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Revision 1.54 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.139 by root, Mon May 26 06:04:38 2008 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, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
…		…
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	my $w = AnyEvent->condvar; # stores whether a condition was flagged	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		20	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	21	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's
22		22
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		24
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	26	nowadays. So what is different about AnyEvent?
…		…
57	as those use one of the supported event loops. It is trivial to add new	57	as those use one of the supported event loops. It is trivial to add new
58	event loops to AnyEvent, too, so it is future-proof).	58	event loops to AnyEvent, too, so it is future-proof).
59		59
60	In addition to being free of having to use I<the one and only true event	60	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	61	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	62	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	63	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	64	offering the functionality that is necessary, in as thin as a wrapper as
65	technically possible.	65	technically possible.
66		66
67	Of course, if you want lots of policy (this can arguably be somewhat	67	Of course, if you 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	68	useful) and you want to force your users to use the one and only event
69	model, you should I<not> use this module.	69	model, you should I<not> use this module.
70
71		70
72	=head1 DESCRIPTION	71	=head1 DESCRIPTION
73		72
74	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
75	allows module authors to utilise an event loop without forcing module	74	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>	78	The interface itself is vaguely similar, but not identical to the L<Event>
80	module.	79	module.
81		80
82	During the first call of any watcher-creation method, the module tries	81	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	82	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>,	83	following modules is already loaded: L<EV>,
85	L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found,	84	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	85	L<POE>. The first one found is used. If none are found, the module tries
		86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		87	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	88	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	89	found, AnyEvent will fall back to a pure-perl event loop, which is not
89	is not very efficient, but should work everywhere.	90	very efficient, but should work everywhere.
90		91
91	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
92	an event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
93	that model the default. For example:	94	that model the default. For example:
94		95
…		…
107		108
108	=head1 WATCHERS	109	=head1 WATCHERS
109		110
110	AnyEvent has the central concept of a I<watcher>, which is an object that	111	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	112	stores relevant data for each kind of event you are waiting for, such as
112	the callback to call, the filehandle to watch, etc.	113	the callback to call, the file handle to watch, etc.
113		114
114	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
115	creating a watcher it will immediately "watch" for events and invoke the	116	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	117	callback when the event occurs (of course, only when the event model
117	is in control).	118	is in control).
…		…
134		135
135	Note that C<my $w; $w => combination. This is necessary because in Perl,	136	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	137	my variables are only visible after the statement in which they are
137	declared.	138	declared.
138		139
139	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
140		141
141	You can create an I/O watcher by calling the C<< AnyEvent->io >> method	142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
142	with the following mandatory key-value pairs as arguments:	143	with the following mandatory key-value pairs as arguments:
143		144
144	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for	145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
145	events. C<poll> must be a string that is either C<r> or C<w>, which	146	for events. C<poll> must be a string that is either C<r> or C<w>,
146	creates a watcher waiting for "r"eadable or "w"ritable events,	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
147	respectively. C<cb> is the callback to invoke each time the file handle	148	respectively. C<cb> is the callback to invoke each time the file handle
148	becomes ready.	149	becomes ready.
149		150
150	File handles will be kept alive, so as long as the watcher exists, the	151	Although the callback might get passed parameters, their value and
151	file handle exists, too.	152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
152		154
		155	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	156	You must not close a file handle as long as any watcher is active on the
154	on the underlying file descriptor.	157	underlying file descriptor.
155		158
156	Some event loops issue spurious readyness notifications, so you should	159	Some event loops issue spurious readyness notifications, so you should
157	always use non-blocking calls when reading/writing from/to your file	160	always use non-blocking calls when reading/writing from/to your file
158	handles.	161	handles.
159		162
…		…
170		173
171	You can create a time watcher by calling the C<< AnyEvent->timer >>	174	You can create a time watcher by calling the C<< AnyEvent->timer >>
172	method with the following mandatory arguments:	175	method with the following mandatory arguments:
173		176
174	C<after> specifies after how many seconds (fractional values are	177	C<after> specifies after how many seconds (fractional values are
175	supported) should the timer activate. C<cb> the callback to invoke in that	178	supported) the callback should be invoked. C<cb> is the callback to invoke
176	case.	179	in that case.
		180
		181	Although the callback might get passed parameters, their value and
		182	presence is undefined and you cannot rely on them. Portable AnyEvent
		183	callbacks cannot use arguments passed to time watcher callbacks.
177		184
178	The timer callback will be invoked at most once: if you want a repeating	185	The timer callback will be invoked at most once: if you want a repeating
179	timer you have to create a new watcher (this is a limitation by both Tk	186	timer you have to create a new watcher (this is a limitation by both Tk
180	and Glib).	187	and Glib).
181		188
…		…
206		213
207	There are two ways to handle timers: based on real time (relative, "fire	214	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	215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
209	o'clock").	216	o'clock").
210		217
211	While most event loops expect timers to specified in a relative way, they use	218	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",	219	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	220	"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	221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
215	six years to finally fire.	222	fire "after" a second might actually take six years to finally fire.
216		223
217	AnyEvent cannot compensate for this. The only event loop that is conscious	224	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	225	about these issues is L<EV>, which offers both relative (ev_timer, based
219	absolute (ev_periodic) timers.	226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
220		228
221	AnyEvent always prefers relative timers, if available, matching the	229	AnyEvent always prefers relative timers, if available, matching the
222	AnyEvent API.	230	AnyEvent API.
223		231
224	=head2 SIGNAL WATCHERS	232	=head2 SIGNAL WATCHERS
225		233
226	You can watch for signals using a signal watcher, C<signal> is the signal	234	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	235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
228	be invoked whenever a signal occurs.	236	be invoked whenever a signal occurs.
229		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
230	Multiple signals occurances can be clumped together into one callback	242	Multiple signal occurrences can be clumped together into one callback
231	invocation, and callback invocation will be synchronous. synchronous means	243	invocation, and callback invocation will be synchronous. Synchronous means
232	that it might take a while until the signal gets handled by the process,	244	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.	245	but it is guaranteed not to interrupt any other callbacks.
234		246
235	The main advantage of using these watchers is that you can share a signal	247	The main advantage of using these watchers is that you can share a signal
236	between multiple watchers.	248	between multiple watchers.
