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Revision 1.227 by root, Mon Jul 6 23:42:24 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 - 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
…		…
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 the	112	to detect the currently loaded event loop by probing whether one of the
84	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,	113	following modules is already loaded: L<EV>,
85	L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found,	114	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	the module tries to load these modules in the stated order. The first one	115	L<POE>. The first one found is used. If none are found, the module tries
		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
87	that can be successfully loaded will be used. If, after this, still none	118	be successfully loaded will be used. If, after this, still none could be
88	could be found, AnyEvent will fall back to a pure-perl event loop, which	119	found, AnyEvent will fall back to a pure-perl event loop, which is not
89	is not very efficient, but should work everywhere.	120	very efficient, but should work everywhere.
90		121
91	Because AnyEvent first checks for modules that are already loaded, loading	122	Because AnyEvent first checks for modules that are already loaded, loading
92	an event model explicitly before first using AnyEvent will likely make	123	an event model explicitly before first using AnyEvent will likely make
93	that model the default. For example:	124	that model the default. For example:
94		125
…		…
101	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
102	use AnyEvent so their modules work together with others seamlessly...	133	use AnyEvent so their modules work together with others seamlessly...
103		134
104	The pure-perl implementation of AnyEvent is called	135	The pure-perl implementation of AnyEvent is called
105	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
106	explicitly.	137	explicitly and enjoy the high availability of that event loop :)
107		138
108	=head1 WATCHERS	139	=head1 WATCHERS
109		140
110	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
111	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
112	the callback to call, the filehandle to watch, etc.	143	the callback to call, the file handle to watch, etc.
113		144
114	These watchers are normal Perl objects with normal Perl lifetime. After	145	These watchers are normal Perl objects with normal Perl lifetime. After
115	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
116	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
117	is in control).	148	is in control).
118		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
119	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
120	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
121	to it).	158	to it).
122		159
123	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.
…		…
125	Many watchers either are used with "recursion" (repeating timers for	162	Many watchers either are used with "recursion" (repeating timers for
126	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.
127		164
128	An any way to achieve that is this pattern:	165	An any way to achieve that is this pattern:
129		166
130	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	167	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
131	# you can use $w here, for example to undef it	168	# you can use $w here, for example to undef it
132	undef $w;	169	undef $w;
133	});	170	});
134		171
135	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,
136	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
137	declared.	174	declared.
138		175
139	=head2 IO WATCHERS	176	=head2 I/O WATCHERS
140		177
141	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
142	with the following mandatory key-value pairs as arguments:	179	with the following mandatory key-value pairs as arguments:
143		180
144	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	181	C<fh> is the Perl I<file handle> (I<not> 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
145	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
146	creates a watcher waiting for "r"eadable or "w"ritable events,	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
147	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.
148	becomes ready.
149		192
150	File handles will be kept alive, so as long as the watcher exists, the	193	Although the callback might get passed parameters, their value and
151	file handle exists, too.	194	presence is undefined and you cannot rely on them. Portable AnyEvent
		195	callbacks cannot use arguments passed to I/O watcher callbacks.
152		196
		197	The I/O watcher might use the underlying file descriptor or a copy of it.
153	It is not allowed to close a file handle as long as any watcher is active	198	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	199	underlying file descriptor.
155		200
156	Some event loops issue spurious readyness notifications, so you should	201	Some event loops issue spurious readyness notifications, so you should
157	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
158	handles.	203	handles.
159		204
160	Example:
161
162	# 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
163	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
164	chomp (my $input = <STDIN>);	209	chomp (my $input = <STDIN>);
165	warn "read: $input\n";	210	warn "read: $input\n";
166	undef $w;	211	undef $w;
167	});	212	});
…		…
170		215
171	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 >>
172	method with the following mandatory arguments:	217	method with the following mandatory arguments:
173		218
174	C<after> specifies after how many seconds (fractional values are	219	C<after> specifies after how many seconds (fractional values are
175	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
176	case.	221	in that case.
177		222
178	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
179	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
180	and Glib).	225	callbacks cannot use arguments passed to time watcher callbacks.
181		226
182	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.
183		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
184	# fire an event after 7.7 seconds	237	Example: fire an event after 7.7 seconds.
		238
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	240	warn "timeout\n";
187	});	241	});
188		242
189	# to cancel the timer:	243	# to cancel the timer:
190	undef $w;	244	undef $w;
191		245
192	Example 2:
193
194	# 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.
195	my $w;
196		247
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		249	warn "timeout\n";
200	};	250	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		251
205	=head3 TIMING ISSUES	252	=head3 TIMING ISSUES
206		253
207	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
208	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
209	o'clock").	256	o'clock").
210		257
211	While most event loops expect timers to specified in a relative way, they use	258	While most event loops expect timers to specified in a relative way, they
212	absolute time internally. This makes a difference when your clock "jumps",	259	use absolute time internally. This makes a difference when your clock
213	for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to	260	"jumps", for example, when ntp decides to set your clock backwards from
214	2008-01-01, a watcher that you created to fire "after" a second might actually take	261	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	262	fire "after" a second might actually take six years to finally fire.
216		263
217	AnyEvent cannot compensate for this. The only event loop that is conscious	264	AnyEvent cannot compensate for this. The only event loop that is conscious
218	about these issues is L<EV>, which offers both relative (ev_timer) and	265	about these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	266	on true relative time) and absolute (ev_periodic, based on wallclock time)
		267	timers.
220		268
221	AnyEvent always prefers relative timers, if available, matching the	269	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	270	AnyEvent API.
223		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
224	=head2 SIGNAL WATCHERS	350	=head2 SIGNAL WATCHERS
225		351
226	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
227	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
228	be invoked whenever a signal occurs.	354	callback to be invoked whenever a signal occurs.
229		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
230	Multiple signals occurances can be clumped together into one callback	360	Multiple signal occurrences can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	361	invocation, and callback invocation will be synchronous. Synchronous means
232	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,
233	but it is guarenteed not to interrupt any other callbacks.	363	but it is guaranteed not to interrupt any other callbacks.
234		364
235	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
236	between multiple watchers.	366	between multiple watchers.
237		367
238	This watcher might use C<%SIG>, so programs overwriting those signals	368	This watcher might use C<%SIG>, so programs overwriting those signals
…		…
245	=head2 CHILD PROCESS WATCHERS	375	=head2 CHILD PROCESS WATCHERS
246		376
247	You can also watch on a child process exit and catch its exit status.	377	You can also watch on a child process exit and catch its exit status.
248		378
249	The child process is specified by the C<pid> argument (if set to C<0>, it	379	The child process is specified by the C<pid> argument (if set to C<0>, it
250	watches for any child process exit). The watcher will trigger as often	380	watches for any child process exit). The watcher will triggered only when
251	as status change for the child are received. This works by installing a	381	the child process has finished and an exit status is available, not on
252	signal handler for C<SIGCHLD>. The callback will be called with the pid	382	any trace events (stopped/continued).
253	and exit status (as returned by waitpid).
254		383
255	Example: wait for pid 1333	384	The callback will be called with the pid and exit status (as returned by
		385	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		386	callback arguments.
256		387
		388	This watcher type works by installing a signal handler for C<SIGCHLD>,
		389	and since it cannot be shared, nothing else should use SIGCHLD or reap
		390	random child processes (waiting for specific child processes, e.g. inside
		391	C<system>, is just fine).
		392
		393	There is a slight catch to child watchers, however: you usually start them
		394	I<after> the child process was created, and this means the process could
		395	have exited already (and no SIGCHLD will be sent anymore).
		396
		397	Not all event models handle this correctly (neither POE nor IO::Async do,
		398	see their AnyEvent::Impl manpages for details), but even for event models
		399	that I<do> handle this correctly, they usually need to be loaded before
		400	the process exits (i.e. before you fork in the first place). AnyEvent's
		401	pure perl event loop handles all cases correctly regardless of when you
		402	start the watcher.
		403
		404	This means you cannot create a child watcher as the very first
		405	thing in an AnyEvent program, you I<have> to create at least one
		406	watcher before you C<fork> the child (alternatively, you can call
		407	C<AnyEvent::detect>).
		408
		409	Example: fork a process and wait for it
		410
		411	my $done = AnyEvent->condvar;
		412
		413	my $pid = fork or exit 5;
		414
257	my $w = AnyEvent->child (	415	my $w = AnyEvent->child (
258	pid => 1333,	416	pid => $pid,
259	cb => sub {	417	cb => sub {
260	my ($pid, $status) = @_;	418	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	419	warn "pid $pid exited with status $status";
		420	$done->send;
262	},	421	},
263	);	422	);
		423
		424	# do something else, then wait for process exit
		425	$done->recv;
		426
		427	=head2 IDLE WATCHERS
		428
		429	Sometimes there is a need to do something, but it is not so important
		430	to do it instantly, but only when there is nothing better to do. This
		431	"nothing better to do" is usually defined to be "no other events need
		432	attention by the event loop".
