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Comparing AnyEvent/README (file contents):
Revision 1.6 by root, Wed Nov 1 01:22:19 2006 UTC vs.
Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC

…		…
1	NAME	1	=> NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - provide framework for multiple event loops
3		3
4	Event, Coro, Glib, Tk, Perl - various supported event loops	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
		5	loops
5		6
6	SYNOPSIS	7	SYNOPSIS
7	use AnyEvent;	8	use AnyEvent;
8		9
9	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
12		13
13	my $w = AnyEvent->timer (after => $seconds, cb => sub {	14	my $w = AnyEvent->timer (after => $seconds, cb => sub {
14	...	15	...
15	});	16	});
16		17
17	my $w = AnyEvent->condvar; # stores wether a condition was flagged	18	my $w = AnyEvent->condvar; # stores whether a condition was flagged
		19	$w->send; # wake up current and all future recv's
18	$w->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->recv; # enters "main loop" till $condvar gets ->send
19	$w->broadcast; # wake up current and all future wait's	21
		22	WHY YOU SHOULD USE THIS MODULE (OR NOT)
		23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
		24	nowadays. So what is different about AnyEvent?
		25
		26	Executive Summary: AnyEvent is compatible, AnyEvent is *free of
		27	policy* and AnyEvent is small and efficient.
		28
		29	First and foremost, AnyEvent is not an event model itself, it only
		30	interfaces to whatever event model the main program happens to use in a
		31	pragmatic way. For event models and certain classes of immortals alike,
		32	the statement "there can only be one" is a bitter reality: In general,
		33	only one event loop can be active at the same time in a process.
		34	AnyEvent helps hiding the differences between those event loops.
		35
		36	The goal of AnyEvent is to offer module authors the ability to do event
		37	programming (waiting for I/O or timer events) without subscribing to a
		38	religion, a way of living, and most importantly: without forcing your
		39	module users into the same thing by forcing them to use the same event
		40	model you use.
		41
		42	For modules like POE or IO::Async (which is a total misnomer as it is
		43	actually doing all I/O synchronously...), using them in your module is
		44	like joining a cult: After you joined, you are dependent on them and you
		45	cannot use anything else, as it is simply incompatible to everything
		46	that isn't itself. What's worse, all the potential users of your module
		47	are also forced to use the same event loop you use.
		48
		49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
		50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
		51	with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
		52	module uses one of those, every user of your module has to use it, too.
		53	But if your module uses AnyEvent, it works transparently with all event
		54	models it supports (including stuff like POE and IO::Async, as long as
		55	those use one of the supported event loops. It is trivial to add new
		56	event loops to AnyEvent, too, so it is future-proof).
		57
		58	In addition to being free of having to use *the one and only true event
		59	model*, AnyEvent also is free of bloat and policy: with POE or similar
		60	modules, you get an enormous amount of code and strict rules you have to
		61	follow. AnyEvent, on the other hand, is lean and up to the point, by
		62	only offering the functionality that is necessary, in as thin as a
		63	wrapper as technically possible.
		64
		65	Of course, AnyEvent comes with a big (and fully optional!) toolbox of
		66	useful functionality, such as an asynchronous DNS resolver, 100%
		67	non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
		68	such as Windows) and lots of real-world knowledge and workarounds for
		69	platform bugs and differences.
		70
		71	Now, if you do want lots of policy (this can arguably be somewhat
		72	useful) and you want to force your users to use the one and only event
		73	model, you should not use this module.
20		74
21	DESCRIPTION	75	DESCRIPTION
22	AnyEvent provides an identical interface to multiple event loops. This	76	AnyEvent provides an identical interface to multiple event loops. This
23	allows module authors to utilise an event loop without forcing module	77	allows module authors to utilise an event loop without forcing module
24	users to use the same event loop (as only a single event loop can	78	users to use the same event loop (as only a single event loop can
25	coexist peacefully at any one time).	79	coexist peacefully at any one time).
26		80
27	The interface itself is vaguely similar but not identical to the Event	81	The interface itself is vaguely similar, but not identical to the Event
28	module.	82	module.
29		83
30	On the first call of any method, the module tries to detect the	84	During the first call of any watcher-creation method, the module tries
31	currently loaded event loop by probing wether any of the following	85	to detect the currently loaded event loop by probing whether one of the
32	modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is	86	following modules is already loaded: EV, Event, Glib,
		87	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
33	used. If none is found, the module tries to load these modules in the	88	used. If none are found, the module tries to load these modules
34	order given. The first one that could be successfully loaded will be	89	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
35	used. If still none could be found, AnyEvent will fall back to a	90	always succeed) in the order given. The first one that can be
36	pure-perl event loop, which is also not very efficient.	91	successfully loaded will be used. If, after this, still none could be
		92	found, AnyEvent will fall back to a pure-perl event loop, which is not
		93	very efficient, but should work everywhere.
37		94
38	Because AnyEvent first checks for modules that are already loaded,	95	Because AnyEvent first checks for modules that are already loaded,
39	loading an Event model explicitly before first using AnyEvent will	96	loading an event model explicitly before first using AnyEvent will
40	likely make that model the default. For example:	97	likely make that model the default. For example:
41		98
42	use Tk;	99	use Tk;
43	use AnyEvent;	100	use AnyEvent;
44		101
45	# .. AnyEvent will likely default to Tk	102	# .. AnyEvent will likely default to Tk
46		103
		104	The likely means that, if any module loads another event model and
		105	starts using it, all bets are off. Maybe you should tell their authors
		106	to use AnyEvent so their modules work together with others seamlessly...
		107
47	The pure-perl implementation of AnyEvent is called	108	The pure-perl implementation of AnyEvent is called
48	"AnyEvent::Impl::Perl". Like other event modules you can load it	109	"AnyEvent::Impl::Perl". Like other event modules you can load it
49	explicitly.	110	explicitly and enjoy the high availability of that event loop :)
50		111
51	WATCHERS	112	WATCHERS
52	AnyEvent has the central concept of a watcher, which is an object that	113	AnyEvent has the central concept of a watcher, which is an object that
53	stores relevant data for each kind of event you are waiting for, such as	114	stores relevant data for each kind of event you are waiting for, such as
54	the callback to call, the filehandle to watch, etc.	115	the callback to call, the file handle to watch, etc.
55		116
56	These watchers are normal Perl objects with normal Perl lifetime. After	117	These watchers are normal Perl objects with normal Perl lifetime. After
57	creating a watcher it will immediately "watch" for events and invoke the	118	creating a watcher it will immediately "watch" for events and invoke the
		119	callback when the event occurs (of course, only when the event model is
		120	in control).
		121
58	callback. To disable the watcher you have to destroy it (e.g. by setting	122	To disable the watcher you have to destroy it (e.g. by setting the
59	the variable that stores it to "undef" or otherwise deleting all	123	variable you store it in to "undef" or otherwise deleting all references
60	references to it).	124	to it).
61		125
62	All watchers are created by calling a method on the "AnyEvent" class.	126	All watchers are created by calling a method on the "AnyEvent" class.
