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Revision 1.6 by root, Mon Dec 19 17:03:29 2005 UTC vs.
Revision 1.112 by root, Sat May 10 01:04:42 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 - 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
11	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
12	my ($poll_got) = @_;
13	...	12	...
14	});	13	});
15
16	- only one io watcher per $fh and $poll type is allowed
17	(i.e. on a socket you can have one r + one w or one rw
18	watcher, not any more.
19
20	- AnyEvent will keep filehandles alive, so as long as the watcher exists,
21	the filehandle exists.
22		14
23	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
24	...	16	...
25	});	17	});
26		18
27	- io and time watchers get canceled whenever $w is destroyed, so keep a copy	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
28
29	- timers can only be used once and must be recreated for repeated operation
30
31	my $w = AnyEvent->condvar; # kind of main loop replacement
32	$w->wait; # enters main loop till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->send
33	$w->broadcast; # wake up current and all future wait's	21	$w->send; # wake up current and all future wait's
34		22
35	- condvars are used to give blocking behaviour when neccessary. Create	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
36	a condvar for any "request" or "event" your module might create, C<<	24
37	->broadcast >> it when the event happens and provide a function that calls	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
38	C<< ->wait >> for it. See the examples below.	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.
39		70
40	=head1 DESCRIPTION	71	=head1 DESCRIPTION
41		72
42	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
43	allows module authors to utilizy an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
44	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
45	peacefully at any one time).	76	peacefully at any one time).
46		77
47	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>
48	module.	79	module.
49		80
50	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
51	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
52	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
53	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>,
54	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
55	used. If still none could be found, it will issue an error.	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		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.
		91
		92	Because AnyEvent first checks for modules that are already loaded, loading
		93	an event model explicitly before first using AnyEvent will likely make
		94	that model the default. For example:
		95
		96	use Tk;
		97	use AnyEvent;
		98
		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...
		104
		105	The pure-perl implementation of AnyEvent is called
		106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		107	explicitly.
		108
		109	=head1 WATCHERS
		110
		111	AnyEvent has the central concept of a I<watcher>, which is an object that
		112	stores relevant data for each kind of event you are waiting for, such as
		113	the callback to call, the filehandle to watch, etc.
		114
		115	These watchers are normal Perl objects with normal Perl lifetime. After
		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
		120	To disable the watcher you have to destroy it (e.g. by setting the
		121	variable you store it in to C<undef> or otherwise deleting all references
		122	to it).
		123
		124	All watchers are created by calling a method on the C<AnyEvent> class.
		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
		140	=head2 I/O WATCHERS
		141
		142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		143	with the following mandatory key-value pairs as arguments:
		144
		145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
		146	for events. C<poll> must be a string that is either C<r> or C<w>,
		147	which creates a watcher waiting for "r"eadable or "w"ritable events,
		148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
		150
		151	Although the callback might get passed parameters, their value and
		152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
		154
		155	The I/O watcher might use the underlying file descriptor or a copy of it.
		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.
		162
		163	Example:
		164
		165	# wait for readability of STDIN, then read a line and disable the watcher
		166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		167	chomp (my $input = <STDIN>);
		168	warn "read: $input\n";
		169	undef $w;
		170	});
		171
		172	=head2 TIME WATCHERS
		173
		174	You can create a time watcher by calling the C<< AnyEvent->timer >>
		175	method with the following mandatory arguments:
		176
		177	C<after> specifies after how many seconds (fractional values are
		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.
		184
		185	The timer callback will be invoked at most once: if you want a repeating
		186	timer you have to create a new watcher (this is a limitation by both Tk
		187	and Glib).
		188
		189	Example:
		190
		191	# fire an event after 7.7 seconds
		192	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		193	warn "timeout\n";
		194	});
		195
		196	# to cancel the timer:
		197	undef $w;
		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->send;
		294	},
		295	);
		296
		297	# do something else, then wait for process exit
		298	$done->wait;
		299
		300	=head2 CONDITION VARIABLES
		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
		312	Condition variables can be created by calling the C<< AnyEvent->condvar
		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.
		316
		317	After creation, the conditon variable is "false" until it becomes "true"
		318	by calling the C<send> method.
		319
		320	Condition variables are similar to callbacks, except that you can
		321	optionally wait for them. They can also be called merge points - points
		322	in time where multiple 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.
		326
		327	Condition variables are very useful to signal that something has finished,
		328	for example, if you write a module that does asynchronous http requests,
		329	then a condition variable would be the ideal candidate to signal the
		330	availability of results. The user can either act when the callback is
		331	called or can synchronously C<< ->wait >> for the results.
		332
		333	You can also use them to simulate traditional event loops - for example,
		334	you can block your main program until an event occurs - for example, you
		335	could C<< ->wait >> in your main program until the user clicks the Quit
		336	button of your app, which would C<< ->send >> the "quit" event.
