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Revision 1.6 by root, Mon Dec 19 17:03:29 2005 UTC vs.
Revision 1.126 by root, Fri May 23 23:44:55 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		20	$w->send; # wake up current and all future recv's
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	21	$w->recv; # enters "main loop" till $condvar gets ->send
33	$w->broadcast; # 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	my $pid = fork or exit 5;
		285
		286	my $w = AnyEvent->child (
		287	pid => $pid,
		288	cb => sub {
		289	my ($pid, $status) = @_;
		290	warn "pid $pid exited with status $status";
		291	$done->send;
		292	},
		293	);
		294
		295	# do something else, then wait for process exit
		296	$done->recv;
		297
		298	=head2 CONDITION VARIABLES
		299
		300	If you are familiar with some event loops you will know that all of them
		301	require you to run some blocking "loop", "run" or similar function that
		302	will actively watch for new events and call your callbacks.
		303
		304	AnyEvent is different, it expects somebody else to run the event loop and
		305	will only block when necessary (usually when told by the user).
		306
		307	The instrument to do that is called a "condition variable", so called
		308	because they represent a condition that must become true.
		309
		310	Condition variables can be created by calling the C<< AnyEvent->condvar
		311	>> method, usually without arguments. The only argument pair allowed is
		312	C<cb>, which specifies a callback to be called when the condition variable
		313	becomes true.
		314
		315	After creation, the conditon variable is "false" until it becomes "true"
		316	by calling the C<send> method.
		317
		318	Condition variables are similar to callbacks, except that you can
		319	optionally wait for them. They can also be called merge points - points
		320	in time where multiple outstandign events have been processed. And yet
		321	another way to call them is transations - each condition variable can be
		322	used to represent a transaction, which finishes at some point and delivers
		323	a result.
		324
		325	Condition variables are very useful to signal that something has finished,
		326	for example, if you write a module that does asynchronous http requests,
		327	then a condition variable would be the ideal candidate to signal the
		328	availability of results. The user can either act when the callback is
		329	called or can synchronously C<< ->recv >> for the results.
		330
		331	You can also use them to simulate traditional event loops - for example,
		332	you can block your main program until an event occurs - for example, you
		333	could C<< ->recv >> in your main program until the user clicks the Quit
		334	button of your app, which would C<< ->send >> the "quit" event.
		335
		336	Note that condition variables recurse into the event loop - if you have
		337	two pieces of code that call C<< ->recv >> in a round-robbin fashion, you
		338	lose. Therefore, condition variables are good to export to your caller, but
		339	you should avoid making a blocking wait yourself, at least in callbacks,
		340	as this asks for trouble.
		341
		342	Condition variables are represented by hash refs in perl, and the keys
		343	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		344	easy (it is often useful to build your own transaction class on top of
		345	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		346	it's C<new> method in your own C<new> method.
		347
		348	There are two "sides" to a condition variable - the "producer side" which
		349	eventually calls C<< -> send >>, and the "consumer side", which waits
		350	for the send to occur.
		351
		352	Example:
		353
		354	# wait till the result is ready
		355	my $result_ready = AnyEvent->condvar;
		356
		357	# do something such as adding a timer
		358	# or socket watcher the calls $result_ready->send
		359	# when the "result" is ready.
		360	# in this case, we simply use a timer:
		361	my $w = AnyEvent->timer (
		362	after => 1,
		363	cb => sub { $result_ready->send },
		364	);
		365
		366	# this "blocks" (while handling events) till the callback
		367	# calls send
		368	$result_ready->recv;
		369
		370	=head3 METHODS FOR PRODUCERS
		371
		372	These methods should only be used by the producing side, i.e. the
		373	code/module that eventually sends the signal. Note that it is also
		374	the producer side which creates the condvar in most cases, but it isn't
		375	uncommon for the consumer to create it as well.
56		376
57	=over 4	377	=over 4
58		378
		379	=item $cv->send (...)
		380
		381	Flag the condition as ready - a running C<< ->recv >> and all further
		382	calls to C<recv> will (eventually) return after this method has been
		383	called. If nobody is waiting the send will be remembered.
		384
		385	If a callback has been set on the condition variable, it is called
		386	immediately from within send.
		387
		388	Any arguments passed to the C<send> call will be returned by all
		389	future C<< ->recv >> calls.
