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Revision 1.44 by root, Mon Apr 7 19:42:18 2008 UTC vs.
Revision 1.140 by root, Mon May 26 06:18:53 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		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?
…		…
29	policy> and AnyEvent is I<small and efficient>.	29	policy> and AnyEvent is I<small and efficient>.
30		30
31	First and foremost, I<AnyEvent is not an event model> itself, it only	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	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,	33	pragmatic way. For event models and certain classes of immortals alike,
34	the statement "there can only be one" is a bitter reality, and AnyEvent	34	the statement "there can only be one" is a bitter reality: In general,
35	helps hiding the differences.	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.
36		37
37	The goal of AnyEvent is to offer module authors the ability to do event	38	The goal of AnyEvent is to offer module authors the ability to do event
38	programming (waiting for I/O or timer events) without subscribing to a	39	programming (waiting for I/O or timer events) without subscribing to a
39	religion, a way of living, and most importantly: without forcing your	40	religion, a way of living, and most importantly: without forcing your
40	module users into the same thing by forcing them to use the same event	41	module users into the same thing by forcing them to use the same event
41	model you use.	42	model you use.
42		43
43	For modules like POE or IO::Async (which is actually doing all I/O	44	For modules like POE or IO::Async (which is a total misnomer as it is
44	I<synchronously>...), using them in your module is like joining a	45	actually doing all I/O I<synchronously>...), using them in your module is
45	cult: After you joined, you are dependent on them and you cannot use	46	like joining a cult: After you joined, you are dependent on them and you
46	anything else, as it is simply incompatible to everything that isn't	47	cannot use anything else, as it is simply incompatible to everything that
47	itself.	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.
48		50
49	AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk	51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	works fine etc. etc. but none of these work together with the rest: POE	52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	+ IO::Async? no go. Tk + Event? no go. If your module uses one of	53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if
52	those, every user of your module has to use it, too. If your module	54	your module uses one of those, every user of your module has to use it,
53	uses AnyEvent, it works transparently with all event models it supports	55	too. But if your module uses AnyEvent, it works transparently with all
54	(including stuff like POE and IO::Async).	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).
55		59
56	In addition of 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
57	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
58	modules, you get an enourmous amount of code and strict rules you have	62	modules, you get an enormous amount of code and strict rules you have to
59	to follow. AnyEvent, on the other hand, is lean and to the point by only	63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
60	offering the functionality that is useful, in as thin as a wrapper as	64	offering the functionality that is necessary, in as thin as a wrapper as
61	technically possible.	65	technically possible.
62		66
63	Of course, if you want lots of policy (this is arguably somewhat useful	67	Of course, if you want lots of policy (this can arguably be somewhat
64	in many cases) and you want to force your users to the one and only event	68	useful) and you want to force your users to use the one and only event
65	model your module forces on them, you should I<not> use this module.	69	model, you should I<not> use this module.
66
67		70
68	=head1 DESCRIPTION	71	=head1 DESCRIPTION
69		72
70	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
71	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
72	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
73	peacefully at any one time).	76	peacefully at any one time).
74		77
75	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>
76	module.	79	module.
77		80
78	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
79	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
80	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
81	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>,
82	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
83	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
84	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.
85		91
86	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
87	an Event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
88	that model the default. For example:	94	that model the default. For example:
89		95
90	use Tk;	96	use Tk;
91	use AnyEvent;	97	use AnyEvent;
92		98
93	# .. 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...
94		104
95	The pure-perl implementation of AnyEvent is called	105	The pure-perl implementation of AnyEvent is called
96	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
97	explicitly.	107	explicitly.
98		108
99	=head1 WATCHERS	109	=head1 WATCHERS
100		110
101	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
102	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
103	the callback to call, the filehandle to watch, etc.	113	the callback to call, the file handle to watch, etc.
104		114
105	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
106	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
107	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
108	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
109	references to it).	122	to it).
110		123
111	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.
112		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
113	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
114		141
115	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
116	the following mandatory arguments:	143	with the following mandatory key-value pairs as arguments:
117		144
118	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
119	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>,
120	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,
121	to invoke everytime the filehandle becomes ready.	148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
122		150
123	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
124	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
125	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.
126		154
127	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.
128	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.
129		162
130	Example:	163	Example:
131		164
132	# 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
133	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
139	=head2 TIME WATCHERS	172	=head2 TIME WATCHERS
140		173
141	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 >>
142	method with the following mandatory arguments:	175	method with the following mandatory arguments:
143		176
144	C<after> after how many seconds (fractions are supported) should the timer	177	C<after> specifies after how many seconds (fractional values are
145	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.
146		184
147	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
148	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
149	and Glib).	187	and Glib).
150		188
…		…
156	});	194	});
157		195
158	# to cancel the timer:	196	# to cancel the timer:
159	undef $w;	197	undef $w;
160		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
161	=head2 CONDITION WATCHERS	298	=head2 CONDITION VARIABLES
162		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
163	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	310	Condition variables can be created by calling the C<< AnyEvent->condvar
164	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.
165		314
166	A condition watcher watches for a condition - precisely that the C<<	315	After creation, the condition variable is "false" until it becomes "true"
167	->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).
168		319
		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,
		328	for example, if you write a module that does asynchronous http requests,
		329	then a condition variable would be the ideal candidate to signal the
		330	availability of results. The user can either act when the callback is
		331	called or can synchronously C<< ->recv >> for the results.
