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Revision 1.15 by root, Mon Oct 30 20:55:05 2006 UTC vs.
Revision 1.105 by root, Thu May 1 12:35:54 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, Coro::EV, Coro::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->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->broadcast
21	$w->broadcast; # wake up current and all future wait's	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 enourmous amount of code and strict rules you have to
		63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		64	offering the functionality that is necessary, in as thin as a wrapper as
		65	technically possible.
		66
		67	Of course, if you want lots of policy (this can arguably be somewhat
		68	useful) and you want to force your users to use the one and only event
		69	model, you should I<not> use this module.
22		70
23	=head1 DESCRIPTION	71	=head1 DESCRIPTION
24		72
25	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
26	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
27	users to use the same event loop (as only a single event loop can coexist	75	users to use the same event loop (as only a single event loop can coexist
28	peacefully at any one time).	76	peacefully at any one time).
29		77
30	The interface itself is vaguely similar but not identical to the Event	78	The interface itself is vaguely similar, but not identical to the L<Event>
31	module.	79	module.
32		80
33	On the first call of any method, the module tries to detect the currently	81	During the first call of any watcher-creation method, the module tries
34	loaded event loop by probing wether any of the following modules is	82	to detect the currently loaded event loop by probing whether one of the
35	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
36	used. If none is found, the module tries to load these modules in the	84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
37	order given. The first one that could be successfully loaded will be	85	L<POE>. The first one found is used. If none are found, the module tries
38	used. If still none could be found, AnyEvent will fall back to a pure-perl	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
39	event loop, which is also not very efficient.	87	adaptor should always succeed) in the order given. The first one that can
		88	be successfully loaded will be used. If, after this, still none could be
		89	found, AnyEvent will fall back to a pure-perl event loop, which is not
		90	very efficient, but should work everywhere.
40		91
41	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
42	an Event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
43	that model the default. For example:	94	that model the default. For example:
44		95
45	use Tk;	96	use Tk;
46	use AnyEvent;	97	use AnyEvent;
47		98
48	# .. AnyEvent will likely default to Tk	99	# .. AnyEvent will likely default to Tk
		100
		101	The I<likely> means that, if any module loads another event model and
		102	starts using it, all bets are off. Maybe you should tell their authors to
		103	use AnyEvent so their modules work together with others seamlessly...
49		104
50	The pure-perl implementation of AnyEvent is called	105	The pure-perl implementation of AnyEvent is called
51	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
52	explicitly.	107	explicitly.
53		108
…		…
56	AnyEvent has the central concept of a I<watcher>, which is an object that	111	AnyEvent has the central concept of a I<watcher>, which is an object that
57	stores relevant data for each kind of event you are waiting for, such as	112	stores relevant data for each kind of event you are waiting for, such as
58	the callback to call, the filehandle to watch, etc.	113	the callback to call, the filehandle to watch, etc.
59		114
60	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
61	creating a watcher it will immediately "watch" for events and invoke	116	creating a watcher it will immediately "watch" for events and invoke the
		117	callback when the event occurs (of course, only when the event model
		118	is in control).
		119
62	the callback. To disable the watcher you have to destroy it (e.g. by	120	To disable the watcher you have to destroy it (e.g. by setting the
63	setting the variable that stores it to C<undef> or otherwise deleting all	121	variable you store it in to C<undef> or otherwise deleting all references
64	references to it).	122	to it).
65		123
66	All watchers are created by calling a method on the C<AnyEvent> class.	124	All watchers are created by calling a method on the C<AnyEvent> class.
67		125
		126	Many watchers either are used with "recursion" (repeating timers for
		127	example), or need to refer to their watcher object in other ways.
		128
		129	An any way to achieve that is this pattern:
		130
		131	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		132	# you can use $w here, for example to undef it
		133	undef $w;
		134	});
		135
		136	Note that C<my $w; $w => combination. This is necessary because in Perl,
		137	my variables are only visible after the statement in which they are
		138	declared.
		139
68	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
69		141
70	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
71	the following mandatory arguments:	143	with the following mandatory key-value pairs as arguments:
72		144
73	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
74	events. C<poll> must be a string that is either C<r> or C<w>, that creates	146	for events. C<poll> must be a string that is either C<r> or C<w>,
75	a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
76	to invoke everytime the filehandle becomes ready.	148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
77		150
78	Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on	151	Although the callback might get passed parameters, their value and
79	a socket you can have one r + one w, not any more (limitation comes from	152	presence is undefined and you cannot rely on them. Portable AnyEvent
80	Tk - if you are sure you are not using Tk this limitation is gone).	153	callbacks cannot use arguments passed to I/O watcher callbacks.
81		154
82	Filehandles will be kept alive, so as long as the watcher exists, the	155	The I/O watcher might use the underlying file descriptor or a copy of it.
83	filehandle exists, too.	156	You must not close a file handle as long as any watcher is active on the
		157	underlying file descriptor.
		158
		159	Some event loops issue spurious readyness notifications, so you should
		160	always use non-blocking calls when reading/writing from/to your file
		161	handles.
84		162
85	Example:	163	Example:
86		164
87	# wait for readability of STDIN, then read a line and disable the watcher	165	# wait for readability of STDIN, then read a line and disable the watcher
88	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
89	chomp (my $input = <STDIN>);	167	chomp (my $input = <STDIN>);
90	warn "read: $input\n";	168	warn "read: $input\n";
91	undef $w;	169	undef $w;
92	});	170	});
93		171
94	=head2 TIMER WATCHERS	172	=head2 TIME WATCHERS
95		173
96	You can create a timer watcher by calling the C<< AnyEvent->timer >>	174	You can create a time watcher by calling the C<< AnyEvent->timer >>
97	method with the following mandatory arguments:	175	method with the following mandatory arguments:
98		176
99	C<after> after how many seconds (fractions are supported) should the timer	177	C<after> specifies after how many seconds (fractional values are
100	activate. C<cb> the callback to invoke.	178	supported) the callback should be invoked. C<cb> is the callback to invoke
		179	in that case.