237		249
238	This watcher might use C<%SIG>, so programs overwriting those signals	250	This watcher might use C<%SIG>, so programs overwriting those signals
…		…
248		260
249	The child process is specified by the C<pid> argument (if set to C<0>, it	261	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	262	watches for any child process exit). The watcher will trigger as often
251	as status change for the child are received. This works by installing a	263	as status change for the child are received. This works by installing a
252	signal handler for C<SIGCHLD>. The callback will be called with the pid	264	signal handler for C<SIGCHLD>. The callback will be called with the pid
253	and exit status (as returned by waitpid).	265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
254		267
255	Example: wait for pid 1333	268	There is a slight catch to child watchers, however: you usually start them
		269	I<after> the child process was created, and this means the process could
		270	have exited already (and no SIGCHLD will be sent anymore).
		271
		272	Not all event models handle this correctly (POE doesn't), but even for
		273	event models that I<do> handle this correctly, they usually need to be
		274	loaded before the process exits (i.e. before you fork in the first place).
		275
		276	This means you cannot create a child watcher as the very first thing in an
		277	AnyEvent program, you I<have> to create at least one watcher before you
		278	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		279
		280	Example: fork a process and wait for it
		281
		282	my $done = AnyEvent->condvar;
		283
		284	my $pid = fork or exit 5;
256		285
257	my $w = AnyEvent->child (	286	my $w = AnyEvent->child (
258	pid => 1333,	287	pid => $pid,
259	cb => sub {	288	cb => sub {
260	my ($pid, $status) = @_;	289	my ($pid, $status) = @_;
261	warn "pid $pid exited with status $status";	290	warn "pid $pid exited with status $status";
		291	$done->send;
262	},	292	},
263	);	293	);
264		294
		295	# do something else, then wait for process exit
		296	$done->recv;
		297
265	=head2 CONDITION VARIABLES	298	=head2 CONDITION VARIABLES
266		299
		300	If you are familiar with some event loops you will know that all of them
		301	require you to run some blocking "loop", "run" or similar function that
		302	will actively watch for new events and call your callbacks.
		303
		304	AnyEvent is different, it expects somebody else to run the event loop and
		305	will only block when necessary (usually when told by the user).
		306
		307	The instrument to do that is called a "condition variable", so called
		308	because they represent a condition that must become true.
		309
267	Condition variables can be created by calling the C<< AnyEvent->condvar >>	310	Condition variables can be created by calling the C<< AnyEvent->condvar
268	method without any arguments.	311	>> method, usually without arguments. The only argument pair allowed is
		312	C<cb>, which specifies a callback to be called when the condition variable
		313	becomes true.
269		314
270	A condition variable waits for a condition - precisely that the C<<	315	After creation, the condition variable is "false" until it becomes "true"
271	->broadcast >> method has been called.	316	by calling the C<send> method (or calling the condition variable as if it
		317	were a callback, read about the caveats in the description for the C<<
		318	->send >> method).
272		319
273	They are very useful to signal that a condition has been fulfilled, for	320	Condition variables are similar to callbacks, except that you can
		321	optionally wait for them. They can also be called merge points - points
		322	in time where multiple outstanding events have been processed. And yet
		323	another way to call them is transactions - each condition variable can be
		324	used to represent a transaction, which finishes at some point and delivers
		325	a result.
		326
		327	Condition variables are very useful to signal that something has finished,
274	example, if you write a module that does asynchronous http requests,	328	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	329	then a condition variable would be the ideal candidate to signal the
276	availability of results.	330	availability of results. The user can either act when the callback is
		331	called or can synchronously C<< ->recv >> for the results.
277		332
278	You can also use condition variables to block your main program until	333	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	334	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<<	335	could C<< ->recv >> in your main program until the user clicks the Quit
281	->broadcast >> the "quit" event.	336	button of your app, which would C<< ->send >> the "quit" event.
282		337
283	Note that condition variables recurse into the event loop - if you have	338	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	339	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	340	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,	341	you should avoid making a blocking wait yourself, at least in callbacks,
287	as this asks for trouble.	342	as this asks for trouble.
288		343
289	This object has two methods:	344	Condition variables are represented by hash refs in perl, and the keys
		345	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		346	easy (it is often useful to build your own transaction class on top of
		347	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		348	it's C<new> method in your own C<new> method.
		349
		350	There are two "sides" to a condition variable - the "producer side" which
		351	eventually calls C<< -> send >>, and the "consumer side", which waits
		352	for the send to occur.
		353
		354	Example: wait for a timer.
		355
		356	# wait till the result is ready
		357	my $result_ready = AnyEvent->condvar;
		358
		359	# do something such as adding a timer
		360	# or socket watcher the calls $result_ready->send
		361	# when the "result" is ready.
		362	# in this case, we simply use a timer:
		363	my $w = AnyEvent->timer (
		364	after => 1,
		365	cb => sub { $result_ready->send },
		366	);
		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls send
		370	$result_ready->recv;
		371
		372	Example: wait for a timer, but take advantage of the fact that
		373	condition variables are also code references.
		374
		375	my $done = AnyEvent->condvar;
		376	my $delay = AnyEvent->timer (after => 5, cb => $done);
		377	$done->recv;
		378
		379	=head3 METHODS FOR PRODUCERS
		380
		381	These methods should only be used by the producing side, i.e. the
		382	code/module that eventually sends the signal. Note that it is also
		383	the producer side which creates the condvar in most cases, but it isn't
		384	uncommon for the consumer to create it as well.
290		385
291	=over 4	386	=over 4
292		387
		388	=item $cv->send (...)
		389
		390	Flag the condition as ready - a running C<< ->recv >> and all further
		391	calls to C<recv> will (eventually) return after this method has been
		392	called. If nobody is waiting the send will be remembered.
		393
		394	If a callback has been set on the condition variable, it is called
		395	immediately from within send.
		396
		397	Any arguments passed to the C<send> call will be returned by all
		398	future C<< ->recv >> calls.
