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Revision 1.297 by root, Thu Nov 19 01:55:57 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - the DBI of event loop programming
4		4
5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, Qt
		6	and POE are various supported event loops/environments.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# file descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	13	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		14
		15	# one-shot or repeating timers
		16	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		17	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		18
		19	print AnyEvent->now; # prints current event loop time
		20	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		21
		22	# POSIX signal
		23	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		24
		25	# child process exit
		26	my $w = AnyEvent->child (pid => $pid, cb => sub {
		27	my ($pid, $status) = @_;
12	...	28	...
13	});	29	});
14		30
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	31	# called when event loop idle (if applicable)
16	...	32	my $w = AnyEvent->idle (cb => sub { ... });
17	});
18		33
19	my $w = AnyEvent->condvar; # stores whether a condition was flagged	34	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		35	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	36	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	37	# use a condvar in callback mode:
		38	$w->cb (sub { $_[0]->recv });
		39
		40	=head1 INTRODUCTION/TUTORIAL
		41
		42	This manpage is mainly a reference manual. If you are interested
		43	in a tutorial or some gentle introduction, have a look at the
		44	L<AnyEvent::Intro> manpage.
		45
		46	=head1 SUPPORT
		47
		48	There is a mailinglist for discussing all things AnyEvent, and an IRC
		49	channel, too.
		50
		51	See the AnyEvent project page at the B<Schmorpforge Ta-Sa Software
		52	Repository>, at L<http://anyevent.schmorp.de>, for more info.
22		53
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	54	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		55
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	56	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	57	nowadays. So what is different about AnyEvent?
27		58
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	59	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
29	policy> and AnyEvent is I<small and efficient>.	60	policy> and AnyEvent is I<small and efficient>.
30		61
31	First and foremost, I<AnyEvent is not an event model> itself, it only	62	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	63	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,	64	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,	65	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	66	only one event loop can be active at the same time in a process. AnyEvent
36	helps hiding the differences between those event loops.	67	cannot change this, but it can hide the differences between those event
		68	loops.
37		69
38	The goal of AnyEvent is to offer module authors the ability to do event	70	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	71	programming (waiting for I/O or timer events) without subscribing to a
40	religion, a way of living, and most importantly: without forcing your	72	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	73	module users into the same thing by forcing them to use the same event
42	model you use.	74	model you use.
43		75
44	For modules like POE or IO::Async (which is a total misnomer as it is	76	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	77	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	78	like joining a cult: After you joined, you are dependent on them and you
47	cannot use anything else, as it is simply incompatible to everything that	79	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	80	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.	81	module are I<also> forced to use the same event loop you use.
50		82
51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	83	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	84	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	85	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
54	your module uses one of those, every user of your module has to use it,	86	your module uses one of those, every user of your module has to use it,
55	too. But if your module uses AnyEvent, it works transparently with all	87	too. But if your module uses AnyEvent, it works transparently with all
56	event models it supports (including stuff like POE and IO::Async, as long	88	event models it supports (including stuff like IO::Async, as long as those
57	as those use one of the supported event loops. It is trivial to add new	89	use one of the supported event loops. It is trivial to add new event loops
58	event loops to AnyEvent, too, so it is future-proof).	90	to AnyEvent, too, so it is future-proof).
59		91
60	In addition to being free of having to use I<the one and only true event	92	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	93	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	94	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	95	follow. AnyEvent, on the other hand, is lean and up to the point, by only
64	offering the functionality that is necessary, in as thin as a wrapper as	96	offering the functionality that is necessary, in as thin as a wrapper as
65	technically possible.	97	technically possible.
66		98
		99	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		100	of useful functionality, such as an asynchronous DNS resolver, 100%
		101	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		102	such as Windows) and lots of real-world knowledge and workarounds for
		103	platform bugs and differences.
		104
67	Of course, if you want lots of policy (this can arguably be somewhat	105	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	106	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	107	model, you should I<not> use this module.
70
71		108
72	=head1 DESCRIPTION	109	=head1 DESCRIPTION
73		110
74	L<AnyEvent> provides an identical interface to multiple event loops. This	111	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	112	allows module authors to utilise an event loop without forcing module
…		…
79	The interface itself is vaguely similar, but not identical to the L<Event>	116	The interface itself is vaguely similar, but not identical to the L<Event>
80	module.	117	module.
81		118
82	During the first call of any watcher-creation method, the module tries	119	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	120	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>,	121	following modules is already loaded: L<EV>,
85	L<Event>, L<Glib>, L<Tk>, L<AnyEvent::Impl::Perl>, L<Event::Lib>, L<Qt>,	122	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	L<POE>. The first one found is used. If none are found, the module tries	123	L<POE>. The first one found is used. If none are found, the module tries
87	to load these modules (excluding Event::Lib, Qt and POE as the pure perl	124	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
88	adaptor should always succeed) in the order given. The first one that can	125	adaptor should always succeed) in the order given. The first one that can
89	be successfully loaded will be used. If, after this, still none could be	126	be successfully loaded will be used. If, after this, still none could be
90	found, AnyEvent will fall back to a pure-perl event loop, which is not	127	found, AnyEvent will fall back to a pure-perl event loop, which is not
91	very efficient, but should work everywhere.	128	very efficient, but should work everywhere.
92		129
…		…
103	starts using it, all bets are off. Maybe you should tell their authors to	140	starts using it, all bets are off. Maybe you should tell their authors to
104	use AnyEvent so their modules work together with others seamlessly...	141	use AnyEvent so their modules work together with others seamlessly...
105		142
106	The pure-perl implementation of AnyEvent is called	143	The pure-perl implementation of AnyEvent is called
107	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	144	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
108	explicitly.	145	explicitly and enjoy the high availability of that event loop :)
109		146
110	=head1 WATCHERS	147	=head1 WATCHERS
111		148
112	AnyEvent has the central concept of a I<watcher>, which is an object that	149	AnyEvent has the central concept of a I<watcher>, which is an object that
113	stores relevant data for each kind of event you are waiting for, such as	150	stores relevant data for each kind of event you are waiting for, such as
114	the callback to call, the filehandle to watch, etc.	151	the callback to call, the file handle to watch, etc.
115		152
116	These watchers are normal Perl objects with normal Perl lifetime. After	153	These watchers are normal Perl objects with normal Perl lifetime. After
117	creating a watcher it will immediately "watch" for events and invoke the	154	creating a watcher it will immediately "watch" for events and invoke the
118	callback when the event occurs (of course, only when the event model	155	callback when the event occurs (of course, only when the event model
119	is in control).	156	is in control).
120		157
		158	Note that B<callbacks must not permanently change global variables>
		159	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		160	callbacks must not C<die> >>. The former is good programming practise in
		161	Perl and the latter stems from the fact that exception handling differs
		162	widely between event loops.
		163
121	To disable the watcher you have to destroy it (e.g. by setting the	164	To disable the watcher you have to destroy it (e.g. by setting the
122	variable you store it in to C<undef> or otherwise deleting all references	165	variable you store it in to C<undef> or otherwise deleting all references
123	to it).	166	to it).
124		167
125	All watchers are created by calling a method on the C<AnyEvent> class.	168	All watchers are created by calling a method on the C<AnyEvent> class.
…		…
127	Many watchers either are used with "recursion" (repeating timers for	170	Many watchers either are used with "recursion" (repeating timers for
128	example), or need to refer to their watcher object in other ways.	171	example), or need to refer to their watcher object in other ways.
129		172
130	An any way to achieve that is this pattern:	173	An any way to achieve that is this pattern:
131		174
132	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	175	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
133	# you can use $w here, for example to undef it	176	# you can use $w here, for example to undef it
134	undef $w;	177	undef $w;
135	});	178	});
136		179
137	Note that C<my $w; $w => combination. This is necessary because in Perl,	180	Note that C<my $w; $w => combination. This is necessary because in Perl,
138	my variables are only visible after the statement in which they are	181	my variables are only visible after the statement in which they are
139	declared.	182	declared.
140		183
141	=head2 IO WATCHERS	184	=head2 I/O WATCHERS
		185
		186	$w = AnyEvent->io (
		187	fh => <filehandle_or_fileno>,
		188	poll => <"r" or "w">,
		189	cb => <callback>,
		190	);
142		191
143	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	192	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
144	with the following mandatory key-value pairs as arguments:	193	with the following mandatory key-value pairs as arguments:
145		194
146	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	195	C<fh> is the Perl I<file handle> (or a naked file descriptor) to watch
		196	for events (AnyEvent might or might not keep a reference to this file
		197	handle). Note that only file handles pointing to things for which
		198	non-blocking operation makes sense are allowed. This includes sockets,
		199	most character devices, pipes, fifos and so on, but not for example files
		200	or block devices.
		201
147	events. C<poll> must be a string that is either C<r> or C<w>, which	202	C<poll> must be a string that is either C<r> or C<w>, which creates a
148	creates a watcher waiting for "r"eadable or "w"ritable events,	203	watcher waiting for "r"eadable or "w"ritable events, respectively.
		204
149	respectively. C<cb> is the callback to invoke each time the file handle	205	C<cb> is the callback to invoke each time the file handle becomes ready.
150	becomes ready.
151		206
152	As long as the I/O watcher exists it will keep the file descriptor or a	207	Although the callback might get passed parameters, their value and
153	copy of it alive/open.	208	presence is undefined and you cannot rely on them. Portable AnyEvent
		209	callbacks cannot use arguments passed to I/O watcher callbacks.
154		210
		211	The I/O watcher might use the underlying file descriptor or a copy of it.
155	It is not allowed to close a file handle as long as any watcher is active	212	You must not close a file handle as long as any watcher is active on the
156	on the underlying file descriptor.	213	underlying file descriptor.
157		214
158	Some event loops issue spurious readyness notifications, so you should	215	Some event loops issue spurious readyness notifications, so you should
159	always use non-blocking calls when reading/writing from/to your file	216	always use non-blocking calls when reading/writing from/to your file
160	handles.	217	handles.
161		218
162	Example:
163
164	# wait for readability of STDIN, then read a line and disable the watcher	219	Example: wait for readability of STDIN, then read a line and disable the
		220	watcher.
		221
165	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	222	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
166	chomp (my $input = <STDIN>);	223	chomp (my $input = <STDIN>);
167	warn "read: $input\n";	224	warn "read: $input\n";
168	undef $w;	225	undef $w;
169	});	226	});
170		227
171	=head2 TIME WATCHERS	228	=head2 TIME WATCHERS
172		229
		230	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		231
		232	$w = AnyEvent->timer (
		233	after => <fractional_seconds>,
		234	interval => <fractional_seconds>,
		235	cb => <callback>,
		236	);
		237
173	You can create a time watcher by calling the C<< AnyEvent->timer >>	238	You can create a time watcher by calling the C<< AnyEvent->timer >>
174	method with the following mandatory arguments:	239	method with the following mandatory arguments:
175		240
176	C<after> specifies after how many seconds (fractional values are	241	C<after> specifies after how many seconds (fractional values are
177	supported) should the timer activate. C<cb> the callback to invoke in that	242	supported) the callback should be invoked. C<cb> is the callback to invoke
178	case.	243	in that case.
179		244
180	The timer callback will be invoked at most once: if you want a repeating	245	Although the callback might get passed parameters, their value and
181	timer you have to create a new watcher (this is a limitation by both Tk	246	presence is undefined and you cannot rely on them. Portable AnyEvent
182	and Glib).	247	callbacks cannot use arguments passed to time watcher callbacks.
183		248
184	Example:	249	The callback will normally be invoked once only. If you specify another
		250	parameter, C<interval>, as a strictly positive number (> 0), then the
		251	callback will be invoked regularly at that interval (in fractional
		252	seconds) after the first invocation. If C<interval> is specified with a
		253	false value, then it is treated as if it were missing.
185		254
		255	The callback will be rescheduled before invoking the callback, but no
		256	attempt is done to avoid timer drift in most backends, so the interval is
		257	only approximate.
		258
186	# fire an event after 7.7 seconds	259	Example: fire an event after 7.7 seconds.
		260
187	my $w = AnyEvent->timer (after => 7.7, cb => sub {	261	my $w = AnyEvent->timer (after => 7.7, cb => sub {
188	warn "timeout\n";	262	warn "timeout\n";
189	});	263	});
190		264
191	# to cancel the timer:	265	# to cancel the timer:
192	undef $w;	266	undef $w;
193		267
194	Example 2:
195
196	# fire an event after 0.5 seconds, then roughly every second	268	Example 2: fire an event after 0.5 seconds, then roughly every second.
197	my $w;
198		269
199	my $cb = sub {
200	# cancel the old timer while creating a new one
201	$w = AnyEvent->timer (after => 1, cb => $cb);	270	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		271	warn "timeout\n";
202	};	272	};
203
204	# start the "loop" by creating the first watcher
205	$w = AnyEvent->timer (after => 0.5, cb => $cb);
206		273
207	=head3 TIMING ISSUES	274	=head3 TIMING ISSUES
208		275
209	There are two ways to handle timers: based on real time (relative, "fire	276	There are two ways to handle timers: based on real time (relative, "fire
210	in 10 seconds") and based on wallclock time (absolute, "fire at 12	277	in 10 seconds") and based on wallclock time (absolute, "fire at 12
…		…
222	timers.	289	timers.