		390
		391	=item $cv->croak ($error)
		392
		393	Similar to send, but causes all call's to C<< ->recv >> to invoke
		394	C<Carp::croak> with the given error message/object/scalar.
		395
		396	This can be used to signal any errors to the condition variable
		397	user/consumer.
		398
		399	=item $cv->begin ([group callback])
		400
		401	=item $cv->end
		402
		403	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		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 $cv->recv
		460
		461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		462	>> methods have been called on c<$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<< ->recv >> in a module is that you cannot
		483	sensibly have two C<< ->recv >>'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<< ->recv >> 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<< -recv >> never blocks by setting a callback and
		494	only calling C<< ->recv >> 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<recv> 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<< ->recv >> 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<< ->recv >> 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<< ->recv >>
		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 various utility functions for (internet protocol) sockets,
		639	addresses and name resolution. Also functions to create non-blocking tcp
		640	connections or tcp servers, with IPv6 and SRV record support and more.
		641
		642	=item L<AnyEvent::HTTPD>
		643
		644	Provides a simple web application server framework.
		645
		646	=item L<AnyEvent::DNS>
		647
		648	Provides rich asynchronous DNS resolver capabilities.
		649
		650	=item L<AnyEvent::FastPing>
		651
		652	The fastest ping in the west.
		653
		654	=item L<Net::IRC3>
		655
		656	AnyEvent based IRC client module family.
		657
		658	=item L<Net::XMPP2>
		659
		660	AnyEvent based XMPP (Jabber protocol) module family.
		661
		662	=item L<Net::FCP>
		663
		664	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		665	of AnyEvent.
		666
		667	=item L<Event::ExecFlow>
		668
		669	High level API for event-based execution flow control.
		670
		671	=item L<Coro>
		672
		673	Has special support for AnyEvent via L<Coro::AnyEvent>.
		674
		675	=item L<AnyEvent::AIO>, L<IO::AIO>
		676
		677	Truly asynchronous I/O, should be in the toolbox of every event
		678	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		679	together.
		680
		681	=item L<AnyEvent::BDB>, L<BDB>
		682
		683	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		684	IO::AIO and AnyEvent together.
		685
		686	=item L<IO::Lambda>
		687
		688	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		689
		690	=back
		691
59	=cut	692	=cut
60		693
61	package AnyEvent;	694	package AnyEvent;
62		695
63	no warnings;	696	no warnings;
64	use strict 'vars';	697	use strict;
		698
65	use Carp;	699	use Carp;
66		700
67	our $VERSION = 0.3;	701	our $VERSION = '3.6';
68	our $MODEL;	702	our $MODEL;
69		703
70	our $AUTOLOAD;	704	our $AUTOLOAD;
71	our @ISA;	705	our @ISA;
72		706
		707	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		708
		709	our @REGISTRY;
		710
		711	our %PROTOCOL; # (ipv4|ipv6) => (1|2)
		712
		713	{
		714	my $idx;
		715	$PROTOCOL{$_} = ++$idx
		716	for split /\s*,\s*/, $ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		717	}
		718
73	my @models = (	719	my @models = (
74	[Coro => Coro::Event::],	720	[EV:: => AnyEvent::Impl::EV::],
75	[Event => Event::],	721	[Event:: => AnyEvent::Impl::Event::],
76	[Glib => Glib::],	722	[Tk:: => AnyEvent::Impl::Tk::],
77	[Tk => Tk::],	723	[Wx:: => AnyEvent::Impl::POE::],
		724	[Prima:: => AnyEvent::Impl::POE::],
		725	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		726	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		727	[Glib:: => AnyEvent::Impl::Glib::],
		728	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		729	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		730	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
78	);	731	);
79		732
