ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.17 by root, Fri Nov 24 14:40:13 2006 UTC vs.
Revision 1.115 by root, Sat May 10 21:47:28 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, Perl - 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
…		…
14		14
15	my $w = AnyEvent->timer (after => $seconds, cb => sub {	15	my $w = AnyEvent->timer (after => $seconds, cb => sub {
16	...	16	...
17	});	17	});
18		18
19	my $w = AnyEvent->condvar; # stores wether a condition was flagged	19	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		20	$w->send; # wake up current and all future recv's
20	$w->wait; # enters "main loop" till $condvar gets ->broadcast	21	$w->recv; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all 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 enourmous amount of code and strict rules you have to
		63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
		64	offering the functionality that is necessary, in as thin as a wrapper as
		65	technically possible.
		66
		67	Of course, if you want lots of policy (this can arguably be somewhat
		68	useful) and you want to force your users to use the one and only event
		69	model, you should I<not> use this module.
22		70
23	=head1 DESCRIPTION	71	=head1 DESCRIPTION
24		72
25	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
26	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
27	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
28	peacefully at any one time).	76	peacefully at any one time).
29		77
30	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>
31	module.	79	module.
32		80
33	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
34	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
35	loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is	83	following modules is already loaded: L<EV>,
36	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>,
37	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
38	used. If still none could be found, AnyEvent will fall back to a pure-perl	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
39	event loop, which is also not very efficient.	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.
40		91
41	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
42	an Event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
43	that model the default. For example:	94	that model the default. For example:
44		95
45	use Tk;	96	use Tk;
46	use AnyEvent;	97	use AnyEvent;
47		98
48	# .. AnyEvent will likely default to Tk	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...
49		104
50	The pure-perl implementation of AnyEvent is called	105	The pure-perl implementation of AnyEvent is called
51	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	106	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
52	explicitly.	107	explicitly.
53		108
…		…
56	AnyEvent has the central concept of a I<watcher>, which is an object that	111	AnyEvent has the central concept of a I<watcher>, which is an object that
57	stores relevant data for each kind of event you are waiting for, such as	112	stores relevant data for each kind of event you are waiting for, such as
58	the callback to call, the filehandle to watch, etc.	113	the callback to call, the filehandle to watch, etc.
59		114
60	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
61	creating a watcher it will immediately "watch" for events and invoke	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
62	the callback. To disable the watcher you have to destroy it (e.g. by	120	To disable the watcher you have to destroy it (e.g. by setting the
63	setting the variable that stores it to C<undef> or otherwise deleting all	121	variable you store it in to C<undef> or otherwise deleting all references
64	references to it).	122	to it).
65		123
66	All watchers are created by calling a method on the C<AnyEvent> class.	124	All watchers are created by calling a method on the C<AnyEvent> class.
67		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
68	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
69		141
70	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	142	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
71	the following mandatory arguments:	143	with the following mandatory key-value pairs as arguments:
72		144
73	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	145	C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
74	events. C<poll> must be a string that is either C<r> or C<w>, that creates	146	for events. C<poll> must be a string that is either C<r> or C<w>,
75	a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
76	to invoke everytime the filehandle becomes ready.	148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
77		150
78	Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on	151	Although the callback might get passed parameters, their value and
79	a socket you can have one r + one w, not any more (limitation comes from	152	presence is undefined and you cannot rely on them. Portable AnyEvent
80	Tk - if you are sure you are not using Tk this limitation is gone).	153	callbacks cannot use arguments passed to I/O watcher callbacks.
81		154
82	Filehandles will be kept alive, so as long as the watcher exists, the	155	The I/O watcher might use the underlying file descriptor or a copy of it.
83	filehandle exists, too.	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.
84		162
85	Example:	163	Example:
86		164
87	# wait for readability of STDIN, then read a line and disable the watcher	165	# wait for readability of STDIN, then read a line and disable the watcher
88	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
89	chomp (my $input = <STDIN>);	167	chomp (my $input = <STDIN>);
90	warn "read: $input\n";	168	warn "read: $input\n";
91	undef $w;	169	undef $w;
92	});	170	});
93		171
94	=head2 TIMER WATCHERS	172	=head2 TIME WATCHERS
95		173
96	You can create a timer watcher by calling the C<< AnyEvent->timer >>	174	You can create a time watcher by calling the C<< AnyEvent->timer >>
97	method with the following mandatory arguments:	175	method with the following mandatory arguments:
98		176
99	C<after> after how many seconds (fractions are supported) should the timer	177	C<after> specifies after how many seconds (fractional values are
100	activate. C<cb> the callback to invoke.	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.
101		184
102	The timer callback will be invoked at most once: if you want a repeating	185	The timer callback will be invoked at most once: if you want a repeating
103	timer you have to create a new watcher (this is a limitation by both Tk	186	timer you have to create a new watcher (this is a limitation by both Tk
104	and Glib).	187	and Glib).
105		188
…		…
109	my $w = AnyEvent->timer (after => 7.7, cb => sub {	192	my $w = AnyEvent->timer (after => 7.7, cb => sub {
110	warn "timeout\n";	193	warn "timeout\n";
111	});	194	});
112		195
113	# to cancel the timer:	196	# to cancel the timer:
114	undef $w	197	undef $w;
115		198
		199	Example 2:
		200
		201	# fire an event after 0.5 seconds, then roughly every second
		202	my $w;
		203
		204	my $cb = sub {
		205	# cancel the old timer while creating a new one
		206	$w = AnyEvent->timer (after => 1, cb => $cb);
		207	};
		208
		209	# start the "loop" by creating the first watcher
		210	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		211
		212	=head3 TIMING ISSUES
		213
		214	There are two ways to handle timers: based on real time (relative, "fire
		215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		216	o'clock").
		217
		218	While most event loops expect timers to specified in a relative way, they
		219	use absolute time internally. This makes a difference when your clock
		220	"jumps", for example, when ntp decides to set your clock backwards from
		221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		222	fire "after" a second might actually take six years to finally fire.
		223
		224	AnyEvent cannot compensate for this. The only event loop that is conscious
		225	about these issues is L<EV>, which offers both relative (ev_timer, based
		226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
		228
		229	AnyEvent always prefers relative timers, if available, matching the
		230	AnyEvent API.
		231
		232	=head2 SIGNAL WATCHERS
		233
		234	You can watch for signals using a signal watcher, C<signal> is the signal
		235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		236	be invoked whenever a signal occurs.
