ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.4 by root, Thu Dec 1 22:04:50 2005 UTC vs.
Revision 1.133 by root, Sun May 25 03:44:03 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->timer (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	});
		14
15	my $w = AnyEvent->io (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	# watchers get canceled whenever $w is destroyed	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
20	# only one watcher per $fh and $poll type is allowed	20	$w->send; # wake up current and all future recv's
21	# (i.e. on a socket you cna have one r + one w or one rw
22	# watcher, not any more.
23	# timers can only be used once
24
25	my $w = AnyEvent->condvar; # kind of main loop replacement
26	# can only be used once
27	$w->wait; # enters main loop till $condvar gets ->send	21	$w->recv; # enters "main loop" till $condvar gets ->send
28	$w->broadcast; # wake up waiting and future wait's	22
		23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
		24
		25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		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.
29		70
30	=head1 DESCRIPTION	71	=head1 DESCRIPTION
31		72
32	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
33	allows module authors to utilizy an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
34	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
35	peacefully at any one time).	76	peacefully at any one time).
36		77
37	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>
38	module.	79	module.
39		80
40	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
41	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
42	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
43	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>,
44	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
45	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).
		318
		319	Condition variables are similar to callbacks, except that you can
		320	optionally wait for them. They can also be called merge points - points
		321	in time where multiple outstanding events have been processed. And yet
		322	another way to call them is transactions - each condition variable can be
		323	used to represent a transaction, which finishes at some point and delivers
		324	a result.
		325
		326	Condition variables are very useful to signal that something has finished,
		327	for example, if you write a module that does asynchronous http requests,
		328	then a condition variable would be the ideal candidate to signal the
		329	availability of results. The user can either act when the callback is
		330	called or can synchronously C<< ->recv >> for the results.
		331
		332	You can also use them to simulate traditional event loops - for example,
		333	you can block your main program until an event occurs - for example, you
		334	could C<< ->recv >> in your main program until the user clicks the Quit
		335	button of your app, which would C<< ->send >> the "quit" event.
		336
		337	Note that condition variables recurse into the event loop - if you have
		338	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		339	lose. Therefore, condition variables are good to export to your caller, but
		340	you should avoid making a blocking wait yourself, at least in callbacks,
		341	as this asks for trouble.
		342
		343	Condition variables are represented by hash refs in perl, and the keys
		344	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		345	easy (it is often useful to build your own transaction class on top of
		346	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		347	it's C<new> method in your own C<new> method.
		348
		349	There are two "sides" to a condition variable - the "producer side" which
		350	eventually calls C<< -> send >>, and the "consumer side", which waits
		351	for the send to occur.
		352
		353	Example: wait for a timer.
		354
		355	# wait till the result is ready
		356	my $result_ready = AnyEvent->condvar;
		357
		358	# do something such as adding a timer
		359	# or socket watcher the calls $result_ready->send
		360	# when the "result" is ready.
		361	# in this case, we simply use a timer:
		362	my $w = AnyEvent->timer (
		363	after => 1,
		364	cb => sub { $result_ready->send },
		365	);
		366
		367	# this "blocks" (while handling events) till the callback
		368	# calls send
		369	$result_ready->recv;
		370
		371	Example: wait for a timer, but take advantage of the fact that
		372	condition variables are also code references.
		373
		374	my $done = AnyEvent->condvar;
		375	my $delay = AnyEvent->timer (after => 5, cb => $done);
		376	$done->recv;
		377
		378	=head3 METHODS FOR PRODUCERS
		379
		380	These methods should only be used by the producing side, i.e. the
		381	code/module that eventually sends the signal. Note that it is also
		382	the producer side which creates the condvar in most cases, but it isn't
		383	uncommon for the consumer to create it as well.
46		384
47	=over 4	385	=over 4
48		386
		387	=item $cv->send (...)
		388
		389	Flag the condition as ready - a running C<< ->recv >> and all further
		390	calls to C<recv> will (eventually) return after this method has been
		391	called. If nobody is waiting the send will be remembered.
		392
		393	If a callback has been set on the condition variable, it is called
		394	immediately from within send.
		395
		396	Any arguments passed to the C<send> call will be returned by all
		397	future C<< ->recv >> calls.
		398
		399	Condition variables are overloaded so one can call them directly (as a
		400	code reference). Calling them directly is the same as calling C<send>.
		401
		402	=item $cv->croak ($error)
		403
		404	Similar to send, but causes all call's to C<< ->recv >> to invoke
		405	C<Carp::croak> with the given error message/object/scalar.
		406
		407	This can be used to signal any errors to the condition variable
		408	user/consumer.
		409
		410	=item $cv->begin ([group callback])
		411
		412	=item $cv->end
		413
		414	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		415
		416	These two methods can be used to combine many transactions/events into
		417	one. For example, a function that pings many hosts in parallel might want
		418	to use a condition variable for the whole process.
		419
		420	Every call to C<< ->begin >> will increment a counter, and every call to
		421	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		422	>>, the (last) callback passed to C<begin> will be executed. That callback
		423	is I<supposed> to call C<< ->send >>, but that is not required. If no
		424	callback was set, C<send> will be called without any arguments.
		425
		426	Let's clarify this with the ping example:
		427
		428	my $cv = AnyEvent->condvar;
		429
		430	my %result;
		431	$cv->begin (sub { $cv->send (\%result) });
		432
		433	for my $host (@list_of_hosts) {
		434	$cv->begin;
		435	ping_host_then_call_callback $host, sub {
		436	$result{$host} = ...;
		437	$cv->end;
		438	};
		439	}
		440
		441	$cv->end;
		442
		443	This code fragment supposedly pings a number of hosts and calls
		444	C<send> after results for all then have have been gathered - in any
		445	order. To achieve this, the code issues a call to C<begin> when it starts
		446	each ping request and calls C<end> when it has received some result for
		447	it. Since C<begin> and C<end> only maintain a counter, the order in which
		448	results arrive is not relevant.
