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Revision 1.42 by root, Mon Apr 7 19:40:12 2008 UTC vs.
Revision 1.139 by root, Mon May 26 06:04:38 2008 UTC

1	=head1 NAME	1	=head1 => NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	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	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?
27		27
28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of	28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
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
		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.
63		70
64	=head1 DESCRIPTION	71	=head1 DESCRIPTION
65		72
66	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
67	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
68	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
69	peacefully at any one time).	76	peacefully at any one time).
70		77
71	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>
72	module.	79	module.
73		80
74	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
75	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
76	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
77	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>,
78	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
79	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
80	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.
81		91
82	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
83	an Event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
84	that model the default. For example:	94	that model the default. For example:
85		95
86	use Tk;	96	use Tk;
87	use AnyEvent;	97	use AnyEvent;
88		98
89	# .. 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...
90		104
91	The pure-perl implementation of AnyEvent is called	105	The pure-perl implementation of AnyEvent is called
92	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
93	explicitly.	107	explicitly.
94		108
95	=head1 WATCHERS	109	=head1 WATCHERS
96		110
97	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
98	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
99	the callback to call, the filehandle to watch, etc.	113	the callback to call, the file handle to watch, etc.
100		114
101	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
102	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
103	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
104	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
105	references to it).	122	to it).
106		123
107	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.
108		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
109	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
110		141
111	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
112	the following mandatory arguments:	143	with the following mandatory key-value pairs as arguments:
113		144
114	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
115	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>,
116	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,
117	to invoke everytime the filehandle becomes ready.	148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
118		150
119	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
120	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
121	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.
122		154
123	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.
124	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.
125		162
126	Example:	163	Example:
127		164
128	# 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
129	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
135	=head2 TIME WATCHERS	172	=head2 TIME WATCHERS
136		173
137	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 >>
138	method with the following mandatory arguments:	175	method with the following mandatory arguments:
139		176
140	C<after> after how many seconds (fractions are supported) should the timer	177	C<after> specifies after how many seconds (fractional values are
141	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.
142		184
143	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
144	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
145	and Glib).	187	and Glib).
146		188
…		…
152	});	194	});
153		195
154	# to cancel the timer:	196	# to cancel the timer:
155	undef $w;	197	undef $w;
156		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
157	=head2 CONDITION WATCHERS	298	=head2 CONDITION VARIABLES
158		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
159	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	310	Condition variables can be created by calling the C<< AnyEvent->condvar
160	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.
161		314
162	A condition watcher watches for a condition - precisely that the C<<	315	After creation, the condition variable is "false" until it becomes "true"
163	->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).
164		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
165	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
166	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
167	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
168	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,
169	usually asks for trouble.	342	as this asks for trouble.
170		343
171	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.
172		349
173	=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.
174		353
175	=item $cv->wait	354	Example: wait for a timer.
176
177	Wait (blocking if necessary) until the C<< ->broadcast >> method has been
178	called on c<$cv>, while servicing other watchers normally.
179
180	Not all event models support a blocking wait - some die in that case, so
181	if you are using this from a module, never require a blocking wait, but
182	let the caller decide wether the call will block or not (for example,
183	by coupling condition variables with some kind of request results and
184	supporting callbacks so the caller knows that getting the result will not
185	block, while still suppporting blockign waits if the caller so desires).
186
187	You can only wait once on a condition - additional calls will return
188	immediately.
189
190	=item $cv->broadcast
191
192	Flag the condition as ready - a running C<< ->wait >> and all further
193	calls to C<wait> will return after this method has been called. If nobody
194	is waiting the broadcast will be remembered..
195
196	Example:
197		355
198	# wait till the result is ready	356	# wait till the result is ready
199	my $result_ready = AnyEvent->condvar;	357	my $result_ready = AnyEvent->condvar;
200		358
201	# do something such as adding a timer	359	# do something such as adding a timer
202	# or socket watcher the calls $result_ready->broadcast	360	# or socket watcher the calls $result_ready->send
203	# 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	);
204		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls send
205	$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>.
206		467
207	=back	468	=back
208		469
209	=head2 SIGNAL WATCHERS	470	=head3 METHODS FOR CONSUMERS
210		471
211	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
212	I<name> without any C<SIG> prefix. Multiple signals events can be clumped	473	code awaits the condition.
213	together into one callback invocation, and callback invocation might or
214	might not be asynchronous.
215		474
216	These watchers might use C<%SIG>, so programs overwriting those signals	475	=over 4
217	directly will likely not work correctly.
218		476
219	Example: exit on SIGINT	477	=item $cv->recv
220		478
221	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.