		332
		333	You can also use them to simulate traditional event loops - for example,
		334	you can block your main program until an event occurs - for example, you
		335	could C<< ->recv >> in your main program until the user clicks the Quit
		336	button of your app, which would C<< ->send >> the "quit" event.
		337
169	Note that condition watchers recurse into the event loop - if you have	338	Note that condition variables recurse into the event loop - if you have
170	two watchers 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
171	lose. Therefore, condition watchers are good to export to your caller, but	340	lose. Therefore, condition variables are good to export to your caller, but
172	you should avoid making a blocking wait, at least in callbacks, as this	341	you should avoid making a blocking wait yourself, at least in callbacks,
173	usually asks for trouble.	342	as this asks for trouble.
174		343
175	The watcher has only 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.
176		349
177	=over 4	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.
178		353
179	=item $cv->wait	354	Example: wait for a timer.
180
181	Wait (blocking if necessary) until the C<< ->broadcast >> method has been
182	called on c<$cv>, while servicing other watchers normally.
183
184	Not all event models support a blocking wait - some die in that case, so
185	if you are using this from a module, never require a blocking wait, but
186	let the caller decide wether the call will block or not (for example,
187	by coupling condition variables with some kind of request results and
188	supporting callbacks so the caller knows that getting the result will not
189	block, while still suppporting blockign waits if the caller so desires).
190
191	You can only wait once on a condition - additional calls will return
192	immediately.
193
194	=item $cv->broadcast
195
196	Flag the condition as ready - a running C<< ->wait >> and all further
197	calls to C<wait> will return after this method has been called. If nobody
198	is waiting the broadcast will be remembered..
199
200	Example:
201		355
202	# wait till the result is ready	356	# wait till the result is ready
203	my $result_ready = AnyEvent->condvar;	357	my $result_ready = AnyEvent->condvar;
204		358
205	# do something such as adding a timer	359	# do something such as adding a timer
206	# or socket watcher the calls $result_ready->broadcast	360	# or socket watcher the calls $result_ready->send
207	# when the "result" is ready.	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	);
208		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls send
209	$result_ready->wait;	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.
		385
		386	=over 4
		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
		419	=item $cv->end
		420
		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>.
210		467
211	=back	468	=back
212		469
213	=head2 SIGNAL WATCHERS	470	=head3 METHODS FOR CONSUMERS
214		471
215	You can listen for signals using a signal watcher, C<signal> is the signal	472	These methods should only be used by the consuming side, i.e. the
216	I<name> without any C<SIG> prefix. Multiple signals events can be clumped	473	code awaits the condition.
217	together into one callback invocation, and callback invocation might or
218	might not be asynchronous.
219		474
220	These watchers might use C<%SIG>, so programs overwriting those signals	475	=over 4
221	directly will likely not work correctly.
222		476
223	Example: exit on SIGINT	477	=item $cv->recv
224		478
225	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	479	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		480	>> methods have been called on c<$cv>, while servicing other watchers
		481	normally.
226		482
227	=head2 CHILD PROCESS WATCHERS	483	You can only wait once on a condition - additional calls are valid but
		484	will return immediately.
228		485
229	You can also listen for the status of a child process specified by the	486	If an error condition has been set by calling C<< ->croak >>, then this
230	C<pid> argument (or any child if the pid argument is 0). The watcher will	487	function will call C<croak>.
231	trigger as often as status change for the child are received. This works
232	by installing a signal handler for C<SIGCHLD>. The callback will be called with
233	the pid and exit status (as returned by waitpid).
234		488
235	Example: wait for pid 1333	489	In list context, all parameters passed to C<send> will be returned,
		490	in scalar context only the first one will be returned.
236		491
237	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });	492	Not all event models support a blocking wait - some die in that case
		493	(programs might want to do that to stay interactive), so I<if you are
		494	using this from a module, never require a blocking wait>, but let the
		495	caller decide whether the call will block or not (for example, by coupling
		496	condition variables with some kind of request results and supporting
		497	callbacks so the caller knows that getting the result will not block,
		498	while still supporting blocking waits if the caller so desires).
238		499
239	=head1 GLOBALS	500	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		501	sensibly have two C<< ->recv >>'s in parallel, as that would require
		502	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		503	can supply.
		504
		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).
		510
		511	You can ensure that C<< -recv >> never blocks by setting a callback and
		512	only calling C<< ->recv >> from within that callback (or at a later
		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.
		529
		530	=back
		531
		532	=head1 GLOBAL VARIABLES AND FUNCTIONS
240		533
241	=over 4	534	=over 4
242		535
243	=item $AnyEvent::MODEL	536	=item $AnyEvent::MODEL
244		537
…		…
248	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	541	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
249	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	542	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
250		543
251	The known classes so far are:	544	The known classes so far are:
252		545
253	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
254	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	546	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
255	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
256	AnyEvent::Impl::Event based on Event, also second best choice :)	547	AnyEvent::Impl::Event based on Event, second best choice.
		548	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
257	AnyEvent::Impl::Glib based on Glib, second-best choice.	549	AnyEvent::Impl::Glib based on Glib, third-best choice.
258	AnyEvent::Impl::Tk based on Tk, very bad choice.	550	AnyEvent::Impl::Tk based on Tk, very bad choice.
259	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	551	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		552	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		553	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		554
		555	There is no support for WxWidgets, as WxWidgets has no support for
		556	watching file handles. However, you can use WxWidgets through the
		557	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		558	second, which was considered to be too horrible to even consider for
		559	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		560	it's adaptor.