		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
		242	Multiple signal occurances can be clumped together into one callback
		243	invocation, and callback invocation will be synchronous. synchronous means
		244	that it might take a while until the signal gets handled by the process,
		245	but it is guarenteed not to interrupt any other callbacks.
		246
		247	The main advantage of using these watchers is that you can share a signal
		248	between multiple watchers.
		249
		250	This watcher might use C<%SIG>, so programs overwriting those signals
		251	directly will likely not work correctly.
		252
		253	Example: exit on SIGINT
		254
		255	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		256
		257	=head2 CHILD PROCESS WATCHERS
		258
		259	You can also watch on a child process exit and catch its exit status.
		260
		261	The child process is specified by the C<pid> argument (if set to C<0>, it
		262	watches for any child process exit). The watcher will trigger as often
		263	as status change for the child are received. This works by installing a
		264	signal handler for C<SIGCHLD>. The callback will be called with the pid
		265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
		267
		268	There is a slight catch to child watchers, however: you usually start them
		269	I<after> the child process was created, and this means the process could
		270	have exited already (and no SIGCHLD will be sent anymore).
		271
		272	Not all event models handle this correctly (POE doesn't), but even for
		273	event models that I<do> handle this correctly, they usually need to be
		274	loaded before the process exits (i.e. before you fork in the first place).
		275
		276	This means you cannot create a child watcher as the very first thing in an
		277	AnyEvent program, you I<have> to create at least one watcher before you
		278	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		279
		280	Example: fork a process and wait for it
		281
		282	my $done = AnyEvent->condvar;
		283
		284	my $pid = fork or exit 5;
		285
		286	my $w = AnyEvent->child (
		287	pid => $pid,
		288	cb => sub {
		289	my ($pid, $status) = @_;
		290	warn "pid $pid exited with status $status";
		291	$done->send;
		292	},
		293	);
		294
		295	# do something else, then wait for process exit
		296	$done->recv;
		297
116	=head2 CONDITION WATCHERS	298	=head2 CONDITION VARIABLES
117		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
118	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	310	Condition variables can be created by calling the C<< AnyEvent->condvar
119	method without any arguments.	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.
120		314
121	A condition watcher watches for a condition - precisely that the C<<	315	After creation, the conditon variable is "false" until it becomes "true"
122	->broadcast >> method has been called.	316	by calling the C<send> method.
123		317
124	The watcher has only two methods:	318	Condition variables are similar to callbacks, except that you can
		319	optionally wait for them. They can also be called merge points - points
		320	in time where multiple outstandign events have been processed. And yet
		321	another way to call them is transations - each condition variable can be
		322	used to represent a transaction, which finishes at some point and delivers
		323	a result.
125		324
126	=over 4	325	Condition variables are very useful to signal that something has finished,
		326	for example, if you write a module that does asynchronous http requests,
		327	then a condition variable would be the ideal candidate to signal the
		328	availability of results. The user can either act when the callback is
		329	called or can synchronously C<< ->recv >> for the results.
127		330
128	=item $cv->wait	331	You can also use them to simulate traditional event loops - for example,
		332	you can block your main program until an event occurs - for example, you
		333	could C<< ->recv >> in your main program until the user clicks the Quit
		334	button of your app, which would C<< ->send >> the "quit" event.
129		335
130	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	336	Note that condition variables recurse into the event loop - if you have
131	called on c<$cv>, while servicing other watchers normally.	337	two pieces of code that call C<< ->recv >> in a round-robbin fashion, you
		338	lose. Therefore, condition variables are good to export to your caller, but
		339	you should avoid making a blocking wait yourself, at least in callbacks,
		340	as this asks for trouble.
132		341
133	Not all event models support a blocking wait - some die in that case, so	342	Condition variables are represented by hash refs in perl, and the keys
134	if you are using this from a module, never require a blocking wait, but	343	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
135	let the caller decide wether the call will block or not (for example,	344	easy (it is often useful to build your own transaction class on top of
136	by coupling condition variables with some kind of request results and	345	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
137	supporting callbacks so the caller knows that getting the result will not	346	it's C<new> method in your own C<new> method.
138	block, while still suppporting blockign waits if the caller so desires).
139		347
140	You can only wait once on a condition - additional calls will return	348	There are two "sides" to a condition variable - the "producer side" which
141	immediately.	349	eventually calls C<< -> send >>, and the "consumer side", which waits
142		350	for the send to occur.
143	=item $cv->broadcast
144
145	Flag the condition as ready - a running C<< ->wait >> and all further
146	calls to C<wait> will return after this method has been called. If nobody
147	is waiting the broadcast will be remembered..
148		351
149	Example:	352	Example:
150		353
151	# wait till the result is ready	354	# wait till the result is ready
152	my $result_ready = AnyEvent->condvar;	355	my $result_ready = AnyEvent->condvar;
153		356
154	# do something such as adding a timer	357	# do something such as adding a timer
155	# or socket watcher the calls $result_ready->broadcast	358	# or socket watcher the calls $result_ready->send
156	# when the "result" is ready.	359	# when the "result" is ready.
		360	# in this case, we simply use a timer:
		361	my $w = AnyEvent->timer (
		362	after => 1,
		363	cb => sub { $result_ready->send },
		364	);
157		365
		366	# this "blocks" (while handling events) till the callback
		367	# calls send
158	$result_ready->wait;	368	$result_ready->recv;
		369
		370	=head3 METHODS FOR PRODUCERS
		371
		372	These methods should only be used by the producing side, i.e. the
		373	code/module that eventually sends the signal. Note that it is also
		374	the producer side which creates the condvar in most cases, but it isn't
		375	uncommon for the consumer to create it as well.
		376
		377	=over 4
		378
		379	=item $cv->send (...)
		380
		381	Flag the condition as ready - a running C<< ->recv >> and all further
		382	calls to C<recv> will (eventually) return after this method has been
		383	called. If nobody is waiting the send will be remembered.
		384
		385	If a callback has been set on the condition variable, it is called
		386	immediately from within send.
		387
		388	Any arguments passed to the C<send> call will be returned by all
		389	future C<< ->recv >> calls.
		390
		391	=item $cv->croak ($error)
		392
		393	Similar to send, but causes all call's to C<< ->recv >> to invoke
		394	C<Carp::croak> with the given error message/object/scalar.
		395
		396	This can be used to signal any errors to the condition variable
		397	user/consumer.
		398
		399	=item $cv->begin ([group callback])
		400
		401	=item $cv->end
		402
		403	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		404
		405	These two methods can be used to combine many transactions/events into
		406	one. For example, a function that pings many hosts in parallel might want
		407	to use a condition variable for the whole process.
		408
		409	Every call to C<< ->begin >> will increment a counter, and every call to
		410	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		411	>>, the (last) callback passed to C<begin> will be executed. That callback
		412	is I<supposed> to call C<< ->send >>, but that is not required. If no
		413	callback was set, C<send> will be called without any arguments.
		414
		415	Let's clarify this with the ping example:
		416
		417	my $cv = AnyEvent->condvar;
		418
		419	my %result;
		420	$cv->begin (sub { $cv->send (\%result) });
		421
		422	for my $host (@list_of_hosts) {
		423	$cv->begin;
		424	ping_host_then_call_callback $host, sub {
		425	$result{$host} = ...;
		426	$cv->end;
		427	};
		428	}
		429
		430	$cv->end;
		431
		432	This code fragment supposedly pings a number of hosts and calls
		433	C<send> after results for all then have have been gathered - in any
		434	order. To achieve this, the code issues a call to C<begin> when it starts
		435	each ping request and calls C<end> when it has received some result for
		436	it. Since C<begin> and C<end> only maintain a counter, the order in which
		437	results arrive is not relevant.
		438
		439	There is an additional bracketing call to C<begin> and C<end> outside the
		440	loop, which serves two important purposes: first, it sets the callback
		441	to be called once the counter reaches C<0>, and second, it ensures that
		442	C<send> is called even when C<no> hosts are being pinged (the loop
		443	doesn't execute once).
		444
		445	This is the general pattern when you "fan out" into multiple subrequests:
		446	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		447	is called at least once, and then, for each subrequest you start, call
		448	C<begin> and for eahc subrequest you finish, call C<end>.
159		449
160	=back	450	=back
161		451
162	=head1 GLOBALS	452	=head3 METHODS FOR CONSUMERS
		453
		454	These methods should only be used by the consuming side, i.e. the
		455	code awaits the condition.
		456
		457	=over 4
		458
		459	=item $cv->recv
		460
		461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
		462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
		464
		465	You can only wait once on a condition - additional calls are valid but
		466	will return immediately.
		467
		468	If an error condition has been set by calling C<< ->croak >>, then this
		469	function will call C<croak>.
		470
		471	In list context, all parameters passed to C<send> will be returned,
		472	in scalar context only the first one will be returned.
		473
		474	Not all event models support a blocking wait - some die in that case
		475	(programs might want to do that to stay interactive), so I<if you are
		476	using this from a module, never require a blocking wait>, but let the
		477	caller decide whether the call will block or not (for example, by coupling
		478	condition variables with some kind of request results and supporting
		479	callbacks so the caller knows that getting the result will not block,
		480	while still suppporting blocking waits if the caller so desires).
		481
		482	Another reason I<never> to C<< ->recv >> in a module is that you cannot
		483	sensibly have two C<< ->recv >>'s in parallel, as that would require
		484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
		485	can supply.
		486
		487	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		488	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		489	versions and also integrates coroutines into AnyEvent, making blocking
		490	C<< ->recv >> calls perfectly safe as long as they are done from another
		491	coroutine (one that doesn't run the event loop).
		492
		493	You can ensure that C<< -recv >> never blocks by setting a callback and
		494	only calling C<< ->recv >> from within that callback (or at a later
		495	time). This will work even when the event loop does not support blocking
		496	waits otherwise.
		497
		498	=item $bool = $cv->ready
		499
		500	Returns true when the condition is "true", i.e. whether C<send> or
		501	C<croak> have been called.
		502
		503	=item $cb = $cv->cb ([new callback])
		504
		505	This is a mutator function that returns the callback set and optionally
		506	replaces it before doing so.
		507
		508	The callback will be called when the condition becomes "true", i.e. when
		509	C<send> or C<croak> are called. Calling C<recv> inside the callback
		510	or at any later time is guaranteed not to block.
		511
		512	=back
		513
		514	=head1 GLOBAL VARIABLES AND FUNCTIONS
163		515
164	=over 4	516	=over 4
165		517
166	=item $AnyEvent::MODEL	518	=item $AnyEvent::MODEL
167		519
…		…
171	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	523	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
172	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).	524	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
173		525
174	The known classes so far are:	526	The known classes so far are:
175		527
176	AnyEvent::Impl::Coro based on Coro::Event, best choise.	528	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
177	AnyEvent::Impl::Event based on Event, also best choice :)	529	AnyEvent::Impl::Event based on Event, second best choice.
		530	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
178	AnyEvent::Impl::Glib based on Glib, second-best choice.	531	AnyEvent::Impl::Glib based on Glib, third-best choice.
179	AnyEvent::Impl::Tk based on Tk, very bad choice.	532	AnyEvent::Impl::Tk based on Tk, very bad choice.
180	AnyEvent::Impl::Perl pure-perl implementation, inefficient.	533	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		534	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		535	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		536
		537	There is no support for WxWidgets, as WxWidgets has no support for
		538	watching file handles. However, you can use WxWidgets through the
		539	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		540	second, which was considered to be too horrible to even consider for
		541	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		542	it's adaptor.
		543
		544	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		545	autodetecting them.
		546
		547	=item AnyEvent::detect
		548
		549	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
		550	if necessary. You should only call this function right before you would
		551	have created an AnyEvent watcher anyway, that is, as late as possible at
		552	runtime.
		553
		554	=item $guard = AnyEvent::post_detect { BLOCK }
		555
		556	Arranges for the code block to be executed as soon as the event model is
		557	autodetected (or immediately if this has already happened).
		558
		559	If called in scalar or list context, then it creates and returns an object
		560	that automatically removes the callback again when it is destroyed. See
		561	L<Coro::BDB> for a case where this is useful.
		562
		563	=item @AnyEvent::post_detect
		564
		565	If there are any code references in this array (you can C<push> to it
		566	before or after loading AnyEvent), then they will called directly after
		567	the event loop has been chosen.
		568
		569	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		570	if it contains a true value then the event loop has already been detected,
		571	and the array will be ignored.
		572
		573	Best use C<AnyEvent::post_detect { BLOCK }> instead.
181		574
182	=back	575	=back
183		576
184	=head1 WHAT TO DO IN A MODULE	577	=head1 WHAT TO DO IN A MODULE
185		578
186	As a module author, you should "use AnyEvent" and call AnyEvent methods	579	As a module author, you should C<use AnyEvent> and call AnyEvent methods
187	freely, but you should not load a specific event module or rely on it.	580	freely, but you should not load a specific event module or rely on it.
188		581
189	Be careful when you create watchers in the module body - Anyevent will	582	Be careful when you create watchers in the module body - AnyEvent will
190	decide which event module to use as soon as the first method is called, so	583	decide which event module to use as soon as the first method is called, so
191	by calling AnyEvent in your module body you force the user of your module	584	by calling AnyEvent in your module body you force the user of your module
192	to load the event module first.	585	to load the event module first.
193		586
		587	Never call C<< ->recv >> on a condition variable unless you I<know> that
		588	the C<< ->send >> method has been called on it already. This is
		589	because it will stall the whole program, and the whole point of using
		590	events is to stay interactive.
		591
		592	It is fine, however, to call C<< ->recv >> when the user of your module
		593	requests it (i.e. if you create a http request object ad have a method
		594	called C<results> that returns the results, it should call C<< ->recv >>
		595	freely, as the user of your module knows what she is doing. always).
		596
194	=head1 WHAT TO DO IN THE MAIN PROGRAM	597	=head1 WHAT TO DO IN THE MAIN PROGRAM
195		598
196	There will always be a single main program - the only place that should	599	There will always be a single main program - the only place that should
197	dictate which event model to use.	600	dictate which event model to use.
198		601
199	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	602	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
200	do anything special and let AnyEvent decide which implementation to chose.	603	do anything special (it does not need to be event-based) and let AnyEvent
		604	decide which implementation to chose if some module relies on it.
201		605
202	If the main program relies on a specific event model (for example, in Gtk2	606	If the main program relies on a specific event model. For example, in
203	programs you have to rely on either Glib or Glib::Event), you should load	607	Gtk2 programs you have to rely on the Glib module. You should load the
204	it before loading AnyEvent or any module that uses it, generally, as early	608	event module before loading AnyEvent or any module that uses it: generally
205	as possible. The reason is that modules might create watchers when they	609	speaking, you should load it as early as possible. The reason is that
206	are loaded, and AnyEvent will decide on the event model to use as soon as	610	modules might create watchers when they are loaded, and AnyEvent will
207	it creates watchers, and it might chose the wrong one unless you load the	611	decide on the event model to use as soon as it creates watchers, and it
208	correct one yourself.	612	might chose the wrong one unless you load the correct one yourself.
209		613
210	You can chose to use a rather inefficient pure-perl implementation by	614	You can chose to use a rather inefficient pure-perl implementation by
211	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	615	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
212	generally better.	616	behaviour everywhere, but letting AnyEvent chose is generally better.
		617
		618	=head1 OTHER MODULES
		619
		620	The following is a non-exhaustive list of additional modules that use
		621	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		622	in the same program. Some of the modules come with AnyEvent, some are
		623	available via CPAN.
		624
		625	=over 4
		626
		627	=item L<AnyEvent::Util>
		628
		629	Contains various utility functions that replace often-used but blocking
		630	functions such as C<inet_aton> by event-/callback-based versions.
		631
		632	=item L<AnyEvent::Handle>
		633
		634	Provide read and write buffers and manages watchers for reads and writes.
		635
		636	=item L<AnyEvent::HTTPD>
		637
		638	Provides a simple web application server framework.
		639
		640	=item L<AnyEvent::DNS>
		641
		642	Provides asynchronous DNS resolver capabilities, beyond what
		643	L<AnyEvent::Util> offers.
		644
		645	=item L<AnyEvent::FastPing>
		646
		647	The fastest ping in the west.
		648
		649	=item L<Net::IRC3>
		650
		651	AnyEvent based IRC client module family.
		652
		653	=item L<Net::XMPP2>
		654
		655	AnyEvent based XMPP (Jabber protocol) module family.
		656
		657	=item L<Net::FCP>
		658
		659	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		660	of AnyEvent.
		661
		662	=item L<Event::ExecFlow>
		663
		664	High level API for event-based execution flow control.
		665
		666	=item L<Coro>
		667
		668	Has special support for AnyEvent via L<Coro::AnyEvent>.
		669
		670	=item L<AnyEvent::AIO>, L<IO::AIO>
		671
		672	Truly asynchronous I/O, should be in the toolbox of every event
		673	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		674	together.
		675
		676	=item L<AnyEvent::BDB>, L<BDB>
		677
		678	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		679	IO::AIO and AnyEvent together.
		680
		681	=item L<IO::Lambda>
		682
		683	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		684
		685	=back
213		686
214	=cut	687	=cut
215		688
216	package AnyEvent;	689	package AnyEvent;
217		690
218	no warnings;	691	no warnings;
219	use strict 'vars';	692	use strict;
		693
220	use Carp;	694	use Carp;
221		695
222	our $VERSION = '2.1';	696	our $VERSION = '3.4';
223	our $MODEL;	697	our $MODEL;
224		698
225	our $AUTOLOAD;	699	our $AUTOLOAD;
226	our @ISA;	700	our @ISA;
227		701
228	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	702	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
229		703
230	our @REGISTRY;	704	our @REGISTRY;
231		705
232	my @models = (	706	my @models = (
233	[Coro::Event:: => AnyEvent::Impl::Coro::],	707	[EV:: => AnyEvent::Impl::EV::],
234	[Event:: => AnyEvent::Impl::Event::],	708	[Event:: => AnyEvent::Impl::Event::],
235	[Glib:: => AnyEvent::Impl::Glib::],
236	[Tk:: => AnyEvent::Impl::Tk::],	709	[Tk:: => AnyEvent::Impl::Tk::],
		710	[Wx:: => AnyEvent::Impl::POE::],
		711	[Prima:: => AnyEvent::Impl::POE::],
237	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	712	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		713	# everything below here will not be autoprobed as the pureperl backend should work everywhere
		714	[Glib:: => AnyEvent::Impl::Glib::],
		715	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		716	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		717	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
238	);	718	);
239		719
240	our %method = map +($_ => 1), qw(io timer condvar broadcast wait DESTROY);	720	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
241		721
242	sub AUTOLOAD {	722	our @post_detect;
243	$AUTOLOAD =~ s/.*://;
244		723
245	$method{$AUTOLOAD}	724	sub post_detect(&) {
246	or croak "$AUTOLOAD: not a valid method for AnyEvent objects";	725	my ($cb) = @_;
247		726
		727	if ($MODEL) {
		728	$cb->();
		729
		730	1
		731	} else {
		732	push @post_detect, $cb;
		733
		734	defined wantarray
		735	? bless \$cb, "AnyEvent::Util::Guard"
		736	: ()
		737	}
		738	}
		739
		740	sub AnyEvent::Util::Guard::DESTROY {
		741	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		742	}
		743
		744	sub detect() {
248	unless ($MODEL) {	745	unless ($MODEL) {
		746	no strict 'refs';
		747
		748	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		749	my $model = "AnyEvent::Impl::$1";
		750	if (eval "require $model") {
		751	$MODEL = $model;
		752	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		753	} else {
		754	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		755	}
		756	}
		757
249	# check for already loaded models	758	# check for already loaded models
		759	unless ($MODEL) {
250	for (@REGISTRY, @models) {	760	for (@REGISTRY, @models) {
251	my ($package, $model) = @$_;	761	my ($package, $model) = @$_;
252	if (${"$package\::VERSION"} > 0) {	762	if (${"$package\::VERSION"} > 0) {
253	if (eval "require $model") {	763	if (eval "require $model") {
254	$MODEL = $model;	764	$MODEL = $model;
255	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	765	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
256	last;	766	last;
		767	}
257	}	768	}
258	}	769	}
		770
		771	unless ($MODEL) {
		772	# try to load a model
		773
		774	for (@REGISTRY, @models) {
		775	my ($package, $model) = @$_;
		776	if (eval "require $package"
		777	and ${"$package\::VERSION"} > 0
		778	and eval "require $model") {
		779	$MODEL = $model;
		780	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
		781	last;
		782	}
		783	}
		784
		785	$MODEL
		786	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
		787	}
259	}	788	}
260		789
261	unless ($MODEL) {	790	unshift @ISA, $MODEL;
262	# try to load a model	791	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
263		792
264	for (@REGISTRY, @models) {	793	(shift @post_detect)->() while @post_detect;
265	my ($package, $model) = @$_;
266	if (eval "require $model") {
267	$MODEL = $model;
268	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
269	last;
270	}
271	}
272
273	$MODEL
274	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Coro, Event, Glib or Tk.";
275	}
276	}	794	}
277		795
278	@ISA = $MODEL;	796	$MODEL
		797	}
		798
		799	sub AUTOLOAD {
		800	(my $func = $AUTOLOAD) =~ s/.*://;
		801
		802	$method{$func}
		803	or croak "$func: not a valid method for AnyEvent objects";
		804
		805	detect unless $MODEL;
279		806
280	my $class = shift;	807	my $class = shift;
281	$class->$AUTOLOAD (@_);	808	$class->$func (@_);
282	}	809	}
		810
		811	package AnyEvent::Base;
		812
		813	# default implementation for ->condvar
		814
		815	sub condvar {
		816	bless {}, "AnyEvent::Base::CondVar"
		817	}
		818
		819	# default implementation for ->signal
		820
		821	our %SIG_CB;
		822
		823	sub signal {
		824	my (undef, %arg) = @_;
		825
		826	my $signal = uc $arg{signal}
		827	or Carp::croak "required option 'signal' is missing";
		828
		829	$SIG_CB{$signal}{$arg{cb}} = $arg{cb};
		830	$SIG{$signal} ||= sub {
		831	$_->() for values %{ $SIG_CB{$signal} || {} };
		832	};
		833
		834	bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
		835	}
		836
		837	sub AnyEvent::Base::Signal::DESTROY {
		838	my ($signal, $cb) = @{$_[0]};
		839
		840	delete $SIG_CB{$signal}{$cb};
		841
		842	$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
		843	}
		844
		845	# default implementation for ->child
		846
		847	our %PID_CB;
		848	our $CHLD_W;
		849	our $CHLD_DELAY_W;
		850	our $PID_IDLE;
		851	our $WNOHANG;
		852
		853	sub _child_wait {
		854	while (0 < (my $pid = waitpid -1, $WNOHANG)) {
		855	$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
		856	(values %{ $PID_CB{0} || {} });
		857	}
		858
		859	undef $PID_IDLE;
		860	}
		861
		862	sub _sigchld {
		863	# make sure we deliver these changes "synchronous" with the event loop.
		864	$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
		865	undef $CHLD_DELAY_W;
		866	&_child_wait;
		867	});
		868	}
		869
		870	sub child {
		871	my (undef, %arg) = @_;
		872
		873	defined (my $pid = $arg{pid} + 0)
		874	or Carp::croak "required option 'pid' is missing";
		875
		876	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
		877
		878	unless ($WNOHANG) {
		879	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
		880	}
		881
		882	unless ($CHLD_W) {
		883	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
		884	# child could be a zombie already, so make at least one round
		885	&_sigchld;
		886	}
		887
		888	bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
		889	}
		890
		891	sub AnyEvent::Base::Child::DESTROY {
		892	my ($pid, $cb) = @{$_[0]};
		893
		894	delete $PID_CB{$pid}{$cb};
		895	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
		896
		897	undef $CHLD_W unless keys %PID_CB;
		898	}
		899
		900	package AnyEvent::Base::CondVar;
		901
		902	# wake up the waiter
		903	sub _send {
		904	&{ delete $_[0]{_ae_cb} } if $_[0]{_ae_cb};
		905	}
		906
		907	sub send {
		908	my $cv = shift;
		909	$cv->{_ae_sent} = [@_];
		910	$cv->_send;
		911	}
		912
		913	sub croak {
		914	$_[0]{_ae_croak} = $_[1];
		915	$_[0]->send;
		916	}
		917
		918	sub ready {
		919	$_[0]{_ae_sent}
		920	}
		921
		922	sub recv {
		923	AnyEvent->one_event while !$_[0]{_ae_sent};
		924
		925	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		926	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		927	}
		928
		929	sub cb {
		930	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		931	$_[0]{_ae_cb}
		932	}
		933
		934	sub begin {
		935	++$_[0]{_ae_counter};
		936	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		937	}
		938
		939	sub end {
		940	return if --$_[0]{_ae_counter};
		941	&{ $_[0]{_ae_end_cb} } if $_[0]{_ae_end_cb};
		942	}
		943
		944	# undocumented/compatibility with pre-3.4
		945	*broadcast = \&send;
		946	*wait = \&recv;
283		947
284	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	948	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		949
		950	This is an advanced topic that you do not normally need to use AnyEvent in
		951	a module. This section is only of use to event loop authors who want to
		952	provide AnyEvent compatibility.
285		953
286	If you need to support another event library which isn't directly	954	If you need to support another event library which isn't directly
287	supported by AnyEvent, you can supply your own interface to it by	955	supported by AnyEvent, you can supply your own interface to it by
288	pushing, before the first watcher gets created, the package name of	956	pushing, before the first watcher gets created, the package name of
289	the event module and the package name of the interface to use onto	957	the event module and the package name of the interface to use onto
290	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	958	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
291	AnyEvent.	959	AnyEvent, so it is reasonably cheap.
292		960
293	Example:	961	Example:
294		962
295	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	963	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
296		964
297	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	965	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
298	package/class when it finds the C<urxvt> package/module is loaded. When	966	package/class when it finds the C<urxvt> package/module is already loaded.
		967
299	AnyEvent is loaded and asked to find a suitable event model, it will	968	When AnyEvent is loaded and asked to find a suitable event model, it
300	first check for the presence of urxvt.	969	will first check for the presence of urxvt by trying to C<use> the
		970	C<urxvt::anyevent> module.
301		971
302	The class should prove implementations for all watcher types (see	972	The class should provide implementations for all watcher types. See
303	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	973	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
304	(Source code) and so on for actual examples, use C<perldoc -m	974	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
305	AnyEvent::Impl::Glib> to see the sources).	975	see the sources.
306		976
		977	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		978	provide suitable (hopefully) replacements.
		979
307	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	980	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
308	uses the above line as-is. An interface isn't included in AnyEvent	981	terminal emulator uses the above line as-is. An interface isn't included
309	because it doesn't make sense outside the embedded interpreter inside	982	in AnyEvent because it doesn't make sense outside the embedded interpreter
310	I<rxvt-unicode>, and it is updated and maintained as part of the	983	inside I<rxvt-unicode>, and it is updated and maintained as part of the
311	I<rxvt-unicode> distribution.	984	I<rxvt-unicode> distribution.
312		985
313	I<rxvt-unicode> also cheats a bit by not providing blocking access to	986	I<rxvt-unicode> also cheats a bit by not providing blocking access to
314	condition variables: code blocking while waiting for a condition will	987	condition variables: code blocking while waiting for a condition will
315	C<die>. This still works with most modules/usages, and blocking calls must	988	C<die>. This still works with most modules/usages, and blocking calls must
316	not be in an interactive appliation, so it makes sense.	989	not be done in an interactive application, so it makes sense.
317		990
318	=head1 ENVIRONMENT VARIABLES	991	=head1 ENVIRONMENT VARIABLES
319		992
320	The following environment variables are used by this module:	993	The following environment variables are used by this module:
321		994
322	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	995	=over 4
323	model gets used.
324		996
		997	=item C<PERL_ANYEVENT_VERBOSE>
		998
		999	By default, AnyEvent will be completely silent except in fatal
		1000	conditions. You can set this environment variable to make AnyEvent more
		1001	talkative.
		1002
		1003	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1004	conditions, such as not being able to load the event model specified by
		1005	C<PERL_ANYEVENT_MODEL>.
		1006
		1007	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1008	model it chooses.
		1009
		1010	=item C<PERL_ANYEVENT_MODEL>
		1011
		1012	This can be used to specify the event model to be used by AnyEvent, before
		1013	autodetection and -probing kicks in. It must be a string consisting
		1014	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1015	and the resulting module name is loaded and if the load was successful,
		1016	used as event model. If it fails to load AnyEvent will proceed with
		1017	autodetection and -probing.
		1018
		1019	This functionality might change in future versions.
		1020
		1021	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1022	could start your program like this:
		1023
		1024	PERL_ANYEVENT_MODEL=Perl perl ...
		1025
		1026	=back
		1027
325	=head1 EXAMPLE	1028	=head1 EXAMPLE PROGRAM
326		1029
327	The following program uses an io watcher to read data from stdin, a timer	1030	The following program uses an I/O watcher to read data from STDIN, a timer
328	to display a message once per second, and a condvar to exit the program	1031	to display a message once per second, and a condition variable to quit the
329	when the user enters quit:	1032	program when the user enters quit:
330		1033
331	use AnyEvent;	1034	use AnyEvent;
332		1035
333	my $cv = AnyEvent->condvar;	1036	my $cv = AnyEvent->condvar;
334		1037
335	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1038	my $io_watcher = AnyEvent->io (
		1039	fh => \*STDIN,
		1040	poll => 'r',
		1041	cb => sub {
336	warn "io event <$_[0]>\n"; # will always output <r>	1042	warn "io event <$_[0]>\n"; # will always output <r>
337	chomp (my $input = <STDIN>); # read a line	1043	chomp (my $input = <STDIN>); # read a line
338	warn "read: $input\n"; # output what has been read	1044	warn "read: $input\n"; # output what has been read
339	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1045	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		1046	},
340	});	1047	);
341		1048
342	my $time_watcher; # can only be used once	1049	my $time_watcher; # can only be used once
343		1050
344	sub new_timer {	1051	sub new_timer {
345	$timer = AnyEvent->timer (after => 1, cb => sub {	1052	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
427	$txn->{finished}->wait;	1134	$txn->{finished}->wait;
428	return $txn->{result};	1135	return $txn->{result};
429		1136
430	The actual code goes further and collects all errors (C<die>s, exceptions)	1137	The actual code goes further and collects all errors (C<die>s, exceptions)
431	that occured during request processing. The C<result> method detects	1138	that occured during request processing. The C<result> method detects
432	wether an exception as thrown (it is stored inside the $txn object)	1139	whether an exception as thrown (it is stored inside the $txn object)
433	and just throws the exception, which means connection errors and other	1140	and just throws the exception, which means connection errors and other
434	problems get reported tot he code that tries to use the result, not in a	1141	problems get reported tot he code that tries to use the result, not in a
435	random callback.	1142	random callback.
436		1143
437	All of this enables the following usage styles:	1144	All of this enables the following usage styles:
438		1145
439	1. Blocking:	1146	1. Blocking:
440		1147
441	my $data = $fcp->client_get ($url);	1148	my $data = $fcp->client_get ($url);
442		1149
443	2. Blocking, but parallelizing:	1150	2. Blocking, but running in parallel:
444		1151
445	my @datas = map $_->result,	1152	my @datas = map $_->result,
446	map $fcp->txn_client_get ($_),	1153	map $fcp->txn_client_get ($_),
447	@urls;	1154	@urls;
448		1155
449	Both blocking examples work without the module user having to know	1156	Both blocking examples work without the module user having to know
450	anything about events.	1157	anything about events.
451		1158
452	3a. Event-based in a main program, using any support Event module:	1159	3a. Event-based in a main program, using any supported event module:
453		1160
454	use Event;	1161	use EV;
455		1162
456	$fcp->txn_client_get ($url)->cb (sub {	1163	$fcp->txn_client_get ($url)->cb (sub {
457	my $txn = shift;	1164	my $txn = shift;
458	my $data = $txn->result;	1165	my $data = $txn->result;
459	...	1166	...
460	});	1167	});
461		1168
462	Event::loop;	1169	EV::loop;
463		1170
464	3b. The module user could use AnyEvent, too:	1171	3b. The module user could use AnyEvent, too:
465		1172
466	use AnyEvent;	1173	use AnyEvent;
467		1174
…		…
472	$quit->broadcast;	1179	$quit->broadcast;
473	});	1180	});
474		1181
475	$quit->wait;	1182	$quit->wait;
476		1183
		1184
		1185	=head1 BENCHMARKS
		1186
		1187	To give you an idea of the performance and overheads that AnyEvent adds
		1188	over the event loops themselves and to give you an impression of the speed
		1189	of various event loops I prepared some benchmarks.
		1190
		1191	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1192
		1193	Here is a benchmark of various supported event models used natively and
		1194	through anyevent. The benchmark creates a lot of timers (with a zero
		1195	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1196	which it is), lets them fire exactly once and destroys them again.
		1197
		1198	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1199	distribution.
		1200
		1201	=head3 Explanation of the columns
		1202
		1203	I<watcher> is the number of event watchers created/destroyed. Since
		1204	different event models feature vastly different performances, each event
		1205	loop was given a number of watchers so that overall runtime is acceptable
		1206	and similar between tested event loop (and keep them from crashing): Glib
		1207	would probably take thousands of years if asked to process the same number
		1208	of watchers as EV in this benchmark.
		1209
		1210	I<bytes> is the number of bytes (as measured by the resident set size,
		1211	RSS) consumed by each watcher. This method of measuring captures both C
		1212	and Perl-based overheads.
		1213
		1214	I<create> is the time, in microseconds (millionths of seconds), that it
		1215	takes to create a single watcher. The callback is a closure shared between
		1216	all watchers, to avoid adding memory overhead. That means closure creation
		1217	and memory usage is not included in the figures.
		1218
		1219	I<invoke> is the time, in microseconds, used to invoke a simple
		1220	callback. The callback simply counts down a Perl variable and after it was
		1221	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1222	signal the end of this phase.
		1223
		1224	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1225	watcher.
		1226
		1227	=head3 Results
		1228
		1229	name watchers bytes create invoke destroy comment
		1230	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1231	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1232	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1233	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1234	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1235	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1236	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1237	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1238	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1239	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1240
		1241	=head3 Discussion
		1242
		1243	The benchmark does I<not> measure scalability of the event loop very
		1244	well. For example, a select-based event loop (such as the pure perl one)
		1245	can never compete with an event loop that uses epoll when the number of
		1246	file descriptors grows high. In this benchmark, all events become ready at
		1247	the same time, so select/poll-based implementations get an unnatural speed
		1248	boost.
		1249
		1250	Also, note that the number of watchers usually has a nonlinear effect on
		1251	overall speed, that is, creating twice as many watchers doesn't take twice
		1252	the time - usually it takes longer. This puts event loops tested with a
		1253	higher number of watchers at a disadvantage.
		1254
		1255	To put the range of results into perspective, consider that on the
		1256	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1257	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1258	cycles with POE.
		1259
		1260	C<EV> is the sole leader regarding speed and memory use, which are both
		1261	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1262	far less memory than any other event loop and is still faster than Event
		1263	natively.
		1264
		1265	The pure perl implementation is hit in a few sweet spots (both the
		1266	constant timeout and the use of a single fd hit optimisations in the perl
		1267	interpreter and the backend itself). Nevertheless this shows that it
		1268	adds very little overhead in itself. Like any select-based backend its
		1269	performance becomes really bad with lots of file descriptors (and few of
		1270	them active), of course, but this was not subject of this benchmark.
		1271
		1272	The C<Event> module has a relatively high setup and callback invocation
		1273	cost, but overall scores in on the third place.
		1274
		1275	C<Glib>'s memory usage is quite a bit higher, but it features a
		1276	faster callback invocation and overall ends up in the same class as
		1277	C<Event>. However, Glib scales extremely badly, doubling the number of
		1278	watchers increases the processing time by more than a factor of four,
		1279	making it completely unusable when using larger numbers of watchers
		1280	(note that only a single file descriptor was used in the benchmark, so
		1281	inefficiencies of C<poll> do not account for this).
		1282
		1283	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1284	more than 2000 watchers is a big setback, however, as correctness takes
		1285	precedence over speed. Nevertheless, its performance is surprising, as the
		1286	file descriptor is dup()ed for each watcher. This shows that the dup()
		1287	employed by some adaptors is not a big performance issue (it does incur a
		1288	hidden memory cost inside the kernel which is not reflected in the figures
		1289	above).
		1290
		1291	C<POE>, regardless of underlying event loop (whether using its pure perl
		1292	select-based backend or the Event module, the POE-EV backend couldn't
		1293	be tested because it wasn't working) shows abysmal performance and
		1294	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1295	as EV watchers, and 10 times as much memory as Event (the high memory
		1296	requirements are caused by requiring a session for each watcher). Watcher
		1297	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1298	implementation.
		1299
		1300	The design of the POE adaptor class in AnyEvent can not really account
		1301	for the performance issues, though, as session creation overhead is
		1302	small compared to execution of the state machine, which is coded pretty
		1303	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1304	using multiple sessions is not a good approach, especially regarding
		1305	memory usage, even the author of POE could not come up with a faster
		1306	design).
		1307
		1308	=head3 Summary
		1309
		1310	=over 4
		1311
		1312	=item * Using EV through AnyEvent is faster than any other event loop
		1313	(even when used without AnyEvent), but most event loops have acceptable
		1314	performance with or without AnyEvent.
		1315
		1316	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1317	the actual event loop, only with extremely fast event loops such as EV
		1318	adds AnyEvent significant overhead.
		1319
		1320	=item * You should avoid POE like the plague if you want performance or
		1321	reasonable memory usage.
		1322
		1323	=back
		1324
		1325	=head2 BENCHMARKING THE LARGE SERVER CASE
		1326
		1327	This benchmark atcually benchmarks the event loop itself. It works by
		1328	creating a number of "servers": each server consists of a socketpair, a
		1329	timeout watcher that gets reset on activity (but never fires), and an I/O
		1330	watcher waiting for input on one side of the socket. Each time the socket
		1331	watcher reads a byte it will write that byte to a random other "server".
		1332
		1333	The effect is that there will be a lot of I/O watchers, only part of which
		1334	are active at any one point (so there is a constant number of active
		1335	fds for each loop iterstaion, but which fds these are is random). The
		1336	timeout is reset each time something is read because that reflects how
		1337	most timeouts work (and puts extra pressure on the event loops).
		1338
		1339	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1340	(1%) are active. This mirrors the activity of large servers with many
		1341	connections, most of which are idle at any one point in time.
		1342
		1343	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1344	distribution.
		1345
		1346	=head3 Explanation of the columns
		1347
		1348	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1349	each server has a read and write socket end).
		1350
		1351	I<create> is the time it takes to create a socketpair (which is
		1352	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1353
		1354	I<request>, the most important value, is the time it takes to handle a
		1355	single "request", that is, reading the token from the pipe and forwarding
		1356	it to another server. This includes deleting the old timeout and creating
		1357	a new one that moves the timeout into the future.
		1358
		1359	=head3 Results
		1360
		1361	name sockets create request
		1362	EV 20000 69.01 11.16
		1363	Perl 20000 73.32 35.87
		1364	Event 20000 212.62 257.32
		1365	Glib 20000 651.16 1896.30
		1366	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1367
		1368	=head3 Discussion
		1369
		1370	This benchmark I<does> measure scalability and overall performance of the
		1371	particular event loop.
		1372
		1373	EV is again fastest. Since it is using epoll on my system, the setup time
		1374	is relatively high, though.
		1375
		1376	Perl surprisingly comes second. It is much faster than the C-based event
		1377	loops Event and Glib.
		1378
		1379	Event suffers from high setup time as well (look at its code and you will
		1380	understand why). Callback invocation also has a high overhead compared to
		1381	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1382	uses select or poll in basically all documented configurations.
		1383
		1384	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1385	clearly fails to perform with many filehandles or in busy servers.
		1386
		1387	POE is still completely out of the picture, taking over 1000 times as long
		1388	as EV, and over 100 times as long as the Perl implementation, even though
		1389	it uses a C-based event loop in this case.
		1390
		1391	=head3 Summary
		1392
		1393	=over 4
		1394
		1395	=item * The pure perl implementation performs extremely well.
		1396
		1397	=item * Avoid Glib or POE in large projects where performance matters.
		1398
		1399	=back
		1400
		1401	=head2 BENCHMARKING SMALL SERVERS
		1402
		1403	While event loops should scale (and select-based ones do not...) even to
		1404	large servers, most programs we (or I :) actually write have only a few
		1405	I/O watchers.
		1406
		1407	In this benchmark, I use the same benchmark program as in the large server
		1408	case, but it uses only eight "servers", of which three are active at any
		1409	one time. This should reflect performance for a small server relatively
		1410	well.
		1411
		1412	The columns are identical to the previous table.
		1413
		1414	=head3 Results
		1415
		1416	name sockets create request
		1417	EV 16 20.00 6.54
		1418	Perl 16 25.75 12.62
		1419	Event 16 81.27 35.86
		1420	Glib 16 32.63 15.48
		1421	POE 16 261.87 276.28 uses POE::Loop::Event
		1422
		1423	=head3 Discussion
		1424
		1425	The benchmark tries to test the performance of a typical small
		1426	server. While knowing how various event loops perform is interesting, keep
		1427	in mind that their overhead in this case is usually not as important, due
		1428	to the small absolute number of watchers (that is, you need efficiency and
		1429	speed most when you have lots of watchers, not when you only have a few of
		1430	them).
		1431
		1432	EV is again fastest.
		1433
		1434	Perl again comes second. It is noticably faster than the C-based event
		1435	loops Event and Glib, although the difference is too small to really
		1436	matter.
		1437
		1438	POE also performs much better in this case, but is is still far behind the
		1439	others.
		1440
		1441	=head3 Summary
		1442
		1443	=over 4
		1444
		1445	=item * C-based event loops perform very well with small number of
		1446	watchers, as the management overhead dominates.
		1447
		1448	=back
		1449
		1450
		1451	=head1 FORK
		1452
		1453	Most event libraries are not fork-safe. The ones who are usually are
		1454	because they rely on inefficient but fork-safe C<select> or C<poll>
		1455	calls. Only L<EV> is fully fork-aware.
		1456
		1457	If you have to fork, you must either do so I<before> creating your first
		1458	watcher OR you must not use AnyEvent at all in the child.
		1459
		1460
		1461	=head1 SECURITY CONSIDERATIONS
		1462
		1463	AnyEvent can be forced to load any event model via
		1464	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1465	execute arbitrary code or directly gain access, it can easily be used to
		1466	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1467	will not be active when the program uses a different event model than
		1468	specified in the variable.
		1469
		1470	You can make AnyEvent completely ignore this variable by deleting it
		1471	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1472
		1473	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1474
		1475	use AnyEvent;
		1476
		1477	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1478	be used to probe what backend is used and gain other information (which is
		1479	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1480
		1481
477	=head1 SEE ALSO	1482	=head1 SEE ALSO
478		1483
479	Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.	1484	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1485	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
480		1486
481	Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.	1487	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
		1488	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1489	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1490	L<AnyEvent::Impl::POE>.
482		1491
		1492	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1493
483	Nontrivial usage example: L<Net::FCP>.	1494	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
484		1495
485	=head1	1496
		1497	=head1 AUTHOR
		1498
		1499	Marc Lehmann <schmorp@schmorp.de>
		1500	http://home.schmorp.de/
486		1501
487	=cut	1502	=cut
488		1503
489	1	1504	1
490		1505

Diff Legend

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