222		482
223	=head2 CHILD PROCESS WATCHERS	483	You can only wait once on a condition - additional calls are valid but
		484	will return immediately.
224		485
225	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
226	C<pid> argument (or any child if the pid argument is 0). The watcher will	487	function will call C<croak>.
227	trigger as often as status change for the child are received. This works
228	by installing a signal handler for C<SIGCHLD>. The callback will be called with
229	the pid and exit status (as returned by waitpid).
230		488
231	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.
232		491
233	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).
234		499
235	=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
236		533
237	=over 4	534	=over 4
238		535
239	=item $AnyEvent::MODEL	536	=item $AnyEvent::MODEL
240		537
…		…
244	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	541	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
245	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	542	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
246		543
247	The known classes so far are:	544	The known classes so far are:
248		545
249	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
250	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	546	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
251	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
252	AnyEvent::Impl::Event based on Event, also second best choice :)	547	AnyEvent::Impl::Event based on Event, second best choice.
		548	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
253	AnyEvent::Impl::Glib based on Glib, second-best choice.	549	AnyEvent::Impl::Glib based on Glib, third-best choice.
254	AnyEvent::Impl::Tk based on Tk, very bad choice.	550	AnyEvent::Impl::Tk based on Tk, very bad choice.
255	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	551	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		552	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		553	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		554
		555	There is no support for WxWidgets, as WxWidgets has no support for
		556	watching file handles. However, you can use WxWidgets through the
		557	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		558	second, which was considered to be too horrible to even consider for
		559	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		560	it's adaptor.
		561
		562	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		563	autodetecting them.
256		564
257	=item AnyEvent::detect	565	=item AnyEvent::detect
258		566
259	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	567	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
260	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
261	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.
262		592
263	=back	593	=back
264		594
265	=head1 WHAT TO DO IN A MODULE	595	=head1 WHAT TO DO IN A MODULE
266		596
267	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
268	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.
269		599
270	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
271	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
272	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
273	to load the event module first.	603	to load the event module first.
274		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
275	=head1 WHAT TO DO IN THE MAIN PROGRAM	615	=head1 WHAT TO DO IN THE MAIN PROGRAM
276		616
277	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
278	dictate which event model to use.	618	dictate which event model to use.
279		619
280	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
281	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.
282		623
283	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
284	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
285	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
286	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
287	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
288	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
289	correct one yourself.	630	might chose the wrong one unless you load the correct one yourself.
290		631
291	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
292	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	633	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
293	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
294		726
295	=cut	727	=cut
296		728
297	package AnyEvent;	729	package AnyEvent;
298		730
299	no warnings;	731	no warnings;
300	use strict;	732	use strict;
301		733
302	use Carp;	734	use Carp;
303		735
304	our $VERSION = '3.0';	736	our $VERSION = '4.04';
305	our $MODEL;	737	our $MODEL;
306		738
307	our $AUTOLOAD;	739	our $AUTOLOAD;
308	our @ISA;	740	our @ISA;
309		741
		742	our @REGISTRY;
		743
		744	our $WIN32;
		745
		746	BEGIN {
		747	my $win32 = ! ! ($^O =~ /mswin32/i);
		748	eval "sub WIN32(){ $win32 }";
		749	}
		750
310	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	751	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
311		752
312	our @REGISTRY;	753	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		754
		755	{
		756	my $idx;
		757	$PROTOCOL{$_} = ++$idx
		758	for reverse split /\s*,\s*/,
		759	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		760	}
		761
		762	sub import {
		763	shift;
		764	return unless @_;
		765
		766	my $pkg = caller;
		767
		768	no strict 'refs';
		769
		770	for (@_) {
		771	*{"$pkg\::WIN32"} = *WIN32 if $_ eq "WIN32";
		772	}
		773	}
313		774
314	my @models = (	775	my @models = (
315	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
316	[EV:: => AnyEvent::Impl::EV::],	776	[EV:: => AnyEvent::Impl::EV::],
317	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
318	[Event:: => AnyEvent::Impl::Event::],	777	[Event:: => AnyEvent::Impl::Event::],
319	[Glib:: => AnyEvent::Impl::Glib::],
320	[Tk:: => AnyEvent::Impl::Tk::],
321	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	778	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		779	# everything below here will not be autoprobed
		780	# as the pureperl backend should work everywhere
		781	# and is usually faster
