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Revision 1.232 by root, Thu Jul 9 01:08:22 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 - 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> (or a naked file descriptor) to watch
		182	for events (AnyEvent might or might not keep a reference to this file
		183	handle). Note that only file handles pointing to things for which
		184	non-blocking operation makes sense are allowed. This includes sockets,
		185	most character devices, pipes, fifos and so on, but not for example files
		186	or block devices.
		187
145	events. C<poll> must be a string that is either C<r> or C<w>, which	188	C<poll> must be a string that is either C<r> or C<w>, which creates a
146	creates a watcher waiting for "r"eadable or "w"ritable events,	189	watcher waiting for "r"eadable or "w"ritable events, respectively.
		190
147	respectively. C<cb> is the callback to invoke each time the file handle	191	C<cb> is the callback to invoke each time the file handle becomes ready.
148	becomes ready.
149		192
150	File handles will be kept alive, so as long as the watcher exists, the	193	Although the callback might get passed parameters, their value and
151	file handle exists, too.	194	presence is undefined and you cannot rely on them. Portable AnyEvent
		195	callbacks cannot use arguments passed to I/O watcher callbacks.
152		196
		197	The I/O watcher might use the underlying file descriptor or a copy of it.
153	It is not allowed to close a file handle as long as any watcher is active	198	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	199	underlying file descriptor.
155		200
156	Some event loops issue spurious readyness notifications, so you should	201	Some event loops issue spurious readyness notifications, so you should
157	always use non-blocking calls when reading/writing from/to your file	202	always use non-blocking calls when reading/writing from/to your file
158	handles.	203	handles.
159		204
160	Example:
161
162	# wait for readability of STDIN, then read a line and disable the watcher	205	Example: wait for readability of STDIN, then read a line and disable the
		206	watcher.
		207
163	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	208	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
164	chomp (my $input = <STDIN>);	209	chomp (my $input = <STDIN>);
165	warn "read: $input\n";	210	warn "read: $input\n";
166	undef $w;	211	undef $w;
167	});	212	});
…		…
170		215
171	You can create a time watcher by calling the C<< AnyEvent->timer >>	216	You can create a time watcher by calling the C<< AnyEvent->timer >>
172	method with the following mandatory arguments:	217	method with the following mandatory arguments:
173		218
174	C<after> specifies after how many seconds (fractional values are	219	C<after> specifies after how many seconds (fractional values are
175	supported) should the timer activate. C<cb> the callback to invoke in that	220	supported) the callback should be invoked. C<cb> is the callback to invoke
176	case.	221	in that case.
177		222
178	The timer callback will be invoked at most once: if you want a repeating	223	Although the callback might get passed parameters, their value and
179	timer you have to create a new watcher (this is a limitation by both Tk	224	presence is undefined and you cannot rely on them. Portable AnyEvent
180	and Glib).	225	callbacks cannot use arguments passed to time watcher callbacks.
181		226
182	Example:	227	The callback will normally be invoked once only. If you specify another
		228	parameter, C<interval>, as a strictly positive number (> 0), then the
		229	callback will be invoked regularly at that interval (in fractional
		230	seconds) after the first invocation. If C<interval> is specified with a
		231	false value, then it is treated as if it were missing.
183		232
		233	The callback will be rescheduled before invoking the callback, but no
		234	attempt is done to avoid timer drift in most backends, so the interval is
		235	only approximate.
		236
184	# fire an event after 7.7 seconds	237	Example: fire an event after 7.7 seconds.
		238
185	my $w = AnyEvent->timer (after => 7.7, cb => sub {	239	my $w = AnyEvent->timer (after => 7.7, cb => sub {
186	warn "timeout\n";	240	warn "timeout\n";
187	});	241	});
188		242
189	# to cancel the timer:	243	# to cancel the timer:
190	undef $w;	244	undef $w;
191		245
192	Example 2:
193
194	# fire an event after 0.5 seconds, then roughly every second	246	Example 2: fire an event after 0.5 seconds, then roughly every second.
195	my $w;
196		247
197	my $cb = sub {
198	# cancel the old timer while creating a new one
199	$w = AnyEvent->timer (after => 1, cb => $cb);	248	my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
		249	warn "timeout\n";
200	};	250	};
201
202	# start the "loop" by creating the first watcher
203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
204		251
205	=head3 TIMING ISSUES	252	=head3 TIMING ISSUES
206		253
207	There are two ways to handle timers: based on real time (relative, "fire	254	There are two ways to handle timers: based on real time (relative, "fire
208	in 10 seconds") and based on wallclock time (absolute, "fire at 12	255	in 10 seconds") and based on wallclock time (absolute, "fire at 12
209	o'clock").	256	o'clock").
210		257
211	While most event loops expect timers to specified in a relative way, they use	258	While most event loops expect timers to specified in a relative way, they
212	absolute time internally. This makes a difference when your clock "jumps",	259	use absolute time internally. This makes a difference when your clock
213	for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to	260	"jumps", for example, when ntp decides to set your clock backwards from
214	2008-01-01, a watcher that you created to fire "after" a second might actually take	261	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	262	fire "after" a second might actually take six years to finally fire.
216		263
217	AnyEvent cannot compensate for this. The only event loop that is conscious	264	AnyEvent cannot compensate for this. The only event loop that is conscious
218	about these issues is L<EV>, which offers both relative (ev_timer) and	265	about these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	266	on true relative time) and absolute (ev_periodic, based on wallclock time)
		267	timers.
220		268
221	AnyEvent always prefers relative timers, if available, matching the	269	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	270	AnyEvent API.
223		271
		272	AnyEvent has two additional methods that return the "current time":
		273
		274	=over 4
		275
		276	=item AnyEvent->time
		277
		278	This returns the "current wallclock time" as a fractional number of
		279	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		280	return, and the result is guaranteed to be compatible with those).
		281
		282	It progresses independently of any event loop processing, i.e. each call
		283	will check the system clock, which usually gets updated frequently.
		284
		285	=item AnyEvent->now
		286
		287	This also returns the "current wallclock time", but unlike C<time>, above,
		288	this value might change only once per event loop iteration, depending on
		289	the event loop (most return the same time as C<time>, above). This is the
		290	time that AnyEvent's timers get scheduled against.
		291
		292	I<In almost all cases (in all cases if you don't care), this is the
		293	function to call when you want to know the current time.>
		294
		295	This function is also often faster then C<< AnyEvent->time >>, and
		296	thus the preferred method if you want some timestamp (for example,
		297	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		298
		299	The rest of this section is only of relevance if you try to be very exact
		300	with your timing, you can skip it without bad conscience.
		301
		302	For a practical example of when these times differ, consider L<Event::Lib>
		303	and L<EV> and the following set-up:
		304
		305	The event loop is running and has just invoked one of your callback at
		306	time=500 (assume no other callbacks delay processing). In your callback,
		307	you wait a second by executing C<sleep 1> (blocking the process for a
		308	second) and then (at time=501) you create a relative timer that fires
		309	after three seconds.
		310
		311	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		312	both return C<501>, because that is the current time, and the timer will
		313	be scheduled to fire at time=504 (C<501> + C<3>).
		314
		315	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		316	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		317	last event processing phase started. With L<EV>, your timer gets scheduled
		318	to run at time=503 (C<500> + C<3>).
		319
		320	In one sense, L<Event::Lib> is more exact, as it uses the current time
		321	regardless of any delays introduced by event processing. However, most
		322	callbacks do not expect large delays in processing, so this causes a
		323	higher drift (and a lot more system calls to get the current time).
		324
		325	In another sense, L<EV> is more exact, as your timer will be scheduled at
		326	the same time, regardless of how long event processing actually took.
		327
		328	In either case, if you care (and in most cases, you don't), then you
		329	can get whatever behaviour you want with any event loop, by taking the
		330	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		331	account.
		332
		333	=item AnyEvent->now_update
		334
		335	Some event loops (such as L<EV> or L<AnyEvent::Impl::Perl>) cache
		336	the current time for each loop iteration (see the discussion of L<<
		337	AnyEvent->now >>, above).
		338
		339	When a callback runs for a long time (or when the process sleeps), then
		340	this "current" time will differ substantially from the real time, which
		341	might affect timers and time-outs.
		342
		343	When this is the case, you can call this method, which will update the
		344	event loop's idea of "current time".
		345
		346	Note that updating the time I<might> cause some events to be handled.
		347
		348	=back
		349
224	=head2 SIGNAL WATCHERS	350	=head2 SIGNAL WATCHERS
225		351
226	You can watch for signals using a signal watcher, C<signal> is the signal	352	You can watch for signals using a signal watcher, C<signal> is the signal
227	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to	353	I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
228	be invoked whenever a signal occurs.	354	callback to be invoked whenever a signal occurs.
229		355
		356	Although the callback might get passed parameters, their value and
		357	presence is undefined and you cannot rely on them. Portable AnyEvent
		358	callbacks cannot use arguments passed to signal watcher callbacks.
		359
230	Multiple signals occurances can be clumped together into one callback	360	Multiple signal occurrences can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	361	invocation, and callback invocation will be synchronous. Synchronous means
232	that it might take a while until the signal gets handled by the process,	362	that it might take a while until the signal gets handled by the process,
233	but it is guarenteed not to interrupt any other callbacks.	363	but it is guaranteed not to interrupt any other callbacks.
234		364
235	The main advantage of using these watchers is that you can share a signal	365	The main advantage of using these watchers is that you can share a signal
236	between multiple watchers.	366	between multiple watchers.