		180
		181	Although the callback might get passed parameters, their value and
		182	presence is undefined and you cannot rely on them. Portable AnyEvent
		183	callbacks cannot use arguments passed to time watcher callbacks.
101		184
102	The timer callback will be invoked at most once: if you want a repeating	185	The timer callback will be invoked at most once: if you want a repeating
103	timer you have to create a new watcher (this is a limitation by both Tk	186	timer you have to create a new watcher (this is a limitation by both Tk
104	and Glib).	187	and Glib).
105		188
…		…
109	my $w = AnyEvent->timer (after => 7.7, cb => sub {	192	my $w = AnyEvent->timer (after => 7.7, cb => sub {
110	warn "timeout\n";	193	warn "timeout\n";
111	});	194	});
112		195
113	# to cancel the timer:	196	# to cancel the timer:
114	undef $w	197	undef $w;
115		198
		199	Example 2:
		200
		201	# fire an event after 0.5 seconds, then roughly every second
		202	my $w;
		203
		204	my $cb = sub {
		205	# cancel the old timer while creating a new one
		206	$w = AnyEvent->timer (after => 1, cb => $cb);
		207	};
		208
		209	# start the "loop" by creating the first watcher
		210	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		211
		212	=head3 TIMING ISSUES
		213
		214	There are two ways to handle timers: based on real time (relative, "fire
		215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		216	o'clock").
		217
		218	While most event loops expect timers to specified in a relative way, they
		219	use absolute time internally. This makes a difference when your clock
		220	"jumps", for example, when ntp decides to set your clock backwards from
		221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		222	fire "after" a second might actually take six years to finally fire.
		223
		224	AnyEvent cannot compensate for this. The only event loop that is conscious
		225	about these issues is L<EV>, which offers both relative (ev_timer, based
		226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
		228
		229	AnyEvent always prefers relative timers, if available, matching the
		230	AnyEvent API.
		231
		232	=head2 SIGNAL WATCHERS
		233
		234	You can watch for signals using a signal watcher, C<signal> is the signal
		235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		236	be invoked whenever a signal occurs.
		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
		242	Multiple signal occurances 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 guarenteed 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	AnyEvent::detect; # force event module to be initialised
		285
		286	my $pid = fork or exit 5;
		287
		288	my $w = AnyEvent->child (
		289	pid => $pid,
		290	cb => sub {
		291	my ($pid, $status) = @_;
		292	warn "pid $pid exited with status $status";
		293	$done->broadcast;
		294	},
		295	);
		296
		297	# do something else, then wait for process exit
		298	$done->wait;
		299
116	=head2 CONDITION WATCHERS	300	=head2 CONDITION VARIABLES
117		301
		302	If you are familiar with some event loops you will know that all of them
		303	require you to run some blocking "loop", "run" or similar function that
		304	will actively watch for new events and call your callbacks.
		305
		306	AnyEvent is different, it expects somebody else to run the event loop and
		307	will only block when necessary (usually when told by the user).
		308
		309	The instrument to do that is called a "condition variable", so called
		310	because they represent a condition that must become true.
		311
118	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	312	Condition variables can be created by calling the C<< AnyEvent->condvar
119	method without any arguments.	313	>> method, usually without arguments. The only argument pair allowed is
		314	C<cb>, which specifies a callback to be called when the condition variable
		315	becomes true.
120		316
121	A condition watcher watches for a condition - precisely that the C<<	317	After creation, the conditon variable is "false" until it becomes "true"
122	->broadcast >> method has been called.	318	by calling the C<broadcast> method.
123		319
124	The watcher has only two methods:	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 outstandign events have been processed. And yet
		323	another way to call them is transations - each condition variable can be
		324	used to represent a transaction, which finishes at some point and delivers
		325	a result.
125		326
126	=over 4	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<< ->wait >> for the results.
127		332
128	=item $cv->wait	333	You can also use them to simulate traditional event loops - for example,
		334	you can block your main program until an event occurs - for example, you
		335	could C<< ->wait >> in your main program until the user clicks the Quit
		336	button of your app, which would C<< ->broadcast >> the "quit" event.
129		337
130	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	338	Note that condition variables recurse into the event loop - if you have
131	called on c<$cv>, while servicing other watchers normally.	339	two pieces of code that call C<< ->wait >> in a round-robbin fashion, you
		340	lose. Therefore, condition variables are good to export to your caller, but
		341	you should avoid making a blocking wait yourself, at least in callbacks,
		342	as this asks for trouble.
132		343
133	Not all event models support a blocking wait - some die in that case, so	344	Condition variables are represented by hash refs in perl, and the keys
134	if you are using this from a module, never require a blocking wait, but	345	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
135	let the caller decide wether the call will block or not (for example,	346	easy (it is often useful to build your own transaction class on top of
136	by coupling condition variables with some kind of request results and	347	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
137	supporting callbacks so the caller knows that getting the result will not	348	it's C<new> method in your own C<new> method.
138	block, while still suppporting blockign waits if the caller so desires).
139		349
140	You can only wait once on a condition - additional calls will return	350	There are two "sides" to a condition variable - the "producer side" which
141	immediately.	351	eventually calls C<< -> broadcast >>, and the "consumer side", which waits
142		352	for the broadcast to occur.
143	=item $cv->broadcast
144
145	Flag the condition as ready - a running C<< ->wait >> and all further
146	calls to C<wait> will return after this method has been called. If nobody
147	is waiting the broadcast will be remembered..
148		353
149	Example:	354	Example:
150		355
151	# wait till the result is ready	356	# wait till the result is ready
152	my $result_ready = AnyEvent->condvar;	357	my $result_ready = AnyEvent->condvar;
153		358
154	# do something such as adding a timer	359	# do something such as adding a timer
155	# or socket watcher the calls $result_ready->broadcast	360	# or socket watcher the calls $result_ready->broadcast
156	# 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->broadcast },
		366	);
157		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls broadcast
158	$result_ready->wait;	370	$result_ready->wait;
159		371
		372	=head3 METHODS FOR PRODUCERS
		373
		374	These methods should only be used by the producing side, i.e. the
		375	code/module that eventually broadcasts the signal. Note that it is also
		376	the producer side which creates the condvar in most cases, but it isn't
		377	uncommon for the consumer to create it as well.
