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Revision 1.52 by root, Sat Apr 19 03:47:24 2008 UTC vs.
Revision 1.147 by root, Fri May 30 21:43:26 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
…		…
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 whether 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		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 enormous 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
		67	Of course, AnyEvent comes with a big (and fully optional!) toolbox
		68	of useful functionality, such as an asynchronous DNS resolver, 100%
		69	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		70	such as Windows) and lots of real-world knowledge and workarounds for
		71	platform bugs and differences.
		72
63	Of course, if you want lots of policy (this can arguably be somewhat	73	Now, if you I<do 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	74	useful) and you want to force your users to use the one and only event
65	model, you should I<not> use this module.	75	model, you should I<not> use this module.
66
67		76
68	=head1 DESCRIPTION	77	=head1 DESCRIPTION
69		78
70	L<AnyEvent> provides an identical interface to multiple event loops. This	79	L<AnyEvent> provides an identical interface to multiple event loops. This
71	allows module authors to utilise an event loop without forcing module	80	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	81	users to use the same event loop (as only a single event loop can coexist
73	peacefully at any one time).	82	peacefully at any one time).
74		83
75	The interface itself is vaguely similar but not identical to the Event	84	The interface itself is vaguely similar, but not identical to the L<Event>
76	module.	85	module.
77		86
78	On the first call of any method, the module tries to detect the currently	87	During the first call of any watcher-creation method, the module tries
79	loaded event loop by probing whether any of the following modules is	88	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	89	following modules is already loaded: L<EV>,
		90	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	91	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	92	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	93	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.	94	be successfully loaded will be used. If, after this, still none could be
		95	found, AnyEvent will fall back to a pure-perl event loop, which is not
		96	very efficient, but should work everywhere.
85		97
86	Because AnyEvent first checks for modules that are already loaded, loading	98	Because AnyEvent first checks for modules that are already loaded, loading
87	an Event model explicitly before first using AnyEvent will likely make	99	an event model explicitly before first using AnyEvent will likely make
88	that model the default. For example:	100	that model the default. For example:
89		101
90	use Tk;	102	use Tk;
91	use AnyEvent;	103	use AnyEvent;
92		104
93	# .. AnyEvent will likely default to Tk	105	# .. AnyEvent will likely default to Tk
94		106
		107	The I<likely> means that, if any module loads another event model and
		108	starts using it, all bets are off. Maybe you should tell their authors to
		109	use AnyEvent so their modules work together with others seamlessly...
		110
95	The pure-perl implementation of AnyEvent is called	111	The pure-perl implementation of AnyEvent is called
96	C<AnyEvent::Impl::Perl>. Like other event modules you can load it	112	C<AnyEvent::Impl::Perl>. Like other event modules you can load it
97	explicitly.	113	explicitly and enjoy the high availability of that event loop :)
98		114
99	=head1 WATCHERS	115	=head1 WATCHERS
100		116
101	AnyEvent has the central concept of a I<watcher>, which is an object that	117	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	118	stores relevant data for each kind of event you are waiting for, such as
103	the callback to call, the filehandle to watch, etc.	119	the callback to call, the file handle to watch, etc.
104		120
105	These watchers are normal Perl objects with normal Perl lifetime. After	121	These watchers are normal Perl objects with normal Perl lifetime. After
106	creating a watcher it will immediately "watch" for events and invoke	122	creating a watcher it will immediately "watch" for events and invoke the
		123	callback when the event occurs (of course, only when the event model
		124	is in control).
		125
107	the callback. To disable the watcher you have to destroy it (e.g. by	126	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	127	variable you store it in to C<undef> or otherwise deleting all references
109	references to it).	128	to it).
110		129
111	All watchers are created by calling a method on the C<AnyEvent> class.	130	All watchers are created by calling a method on the C<AnyEvent> class.
112		131
		132	Many watchers either are used with "recursion" (repeating timers for
		133	example), or need to refer to their watcher object in other ways.
		134
		135	An any way to achieve that is this pattern:
		136
		137	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		138	# you can use $w here, for example to undef it
		139	undef $w;
		140	});
		141
		142	Note that C<my $w; $w => combination. This is necessary because in Perl,
		143	my variables are only visible after the statement in which they are
		144	declared.
		145
113	=head2 IO WATCHERS	146	=head2 I/O WATCHERS
114		147
115	You can create I/O watcher by calling the C<< AnyEvent->io >> method with	148	You can create an I/O watcher by calling the C<< AnyEvent->io >> method
116	the following mandatory arguments:	149	with the following mandatory key-value pairs as arguments:
117		150
118	C<fh> the Perl I<filehandle> (not filedescriptor) to watch for	151	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	152	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	153	which creates a watcher waiting for "r"eadable or "w"ritable events,
121	to invoke everytime the filehandle becomes ready.	154	respectively. C<cb> is the callback to invoke each time the file handle
		155	becomes ready.
122		156
123	Filehandles will be kept alive, so as long as the watcher exists, the	157	Although the callback might get passed parameters, their value and
124	filehandle exists, too.	158	presence is undefined and you cannot rely on them. Portable AnyEvent
		159	callbacks cannot use arguments passed to I/O watcher callbacks.
		160
		161	The I/O watcher might use the underlying file descriptor or a copy of it.
		162	You must not close a file handle as long as any watcher is active on the
		163	underlying file descriptor.
		164
		165	Some event loops issue spurious readyness notifications, so you should
		166	always use non-blocking calls when reading/writing from/to your file
		167	handles.
125		168
126	Example:	169	Example:
127		170
128	# wait for readability of STDIN, then read a line and disable the watcher	171	# 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 {	172	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
135	=head2 TIME WATCHERS	178	=head2 TIME WATCHERS
136		179
137	You can create a time watcher by calling the C<< AnyEvent->timer >>	180	You can create a time watcher by calling the C<< AnyEvent->timer >>
138	method with the following mandatory arguments:	181	method with the following mandatory arguments:
139		182
140	C<after> after how many seconds (fractions are supported) should the timer	183	C<after> specifies after how many seconds (fractional values are
141	activate. C<cb> the callback to invoke.	184	supported) the callback should be invoked. C<cb> is the callback to invoke
		185	in that case.
		186
		187	Although the callback might get passed parameters, their value and
		188	presence is undefined and you cannot rely on them. Portable AnyEvent
		189	callbacks cannot use arguments passed to time watcher callbacks.
142		190
143	The timer callback will be invoked at most once: if you want a repeating	191	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	192	timer you have to create a new watcher (this is a limitation by both Tk
145	and Glib).	193	and Glib).
146		194
…		…
152	});	200	});
153		201
154	# to cancel the timer:	202	# to cancel the timer:
155	undef $w;	203	undef $w;
156		204
157	=head2 CONDITION WATCHERS	205	Example 2:
158		206
159	Condition watchers can be created by calling the C<< AnyEvent->condvar >>	207	# fire an event after 0.5 seconds, then roughly every second
160	method without any arguments.	208	my $w;
161		209
162	A condition watcher watches for a condition - precisely that the C<<	210	my $cb = sub {
163	->broadcast >> method has been called.	211	# cancel the old timer while creating a new one
		212	$w = AnyEvent->timer (after => 1, cb => $cb);
		213	};
164		214
165	Note that condition watchers recurse into the event loop - if you have	215	# start the "loop" by creating the first watcher
166	two watchers that call C<< ->wait >> in a round-robbin fashion, you	216	$w = AnyEvent->timer (after => 0.5, cb => $cb);
167	lose. Therefore, condition watchers are good to export to your caller, but
168	you should avoid making a blocking wait, at least in callbacks, as this
169	usually asks for trouble.
