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Revision 1.6 by root, Mon Dec 19 17:03:29 2005 UTC vs.
Revision 1.136 by root, Sun May 25 23:52:02 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 enormous 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 file handle 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 occurrences 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 guaranteed 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 condition variable is "false" until it becomes "true"
		316	by calling the C<send> method (or calling the condition variable as if it
		317	were a callback, read about the caveats in the description for the C<<
		318	->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 outstanding events have been processed. And yet
		323	another way to call them is transactions - 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<< ->recv >> 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<< ->recv >> 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<< ->recv >> in a round-robin 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: wait for a timer.
		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->recv;
		371
		372	Example: wait for a timer, but take advantage of the fact that
		373	condition variables are also code references.
		374
		375	my $done = AnyEvent->condvar;
		376	my $delay = AnyEvent->timer (after => 5, cb => $done);
		377	$done->recv;
		378
		379	=head3 METHODS FOR PRODUCERS
		380
		381	These methods should only be used by the producing side, i.e. the
		382	code/module that eventually sends the signal. Note that it is also
		383	the producer side which creates the condvar in most cases, but it isn't
		384	uncommon for the consumer to create it as well.
56		385
57	=over 4	386	=over 4
58		387
		388	=item $cv->send (...)
		389
		390	Flag the condition as ready - a running C<< ->recv >> and all further
		391	calls to C<recv> will (eventually) return after this method has been
		392	called. If nobody is waiting the send will be remembered.
		393
		394	If a callback has been set on the condition variable, it is called
		395	immediately from within send.
		396
		397	Any arguments passed to the C<send> call will be returned by all
		398	future C<< ->recv >> calls.
		399
		400	Condition variables are overloaded so one can call them directly
		401	(as a code reference). Calling them directly is the same as calling
		402	C<send>. Note, however, that many C-based event loops do not handle
		403	overloading, so as tempting as it may be, passing a condition variable
		404	instead of a callback does not work. Both the pure perl and EV loops
		405	support overloading, however, as well as all functions that use perl to
		406	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		407	example).
		408
		409	=item $cv->croak ($error)
		410
		411	Similar to send, but causes all call's to C<< ->recv >> to invoke
		412	C<Carp::croak> with the given error message/object/scalar.
		413
		414	This can be used to signal any errors to the condition variable
		415	user/consumer.
		416
		417	=item $cv->begin ([group callback])
		418
		419	=item $cv->end
		420
		421	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		422
		423	These two methods can be used to combine many transactions/events into
		424	one. For example, a function that pings many hosts in parallel might want
		425	to use a condition variable for the whole process.
		426
		427	Every call to C<< ->begin >> will increment a counter, and every call to
		428	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		429	>>, the (last) callback passed to C<begin> will be executed. That callback
		430	is I<supposed> to call C<< ->send >>, but that is not required. If no
		431	callback was set, C<send> will be called without any arguments.
		432
		433	Let's clarify this with the ping example:
		434
		435	my $cv = AnyEvent->condvar;
		436
		437	my %result;
		438	$cv->begin (sub { $cv->send (\%result) });
		439
		440	for my $host (@list_of_hosts) {
		441	$cv->begin;
		442	ping_host_then_call_callback $host, sub {
		443	$result{$host} = ...;
		444	$cv->end;
		445	};
		446	}
		447
		448	$cv->end;
		449
		450	This code fragment supposedly pings a number of hosts and calls
		451	C<send> after results for all then have have been gathered - in any
		452	order. To achieve this, the code issues a call to C<begin> when it starts
		453	each ping request and calls C<end> when it has received some result for
		454	it. Since C<begin> and C<end> only maintain a counter, the order in which
		455	results arrive is not relevant.
		456
		457	There is an additional bracketing call to C<begin> and C<end> outside the
		458	loop, which serves two important purposes: first, it sets the callback
		459	to be called once the counter reaches C<0>, and second, it ensures that
		460	C<send> is called even when C<no> hosts are being pinged (the loop
		461	doesn't execute once).
		462
		463	This is the general pattern when you "fan out" into multiple subrequests:
		464	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		465	is called at least once, and then, for each subrequest you start, call
		466	C<begin> and for each subrequest you finish, call C<end>.
		467
		468	=back
		469
		470	=head3 METHODS FOR CONSUMERS
		471
		472	These methods should only be used by the consuming side, i.e. the
		473	code awaits the condition.
		474
		475	=over 4
		476
		477	=item $cv->recv
		478
		479	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		480	>> methods have been called on c<$cv>, while servicing other watchers
		481	normally.
		482
		483	You can only wait once on a condition - additional calls are valid but
		484	will return immediately.
		485
		486	If an error condition has been set by calling C<< ->croak >>, then this
		487	function will call C<croak>.
		488
		489	In list context, all parameters passed to C<send> will be returned,
		490	in scalar context only the first one will be returned.
		491
		492	Not all event models support a blocking wait - some die in that case
		493	(programs might want to do that to stay interactive), so I<if you are
		494	using this from a module, never require a blocking wait>, but let the
		495	caller decide whether the call will block or not (for example, by coupling
		496	condition variables with some kind of request results and supporting
		497	callbacks so the caller knows that getting the result will not block,
		498	while still supporting blocking waits if the caller so desires).