		399
		400	Condition variables are overloaded so one can call them directly
		401	(as a code reference). Calling them directly is the same as calling
		402	C<send>. Note, however, that many C-based event loops do not handle
		403	overloading, so as tempting as it may be, passing a condition variable
		404	instead of a callback does not work. Both the pure perl and EV loops
		405	support overloading, however, as well as all functions that use perl to
		406	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		407	example).
		408
		409	=item $cv->croak ($error)
		410
		411	Similar to send, but causes all call's to C<< ->recv >> to invoke
		412	C<Carp::croak> with the given error message/object/scalar.
		413
		414	This can be used to signal any errors to the condition variable
		415	user/consumer.
		416
		417	=item $cv->begin ([group callback])
		418
293	=item $cv->wait	419	=item $cv->end
294		420
295	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	421	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		422
		423	These two methods can be used to combine many transactions/events into
		424	one. For example, a function that pings many hosts in parallel might want
		425	to use a condition variable for the whole process.
		426
		427	Every call to C<< ->begin >> will increment a counter, and every call to
		428	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		429	>>, the (last) callback passed to C<begin> will be executed. That callback
		430	is I<supposed> to call C<< ->send >>, but that is not required. If no
		431	callback was set, C<send> will be called without any arguments.
		432
		433	Let's clarify this with the ping example:
		434
		435	my $cv = AnyEvent->condvar;
		436
		437	my %result;
		438	$cv->begin (sub { $cv->send (\%result) });
		439
		440	for my $host (@list_of_hosts) {
		441	$cv->begin;
		442	ping_host_then_call_callback $host, sub {
		443	$result{$host} = ...;
		444	$cv->end;
		445	};
		446	}
		447
		448	$cv->end;
		449
		450	This code fragment supposedly pings a number of hosts and calls
		451	C<send> after results for all then have have been gathered - in any
		452	order. To achieve this, the code issues a call to C<begin> when it starts
		453	each ping request and calls C<end> when it has received some result for
		454	it. Since C<begin> and C<end> only maintain a counter, the order in which
		455	results arrive is not relevant.
		456
		457	There is an additional bracketing call to C<begin> and C<end> outside the
		458	loop, which serves two important purposes: first, it sets the callback
		459	to be called once the counter reaches C<0>, and second, it ensures that
		460	C<send> is called even when C<no> hosts are being pinged (the loop
		461	doesn't execute once).
		462
		463	This is the general pattern when you "fan out" into multiple subrequests:
		464	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		465	is called at least once, and then, for each subrequest you start, call
		466	C<begin> and for each subrequest you finish, call C<end>.
		467
		468	=back
		469
		470	=head3 METHODS FOR CONSUMERS
		471
		472	These methods should only be used by the consuming side, i.e. the
		473	code awaits the condition.
		474
		475	=over 4
		476
		477	=item $cv->recv
		478
		479	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
296	called on c<$cv>, while servicing other watchers normally.	480	>> methods have been called on c<$cv>, while servicing other watchers
		481	normally.
297		482
298	You can only wait once on a condition - additional calls will return	483	You can only wait once on a condition - additional calls are valid but
299	immediately.	484	will return immediately.
		485
		486	If an error condition has been set by calling C<< ->croak >>, then this
		487	function will call C<croak>.
		488
		489	In list context, all parameters passed to C<send> will be returned,
		490	in scalar context only the first one will be returned.
300		491
301	Not all event models support a blocking wait - some die in that case	492	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	493	(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	494	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	495	caller decide whether the call will block or not (for example, by coupling
305	condition variables with some kind of request results and supporting	496	condition variables with some kind of request results and supporting
306	callbacks so the caller knows that getting the result will not block,	497	callbacks so the caller knows that getting the result will not block,
307	while still suppporting blocking waits if the caller so desires).	498	while still supporting blocking waits if the caller so desires).
308		499
309	Another reason I<never> to C<< ->wait >> in a module is that you cannot	500	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	501	sensibly have two C<< ->recv >>'s in parallel, as that would require
311	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	502	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
312	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and	503	can supply.
313	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
314	from different coroutines, however).
315		504
316	=item $cv->broadcast	505	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		506	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		507	versions and also integrates coroutines into AnyEvent, making blocking
		508	C<< ->recv >> calls perfectly safe as long as they are done from another
		509	coroutine (one that doesn't run the event loop).
317		510
318	Flag the condition as ready - a running C<< ->wait >> and all further	511	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	512	only calling C<< ->recv >> from within that callback (or at a later
320	called. If nobody is waiting the broadcast will be remembered..	513	time). This will work even when the event loop does not support blocking
		514	waits otherwise.
		515
		516	=item $bool = $cv->ready
		517
		518	Returns true when the condition is "true", i.e. whether C<send> or
		519	C<croak> have been called.
		520
		521	=item $cb = $cv->cb ([new callback])
		522
		523	This is a mutator function that returns the callback set and optionally
		524	replaces it before doing so.
		525
		526	The callback will be called when the condition becomes "true", i.e. when
		527	C<send> or C<croak> are called. Calling C<recv> inside the callback
		528	or at any later time is guaranteed not to block.
321		529
322	=back	530	=back
323
324	Example:
325
326	# wait till the result is ready
327	my $result_ready = AnyEvent->condvar;
328
329	# do something such as adding a timer
330	# or socket watcher the calls $result_ready->broadcast
331	# when the "result" is ready.
332	# in this case, we simply use a timer:
333	my $w = AnyEvent->timer (
334	after => 1,
335	cb => sub { $result_ready->broadcast },
336	);
337
338	# this "blocks" (while handling events) till the watcher
339	# calls broadcast
340	$result_ready->wait;
341		531
342	=head1 GLOBAL VARIABLES AND FUNCTIONS	532	=head1 GLOBAL VARIABLES AND FUNCTIONS
343		533
344	=over 4	534	=over 4
345		535
…		…
351	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	541	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>).	542	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
353		543
354	The known classes so far are:	544	The known classes so far are:
355		545
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).	546	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
359	AnyEvent::Impl::Event based on Event, also second best choice :)	547	AnyEvent::Impl::Event based on Event, second best choice.
