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Revision 1.38 by root, Sun Nov 25 14:08:12 2007 UTC vs.
Revision 1.132 by root, Sun May 25 01:05:27 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	Event, Coro, 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
…		…
14		14
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 wether 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
		23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		24
		25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		26	nowadays. So what is different about AnyEvent?
		27
		28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		29	policy> and AnyEvent is I<small and efficient>.
		30
		31	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
		33	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,
		35	only one event loop can be active at the same time in a process. AnyEvent
		36	helps hiding the differences between those event loops.
		37
		38	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
		40	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
		42	model you use.
		43
		44	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
		46	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
		48	isn't itself. What's worse, all the potential users of your module are
		49	I<also> forced to use the same event loop you use.
		50
		51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		52	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
		54	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
		56	event models it supports (including stuff like POE and IO::Async, as long
		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).
		59
		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
		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
		64	offering the functionality that is necessary, in as thin as a wrapper as
		65	technically possible.
		66
		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
		69	model, you should I<not> use this module.
22		70
23	=head1 DESCRIPTION	71	=head1 DESCRIPTION
24		72
25	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
26	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
27	users to use the same event loop (as only a single event loop can coexist	75	users to use the same event loop (as only a single event loop can coexist
28	peacefully at any one time).	76	peacefully at any one time).
29		77
30	The interface itself is vaguely similar but not identical to the Event	78	The interface itself is vaguely similar, but not identical to the L<Event>
31	module.	79	module.
32		80
33	On the first call of any method, the module tries to detect the currently	81	During the first call of any watcher-creation method, the module tries
34	loaded event loop by probing wether any of the following modules is	82	to detect the currently loaded event loop by probing whether one of the
35	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
36	used. If none is found, the module tries to load these modules in the	84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
37	order given. The first one that could be successfully loaded will be	85	L<POE>. The first one found is used. If none are found, the module tries
38	used. If still none could be found, AnyEvent will fall back to a pure-perl	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
39	event loop, which is also not very efficient.	87	adaptor should always succeed) in the order given. The first one that can
		88	be successfully loaded will be used. If, after this, still none could be
		89	found, AnyEvent will fall back to a pure-perl event loop, which is not
		90	very efficient, but should work everywhere.
40		91
41	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
42	an Event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
43	that model the default. For example:	94	that model the default. For example:
44		95
45	use Tk;	96	use Tk;
46	use AnyEvent;	97	use AnyEvent;
47		98
48	# .. AnyEvent will likely default to Tk	99	# .. AnyEvent will likely default to Tk
		100
		101	The I<likely> means that, if any module loads another event model and
		102	starts using it, all bets are off. Maybe you should tell their authors to
		103	use AnyEvent so their modules work together with others seamlessly...
49		104
50	The pure-perl implementation of AnyEvent is called	105	The pure-perl implementation of AnyEvent is called
51	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
52	explicitly.	107	explicitly.
53		108
54	=head1 WATCHERS	109	=head1 WATCHERS
55		110
56	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
57	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
58	the callback to call, the filehandle to watch, etc.	113	the callback to call, the file handle to watch, etc.
59		114
60	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
61	creating a watcher it will immediately "watch" for events and invoke	116	creating a watcher it will immediately "watch" for events and invoke the
		117	callback when the event occurs (of course, only when the event model
		118	is in control).
		119
62	the callback. To disable the watcher you have to destroy it (e.g. by	120	To disable the watcher you have to destroy it (e.g. by setting the
63	setting the variable that stores it to C<undef> or otherwise deleting all	121	variable you store it in to C<undef> or otherwise deleting all references
64	references to it).	122	to it).
65		123
66	All watchers are created by calling a method on the C<AnyEvent> class.	124	All watchers are created by calling a method on the C<AnyEvent> class.
67		125
		126	Many watchers either are used with "recursion" (repeating timers for
		127	example), or need to refer to their watcher object in other ways.
		128
		129	An any way to achieve that is this pattern:
		130
		131	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		132	# you can use $w here, for example to undef it
		133	undef $w;
		134	});
		135
		136	Note that C<my $w; $w => combination. This is necessary because in Perl,
		137	my variables are only visible after the statement in which they are
		138	declared.
		139
68	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
69		141
70	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
71	the following mandatory arguments:	143	with the following mandatory key-value pairs as arguments:
72		144
73	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
74	events. C<poll> must be a string that is either C<r> or C<w>, that creates	146	for events. C<poll> must be a string that is either C<r> or C<w>,
75	a watcher waiting for "r"eadable or "w"ritable events. C<cb> the callback	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
76	to invoke everytime the filehandle becomes ready.	148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
77		150
78	Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on	151	Although the callback might get passed parameters, their value and
79	a socket you can have one r + one w, not any more (limitation comes from	152	presence is undefined and you cannot rely on them. Portable AnyEvent
80	Tk - if you are sure you are not using Tk this limitation is gone).	153	callbacks cannot use arguments passed to I/O watcher callbacks.
81		154
82	Filehandles will be kept alive, so as long as the watcher exists, the	155	The I/O watcher might use the underlying file descriptor or a copy of it.
83	filehandle exists, too.	156	You must not close a file handle as long as any watcher is active on the
		157	underlying file descriptor.
		158
		159	Some event loops issue spurious readyness notifications, so you should
		160	always use non-blocking calls when reading/writing from/to your file
		161	handles.
84		162
85	Example:	163	Example:
86		164
87	# wait for readability of STDIN, then read a line and disable the watcher	165	# wait for readability of STDIN, then read a line and disable the watcher
88	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
94	=head2 TIME WATCHERS	172	=head2 TIME WATCHERS
95		173
96	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 >>
97	method with the following mandatory arguments:	175	method with the following mandatory arguments:
98		176
99	C<after> after how many seconds (fractions are supported) should the timer	177	C<after> specifies after how many seconds (fractional values are
100	activate. C<cb> the callback to invoke.	178	supported) the callback should be invoked. C<cb> is the callback to invoke
		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.
101		184
102	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
103	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
104	and Glib).	187	and Glib).
105		188
…		…
111	});	194	});
112		195
113	# to cancel the timer:	196	# to cancel the timer:
114	undef $w;	197	undef $w;
115		198
		199	Example 2:
		200
		201	# fire an event after 0.5 seconds, then roughly every second
		202	my $w;
		203
		204	my $cb = sub {
		205	# cancel the old timer while creating a new one
		206	$w = AnyEvent->timer (after => 1, cb => $cb);
		207	};
		208
		209	# start the "loop" by creating the first watcher
		210	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		211
		212	=head3 TIMING ISSUES
		213
		214	There are two ways to handle timers: based on real time (relative, "fire
		215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		216	o'clock").