63		127
		128	Many watchers either are used with "recursion" (repeating timers for
		129	example), or need to refer to their watcher object in other ways.
		130
		131	An any way to achieve that is this pattern:
		132
		133	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		134	# you can use $w here, for example to undef it
		135	undef $w;
		136	});
		137
		138	Note that "my $w; $w =" combination. This is necessary because in Perl,
		139	my variables are only visible after the statement in which they are
		140	declared.
		141
64	IO WATCHERS	142	I/O WATCHERS
65	You can create I/O watcher by calling the "AnyEvent->io" method with the	143	You can create an I/O watcher by calling the "AnyEvent->io" method with
66	following mandatory arguments:	144	the following mandatory key-value pairs as arguments:
67		145
68	"fh" the Perl filehandle (not filedescriptor) to watch for events.	146	"fh" the Perl file handle (not file descriptor) to watch for events.
69	"poll" must be a string that is either "r" or "w", that creates a	147	"poll" must be a string that is either "r" or "w", which creates a
70	watcher waiting for "r"eadable or "w"ritable events. "cb" teh callback	148	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
71	to invoke everytime the filehandle becomes ready.	149	is the callback to invoke each time the file handle becomes ready.
72		150
73	Only one io watcher per "fh" and "poll" combination is allowed (i.e. on	151	Although the callback might get passed parameters, their value and
74	a socket you can have one r + one w, not any more (limitation comes from	152	presence is undefined and you cannot rely on them. Portable AnyEvent
75	Tk - if you are sure you are not using Tk this limitation is gone).	153	callbacks cannot use arguments passed to I/O watcher callbacks.
76		154
77	Filehandles will be kept alive, so as long as the watcher exists, the	155	The I/O watcher might use the underlying file descriptor or a copy of
78	filehandle exists, too.	156	it. You must not close a file handle as long as any watcher is active on
		157	the 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.
79		162
80	Example:	163	Example:
81		164
82	# 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
83	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	166	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
84	chomp (my $input = <STDIN>);	167	chomp (my $input = <STDIN>);
85	warn "read: $input\n";	168	warn "read: $input\n";
86	undef $w;	169	undef $w;
87	});	170	});
88		171
89	TIMER WATCHERS	172	TIME WATCHERS
90	You can create a timer watcher by calling the "AnyEvent->timer" method	173	You can create a time watcher by calling the "AnyEvent->timer" method
91	with the following mandatory arguments:	174	with the following mandatory arguments:
92		175
93	"after" after how many seconds (fractions are supported) should the	176	"after" specifies after how many seconds (fractional values are
94	timer activate. "cb" the callback to invoke.	177	supported) the callback should be invoked. "cb" is the callback to
		178	invoke in that case.
		179
		180	Although the callback might get passed parameters, their value and
		181	presence is undefined and you cannot rely on them. Portable AnyEvent
		182	callbacks cannot use arguments passed to time watcher callbacks.
95		183
96	The timer callback will be invoked at most once: if you want a repeating	184	The timer callback will be invoked at most once: if you want a repeating
97	timer you have to create a new watcher (this is a limitation by both Tk	185	timer you have to create a new watcher (this is a limitation by both Tk
98	and Glib).	186	and Glib).
99		187
…		…
103	my $w = AnyEvent->timer (after => 7.7, cb => sub {	191	my $w = AnyEvent->timer (after => 7.7, cb => sub {
104	warn "timeout\n";	192	warn "timeout\n";
105	});	193	});
106		194
107	# to cancel the timer:	195	# to cancel the timer:
108	undef $w	196	undef $w;
109		197
110	CONDITION WATCHERS	198	Example 2:
		199
		200	# fire an event after 0.5 seconds, then roughly every second
		201	my $w;
		202
		203	my $cb = sub {
		204	# cancel the old timer while creating a new one
		205	$w = AnyEvent->timer (after => 1, cb => $cb);
		206	};
		207
		208	# start the "loop" by creating the first watcher
		209	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		210
		211	TIMING ISSUES
		212	There are two ways to handle timers: based on real time (relative, "fire
		213	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		214	o'clock").
		215
		216	While most event loops expect timers to specified in a relative way,
		217	they use absolute time internally. This makes a difference when your
		218	clock "jumps", for example, when ntp decides to set your clock backwards
		219	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
		220	supposed to fire "after" a second might actually take six years to
		221	finally fire.
		222
		223	AnyEvent cannot compensate for this. The only event loop that is
		224	conscious about these issues is EV, which offers both relative
		225	(ev_timer, based on true relative time) and absolute (ev_periodic, based
		226	on wallclock time) timers.
		227
		228	AnyEvent always prefers relative timers, if available, matching the
		229	AnyEvent API.
		230
		231	AnyEvent has two additional methods that return the "current time":
		232
		233	AnyEvent->time
		234	This returns the "current wallclock time" as a fractional number of
		235	seconds since the Epoch (the same thing as "time" or
		236	"Time::HiRes::time" return, and the result is guaranteed to be
		237	compatible with those).
		238
		239	It progresses independently of any event loop processing, i.e. each
		240	call will check the system clock, which usually gets updated
		241	frequently.
		242
		243	AnyEvent->now
		244	This also returns the "current wallclock time", but unlike "time",
		245	above, this value might change only once per event loop iteration,
		246	depending on the event loop (most return the same time as "time",
		247	above). This is the time that AnyEvent's timers get scheduled
		248	against.
		249
		250	*In almost all cases (in all cases if you don't care), this is the
		251	function to call when you want to know the current time.*
		252
		253	This function is also often faster then "AnyEvent->time", and thus
		254	the preferred method if you want some timestamp (for example,
		255	AnyEvent::Handle uses this to update it's activity timeouts).
		256
		257	The rest of this section is only of relevance if you try to be very
		258	exact with your timing, you can skip it without bad conscience.
		259
		260	For a practical example of when these times differ, consider
		261	Event::Lib and EV and the following set-up:
		262
		263	The event loop is running and has just invoked one of your callback
		264	at time=500 (assume no other callbacks delay processing). In your
		265	callback, you wait a second by executing "sleep 1" (blocking the
		266	process for a second) and then (at time=501) you create a relative
		267	timer that fires after three seconds.
		268
		269	With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
		270	return 501, because that is the current time, and the timer will be
		271	scheduled to fire at time=504 (501 + 3).
		272
		273	With EV, "AnyEvent->time" returns 501 (as that is the current time),
		274	but "AnyEvent->now" returns 500, as that is the time the last event
		275	processing phase started. With EV, your timer gets scheduled to run
		276	at time=503 (500 + 3).
		277
		278	In one sense, Event::Lib is more exact, as it uses the current time
		279	regardless of any delays introduced by event processing. However,
		280	most callbacks do not expect large delays in processing, so this
		281	causes a higher drift (and a lot more system calls to get the
		282	current time).
		283
		284	In another sense, EV is more exact, as your timer will be scheduled
		285	at the same time, regardless of how long event processing actually
		286	took.