		561
		562	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		563	autodetecting them.
260		564
261	=item AnyEvent::detect	565	=item AnyEvent::detect
262		566
263	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	567	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
264	necessary. You should only call this function right before you would have	568	if necessary. You should only call this function right before you would
265	created an AnyEvent watcher anyway, that is, very late at runtime.	569	have created an AnyEvent watcher anyway, that is, as late as possible at
		570	runtime.
		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.
266		592
267	=back	593	=back
268		594
269	=head1 WHAT TO DO IN A MODULE	595	=head1 WHAT TO DO IN A MODULE
270		596
271	As a module author, you should "use AnyEvent" and call AnyEvent methods	597	As a module author, you should C<use AnyEvent> and call AnyEvent methods
272	freely, but you should not load a specific event module or rely on it.	598	freely, but you should not load a specific event module or rely on it.
273		599
274	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
275	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
276	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
277	to load the event module first.	603	to load the event module first.
278		604
		605	Never call C<< ->recv >> on a condition variable unless you I<know> that
		606	the C<< ->send >> method has been called on it already. This is
		607	because it will stall the whole program, and the whole point of using
		608	events is to stay interactive.
		609
		610	It is fine, however, to call C<< ->recv >> when the user of your module
		611	requests it (i.e. if you create a http request object ad have a method
		612	called C<results> that returns the results, it should call C<< ->recv >>
		613	freely, as the user of your module knows what she is doing. always).
		614
279	=head1 WHAT TO DO IN THE MAIN PROGRAM	615	=head1 WHAT TO DO IN THE MAIN PROGRAM
280		616
281	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
282	dictate which event model to use.	618	dictate which event model to use.
283		619
284	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
285	do anything special and let AnyEvent decide which implementation to chose.	621	do anything special (it does not need to be event-based) and let AnyEvent
		622	decide which implementation to chose if some module relies on it.
286		623
287	If the main program relies on a specific event model (for example, in Gtk2	624	If the main program relies on a specific event model - for example, in
288	programs you have to rely on either Glib or Glib::Event), you should load	625	Gtk2 programs you have to rely on the Glib module - you should load the
289	it before loading AnyEvent or any module that uses it, generally, as early	626	event module before loading AnyEvent or any module that uses it: generally
290	as possible. The reason is that modules might create watchers when they	627	speaking, you should load it as early as possible. The reason is that
291	are loaded, and AnyEvent will decide on the event model to use as soon as	628	modules might create watchers when they are loaded, and AnyEvent will
292	it creates watchers, and it might chose the wrong one unless you load the	629	decide on the event model to use as soon as it creates watchers, and it
293	correct one yourself.	630	might chose the wrong one unless you load the correct one yourself.
294		631
295	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
296	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	633	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
297	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
298		726
299	=cut	727	=cut
300		728
301	package AnyEvent;	729	package AnyEvent;
302		730
303	no warnings;	731	no warnings;
304	use strict;	732	use strict;
305		733
306	use Carp;	734	use Carp;
307		735
308	our $VERSION = '3.0';	736	our $VERSION = '4.04';
309	our $MODEL;	737	our $MODEL;
310		738
311	our $AUTOLOAD;	739	our $AUTOLOAD;
312	our @ISA;	740	our @ISA;
313		741
		742	our @REGISTRY;
		743
		744	our $WIN32;
		745
		746	BEGIN {
		747	my $win32 = ! ! ($^O =~ /mswin32/i);
		748	eval "sub WIN32(){ $win32 }";
		749	}
		750
314	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	751	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
315		752
316	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	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		760	}
317		761
318	my @models = (	762	my @models = (
319	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
320	[EV:: => AnyEvent::Impl::EV::],	763	[EV:: => AnyEvent::Impl::EV::],
321	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
322	[Event:: => AnyEvent::Impl::Event::],	764	[Event:: => AnyEvent::Impl::Event::],
323	[Glib:: => AnyEvent::Impl::Glib::],
324	[Tk:: => AnyEvent::Impl::Tk::],
325	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	765	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		766	# everything below here will not be autoprobed
		767	# as the pureperl backend should work everywhere
		768	# and is usually faster
		769	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		770	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		771	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		772	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		773	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		774	[Wx:: => AnyEvent::Impl::POE::],
		775	[Prima:: => AnyEvent::Impl::POE::],
326	);	776	);
327		777
328	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	778	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		779
		780	our @post_detect;
		781
		782	sub post_detect(&) {
		783	my ($cb) = @_;
		784
		785	if ($MODEL) {
		786	$cb->();
		787
		788	1
		789	} else {
		790	push @post_detect, $cb;
		791
		792	defined wantarray
		793	? bless \$cb, "AnyEvent::Util::PostDetect"
		794	: ()
		795	}
		796	}
		797
		798	sub AnyEvent::Util::PostDetect::DESTROY {
		799	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		800	}
329		801
330	sub detect() {	802	sub detect() {
331	unless ($MODEL) {	803	unless ($MODEL) {
332	no strict 'refs';	804	no strict 'refs';
		805	local $SIG{__DIE__};
		806
		807	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		808	my $model = "AnyEvent::Impl::$1";
		809	if (eval "require $model") {
		810	$MODEL = $model;
		811	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		812	} else {
		813	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		814	}
		815	}
333		816
334	# check for already loaded models	817	# check for already loaded models
		818	unless ($MODEL) {
335	for (@REGISTRY, @models) {	819	for (@REGISTRY, @models) {
336	my ($package, $model) = @$_;	820	my ($package, $model) = @$_;
337	if (${"$package\::VERSION"} > 0) {	821	if (${"$package\::VERSION"} > 0) {
338	if (eval "require $model") {	822	if (eval "require $model") {
339	$MODEL = $model;	823	$MODEL = $model;
340	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	824	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
341	last;	825	last;
		826	}
342	}	827	}
343	}	828	}
344	}
345		829
346	unless ($MODEL) {	830	unless ($MODEL) {
347	# try to load a model	831	# try to load a model
348		832
349	for (@REGISTRY, @models) {	833	for (@REGISTRY, @models) {
350	my ($package, $model) = @$_;	834	my ($package, $model) = @$_;
351	if (eval "require $package"	835	if (eval "require $package"
352	and ${"$package\::VERSION"} > 0	836	and ${"$package\::VERSION"} > 0
353	and eval "require $model") {	837	and eval "require $model") {
354	$MODEL = $model;	838	$MODEL = $model;
355	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	839	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
356	last;	840	last;
		841	}
357	}	842	}
		843
		844	$MODEL
		845	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
358	}	846	}
359
360	$MODEL
361	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.";
362	}	847	}
363		848
364	unshift @ISA, $MODEL;	849	unshift @ISA, $MODEL;
365	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	850	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		851
		852	(shift @post_detect)->() while @post_detect;
366	}	853	}
367		854
368	$MODEL	855	$MODEL
369	}	856	}
370		857
…		…
380	$class->$func (@_);	867	$class->$func (@_);
381	}	868	}
382		869
383	package AnyEvent::Base;	870	package AnyEvent::Base;
384		871
385	# default implementation for ->condvar, ->wait, ->broadcast	872	# default implementation for ->condvar
386		873
387	sub condvar {	874	sub condvar {
388	bless \my $flag, "AnyEvent::Base::CondVar"	875	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
389	}
390
391	sub AnyEvent::Base::CondVar::broadcast {
392	${$_[0]}++;
393	}
394
395	sub AnyEvent::Base::CondVar::wait {
396	AnyEvent->one_event while !${$_[0]};
397	}	876	}
398		877
399	# default implementation for ->signal	878	# default implementation for ->signal
400		879
401	our %SIG_CB;	880	our %SIG_CB;
…		…
454	or Carp::croak "required option 'pid' is missing";	933	or Carp::croak "required option 'pid' is missing";
455		934
456	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	935	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
457		936
458	unless ($WNOHANG) {	937	unless ($WNOHANG) {
459	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	938	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
460	}	939	}
461		940
462	unless ($CHLD_W) {	941	unless ($CHLD_W) {
463	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	942	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
464	# child could be a zombie already, so make at least one round	943	# child could be a zombie already, so make at least one round
…		…
475	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	954	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
476		955
477	undef $CHLD_W unless keys %PID_CB;	956	undef $CHLD_W unless keys %PID_CB;
478	}	957	}
479		958
		959	package AnyEvent::CondVar;
		960
		961	our @ISA = AnyEvent::CondVar::Base::;
		962
		963	package AnyEvent::CondVar::Base;
		964
		965	use overload
		966	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		967	fallback => 1;
		968
		969	sub _send {
		970	# nop
		971	}
		972
		973	sub send {
		974	my $cv = shift;
		975	$cv->{_ae_sent} = [@_];
		976	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		977	$cv->_send;
		978	}
		979
		980	sub croak {
		981	$_[0]{_ae_croak} = $_[1];
		982	$_[0]->send;
		983	}
		984
		985	sub ready {
		986	$_[0]{_ae_sent}
		987	}
		988
		989	sub _wait {
		990	AnyEvent->one_event while !$_[0]{_ae_sent};
		991	}
		992
		993	sub recv {
		994	$_[0]->_wait;
		995
		996	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		997	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		998	}
		999
		1000	sub cb {
		1001	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1002	$_[0]{_ae_cb}
		1003	}
		1004
		1005	sub begin {
		1006	++$_[0]{_ae_counter};
		1007	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1008	}
		1009
		1010	sub end {
		1011	return if --$_[0]{_ae_counter};
		1012	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1013	}
		1014
		1015	# undocumented/compatibility with pre-3.4
		1016	*broadcast = \&send;
		1017	*wait = \&_wait;
		1018
480	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1019	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1020
		1021	This is an advanced topic that you do not normally need to use AnyEvent in
		1022	a module. This section is only of use to event loop authors who want to
		1023	provide AnyEvent compatibility.
481		1024
482	If you need to support another event library which isn't directly	1025	If you need to support another event library which isn't directly
483	supported by AnyEvent, you can supply your own interface to it by	1026	supported by AnyEvent, you can supply your own interface to it by
484	pushing, before the first watcher gets created, the package name of	1027	pushing, before the first watcher gets created, the package name of
485	the event module and the package name of the interface to use onto	1028	the event module and the package name of the interface to use onto
486	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	1029	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
487	AnyEvent.	1030	AnyEvent, so it is reasonably cheap.
488		1031
489	Example:	1032	Example:
490		1033
491	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1034	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
492		1035
493	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1036	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
494	package/class when it finds the C<urxvt> package/module is loaded. When	1037	package/class when it finds the C<urxvt> package/module is already loaded.
		1038
495	AnyEvent is loaded and asked to find a suitable event model, it will	1039	When AnyEvent is loaded and asked to find a suitable event model, it
496	first check for the presence of urxvt.	1040	will first check for the presence of urxvt by trying to C<use> the
		1041	C<urxvt::anyevent> module.
497		1042
498	The class should provide implementations for all watcher types (see	1043	The class should provide implementations for all watcher types. See
499	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1044	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
500	(Source code) and so on for actual examples, use C<perldoc -m	1045	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
501	AnyEvent::Impl::Glib> to see the sources).	1046	see the sources.
502		1047
		1048	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1049	provide suitable (hopefully) replacements.
		1050
503	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1051	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
504	uses the above line as-is. An interface isn't included in AnyEvent	1052	terminal emulator uses the above line as-is. An interface isn't included
505	because it doesn't make sense outside the embedded interpreter inside	1053	in AnyEvent because it doesn't make sense outside the embedded interpreter
506	I<rxvt-unicode>, and it is updated and maintained as part of the	1054	inside I<rxvt-unicode>, and it is updated and maintained as part of the
507	I<rxvt-unicode> distribution.	1055	I<rxvt-unicode> distribution.
508		1056
509	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1057	I<rxvt-unicode> also cheats a bit by not providing blocking access to
510	condition variables: code blocking while waiting for a condition will	1058	condition variables: code blocking while waiting for a condition will
511	C<die>. This still works with most modules/usages, and blocking calls must	1059	C<die>. This still works with most modules/usages, and blocking calls must
512	not be in an interactive application, so it makes sense.	1060	not be done in an interactive application, so it makes sense.
513		1061
514	=head1 ENVIRONMENT VARIABLES	1062	=head1 ENVIRONMENT VARIABLES
515		1063
516	The following environment variables are used by this module:	1064	The following environment variables are used by this module:
517		1065
518	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	1066	=over 4
519	model gets used.
520		1067
		1068	=item C<PERL_ANYEVENT_VERBOSE>
		1069
		1070	By default, AnyEvent will be completely silent except in fatal
		1071	conditions. You can set this environment variable to make AnyEvent more
		1072	talkative.
		1073
		1074	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1075	conditions, such as not being able to load the event model specified by
		1076	C<PERL_ANYEVENT_MODEL>.
		1077
		1078	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1079	model it chooses.
		1080
		1081	=item C<PERL_ANYEVENT_MODEL>
		1082
		1083	This can be used to specify the event model to be used by AnyEvent, before
		1084	auto detection and -probing kicks in. It must be a string consisting
		1085	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1086	and the resulting module name is loaded and if the load was successful,
		1087	used as event model. If it fails to load AnyEvent will proceed with
		1088	auto detection and -probing.
		1089
		1090	This functionality might change in future versions.
		1091
		1092	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1093	could start your program like this:
		1094
		1095	PERL_ANYEVENT_MODEL=Perl perl ...
		1096
		1097	=item C<PERL_ANYEVENT_PROTOCOLS>
		1098
		1099	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1100	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1101	of auto probing).
		1102
		1103	Must be set to a comma-separated list of protocols or address families,
		1104	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1105	used, and preference will be given to protocols mentioned earlier in the
		1106	list.
		1107
		1108	This variable can effectively be used for denial-of-service attacks
		1109	against local programs (e.g. when setuid), although the impact is likely
		1110	small, as the program has to handle connection errors already-
		1111
		1112	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1113	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1114	- only support IPv4, never try to resolve or contact IPv6
		1115	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1116	IPv6, but prefer IPv6 over IPv4.
		1117
		1118	=item C<PERL_ANYEVENT_EDNS0>
		1119
		1120	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1121	for DNS. This extension is generally useful to reduce DNS traffic, but
		1122	some (broken) firewalls drop such DNS packets, which is why it is off by
		1123	default.
		1124
		1125	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1126	EDNS0 in its DNS requests.
		1127
		1128	=back
		1129
521	=head1 EXAMPLE	1130	=head1 EXAMPLE PROGRAM
522		1131
523	The following program uses an io watcher to read data from stdin, a timer	1132	The following program uses an I/O watcher to read data from STDIN, a timer
524	to display a message once per second, and a condvar to exit the program	1133	to display a message once per second, and a condition variable to quit the
525	when the user enters quit:	1134	program when the user enters quit:
526		1135
527	use AnyEvent;	1136	use AnyEvent;
528		1137
529	my $cv = AnyEvent->condvar;	1138	my $cv = AnyEvent->condvar;
530		1139
531	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1140	my $io_watcher = AnyEvent->io (
		1141	fh => \*STDIN,
		1142	poll => 'r',
		1143	cb => sub {
532	warn "io event <$_[0]>\n"; # will always output <r>	1144	warn "io event <$_[0]>\n"; # will always output <r>
533	chomp (my $input = <STDIN>); # read a line	1145	chomp (my $input = <STDIN>); # read a line
534	warn "read: $input\n"; # output what has been read	1146	warn "read: $input\n"; # output what has been read
535	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1147	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1148	},
536	});	1149	);
537		1150
538	my $time_watcher; # can only be used once	1151	my $time_watcher; # can only be used once
539		1152
540	sub new_timer {	1153	sub new_timer {
541	$timer = AnyEvent->timer (after => 1, cb => sub {	1154	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
544	});	1157	});
545	}	1158	}
546		1159
547	new_timer; # create first timer	1160	new_timer; # create first timer
548		1161
549	$cv->wait; # wait until user enters /^q/i	1162	$cv->recv; # wait until user enters /^q/i
550		1163
551	=head1 REAL-WORLD EXAMPLE	1164	=head1 REAL-WORLD EXAMPLE
552		1165
553	Consider the L<Net::FCP> module. It features (among others) the following	1166	Consider the L<Net::FCP> module. It features (among others) the following
554	API calls, which are to freenet what HTTP GET requests are to http:	1167	API calls, which are to freenet what HTTP GET requests are to http:
…		…
604	syswrite $txn->{fh}, $txn->{request}	1217	syswrite $txn->{fh}, $txn->{request}
605	or die "connection or write error";	1218	or die "connection or write error";
606	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1219	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
607		1220
608	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1221	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
609	result and signals any possible waiters that the request ahs finished:	1222	result and signals any possible waiters that the request has finished:
610		1223
611	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1224	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
612		1225
613	if (end-of-file or data complete) {	1226	if (end-of-file or data complete) {
614	$txn->{result} = $txn->{buf};	1227	$txn->{result} = $txn->{buf};
615	$txn->{finished}->broadcast;	1228	$txn->{finished}->send;
616	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1229	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
617	}	1230	}
618		1231
619	The C<result> method, finally, just waits for the finished signal (if the	1232	The C<result> method, finally, just waits for the finished signal (if the
620	request was already finished, it doesn't wait, of course, and returns the	1233	request was already finished, it doesn't wait, of course, and returns the
621	data:	1234	data:
622		1235
623	$txn->{finished}->wait;	1236	$txn->{finished}->recv;
624	return $txn->{result};	1237	return $txn->{result};
625		1238
626	The actual code goes further and collects all errors (C<die>s, exceptions)	1239	The actual code goes further and collects all errors (C<die>s, exceptions)
627	that occured during request processing. The C<result> method detects	1240	that occurred during request processing. The C<result> method detects
628	wether an exception as thrown (it is stored inside the $txn object)	1241	whether an exception as thrown (it is stored inside the $txn object)
629	and just throws the exception, which means connection errors and other	1242	and just throws the exception, which means connection errors and other
630	problems get reported tot he code that tries to use the result, not in a	1243	problems get reported tot he code that tries to use the result, not in a
631	random callback.	1244	random callback.
632		1245
633	All of this enables the following usage styles:	1246	All of this enables the following usage styles:
634		1247
635	1. Blocking:	1248	1. Blocking:
636		1249
637	my $data = $fcp->client_get ($url);	1250	my $data = $fcp->client_get ($url);
638		1251
639	2. Blocking, but parallelizing:	1252	2. Blocking, but running in parallel:
640		1253
641	my @datas = map $_->result,	1254	my @datas = map $_->result,
642	map $fcp->txn_client_get ($_),	1255	map $fcp->txn_client_get ($_),
643	@urls;	1256	@urls;
644		1257
645	Both blocking examples work without the module user having to know	1258	Both blocking examples work without the module user having to know
646	anything about events.	1259	anything about events.
647		1260
648	3a. Event-based in a main program, using any support Event module:	1261	3a. Event-based in a main program, using any supported event module:
649		1262
650	use Event;	1263	use EV;
651		1264
652	$fcp->txn_client_get ($url)->cb (sub {	1265	$fcp->txn_client_get ($url)->cb (sub {
653	my $txn = shift;	1266	my $txn = shift;
654	my $data = $txn->result;	1267	my $data = $txn->result;
655	...	1268	...
656	});	1269	});
657		1270
658	Event::loop;	1271	EV::loop;
659		1272
660	3b. The module user could use AnyEvent, too:	1273	3b. The module user could use AnyEvent, too:
661		1274
662	use AnyEvent;	1275	use AnyEvent;
663		1276
664	my $quit = AnyEvent->condvar;	1277	my $quit = AnyEvent->condvar;
665		1278
666	$fcp->txn_client_get ($url)->cb (sub {	1279	$fcp->txn_client_get ($url)->cb (sub {
667	...	1280	...
668	$quit->broadcast;	1281	$quit->send;
669	});	1282	});
670		1283
671	$quit->wait;	1284	$quit->recv;
		1285
		1286
		1287	=head1 BENCHMARKS
		1288
		1289	To give you an idea of the performance and overheads that AnyEvent adds
		1290	over the event loops themselves and to give you an impression of the speed
		1291	of various event loops I prepared some benchmarks.
		1292
		1293	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1294
		1295	Here is a benchmark of various supported event models used natively and
		1296	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1297	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1298	which it is), lets them fire exactly once and destroys them again.
		1299
		1300	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1301	distribution.
		1302
		1303	=head3 Explanation of the columns
		1304
		1305	I<watcher> is the number of event watchers created/destroyed. Since
		1306	different event models feature vastly different performances, each event
		1307	loop was given a number of watchers so that overall runtime is acceptable
		1308	and similar between tested event loop (and keep them from crashing): Glib
		1309	would probably take thousands of years if asked to process the same number
		1310	of watchers as EV in this benchmark.
		1311
		1312	I<bytes> is the number of bytes (as measured by the resident set size,
		1313	RSS) consumed by each watcher. This method of measuring captures both C
		1314	and Perl-based overheads.
		1315
		1316	I<create> is the time, in microseconds (millionths of seconds), that it
		1317	takes to create a single watcher. The callback is a closure shared between
		1318	all watchers, to avoid adding memory overhead. That means closure creation
		1319	and memory usage is not included in the figures.
		1320
		1321	I<invoke> is the time, in microseconds, used to invoke a simple
		1322	callback. The callback simply counts down a Perl variable and after it was
		1323	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1324	signal the end of this phase.
		1325
		1326	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1327	watcher.
		1328
		1329	=head3 Results
		1330
		1331	name watchers bytes create invoke destroy comment
		1332	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1333	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1334	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1335	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1336	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1337	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1338	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1339	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1340	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1341	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1342
		1343	=head3 Discussion
		1344
		1345	The benchmark does I<not> measure scalability of the event loop very
		1346	well. For example, a select-based event loop (such as the pure perl one)
		1347	can never compete with an event loop that uses epoll when the number of
		1348	file descriptors grows high. In this benchmark, all events become ready at
		1349	the same time, so select/poll-based implementations get an unnatural speed
		1350	boost.
		1351
		1352	Also, note that the number of watchers usually has a nonlinear effect on
		1353	overall speed, that is, creating twice as many watchers doesn't take twice
		1354	the time - usually it takes longer. This puts event loops tested with a
		1355	higher number of watchers at a disadvantage.
		1356
		1357	To put the range of results into perspective, consider that on the
		1358	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1359	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1360	cycles with POE.
		1361
		1362	C<EV> is the sole leader regarding speed and memory use, which are both
		1363	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1364	far less memory than any other event loop and is still faster than Event
		1365	natively.
		1366
		1367	The pure perl implementation is hit in a few sweet spots (both the
		1368	constant timeout and the use of a single fd hit optimisations in the perl
		1369	interpreter and the backend itself). Nevertheless this shows that it
		1370	adds very little overhead in itself. Like any select-based backend its
		1371	performance becomes really bad with lots of file descriptors (and few of
		1372	them active), of course, but this was not subject of this benchmark.
		1373
		1374	The C<Event> module has a relatively high setup and callback invocation
		1375	cost, but overall scores in on the third place.
		1376
		1377	C<Glib>'s memory usage is quite a bit higher, but it features a
		1378	faster callback invocation and overall ends up in the same class as
		1379	C<Event>. However, Glib scales extremely badly, doubling the number of
		1380	watchers increases the processing time by more than a factor of four,
		1381	making it completely unusable when using larger numbers of watchers
		1382	(note that only a single file descriptor was used in the benchmark, so
		1383	inefficiencies of C<poll> do not account for this).
		1384
		1385	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1386	more than 2000 watchers is a big setback, however, as correctness takes
		1387	precedence over speed. Nevertheless, its performance is surprising, as the
		1388	file descriptor is dup()ed for each watcher. This shows that the dup()
		1389	employed by some adaptors is not a big performance issue (it does incur a
		1390	hidden memory cost inside the kernel which is not reflected in the figures
		1391	above).
		1392
		1393	C<POE>, regardless of underlying event loop (whether using its pure perl
		1394	select-based backend or the Event module, the POE-EV backend couldn't
		1395	be tested because it wasn't working) shows abysmal performance and
		1396	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1397	as EV watchers, and 10 times as much memory as Event (the high memory
		1398	requirements are caused by requiring a session for each watcher). Watcher
		1399	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1400	implementation.
		1401
		1402	The design of the POE adaptor class in AnyEvent can not really account
		1403	for the performance issues, though, as session creation overhead is
		1404	small compared to execution of the state machine, which is coded pretty
		1405	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1406	using multiple sessions is not a good approach, especially regarding
		1407	memory usage, even the author of POE could not come up with a faster
		1408	design).
		1409
		1410	=head3 Summary
		1411
		1412	=over 4
		1413
		1414	=item * Using EV through AnyEvent is faster than any other event loop
		1415	(even when used without AnyEvent), but most event loops have acceptable
		1416	performance with or without AnyEvent.
		1417
		1418	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1419	the actual event loop, only with extremely fast event loops such as EV
		1420	adds AnyEvent significant overhead.
		1421
		1422	=item * You should avoid POE like the plague if you want performance or
		1423	reasonable memory usage.
		1424
		1425	=back
		1426
		1427	=head2 BENCHMARKING THE LARGE SERVER CASE
		1428
		1429	This benchmark actually benchmarks the event loop itself. It works by
		1430	creating a number of "servers": each server consists of a socket pair, a
		1431	timeout watcher that gets reset on activity (but never fires), and an I/O
		1432	watcher waiting for input on one side of the socket. Each time the socket
		1433	watcher reads a byte it will write that byte to a random other "server".
		1434
		1435	The effect is that there will be a lot of I/O watchers, only part of which
		1436	are active at any one point (so there is a constant number of active
		1437	fds for each loop iteration, but which fds these are is random). The
		1438	timeout is reset each time something is read because that reflects how
		1439	most timeouts work (and puts extra pressure on the event loops).
		1440
		1441	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1442	(1%) are active. This mirrors the activity of large servers with many
		1443	connections, most of which are idle at any one point in time.
		1444
		1445	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1446	distribution.
		1447
		1448	=head3 Explanation of the columns
		1449
		1450	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1451	each server has a read and write socket end).
		1452
		1453	I<create> is the time it takes to create a socket pair (which is
		1454	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1455
		1456	I<request>, the most important value, is the time it takes to handle a
		1457	single "request", that is, reading the token from the pipe and forwarding
		1458	it to another server. This includes deleting the old timeout and creating
		1459	a new one that moves the timeout into the future.
		1460
		1461	=head3 Results
		1462
		1463	name sockets create request
		1464	EV 20000 69.01 11.16
		1465	Perl 20000 73.32 35.87
		1466	Event 20000 212.62 257.32
		1467	Glib 20000 651.16 1896.30
		1468	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1469
		1470	=head3 Discussion
		1471
		1472	This benchmark I<does> measure scalability and overall performance of the
		1473	particular event loop.
		1474
		1475	EV is again fastest. Since it is using epoll on my system, the setup time
		1476	is relatively high, though.
		1477
		1478	Perl surprisingly comes second. It is much faster than the C-based event
		1479	loops Event and Glib.
		1480
		1481	Event suffers from high setup time as well (look at its code and you will
		1482	understand why). Callback invocation also has a high overhead compared to
		1483	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1484	uses select or poll in basically all documented configurations.
		1485
		1486	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1487	clearly fails to perform with many filehandles or in busy servers.
		1488
		1489	POE is still completely out of the picture, taking over 1000 times as long
		1490	as EV, and over 100 times as long as the Perl implementation, even though
		1491	it uses a C-based event loop in this case.
		1492
		1493	=head3 Summary
		1494
		1495	=over 4
		1496
		1497	=item * The pure perl implementation performs extremely well.
		1498
		1499	=item * Avoid Glib or POE in large projects where performance matters.
		1500
		1501	=back
		1502
		1503	=head2 BENCHMARKING SMALL SERVERS
		1504
		1505	While event loops should scale (and select-based ones do not...) even to
		1506	large servers, most programs we (or I :) actually write have only a few
		1507	I/O watchers.
		1508
		1509	In this benchmark, I use the same benchmark program as in the large server
		1510	case, but it uses only eight "servers", of which three are active at any
		1511	one time. This should reflect performance for a small server relatively
		1512	well.
		1513
		1514	The columns are identical to the previous table.
		1515
		1516	=head3 Results
		1517
		1518	name sockets create request
		1519	EV 16 20.00 6.54
		1520	Perl 16 25.75 12.62
		1521	Event 16 81.27 35.86
		1522	Glib 16 32.63 15.48
		1523	POE 16 261.87 276.28 uses POE::Loop::Event
		1524
		1525	=head3 Discussion
		1526
		1527	The benchmark tries to test the performance of a typical small
		1528	server. While knowing how various event loops perform is interesting, keep
		1529	in mind that their overhead in this case is usually not as important, due
		1530	to the small absolute number of watchers (that is, you need efficiency and
		1531	speed most when you have lots of watchers, not when you only have a few of
		1532	them).
		1533
		1534	EV is again fastest.
		1535
		1536	Perl again comes second. It is noticeably faster than the C-based event
		1537	loops Event and Glib, although the difference is too small to really
		1538	matter.
		1539
		1540	POE also performs much better in this case, but is is still far behind the
		1541	others.
		1542
		1543	=head3 Summary
		1544
		1545	=over 4
		1546
		1547	=item * C-based event loops perform very well with small number of
		1548	watchers, as the management overhead dominates.
		1549
		1550	=back
		1551
		1552
		1553	=head1 FORK
		1554
		1555	Most event libraries are not fork-safe. The ones who are usually are
		1556	because they rely on inefficient but fork-safe C<select> or C<poll>
		1557	calls. Only L<EV> is fully fork-aware.
		1558
		1559	If you have to fork, you must either do so I<before> creating your first
		1560	watcher OR you must not use AnyEvent at all in the child.
		1561
		1562
		1563	=head1 SECURITY CONSIDERATIONS
		1564
		1565	AnyEvent can be forced to load any event model via
		1566	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1567	execute arbitrary code or directly gain access, it can easily be used to
		1568	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1569	will not be active when the program uses a different event model than
		1570	specified in the variable.
		1571
		1572	You can make AnyEvent completely ignore this variable by deleting it
		1573	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1574
		1575	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1576
		1577	use AnyEvent;
		1578
		1579	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1580	be used to probe what backend is used and gain other information (which is
		1581	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1582
672		1583
673	=head1 SEE ALSO	1584	=head1 SEE ALSO
674		1585
675	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1586	Utility functions: L<AnyEvent::Util>.
676		1587
677	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1588	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1589	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
678		1590
679	Nontrivial usage example: L<Net::FCP>.	1591	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1592	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1593	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1594	L<AnyEvent::Impl::POE>.
680		1595
681	=head1	1596	Non-blocking file handles, sockets, TCP clients and
		1597	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1598
		1599	Asynchronous DNS: L<AnyEvent::DNS>.
		1600
		1601	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1602
		1603	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1604
		1605
		1606	=head1 AUTHOR
		1607
		1608	Marc Lehmann <schmorp@schmorp.de>
		1609	http://home.schmorp.de/
682		1610
683	=cut	1611	=cut
684		1612
685	1	1613	1
686		1614

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