		378
		379	=over 4
		380
		381	=item $cv->broadcast (...)
		382
		383	Flag the condition as ready - a running C<< ->wait >> and all further
		384	calls to C<wait> will (eventually) return after this method has been
		385	called. If nobody is waiting the broadcast will be remembered.
		386
		387	If a callback has been set on the condition variable, it is called
		388	immediately from within broadcast.
		389
		390	Any arguments passed to the C<broadcast> call will be returned by all
		391	future C<< ->wait >> calls.
		392
		393	=item $cv->croak ($error)
		394
		395	Similar to broadcast, but causes all call's wait C<< ->wait >> to invoke
		396	C<Carp::croak> with the given error message/object/scalar.
		397
		398	This can be used to signal any errors to the condition variable
		399	user/consumer.
		400
		401	=item $cv->begin ([group callback])
		402
		403	=item $cv->end
		404
		405	These two methods can be used to combine many transactions/events into
		406	one. For example, a function that pings many hosts in parallel might want
		407	to use a condition variable for the whole process.
		408
		409	Every call to C<< ->begin >> will increment a counter, and every call to
		410	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		411	>>, the (last) callback passed to C<begin> will be executed. That callback
		412	is I<supposed> to call C<< ->broadcast >>, but that is not required. If no
		413	callback was set, C<broadcast> will be called without any arguments.
		414
		415	Let's clarify this with the ping example:
		416
		417	my $cv = AnyEvent->condvar;
		418
		419	my %result;
		420	$cv->begin (sub { $cv->broadcast (\%result) });
		421
		422	for my $host (@list_of_hosts) {
		423	$cv->begin;
		424	ping_host_then_call_callback $host, sub {
		425	$result{$host} = ...;
		426	$cv->end;
		427	};
		428	}
		429
		430	$cv->end;
		431
		432	This code fragment supposedly pings a number of hosts and calls
		433	C<broadcast> after results for all then have have been gathered - in any
		434	order. To achieve this, the code issues a call to C<begin> when it starts
		435	each ping request and calls C<end> when it has received some result for
		436	it. Since C<begin> and C<end> only maintain a counter, the order in which
		437	results arrive is not relevant.
		438
		439	There is an additional bracketing call to C<begin> and C<end> outside the
		440	loop, which serves two important purposes: first, it sets the callback
		441	to be called once the counter reaches C<0>, and second, it ensures that
		442	broadcast is called even when C<no> hosts are being pinged (the loop
		443	doesn't execute once).
		444
		445	This is the general pattern when you "fan out" into multiple subrequests:
		446	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		447	is called at least once, and then, for each subrequest you start, call
		448	C<begin> and for eahc subrequest you finish, call C<end>.
		449
160	=back	450	=back
161		451
		452	=head3 METHODS FOR CONSUMERS
		453
		454	These methods should only be used by the consuming side, i.e. the
		455	code awaits the condition.
		456
		457	=item $cv->wait
		458
		459	Wait (blocking if necessary) until the C<< ->broadcast >> or C<< ->croak
		460	>> methods have been called on c<$cv>, while servicing other watchers
		461	normally.
		462
		463	You can only wait once on a condition - additional calls are valid but
		464	will return immediately.
		465
		466	If an error condition has been set by calling C<< ->croak >>, then this
		467	function will call C<croak>.
		468
		469	In list context, all parameters passed to C<broadcast> will be returned,
		470	in scalar context only the first one will be returned.
		471
		472	Not all event models support a blocking wait - some die in that case
		473	(programs might want to do that to stay interactive), so I<if you are
		474	using this from a module, never require a blocking wait>, but let the
		475	caller decide whether the call will block or not (for example, by coupling
		476	condition variables with some kind of request results and supporting
		477	callbacks so the caller knows that getting the result will not block,
		478	while still suppporting blocking waits if the caller so desires).
		479
		480	Another reason I<never> to C<< ->wait >> in a module is that you cannot
		481	sensibly have two C<< ->wait >>'s in parallel, as that would require
		482	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		483	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
		484	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
		485	from different coroutines, however).
		486
		487	You can ensure that C<< -wait >> never blocks by setting a callback and
		488	only calling C<< ->wait >> from within that callback (or at a later
		489	time). This will work even when the event loop does not support blocking
		490	waits otherwise.
		491
		492	=back
		493
		494	=head1 GLOBAL VARIABLES AND FUNCTIONS
		495
		496	=over 4
		497
		498	=item $AnyEvent::MODEL
		499
		500	Contains C<undef> until the first watcher is being created. Then it
		501	contains the event model that is being used, which is the name of the
		502	Perl class implementing the model. This class is usually one of the
		503	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		504	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		505
		506	The known classes so far are:
		507
		508	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
		509	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
		510	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		511	AnyEvent::Impl::Event based on Event, second best choice.
		512	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		513	AnyEvent::Impl::Glib based on Glib, third-best choice.
		514	AnyEvent::Impl::Tk based on Tk, very bad choice.
		515	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		516	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		517	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		518
		519	There is no support for WxWidgets, as WxWidgets has no support for
		520	watching file handles. However, you can use WxWidgets through the
		521	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		522	second, which was considered to be too horrible to even consider for
		523	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		524	it's adaptor.
		525
		526	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		527	autodetecting them.
		528
		529	=item AnyEvent::detect
		530
		531	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		532	if necessary. You should only call this function right before you would
		533	have created an AnyEvent watcher anyway, that is, as late as possible at
		534	runtime.
		535
		536	=back
		537
162	=head1 WHAT TO DO IN A MODULE	538	=head1 WHAT TO DO IN A MODULE
163		539
164	As a module author, you should "use AnyEvent" and call AnyEvent methods	540	As a module author, you should C<use AnyEvent> and call AnyEvent methods
165	freely, but you should not load a specific event module or rely on it.	541	freely, but you should not load a specific event module or rely on it.