		287
		288	In either case, if you care (and in most cases, you don't), then you
		289	can get whatever behaviour you want with any event loop, by taking
		290	the difference between "AnyEvent->time" and "AnyEvent->now" into
		291	account.
		292
		293	SIGNAL WATCHERS
		294	You can watch for signals using a signal watcher, "signal" is the signal
		295	name without any "SIG" prefix, "cb" is the Perl callback to be invoked
		296	whenever a signal occurs.
		297
		298	Although the callback might get passed parameters, their value and
		299	presence is undefined and you cannot rely on them. Portable AnyEvent
		300	callbacks cannot use arguments passed to signal watcher callbacks.
		301
		302	Multiple signal occurrences can be clumped together into one callback
		303	invocation, and callback invocation will be synchronous. Synchronous
		304	means that it might take a while until the signal gets handled by the
		305	process, but it is guaranteed not to interrupt any other callbacks.
		306
		307	The main advantage of using these watchers is that you can share a
		308	signal between multiple watchers.
		309
		310	This watcher might use %SIG, so programs overwriting those signals
		311	directly will likely not work correctly.
		312
		313	Example: exit on SIGINT
		314
		315	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		316
		317	CHILD PROCESS WATCHERS
		318	You can also watch on a child process exit and catch its exit status.
		319
		320	The child process is specified by the "pid" argument (if set to 0, it
		321	watches for any child process exit). The watcher will trigger as often
		322	as status change for the child are received. This works by installing a
		323	signal handler for "SIGCHLD". The callback will be called with the pid
		324	and exit status (as returned by waitpid), so unlike other watcher types,
		325	you can rely on child watcher callback arguments.
		326
		327	There is a slight catch to child watchers, however: you usually start
		328	them after the child process was created, and this means the process
		329	could have exited already (and no SIGCHLD will be sent anymore).
		330
		331	Not all event models handle this correctly (POE doesn't), but even for
		332	event models that do handle this correctly, they usually need to be
		333	loaded before the process exits (i.e. before you fork in the first
		334	place).
		335
		336	This means you cannot create a child watcher as the very first thing in
		337	an AnyEvent program, you have to create at least one watcher before
		338	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		339
		340	Example: fork a process and wait for it
		341
		342	my $done = AnyEvent->condvar;
		343
		344	my $pid = fork or exit 5;
		345
		346	my $w = AnyEvent->child (
		347	pid => $pid,
		348	cb => sub {
		349	my ($pid, $status) = @_;
		350	warn "pid $pid exited with status $status";
		351	$done->send;
		352	},
		353	);
		354
		355	# do something else, then wait for process exit
		356	$done->recv;
		357
		358	CONDITION VARIABLES
		359	If you are familiar with some event loops you will know that all of them
		360	require you to run some blocking "loop", "run" or similar function that
		361	will actively watch for new events and call your callbacks.
		362
		363	AnyEvent is different, it expects somebody else to run the event loop
		364	and will only block when necessary (usually when told by the user).
		365
		366	The instrument to do that is called a "condition variable", so called
		367	because they represent a condition that must become true.
		368
111	Condition watchers can be created by calling the "AnyEvent->condvar"	369	Condition variables can be created by calling the "AnyEvent->condvar"
112	method without any arguments.	370	method, usually without arguments. The only argument pair allowed is
		371	"cb", which specifies a callback to be called when the condition
		372	variable becomes true.
113		373
114	A condition watcher watches for a condition - precisely that the	374	After creation, the condition variable is "false" until it becomes
115	"->broadcast" method has been called.	375	"true" by calling the "send" method (or calling the condition variable
		376	as if it were a callback, read about the caveats in the description for
		377	the "->send" method).
116		378
117	The watcher has only two methods:	379	Condition variables are similar to callbacks, except that you can
		380	optionally wait for them. They can also be called merge points - points
		381	in time where multiple outstanding events have been processed. And yet
		382	another way to call them is transactions - each condition variable can
		383	be used to represent a transaction, which finishes at some point and
		384	delivers a result.
118		385
119	$cv->wait	386	Condition variables are very useful to signal that something has
		387	finished, for example, if you write a module that does asynchronous http
		388	requests, then a condition variable would be the ideal candidate to
		389	signal the availability of results. The user can either act when the
		390	callback is called or can synchronously "->recv" for the results.
		391
		392	You can also use them to simulate traditional event loops - for example,
		393	you can block your main program until an event occurs - for example, you
		394	could "->recv" in your main program until the user clicks the Quit
		395	button of your app, which would "->send" the "quit" event.
		396
		397	Note that condition variables recurse into the event loop - if you have
		398	two pieces of code that call "->recv" in a round-robin fashion, you
		399	lose. Therefore, condition variables are good to export to your caller,
		400	but you should avoid making a blocking wait yourself, at least in
		401	callbacks, as this asks for trouble.
		402
		403	Condition variables are represented by hash refs in perl, and the keys
		404	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		405	(it is often useful to build your own transaction class on top of
		406	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		407	it's "new" method in your own "new" method.
		408
		409	There are two "sides" to a condition variable - the "producer side"
		410	which eventually calls "-> send", and the "consumer side", which waits
		411	for the send to occur.
		412
		413	Example: wait for a timer.
		414
		415	# wait till the result is ready
		416	my $result_ready = AnyEvent->condvar;
		417
		418	# do something such as adding a timer
		419	# or socket watcher the calls $result_ready->send
		420	# when the "result" is ready.
		421	# in this case, we simply use a timer:
		422	my $w = AnyEvent->timer (
		423	after => 1,
		424	cb => sub { $result_ready->send },
		425	);
		426
		427	# this "blocks" (while handling events) till the callback
		428	# calls send
		429	$result_ready->recv;
		430
		431	Example: wait for a timer, but take advantage of the fact that condition
		432	variables are also code references.
		433
		434	my $done = AnyEvent->condvar;
		435	my $delay = AnyEvent->timer (after => 5, cb => $done);
		436	$done->recv;
		437
		438	METHODS FOR PRODUCERS
		439	These methods should only be used by the producing side, i.e. the
		440	code/module that eventually sends the signal. Note that it is also the
		441	producer side which creates the condvar in most cases, but it isn't
		442	uncommon for the consumer to create it as well.
		443
		444	$cv->send (...)
		445	Flag the condition as ready - a running "->recv" and all further
		446	calls to "recv" will (eventually) return after this method has been
		447	called. If nobody is waiting the send will be remembered.
		448
		449	If a callback has been set on the condition variable, it is called
		450	immediately from within send.
		451
		452	Any arguments passed to the "send" call will be returned by all
		453	future "->recv" calls.
		454
		455	Condition variables are overloaded so one can call them directly (as
		456	a code reference). Calling them directly is the same as calling
		457	"send". Note, however, that many C-based event loops do not handle
		458	overloading, so as tempting as it may be, passing a condition
		459	variable instead of a callback does not work. Both the pure perl and
		460	EV loops support overloading, however, as well as all functions that
		461	use perl to invoke a callback (as in AnyEvent::Socket and
		462	AnyEvent::DNS for example).
		463
		464	$cv->croak ($error)
		465	Similar to send, but causes all call's to "->recv" to invoke
		466	"Carp::croak" with the given error message/object/scalar.