		217
		218	While most event loops expect timers to specified in a relative way, they
		219	use absolute time internally. This makes a difference when your clock
		220	"jumps", for example, when ntp decides to set your clock backwards from
		221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		222	fire "after" a second might actually take six years to finally fire.
		223
		224	AnyEvent cannot compensate for this. The only event loop that is conscious
		225	about these issues is L<EV>, which offers both relative (ev_timer, based
		226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
		228
		229	AnyEvent always prefers relative timers, if available, matching the
		230	AnyEvent API.
		231
		232	=head2 SIGNAL WATCHERS
		233
		234	You can watch for signals using a signal watcher, C<signal> is the signal
		235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		236	be invoked whenever a signal occurs.
		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
		242	Multiple signal occurrences can be clumped together into one callback
		243	invocation, and callback invocation will be synchronous. Synchronous means
		244	that it might take a while until the signal gets handled by the process,
		245	but it is guaranteed not to interrupt any other callbacks.
		246
		247	The main advantage of using these watchers is that you can share a signal
		248	between multiple watchers.
		249
		250	This watcher might use C<%SIG>, so programs overwriting those signals
		251	directly will likely not work correctly.
		252
		253	Example: exit on SIGINT
		254
		255	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		256
		257	=head2 CHILD PROCESS WATCHERS
		258
		259	You can also watch on a child process exit and catch its exit status.
		260
		261	The child process is specified by the C<pid> argument (if set to C<0>, it
		262	watches for any child process exit). The watcher will trigger as often
		263	as status change for the child are received. This works by installing a
		264	signal handler for C<SIGCHLD>. The callback will be called with the pid
		265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
		267
		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;
		285
		286	my $w = AnyEvent->child (
		287	pid => $pid,
		288	cb => sub {
		289	my ($pid, $status) = @_;
		290	warn "pid $pid exited with status $status";
		291	$done->send;
		292	},
		293	);
		294
		295	# do something else, then wait for process exit
		296	$done->recv;
		297
116	=head2 CONDITION WATCHERS	298	=head2 CONDITION VARIABLES
117		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
118	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	310	Condition variables can be created by calling the C<< AnyEvent->condvar
119	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.
120		314
121	A condition watcher watches for a condition - precisely that the C<<	315	After creation, the condition variable is "false" until it becomes "true"
122	->broadcast >> method has been called.	316	by calling the C<send> method (or calling the condition variable as if it
		317	were a callback).
123		318
124	The watcher has only two methods:	319	Condition variables are similar to callbacks, except that you can
		320	optionally wait for them. They can also be called merge points - points
		321	in time where multiple outstanding events have been processed. And yet
		322	another way to call them is transactions - each condition variable can be
		323	used to represent a transaction, which finishes at some point and delivers
		324	a result.
125		325
126	=over 4	326	Condition variables are very useful to signal that something has finished,
		327	for example, if you write a module that does asynchronous http requests,
		328	then a condition variable would be the ideal candidate to signal the
		329	availability of results. The user can either act when the callback is
		330	called or can synchronously C<< ->recv >> for the results.
127		331
128	=item $cv->wait	332	You can also use them to simulate traditional event loops - for example,
		333	you can block your main program until an event occurs - for example, you
		334	could C<< ->recv >> in your main program until the user clicks the Quit
		335	button of your app, which would C<< ->send >> the "quit" event.
129		336
130	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	337	Note that condition variables recurse into the event loop - if you have
131	called on c<$cv>, while servicing other watchers normally.	338	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		339	lose. Therefore, condition variables are good to export to your caller, but
		340	you should avoid making a blocking wait yourself, at least in callbacks,
		341	as this asks for trouble.
132		342
133	Not all event models support a blocking wait - some die in that case, so	343	Condition variables are represented by hash refs in perl, and the keys
134	if you are using this from a module, never require a blocking wait, but	344	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
135	let the caller decide wether the call will block or not (for example,	345	easy (it is often useful to build your own transaction class on top of
136	by coupling condition variables with some kind of request results and	346	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
137	supporting callbacks so the caller knows that getting the result will not	347	it's C<new> method in your own C<new> method.
138	block, while still suppporting blockign waits if the caller so desires).
139		348
140	You can only wait once on a condition - additional calls will return	349	There are two "sides" to a condition variable - the "producer side" which
141	immediately.	350	eventually calls C<< -> send >>, and the "consumer side", which waits
		351	for the send to occur.
142		352
143	=item $cv->broadcast	353	Example: wait for a timer.
144
145	Flag the condition as ready - a running C<< ->wait >> and all further
146	calls to C<wait> will return after this method has been called. If nobody
147	is waiting the broadcast will be remembered..
148
149	Example:
150		354
151	# wait till the result is ready	355	# wait till the result is ready
152	my $result_ready = AnyEvent->condvar;	356	my $result_ready = AnyEvent->condvar;
153		357
154	# do something such as adding a timer	358	# do something such as adding a timer
155	# or socket watcher the calls $result_ready->broadcast	359	# or socket watcher the calls $result_ready->send
156	# when the "result" is ready.	360	# when the "result" is ready.
		361	# in this case, we simply use a timer:
		362	my $w = AnyEvent->timer (
		363	after => 1,
		364	cb => sub { $result_ready->send },
		365	);
157		366
		367	# this "blocks" (while handling events) till the callback
		368	# calls send
158	$result_ready->wait;	369	$result_ready->recv;
		370
		371	Example: wait for a timer, but take advantage of the fact that
		372	condition variables are also code references.
		373
		374	my $done = AnyEvent->condvar;
		375	my $delay = AnyEvent->timer (after => 5, cb => $done);
		376	$done->recv;
		377
		378	=head3 METHODS FOR PRODUCERS
		379
		380	These methods should only be used by the producing side, i.e. the
		381	code/module that eventually sends the signal. Note that it is also
		382	the producer side which creates the condvar in most cases, but it isn't
		383	uncommon for the consumer to create it as well.
		384
		385	=over 4
		386
		387	=item $cv->send (...)
		388
		389	Flag the condition as ready - a running C<< ->recv >> and all further
		390	calls to C<recv> will (eventually) return after this method has been
		391	called. If nobody is waiting the send will be remembered.
		392
		393	If a callback has been set on the condition variable, it is called
		394	immediately from within send.
		395
		396	Any arguments passed to the C<send> call will be returned by all
		397	future C<< ->recv >> calls.
		398
		399	Condition variables are overloaded so one can call them directly (as a
		400	code reference). Calling them directly is the same as calling C<send>.
		401
		402	=item $cv->croak ($error)
		403
		404	Similar to send, but causes all call's to C<< ->recv >> to invoke
		405	C<Carp::croak> with the given error message/object/scalar.
		406
		407	This can be used to signal any errors to the condition variable
		408	user/consumer.