166		542
167	Be careful when you create watchers in the module body - Anyevent will	543	Be careful when you create watchers in the module body - AnyEvent will
168	decide which event module to use as soon as the first method is called, so	544	decide which event module to use as soon as the first method is called, so
169	by calling AnyEvent in your module body you force the user of your module	545	by calling AnyEvent in your module body you force the user of your module
170	to load the event module first.	546	to load the event module first.
171		547
		548	Never call C<< ->wait >> on a condition variable unless you I<know> that
		549	the C<< ->broadcast >> method has been called on it already. This is
		550	because it will stall the whole program, and the whole point of using
		551	events is to stay interactive.
		552
		553	It is fine, however, to call C<< ->wait >> when the user of your module
		554	requests it (i.e. if you create a http request object ad have a method
		555	called C<results> that returns the results, it should call C<< ->wait >>
		556	freely, as the user of your module knows what she is doing. always).
		557
172	=head1 WHAT TO DO IN THE MAIN PROGRAM	558	=head1 WHAT TO DO IN THE MAIN PROGRAM
173		559
174	There will always be a single main program - the only place that should	560	There will always be a single main program - the only place that should
175	dictate which event model to use.	561	dictate which event model to use.
176		562
177	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	563	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
178	do anything special and let AnyEvent decide which implementation to chose.	564	do anything special (it does not need to be event-based) and let AnyEvent
		565	decide which implementation to chose if some module relies on it.
179		566
180	If the main program relies on a specific event model (for example, in Gtk2	567	If the main program relies on a specific event model. For example, in
181	programs you have to rely on either Glib or Glib::Event), you should load	568	Gtk2 programs you have to rely on the Glib module. You should load the
182	it before loading AnyEvent or any module that uses it, generally, as early	569	event module before loading AnyEvent or any module that uses it: generally
183	as possible. The reason is that modules might create watchers when they	570	speaking, you should load it as early as possible. The reason is that
184	are loaded, and AnyEvent will decide on the event model to use as soon as	571	modules might create watchers when they are loaded, and AnyEvent will
185	it creates watchers, and it might chose the wrong one unless you load the	572	decide on the event model to use as soon as it creates watchers, and it
186	correct one yourself.	573	might chose the wrong one unless you load the correct one yourself.
187		574
188	You can chose to use a rather inefficient pure-perl implementation by	575	You can chose to use a rather inefficient pure-perl implementation by
189	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	576	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
190	generally better.	577	behaviour everywhere, but letting AnyEvent chose is generally better.
		578
		579	=head1 OTHER MODULES
		580
		581	The following is a non-exhaustive list of additional modules that use
		582	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		583	in the same program. Some of the modules come with AnyEvent, some are
		584	available via CPAN.
		585
		586	=over 4
		587
		588	=item L<AnyEvent::Util>
		589
		590	Contains various utility functions that replace often-used but blocking
		591	functions such as C<inet_aton> by event-/callback-based versions.
		592
		593	=item L<AnyEvent::Handle>
		594
		595	Provide read and write buffers and manages watchers for reads and writes.
		596
		597	=item L<AnyEvent::Socket>
		598
		599	Provides a means to do non-blocking connects, accepts etc.
		600
		601	=item L<AnyEvent::HTTPD>
		602
		603	Provides a simple web application server framework.
		604
		605	=item L<AnyEvent::DNS>
		606
		607	Provides asynchronous DNS resolver capabilities, beyond what
		608	L<AnyEvent::Util> offers.
		609
		610	=item L<AnyEvent::FastPing>
		611
		612	The fastest ping in the west.
		613
		614	=item L<Net::IRC3>
		615
		616	AnyEvent based IRC client module family.
		617
		618	=item L<Net::XMPP2>
		619
		620	AnyEvent based XMPP (Jabber protocol) module family.
		621
		622	=item L<Net::FCP>
		623
		624	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		625	of AnyEvent.
		626
		627	=item L<Event::ExecFlow>
		628
		629	High level API for event-based execution flow control.
		630
		631	=item L<Coro>
		632
		633	Has special support for AnyEvent.
		634
		635	=item L<IO::Lambda>
		636
		637	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		638
		639	=item L<IO::AIO>
		640
		641	Truly asynchronous I/O, should be in the toolbox of every event
		642	programmer. Can be trivially made to use AnyEvent.