		467
		468	This can be used to signal any errors to the condition variable
		469	user/consumer.
		470
		471	$cv->begin ([group callback])
		472	$cv->end
		473	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		474
		475	These two methods can be used to combine many transactions/events
		476	into one. For example, a function that pings many hosts in parallel
		477	might want to use a condition variable for the whole process.
		478
		479	Every call to "->begin" will increment a counter, and every call to
		480	"->end" will decrement it. If the counter reaches 0 in "->end", the
		481	(last) callback passed to "begin" will be executed. That callback is
		482	supposed to call "->send", but that is not required. If no
		483	callback was set, "send" will be called without any arguments.
		484
		485	Let's clarify this with the ping example:
		486
		487	my $cv = AnyEvent->condvar;
		488
		489	my %result;
		490	$cv->begin (sub { $cv->send (\%result) });
		491
		492	for my $host (@list_of_hosts) {
		493	$cv->begin;
		494	ping_host_then_call_callback $host, sub {
		495	$result{$host} = ...;
		496	$cv->end;
		497	};
		498	}
		499
		500	$cv->end;
		501
		502	This code fragment supposedly pings a number of hosts and calls
		503	"send" after results for all then have have been gathered - in any
		504	order. To achieve this, the code issues a call to "begin" when it
		505	starts each ping request and calls "end" when it has received some
		506	result for it. Since "begin" and "end" only maintain a counter, the
		507	order in which results arrive is not relevant.
		508
		509	There is an additional bracketing call to "begin" and "end" outside
		510	the loop, which serves two important purposes: first, it sets the
		511	callback to be called once the counter reaches 0, and second, it
		512	ensures that "send" is called even when "no" hosts are being pinged
		513	(the loop doesn't execute once).
		514
		515	This is the general pattern when you "fan out" into multiple
		516	subrequests: use an outer "begin"/"end" pair to set the callback and
		517	ensure "end" is called at least once, and then, for each subrequest
		518	you start, call "begin" and for each subrequest you finish, call
		519	"end".
		520
		521	METHODS FOR CONSUMERS
		522	These methods should only be used by the consuming side, i.e. the code
		523	awaits the condition.
		524
		525	$cv->recv
120	Wait (blocking if necessary) until the "->broadcast" method has been	526	Wait (blocking if necessary) until the "->send" or "->croak" methods
121	called on c<$cv>, while servicing other watchers normally.	527	have been called on c<$cv>, while servicing other watchers normally.
122		528
		529	You can only wait once on a condition - additional calls are valid
		530	but will return immediately.
		531
		532	If an error condition has been set by calling "->croak", then this
		533	function will call "croak".
		534
		535	In list context, all parameters passed to "send" will be returned,
		536	in scalar context only the first one will be returned.
		537
123	Not all event models support a blocking wait - some die in that	538	Not all event models support a blocking wait - some die in that case
124	case, so if you are using this from a module, never require a	539	(programs might want to do that to stay interactive), so *if you are
125	blocking wait, but let the caller decide wether the call will block	540	using this from a module, never require a blocking wait*, but let
126	or not (for example, by coupling condition variables with some kind	541	the caller decide whether the call will block or not (for example,
		542	by coupling condition variables with some kind of request results
127	of request results and supporting callbacks so the caller knows that	543	and supporting callbacks so the caller knows that getting the result
128	getting the result will not block, while still suppporting blockign	544	will not block, while still supporting blocking waits if the caller
129	waits if the caller so desires).	545	so desires).
130		546
131	You can only wait once on a condition - additional calls will return	547	Another reason never to "->recv" in a module is that you cannot
132	immediately.	548	sensibly have two "->recv"'s in parallel, as that would require
		549	multiple interpreters or coroutines/threads, none of which
		550	"AnyEvent" can supply.
133		551
134	$cv->broadcast	552	The Coro module, however, can and does supply coroutines and, in
135	Flag the condition as ready - a running "->wait" and all further	553	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
136	calls to "wait" will return after this method has been called. If	554	versions and also integrates coroutines into AnyEvent, making
137	nobody is waiting the broadcast will be remembered..	555	blocking "->recv" calls perfectly safe as long as they are done from
		556	another coroutine (one that doesn't run the event loop).
138		557
139	Example:	558	You can ensure that "-recv" never blocks by setting a callback and
		559	only calling "->recv" from within that callback (or at a later
		560	time). This will work even when the event loop does not support
		561	blocking waits otherwise.
140		562
141	# wait till the result is ready	563	$bool = $cv->ready
142	my $result_ready = AnyEvent->condvar;	564	Returns true when the condition is "true", i.e. whether "send" or
		565	"croak" have been called.
143		566
144	# do something such as adding a timer	567	$cb = $cv->cb ([new callback])
145	# or socket watcher the calls $result_ready->broadcast	568	This is a mutator function that returns the callback set and
146	# when the "result" is ready.	569	optionally replaces it before doing so.
147		570
148	$result_ready->wait;	571	The callback will be called when the condition becomes "true", i.e.
		572	when "send" or "croak" are called. Calling "recv" inside the
		573	callback or at any later time is guaranteed not to block.
		574
		575	GLOBAL VARIABLES AND FUNCTIONS
		576	$AnyEvent::MODEL
		577	Contains "undef" until the first watcher is being created. Then it
		578	contains the event model that is being used, which is the name of
		579	the Perl class implementing the model. This class is usually one of
		580	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
		581	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
		582
		583	The known classes so far are:
		584
		585	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
		586	AnyEvent::Impl::Event based on Event, second best choice.
		587	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		588	AnyEvent::Impl::Glib based on Glib, third-best choice.
		589	AnyEvent::Impl::Tk based on Tk, very bad choice.
		590	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		591	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		592	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		593
		594	There is no support for WxWidgets, as WxWidgets has no support for
		595	watching file handles. However, you can use WxWidgets through the
		596	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		597	second, which was considered to be too horrible to even consider for
		598	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		599	using it's adaptor.
		600
		601	AnyEvent knows about Prima and Wx and will try to use POE when
		602	autodetecting them.
		603
		604	AnyEvent::detect
		605	Returns $AnyEvent::MODEL, forcing autodetection of the event model
		606	if necessary. You should only call this function right before you
		607	would have created an AnyEvent watcher anyway, that is, as late as
		608	possible at runtime.
		609
		610	$guard = AnyEvent::post_detect { BLOCK }
		611	Arranges for the code block to be executed as soon as the event
		612	model is autodetected (or immediately if this has already happened).
		613
		614	If called in scalar or list context, then it creates and returns an
		615	object that automatically removes the callback again when it is
		616	destroyed. See Coro::BDB for a case where this is useful.
		617
		618	@AnyEvent::post_detect
		619	If there are any code references in this array (you can "push" to it
		620	before or after loading AnyEvent), then they will called directly
		621	after the event loop has been chosen.