		409
		410	=item $cv->begin ([group callback])
		411
		412	=item $cv->end
		413
		414	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		415
		416	These two methods can be used to combine many transactions/events into
		417	one. For example, a function that pings many hosts in parallel might want
		418	to use a condition variable for the whole process.
		419
		420	Every call to C<< ->begin >> will increment a counter, and every call to
		421	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		422	>>, the (last) callback passed to C<begin> will be executed. That callback
		423	is I<supposed> to call C<< ->send >>, but that is not required. If no
		424	callback was set, C<send> will be called without any arguments.
		425
		426	Let's clarify this with the ping example:
		427
		428	my $cv = AnyEvent->condvar;
		429
		430	my %result;
		431	$cv->begin (sub { $cv->send (\%result) });
		432
		433	for my $host (@list_of_hosts) {
		434	$cv->begin;
		435	ping_host_then_call_callback $host, sub {
		436	$result{$host} = ...;
		437	$cv->end;
		438	};
		439	}
		440
		441	$cv->end;
		442
		443	This code fragment supposedly pings a number of hosts and calls
		444	C<send> after results for all then have have been gathered - in any
		445	order. To achieve this, the code issues a call to C<begin> when it starts
		446	each ping request and calls C<end> when it has received some result for
		447	it. Since C<begin> and C<end> only maintain a counter, the order in which
		448	results arrive is not relevant.
		449
		450	There is an additional bracketing call to C<begin> and C<end> outside the
		451	loop, which serves two important purposes: first, it sets the callback
		452	to be called once the counter reaches C<0>, and second, it ensures that
		453	C<send> is called even when C<no> hosts are being pinged (the loop
		454	doesn't execute once).
		455
		456	This is the general pattern when you "fan out" into multiple subrequests:
		457	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		458	is called at least once, and then, for each subrequest you start, call
		459	C<begin> and for each subrequest you finish, call C<end>.
159		460
160	=back	461	=back
161		462
162	=head2 SIGNAL WATCHERS	463	=head3 METHODS FOR CONSUMERS
163		464
164	You can listen for signals using a signal watcher, C<signal> is the signal	465	These methods should only be used by the consuming side, i.e. the
165	I<name> without any C<SIG> prefix. Multiple signals events can be clumped	466	code awaits the condition.
166	together into one callback invocation, and callback invocation might or
167	might not be asynchronous.
168		467
169	These watchers might use C<%SIG>, so programs overwriting those signals	468	=over 4
170	directly will likely not work correctly.
171		469
172	Example: exit on SIGINT	470	=item $cv->recv
173		471
174	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	472	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		473	>> methods have been called on c<$cv>, while servicing other watchers
		474	normally.
175		475
176	=head2 CHILD PROCESS WATCHERS	476	You can only wait once on a condition - additional calls are valid but
		477	will return immediately.
177		478
178	You can also listen for the status of a child process specified by the	479	If an error condition has been set by calling C<< ->croak >>, then this
179	C<pid> argument (or any child if the pid argument is 0). The watcher will	480	function will call C<croak>.
180	trigger as often as status change for the child are received. This works
181	by installing a signal handler for C<SIGCHLD>. The callback will be called with
182	the pid and exit status (as returned by waitpid).
183		481
184	Example: wait for pid 1333	482	In list context, all parameters passed to C<send> will be returned,
		483	in scalar context only the first one will be returned.
185		484
186	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });	485	Not all event models support a blocking wait - some die in that case
		486	(programs might want to do that to stay interactive), so I<if you are
		487	using this from a module, never require a blocking wait>, but let the
		488	caller decide whether the call will block or not (for example, by coupling
		489	condition variables with some kind of request results and supporting
		490	callbacks so the caller knows that getting the result will not block,
		491	while still supporting blocking waits if the caller so desires).
187		492
188	=head1 GLOBALS	493	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		494	sensibly have two C<< ->recv >>'s in parallel, as that would require
		495	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		496	can supply.
		497
		498	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		499	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		500	versions and also integrates coroutines into AnyEvent, making blocking
		501	C<< ->recv >> calls perfectly safe as long as they are done from another
		502	coroutine (one that doesn't run the event loop).
		503
		504	You can ensure that C<< -recv >> never blocks by setting a callback and
		505	only calling C<< ->recv >> from within that callback (or at a later
		506	time). This will work even when the event loop does not support blocking
		507	waits otherwise.
		508
		509	=item $bool = $cv->ready
		510
		511	Returns true when the condition is "true", i.e. whether C<send> or
		512	C<croak> have been called.
		513
		514	=item $cb = $cv->cb ([new callback])
		515
		516	This is a mutator function that returns the callback set and optionally
		517	replaces it before doing so.
		518
		519	The callback will be called when the condition becomes "true", i.e. when
		520	C<send> or C<croak> are called. Calling C<recv> inside the callback
		521	or at any later time is guaranteed not to block.
		522
		523	=back
		524
		525	=head1 GLOBAL VARIABLES AND FUNCTIONS
189		526
190	=over 4	527	=over 4
191		528
192	=item $AnyEvent::MODEL	529	=item $AnyEvent::MODEL
193		530
…		…
197	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	534	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
198	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	535	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
199		536
200	The known classes so far are:	537	The known classes so far are:
201		538
202	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
203	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	539	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
204	AnyEvent::Impl::Coro based on Coro::Event, second best choice.
205	AnyEvent::Impl::Event based on Event, also second best choice :)	540	AnyEvent::Impl::Event based on Event, second best choice.
		541	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
206	AnyEvent::Impl::Glib based on Glib, second-best choice.	542	AnyEvent::Impl::Glib based on Glib, third-best choice.
207	AnyEvent::Impl::Tk based on Tk, very bad choice.	543	AnyEvent::Impl::Tk based on Tk, very bad choice.
208	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	544	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		545	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		546	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		547
		548	There is no support for WxWidgets, as WxWidgets has no support for
		549	watching file handles. However, you can use WxWidgets through the
		550	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		551	second, which was considered to be too horrible to even consider for
		552	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		553	it's adaptor.
		554
		555	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		556	autodetecting them.
209		557
210	=item AnyEvent::detect	558	=item AnyEvent::detect
211		559
212	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	560	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
213	necessary. You should only call this function right before you would have	561	if necessary. You should only call this function right before you would
214	created an AnyEvent watcher anyway, that is, very late at runtime.	562	have created an AnyEvent watcher anyway, that is, as late as possible at
		563	runtime.
		564
		565	=item $guard = AnyEvent::post_detect { BLOCK }
		566
		567	Arranges for the code block to be executed as soon as the event model is
		568	autodetected (or immediately if this has already happened).
		569
		570	If called in scalar or list context, then it creates and returns an object
		571	that automatically removes the callback again when it is destroyed. See
		572	L<Coro::BDB> for a case where this is useful.
		573
		574	=item @AnyEvent::post_detect
		575
		576	If there are any code references in this array (you can C<push> to it
		577	before or after loading AnyEvent), then they will called directly after
		578	the event loop has been chosen.