		499
		500	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		501	sensibly have two C<< ->recv >>'s in parallel, as that would require
		502	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		503	can supply.
		504
		505	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		506	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		507	versions and also integrates coroutines into AnyEvent, making blocking
		508	C<< ->recv >> calls perfectly safe as long as they are done from another
		509	coroutine (one that doesn't run the event loop).
		510
		511	You can ensure that C<< -recv >> never blocks by setting a callback and
		512	only calling C<< ->recv >> from within that callback (or at a later
		513	time). This will work even when the event loop does not support blocking
		514	waits otherwise.
		515
		516	=item $bool = $cv->ready
		517
		518	Returns true when the condition is "true", i.e. whether C<send> or
		519	C<croak> have been called.
		520
		521	=item $cb = $cv->cb ([new callback])
		522
		523	This is a mutator function that returns the callback set and optionally
		524	replaces it before doing so.
		525
		526	The callback will be called when the condition becomes "true", i.e. when
		527	C<send> or C<croak> are called. Calling C<recv> inside the callback
		528	or at any later time is guaranteed not to block.
		529
		530	=back
		531
		532	=head1 GLOBAL VARIABLES AND FUNCTIONS
		533
		534	=over 4
		535
		536	=item $AnyEvent::MODEL
		537
		538	Contains C<undef> until the first watcher is being created. Then it
		539	contains the event model that is being used, which is the name of the
		540	Perl class implementing the model. This class is usually one of the
		541	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		542	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		543
		544	The known classes so far are:
		545
		546	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		547	AnyEvent::Impl::Event based on Event, second best choice.
		548	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		549	AnyEvent::Impl::Glib based on Glib, third-best choice.
		550	AnyEvent::Impl::Tk based on Tk, very bad choice.
		551	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		552	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		553	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		554
		555	There is no support for WxWidgets, as WxWidgets has no support for
		556	watching file handles. However, you can use WxWidgets through the
		557	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		558	second, which was considered to be too horrible to even consider for
		559	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		560	it's adaptor.
		561
		562	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		563	autodetecting them.
		564
		565	=item AnyEvent::detect
		566
		567	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		568	if necessary. You should only call this function right before you would
		569	have created an AnyEvent watcher anyway, that is, as late as possible at
		570	runtime.
		571
		572	=item $guard = AnyEvent::post_detect { BLOCK }
		573
		574	Arranges for the code block to be executed as soon as the event model is
		575	autodetected (or immediately if this has already happened).
		576
		577	If called in scalar or list context, then it creates and returns an object
		578	that automatically removes the callback again when it is destroyed. See
		579	L<Coro::BDB> for a case where this is useful.
		580
		581	=item @AnyEvent::post_detect
		582
		583	If there are any code references in this array (you can C<push> to it
		584	before or after loading AnyEvent), then they will called directly after
		585	the event loop has been chosen.
		586
		587	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		588	if it contains a true value then the event loop has already been detected,
		589	and the array will be ignored.
		590
		591	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		592
		593	=back
		594
		595	=head1 WHAT TO DO IN A MODULE
		596
		597	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		598	freely, but you should not load a specific event module or rely on it.
		599
		600	Be careful when you create watchers in the module body - AnyEvent will
		601	decide which event module to use as soon as the first method is called, so
		602	by calling AnyEvent in your module body you force the user of your module
		603	to load the event module first.
		604
		605	Never call C<< ->recv >> on a condition variable unless you I<know> that
		606	the C<< ->send >> method has been called on it already. This is
		607	because it will stall the whole program, and the whole point of using
		608	events is to stay interactive.
		609
		610	It is fine, however, to call C<< ->recv >> when the user of your module
		611	requests it (i.e. if you create a http request object ad have a method
		612	called C<results> that returns the results, it should call C<< ->recv >>
		613	freely, as the user of your module knows what she is doing. always).
		614
		615	=head1 WHAT TO DO IN THE MAIN PROGRAM
		616
		617	There will always be a single main program - the only place that should
		618	dictate which event model to use.
		619
		620	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		621	do anything special (it does not need to be event-based) and let AnyEvent
		622	decide which implementation to chose if some module relies on it.
		623
		624	If the main program relies on a specific event model - for example, in
		625	Gtk2 programs you have to rely on the Glib module - you should load the
		626	event module before loading AnyEvent or any module that uses it: generally
		627	speaking, you should load it as early as possible. The reason is that
		628	modules might create watchers when they are loaded, and AnyEvent will
		629	decide on the event model to use as soon as it creates watchers, and it
		630	might chose the wrong one unless you load the correct one yourself.
		631
		632	You can chose to use a pure-perl implementation by loading the
		633	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
		634	everywhere, but letting AnyEvent chose the model is generally better.
		635
		636	=head2 MAINLOOP EMULATION
		637
		638	Sometimes (often for short test scripts, or even standalone programs who
		639	only want to use AnyEvent), you do not want to run a specific event loop.
