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Revision 1.11 by root, Thu Jul 20 01:32:11 2006 UTC vs.
Revision 1.110 by root, Sat May 10 00:57:31 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 $poll type is allowed (i.e. on a socket
17	you can have one r + one w or one rw watcher, not any more (limitation by
18	Tk).
19
20	* the C<$poll_got> passed to the handler needs to be checked by looking
21	for single characters (e.g. with a regex), as it can contain more event
22	types than were requested (e.g. a 'w' watcher might generate 'rw' events,
23	limitation by Glib).
24
25	* AnyEvent will keep filehandles alive, so as long as the watcher exists,
26	the filehandle exists.
27		14
28	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
29	...	16	...
30	});	17	});
31		18
32	* 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
33
34	* timers can only be used once and must be recreated for repeated
35	operation (limitation by Glib and Tk).
36
37	my $w = AnyEvent->condvar; # kind of main loop replacement
38	$w->wait; # enters main loop till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->send
39	$w->broadcast; # wake up current and all future wait's	21	$w->send; # wake up current and all future wait's
40		22
41	* condvars are used to give blocking behaviour when neccessary. Create	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
42	a condvar for any "request" or "event" your module might create, C<<	24
43	->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
44	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.
45		70
46	=head1 DESCRIPTION	71	=head1 DESCRIPTION
47		72
48	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
49	allows module authors to utilizy an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
50	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
51	peacefully at any one time).	76	peacefully at any one time).
52		77
53	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>
54	module.	79	module.
55		80
56	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
57	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
58	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
59	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>,
60	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
61	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.
62		378
63	=over 4	379	=over 4
64		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 $guard = AnyEvent::on_detect { BLOCK }
		555
		556	Arranges for the code block to be executed as soon as the event model is
		557	autodetected (or immediately if this has already happened).
		558
		559	If called in scalar or list context, then it creates and returns an object
		560	that automatically removes the callback again when it is destroyed.
		561
		562	=item @AnyEvent::on_detect
		563
		564	If there are any code references in this array (you can C<push> to it
		565	before or after loading AnyEvent), then they will called directly after
		566	the event loop has been chosen.
		567
		568	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		569	if it contains a true value then the event loop has already been detected,
		570	and the array will be ignored.
		571
		572	Best use C<AnyEvent::on_detect { BLOCK }> instead.
		573
		574	=back
		575
		576	=head1 WHAT TO DO IN A MODULE
		577
		578	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		579	freely, but you should not load a specific event module or rely on it.
		580
		581	Be careful when you create watchers in the module body - AnyEvent will
		582	decide which event module to use as soon as the first method is called, so
		583	by calling AnyEvent in your module body you force the user of your module
		584	to load the event module first.
		585
		586	Never call C<< ->wait >> on a condition variable unless you I<know> that
		587	the C<< ->send >> method has been called on it already. This is
		588	because it will stall the whole program, and the whole point of using
		589	events is to stay interactive.
		590
		591	It is fine, however, to call C<< ->wait >> when the user of your module
		592	requests it (i.e. if you create a http request object ad have a method
		593	called C<results> that returns the results, it should call C<< ->wait >>
		594	freely, as the user of your module knows what she is doing. always).
		595
		596	=head1 WHAT TO DO IN THE MAIN PROGRAM
		597
		598	There will always be a single main program - the only place that should
		599	dictate which event model to use.
		600
		601	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		602	do anything special (it does not need to be event-based) and let AnyEvent
		603	decide which implementation to chose if some module relies on it.
		604
		605	If the main program relies on a specific event model. For example, in
		606	Gtk2 programs you have to rely on the Glib module. You should load the
		607	event module before loading AnyEvent or any module that uses it: generally
		608	speaking, you should load it as early as possible. The reason is that
		609	modules might create watchers when they are loaded, and AnyEvent will
		610	decide on the event model to use as soon as it creates watchers, and it
		611	might chose the wrong one unless you load the correct one yourself.
