	2395	$quit->send;
285	});	2396	});
286		2397
287	$quit->wait;	2398	$quit->recv;
		2399
		2400
		2401	=head1 BENCHMARKS
		2402
		2403	To give you an idea of the performance and overheads that AnyEvent adds
		2404	over the event loops themselves and to give you an impression of the speed
		2405	of various event loops I prepared some benchmarks.
		2406
		2407	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2408
		2409	Here is a benchmark of various supported event models used natively and
		2410	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2411	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2412	which it is), lets them fire exactly once and destroys them again.
		2413
		2414	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2415	distribution. It uses the L<AE> interface, which makes a real difference
		2416	for the EV and Perl backends only.
		2417
		2418	=head3 Explanation of the columns
		2419
		2420	I<watcher> is the number of event watchers created/destroyed. Since
		2421	different event models feature vastly different performances, each event
		2422	loop was given a number of watchers so that overall runtime is acceptable
		2423	and similar between tested event loop (and keep them from crashing): Glib
		2424	would probably take thousands of years if asked to process the same number
		2425	of watchers as EV in this benchmark.
		2426
		2427	I<bytes> is the number of bytes (as measured by the resident set size,
		2428	RSS) consumed by each watcher. This method of measuring captures both C
		2429	and Perl-based overheads.
		2430
		2431	I<create> is the time, in microseconds (millionths of seconds), that it
		2432	takes to create a single watcher. The callback is a closure shared between
		2433	all watchers, to avoid adding memory overhead. That means closure creation
		2434	and memory usage is not included in the figures.
		2435
		2436	I<invoke> is the time, in microseconds, used to invoke a simple
		2437	callback. The callback simply counts down a Perl variable and after it was
		2438	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2439	signal the end of this phase.
		2440
		2441	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2442	watcher.
		2443
		2444	=head3 Results
		2445
		2446	name watchers bytes create invoke destroy comment
		2447	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2448	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2449	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2450	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2451	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2452	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2453	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2454	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2455	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2456	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2457	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2458	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2459
		2460	=head3 Discussion
		2461
		2462	The benchmark does I<not> measure scalability of the event loop very
		2463	well. For example, a select-based event loop (such as the pure perl one)
		2464	can never compete with an event loop that uses epoll when the number of
		2465	file descriptors grows high. In this benchmark, all events become ready at
		2466	the same time, so select/poll-based implementations get an unnatural speed
		2467	boost.
		2468
		2469	Also, note that the number of watchers usually has a nonlinear effect on
		2470	overall speed, that is, creating twice as many watchers doesn't take twice
		2471	the time - usually it takes longer. This puts event loops tested with a
		2472	higher number of watchers at a disadvantage.
		2473
		2474	To put the range of results into perspective, consider that on the
		2475	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2476	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2477	cycles with POE.
		2478
		2479	C<EV> is the sole leader regarding speed and memory use, which are both
		2480	maximal/minimal, respectively. When using the L<AE> API there is zero
		2481	overhead (when going through the AnyEvent API create is about 5-6 times
		2482	slower, with other times being equal, so still uses far less memory than
		2483	any other event loop and is still faster than Event natively).
		2484
		2485	The pure perl implementation is hit in a few sweet spots (both the
		2486	constant timeout and the use of a single fd hit optimisations in the perl
		2487	interpreter and the backend itself). Nevertheless this shows that it
		2488	adds very little overhead in itself. Like any select-based backend its
		2489	performance becomes really bad with lots of file descriptors (and few of
		2490	them active), of course, but this was not subject of this benchmark.
		2491
		2492	The C<Event> module has a relatively high setup and callback invocation
		2493	cost, but overall scores in on the third place.
		2494
		2495	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2496	when using its pure perl backend.
		2497
		2498	C<Glib>'s memory usage is quite a bit higher, but it features a
		2499	faster callback invocation and overall ends up in the same class as
		2500	C<Event>. However, Glib scales extremely badly, doubling the number of
		2501	watchers increases the processing time by more than a factor of four,
		2502	making it completely unusable when using larger numbers of watchers
		2503	(note that only a single file descriptor was used in the benchmark, so
		2504	inefficiencies of C<poll> do not account for this).
		2505
		2506	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2507	more than 2000 watchers is a big setback, however, as correctness takes
		2508	precedence over speed. Nevertheless, its performance is surprising, as the
		2509	file descriptor is dup()ed for each watcher. This shows that the dup()
		2510	employed by some adaptors is not a big performance issue (it does incur a
		2511	hidden memory cost inside the kernel which is not reflected in the figures
		2512	above).
		2513
		2514	C<POE>, regardless of underlying event loop (whether using its pure perl
		2515	select-based backend or the Event module, the POE-EV backend couldn't
		2516	be tested because it wasn't working) shows abysmal performance and
		2517	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2518	as EV watchers, and 10 times as much memory as Event (the high memory
		2519	requirements are caused by requiring a session for each watcher). Watcher
		2520	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2521	implementation.
		2522
		2523	The design of the POE adaptor class in AnyEvent can not really account
		2524	for the performance issues, though, as session creation overhead is
		2525	small compared to execution of the state machine, which is coded pretty
		2526	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2527	using multiple sessions is not a good approach, especially regarding
		2528	memory usage, even the author of POE could not come up with a faster
		2529	design).
		2530
		2531	=head3 Summary
		2532
		2533	=over 4
		2534
		2535	=item * Using EV through AnyEvent is faster than any other event loop
		2536	(even when used without AnyEvent), but most event loops have acceptable
		2537	performance with or without AnyEvent.
		2538
		2539	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2540	the actual event loop, only with extremely fast event loops such as EV
		2541	does AnyEvent add significant overhead.
		2542
		2543	=item * You should avoid POE like the plague if you want performance or
		2544	reasonable memory usage.
		2545
		2546	=back
		2547
		2548	=head2 BENCHMARKING THE LARGE SERVER CASE
		2549
		2550	This benchmark actually benchmarks the event loop itself. It works by
		2551	creating a number of "servers": each server consists of a socket pair, a
		2552	timeout watcher that gets reset on activity (but never fires), and an I/O
		2553	watcher waiting for input on one side of the socket. Each time the socket
		2554	watcher reads a byte it will write that byte to a random other "server".
		2555
		2556	The effect is that there will be a lot of I/O watchers, only part of which
		2557	are active at any one point (so there is a constant number of active
		2558	fds for each loop iteration, but which fds these are is random). The
		2559	timeout is reset each time something is read because that reflects how
		2560	most timeouts work (and puts extra pressure on the event loops).
		2561
		2562	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2563	(1%) are active. This mirrors the activity of large servers with many
		2564	connections, most of which are idle at any one point in time.
		2565
		2566	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2567	distribution. It uses the L<AE> interface, which makes a real difference
		2568	for the EV and Perl backends only.
		2569
		2570	=head3 Explanation of the columns
		2571
		2572	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2573	each server has a read and write socket end).
		2574
		2575	I<create> is the time it takes to create a socket pair (which is
		2576	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2577
		2578	I<request>, the most important value, is the time it takes to handle a
		2579	single "request", that is, reading the token from the pipe and forwarding
		2580	it to another server. This includes deleting the old timeout and creating
		2581	a new one that moves the timeout into the future.
		2582
		2583	=head3 Results
		2584
		2585	name sockets create request
		2586	EV 20000 62.66 7.99
		2587	Perl 20000 68.32 32.64
		2588	IOAsync 20000 174.06 101.15 epoll
		2589	IOAsync 20000 174.67 610.84 poll
		2590	Event 20000 202.69 242.91
		2591	Glib 20000 557.01 1689.52
		2592	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2593
		2594	=head3 Discussion
		2595
		2596	This benchmark I<does> measure scalability and overall performance of the
		2597	particular event loop.
		2598
		2599	EV is again fastest. Since it is using epoll on my system, the setup time
		2600	is relatively high, though.
		2601
		2602	Perl surprisingly comes second. It is much faster than the C-based event
		2603	loops Event and Glib.
		2604
		2605	IO::Async performs very well when using its epoll backend, and still quite
		2606	good compared to Glib when using its pure perl backend.
		2607
		2608	Event suffers from high setup time as well (look at its code and you will
		2609	understand why). Callback invocation also has a high overhead compared to
		2610	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2611	uses select or poll in basically all documented configurations.
		2612
		2613	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2614	clearly fails to perform with many filehandles or in busy servers.
		2615
		2616	POE is still completely out of the picture, taking over 1000 times as long
		2617	as EV, and over 100 times as long as the Perl implementation, even though
		2618	it uses a C-based event loop in this case.
		2619
		2620	=head3 Summary
		2621
		2622	=over 4
		2623
		2624	=item * The pure perl implementation performs extremely well.
		2625
		2626	=item * Avoid Glib or POE in large projects where performance matters.
		2627
		2628	=back
		2629
		2630	=head2 BENCHMARKING SMALL SERVERS
		2631
		2632	While event loops should scale (and select-based ones do not...) even to
		2633	large servers, most programs we (or I :) actually write have only a few
		2634	I/O watchers.
		2635
		2636	In this benchmark, I use the same benchmark program as in the large server
		2637	case, but it uses only eight "servers", of which three are active at any
		2638	one time. This should reflect performance for a small server relatively
		2639	well.
		2640
		2641	The columns are identical to the previous table.
		2642
		2643	=head3 Results
		2644
		2645	name sockets create request
		2646	EV 16 20.00 6.54
		2647	Perl 16 25.75 12.62
		2648	Event 16 81.27 35.86
		2649	Glib 16 32.63 15.48
		2650	POE 16 261.87 276.28 uses POE::Loop::Event
		2651
		2652	=head3 Discussion
		2653
		2654	The benchmark tries to test the performance of a typical small
		2655	server. While knowing how various event loops perform is interesting, keep
		2656	in mind that their overhead in this case is usually not as important, due
		2657	to the small absolute number of watchers (that is, you need efficiency and
		2658	speed most when you have lots of watchers, not when you only have a few of
		2659	them).
		2660
		2661	EV is again fastest.
		2662
		2663	Perl again comes second. It is noticeably faster than the C-based event
		2664	loops Event and Glib, although the difference is too small to really
		2665	matter.
		2666
		2667	POE also performs much better in this case, but is is still far behind the
		2668	others.
		2669
		2670	=head3 Summary
		2671
		2672	=over 4
		2673
		2674	=item * C-based event loops perform very well with small number of
		2675	watchers, as the management overhead dominates.
		2676
		2677	=back
		2678
		2679	=head2 THE IO::Lambda BENCHMARK
		2680
		2681	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2682	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2683	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2684	shouldn't come as a surprise to anybody). As such, the benchmark is
		2685	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2686	very optimal. But how would AnyEvent compare when used without the extra
		2687	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2688
		2689	The benchmark itself creates an echo-server, and then, for 500 times,
		2690	connects to the echo server, sends a line, waits for the reply, and then
		2691	creates the next connection. This is a rather bad benchmark, as it doesn't
		2692	test the efficiency of the framework or much non-blocking I/O, but it is a
		2693	benchmark nevertheless.
		2694
		2695	name runtime
		2696	Lambda/select 0.330 sec
		2697	+ optimized 0.122 sec
		2698	Lambda/AnyEvent 0.327 sec
		2699	+ optimized 0.138 sec
		2700	Raw sockets/select 0.077 sec
		2701	POE/select, components 0.662 sec
		2702	POE/select, raw sockets 0.226 sec
		2703	POE/select, optimized 0.404 sec
		2704
		2705	AnyEvent/select/nb 0.085 sec
		2706	AnyEvent/EV/nb 0.068 sec
		2707	+state machine 0.134 sec
		2708
		2709	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2710	benchmarks actually make blocking connects and use 100% blocking I/O,
		2711	defeating the purpose of an event-based solution. All of the newly
		2712	written AnyEvent benchmarks use 100% non-blocking connects (using
		2713	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2714	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2715	generally require a lot more bookkeeping and event handling than blocking
		2716	connects (which involve a single syscall only).
		2717
		2718	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2719	offers similar expressive power as POE and IO::Lambda, using conventional
		2720	Perl syntax. This means that both the echo server and the client are 100%
		2721	non-blocking, further placing it at a disadvantage.
		2722
		2723	As you can see, the AnyEvent + EV combination even beats the
		2724	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2725	backend easily beats IO::Lambda and POE.
		2726
		2727	And even the 100% non-blocking version written using the high-level (and
		2728	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2729	higher level ("unoptimised") abstractions by a large margin, even though
		2730	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2731
		2732	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2733	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2734	part of the IO::Lambda distribution and were used without any changes.
		2735
		2736
		2737	=head1 SIGNALS
		2738
		2739	AnyEvent currently installs handlers for these signals:
		2740
		2741	=over 4
		2742
		2743	=item SIGCHLD
		2744
		2745	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2746	emulation for event loops that do not support them natively. Also, some
		2747	event loops install a similar handler.
		2748
		2749	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2750	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2751
		2752	=item SIGPIPE
		2753
		2754	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2755	when AnyEvent gets loaded.
		2756
		2757	The rationale for this is that AnyEvent users usually do not really depend
		2758	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2759	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2760	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2761	some random socket.
		2762
		2763	The rationale for installing a no-op handler as opposed to ignoring it is
		2764	that this way, the handler will be restored to defaults on exec.
		2765
		2766	Feel free to install your own handler, or reset it to defaults.
		2767
		2768	=back
		2769
		2770	=cut
		2771
		2772	undef $SIG{CHLD}
		2773	if $SIG{CHLD} eq 'IGNORE';
		2774
		2775	$SIG{PIPE} = sub { }
		2776	unless defined $SIG{PIPE};
		2777
		2778	=head1 RECOMMENDED/OPTIONAL MODULES
		2779
		2780	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2781	its built-in modules) are required to use it.
		2782
		2783	That does not mean that AnyEvent won't take advantage of some additional
		2784	modules if they are installed.
		2785
		2786	This section explains which additional modules will be used, and how they
		2787	affect AnyEvent's operation.
		2788
		2789	=over 4
		2790
		2791	=item L<Async::Interrupt>
		2792
		2793	This slightly arcane module is used to implement fast signal handling: To
		2794	my knowledge, there is no way to do completely race-free and quick
		2795	signal handling in pure perl. To ensure that signals still get
		2796	delivered, AnyEvent will start an interval timer to wake up perl (and
		2797	catch the signals) with some delay (default is 10 seconds, look for
		2798	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2799
		2800	If this module is available, then it will be used to implement signal
		2801	catching, which means that signals will not be delayed, and the event loop
		2802	will not be interrupted regularly, which is more efficient (and good for
		2803	battery life on laptops).
		2804
		2805	This affects not just the pure-perl event loop, but also other event loops
		2806	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2807
		2808	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2809	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2810	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2811	does nothing for those backends.
		2812
		2813	=item L<EV>
		2814
		2815	This module isn't really "optional", as it is simply one of the backend
		2816	event loops that AnyEvent can use. However, it is simply the best event
		2817	loop available in terms of features, speed and stability: It supports
		2818	the AnyEvent API optimally, implements all the watcher types in XS, does
		2819	automatic timer adjustments even when no monotonic clock is available,
		2820	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2821	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2822	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2823
		2824	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2825	then this module will do nothing for you.
		2826
		2827	=item L<Guard>
		2828
		2829	The guard module, when used, will be used to implement
		2830	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2831	lot less memory), but otherwise doesn't affect guard operation much. It is
		2832	purely used for performance.
		2833
		2834	=item L<JSON> and L<JSON::XS>
		2835
		2836	One of these modules is required when you want to read or write JSON data
		2837	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2838	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2839
		2840	=item L<Net::SSLeay>
		2841
		2842	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2843	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2844	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2845
		2846	=item L<Time::HiRes>
		2847
		2848	This module is part of perl since release 5.008. It will be used when the
		2849	chosen event library does not come with a timing source of its own. The
		2850	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2851	try to use a monotonic clock for timing stability.
		2852
		2853	=back
		2854
		2855
		2856	=head1 FORK
		2857
		2858	Most event libraries are not fork-safe. The ones who are usually are
		2859	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2860	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2861	are usually badly thought-out hacks that are incompatible with fork in
		2862	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2863	continue event-processing in both parent and child (or both, if you know
		2864	what you are doing).
		2865
		2866	This means that, in general, you cannot fork and do event processing in
		2867	the child if the event library was initialised before the fork (which
		2868	usually happens when the first AnyEvent watcher is created, or the library
		2869	is loaded).
		2870
		2871	If you have to fork, you must either do so I<before> creating your first
		2872	watcher OR you must not use AnyEvent at all in the child OR you must do
		2873	something completely out of the scope of AnyEvent.
		2874
		2875	The problem of doing event processing in the parent I<and> the child
		2876	is much more complicated: even for backends that I<are> fork-aware or
		2877	fork-safe, their behaviour is not usually what you want: fork clones all
		2878	watchers, that means all timers, I/O watchers etc. are active in both
		2879	parent and child, which is almost never what you want. USing C<exec>
		2880	to start worker children from some kind of manage rprocess is usually
		2881	preferred, because it is much easier and cleaner, at the expense of having
		2882	to have another binary.
		2883
		2884
		2885	=head1 SECURITY CONSIDERATIONS
		2886
		2887	AnyEvent can be forced to load any event model via
		2888	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2889	execute arbitrary code or directly gain access, it can easily be used to
		2890	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2891	will not be active when the program uses a different event model than
		2892	specified in the variable.
		2893
		2894	You can make AnyEvent completely ignore this variable by deleting it
		2895	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2896
		2897	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2898
		2899	use AnyEvent;
		2900
		2901	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2902	be used to probe what backend is used and gain other information (which is
		2903	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2904	$ENV{PERL_ANYEVENT_STRICT}.
		2905
		2906	Note that AnyEvent will remove I<all> environment variables starting with
		2907	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2908	enabled.
		2909
		2910
		2911	=head1 BUGS
		2912
		2913	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2914	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2915	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2916	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2917	pronounced).
		2918
288		2919
289	=head1 SEE ALSO	2920	=head1 SEE ALSO
290		2921
291	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	2922	Tutorial/Introduction: L<AnyEvent::Intro>.
292		2923
293	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	2924	FAQ: L<AnyEvent::FAQ>.
294		2925
295	Nontrivial usage example: L<Net::FCP>.	2926	Utility functions: L<AnyEvent::Util> (misc. grab-bag), L<AnyEvent::Log>
		2927	(simply logging).
296		2928
297	=head1	2929	Development/Debugging: L<AnyEvent::Strict> (stricter checking),
		2930	L<AnyEvent::Debug> (interactive shell, watcher tracing).
		2931
		2932	Supported event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>,
		2933	L<Glib::EV>, L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>,
		2934	L<Qt>, L<POE>, L<FLTK>.
		2935
		2936	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2937	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2938	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2939	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>,
		2940	L<AnyEvent::Impl::FLTK>.
		2941
		2942	Non-blocking handles, pipes, stream sockets, TCP clients and
		2943	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2944
		2945	Asynchronous DNS: L<AnyEvent::DNS>.
		2946
		2947	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2948
		2949	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2950	L<AnyEvent::HTTP>.
		2951
		2952
		2953	=head1 AUTHOR
		2954
		2955	Marc Lehmann <schmorp@schmorp.de>
		2956	http://home.schmorp.de/
298		2957
299	=cut	2958	=cut
300		2959
301	1	2960	1
302		2961

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