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Revision 1.21 by root, Mon Dec 11 20:36:50 2006 UTC vs.
Revision 1.145 by root, Thu May 29 03:45:37 2008 UTC

1	=head1 NAME	1	=head1 => NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	Event, Coro, Glib, Tk, Perl - various supported event loops	5	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
…		…
14		14
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	my $w = AnyEvent->condvar; # stores wether a condition was flagged	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		20	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	21	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	22
		23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		24
		25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		26	nowadays. So what is different about AnyEvent?
		27
		28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		29	policy> and AnyEvent is I<small and efficient>.
		30
		31	First and foremost, I<AnyEvent is not an event model> itself, it only
		32	interfaces to whatever event model the main program happens to use in a
		33	pragmatic way. For event models and certain classes of immortals alike,
		34	the statement "there can only be one" is a bitter reality: In general,
		35	only one event loop can be active at the same time in a process. AnyEvent
		36	helps hiding the differences between those event loops.
		37
		38	The goal of AnyEvent is to offer module authors the ability to do event
		39	programming (waiting for I/O or timer events) without subscribing to a
		40	religion, a way of living, and most importantly: without forcing your
		41	module users into the same thing by forcing them to use the same event
		42	model you use.
		43
		44	For modules like POE or IO::Async (which is a total misnomer as it is
		45	actually doing all I/O I<synchronously>...), using them in your module is
		46	like joining a cult: After you joined, you are dependent on them and you
		47	cannot use anything else, as it is simply incompatible to everything that
		48	isn't itself. What's worse, all the potential users of your module are
		49	I<also> forced to use the same event loop you use.
		50
		51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		53	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if
		54	your module uses one of those, every user of your module has to use it,
		55	too. But if your module uses AnyEvent, it works transparently with all
		56	event models it supports (including stuff like POE and IO::Async, as long
		57	as those use one of the supported event loops. It is trivial to add new
		58	event loops to AnyEvent, too, so it is future-proof).
		59
		60	In addition to being free of having to use I<the one and only true event
		61	model>, AnyEvent also is free of bloat and policy: with POE or similar
		62	modules, you get an enormous amount of code and strict rules you have to
		63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		64	offering the functionality that is necessary, in as thin as a wrapper as
		65	technically possible.
		66
		67	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		68	of useful functionality, such as an asynchronous DNS resolver, 100%
		69	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		70	such as Windows) and lots of real-world knowledge and workarounds for
		71	platform bugs and differences.
		72
		73	Now, if you I<do want> lots of policy (this can arguably be somewhat
		74	useful) and you want to force your users to use the one and only event
		75	model, you should I<not> use this module.
22		76
23	=head1 DESCRIPTION	77	=head1 DESCRIPTION
24		78
25	L<AnyEvent> provides an identical interface to multiple event loops. This	79	L<AnyEvent> provides an identical interface to multiple event loops. This
26	allows module authors to utilise an event loop without forcing module	80	allows module authors to utilise an event loop without forcing module
27	users to use the same event loop (as only a single event loop can coexist	81	users to use the same event loop (as only a single event loop can coexist
28	peacefully at any one time).	82	peacefully at any one time).
29		83
30	The interface itself is vaguely similar but not identical to the Event	84	The interface itself is vaguely similar, but not identical to the L<Event>
31	module.	85	module.
32		86
33	On the first call of any method, the module tries to detect the currently	87	During the first call of any watcher-creation method, the module tries
34	loaded event loop by probing wether any of the following modules is	88	to detect the currently loaded event loop by probing whether one of the
35	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	89	following modules is already loaded: L<EV>,
36	used. If none is found, the module tries to load these modules in the	90	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
37	order given. The first one that could be successfully loaded will be	91	L<POE>. The first one found is used. If none are found, the module tries
38	used. If still none could be found, AnyEvent will fall back to a pure-perl	92	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
39	event loop, which is also not very efficient.	93	adaptor should always succeed) in the order given. The first one that can
		94	be successfully loaded will be used. If, after this, still none could be
		95	found, AnyEvent will fall back to a pure-perl event loop, which is not
		96	very efficient, but should work everywhere.
40		97
41	Because AnyEvent first checks for modules that are already loaded, loading	98	Because AnyEvent first checks for modules that are already loaded, loading
42	an Event model explicitly before first using AnyEvent will likely make	99	an event model explicitly before first using AnyEvent will likely make
43	that model the default. For example:	100	that model the default. For example:
44		101
45	use Tk;	102	use Tk;
46	use AnyEvent;	103	use AnyEvent;
47		104
48	# .. AnyEvent will likely default to Tk	105	# .. AnyEvent will likely default to Tk
49		106
		107	The I<likely> means that, if any module loads another event model and
		108	starts using it, all bets are off. Maybe you should tell their authors to
		109	use AnyEvent so their modules work together with others seamlessly...
		110
50	The pure-perl implementation of AnyEvent is called	111	The pure-perl implementation of AnyEvent is called
51	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	112	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
52	explicitly.	113	explicitly and enjoy the high availability of that event loop :)
53		114
54	=head1 WATCHERS	115	=head1 WATCHERS
55		116
56	AnyEvent has the central concept of a I<watcher>, which is an object that	117	AnyEvent has the central concept of a I<watcher>, which is an object that
57	stores relevant data for each kind of event you are waiting for, such as	118	stores relevant data for each kind of event you are waiting for, such as
58	the callback to call, the filehandle to watch, etc.	119	the callback to call, the file handle to watch, etc.
59		120
60	These watchers are normal Perl objects with normal Perl lifetime. After	121	These watchers are normal Perl objects with normal Perl lifetime. After
61	creating a watcher it will immediately "watch" for events and invoke	122	creating a watcher it will immediately "watch" for events and invoke the
		123	callback when the event occurs (of course, only when the event model
		124	is in control).
		125
62	the callback. To disable the watcher you have to destroy it (e.g. by	126	To disable the watcher you have to destroy it (e.g. by setting the
63	setting the variable that stores it to C<undef> or otherwise deleting all	127	variable you store it in to C<undef> or otherwise deleting all references
64	references to it).	128	to it).
65		129
66	All watchers are created by calling a method on the C<AnyEvent> class.	130	All watchers are created by calling a method on the C<AnyEvent> class.
67		131
		132	Many watchers either are used with "recursion" (repeating timers for
		133	example), or need to refer to their watcher object in other ways.
		134
		135	An any way to achieve that is this pattern:
		136
		137	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		138	# you can use $w here, for example to undef it
		139	undef $w;
		140	});
		141
		142	Note that C<my $w; $w => combination. This is necessary because in Perl,
		143	my variables are only visible after the statement in which they are
		144	declared.
		145
68	=head2 IO WATCHERS	146	=head2 I/O WATCHERS
69		147
70	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	148	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
71	the following mandatory arguments:	149	with the following mandatory key-value pairs as arguments:
72		150
73	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	151	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
74	events. C<poll> must be a string that is either C<r> or C<w>, that creates	152	for events. C<poll> must be a string that is either C<r> or C<w>,
75	a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback	153	which creates a watcher waiting for "r"eadable or "w"ritable events,
76	to invoke everytime the filehandle becomes ready.	154	respectively. C<cb> is the callback to invoke each time the file handle
		155	becomes ready.
77		156
78	Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on	157	Although the callback might get passed parameters, their value and
79	a socket you can have one r + one w, not any more (limitation comes from	158	presence is undefined and you cannot rely on them. Portable AnyEvent
80	Tk - if you are sure you are not using Tk this limitation is gone).	159	callbacks cannot use arguments passed to I/O watcher callbacks.
81		160
82	Filehandles will be kept alive, so as long as the watcher exists, the	161	The I/O watcher might use the underlying file descriptor or a copy of it.
83	filehandle exists, too.	162	You must not close a file handle as long as any watcher is active on the
		163	underlying file descriptor.
		164
		165	Some event loops issue spurious readyness notifications, so you should
		166	always use non-blocking calls when reading/writing from/to your file
		167	handles.