		643
		644	=item L<BDB>
		645
		646	Truly asynchronous Berkeley DB access. Can be trivially made to use
		647	AnyEvent.
		648
		649	=back
191		650
192	=cut	651	=cut
193		652
194	package AnyEvent;	653	package AnyEvent;
195		654
196	no warnings;	655	no warnings;
197	use strict 'vars';	656	use strict;
		657
198	use Carp;	658	use Carp;
199		659
200	our $VERSION = '2.0';	660	our $VERSION = '3.3';
201	our $MODEL;	661	our $MODEL;
202		662
203	our $AUTOLOAD;	663	our $AUTOLOAD;
204	our @ISA;	664	our @ISA;
205		665
206	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	666	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
207		667
208	our @REGISTRY;	668	our @REGISTRY;
209		669
210	my @models = (	670	my @models = (
		671	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
211	[Coro::Event:: => AnyEvent::Impl::Coro::],	672	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
		673	[EV:: => AnyEvent::Impl::EV::],
212	[Event:: => AnyEvent::Impl::Event::],	674	[Event:: => AnyEvent::Impl::Event::],
213	[Glib:: => AnyEvent::Impl::Glib::],
214	[Tk:: => AnyEvent::Impl::Tk::],	675	[Tk:: => AnyEvent::Impl::Tk::],
		676	[Wx:: => AnyEvent::Impl::POE::],
		677	[Prima:: => AnyEvent::Impl::POE::],
215	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	678	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		679	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		680	[Glib:: => AnyEvent::Impl::Glib::],
		681	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		682	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		683	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
216	);	684	);
217		685
218	our %method = map +($_ => 1), qw(io timer condvar broadcast wait DESTROY);	686	our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);
219		687
220	sub AUTOLOAD {	688	sub detect() {
221	$AUTOLOAD =~ s/.*://;
222
223	$method{$AUTOLOAD}
224	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";
225
226	unless ($MODEL) {	689	unless ($MODEL) {
		690	no strict 'refs';
		691
		692	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		693	my $model = "AnyEvent::Impl::$1";
		694	if (eval "require $model") {
		695	$MODEL = $model;
		696	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		697	} else {
		698	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		699	}
		700	}
		701
227	# check for already loaded models	702	# check for already loaded models
		703	unless ($MODEL) {
228	for (@REGISTRY, @models) {	704	for (@REGISTRY, @models) {
229	my ($package, $model) = @$_;	705	my ($package, $model) = @$_;
230	if (${"$package\::VERSION"} > 0) {	706	if (${"$package\::VERSION"} > 0) {
231	if (eval "require $model") {	707	if (eval "require $model") {
232	$MODEL = $model;	708	$MODEL = $model;
233	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	709	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
234	last;	710	last;
		711	}
235	}	712	}
236	}	713	}
		714
		715	unless ($MODEL) {
		716	# try to load a model
		717
		718	for (@REGISTRY, @models) {
		719	my ($package, $model) = @$_;
		720	if (eval "require $package"
		721	and ${"$package\::VERSION"} > 0
		722	and eval "require $model") {
		723	$MODEL = $model;
		724	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		725	last;
		726	}
		727	}
		728
		729	$MODEL
		730	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";
		731	}
237	}	732	}
238		733
239	unless ($MODEL) {	734	unshift @ISA, $MODEL;
240	# try to load a model	735	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
241
242	for (@REGISTRY, @models) {
243	my ($package, $model) = @$_;
244	if (eval "require $model") {
245	$MODEL = $model;
246	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
247	last;
248	}
249	}
250
251	$MODEL
252	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";
253	}
254	}	736	}
255		737
256	@ISA = $MODEL;	738	$MODEL
		739	}
		740
		741	sub AUTOLOAD {
		742	(my $func = $AUTOLOAD) =~ s/.*://;
		743
		744	$method{$func}
		745	or croak "$func: not a valid method for AnyEvent objects";
		746
		747	detect unless $MODEL;
257		748
258	my $class = shift;	749	my $class = shift;
259	$class->$AUTOLOAD (@_);	750	$class->$func (@_);
260	}	751	}
261		752
		753	package AnyEvent::Base;
		754
		755	# default implementation for ->condvar, ->wait, ->broadcast
		756
		757	sub condvar {
		758	bless \my $flag, "AnyEvent::Base::CondVar"
		759	}
		760
		761	sub AnyEvent::Base::CondVar::broadcast {
		762	${$_[0]}++;
		763	}
		764
		765	sub AnyEvent::Base::CondVar::wait {
		766	AnyEvent->one_event while !${$_[0]};
		767	}
		768
		769	# default implementation for ->signal
		770
		771	our %SIG_CB;
		772
		773	sub signal {
		774	my (undef, %arg) = @_;
		775
		776	my $signal = uc $arg{signal}
		777	or Carp::croak "required option 'signal' is missing";
		778
		779	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		780	$SIG{$signal} ||= sub {
		781	$_->() for values %{ $SIG_CB{$signal} || {} };
		782	};
		783
		784	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		785	}
		786
		787	sub AnyEvent::Base::Signal::DESTROY {
		788	my ($signal, $cb) = @{$_[0]};
		789
		790	delete $SIG_CB{$signal}{$cb};
		791
		792	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		793	}
		794
		795	# default implementation for ->child
		796
		797	our %PID_CB;
		798	our $CHLD_W;
		799	our $CHLD_DELAY_W;
		800	our $PID_IDLE;
		801	our $WNOHANG;
		802
		803	sub _child_wait {
		804	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		805	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		806	(values %{ $PID_CB{0} || {} });
		807	}
		808
		809	undef $PID_IDLE;
		810	}
		811
		812	sub _sigchld {
		813	# make sure we deliver these changes "synchronous" with the event loop.
		814	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		815	undef $CHLD_DELAY_W;
		816	&_child_wait;
		817	});
		818	}
		819
		820	sub child {
		821	my (undef, %arg) = @_;
		822
		823	defined (my $pid = $arg{pid} + 0)
		824	or Carp::croak "required option 'pid' is missing";
		825
		826	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		827
		828	unless ($WNOHANG) {
		829	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		830	}
		831
		832	unless ($CHLD_W) {
		833	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		834	# child could be a zombie already, so make at least one round
		835	&_sigchld;
		836	}
		837
		838	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		839	}
		840
		841	sub AnyEvent::Base::Child::DESTROY {
		842	my ($pid, $cb) = @{$_[0]};
		843
		844	delete $PID_CB{$pid}{$cb};
		845	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		846
		847	undef $CHLD_W unless keys %PID_CB;
		848	}
		849
262	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	850	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		851
		852	This is an advanced topic that you do not normally need to use AnyEvent in
		853	a module. This section is only of use to event loop authors who want to
		854	provide AnyEvent compatibility.
263		855
264	If you need to support another event library which isn't directly	856	If you need to support another event library which isn't directly
265	supported by AnyEvent, you can supply your own interface to it by	857	supported by AnyEvent, you can supply your own interface to it by
266	pushing, before the first watcher gets created, the package name of	858	pushing, before the first watcher gets created, the package name of
267	the event module and the package name of the interface to use onto	859	the event module and the package name of the interface to use onto
268	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	860	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
269	AnyEvent.	861	AnyEvent, so it is reasonably cheap.
270		862
271	Example:	863	Example:
272		864
273	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	865	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
274		866
275	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	867	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
276	package/class when it finds the C<urxvt> package/module is loaded. When	868	package/class when it finds the C<urxvt> package/module is already loaded.