		449
		450	There is an additional bracketing call to C<begin> and C<end> outside the
		451	loop, which serves two important purposes: first, it sets the callback
		452	to be called once the counter reaches C<0>, and second, it ensures that
		453	C<send> is called even when C<no> hosts are being pinged (the loop
		454	doesn't execute once).
		455
		456	This is the general pattern when you "fan out" into multiple subrequests:
		457	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		458	is called at least once, and then, for each subrequest you start, call
		459	C<begin> and for each subrequest you finish, call C<end>.
		460
		461	=back
		462
		463	=head3 METHODS FOR CONSUMERS
		464
		465	These methods should only be used by the consuming side, i.e. the
		466	code awaits the condition.
		467
		468	=over 4
		469
		470	=item $cv->recv
		471
		472	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		473	>> methods have been called on c<$cv>, while servicing other watchers
		474	normally.
		475
		476	You can only wait once on a condition - additional calls are valid but
		477	will return immediately.
		478
		479	If an error condition has been set by calling C<< ->croak >>, then this
		480	function will call C<croak>.
		481
		482	In list context, all parameters passed to C<send> will be returned,
		483	in scalar context only the first one will be returned.
		484
		485	Not all event models support a blocking wait - some die in that case
		486	(programs might want to do that to stay interactive), so I<if you are
		487	using this from a module, never require a blocking wait>, but let the
		488	caller decide whether the call will block or not (for example, by coupling
		489	condition variables with some kind of request results and supporting
		490	callbacks so the caller knows that getting the result will not block,
		491	while still supporting blocking waits if the caller so desires).
		492
		493	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		494	sensibly have two C<< ->recv >>'s in parallel, as that would require
		495	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		496	can supply.
		497
		498	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		499	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		500	versions and also integrates coroutines into AnyEvent, making blocking
		501	C<< ->recv >> calls perfectly safe as long as they are done from another
		502	coroutine (one that doesn't run the event loop).
		503
		504	You can ensure that C<< -recv >> never blocks by setting a callback and
		505	only calling C<< ->recv >> from within that callback (or at a later
		506	time). This will work even when the event loop does not support blocking
		507	waits otherwise.
		508
		509	=item $bool = $cv->ready
		510
		511	Returns true when the condition is "true", i.e. whether C<send> or
		512	C<croak> have been called.
		513
		514	=item $cb = $cv->cb ([new callback])
		515
		516	This is a mutator function that returns the callback set and optionally
		517	replaces it before doing so.
		518
		519	The callback will be called when the condition becomes "true", i.e. when
		520	C<send> or C<croak> are called. Calling C<recv> inside the callback
		521	or at any later time is guaranteed not to block.
		522
		523	=back
		524
		525	=head3 MAINLOOP EMULATION
		526
		527	Sometimes (often for short test scripts, or even standalone programs
		528	who only want to use AnyEvent), you I<do> want your program to block
		529	indefinitely in some event loop.
		530
		531	In that case, you cna use a condition variable like this:
		532
		533	AnyEvent->condvar->recv;
		534
		535	This has the effect of entering the event loop and looping forever.
		536
		537	Note that usually your program has some exit condition, in which case
		538	it is better to use the "traditional" approach of storing a condition
		539	variable, waiting for it, and sending it when the program should exit
		540	cleanly.
		541
		542
		543	=head1 GLOBAL VARIABLES AND FUNCTIONS
		544
		545	=over 4
		546
		547	=item $AnyEvent::MODEL
		548
		549	Contains C<undef> until the first watcher is being created. Then it
		550	contains the event model that is being used, which is the name of the
		551	Perl class implementing the model. This class is usually one of the
		552	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
		553	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
		554
		555	The known classes so far are:
		556
		557	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		558	AnyEvent::Impl::Event based on Event, second best choice.
		559	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		560	AnyEvent::Impl::Glib based on Glib, third-best choice.
		561	AnyEvent::Impl::Tk based on Tk, very bad choice.
		562	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		563	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		564	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		565
		566	There is no support for WxWidgets, as WxWidgets has no support for
		567	watching file handles. However, you can use WxWidgets through the
		568	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		569	second, which was considered to be too horrible to even consider for
		570	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		571	it's adaptor.
		572
		573	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		574	autodetecting them.
		575
		576	=item AnyEvent::detect
		577
		578	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		579	if necessary. You should only call this function right before you would
		580	have created an AnyEvent watcher anyway, that is, as late as possible at
		581	runtime.
		582
		583	=item $guard = AnyEvent::post_detect { BLOCK }
		584
		585	Arranges for the code block to be executed as soon as the event model is
		586	autodetected (or immediately if this has already happened).
		587
		588	If called in scalar or list context, then it creates and returns an object
		589	that automatically removes the callback again when it is destroyed. See
		590	L<Coro::BDB> for a case where this is useful.
		591
		592	=item @AnyEvent::post_detect
		593
		594	If there are any code references in this array (you can C<push> to it
		595	before or after loading AnyEvent), then they will called directly after
		596	the event loop has been chosen.
		597
		598	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		599	if it contains a true value then the event loop has already been detected,
		600	and the array will be ignored.