237		367
238	This watcher might use C<%SIG>, so programs overwriting those signals	368	This watcher might use C<%SIG>, so programs overwriting those signals
…		…
245	=head2 CHILD PROCESS WATCHERS	375	=head2 CHILD PROCESS WATCHERS
246		376
247	You can also watch on a child process exit and catch its exit status.	377	You can also watch on a child process exit and catch its exit status.
248		378
249	The child process is specified by the C<pid> argument (if set to C<0>, it	379	The child process is specified by the C<pid> argument (if set to C<0>, it
250	watches for any child process exit). The watcher will trigger as often	380	watches for any child process exit). The watcher will triggered only when
251	as status change for the child are received. This works by installing a	381	the child process has finished and an exit status is available, not on
252	signal handler for C<SIGCHLD>. The callback will be called with the pid	382	any trace events (stopped/continued).
253	and exit status (as returned by waitpid).
254		383
255	Example: wait for pid 1333	384	The callback will be called with the pid and exit status (as returned by
		385	waitpid), so unlike other watcher types, you I<can> rely on child watcher
		386	callback arguments.
256		387
		388	This watcher type works by installing a signal handler for C<SIGCHLD>,
		389	and since it cannot be shared, nothing else should use SIGCHLD or reap
		390	random child processes (waiting for specific child processes, e.g. inside
		391	C<system>, is just fine).
		392
		393	There is a slight catch to child watchers, however: you usually start them
		394	I<after> the child process was created, and this means the process could
		395	have exited already (and no SIGCHLD will be sent anymore).
		396
		397	Not all event models handle this correctly (neither POE nor IO::Async do,
		398	see their AnyEvent::Impl manpages for details), but even for event models
		399	that I<do> handle this correctly, they usually need to be loaded before
		400	the process exits (i.e. before you fork in the first place). AnyEvent's
		401	pure perl event loop handles all cases correctly regardless of when you
		402	start the watcher.
		403
		404	This means you cannot create a child watcher as the very first
		405	thing in an AnyEvent program, you I<have> to create at least one
		406	watcher before you C<fork> the child (alternatively, you can call
		407	C<AnyEvent::detect>).
		408
		409	Example: fork a process and wait for it
		410
		411	my $done = AnyEvent->condvar;
		412
		413	my $pid = fork or exit 5;
		414
257	my $w = AnyEvent->child (	415	my $w = AnyEvent->child (
258	pid => 1333,	416	pid => $pid,
259	cb => sub {	417	cb => sub {
260	my ($pid, $status) = @_;	418	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	419	warn "pid $pid exited with status $status";
		420	$done->send;
262	},	421	},
263	);	422	);
		423
		424	# do something else, then wait for process exit
		425	$done->recv;
		426
		427	=head2 IDLE WATCHERS
		428
		429	Sometimes there is a need to do something, but it is not so important
		430	to do it instantly, but only when there is nothing better to do. This
		431	"nothing better to do" is usually defined to be "no other events need
		432	attention by the event loop".
		433
		434	Idle watchers ideally get invoked when the event loop has nothing
		435	better to do, just before it would block the process to wait for new
		436	events. Instead of blocking, the idle watcher is invoked.
		437
		438	Most event loops unfortunately do not really support idle watchers (only
		439	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		440	will simply call the callback "from time to time".
		441
		442	Example: read lines from STDIN, but only process them when the
		443	program is otherwise idle:
		444
		445	my @lines; # read data
		446	my $idle_w;
		447	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		448	push @lines, scalar <STDIN>;
		449
		450	# start an idle watcher, if not already done
		451	$idle_w ||= AnyEvent->idle (cb => sub {
		452	# handle only one line, when there are lines left
		453	if (my $line = shift @lines) {
		454	print "handled when idle: $line";
		455	} else {
		456	# otherwise disable the idle watcher again
		457	undef $idle_w;
		458	}
		459	});
		460	});
264		461
265	=head2 CONDITION VARIABLES	462	=head2 CONDITION VARIABLES
266		463
		464	If you are familiar with some event loops you will know that all of them
		465	require you to run some blocking "loop", "run" or similar function that
		466	will actively watch for new events and call your callbacks.
		467
		468	AnyEvent is different, it expects somebody else to run the event loop and
		469	will only block when necessary (usually when told by the user).
		470
		471	The instrument to do that is called a "condition variable", so called
		472	because they represent a condition that must become true.
		473
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	474	Condition variables can be created by calling the C<< AnyEvent->condvar
268	method without any arguments.	475	>> method, usually without arguments. The only argument pair allowed is
269		476
270	A condition variable waits for a condition - precisely that the C<<	477	C<cb>, which specifies a callback to be called when the condition variable
271	->broadcast >> method has been called.	478	becomes true, with the condition variable as the first argument (but not
		479	the results).
272		480
273	They are very useful to signal that a condition has been fulfilled, for	481	After creation, the condition variable is "false" until it becomes "true"
		482	by calling the C<send> method (or calling the condition variable as if it
		483	were a callback, read about the caveats in the description for the C<<
		484	->send >> method).
		485
		486	Condition variables are similar to callbacks, except that you can
		487	optionally wait for them. They can also be called merge points - points
		488	in time where multiple outstanding events have been processed. And yet
		489	another way to call them is transactions - each condition variable can be
		490	used to represent a transaction, which finishes at some point and delivers
		491	a result.
		492
		493	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	494	for example, if you write a module that does asynchronous http requests,
275	then a condition variable would be the ideal candidate to signal the	495	then a condition variable would be the ideal candidate to signal the
276	availability of results.	496	availability of results. The user can either act when the callback is
		497	called or can synchronously C<< ->recv >> for the results.
277		498
278	You can also use condition variables to block your main program until	499	You can also use them to simulate traditional event loops - for example,
279	an event occurs - for example, you could C<< ->wait >> in your main	500	you can block your main program until an event occurs - for example, you
280	program until the user clicks the Quit button in your app, which would C<<	501	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	502	button of your app, which would C<< ->send >> the "quit" event.
282		503
283	Note that condition variables recurse into the event loop - if you have	504	Note that condition variables recurse into the event loop - if you have
284	two pirces of code that call C<< ->wait >> in a round-robbin fashion, you	505	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
285	lose. Therefore, condition variables are good to export to your caller, but	506	lose. Therefore, condition variables are good to export to your caller, but
286	you should avoid making a blocking wait yourself, at least in callbacks,	507	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	508	as this asks for trouble.
288		509
289	This object has two methods:	510	Condition variables are represented by hash refs in perl, and the keys
		511	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		512	easy (it is often useful to build your own transaction class on top of
		513	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		514	it's C<new> method in your own C<new> method.
		515
		516	There are two "sides" to a condition variable - the "producer side" which
		517	eventually calls C<< -> send >>, and the "consumer side", which waits
		518	for the send to occur.
		519
		520	Example: wait for a timer.
		521
		522	# wait till the result is ready
		523	my $result_ready = AnyEvent->condvar;
		524
		525	# do something such as adding a timer
		526	# or socket watcher the calls $result_ready->send
		527	# when the "result" is ready.
		528	# in this case, we simply use a timer:
		529	my $w = AnyEvent->timer (
		530	after => 1,
		531	cb => sub { $result_ready->send },
		532	);
		533
		534	# this "blocks" (while handling events) till the callback
		535	# calls send
		536	$result_ready->recv;
		537
		538	Example: wait for a timer, but take advantage of the fact that
		539	condition variables are also code references.
		540
		541	my $done = AnyEvent->condvar;
		542	my $delay = AnyEvent->timer (after => 5, cb => $done);
		543	$done->recv;
		544
		545	Example: Imagine an API that returns a condvar and doesn't support
		546	callbacks. This is how you make a synchronous call, for example from
		547	the main program:
		548
		549	use AnyEvent::CouchDB;
		550
		551	...
		552
		553	my @info = $couchdb->info->recv;
		554
		555	And this is how you would just ste a callback to be called whenever the
		556	results are available:
		557
		558	$couchdb->info->cb (sub {
		559	my @info = $_[0]->recv;
		560	});
		561
		562	=head3 METHODS FOR PRODUCERS
		563
		564	These methods should only be used by the producing side, i.e. the
		565	code/module that eventually sends the signal. Note that it is also
		566	the producer side which creates the condvar in most cases, but it isn't
		567	uncommon for the consumer to create it as well.
290		568
291	=over 4	569	=over 4
292		570
		571	=item $cv->send (...)
		572
		573	Flag the condition as ready - a running C<< ->recv >> and all further
		574	calls to C<recv> will (eventually) return after this method has been
		575	called. If nobody is waiting the send will be remembered.
		576
		577	If a callback has been set on the condition variable, it is called
		578	immediately from within send.
		579
		580	Any arguments passed to the C<send> call will be returned by all
		581	future C<< ->recv >> calls.
		582
		583	Condition variables are overloaded so one can call them directly
		584	(as a code reference). Calling them directly is the same as calling
		585	C<send>. Note, however, that many C-based event loops do not handle
		586	overloading, so as tempting as it may be, passing a condition variable
		587	instead of a callback does not work. Both the pure perl and EV loops
		588	support overloading, however, as well as all functions that use perl to
		589	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		590	example).
		591
		592	=item $cv->croak ($error)
		593
		594	Similar to send, but causes all call's to C<< ->recv >> to invoke
		595	C<Carp::croak> with the given error message/object/scalar.
		596
		597	This can be used to signal any errors to the condition variable
		598	user/consumer.