		548	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
360	AnyEvent::Impl::Glib based on Glib, third-best choice.	549	AnyEvent::Impl::Glib based on Glib, third-best choice.
361	AnyEvent::Impl::Tk based on Tk, very bad choice.	550	AnyEvent::Impl::Tk based on Tk, very bad choice.
362	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	551	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		552	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		553	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		554
		555	There is no support for WxWidgets, as WxWidgets has no support for
		556	watching file handles. However, you can use WxWidgets through the
		557	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		558	second, which was considered to be too horrible to even consider for
		559	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		560	it's adaptor.
		561
		562	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		563	autodetecting them.
363		564
364	=item AnyEvent::detect	565	=item AnyEvent::detect
365		566
366	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model	567	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
367	if necessary. You should only call this function right before you would	568	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	569	have created an AnyEvent watcher anyway, that is, as late as possible at
369	runtime.	570	runtime.
370		571
		572	=item $guard = AnyEvent::post_detect { BLOCK }
		573
		574	Arranges for the code block to be executed as soon as the event model is
		575	autodetected (or immediately if this has already happened).
		576
		577	If called in scalar or list context, then it creates and returns an object
		578	that automatically removes the callback again when it is destroyed. See
		579	L<Coro::BDB> for a case where this is useful.
		580
		581	=item @AnyEvent::post_detect
		582
		583	If there are any code references in this array (you can C<push> to it
		584	before or after loading AnyEvent), then they will called directly after
		585	the event loop has been chosen.
		586
		587	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		588	if it contains a true value then the event loop has already been detected,
		589	and the array will be ignored.
		590
		591	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		592
371	=back	593	=back
372		594
373	=head1 WHAT TO DO IN A MODULE	595	=head1 WHAT TO DO IN A MODULE
374		596
375	As a module author, you should C<use AnyEvent> and call AnyEvent methods	597	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	600	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	601	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	602	by calling AnyEvent in your module body you force the user of your module
381	to load the event module first.	603	to load the event module first.
382		604
383	Never call C<< ->wait >> on a condition variable unless you I<know> that	605	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	606	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	607	because it will stall the whole program, and the whole point of using
386	events is to stay interactive.	608	events is to stay interactive.
387		609
388	It is fine, however, to call C<< ->wait >> when the user of your module	610	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	611	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 >>	612	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).	613	freely, as the user of your module knows what she is doing. always).
392		614
393	=head1 WHAT TO DO IN THE MAIN PROGRAM	615	=head1 WHAT TO DO IN THE MAIN PROGRAM
394		616
395	There will always be a single main program - the only place that should	617	There will always be a single main program - the only place that should
…		…
397		619
398	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	620	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	621	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.	622	decide which implementation to chose if some module relies on it.
401		623
402	If the main program relies on a specific event model. For example, in	624	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	625	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	626	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	627	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	628	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	629	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.	630	might chose the wrong one unless you load the correct one yourself.
409		631
410	You can chose to use a rather inefficient pure-perl implementation by	632	You can chose to use a pure-perl implementation by loading the
411	loading the C<AnyEvent::Impl::Perl> module, which gives you similar	633	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
412	behaviour everywhere, but letting AnyEvent chose is generally better.	634	everywhere, but letting AnyEvent chose the model is generally better.
		635
		636	=head2 MAINLOOP EMULATION
		637
		638	Sometimes (often for short test scripts, or even standalone programs who
		639	only want to use AnyEvent), you do not want to run a specific event loop.
		640
		641	In that case, you can use a condition variable like this:
		642
		643	AnyEvent->condvar->recv;
		644
		645	This has the effect of entering the event loop and looping forever.
		646
		647	Note that usually your program has some exit condition, in which case
		648	it is better to use the "traditional" approach of storing a condition
		649	variable somewhere, waiting for it, and sending it when the program should
		650	exit cleanly.
		651
		652
		653	=head1 OTHER MODULES
		654
		655	The following is a non-exhaustive list of additional modules that use
		656	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		657	in the same program. Some of the modules come with AnyEvent, some are
		658	available via CPAN.
		659
		660	=over 4
		661
		662	=item L<AnyEvent::Util>
		663
		664	Contains various utility functions that replace often-used but blocking
		665	functions such as C<inet_aton> by event-/callback-based versions.
		666
		667	=item L<AnyEvent::Handle>
		668
		669	Provide read and write buffers and manages watchers for reads and writes.
		670
		671	=item L<AnyEvent::Socket>
		672
		673	Provides various utility functions for (internet protocol) sockets,
		674	addresses and name resolution. Also functions to create non-blocking tcp
		675	connections or tcp servers, with IPv6 and SRV record support and more.
		676
		677	=item L<AnyEvent::DNS>
		678
		679	Provides rich asynchronous DNS resolver capabilities.
		680
		681	=item L<AnyEvent::HTTPD>
		682
		683	Provides a simple web application server framework.
		684
		685	=item L<AnyEvent::FastPing>
		686
		687	The fastest ping in the west.
		688
		689	=item L<Net::IRC3>
		690
		691	AnyEvent based IRC client module family.
		692
		693	=item L<Net::XMPP2>
		694
		695	AnyEvent based XMPP (Jabber protocol) module family.
		696
		697	=item L<Net::FCP>
		698
		699	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		700	of AnyEvent.
		701
		702	=item L<Event::ExecFlow>
		703
		704	High level API for event-based execution flow control.
		705
		706	=item L<Coro>
		707
		708	Has special support for AnyEvent via L<Coro::AnyEvent>.
		709
		710	=item L<AnyEvent::AIO>, L<IO::AIO>
		711
		712	Truly asynchronous I/O, should be in the toolbox of every event
		713	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		714	together.
		715
		716	=item L<AnyEvent::BDB>, L<BDB>
		717
		718	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		719	IO::AIO and AnyEvent together.
		720
		721	=item L<IO::Lambda>
		722
		723	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		724
		725	=back
413		726
414	=cut	727	=cut
415		728
416	package AnyEvent;	729	package AnyEvent;
417		730
418	no warnings;	731	no warnings;
419	use strict;	732	use strict;
420		733
421	use Carp;	734	use Carp;
422		735
423	our $VERSION = '3.12';	736	our $VERSION = '4.04';
424	our $MODEL;	737	our $MODEL;
425		738
426	our $AUTOLOAD;	739	our $AUTOLOAD;
427	our @ISA;	740	our @ISA;
428		741
		742	our @REGISTRY;
		743
		744	our $WIN32;
		745
		746	BEGIN {
		747	my $win32 = ! ! ($^O =~ /mswin32/i);
		748	eval "sub WIN32(){ $win32 }";
		749	}
		750
429	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	751	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
430		752
431	our @REGISTRY;	753	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		754
		755	{
		756	my $idx;
		757	$PROTOCOL{$_} = ++$idx
		758	for reverse split /\s*,\s*/,
		759	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		760	}
		761
		762	sub import {
		763	shift;
		764	return unless @_;
		765
		766	my $pkg = caller;
		767
		768	no strict 'refs';
		769
		770	for (@_) {
		771	*{"$pkg\::WIN32"} = *WIN32 if $_ eq "WIN32";
		772	}
		773	}
432		774
433	my @models = (	775	my @models = (
434	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
435	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
436	[EV:: => AnyEvent::Impl::EV::],	776	[EV:: => AnyEvent::Impl::EV::],
437	[Event:: => AnyEvent::Impl::Event::],	777	[Event:: => AnyEvent::Impl::Event::],
438	[Glib:: => AnyEvent::Impl::Glib::],
439	[Tk:: => AnyEvent::Impl::Tk::],
440	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	778	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		779	# everything below here will not be autoprobed
		780	# as the pureperl backend should work everywhere
		781	# and is usually faster
		782	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		783	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		784	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		785	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		786	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		787	[Wx:: => AnyEvent::Impl::POE::],
		788	[Prima:: => AnyEvent::Impl::POE::],
441	);	789	);
442		790
443	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	791	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		792
		793	our @post_detect;
		794
		795	sub post_detect(&) {
		796	my ($cb) = @_;
		797
		798	if ($MODEL) {
		799	$cb->();
		800
		801	1
		802	} else {
		803	push @post_detect, $cb;
		804
		805	defined wantarray
		806	? bless \$cb, "AnyEvent::Util::PostDetect"
		807	: ()
		808	}
		809	}
		810
		811	sub AnyEvent::Util::PostDetect::DESTROY {
		812	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		813	}
444		814
445	sub detect() {	815	sub detect() {
446	unless ($MODEL) {	816	unless ($MODEL) {
447	no strict 'refs';	817	no strict 'refs';
		818	local $SIG{__DIE__};
		819
		820	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		821	my $model = "AnyEvent::Impl::$1";
		822	if (eval "require $model") {
		823	$MODEL = $model;
		824	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		825	} else {
		826	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		827	}
		828	}
448		829
449	# check for already loaded models	830	# check for already loaded models
		831	unless ($MODEL) {
450	for (@REGISTRY, @models) {	832	for (@REGISTRY, @models) {
451	my ($package, $model) = @$_;	833	my ($package, $model) = @$_;
452	if (${"$package\::VERSION"} > 0) {	834	if (${"$package\::VERSION"} > 0) {
453	if (eval "require $model") {	835	if (eval "require $model") {
454	$MODEL = $model;	836	$MODEL = $model;
455	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	837	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
456	last;	838	last;
		839	}
457	}	840	}
458	}	841	}
459	}
460		842
461	unless ($MODEL) {	843	unless ($MODEL) {
462	# try to load a model	844	# try to load a model
463		845
464	for (@REGISTRY, @models) {	846	for (@REGISTRY, @models) {
465	my ($package, $model) = @$_;	847	my ($package, $model) = @$_;
466	if (eval "require $package"	848	if (eval "require $package"
467	and ${"$package\::VERSION"} > 0	849	and ${"$package\::VERSION"} > 0
468	and eval "require $model") {	850	and eval "require $model") {
469	$MODEL = $model;	851	$MODEL = $model;
470	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	852	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
471	last;	853	last;
		854	}
472	}	855	}
		856
		857	$MODEL
		858	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
473	}	859	}
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	}	860	}
478		861
479	unshift @ISA, $MODEL;	862	unshift @ISA, $MODEL;
480	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	863	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		864
		865	(shift @post_detect)->() while @post_detect;
481	}	866	}
482		867
483	$MODEL	868	$MODEL
484	}	869	}
485		870
…		…
495	$class->$func (@_);	880	$class->$func (@_);
496	}	881	}
497		882
498	package AnyEvent::Base;	883	package AnyEvent::Base;
499		884
500	# default implementation for ->condvar, ->wait, ->broadcast	885	# default implementation for ->condvar
501		886
502	sub condvar {	887	sub condvar {
503	bless \my $flag, "AnyEvent::Base::CondVar"	888	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	}	889	}
513		890
514	# default implementation for ->signal	891	# default implementation for ->signal
515		892
516	our %SIG_CB;	893	our %SIG_CB;
…		…
569	or Carp::croak "required option 'pid' is missing";	946	or Carp::croak "required option 'pid' is missing";
570		947
571	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	948	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
572		949
573	unless ($WNOHANG) {	950	unless ($WNOHANG) {
574	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	951	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
575	}	952	}
576		953
577	unless ($CHLD_W) {	954	unless ($CHLD_W) {
578	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	955	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
579	# child could be a zombie already, so make at least one round	956	# child could be a zombie already, so make at least one round
…		…
589	delete $PID_CB{$pid}{$cb};	966	delete $PID_CB{$pid}{$cb};
590	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	967	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
591		968
592	undef $CHLD_W unless keys %PID_CB;	969	undef $CHLD_W unless keys %PID_CB;
593	}	970	}
		971
		972	package AnyEvent::CondVar;
		973
		974	our @ISA = AnyEvent::CondVar::Base::;
		975
		976	package AnyEvent::CondVar::Base;
		977
		978	use overload
		979	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		980	fallback => 1;
		981
		982	sub _send {
		983	# nop
		984	}
		985
		986	sub send {
		987	my $cv = shift;
		988	$cv->{_ae_sent} = [@_];
		989	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		990	$cv->_send;
		991	}
		992
		993	sub croak {
		994	$_[0]{_ae_croak} = $_[1];
		995	$_[0]->send;
		996	}
		997
		998	sub ready {
		999	$_[0]{_ae_sent}
		1000	}
		1001
		1002	sub _wait {
		1003	AnyEvent->one_event while !$_[0]{_ae_sent};
		1004	}
		1005
		1006	sub recv {
		1007	$_[0]->_wait;
		1008
		1009	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1010	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1011	}
		1012
		1013	sub cb {
		1014	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1015	$_[0]{_ae_cb}
		1016	}
		1017
		1018	sub begin {
		1019	++$_[0]{_ae_counter};
		1020	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1021	}
		1022
		1023	sub end {
		1024	return if --$_[0]{_ae_counter};
		1025	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1026	}
		1027
		1028	# undocumented/compatibility with pre-3.4
		1029	*broadcast = \&send;
		1030	*wait = \&_wait;
594		1031
595	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1032	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
596		1033
597	This is an advanced topic that you do not normally need to use AnyEvent in	1034	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	1035	a module. This section is only of use to event loop authors who want to
…		…
637		1074
638	=head1 ENVIRONMENT VARIABLES	1075	=head1 ENVIRONMENT VARIABLES
639		1076
640	The following environment variables are used by this module:	1077	The following environment variables are used by this module:
641		1078
642	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to	1079	=over 4
643	report to STDERR which event model it chooses.	1080
		1081	=item C<PERL_ANYEVENT_VERBOSE>
		1082
		1083	By default, AnyEvent will be completely silent except in fatal
		1084	conditions. You can set this environment variable to make AnyEvent more
		1085	talkative.
		1086
		1087	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1088	conditions, such as not being able to load the event model specified by
		1089	C<PERL_ANYEVENT_MODEL>.
		1090
		1091	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1092	model it chooses.
		1093
		1094	=item C<PERL_ANYEVENT_MODEL>
		1095
		1096	This can be used to specify the event model to be used by AnyEvent, before
		1097	auto detection and -probing kicks in. It must be a string consisting
		1098	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1099	and the resulting module name is loaded and if the load was successful,
		1100	used as event model. If it fails to load AnyEvent will proceed with
		1101	auto detection and -probing.
		1102
		1103	This functionality might change in future versions.
		1104
		1105	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1106	could start your program like this:
		1107
		1108	PERL_ANYEVENT_MODEL=Perl perl ...
		1109
		1110	=item C<PERL_ANYEVENT_PROTOCOLS>
		1111
		1112	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1113	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1114	of auto probing).
		1115
		1116	Must be set to a comma-separated list of protocols or address families,
		1117	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1118	used, and preference will be given to protocols mentioned earlier in the
		1119	list.
		1120
		1121	This variable can effectively be used for denial-of-service attacks
		1122	against local programs (e.g. when setuid), although the impact is likely
		1123	small, as the program has to handle connection errors already-
		1124
		1125	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1126	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1127	- only support IPv4, never try to resolve or contact IPv6
		1128	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1129	IPv6, but prefer IPv6 over IPv4.
		1130
		1131	=item C<PERL_ANYEVENT_EDNS0>
		1132
		1133	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1134	for DNS. This extension is generally useful to reduce DNS traffic, but
		1135	some (broken) firewalls drop such DNS packets, which is why it is off by
		1136	default.
		1137
		1138	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1139	EDNS0 in its DNS requests.
		1140
		1141	=back
644		1142
645	=head1 EXAMPLE PROGRAM	1143	=head1 EXAMPLE PROGRAM
646		1144
647	The following program uses an IO watcher to read data from STDIN, a timer	1145	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	1146	to display a message once per second, and a condition variable to quit the
649	program when the user enters quit:	1147	program when the user enters quit:
650		1148
651	use AnyEvent;	1149	use AnyEvent;
652		1150
…		…
657	poll => 'r',	1155	poll => 'r',
658	cb => sub {	1156	cb => sub {
659	warn "io event <$_[0]>\n"; # will always output <r>	1157	warn "io event <$_[0]>\n"; # will always output <r>
660	chomp (my $input = <STDIN>); # read a line	1158	chomp (my $input = <STDIN>); # read a line
661	warn "read: $input\n"; # output what has been read	1159	warn "read: $input\n"; # output what has been read
662	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1160	$cv->send if $input =~ /^q/i; # quit program if /^q/i
663	},	1161	},
664	);	1162	);
665		1163
666	my $time_watcher; # can only be used once	1164	my $time_watcher; # can only be used once
667		1165
…		…
672	});	1170	});
673	}	1171	}
674		1172
675	new_timer; # create first timer	1173	new_timer; # create first timer
676		1174
677	$cv->wait; # wait until user enters /^q/i	1175	$cv->recv; # wait until user enters /^q/i
678		1176
679	=head1 REAL-WORLD EXAMPLE	1177	=head1 REAL-WORLD EXAMPLE
680		1178
681	Consider the L<Net::FCP> module. It features (among others) the following	1179	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:	1180	API calls, which are to freenet what HTTP GET requests are to http:
…		…
732	syswrite $txn->{fh}, $txn->{request}	1230	syswrite $txn->{fh}, $txn->{request}
733	or die "connection or write error";	1231	or die "connection or write error";
734	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1232	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
735		1233
736	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1234	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:	1235	result and signals any possible waiters that the request has finished:
738		1236
739	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1237	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
740		1238
741	if (end-of-file or data complete) {	1239	if (end-of-file or data complete) {
742	$txn->{result} = $txn->{buf};	1240	$txn->{result} = $txn->{buf};
743	$txn->{finished}->broadcast;	1241	$txn->{finished}->send;
744	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1242	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
745	}	1243	}
746		1244
747	The C<result> method, finally, just waits for the finished signal (if the	1245	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	1246	request was already finished, it doesn't wait, of course, and returns the
749	data:	1247	data:
750		1248
751	$txn->{finished}->wait;	1249	$txn->{finished}->recv;
752	return $txn->{result};	1250	return $txn->{result};
753		1251
754	The actual code goes further and collects all errors (C<die>s, exceptions)	1252	The actual code goes further and collects all errors (C<die>s, exceptions)
755	that occured during request processing. The C<result> method detects	1253	that occurred during request processing. The C<result> method detects
756	whether an exception as thrown (it is stored inside the $txn object)	1254	whether an exception as thrown (it is stored inside the $txn object)
757	and just throws the exception, which means connection errors and other	1255	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	1256	problems get reported tot he code that tries to use the result, not in a
759	random callback.	1257	random callback.
760		1258
…		…
791		1289
792	my $quit = AnyEvent->condvar;	1290	my $quit = AnyEvent->condvar;
793		1291
794	$fcp->txn_client_get ($url)->cb (sub {	1292	$fcp->txn_client_get ($url)->cb (sub {
795	...	1293	...
796	$quit->broadcast;	1294	$quit->send;
797	});	1295	});
798		1296
799	$quit->wait;	1297	$quit->recv;
		1298
		1299
		1300	=head1 BENCHMARKS
		1301
		1302	To give you an idea of the performance and overheads that AnyEvent adds
		1303	over the event loops themselves and to give you an impression of the speed
		1304	of various event loops I prepared some benchmarks.
		1305
		1306	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1307
		1308	Here is a benchmark of various supported event models used natively and
		1309	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1310	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1311	which it is), lets them fire exactly once and destroys them again.
		1312
		1313	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1314	distribution.
		1315
		1316	=head3 Explanation of the columns
		1317
		1318	I<watcher> is the number of event watchers created/destroyed. Since
		1319	different event models feature vastly different performances, each event
		1320	loop was given a number of watchers so that overall runtime is acceptable
		1321	and similar between tested event loop (and keep them from crashing): Glib
		1322	would probably take thousands of years if asked to process the same number
		1323	of watchers as EV in this benchmark.
		1324
		1325	I<bytes> is the number of bytes (as measured by the resident set size,
		1326	RSS) consumed by each watcher. This method of measuring captures both C
		1327	and Perl-based overheads.
		1328
		1329	I<create> is the time, in microseconds (millionths of seconds), that it
		1330	takes to create a single watcher. The callback is a closure shared between
		1331	all watchers, to avoid adding memory overhead. That means closure creation
		1332	and memory usage is not included in the figures.
		1333
		1334	I<invoke> is the time, in microseconds, used to invoke a simple
		1335	callback. The callback simply counts down a Perl variable and after it was
		1336	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1337	signal the end of this phase.
		1338
		1339	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1340	watcher.
		1341
		1342	=head3 Results
		1343
		1344	name watchers bytes create invoke destroy comment
		1345	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1346	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1347	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1348	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1349	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1350	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1351	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1352	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1353	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1354	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1355
		1356	=head3 Discussion
		1357
		1358	The benchmark does I<not> measure scalability of the event loop very
		1359	well. For example, a select-based event loop (such as the pure perl one)
		1360	can never compete with an event loop that uses epoll when the number of
		1361	file descriptors grows high. In this benchmark, all events become ready at
		1362	the same time, so select/poll-based implementations get an unnatural speed
		1363	boost.
		1364
		1365	Also, note that the number of watchers usually has a nonlinear effect on
		1366	overall speed, that is, creating twice as many watchers doesn't take twice
		1367	the time - usually it takes longer. This puts event loops tested with a
		1368	higher number of watchers at a disadvantage.
		1369
		1370	To put the range of results into perspective, consider that on the
		1371	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1372	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1373	cycles with POE.
		1374
		1375	C<EV> is the sole leader regarding speed and memory use, which are both
		1376	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1377	far less memory than any other event loop and is still faster than Event
		1378	natively.
		1379
		1380	The pure perl implementation is hit in a few sweet spots (both the
		1381	constant timeout and the use of a single fd hit optimisations in the perl
		1382	interpreter and the backend itself). Nevertheless this shows that it
		1383	adds very little overhead in itself. Like any select-based backend its
		1384	performance becomes really bad with lots of file descriptors (and few of
		1385	them active), of course, but this was not subject of this benchmark.
		1386
		1387	The C<Event> module has a relatively high setup and callback invocation
		1388	cost, but overall scores in on the third place.
		1389
		1390	C<Glib>'s memory usage is quite a bit higher, but it features a
		1391	faster callback invocation and overall ends up in the same class as
		1392	C<Event>. However, Glib scales extremely badly, doubling the number of
		1393	watchers increases the processing time by more than a factor of four,
		1394	making it completely unusable when using larger numbers of watchers
		1395	(note that only a single file descriptor was used in the benchmark, so
		1396	inefficiencies of C<poll> do not account for this).
		1397
		1398	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1399	more than 2000 watchers is a big setback, however, as correctness takes
		1400	precedence over speed. Nevertheless, its performance is surprising, as the
		1401	file descriptor is dup()ed for each watcher. This shows that the dup()
		1402	employed by some adaptors is not a big performance issue (it does incur a
		1403	hidden memory cost inside the kernel which is not reflected in the figures
		1404	above).
		1405
		1406	C<POE>, regardless of underlying event loop (whether using its pure perl
		1407	select-based backend or the Event module, the POE-EV backend couldn't
		1408	be tested because it wasn't working) shows abysmal performance and
		1409	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1410	as EV watchers, and 10 times as much memory as Event (the high memory
		1411	requirements are caused by requiring a session for each watcher). Watcher
		1412	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1413	implementation.
		1414
		1415	The design of the POE adaptor class in AnyEvent can not really account
		1416	for the performance issues, though, as session creation overhead is
		1417	small compared to execution of the state machine, which is coded pretty
		1418	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1419	using multiple sessions is not a good approach, especially regarding
		1420	memory usage, even the author of POE could not come up with a faster
		1421	design).
		1422
		1423	=head3 Summary
		1424
		1425	=over 4
		1426
		1427	=item * Using EV through AnyEvent is faster than any other event loop
		1428	(even when used without AnyEvent), but most event loops have acceptable
		1429	performance with or without AnyEvent.
		1430
		1431	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1432	the actual event loop, only with extremely fast event loops such as EV
		1433	adds AnyEvent significant overhead.
		1434
		1435	=item * You should avoid POE like the plague if you want performance or
		1436	reasonable memory usage.
		1437
		1438	=back
		1439
		1440	=head2 BENCHMARKING THE LARGE SERVER CASE
		1441
		1442	This benchmark actually benchmarks the event loop itself. It works by
		1443	creating a number of "servers": each server consists of a socket pair, a
		1444	timeout watcher that gets reset on activity (but never fires), and an I/O
		1445	watcher waiting for input on one side of the socket. Each time the socket
		1446	watcher reads a byte it will write that byte to a random other "server".
		1447
		1448	The effect is that there will be a lot of I/O watchers, only part of which
		1449	are active at any one point (so there is a constant number of active
		1450	fds for each loop iteration, but which fds these are is random). The
		1451	timeout is reset each time something is read because that reflects how
		1452	most timeouts work (and puts extra pressure on the event loops).
		1453
		1454	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1455	(1%) are active. This mirrors the activity of large servers with many
		1456	connections, most of which are idle at any one point in time.
		1457
		1458	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1459	distribution.
		1460
		1461	=head3 Explanation of the columns
		1462
		1463	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1464	each server has a read and write socket end).
		1465
		1466	I<create> is the time it takes to create a socket pair (which is
		1467	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1468
		1469	I<request>, the most important value, is the time it takes to handle a
		1470	single "request", that is, reading the token from the pipe and forwarding
		1471	it to another server. This includes deleting the old timeout and creating
		1472	a new one that moves the timeout into the future.
		1473
		1474	=head3 Results
		1475
		1476	name sockets create request
		1477	EV 20000 69.01 11.16
		1478	Perl 20000 73.32 35.87
		1479	Event 20000 212.62 257.32
		1480	Glib 20000 651.16 1896.30
		1481	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1482
		1483	=head3 Discussion
		1484
		1485	This benchmark I<does> measure scalability and overall performance of the
		1486	particular event loop.
		1487
		1488	EV is again fastest. Since it is using epoll on my system, the setup time
		1489	is relatively high, though.
		1490
		1491	Perl surprisingly comes second. It is much faster than the C-based event
		1492	loops Event and Glib.
		1493
		1494	Event suffers from high setup time as well (look at its code and you will
		1495	understand why). Callback invocation also has a high overhead compared to
		1496	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1497	uses select or poll in basically all documented configurations.
		1498
		1499	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1500	clearly fails to perform with many filehandles or in busy servers.
		1501
		1502	POE is still completely out of the picture, taking over 1000 times as long
		1503	as EV, and over 100 times as long as the Perl implementation, even though
		1504	it uses a C-based event loop in this case.
		1505
		1506	=head3 Summary
		1507
		1508	=over 4
		1509
		1510	=item * The pure perl implementation performs extremely well.
		1511
		1512	=item * Avoid Glib or POE in large projects where performance matters.
		1513
		1514	=back
		1515
		1516	=head2 BENCHMARKING SMALL SERVERS
		1517
		1518	While event loops should scale (and select-based ones do not...) even to
		1519	large servers, most programs we (or I :) actually write have only a few
		1520	I/O watchers.
		1521
		1522	In this benchmark, I use the same benchmark program as in the large server
		1523	case, but it uses only eight "servers", of which three are active at any
		1524	one time. This should reflect performance for a small server relatively
		1525	well.
		1526
		1527	The columns are identical to the previous table.
		1528
		1529	=head3 Results
		1530
		1531	name sockets create request
		1532	EV 16 20.00 6.54
		1533	Perl 16 25.75 12.62
		1534	Event 16 81.27 35.86
		1535	Glib 16 32.63 15.48
		1536	POE 16 261.87 276.28 uses POE::Loop::Event
		1537
		1538	=head3 Discussion
		1539
		1540	The benchmark tries to test the performance of a typical small
		1541	server. While knowing how various event loops perform is interesting, keep
		1542	in mind that their overhead in this case is usually not as important, due
		1543	to the small absolute number of watchers (that is, you need efficiency and
		1544	speed most when you have lots of watchers, not when you only have a few of
		1545	them).
		1546
		1547	EV is again fastest.
		1548
		1549	Perl again comes second. It is noticeably faster than the C-based event
		1550	loops Event and Glib, although the difference is too small to really
		1551	matter.
		1552
		1553	POE also performs much better in this case, but is is still far behind the
		1554	others.
		1555
		1556	=head3 Summary
		1557
		1558	=over 4
		1559
		1560	=item * C-based event loops perform very well with small number of
		1561	watchers, as the management overhead dominates.
		1562
		1563	=back
		1564
		1565
		1566	=head1 FORK
		1567
		1568	Most event libraries are not fork-safe. The ones who are usually are
		1569	because they rely on inefficient but fork-safe C<select> or C<poll>
		1570	calls. Only L<EV> is fully fork-aware.
		1571
		1572	If you have to fork, you must either do so I<before> creating your first
		1573	watcher OR you must not use AnyEvent at all in the child.
		1574
		1575
		1576	=head1 SECURITY CONSIDERATIONS
		1577
		1578	AnyEvent can be forced to load any event model via
		1579	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1580	execute arbitrary code or directly gain access, it can easily be used to
		1581	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1582	will not be active when the program uses a different event model than
		1583	specified in the variable.
		1584
		1585	You can make AnyEvent completely ignore this variable by deleting it
		1586	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1587
		1588	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1589
		1590	use AnyEvent;
		1591
		1592	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1593	be used to probe what backend is used and gain other information (which is
		1594	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1595
800		1596
801	=head1 SEE ALSO	1597	=head1 SEE ALSO
802		1598
803	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1599	Utility functions: L<AnyEvent::Util>.
804	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.
805		1600
806	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1601	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1602	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1603
807	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1604	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
808	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	1605	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1606	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1607	L<AnyEvent::Impl::POE>.
809		1608
		1609	Non-blocking file handles, sockets, TCP clients and
		1610	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1611
		1612	Asynchronous DNS: L<AnyEvent::DNS>.
		1613
		1614	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1615
810	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1616	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1617
811		1618
812	=head1 AUTHOR	1619	=head1 AUTHOR
813		1620
814	Marc Lehmann <schmorp@schmorp.de>	1621	Marc Lehmann <schmorp@schmorp.de>
815	http://home.schmorp.de/	1622	http://home.schmorp.de/

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