		622
		623	You should check $AnyEvent::MODEL before adding to this array,
		624	though: if it contains a true value then the event loop has already
		625	been detected, and the array will be ignored.
		626
		627	Best use "AnyEvent::post_detect { BLOCK }" instead.
149		628
150	WHAT TO DO IN A MODULE	629	WHAT TO DO IN A MODULE
151	As a module author, you should "use AnyEvent" and call AnyEvent methods	630	As a module author, you should "use AnyEvent" and call AnyEvent methods
152	freely, but you should not load a specific event module or rely on it.	631	freely, but you should not load a specific event module or rely on it.
153		632
154	Be careful when you create watchers in the module body - Anyevent will	633	Be careful when you create watchers in the module body - AnyEvent will
155	decide which event module to use as soon as the first method is called,	634	decide which event module to use as soon as the first method is called,
156	so by calling AnyEvent in your module body you force the user of your	635	so by calling AnyEvent in your module body you force the user of your
157	module to load the event module first.	636	module to load the event module first.
158		637
		638	Never call "->recv" on a condition variable unless you know that the
		639	"->send" method has been called on it already. This is because it will
		640	stall the whole program, and the whole point of using events is to stay
		641	interactive.
		642
		643	It is fine, however, to call "->recv" when the user of your module
		644	requests it (i.e. if you create a http request object ad have a method
		645	called "results" that returns the results, it should call "->recv"
		646	freely, as the user of your module knows what she is doing. always).
		647
159	WHAT TO DO IN THE MAIN PROGRAM	648	WHAT TO DO IN THE MAIN PROGRAM
160	There will always be a single main program - the only place that should	649	There will always be a single main program - the only place that should
161	dictate which event model to use.	650	dictate which event model to use.
162		651
163	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	652	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
164	do anything special and let AnyEvent decide which implementation to	653	do anything special (it does not need to be event-based) and let
165	chose.	654	AnyEvent decide which implementation to chose if some module relies on
		655	it.
166		656
167	If the main program relies on a specific event model (for example, in	657	If the main program relies on a specific event model - for example, in
168	Gtk2 programs you have to rely on either Glib or Glib::Event), you	658	Gtk2 programs you have to rely on the Glib module - you should load the
169	should load it before loading AnyEvent or any module that uses it,	659	event module before loading AnyEvent or any module that uses it:
170	generally, as early as possible. The reason is that modules might create	660	generally speaking, you should load it as early as possible. The reason
171	watchers when they are loaded, and AnyEvent will decide on the event	661	is that modules might create watchers when they are loaded, and AnyEvent
172	model to use as soon as it creates watchers, and it might chose the	662	will decide on the event model to use as soon as it creates watchers,
173	wrong one unless you load the correct one yourself.	663	and it might chose the wrong one unless you load the correct one
		664	yourself.
174		665
175	You can chose to use a rather inefficient pure-perl implementation by	666	You can chose to use a pure-perl implementation by loading the
176	loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is	667	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
177	generally better.	668	everywhere, but letting AnyEvent chose the model is generally better.
		669
		670	MAINLOOP EMULATION
		671	Sometimes (often for short test scripts, or even standalone programs who
		672	only want to use AnyEvent), you do not want to run a specific event
		673	loop.
		674
		675	In that case, you can use a condition variable like this:
		676
		677	AnyEvent->condvar->recv;
		678
		679	This has the effect of entering the event loop and looping forever.
		680
		681	Note that usually your program has some exit condition, in which case it
		682	is better to use the "traditional" approach of storing a condition
		683	variable somewhere, waiting for it, and sending it when the program
		684	should exit cleanly.
		685
		686	OTHER MODULES
		687	The following is a non-exhaustive list of additional modules that use
		688	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		689	in the same program. Some of the modules come with AnyEvent, some are
		690	available via CPAN.
		691
		692	AnyEvent::Util
		693	Contains various utility functions that replace often-used but
		694	blocking functions such as "inet_aton" by event-/callback-based
		695	versions.
		696
		697	AnyEvent::Handle
		698	Provide read and write buffers and manages watchers for reads and
		699	writes.
		700
		701	AnyEvent::Socket
		702	Provides various utility functions for (internet protocol) sockets,
		703	addresses and name resolution. Also functions to create non-blocking
		704	tcp connections or tcp servers, with IPv6 and SRV record support and
		705	more.
		706
		707	AnyEvent::DNS
		708	Provides rich asynchronous DNS resolver capabilities.
		709
		710	AnyEvent::HTTPD
		711	Provides a simple web application server framework.
		712
		713	AnyEvent::FastPing
		714	The fastest ping in the west.
		715
		716	Net::IRC3
		717	AnyEvent based IRC client module family.
		718
		719	Net::XMPP2
		720	AnyEvent based XMPP (Jabber protocol) module family.
		721
		722	Net::FCP
		723	AnyEvent-based implementation of the Freenet Client Protocol,
		724	birthplace of AnyEvent.
		725
		726	Event::ExecFlow
		727	High level API for event-based execution flow control.
		728
		729	Coro
		730	Has special support for AnyEvent via Coro::AnyEvent.
		731
		732	AnyEvent::AIO, IO::AIO
		733	Truly asynchronous I/O, should be in the toolbox of every event
		734	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		735	together.
		736
		737	AnyEvent::BDB, BDB
		738	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
		739	fuses IO::AIO and AnyEvent together.
		740
		741	IO::Lambda
		742	The lambda approach to I/O - don't ask, look there. Can use
		743	AnyEvent.
178		744
179	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	745	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		746	This is an advanced topic that you do not normally need to use AnyEvent
		747	in a module. This section is only of use to event loop authors who want
		748	to provide AnyEvent compatibility.
		749
180	If you need to support another event library which isn't directly	750	If you need to support another event library which isn't directly
181	supported by AnyEvent, you can supply your own interface to it by	751	supported by AnyEvent, you can supply your own interface to it by
182	pushing, before the first watcher gets created, the package name of the	752	pushing, before the first watcher gets created, the package name of the
183	event module and the package name of the interface to use onto	753	event module and the package name of the interface to use onto
184	@AnyEvent::REGISTRY. You can do that before and even without loading	754	@AnyEvent::REGISTRY. You can do that before and even without loading
185	AnyEvent.	755	AnyEvent, so it is reasonably cheap.
186		756
187	Example:	757	Example:
188		758
189	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	759	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
190		760
191	This tells AnyEvent to (literally) use the "urxvt::anyevent::"	761	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
192	package/class when it finds the "urxvt" package/module is loaded. When	762	package/class when it finds the "urxvt" package/module is already
		763	loaded.
		764
193	AnyEvent is loaded and asked to find a suitable event model, it will	765	When AnyEvent is loaded and asked to find a suitable event model, it
194	first check for the presence of urxvt.	766	will first check for the presence of urxvt by trying to "use" the
		767	"urxvt::anyevent" module.
195		768
196	The class should prove implementations for all watcher types (see	769	The class should provide implementations for all watcher types. See
197	AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code)	770	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
198	and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to	771	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
199	see the sources).	772	the sources.
