[ViewVC] Diff of: cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.50 by root, Wed Apr 16 14:04:45 2008 UTC vs.
Revision 1.108 by root, Sat May 10 00:22:02 2008 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent - provide framework for multiple event loops	3	AnyEvent - provide framework for multiple event loops
4		4
5	EV, Event, Coro::EV, Coro::Event, 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->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->wait; # enters "main loop" till $condvar gets ->send
21	$w->broadcast; # wake up current and all future wait's	21	$w->send; # wake up current and all future wait's
22		22
23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)	23	=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
24		24
25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	25	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
26	nowadays. So what is different about AnyEvent?	26	nowadays. So what is different about AnyEvent?
…		…
29	policy> and AnyEvent is I<small and efficient>.	29	policy> and AnyEvent is I<small and efficient>.
30		30
31	First and foremost, I<AnyEvent is not an event model> itself, it only	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	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,	33	pragmatic way. For event models and certain classes of immortals alike,
34	the statement "there can only be one" is a bitter reality, and AnyEvent	34	the statement "there can only be one" is a bitter reality: In general,
35	helps hiding the differences.	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.
36		37
37	The goal of AnyEvent is to offer module authors the ability to do event	38	The goal of AnyEvent is to offer module authors the ability to do event
38	programming (waiting for I/O or timer events) without subscribing to a	39	programming (waiting for I/O or timer events) without subscribing to a
39	religion, a way of living, and most importantly: without forcing your	40	religion, a way of living, and most importantly: without forcing your
40	module users into the same thing by forcing them to use the same event	41	module users into the same thing by forcing them to use the same event
41	model you use.	42	model you use.
42		43
43	For modules like POE or IO::Async (which is actually doing all I/O	44	For modules like POE or IO::Async (which is a total misnomer as it is
44	I<synchronously>...), using them in your module is like joining a	45	actually doing all I/O I<synchronously>...), using them in your module is
45	cult: After you joined, you are dependent on them and you cannot use	46	like joining a cult: After you joined, you are dependent on them and you
46	anything else, as it is simply incompatible to everything that isn't	47	cannot use anything else, as it is simply incompatible to everything that
47	itself.	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.
48		50
49	AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk	51	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50	works fine etc. etc. but none of these work together with the rest: POE	52	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51	+ IO::Async? no go. Tk + Event? no go. If your module uses one of	53	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if
52	those, every user of your module has to use it, too. If your module	54	your module uses one of those, every user of your module has to use it,
53	uses AnyEvent, it works transparently with all event models it supports	55	too. But if your module uses AnyEvent, it works transparently with all
54	(including stuff like POE and IO::Async).	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).
55		59
56	In addition of being free of having to use I<the one and only true event	60	In addition to being free of having to use I<the one and only true event
57	model>, AnyEvent also is free of bloat and policy: with POE or similar	61	model>, AnyEvent also is free of bloat and policy: with POE or similar
58	modules, you get an enourmous amount of code and strict rules you have	62	modules, you get an enourmous amount of code and strict rules you have to
59	to follow. AnyEvent, on the other hand, is lean and to the point by only	63	follow. AnyEvent, on the other hand, is lean and up to the point, by only
60	offering the functionality that is useful, in as thin as a wrapper as	64	offering the functionality that is necessary, in as thin as a wrapper as
61	technically possible.	65	technically possible.
62		66
63	Of course, if you want lots of policy (this can arguably be somewhat	67	Of course, if you want lots of policy (this can arguably be somewhat
64	useful) and you want to force your users to use the one and only event	68	useful) and you want to force your users to use the one and only event
65	model, you should I<not> use this module.	69	model, you should I<not> use this module.
66
67		70
68	=head1 DESCRIPTION	71	=head1 DESCRIPTION
69		72
70	L<AnyEvent> provides an identical interface to multiple event loops. This	73	L<AnyEvent> provides an identical interface to multiple event loops. This
71	allows module authors to utilise an event loop without forcing module	74	allows module authors to utilise an event loop without forcing module
72	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
73	peacefully at any one time).	76	peacefully at any one time).
74		77
75	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>
76	module.	79	module.
77		80
78	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
79	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
80	loaded: L<Coro::EV>, L<Coro::Event>, L<EV>, L<Event>, L<Glib>, L<Tk>. The	83	following modules is already loaded: L<EV>,
		84	L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
81	first one found is used. If none are found, the module tries to load these	85	L<POE>. The first one found is used. If none are found, the module tries
82	modules in the order given. The first one that could be successfully	86	to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
83	loaded will be used. If still none could be found, AnyEvent will fall back	87	adaptor should always succeed) in the order given. The first one that can
84	to a pure-perl event loop, which is also not very efficient.	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.
85		91
86	Because AnyEvent first checks for modules that are already loaded, loading	92	Because AnyEvent first checks for modules that are already loaded, loading
87	an Event model explicitly before first using AnyEvent will likely make	93	an event model explicitly before first using AnyEvent will likely make
88	that model the default. For example:	94	that model the default. For example:
89		95
90	use Tk;	96	use Tk;
91	use AnyEvent;	97	use AnyEvent;
92		98
93	# .. 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...
94		104
95	The pure-perl implementation of AnyEvent is called	105	The pure-perl implementation of AnyEvent is called
96	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
97	explicitly.	107	explicitly.
98		108
…		…
101	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
102	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
103	the callback to call, the filehandle to watch, etc.	113	the callback to call, the filehandle to watch, etc.
104		114
105	These watchers are normal Perl objects with normal Perl lifetime. After	115	These watchers are normal Perl objects with normal Perl lifetime. After
106	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
107	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
108	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
109	references to it).	122	to it).
110		123
111	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.
112		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
113	=head2 IO WATCHERS	140	=head2 I/O WATCHERS
114		141
115	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
116	the following mandatory arguments:	143	with the following mandatory key-value pairs as arguments:
117		144
118	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
119	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>,
120	a watcher waiting for "r"eadable or "w"ritable events. C<cb> the callback	147	which creates a watcher waiting for "r"eadable or "w"ritable events,
121	to invoke everytime the filehandle becomes ready.	148	respectively. C<cb> is the callback to invoke each time the file handle
		149	becomes ready.