		612
		613	You can chose to use a rather inefficient pure-perl implementation by
		614	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
		615	behaviour everywhere, but letting AnyEvent chose is generally better.
		616
		617	=head1 OTHER MODULES
		618
		619	The following is a non-exhaustive list of additional modules that use
		620	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		621	in the same program. Some of the modules come with AnyEvent, some are
		622	available via CPAN.
		623
		624	=over 4
		625
		626	=item L<AnyEvent::Util>
		627
		628	Contains various utility functions that replace often-used but blocking
		629	functions such as C<inet_aton> by event-/callback-based versions.
		630
		631	=item L<AnyEvent::Handle>
		632
		633	Provide read and write buffers and manages watchers for reads and writes.
		634
		635	=item L<AnyEvent::Socket>
		636
		637	Provides a means to do non-blocking connects, accepts etc.
		638
		639	=item L<AnyEvent::HTTPD>
		640
		641	Provides a simple web application server framework.
		642
		643	=item L<AnyEvent::DNS>
		644
		645	Provides asynchronous DNS resolver capabilities, beyond what
		646	L<AnyEvent::Util> offers.
		647
		648	=item L<AnyEvent::FastPing>
		649
		650	The fastest ping in the west.
		651
		652	=item L<Net::IRC3>
		653
		654	AnyEvent based IRC client module family.
		655
		656	=item L<Net::XMPP2>
		657
		658	AnyEvent based XMPP (Jabber protocol) module family.
		659
		660	=item L<Net::FCP>
		661
		662	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		663	of AnyEvent.
		664
		665	=item L<Event::ExecFlow>
		666
		667	High level API for event-based execution flow control.
		668
		669	=item L<Coro>
		670
		671	Has special support for AnyEvent via L<Coro::AnyEvent>.
		672
		673	=item L<IO::Lambda>
		674
		675	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		676
		677	=item L<IO::AIO>
		678
		679	Truly asynchronous I/O, should be in the toolbox of every event
		680	programmer. Can be trivially made to use AnyEvent.
		681
		682	=item L<BDB>
		683
		684	Truly asynchronous Berkeley DB access. Can be trivially made to use
		685	AnyEvent.
		686
		687	=back
		688
65	=cut	689	=cut
66		690
67	package AnyEvent;	691	package AnyEvent;
68		692
69	no warnings;	693	no warnings;
70	use strict 'vars';	694	use strict;
		695
71	use Carp;	696	use Carp;
72		697
73	our $VERSION = '1.02';	698	our $VERSION = '3.4';
74	our $MODEL;	699	our $MODEL;
75		700
76	our $AUTOLOAD;	701	our $AUTOLOAD;
77	our @ISA;	702	our @ISA;
78		703
79	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	704	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
80		705
81	our @REGISTRY;	706	our @REGISTRY;
82		707
83	my @models = (	708	my @models = (
84	[Coro::Event:: => AnyEvent::Impl::Coro::],	709	[EV:: => AnyEvent::Impl::EV::],
85	[Event:: => AnyEvent::Impl::Event::],	710	[Event:: => AnyEvent::Impl::Event::],
		711	[Tk:: => AnyEvent::Impl::Tk::],
		712	[Wx:: => AnyEvent::Impl::POE::],
		713	[Prima:: => AnyEvent::Impl::POE::],
		714	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		715	# everything below here will not be autoprobed as the pureperl backend should work everywhere
86	[Glib:: => AnyEvent::Impl::Glib::],	716	[Glib:: => AnyEvent::Impl::Glib::],
87	[Tk:: => AnyEvent::Impl::Tk::],	717	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		718	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		719	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
88	);	720	);
89		721
90	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	722	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
91		723
92	sub AUTOLOAD {	724	our @on_detect;
93	$AUTOLOAD =~ s/.*://;
94		725
95	$method{$AUTOLOAD}	726	sub on_detect(&) {
96	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	727	my ($cb) = @_;
97		728
		729	if ($MODEL) {
		730	$cb->();
		731
		732	1
		733	} else {
		734	push @on_detect, $cb;
		735
		736	defined wantarray
		737	? bless \$cb, "AnyEvent::Util::Guard"