200		773
		774	If you don't provide "signal" and "child" watchers than AnyEvent will
		775	provide suitable (hopefully) replacements.
		776
201	The above isn't fictitious, the rxvt-unicode (a.k.a. urxvt) uses the	777	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
202	above line as-is. An interface isn't included in AnyEvent because it	778	terminal emulator uses the above line as-is. An interface isn't included
203	doesn't make sense outside the embedded interpreter inside	779	in AnyEvent because it doesn't make sense outside the embedded
204	rxvt-unicode, and it is updated and maintained as part of the	780	interpreter inside rxvt-unicode, and it is updated and maintained as
205	rxvt-unicode distribution.	781	part of the rxvt-unicode distribution.
206		782
207	rxvt-unicode also cheats a bit by not providing blocking access to	783	rxvt-unicode also cheats a bit by not providing blocking access to
208	condition variables: code blocking while waiting for a condition will	784	condition variables: code blocking while waiting for a condition will
209	"die". This still works with most modules/usages, and blocking calls	785	"die". This still works with most modules/usages, and blocking calls
210	must not be in an interactive appliation, so it makes sense.	786	must not be done in an interactive application, so it makes sense.
211		787
212	ENVIRONMENT VARIABLES	788	ENVIRONMENT VARIABLES
213	The following environment variables are used by this module:	789	The following environment variables are used by this module:
214		790
215	"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event	791	"PERL_ANYEVENT_VERBOSE"
216	model gets used.	792	By default, AnyEvent will be completely silent except in fatal
		793	conditions. You can set this environment variable to make AnyEvent
		794	more talkative.
217		795
218	EXAMPLE	796	When set to 1 or higher, causes AnyEvent to warn about unexpected
		797	conditions, such as not being able to load the event model specified
		798	by "PERL_ANYEVENT_MODEL".
		799
		800	When set to 2 or higher, cause AnyEvent to report to STDERR which
		801	event model it chooses.
		802
		803	"PERL_ANYEVENT_MODEL"
		804	This can be used to specify the event model to be used by AnyEvent,
		805	before auto detection and -probing kicks in. It must be a string
		806	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		807	gets prepended and the resulting module name is loaded and if the
		808	load was successful, used as event model. If it fails to load
		809	AnyEvent will proceed with auto detection and -probing.
		810
		811	This functionality might change in future versions.
		812
		813	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		814	could start your program like this:
		815
		816	PERL_ANYEVENT_MODEL=Perl perl ...
		817
		818	"PERL_ANYEVENT_PROTOCOLS"
		819	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		820	preferences for IPv4 or IPv6. The default is unspecified (and might
		821	change, or be the result of auto probing).
		822
		823	Must be set to a comma-separated list of protocols or address
		824	families, current supported: "ipv4" and "ipv6". Only protocols
		825	mentioned will be used, and preference will be given to protocols
		826	mentioned earlier in the list.
		827
		828	This variable can effectively be used for denial-of-service attacks
		829	against local programs (e.g. when setuid), although the impact is
		830	likely small, as the program has to handle connection errors
		831	already-
		832
		833	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		834	IPv6, but support both and try to use both.
		835	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		836	resolve or contact IPv6 addresses.
		837	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		838	prefer IPv6 over IPv4.
		839
		840	"PERL_ANYEVENT_EDNS0"
		841	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		842	for DNS. This extension is generally useful to reduce DNS traffic,
		843	but some (broken) firewalls drop such DNS packets, which is why it
		844	is off by default.
		845
		846	Setting this variable to 1 will cause AnyEvent::DNS to announce
		847	EDNS0 in its DNS requests.
		848
		849	"PERL_ANYEVENT_MAX_FORKS"
		850	The maximum number of child processes that
		851	"AnyEvent::Util::fork_call" will create in parallel.
		852
		853	EXAMPLE PROGRAM
219	The following program uses an io watcher to read data from stdin, a	854	The following program uses an I/O watcher to read data from STDIN, a
220	timer to display a message once per second, and a condvar to exit the	855	timer to display a message once per second, and a condition variable to
221	program when the user enters quit:	856	quit the program when the user enters quit:
222		857
223	use AnyEvent;	858	use AnyEvent;
224		859
225	my $cv = AnyEvent->condvar;	860	my $cv = AnyEvent->condvar;
226		861
227	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	862	my $io_watcher = AnyEvent->io (
		863	fh => \*STDIN,
		864	poll => 'r',
		865	cb => sub {
228	warn "io event <$_[0]>\n"; # will always output <r>	866	warn "io event <$_[0]>\n"; # will always output <r>
229	chomp (my $input = <STDIN>); # read a line	867	chomp (my $input = <STDIN>); # read a line
230	warn "read: $input\n"; # output what has been read	868	warn "read: $input\n"; # output what has been read
231	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	869	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		870	},
232	});	871	);
233		872
234	my $time_watcher; # can only be used once	873	my $time_watcher; # can only be used once
235		874
236	sub new_timer {	875	sub new_timer {
237	$timer = AnyEvent->timer (after => 1, cb => sub {	876	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
240	});	879	});
241	}	880	}
242		881
243	new_timer; # create first timer	882	new_timer; # create first timer
244		883
245	$cv->wait; # wait until user enters /^q/i	884	$cv->recv; # wait until user enters /^q/i
246		885
247	REAL-WORLD EXAMPLE	886	REAL-WORLD EXAMPLE
248	Consider the Net::FCP module. It features (among others) the following	887	Consider the Net::FCP module. It features (among others) the following
249	API calls, which are to freenet what HTTP GET requests are to http:	888	API calls, which are to freenet what HTTP GET requests are to http:
250		889
…		…
299	syswrite $txn->{fh}, $txn->{request}	938	syswrite $txn->{fh}, $txn->{request}
300	or die "connection or write error";	939	or die "connection or write error";
301	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	940	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
302		941
303	Again, "fh_ready_r" waits till all data has arrived, and then stores the	942	Again, "fh_ready_r" waits till all data has arrived, and then stores the
304	result and signals any possible waiters that the request ahs finished:	943	result and signals any possible waiters that the request has finished:
305		944
306	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	945	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
307		946
308	if (end-of-file or data complete) {	947	if (end-of-file or data complete) {
309	$txn->{result} = $txn->{buf};	948	$txn->{result} = $txn->{buf};
310	$txn->{finished}->broadcast;	949	$txn->{finished}->send;
311	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	950	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
312	}	951	}
313		952
314	The "result" method, finally, just waits for the finished signal (if the	953	The "result" method, finally, just waits for the finished signal (if the
315	request was already finished, it doesn't wait, of course, and returns	954	request was already finished, it doesn't wait, of course, and returns
316	the data:	955	the data:
317		956
318	$txn->{finished}->wait;	957	$txn->{finished}->recv;
319	return $txn->{result};	958	return $txn->{result};
320		959
321	The actual code goes further and collects all errors ("die"s,	960	The actual code goes further and collects all errors ("die"s,
322	exceptions) that occured during request processing. The "result" method	961	exceptions) that occurred during request processing. The "result" method
323	detects wether an exception as thrown (it is stored inside the $txn	962	detects whether an exception as thrown (it is stored inside the $txn
324	object) and just throws the exception, which means connection errors and	963	object) and just throws the exception, which means connection errors and
325	other problems get reported tot he code that tries to use the result,	964	other problems get reported tot he code that tries to use the result,
326	not in a random callback.	965	not in a random callback.