		640
		641	In that case, you can use a condition variable like this:
		642
		643	AnyEvent->condvar->recv;
		644
		645	This has the effect of entering the event loop and looping forever.
		646
		647	Note that usually your program has some exit condition, in which case
		648	it is better to use the "traditional" approach of storing a condition
		649	variable somewhere, waiting for it, and sending it when the program should
		650	exit cleanly.
		651
		652
		653	=head1 OTHER MODULES
		654
		655	The following is a non-exhaustive list of additional modules that use
		656	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		657	in the same program. Some of the modules come with AnyEvent, some are
		658	available via CPAN.
		659
		660	=over 4
		661
		662	=item L<AnyEvent::Util>
		663
		664	Contains various utility functions that replace often-used but blocking
		665	functions such as C<inet_aton> by event-/callback-based versions.
		666
		667	=item L<AnyEvent::Handle>
		668
		669	Provide read and write buffers and manages watchers for reads and writes.
		670
		671	=item L<AnyEvent::Socket>
		672
		673	Provides various utility functions for (internet protocol) sockets,
		674	addresses and name resolution. Also functions to create non-blocking tcp
		675	connections or tcp servers, with IPv6 and SRV record support and more.
		676
		677	=item L<AnyEvent::DNS>
		678
		679	Provides rich asynchronous DNS resolver capabilities.
		680
		681	=item L<AnyEvent::HTTPD>
		682
		683	Provides a simple web application server framework.
		684
		685	=item L<AnyEvent::FastPing>
		686
		687	The fastest ping in the west.
		688
		689	=item L<Net::IRC3>
		690
		691	AnyEvent based IRC client module family.
		692
		693	=item L<Net::XMPP2>
		694
		695	AnyEvent based XMPP (Jabber protocol) module family.
		696
		697	=item L<Net::FCP>
		698
		699	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		700	of AnyEvent.
		701
		702	=item L<Event::ExecFlow>
		703
		704	High level API for event-based execution flow control.
		705
		706	=item L<Coro>
		707
		708	Has special support for AnyEvent via L<Coro::AnyEvent>.
		709
		710	=item L<AnyEvent::AIO>, L<IO::AIO>
		711
		712	Truly asynchronous I/O, should be in the toolbox of every event
		713	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		714	together.
		715
		716	=item L<AnyEvent::BDB>, L<BDB>
		717
		718	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		719	IO::AIO and AnyEvent together.
		720
		721	=item L<IO::Lambda>
		722
		723	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		724
		725	=back
		726
59	=cut	727	=cut
60		728
61	package AnyEvent;	729	package AnyEvent;
62		730
63	no warnings;	731	no warnings;
64	use strict 'vars';	732	use strict;
		733
65	use Carp;	734	use Carp;
66		735
67	our $VERSION = 0.3;	736	our $VERSION = '4.03';
68	our $MODEL;	737	our $MODEL;
69		738
70	our $AUTOLOAD;	739	our $AUTOLOAD;
71	our @ISA;	740	our @ISA;
72		741
		742	our @REGISTRY;
		743
		744	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		745
		746	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		747
		748	{
		749	my $idx;
		750	$PROTOCOL{$_} = ++$idx
		751	for reverse split /\s*,\s*/,
		752	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		753	}
		754
73	my @models = (	755	my @models = (
74	[Coro => Coro::Event::],	756	[EV:: => AnyEvent::Impl::EV::],
75	[Event => Event::],	757	[Event:: => AnyEvent::Impl::Event::],
76	[Glib => Glib::],	758	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
77	[Tk => Tk::],	759	# everything below here will not be autoprobed
		760	# as the pureperl backend should work everywhere
		761	# and is usually faster
		762	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		763	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		764	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		765	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		766	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		767	[Wx:: => AnyEvent::Impl::POE::],
		768	[Prima:: => AnyEvent::Impl::POE::],
78	);	769	);
79		770
80	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	771	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
81		772
82	sub AUTOLOAD {	773	our @post_detect;
83	$AUTOLOAD =~ s/.*://;
84		774
85	$method{$AUTOLOAD}	775	sub post_detect(&) {
86	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	776	my ($cb) = @_;
87		777
		778	if ($MODEL) {
		779	$cb->();
		780
		781	1
		782	} else {
		783	push @post_detect, $cb;
		784
		785	defined wantarray
		786	? bless \$cb, "AnyEvent::Util::PostDetect"
		787	: ()
		788	}
		789	}
		790
		791	sub AnyEvent::Util::PostDetect::DESTROY {
		792	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		793	}
		794
		795	sub detect() {
88	unless ($MODEL) {	796	unless ($MODEL) {
89	# check for already loaded models	797	no strict 'refs';
90	for (@models) {	798
91	my ($model, $package) = @$_;	799	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
92	if (scalar keys %{ *{"$package\::"} }) {	800	my $model = "AnyEvent::Impl::$1";
93	eval "require AnyEvent::Impl::$model";	801	if (eval "require $model") {
94	last if $MODEL;	802	$MODEL = $model;
		803	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		804	} else {
		805	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
95	}	806	}
96	}	807	}
97		808
		809	# check for already loaded models