		601
		602	Best use C<AnyEvent::post_detect { BLOCK }> instead.
		603
		604	=back
		605
		606	=head1 WHAT TO DO IN A MODULE
		607
		608	As a module author, you should C<use AnyEvent> and call AnyEvent methods
		609	freely, but you should not load a specific event module or rely on it.
		610
		611	Be careful when you create watchers in the module body - AnyEvent will
		612	decide which event module to use as soon as the first method is called, so
		613	by calling AnyEvent in your module body you force the user of your module
		614	to load the event module first.
		615
		616	Never call C<< ->recv >> on a condition variable unless you I<know> that
		617	the C<< ->send >> method has been called on it already. This is
		618	because it will stall the whole program, and the whole point of using
		619	events is to stay interactive.
		620
		621	It is fine, however, to call C<< ->recv >> when the user of your module
		622	requests it (i.e. if you create a http request object ad have a method
		623	called C<results> that returns the results, it should call C<< ->recv >>
		624	freely, as the user of your module knows what she is doing. always).
		625
		626	=head1 WHAT TO DO IN THE MAIN PROGRAM
		627
		628	There will always be a single main program - the only place that should
		629	dictate which event model to use.
		630
		631	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
		632	do anything special (it does not need to be event-based) and let AnyEvent
		633	decide which implementation to chose if some module relies on it.
		634
		635	If the main program relies on a specific event model. For example, in
		636	Gtk2 programs you have to rely on the Glib module. You should load the
		637	event module before loading AnyEvent or any module that uses it: generally
		638	speaking, you should load it as early as possible. The reason is that
		639	modules might create watchers when they are loaded, and AnyEvent will
		640	decide on the event model to use as soon as it creates watchers, and it
		641	might chose the wrong one unless you load the correct one yourself.
		642
		643	You can chose to use a rather inefficient pure-perl implementation by
		644	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
		645	behaviour everywhere, but letting AnyEvent chose is generally better.
		646
		647	=head1 OTHER MODULES
		648
		649	The following is a non-exhaustive list of additional modules that use
		650	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		651	in the same program. Some of the modules come with AnyEvent, some are
		652	available via CPAN.
		653
		654	=over 4
		655
		656	=item L<AnyEvent::Util>
		657
		658	Contains various utility functions that replace often-used but blocking
		659	functions such as C<inet_aton> by event-/callback-based versions.
		660
		661	=item L<AnyEvent::Handle>
		662
		663	Provide read and write buffers and manages watchers for reads and writes.
		664
		665	=item L<AnyEvent::Socket>
		666
		667	Provides various utility functions for (internet protocol) sockets,
		668	addresses and name resolution. Also functions to create non-blocking tcp
		669	connections or tcp servers, with IPv6 and SRV record support and more.
		670
		671	=item L<AnyEvent::HTTPD>
		672
		673	Provides a simple web application server framework.
		674
		675	=item L<AnyEvent::DNS>
		676
		677	Provides rich asynchronous DNS resolver capabilities.
		678
		679	=item L<AnyEvent::FastPing>
		680
		681	The fastest ping in the west.
		682
		683	=item L<Net::IRC3>
		684
		685	AnyEvent based IRC client module family.
		686
		687	=item L<Net::XMPP2>
		688
		689	AnyEvent based XMPP (Jabber protocol) module family.
		690
		691	=item L<Net::FCP>
		692
		693	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		694	of AnyEvent.
		695
		696	=item L<Event::ExecFlow>
		697
		698	High level API for event-based execution flow control.
		699
		700	=item L<Coro>
		701
		702	Has special support for AnyEvent via L<Coro::AnyEvent>.
		703
		704	=item L<AnyEvent::AIO>, L<IO::AIO>
		705
		706	Truly asynchronous I/O, should be in the toolbox of every event
		707	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		708	together.
		709
		710	=item L<AnyEvent::BDB>, L<BDB>
		711
		712	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		713	IO::AIO and AnyEvent together.
		714
		715	=item L<IO::Lambda>
		716
		717	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		718
		719	=back
		720
49	=cut	721	=cut
50		722
51	package AnyEvent;	723	package AnyEvent;
52		724
53	no warnings;	725	no warnings;
54	use strict 'vars';	726	use strict;
		727
55	use Carp;	728	use Carp;
56		729
57	our $VERSION = 0.2;	730	our $VERSION = '4.03';
58	our $MODEL;	731	our $MODEL;
59		732
60	our $AUTOLOAD;	733	our $AUTOLOAD;
61	our @ISA;	734	our @ISA;
62		735
		736	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
		737
		738	our @REGISTRY;
		739
		740	our %PROTOCOL; # (ipv4|ipv6) => (1|2)
		741
		742	{
		743	my $idx;
		744	$PROTOCOL{$_} = ++$idx
		745	for split /\s*,\s*/, $ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		746	}
		747
63	my @models = (	748	my @models = (
64	[Coro => Coro::Event::],	749	[EV:: => AnyEvent::Impl::EV::],
65	[Event => Event::],	750	[Event:: => AnyEvent::Impl::Event::],
66	[Glib => Glib::],	751	[Tk:: => AnyEvent::Impl::Tk::],
67	[Tk => Tk::],	752	[Wx:: => AnyEvent::Impl::POE::],
		753	[Prima:: => AnyEvent::Impl::POE::],
		754	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		755	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		756	[Glib:: => AnyEvent::Impl::Glib::],
		757	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		758	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		759	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
68	);	760	);
69		761
70	our %method = map +($_ => 1), qw(io timer condvar broadcast wait cancel DESTROY);	762	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
71		763
72	sub AUTOLOAD {	764	our @post_detect;
73	$AUTOLOAD =~ s/.*://;
74		765
75	$method{$AUTOLOAD}	766	sub post_detect(&) {
76	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	767	my ($cb) = @_;
77		768
		769	if ($MODEL) {
		770	$cb->();
		771
		772	1
		773	} else {
		774	push @post_detect, $cb;