		782	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		783	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		784	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		785	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		786	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		787	[Wx:: => AnyEvent::Impl::POE::],
		788	[Prima:: => AnyEvent::Impl::POE::],
322	);	789	);
323		790
324	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	791	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		792
		793	our @post_detect;
		794
		795	sub post_detect(&) {
		796	my ($cb) = @_;
		797
		798	if ($MODEL) {
		799	$cb->();
		800
		801	1
		802	} else {
		803	push @post_detect, $cb;
		804
		805	defined wantarray
		806	? bless \$cb, "AnyEvent::Util::PostDetect"
		807	: ()
		808	}
		809	}
		810
		811	sub AnyEvent::Util::PostDetect::DESTROY {
		812	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		813	}
325		814
326	sub detect() {	815	sub detect() {
327	unless ($MODEL) {	816	unless ($MODEL) {
328	no strict 'refs';	817	no strict 'refs';
		818	local $SIG{__DIE__};
		819
		820	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		821	my $model = "AnyEvent::Impl::$1";
		822	if (eval "require $model") {
		823	$MODEL = $model;
		824	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		825	} else {
		826	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		827	}
		828	}
329		829
330	# check for already loaded models	830	# check for already loaded models
		831	unless ($MODEL) {
331	for (@REGISTRY, @models) {	832	for (@REGISTRY, @models) {
332	my ($package, $model) = @$_;	833	my ($package, $model) = @$_;
333	if (${"$package\::VERSION"} > 0) {	834	if (${"$package\::VERSION"} > 0) {
334	if (eval "require $model") {	835	if (eval "require $model") {
335	$MODEL = $model;	836	$MODEL = $model;
336	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	837	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
337	last;	838	last;
		839	}
338	}	840	}
339	}	841	}
340	}
341		842
342	unless ($MODEL) {	843	unless ($MODEL) {
343	# try to load a model	844	# try to load a model
344		845
345	for (@REGISTRY, @models) {	846	for (@REGISTRY, @models) {
346	my ($package, $model) = @$_;	847	my ($package, $model) = @$_;
347	if (eval "require $package"	848	if (eval "require $package"
348	and ${"$package\::VERSION"} > 0	849	and ${"$package\::VERSION"} > 0
349	and eval "require $model") {	850	and eval "require $model") {
350	$MODEL = $model;	851	$MODEL = $model;
351	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	852	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
352	last;	853	last;
		854	}
353	}	855	}
		856
		857	$MODEL
		858	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
354	}	859	}
355
356	$MODEL
357	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.";
358	}	860	}
359		861
360	unshift @ISA, $MODEL;	862	unshift @ISA, $MODEL;
361	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	863	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		864
		865	(shift @post_detect)->() while @post_detect;
362	}	866	}
363		867
364	$MODEL	868	$MODEL
365	}	869	}
366		870
…		…
376	$class->$func (@_);	880	$class->$func (@_);
377	}	881	}
378		882
379	package AnyEvent::Base;	883	package AnyEvent::Base;
380		884
381	# default implementation for ->condvar, ->wait, ->broadcast	885	# default implementation for ->condvar
382		886
383	sub condvar {	887	sub condvar {
384	bless \my $flag, "AnyEvent::Base::CondVar"	888	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
385	}
386
387	sub AnyEvent::Base::CondVar::broadcast {
388	${$_[0]}++;
389	}
390
391	sub AnyEvent::Base::CondVar::wait {
392	AnyEvent->one_event while !${$_[0]};
393	}	889	}
394		890
395	# default implementation for ->signal	891	# default implementation for ->signal
396		892
397	our %SIG_CB;	893	our %SIG_CB;
…		…
450	or Carp::croak "required option 'pid' is missing";	946	or Carp::croak "required option 'pid' is missing";
451		947
452	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	948	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
453		949
454	unless ($WNOHANG) {	950	unless ($WNOHANG) {
455	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	951	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
456	}	952	}
457		953
458	unless ($CHLD_W) {	954	unless ($CHLD_W) {
459	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	955	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
460	# child could be a zombie already, so make at least one round	956	# child could be a zombie already, so make at least one round
…		…
471	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	967	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
472		968
473	undef $CHLD_W unless keys %PID_CB;	969	undef $CHLD_W unless keys %PID_CB;
474	}	970	}
475		971
		972	package AnyEvent::CondVar;
		973
		974	our @ISA = AnyEvent::CondVar::Base::;
		975
		976	package AnyEvent::CondVar::Base;
		977
		978	use overload
		979	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		980	fallback => 1;
		981
		982	sub _send {
		983	# nop
		984	}
		985
		986	sub send {
		987	my $cv = shift;
		988	$cv->{_ae_sent} = [@_];
		989	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		990	$cv->_send;
		991	}
		992
		993	sub croak {
		994	$_[0]{_ae_croak} = $_[1];
		995	$_[0]->send;
		996	}
		997
		998	sub ready {
		999	$_[0]{_ae_sent}
		1000	}
		1001
		1002	sub _wait {
		1003	AnyEvent->one_event while !$_[0]{_ae_sent};
		1004	}
		1005
		1006	sub recv {
		1007	$_[0]->_wait;
		1008
		1009	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1010	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1011	}
		1012
		1013	sub cb {
		1014	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1015	$_[0]{_ae_cb}
		1016	}
		1017
		1018	sub begin {
		1019	++$_[0]{_ae_counter};
		1020	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1021	}
		1022
		1023	sub end {
		1024	return if --$_[0]{_ae_counter};
		1025	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1026	}
		1027
		1028	# undocumented/compatibility with pre-3.4
		1029	*broadcast = \&send;
		1030	*wait = \&_wait;
		1031
476	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1032	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1033
		1034	This is an advanced topic that you do not normally need to use AnyEvent in
		1035	a module. This section is only of use to event loop authors who want to
		1036	provide AnyEvent compatibility.