		433
		434	Idle watchers ideally get invoked when the event loop has nothing
		435	better to do, just before it would block the process to wait for new
		436	events. Instead of blocking, the idle watcher is invoked.
		437
		438	Most event loops unfortunately do not really support idle watchers (only
		439	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		440	will simply call the callback "from time to time".
		441
		442	Example: read lines from STDIN, but only process them when the
		443	program is otherwise idle:
		444
		445	my @lines; # read data
		446	my $idle_w;
		447	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		448	push @lines, scalar <STDIN>;
		449
		450	# start an idle watcher, if not already done
		451	$idle_w ||= AnyEvent->idle (cb => sub {
		452	# handle only one line, when there are lines left
		453	if (my $line = shift @lines) {
		454	print "handled when idle: $line";
		455	} else {
		456	# otherwise disable the idle watcher again
		457	undef $idle_w;
		458	}
		459	});
		460	});
264		461
265	=head2 CONDITION VARIABLES	462	=head2 CONDITION VARIABLES
266		463
		464	If you are familiar with some event loops you will know that all of them
		465	require you to run some blocking "loop", "run" or similar function that
		466	will actively watch for new events and call your callbacks.
		467
		468	AnyEvent is different, it expects somebody else to run the event loop and
		469	will only block when necessary (usually when told by the user).
		470
		471	The instrument to do that is called a "condition variable", so called
		472	because they represent a condition that must become true.
		473
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	474	Condition variables can be created by calling the C<< AnyEvent->condvar
268	method without any arguments.	475	>> method, usually without arguments. The only argument pair allowed is
269		476
270	A condition variable waits for a condition - precisely that the C<<	477	C<cb>, which specifies a callback to be called when the condition variable
271	->broadcast >> method has been called.	478	becomes true, with the condition variable as the first argument (but not
		479	the results).
272		480
273	They are very useful to signal that a condition has been fulfilled, for	481	After creation, the condition variable is "false" until it becomes "true"
		482	by calling the C<send> method (or calling the condition variable as if it
		483	were a callback, read about the caveats in the description for the C<<
		484	->send >> method).
		485
		486	Condition variables are similar to callbacks, except that you can
		487	optionally wait for them. They can also be called merge points - points
		488	in time where multiple outstanding events have been processed. And yet
		489	another way to call them is transactions - each condition variable can be
		490	used to represent a transaction, which finishes at some point and delivers
		491	a result.
		492
		493	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	494	for example, if you write a module that does asynchronous http requests,
275	then a condition variable would be the ideal candidate to signal the	495	then a condition variable would be the ideal candidate to signal the
276	availability of results.	496	availability of results. The user can either act when the callback is
		497	called or can synchronously C<< ->recv >> for the results.
277		498
278	You can also use condition variables to block your main program until	499	You can also use them to simulate traditional event loops - for example,
279	an event occurs - for example, you could C<< ->wait >> in your main	500	you can block your main program until an event occurs - for example, you
280	program until the user clicks the Quit button in your app, which would C<<	501	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	502	button of your app, which would C<< ->send >> the "quit" event.
282		503
283	Note that condition variables recurse into the event loop - if you have	504	Note that condition variables recurse into the event loop - if you have
284	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	505	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
285	lose. Therefore, condition variables are good to export to your caller, but	506	lose. Therefore, condition variables are good to export to your caller, but
286	you should avoid making a blocking wait yourself, at least in callbacks,	507	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	508	as this asks for trouble.
288		509
289	This object has two methods:	510	Condition variables are represented by hash refs in perl, and the keys
		511	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		512	easy (it is often useful to build your own transaction class on top of
		513	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		514	it's C<new> method in your own C<new> method.
		515
		516	There are two "sides" to a condition variable - the "producer side" which
		517	eventually calls C<< -> send >>, and the "consumer side", which waits
		518	for the send to occur.
		519
		520	Example: wait for a timer.
		521
		522	# wait till the result is ready
		523	my $result_ready = AnyEvent->condvar;
		524
		525	# do something such as adding a timer
		526	# or socket watcher the calls $result_ready->send
		527	# when the "result" is ready.
		528	# in this case, we simply use a timer:
		529	my $w = AnyEvent->timer (
		530	after => 1,
		531	cb => sub { $result_ready->send },
		532	);
		533
		534	# this "blocks" (while handling events) till the callback
		535	# calls send
		536	$result_ready->recv;
		537
		538	Example: wait for a timer, but take advantage of the fact that
		539	condition variables are also code references.
		540
		541	my $done = AnyEvent->condvar;
		542	my $delay = AnyEvent->timer (after => 5, cb => $done);
		543	$done->recv;
		544
		545	Example: Imagine an API that returns a condvar and doesn't support
		546	callbacks. This is how you make a synchronous call, for example from
		547	the main program:
		548
		549	use AnyEvent::CouchDB;
		550
		551	...
		552
		553	my @info = $couchdb->info->recv;
		554
		555	And this is how you would just ste a callback to be called whenever the
		556	results are available:
		557
		558	$couchdb->info->cb (sub {
		559	my @info = $_[0]->recv;
		560	});
		561
		562	=head3 METHODS FOR PRODUCERS
		563
		564	These methods should only be used by the producing side, i.e. the
		565	code/module that eventually sends the signal. Note that it is also
		566	the producer side which creates the condvar in most cases, but it isn't
		567	uncommon for the consumer to create it as well.
290		568
291	=over 4	569	=over 4
292		570
		571	=item $cv->send (...)
		572
		573	Flag the condition as ready - a running C<< ->recv >> and all further
		574	calls to C<recv> will (eventually) return after this method has been
		575	called. If nobody is waiting the send will be remembered.
		576
		577	If a callback has been set on the condition variable, it is called
		578	immediately from within send.
		579
		580	Any arguments passed to the C<send> call will be returned by all
		581	future C<< ->recv >> calls.
		582
		583	Condition variables are overloaded so one can call them directly
		584	(as a code reference). Calling them directly is the same as calling
		585	C<send>. Note, however, that many C-based event loops do not handle
		586	overloading, so as tempting as it may be, passing a condition variable
		587	instead of a callback does not work. Both the pure perl and EV loops
		588	support overloading, however, as well as all functions that use perl to
		589	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		590	example).
		591
		592	=item $cv->croak ($error)
		593
		594	Similar to send, but causes all call's to C<< ->recv >> to invoke
		595	C<Carp::croak> with the given error message/object/scalar.
		596
		597	This can be used to signal any errors to the condition variable
		598	user/consumer.
		599
		600	=item $cv->begin ([group callback])
		601
293	=item $cv->wait	602	=item $cv->end
294		603
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	604	These two methods can be used to combine many transactions/events into
		605	one. For example, a function that pings many hosts in parallel might want
		606	to use a condition variable for the whole process.
		607
		608	Every call to C<< ->begin >> will increment a counter, and every call to
		609	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		610	>>, the (last) callback passed to C<begin> will be executed. That callback
		611	is I<supposed> to call C<< ->send >>, but that is not required. If no
		612	callback was set, C<send> will be called without any arguments.
		613
		614	You can think of C<< $cv->send >> giving you an OR condition (one call
		615	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		616	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		617
		618	Let's start with a simple example: you have two I/O watchers (for example,
		619	STDOUT and STDERR for a program), and you want to wait for both streams to
		620	close before activating a condvar:
		621
		622	my $cv = AnyEvent->condvar;
		623
		624	$cv->begin; # first watcher
		625	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		626	defined sysread $fh1, my $buf, 4096
		627	or $cv->end;
		628	});
		629
		630	$cv->begin; # second watcher
		631	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		632	defined sysread $fh2, my $buf, 4096
		633	or $cv->end;
		634	});
		635
		636	$cv->recv;
		637
		638	This works because for every event source (EOF on file handle), there is
		639	one call to C<begin>, so the condvar waits for all calls to C<end> before
		640	sending.
