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Revision 1.211 by root, Sat Jun 6 12:04:30 2009 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
		6	event loops.
6		7
7	=head1 SYNOPSIS	8	=head1 SYNOPSIS
8		9
9	use AnyEvent;	10	use AnyEvent;
10		11
		12	# file descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {	13	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
		14
		15	# one-shot or repeating timers
		16	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
		17	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
		18
		19	print AnyEvent->now; # prints current event loop time
		20	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
		21
		22	# POSIX signal
		23	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
		24
		25	# child process exit
		26	my $w = AnyEvent->child (pid => $pid, cb => sub {
		27	my ($pid, $status) = @_;
12	...	28	...
13	});	29	});
14		30
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	31	# called when event loop idle (if applicable)
16	...	32	my $w = AnyEvent->idle (cb => sub { ... });
17	});
18		33
19	my $w = AnyEvent->condvar; # stores whether a condition was flagged	34	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		35	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	36	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	37	# use a condvar in callback mode:
		38	$w->cb (sub { $_[0]->recv });
		39
		40	=head1 INTRODUCTION/TUTORIAL
		41
		42	This manpage is mainly a reference manual. If you are interested
		43	in a tutorial or some gentle introduction, have a look at the
		44	L<AnyEvent::Intro> manpage.
22		45
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	46	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		47
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	48	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	49	nowadays. So what is different about AnyEvent?
27		50
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	51	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
29	policy> and AnyEvent is I<small and efficient>.	52	policy> and AnyEvent is I<small and efficient>.
30		53
31	First and foremost, I<AnyEvent is not an event model> itself, it only	54	First and foremost, I<AnyEvent is not an event model> itself, it only
32	interfaces to whatever event model the main program happens to use in a	55	interfaces to whatever event model the main program happens to use, in a
33	pragmatic way. For event models and certain classes of immortals alike,	56	pragmatic way. For event models and certain classes of immortals alike,
34	the statement "there can only be one" is a bitter reality: In general,	57	the statement "there can only be one" is a bitter reality: In general,
35	only one event loop can be active at the same time in a process. AnyEvent	58	only one event loop can be active at the same time in a process. AnyEvent
36	helps hiding the differences between those event loops.	59	cannot change this, but it can hide the differences between those event
		60	loops.
37		61
38	The goal of AnyEvent is to offer module authors the ability to do event	62	The goal of AnyEvent is to offer module authors the ability to do event
39	programming (waiting for I/O or timer events) without subscribing to a	63	programming (waiting for I/O or timer events) without subscribing to a
40	religion, a way of living, and most importantly: without forcing your	64	religion, a way of living, and most importantly: without forcing your
41	module users into the same thing by forcing them to use the same event	65	module users into the same thing by forcing them to use the same event
42	model you use.	66	model you use.
43		67
44	For modules like POE or IO::Async (which is a total misnomer as it is	68	For modules like POE or IO::Async (which is a total misnomer as it is
45	actually doing all I/O I<synchronously>...), using them in your module is	69	actually doing all I/O I<synchronously>...), using them in your module is
46	like joining a cult: After you joined, you are dependent on them and you	70	like joining a cult: After you joined, you are dependent on them and you
47	cannot use anything else, as it is simply incompatible to everything that	71	cannot use anything else, as they are simply incompatible to everything
48	isn't itself. What's worse, all the potential users of your module are	72	that isn't them. What's worse, all the potential users of your
49	I<also> forced to use the same event loop you use.	73	module are I<also> forced to use the same event loop you use.
50		74
51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	75	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together	76	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if	77	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
54	your module uses one of those, every user of your module has to use it,	78	your module uses one of those, every user of your module has to use it,
55	too. But if your module uses AnyEvent, it works transparently with all	79	too. But if your module uses AnyEvent, it works transparently with all
56	event models it supports (including stuff like POE and IO::Async, as long	80	event models it supports (including stuff like IO::Async, as long as those
57	as those use one of the supported event loops. It is trivial to add new	81	use one of the supported event loops. It is trivial to add new event loops
58	event loops to AnyEvent, too, so it is future-proof).	82	to AnyEvent, too, so it is future-proof).
59		83
60	In addition to being free of having to use I<the one and only true event	84	In addition to being free of having to use I<the one and only true event
61	model>, AnyEvent also is free of bloat and policy: with POE or similar	85	model>, AnyEvent also is free of bloat and policy: with POE or similar
62	modules, you get an enourmous amount of code and strict rules you have to	86	modules, you get an enormous amount of code and strict rules you have to
63	follow. AnyEvent, on the other hand, is lean and up to the point, by only	87	follow. AnyEvent, on the other hand, is lean and up to the point, by only
64	offering the functionality that is necessary, in as thin as a wrapper as	88	offering the functionality that is necessary, in as thin as a wrapper as
65	technically possible.	89	technically possible.
66		90
		91	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		92	of useful functionality, such as an asynchronous DNS resolver, 100%
		93	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		94	such as Windows) and lots of real-world knowledge and workarounds for
		95	platform bugs and differences.
		96
67	Of course, if you want lots of policy (this can arguably be somewhat	97	Now, if you I<do want> lots of policy (this can arguably be somewhat
68	useful) and you want to force your users to use the one and only event	98	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	99	model, you should I<not> use this module.
70
71		100
72	=head1 DESCRIPTION	101	=head1 DESCRIPTION
73		102
74	L<AnyEvent> provides an identical interface to multiple event loops. This	103	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	104	allows module authors to utilise an event loop without forcing module
…		…
79	The interface itself is vaguely similar, but not identical to the L<Event>	108	The interface itself is vaguely similar, but not identical to the L<Event>
80	module.	109	module.
81		110
82	During the first call of any watcher-creation method, the module tries	111	During the first call of any watcher-creation method, the module tries
83	to detect the currently loaded event loop by probing whether one of the	112	to detect the currently loaded event loop by probing whether one of the
84	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,	113	following modules is already loaded: L<EV>,
85	L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found,	114	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
86	the module tries to load these modules in the stated order. The first one	115	L<POE>. The first one found is used. If none are found, the module tries
		116	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		117	adaptor should always succeed) in the order given. The first one that can
87	that can be successfully loaded will be used. If, after this, still none	118	be successfully loaded will be used. If, after this, still none could be
88	could be found, AnyEvent will fall back to a pure-perl event loop, which	119	found, AnyEvent will fall back to a pure-perl event loop, which is not
89	is not very efficient, but should work everywhere.	120	very efficient, but should work everywhere.
90		121
91	Because AnyEvent first checks for modules that are already loaded, loading	122	Because AnyEvent first checks for modules that are already loaded, loading
92	an event model explicitly before first using AnyEvent will likely make	123	an event model explicitly before first using AnyEvent will likely make
93	that model the default. For example:	124	that model the default. For example:
94		125
…		…
101	starts using it, all bets are off. Maybe you should tell their authors to	132	starts using it, all bets are off. Maybe you should tell their authors to
102	use AnyEvent so their modules work together with others seamlessly...	133	use AnyEvent so their modules work together with others seamlessly...
103		134
104	The pure-perl implementation of AnyEvent is called	135	The pure-perl implementation of AnyEvent is called
105	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	136	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
106	explicitly.	137	explicitly and enjoy the high availability of that event loop :)
107		138
108	=head1 WATCHERS	139	=head1 WATCHERS
109		140
110	AnyEvent has the central concept of a I<watcher>, which is an object that	141	AnyEvent has the central concept of a I<watcher>, which is an object that
111	stores relevant data for each kind of event you are waiting for, such as	142	stores relevant data for each kind of event you are waiting for, such as
112	the callback to call, the filehandle to watch, etc.	143	the callback to call, the file handle to watch, etc.
113		144
114	These watchers are normal Perl objects with normal Perl lifetime. After	145	These watchers are normal Perl objects with normal Perl lifetime. After
115	creating a watcher it will immediately "watch" for events and invoke the	146	creating a watcher it will immediately "watch" for events and invoke the
116	callback when the event occurs (of course, only when the event model	147	callback when the event occurs (of course, only when the event model
117	is in control).	148	is in control).
118		149
		150	Note that B<callbacks must not permanently change global variables>
		151	potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
		152	callbacks must not C<die> >>. The former is good programming practise in
		153	Perl and the latter stems from the fact that exception handling differs
		154	widely between event loops.
		155
119	To disable the watcher you have to destroy it (e.g. by setting the	156	To disable the watcher you have to destroy it (e.g. by setting the
120	variable you store it in to C<undef> or otherwise deleting all references	157	variable you store it in to C<undef> or otherwise deleting all references
121	to it).	158	to it).
122		159
123	All watchers are created by calling a method on the C<AnyEvent> class.	160	All watchers are created by calling a method on the C<AnyEvent> class.
…		…
125	Many watchers either are used with "recursion" (repeating timers for	162	Many watchers either are used with "recursion" (repeating timers for
126	example), or need to refer to their watcher object in other ways.	163	example), or need to refer to their watcher object in other ways.
127		164
128	An any way to achieve that is this pattern:	165	An any way to achieve that is this pattern:
129		166
130	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {	167	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
131	# you can use $w here, for example to undef it	168	# you can use $w here, for example to undef it
132	undef $w;	169	undef $w;
133	});	170	});
134		171
135	Note that C<my $w; $w => combination. This is necessary because in Perl,	172	Note that C<my $w; $w => combination. This is necessary because in Perl,
136	my variables are only visible after the statement in which they are	173	my variables are only visible after the statement in which they are
137	declared.	174	declared.