477		1037
478	If you need to support another event library which isn't directly	1038	If you need to support another event library which isn't directly
479	supported by AnyEvent, you can supply your own interface to it by	1039	supported by AnyEvent, you can supply your own interface to it by
480	pushing, before the first watcher gets created, the package name of	1040	pushing, before the first watcher gets created, the package name of
481	the event module and the package name of the interface to use onto	1041	the event module and the package name of the interface to use onto
482	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	1042	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
483	AnyEvent.	1043	AnyEvent, so it is reasonably cheap.
484		1044
485	Example:	1045	Example:
486		1046
487	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1047	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
488		1048
489	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1049	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
490	package/class when it finds the C<urxvt> package/module is loaded. When	1050	package/class when it finds the C<urxvt> package/module is already loaded.
		1051
491	AnyEvent is loaded and asked to find a suitable event model, it will	1052	When AnyEvent is loaded and asked to find a suitable event model, it
492	first check for the presence of urxvt.	1053	will first check for the presence of urxvt by trying to C<use> the
		1054	C<urxvt::anyevent> module.
493		1055
494	The class should provide implementations for all watcher types (see	1056	The class should provide implementations for all watcher types. See
495	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1057	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
496	(Source code) and so on for actual examples, use C<perldoc -m	1058	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
497	AnyEvent::Impl::Glib> to see the sources).	1059	see the sources.
498		1060
		1061	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1062	provide suitable (hopefully) replacements.
		1063
499	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1064	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
500	uses the above line as-is. An interface isn't included in AnyEvent	1065	terminal emulator uses the above line as-is. An interface isn't included
501	because it doesn't make sense outside the embedded interpreter inside	1066	in AnyEvent because it doesn't make sense outside the embedded interpreter
502	I<rxvt-unicode>, and it is updated and maintained as part of the	1067	inside I<rxvt-unicode>, and it is updated and maintained as part of the
503	I<rxvt-unicode> distribution.	1068	I<rxvt-unicode> distribution.
504		1069
505	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1070	I<rxvt-unicode> also cheats a bit by not providing blocking access to
506	condition variables: code blocking while waiting for a condition will	1071	condition variables: code blocking while waiting for a condition will
507	C<die>. This still works with most modules/usages, and blocking calls must	1072	C<die>. This still works with most modules/usages, and blocking calls must
508	not be in an interactive application, so it makes sense.	1073	not be done in an interactive application, so it makes sense.
509		1074
510	=head1 ENVIRONMENT VARIABLES	1075	=head1 ENVIRONMENT VARIABLES
511		1076
512	The following environment variables are used by this module:	1077	The following environment variables are used by this module:
513		1078
514	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	1079	=over 4
515	model gets used.
516		1080
		1081	=item C<PERL_ANYEVENT_VERBOSE>
		1082
		1083	By default, AnyEvent will be completely silent except in fatal
		1084	conditions. You can set this environment variable to make AnyEvent more
		1085	talkative.
		1086
		1087	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1088	conditions, such as not being able to load the event model specified by
		1089	C<PERL_ANYEVENT_MODEL>.
		1090
		1091	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1092	model it chooses.
		1093
		1094	=item C<PERL_ANYEVENT_MODEL>
		1095
		1096	This can be used to specify the event model to be used by AnyEvent, before
		1097	auto detection and -probing kicks in. It must be a string consisting
		1098	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1099	and the resulting module name is loaded and if the load was successful,
		1100	used as event model. If it fails to load AnyEvent will proceed with
		1101	auto detection and -probing.