		738	: ()
		739	}
		740	}
		741
		742	sub AnyEvent::Util::Guard::DESTROY {
		743	@on_detect = grep $_ != ${$_[0]}, @on_detect;
		744	}
		745
		746	sub detect() {
98	unless ($MODEL) {	747	unless ($MODEL) {
		748	no strict 'refs';
		749
		750	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		751	my $model = "AnyEvent::Impl::$1";
		752	if (eval "require $model") {
		753	$MODEL = $model;
		754	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		755	} else {
		756	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		757	}
		758	}
		759
99	# check for already loaded models	760	# check for already loaded models
		761	unless ($MODEL) {
100	for (@REGISTRY, @models) {	762	for (@REGISTRY, @models) {
101	my ($package, $model) = @$_;	763	my ($package, $model) = @$_;
102	if (${"$package\::VERSION"} > 0) {	764	if (${"$package\::VERSION"} > 0) {
103	if (eval "require $model") {	765	if (eval "require $model") {
104	$MODEL = $model;	766	$MODEL = $model;
105	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	767	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
106	last;	768	last;
		769	}
107	}	770	}
108	}	771	}
		772
		773	unless ($MODEL) {
		774	# try to load a model
		775
		776	for (@REGISTRY, @models) {
		777	my ($package, $model) = @$_;
		778	if (eval "require $package"
		779	and ${"$package\::VERSION"} > 0
		780	and eval "require $model") {
		781	$MODEL = $model;
		782	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		783	last;
		784	}
		785	}
		786
		787	$MODEL
		788	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		789	}
109	}	790	}
110		791
111	unless ($MODEL) {	792	unshift @ISA, $MODEL;
112	# try to load a model	793	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
113		794
114	for (@REGISTRY, @models) {	795	(shift @on_detect)->() while @on_detect;
115	my ($package, $model) = @$_;
116	if (eval "require $model") {
117	$MODEL = $model;
118	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
119	last;
120	}
121	}
122
123	$MODEL
124	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";
125	}
126	}	796	}
127		797
128	@ISA = $MODEL;	798	$MODEL
		799	}
		800
		801	sub AUTOLOAD {
		802	(my $func = $AUTOLOAD) =~ s/.*://;
		803
		804	$method{$func}
		805	or croak "$func: not a valid method for AnyEvent objects";
		806
		807	detect unless $MODEL;
129		808
130	my $class = shift;	809	my $class = shift;
131	$class->$AUTOLOAD (@_);	810	$class->$func (@_);
132	}	811	}
133		812
134	=back	813	package AnyEvent::Base;
		814
		815	# default implementation for ->condvar, ->wait, ->broadcast
		816
		817	sub condvar {
		818	bless \my $flag, "AnyEvent::Base::CondVar"
		819	}
		820
		821	sub AnyEvent::Base::CondVar::broadcast {
		822	${$_[0]}++;
		823	}
		824
		825	sub AnyEvent::Base::CondVar::wait {
		826	AnyEvent->one_event while !${$_[0]};
		827	}
		828
		829	# default implementation for ->signal
		830
		831	our %SIG_CB;
		832
		833	sub signal {
		834	my (undef, %arg) = @_;
		835
		836	my $signal = uc $arg{signal}
		837	or Carp::croak "required option 'signal' is missing";
		838
		839	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		840	$SIG{$signal} ||= sub {
		841	$_->() for values %{ $SIG_CB{$signal} || {} };
		842	};
		843
		844	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		845	}
		846
		847	sub AnyEvent::Base::Signal::DESTROY {
		848	my ($signal, $cb) = @{$_[0]};
		849
		850	delete $SIG_CB{$signal}{$cb};
		851
		852	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		853	}
		854
		855	# default implementation for ->child
		856
		857	our %PID_CB;
		858	our $CHLD_W;
		859	our $CHLD_DELAY_W;
		860	our $PID_IDLE;
		861	our $WNOHANG;
		862
		863	sub _child_wait {
		864	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		865	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		866	(values %{ $PID_CB{0} || {} });
		867	}
		868
		869	undef $PID_IDLE;
		870	}
		871
		872	sub _sigchld {
		873	# make sure we deliver these changes "synchronous" with the event loop.