		599
		600	=item $cv->begin ([group callback])
		601
293	=item $cv->wait	602	=item $cv->end
294		603
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	604	These two methods can be used to combine many transactions/events into
		605	one. For example, a function that pings many hosts in parallel might want
		606	to use a condition variable for the whole process.
		607
		608	Every call to C<< ->begin >> will increment a counter, and every call to
		609	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		610	>>, the (last) callback passed to C<begin> will be executed. That callback
		611	is I<supposed> to call C<< ->send >>, but that is not required. If no
		612	callback was set, C<send> will be called without any arguments.
		613
		614	You can think of C<< $cv->send >> giving you an OR condition (one call
		615	sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
		616	condition (all C<begin> calls must be C<end>'ed before the condvar sends).
		617
		618	Let's start with a simple example: you have two I/O watchers (for example,
		619	STDOUT and STDERR for a program), and you want to wait for both streams to
		620	close before activating a condvar:
		621
		622	my $cv = AnyEvent->condvar;
		623
		624	$cv->begin; # first watcher
		625	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		626	defined sysread $fh1, my $buf, 4096
		627	or $cv->end;
		628	});
		629
		630	$cv->begin; # second watcher
		631	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		632	defined sysread $fh2, my $buf, 4096
		633	or $cv->end;
		634	});
		635
		636	$cv->recv;
		637
		638	This works because for every event source (EOF on file handle), there is
		639	one call to C<begin>, so the condvar waits for all calls to C<end> before
		640	sending.
		641
		642	The ping example mentioned above is slightly more complicated, as the
		643	there are results to be passwd back, and the number of tasks that are
		644	begung can potentially be zero:
		645
		646	my $cv = AnyEvent->condvar;
		647
		648	my %result;
		649	$cv->begin (sub { $cv->send (\%result) });
		650
		651	for my $host (@list_of_hosts) {
		652	$cv->begin;
		653	ping_host_then_call_callback $host, sub {
		654	$result{$host} = ...;
		655	$cv->end;
		656	};
		657	}
		658
		659	$cv->end;
		660
		661	This code fragment supposedly pings a number of hosts and calls
		662	C<send> after results for all then have have been gathered - in any
		663	order. To achieve this, the code issues a call to C<begin> when it starts
		664	each ping request and calls C<end> when it has received some result for
		665	it. Since C<begin> and C<end> only maintain a counter, the order in which
		666	results arrive is not relevant.
		667
		668	There is an additional bracketing call to C<begin> and C<end> outside the
		669	loop, which serves two important purposes: first, it sets the callback
		670	to be called once the counter reaches C<0>, and second, it ensures that
		671	C<send> is called even when C<no> hosts are being pinged (the loop
		672	doesn't execute once).
		673
		674	This is the general pattern when you "fan out" into multiple (but
		675	potentially none) subrequests: use an outer C<begin>/C<end> pair to set
		676	the callback and ensure C<end> is called at least once, and then, for each
		677	subrequest you start, call C<begin> and for each subrequest you finish,
		678	call C<end>.
		679
		680	=back
		681
		682	=head3 METHODS FOR CONSUMERS
		683
		684	These methods should only be used by the consuming side, i.e. the
		685	code awaits the condition.
		686
		687	=over 4
		688
		689	=item $cv->recv
		690
		691	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
296	called on c<$cv>, while servicing other watchers normally.	692	>> methods have been called on c<$cv>, while servicing other watchers
		693	normally.
297		694
298	You can only wait once on a condition - additional calls will return	695	You can only wait once on a condition - additional calls are valid but
299	immediately.	696	will return immediately.
		697
		698	If an error condition has been set by calling C<< ->croak >>, then this
		699	function will call C<croak>.
		700
		701	In list context, all parameters passed to C<send> will be returned,
		702	in scalar context only the first one will be returned.
300		703
301	Not all event models support a blocking wait - some die in that case	704	Not all event models support a blocking wait - some die in that case
302	(programs might want to do that to stay interactive), so I<if you are	705	(programs might want to do that to stay interactive), so I<if you are
303	using this from a module, never require a blocking wait>, but let the	706	using this from a module, never require a blocking wait>, but let the
304	caller decide whether the call will block or not (for example, by coupling	707	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	708	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	709	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	710	while still supporting blocking waits if the caller so desires).
308		711
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	712	Another reason I<never> to C<< ->recv >> in a module is that you cannot
310	sensibly have two C<< ->wait >>'s in parallel, as that would require	713	sensibly have two C<< ->recv >>'s in parallel, as that would require
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	714	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	715	can supply.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		716
316	=item $cv->broadcast	717	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		718	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		719	versions and also integrates coroutines into AnyEvent, making blocking
		720	C<< ->recv >> calls perfectly safe as long as they are done from another
		721	coroutine (one that doesn't run the event loop).
317		722
318	Flag the condition as ready - a running C<< ->wait >> and all further	723	You can ensure that C<< -recv >> never blocks by setting a callback and
319	calls to C<wait> will (eventually) return after this method has been	724	only calling C<< ->recv >> from within that callback (or at a later
320	called. If nobody is waiting the broadcast will be remembered..	725	time). This will work even when the event loop does not support blocking
		726	waits otherwise.
		727
		728	=item $bool = $cv->ready
		729
		730	Returns true when the condition is "true", i.e. whether C<send> or
		731	C<croak> have been called.
		732
		733	=item $cb = $cv->cb ($cb->($cv))
		734
		735	This is a mutator function that returns the callback set and optionally
		736	replaces it before doing so.
		737
		738	The callback will be called when the condition becomes "true", i.e. when
		739	C<send> or C<croak> are called, with the only argument being the condition
		740	variable itself. Calling C<recv> inside the callback or at any later time
		741	is guaranteed not to block.
321		742
322	=back	743	=back
323		744
324	Example:	745	=head1 SUPPORTED EVENT LOOPS/BACKENDS
325		746
326	# wait till the result is ready	747	The available backend classes are (every class has its own manpage):
327	my $result_ready = AnyEvent->condvar;
328		748
329	# do something such as adding a timer	749	=over 4
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		750
338	# this "blocks" (while handling events) till the watcher	751	=item Backends that are autoprobed when no other event loop can be found.
339	# calls broadcast	752
340	$result_ready->wait;	753	EV is the preferred backend when no other event loop seems to be in
		754	use. If EV is not installed, then AnyEvent will try Event, and, failing
		755	that, will fall back to its own pure-perl implementation, which is
		756	available everywhere as it comes with AnyEvent itself.
		757
		758	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		759	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		760	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		761
		762	=item Backends that are transparently being picked up when they are used.
		763
		764	These will be used when they are currently loaded when the first watcher
		765	is created, in which case it is assumed that the application is using
		766	them. This means that AnyEvent will automatically pick the right backend
		767	when the main program loads an event module before anything starts to
		768	create watchers. Nothing special needs to be done by the main program.
		769
		770	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		771	AnyEvent::Impl::Tk based on Tk, very broken.
		772	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		773	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		774
		775	=item Backends with special needs.
		776
		777	Qt requires the Qt::Application to be instantiated first, but will
		778	otherwise be picked up automatically. As long as the main program
		779	instantiates the application before any AnyEvent watchers are created,
		780	everything should just work.
		781
		782	AnyEvent::Impl::Qt based on Qt.
		783
		784	Support for IO::Async can only be partial, as it is too broken and
		785	architecturally limited to even support the AnyEvent API. It also
		786	is the only event loop that needs the loop to be set explicitly, so
		787	it can only be used by a main program knowing about AnyEvent. See
		788	L<AnyEvent::Impl::Async> for the gory details.
		789
		790	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		791
		792	=item Event loops that are indirectly supported via other backends.
		793
		794	Some event loops can be supported via other modules:
		795
		796	There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
		797
		798	B<WxWidgets> has no support for watching file handles. However, you can
		799	use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
		800	polls 20 times per second, which was considered to be too horrible to even
		801	consider for AnyEvent.
		802
		803	B<Prima> is not supported as nobody seems to be using it, but it has a POE
		804	backend, so it can be supported through POE.
		805
		806	AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
		807	load L<POE> when detecting them, in the hope that POE will pick them up,
		808	in which case everything will be automatic.
		809
		810	=back
341		811
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	812	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		813
344	=over 4	814	=over 4
345		815
…		…
349	contains the event model that is being used, which is the name of the	819	contains the event model that is being used, which is the name of the
350	Perl class implementing the model. This class is usually one of the	820	Perl class implementing the model. This class is usually one of the
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	821	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>).	822	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
353		823
354	The known classes so far are:
355
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).
359	AnyEvent::Impl::Event based on Event, also second best choice :)
360	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
363
364	=item AnyEvent::detect	824	=item AnyEvent::detect
365		825
366	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	826	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
367	if necessary. You should only call this function right before you would	827	if necessary. You should only call this function right before you would
368	have created an AnyEvent watcher anyway, that is, as late as possible at	828	have created an AnyEvent watcher anyway, that is, as late as possible at
369	runtime.	829	runtime.
370		830
		831	=item $guard = AnyEvent::post_detect { BLOCK }
		832
		833	Arranges for the code block to be executed as soon as the event model is
		834	autodetected (or immediately if this has already happened).
		835
		836	If called in scalar or list context, then it creates and returns an object
		837	that automatically removes the callback again when it is destroyed. See
		838	L<Coro::BDB> for a case where this is useful.
		839
		840	=item @AnyEvent::post_detect
		841
		842	If there are any code references in this array (you can C<push> to it
		843	before or after loading AnyEvent), then they will called directly after
		844	the event loop has been chosen.