		775
		776	defined wantarray
		777	? bless \$cb, "AnyEvent::Util::PostDetect"
		778	: ()
		779	}
		780	}
		781
		782	sub AnyEvent::Util::PostDetect::DESTROY {
		783	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		784	}
		785
		786	sub detect() {
78	unless ($MODEL) {	787	unless ($MODEL) {
79	# check for already loaded models	788	no strict 'refs';
80	for (@models) {	789
81	my ($model, $package) = @$_;	790	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
82	if (scalar keys %{ *{"$package\::"} }) {	791	my $model = "AnyEvent::Impl::$1";
83	eval "require AnyEvent::Impl::$model";	792	if (eval "require $model") {
84	last if $MODEL;	793	$MODEL = $model;
		794	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		795	} else {
		796	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
85	}	797	}
86	}	798	}
87		799
		800	# check for already loaded models
88	unless ($MODEL) {	801	unless ($MODEL) {
89	# try to load a model
90
91	for (@models) {	802	for (@REGISTRY, @models) {
92	my ($model, $package) = @$_;	803	my ($package, $model) = @$_;
93	eval "require AnyEvent::Impl::$model";	804	if (${"$package\::VERSION"} > 0) {
94	last if $MODEL;	805	if (eval "require $model") {
		806	$MODEL = $model;
		807	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
		808	last;
		809	}
		810	}
95	}	811	}
96		812
		813	unless ($MODEL) {
		814	# try to load a model
		815
		816	for (@REGISTRY, @models) {
		817	my ($package, $model) = @$_;
		818	if (eval "require $package"
		819	and ${"$package\::VERSION"} > 0
		820	and eval "require $model") {
		821	$MODEL = $model;
		822	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		823	last;
		824	}
		825	}
		826
97	$MODEL	827	$MODEL
98	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";	828	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		829	}
99	}	830	}
		831
		832	unshift @ISA, $MODEL;
		833	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		834
		835	(shift @post_detect)->() while @post_detect;
100	}	836	}
101		837
102	@ISA = $MODEL;	838	$MODEL
		839	}
		840
		841	sub AUTOLOAD {
		842	(my $func = $AUTOLOAD) =~ s/.*://;
		843
		844	$method{$func}
		845	or croak "$func: not a valid method for AnyEvent objects";
		846
		847	detect unless $MODEL;
103		848
104	my $class = shift;	849	my $class = shift;
105	$class->$AUTOLOAD (@_);	850	$class->$func (@_);
106	}	851	}
		852
		853	package AnyEvent::Base;
		854
		855	# default implementation for ->condvar
		856
		857	sub condvar {
		858	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
		859	}
		860
		861	# default implementation for ->signal
		862
		863	our %SIG_CB;
		864
		865	sub signal {
		866	my (undef, %arg) = @_;
		867
		868	my $signal = uc $arg{signal}
		869	or Carp::croak "required option 'signal' is missing";
		870
		871	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		872	$SIG{$signal} ||= sub {
		873	$_->() for values %{ $SIG_CB{$signal} || {} };
		874	};
		875
		876	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		877	}
		878
		879	sub AnyEvent::Base::Signal::DESTROY {
		880	my ($signal, $cb) = @{$_[0]};
		881
		882	delete $SIG_CB{$signal}{$cb};
		883
		884	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		885	}
		886
		887	# default implementation for ->child
		888
		889	our %PID_CB;
		890	our $CHLD_W;
		891	our $CHLD_DELAY_W;
		892	our $PID_IDLE;
		893	our $WNOHANG;
		894
		895	sub _child_wait {
		896	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		897	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		898	(values %{ $PID_CB{0} || {} });
		899	}
		900
		901	undef $PID_IDLE;
		902	}
		903
		904	sub _sigchld {
		905	# make sure we deliver these changes "synchronous" with the event loop.
		906	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		907	undef $CHLD_DELAY_W;
		908	&_child_wait;
		909	});
		910	}
		911
		912	sub child {
		913	my (undef, %arg) = @_;
		914
		915	defined (my $pid = $arg{pid} + 0)
		916	or Carp::croak "required option 'pid' is missing";
		917
		918	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		919
		920	unless ($WNOHANG) {
		921	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		922	}
		923
		924	unless ($CHLD_W) {
		925	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		926	# child could be a zombie already, so make at least one round
		927	&_sigchld;
		928	}
		929
		930	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		931	}
		932
		933	sub AnyEvent::Base::Child::DESTROY {
		934	my ($pid, $cb) = @{$_[0]};
		935
		936	delete $PID_CB{$pid}{$cb};
		937	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		938
		939	undef $CHLD_W unless keys %PID_CB;
		940	}
		941
		942	package AnyEvent::CondVar;
		943
		944	our @ISA = AnyEvent::CondVar::Base::;
		945
		946	package AnyEvent::CondVar::Base;
		947
		948	use overload
		949	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		950	fallback => 1;
		951
		952	sub _send {
		953	# nop
		954	}
		955
		956	sub send {
		957	my $cv = shift;
		958	$cv->{_ae_sent} = [@_];
		959	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		960	$cv->_send;
		961	}
		962
		963	sub croak {
		964	$_[0]{_ae_croak} = $_[1];
		965	$_[0]->send;
		966	}
		967
		968	sub ready {
		969	$_[0]{_ae_sent}
		970	}
		971
		972	sub _wait {
		973	AnyEvent->one_event while !$_[0]{_ae_sent};
		974	}
		975
		976	sub recv {
		977	$_[0]->_wait;
		978
		979	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		980	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		981	}
		982
		983	sub cb {
		984	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		985	$_[0]{_ae_cb}
		986	}
		987
		988	sub begin {
		989	++$_[0]{_ae_counter};
		990	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		991	}
		992
		993	sub end {
		994	return if --$_[0]{_ae_counter};
		995	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		996	}
		997
		998	# undocumented/compatibility with pre-3.4
		999	*broadcast = \&send;
		1000	*wait = \&_wait;
		1001
		1002	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1003
		1004	This is an advanced topic that you do not normally need to use AnyEvent in
		1005	a module. This section is only of use to event loop authors who want to
		1006	provide AnyEvent compatibility.
		1007
		1008	If you need to support another event library which isn't directly
		1009	supported by AnyEvent, you can supply your own interface to it by
		1010	pushing, before the first watcher gets created, the package name of
		1011	the event module and the package name of the interface to use onto
		1012	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
		1013	AnyEvent, so it is reasonably cheap.
		1014
		1015	Example:
		1016
		1017	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1018
		1019	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
		1020	package/class when it finds the C<urxvt> package/module is already loaded.
		1021
		1022	When AnyEvent is loaded and asked to find a suitable event model, it
		1023	will first check for the presence of urxvt by trying to C<use> the
		1024	C<urxvt::anyevent> module.
		1025
		1026	The class should provide implementations for all watcher types. See
		1027	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
		1028	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
		1029	see the sources.
		1030
		1031	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1032	provide suitable (hopefully) replacements.
		1033
		1034	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
		1035	terminal emulator uses the above line as-is. An interface isn't included
		1036	in AnyEvent because it doesn't make sense outside the embedded interpreter
		1037	inside I<rxvt-unicode>, and it is updated and maintained as part of the
		1038	I<rxvt-unicode> distribution.
		1039
		1040	I<rxvt-unicode> also cheats a bit by not providing blocking access to
		1041	condition variables: code blocking while waiting for a condition will
		1042	C<die>. This still works with most modules/usages, and blocking calls must
		1043	not be done in an interactive application, so it makes sense.
		1044
		1045	=head1 ENVIRONMENT VARIABLES
		1046
		1047	The following environment variables are used by this module:
		1048
		1049	=over 4
		1050
		1051	=item C<PERL_ANYEVENT_VERBOSE>
		1052
		1053	By default, AnyEvent will be completely silent except in fatal
		1054	conditions. You can set this environment variable to make AnyEvent more
		1055	talkative.
		1056
		1057	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1058	conditions, such as not being able to load the event model specified by
		1059	C<PERL_ANYEVENT_MODEL>.
		1060
		1061	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1062	model it chooses.
		1063
		1064	=item C<PERL_ANYEVENT_MODEL>
		1065
		1066	This can be used to specify the event model to be used by AnyEvent, before
		1067	auto detection and -probing kicks in. It must be a string consisting
		1068	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1069	and the resulting module name is loaded and if the load was successful,
		1070	used as event model. If it fails to load AnyEvent will proceed with
		1071	auto detection and -probing.
		1072
		1073	This functionality might change in future versions.
		1074
		1075	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1076	could start your program like this:
		1077
		1078	PERL_ANYEVENT_MODEL=Perl perl ...
		1079
		1080	=item C<PERL_ANYEVENT_PROTOCOLS>
		1081
		1082	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1083	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1084	of auto probing).
		1085
		1086	Must be set to a comma-separated list of protocols or address families,
		1087	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1088	used, and preference will be given to protocols mentioned earlier in the
		1089	list.
		1090
		1091	This variable can effectively be used for denial-of-service attacks
		1092	against local programs (e.g. when setuid), although the impact is likely
		1093	small, as the program has to handle connection errors already-
		1094
		1095	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1096	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1097	- only support IPv4, never try to resolve or contact IPv6
		1098	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1099	IPv6, but prefer IPv6 over IPv4.
		1100
		1101	=item C<PERL_ANYEVENT_EDNS0>
		1102
		1103	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1104	for DNS. This extension is generally useful to reduce DNS traffic, but
		1105	some (broken) firewalls drop such DNS packets, which is why it is off by
		1106	default.
		1107
		1108	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1109	EDNS0 in its DNS requests.