		874	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		875	undef $CHLD_DELAY_W;
		876	&_child_wait;
		877	});
		878	}
		879
		880	sub child {
		881	my (undef, %arg) = @_;
		882
		883	defined (my $pid = $arg{pid} + 0)
		884	or Carp::croak "required option 'pid' is missing";
		885
		886	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		887
		888	unless ($WNOHANG) {
		889	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		890	}
		891
		892	unless ($CHLD_W) {
		893	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		894	# child could be a zombie already, so make at least one round
		895	&_sigchld;
		896	}
		897
		898	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		899	}
		900
		901	sub AnyEvent::Base::Child::DESTROY {
		902	my ($pid, $cb) = @{$_[0]};
		903
		904	delete $PID_CB{$pid}{$cb};
		905	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		906
		907	undef $CHLD_W unless keys %PID_CB;
		908	}
135		909
136	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	910	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		911
		912	This is an advanced topic that you do not normally need to use AnyEvent in
		913	a module. This section is only of use to event loop authors who want to
		914	provide AnyEvent compatibility.
137		915
138	If you need to support another event library which isn't directly	916	If you need to support another event library which isn't directly
139	supported by AnyEvent, you can supply your own interface to it by	917	supported by AnyEvent, you can supply your own interface to it by
140	pushing, before the first watcher gets created, the package name of	918	pushing, before the first watcher gets created, the package name of
141	the event module and the package name of the interface to use onto	919	the event module and the package name of the interface to use onto
142	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	920	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
143	AnyEvent.	921	AnyEvent, so it is reasonably cheap.
144		922
145	Example:	923	Example:
146		924
147	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	925	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
148		926
149	This tells AnyEvent to (literally) use the C<urxvt::anyevent::> module	927	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
150	when it finds the C<urxvt> module is loaded. When AnyEvent is loaded and	928	package/class when it finds the C<urxvt> package/module is already loaded.
151	requested to find a suitable event model, it will first check for the
152	urxvt module.
153		929
		930	When AnyEvent is loaded and asked to find a suitable event model, it
		931	will first check for the presence of urxvt by trying to C<use> the
		932	C<urxvt::anyevent> module.
		933
		934	The class should provide implementations for all watcher types. See
		935	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		936	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		937	see the sources.
		938
		939	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		940	provide suitable (hopefully) replacements.
		941
154	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt) uses	942	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
155	the above line exactly. An interface isn't included in AnyEvent	943	terminal emulator uses the above line as-is. An interface isn't included
156	because it doesn't make sense outside the embedded interpreter inside	944	in AnyEvent because it doesn't make sense outside the embedded interpreter
157	I<rxvt-unicode>, and it is updated and maintained as part of the	945	inside I<rxvt-unicode>, and it is updated and maintained as part of the
158	I<rxvt-unicode> distribution.	946	I<rxvt-unicode> distribution.
159		947
		948	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		949	condition variables: code blocking while waiting for a condition will
		950	C<die>. This still works with most modules/usages, and blocking calls must
		951	not be done in an interactive application, so it makes sense.
		952
160	=head1 ENVIRONMENT VARIABLES	953	=head1 ENVIRONMENT VARIABLES
161		954
162	The following environment variables are used by this module:	955	The following environment variables are used by this module:
163		956
164	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	957	=over 4
165	model gets used.
166		958
		959	=item C<PERL_ANYEVENT_VERBOSE>
		960
		961	By default, AnyEvent will be completely silent except in fatal
		962	conditions. You can set this environment variable to make AnyEvent more
		963	talkative.
		964
		965	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		966	conditions, such as not being able to load the event model specified by
		967	C<PERL_ANYEVENT_MODEL>.
		968
		969	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		970	model it chooses.
		971
		972	=item C<PERL_ANYEVENT_MODEL>
		973
		974	This can be used to specify the event model to be used by AnyEvent, before
		975	autodetection and -probing kicks in. It must be a string consisting
		976	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		977	and the resulting module name is loaded and if the load was successful,
		978	used as event model. If it fails to load AnyEvent will proceed with
		979	autodetection and -probing.
		980
		981	This functionality might change in future versions.
		982
		983	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		984	could start your program like this:
		985
		986	PERL_ANYEVENT_MODEL=Perl perl ...
		987
		988	=back
		989
167	=head1 EXAMPLE	990	=head1 EXAMPLE PROGRAM
168		991
169	The following program uses an io watcher to read data from stdin, a timer	992	The following program uses an I/O watcher to read data from STDIN, a timer
170	to display a message once per second, and a condvar to exit the program	993	to display a message once per second, and a condition variable to quit the
171	when the user enters quit:	994	program when the user enters quit:
172		995
173	use AnyEvent;	996	use AnyEvent;
174		997
175	my $cv = AnyEvent->condvar;	998	my $cv = AnyEvent->condvar;
176		999
177	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1000	my $io_watcher = AnyEvent->io (
		1001	fh => \*STDIN,
		1002	poll => 'r',
		1003	cb => sub {
178	warn "io event <$_[0]>\n"; # will always output <r>	1004	warn "io event <$_[0]>\n"; # will always output <r>
179	chomp (my $input = <STDIN>); # read a line	1005	chomp (my $input = <STDIN>); # read a line
180	warn "read: $input\n"; # output what has been read	1006	warn "read: $input\n"; # output what has been read
181	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1007	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		1008	},
182	});	1009	);
183		1010
184	my $time_watcher; # can only be used once	1011	my $time_watcher; # can only be used once
185		1012
186	sub new_timer {	1013	sub new_timer {
187	$timer = AnyEvent->timer (after => 1, cb => sub {	1014	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
269	$txn->{finished}->wait;	1096	$txn->{finished}->wait;
270	return $txn->{result};	1097	return $txn->{result};
271		1098
272	The actual code goes further and collects all errors (C<die>s, exceptions)	1099	The actual code goes further and collects all errors (C<die>s, exceptions)
273	that occured during request processing. The C<result> method detects	1100	that occured during request processing. The C<result> method detects
274	wether an exception as thrown (it is stored inside the $txn object)	1101	whether an exception as thrown (it is stored inside the $txn object)
275	and just throws the exception, which means connection errors and other	1102	and just throws the exception, which means connection errors and other
276	problems get reported tot he code that tries to use the result, not in a	1103	problems get reported tot he code that tries to use the result, not in a
277	random callback.	1104	random callback.
278		1105
279	All of this enables the following usage styles:	1106	All of this enables the following usage styles:
280		1107
281	1. Blocking:	1108	1. Blocking:
282		1109
283	my $data = $fcp->client_get ($url);	1110	my $data = $fcp->client_get ($url);
284		1111
285	2. Blocking, but parallelizing:	1112	2. Blocking, but running in parallel:
286		1113
287	my @datas = map $_->result,	1114	my @datas = map $_->result,
288	map $fcp->txn_client_get ($_),	1115	map $fcp->txn_client_get ($_),
289	@urls;	1116	@urls;
290		1117
291	Both blocking examples work without the module user having to know	1118	Both blocking examples work without the module user having to know
292	anything about events.	1119	anything about events.
293		1120
294	3a. Event-based in a main program, using any support Event module:	1121	3a. Event-based in a main program, using any supported event module:
295		1122
296	use Event;	1123	use EV;
297		1124
298	$fcp->txn_client_get ($url)->cb (sub {	1125	$fcp->txn_client_get ($url)->cb (sub {
299	my $txn = shift;	1126	my $txn = shift;
300	my $data = $txn->result;	1127	my $data = $txn->result;
301	...	1128	...
