[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.15 by root, Wed Apr 16 15:10:10 2008 UTC vs.
Revision 1.22 by root, Sat May 24 17:58:33 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	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
5	event loops	5	loops
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {	10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub {
13		13
14	my $w = AnyEvent->timer (after => $seconds, cb => sub {	14	my $w = AnyEvent->timer (after => $seconds, cb => sub {
15	...	15	...
16	});	16	});
17		17
18	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
19	$w->wait; # enters "main loop" till $condvar gets ->broadcast	20	$w->recv; # enters "main loop" till $condvar gets ->send
20	$w->broadcast; # wake up current and all future wait's
21		21
22	WHY YOU SHOULD USE THIS MODULE (OR NOT)	22	WHY YOU SHOULD USE THIS MODULE (OR NOT)
23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	23	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24	nowadays. So what is different about AnyEvent?	24	nowadays. So what is different about AnyEvent?
25		25
…		…
27	policy* and AnyEvent is small and efficient.	27	policy* and AnyEvent is small and efficient.
28		28
29	First and foremost, AnyEvent is not an event model itself, it only	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	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,	31	pragmatic way. For event models and certain classes of immortals alike,
32	the statement "there can only be one" is a bitter reality, and AnyEvent	32	the statement "there can only be one" is a bitter reality: In general,
33	helps hiding the differences.	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.
34		35
35	The goal of AnyEvent is to offer module authors the ability to do event	36	The goal of AnyEvent is to offer module authors the ability to do event
36	programming (waiting for I/O or timer events) without subscribing to a	37	programming (waiting for I/O or timer events) without subscribing to a
37	religion, a way of living, and most importantly: without forcing your	38	religion, a way of living, and most importantly: without forcing your
38	module users into the same thing by forcing them to use the same event	39	module users into the same thing by forcing them to use the same event
39	model you use.	40	model you use.
40		41
41	For modules like POE or IO::Async (which is actually doing all I/O	42	For modules like POE or IO::Async (which is a total misnomer as it is
42	synchronously...), using them in your module is like joining a cult:	43	actually doing all I/O synchronously...), using them in your module is
43	After you joined, you are dependent on them and you cannot use anything	44	like joining a cult: After you joined, you are dependent on them and you
44	else, as it is simply incompatible to everything that isn't itself.	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.
45		48
46	AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk	49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
47	works fine etc. etc. but none of these work together with the rest: POE	50	fine. AnyEvent + Tk works fine etc. etc. but none of these work together
48	+ IO::Async? no go. Tk + Event? no go. If your module uses one of those,	51	with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your
49	every user of your module has to use it, too. If your module uses	52	module uses one of those, every user of your module has to use it, too.
50	AnyEvent, it works transparently with all event models it supports	53	But if your module uses AnyEvent, it works transparently with all event
51	(including stuff like POE and IO::Async).	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).
52		57
53	In addition of being free of having to use *the one and only true event	58	In addition to being free of having to use *the one and only true event
54	model*, AnyEvent also is free of bloat and policy: with POE or similar	59	model*, AnyEvent also is free of bloat and policy: with POE or similar
55	modules, you get an enourmous amount of code and strict rules you have	60	modules, you get an enormous amount of code and strict rules you have to
56	to follow. AnyEvent, on the other hand, is lean and to the point by only	61	follow. AnyEvent, on the other hand, is lean and up to the point, by
57	offering the functionality that is useful, in as thin as a wrapper as	62	only offering the functionality that is necessary, in as thin as a
58	technically possible.	63	wrapper as technically possible.
59		64
60	Of course, if you want lots of policy (this can arguably be somewhat	65	Of course, if you want lots of policy (this can arguably be somewhat
61	useful) and you want to force your users to use the one and only event	66	useful) and you want to force your users to use the one and only event
62	model, you should not use this module.	67	model, you should not use this module.
63		68
…		…
65	AnyEvent provides an identical interface to multiple event loops. This	70	AnyEvent provides an identical interface to multiple event loops. This
66	allows module authors to utilise an event loop without forcing module	71	allows module authors to utilise an event loop without forcing module
67	users to use the same event loop (as only a single event loop can	72	users to use the same event loop (as only a single event loop can
68	coexist peacefully at any one time).	73	coexist peacefully at any one time).
69		74
70	The interface itself is vaguely similar but not identical to the Event	75	The interface itself is vaguely similar, but not identical to the Event
71	module.	76	module.