84		168
85	Example:	169	Example:
86		170
87	# wait for readability of STDIN, then read a line and disable the watcher	171	# wait for readability of STDIN, then read a line and disable the watcher
88	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	172	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
94	=head2 TIME WATCHERS	178	=head2 TIME WATCHERS
95		179
96	You can create a time watcher by calling the C<< AnyEvent->timer >>	180	You can create a time watcher by calling the C<< AnyEvent->timer >>
97	method with the following mandatory arguments:	181	method with the following mandatory arguments:
98		182
99	C<after> after how many seconds (fractions are supported) should the timer	183	C<after> specifies after how many seconds (fractional values are
100	activate. C<cb> the callback to invoke.	184	supported) the callback should be invoked. C<cb> is the callback to invoke
		185	in that case.
		186
		187	Although the callback might get passed parameters, their value and
		188	presence is undefined and you cannot rely on them. Portable AnyEvent
		189	callbacks cannot use arguments passed to time watcher callbacks.
101		190
102	The timer callback will be invoked at most once: if you want a repeating	191	The timer callback will be invoked at most once: if you want a repeating
103	timer you have to create a new watcher (this is a limitation by both Tk	192	timer you have to create a new watcher (this is a limitation by both Tk
104	and Glib).	193	and Glib).
105		194
…		…
109	my $w = AnyEvent->timer (after => 7.7, cb => sub {	198	my $w = AnyEvent->timer (after => 7.7, cb => sub {
110	warn "timeout\n";	199	warn "timeout\n";
111	});	200	});
112		201
113	# to cancel the timer:	202	# to cancel the timer:
114	undef $w	203	undef $w;
115		204
116	=head2 CONDITION WATCHERS	205	Example 2:
117		206
118	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	207	# fire an event after 0.5 seconds, then roughly every second
119	method without any arguments.	208	my $w;
120		209
121	A condition watcher watches for a condition - precisely that the C<<	210	my $cb = sub {
122	->broadcast >> method has been called.	211	# cancel the old timer while creating a new one
		212	$w = AnyEvent->timer (after => 1, cb => $cb);
		213	};
123		214
124	The watcher has only two methods:	215	# start the "loop" by creating the first watcher
		216	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		217
		218	=head3 TIMING ISSUES
		219
		220	There are two ways to handle timers: based on real time (relative, "fire
		221	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		222	o'clock").
		223
		224	While most event loops expect timers to specified in a relative way, they
		225	use absolute time internally. This makes a difference when your clock
		226	"jumps", for example, when ntp decides to set your clock backwards from
		227	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		228	fire "after" a second might actually take six years to finally fire.
		229
		230	AnyEvent cannot compensate for this. The only event loop that is conscious
		231	about these issues is L<EV>, which offers both relative (ev_timer, based
		232	on true relative time) and absolute (ev_periodic, based on wallclock time)
		233	timers.
		234
		235	AnyEvent always prefers relative timers, if available, matching the
		236	AnyEvent API.
		237
		238	AnyEvent has two additional methods that return the "current time":
125		239
126	=over 4	240	=over 4
127		241
128	=item $cv->wait	242	=item AnyEvent->time
129		243
130	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	244	This returns the "current wallclock time" as a fractional number of
131	called on c<$cv>, while servicing other watchers normally.	245	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		246	return, and the result is guaranteed to be compatible with those).
132		247
133	Not all event models support a blocking wait - some die in that case, so	248	It progresses independently of any event loop processing, i.e. each call
134	if you are using this from a module, never require a blocking wait, but	249	will check the system clock, which usually gets updated frequently.
135	let the caller decide wether the call will block or not (for example,
136	by coupling condition variables with some kind of request results and
137	supporting callbacks so the caller knows that getting the result will not
138	block, while still suppporting blockign waits if the caller so desires).
139		250
140	You can only wait once on a condition - additional calls will return	251	=item AnyEvent->now
141	immediately.
142		252
143	=item $cv->broadcast	253	This also returns the "current wallclock time", but unlike C<time>, above,
		254	this value might change only once per event loop iteration, depending on
		255	the event loop (most return the same time as C<time>, above). This is the
		256	time that AnyEvent's timers get scheduled against.
144		257
145	Flag the condition as ready - a running C<< ->wait >> and all further	258	I<In almost all cases (in all cases if you don't care), this is the
146	calls to C<wait> will return after this method has been called. If nobody	259	function to call when you want to know the current time.>
147	is waiting the broadcast will be remembered..
148		260
149	Example:	261	This function is also often faster then C<< AnyEvent->time >>, and
		262	thus the preferred method if you want some timestamp (for example,
		263	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		264
		265	The rest of this section is only of relevance if you try to be very exact
		266	with your timing, you can skip it without bad conscience.
		267
		268	For a practical example of when these times differ, consider L<Event::Lib>
		269	and L<EV> and the following set-up:
		270
		271	The event loop is running and has just invoked one of your callback at
		272	time=500 (assume no other callbacks delay processing). In your callback,
		273	you wait a second by executing C<sleep 1> (blocking the process for a
		274	second) and then (at time=501) you create a relative timer that fires
		275	after three seconds.
		276
		277	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		278	both return C<501>, because that is the current time, and the timer will
		279	be scheduled to fire at time=504 (C<501> + C<3>).
		280
		281	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		282	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		283	last event processing phase started. With L<EV>, your timer gets scheduled
		284	to run at time=503 (C<500> + C<3>).
		285
		286	In one sense, L<Event::Lib> is more exact, as it uses the current time
		287	regardless of any delays introduced by event processing. However, most
		288	callbacks do not expect large delays in processing, so this causes a
		289	higher drift (and a lot more system calls to get the current time).
		290
		291	In another sense, L<EV> is more exact, as your timer will be scheduled at
		292	the same time, regardless of how long event processing actually took.
		293
		294	In either case, if you care (and in most cases, you don't), then you
		295	can get whatever behaviour you want with any event loop, by taking the
		296	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		297	account.
		298
		299	=back
		300
		301	=head2 SIGNAL WATCHERS
		302
		303	You can watch for signals using a signal watcher, C<signal> is the signal
		304	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		305	be invoked whenever a signal occurs.
		306
		307	Although the callback might get passed parameters, their value and
		308	presence is undefined and you cannot rely on them. Portable AnyEvent
		309	callbacks cannot use arguments passed to signal watcher callbacks.
		310
		311	Multiple signal occurrences can be clumped together into one callback
		312	invocation, and callback invocation will be synchronous. Synchronous means
		313	that it might take a while until the signal gets handled by the process,
		314	but it is guaranteed not to interrupt any other callbacks.
		315
		316	The main advantage of using these watchers is that you can share a signal
		317	between multiple watchers.
		318
		319	This watcher might use C<%SIG>, so programs overwriting those signals
		320	directly will likely not work correctly.
		321
		322	Example: exit on SIGINT
		323
		324	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		325
		326	=head2 CHILD PROCESS WATCHERS
		327
		328	You can also watch on a child process exit and catch its exit status.
		329
		330	The child process is specified by the C<pid> argument (if set to C<0>, it
		331	watches for any child process exit). The watcher will trigger as often
		332	as status change for the child are received. This works by installing a
		333	signal handler for C<SIGCHLD>. The callback will be called with the pid
		334	and exit status (as returned by waitpid), so unlike other watcher types,
		335	you I<can> rely on child watcher callback arguments.
		336
		337	There is a slight catch to child watchers, however: you usually start them
		338	I<after> the child process was created, and this means the process could
		339	have exited already (and no SIGCHLD will be sent anymore).
		340
		341	Not all event models handle this correctly (POE doesn't), but even for
		342	event models that I<do> handle this correctly, they usually need to be
		343	loaded before the process exits (i.e. before you fork in the first place).
		344
		345	This means you cannot create a child watcher as the very first thing in an
		346	AnyEvent program, you I<have> to create at least one watcher before you
		347	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		348
		349	Example: fork a process and wait for it
		350
		351	my $done = AnyEvent->condvar;
		352
		353	my $pid = fork or exit 5;
		354
		355	my $w = AnyEvent->child (
		356	pid => $pid,
		357	cb => sub {
		358	my ($pid, $status) = @_;
		359	warn "pid $pid exited with status $status";
		360	$done->send;
		361	},
		362	);
		363
		364	# do something else, then wait for process exit
		365	$done->recv;
		366
		367	=head2 CONDITION VARIABLES
		368
		369	If you are familiar with some event loops you will know that all of them
		370	require you to run some blocking "loop", "run" or similar function that
		371	will actively watch for new events and call your callbacks.
