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Revision 1.221 by root, Fri Jun 26 06:33:17 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - 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	#TODO#
72
73	Net::IRC3
74	AnyEvent::HTTPD
75	AnyEvent::DNS
76	IO::AnyEvent
77	Net::FPing
78	Net::XMPP2
79	Coro
80
81	AnyEvent::IRC
82	AnyEvent::HTTPD
83	AnyEvent::DNS
84	AnyEvent::Handle
85	AnyEvent::Socket
86	AnyEvent::FPing
87	AnyEvent::XMPP
88	AnyEvent::SNMP
89	Coro
90		100
91	=head1 DESCRIPTION	101	=head1 DESCRIPTION
92		102
93	L<AnyEvent> provides an identical interface to multiple event loops. This	103	L<AnyEvent> provides an identical interface to multiple event loops. This
94	allows module authors to utilise an event loop without forcing module	104	allows module authors to utilise an event loop without forcing module
…		…
98	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>
99	module.	109	module.
100		110
101	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
102	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
103	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,	113	following modules is already loaded: L<EV>,
104	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,	114	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
105	L<POE>. The first one found is used. If none are found, the module tries	115	L<POE>. The first one found is used. If none are found, the module tries
106	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl	116	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
107	adaptor should always succeed) in the order given. The first one that can	117	adaptor should always succeed) in the order given. The first one that can
108	be successfully loaded will be used. If, after this, still none could be	118	be successfully loaded will be used. If, after this, still none could be
…		…
122	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
123	use AnyEvent so their modules work together with others seamlessly...	133	use AnyEvent so their modules work together with others seamlessly...
124		134
125	The pure-perl implementation of AnyEvent is called	135	The pure-perl implementation of AnyEvent is called
126	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
127	explicitly.	137	explicitly and enjoy the high availability of that event loop :)
128		138
129	=head1 WATCHERS	139	=head1 WATCHERS
130		140
131	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
132	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
133	the callback to call, the filehandle to watch, etc.	143	the callback to call, the file handle to watch, etc.
134		144
135	These watchers are normal Perl objects with normal Perl lifetime. After	145	These watchers are normal Perl objects with normal Perl lifetime. After
136	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
137	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
138	is in control).	148	is in control).
139		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
140	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
141	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
142	to it).	158	to it).
143		159
144	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.
…		…
146	Many watchers either are used with "recursion" (repeating timers for	162	Many watchers either are used with "recursion" (repeating timers for
147	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.
148		164
149	An any way to achieve that is this pattern:	165	An any way to achieve that is this pattern:
150		166
151	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	167	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
152	# you can use $w here, for example to undef it	168	# you can use $w here, for example to undef it
153	undef $w;	169	undef $w;
154	});	170	});
155		171
156	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,
157	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
158	declared.	174	declared.
159		175
160	=head2 I/O WATCHERS	176	=head2 I/O WATCHERS
161		177
162	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
163	with the following mandatory key-value pairs as arguments:	179	with the following mandatory key-value pairs as arguments:
164		180
165	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch	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
166	for events. C<poll> must be a string that is either C<r> or C<w>,	188	C<poll> must be a string that is either C<r> or C<w>, which creates a
167	which creates a watcher waiting for "r"eadable or "w"ritable events,	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
168	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.
169	becomes ready.
170		192
171	Although the callback might get passed parameters, their value and	193	Although the callback might get passed parameters, their value and
172	presence is undefined and you cannot rely on them. Portable AnyEvent	194	presence is undefined and you cannot rely on them. Portable AnyEvent
173	callbacks cannot use arguments passed to I/O watcher callbacks.	195	callbacks cannot use arguments passed to I/O watcher callbacks.
174		196
…		…
178		200
179	Some event loops issue spurious readyness notifications, so you should	201	Some event loops issue spurious readyness notifications, so you should
180	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
181	handles.	203	handles.
182		204
183	Example:
184
185	# 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
186	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
187	chomp (my $input = <STDIN>);	209	chomp (my $input = <STDIN>);
188	warn "read: $input\n";	210	warn "read: $input\n";
189	undef $w;	211	undef $w;
190	});	212	});
…		…
200		222
201	Although the callback might get passed parameters, their value and	223	Although the callback might get passed parameters, their value and
202	presence is undefined and you cannot rely on them. Portable AnyEvent	224	presence is undefined and you cannot rely on them. Portable AnyEvent
203	callbacks cannot use arguments passed to time watcher callbacks.	225	callbacks cannot use arguments passed to time watcher callbacks.
204		226
205	The timer callback will be invoked at most once: if you want a repeating	227	The callback will normally be invoked once only. If you specify another
206	timer you have to create a new watcher (this is a limitation by both Tk	228	parameter, C<interval>, as a strictly positive number (> 0), then the
207	and Glib).	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.
208		232
209	Example:	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.
210		236
211	# fire an event after 7.7 seconds	237	Example: fire an event after 7.7 seconds.
		238
212	my $w = AnyEvent->timer (after => 7.7, cb => sub {	239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
213	warn "timeout\n";	240	warn "timeout\n";
214	});	241	});
215		242
216	# to cancel the timer:	243	# to cancel the timer:
217	undef $w;	244	undef $w;
218		245
219	Example 2:
220
221	# 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.
222	my $w;
223		247
224	my $cb = sub {
225	# cancel the old timer while creating a new one
226	$w = AnyEvent->timer (after => 1, cb => $cb);	248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		249	warn "timeout\n";
227	};	250	};
228
229	# start the "loop" by creating the first watcher
230	$w = AnyEvent->timer (after => 0.5, cb => $cb);
231		251
232	=head3 TIMING ISSUES	252	=head3 TIMING ISSUES
233		253
234	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
235	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
…		…
247	timers.	267	timers.
248		268
249	AnyEvent always prefers relative timers, if available, matching the	269	AnyEvent always prefers relative timers, if available, matching the
250	AnyEvent API.	270	AnyEvent API.
251		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
252	=head2 SIGNAL WATCHERS	350	=head2 SIGNAL WATCHERS
253		351
254	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
255	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
256	be invoked whenever a signal occurs.	354	callback to be invoked whenever a signal occurs.
257		355
258	Although the callback might get passed parameters, their value and	356	Although the callback might get passed parameters, their value and
259	presence is undefined and you cannot rely on them. Portable AnyEvent	357	presence is undefined and you cannot rely on them. Portable AnyEvent
260	callbacks cannot use arguments passed to signal watcher callbacks.	358	callbacks cannot use arguments passed to signal watcher callbacks.
261		359
262	Multiple signal occurances can be clumped together into one callback	360	Multiple signal occurrences can be clumped together into one callback
263	invocation, and callback invocation will be synchronous. synchronous means	361	invocation, and callback invocation will be synchronous. Synchronous means
264	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,
265	but it is guarenteed not to interrupt any other callbacks.	363	but it is guaranteed not to interrupt any other callbacks.
266		364
267	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
268	between multiple watchers.	366	between multiple watchers.
269		367
270	This watcher might use C<%SIG>, so programs overwriting those signals	368	This watcher might use C<%SIG>, so programs overwriting those signals
…		…
277	=head2 CHILD PROCESS WATCHERS	375	=head2 CHILD PROCESS WATCHERS
278		376
279	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.
280		378
281	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
282	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
283	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
284	signal handler for C<SIGCHLD>. The callback will be called with the pid	382	any trace events (stopped/continued).
285	and exit status (as returned by waitpid), so unlike other watcher types,	383
286	you I<can> rely on child watcher callback arguments.	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.
		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).
287		392
288	There is a slight catch to child watchers, however: you usually start them	393	There is a slight catch to child watchers, however: you usually start them
289	I<after> the child process was created, and this means the process could	394	I<after> the child process was created, and this means the process could
290	have exited already (and no SIGCHLD will be sent anymore).	395	have exited already (and no SIGCHLD will be sent anymore).
291		396
292	Not all event models handle this correctly (POE doesn't), but even for	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
293	event models that I<do> handle this correctly, they usually need to be	399	that I<do> handle this correctly, they usually need to be loaded before
294	loaded before the process exits (i.e. before you fork in the first place).	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.
295		403
296	This means you cannot create a child watcher as the very first thing in an	404	This means you cannot create a child watcher as the very first
297	AnyEvent program, you I<have> to create at least one watcher before you	405	thing in an AnyEvent program, you I<have> to create at least one
298	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).	406	watcher before you C<fork> the child (alternatively, you can call
		407	C<AnyEvent::detect>).
299		408
300	Example: fork a process and wait for it	409	Example: fork a process and wait for it
301		410
302	my $done = AnyEvent->condvar;	411	my $done = AnyEvent->condvar;
303		412
304	AnyEvent::detect; # force event module to be initialised
305
306	my $pid = fork or exit 5;	413	my $pid = fork or exit 5;
307		414
308	my $w = AnyEvent->child (	415	my $w = AnyEvent->child (
309	pid => $pid,	416	pid => $pid,
310	cb => sub {	417	cb => sub {
311	my ($pid, $status) = @_;	418	my ($pid, $status) = @_;
312	warn "pid $pid exited with status $status";	419	warn "pid $pid exited with status $status";
313	$done->broadcast;	420	$done->send;
314	},	421	},
315	);	422	);
316		423
317	# do something else, then wait for process exit	424	# do something else, then wait for process exit
318	$done->wait;	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	});
319		461
320	=head2 CONDITION VARIABLES	462	=head2 CONDITION VARIABLES
321		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
322	Condition variables can be created by calling the C<< AnyEvent->condvar >>	474	Condition variables can be created by calling the C<< AnyEvent->condvar
323	method without any arguments.	475	>> method, usually without arguments. The only argument pair allowed is
324		476
325	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
326	->broadcast >> method has been called.	478	becomes true, with the condition variable as the first argument (but not
		479	the results).
327		480
328	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,
329	example, if you write a module that does asynchronous http requests,	494	for example, if you write a module that does asynchronous http requests,
330	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
331	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.
332		498
333	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,
334	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
335	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
336	->broadcast >> the "quit" event.	502	button of your app, which would C<< ->send >> the "quit" event.
337		503
338	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
339	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
340	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
341	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,
342	as this asks for trouble.	508	as this asks for trouble.
343		509
344	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.
345		568
346	=over 4	569	=over 4
347		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
348	=item $cv->wait	602	=item $cv->end
349		603
350	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	604	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		605
		606	These two methods can be used to combine many transactions/events into
		607	one. For example, a function that pings many hosts in parallel might want
		608	to use a condition variable for the whole process.
		609
		610	Every call to C<< ->begin >> will increment a counter, and every call to
		611	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		612	>>, the (last) callback passed to C<begin> will be executed. That callback
		613	is I<supposed> to call C<< ->send >>, but that is not required. If no
		614	callback was set, C<send> will be called without any arguments.
		615
		616	Let's clarify this with the ping example:
		617
		618	my $cv = AnyEvent->condvar;
		619
		620	my %result;
		621	$cv->begin (sub { $cv->send (\%result) });
		622
		623	for my $host (@list_of_hosts) {
		624	$cv->begin;
		625	ping_host_then_call_callback $host, sub {
		626	$result{$host} = ...;
		627	$cv->end;
		628	};
		629	}
		630
		631	$cv->end;
		632
		633	This code fragment supposedly pings a number of hosts and calls
		634	C<send> after results for all then have have been gathered - in any
		635	order. To achieve this, the code issues a call to C<begin> when it starts
		636	each ping request and calls C<end> when it has received some result for
		637	it. Since C<begin> and C<end> only maintain a counter, the order in which
		638	results arrive is not relevant.
		639
		640	There is an additional bracketing call to C<begin> and C<end> outside the
		641	loop, which serves two important purposes: first, it sets the callback
		642	to be called once the counter reaches C<0>, and second, it ensures that
		643	C<send> is called even when C<no> hosts are being pinged (the loop
		644	doesn't execute once).
		645
		646	This is the general pattern when you "fan out" into multiple subrequests:
		647	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		648	is called at least once, and then, for each subrequest you start, call
		649	C<begin> and for each subrequest you finish, call C<end>.
		650
		651	=back
		652
		653	=head3 METHODS FOR CONSUMERS
		654
		655	These methods should only be used by the consuming side, i.e. the
		656	code awaits the condition.
		657
		658	=over 4
		659
		660	=item $cv->recv
		661
		662	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
351	called on c<$cv>, while servicing other watchers normally.	663	>> methods have been called on c<$cv>, while servicing other watchers
		664	normally.
352		665
353	You can only wait once on a condition - additional calls will return	666	You can only wait once on a condition - additional calls are valid but
354	immediately.	667	will return immediately.
		668
		669	If an error condition has been set by calling C<< ->croak >>, then this
		670	function will call C<croak>.
		671
		672	In list context, all parameters passed to C<send> will be returned,
		673	in scalar context only the first one will be returned.
355		674
356	Not all event models support a blocking wait - some die in that case	675	Not all event models support a blocking wait - some die in that case
357	(programs might want to do that to stay interactive), so I<if you are	676	(programs might want to do that to stay interactive), so I<if you are
358	using this from a module, never require a blocking wait>, but let the	677	using this from a module, never require a blocking wait>, but let the
359	caller decide whether the call will block or not (for example, by coupling	678	caller decide whether the call will block or not (for example, by coupling
360	condition variables with some kind of request results and supporting	679	condition variables with some kind of request results and supporting
361	callbacks so the caller knows that getting the result will not block,	680	callbacks so the caller knows that getting the result will not block,
362	while still suppporting blocking waits if the caller so desires).	681	while still supporting blocking waits if the caller so desires).
363		682
364	Another reason I<never> to C<< ->wait >> in a module is that you cannot	683	Another reason I<never> to C<< ->recv >> in a module is that you cannot
365	sensibly have two C<< ->wait >>'s in parallel, as that would require	684	sensibly have two C<< ->recv >>'s in parallel, as that would require
366	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	685	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
367	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	686	can supply.
368	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
369	from different coroutines, however).
370		687
371	=item $cv->broadcast	688	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		689	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		690	versions and also integrates coroutines into AnyEvent, making blocking
		691	C<< ->recv >> calls perfectly safe as long as they are done from another
		692	coroutine (one that doesn't run the event loop).
372		693
373	Flag the condition as ready - a running C<< ->wait >> and all further	694	You can ensure that C<< -recv >> never blocks by setting a callback and
374	calls to C<wait> will (eventually) return after this method has been	695	only calling C<< ->recv >> from within that callback (or at a later
375	called. If nobody is waiting the broadcast will be remembered..	696	time). This will work even when the event loop does not support blocking
		697	waits otherwise.
		698
		699	=item $bool = $cv->ready
		700
		701	Returns true when the condition is "true", i.e. whether C<send> or
		702	C<croak> have been called.
		703
		704	=item $cb = $cv->cb ($cb->($cv))
		705
		706	This is a mutator function that returns the callback set and optionally
		707	replaces it before doing so.
		708
		709	The callback will be called when the condition becomes "true", i.e. when
		710	C<send> or C<croak> are called, with the only argument being the condition
		711	variable itself. Calling C<recv> inside the callback or at any later time
		712	is guaranteed not to block.
376		713
377	=back	714	=back
378
379	Example:
380
381	# wait till the result is ready
382	my $result_ready = AnyEvent->condvar;
383
384	# do something such as adding a timer
385	# or socket watcher the calls $result_ready->broadcast
386	# when the "result" is ready.
387	# in this case, we simply use a timer:
388	my $w = AnyEvent->timer (
389	after => 1,
390	cb => sub { $result_ready->broadcast },
391	);
392
393	# this "blocks" (while handling events) till the watcher
394	# calls broadcast
395	$result_ready->wait;
396		715
397	=head1 GLOBAL VARIABLES AND FUNCTIONS	716	=head1 GLOBAL VARIABLES AND FUNCTIONS
398		717
399	=over 4	718	=over 4
400		719
…		…
406	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	725	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
407	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	726	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
408		727
409	The known classes so far are:	728	The known classes so far are:
410		729
411	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
412	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
413	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	730	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
414	AnyEvent::Impl::Event based on Event, second best choice.	731	AnyEvent::Impl::Event based on Event, second best choice.
		732	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
415	AnyEvent::Impl::Glib based on Glib, third-best choice.	733	AnyEvent::Impl::Glib based on Glib, third-best choice.
416	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
417	AnyEvent::Impl::Tk based on Tk, very bad choice.	734	AnyEvent::Impl::Tk based on Tk, very bad choice.
418	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	735	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
419	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	736	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
420	AnyEvent::Impl::POE based on POE, not generic enough for full support.	737	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		738
		739	# warning, support for IO::Async is only partial, as it is too broken
		740	# and limited toe ven support the AnyEvent API. See AnyEvent::Impl::Async.
		741	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed (see its docs).
421		742
422	There is no support for WxWidgets, as WxWidgets has no support for	743	There is no support for WxWidgets, as WxWidgets has no support for
423	watching file handles. However, you can use WxWidgets through the	744	watching file handles. However, you can use WxWidgets through the
424	POE Adaptor, as POE has a Wx backend that simply polls 20 times per	745	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
425	second, which was considered to be too horrible to even consider for	746	second, which was considered to be too horrible to even consider for
…		…
434	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	755	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
435	if necessary. You should only call this function right before you would	756	if necessary. You should only call this function right before you would
436	have created an AnyEvent watcher anyway, that is, as late as possible at	757	have created an AnyEvent watcher anyway, that is, as late as possible at
437	runtime.	758	runtime.
438		759
		760	=item $guard = AnyEvent::post_detect { BLOCK }
		761
		762	Arranges for the code block to be executed as soon as the event model is
		763	autodetected (or immediately if this has already happened).
		764
		765	If called in scalar or list context, then it creates and returns an object
		766	that automatically removes the callback again when it is destroyed. See
		767	L<Coro::BDB> for a case where this is useful.
		768
		769	=item @AnyEvent::post_detect
		770
		771	If there are any code references in this array (you can C<push> to it
		772	before or after loading AnyEvent), then they will called directly after
		773	the event loop has been chosen.
		774
		775	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		776	if it contains a true value then the event loop has already been detected,
		777	and the array will be ignored.
		778
		779	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		780
439	=back	781	=back
440		782
441	=head1 WHAT TO DO IN A MODULE	783	=head1 WHAT TO DO IN A MODULE
442		784
443	As a module author, you should C<use AnyEvent> and call AnyEvent methods	785	As a module author, you should C<use AnyEvent> and call AnyEvent methods
…		…
446	Be careful when you create watchers in the module body - AnyEvent will	788	Be careful when you create watchers in the module body - AnyEvent will
447	decide which event module to use as soon as the first method is called, so	789	decide which event module to use as soon as the first method is called, so
448	by calling AnyEvent in your module body you force the user of your module	790	by calling AnyEvent in your module body you force the user of your module
449	to load the event module first.	791	to load the event module first.
450		792
451	Never call C<< ->wait >> on a condition variable unless you I<know> that	793	Never call C<< ->recv >> on a condition variable unless you I<know> that
452	the C<< ->broadcast >> method has been called on it already. This is	794	the C<< ->send >> method has been called on it already. This is
453	because it will stall the whole program, and the whole point of using	795	because it will stall the whole program, and the whole point of using
454	events is to stay interactive.	796	events is to stay interactive.
455		797
456	It is fine, however, to call C<< ->wait >> when the user of your module	798	It is fine, however, to call C<< ->recv >> when the user of your module
457	requests it (i.e. if you create a http request object ad have a method	799	requests it (i.e. if you create a http request object ad have a method
458	called C<results> that returns the results, it should call C<< ->wait >>	800	called C<results> that returns the results, it should call C<< ->recv >>
459	freely, as the user of your module knows what she is doing. always).	801	freely, as the user of your module knows what she is doing. always).
460		802
461	=head1 WHAT TO DO IN THE MAIN PROGRAM	803	=head1 WHAT TO DO IN THE MAIN PROGRAM
462		804
463	There will always be a single main program - the only place that should	805	There will always be a single main program - the only place that should
…		…
465		807
466	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	808	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
467	do anything special (it does not need to be event-based) and let AnyEvent	809	do anything special (it does not need to be event-based) and let AnyEvent
468	decide which implementation to chose if some module relies on it.	810	decide which implementation to chose if some module relies on it.
469		811
470	If the main program relies on a specific event model. For example, in	812	If the main program relies on a specific event model - for example, in
471	Gtk2 programs you have to rely on the Glib module. You should load the	813	Gtk2 programs you have to rely on the Glib module - you should load the
472	event module before loading AnyEvent or any module that uses it: generally	814	event module before loading AnyEvent or any module that uses it: generally
473	speaking, you should load it as early as possible. The reason is that	815	speaking, you should load it as early as possible. The reason is that
474	modules might create watchers when they are loaded, and AnyEvent will	816	modules might create watchers when they are loaded, and AnyEvent will
475	decide on the event model to use as soon as it creates watchers, and it	817	decide on the event model to use as soon as it creates watchers, and it
476	might chose the wrong one unless you load the correct one yourself.	818	might chose the wrong one unless you load the correct one yourself.
477		819
478	You can chose to use a rather inefficient pure-perl implementation by	820	You can chose to use a pure-perl implementation by loading the
479	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	821	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
480	behaviour everywhere, but letting AnyEvent chose is generally better.	822	everywhere, but letting AnyEvent chose the model is generally better.
		823
		824	=head2 MAINLOOP EMULATION
		825
		826	Sometimes (often for short test scripts, or even standalone programs who
		827	only want to use AnyEvent), you do not want to run a specific event loop.
		828
		829	In that case, you can use a condition variable like this:
		830
		831	AnyEvent->condvar->recv;
		832
		833	This has the effect of entering the event loop and looping forever.
		834
		835	Note that usually your program has some exit condition, in which case
		836	it is better to use the "traditional" approach of storing a condition
		837	variable somewhere, waiting for it, and sending it when the program should
		838	exit cleanly.
		839
		840
		841	=head1 OTHER MODULES
		842
		843	The following is a non-exhaustive list of additional modules that use
		844	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		845	in the same program. Some of the modules come with AnyEvent, some are
		846	available via CPAN.
		847
		848	=over 4
		849
		850	=item L<AnyEvent::Util>
		851
		852	Contains various utility functions that replace often-used but blocking
		853	functions such as C<inet_aton> by event-/callback-based versions.
		854
		855	=item L<AnyEvent::Socket>
		856
		857	Provides various utility functions for (internet protocol) sockets,
		858	addresses and name resolution. Also functions to create non-blocking tcp
		859	connections or tcp servers, with IPv6 and SRV record support and more.
		860
		861	=item L<AnyEvent::Handle>
		862
		863	Provide read and write buffers, manages watchers for reads and writes,
		864	supports raw and formatted I/O, I/O queued and fully transparent and
		865	non-blocking SSL/TLS.
		866
		867	=item L<AnyEvent::DNS>
		868
		869	Provides rich asynchronous DNS resolver capabilities.
		870
		871	=item L<AnyEvent::HTTP>
		872
		873	A simple-to-use HTTP library that is capable of making a lot of concurrent
		874	HTTP requests.
		875
		876	=item L<AnyEvent::HTTPD>
		877
		878	Provides a simple web application server framework.
		879
		880	=item L<AnyEvent::FastPing>
		881
		882	The fastest ping in the west.
		883
		884	=item L<AnyEvent::DBI>
		885
		886	Executes L<DBI> requests asynchronously in a proxy process.
		887
		888	=item L<AnyEvent::AIO>
		889
		890	Truly asynchronous I/O, should be in the toolbox of every event
		891	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		892	together.
		893
		894	=item L<AnyEvent::BDB>
		895
		896	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		897	L<BDB> and AnyEvent together.
		898
		899	=item L<AnyEvent::GPSD>
		900
		901	A non-blocking interface to gpsd, a daemon delivering GPS information.
		902
		903	=item L<AnyEvent::IGS>
		904
		905	A non-blocking interface to the Internet Go Server protocol (used by
		906	L<App::IGS>).
		907
		908	=item L<AnyEvent::IRC>
		909
		910	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		911
		912	=item L<Net::XMPP2>
		913
		914	AnyEvent based XMPP (Jabber protocol) module family.
		915
		916	=item L<Net::FCP>
		917
		918	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		919	of AnyEvent.
		920
		921	=item L<Event::ExecFlow>
		922
		923	High level API for event-based execution flow control.
		924
		925	=item L<Coro>
		926
		927	Has special support for AnyEvent via L<Coro::AnyEvent>.
		928
		929	=item L<IO::Lambda>
		930
		931	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		932
		933	=back
481		934
482	=cut	935	=cut
483		936
484	package AnyEvent;	937	package AnyEvent;
485		938
486	no warnings;	939	no warnings;
487	use strict;	940	use strict qw(vars subs);
488		941
489	use Carp;	942	use Carp;
490		943
491	our $VERSION = '3.3';	944	our $VERSION = 4.42;
492	our $MODEL;	945	our $MODEL;
493		946
494	our $AUTOLOAD;	947	our $AUTOLOAD;
495	our @ISA;	948	our @ISA;
496		949
		950	our @REGISTRY;
		951
		952	our $WIN32;
		953
		954	BEGIN {
		955	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		956	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		957
		958	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		959	if ${^TAINT};
		960	}
		961
497	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	962	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
498		963
499	our @REGISTRY;	964	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		965
		966	{
		967	my $idx;
		968	$PROTOCOL{$_} = ++$idx
		969	for reverse split /\s*,\s*/,
		970	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		971	}
500		972
501	my @models = (	973	my @models = (
502	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
503	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
504	[EV:: => AnyEvent::Impl::EV::],	974	[EV:: => AnyEvent::Impl::EV::],
505	[Event:: => AnyEvent::Impl::Event::],	975	[Event:: => AnyEvent::Impl::Event::],
506	[Glib:: => AnyEvent::Impl::Glib::],
507	[Tk:: => AnyEvent::Impl::Tk::],
508	[Wx:: => AnyEvent::Impl::POE::],
509	[Prima:: => AnyEvent::Impl::POE::],
510	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	976	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
511	# everything below here will not be autoprobed as the pureperl backend should work everywhere	977	# everything below here will not be autoprobed
		978	# as the pureperl backend should work everywhere
		979	# and is usually faster
		980	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		981	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
512	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy	982	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
513	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program	983	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
514	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza	984	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		985	[Wx:: => AnyEvent::Impl::POE::],
		986	[Prima:: => AnyEvent::Impl::POE::],
		987	# IO::Async is just too broken - we would need workaorunds for its
		988	# byzantine signal and broken child handling, among others.
		989	# IO::Async is rather hard to detect, as it doesn't have any
		990	# obvious default class.
		991	# [IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		992	# [IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		993	# [IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
515	);	994	);
516		995
517	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);	996	our %method = map +($_ => 1),
		997	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
		998
		999	our @post_detect;
		1000
		1001	sub post_detect(&) {
		1002	my ($cb) = @_;
		1003
		1004	if ($MODEL) {
		1005	$cb->();
		1006
		1007	1
		1008	} else {
		1009	push @post_detect, $cb;
		1010
		1011	defined wantarray
		1012	? bless \$cb, "AnyEvent::Util::postdetect"
		1013	: ()
		1014	}
		1015	}
		1016
		1017	sub AnyEvent::Util::postdetect::DESTROY {
		1018	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1019	}
518		1020
519	sub detect() {	1021	sub detect() {
520	unless ($MODEL) {	1022	unless ($MODEL) {
521	no strict 'refs';	1023	no strict 'refs';
		1024	local $SIG{__DIE__};
522		1025
523	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {	1026	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
524	my $model = "AnyEvent::Impl::$1";	1027	my $model = "AnyEvent::Impl::$1";
525	if (eval "require $model") {	1028	if (eval "require $model") {
526	$MODEL = $model;	1029	$MODEL = $model;
…		…
556	last;	1059	last;
557	}	1060	}
558	}	1061	}
559		1062
560	$MODEL	1063	$MODEL
561	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";	1064	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
562	}	1065	}
563	}	1066	}
564		1067
		1068	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1069
565	unshift @ISA, $MODEL;	1070	unshift @ISA, $MODEL;
566	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	1071
		1072	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1073
		1074	(shift @post_detect)->() while @post_detect;
567	}	1075	}
568		1076
569	$MODEL	1077	$MODEL
570	}	1078	}
571		1079
…		…
579		1087
580	my $class = shift;	1088	my $class = shift;
581	$class->$func (@_);	1089	$class->$func (@_);
582	}	1090	}
583		1091
		1092	# utility function to dup a filehandle. this is used by many backends
		1093	# to support binding more than one watcher per filehandle (they usually
		1094	# allow only one watcher per fd, so we dup it to get a different one).
		1095	sub _dupfh($$;$$) {
		1096	my ($poll, $fh, $r, $w) = @_;
		1097
		1098	# cygwin requires the fh mode to be matching, unix doesn't
		1099	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1100	: $poll eq "w" ? ($w, ">")
		1101	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1102
		1103	open my $fh2, "$mode&" . fileno $fh
		1104	or die "cannot dup() filehandle: $!,";
		1105
		1106	# we assume CLOEXEC is already set by perl in all important cases
		1107
		1108	($fh2, $rw)
		1109	}
		1110
584	package AnyEvent::Base;	1111	package AnyEvent::Base;
585		1112
		1113	# default implementations for many methods
		1114
		1115	BEGIN {
		1116	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1117	*_time = \&Time::HiRes::time;
		1118	# if (eval "use POSIX (); (POSIX::times())...
		1119	} else {
		1120	*_time = sub { time }; # epic fail
		1121	}
		1122	}
		1123
		1124	sub time { _time }
		1125	sub now { _time }
		1126	sub now_update { }
		1127
586	# default implementation for ->condvar, ->wait, ->broadcast	1128	# default implementation for ->condvar
587		1129
588	sub condvar {	1130	sub condvar {
589	bless \my $flag, "AnyEvent::Base::CondVar"	1131	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
590	}
591
592	sub AnyEvent::Base::CondVar::broadcast {
593	${$_[0]}++;
594	}
595
596	sub AnyEvent::Base::CondVar::wait {
597	AnyEvent->one_event while !${$_[0]};
598	}	1132	}
599		1133
600	# default implementation for ->signal	1134	# default implementation for ->signal
601		1135
602	our %SIG_CB;	1136	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1137
		1138	sub _signal_exec {
		1139	sysread $SIGPIPE_R, my $dummy, 4;
		1140
		1141	while (%SIG_EV) {
		1142	for (keys %SIG_EV) {
		1143	delete $SIG_EV{$_};
		1144	$_->() for values %{ $SIG_CB{$_} || {} };
		1145	}
		1146	}
		1147	}
603		1148
604	sub signal {	1149	sub signal {
605	my (undef, %arg) = @_;	1150	my (undef, %arg) = @_;
606		1151
		1152	unless ($SIGPIPE_R) {
		1153	require Fcntl;
		1154
		1155	if (AnyEvent::WIN32) {
		1156	require AnyEvent::Util;
		1157
		1158	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1159	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1160	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1161	} else {
		1162	pipe $SIGPIPE_R, $SIGPIPE_W;
		1163	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1164	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1165
		1166	# not strictly required, as $^F is normally 2, but let's make sure...
		1167	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1168	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1169	}
		1170
		1171	$SIGPIPE_R
		1172	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1173
		1174	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1175	}
		1176
607	my $signal = uc $arg{signal}	1177	my $signal = uc $arg{signal}
608	or Carp::croak "required option 'signal' is missing";	1178	or Carp::croak "required option 'signal' is missing";
609		1179
610	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1180	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
611	$SIG{$signal} ||= sub {	1181	$SIG{$signal} ||= sub {
612	$_->() for values %{ $SIG_CB{$signal} || {} };	1182	local $!;
		1183	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1184	undef $SIG_EV{$signal};
613	};	1185	};
614		1186
615	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1187	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
616	}	1188	}
617		1189
618	sub AnyEvent::Base::Signal::DESTROY {	1190	sub AnyEvent::Base::signal::DESTROY {
619	my ($signal, $cb) = @{$_[0]};	1191	my ($signal, $cb) = @{$_[0]};
620		1192
621	delete $SIG_CB{$signal}{$cb};	1193	delete $SIG_CB{$signal}{$cb};
622		1194
		1195	# delete doesn't work with older perls - they then
		1196	# print weird messages, or just unconditionally exit
		1197	# instead of getting the default action.
623	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1198	undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
624	}	1199	}
625		1200
626	# default implementation for ->child	1201	# default implementation for ->child
627		1202
628	our %PID_CB;	1203	our %PID_CB;
629	our $CHLD_W;	1204	our $CHLD_W;
630	our $CHLD_DELAY_W;	1205	our $CHLD_DELAY_W;
631	our $PID_IDLE;
632	our $WNOHANG;	1206	our $WNOHANG;
633		1207
634	sub _child_wait {	1208	sub _sigchld {
635	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	1209	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
636	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1210	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
637	(values %{ $PID_CB{0} || {} });	1211	(values %{ $PID_CB{0} || {} });
638	}	1212	}
639
640	undef $PID_IDLE;
641	}
642
643	sub _sigchld {
644	# make sure we deliver these changes "synchronous" with the event loop.
645	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
646	undef $CHLD_DELAY_W;
647	&_child_wait;
648	});
649	}	1213	}
650		1214
651	sub child {	1215	sub child {
652	my (undef, %arg) = @_;	1216	my (undef, %arg) = @_;
653		1217
654	defined (my $pid = $arg{pid} + 0)	1218	defined (my $pid = $arg{pid} + 0)
655	or Carp::croak "required option 'pid' is missing";	1219	or Carp::croak "required option 'pid' is missing";
656		1220
657	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1221	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
658		1222
659	unless ($WNOHANG) {
660	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1223	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
661	}
662		1224
663	unless ($CHLD_W) {	1225	unless ($CHLD_W) {
664	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1226	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
665	# child could be a zombie already, so make at least one round	1227	# child could be a zombie already, so make at least one round
666	&_sigchld;	1228	&_sigchld;
667	}	1229	}
668		1230
669	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1231	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
670	}	1232	}
671		1233
672	sub AnyEvent::Base::Child::DESTROY {	1234	sub AnyEvent::Base::child::DESTROY {
673	my ($pid, $cb) = @{$_[0]};	1235	my ($pid, $cb) = @{$_[0]};
674		1236
675	delete $PID_CB{$pid}{$cb};	1237	delete $PID_CB{$pid}{$cb};
676	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1238	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
677		1239
678	undef $CHLD_W unless keys %PID_CB;	1240	undef $CHLD_W unless keys %PID_CB;
679	}	1241	}
		1242
		1243	# idle emulation is done by simply using a timer, regardless
		1244	# of whether the process is idle or not, and not letting
		1245	# the callback use more than 50% of the time.
		1246	sub idle {
		1247	my (undef, %arg) = @_;
		1248
		1249	my ($cb, $w, $rcb) = $arg{cb};
		1250
		1251	$rcb = sub {
		1252	if ($cb) {
		1253	$w = _time;
		1254	&$cb;
		1255	$w = _time - $w;
		1256
		1257	# never use more then 50% of the time for the idle watcher,
		1258	# within some limits
		1259	$w = 0.0001 if $w < 0.0001;
		1260	$w = 5 if $w > 5;
		1261
		1262	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1263	} else {
		1264	# clean up...
		1265	undef $w;
		1266	undef $rcb;
		1267	}
		1268	};
		1269
		1270	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1271
		1272	bless \\$cb, "AnyEvent::Base::idle"
		1273	}
		1274
		1275	sub AnyEvent::Base::idle::DESTROY {
		1276	undef $${$_[0]};
		1277	}
		1278
		1279	package AnyEvent::CondVar;
		1280
		1281	our @ISA = AnyEvent::CondVar::Base::;
		1282
		1283	package AnyEvent::CondVar::Base;
		1284
		1285	use overload
		1286	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1287	fallback => 1;
		1288
		1289	sub _send {
		1290	# nop
		1291	}
		1292
		1293	sub send {
		1294	my $cv = shift;
		1295	$cv->{_ae_sent} = [@_];
		1296	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1297	$cv->_send;
		1298	}
		1299
		1300	sub croak {
		1301	$_[0]{_ae_croak} = $_[1];
		1302	$_[0]->send;
		1303	}
		1304
		1305	sub ready {
		1306	$_[0]{_ae_sent}
		1307	}
		1308
		1309	sub _wait {
		1310	AnyEvent->one_event while !$_[0]{_ae_sent};
		1311	}
		1312
		1313	sub recv {
		1314	$_[0]->_wait;
		1315
		1316	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1317	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1318	}
		1319
		1320	sub cb {
		1321	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1322	$_[0]{_ae_cb}
		1323	}
		1324
		1325	sub begin {
		1326	++$_[0]{_ae_counter};
		1327	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1328	}
		1329
		1330	sub end {
		1331	return if --$_[0]{_ae_counter};
		1332	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1333	}
		1334
		1335	# undocumented/compatibility with pre-3.4
		1336	*broadcast = \&send;
		1337	*wait = \&_wait;
		1338
		1339	=head1 ERROR AND EXCEPTION HANDLING
		1340
		1341	In general, AnyEvent does not do any error handling - it relies on the
		1342	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1343	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1344	checking of all AnyEvent methods, however, which is highly useful during
		1345	development.
		1346
		1347	As for exception handling (i.e. runtime errors and exceptions thrown while
		1348	executing a callback), this is not only highly event-loop specific, but
		1349	also not in any way wrapped by this module, as this is the job of the main
		1350	program.
		1351
		1352	The pure perl event loop simply re-throws the exception (usually
		1353	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1354	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1355	so on.
		1356
		1357	=head1 ENVIRONMENT VARIABLES
		1358
		1359	The following environment variables are used by this module or its
		1360	submodules.
		1361
		1362	Note that AnyEvent will remove I<all> environment variables starting with
		1363	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1364	enabled.
		1365
		1366	=over 4
		1367
		1368	=item C<PERL_ANYEVENT_VERBOSE>
		1369
		1370	By default, AnyEvent will be completely silent except in fatal
		1371	conditions. You can set this environment variable to make AnyEvent more
		1372	talkative.
		1373
		1374	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1375	conditions, such as not being able to load the event model specified by
		1376	C<PERL_ANYEVENT_MODEL>.
		1377
		1378	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1379	model it chooses.
		1380
		1381	=item C<PERL_ANYEVENT_STRICT>
		1382
		1383	AnyEvent does not do much argument checking by default, as thorough
		1384	argument checking is very costly. Setting this variable to a true value
		1385	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1386	check the arguments passed to most method calls. If it finds any problems,
		1387	it will croak.
		1388
		1389	In other words, enables "strict" mode.
		1390
		1391	Unlike C<use strict>, it is definitely recommended to keep it off in
		1392	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1393	developing programs can be very useful, however.
		1394
		1395	=item C<PERL_ANYEVENT_MODEL>
		1396
		1397	This can be used to specify the event model to be used by AnyEvent, before
		1398	auto detection and -probing kicks in. It must be a string consisting
		1399	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1400	and the resulting module name is loaded and if the load was successful,
		1401	used as event model. If it fails to load AnyEvent will proceed with
		1402	auto detection and -probing.
		1403
		1404	This functionality might change in future versions.
		1405
		1406	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1407	could start your program like this:
		1408
		1409	PERL_ANYEVENT_MODEL=Perl perl ...
		1410
		1411	=item C<PERL_ANYEVENT_PROTOCOLS>
		1412
		1413	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1414	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1415	of auto probing).
		1416
		1417	Must be set to a comma-separated list of protocols or address families,
		1418	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1419	used, and preference will be given to protocols mentioned earlier in the
		1420	list.
		1421
		1422	This variable can effectively be used for denial-of-service attacks
		1423	against local programs (e.g. when setuid), although the impact is likely
		1424	small, as the program has to handle conenction and other failures anyways.
		1425
		1426	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1427	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1428	- only support IPv4, never try to resolve or contact IPv6
		1429	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1430	IPv6, but prefer IPv6 over IPv4.
		1431
		1432	=item C<PERL_ANYEVENT_EDNS0>
		1433
		1434	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1435	for DNS. This extension is generally useful to reduce DNS traffic, but
		1436	some (broken) firewalls drop such DNS packets, which is why it is off by
		1437	default.
		1438
		1439	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1440	EDNS0 in its DNS requests.
		1441
		1442	=item C<PERL_ANYEVENT_MAX_FORKS>
		1443
		1444	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1445	will create in parallel.
		1446
		1447	=back
680		1448
681	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1449	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
682		1450
683	This is an advanced topic that you do not normally need to use AnyEvent in	1451	This is an advanced topic that you do not normally need to use AnyEvent in
684	a module. This section is only of use to event loop authors who want to	1452	a module. This section is only of use to event loop authors who want to
…		…
718		1486
719	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1487	I<rxvt-unicode> also cheats a bit by not providing blocking access to
720	condition variables: code blocking while waiting for a condition will	1488	condition variables: code blocking while waiting for a condition will
721	C<die>. This still works with most modules/usages, and blocking calls must	1489	C<die>. This still works with most modules/usages, and blocking calls must
722	not be done in an interactive application, so it makes sense.	1490	not be done in an interactive application, so it makes sense.
723
724	=head1 ENVIRONMENT VARIABLES
725
726	The following environment variables are used by this module:
727
728	=over 4
729
730	=item C<PERL_ANYEVENT_VERBOSE>
731
732	By default, AnyEvent will be completely silent except in fatal
733	conditions. You can set this environment variable to make AnyEvent more
734	talkative.
735
736	When set to C<1> or higher, causes AnyEvent to warn about unexpected
737	conditions, such as not being able to load the event model specified by
738	C<PERL_ANYEVENT_MODEL>.
739
740	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
741	model it chooses.
742
743	=item C<PERL_ANYEVENT_MODEL>
744
745	This can be used to specify the event model to be used by AnyEvent, before
746	autodetection and -probing kicks in. It must be a string consisting
747	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
748	and the resulting module name is loaded and if the load was successful,
749	used as event model. If it fails to load AnyEvent will proceed with
750	autodetection and -probing.
751
752	This functionality might change in future versions.
753
754	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
755	could start your program like this:
756
757	PERL_ANYEVENT_MODEL=Perl perl ...
758
759	=back
760		1491
761	=head1 EXAMPLE PROGRAM	1492	=head1 EXAMPLE PROGRAM
762		1493
763	The following program uses an I/O watcher to read data from STDIN, a timer	1494	The following program uses an I/O watcher to read data from STDIN, a timer
764	to display a message once per second, and a condition variable to quit the	1495	to display a message once per second, and a condition variable to quit the
…		…
773	poll => 'r',	1504	poll => 'r',
774	cb => sub {	1505	cb => sub {
775	warn "io event <$_[0]>\n"; # will always output <r>	1506	warn "io event <$_[0]>\n"; # will always output <r>
776	chomp (my $input = <STDIN>); # read a line	1507	chomp (my $input = <STDIN>); # read a line
777	warn "read: $input\n"; # output what has been read	1508	warn "read: $input\n"; # output what has been read
778	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1509	$cv->send if $input =~ /^q/i; # quit program if /^q/i
779	},	1510	},
780	);	1511	);
781		1512
782	my $time_watcher; # can only be used once	1513	my $time_watcher; # can only be used once
783		1514
…		…
788	});	1519	});
789	}	1520	}
790		1521
791	new_timer; # create first timer	1522	new_timer; # create first timer
792		1523
793	$cv->wait; # wait until user enters /^q/i	1524	$cv->recv; # wait until user enters /^q/i
794		1525
795	=head1 REAL-WORLD EXAMPLE	1526	=head1 REAL-WORLD EXAMPLE
796		1527
797	Consider the L<Net::FCP> module. It features (among others) the following	1528	Consider the L<Net::FCP> module. It features (among others) the following
798	API calls, which are to freenet what HTTP GET requests are to http:	1529	API calls, which are to freenet what HTTP GET requests are to http:
…		…
848	syswrite $txn->{fh}, $txn->{request}	1579	syswrite $txn->{fh}, $txn->{request}
849	or die "connection or write error";	1580	or die "connection or write error";
850	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1581	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
851		1582
852	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1583	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
853	result and signals any possible waiters that the request ahs finished:	1584	result and signals any possible waiters that the request has finished:
854		1585
855	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1586	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
856		1587
857	if (end-of-file or data complete) {	1588	if (end-of-file or data complete) {
858	$txn->{result} = $txn->{buf};	1589	$txn->{result} = $txn->{buf};
859	$txn->{finished}->broadcast;	1590	$txn->{finished}->send;
860	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1591	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
861	}	1592	}
862		1593
863	The C<result> method, finally, just waits for the finished signal (if the	1594	The C<result> method, finally, just waits for the finished signal (if the
864	request was already finished, it doesn't wait, of course, and returns the	1595	request was already finished, it doesn't wait, of course, and returns the
865	data:	1596	data:
866		1597
867	$txn->{finished}->wait;	1598	$txn->{finished}->recv;
868	return $txn->{result};	1599	return $txn->{result};
869		1600
870	The actual code goes further and collects all errors (C<die>s, exceptions)	1601	The actual code goes further and collects all errors (C<die>s, exceptions)
871	that occured during request processing. The C<result> method detects	1602	that occurred during request processing. The C<result> method detects
872	whether an exception as thrown (it is stored inside the $txn object)	1603	whether an exception as thrown (it is stored inside the $txn object)
873	and just throws the exception, which means connection errors and other	1604	and just throws the exception, which means connection errors and other
874	problems get reported tot he code that tries to use the result, not in a	1605	problems get reported tot he code that tries to use the result, not in a
875	random callback.	1606	random callback.
876		1607
…		…
907		1638
908	my $quit = AnyEvent->condvar;	1639	my $quit = AnyEvent->condvar;
909		1640
910	$fcp->txn_client_get ($url)->cb (sub {	1641	$fcp->txn_client_get ($url)->cb (sub {
911	...	1642	...
912	$quit->broadcast;	1643	$quit->send;
913	});	1644	});
914		1645
915	$quit->wait;	1646	$quit->recv;
916		1647
917		1648
918	=head1 BENCHMARKS	1649	=head1 BENCHMARKS
919		1650
920	To give you an idea of the performance and overheads that AnyEvent adds	1651	To give you an idea of the performance and overheads that AnyEvent adds
…		…
922	of various event loops I prepared some benchmarks.	1653	of various event loops I prepared some benchmarks.
923		1654
924	=head2 BENCHMARKING ANYEVENT OVERHEAD	1655	=head2 BENCHMARKING ANYEVENT OVERHEAD
925		1656
926	Here is a benchmark of various supported event models used natively and	1657	Here is a benchmark of various supported event models used natively and
927	through anyevent. The benchmark creates a lot of timers (with a zero	1658	through AnyEvent. The benchmark creates a lot of timers (with a zero
928	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1659	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
929	which it is), lets them fire exactly once and destroys them again.	1660	which it is), lets them fire exactly once and destroys them again.
930		1661
931	Source code for this benchmark is found as F<eg/bench> in the AnyEvent	1662	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
932	distribution.	1663	distribution.
…		…
949	all watchers, to avoid adding memory overhead. That means closure creation	1680	all watchers, to avoid adding memory overhead. That means closure creation
950	and memory usage is not included in the figures.	1681	and memory usage is not included in the figures.
951		1682
952	I<invoke> is the time, in microseconds, used to invoke a simple	1683	I<invoke> is the time, in microseconds, used to invoke a simple
953	callback. The callback simply counts down a Perl variable and after it was	1684	callback. The callback simply counts down a Perl variable and after it was
954	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to	1685	invoked "watcher" times, it would C<< ->send >> a condvar once to
955	signal the end of this phase.	1686	signal the end of this phase.
956		1687
957	I<destroy> is the time, in microseconds, that it takes to destroy a single	1688	I<destroy> is the time, in microseconds, that it takes to destroy a single
958	watcher.	1689	watcher.
959		1690
960	=head3 Results	1691	=head3 Results
961		1692
962	name watchers bytes create invoke destroy comment	1693	name watchers bytes create invoke destroy comment
963	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1694	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
964	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1695	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
965	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1696	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
966	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1697	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
967	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1698	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
968	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1699	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1700	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1701	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
969	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1702	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
970	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1703	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
971	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1704	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
972	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1705	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
973		1706
974	=head3 Discussion	1707	=head3 Discussion
975		1708
976	The benchmark does I<not> measure scalability of the event loop very	1709	The benchmark does I<not> measure scalability of the event loop very
977	well. For example, a select-based event loop (such as the pure perl one)	1710	well. For example, a select-based event loop (such as the pure perl one)
…		…
1002	performance becomes really bad with lots of file descriptors (and few of	1735	performance becomes really bad with lots of file descriptors (and few of
1003	them active), of course, but this was not subject of this benchmark.	1736	them active), of course, but this was not subject of this benchmark.
1004		1737
1005	The C<Event> module has a relatively high setup and callback invocation	1738	The C<Event> module has a relatively high setup and callback invocation
1006	cost, but overall scores in on the third place.	1739	cost, but overall scores in on the third place.
		1740
		1741	C<IO::Async> performs admirably well, about on par with C<Event>, even
		1742	when using its pure perl backend.
1007		1743
1008	C<Glib>'s memory usage is quite a bit higher, but it features a	1744	C<Glib>'s memory usage is quite a bit higher, but it features a
1009	faster callback invocation and overall ends up in the same class as	1745	faster callback invocation and overall ends up in the same class as
1010	C<Event>. However, Glib scales extremely badly, doubling the number of	1746	C<Event>. However, Glib scales extremely badly, doubling the number of
1011	watchers increases the processing time by more than a factor of four,	1747	watchers increases the processing time by more than a factor of four,
…		…
1019	file descriptor is dup()ed for each watcher. This shows that the dup()	1755	file descriptor is dup()ed for each watcher. This shows that the dup()
1020	employed by some adaptors is not a big performance issue (it does incur a	1756	employed by some adaptors is not a big performance issue (it does incur a
1021	hidden memory cost inside the kernel which is not reflected in the figures	1757	hidden memory cost inside the kernel which is not reflected in the figures
1022	above).	1758	above).
1023		1759
1024	C<POE>, regardless of underlying event loop (whether using its pure	1760	C<POE>, regardless of underlying event loop (whether using its pure perl
1025	perl select-based backend or the Event module, the POE-EV backend	1761	select-based backend or the Event module, the POE-EV backend couldn't
1026	couldn't be tested because it wasn't working) shows abysmal performance	1762	be tested because it wasn't working) shows abysmal performance and
1027	and memory usage: Watchers use almost 30 times as much memory as	1763	memory usage with AnyEvent: Watchers use almost 30 times as much memory
1028	EV watchers, and 10 times as much memory as Event (the high memory	1764	as EV watchers, and 10 times as much memory as Event (the high memory
1029	requirements are caused by requiring a session for each watcher). Watcher	1765	requirements are caused by requiring a session for each watcher). Watcher
1030	invocation speed is almost 900 times slower than with AnyEvent's pure perl	1766	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1767	implementation.
		1768
1031	implementation. The design of the POE adaptor class in AnyEvent can not	1769	The design of the POE adaptor class in AnyEvent can not really account
1032	really account for this, as session creation overhead is small compared	1770	for the performance issues, though, as session creation overhead is
1033	to execution of the state machine, which is coded pretty optimally within	1771	small compared to execution of the state machine, which is coded pretty
1034	L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.	1772	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1773	using multiple sessions is not a good approach, especially regarding
		1774	memory usage, even the author of POE could not come up with a faster
		1775	design).
1035		1776
1036	=head3 Summary	1777	=head3 Summary
1037		1778
1038	=over 4	1779	=over 4
1039		1780
…		…
1050		1791
1051	=back	1792	=back
1052		1793
1053	=head2 BENCHMARKING THE LARGE SERVER CASE	1794	=head2 BENCHMARKING THE LARGE SERVER CASE
1054		1795
1055	This benchmark atcually benchmarks the event loop itself. It works by	1796	This benchmark actually benchmarks the event loop itself. It works by
1056	creating a number of "servers": each server consists of a socketpair, a	1797	creating a number of "servers": each server consists of a socket pair, a
1057	timeout watcher that gets reset on activity (but never fires), and an I/O	1798	timeout watcher that gets reset on activity (but never fires), and an I/O
1058	watcher waiting for input on one side of the socket. Each time the socket	1799	watcher waiting for input on one side of the socket. Each time the socket
1059	watcher reads a byte it will write that byte to a random other "server".	1800	watcher reads a byte it will write that byte to a random other "server".
1060		1801
1061	The effect is that there will be a lot of I/O watchers, only part of which	1802	The effect is that there will be a lot of I/O watchers, only part of which
1062	are active at any one point (so there is a constant number of active	1803	are active at any one point (so there is a constant number of active
1063	fds for each loop iterstaion, but which fds these are is random). The	1804	fds for each loop iteration, but which fds these are is random). The
1064	timeout is reset each time something is read because that reflects how	1805	timeout is reset each time something is read because that reflects how
1065	most timeouts work (and puts extra pressure on the event loops).	1806	most timeouts work (and puts extra pressure on the event loops).
1066		1807
1067	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100	1808	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
1068	(1%) are active. This mirrors the activity of large servers with many	1809	(1%) are active. This mirrors the activity of large servers with many
1069	connections, most of which are idle at any one point in time.	1810	connections, most of which are idle at any one point in time.
1070		1811
1071	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent	1812	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
1072	distribution.	1813	distribution.
…		…
1074	=head3 Explanation of the columns	1815	=head3 Explanation of the columns
1075		1816
1076	I<sockets> is the number of sockets, and twice the number of "servers" (as	1817	I<sockets> is the number of sockets, and twice the number of "servers" (as
1077	each server has a read and write socket end).	1818	each server has a read and write socket end).
1078		1819
1079	I<create> is the time it takes to create a socketpair (which is	1820	I<create> is the time it takes to create a socket pair (which is
1080	nontrivial) and two watchers: an I/O watcher and a timeout watcher.	1821	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1081		1822
1082	I<request>, the most important value, is the time it takes to handle a	1823	I<request>, the most important value, is the time it takes to handle a
1083	single "request", that is, reading the token from the pipe and forwarding	1824	single "request", that is, reading the token from the pipe and forwarding
1084	it to another server. This includes deleting the old timeout and creating	1825	it to another server. This includes deleting the old timeout and creating
1085	a new one that moves the timeout into the future.	1826	a new one that moves the timeout into the future.
1086		1827
1087	=head3 Results	1828	=head3 Results
1088		1829
1089	name sockets create request	1830	name sockets create request
1090	EV 20000 69.01 11.16	1831	EV 20000 69.01 11.16
1091	Perl 20000 75.28 112.76	1832	Perl 20000 73.32 35.87
		1833	IOAsync 20000 157.00 98.14 epoll
		1834	IOAsync 20000 159.31 616.06 poll
1092	Event 20000 212.62 257.32	1835	Event 20000 212.62 257.32
1093	Glib 20000 651.16 1896.30	1836	Glib 20000 651.16 1896.30
1094	POE 20000 349.67 12317.24 uses POE::Loop::Event	1837	POE 20000 349.67 12317.24 uses POE::Loop::Event
1095		1838
1096	=head3 Discussion	1839	=head3 Discussion
1097		1840
1098	This benchmark I<does> measure scalability and overall performance of the	1841	This benchmark I<does> measure scalability and overall performance of the
1099	particular event loop.	1842	particular event loop.
…		…
1101	EV is again fastest. Since it is using epoll on my system, the setup time	1844	EV is again fastest. Since it is using epoll on my system, the setup time
1102	is relatively high, though.	1845	is relatively high, though.
1103		1846
1104	Perl surprisingly comes second. It is much faster than the C-based event	1847	Perl surprisingly comes second. It is much faster than the C-based event
1105	loops Event and Glib.	1848	loops Event and Glib.
		1849
		1850	IO::Async performs very well when using its epoll backend, and still quite
		1851	good compared to Glib when using its pure perl backend.
1106		1852
1107	Event suffers from high setup time as well (look at its code and you will	1853	Event suffers from high setup time as well (look at its code and you will
1108	understand why). Callback invocation also has a high overhead compared to	1854	understand why). Callback invocation also has a high overhead compared to
1109	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event	1855	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
1110	uses select or poll in basically all documented configurations.	1856	uses select or poll in basically all documented configurations.
…		…
1118		1864
1119	=head3 Summary	1865	=head3 Summary
1120		1866
1121	=over 4	1867	=over 4
1122		1868
1123	=item * The pure perl implementation performs extremely well, considering	1869	=item * The pure perl implementation performs extremely well.
1124	that it uses select.
1125		1870
1126	=item * Avoid Glib or POE in large projects where performance matters.	1871	=item * Avoid Glib or POE in large projects where performance matters.
1127		1872
1128	=back	1873	=back
1129		1874
…		…
1142		1887
1143	=head3 Results	1888	=head3 Results
1144		1889
1145	name sockets create request	1890	name sockets create request
1146	EV 16 20.00 6.54	1891	EV 16 20.00 6.54
		1892	Perl 16 25.75 12.62
1147	Event 16 81.27 35.86	1893	Event 16 81.27 35.86
1148	Glib 16 32.63 15.48	1894	Glib 16 32.63 15.48
1149	Perl 16 24.62 162.37
1150	POE 16 261.87 276.28 uses POE::Loop::Event	1895	POE 16 261.87 276.28 uses POE::Loop::Event
1151		1896
1152	=head3 Discussion	1897	=head3 Discussion
1153		1898
1154	The benchmark tries to test the performance of a typical small	1899	The benchmark tries to test the performance of a typical small
…		…
1158	speed most when you have lots of watchers, not when you only have a few of	1903	speed most when you have lots of watchers, not when you only have a few of
1159	them).	1904	them).
1160		1905
1161	EV is again fastest.	1906	EV is again fastest.
1162		1907
1163	The C-based event loops Event and Glib come in second this time, as the	1908	Perl again comes second. It is noticeably faster than the C-based event
1164	overhead of running an iteration is much smaller in C than in Perl (little	1909	loops Event and Glib, although the difference is too small to really
1165	code to execute in the inner loop, and perl's function calling overhead is	1910	matter.
1166	high, and updating all the data structures is costly).
1167
1168	The pure perl event loop is much slower, but still competitive.
1169		1911
1170	POE also performs much better in this case, but is is still far behind the	1912	POE also performs much better in this case, but is is still far behind the
1171	others.	1913	others.
1172		1914
1173	=head3 Summary	1915	=head3 Summary
…		…
1177	=item * C-based event loops perform very well with small number of	1919	=item * C-based event loops perform very well with small number of
1178	watchers, as the management overhead dominates.	1920	watchers, as the management overhead dominates.
1179		1921
1180	=back	1922	=back
1181		1923
		1924	=head2 THE IO::Lambda BENCHMARK
		1925
		1926	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1927	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		1928	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		1929	shouldn't come as a surprise to anybody). As such, the benchmark is
		1930	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		1931	very optimal. But how would AnyEvent compare when used without the extra
		1932	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		1933
		1934	The benchmark itself creates an echo-server, and then, for 500 times,
		1935	connects to the echo server, sends a line, waits for the reply, and then
		1936	creates the next connection. This is a rather bad benchmark, as it doesn't
		1937	test the efficiency of the framework or much non-blocking I/O, but it is a
		1938	benchmark nevertheless.
		1939
		1940	name runtime
		1941	Lambda/select 0.330 sec
		1942	+ optimized 0.122 sec
		1943	Lambda/AnyEvent 0.327 sec
		1944	+ optimized 0.138 sec
		1945	Raw sockets/select 0.077 sec
		1946	POE/select, components 0.662 sec
		1947	POE/select, raw sockets 0.226 sec
		1948	POE/select, optimized 0.404 sec
		1949
		1950	AnyEvent/select/nb 0.085 sec
		1951	AnyEvent/EV/nb 0.068 sec
		1952	+state machine 0.134 sec
		1953
		1954	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1955	benchmarks actually make blocking connects and use 100% blocking I/O,
		1956	defeating the purpose of an event-based solution. All of the newly
		1957	written AnyEvent benchmarks use 100% non-blocking connects (using
		1958	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1959	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		1960	generally require a lot more bookkeeping and event handling than blocking
		1961	connects (which involve a single syscall only).
		1962
		1963	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		1964	offers similar expressive power as POE and IO::Lambda, using conventional
		1965	Perl syntax. This means that both the echo server and the client are 100%
		1966	non-blocking, further placing it at a disadvantage.
		1967
		1968	As you can see, the AnyEvent + EV combination even beats the
		1969	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1970	backend easily beats IO::Lambda and POE.
		1971
		1972	And even the 100% non-blocking version written using the high-level (and
		1973	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
		1974	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1975	in a non-blocking way.
		1976
		1977	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		1978	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		1979	part of the IO::lambda distribution and were used without any changes.
		1980
		1981
		1982	=head1 SIGNALS
		1983
		1984	AnyEvent currently installs handlers for these signals:
		1985
		1986	=over 4
		1987
		1988	=item SIGCHLD
		1989
		1990	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		1991	emulation for event loops that do not support them natively. Also, some
		1992	event loops install a similar handler.
		1993
		1994	If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent will
		1995	reset it to default, to avoid losing child exit statuses.
		1996
		1997	=item SIGPIPE
		1998
		1999	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2000	when AnyEvent gets loaded.
		2001
		2002	The rationale for this is that AnyEvent users usually do not really depend
		2003	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2004	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2005	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2006	some random socket.
		2007
		2008	The rationale for installing a no-op handler as opposed to ignoring it is
		2009	that this way, the handler will be restored to defaults on exec.
		2010
		2011	Feel free to install your own handler, or reset it to defaults.
		2012
		2013	=back
		2014
		2015	=cut
		2016
		2017	undef $SIG{CHLD}
		2018	if $SIG{CHLD} eq 'IGNORE';
		2019
		2020	$SIG{PIPE} = sub { }
		2021	unless defined $SIG{PIPE};
1182		2022
1183	=head1 FORK	2023	=head1 FORK
1184		2024
1185	Most event libraries are not fork-safe. The ones who are usually are	2025	Most event libraries are not fork-safe. The ones who are usually are
1186	because they are so inefficient. Only L<EV> is fully fork-aware.	2026	because they rely on inefficient but fork-safe C<select> or C<poll>
		2027	calls. Only L<EV> is fully fork-aware.
1187		2028
1188	If you have to fork, you must either do so I<before> creating your first	2029	If you have to fork, you must either do so I<before> creating your first
1189	watcher OR you must not use AnyEvent at all in the child.	2030	watcher OR you must not use AnyEvent at all in the child.
1190		2031
1191		2032
…		…
1199	specified in the variable.	2040	specified in the variable.
1200		2041
1201	You can make AnyEvent completely ignore this variable by deleting it	2042	You can make AnyEvent completely ignore this variable by deleting it
1202	before the first watcher gets created, e.g. with a C<BEGIN> block:	2043	before the first watcher gets created, e.g. with a C<BEGIN> block:
1203		2044
1204	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	2045	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1205		2046
1206	use AnyEvent;	2047	use AnyEvent;
		2048
		2049	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2050	be used to probe what backend is used and gain other information (which is
		2051	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2052	$ENV{PERL_ANYEVENT_STRICT}.
		2053
		2054	Note that AnyEvent will remove I<all> environment variables starting with
		2055	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2056	enabled.
		2057
		2058
		2059	=head1 BUGS
		2060
		2061	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2062	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2063	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2064	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2065	pronounced).
1207		2066
1208		2067
1209	=head1 SEE ALSO	2068	=head1 SEE ALSO
1210		2069
1211	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	2070	Utility functions: L<AnyEvent::Util>.
1212	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,	2071
		2072	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
1213	L<Event::Lib>, L<Qt>, L<POE>.	2073	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
1214		2074
1215	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	2075	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
1216	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,	2076	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
1217	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,	2077	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
1218	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.	2078	L<AnyEvent::Impl::POE>.
1219		2079
		2080	Non-blocking file handles, sockets, TCP clients and
		2081	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		2082
		2083	Asynchronous DNS: L<AnyEvent::DNS>.
		2084
		2085	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		2086
1220	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	2087	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
1221		2088
1222		2089
1223	=head1 AUTHOR	2090	=head1 AUTHOR
1224		2091
1225	Marc Lehmann <schmorp@schmorp.de>	2092	Marc Lehmann <schmorp@schmorp.de>
1226	http://home.schmorp.de/	2093	http://home.schmorp.de/
1227		2094
1228	=cut	2095	=cut
1229		2096
1230	1	2097	1
1231		2098

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