		337
		338	Note that condition variables recurse into the event loop - if you have
		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.
		343
		344	Condition variables are represented by hash refs in perl, and the keys
		345	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		346	easy (it is often useful to build your own transaction class on top of
		347	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		348	it's C<new> method in your own C<new> method.
		349
		350	There are two "sides" to a condition variable - the "producer side" which
		351	eventually calls C<< -> send >>, and the "consumer side", which waits
		352	for the send to occur.
		353
		354	Example:
		355
		356	# wait till the result is ready
		357	my $result_ready = AnyEvent->condvar;
		358
		359	# do something such as adding a timer
		360	# or socket watcher the calls $result_ready->send
		361	# when the "result" is ready.
		362	# in this case, we simply use a timer:
		363	my $w = AnyEvent->timer (
		364	after => 1,
		365	cb => sub { $result_ready->send },
		366	);
		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls send
		370	$result_ready->wait;
		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 sends 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.
56		378
57	=over 4	379	=over 4
58		380
		381	=item $cv->send (...)
		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 send will be remembered.
		386
		387	If a callback has been set on the condition variable, it is called
		388	immediately from within send.
		389
		390	Any arguments passed to the C<send> call will be returned by all
		391	future C<< ->wait >> calls.
		392
		393	=item $cv->croak ($error)
		394
		395	Similar to send, 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<< ->send >>, but that is not required. If no
		413	callback was set, C<send> 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->send (\%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<send> 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	C<send> 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
		450	=back
		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	=over 4
		458
		459	=item $cv->wait
		460
		461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
		464
		465	You can only wait once on a condition - additional calls are valid but
		466	will return immediately.
		467
		468	If an error condition has been set by calling C<< ->croak >>, then this
		469	function will call C<croak>.
		470
		471	In list context, all parameters passed to C<send> will be returned,
		472	in scalar context only the first one will be returned.
		473
		474	Not all event models support a blocking wait - some die in that case
		475	(programs might want to do that to stay interactive), so I<if you are
		476	using this from a module, never require a blocking wait>, but let the
		477	caller decide whether the call will block or not (for example, by coupling
		478	condition variables with some kind of request results and supporting
		479	callbacks so the caller knows that getting the result will not block,
		480	while still suppporting blocking waits if the caller so desires).
		481
		482	Another reason I<never> to C<< ->wait >> in a module is that you cannot
		483	sensibly have two C<< ->wait >>'s in parallel, as that would require
		484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		485	can supply.
		486
		487	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		488	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		489	versions and also integrates coroutines into AnyEvent, making blocking
		490	C<< ->wait >> calls perfectly safe as long as they are done from another
		491	coroutine (one that doesn't run the event loop).
		492
		493	You can ensure that C<< -wait >> never blocks by setting a callback and
		494	only calling C<< ->wait >> from within that callback (or at a later
		495	time). This will work even when the event loop does not support blocking
		496	waits otherwise.
		497
		498	=item $bool = $cv->ready
		499
		500	Returns true when the condition is "true", i.e. whether C<send> or
		501	C<croak> have been called.
		502
		503	=item $cb = $cv->cb ([new callback])
		504
		505	This is a mutator function that returns the callback set and optionally
		506	replaces it before doing so.
		507
		508	The callback will be called when the condition becomes "true", i.e. when
		509	C<send> or C<croak> are called. Calling C<wait> inside the callback
		510	or at any later time is guaranteed not to block.
		511
		512	=back
		513
		514	=head1 GLOBAL VARIABLES AND FUNCTIONS
		515
		516	=over 4
		517
		518	=item $AnyEvent::MODEL
		519
		520	Contains C<undef> until the first watcher is being created. Then it
		521	contains the event model that is being used, which is the name of the
		522	Perl class implementing the model. This class is usually one of the
		523	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		524	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		525
		526	The known classes so far are:
		527
		528	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		529	AnyEvent::Impl::Event based on Event, second best choice.
		530	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		531	AnyEvent::Impl::Glib based on Glib, third-best choice.
		532	AnyEvent::Impl::Tk based on Tk, very bad choice.
		533	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		534	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		535	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		536
		537	There is no support for WxWidgets, as WxWidgets has no support for
		538	watching file handles. However, you can use WxWidgets through the
		539	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		540	second, which was considered to be too horrible to even consider for
		541	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		542	it's adaptor.
		543
		544	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		545	autodetecting them.
		546
		547	=item AnyEvent::detect
		548
		549	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		550	if necessary. You should only call this function right before you would
		551	have created an AnyEvent watcher anyway, that is, as late as possible at
		552	runtime.
		553
		554	=item $guard = AnyEvent::post_detect { BLOCK }
		555
		556	Arranges for the code block to be executed as soon as the event model is
		557	autodetected (or immediately if this has already happened).