		372
		373	AnyEvent is different, it expects somebody else to run the event loop and
		374	will only block when necessary (usually when told by the user).
		375
		376	The instrument to do that is called a "condition variable", so called
		377	because they represent a condition that must become true.
		378
		379	Condition variables can be created by calling the C<< AnyEvent->condvar
		380	>> method, usually without arguments. The only argument pair allowed is
		381	C<cb>, which specifies a callback to be called when the condition variable
		382	becomes true.
		383
		384	After creation, the condition variable is "false" until it becomes "true"
		385	by calling the C<send> method (or calling the condition variable as if it
		386	were a callback, read about the caveats in the description for the C<<
		387	->send >> method).
		388
		389	Condition variables are similar to callbacks, except that you can
		390	optionally wait for them. They can also be called merge points - points
		391	in time where multiple outstanding events have been processed. And yet
		392	another way to call them is transactions - each condition variable can be
		393	used to represent a transaction, which finishes at some point and delivers
		394	a result.
		395
		396	Condition variables are very useful to signal that something has finished,
		397	for example, if you write a module that does asynchronous http requests,
		398	then a condition variable would be the ideal candidate to signal the
		399	availability of results. The user can either act when the callback is
		400	called or can synchronously C<< ->recv >> for the results.
		401
		402	You can also use them to simulate traditional event loops - for example,
		403	you can block your main program until an event occurs - for example, you
		404	could C<< ->recv >> in your main program until the user clicks the Quit
		405	button of your app, which would C<< ->send >> the "quit" event.
		406
		407	Note that condition variables recurse into the event loop - if you have
		408	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		409	lose. Therefore, condition variables are good to export to your caller, but
		410	you should avoid making a blocking wait yourself, at least in callbacks,
		411	as this asks for trouble.
		412
		413	Condition variables are represented by hash refs in perl, and the keys
		414	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		415	easy (it is often useful to build your own transaction class on top of
		416	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		417	it's C<new> method in your own C<new> method.
		418
		419	There are two "sides" to a condition variable - the "producer side" which
		420	eventually calls C<< -> send >>, and the "consumer side", which waits
		421	for the send to occur.
		422
		423	Example: wait for a timer.
150		424
151	# wait till the result is ready	425	# wait till the result is ready
152	my $result_ready = AnyEvent->condvar;	426	my $result_ready = AnyEvent->condvar;
153		427
154	# do something such as adding a timer	428	# do something such as adding a timer
155	# or socket watcher the calls $result_ready->broadcast	429	# or socket watcher the calls $result_ready->send
156	# when the "result" is ready.	430	# when the "result" is ready.
		431	# in this case, we simply use a timer:
		432	my $w = AnyEvent->timer (
		433	after => 1,
		434	cb => sub { $result_ready->send },
		435	);
157		436
		437	# this "blocks" (while handling events) till the callback
		438	# calls send
158	$result_ready->wait;	439	$result_ready->recv;
		440
		441	Example: wait for a timer, but take advantage of the fact that
		442	condition variables are also code references.
		443
		444	my $done = AnyEvent->condvar;
		445	my $delay = AnyEvent->timer (after => 5, cb => $done);
		446	$done->recv;
		447
		448	=head3 METHODS FOR PRODUCERS
		449
		450	These methods should only be used by the producing side, i.e. the
		451	code/module that eventually sends the signal. Note that it is also
		452	the producer side which creates the condvar in most cases, but it isn't
		453	uncommon for the consumer to create it as well.
		454
		455	=over 4
		456
		457	=item $cv->send (...)
		458
		459	Flag the condition as ready - a running C<< ->recv >> and all further
		460	calls to C<recv> will (eventually) return after this method has been
		461	called. If nobody is waiting the send will be remembered.
		462
		463	If a callback has been set on the condition variable, it is called
		464	immediately from within send.
		465
		466	Any arguments passed to the C<send> call will be returned by all
		467	future C<< ->recv >> calls.
		468
		469	Condition variables are overloaded so one can call them directly
		470	(as a code reference). Calling them directly is the same as calling
		471	C<send>. Note, however, that many C-based event loops do not handle
		472	overloading, so as tempting as it may be, passing a condition variable
		473	instead of a callback does not work. Both the pure perl and EV loops
		474	support overloading, however, as well as all functions that use perl to
		475	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		476	example).
		477
		478	=item $cv->croak ($error)
		479
		480	Similar to send, but causes all call's to C<< ->recv >> to invoke
		481	C<Carp::croak> with the given error message/object/scalar.
		482
		483	This can be used to signal any errors to the condition variable
		484	user/consumer.
		485
		486	=item $cv->begin ([group callback])
		487
		488	=item $cv->end
		489
		490	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		491
		492	These two methods can be used to combine many transactions/events into
		493	one. For example, a function that pings many hosts in parallel might want
		494	to use a condition variable for the whole process.
		495
		496	Every call to C<< ->begin >> will increment a counter, and every call to
		497	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		498	>>, the (last) callback passed to C<begin> will be executed. That callback
		499	is I<supposed> to call C<< ->send >>, but that is not required. If no
		500	callback was set, C<send> will be called without any arguments.
		501
		502	Let's clarify this with the ping example:
		503
		504	my $cv = AnyEvent->condvar;
		505
		506	my %result;
		507	$cv->begin (sub { $cv->send (\%result) });
		508
		509	for my $host (@list_of_hosts) {
		510	$cv->begin;
		511	ping_host_then_call_callback $host, sub {
		512	$result{$host} = ...;
		513	$cv->end;
		514	};
		515	}
		516
		517	$cv->end;
		518
		519	This code fragment supposedly pings a number of hosts and calls
		520	C<send> after results for all then have have been gathered - in any
		521	order. To achieve this, the code issues a call to C<begin> when it starts
		522	each ping request and calls C<end> when it has received some result for
		523	it. Since C<begin> and C<end> only maintain a counter, the order in which
		524	results arrive is not relevant.
		525
		526	There is an additional bracketing call to C<begin> and C<end> outside the
		527	loop, which serves two important purposes: first, it sets the callback
		528	to be called once the counter reaches C<0>, and second, it ensures that
		529	C<send> is called even when C<no> hosts are being pinged (the loop
		530	doesn't execute once).
		531
		532	This is the general pattern when you "fan out" into multiple subrequests:
		533	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		534	is called at least once, and then, for each subrequest you start, call
		535	C<begin> and for each subrequest you finish, call C<end>.
159		536
160	=back	537	=back
161		538
162	=head2 SIGNAL WATCHERS	539	=head3 METHODS FOR CONSUMERS
163		540
164	You can listen for signals using a signal watcher, C<signal> is the signal	541	These methods should only be used by the consuming side, i.e. the
165	I<name> without any C<SIG> prefix. Multiple signals events can be clumped	542	code awaits the condition.
166	together into one callback invocation, and callbakc invocation might or
167	might not be asynchronous.
168		543
169	These watchers might use C<%SIG>, so programs overwriting those signals	544	=over 4
170	directly will likely not work correctly.
171		545
172	Example: exit on SIGINT	546	=item $cv->recv
173		547
174	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	548	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		549	>> methods have been called on c<$cv>, while servicing other watchers
		550	normally.
175		551
176	=head2 CHILD PROCESS WATCHERS	552	You can only wait once on a condition - additional calls are valid but
		553	will return immediately.
177		554
178	You can also listen for the status of a child process specified by the	555	If an error condition has been set by calling C<< ->croak >>, then this
179	C<pid> argument. The watcher will only trigger once. This works by	556	function will call C<croak>.
180	installing a signal handler for C<SIGCHLD>.
181		557
182	Example: wait for pid 1333	558	In list context, all parameters passed to C<send> will be returned,
		559	in scalar context only the first one will be returned.