98	unless ($MODEL) {	810	unless ($MODEL) {
99	# try to load a model
100
101	for (@models) {	811	for (@REGISTRY, @models) {
102	my ($model, $package) = @$_;	812	my ($package, $model) = @$_;
103	eval "require AnyEvent::Impl::$model";	813	if (${"$package\::VERSION"} > 0) {
104	last if $MODEL;	814	if (eval "require $model") {
		815	$MODEL = $model;
		816	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		817	last;
		818	}
		819	}
105	}	820	}
106		821
		822	unless ($MODEL) {
		823	# try to load a model
		824
		825	for (@REGISTRY, @models) {
		826	my ($package, $model) = @$_;
		827	if (eval "require $package"
		828	and ${"$package\::VERSION"} > 0
		829	and eval "require $model") {
		830	$MODEL = $model;
		831	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		832	last;
		833	}
		834	}
		835
107	$MODEL	836	$MODEL
108	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	837	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		838	}
109	}	839	}
		840
		841	unshift @ISA, $MODEL;
		842	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		843
		844	(shift @post_detect)->() while @post_detect;
110	}	845	}
111		846
112	@ISA = $MODEL;	847	$MODEL
		848	}
		849
		850	sub AUTOLOAD {
		851	(my $func = $AUTOLOAD) =~ s/.*://;
		852
		853	$method{$func}
		854	or croak "$func: not a valid method for AnyEvent objects";
		855
		856	detect unless $MODEL;
113		857
114	my $class = shift;	858	my $class = shift;
115	$class->$AUTOLOAD (@_);	859	$class->$func (@_);
116	}	860	}
		861
		862	package AnyEvent::Base;
		863
		864	# default implementation for ->condvar
		865
		866	sub condvar {
		867	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		868	}
		869
		870	# default implementation for ->signal
		871
		872	our %SIG_CB;
		873
		874	sub signal {
		875	my (undef, %arg) = @_;
		876
		877	my $signal = uc $arg{signal}
		878	or Carp::croak "required option 'signal' is missing";
		879
		880	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		881	$SIG{$signal} ||= sub {
		882	$_->() for values %{ $SIG_CB{$signal} || {} };
		883	};
		884
		885	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		886	}
		887
		888	sub AnyEvent::Base::Signal::DESTROY {
		889	my ($signal, $cb) = @{$_[0]};
		890
		891	delete $SIG_CB{$signal}{$cb};
		892
		893	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		894	}
		895
		896	# default implementation for ->child
		897
		898	our %PID_CB;
		899	our $CHLD_W;
		900	our $CHLD_DELAY_W;
		901	our $PID_IDLE;
		902	our $WNOHANG;
		903
		904	sub _child_wait {
		905	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		906	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		907	(values %{ $PID_CB{0} || {} });
		908	}
		909
		910	undef $PID_IDLE;
		911	}
		912
		913	sub _sigchld {
		914	# make sure we deliver these changes "synchronous" with the event loop.
		915	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		916	undef $CHLD_DELAY_W;
		917	&_child_wait;
		918	});
		919	}
		920
		921	sub child {
		922	my (undef, %arg) = @_;
		923
		924	defined (my $pid = $arg{pid} + 0)
		925	or Carp::croak "required option 'pid' is missing";
		926
		927	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		928
		929	unless ($WNOHANG) {
		930	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		931	}
		932
		933	unless ($CHLD_W) {
		934	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		935	# child could be a zombie already, so make at least one round
		936	&_sigchld;
		937	}
		938
		939	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		940	}
		941
		942	sub AnyEvent::Base::Child::DESTROY {
		943	my ($pid, $cb) = @{$_[0]};
		944
		945	delete $PID_CB{$pid}{$cb};
		946	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		947
		948	undef $CHLD_W unless keys %PID_CB;
		949	}
		950
		951	package AnyEvent::CondVar;
		952
		953	our @ISA = AnyEvent::CondVar::Base::;
		954
		955	package AnyEvent::CondVar::Base;
		956
		957	use overload
		958	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		959	fallback => 1;
		960
		961	sub _send {
		962	# nop
		963	}
		964
		965	sub send {
		966	my $cv = shift;
		967	$cv->{_ae_sent} = [@_];
		968	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		969	$cv->_send;
		970	}
		971
		972	sub croak {
		973	$_[0]{_ae_croak} = $_[1];
		974	$_[0]->send;
		975	}
		976
		977	sub ready {
		978	$_[0]{_ae_sent}
		979	}
		980
		981	sub _wait {
		982	AnyEvent->one_event while !$_[0]{_ae_sent};
		983	}
		984
		985	sub recv {
		986	$_[0]->_wait;
		987
		988	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		989	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		990	}
		991
		992	sub cb {
		993	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		994	$_[0]{_ae_cb}
		995	}
		996
		997	sub begin {
		998	++$_[0]{_ae_counter};
		999	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1000	}
		1001
		1002	sub end {
		1003	return if --$_[0]{_ae_counter};
		1004	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1005	}
		1006
		1007	# undocumented/compatibility with pre-3.4
		1008	*broadcast = \&send;
		1009	*wait = \&_wait;
		1010
		1011	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1012
		1013	This is an advanced topic that you do not normally need to use AnyEvent in
		1014	a module. This section is only of use to event loop authors who want to
		1015	provide AnyEvent compatibility.
		1016
		1017	If you need to support another event library which isn't directly
		1018	supported by AnyEvent, you can supply your own interface to it by
		1019	pushing, before the first watcher gets created, the package name of
		1020	the event module and the package name of the interface to use onto
		1021	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1022	AnyEvent, so it is reasonably cheap.
		1023
		1024	Example:
		1025
		1026	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1027
		1028	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1029	package/class when it finds the C<urxvt> package/module is already loaded.
		1030
		1031	When AnyEvent is loaded and asked to find a suitable event model, it
		1032	will first check for the presence of urxvt by trying to C<use> the
		1033	C<urxvt::anyevent> module.
		1034
		1035	The class should provide implementations for all watcher types. See
		1036	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1037	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1038	see the sources.
		1039
		1040	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1041	provide suitable (hopefully) replacements.
		1042
		1043	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1044	terminal emulator uses the above line as-is. An interface isn't included
		1045	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1046	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1047	I<rxvt-unicode> distribution.
		1048
		1049	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1050	condition variables: code blocking while waiting for a condition will
		1051	C<die>. This still works with most modules/usages, and blocking calls must
		1052	not be done in an interactive application, so it makes sense.
		1053
		1054	=head1 ENVIRONMENT VARIABLES
		1055
		1056	The following environment variables are used by this module:
		1057
		1058	=over 4
		1059
		1060	=item C<PERL_ANYEVENT_VERBOSE>
		1061
		1062	By default, AnyEvent will be completely silent except in fatal
		1063	conditions. You can set this environment variable to make AnyEvent more
		1064	talkative.
		1065
		1066	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1067	conditions, such as not being able to load the event model specified by
		1068	C<PERL_ANYEVENT_MODEL>.
		1069
		1070	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1071	model it chooses.
		1072
		1073	=item C<PERL_ANYEVENT_MODEL>
		1074
		1075	This can be used to specify the event model to be used by AnyEvent, before
		1076	auto detection and -probing kicks in. It must be a string consisting
		1077	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1078	and the resulting module name is loaded and if the load was successful,
		1079	used as event model. If it fails to load AnyEvent will proceed with
		1080	auto detection and -probing.
		1081
		1082	This functionality might change in future versions.
		1083
		1084	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1085	could start your program like this:
		1086
		1087	PERL_ANYEVENT_MODEL=Perl perl ...
		1088
		1089	=item C<PERL_ANYEVENT_PROTOCOLS>
		1090
		1091	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1092	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1093	of auto probing).
		1094
		1095	Must be set to a comma-separated list of protocols or address families,
		1096	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1097	used, and preference will be given to protocols mentioned earlier in the
		1098	list.
		1099
		1100	This variable can effectively be used for denial-of-service attacks
		1101	against local programs (e.g. when setuid), although the impact is likely
		1102	small, as the program has to handle connection errors already-
		1103
		1104	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1105	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1106	- only support IPv4, never try to resolve or contact IPv6
		1107	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1108	IPv6, but prefer IPv6 over IPv4.
		1109
		1110	=item C<PERL_ANYEVENT_EDNS0>
		1111
		1112	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1113	for DNS. This extension is generally useful to reduce DNS traffic, but
		1114	some (broken) firewalls drop such DNS packets, which is why it is off by
		1115	default.
		1116
		1117	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1118	EDNS0 in its DNS requests.
117		1119
118	=back	1120	=back
119		1121
120	=head1 EXAMPLE	1122	=head1 EXAMPLE PROGRAM
121		1123
122	The following program uses an io watcher to read data from stdin, a timer	1124	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	1125	to display a message once per second, and a condition variable to quit the
124	when the user enters quit:	1126	program when the user enters quit:
125		1127
126	use AnyEvent;	1128	use AnyEvent;
127		1129
128	my $cv = AnyEvent->condvar;	1130	my $cv = AnyEvent->condvar;
129		1131
130	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1132	my $io_watcher = AnyEvent->io (
		1133	fh => \*STDIN,
		1134	poll => 'r',
		1135	cb => sub {
131	warn "io event <$_[0]>\n"; # will always output <r>	1136	warn "io event <$_[0]>\n"; # will always output <r>
132	chomp (my $input = <STDIN>); # read a line	1137	chomp (my $input = <STDIN>); # read a line
133	warn "read: $input\n"; # output what has been read	1138	warn "read: $input\n"; # output what has been read
134	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1139	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1140	},
135	});	1141	);
136		1142
137	my $time_watcher; # can only be used once	1143	my $time_watcher; # can only be used once
138		1144
139	sub new_timer {	1145	sub new_timer {
140	$timer = AnyEvent->timer (after => 1, cb => sub {	1146	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
143	});	1149	});
144	}	1150	}
145		1151
146	new_timer; # create first timer	1152	new_timer; # create first timer