		641
		642	The ping example mentioned above is slightly more complicated, as the
		643	there are results to be passwd back, and the number of tasks that are
		644	begung can potentially be zero:
		645
		646	my $cv = AnyEvent->condvar;
		647
		648	my %result;
		649	$cv->begin (sub { $cv->send (\%result) });
		650
		651	for my $host (@list_of_hosts) {
		652	$cv->begin;
		653	ping_host_then_call_callback $host, sub {
		654	$result{$host} = ...;
		655	$cv->end;
		656	};
		657	}
		658
		659	$cv->end;
		660
		661	This code fragment supposedly pings a number of hosts and calls
		662	C<send> after results for all then have have been gathered - in any
		663	order. To achieve this, the code issues a call to C<begin> when it starts
		664	each ping request and calls C<end> when it has received some result for
		665	it. Since C<begin> and C<end> only maintain a counter, the order in which
		666	results arrive is not relevant.
		667
		668	There is an additional bracketing call to C<begin> and C<end> outside the
		669	loop, which serves two important purposes: first, it sets the callback
		670	to be called once the counter reaches C<0>, and second, it ensures that
		671	C<send> is called even when C<no> hosts are being pinged (the loop
		672	doesn't execute once).
		673
		674	This is the general pattern when you "fan out" into multiple (but
		675	potentially none) subrequests: use an outer C<begin>/C<end> pair to set
		676	the callback and ensure C<end> is called at least once, and then, for each
		677	subrequest you start, call C<begin> and for each subrequest you finish,
		678	call C<end>.
		679
		680	=back
		681
		682	=head3 METHODS FOR CONSUMERS
		683
		684	These methods should only be used by the consuming side, i.e. the
		685	code awaits the condition.
		686
		687	=over 4
		688
		689	=item $cv->recv
		690
		691	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
296	called on c<$cv>, while servicing other watchers normally.	692	>> methods have been called on c<$cv>, while servicing other watchers
		693	normally.
297		694
298	You can only wait once on a condition - additional calls will return	695	You can only wait once on a condition - additional calls are valid but
299	immediately.	696	will return immediately.
		697
		698	If an error condition has been set by calling C<< ->croak >>, then this
		699	function will call C<croak>.
		700
		701	In list context, all parameters passed to C<send> will be returned,
		702	in scalar context only the first one will be returned.
300		703
301	Not all event models support a blocking wait - some die in that case	704	Not all event models support a blocking wait - some die in that case
302	(programs might want to do that to stay interactive), so I<if you are	705	(programs might want to do that to stay interactive), so I<if you are
303	using this from a module, never require a blocking wait>, but let the	706	using this from a module, never require a blocking wait>, but let the
304	caller decide whether the call will block or not (for example, by coupling	707	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	708	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	709	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	710	while still supporting blocking waits if the caller so desires).
308		711
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	712	Another reason I<never> to C<< ->recv >> in a module is that you cannot
310	sensibly have two C<< ->wait >>'s in parallel, as that would require	713	sensibly have two C<< ->recv >>'s in parallel, as that would require
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	714	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	715	can supply.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		716
316	=item $cv->broadcast	717	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		718	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		719	versions and also integrates coroutines into AnyEvent, making blocking
		720	C<< ->recv >> calls perfectly safe as long as they are done from another
		721	coroutine (one that doesn't run the event loop).
317		722
318	Flag the condition as ready - a running C<< ->wait >> and all further	723	You can ensure that C<< -recv >> never blocks by setting a callback and
319	calls to C<wait> will (eventually) return after this method has been	724	only calling C<< ->recv >> from within that callback (or at a later
320	called. If nobody is waiting the broadcast will be remembered..	725	time). This will work even when the event loop does not support blocking
		726	waits otherwise.
		727
		728	=item $bool = $cv->ready
		729
		730	Returns true when the condition is "true", i.e. whether C<send> or
		731	C<croak> have been called.
		732
		733	=item $cb = $cv->cb ($cb->($cv))
		734
		735	This is a mutator function that returns the callback set and optionally
		736	replaces it before doing so.
		737
		738	The callback will be called when the condition becomes "true", i.e. when
		739	C<send> or C<croak> are called, with the only argument being the condition
		740	variable itself. Calling C<recv> inside the callback or at any later time
		741	is guaranteed not to block.
321		742
322	=back	743	=back
323
324	Example:
325
326	# wait till the result is ready
327	my $result_ready = AnyEvent->condvar;
328
329	# do something such as adding a timer
330	# or socket watcher the calls $result_ready->broadcast
331	# when the "result" is ready.
332	# in this case, we simply use a timer:
333	my $w = AnyEvent->timer (
334	after => 1,
335	cb => sub { $result_ready->broadcast },
336	);
337
338	# this "blocks" (while handling events) till the watcher
339	# calls broadcast
340	$result_ready->wait;
341		744
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	745	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		746
344	=over 4	747	=over 4
345		748
…		…
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	754	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
352	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	755	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
353		756
354	The known classes so far are:	757	The known classes so far are:
355		758
356	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
357	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
358	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	759	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)	760	AnyEvent::Impl::Event based on Event, second best choice.
		761	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
360	AnyEvent::Impl::Glib based on Glib, third-best choice.	762	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.	763	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	764	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
363	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	765	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		766	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		767
		768	# warning, support for IO::Async is only partial, as it is too broken
		769	# and limited toe ven support the AnyEvent API. See AnyEvent::Impl::Async.
		770	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed (see its docs).
		771
		772	There is no support for WxWidgets, as WxWidgets has no support for
		773	watching file handles. However, you can use WxWidgets through the
		774	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		775	second, which was considered to be too horrible to even consider for
		776	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		777	it's adaptor.
		778
		779	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		780	autodetecting them.
364		781
365	=item AnyEvent::detect	782	=item AnyEvent::detect
366		783
367	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	784	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
368	if necessary. You should only call this function right before you would	785	if necessary. You should only call this function right before you would
369	have created an AnyEvent watcher anyway, that is, as late as possible at	786	have created an AnyEvent watcher anyway, that is, as late as possible at
370	runtime.	787	runtime.
371		788
		789	=item $guard = AnyEvent::post_detect { BLOCK }
		790
		791	Arranges for the code block to be executed as soon as the event model is
		792	autodetected (or immediately if this has already happened).
		793
		794	If called in scalar or list context, then it creates and returns an object
		795	that automatically removes the callback again when it is destroyed. See
		796	L<Coro::BDB> for a case where this is useful.
		797
		798	=item @AnyEvent::post_detect
		799
		800	If there are any code references in this array (you can C<push> to it
		801	before or after loading AnyEvent), then they will called directly after
		802	the event loop has been chosen.
		803
		804	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		805	if it contains a true value then the event loop has already been detected,
		806	and the array will be ignored.
		807
		808	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		809
372	=back	810	=back
373		811
374	=head1 WHAT TO DO IN A MODULE	812	=head1 WHAT TO DO IN A MODULE
375		813
376	As a module author, you should C<use AnyEvent> and call AnyEvent methods	814	As a module author, you should C<use AnyEvent> and call AnyEvent methods
…		…
379	Be careful when you create watchers in the module body - AnyEvent will	817	Be careful when you create watchers in the module body - AnyEvent will
380	decide which event module to use as soon as the first method is called, so	818	decide which event module to use as soon as the first method is called, so
381	by calling AnyEvent in your module body you force the user of your module	819	by calling AnyEvent in your module body you force the user of your module
382	to load the event module first.	820	to load the event module first.
383		821
384	Never call C<< ->wait >> on a condition variable unless you I<know> that	822	Never call C<< ->recv >> on a condition variable unless you I<know> that
385	the C<< ->broadcast >> method has been called on it already. This is	823	the C<< ->send >> method has been called on it already. This is
386	because it will stall the whole program, and the whole point of using	824	because it will stall the whole program, and the whole point of using
387	events is to stay interactive.	825	events is to stay interactive.
388		826
389	It is fine, however, to call C<< ->wait >> when the user of your module	827	It is fine, however, to call C<< ->recv >> when the user of your module
390	requests it (i.e. if you create a http request object ad have a method	828	requests it (i.e. if you create a http request object ad have a method
391	called C<results> that returns the results, it should call C<< ->wait >>	829	called C<results> that returns the results, it should call C<< ->recv >>
392	freely, as the user of your module knows what she is doing. always).	830	freely, as the user of your module knows what she is doing. always).
393		831
394	=head1 WHAT TO DO IN THE MAIN PROGRAM	832	=head1 WHAT TO DO IN THE MAIN PROGRAM
395		833
396	There will always be a single main program - the only place that should	834	There will always be a single main program - the only place that should
…		…
398		836
399	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	837	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
400	do anything special (it does not need to be event-based) and let AnyEvent	838	do anything special (it does not need to be event-based) and let AnyEvent
401	decide which implementation to chose if some module relies on it.	839	decide which implementation to chose if some module relies on it.