183		560
184	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });	561	Not all event models support a blocking wait - some die in that case
		562	(programs might want to do that to stay interactive), so I<if you are
		563	using this from a module, never require a blocking wait>, but let the
		564	caller decide whether the call will block or not (for example, by coupling
		565	condition variables with some kind of request results and supporting
		566	callbacks so the caller knows that getting the result will not block,
		567	while still supporting blocking waits if the caller so desires).
185		568
186	=head1 GLOBALS	569	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		570	sensibly have two C<< ->recv >>'s in parallel, as that would require
		571	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		572	can supply.
		573
		574	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		575	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		576	versions and also integrates coroutines into AnyEvent, making blocking
		577	C<< ->recv >> calls perfectly safe as long as they are done from another
		578	coroutine (one that doesn't run the event loop).
		579
		580	You can ensure that C<< -recv >> never blocks by setting a callback and
		581	only calling C<< ->recv >> from within that callback (or at a later
		582	time). This will work even when the event loop does not support blocking
		583	waits otherwise.
		584
		585	=item $bool = $cv->ready
		586
		587	Returns true when the condition is "true", i.e. whether C<send> or
		588	C<croak> have been called.
		589
		590	=item $cb = $cv->cb ([new callback])
		591
		592	This is a mutator function that returns the callback set and optionally
		593	replaces it before doing so.
		594
		595	The callback will be called when the condition becomes "true", i.e. when
		596	C<send> or C<croak> are called. Calling C<recv> inside the callback
		597	or at any later time is guaranteed not to block.
		598
		599	=back
		600
		601	=head1 GLOBAL VARIABLES AND FUNCTIONS
187		602
188	=over 4	603	=over 4
189		604
190	=item $AnyEvent::MODEL	605	=item $AnyEvent::MODEL
191		606
…		…
195	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	610	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
196	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	611	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
197		612
198	The known classes so far are:	613	The known classes so far are:
199		614
200	AnyEvent::Impl::Coro based on Coro::Event, best choise.	615	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
201	AnyEvent::Impl::Event based on Event, also best choice :)	616	AnyEvent::Impl::Event based on Event, second best choice.
		617	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
202	AnyEvent::Impl::Glib based on Glib, second-best choice.	618	AnyEvent::Impl::Glib based on Glib, third-best choice.
203	AnyEvent::Impl::Tk based on Tk, very bad choice.	619	AnyEvent::Impl::Tk based on Tk, very bad choice.
204	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	620	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		621	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		622	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		623
		624	There is no support for WxWidgets, as WxWidgets has no support for
		625	watching file handles. However, you can use WxWidgets through the
		626	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		627	second, which was considered to be too horrible to even consider for
		628	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		629	it's adaptor.
		630
		631	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		632	autodetecting them.
205		633
206	=item AnyEvent::detect	634	=item AnyEvent::detect
207		635
208	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	636	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
209	necessary. You should only call this function right before you would have	637	if necessary. You should only call this function right before you would
210	created an AnyEvent watcher anyway, that is, very late at runtime.	638	have created an AnyEvent watcher anyway, that is, as late as possible at
		639	runtime.
		640
		641	=item $guard = AnyEvent::post_detect { BLOCK }
		642
		643	Arranges for the code block to be executed as soon as the event model is
		644	autodetected (or immediately if this has already happened).
		645
		646	If called in scalar or list context, then it creates and returns an object
		647	that automatically removes the callback again when it is destroyed. See
		648	L<Coro::BDB> for a case where this is useful.
		649
		650	=item @AnyEvent::post_detect
		651
		652	If there are any code references in this array (you can C<push> to it
		653	before or after loading AnyEvent), then they will called directly after
		654	the event loop has been chosen.
		655
		656	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		657	if it contains a true value then the event loop has already been detected,
		658	and the array will be ignored.
		659
		660	Best use C<AnyEvent::post_detect { BLOCK }> instead.
211		661
212	=back	662	=back
213		663
214	=head1 WHAT TO DO IN A MODULE	664	=head1 WHAT TO DO IN A MODULE
215		665
216	As a module author, you should "use AnyEvent" and call AnyEvent methods	666	As a module author, you should C<use AnyEvent> and call AnyEvent methods
217	freely, but you should not load a specific event module or rely on it.	667	freely, but you should not load a specific event module or rely on it.
218		668
219	Be careful when you create watchers in the module body - Anyevent will	669	Be careful when you create watchers in the module body - AnyEvent will
220	decide which event module to use as soon as the first method is called, so	670	decide which event module to use as soon as the first method is called, so
221	by calling AnyEvent in your module body you force the user of your module	671	by calling AnyEvent in your module body you force the user of your module
222	to load the event module first.	672	to load the event module first.
223		673
		674	Never call C<< ->recv >> on a condition variable unless you I<know> that
		675	the C<< ->send >> method has been called on it already. This is
		676	because it will stall the whole program, and the whole point of using
		677	events is to stay interactive.
		678
		679	It is fine, however, to call C<< ->recv >> when the user of your module
		680	requests it (i.e. if you create a http request object ad have a method
		681	called C<results> that returns the results, it should call C<< ->recv >>
		682	freely, as the user of your module knows what she is doing. always).
		683
224	=head1 WHAT TO DO IN THE MAIN PROGRAM	684	=head1 WHAT TO DO IN THE MAIN PROGRAM
225		685
226	There will always be a single main program - the only place that should	686	There will always be a single main program - the only place that should
227	dictate which event model to use.	687	dictate which event model to use.
228		688
229	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	689	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
230	do anything special and let AnyEvent decide which implementation to chose.	690	do anything special (it does not need to be event-based) and let AnyEvent
		691	decide which implementation to chose if some module relies on it.
231		692
232	If the main program relies on a specific event model (for example, in Gtk2	693	If the main program relies on a specific event model - for example, in
233	programs you have to rely on either Glib or Glib::Event), you should load	694	Gtk2 programs you have to rely on the Glib module - you should load the
234	it before loading AnyEvent or any module that uses it, generally, as early	695	event module before loading AnyEvent or any module that uses it: generally
235	as possible. The reason is that modules might create watchers when they	696	speaking, you should load it as early as possible. The reason is that
236	are loaded, and AnyEvent will decide on the event model to use as soon as	697	modules might create watchers when they are loaded, and AnyEvent will
237	it creates watchers, and it might chose the wrong one unless you load the	698	decide on the event model to use as soon as it creates watchers, and it
238	correct one yourself.	699	might chose the wrong one unless you load the correct one yourself.
239		700
240	You can chose to use a rather inefficient pure-perl implementation by	701	You can chose to use a pure-perl implementation by loading the
241	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	702	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
242	generally better.	703	everywhere, but letting AnyEvent chose the model is generally better.
		704
		705	=head2 MAINLOOP EMULATION
		706
		707	Sometimes (often for short test scripts, or even standalone programs who
		708	only want to use AnyEvent), you do not want to run a specific event loop.
		709
		710	In that case, you can use a condition variable like this:
		711
		712	AnyEvent->condvar->recv;
		713
		714	This has the effect of entering the event loop and looping forever.
		715
		716	Note that usually your program has some exit condition, in which case
		717	it is better to use the "traditional" approach of storing a condition
		718	variable somewhere, waiting for it, and sending it when the program should
		719	exit cleanly.
		720
		721
		722	=head1 OTHER MODULES
		723
		724	The following is a non-exhaustive list of additional modules that use
		725	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		726	in the same program. Some of the modules come with AnyEvent, some are
		727	available via CPAN.
		728
		729	=over 4
		730
		731	=item L<AnyEvent::Util>
		732
		733	Contains various utility functions that replace often-used but blocking
		734	functions such as C<inet_aton> by event-/callback-based versions.
		735
		736	=item L<AnyEvent::Handle>
		737
		738	Provide read and write buffers and manages watchers for reads and writes.
		739
		740	=item L<AnyEvent::Socket>
		741
		742	Provides various utility functions for (internet protocol) sockets,
		743	addresses and name resolution. Also functions to create non-blocking tcp
		744	connections or tcp servers, with IPv6 and SRV record support and more.
		745
		746	=item L<AnyEvent::DNS>
		747
		748	Provides rich asynchronous DNS resolver capabilities.
		749
		750	=item L<AnyEvent::HTTPD>
		751
		752	Provides a simple web application server framework.
		753
		754	=item L<AnyEvent::FastPing>
		755
		756	The fastest ping in the west.
		757
		758	=item L<Net::IRC3>
		759
		760	AnyEvent based IRC client module family.
		761
		762	=item L<Net::XMPP2>
		763
		764	AnyEvent based XMPP (Jabber protocol) module family.
		765
		766	=item L<Net::FCP>
		767
		768	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		769	of AnyEvent.
		770
		771	=item L<Event::ExecFlow>
		772
		773	High level API for event-based execution flow control.
		774
		775	=item L<Coro>
		776
		777	Has special support for AnyEvent via L<Coro::AnyEvent>.
		778
		779	=item L<AnyEvent::AIO>, L<IO::AIO>
		780
		781	Truly asynchronous I/O, should be in the toolbox of every event
		782	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		783	together.
		784
		785	=item L<AnyEvent::BDB>, L<BDB>
		786
		787	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		788	IO::AIO and AnyEvent together.
		789
		790	=item L<IO::Lambda>
		791
		792	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		793
		794	=back
243		795
244	=cut	796	=cut
245		797
246	package AnyEvent;	798	package AnyEvent;
247		799
248	no warnings;	800	no warnings;
249	use strict;	801	use strict;
		802
250	use Carp;	803	use Carp;
251		804
252	our $VERSION = '2.51';	805	our $VERSION = '4.1';
253	our $MODEL;	806	our $MODEL;
254		807
255	our $AUTOLOAD;	808	our $AUTOLOAD;
256	our @ISA;	809	our @ISA;
257		810
		811	our @REGISTRY;
		812
		813	our $WIN32;
		814
		815	BEGIN {
		816	my $win32 = ! ! ($^O =~ /mswin32/i);
		817	eval "sub WIN32(){ $win32 }";
		818	}
		819
258	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	820	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
259		821
260	our @REGISTRY;	822	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		823
		824	{
		825	my $idx;
		826	$PROTOCOL{$_} = ++$idx
		827	for reverse split /\s*,\s*/,
		828	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		829	}
261		830
262	my @models = (	831	my @models = (
263	[Coro::Event:: => AnyEvent::Impl::Coro::],	832	[EV:: => AnyEvent::Impl::EV::],
264	[Event:: => AnyEvent::Impl::Event::],	833	[Event:: => AnyEvent::Impl::Event::],
265	[Glib:: => AnyEvent::Impl::Glib::],
266	[Tk:: => AnyEvent::Impl::Tk::],
267	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	834	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		835	# everything below here will not be autoprobed
		836	# as the pureperl backend should work everywhere
		837	# and is usually faster
		838	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		839	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		840	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		841	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		842	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		843	[Wx:: => AnyEvent::Impl::POE::],
		844	[Prima:: => AnyEvent::Impl::POE::],
268	);	845	);
269		846
270	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	847	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
		848
		849	our @post_detect;
		850
		851	sub post_detect(&) {
		852	my ($cb) = @_;
		853
		854	if ($MODEL) {
		855	$cb->();
		856
		857	1
		858	} else {
		859	push @post_detect, $cb;
		860
		861	defined wantarray
		862	? bless \$cb, "AnyEvent::Util::PostDetect"
		863	: ()
		864	}
		865	}
		866
		867	sub AnyEvent::Util::PostDetect::DESTROY {
		868	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		869	}
271		870
272	sub detect() {	871	sub detect() {
273	unless ($MODEL) {	872	unless ($MODEL) {
274	no strict 'refs';	873	no strict 'refs';
		874	local $SIG{__DIE__};
		875
		876	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		877	my $model = "AnyEvent::Impl::$1";
		878	if (eval "require $model") {
		879	$MODEL = $model;
		880	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		881	} else {
		882	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		883	}
		884	}
275		885
276	# check for already loaded models	886	# check for already loaded models
		887	unless ($MODEL) {
277	for (@REGISTRY, @models) {	888	for (@REGISTRY, @models) {
278	my ($package, $model) = @$_;	889	my ($package, $model) = @$_;
279	if (${"$package\::VERSION"} > 0) {	890	if (${"$package\::VERSION"} > 0) {
280	if (eval "require $model") {	891	if (eval "require $model") {
281	$MODEL = $model;	892	$MODEL = $model;
282	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	893	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
283	last;	894	last;
		895	}
284	}	896	}
285	}	897	}
286	}
287		898
288	unless ($MODEL) {	899	unless ($MODEL) {
289	# try to load a model	900	# try to load a model
290		901
291	for (@REGISTRY, @models) {	902	for (@REGISTRY, @models) {
292	my ($package, $model) = @$_;	903	my ($package, $model) = @$_;
293	if (eval "require $package"	904	if (eval "require $package"
294	and ${"$package\::VERSION"} > 0	905	and ${"$package\::VERSION"} > 0
295	and eval "require $model") {	906	and eval "require $model") {
296	$MODEL = $model;	907	$MODEL = $model;
297	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	908	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
298	last;	909	last;
		910	}
299	}	911	}
		912
		913	$MODEL
		914	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
300	}	915	}
301
302	$MODEL
303	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Event (or Coro+Event), Glib or Tk.";
304	}	916	}
305		917
306	unshift @ISA, $MODEL;	918	unshift @ISA, $MODEL;
307	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	919	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		920
		921	(shift @post_detect)->() while @post_detect;
308	}	922	}
309		923
310	$MODEL	924	$MODEL
311	}	925	}
312		926
…		…
322	$class->$func (@_);	936	$class->$func (@_);
323	}	937	}
324		938
325	package AnyEvent::Base;	939	package AnyEvent::Base;
326		940
		941	# default implementation for now and time
		942
		943	use Time::HiRes ();
		944
		945	sub time { Time::HiRes::time }
		946	sub now { Time::HiRes::time }
		947
327	# default implementation for ->condvar, ->wait, ->broadcast	948	# default implementation for ->condvar
328		949
329	sub condvar {	950	sub condvar {
330	bless \my $flag, "AnyEvent::Base::CondVar"	951	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
331	}
332
333	sub AnyEvent::Base::CondVar::broadcast {
334	${$_[0]}++;
335	}
336
337	sub AnyEvent::Base::CondVar::wait {
338	AnyEvent->one_event while !${$_[0]};
339	}	952	}
340		953
341	# default implementation for ->signal	954	# default implementation for ->signal
342		955
343	our %SIG_CB;	956	our %SIG_CB;
…		…
366		979
367	# default implementation for ->child	980	# default implementation for ->child
368		981
369	our %PID_CB;	982	our %PID_CB;
370	our $CHLD_W;	983	our $CHLD_W;
		984	our $CHLD_DELAY_W;
371	our $PID_IDLE;	985	our $PID_IDLE;
372	our $WNOHANG;	986	our $WNOHANG;
373		987
374	sub _child_wait {	988	sub _child_wait {
375	while (0 < (my $pid = waitpid -1, $WNOHANG)) {	989	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
376	$_->() for values %{ (delete $PID_CB{$pid}) || {} };	990	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		991	(values %{ $PID_CB{0} || {} });
377	}	992	}
378		993
379	undef $PID_IDLE;	994	undef $PID_IDLE;
		995	}
		996
		997	sub _sigchld {
		998	# make sure we deliver these changes "synchronous" with the event loop.
		999	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		1000	undef $CHLD_DELAY_W;
		1001	&_child_wait;
		1002	});
380	}	1003	}
381		1004
382	sub child {	1005	sub child {
383	my (undef, %arg) = @_;	1006	my (undef, %arg) = @_;
384		1007
385	my $pid = uc $arg{pid}	1008	defined (my $pid = $arg{pid} + 0)
386	or Carp::croak "required option 'pid' is missing";	1009	or Carp::croak "required option 'pid' is missing";
387		1010
388	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1011	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
389		1012
390	unless ($WNOHANG) {	1013	unless ($WNOHANG) {
391	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_child_wait);
392	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1014	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
393	}	1015	}
394		1016
395	# child could be a zombie already	1017	unless ($CHLD_W) {
396	$PID_IDLE ||= AnyEvent->timer (after => 0, cb => \&_child_wait);	1018	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		1019	# child could be a zombie already, so make at least one round
		1020	&_sigchld;
		1021	}
397		1022
398	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"	1023	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
399	}	1024	}
400		1025
401	sub AnyEvent::Base::Child::DESTROY {	1026	sub AnyEvent::Base::Child::DESTROY {
…		…
405	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1030	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
406		1031
407	undef $CHLD_W unless keys %PID_CB;	1032	undef $CHLD_W unless keys %PID_CB;
408	}	1033	}
409		1034
		1035	package AnyEvent::CondVar;
		1036
		1037	our @ISA = AnyEvent::CondVar::Base::;
		1038
		1039	package AnyEvent::CondVar::Base;
		1040
		1041	use overload
		1042	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1043	fallback => 1;
		1044
		1045	sub _send {
		1046	# nop
		1047	}
		1048
		1049	sub send {
		1050	my $cv = shift;
		1051	$cv->{_ae_sent} = [@_];
		1052	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1053	$cv->_send;
		1054	}
		1055
		1056	sub croak {
		1057	$_[0]{_ae_croak} = $_[1];
		1058	$_[0]->send;
		1059	}
		1060
		1061	sub ready {
		1062	$_[0]{_ae_sent}
		1063	}
		1064
		1065	sub _wait {
		1066	AnyEvent->one_event while !$_[0]{_ae_sent};
		1067	}
		1068
		1069	sub recv {
		1070	$_[0]->_wait;
		1071
		1072	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1073	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1074	}
		1075
		1076	sub cb {
		1077	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1078	$_[0]{_ae_cb}
		1079	}
		1080
		1081	sub begin {
		1082	++$_[0]{_ae_counter};
		1083	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1084	}
		1085
		1086	sub end {
		1087	return if --$_[0]{_ae_counter};
		1088	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1089	}
		1090
		1091	# undocumented/compatibility with pre-3.4
		1092	*broadcast = \&send;
		1093	*wait = \&_wait;
		1094
410	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1095	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1096
		1097	This is an advanced topic that you do not normally need to use AnyEvent in
		1098	a module. This section is only of use to event loop authors who want to
		1099	provide AnyEvent compatibility.
411		1100
412	If you need to support another event library which isn't directly	1101	If you need to support another event library which isn't directly
413	supported by AnyEvent, you can supply your own interface to it by	1102	supported by AnyEvent, you can supply your own interface to it by
414	pushing, before the first watcher gets created, the package name of	1103	pushing, before the first watcher gets created, the package name of
415	the event module and the package name of the interface to use onto	1104	the event module and the package name of the interface to use onto
416	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	1105	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
417	AnyEvent.	1106	AnyEvent, so it is reasonably cheap.
418		1107
419	Example:	1108	Example:
420		1109
421	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1110	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
422		1111
423	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1112	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
424	package/class when it finds the C<urxvt> package/module is loaded. When	1113	package/class when it finds the C<urxvt> package/module is already loaded.
		1114
425	AnyEvent is loaded and asked to find a suitable event model, it will	1115	When AnyEvent is loaded and asked to find a suitable event model, it
426	first check for the presence of urxvt.	1116	will first check for the presence of urxvt by trying to C<use> the
		1117	C<urxvt::anyevent> module.
427		1118
428	The class should provide implementations for all watcher types (see	1119	The class should provide implementations for all watcher types. See
429	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1120	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
430	(Source code) and so on for actual examples, use C<perldoc -m	1121	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
431	AnyEvent::Impl::Glib> to see the sources).	1122	see the sources.
432		1123
		1124	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1125	provide suitable (hopefully) replacements.
		1126
433	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1127	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
434	uses the above line as-is. An interface isn't included in AnyEvent	1128	terminal emulator uses the above line as-is. An interface isn't included
435	because it doesn't make sense outside the embedded interpreter inside	1129	in AnyEvent because it doesn't make sense outside the embedded interpreter
436	I<rxvt-unicode>, and it is updated and maintained as part of the	1130	inside I<rxvt-unicode>, and it is updated and maintained as part of the
437	I<rxvt-unicode> distribution.	1131	I<rxvt-unicode> distribution.
438		1132
439	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1133	I<rxvt-unicode> also cheats a bit by not providing blocking access to
440	condition variables: code blocking while waiting for a condition will	1134	condition variables: code blocking while waiting for a condition will
441	C<die>. This still works with most modules/usages, and blocking calls must	1135	C<die>. This still works with most modules/usages, and blocking calls must
442	not be in an interactive appliation, so it makes sense.	1136	not be done in an interactive application, so it makes sense.
443		1137
444	=head1 ENVIRONMENT VARIABLES	1138	=head1 ENVIRONMENT VARIABLES
445		1139
446	The following environment variables are used by this module:	1140	The following environment variables are used by this module:
447		1141
448	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	1142	=over 4
449	model gets used.
450		1143
		1144	=item C<PERL_ANYEVENT_VERBOSE>
		1145
		1146	By default, AnyEvent will be completely silent except in fatal
		1147	conditions. You can set this environment variable to make AnyEvent more
		1148	talkative.
		1149
		1150	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1151	conditions, such as not being able to load the event model specified by
		1152	C<PERL_ANYEVENT_MODEL>.
		1153
		1154	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1155	model it chooses.
		1156
		1157	=item C<PERL_ANYEVENT_MODEL>
		1158
		1159	This can be used to specify the event model to be used by AnyEvent, before
		1160	auto detection and -probing kicks in. It must be a string consisting
		1161	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1162	and the resulting module name is loaded and if the load was successful,
		1163	used as event model. If it fails to load AnyEvent will proceed with
		1164	auto detection and -probing.
		1165
		1166	This functionality might change in future versions.
		1167
		1168	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1169	could start your program like this:
		1170
		1171	PERL_ANYEVENT_MODEL=Perl perl ...
		1172
		1173	=item C<PERL_ANYEVENT_PROTOCOLS>
		1174
		1175	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1176	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1177	of auto probing).
		1178
		1179	Must be set to a comma-separated list of protocols or address families,
		1180	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1181	used, and preference will be given to protocols mentioned earlier in the
		1182	list.
		1183
		1184	This variable can effectively be used for denial-of-service attacks
		1185	against local programs (e.g. when setuid), although the impact is likely
		1186	small, as the program has to handle connection errors already-
		1187
		1188	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1189	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1190	- only support IPv4, never try to resolve or contact IPv6
		1191	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1192	IPv6, but prefer IPv6 over IPv4.
		1193
		1194	=item C<PERL_ANYEVENT_EDNS0>
		1195
		1196	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1197	for DNS. This extension is generally useful to reduce DNS traffic, but
		1198	some (broken) firewalls drop such DNS packets, which is why it is off by
		1199	default.
		1200
		1201	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1202	EDNS0 in its DNS requests.
		1203
		1204	=item C<PERL_ANYEVENT_MAX_FORKS>
		1205
		1206	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1207	will create in parallel.