		558
		559	If called in scalar or list context, then it creates and returns an object
		560	that automatically removes the callback again when it is destroyed. See
		561	L<Coro::BDB> for a case where this is useful.
		562
		563	=item @AnyEvent::post_detect
		564
		565	If there are any code references in this array (you can C<push> to it
		566	before or after loading AnyEvent), then they will called directly after
		567	the event loop has been chosen.
		568
		569	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		570	if it contains a true value then the event loop has already been detected,
		571	and the array will be ignored.
		572
		573	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		574
		575	=back
		576
		577	=head1 WHAT TO DO IN A MODULE
		578
		579	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		580	freely, but you should not load a specific event module or rely on it.
		581
		582	Be careful when you create watchers in the module body - AnyEvent will
		583	decide which event module to use as soon as the first method is called, so
		584	by calling AnyEvent in your module body you force the user of your module
		585	to load the event module first.
		586
		587	Never call C<< ->wait >> on a condition variable unless you I<know> that
		588	the C<< ->send >> method has been called on it already. This is
		589	because it will stall the whole program, and the whole point of using
		590	events is to stay interactive.
		591
		592	It is fine, however, to call C<< ->wait >> when the user of your module
		593	requests it (i.e. if you create a http request object ad have a method
		594	called C<results> that returns the results, it should call C<< ->wait >>
		595	freely, as the user of your module knows what she is doing. always).
		596
		597	=head1 WHAT TO DO IN THE MAIN PROGRAM
		598
		599	There will always be a single main program - the only place that should
		600	dictate which event model to use.
		601
		602	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		603	do anything special (it does not need to be event-based) and let AnyEvent
		604	decide which implementation to chose if some module relies on it.
		605
		606	If the main program relies on a specific event model. For example, in
		607	Gtk2 programs you have to rely on the Glib module. You should load the
		608	event module before loading AnyEvent or any module that uses it: generally
		609	speaking, you should load it as early as possible. The reason is that
		610	modules might create watchers when they are loaded, and AnyEvent will
		611	decide on the event model to use as soon as it creates watchers, and it
		612	might chose the wrong one unless you load the correct one yourself.
		613
		614	You can chose to use a rather inefficient pure-perl implementation by
		615	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
		616	behaviour everywhere, but letting AnyEvent chose is generally better.
		617
		618	=head1 OTHER MODULES
		619
		620	The following is a non-exhaustive list of additional modules that use
		621	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		622	in the same program. Some of the modules come with AnyEvent, some are
		623	available via CPAN.
		624
		625	=over 4
		626
		627	=item L<AnyEvent::Util>
		628
		629	Contains various utility functions that replace often-used but blocking
		630	functions such as C<inet_aton> by event-/callback-based versions.
		631
		632	=item L<AnyEvent::Handle>
		633
		634	Provide read and write buffers and manages watchers for reads and writes.
		635
		636	=item L<AnyEvent::Socket>
		637
		638	Provides a means to do non-blocking connects, accepts etc.
		639
		640	=item L<AnyEvent::HTTPD>
		641
		642	Provides a simple web application server framework.
		643
		644	=item L<AnyEvent::DNS>
		645
		646	Provides asynchronous DNS resolver capabilities, beyond what
		647	L<AnyEvent::Util> offers.
		648
		649	=item L<AnyEvent::FastPing>
		650
		651	The fastest ping in the west.
		652
		653	=item L<Net::IRC3>
		654
		655	AnyEvent based IRC client module family.
		656
		657	=item L<Net::XMPP2>
		658
		659	AnyEvent based XMPP (Jabber protocol) module family.
		660
		661	=item L<Net::FCP>
		662
		663	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		664	of AnyEvent.
		665
		666	=item L<Event::ExecFlow>
		667
		668	High level API for event-based execution flow control.
		669
		670	=item L<Coro>
		671
		672	Has special support for AnyEvent via L<Coro::AnyEvent>.
		673
		674	=item L<IO::Lambda>
		675
		676	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		677
		678	=item L<IO::AIO>
		679
		680	Truly asynchronous I/O, should be in the toolbox of every event
		681	programmer. Can be trivially made to use AnyEvent.