170		217
171	The watcher has only two methods:	218	=head3 TIMING ISSUES
		219
		220	There are two ways to handle timers: based on real time (relative, "fire
		221	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		222	o'clock").
		223
		224	While most event loops expect timers to specified in a relative way, they
		225	use absolute time internally. This makes a difference when your clock
		226	"jumps", for example, when ntp decides to set your clock backwards from
		227	the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
		228	fire "after" a second might actually take six years to finally fire.
		229
		230	AnyEvent cannot compensate for this. The only event loop that is conscious
		231	about these issues is L<EV>, which offers both relative (ev_timer, based
		232	on true relative time) and absolute (ev_periodic, based on wallclock time)
		233	timers.
		234
		235	AnyEvent always prefers relative timers, if available, matching the
		236	AnyEvent API.
		237
		238	AnyEvent has two additional methods that return the "current time":
172		239
173	=over 4	240	=over 4
174		241
		242	=item AnyEvent->time
		243
		244	This returns the "current wallclock time" as a fractional number of
		245	seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
		246	return, and the result is guaranteed to be compatible with those).
		247
		248	It progresses independently of any event loop processing, i.e. each call
		249	will check the system clock, which usually gets updated frequently.
		250
		251	=item AnyEvent->now
		252
		253	This also returns the "current wallclock time", but unlike C<time>, above,
		254	this value might change only once per event loop iteration, depending on
		255	the event loop (most return the same time as C<time>, above). This is the
		256	time that AnyEvent's timers get scheduled against.
		257
		258	I<In almost all cases (in all cases if you don't care), this is the
		259	function to call when you want to know the current time.>
		260
		261	This function is also often faster then C<< AnyEvent->time >>, and
		262	thus the preferred method if you want some timestamp (for example,
		263	L<AnyEvent::Handle> uses this to update it's activity timeouts).
		264
		265	The rest of this section is only of relevance if you try to be very exact
		266	with your timing, you can skip it without bad conscience.
		267
		268	For a practical example of when these times differ, consider L<Event::Lib>
		269	and L<EV> and the following set-up:
		270
		271	The event loop is running and has just invoked one of your callback at
		272	time=500 (assume no other callbacks delay processing). In your callback,
		273	you wait a second by executing C<sleep 1> (blocking the process for a
		274	second) and then (at time=501) you create a relative timer that fires
		275	after three seconds.
		276
		277	With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
		278	both return C<501>, because that is the current time, and the timer will
		279	be scheduled to fire at time=504 (C<501> + C<3>).
		280
		281	With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
		282	time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
		283	last event processing phase started. With L<EV>, your timer gets scheduled
		284	to run at time=503 (C<500> + C<3>).
		285
		286	In one sense, L<Event::Lib> is more exact, as it uses the current time
		287	regardless of any delays introduced by event processing. However, most
		288	callbacks do not expect large delays in processing, so this causes a
		289	higher drift (and a lot more system calls to get the current time).
		290
		291	In another sense, L<EV> is more exact, as your timer will be scheduled at
		292	the same time, regardless of how long event processing actually took.
		293
		294	In either case, if you care (and in most cases, you don't), then you
		295	can get whatever behaviour you want with any event loop, by taking the
		296	difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
		297	account.
		298
		299	=back
		300
		301	=head2 SIGNAL WATCHERS
		302
		303	You can watch for signals using a signal watcher, C<signal> is the signal
		304	I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
		305	be invoked whenever a signal occurs.
		306
		307	Although the callback might get passed parameters, their value and
		308	presence is undefined and you cannot rely on them. Portable AnyEvent
		309	callbacks cannot use arguments passed to signal watcher callbacks.
		310
		311	Multiple signal occurrences can be clumped together into one callback
		312	invocation, and callback invocation will be synchronous. Synchronous means
		313	that it might take a while until the signal gets handled by the process,
		314	but it is guaranteed not to interrupt any other callbacks.
		315
		316	The main advantage of using these watchers is that you can share a signal
		317	between multiple watchers.
		318
		319	This watcher might use C<%SIG>, so programs overwriting those signals
		320	directly will likely not work correctly.
		321
		322	Example: exit on SIGINT
		323
		324	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		325
		326	=head2 CHILD PROCESS WATCHERS
		327
		328	You can also watch on a child process exit and catch its exit status.
		329
		330	The child process is specified by the C<pid> argument (if set to C<0>, it
		331	watches for any child process exit). The watcher will trigger as often
		332	as status change for the child are received. This works by installing a
		333	signal handler for C<SIGCHLD>. The callback will be called with the pid
		334	and exit status (as returned by waitpid), so unlike other watcher types,
		335	you I<can> rely on child watcher callback arguments.
		336
		337	There is a slight catch to child watchers, however: you usually start them
		338	I<after> the child process was created, and this means the process could
		339	have exited already (and no SIGCHLD will be sent anymore).
		340
		341	Not all event models handle this correctly (POE doesn't), but even for
		342	event models that I<do> handle this correctly, they usually need to be
		343	loaded before the process exits (i.e. before you fork in the first place).
		344
		345	This means you cannot create a child watcher as the very first thing in an
		346	AnyEvent program, you I<have> to create at least one watcher before you
		347	C<fork> the child (alternatively, you can call C<AnyEvent::detect>).
		348
		349	Example: fork a process and wait for it
		350
		351	my $done = AnyEvent->condvar;
		352
		353	my $pid = fork or exit 5;
		354
		355	my $w = AnyEvent->child (
		356	pid => $pid,
		357	cb => sub {
		358	my ($pid, $status) = @_;
		359	warn "pid $pid exited with status $status";
		360	$done->send;
		361	},
		362	);
		363
		364	# do something else, then wait for process exit
		365	$done->recv;
		366
		367	=head2 CONDITION VARIABLES
		368
		369	If you are familiar with some event loops you will know that all of them
		370	require you to run some blocking "loop", "run" or similar function that
		371	will actively watch for new events and call your callbacks.
		372
		373	AnyEvent is different, it expects somebody else to run the event loop and
		374	will only block when necessary (usually when told by the user).
		375
		376	The instrument to do that is called a "condition variable", so called
		377	because they represent a condition that must become true.
		378
		379	Condition variables can be created by calling the C<< AnyEvent->condvar
		380	>> method, usually without arguments. The only argument pair allowed is
		381	C<cb>, which specifies a callback to be called when the condition variable
		382	becomes true.
		383
		384	After creation, the condition variable is "false" until it becomes "true"
		385	by calling the C<send> method (or calling the condition variable as if it
		386	were a callback, read about the caveats in the description for the C<<
		387	->send >> method).
		388
		389	Condition variables are similar to callbacks, except that you can
		390	optionally wait for them. They can also be called merge points - points
		391	in time where multiple outstanding events have been processed. And yet
		392	another way to call them is transactions - each condition variable can be
		393	used to represent a transaction, which finishes at some point and delivers
		394	a result.
		395
		396	Condition variables are very useful to signal that something has finished,
		397	for example, if you write a module that does asynchronous http requests,
		398	then a condition variable would be the ideal candidate to signal the
		399	availability of results. The user can either act when the callback is
		400	called or can synchronously C<< ->recv >> for the results.
		401
		402	You can also use them to simulate traditional event loops - for example,
		403	you can block your main program until an event occurs - for example, you
		404	could C<< ->recv >> in your main program until the user clicks the Quit
		405	button of your app, which would C<< ->send >> the "quit" event.
		406
		407	Note that condition variables recurse into the event loop - if you have
		408	two pieces of code that call C<< ->recv >> in a round-robin fashion, you
		409	lose. Therefore, condition variables are good to export to your caller, but
		410	you should avoid making a blocking wait yourself, at least in callbacks,
		411	as this asks for trouble.
		412
		413	Condition variables are represented by hash refs in perl, and the keys
		414	used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
		415	easy (it is often useful to build your own transaction class on top of
		416	AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
		417	it's C<new> method in your own C<new> method.
		418
		419	There are two "sides" to a condition variable - the "producer side" which
		420	eventually calls C<< -> send >>, and the "consumer side", which waits
		421	for the send to occur.
		422
		423	Example: wait for a timer.
		424
		425	# wait till the result is ready
		426	my $result_ready = AnyEvent->condvar;
		427
		428	# do something such as adding a timer
		429	# or socket watcher the calls $result_ready->send
		430	# when the "result" is ready.
		431	# in this case, we simply use a timer:
		432	my $w = AnyEvent->timer (
		433	after => 1,
		434	cb => sub { $result_ready->send },
		435	);
		436
		437	# this "blocks" (while handling events) till the callback
		438	# calls send
		439	$result_ready->recv;
		440
		441	Example: wait for a timer, but take advantage of the fact that
		442	condition variables are also code references.
		443
		444	my $done = AnyEvent->condvar;
		445	my $delay = AnyEvent->timer (after => 5, cb => $done);
		446	$done->recv;
		447
		448	=head3 METHODS FOR PRODUCERS
		449
		450	These methods should only be used by the producing side, i.e. the
		451	code/module that eventually sends the signal. Note that it is also
		452	the producer side which creates the condvar in most cases, but it isn't
		453	uncommon for the consumer to create it as well.
		454
		455	=over 4
		456
		457	=item $cv->send (...)
		458
		459	Flag the condition as ready - a running C<< ->recv >> and all further
		460	calls to C<recv> will (eventually) return after this method has been
		461	called. If nobody is waiting the send will be remembered.
		462
		463	If a callback has been set on the condition variable, it is called
		464	immediately from within send.
		465
		466	Any arguments passed to the C<send> call will be returned by all
		467	future C<< ->recv >> calls.
		468
		469	Condition variables are overloaded so one can call them directly
		470	(as a code reference). Calling them directly is the same as calling
		471	C<send>. Note, however, that many C-based event loops do not handle
		472	overloading, so as tempting as it may be, passing a condition variable
		473	instead of a callback does not work. Both the pure perl and EV loops
		474	support overloading, however, as well as all functions that use perl to
		475	invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
		476	example).
		477
		478	=item $cv->croak ($error)
		479
		480	Similar to send, but causes all call's to C<< ->recv >> to invoke
		481	C<Carp::croak> with the given error message/object/scalar.
		482
		483	This can be used to signal any errors to the condition variable
		484	user/consumer.
		485
		486	=item $cv->begin ([group callback])
		487
175	=item $cv->wait	488	=item $cv->end
176		489
177	Wait (blocking if necessary) until the C<< ->broadcast >> method has been	490	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		491
		492	These two methods can be used to combine many transactions/events into
		493	one. For example, a function that pings many hosts in parallel might want
		494	to use a condition variable for the whole process.
		495
		496	Every call to C<< ->begin >> will increment a counter, and every call to
		497	C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end
		498	>>, the (last) callback passed to C<begin> will be executed. That callback
		499	is I<supposed> to call C<< ->send >>, but that is not required. If no
		500	callback was set, C<send> will be called without any arguments.
		501
		502	Let's clarify this with the ping example:
		503
		504	my $cv = AnyEvent->condvar;
		505
		506	my %result;
		507	$cv->begin (sub { $cv->send (\%result) });
		508
		509	for my $host (@list_of_hosts) {
		510	$cv->begin;
		511	ping_host_then_call_callback $host, sub {
		512	$result{$host} = ...;
		513	$cv->end;
		514	};
		515	}
		516
		517	$cv->end;
		518
		519	This code fragment supposedly pings a number of hosts and calls
		520	C<send> after results for all then have have been gathered - in any
		521	order. To achieve this, the code issues a call to C<begin> when it starts
		522	each ping request and calls C<end> when it has received some result for
		523	it. Since C<begin> and C<end> only maintain a counter, the order in which
		524	results arrive is not relevant.
		525
		526	There is an additional bracketing call to C<begin> and C<end> outside the
		527	loop, which serves two important purposes: first, it sets the callback
		528	to be called once the counter reaches C<0>, and second, it ensures that
		529	C<send> is called even when C<no> hosts are being pinged (the loop
		530	doesn't execute once).
		531
		532	This is the general pattern when you "fan out" into multiple subrequests:
		533	use an outer C<begin>/C<end> pair to set the callback and ensure C<end>
		534	is called at least once, and then, for each subrequest you start, call
		535	C<begin> and for each subrequest you finish, call C<end>.
		536
		537	=back
		538
		539	=head3 METHODS FOR CONSUMERS
		540
		541	These methods should only be used by the consuming side, i.e. the
		542	code awaits the condition.
		543
		544	=over 4
		545
		546	=item $cv->recv
		547
		548	Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
178	called on c<$cv>, while servicing other watchers normally.	549	>> methods have been called on c<$cv>, while servicing other watchers
		550	normally.
179		551
180	You can only wait once on a condition - additional calls will return	552	You can only wait once on a condition - additional calls are valid but
181	immediately.	553	will return immediately.
		554
		555	If an error condition has been set by calling C<< ->croak >>, then this
		556	function will call C<croak>.
		557
		558	In list context, all parameters passed to C<send> will be returned,
		559	in scalar context only the first one will be returned.
182		560
183	Not all event models support a blocking wait - some die in that case	561	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	562	(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	563	using this from a module, never require a blocking wait>, but let the
186	caller decide whether the call will block or not (for example, by coupling	564	caller decide whether the call will block or not (for example, by coupling
187	condition variables with some kind of request results and supporting	565	condition variables with some kind of request results and supporting
188	callbacks so the caller knows that getting the result will not block,	566	callbacks so the caller knows that getting the result will not block,
189	while still suppporting blocking waits if the caller so desires).	567	while still supporting blocking waits if the caller so desires).
190		568
191	Another reason I<never> to C<< ->wait >> in a module is that you cannot	569	Another reason I<never> to C<< ->recv >> in a module is that you cannot
192	sensibly have two C<< ->wait >>'s in parallel, as that would require	570	sensibly have two C<< ->recv >>'s in parallel, as that would require
193	multiple interpreters or coroutines/threads, none of which C<AnyEvent>	571	multiple interpreters or coroutines/threads, none of which C<AnyEvent>
194	can supply (the coroutine-aware backends C<Coro::EV> and C<Coro::Event>	572	can supply.
195	explicitly support concurrent C<< ->wait >>'s from different coroutines,
196	however).
197		573
198	=item $cv->broadcast	574	The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
		575	fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
		576	versions and also integrates coroutines into AnyEvent, making blocking
		577	C<< ->recv >> calls perfectly safe as long as they are done from another
		578	coroutine (one that doesn't run the event loop).
199		579
200	Flag the condition as ready - a running C<< ->wait >> and all further	580	You can ensure that C<< -recv >> never blocks by setting a callback and
201	calls to C<wait> will return after this method has been called. If nobody	581	only calling C<< ->recv >> from within that callback (or at a later
202	is waiting the broadcast will be remembered..	582	time). This will work even when the event loop does not support blocking
		583	waits otherwise.
203		584
204	Example:	585	=item $bool = $cv->ready
205		586
206	# wait till the result is ready	587	Returns true when the condition is "true", i.e. whether C<send> or
207	my $result_ready = AnyEvent->condvar;	588	C<croak> have been called.
208		589
209	# do something such as adding a timer	590	=item $cb = $cv->cb ([new callback])
210	# or socket watcher the calls $result_ready->broadcast
211	# when the "result" is ready.
212		591
213	$result_ready->wait;	592	This is a mutator function that returns the callback set and optionally
		593	replaces it before doing so.
		594
		595	The callback will be called when the condition becomes "true", i.e. when
		596	C<send> or C<croak> are called. Calling C<recv> inside the callback
		597	or at any later time is guaranteed not to block.
214		598
215	=back	599	=back
216		600
217	=head2 SIGNAL WATCHERS	601	=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		602
245	=over 4	603	=over 4
246		604
247	=item $AnyEvent::MODEL	605	=item $AnyEvent::MODEL
248		606
…		…
252	C<AnyEvent::Impl:xxx> modules, but can be any other class in the case	610	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>).	611	AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
254		612
255	The known classes so far are:	613	The known classes so far are:
256		614
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).	615	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
260	AnyEvent::Impl::Event based on Event, also second best choice :)	616	AnyEvent::Impl::Event based on Event, second best choice.
		617	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
261	AnyEvent::Impl::Glib based on Glib, third-best choice.	618	AnyEvent::Impl::Glib based on Glib, third-best choice.
262	AnyEvent::Impl::Tk based on Tk, very bad choice.	619	AnyEvent::Impl::Tk based on Tk, very bad choice.
263	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	620	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		621	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		622	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		623
		624	There is no support for WxWidgets, as WxWidgets has no support for
		625	watching file handles. However, you can use WxWidgets through the
		626	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		627	second, which was considered to be too horrible to even consider for
		628	AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
		629	it's adaptor.
		630
		631	AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
		632	autodetecting them.
264		633
265	=item AnyEvent::detect	634	=item AnyEvent::detect
266		635
267	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if	636	Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
268	necessary. You should only call this function right before you would have	637	if necessary. You should only call this function right before you would
269	created an AnyEvent watcher anyway, that is, very late at runtime.	638	have created an AnyEvent watcher anyway, that is, as late as possible at
		639	runtime.
		640
		641	=item $guard = AnyEvent::post_detect { BLOCK }
		642
		643	Arranges for the code block to be executed as soon as the event model is
		644	autodetected (or immediately if this has already happened).
		645
		646	If called in scalar or list context, then it creates and returns an object
		647	that automatically removes the callback again when it is destroyed. See
		648	L<Coro::BDB> for a case where this is useful.
		649
		650	=item @AnyEvent::post_detect
		651
		652	If there are any code references in this array (you can C<push> to it
		653	before or after loading AnyEvent), then they will called directly after
		654	the event loop has been chosen.
		655
		656	You should check C<$AnyEvent::MODEL> before adding to this array, though:
		657	if it contains a true value then the event loop has already been detected,
		658	and the array will be ignored.
		659
		660	Best use C<AnyEvent::post_detect { BLOCK }> instead.
270		661
271	=back	662	=back
272		663
273	=head1 WHAT TO DO IN A MODULE	664	=head1 WHAT TO DO IN A MODULE
274		665
275	As a module author, you should "use AnyEvent" and call AnyEvent methods	666	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.	667	freely, but you should not load a specific event module or rely on it.
277		668
278	Be careful when you create watchers in the module body - Anyevent will	669	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	670	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	671	by calling AnyEvent in your module body you force the user of your module
281	to load the event module first.	672	to load the event module first.
282		673
		674	Never call C<< ->recv >> on a condition variable unless you I<know> that
		675	the C<< ->send >> method has been called on it already. This is
		676	because it will stall the whole program, and the whole point of using
		677	events is to stay interactive.
		678
		679	It is fine, however, to call C<< ->recv >> when the user of your module
		680	requests it (i.e. if you create a http request object ad have a method
		681	called C<results> that returns the results, it should call C<< ->recv >>
		682	freely, as the user of your module knows what she is doing. always).
		683
283	=head1 WHAT TO DO IN THE MAIN PROGRAM	684	=head1 WHAT TO DO IN THE MAIN PROGRAM
284		685
285	There will always be a single main program - the only place that should	686	There will always be a single main program - the only place that should
286	dictate which event model to use.	687	dictate which event model to use.
287		688
288	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	689	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.	690	do anything special (it does not need to be event-based) and let AnyEvent
		691	decide which implementation to chose if some module relies on it.
290		692
291	If the main program relies on a specific event model (for example, in Gtk2	693	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	694	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	695	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	696	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	697	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	698	decide on the event model to use as soon as it creates watchers, and it
297	correct one yourself.	699	might chose the wrong one unless you load the correct one yourself.
298		700
299	You can chose to use a rather inefficient pure-perl implementation by	701	You can chose to use a pure-perl implementation by loading the
300	loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is	702	C<AnyEvent::Impl::Perl> module, which gives you similar behaviour
301	generally better.	703	everywhere, but letting AnyEvent chose the model is generally better.
		704
		705	=head2 MAINLOOP EMULATION
		706
		707	Sometimes (often for short test scripts, or even standalone programs who
		708	only want to use AnyEvent), you do not want to run a specific event loop.
		709
		710	In that case, you can use a condition variable like this:
		711
		712	AnyEvent->condvar->recv;
		713
		714	This has the effect of entering the event loop and looping forever.
		715
		716	Note that usually your program has some exit condition, in which case
		717	it is better to use the "traditional" approach of storing a condition
		718	variable somewhere, waiting for it, and sending it when the program should
		719	exit cleanly.
		720
		721
		722	=head1 OTHER MODULES
		723
		724	The following is a non-exhaustive list of additional modules that use
		725	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		726	in the same program. Some of the modules come with AnyEvent, some are
		727	available via CPAN.
		728
		729	=over 4
		730
		731	=item L<AnyEvent::Util>
		732
		733	Contains various utility functions that replace often-used but blocking
		734	functions such as C<inet_aton> by event-/callback-based versions.
		735
		736	=item L<AnyEvent::Handle>
		737
		738	Provide read and write buffers and manages watchers for reads and writes.
		739
		740	=item L<AnyEvent::Socket>
		741
		742	Provides various utility functions for (internet protocol) sockets,
		743	addresses and name resolution. Also functions to create non-blocking tcp
		744	connections or tcp servers, with IPv6 and SRV record support and more.
		745
		746	=item L<AnyEvent::DNS>
		747
		748	Provides rich asynchronous DNS resolver capabilities.
		749
		750	=item L<AnyEvent::HTTPD>
		751
		752	Provides a simple web application server framework.
		753
		754	=item L<AnyEvent::FastPing>
		755
		756	The fastest ping in the west.
		757
		758	=item L<Net::IRC3>
		759
		760	AnyEvent based IRC client module family.
		761
		762	=item L<Net::XMPP2>
		763
		764	AnyEvent based XMPP (Jabber protocol) module family.
		765
		766	=item L<Net::FCP>
		767
		768	AnyEvent-based implementation of the Freenet Client Protocol, birthplace
		769	of AnyEvent.
		770
		771	=item L<Event::ExecFlow>
		772
		773	High level API for event-based execution flow control.
		774
		775	=item L<Coro>
		776
		777	Has special support for AnyEvent via L<Coro::AnyEvent>.
		778
		779	=item L<AnyEvent::AIO>, L<IO::AIO>
		780
		781	Truly asynchronous I/O, should be in the toolbox of every event
		782	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		783	together.
		784
		785	=item L<AnyEvent::BDB>, L<BDB>
		786
		787	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses
		788	IO::AIO and AnyEvent together.
		789
		790	=item L<IO::Lambda>
		791
		792	The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
		793
		794	=back
302		795
303	=cut	796	=cut
304		797
305	package AnyEvent;	798	package AnyEvent;
306		799
307	no warnings;	800	no warnings;
308	use strict;	801	use strict;
309		802
310	use Carp;	803	use Carp;
311		804
312	our $VERSION = '3.1';	805	our $VERSION = 4.11;
313	our $MODEL;	806	our $MODEL;
314		807
315	our $AUTOLOAD;	808	our $AUTOLOAD;
316	our @ISA;	809	our @ISA;
317		810
		811	our @REGISTRY;
		812
		813	our $WIN32;
		814
		815	BEGIN {
		816	my $win32 = ! ! ($^O =~ /mswin32/i);
		817	eval "sub WIN32(){ $win32 }";
		818	}
		819
318	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;	820	our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
319		821
320	our @REGISTRY;	822	our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
		823
		824	{
		825	my $idx;
		826	$PROTOCOL{$_} = ++$idx
		827	for reverse split /\s*,\s*/,
		828	$ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
		829	}
321		830
322	my @models = (	831	my @models = (
323	[Coro::EV:: => AnyEvent::Impl::CoroEV::],
324	[Coro::Event:: => AnyEvent::Impl::CoroEvent::],
325	[EV:: => AnyEvent::Impl::EV::],	832	[EV:: => AnyEvent::Impl::EV::],
326	[Event:: => AnyEvent::Impl::Event::],	833	[Event:: => AnyEvent::Impl::Event::],
327	[Glib:: => AnyEvent::Impl::Glib::],
328	[Tk:: => AnyEvent::Impl::Tk::],
329	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],	834	[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
		835	# everything below here will not be autoprobed
		836	# as the pureperl backend should work everywhere
		837	# and is usually faster
		838	[Tk:: => AnyEvent::Impl::Tk::], # crashes with many handles
		839	[Glib:: => AnyEvent::Impl::Glib::], # becomes extremely slow with many watchers
		840	[Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy
		841	[Qt:: => AnyEvent::Impl::Qt::], # requires special main program
		842	[POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza
		843	[Wx:: => AnyEvent::Impl::POE::],
		844	[Prima:: => AnyEvent::Impl::POE::],
330	);	845	);
331		846
332	our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);	847	our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
		848
		849	our @post_detect;
		850
		851	sub post_detect(&) {
		852	my ($cb) = @_;
		853
		854	if ($MODEL) {
		855	$cb->();
		856
		857	1
		858	} else {
		859	push @post_detect, $cb;
		860
		861	defined wantarray
		862	? bless \$cb, "AnyEvent::Util::PostDetect"
		863	: ()
		864	}
		865	}
		866
		867	sub AnyEvent::Util::PostDetect::DESTROY {
		868	@post_detect = grep $_ != ${$_[0]}, @post_detect;
		869	}
333		870
334	sub detect() {	871	sub detect() {
335	unless ($MODEL) {	872	unless ($MODEL) {
336	no strict 'refs';	873	no strict 'refs';
		874	local $SIG{__DIE__};
		875
		876	if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
		877	my $model = "AnyEvent::Impl::$1";
		878	if (eval "require $model") {
		879	$MODEL = $model;
		880	warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
		881	} else {
		882	warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
		883	}
		884	}
337		885
338	# check for already loaded models	886	# check for already loaded models
		887	unless ($MODEL) {
339	for (@REGISTRY, @models) {	888	for (@REGISTRY, @models) {
340	my ($package, $model) = @$_;	889	my ($package, $model) = @$_;
341	if (${"$package\::VERSION"} > 0) {	890	if (${"$package\::VERSION"} > 0) {
342	if (eval "require $model") {	891	if (eval "require $model") {
343	$MODEL = $model;	892	$MODEL = $model;
344	warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;	893	warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
345	last;	894	last;
		895	}
346	}	896	}
347	}	897	}
348	}
349		898
350	unless ($MODEL) {	899	unless ($MODEL) {
351	# try to load a model	900	# try to load a model
352		901
353	for (@REGISTRY, @models) {	902	for (@REGISTRY, @models) {
354	my ($package, $model) = @$_;	903	my ($package, $model) = @$_;
355	if (eval "require $package"	904	if (eval "require $package"
356	and ${"$package\::VERSION"} > 0	905	and ${"$package\::VERSION"} > 0
357	and eval "require $model") {	906	and eval "require $model") {
358	$MODEL = $model;	907	$MODEL = $model;
359	warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;	908	warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
360	last;	909	last;
		910	}
361	}	911	}
		912
		913	$MODEL
		914	or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
362	}	915	}
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	}	916	}
367		917
368	unshift @ISA, $MODEL;	918	unshift @ISA, $MODEL;
369	push @{"$MODEL\::ISA"}, "AnyEvent::Base";	919	push @{"$MODEL\::ISA"}, "AnyEvent::Base";
		920
		921	(shift @post_detect)->() while @post_detect;
370	}	922	}
371		923
372	$MODEL	924	$MODEL
373	}	925	}
374		926
…		…
384	$class->$func (@_);	936	$class->$func (@_);
385	}	937	}
386		938
387	package AnyEvent::Base;	939	package AnyEvent::Base;
388		940
		941	# default implementation for now and time
		942
		943	use Time::HiRes ();
		944
		945	sub time { Time::HiRes::time }
		946	sub now { Time::HiRes::time }
		947
389	# default implementation for ->condvar, ->wait, ->broadcast	948	# default implementation for ->condvar
390		949
391	sub condvar {	950	sub condvar {
392	bless \my $flag, "AnyEvent::Base::CondVar"	951	bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
393	}
394
395	sub AnyEvent::Base::CondVar::broadcast {
396	${$_[0]}++;
397	}
398
399	sub AnyEvent::Base::CondVar::wait {
400	AnyEvent->one_event while !${$_[0]};
401	}	952	}
402		953
403	# default implementation for ->signal	954	# default implementation for ->signal
404		955
405	our %SIG_CB;	956	our %SIG_CB;
…		…
458	or Carp::croak "required option 'pid' is missing";	1009	or Carp::croak "required option 'pid' is missing";
459		1010
460	$PID_CB{$pid}{$arg{cb}} = $arg{cb};	1011	$PID_CB{$pid}{$arg{cb}} = $arg{cb};
461		1012
462	unless ($WNOHANG) {	1013	unless ($WNOHANG) {
463	$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;	1014	$WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
464	}	1015	}
465		1016
466	unless ($CHLD_W) {	1017	unless ($CHLD_W) {
467	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);	1018	$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
468	# child could be a zombie already, so make at least one round	1019	# child could be a zombie already, so make at least one round
…		…
479	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };	1030	delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
480		1031
481	undef $CHLD_W unless keys %PID_CB;	1032	undef $CHLD_W unless keys %PID_CB;
482	}	1033	}
483		1034
		1035	package AnyEvent::CondVar;
		1036
		1037	our @ISA = AnyEvent::CondVar::Base::;
		1038
		1039	package AnyEvent::CondVar::Base;
		1040
		1041	use overload
		1042	'&{}' => sub { my $self = shift; sub { $self->send (@_) } },
		1043	fallback => 1;
		1044
		1045	sub _send {
		1046	# nop
		1047	}
		1048
		1049	sub send {
		1050	my $cv = shift;
		1051	$cv->{_ae_sent} = [@_];
		1052	(delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
		1053	$cv->_send;
		1054	}
		1055
		1056	sub croak {
		1057	$_[0]{_ae_croak} = $_[1];
		1058	$_[0]->send;
		1059	}
		1060
		1061	sub ready {
		1062	$_[0]{_ae_sent}
		1063	}
		1064
		1065	sub _wait {
		1066	AnyEvent->one_event while !$_[0]{_ae_sent};
		1067	}
		1068
		1069	sub recv {
		1070	$_[0]->_wait;
		1071
		1072	Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
		1073	wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
		1074	}
		1075
		1076	sub cb {
		1077	$_[0]{_ae_cb} = $_[1] if @_ > 1;
		1078	$_[0]{_ae_cb}
		1079	}
		1080
		1081	sub begin {
		1082	++$_[0]{_ae_counter};
		1083	$_[0]{_ae_end_cb} = $_[1] if @_ > 1;
		1084	}
		1085
		1086	sub end {
		1087	return if --$_[0]{_ae_counter};
		1088	&{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
		1089	}
		1090
		1091	# undocumented/compatibility with pre-3.4
		1092	*broadcast = \&send;
		1093	*wait = \&_wait;
		1094
484	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1095	=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1096
		1097	This is an advanced topic that you do not normally need to use AnyEvent in
		1098	a module. This section is only of use to event loop authors who want to
		1099	provide AnyEvent compatibility.
485		1100
486	If you need to support another event library which isn't directly	1101	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	1102	supported by AnyEvent, you can supply your own interface to it by
488	pushing, before the first watcher gets created, the package name of	1103	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	1104	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	1105	C<@AnyEvent::REGISTRY>. You can do that before and even without loading
491	AnyEvent.	1106	AnyEvent, so it is reasonably cheap.
492		1107
493	Example:	1108	Example:
494		1109
495	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	1110	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
496		1111
497	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>	1112	This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
498	package/class when it finds the C<urxvt> package/module is loaded. When	1113	package/class when it finds the C<urxvt> package/module is already loaded.
		1114
499	AnyEvent is loaded and asked to find a suitable event model, it will	1115	When AnyEvent is loaded and asked to find a suitable event model, it
500	first check for the presence of urxvt.	1116	will first check for the presence of urxvt by trying to C<use> the
		1117	C<urxvt::anyevent> module.
501		1118
502	The class should provide implementations for all watcher types (see	1119	The class should provide implementations for all watcher types. See
503	L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>	1120	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	1121	and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
505	AnyEvent::Impl::Glib> to see the sources).	1122	see the sources.
506		1123
		1124	If you don't provide C<signal> and C<child> watchers than AnyEvent will
		1125	provide suitable (hopefully) replacements.
		1126
507	The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)	1127	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	1128	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	1129	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	1130	inside I<rxvt-unicode>, and it is updated and maintained as part of the
511	I<rxvt-unicode> distribution.	1131	I<rxvt-unicode> distribution.
512		1132
513	I<rxvt-unicode> also cheats a bit by not providing blocking access to	1133	I<rxvt-unicode> also cheats a bit by not providing blocking access to
514	condition variables: code blocking while waiting for a condition will	1134	condition variables: code blocking while waiting for a condition will
515	C<die>. This still works with most modules/usages, and blocking calls must	1135	C<die>. This still works with most modules/usages, and blocking calls must
516	not be in an interactive application, so it makes sense.	1136	not be done in an interactive application, so it makes sense.
517		1137
518	=head1 ENVIRONMENT VARIABLES	1138	=head1 ENVIRONMENT VARIABLES
519		1139
520	The following environment variables are used by this module:	1140	The following environment variables are used by this module:
521		1141
522	C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, reports which event	1142	=over 4
523	model gets used.
524		1143
		1144	=item C<PERL_ANYEVENT_VERBOSE>
		1145
		1146	By default, AnyEvent will be completely silent except in fatal
		1147	conditions. You can set this environment variable to make AnyEvent more
		1148	talkative.
		1149
		1150	When set to C<1> or higher, causes AnyEvent to warn about unexpected
		1151	conditions, such as not being able to load the event model specified by
		1152	C<PERL_ANYEVENT_MODEL>.
		1153
		1154	When set to C<2> or higher, cause AnyEvent to report to STDERR which event
		1155	model it chooses.
		1156
		1157	=item C<PERL_ANYEVENT_MODEL>
		1158
		1159	This can be used to specify the event model to be used by AnyEvent, before
		1160	auto detection and -probing kicks in. It must be a string consisting
		1161	entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
		1162	and the resulting module name is loaded and if the load was successful,
		1163	used as event model. If it fails to load AnyEvent will proceed with
		1164	auto detection and -probing.
		1165
		1166	This functionality might change in future versions.
		1167
		1168	For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
		1169	could start your program like this:
		1170
		1171	PERL_ANYEVENT_MODEL=Perl perl ...
		1172
		1173	=item C<PERL_ANYEVENT_PROTOCOLS>
		1174
		1175	Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
		1176	for IPv4 or IPv6. The default is unspecified (and might change, or be the result
		1177	of auto probing).
		1178
		1179	Must be set to a comma-separated list of protocols or address families,
		1180	current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
		1181	used, and preference will be given to protocols mentioned earlier in the
		1182	list.
		1183
		1184	This variable can effectively be used for denial-of-service attacks
		1185	against local programs (e.g. when setuid), although the impact is likely
		1186	small, as the program has to handle connection errors already-
		1187
		1188	Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
		1189	but support both and try to use both. C<PERL_ANYEVENT_PROTOCOLS=ipv4>
		1190	- only support IPv4, never try to resolve or contact IPv6
		1191	addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
		1192	IPv6, but prefer IPv6 over IPv4.
		1193
		1194	=item C<PERL_ANYEVENT_EDNS0>
		1195
		1196	Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
		1197	for DNS. This extension is generally useful to reduce DNS traffic, but
		1198	some (broken) firewalls drop such DNS packets, which is why it is off by
		1199	default.
		1200
		1201	Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
		1202	EDNS0 in its DNS requests.
		1203
		1204	=item C<PERL_ANYEVENT_MAX_FORKS>
		1205
		1206	The maximum number of child processes that C<AnyEvent::Util::fork_call>
		1207	will create in parallel.
		1208
		1209	=back
		1210
525	=head1 EXAMPLE	1211	=head1 EXAMPLE PROGRAM
526		1212
527	The following program uses an io watcher to read data from stdin, a timer	1213	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	1214	to display a message once per second, and a condition variable to quit the
529	when the user enters quit:	1215	program when the user enters quit:
530		1216
531	use AnyEvent;	1217	use AnyEvent;
532		1218
533	my $cv = AnyEvent->condvar;	1219	my $cv = AnyEvent->condvar;
534		1220
535	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	1221	my $io_watcher = AnyEvent->io (
		1222	fh => \*STDIN,
		1223	poll => 'r',
		1224	cb => sub {
536	warn "io event <$_[0]>\n"; # will always output <r>	1225	warn "io event <$_[0]>\n"; # will always output <r>
537	chomp (my $input = <STDIN>); # read a line	1226	chomp (my $input = <STDIN>); # read a line
538	warn "read: $input\n"; # output what has been read	1227	warn "read: $input\n"; # output what has been read
539	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	1228	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		1229	},
540	});	1230	);
541		1231
542	my $time_watcher; # can only be used once	1232	my $time_watcher; # can only be used once
543		1233
544	sub new_timer {	1234	sub new_timer {
545	$timer = AnyEvent->timer (after => 1, cb => sub {	1235	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
548	});	1238	});
549	}	1239	}
550		1240
551	new_timer; # create first timer	1241	new_timer; # create first timer
552		1242
553	$cv->wait; # wait until user enters /^q/i	1243	$cv->recv; # wait until user enters /^q/i
554		1244
555	=head1 REAL-WORLD EXAMPLE	1245	=head1 REAL-WORLD EXAMPLE
556		1246
557	Consider the L<Net::FCP> module. It features (among others) the following	1247	Consider the L<Net::FCP> module. It features (among others) the following
558	API calls, which are to freenet what HTTP GET requests are to http:	1248	API calls, which are to freenet what HTTP GET requests are to http:
…		…
608	syswrite $txn->{fh}, $txn->{request}	1298	syswrite $txn->{fh}, $txn->{request}
609	or die "connection or write error";	1299	or die "connection or write error";
610	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	1300	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
611		1301
612	Again, C<fh_ready_r> waits till all data has arrived, and then stores the	1302	Again, C<fh_ready_r> waits till all data has arrived, and then stores the
613	result and signals any possible waiters that the request ahs finished:	1303	result and signals any possible waiters that the request has finished:
614		1304
615	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	1305	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
616		1306
617	if (end-of-file or data complete) {	1307	if (end-of-file or data complete) {
618	$txn->{result} = $txn->{buf};	1308	$txn->{result} = $txn->{buf};
619	$txn->{finished}->broadcast;	1309	$txn->{finished}->send;
620	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	1310	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
621	}	1311	}
622		1312
623	The C<result> method, finally, just waits for the finished signal (if the	1313	The C<result> method, finally, just waits for the finished signal (if the
624	request was already finished, it doesn't wait, of course, and returns the	1314	request was already finished, it doesn't wait, of course, and returns the
625	data:	1315	data:
626		1316
627	$txn->{finished}->wait;	1317	$txn->{finished}->recv;
628	return $txn->{result};	1318	return $txn->{result};
629		1319
630	The actual code goes further and collects all errors (C<die>s, exceptions)	1320	The actual code goes further and collects all errors (C<die>s, exceptions)
631	that occured during request processing. The C<result> method detects	1321	that occurred during request processing. The C<result> method detects
632	whether an exception as thrown (it is stored inside the $txn object)	1322	whether an exception as thrown (it is stored inside the $txn object)
633	and just throws the exception, which means connection errors and other	1323	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	1324	problems get reported tot he code that tries to use the result, not in a
635	random callback.	1325	random callback.
636		1326
…		…
667		1357
668	my $quit = AnyEvent->condvar;	1358	my $quit = AnyEvent->condvar;
669		1359
670	$fcp->txn_client_get ($url)->cb (sub {	1360	$fcp->txn_client_get ($url)->cb (sub {
671	...	1361	...
672	$quit->broadcast;	1362	$quit->send;
673	});	1363	});
674		1364
675	$quit->wait;	1365	$quit->recv;
		1366
		1367
		1368	=head1 BENCHMARKS
		1369
		1370	To give you an idea of the performance and overheads that AnyEvent adds
		1371	over the event loops themselves and to give you an impression of the speed
		1372	of various event loops I prepared some benchmarks.
		1373
		1374	=head2 BENCHMARKING ANYEVENT OVERHEAD
		1375
		1376	Here is a benchmark of various supported event models used natively and
		1377	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1378	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1379	which it is), lets them fire exactly once and destroys them again.
		1380
		1381	Source code for this benchmark is found as F<eg/bench> in the AnyEvent
		1382	distribution.
		1383
		1384	=head3 Explanation of the columns
		1385
		1386	I<watcher> is the number of event watchers created/destroyed. Since
		1387	different event models feature vastly different performances, each event
		1388	loop was given a number of watchers so that overall runtime is acceptable
		1389	and similar between tested event loop (and keep them from crashing): Glib
		1390	would probably take thousands of years if asked to process the same number
		1391	of watchers as EV in this benchmark.
		1392
		1393	I<bytes> is the number of bytes (as measured by the resident set size,
		1394	RSS) consumed by each watcher. This method of measuring captures both C
		1395	and Perl-based overheads.
		1396
		1397	I<create> is the time, in microseconds (millionths of seconds), that it
		1398	takes to create a single watcher. The callback is a closure shared between
		1399	all watchers, to avoid adding memory overhead. That means closure creation
		1400	and memory usage is not included in the figures.
		1401
		1402	I<invoke> is the time, in microseconds, used to invoke a simple
		1403	callback. The callback simply counts down a Perl variable and after it was
		1404	invoked "watcher" times, it would C<< ->send >> a condvar once to
		1405	signal the end of this phase.
		1406
		1407	I<destroy> is the time, in microseconds, that it takes to destroy a single
		1408	watcher.
		1409
		1410	=head3 Results
		1411
		1412	name watchers bytes create invoke destroy comment
		1413	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1414	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1415	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1416	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1417	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1418	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1419	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1420	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1421	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1422	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1423
		1424	=head3 Discussion
		1425
		1426	The benchmark does I<not> measure scalability of the event loop very
		1427	well. For example, a select-based event loop (such as the pure perl one)
		1428	can never compete with an event loop that uses epoll when the number of
		1429	file descriptors grows high. In this benchmark, all events become ready at
		1430	the same time, so select/poll-based implementations get an unnatural speed
		1431	boost.
		1432
		1433	Also, note that the number of watchers usually has a nonlinear effect on
		1434	overall speed, that is, creating twice as many watchers doesn't take twice
		1435	the time - usually it takes longer. This puts event loops tested with a
		1436	higher number of watchers at a disadvantage.
		1437
		1438	To put the range of results into perspective, consider that on the
		1439	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1440	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
		1441	cycles with POE.
		1442
		1443	C<EV> is the sole leader regarding speed and memory use, which are both
		1444	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1445	far less memory than any other event loop and is still faster than Event
		1446	natively.
		1447
		1448	The pure perl implementation is hit in a few sweet spots (both the
		1449	constant timeout and the use of a single fd hit optimisations in the perl
		1450	interpreter and the backend itself). Nevertheless this shows that it
		1451	adds very little overhead in itself. Like any select-based backend its
		1452	performance becomes really bad with lots of file descriptors (and few of
		1453	them active), of course, but this was not subject of this benchmark.
		1454
		1455	The C<Event> module has a relatively high setup and callback invocation
		1456	cost, but overall scores in on the third place.
		1457
		1458	C<Glib>'s memory usage is quite a bit higher, but it features a
		1459	faster callback invocation and overall ends up in the same class as
		1460	C<Event>. However, Glib scales extremely badly, doubling the number of
		1461	watchers increases the processing time by more than a factor of four,
		1462	making it completely unusable when using larger numbers of watchers
		1463	(note that only a single file descriptor was used in the benchmark, so
		1464	inefficiencies of C<poll> do not account for this).
		1465
		1466	The C<Tk> adaptor works relatively well. The fact that it crashes with
		1467	more than 2000 watchers is a big setback, however, as correctness takes
		1468	precedence over speed. Nevertheless, its performance is surprising, as the
		1469	file descriptor is dup()ed for each watcher. This shows that the dup()
		1470	employed by some adaptors is not a big performance issue (it does incur a
		1471	hidden memory cost inside the kernel which is not reflected in the figures
		1472	above).
		1473
		1474	C<POE>, regardless of underlying event loop (whether using its pure perl
		1475	select-based backend or the Event module, the POE-EV backend couldn't
		1476	be tested because it wasn't working) shows abysmal performance and
		1477	memory usage with AnyEvent: Watchers use almost 30 times as much memory
		1478	as EV watchers, and 10 times as much memory as Event (the high memory
		1479	requirements are caused by requiring a session for each watcher). Watcher
		1480	invocation speed is almost 900 times slower than with AnyEvent's pure perl
		1481	implementation.
		1482
		1483	The design of the POE adaptor class in AnyEvent can not really account
		1484	for the performance issues, though, as session creation overhead is
		1485	small compared to execution of the state machine, which is coded pretty
		1486	optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
		1487	using multiple sessions is not a good approach, especially regarding
		1488	memory usage, even the author of POE could not come up with a faster
		1489	design).
		1490
		1491	=head3 Summary
		1492
		1493	=over 4
		1494
		1495	=item * Using EV through AnyEvent is faster than any other event loop
		1496	(even when used without AnyEvent), but most event loops have acceptable
		1497	performance with or without AnyEvent.
		1498
		1499	=item * The overhead AnyEvent adds is usually much smaller than the overhead of
		1500	the actual event loop, only with extremely fast event loops such as EV
		1501	adds AnyEvent significant overhead.
		1502
		1503	=item * You should avoid POE like the plague if you want performance or
		1504	reasonable memory usage.
		1505
		1506	=back
		1507
		1508	=head2 BENCHMARKING THE LARGE SERVER CASE
		1509
		1510	This benchmark actually benchmarks the event loop itself. It works by
		1511	creating a number of "servers": each server consists of a socket pair, a
		1512	timeout watcher that gets reset on activity (but never fires), and an I/O
		1513	watcher waiting for input on one side of the socket. Each time the socket
		1514	watcher reads a byte it will write that byte to a random other "server".
		1515
		1516	The effect is that there will be a lot of I/O watchers, only part of which
		1517	are active at any one point (so there is a constant number of active
		1518	fds for each loop iteration, but which fds these are is random). The
		1519	timeout is reset each time something is read because that reflects how
		1520	most timeouts work (and puts extra pressure on the event loops).
		1521
		1522	In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
		1523	(1%) are active. This mirrors the activity of large servers with many
		1524	connections, most of which are idle at any one point in time.
		1525
		1526	Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
		1527	distribution.
		1528
		1529	=head3 Explanation of the columns
		1530
		1531	I<sockets> is the number of sockets, and twice the number of "servers" (as
		1532	each server has a read and write socket end).
		1533
		1534	I<create> is the time it takes to create a socket pair (which is
		1535	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1536
		1537	I<request>, the most important value, is the time it takes to handle a
		1538	single "request", that is, reading the token from the pipe and forwarding
		1539	it to another server. This includes deleting the old timeout and creating
		1540	a new one that moves the timeout into the future.
		1541
		1542	=head3 Results
		1543
		1544	name sockets create request
		1545	EV 20000 69.01 11.16
		1546	Perl 20000 73.32 35.87
		1547	Event 20000 212.62 257.32
		1548	Glib 20000 651.16 1896.30
		1549	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1550
		1551	=head3 Discussion
		1552
		1553	This benchmark I<does> measure scalability and overall performance of the
		1554	particular event loop.
		1555
		1556	EV is again fastest. Since it is using epoll on my system, the setup time
		1557	is relatively high, though.
		1558
		1559	Perl surprisingly comes second. It is much faster than the C-based event
		1560	loops Event and Glib.
		1561
		1562	Event suffers from high setup time as well (look at its code and you will
		1563	understand why). Callback invocation also has a high overhead compared to
		1564	the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
		1565	uses select or poll in basically all documented configurations.
		1566
		1567	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1568	clearly fails to perform with many filehandles or in busy servers.
		1569
		1570	POE is still completely out of the picture, taking over 1000 times as long
		1571	as EV, and over 100 times as long as the Perl implementation, even though
		1572	it uses a C-based event loop in this case.
		1573
		1574	=head3 Summary
		1575
		1576	=over 4
		1577
		1578	=item * The pure perl implementation performs extremely well.
		1579
		1580	=item * Avoid Glib or POE in large projects where performance matters.
		1581
		1582	=back
		1583
		1584	=head2 BENCHMARKING SMALL SERVERS
		1585
		1586	While event loops should scale (and select-based ones do not...) even to
		1587	large servers, most programs we (or I :) actually write have only a few
		1588	I/O watchers.
		1589
		1590	In this benchmark, I use the same benchmark program as in the large server
		1591	case, but it uses only eight "servers", of which three are active at any
		1592	one time. This should reflect performance for a small server relatively
		1593	well.
		1594
		1595	The columns are identical to the previous table.
		1596
		1597	=head3 Results
		1598
		1599	name sockets create request
		1600	EV 16 20.00 6.54
		1601	Perl 16 25.75 12.62
		1602	Event 16 81.27 35.86
		1603	Glib 16 32.63 15.48
		1604	POE 16 261.87 276.28 uses POE::Loop::Event
		1605
		1606	=head3 Discussion
		1607
		1608	The benchmark tries to test the performance of a typical small
		1609	server. While knowing how various event loops perform is interesting, keep
		1610	in mind that their overhead in this case is usually not as important, due
		1611	to the small absolute number of watchers (that is, you need efficiency and
		1612	speed most when you have lots of watchers, not when you only have a few of
		1613	them).
		1614
		1615	EV is again fastest.
		1616
		1617	Perl again comes second. It is noticeably faster than the C-based event
		1618	loops Event and Glib, although the difference is too small to really
		1619	matter.
		1620
		1621	POE also performs much better in this case, but is is still far behind the
		1622	others.
		1623
		1624	=head3 Summary
		1625
		1626	=over 4
		1627
		1628	=item * C-based event loops perform very well with small number of
		1629	watchers, as the management overhead dominates.
		1630
		1631	=back
		1632
		1633
		1634	=head1 FORK
		1635
		1636	Most event libraries are not fork-safe. The ones who are usually are
		1637	because they rely on inefficient but fork-safe C<select> or C<poll>
		1638	calls. Only L<EV> is fully fork-aware.
		1639
		1640	If you have to fork, you must either do so I<before> creating your first
		1641	watcher OR you must not use AnyEvent at all in the child.
		1642
		1643
		1644	=head1 SECURITY CONSIDERATIONS
		1645
		1646	AnyEvent can be forced to load any event model via
		1647	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
		1648	execute arbitrary code or directly gain access, it can easily be used to
		1649	make the program hang or malfunction in subtle ways, as AnyEvent watchers
		1650	will not be active when the program uses a different event model than
		1651	specified in the variable.
		1652
		1653	You can make AnyEvent completely ignore this variable by deleting it
		1654	before the first watcher gets created, e.g. with a C<BEGIN> block:
		1655
		1656	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1657
		1658	use AnyEvent;
		1659
		1660	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1661	be used to probe what backend is used and gain other information (which is
		1662	probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
		1663
676		1664
677	=head1 SEE ALSO	1665	=head1 SEE ALSO
678		1666
679	Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,	1667	Utility functions: L<AnyEvent::Util>.
680	L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.
681		1668
682	Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,	1669	Event modules: L<EV>, L<EV::Glib>, L<Glib::EV>, L<Event>, L<Glib::Event>,
		1670	L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
		1671
683	L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,	1672	Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
684	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.	1673	L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
		1674	L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
		1675	L<AnyEvent::Impl::POE>.
685		1676
		1677	Non-blocking file handles, sockets, TCP clients and
		1678	servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
		1679
		1680	Asynchronous DNS: L<AnyEvent::DNS>.
		1681
		1682	Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
		1683
686	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.	1684	Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
687		1685
688	=head1	1686
		1687	=head1 AUTHOR
		1688
		1689	Marc Lehmann <schmorp@schmorp.de>
		1690	http://home.schmorp.de/
689		1691
690	=cut	1692	=cut
691		1693
692	1	1694	1
693		1695

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