		1208
		1209	=back
		1210
451	=head1 EXAMPLE	1211	=head1 EXAMPLE PROGRAM
452		1212
453	The following program uses an io watcher to read data from stdin, a timer	1213	The following program uses an I/O watcher to read data from STDIN, a timer
454	to display a message once per second, and a condvar to exit the program	1214	to display a message once per second, and a condition variable to quit the
455	when the user enters quit:	1215	program when the user enters quit:
456		1216
457	use AnyEvent;	1217	use AnyEvent;
458		1218
459	my $cv = AnyEvent->condvar;	1219	my $cv = AnyEvent->condvar;
460		1220
461	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1221	my $io_watcher = AnyEvent->io (
		1222	fh => \*STDIN,
		1223	poll => 'r',
		1224	cb => sub {
462	warn "io event <$_[0]>\n"; # will always output <r>	1225	warn "io event <$_[0]>\n"; # will always output <r>
463	chomp (my $input = <STDIN>); # read a line	1226	chomp (my $input = <STDIN>); # read a line
464	warn "read: $input\n"; # output what has been read	1227	warn "read: $input\n"; # output what has been read
465	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1228	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1229	},
466	});	1230	);
467		1231
468	my $time_watcher; # can only be used once	1232	my $time_watcher; # can only be used once
469		1233
470	sub new_timer {	1234	sub new_timer {
471	$timer = AnyEvent->timer (after => 1, cb => sub {	1235	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
474	});	1238	});
475	}	1239	}
476		1240
477	new_timer; # create first timer	1241	new_timer; # create first timer
478		1242
479	$cv->wait; # wait until user enters /^q/i	1243	$cv->recv; # wait until user enters /^q/i
480		1244
481	=head1 REAL-WORLD EXAMPLE	1245	=head1 REAL-WORLD EXAMPLE
482		1246
483	Consider the L<Net::FCP> module. It features (among others) the following	1247	Consider the L<Net::FCP> module. It features (among others) the following
484	API calls, which are to freenet what HTTP GET requests are to http:	1248	API calls, which are to freenet what HTTP GET requests are to http:
…		…
534	syswrite $txn->{fh}, $txn->{request}	1298	syswrite $txn->{fh}, $txn->{request}
535	or die "connection or write error";	1299	or die "connection or write error";
536	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1300	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
537		1301
538	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1302	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
539	result and signals any possible waiters that the request ahs finished:	1303	result and signals any possible waiters that the request has finished:
540		1304
541	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1305	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
542		1306
543	if (end-of-file or data complete) {	1307	if (end-of-file or data complete) {
544	$txn->{result} = $txn->{buf};	1308	$txn->{result} = $txn->{buf};
545	$txn->{finished}->broadcast;	1309	$txn->{finished}->send;
546	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1310	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
547	}	1311	}
548		1312
549	The C<result> method, finally, just waits for the finished signal (if the	1313	The C<result> method, finally, just waits for the finished signal (if the
550	request was already finished, it doesn't wait, of course, and returns the	1314	request was already finished, it doesn't wait, of course, and returns the
551	data:	1315	data:
552		1316
553	$txn->{finished}->wait;	1317	$txn->{finished}->recv;
554	return $txn->{result};	1318	return $txn->{result};
555		1319
556	The actual code goes further and collects all errors (C<die>s, exceptions)	1320	The actual code goes further and collects all errors (C<die>s, exceptions)
557	that occured during request processing. The C<result> method detects	1321	that occurred during request processing. The C<result> method detects
558	wether an exception as thrown (it is stored inside the $txn object)	1322	whether an exception as thrown (it is stored inside the $txn object)
559	and just throws the exception, which means connection errors and other	1323	and just throws the exception, which means connection errors and other
560	problems get reported tot he code that tries to use the result, not in a	1324	problems get reported tot he code that tries to use the result, not in a
561	random callback.	1325	random callback.
562		1326
563	All of this enables the following usage styles:	1327	All of this enables the following usage styles:
564		1328
565	1. Blocking:	1329	1. Blocking:
566		1330
567	my $data = $fcp->client_get ($url);	1331	my $data = $fcp->client_get ($url);
568		1332
569	2. Blocking, but parallelizing:	1333	2. Blocking, but running in parallel:
570		1334
571	my @datas = map $_->result,	1335	my @datas = map $_->result,
572	map $fcp->txn_client_get ($_),	1336	map $fcp->txn_client_get ($_),
573	@urls;	1337	@urls;
574		1338
575	Both blocking examples work without the module user having to know	1339	Both blocking examples work without the module user having to know
576	anything about events.	1340	anything about events.
577		1341
578	3a. Event-based in a main program, using any support Event module:	1342	3a. Event-based in a main program, using any supported event module:
579		1343
580	use Event;	1344	use EV;
581		1345
582	$fcp->txn_client_get ($url)->cb (sub {	1346	$fcp->txn_client_get ($url)->cb (sub {
583	my $txn = shift;	1347	my $txn = shift;
584	my $data = $txn->result;	1348	my $data = $txn->result;
585	...	1349	...
586	});	1350	});
587		1351
588	Event::loop;	1352	EV::loop;
589		1353
590	3b. The module user could use AnyEvent, too:	1354	3b. The module user could use AnyEvent, too:
591		1355
592	use AnyEvent;	1356	use AnyEvent;
593		1357
594	my $quit = AnyEvent->condvar;	1358	my $quit = AnyEvent->condvar;
595		1359
596	$fcp->txn_client_get ($url)->cb (sub {	1360	$fcp->txn_client_get ($url)->cb (sub {
597	...	1361	...
598	$quit->broadcast;	1362	$quit->send;
599	});	1363	});
600		1364
601	$quit->wait;	1365	$quit->recv;
		1366
		1367
		1368	=head1 BENCHMARKS
		1369
		1370	To give you an idea of the performance and overheads that AnyEvent adds
		1371	over the event loops themselves and to give you an impression of the speed
		1372	of various event loops I prepared some benchmarks.
		1373
		1374	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1375
		1376	Here is a benchmark of various supported event models used natively and
		1377	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1378	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1379	which it is), lets them fire exactly once and destroys them again.
		1380
		1381	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1382	distribution.
		1383
		1384	=head3 Explanation of the columns
		1385
		1386	I<watcher> is the number of event watchers created/destroyed. Since
		1387	different event models feature vastly different performances, each event
		1388	loop was given a number of watchers so that overall runtime is acceptable
		1389	and similar between tested event loop (and keep them from crashing): Glib
		1390	would probably take thousands of years if asked to process the same number
		1391	of watchers as EV in this benchmark.
		1392
		1393	I<bytes> is the number of bytes (as measured by the resident set size,
		1394	RSS) consumed by each watcher. This method of measuring captures both C
		1395	and Perl-based overheads.
		1396
		1397	I<create> is the time, in microseconds (millionths of seconds), that it
		1398	takes to create a single watcher. The callback is a closure shared between
		1399	all watchers, to avoid adding memory overhead. That means closure creation
		1400	and memory usage is not included in the figures.
		1401
		1402	I<invoke> is the time, in microseconds, used to invoke a simple
		1403	callback. The callback simply counts down a Perl variable and after it was
		1404	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1405	signal the end of this phase.
		1406
		1407	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1408	watcher.
		1409
		1410	=head3 Results
		1411
		1412	name watchers bytes create invoke destroy comment
		1413	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1414	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1415	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1416	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1417	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1418	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1419	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1420	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1421	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1422	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1423
		1424	=head3 Discussion
		1425
		1426	The benchmark does I<not> measure scalability of the event loop very
		1427	well. For example, a select-based event loop (such as the pure perl one)
		1428	can never compete with an event loop that uses epoll when the number of
		1429	file descriptors grows high. In this benchmark, all events become ready at
		1430	the same time, so select/poll-based implementations get an unnatural speed
		1431	boost.
		1432
		1433	Also, note that the number of watchers usually has a nonlinear effect on
		1434	overall speed, that is, creating twice as many watchers doesn't take twice
		1435	the time - usually it takes longer. This puts event loops tested with a
		1436	higher number of watchers at a disadvantage.
		1437
		1438	To put the range of results into perspective, consider that on the
		1439	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1440	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1441	cycles with POE.
		1442
		1443	C<EV> is the sole leader regarding speed and memory use, which are both
		1444	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1445	far less memory than any other event loop and is still faster than Event
		1446	natively.
		1447
		1448	The pure perl implementation is hit in a few sweet spots (both the
		1449	constant timeout and the use of a single fd hit optimisations in the perl
		1450	interpreter and the backend itself). Nevertheless this shows that it
		1451	adds very little overhead in itself. Like any select-based backend its
		1452	performance becomes really bad with lots of file descriptors (and few of
		1453	them active), of course, but this was not subject of this benchmark.
		1454
		1455	The C<Event> module has a relatively high setup and callback invocation
		1456	cost, but overall scores in on the third place.
		1457
		1458	C<Glib>'s memory usage is quite a bit higher, but it features a
		1459	faster callback invocation and overall ends up in the same class as
		1460	C<Event>. However, Glib scales extremely badly, doubling the number of
		1461	watchers increases the processing time by more than a factor of four,
		1462	making it completely unusable when using larger numbers of watchers
		1463	(note that only a single file descriptor was used in the benchmark, so
		1464	inefficiencies of C<poll> do not account for this).
		1465
		1466	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1467	more than 2000 watchers is a big setback, however, as correctness takes
		1468	precedence over speed. Nevertheless, its performance is surprising, as the
		1469	file descriptor is dup()ed for each watcher. This shows that the dup()
		1470	employed by some adaptors is not a big performance issue (it does incur a
		1471	hidden memory cost inside the kernel which is not reflected in the figures
		1472	above).
		1473
		1474	C<POE>, regardless of underlying event loop (whether using its pure perl
		1475	select-based backend or the Event module, the POE-EV backend couldn't
		1476	be tested because it wasn't working) shows abysmal performance and
		1477	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1478	as EV watchers, and 10 times as much memory as Event (the high memory
		1479	requirements are caused by requiring a session for each watcher). Watcher
		1480	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1481	implementation.
		1482
		1483	The design of the POE adaptor class in AnyEvent can not really account
		1484	for the performance issues, though, as session creation overhead is
		1485	small compared to execution of the state machine, which is coded pretty
		1486	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1487	using multiple sessions is not a good approach, especially regarding
		1488	memory usage, even the author of POE could not come up with a faster
		1489	design).
		1490
		1491	=head3 Summary
		1492
		1493	=over 4
		1494
		1495	=item * Using EV through AnyEvent is faster than any other event loop
		1496	(even when used without AnyEvent), but most event loops have acceptable
		1497	performance with or without AnyEvent.
		1498
		1499	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1500	the actual event loop, only with extremely fast event loops such as EV
		1501	adds AnyEvent significant overhead.
		1502
		1503	=item * You should avoid POE like the plague if you want performance or
		1504	reasonable memory usage.
		1505
		1506	=back
		1507
		1508	=head2 BENCHMARKING THE LARGE SERVER CASE
		1509
		1510	This benchmark actually benchmarks the event loop itself. It works by
		1511	creating a number of "servers": each server consists of a socket pair, a
		1512	timeout watcher that gets reset on activity (but never fires), and an I/O
		1513	watcher waiting for input on one side of the socket. Each time the socket
		1514	watcher reads a byte it will write that byte to a random other "server".
		1515
		1516	The effect is that there will be a lot of I/O watchers, only part of which
		1517	are active at any one point (so there is a constant number of active
		1518	fds for each loop iteration, but which fds these are is random). The
		1519	timeout is reset each time something is read because that reflects how
		1520	most timeouts work (and puts extra pressure on the event loops).
		1521
		1522	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1523	(1%) are active. This mirrors the activity of large servers with many
		1524	connections, most of which are idle at any one point in time.
		1525
		1526	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1527	distribution.
		1528
		1529	=head3 Explanation of the columns
		1530
		1531	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1532	each server has a read and write socket end).
		1533
		1534	I<create> is the time it takes to create a socket pair (which is
		1535	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1536
		1537	I<request>, the most important value, is the time it takes to handle a
		1538	single "request", that is, reading the token from the pipe and forwarding
		1539	it to another server. This includes deleting the old timeout and creating
		1540	a new one that moves the timeout into the future.
		1541
		1542	=head3 Results
		1543
		1544	name sockets create request
		1545	EV 20000 69.01 11.16
		1546	Perl 20000 73.32 35.87
		1547	Event 20000 212.62 257.32
		1548	Glib 20000 651.16 1896.30
		1549	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1550
		1551	=head3 Discussion
		1552
		1553	This benchmark I<does> measure scalability and overall performance of the
		1554	particular event loop.
		1555
		1556	EV is again fastest. Since it is using epoll on my system, the setup time
		1557	is relatively high, though.
		1558
		1559	Perl surprisingly comes second. It is much faster than the C-based event
		1560	loops Event and Glib.
		1561
		1562	Event suffers from high setup time as well (look at its code and you will
		1563	understand why). Callback invocation also has a high overhead compared to
		1564	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1565	uses select or poll in basically all documented configurations.
		1566
		1567	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1568	clearly fails to perform with many filehandles or in busy servers.
		1569
		1570	POE is still completely out of the picture, taking over 1000 times as long
		1571	as EV, and over 100 times as long as the Perl implementation, even though
		1572	it uses a C-based event loop in this case.
		1573
		1574	=head3 Summary
		1575
		1576	=over 4
		1577
		1578	=item * The pure perl implementation performs extremely well.
		1579
		1580	=item * Avoid Glib or POE in large projects where performance matters.
		1581
		1582	=back
		1583
		1584	=head2 BENCHMARKING SMALL SERVERS
		1585
		1586	While event loops should scale (and select-based ones do not...) even to
		1587	large servers, most programs we (or I :) actually write have only a few
		1588	I/O watchers.
		1589
		1590	In this benchmark, I use the same benchmark program as in the large server
		1591	case, but it uses only eight "servers", of which three are active at any
		1592	one time. This should reflect performance for a small server relatively
		1593	well.
		1594
		1595	The columns are identical to the previous table.
		1596
		1597	=head3 Results
		1598
		1599	name sockets create request
		1600	EV 16 20.00 6.54
		1601	Perl 16 25.75 12.62
		1602	Event 16 81.27 35.86
		1603	Glib 16 32.63 15.48
		1604	POE 16 261.87 276.28 uses POE::Loop::Event
		1605
		1606	=head3 Discussion
		1607
		1608	The benchmark tries to test the performance of a typical small
		1609	server. While knowing how various event loops perform is interesting, keep
		1610	in mind that their overhead in this case is usually not as important, due
		1611	to the small absolute number of watchers (that is, you need efficiency and
		1612	speed most when you have lots of watchers, not when you only have a few of
		1613	them).
		1614
		1615	EV is again fastest.
		1616
		1617	Perl again comes second. It is noticeably faster than the C-based event
		1618	loops Event and Glib, although the difference is too small to really
		1619	matter.
		1620
		1621	POE also performs much better in this case, but is is still far behind the
		1622	others.
		1623
		1624	=head3 Summary
		1625
		1626	=over 4
		1627
		1628	=item * C-based event loops perform very well with small number of
		1629	watchers, as the management overhead dominates.
		1630
		1631	=back
		1632
		1633
		1634	=head1 FORK
		1635
		1636	Most event libraries are not fork-safe. The ones who are usually are
		1637	because they rely on inefficient but fork-safe C<select> or C<poll>
		1638	calls. Only L<EV> is fully fork-aware.
		1639
		1640	If you have to fork, you must either do so I<before> creating your first
		1641	watcher OR you must not use AnyEvent at all in the child.
		1642
		1643
		1644	=head1 SECURITY CONSIDERATIONS
		1645
		1646	AnyEvent can be forced to load any event model via
		1647	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1648	execute arbitrary code or directly gain access, it can easily be used to
		1649	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1650	will not be active when the program uses a different event model than
		1651	specified in the variable.
		1652
		1653	You can make AnyEvent completely ignore this variable by deleting it
		1654	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1655
		1656	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1657
		1658	use AnyEvent;
		1659
		1660	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1661	be used to probe what backend is used and gain other information (which is
		1662	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1663
602		1664
603	=head1 SEE ALSO	1665	=head1 SEE ALSO
604		1666
605	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1667	Utility functions: L<AnyEvent::Util>.
606		1668
607	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1669	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1670	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
608		1671
609	Nontrivial usage example: L<Net::FCP>.	1672	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1673	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1674	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1675	L<AnyEvent::Impl::POE>.
610		1676
611	=head1	1677	Non-blocking file handles, sockets, TCP clients and
		1678	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1679
		1680	Asynchronous DNS: L<AnyEvent::DNS>.
		1681
		1682	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1683
		1684	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1685
		1686
		1687	=head1 AUTHOR
		1688
		1689	Marc Lehmann <schmorp@schmorp.de>
		1690	http://home.schmorp.de/
612		1691
613	=cut	1692	=cut
614		1693
615	1	1694	1
616		1695

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