		845
		846	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		847	if it contains a true value then the event loop has already been detected,
		848	and the array will be ignored.
		849
		850	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		851
371	=back	852	=back
372		853
373	=head1 WHAT TO DO IN A MODULE	854	=head1 WHAT TO DO IN A MODULE
374		855
375	As a module author, you should C<use AnyEvent> and call AnyEvent methods	856	As a module author, you should C<use AnyEvent> and call AnyEvent methods
…		…
378	Be careful when you create watchers in the module body - AnyEvent will	859	Be careful when you create watchers in the module body - AnyEvent will
379	decide which event module to use as soon as the first method is called, so	860	decide which event module to use as soon as the first method is called, so
380	by calling AnyEvent in your module body you force the user of your module	861	by calling AnyEvent in your module body you force the user of your module
381	to load the event module first.	862	to load the event module first.
382		863
383	Never call C<< ->wait >> on a condition variable unless you I<know> that	864	Never call C<< ->recv >> on a condition variable unless you I<know> that
384	the C<< ->broadcast >> method has been called on it already. This is	865	the C<< ->send >> method has been called on it already. This is
385	because it will stall the whole program, and the whole point of using	866	because it will stall the whole program, and the whole point of using
386	events is to stay interactive.	867	events is to stay interactive.
387		868
388	It is fine, however, to call C<< ->wait >> when the user of your module	869	It is fine, however, to call C<< ->recv >> when the user of your module
389	requests it (i.e. if you create a http request object ad have a method	870	requests it (i.e. if you create a http request object ad have a method
390	called C<results> that returns the results, it should call C<< ->wait >>	871	called C<results> that returns the results, it should call C<< ->recv >>
391	freely, as the user of your module knows what she is doing. always).	872	freely, as the user of your module knows what she is doing. always).
392		873
393	=head1 WHAT TO DO IN THE MAIN PROGRAM	874	=head1 WHAT TO DO IN THE MAIN PROGRAM
394		875
395	There will always be a single main program - the only place that should	876	There will always be a single main program - the only place that should
…		…
397		878
398	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	879	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
399	do anything special (it does not need to be event-based) and let AnyEvent	880	do anything special (it does not need to be event-based) and let AnyEvent
400	decide which implementation to chose if some module relies on it.	881	decide which implementation to chose if some module relies on it.
401		882
402	If the main program relies on a specific event model. For example, in	883	If the main program relies on a specific event model - for example, in
403	Gtk2 programs you have to rely on the Glib module. You should load the	884	Gtk2 programs you have to rely on the Glib module - you should load the
404	event module before loading AnyEvent or any module that uses it: generally	885	event module before loading AnyEvent or any module that uses it: generally
405	speaking, you should load it as early as possible. The reason is that	886	speaking, you should load it as early as possible. The reason is that
406	modules might create watchers when they are loaded, and AnyEvent will	887	modules might create watchers when they are loaded, and AnyEvent will
407	decide on the event model to use as soon as it creates watchers, and it	888	decide on the event model to use as soon as it creates watchers, and it
408	might chose the wrong one unless you load the correct one yourself.	889	might chose the wrong one unless you load the correct one yourself.
409		890
410	You can chose to use a rather inefficient pure-perl implementation by	891	You can chose to use a pure-perl implementation by loading the
411	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	892	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
412	behaviour everywhere, but letting AnyEvent chose is generally better.	893	everywhere, but letting AnyEvent chose the model is generally better.
		894
		895	=head2 MAINLOOP EMULATION
		896
		897	Sometimes (often for short test scripts, or even standalone programs who
		898	only want to use AnyEvent), you do not want to run a specific event loop.
		899
		900	In that case, you can use a condition variable like this:
		901
		902	AnyEvent->condvar->recv;
		903
		904	This has the effect of entering the event loop and looping forever.
		905
		906	Note that usually your program has some exit condition, in which case
		907	it is better to use the "traditional" approach of storing a condition
		908	variable somewhere, waiting for it, and sending it when the program should
		909	exit cleanly.
		910
		911
		912	=head1 OTHER MODULES
		913
		914	The following is a non-exhaustive list of additional modules that use
		915	AnyEvent as a client and can therefore be mixed easily with other AnyEvent
		916	modules and other event loops in the same program. Some of the modules
		917	come with AnyEvent, most are available via CPAN.
		918
		919	=over 4
		920
		921	=item L<AnyEvent::Util>
		922
		923	Contains various utility functions that replace often-used but blocking
		924	functions such as C<inet_aton> by event-/callback-based versions.
		925
		926	=item L<AnyEvent::Socket>
		927
		928	Provides various utility functions for (internet protocol) sockets,
		929	addresses and name resolution. Also functions to create non-blocking tcp
		930	connections or tcp servers, with IPv6 and SRV record support and more.
		931
		932	=item L<AnyEvent::Handle>
		933
		934	Provide read and write buffers, manages watchers for reads and writes,
		935	supports raw and formatted I/O, I/O queued and fully transparent and
		936	non-blocking SSL/TLS (via L<AnyEvent::TLS>.
		937
		938	=item L<AnyEvent::DNS>
		939
		940	Provides rich asynchronous DNS resolver capabilities.
		941
		942	=item L<AnyEvent::HTTP>
		943
		944	A simple-to-use HTTP library that is capable of making a lot of concurrent
		945	HTTP requests.
		946
		947	=item L<AnyEvent::HTTPD>
		948
		949	Provides a simple web application server framework.
		950
		951	=item L<AnyEvent::FastPing>
		952
		953	The fastest ping in the west.
		954
		955	=item L<AnyEvent::DBI>
		956
		957	Executes L<DBI> requests asynchronously in a proxy process.
		958
		959	=item L<AnyEvent::AIO>
		960
		961	Truly asynchronous I/O, should be in the toolbox of every event
		962	programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
		963	together.
		964
		965	=item L<AnyEvent::BDB>
		966
		967	Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
		968	L<BDB> and AnyEvent together.
		969
		970	=item L<AnyEvent::GPSD>
		971
		972	A non-blocking interface to gpsd, a daemon delivering GPS information.
		973
		974	=item L<AnyEvent::IRC>
		975
		976	AnyEvent based IRC client module family (replacing the older Net::IRC3).
		977
		978	=item L<AnyEvent::XMPP>
		979
		980	AnyEvent based XMPP (Jabber protocol) module family (replacing the older
		981	Net::XMPP2>.
		982
		983	=item L<AnyEvent::IGS>
		984
		985	A non-blocking interface to the Internet Go Server protocol (used by
		986	L<App::IGS>).
		987
		988	=item L<Net::FCP>
		989
		990	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		991	of AnyEvent.
		992
		993	=item L<Event::ExecFlow>
		994
		995	High level API for event-based execution flow control.
		996
		997	=item L<Coro>
		998
		999	Has special support for AnyEvent via L<Coro::AnyEvent>.
		1000
		1001	=back
413		1002
414	=cut	1003	=cut
415		1004
416	package AnyEvent;	1005	package AnyEvent;
417		1006
418	no warnings;	1007	no warnings;
419	use strict;	1008	use strict qw(vars subs);
420		1009
421	use Carp;	1010	use Carp;
422		1011
423	our $VERSION = '3.11';	1012	our $VERSION = 4.801;
424	our $MODEL;	1013	our $MODEL;
425		1014
426	our $AUTOLOAD;	1015	our $AUTOLOAD;
427	our @ISA;	1016	our @ISA;
428		1017
		1018	our @REGISTRY;
		1019
		1020	our $WIN32;
		1021
		1022	BEGIN {
		1023	eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
		1024	eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
		1025
		1026	delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
		1027	if ${^TAINT};
		1028	}
		1029
429	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	1030	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
430		1031
431	our @REGISTRY;	1032	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		1033
		1034	{
		1035	my $idx;
		1036	$PROTOCOL{$_} = ++$idx
		1037	for reverse split /\s*,\s*/,
		1038	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		1039	}
432		1040
433	my @models = (	1041	my @models = (
434	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
435	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
436	[EV:: => AnyEvent::Impl::EV::],	1042	[EV:: => AnyEvent::Impl::EV::],
437	[Event:: => AnyEvent::Impl::Event::],	1043	[Event:: => AnyEvent::Impl::Event::],
438	[Glib:: => AnyEvent::Impl::Glib::],
439	[Tk:: => AnyEvent::Impl::Tk::],
440	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	1044	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		1045	# everything below here will not be autoprobed
		1046	# as the pureperl backend should work everywhere
		1047	# and is usually faster
		1048	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		1049	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		1050	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		1051	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		1052	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		1053	[Wx:: => AnyEvent::Impl::POE::],
		1054	[Prima:: => AnyEvent::Impl::POE::],
		1055	# IO::Async is just too broken - we would need workarounds for its
		1056	# byzantine signal and broken child handling, among others.
		1057	# IO::Async is rather hard to detect, as it doesn't have any
		1058	# obvious default class.