327		966
328	All of this enables the following usage styles:	967	All of this enables the following usage styles:
329		968
330	1. Blocking:	969	1. Blocking:
331		970
332	my $data = $fcp->client_get ($url);	971	my $data = $fcp->client_get ($url);
333		972
334	2. Blocking, but parallelizing:	973	2. Blocking, but running in parallel:
335		974
336	my @datas = map $_->result,	975	my @datas = map $_->result,
337	map $fcp->txn_client_get ($_),	976	map $fcp->txn_client_get ($_),
338	@urls;	977	@urls;
339		978
340	Both blocking examples work without the module user having to know	979	Both blocking examples work without the module user having to know
341	anything about events.	980	anything about events.
342		981
343	3a. Event-based in a main program, using any support Event module:	982	3a. Event-based in a main program, using any supported event module:
344		983
345	use Event;	984	use EV;
346		985
347	$fcp->txn_client_get ($url)->cb (sub {	986	$fcp->txn_client_get ($url)->cb (sub {
348	my $txn = shift;	987	my $txn = shift;
349	my $data = $txn->result;	988	my $data = $txn->result;
350	...	989	...
351	});	990	});
352		991
353	Event::loop;	992	EV::loop;
354		993
355	3b. The module user could use AnyEvent, too:	994	3b. The module user could use AnyEvent, too:
356		995
357	use AnyEvent;	996	use AnyEvent;
358		997
359	my $quit = AnyEvent->condvar;	998	my $quit = AnyEvent->condvar;
360		999
361	$fcp->txn_client_get ($url)->cb (sub {	1000	$fcp->txn_client_get ($url)->cb (sub {
362	...	1001	...
363	$quit->broadcast;	1002	$quit->send;
364	});	1003	});
365		1004
366	$quit->wait;	1005	$quit->recv;
		1006
		1007	BENCHMARKS
		1008	To give you an idea of the performance and overheads that AnyEvent adds
		1009	over the event loops themselves and to give you an impression of the
		1010	speed of various event loops I prepared some benchmarks.
		1011
		1012	BENCHMARKING ANYEVENT OVERHEAD
		1013	Here is a benchmark of various supported event models used natively and
		1014	through AnyEvent. The benchmark creates a lot of timers (with a zero
		1015	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		1016	which it is), lets them fire exactly once and destroys them again.
		1017
		1018	Source code for this benchmark is found as eg/bench in the AnyEvent
		1019	distribution.
		1020
		1021	Explanation of the columns
		1022	watcher is the number of event watchers created/destroyed. Since
		1023	different event models feature vastly different performances, each event
		1024	loop was given a number of watchers so that overall runtime is
		1025	acceptable and similar between tested event loop (and keep them from
		1026	crashing): Glib would probably take thousands of years if asked to
		1027	process the same number of watchers as EV in this benchmark.
		1028
		1029	bytes is the number of bytes (as measured by the resident set size,
		1030	RSS) consumed by each watcher. This method of measuring captures both C
		1031	and Perl-based overheads.
		1032
		1033	create is the time, in microseconds (millionths of seconds), that it
		1034	takes to create a single watcher. The callback is a closure shared
		1035	between all watchers, to avoid adding memory overhead. That means
		1036	closure creation and memory usage is not included in the figures.
		1037
		1038	invoke is the time, in microseconds, used to invoke a simple callback.
		1039	The callback simply counts down a Perl variable and after it was invoked
		1040	"watcher" times, it would "->send" a condvar once to signal the end of
		1041	this phase.
		1042
		1043	destroy is the time, in microseconds, that it takes to destroy a
		1044	single watcher.
		1045
		1046	Results
		1047	name watchers bytes create invoke destroy comment
		1048	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		1049	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		1050	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		1051	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		1052	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		1053	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		1054	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		1055	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		1056	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		1057	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		1058
		1059	Discussion
		1060	The benchmark does not measure scalability of the event loop very
		1061	well. For example, a select-based event loop (such as the pure perl one)
		1062	can never compete with an event loop that uses epoll when the number of
		1063	file descriptors grows high. In this benchmark, all events become ready
		1064	at the same time, so select/poll-based implementations get an unnatural
		1065	speed boost.
		1066
		1067	Also, note that the number of watchers usually has a nonlinear effect on
		1068	overall speed, that is, creating twice as many watchers doesn't take
		1069	twice the time - usually it takes longer. This puts event loops tested
		1070	with a higher number of watchers at a disadvantage.
		1071
		1072	To put the range of results into perspective, consider that on the
		1073	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1074	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		1075	CPU cycles with POE.
		1076
		1077	"EV" is the sole leader regarding speed and memory use, which are both
		1078	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1079	far less memory than any other event loop and is still faster than Event
		1080	natively.
		1081
		1082	The pure perl implementation is hit in a few sweet spots (both the
		1083	constant timeout and the use of a single fd hit optimisations in the
		1084	perl interpreter and the backend itself). Nevertheless this shows that
		1085	it adds very little overhead in itself. Like any select-based backend
		1086	its performance becomes really bad with lots of file descriptors (and
		1087	few of them active), of course, but this was not subject of this
		1088	benchmark.
		1089
		1090	The "Event" module has a relatively high setup and callback invocation
		1091	cost, but overall scores in on the third place.
		1092
		1093	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1094	callback invocation and overall ends up in the same class as "Event".
		1095	However, Glib scales extremely badly, doubling the number of watchers
		1096	increases the processing time by more than a factor of four, making it
		1097	completely unusable when using larger numbers of watchers (note that
		1098	only a single file descriptor was used in the benchmark, so
		1099	inefficiencies of "poll" do not account for this).
		1100
		1101	The "Tk" adaptor works relatively well. The fact that it crashes with
		1102	more than 2000 watchers is a big setback, however, as correctness takes
		1103	precedence over speed. Nevertheless, its performance is surprising, as
		1104	the file descriptor is dup()ed for each watcher. This shows that the
		1105	dup() employed by some adaptors is not a big performance issue (it does
		1106	incur a hidden memory cost inside the kernel which is not reflected in
		1107	the figures above).
		1108
		1109	"POE", regardless of underlying event loop (whether using its pure perl
		1110	select-based backend or the Event module, the POE-EV backend couldn't be
		1111	tested because it wasn't working) shows abysmal performance and memory
		1112	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1113	watchers, and 10 times as much memory as Event (the high memory
		1114	requirements are caused by requiring a session for each watcher).
		1115	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1116	pure perl implementation.