302	});	1129	});
303		1130
304	Event::loop;	1131	EV::loop;
305		1132
306	3b. The module user could use AnyEvent, too:	1133	3b. The module user could use AnyEvent, too:
307		1134
308	use AnyEvent;	1135	use AnyEvent;
309		1136
…		…
314	$quit->broadcast;	1141	$quit->broadcast;
315	});	1142	});
316		1143
317	$quit->wait;	1144	$quit->wait;
318		1145
		1146
		1147	=head1 BENCHMARKS
		1148
		1149	To give you an idea of the performance and overheads that AnyEvent adds
		1150	over the event loops themselves and to give you an impression of the speed
		1151	of various event loops I prepared some benchmarks.
		1152
		1153	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1154
		1155	Here is a benchmark of various supported event models used natively and
		1156	through anyevent. The benchmark creates a lot of timers (with a zero
		1157	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1158	which it is), lets them fire exactly once and destroys them again.
		1159
		1160	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1161	distribution.
		1162
		1163	=head3 Explanation of the columns
		1164
		1165	I<watcher> is the number of event watchers created/destroyed. Since
		1166	different event models feature vastly different performances, each event
		1167	loop was given a number of watchers so that overall runtime is acceptable
		1168	and similar between tested event loop (and keep them from crashing): Glib
		1169	would probably take thousands of years if asked to process the same number
		1170	of watchers as EV in this benchmark.
		1171
		1172	I<bytes> is the number of bytes (as measured by the resident set size,
		1173	RSS) consumed by each watcher. This method of measuring captures both C
		1174	and Perl-based overheads.
		1175
		1176	I<create> is the time, in microseconds (millionths of seconds), that it
		1177	takes to create a single watcher. The callback is a closure shared between
		1178	all watchers, to avoid adding memory overhead. That means closure creation
		1179	and memory usage is not included in the figures.
		1180
		1181	I<invoke> is the time, in microseconds, used to invoke a simple
		1182	callback. The callback simply counts down a Perl variable and after it was
		1183	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1184	signal the end of this phase.
		1185
		1186	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1187	watcher.
		1188
		1189	=head3 Results
		1190
		1191	name watchers bytes create invoke destroy comment
		1192	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1193	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1194	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1195	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1196	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1197	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1198	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1199	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1200	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1201	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1202
		1203	=head3 Discussion
		1204
		1205	The benchmark does I<not> measure scalability of the event loop very
		1206	well. For example, a select-based event loop (such as the pure perl one)
		1207	can never compete with an event loop that uses epoll when the number of
		1208	file descriptors grows high. In this benchmark, all events become ready at
		1209	the same time, so select/poll-based implementations get an unnatural speed
		1210	boost.
		1211
		1212	Also, note that the number of watchers usually has a nonlinear effect on
		1213	overall speed, that is, creating twice as many watchers doesn't take twice
		1214	the time - usually it takes longer. This puts event loops tested with a
		1215	higher number of watchers at a disadvantage.
		1216
		1217	To put the range of results into perspective, consider that on the
		1218	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1219	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1220	cycles with POE.
		1221
		1222	C<EV> is the sole leader regarding speed and memory use, which are both
		1223	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1224	far less memory than any other event loop and is still faster than Event
		1225	natively.
		1226
		1227	The pure perl implementation is hit in a few sweet spots (both the
		1228	constant timeout and the use of a single fd hit optimisations in the perl
		1229	interpreter and the backend itself). Nevertheless this shows that it
		1230	adds very little overhead in itself. Like any select-based backend its
		1231	performance becomes really bad with lots of file descriptors (and few of
		1232	them active), of course, but this was not subject of this benchmark.
		1233
		1234	The C<Event> module has a relatively high setup and callback invocation
		1235	cost, but overall scores in on the third place.