107		1110
108	=back	1111	=back
109		1112
110	=head1 EXAMPLE	1113	=head1 EXAMPLE PROGRAM
111		1114
112	The following program uses an io watcher to read data from stdin, a timer	1115	The following program uses an I/O watcher to read data from STDIN, a timer
113	to display a message once per second, and a condvar to exit the program	1116	to display a message once per second, and a condition variable to quit the
114	when the user enters quit:	1117	program when the user enters quit:
115		1118
116	use AnyEvent;	1119	use AnyEvent;
117		1120
118	my $cv = AnyEvent->condvar;	1121	my $cv = AnyEvent->condvar;
119		1122
120	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1123	my $io_watcher = AnyEvent->io (
		1124	fh => \*STDIN,
		1125	poll => 'r',
		1126	cb => sub {
121	warn "io event <$_[0]>\n"; # will always output <r>	1127	warn "io event <$_[0]>\n"; # will always output <r>
122	chomp (my $input = <STDIN>); # read a line	1128	chomp (my $input = <STDIN>); # read a line
123	warn "read: $input\n"; # output what has been read	1129	warn "read: $input\n"; # output what has been read
124	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1130	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1131	},
125	});	1132	);
126		1133
127	my $time_watcher; # can only be used once	1134	my $time_watcher; # can only be used once
128		1135
129	sub new_timer {	1136	sub new_timer {
130	$timer = AnyEvent->timer (after => 1, cb => sub {	1137	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
133	});	1140	});
134	}	1141	}
135		1142
136	new_timer; # create first timer	1143	new_timer; # create first timer
137		1144
138	$cv->wait; # wait until user enters /^q/i	1145	$cv->recv; # wait until user enters /^q/i
		1146
		1147	=head1 REAL-WORLD EXAMPLE
		1148
		1149	Consider the L<Net::FCP> module. It features (among others) the following
		1150	API calls, which are to freenet what HTTP GET requests are to http:
		1151
		1152	my $data = $fcp->client_get ($url); # blocks
		1153
		1154	my $transaction = $fcp->txn_client_get ($url); # does not block
		1155	$transaction->cb ( sub { ... } ); # set optional result callback
		1156	my $data = $transaction->result; # possibly blocks
		1157
		1158	The C<client_get> method works like C<LWP::Simple::get>: it requests the
		1159	given URL and waits till the data has arrived. It is defined to be:
		1160
		1161	sub client_get { $_[0]->txn_client_get ($_[1])->result }
		1162
		1163	And in fact is automatically generated. This is the blocking API of
		1164	L<Net::FCP>, and it works as simple as in any other, similar, module.
		1165
		1166	More complicated is C<txn_client_get>: It only creates a transaction
		1167	(completion, result, ...) object and initiates the transaction.
		1168
		1169	my $txn = bless { }, Net::FCP::Txn::;
		1170
		1171	It also creates a condition variable that is used to signal the completion
		1172	of the request:
		1173
		1174	$txn->{finished} = AnyAvent->condvar;
		1175
		1176	It then creates a socket in non-blocking mode.
		1177
		1178	socket $txn->{fh}, ...;
		1179	fcntl $txn->{fh}, F_SETFL, O_NONBLOCK;
		1180	connect $txn->{fh}, ...
		1181	and !$!{EWOULDBLOCK}
		1182	and !$!{EINPROGRESS}
		1183	and Carp::croak "unable to connect: $!\n";
		1184
		1185	Then it creates a write-watcher which gets called whenever an error occurs
		1186	or the connection succeeds:
		1187
		1188	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w });
		1189
		1190	And returns this transaction object. The C<fh_ready_w> callback gets
		1191	called as soon as the event loop detects that the socket is ready for
		1192	writing.
		1193
		1194	The C<fh_ready_w> method makes the socket blocking again, writes the
		1195	request data and replaces the watcher by a read watcher (waiting for reply
		1196	data). The actual code is more complicated, but that doesn't matter for
		1197	this example:
		1198
		1199	fcntl $txn->{fh}, F_SETFL, 0;
		1200	syswrite $txn->{fh}, $txn->{request}
		1201	or die "connection or write error";
		1202	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
		1203
		1204	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
		1205	result and signals any possible waiters that the request has finished:
		1206
		1207	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
		1208
		1209	if (end-of-file or data complete) {
		1210	$txn->{result} = $txn->{buf};
		1211	$txn->{finished}->send;
		1212	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
		1213	}
		1214
		1215	The C<result> method, finally, just waits for the finished signal (if the
		1216	request was already finished, it doesn't wait, of course, and returns the
		1217	data:
		1218
		1219	$txn->{finished}->recv;
		1220	return $txn->{result};
		1221
		1222	The actual code goes further and collects all errors (C<die>s, exceptions)
		1223	that occurred during request processing. The C<result> method detects
		1224	whether an exception as thrown (it is stored inside the $txn object)
		1225	and just throws the exception, which means connection errors and other
		1226	problems get reported tot he code that tries to use the result, not in a
		1227	random callback.
		1228
		1229	All of this enables the following usage styles:
		1230
		1231	1. Blocking:
		1232
		1233	my $data = $fcp->client_get ($url);
		1234
		1235	2. Blocking, but running in parallel:
		1236
		1237	my @datas = map $_->result,
		1238	map $fcp->txn_client_get ($_),
		1239	@urls;
		1240
		1241	Both blocking examples work without the module user having to know
		1242	anything about events.
		1243
		1244	3a. Event-based in a main program, using any supported event module:
		1245
		1246	use EV;
		1247
		1248	$fcp->txn_client_get ($url)->cb (sub {
		1249	my $txn = shift;
		1250	my $data = $txn->result;
		1251	...
		1252	});
		1253
		1254	EV::loop;
		1255
		1256	3b. The module user could use AnyEvent, too:
		1257
		1258	use AnyEvent;
		1259
		1260	my $quit = AnyEvent->condvar;
		1261
		1262	$fcp->txn_client_get ($url)->cb (sub {
		1263	...
		1264	$quit->send;
		1265	});
		1266
		1267	$quit->recv;
		1268
		1269
		1270	=head1 BENCHMARKS
		1271
		1272	To give you an idea of the performance and overheads that AnyEvent adds
		1273	over the event loops themselves and to give you an impression of the speed
		1274	of various event loops I prepared some benchmarks.
		1275
		1276	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1277
		1278	Here is a benchmark of various supported event models used natively and
		1279	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1280	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1281	which it is), lets them fire exactly once and destroys them again.
		1282
		1283	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1284	distribution.
		1285
		1286	=head3 Explanation of the columns
		1287
		1288	I<watcher> is the number of event watchers created/destroyed. Since
		1289	different event models feature vastly different performances, each event
		1290	loop was given a number of watchers so that overall runtime is acceptable
		1291	and similar between tested event loop (and keep them from crashing): Glib
		1292	would probably take thousands of years if asked to process the same number
		1293	of watchers as EV in this benchmark.
		1294
		1295	I<bytes> is the number of bytes (as measured by the resident set size,
		1296	RSS) consumed by each watcher. This method of measuring captures both C
		1297	and Perl-based overheads.
		1298
		1299	I<create> is the time, in microseconds (millionths of seconds), that it
		1300	takes to create a single watcher. The callback is a closure shared between
		1301	all watchers, to avoid adding memory overhead. That means closure creation
		1302	and memory usage is not included in the figures.
		1303
		1304	I<invoke> is the time, in microseconds, used to invoke a simple
		1305	callback. The callback simply counts down a Perl variable and after it was
		1306	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1307	signal the end of this phase.
		1308
		1309	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1310	watcher.
		1311
		1312	=head3 Results
		1313
		1314	name watchers bytes create invoke destroy comment
		1315	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1316	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1317	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1318	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1319	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1320	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1321	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1322	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1323	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1324	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1325
		1326	=head3 Discussion
		1327
		1328	The benchmark does I<not> measure scalability of the event loop very
		1329	well. For example, a select-based event loop (such as the pure perl one)
		1330	can never compete with an event loop that uses epoll when the number of
		1331	file descriptors grows high. In this benchmark, all events become ready at
		1332	the same time, so select/poll-based implementations get an unnatural speed
		1333	boost.
		1334
		1335	Also, note that the number of watchers usually has a nonlinear effect on
		1336	overall speed, that is, creating twice as many watchers doesn't take twice
		1337	the time - usually it takes longer. This puts event loops tested with a
		1338	higher number of watchers at a disadvantage.
		1339
		1340	To put the range of results into perspective, consider that on the
		1341	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1342	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1343	cycles with POE.
		1344
		1345	C<EV> is the sole leader regarding speed and memory use, which are both
		1346	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1347	far less memory than any other event loop and is still faster than Event
		1348	natively.
		1349
		1350	The pure perl implementation is hit in a few sweet spots (both the
		1351	constant timeout and the use of a single fd hit optimisations in the perl
		1352	interpreter and the backend itself). Nevertheless this shows that it
		1353	adds very little overhead in itself. Like any select-based backend its
		1354	performance becomes really bad with lots of file descriptors (and few of
		1355	them active), of course, but this was not subject of this benchmark.
		1356
		1357	The C<Event> module has a relatively high setup and callback invocation
		1358	cost, but overall scores in on the third place.
		1359
		1360	C<Glib>'s memory usage is quite a bit higher, but it features a
		1361	faster callback invocation and overall ends up in the same class as
		1362	C<Event>. However, Glib scales extremely badly, doubling the number of
		1363	watchers increases the processing time by more than a factor of four,
		1364	making it completely unusable when using larger numbers of watchers
		1365	(note that only a single file descriptor was used in the benchmark, so
		1366	inefficiencies of C<poll> do not account for this).
		1367
		1368	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1369	more than 2000 watchers is a big setback, however, as correctness takes
		1370	precedence over speed. Nevertheless, its performance is surprising, as the
		1371	file descriptor is dup()ed for each watcher. This shows that the dup()
		1372	employed by some adaptors is not a big performance issue (it does incur a
		1373	hidden memory cost inside the kernel which is not reflected in the figures
		1374	above).
		1375
		1376	C<POE>, regardless of underlying event loop (whether using its pure perl
		1377	select-based backend or the Event module, the POE-EV backend couldn't
		1378	be tested because it wasn't working) shows abysmal performance and
		1379	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1380	as EV watchers, and 10 times as much memory as Event (the high memory
		1381	requirements are caused by requiring a session for each watcher). Watcher
		1382	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1383	implementation.
		1384
		1385	The design of the POE adaptor class in AnyEvent can not really account
		1386	for the performance issues, though, as session creation overhead is
		1387	small compared to execution of the state machine, which is coded pretty
		1388	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1389	using multiple sessions is not a good approach, especially regarding
		1390	memory usage, even the author of POE could not come up with a faster
		1391	design).
		1392
		1393	=head3 Summary
		1394
		1395	=over 4
		1396
		1397	=item * Using EV through AnyEvent is faster than any other event loop
		1398	(even when used without AnyEvent), but most event loops have acceptable
		1399	performance with or without AnyEvent.
		1400
		1401	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1402	the actual event loop, only with extremely fast event loops such as EV
		1403	adds AnyEvent significant overhead.
		1404
		1405	=item * You should avoid POE like the plague if you want performance or
		1406	reasonable memory usage.
		1407
		1408	=back
		1409
		1410	=head2 BENCHMARKING THE LARGE SERVER CASE
		1411
		1412	This benchmark actually benchmarks the event loop itself. It works by
		1413	creating a number of "servers": each server consists of a socket pair, a
		1414	timeout watcher that gets reset on activity (but never fires), and an I/O
		1415	watcher waiting for input on one side of the socket. Each time the socket
		1416	watcher reads a byte it will write that byte to a random other "server".
		1417
		1418	The effect is that there will be a lot of I/O watchers, only part of which
		1419	are active at any one point (so there is a constant number of active
		1420	fds for each loop iteration, but which fds these are is random). The
		1421	timeout is reset each time something is read because that reflects how
		1422	most timeouts work (and puts extra pressure on the event loops).
		1423
		1424	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1425	(1%) are active. This mirrors the activity of large servers with many
		1426	connections, most of which are idle at any one point in time.
		1427
		1428	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1429	distribution.
		1430
		1431	=head3 Explanation of the columns
		1432
		1433	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1434	each server has a read and write socket end).
		1435
		1436	I<create> is the time it takes to create a socket pair (which is
		1437	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1438
		1439	I<request>, the most important value, is the time it takes to handle a
		1440	single "request", that is, reading the token from the pipe and forwarding
		1441	it to another server. This includes deleting the old timeout and creating
		1442	a new one that moves the timeout into the future.
		1443
		1444	=head3 Results
		1445
		1446	name sockets create request
		1447	EV 20000 69.01 11.16
		1448	Perl 20000 73.32 35.87
		1449	Event 20000 212.62 257.32
		1450	Glib 20000 651.16 1896.30
		1451	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1452
		1453	=head3 Discussion
		1454
		1455	This benchmark I<does> measure scalability and overall performance of the
		1456	particular event loop.
		1457
		1458	EV is again fastest. Since it is using epoll on my system, the setup time
		1459	is relatively high, though.
		1460
		1461	Perl surprisingly comes second. It is much faster than the C-based event
		1462	loops Event and Glib.
		1463
		1464	Event suffers from high setup time as well (look at its code and you will
		1465	understand why). Callback invocation also has a high overhead compared to
		1466	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1467	uses select or poll in basically all documented configurations.
		1468
		1469	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1470	clearly fails to perform with many filehandles or in busy servers.
		1471
		1472	POE is still completely out of the picture, taking over 1000 times as long
		1473	as EV, and over 100 times as long as the Perl implementation, even though
		1474	it uses a C-based event loop in this case.
		1475
		1476	=head3 Summary
		1477
		1478	=over 4
		1479
		1480	=item * The pure perl implementation performs extremely well.
		1481
		1482	=item * Avoid Glib or POE in large projects where performance matters.
		1483
		1484	=back
		1485
		1486	=head2 BENCHMARKING SMALL SERVERS
		1487
		1488	While event loops should scale (and select-based ones do not...) even to
		1489	large servers, most programs we (or I :) actually write have only a few
		1490	I/O watchers.
		1491
		1492	In this benchmark, I use the same benchmark program as in the large server
		1493	case, but it uses only eight "servers", of which three are active at any
		1494	one time. This should reflect performance for a small server relatively
		1495	well.
		1496
		1497	The columns are identical to the previous table.
		1498
		1499	=head3 Results
		1500
		1501	name sockets create request
		1502	EV 16 20.00 6.54
		1503	Perl 16 25.75 12.62
		1504	Event 16 81.27 35.86
		1505	Glib 16 32.63 15.48
		1506	POE 16 261.87 276.28 uses POE::Loop::Event
		1507
		1508	=head3 Discussion
		1509
		1510	The benchmark tries to test the performance of a typical small
		1511	server. While knowing how various event loops perform is interesting, keep
		1512	in mind that their overhead in this case is usually not as important, due
		1513	to the small absolute number of watchers (that is, you need efficiency and
		1514	speed most when you have lots of watchers, not when you only have a few of
		1515	them).
		1516
		1517	EV is again fastest.
		1518
		1519	Perl again comes second. It is noticeably faster than the C-based event
		1520	loops Event and Glib, although the difference is too small to really
		1521	matter.
		1522
		1523	POE also performs much better in this case, but is is still far behind the
		1524	others.
		1525
		1526	=head3 Summary
		1527
		1528	=over 4
		1529
		1530	=item * C-based event loops perform very well with small number of
		1531	watchers, as the management overhead dominates.
		1532
		1533	=back
		1534
		1535
		1536	=head1 FORK
		1537
		1538	Most event libraries are not fork-safe. The ones who are usually are
		1539	because they rely on inefficient but fork-safe C<select> or C<poll>
		1540	calls. Only L<EV> is fully fork-aware.
		1541
		1542	If you have to fork, you must either do so I<before> creating your first
		1543	watcher OR you must not use AnyEvent at all in the child.
		1544
		1545
		1546	=head1 SECURITY CONSIDERATIONS
		1547
		1548	AnyEvent can be forced to load any event model via
		1549	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1550	execute arbitrary code or directly gain access, it can easily be used to
		1551	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1552	will not be active when the program uses a different event model than
		1553	specified in the variable.
		1554
		1555	You can make AnyEvent completely ignore this variable by deleting it
		1556	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1557
		1558	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1559
		1560	use AnyEvent;
		1561
		1562	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1563	be used to probe what backend is used and gain other information (which is
		1564	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1565
139		1566
140	=head1 SEE ALSO	1567	=head1 SEE ALSO
141		1568
142	L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>,	1569	Utility functions: L<AnyEvent::Util>.
143	L<AnyEvent::Impl::Coro>,	1570
144	L<AnyEvent::Impl::Event>,	1571	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
145	L<AnyEvent::Impl::Glib>,	1572	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1573
		1574	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1575	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1576	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
146	L<AnyEvent::Impl::Tk>.	1577	L<AnyEvent::Impl::POE>.
147		1578
148	=head1	1579	Non-blocking file handles, sockets, TCP clients and
		1580	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1581
		1582	Asynchronous DNS: L<AnyEvent::DNS>.
		1583
		1584	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1585
		1586	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
		1587
		1588
		1589	=head1 AUTHOR
		1590
		1591	Marc Lehmann <schmorp@schmorp.de>
		1592	http://home.schmorp.de/
149		1593
150	=cut	1594	=cut
151		1595
152	1	1596	1
153		1597

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines