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Revision 1.6 by root, Mon Dec 19 17:03:29 2005 UTC vs.
Revision 1.107 by root, Tue May 6 12:15:50 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, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
6		6
7	=head1 SYNOPSIS	7	=head1 SYNOPSIS
8		8
9	use AnyEvent;	9	use AnyEvent;
10		10
11	my $w = AnyEvent->io (fh => ..., poll => "[rw]+", cb => sub {	11	my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
12	my ($poll_got) = @_;
13	...	12	...
14	});	13	});
15
16	- only one io watcher per $fh and $poll type is allowed
17	(i.e. on a socket you can have one r + one w or one rw
18	watcher, not any more.
19
20	- AnyEvent will keep filehandles alive, so as long as the watcher exists,
21	the filehandle exists.
22		14
23	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
24	...	16	...
25	});	17	});
26		18
27	- io and time watchers get canceled whenever $w is destroyed, so keep a copy	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
28
29	- timers can only be used once and must be recreated for repeated operation
30
31	my $w = AnyEvent->condvar; # kind of main loop replacement
32	$w->wait; # enters main loop till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->send
33	$w->broadcast; # wake up current and all future wait's	21	$w->send; # wake up current and all future wait's
34		22
35	- condvars are used to give blocking behaviour when neccessary. Create	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
36	a condvar for any "request" or "event" your module might create, C<<	24
37	->broadcast >> it when the event happens and provide a function that calls	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
38	C<< ->wait >> for it. See the examples below.	26	nowadays. So what is different about AnyEvent?
		27
		28	Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
		29	policy> and AnyEvent is I<small and efficient>.
		30
		31	First and foremost, I<AnyEvent is not an event model> itself, it only
		32	interfaces to whatever event model the main program happens to use in a
		33	pragmatic way. For event models and certain classes of immortals alike,
		34	the statement "there can only be one" is a bitter reality: In general,
		35	only one event loop can be active at the same time in a process. AnyEvent
		36	helps hiding the differences between those event loops.
		37
		38	The goal of AnyEvent is to offer module authors the ability to do event
		39	programming (waiting for I/O or timer events) without subscribing to a
		40	religion, a way of living, and most importantly: without forcing your
		41	module users into the same thing by forcing them to use the same event
		42	model you use.
		43
		44	For modules like POE or IO::Async (which is a total misnomer as it is
		45	actually doing all I/O I<synchronously>...), using them in your module is
		46	like joining a cult: After you joined, you are dependent on them and you
		47	cannot use anything else, as it is simply incompatible to everything that
		48	isn't itself. What's worse, all the potential users of your module are
		49	I<also> forced to use the same event loop you use.
		50
		51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if
		54	your module uses one of those, every user of your module has to use it,
		55	too. But if your module uses AnyEvent, it works transparently with all
		56	event models it supports (including stuff like POE and IO::Async, as long
		57	as those use one of the supported event loops. It is trivial to add new
		58	event loops to AnyEvent, too, so it is future-proof).
		59
		60	In addition to being free of having to use I<the one and only true event
		61	model>, AnyEvent also is free of bloat and policy: with POE or similar
		62	modules, you get an enourmous amount of code and strict rules you have to
		63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		64	offering the functionality that is necessary, in as thin as a wrapper as
		65	technically possible.
		66
		67	Of course, if you want lots of policy (this can arguably be somewhat
		68	useful) and you want to force your users to use the one and only event
		69	model, you should I<not> use this module.
39		70
40	=head1 DESCRIPTION	71	=head1 DESCRIPTION
41		72
42	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
43	allows module authors to utilizy an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
44	users to use the same event loop (as only a single event loop can coexist	75	users to use the same event loop (as only a single event loop can coexist
45	peacefully at any one time).	76	peacefully at any one time).
46		77
47	The interface itself is vaguely similar but not identical to the Event	78	The interface itself is vaguely similar, but not identical to the L<Event>
48	module.	79	module.
49		80
50	On the first call of any method, the module tries to detect the currently	81	During the first call of any watcher-creation method, the module tries
51	loaded event loop by probing wether any of the following modules is	82	to detect the currently loaded event loop by probing whether one of the
52	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
53	used. If none is found, the module tries to load these modules in the	84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
54	order given. The first one that could be successfully loaded will be	85	L<POE>. The first one found is used. If none are found, the module tries
55	used. If still none could be found, it will issue an error.	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
		87	adaptor should always succeed) in the order given. The first one that can
		88	be successfully loaded will be used. If, after this, still none could be
		89	found, AnyEvent will fall back to a pure-perl event loop, which is not
		90	very efficient, but should work everywhere.
		91
		92	Because AnyEvent first checks for modules that are already loaded, loading
		93	an event model explicitly before first using AnyEvent will likely make
		94	that model the default. For example:
		95
		96	use Tk;
		97	use AnyEvent;
		98
		99	# .. AnyEvent will likely default to Tk
		100
		101	The I<likely> means that, if any module loads another event model and
		102	starts using it, all bets are off. Maybe you should tell their authors to
		103	use AnyEvent so their modules work together with others seamlessly...
		104
		105	The pure-perl implementation of AnyEvent is called
		106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
		107	explicitly.
		108
		109	=head1 WATCHERS
		110
		111	AnyEvent has the central concept of a I<watcher>, which is an object that
		112	stores relevant data for each kind of event you are waiting for, such as
		113	the callback to call, the filehandle to watch, etc.
		114
		115	These watchers are normal Perl objects with normal Perl lifetime. After
		116	creating a watcher it will immediately "watch" for events and invoke the
		117	callback when the event occurs (of course, only when the event model
		118	is in control).
		119
		120	To disable the watcher you have to destroy it (e.g. by setting the
		121	variable you store it in to C<undef> or otherwise deleting all references
		122	to it).
		123
		124	All watchers are created by calling a method on the C<AnyEvent> class.
		125
		126	Many watchers either are used with "recursion" (repeating timers for
		127	example), or need to refer to their watcher object in other ways.
		128
		129	An any way to achieve that is this pattern:
		130
		131	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		132	# you can use $w here, for example to undef it
		133	undef $w;
		134	});
		135
		136	Note that C<my $w; $w => combination. This is necessary because in Perl,
		137	my variables are only visible after the statement in which they are
		138	declared.
		139
		140	=head2 I/O WATCHERS
		141
		142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
		143	with the following mandatory key-value pairs as arguments:
		144
		145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
		146	for events. C<poll> must be a string that is either C<r> or C<w>,
		147	which creates a watcher waiting for "r"eadable or "w"ritable events,
		148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
		150
		151	Although the callback might get passed parameters, their value and
		152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
		154
		155	The I/O watcher might use the underlying file descriptor or a copy of it.
		156	You must not close a file handle as long as any watcher is active on the
		157	underlying file descriptor.
		158
		159	Some event loops issue spurious readyness notifications, so you should
		160	always use non-blocking calls when reading/writing from/to your file
		161	handles.
		162
		163	Example:
		164
		165	# wait for readability of STDIN, then read a line and disable the watcher
		166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		167	chomp (my $input = <STDIN>);
		168	warn "read: $input\n";
		169	undef $w;
		170	});
		171
		172	=head2 TIME WATCHERS
		173
		174	You can create a time watcher by calling the C<< AnyEvent->timer >>
		175	method with the following mandatory arguments:
		176
		177	C<after> specifies after how many seconds (fractional values are
		178	supported) the callback should be invoked. C<cb> is the callback to invoke
		179	in that case.
		180
		181	Although the callback might get passed parameters, their value and
		182	presence is undefined and you cannot rely on them. Portable AnyEvent
		183	callbacks cannot use arguments passed to time watcher callbacks.
		184
		185	The timer callback will be invoked at most once: if you want a repeating
		186	timer you have to create a new watcher (this is a limitation by both Tk
		187	and Glib).
		188
		189	Example:
		190
		191	# fire an event after 7.7 seconds
		192	my $w = AnyEvent->timer (after => 7.7, cb => sub {
		193	warn "timeout\n";
		194	});
		195
		196	# to cancel the timer:
		197	undef $w;
		198
		199	Example 2:
		200
		201	# fire an event after 0.5 seconds, then roughly every second
		202	my $w;
		203
		204	my $cb = sub {
		205	# cancel the old timer while creating a new one
		206	$w = AnyEvent->timer (after => 1, cb => $cb);
		207	};
		208
		209	# start the "loop" by creating the first watcher
		210	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		211
		212	=head3 TIMING ISSUES
		213
		214	There are two ways to handle timers: based on real time (relative, "fire
		215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		216	o'clock").
		217
		218	While most event loops expect timers to specified in a relative way, they
		219	use absolute time internally. This makes a difference when your clock
		220	"jumps", for example, when ntp decides to set your clock backwards from
		221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		222	fire "after" a second might actually take six years to finally fire.
		223
		224	AnyEvent cannot compensate for this. The only event loop that is conscious
		225	about these issues is L<EV>, which offers both relative (ev_timer, based
		226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
		228
		229	AnyEvent always prefers relative timers, if available, matching the
		230	AnyEvent API.
		231
		232	=head2 SIGNAL WATCHERS
		233
		234	You can watch for signals using a signal watcher, C<signal> is the signal
		235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		236	be invoked whenever a signal occurs.
		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
		242	Multiple signal occurances can be clumped together into one callback
		243	invocation, and callback invocation will be synchronous. synchronous means
		244	that it might take a while until the signal gets handled by the process,
		245	but it is guarenteed not to interrupt any other callbacks.
		246
		247	The main advantage of using these watchers is that you can share a signal
		248	between multiple watchers.
		249
		250	This watcher might use C<%SIG>, so programs overwriting those signals
		251	directly will likely not work correctly.
		252
		253	Example: exit on SIGINT
		254
		255	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		256
		257	=head2 CHILD PROCESS WATCHERS
		258
		259	You can also watch on a child process exit and catch its exit status.
		260
		261	The child process is specified by the C<pid> argument (if set to C<0>, it
		262	watches for any child process exit). The watcher will trigger as often
		263	as status change for the child are received. This works by installing a
		264	signal handler for C<SIGCHLD>. The callback will be called with the pid
		265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
		267
		268	There is a slight catch to child watchers, however: you usually start them
		269	I<after> the child process was created, and this means the process could
		270	have exited already (and no SIGCHLD will be sent anymore).
		271
		272	Not all event models handle this correctly (POE doesn't), but even for
		273	event models that I<do> handle this correctly, they usually need to be
		274	loaded before the process exits (i.e. before you fork in the first place).
		275
		276	This means you cannot create a child watcher as the very first thing in an
		277	AnyEvent program, you I<have> to create at least one watcher before you
		278	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		279
		280	Example: fork a process and wait for it
		281
		282	my $done = AnyEvent->condvar;
		283
		284	AnyEvent::detect; # force event module to be initialised
		285
		286	my $pid = fork or exit 5;
		287
		288	my $w = AnyEvent->child (
		289	pid => $pid,
		290	cb => sub {
		291	my ($pid, $status) = @_;
		292	warn "pid $pid exited with status $status";
		293	$done->send;
		294	},
		295	);
		296
		297	# do something else, then wait for process exit
		298	$done->wait;
		299
		300	=head2 CONDITION VARIABLES
		301
		302	If you are familiar with some event loops you will know that all of them
		303	require you to run some blocking "loop", "run" or similar function that
		304	will actively watch for new events and call your callbacks.
		305
		306	AnyEvent is different, it expects somebody else to run the event loop and
		307	will only block when necessary (usually when told by the user).
		308
		309	The instrument to do that is called a "condition variable", so called
		310	because they represent a condition that must become true.
		311
		312	Condition variables can be created by calling the C<< AnyEvent->condvar
		313	>> method, usually without arguments. The only argument pair allowed is
		314	C<cb>, which specifies a callback to be called when the condition variable
		315	becomes true.
		316
		317	After creation, the conditon variable is "false" until it becomes "true"
		318	by calling the C<send> method.
		319
		320	Condition variables are similar to callbacks, except that you can
		321	optionally wait for them. They can also be called merge points - points
		322	in time where multiple outstandign events have been processed. And yet
		323	another way to call them is transations - each condition variable can be
		324	used to represent a transaction, which finishes at some point and delivers
		325	a result.
		326
		327	Condition variables are very useful to signal that something has finished,
		328	for example, if you write a module that does asynchronous http requests,
		329	then a condition variable would be the ideal candidate to signal the
		330	availability of results. The user can either act when the callback is
		331	called or can synchronously C<< ->wait >> for the results.
		332
		333	You can also use them to simulate traditional event loops - for example,
		334	you can block your main program until an event occurs - for example, you
		335	could C<< ->wait >> in your main program until the user clicks the Quit
		336	button of your app, which would C<< ->send >> the "quit" event.
		337
		338	Note that condition variables recurse into the event loop - if you have
		339	two pieces of code that call C<< ->wait >> in a round-robbin fashion, you
		340	lose. Therefore, condition variables are good to export to your caller, but
		341	you should avoid making a blocking wait yourself, at least in callbacks,
		342	as this asks for trouble.
		343
		344	Condition variables are represented by hash refs in perl, and the keys
		345	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		346	easy (it is often useful to build your own transaction class on top of
		347	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		348	it's C<new> method in your own C<new> method.
		349
		350	There are two "sides" to a condition variable - the "producer side" which
		351	eventually calls C<< -> send >>, and the "consumer side", which waits
		352	for the send to occur.
		353
		354	Example:
		355
		356	# wait till the result is ready
		357	my $result_ready = AnyEvent->condvar;
		358
		359	# do something such as adding a timer
		360	# or socket watcher the calls $result_ready->send
		361	# when the "result" is ready.
		362	# in this case, we simply use a timer:
		363	my $w = AnyEvent->timer (
		364	after => 1,
		365	cb => sub { $result_ready->send },
		366	);
		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls send
		370	$result_ready->wait;
		371
		372	=head3 METHODS FOR PRODUCERS
		373
		374	These methods should only be used by the producing side, i.e. the
		375	code/module that eventually sends the signal. Note that it is also
		376	the producer side which creates the condvar in most cases, but it isn't
		377	uncommon for the consumer to create it as well.
56		378
57	=over 4	379	=over 4
58		380
		381	=item $cv->send (...)
		382
		383	Flag the condition as ready - a running C<< ->wait >> and all further
		384	calls to C<wait> will (eventually) return after this method has been
		385	called. If nobody is waiting the send will be remembered.
		386
		387	If a callback has been set on the condition variable, it is called
		388	immediately from within send.
		389
		390	Any arguments passed to the C<send> call will be returned by all
		391	future C<< ->wait >> calls.
		392
		393	=item $cv->croak ($error)
		394
		395	Similar to send, but causes all call's wait C<< ->wait >> to invoke
		396	C<Carp::croak> with the given error message/object/scalar.
		397
		398	This can be used to signal any errors to the condition variable
		399	user/consumer.
		400
		401	=item $cv->begin ([group callback])
		402
		403	=item $cv->end
		404
		405	These two methods can be used to combine many transactions/events into
		406	one. For example, a function that pings many hosts in parallel might want
		407	to use a condition variable for the whole process.
		408
		409	Every call to C<< ->begin >> will increment a counter, and every call to
		410	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		411	>>, the (last) callback passed to C<begin> will be executed. That callback
		412	is I<supposed> to call C<< ->send >>, but that is not required. If no
		413	callback was set, C<send> will be called without any arguments.
		414
		415	Let's clarify this with the ping example:
		416
		417	my $cv = AnyEvent->condvar;
		418
		419	my %result;
		420	$cv->begin (sub { $cv->send (\%result) });
		421
		422	for my $host (@list_of_hosts) {
		423	$cv->begin;
		424	ping_host_then_call_callback $host, sub {
		425	$result{$host} = ...;
		426	$cv->end;
		427	};
		428	}
		429
		430	$cv->end;
		431
		432	This code fragment supposedly pings a number of hosts and calls
		433	C<send> after results for all then have have been gathered - in any
		434	order. To achieve this, the code issues a call to C<begin> when it starts
		435	each ping request and calls C<end> when it has received some result for
		436	it. Since C<begin> and C<end> only maintain a counter, the order in which
		437	results arrive is not relevant.
		438
		439	There is an additional bracketing call to C<begin> and C<end> outside the
		440	loop, which serves two important purposes: first, it sets the callback
		441	to be called once the counter reaches C<0>, and second, it ensures that
		442	C<send> is called even when C<no> hosts are being pinged (the loop
		443	doesn't execute once).
		444
		445	This is the general pattern when you "fan out" into multiple subrequests:
		446	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		447	is called at least once, and then, for each subrequest you start, call
		448	C<begin> and for eahc subrequest you finish, call C<end>.
		449
		450	=back
		451
		452	=head3 METHODS FOR CONSUMERS
		453
		454	These methods should only be used by the consuming side, i.e. the
		455	code awaits the condition.
		456
		457	=over 4
		458
		459	=item $cv->wait
		460
		461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
		464
		465	You can only wait once on a condition - additional calls are valid but
		466	will return immediately.
		467
		468	If an error condition has been set by calling C<< ->croak >>, then this
		469	function will call C<croak>.
		470
		471	In list context, all parameters passed to C<send> will be returned,
		472	in scalar context only the first one will be returned.
		473
		474	Not all event models support a blocking wait - some die in that case
		475	(programs might want to do that to stay interactive), so I<if you are
		476	using this from a module, never require a blocking wait>, but let the
		477	caller decide whether the call will block or not (for example, by coupling
		478	condition variables with some kind of request results and supporting
		479	callbacks so the caller knows that getting the result will not block,
		480	while still suppporting blocking waits if the caller so desires).
		481
		482	Another reason I<never> to C<< ->wait >> in a module is that you cannot
		483	sensibly have two C<< ->wait >>'s in parallel, as that would require
		484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		485	can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
		486	L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
		487	from different coroutines, however).
		488
		489	You can ensure that C<< -wait >> never blocks by setting a callback and
		490	only calling C<< ->wait >> from within that callback (or at a later
		491	time). This will work even when the event loop does not support blocking
		492	waits otherwise.
		493
		494	=item $bool = $cv->ready
		495
		496	Returns true when the condition is "true", i.e. whether C<send> or
		497	C<croak> have been called.
		498
		499	=item $cb = $cv->cb ([new callback])
		500
		501	This is a mutator function that returns the callback set and optionally
		502	replaces it before doing so.
		503
		504	The callback will be called when the condition becomes "true", i.e. when
		505	C<send> or C<croak> are called. Calling C<wait> inside the callback
		506	or at any later time is guaranteed not to block.
		507
		508	=back
		509
		510	=head1 GLOBAL VARIABLES AND FUNCTIONS
		511
		512	=over 4
		513
		514	=item $AnyEvent::MODEL
		515
		516	Contains C<undef> until the first watcher is being created. Then it
		517	contains the event model that is being used, which is the name of the
		518	Perl class implementing the model. This class is usually one of the
		519	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		520	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		521
		522	The known classes so far are:
		523
		524	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
		525	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
		526	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		527	AnyEvent::Impl::Event based on Event, second best choice.
		528	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		529	AnyEvent::Impl::Glib based on Glib, third-best choice.
		530	AnyEvent::Impl::Tk based on Tk, very bad choice.
		531	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		532	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		533	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		534
		535	There is no support for WxWidgets, as WxWidgets has no support for
		536	watching file handles. However, you can use WxWidgets through the
		537	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		538	second, which was considered to be too horrible to even consider for
		539	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		540	it's adaptor.
		541
		542	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		543	autodetecting them.
		544
		545	=item AnyEvent::detect
		546
		547	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		548	if necessary. You should only call this function right before you would
		549	have created an AnyEvent watcher anyway, that is, as late as possible at
		550	runtime.
		551
		552	=back
		553
		554	=head1 WHAT TO DO IN A MODULE
		555
		556	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		557	freely, but you should not load a specific event module or rely on it.
		558
		559	Be careful when you create watchers in the module body - AnyEvent will
		560	decide which event module to use as soon as the first method is called, so
		561	by calling AnyEvent in your module body you force the user of your module
		562	to load the event module first.
		563
		564	Never call C<< ->wait >> on a condition variable unless you I<know> that
		565	the C<< ->send >> method has been called on it already. This is
		566	because it will stall the whole program, and the whole point of using
		567	events is to stay interactive.
		568
		569	It is fine, however, to call C<< ->wait >> when the user of your module
		570	requests it (i.e. if you create a http request object ad have a method
		571	called C<results> that returns the results, it should call C<< ->wait >>
		572	freely, as the user of your module knows what she is doing. always).
		573
		574	=head1 WHAT TO DO IN THE MAIN PROGRAM
		575
		576	There will always be a single main program - the only place that should
		577	dictate which event model to use.
		578
		579	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		580	do anything special (it does not need to be event-based) and let AnyEvent
		581	decide which implementation to chose if some module relies on it.
		582
		583	If the main program relies on a specific event model. For example, in
		584	Gtk2 programs you have to rely on the Glib module. You should load the
		585	event module before loading AnyEvent or any module that uses it: generally
		586	speaking, you should load it as early as possible. The reason is that
		587	modules might create watchers when they are loaded, and AnyEvent will
		588	decide on the event model to use as soon as it creates watchers, and it
		589	might chose the wrong one unless you load the correct one yourself.
		590
		591	You can chose to use a rather inefficient pure-perl implementation by
		592	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
		593	behaviour everywhere, but letting AnyEvent chose is generally better.
		594
		595	=head1 OTHER MODULES
		596
		597	The following is a non-exhaustive list of additional modules that use
		598	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		599	in the same program. Some of the modules come with AnyEvent, some are
		600	available via CPAN.
		601
		602	=over 4
		603
		604	=item L<AnyEvent::Util>
		605
		606	Contains various utility functions that replace often-used but blocking
		607	functions such as C<inet_aton> by event-/callback-based versions.
		608
		609	=item L<AnyEvent::Handle>
		610
		611	Provide read and write buffers and manages watchers for reads and writes.
		612
		613	=item L<AnyEvent::Socket>
		614
		615	Provides a means to do non-blocking connects, accepts etc.
		616
		617	=item L<AnyEvent::HTTPD>
		618
		619	Provides a simple web application server framework.
		620
		621	=item L<AnyEvent::DNS>
		622
		623	Provides asynchronous DNS resolver capabilities, beyond what
		624	L<AnyEvent::Util> offers.
		625
		626	=item L<AnyEvent::FastPing>
		627
		628	The fastest ping in the west.
		629
		630	=item L<Net::IRC3>
		631
		632	AnyEvent based IRC client module family.
		633
		634	=item L<Net::XMPP2>
		635
		636	AnyEvent based XMPP (Jabber protocol) module family.
		637
		638	=item L<Net::FCP>
		639
		640	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		641	of AnyEvent.
		642
		643	=item L<Event::ExecFlow>
		644
		645	High level API for event-based execution flow control.
		646
		647	=item L<Coro>
		648
		649	Has special support for AnyEvent.
		650
		651	=item L<IO::Lambda>
		652
		653	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		654
		655	=item L<IO::AIO>
		656
		657	Truly asynchronous I/O, should be in the toolbox of every event
		658	programmer. Can be trivially made to use AnyEvent.
		659
		660	=item L<BDB>
		661
		662	Truly asynchronous Berkeley DB access. Can be trivially made to use
		663	AnyEvent.
		664
		665	=back
		666
59	=cut	667	=cut
60		668
61	package AnyEvent;	669	package AnyEvent;
62		670
63	no warnings;	671	no warnings;
64	use strict 'vars';	672	use strict;
		673
65	use Carp;	674	use Carp;
66		675
67	our $VERSION = 0.3;	676	our $VERSION = '3.3';
68	our $MODEL;	677	our $MODEL;
69		678
70	our $AUTOLOAD;	679	our $AUTOLOAD;
71	our @ISA;	680	our @ISA;
72		681
		682	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		683
		684	our @REGISTRY;
		685
73	my @models = (	686	my @models = (
74	[Coro => Coro::Event::],	687	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
75	[Event => Event::],	688	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
76	[Glib => Glib::],	689	[EV:: => AnyEvent::Impl::EV::],
77	[Tk => Tk::],	690	[Event:: => AnyEvent::Impl::Event::],
		691	[Tk:: => AnyEvent::Impl::Tk::],
		692	[Wx:: => AnyEvent::Impl::POE::],
		693	[Prima:: => AnyEvent::Impl::POE::],
		694	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		695	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		696	[Glib:: => AnyEvent::Impl::Glib::],
		697	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		698	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		699	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
78	);	700	);
79		701
80	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	702	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
81		703
82	sub AUTOLOAD {	704	sub detect() {
83	$AUTOLOAD =~ s/.*://;
84
85	$method{$AUTOLOAD}
86	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";
87
88	unless ($MODEL) {	705	unless ($MODEL) {
89	# check for already loaded models	706	no strict 'refs';
90	for (@models) {	707
91	my ($model, $package) = @$_;	708	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
92	if (scalar keys %{ *{"$package\::"} }) {	709	my $model = "AnyEvent::Impl::$1";
93	eval "require AnyEvent::Impl::$model";	710	if (eval "require $model") {
94	last if $MODEL;	711	$MODEL = $model;
		712	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		713	} else {
		714	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
95	}	715	}
96	}	716	}
97		717
		718	# check for already loaded models
98	unless ($MODEL) {	719	unless ($MODEL) {
99	# try to load a model
100
101	for (@models) {	720	for (@REGISTRY, @models) {
102	my ($model, $package) = @$_;	721	my ($package, $model) = @$_;
103	eval "require AnyEvent::Impl::$model";	722	if (${"$package\::VERSION"} > 0) {
104	last if $MODEL;	723	if (eval "require $model") {
		724	$MODEL = $model;
		725	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		726	last;
		727	}
		728	}
105	}	729	}
106		730
		731	unless ($MODEL) {
		732	# try to load a model
		733
		734	for (@REGISTRY, @models) {
		735	my ($package, $model) = @$_;
		736	if (eval "require $package"
		737	and ${"$package\::VERSION"} > 0
		738	and eval "require $model") {
		739	$MODEL = $model;
		740	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		741	last;
		742	}
		743	}
		744
107	$MODEL	745	$MODEL
108	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	746	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib.";
		747	}
109	}	748	}
		749
		750	unshift @ISA, $MODEL;
		751	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
110	}	752	}
111		753
112	@ISA = $MODEL;	754	$MODEL
		755	}
		756
		757	sub AUTOLOAD {
		758	(my $func = $AUTOLOAD) =~ s/.*://;
		759
		760	$method{$func}
		761	or croak "$func: not a valid method for AnyEvent objects";
		762
		763	detect unless $MODEL;
113		764
114	my $class = shift;	765	my $class = shift;
115	$class->$AUTOLOAD (@_);	766	$class->$func (@_);
116	}	767	}
117		768
		769	package AnyEvent::Base;
		770
		771	# default implementation for ->condvar, ->wait, ->broadcast
		772
		773	sub condvar {
		774	bless \my $flag, "AnyEvent::Base::CondVar"
		775	}
		776
		777	sub AnyEvent::Base::CondVar::broadcast {
		778	${$_[0]}++;
		779	}
		780
		781	sub AnyEvent::Base::CondVar::wait {
		782	AnyEvent->one_event while !${$_[0]};
		783	}
		784
		785	# default implementation for ->signal
		786
		787	our %SIG_CB;
		788
		789	sub signal {
		790	my (undef, %arg) = @_;
		791
		792	my $signal = uc $arg{signal}
		793	or Carp::croak "required option 'signal' is missing";
		794
		795	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		796	$SIG{$signal} ||= sub {
		797	$_->() for values %{ $SIG_CB{$signal} || {} };
		798	};
		799
		800	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		801	}
		802
		803	sub AnyEvent::Base::Signal::DESTROY {
		804	my ($signal, $cb) = @{$_[0]};
		805
		806	delete $SIG_CB{$signal}{$cb};
		807
		808	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		809	}
		810
		811	# default implementation for ->child
		812
		813	our %PID_CB;
		814	our $CHLD_W;
		815	our $CHLD_DELAY_W;
		816	our $PID_IDLE;
		817	our $WNOHANG;
		818
		819	sub _child_wait {
		820	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		821	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		822	(values %{ $PID_CB{0} || {} });
		823	}
		824
		825	undef $PID_IDLE;
		826	}
		827
		828	sub _sigchld {
		829	# make sure we deliver these changes "synchronous" with the event loop.
		830	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		831	undef $CHLD_DELAY_W;
		832	&_child_wait;
		833	});
		834	}
		835
		836	sub child {
		837	my (undef, %arg) = @_;
		838
		839	defined (my $pid = $arg{pid} + 0)
		840	or Carp::croak "required option 'pid' is missing";
		841
		842	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		843
		844	unless ($WNOHANG) {
		845	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		846	}
		847
		848	unless ($CHLD_W) {
		849	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		850	# child could be a zombie already, so make at least one round
		851	&_sigchld;
		852	}
		853
		854	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		855	}
		856
		857	sub AnyEvent::Base::Child::DESTROY {
		858	my ($pid, $cb) = @{$_[0]};
		859
		860	delete $PID_CB{$pid}{$cb};
		861	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		862
		863	undef $CHLD_W unless keys %PID_CB;
		864	}
		865
		866	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		867
		868	This is an advanced topic that you do not normally need to use AnyEvent in
		869	a module. This section is only of use to event loop authors who want to
		870	provide AnyEvent compatibility.
		871
		872	If you need to support another event library which isn't directly
		873	supported by AnyEvent, you can supply your own interface to it by
		874	pushing, before the first watcher gets created, the package name of
		875	the event module and the package name of the interface to use onto
		876	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		877	AnyEvent, so it is reasonably cheap.
		878
		879	Example:
		880
		881	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		882
		883	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		884	package/class when it finds the C<urxvt> package/module is already loaded.
		885
		886	When AnyEvent is loaded and asked to find a suitable event model, it
		887	will first check for the presence of urxvt by trying to C<use> the
		888	C<urxvt::anyevent> module.
		889
		890	The class should provide implementations for all watcher types. See
		891	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		892	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		893	see the sources.
		894
		895	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		896	provide suitable (hopefully) replacements.
		897
		898	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		899	terminal emulator uses the above line as-is. An interface isn't included
		900	in AnyEvent because it doesn't make sense outside the embedded interpreter
		901	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		902	I<rxvt-unicode> distribution.
		903
		904	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		905	condition variables: code blocking while waiting for a condition will
		906	C<die>. This still works with most modules/usages, and blocking calls must
		907	not be done in an interactive application, so it makes sense.
		908
		909	=head1 ENVIRONMENT VARIABLES
		910
		911	The following environment variables are used by this module:
		912
		913	=over 4
		914
		915	=item C<PERL_ANYEVENT_VERBOSE>
		916
		917	By default, AnyEvent will be completely silent except in fatal
		918	conditions. You can set this environment variable to make AnyEvent more
		919	talkative.
		920
		921	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		922	conditions, such as not being able to load the event model specified by
		923	C<PERL_ANYEVENT_MODEL>.
		924
		925	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		926	model it chooses.
		927
		928	=item C<PERL_ANYEVENT_MODEL>
		929
		930	This can be used to specify the event model to be used by AnyEvent, before
		931	autodetection and -probing kicks in. It must be a string consisting
		932	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		933	and the resulting module name is loaded and if the load was successful,
		934	used as event model. If it fails to load AnyEvent will proceed with
		935	autodetection and -probing.
		936
		937	This functionality might change in future versions.
		938
		939	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		940	could start your program like this:
		941
		942	PERL_ANYEVENT_MODEL=Perl perl ...
		943
118	=back	944	=back
119		945
120	=head1 EXAMPLE	946	=head1 EXAMPLE PROGRAM
121		947
122	The following program uses an io watcher to read data from stdin, a timer	948	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	949	to display a message once per second, and a condition variable to quit the
124	when the user enters quit:	950	program when the user enters quit:
125		951
126	use AnyEvent;	952	use AnyEvent;
127		953
128	my $cv = AnyEvent->condvar;	954	my $cv = AnyEvent->condvar;
129		955
130	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	956	my $io_watcher = AnyEvent->io (
		957	fh => \*STDIN,
		958	poll => 'r',
		959	cb => sub {
131	warn "io event <$_[0]>\n"; # will always output <r>	960	warn "io event <$_[0]>\n"; # will always output <r>
132	chomp (my $input = <STDIN>); # read a line	961	chomp (my $input = <STDIN>); # read a line
133	warn "read: $input\n"; # output what has been read	962	warn "read: $input\n"; # output what has been read
134	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	963	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		964	},
135	});	965	);
136		966
137	my $time_watcher; # can only be used once	967	my $time_watcher; # can only be used once
138		968
139	sub new_timer {	969	sub new_timer {
140	$timer = AnyEvent->timer (after => 1, cb => sub {	970	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
222	$txn->{finished}->wait;	1052	$txn->{finished}->wait;
223	return $txn->{result};	1053	return $txn->{result};
224		1054
225	The actual code goes further and collects all errors (C<die>s, exceptions)	1055	The actual code goes further and collects all errors (C<die>s, exceptions)
226	that occured during request processing. The C<result> method detects	1056	that occured during request processing. The C<result> method detects
227	wether an exception as thrown (it is stored inside the $txn object)	1057	whether an exception as thrown (it is stored inside the $txn object)
228	and just throws the exception, which means connection errors and other	1058	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	1059	problems get reported tot he code that tries to use the result, not in a
230	random callback.	1060	random callback.
231		1061
232	All of this enables the following usage styles:	1062	All of this enables the following usage styles:
233		1063
234	1. Blocking:	1064	1. Blocking:
235		1065
236	my $data = $fcp->client_get ($url);	1066	my $data = $fcp->client_get ($url);
237		1067
238	2. Blocking, but parallelizing:	1068	2. Blocking, but running in parallel:
239		1069
240	my @datas = map $_->result,	1070	my @datas = map $_->result,
241	map $fcp->txn_client_get ($_),	1071	map $fcp->txn_client_get ($_),
242	@urls;	1072	@urls;
243		1073
244	Both blocking examples work without the module user having to know	1074	Both blocking examples work without the module user having to know
245	anything about events.	1075	anything about events.
246		1076
247	3a. Event-based in a main program, using any support Event module:	1077	3a. Event-based in a main program, using any supported event module:
248		1078
249	use Event;	1079	use EV;
250		1080
251	$fcp->txn_client_get ($url)->cb (sub {	1081	$fcp->txn_client_get ($url)->cb (sub {
252	my $txn = shift;	1082	my $txn = shift;
253	my $data = $txn->result;	1083	my $data = $txn->result;
254	...	1084	...
255	});	1085	});
256		1086
257	Event::loop;	1087	EV::loop;
258		1088
259	3b. The module user could use AnyEvent, too:	1089	3b. The module user could use AnyEvent, too:
260		1090
261	use AnyEvent;	1091	use AnyEvent;
262		1092
…		…
267	$quit->broadcast;	1097	$quit->broadcast;
268	});	1098	});
269		1099
270	$quit->wait;	1100	$quit->wait;
271		1101
		1102
		1103	=head1 BENCHMARKS
		1104
		1105	To give you an idea of the performance and overheads that AnyEvent adds
		1106	over the event loops themselves and to give you an impression of the speed
		1107	of various event loops I prepared some benchmarks.
		1108
		1109	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1110
		1111	Here is a benchmark of various supported event models used natively and
		1112	through anyevent. The benchmark creates a lot of timers (with a zero
		1113	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1114	which it is), lets them fire exactly once and destroys them again.
		1115
		1116	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1117	distribution.
		1118
		1119	=head3 Explanation of the columns
		1120
		1121	I<watcher> is the number of event watchers created/destroyed. Since
		1122	different event models feature vastly different performances, each event
		1123	loop was given a number of watchers so that overall runtime is acceptable
		1124	and similar between tested event loop (and keep them from crashing): Glib
		1125	would probably take thousands of years if asked to process the same number
		1126	of watchers as EV in this benchmark.
		1127
		1128	I<bytes> is the number of bytes (as measured by the resident set size,
		1129	RSS) consumed by each watcher. This method of measuring captures both C
		1130	and Perl-based overheads.
		1131
		1132	I<create> is the time, in microseconds (millionths of seconds), that it
		1133	takes to create a single watcher. The callback is a closure shared between
		1134	all watchers, to avoid adding memory overhead. That means closure creation
		1135	and memory usage is not included in the figures.
		1136
		1137	I<invoke> is the time, in microseconds, used to invoke a simple
		1138	callback. The callback simply counts down a Perl variable and after it was
		1139	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1140	signal the end of this phase.
		1141
		1142	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1143	watcher.
		1144
		1145	=head3 Results
		1146
		1147	name watchers bytes create invoke destroy comment
		1148	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1149	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1150	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1151	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1152	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1153	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1154	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1155	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1156	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1157	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1158
		1159	=head3 Discussion
		1160
		1161	The benchmark does I<not> measure scalability of the event loop very
		1162	well. For example, a select-based event loop (such as the pure perl one)
		1163	can never compete with an event loop that uses epoll when the number of
		1164	file descriptors grows high. In this benchmark, all events become ready at
		1165	the same time, so select/poll-based implementations get an unnatural speed
		1166	boost.
		1167
		1168	Also, note that the number of watchers usually has a nonlinear effect on
		1169	overall speed, that is, creating twice as many watchers doesn't take twice
		1170	the time - usually it takes longer. This puts event loops tested with a
		1171	higher number of watchers at a disadvantage.
		1172
		1173	To put the range of results into perspective, consider that on the
		1174	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1175	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1176	cycles with POE.
		1177
		1178	C<EV> is the sole leader regarding speed and memory use, which are both
		1179	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1180	far less memory than any other event loop and is still faster than Event
		1181	natively.
		1182
		1183	The pure perl implementation is hit in a few sweet spots (both the
		1184	constant timeout and the use of a single fd hit optimisations in the perl
		1185	interpreter and the backend itself). Nevertheless this shows that it
		1186	adds very little overhead in itself. Like any select-based backend its
		1187	performance becomes really bad with lots of file descriptors (and few of
		1188	them active), of course, but this was not subject of this benchmark.
		1189
		1190	The C<Event> module has a relatively high setup and callback invocation
		1191	cost, but overall scores in on the third place.
		1192
		1193	C<Glib>'s memory usage is quite a bit higher, but it features a
		1194	faster callback invocation and overall ends up in the same class as
		1195	C<Event>. However, Glib scales extremely badly, doubling the number of
		1196	watchers increases the processing time by more than a factor of four,
		1197	making it completely unusable when using larger numbers of watchers
		1198	(note that only a single file descriptor was used in the benchmark, so
		1199	inefficiencies of C<poll> do not account for this).
		1200
		1201	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1202	more than 2000 watchers is a big setback, however, as correctness takes
		1203	precedence over speed. Nevertheless, its performance is surprising, as the
		1204	file descriptor is dup()ed for each watcher. This shows that the dup()
		1205	employed by some adaptors is not a big performance issue (it does incur a
		1206	hidden memory cost inside the kernel which is not reflected in the figures
		1207	above).
		1208
		1209	C<POE>, regardless of underlying event loop (whether using its pure perl
		1210	select-based backend or the Event module, the POE-EV backend couldn't
		1211	be tested because it wasn't working) shows abysmal performance and
		1212	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1213	as EV watchers, and 10 times as much memory as Event (the high memory
		1214	requirements are caused by requiring a session for each watcher). Watcher
		1215	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1216	implementation.
		1217
		1218	The design of the POE adaptor class in AnyEvent can not really account
		1219	for the performance issues, though, as session creation overhead is
		1220	small compared to execution of the state machine, which is coded pretty
		1221	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1222	using multiple sessions is not a good approach, especially regarding
		1223	memory usage, even the author of POE could not come up with a faster
		1224	design).
		1225
		1226	=head3 Summary
		1227
		1228	=over 4
		1229
		1230	=item * Using EV through AnyEvent is faster than any other event loop
		1231	(even when used without AnyEvent), but most event loops have acceptable
		1232	performance with or without AnyEvent.
		1233
		1234	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1235	the actual event loop, only with extremely fast event loops such as EV
		1236	adds AnyEvent significant overhead.
		1237
		1238	=item * You should avoid POE like the plague if you want performance or
		1239	reasonable memory usage.
		1240
		1241	=back
		1242
		1243	=head2 BENCHMARKING THE LARGE SERVER CASE
		1244
		1245	This benchmark atcually benchmarks the event loop itself. It works by
		1246	creating a number of "servers": each server consists of a socketpair, a
		1247	timeout watcher that gets reset on activity (but never fires), and an I/O
		1248	watcher waiting for input on one side of the socket. Each time the socket
		1249	watcher reads a byte it will write that byte to a random other "server".
		1250
		1251	The effect is that there will be a lot of I/O watchers, only part of which
		1252	are active at any one point (so there is a constant number of active
		1253	fds for each loop iterstaion, but which fds these are is random). The
		1254	timeout is reset each time something is read because that reflects how
		1255	most timeouts work (and puts extra pressure on the event loops).
		1256
		1257	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1258	(1%) are active. This mirrors the activity of large servers with many
		1259	connections, most of which are idle at any one point in time.
		1260
		1261	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1262	distribution.
		1263
		1264	=head3 Explanation of the columns
		1265
		1266	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1267	each server has a read and write socket end).
		1268
		1269	I<create> is the time it takes to create a socketpair (which is
		1270	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1271
		1272	I<request>, the most important value, is the time it takes to handle a
		1273	single "request", that is, reading the token from the pipe and forwarding
		1274	it to another server. This includes deleting the old timeout and creating
		1275	a new one that moves the timeout into the future.
		1276
		1277	=head3 Results
		1278
		1279	name sockets create request
		1280	EV 20000 69.01 11.16
		1281	Perl 20000 73.32 35.87
		1282	Event 20000 212.62 257.32
		1283	Glib 20000 651.16 1896.30
		1284	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1285
		1286	=head3 Discussion
		1287
		1288	This benchmark I<does> measure scalability and overall performance of the
		1289	particular event loop.
		1290
		1291	EV is again fastest. Since it is using epoll on my system, the setup time
		1292	is relatively high, though.
		1293
		1294	Perl surprisingly comes second. It is much faster than the C-based event
		1295	loops Event and Glib.
		1296
		1297	Event suffers from high setup time as well (look at its code and you will
		1298	understand why). Callback invocation also has a high overhead compared to
		1299	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1300	uses select or poll in basically all documented configurations.
		1301
		1302	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1303	clearly fails to perform with many filehandles or in busy servers.
		1304
		1305	POE is still completely out of the picture, taking over 1000 times as long
		1306	as EV, and over 100 times as long as the Perl implementation, even though
		1307	it uses a C-based event loop in this case.
		1308
		1309	=head3 Summary
		1310
		1311	=over 4
		1312
		1313	=item * The pure perl implementation performs extremely well.
		1314
		1315	=item * Avoid Glib or POE in large projects where performance matters.
		1316
		1317	=back
		1318
		1319	=head2 BENCHMARKING SMALL SERVERS
		1320
		1321	While event loops should scale (and select-based ones do not...) even to
		1322	large servers, most programs we (or I :) actually write have only a few
		1323	I/O watchers.
		1324
		1325	In this benchmark, I use the same benchmark program as in the large server
		1326	case, but it uses only eight "servers", of which three are active at any
		1327	one time. This should reflect performance for a small server relatively
		1328	well.
		1329
		1330	The columns are identical to the previous table.
		1331
		1332	=head3 Results
		1333
		1334	name sockets create request
		1335	EV 16 20.00 6.54
		1336	Perl 16 25.75 12.62
		1337	Event 16 81.27 35.86
		1338	Glib 16 32.63 15.48
		1339	POE 16 261.87 276.28 uses POE::Loop::Event
		1340
		1341	=head3 Discussion
		1342
		1343	The benchmark tries to test the performance of a typical small
		1344	server. While knowing how various event loops perform is interesting, keep
		1345	in mind that their overhead in this case is usually not as important, due
		1346	to the small absolute number of watchers (that is, you need efficiency and
		1347	speed most when you have lots of watchers, not when you only have a few of
		1348	them).
		1349
		1350	EV is again fastest.
		1351
		1352	Perl again comes second. It is noticably faster than the C-based event
		1353	loops Event and Glib, although the difference is too small to really
		1354	matter.
		1355
		1356	POE also performs much better in this case, but is is still far behind the
		1357	others.
		1358
		1359	=head3 Summary
		1360
		1361	=over 4
		1362
		1363	=item * C-based event loops perform very well with small number of
		1364	watchers, as the management overhead dominates.
		1365
		1366	=back
		1367
		1368
		1369	=head1 FORK
		1370
		1371	Most event libraries are not fork-safe. The ones who are usually are
		1372	because they rely on inefficient but fork-safe C<select> or C<poll>
		1373	calls. Only L<EV> is fully fork-aware.
		1374
		1375	If you have to fork, you must either do so I<before> creating your first
		1376	watcher OR you must not use AnyEvent at all in the child.
		1377
		1378
		1379	=head1 SECURITY CONSIDERATIONS
		1380
		1381	AnyEvent can be forced to load any event model via
		1382	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1383	execute arbitrary code or directly gain access, it can easily be used to
		1384	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1385	will not be active when the program uses a different event model than
		1386	specified in the variable.
		1387
		1388	You can make AnyEvent completely ignore this variable by deleting it
		1389	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1390
		1391	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1392
		1393	use AnyEvent;
		1394
		1395	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1396	be used to probe what backend is used and gain other information (which is
		1397	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1398
		1399
272	=head1 SEE ALSO	1400	=head1 SEE ALSO
273		1401
274	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1402	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
		1403	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
		1404	L<Event::Lib>, L<Qt>, L<POE>.
275		1405
		1406	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
276	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1407	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
		1408	L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
		1409	L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
277		1410
278	Nontrivial usage example: L<Net::FCP>.	1411	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
279		1412
280	=head1	1413
		1414	=head1 AUTHOR
		1415
		1416	Marc Lehmann <schmorp@schmorp.de>
		1417	http://home.schmorp.de/
281		1418
282	=cut	1419	=cut
283		1420
284	1	1421	1
285		1422

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