		1236
		1237	C<Glib>'s memory usage is quite a bit higher, but it features a
		1238	faster callback invocation and overall ends up in the same class as
		1239	C<Event>. However, Glib scales extremely badly, doubling the number of
		1240	watchers increases the processing time by more than a factor of four,
		1241	making it completely unusable when using larger numbers of watchers
		1242	(note that only a single file descriptor was used in the benchmark, so
		1243	inefficiencies of C<poll> do not account for this).
		1244
		1245	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1246	more than 2000 watchers is a big setback, however, as correctness takes
		1247	precedence over speed. Nevertheless, its performance is surprising, as the
		1248	file descriptor is dup()ed for each watcher. This shows that the dup()
		1249	employed by some adaptors is not a big performance issue (it does incur a
		1250	hidden memory cost inside the kernel which is not reflected in the figures
		1251	above).
		1252
		1253	C<POE>, regardless of underlying event loop (whether using its pure perl
		1254	select-based backend or the Event module, the POE-EV backend couldn't
		1255	be tested because it wasn't working) shows abysmal performance and
		1256	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1257	as EV watchers, and 10 times as much memory as Event (the high memory
		1258	requirements are caused by requiring a session for each watcher). Watcher
		1259	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1260	implementation.
		1261
		1262	The design of the POE adaptor class in AnyEvent can not really account
		1263	for the performance issues, though, as session creation overhead is
		1264	small compared to execution of the state machine, which is coded pretty
		1265	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1266	using multiple sessions is not a good approach, especially regarding
		1267	memory usage, even the author of POE could not come up with a faster
		1268	design).
		1269
		1270	=head3 Summary
		1271
		1272	=over 4
		1273
		1274	=item * Using EV through AnyEvent is faster than any other event loop
		1275	(even when used without AnyEvent), but most event loops have acceptable
		1276	performance with or without AnyEvent.
		1277
		1278	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1279	the actual event loop, only with extremely fast event loops such as EV
		1280	adds AnyEvent significant overhead.
		1281
		1282	=item * You should avoid POE like the plague if you want performance or
		1283	reasonable memory usage.
		1284
		1285	=back
		1286
		1287	=head2 BENCHMARKING THE LARGE SERVER CASE
		1288
		1289	This benchmark atcually benchmarks the event loop itself. It works by
		1290	creating a number of "servers": each server consists of a socketpair, a
		1291	timeout watcher that gets reset on activity (but never fires), and an I/O
		1292	watcher waiting for input on one side of the socket. Each time the socket
		1293	watcher reads a byte it will write that byte to a random other "server".
		1294
		1295	The effect is that there will be a lot of I/O watchers, only part of which
		1296	are active at any one point (so there is a constant number of active
		1297	fds for each loop iterstaion, but which fds these are is random). The
		1298	timeout is reset each time something is read because that reflects how
		1299	most timeouts work (and puts extra pressure on the event loops).
		1300
		1301	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1302	(1%) are active. This mirrors the activity of large servers with many
		1303	connections, most of which are idle at any one point in time.
		1304
		1305	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1306	distribution.
		1307
		1308	=head3 Explanation of the columns
		1309
		1310	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1311	each server has a read and write socket end).
		1312
		1313	I<create> is the time it takes to create a socketpair (which is
		1314	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1315
		1316	I<request>, the most important value, is the time it takes to handle a
		1317	single "request", that is, reading the token from the pipe and forwarding
		1318	it to another server. This includes deleting the old timeout and creating
		1319	a new one that moves the timeout into the future.
		1320
		1321	=head3 Results
		1322
		1323	name sockets create request
		1324	EV 20000 69.01 11.16
		1325	Perl 20000 73.32 35.87
		1326	Event 20000 212.62 257.32
		1327	Glib 20000 651.16 1896.30
		1328	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1329
		1330	=head3 Discussion
		1331
		1332	This benchmark I<does> measure scalability and overall performance of the
		1333	particular event loop.
		1334
		1335	EV is again fastest. Since it is using epoll on my system, the setup time
		1336	is relatively high, though.
		1337
		1338	Perl surprisingly comes second. It is much faster than the C-based event
		1339	loops Event and Glib.
		1340
		1341	Event suffers from high setup time as well (look at its code and you will
		1342	understand why). Callback invocation also has a high overhead compared to
		1343	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1344	uses select or poll in basically all documented configurations.
		1345
		1346	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1347	clearly fails to perform with many filehandles or in busy servers.
		1348
		1349	POE is still completely out of the picture, taking over 1000 times as long
		1350	as EV, and over 100 times as long as the Perl implementation, even though
		1351	it uses a C-based event loop in this case.
		1352
		1353	=head3 Summary
		1354
		1355	=over 4
		1356
		1357	=item * The pure perl implementation performs extremely well.
		1358
		1359	=item * Avoid Glib or POE in large projects where performance matters.
		1360
		1361	=back
		1362
		1363	=head2 BENCHMARKING SMALL SERVERS
		1364
		1365	While event loops should scale (and select-based ones do not...) even to
		1366	large servers, most programs we (or I :) actually write have only a few
		1367	I/O watchers.
		1368
		1369	In this benchmark, I use the same benchmark program as in the large server
		1370	case, but it uses only eight "servers", of which three are active at any
		1371	one time. This should reflect performance for a small server relatively
		1372	well.
		1373
		1374	The columns are identical to the previous table.
		1375
		1376	=head3 Results
		1377
		1378	name sockets create request
		1379	EV 16 20.00 6.54
		1380	Perl 16 25.75 12.62
		1381	Event 16 81.27 35.86
		1382	Glib 16 32.63 15.48
		1383	POE 16 261.87 276.28 uses POE::Loop::Event
		1384
		1385	=head3 Discussion
		1386
		1387	The benchmark tries to test the performance of a typical small
		1388	server. While knowing how various event loops perform is interesting, keep
		1389	in mind that their overhead in this case is usually not as important, due
		1390	to the small absolute number of watchers (that is, you need efficiency and
		1391	speed most when you have lots of watchers, not when you only have a few of
		1392	them).
		1393
		1394	EV is again fastest.
		1395
		1396	Perl again comes second. It is noticably faster than the C-based event
		1397	loops Event and Glib, although the difference is too small to really
		1398	matter.
		1399
		1400	POE also performs much better in this case, but is is still far behind the
		1401	others.
		1402
		1403	=head3 Summary
		1404
		1405	=over 4
		1406
		1407	=item * C-based event loops perform very well with small number of
		1408	watchers, as the management overhead dominates.
		1409
		1410	=back
		1411
		1412
		1413	=head1 FORK
		1414
		1415	Most event libraries are not fork-safe. The ones who are usually are
		1416	because they rely on inefficient but fork-safe C<select> or C<poll>
		1417	calls. Only L<EV> is fully fork-aware.
		1418
		1419	If you have to fork, you must either do so I<before> creating your first
		1420	watcher OR you must not use AnyEvent at all in the child.
		1421
		1422
		1423	=head1 SECURITY CONSIDERATIONS
		1424
		1425	AnyEvent can be forced to load any event model via
		1426	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1427	execute arbitrary code or directly gain access, it can easily be used to
		1428	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1429	will not be active when the program uses a different event model than
		1430	specified in the variable.
		1431
		1432	You can make AnyEvent completely ignore this variable by deleting it
		1433	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1434
		1435	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1436
		1437	use AnyEvent;
		1438
		1439	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1440	be used to probe what backend is used and gain other information (which is
		1441	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1442
		1443
319	=head1 SEE ALSO	1444	=head1 SEE ALSO
320		1445
321	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1446	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1447	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
322		1448
323	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1449	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1450	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1451	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1452	L<AnyEvent::Impl::POE>.
324		1453
		1454	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1455
325	Nontrivial usage example: L<Net::FCP>.	1456	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
326		1457
327	=head1	1458
		1459	=head1 AUTHOR
		1460
		1461	Marc Lehmann <schmorp@schmorp.de>
		1462	http://home.schmorp.de/
328		1463
329	=cut	1464	=cut
330		1465
331	1	1466	1
332		1467

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