147		1153
148	$cv->wait; # wait until user enters /^q/i	1154	$cv->recv; # wait until user enters /^q/i
149		1155
150	=head1 REAL-WORLD EXAMPLE	1156	=head1 REAL-WORLD EXAMPLE
151		1157
152	Consider the L<Net::FCP> module. It features (among others) the following	1158	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:	1159	API calls, which are to freenet what HTTP GET requests are to http:
…		…
203	syswrite $txn->{fh}, $txn->{request}	1209	syswrite $txn->{fh}, $txn->{request}
204	or die "connection or write error";	1210	or die "connection or write error";
205	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1211	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
206		1212
207	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1213	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
208	result and signals any possible waiters that the request ahs finished:	1214	result and signals any possible waiters that the request has finished:
209		1215
210	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1216	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
211		1217
212	if (end-of-file or data complete) {	1218	if (end-of-file or data complete) {
213	$txn->{result} = $txn->{buf};	1219	$txn->{result} = $txn->{buf};
214	$txn->{finished}->broadcast;	1220	$txn->{finished}->send;
215	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1221	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
216	}	1222	}
217		1223
218	The C<result> method, finally, just waits for the finished signal (if the	1224	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	1225	request was already finished, it doesn't wait, of course, and returns the
220	data:	1226	data:
221		1227
222	$txn->{finished}->wait;	1228	$txn->{finished}->recv;
223	return $txn->{result};	1229	return $txn->{result};
224		1230
225	The actual code goes further and collects all errors (C<die>s, exceptions)	1231	The actual code goes further and collects all errors (C<die>s, exceptions)
226	that occured during request processing. The C<result> method detects	1232	that occurred during request processing. The C<result> method detects
227	wether an exception as thrown (it is stored inside the $txn object)	1233	whether an exception as thrown (it is stored inside the $txn object)
228	and just throws the exception, which means connection errors and other	1234	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	1235	problems get reported tot he code that tries to use the result, not in a
230	random callback.	1236	random callback.
231		1237
232	All of this enables the following usage styles:	1238	All of this enables the following usage styles:
233		1239
234	1. Blocking:	1240	1. Blocking:
235		1241
236	my $data = $fcp->client_get ($url);	1242	my $data = $fcp->client_get ($url);
237		1243
238	2. Blocking, but parallelizing:	1244	2. Blocking, but running in parallel:
239		1245
240	my @datas = map $_->result,	1246	my @datas = map $_->result,
241	map $fcp->txn_client_get ($_),	1247	map $fcp->txn_client_get ($_),
242	@urls;	1248	@urls;
243		1249
244	Both blocking examples work without the module user having to know	1250	Both blocking examples work without the module user having to know
245	anything about events.	1251	anything about events.
246		1252
247	3a. Event-based in a main program, using any support Event module:	1253	3a. Event-based in a main program, using any supported event module:
248		1254
249	use Event;	1255	use EV;
250		1256
251	$fcp->txn_client_get ($url)->cb (sub {	1257	$fcp->txn_client_get ($url)->cb (sub {
252	my $txn = shift;	1258	my $txn = shift;
253	my $data = $txn->result;	1259	my $data = $txn->result;
254	...	1260	...
255	});	1261	});
256		1262
257	Event::loop;	1263	EV::loop;
258		1264
259	3b. The module user could use AnyEvent, too:	1265	3b. The module user could use AnyEvent, too:
260		1266
261	use AnyEvent;	1267	use AnyEvent;
262		1268
263	my $quit = AnyEvent->condvar;	1269	my $quit = AnyEvent->condvar;
264		1270
265	$fcp->txn_client_get ($url)->cb (sub {	1271	$fcp->txn_client_get ($url)->cb (sub {
266	...	1272	...
267	$quit->broadcast;	1273	$quit->send;
268	});	1274	});
269		1275
270	$quit->wait;	1276	$quit->recv;
		1277
		1278
		1279	=head1 BENCHMARKS
		1280
		1281	To give you an idea of the performance and overheads that AnyEvent adds
		1282	over the event loops themselves and to give you an impression of the speed
		1283	of various event loops I prepared some benchmarks.
		1284
		1285	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1286
		1287	Here is a benchmark of various supported event models used natively and
		1288	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1289	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1290	which it is), lets them fire exactly once and destroys them again.
		1291
		1292	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1293	distribution.
		1294
		1295	=head3 Explanation of the columns
		1296
		1297	I<watcher> is the number of event watchers created/destroyed. Since
		1298	different event models feature vastly different performances, each event
		1299	loop was given a number of watchers so that overall runtime is acceptable
		1300	and similar between tested event loop (and keep them from crashing): Glib
		1301	would probably take thousands of years if asked to process the same number
		1302	of watchers as EV in this benchmark.
		1303
		1304	I<bytes> is the number of bytes (as measured by the resident set size,
		1305	RSS) consumed by each watcher. This method of measuring captures both C
		1306	and Perl-based overheads.
		1307
		1308	I<create> is the time, in microseconds (millionths of seconds), that it
		1309	takes to create a single watcher. The callback is a closure shared between
		1310	all watchers, to avoid adding memory overhead. That means closure creation
		1311	and memory usage is not included in the figures.
		1312
		1313	I<invoke> is the time, in microseconds, used to invoke a simple
		1314	callback. The callback simply counts down a Perl variable and after it was
		1315	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1316	signal the end of this phase.
		1317
		1318	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1319	watcher.
		1320
		1321	=head3 Results
		1322
		1323	name watchers bytes create invoke destroy comment
		1324	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1325	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1326	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1327	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1328	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1329	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1330	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1331	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1332	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1333	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1334
		1335	=head3 Discussion
		1336
		1337	The benchmark does I<not> measure scalability of the event loop very
		1338	well. For example, a select-based event loop (such as the pure perl one)
		1339	can never compete with an event loop that uses epoll when the number of
		1340	file descriptors grows high. In this benchmark, all events become ready at
		1341	the same time, so select/poll-based implementations get an unnatural speed
		1342	boost.
		1343
		1344	Also, note that the number of watchers usually has a nonlinear effect on
		1345	overall speed, that is, creating twice as many watchers doesn't take twice
		1346	the time - usually it takes longer. This puts event loops tested with a
		1347	higher number of watchers at a disadvantage.
		1348
		1349	To put the range of results into perspective, consider that on the
		1350	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1351	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1352	cycles with POE.
		1353
		1354	C<EV> is the sole leader regarding speed and memory use, which are both
		1355	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1356	far less memory than any other event loop and is still faster than Event
		1357	natively.
		1358
		1359	The pure perl implementation is hit in a few sweet spots (both the
		1360	constant timeout and the use of a single fd hit optimisations in the perl
		1361	interpreter and the backend itself). Nevertheless this shows that it
		1362	adds very little overhead in itself. Like any select-based backend its
		1363	performance becomes really bad with lots of file descriptors (and few of
		1364	them active), of course, but this was not subject of this benchmark.
		1365
		1366	The C<Event> module has a relatively high setup and callback invocation
		1367	cost, but overall scores in on the third place.
		1368
		1369	C<Glib>'s memory usage is quite a bit higher, but it features a
		1370	faster callback invocation and overall ends up in the same class as
		1371	C<Event>. However, Glib scales extremely badly, doubling the number of
		1372	watchers increases the processing time by more than a factor of four,
		1373	making it completely unusable when using larger numbers of watchers
		1374	(note that only a single file descriptor was used in the benchmark, so
		1375	inefficiencies of C<poll> do not account for this).
		1376
		1377	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1378	more than 2000 watchers is a big setback, however, as correctness takes
		1379	precedence over speed. Nevertheless, its performance is surprising, as the
		1380	file descriptor is dup()ed for each watcher. This shows that the dup()
		1381	employed by some adaptors is not a big performance issue (it does incur a
		1382	hidden memory cost inside the kernel which is not reflected in the figures
		1383	above).
		1384
		1385	C<POE>, regardless of underlying event loop (whether using its pure perl
		1386	select-based backend or the Event module, the POE-EV backend couldn't
		1387	be tested because it wasn't working) shows abysmal performance and
		1388	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1389	as EV watchers, and 10 times as much memory as Event (the high memory
		1390	requirements are caused by requiring a session for each watcher). Watcher
		1391	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1392	implementation.
		1393
		1394	The design of the POE adaptor class in AnyEvent can not really account
		1395	for the performance issues, though, as session creation overhead is
		1396	small compared to execution of the state machine, which is coded pretty
		1397	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1398	using multiple sessions is not a good approach, especially regarding
		1399	memory usage, even the author of POE could not come up with a faster
		1400	design).
		1401
		1402	=head3 Summary
		1403
		1404	=over 4
		1405
		1406	=item * Using EV through AnyEvent is faster than any other event loop
		1407	(even when used without AnyEvent), but most event loops have acceptable
		1408	performance with or without AnyEvent.
		1409
		1410	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1411	the actual event loop, only with extremely fast event loops such as EV
		1412	adds AnyEvent significant overhead.
		1413
		1414	=item * You should avoid POE like the plague if you want performance or
		1415	reasonable memory usage.
		1416
		1417	=back
		1418
		1419	=head2 BENCHMARKING THE LARGE SERVER CASE
		1420
		1421	This benchmark actually benchmarks the event loop itself. It works by
		1422	creating a number of "servers": each server consists of a socket pair, a
		1423	timeout watcher that gets reset on activity (but never fires), and an I/O
		1424	watcher waiting for input on one side of the socket. Each time the socket
		1425	watcher reads a byte it will write that byte to a random other "server".
		1426
		1427	The effect is that there will be a lot of I/O watchers, only part of which
		1428	are active at any one point (so there is a constant number of active
		1429	fds for each loop iteration, but which fds these are is random). The
		1430	timeout is reset each time something is read because that reflects how
		1431	most timeouts work (and puts extra pressure on the event loops).
		1432
		1433	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1434	(1%) are active. This mirrors the activity of large servers with many
		1435	connections, most of which are idle at any one point in time.
		1436
		1437	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1438	distribution.
		1439
		1440	=head3 Explanation of the columns
		1441
		1442	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1443	each server has a read and write socket end).
		1444
		1445	I<create> is the time it takes to create a socket pair (which is
		1446	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1447
		1448	I<request>, the most important value, is the time it takes to handle a
		1449	single "request", that is, reading the token from the pipe and forwarding
		1450	it to another server. This includes deleting the old timeout and creating
		1451	a new one that moves the timeout into the future.
		1452
		1453	=head3 Results
		1454
		1455	name sockets create request
		1456	EV 20000 69.01 11.16
		1457	Perl 20000 73.32 35.87
		1458	Event 20000 212.62 257.32
		1459	Glib 20000 651.16 1896.30
		1460	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1461
		1462	=head3 Discussion
		1463
		1464	This benchmark I<does> measure scalability and overall performance of the
		1465	particular event loop.
		1466
		1467	EV is again fastest. Since it is using epoll on my system, the setup time
		1468	is relatively high, though.
		1469
		1470	Perl surprisingly comes second. It is much faster than the C-based event
		1471	loops Event and Glib.
		1472
		1473	Event suffers from high setup time as well (look at its code and you will
		1474	understand why). Callback invocation also has a high overhead compared to
		1475	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1476	uses select or poll in basically all documented configurations.
		1477
		1478	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1479	clearly fails to perform with many filehandles or in busy servers.
		1480
		1481	POE is still completely out of the picture, taking over 1000 times as long
		1482	as EV, and over 100 times as long as the Perl implementation, even though
		1483	it uses a C-based event loop in this case.
		1484
		1485	=head3 Summary
		1486
		1487	=over 4
		1488
		1489	=item * The pure perl implementation performs extremely well.
		1490
		1491	=item * Avoid Glib or POE in large projects where performance matters.
		1492
		1493	=back
		1494
		1495	=head2 BENCHMARKING SMALL SERVERS
		1496
		1497	While event loops should scale (and select-based ones do not...) even to
		1498	large servers, most programs we (or I :) actually write have only a few
		1499	I/O watchers.
		1500
		1501	In this benchmark, I use the same benchmark program as in the large server
		1502	case, but it uses only eight "servers", of which three are active at any
		1503	one time. This should reflect performance for a small server relatively
		1504	well.
		1505
		1506	The columns are identical to the previous table.
		1507
		1508	=head3 Results
		1509
		1510	name sockets create request
		1511	EV 16 20.00 6.54
		1512	Perl 16 25.75 12.62
		1513	Event 16 81.27 35.86
		1514	Glib 16 32.63 15.48
		1515	POE 16 261.87 276.28 uses POE::Loop::Event
		1516
		1517	=head3 Discussion
		1518
		1519	The benchmark tries to test the performance of a typical small
		1520	server. While knowing how various event loops perform is interesting, keep
		1521	in mind that their overhead in this case is usually not as important, due
		1522	to the small absolute number of watchers (that is, you need efficiency and
		1523	speed most when you have lots of watchers, not when you only have a few of
		1524	them).
		1525
		1526	EV is again fastest.
		1527
		1528	Perl again comes second. It is noticeably faster than the C-based event
		1529	loops Event and Glib, although the difference is too small to really
		1530	matter.
		1531
		1532	POE also performs much better in this case, but is is still far behind the
		1533	others.
		1534
		1535	=head3 Summary
		1536
		1537	=over 4
		1538
		1539	=item * C-based event loops perform very well with small number of
		1540	watchers, as the management overhead dominates.
		1541
		1542	=back
		1543
		1544
		1545	=head1 FORK
		1546
		1547	Most event libraries are not fork-safe. The ones who are usually are
		1548	because they rely on inefficient but fork-safe C<select> or C<poll>
		1549	calls. Only L<EV> is fully fork-aware.
		1550
		1551	If you have to fork, you must either do so I<before> creating your first
		1552	watcher OR you must not use AnyEvent at all in the child.
		1553
		1554
		1555	=head1 SECURITY CONSIDERATIONS
		1556
		1557	AnyEvent can be forced to load any event model via
		1558	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1559	execute arbitrary code or directly gain access, it can easily be used to
		1560	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1561	will not be active when the program uses a different event model than
		1562	specified in the variable.
		1563
		1564	You can make AnyEvent completely ignore this variable by deleting it
		1565	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1566
		1567	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1568
		1569	use AnyEvent;
		1570
		1571	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1572	be used to probe what backend is used and gain other information (which is
		1573	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1574
271		1575
272	=head1 SEE ALSO	1576	=head1 SEE ALSO
273		1577
274	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1578	Utility functions: L<AnyEvent::Util>.
275		1579
276	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1580	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1581	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
277		1582
278	Nontrivial usage example: L<Net::FCP>.	1583	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1584	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1585	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1586	L<AnyEvent::Impl::POE>.
279		1587
280	=head1	1588	Non-blocking file handles, sockets, TCP clients and
		1589	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1590
		1591	Asynchronous DNS: L<AnyEvent::DNS>.
		1592
		1593	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1594
		1595	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1596
		1597
		1598	=head1 AUTHOR
		1599
		1600	Marc Lehmann <schmorp@schmorp.de>
		1601	http://home.schmorp.de/
281		1602
282	=cut	1603	=cut
283		1604
284	1	1605	1
285		1606

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