122		150
123	Filehandles will be kept alive, so as long as the watcher exists, the	151	Although the callback might get passed parameters, their value and
124	filehandle exists, too.	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.
125		162
126	Example:	163	Example:
127		164
128	# 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
129	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
135	=head2 TIME WATCHERS	172	=head2 TIME WATCHERS
136		173
137	You can create a time watcher by calling the C<< AnyEvent->timer >>	174	You can create a time watcher by calling the C<< AnyEvent->timer >>
138	method with the following mandatory arguments:	175	method with the following mandatory arguments:
139		176
140	C<after> after how many seconds (fractions are supported) should the timer	177	C<after> specifies after how many seconds (fractional values are
141	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.
142		184
143	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
144	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
145	and Glib).	187	and Glib).
146		188
…		…
152	});	194	});
153		195
154	# to cancel the timer:	196	# to cancel the timer:
155	undef $w;	197	undef $w;
156		198
		199	Example 2:
		200
		201	# fire an event after 0.5 seconds, then roughly every second
		202	my $w;
		203
		204	my $cb = sub {
		205	# cancel the old timer while creating a new one
		206	$w = AnyEvent->timer (after => 1, cb => $cb);
		207	};
		208
		209	# start the "loop" by creating the first watcher
		210	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		211
		212	=head3 TIMING ISSUES
		213
		214	There are two ways to handle timers: based on real time (relative, "fire
		215	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		216	o'clock").
		217
		218	While most event loops expect timers to specified in a relative way, they
		219	use absolute time internally. This makes a difference when your clock
		220	"jumps", for example, when ntp decides to set your clock backwards from
		221	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		222	fire "after" a second might actually take six years to finally fire.
		223
		224	AnyEvent cannot compensate for this. The only event loop that is conscious
		225	about these issues is L<EV>, which offers both relative (ev_timer, based
		226	on true relative time) and absolute (ev_periodic, based on wallclock time)
		227	timers.
		228
		229	AnyEvent always prefers relative timers, if available, matching the
		230	AnyEvent API.
		231
		232	=head2 SIGNAL WATCHERS
		233
		234	You can watch for signals using a signal watcher, C<signal> is the signal
		235	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		236	be invoked whenever a signal occurs.
		237
		238	Although the callback might get passed parameters, their value and
		239	presence is undefined and you cannot rely on them. Portable AnyEvent
		240	callbacks cannot use arguments passed to signal watcher callbacks.
		241
		242	Multiple signal occurances can be clumped together into one callback
		243	invocation, and callback invocation will be synchronous. synchronous means
		244	that it might take a while until the signal gets handled by the process,
		245	but it is guarenteed not to interrupt any other callbacks.
		246
		247	The main advantage of using these watchers is that you can share a signal
		248	between multiple watchers.
		249
		250	This watcher might use C<%SIG>, so programs overwriting those signals
		251	directly will likely not work correctly.
		252
		253	Example: exit on SIGINT
		254
		255	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		256
		257	=head2 CHILD PROCESS WATCHERS
		258
		259	You can also watch on a child process exit and catch its exit status.
		260
		261	The child process is specified by the C<pid> argument (if set to C<0>, it
		262	watches for any child process exit). The watcher will trigger as often
		263	as status change for the child are received. This works by installing a
		264	signal handler for C<SIGCHLD>. The callback will be called with the pid
		265	and exit status (as returned by waitpid), so unlike other watcher types,
		266	you I<can> rely on child watcher callback arguments.
		267
		268	There is a slight catch to child watchers, however: you usually start them
		269	I<after> the child process was created, and this means the process could
		270	have exited already (and no SIGCHLD will be sent anymore).
		271
		272	Not all event models handle this correctly (POE doesn't), but even for
		273	event models that I<do> handle this correctly, they usually need to be
		274	loaded before the process exits (i.e. before you fork in the first place).
		275
		276	This means you cannot create a child watcher as the very first thing in an
		277	AnyEvent program, you I<have> to create at least one watcher before you
		278	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		279
		280	Example: fork a process and wait for it
		281
		282	my $done = AnyEvent->condvar;
		283
		284	AnyEvent::detect; # force event module to be initialised
		285
		286	my $pid = fork or exit 5;
		287
		288	my $w = AnyEvent->child (
		289	pid => $pid,
		290	cb => sub {
		291	my ($pid, $status) = @_;
		292	warn "pid $pid exited with status $status";
		293	$done->send;
		294	},
		295	);
		296
		297	# do something else, then wait for process exit
		298	$done->wait;
		299
157	=head2 CONDITION WATCHERS	300	=head2 CONDITION VARIABLES
158		301
		302	If you are familiar with some event loops you will know that all of them
		303	require you to run some blocking "loop", "run" or similar function that
		304	will actively watch for new events and call your callbacks.
		305
		306	AnyEvent is different, it expects somebody else to run the event loop and
		307	will only block when necessary (usually when told by the user).
		308
		309	The instrument to do that is called a "condition variable", so called
		310	because they represent a condition that must become true.
		311
159	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	312	Condition variables can be created by calling the C<< AnyEvent->condvar
160	method without any arguments.	313	>> method, usually without arguments. The only argument pair allowed is
		314	C<cb>, which specifies a callback to be called when the condition variable
		315	becomes true.
161		316
162	A condition watcher watches for a condition - precisely that the C<<	317	After creation, the conditon variable is "false" until it becomes "true"
163	->broadcast >> method has been called.	318	by calling the C<send> method.
164		319
		320	Condition variables are similar to callbacks, except that you can
		321	optionally wait for them. They can also be called merge points - points
		322	in time where multiple outstandign events have been processed. And yet
		323	another way to call them is transations - each condition variable can be
		324	used to represent a transaction, which finishes at some point and delivers
		325	a result.
		326
		327	Condition variables are very useful to signal that something has finished,
		328	for example, if you write a module that does asynchronous http requests,
		329	then a condition variable would be the ideal candidate to signal the
		330	availability of results. The user can either act when the callback is
		331	called or can synchronously C<< ->wait >> for the results.