		1102
		1103	This functionality might change in future versions.
		1104
		1105	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1106	could start your program like this:
		1107
		1108	PERL_ANYEVENT_MODEL=Perl perl ...
		1109
		1110	=item C<PERL_ANYEVENT_PROTOCOLS>
		1111
		1112	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1113	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1114	of auto probing).
		1115
		1116	Must be set to a comma-separated list of protocols or address families,
		1117	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1118	used, and preference will be given to protocols mentioned earlier in the
		1119	list.
		1120
		1121	This variable can effectively be used for denial-of-service attacks
		1122	against local programs (e.g. when setuid), although the impact is likely
		1123	small, as the program has to handle connection errors already-
		1124
		1125	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1126	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1127	- only support IPv4, never try to resolve or contact IPv6
		1128	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1129	IPv6, but prefer IPv6 over IPv4.
		1130
		1131	=item C<PERL_ANYEVENT_EDNS0>
		1132
		1133	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1134	for DNS. This extension is generally useful to reduce DNS traffic, but
		1135	some (broken) firewalls drop such DNS packets, which is why it is off by
		1136	default.
		1137
		1138	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1139	EDNS0 in its DNS requests.
		1140
		1141	=back
		1142
517	=head1 EXAMPLE	1143	=head1 EXAMPLE PROGRAM
518		1144
519	The following program uses an io watcher to read data from stdin, a timer	1145	The following program uses an I/O watcher to read data from STDIN, a timer
520	to display a message once per second, and a condvar to exit the program	1146	to display a message once per second, and a condition variable to quit the
521	when the user enters quit:	1147	program when the user enters quit:
522		1148
523	use AnyEvent;	1149	use AnyEvent;
524		1150
525	my $cv = AnyEvent->condvar;	1151	my $cv = AnyEvent->condvar;
526		1152
527	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1153	my $io_watcher = AnyEvent->io (
		1154	fh => \*STDIN,
		1155	poll => 'r',
		1156	cb => sub {
528	warn "io event <$_[0]>\n"; # will always output <r>	1157	warn "io event <$_[0]>\n"; # will always output <r>
529	chomp (my $input = <STDIN>); # read a line	1158	chomp (my $input = <STDIN>); # read a line
530	warn "read: $input\n"; # output what has been read	1159	warn "read: $input\n"; # output what has been read
531	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1160	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1161	},
532	});	1162	);
533		1163
534	my $time_watcher; # can only be used once	1164	my $time_watcher; # can only be used once
535		1165
536	sub new_timer {	1166	sub new_timer {
537	$timer = AnyEvent->timer (after => 1, cb => sub {	1167	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
540	});	1170	});
541	}	1171	}
542		1172
543	new_timer; # create first timer	1173	new_timer; # create first timer
544		1174
545	$cv->wait; # wait until user enters /^q/i	1175	$cv->recv; # wait until user enters /^q/i
546		1176
547	=head1 REAL-WORLD EXAMPLE	1177	=head1 REAL-WORLD EXAMPLE
548		1178
549	Consider the L<Net::FCP> module. It features (among others) the following	1179	Consider the L<Net::FCP> module. It features (among others) the following
550	API calls, which are to freenet what HTTP GET requests are to http:	1180	API calls, which are to freenet what HTTP GET requests are to http:
…		…
600	syswrite $txn->{fh}, $txn->{request}	1230	syswrite $txn->{fh}, $txn->{request}
601	or die "connection or write error";	1231	or die "connection or write error";
602	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1232	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
603		1233
604	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1234	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
605	result and signals any possible waiters that the request ahs finished:	1235	result and signals any possible waiters that the request has finished:
606		1236
607	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1237	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
608		1238
609	if (end-of-file or data complete) {	1239	if (end-of-file or data complete) {
610	$txn->{result} = $txn->{buf};	1240	$txn->{result} = $txn->{buf};
611	$txn->{finished}->broadcast;	1241	$txn->{finished}->send;
612	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1242	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
613	}	1243	}
614		1244
615	The C<result> method, finally, just waits for the finished signal (if the	1245	The C<result> method, finally, just waits for the finished signal (if the
616	request was already finished, it doesn't wait, of course, and returns the	1246	request was already finished, it doesn't wait, of course, and returns the
617	data:	1247	data:
618		1248
619	$txn->{finished}->wait;	1249	$txn->{finished}->recv;
620	return $txn->{result};	1250	return $txn->{result};
621		1251
622	The actual code goes further and collects all errors (C<die>s, exceptions)	1252	The actual code goes further and collects all errors (C<die>s, exceptions)
623	that occured during request processing. The C<result> method detects	1253	that occurred during request processing. The C<result> method detects
624	wether an exception as thrown (it is stored inside the $txn object)	1254	whether an exception as thrown (it is stored inside the $txn object)
625	and just throws the exception, which means connection errors and other	1255	and just throws the exception, which means connection errors and other
626	problems get reported tot he code that tries to use the result, not in a	1256	problems get reported tot he code that tries to use the result, not in a
627	random callback.	1257	random callback.
