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Revision 1.53 by root, Sat Apr 19 04:58:14 2008 UTC vs.
Revision 1.356 by root, Fri Aug 12 18:41:25 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	EV, Event, Coro::EV, Coro::Event, 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 whether 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.
22		58
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	59	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		60
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	61	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	62	nowadays. So what is different about AnyEvent?
27		63
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	64	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
29	policy> and AnyEvent is I<small and efficient>.	65	policy> and AnyEvent is I<small and efficient>.
30		66
31	First and foremost, I<AnyEvent is not an event model> itself, it only	67	First and foremost, I<AnyEvent is not an event model> itself, it only
32	interfaces to whatever event model the main program happens to use in a	68	interfaces to whatever event model the main program happens to use, in a
33	pragmatic way. For event models and certain classes of immortals alike,	69	pragmatic way. For event models and certain classes of immortals alike,
34	the statement "there can only be one" is a bitter reality: In general,	70	the statement "there can only be one" is a bitter reality: In general,
35	only one event loop can be active at the same time in a process. AnyEvent	71	only one event loop can be active at the same time in a process. AnyEvent
36	helps hiding the differences between those event loops.	72	cannot change this, but it can hide the differences between those event
		73	loops.
37		74
38	The goal of AnyEvent is to offer module authors the ability to do event	75	The goal of AnyEvent is to offer module authors the ability to do event
39	programming (waiting for I/O or timer events) without subscribing to a	76	programming (waiting for I/O or timer events) without subscribing to a
40	religion, a way of living, and most importantly: without forcing your	77	religion, a way of living, and most importantly: without forcing your
41	module users into the same thing by forcing them to use the same event	78	module users into the same thing by forcing them to use the same event
42	model you use.	79	model you use.
43		80
44	For modules like POE or IO::Async (which is a total misnomer as it is	81	For modules like POE or IO::Async (which is a total misnomer as it is
45	actually doing all I/O I<synchronously>...), using them in your module is	82	actually doing all I/O I<synchronously>...), using them in your module is
46	like joining a cult: After you joined, you are dependent on them and you	83	like joining a cult: After you join, you are dependent on them and you
47	cannot use anything else, as it is simply incompatible to everything that	84	cannot use anything else, as they are simply incompatible to everything
48	isn't itself. What's worse, all the potential users of your module are	85	that isn't them. What's worse, all the potential users of your
49	I<also> forced to use the same event loop you use.	86	module are I<also> forced to use the same event loop you use.
50		87
51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	88	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	89	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if	90	with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
54	your module uses one of those, every user of your module has to use it,	91	uses one of those, every user of your module has to use it, too. But if
55	too. But if your module uses AnyEvent, it works transparently with all	92	your module uses AnyEvent, it works transparently with all event models it
56	event models it supports (including stuff like POE and IO::Async, as long	93	supports (including stuff like IO::Async, as long as those use one of the
57	as those use one of the supported event loops. It is trivial to add new	94	supported event loops. It is easy to add new event loops to AnyEvent, too,
58	event loops to AnyEvent, too, so it is future-proof).	95	so it is future-proof).
59		96
60	In addition to being free of having to use I<the one and only true event	97	In addition to being free of having to use I<the one and only true event
61	model>, AnyEvent also is free of bloat and policy: with POE or similar	98	model>, AnyEvent also is free of bloat and policy: with POE or similar
62	modules, you get an enourmous amount of code and strict rules you have to	99	modules, you get an enormous amount of code and strict rules you have to
63	follow. AnyEvent, on the other hand, is lean and up to the point, by only	100	follow. AnyEvent, on the other hand, is lean and to the point, by only
64	offering the functionality that is necessary, in as thin as a wrapper as	101	offering the functionality that is necessary, in as thin as a wrapper as
65	technically possible.	102	technically possible.
66		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
67	Of course, if you want lots of policy (this can arguably be somewhat	110	Now, if you I<do want> lots of policy (this can arguably be somewhat
68	useful) and you want to force your users to use the one and only event	111	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	112	model, you should I<not> use this module.
70		113
71
72	=head1 DESCRIPTION	114	=head1 DESCRIPTION
73		115
74	L<AnyEvent> provides an identical interface to multiple event loops. This	116	L<AnyEvent> provides a uniform interface to various event loops. This
75	allows module authors to utilise an event loop without forcing module	117	allows module authors to use event loop functionality without forcing
76	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
77	peacefully at any one time).	119	than one event loop cannot coexist peacefully).
78		120
79	The interface itself is vaguely similar, but not identical to the L<Event>	121	The interface itself is vaguely similar, but not identical to the L<Event>
80	module.	122	module.
81		123
82	During the first call of any watcher-creation method, the module tries	124	During the first call of any watcher-creation method, the module tries
83	to detect the currently loaded event loop by probing whether one of the	125	to detect the currently loaded event loop by probing whether one of the
84	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,	126	following modules is already loaded: L<EV>, L<AnyEvent::Loop>,
85	L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found,	127	L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>. The first one
86	the module tries to load these modules in the stated order. The first one	128	found is used. If none are detected, the module tries to load the first
87	that can be successfully loaded will be used. If, after this, still none	129	four modules in the order given; but note that if L<EV> is not
88	could be found, AnyEvent will fall back to a pure-perl event loop, which	130	available, the pure-perl L<AnyEvent::Loop> should always work, so
89	is not very efficient, but should work everywhere.	131	the other two are not normally tried.
90		132
91	Because AnyEvent first checks for modules that are already loaded, loading	133	Because AnyEvent first checks for modules that are already loaded, loading
92	an event model explicitly before first using AnyEvent will likely make	134	an event model explicitly before first using AnyEvent will likely make
93	that model the default. For example:	135	that model the default. For example:
94		136
…		…
96	use AnyEvent;	138	use AnyEvent;
97		139
98	# .. AnyEvent will likely default to Tk	140	# .. AnyEvent will likely default to Tk
99		141
100	The I<likely> means that, if any module loads another event model and	142	The I<likely> means that, if any module loads another event model and
101	starts using it, all bets are off. Maybe you should tell their authors to	143	starts using it, all bets are off - this case should be very rare though,
102	use AnyEvent so their modules work together with others seamlessly...	144	as very few modules hardcode event loops without announcing this very
		145	loudly.
103		146
104	The pure-perl implementation of AnyEvent is called	147	The pure-perl implementation of AnyEvent is called C<AnyEvent::Loop>. Like
105	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
106	explicitly.	149	availability of that event loop :)
107		150
108	=head1 WATCHERS	151	=head1 WATCHERS
109		152
110	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
111	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
112	the callback to call, the filehandle to watch, etc.	155	the callback to call, the file handle to watch, etc.
113		156
114	These watchers are normal Perl objects with normal Perl lifetime. After	157	These watchers are normal Perl objects with normal Perl lifetime. After
115	creating a watcher it will immediately "watch" for events and invoke the	158	creating a watcher it will immediately "watch" for events and invoke the
116	callback when the event occurs (of course, only when the event model	159	callback when the event occurs (of course, only when the event model
117	is in control).	160	is in control).
118		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
119	To disable the watcher you have to destroy it (e.g. by setting the	168	To disable a watcher you have to destroy it (e.g. by setting the
120	variable you store it in to C<undef> or otherwise deleting all references	169	variable you store it in to C<undef> or otherwise deleting all references
121	to it).	170	to it).
122		171
123	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.
124		173
125	Many watchers either are used with "recursion" (repeating timers for	174	Many watchers either are used with "recursion" (repeating timers for
126	example), or need to refer to their watcher object in other ways.	175	example), or need to refer to their watcher object in other ways.
127		176
128	An any way to achieve that is this pattern:	177	One way to achieve that is this pattern:
129		178
130	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	179	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
131	# you can use $w here, for example to undef it	180	# you can use $w here, for example to undef it
132	undef $w;	181	undef $w;
133	});	182	});
134		183
135	Note that C<my $w; $w => combination. This is necessary because in Perl,	184	Note that C<my $w; $w => combination. This is necessary because in Perl,
136	my variables are only visible after the statement in which they are	185	my variables are only visible after the statement in which they are
137	declared.	186	declared.
138		187
139	=head2 IO WATCHERS	188	=head2 I/O WATCHERS
		189
		190	$w = AnyEvent->io (
		191	fh => <filehandle_or_fileno>,
		192	poll => <"r" or "w">,
		193	cb => <callback>,
		194	);
140		195
141	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	196	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
142	with the following mandatory key-value pairs as arguments:	197	with the following mandatory key-value pairs as arguments:
143		198
144	C<fh> the Perl I<file handle> (I<not> file descriptor) 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
145	events. C<poll> must be a string that is either C<r> or C<w>, which	206	C<poll> must be a string that is either C<r> or C<w>, which creates a
146	creates a watcher waiting for "r"eadable or "w"ritable events,	207	watcher waiting for "r"eadable or "w"ritable events, respectively.
		208
147	respectively. C<cb> is the callback to invoke each time the file handle	209	C<cb> is the callback to invoke each time the file handle becomes ready.
148	becomes ready.
149		210
150	File handles will be kept alive, so as long as the watcher exists, the	211	Although the callback might get passed parameters, their value and
151	file handle 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.
152		214
		215	The I/O watcher might use the underlying file descriptor or a copy of it.
153	It is not allowed to close a file handle as long as any watcher is active	216	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	217	underlying file descriptor.
155		218
156	Some event loops issue spurious readyness notifications, so you should	219	Some event loops issue spurious readiness notifications, so you should
157	always use non-blocking calls when reading/writing from/to your file	220	always use non-blocking calls when reading/writing from/to your file
158	handles.	221	handles.
159		222
160	Example:
161
162	# 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
163	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	226	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
164	chomp (my $input = <STDIN>);	227	chomp (my $input = <STDIN>);
165	warn "read: $input\n";	228	warn "read: $input\n";
166	undef $w;	229	undef $w;
167	});	230	});
168		231
169	=head2 TIME WATCHERS	232	=head2 TIME WATCHERS
170		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
171	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 >>
172	method with the following mandatory arguments:	243	method with the following mandatory arguments:
173		244
174	C<after> specifies after how many seconds (fractional values are	245	C<after> specifies after how many seconds (fractional values are
175	supported) should the timer activate. C<cb> the callback to invoke in that	246	supported) the callback should be invoked. C<cb> is the callback to invoke
176	case.	247	in that case.
177		248
178	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
179	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
180	and Glib).	251	callbacks cannot use arguments passed to time watcher callbacks.
181		252
182	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.
183		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
184	# fire an event after 7.7 seconds	263	Example: fire an event after 7.7 seconds.
		264
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	265	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	266	warn "timeout\n";
187	});	267	});
188		268
189	# to cancel the timer:	269	# to cancel the timer:
190	undef $w;	270	undef $w;
191		271
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	272	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		273
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	274	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		275	warn "timeout\n";
200	};	276	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		277
205	=head3 TIMING ISSUES	278	=head3 TIMING ISSUES
206		279
207	There are two ways to handle timers: based on real time (relative, "fire	280	There are two ways to handle timers: based on real time (relative, "fire
208	in 10 seconds") and based on wallclock time (absolute, "fire at 12	281	in 10 seconds") and based on wallclock time (absolute, "fire at 12
209	o'clock").	282	o'clock").
210		283
211	While most event loops expect timers to specified in a relative way, they use	284	While most event loops expect timers to specified in a relative way, they
212	absolute time internally. This makes a difference when your clock "jumps",	285	use absolute time internally. This makes a difference when your clock
213	for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to	286	"jumps", for example, when ntp decides to set your clock backwards from
214	2008-01-01, a watcher that you created to fire "after" a second might actually take	287	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	288	fire "after a second" might actually take six years to finally fire.
216		289
217	AnyEvent cannot compensate for this. The only event loop that is conscious	290	AnyEvent cannot compensate for this. The only event loop that is conscious
218	about these issues is L<EV>, which offers both relative (ev_timer) and	291	of these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	292	on true relative time) and absolute (ev_periodic, based on wallclock time)
		293	timers.
220		294
221	AnyEvent always prefers relative timers, if available, matching the	295	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	296	AnyEvent API.
223		297
		298	AnyEvent has two additional methods that return the "current time":
		299
		300	=over 4
		301
		302	=item AnyEvent->time
		303
		304	This returns the "current wallclock time" as a fractional number of
		305	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		306	return, and the result is guaranteed to be compatible with those).
		307
		308	It progresses independently of any event loop processing, i.e. each call
		309	will check the system clock, which usually gets updated frequently.
		310
		311	=item AnyEvent->now
		312
		313	This also returns the "current wallclock time", but unlike C<time>, above,
		314	this value might change only once per event loop iteration, depending on
		315	the event loop (most return the same time as C<time>, above). This is the
		316	time that AnyEvent's timers get scheduled against.
		317
		318	I<In almost all cases (in all cases if you don't care), this is the
		319	function to call when you want to know the current time.>
		320
		321	This function is also often faster then C<< AnyEvent->time >>, and
		322	thus the preferred method if you want some timestamp (for example,
		323	L<AnyEvent::Handle> uses this to update its activity timeouts).
		324
		325	The rest of this section is only of relevance if you try to be very exact
		326	with your timing; you can skip it without a bad conscience.
		327
		328	For a practical example of when these times differ, consider L<Event::Lib>
		329	and L<EV> and the following set-up:
		330
		331	The event loop is running and has just invoked one of your callbacks at
		332	time=500 (assume no other callbacks delay processing). In your callback,
		333	you wait a second by executing C<sleep 1> (blocking the process for a
		334	second) and then (at time=501) you create a relative timer that fires
		335	after three seconds.
		336
		337	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		338	both return C<501>, because that is the current time, and the timer will
		339	be scheduled to fire at time=504 (C<501> + C<3>).
		340
		341	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		342	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		343	last event processing phase started. With L<EV>, your timer gets scheduled
		344	to run at time=503 (C<500> + C<3>).
		345
		346	In one sense, L<Event::Lib> is more exact, as it uses the current time
		347	regardless of any delays introduced by event processing. However, most
		348	callbacks do not expect large delays in processing, so this causes a
		349	higher drift (and a lot more system calls to get the current time).
		350
		351	In another sense, L<EV> is more exact, as your timer will be scheduled at
		352	the same time, regardless of how long event processing actually took.
		353
		354	In either case, if you care (and in most cases, you don't), then you
		355	can get whatever behaviour you want with any event loop, by taking the
		356	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		357	account.
		358
		359	=item AnyEvent->now_update
		360
		361	Some event loops (such as L<EV> or L<AnyEvent::Loop>) cache the current
		362	time for each loop iteration (see the discussion of L<< AnyEvent->now >>,
		363	above).
		364
		365	When a callback runs for a long time (or when the process sleeps), then
		366	this "current" time will differ substantially from the real time, which
		367	might affect timers and time-outs.
		368
		369	When this is the case, you can call this method, which will update the
		370	event loop's idea of "current time".
		371
		372	A typical example would be a script in a web server (e.g. C<mod_perl>) -
		373	when mod_perl executes the script, then the event loop will have the wrong
		374	idea about the "current time" (being potentially far in the past, when the
		375	script ran the last time). In that case you should arrange a call to C<<
		376	AnyEvent->now_update >> each time the web server process wakes up again
		377	(e.g. at the start of your script, or in a handler).
		378
		379	Note that updating the time I<might> cause some events to be handled.
		380
		381	=back
		382
224	=head2 SIGNAL WATCHERS	383	=head2 SIGNAL WATCHERS
225		384
		385	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		386
226	You can watch 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
227	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	388	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
228	be invoked whenever a signal occurs.	389	callback to be invoked whenever a signal occurs.
229		390
		391	Although the callback might get passed parameters, their value and
		392	presence is undefined and you cannot rely on them. Portable AnyEvent
		393	callbacks cannot use arguments passed to signal watcher callbacks.
		394
230	Multiple signals occurances can be clumped together into one callback	395	Multiple signal occurrences can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	396	invocation, and callback invocation will be synchronous. Synchronous means
232	that it might take a while until the signal gets handled by the process,	397	that it might take a while until the signal gets handled by the process,
233	but it is guarenteed not to interrupt any other callbacks.	398	but it is guaranteed not to interrupt any other callbacks.
234		399
235	The main advantage of using these watchers is that you can share a signal	400	The main advantage of using these watchers is that you can share a signal
236	between multiple watchers.	401	between multiple watchers, and AnyEvent will ensure that signals will not
		402	interrupt your program at bad times.
237		403
238	This watcher might use C<%SIG>, so programs overwriting those signals	404	This watcher might use C<%SIG> (depending on the event loop used),
239	directly will likely not work correctly.	405	so programs overwriting those signals directly will likely not work
		406	correctly.
240		407
241	Example: exit on SIGINT	408	Example: exit on SIGINT
242		409
243	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	410	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
244		411
		412	=head3 Restart Behaviour
		413
		414	While restart behaviour is up to the event loop implementation, most will
		415	not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
		416	pure perl implementation).
		417
		418	=head3 Safe/Unsafe Signals
		419
		420	Perl signals can be either "safe" (synchronous to opcode handling) or
		421	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		422	latter might corrupt your memory.
		423
		424	AnyEvent signal handlers are, in addition, synchronous to the event loop,
		425	i.e. they will not interrupt your running perl program but will only be
		426	called as part of the normal event handling (just like timer, I/O etc.
		427	callbacks, too).
		428
		429	=head3 Signal Races, Delays and Workarounds
		430
		431	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		432	callbacks to signals in a generic way, which is a pity, as you cannot
		433	do race-free signal handling in perl, requiring C libraries for
		434	this. AnyEvent will try to do its best, which means in some cases,
		435	signals will be delayed. The maximum time a signal might be delayed is
		436	specified in C<$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
245	=head2 CHILD PROCESS WATCHERS	449	=head2 CHILD PROCESS WATCHERS
246		450
		451	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		452
247	You can also watch on a child process exit and catch its exit status.	453	You can also watch for a child process exit and catch its exit status.
248		454
249	The child process is specified by the C<pid> argument (if set to C<0>, it	455	The child process is specified by the C<pid> argument (on some backends,
250	watches for any child process exit). The watcher will trigger as often	456	using C<0> watches for any child process exit, on others this will
251	as status change for the child are received. This works by installing a	457	croak). The watcher will be triggered only when the child process has
252	signal handler for C<SIGCHLD>. The callback will be called with the pid	458	finished and an exit status is available, not on any trace events
253	and exit status (as returned by waitpid).	459	(stopped/continued).
254		460
255	Example: wait for pid 1333	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.
256		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
257	my $w = AnyEvent->child (	496	my $w = AnyEvent->child (
258	pid => 1333,	497	pid => $pid,
259	cb => sub {	498	cb => sub {
260	my ($pid, $status) = @_;	499	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	500	warn "pid $pid exited with status $status";
		501	$done->send;
262	},	502	},
263	);	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	});
264		547
265	=head2 CONDITION VARIABLES	548	=head2 CONDITION VARIABLES
266		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
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	567	Condition variables can be created by calling the C<< AnyEvent->condvar
268	method without any arguments.	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).
269		572
270	A condition variable waits for a condition - precisely that the C<<	573	After creation, the condition variable is "false" until it becomes "true"
271	->broadcast >> method has been called.	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).
272		577
273	They are very useful to signal that a condition has been fulfilled, for	578	Since condition variables are the most complex part of the AnyEvent API, here are
		579	some different mental models of what they are - pick the ones you can connect to:
		580
		581	=over 4
		582
		583	=item * Condition variables are like callbacks - you can call them (and pass them instead
		584	of callbacks). Unlike callbacks however, you can also wait for them to be called.
		585
		586	=item * Condition variables are signals - one side can emit or send them,
		587	the other side can wait for them, or install a handler that is called when
		588	the signal fires.
		589
		590	=item * Condition variables are like "Merge Points" - points in your program
		591	where you merge multiple independent results/control flows into one.
		592
		593	=item * Condition variables represent a transaction - functions that start
		594	some kind of transaction can return them, leaving the caller the choice
		595	between waiting in a blocking fashion, or setting a callback.
		596
		597	=item * Condition variables represent future values, or promises to deliver
		598	some result, long before the result is available.
		599
		600	=back
		601
		602	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	603	for example, if you write a module that does asynchronous http requests,
275	then a condition variable would be the ideal candidate to signal the	604	then a condition variable would be the ideal candidate to signal the
276	availability of results.	605	availability of results. The user can either act when the callback is
		606	called or can synchronously C<< ->recv >> for the results.
277		607
278	You can also use condition variables to block your main program until	608	You can also use them to simulate traditional event loops - for example,
279	an event occurs - for example, you could C<< ->wait >> in your main	609	you can block your main program until an event occurs - for example, you
280	program until the user clicks the Quit button in your app, which would C<<	610	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	611	button of your app, which would C<< ->send >> the "quit" event.
282		612
283	Note that condition variables recurse into the event loop - if you have	613	Note that condition variables recurse into the event loop - if you have
284	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	614	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
285	lose. Therefore, condition variables are good to export to your caller, but	615	lose. Therefore, condition variables are good to export to your caller, but
286	you should avoid making a blocking wait yourself, at least in callbacks,	616	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	617	as this asks for trouble.
288		618
289	This object has two methods:	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.
290		677
291	=over 4	678	=over 4
292		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
293	=item $cv->wait	710	=item $cv->end
294		711
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	712	These two methods can be used to combine many transactions/events into
296	called on c<$cv>, while servicing other watchers normally.	713	one. For example, a function that pings many hosts in parallel might want
		714	to use a condition variable for the whole process.
297		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
298	You can only wait once on a condition - additional calls will return	804	You can only wait once on a condition - additional calls are valid but
299	immediately.	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.
300		819
301	Not all event models support a blocking wait - some die in that case	820	Not all event models support a blocking wait - some die in that case
302	(programs might want to do that to stay interactive), so I<if you are	821	(programs might want to do that to stay interactive), so I<if you are
303	using this from a module, never require a blocking wait>, but let the	822	using this from a module, never require a blocking wait>. Instead, let the
304	caller decide whether the call will block or not (for example, by coupling	823	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	824	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	825	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	826	while still supporting blocking waits if the caller so desires).
308		827
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	828	You can ensure that C<< ->recv >> never blocks by setting a callback and
310	sensibly have two C<< ->wait >>'s in parallel, as that would require	829	only calling C<< ->recv >> from within that callback (or at a later
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	830	time). This will work even when the event loop does not support blocking
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	831	waits otherwise.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		832
316	=item $cv->broadcast	833	=item $bool = $cv->ready
317		834
318	Flag the condition as ready - a running C<< ->wait >> and all further	835	Returns true when the condition is "true", i.e. whether C<send> or
319	calls to C<wait> will (eventually) return after this method has been	836	C<croak> have been called.
320	called. If nobody is waiting the broadcast will be remembered..	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.
321		848
322	=back	849	=back
323		850
324	Example:	851	=head1 SUPPORTED EVENT LOOPS/BACKENDS
325		852
326	# wait till the result is ready	853	The available backend classes are (every class has its own manpage):
327	my $result_ready = AnyEvent->condvar;
328		854
329	# do something such as adding a timer	855	=over 4
330	# or socket watcher the calls $result_ready->broadcast
331	# when the "result" is ready.
332	# in this case, we simply use a timer:
333	my $w = AnyEvent->timer (
334	after => 1,
335	cb => sub { $result_ready->broadcast },
336	);
337		856
338	# this "blocks" (while handling events) till the watcher	857	=item Backends that are autoprobed when no other event loop can be found.
339	# calls broadcast	858
340	$result_ready->wait;	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
341		913
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	914	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		915
		916	These are not normally required to use AnyEvent, but can be useful to
		917	write AnyEvent extension modules.
		918
344	=over 4	919	=over 4
345		920
346	=item $AnyEvent::MODEL	921	=item $AnyEvent::MODEL
347		922
348	Contains C<undef> until the first watcher is being created. Then it	923	Contains C<undef> until the first watcher is being created, before the
		924	backend has been autodetected.
		925
349	contains the event model that is being used, which is the name of the	926	Afterwards it contains the event model that is being used, which is the
350	Perl class implementing the model. This class is usually one of the	927	name of the Perl class implementing the model. This class is usually one
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	928	of the C<AnyEvent::Impl::xxx> modules, but can be any other class in the
352	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	929	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
353		930	will be C<urxvt::anyevent>).
354	The known classes so far are:
355
356	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
357	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
358	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)
360	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
363		931
364	=item AnyEvent::detect	932	=item AnyEvent::detect
365		933
366	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	934	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
367	if necessary. You should only call this function right before you would	935	if necessary. You should only call this function right before you would
368	have created an AnyEvent watcher anyway, that is, as late as possible at	936	have created an AnyEvent watcher anyway, that is, as late as possible at
369	runtime.	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;
370		1049
371	=back	1050	=back
372		1051
373	=head1 WHAT TO DO IN A MODULE	1052	=head1 WHAT TO DO IN A MODULE
374		1053
…		…
378	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
379	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
380	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
381	to load the event module first.	1060	to load the event module first.
382		1061
383	Never call C<< ->wait >> on a condition variable unless you I<know> that	1062	Never call C<< ->recv >> on a condition variable unless you I<know> that
384	the C<< ->broadcast >> method has been called on it already. This is	1063	the C<< ->send >> method has been called on it already. This is
385	because it will stall the whole program, and the whole point of using	1064	because it will stall the whole program, and the whole point of using
386	events is to stay interactive.	1065	events is to stay interactive.
387		1066
388	It is fine, however, to call C<< ->wait >> when the user of your module	1067	It is fine, however, to call C<< ->recv >> when the user of your module
389	requests it (i.e. if you create a http request object ad have a method	1068	requests it (i.e. if you create a http request object ad have a method
390	called C<results> that returns the results, it should call C<< ->wait >>	1069	called C<results> that returns the results, it may call C<< ->recv >>
391	freely, as the user of your module knows what she is doing. always).	1070	freely, as the user of your module knows what she is doing. Always).
392		1071
393	=head1 WHAT TO DO IN THE MAIN PROGRAM	1072	=head1 WHAT TO DO IN THE MAIN PROGRAM
394		1073
395	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
396	dictate which event model to use.	1075	dictate which event model to use.
397		1076
398	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
399	do anything special (it does not need to be event-based) and let AnyEvent	1078	when it depends on a module that uses an AnyEvent. If the program itself
400	decide which implementation to chose if some module relies on it.	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.
401		1082
402	If the main program relies on a specific event model. For example, in	1083	If the main program relies on a specific event model - for example, in
403	Gtk2 programs you have to rely on the Glib module. You should load the	1084	Gtk2 programs you have to rely on the Glib module - you should load the
404	event module before loading AnyEvent or any module that uses it: generally	1085	event module before loading AnyEvent or any module that uses it: generally
405	speaking, you should load it as early as possible. The reason is that	1086	speaking, you should load it as early as possible. The reason is that
406	modules might create watchers when they are loaded, and AnyEvent will	1087	modules might create watchers when they are loaded, and AnyEvent will
407	decide on the event model to use as soon as it creates watchers, and it	1088	decide on the event model to use as soon as it creates watchers, and it
408	might chose the wrong one unless you load the correct one yourself.	1089	might choose the wrong one unless you load the correct one yourself.
409		1090
410	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
411	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	1092	C<AnyEvent::Loop> module, which gives you similar behaviour
412	behaviour everywhere, but letting AnyEvent chose is 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
413		1190
414	=cut	1191	=cut
415		1192
416	package AnyEvent;	1193	package AnyEvent;
417		1194
418	no warnings;	1195	# basically a tuned-down version of common::sense
419	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	}
420		1202
		1203	BEGIN { AnyEvent::common_sense }
		1204
421	use Carp;	1205	use Carp ();
422		1206
423	our $VERSION = '3.11';	1207	our $VERSION = '5.34';
424	our $MODEL;	1208	our $MODEL;
425		1209
426	our $AUTOLOAD;	1210	our $AUTOLOAD;
427	our @ISA;	1211	our @ISA;
428		1212
429	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
430
431	our @REGISTRY;	1213	our @REGISTRY;
432		1214
		1215	our $VERBOSE;
		1216
		1217	BEGIN {
		1218	require "AnyEvent/constants.pl";
		1219
		1220	eval "sub TAINT (){" . (${^TAINT}*1) . "}";
		1221
		1222	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1223	if ${^TAINT};
		1224
		1225	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1226
		1227	}
		1228
		1229	our $MAX_SIGNAL_LATENCY = 10;
		1230
		1231	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1232
		1233	{
		1234	my $idx;
		1235	$PROTOCOL{$_} = ++$idx
		1236	for reverse split /\s*,\s*/,
		1237	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1238	}
		1239
		1240	our @post_detect;
		1241
		1242	sub post_detect(&) {
		1243	my ($cb) = @_;
		1244
		1245	push @post_detect, $cb;
		1246
		1247	defined wantarray
		1248	? bless \$cb, "AnyEvent::Util::postdetect"
		1249	: ()
		1250	}
		1251
		1252	sub AnyEvent::Util::postdetect::DESTROY {
		1253	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1254	}
		1255
		1256	our $POSTPONE_W;
		1257	our @POSTPONE;
		1258
		1259	sub _postpone_exec {
		1260	undef $POSTPONE_W;
		1261
		1262	&{ shift @POSTPONE }
		1263	while @POSTPONE;
		1264	}
		1265
		1266	sub postpone(&) {
		1267	push @POSTPONE, shift;
		1268
		1269	$POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
		1270
		1271	()
		1272	}
		1273
433	my @models = (	1274	our @models = (
434	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
435	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
436	[EV:: => AnyEvent::Impl::EV::],	1275	[EV:: => AnyEvent::Impl::EV:: , 1],
		1276	[AnyEvent::Loop:: => AnyEvent::Impl::Perl:: , 1],
		1277	# everything below here will not (normally) be autoprobed
		1278	# as the pure perl backend should work everywhere
		1279	# and is usually faster
437	[Event:: => AnyEvent::Impl::Event::],	1280	[Event:: => AnyEvent::Impl::Event::, 1],
438	[Glib:: => AnyEvent::Impl::Glib::],	1281	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1282	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1283	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
		1284	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1285	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1286	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
439	[Tk:: => AnyEvent::Impl::Tk::],	1287	[Wx:: => AnyEvent::Impl::POE::],
440	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	1288	[Prima:: => AnyEvent::Impl::POE::],
		1289	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # a bitch to autodetect
		1290	[Cocoa::EventLoop:: => AnyEvent::Impl::Cocoa::],
		1291	[FLTK:: => AnyEvent::Impl::FLTK2::],
441	);	1292	);
442		1293
443	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);
444
445	sub detect() {	1294	sub detect() {
		1295	# free some memory
		1296	*detect = sub () { $MODEL };
		1297
		1298	local $!; # for good measure
		1299	local $SIG{__DIE__};
		1300
		1301	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
		1302	my $model = $1;
		1303	$model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
		1304	if (eval "require $model") {
		1305	$MODEL = $model;
		1306	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1307	} else {
		1308	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
		1309	}
		1310	}
		1311
		1312	# check for already loaded models
446	unless ($MODEL) {	1313	unless ($MODEL) {
447	no strict 'refs';
448
449	# check for already loaded models
450	for (@REGISTRY, @models) {	1314	for (@REGISTRY, @models) {
451	my ($package, $model) = @$_;	1315	my ($package, $model) = @$_;
452	if (${"$package\::VERSION"} > 0) {	1316	if (${"$package\::VERSION"} > 0) {
453	if (eval "require $model") {	1317	if (eval "require $model") {
454	$MODEL = $model;	1318	$MODEL = $model;
455	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1319	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
456	last;	1320	last;
457	}	1321	}
458	}	1322	}
459	}	1323	}
460		1324
461	unless ($MODEL) {	1325	unless ($MODEL) {
462	# try to load a model	1326	# try to autoload a model
463
464	for (@REGISTRY, @models) {	1327	for (@REGISTRY, @models) {
465	my ($package, $model) = @$_;	1328	my ($package, $model, $autoload) = @$_;
		1329	if (
		1330	$autoload
466	if (eval "require $package"	1331	and eval "require $package"
467	and ${"$package\::VERSION"} > 0	1332	and ${"$package\::VERSION"} > 0
468	and eval "require $model") {	1333	and eval "require $model"
		1334	) {
469	$MODEL = $model;	1335	$MODEL = $model;
470	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	1336	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
471	last;	1337	last;
472	}	1338	}
473	}	1339	}
474		1340
475	$MODEL	1341	$MODEL
476	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk.";	1342	or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?\n";
477	}	1343	}
478
479	unshift @ISA, $MODEL;
480	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
481	}	1344	}
482		1345
		1346	# free memory only needed for probing
		1347	undef @models;
		1348	undef @REGISTRY;
		1349
		1350	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1351	unshift @ISA, $MODEL;
		1352
		1353	# now nuke some methods that are overridden by the backend.
		1354	# SUPER usage is not allowed in these.
		1355	for (qw(time signal child idle)) {
		1356	undef &{"AnyEvent::Base::$_"}
		1357	if defined &{"$MODEL\::$_"};
		1358	}
		1359
		1360	if ($ENV{PERL_ANYEVENT_STRICT}) {
		1361	eval { require AnyEvent::Strict };
		1362	warn "AnyEvent: cannot load AnyEvent::Strict: $@"
		1363	if $@ && $VERBOSE;
		1364	}
		1365
		1366	(shift @post_detect)->() while @post_detect;
		1367	undef @post_detect;
		1368
		1369	*post_detect = sub(&) {
		1370	shift->();
		1371
		1372	undef
		1373	};
		1374
		1375	# recover a few more bytes
		1376	postpone {
		1377	undef &AUTOLOAD;
		1378	};
		1379
483	$MODEL	1380	$MODEL
484	}	1381	}
		1382
		1383	our %method = map +($_ => 1),
		1384	qw(io timer time now now_update signal child idle condvar DESTROY);
485		1385
486	sub AUTOLOAD {	1386	sub AUTOLOAD {
487	(my $func = $AUTOLOAD) =~ s/.*://;	1387	(my $func = $AUTOLOAD) =~ s/.*://;
488		1388
489	$method{$func}	1389	$method{$func}
490	or croak "$func: not a valid method for AnyEvent objects";	1390	or Carp::croak "$func: not a valid AnyEvent class method";
491		1391
492	detect unless $MODEL;	1392	# free some memory
		1393	undef %method;
		1394
		1395	detect;
493		1396
494	my $class = shift;	1397	my $class = shift;
495	$class->$func (@_);	1398	$class->$func (@_);
496	}	1399	}
497		1400
		1401	# utility function to dup a filehandle. this is used by many backends
		1402	# to support binding more than one watcher per filehandle (they usually
		1403	# allow only one watcher per fd, so we dup it to get a different one).
		1404	sub _dupfh($$;$$) {
		1405	my ($poll, $fh, $r, $w) = @_;
		1406
		1407	# cygwin requires the fh mode to be matching, unix doesn't
		1408	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1409
		1410	open my $fh2, $mode, $fh
		1411	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1412
		1413	# we assume CLOEXEC is already set by perl in all important cases
		1414
		1415	($fh2, $rw)
		1416	}
		1417
		1418	=head1 SIMPLIFIED AE API
		1419
		1420	Starting with version 5.0, AnyEvent officially supports a second, much
		1421	simpler, API that is designed to reduce the calling, typing and memory
		1422	overhead by using function call syntax and a fixed number of parameters.
		1423
		1424	See the L<AE> manpage for details.
		1425
		1426	=cut
		1427
		1428	package AE;
		1429
		1430	our $VERSION = $AnyEvent::VERSION;
		1431
		1432
		1433	sub _reset() {
		1434	eval q{
		1435	# fall back to the main API by default - backends and AnyEvent::Base
		1436	# implementations can overwrite these.
		1437
		1438	sub io($$$) {
		1439	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1440	}
		1441
		1442	sub timer($$$) {
		1443	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1444	}
		1445
		1446	sub signal($$) {
		1447	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1448	}
		1449
		1450	sub child($$) {
		1451	AnyEvent->child (pid => $_[0], cb => $_[1])
		1452	}
		1453
		1454	sub idle($) {
		1455	AnyEvent->idle (cb => $_[0])
		1456	}
		1457
		1458	sub cv(;&) {
		1459	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1460	}
		1461
		1462	sub now() {
		1463	AnyEvent->now
		1464	}
		1465
		1466	sub now_update() {
		1467	AnyEvent->now_update
		1468	}
		1469
		1470	sub time() {
		1471	AnyEvent->time
		1472	}
		1473
		1474	*postpone = \&AnyEvent::postpone;
		1475	};
		1476	die if $@;
		1477	}
		1478
		1479	BEGIN { _reset }
		1480
498	package AnyEvent::Base;	1481	package AnyEvent::Base;
499		1482
		1483	# default implementations for many methods
		1484
		1485	sub time {
		1486	eval q{ # poor man's autoloading {}
		1487	# probe for availability of Time::HiRes
		1488	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1489	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1490	*AE::time = \&Time::HiRes::time;
		1491	# if (eval "use POSIX (); (POSIX::times())...
		1492	} else {
		1493	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1494	*AE::time = sub (){ time }; # epic fail
		1495	}
		1496
		1497	*time = sub { AE::time }; # different prototypes
		1498	};
		1499	die if $@;
		1500
		1501	&time
		1502	}
		1503
		1504	*now = \&time;
		1505
		1506	sub now_update { }
		1507
		1508	sub _poll {
		1509	Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
		1510	}
		1511
500	# default implementation for ->condvar, ->wait, ->broadcast	1512	# default implementation for ->condvar
		1513	# in fact, the default should not be overwritten
501		1514
502	sub condvar {	1515	sub condvar {
503	bless \my $flag, "AnyEvent::Base::CondVar"	1516	eval q{ # poor man's autoloading {}
504	}	1517	*condvar = sub {
		1518	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
		1519	};
505		1520
506	sub AnyEvent::Base::CondVar::broadcast {	1521	*AE::cv = sub (;&) {
507	${$_[0]}++;	1522	bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
508	}	1523	};
		1524	};
		1525	die if $@;
509		1526
510	sub AnyEvent::Base::CondVar::wait {	1527	&condvar
511	AnyEvent->one_event while !${$_[0]};
512	}	1528	}
513		1529
514	# default implementation for ->signal	1530	# default implementation for ->signal
515		1531
516	our %SIG_CB;	1532	our $HAVE_ASYNC_INTERRUPT;
		1533
		1534	sub _have_async_interrupt() {
		1535	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1536	&& eval "use Async::Interrupt 1.02 (); 1")
		1537	unless defined $HAVE_ASYNC_INTERRUPT;
		1538
		1539	$HAVE_ASYNC_INTERRUPT
		1540	}
		1541
		1542	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1543	our (%SIG_ASY, %SIG_ASY_W);
		1544	our ($SIG_COUNT, $SIG_TW);
		1545
		1546	# install a dummy wakeup watcher to reduce signal catching latency
		1547	# used by Impls
		1548	sub _sig_add() {
		1549	unless ($SIG_COUNT++) {
		1550	# try to align timer on a full-second boundary, if possible
		1551	my $NOW = AE::now;
		1552
		1553	$SIG_TW = AE::timer
		1554	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1555	$MAX_SIGNAL_LATENCY,
		1556	sub { } # just for the PERL_ASYNC_CHECK
		1557	;
		1558	}
		1559	}
		1560
		1561	sub _sig_del {
		1562	undef $SIG_TW
		1563	unless --$SIG_COUNT;
		1564	}
		1565
		1566	our $_sig_name_init; $_sig_name_init = sub {
		1567	eval q{ # poor man's autoloading {}
		1568	undef $_sig_name_init;
		1569
		1570	if (_have_async_interrupt) {
		1571	*sig2num = \&Async::Interrupt::sig2num;
		1572	*sig2name = \&Async::Interrupt::sig2name;
		1573	} else {
		1574	require Config;
		1575
		1576	my %signame2num;
		1577	@signame2num{ split ' ', $Config::Config{sig_name} }
		1578	= split ' ', $Config::Config{sig_num};
		1579
		1580	my @signum2name;
		1581	@signum2name[values %signame2num] = keys %signame2num;
		1582
		1583	*sig2num = sub($) {
		1584	$_[0] > 0 ? shift : $signame2num{+shift}
		1585	};
		1586	*sig2name = sub ($) {
		1587	$_[0] > 0 ? $signum2name[+shift] : shift
		1588	};
		1589	}
		1590	};
		1591	die if $@;
		1592	};
		1593
		1594	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1595	sub sig2name($) { &$_sig_name_init; &sig2name }
517		1596
518	sub signal {	1597	sub signal {
		1598	eval q{ # poor man's autoloading {}
		1599	# probe for availability of Async::Interrupt
		1600	if (_have_async_interrupt) {
		1601	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1602
		1603	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1604	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1605
		1606	} else {
		1607	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1608
		1609	if (AnyEvent::WIN32) {
		1610	require AnyEvent::Util;
		1611
		1612	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1613	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1614	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1615	} else {
		1616	pipe $SIGPIPE_R, $SIGPIPE_W;
		1617	fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
		1618	fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
		1619
		1620	# not strictly required, as $^F is normally 2, but let's make sure...
		1621	fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1622	fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
		1623	}
		1624
		1625	$SIGPIPE_R
		1626	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1627
		1628	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1629	}
		1630
		1631	*signal = $HAVE_ASYNC_INTERRUPT
		1632	? sub {
519	my (undef, %arg) = @_;	1633	my (undef, %arg) = @_;
520		1634
		1635	# async::interrupt
521	my $signal = uc $arg{signal}	1636	my $signal = sig2num $arg{signal};
522	or Carp::croak "required option 'signal' is missing";
523
524	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1637	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1638
		1639	$SIG_ASY{$signal} ||= new Async::Interrupt
		1640	cb => sub { undef $SIG_EV{$signal} },
		1641	signal => $signal,
		1642	pipe => [$SIGPIPE_R->filenos],
		1643	pipe_autodrain => 0,
		1644	;
		1645
		1646	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1647	}
		1648	: sub {
		1649	my (undef, %arg) = @_;
		1650
		1651	# pure perl
		1652	my $signal = sig2name $arg{signal};
		1653	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1654
525	$SIG{$signal} ||= sub {	1655	$SIG{$signal} ||= sub {
		1656	local $!;
		1657	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1658	undef $SIG_EV{$signal};
		1659	};
		1660
		1661	# can't do signal processing without introducing races in pure perl,
		1662	# so limit the signal latency.
		1663	_sig_add;
		1664
		1665	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1666	}
		1667	;
		1668
		1669	*AnyEvent::Base::signal::DESTROY = sub {
		1670	my ($signal, $cb) = @{$_[0]};
		1671
		1672	_sig_del;
		1673
		1674	delete $SIG_CB{$signal}{$cb};
		1675
		1676	$HAVE_ASYNC_INTERRUPT
		1677	? delete $SIG_ASY{$signal}
		1678	: # delete doesn't work with older perls - they then
		1679	# print weird messages, or just unconditionally exit
		1680	# instead of getting the default action.
		1681	undef $SIG{$signal}
		1682	unless keys %{ $SIG_CB{$signal} };
		1683	};
		1684
		1685	*_signal_exec = sub {
		1686	$HAVE_ASYNC_INTERRUPT
		1687	? $SIGPIPE_R->drain
		1688	: sysread $SIGPIPE_R, (my $dummy), 9;
		1689
		1690	while (%SIG_EV) {
		1691	for (keys %SIG_EV) {
		1692	delete $SIG_EV{$_};
526	$_->() for values %{ $SIG_CB{$signal} || {} };	1693	&$_ for values %{ $SIG_CB{$_} || {} };
		1694	}
		1695	}
		1696	};
527	};	1697	};
		1698	die if $@;
528		1699
529	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1700	&signal
530	}
531
532	sub AnyEvent::Base::Signal::DESTROY {
533	my ($signal, $cb) = @{$_[0]};
534
535	delete $SIG_CB{$signal}{$cb};
536
537	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
538	}	1701	}
539		1702
540	# default implementation for ->child	1703	# default implementation for ->child
541		1704
542	our %PID_CB;	1705	our %PID_CB;
543	our $CHLD_W;	1706	our $CHLD_W;
544	our $CHLD_DELAY_W;	1707	our $CHLD_DELAY_W;
545	our $PID_IDLE;
546	our $WNOHANG;
547		1708
548	sub _child_wait {	1709	# used by many Impl's
549	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	1710	sub _emit_childstatus($$) {
		1711	my (undef, $rpid, $rstatus) = @_;
		1712
		1713	$_->($rpid, $rstatus)
550	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1714	for values %{ $PID_CB{$rpid} || {} },
551	(values %{ $PID_CB{0} || {} });	1715	values %{ $PID_CB{0} || {} };
		1716	}
		1717
		1718	sub child {
		1719	eval q{ # poor man's autoloading {}
		1720	*_sigchld = sub {
		1721	my $pid;
		1722
		1723	AnyEvent->_emit_childstatus ($pid, $?)
		1724	while ($pid = waitpid -1, WNOHANG) > 0;
		1725	};
		1726
		1727	*child = sub {
		1728	my (undef, %arg) = @_;
		1729
		1730	my $pid = $arg{pid};
		1731	my $cb = $arg{cb};
		1732
		1733	$PID_CB{$pid}{$cb+0} = $cb;
		1734
		1735	unless ($CHLD_W) {
		1736	$CHLD_W = AE::signal CHLD => \&_sigchld;
		1737	# child could be a zombie already, so make at least one round
		1738	&_sigchld;
		1739	}
		1740
		1741	bless [$pid, $cb+0], "AnyEvent::Base::child"
		1742	};
		1743
		1744	*AnyEvent::Base::child::DESTROY = sub {
		1745	my ($pid, $icb) = @{$_[0]};
		1746
		1747	delete $PID_CB{$pid}{$icb};
		1748	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		1749
		1750	undef $CHLD_W unless keys %PID_CB;
		1751	};
		1752	};
		1753	die if $@;
		1754
		1755	&child
		1756	}
		1757
		1758	# idle emulation is done by simply using a timer, regardless
		1759	# of whether the process is idle or not, and not letting
		1760	# the callback use more than 50% of the time.
		1761	sub idle {
		1762	eval q{ # poor man's autoloading {}
		1763	*idle = sub {
		1764	my (undef, %arg) = @_;
		1765
		1766	my ($cb, $w, $rcb) = $arg{cb};
		1767
		1768	$rcb = sub {
		1769	if ($cb) {
		1770	$w = AE::time;
		1771	&$cb;
		1772	$w = AE::time - $w;
		1773
		1774	# never use more then 50% of the time for the idle watcher,
		1775	# within some limits
		1776	$w = 0.0001 if $w < 0.0001;
		1777	$w = 5 if $w > 5;
		1778
		1779	$w = AE::timer $w, 0, $rcb;
		1780	} else {
		1781	# clean up...
		1782	undef $w;
		1783	undef $rcb;
		1784	}
		1785	};
		1786
		1787	$w = AE::timer 0.05, 0, $rcb;
		1788
		1789	bless \\$cb, "AnyEvent::Base::idle"
		1790	};
		1791
		1792	*AnyEvent::Base::idle::DESTROY = sub {
		1793	undef $${$_[0]};
		1794	};
		1795	};
		1796	die if $@;
		1797
		1798	&idle
		1799	}
		1800
		1801	package AnyEvent::CondVar;
		1802
		1803	our @ISA = AnyEvent::CondVar::Base::;
		1804
		1805	# only to be used for subclassing
		1806	sub new {
		1807	my $class = shift;
		1808	bless AnyEvent->condvar (@_), $class
		1809	}
		1810
		1811	package AnyEvent::CondVar::Base;
		1812
		1813	#use overload
		1814	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1815	# fallback => 1;
		1816
		1817	# save 300+ kilobytes by dirtily hardcoding overloading
		1818	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1819	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1820	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1821	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1822
		1823	our $WAITING;
		1824
		1825	sub _send {
		1826	# nop
		1827	}
		1828
		1829	sub _wait {
		1830	AnyEvent->_poll until $_[0]{_ae_sent};
		1831	}
		1832
		1833	sub send {
		1834	my $cv = shift;
		1835	$cv->{_ae_sent} = [@_];
		1836	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1837	$cv->_send;
		1838	}
		1839
		1840	sub croak {
		1841	$_[0]{_ae_croak} = $_[1];
		1842	$_[0]->send;
		1843	}
		1844
		1845	sub ready {
		1846	$_[0]{_ae_sent}
		1847	}
		1848
		1849	sub recv {
		1850	unless ($_[0]{_ae_sent}) {
		1851	$WAITING
		1852	and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
		1853
		1854	local $WAITING = 1;
		1855	$_[0]->_wait;
552	}	1856	}
553		1857
554	undef $PID_IDLE;	1858	$_[0]{_ae_croak}
555	}	1859	and Carp::croak $_[0]{_ae_croak};
556		1860
557	sub _sigchld {	1861	wantarray
558	# make sure we deliver these changes "synchronous" with the event loop.	1862	? @{ $_[0]{_ae_sent} }
559	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {	1863	: $_[0]{_ae_sent}[0]
560	undef $CHLD_DELAY_W;
561	&_child_wait;
562	});
563	}	1864	}
564		1865
565	sub child {	1866	sub cb {
566	my (undef, %arg) = @_;	1867	my $cv = shift;
567		1868
568	defined (my $pid = $arg{pid} + 0)	1869	@_
569	or Carp::croak "required option 'pid' is missing";	1870	and $cv->{_ae_cb} = shift
		1871	and $cv->{_ae_sent}
		1872	and (delete $cv->{_ae_cb})->($cv);
570		1873
571	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1874	$cv->{_ae_cb}
572
573	unless ($WNOHANG) {
574	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
575	}
576
577	unless ($CHLD_W) {
578	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
579	# child could be a zombie already, so make at least one round
580	&_sigchld;
581	}
582
583	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
584	}	1875	}
585		1876
586	sub AnyEvent::Base::Child::DESTROY {	1877	sub begin {
587	my ($pid, $cb) = @{$_[0]};	1878	++$_[0]{_ae_counter};
588		1879	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
589	delete $PID_CB{$pid}{$cb};
590	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
591
592	undef $CHLD_W unless keys %PID_CB;
593	}	1880	}
		1881
		1882	sub end {
		1883	return if --$_[0]{_ae_counter};
		1884	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1885	}
		1886
		1887	# undocumented/compatibility with pre-3.4
		1888	*broadcast = \&send;
		1889	*wait = \&recv;
		1890
		1891	=head1 ERROR AND EXCEPTION HANDLING
		1892
		1893	In general, AnyEvent does not do any error handling - it relies on the
		1894	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1895	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1896	checking of all AnyEvent methods, however, which is highly useful during
		1897	development.
		1898
		1899	As for exception handling (i.e. runtime errors and exceptions thrown while
		1900	executing a callback), this is not only highly event-loop specific, but
		1901	also not in any way wrapped by this module, as this is the job of the main
		1902	program.
		1903
		1904	The pure perl event loop simply re-throws the exception (usually
		1905	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1906	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1907	so on.
		1908
		1909	=head1 ENVIRONMENT VARIABLES
		1910
		1911	The following environment variables are used by this module or its
		1912	submodules.
		1913
		1914	Note that AnyEvent will remove I<all> environment variables starting with
		1915	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1916	enabled.
		1917
		1918	=over 4
		1919
		1920	=item C<PERL_ANYEVENT_VERBOSE>
		1921
		1922	By default, AnyEvent will be completely silent except in fatal
		1923	conditions. You can set this environment variable to make AnyEvent more
		1924	talkative.
		1925
		1926	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1927	conditions, such as not being able to load the event model specified by
		1928	C<PERL_ANYEVENT_MODEL>.
		1929
		1930	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1931	model it chooses.
		1932
		1933	When set to C<8> or higher, then AnyEvent will report extra information on
		1934	which optional modules it loads and how it implements certain features.
		1935
		1936	=item C<PERL_ANYEVENT_STRICT>
		1937
		1938	AnyEvent does not do much argument checking by default, as thorough
		1939	argument checking is very costly. Setting this variable to a true value
		1940	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1941	check the arguments passed to most method calls. If it finds any problems,
		1942	it will croak.
		1943
		1944	In other words, enables "strict" mode.
		1945
		1946	Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
		1947	>>, it is definitely recommended to keep it off in production. Keeping
		1948	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1949	can be very useful, however.
		1950
		1951	=item C<PERL_ANYEVENT_MODEL>
		1952
		1953	This can be used to specify the event model to be used by AnyEvent, before
		1954	auto detection and -probing kicks in.
		1955
		1956	It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
		1957	or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
		1958	resulting module name is loaded and - if the load was successful - used as
		1959	event model backend. If it fails to load then AnyEvent will proceed with
		1960	auto detection and -probing.
		1961
		1962	If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
		1963	nothing gets prepended and the module name is used as-is (hint: C<::> at
		1964	the end of a string designates a module name and quotes it appropriately).
		1965
		1966	For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
		1967	could start your program like this:
		1968
		1969	PERL_ANYEVENT_MODEL=Perl perl ...
		1970
		1971	=item C<PERL_ANYEVENT_PROTOCOLS>
		1972
		1973	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1974	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1975	of auto probing).
		1976
		1977	Must be set to a comma-separated list of protocols or address families,
		1978	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1979	used, and preference will be given to protocols mentioned earlier in the
		1980	list.
		1981
		1982	This variable can effectively be used for denial-of-service attacks
		1983	against local programs (e.g. when setuid), although the impact is likely
		1984	small, as the program has to handle conenction and other failures anyways.
		1985
		1986	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1987	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1988	- only support IPv4, never try to resolve or contact IPv6
		1989	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1990	IPv6, but prefer IPv6 over IPv4.
		1991
		1992	=item C<PERL_ANYEVENT_EDNS0>
		1993
		1994	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1995	for DNS. This extension is generally useful to reduce DNS traffic, but
		1996	some (broken) firewalls drop such DNS packets, which is why it is off by
		1997	default.
		1998
		1999	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		2000	EDNS0 in its DNS requests.
		2001
		2002	=item C<PERL_ANYEVENT_MAX_FORKS>
		2003
		2004	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		2005	will create in parallel.
		2006
		2007	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		2008
		2009	The default value for the C<max_outstanding> parameter for the default DNS
		2010	resolver - this is the maximum number of parallel DNS requests that are
		2011	sent to the DNS server.
		2012
		2013	=item C<PERL_ANYEVENT_RESOLV_CONF>
		2014
		2015	The file to use instead of F</etc/resolv.conf> (or OS-specific
		2016	configuration) in the default resolver. When set to the empty string, no
		2017	default config will be used.
		2018
		2019	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		2020
		2021	When neither C<ca_file> nor C<ca_path> was specified during
		2022	L<AnyEvent::TLS> context creation, and either of these environment
		2023	variables exist, they will be used to specify CA certificate locations
		2024	instead of a system-dependent default.
		2025
		2026	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		2027
		2028	When these are set to C<1>, then the respective modules are not
		2029	loaded. Mostly good for testing AnyEvent itself.
		2030
		2031	=back
594		2032
595	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	2033	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
596		2034
597	This is an advanced topic that you do not normally need to use AnyEvent in	2035	This is an advanced topic that you do not normally need to use AnyEvent in
598	a module. This section is only of use to event loop authors who want to	2036	a module. This section is only of use to event loop authors who want to
…		…
633	I<rxvt-unicode> also cheats a bit by not providing blocking access to	2071	I<rxvt-unicode> also cheats a bit by not providing blocking access to
634	condition variables: code blocking while waiting for a condition will	2072	condition variables: code blocking while waiting for a condition will
635	C<die>. This still works with most modules/usages, and blocking calls must	2073	C<die>. This still works with most modules/usages, and blocking calls must
636	not be done in an interactive application, so it makes sense.	2074	not be done in an interactive application, so it makes sense.
637		2075
638	=head1 ENVIRONMENT VARIABLES
639
640	The following environment variables are used by this module:
641
642	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to
643	report to STDERR which event model it chooses.
644
645	=head1 EXAMPLE PROGRAM	2076	=head1 EXAMPLE PROGRAM
646		2077
647	The following program uses an IO watcher to read data from STDIN, a timer	2078	The following program uses an I/O watcher to read data from STDIN, a timer
648	to display a message once per second, and a condition variable to quit the	2079	to display a message once per second, and a condition variable to quit the
649	program when the user enters quit:	2080	program when the user enters quit:
650		2081
651	use AnyEvent;	2082	use AnyEvent;
652		2083
…		…
657	poll => 'r',	2088	poll => 'r',
658	cb => sub {	2089	cb => sub {
659	warn "io event <$_[0]>\n"; # will always output <r>	2090	warn "io event <$_[0]>\n"; # will always output <r>
660	chomp (my $input = <STDIN>); # read a line	2091	chomp (my $input = <STDIN>); # read a line
661	warn "read: $input\n"; # output what has been read	2092	warn "read: $input\n"; # output what has been read
662	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	2093	$cv->send if $input =~ /^q/i; # quit program if /^q/i
663	},	2094	},
664	);	2095	);
665		2096
666	my $time_watcher; # can only be used once
667
668	sub new_timer {
669	$timer = AnyEvent->timer (after => 1, cb => sub {	2097	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
670	warn "timeout\n"; # print 'timeout' about every second	2098	warn "timeout\n"; # print 'timeout' at most every second
671	&new_timer; # and restart the time
672	});	2099	});
673	}
674		2100
675	new_timer; # create first timer
676
677	$cv->wait; # wait until user enters /^q/i	2101	$cv->recv; # wait until user enters /^q/i
678		2102
679	=head1 REAL-WORLD EXAMPLE	2103	=head1 REAL-WORLD EXAMPLE
680		2104
681	Consider the L<Net::FCP> module. It features (among others) the following	2105	Consider the L<Net::FCP> module. It features (among others) the following
682	API calls, which are to freenet what HTTP GET requests are to http:	2106	API calls, which are to freenet what HTTP GET requests are to http:
…		…
732	syswrite $txn->{fh}, $txn->{request}	2156	syswrite $txn->{fh}, $txn->{request}
733	or die "connection or write error";	2157	or die "connection or write error";
734	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	2158	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
735		2159
736	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	2160	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
737	result and signals any possible waiters that the request ahs finished:	2161	result and signals any possible waiters that the request has finished:
738		2162
739	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	2163	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
740		2164
741	if (end-of-file or data complete) {	2165	if (end-of-file or data complete) {
742	$txn->{result} = $txn->{buf};	2166	$txn->{result} = $txn->{buf};
743	$txn->{finished}->broadcast;	2167	$txn->{finished}->send;
744	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	2168	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
745	}	2169	}
746		2170
747	The C<result> method, finally, just waits for the finished signal (if the	2171	The C<result> method, finally, just waits for the finished signal (if the
748	request was already finished, it doesn't wait, of course, and returns the	2172	request was already finished, it doesn't wait, of course, and returns the
749	data:	2173	data:
750		2174
751	$txn->{finished}->wait;	2175	$txn->{finished}->recv;
752	return $txn->{result};	2176	return $txn->{result};
753		2177
754	The actual code goes further and collects all errors (C<die>s, exceptions)	2178	The actual code goes further and collects all errors (C<die>s, exceptions)
755	that occured during request processing. The C<result> method detects	2179	that occurred during request processing. The C<result> method detects
756	whether an exception as thrown (it is stored inside the $txn object)	2180	whether an exception as thrown (it is stored inside the $txn object)
757	and just throws the exception, which means connection errors and other	2181	and just throws the exception, which means connection errors and other
758	problems get reported tot he code that tries to use the result, not in a	2182	problems get reported to the code that tries to use the result, not in a
759	random callback.	2183	random callback.
760		2184
761	All of this enables the following usage styles:	2185	All of this enables the following usage styles:
762		2186
763	1. Blocking:	2187	1. Blocking:
…		…
791		2215
792	my $quit = AnyEvent->condvar;	2216	my $quit = AnyEvent->condvar;
793		2217
794	$fcp->txn_client_get ($url)->cb (sub {	2218	$fcp->txn_client_get ($url)->cb (sub {
795	...	2219	...
796	$quit->broadcast;	2220	$quit->send;
797	});	2221	});
798		2222
799	$quit->wait;	2223	$quit->recv;
		2224
		2225
		2226	=head1 BENCHMARKS
		2227
		2228	To give you an idea of the performance and overheads that AnyEvent adds
		2229	over the event loops themselves and to give you an impression of the speed
		2230	of various event loops I prepared some benchmarks.
		2231
		2232	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2233
		2234	Here is a benchmark of various supported event models used natively and
		2235	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2236	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		2237	which it is), lets them fire exactly once and destroys them again.
		2238
		2239	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2240	distribution. It uses the L<AE> interface, which makes a real difference
		2241	for the EV and Perl backends only.
		2242
		2243	=head3 Explanation of the columns
		2244
		2245	I<watcher> is the number of event watchers created/destroyed. Since
		2246	different event models feature vastly different performances, each event
		2247	loop was given a number of watchers so that overall runtime is acceptable
		2248	and similar between tested event loop (and keep them from crashing): Glib
		2249	would probably take thousands of years if asked to process the same number
		2250	of watchers as EV in this benchmark.
		2251
		2252	I<bytes> is the number of bytes (as measured by the resident set size,
		2253	RSS) consumed by each watcher. This method of measuring captures both C
		2254	and Perl-based overheads.
		2255
		2256	I<create> is the time, in microseconds (millionths of seconds), that it
		2257	takes to create a single watcher. The callback is a closure shared between
		2258	all watchers, to avoid adding memory overhead. That means closure creation
		2259	and memory usage is not included in the figures.
		2260
		2261	I<invoke> is the time, in microseconds, used to invoke a simple
		2262	callback. The callback simply counts down a Perl variable and after it was
		2263	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2264	signal the end of this phase.
		2265
		2266	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2267	watcher.
		2268
		2269	=head3 Results
		2270
		2271	name watchers bytes create invoke destroy comment
		2272	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
		2273	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
		2274	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
		2275	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
		2276	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
		2277	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2278	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2279	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
		2280	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
		2281	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
		2282	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
		2283	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
		2284
		2285	=head3 Discussion
		2286
		2287	The benchmark does I<not> measure scalability of the event loop very
		2288	well. For example, a select-based event loop (such as the pure perl one)
		2289	can never compete with an event loop that uses epoll when the number of
		2290	file descriptors grows high. In this benchmark, all events become ready at
		2291	the same time, so select/poll-based implementations get an unnatural speed
		2292	boost.
		2293
		2294	Also, note that the number of watchers usually has a nonlinear effect on
		2295	overall speed, that is, creating twice as many watchers doesn't take twice
		2296	the time - usually it takes longer. This puts event loops tested with a
		2297	higher number of watchers at a disadvantage.
		2298
		2299	To put the range of results into perspective, consider that on the
		2300	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2301	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2302	cycles with POE.
		2303
		2304	C<EV> is the sole leader regarding speed and memory use, which are both
		2305	maximal/minimal, respectively. When using the L<AE> API there is zero
		2306	overhead (when going through the AnyEvent API create is about 5-6 times
		2307	slower, with other times being equal, so still uses far less memory than
		2308	any other event loop and is still faster than Event natively).
		2309
		2310	The pure perl implementation is hit in a few sweet spots (both the
		2311	constant timeout and the use of a single fd hit optimisations in the perl
		2312	interpreter and the backend itself). Nevertheless this shows that it
		2313	adds very little overhead in itself. Like any select-based backend its
		2314	performance becomes really bad with lots of file descriptors (and few of
		2315	them active), of course, but this was not subject of this benchmark.
		2316
		2317	The C<Event> module has a relatively high setup and callback invocation
		2318	cost, but overall scores in on the third place.
		2319
		2320	C<IO::Async> performs admirably well, about on par with C<Event>, even
		2321	when using its pure perl backend.
		2322
		2323	C<Glib>'s memory usage is quite a bit higher, but it features a
		2324	faster callback invocation and overall ends up in the same class as
		2325	C<Event>. However, Glib scales extremely badly, doubling the number of
		2326	watchers increases the processing time by more than a factor of four,
		2327	making it completely unusable when using larger numbers of watchers
		2328	(note that only a single file descriptor was used in the benchmark, so
		2329	inefficiencies of C<poll> do not account for this).
		2330
		2331	The C<Tk> adaptor works relatively well. The fact that it crashes with
		2332	more than 2000 watchers is a big setback, however, as correctness takes
		2333	precedence over speed. Nevertheless, its performance is surprising, as the
		2334	file descriptor is dup()ed for each watcher. This shows that the dup()
		2335	employed by some adaptors is not a big performance issue (it does incur a
		2336	hidden memory cost inside the kernel which is not reflected in the figures
		2337	above).
		2338
		2339	C<POE>, regardless of underlying event loop (whether using its pure perl
		2340	select-based backend or the Event module, the POE-EV backend couldn't
		2341	be tested because it wasn't working) shows abysmal performance and
		2342	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2343	as EV watchers, and 10 times as much memory as Event (the high memory
		2344	requirements are caused by requiring a session for each watcher). Watcher
		2345	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2346	implementation.
		2347
		2348	The design of the POE adaptor class in AnyEvent can not really account
		2349	for the performance issues, though, as session creation overhead is
		2350	small compared to execution of the state machine, which is coded pretty
		2351	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2352	using multiple sessions is not a good approach, especially regarding
		2353	memory usage, even the author of POE could not come up with a faster
		2354	design).
		2355
		2356	=head3 Summary
		2357
		2358	=over 4
		2359
		2360	=item * Using EV through AnyEvent is faster than any other event loop
		2361	(even when used without AnyEvent), but most event loops have acceptable
		2362	performance with or without AnyEvent.
		2363
		2364	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2365	the actual event loop, only with extremely fast event loops such as EV
		2366	adds AnyEvent significant overhead.
		2367
		2368	=item * You should avoid POE like the plague if you want performance or
		2369	reasonable memory usage.
		2370
		2371	=back
		2372
		2373	=head2 BENCHMARKING THE LARGE SERVER CASE
		2374
		2375	This benchmark actually benchmarks the event loop itself. It works by
		2376	creating a number of "servers": each server consists of a socket pair, a
		2377	timeout watcher that gets reset on activity (but never fires), and an I/O
		2378	watcher waiting for input on one side of the socket. Each time the socket
		2379	watcher reads a byte it will write that byte to a random other "server".
		2380
		2381	The effect is that there will be a lot of I/O watchers, only part of which
		2382	are active at any one point (so there is a constant number of active
		2383	fds for each loop iteration, but which fds these are is random). The
		2384	timeout is reset each time something is read because that reflects how
		2385	most timeouts work (and puts extra pressure on the event loops).
		2386
		2387	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2388	(1%) are active. This mirrors the activity of large servers with many
		2389	connections, most of which are idle at any one point in time.
		2390
		2391	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2392	distribution. It uses the L<AE> interface, which makes a real difference
		2393	for the EV and Perl backends only.
		2394
		2395	=head3 Explanation of the columns
		2396
		2397	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2398	each server has a read and write socket end).
		2399
		2400	I<create> is the time it takes to create a socket pair (which is
		2401	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2402
		2403	I<request>, the most important value, is the time it takes to handle a
		2404	single "request", that is, reading the token from the pipe and forwarding
		2405	it to another server. This includes deleting the old timeout and creating
		2406	a new one that moves the timeout into the future.
		2407
		2408	=head3 Results
		2409
		2410	name sockets create request
		2411	EV 20000 62.66 7.99
		2412	Perl 20000 68.32 32.64
		2413	IOAsync 20000 174.06 101.15 epoll
		2414	IOAsync 20000 174.67 610.84 poll
		2415	Event 20000 202.69 242.91
		2416	Glib 20000 557.01 1689.52
		2417	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2418
		2419	=head3 Discussion
		2420
		2421	This benchmark I<does> measure scalability and overall performance of the
		2422	particular event loop.
		2423
		2424	EV is again fastest. Since it is using epoll on my system, the setup time
		2425	is relatively high, though.
		2426
		2427	Perl surprisingly comes second. It is much faster than the C-based event
		2428	loops Event and Glib.
		2429
		2430	IO::Async performs very well when using its epoll backend, and still quite
		2431	good compared to Glib when using its pure perl backend.
		2432
		2433	Event suffers from high setup time as well (look at its code and you will
		2434	understand why). Callback invocation also has a high overhead compared to
		2435	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2436	uses select or poll in basically all documented configurations.
		2437
		2438	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2439	clearly fails to perform with many filehandles or in busy servers.
		2440
		2441	POE is still completely out of the picture, taking over 1000 times as long
		2442	as EV, and over 100 times as long as the Perl implementation, even though
		2443	it uses a C-based event loop in this case.
		2444
		2445	=head3 Summary
		2446
		2447	=over 4
		2448
		2449	=item * The pure perl implementation performs extremely well.
		2450
		2451	=item * Avoid Glib or POE in large projects where performance matters.
		2452
		2453	=back
		2454
		2455	=head2 BENCHMARKING SMALL SERVERS
		2456
		2457	While event loops should scale (and select-based ones do not...) even to
		2458	large servers, most programs we (or I :) actually write have only a few
		2459	I/O watchers.
		2460
		2461	In this benchmark, I use the same benchmark program as in the large server
		2462	case, but it uses only eight "servers", of which three are active at any
		2463	one time. This should reflect performance for a small server relatively
		2464	well.
		2465
		2466	The columns are identical to the previous table.
		2467
		2468	=head3 Results
		2469
		2470	name sockets create request
		2471	EV 16 20.00 6.54
		2472	Perl 16 25.75 12.62
		2473	Event 16 81.27 35.86
		2474	Glib 16 32.63 15.48
		2475	POE 16 261.87 276.28 uses POE::Loop::Event
		2476
		2477	=head3 Discussion
		2478
		2479	The benchmark tries to test the performance of a typical small
		2480	server. While knowing how various event loops perform is interesting, keep
		2481	in mind that their overhead in this case is usually not as important, due
		2482	to the small absolute number of watchers (that is, you need efficiency and
		2483	speed most when you have lots of watchers, not when you only have a few of
		2484	them).
		2485
		2486	EV is again fastest.
		2487
		2488	Perl again comes second. It is noticeably faster than the C-based event
		2489	loops Event and Glib, although the difference is too small to really
		2490	matter.
		2491
		2492	POE also performs much better in this case, but is is still far behind the
		2493	others.
		2494
		2495	=head3 Summary
		2496
		2497	=over 4
		2498
		2499	=item * C-based event loops perform very well with small number of
		2500	watchers, as the management overhead dominates.
		2501
		2502	=back
		2503
		2504	=head2 THE IO::Lambda BENCHMARK
		2505
		2506	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2507	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2508	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2509	shouldn't come as a surprise to anybody). As such, the benchmark is
		2510	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2511	very optimal. But how would AnyEvent compare when used without the extra
		2512	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2513
		2514	The benchmark itself creates an echo-server, and then, for 500 times,
		2515	connects to the echo server, sends a line, waits for the reply, and then
		2516	creates the next connection. This is a rather bad benchmark, as it doesn't
		2517	test the efficiency of the framework or much non-blocking I/O, but it is a
		2518	benchmark nevertheless.
		2519
		2520	name runtime
		2521	Lambda/select 0.330 sec
		2522	+ optimized 0.122 sec
		2523	Lambda/AnyEvent 0.327 sec
		2524	+ optimized 0.138 sec
		2525	Raw sockets/select 0.077 sec
		2526	POE/select, components 0.662 sec
		2527	POE/select, raw sockets 0.226 sec
		2528	POE/select, optimized 0.404 sec
		2529
		2530	AnyEvent/select/nb 0.085 sec
		2531	AnyEvent/EV/nb 0.068 sec
		2532	+state machine 0.134 sec
		2533
		2534	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2535	benchmarks actually make blocking connects and use 100% blocking I/O,
		2536	defeating the purpose of an event-based solution. All of the newly
		2537	written AnyEvent benchmarks use 100% non-blocking connects (using
		2538	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2539	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2540	generally require a lot more bookkeeping and event handling than blocking
		2541	connects (which involve a single syscall only).
		2542
		2543	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2544	offers similar expressive power as POE and IO::Lambda, using conventional
		2545	Perl syntax. This means that both the echo server and the client are 100%
		2546	non-blocking, further placing it at a disadvantage.
		2547
		2548	As you can see, the AnyEvent + EV combination even beats the
		2549	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2550	backend easily beats IO::Lambda and POE.
		2551
		2552	And even the 100% non-blocking version written using the high-level (and
		2553	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2554	higher level ("unoptimised") abstractions by a large margin, even though
		2555	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2556
		2557	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2558	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2559	part of the IO::Lambda distribution and were used without any changes.
		2560
		2561
		2562	=head1 SIGNALS
		2563
		2564	AnyEvent currently installs handlers for these signals:
		2565
		2566	=over 4
		2567
		2568	=item SIGCHLD
		2569
		2570	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2571	emulation for event loops that do not support them natively. Also, some
		2572	event loops install a similar handler.
		2573
		2574	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2575	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2576
		2577	=item SIGPIPE
		2578
		2579	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2580	when AnyEvent gets loaded.
		2581
		2582	The rationale for this is that AnyEvent users usually do not really depend
		2583	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2584	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2585	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2586	some random socket.
		2587
		2588	The rationale for installing a no-op handler as opposed to ignoring it is
		2589	that this way, the handler will be restored to defaults on exec.
		2590
		2591	Feel free to install your own handler, or reset it to defaults.
		2592
		2593	=back
		2594
		2595	=cut
		2596
		2597	undef $SIG{CHLD}
		2598	if $SIG{CHLD} eq 'IGNORE';
		2599
		2600	$SIG{PIPE} = sub { }
		2601	unless defined $SIG{PIPE};
		2602
		2603	=head1 RECOMMENDED/OPTIONAL MODULES
		2604
		2605	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2606	its built-in modules) are required to use it.
		2607
		2608	That does not mean that AnyEvent won't take advantage of some additional
		2609	modules if they are installed.
		2610
		2611	This section explains which additional modules will be used, and how they
		2612	affect AnyEvent's operation.
		2613
		2614	=over 4
		2615
		2616	=item L<Async::Interrupt>
		2617
		2618	This slightly arcane module is used to implement fast signal handling: To
		2619	my knowledge, there is no way to do completely race-free and quick
		2620	signal handling in pure perl. To ensure that signals still get
		2621	delivered, AnyEvent will start an interval timer to wake up perl (and
		2622	catch the signals) with some delay (default is 10 seconds, look for
		2623	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2624
		2625	If this module is available, then it will be used to implement signal
		2626	catching, which means that signals will not be delayed, and the event loop
		2627	will not be interrupted regularly, which is more efficient (and good for
		2628	battery life on laptops).
		2629
		2630	This affects not just the pure-perl event loop, but also other event loops
		2631	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2632
		2633	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2634	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2635	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2636	does nothing for those backends.
		2637
		2638	=item L<EV>
		2639
		2640	This module isn't really "optional", as it is simply one of the backend
		2641	event loops that AnyEvent can use. However, it is simply the best event
		2642	loop available in terms of features, speed and stability: It supports
		2643	the AnyEvent API optimally, implements all the watcher types in XS, does
		2644	automatic timer adjustments even when no monotonic clock is available,
		2645	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2646	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2647	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2648
		2649	If you only use backends that rely on another event loop (e.g. C<Tk>),
		2650	then this module will do nothing for you.
		2651
		2652	=item L<Guard>
		2653
		2654	The guard module, when used, will be used to implement
		2655	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2656	lot less memory), but otherwise doesn't affect guard operation much. It is
		2657	purely used for performance.
		2658
		2659	=item L<JSON> and L<JSON::XS>
		2660
		2661	One of these modules is required when you want to read or write JSON data
		2662	via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
		2663	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2664
		2665	=item L<Net::SSLeay>
		2666
		2667	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2668	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2669	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2670
		2671	=item L<Time::HiRes>
		2672
		2673	This module is part of perl since release 5.008. It will be used when the
		2674	chosen event library does not come with a timing source of its own. The
		2675	pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
		2676	try to use a monotonic clock for timing stability.
		2677
		2678	=back
		2679
		2680
		2681	=head1 FORK
		2682
		2683	Most event libraries are not fork-safe. The ones who are usually are
		2684	because they rely on inefficient but fork-safe C<select> or C<poll> calls
		2685	- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
		2686	are usually badly thought-out hacks that are incompatible with fork in
		2687	one way or another. Only L<EV> is fully fork-aware and ensures that you
		2688	continue event-processing in both parent and child (or both, if you know
		2689	what you are doing).
		2690
		2691	This means that, in general, you cannot fork and do event processing in
		2692	the child if the event library was initialised before the fork (which
		2693	usually happens when the first AnyEvent watcher is created, or the library
		2694	is loaded).
		2695
		2696	If you have to fork, you must either do so I<before> creating your first
		2697	watcher OR you must not use AnyEvent at all in the child OR you must do
		2698	something completely out of the scope of AnyEvent.
		2699
		2700	The problem of doing event processing in the parent I<and> the child
		2701	is much more complicated: even for backends that I<are> fork-aware or
		2702	fork-safe, their behaviour is not usually what you want: fork clones all
		2703	watchers, that means all timers, I/O watchers etc. are active in both
		2704	parent and child, which is almost never what you want. USing C<exec>
		2705	to start worker children from some kind of manage rprocess is usually
		2706	preferred, because it is much easier and cleaner, at the expense of having
		2707	to have another binary.
		2708
		2709
		2710	=head1 SECURITY CONSIDERATIONS
		2711
		2712	AnyEvent can be forced to load any event model via
		2713	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2714	execute arbitrary code or directly gain access, it can easily be used to
		2715	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2716	will not be active when the program uses a different event model than
		2717	specified in the variable.
		2718
		2719	You can make AnyEvent completely ignore this variable by deleting it
		2720	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2721
		2722	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2723
		2724	use AnyEvent;
		2725
		2726	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2727	be used to probe what backend is used and gain other information (which is
		2728	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2729	$ENV{PERL_ANYEVENT_STRICT}.
		2730
		2731	Note that AnyEvent will remove I<all> environment variables starting with
		2732	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2733	enabled.
		2734
		2735
		2736	=head1 BUGS
		2737
		2738	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2739	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2740	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2741	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2742	pronounced).
		2743
800		2744
801	=head1 SEE ALSO	2745	=head1 SEE ALSO
802		2746
		2747	Tutorial/Introduction: L<AnyEvent::Intro>.
		2748
		2749	FAQ: L<AnyEvent::FAQ>.
		2750
		2751	Utility functions: L<AnyEvent::Util>.
		2752
803	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	2753	Event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>, L<Glib::EV>,
804	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.	2754	L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
805		2755
806	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
807	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	2756	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	2757	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2758	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2759	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
809		2760
		2761	Non-blocking file handles, sockets, TCP clients and
		2762	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2763
		2764	Asynchronous DNS: L<AnyEvent::DNS>.
		2765
		2766	Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
		2767
810	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	2768	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
		2769	L<AnyEvent::HTTP>.
811		2770
812	=head1	2771
		2772	=head1 AUTHOR
		2773
		2774	Marc Lehmann <schmorp@schmorp.de>
		2775	http://home.schmorp.de/
813		2776
814	=cut	2777	=cut
815		2778
816	1	2779	1
817		2780

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