80	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	733	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
81		734
82	sub AUTOLOAD {	735	our @post_detect;
83	$AUTOLOAD =~ s/.*://;
84		736
85	$method{$AUTOLOAD}	737	sub post_detect(&) {
86	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	738	my ($cb) = @_;
87		739
		740	if ($MODEL) {
		741	$cb->();
		742
		743	1
		744	} else {
		745	push @post_detect, $cb;
		746
		747	defined wantarray
		748	? bless \$cb, "AnyEvent::Util::PostDetect"
		749	: ()
		750	}
		751	}
		752
		753	sub AnyEvent::Util::PostDetect::DESTROY {
		754	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		755	}
		756
		757	sub detect() {
88	unless ($MODEL) {	758	unless ($MODEL) {
89	# check for already loaded models	759	no strict 'refs';
90	for (@models) {	760
91	my ($model, $package) = @$_;	761	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
92	if (scalar keys %{ *{"$package\::"} }) {	762	my $model = "AnyEvent::Impl::$1";
93	eval "require AnyEvent::Impl::$model";	763	if (eval "require $model") {
94	last if $MODEL;	764	$MODEL = $model;
		765	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		766	} else {
		767	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
95	}	768	}
96	}	769	}
97		770
		771	# check for already loaded models
98	unless ($MODEL) {	772	unless ($MODEL) {
99	# try to load a model
100
101	for (@models) {	773	for (@REGISTRY, @models) {
102	my ($model, $package) = @$_;	774	my ($package, $model) = @$_;
103	eval "require AnyEvent::Impl::$model";	775	if (${"$package\::VERSION"} > 0) {
104	last if $MODEL;	776	if (eval "require $model") {
		777	$MODEL = $model;
		778	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		779	last;
		780	}
		781	}
105	}	782	}
106		783
		784	unless ($MODEL) {
		785	# try to load a model
		786
		787	for (@REGISTRY, @models) {
		788	my ($package, $model) = @$_;
		789	if (eval "require $package"
		790	and ${"$package\::VERSION"} > 0
		791	and eval "require $model") {
		792	$MODEL = $model;
		793	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		794	last;
		795	}
		796	}
		797
107	$MODEL	798	$MODEL
108	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	799	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		800	}
109	}	801	}
		802
		803	unshift @ISA, $MODEL;
		804	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		805
		806	(shift @post_detect)->() while @post_detect;
110	}	807	}
111		808
112	@ISA = $MODEL;	809	$MODEL
		810	}
		811
		812	sub AUTOLOAD {
		813	(my $func = $AUTOLOAD) =~ s/.*://;
		814
		815	$method{$func}
		816	or croak "$func: not a valid method for AnyEvent objects";
		817
		818	detect unless $MODEL;
113		819
114	my $class = shift;	820	my $class = shift;
115	$class->$AUTOLOAD (@_);	821	$class->$func (@_);
116	}	822	}
		823
		824	package AnyEvent::Base;
		825
		826	# default implementation for ->condvar
		827
		828	sub condvar {
		829	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		830	}
		831
		832	# default implementation for ->signal
		833
		834	our %SIG_CB;
		835
		836	sub signal {
		837	my (undef, %arg) = @_;
		838
		839	my $signal = uc $arg{signal}
		840	or Carp::croak "required option 'signal' is missing";
		841
		842	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		843	$SIG{$signal} ||= sub {
		844	$_->() for values %{ $SIG_CB{$signal} || {} };
		845	};
		846
		847	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		848	}
		849
		850	sub AnyEvent::Base::Signal::DESTROY {
		851	my ($signal, $cb) = @{$_[0]};
		852
		853	delete $SIG_CB{$signal}{$cb};
		854
		855	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		856	}
		857
		858	# default implementation for ->child
		859
		860	our %PID_CB;
		861	our $CHLD_W;
		862	our $CHLD_DELAY_W;
		863	our $PID_IDLE;
		864	our $WNOHANG;
		865
		866	sub _child_wait {
		867	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		868	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		869	(values %{ $PID_CB{0} || {} });
		870	}
		871
		872	undef $PID_IDLE;
		873	}
		874
		875	sub _sigchld {
		876	# make sure we deliver these changes "synchronous" with the event loop.
		877	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		878	undef $CHLD_DELAY_W;
		879	&_child_wait;
		880	});
		881	}
		882
		883	sub child {
		884	my (undef, %arg) = @_;
		885
		886	defined (my $pid = $arg{pid} + 0)
		887	or Carp::croak "required option 'pid' is missing";
		888
		889	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		890
		891	unless ($WNOHANG) {
		892	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		893	}
		894
		895	unless ($CHLD_W) {
		896	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		897	# child could be a zombie already, so make at least one round
		898	&_sigchld;
		899	}
		900
		901	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		902	}
		903
		904	sub AnyEvent::Base::Child::DESTROY {
		905	my ($pid, $cb) = @{$_[0]};
		906
		907	delete $PID_CB{$pid}{$cb};
		908	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		909
		910	undef $CHLD_W unless keys %PID_CB;
		911	}
		912
		913	package AnyEvent::CondVar;
		914
		915	our @ISA = AnyEvent::CondVar::Base::;
		916
		917	package AnyEvent::CondVar::Base;
		918
		919	sub _send {
		920	# nop
		921	}
		922
		923	sub send {
		924	my $cv = shift;
		925	$cv->{_ae_sent} = [@_];
		926	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		927	$cv->_send;
		928	}
		929
		930	sub croak {
		931	$_[0]{_ae_croak} = $_[1];
		932	$_[0]->send;
		933	}
		934
		935	sub ready {
		936	$_[0]{_ae_sent}
		937	}
		938
		939	sub _wait {
		940	AnyEvent->one_event while !$_[0]{_ae_sent};
		941	}
		942
		943	sub recv {
		944	$_[0]->_wait;
		945
		946	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		947	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		948	}
		949
		950	sub cb {
		951	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		952	$_[0]{_ae_cb}
		953	}
		954
		955	sub begin {
		956	++$_[0]{_ae_counter};
		957	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		958	}
		959
		960	sub end {
		961	return if --$_[0]{_ae_counter};
		962	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		963	}
		964
		965	# undocumented/compatibility with pre-3.4
		966	*broadcast = \&send;
		967	*wait = \&_wait;
		968
		969	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		970
		971	This is an advanced topic that you do not normally need to use AnyEvent in
		972	a module. This section is only of use to event loop authors who want to
		973	provide AnyEvent compatibility.
		974
		975	If you need to support another event library which isn't directly
		976	supported by AnyEvent, you can supply your own interface to it by
		977	pushing, before the first watcher gets created, the package name of
		978	the event module and the package name of the interface to use onto
		979	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		980	AnyEvent, so it is reasonably cheap.
		981
		982	Example:
		983
		984	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		985
		986	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		987	package/class when it finds the C<urxvt> package/module is already loaded.
		988
		989	When AnyEvent is loaded and asked to find a suitable event model, it
		990	will first check for the presence of urxvt by trying to C<use> the
		991	C<urxvt::anyevent> module.
		992
		993	The class should provide implementations for all watcher types. See
		994	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		995	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		996	see the sources.
		997
		998	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		999	provide suitable (hopefully) replacements.
		1000
		1001	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1002	terminal emulator uses the above line as-is. An interface isn't included
		1003	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1004	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1005	I<rxvt-unicode> distribution.
		1006
		1007	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1008	condition variables: code blocking while waiting for a condition will
		1009	C<die>. This still works with most modules/usages, and blocking calls must
		1010	not be done in an interactive application, so it makes sense.
		1011
		1012	=head1 ENVIRONMENT VARIABLES
		1013
		1014	The following environment variables are used by this module:
		1015
		1016	=over 4
		1017
		1018	=item C<PERL_ANYEVENT_VERBOSE>
		1019
		1020	By default, AnyEvent will be completely silent except in fatal
		1021	conditions. You can set this environment variable to make AnyEvent more
		1022	talkative.
		1023
		1024	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1025	conditions, such as not being able to load the event model specified by
		1026	C<PERL_ANYEVENT_MODEL>.
		1027
		1028	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1029	model it chooses.
		1030
		1031	=item C<PERL_ANYEVENT_MODEL>
		1032
		1033	This can be used to specify the event model to be used by AnyEvent, before
		1034	autodetection and -probing kicks in. It must be a string consisting
		1035	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1036	and the resulting module name is loaded and if the load was successful,
		1037	used as event model. If it fails to load AnyEvent will proceed with
		1038	autodetection and -probing.
		1039
		1040	This functionality might change in future versions.
		1041
		1042	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1043	could start your program like this:
		1044
		1045	PERL_ANYEVENT_MODEL=Perl perl ...
		1046
		1047	=item C<PERL_ANYEVENT_PROTOCOLS>
		1048
		1049	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1050	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1051	of autoprobing).
		1052
		1053	Must be set to a comma-separated list of protocols or address families,
		1054	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1055	used, and preference will be given to protocols mentioned earlier in the
		1056	list.
		1057
		1058	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1059	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1060	- only support IPv4, never try to resolve or contact IPv6
		1061	addressses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1062	IPv6, but prefer IPv6 over IPv4.
117		1063
118	=back	1064	=back
119		1065
120	=head1 EXAMPLE	1066	=head1 EXAMPLE PROGRAM
121		1067
122	The following program uses an io watcher to read data from stdin, a timer	1068	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	1069	to display a message once per second, and a condition variable to quit the
124	when the user enters quit:	1070	program when the user enters quit:
125		1071
126	use AnyEvent;	1072	use AnyEvent;
127		1073
128	my $cv = AnyEvent->condvar;	1074	my $cv = AnyEvent->condvar;
129		1075
130	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1076	my $io_watcher = AnyEvent->io (
		1077	fh => \*STDIN,
		1078	poll => 'r',
		1079	cb => sub {
131	warn "io event <$_[0]>\n"; # will always output <r>	1080	warn "io event <$_[0]>\n"; # will always output <r>
132	chomp (my $input = <STDIN>); # read a line	1081	chomp (my $input = <STDIN>); # read a line
133	warn "read: $input\n"; # output what has been read	1082	warn "read: $input\n"; # output what has been read
134	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1083	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1084	},
135	});	1085	);
136		1086
137	my $time_watcher; # can only be used once	1087	my $time_watcher; # can only be used once
138		1088
139	sub new_timer {	1089	sub new_timer {
140	$timer = AnyEvent->timer (after => 1, cb => sub {	1090	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
143	});	1093	});
144	}	1094	}
145		1095
146	new_timer; # create first timer	1096	new_timer; # create first timer
147		1097
148	$cv->wait; # wait until user enters /^q/i	1098	$cv->recv; # wait until user enters /^q/i
149		1099
150	=head1 REAL-WORLD EXAMPLE	1100	=head1 REAL-WORLD EXAMPLE
151		1101
152	Consider the L<Net::FCP> module. It features (among others) the following	1102	Consider the L<Net::FCP> module. It features (among others) the following
153	API calls, which are to freenet what HTTP GET requests are to http:	1103	API calls, which are to freenet what HTTP GET requests are to http:
…		…
209		1159
210	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1160	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
211		1161
212	if (end-of-file or data complete) {	1162	if (end-of-file or data complete) {
213	$txn->{result} = $txn->{buf};	1163	$txn->{result} = $txn->{buf};
214	$txn->{finished}->broadcast;	1164	$txn->{finished}->send;
215	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1165	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
216	}	1166	}
217		1167
218	The C<result> method, finally, just waits for the finished signal (if the	1168	The C<result> method, finally, just waits for the finished signal (if the
219	request was already finished, it doesn't wait, of course, and returns the	1169	request was already finished, it doesn't wait, of course, and returns the
220	data:	1170	data:
221		1171
222	$txn->{finished}->wait;	1172	$txn->{finished}->recv;
223	return $txn->{result};	1173	return $txn->{result};
224		1174
225	The actual code goes further and collects all errors (C<die>s, exceptions)	1175	The actual code goes further and collects all errors (C<die>s, exceptions)
226	that occured during request processing. The C<result> method detects	1176	that occured during request processing. The C<result> method detects
227	wether an exception as thrown (it is stored inside the $txn object)	1177	whether an exception as thrown (it is stored inside the $txn object)
228	and just throws the exception, which means connection errors and other	1178	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	1179	problems get reported tot he code that tries to use the result, not in a
230	random callback.	1180	random callback.
231		1181
232	All of this enables the following usage styles:	1182	All of this enables the following usage styles:
233		1183
234	1. Blocking:	1184	1. Blocking:
235		1185
236	my $data = $fcp->client_get ($url);	1186	my $data = $fcp->client_get ($url);
237		1187
238	2. Blocking, but parallelizing:	1188	2. Blocking, but running in parallel:
239		1189
240	my @datas = map $_->result,	1190	my @datas = map $_->result,
241	map $fcp->txn_client_get ($_),	1191	map $fcp->txn_client_get ($_),
242	@urls;	1192	@urls;
243		1193
244	Both blocking examples work without the module user having to know	1194	Both blocking examples work without the module user having to know
245	anything about events.	1195	anything about events.
246		1196
247	3a. Event-based in a main program, using any support Event module:	1197	3a. Event-based in a main program, using any supported event module:
248		1198
249	use Event;	1199	use EV;
250		1200
251	$fcp->txn_client_get ($url)->cb (sub {	1201	$fcp->txn_client_get ($url)->cb (sub {
252	my $txn = shift;	1202	my $txn = shift;
253	my $data = $txn->result;	1203	my $data = $txn->result;
254	...	1204	...
255	});	1205	});
256		1206
257	Event::loop;	1207	EV::loop;
258		1208
259	3b. The module user could use AnyEvent, too:	1209	3b. The module user could use AnyEvent, too:
260		1210
261	use AnyEvent;	1211	use AnyEvent;
262		1212
263	my $quit = AnyEvent->condvar;	1213	my $quit = AnyEvent->condvar;
264		1214
265	$fcp->txn_client_get ($url)->cb (sub {	1215	$fcp->txn_client_get ($url)->cb (sub {
266	...	1216	...
267	$quit->broadcast;	1217	$quit->send;
268	});	1218	});
269		1219
270	$quit->wait;	1220	$quit->recv;
		1221
		1222
		1223	=head1 BENCHMARKS
		1224
		1225	To give you an idea of the performance and overheads that AnyEvent adds
		1226	over the event loops themselves and to give you an impression of the speed
		1227	of various event loops I prepared some benchmarks.
		1228
		1229	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1230
		1231	Here is a benchmark of various supported event models used natively and
		1232	through anyevent. The benchmark creates a lot of timers (with a zero
		1233	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1234	which it is), lets them fire exactly once and destroys them again.
		1235
		1236	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1237	distribution.
		1238
		1239	=head3 Explanation of the columns
		1240
		1241	I<watcher> is the number of event watchers created/destroyed. Since
		1242	different event models feature vastly different performances, each event
		1243	loop was given a number of watchers so that overall runtime is acceptable
		1244	and similar between tested event loop (and keep them from crashing): Glib
		1245	would probably take thousands of years if asked to process the same number
		1246	of watchers as EV in this benchmark.
		1247
		1248	I<bytes> is the number of bytes (as measured by the resident set size,
		1249	RSS) consumed by each watcher. This method of measuring captures both C
		1250	and Perl-based overheads.
		1251
		1252	I<create> is the time, in microseconds (millionths of seconds), that it
		1253	takes to create a single watcher. The callback is a closure shared between
		1254	all watchers, to avoid adding memory overhead. That means closure creation
		1255	and memory usage is not included in the figures.
		1256
		1257	I<invoke> is the time, in microseconds, used to invoke a simple
		1258	callback. The callback simply counts down a Perl variable and after it was
		1259	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1260	signal the end of this phase.
		1261
		1262	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1263	watcher.
		1264
		1265	=head3 Results
		1266
		1267	name watchers bytes create invoke destroy comment
		1268	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1269	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1270	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1271	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1272	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1273	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1274	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1275	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1276	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1277	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1278
		1279	=head3 Discussion
		1280
		1281	The benchmark does I<not> measure scalability of the event loop very
		1282	well. For example, a select-based event loop (such as the pure perl one)
		1283	can never compete with an event loop that uses epoll when the number of
		1284	file descriptors grows high. In this benchmark, all events become ready at
		1285	the same time, so select/poll-based implementations get an unnatural speed
		1286	boost.
		1287
		1288	Also, note that the number of watchers usually has a nonlinear effect on
		1289	overall speed, that is, creating twice as many watchers doesn't take twice
		1290	the time - usually it takes longer. This puts event loops tested with a
		1291	higher number of watchers at a disadvantage.
		1292
		1293	To put the range of results into perspective, consider that on the
		1294	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1295	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1296	cycles with POE.
		1297
		1298	C<EV> is the sole leader regarding speed and memory use, which are both
		1299	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1300	far less memory than any other event loop and is still faster than Event
		1301	natively.
		1302
		1303	The pure perl implementation is hit in a few sweet spots (both the
		1304	constant timeout and the use of a single fd hit optimisations in the perl
		1305	interpreter and the backend itself). Nevertheless this shows that it
		1306	adds very little overhead in itself. Like any select-based backend its
		1307	performance becomes really bad with lots of file descriptors (and few of
		1308	them active), of course, but this was not subject of this benchmark.
		1309
		1310	The C<Event> module has a relatively high setup and callback invocation
		1311	cost, but overall scores in on the third place.
		1312
		1313	C<Glib>'s memory usage is quite a bit higher, but it features a
		1314	faster callback invocation and overall ends up in the same class as
		1315	C<Event>. However, Glib scales extremely badly, doubling the number of
		1316	watchers increases the processing time by more than a factor of four,
		1317	making it completely unusable when using larger numbers of watchers
		1318	(note that only a single file descriptor was used in the benchmark, so
		1319	inefficiencies of C<poll> do not account for this).
		1320
		1321	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1322	more than 2000 watchers is a big setback, however, as correctness takes
		1323	precedence over speed. Nevertheless, its performance is surprising, as the
		1324	file descriptor is dup()ed for each watcher. This shows that the dup()
		1325	employed by some adaptors is not a big performance issue (it does incur a
		1326	hidden memory cost inside the kernel which is not reflected in the figures
		1327	above).
		1328
		1329	C<POE>, regardless of underlying event loop (whether using its pure perl
		1330	select-based backend or the Event module, the POE-EV backend couldn't
		1331	be tested because it wasn't working) shows abysmal performance and
		1332	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1333	as EV watchers, and 10 times as much memory as Event (the high memory
		1334	requirements are caused by requiring a session for each watcher). Watcher
		1335	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1336	implementation.
		1337
		1338	The design of the POE adaptor class in AnyEvent can not really account
		1339	for the performance issues, though, as session creation overhead is
		1340	small compared to execution of the state machine, which is coded pretty
		1341	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1342	using multiple sessions is not a good approach, especially regarding
		1343	memory usage, even the author of POE could not come up with a faster
		1344	design).
		1345
		1346	=head3 Summary
		1347
		1348	=over 4
		1349
		1350	=item * Using EV through AnyEvent is faster than any other event loop
		1351	(even when used without AnyEvent), but most event loops have acceptable
		1352	performance with or without AnyEvent.
		1353
		1354	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1355	the actual event loop, only with extremely fast event loops such as EV
		1356	adds AnyEvent significant overhead.
		1357
		1358	=item * You should avoid POE like the plague if you want performance or
		1359	reasonable memory usage.
		1360
		1361	=back
		1362
		1363	=head2 BENCHMARKING THE LARGE SERVER CASE
		1364
		1365	This benchmark atcually benchmarks the event loop itself. It works by
		1366	creating a number of "servers": each server consists of a socketpair, a
		1367	timeout watcher that gets reset on activity (but never fires), and an I/O
		1368	watcher waiting for input on one side of the socket. Each time the socket
		1369	watcher reads a byte it will write that byte to a random other "server".
		1370
		1371	The effect is that there will be a lot of I/O watchers, only part of which
		1372	are active at any one point (so there is a constant number of active
		1373	fds for each loop iterstaion, but which fds these are is random). The
		1374	timeout is reset each time something is read because that reflects how
		1375	most timeouts work (and puts extra pressure on the event loops).
		1376
		1377	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1378	(1%) are active. This mirrors the activity of large servers with many
		1379	connections, most of which are idle at any one point in time.
		1380
		1381	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1382	distribution.
		1383
		1384	=head3 Explanation of the columns
		1385
		1386	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1387	each server has a read and write socket end).
		1388
		1389	I<create> is the time it takes to create a socketpair (which is
		1390	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1391
		1392	I<request>, the most important value, is the time it takes to handle a
		1393	single "request", that is, reading the token from the pipe and forwarding
		1394	it to another server. This includes deleting the old timeout and creating
		1395	a new one that moves the timeout into the future.
		1396
		1397	=head3 Results
		1398
		1399	name sockets create request
		1400	EV 20000 69.01 11.16
		1401	Perl 20000 73.32 35.87
		1402	Event 20000 212.62 257.32
		1403	Glib 20000 651.16 1896.30
		1404	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1405
		1406	=head3 Discussion
		1407
		1408	This benchmark I<does> measure scalability and overall performance of the
		1409	particular event loop.
		1410
		1411	EV is again fastest. Since it is using epoll on my system, the setup time
		1412	is relatively high, though.
		1413
		1414	Perl surprisingly comes second. It is much faster than the C-based event
		1415	loops Event and Glib.
		1416
		1417	Event suffers from high setup time as well (look at its code and you will
		1418	understand why). Callback invocation also has a high overhead compared to
		1419	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1420	uses select or poll in basically all documented configurations.
		1421
		1422	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1423	clearly fails to perform with many filehandles or in busy servers.
		1424
		1425	POE is still completely out of the picture, taking over 1000 times as long
		1426	as EV, and over 100 times as long as the Perl implementation, even though
		1427	it uses a C-based event loop in this case.
		1428
		1429	=head3 Summary
		1430
		1431	=over 4
		1432
		1433	=item * The pure perl implementation performs extremely well.
		1434
		1435	=item * Avoid Glib or POE in large projects where performance matters.
		1436
		1437	=back
		1438
		1439	=head2 BENCHMARKING SMALL SERVERS
		1440
		1441	While event loops should scale (and select-based ones do not...) even to
		1442	large servers, most programs we (or I :) actually write have only a few
		1443	I/O watchers.
		1444
		1445	In this benchmark, I use the same benchmark program as in the large server
		1446	case, but it uses only eight "servers", of which three are active at any
		1447	one time. This should reflect performance for a small server relatively
		1448	well.
		1449
		1450	The columns are identical to the previous table.
		1451
		1452	=head3 Results
		1453
		1454	name sockets create request
		1455	EV 16 20.00 6.54
		1456	Perl 16 25.75 12.62
		1457	Event 16 81.27 35.86
		1458	Glib 16 32.63 15.48
		1459	POE 16 261.87 276.28 uses POE::Loop::Event
		1460
		1461	=head3 Discussion
		1462
		1463	The benchmark tries to test the performance of a typical small
		1464	server. While knowing how various event loops perform is interesting, keep
		1465	in mind that their overhead in this case is usually not as important, due
		1466	to the small absolute number of watchers (that is, you need efficiency and
		1467	speed most when you have lots of watchers, not when you only have a few of
		1468	them).
		1469
		1470	EV is again fastest.
		1471
		1472	Perl again comes second. It is noticably faster than the C-based event
		1473	loops Event and Glib, although the difference is too small to really
		1474	matter.
		1475
		1476	POE also performs much better in this case, but is is still far behind the
		1477	others.
		1478
		1479	=head3 Summary
		1480
		1481	=over 4
		1482
		1483	=item * C-based event loops perform very well with small number of
		1484	watchers, as the management overhead dominates.
		1485
		1486	=back
		1487
		1488
		1489	=head1 FORK
		1490
		1491	Most event libraries are not fork-safe. The ones who are usually are
		1492	because they rely on inefficient but fork-safe C<select> or C<poll>
		1493	calls. Only L<EV> is fully fork-aware.
		1494
		1495	If you have to fork, you must either do so I<before> creating your first
		1496	watcher OR you must not use AnyEvent at all in the child.
		1497
		1498
		1499	=head1 SECURITY CONSIDERATIONS
		1500
		1501	AnyEvent can be forced to load any event model via
		1502	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1503	execute arbitrary code or directly gain access, it can easily be used to
		1504	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1505	will not be active when the program uses a different event model than
		1506	specified in the variable.
		1507
		1508	You can make AnyEvent completely ignore this variable by deleting it
		1509	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1510
		1511	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1512
		1513	use AnyEvent;
		1514
		1515	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1516	be used to probe what backend is used and gain other information (which is
		1517	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1518
271		1519
272	=head1 SEE ALSO	1520	=head1 SEE ALSO
273		1521
274	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1522	Utility functions: L<AnyEvent::Util>.
275		1523
276	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1524	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1525	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
277		1526
278	Nontrivial usage example: L<Net::FCP>.	1527	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1528	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1529	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1530	L<AnyEvent::Impl::POE>.
279		1531
280	=head1	1532	Non-blocking file handles, sockets, TCP clients and
		1533	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1534
		1535	Asynchronous DNS: L<AnyEvent::DNS>.
		1536
		1537	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1538
		1539	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1540
		1541
		1542	=head1 AUTHOR
		1543
		1544	Marc Lehmann <schmorp@schmorp.de>
		1545	http://home.schmorp.de/
281		1546
282	=cut	1547	=cut
283		1548
284	1	1549	1
285		1550

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