		869
277	AnyEvent is loaded and asked to find a suitable event model, it will	870	When AnyEvent is loaded and asked to find a suitable event model, it
278	first check for the presence of urxvt.	871	will first check for the presence of urxvt by trying to C<use> the
		872	C<urxvt::anyevent> module.
279		873
280	The class should prove implementations for all watcher types (see	874	The class should provide implementations for all watcher types. See
281	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	875	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
282	(Source code) and so on for actual examples, use C<perldoc -m	876	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
283	AnyEvent::Impl::Glib> to see the sources).	877	see the sources.
284		878
		879	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		880	provide suitable (hopefully) replacements.
		881
285	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	882	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
286	uses the above line as-is. An interface isn't included in AnyEvent	883	terminal emulator uses the above line as-is. An interface isn't included
287	because it doesn't make sense outside the embedded interpreter inside	884	in AnyEvent because it doesn't make sense outside the embedded interpreter
288	I<rxvt-unicode>, and it is updated and maintained as part of the	885	inside I<rxvt-unicode>, and it is updated and maintained as part of the
289	I<rxvt-unicode> distribution.	886	I<rxvt-unicode> distribution.
290		887
291	I<rxvt-unicode> also cheats a bit by not providing blocking access to	888	I<rxvt-unicode> also cheats a bit by not providing blocking access to
292	condition variables: code blocking while waiting for a condition will	889	condition variables: code blocking while waiting for a condition will
293	C<die>. This still works with most modules/usages, and blocking calls must	890	C<die>. This still works with most modules/usages, and blocking calls must
294	not be in an interactive appliation, so it makes sense.	891	not be done in an interactive application, so it makes sense.
295		892
296	=head1 ENVIRONMENT VARIABLES	893	=head1 ENVIRONMENT VARIABLES
297		894
298	The following environment variables are used by this module:	895	The following environment variables are used by this module:
299		896
300	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	897	=over 4
301	model gets used.
302		898
		899	=item C<PERL_ANYEVENT_VERBOSE>
		900
		901	By default, AnyEvent will be completely silent except in fatal
		902	conditions. You can set this environment variable to make AnyEvent more
		903	talkative.
		904
		905	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		906	conditions, such as not being able to load the event model specified by
		907	C<PERL_ANYEVENT_MODEL>.
		908
		909	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		910	model it chooses.
		911
		912	=item C<PERL_ANYEVENT_MODEL>
		913
		914	This can be used to specify the event model to be used by AnyEvent, before
		915	autodetection and -probing kicks in. It must be a string consisting
		916	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		917	and the resulting module name is loaded and if the load was successful,
		918	used as event model. If it fails to load AnyEvent will proceed with
		919	autodetection and -probing.
		920
		921	This functionality might change in future versions.
		922
		923	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		924	could start your program like this:
		925
		926	PERL_ANYEVENT_MODEL=Perl perl ...
		927
		928	=back
		929
303	=head1 EXAMPLE	930	=head1 EXAMPLE PROGRAM
304		931
305	The following program uses an io watcher to read data from stdin, a timer	932	The following program uses an I/O watcher to read data from STDIN, a timer
306	to display a message once per second, and a condvar to exit the program	933	to display a message once per second, and a condition variable to quit the
307	when the user enters quit:	934	program when the user enters quit:
308		935
309	use AnyEvent;	936	use AnyEvent;
310		937
311	my $cv = AnyEvent->condvar;	938	my $cv = AnyEvent->condvar;
312		939
313	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	940	my $io_watcher = AnyEvent->io (
		941	fh => \*STDIN,
		942	poll => 'r',
		943	cb => sub {
314	warn "io event <$_[0]>\n"; # will always output <r>	944	warn "io event <$_[0]>\n"; # will always output <r>
315	chomp (my $input = <STDIN>); # read a line	945	chomp (my $input = <STDIN>); # read a line
316	warn "read: $input\n"; # output what has been read	946	warn "read: $input\n"; # output what has been read
317	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	947	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		948	},
318	});	949	);
319		950
320	my $time_watcher; # can only be used once	951	my $time_watcher; # can only be used once
321		952
322	sub new_timer {	953	sub new_timer {
323	$timer = AnyEvent->timer (after => 1, cb => sub {	954	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
405	$txn->{finished}->wait;	1036	$txn->{finished}->wait;
406	return $txn->{result};	1037	return $txn->{result};
407		1038
408	The actual code goes further and collects all errors (C<die>s, exceptions)	1039	The actual code goes further and collects all errors (C<die>s, exceptions)
409	that occured during request processing. The C<result> method detects	1040	that occured during request processing. The C<result> method detects
410	wether an exception as thrown (it is stored inside the $txn object)	1041	whether an exception as thrown (it is stored inside the $txn object)
411	and just throws the exception, which means connection errors and other	1042	and just throws the exception, which means connection errors and other
412	problems get reported tot he code that tries to use the result, not in a	1043	problems get reported tot he code that tries to use the result, not in a
413	random callback.	1044	random callback.
414		1045
415	All of this enables the following usage styles:	1046	All of this enables the following usage styles:
416		1047
417	1. Blocking:	1048	1. Blocking:
418		1049
419	my $data = $fcp->client_get ($url);	1050	my $data = $fcp->client_get ($url);
420		1051
421	2. Blocking, but parallelizing:	1052	2. Blocking, but running in parallel:
422		1053
423	my @datas = map $_->result,	1054	my @datas = map $_->result,
424	map $fcp->txn_client_get ($_),	1055	map $fcp->txn_client_get ($_),
425	@urls;	1056	@urls;
426		1057
427	Both blocking examples work without the module user having to know	1058	Both blocking examples work without the module user having to know
428	anything about events.	1059	anything about events.
429		1060
430	3a. Event-based in a main program, using any support Event module:	1061	3a. Event-based in a main program, using any supported event module:
431		1062
432	use Event;	1063	use EV;
433		1064
434	$fcp->txn_client_get ($url)->cb (sub {	1065	$fcp->txn_client_get ($url)->cb (sub {
435	my $txn = shift;	1066	my $txn = shift;
436	my $data = $txn->result;	1067	my $data = $txn->result;
437	...	1068	...