402		840
403	If the main program relies on a specific event model. For example, in	841	If the main program relies on a specific event model - for example, in
404	Gtk2 programs you have to rely on the Glib module. You should load the	842	Gtk2 programs you have to rely on the Glib module - you should load the
405	event module before loading AnyEvent or any module that uses it: generally	843	event module before loading AnyEvent or any module that uses it: generally
406	speaking, you should load it as early as possible. The reason is that	844	speaking, you should load it as early as possible. The reason is that
407	modules might create watchers when they are loaded, and AnyEvent will	845	modules might create watchers when they are loaded, and AnyEvent will
408	decide on the event model to use as soon as it creates watchers, and it	846	decide on the event model to use as soon as it creates watchers, and it
409	might chose the wrong one unless you load the correct one yourself.	847	might chose the wrong one unless you load the correct one yourself.
410		848
411	You can chose to use a rather inefficient pure-perl implementation by	849	You can chose to use a pure-perl implementation by loading the
412	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	850	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
413	behaviour everywhere, but letting AnyEvent chose is generally better.	851	everywhere, but letting AnyEvent chose the model is generally better.
		852
		853	=head2 MAINLOOP EMULATION
		854
		855	Sometimes (often for short test scripts, or even standalone programs who
		856	only want to use AnyEvent), you do not want to run a specific event loop.
		857
		858	In that case, you can use a condition variable like this:
		859
		860	AnyEvent->condvar->recv;
		861
		862	This has the effect of entering the event loop and looping forever.
		863
		864	Note that usually your program has some exit condition, in which case
		865	it is better to use the "traditional" approach of storing a condition
		866	variable somewhere, waiting for it, and sending it when the program should
		867	exit cleanly.
		868
		869
		870	=head1 OTHER MODULES
		871
		872	The following is a non-exhaustive list of additional modules that use
		873	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		874	in the same program. Some of the modules come with AnyEvent, some are
		875	available via CPAN.
		876
		877	=over 4
		878
		879	=item L<AnyEvent::Util>
		880
		881	Contains various utility functions that replace often-used but blocking
		882	functions such as C<inet_aton> by event-/callback-based versions.
		883
		884	=item L<AnyEvent::Socket>
		885
		886	Provides various utility functions for (internet protocol) sockets,
		887	addresses and name resolution. Also functions to create non-blocking tcp
		888	connections or tcp servers, with IPv6 and SRV record support and more.
		889
		890	=item L<AnyEvent::Handle>
		891
		892	Provide read and write buffers, manages watchers for reads and writes,
		893	supports raw and formatted I/O, I/O queued and fully transparent and
		894	non-blocking SSL/TLS.
		895
		896	=item L<AnyEvent::DNS>
		897
		898	Provides rich asynchronous DNS resolver capabilities.
		899
		900	=item L<AnyEvent::HTTP>
		901
		902	A simple-to-use HTTP library that is capable of making a lot of concurrent
		903	HTTP requests.
		904
		905	=item L<AnyEvent::HTTPD>
		906
		907	Provides a simple web application server framework.
		908
		909	=item L<AnyEvent::FastPing>
		910
		911	The fastest ping in the west.
		912
		913	=item L<AnyEvent::DBI>
		914
		915	Executes L<DBI> requests asynchronously in a proxy process.
		916
		917	=item L<AnyEvent::AIO>
		918
		919	Truly asynchronous I/O, should be in the toolbox of every event
		920	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		921	together.
		922
		923	=item L<AnyEvent::BDB>
		924
		925	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		926	L<BDB> and AnyEvent together.
		927
		928	=item L<AnyEvent::GPSD>
		929
		930	A non-blocking interface to gpsd, a daemon delivering GPS information.
		931
		932	=item L<AnyEvent::IGS>
		933
		934	A non-blocking interface to the Internet Go Server protocol (used by
		935	L<App::IGS>).
		936
		937	=item L<AnyEvent::IRC>
		938
		939	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		940
		941	=item L<Net::XMPP2>
		942
		943	AnyEvent based XMPP (Jabber protocol) module family.
		944
		945	=item L<Net::FCP>
		946
		947	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		948	of AnyEvent.
		949
		950	=item L<Event::ExecFlow>
		951
		952	High level API for event-based execution flow control.
		953
		954	=item L<Coro>
		955
		956	Has special support for AnyEvent via L<Coro::AnyEvent>.
		957
		958	=item L<IO::Lambda>
		959
		960	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		961
		962	=back
414		963
415	=cut	964	=cut
416		965
417	package AnyEvent;	966	package AnyEvent;
418		967
419	no warnings;	968	no warnings;
420	use strict;	969	use strict qw(vars subs);
421		970
422	use Carp;	971	use Carp;
423		972
424	our $VERSION = '3.12';	973	our $VERSION = 4.8;
425	our $MODEL;	974	our $MODEL;
426		975
427	our $AUTOLOAD;	976	our $AUTOLOAD;
428	our @ISA;	977	our @ISA;
429		978
		979	our @REGISTRY;
		980
		981	our $WIN32;
		982
		983	BEGIN {
		984	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		985	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		986
		987	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		988	if ${^TAINT};
		989	}
		990
430	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	991	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
431		992
432	our @REGISTRY;	993	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		994
		995	{
		996	my $idx;
		997	$PROTOCOL{$_} = ++$idx
		998	for reverse split /\s*,\s*/,
		999	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1000	}
433		1001
434	my @models = (	1002	my @models = (
435	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
436	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
437	[EV:: => AnyEvent::Impl::EV::],	1003	[EV:: => AnyEvent::Impl::EV::],
438	[Event:: => AnyEvent::Impl::Event::],	1004	[Event:: => AnyEvent::Impl::Event::],
439	[Glib:: => AnyEvent::Impl::Glib::],
440	[Tk:: => AnyEvent::Impl::Tk::],
441	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	1005	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		1006	# everything below here will not be autoprobed
		1007	# as the pureperl backend should work everywhere
		1008	# and is usually faster
		1009	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1010	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
442	[Event::Lib:: => AnyEvent::Impl::EventLib::],	1011	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1012	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1013	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1014	[Wx:: => AnyEvent::Impl::POE::],
		1015	[Prima:: => AnyEvent::Impl::POE::],
		1016	# IO::Async is just too broken - we would need workaorunds for its
		1017	# byzantine signal and broken child handling, among others.
		1018	# IO::Async is rather hard to detect, as it doesn't have any
		1019	# obvious default class.
		1020	# [IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1021	# [IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1022	# [IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
443	);	1023	);
444		1024
445	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	1025	our %method = map +($_ => 1),
		1026	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
		1027
		1028	our @post_detect;
		1029
		1030	sub post_detect(&) {
		1031	my ($cb) = @_;
		1032
		1033	if ($MODEL) {
		1034	$cb->();
		1035
		1036	1
		1037	} else {
		1038	push @post_detect, $cb;
		1039
		1040	defined wantarray
		1041	? bless \$cb, "AnyEvent::Util::postdetect"
		1042	: ()
		1043	}
		1044	}
		1045
		1046	sub AnyEvent::Util::postdetect::DESTROY {
		1047	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1048	}
446		1049
447	sub detect() {	1050	sub detect() {
448	unless ($MODEL) {	1051	unless ($MODEL) {
449	no strict 'refs';	1052	no strict 'refs';
		1053	local $SIG{__DIE__};
450		1054
451	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {	1055	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
452	my $model = "AnyEvent::Impl::$1";	1056	my $model = "AnyEvent::Impl::$1";
453	if (eval "require $model") {	1057	if (eval "require $model") {
454	$MODEL = $model;	1058	$MODEL = $model;
455	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;	1059	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		1060	} else {
		1061	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
456	}	1062	}
457	}	1063	}
458		1064
459	# check for already loaded models	1065	# check for already loaded models
460	unless ($MODEL) {	1066	unless ($MODEL) {
…		…
482	last;	1088	last;
483	}	1089	}
484	}	1090	}
485		1091
486	$MODEL	1092	$MODEL
487	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";	1093	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
488	}	1094	}
489	}	1095	}
490		1096
		1097	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1098
491	unshift @ISA, $MODEL;	1099	unshift @ISA, $MODEL;
492	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	1100
		1101	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1102
		1103	(shift @post_detect)->() while @post_detect;
493	}	1104	}
494		1105
495	$MODEL	1106	$MODEL
496	}	1107	}
497		1108
…		…
505		1116
506	my $class = shift;	1117	my $class = shift;
507	$class->$func (@_);	1118	$class->$func (@_);
508	}	1119	}
509		1120
		1121	# utility function to dup a filehandle. this is used by many backends
		1122	# to support binding more than one watcher per filehandle (they usually
		1123	# allow only one watcher per fd, so we dup it to get a different one).
		1124	sub _dupfh($$;$$) {
		1125	my ($poll, $fh, $r, $w) = @_;
		1126
		1127	# cygwin requires the fh mode to be matching, unix doesn't
		1128	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1129	: $poll eq "w" ? ($w, ">")
		1130	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1131
		1132	open my $fh2, "$mode&" . fileno $fh
		1133	or die "cannot dup() filehandle: $!,";
		1134
		1135	# we assume CLOEXEC is already set by perl in all important cases
		1136
		1137	($fh2, $rw)
		1138	}
		1139
510	package AnyEvent::Base;	1140	package AnyEvent::Base;
511		1141
		1142	# default implementations for many methods
		1143
		1144	BEGIN {
		1145	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1146	*_time = \&Time::HiRes::time;
		1147	# if (eval "use POSIX (); (POSIX::times())...
		1148	} else {
		1149	*_time = sub { time }; # epic fail
		1150	}
		1151	}
		1152
		1153	sub time { _time }
		1154	sub now { _time }
		1155	sub now_update { }
		1156
512	# default implementation for ->condvar, ->wait, ->broadcast	1157	# default implementation for ->condvar
513		1158
514	sub condvar {	1159	sub condvar {
515	bless \my $flag, "AnyEvent::Base::CondVar"	1160	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
516	}
517
518	sub AnyEvent::Base::CondVar::broadcast {
519	${$_[0]}++;
520	}
521
522	sub AnyEvent::Base::CondVar::wait {
523	AnyEvent->one_event while !${$_[0]};
524	}	1161	}
525		1162
526	# default implementation for ->signal	1163	# default implementation for ->signal
527		1164
528	our %SIG_CB;	1165	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1166
		1167	sub _signal_exec {
		1168	sysread $SIGPIPE_R, my $dummy, 4;
		1169
		1170	while (%SIG_EV) {
		1171	for (keys %SIG_EV) {
		1172	delete $SIG_EV{$_};
		1173	$_->() for values %{ $SIG_CB{$_} || {} };
		1174	}
		1175	}
		1176	}
529		1177
530	sub signal {	1178	sub signal {
531	my (undef, %arg) = @_;	1179	my (undef, %arg) = @_;
532		1180
		1181	unless ($SIGPIPE_R) {
		1182	require Fcntl;
		1183
		1184	if (AnyEvent::WIN32) {
		1185	require AnyEvent::Util;
		1186
		1187	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1188	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1189	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1190	} else {
		1191	pipe $SIGPIPE_R, $SIGPIPE_W;
		1192	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1193	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1194
		1195	# not strictly required, as $^F is normally 2, but let's make sure...
		1196	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1197	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1198	}
		1199
		1200	$SIGPIPE_R
		1201	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1202
		1203	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1204	}
		1205
533	my $signal = uc $arg{signal}	1206	my $signal = uc $arg{signal}
534	or Carp::croak "required option 'signal' is missing";	1207	or Carp::croak "required option 'signal' is missing";
535		1208
536	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1209	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
537	$SIG{$signal} ||= sub {	1210	$SIG{$signal} ||= sub {
538	$_->() for values %{ $SIG_CB{$signal} || {} };	1211	local $!;
		1212	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1213	undef $SIG_EV{$signal};
539	};	1214	};
540		1215
541	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1216	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
542	}	1217	}
543		1218
544	sub AnyEvent::Base::Signal::DESTROY {	1219	sub AnyEvent::Base::signal::DESTROY {
545	my ($signal, $cb) = @{$_[0]};	1220	my ($signal, $cb) = @{$_[0]};
546		1221
547	delete $SIG_CB{$signal}{$cb};	1222	delete $SIG_CB{$signal}{$cb};
548		1223
		1224	# delete doesn't work with older perls - they then
		1225	# print weird messages, or just unconditionally exit
		1226	# instead of getting the default action.
549	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1227	undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
550	}	1228	}
551		1229
552	# default implementation for ->child	1230	# default implementation for ->child
553		1231
554	our %PID_CB;	1232	our %PID_CB;
555	our $CHLD_W;	1233	our $CHLD_W;
556	our $CHLD_DELAY_W;	1234	our $CHLD_DELAY_W;
557	our $PID_IDLE;
558	our $WNOHANG;	1235	our $WNOHANG;
559		1236
560	sub _child_wait {	1237	sub _sigchld {
561	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	1238	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
562	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1239	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
563	(values %{ $PID_CB{0} || {} });	1240	(values %{ $PID_CB{0} || {} });
564	}	1241	}
565
566	undef $PID_IDLE;
567	}
568
569	sub _sigchld {
570	# make sure we deliver these changes "synchronous" with the event loop.
571	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
572	undef $CHLD_DELAY_W;
573	&_child_wait;
574	});
575	}	1242	}
576		1243
577	sub child {	1244	sub child {
578	my (undef, %arg) = @_;	1245	my (undef, %arg) = @_;
579		1246
580	defined (my $pid = $arg{pid} + 0)	1247	defined (my $pid = $arg{pid} + 0)
581	or Carp::croak "required option 'pid' is missing";	1248	or Carp::croak "required option 'pid' is missing";
582		1249
583	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1250	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
584		1251
585	unless ($WNOHANG) {
586	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1252	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
587	}
588		1253
589	unless ($CHLD_W) {	1254	unless ($CHLD_W) {
590	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1255	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
591	# child could be a zombie already, so make at least one round	1256	# child could be a zombie already, so make at least one round
592	&_sigchld;	1257	&_sigchld;
593	}	1258	}
594		1259
595	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1260	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
596	}	1261	}
597		1262
598	sub AnyEvent::Base::Child::DESTROY {	1263	sub AnyEvent::Base::child::DESTROY {
599	my ($pid, $cb) = @{$_[0]};	1264	my ($pid, $cb) = @{$_[0]};
600		1265
601	delete $PID_CB{$pid}{$cb};	1266	delete $PID_CB{$pid}{$cb};
602	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1267	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
603		1268
604	undef $CHLD_W unless keys %PID_CB;	1269	undef $CHLD_W unless keys %PID_CB;
605	}	1270	}
		1271
		1272	# idle emulation is done by simply using a timer, regardless
		1273	# of whether the process is idle or not, and not letting
		1274	# the callback use more than 50% of the time.
		1275	sub idle {
		1276	my (undef, %arg) = @_;
		1277
		1278	my ($cb, $w, $rcb) = $arg{cb};
		1279
		1280	$rcb = sub {
		1281	if ($cb) {
		1282	$w = _time;
		1283	&$cb;
		1284	$w = _time - $w;
		1285
		1286	# never use more then 50% of the time for the idle watcher,
		1287	# within some limits
		1288	$w = 0.0001 if $w < 0.0001;
		1289	$w = 5 if $w > 5;
		1290
		1291	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1292	} else {
		1293	# clean up...
		1294	undef $w;
		1295	undef $rcb;
		1296	}
		1297	};
		1298
		1299	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1300
		1301	bless \\$cb, "AnyEvent::Base::idle"
		1302	}
		1303
		1304	sub AnyEvent::Base::idle::DESTROY {
		1305	undef $${$_[0]};
		1306	}
		1307
		1308	package AnyEvent::CondVar;
		1309
		1310	our @ISA = AnyEvent::CondVar::Base::;
		1311
		1312	package AnyEvent::CondVar::Base;
		1313
		1314	use overload
		1315	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1316	fallback => 1;
		1317
		1318	sub _send {
		1319	# nop
		1320	}
		1321
		1322	sub send {
		1323	my $cv = shift;
		1324	$cv->{_ae_sent} = [@_];
		1325	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1326	$cv->_send;
		1327	}
		1328
		1329	sub croak {
		1330	$_[0]{_ae_croak} = $_[1];
		1331	$_[0]->send;
		1332	}
		1333
		1334	sub ready {
		1335	$_[0]{_ae_sent}
		1336	}
		1337
		1338	sub _wait {
		1339	AnyEvent->one_event while !$_[0]{_ae_sent};
		1340	}
		1341
		1342	sub recv {
		1343	$_[0]->_wait;
		1344
		1345	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1346	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1347	}
		1348
		1349	sub cb {
		1350	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1351	$_[0]{_ae_cb}
		1352	}
		1353
		1354	sub begin {
		1355	++$_[0]{_ae_counter};
		1356	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1357	}
		1358
		1359	sub end {
		1360	return if --$_[0]{_ae_counter};
		1361	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1362	}
		1363
		1364	# undocumented/compatibility with pre-3.4
		1365	*broadcast = \&send;
		1366	*wait = \&_wait;
		1367
		1368	=head1 ERROR AND EXCEPTION HANDLING
		1369
		1370	In general, AnyEvent does not do any error handling - it relies on the
		1371	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1372	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1373	checking of all AnyEvent methods, however, which is highly useful during
		1374	development.
		1375
		1376	As for exception handling (i.e. runtime errors and exceptions thrown while
		1377	executing a callback), this is not only highly event-loop specific, but
		1378	also not in any way wrapped by this module, as this is the job of the main
		1379	program.
		1380
		1381	The pure perl event loop simply re-throws the exception (usually
		1382	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1383	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1384	so on.
		1385
		1386	=head1 ENVIRONMENT VARIABLES
		1387
		1388	The following environment variables are used by this module or its
		1389	submodules.
		1390
		1391	Note that AnyEvent will remove I<all> environment variables starting with
		1392	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1393	enabled.
		1394
		1395	=over 4
		1396
		1397	=item C<PERL_ANYEVENT_VERBOSE>
		1398
		1399	By default, AnyEvent will be completely silent except in fatal
		1400	conditions. You can set this environment variable to make AnyEvent more
		1401	talkative.
		1402
		1403	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1404	conditions, such as not being able to load the event model specified by
		1405	C<PERL_ANYEVENT_MODEL>.
		1406
		1407	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1408	model it chooses.
		1409
		1410	=item C<PERL_ANYEVENT_STRICT>
		1411
		1412	AnyEvent does not do much argument checking by default, as thorough
		1413	argument checking is very costly. Setting this variable to a true value
		1414	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1415	check the arguments passed to most method calls. If it finds any problems,
		1416	it will croak.
		1417
		1418	In other words, enables "strict" mode.
		1419
		1420	Unlike C<use strict>, it is definitely recommended to keep it off in
		1421	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1422	developing programs can be very useful, however.
		1423
		1424	=item C<PERL_ANYEVENT_MODEL>
		1425
		1426	This can be used to specify the event model to be used by AnyEvent, before
		1427	auto detection and -probing kicks in. It must be a string consisting
		1428	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1429	and the resulting module name is loaded and if the load was successful,
		1430	used as event model. If it fails to load AnyEvent will proceed with
		1431	auto detection and -probing.
		1432
		1433	This functionality might change in future versions.
		1434
		1435	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1436	could start your program like this:
		1437
		1438	PERL_ANYEVENT_MODEL=Perl perl ...
		1439
		1440	=item C<PERL_ANYEVENT_PROTOCOLS>
		1441
		1442	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1443	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1444	of auto probing).
		1445
		1446	Must be set to a comma-separated list of protocols or address families,
		1447	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1448	used, and preference will be given to protocols mentioned earlier in the
		1449	list.
		1450
		1451	This variable can effectively be used for denial-of-service attacks
		1452	against local programs (e.g. when setuid), although the impact is likely
		1453	small, as the program has to handle conenction and other failures anyways.
		1454
		1455	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1456	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1457	- only support IPv4, never try to resolve or contact IPv6
		1458	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1459	IPv6, but prefer IPv6 over IPv4.
		1460
		1461	=item C<PERL_ANYEVENT_EDNS0>
		1462
		1463	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1464	for DNS. This extension is generally useful to reduce DNS traffic, but
		1465	some (broken) firewalls drop such DNS packets, which is why it is off by
		1466	default.
		1467
		1468	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1469	EDNS0 in its DNS requests.
		1470
		1471	=item C<PERL_ANYEVENT_MAX_FORKS>
		1472
		1473	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1474	will create in parallel.
		1475
		1476	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1477
		1478	The default value for the C<max_outstanding> parameter for the default DNS
		1479	resolver - this is the maximum number of parallel DNS requests that are
		1480	sent to the DNS server.
		1481
		1482	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1483
		1484	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1485	configuration) in the default resolver. When set to the empty string, no
		1486	default config will be used.
		1487
		1488	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1489
		1490	When neither C<ca_file> nor C<ca_path> was specified during
		1491	L<AnyEvent::TLS> context creation, and either of these environment
		1492	variables exist, they will be used to specify CA certificate locations
		1493	instead of a system-dependent default.
		1494
		1495	=back
606		1496
607	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1497	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
608		1498
609	This is an advanced topic that you do not normally need to use AnyEvent in	1499	This is an advanced topic that you do not normally need to use AnyEvent in
610	a module. This section is only of use to event loop authors who want to	1500	a module. This section is only of use to event loop authors who want to
…		…
645	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1535	I<rxvt-unicode> also cheats a bit by not providing blocking access to
646	condition variables: code blocking while waiting for a condition will	1536	condition variables: code blocking while waiting for a condition will
647	C<die>. This still works with most modules/usages, and blocking calls must	1537	C<die>. This still works with most modules/usages, and blocking calls must
648	not be done in an interactive application, so it makes sense.	1538	not be done in an interactive application, so it makes sense.
649		1539
650	=head1 ENVIRONMENT VARIABLES
651
652	The following environment variables are used by this module:
653
654	=over 4
655
656	=item C<PERL_ANYEVENT_VERBOSE>
657
658	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
659	model it chooses.
660
661	=item C<PERL_ANYEVENT_MODEL>
662
663	This can be used to specify the event model to be used by AnyEvent, before
664	autodetection and -probing kicks in. It must be a string consisting
665	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
666	and the resulting module name is loaded and if the load was successful,
667	used as event model. If it fails to load AnyEvent will proceed with
668	autodetection and -probing.
669
670	This functionality might change in future versions.
671
672	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
673	could start your program like this:
674
675	PERL_ANYEVENT_MODEL=Perl perl ...
676
677	=back
678
679	=head1 EXAMPLE PROGRAM	1540	=head1 EXAMPLE PROGRAM
680		1541
681	The following program uses an IO watcher to read data from STDIN, a timer	1542	The following program uses an I/O watcher to read data from STDIN, a timer
682	to display a message once per second, and a condition variable to quit the	1543	to display a message once per second, and a condition variable to quit the
683	program when the user enters quit:	1544	program when the user enters quit:
684		1545
685	use AnyEvent;	1546	use AnyEvent;
686		1547
…		…
691	poll => 'r',	1552	poll => 'r',
692	cb => sub {	1553	cb => sub {
693	warn "io event <$_[0]>\n"; # will always output <r>	1554	warn "io event <$_[0]>\n"; # will always output <r>
694	chomp (my $input = <STDIN>); # read a line	1555	chomp (my $input = <STDIN>); # read a line
695	warn "read: $input\n"; # output what has been read	1556	warn "read: $input\n"; # output what has been read
696	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1557	$cv->send if $input =~ /^q/i; # quit program if /^q/i
697	},	1558	},
698	);	1559	);
699		1560
700	my $time_watcher; # can only be used once	1561	my $time_watcher; # can only be used once
701		1562
…		…
706	});	1567	});
707	}	1568	}
708		1569
709	new_timer; # create first timer	1570	new_timer; # create first timer
710		1571
711	$cv->wait; # wait until user enters /^q/i	1572	$cv->recv; # wait until user enters /^q/i
712		1573
713	=head1 REAL-WORLD EXAMPLE	1574	=head1 REAL-WORLD EXAMPLE
714		1575
715	Consider the L<Net::FCP> module. It features (among others) the following	1576	Consider the L<Net::FCP> module. It features (among others) the following
716	API calls, which are to freenet what HTTP GET requests are to http:	1577	API calls, which are to freenet what HTTP GET requests are to http:
…		…
766	syswrite $txn->{fh}, $txn->{request}	1627	syswrite $txn->{fh}, $txn->{request}
767	or die "connection or write error";	1628	or die "connection or write error";
768	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1629	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
769		1630
770	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1631	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
771	result and signals any possible waiters that the request ahs finished:	1632	result and signals any possible waiters that the request has finished:
772		1633
773	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1634	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
774		1635
775	if (end-of-file or data complete) {	1636	if (end-of-file or data complete) {
776	$txn->{result} = $txn->{buf};	1637	$txn->{result} = $txn->{buf};
777	$txn->{finished}->broadcast;	1638	$txn->{finished}->send;
778	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1639	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
779	}	1640	}
780		1641
781	The C<result> method, finally, just waits for the finished signal (if the	1642	The C<result> method, finally, just waits for the finished signal (if the
782	request was already finished, it doesn't wait, of course, and returns the	1643	request was already finished, it doesn't wait, of course, and returns the
783	data:	1644	data:
784		1645
785	$txn->{finished}->wait;	1646	$txn->{finished}->recv;
786	return $txn->{result};	1647	return $txn->{result};
787		1648
788	The actual code goes further and collects all errors (C<die>s, exceptions)	1649	The actual code goes further and collects all errors (C<die>s, exceptions)
789	that occured during request processing. The C<result> method detects	1650	that occurred during request processing. The C<result> method detects
790	whether an exception as thrown (it is stored inside the $txn object)	1651	whether an exception as thrown (it is stored inside the $txn object)
791	and just throws the exception, which means connection errors and other	1652	and just throws the exception, which means connection errors and other
792	problems get reported tot he code that tries to use the result, not in a	1653	problems get reported tot he code that tries to use the result, not in a
793	random callback.	1654	random callback.
794		1655
…		…
825		1686
826	my $quit = AnyEvent->condvar;	1687	my $quit = AnyEvent->condvar;
827		1688
828	$fcp->txn_client_get ($url)->cb (sub {	1689	$fcp->txn_client_get ($url)->cb (sub {
829	...	1690	...
830	$quit->broadcast;	1691	$quit->send;
831	});	1692	});
832		1693
833	$quit->wait;	1694	$quit->recv;
		1695
		1696
		1697	=head1 BENCHMARKS
		1698
		1699	To give you an idea of the performance and overheads that AnyEvent adds
		1700	over the event loops themselves and to give you an impression of the speed
		1701	of various event loops I prepared some benchmarks.
		1702
		1703	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1704
		1705	Here is a benchmark of various supported event models used natively and
		1706	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1707	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1708	which it is), lets them fire exactly once and destroys them again.
		1709
		1710	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1711	distribution.
		1712
		1713	=head3 Explanation of the columns
		1714
		1715	I<watcher> is the number of event watchers created/destroyed. Since
		1716	different event models feature vastly different performances, each event
		1717	loop was given a number of watchers so that overall runtime is acceptable
		1718	and similar between tested event loop (and keep them from crashing): Glib
		1719	would probably take thousands of years if asked to process the same number
		1720	of watchers as EV in this benchmark.
		1721
		1722	I<bytes> is the number of bytes (as measured by the resident set size,
		1723	RSS) consumed by each watcher. This method of measuring captures both C
		1724	and Perl-based overheads.
		1725
		1726	I<create> is the time, in microseconds (millionths of seconds), that it
		1727	takes to create a single watcher. The callback is a closure shared between
		1728	all watchers, to avoid adding memory overhead. That means closure creation
		1729	and memory usage is not included in the figures.
		1730
		1731	I<invoke> is the time, in microseconds, used to invoke a simple
		1732	callback. The callback simply counts down a Perl variable and after it was
		1733	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1734	signal the end of this phase.
		1735
		1736	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1737	watcher.
		1738
		1739	=head3 Results
		1740
		1741	name watchers bytes create invoke destroy comment
		1742	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1743	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1744	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1745	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1746	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1747	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1748	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1749	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
		1750	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1751	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1752	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1753	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1754
		1755	=head3 Discussion
		1756
		1757	The benchmark does I<not> measure scalability of the event loop very
		1758	well. For example, a select-based event loop (such as the pure perl one)
		1759	can never compete with an event loop that uses epoll when the number of
		1760	file descriptors grows high. In this benchmark, all events become ready at
		1761	the same time, so select/poll-based implementations get an unnatural speed
		1762	boost.
		1763
		1764	Also, note that the number of watchers usually has a nonlinear effect on
		1765	overall speed, that is, creating twice as many watchers doesn't take twice
		1766	the time - usually it takes longer. This puts event loops tested with a
		1767	higher number of watchers at a disadvantage.
		1768
		1769	To put the range of results into perspective, consider that on the
		1770	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1771	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1772	cycles with POE.
		1773
		1774	C<EV> is the sole leader regarding speed and memory use, which are both
		1775	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1776	far less memory than any other event loop and is still faster than Event
		1777	natively.
		1778
		1779	The pure perl implementation is hit in a few sweet spots (both the
		1780	constant timeout and the use of a single fd hit optimisations in the perl
		1781	interpreter and the backend itself). Nevertheless this shows that it
		1782	adds very little overhead in itself. Like any select-based backend its
		1783	performance becomes really bad with lots of file descriptors (and few of
		1784	them active), of course, but this was not subject of this benchmark.
		1785
		1786	The C<Event> module has a relatively high setup and callback invocation
		1787	cost, but overall scores in on the third place.
		1788
		1789	C<IO::Async> performs admirably well, about on par with C<Event>, even
		1790	when using its pure perl backend.
		1791
		1792	C<Glib>'s memory usage is quite a bit higher, but it features a
		1793	faster callback invocation and overall ends up in the same class as
		1794	C<Event>. However, Glib scales extremely badly, doubling the number of
		1795	watchers increases the processing time by more than a factor of four,
		1796	making it completely unusable when using larger numbers of watchers
		1797	(note that only a single file descriptor was used in the benchmark, so
		1798	inefficiencies of C<poll> do not account for this).
		1799
		1800	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1801	more than 2000 watchers is a big setback, however, as correctness takes
		1802	precedence over speed. Nevertheless, its performance is surprising, as the
		1803	file descriptor is dup()ed for each watcher. This shows that the dup()
		1804	employed by some adaptors is not a big performance issue (it does incur a
		1805	hidden memory cost inside the kernel which is not reflected in the figures
		1806	above).
		1807
		1808	C<POE>, regardless of underlying event loop (whether using its pure perl
		1809	select-based backend or the Event module, the POE-EV backend couldn't
		1810	be tested because it wasn't working) shows abysmal performance and
		1811	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1812	as EV watchers, and 10 times as much memory as Event (the high memory
		1813	requirements are caused by requiring a session for each watcher). Watcher
		1814	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1815	implementation.
		1816
		1817	The design of the POE adaptor class in AnyEvent can not really account
		1818	for the performance issues, though, as session creation overhead is
		1819	small compared to execution of the state machine, which is coded pretty
		1820	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1821	using multiple sessions is not a good approach, especially regarding
		1822	memory usage, even the author of POE could not come up with a faster
		1823	design).
		1824
		1825	=head3 Summary
		1826
		1827	=over 4
		1828
		1829	=item * Using EV through AnyEvent is faster than any other event loop
		1830	(even when used without AnyEvent), but most event loops have acceptable
		1831	performance with or without AnyEvent.
		1832
		1833	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1834	the actual event loop, only with extremely fast event loops such as EV
		1835	adds AnyEvent significant overhead.
		1836
		1837	=item * You should avoid POE like the plague if you want performance or
		1838	reasonable memory usage.
		1839
		1840	=back
		1841
		1842	=head2 BENCHMARKING THE LARGE SERVER CASE
		1843
		1844	This benchmark actually benchmarks the event loop itself. It works by
		1845	creating a number of "servers": each server consists of a socket pair, a
		1846	timeout watcher that gets reset on activity (but never fires), and an I/O
		1847	watcher waiting for input on one side of the socket. Each time the socket
		1848	watcher reads a byte it will write that byte to a random other "server".
		1849
		1850	The effect is that there will be a lot of I/O watchers, only part of which
		1851	are active at any one point (so there is a constant number of active
		1852	fds for each loop iteration, but which fds these are is random). The
		1853	timeout is reset each time something is read because that reflects how
		1854	most timeouts work (and puts extra pressure on the event loops).
		1855
		1856	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1857	(1%) are active. This mirrors the activity of large servers with many
		1858	connections, most of which are idle at any one point in time.
		1859
		1860	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1861	distribution.
		1862
		1863	=head3 Explanation of the columns
		1864
		1865	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1866	each server has a read and write socket end).
		1867
		1868	I<create> is the time it takes to create a socket pair (which is
		1869	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1870
		1871	I<request>, the most important value, is the time it takes to handle a
		1872	single "request", that is, reading the token from the pipe and forwarding
		1873	it to another server. This includes deleting the old timeout and creating
		1874	a new one that moves the timeout into the future.
		1875
		1876	=head3 Results
		1877
		1878	name sockets create request
		1879	EV 20000 69.01 11.16
		1880	Perl 20000 73.32 35.87
		1881	IOAsync 20000 157.00 98.14 epoll
		1882	IOAsync 20000 159.31 616.06 poll
		1883	Event 20000 212.62 257.32
		1884	Glib 20000 651.16 1896.30
		1885	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1886
		1887	=head3 Discussion
		1888
		1889	This benchmark I<does> measure scalability and overall performance of the
		1890	particular event loop.
		1891
		1892	EV is again fastest. Since it is using epoll on my system, the setup time
		1893	is relatively high, though.
		1894
		1895	Perl surprisingly comes second. It is much faster than the C-based event
		1896	loops Event and Glib.
		1897
		1898	IO::Async performs very well when using its epoll backend, and still quite
		1899	good compared to Glib when using its pure perl backend.
		1900
		1901	Event suffers from high setup time as well (look at its code and you will
		1902	understand why). Callback invocation also has a high overhead compared to
		1903	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1904	uses select or poll in basically all documented configurations.
		1905
		1906	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1907	clearly fails to perform with many filehandles or in busy servers.
		1908
		1909	POE is still completely out of the picture, taking over 1000 times as long
		1910	as EV, and over 100 times as long as the Perl implementation, even though
		1911	it uses a C-based event loop in this case.
		1912
		1913	=head3 Summary
		1914
		1915	=over 4
		1916
		1917	=item * The pure perl implementation performs extremely well.
		1918
		1919	=item * Avoid Glib or POE in large projects where performance matters.
		1920
		1921	=back
		1922
		1923	=head2 BENCHMARKING SMALL SERVERS
		1924
		1925	While event loops should scale (and select-based ones do not...) even to
		1926	large servers, most programs we (or I :) actually write have only a few
		1927	I/O watchers.
		1928
		1929	In this benchmark, I use the same benchmark program as in the large server
		1930	case, but it uses only eight "servers", of which three are active at any
		1931	one time. This should reflect performance for a small server relatively
		1932	well.
		1933
		1934	The columns are identical to the previous table.
		1935
		1936	=head3 Results
		1937
		1938	name sockets create request
		1939	EV 16 20.00 6.54
		1940	Perl 16 25.75 12.62
		1941	Event 16 81.27 35.86
		1942	Glib 16 32.63 15.48
		1943	POE 16 261.87 276.28 uses POE::Loop::Event
		1944
		1945	=head3 Discussion
		1946
		1947	The benchmark tries to test the performance of a typical small
		1948	server. While knowing how various event loops perform is interesting, keep
		1949	in mind that their overhead in this case is usually not as important, due
		1950	to the small absolute number of watchers (that is, you need efficiency and
		1951	speed most when you have lots of watchers, not when you only have a few of
		1952	them).
		1953
		1954	EV is again fastest.
		1955
		1956	Perl again comes second. It is noticeably faster than the C-based event
		1957	loops Event and Glib, although the difference is too small to really
		1958	matter.
		1959
		1960	POE also performs much better in this case, but is is still far behind the
		1961	others.
		1962
		1963	=head3 Summary
		1964
		1965	=over 4
		1966
		1967	=item * C-based event loops perform very well with small number of
		1968	watchers, as the management overhead dominates.
		1969
		1970	=back
		1971
		1972	=head2 THE IO::Lambda BENCHMARK
		1973
		1974	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1975	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		1976	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		1977	shouldn't come as a surprise to anybody). As such, the benchmark is
		1978	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		1979	very optimal. But how would AnyEvent compare when used without the extra
		1980	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		1981
		1982	The benchmark itself creates an echo-server, and then, for 500 times,
		1983	connects to the echo server, sends a line, waits for the reply, and then
		1984	creates the next connection. This is a rather bad benchmark, as it doesn't
		1985	test the efficiency of the framework or much non-blocking I/O, but it is a
		1986	benchmark nevertheless.
		1987
		1988	name runtime
		1989	Lambda/select 0.330 sec
		1990	+ optimized 0.122 sec
		1991	Lambda/AnyEvent 0.327 sec
		1992	+ optimized 0.138 sec
		1993	Raw sockets/select 0.077 sec
		1994	POE/select, components 0.662 sec
		1995	POE/select, raw sockets 0.226 sec
		1996	POE/select, optimized 0.404 sec
		1997
		1998	AnyEvent/select/nb 0.085 sec
		1999	AnyEvent/EV/nb 0.068 sec
		2000	+state machine 0.134 sec
		2001
		2002	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2003	benchmarks actually make blocking connects and use 100% blocking I/O,
		2004	defeating the purpose of an event-based solution. All of the newly
		2005	written AnyEvent benchmarks use 100% non-blocking connects (using
		2006	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2007	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2008	generally require a lot more bookkeeping and event handling than blocking
		2009	connects (which involve a single syscall only).
		2010
		2011	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2012	offers similar expressive power as POE and IO::Lambda, using conventional
		2013	Perl syntax. This means that both the echo server and the client are 100%
		2014	non-blocking, further placing it at a disadvantage.
		2015
		2016	As you can see, the AnyEvent + EV combination even beats the
		2017	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2018	backend easily beats IO::Lambda and POE.
		2019
		2020	And even the 100% non-blocking version written using the high-level (and
		2021	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
		2022	large margin, even though it does all of DNS, tcp-connect and socket I/O
		2023	in a non-blocking way.
		2024
		2025	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2026	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2027	part of the IO::lambda distribution and were used without any changes.
		2028
		2029
		2030	=head1 SIGNALS
		2031
		2032	AnyEvent currently installs handlers for these signals:
		2033
		2034	=over 4
		2035
		2036	=item SIGCHLD
		2037
		2038	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2039	emulation for event loops that do not support them natively. Also, some
		2040	event loops install a similar handler.
		2041
		2042	If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent will
		2043	reset it to default, to avoid losing child exit statuses.
		2044
		2045	=item SIGPIPE
		2046
		2047	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2048	when AnyEvent gets loaded.
		2049
		2050	The rationale for this is that AnyEvent users usually do not really depend
		2051	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2052	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2053	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2054	some random socket.
		2055
		2056	The rationale for installing a no-op handler as opposed to ignoring it is
		2057	that this way, the handler will be restored to defaults on exec.
		2058
		2059	Feel free to install your own handler, or reset it to defaults.
		2060
		2061	=back
		2062
		2063	=cut
		2064
		2065	undef $SIG{CHLD}
		2066	if $SIG{CHLD} eq 'IGNORE';
		2067
		2068	$SIG{PIPE} = sub { }
		2069	unless defined $SIG{PIPE};
834		2070
835	=head1 FORK	2071	=head1 FORK
836		2072
837	Most event libraries are not fork-safe. The ones who are usually are	2073	Most event libraries are not fork-safe. The ones who are usually are
838	because they are so inefficient. Only L<EV> is fully fork-aware.	2074	because they rely on inefficient but fork-safe C<select> or C<poll>
		2075	calls. Only L<EV> is fully fork-aware.
839		2076
840	If you have to fork, you must either do so I<before> creating your first	2077	If you have to fork, you must either do so I<before> creating your first
841	watcher OR you must not use AnyEvent at all in the child.	2078	watcher OR you must not use AnyEvent at all in the child.
		2079
842		2080
843	=head1 SECURITY CONSIDERATIONS	2081	=head1 SECURITY CONSIDERATIONS
844		2082
845	AnyEvent can be forced to load any event model via	2083	AnyEvent can be forced to load any event model via
846	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to	2084	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
…		…
850	specified in the variable.	2088	specified in the variable.
851		2089
852	You can make AnyEvent completely ignore this variable by deleting it	2090	You can make AnyEvent completely ignore this variable by deleting it
853	before the first watcher gets created, e.g. with a C<BEGIN> block:	2091	before the first watcher gets created, e.g. with a C<BEGIN> block:
854		2092
855	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2093	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
856		2094
857	use AnyEvent;	2095	use AnyEvent;
		2096
		2097	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2098	be used to probe what backend is used and gain other information (which is
		2099	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2100	$ENV{PERL_ANYEVENT_STRICT}.
		2101
		2102	Note that AnyEvent will remove I<all> environment variables starting with
		2103	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2104	enabled.
		2105
		2106
		2107	=head1 BUGS
		2108
		2109	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2110	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2111	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2112	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2113	pronounced).
		2114
858		2115
859	=head1 SEE ALSO	2116	=head1 SEE ALSO
860		2117
861	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	2118	Utility functions: L<AnyEvent::Util>.
862	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
863	L<Event::Lib>.
864		2119
865	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	2120	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
866	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,	2121	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
867	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>.
868		2122
		2123	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		2124	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2125	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2126	L<AnyEvent::Impl::POE>.
		2127
		2128	Non-blocking file handles, sockets, TCP clients and
		2129	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		2130
		2131	Asynchronous DNS: L<AnyEvent::DNS>.
		2132
		2133	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		2134
869	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	2135	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		2136
870		2137
871	=head1 AUTHOR	2138	=head1 AUTHOR
872		2139
873	Marc Lehmann <schmorp@schmorp.de>	2140	Marc Lehmann <schmorp@schmorp.de>
874	http://home.schmorp.de/	2141	http://home.schmorp.de/
875		2142
876	=cut	2143	=cut
877		2144
878	1	2145	1
879		2146

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