628		1258
629	All of this enables the following usage styles:	1259	All of this enables the following usage styles:
630		1260
631	1. Blocking:	1261	1. Blocking:
632		1262
633	my $data = $fcp->client_get ($url);	1263	my $data = $fcp->client_get ($url);
634		1264
635	2. Blocking, but parallelizing:	1265	2. Blocking, but running in parallel:
636		1266
637	my @datas = map $_->result,	1267	my @datas = map $_->result,
638	map $fcp->txn_client_get ($_),	1268	map $fcp->txn_client_get ($_),
639	@urls;	1269	@urls;
640		1270
641	Both blocking examples work without the module user having to know	1271	Both blocking examples work without the module user having to know
642	anything about events.	1272	anything about events.
643		1273
644	3a. Event-based in a main program, using any support Event module:	1274	3a. Event-based in a main program, using any supported event module:
645		1275
646	use Event;	1276	use EV;
647		1277
648	$fcp->txn_client_get ($url)->cb (sub {	1278	$fcp->txn_client_get ($url)->cb (sub {
649	my $txn = shift;	1279	my $txn = shift;
650	my $data = $txn->result;	1280	my $data = $txn->result;
651	...	1281	...
652	});	1282	});
653		1283
654	Event::loop;	1284	EV::loop;
655		1285
656	3b. The module user could use AnyEvent, too:	1286	3b. The module user could use AnyEvent, too:
657		1287
658	use AnyEvent;	1288	use AnyEvent;
659		1289
660	my $quit = AnyEvent->condvar;	1290	my $quit = AnyEvent->condvar;
661		1291
662	$fcp->txn_client_get ($url)->cb (sub {	1292	$fcp->txn_client_get ($url)->cb (sub {
663	...	1293	...
664	$quit->broadcast;	1294	$quit->send;
665	});	1295	});
666		1296
667	$quit->wait;	1297	$quit->recv;
		1298
		1299
		1300	=head1 BENCHMARKS
		1301
		1302	To give you an idea of the performance and overheads that AnyEvent adds
		1303	over the event loops themselves and to give you an impression of the speed
		1304	of various event loops I prepared some benchmarks.
		1305
		1306	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1307
		1308	Here is a benchmark of various supported event models used natively and
		1309	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1310	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1311	which it is), lets them fire exactly once and destroys them again.
		1312
		1313	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1314	distribution.
		1315
		1316	=head3 Explanation of the columns
		1317
		1318	I<watcher> is the number of event watchers created/destroyed. Since
		1319	different event models feature vastly different performances, each event
		1320	loop was given a number of watchers so that overall runtime is acceptable
		1321	and similar between tested event loop (and keep them from crashing): Glib
		1322	would probably take thousands of years if asked to process the same number
		1323	of watchers as EV in this benchmark.
		1324
		1325	I<bytes> is the number of bytes (as measured by the resident set size,
		1326	RSS) consumed by each watcher. This method of measuring captures both C
		1327	and Perl-based overheads.
		1328
		1329	I<create> is the time, in microseconds (millionths of seconds), that it
		1330	takes to create a single watcher. The callback is a closure shared between
		1331	all watchers, to avoid adding memory overhead. That means closure creation
		1332	and memory usage is not included in the figures.
		1333
		1334	I<invoke> is the time, in microseconds, used to invoke a simple
		1335	callback. The callback simply counts down a Perl variable and after it was
		1336	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1337	signal the end of this phase.
		1338
		1339	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1340	watcher.
		1341
		1342	=head3 Results
		1343
		1344	name watchers bytes create invoke destroy comment
		1345	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1346	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1347	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1348	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1349	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1350	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1351	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1352	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1353	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1354	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1355
		1356	=head3 Discussion
		1357
		1358	The benchmark does I<not> measure scalability of the event loop very
		1359	well. For example, a select-based event loop (such as the pure perl one)
		1360	can never compete with an event loop that uses epoll when the number of
		1361	file descriptors grows high. In this benchmark, all events become ready at
		1362	the same time, so select/poll-based implementations get an unnatural speed
		1363	boost.
		1364
		1365	Also, note that the number of watchers usually has a nonlinear effect on
		1366	overall speed, that is, creating twice as many watchers doesn't take twice
		1367	the time - usually it takes longer. This puts event loops tested with a
		1368	higher number of watchers at a disadvantage.