438	});	1069	});
439		1070
440	Event::loop;	1071	EV::loop;
441		1072
442	3b. The module user could use AnyEvent, too:	1073	3b. The module user could use AnyEvent, too:
443		1074
444	use AnyEvent;	1075	use AnyEvent;
445		1076
…		…
450	$quit->broadcast;	1081	$quit->broadcast;
451	});	1082	});
452		1083
453	$quit->wait;	1084	$quit->wait;
454		1085
		1086
		1087	=head1 BENCHMARKS
		1088
		1089	To give you an idea of the performance and overheads that AnyEvent adds
		1090	over the event loops themselves and to give you an impression of the speed
		1091	of various event loops I prepared some benchmarks.
		1092
		1093	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1094
		1095	Here is a benchmark of various supported event models used natively and
		1096	through anyevent. The benchmark creates a lot of timers (with a zero
		1097	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1098	which it is), lets them fire exactly once and destroys them again.
		1099
		1100	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1101	distribution.
		1102
		1103	=head3 Explanation of the columns
		1104
		1105	I<watcher> is the number of event watchers created/destroyed. Since
		1106	different event models feature vastly different performances, each event
		1107	loop was given a number of watchers so that overall runtime is acceptable
		1108	and similar between tested event loop (and keep them from crashing): Glib
		1109	would probably take thousands of years if asked to process the same number
		1110	of watchers as EV in this benchmark.
		1111
		1112	I<bytes> is the number of bytes (as measured by the resident set size,
		1113	RSS) consumed by each watcher. This method of measuring captures both C
		1114	and Perl-based overheads.
		1115
		1116	I<create> is the time, in microseconds (millionths of seconds), that it
		1117	takes to create a single watcher. The callback is a closure shared between
		1118	all watchers, to avoid adding memory overhead. That means closure creation
		1119	and memory usage is not included in the figures.
		1120
		1121	I<invoke> is the time, in microseconds, used to invoke a simple
		1122	callback. The callback simply counts down a Perl variable and after it was
		1123	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1124	signal the end of this phase.
		1125
		1126	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1127	watcher.
		1128
		1129	=head3 Results
		1130
		1131	name watchers bytes create invoke destroy comment
		1132	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1133	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1134	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1135	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1136	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1137	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1138	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1139	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1140	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1141	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1142
		1143	=head3 Discussion
		1144
		1145	The benchmark does I<not> measure scalability of the event loop very
		1146	well. For example, a select-based event loop (such as the pure perl one)
		1147	can never compete with an event loop that uses epoll when the number of
		1148	file descriptors grows high. In this benchmark, all events become ready at
		1149	the same time, so select/poll-based implementations get an unnatural speed
		1150	boost.
		1151
		1152	Also, note that the number of watchers usually has a nonlinear effect on
		1153	overall speed, that is, creating twice as many watchers doesn't take twice
		1154	the time - usually it takes longer. This puts event loops tested with a
		1155	higher number of watchers at a disadvantage.
		1156
		1157	To put the range of results into perspective, consider that on the
		1158	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1159	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1160	cycles with POE.
		1161
		1162	C<EV> is the sole leader regarding speed and memory use, which are both
		1163	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1164	far less memory than any other event loop and is still faster than Event
		1165	natively.
		1166
		1167	The pure perl implementation is hit in a few sweet spots (both the
		1168	constant timeout and the use of a single fd hit optimisations in the perl
		1169	interpreter and the backend itself). Nevertheless this shows that it
		1170	adds very little overhead in itself. Like any select-based backend its
		1171	performance becomes really bad with lots of file descriptors (and few of
		1172	them active), of course, but this was not subject of this benchmark.
		1173
		1174	The C<Event> module has a relatively high setup and callback invocation
		1175	cost, but overall scores in on the third place.
		1176
		1177	C<Glib>'s memory usage is quite a bit higher, but it features a
		1178	faster callback invocation and overall ends up in the same class as
		1179	C<Event>. However, Glib scales extremely badly, doubling the number of
		1180	watchers increases the processing time by more than a factor of four,
		1181	making it completely unusable when using larger numbers of watchers
		1182	(note that only a single file descriptor was used in the benchmark, so
		1183	inefficiencies of C<poll> do not account for this).
		1184
		1185	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1186	more than 2000 watchers is a big setback, however, as correctness takes
		1187	precedence over speed. Nevertheless, its performance is surprising, as the
		1188	file descriptor is dup()ed for each watcher. This shows that the dup()
		1189	employed by some adaptors is not a big performance issue (it does incur a
		1190	hidden memory cost inside the kernel which is not reflected in the figures
		1191	above).
		1192
		1193	C<POE>, regardless of underlying event loop (whether using its pure perl
		1194	select-based backend or the Event module, the POE-EV backend couldn't
		1195	be tested because it wasn't working) shows abysmal performance and
		1196	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1197	as EV watchers, and 10 times as much memory as Event (the high memory
		1198	requirements are caused by requiring a session for each watcher). Watcher
		1199	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1200	implementation.
		1201
		1202	The design of the POE adaptor class in AnyEvent can not really account
		1203	for the performance issues, though, as session creation overhead is
		1204	small compared to execution of the state machine, which is coded pretty
		1205	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1206	using multiple sessions is not a good approach, especially regarding
		1207	memory usage, even the author of POE could not come up with a faster
		1208	design).
		1209
		1210	=head3 Summary
		1211
		1212	=over 4
		1213
		1214	=item * Using EV through AnyEvent is faster than any other event loop
		1215	(even when used without AnyEvent), but most event loops have acceptable
		1216	performance with or without AnyEvent.
		1217
		1218	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1219	the actual event loop, only with extremely fast event loops such as EV
		1220	adds AnyEvent significant overhead.
		1221
		1222	=item * You should avoid POE like the plague if you want performance or
		1223	reasonable memory usage.
		1224
		1225	=back
		1226
		1227	=head2 BENCHMARKING THE LARGE SERVER CASE
		1228
		1229	This benchmark atcually benchmarks the event loop itself. It works by
		1230	creating a number of "servers": each server consists of a socketpair, a
		1231	timeout watcher that gets reset on activity (but never fires), and an I/O
		1232	watcher waiting for input on one side of the socket. Each time the socket
		1233	watcher reads a byte it will write that byte to a random other "server".
		1234
		1235	The effect is that there will be a lot of I/O watchers, only part of which
		1236	are active at any one point (so there is a constant number of active
		1237	fds for each loop iterstaion, but which fds these are is random). The
		1238	timeout is reset each time something is read because that reflects how
		1239	most timeouts work (and puts extra pressure on the event loops).
		1240
		1241	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1242	(1%) are active. This mirrors the activity of large servers with many
		1243	connections, most of which are idle at any one point in time.
		1244
		1245	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1246	distribution.
		1247
		1248	=head3 Explanation of the columns
		1249
		1250	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1251	each server has a read and write socket end).
		1252
		1253	I<create> is the time it takes to create a socketpair (which is
		1254	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1255
		1256	I<request>, the most important value, is the time it takes to handle a
		1257	single "request", that is, reading the token from the pipe and forwarding
		1258	it to another server. This includes deleting the old timeout and creating
		1259	a new one that moves the timeout into the future.
		1260
		1261	=head3 Results
		1262
		1263	name sockets create request
		1264	EV 20000 69.01 11.16
		1265	Perl 20000 73.32 35.87
		1266	Event 20000 212.62 257.32
		1267	Glib 20000 651.16 1896.30
		1268	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1269
		1270	=head3 Discussion
		1271
		1272	This benchmark I<does> measure scalability and overall performance of the
		1273	particular event loop.
		1274
		1275	EV is again fastest. Since it is using epoll on my system, the setup time
		1276	is relatively high, though.
		1277
		1278	Perl surprisingly comes second. It is much faster than the C-based event
		1279	loops Event and Glib.
		1280
		1281	Event suffers from high setup time as well (look at its code and you will
		1282	understand why). Callback invocation also has a high overhead compared to
		1283	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1284	uses select or poll in basically all documented configurations.
		1285
		1286	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1287	clearly fails to perform with many filehandles or in busy servers.
		1288
		1289	POE is still completely out of the picture, taking over 1000 times as long
		1290	as EV, and over 100 times as long as the Perl implementation, even though
		1291	it uses a C-based event loop in this case.
		1292
		1293	=head3 Summary
		1294
		1295	=over 4
		1296
		1297	=item * The pure perl implementation performs extremely well.
		1298
		1299	=item * Avoid Glib or POE in large projects where performance matters.
		1300
		1301	=back
		1302
		1303	=head2 BENCHMARKING SMALL SERVERS
		1304
		1305	While event loops should scale (and select-based ones do not...) even to
		1306	large servers, most programs we (or I :) actually write have only a few
		1307	I/O watchers.
		1308
		1309	In this benchmark, I use the same benchmark program as in the large server
		1310	case, but it uses only eight "servers", of which three are active at any
		1311	one time. This should reflect performance for a small server relatively
		1312	well.
		1313
		1314	The columns are identical to the previous table.
		1315
		1316	=head3 Results
		1317
		1318	name sockets create request
		1319	EV 16 20.00 6.54
		1320	Perl 16 25.75 12.62
		1321	Event 16 81.27 35.86
		1322	Glib 16 32.63 15.48
		1323	POE 16 261.87 276.28 uses POE::Loop::Event
		1324
		1325	=head3 Discussion
		1326
		1327	The benchmark tries to test the performance of a typical small
		1328	server. While knowing how various event loops perform is interesting, keep
		1329	in mind that their overhead in this case is usually not as important, due
		1330	to the small absolute number of watchers (that is, you need efficiency and
		1331	speed most when you have lots of watchers, not when you only have a few of
		1332	them).
		1333
		1334	EV is again fastest.
		1335
		1336	Perl again comes second. It is noticably faster than the C-based event
		1337	loops Event and Glib, although the difference is too small to really
		1338	matter.
		1339
		1340	POE also performs much better in this case, but is is still far behind the
		1341	others.
		1342
		1343	=head3 Summary
		1344
		1345	=over 4
		1346
		1347	=item * C-based event loops perform very well with small number of
		1348	watchers, as the management overhead dominates.
		1349
		1350	=back
		1351
		1352
		1353	=head1 FORK
		1354
		1355	Most event libraries are not fork-safe. The ones who are usually are
		1356	because they rely on inefficient but fork-safe C<select> or C<poll>
		1357	calls. Only L<EV> is fully fork-aware.
		1358
		1359	If you have to fork, you must either do so I<before> creating your first
		1360	watcher OR you must not use AnyEvent at all in the child.
		1361
		1362
		1363	=head1 SECURITY CONSIDERATIONS
		1364
		1365	AnyEvent can be forced to load any event model via
		1366	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1367	execute arbitrary code or directly gain access, it can easily be used to
		1368	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1369	will not be active when the program uses a different event model than
		1370	specified in the variable.
		1371
		1372	You can make AnyEvent completely ignore this variable by deleting it
		1373	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1374
		1375	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1376
		1377	use AnyEvent;
		1378
		1379
455	=head1 SEE ALSO	1380	=head1 SEE ALSO
456		1381
457	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1382	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
		1383	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
		1384	L<Event::Lib>, L<Qt>, L<POE>.
458		1385
		1386	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
459	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1387	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
		1388	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
		1389	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
460		1390
461	Nontrivial usage example: L<Net::FCP>.	1391	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
462		1392
463	=head1	1393
		1394	=head1 AUTHOR
		1395
		1396	Marc Lehmann <schmorp@schmorp.de>
		1397	http://home.schmorp.de/
464		1398
465	=cut	1399	=cut
466		1400
467	1	1401	1
468		1402

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