		682
		683	=item L<BDB>
		684
		685	Truly asynchronous Berkeley DB access. Can be trivially made to use
		686	AnyEvent.
		687
		688	=back
		689
59	=cut	690	=cut
60		691
61	package AnyEvent;	692	package AnyEvent;
62		693
63	no warnings;	694	no warnings;
64	use strict 'vars';	695	use strict;
		696
65	use Carp;	697	use Carp;
66		698
67	our $VERSION = 0.3;	699	our $VERSION = '3.4';
68	our $MODEL;	700	our $MODEL;
69		701
70	our $AUTOLOAD;	702	our $AUTOLOAD;
71	our @ISA;	703	our @ISA;
72		704
		705	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		706
		707	our @REGISTRY;
		708
73	my @models = (	709	my @models = (
74	[Coro => Coro::Event::],	710	[EV:: => AnyEvent::Impl::EV::],
75	[Event => Event::],	711	[Event:: => AnyEvent::Impl::Event::],
76	[Glib => Glib::],	712	[Tk:: => AnyEvent::Impl::Tk::],
77	[Tk => Tk::],	713	[Wx:: => AnyEvent::Impl::POE::],
		714	[Prima:: => AnyEvent::Impl::POE::],
		715	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		716	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		717	[Glib:: => AnyEvent::Impl::Glib::],
		718	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		719	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		720	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
78	);	721	);
79		722
80	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	723	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
81		724
82	sub AUTOLOAD {	725	our @post_detect;
83	$AUTOLOAD =~ s/.*://;
84		726
85	$method{$AUTOLOAD}	727	sub post_detect(&) {
86	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	728	my ($cb) = @_;
87		729
		730	if ($MODEL) {
		731	$cb->();
		732
		733	1
		734	} else {
		735	push @post_detect, $cb;
		736
		737	defined wantarray
		738	? bless \$cb, "AnyEvent::Util::Guard"
		739	: ()
		740	}
		741	}
		742
		743	sub AnyEvent::Util::Guard::DESTROY {
		744	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		745	}
		746
		747	sub detect() {
88	unless ($MODEL) {	748	unless ($MODEL) {
89	# check for already loaded models	749	no strict 'refs';
90	for (@models) {	750
91	my ($model, $package) = @$_;	751	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
92	if (scalar keys %{ *{"$package\::"} }) {	752	my $model = "AnyEvent::Impl::$1";
93	eval "require AnyEvent::Impl::$model";	753	if (eval "require $model") {
94	last if $MODEL;	754	$MODEL = $model;
		755	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		756	} else {
		757	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
95	}	758	}
96	}	759	}
97		760
		761	# check for already loaded models
98	unless ($MODEL) {	762	unless ($MODEL) {
99	# try to load a model
100
101	for (@models) {	763	for (@REGISTRY, @models) {
102	my ($model, $package) = @$_;	764	my ($package, $model) = @$_;
103	eval "require AnyEvent::Impl::$model";	765	if (${"$package\::VERSION"} > 0) {
104	last if $MODEL;	766	if (eval "require $model") {
		767	$MODEL = $model;
		768	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		769	last;
		770	}
		771	}
105	}	772	}
106		773
		774	unless ($MODEL) {
		775	# try to load a model
		776
		777	for (@REGISTRY, @models) {
		778	my ($package, $model) = @$_;
		779	if (eval "require $package"
		780	and ${"$package\::VERSION"} > 0
		781	and eval "require $model") {
		782	$MODEL = $model;
		783	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		784	last;
		785	}
		786	}
		787
107	$MODEL	788	$MODEL
108	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	789	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		790	}
109	}	791	}
		792
		793	unshift @ISA, $MODEL;
		794	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		795
		796	(shift @post_detect)->() while @post_detect;
110	}	797	}
111		798
112	@ISA = $MODEL;	799	$MODEL
		800	}
		801
		802	sub AUTOLOAD {
		803	(my $func = $AUTOLOAD) =~ s/.*://;
		804
		805	$method{$func}
		806	or croak "$func: not a valid method for AnyEvent objects";
		807
		808	detect unless $MODEL;
113		809
114	my $class = shift;	810	my $class = shift;
115	$class->$AUTOLOAD (@_);	811	$class->$func (@_);
116	}	812	}
117		813
		814	package AnyEvent::Base;
		815
		816	# default implementation for ->condvar, ->wait, ->broadcast
		817
		818	sub condvar {
		819	bless \my $flag, "AnyEvent::Base::CondVar"
		820	}
		821
		822	sub AnyEvent::Base::CondVar::broadcast {
		823	${$_[0]}++;
		824	}
		825
		826	sub AnyEvent::Base::CondVar::wait {
		827	AnyEvent->one_event while !${$_[0]};
		828	}
		829
		830	# default implementation for ->signal
		831
		832	our %SIG_CB;
		833
		834	sub signal {
		835	my (undef, %arg) = @_;
		836
		837	my $signal = uc $arg{signal}
		838	or Carp::croak "required option 'signal' is missing";
		839
		840	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		841	$SIG{$signal} ||= sub {
		842	$_->() for values %{ $SIG_CB{$signal} || {} };
		843	};
		844
		845	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		846	}
		847
		848	sub AnyEvent::Base::Signal::DESTROY {
		849	my ($signal, $cb) = @{$_[0]};
		850
		851	delete $SIG_CB{$signal}{$cb};
		852
		853	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		854	}
		855
		856	# default implementation for ->child
		857
		858	our %PID_CB;
		859	our $CHLD_W;
		860	our $CHLD_DELAY_W;
		861	our $PID_IDLE;
		862	our $WNOHANG;
		863
		864	sub _child_wait {
		865	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		866	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		867	(values %{ $PID_CB{0} || {} });
		868	}
		869
		870	undef $PID_IDLE;
		871	}
		872
		873	sub _sigchld {
		874	# make sure we deliver these changes "synchronous" with the event loop.
		875	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		876	undef $CHLD_DELAY_W;
		877	&_child_wait;
		878	});
		879	}
		880
		881	sub child {
		882	my (undef, %arg) = @_;
		883
		884	defined (my $pid = $arg{pid} + 0)
		885	or Carp::croak "required option 'pid' is missing";
		886
		887	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		888
		889	unless ($WNOHANG) {
		890	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		891	}
		892
		893	unless ($CHLD_W) {
		894	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		895	# child could be a zombie already, so make at least one round
		896	&_sigchld;
		897	}
		898
		899	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		900	}
		901
		902	sub AnyEvent::Base::Child::DESTROY {
		903	my ($pid, $cb) = @{$_[0]};
		904
		905	delete $PID_CB{$pid}{$cb};
		906	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		907
		908	undef $CHLD_W unless keys %PID_CB;
		909	}
		910
		911	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		912
		913	This is an advanced topic that you do not normally need to use AnyEvent in
		914	a module. This section is only of use to event loop authors who want to
		915	provide AnyEvent compatibility.
		916
		917	If you need to support another event library which isn't directly
		918	supported by AnyEvent, you can supply your own interface to it by
		919	pushing, before the first watcher gets created, the package name of
		920	the event module and the package name of the interface to use onto
		921	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		922	AnyEvent, so it is reasonably cheap.
		923
		924	Example:
		925
		926	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		927
		928	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		929	package/class when it finds the C<urxvt> package/module is already loaded.
		930
		931	When AnyEvent is loaded and asked to find a suitable event model, it
		932	will first check for the presence of urxvt by trying to C<use> the
		933	C<urxvt::anyevent> module.
		934
		935	The class should provide implementations for all watcher types. See
		936	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		937	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		938	see the sources.
		939
		940	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		941	provide suitable (hopefully) replacements.
		942
		943	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		944	terminal emulator uses the above line as-is. An interface isn't included
		945	in AnyEvent because it doesn't make sense outside the embedded interpreter
		946	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		947	I<rxvt-unicode> distribution.
		948
		949	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		950	condition variables: code blocking while waiting for a condition will
		951	C<die>. This still works with most modules/usages, and blocking calls must
		952	not be done in an interactive application, so it makes sense.
		953
		954	=head1 ENVIRONMENT VARIABLES
		955
		956	The following environment variables are used by this module:
		957
		958	=over 4
		959
		960	=item C<PERL_ANYEVENT_VERBOSE>
		961
		962	By default, AnyEvent will be completely silent except in fatal
		963	conditions. You can set this environment variable to make AnyEvent more
		964	talkative.
		965
		966	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		967	conditions, such as not being able to load the event model specified by
		968	C<PERL_ANYEVENT_MODEL>.
		969
		970	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		971	model it chooses.
		972
		973	=item C<PERL_ANYEVENT_MODEL>
		974
		975	This can be used to specify the event model to be used by AnyEvent, before
		976	autodetection and -probing kicks in. It must be a string consisting
		977	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		978	and the resulting module name is loaded and if the load was successful,
		979	used as event model. If it fails to load AnyEvent will proceed with
		980	autodetection and -probing.
		981
		982	This functionality might change in future versions.
		983
		984	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		985	could start your program like this:
		986
		987	PERL_ANYEVENT_MODEL=Perl perl ...
		988
118	=back	989	=back
119		990
120	=head1 EXAMPLE	991	=head1 EXAMPLE PROGRAM
121		992
122	The following program uses an io watcher to read data from stdin, a timer	993	The following program uses an I/O watcher to read data from STDIN, a timer
123	to display a message once per second, and a condvar to exit the program	994	to display a message once per second, and a condition variable to quit the
124	when the user enters quit:	995	program when the user enters quit:
125		996
126	use AnyEvent;	997	use AnyEvent;
127		998
128	my $cv = AnyEvent->condvar;	999	my $cv = AnyEvent->condvar;
129		1000
130	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1001	my $io_watcher = AnyEvent->io (
		1002	fh => \*STDIN,
		1003	poll => 'r',
		1004	cb => sub {
131	warn "io event <$_[0]>\n"; # will always output <r>	1005	warn "io event <$_[0]>\n"; # will always output <r>
132	chomp (my $input = <STDIN>); # read a line	1006	chomp (my $input = <STDIN>); # read a line
133	warn "read: $input\n"; # output what has been read	1007	warn "read: $input\n"; # output what has been read
134	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1008	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		1009	},
135	});	1010	);
136		1011
137	my $time_watcher; # can only be used once	1012	my $time_watcher; # can only be used once
138		1013
139	sub new_timer {	1014	sub new_timer {
140	$timer = AnyEvent->timer (after => 1, cb => sub {	1015	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
222	$txn->{finished}->wait;	1097	$txn->{finished}->wait;
223	return $txn->{result};	1098	return $txn->{result};
224		1099
225	The actual code goes further and collects all errors (C<die>s, exceptions)	1100	The actual code goes further and collects all errors (C<die>s, exceptions)
226	that occured during request processing. The C<result> method detects	1101	that occured during request processing. The C<result> method detects
227	wether an exception as thrown (it is stored inside the $txn object)	1102	whether an exception as thrown (it is stored inside the $txn object)
228	and just throws the exception, which means connection errors and other	1103	and just throws the exception, which means connection errors and other
229	problems get reported tot he code that tries to use the result, not in a	1104	problems get reported tot he code that tries to use the result, not in a
230	random callback.	1105	random callback.
231		1106
232	All of this enables the following usage styles:	1107	All of this enables the following usage styles:
233		1108
234	1. Blocking:	1109	1. Blocking:
235		1110
236	my $data = $fcp->client_get ($url);	1111	my $data = $fcp->client_get ($url);
237		1112
238	2. Blocking, but parallelizing:	1113	2. Blocking, but running in parallel:
239		1114
240	my @datas = map $_->result,	1115	my @datas = map $_->result,
241	map $fcp->txn_client_get ($_),	1116	map $fcp->txn_client_get ($_),
242	@urls;	1117	@urls;
243		1118
244	Both blocking examples work without the module user having to know	1119	Both blocking examples work without the module user having to know
245	anything about events.	1120	anything about events.
246		1121
247	3a. Event-based in a main program, using any support Event module:	1122	3a. Event-based in a main program, using any supported event module:
248		1123
249	use Event;	1124	use EV;
250		1125
251	$fcp->txn_client_get ($url)->cb (sub {	1126	$fcp->txn_client_get ($url)->cb (sub {
252	my $txn = shift;	1127	my $txn = shift;
253	my $data = $txn->result;	1128	my $data = $txn->result;
254	...	1129	...
255	});	1130	});
256		1131
257	Event::loop;	1132	EV::loop;
258		1133
259	3b. The module user could use AnyEvent, too:	1134	3b. The module user could use AnyEvent, too:
260		1135
261	use AnyEvent;	1136	use AnyEvent;
262		1137
…		…
267	$quit->broadcast;	1142	$quit->broadcast;
268	});	1143	});
269		1144
270	$quit->wait;	1145	$quit->wait;
271		1146
		1147
		1148	=head1 BENCHMARKS
		1149
		1150	To give you an idea of the performance and overheads that AnyEvent adds
		1151	over the event loops themselves and to give you an impression of the speed
		1152	of various event loops I prepared some benchmarks.
		1153
		1154	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1155
		1156	Here is a benchmark of various supported event models used natively and
		1157	through anyevent. The benchmark creates a lot of timers (with a zero
		1158	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1159	which it is), lets them fire exactly once and destroys them again.
		1160
		1161	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1162	distribution.
		1163
		1164	=head3 Explanation of the columns
		1165
		1166	I<watcher> is the number of event watchers created/destroyed. Since
		1167	different event models feature vastly different performances, each event
		1168	loop was given a number of watchers so that overall runtime is acceptable
		1169	and similar between tested event loop (and keep them from crashing): Glib
		1170	would probably take thousands of years if asked to process the same number
		1171	of watchers as EV in this benchmark.
		1172
		1173	I<bytes> is the number of bytes (as measured by the resident set size,
		1174	RSS) consumed by each watcher. This method of measuring captures both C
		1175	and Perl-based overheads.
		1176
		1177	I<create> is the time, in microseconds (millionths of seconds), that it
		1178	takes to create a single watcher. The callback is a closure shared between
		1179	all watchers, to avoid adding memory overhead. That means closure creation
		1180	and memory usage is not included in the figures.
		1181
		1182	I<invoke> is the time, in microseconds, used to invoke a simple
		1183	callback. The callback simply counts down a Perl variable and after it was
		1184	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1185	signal the end of this phase.
		1186
		1187	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1188	watcher.
		1189
		1190	=head3 Results
		1191
		1192	name watchers bytes create invoke destroy comment
		1193	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1194	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1195	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1196	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1197	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1198	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1199	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1200	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1201	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1202	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1203
		1204	=head3 Discussion
		1205
		1206	The benchmark does I<not> measure scalability of the event loop very
		1207	well. For example, a select-based event loop (such as the pure perl one)
		1208	can never compete with an event loop that uses epoll when the number of
		1209	file descriptors grows high. In this benchmark, all events become ready at
		1210	the same time, so select/poll-based implementations get an unnatural speed
		1211	boost.
		1212
		1213	Also, note that the number of watchers usually has a nonlinear effect on
		1214	overall speed, that is, creating twice as many watchers doesn't take twice
		1215	the time - usually it takes longer. This puts event loops tested with a
		1216	higher number of watchers at a disadvantage.
		1217
		1218	To put the range of results into perspective, consider that on the
		1219	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1220	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1221	cycles with POE.
		1222
		1223	C<EV> is the sole leader regarding speed and memory use, which are both
		1224	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1225	far less memory than any other event loop and is still faster than Event
		1226	natively.
		1227
		1228	The pure perl implementation is hit in a few sweet spots (both the
		1229	constant timeout and the use of a single fd hit optimisations in the perl
		1230	interpreter and the backend itself). Nevertheless this shows that it
		1231	adds very little overhead in itself. Like any select-based backend its
		1232	performance becomes really bad with lots of file descriptors (and few of
		1233	them active), of course, but this was not subject of this benchmark.
		1234
		1235	The C<Event> module has a relatively high setup and callback invocation
		1236	cost, but overall scores in on the third place.
		1237
		1238	C<Glib>'s memory usage is quite a bit higher, but it features a
		1239	faster callback invocation and overall ends up in the same class as
		1240	C<Event>. However, Glib scales extremely badly, doubling the number of
		1241	watchers increases the processing time by more than a factor of four,
		1242	making it completely unusable when using larger numbers of watchers
		1243	(note that only a single file descriptor was used in the benchmark, so
		1244	inefficiencies of C<poll> do not account for this).
		1245
		1246	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1247	more than 2000 watchers is a big setback, however, as correctness takes
		1248	precedence over speed. Nevertheless, its performance is surprising, as the
		1249	file descriptor is dup()ed for each watcher. This shows that the dup()
		1250	employed by some adaptors is not a big performance issue (it does incur a
		1251	hidden memory cost inside the kernel which is not reflected in the figures
		1252	above).
		1253
		1254	C<POE>, regardless of underlying event loop (whether using its pure perl
		1255	select-based backend or the Event module, the POE-EV backend couldn't
		1256	be tested because it wasn't working) shows abysmal performance and
		1257	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1258	as EV watchers, and 10 times as much memory as Event (the high memory
		1259	requirements are caused by requiring a session for each watcher). Watcher
		1260	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1261	implementation.
		1262
		1263	The design of the POE adaptor class in AnyEvent can not really account
		1264	for the performance issues, though, as session creation overhead is
		1265	small compared to execution of the state machine, which is coded pretty
		1266	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1267	using multiple sessions is not a good approach, especially regarding
		1268	memory usage, even the author of POE could not come up with a faster
		1269	design).
		1270
		1271	=head3 Summary
		1272
		1273	=over 4
		1274
		1275	=item * Using EV through AnyEvent is faster than any other event loop
		1276	(even when used without AnyEvent), but most event loops have acceptable
		1277	performance with or without AnyEvent.
		1278
		1279	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1280	the actual event loop, only with extremely fast event loops such as EV
		1281	adds AnyEvent significant overhead.
		1282
		1283	=item * You should avoid POE like the plague if you want performance or
		1284	reasonable memory usage.
		1285
		1286	=back
		1287
		1288	=head2 BENCHMARKING THE LARGE SERVER CASE
		1289
		1290	This benchmark atcually benchmarks the event loop itself. It works by
		1291	creating a number of "servers": each server consists of a socketpair, a
		1292	timeout watcher that gets reset on activity (but never fires), and an I/O
		1293	watcher waiting for input on one side of the socket. Each time the socket
		1294	watcher reads a byte it will write that byte to a random other "server".
		1295
		1296	The effect is that there will be a lot of I/O watchers, only part of which
		1297	are active at any one point (so there is a constant number of active
		1298	fds for each loop iterstaion, but which fds these are is random). The
		1299	timeout is reset each time something is read because that reflects how
		1300	most timeouts work (and puts extra pressure on the event loops).
		1301
		1302	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1303	(1%) are active. This mirrors the activity of large servers with many
		1304	connections, most of which are idle at any one point in time.
		1305
		1306	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1307	distribution.
		1308
		1309	=head3 Explanation of the columns
		1310
		1311	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1312	each server has a read and write socket end).
		1313
		1314	I<create> is the time it takes to create a socketpair (which is
		1315	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1316
		1317	I<request>, the most important value, is the time it takes to handle a
		1318	single "request", that is, reading the token from the pipe and forwarding
		1319	it to another server. This includes deleting the old timeout and creating
		1320	a new one that moves the timeout into the future.
		1321
		1322	=head3 Results
		1323
		1324	name sockets create request
		1325	EV 20000 69.01 11.16
		1326	Perl 20000 73.32 35.87
		1327	Event 20000 212.62 257.32
		1328	Glib 20000 651.16 1896.30
		1329	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1330
		1331	=head3 Discussion
		1332
		1333	This benchmark I<does> measure scalability and overall performance of the
		1334	particular event loop.
		1335
		1336	EV is again fastest. Since it is using epoll on my system, the setup time
		1337	is relatively high, though.
		1338
		1339	Perl surprisingly comes second. It is much faster than the C-based event
		1340	loops Event and Glib.
		1341
		1342	Event suffers from high setup time as well (look at its code and you will
		1343	understand why). Callback invocation also has a high overhead compared to
		1344	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1345	uses select or poll in basically all documented configurations.
		1346
		1347	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1348	clearly fails to perform with many filehandles or in busy servers.
		1349
		1350	POE is still completely out of the picture, taking over 1000 times as long
		1351	as EV, and over 100 times as long as the Perl implementation, even though
		1352	it uses a C-based event loop in this case.
		1353
		1354	=head3 Summary
		1355
		1356	=over 4
		1357
		1358	=item * The pure perl implementation performs extremely well.
		1359
		1360	=item * Avoid Glib or POE in large projects where performance matters.
		1361
		1362	=back
		1363
		1364	=head2 BENCHMARKING SMALL SERVERS
		1365
		1366	While event loops should scale (and select-based ones do not...) even to
		1367	large servers, most programs we (or I :) actually write have only a few
		1368	I/O watchers.
		1369
		1370	In this benchmark, I use the same benchmark program as in the large server
		1371	case, but it uses only eight "servers", of which three are active at any
		1372	one time. This should reflect performance for a small server relatively
		1373	well.
		1374
		1375	The columns are identical to the previous table.
		1376
		1377	=head3 Results
		1378
		1379	name sockets create request
		1380	EV 16 20.00 6.54
		1381	Perl 16 25.75 12.62
		1382	Event 16 81.27 35.86
		1383	Glib 16 32.63 15.48
		1384	POE 16 261.87 276.28 uses POE::Loop::Event
		1385
		1386	=head3 Discussion
		1387
		1388	The benchmark tries to test the performance of a typical small
		1389	server. While knowing how various event loops perform is interesting, keep
		1390	in mind that their overhead in this case is usually not as important, due
		1391	to the small absolute number of watchers (that is, you need efficiency and
		1392	speed most when you have lots of watchers, not when you only have a few of
		1393	them).
		1394
		1395	EV is again fastest.
		1396
		1397	Perl again comes second. It is noticably faster than the C-based event
		1398	loops Event and Glib, although the difference is too small to really
		1399	matter.
		1400
		1401	POE also performs much better in this case, but is is still far behind the
		1402	others.
		1403
		1404	=head3 Summary
		1405
		1406	=over 4
		1407
		1408	=item * C-based event loops perform very well with small number of
		1409	watchers, as the management overhead dominates.
		1410
		1411	=back
		1412
		1413
		1414	=head1 FORK
		1415
		1416	Most event libraries are not fork-safe. The ones who are usually are
		1417	because they rely on inefficient but fork-safe C<select> or C<poll>
		1418	calls. Only L<EV> is fully fork-aware.
		1419
		1420	If you have to fork, you must either do so I<before> creating your first
		1421	watcher OR you must not use AnyEvent at all in the child.
		1422
		1423
		1424	=head1 SECURITY CONSIDERATIONS
		1425
		1426	AnyEvent can be forced to load any event model via
		1427	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1428	execute arbitrary code or directly gain access, it can easily be used to
		1429	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1430	will not be active when the program uses a different event model than
		1431	specified in the variable.
		1432
		1433	You can make AnyEvent completely ignore this variable by deleting it
		1434	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1435
		1436	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1437
		1438	use AnyEvent;
		1439
		1440	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1441	be used to probe what backend is used and gain other information (which is
		1442	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1443
		1444
272	=head1 SEE ALSO	1445	=head1 SEE ALSO
273		1446
274	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1447	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1448	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
275		1449
276	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1450	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1451	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1452	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1453	L<AnyEvent::Impl::POE>.
277		1454
		1455	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1456
278	Nontrivial usage example: L<Net::FCP>.	1457	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
279		1458
280	=head1	1459
		1460	=head1 AUTHOR
		1461
		1462	Marc Lehmann <schmorp@schmorp.de>
		1463	http://home.schmorp.de/
281		1464
282	=cut	1465	=cut
283		1466
284	1	1467	1
285		1468

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