		1369
		1370	To put the range of results into perspective, consider that on the
		1371	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1372	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1373	cycles with POE.
		1374
		1375	C<EV> is the sole leader regarding speed and memory use, which are both
		1376	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1377	far less memory than any other event loop and is still faster than Event
		1378	natively.
		1379
		1380	The pure perl implementation is hit in a few sweet spots (both the
		1381	constant timeout and the use of a single fd hit optimisations in the perl
		1382	interpreter and the backend itself). Nevertheless this shows that it
		1383	adds very little overhead in itself. Like any select-based backend its
		1384	performance becomes really bad with lots of file descriptors (and few of
		1385	them active), of course, but this was not subject of this benchmark.
		1386
		1387	The C<Event> module has a relatively high setup and callback invocation
		1388	cost, but overall scores in on the third place.
		1389
		1390	C<Glib>'s memory usage is quite a bit higher, but it features a
		1391	faster callback invocation and overall ends up in the same class as
		1392	C<Event>. However, Glib scales extremely badly, doubling the number of
		1393	watchers increases the processing time by more than a factor of four,
		1394	making it completely unusable when using larger numbers of watchers
		1395	(note that only a single file descriptor was used in the benchmark, so
		1396	inefficiencies of C<poll> do not account for this).
		1397
		1398	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1399	more than 2000 watchers is a big setback, however, as correctness takes
		1400	precedence over speed. Nevertheless, its performance is surprising, as the
		1401	file descriptor is dup()ed for each watcher. This shows that the dup()
		1402	employed by some adaptors is not a big performance issue (it does incur a
		1403	hidden memory cost inside the kernel which is not reflected in the figures
		1404	above).
		1405
		1406	C<POE>, regardless of underlying event loop (whether using its pure perl
		1407	select-based backend or the Event module, the POE-EV backend couldn't
		1408	be tested because it wasn't working) shows abysmal performance and
		1409	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1410	as EV watchers, and 10 times as much memory as Event (the high memory
		1411	requirements are caused by requiring a session for each watcher). Watcher
		1412	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1413	implementation.
		1414
		1415	The design of the POE adaptor class in AnyEvent can not really account
		1416	for the performance issues, though, as session creation overhead is
		1417	small compared to execution of the state machine, which is coded pretty
		1418	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1419	using multiple sessions is not a good approach, especially regarding
		1420	memory usage, even the author of POE could not come up with a faster
		1421	design).
		1422
		1423	=head3 Summary
		1424
		1425	=over 4
		1426
		1427	=item * Using EV through AnyEvent is faster than any other event loop
		1428	(even when used without AnyEvent), but most event loops have acceptable
		1429	performance with or without AnyEvent.
		1430
		1431	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1432	the actual event loop, only with extremely fast event loops such as EV
		1433	adds AnyEvent significant overhead.
		1434
		1435	=item * You should avoid POE like the plague if you want performance or
		1436	reasonable memory usage.
		1437
		1438	=back
		1439
		1440	=head2 BENCHMARKING THE LARGE SERVER CASE
		1441
		1442	This benchmark actually benchmarks the event loop itself. It works by
		1443	creating a number of "servers": each server consists of a socket pair, a
		1444	timeout watcher that gets reset on activity (but never fires), and an I/O
		1445	watcher waiting for input on one side of the socket. Each time the socket
		1446	watcher reads a byte it will write that byte to a random other "server".
		1447
		1448	The effect is that there will be a lot of I/O watchers, only part of which
		1449	are active at any one point (so there is a constant number of active
		1450	fds for each loop iteration, but which fds these are is random). The
		1451	timeout is reset each time something is read because that reflects how
		1452	most timeouts work (and puts extra pressure on the event loops).
		1453
		1454	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1455	(1%) are active. This mirrors the activity of large servers with many
		1456	connections, most of which are idle at any one point in time.
		1457
		1458	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1459	distribution.
		1460
		1461	=head3 Explanation of the columns
		1462
		1463	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1464	each server has a read and write socket end).
		1465
		1466	I<create> is the time it takes to create a socket pair (which is
		1467	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1468
		1469	I<request>, the most important value, is the time it takes to handle a
		1470	single "request", that is, reading the token from the pipe and forwarding
		1471	it to another server. This includes deleting the old timeout and creating
		1472	a new one that moves the timeout into the future.
		1473
		1474	=head3 Results
		1475
		1476	name sockets create request
		1477	EV 20000 69.01 11.16
		1478	Perl 20000 73.32 35.87
		1479	Event 20000 212.62 257.32
		1480	Glib 20000 651.16 1896.30
		1481	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1482
		1483	=head3 Discussion
		1484
		1485	This benchmark I<does> measure scalability and overall performance of the
		1486	particular event loop.