223		290
224	AnyEvent always prefers relative timers, if available, matching the	291	AnyEvent always prefers relative timers, if available, matching the
225	AnyEvent API.	292	AnyEvent API.
226		293
		294	AnyEvent has two additional methods that return the "current time":
		295
		296	=over 4
		297
		298	=item AnyEvent->time
		299
		300	This returns the "current wallclock time" as a fractional number of
		301	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		302	return, and the result is guaranteed to be compatible with those).
		303
		304	It progresses independently of any event loop processing, i.e. each call
		305	will check the system clock, which usually gets updated frequently.
		306
		307	=item AnyEvent->now
		308
		309	This also returns the "current wallclock time", but unlike C<time>, above,
		310	this value might change only once per event loop iteration, depending on
		311	the event loop (most return the same time as C<time>, above). This is the
		312	time that AnyEvent's timers get scheduled against.
		313
		314	I<In almost all cases (in all cases if you don't care), this is the
		315	function to call when you want to know the current time.>
		316
		317	This function is also often faster then C<< AnyEvent->time >>, and
		318	thus the preferred method if you want some timestamp (for example,
		319	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		320
		321	The rest of this section is only of relevance if you try to be very exact
		322	with your timing, you can skip it without bad conscience.
		323
		324	For a practical example of when these times differ, consider L<Event::Lib>
		325	and L<EV> and the following set-up:
		326
		327	The event loop is running and has just invoked one of your callback at
		328	time=500 (assume no other callbacks delay processing). In your callback,
		329	you wait a second by executing C<sleep 1> (blocking the process for a
		330	second) and then (at time=501) you create a relative timer that fires
		331	after three seconds.
		332
		333	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		334	both return C<501>, because that is the current time, and the timer will
		335	be scheduled to fire at time=504 (C<501> + C<3>).
		336
		337	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		338	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		339	last event processing phase started. With L<EV>, your timer gets scheduled
		340	to run at time=503 (C<500> + C<3>).
		341
		342	In one sense, L<Event::Lib> is more exact, as it uses the current time
		343	regardless of any delays introduced by event processing. However, most
		344	callbacks do not expect large delays in processing, so this causes a
		345	higher drift (and a lot more system calls to get the current time).
		346
		347	In another sense, L<EV> is more exact, as your timer will be scheduled at
		348	the same time, regardless of how long event processing actually took.
		349
		350	In either case, if you care (and in most cases, you don't), then you
		351	can get whatever behaviour you want with any event loop, by taking the
		352	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		353	account.
		354
		355	=item AnyEvent->now_update
		356
		357	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		358	the current time for each loop iteration (see the discussion of L<<
		359	AnyEvent->now >>, above).
		360
		361	When a callback runs for a long time (or when the process sleeps), then
		362	this "current" time will differ substantially from the real time, which
		363	might affect timers and time-outs.
		364
		365	When this is the case, you can call this method, which will update the
		366	event loop's idea of "current time".
		367
		368	A typical example would be a script in a web server (e.g. C<mod_perl>) -
		369	when mod_perl executes the script, then the event loop will have the wrong
		370	idea about the "current time" (being potentially far in the past, when the
		371	script ran the last time). In that case you should arrange a call to C<<
		372	AnyEvent->now_update >> each time the web server process wakes up again
		373	(e.g. at the start of your script, or in a handler).
		374
		375	Note that updating the time I<might> cause some events to be handled.
		376
		377	=back
		378
227	=head2 SIGNAL WATCHERS	379	=head2 SIGNAL WATCHERS
228		380
		381	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		382
229	You can watch for signals using a signal watcher, C<signal> is the signal	383	You can watch for signals using a signal watcher, C<signal> is the signal
230	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	384	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
231	be invoked whenever a signal occurs.	385	callback to be invoked whenever a signal occurs.
232		386
		387	Although the callback might get passed parameters, their value and
		388	presence is undefined and you cannot rely on them. Portable AnyEvent
		389	callbacks cannot use arguments passed to signal watcher callbacks.
		390
233	Multiple signal occurances can be clumped together into one callback	391	Multiple signal occurrences can be clumped together into one callback
234	invocation, and callback invocation will be synchronous. synchronous means	392	invocation, and callback invocation will be synchronous. Synchronous means
235	that it might take a while until the signal gets handled by the process,	393	that it might take a while until the signal gets handled by the process,
236	but it is guarenteed not to interrupt any other callbacks.	394	but it is guaranteed not to interrupt any other callbacks.
237		395
238	The main advantage of using these watchers is that you can share a signal	396	The main advantage of using these watchers is that you can share a signal
239	between multiple watchers.	397	between multiple watchers, and AnyEvent will ensure that signals will not
		398	interrupt your program at bad times.
240		399
241	This watcher might use C<%SIG>, so programs overwriting those signals	400	This watcher might use C<%SIG> (depending on the event loop used),
242	directly will likely not work correctly.	401	so programs overwriting those signals directly will likely not work
		402	correctly.
243		403
244	Example: exit on SIGINT	404	Example: exit on SIGINT
245		405
246	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	406	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
247		407
		408	=head3 Signal Races, Delays and Workarounds
		409
		410	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		411	callbacks to signals in a generic way, which is a pity, as you cannot
		412	do race-free signal handling in perl, requiring C libraries for
		413	this. AnyEvent will try to do it's best, which means in some cases,
		414	signals will be delayed. The maximum time a signal might be delayed is
		415	specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10 seconds). This
		416	variable can be changed only before the first signal watcher is created,
		417	and should be left alone otherwise. This variable determines how often
		418	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		419	will cause fewer spurious wake-ups, which is better for power and CPU
		420	saving.
		421
		422	All these problems can be avoided by installing the optional
		423	L<Async::Interrupt> module, which works with most event loops. It will not
		424	work with inherently broken event loops such as L<Event> or L<Event::Lib>
		425	(and not with L<POE> currently, as POE does it's own workaround with
		426	one-second latency). For those, you just have to suffer the delays.
		427
248	=head2 CHILD PROCESS WATCHERS	428	=head2 CHILD PROCESS WATCHERS
249		429
		430	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		431
250	You can also watch on a child process exit and catch its exit status.	432	You can also watch on a child process exit and catch its exit status.
251		433
252	The child process is specified by the C<pid> argument (if set to C<0>, it	434	The child process is specified by the C<pid> argument (one some backends,
253	watches for any child process exit). The watcher will trigger as often	435	using C<0> watches for any child process exit, on others this will
254	as status change for the child are received. This works by installing a	436	croak). The watcher will be triggered only when the child process has
255	signal handler for C<SIGCHLD>. The callback will be called with the pid	437	finished and an exit status is available, not on any trace events
256	and exit status (as returned by waitpid).	438	(stopped/continued).
257		439
258	Example: wait for pid 1333	440	The callback will be called with the pid and exit status (as returned by
		441	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		442	callback arguments.
259		443
		444	This watcher type works by installing a signal handler for C<SIGCHLD>,
		445	and since it cannot be shared, nothing else should use SIGCHLD or reap
		446	random child processes (waiting for specific child processes, e.g. inside
		447	C<system>, is just fine).
		448
		449	There is a slight catch to child watchers, however: you usually start them
		450	I<after> the child process was created, and this means the process could
		451	have exited already (and no SIGCHLD will be sent anymore).
		452
		453	Not all event models handle this correctly (neither POE nor IO::Async do,
		454	see their AnyEvent::Impl manpages for details), but even for event models
		455	that I<do> handle this correctly, they usually need to be loaded before
		456	the process exits (i.e. before you fork in the first place). AnyEvent's
		457	pure perl event loop handles all cases correctly regardless of when you
		458	start the watcher.
		459
		460	This means you cannot create a child watcher as the very first
		461	thing in an AnyEvent program, you I<have> to create at least one
		462	watcher before you C<fork> the child (alternatively, you can call
		463	C<AnyEvent::detect>).
		464
		465	As most event loops do not support waiting for child events, they will be
		466	emulated by AnyEvent in most cases, in which the latency and race problems
		467	mentioned in the description of signal watchers apply.
		468
		469	Example: fork a process and wait for it
		470
		471	my $done = AnyEvent->condvar;
		472
		473	my $pid = fork or exit 5;
		474
260	my $w = AnyEvent->child (	475	my $w = AnyEvent->child (
261	pid => 1333,	476	pid => $pid,
262	cb => sub {	477	cb => sub {
263	my ($pid, $status) = @_;	478	my ($pid, $status) = @_;
264	warn "pid $pid exited with status $status";	479	warn "pid $pid exited with status $status";
		480	$done->send;
265	},	481	},
266	);	482	);
		483
		484	# do something else, then wait for process exit
		485	$done->recv;
		486
		487	=head2 IDLE WATCHERS
		488
		489	$w = AnyEvent->idle (cb => <callback>);
		490
		491	Sometimes there is a need to do something, but it is not so important
		492	to do it instantly, but only when there is nothing better to do. This
		493	"nothing better to do" is usually defined to be "no other events need
		494	attention by the event loop".
		495
		496	Idle watchers ideally get invoked when the event loop has nothing
		497	better to do, just before it would block the process to wait for new
		498	events. Instead of blocking, the idle watcher is invoked.
		499
		500	Most event loops unfortunately do not really support idle watchers (only
		501	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		502	will simply call the callback "from time to time".
		503
		504	Example: read lines from STDIN, but only process them when the
		505	program is otherwise idle:
		506
		507	my @lines; # read data
		508	my $idle_w;
		509	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		510	push @lines, scalar <STDIN>;
		511
		512	# start an idle watcher, if not already done
		513	$idle_w ||= AnyEvent->idle (cb => sub {
		514	# handle only one line, when there are lines left
		515	if (my $line = shift @lines) {
		516	print "handled when idle: $line";
		517	} else {
		518	# otherwise disable the idle watcher again
		519	undef $idle_w;
		520	}
		521	});
		522	});
267		523
268	=head2 CONDITION VARIABLES	524	=head2 CONDITION VARIABLES
269		525
		526	$cv = AnyEvent->condvar;
		527
		528	$cv->send (<list>);
		529	my @res = $cv->recv;
		530
		531	If you are familiar with some event loops you will know that all of them
		532	require you to run some blocking "loop", "run" or similar function that
		533	will actively watch for new events and call your callbacks.
		534
		535	AnyEvent is slightly different: it expects somebody else to run the event
		536	loop and will only block when necessary (usually when told by the user).
		537
		538	The instrument to do that is called a "condition variable", so called
		539	because they represent a condition that must become true.
		540
		541	Now is probably a good time to look at the examples further below.
		542
270	Condition variables can be created by calling the C<< AnyEvent->condvar >>	543	Condition variables can be created by calling the C<< AnyEvent->condvar
271	method without any arguments.	544	>> method, usually without arguments. The only argument pair allowed is
		545	C<cb>, which specifies a callback to be called when the condition variable
		546	becomes true, with the condition variable as the first argument (but not
		547	the results).
272		548
273	A condition variable waits for a condition - precisely that the C<<	549	After creation, the condition variable is "false" until it becomes "true"
274	->broadcast >> method has been called.	550	by calling the C<send> method (or calling the condition variable as if it
		551	were a callback, read about the caveats in the description for the C<<
		552	->send >> method).
275		553
276	They are very useful to signal that a condition has been fulfilled, for	554	Condition variables are similar to callbacks, except that you can
		555	optionally wait for them. They can also be called merge points - points
		556	in time where multiple outstanding events have been processed. And yet
		557	another way to call them is transactions - each condition variable can be
		558	used to represent a transaction, which finishes at some point and delivers
		559	a result. And yet some people know them as "futures" - a promise to
		560	compute/deliver something that you can wait for.
		561
		562	Condition variables are very useful to signal that something has finished,
277	example, if you write a module that does asynchronous http requests,	563	for example, if you write a module that does asynchronous http requests,
278	then a condition variable would be the ideal candidate to signal the	564	then a condition variable would be the ideal candidate to signal the
279	availability of results.	565	availability of results. The user can either act when the callback is
		566	called or can synchronously C<< ->recv >> for the results.
280		567
281	You can also use condition variables to block your main program until	568	You can also use them to simulate traditional event loops - for example,
282	an event occurs - for example, you could C<< ->wait >> in your main	569	you can block your main program until an event occurs - for example, you
283	program until the user clicks the Quit button in your app, which would C<<	570	could C<< ->recv >> in your main program until the user clicks the Quit
284	->broadcast >> the "quit" event.	571	button of your app, which would C<< ->send >> the "quit" event.
285		572
286	Note that condition variables recurse into the event loop - if you have	573	Note that condition variables recurse into the event loop - if you have
287	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	574	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
288	lose. Therefore, condition variables are good to export to your caller, but	575	lose. Therefore, condition variables are good to export to your caller, but
289	you should avoid making a blocking wait yourself, at least in callbacks,	576	you should avoid making a blocking wait yourself, at least in callbacks,
290	as this asks for trouble.	577	as this asks for trouble.
291		578
292	This object has two methods:	579	Condition variables are represented by hash refs in perl, and the keys
		580	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		581	easy (it is often useful to build your own transaction class on top of
		582	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		583	it's C<new> method in your own C<new> method.
293		584
294	=over 4	585	There are two "sides" to a condition variable - the "producer side" which
		586	eventually calls C<< -> send >>, and the "consumer side", which waits
		587	for the send to occur.
295		588
296	=item $cv->wait	589	Example: wait for a timer.
297
298	Wait (blocking if necessary) until the C<< ->broadcast >> method has been
299	called on c<$cv>, while servicing other watchers normally.
300
301	You can only wait once on a condition - additional calls will return
302	immediately.
303
304	Not all event models support a blocking wait - some die in that case
305	(programs might want to do that to stay interactive), so I<if you are
306	using this from a module, never require a blocking wait>, but let the
307	caller decide whether the call will block or not (for example, by coupling
308	condition variables with some kind of request results and supporting
309	callbacks so the caller knows that getting the result will not block,
310	while still suppporting blocking waits if the caller so desires).
311
312	Another reason I<never> to C<< ->wait >> in a module is that you cannot
313	sensibly have two C<< ->wait >>'s in parallel, as that would require
314	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
315	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
316	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
317	from different coroutines, however).
318
319	=item $cv->broadcast
320
321	Flag the condition as ready - a running C<< ->wait >> and all further
322	calls to C<wait> will (eventually) return after this method has been
323	called. If nobody is waiting the broadcast will be remembered..
324
325	=back
326
327	Example:
328		590
329	# wait till the result is ready	591	# wait till the result is ready
330	my $result_ready = AnyEvent->condvar;	592	my $result_ready = AnyEvent->condvar;
331		593
332	# do something such as adding a timer	594	# do something such as adding a timer
333	# or socket watcher the calls $result_ready->broadcast	595	# or socket watcher the calls $result_ready->send
334	# when the "result" is ready.	596	# when the "result" is ready.
335	# in this case, we simply use a timer:	597	# in this case, we simply use a timer:
336	my $w = AnyEvent->timer (	598	my $w = AnyEvent->timer (
337	after => 1,	599	after => 1,
338	cb => sub { $result_ready->broadcast },	600	cb => sub { $result_ready->send },
339	);	601	);
340		602
341	# this "blocks" (while handling events) till the watcher	603	# this "blocks" (while handling events) till the callback
342	# calls broadcast	604	# calls ->send
343	$result_ready->wait;	605	$result_ready->recv;
		606
		607	Example: wait for a timer, but take advantage of the fact that condition
		608	variables are also callable directly.
		609
		610	my $done = AnyEvent->condvar;
		611	my $delay = AnyEvent->timer (after => 5, cb => $done);
		612	$done->recv;
		613
		614	Example: Imagine an API that returns a condvar and doesn't support
		615	callbacks. This is how you make a synchronous call, for example from
		616	the main program:
		617
		618	use AnyEvent::CouchDB;
		619
		620	...
		621
		622	my @info = $couchdb->info->recv;
		623
		624	And this is how you would just set a callback to be called whenever the
		625	results are available:
		626
		627	$couchdb->info->cb (sub {
		628	my @info = $_[0]->recv;
		629	});
		630
		631	=head3 METHODS FOR PRODUCERS
		632
		633	These methods should only be used by the producing side, i.e. the
		634	code/module that eventually sends the signal. Note that it is also
		635	the producer side which creates the condvar in most cases, but it isn't
		636	uncommon for the consumer to create it as well.
		637
		638	=over 4
		639
		640	=item $cv->send (...)
		641
		642	Flag the condition as ready - a running C<< ->recv >> and all further
		643	calls to C<recv> will (eventually) return after this method has been
		644	called. If nobody is waiting the send will be remembered.
		645
		646	If a callback has been set on the condition variable, it is called
		647	immediately from within send.
		648
		649	Any arguments passed to the C<send> call will be returned by all
		650	future C<< ->recv >> calls.
		651
		652	Condition variables are overloaded so one can call them directly (as if
		653	they were a code reference). Calling them directly is the same as calling
		654	C<send>.
		655
		656	=item $cv->croak ($error)
		657
		658	Similar to send, but causes all call's to C<< ->recv >> to invoke
		659	C<Carp::croak> with the given error message/object/scalar.
		660
		661	This can be used to signal any errors to the condition variable
		662	user/consumer. Doing it this way instead of calling C<croak> directly
		663	delays the error detetcion, but has the overwhelmign advantage that it
		664	diagnoses the error at the place where the result is expected, and not
		665	deep in some event clalback without connection to the actual code causing
		666	the problem.
		667
		668	=item $cv->begin ([group callback])
		669
		670	=item $cv->end
		671
		672	These two methods can be used to combine many transactions/events into
		673	one. For example, a function that pings many hosts in parallel might want
		674	to use a condition variable for the whole process.
		675
		676	Every call to C<< ->begin >> will increment a counter, and every call to
		677	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		678	>>, the (last) callback passed to C<begin> will be executed, passing the
		679	condvar as first argument. That callback is I<supposed> to call C<< ->send
		680	>>, but that is not required. If no group callback was set, C<send> will
		681	be called without any arguments.
		682
		683	You can think of C<< $cv->send >> giving you an OR condition (one call
		684	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		685	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		686
		687	Let's start with a simple example: you have two I/O watchers (for example,
		688	STDOUT and STDERR for a program), and you want to wait for both streams to
		689	close before activating a condvar:
		690
		691	my $cv = AnyEvent->condvar;
		692
		693	$cv->begin; # first watcher
		694	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		695	defined sysread $fh1, my $buf, 4096
		696	or $cv->end;
		697	});
		698
		699	$cv->begin; # second watcher
		700	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		701	defined sysread $fh2, my $buf, 4096
		702	or $cv->end;
		703	});
		704
		705	$cv->recv;
		706
		707	This works because for every event source (EOF on file handle), there is
		708	one call to C<begin>, so the condvar waits for all calls to C<end> before
		709	sending.
		710
		711	The ping example mentioned above is slightly more complicated, as the
		712	there are results to be passwd back, and the number of tasks that are
		713	begung can potentially be zero:
		714
		715	my $cv = AnyEvent->condvar;
		716
		717	my %result;
		718	$cv->begin (sub { shift->send (\%result) });
		719
		720	for my $host (@list_of_hosts) {
		721	$cv->begin;
		722	ping_host_then_call_callback $host, sub {
		723	$result{$host} = ...;
		724	$cv->end;
		725	};
		726	}
		727
		728	$cv->end;
		729
		730	This code fragment supposedly pings a number of hosts and calls
		731	C<send> after results for all then have have been gathered - in any
		732	order. To achieve this, the code issues a call to C<begin> when it starts
		733	each ping request and calls C<end> when it has received some result for
		734	it. Since C<begin> and C<end> only maintain a counter, the order in which
		735	results arrive is not relevant.
		736
		737	There is an additional bracketing call to C<begin> and C<end> outside the
		738	loop, which serves two important purposes: first, it sets the callback
		739	to be called once the counter reaches C<0>, and second, it ensures that
		740	C<send> is called even when C<no> hosts are being pinged (the loop
		741	doesn't execute once).
		742
		743	This is the general pattern when you "fan out" into multiple (but
		744	potentially none) subrequests: use an outer C<begin>/C<end> pair to set
		745	the callback and ensure C<end> is called at least once, and then, for each
		746	subrequest you start, call C<begin> and for each subrequest you finish,
		747	call C<end>.
		748
		749	=back
		750
		751	=head3 METHODS FOR CONSUMERS
		752
		753	These methods should only be used by the consuming side, i.e. the
		754	code awaits the condition.
		755
		756	=over 4
		757
		758	=item $cv->recv
		759
		760	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		761	>> methods have been called on c<$cv>, while servicing other watchers
		762	normally.
		763
		764	You can only wait once on a condition - additional calls are valid but
		765	will return immediately.
		766
		767	If an error condition has been set by calling C<< ->croak >>, then this
		768	function will call C<croak>.
		769
		770	In list context, all parameters passed to C<send> will be returned,
		771	in scalar context only the first one will be returned.
		772
		773	Note that doing a blocking wait in a callback is not supported by any
		774	event loop, that is, recursive invocation of a blocking C<< ->recv
		775	>> is not allowed, and the C<recv> call will C<croak> if such a
		776	condition is detected. This condition can be slightly loosened by using
		777	L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
		778	any thread that doesn't run the event loop itself.
		779
		780	Not all event models support a blocking wait - some die in that case
		781	(programs might want to do that to stay interactive), so I<if you are
		782	using this from a module, never require a blocking wait>. Instead, let the
		783	caller decide whether the call will block or not (for example, by coupling
		784	condition variables with some kind of request results and supporting
		785	callbacks so the caller knows that getting the result will not block,
		786	while still supporting blocking waits if the caller so desires).
		787
		788	You can ensure that C<< -recv >> never blocks by setting a callback and
		789	only calling C<< ->recv >> from within that callback (or at a later
		790	time). This will work even when the event loop does not support blocking
		791	waits otherwise.
		792
		793	=item $bool = $cv->ready
		794
		795	Returns true when the condition is "true", i.e. whether C<send> or
		796	C<croak> have been called.
		797
		798	=item $cb = $cv->cb ($cb->($cv))
		799
		800	This is a mutator function that returns the callback set and optionally
		801	replaces it before doing so.
		802
		803	The callback will be called when the condition becomes (or already was)
		804	"true", i.e. when C<send> or C<croak> are called (or were called), with
		805	the only argument being the condition variable itself. Calling C<recv>
		806	inside the callback or at any later time is guaranteed not to block.
		807
		808	=back
		809
		810	=head1 SUPPORTED EVENT LOOPS/BACKENDS
		811
		812	The available backend classes are (every class has its own manpage):
		813
		814	=over 4
		815
		816	=item Backends that are autoprobed when no other event loop can be found.
		817
		818	EV is the preferred backend when no other event loop seems to be in
		819	use. If EV is not installed, then AnyEvent will fall back to its own
		820	pure-perl implementation, which is available everywhere as it comes with
		821	AnyEvent itself.
		822
		823	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		824	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		825
		826	=item Backends that are transparently being picked up when they are used.
		827
		828	These will be used when they are currently loaded when the first watcher
		829	is created, in which case it is assumed that the application is using
		830	them. This means that AnyEvent will automatically pick the right backend
		831	when the main program loads an event module before anything starts to
		832	create watchers. Nothing special needs to be done by the main program.
		833
		834	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		835	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		836	AnyEvent::Impl::Tk based on Tk, very broken.
		837	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		838	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		839	AnyEvent::Impl::Irssi used when running within irssi.
		840
		841	=item Backends with special needs.
		842
		843	Qt requires the Qt::Application to be instantiated first, but will
		844	otherwise be picked up automatically. As long as the main program
		845	instantiates the application before any AnyEvent watchers are created,
		846	everything should just work.
		847
		848	AnyEvent::Impl::Qt based on Qt.
		849
		850	Support for IO::Async can only be partial, as it is too broken and
		851	architecturally limited to even support the AnyEvent API. It also
		852	is the only event loop that needs the loop to be set explicitly, so
		853	it can only be used by a main program knowing about AnyEvent. See
		854	L<AnyEvent::Impl::Async> for the gory details.
		855
		856	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		857
		858	=item Event loops that are indirectly supported via other backends.
		859
		860	Some event loops can be supported via other modules:
		861
		862	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		863
		864	B<WxWidgets> has no support for watching file handles. However, you can
		865	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		866	polls 20 times per second, which was considered to be too horrible to even
		867	consider for AnyEvent.
		868
		869	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		870	backend, so it can be supported through POE.
		871
		872	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		873	load L<POE> when detecting them, in the hope that POE will pick them up,
		874	in which case everything will be automatic.
		875
		876	=back
344		877
345	=head1 GLOBAL VARIABLES AND FUNCTIONS	878	=head1 GLOBAL VARIABLES AND FUNCTIONS
346		879
		880	These are not normally required to use AnyEvent, but can be useful to
		881	write AnyEvent extension modules.
		882
347	=over 4	883	=over 4
348		884
349	=item $AnyEvent::MODEL	885	=item $AnyEvent::MODEL
350		886
351	Contains C<undef> until the first watcher is being created. Then it	887	Contains C<undef> until the first watcher is being created, before the
		888	backend has been autodetected.
		889
352	contains the event model that is being used, which is the name of the	890	Afterwards it contains the event model that is being used, which is the
353	Perl class implementing the model. This class is usually one of the	891	name of the Perl class implementing the model. This class is usually one
354	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	892	of the C<AnyEvent::Impl:xxx> modules, but can be any other class in the
355	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	893	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
356		894	will be C<urxvt::anyevent>).
357	The known classes so far are:
358
359	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
360	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
361	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
362	AnyEvent::Impl::Event based on Event, second best choice.
363	AnyEvent::Impl::Glib based on Glib, third-best choice.
364	AnyEvent::Impl::Tk based on Tk, very bad choice.
365	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
366	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
367	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
368	AnyEvent::Impl::POE based on POE, not generic enough for full support.
369
370	There is no support for WxWidgets, as WxWidgets has no support for
371	watching file handles. However, you can use WxWidgets through the
372	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
373	second, which was considered to be too horrible to even consider for
374	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
375	it's adaptor.
376
377	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
378	autodetecting them.
379		895
380	=item AnyEvent::detect	896	=item AnyEvent::detect
381		897
382	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	898	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
383	if necessary. You should only call this function right before you would	899	if necessary. You should only call this function right before you would
384	have created an AnyEvent watcher anyway, that is, as late as possible at	900	have created an AnyEvent watcher anyway, that is, as late as possible at
385	runtime.	901	runtime, and not e.g. while initialising of your module.
		902
		903	If you need to do some initialisation before AnyEvent watchers are
		904	created, use C<post_detect>.
		905
		906	=item $guard = AnyEvent::post_detect { BLOCK }
		907
		908	Arranges for the code block to be executed as soon as the event model is
		909	autodetected (or immediately if this has already happened).
		910
		911	The block will be executed I<after> the actual backend has been detected
		912	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		913	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		914	other initialisations - see the sources of L<AnyEvent::Strict> or
		915	L<AnyEvent::AIO> to see how this is used.
		916
		917	The most common usage is to create some global watchers, without forcing
		918	event module detection too early, for example, L<AnyEvent::AIO> creates
		919	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		920	avoid autodetecting the event module at load time.
		921
		922	If called in scalar or list context, then it creates and returns an object
		923	that automatically removes the callback again when it is destroyed (or
		924	C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
		925	a case where this is useful.
		926
		927	Example: Create a watcher for the IO::AIO module and store it in
		928	C<$WATCHER>. Only do so after the event loop is initialised, though.
		929
		930	our WATCHER;
		931
		932	my $guard = AnyEvent::post_detect {
		933	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		934	};
		935
		936	# the ||= is important in case post_detect immediately runs the block,
		937	# as to not clobber the newly-created watcher. assigning both watcher and
		938	# post_detect guard to the same variable has the advantage of users being
		939	# able to just C<undef $WATCHER> if the watcher causes them grief.
		940
		941	$WATCHER ||= $guard;
		942
		943	=item @AnyEvent::post_detect
		944
		945	If there are any code references in this array (you can C<push> to it
		946	before or after loading AnyEvent), then they will called directly after
		947	the event loop has been chosen.
		948
		949	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		950	if it is defined then the event loop has already been detected, and the
		951	array will be ignored.
		952
		953	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		954	it,as it takes care of these details.
		955
		956	This variable is mainly useful for modules that can do something useful
		957	when AnyEvent is used and thus want to know when it is initialised, but do
		958	not need to even load it by default. This array provides the means to hook
		959	into AnyEvent passively, without loading it.
386		960
387	=back	961	=back
388		962
389	=head1 WHAT TO DO IN A MODULE	963	=head1 WHAT TO DO IN A MODULE
390		964
…		…
394	Be careful when you create watchers in the module body - AnyEvent will	968	Be careful when you create watchers in the module body - AnyEvent will
395	decide which event module to use as soon as the first method is called, so	969	decide which event module to use as soon as the first method is called, so
396	by calling AnyEvent in your module body you force the user of your module	970	by calling AnyEvent in your module body you force the user of your module
397	to load the event module first.	971	to load the event module first.
398		972
399	Never call C<< ->wait >> on a condition variable unless you I<know> that	973	Never call C<< ->recv >> on a condition variable unless you I<know> that
400	the C<< ->broadcast >> method has been called on it already. This is	974	the C<< ->send >> method has been called on it already. This is
401	because it will stall the whole program, and the whole point of using	975	because it will stall the whole program, and the whole point of using
402	events is to stay interactive.	976	events is to stay interactive.
403		977
404	It is fine, however, to call C<< ->wait >> when the user of your module	978	It is fine, however, to call C<< ->recv >> when the user of your module
405	requests it (i.e. if you create a http request object ad have a method	979	requests it (i.e. if you create a http request object ad have a method
406	called C<results> that returns the results, it should call C<< ->wait >>	980	called C<results> that returns the results, it should call C<< ->recv >>
407	freely, as the user of your module knows what she is doing. always).	981	freely, as the user of your module knows what she is doing. always).
408		982
409	=head1 WHAT TO DO IN THE MAIN PROGRAM	983	=head1 WHAT TO DO IN THE MAIN PROGRAM
410		984
411	There will always be a single main program - the only place that should	985	There will always be a single main program - the only place that should
…		…
413		987
414	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	988	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
415	do anything special (it does not need to be event-based) and let AnyEvent	989	do anything special (it does not need to be event-based) and let AnyEvent
416	decide which implementation to chose if some module relies on it.	990	decide which implementation to chose if some module relies on it.
417		991
418	If the main program relies on a specific event model. For example, in	992	If the main program relies on a specific event model - for example, in
419	Gtk2 programs you have to rely on the Glib module. You should load the	993	Gtk2 programs you have to rely on the Glib module - you should load the
420	event module before loading AnyEvent or any module that uses it: generally	994	event module before loading AnyEvent or any module that uses it: generally
421	speaking, you should load it as early as possible. The reason is that	995	speaking, you should load it as early as possible. The reason is that
422	modules might create watchers when they are loaded, and AnyEvent will	996	modules might create watchers when they are loaded, and AnyEvent will
423	decide on the event model to use as soon as it creates watchers, and it	997	decide on the event model to use as soon as it creates watchers, and it
424	might chose the wrong one unless you load the correct one yourself.	998	might chose the wrong one unless you load the correct one yourself.
425		999
426	You can chose to use a rather inefficient pure-perl implementation by	1000	You can chose to use a pure-perl implementation by loading the
427	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	1001	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
428	behaviour everywhere, but letting AnyEvent chose is generally better.	1002	everywhere, but letting AnyEvent chose the model is generally better.
		1003
		1004	=head2 MAINLOOP EMULATION
		1005
		1006	Sometimes (often for short test scripts, or even standalone programs who
		1007	only want to use AnyEvent), you do not want to run a specific event loop.
		1008
		1009	In that case, you can use a condition variable like this:
		1010
		1011	AnyEvent->condvar->recv;
		1012
		1013	This has the effect of entering the event loop and looping forever.
		1014
		1015	Note that usually your program has some exit condition, in which case
		1016	it is better to use the "traditional" approach of storing a condition
		1017	variable somewhere, waiting for it, and sending it when the program should
		1018	exit cleanly.
		1019
		1020
		1021	=head1 OTHER MODULES
		1022
		1023	The following is a non-exhaustive list of additional modules that use
		1024	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		1025	modules and other event loops in the same program. Some of the modules
		1026	come with AnyEvent, most are available via CPAN.
		1027
		1028	=over 4
		1029
		1030	=item L<AnyEvent::Util>
		1031
		1032	Contains various utility functions that replace often-used but blocking
		1033	functions such as C<inet_aton> by event-/callback-based versions.
		1034
		1035	=item L<AnyEvent::Socket>
		1036
		1037	Provides various utility functions for (internet protocol) sockets,
		1038	addresses and name resolution. Also functions to create non-blocking tcp
		1039	connections or tcp servers, with IPv6 and SRV record support and more.
		1040
		1041	=item L<AnyEvent::Handle>
		1042
		1043	Provide read and write buffers, manages watchers for reads and writes,
		1044	supports raw and formatted I/O, I/O queued and fully transparent and
		1045	non-blocking SSL/TLS (via L<AnyEvent::TLS>.
		1046
		1047	=item L<AnyEvent::DNS>
		1048
		1049	Provides rich asynchronous DNS resolver capabilities.
		1050
		1051	=item L<AnyEvent::HTTP>
		1052
		1053	A simple-to-use HTTP library that is capable of making a lot of concurrent
		1054	HTTP requests.
		1055
		1056	=item L<AnyEvent::HTTPD>
		1057
		1058	Provides a simple web application server framework.
		1059
		1060	=item L<AnyEvent::FastPing>
		1061
		1062	The fastest ping in the west.
		1063
		1064	=item L<AnyEvent::DBI>
		1065
		1066	Executes L<DBI> requests asynchronously in a proxy process.
		1067
		1068	=item L<AnyEvent::AIO>
		1069
		1070	Truly asynchronous I/O, should be in the toolbox of every event
		1071	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		1072	together.
		1073
		1074	=item L<AnyEvent::BDB>
		1075
		1076	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		1077	L<BDB> and AnyEvent together.
		1078
		1079	=item L<AnyEvent::GPSD>
		1080
		1081	A non-blocking interface to gpsd, a daemon delivering GPS information.
		1082
		1083	=item L<AnyEvent::IRC>
		1084
		1085	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		1086
		1087	=item L<AnyEvent::XMPP>
		1088
		1089	AnyEvent based XMPP (Jabber protocol) module family (replacing the older
		1090	Net::XMPP2>.
		1091
		1092	=item L<AnyEvent::IGS>
		1093
		1094	A non-blocking interface to the Internet Go Server protocol (used by
		1095	L<App::IGS>).
		1096
		1097	=item L<Net::FCP>
		1098
		1099	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		1100	of AnyEvent.
		1101
		1102	=item L<Event::ExecFlow>
		1103
		1104	High level API for event-based execution flow control.
		1105
		1106	=item L<Coro>
		1107
		1108	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1109
		1110	=back
429		1111
430	=cut	1112	=cut
431		1113
432	package AnyEvent;	1114	package AnyEvent;
433		1115
434	no warnings;	1116	# basically a tuned-down version of common::sense
435	use strict;	1117	sub common_sense {
		1118	# from common:.sense 1.0
		1119	${^WARNING_BITS} = "\xfc\x3f\xf3\x00\x0f\xf3\xcf\xc0\xf3\xfc\x33\x03";
		1120	# use strict vars subs
		1121	$^H |= 0x00000600;
		1122	}
436		1123
		1124	BEGIN { AnyEvent::common_sense }
		1125
437	use Carp;	1126	use Carp ();
438		1127
439	our $VERSION = '3.3';	1128	our $VERSION = '5.21';
440	our $MODEL;	1129	our $MODEL;
441		1130
442	our $AUTOLOAD;	1131	our $AUTOLOAD;
443	our @ISA;	1132	our @ISA;
444		1133
445	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
446
447	our @REGISTRY;	1134	our @REGISTRY;
448		1135
		1136	our $VERBOSE;
		1137
		1138	BEGIN {
		1139	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		1140	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		1141
		1142	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1143	if ${^TAINT};
		1144
		1145	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1146
		1147	}
		1148
		1149	our $MAX_SIGNAL_LATENCY = 10;
		1150
		1151	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1152
		1153	{
		1154	my $idx;
		1155	$PROTOCOL{$_} = ++$idx
		1156	for reverse split /\s*,\s*/,
		1157	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1158	}
		1159
449	my @models = (	1160	my @models = (
450	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
451	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
452	[EV:: => AnyEvent::Impl::EV::],	1161	[EV:: => AnyEvent::Impl::EV:: , 1],
		1162	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl:: , 1],
		1163	# everything below here will not (normally) be autoprobed
		1164	# as the pureperl backend should work everywhere
		1165	# and is usually faster
453	[Event:: => AnyEvent::Impl::Event::],	1166	[Event:: => AnyEvent::Impl::Event::, 1],
454	[Glib:: => AnyEvent::Impl::Glib::],	1167	[Glib:: => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
		1168	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1169	[Irssi:: => AnyEvent::Impl::Irssi::], # Irssi has a bogus "Event" package
455	[Tk:: => AnyEvent::Impl::Tk::],	1170	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1171	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1172	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
456	[Wx:: => AnyEvent::Impl::POE::],	1173	[Wx:: => AnyEvent::Impl::POE::],
457	[Prima:: => AnyEvent::Impl::POE::],	1174	[Prima:: => AnyEvent::Impl::POE::],
458	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	1175	# IO::Async is just too broken - we would need workarounds for its
459	# everything below here will not be autoprobed as the pureperl backend should work everywhere	1176	# byzantine signal and broken child handling, among others.
460	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy	1177	# IO::Async is rather hard to detect, as it doesn't have any
		1178	# obvious default class.
461	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program	1179	[IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
462	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza	1180	[IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1181	[IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1182	[AnyEvent::Impl::IOAsync:: => AnyEvent::Impl::IOAsync::], # requires special main program
463	);	1183	);
464		1184
465	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);	1185	our %method = map +($_ => 1),
		1186	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
		1187
		1188	our @post_detect;
		1189
		1190	sub post_detect(&) {
		1191	my ($cb) = @_;
		1192
		1193	if ($MODEL) {
		1194	$cb->();
		1195
		1196	undef
		1197	} else {
		1198	push @post_detect, $cb;
		1199
		1200	defined wantarray
		1201	? bless \$cb, "AnyEvent::Util::postdetect"
		1202	: ()
		1203	}
		1204	}
		1205
		1206	sub AnyEvent::Util::postdetect::DESTROY {
		1207	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1208	}
466		1209
467	sub detect() {	1210	sub detect() {
468	unless ($MODEL) {	1211	unless ($MODEL) {
469	no strict 'refs';	1212	local $SIG{__DIE__};
470		1213
471	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {	1214	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
472	my $model = "AnyEvent::Impl::$1";	1215	my $model = "AnyEvent::Impl::$1";
473	if (eval "require $model") {	1216	if (eval "require $model") {
474	$MODEL = $model;	1217	$MODEL = $model;
475	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;	1218	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
476	} else {	1219	} else {
477	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;	1220	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
478	}	1221	}
479	}	1222	}
480		1223
481	# check for already loaded models	1224	# check for already loaded models
482	unless ($MODEL) {	1225	unless ($MODEL) {
483	for (@REGISTRY, @models) {	1226	for (@REGISTRY, @models) {
484	my ($package, $model) = @$_;	1227	my ($package, $model) = @$_;
485	if (${"$package\::VERSION"} > 0) {	1228	if (${"$package\::VERSION"} > 0) {
486	if (eval "require $model") {	1229	if (eval "require $model") {
487	$MODEL = $model;	1230	$MODEL = $model;
488	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;	1231	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
489	last;	1232	last;
490	}	1233	}
491	}	1234	}
492	}	1235	}
493		1236
494	unless ($MODEL) {	1237	unless ($MODEL) {
495	# try to load a model	1238	# try to autoload a model
496
497	for (@REGISTRY, @models) {	1239	for (@REGISTRY, @models) {
498	my ($package, $model) = @$_;	1240	my ($package, $model, $autoload) = @$_;
		1241	if (
		1242	$autoload
499	if (eval "require $package"	1243	and eval "require $package"
500	and ${"$package\::VERSION"} > 0	1244	and ${"$package\::VERSION"} > 0
501	and eval "require $model") {	1245	and eval "require $model"
		1246	) {
502	$MODEL = $model;	1247	$MODEL = $model;
503	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;	1248	warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
504	last;	1249	last;
505	}	1250	}
506	}	1251	}
507		1252
508	$MODEL	1253	$MODEL
509	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";	1254	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
510	}	1255	}
511	}	1256	}
512		1257
		1258	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1259
513	unshift @ISA, $MODEL;	1260	unshift @ISA, $MODEL;
514	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	1261
		1262	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1263
		1264	(shift @post_detect)->() while @post_detect;
515	}	1265	}
516		1266
517	$MODEL	1267	$MODEL
518	}	1268	}
519		1269
520	sub AUTOLOAD {	1270	sub AUTOLOAD {
521	(my $func = $AUTOLOAD) =~ s/.*://;	1271	(my $func = $AUTOLOAD) =~ s/.*://;
522		1272
523	$method{$func}	1273	$method{$func}
524	or croak "$func: not a valid method for AnyEvent objects";	1274	or Carp::croak "$func: not a valid method for AnyEvent objects";
525		1275
526	detect unless $MODEL;	1276	detect unless $MODEL;
527		1277
528	my $class = shift;	1278	my $class = shift;
529	$class->$func (@_);	1279	$class->$func (@_);
530	}	1280	}
531		1281
		1282	# utility function to dup a filehandle. this is used by many backends
		1283	# to support binding more than one watcher per filehandle (they usually
		1284	# allow only one watcher per fd, so we dup it to get a different one).
		1285	sub _dupfh($$;$$) {
		1286	my ($poll, $fh, $r, $w) = @_;
		1287
		1288	# cygwin requires the fh mode to be matching, unix doesn't
		1289	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1290
		1291	open my $fh2, $mode, $fh
		1292	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1293
		1294	# we assume CLOEXEC is already set by perl in all important cases
		1295
		1296	($fh2, $rw)
		1297	}
		1298
		1299	=head1 SIMPLIFIED AE API
		1300
		1301	Starting with version 5.0, AnyEvent officially supports a second, much
		1302	simpler, API that is designed to reduce the calling, typing and memory
		1303	overhead.
		1304
		1305	See the L<AE> manpage for details.
		1306
		1307	=cut
		1308
		1309	package AE;
		1310
		1311	our $VERSION = $AnyEvent::VERSION;
		1312
		1313	sub io($$$) {
		1314	AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
		1315	}
		1316
		1317	sub timer($$$) {
		1318	AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
		1319	}
		1320
		1321	sub signal($$) {
		1322	AnyEvent->signal (signal => $_[0], cb => $_[1])
		1323	}
		1324
		1325	sub child($$) {
		1326	AnyEvent->child (pid => $_[0], cb => $_[1])
		1327	}
		1328
		1329	sub idle($) {
		1330	AnyEvent->idle (cb => $_[0])
		1331	}
		1332
		1333	sub cv(;&) {
		1334	AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
		1335	}
		1336
		1337	sub now() {
		1338	AnyEvent->now
		1339	}
		1340
		1341	sub now_update() {
		1342	AnyEvent->now_update
		1343	}
		1344
		1345	sub time() {
		1346	AnyEvent->time
		1347	}
		1348
532	package AnyEvent::Base;	1349	package AnyEvent::Base;
533		1350
		1351	# default implementations for many methods
		1352
		1353	sub _time() {
		1354	# probe for availability of Time::HiRes
		1355	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1356	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1357	*_time = \&Time::HiRes::time;
		1358	# if (eval "use POSIX (); (POSIX::times())...
		1359	} else {
		1360	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1361	*_time = sub { time }; # epic fail
		1362	}
		1363
		1364	&_time
		1365	}
		1366
		1367	sub time { _time }
		1368	sub now { _time }
		1369	sub now_update { }
		1370
534	# default implementation for ->condvar, ->wait, ->broadcast	1371	# default implementation for ->condvar
535		1372
536	sub condvar {	1373	sub condvar {
537	bless \my $flag, "AnyEvent::Base::CondVar"	1374	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
538	}
539
540	sub AnyEvent::Base::CondVar::broadcast {
541	${$_[0]}++;
542	}
543
544	sub AnyEvent::Base::CondVar::wait {
545	AnyEvent->one_event while !${$_[0]};
546	}	1375	}
547		1376
548	# default implementation for ->signal	1377	# default implementation for ->signal
549		1378
550	our %SIG_CB;	1379	our $HAVE_ASYNC_INTERRUPT;
		1380
		1381	sub _have_async_interrupt() {
		1382	$HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
		1383	&& eval "use Async::Interrupt 1.02 (); 1")
		1384	unless defined $HAVE_ASYNC_INTERRUPT;
		1385
		1386	$HAVE_ASYNC_INTERRUPT
		1387	}
		1388
		1389	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1390	our (%SIG_ASY, %SIG_ASY_W);
		1391	our ($SIG_COUNT, $SIG_TW);
		1392
		1393	sub _signal_exec {
		1394	$HAVE_ASYNC_INTERRUPT
		1395	? $SIGPIPE_R->drain
		1396	: sysread $SIGPIPE_R, (my $dummy), 9;
		1397
		1398	while (%SIG_EV) {
		1399	for (keys %SIG_EV) {
		1400	delete $SIG_EV{$_};
		1401	$_->() for values %{ $SIG_CB{$_} || {} };
		1402	}
		1403	}
		1404	}
		1405
		1406	# install a dummy wakeup watcher to reduce signal catching latency
		1407	sub _sig_add() {
		1408	unless ($SIG_COUNT++) {
		1409	# try to align timer on a full-second boundary, if possible
		1410	my $NOW = AE::now;
		1411
		1412	$SIG_TW = AE::timer
		1413	$MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1414	$MAX_SIGNAL_LATENCY,
		1415	sub { } # just for the PERL_ASYNC_CHECK
		1416	;
		1417	}
		1418	}
		1419
		1420	sub _sig_del {
		1421	undef $SIG_TW
		1422	unless --$SIG_COUNT;
		1423	}
		1424
		1425	our $_sig_name_init; $_sig_name_init = sub {
		1426	eval q{ # poor man's autoloading
		1427	undef $_sig_name_init;
		1428
		1429	if (_have_async_interrupt) {
		1430	*sig2num = \&Async::Interrupt::sig2num;
		1431	*sig2name = \&Async::Interrupt::sig2name;
		1432	} else {
		1433	require Config;
		1434
		1435	my %signame2num;
		1436	@signame2num{ split ' ', $Config::Config{sig_name} }
		1437	= split ' ', $Config::Config{sig_num};
		1438
		1439	my @signum2name;
		1440	@signum2name[values %signame2num] = keys %signame2num;
		1441
		1442	*sig2num = sub($) {
		1443	$_[0] > 0 ? shift : $signame2num{+shift}
		1444	};
		1445	*sig2name = sub ($) {
		1446	$_[0] > 0 ? $signum2name[+shift] : shift
		1447	};
		1448	}
		1449	};
		1450	die if $@;
		1451	};
		1452
		1453	sub sig2num ($) { &$_sig_name_init; &sig2num }
		1454	sub sig2name($) { &$_sig_name_init; &sig2name }
551		1455
552	sub signal {	1456	sub signal {
		1457	eval q{ # poor man's autoloading {}
		1458	# probe for availability of Async::Interrupt
		1459	if (_have_async_interrupt) {
		1460	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1461
		1462	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1463	$SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
		1464
		1465	} else {
		1466	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1467
		1468	require Fcntl;
		1469
		1470	if (AnyEvent::WIN32) {
		1471	require AnyEvent::Util;
		1472
		1473	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1474	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
		1475	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
		1476	} else {
		1477	pipe $SIGPIPE_R, $SIGPIPE_W;
		1478	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1479	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1480
		1481	# not strictly required, as $^F is normally 2, but let's make sure...
		1482	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1483	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1484	}
		1485
		1486	$SIGPIPE_R
		1487	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1488
		1489	$SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
		1490	}
		1491
		1492	*signal = sub {
553	my (undef, %arg) = @_;	1493	my (undef, %arg) = @_;
554		1494
555	my $signal = uc $arg{signal}	1495	my $signal = uc $arg{signal}
556	or Carp::croak "required option 'signal' is missing";	1496	or Carp::croak "required option 'signal' is missing";
557		1497
		1498	if ($HAVE_ASYNC_INTERRUPT) {
		1499	# async::interrupt
		1500
		1501	$signal = sig2num $signal;
558	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1502	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1503
		1504	$SIG_ASY{$signal} ||= new Async::Interrupt
		1505	cb => sub { undef $SIG_EV{$signal} },
		1506	signal => $signal,
		1507	pipe => [$SIGPIPE_R->filenos],
		1508	pipe_autodrain => 0,
		1509	;
		1510
		1511	} else {
		1512	# pure perl
		1513
		1514	# AE::Util has been loaded in signal
		1515	$signal = sig2name $signal;
		1516	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1517
559	$SIG{$signal} ||= sub {	1518	$SIG{$signal} ||= sub {
560	$_->() for values %{ $SIG_CB{$signal} || {} };	1519	local $!;
		1520	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1521	undef $SIG_EV{$signal};
		1522	};
		1523
		1524	# can't do signal processing without introducing races in pure perl,
		1525	# so limit the signal latency.
		1526	_sig_add;
		1527	}
		1528
		1529	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
		1530	};
		1531
		1532	*AnyEvent::Base::signal::DESTROY = sub {
		1533	my ($signal, $cb) = @{$_[0]};
		1534
		1535	_sig_del;
		1536
		1537	delete $SIG_CB{$signal}{$cb};
		1538
		1539	$HAVE_ASYNC_INTERRUPT
		1540	? delete $SIG_ASY{$signal}
		1541	: # delete doesn't work with older perls - they then
		1542	# print weird messages, or just unconditionally exit
		1543	# instead of getting the default action.
		1544	undef $SIG{$signal}
		1545	unless keys %{ $SIG_CB{$signal} };
		1546	};
561	};	1547	};
562		1548	die if $@;
563	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1549	&signal
564	}
565
566	sub AnyEvent::Base::Signal::DESTROY {
567	my ($signal, $cb) = @{$_[0]};
568
569	delete $SIG_CB{$signal}{$cb};
570
571	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
572	}	1550	}
573		1551
574	# default implementation for ->child	1552	# default implementation for ->child
575		1553
576	our %PID_CB;	1554	our %PID_CB;
577	our $CHLD_W;	1555	our $CHLD_W;
578	our $CHLD_DELAY_W;	1556	our $CHLD_DELAY_W;
579	our $PID_IDLE;
580	our $WNOHANG;	1557	our $WNOHANG;
581		1558
582	sub _child_wait {	1559	sub _emit_childstatus($$) {
583	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	1560	my (undef, $rpid, $rstatus) = @_;
		1561
		1562	$_->($rpid, $rstatus)
584	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1563	for values %{ $PID_CB{$rpid} || {} },
585	(values %{ $PID_CB{0} || {} });	1564	values %{ $PID_CB{0} || {} };
586	}
587
588	undef $PID_IDLE;
589	}	1565	}
590		1566
591	sub _sigchld {	1567	sub _sigchld {
592	# make sure we deliver these changes "synchronous" with the event loop.	1568	my $pid;
593	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {	1569
594	undef $CHLD_DELAY_W;	1570	AnyEvent->_emit_childstatus ($pid, $?)
595	&_child_wait;	1571	while ($pid = waitpid -1, $WNOHANG) > 0;
596	});
597	}	1572	}
598		1573
599	sub child {	1574	sub child {
600	my (undef, %arg) = @_;	1575	my (undef, %arg) = @_;
601		1576
602	defined (my $pid = $arg{pid} + 0)	1577	defined (my $pid = $arg{pid} + 0)
603	or Carp::croak "required option 'pid' is missing";	1578	or Carp::croak "required option 'pid' is missing";
604		1579
605	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1580	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
606		1581
607	unless ($WNOHANG) {	1582	# WNOHANG is almost cetrainly 1 everywhere
608	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1583	$WNOHANG ||= $^O =~ /^(?:openbsd|netbsd|linux|freebsd|cygwin|MSWin32)$/
609	}	1584	? 1
		1585	: eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
610		1586
611	unless ($CHLD_W) {	1587	unless ($CHLD_W) {
612	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1588	$CHLD_W = AE::signal CHLD => \&_sigchld;
613	# child could be a zombie already, so make at least one round	1589	# child could be a zombie already, so make at least one round
614	&_sigchld;	1590	&_sigchld;
615	}	1591	}
616		1592
617	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1593	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
618	}	1594	}
619		1595
620	sub AnyEvent::Base::Child::DESTROY {	1596	sub AnyEvent::Base::child::DESTROY {
621	my ($pid, $cb) = @{$_[0]};	1597	my ($pid, $cb) = @{$_[0]};
622		1598
623	delete $PID_CB{$pid}{$cb};	1599	delete $PID_CB{$pid}{$cb};
624	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1600	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
625		1601
626	undef $CHLD_W unless keys %PID_CB;	1602	undef $CHLD_W unless keys %PID_CB;
627	}	1603	}
		1604
		1605	# idle emulation is done by simply using a timer, regardless
		1606	# of whether the process is idle or not, and not letting
		1607	# the callback use more than 50% of the time.
		1608	sub idle {
		1609	my (undef, %arg) = @_;
		1610
		1611	my ($cb, $w, $rcb) = $arg{cb};
		1612
		1613	$rcb = sub {
		1614	if ($cb) {
		1615	$w = _time;
		1616	&$cb;
		1617	$w = _time - $w;
		1618
		1619	# never use more then 50% of the time for the idle watcher,
		1620	# within some limits
		1621	$w = 0.0001 if $w < 0.0001;
		1622	$w = 5 if $w > 5;
		1623
		1624	$w = AE::timer $w, 0, $rcb;
		1625	} else {
		1626	# clean up...
		1627	undef $w;
		1628	undef $rcb;
		1629	}
		1630	};
		1631
		1632	$w = AE::timer 0.05, 0, $rcb;
		1633
		1634	bless \\$cb, "AnyEvent::Base::idle"
		1635	}
		1636
		1637	sub AnyEvent::Base::idle::DESTROY {
		1638	undef $${$_[0]};
		1639	}
		1640
		1641	package AnyEvent::CondVar;
		1642
		1643	our @ISA = AnyEvent::CondVar::Base::;
		1644
		1645	package AnyEvent::CondVar::Base;
		1646
		1647	#use overload
		1648	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1649	# fallback => 1;
		1650
		1651	# save 300+ kilobytes by dirtily hardcoding overloading
		1652	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1653	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1654	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1655	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1656
		1657	our $WAITING;
		1658
		1659	sub _send {
		1660	# nop
		1661	}
		1662
		1663	sub send {
		1664	my $cv = shift;
		1665	$cv->{_ae_sent} = [@_];
		1666	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1667	$cv->_send;
		1668	}
		1669
		1670	sub croak {
		1671	$_[0]{_ae_croak} = $_[1];
		1672	$_[0]->send;
		1673	}
		1674
		1675	sub ready {
		1676	$_[0]{_ae_sent}
		1677	}
		1678
		1679	sub _wait {
		1680	$WAITING
		1681	and !$_[0]{_ae_sent}
		1682	and Carp::croak "AnyEvent::CondVar: recursive blocking wait detected";
		1683
		1684	local $WAITING = 1;
		1685	AnyEvent->one_event while !$_[0]{_ae_sent};
		1686	}
		1687
		1688	sub recv {
		1689	$_[0]->_wait;
		1690
		1691	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1692	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1693	}
		1694
		1695	sub cb {
		1696	my $cv = shift;
		1697
		1698	@_
		1699	and $cv->{_ae_cb} = shift
		1700	and $cv->{_ae_sent}
		1701	and (delete $cv->{_ae_cb})->($cv);
		1702
		1703	$cv->{_ae_cb}
		1704	}
		1705
		1706	sub begin {
		1707	++$_[0]{_ae_counter};
		1708	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1709	}
		1710
		1711	sub end {
		1712	return if --$_[0]{_ae_counter};
		1713	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1714	}
		1715
		1716	# undocumented/compatibility with pre-3.4
		1717	*broadcast = \&send;
		1718	*wait = \&_wait;
		1719
		1720	=head1 ERROR AND EXCEPTION HANDLING
		1721
		1722	In general, AnyEvent does not do any error handling - it relies on the
		1723	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1724	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1725	checking of all AnyEvent methods, however, which is highly useful during
		1726	development.
		1727
		1728	As for exception handling (i.e. runtime errors and exceptions thrown while
		1729	executing a callback), this is not only highly event-loop specific, but
		1730	also not in any way wrapped by this module, as this is the job of the main
		1731	program.
		1732
		1733	The pure perl event loop simply re-throws the exception (usually
		1734	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1735	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1736	so on.
		1737
		1738	=head1 ENVIRONMENT VARIABLES
		1739
		1740	The following environment variables are used by this module or its
		1741	submodules.
		1742
		1743	Note that AnyEvent will remove I<all> environment variables starting with
		1744	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1745	enabled.
		1746
		1747	=over 4
		1748
		1749	=item C<PERL_ANYEVENT_VERBOSE>
		1750
		1751	By default, AnyEvent will be completely silent except in fatal
		1752	conditions. You can set this environment variable to make AnyEvent more
		1753	talkative.
		1754
		1755	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1756	conditions, such as not being able to load the event model specified by
		1757	C<PERL_ANYEVENT_MODEL>.
		1758
		1759	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1760	model it chooses.
		1761
		1762	When set to C<8> or higher, then AnyEvent will report extra information on
		1763	which optional modules it loads and how it implements certain features.
		1764
		1765	=item C<PERL_ANYEVENT_STRICT>
		1766
		1767	AnyEvent does not do much argument checking by default, as thorough
		1768	argument checking is very costly. Setting this variable to a true value
		1769	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1770	check the arguments passed to most method calls. If it finds any problems,
		1771	it will croak.
		1772
		1773	In other words, enables "strict" mode.
		1774
		1775	Unlike C<use strict> (or it's modern cousin, C<< use L<common::sense>
		1776	>>, it is definitely recommended to keep it off in production. Keeping
		1777	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1778	can be very useful, however.
		1779
		1780	=item C<PERL_ANYEVENT_MODEL>
		1781
		1782	This can be used to specify the event model to be used by AnyEvent, before
		1783	auto detection and -probing kicks in. It must be a string consisting
		1784	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1785	and the resulting module name is loaded and if the load was successful,
		1786	used as event model. If it fails to load AnyEvent will proceed with
		1787	auto detection and -probing.
		1788
		1789	This functionality might change in future versions.
		1790
		1791	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1792	could start your program like this:
		1793
		1794	PERL_ANYEVENT_MODEL=Perl perl ...
		1795
		1796	=item C<PERL_ANYEVENT_PROTOCOLS>
		1797
		1798	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1799	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1800	of auto probing).
		1801
		1802	Must be set to a comma-separated list of protocols or address families,
		1803	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1804	used, and preference will be given to protocols mentioned earlier in the
		1805	list.
		1806
		1807	This variable can effectively be used for denial-of-service attacks
		1808	against local programs (e.g. when setuid), although the impact is likely
		1809	small, as the program has to handle conenction and other failures anyways.
		1810
		1811	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1812	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1813	- only support IPv4, never try to resolve or contact IPv6
		1814	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1815	IPv6, but prefer IPv6 over IPv4.
		1816
		1817	=item C<PERL_ANYEVENT_EDNS0>
		1818
		1819	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1820	for DNS. This extension is generally useful to reduce DNS traffic, but
		1821	some (broken) firewalls drop such DNS packets, which is why it is off by
		1822	default.
		1823
		1824	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1825	EDNS0 in its DNS requests.
		1826
		1827	=item C<PERL_ANYEVENT_MAX_FORKS>
		1828
		1829	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1830	will create in parallel.
		1831
		1832	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1833
		1834	The default value for the C<max_outstanding> parameter for the default DNS
		1835	resolver - this is the maximum number of parallel DNS requests that are
		1836	sent to the DNS server.
		1837
		1838	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1839
		1840	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1841	configuration) in the default resolver. When set to the empty string, no
		1842	default config will be used.
		1843
		1844	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1845
		1846	When neither C<ca_file> nor C<ca_path> was specified during
		1847	L<AnyEvent::TLS> context creation, and either of these environment
		1848	variables exist, they will be used to specify CA certificate locations
		1849	instead of a system-dependent default.
		1850
		1851	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		1852
		1853	When these are set to C<1>, then the respective modules are not
		1854	loaded. Mostly good for testing AnyEvent itself.
		1855
		1856	=back
628		1857
629	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1858	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
630		1859
631	This is an advanced topic that you do not normally need to use AnyEvent in	1860	This is an advanced topic that you do not normally need to use AnyEvent in
632	a module. This section is only of use to event loop authors who want to	1861	a module. This section is only of use to event loop authors who want to
…		…
667	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1896	I<rxvt-unicode> also cheats a bit by not providing blocking access to
668	condition variables: code blocking while waiting for a condition will	1897	condition variables: code blocking while waiting for a condition will
669	C<die>. This still works with most modules/usages, and blocking calls must	1898	C<die>. This still works with most modules/usages, and blocking calls must
670	not be done in an interactive application, so it makes sense.	1899	not be done in an interactive application, so it makes sense.
671		1900
672	=head1 ENVIRONMENT VARIABLES
673
674	The following environment variables are used by this module:
675
676	=over 4
677
678	=item C<PERL_ANYEVENT_VERBOSE>
679
680	By default, AnyEvent will be completely silent except in fatal
681	conditions. You can set this environment variable to make AnyEvent more
682	talkative.
683
684	When set to C<1> or higher, causes AnyEvent to warn about unexpected
685	conditions, such as not being able to load the event model specified by
686	C<PERL_ANYEVENT_MODEL>.
687
688	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
689	model it chooses.
690
691	=item C<PERL_ANYEVENT_MODEL>
692
693	This can be used to specify the event model to be used by AnyEvent, before
694	autodetection and -probing kicks in. It must be a string consisting
695	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
696	and the resulting module name is loaded and if the load was successful,
697	used as event model. If it fails to load AnyEvent will proceed with
698	autodetection and -probing.
699
700	This functionality might change in future versions.
701
702	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
703	could start your program like this:
704
705	PERL_ANYEVENT_MODEL=Perl perl ...
706
707	=back
708
709	=head1 EXAMPLE PROGRAM	1901	=head1 EXAMPLE PROGRAM
710		1902
711	The following program uses an IO watcher to read data from STDIN, a timer	1903	The following program uses an I/O watcher to read data from STDIN, a timer
712	to display a message once per second, and a condition variable to quit the	1904	to display a message once per second, and a condition variable to quit the
713	program when the user enters quit:	1905	program when the user enters quit:
714		1906
715	use AnyEvent;	1907	use AnyEvent;
716		1908
…		…
721	poll => 'r',	1913	poll => 'r',
722	cb => sub {	1914	cb => sub {
723	warn "io event <$_[0]>\n"; # will always output <r>	1915	warn "io event <$_[0]>\n"; # will always output <r>
724	chomp (my $input = <STDIN>); # read a line	1916	chomp (my $input = <STDIN>); # read a line
725	warn "read: $input\n"; # output what has been read	1917	warn "read: $input\n"; # output what has been read
726	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1918	$cv->send if $input =~ /^q/i; # quit program if /^q/i
727	},	1919	},
728	);	1920	);
729		1921
730	my $time_watcher; # can only be used once
731
732	sub new_timer {
733	$timer = AnyEvent->timer (after => 1, cb => sub {	1922	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
734	warn "timeout\n"; # print 'timeout' about every second	1923	warn "timeout\n"; # print 'timeout' at most every second
735	&new_timer; # and restart the time
736	});	1924	});
737	}
738		1925
739	new_timer; # create first timer
740
741	$cv->wait; # wait until user enters /^q/i	1926	$cv->recv; # wait until user enters /^q/i
742		1927
743	=head1 REAL-WORLD EXAMPLE	1928	=head1 REAL-WORLD EXAMPLE
744		1929
745	Consider the L<Net::FCP> module. It features (among others) the following	1930	Consider the L<Net::FCP> module. It features (among others) the following
746	API calls, which are to freenet what HTTP GET requests are to http:	1931	API calls, which are to freenet what HTTP GET requests are to http:
…		…
796	syswrite $txn->{fh}, $txn->{request}	1981	syswrite $txn->{fh}, $txn->{request}
797	or die "connection or write error";	1982	or die "connection or write error";
798	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1983	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
799		1984
800	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1985	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
801	result and signals any possible waiters that the request ahs finished:	1986	result and signals any possible waiters that the request has finished:
802		1987
803	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1988	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
804		1989
805	if (end-of-file or data complete) {	1990	if (end-of-file or data complete) {
806	$txn->{result} = $txn->{buf};	1991	$txn->{result} = $txn->{buf};
807	$txn->{finished}->broadcast;	1992	$txn->{finished}->send;
808	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1993	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
809	}	1994	}
810		1995
811	The C<result> method, finally, just waits for the finished signal (if the	1996	The C<result> method, finally, just waits for the finished signal (if the
812	request was already finished, it doesn't wait, of course, and returns the	1997	request was already finished, it doesn't wait, of course, and returns the
813	data:	1998	data:
814		1999
815	$txn->{finished}->wait;	2000	$txn->{finished}->recv;
816	return $txn->{result};	2001	return $txn->{result};
817		2002
818	The actual code goes further and collects all errors (C<die>s, exceptions)	2003	The actual code goes further and collects all errors (C<die>s, exceptions)
819	that occured during request processing. The C<result> method detects	2004	that occurred during request processing. The C<result> method detects
820	whether an exception as thrown (it is stored inside the $txn object)	2005	whether an exception as thrown (it is stored inside the $txn object)
821	and just throws the exception, which means connection errors and other	2006	and just throws the exception, which means connection errors and other
822	problems get reported tot he code that tries to use the result, not in a	2007	problems get reported tot he code that tries to use the result, not in a
823	random callback.	2008	random callback.
824		2009
…		…
855		2040
856	my $quit = AnyEvent->condvar;	2041	my $quit = AnyEvent->condvar;
857		2042
858	$fcp->txn_client_get ($url)->cb (sub {	2043	$fcp->txn_client_get ($url)->cb (sub {
859	...	2044	...
860	$quit->broadcast;	2045	$quit->send;
861	});	2046	});
862		2047
863	$quit->wait;	2048	$quit->recv;
864		2049
865		2050
866	=head1 BENCHMARK	2051	=head1 BENCHMARKS
867		2052
868	To give you an idea of the performance and overheads that AnyEvent adds	2053	To give you an idea of the performance and overheads that AnyEvent adds
869	over the backends directly, here is a benchmark of various supported event	2054	over the event loops themselves and to give you an impression of the speed
870	models natively and with anyevent. The benchmark creates a lot of timers	2055	of various event loops I prepared some benchmarks.
871	(with a zero timeout) and io events (watching STDOUT, a pty, to become	2056
		2057	=head2 BENCHMARKING ANYEVENT OVERHEAD
		2058
		2059	Here is a benchmark of various supported event models used natively and
		2060	through AnyEvent. The benchmark creates a lot of timers (with a zero
		2061	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
872	writable), lets them fire exactly once and destroys them again.	2062	which it is), lets them fire exactly once and destroys them again.
873		2063
874	Explanation of the fields:	2064	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		2065	distribution. It uses the L<AE> interface, which makes a real difference
		2066	for the EV and Perl backends only.
875		2067
		2068	=head3 Explanation of the columns
		2069
876	I<watcher> is the number of event watchers created/destroyed. Sicne	2070	I<watcher> is the number of event watchers created/destroyed. Since
877	different event models have vastly different performance each backend was	2071	different event models feature vastly different performances, each event
878	handed a number of watchers so that overall runtime is acceptable and	2072	loop was given a number of watchers so that overall runtime is acceptable
879	similar to all backends (and keep them from crashing).	2073	and similar between tested event loop (and keep them from crashing): Glib
		2074	would probably take thousands of years if asked to process the same number
		2075	of watchers as EV in this benchmark.
880		2076
881	I<bytes> is the number of bytes (as measured by resident set size) used by	2077	I<bytes> is the number of bytes (as measured by the resident set size,
882	each watcher.	2078	RSS) consumed by each watcher. This method of measuring captures both C
		2079	and Perl-based overheads.
883		2080
884	I<create> is the time, in microseconds, to create a single watcher.	2081	I<create> is the time, in microseconds (millionths of seconds), that it
		2082	takes to create a single watcher. The callback is a closure shared between
		2083	all watchers, to avoid adding memory overhead. That means closure creation
		2084	and memory usage is not included in the figures.
885		2085
886	I<invoke> is the time, in microseconds, used to invoke a simple callback	2086	I<invoke> is the time, in microseconds, used to invoke a simple
887	that simply counts down.	2087	callback. The callback simply counts down a Perl variable and after it was
		2088	invoked "watcher" times, it would C<< ->send >> a condvar once to
		2089	signal the end of this phase.
888		2090
889	I<destroy> is the time, in microseconds, to destroy a single watcher.	2091	I<destroy> is the time, in microseconds, that it takes to destroy a single
		2092	watcher.
890		2093
		2094	=head3 Results
		2095
891	name watcher bytes create invoke destroy comment	2096	name watchers bytes create invoke destroy comment
892	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	2097	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
893	EV/Any 100000 610 3.52 0.91 0.75	2098	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
894	CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal	2099	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
895	Perl/Any 10000 654 4.64 1.22 0.77 pure perl implementation	2100	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
896	Event/Event 10000 523 28.05 21.38 5.22 Event native interface	2101	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
897	Event/Any 10000 943 34.43 20.48 1.39	2102	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		2103	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		2104	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
898	Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour	2105	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
899	Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers	2106	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
900	POE/Select 2000 6343 94.69 807.65 562.69 POE::Loop::Select	2107	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
901	POE/Event 2000 6644 108.15 768.19 14.33 POE::Loop::Event	2108	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
902		2109
903	Discussion: The benchmark does I<not> bench scalability of the	2110	=head3 Discussion
		2111
		2112	The benchmark does I<not> measure scalability of the event loop very
904	backend. For example a select-based backend (such as the pureperl one) can	2113	well. For example, a select-based event loop (such as the pure perl one)
905	never compete with a backend using epoll. In this benchmark, only a single	2114	can never compete with an event loop that uses epoll when the number of
906	filehandle is used.	2115	file descriptors grows high. In this benchmark, all events become ready at
		2116	the same time, so select/poll-based implementations get an unnatural speed
		2117	boost.
907		2118
		2119	Also, note that the number of watchers usually has a nonlinear effect on
		2120	overall speed, that is, creating twice as many watchers doesn't take twice
		2121	the time - usually it takes longer. This puts event loops tested with a
		2122	higher number of watchers at a disadvantage.
		2123
		2124	To put the range of results into perspective, consider that on the
		2125	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		2126	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		2127	cycles with POE.
		2128
908	EV is the sole leader regarding speed and memory use, which are both	2129	C<EV> is the sole leader regarding speed and memory use, which are both
909	maximal/minimal. Even when going through AnyEvent, there is only one event	2130	maximal/minimal, respectively. When using the L<AE> API there is zero
910	loop that uses less memory (the Event module natively), and no faster	2131	overhead (when going through the AnyEvent API create is about 5-6 times
911	event model.	2132	slower, with other times being equal, so still uses far less memory than
		2133	any other event loop and is still faster than Event natively).
912		2134
913	The pure perl implementation is hit in a few sweet spots (both the	2135	The pure perl implementation is hit in a few sweet spots (both the
914	zero timeout and the use of a single fd hit optimisations in the perl	2136	constant timeout and the use of a single fd hit optimisations in the perl
915	interpreter and the backend itself), but it shows that it adds very little	2137	interpreter and the backend itself). Nevertheless this shows that it
916	overhead in itself. Like any select-based backend it's performance becomes	2138	adds very little overhead in itself. Like any select-based backend its
917	really bad with lots of file descriptors.	2139	performance becomes really bad with lots of file descriptors (and few of
		2140	them active), of course, but this was not subject of this benchmark.
918		2141
919	The Event module has a relatively high setup and callback invocation cost,	2142	The C<Event> module has a relatively high setup and callback invocation
920	but overall scores on the third place.	2143	cost, but overall scores in on the third place.
921		2144
922	Glib has a little higher memory cost, a bit fster callback invocation and	2145	C<IO::Async> performs admirably well, about on par with C<Event>, even
923	has a similar speed as Event.	2146	when using its pure perl backend.
924		2147
		2148	C<Glib>'s memory usage is quite a bit higher, but it features a
		2149	faster callback invocation and overall ends up in the same class as
		2150	C<Event>. However, Glib scales extremely badly, doubling the number of
		2151	watchers increases the processing time by more than a factor of four,
		2152	making it completely unusable when using larger numbers of watchers
		2153	(note that only a single file descriptor was used in the benchmark, so
		2154	inefficiencies of C<poll> do not account for this).
		2155
925	The Tk backend works relatively well, the fact that it crashes with	2156	The C<Tk> adaptor works relatively well. The fact that it crashes with
926	more than 2000 watchers is a big setback, however, as correctness takes	2157	more than 2000 watchers is a big setback, however, as correctness takes
927	precedence over speed.	2158	precedence over speed. Nevertheless, its performance is surprising, as the
		2159	file descriptor is dup()ed for each watcher. This shows that the dup()
		2160	employed by some adaptors is not a big performance issue (it does incur a
		2161	hidden memory cost inside the kernel which is not reflected in the figures
		2162	above).
928		2163
929	POE, regardless of backend (wether it's pure perl select backend or the	2164	C<POE>, regardless of underlying event loop (whether using its pure perl
930	Event backend) shows abysmal performance and memory usage: Watchers use	2165	select-based backend or the Event module, the POE-EV backend couldn't
931	almost 30 times as much memory as EV watchers, and 10 times as much memory	2166	be tested because it wasn't working) shows abysmal performance and
932	as both Event or EV via AnyEvent.	2167	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		2168	as EV watchers, and 10 times as much memory as Event (the high memory
		2169	requirements are caused by requiring a session for each watcher). Watcher
		2170	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2171	implementation.
933		2172
		2173	The design of the POE adaptor class in AnyEvent can not really account
		2174	for the performance issues, though, as session creation overhead is
		2175	small compared to execution of the state machine, which is coded pretty
		2176	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2177	using multiple sessions is not a good approach, especially regarding
		2178	memory usage, even the author of POE could not come up with a faster
		2179	design).
		2180
		2181	=head3 Summary
		2182
		2183	=over 4
		2184
934	Summary: using EV through AnyEvent is faster than any other event	2185	=item * Using EV through AnyEvent is faster than any other event loop
935	loop. The overhead AnyEvent adds can be very small, and you should avoid	2186	(even when used without AnyEvent), but most event loops have acceptable
936	POE like the plague if you want performance or reasonable memory usage.	2187	performance with or without AnyEvent.
		2188
		2189	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2190	the actual event loop, only with extremely fast event loops such as EV
		2191	adds AnyEvent significant overhead.
		2192
		2193	=item * You should avoid POE like the plague if you want performance or
		2194	reasonable memory usage.
		2195
		2196	=back
		2197
		2198	=head2 BENCHMARKING THE LARGE SERVER CASE
		2199
		2200	This benchmark actually benchmarks the event loop itself. It works by
		2201	creating a number of "servers": each server consists of a socket pair, a
		2202	timeout watcher that gets reset on activity (but never fires), and an I/O
		2203	watcher waiting for input on one side of the socket. Each time the socket
		2204	watcher reads a byte it will write that byte to a random other "server".
		2205
		2206	The effect is that there will be a lot of I/O watchers, only part of which
		2207	are active at any one point (so there is a constant number of active
		2208	fds for each loop iteration, but which fds these are is random). The
		2209	timeout is reset each time something is read because that reflects how
		2210	most timeouts work (and puts extra pressure on the event loops).
		2211
		2212	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2213	(1%) are active. This mirrors the activity of large servers with many
		2214	connections, most of which are idle at any one point in time.
		2215
		2216	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2217	distribution. It uses the L<AE> interface, which makes a real difference
		2218	for the EV and Perl backends only.
		2219
		2220	=head3 Explanation of the columns
		2221
		2222	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2223	each server has a read and write socket end).
		2224
		2225	I<create> is the time it takes to create a socket pair (which is
		2226	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2227
		2228	I<request>, the most important value, is the time it takes to handle a
		2229	single "request", that is, reading the token from the pipe and forwarding
		2230	it to another server. This includes deleting the old timeout and creating
		2231	a new one that moves the timeout into the future.
		2232
		2233	=head3 Results
		2234
		2235	name sockets create request
		2236	EV 20000 62.66 7.99
		2237	Perl 20000 68.32 32.64
		2238	IOAsync 20000 174.06 101.15 epoll
		2239	IOAsync 20000 174.67 610.84 poll
		2240	Event 20000 202.69 242.91
		2241	Glib 20000 557.01 1689.52
		2242	POE 20000 341.54 12086.32 uses POE::Loop::Event
		2243
		2244	=head3 Discussion
		2245
		2246	This benchmark I<does> measure scalability and overall performance of the
		2247	particular event loop.
		2248
		2249	EV is again fastest. Since it is using epoll on my system, the setup time
		2250	is relatively high, though.
		2251
		2252	Perl surprisingly comes second. It is much faster than the C-based event
		2253	loops Event and Glib.
		2254
		2255	IO::Async performs very well when using its epoll backend, and still quite
		2256	good compared to Glib when using its pure perl backend.
		2257
		2258	Event suffers from high setup time as well (look at its code and you will
		2259	understand why). Callback invocation also has a high overhead compared to
		2260	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2261	uses select or poll in basically all documented configurations.
		2262
		2263	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2264	clearly fails to perform with many filehandles or in busy servers.
		2265
		2266	POE is still completely out of the picture, taking over 1000 times as long
		2267	as EV, and over 100 times as long as the Perl implementation, even though
		2268	it uses a C-based event loop in this case.
		2269
		2270	=head3 Summary
		2271
		2272	=over 4
		2273
		2274	=item * The pure perl implementation performs extremely well.
		2275
		2276	=item * Avoid Glib or POE in large projects where performance matters.
		2277
		2278	=back
		2279
		2280	=head2 BENCHMARKING SMALL SERVERS
		2281
		2282	While event loops should scale (and select-based ones do not...) even to
		2283	large servers, most programs we (or I :) actually write have only a few
		2284	I/O watchers.
		2285
		2286	In this benchmark, I use the same benchmark program as in the large server
		2287	case, but it uses only eight "servers", of which three are active at any
		2288	one time. This should reflect performance for a small server relatively
		2289	well.
		2290
		2291	The columns are identical to the previous table.
		2292
		2293	=head3 Results
		2294
		2295	name sockets create request
		2296	EV 16 20.00 6.54
		2297	Perl 16 25.75 12.62
		2298	Event 16 81.27 35.86
		2299	Glib 16 32.63 15.48
		2300	POE 16 261.87 276.28 uses POE::Loop::Event
		2301
		2302	=head3 Discussion
		2303
		2304	The benchmark tries to test the performance of a typical small
		2305	server. While knowing how various event loops perform is interesting, keep
		2306	in mind that their overhead in this case is usually not as important, due
		2307	to the small absolute number of watchers (that is, you need efficiency and
		2308	speed most when you have lots of watchers, not when you only have a few of
		2309	them).
		2310
		2311	EV is again fastest.
		2312
		2313	Perl again comes second. It is noticeably faster than the C-based event
		2314	loops Event and Glib, although the difference is too small to really
		2315	matter.
		2316
		2317	POE also performs much better in this case, but is is still far behind the
		2318	others.
		2319
		2320	=head3 Summary
		2321
		2322	=over 4
		2323
		2324	=item * C-based event loops perform very well with small number of
		2325	watchers, as the management overhead dominates.
		2326
		2327	=back
		2328
		2329	=head2 THE IO::Lambda BENCHMARK
		2330
		2331	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2332	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2333	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2334	shouldn't come as a surprise to anybody). As such, the benchmark is
		2335	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2336	very optimal. But how would AnyEvent compare when used without the extra
		2337	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2338
		2339	The benchmark itself creates an echo-server, and then, for 500 times,
		2340	connects to the echo server, sends a line, waits for the reply, and then
		2341	creates the next connection. This is a rather bad benchmark, as it doesn't
		2342	test the efficiency of the framework or much non-blocking I/O, but it is a
		2343	benchmark nevertheless.
		2344
		2345	name runtime
		2346	Lambda/select 0.330 sec
		2347	+ optimized 0.122 sec
		2348	Lambda/AnyEvent 0.327 sec
		2349	+ optimized 0.138 sec
		2350	Raw sockets/select 0.077 sec
		2351	POE/select, components 0.662 sec
		2352	POE/select, raw sockets 0.226 sec
		2353	POE/select, optimized 0.404 sec
		2354
		2355	AnyEvent/select/nb 0.085 sec
		2356	AnyEvent/EV/nb 0.068 sec
		2357	+state machine 0.134 sec
		2358
		2359	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2360	benchmarks actually make blocking connects and use 100% blocking I/O,
		2361	defeating the purpose of an event-based solution. All of the newly
		2362	written AnyEvent benchmarks use 100% non-blocking connects (using
		2363	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2364	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2365	generally require a lot more bookkeeping and event handling than blocking
		2366	connects (which involve a single syscall only).
		2367
		2368	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2369	offers similar expressive power as POE and IO::Lambda, using conventional
		2370	Perl syntax. This means that both the echo server and the client are 100%
		2371	non-blocking, further placing it at a disadvantage.
		2372
		2373	As you can see, the AnyEvent + EV combination even beats the
		2374	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2375	backend easily beats IO::Lambda and POE.
		2376
		2377	And even the 100% non-blocking version written using the high-level (and
		2378	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
		2379	higher level ("unoptimised") abstractions by a large margin, even though
		2380	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		2381
		2382	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2383	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2384	part of the IO::Lambda distribution and were used without any changes.
		2385
		2386
		2387	=head1 SIGNALS
		2388
		2389	AnyEvent currently installs handlers for these signals:
		2390
		2391	=over 4
		2392
		2393	=item SIGCHLD
		2394
		2395	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2396	emulation for event loops that do not support them natively. Also, some
		2397	event loops install a similar handler.
		2398
		2399	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2400	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2401
		2402	=item SIGPIPE
		2403
		2404	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2405	when AnyEvent gets loaded.
		2406
		2407	The rationale for this is that AnyEvent users usually do not really depend
		2408	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2409	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2410	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2411	some random socket.
		2412
		2413	The rationale for installing a no-op handler as opposed to ignoring it is
		2414	that this way, the handler will be restored to defaults on exec.
		2415
		2416	Feel free to install your own handler, or reset it to defaults.
		2417
		2418	=back
		2419
		2420	=cut
		2421
		2422	undef $SIG{CHLD}
		2423	if $SIG{CHLD} eq 'IGNORE';
		2424
		2425	$SIG{PIPE} = sub { }
		2426	unless defined $SIG{PIPE};
		2427
		2428	=head1 RECOMMENDED/OPTIONAL MODULES
		2429
		2430	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2431	it's built-in modules) are required to use it.
		2432
		2433	That does not mean that AnyEvent won't take advantage of some additional
		2434	modules if they are installed.
		2435
		2436	This section epxlains which additional modules will be used, and how they
		2437	affect AnyEvent's operetion.
		2438
		2439	=over 4
		2440
		2441	=item L<Async::Interrupt>
		2442
		2443	This slightly arcane module is used to implement fast signal handling: To
		2444	my knowledge, there is no way to do completely race-free and quick
		2445	signal handling in pure perl. To ensure that signals still get
		2446	delivered, AnyEvent will start an interval timer to wake up perl (and
		2447	catch the signals) with some delay (default is 10 seconds, look for
		2448	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2449
		2450	If this module is available, then it will be used to implement signal
		2451	catching, which means that signals will not be delayed, and the event loop
		2452	will not be interrupted regularly, which is more efficient (And good for
		2453	battery life on laptops).
		2454
		2455	This affects not just the pure-perl event loop, but also other event loops
		2456	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2457
		2458	Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
		2459	and either employ their own workarounds (POE) or use AnyEvent's workaround
		2460	(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
		2461	does nothing for those backends.
		2462
		2463	=item L<EV>
		2464
		2465	This module isn't really "optional", as it is simply one of the backend
		2466	event loops that AnyEvent can use. However, it is simply the best event
		2467	loop available in terms of features, speed and stability: It supports
		2468	the AnyEvent API optimally, implements all the watcher types in XS, does
		2469	automatic timer adjustments even when no monotonic clock is available,
		2470	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2471	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2472	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2473
		2474	=item L<Guard>
		2475
		2476	The guard module, when used, will be used to implement
		2477	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2478	lot less memory), but otherwise doesn't affect guard operation much. It is
		2479	purely used for performance.
		2480
		2481	=item L<JSON> and L<JSON::XS>
		2482
		2483	One of these modules is required when you want to read or write JSON data
		2484	via L<AnyEvent::Handle>. It is also written in pure-perl, but can take
		2485	advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
		2486
		2487	In fact, L<AnyEvent::Handle> will use L<JSON::XS> by default if it is
		2488	installed.
		2489
		2490	=item L<Net::SSLeay>
		2491
		2492	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2493	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2494	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2495
		2496	=item L<Time::HiRes>
		2497
		2498	This module is part of perl since release 5.008. It will be used when the
		2499	chosen event library does not come with a timing source on it's own. The
		2500	pure-perl event loop (L<AnyEvent::Impl::Perl>) will additionally use it to
		2501	try to use a monotonic clock for timing stability.
		2502
		2503	=back
937		2504
938		2505
939	=head1 FORK	2506	=head1 FORK
940		2507
941	Most event libraries are not fork-safe. The ones who are usually are	2508	Most event libraries are not fork-safe. The ones who are usually are
942	because they are so inefficient. Only L<EV> is fully fork-aware.	2509	because they rely on inefficient but fork-safe C<select> or C<poll>
		2510	calls. Only L<EV> is fully fork-aware.
943		2511
944	If you have to fork, you must either do so I<before> creating your first	2512	If you have to fork, you must either do so I<before> creating your first
945	watcher OR you must not use AnyEvent at all in the child.	2513	watcher OR you must not use AnyEvent at all in the child OR you must do
		2514	something completely out of the scope of AnyEvent.
946		2515
947		2516
948	=head1 SECURITY CONSIDERATIONS	2517	=head1 SECURITY CONSIDERATIONS
949		2518
950	AnyEvent can be forced to load any event model via	2519	AnyEvent can be forced to load any event model via
…		…
955	specified in the variable.	2524	specified in the variable.
956		2525
957	You can make AnyEvent completely ignore this variable by deleting it	2526	You can make AnyEvent completely ignore this variable by deleting it
958	before the first watcher gets created, e.g. with a C<BEGIN> block:	2527	before the first watcher gets created, e.g. with a C<BEGIN> block:
959		2528
960	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2529	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
961		2530
962	use AnyEvent;	2531	use AnyEvent;
		2532
		2533	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2534	be used to probe what backend is used and gain other information (which is
		2535	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2536	$ENV{PERL_ANYEVENT_STRICT}.
		2537
		2538	Note that AnyEvent will remove I<all> environment variables starting with
		2539	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2540	enabled.
		2541
		2542
		2543	=head1 BUGS
		2544
		2545	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2546	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2547	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2548	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2549	pronounced).
963		2550
964		2551
965	=head1 SEE ALSO	2552	=head1 SEE ALSO
966		2553
967	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	2554	Utility functions: L<AnyEvent::Util>.
968	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,	2555
		2556	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
969	L<Event::Lib>, L<Qt>, L<POE>.	2557	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
970		2558
971	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	2559	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2560	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2561	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
972	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,	2562	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
973	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
974	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
975		2563
		2564	Non-blocking file handles, sockets, TCP clients and
		2565	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2566
		2567	Asynchronous DNS: L<AnyEvent::DNS>.
		2568
		2569	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>,
		2570	L<Coro::Event>,
		2571
976	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	2572	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::XMPP>,
		2573	L<AnyEvent::HTTP>.
977		2574
978		2575
979	=head1 AUTHOR	2576	=head1 AUTHOR
980		2577
981	Marc Lehmann <schmorp@schmorp.de>	2578	Marc Lehmann <schmorp@schmorp.de>
982	http://home.schmorp.de/	2579	http://home.schmorp.de/
983		2580
984	=cut	2581	=cut
985		2582
986	1	2583	1
987		2584

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