		1059	# [IO::Async:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1060	# [IO::Async::Loop:: => AnyEvent::Impl::IOAsync::], # requires special main program
		1061	# [IO::Async::Notifier:: => AnyEvent::Impl::IOAsync::], # requires special main program
441	);	1062	);
442		1063
443	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	1064	our %method = map +($_ => 1),
		1065	qw(io timer time now now_update signal child idle condvar one_event DESTROY);
		1066
		1067	our @post_detect;
		1068
		1069	sub post_detect(&) {
		1070	my ($cb) = @_;
		1071
		1072	if ($MODEL) {
		1073	$cb->();
		1074
		1075	1
		1076	} else {
		1077	push @post_detect, $cb;
		1078
		1079	defined wantarray
		1080	? bless \$cb, "AnyEvent::Util::postdetect"
		1081	: ()
		1082	}
		1083	}
		1084
		1085	sub AnyEvent::Util::postdetect::DESTROY {
		1086	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		1087	}
444		1088
445	sub detect() {	1089	sub detect() {
446	unless ($MODEL) {	1090	unless ($MODEL) {
447	no strict 'refs';	1091	no strict 'refs';
		1092	local $SIG{__DIE__};
		1093
		1094	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		1095	my $model = "AnyEvent::Impl::$1";
		1096	if (eval "require $model") {
		1097	$MODEL = $model;
		1098	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		1099	} else {
		1100	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		1101	}
		1102	}
448		1103
449	# check for already loaded models	1104	# check for already loaded models
		1105	unless ($MODEL) {
450	for (@REGISTRY, @models) {	1106	for (@REGISTRY, @models) {
451	my ($package, $model) = @$_;	1107	my ($package, $model) = @$_;
452	if (${"$package\::VERSION"} > 0) {	1108	if (${"$package\::VERSION"} > 0) {
453	if (eval "require $model") {	1109	if (eval "require $model") {
454	$MODEL = $model;	1110	$MODEL = $model;
455	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	1111	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
456	last;	1112	last;
		1113	}
457	}	1114	}
458	}	1115	}
		1116
		1117	unless ($MODEL) {
		1118	# try to load a model
		1119
		1120	for (@REGISTRY, @models) {
		1121	my ($package, $model) = @$_;
		1122	if (eval "require $package"
		1123	and ${"$package\::VERSION"} > 0
		1124	and eval "require $model") {
		1125	$MODEL = $model;
		1126	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		1127	last;
		1128	}
		1129	}
		1130
		1131	$MODEL
		1132	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.\n";
		1133	}
459	}	1134	}
460		1135
461	unless ($MODEL) {	1136	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
462	# try to load a model
463
464	for (@REGISTRY, @models) {
465	my ($package, $model) = @$_;
466	if (eval "require $package"
467	and ${"$package\::VERSION"} > 0
468	and eval "require $model") {
469	$MODEL = $model;
470	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
471	last;
472	}
473	}
474
475	$MODEL
476	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), Glib or Tk.";
477	}
478		1137
479	unshift @ISA, $MODEL;	1138	unshift @ISA, $MODEL;
480	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	1139
		1140	require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
		1141
		1142	(shift @post_detect)->() while @post_detect;
481	}	1143	}
482		1144
483	$MODEL	1145	$MODEL
484	}	1146	}
485		1147
…		…
493		1155
494	my $class = shift;	1156	my $class = shift;
495	$class->$func (@_);	1157	$class->$func (@_);
496	}	1158	}
497		1159
		1160	# utility function to dup a filehandle. this is used by many backends
		1161	# to support binding more than one watcher per filehandle (they usually
		1162	# allow only one watcher per fd, so we dup it to get a different one).
		1163	sub _dupfh($$;$$) {
		1164	my ($poll, $fh, $r, $w) = @_;
		1165
		1166	# cygwin requires the fh mode to be matching, unix doesn't
		1167	my ($rw, $mode) = $poll eq "r" ? ($r, "<") : ($w, ">");
		1168
		1169	open my $fh2, "$mode&", $fh
		1170	or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
		1171
		1172	# we assume CLOEXEC is already set by perl in all important cases
		1173
		1174	($fh2, $rw)
		1175	}
		1176
498	package AnyEvent::Base;	1177	package AnyEvent::Base;
499		1178
		1179	# default implementations for many methods
		1180
		1181	BEGIN {
		1182	if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
		1183	*_time = \&Time::HiRes::time;
		1184	# if (eval "use POSIX (); (POSIX::times())...
		1185	} else {
		1186	*_time = sub { time }; # epic fail
		1187	}
		1188	}
		1189
		1190	sub time { _time }
		1191	sub now { _time }
		1192	sub now_update { }
		1193
500	# default implementation for ->condvar, ->wait, ->broadcast	1194	# default implementation for ->condvar
501		1195
502	sub condvar {	1196	sub condvar {
503	bless \my $flag, "AnyEvent::Base::CondVar"	1197	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
504	}
505
506	sub AnyEvent::Base::CondVar::broadcast {
507	${$_[0]}++;
508	}
509
510	sub AnyEvent::Base::CondVar::wait {
511	AnyEvent->one_event while !${$_[0]};
512	}	1198	}
513		1199
514	# default implementation for ->signal	1200	# default implementation for ->signal
515		1201
516	our %SIG_CB;	1202	our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
		1203
		1204	sub _signal_exec {
		1205	sysread $SIGPIPE_R, my $dummy, 4;
		1206
		1207	while (%SIG_EV) {
		1208	for (keys %SIG_EV) {
		1209	delete $SIG_EV{$_};
		1210	$_->() for values %{ $SIG_CB{$_} || {} };
		1211	}
		1212	}
		1213	}
517		1214
518	sub signal {	1215	sub signal {
519	my (undef, %arg) = @_;	1216	my (undef, %arg) = @_;
520		1217
		1218	unless ($SIGPIPE_R) {
		1219	require Fcntl;
		1220
		1221	if (AnyEvent::WIN32) {
		1222	require AnyEvent::Util;
		1223
		1224	($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
		1225	AnyEvent::Util::fh_nonblocking ($SIGPIPE_R) if $SIGPIPE_R;
		1226	AnyEvent::Util::fh_nonblocking ($SIGPIPE_W) if $SIGPIPE_W; # just in case
		1227	} else {
		1228	pipe $SIGPIPE_R, $SIGPIPE_W;
		1229	fcntl $SIGPIPE_R, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_R;
		1230	fcntl $SIGPIPE_W, &Fcntl::F_SETFL, &Fcntl::O_NONBLOCK if $SIGPIPE_W; # just in case
		1231
		1232	# not strictly required, as $^F is normally 2, but let's make sure...
		1233	fcntl $SIGPIPE_R, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1234	fcntl $SIGPIPE_W, &Fcntl::F_SETFD, &Fcntl::FD_CLOEXEC;
		1235	}
		1236
		1237	$SIGPIPE_R
		1238	or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
		1239
		1240	$SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
		1241	}
		1242
521	my $signal = uc $arg{signal}	1243	my $signal = uc $arg{signal}
522	or Carp::croak "required option 'signal' is missing";	1244	or Carp::croak "required option 'signal' is missing";
523		1245
524	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};	1246	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
525	$SIG{$signal} ||= sub {	1247	$SIG{$signal} ||= sub {
526	$_->() for values %{ $SIG_CB{$signal} || {} };	1248	local $!;
		1249	syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
		1250	undef $SIG_EV{$signal};
527	};	1251	};
528		1252
529	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"	1253	bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
530	}	1254	}
531		1255
532	sub AnyEvent::Base::Signal::DESTROY {	1256	sub AnyEvent::Base::signal::DESTROY {
533	my ($signal, $cb) = @{$_[0]};	1257	my ($signal, $cb) = @{$_[0]};
534		1258
535	delete $SIG_CB{$signal}{$cb};	1259	delete $SIG_CB{$signal}{$cb};
536		1260
		1261	# delete doesn't work with older perls - they then
		1262	# print weird messages, or just unconditionally exit
		1263	# instead of getting the default action.
537	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };	1264	undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
538	}	1265	}
539		1266
540	# default implementation for ->child	1267	# default implementation for ->child
541		1268
542	our %PID_CB;	1269	our %PID_CB;
543	our $CHLD_W;	1270	our $CHLD_W;
544	our $CHLD_DELAY_W;	1271	our $CHLD_DELAY_W;
545	our $PID_IDLE;
546	our $WNOHANG;	1272	our $WNOHANG;
547		1273
548	sub _child_wait {	1274	sub _sigchld {
549	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	1275	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
550	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),	1276	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
551	(values %{ $PID_CB{0} || {} });	1277	(values %{ $PID_CB{0} || {} });
552	}	1278	}
553
554	undef $PID_IDLE;
555	}
556
557	sub _sigchld {
558	# make sure we deliver these changes "synchronous" with the event loop.
559	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
560	undef $CHLD_DELAY_W;
561	&_child_wait;
562	});
563	}	1279	}
564		1280
565	sub child {	1281	sub child {
566	my (undef, %arg) = @_;	1282	my (undef, %arg) = @_;
567		1283
568	defined (my $pid = $arg{pid} + 0)	1284	defined (my $pid = $arg{pid} + 0)
569	or Carp::croak "required option 'pid' is missing";	1285	or Carp::croak "required option 'pid' is missing";
570		1286
571	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1287	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
572		1288
573	unless ($WNOHANG) {
574	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1289	$WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
575	}
576		1290
577	unless ($CHLD_W) {	1291	unless ($CHLD_W) {
578	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1292	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
579	# child could be a zombie already, so make at least one round	1293	# child could be a zombie already, so make at least one round
580	&_sigchld;	1294	&_sigchld;
581	}	1295	}
582		1296
583	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1297	bless [$pid, $arg{cb}], "AnyEvent::Base::child"
584	}	1298	}
585		1299
586	sub AnyEvent::Base::Child::DESTROY {	1300	sub AnyEvent::Base::child::DESTROY {
587	my ($pid, $cb) = @{$_[0]};	1301	my ($pid, $cb) = @{$_[0]};
588		1302
589	delete $PID_CB{$pid}{$cb};	1303	delete $PID_CB{$pid}{$cb};
590	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1304	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
591		1305
592	undef $CHLD_W unless keys %PID_CB;	1306	undef $CHLD_W unless keys %PID_CB;
593	}	1307	}
		1308
		1309	# idle emulation is done by simply using a timer, regardless
		1310	# of whether the process is idle or not, and not letting
		1311	# the callback use more than 50% of the time.
		1312	sub idle {
		1313	my (undef, %arg) = @_;
		1314
		1315	my ($cb, $w, $rcb) = $arg{cb};
		1316
		1317	$rcb = sub {
		1318	if ($cb) {
		1319	$w = _time;
		1320	&$cb;
		1321	$w = _time - $w;
		1322
		1323	# never use more then 50% of the time for the idle watcher,
		1324	# within some limits
		1325	$w = 0.0001 if $w < 0.0001;
		1326	$w = 5 if $w > 5;
		1327
		1328	$w = AnyEvent->timer (after => $w, cb => $rcb);
		1329	} else {
		1330	# clean up...
		1331	undef $w;
		1332	undef $rcb;
		1333	}
		1334	};
		1335
		1336	$w = AnyEvent->timer (after => 0.05, cb => $rcb);
		1337
		1338	bless \\$cb, "AnyEvent::Base::idle"
		1339	}
		1340
		1341	sub AnyEvent::Base::idle::DESTROY {
		1342	undef $${$_[0]};
		1343	}
		1344
		1345	package AnyEvent::CondVar;
		1346
		1347	our @ISA = AnyEvent::CondVar::Base::;
		1348
		1349	package AnyEvent::CondVar::Base;
		1350
		1351	use overload
		1352	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1353	fallback => 1;
		1354
		1355	sub _send {
		1356	# nop
		1357	}
		1358
		1359	sub send {
		1360	my $cv = shift;
		1361	$cv->{_ae_sent} = [@_];
		1362	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1363	$cv->_send;
		1364	}
		1365
		1366	sub croak {
		1367	$_[0]{_ae_croak} = $_[1];
		1368	$_[0]->send;
		1369	}
		1370
		1371	sub ready {
		1372	$_[0]{_ae_sent}
		1373	}
		1374
		1375	sub _wait {
		1376	AnyEvent->one_event while !$_[0]{_ae_sent};
		1377	}
		1378
		1379	sub recv {
		1380	$_[0]->_wait;
		1381
		1382	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1383	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1384	}
		1385
		1386	sub cb {
		1387	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1388	$_[0]{_ae_cb}
		1389	}
		1390
		1391	sub begin {
		1392	++$_[0]{_ae_counter};
		1393	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1394	}
		1395
		1396	sub end {
		1397	return if --$_[0]{_ae_counter};
		1398	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1399	}
		1400
		1401	# undocumented/compatibility with pre-3.4
		1402	*broadcast = \&send;
		1403	*wait = \&_wait;
		1404
		1405	=head1 ERROR AND EXCEPTION HANDLING
		1406
		1407	In general, AnyEvent does not do any error handling - it relies on the
		1408	caller to do that if required. The L<AnyEvent::Strict> module (see also
		1409	the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
		1410	checking of all AnyEvent methods, however, which is highly useful during
		1411	development.
		1412
		1413	As for exception handling (i.e. runtime errors and exceptions thrown while
		1414	executing a callback), this is not only highly event-loop specific, but
		1415	also not in any way wrapped by this module, as this is the job of the main
		1416	program.
		1417
		1418	The pure perl event loop simply re-throws the exception (usually
		1419	within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
		1420	$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
		1421	so on.
		1422
		1423	=head1 ENVIRONMENT VARIABLES
		1424
		1425	The following environment variables are used by this module or its
		1426	submodules.
		1427
		1428	Note that AnyEvent will remove I<all> environment variables starting with
		1429	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		1430	enabled.
		1431
		1432	=over 4
		1433
		1434	=item C<PERL_ANYEVENT_VERBOSE>
		1435
		1436	By default, AnyEvent will be completely silent except in fatal
		1437	conditions. You can set this environment variable to make AnyEvent more
		1438	talkative.
		1439
		1440	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1441	conditions, such as not being able to load the event model specified by
		1442	C<PERL_ANYEVENT_MODEL>.
		1443
		1444	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1445	model it chooses.
		1446
		1447	=item C<PERL_ANYEVENT_STRICT>
		1448
		1449	AnyEvent does not do much argument checking by default, as thorough
		1450	argument checking is very costly. Setting this variable to a true value
		1451	will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
		1452	check the arguments passed to most method calls. If it finds any problems,
		1453	it will croak.
		1454
		1455	In other words, enables "strict" mode.
		1456
		1457	Unlike C<use strict>, it is definitely recommended to keep it off in
		1458	production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
		1459	developing programs can be very useful, however.
		1460
		1461	=item C<PERL_ANYEVENT_MODEL>
		1462
		1463	This can be used to specify the event model to be used by AnyEvent, before
		1464	auto detection and -probing kicks in. It must be a string consisting
		1465	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1466	and the resulting module name is loaded and if the load was successful,
		1467	used as event model. If it fails to load AnyEvent will proceed with
		1468	auto detection and -probing.
		1469
		1470	This functionality might change in future versions.
		1471
		1472	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1473	could start your program like this:
		1474
		1475	PERL_ANYEVENT_MODEL=Perl perl ...
		1476
		1477	=item C<PERL_ANYEVENT_PROTOCOLS>
		1478
		1479	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1480	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1481	of auto probing).
		1482
		1483	Must be set to a comma-separated list of protocols or address families,
		1484	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1485	used, and preference will be given to protocols mentioned earlier in the
		1486	list.
		1487
		1488	This variable can effectively be used for denial-of-service attacks
		1489	against local programs (e.g. when setuid), although the impact is likely
		1490	small, as the program has to handle conenction and other failures anyways.
		1491
		1492	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1493	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1494	- only support IPv4, never try to resolve or contact IPv6
		1495	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1496	IPv6, but prefer IPv6 over IPv4.
		1497
		1498	=item C<PERL_ANYEVENT_EDNS0>
		1499
		1500	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1501	for DNS. This extension is generally useful to reduce DNS traffic, but
		1502	some (broken) firewalls drop such DNS packets, which is why it is off by
		1503	default.
		1504
		1505	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1506	EDNS0 in its DNS requests.
		1507
		1508	=item C<PERL_ANYEVENT_MAX_FORKS>
		1509
		1510	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1511	will create in parallel.
		1512
		1513	=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
		1514
		1515	The default value for the C<max_outstanding> parameter for the default DNS
		1516	resolver - this is the maximum number of parallel DNS requests that are
		1517	sent to the DNS server.
		1518
		1519	=item C<PERL_ANYEVENT_RESOLV_CONF>
		1520
		1521	The file to use instead of F</etc/resolv.conf> (or OS-specific
		1522	configuration) in the default resolver. When set to the empty string, no
		1523	default config will be used.
		1524
		1525	=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
		1526
		1527	When neither C<ca_file> nor C<ca_path> was specified during
		1528	L<AnyEvent::TLS> context creation, and either of these environment
		1529	variables exist, they will be used to specify CA certificate locations
		1530	instead of a system-dependent default.
		1531
		1532	=back
594		1533
595	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1534	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
596		1535
597	This is an advanced topic that you do not normally need to use AnyEvent in	1536	This is an advanced topic that you do not normally need to use AnyEvent in
598	a module. This section is only of use to event loop authors who want to	1537	a module. This section is only of use to event loop authors who want to
…		…
633	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1572	I<rxvt-unicode> also cheats a bit by not providing blocking access to
634	condition variables: code blocking while waiting for a condition will	1573	condition variables: code blocking while waiting for a condition will
635	C<die>. This still works with most modules/usages, and blocking calls must	1574	C<die>. This still works with most modules/usages, and blocking calls must
636	not be done in an interactive application, so it makes sense.	1575	not be done in an interactive application, so it makes sense.
637		1576
638	=head1 ENVIRONMENT VARIABLES
639
640	The following environment variables are used by this module:
641
642	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to
643	report to STDERR which event model it chooses.
644
645	=head1 EXAMPLE PROGRAM	1577	=head1 EXAMPLE PROGRAM
646		1578
647	The following program uses an IO watcher to read data from STDIN, a timer	1579	The following program uses an I/O watcher to read data from STDIN, a timer
648	to display a message once per second, and a condition variable to quit the	1580	to display a message once per second, and a condition variable to quit the
649	program when the user enters quit:	1581	program when the user enters quit:
650		1582
651	use AnyEvent;	1583	use AnyEvent;
652		1584
…		…
657	poll => 'r',	1589	poll => 'r',
658	cb => sub {	1590	cb => sub {
659	warn "io event <$_[0]>\n"; # will always output <r>	1591	warn "io event <$_[0]>\n"; # will always output <r>
660	chomp (my $input = <STDIN>); # read a line	1592	chomp (my $input = <STDIN>); # read a line
661	warn "read: $input\n"; # output what has been read	1593	warn "read: $input\n"; # output what has been read
662	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1594	$cv->send if $input =~ /^q/i; # quit program if /^q/i
663	},	1595	},
664	);	1596	);
665		1597
666	my $time_watcher; # can only be used once	1598	my $time_watcher; # can only be used once
667		1599
…		…
672	});	1604	});
673	}	1605	}
674		1606
675	new_timer; # create first timer	1607	new_timer; # create first timer
676		1608
677	$cv->wait; # wait until user enters /^q/i	1609	$cv->recv; # wait until user enters /^q/i
678		1610
679	=head1 REAL-WORLD EXAMPLE	1611	=head1 REAL-WORLD EXAMPLE
680		1612
681	Consider the L<Net::FCP> module. It features (among others) the following	1613	Consider the L<Net::FCP> module. It features (among others) the following
682	API calls, which are to freenet what HTTP GET requests are to http:	1614	API calls, which are to freenet what HTTP GET requests are to http:
…		…
732	syswrite $txn->{fh}, $txn->{request}	1664	syswrite $txn->{fh}, $txn->{request}
733	or die "connection or write error";	1665	or die "connection or write error";
734	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1666	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
735		1667
736	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1668	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
737	result and signals any possible waiters that the request ahs finished:	1669	result and signals any possible waiters that the request has finished:
738		1670
739	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1671	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
740		1672
741	if (end-of-file or data complete) {	1673	if (end-of-file or data complete) {
742	$txn->{result} = $txn->{buf};	1674	$txn->{result} = $txn->{buf};
743	$txn->{finished}->broadcast;	1675	$txn->{finished}->send;
744	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1676	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
745	}	1677	}
746		1678
747	The C<result> method, finally, just waits for the finished signal (if the	1679	The C<result> method, finally, just waits for the finished signal (if the
748	request was already finished, it doesn't wait, of course, and returns the	1680	request was already finished, it doesn't wait, of course, and returns the
749	data:	1681	data:
750		1682
751	$txn->{finished}->wait;	1683	$txn->{finished}->recv;
752	return $txn->{result};	1684	return $txn->{result};
753		1685
754	The actual code goes further and collects all errors (C<die>s, exceptions)	1686	The actual code goes further and collects all errors (C<die>s, exceptions)
755	that occured during request processing. The C<result> method detects	1687	that occurred during request processing. The C<result> method detects
756	whether an exception as thrown (it is stored inside the $txn object)	1688	whether an exception as thrown (it is stored inside the $txn object)
757	and just throws the exception, which means connection errors and other	1689	and just throws the exception, which means connection errors and other
758	problems get reported tot he code that tries to use the result, not in a	1690	problems get reported tot he code that tries to use the result, not in a
759	random callback.	1691	random callback.
760		1692
…		…
791		1723
792	my $quit = AnyEvent->condvar;	1724	my $quit = AnyEvent->condvar;
793		1725
794	$fcp->txn_client_get ($url)->cb (sub {	1726	$fcp->txn_client_get ($url)->cb (sub {
795	...	1727	...
796	$quit->broadcast;	1728	$quit->send;
797	});	1729	});
798		1730
799	$quit->wait;	1731	$quit->recv;
		1732
		1733
		1734	=head1 BENCHMARKS
		1735
		1736	To give you an idea of the performance and overheads that AnyEvent adds
		1737	over the event loops themselves and to give you an impression of the speed
		1738	of various event loops I prepared some benchmarks.
		1739
		1740	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1741
		1742	Here is a benchmark of various supported event models used natively and
		1743	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1744	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1745	which it is), lets them fire exactly once and destroys them again.
		1746
		1747	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1748	distribution.
		1749
		1750	=head3 Explanation of the columns
		1751
		1752	I<watcher> is the number of event watchers created/destroyed. Since
		1753	different event models feature vastly different performances, each event
		1754	loop was given a number of watchers so that overall runtime is acceptable
		1755	and similar between tested event loop (and keep them from crashing): Glib
		1756	would probably take thousands of years if asked to process the same number
		1757	of watchers as EV in this benchmark.
		1758
		1759	I<bytes> is the number of bytes (as measured by the resident set size,
		1760	RSS) consumed by each watcher. This method of measuring captures both C
		1761	and Perl-based overheads.
		1762
		1763	I<create> is the time, in microseconds (millionths of seconds), that it
		1764	takes to create a single watcher. The callback is a closure shared between
		1765	all watchers, to avoid adding memory overhead. That means closure creation
		1766	and memory usage is not included in the figures.
		1767
		1768	I<invoke> is the time, in microseconds, used to invoke a simple
		1769	callback. The callback simply counts down a Perl variable and after it was
		1770	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1771	signal the end of this phase.
		1772
		1773	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1774	watcher.
		1775
		1776	=head3 Results
		1777
		1778	name watchers bytes create invoke destroy comment
		1779	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
		1780	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
		1781	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
		1782	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
		1783	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
		1784	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1785	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1786	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
		1787	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
		1788	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
		1789	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
		1790	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
		1791
		1792	=head3 Discussion
		1793
		1794	The benchmark does I<not> measure scalability of the event loop very
		1795	well. For example, a select-based event loop (such as the pure perl one)
		1796	can never compete with an event loop that uses epoll when the number of
		1797	file descriptors grows high. In this benchmark, all events become ready at
		1798	the same time, so select/poll-based implementations get an unnatural speed
		1799	boost.
		1800
		1801	Also, note that the number of watchers usually has a nonlinear effect on
		1802	overall speed, that is, creating twice as many watchers doesn't take twice
		1803	the time - usually it takes longer. This puts event loops tested with a
		1804	higher number of watchers at a disadvantage.
		1805
		1806	To put the range of results into perspective, consider that on the
		1807	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1808	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1809	cycles with POE.
		1810
		1811	C<EV> is the sole leader regarding speed and memory use, which are both
		1812	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1813	far less memory than any other event loop and is still faster than Event
		1814	natively.
		1815
		1816	The pure perl implementation is hit in a few sweet spots (both the
		1817	constant timeout and the use of a single fd hit optimisations in the perl
		1818	interpreter and the backend itself). Nevertheless this shows that it
		1819	adds very little overhead in itself. Like any select-based backend its
		1820	performance becomes really bad with lots of file descriptors (and few of
		1821	them active), of course, but this was not subject of this benchmark.
		1822
		1823	The C<Event> module has a relatively high setup and callback invocation
		1824	cost, but overall scores in on the third place.
		1825
		1826	C<IO::Async> performs admirably well, about on par with C<Event>, even
		1827	when using its pure perl backend.
		1828
		1829	C<Glib>'s memory usage is quite a bit higher, but it features a
		1830	faster callback invocation and overall ends up in the same class as
		1831	C<Event>. However, Glib scales extremely badly, doubling the number of
		1832	watchers increases the processing time by more than a factor of four,
		1833	making it completely unusable when using larger numbers of watchers
		1834	(note that only a single file descriptor was used in the benchmark, so
		1835	inefficiencies of C<poll> do not account for this).
		1836
		1837	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1838	more than 2000 watchers is a big setback, however, as correctness takes
		1839	precedence over speed. Nevertheless, its performance is surprising, as the
		1840	file descriptor is dup()ed for each watcher. This shows that the dup()
		1841	employed by some adaptors is not a big performance issue (it does incur a
		1842	hidden memory cost inside the kernel which is not reflected in the figures
		1843	above).
		1844
		1845	C<POE>, regardless of underlying event loop (whether using its pure perl
		1846	select-based backend or the Event module, the POE-EV backend couldn't
		1847	be tested because it wasn't working) shows abysmal performance and
		1848	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1849	as EV watchers, and 10 times as much memory as Event (the high memory
		1850	requirements are caused by requiring a session for each watcher). Watcher
		1851	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1852	implementation.
		1853
		1854	The design of the POE adaptor class in AnyEvent can not really account
		1855	for the performance issues, though, as session creation overhead is
		1856	small compared to execution of the state machine, which is coded pretty
		1857	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1858	using multiple sessions is not a good approach, especially regarding
		1859	memory usage, even the author of POE could not come up with a faster
		1860	design).
		1861
		1862	=head3 Summary
		1863
		1864	=over 4
		1865
		1866	=item * Using EV through AnyEvent is faster than any other event loop
		1867	(even when used without AnyEvent), but most event loops have acceptable
		1868	performance with or without AnyEvent.
		1869
		1870	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1871	the actual event loop, only with extremely fast event loops such as EV
		1872	adds AnyEvent significant overhead.
		1873
		1874	=item * You should avoid POE like the plague if you want performance or
		1875	reasonable memory usage.
		1876
		1877	=back
		1878
		1879	=head2 BENCHMARKING THE LARGE SERVER CASE
		1880
		1881	This benchmark actually benchmarks the event loop itself. It works by
		1882	creating a number of "servers": each server consists of a socket pair, a
		1883	timeout watcher that gets reset on activity (but never fires), and an I/O
		1884	watcher waiting for input on one side of the socket. Each time the socket
		1885	watcher reads a byte it will write that byte to a random other "server".
		1886
		1887	The effect is that there will be a lot of I/O watchers, only part of which
		1888	are active at any one point (so there is a constant number of active
		1889	fds for each loop iteration, but which fds these are is random). The
		1890	timeout is reset each time something is read because that reflects how
		1891	most timeouts work (and puts extra pressure on the event loops).
		1892
		1893	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1894	(1%) are active. This mirrors the activity of large servers with many
		1895	connections, most of which are idle at any one point in time.
		1896
		1897	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1898	distribution.
		1899
		1900	=head3 Explanation of the columns
		1901
		1902	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1903	each server has a read and write socket end).
		1904
		1905	I<create> is the time it takes to create a socket pair (which is
		1906	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1907
		1908	I<request>, the most important value, is the time it takes to handle a
		1909	single "request", that is, reading the token from the pipe and forwarding
		1910	it to another server. This includes deleting the old timeout and creating
		1911	a new one that moves the timeout into the future.
		1912
		1913	=head3 Results
		1914
		1915	name sockets create request
		1916	EV 20000 69.01 11.16
		1917	Perl 20000 73.32 35.87
		1918	IOAsync 20000 157.00 98.14 epoll
		1919	IOAsync 20000 159.31 616.06 poll
		1920	Event 20000 212.62 257.32
		1921	Glib 20000 651.16 1896.30
		1922	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1923
		1924	=head3 Discussion
		1925
		1926	This benchmark I<does> measure scalability and overall performance of the
		1927	particular event loop.
		1928
		1929	EV is again fastest. Since it is using epoll on my system, the setup time
		1930	is relatively high, though.
		1931
		1932	Perl surprisingly comes second. It is much faster than the C-based event
		1933	loops Event and Glib.
		1934
		1935	IO::Async performs very well when using its epoll backend, and still quite
		1936	good compared to Glib when using its pure perl backend.
		1937
		1938	Event suffers from high setup time as well (look at its code and you will
		1939	understand why). Callback invocation also has a high overhead compared to
		1940	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1941	uses select or poll in basically all documented configurations.
		1942
		1943	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1944	clearly fails to perform with many filehandles or in busy servers.
		1945
		1946	POE is still completely out of the picture, taking over 1000 times as long
		1947	as EV, and over 100 times as long as the Perl implementation, even though
		1948	it uses a C-based event loop in this case.
		1949
		1950	=head3 Summary
		1951
		1952	=over 4
		1953
		1954	=item * The pure perl implementation performs extremely well.
		1955
		1956	=item * Avoid Glib or POE in large projects where performance matters.
		1957
		1958	=back
		1959
		1960	=head2 BENCHMARKING SMALL SERVERS
		1961
		1962	While event loops should scale (and select-based ones do not...) even to
		1963	large servers, most programs we (or I :) actually write have only a few
		1964	I/O watchers.
		1965
		1966	In this benchmark, I use the same benchmark program as in the large server
		1967	case, but it uses only eight "servers", of which three are active at any
		1968	one time. This should reflect performance for a small server relatively
		1969	well.
		1970
		1971	The columns are identical to the previous table.
		1972
		1973	=head3 Results
		1974
		1975	name sockets create request
		1976	EV 16 20.00 6.54
		1977	Perl 16 25.75 12.62
		1978	Event 16 81.27 35.86
		1979	Glib 16 32.63 15.48
		1980	POE 16 261.87 276.28 uses POE::Loop::Event
		1981
		1982	=head3 Discussion
		1983
		1984	The benchmark tries to test the performance of a typical small
		1985	server. While knowing how various event loops perform is interesting, keep
		1986	in mind that their overhead in this case is usually not as important, due
		1987	to the small absolute number of watchers (that is, you need efficiency and
		1988	speed most when you have lots of watchers, not when you only have a few of
		1989	them).
		1990
		1991	EV is again fastest.
		1992
		1993	Perl again comes second. It is noticeably faster than the C-based event
		1994	loops Event and Glib, although the difference is too small to really
		1995	matter.
		1996
		1997	POE also performs much better in this case, but is is still far behind the
		1998	others.
		1999
		2000	=head3 Summary
		2001
		2002	=over 4
		2003
		2004	=item * C-based event loops perform very well with small number of
		2005	watchers, as the management overhead dominates.
		2006
		2007	=back
		2008
		2009	=head2 THE IO::Lambda BENCHMARK
		2010
		2011	Recently I was told about the benchmark in the IO::Lambda manpage, which
		2012	could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
		2013	simply compares IO::Lambda with POE, and IO::Lambda looks better (which
		2014	shouldn't come as a surprise to anybody). As such, the benchmark is
		2015	fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
		2016	very optimal. But how would AnyEvent compare when used without the extra
		2017	baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
		2018
		2019	The benchmark itself creates an echo-server, and then, for 500 times,
		2020	connects to the echo server, sends a line, waits for the reply, and then
		2021	creates the next connection. This is a rather bad benchmark, as it doesn't
		2022	test the efficiency of the framework or much non-blocking I/O, but it is a
		2023	benchmark nevertheless.
		2024
		2025	name runtime
		2026	Lambda/select 0.330 sec
		2027	+ optimized 0.122 sec
		2028	Lambda/AnyEvent 0.327 sec
		2029	+ optimized 0.138 sec
		2030	Raw sockets/select 0.077 sec
		2031	POE/select, components 0.662 sec
		2032	POE/select, raw sockets 0.226 sec
		2033	POE/select, optimized 0.404 sec
		2034
		2035	AnyEvent/select/nb 0.085 sec
		2036	AnyEvent/EV/nb 0.068 sec
		2037	+state machine 0.134 sec
		2038
		2039	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		2040	benchmarks actually make blocking connects and use 100% blocking I/O,
		2041	defeating the purpose of an event-based solution. All of the newly
		2042	written AnyEvent benchmarks use 100% non-blocking connects (using
		2043	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		2044	resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
		2045	generally require a lot more bookkeeping and event handling than blocking
		2046	connects (which involve a single syscall only).
		2047
		2048	The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
		2049	offers similar expressive power as POE and IO::Lambda, using conventional
		2050	Perl syntax. This means that both the echo server and the client are 100%
		2051	non-blocking, further placing it at a disadvantage.
		2052
		2053	As you can see, the AnyEvent + EV combination even beats the
		2054	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		2055	backend easily beats IO::Lambda and POE.
		2056
		2057	And even the 100% non-blocking version written using the high-level (and
		2058	slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
		2059	large margin, even though it does all of DNS, tcp-connect and socket I/O
		2060	in a non-blocking way.
		2061
		2062	The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
		2063	F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
		2064	part of the IO::lambda distribution and were used without any changes.
		2065
		2066
		2067	=head1 SIGNALS
		2068
		2069	AnyEvent currently installs handlers for these signals:
		2070
		2071	=over 4
		2072
		2073	=item SIGCHLD
		2074
		2075	A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
		2076	emulation for event loops that do not support them natively. Also, some
		2077	event loops install a similar handler.
		2078
		2079	If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent will
		2080	reset it to default, to avoid losing child exit statuses.
		2081
		2082	=item SIGPIPE
		2083
		2084	A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
		2085	when AnyEvent gets loaded.
		2086
		2087	The rationale for this is that AnyEvent users usually do not really depend
		2088	on SIGPIPE delivery (which is purely an optimisation for shell use, or
		2089	badly-written programs), but C<SIGPIPE> can cause spurious and rare
		2090	program exits as a lot of people do not expect C<SIGPIPE> when writing to
		2091	some random socket.
		2092
		2093	The rationale for installing a no-op handler as opposed to ignoring it is
		2094	that this way, the handler will be restored to defaults on exec.
		2095
		2096	Feel free to install your own handler, or reset it to defaults.
		2097
		2098	=back
		2099
		2100	=cut
		2101
		2102	undef $SIG{CHLD}
		2103	if $SIG{CHLD} eq 'IGNORE';
		2104
		2105	$SIG{PIPE} = sub { }
		2106	unless defined $SIG{PIPE};
		2107
		2108	=head1 FORK
		2109
		2110	Most event libraries are not fork-safe. The ones who are usually are
		2111	because they rely on inefficient but fork-safe C<select> or C<poll>
		2112	calls. Only L<EV> is fully fork-aware.
		2113
		2114	If you have to fork, you must either do so I<before> creating your first
		2115	watcher OR you must not use AnyEvent at all in the child.
		2116
		2117
		2118	=head1 SECURITY CONSIDERATIONS
		2119
		2120	AnyEvent can be forced to load any event model via
		2121	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		2122	execute arbitrary code or directly gain access, it can easily be used to
		2123	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		2124	will not be active when the program uses a different event model than
		2125	specified in the variable.
		2126
		2127	You can make AnyEvent completely ignore this variable by deleting it
		2128	before the first watcher gets created, e.g. with a C<BEGIN> block:
		2129
		2130	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		2131
		2132	use AnyEvent;
		2133
		2134	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		2135	be used to probe what backend is used and gain other information (which is
		2136	probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
		2137	$ENV{PERL_ANYEVENT_STRICT}.
		2138
		2139	Note that AnyEvent will remove I<all> environment variables starting with
		2140	C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
		2141	enabled.
		2142
		2143
		2144	=head1 BUGS
		2145
		2146	Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
		2147	to work around. If you suffer from memleaks, first upgrade to Perl 5.10
		2148	and check wether the leaks still show up. (Perl 5.10.0 has other annoying
		2149	memleaks, such as leaking on C<map> and C<grep> but it is usually not as
		2150	pronounced).
		2151
800		2152
801	=head1 SEE ALSO	2153	=head1 SEE ALSO
802		2154
803	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	2155	Utility functions: L<AnyEvent::Util>.
804	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.
805		2156
806	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	2157	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		2158	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		2159
807	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	2160	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	2161	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		2162	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		2163	L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>.
809		2164
		2165	Non-blocking file handles, sockets, TCP clients and
		2166	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
		2167
		2168	Asynchronous DNS: L<AnyEvent::DNS>.
		2169
		2170	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>,
		2171	L<Coro::Event>,
		2172
810	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	2173	Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::XMPP>,
		2174	L<AnyEvent::HTTP>.
811		2175
812	=head1	2176
		2177	=head1 AUTHOR
		2178
		2179	Marc Lehmann <schmorp@schmorp.de>
		2180	http://home.schmorp.de/
813		2181
814	=cut	2182	=cut
815		2183
816	1	2184	1
817		2185

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