		579
		580	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		581	if it contains a true value then the event loop has already been detected,
		582	and the array will be ignored.
		583
		584	Best use C<AnyEvent::post_detect { BLOCK }> instead.
215		585
216	=back	586	=back
217		587
218	=head1 WHAT TO DO IN A MODULE	588	=head1 WHAT TO DO IN A MODULE
219		589
220	As a module author, you should "use AnyEvent" and call AnyEvent methods	590	As a module author, you should C<use AnyEvent> and call AnyEvent methods
221	freely, but you should not load a specific event module or rely on it.	591	freely, but you should not load a specific event module or rely on it.
222		592
223	Be careful when you create watchers in the module body - Anyevent will	593	Be careful when you create watchers in the module body - AnyEvent will
224	decide which event module to use as soon as the first method is called, so	594	decide which event module to use as soon as the first method is called, so
225	by calling AnyEvent in your module body you force the user of your module	595	by calling AnyEvent in your module body you force the user of your module
226	to load the event module first.	596	to load the event module first.
227		597
		598	Never call C<< ->recv >> on a condition variable unless you I<know> that
		599	the C<< ->send >> method has been called on it already. This is
		600	because it will stall the whole program, and the whole point of using
		601	events is to stay interactive.
		602
		603	It is fine, however, to call C<< ->recv >> when the user of your module
		604	requests it (i.e. if you create a http request object ad have a method
		605	called C<results> that returns the results, it should call C<< ->recv >>
		606	freely, as the user of your module knows what she is doing. always).
		607
228	=head1 WHAT TO DO IN THE MAIN PROGRAM	608	=head1 WHAT TO DO IN THE MAIN PROGRAM
229		609
230	There will always be a single main program - the only place that should	610	There will always be a single main program - the only place that should
231	dictate which event model to use.	611	dictate which event model to use.
232		612
233	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	613	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
234	do anything special and let AnyEvent decide which implementation to chose.	614	do anything special (it does not need to be event-based) and let AnyEvent
		615	decide which implementation to chose if some module relies on it.
235		616
236	If the main program relies on a specific event model (for example, in Gtk2	617	If the main program relies on a specific event model. For example, in
237	programs you have to rely on either Glib or Glib::Event), you should load	618	Gtk2 programs you have to rely on the Glib module. You should load the
238	it before loading AnyEvent or any module that uses it, generally, as early	619	event module before loading AnyEvent or any module that uses it: generally
239	as possible. The reason is that modules might create watchers when they	620	speaking, you should load it as early as possible. The reason is that
240	are loaded, and AnyEvent will decide on the event model to use as soon as	621	modules might create watchers when they are loaded, and AnyEvent will
241	it creates watchers, and it might chose the wrong one unless you load the	622	decide on the event model to use as soon as it creates watchers, and it
242	correct one yourself.	623	might chose the wrong one unless you load the correct one yourself.
243		624
244	You can chose to use a rather inefficient pure-perl implementation by	625	You can chose to use a rather inefficient pure-perl implementation by
245	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	626	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
246	generally better.	627	behaviour everywhere, but letting AnyEvent chose is generally better.
		628
		629	=head1 OTHER MODULES
		630
		631	The following is a non-exhaustive list of additional modules that use
		632	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		633	in the same program. Some of the modules come with AnyEvent, some are
		634	available via CPAN.
		635
		636	=over 4
		637
		638	=item L<AnyEvent::Util>
		639
		640	Contains various utility functions that replace often-used but blocking
		641	functions such as C<inet_aton> by event-/callback-based versions.
		642
		643	=item L<AnyEvent::Handle>
		644
		645	Provide read and write buffers and manages watchers for reads and writes.
		646
		647	=item L<AnyEvent::Socket>
		648
		649	Provides various utility functions for (internet protocol) sockets,
		650	addresses and name resolution. Also functions to create non-blocking tcp
		651	connections or tcp servers, with IPv6 and SRV record support and more.
		652
		653	=item L<AnyEvent::HTTPD>
		654
		655	Provides a simple web application server framework.
		656
		657	=item L<AnyEvent::DNS>
		658
		659	Provides rich asynchronous DNS resolver capabilities.
		660
		661	=item L<AnyEvent::FastPing>
		662
		663	The fastest ping in the west.
		664
		665	=item L<Net::IRC3>
		666
		667	AnyEvent based IRC client module family.
		668
		669	=item L<Net::XMPP2>
		670
		671	AnyEvent based XMPP (Jabber protocol) module family.
		672
		673	=item L<Net::FCP>
		674
		675	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		676	of AnyEvent.
		677
		678	=item L<Event::ExecFlow>
		679
		680	High level API for event-based execution flow control.
		681
		682	=item L<Coro>
		683
		684	Has special support for AnyEvent via L<Coro::AnyEvent>.
		685
		686	=item L<AnyEvent::AIO>, L<IO::AIO>
		687
		688	Truly asynchronous I/O, should be in the toolbox of every event
		689	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		690	together.
		691
		692	=item L<AnyEvent::BDB>, L<BDB>
		693
		694	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		695	IO::AIO and AnyEvent together.