		332
		333	You can also use them to simulate traditional event loops - for example,
		334	you can block your main program until an event occurs - for example, you
		335	could C<< ->wait >> in your main program until the user clicks the Quit
		336	button of your app, which would C<< ->send >> the "quit" event.
		337
165	Note that condition watchers recurse into the event loop - if you have	338	Note that condition variables recurse into the event loop - if you have
166	two watchers that call C<< ->wait >> in a round-robbin fashion, you	339	two pieces of code that call C<< ->wait >> in a round-robbin fashion, you
167	lose. Therefore, condition watchers are good to export to your caller, but	340	lose. Therefore, condition variables are good to export to your caller, but
168	you should avoid making a blocking wait, at least in callbacks, as this	341	you should avoid making a blocking wait yourself, at least in callbacks,
169	usually asks for trouble.	342	as this asks for trouble.
170		343
171	The watcher has only two methods:	344	Condition variables are represented by hash refs in perl, and the keys
		345	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		346	easy (it is often useful to build your own transaction class on top of
		347	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		348	it's C<new> method in your own C<new> method.
		349
		350	There are two "sides" to a condition variable - the "producer side" which
		351	eventually calls C<< -> send >>, and the "consumer side", which waits
		352	for the send to occur.
		353
		354	Example:
		355
		356	# wait till the result is ready
		357	my $result_ready = AnyEvent->condvar;
		358
		359	# do something such as adding a timer
		360	# or socket watcher the calls $result_ready->send
		361	# when the "result" is ready.
		362	# in this case, we simply use a timer:
		363	my $w = AnyEvent->timer (
		364	after => 1,
		365	cb => sub { $result_ready->send },
		366	);
		367
		368	# this "blocks" (while handling events) till the callback
		369	# calls send
		370	$result_ready->wait;
		371
		372	=head3 METHODS FOR PRODUCERS
		373
		374	These methods should only be used by the producing side, i.e. the
		375	code/module that eventually sends the signal. Note that it is also
		376	the producer side which creates the condvar in most cases, but it isn't
		377	uncommon for the consumer to create it as well.
172		378
173	=over 4	379	=over 4
174		380
		381	=item $cv->send (...)
		382
		383	Flag the condition as ready - a running C<< ->wait >> and all further
		384	calls to C<wait> will (eventually) return after this method has been
		385	called. If nobody is waiting the send will be remembered.
		386
		387	If a callback has been set on the condition variable, it is called
		388	immediately from within send.
		389
		390	Any arguments passed to the C<send> call will be returned by all
		391	future C<< ->wait >> calls.
		392
		393	=item $cv->croak ($error)
		394
		395	Similar to send, but causes all call's wait C<< ->wait >> to invoke
		396	C<Carp::croak> with the given error message/object/scalar.
		397
		398	This can be used to signal any errors to the condition variable
		399	user/consumer.
		400
		401	=item $cv->begin ([group callback])
		402
		403	=item $cv->end
		404
		405	These two methods can be used to combine many transactions/events into
		406	one. For example, a function that pings many hosts in parallel might want
		407	to use a condition variable for the whole process.
		408
		409	Every call to C<< ->begin >> will increment a counter, and every call to
		410	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		411	>>, the (last) callback passed to C<begin> will be executed. That callback
		412	is I<supposed> to call C<< ->send >>, but that is not required. If no
		413	callback was set, C<send> will be called without any arguments.
		414
		415	Let's clarify this with the ping example:
		416
		417	my $cv = AnyEvent->condvar;
		418
		419	my %result;
		420	$cv->begin (sub { $cv->send (\%result) });
		421
		422	for my $host (@list_of_hosts) {
		423	$cv->begin;
		424	ping_host_then_call_callback $host, sub {
		425	$result{$host} = ...;
		426	$cv->end;
		427	};
		428	}
		429
		430	$cv->end;
		431
		432	This code fragment supposedly pings a number of hosts and calls
		433	C<send> after results for all then have have been gathered - in any
		434	order. To achieve this, the code issues a call to C<begin> when it starts
		435	each ping request and calls C<end> when it has received some result for
		436	it. Since C<begin> and C<end> only maintain a counter, the order in which
		437	results arrive is not relevant.
		438
		439	There is an additional bracketing call to C<begin> and C<end> outside the
		440	loop, which serves two important purposes: first, it sets the callback
		441	to be called once the counter reaches C<0>, and second, it ensures that
		442	C<send> is called even when C<no> hosts are being pinged (the loop
		443	doesn't execute once).
		444
		445	This is the general pattern when you "fan out" into multiple subrequests:
		446	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		447	is called at least once, and then, for each subrequest you start, call
		448	C<begin> and for eahc subrequest you finish, call C<end>.
		449
		450	=back
		451
		452	=head3 METHODS FOR CONSUMERS
		453
		454	These methods should only be used by the consuming side, i.e. the
		455	code awaits the condition.
		456
		457	=over 4
		458
175	=item $cv->wait	459	=item $cv->wait
176		460
177	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	461	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
178	called on c<$cv>, while servicing other watchers normally.	462	>> methods have been called on c<$cv>, while servicing other watchers
		463	normally.
179		464
180	You can only wait once on a condition - additional calls will return	465	You can only wait once on a condition - additional calls are valid but
181	immediately.	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.
182		473
183	Not all event models support a blocking wait - some die in that case	474	Not all event models support a blocking wait - some die in that case
184	(programs might want to do that so they stay interactive), so I<if you	475	(programs might want to do that to stay interactive), so I<if you are
185	are using this from a module, never require a blocking wait>, but let the	476	using this from a module, never require a blocking wait>, but let the
186	caller decide wether the call will block or not (for example, by coupling	477	caller decide whether the call will block or not (for example, by coupling
187	condition variables with some kind of request results and supporting	478	condition variables with some kind of request results and supporting
188	callbacks so the caller knows that getting the result will not block,	479	callbacks so the caller knows that getting the result will not block,
189	while still suppporting blocking waits if the caller so desires).	480	while still suppporting blocking waits if the caller so desires).
190		481
191	Another reason I<never> to C<< ->wait >> in a module is that you cannot	482	Another reason I<never> to C<< ->wait >> in a module is that you cannot
192	sensibly have two C<< ->wait >>'s in parallel, as that would require	483	sensibly have two C<< ->wait >>'s in parallel, as that would require
193	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	484	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
194	can supply (the coroutine-aware backends C<Coro::EV> and C<Coro::Event>	485	can supply.
195	explicitly support concurrent C<< ->wait >>'s from different coroutines,
196	however).
197		486
198	=item $cv->broadcast	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<< ->wait >> calls perfectly safe as long as they are done from another
		491	coroutine (one that doesn't run the event loop).
199		492
200	Flag the condition as ready - a running C<< ->wait >> and all further	493	You can ensure that C<< -wait >> never blocks by setting a callback and
201	calls to C<wait> will return after this method has been called. If nobody	494	only calling C<< ->wait >> from within that callback (or at a later
202	is waiting the broadcast will be remembered..	495	time). This will work even when the event loop does not support blocking
		496	waits otherwise.
203		497
204	Example:	498	=item $bool = $cv->ready
205		499
206	# wait till the result is ready	500	Returns true when the condition is "true", i.e. whether C<send> or
207	my $result_ready = AnyEvent->condvar;	501	C<croak> have been called.
208		502
209	# do something such as adding a timer	503	=item $cb = $cv->cb ([new callback])
210	# or socket watcher the calls $result_ready->broadcast
211	# when the "result" is ready.
212		504
213	$result_ready->wait;	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<wait> inside the callback
		510	or at any later time is guaranteed not to block.
214		511
215	=back	512	=back
216		513
217	=head2 SIGNAL WATCHERS	514	=head1 GLOBAL VARIABLES AND FUNCTIONS
218
219	You can listen for signals using a signal watcher, C<signal> is the signal
220	I<name> without any C<SIG> prefix. Multiple signals events can be clumped
221	together into one callback invocation, and callback invocation might or
222	might not be asynchronous.
223
224	These watchers might use C<%SIG>, so programs overwriting those signals
225	directly will likely not work correctly.
226
227	Example: exit on SIGINT
228
229	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
230
231	=head2 CHILD PROCESS WATCHERS
232
233	You can also listen for the status of a child process specified by the
234	C<pid> argument (or any child if the pid argument is 0). The watcher will
235	trigger as often as status change for the child are received. This works
236	by installing a signal handler for C<SIGCHLD>. The callback will be called with
237	the pid and exit status (as returned by waitpid).
238
239	Example: wait for pid 1333
240
241	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
242
243	=head1 GLOBALS
244		515
245	=over 4	516	=over 4
246		517
247	=item $AnyEvent::MODEL	518	=item $AnyEvent::MODEL
248		519
…		…
252	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
253	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>).
254		525
255	The known classes so far are:	526	The known classes so far are:
256		527
257	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
258	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
259	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	528	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
260	AnyEvent::Impl::Event based on Event, also second best choice :)	529	AnyEvent::Impl::Event based on Event, second best choice.
		530	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
261	AnyEvent::Impl::Glib based on Glib, third-best choice.	531	AnyEvent::Impl::Glib based on Glib, third-best choice.
262	AnyEvent::Impl::Tk based on Tk, very bad choice.	532	AnyEvent::Impl::Tk based on Tk, very bad choice.
263	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	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.
264		546
265	=item AnyEvent::detect	547	=item AnyEvent::detect
266		548
267	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	549	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
268	necessary. You should only call this function right before you would have	550	if necessary. You should only call this function right before you would
269	created an AnyEvent watcher anyway, that is, very late at runtime.	551	have created an AnyEvent watcher anyway, that is, as late as possible at
		552	runtime.
		553
		554	=item @AnyEvent::detect
		555
		556	If there are any code references in this array (you can C<push> to it
		557	before or after loading AnyEvent), then they will called directly after
		558	the event loop has been chosen.
		559
		560	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		561	if it contains a true value then the event loop has already been detected,
		562	and the array will be ignored.
270		563
271	=back	564	=back
272		565
273	=head1 WHAT TO DO IN A MODULE	566	=head1 WHAT TO DO IN A MODULE
274		567
275	As a module author, you should "use AnyEvent" and call AnyEvent methods	568	As a module author, you should C<use AnyEvent> and call AnyEvent methods
276	freely, but you should not load a specific event module or rely on it.	569	freely, but you should not load a specific event module or rely on it.
277		570
278	Be careful when you create watchers in the module body - Anyevent will	571	Be careful when you create watchers in the module body - AnyEvent will
279	decide which event module to use as soon as the first method is called, so	572	decide which event module to use as soon as the first method is called, so
280	by calling AnyEvent in your module body you force the user of your module	573	by calling AnyEvent in your module body you force the user of your module
281	to load the event module first.	574	to load the event module first.
282		575
		576	Never call C<< ->wait >> on a condition variable unless you I<know> that
		577	the C<< ->send >> method has been called on it already. This is
		578	because it will stall the whole program, and the whole point of using
		579	events is to stay interactive.
		580
		581	It is fine, however, to call C<< ->wait >> when the user of your module
		582	requests it (i.e. if you create a http request object ad have a method
		583	called C<results> that returns the results, it should call C<< ->wait >>
		584	freely, as the user of your module knows what she is doing. always).
		585
283	=head1 WHAT TO DO IN THE MAIN PROGRAM	586	=head1 WHAT TO DO IN THE MAIN PROGRAM
284		587
285	There will always be a single main program - the only place that should	588	There will always be a single main program - the only place that should
286	dictate which event model to use.	589	dictate which event model to use.
287		590
288	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	591	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
289	do anything special and let AnyEvent decide which implementation to chose.	592	do anything special (it does not need to be event-based) and let AnyEvent
		593	decide which implementation to chose if some module relies on it.
290		594
291	If the main program relies on a specific event model (for example, in Gtk2	595	If the main program relies on a specific event model. For example, in
292	programs you have to rely on either Glib or Glib::Event), you should load	596	Gtk2 programs you have to rely on the Glib module. You should load the
293	it before loading AnyEvent or any module that uses it, generally, as early	597	event module before loading AnyEvent or any module that uses it: generally
294	as possible. The reason is that modules might create watchers when they	598	speaking, you should load it as early as possible. The reason is that
295	are loaded, and AnyEvent will decide on the event model to use as soon as	599	modules might create watchers when they are loaded, and AnyEvent will
296	it creates watchers, and it might chose the wrong one unless you load the	600	decide on the event model to use as soon as it creates watchers, and it
297	correct one yourself.	601	might chose the wrong one unless you load the correct one yourself.
298		602
299	You can chose to use a rather inefficient pure-perl implementation by	603	You can chose to use a rather inefficient pure-perl implementation by
300	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	604	loading the C<AnyEvent::Impl::Perl> module, which gives you similar
301	generally better.	605	behaviour everywhere, but letting AnyEvent chose is generally better.
		606
		607	=head1 OTHER MODULES
		608
		609	The following is a non-exhaustive list of additional modules that use
		610	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		611	in the same program. Some of the modules come with AnyEvent, some are
		612	available via CPAN.
		613
		614	=over 4
		615
		616	=item L<AnyEvent::Util>
		617
		618	Contains various utility functions that replace often-used but blocking
		619	functions such as C<inet_aton> by event-/callback-based versions.
		620
		621	=item L<AnyEvent::Handle>
		622
		623	Provide read and write buffers and manages watchers for reads and writes.
		624
		625	=item L<AnyEvent::Socket>
		626
		627	Provides a means to do non-blocking connects, accepts etc.
		628
		629	=item L<AnyEvent::HTTPD>
		630
		631	Provides a simple web application server framework.
		632
		633	=item L<AnyEvent::DNS>
		634
		635	Provides asynchronous DNS resolver capabilities, beyond what
		636	L<AnyEvent::Util> offers.
		637
		638	=item L<AnyEvent::FastPing>
		639
		640	The fastest ping in the west.
		641
		642	=item L<Net::IRC3>
		643
		644	AnyEvent based IRC client module family.
		645
		646	=item L<Net::XMPP2>
		647
		648	AnyEvent based XMPP (Jabber protocol) module family.
		649
		650	=item L<Net::FCP>
		651
		652	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		653	of AnyEvent.
		654
		655	=item L<Event::ExecFlow>
		656
		657	High level API for event-based execution flow control.
		658
		659	=item L<Coro>
		660
		661	Has special support for AnyEvent via L<Coro::AnyEvent>.
		662
		663	=item L<IO::Lambda>
		664
		665	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		666
		667	=item L<IO::AIO>
		668
		669	Truly asynchronous I/O, should be in the toolbox of every event
		670	programmer. Can be trivially made to use AnyEvent.
		671
		672	=item L<BDB>
		673
		674	Truly asynchronous Berkeley DB access. Can be trivially made to use
		675	AnyEvent.
		676
		677	=back
302		678
303	=cut	679	=cut
304		680
305	package AnyEvent;	681	package AnyEvent;
306		682
307	no warnings;	683	no warnings;
308	use strict;	684	use strict;
309		685
310	use Carp;	686	use Carp;
311		687
312	our $VERSION = '3.0';	688	our $VERSION = '3.4';
313	our $MODEL;	689	our $MODEL;
314		690
315	our $AUTOLOAD;	691	our $AUTOLOAD;
316	our @ISA;	692	our @ISA;
317		693
318	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	694	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
319		695
320	our @REGISTRY;	696	our @REGISTRY;
321		697
322	my @models = (	698	my @models = (
323	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
324	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
325	[EV:: => AnyEvent::Impl::EV::],	699	[EV:: => AnyEvent::Impl::EV::],
326	[Event:: => AnyEvent::Impl::Event::],	700	[Event:: => AnyEvent::Impl::Event::],
		701	[Tk:: => AnyEvent::Impl::Tk::],
		702	[Wx:: => AnyEvent::Impl::POE::],
		703	[Prima:: => AnyEvent::Impl::POE::],
		704	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		705	# everything below here will not be autoprobed as the pureperl backend should work everywhere
327	[Glib:: => AnyEvent::Impl::Glib::],	706	[Glib:: => AnyEvent::Impl::Glib::],
328	[Tk:: => AnyEvent::Impl::Tk::],	707	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
329	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	708	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		709	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
330	);	710	);
331		711
332	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	712	our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY);
		713
		714	our @detect;
333		715
334	sub detect() {	716	sub detect() {
335	unless ($MODEL) {	717	unless ($MODEL) {
336	no strict 'refs';	718	no strict 'refs';
337		719
		720	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		721	my $model = "AnyEvent::Impl::$1";
		722	if (eval "require $model") {
		723	$MODEL = $model;
		724	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		725	} else {
		726	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		727	}
		728	}
		729
338	# check for already loaded models	730	# check for already loaded models
		731	unless ($MODEL) {
339	for (@REGISTRY, @models) {	732	for (@REGISTRY, @models) {
340	my ($package, $model) = @$_;	733	my ($package, $model) = @$_;
341	if (${"$package\::VERSION"} > 0) {	734	if (${"$package\::VERSION"} > 0) {
342	if (eval "require $model") {	735	if (eval "require $model") {
343	$MODEL = $model;	736	$MODEL = $model;
344	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	737	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
345	last;	738	last;
		739	}
346	}	740	}
347	}	741	}
348	}
349		742
350	unless ($MODEL) {	743	unless ($MODEL) {
351	# try to load a model	744	# try to load a model
352		745
353	for (@REGISTRY, @models) {	746	for (@REGISTRY, @models) {
354	my ($package, $model) = @$_;	747	my ($package, $model) = @$_;
355	if (eval "require $package"	748	if (eval "require $package"
356	and ${"$package\::VERSION"} > 0	749	and ${"$package\::VERSION"} > 0
357	and eval "require $model") {	750	and eval "require $model") {
358	$MODEL = $model;	751	$MODEL = $model;
359	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	752	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
360	last;	753	last;
		754	}
361	}	755	}
		756
		757	$MODEL
		758	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
362	}	759	}
363
364	$MODEL
365	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk.";
366	}	760	}
367		761
368	unshift @ISA, $MODEL;	762	unshift @ISA, $MODEL;
369	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	763	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		764
		765	(shift @detect)->() while @detect;
370	}	766	}
371		767
372	$MODEL	768	$MODEL
373	}	769	}
374		770
…		…
481	undef $CHLD_W unless keys %PID_CB;	877	undef $CHLD_W unless keys %PID_CB;
482	}	878	}
483		879
484	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	880	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
485		881
		882	This is an advanced topic that you do not normally need to use AnyEvent in
		883	a module. This section is only of use to event loop authors who want to
		884	provide AnyEvent compatibility.
		885
486	If you need to support another event library which isn't directly	886	If you need to support another event library which isn't directly
487	supported by AnyEvent, you can supply your own interface to it by	887	supported by AnyEvent, you can supply your own interface to it by
488	pushing, before the first watcher gets created, the package name of	888	pushing, before the first watcher gets created, the package name of
489	the event module and the package name of the interface to use onto	889	the event module and the package name of the interface to use onto
490	C<@AnyEvent::REGISTRY>. You can do that before and even without loading	890	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
491	AnyEvent.	891	AnyEvent, so it is reasonably cheap.
492		892
493	Example:	893	Example:
494		894
495	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	895	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
496		896
497	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	897	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
498	package/class when it finds the C<urxvt> package/module is loaded. When	898	package/class when it finds the C<urxvt> package/module is already loaded.
		899
499	AnyEvent is loaded and asked to find a suitable event model, it will	900	When AnyEvent is loaded and asked to find a suitable event model, it
500	first check for the presence of urxvt.	901	will first check for the presence of urxvt by trying to C<use> the
		902	C<urxvt::anyevent> module.
501		903
502	The class should provide implementations for all watcher types (see	904	The class should provide implementations for all watcher types. See
503	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	905	L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
504	(Source code) and so on for actual examples, use C<perldoc -m	906	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
505	AnyEvent::Impl::Glib> to see the sources).	907	see the sources.
506		908
		909	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		910	provide suitable (hopefully) replacements.
		911
507	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	912	The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
508	uses the above line as-is. An interface isn't included in AnyEvent	913	terminal emulator uses the above line as-is. An interface isn't included
509	because it doesn't make sense outside the embedded interpreter inside	914	in AnyEvent because it doesn't make sense outside the embedded interpreter
510	I<rxvt-unicode>, and it is updated and maintained as part of the	915	inside I<rxvt-unicode>, and it is updated and maintained as part of the
511	I<rxvt-unicode> distribution.	916	I<rxvt-unicode> distribution.
512		917
513	I<rxvt-unicode> also cheats a bit by not providing blocking access to	918	I<rxvt-unicode> also cheats a bit by not providing blocking access to
514	condition variables: code blocking while waiting for a condition will	919	condition variables: code blocking while waiting for a condition will
515	C<die>. This still works with most modules/usages, and blocking calls must	920	C<die>. This still works with most modules/usages, and blocking calls must
516	not be in an interactive application, so it makes sense.	921	not be done in an interactive application, so it makes sense.
517		922
518	=head1 ENVIRONMENT VARIABLES	923	=head1 ENVIRONMENT VARIABLES
519		924
520	The following environment variables are used by this module:	925	The following environment variables are used by this module:
521		926
522	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	927	=over 4
523	model gets used.
524		928
		929	=item C<PERL_ANYEVENT_VERBOSE>
		930
		931	By default, AnyEvent will be completely silent except in fatal
		932	conditions. You can set this environment variable to make AnyEvent more
		933	talkative.
		934
		935	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		936	conditions, such as not being able to load the event model specified by
		937	C<PERL_ANYEVENT_MODEL>.
		938
		939	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		940	model it chooses.
		941
		942	=item C<PERL_ANYEVENT_MODEL>
		943
		944	This can be used to specify the event model to be used by AnyEvent, before
		945	autodetection and -probing kicks in. It must be a string consisting
		946	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		947	and the resulting module name is loaded and if the load was successful,
		948	used as event model. If it fails to load AnyEvent will proceed with
		949	autodetection and -probing.
		950
		951	This functionality might change in future versions.
		952
		953	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		954	could start your program like this:
		955
		956	PERL_ANYEVENT_MODEL=Perl perl ...
		957
		958	=back
		959
525	=head1 EXAMPLE	960	=head1 EXAMPLE PROGRAM
526		961
527	The following program uses an io watcher to read data from stdin, a timer	962	The following program uses an I/O watcher to read data from STDIN, a timer
528	to display a message once per second, and a condvar to exit the program	963	to display a message once per second, and a condition variable to quit the
529	when the user enters quit:	964	program when the user enters quit:
530		965
531	use AnyEvent;	966	use AnyEvent;
532		967
533	my $cv = AnyEvent->condvar;	968	my $cv = AnyEvent->condvar;
534		969
535	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	970	my $io_watcher = AnyEvent->io (
		971	fh => \*STDIN,
		972	poll => 'r',
		973	cb => sub {
536	warn "io event <$_[0]>\n"; # will always output <r>	974	warn "io event <$_[0]>\n"; # will always output <r>
537	chomp (my $input = <STDIN>); # read a line	975	chomp (my $input = <STDIN>); # read a line
538	warn "read: $input\n"; # output what has been read	976	warn "read: $input\n"; # output what has been read
539	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	977	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
		978	},
540	});	979	);
541		980
542	my $time_watcher; # can only be used once	981	my $time_watcher; # can only be used once
543		982
544	sub new_timer {	983	sub new_timer {
545	$timer = AnyEvent->timer (after => 1, cb => sub {	984	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
627	$txn->{finished}->wait;	1066	$txn->{finished}->wait;
628	return $txn->{result};	1067	return $txn->{result};
629		1068
630	The actual code goes further and collects all errors (C<die>s, exceptions)	1069	The actual code goes further and collects all errors (C<die>s, exceptions)
631	that occured during request processing. The C<result> method detects	1070	that occured during request processing. The C<result> method detects
632	wether an exception as thrown (it is stored inside the $txn object)	1071	whether an exception as thrown (it is stored inside the $txn object)
633	and just throws the exception, which means connection errors and other	1072	and just throws the exception, which means connection errors and other
634	problems get reported tot he code that tries to use the result, not in a	1073	problems get reported tot he code that tries to use the result, not in a
635	random callback.	1074	random callback.
636		1075
637	All of this enables the following usage styles:	1076	All of this enables the following usage styles:
…		…
672	$quit->broadcast;	1111	$quit->broadcast;
673	});	1112	});
674		1113
675	$quit->wait;	1114	$quit->wait;
676		1115
		1116
		1117	=head1 BENCHMARKS
		1118
		1119	To give you an idea of the performance and overheads that AnyEvent adds
		1120	over the event loops themselves and to give you an impression of the speed
		1121	of various event loops I prepared some benchmarks.
		1122
		1123	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1124
		1125	Here is a benchmark of various supported event models used natively and
		1126	through anyevent. The benchmark creates a lot of timers (with a zero
		1127	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1128	which it is), lets them fire exactly once and destroys them again.
		1129
		1130	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1131	distribution.
		1132
		1133	=head3 Explanation of the columns
		1134
		1135	I<watcher> is the number of event watchers created/destroyed. Since
		1136	different event models feature vastly different performances, each event
		1137	loop was given a number of watchers so that overall runtime is acceptable
		1138	and similar between tested event loop (and keep them from crashing): Glib
		1139	would probably take thousands of years if asked to process the same number
		1140	of watchers as EV in this benchmark.
		1141
		1142	I<bytes> is the number of bytes (as measured by the resident set size,
		1143	RSS) consumed by each watcher. This method of measuring captures both C
		1144	and Perl-based overheads.
		1145
		1146	I<create> is the time, in microseconds (millionths of seconds), that it
		1147	takes to create a single watcher. The callback is a closure shared between
		1148	all watchers, to avoid adding memory overhead. That means closure creation
		1149	and memory usage is not included in the figures.
		1150
		1151	I<invoke> is the time, in microseconds, used to invoke a simple
		1152	callback. The callback simply counts down a Perl variable and after it was
		1153	invoked "watcher" times, it would C<< ->broadcast >> a condvar once to
		1154	signal the end of this phase.
		1155
		1156	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1157	watcher.
		1158
		1159	=head3 Results
		1160
		1161	name watchers bytes create invoke destroy comment
		1162	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1163	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1164	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1165	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1166	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1167	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1168	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1169	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1170	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1171	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1172
		1173	=head3 Discussion
		1174
		1175	The benchmark does I<not> measure scalability of the event loop very
		1176	well. For example, a select-based event loop (such as the pure perl one)
		1177	can never compete with an event loop that uses epoll when the number of
		1178	file descriptors grows high. In this benchmark, all events become ready at
		1179	the same time, so select/poll-based implementations get an unnatural speed
		1180	boost.
		1181
		1182	Also, note that the number of watchers usually has a nonlinear effect on
		1183	overall speed, that is, creating twice as many watchers doesn't take twice
		1184	the time - usually it takes longer. This puts event loops tested with a
		1185	higher number of watchers at a disadvantage.
		1186
		1187	To put the range of results into perspective, consider that on the
		1188	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1189	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1190	cycles with POE.
		1191
		1192	C<EV> is the sole leader regarding speed and memory use, which are both
		1193	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1194	far less memory than any other event loop and is still faster than Event
		1195	natively.
		1196
		1197	The pure perl implementation is hit in a few sweet spots (both the
		1198	constant timeout and the use of a single fd hit optimisations in the perl
		1199	interpreter and the backend itself). Nevertheless this shows that it
		1200	adds very little overhead in itself. Like any select-based backend its
		1201	performance becomes really bad with lots of file descriptors (and few of
		1202	them active), of course, but this was not subject of this benchmark.
		1203
		1204	The C<Event> module has a relatively high setup and callback invocation
		1205	cost, but overall scores in on the third place.
		1206
		1207	C<Glib>'s memory usage is quite a bit higher, but it features a
		1208	faster callback invocation and overall ends up in the same class as
		1209	C<Event>. However, Glib scales extremely badly, doubling the number of
		1210	watchers increases the processing time by more than a factor of four,
		1211	making it completely unusable when using larger numbers of watchers
		1212	(note that only a single file descriptor was used in the benchmark, so
		1213	inefficiencies of C<poll> do not account for this).
		1214
		1215	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1216	more than 2000 watchers is a big setback, however, as correctness takes
		1217	precedence over speed. Nevertheless, its performance is surprising, as the
		1218	file descriptor is dup()ed for each watcher. This shows that the dup()
		1219	employed by some adaptors is not a big performance issue (it does incur a
		1220	hidden memory cost inside the kernel which is not reflected in the figures
		1221	above).
		1222
		1223	C<POE>, regardless of underlying event loop (whether using its pure perl
		1224	select-based backend or the Event module, the POE-EV backend couldn't
		1225	be tested because it wasn't working) shows abysmal performance and
		1226	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1227	as EV watchers, and 10 times as much memory as Event (the high memory
		1228	requirements are caused by requiring a session for each watcher). Watcher
		1229	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1230	implementation.
		1231
		1232	The design of the POE adaptor class in AnyEvent can not really account
		1233	for the performance issues, though, as session creation overhead is
		1234	small compared to execution of the state machine, which is coded pretty
		1235	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1236	using multiple sessions is not a good approach, especially regarding
		1237	memory usage, even the author of POE could not come up with a faster
		1238	design).
		1239
		1240	=head3 Summary
		1241
		1242	=over 4
		1243
		1244	=item * Using EV through AnyEvent is faster than any other event loop
		1245	(even when used without AnyEvent), but most event loops have acceptable
		1246	performance with or without AnyEvent.
		1247
		1248	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1249	the actual event loop, only with extremely fast event loops such as EV
		1250	adds AnyEvent significant overhead.
		1251
		1252	=item * You should avoid POE like the plague if you want performance or
		1253	reasonable memory usage.
		1254
		1255	=back
		1256
		1257	=head2 BENCHMARKING THE LARGE SERVER CASE
		1258
		1259	This benchmark atcually benchmarks the event loop itself. It works by
		1260	creating a number of "servers": each server consists of a socketpair, a
		1261	timeout watcher that gets reset on activity (but never fires), and an I/O
		1262	watcher waiting for input on one side of the socket. Each time the socket
		1263	watcher reads a byte it will write that byte to a random other "server".
		1264
		1265	The effect is that there will be a lot of I/O watchers, only part of which
		1266	are active at any one point (so there is a constant number of active
		1267	fds for each loop iterstaion, but which fds these are is random). The
		1268	timeout is reset each time something is read because that reflects how
		1269	most timeouts work (and puts extra pressure on the event loops).
		1270
		1271	In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100
		1272	(1%) are active. This mirrors the activity of large servers with many
		1273	connections, most of which are idle at any one point in time.
		1274
		1275	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1276	distribution.
		1277
		1278	=head3 Explanation of the columns
		1279
		1280	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1281	each server has a read and write socket end).
		1282
		1283	I<create> is the time it takes to create a socketpair (which is
		1284	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1285
		1286	I<request>, the most important value, is the time it takes to handle a
		1287	single "request", that is, reading the token from the pipe and forwarding
		1288	it to another server. This includes deleting the old timeout and creating
		1289	a new one that moves the timeout into the future.
		1290
		1291	=head3 Results
		1292
		1293	name sockets create request
		1294	EV 20000 69.01 11.16
		1295	Perl 20000 73.32 35.87
		1296	Event 20000 212.62 257.32
		1297	Glib 20000 651.16 1896.30
		1298	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1299
		1300	=head3 Discussion
		1301
		1302	This benchmark I<does> measure scalability and overall performance of the
		1303	particular event loop.
		1304
		1305	EV is again fastest. Since it is using epoll on my system, the setup time
		1306	is relatively high, though.
		1307
		1308	Perl surprisingly comes second. It is much faster than the C-based event
		1309	loops Event and Glib.
		1310
		1311	Event suffers from high setup time as well (look at its code and you will
		1312	understand why). Callback invocation also has a high overhead compared to
		1313	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1314	uses select or poll in basically all documented configurations.
		1315
		1316	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1317	clearly fails to perform with many filehandles or in busy servers.
		1318
		1319	POE is still completely out of the picture, taking over 1000 times as long
		1320	as EV, and over 100 times as long as the Perl implementation, even though
		1321	it uses a C-based event loop in this case.
		1322
		1323	=head3 Summary
		1324
		1325	=over 4
		1326
		1327	=item * The pure perl implementation performs extremely well.
		1328
		1329	=item * Avoid Glib or POE in large projects where performance matters.
		1330
		1331	=back
		1332
		1333	=head2 BENCHMARKING SMALL SERVERS
		1334
		1335	While event loops should scale (and select-based ones do not...) even to
		1336	large servers, most programs we (or I :) actually write have only a few
		1337	I/O watchers.
		1338
		1339	In this benchmark, I use the same benchmark program as in the large server
		1340	case, but it uses only eight "servers", of which three are active at any
		1341	one time. This should reflect performance for a small server relatively
		1342	well.
		1343
		1344	The columns are identical to the previous table.
		1345
		1346	=head3 Results
		1347
		1348	name sockets create request
		1349	EV 16 20.00 6.54
		1350	Perl 16 25.75 12.62
		1351	Event 16 81.27 35.86
		1352	Glib 16 32.63 15.48
		1353	POE 16 261.87 276.28 uses POE::Loop::Event
		1354
		1355	=head3 Discussion
		1356
		1357	The benchmark tries to test the performance of a typical small
		1358	server. While knowing how various event loops perform is interesting, keep
		1359	in mind that their overhead in this case is usually not as important, due
		1360	to the small absolute number of watchers (that is, you need efficiency and
		1361	speed most when you have lots of watchers, not when you only have a few of
		1362	them).
		1363
		1364	EV is again fastest.
		1365
		1366	Perl again comes second. It is noticably faster than the C-based event
		1367	loops Event and Glib, although the difference is too small to really
		1368	matter.
		1369
		1370	POE also performs much better in this case, but is is still far behind the
		1371	others.
		1372
		1373	=head3 Summary
		1374
		1375	=over 4
		1376
		1377	=item * C-based event loops perform very well with small number of
		1378	watchers, as the management overhead dominates.
		1379
		1380	=back
		1381
		1382
		1383	=head1 FORK
		1384
		1385	Most event libraries are not fork-safe. The ones who are usually are
		1386	because they rely on inefficient but fork-safe C<select> or C<poll>
		1387	calls. Only L<EV> is fully fork-aware.
		1388
		1389	If you have to fork, you must either do so I<before> creating your first
		1390	watcher OR you must not use AnyEvent at all in the child.
		1391
		1392
		1393	=head1 SECURITY CONSIDERATIONS
		1394
		1395	AnyEvent can be forced to load any event model via
		1396	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1397	execute arbitrary code or directly gain access, it can easily be used to
		1398	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1399	will not be active when the program uses a different event model than
		1400	specified in the variable.
		1401
		1402	You can make AnyEvent completely ignore this variable by deleting it
		1403	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1404
		1405	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1406
		1407	use AnyEvent;
		1408
		1409	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1410	be used to probe what backend is used and gain other information (which is
		1411	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1412
		1413
677	=head1 SEE ALSO	1414	=head1 SEE ALSO
678		1415
679	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1416	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
680	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.	1417	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
681		1418
682	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
683	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1419	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
684	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	1420	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1421	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1422	L<AnyEvent::Impl::POE>.
		1423
		1424	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
685		1425
686	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1426	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
687		1427
688	=head1	1428
		1429	=head1 AUTHOR
		1430
		1431	Marc Lehmann <schmorp@schmorp.de>
		1432	http://home.schmorp.de/
689		1433
690	=cut	1434	=cut
691		1435
692	1	1436	1
693		1437

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.50 by root, Wed Apr 16 14:04:45 2008 UTC vs.
Revision 1.108 by root, Sat May 10 00:22:02 2008 UTC