138		175
139	=head2 IO WATCHERS	176	=head2 I/O WATCHERS
140		177
141	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	178	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
142	with the following mandatory key-value pairs as arguments:	179	with the following mandatory key-value pairs as arguments:
143		180
144	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	181	C<fh> is the Perl I<file handle> (I<not> file descriptor) to watch
		182	for events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example files
		186	or block devices.
		187
145	events. C<poll> must be a string that is either C<r> or C<w>, which	188	C<poll> must be a string that is either C<r> or C<w>, which creates a
146	creates a watcher waiting for "r"eadable or "w"ritable events,	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
147	respectively. C<cb> is the callback to invoke each time the file handle	191	C<cb> is the callback to invoke each time the file handle becomes ready.
148	becomes ready.
149		192
150	File handles will be kept alive, so as long as the watcher exists, the	193	Although the callback might get passed parameters, their value and
151	file handle exists, too.	194	presence is undefined and you cannot rely on them. Portable AnyEvent
		195	callbacks cannot use arguments passed to I/O watcher callbacks.
152		196
		197	The I/O watcher might use the underlying file descriptor or a copy of it.
153	It is not allowed to close a file handle as long as any watcher is active	198	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	199	underlying file descriptor.
155		200
156	Some event loops issue spurious readyness notifications, so you should	201	Some event loops issue spurious readyness notifications, so you should
157	always use non-blocking calls when reading/writing from/to your file	202	always use non-blocking calls when reading/writing from/to your file
158	handles.	203	handles.
159		204
160	Example:
161
162	# wait for readability of STDIN, then read a line and disable the watcher	205	Example: wait for readability of STDIN, then read a line and disable the
		206	watcher.
		207
163	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
164	chomp (my $input = <STDIN>);	209	chomp (my $input = <STDIN>);
165	warn "read: $input\n";	210	warn "read: $input\n";
166	undef $w;	211	undef $w;
167	});	212	});
…		…
170		215
171	You can create a time watcher by calling the C<< AnyEvent->timer >>	216	You can create a time watcher by calling the C<< AnyEvent->timer >>
172	method with the following mandatory arguments:	217	method with the following mandatory arguments:
173		218
174	C<after> specifies after how many seconds (fractional values are	219	C<after> specifies after how many seconds (fractional values are
175	supported) should the timer activate. C<cb> the callback to invoke in that	220	supported) the callback should be invoked. C<cb> is the callback to invoke
176	case.	221	in that case.
177		222
178	The timer callback will be invoked at most once: if you want a repeating	223	Although the callback might get passed parameters, their value and
179	timer you have to create a new watcher (this is a limitation by both Tk	224	presence is undefined and you cannot rely on them. Portable AnyEvent
180	and Glib).	225	callbacks cannot use arguments passed to time watcher callbacks.
181		226
182	Example:	227	The callback will normally be invoked once only. If you specify another
		228	parameter, C<interval>, as a strictly positive number (> 0), then the
		229	callback will be invoked regularly at that interval (in fractional
		230	seconds) after the first invocation. If C<interval> is specified with a
		231	false value, then it is treated as if it were missing.
183		232
		233	The callback will be rescheduled before invoking the callback, but no
		234	attempt is done to avoid timer drift in most backends, so the interval is
		235	only approximate.
		236
184	# fire an event after 7.7 seconds	237	Example: fire an event after 7.7 seconds.
		238
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	240	warn "timeout\n";
187	});	241	});
188		242
189	# to cancel the timer:	243	# to cancel the timer:
190	undef $w;	244	undef $w;
191		245
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	246	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		247
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		249	warn "timeout\n";
200	};	250	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		251
205	=head3 TIMING ISSUES	252	=head3 TIMING ISSUES
206		253
207	There are two ways to handle timers: based on real time (relative, "fire	254	There are two ways to handle timers: based on real time (relative, "fire
208	in 10 seconds") and based on wallclock time (absolute, "fire at 12	255	in 10 seconds") and based on wallclock time (absolute, "fire at 12
209	o'clock").	256	o'clock").
210		257
211	While most event loops expect timers to specified in a relative way, they use	258	While most event loops expect timers to specified in a relative way, they
212	absolute time internally. This makes a difference when your clock "jumps",	259	use absolute time internally. This makes a difference when your clock
213	for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to	260	"jumps", for example, when ntp decides to set your clock backwards from
214	2008-01-01, a watcher that you created to fire "after" a second might actually take	261	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	262	fire "after" a second might actually take six years to finally fire.
216		263
217	AnyEvent cannot compensate for this. The only event loop that is conscious	264	AnyEvent cannot compensate for this. The only event loop that is conscious
218	about these issues is L<EV>, which offers both relative (ev_timer) and	265	about these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	266	on true relative time) and absolute (ev_periodic, based on wallclock time)
		267	timers.
220		268
221	AnyEvent always prefers relative timers, if available, matching the	269	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	270	AnyEvent API.
223		271
		272	AnyEvent has two additional methods that return the "current time":
		273
		274	=over 4
		275
		276	=item AnyEvent->time
		277
		278	This returns the "current wallclock time" as a fractional number of
		279	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		280	return, and the result is guaranteed to be compatible with those).
		281
		282	It progresses independently of any event loop processing, i.e. each call
		283	will check the system clock, which usually gets updated frequently.
		284
		285	=item AnyEvent->now
		286
		287	This also returns the "current wallclock time", but unlike C<time>, above,
		288	this value might change only once per event loop iteration, depending on
		289	the event loop (most return the same time as C<time>, above). This is the
		290	time that AnyEvent's timers get scheduled against.
		291
		292	I<In almost all cases (in all cases if you don't care), this is the
		293	function to call when you want to know the current time.>
		294
		295	This function is also often faster then C<< AnyEvent->time >>, and
		296	thus the preferred method if you want some timestamp (for example,
		297	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		298
		299	The rest of this section is only of relevance if you try to be very exact
		300	with your timing, you can skip it without bad conscience.
		301
		302	For a practical example of when these times differ, consider L<Event::Lib>
		303	and L<EV> and the following set-up:
		304
		305	The event loop is running and has just invoked one of your callback at
		306	time=500 (assume no other callbacks delay processing). In your callback,
		307	you wait a second by executing C<sleep 1> (blocking the process for a
		308	second) and then (at time=501) you create a relative timer that fires
		309	after three seconds.
		310
		311	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		312	both return C<501>, because that is the current time, and the timer will
		313	be scheduled to fire at time=504 (C<501> + C<3>).
		314
		315	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		316	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		317	last event processing phase started. With L<EV>, your timer gets scheduled
		318	to run at time=503 (C<500> + C<3>).
		319
		320	In one sense, L<Event::Lib> is more exact, as it uses the current time
		321	regardless of any delays introduced by event processing. However, most
		322	callbacks do not expect large delays in processing, so this causes a
		323	higher drift (and a lot more system calls to get the current time).
		324
		325	In another sense, L<EV> is more exact, as your timer will be scheduled at
		326	the same time, regardless of how long event processing actually took.
		327
		328	In either case, if you care (and in most cases, you don't), then you
		329	can get whatever behaviour you want with any event loop, by taking the
		330	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		331	account.
		332
		333	=item AnyEvent->now_update
		334
		335	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		336	the current time for each loop iteration (see the discussion of L<<
		337	AnyEvent->now >>, above).
		338
		339	When a callback runs for a long time (or when the process sleeps), then
		340	this "current" time will differ substantially from the real time, which
		341	might affect timers and time-outs.
		342
		343	When this is the case, you can call this method, which will update the
		344	event loop's idea of "current time".
		345
		346	Note that updating the time I<might> cause some events to be handled.
		347
		348	=back
		349
224	=head2 SIGNAL WATCHERS	350	=head2 SIGNAL WATCHERS
225		351
226	You can watch for signals using a signal watcher, C<signal> is the signal	352	You can watch for signals using a signal watcher, C<signal> is the signal
227	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	353	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
228	be invoked whenever a signal occurs.	354	callback to be invoked whenever a signal occurs.
229		355
		356	Although the callback might get passed parameters, their value and
		357	presence is undefined and you cannot rely on them. Portable AnyEvent
		358	callbacks cannot use arguments passed to signal watcher callbacks.
		359
230	Multiple signals occurances can be clumped together into one callback	360	Multiple signal occurrences can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	361	invocation, and callback invocation will be synchronous. Synchronous means
232	that it might take a while until the signal gets handled by the process,	362	that it might take a while until the signal gets handled by the process,
233	but it is guarenteed not to interrupt any other callbacks.	363	but it is guaranteed not to interrupt any other callbacks.
234		364
235	The main advantage of using these watchers is that you can share a signal	365	The main advantage of using these watchers is that you can share a signal
236	between multiple watchers.	366	between multiple watchers.
237		367
238	This watcher might use C<%SIG>, so programs overwriting those signals	368	This watcher might use C<%SIG>, so programs overwriting those signals
…		…
245	=head2 CHILD PROCESS WATCHERS	375	=head2 CHILD PROCESS WATCHERS
246		376
247	You can also watch on a child process exit and catch its exit status.	377	You can also watch on a child process exit and catch its exit status.
248		378
249	The child process is specified by the C<pid> argument (if set to C<0>, it	379	The child process is specified by the C<pid> argument (if set to C<0>, it
250	watches for any child process exit). The watcher will trigger as often	380	watches for any child process exit). The watcher will triggered only when
251	as status change for the child are received. This works by installing a	381	the child process has finished and an exit status is available, not on
252	signal handler for C<SIGCHLD>. The callback will be called with the pid	382	any trace events (stopped/continued).