		1487
		1488	EV is again fastest. Since it is using epoll on my system, the setup time
		1489	is relatively high, though.
		1490
		1491	Perl surprisingly comes second. It is much faster than the C-based event
		1492	loops Event and Glib.
		1493
		1494	Event suffers from high setup time as well (look at its code and you will
		1495	understand why). Callback invocation also has a high overhead compared to
		1496	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1497	uses select or poll in basically all documented configurations.
		1498
		1499	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1500	clearly fails to perform with many filehandles or in busy servers.
		1501
		1502	POE is still completely out of the picture, taking over 1000 times as long
		1503	as EV, and over 100 times as long as the Perl implementation, even though
		1504	it uses a C-based event loop in this case.
		1505
		1506	=head3 Summary
		1507
		1508	=over 4
		1509
		1510	=item * The pure perl implementation performs extremely well.
		1511
		1512	=item * Avoid Glib or POE in large projects where performance matters.
		1513
		1514	=back
		1515
		1516	=head2 BENCHMARKING SMALL SERVERS
		1517
		1518	While event loops should scale (and select-based ones do not...) even to
		1519	large servers, most programs we (or I :) actually write have only a few
		1520	I/O watchers.
		1521
		1522	In this benchmark, I use the same benchmark program as in the large server
		1523	case, but it uses only eight "servers", of which three are active at any
		1524	one time. This should reflect performance for a small server relatively
		1525	well.
		1526
		1527	The columns are identical to the previous table.
		1528
		1529	=head3 Results
		1530
		1531	name sockets create request
		1532	EV 16 20.00 6.54
		1533	Perl 16 25.75 12.62
		1534	Event 16 81.27 35.86
		1535	Glib 16 32.63 15.48
		1536	POE 16 261.87 276.28 uses POE::Loop::Event
		1537
		1538	=head3 Discussion
		1539
		1540	The benchmark tries to test the performance of a typical small
		1541	server. While knowing how various event loops perform is interesting, keep
		1542	in mind that their overhead in this case is usually not as important, due
		1543	to the small absolute number of watchers (that is, you need efficiency and
		1544	speed most when you have lots of watchers, not when you only have a few of
		1545	them).
		1546
		1547	EV is again fastest.
		1548
		1549	Perl again comes second. It is noticeably faster than the C-based event
		1550	loops Event and Glib, although the difference is too small to really
		1551	matter.
		1552
		1553	POE also performs much better in this case, but is is still far behind the
		1554	others.
		1555
		1556	=head3 Summary
		1557
		1558	=over 4
		1559
		1560	=item * C-based event loops perform very well with small number of
		1561	watchers, as the management overhead dominates.
		1562
		1563	=back
		1564
		1565
		1566	=head1 FORK
		1567
		1568	Most event libraries are not fork-safe. The ones who are usually are
		1569	because they rely on inefficient but fork-safe C<select> or C<poll>
		1570	calls. Only L<EV> is fully fork-aware.
		1571
		1572	If you have to fork, you must either do so I<before> creating your first
		1573	watcher OR you must not use AnyEvent at all in the child.
		1574
		1575
		1576	=head1 SECURITY CONSIDERATIONS
		1577
		1578	AnyEvent can be forced to load any event model via
		1579	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1580	execute arbitrary code or directly gain access, it can easily be used to
		1581	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1582	will not be active when the program uses a different event model than
		1583	specified in the variable.
		1584
		1585	You can make AnyEvent completely ignore this variable by deleting it
		1586	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1587
		1588	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1589
		1590	use AnyEvent;
		1591
		1592	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1593	be used to probe what backend is used and gain other information (which is
		1594	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1595
668		1596
669	=head1 SEE ALSO	1597	=head1 SEE ALSO
670		1598
671	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1599	Utility functions: L<AnyEvent::Util>.
672		1600
673	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1601	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1602	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
674		1603
675	Nontrivial usage example: L<Net::FCP>.	1604	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1605	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1606	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1607	L<AnyEvent::Impl::POE>.
676		1608
677	=head1	1609	Non-blocking file handles, sockets, TCP clients and
		1610	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1611
		1612	Asynchronous DNS: L<AnyEvent::DNS>.
		1613
		1614	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1615
		1616	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1617
		1618
		1619	=head1 AUTHOR
		1620
		1621	Marc Lehmann <schmorp@schmorp.de>
		1622	http://home.schmorp.de/
678		1623
679	=cut	1624	=cut
680		1625
681	1	1626	1
682		1627

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