		1117
		1118	The design of the POE adaptor class in AnyEvent can not really account
		1119	for the performance issues, though, as session creation overhead is
		1120	small compared to execution of the state machine, which is coded pretty
		1121	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1122	using multiple sessions is not a good approach, especially regarding
		1123	memory usage, even the author of POE could not come up with a faster
		1124	design).
		1125
		1126	Summary
		1127	* Using EV through AnyEvent is faster than any other event loop (even
		1128	when used without AnyEvent), but most event loops have acceptable
		1129	performance with or without AnyEvent.
		1130
		1131	* The overhead AnyEvent adds is usually much smaller than the overhead
		1132	of the actual event loop, only with extremely fast event loops such
		1133	as EV adds AnyEvent significant overhead.
		1134
		1135	* You should avoid POE like the plague if you want performance or
		1136	reasonable memory usage.
		1137
		1138	BENCHMARKING THE LARGE SERVER CASE
		1139	This benchmark actually benchmarks the event loop itself. It works by
		1140	creating a number of "servers": each server consists of a socket pair, a
		1141	timeout watcher that gets reset on activity (but never fires), and an
		1142	I/O watcher waiting for input on one side of the socket. Each time the
		1143	socket watcher reads a byte it will write that byte to a random other
		1144	"server".
		1145
		1146	The effect is that there will be a lot of I/O watchers, only part of
		1147	which are active at any one point (so there is a constant number of
		1148	active fds for each loop iteration, but which fds these are is random).
		1149	The timeout is reset each time something is read because that reflects
		1150	how most timeouts work (and puts extra pressure on the event loops).
		1151
		1152	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1153	100 (1%) are active. This mirrors the activity of large servers with
		1154	many connections, most of which are idle at any one point in time.
		1155
		1156	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1157	distribution.
		1158
		1159	Explanation of the columns
		1160	sockets is the number of sockets, and twice the number of "servers"
		1161	(as each server has a read and write socket end).
		1162
		1163	create is the time it takes to create a socket pair (which is
		1164	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1165
		1166	request, the most important value, is the time it takes to handle a
		1167	single "request", that is, reading the token from the pipe and
		1168	forwarding it to another server. This includes deleting the old timeout
		1169	and creating a new one that moves the timeout into the future.
		1170
		1171	Results
		1172	name sockets create request
		1173	EV 20000 69.01 11.16
		1174	Perl 20000 73.32 35.87
		1175	Event 20000 212.62 257.32
		1176	Glib 20000 651.16 1896.30
		1177	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1178
		1179	Discussion
		1180	This benchmark does measure scalability and overall performance of the
		1181	particular event loop.
		1182
		1183	EV is again fastest. Since it is using epoll on my system, the setup
		1184	time is relatively high, though.
		1185
		1186	Perl surprisingly comes second. It is much faster than the C-based event
		1187	loops Event and Glib.
		1188
		1189	Event suffers from high setup time as well (look at its code and you
		1190	will understand why). Callback invocation also has a high overhead
		1191	compared to the "$_->() for .."-style loop that the Perl event loop
		1192	uses. Event uses select or poll in basically all documented
		1193	configurations.
		1194
		1195	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1196	clearly fails to perform with many filehandles or in busy servers.
		1197
		1198	POE is still completely out of the picture, taking over 1000 times as
		1199	long as EV, and over 100 times as long as the Perl implementation, even
		1200	though it uses a C-based event loop in this case.
		1201
		1202	Summary
		1203	* The pure perl implementation performs extremely well.
		1204
		1205	* Avoid Glib or POE in large projects where performance matters.
		1206
		1207	BENCHMARKING SMALL SERVERS
		1208	While event loops should scale (and select-based ones do not...) even to
		1209	large servers, most programs we (or I :) actually write have only a few
		1210	I/O watchers.
		1211
		1212	In this benchmark, I use the same benchmark program as in the large
		1213	server case, but it uses only eight "servers", of which three are active
		1214	at any one time. This should reflect performance for a small server
		1215	relatively well.
		1216
		1217	The columns are identical to the previous table.
		1218
		1219	Results
		1220	name sockets create request
		1221	EV 16 20.00 6.54
		1222	Perl 16 25.75 12.62
		1223	Event 16 81.27 35.86
		1224	Glib 16 32.63 15.48
		1225	POE 16 261.87 276.28 uses POE::Loop::Event
		1226
		1227	Discussion
		1228	The benchmark tries to test the performance of a typical small server.
		1229	While knowing how various event loops perform is interesting, keep in
		1230	mind that their overhead in this case is usually not as important, due
		1231	to the small absolute number of watchers (that is, you need efficiency
		1232	and speed most when you have lots of watchers, not when you only have a
		1233	few of them).
		1234
		1235	EV is again fastest.
		1236
		1237	Perl again comes second. It is noticeably faster than the C-based event
		1238	loops Event and Glib, although the difference is too small to really
		1239	matter.
		1240
		1241	POE also performs much better in this case, but is is still far behind
		1242	the others.
		1243
		1244	Summary
		1245	* C-based event loops perform very well with small number of watchers,
		1246	as the management overhead dominates.
		1247
		1248	FORK
		1249	Most event libraries are not fork-safe. The ones who are usually are
		1250	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1251	Only EV is fully fork-aware.
		1252
		1253	If you have to fork, you must either do so before creating your first
		1254	watcher OR you must not use AnyEvent at all in the child.
		1255
		1256	SECURITY CONSIDERATIONS
		1257	AnyEvent can be forced to load any event model via
		1258	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
		1259	to execute arbitrary code or directly gain access, it can easily be used
		1260	to make the program hang or malfunction in subtle ways, as AnyEvent
		1261	watchers will not be active when the program uses a different event
		1262	model than specified in the variable.
		1263
		1264	You can make AnyEvent completely ignore this variable by deleting it
		1265	before the first watcher gets created, e.g. with a "BEGIN" block:
		1266
		1267	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1268
		1269	use AnyEvent;
		1270
		1271	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1272	be used to probe what backend is used and gain other information (which
		1273	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
367		1274
368	SEE ALSO	1275	SEE ALSO
369	Event modules: Coro::Event, Coro, Event, Glib::Event, Glib.	1276	Utility functions: AnyEvent::Util.
370		1277
		1278	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
		1279	Event::Lib, Qt, POE.
		1280
371	Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event,	1281	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
372	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk.	1282	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1283	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
373		1284
374	Nontrivial usage example: Net::FCP.	1285	Non-blocking file handles, sockets, TCP clients and servers:
		1286	AnyEvent::Handle, AnyEvent::Socket.
375		1287
		1288	Asynchronous DNS: AnyEvent::DNS.
376		1289
		1290	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1291
		1292	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
		1293
		1294	AUTHOR
		1295	Marc Lehmann <schmorp@schmorp.de>
		1296	http://home.schmorp.de/
		1297

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Comparing AnyEvent/README (file contents): Revision 1.6 by root, Wed Nov 1 01:22:19 2006 UTC vs. Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC

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Revision 1.6 by root, Wed Nov 1 01:22:19 2006 UTC vs.
Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC