ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.32 by root, Sat Nov 3 09:29:51 2007 UTC vs.
Revision 1.358 by root, Sat Aug 13 02:35:32 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, Perl - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, Qt
		6	and POE are various supported event loops/environments.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# 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 => $fh, poll => "r|w", cb => sub {	16	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		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) = @_;
12	...	31	...
13	});	32	});
14		33
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	34	# called when event loop idle (if applicable)
16	...	35	my $w = AnyEvent->idle (cb => sub { ... });
17	});
18		36
19	my $w = AnyEvent->condvar; # stores wether a condition was flagged	37	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		38	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	39	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	40	# use a condvar in callback mode:
		41	$w->cb (sub { $_[0]->recv });
		42
		43	=head1 INTRODUCTION/TUTORIAL
		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.
22		113
23	=head1 DESCRIPTION	114	=head1 DESCRIPTION
24		115
25	L<AnyEvent> provides an identical interface to multiple event loops. This	116	L<AnyEvent> provides a uniform interface to various event loops. This
26	allows module authors to utilise an event loop without forcing module	117	allows module authors to use event loop functionality without forcing
27	users to use the same event loop (as only a single event loop can coexist	118	module users to use a specific event loop implementation (since more
28	peacefully at any one time).	119	than one event loop cannot coexist peacefully).
29		120
30	The interface itself is vaguely similar but not identical to the Event	121	The interface itself is vaguely similar, but not identical to the L<Event>
31	module.	122	module.
32		123
33	On the first call of any method, the module tries to detect the currently	124	During the first call of any watcher-creation method, the module tries
34	loaded event loop by probing wether any of the following modules is	125	to detect the currently loaded event loop by probing whether one of the
35	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	126	following modules is already loaded: L<EV>, L<AnyEvent::Loop>,
36	used. If none is found, the module tries to load these modules in the	127	L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>. The first one
37	order given. The first one that could be successfully loaded will be	128	found is used. If none are detected, the module tries to load the first
38	used. If still none could be found, AnyEvent will fall back to a pure-perl	129	four modules in the order given; but note that if L<EV> is not
39	event loop, which is also not very efficient.	130	available, the pure-perl L<AnyEvent::Loop> should always work, so
		131	the other two are not normally tried.
40		132
41	Because AnyEvent first checks for modules that are already loaded, loading	133	Because AnyEvent first checks for modules that are already loaded, loading
42	an Event model explicitly before first using AnyEvent will likely make	134	an event model explicitly before first using AnyEvent will likely make
43	that model the default. For example:	135	that model the default. For example:
44		136
45	use Tk;	137	use Tk;
46	use AnyEvent;	138	use AnyEvent;
47		139
48	# .. AnyEvent will likely default to Tk	140	# .. AnyEvent will likely default to Tk
49		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
50	The pure-perl implementation of AnyEvent is called	147	The pure-perl implementation of AnyEvent is called C<AnyEvent::Loop>. Like
51	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	148	other event modules you can load it explicitly and enjoy the high
52	explicitly.	149	availability of that event loop :)
53		150
54	=head1 WATCHERS	151	=head1 WATCHERS
55		152
56	AnyEvent has the central concept of a I<watcher>, which is an object that	153	AnyEvent has the central concept of a I<watcher>, which is an object that
57	stores relevant data for each kind of event you are waiting for, such as	154	stores relevant data for each kind of event you are waiting for, such as
58	the callback to call, the filehandle to watch, etc.	155	the callback to call, the file handle to watch, etc.
59		156
60	These watchers are normal Perl objects with normal Perl lifetime. After	157	These watchers are normal Perl objects with normal Perl lifetime. After
61	creating a watcher it will immediately "watch" for events and invoke	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
62	the callback. To disable the watcher you have to destroy it (e.g. by	168	To disable a watcher you have to destroy it (e.g. by setting the
63	setting the variable that stores it to C<undef> or otherwise deleting all	169	variable you store it in to C<undef> or otherwise deleting all references
64	references to it).	170	to it).
65		171
66	All watchers are created by calling a method on the C<AnyEvent> class.	172	All watchers are created by calling a method on the C<AnyEvent> class.
67		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
68	=head2 IO WATCHERS	188	=head2 I/O WATCHERS
69		189
		190	$w = AnyEvent->io (
		191	fh => <filehandle_or_fileno>,
		192	poll => <"r" or "w">,
		193	cb => <callback>,
		194	);
		195
70	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	196	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
71	the following mandatory arguments:	197	with the following mandatory key-value pairs as arguments:
72		198
73	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	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
74	events. C<poll> must be a string that is either C<r> or C<w>, that creates	206	C<poll> must be a string that is either C<r> or C<w>, which creates a
75	a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback	207	watcher waiting for "r"eadable or "w"ritable events, respectively.
76	to invoke everytime the filehandle becomes ready.
77		208
78	Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on	209	C<cb> is the callback to invoke each time the file handle becomes ready.
79	a socket you can have one r + one w, not any more (limitation comes from
80	Tk - if you are sure you are not using Tk this limitation is gone).
81		210
82	Filehandles will be kept alive, so as long as the watcher exists, the	211	Although the callback might get passed parameters, their value and
83	filehandle exists, too.	212	presence is undefined and you cannot rely on them. Portable AnyEvent
		213	callbacks cannot use arguments passed to I/O watcher callbacks.
84		214
85	Example:	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.
86		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
87	# wait for readability of STDIN, then read a line and disable the watcher	223	Example: wait for readability of STDIN, then read a line and disable the
		224	watcher.
		225
88	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	226	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
89	chomp (my $input = <STDIN>);	227	chomp (my $input = <STDIN>);
90	warn "read: $input\n";	228	warn "read: $input\n";
91	undef $w;	229	undef $w;
92	});	230	});
93		231
94	=head2 TIME WATCHERS	232	=head2 TIME WATCHERS
95		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
96	You can create a time watcher by calling the C<< AnyEvent->timer >>	242	You can create a time watcher by calling the C<< AnyEvent->timer >>
97	method with the following mandatory arguments:	243	method with the following mandatory arguments:
98		244
99	C<after> after how many seconds (fractions are supported) should the timer	245	C<after> specifies after how many seconds (fractional values are
100	activate. C<cb> the callback to invoke.	246	supported) the callback should be invoked. C<cb> is the callback to invoke
		247	in that case.
101		248
102	The timer callback will be invoked at most once: if you want a repeating	249	Although the callback might get passed parameters, their value and
103	timer you have to create a new watcher (this is a limitation by both Tk	250	presence is undefined and you cannot rely on them. Portable AnyEvent
104	and Glib).	251	callbacks cannot use arguments passed to time watcher callbacks.
105		252
106	Example:	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.
107		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
108	# fire an event after 7.7 seconds	263	Example: fire an event after 7.7 seconds.
		264
109	my $w = AnyEvent->timer (after => 7.7, cb => sub {	265	my $w = AnyEvent->timer (after => 7.7, cb => sub {
110	warn "timeout\n";	266	warn "timeout\n";
111	});	267	});
112		268
113	# to cancel the timer:	269	# to cancel the timer:
114	undef $w	270	undef $w;
115		271
116	=head2 CONDITION WATCHERS	272	Example 2: fire an event after 0.5 seconds, then roughly every second.
117		273
118	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	274	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
119	method without any arguments.	275	warn "timeout\n";
		276	};
120		277
121	A condition watcher watches for a condition - precisely that the C<<	278	=head3 TIMING ISSUES
122	->broadcast >> method has been called.
123		279
124	The watcher has only two methods:	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":
125		299
126	=over 4	300	=over 4
127		301
128	=item $cv->wait	302	=item AnyEvent->time
129		303
130	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	304	This returns the "current wallclock time" as a fractional number of
131	called on c<$cv>, while servicing other watchers normally.	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).
132		307
133	Not all event models support a blocking wait - some die in that case, so	308	It progresses independently of any event loop processing, i.e. each call
134	if you are using this from a module, never require a blocking wait, but	309	will check the system clock, which usually gets updated frequently.
135	let the caller decide wether the call will block or not (for example,
136	by coupling condition variables with some kind of request results and
137	supporting callbacks so the caller knows that getting the result will not
138	block, while still suppporting blockign waits if the caller so desires).
139		310
140	You can only wait once on a condition - additional calls will return	311	=item AnyEvent->now
141	immediately.
142		312
143	=item $cv->broadcast	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.
144		317
145	Flag the condition as ready - a running C<< ->wait >> and all further	318	I<In almost all cases (in all cases if you don't care), this is the
146	calls to C<wait> will return after this method has been called. If nobody	319	function to call when you want to know the current time.>
147	is waiting the broadcast will be remembered..
148		320
149	Example:	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).
150		324
151	# wait till the result is ready	325	The rest of this section is only of relevance if you try to be very exact
152	my $result_ready = AnyEvent->condvar;	326	with your timing; you can skip it without a bad conscience.
153		327
154	# do something such as adding a timer	328	For a practical example of when these times differ, consider L<Event::Lib>
155	# or socket watcher the calls $result_ready->broadcast	329	and L<EV> and the following set-up:
156	# when the "result" is ready.
157		330
158	$result_ready->wait;	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.
159		380
160	=back	381	=back
161		382
162	=head2 SIGNAL WATCHERS	383	=head2 SIGNAL WATCHERS
163		384
		385	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		386
164	You can listen for signals using a signal watcher, C<signal> is the signal	387	You can watch for signals using a signal watcher, C<signal> is the signal
165	I<name> without any C<SIG> prefix. Multiple signals events can be clumped	388	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
166	together into one callback invocation, and callback invocation might or	389	callback to be invoked whenever a signal occurs.
167	might not be asynchronous.
168		390
169	These watchers might use C<%SIG>, so programs overwriting those signals	391	Although the callback might get passed parameters, their value and
170	directly will likely not work correctly.	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.
171		407
172	Example: exit on SIGINT	408	Example: exit on SIGINT
173		409
174	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	410	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
175		411
		412	=head3 Restart Behaviour
		413
		414	While restart behaviour is up to the event loop implementation, most will
		415	not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
		416	pure perl implementation).
		417
		418	=head3 Safe/Unsafe Signals
		419
		420	Perl signals can be either "safe" (synchronous to opcode handling) or
		421	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		422	latter might corrupt your memory.
		423
		424	AnyEvent signal handlers are, in addition, synchronous to the event loop,
		425	i.e. they will not interrupt your running perl program but will only be
		426	called as part of the normal event handling (just like timer, I/O etc.
		427	callbacks, too).
		428
		429	=head3 Signal Races, Delays and Workarounds
		430
		431	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		432	callbacks to signals in a generic way, which is a pity, as you cannot
		433	do race-free signal handling in perl, requiring C libraries for
		434	this. AnyEvent will try to do its best, which means in some cases,
		435	signals will be delayed. The maximum time a signal might be delayed is
		436	specified in C<$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
176	=head2 CHILD PROCESS WATCHERS	449	=head2 CHILD PROCESS WATCHERS
177		450
178	You can also listen for the status of a child process specified by the	451	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
179	C<pid> argument (or any child if the pid argument is 0). The watcher will
180	trigger as often as status change for the child are received. This works
181	by installing a signal handler for C<SIGCHLD>. The callback will be called with
182	the pid and exit status (as returned by waitpid).
183		452
184	Example: wait for pid 1333	453	You can also watch for a child process exit and catch its exit status.
185		454
186	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });	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).
187		460
188	=head1 GLOBALS	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:
189		580
190	=over 4	581	=over 4
191		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::FLTK2 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
192	=item $AnyEvent::MODEL	921	=item $AnyEvent::MODEL
193		922
194	Contains C<undef> until the first watcher is being created. Then it	923	Contains C<undef> until the first watcher is being created, before the
		924	backend has been autodetected.
		925
195	contains the event model that is being used, which is the name of the	926	Afterwards it contains the event model that is being used, which is the
196	Perl class implementing the model. This class is usually one of the	927	name of the Perl class implementing the model. This class is usually one
197	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	928	of the C<AnyEvent::Impl::xxx> modules, but can be any other class in the
198	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	929	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
199		930	will be C<urxvt::anyevent>).
200	The known classes so far are:
201
202	EV::AnyEvent based on EV (an interface to libev, best choice)
203	AnyEvent::Impl::Coro based on Coro::Event, second best choice.
204	AnyEvent::Impl::Event based on Event, also second best choice :)
205	AnyEvent::Impl::Glib based on Glib, second-best choice.
206	AnyEvent::Impl::Tk based on Tk, very bad choice.
207	AnyEvent::Impl::Perl pure-perl implementation, inefficient.
208		931
209	=item AnyEvent::detect	932	=item AnyEvent::detect
210		933
211	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	934	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
212	necessary. You should only call this function right before you would have	935	if necessary. You should only call this function right before you would
213	created an AnyEvent watcher anyway, that is, very late at runtime.	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	If you need to do some initialisation before AnyEvent watchers are
		940	created, use C<post_detect>.
		941
		942	=item $guard = AnyEvent::post_detect { BLOCK }
		943
		944	Arranges for the code block to be executed as soon as the event model is
		945	autodetected (or immediately if that has already happened).
		946
		947	The block will be executed I<after> the actual backend has been detected
		948	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		949	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		950	other initialisations - see the sources of L<AnyEvent::Strict> or
		951	L<AnyEvent::AIO> to see how this is used.
		952
		953	The most common usage is to create some global watchers, without forcing
		954	event module detection too early, for example, L<AnyEvent::AIO> creates
		955	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		956	avoid autodetecting the event module at load time.
		957
		958	If called in scalar or list context, then it creates and returns an object
		959	that automatically removes the callback again when it is destroyed (or
		960	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		961	a case where this is useful.
		962
		963	Example: Create a watcher for the IO::AIO module and store it in
		964	C<$WATCHER>, but do so only do so after the event loop is initialised.
		965
		966	our WATCHER;
		967
		968	my $guard = AnyEvent::post_detect {
		969	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		970	};
		971
		972	# the ||= is important in case post_detect immediately runs the block,
		973	# as to not clobber the newly-created watcher. assigning both watcher and
		974	# post_detect guard to the same variable has the advantage of users being
		975	# able to just C<undef $WATCHER> if the watcher causes them grief.
		976
		977	$WATCHER ||= $guard;
		978
		979	=item @AnyEvent::post_detect
		980
		981	If there are any code references in this array (you can C<push> to it
		982	before or after loading AnyEvent), then they will be called directly
		983	after the event loop has been chosen.
		984
		985	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		986	if it is defined then the event loop has already been detected, and the
		987	array will be ignored.
		988
		989	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		990	it, as it takes care of these details.
		991
		992	This variable is mainly useful for modules that can do something useful
		993	when AnyEvent is used and thus want to know when it is initialised, but do
		994	not need to even load it by default. This array provides the means to hook
		995	into AnyEvent passively, without loading it.
		996
		997	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		998	together, you could put this into Coro (this is the actual code used by
		999	Coro to accomplish this):
		1000
		1001	if (defined $AnyEvent::MODEL) {
		1002	# AnyEvent already initialised, so load Coro::AnyEvent
		1003	require Coro::AnyEvent;
		1004	} else {
		1005	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		1006	# as soon as it is
		1007	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		1008	}
		1009
		1010	=item AnyEvent::postpone { BLOCK }
		1011
		1012	Arranges for the block to be executed as soon as possible, but not before
		1013	the call itself returns. In practise, the block will be executed just
		1014	before the event loop polls for new events, or shortly afterwards.
		1015
		1016	This function never returns anything (to make the C<return postpone { ...
		1017	}> idiom more useful.
		1018
		1019	To understand the usefulness of this function, consider a function that
		1020	asynchronously does something for you and returns some transaction
		1021	object or guard to let you cancel the operation. For example,
		1022	C<AnyEvent::Socket::tcp_connect>:
		1023
		1024	# start a conenction attempt unless one is active
		1025	$self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
		1026	delete $self->{connect_guard};
		1027	...
		1028	};
		1029
		1030	Imagine that this function could instantly call the callback, for
		1031	example, because it detects an obvious error such as a negative port
		1032	number. Invoking the callback before the function returns causes problems
		1033	however: the callback will be called and will try to delete the guard
		1034	object. But since the function hasn't returned yet, there is nothing to
		1035	delete. When the function eventually returns it will assign the guard
		1036	object to C<< $self->{connect_guard} >>, where it will likely never be
		1037	deleted, so the program thinks it is still trying to connect.
		1038
		1039	This is where C<AnyEvent::postpone> should be used. Instead of calling the
		1040	callback directly on error:
		1041
		1042	$cb->(undef), return # signal error to callback, BAD!
		1043	if $some_error_condition;
		1044
		1045	It should use C<postpone>:
		1046
		1047	AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
		1048	if $some_error_condition;
214		1049
215	=back	1050	=back
216		1051
217	=head1 WHAT TO DO IN A MODULE	1052	=head1 WHAT TO DO IN A MODULE
218		1053
219	As a module author, you should "use AnyEvent" and call AnyEvent methods	1054	As a module author, you should C<use AnyEvent> and call AnyEvent methods
220	freely, but you should not load a specific event module or rely on it.	1055	freely, but you should not load a specific event module or rely on it.
221		1056
222	Be careful when you create watchers in the module body - Anyevent will	1057	Be careful when you create watchers in the module body - AnyEvent will
223	decide which event module to use as soon as the first method is called, so	1058	decide which event module to use as soon as the first method is called, so
224	by calling AnyEvent in your module body you force the user of your module	1059	by calling AnyEvent in your module body you force the user of your module
225	to load the event module first.	1060	to load the event module first.
226		1061
		1062	Never call C<< ->recv >> on a condition variable unless you I<know> that
		1063	the C<< ->send >> method has been called on it already. This is
		1064	because it will stall the whole program, and the whole point of using
		1065	events is to stay interactive.
		1066
		1067	It is fine, however, to call C<< ->recv >> when the user of your module
		1068	requests it (i.e. if you create a http request object ad have a method
		1069	called C<results> that returns the results, it may call C<< ->recv >>
		1070	freely, as the user of your module knows what she is doing. Always).
		1071
227	=head1 WHAT TO DO IN THE MAIN PROGRAM	1072	=head1 WHAT TO DO IN THE MAIN PROGRAM
228		1073
229	There will always be a single main program - the only place that should	1074	There will always be a single main program - the only place that should
230	dictate which event model to use.	1075	dictate which event model to use.
231		1076
232	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	1077	If the program is not event-based, it need not do anything special, even
233	do anything special and let AnyEvent decide which implementation to chose.	1078	when it depends on a module that uses an AnyEvent. If the program itself
		1079	uses AnyEvent, but does not care which event loop is used, all it needs
		1080	to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
		1081	available loop implementation.
234		1082
235	If the main program relies on a specific event model (for example, in Gtk2	1083	If the main program relies on a specific event model - for example, in
236	programs you have to rely on either Glib or Glib::Event), you should load	1084	Gtk2 programs you have to rely on the Glib module - you should load the
237	it before loading AnyEvent or any module that uses it, generally, as early	1085	event module before loading AnyEvent or any module that uses it: generally
238	as possible. The reason is that modules might create watchers when they	1086	speaking, you should load it as early as possible. The reason is that
239	are loaded, and AnyEvent will decide on the event model to use as soon as	1087	modules might create watchers when they are loaded, and AnyEvent will
240	it creates watchers, and it might chose the wrong one unless you load the	1088	decide on the event model to use as soon as it creates watchers, and it
241	correct one yourself.	1089	might choose the wrong one unless you load the correct one yourself.
242		1090
243	You can chose to use a rather inefficient pure-perl implementation by	1091	You can chose to use a pure-perl implementation by loading the
244	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	1092	C<AnyEvent::Loop> module, which gives you similar behaviour
245	generally better.	1093	everywhere, but letting AnyEvent chose the model is generally better.
		1094
		1095	=head2 MAINLOOP EMULATION
		1096
		1097	Sometimes (often for short test scripts, or even standalone programs who
		1098	only want to use AnyEvent), you do not want to run a specific event loop.
		1099
		1100	In that case, you can use a condition variable like this:
		1101
		1102	AnyEvent->condvar->recv;
		1103
		1104	This has the effect of entering the event loop and looping forever.
		1105
		1106	Note that usually your program has some exit condition, in which case
		1107	it is better to use the "traditional" approach of storing a condition
		1108	variable somewhere, waiting for it, and sending it when the program should
		1109	exit cleanly.
		1110
		1111
		1112	=head1 OTHER MODULES
		1113
		1114	The following is a non-exhaustive list of additional modules that use
		1115	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		1116	modules and other event loops in the same program. Some of the modules
		1117	come as part of AnyEvent, the others are available via CPAN.
		1118
		1119	=over 4
		1120
		1121	=item L<AnyEvent::Util>
		1122
		1123	Contains various utility functions that replace often-used blocking
		1124	functions such as C<inet_aton> with event/callback-based versions.
		1125
		1126	=item L<AnyEvent::Socket>
		1127
		1128	Provides various utility functions for (internet protocol) sockets,
		1129	addresses and name resolution. Also functions to create non-blocking tcp
		1130	connections or tcp servers, with IPv6 and SRV record support and more.
		1131
		1132	=item L<AnyEvent::Handle>
		1133
		1134	Provide read and write buffers, manages watchers for reads and writes,
		1135	supports raw and formatted I/O, I/O queued and fully transparent and
		1136	non-blocking SSL/TLS (via L<AnyEvent::TLS>).
		1137
		1138	=item L<AnyEvent::DNS>
		1139
		1140	Provides rich asynchronous DNS resolver capabilities.
		1141
		1142	=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
		1143
		1144	Implement event-based interfaces to the protocols of the same name (for
		1145	the curious, IGS is the International Go Server and FCP is the Freenet
		1146	Client Protocol).
		1147
		1148	=item L<AnyEvent::Handle::UDP>
		1149
		1150	Here be danger!
		1151
		1152	As Pauli would put it, "Not only is it not right, it's not even wrong!" -
		1153	there are so many things wrong with AnyEvent::Handle::UDP, most notably
		1154	its use of a stream-based API with a protocol that isn't streamable, that
		1155	the only way to improve it is to delete it.
		1156
		1157	It features data corruption (but typically only under load) and general
		1158	confusion. On top, the author is not only clueless about UDP but also
		1159	fact-resistant - some gems of his understanding: "connect doesn't work
		1160	with UDP", "UDP packets are not IP packets", "UDP only has datagrams, not
		1161	packets", "I don't need to implement proper error checking as UDP doesn't
		1162	support error checking" and so on - he doesn't even understand what's
		1163	wrong with his module when it is explained to him.
		1164
		1165	=item L<AnyEvent::DBI>
		1166
		1167	Executes L<DBI> requests asynchronously in a proxy process for you,
		1168	notifying you in an event-based way when the operation is finished.
		1169
		1170	=item L<AnyEvent::AIO>
		1171
		1172	Truly asynchronous (as opposed to non-blocking) I/O, should be in the
		1173	toolbox of every event programmer. AnyEvent::AIO transparently fuses
		1174	L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
		1175	file I/O, and much more.
		1176
		1177	=item L<AnyEvent::HTTPD>
		1178
		1179	A simple embedded webserver.
		1180
		1181	=item L<AnyEvent::FastPing>
		1182
		1183	The fastest ping in the west.
		1184
		1185	=item L<Coro>
		1186
		1187	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1188
		1189	=back
246		1190
247	=cut	1191	=cut
248		1192
249	package AnyEvent;	1193	package AnyEvent;
250		1194
251	no warnings;	1195	# basically a tuned-down version of common::sense
252	use strict;	1196	sub common_sense {
		1197	# from common:.sense 3.4
		1198	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
		1199	# use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
		1200	$^H |= 0x00000600;
		1201	}
253		1202
		1203	BEGIN { AnyEvent::common_sense }
		1204
254	use Carp;	1205	use Carp ();
255		1206
256	our $VERSION = '2.55';	1207	our $VERSION = '5.34';
257	our $MODEL;	1208	our $MODEL;
258		1209
259	our $AUTOLOAD;
260	our @ISA;	1210	our @ISA;
261		1211
262	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
263
264	our @REGISTRY;	1212	our @REGISTRY;
265		1213
		1214	our $VERBOSE;
		1215
		1216	BEGIN {
		1217	require "AnyEvent/constants.pl";
		1218
		1219	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1220
		1221	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1222	if ${^TAINT};
		1223
		1224	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1225
		1226	}
		1227
		1228	our $MAX_SIGNAL_LATENCY = 10;
		1229
		1230	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1231
		1232	{
		1233	my $idx;
		1234	$PROTOCOL{$_} = ++$idx
		1235	for reverse split /\s*,\s*/,
		1236	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1237	}
		1238
		1239	our @post_detect;
		1240
		1241	sub post_detect(&) {
		1242	my ($cb) = @_;
		1243
		1244	push @post_detect, $cb;
		1245
		1246	defined wantarray
		1247	? bless \$cb, "AnyEvent::Util::postdetect"
		1248	: ()
		1249	}
		1250
		1251	sub AnyEvent::Util::postdetect::DESTROY {
		1252	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1253	}
		1254
		1255	our $POSTPONE_W;
		1256	our @POSTPONE;
		1257
		1258	sub _postpone_exec {
		1259	undef $POSTPONE_W;
		1260
		1261	&{ shift @POSTPONE }
		1262	while @POSTPONE;
		1263	}
		1264
		1265	sub postpone(&) {
		1266	push @POSTPONE, shift;
		1267
		1268	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1269
		1270	()
		1271	}
		1272
266	my @models = (	1273	our @models = (
267	[Coro::Event:: => AnyEvent::Impl::Coro::],
268	[EV:: => EV::AnyEvent::],	1274	[EV:: => AnyEvent::Impl::EV:: , 1],
		1275	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
		1276	# everything below here will not (normally) be autoprobed
		1277	# as the pure perl backend should work everywhere
		1278	# and is usually faster
269	[Event:: => AnyEvent::Impl::Event::],	1279	[Event:: => AnyEvent::Impl::Event::, 1],
270	[Glib:: => AnyEvent::Impl::Glib::],	1280	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1281	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1282	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1283	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1284	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1285	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
271	[Tk:: => AnyEvent::Impl::Tk::],	1286	[Wx:: => AnyEvent::Impl::POE::],
272	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	1287	[Prima:: => AnyEvent::Impl::POE::],
		1288	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1289	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
		1290	[FLTK:: => AnyEvent::Impl::FLTK2::],
273	);	1291	);
274		1292
275	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	1293	# all autoloaded methods reserve the complete glob, not just the method slot.
		1294	# due to bugs in perls method cache implementation.
		1295	our @methods = qw(io timer time now now_update signal child idle condvar);
276		1296
277	sub detect() {	1297	sub detect() {
		1298	local $!; # for good measure
		1299	local $SIG{__DIE__}; # we use eval
		1300
		1301	# free some memory
		1302	*detect = sub () { $MODEL };
		1303	# undef &func doesn't correctly update the method cache. grmbl.
		1304	# so we delete the whole glob. grmbl.
		1305	# otoh, perl doesn't let me undef an active usb, but it lets me free
		1306	# a glob with an active sub. hrm. i hope it works, but perl is
		1307	# usually buggy in this department. sigh.
		1308	delete @{"AnyEvent::"}{@methods};
		1309	undef @methods;
		1310
		1311	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1312	my $model = $1;
		1313	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1314	if (eval "require $model") {
		1315	$MODEL = $model;
		1316	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1317	} else {
		1318	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
		1319	}
		1320	}
		1321
		1322	# check for already loaded models
278	unless ($MODEL) {	1323	unless ($MODEL) {
279	no strict 'refs';
280
281	# check for already loaded models
282	for (@REGISTRY, @models) {	1324	for (@REGISTRY, @models) {
283	my ($package, $model) = @$_;	1325	my ($package, $model) = @$_;
284	if (${"$package\::VERSION"} > 0) {	1326	if (${"$package\::VERSION"} > 0) {
285	if (eval "require $model") {	1327	if (eval "require $model") {
286	$MODEL = $model;	1328	$MODEL = $model;
287	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1329	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
288	last;	1330	last;
289	}	1331	}
290	}	1332	}
291	}	1333	}
292		1334
293	unless ($MODEL) {	1335	unless ($MODEL) {
294	# try to load a model	1336	# try to autoload a model
295
296	for (@REGISTRY, @models) {	1337	for (@REGISTRY, @models) {
297	my ($package, $model) = @$_;	1338	my ($package, $model, $autoload) = @$_;
		1339	if (
		1340	$autoload
298	if (eval "require $package"	1341	and eval "require $package"
299	and ${"$package\::VERSION"} > 0	1342	and ${"$package\::VERSION"} > 0
300	and eval "require $model") {	1343	and eval "require $model"
		1344	) {
301	$MODEL = $model;	1345	$MODEL = $model;
302	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	1346	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
303	last;	1347	last;
304	}	1348	}
305	}	1349	}
306		1350
307	$MODEL	1351	$MODEL
308	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Event (or Coro+Event), Glib or Tk.";	1352	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?\n";
309	}	1353	}
310
311	unshift @ISA, $MODEL;
312	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
313	}	1354	}
314		1355
		1356	# free memory only needed for probing
		1357	undef @models;
		1358	undef @REGISTRY;
		1359
		1360	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1361	unshift @ISA, $MODEL;
		1362
		1363	# now nuke some methods that are overridden by the backend.
		1364	# SUPER usage is not allowed in these.
		1365	for (qw(time signal child idle)) {
		1366	undef &{"AnyEvent::Base::$_"}
		1367	if defined &{"$MODEL\::$_"};
		1368	}
		1369
		1370	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1371	require AnyEvent::Strict;
		1372	}
		1373
		1374	if ($ENV{PERL_ANYEVENT_DEBUG_WRAP}) {
		1375	require AnyEvent::Debug;
		1376	AnyEvent::Debug::wrap ($ENV{PERL_ANYEVENT_DEBUG_WRAP});
		1377	}
		1378
		1379	if (exists $ENV{PERL_ANYEVENT_DEBUG_SHELL}) {
		1380	require AnyEvent::Socket;
		1381	require AnyEvent::Debug;
		1382
		1383	my ($host, $service) = AnyEvent::Socket::parse_hostport ($ENV{PERL_ANYEVENT_DEBUG_SHELL});
		1384	$AnyEvent::Debug::SHELL = AnyEvent::Debug::shell ($host, $service);
		1385	}
		1386
		1387	(shift @post_detect)->() while @post_detect;
		1388	undef @post_detect;
		1389
		1390	*post_detect = sub(&) {
		1391	shift->();
		1392
		1393	undef
		1394	};
		1395
315	$MODEL	1396	$MODEL
316	}	1397	}
317		1398
318	sub AUTOLOAD {	1399	for my $name (@methods) {
319	(my $func = $AUTOLOAD) =~ s/.*://;	1400	*$name = sub {
320		1401	detect;
321	$method{$func}	1402	# we use goto because
322	or croak "$func: not a valid method for AnyEvent objects";	1403	# a) it makes the thunk more transparent
323		1404	# b) it allows us to delete the thunk later
324	detect unless $MODEL;	1405	goto &{ UNIVERSAL::can AnyEvent => "SUPER::$name" }
325		1406	};
326	my $class = shift;
327	$class->$func (@_);
328	}	1407	}
		1408
		1409	# utility function to dup a filehandle. this is used by many backends
		1410	# to support binding more than one watcher per filehandle (they usually
		1411	# allow only one watcher per fd, so we dup it to get a different one).
		1412	sub _dupfh($$;$$) {
		1413	my ($poll, $fh, $r, $w) = @_;
		1414
		1415	# cygwin requires the fh mode to be matching, unix doesn't
		1416	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1417
		1418	open my $fh2, $mode, $fh
		1419	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1420
		1421	# we assume CLOEXEC is already set by perl in all important cases
		1422
		1423	($fh2, $rw)
		1424	}
		1425
		1426	=head1 SIMPLIFIED AE API
		1427
		1428	Starting with version 5.0, AnyEvent officially supports a second, much
		1429	simpler, API that is designed to reduce the calling, typing and memory
		1430	overhead by using function call syntax and a fixed number of parameters.
		1431
		1432	See the L<AE> manpage for details.
		1433
		1434	=cut
		1435
		1436	package AE;
		1437
		1438	our $VERSION = $AnyEvent::VERSION;
		1439
		1440	sub _reset() {
		1441	eval q{
		1442	# fall back to the main API by default - backends and AnyEvent::Base
		1443	# implementations can overwrite these.
		1444
		1445	sub io($$$) {
		1446	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1447	}
		1448
		1449	sub timer($$$) {
		1450	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1451	}
		1452
		1453	sub signal($$) {
		1454	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1455	}
		1456
		1457	sub child($$) {
		1458	AnyEvent->child (pid => $_[0], cb => $_[1])
		1459	}
		1460
		1461	sub idle($) {
		1462	AnyEvent->idle (cb => $_[0]);
		1463	}
		1464
		1465	sub cv(;&) {
		1466	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1467	}
		1468
		1469	sub now() {
		1470	AnyEvent->now
		1471	}
		1472
		1473	sub now_update() {
		1474	AnyEvent->now_update
		1475	}
		1476
		1477	sub time() {
		1478	AnyEvent->time
		1479	}
		1480
		1481	*postpone = \&AnyEvent::postpone;
		1482	};
		1483	die if $@;
		1484	}
		1485
		1486	BEGIN { _reset }
329		1487
330	package AnyEvent::Base;	1488	package AnyEvent::Base;
331		1489
		1490	# default implementations for many methods
		1491
		1492	sub time {
		1493	eval q{ # poor man's autoloading {}
		1494	# probe for availability of Time::HiRes
		1495	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1496	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1497	*AE::time = \&Time::HiRes::time;
		1498	# if (eval "use POSIX (); (POSIX::times())...
		1499	} else {
		1500	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1501	*AE::time = sub (){ time }; # epic fail
		1502	}
		1503
		1504	*time = sub { AE::time }; # different prototypes
		1505	};
		1506	die if $@;
		1507
		1508	&time
		1509	}
		1510
		1511	*now = \&time;
		1512
		1513	sub now_update { }
		1514
		1515	sub _poll {
		1516	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1517	}
		1518
332	# default implementation for ->condvar, ->wait, ->broadcast	1519	# default implementation for ->condvar
		1520	# in fact, the default should not be overwritten
333		1521
334	sub condvar {	1522	sub condvar {
335	bless \my $flag, "AnyEvent::Base::CondVar"	1523	eval q{ # poor man's autoloading {}
336	}	1524	*condvar = sub {
		1525	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1526	};
337		1527
338	sub AnyEvent::Base::CondVar::broadcast {	1528	*AE::cv = sub (;&) {
339	${$_[0]}++;	1529	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
340	}	1530	};
		1531	};
		1532	die if $@;
341		1533
342	sub AnyEvent::Base::CondVar::wait {	1534	&condvar
343	AnyEvent->one_event while !${$_[0]};
344	}	1535	}
345		1536
346	# default implementation for ->signal	1537	# default implementation for ->signal
347		1538
348	our %SIG_CB;	1539	our $HAVE_ASYNC_INTERRUPT;
		1540
		1541	sub _have_async_interrupt() {
		1542	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1543	&& eval "use Async::Interrupt 1.02 (); 1")
		1544	unless defined $HAVE_ASYNC_INTERRUPT;
		1545
		1546	$HAVE_ASYNC_INTERRUPT
		1547	}
		1548
		1549	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1550	our (%SIG_ASY, %SIG_ASY_W);
		1551	our ($SIG_COUNT, $SIG_TW);
		1552
		1553	# install a dummy wakeup watcher to reduce signal catching latency
		1554	# used by Impls
		1555	sub _sig_add() {
		1556	unless ($SIG_COUNT++) {
		1557	# try to align timer on a full-second boundary, if possible
		1558	my $NOW = AE::now;
		1559
		1560	$SIG_TW = AE::timer
		1561	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1562	$MAX_SIGNAL_LATENCY,
		1563	sub { } # just for the PERL_ASYNC_CHECK
		1564	;
		1565	}
		1566	}
		1567
		1568	sub _sig_del {
		1569	undef $SIG_TW
		1570	unless --$SIG_COUNT;
		1571	}
		1572
		1573	our $_sig_name_init; $_sig_name_init = sub {
		1574	eval q{ # poor man's autoloading {}
		1575	undef $_sig_name_init;
		1576
		1577	if (_have_async_interrupt) {
		1578	*sig2num = \&Async::Interrupt::sig2num;
		1579	*sig2name = \&Async::Interrupt::sig2name;
		1580	} else {
		1581	require Config;
		1582
		1583	my %signame2num;
		1584	@signame2num{ split ' ', $Config::Config{sig_name} }
		1585	= split ' ', $Config::Config{sig_num};
		1586
		1587	my @signum2name;
		1588	@signum2name[values %signame2num] = keys %signame2num;
		1589
		1590	*sig2num = sub($) {
		1591	$_[0] > 0 ? shift : $signame2num{+shift}
		1592	};
		1593	*sig2name = sub ($) {
		1594	$_[0] > 0 ? $signum2name[+shift] : shift
		1595	};
		1596	}
		1597	};
		1598	die if $@;
		1599	};
		1600
		1601	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1602	sub sig2name($) { &$_sig_name_init; &sig2name }
349		1603
350	sub signal {	1604	sub signal {
		1605	eval q{ # poor man's autoloading {}
		1606	# probe for availability of Async::Interrupt
		1607	if (_have_async_interrupt) {
		1608	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1609
		1610	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1611	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1612
		1613	} else {
		1614	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1615
		1616	if (AnyEvent::WIN32) {
		1617	require AnyEvent::Util;
		1618
		1619	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1620	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1621	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1622	} else {
		1623	pipe $SIGPIPE_R, $SIGPIPE_W;
		1624	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1625	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1626
		1627	# not strictly required, as $^F is normally 2, but let's make sure...
		1628	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1629	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1630	}
		1631
		1632	$SIGPIPE_R
		1633	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1634
		1635	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1636	}
		1637
		1638	*signal = $HAVE_ASYNC_INTERRUPT
		1639	? sub {
351	my (undef, %arg) = @_;	1640	my (undef, %arg) = @_;
352		1641
		1642	# async::interrupt
353	my $signal = uc $arg{signal}	1643	my $signal = sig2num $arg{signal};
354	or Carp::croak "required option 'signal' is missing";
355
356	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1644	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1645
		1646	$SIG_ASY{$signal} ||= new Async::Interrupt
		1647	cb => sub { undef $SIG_EV{$signal} },
		1648	signal => $signal,
		1649	pipe => [$SIGPIPE_R->filenos],
		1650	pipe_autodrain => 0,
		1651	;
		1652
		1653	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1654	}
		1655	: sub {
		1656	my (undef, %arg) = @_;
		1657
		1658	# pure perl
		1659	my $signal = sig2name $arg{signal};
		1660	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1661
357	$SIG{$signal} ||= sub {	1662	$SIG{$signal} ||= sub {
		1663	local $!;
		1664	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1665	undef $SIG_EV{$signal};
		1666	};
		1667
		1668	# can't do signal processing without introducing races in pure perl,
		1669	# so limit the signal latency.
		1670	_sig_add;
		1671
		1672	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1673	}
		1674	;
		1675
		1676	*AnyEvent::Base::signal::DESTROY = sub {
		1677	my ($signal, $cb) = @{$_[0]};
		1678
		1679	_sig_del;
		1680
		1681	delete $SIG_CB{$signal}{$cb};
		1682
		1683	$HAVE_ASYNC_INTERRUPT
		1684	? delete $SIG_ASY{$signal}
		1685	: # delete doesn't work with older perls - they then
		1686	# print weird messages, or just unconditionally exit
		1687	# instead of getting the default action.
		1688	undef $SIG{$signal}
		1689	unless keys %{ $SIG_CB{$signal} };
		1690	};
		1691
		1692	*_signal_exec = sub {
		1693	$HAVE_ASYNC_INTERRUPT
		1694	? $SIGPIPE_R->drain
		1695	: sysread $SIGPIPE_R, (my $dummy), 9;
		1696
		1697	while (%SIG_EV) {
		1698	for (keys %SIG_EV) {
		1699	delete $SIG_EV{$_};
358	$_->() for values %{ $SIG_CB{$signal} || {} };	1700	&$_ for values %{ $SIG_CB{$_} || {} };
		1701	}
		1702	}
		1703	};
359	};	1704	};
		1705	die if $@;
360		1706
361	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1707	&signal
362	}
363
364	sub AnyEvent::Base::Signal::DESTROY {
365	my ($signal, $cb) = @{$_[0]};
366
367	delete $SIG_CB{$signal}{$cb};
368
369	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
370	}	1708	}
371		1709
372	# default implementation for ->child	1710	# default implementation for ->child
373		1711
374	our %PID_CB;	1712	our %PID_CB;
375	our $CHLD_W;	1713	our $CHLD_W;
376	our $PID_IDLE;	1714	our $CHLD_DELAY_W;
377	our $WNOHANG;
378		1715
379	sub _child_wait {	1716	# used by many Impl's
380	while (0 <= (my $pid = waitpid -1, $WNOHANG)) {	1717	sub _emit_childstatus($$) {
		1718	my (undef, $rpid, $rstatus) = @_;
		1719
		1720	$_->($rpid, $rstatus)
381	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1721	for values %{ $PID_CB{$rpid} || {} },
382	(values %{ $PID_CB{0} || {} });	1722	values %{ $PID_CB{0} || {} };
		1723	}
		1724
		1725	sub child {
		1726	eval q{ # poor man's autoloading {}
		1727	*_sigchld = sub {
		1728	my $pid;
		1729
		1730	AnyEvent->_emit_childstatus ($pid, $?)
		1731	while ($pid = waitpid -1, WNOHANG) > 0;
		1732	};
		1733
		1734	*child = sub {
		1735	my (undef, %arg) = @_;
		1736
		1737	my $pid = $arg{pid};
		1738	my $cb = $arg{cb};
		1739
		1740	$PID_CB{$pid}{$cb+0} = $cb;
		1741
		1742	unless ($CHLD_W) {
		1743	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1744	# child could be a zombie already, so make at least one round
		1745	&_sigchld;
		1746	}
		1747
		1748	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1749	};
		1750
		1751	*AnyEvent::Base::child::DESTROY = sub {
		1752	my ($pid, $icb) = @{$_[0]};
		1753
		1754	delete $PID_CB{$pid}{$icb};
		1755	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1756
		1757	undef $CHLD_W unless keys %PID_CB;
		1758	};
		1759	};
		1760	die if $@;
		1761
		1762	&child
		1763	}
		1764
		1765	# idle emulation is done by simply using a timer, regardless
		1766	# of whether the process is idle or not, and not letting
		1767	# the callback use more than 50% of the time.
		1768	sub idle {
		1769	eval q{ # poor man's autoloading {}
		1770	*idle = sub {
		1771	my (undef, %arg) = @_;
		1772
		1773	my ($cb, $w, $rcb) = $arg{cb};
		1774
		1775	$rcb = sub {
		1776	if ($cb) {
		1777	$w = AE::time;
		1778	&$cb;
		1779	$w = AE::time - $w;
		1780
		1781	# never use more then 50% of the time for the idle watcher,
		1782	# within some limits
		1783	$w = 0.0001 if $w < 0.0001;
		1784	$w = 5 if $w > 5;
		1785
		1786	$w = AE::timer $w, 0, $rcb;
		1787	} else {
		1788	# clean up...
		1789	undef $w;
		1790	undef $rcb;
		1791	}
		1792	};
		1793
		1794	$w = AE::timer 0.05, 0, $rcb;
		1795
		1796	bless \\$cb, "AnyEvent::Base::idle"
		1797	};
		1798
		1799	*AnyEvent::Base::idle::DESTROY = sub {
		1800	undef $${$_[0]};
		1801	};
		1802	};
		1803	die if $@;
		1804
		1805	&idle
		1806	}
		1807
		1808	package AnyEvent::CondVar;
		1809
		1810	our @ISA = AnyEvent::CondVar::Base::;
		1811
		1812	# only to be used for subclassing
		1813	sub new {
		1814	my $class = shift;
		1815	bless AnyEvent->condvar (@_), $class
		1816	}
		1817
		1818	package AnyEvent::CondVar::Base;
		1819
		1820	#use overload
		1821	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1822	# fallback => 1;
		1823
		1824	# save 300+ kilobytes by dirtily hardcoding overloading
		1825	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1826	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1827	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1828	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1829
		1830	our $WAITING;
		1831
		1832	sub _send {
		1833	# nop
		1834	}
		1835
		1836	sub _wait {
		1837	AnyEvent->_poll until $_[0]{_ae_sent};
		1838	}
		1839
		1840	sub send {
		1841	my $cv = shift;
		1842	$cv->{_ae_sent} = [@_];
		1843	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1844	$cv->_send;
		1845	}
		1846
		1847	sub croak {
		1848	$_[0]{_ae_croak} = $_[1];
		1849	$_[0]->send;
		1850	}
		1851
		1852	sub ready {
		1853	$_[0]{_ae_sent}
		1854	}
		1855
		1856	sub recv {
		1857	unless ($_[0]{_ae_sent}) {
		1858	$WAITING
		1859	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1860
		1861	local $WAITING = 1;
		1862	$_[0]->_wait;
383	}	1863	}
384		1864
385	undef $PID_IDLE;	1865	$_[0]{_ae_croak}
386	}	1866	and Carp::croak $_[0]{_ae_croak};
387		1867
388	sub child {	1868	wantarray
389	my (undef, %arg) = @_;	1869	? @{ $_[0]{_ae_sent} }
390		1870	: $_[0]{_ae_sent}[0]
391	defined (my $pid = $arg{pid} + 0)
392	or Carp::croak "required option 'pid' is missing";
393
394	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
395
396	unless ($WNOHANG) {
397	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
398	}
399
400	unless ($CHLD_W) {
401	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_child_wait);
402	# child could be a zombie already
403	$PID_IDLE ||= AnyEvent->timer (after => 0, cb => \&_child_wait);
404	}
405
406	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
407	}	1871	}
408		1872
409	sub AnyEvent::Base::Child::DESTROY {	1873	sub cb {
410	my ($pid, $cb) = @{$_[0]};	1874	my $cv = shift;
411		1875
412	delete $PID_CB{$pid}{$cb};	1876	@_
413	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1877	and $cv->{_ae_cb} = shift
		1878	and $cv->{_ae_sent}
		1879	and (delete $cv->{_ae_cb})->($cv);
414		1880
415	undef $CHLD_W unless keys %PID_CB;	1881	$cv->{_ae_cb}
416	}	1882	}
		1883
		1884	sub begin {
		1885	++$_[0]{_ae_counter};
		1886	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1887	}
		1888
		1889	sub end {
		1890	return if --$_[0]{_ae_counter};
		1891	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1892	}
		1893
		1894	# undocumented/compatibility with pre-3.4
		1895	*broadcast = \&send;
		1896	*wait = \&recv;
		1897
		1898	=head1 ERROR AND EXCEPTION HANDLING
		1899
		1900	In general, AnyEvent does not do any error handling - it relies on the
		1901	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1902	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1903	checking of all AnyEvent methods, however, which is highly useful during
		1904	development.
		1905
		1906	As for exception handling (i.e. runtime errors and exceptions thrown while
		1907	executing a callback), this is not only highly event-loop specific, but
		1908	also not in any way wrapped by this module, as this is the job of the main
		1909	program.
		1910
		1911	The pure perl event loop simply re-throws the exception (usually
		1912	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1913	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1914	so on.
		1915
		1916	=head1 ENVIRONMENT VARIABLES
		1917
		1918	The following environment variables are used by this module or its
		1919	submodules.
		1920
		1921	Note that AnyEvent will remove I<all> environment variables starting with
		1922	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1923	enabled.
		1924
		1925	=over 4
		1926
		1927	=item C<PERL_ANYEVENT_VERBOSE>
		1928
		1929	By default, AnyEvent will be completely silent except in fatal
		1930	conditions. You can set this environment variable to make AnyEvent more
		1931	talkative.
		1932
		1933	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1934	conditions, such as not being able to load the event model specified by
		1935	C<PERL_ANYEVENT_MODEL>.
		1936
		1937	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1938	model it chooses.
		1939
		1940	When set to C<8> or higher, then AnyEvent will report extra information on
		1941	which optional modules it loads and how it implements certain features.
		1942
		1943	=item C<PERL_ANYEVENT_STRICT>
		1944
		1945	AnyEvent does not do much argument checking by default, as thorough
		1946	argument checking is very costly. Setting this variable to a true value
		1947	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1948	check the arguments passed to most method calls. If it finds any problems,
		1949	it will croak.
		1950
		1951	In other words, enables "strict" mode.
		1952
		1953	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		1954	>>, it is definitely recommended to keep it off in production. Keeping
		1955	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1956	can be very useful, however.
		1957
		1958	=item C<PERL_ANYEVENT_DEBUG_SHELL>
		1959
		1960	If this env variable is set, then its contents will be
		1961	interpreted by C<AnyEvent::Socket::parse_hostport> and an
		1962	C<AnyEvent::Debug::shell> is bound on that port. The shell object is saved
		1963	in C<$AnyEvent::Debug::SHELL>.
		1964
		1965	For example, to bind a debug shell on a unix domain socket in
		1966	F</tmp/debug.sock>, you could use this:
		1967
		1968	PERL_ANYEVENT_DEBUG_SHELL=unix/:/tmp/debug.sock perlprog
		1969
		1970	=item C<PERL_ANYEVENT_DEBUG_WRAP>
		1971
		1972	Can be set to C<0>, C<1> or C<2> and enables wrapping of all watchers for
		1973	debugging purposes. See C<AnyEvent::Debug::wrap> for details.
		1974
		1975	=item C<PERL_ANYEVENT_MODEL>
		1976
		1977	This can be used to specify the event model to be used by AnyEvent, before
		1978	auto detection and -probing kicks in.
		1979
		1980	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		1981	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		1982	resulting module name is loaded and - if the load was successful - used as
		1983	event model backend. If it fails to load then AnyEvent will proceed with
		1984	auto detection and -probing.
		1985
		1986	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		1987	nothing gets prepended and the module name is used as-is (hint: C<::> at
		1988	the end of a string designates a module name and quotes it appropriately).
		1989
		1990	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		1991	could start your program like this:
		1992
		1993	PERL_ANYEVENT_MODEL=Perl perl ...
		1994
		1995	=item C<PERL_ANYEVENT_PROTOCOLS>
		1996
		1997	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1998	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1999	of auto probing).
		2000
		2001	Must be set to a comma-separated list of protocols or address families,
		2002	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		2003	used, and preference will be given to protocols mentioned earlier in the
		2004	list.
		2005
		2006	This variable can effectively be used for denial-of-service attacks
		2007	against local programs (e.g. when setuid), although the impact is likely
		2008	small, as the program has to handle conenction and other failures anyways.
		2009
		2010	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		2011	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		2012	- only support IPv4, never try to resolve or contact IPv6
		2013	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		2014	IPv6, but prefer IPv6 over IPv4.
		2015
		2016	=item C<PERL_ANYEVENT_EDNS0>
		2017
		2018	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		2019	for DNS. This extension is generally useful to reduce DNS traffic, but
		2020	some (broken) firewalls drop such DNS packets, which is why it is off by
		2021	default.
		2022
		2023	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2024	EDNS0 in its DNS requests.
		2025
		2026	=item C<PERL_ANYEVENT_MAX_FORKS>
		2027
		2028	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2029	will create in parallel.
		2030
		2031	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2032
		2033	The default value for the C<max_outstanding> parameter for the default DNS
		2034	resolver - this is the maximum number of parallel DNS requests that are
		2035	sent to the DNS server.
		2036
		2037	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2038
		2039	The file to use instead of F</etc/resolv.conf> (or OS-specific
		2040	configuration) in the default resolver. When set to the empty string, no
		2041	default config will be used.
		2042
		2043	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2044
		2045	When neither C<ca_file> nor C<ca_path> was specified during
		2046	L<AnyEvent::TLS> context creation, and either of these environment
		2047	variables exist, they will be used to specify CA certificate locations
		2048	instead of a system-dependent default.
		2049
		2050	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2051
		2052	When these are set to C<1>, then the respective modules are not
		2053	loaded. Mostly good for testing AnyEvent itself.
		2054
		2055	=back
417		2056
418	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	2057	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		2058
		2059	This is an advanced topic that you do not normally need to use AnyEvent in
		2060	a module. This section is only of use to event loop authors who want to
		2061	provide AnyEvent compatibility.
419		2062
420	If you need to support another event library which isn't directly	2063	If you need to support another event library which isn't directly
421	supported by AnyEvent, you can supply your own interface to it by	2064	supported by AnyEvent, you can supply your own interface to it by
422	pushing, before the first watcher gets created, the package name of	2065	pushing, before the first watcher gets created, the package name of
423	the event module and the package name of the interface to use onto	2066	the event module and the package name of the interface to use onto
424	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	2067	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
425	AnyEvent.	2068	AnyEvent, so it is reasonably cheap.
426		2069
427	Example:	2070	Example:
428		2071
429	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	2072	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
430		2073
431	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	2074	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
432	package/class when it finds the C<urxvt> package/module is loaded. When	2075	package/class when it finds the C<urxvt> package/module is already loaded.
		2076
433	AnyEvent is loaded and asked to find a suitable event model, it will	2077	When AnyEvent is loaded and asked to find a suitable event model, it
434	first check for the presence of urxvt.	2078	will first check for the presence of urxvt by trying to C<use> the
		2079	C<urxvt::anyevent> module.
435		2080
436	The class should provide implementations for all watcher types (see	2081	The class should provide implementations for all watcher types. See
437	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	2082	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
438	(Source code) and so on for actual examples, use C<perldoc -m	2083	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
439	AnyEvent::Impl::Glib> to see the sources).	2084	see the sources.
440		2085
		2086	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		2087	provide suitable (hopefully) replacements.
		2088
441	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	2089	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
442	uses the above line as-is. An interface isn't included in AnyEvent	2090	terminal emulator uses the above line as-is. An interface isn't included
443	because it doesn't make sense outside the embedded interpreter inside	2091	in AnyEvent because it doesn't make sense outside the embedded interpreter
444	I<rxvt-unicode>, and it is updated and maintained as part of the	2092	inside I<rxvt-unicode>, and it is updated and maintained as part of the
445	I<rxvt-unicode> distribution.	2093	I<rxvt-unicode> distribution.
446		2094
447	I<rxvt-unicode> also cheats a bit by not providing blocking access to	2095	I<rxvt-unicode> also cheats a bit by not providing blocking access to
448	condition variables: code blocking while waiting for a condition will	2096	condition variables: code blocking while waiting for a condition will
449	C<die>. This still works with most modules/usages, and blocking calls must	2097	C<die>. This still works with most modules/usages, and blocking calls must
450	not be in an interactive application, so it makes sense.	2098	not be done in an interactive application, so it makes sense.
451		2099
452	=head1 ENVIRONMENT VARIABLES
453
454	The following environment variables are used by this module:
455
456	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event
457	model gets used.
458
459	=head1 EXAMPLE	2100	=head1 EXAMPLE PROGRAM
460		2101
461	The following program uses an io watcher to read data from stdin, a timer	2102	The following program uses an I/O watcher to read data from STDIN, a timer
462	to display a message once per second, and a condvar to exit the program	2103	to display a message once per second, and a condition variable to quit the
463	when the user enters quit:	2104	program when the user enters quit:
464		2105
465	use AnyEvent;	2106	use AnyEvent;
466		2107
467	my $cv = AnyEvent->condvar;	2108	my $cv = AnyEvent->condvar;
468		2109
469	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	2110	my $io_watcher = AnyEvent->io (
		2111	fh => \*STDIN,
		2112	poll => 'r',
		2113	cb => sub {
470	warn "io event <$_[0]>\n"; # will always output <r>	2114	warn "io event <$_[0]>\n"; # will always output <r>
471	chomp (my $input = <STDIN>); # read a line	2115	chomp (my $input = <STDIN>); # read a line
472	warn "read: $input\n"; # output what has been read	2116	warn "read: $input\n"; # output what has been read
473	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	2117	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		2118	},
		2119	);
		2120
		2121	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
		2122	warn "timeout\n"; # print 'timeout' at most every second
474	});	2123	});
475		2124
476	my $time_watcher; # can only be used once
477
478	sub new_timer {
479	$timer = AnyEvent->timer (after => 1, cb => sub {
480	warn "timeout\n"; # print 'timeout' about every second
481	&new_timer; # and restart the time
482	});
483	}
484
485	new_timer; # create first timer
486
487	$cv->wait; # wait until user enters /^q/i	2125	$cv->recv; # wait until user enters /^q/i
488		2126
489	=head1 REAL-WORLD EXAMPLE	2127	=head1 REAL-WORLD EXAMPLE
490		2128
491	Consider the L<Net::FCP> module. It features (among others) the following	2129	Consider the L<Net::FCP> module. It features (among others) the following
492	API calls, which are to freenet what HTTP GET requests are to http:	2130	API calls, which are to freenet what HTTP GET requests are to http:
…		…
542	syswrite $txn->{fh}, $txn->{request}	2180	syswrite $txn->{fh}, $txn->{request}
543	or die "connection or write error";	2181	or die "connection or write error";
544	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	2182	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
545		2183
546	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	2184	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
547	result and signals any possible waiters that the request ahs finished:	2185	result and signals any possible waiters that the request has finished:
548		2186
549	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	2187	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
550		2188
551	if (end-of-file or data complete) {	2189	if (end-of-file or data complete) {
552	$txn->{result} = $txn->{buf};	2190	$txn->{result} = $txn->{buf};
553	$txn->{finished}->broadcast;	2191	$txn->{finished}->send;
554	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	2192	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
555	}	2193	}
556		2194
557	The C<result> method, finally, just waits for the finished signal (if the	2195	The C<result> method, finally, just waits for the finished signal (if the
558	request was already finished, it doesn't wait, of course, and returns the	2196	request was already finished, it doesn't wait, of course, and returns the
559	data:	2197	data:
560		2198
561	$txn->{finished}->wait;	2199	$txn->{finished}->recv;
562	return $txn->{result};	2200	return $txn->{result};
563		2201
564	The actual code goes further and collects all errors (C<die>s, exceptions)	2202	The actual code goes further and collects all errors (C<die>s, exceptions)
565	that occured during request processing. The C<result> method detects	2203	that occurred during request processing. The C<result> method detects
566	wether an exception as thrown (it is stored inside the $txn object)	2204	whether an exception as thrown (it is stored inside the $txn object)
567	and just throws the exception, which means connection errors and other	2205	and just throws the exception, which means connection errors and other
568	problems get reported tot he code that tries to use the result, not in a	2206	problems get reported to the code that tries to use the result, not in a
569	random callback.	2207	random callback.
570		2208
571	All of this enables the following usage styles:	2209	All of this enables the following usage styles:
572		2210
573	1. Blocking:	2211	1. Blocking:
574		2212
575	my $data = $fcp->client_get ($url);	2213	my $data = $fcp->client_get ($url);
576		2214
577	2. Blocking, but parallelizing:	2215	2. Blocking, but running in parallel:
578		2216
579	my @datas = map $_->result,	2217	my @datas = map $_->result,
580	map $fcp->txn_client_get ($_),	2218	map $fcp->txn_client_get ($_),
581	@urls;	2219	@urls;
582		2220
583	Both blocking examples work without the module user having to know	2221	Both blocking examples work without the module user having to know
584	anything about events.	2222	anything about events.
585		2223
586	3a. Event-based in a main program, using any support Event module:	2224	3a. Event-based in a main program, using any supported event module:
587		2225
588	use Event;	2226	use EV;
589		2227
590	$fcp->txn_client_get ($url)->cb (sub {	2228	$fcp->txn_client_get ($url)->cb (sub {
591	my $txn = shift;	2229	my $txn = shift;
592	my $data = $txn->result;	2230	my $data = $txn->result;
593	...	2231	...
594	});	2232	});
595		2233
596	Event::loop;	2234	EV::loop;
597		2235
598	3b. The module user could use AnyEvent, too:	2236	3b. The module user could use AnyEvent, too:
599		2237
600	use AnyEvent;	2238	use AnyEvent;
601		2239
602	my $quit = AnyEvent->condvar;	2240	my $quit = AnyEvent->condvar;
603		2241
604	$fcp->txn_client_get ($url)->cb (sub {	2242	$fcp->txn_client_get ($url)->cb (sub {
605	...	2243	...
606	$quit->broadcast;	2244	$quit->send;
607	});	2245	});
608		2246
609	$quit->wait;	2247	$quit->recv;
		2248
		2249
		2250	=head1 BENCHMARKS
		2251
		2252	To give you an idea of the performance and overheads that AnyEvent adds
		2253	over the event loops themselves and to give you an impression of the speed
		2254	of various event loops I prepared some benchmarks.
		2255
		2256	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2257
		2258	Here is a benchmark of various supported event models used natively and
		2259	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2260	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2261	which it is), lets them fire exactly once and destroys them again.
		2262
		2263	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2264	distribution. It uses the L<AE> interface, which makes a real difference
		2265	for the EV and Perl backends only.
		2266
		2267	=head3 Explanation of the columns
		2268
		2269	I<watcher> is the number of event watchers created/destroyed. Since
		2270	different event models feature vastly different performances, each event
		2271	loop was given a number of watchers so that overall runtime is acceptable
		2272	and similar between tested event loop (and keep them from crashing): Glib
		2273	would probably take thousands of years if asked to process the same number
		2274	of watchers as EV in this benchmark.
		2275
		2276	I<bytes> is the number of bytes (as measured by the resident set size,
		2277	RSS) consumed by each watcher. This method of measuring captures both C
		2278	and Perl-based overheads.
		2279
		2280	I<create> is the time, in microseconds (millionths of seconds), that it
		2281	takes to create a single watcher. The callback is a closure shared between
		2282	all watchers, to avoid adding memory overhead. That means closure creation
		2283	and memory usage is not included in the figures.
		2284
		2285	I<invoke> is the time, in microseconds, used to invoke a simple
		2286	callback. The callback simply counts down a Perl variable and after it was
		2287	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2288	signal the end of this phase.
		2289
		2290	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2291	watcher.
		2292
		2293	=head3 Results
		2294
		2295	name watchers bytes create invoke destroy comment
		2296	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2297	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2298	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2299	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2300	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2301	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2302	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2303	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2304	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2305	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2306	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2307	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2308
		2309	=head3 Discussion
		2310
		2311	The benchmark does I<not> measure scalability of the event loop very
		2312	well. For example, a select-based event loop (such as the pure perl one)
		2313	can never compete with an event loop that uses epoll when the number of
		2314	file descriptors grows high. In this benchmark, all events become ready at
		2315	the same time, so select/poll-based implementations get an unnatural speed
		2316	boost.
		2317
		2318	Also, note that the number of watchers usually has a nonlinear effect on
		2319	overall speed, that is, creating twice as many watchers doesn't take twice
		2320	the time - usually it takes longer. This puts event loops tested with a
		2321	higher number of watchers at a disadvantage.
		2322
		2323	To put the range of results into perspective, consider that on the
		2324	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2325	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2326	cycles with POE.
		2327
		2328	C<EV> is the sole leader regarding speed and memory use, which are both
		2329	maximal/minimal, respectively. When using the L<AE> API there is zero
		2330	overhead (when going through the AnyEvent API create is about 5-6 times
		2331	slower, with other times being equal, so still uses far less memory than
		2332	any other event loop and is still faster than Event natively).
		2333
		2334	The pure perl implementation is hit in a few sweet spots (both the
		2335	constant timeout and the use of a single fd hit optimisations in the perl
		2336	interpreter and the backend itself). Nevertheless this shows that it
		2337	adds very little overhead in itself. Like any select-based backend its
		2338	performance becomes really bad with lots of file descriptors (and few of
		2339	them active), of course, but this was not subject of this benchmark.
		2340
		2341	The C<Event> module has a relatively high setup and callback invocation
		2342	cost, but overall scores in on the third place.
		2343
		2344	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2345	when using its pure perl backend.
		2346
		2347	C<Glib>'s memory usage is quite a bit higher, but it features a
		2348	faster callback invocation and overall ends up in the same class as
		2349	C<Event>. However, Glib scales extremely badly, doubling the number of
		2350	watchers increases the processing time by more than a factor of four,
		2351	making it completely unusable when using larger numbers of watchers
		2352	(note that only a single file descriptor was used in the benchmark, so
		2353	inefficiencies of C<poll> do not account for this).
		2354
		2355	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2356	more than 2000 watchers is a big setback, however, as correctness takes
		2357	precedence over speed. Nevertheless, its performance is surprising, as the
		2358	file descriptor is dup()ed for each watcher. This shows that the dup()
		2359	employed by some adaptors is not a big performance issue (it does incur a
		2360	hidden memory cost inside the kernel which is not reflected in the figures
		2361	above).
		2362
		2363	C<POE>, regardless of underlying event loop (whether using its pure perl
		2364	select-based backend or the Event module, the POE-EV backend couldn't
		2365	be tested because it wasn't working) shows abysmal performance and
		2366	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2367	as EV watchers, and 10 times as much memory as Event (the high memory
		2368	requirements are caused by requiring a session for each watcher). Watcher
		2369	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2370	implementation.
		2371
		2372	The design of the POE adaptor class in AnyEvent can not really account
		2373	for the performance issues, though, as session creation overhead is
		2374	small compared to execution of the state machine, which is coded pretty
		2375	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2376	using multiple sessions is not a good approach, especially regarding
		2377	memory usage, even the author of POE could not come up with a faster
		2378	design).
		2379
		2380	=head3 Summary
		2381
		2382	=over 4
		2383
		2384	=item * Using EV through AnyEvent is faster than any other event loop
		2385	(even when used without AnyEvent), but most event loops have acceptable
		2386	performance with or without AnyEvent.
		2387
		2388	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2389	the actual event loop, only with extremely fast event loops such as EV
		2390	adds AnyEvent significant overhead.
		2391
		2392	=item * You should avoid POE like the plague if you want performance or
		2393	reasonable memory usage.
		2394
		2395	=back
		2396
		2397	=head2 BENCHMARKING THE LARGE SERVER CASE
		2398
		2399	This benchmark actually benchmarks the event loop itself. It works by
		2400	creating a number of "servers": each server consists of a socket pair, a
		2401	timeout watcher that gets reset on activity (but never fires), and an I/O
		2402	watcher waiting for input on one side of the socket. Each time the socket
		2403	watcher reads a byte it will write that byte to a random other "server".
		2404
		2405	The effect is that there will be a lot of I/O watchers, only part of which
		2406	are active at any one point (so there is a constant number of active
		2407	fds for each loop iteration, but which fds these are is random). The
		2408	timeout is reset each time something is read because that reflects how
		2409	most timeouts work (and puts extra pressure on the event loops).
		2410
		2411	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2412	(1%) are active. This mirrors the activity of large servers with many
		2413	connections, most of which are idle at any one point in time.
		2414
		2415	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2416	distribution. It uses the L<AE> interface, which makes a real difference
		2417	for the EV and Perl backends only.
		2418
		2419	=head3 Explanation of the columns
		2420
		2421	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2422	each server has a read and write socket end).
		2423
		2424	I<create> is the time it takes to create a socket pair (which is
		2425	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2426
		2427	I<request>, the most important value, is the time it takes to handle a
		2428	single "request", that is, reading the token from the pipe and forwarding
		2429	it to another server. This includes deleting the old timeout and creating
		2430	a new one that moves the timeout into the future.
		2431
		2432	=head3 Results
		2433
		2434	name sockets create request
		2435	EV 20000 62.66 7.99
		2436	Perl 20000 68.32 32.64
		2437	IOAsync 20000 174.06 101.15 epoll
		2438	IOAsync 20000 174.67 610.84 poll
		2439	Event 20000 202.69 242.91
		2440	Glib 20000 557.01 1689.52
		2441	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2442
		2443	=head3 Discussion
		2444
		2445	This benchmark I<does> measure scalability and overall performance of the
		2446	particular event loop.
		2447
		2448	EV is again fastest. Since it is using epoll on my system, the setup time
		2449	is relatively high, though.
		2450
		2451	Perl surprisingly comes second. It is much faster than the C-based event
		2452	loops Event and Glib.
		2453
		2454	IO::Async performs very well when using its epoll backend, and still quite
		2455	good compared to Glib when using its pure perl backend.
		2456
		2457	Event suffers from high setup time as well (look at its code and you will
		2458	understand why). Callback invocation also has a high overhead compared to
		2459	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2460	uses select or poll in basically all documented configurations.
		2461
		2462	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2463	clearly fails to perform with many filehandles or in busy servers.
		2464
		2465	POE is still completely out of the picture, taking over 1000 times as long
		2466	as EV, and over 100 times as long as the Perl implementation, even though
		2467	it uses a C-based event loop in this case.
		2468
		2469	=head3 Summary
		2470
		2471	=over 4
		2472
		2473	=item * The pure perl implementation performs extremely well.
		2474
		2475	=item * Avoid Glib or POE in large projects where performance matters.
		2476
		2477	=back
		2478
		2479	=head2 BENCHMARKING SMALL SERVERS
		2480
		2481	While event loops should scale (and select-based ones do not...) even to
		2482	large servers, most programs we (or I :) actually write have only a few
		2483	I/O watchers.
		2484
		2485	In this benchmark, I use the same benchmark program as in the large server
		2486	case, but it uses only eight "servers", of which three are active at any
		2487	one time. This should reflect performance for a small server relatively
		2488	well.
		2489
		2490	The columns are identical to the previous table.
		2491
		2492	=head3 Results
		2493
		2494	name sockets create request
		2495	EV 16 20.00 6.54
		2496	Perl 16 25.75 12.62
		2497	Event 16 81.27 35.86
		2498	Glib 16 32.63 15.48
		2499	POE 16 261.87 276.28 uses POE::Loop::Event
		2500
		2501	=head3 Discussion
		2502
		2503	The benchmark tries to test the performance of a typical small
		2504	server. While knowing how various event loops perform is interesting, keep
		2505	in mind that their overhead in this case is usually not as important, due
		2506	to the small absolute number of watchers (that is, you need efficiency and
		2507	speed most when you have lots of watchers, not when you only have a few of
		2508	them).
		2509
		2510	EV is again fastest.
		2511
		2512	Perl again comes second. It is noticeably faster than the C-based event
		2513	loops Event and Glib, although the difference is too small to really
		2514	matter.
		2515
		2516	POE also performs much better in this case, but is is still far behind the
		2517	others.
		2518
		2519	=head3 Summary
		2520
		2521	=over 4
		2522
		2523	=item * C-based event loops perform very well with small number of
		2524	watchers, as the management overhead dominates.
		2525
		2526	=back
		2527
		2528	=head2 THE IO::Lambda BENCHMARK
		2529
		2530	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2531	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2532	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2533	shouldn't come as a surprise to anybody). As such, the benchmark is
		2534	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2535	very optimal. But how would AnyEvent compare when used without the extra
		2536	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2537
		2538	The benchmark itself creates an echo-server, and then, for 500 times,
		2539	connects to the echo server, sends a line, waits for the reply, and then
		2540	creates the next connection. This is a rather bad benchmark, as it doesn't
		2541	test the efficiency of the framework or much non-blocking I/O, but it is a
		2542	benchmark nevertheless.
		2543
		2544	name runtime
		2545	Lambda/select 0.330 sec
		2546	+ optimized 0.122 sec
		2547	Lambda/AnyEvent 0.327 sec
		2548	+ optimized 0.138 sec
		2549	Raw sockets/select 0.077 sec
		2550	POE/select, components 0.662 sec
		2551	POE/select, raw sockets 0.226 sec
		2552	POE/select, optimized 0.404 sec
		2553
		2554	AnyEvent/select/nb 0.085 sec
		2555	AnyEvent/EV/nb 0.068 sec
		2556	+state machine 0.134 sec
		2557
		2558	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2559	benchmarks actually make blocking connects and use 100% blocking I/O,
		2560	defeating the purpose of an event-based solution. All of the newly
		2561	written AnyEvent benchmarks use 100% non-blocking connects (using
		2562	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2563	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2564	generally require a lot more bookkeeping and event handling than blocking
		2565	connects (which involve a single syscall only).
		2566
		2567	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2568	offers similar expressive power as POE and IO::Lambda, using conventional
		2569	Perl syntax. This means that both the echo server and the client are 100%
		2570	non-blocking, further placing it at a disadvantage.
		2571
		2572	As you can see, the AnyEvent + EV combination even beats the
		2573	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2574	backend easily beats IO::Lambda and POE.
		2575
		2576	And even the 100% non-blocking version written using the high-level (and
		2577	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2578	higher level ("unoptimised") abstractions by a large margin, even though
		2579	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2580
		2581	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2582	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2583	part of the IO::Lambda distribution and were used without any changes.
		2584
		2585
		2586	=head1 SIGNALS
		2587
		2588	AnyEvent currently installs handlers for these signals:
		2589
		2590	=over 4
		2591
		2592	=item SIGCHLD
		2593
		2594	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2595	emulation for event loops that do not support them natively. Also, some
		2596	event loops install a similar handler.
		2597
		2598	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2599	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2600
		2601	=item SIGPIPE
		2602
		2603	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2604	when AnyEvent gets loaded.
		2605
		2606	The rationale for this is that AnyEvent users usually do not really depend
		2607	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2608	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2609	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2610	some random socket.
		2611
		2612	The rationale for installing a no-op handler as opposed to ignoring it is
		2613	that this way, the handler will be restored to defaults on exec.
		2614
		2615	Feel free to install your own handler, or reset it to defaults.
		2616
		2617	=back
		2618
		2619	=cut
		2620
		2621	undef $SIG{CHLD}
		2622	if $SIG{CHLD} eq 'IGNORE';
		2623
		2624	$SIG{PIPE} = sub { }
		2625	unless defined $SIG{PIPE};
		2626
		2627	=head1 RECOMMENDED/OPTIONAL MODULES
		2628
		2629	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2630	its built-in modules) are required to use it.
		2631
		2632	That does not mean that AnyEvent won't take advantage of some additional
		2633	modules if they are installed.
		2634
		2635	This section explains which additional modules will be used, and how they
		2636	affect AnyEvent's operation.
		2637
		2638	=over 4
		2639
		2640	=item L<Async::Interrupt>
		2641
		2642	This slightly arcane module is used to implement fast signal handling: To
		2643	my knowledge, there is no way to do completely race-free and quick
		2644	signal handling in pure perl. To ensure that signals still get
		2645	delivered, AnyEvent will start an interval timer to wake up perl (and
		2646	catch the signals) with some delay (default is 10 seconds, look for
		2647	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2648
		2649	If this module is available, then it will be used to implement signal
		2650	catching, which means that signals will not be delayed, and the event loop
		2651	will not be interrupted regularly, which is more efficient (and good for
		2652	battery life on laptops).
		2653
		2654	This affects not just the pure-perl event loop, but also other event loops
		2655	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2656
		2657	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2658	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2659	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2660	does nothing for those backends.
		2661
		2662	=item L<EV>
		2663
		2664	This module isn't really "optional", as it is simply one of the backend
		2665	event loops that AnyEvent can use. However, it is simply the best event
		2666	loop available in terms of features, speed and stability: It supports
		2667	the AnyEvent API optimally, implements all the watcher types in XS, does
		2668	automatic timer adjustments even when no monotonic clock is available,
		2669	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2670	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2671	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2672
		2673	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2674	then this module will do nothing for you.
		2675
		2676	=item L<Guard>
		2677
		2678	The guard module, when used, will be used to implement
		2679	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2680	lot less memory), but otherwise doesn't affect guard operation much. It is
		2681	purely used for performance.
		2682
		2683	=item L<JSON> and L<JSON::XS>
		2684
		2685	One of these modules is required when you want to read or write JSON data
		2686	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2687	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2688
		2689	=item L<Net::SSLeay>
		2690
		2691	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2692	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2693	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2694
		2695	=item L<Time::HiRes>
		2696
		2697	This module is part of perl since release 5.008. It will be used when the
		2698	chosen event library does not come with a timing source of its own. The
		2699	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2700	try to use a monotonic clock for timing stability.
		2701
		2702	=back
		2703
		2704
		2705	=head1 FORK
		2706
		2707	Most event libraries are not fork-safe. The ones who are usually are
		2708	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2709	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2710	are usually badly thought-out hacks that are incompatible with fork in
		2711	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2712	continue event-processing in both parent and child (or both, if you know
		2713	what you are doing).
		2714
		2715	This means that, in general, you cannot fork and do event processing in
		2716	the child if the event library was initialised before the fork (which
		2717	usually happens when the first AnyEvent watcher is created, or the library
		2718	is loaded).
		2719
		2720	If you have to fork, you must either do so I<before> creating your first
		2721	watcher OR you must not use AnyEvent at all in the child OR you must do
		2722	something completely out of the scope of AnyEvent.
		2723
		2724	The problem of doing event processing in the parent I<and> the child
		2725	is much more complicated: even for backends that I<are> fork-aware or
		2726	fork-safe, their behaviour is not usually what you want: fork clones all
		2727	watchers, that means all timers, I/O watchers etc. are active in both
		2728	parent and child, which is almost never what you want. USing C<exec>
		2729	to start worker children from some kind of manage rprocess is usually
		2730	preferred, because it is much easier and cleaner, at the expense of having
		2731	to have another binary.
		2732
		2733
		2734	=head1 SECURITY CONSIDERATIONS
		2735
		2736	AnyEvent can be forced to load any event model via
		2737	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2738	execute arbitrary code or directly gain access, it can easily be used to
		2739	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2740	will not be active when the program uses a different event model than
		2741	specified in the variable.
		2742
		2743	You can make AnyEvent completely ignore this variable by deleting it
		2744	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2745
		2746	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2747
		2748	use AnyEvent;
		2749
		2750	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2751	be used to probe what backend is used and gain other information (which is
		2752	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2753	$ENV{PERL_ANYEVENT_STRICT}.
		2754
		2755	Note that AnyEvent will remove I<all> environment variables starting with
		2756	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2757	enabled.
		2758
		2759
		2760	=head1 BUGS
		2761
		2762	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2763	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2764	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2765	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2766	pronounced).
		2767
610		2768
611	=head1 SEE ALSO	2769	=head1 SEE ALSO
612		2770
613	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	2771	Tutorial/Introduction: L<AnyEvent::Intro>.
614		2772
615	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	2773	FAQ: L<AnyEvent::FAQ>.
616		2774
617	Nontrivial usage example: L<Net::FCP>.	2775	Utility functions: L<AnyEvent::Util>.
618		2776
619	=head1	2777	Event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>, L<Glib::EV>,
		2778	L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		2779
		2780	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2781	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2782	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2783	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
		2784
		2785	Non-blocking file handles, sockets, TCP clients and
		2786	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2787
		2788	Asynchronous DNS: L<AnyEvent::DNS>.
		2789
		2790	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2791
		2792	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2793	L<AnyEvent::HTTP>.
		2794
		2795
		2796	=head1 AUTHOR
		2797
		2798	Marc Lehmann <schmorp@schmorp.de>
		2799	http://home.schmorp.de/
620		2800
621	=cut	2801	=cut
622		2802
623	1	2803	1
624		2804

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines