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Revision 1.246 by root, Sat Jul 18 15:51:52 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
		6	event loops.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# file descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	13	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		14
		15	# one-shot or repeating timers
		16	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		17	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		18
		19	print AnyEvent->now; # prints current event loop time
		20	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		21
		22	# POSIX signal
		23	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		24
		25	# child process exit
		26	my $w = AnyEvent->child (pid => $pid, cb => sub {
		27	my ($pid, $status) = @_;
12	...	28	...
13	});	29	});
14		30
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	31	# called when event loop idle (if applicable)
16	...	32	my $w = AnyEvent->idle (cb => sub { ... });
17	});
18		33
19	my $w = AnyEvent->condvar; # stores 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.
22		45
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	46	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		47
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	48	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	49	nowadays. So what is different about AnyEvent?
27		50
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	51	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
29	policy> and AnyEvent is I<small and efficient>.	52	policy> and AnyEvent is I<small and efficient>.
30		53
31	First and foremost, I<AnyEvent is not an event model> itself, it only	54	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	55	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,	56	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,	57	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	58	only one event loop can be active at the same time in a process. AnyEvent
36	helps hiding the differences between those event loops.	59	cannot change this, but it can hide the differences between those event
		60	loops.
37		61
38	The goal of AnyEvent is to offer module authors the ability to do event	62	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	63	programming (waiting for I/O or timer events) without subscribing to a
40	religion, a way of living, and most importantly: without forcing your	64	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	65	module users into the same thing by forcing them to use the same event
42	model you use.	66	model you use.
43		67
44	For modules like POE or IO::Async (which is a total misnomer as it is	68	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	69	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	70	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	71	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	72	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.	73	module are I<also> forced to use the same event loop you use.
50		74
51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	75	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	76	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	77	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,	78	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	79	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	80	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	81	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).	82	to AnyEvent, too, so it is future-proof).
59		83
60	In addition to being free of having to use I<the one and only true event	84	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	85	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	86	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	87	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	88	offering the functionality that is necessary, in as thin as a wrapper as
65	technically possible.	89	technically possible.
66		90
		91	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		92	of useful functionality, such as an asynchronous DNS resolver, 100%
		93	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		94	such as Windows) and lots of real-world knowledge and workarounds for
		95	platform bugs and differences.
		96
67	Of course, if you want lots of policy (this can arguably be somewhat	97	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	98	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	99	model, you should I<not> use this module.
70
71		100
72	=head1 DESCRIPTION	101	=head1 DESCRIPTION
73		102
74	L<AnyEvent> provides an identical interface to multiple event loops. This	103	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	104	allows module authors to utilise an event loop without forcing module
…		…
78		107
79	The interface itself is vaguely similar, but not identical to the L<Event>	108	The interface itself is vaguely similar, but not identical to the L<Event>
80	module.	109	module.
81		110
82	During the first call of any watcher-creation method, the module tries	111	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	112	to detect the currently loaded event loop by probing whether one of the
84	the following modules is already loaded: L<Coro::EV>, L<Coro::Event>,	113	following modules is already loaded: L<EV>,
85	L<EV>, L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>. The first one	114	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	found is used. If none are found, the module tries to load these modules	115	L<POE>. The first one found is used. If none are found, the module tries
87	(excluding Event::Lib and Qt) in the order given. The first one that can	116	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		117	adaptor should always succeed) in the order given. The first one that can
88	be successfully loaded will be used. If, after this, still none could be	118	be successfully loaded will be used. If, after this, still none could be
89	found, AnyEvent will fall back to a pure-perl event loop, which is not	119	found, AnyEvent will fall back to a pure-perl event loop, which is not
90	very efficient, but should work everywhere.	120	very efficient, but should work everywhere.
91		121
92	Because AnyEvent first checks for modules that are already loaded, loading	122	Because AnyEvent first checks for modules that are already loaded, loading
…		…
102	starts using it, all bets are off. Maybe you should tell their authors to	132	starts using it, all bets are off. Maybe you should tell their authors to
103	use AnyEvent so their modules work together with others seamlessly...	133	use AnyEvent so their modules work together with others seamlessly...
104		134
105	The pure-perl implementation of AnyEvent is called	135	The pure-perl implementation of AnyEvent is called
106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	136	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
107	explicitly.	137	explicitly and enjoy the high availability of that event loop :)
108		138
109	=head1 WATCHERS	139	=head1 WATCHERS
110		140
111	AnyEvent has the central concept of a I<watcher>, which is an object that	141	AnyEvent has the central concept of a I<watcher>, which is an object that
112	stores relevant data for each kind of event you are waiting for, such as	142	stores relevant data for each kind of event you are waiting for, such as
113	the callback to call, the filehandle to watch, etc.	143	the callback to call, the file handle to watch, etc.
114		144
115	These watchers are normal Perl objects with normal Perl lifetime. After	145	These watchers are normal Perl objects with normal Perl lifetime. After
116	creating a watcher it will immediately "watch" for events and invoke the	146	creating a watcher it will immediately "watch" for events and invoke the
117	callback when the event occurs (of course, only when the event model	147	callback when the event occurs (of course, only when the event model
118	is in control).	148	is in control).
119		149
		150	Note that B<callbacks must not permanently change global variables>
		151	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		152	callbacks must not C<die> >>. The former is good programming practise in
		153	Perl and the latter stems from the fact that exception handling differs
		154	widely between event loops.
		155
120	To disable the watcher you have to destroy it (e.g. by setting the	156	To disable the watcher you have to destroy it (e.g. by setting the
121	variable you store it in to C<undef> or otherwise deleting all references	157	variable you store it in to C<undef> or otherwise deleting all references
122	to it).	158	to it).
123		159
124	All watchers are created by calling a method on the C<AnyEvent> class.	160	All watchers are created by calling a method on the C<AnyEvent> class.
…		…
126	Many watchers either are used with "recursion" (repeating timers for	162	Many watchers either are used with "recursion" (repeating timers for
127	example), or need to refer to their watcher object in other ways.	163	example), or need to refer to their watcher object in other ways.
128		164
129	An any way to achieve that is this pattern:	165	An any way to achieve that is this pattern:
130		166
131	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	167	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
132	# you can use $w here, for example to undef it	168	# you can use $w here, for example to undef it
133	undef $w;	169	undef $w;
134	});	170	});
135		171
136	Note that C<my $w; $w => combination. This is necessary because in Perl,	172	Note that C<my $w; $w => combination. This is necessary because in Perl,
137	my variables are only visible after the statement in which they are	173	my variables are only visible after the statement in which they are
138	declared.	174	declared.
139		175
140	=head2 IO WATCHERS	176	=head2 I/O WATCHERS
141		177
142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	178	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
143	with the following mandatory key-value pairs as arguments:	179	with the following mandatory key-value pairs as arguments:
144		180
145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	181	C<fh> is the Perl I<file handle> (or a naked file descriptor) to watch
		182	for events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example files
		186	or block devices.
		187
146	events. C<poll> must be a string that is either C<r> or C<w>, which	188	C<poll> must be a string that is either C<r> or C<w>, which creates a
147	creates a watcher waiting for "r"eadable or "w"ritable events,	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
148	respectively. C<cb> is the callback to invoke each time the file handle	191	C<cb> is the callback to invoke each time the file handle becomes ready.
149	becomes ready.
150		192
151	As long as the I/O watcher exists it will keep the file descriptor or a	193	Although the callback might get passed parameters, their value and
152	copy of it alive/open.	194	presence is undefined and you cannot rely on them. Portable AnyEvent
		195	callbacks cannot use arguments passed to I/O watcher callbacks.
153		196
		197	The I/O watcher might use the underlying file descriptor or a copy of it.
154	It is not allowed to close a file handle as long as any watcher is active	198	You must not close a file handle as long as any watcher is active on the
155	on the underlying file descriptor.	199	underlying file descriptor.
156		200
157	Some event loops issue spurious readyness notifications, so you should	201	Some event loops issue spurious readyness notifications, so you should
158	always use non-blocking calls when reading/writing from/to your file	202	always use non-blocking calls when reading/writing from/to your file
159	handles.	203	handles.
160		204
161	Example:
162
163	# wait for readability of STDIN, then read a line and disable the watcher	205	Example: wait for readability of STDIN, then read a line and disable the
		206	watcher.
		207
164	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
165	chomp (my $input = <STDIN>);	209	chomp (my $input = <STDIN>);
166	warn "read: $input\n";	210	warn "read: $input\n";
167	undef $w;	211	undef $w;
168	});	212	});
…		…
171		215
172	You can create a time watcher by calling the C<< AnyEvent->timer >>	216	You can create a time watcher by calling the C<< AnyEvent->timer >>
173	method with the following mandatory arguments:	217	method with the following mandatory arguments:
174		218
175	C<after> specifies after how many seconds (fractional values are	219	C<after> specifies after how many seconds (fractional values are
176	supported) should the timer activate. C<cb> the callback to invoke in that	220	supported) the callback should be invoked. C<cb> is the callback to invoke
177	case.	221	in that case.
178		222
179	The timer callback will be invoked at most once: if you want a repeating	223	Although the callback might get passed parameters, their value and
180	timer you have to create a new watcher (this is a limitation by both Tk	224	presence is undefined and you cannot rely on them. Portable AnyEvent
181	and Glib).	225	callbacks cannot use arguments passed to time watcher callbacks.
182		226
183	Example:	227	The callback will normally be invoked once only. If you specify another
		228	parameter, C<interval>, as a strictly positive number (> 0), then the
		229	callback will be invoked regularly at that interval (in fractional
		230	seconds) after the first invocation. If C<interval> is specified with a
		231	false value, then it is treated as if it were missing.
184		232
		233	The callback will be rescheduled before invoking the callback, but no
		234	attempt is done to avoid timer drift in most backends, so the interval is
		235	only approximate.
		236
185	# fire an event after 7.7 seconds	237	Example: fire an event after 7.7 seconds.
		238
186	my $w = AnyEvent->timer (after => 7.7, cb => sub {	239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
187	warn "timeout\n";	240	warn "timeout\n";
188	});	241	});
189		242
190	# to cancel the timer:	243	# to cancel the timer:
191	undef $w;	244	undef $w;
192		245
193	Example 2:
194
195	# fire an event after 0.5 seconds, then roughly every second	246	Example 2: fire an event after 0.5 seconds, then roughly every second.
196	my $w;
197		247
198	my $cb = sub {
199	# cancel the old timer while creating a new one
200	$w = AnyEvent->timer (after => 1, cb => $cb);	248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		249	warn "timeout\n";
201	};	250	};
202
203	# start the "loop" by creating the first watcher
204	$w = AnyEvent->timer (after => 0.5, cb => $cb);
205		251
206	=head3 TIMING ISSUES	252	=head3 TIMING ISSUES
207		253
208	There are two ways to handle timers: based on real time (relative, "fire	254	There are two ways to handle timers: based on real time (relative, "fire
209	in 10 seconds") and based on wallclock time (absolute, "fire at 12	255	in 10 seconds") and based on wallclock time (absolute, "fire at 12
…		…
221	timers.	267	timers.
222		268
223	AnyEvent always prefers relative timers, if available, matching the	269	AnyEvent always prefers relative timers, if available, matching the
224	AnyEvent API.	270	AnyEvent API.
225		271
		272	AnyEvent has two additional methods that return the "current time":
		273
		274	=over 4
		275
		276	=item AnyEvent->time
		277
		278	This returns the "current wallclock time" as a fractional number of
		279	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		280	return, and the result is guaranteed to be compatible with those).
		281
		282	It progresses independently of any event loop processing, i.e. each call
		283	will check the system clock, which usually gets updated frequently.
		284
		285	=item AnyEvent->now
		286
		287	This also returns the "current wallclock time", but unlike C<time>, above,
		288	this value might change only once per event loop iteration, depending on
		289	the event loop (most return the same time as C<time>, above). This is the
		290	time that AnyEvent's timers get scheduled against.
		291
		292	I<In almost all cases (in all cases if you don't care), this is the
		293	function to call when you want to know the current time.>
		294
		295	This function is also often faster then C<< AnyEvent->time >>, and
		296	thus the preferred method if you want some timestamp (for example,
		297	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		298
		299	The rest of this section is only of relevance if you try to be very exact
		300	with your timing, you can skip it without bad conscience.
		301
		302	For a practical example of when these times differ, consider L<Event::Lib>
		303	and L<EV> and the following set-up:
		304
		305	The event loop is running and has just invoked one of your callback at
		306	time=500 (assume no other callbacks delay processing). In your callback,
		307	you wait a second by executing C<sleep 1> (blocking the process for a
		308	second) and then (at time=501) you create a relative timer that fires
		309	after three seconds.
		310
		311	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		312	both return C<501>, because that is the current time, and the timer will
		313	be scheduled to fire at time=504 (C<501> + C<3>).
		314
		315	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		316	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		317	last event processing phase started. With L<EV>, your timer gets scheduled
		318	to run at time=503 (C<500> + C<3>).
		319
		320	In one sense, L<Event::Lib> is more exact, as it uses the current time
		321	regardless of any delays introduced by event processing. However, most
		322	callbacks do not expect large delays in processing, so this causes a
		323	higher drift (and a lot more system calls to get the current time).
		324
		325	In another sense, L<EV> is more exact, as your timer will be scheduled at
		326	the same time, regardless of how long event processing actually took.
		327
		328	In either case, if you care (and in most cases, you don't), then you
		329	can get whatever behaviour you want with any event loop, by taking the
		330	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		331	account.
		332
		333	=item AnyEvent->now_update
		334
		335	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		336	the current time for each loop iteration (see the discussion of L<<
		337	AnyEvent->now >>, above).
		338
		339	When a callback runs for a long time (or when the process sleeps), then
		340	this "current" time will differ substantially from the real time, which
		341	might affect timers and time-outs.
		342
		343	When this is the case, you can call this method, which will update the
		344	event loop's idea of "current time".
		345
		346	Note that updating the time I<might> cause some events to be handled.
		347
		348	=back
		349
226	=head2 SIGNAL WATCHERS	350	=head2 SIGNAL WATCHERS
227		351
228	You can watch for signals using a signal watcher, C<signal> is the signal	352	You can watch for signals using a signal watcher, C<signal> is the signal
229	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	353	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
230	be invoked whenever a signal occurs.	354	callback to be invoked whenever a signal occurs.
231		355
		356	Although the callback might get passed parameters, their value and
		357	presence is undefined and you cannot rely on them. Portable AnyEvent
		358	callbacks cannot use arguments passed to signal watcher callbacks.
		359
232	Multiple signal occurances can be clumped together into one callback	360	Multiple signal occurrences can be clumped together into one callback
233	invocation, and callback invocation will be synchronous. synchronous means	361	invocation, and callback invocation will be synchronous. Synchronous means
234	that it might take a while until the signal gets handled by the process,	362	that it might take a while until the signal gets handled by the process,
235	but it is guarenteed not to interrupt any other callbacks.	363	but it is guaranteed not to interrupt any other callbacks.
236		364
237	The main advantage of using these watchers is that you can share a signal	365	The main advantage of using these watchers is that you can share a signal
238	between multiple watchers.	366	between multiple watchers, and AnyEvent will ensure that signals will not
		367	interrupt your program at bad times.
239		368
240	This watcher might use C<%SIG>, so programs overwriting those signals	369	This watcher might use C<%SIG> (depending on the event loop used),
241	directly will likely not work correctly.	370	so programs overwriting those signals directly will likely not work
		371	correctly.
		372
		373	Also note that many event loops (e.g. Glib, Tk, Qt, IO::Async) do not
		374	support attaching callbacks to signals, which is a pity, as you cannot do
		375	race-free signal handling in perl. AnyEvent will try to do it's best, but
		376	in some cases, signals will be delayed. The maximum time a signal might
		377	be delayed is specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10
		378	seconds). This variable can be changed only before the first signal
		379	watcher is created, and should be left alone otherwise. Higher values
		380	will cause fewer spurious wake-ups, which is better for power and CPU
		381	saving. All these problems can be avoided by installing the optional
		382	L<Async::Interrupt> module.
242		383
243	Example: exit on SIGINT	384	Example: exit on SIGINT
244		385
245	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	386	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
246		387
247	=head2 CHILD PROCESS WATCHERS	388	=head2 CHILD PROCESS WATCHERS
248		389
249	You can also watch on a child process exit and catch its exit status.	390	You can also watch on a child process exit and catch its exit status.
250		391
251	The child process is specified by the C<pid> argument (if set to C<0>, it	392	The child process is specified by the C<pid> argument (if set to C<0>, it
252	watches for any child process exit). The watcher will trigger as often	393	watches for any child process exit). The watcher will triggered only when
253	as status change for the child are received. This works by installing a	394	the child process has finished and an exit status is available, not on
254	signal handler for C<SIGCHLD>. The callback will be called with the pid	395	any trace events (stopped/continued).
255	and exit status (as returned by waitpid).
256		396
257	Example: wait for pid 1333	397	The callback will be called with the pid and exit status (as returned by
		398	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		399	callback arguments.
258		400
		401	This watcher type works by installing a signal handler for C<SIGCHLD>,
		402	and since it cannot be shared, nothing else should use SIGCHLD or reap
		403	random child processes (waiting for specific child processes, e.g. inside
		404	C<system>, is just fine).
		405
		406	There is a slight catch to child watchers, however: you usually start them
		407	I<after> the child process was created, and this means the process could
		408	have exited already (and no SIGCHLD will be sent anymore).
		409
		410	Not all event models handle this correctly (neither POE nor IO::Async do,
		411	see their AnyEvent::Impl manpages for details), but even for event models
		412	that I<do> handle this correctly, they usually need to be loaded before
		413	the process exits (i.e. before you fork in the first place). AnyEvent's
		414	pure perl event loop handles all cases correctly regardless of when you
		415	start the watcher.
		416
		417	This means you cannot create a child watcher as the very first
		418	thing in an AnyEvent program, you I<have> to create at least one
		419	watcher before you C<fork> the child (alternatively, you can call
		420	C<AnyEvent::detect>).
		421
		422	As most event loops do not support waiting for child events, they will be
		423	emulated by AnyEvent in most cases, in which the latency and race problems
		424	mentioned in the description of signal watchers apply.
		425
		426	Example: fork a process and wait for it
		427
		428	my $done = AnyEvent->condvar;
		429
		430	my $pid = fork or exit 5;
		431
259	my $w = AnyEvent->child (	432	my $w = AnyEvent->child (
260	pid => 1333,	433	pid => $pid,
261	cb => sub {	434	cb => sub {
262	my ($pid, $status) = @_;	435	my ($pid, $status) = @_;
263	warn "pid $pid exited with status $status";	436	warn "pid $pid exited with status $status";
		437	$done->send;
264	},	438	},
265	);	439	);
		440
		441	# do something else, then wait for process exit
		442	$done->recv;
		443
		444	=head2 IDLE WATCHERS
		445
		446	Sometimes there is a need to do something, but it is not so important
		447	to do it instantly, but only when there is nothing better to do. This
		448	"nothing better to do" is usually defined to be "no other events need
		449	attention by the event loop".
		450
		451	Idle watchers ideally get invoked when the event loop has nothing
		452	better to do, just before it would block the process to wait for new
		453	events. Instead of blocking, the idle watcher is invoked.
		454
		455	Most event loops unfortunately do not really support idle watchers (only
		456	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		457	will simply call the callback "from time to time".
		458
		459	Example: read lines from STDIN, but only process them when the
		460	program is otherwise idle:
		461
		462	my @lines; # read data
		463	my $idle_w;
		464	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		465	push @lines, scalar <STDIN>;
		466
		467	# start an idle watcher, if not already done
		468	$idle_w ||= AnyEvent->idle (cb => sub {
		469	# handle only one line, when there are lines left
		470	if (my $line = shift @lines) {
		471	print "handled when idle: $line";
		472	} else {
		473	# otherwise disable the idle watcher again
		474	undef $idle_w;
		475	}
		476	});
		477	});
266		478
267	=head2 CONDITION VARIABLES	479	=head2 CONDITION VARIABLES
268		480
		481	If you are familiar with some event loops you will know that all of them
		482	require you to run some blocking "loop", "run" or similar function that
		483	will actively watch for new events and call your callbacks.
		484
		485	AnyEvent is slightly different: it expects somebody else to run the event
		486	loop and will only block when necessary (usually when told by the user).
		487
		488	The instrument to do that is called a "condition variable", so called
		489	because they represent a condition that must become true.
		490
		491	Now is probably a good time to look at the examples further below.
		492
269	Condition variables can be created by calling the C<< AnyEvent->condvar >>	493	Condition variables can be created by calling the C<< AnyEvent->condvar
270	method without any arguments.	494	>> method, usually without arguments. The only argument pair allowed is
		495	C<cb>, which specifies a callback to be called when the condition variable
		496	becomes true, with the condition variable as the first argument (but not
		497	the results).
271		498
272	A condition variable waits for a condition - precisely that the C<<	499	After creation, the condition variable is "false" until it becomes "true"
273	->broadcast >> method has been called.	500	by calling the C<send> method (or calling the condition variable as if it
		501	were a callback, read about the caveats in the description for the C<<
		502	->send >> method).
274		503
275	They are very useful to signal that a condition has been fulfilled, for	504	Condition variables are similar to callbacks, except that you can
		505	optionally wait for them. They can also be called merge points - points
		506	in time where multiple outstanding events have been processed. And yet
		507	another way to call them is transactions - each condition variable can be
		508	used to represent a transaction, which finishes at some point and delivers
		509	a result.
		510
		511	Condition variables are very useful to signal that something has finished,
276	example, if you write a module that does asynchronous http requests,	512	for example, if you write a module that does asynchronous http requests,
277	then a condition variable would be the ideal candidate to signal the	513	then a condition variable would be the ideal candidate to signal the
278	availability of results.	514	availability of results. The user can either act when the callback is
		515	called or can synchronously C<< ->recv >> for the results.
279		516
280	You can also use condition variables to block your main program until	517	You can also use them to simulate traditional event loops - for example,
281	an event occurs - for example, you could C<< ->wait >> in your main	518	you can block your main program until an event occurs - for example, you
282	program until the user clicks the Quit button in your app, which would C<<	519	could C<< ->recv >> in your main program until the user clicks the Quit
283	->broadcast >> the "quit" event.	520	button of your app, which would C<< ->send >> the "quit" event.
284		521
285	Note that condition variables recurse into the event loop - if you have	522	Note that condition variables recurse into the event loop - if you have
286	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	523	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
287	lose. Therefore, condition variables are good to export to your caller, but	524	lose. Therefore, condition variables are good to export to your caller, but
288	you should avoid making a blocking wait yourself, at least in callbacks,	525	you should avoid making a blocking wait yourself, at least in callbacks,
289	as this asks for trouble.	526	as this asks for trouble.
290		527
291	This object has two methods:	528	Condition variables are represented by hash refs in perl, and the keys
		529	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		530	easy (it is often useful to build your own transaction class on top of
		531	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		532	it's C<new> method in your own C<new> method.
292		533
293	=over 4	534	There are two "sides" to a condition variable - the "producer side" which
		535	eventually calls C<< -> send >>, and the "consumer side", which waits
		536	for the send to occur.
294		537
295	=item $cv->wait	538	Example: wait for a timer.
296
297	Wait (blocking if necessary) until the C<< ->broadcast >> method has been
298	called on c<$cv>, while servicing other watchers normally.
299
300	You can only wait once on a condition - additional calls will return
301	immediately.
302
303	Not all event models support a blocking wait - some die in that case
304	(programs might want to do that to stay interactive), so I<if you are
305	using this from a module, never require a blocking wait>, but let the
306	caller decide whether the call will block or not (for example, by coupling
307	condition variables with some kind of request results and supporting
308	callbacks so the caller knows that getting the result will not block,
309	while still suppporting blocking waits if the caller so desires).
310
311	Another reason I<never> to C<< ->wait >> in a module is that you cannot
312	sensibly have two C<< ->wait >>'s in parallel, as that would require
313	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
314	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
315	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
316	from different coroutines, however).
317
318	=item $cv->broadcast
319
320	Flag the condition as ready - a running C<< ->wait >> and all further
321	calls to C<wait> will (eventually) return after this method has been
322	called. If nobody is waiting the broadcast will be remembered..
323
324	=back
325
326	Example:
327		539
328	# wait till the result is ready	540	# wait till the result is ready
329	my $result_ready = AnyEvent->condvar;	541	my $result_ready = AnyEvent->condvar;
330		542
331	# do something such as adding a timer	543	# do something such as adding a timer
332	# or socket watcher the calls $result_ready->broadcast	544	# or socket watcher the calls $result_ready->send
333	# when the "result" is ready.	545	# when the "result" is ready.
334	# in this case, we simply use a timer:	546	# in this case, we simply use a timer:
335	my $w = AnyEvent->timer (	547	my $w = AnyEvent->timer (
336	after => 1,	548	after => 1,
337	cb => sub { $result_ready->broadcast },	549	cb => sub { $result_ready->send },
338	);	550	);
339		551
340	# this "blocks" (while handling events) till the watcher	552	# this "blocks" (while handling events) till the callback
341	# calls broadcast	553	# calls -<send
342	$result_ready->wait;	554	$result_ready->recv;
		555
		556	Example: wait for a timer, but take advantage of the fact that condition
		557	variables are also callable directly.
		558
		559	my $done = AnyEvent->condvar;
		560	my $delay = AnyEvent->timer (after => 5, cb => $done);
		561	$done->recv;
		562
		563	Example: Imagine an API that returns a condvar and doesn't support
		564	callbacks. This is how you make a synchronous call, for example from
		565	the main program:
		566
		567	use AnyEvent::CouchDB;
		568
		569	...
		570
		571	my @info = $couchdb->info->recv;
		572
		573	And this is how you would just set a callback to be called whenever the
		574	results are available:
		575
		576	$couchdb->info->cb (sub {
		577	my @info = $_[0]->recv;
		578	});
		579
		580	=head3 METHODS FOR PRODUCERS
		581
		582	These methods should only be used by the producing side, i.e. the
		583	code/module that eventually sends the signal. Note that it is also
		584	the producer side which creates the condvar in most cases, but it isn't
		585	uncommon for the consumer to create it as well.
		586
		587	=over 4
		588
		589	=item $cv->send (...)
		590
		591	Flag the condition as ready - a running C<< ->recv >> and all further
		592	calls to C<recv> will (eventually) return after this method has been
		593	called. If nobody is waiting the send will be remembered.
		594
		595	If a callback has been set on the condition variable, it is called
		596	immediately from within send.
		597
		598	Any arguments passed to the C<send> call will be returned by all
		599	future C<< ->recv >> calls.
		600
		601	Condition variables are overloaded so one can call them directly (as if
		602	they were a code reference). Calling them directly is the same as calling
		603	C<send>.
		604
		605	=item $cv->croak ($error)
		606
		607	Similar to send, but causes all call's to C<< ->recv >> to invoke
		608	C<Carp::croak> with the given error message/object/scalar.
		609
		610	This can be used to signal any errors to the condition variable
		611	user/consumer. Doing it this way instead of calling C<croak> directly
		612	delays the error detetcion, but has the overwhelmign advantage that it
		613	diagnoses the error at the place where the result is expected, and not
		614	deep in some event clalback without connection to the actual code causing
		615	the problem.
		616
		617	=item $cv->begin ([group callback])
		618
		619	=item $cv->end
		620
		621	These two methods can be used to combine many transactions/events into
		622	one. For example, a function that pings many hosts in parallel might want
		623	to use a condition variable for the whole process.
		624
		625	Every call to C<< ->begin >> will increment a counter, and every call to
		626	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		627	>>, the (last) callback passed to C<begin> will be executed. That callback
		628	is I<supposed> to call C<< ->send >>, but that is not required. If no
		629	callback was set, C<send> will be called without any arguments.
		630
		631	You can think of C<< $cv->send >> giving you an OR condition (one call
		632	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		633	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		634
		635	Let's start with a simple example: you have two I/O watchers (for example,
		636	STDOUT and STDERR for a program), and you want to wait for both streams to
		637	close before activating a condvar:
		638
		639	my $cv = AnyEvent->condvar;
		640
		641	$cv->begin; # first watcher
		642	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		643	defined sysread $fh1, my $buf, 4096
		644	or $cv->end;
		645	});
		646
		647	$cv->begin; # second watcher
		648	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		649	defined sysread $fh2, my $buf, 4096
		650	or $cv->end;
		651	});
		652
		653	$cv->recv;
		654
		655	This works because for every event source (EOF on file handle), there is
		656	one call to C<begin>, so the condvar waits for all calls to C<end> before
		657	sending.
		658
		659	The ping example mentioned above is slightly more complicated, as the
		660	there are results to be passwd back, and the number of tasks that are
		661	begung can potentially be zero:
		662
		663	my $cv = AnyEvent->condvar;
		664
		665	my %result;
		666	$cv->begin (sub { $cv->send (\%result) });
		667
		668	for my $host (@list_of_hosts) {
		669	$cv->begin;
		670	ping_host_then_call_callback $host, sub {
		671	$result{$host} = ...;
		672	$cv->end;
		673	};
		674	}
		675
		676	$cv->end;
		677
		678	This code fragment supposedly pings a number of hosts and calls
		679	C<send> after results for all then have have been gathered - in any
		680	order. To achieve this, the code issues a call to C<begin> when it starts
		681	each ping request and calls C<end> when it has received some result for
		682	it. Since C<begin> and C<end> only maintain a counter, the order in which
		683	results arrive is not relevant.
		684
		685	There is an additional bracketing call to C<begin> and C<end> outside the
		686	loop, which serves two important purposes: first, it sets the callback
		687	to be called once the counter reaches C<0>, and second, it ensures that
		688	C<send> is called even when C<no> hosts are being pinged (the loop
		689	doesn't execute once).
		690
		691	This is the general pattern when you "fan out" into multiple (but
		692	potentially none) subrequests: use an outer C<begin>/C<end> pair to set
		693	the callback and ensure C<end> is called at least once, and then, for each
		694	subrequest you start, call C<begin> and for each subrequest you finish,
		695	call C<end>.
		696
		697	=back
		698
		699	=head3 METHODS FOR CONSUMERS
		700
		701	These methods should only be used by the consuming side, i.e. the
		702	code awaits the condition.
		703
		704	=over 4
		705
		706	=item $cv->recv
		707
		708	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		709	>> methods have been called on c<$cv>, while servicing other watchers
		710	normally.
		711
		712	You can only wait once on a condition - additional calls are valid but
		713	will return immediately.
		714
		715	If an error condition has been set by calling C<< ->croak >>, then this
		716	function will call C<croak>.
		717
		718	In list context, all parameters passed to C<send> will be returned,
		719	in scalar context only the first one will be returned.
		720
		721	Note that doing a blocking wait in a callback is not supported by any
		722	event loop, that is, recursive invocation of a blocking C<< ->recv
		723	>> is not allowed, and the C<recv> call will C<croak> if such a
		724	condition is detected. This condition can be slightly loosened by using
		725	L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
		726	any thread that doesn't run the event loop itself.
		727
		728	Not all event models support a blocking wait - some die in that case
		729	(programs might want to do that to stay interactive), so I<if you are
		730	using this from a module, never require a blocking wait>. Instead, let the
		731	caller decide whether the call will block or not (for example, by coupling
		732	condition variables with some kind of request results and supporting
		733	callbacks so the caller knows that getting the result will not block,
		734	while still supporting blocking waits if the caller so desires).
		735
		736	You can ensure that C<< -recv >> never blocks by setting a callback and
		737	only calling C<< ->recv >> from within that callback (or at a later
		738	time). This will work even when the event loop does not support blocking
		739	waits otherwise.
		740
		741	=item $bool = $cv->ready
		742
		743	Returns true when the condition is "true", i.e. whether C<send> or
		744	C<croak> have been called.
		745
		746	=item $cb = $cv->cb ($cb->($cv))
		747
		748	This is a mutator function that returns the callback set and optionally
		749	replaces it before doing so.
		750
		751	The callback will be called when the condition becomes "true", i.e. when
		752	C<send> or C<croak> are called, with the only argument being the condition
		753	variable itself. Calling C<recv> inside the callback or at any later time
		754	is guaranteed not to block.
		755
		756	=back
		757
		758	=head1 SUPPORTED EVENT LOOPS/BACKENDS
		759
		760	The available backend classes are (every class has its own manpage):
		761
		762	=over 4
		763
		764	=item Backends that are autoprobed when no other event loop can be found.
		765
		766	EV is the preferred backend when no other event loop seems to be in
		767	use. If EV is not installed, then AnyEvent will try Event, and, failing
		768	that, will fall back to its own pure-perl implementation, which is
		769	available everywhere as it comes with AnyEvent itself.
		770
		771	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		772	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		773	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		774
		775	=item Backends that are transparently being picked up when they are used.
		776
		777	These will be used when they are currently loaded when the first watcher
		778	is created, in which case it is assumed that the application is using
		779	them. This means that AnyEvent will automatically pick the right backend
		780	when the main program loads an event module before anything starts to
		781	create watchers. Nothing special needs to be done by the main program.
		782
		783	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		784	AnyEvent::Impl::Tk based on Tk, very broken.
		785	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		786	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		787
		788	=item Backends with special needs.
		789
		790	Qt requires the Qt::Application to be instantiated first, but will
		791	otherwise be picked up automatically. As long as the main program
		792	instantiates the application before any AnyEvent watchers are created,
		793	everything should just work.
		794
		795	AnyEvent::Impl::Qt based on Qt.
		796
		797	Support for IO::Async can only be partial, as it is too broken and
		798	architecturally limited to even support the AnyEvent API. It also
		799	is the only event loop that needs the loop to be set explicitly, so
		800	it can only be used by a main program knowing about AnyEvent. See
		801	L<AnyEvent::Impl::Async> for the gory details.
		802
		803	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		804
		805	=item Event loops that are indirectly supported via other backends.
		806
		807	Some event loops can be supported via other modules:
		808
		809	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		810
		811	B<WxWidgets> has no support for watching file handles. However, you can
		812	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		813	polls 20 times per second, which was considered to be too horrible to even
		814	consider for AnyEvent.
		815
		816	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		817	backend, so it can be supported through POE.
		818
		819	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		820	load L<POE> when detecting them, in the hope that POE will pick them up,
		821	in which case everything will be automatic.
		822
		823	=back
343		824
344	=head1 GLOBAL VARIABLES AND FUNCTIONS	825	=head1 GLOBAL VARIABLES AND FUNCTIONS
345		826
		827	These are not normally required to use AnyEvent, but can be useful to
		828	write AnyEvent extension modules.
		829
346	=over 4	830	=over 4
347		831
348	=item $AnyEvent::MODEL	832	=item $AnyEvent::MODEL
349		833
350	Contains C<undef> until the first watcher is being created. Then it	834	Contains C<undef> until the first watcher is being created, before the
		835	backend has been autodetected.
		836
351	contains the event model that is being used, which is the name of the	837	Afterwards it contains the event model that is being used, which is the
352	Perl class implementing the model. This class is usually one of the	838	name of the Perl class implementing the model. This class is usually one
353	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	839	of the C<AnyEvent::Impl:xxx> modules, but can be any other class in the
354	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	840	case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
355		841	will be C<urxvt::anyevent>).
356	The known classes so far are:
357
358	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
359	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
360	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
361	AnyEvent::Impl::Event based on Event, second best choice.
362	AnyEvent::Impl::Glib based on Glib, third-best choice.
363	AnyEvent::Impl::Tk based on Tk, very bad choice.
364	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
365	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
366	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
367		842
368	=item AnyEvent::detect	843	=item AnyEvent::detect
369		844
370	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	845	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
371	if necessary. You should only call this function right before you would	846	if necessary. You should only call this function right before you would
372	have created an AnyEvent watcher anyway, that is, as late as possible at	847	have created an AnyEvent watcher anyway, that is, as late as possible at
373	runtime.	848	runtime, and not e.g. while initialising of your module.
		849
		850	If you need to do some initialisation before AnyEvent watchers are
		851	created, use C<post_detect>.
		852
		853	=item $guard = AnyEvent::post_detect { BLOCK }
		854
		855	Arranges for the code block to be executed as soon as the event model is
		856	autodetected (or immediately if this has already happened).
		857
		858	The block will be executed I<after> the actual backend has been detected
		859	(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
		860	created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
		861	other initialisations - see the sources of L<AnyEvent::Strict> or
		862	L<AnyEvent::AIO> to see how this is used.
		863
		864	The most common usage is to create some global watchers, without forcing
		865	event module detection too early, for example, L<AnyEvent::AIO> creates
		866	and installs the global L<IO::AIO> watcher in a C<post_detect> block to
		867	avoid autodetecting the event module at load time.
		868
		869	If called in scalar or list context, then it creates and returns an object
		870	that automatically removes the callback again when it is destroyed. See
		871	L<Coro::BDB> for a case where this is useful.
		872
		873	=item @AnyEvent::post_detect
		874
		875	If there are any code references in this array (you can C<push> to it
		876	before or after loading AnyEvent), then they will called directly after
		877	the event loop has been chosen.
		878
		879	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		880	if it is defined then the event loop has already been detected, and the
		881	array will be ignored.
		882
		883	Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
		884	it,as it takes care of these details.
		885
		886	This variable is mainly useful for modules that can do something useful
		887	when AnyEvent is used and thus want to know when it is initialised, but do
		888	not need to even load it by default. This array provides the means to hook
		889	into AnyEvent passively, without loading it.
374		890
375	=back	891	=back
376		892
377	=head1 WHAT TO DO IN A MODULE	893	=head1 WHAT TO DO IN A MODULE
378		894
…		…
382	Be careful when you create watchers in the module body - AnyEvent will	898	Be careful when you create watchers in the module body - AnyEvent will
383	decide which event module to use as soon as the first method is called, so	899	decide which event module to use as soon as the first method is called, so
384	by calling AnyEvent in your module body you force the user of your module	900	by calling AnyEvent in your module body you force the user of your module
385	to load the event module first.	901	to load the event module first.
386		902
387	Never call C<< ->wait >> on a condition variable unless you I<know> that	903	Never call C<< ->recv >> on a condition variable unless you I<know> that
388	the C<< ->broadcast >> method has been called on it already. This is	904	the C<< ->send >> method has been called on it already. This is
389	because it will stall the whole program, and the whole point of using	905	because it will stall the whole program, and the whole point of using
390	events is to stay interactive.	906	events is to stay interactive.
391		907
392	It is fine, however, to call C<< ->wait >> when the user of your module	908	It is fine, however, to call C<< ->recv >> when the user of your module
393	requests it (i.e. if you create a http request object ad have a method	909	requests it (i.e. if you create a http request object ad have a method
394	called C<results> that returns the results, it should call C<< ->wait >>	910	called C<results> that returns the results, it should call C<< ->recv >>
395	freely, as the user of your module knows what she is doing. always).	911	freely, as the user of your module knows what she is doing. always).
396		912
397	=head1 WHAT TO DO IN THE MAIN PROGRAM	913	=head1 WHAT TO DO IN THE MAIN PROGRAM
398		914
399	There will always be a single main program - the only place that should	915	There will always be a single main program - the only place that should
…		…
401		917
402	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	918	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
403	do anything special (it does not need to be event-based) and let AnyEvent	919	do anything special (it does not need to be event-based) and let AnyEvent
404	decide which implementation to chose if some module relies on it.	920	decide which implementation to chose if some module relies on it.
405		921
406	If the main program relies on a specific event model. For example, in	922	If the main program relies on a specific event model - for example, in
407	Gtk2 programs you have to rely on the Glib module. You should load the	923	Gtk2 programs you have to rely on the Glib module - you should load the
408	event module before loading AnyEvent or any module that uses it: generally	924	event module before loading AnyEvent or any module that uses it: generally
409	speaking, you should load it as early as possible. The reason is that	925	speaking, you should load it as early as possible. The reason is that
410	modules might create watchers when they are loaded, and AnyEvent will	926	modules might create watchers when they are loaded, and AnyEvent will
411	decide on the event model to use as soon as it creates watchers, and it	927	decide on the event model to use as soon as it creates watchers, and it
412	might chose the wrong one unless you load the correct one yourself.	928	might chose the wrong one unless you load the correct one yourself.
413		929
414	You can chose to use a rather inefficient pure-perl implementation by	930	You can chose to use a pure-perl implementation by loading the
415	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	931	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
416	behaviour everywhere, but letting AnyEvent chose is generally better.	932	everywhere, but letting AnyEvent chose the model is generally better.
		933
		934	=head2 MAINLOOP EMULATION
		935
		936	Sometimes (often for short test scripts, or even standalone programs who
		937	only want to use AnyEvent), you do not want to run a specific event loop.
		938
		939	In that case, you can use a condition variable like this:
		940
		941	AnyEvent->condvar->recv;
		942
		943	This has the effect of entering the event loop and looping forever.
		944
		945	Note that usually your program has some exit condition, in which case
		946	it is better to use the "traditional" approach of storing a condition
		947	variable somewhere, waiting for it, and sending it when the program should
		948	exit cleanly.
		949
		950
		951	=head1 OTHER MODULES
		952
		953	The following is a non-exhaustive list of additional modules that use
		954	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		955	modules and other event loops in the same program. Some of the modules
		956	come with AnyEvent, most are available via CPAN.
		957
		958	=over 4
		959
		960	=item L<AnyEvent::Util>
		961
		962	Contains various utility functions that replace often-used but blocking
		963	functions such as C<inet_aton> by event-/callback-based versions.
		964
		965	=item L<AnyEvent::Socket>
		966
		967	Provides various utility functions for (internet protocol) sockets,
		968	addresses and name resolution. Also functions to create non-blocking tcp
		969	connections or tcp servers, with IPv6 and SRV record support and more.
		970
		971	=item L<AnyEvent::Handle>
		972
		973	Provide read and write buffers, manages watchers for reads and writes,
		974	supports raw and formatted I/O, I/O queued and fully transparent and
		975	non-blocking SSL/TLS (via L<AnyEvent::TLS>.
		976
		977	=item L<AnyEvent::DNS>
		978
		979	Provides rich asynchronous DNS resolver capabilities.
		980
		981	=item L<AnyEvent::HTTP>
		982
		983	A simple-to-use HTTP library that is capable of making a lot of concurrent
		984	HTTP requests.
		985
		986	=item L<AnyEvent::HTTPD>
		987
		988	Provides a simple web application server framework.
		989
		990	=item L<AnyEvent::FastPing>
		991
		992	The fastest ping in the west.
		993
		994	=item L<AnyEvent::DBI>
		995
		996	Executes L<DBI> requests asynchronously in a proxy process.
		997
		998	=item L<AnyEvent::AIO>
		999
		1000	Truly asynchronous I/O, should be in the toolbox of every event
		1001	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		1002	together.
		1003
		1004	=item L<AnyEvent::BDB>
		1005
		1006	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		1007	L<BDB> and AnyEvent together.
		1008
		1009	=item L<AnyEvent::GPSD>
		1010
		1011	A non-blocking interface to gpsd, a daemon delivering GPS information.
		1012
		1013	=item L<AnyEvent::IRC>
		1014
		1015	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		1016
		1017	=item L<AnyEvent::XMPP>
		1018
		1019	AnyEvent based XMPP (Jabber protocol) module family (replacing the older
		1020	Net::XMPP2>.
		1021
		1022	=item L<AnyEvent::IGS>
		1023
		1024	A non-blocking interface to the Internet Go Server protocol (used by
		1025	L<App::IGS>).
		1026
		1027	=item L<Net::FCP>
		1028
		1029	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		1030	of AnyEvent.
		1031
		1032	=item L<Event::ExecFlow>
		1033
		1034	High level API for event-based execution flow control.
		1035
		1036	=item L<Coro>
		1037
		1038	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1039
		1040	=back
417		1041
418	=cut	1042	=cut
419		1043
420	package AnyEvent;	1044	package AnyEvent;
421		1045
		1046	# basically a tuned-down version of common::sense
		1047	sub common_sense {
422	no warnings;	1048	# no warnings
423	use strict;	1049	${^WARNING_BITS} ^= ${^WARNING_BITS};
		1050	# use strict vars subs
		1051	$^H |= 0x00000600;
		1052	}
424		1053
		1054	BEGIN { AnyEvent::common_sense }
		1055
425	use Carp;	1056	use Carp ();
426		1057
427	our $VERSION = '3.2';	1058	our $VERSION = 4.85;
428	our $MODEL;	1059	our $MODEL;
429		1060
430	our $AUTOLOAD;	1061	our $AUTOLOAD;
431	our @ISA;	1062	our @ISA;
432		1063
433	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
434
435	our @REGISTRY;	1064	our @REGISTRY;
436		1065
		1066	our $WIN32;
		1067
		1068	our $VERBOSE;
		1069
		1070	BEGIN {
		1071	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		1072	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		1073
		1074	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1075	if ${^TAINT};
		1076
		1077	$VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		1078
		1079	}
		1080
		1081	our $MAX_SIGNAL_LATENCY = 10;
		1082
		1083	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1084
		1085	{
		1086	my $idx;
		1087	$PROTOCOL{$_} = ++$idx
		1088	for reverse split /\s*,\s*/,
		1089	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1090	}
		1091
437	my @models = (	1092	my @models = (
438	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
439	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
440	[EV:: => AnyEvent::Impl::EV::],	1093	[EV:: => AnyEvent::Impl::EV::],
441	[Event:: => AnyEvent::Impl::Event::],	1094	[Event:: => AnyEvent::Impl::Event::],
442	[Glib:: => AnyEvent::Impl::Glib::],
443	[Tk:: => AnyEvent::Impl::Tk::],
444	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	1095	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		1096	# everything below here will not be autoprobed
		1097	# as the pureperl backend should work everywhere
		1098	# and is usually faster
		1099	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		1100	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1101	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1102	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1103	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1104	[Wx:: => AnyEvent::Impl::POE::],
		1105	[Prima:: => AnyEvent::Impl::POE::],
		1106	# IO::Async is just too broken - we would need workarounds for its
		1107	# byzantine signal and broken child handling, among others.
		1108	# IO::Async is rather hard to detect, as it doesn't have any
		1109	# obvious default class.
		1110	# [IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1111	# [IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1112	# [IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
445	);	1113	);
446	my @models_detect = (
447	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
448	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
449	);
450		1114
451	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);	1115	our %method = map +($_ => 1),
		1116	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
		1117
		1118	our @post_detect;
		1119
		1120	sub post_detect(&) {
		1121	my ($cb) = @_;
		1122
		1123	if ($MODEL) {
		1124	$cb->();
		1125
		1126	1
		1127	} else {
		1128	push @post_detect, $cb;
		1129
		1130	defined wantarray
		1131	? bless \$cb, "AnyEvent::Util::postdetect"
		1132	: ()
		1133	}
		1134	}
		1135
		1136	sub AnyEvent::Util::postdetect::DESTROY {
		1137	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1138	}
452		1139
453	sub detect() {	1140	sub detect() {
454	unless ($MODEL) {	1141	unless ($MODEL) {
455	no strict 'refs';	1142	local $SIG{__DIE__};
456		1143
457	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {	1144	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
458	my $model = "AnyEvent::Impl::$1";	1145	my $model = "AnyEvent::Impl::$1";
459	if (eval "require $model") {	1146	if (eval "require $model") {
460	$MODEL = $model;	1147	$MODEL = $model;
461	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;	1148	warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
		1149	} else {
		1150	warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
462	}	1151	}
463	}	1152	}
464		1153
465	# check for already loaded models	1154	# check for already loaded models
466	unless ($MODEL) {	1155	unless ($MODEL) {
467	for (@REGISTRY, @models, @models_detect) {	1156	for (@REGISTRY, @models) {
468	my ($package, $model) = @$_;	1157	my ($package, $model) = @$_;
469	if (${"$package\::VERSION"} > 0) {	1158	if (${"$package\::VERSION"} > 0) {
470	if (eval "require $model") {	1159	if (eval "require $model") {
471	$MODEL = $model;	1160	$MODEL = $model;
472	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;	1161	warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
473	last;	1162	last;
474	}	1163	}
475	}	1164	}
476	}	1165	}
477		1166
…		…
482	my ($package, $model) = @$_;	1171	my ($package, $model) = @$_;
483	if (eval "require $package"	1172	if (eval "require $package"
484	and ${"$package\::VERSION"} > 0	1173	and ${"$package\::VERSION"} > 0
485	and eval "require $model") {	1174	and eval "require $model") {
486	$MODEL = $model;	1175	$MODEL = $model;
487	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;	1176	warn "AnyEvent: autoprobed model '$model', using it.\n" if $VERBOSE >= 2;
488	last;	1177	last;
489	}	1178	}
490	}	1179	}
491		1180
492	$MODEL	1181	$MODEL
493	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";	1182	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
494	}	1183	}
495	}	1184	}
496		1185
		1186	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1187
497	unshift @ISA, $MODEL;	1188	unshift @ISA, $MODEL;
498	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	1189
		1190	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1191
		1192	(shift @post_detect)->() while @post_detect;
499	}	1193	}
500		1194
501	$MODEL	1195	$MODEL
502	}	1196	}
503		1197
504	sub AUTOLOAD {	1198	sub AUTOLOAD {
505	(my $func = $AUTOLOAD) =~ s/.*://;	1199	(my $func = $AUTOLOAD) =~ s/.*://;
506		1200
507	$method{$func}	1201	$method{$func}
508	or croak "$func: not a valid method for AnyEvent objects";	1202	or Carp::croak "$func: not a valid method for AnyEvent objects";
509		1203
510	detect unless $MODEL;	1204	detect unless $MODEL;
511		1205
512	my $class = shift;	1206	my $class = shift;
513	$class->$func (@_);	1207	$class->$func (@_);
514	}	1208	}
515		1209
		1210	# utility function to dup a filehandle. this is used by many backends
		1211	# to support binding more than one watcher per filehandle (they usually
		1212	# allow only one watcher per fd, so we dup it to get a different one).
		1213	sub _dupfh($$;$$) {
		1214	my ($poll, $fh, $r, $w) = @_;
		1215
		1216	# cygwin requires the fh mode to be matching, unix doesn't
		1217	my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
		1218
		1219	open my $fh2, $mode, $fh
		1220	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1221
		1222	# we assume CLOEXEC is already set by perl in all important cases
		1223
		1224	($fh2, $rw)
		1225	}
		1226
516	package AnyEvent::Base;	1227	package AnyEvent::Base;
517		1228
		1229	# default implementations for many methods
		1230
		1231	sub _time {
		1232	# probe for availability of Time::HiRes
		1233	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1234	warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
		1235	*_time = \&Time::HiRes::time;
		1236	# if (eval "use POSIX (); (POSIX::times())...
		1237	} else {
		1238	warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
		1239	*_time = sub { time }; # epic fail
		1240	}
		1241
		1242	&_time
		1243	}
		1244
		1245	sub time { _time }
		1246	sub now { _time }
		1247	sub now_update { }
		1248
518	# default implementation for ->condvar, ->wait, ->broadcast	1249	# default implementation for ->condvar
519		1250
520	sub condvar {	1251	sub condvar {
521	bless \my $flag, "AnyEvent::Base::CondVar"	1252	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
522	}
523
524	sub AnyEvent::Base::CondVar::broadcast {
525	${$_[0]}++;
526	}
527
528	sub AnyEvent::Base::CondVar::wait {
529	AnyEvent->one_event while !${$_[0]};
530	}	1253	}
531		1254
532	# default implementation for ->signal	1255	# default implementation for ->signal
533		1256
534	our %SIG_CB;	1257	our $HAVE_ASYNC_INTERRUPT;
		1258	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1259	our (%SIG_ASY, %SIG_ASY_W);
		1260	our ($SIG_COUNT, $SIG_TW);
535		1261
		1262	sub _signal_exec {
		1263	$HAVE_ASYNC_INTERRUPT
		1264	? $SIGPIPE_R->drain
		1265	: sysread $SIGPIPE_R, my $dummy, 9;
		1266
		1267	while (%SIG_EV) {
		1268	for (keys %SIG_EV) {
		1269	delete $SIG_EV{$_};
		1270	$_->() for values %{ $SIG_CB{$_} || {} };
		1271	}
		1272	}
		1273	}
		1274
		1275	# install a dumym wakeupw atcher to reduce signal catching latency
		1276	sub _sig_add() {
		1277	unless ($SIG_COUNT++) {
		1278	# try to align timer on a full-second boundary, if possible
		1279	my $NOW = AnyEvent->now;
		1280
		1281	$SIG_TW = AnyEvent->timer (
		1282	after => $MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
		1283	interval => $MAX_SIGNAL_LATENCY,
		1284	cb => sub { }, # just for the PERL_ASYNC_CHECK
		1285	);
		1286	}
		1287	}
		1288
		1289	sub _sig_del {
		1290	undef $SIG_TW
		1291	unless --$SIG_COUNT;
		1292	}
		1293
536	sub signal {	1294	sub _signal {
537	my (undef, %arg) = @_;	1295	my (undef, %arg) = @_;
538		1296
539	my $signal = uc $arg{signal}	1297	my $signal = uc $arg{signal}
540	or Carp::croak "required option 'signal' is missing";	1298	or Carp::croak "required option 'signal' is missing";
541		1299
542	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1300	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		1301
		1302	if ($HAVE_ASYNC_INTERRUPT) {
		1303	# async::interrupt
		1304
		1305	$SIG_ASY{$signal} ||= do {
		1306	my $asy = new Async::Interrupt
		1307	cb => sub { undef $SIG_EV{$signal} },
		1308	signal => $signal,
		1309	pipe => [$SIGPIPE_R->filenos],
		1310	;
		1311	$asy->pipe_autodrain (0);
		1312
		1313	$asy
		1314	};
		1315
		1316	} else {
		1317	# pure perl
		1318
543	$SIG{$signal} ||= sub {	1319	$SIG{$signal} ||= sub {
544	$_->() for values %{ $SIG_CB{$signal} || {} };	1320	local $!;
		1321	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1322	undef $SIG_EV{$signal};
		1323	};
		1324
		1325	# can't do signal processing without introducing races in pure perl,
		1326	# so limit the signal latency.
		1327	_sig_add;
545	};	1328	}
546		1329
547	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1330	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
548	}	1331	}
549		1332
		1333	sub signal {
		1334	# probe for availability of Async::Interrupt
		1335	if (!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT} && eval "use Async::Interrupt 0.6 (); 1") {
		1336	warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
		1337
		1338	$HAVE_ASYNC_INTERRUPT = 1;
		1339	$SIGPIPE_R = new Async::Interrupt::EventPipe;
		1340	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R->fileno, poll => "r", cb => \&_signal_exec);
		1341
		1342	} else {
		1343	warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
		1344
		1345	require Fcntl;
		1346
		1347	if (AnyEvent::WIN32) {
		1348	require AnyEvent::Util;
		1349
		1350	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1351	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1352	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1353	} else {
		1354	pipe $SIGPIPE_R, $SIGPIPE_W;
		1355	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1356	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1357
		1358	# not strictly required, as $^F is normally 2, but let's make sure...
		1359	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1360	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1361	}
		1362
		1363	$SIGPIPE_R
		1364	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1365
		1366	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1367	}
		1368
		1369	*signal = \&_signal;
		1370	&signal
		1371	}
		1372
550	sub AnyEvent::Base::Signal::DESTROY {	1373	sub AnyEvent::Base::signal::DESTROY {
551	my ($signal, $cb) = @{$_[0]};	1374	my ($signal, $cb) = @{$_[0]};
552		1375
		1376	_sig_del;
		1377
553	delete $SIG_CB{$signal}{$cb};	1378	delete $SIG_CB{$signal}{$cb};
554		1379
555	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1380	$HAVE_ASYNC_INTERRUPT
		1381	? delete $SIG_ASY{$signal}
		1382	: # delete doesn't work with older perls - they then
		1383	# print weird messages, or just unconditionally exit
		1384	# instead of getting the default action.
		1385	undef $SIG{$signal}
		1386	unless keys %{ $SIG_CB{$signal} };
556	}	1387	}
557		1388
558	# default implementation for ->child	1389	# default implementation for ->child
559		1390
560	our %PID_CB;	1391	our %PID_CB;
561	our $CHLD_W;	1392	our $CHLD_W;
562	our $CHLD_DELAY_W;	1393	our $CHLD_DELAY_W;
563	our $PID_IDLE;
564	our $WNOHANG;	1394	our $WNOHANG;
565		1395
566	sub _child_wait {	1396	sub _sigchld {
567	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	1397	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		1398	$_->($pid, $?)
568	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1399	for values %{ $PID_CB{$pid} || {} },
569	(values %{ $PID_CB{0} || {} });	1400	values %{ $PID_CB{0} || {} };
570	}	1401	}
571
572	undef $PID_IDLE;
573	}
574
575	sub _sigchld {
576	# make sure we deliver these changes "synchronous" with the event loop.
577	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
578	undef $CHLD_DELAY_W;
579	&_child_wait;
580	});
581	}	1402	}
582		1403
583	sub child {	1404	sub child {
584	my (undef, %arg) = @_;	1405	my (undef, %arg) = @_;
585		1406
586	defined (my $pid = $arg{pid} + 0)	1407	defined (my $pid = $arg{pid} + 0)
587	or Carp::croak "required option 'pid' is missing";	1408	or Carp::croak "required option 'pid' is missing";
588		1409
589	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1410	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
590		1411
591	unless ($WNOHANG) {	1412	# WNOHANG is almost cetrainly 1 everywhere
592	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1413	$WNOHANG ||= $^O =~ /^(?:openbsd|netbsd|linux|freebsd|cygwin|MSWin32)$/
593	}	1414	? 1
		1415	: eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
594		1416
595	unless ($CHLD_W) {	1417	unless ($CHLD_W) {
596	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1418	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
597	# child could be a zombie already, so make at least one round	1419	# child could be a zombie already, so make at least one round
598	&_sigchld;	1420	&_sigchld;
599	}	1421	}
600		1422
601	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1423	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
602	}	1424	}
603		1425
604	sub AnyEvent::Base::Child::DESTROY {	1426	sub AnyEvent::Base::child::DESTROY {
605	my ($pid, $cb) = @{$_[0]};	1427	my ($pid, $cb) = @{$_[0]};
606		1428
607	delete $PID_CB{$pid}{$cb};	1429	delete $PID_CB{$pid}{$cb};
608	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1430	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
609		1431
610	undef $CHLD_W unless keys %PID_CB;	1432	undef $CHLD_W unless keys %PID_CB;
611	}	1433	}
		1434
		1435	# idle emulation is done by simply using a timer, regardless
		1436	# of whether the process is idle or not, and not letting
		1437	# the callback use more than 50% of the time.
		1438	sub idle {
		1439	my (undef, %arg) = @_;
		1440
		1441	my ($cb, $w, $rcb) = $arg{cb};
		1442
		1443	$rcb = sub {
		1444	if ($cb) {
		1445	$w = _time;
		1446	&$cb;
		1447	$w = _time - $w;
		1448
		1449	# never use more then 50% of the time for the idle watcher,
		1450	# within some limits
		1451	$w = 0.0001 if $w < 0.0001;
		1452	$w = 5 if $w > 5;
		1453
		1454	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1455	} else {
		1456	# clean up...
		1457	undef $w;
		1458	undef $rcb;
		1459	}
		1460	};
		1461
		1462	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1463
		1464	bless \\$cb, "AnyEvent::Base::idle"
		1465	}
		1466
		1467	sub AnyEvent::Base::idle::DESTROY {
		1468	undef $${$_[0]};
		1469	}
		1470
		1471	package AnyEvent::CondVar;
		1472
		1473	our @ISA = AnyEvent::CondVar::Base::;
		1474
		1475	package AnyEvent::CondVar::Base;
		1476
		1477	#use overload
		1478	# '&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1479	# fallback => 1;
		1480
		1481	# save 300+ kilobytes by dirtily hardcoding overloading
		1482	${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
		1483	*{'AnyEvent::CondVar::Base::()'} = sub { }; # "Make it findable via fetchmethod."
		1484	*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
		1485	${'AnyEvent::CondVar::Base::()'} = 1; # fallback
		1486
		1487	our $WAITING;
		1488
		1489	sub _send {
		1490	# nop
		1491	}
		1492
		1493	sub send {
		1494	my $cv = shift;
		1495	$cv->{_ae_sent} = [@_];
		1496	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1497	$cv->_send;
		1498	}
		1499
		1500	sub croak {
		1501	$_[0]{_ae_croak} = $_[1];
		1502	$_[0]->send;
		1503	}
		1504
		1505	sub ready {
		1506	$_[0]{_ae_sent}
		1507	}
		1508
		1509	sub _wait {
		1510	$WAITING
		1511	and !$_[0]{_ae_sent}
		1512	and Carp::croak "AnyEvent::CondVar: recursive blocking wait detected";
		1513
		1514	local $WAITING = 1;
		1515	AnyEvent->one_event while !$_[0]{_ae_sent};
		1516	}
		1517
		1518	sub recv {
		1519	$_[0]->_wait;
		1520
		1521	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1522	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1523	}
		1524
		1525	sub cb {
		1526	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1527	$_[0]{_ae_cb}
		1528	}
		1529
		1530	sub begin {
		1531	++$_[0]{_ae_counter};
		1532	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1533	}
		1534
		1535	sub end {
		1536	return if --$_[0]{_ae_counter};
		1537	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1538	}
		1539
		1540	# undocumented/compatibility with pre-3.4
		1541	*broadcast = \&send;
		1542	*wait = \&_wait;
		1543
		1544	=head1 ERROR AND EXCEPTION HANDLING
		1545
		1546	In general, AnyEvent does not do any error handling - it relies on the
		1547	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1548	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1549	checking of all AnyEvent methods, however, which is highly useful during
		1550	development.
		1551
		1552	As for exception handling (i.e. runtime errors and exceptions thrown while
		1553	executing a callback), this is not only highly event-loop specific, but
		1554	also not in any way wrapped by this module, as this is the job of the main
		1555	program.
		1556
		1557	The pure perl event loop simply re-throws the exception (usually
		1558	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1559	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1560	so on.
		1561
		1562	=head1 ENVIRONMENT VARIABLES
		1563
		1564	The following environment variables are used by this module or its
		1565	submodules.
		1566
		1567	Note that AnyEvent will remove I<all> environment variables starting with
		1568	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1569	enabled.
		1570
		1571	=over 4
		1572
		1573	=item C<PERL_ANYEVENT_VERBOSE>
		1574
		1575	By default, AnyEvent will be completely silent except in fatal
		1576	conditions. You can set this environment variable to make AnyEvent more
		1577	talkative.
		1578
		1579	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1580	conditions, such as not being able to load the event model specified by
		1581	C<PERL_ANYEVENT_MODEL>.
		1582
		1583	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1584	model it chooses.
		1585
		1586	When set to C<8> or higher, then AnyEvent will report extra information on
		1587	which optional modules it loads and how it implements certain features.
		1588
		1589	=item C<PERL_ANYEVENT_STRICT>
		1590
		1591	AnyEvent does not do much argument checking by default, as thorough
		1592	argument checking is very costly. Setting this variable to a true value
		1593	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1594	check the arguments passed to most method calls. If it finds any problems,
		1595	it will croak.
		1596
		1597	In other words, enables "strict" mode.
		1598
		1599	Unlike C<use strict> (or it's modern cousin, C<< use L<common::sense>
		1600	>>, it is definitely recommended to keep it off in production. Keeping
		1601	C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
		1602	can be very useful, however.
		1603
		1604	=item C<PERL_ANYEVENT_MODEL>
		1605
		1606	This can be used to specify the event model to be used by AnyEvent, before
		1607	auto detection and -probing kicks in. It must be a string consisting
		1608	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1609	and the resulting module name is loaded and if the load was successful,
		1610	used as event model. If it fails to load AnyEvent will proceed with
		1611	auto detection and -probing.
		1612
		1613	This functionality might change in future versions.
		1614
		1615	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1616	could start your program like this:
		1617
		1618	PERL_ANYEVENT_MODEL=Perl perl ...
		1619
		1620	=item C<PERL_ANYEVENT_PROTOCOLS>
		1621
		1622	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1623	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1624	of auto probing).
		1625
		1626	Must be set to a comma-separated list of protocols or address families,
		1627	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1628	used, and preference will be given to protocols mentioned earlier in the
		1629	list.
		1630
		1631	This variable can effectively be used for denial-of-service attacks
		1632	against local programs (e.g. when setuid), although the impact is likely
		1633	small, as the program has to handle conenction and other failures anyways.
		1634
		1635	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1636	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1637	- only support IPv4, never try to resolve or contact IPv6
		1638	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1639	IPv6, but prefer IPv6 over IPv4.
		1640
		1641	=item C<PERL_ANYEVENT_EDNS0>
		1642
		1643	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1644	for DNS. This extension is generally useful to reduce DNS traffic, but
		1645	some (broken) firewalls drop such DNS packets, which is why it is off by
		1646	default.
		1647
		1648	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1649	EDNS0 in its DNS requests.
		1650
		1651	=item C<PERL_ANYEVENT_MAX_FORKS>
		1652
		1653	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1654	will create in parallel.
		1655
		1656	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1657
		1658	The default value for the C<max_outstanding> parameter for the default DNS
		1659	resolver - this is the maximum number of parallel DNS requests that are
		1660	sent to the DNS server.
		1661
		1662	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1663
		1664	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1665	configuration) in the default resolver. When set to the empty string, no
		1666	default config will be used.
		1667
		1668	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1669
		1670	When neither C<ca_file> nor C<ca_path> was specified during
		1671	L<AnyEvent::TLS> context creation, and either of these environment
		1672	variables exist, they will be used to specify CA certificate locations
		1673	instead of a system-dependent default.
		1674
		1675	=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
		1676
		1677	When these are set to C<1>, then the respective modules are not
		1678	loaded. Mostly good for testing AnyEvent itself.
		1679
		1680	=back
612		1681
613	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1682	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
614		1683
615	This is an advanced topic that you do not normally need to use AnyEvent in	1684	This is an advanced topic that you do not normally need to use AnyEvent in
616	a module. This section is only of use to event loop authors who want to	1685	a module. This section is only of use to event loop authors who want to
…		…
651	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1720	I<rxvt-unicode> also cheats a bit by not providing blocking access to
652	condition variables: code blocking while waiting for a condition will	1721	condition variables: code blocking while waiting for a condition will
653	C<die>. This still works with most modules/usages, and blocking calls must	1722	C<die>. This still works with most modules/usages, and blocking calls must
654	not be done in an interactive application, so it makes sense.	1723	not be done in an interactive application, so it makes sense.
655		1724
656	=head1 ENVIRONMENT VARIABLES
657
658	The following environment variables are used by this module:
659
660	=over 4
661
662	=item C<PERL_ANYEVENT_VERBOSE>
663
664	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
665	model it chooses.
666
667	=item C<PERL_ANYEVENT_MODEL>
668
669	This can be used to specify the event model to be used by AnyEvent, before
670	autodetection and -probing kicks in. It must be a string consisting
671	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
672	and the resulting module name is loaded and if the load was successful,
673	used as event model. If it fails to load AnyEvent will proceed with
674	autodetection and -probing.
675
676	This functionality might change in future versions.
677
678	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
679	could start your program like this:
680
681	PERL_ANYEVENT_MODEL=Perl perl ...
682
683	=back
684
685	=head1 EXAMPLE PROGRAM	1725	=head1 EXAMPLE PROGRAM
686		1726
687	The following program uses an IO watcher to read data from STDIN, a timer	1727	The following program uses an I/O watcher to read data from STDIN, a timer
688	to display a message once per second, and a condition variable to quit the	1728	to display a message once per second, and a condition variable to quit the
689	program when the user enters quit:	1729	program when the user enters quit:
690		1730
691	use AnyEvent;	1731	use AnyEvent;
692		1732
…		…
697	poll => 'r',	1737	poll => 'r',
698	cb => sub {	1738	cb => sub {
699	warn "io event <$_[0]>\n"; # will always output <r>	1739	warn "io event <$_[0]>\n"; # will always output <r>
700	chomp (my $input = <STDIN>); # read a line	1740	chomp (my $input = <STDIN>); # read a line
701	warn "read: $input\n"; # output what has been read	1741	warn "read: $input\n"; # output what has been read
702	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1742	$cv->send if $input =~ /^q/i; # quit program if /^q/i
703	},	1743	},
704	);	1744	);
705		1745
706	my $time_watcher; # can only be used once	1746	my $time_watcher; # can only be used once
707		1747
…		…
712	});	1752	});
713	}	1753	}
714		1754
715	new_timer; # create first timer	1755	new_timer; # create first timer
716		1756
717	$cv->wait; # wait until user enters /^q/i	1757	$cv->recv; # wait until user enters /^q/i
718		1758
719	=head1 REAL-WORLD EXAMPLE	1759	=head1 REAL-WORLD EXAMPLE
720		1760
721	Consider the L<Net::FCP> module. It features (among others) the following	1761	Consider the L<Net::FCP> module. It features (among others) the following
722	API calls, which are to freenet what HTTP GET requests are to http:	1762	API calls, which are to freenet what HTTP GET requests are to http:
…		…
772	syswrite $txn->{fh}, $txn->{request}	1812	syswrite $txn->{fh}, $txn->{request}
773	or die "connection or write error";	1813	or die "connection or write error";
774	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1814	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
775		1815
776	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1816	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
777	result and signals any possible waiters that the request ahs finished:	1817	result and signals any possible waiters that the request has finished:
778		1818
779	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1819	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
780		1820
781	if (end-of-file or data complete) {	1821	if (end-of-file or data complete) {
782	$txn->{result} = $txn->{buf};	1822	$txn->{result} = $txn->{buf};
783	$txn->{finished}->broadcast;	1823	$txn->{finished}->send;
784	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1824	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
785	}	1825	}
786		1826
787	The C<result> method, finally, just waits for the finished signal (if the	1827	The C<result> method, finally, just waits for the finished signal (if the
788	request was already finished, it doesn't wait, of course, and returns the	1828	request was already finished, it doesn't wait, of course, and returns the
789	data:	1829	data:
790		1830
791	$txn->{finished}->wait;	1831	$txn->{finished}->recv;
792	return $txn->{result};	1832	return $txn->{result};
793		1833
794	The actual code goes further and collects all errors (C<die>s, exceptions)	1834	The actual code goes further and collects all errors (C<die>s, exceptions)
795	that occured during request processing. The C<result> method detects	1835	that occurred during request processing. The C<result> method detects
796	whether an exception as thrown (it is stored inside the $txn object)	1836	whether an exception as thrown (it is stored inside the $txn object)
797	and just throws the exception, which means connection errors and other	1837	and just throws the exception, which means connection errors and other
798	problems get reported tot he code that tries to use the result, not in a	1838	problems get reported tot he code that tries to use the result, not in a
799	random callback.	1839	random callback.
800		1840
…		…
831		1871
832	my $quit = AnyEvent->condvar;	1872	my $quit = AnyEvent->condvar;
833		1873
834	$fcp->txn_client_get ($url)->cb (sub {	1874	$fcp->txn_client_get ($url)->cb (sub {
835	...	1875	...
836	$quit->broadcast;	1876	$quit->send;
837	});	1877	});
838		1878
839	$quit->wait;	1879	$quit->recv;
		1880
		1881
		1882	=head1 BENCHMARKS
		1883
		1884	To give you an idea of the performance and overheads that AnyEvent adds
		1885	over the event loops themselves and to give you an impression of the speed
		1886	of various event loops I prepared some benchmarks.
		1887
		1888	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1889
		1890	Here is a benchmark of various supported event models used natively and
		1891	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1892	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1893	which it is), lets them fire exactly once and destroys them again.
		1894
		1895	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1896	distribution.
		1897
		1898	=head3 Explanation of the columns
		1899
		1900	I<watcher> is the number of event watchers created/destroyed. Since
		1901	different event models feature vastly different performances, each event
		1902	loop was given a number of watchers so that overall runtime is acceptable
		1903	and similar between tested event loop (and keep them from crashing): Glib
		1904	would probably take thousands of years if asked to process the same number
		1905	of watchers as EV in this benchmark.
		1906
		1907	I<bytes> is the number of bytes (as measured by the resident set size,
		1908	RSS) consumed by each watcher. This method of measuring captures both C
		1909	and Perl-based overheads.
		1910
		1911	I<create> is the time, in microseconds (millionths of seconds), that it
		1912	takes to create a single watcher. The callback is a closure shared between
		1913	all watchers, to avoid adding memory overhead. That means closure creation
		1914	and memory usage is not included in the figures.
		1915
		1916	I<invoke> is the time, in microseconds, used to invoke a simple
		1917	callback. The callback simply counts down a Perl variable and after it was
		1918	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1919	signal the end of this phase.
		1920
		1921	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1922	watcher.
		1923
		1924	=head3 Results
		1925
		1926	name watchers bytes create invoke destroy comment
		1927	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1928	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1929	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1930	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1931	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1932	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1933	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1934	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
		1935	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1936	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1937	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1938	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1939
		1940	=head3 Discussion
		1941
		1942	The benchmark does I<not> measure scalability of the event loop very
		1943	well. For example, a select-based event loop (such as the pure perl one)
		1944	can never compete with an event loop that uses epoll when the number of
		1945	file descriptors grows high. In this benchmark, all events become ready at
		1946	the same time, so select/poll-based implementations get an unnatural speed
		1947	boost.
		1948
		1949	Also, note that the number of watchers usually has a nonlinear effect on
		1950	overall speed, that is, creating twice as many watchers doesn't take twice
		1951	the time - usually it takes longer. This puts event loops tested with a
		1952	higher number of watchers at a disadvantage.
		1953
		1954	To put the range of results into perspective, consider that on the
		1955	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1956	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1957	cycles with POE.
		1958
		1959	C<EV> is the sole leader regarding speed and memory use, which are both
		1960	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1961	far less memory than any other event loop and is still faster than Event
		1962	natively.
		1963
		1964	The pure perl implementation is hit in a few sweet spots (both the
		1965	constant timeout and the use of a single fd hit optimisations in the perl
		1966	interpreter and the backend itself). Nevertheless this shows that it
		1967	adds very little overhead in itself. Like any select-based backend its
		1968	performance becomes really bad with lots of file descriptors (and few of
		1969	them active), of course, but this was not subject of this benchmark.
		1970
		1971	The C<Event> module has a relatively high setup and callback invocation
		1972	cost, but overall scores in on the third place.
		1973
		1974	C<IO::Async> performs admirably well, about on par with C<Event>, even
		1975	when using its pure perl backend.
		1976
		1977	C<Glib>'s memory usage is quite a bit higher, but it features a
		1978	faster callback invocation and overall ends up in the same class as
		1979	C<Event>. However, Glib scales extremely badly, doubling the number of
		1980	watchers increases the processing time by more than a factor of four,
		1981	making it completely unusable when using larger numbers of watchers
		1982	(note that only a single file descriptor was used in the benchmark, so
		1983	inefficiencies of C<poll> do not account for this).
		1984
		1985	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1986	more than 2000 watchers is a big setback, however, as correctness takes
		1987	precedence over speed. Nevertheless, its performance is surprising, as the
		1988	file descriptor is dup()ed for each watcher. This shows that the dup()
		1989	employed by some adaptors is not a big performance issue (it does incur a
		1990	hidden memory cost inside the kernel which is not reflected in the figures
		1991	above).
		1992
		1993	C<POE>, regardless of underlying event loop (whether using its pure perl
		1994	select-based backend or the Event module, the POE-EV backend couldn't
		1995	be tested because it wasn't working) shows abysmal performance and
		1996	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1997	as EV watchers, and 10 times as much memory as Event (the high memory
		1998	requirements are caused by requiring a session for each watcher). Watcher
		1999	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		2000	implementation.
		2001
		2002	The design of the POE adaptor class in AnyEvent can not really account
		2003	for the performance issues, though, as session creation overhead is
		2004	small compared to execution of the state machine, which is coded pretty
		2005	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		2006	using multiple sessions is not a good approach, especially regarding
		2007	memory usage, even the author of POE could not come up with a faster
		2008	design).
		2009
		2010	=head3 Summary
		2011
		2012	=over 4
		2013
		2014	=item * Using EV through AnyEvent is faster than any other event loop
		2015	(even when used without AnyEvent), but most event loops have acceptable
		2016	performance with or without AnyEvent.
		2017
		2018	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		2019	the actual event loop, only with extremely fast event loops such as EV
		2020	adds AnyEvent significant overhead.
		2021
		2022	=item * You should avoid POE like the plague if you want performance or
		2023	reasonable memory usage.
		2024
		2025	=back
		2026
		2027	=head2 BENCHMARKING THE LARGE SERVER CASE
		2028
		2029	This benchmark actually benchmarks the event loop itself. It works by
		2030	creating a number of "servers": each server consists of a socket pair, a
		2031	timeout watcher that gets reset on activity (but never fires), and an I/O
		2032	watcher waiting for input on one side of the socket. Each time the socket
		2033	watcher reads a byte it will write that byte to a random other "server".
		2034
		2035	The effect is that there will be a lot of I/O watchers, only part of which
		2036	are active at any one point (so there is a constant number of active
		2037	fds for each loop iteration, but which fds these are is random). The
		2038	timeout is reset each time something is read because that reflects how
		2039	most timeouts work (and puts extra pressure on the event loops).
		2040
		2041	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		2042	(1%) are active. This mirrors the activity of large servers with many
		2043	connections, most of which are idle at any one point in time.
		2044
		2045	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		2046	distribution.
		2047
		2048	=head3 Explanation of the columns
		2049
		2050	I<sockets> is the number of sockets, and twice the number of "servers" (as
		2051	each server has a read and write socket end).
		2052
		2053	I<create> is the time it takes to create a socket pair (which is
		2054	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		2055
		2056	I<request>, the most important value, is the time it takes to handle a
		2057	single "request", that is, reading the token from the pipe and forwarding
		2058	it to another server. This includes deleting the old timeout and creating
		2059	a new one that moves the timeout into the future.
		2060
		2061	=head3 Results
		2062
		2063	name sockets create request
		2064	EV 20000 69.01 11.16
		2065	Perl 20000 73.32 35.87
		2066	IOAsync 20000 157.00 98.14 epoll
		2067	IOAsync 20000 159.31 616.06 poll
		2068	Event 20000 212.62 257.32
		2069	Glib 20000 651.16 1896.30
		2070	POE 20000 349.67 12317.24 uses POE::Loop::Event
		2071
		2072	=head3 Discussion
		2073
		2074	This benchmark I<does> measure scalability and overall performance of the
		2075	particular event loop.
		2076
		2077	EV is again fastest. Since it is using epoll on my system, the setup time
		2078	is relatively high, though.
		2079
		2080	Perl surprisingly comes second. It is much faster than the C-based event
		2081	loops Event and Glib.
		2082
		2083	IO::Async performs very well when using its epoll backend, and still quite
		2084	good compared to Glib when using its pure perl backend.
		2085
		2086	Event suffers from high setup time as well (look at its code and you will
		2087	understand why). Callback invocation also has a high overhead compared to
		2088	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		2089	uses select or poll in basically all documented configurations.
		2090
		2091	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		2092	clearly fails to perform with many filehandles or in busy servers.
		2093
		2094	POE is still completely out of the picture, taking over 1000 times as long
		2095	as EV, and over 100 times as long as the Perl implementation, even though
		2096	it uses a C-based event loop in this case.
		2097
		2098	=head3 Summary
		2099
		2100	=over 4
		2101
		2102	=item * The pure perl implementation performs extremely well.
		2103
		2104	=item * Avoid Glib or POE in large projects where performance matters.
		2105
		2106	=back
		2107
		2108	=head2 BENCHMARKING SMALL SERVERS
		2109
		2110	While event loops should scale (and select-based ones do not...) even to
		2111	large servers, most programs we (or I :) actually write have only a few
		2112	I/O watchers.
		2113
		2114	In this benchmark, I use the same benchmark program as in the large server
		2115	case, but it uses only eight "servers", of which three are active at any
		2116	one time. This should reflect performance for a small server relatively
		2117	well.
		2118
		2119	The columns are identical to the previous table.
		2120
		2121	=head3 Results
		2122
		2123	name sockets create request
		2124	EV 16 20.00 6.54
		2125	Perl 16 25.75 12.62
		2126	Event 16 81.27 35.86
		2127	Glib 16 32.63 15.48
		2128	POE 16 261.87 276.28 uses POE::Loop::Event
		2129
		2130	=head3 Discussion
		2131
		2132	The benchmark tries to test the performance of a typical small
		2133	server. While knowing how various event loops perform is interesting, keep
		2134	in mind that their overhead in this case is usually not as important, due
		2135	to the small absolute number of watchers (that is, you need efficiency and
		2136	speed most when you have lots of watchers, not when you only have a few of
		2137	them).
		2138
		2139	EV is again fastest.
		2140
		2141	Perl again comes second. It is noticeably faster than the C-based event
		2142	loops Event and Glib, although the difference is too small to really
		2143	matter.
		2144
		2145	POE also performs much better in this case, but is is still far behind the
		2146	others.
		2147
		2148	=head3 Summary
		2149
		2150	=over 4
		2151
		2152	=item * C-based event loops perform very well with small number of
		2153	watchers, as the management overhead dominates.
		2154
		2155	=back
		2156
		2157	=head2 THE IO::Lambda BENCHMARK
		2158
		2159	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2160	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2161	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2162	shouldn't come as a surprise to anybody). As such, the benchmark is
		2163	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2164	very optimal. But how would AnyEvent compare when used without the extra
		2165	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2166
		2167	The benchmark itself creates an echo-server, and then, for 500 times,
		2168	connects to the echo server, sends a line, waits for the reply, and then
		2169	creates the next connection. This is a rather bad benchmark, as it doesn't
		2170	test the efficiency of the framework or much non-blocking I/O, but it is a
		2171	benchmark nevertheless.
		2172
		2173	name runtime
		2174	Lambda/select 0.330 sec
		2175	+ optimized 0.122 sec
		2176	Lambda/AnyEvent 0.327 sec
		2177	+ optimized 0.138 sec
		2178	Raw sockets/select 0.077 sec
		2179	POE/select, components 0.662 sec
		2180	POE/select, raw sockets 0.226 sec
		2181	POE/select, optimized 0.404 sec
		2182
		2183	AnyEvent/select/nb 0.085 sec
		2184	AnyEvent/EV/nb 0.068 sec
		2185	+state machine 0.134 sec
		2186
		2187	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2188	benchmarks actually make blocking connects and use 100% blocking I/O,
		2189	defeating the purpose of an event-based solution. All of the newly
		2190	written AnyEvent benchmarks use 100% non-blocking connects (using
		2191	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2192	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2193	generally require a lot more bookkeeping and event handling than blocking
		2194	connects (which involve a single syscall only).
		2195
		2196	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2197	offers similar expressive power as POE and IO::Lambda, using conventional
		2198	Perl syntax. This means that both the echo server and the client are 100%
		2199	non-blocking, further placing it at a disadvantage.
		2200
		2201	As you can see, the AnyEvent + EV combination even beats the
		2202	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2203	backend easily beats IO::Lambda and POE.
		2204
		2205	And even the 100% non-blocking version written using the high-level (and
		2206	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
		2207	large margin, even though it does all of DNS, tcp-connect and socket I/O
		2208	in a non-blocking way.
		2209
		2210	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2211	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2212	part of the IO::lambda distribution and were used without any changes.
		2213
		2214
		2215	=head1 SIGNALS
		2216
		2217	AnyEvent currently installs handlers for these signals:
		2218
		2219	=over 4
		2220
		2221	=item SIGCHLD
		2222
		2223	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2224	emulation for event loops that do not support them natively. Also, some
		2225	event loops install a similar handler.
		2226
		2227	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
		2228	AnyEvent will reset it to default, to avoid losing child exit statuses.
		2229
		2230	=item SIGPIPE
		2231
		2232	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2233	when AnyEvent gets loaded.
		2234
		2235	The rationale for this is that AnyEvent users usually do not really depend
		2236	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2237	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2238	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2239	some random socket.
		2240
		2241	The rationale for installing a no-op handler as opposed to ignoring it is
		2242	that this way, the handler will be restored to defaults on exec.
		2243
		2244	Feel free to install your own handler, or reset it to defaults.
		2245
		2246	=back
		2247
		2248	=cut
		2249
		2250	undef $SIG{CHLD}
		2251	if $SIG{CHLD} eq 'IGNORE';
		2252
		2253	$SIG{PIPE} = sub { }
		2254	unless defined $SIG{PIPE};
		2255
		2256	=head1 RECOMMENDED/OPTIONAL MODULES
		2257
		2258	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		2259	it's built-in modules) are required to use it.
		2260
		2261	That does not mean that AnyEvent won't take advantage of some additional
		2262	modules if they are installed.
		2263
		2264	This section epxlains which additional modules will be used, and how they
		2265	affect AnyEvent's operetion.
		2266
		2267	=over 4
		2268
		2269	=item L<Async::Interrupt>
		2270
		2271	This slightly arcane module is used to implement fast signal handling: To
		2272	my knowledge, there is no way to do completely race-free and quick
		2273	signal handling in pure perl. To ensure that signals still get
		2274	delivered, AnyEvent will start an interval timer to wake up perl (and
		2275	catch the signals) with soemd elay (default is 10 seconds, look for
		2276	C<$AnyEvent::MAX_SIGNAL_LATENCY>).
		2277
		2278	If this module is available, then it will be used to implement signal
		2279	catching, which means that signals will not be delayed, and the event loop
		2280	will not be interrupted regularly, which is more efficient (And good for
		2281	battery life on laptops).
		2282
		2283	This affects not just the pure-perl event loop, but also other event loops
		2284	that have no signal handling on their own (e.g. Glib, Tk, Qt).
		2285
		2286	=item L<EV>
		2287
		2288	This module isn't really "optional", as it is simply one of the backend
		2289	event loops that AnyEvent can use. However, it is simply the best event
		2290	loop available in terms of features, speed and stability: It supports
		2291	the AnyEvent API optimally, implements all the watcher types in XS, does
		2292	automatic timer adjustments even when no monotonic clock is available,
		2293	can take avdantage of advanced kernel interfaces such as C<epoll> and
		2294	C<kqueue>, and is the fastest backend I<by far>. You can even embed
		2295	L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
		2296
		2297	=item L<Guard>
		2298
		2299	The guard module, when used, will be used to implement
		2300	C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
		2301	lot less memory), but otherwise doesn't affect guard operation much. It is
		2302	purely used for performance.
		2303
		2304	=item L<JSON> and L<JSON::XS>
		2305
		2306	This module is required when you want to read or write JSON data via
		2307	L<AnyEvent::Handle>. It is also written in pure-perl, but can take
		2308	advantage of the ulta-high-speed L<JSON::XS> module when it is installed.
		2309
		2310	In fact, L<AnyEvent::Handle> will use L<JSON::XS> by default if it is
		2311	installed.
		2312
		2313	=item L<Net::SSLeay>
		2314
		2315	Implementing TLS/SSL in Perl is certainly interesting, but not very
		2316	worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
		2317	the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
		2318
		2319	=item L<Time::HiRes>
		2320
		2321	This module is part of perl since release 5.008. It will be used when the
		2322	chosen event library does not come with a timing source on it's own. The
		2323	pure-perl event loop (L<AnyEvent::Impl::Perl>) will additionally use it to
		2324	try to use a monotonic clock for timing stability.
		2325
		2326	=back
		2327
840		2328
841	=head1 FORK	2329	=head1 FORK
842		2330
843	Most event libraries are not fork-safe. The ones who are usually are	2331	Most event libraries are not fork-safe. The ones who are usually are
844	because they are so inefficient. Only L<EV> is fully fork-aware.	2332	because they rely on inefficient but fork-safe C<select> or C<poll>
		2333	calls. Only L<EV> is fully fork-aware.
845		2334
846	If you have to fork, you must either do so I<before> creating your first	2335	If you have to fork, you must either do so I<before> creating your first
847	watcher OR you must not use AnyEvent at all in the child.	2336	watcher OR you must not use AnyEvent at all in the child OR you must do
		2337	something completely out of the scope of AnyEvent.
		2338
848		2339
849	=head1 SECURITY CONSIDERATIONS	2340	=head1 SECURITY CONSIDERATIONS
850		2341
851	AnyEvent can be forced to load any event model via	2342	AnyEvent can be forced to load any event model via
852	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to	2343	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
…		…
856	specified in the variable.	2347	specified in the variable.
857		2348
858	You can make AnyEvent completely ignore this variable by deleting it	2349	You can make AnyEvent completely ignore this variable by deleting it
859	before the first watcher gets created, e.g. with a C<BEGIN> block:	2350	before the first watcher gets created, e.g. with a C<BEGIN> block:
860		2351
861	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2352	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
862		2353
863	use AnyEvent;	2354	use AnyEvent;
		2355
		2356	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2357	be used to probe what backend is used and gain other information (which is
		2358	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2359	$ENV{PERL_ANYEVENT_STRICT}.
		2360
		2361	Note that AnyEvent will remove I<all> environment variables starting with
		2362	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2363	enabled.
		2364
		2365
		2366	=head1 BUGS
		2367
		2368	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2369	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2370	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2371	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2372	pronounced).
		2373
864		2374
865	=head1 SEE ALSO	2375	=head1 SEE ALSO
866		2376
867	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	2377	Utility functions: L<AnyEvent::Util>.
868	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
869	L<Event::Lib>, L<Qt>.
870		2378
871	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	2379	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
872	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,	2380	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
873	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
874	L<AnyEvent::Impl::Qt>.
875		2381
		2382	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2383	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2384	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2385	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>.
		2386
		2387	Non-blocking file handles, sockets, TCP clients and
		2388	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2389
		2390	Asynchronous DNS: L<AnyEvent::DNS>.
		2391
		2392	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>,
		2393	L<Coro::Event>,
		2394
876	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	2395	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::XMPP>,
		2396	L<AnyEvent::HTTP>.
		2397
877		2398
878	=head1 AUTHOR	2399	=head1 AUTHOR
879		2400
880	Marc Lehmann <schmorp@schmorp.de>	2401	Marc Lehmann <schmorp@schmorp.de>
881	http://home.schmorp.de/	2402	http://home.schmorp.de/
882		2403
883	=cut	2404	=cut
884		2405
885	1	2406	1
886		2407

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