253	and exit status (as returned by waitpid).
254		383
255	Example: wait for pid 1333	384	The callback will be called with the pid and exit status (as returned by
		385	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		386	callback arguments.
256		387
		388	This watcher type works by installing a signal handler for C<SIGCHLD>,
		389	and since it cannot be shared, nothing else should use SIGCHLD or reap
		390	random child processes (waiting for specific child processes, e.g. inside
		391	C<system>, is just fine).
		392
		393	There is a slight catch to child watchers, however: you usually start them
		394	I<after> the child process was created, and this means the process could
		395	have exited already (and no SIGCHLD will be sent anymore).
		396
		397	Not all event models handle this correctly (POE doesn't), but even for
		398	event models that I<do> handle this correctly, they usually need to be
		399	loaded before the process exits (i.e. before you fork in the first place).
		400
		401	This means you cannot create a child watcher as the very first thing in an
		402	AnyEvent program, you I<have> to create at least one watcher before you
		403	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		404
		405	Example: fork a process and wait for it
		406
		407	my $done = AnyEvent->condvar;
		408
		409	my $pid = fork or exit 5;
		410
257	my $w = AnyEvent->child (	411	my $w = AnyEvent->child (
258	pid => 1333,	412	pid => $pid,
259	cb => sub {	413	cb => sub {
260	my ($pid, $status) = @_;	414	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	415	warn "pid $pid exited with status $status";
		416	$done->send;
262	},	417	},
263	);	418	);
		419
		420	# do something else, then wait for process exit
		421	$done->recv;
		422
		423	=head2 IDLE WATCHERS
		424
		425	Sometimes there is a need to do something, but it is not so important
		426	to do it instantly, but only when there is nothing better to do. This
		427	"nothing better to do" is usually defined to be "no other events need
		428	attention by the event loop".
		429
		430	Idle watchers ideally get invoked when the event loop has nothing
		431	better to do, just before it would block the process to wait for new
		432	events. Instead of blocking, the idle watcher is invoked.
		433
		434	Most event loops unfortunately do not really support idle watchers (only
		435	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		436	will simply call the callback "from time to time".
		437
		438	Example: read lines from STDIN, but only process them when the
		439	program is otherwise idle:
		440
		441	my @lines; # read data
		442	my $idle_w;
		443	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		444	push @lines, scalar <STDIN>;
		445
		446	# start an idle watcher, if not already done
		447	$idle_w ||= AnyEvent->idle (cb => sub {
		448	# handle only one line, when there are lines left
		449	if (my $line = shift @lines) {
		450	print "handled when idle: $line";
		451	} else {
		452	# otherwise disable the idle watcher again
		453	undef $idle_w;
		454	}
		455	});
		456	});
264		457
265	=head2 CONDITION VARIABLES	458	=head2 CONDITION VARIABLES
266		459
		460	If you are familiar with some event loops you will know that all of them
		461	require you to run some blocking "loop", "run" or similar function that
		462	will actively watch for new events and call your callbacks.
		463
		464	AnyEvent is different, it expects somebody else to run the event loop and
		465	will only block when necessary (usually when told by the user).
		466
		467	The instrument to do that is called a "condition variable", so called
		468	because they represent a condition that must become true.
		469
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	470	Condition variables can be created by calling the C<< AnyEvent->condvar
268	method without any arguments.	471	>> method, usually without arguments. The only argument pair allowed is
269		472
270	A condition variable waits for a condition - precisely that the C<<	473	C<cb>, which specifies a callback to be called when the condition variable
271	->broadcast >> method has been called.	474	becomes true, with the condition variable as the first argument (but not
		475	the results).
272		476
273	They are very useful to signal that a condition has been fulfilled, for	477	After creation, the condition variable is "false" until it becomes "true"
		478	by calling the C<send> method (or calling the condition variable as if it
		479	were a callback, read about the caveats in the description for the C<<
		480	->send >> method).
		481
		482	Condition variables are similar to callbacks, except that you can
		483	optionally wait for them. They can also be called merge points - points
		484	in time where multiple outstanding events have been processed. And yet
		485	another way to call them is transactions - each condition variable can be
		486	used to represent a transaction, which finishes at some point and delivers
		487	a result.
		488
		489	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	490	for example, if you write a module that does asynchronous http requests,
275	then a condition variable would be the ideal candidate to signal the	491	then a condition variable would be the ideal candidate to signal the
276	availability of results.	492	availability of results. The user can either act when the callback is
		493	called or can synchronously C<< ->recv >> for the results.
277		494
278	You can also use condition variables to block your main program until	495	You can also use them to simulate traditional event loops - for example,
279	an event occurs - for example, you could C<< ->wait >> in your main	496	you can block your main program until an event occurs - for example, you
280	program until the user clicks the Quit button in your app, which would C<<	497	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	498	button of your app, which would C<< ->send >> the "quit" event.
282		499
283	Note that condition variables recurse into the event loop - if you have	500	Note that condition variables recurse into the event loop - if you have
284	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	501	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
285	lose. Therefore, condition variables are good to export to your caller, but	502	lose. Therefore, condition variables are good to export to your caller, but
286	you should avoid making a blocking wait yourself, at least in callbacks,	503	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	504	as this asks for trouble.
288		505
289	This object has two methods:	506	Condition variables are represented by hash refs in perl, and the keys
		507	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		508	easy (it is often useful to build your own transaction class on top of
		509	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		510	it's C<new> method in your own C<new> method.
		511
		512	There are two "sides" to a condition variable - the "producer side" which
		513	eventually calls C<< -> send >>, and the "consumer side", which waits
		514	for the send to occur.
		515
		516	Example: wait for a timer.
		517
		518	# wait till the result is ready
		519	my $result_ready = AnyEvent->condvar;
		520
		521	# do something such as adding a timer
		522	# or socket watcher the calls $result_ready->send
		523	# when the "result" is ready.
		524	# in this case, we simply use a timer:
		525	my $w = AnyEvent->timer (
		526	after => 1,
		527	cb => sub { $result_ready->send },
		528	);
		529
		530	# this "blocks" (while handling events) till the callback
		531	# calls send
		532	$result_ready->recv;
		533
		534	Example: wait for a timer, but take advantage of the fact that
		535	condition variables are also code references.
		536
		537	my $done = AnyEvent->condvar;
		538	my $delay = AnyEvent->timer (after => 5, cb => $done);
		539	$done->recv;
		540
		541	Example: Imagine an API that returns a condvar and doesn't support
		542	callbacks. This is how you make a synchronous call, for example from
		543	the main program:
		544
		545	use AnyEvent::CouchDB;
		546
		547	...
		548
		549	my @info = $couchdb->info->recv;
		550
		551	And this is how you would just ste a callback to be called whenever the
		552	results are available:
		553
		554	$couchdb->info->cb (sub {
		555	my @info = $_[0]->recv;
		556	});
		557
		558	=head3 METHODS FOR PRODUCERS
		559
		560	These methods should only be used by the producing side, i.e. the
		561	code/module that eventually sends the signal. Note that it is also
		562	the producer side which creates the condvar in most cases, but it isn't
		563	uncommon for the consumer to create it as well.
290		564
291	=over 4	565	=over 4
292		566
		567	=item $cv->send (...)
		568
		569	Flag the condition as ready - a running C<< ->recv >> and all further
		570	calls to C<recv> will (eventually) return after this method has been
		571	called. If nobody is waiting the send will be remembered.
		572
		573	If a callback has been set on the condition variable, it is called
		574	immediately from within send.
		575
		576	Any arguments passed to the C<send> call will be returned by all
		577	future C<< ->recv >> calls.
		578
		579	Condition variables are overloaded so one can call them directly
		580	(as a code reference). Calling them directly is the same as calling
		581	C<send>. Note, however, that many C-based event loops do not handle
		582	overloading, so as tempting as it may be, passing a condition variable
		583	instead of a callback does not work. Both the pure perl and EV loops
		584	support overloading, however, as well as all functions that use perl to
		585	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		586	example).
		587
		588	=item $cv->croak ($error)
		589
		590	Similar to send, but causes all call's to C<< ->recv >> to invoke
		591	C<Carp::croak> with the given error message/object/scalar.
		592
		593	This can be used to signal any errors to the condition variable
		594	user/consumer.
		595
		596	=item $cv->begin ([group callback])
		597
293	=item $cv->wait	598	=item $cv->end
294		599
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	600	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		601
		602	These two methods can be used to combine many transactions/events into
		603	one. For example, a function that pings many hosts in parallel might want
		604	to use a condition variable for the whole process.
		605
		606	Every call to C<< ->begin >> will increment a counter, and every call to
		607	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		608	>>, the (last) callback passed to C<begin> will be executed. That callback
		609	is I<supposed> to call C<< ->send >>, but that is not required. If no
		610	callback was set, C<send> will be called without any arguments.
		611
		612	Let's clarify this with the ping example:
		613
		614	my $cv = AnyEvent->condvar;
		615
		616	my %result;
		617	$cv->begin (sub { $cv->send (\%result) });
		618
		619	for my $host (@list_of_hosts) {
		620	$cv->begin;
		621	ping_host_then_call_callback $host, sub {
		622	$result{$host} = ...;
		623	$cv->end;
		624	};
		625	}
		626
		627	$cv->end;
		628
		629	This code fragment supposedly pings a number of hosts and calls
		630	C<send> after results for all then have have been gathered - in any
		631	order. To achieve this, the code issues a call to C<begin> when it starts
		632	each ping request and calls C<end> when it has received some result for
		633	it. Since C<begin> and C<end> only maintain a counter, the order in which
		634	results arrive is not relevant.
		635
		636	There is an additional bracketing call to C<begin> and C<end> outside the
		637	loop, which serves two important purposes: first, it sets the callback
		638	to be called once the counter reaches C<0>, and second, it ensures that
		639	C<send> is called even when C<no> hosts are being pinged (the loop
		640	doesn't execute once).
		641
		642	This is the general pattern when you "fan out" into multiple subrequests:
		643	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		644	is called at least once, and then, for each subrequest you start, call
		645	C<begin> and for each subrequest you finish, call C<end>.
		646
		647	=back
		648
		649	=head3 METHODS FOR CONSUMERS
		650
		651	These methods should only be used by the consuming side, i.e. the
		652	code awaits the condition.
		653
		654	=over 4
		655
		656	=item $cv->recv
		657
		658	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
296	called on c<$cv>, while servicing other watchers normally.	659	>> methods have been called on c<$cv>, while servicing other watchers
		660	normally.
297		661
298	You can only wait once on a condition - additional calls will return	662	You can only wait once on a condition - additional calls are valid but
299	immediately.	663	will return immediately.
		664
		665	If an error condition has been set by calling C<< ->croak >>, then this
		666	function will call C<croak>.
		667
		668	In list context, all parameters passed to C<send> will be returned,
		669	in scalar context only the first one will be returned.
300		670
301	Not all event models support a blocking wait - some die in that case	671	Not all event models support a blocking wait - some die in that case
302	(programs might want to do that to stay interactive), so I<if you are	672	(programs might want to do that to stay interactive), so I<if you are
303	using this from a module, never require a blocking wait>, but let the	673	using this from a module, never require a blocking wait>, but let the
304	caller decide whether the call will block or not (for example, by coupling	674	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	675	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	676	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	677	while still supporting blocking waits if the caller so desires).
308		678
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	679	Another reason I<never> to C<< ->recv >> in a module is that you cannot
310	sensibly have two C<< ->wait >>'s in parallel, as that would require	680	sensibly have two C<< ->recv >>'s in parallel, as that would require
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	681	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	682	can supply.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		683
316	=item $cv->broadcast	684	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		685	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		686	versions and also integrates coroutines into AnyEvent, making blocking
		687	C<< ->recv >> calls perfectly safe as long as they are done from another
		688	coroutine (one that doesn't run the event loop).
317		689
318	Flag the condition as ready - a running C<< ->wait >> and all further	690	You can ensure that C<< -recv >> never blocks by setting a callback and
319	calls to C<wait> will (eventually) return after this method has been	691	only calling C<< ->recv >> from within that callback (or at a later
320	called. If nobody is waiting the broadcast will be remembered..	692	time). This will work even when the event loop does not support blocking
		693	waits otherwise.
		694
		695	=item $bool = $cv->ready
		696
		697	Returns true when the condition is "true", i.e. whether C<send> or
		698	C<croak> have been called.
		699
		700	=item $cb = $cv->cb ($cb->($cv))
		701
		702	This is a mutator function that returns the callback set and optionally
		703	replaces it before doing so.
		704
		705	The callback will be called when the condition becomes "true", i.e. when
		706	C<send> or C<croak> are called, with the only argument being the condition
		707	variable itself. Calling C<recv> inside the callback or at any later time
		708	is guaranteed not to block.
321		709
322	=back	710	=back
323
324	Example:
325
326	# wait till the result is ready
327	my $result_ready = AnyEvent->condvar;
328
329	# do something such as adding a timer
330	# or socket watcher the calls $result_ready->broadcast
331	# when the "result" is ready.
332	# in this case, we simply use a timer:
333	my $w = AnyEvent->timer (
334	after => 1,
335	cb => sub { $result_ready->broadcast },
336	);
337
338	# this "blocks" (while handling events) till the watcher
339	# calls broadcast
340	$result_ready->wait;
341		711
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	712	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		713
344	=over 4	714	=over 4
345		715
…		…
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	721	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
352	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	722	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
353		723
354	The known classes so far are:	724	The known classes so far are:
355		725
356	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
357	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
358	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	726	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)	727	AnyEvent::Impl::Event based on Event, second best choice.
		728	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
360	AnyEvent::Impl::Glib based on Glib, third-best choice.	729	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.	730	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	731	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
363	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	732	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		733	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		734
		735	There is no support for WxWidgets, as WxWidgets has no support for
		736	watching file handles. However, you can use WxWidgets through the
		737	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		738	second, which was considered to be too horrible to even consider for
		739	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		740	it's adaptor.
		741
		742	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		743	autodetecting them.
364		744
365	=item AnyEvent::detect	745	=item AnyEvent::detect
366		746
367	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	747	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
368	if necessary. You should only call this function right before you would	748	if necessary. You should only call this function right before you would
369	have created an AnyEvent watcher anyway, that is, as late as possible at	749	have created an AnyEvent watcher anyway, that is, as late as possible at
370	runtime.	750	runtime.
371		751
		752	=item $guard = AnyEvent::post_detect { BLOCK }
		753
		754	Arranges for the code block to be executed as soon as the event model is
		755	autodetected (or immediately if this has already happened).
		756
		757	If called in scalar or list context, then it creates and returns an object
		758	that automatically removes the callback again when it is destroyed. See
		759	L<Coro::BDB> for a case where this is useful.
		760
		761	=item @AnyEvent::post_detect
		762
		763	If there are any code references in this array (you can C<push> to it
		764	before or after loading AnyEvent), then they will called directly after
		765	the event loop has been chosen.
		766
		767	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		768	if it contains a true value then the event loop has already been detected,
		769	and the array will be ignored.
		770
		771	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		772
372	=back	773	=back
373		774
374	=head1 WHAT TO DO IN A MODULE	775	=head1 WHAT TO DO IN A MODULE
375		776
376	As a module author, you should C<use AnyEvent> and call AnyEvent methods	777	As a module author, you should C<use AnyEvent> and call AnyEvent methods
…		…
379	Be careful when you create watchers in the module body - AnyEvent will	780	Be careful when you create watchers in the module body - AnyEvent will
380	decide which event module to use as soon as the first method is called, so	781	decide which event module to use as soon as the first method is called, so
381	by calling AnyEvent in your module body you force the user of your module	782	by calling AnyEvent in your module body you force the user of your module
382	to load the event module first.	783	to load the event module first.
383		784
384	Never call C<< ->wait >> on a condition variable unless you I<know> that	785	Never call C<< ->recv >> on a condition variable unless you I<know> that
385	the C<< ->broadcast >> method has been called on it already. This is	786	the C<< ->send >> method has been called on it already. This is
386	because it will stall the whole program, and the whole point of using	787	because it will stall the whole program, and the whole point of using
387	events is to stay interactive.	788	events is to stay interactive.
388		789
389	It is fine, however, to call C<< ->wait >> when the user of your module	790	It is fine, however, to call C<< ->recv >> when the user of your module
390	requests it (i.e. if you create a http request object ad have a method	791	requests it (i.e. if you create a http request object ad have a method
391	called C<results> that returns the results, it should call C<< ->wait >>	792	called C<results> that returns the results, it should call C<< ->recv >>
392	freely, as the user of your module knows what she is doing. always).	793	freely, as the user of your module knows what she is doing. always).
393		794
394	=head1 WHAT TO DO IN THE MAIN PROGRAM	795	=head1 WHAT TO DO IN THE MAIN PROGRAM
395		796
396	There will always be a single main program - the only place that should	797	There will always be a single main program - the only place that should
…		…
398		799
399	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	800	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
400	do anything special (it does not need to be event-based) and let AnyEvent	801	do anything special (it does not need to be event-based) and let AnyEvent
401	decide which implementation to chose if some module relies on it.	802	decide which implementation to chose if some module relies on it.
402		803
403	If the main program relies on a specific event model. For example, in	804	If the main program relies on a specific event model - for example, in
404	Gtk2 programs you have to rely on the Glib module. You should load the	805	Gtk2 programs you have to rely on the Glib module - you should load the
405	event module before loading AnyEvent or any module that uses it: generally	806	event module before loading AnyEvent or any module that uses it: generally
406	speaking, you should load it as early as possible. The reason is that	807	speaking, you should load it as early as possible. The reason is that
407	modules might create watchers when they are loaded, and AnyEvent will	808	modules might create watchers when they are loaded, and AnyEvent will
408	decide on the event model to use as soon as it creates watchers, and it	809	decide on the event model to use as soon as it creates watchers, and it
409	might chose the wrong one unless you load the correct one yourself.	810	might chose the wrong one unless you load the correct one yourself.
410		811
411	You can chose to use a rather inefficient pure-perl implementation by	812	You can chose to use a pure-perl implementation by loading the
412	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	813	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
413	behaviour everywhere, but letting AnyEvent chose is generally better.	814	everywhere, but letting AnyEvent chose the model is generally better.
		815
		816	=head2 MAINLOOP EMULATION
		817
		818	Sometimes (often for short test scripts, or even standalone programs who
		819	only want to use AnyEvent), you do not want to run a specific event loop.
		820
		821	In that case, you can use a condition variable like this:
		822
		823	AnyEvent->condvar->recv;
		824
		825	This has the effect of entering the event loop and looping forever.
		826
		827	Note that usually your program has some exit condition, in which case
		828	it is better to use the "traditional" approach of storing a condition
		829	variable somewhere, waiting for it, and sending it when the program should
		830	exit cleanly.
		831
		832
		833	=head1 OTHER MODULES
		834
		835	The following is a non-exhaustive list of additional modules that use
		836	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		837	in the same program. Some of the modules come with AnyEvent, some are
		838	available via CPAN.
		839
		840	=over 4
		841
		842	=item L<AnyEvent::Util>
		843
		844	Contains various utility functions that replace often-used but blocking
		845	functions such as C<inet_aton> by event-/callback-based versions.
		846
		847	=item L<AnyEvent::Socket>
		848
		849	Provides various utility functions for (internet protocol) sockets,
		850	addresses and name resolution. Also functions to create non-blocking tcp
		851	connections or tcp servers, with IPv6 and SRV record support and more.
		852
		853	=item L<AnyEvent::Handle>
		854
		855	Provide read and write buffers, manages watchers for reads and writes,
		856	supports raw and formatted I/O, I/O queued and fully transparent and
		857	non-blocking SSL/TLS.
		858
		859	=item L<AnyEvent::DNS>
		860
		861	Provides rich asynchronous DNS resolver capabilities.
		862
		863	=item L<AnyEvent::HTTP>
		864
		865	A simple-to-use HTTP library that is capable of making a lot of concurrent
		866	HTTP requests.
		867
		868	=item L<AnyEvent::HTTPD>
		869
		870	Provides a simple web application server framework.
		871
		872	=item L<AnyEvent::FastPing>
		873
		874	The fastest ping in the west.
		875
		876	=item L<AnyEvent::DBI>
		877
		878	Executes L<DBI> requests asynchronously in a proxy process.
		879
		880	=item L<AnyEvent::AIO>
		881
		882	Truly asynchronous I/O, should be in the toolbox of every event
		883	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		884	together.
		885
		886	=item L<AnyEvent::BDB>
		887
		888	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		889	L<BDB> and AnyEvent together.
		890
		891	=item L<AnyEvent::GPSD>
		892
		893	A non-blocking interface to gpsd, a daemon delivering GPS information.
		894
		895	=item L<AnyEvent::IGS>
		896
		897	A non-blocking interface to the Internet Go Server protocol (used by
		898	L<App::IGS>).
		899
		900	=item L<AnyEvent::IRC>
		901
		902	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		903
		904	=item L<Net::XMPP2>
		905
		906	AnyEvent based XMPP (Jabber protocol) module family.
		907
		908	=item L<Net::FCP>
		909
		910	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		911	of AnyEvent.
		912
		913	=item L<Event::ExecFlow>
		914
		915	High level API for event-based execution flow control.
		916
		917	=item L<Coro>
		918
		919	Has special support for AnyEvent via L<Coro::AnyEvent>.
		920
		921	=item L<IO::Lambda>
		922
		923	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		924
		925	=back
414		926
415	=cut	927	=cut
416		928
417	package AnyEvent;	929	package AnyEvent;
418		930
419	no warnings;	931	no warnings;
420	use strict;	932	use strict qw(vars subs);
421		933
422	use Carp;	934	use Carp;
423		935
424	our $VERSION = '3.12';	936	our $VERSION = 4.41;
425	our $MODEL;	937	our $MODEL;
426		938
427	our $AUTOLOAD;	939	our $AUTOLOAD;
428	our @ISA;	940	our @ISA;
429		941
		942	our @REGISTRY;
		943
		944	our $WIN32;
		945
		946	BEGIN {
		947	my $win32 = ! ! ($^O =~ /mswin32/i);
		948	eval "sub WIN32(){ $win32 }";
		949	}
		950
430	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	951	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
431		952
432	our @REGISTRY;	953	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		954
		955	{
		956	my $idx;
		957	$PROTOCOL{$_} = ++$idx
		958	for reverse split /\s*,\s*/,
		959	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		960	}
433		961
434	my @models = (	962	my @models = (
435	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
436	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
437	[EV:: => AnyEvent::Impl::EV::],	963	[EV:: => AnyEvent::Impl::EV::],
438	[Event:: => AnyEvent::Impl::Event::],	964	[Event:: => AnyEvent::Impl::Event::],
439	[Glib:: => AnyEvent::Impl::Glib::],
440	[Tk:: => AnyEvent::Impl::Tk::],
441	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	965	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		966	# everything below here will not be autoprobed
		967	# as the pureperl backend should work everywhere
		968	# and is usually faster
		969	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		970	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
442	[Event::Lib:: => AnyEvent::Impl::EventLib::],	971	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		972	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		973	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		974	[Wx:: => AnyEvent::Impl::POE::],
		975	[Prima:: => AnyEvent::Impl::POE::],
443	);	976	);
444		977
445	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	978	our %method = map +($_ => 1),
		979	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
		980
		981	our @post_detect;
		982
		983	sub post_detect(&) {
		984	my ($cb) = @_;
		985
		986	if ($MODEL) {
		987	$cb->();
		988
		989	1
		990	} else {
		991	push @post_detect, $cb;
		992
		993	defined wantarray
		994	? bless \$cb, "AnyEvent::Util::postdetect"
		995	: ()
		996	}
		997	}
		998
		999	sub AnyEvent::Util::postdetect::DESTROY {
		1000	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1001	}
446		1002
447	sub detect() {	1003	sub detect() {
448	unless ($MODEL) {	1004	unless ($MODEL) {
449	no strict 'refs';	1005	no strict 'refs';
		1006	local $SIG{__DIE__};
450		1007
451	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {	1008	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
452	my $model = "AnyEvent::Impl::$1";	1009	my $model = "AnyEvent::Impl::$1";
453	if (eval "require $model") {	1010	if (eval "require $model") {
454	$MODEL = $model;	1011	$MODEL = $model;
455	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;	1012	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		1013	} else {
		1014	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
456	}	1015	}
457	}	1016	}
458		1017
459	# check for already loaded models	1018	# check for already loaded models
460	unless ($MODEL) {	1019	unless ($MODEL) {
…		…
482	last;	1041	last;
483	}	1042	}
484	}	1043	}
485		1044
486	$MODEL	1045	$MODEL
487	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";	1046	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
488	}	1047	}
489	}	1048	}
490		1049
		1050	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		1051
491	unshift @ISA, $MODEL;	1052	unshift @ISA, $MODEL;
492	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	1053
		1054	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1055
		1056	(shift @post_detect)->() while @post_detect;
493	}	1057	}
494		1058
495	$MODEL	1059	$MODEL
496	}	1060	}
497		1061
…		…
505		1069
506	my $class = shift;	1070	my $class = shift;
507	$class->$func (@_);	1071	$class->$func (@_);
508	}	1072	}
509		1073
		1074	# utility function to dup a filehandle. this is used by many backends
		1075	# to support binding more than one watcher per filehandle (they usually
		1076	# allow only one watcher per fd, so we dup it to get a different one).
		1077	sub _dupfh($$$$) {
		1078	my ($poll, $fh, $r, $w) = @_;
		1079
		1080	# cygwin requires the fh mode to be matching, unix doesn't
		1081	my ($rw, $mode) = $poll eq "r" ? ($r, "<")
		1082	: $poll eq "w" ? ($w, ">")
		1083	: Carp::croak "AnyEvent->io requires poll set to either 'r' or 'w'";
		1084
		1085	open my $fh2, "$mode&" . fileno $fh
		1086	or die "cannot dup() filehandle: $!,";
		1087
		1088	# we assume CLOEXEC is already set by perl in all important cases
		1089
		1090	($fh2, $rw)
		1091	}
		1092
510	package AnyEvent::Base;	1093	package AnyEvent::Base;
511		1094
		1095	# default implementations for many methods
		1096
		1097	BEGIN {
		1098	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1099	*_time = \&Time::HiRes::time;
		1100	# if (eval "use POSIX (); (POSIX::times())...
		1101	} else {
		1102	*_time = sub { time }; # epic fail
		1103	}
		1104	}
		1105
		1106	sub time { _time }
		1107	sub now { _time }
		1108	sub now_update { }
		1109
512	# default implementation for ->condvar, ->wait, ->broadcast	1110	# default implementation for ->condvar
513		1111
514	sub condvar {	1112	sub condvar {
515	bless \my $flag, "AnyEvent::Base::CondVar"	1113	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
516	}
517
518	sub AnyEvent::Base::CondVar::broadcast {
519	${$_[0]}++;
520	}
521
522	sub AnyEvent::Base::CondVar::wait {
523	AnyEvent->one_event while !${$_[0]};
524	}	1114	}
525		1115
526	# default implementation for ->signal	1116	# default implementation for ->signal
527		1117
528	our %SIG_CB;	1118	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1119
		1120	sub _signal_exec {
		1121	sysread $SIGPIPE_R, my $dummy, 4;
		1122
		1123	while (%SIG_EV) {
		1124	for (keys %SIG_EV) {
		1125	delete $SIG_EV{$_};
		1126	$_->() for values %{ $SIG_CB{$_} || {} };
		1127	}
		1128	}
		1129	}
529		1130
530	sub signal {	1131	sub signal {
531	my (undef, %arg) = @_;	1132	my (undef, %arg) = @_;
532		1133
		1134	unless ($SIGPIPE_R) {
		1135	require Fcntl;
		1136
		1137	if (AnyEvent::WIN32) {
		1138	require AnyEvent::Util;
		1139
		1140	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1141	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1142	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1143	} else {
		1144	pipe $SIGPIPE_R, $SIGPIPE_W;
		1145	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1146	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1147
		1148	# not strictly required, as $^F is normally 2, but let's make sure...
		1149	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1150	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1151	}
		1152
		1153	$SIGPIPE_R
		1154	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1155
		1156	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1157	}
		1158
533	my $signal = uc $arg{signal}	1159	my $signal = uc $arg{signal}
534	or Carp::croak "required option 'signal' is missing";	1160	or Carp::croak "required option 'signal' is missing";
535		1161
536	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1162	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
537	$SIG{$signal} ||= sub {	1163	$SIG{$signal} ||= sub {
538	$_->() for values %{ $SIG_CB{$signal} || {} };	1164	local $!;
		1165	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1166	undef $SIG_EV{$signal};
539	};	1167	};
540		1168
541	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1169	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
542	}	1170	}
543		1171
544	sub AnyEvent::Base::Signal::DESTROY {	1172	sub AnyEvent::Base::signal::DESTROY {
545	my ($signal, $cb) = @{$_[0]};	1173	my ($signal, $cb) = @{$_[0]};
546		1174
547	delete $SIG_CB{$signal}{$cb};	1175	delete $SIG_CB{$signal}{$cb};
548		1176
		1177	# delete doesn't work with older perls - they then
		1178	# print weird messages, or just unconditionally exit
		1179	# instead of getting the default action.
549	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1180	undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
550	}	1181	}
551		1182
552	# default implementation for ->child	1183	# default implementation for ->child
553		1184
554	our %PID_CB;	1185	our %PID_CB;
555	our $CHLD_W;	1186	our $CHLD_W;
556	our $CHLD_DELAY_W;	1187	our $CHLD_DELAY_W;
557	our $PID_IDLE;
558	our $WNOHANG;	1188	our $WNOHANG;
559		1189
560	sub _child_wait {	1190	sub _sigchld {
561	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	1191	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
562	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1192	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
563	(values %{ $PID_CB{0} || {} });	1193	(values %{ $PID_CB{0} || {} });
564	}	1194	}
565
566	undef $PID_IDLE;
567	}
568
569	sub _sigchld {
570	# make sure we deliver these changes "synchronous" with the event loop.
571	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
572	undef $CHLD_DELAY_W;
573	&_child_wait;
574	});
575	}	1195	}
576		1196
577	sub child {	1197	sub child {
578	my (undef, %arg) = @_;	1198	my (undef, %arg) = @_;
579		1199
580	defined (my $pid = $arg{pid} + 0)	1200	defined (my $pid = $arg{pid} + 0)
581	or Carp::croak "required option 'pid' is missing";	1201	or Carp::croak "required option 'pid' is missing";
582		1202
583	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1203	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
584		1204
585	unless ($WNOHANG) {
586	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1205	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
587	}
588		1206
589	unless ($CHLD_W) {	1207	unless ($CHLD_W) {
590	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1208	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
591	# child could be a zombie already, so make at least one round	1209	# child could be a zombie already, so make at least one round
592	&_sigchld;	1210	&_sigchld;
593	}	1211	}
594		1212
595	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1213	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
596	}	1214	}
597		1215
598	sub AnyEvent::Base::Child::DESTROY {	1216	sub AnyEvent::Base::child::DESTROY {
599	my ($pid, $cb) = @{$_[0]};	1217	my ($pid, $cb) = @{$_[0]};
600		1218
601	delete $PID_CB{$pid}{$cb};	1219	delete $PID_CB{$pid}{$cb};
602	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1220	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
603		1221
604	undef $CHLD_W unless keys %PID_CB;	1222	undef $CHLD_W unless keys %PID_CB;
605	}	1223	}
		1224
		1225	# idle emulation is done by simply using a timer, regardless
		1226	# of whether the process is idle or not, and not letting
		1227	# the callback use more than 50% of the time.
		1228	sub idle {
		1229	my (undef, %arg) = @_;
		1230
		1231	my ($cb, $w, $rcb) = $arg{cb};
		1232
		1233	$rcb = sub {
		1234	if ($cb) {
		1235	$w = _time;
		1236	&$cb;
		1237	$w = _time - $w;
		1238
		1239	# never use more then 50% of the time for the idle watcher,
		1240	# within some limits
		1241	$w = 0.0001 if $w < 0.0001;
		1242	$w = 5 if $w > 5;
		1243
		1244	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1245	} else {
		1246	# clean up...
		1247	undef $w;
		1248	undef $rcb;
		1249	}
		1250	};
		1251
		1252	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1253
		1254	bless \\$cb, "AnyEvent::Base::idle"
		1255	}
		1256
		1257	sub AnyEvent::Base::idle::DESTROY {
		1258	undef $${$_[0]};
		1259	}
		1260
		1261	package AnyEvent::CondVar;
		1262
		1263	our @ISA = AnyEvent::CondVar::Base::;
		1264
		1265	package AnyEvent::CondVar::Base;
		1266
		1267	use overload
		1268	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1269	fallback => 1;
		1270
		1271	sub _send {
		1272	# nop
		1273	}
		1274
		1275	sub send {
		1276	my $cv = shift;
		1277	$cv->{_ae_sent} = [@_];
		1278	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1279	$cv->_send;
		1280	}
		1281
		1282	sub croak {
		1283	$_[0]{_ae_croak} = $_[1];
		1284	$_[0]->send;
		1285	}
		1286
		1287	sub ready {
		1288	$_[0]{_ae_sent}
		1289	}
		1290
		1291	sub _wait {
		1292	AnyEvent->one_event while !$_[0]{_ae_sent};
		1293	}
		1294
		1295	sub recv {
		1296	$_[0]->_wait;
		1297
		1298	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1299	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1300	}
		1301
		1302	sub cb {
		1303	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1304	$_[0]{_ae_cb}
		1305	}
		1306
		1307	sub begin {
		1308	++$_[0]{_ae_counter};
		1309	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1310	}
		1311
		1312	sub end {
		1313	return if --$_[0]{_ae_counter};
		1314	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1315	}
		1316
		1317	# undocumented/compatibility with pre-3.4
		1318	*broadcast = \&send;
		1319	*wait = \&_wait;
		1320
		1321	=head1 ERROR AND EXCEPTION HANDLING
		1322
		1323	In general, AnyEvent does not do any error handling - it relies on the
		1324	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1325	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1326	checking of all AnyEvent methods, however, which is highly useful during
		1327	development.
		1328
		1329	As for exception handling (i.e. runtime errors and exceptions thrown while
		1330	executing a callback), this is not only highly event-loop specific, but
		1331	also not in any way wrapped by this module, as this is the job of the main
		1332	program.
		1333
		1334	The pure perl event loop simply re-throws the exception (usually
		1335	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1336	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1337	so on.
		1338
		1339	=head1 ENVIRONMENT VARIABLES
		1340
		1341	The following environment variables are used by this module or its
		1342	submodules:
		1343
		1344	=over 4
		1345
		1346	=item C<PERL_ANYEVENT_VERBOSE>
		1347
		1348	By default, AnyEvent will be completely silent except in fatal
		1349	conditions. You can set this environment variable to make AnyEvent more
		1350	talkative.
		1351
		1352	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1353	conditions, such as not being able to load the event model specified by
		1354	C<PERL_ANYEVENT_MODEL>.
		1355
		1356	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1357	model it chooses.
		1358
		1359	=item C<PERL_ANYEVENT_STRICT>
		1360
		1361	AnyEvent does not do much argument checking by default, as thorough
		1362	argument checking is very costly. Setting this variable to a true value
		1363	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1364	check the arguments passed to most method calls. If it finds any problems
		1365	it will croak.
		1366
		1367	In other words, enables "strict" mode.
		1368
		1369	Unlike C<use strict>, it is definitely recommended ot keep it off in
		1370	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1371	developing programs can be very useful, however.
		1372
		1373	=item C<PERL_ANYEVENT_MODEL>
		1374
		1375	This can be used to specify the event model to be used by AnyEvent, before
		1376	auto detection and -probing kicks in. It must be a string consisting
		1377	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1378	and the resulting module name is loaded and if the load was successful,
		1379	used as event model. If it fails to load AnyEvent will proceed with
		1380	auto detection and -probing.
		1381
		1382	This functionality might change in future versions.
		1383
		1384	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1385	could start your program like this:
		1386
		1387	PERL_ANYEVENT_MODEL=Perl perl ...
		1388
		1389	=item C<PERL_ANYEVENT_PROTOCOLS>
		1390
		1391	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1392	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1393	of auto probing).
		1394
		1395	Must be set to a comma-separated list of protocols or address families,
		1396	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1397	used, and preference will be given to protocols mentioned earlier in the
		1398	list.
		1399
		1400	This variable can effectively be used for denial-of-service attacks
		1401	against local programs (e.g. when setuid), although the impact is likely
		1402	small, as the program has to handle conenction and other failures anyways.
		1403
		1404	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1405	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1406	- only support IPv4, never try to resolve or contact IPv6
		1407	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1408	IPv6, but prefer IPv6 over IPv4.
		1409
		1410	=item C<PERL_ANYEVENT_EDNS0>
		1411
		1412	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1413	for DNS. This extension is generally useful to reduce DNS traffic, but
		1414	some (broken) firewalls drop such DNS packets, which is why it is off by
		1415	default.
		1416
		1417	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1418	EDNS0 in its DNS requests.
		1419
		1420	=item C<PERL_ANYEVENT_MAX_FORKS>
		1421
		1422	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1423	will create in parallel.
		1424
		1425	=back
606		1426
607	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1427	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
608		1428
609	This is an advanced topic that you do not normally need to use AnyEvent in	1429	This is an advanced topic that you do not normally need to use AnyEvent in
610	a module. This section is only of use to event loop authors who want to	1430	a module. This section is only of use to event loop authors who want to
…		…
645	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1465	I<rxvt-unicode> also cheats a bit by not providing blocking access to
646	condition variables: code blocking while waiting for a condition will	1466	condition variables: code blocking while waiting for a condition will
647	C<die>. This still works with most modules/usages, and blocking calls must	1467	C<die>. This still works with most modules/usages, and blocking calls must
648	not be done in an interactive application, so it makes sense.	1468	not be done in an interactive application, so it makes sense.
649		1469
650	=head1 ENVIRONMENT VARIABLES
651
652	The following environment variables are used by this module:
653
654	=over 4
655
656	=item C<PERL_ANYEVENT_VERBOSE>
657
658	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
659	model it chooses.
660
661	=item C<PERL_ANYEVENT_MODEL>
662
663	This can be used to specify the event model to be used by AnyEvent, before
664	autodetection and -probing kicks in. It must be a string consisting
665	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
666	and the resulting module name is loaded and if the load was successful,
667	used as event model. If it fails to load AnyEvent will proceed with
668	autodetection and -probing.
669
670	This functionality might change in future versions.
671
672	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
673	could start your program like this:
674
675	PERL_ANYEVENT_MODEL=Perl perl ...
676
677	=back
678
679	=head1 EXAMPLE PROGRAM	1470	=head1 EXAMPLE PROGRAM
680		1471
681	The following program uses an IO watcher to read data from STDIN, a timer	1472	The following program uses an I/O watcher to read data from STDIN, a timer
682	to display a message once per second, and a condition variable to quit the	1473	to display a message once per second, and a condition variable to quit the
683	program when the user enters quit:	1474	program when the user enters quit:
684		1475
685	use AnyEvent;	1476	use AnyEvent;
686		1477
…		…
691	poll => 'r',	1482	poll => 'r',
692	cb => sub {	1483	cb => sub {
693	warn "io event <$_[0]>\n"; # will always output <r>	1484	warn "io event <$_[0]>\n"; # will always output <r>
694	chomp (my $input = <STDIN>); # read a line	1485	chomp (my $input = <STDIN>); # read a line
695	warn "read: $input\n"; # output what has been read	1486	warn "read: $input\n"; # output what has been read
696	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1487	$cv->send if $input =~ /^q/i; # quit program if /^q/i
697	},	1488	},
698	);	1489	);
699		1490
700	my $time_watcher; # can only be used once	1491	my $time_watcher; # can only be used once
701		1492
…		…
706	});	1497	});
707	}	1498	}
708		1499
709	new_timer; # create first timer	1500	new_timer; # create first timer
710		1501
711	$cv->wait; # wait until user enters /^q/i	1502	$cv->recv; # wait until user enters /^q/i
712		1503
713	=head1 REAL-WORLD EXAMPLE	1504	=head1 REAL-WORLD EXAMPLE
714		1505
715	Consider the L<Net::FCP> module. It features (among others) the following	1506	Consider the L<Net::FCP> module. It features (among others) the following
716	API calls, which are to freenet what HTTP GET requests are to http:	1507	API calls, which are to freenet what HTTP GET requests are to http:
…		…
766	syswrite $txn->{fh}, $txn->{request}	1557	syswrite $txn->{fh}, $txn->{request}
767	or die "connection or write error";	1558	or die "connection or write error";
768	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1559	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
769		1560
770	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1561	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
771	result and signals any possible waiters that the request ahs finished:	1562	result and signals any possible waiters that the request has finished:
772		1563
773	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1564	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
774		1565
775	if (end-of-file or data complete) {	1566	if (end-of-file or data complete) {
776	$txn->{result} = $txn->{buf};	1567	$txn->{result} = $txn->{buf};
777	$txn->{finished}->broadcast;	1568	$txn->{finished}->send;
778	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1569	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
779	}	1570	}
780		1571
781	The C<result> method, finally, just waits for the finished signal (if the	1572	The C<result> method, finally, just waits for the finished signal (if the
782	request was already finished, it doesn't wait, of course, and returns the	1573	request was already finished, it doesn't wait, of course, and returns the
783	data:	1574	data:
784		1575
785	$txn->{finished}->wait;	1576	$txn->{finished}->recv;
786	return $txn->{result};	1577	return $txn->{result};
787		1578
788	The actual code goes further and collects all errors (C<die>s, exceptions)	1579	The actual code goes further and collects all errors (C<die>s, exceptions)
789	that occured during request processing. The C<result> method detects	1580	that occurred during request processing. The C<result> method detects
790	whether an exception as thrown (it is stored inside the $txn object)	1581	whether an exception as thrown (it is stored inside the $txn object)
791	and just throws the exception, which means connection errors and other	1582	and just throws the exception, which means connection errors and other
792	problems get reported tot he code that tries to use the result, not in a	1583	problems get reported tot he code that tries to use the result, not in a
793	random callback.	1584	random callback.
794		1585
…		…
825		1616
826	my $quit = AnyEvent->condvar;	1617	my $quit = AnyEvent->condvar;
827		1618
828	$fcp->txn_client_get ($url)->cb (sub {	1619	$fcp->txn_client_get ($url)->cb (sub {
829	...	1620	...
830	$quit->broadcast;	1621	$quit->send;
831	});	1622	});
832		1623
833	$quit->wait;	1624	$quit->recv;
		1625
		1626
		1627	=head1 BENCHMARKS
		1628
		1629	To give you an idea of the performance and overheads that AnyEvent adds
		1630	over the event loops themselves and to give you an impression of the speed
		1631	of various event loops I prepared some benchmarks.
		1632
		1633	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1634
		1635	Here is a benchmark of various supported event models used natively and
		1636	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1637	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1638	which it is), lets them fire exactly once and destroys them again.
		1639
		1640	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1641	distribution.
		1642
		1643	=head3 Explanation of the columns
		1644
		1645	I<watcher> is the number of event watchers created/destroyed. Since
		1646	different event models feature vastly different performances, each event
		1647	loop was given a number of watchers so that overall runtime is acceptable
		1648	and similar between tested event loop (and keep them from crashing): Glib
		1649	would probably take thousands of years if asked to process the same number
		1650	of watchers as EV in this benchmark.
		1651
		1652	I<bytes> is the number of bytes (as measured by the resident set size,
		1653	RSS) consumed by each watcher. This method of measuring captures both C
		1654	and Perl-based overheads.
		1655
		1656	I<create> is the time, in microseconds (millionths of seconds), that it
		1657	takes to create a single watcher. The callback is a closure shared between
		1658	all watchers, to avoid adding memory overhead. That means closure creation
		1659	and memory usage is not included in the figures.
		1660
		1661	I<invoke> is the time, in microseconds, used to invoke a simple
		1662	callback. The callback simply counts down a Perl variable and after it was
		1663	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1664	signal the end of this phase.
		1665
		1666	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1667	watcher.
		1668
		1669	=head3 Results
		1670
		1671	name watchers bytes create invoke destroy comment
		1672	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1673	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1674	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1675	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1676	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1677	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1678	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1679	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1680	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1681	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1682
		1683	=head3 Discussion
		1684
		1685	The benchmark does I<not> measure scalability of the event loop very
		1686	well. For example, a select-based event loop (such as the pure perl one)
		1687	can never compete with an event loop that uses epoll when the number of
		1688	file descriptors grows high. In this benchmark, all events become ready at
		1689	the same time, so select/poll-based implementations get an unnatural speed
		1690	boost.
		1691
		1692	Also, note that the number of watchers usually has a nonlinear effect on
		1693	overall speed, that is, creating twice as many watchers doesn't take twice
		1694	the time - usually it takes longer. This puts event loops tested with a
		1695	higher number of watchers at a disadvantage.
		1696
		1697	To put the range of results into perspective, consider that on the
		1698	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1699	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1700	cycles with POE.
		1701
		1702	C<EV> is the sole leader regarding speed and memory use, which are both
		1703	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1704	far less memory than any other event loop and is still faster than Event
		1705	natively.
		1706
		1707	The pure perl implementation is hit in a few sweet spots (both the
		1708	constant timeout and the use of a single fd hit optimisations in the perl
		1709	interpreter and the backend itself). Nevertheless this shows that it
		1710	adds very little overhead in itself. Like any select-based backend its
		1711	performance becomes really bad with lots of file descriptors (and few of
		1712	them active), of course, but this was not subject of this benchmark.
		1713
		1714	The C<Event> module has a relatively high setup and callback invocation
		1715	cost, but overall scores in on the third place.
		1716
		1717	C<Glib>'s memory usage is quite a bit higher, but it features a
		1718	faster callback invocation and overall ends up in the same class as
		1719	C<Event>. However, Glib scales extremely badly, doubling the number of
		1720	watchers increases the processing time by more than a factor of four,
		1721	making it completely unusable when using larger numbers of watchers
		1722	(note that only a single file descriptor was used in the benchmark, so
		1723	inefficiencies of C<poll> do not account for this).
		1724
		1725	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1726	more than 2000 watchers is a big setback, however, as correctness takes
		1727	precedence over speed. Nevertheless, its performance is surprising, as the
		1728	file descriptor is dup()ed for each watcher. This shows that the dup()
		1729	employed by some adaptors is not a big performance issue (it does incur a
		1730	hidden memory cost inside the kernel which is not reflected in the figures
		1731	above).
		1732
		1733	C<POE>, regardless of underlying event loop (whether using its pure perl
		1734	select-based backend or the Event module, the POE-EV backend couldn't
		1735	be tested because it wasn't working) shows abysmal performance and
		1736	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1737	as EV watchers, and 10 times as much memory as Event (the high memory
		1738	requirements are caused by requiring a session for each watcher). Watcher
		1739	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1740	implementation.
		1741
		1742	The design of the POE adaptor class in AnyEvent can not really account
		1743	for the performance issues, though, as session creation overhead is
		1744	small compared to execution of the state machine, which is coded pretty
		1745	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1746	using multiple sessions is not a good approach, especially regarding
		1747	memory usage, even the author of POE could not come up with a faster
		1748	design).
		1749
		1750	=head3 Summary
		1751
		1752	=over 4
		1753
		1754	=item * Using EV through AnyEvent is faster than any other event loop
		1755	(even when used without AnyEvent), but most event loops have acceptable
		1756	performance with or without AnyEvent.
		1757
		1758	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1759	the actual event loop, only with extremely fast event loops such as EV
		1760	adds AnyEvent significant overhead.
		1761
		1762	=item * You should avoid POE like the plague if you want performance or
		1763	reasonable memory usage.
		1764
		1765	=back
		1766
		1767	=head2 BENCHMARKING THE LARGE SERVER CASE
		1768
		1769	This benchmark actually benchmarks the event loop itself. It works by
		1770	creating a number of "servers": each server consists of a socket pair, a
		1771	timeout watcher that gets reset on activity (but never fires), and an I/O
		1772	watcher waiting for input on one side of the socket. Each time the socket
		1773	watcher reads a byte it will write that byte to a random other "server".
		1774
		1775	The effect is that there will be a lot of I/O watchers, only part of which
		1776	are active at any one point (so there is a constant number of active
		1777	fds for each loop iteration, but which fds these are is random). The
		1778	timeout is reset each time something is read because that reflects how
		1779	most timeouts work (and puts extra pressure on the event loops).
		1780
		1781	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1782	(1%) are active. This mirrors the activity of large servers with many
		1783	connections, most of which are idle at any one point in time.
		1784
		1785	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1786	distribution.
		1787
		1788	=head3 Explanation of the columns
		1789
		1790	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1791	each server has a read and write socket end).
		1792
		1793	I<create> is the time it takes to create a socket pair (which is
		1794	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1795
		1796	I<request>, the most important value, is the time it takes to handle a
		1797	single "request", that is, reading the token from the pipe and forwarding
		1798	it to another server. This includes deleting the old timeout and creating
		1799	a new one that moves the timeout into the future.
		1800
		1801	=head3 Results
		1802
		1803	name sockets create request
		1804	EV 20000 69.01 11.16
		1805	Perl 20000 73.32 35.87
		1806	Event 20000 212.62 257.32
		1807	Glib 20000 651.16 1896.30
		1808	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1809
		1810	=head3 Discussion
		1811
		1812	This benchmark I<does> measure scalability and overall performance of the
		1813	particular event loop.
		1814
		1815	EV is again fastest. Since it is using epoll on my system, the setup time
		1816	is relatively high, though.
		1817
		1818	Perl surprisingly comes second. It is much faster than the C-based event
		1819	loops Event and Glib.
		1820
		1821	Event suffers from high setup time as well (look at its code and you will
		1822	understand why). Callback invocation also has a high overhead compared to
		1823	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1824	uses select or poll in basically all documented configurations.
		1825
		1826	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1827	clearly fails to perform with many filehandles or in busy servers.
		1828
		1829	POE is still completely out of the picture, taking over 1000 times as long
		1830	as EV, and over 100 times as long as the Perl implementation, even though
		1831	it uses a C-based event loop in this case.
		1832
		1833	=head3 Summary
		1834
		1835	=over 4
		1836
		1837	=item * The pure perl implementation performs extremely well.
		1838
		1839	=item * Avoid Glib or POE in large projects where performance matters.
		1840
		1841	=back
		1842
		1843	=head2 BENCHMARKING SMALL SERVERS
		1844
		1845	While event loops should scale (and select-based ones do not...) even to
		1846	large servers, most programs we (or I :) actually write have only a few
		1847	I/O watchers.
		1848
		1849	In this benchmark, I use the same benchmark program as in the large server
		1850	case, but it uses only eight "servers", of which three are active at any
		1851	one time. This should reflect performance for a small server relatively
		1852	well.
		1853
		1854	The columns are identical to the previous table.
		1855
		1856	=head3 Results
		1857
		1858	name sockets create request
		1859	EV 16 20.00 6.54
		1860	Perl 16 25.75 12.62
		1861	Event 16 81.27 35.86
		1862	Glib 16 32.63 15.48
		1863	POE 16 261.87 276.28 uses POE::Loop::Event
		1864
		1865	=head3 Discussion
		1866
		1867	The benchmark tries to test the performance of a typical small
		1868	server. While knowing how various event loops perform is interesting, keep
		1869	in mind that their overhead in this case is usually not as important, due
		1870	to the small absolute number of watchers (that is, you need efficiency and
		1871	speed most when you have lots of watchers, not when you only have a few of
		1872	them).
		1873
		1874	EV is again fastest.
		1875
		1876	Perl again comes second. It is noticeably faster than the C-based event
		1877	loops Event and Glib, although the difference is too small to really
		1878	matter.
		1879
		1880	POE also performs much better in this case, but is is still far behind the
		1881	others.
		1882
		1883	=head3 Summary
		1884
		1885	=over 4
		1886
		1887	=item * C-based event loops perform very well with small number of
		1888	watchers, as the management overhead dominates.
		1889
		1890	=back
		1891
		1892
		1893	=head1 SIGNALS
		1894
		1895	AnyEvent currently installs handlers for these signals:
		1896
		1897	=over 4
		1898
		1899	=item SIGCHLD
		1900
		1901	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		1902	emulation for event loops that do not support them natively. Also, some
		1903	event loops install a similar handler.
		1904
		1905	=item SIGPIPE
		1906
		1907	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		1908	when AnyEvent gets loaded.
		1909
		1910	The rationale for this is that AnyEvent users usually do not really depend
		1911	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		1912	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		1913	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		1914	some random socket.
		1915
		1916	The rationale for installing a no-op handler as opposed to ignoring it is
		1917	that this way, the handler will be restored to defaults on exec.
		1918
		1919	Feel free to install your own handler, or reset it to defaults.
		1920
		1921	=back
		1922
		1923	=cut
		1924
		1925	$SIG{PIPE} = sub { }
		1926	unless defined $SIG{PIPE};
		1927
834		1928
835	=head1 FORK	1929	=head1 FORK
836		1930
837	Most event libraries are not fork-safe. The ones who are usually are	1931	Most event libraries are not fork-safe. The ones who are usually are
838	because they are so inefficient. Only L<EV> is fully fork-aware.	1932	because they rely on inefficient but fork-safe C<select> or C<poll>
		1933	calls. Only L<EV> is fully fork-aware.
839		1934
840	If you have to fork, you must either do so I<before> creating your first	1935	If you have to fork, you must either do so I<before> creating your first
841	watcher OR you must not use AnyEvent at all in the child.	1936	watcher OR you must not use AnyEvent at all in the child.
		1937
842		1938
843	=head1 SECURITY CONSIDERATIONS	1939	=head1 SECURITY CONSIDERATIONS
844		1940
845	AnyEvent can be forced to load any event model via	1941	AnyEvent can be forced to load any event model via
846	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to	1942	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
…		…
850	specified in the variable.	1946	specified in the variable.
851		1947
852	You can make AnyEvent completely ignore this variable by deleting it	1948	You can make AnyEvent completely ignore this variable by deleting it
853	before the first watcher gets created, e.g. with a C<BEGIN> block:	1949	before the first watcher gets created, e.g. with a C<BEGIN> block:
854		1950
855	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1951	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
856		1952
857	use AnyEvent;	1953	use AnyEvent;
		1954
		1955	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1956	be used to probe what backend is used and gain other information (which is
		1957	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		1958	$ENV{PERL_ANYEGENT_STRICT}.
		1959
		1960
		1961	=head1 BUGS
		1962
		1963	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		1964	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		1965	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		1966	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		1967	pronounced).
		1968
858		1969
859	=head1 SEE ALSO	1970	=head1 SEE ALSO
860		1971
861	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1972	Utility functions: L<AnyEvent::Util>.
862	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
863	L<Event::Lib>.
864		1973
865	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1974	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
866	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,	1975	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
867	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>.
868		1976
		1977	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1978	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1979	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1980	L<AnyEvent::Impl::POE>.
		1981
		1982	Non-blocking file handles, sockets, TCP clients and
		1983	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1984
		1985	Asynchronous DNS: L<AnyEvent::DNS>.
		1986
		1987	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1988
869	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1989	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1990
870		1991
871	=head1 AUTHOR	1992	=head1 AUTHOR
872		1993
873	Marc Lehmann <schmorp@schmorp.de>	1994	Marc Lehmann <schmorp@schmorp.de>
874	http://home.schmorp.de/	1995	http://home.schmorp.de/
875		1996
876	=cut	1997	=cut
877		1998
878	1	1999	1
879		2000

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