		696
		697	=item L<IO::Lambda>
		698
		699	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		700
		701	=back
247		702
248	=cut	703	=cut
249		704
250	package AnyEvent;	705	package AnyEvent;
251		706
252	no warnings;	707	no warnings;
253	use strict;	708	use strict;
254		709
255	use Carp;	710	use Carp;
256		711
257	our $VERSION = '2.8';	712	our $VERSION = '4.03';
258	our $MODEL;	713	our $MODEL;
259		714
260	our $AUTOLOAD;	715	our $AUTOLOAD;
261	our @ISA;	716	our @ISA;
262		717
263	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	718	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
264		719
265	our @REGISTRY;	720	our @REGISTRY;
266		721
		722	our %PROTOCOL; # (ipv4|ipv6) => (1|2)
		723
		724	{
		725	my $idx;
		726	$PROTOCOL{$_} = ++$idx
		727	for split /\s*,\s*/, $ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		728	}
		729
267	my @models = (	730	my @models = (
268	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
269	[EV:: => AnyEvent::Impl::EV::],	731	[EV:: => AnyEvent::Impl::EV::],
270	[Coro::Event:: => AnyEvent::Impl::Coro::],
271	[Event:: => AnyEvent::Impl::Event::],	732	[Event:: => AnyEvent::Impl::Event::],
		733	[Tk:: => AnyEvent::Impl::Tk::],
		734	[Wx:: => AnyEvent::Impl::POE::],
		735	[Prima:: => AnyEvent::Impl::POE::],
		736	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		737	# everything below here will not be autoprobed as the pureperl backend should work everywhere
272	[Glib:: => AnyEvent::Impl::Glib::],	738	[Glib:: => AnyEvent::Impl::Glib::],
273	[Tk:: => AnyEvent::Impl::Tk::],	739	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
274	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	740	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		741	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
275	);	742	);
276		743
277	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	744	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		745
		746	our @post_detect;
		747
		748	sub post_detect(&) {
		749	my ($cb) = @_;
		750
		751	if ($MODEL) {
		752	$cb->();
		753
		754	1
		755	} else {
		756	push @post_detect, $cb;
		757
		758	defined wantarray
		759	? bless \$cb, "AnyEvent::Util::PostDetect"
		760	: ()
		761	}
		762	}
		763
		764	sub AnyEvent::Util::PostDetect::DESTROY {
		765	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		766	}
278		767
279	sub detect() {	768	sub detect() {
280	unless ($MODEL) {	769	unless ($MODEL) {
281	no strict 'refs';	770	no strict 'refs';
282		771
		772	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		773	my $model = "AnyEvent::Impl::$1";
		774	if (eval "require $model") {
		775	$MODEL = $model;
		776	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		777	} else {
		778	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		779	}
		780	}
		781
283	# check for already loaded models	782	# check for already loaded models
		783	unless ($MODEL) {
284	for (@REGISTRY, @models) {	784	for (@REGISTRY, @models) {
285	my ($package, $model) = @$_;	785	my ($package, $model) = @$_;
286	if (${"$package\::VERSION"} > 0) {	786	if (${"$package\::VERSION"} > 0) {
287	if (eval "require $model") {	787	if (eval "require $model") {
288	$MODEL = $model;	788	$MODEL = $model;
289	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	789	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
290	last;	790	last;
		791	}
291	}	792	}
292	}	793	}
293	}
294		794
295	unless ($MODEL) {	795	unless ($MODEL) {
296	# try to load a model	796	# try to load a model
297		797
298	for (@REGISTRY, @models) {	798	for (@REGISTRY, @models) {
299	my ($package, $model) = @$_;	799	my ($package, $model) = @$_;
300	if (eval "require $package"	800	if (eval "require $package"
301	and ${"$package\::VERSION"} > 0	801	and ${"$package\::VERSION"} > 0
302	and eval "require $model") {	802	and eval "require $model") {
303	$MODEL = $model;	803	$MODEL = $model;
304	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	804	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
305	last;	805	last;
		806	}
306	}	807	}
		808
		809	$MODEL
		810	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
307	}	811	}
308
309	$MODEL
310	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.";
311	}	812	}
312		813
313	unshift @ISA, $MODEL;	814	unshift @ISA, $MODEL;
314	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	815	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		816
		817	(shift @post_detect)->() while @post_detect;
315	}	818	}
316		819
317	$MODEL	820	$MODEL
318	}	821	}
319		822
…		…
329	$class->$func (@_);	832	$class->$func (@_);
330	}	833	}
331		834
332	package AnyEvent::Base;	835	package AnyEvent::Base;
333		836
334	# default implementation for ->condvar, ->wait, ->broadcast	837	# default implementation for ->condvar
335		838
336	sub condvar {	839	sub condvar {
337	bless \my $flag, "AnyEvent::Base::CondVar"	840	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
338	}
339
340	sub AnyEvent::Base::CondVar::broadcast {
341	${$_[0]}++;
342	}
343
344	sub AnyEvent::Base::CondVar::wait {
345	AnyEvent->one_event while !${$_[0]};
346	}	841	}
347		842
348	# default implementation for ->signal	843	# default implementation for ->signal
349		844
350	our %SIG_CB;	845	our %SIG_CB;
…		…
424	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	919	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
425		920
426	undef $CHLD_W unless keys %PID_CB;	921	undef $CHLD_W unless keys %PID_CB;
427	}	922	}
428		923
		924	package AnyEvent::CondVar;
		925
		926	our @ISA = AnyEvent::CondVar::Base::;
		927
		928	package AnyEvent::CondVar::Base;
		929
		930	use overload
		931	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		932	fallback => 1;
		933
		934	sub _send {
		935	# nop
		936	}
		937
		938	sub send {
		939	my $cv = shift;
		940	$cv->{_ae_sent} = [@_];
		941	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		942	$cv->_send;
		943	}
		944
		945	sub croak {
		946	$_[0]{_ae_croak} = $_[1];
		947	$_[0]->send;
		948	}
		949
		950	sub ready {
		951	$_[0]{_ae_sent}
		952	}
		953
		954	sub _wait {
		955	AnyEvent->one_event while !$_[0]{_ae_sent};
		956	}
		957
		958	sub recv {
		959	$_[0]->_wait;
		960
		961	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		962	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		963	}
		964
		965	sub cb {
		966	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		967	$_[0]{_ae_cb}
		968	}
		969
		970	sub begin {
		971	++$_[0]{_ae_counter};
		972	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		973	}
		974
		975	sub end {
		976	return if --$_[0]{_ae_counter};
		977	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		978	}
		979
		980	# undocumented/compatibility with pre-3.4
		981	*broadcast = \&send;
		982	*wait = \&_wait;
		983
429	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	984	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		985
		986	This is an advanced topic that you do not normally need to use AnyEvent in
		987	a module. This section is only of use to event loop authors who want to
		988	provide AnyEvent compatibility.
430		989
431	If you need to support another event library which isn't directly	990	If you need to support another event library which isn't directly
432	supported by AnyEvent, you can supply your own interface to it by	991	supported by AnyEvent, you can supply your own interface to it by
433	pushing, before the first watcher gets created, the package name of	992	pushing, before the first watcher gets created, the package name of
434	the event module and the package name of the interface to use onto	993	the event module and the package name of the interface to use onto
435	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	994	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
436	AnyEvent.	995	AnyEvent, so it is reasonably cheap.
437		996
438	Example:	997	Example:
439		998
440	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	999	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
441		1000
442	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1001	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
443	package/class when it finds the C<urxvt> package/module is loaded. When	1002	package/class when it finds the C<urxvt> package/module is already loaded.
		1003
444	AnyEvent is loaded and asked to find a suitable event model, it will	1004	When AnyEvent is loaded and asked to find a suitable event model, it
445	first check for the presence of urxvt.	1005	will first check for the presence of urxvt by trying to C<use> the
		1006	C<urxvt::anyevent> module.
446		1007
447	The class should provide implementations for all watcher types (see	1008	The class should provide implementations for all watcher types. See
448	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1009	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
449	(Source code) and so on for actual examples, use C<perldoc -m	1010	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
450	AnyEvent::Impl::Glib> to see the sources).	1011	see the sources.
451		1012
		1013	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1014	provide suitable (hopefully) replacements.
		1015
452	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1016	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
453	uses the above line as-is. An interface isn't included in AnyEvent	1017	terminal emulator uses the above line as-is. An interface isn't included
454	because it doesn't make sense outside the embedded interpreter inside	1018	in AnyEvent because it doesn't make sense outside the embedded interpreter
455	I<rxvt-unicode>, and it is updated and maintained as part of the	1019	inside I<rxvt-unicode>, and it is updated and maintained as part of the
456	I<rxvt-unicode> distribution.	1020	I<rxvt-unicode> distribution.
457		1021
458	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1022	I<rxvt-unicode> also cheats a bit by not providing blocking access to
459	condition variables: code blocking while waiting for a condition will	1023	condition variables: code blocking while waiting for a condition will
460	C<die>. This still works with most modules/usages, and blocking calls must	1024	C<die>. This still works with most modules/usages, and blocking calls must
461	not be in an interactive application, so it makes sense.	1025	not be done in an interactive application, so it makes sense.
462		1026
463	=head1 ENVIRONMENT VARIABLES	1027	=head1 ENVIRONMENT VARIABLES
464		1028
465	The following environment variables are used by this module:	1029	The following environment variables are used by this module:
466		1030
467	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	1031	=over 4
468	model gets used.
469		1032
		1033	=item C<PERL_ANYEVENT_VERBOSE>
		1034
		1035	By default, AnyEvent will be completely silent except in fatal
		1036	conditions. You can set this environment variable to make AnyEvent more
		1037	talkative.
		1038
		1039	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1040	conditions, such as not being able to load the event model specified by
		1041	C<PERL_ANYEVENT_MODEL>.
		1042
		1043	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1044	model it chooses.
		1045
		1046	=item C<PERL_ANYEVENT_MODEL>
		1047
		1048	This can be used to specify the event model to be used by AnyEvent, before
		1049	auto detection and -probing kicks in. It must be a string consisting
		1050	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1051	and the resulting module name is loaded and if the load was successful,
		1052	used as event model. If it fails to load AnyEvent will proceed with
		1053	auto detection and -probing.
		1054
		1055	This functionality might change in future versions.
		1056
		1057	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1058	could start your program like this:
		1059
		1060	PERL_ANYEVENT_MODEL=Perl perl ...
		1061
		1062	=item C<PERL_ANYEVENT_PROTOCOLS>
		1063
		1064	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1065	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1066	of auto probing).
		1067
		1068	Must be set to a comma-separated list of protocols or address families,
		1069	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1070	used, and preference will be given to protocols mentioned earlier in the
		1071	list.
		1072
		1073	This variable can effectively be used for denial-of-service attacks
		1074	against local programs (e.g. when setuid), although the impact is likely
		1075	small, as the program has to handle connection errors already-
		1076
		1077	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1078	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1079	- only support IPv4, never try to resolve or contact IPv6
		1080	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1081	IPv6, but prefer IPv6 over IPv4.
		1082
		1083	=item C<PERL_ANYEVENT_EDNS0>
		1084
		1085	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1086	for DNS. This extension is generally useful to reduce DNS traffic, but
		1087	some (broken) firewalls drop such DNS packets, which is why it is off by
		1088	default.
		1089
		1090	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1091	EDNS0 in its DNS requests.
		1092
		1093	=back
		1094
470	=head1 EXAMPLE	1095	=head1 EXAMPLE PROGRAM
471		1096
472	The following program uses an io watcher to read data from stdin, a timer	1097	The following program uses an I/O watcher to read data from STDIN, a timer
473	to display a message once per second, and a condvar to exit the program	1098	to display a message once per second, and a condition variable to quit the
474	when the user enters quit:	1099	program when the user enters quit:
475		1100
476	use AnyEvent;	1101	use AnyEvent;
477		1102
478	my $cv = AnyEvent->condvar;	1103	my $cv = AnyEvent->condvar;
479		1104
480	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1105	my $io_watcher = AnyEvent->io (
		1106	fh => \*STDIN,
		1107	poll => 'r',
		1108	cb => sub {
481	warn "io event <$_[0]>\n"; # will always output <r>	1109	warn "io event <$_[0]>\n"; # will always output <r>
482	chomp (my $input = <STDIN>); # read a line	1110	chomp (my $input = <STDIN>); # read a line
483	warn "read: $input\n"; # output what has been read	1111	warn "read: $input\n"; # output what has been read
484	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1112	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1113	},
485	});	1114	);
486		1115
487	my $time_watcher; # can only be used once	1116	my $time_watcher; # can only be used once
488		1117
489	sub new_timer {	1118	sub new_timer {
490	$timer = AnyEvent->timer (after => 1, cb => sub {	1119	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
493	});	1122	});
494	}	1123	}
495		1124
496	new_timer; # create first timer	1125	new_timer; # create first timer
497		1126
498	$cv->wait; # wait until user enters /^q/i	1127	$cv->recv; # wait until user enters /^q/i
499		1128
500	=head1 REAL-WORLD EXAMPLE	1129	=head1 REAL-WORLD EXAMPLE
501		1130
502	Consider the L<Net::FCP> module. It features (among others) the following	1131	Consider the L<Net::FCP> module. It features (among others) the following
503	API calls, which are to freenet what HTTP GET requests are to http:	1132	API calls, which are to freenet what HTTP GET requests are to http:
…		…
553	syswrite $txn->{fh}, $txn->{request}	1182	syswrite $txn->{fh}, $txn->{request}
554	or die "connection or write error";	1183	or die "connection or write error";
555	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1184	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
556		1185
557	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1186	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
558	result and signals any possible waiters that the request ahs finished:	1187	result and signals any possible waiters that the request has finished:
559		1188
560	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1189	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
561		1190
562	if (end-of-file or data complete) {	1191	if (end-of-file or data complete) {
563	$txn->{result} = $txn->{buf};	1192	$txn->{result} = $txn->{buf};
564	$txn->{finished}->broadcast;	1193	$txn->{finished}->send;
565	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1194	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
566	}	1195	}
567		1196
568	The C<result> method, finally, just waits for the finished signal (if the	1197	The C<result> method, finally, just waits for the finished signal (if the
569	request was already finished, it doesn't wait, of course, and returns the	1198	request was already finished, it doesn't wait, of course, and returns the
570	data:	1199	data:
571		1200
572	$txn->{finished}->wait;	1201	$txn->{finished}->recv;
573	return $txn->{result};	1202	return $txn->{result};
574		1203
575	The actual code goes further and collects all errors (C<die>s, exceptions)	1204	The actual code goes further and collects all errors (C<die>s, exceptions)
576	that occured during request processing. The C<result> method detects	1205	that occurred during request processing. The C<result> method detects
577	wether an exception as thrown (it is stored inside the $txn object)	1206	whether an exception as thrown (it is stored inside the $txn object)
578	and just throws the exception, which means connection errors and other	1207	and just throws the exception, which means connection errors and other
579	problems get reported tot he code that tries to use the result, not in a	1208	problems get reported tot he code that tries to use the result, not in a
580	random callback.	1209	random callback.
581		1210
582	All of this enables the following usage styles:	1211	All of this enables the following usage styles:
583		1212
584	1. Blocking:	1213	1. Blocking:
585		1214
586	my $data = $fcp->client_get ($url);	1215	my $data = $fcp->client_get ($url);
587		1216
588	2. Blocking, but parallelizing:	1217	2. Blocking, but running in parallel:
589		1218
590	my @datas = map $_->result,	1219	my @datas = map $_->result,
591	map $fcp->txn_client_get ($_),	1220	map $fcp->txn_client_get ($_),
592	@urls;	1221	@urls;
593		1222
594	Both blocking examples work without the module user having to know	1223	Both blocking examples work without the module user having to know
595	anything about events.	1224	anything about events.
596		1225
597	3a. Event-based in a main program, using any support Event module:	1226	3a. Event-based in a main program, using any supported event module:
598		1227
599	use Event;	1228	use EV;
600		1229
601	$fcp->txn_client_get ($url)->cb (sub {	1230	$fcp->txn_client_get ($url)->cb (sub {
602	my $txn = shift;	1231	my $txn = shift;
603	my $data = $txn->result;	1232	my $data = $txn->result;
604	...	1233	...
605	});	1234	});
606		1235
607	Event::loop;	1236	EV::loop;
608		1237
609	3b. The module user could use AnyEvent, too:	1238	3b. The module user could use AnyEvent, too:
610		1239
611	use AnyEvent;	1240	use AnyEvent;
612		1241
613	my $quit = AnyEvent->condvar;	1242	my $quit = AnyEvent->condvar;
614		1243
615	$fcp->txn_client_get ($url)->cb (sub {	1244	$fcp->txn_client_get ($url)->cb (sub {
616	...	1245	...
617	$quit->broadcast;	1246	$quit->send;
618	});	1247	});
619		1248
620	$quit->wait;	1249	$quit->recv;
		1250
		1251
		1252	=head1 BENCHMARKS
		1253
		1254	To give you an idea of the performance and overheads that AnyEvent adds
		1255	over the event loops themselves and to give you an impression of the speed
		1256	of various event loops I prepared some benchmarks.
		1257
		1258	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1259
		1260	Here is a benchmark of various supported event models used natively and
		1261	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1262	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1263	which it is), lets them fire exactly once and destroys them again.
		1264
		1265	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1266	distribution.
		1267
		1268	=head3 Explanation of the columns
		1269
		1270	I<watcher> is the number of event watchers created/destroyed. Since
		1271	different event models feature vastly different performances, each event
		1272	loop was given a number of watchers so that overall runtime is acceptable
		1273	and similar between tested event loop (and keep them from crashing): Glib
		1274	would probably take thousands of years if asked to process the same number
		1275	of watchers as EV in this benchmark.
		1276
		1277	I<bytes> is the number of bytes (as measured by the resident set size,
		1278	RSS) consumed by each watcher. This method of measuring captures both C
		1279	and Perl-based overheads.
		1280
		1281	I<create> is the time, in microseconds (millionths of seconds), that it
		1282	takes to create a single watcher. The callback is a closure shared between
		1283	all watchers, to avoid adding memory overhead. That means closure creation
		1284	and memory usage is not included in the figures.
		1285
		1286	I<invoke> is the time, in microseconds, used to invoke a simple
		1287	callback. The callback simply counts down a Perl variable and after it was
		1288	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1289	signal the end of this phase.
		1290
		1291	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1292	watcher.
		1293
		1294	=head3 Results
		1295
		1296	name watchers bytes create invoke destroy comment
		1297	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1298	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1299	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1300	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1301	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1302	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1303	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1304	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1305	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1306	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1307
		1308	=head3 Discussion
		1309
		1310	The benchmark does I<not> measure scalability of the event loop very
		1311	well. For example, a select-based event loop (such as the pure perl one)
		1312	can never compete with an event loop that uses epoll when the number of
		1313	file descriptors grows high. In this benchmark, all events become ready at
		1314	the same time, so select/poll-based implementations get an unnatural speed
		1315	boost.
		1316
		1317	Also, note that the number of watchers usually has a nonlinear effect on
		1318	overall speed, that is, creating twice as many watchers doesn't take twice
		1319	the time - usually it takes longer. This puts event loops tested with a
		1320	higher number of watchers at a disadvantage.
		1321
		1322	To put the range of results into perspective, consider that on the
		1323	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1324	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1325	cycles with POE.
		1326
		1327	C<EV> is the sole leader regarding speed and memory use, which are both
		1328	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1329	far less memory than any other event loop and is still faster than Event
		1330	natively.
		1331
		1332	The pure perl implementation is hit in a few sweet spots (both the
		1333	constant timeout and the use of a single fd hit optimisations in the perl
		1334	interpreter and the backend itself). Nevertheless this shows that it
		1335	adds very little overhead in itself. Like any select-based backend its
		1336	performance becomes really bad with lots of file descriptors (and few of
		1337	them active), of course, but this was not subject of this benchmark.
		1338
		1339	The C<Event> module has a relatively high setup and callback invocation
		1340	cost, but overall scores in on the third place.
		1341
		1342	C<Glib>'s memory usage is quite a bit higher, but it features a
		1343	faster callback invocation and overall ends up in the same class as
		1344	C<Event>. However, Glib scales extremely badly, doubling the number of
		1345	watchers increases the processing time by more than a factor of four,
		1346	making it completely unusable when using larger numbers of watchers
		1347	(note that only a single file descriptor was used in the benchmark, so
		1348	inefficiencies of C<poll> do not account for this).
		1349
		1350	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1351	more than 2000 watchers is a big setback, however, as correctness takes
		1352	precedence over speed. Nevertheless, its performance is surprising, as the
		1353	file descriptor is dup()ed for each watcher. This shows that the dup()
		1354	employed by some adaptors is not a big performance issue (it does incur a
		1355	hidden memory cost inside the kernel which is not reflected in the figures
		1356	above).
		1357
		1358	C<POE>, regardless of underlying event loop (whether using its pure perl
		1359	select-based backend or the Event module, the POE-EV backend couldn't
		1360	be tested because it wasn't working) shows abysmal performance and
		1361	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1362	as EV watchers, and 10 times as much memory as Event (the high memory
		1363	requirements are caused by requiring a session for each watcher). Watcher
		1364	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1365	implementation.
		1366
		1367	The design of the POE adaptor class in AnyEvent can not really account
		1368	for the performance issues, though, as session creation overhead is
		1369	small compared to execution of the state machine, which is coded pretty
		1370	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1371	using multiple sessions is not a good approach, especially regarding
		1372	memory usage, even the author of POE could not come up with a faster
		1373	design).
		1374
		1375	=head3 Summary
		1376
		1377	=over 4
		1378
		1379	=item * Using EV through AnyEvent is faster than any other event loop
		1380	(even when used without AnyEvent), but most event loops have acceptable
		1381	performance with or without AnyEvent.
		1382
		1383	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1384	the actual event loop, only with extremely fast event loops such as EV
		1385	adds AnyEvent significant overhead.
		1386
		1387	=item * You should avoid POE like the plague if you want performance or
		1388	reasonable memory usage.
		1389
		1390	=back
		1391
		1392	=head2 BENCHMARKING THE LARGE SERVER CASE
		1393
		1394	This benchmark actually benchmarks the event loop itself. It works by
		1395	creating a number of "servers": each server consists of a socket pair, a
		1396	timeout watcher that gets reset on activity (but never fires), and an I/O
		1397	watcher waiting for input on one side of the socket. Each time the socket
		1398	watcher reads a byte it will write that byte to a random other "server".
		1399
		1400	The effect is that there will be a lot of I/O watchers, only part of which
		1401	are active at any one point (so there is a constant number of active
		1402	fds for each loop iteration, but which fds these are is random). The
		1403	timeout is reset each time something is read because that reflects how
		1404	most timeouts work (and puts extra pressure on the event loops).
		1405
		1406	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1407	(1%) are active. This mirrors the activity of large servers with many
		1408	connections, most of which are idle at any one point in time.
		1409
		1410	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1411	distribution.
		1412
		1413	=head3 Explanation of the columns
		1414
		1415	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1416	each server has a read and write socket end).
		1417
		1418	I<create> is the time it takes to create a socket pair (which is
		1419	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1420
		1421	I<request>, the most important value, is the time it takes to handle a
		1422	single "request", that is, reading the token from the pipe and forwarding
		1423	it to another server. This includes deleting the old timeout and creating
		1424	a new one that moves the timeout into the future.
		1425
		1426	=head3 Results
		1427
		1428	name sockets create request
		1429	EV 20000 69.01 11.16
		1430	Perl 20000 73.32 35.87
		1431	Event 20000 212.62 257.32
		1432	Glib 20000 651.16 1896.30
		1433	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1434
		1435	=head3 Discussion
		1436
		1437	This benchmark I<does> measure scalability and overall performance of the
		1438	particular event loop.
		1439
		1440	EV is again fastest. Since it is using epoll on my system, the setup time
		1441	is relatively high, though.
		1442
		1443	Perl surprisingly comes second. It is much faster than the C-based event
		1444	loops Event and Glib.
		1445
		1446	Event suffers from high setup time as well (look at its code and you will
		1447	understand why). Callback invocation also has a high overhead compared to
		1448	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1449	uses select or poll in basically all documented configurations.
		1450
		1451	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1452	clearly fails to perform with many filehandles or in busy servers.
		1453
		1454	POE is still completely out of the picture, taking over 1000 times as long
		1455	as EV, and over 100 times as long as the Perl implementation, even though
		1456	it uses a C-based event loop in this case.
		1457
		1458	=head3 Summary
		1459
		1460	=over 4
		1461
		1462	=item * The pure perl implementation performs extremely well.
		1463
		1464	=item * Avoid Glib or POE in large projects where performance matters.
		1465
		1466	=back
		1467
		1468	=head2 BENCHMARKING SMALL SERVERS
		1469
		1470	While event loops should scale (and select-based ones do not...) even to
		1471	large servers, most programs we (or I :) actually write have only a few
		1472	I/O watchers.
		1473
		1474	In this benchmark, I use the same benchmark program as in the large server
		1475	case, but it uses only eight "servers", of which three are active at any
		1476	one time. This should reflect performance for a small server relatively
		1477	well.
		1478
		1479	The columns are identical to the previous table.
		1480
		1481	=head3 Results
		1482
		1483	name sockets create request
		1484	EV 16 20.00 6.54
		1485	Perl 16 25.75 12.62
		1486	Event 16 81.27 35.86
		1487	Glib 16 32.63 15.48
		1488	POE 16 261.87 276.28 uses POE::Loop::Event
		1489
		1490	=head3 Discussion
		1491
		1492	The benchmark tries to test the performance of a typical small
		1493	server. While knowing how various event loops perform is interesting, keep
		1494	in mind that their overhead in this case is usually not as important, due
		1495	to the small absolute number of watchers (that is, you need efficiency and
		1496	speed most when you have lots of watchers, not when you only have a few of
		1497	them).
		1498
		1499	EV is again fastest.
		1500
		1501	Perl again comes second. It is noticeably faster than the C-based event
		1502	loops Event and Glib, although the difference is too small to really
		1503	matter.
		1504
		1505	POE also performs much better in this case, but is is still far behind the
		1506	others.
		1507
		1508	=head3 Summary
		1509
		1510	=over 4
		1511
		1512	=item * C-based event loops perform very well with small number of
		1513	watchers, as the management overhead dominates.
		1514
		1515	=back
		1516
		1517
		1518	=head1 FORK
		1519
		1520	Most event libraries are not fork-safe. The ones who are usually are
		1521	because they rely on inefficient but fork-safe C<select> or C<poll>
		1522	calls. Only L<EV> is fully fork-aware.
		1523
		1524	If you have to fork, you must either do so I<before> creating your first
		1525	watcher OR you must not use AnyEvent at all in the child.
		1526
		1527
		1528	=head1 SECURITY CONSIDERATIONS
		1529
		1530	AnyEvent can be forced to load any event model via
		1531	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1532	execute arbitrary code or directly gain access, it can easily be used to
		1533	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1534	will not be active when the program uses a different event model than
		1535	specified in the variable.
		1536
		1537	You can make AnyEvent completely ignore this variable by deleting it
		1538	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1539
		1540	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1541
		1542	use AnyEvent;
		1543
		1544	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1545	be used to probe what backend is used and gain other information (which is
		1546	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1547
621		1548
622	=head1 SEE ALSO	1549	=head1 SEE ALSO
623		1550
624	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1551	Utility functions: L<AnyEvent::Util>.
625		1552
626	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1553	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1554	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
627		1555
628	Nontrivial usage example: L<Net::FCP>.	1556	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1557	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1558	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1559	L<AnyEvent::Impl::POE>.
629		1560
630	=head1	1561	Non-blocking file handles, sockets, TCP clients and
		1562	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1563
		1564	Asynchronous DNS: L<AnyEvent::DNS>.
		1565
		1566	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1567
		1568	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1569
		1570
		1571	=head1 AUTHOR
		1572
		1573	Marc Lehmann <schmorp@schmorp.de>
		1574	http://home.schmorp.de/
631		1575
632	=cut	1576	=cut
633		1577
634	1	1578	1
635		1579

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