72		77
73	On the first call of any method, the module tries to detect the	78	During the first call of any watcher-creation method, the module tries
74	currently loaded event loop by probing wether any of the following	79	to detect the currently loaded event loop by probing whether one of the
75	modules is loaded: Coro::EV, Coro::Event, EV, Event, Glib, Tk. The first	80	following modules is already loaded: EV, Event, Glib,
		81	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
76	one found is used. If none are found, the module tries to load these	82	used. If none are found, the module tries to load these modules
77	modules in the order given. The first one that could be successfully	83	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
78	loaded will be used. If still none could be found, AnyEvent will fall	84	always succeed) in the order given. The first one that can be
79	back to a pure-perl event loop, which is also not very efficient.	85	successfully loaded will be used. If, after this, still none could be
		86	found, AnyEvent will fall back to a pure-perl event loop, which is not
		87	very efficient, but should work everywhere.
80		88
81	Because AnyEvent first checks for modules that are already loaded,	89	Because AnyEvent first checks for modules that are already loaded,
82	loading an Event model explicitly before first using AnyEvent will	90	loading an event model explicitly before first using AnyEvent will
83	likely make that model the default. For example:	91	likely make that model the default. For example:
84		92
85	use Tk;	93	use Tk;
86	use AnyEvent;	94	use AnyEvent;
87		95
88	# .. AnyEvent will likely default to Tk	96	# .. AnyEvent will likely default to Tk
		97
		98	The likely means that, if any module loads another event model and
		99	starts using it, all bets are off. Maybe you should tell their authors
		100	to use AnyEvent so their modules work together with others seamlessly...
89		101
90	The pure-perl implementation of AnyEvent is called	102	The pure-perl implementation of AnyEvent is called
91	"AnyEvent::Impl::Perl". Like other event modules you can load it	103	"AnyEvent::Impl::Perl". Like other event modules you can load it
92	explicitly.	104	explicitly.
93		105
94	WATCHERS	106	WATCHERS
95	AnyEvent has the central concept of a watcher, which is an object that	107	AnyEvent has the central concept of a watcher, which is an object that
96	stores relevant data for each kind of event you are waiting for, such as	108	stores relevant data for each kind of event you are waiting for, such as
97	the callback to call, the filehandle to watch, etc.	109	the callback to call, the file handle to watch, etc.
98		110
99	These watchers are normal Perl objects with normal Perl lifetime. After	111	These watchers are normal Perl objects with normal Perl lifetime. After
100	creating a watcher it will immediately "watch" for events and invoke the	112	creating a watcher it will immediately "watch" for events and invoke the
		113	callback when the event occurs (of course, only when the event model is
		114	in control).
		115
101	callback. To disable the watcher you have to destroy it (e.g. by setting	116	To disable the watcher you have to destroy it (e.g. by setting the
102	the variable that stores it to "undef" or otherwise deleting all	117	variable you store it in to "undef" or otherwise deleting all references
103	references to it).	118	to it).
104		119
105	All watchers are created by calling a method on the "AnyEvent" class.	120	All watchers are created by calling a method on the "AnyEvent" class.
106		121
		122	Many watchers either are used with "recursion" (repeating timers for
		123	example), or need to refer to their watcher object in other ways.
		124
		125	An any way to achieve that is this pattern:
		126
		127	my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
		128	# you can use $w here, for example to undef it
		129	undef $w;
		130	});
		131
		132	Note that "my $w; $w =" combination. This is necessary because in Perl,
		133	my variables are only visible after the statement in which they are
		134	declared.
		135
107	IO WATCHERS	136	I/O WATCHERS
108	You can create I/O watcher by calling the "AnyEvent->io" method with the	137	You can create an I/O watcher by calling the "AnyEvent->io" method with
109	following mandatory arguments:	138	the following mandatory key-value pairs as arguments:
110		139
111	"fh" the Perl filehandle (not filedescriptor) to watch for events.	140	"fh" the Perl file handle (not file descriptor) to watch for events.
112	"poll" must be a string that is either "r" or "w", that creates a	141	"poll" must be a string that is either "r" or "w", which creates a
113	watcher waiting for "r"eadable or "w"ritable events. "cb" the callback	142	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
114	to invoke everytime the filehandle becomes ready.	143	is the callback to invoke each time the file handle becomes ready.
115		144
116	Filehandles will be kept alive, so as long as the watcher exists, the	145	Although the callback might get passed parameters, their value and
117	filehandle exists, too.	146	presence is undefined and you cannot rely on them. Portable AnyEvent
		147	callbacks cannot use arguments passed to I/O watcher callbacks.
		148
		149	The I/O watcher might use the underlying file descriptor or a copy of
		150	it. You must not close a file handle as long as any watcher is active on
		151	the underlying file descriptor.
		152
		153	Some event loops issue spurious readyness notifications, so you should
		154	always use non-blocking calls when reading/writing from/to your file
		155	handles.
118		156
119	Example:	157	Example:
120		158
121	# wait for readability of STDIN, then read a line and disable the watcher	159	# wait for readability of STDIN, then read a line and disable the watcher
122	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	160	my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
…		…
127		165
128	TIME WATCHERS	166	TIME WATCHERS
129	You can create a time watcher by calling the "AnyEvent->timer" method	167	You can create a time watcher by calling the "AnyEvent->timer" method
130	with the following mandatory arguments:	168	with the following mandatory arguments:
131		169
132	"after" after how many seconds (fractions are supported) should the	170	"after" specifies after how many seconds (fractional values are
133	timer activate. "cb" the callback to invoke.	171	supported) the callback should be invoked. "cb" is the callback to
		172	invoke in that case.
		173
		174	Although the callback might get passed parameters, their value and
		175	presence is undefined and you cannot rely on them. Portable AnyEvent
		176	callbacks cannot use arguments passed to time watcher callbacks.
134		177
135	The timer callback will be invoked at most once: if you want a repeating	178	The timer callback will be invoked at most once: if you want a repeating
136	timer you have to create a new watcher (this is a limitation by both Tk	179	timer you have to create a new watcher (this is a limitation by both Tk
137	and Glib).	180	and Glib).
138		181
…		…
144	});	187	});
145		188
146	# to cancel the timer:	189	# to cancel the timer:
147	undef $w;	190	undef $w;
148		191
149	CONDITION WATCHERS	192	Example 2:
		193
		194	# fire an event after 0.5 seconds, then roughly every second
		195	my $w;
		196
		197	my $cb = sub {
		198	# cancel the old timer while creating a new one
		199	$w = AnyEvent->timer (after => 1, cb => $cb);
		200	};
		201
		202	# start the "loop" by creating the first watcher
		203	$w = AnyEvent->timer (after => 0.5, cb => $cb);
		204
		205	TIMING ISSUES
		206	There are two ways to handle timers: based on real time (relative, "fire
		207	in 10 seconds") and based on wallclock time (absolute, "fire at 12
		208	o'clock").
		209
		210	While most event loops expect timers to specified in a relative way,
		211	they use absolute time internally. This makes a difference when your
		212	clock "jumps", for example, when ntp decides to set your clock backwards
		213	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
		214	supposed to fire "after" a second might actually take six years to
		215	finally fire.
		216
		217	AnyEvent cannot compensate for this. The only event loop that is
		218	conscious about these issues is EV, which offers both relative
		219	(ev_timer, based on true relative time) and absolute (ev_periodic, based
		220	on wallclock time) timers.
		221
		222	AnyEvent always prefers relative timers, if available, matching the
		223	AnyEvent API.
		224
		225	SIGNAL WATCHERS
		226	You can watch for signals using a signal watcher, "signal" is the signal
		227	name without any "SIG" prefix, "cb" is the Perl callback to be invoked
		228	whenever a signal occurs.
		229
		230	Although the callback might get passed parameters, their value and
		231	presence is undefined and you cannot rely on them. Portable AnyEvent
		232	callbacks cannot use arguments passed to signal watcher callbacks.
		233
		234	Multiple signal occurrences can be clumped together into one callback
		235	invocation, and callback invocation will be synchronous. Synchronous
		236	means that it might take a while until the signal gets handled by the
		237	process, but it is guaranteed not to interrupt any other callbacks.
		238
		239	The main advantage of using these watchers is that you can share a
		240	signal between multiple watchers.
		241
		242	This watcher might use %SIG, so programs overwriting those signals
		243	directly will likely not work correctly.
		244
		245	Example: exit on SIGINT
		246
		247	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
		248
		249	CHILD PROCESS WATCHERS
		250	You can also watch on a child process exit and catch its exit status.
		251
		252	The child process is specified by the "pid" argument (if set to 0, it
		253	watches for any child process exit). The watcher will trigger as often
		254	as status change for the child are received. This works by installing a
		255	signal handler for "SIGCHLD". The callback will be called with the pid
		256	and exit status (as returned by waitpid), so unlike other watcher types,
		257	you can rely on child watcher callback arguments.
		258
		259	There is a slight catch to child watchers, however: you usually start
		260	them after the child process was created, and this means the process
		261	could have exited already (and no SIGCHLD will be sent anymore).
		262
		263	Not all event models handle this correctly (POE doesn't), but even for
		264	event models that do handle this correctly, they usually need to be
		265	loaded before the process exits (i.e. before you fork in the first
		266	place).
		267
		268	This means you cannot create a child watcher as the very first thing in
		269	an AnyEvent program, you have to create at least one watcher before
		270	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		271
		272	Example: fork a process and wait for it
		273
		274	my $done = AnyEvent->condvar;
		275
		276	my $pid = fork or exit 5;
		277
		278	my $w = AnyEvent->child (
		279	pid => $pid,
		280	cb => sub {
		281	my ($pid, $status) = @_;
		282	warn "pid $pid exited with status $status";
		283	$done->send;
		284	},
		285	);
		286
		287	# do something else, then wait for process exit
		288	$done->recv;
		289
		290	CONDITION VARIABLES
		291	If you are familiar with some event loops you will know that all of them
		292	require you to run some blocking "loop", "run" or similar function that
		293	will actively watch for new events and call your callbacks.
		294
		295	AnyEvent is different, it expects somebody else to run the event loop
		296	and will only block when necessary (usually when told by the user).
		297
		298	The instrument to do that is called a "condition variable", so called
		299	because they represent a condition that must become true.
		300
150	Condition watchers can be created by calling the "AnyEvent->condvar"	301	Condition variables can be created by calling the "AnyEvent->condvar"
151	method without any arguments.	302	method, usually without arguments. The only argument pair allowed is
		303	"cb", which specifies a callback to be called when the condition
		304	variable becomes true.
152		305
153	A condition watcher watches for a condition - precisely that the	306	After creation, the condition variable is "false" until it becomes
154	"->broadcast" method has been called.	307	"true" by calling the "send" method (or calling the condition variable
		308	as if it were a callback).
155		309
		310	Condition variables are similar to callbacks, except that you can
		311	optionally wait for them. They can also be called merge points - points
		312	in time where multiple outstanding events have been processed. And yet
		313	another way to call them is transactions - each condition variable can
		314	be used to represent a transaction, which finishes at some point and
		315	delivers a result.
		316
		317	Condition variables are very useful to signal that something has
		318	finished, for example, if you write a module that does asynchronous http
		319	requests, then a condition variable would be the ideal candidate to
		320	signal the availability of results. The user can either act when the
		321	callback is called or can synchronously "->recv" for the results.
		322
		323	You can also use them to simulate traditional event loops - for example,
		324	you can block your main program until an event occurs - for example, you
		325	could "->recv" in your main program until the user clicks the Quit
		326	button of your app, which would "->send" the "quit" event.
		327
156	Note that condition watchers recurse into the event loop - if you have	328	Note that condition variables recurse into the event loop - if you have
157	two watchers that call "->wait" in a round-robbin fashion, you lose.	329	two pieces of code that call "->recv" in a round-robin fashion, you
158	Therefore, condition watchers are good to export to your caller, but you	330	lose. Therefore, condition variables are good to export to your caller,
159	should avoid making a blocking wait, at least in callbacks, as this	331	but you should avoid making a blocking wait yourself, at least in
160	usually asks for trouble.	332	callbacks, as this asks for trouble.
161		333
162	The watcher has only two methods:	334	Condition variables are represented by hash refs in perl, and the keys
		335	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		336	(it is often useful to build your own transaction class on top of
		337	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		338	it's "new" method in your own "new" method.
163		339
164	$cv->wait	340	There are two "sides" to a condition variable - the "producer side"
		341	which eventually calls "-> send", and the "consumer side", which waits
		342	for the send to occur.
		343
		344	Example: wait for a timer.
		345
		346	# wait till the result is ready
		347	my $result_ready = AnyEvent->condvar;
		348
		349	# do something such as adding a timer
		350	# or socket watcher the calls $result_ready->send
		351	# when the "result" is ready.
		352	# in this case, we simply use a timer:
		353	my $w = AnyEvent->timer (
		354	after => 1,
		355	cb => sub { $result_ready->send },
		356	);
		357
		358	# this "blocks" (while handling events) till the callback
		359	# calls send
		360	$result_ready->recv;
		361
		362	Example: wait for a timer, but take advantage of the fact that condition
		363	variables are also code references.
		364
		365	my $done = AnyEvent->condvar;
		366	my $delay = AnyEvent->timer (after => 5, cb => $done);
		367	$done->recv;
		368
		369	METHODS FOR PRODUCERS
		370	These methods should only be used by the producing side, i.e. the
		371	code/module that eventually sends the signal. Note that it is also the
		372	producer side which creates the condvar in most cases, but it isn't
		373	uncommon for the consumer to create it as well.
		374
		375	$cv->send (...)
		376	Flag the condition as ready - a running "->recv" and all further
		377	calls to "recv" will (eventually) return after this method has been
		378	called. If nobody is waiting the send will be remembered.
		379
		380	If a callback has been set on the condition variable, it is called
		381	immediately from within send.
		382
		383	Any arguments passed to the "send" call will be returned by all
		384	future "->recv" calls.
		385
		386	Condition variables are overloaded so one can call them directly (as
		387	a code reference). Calling them directly is the same as calling
		388	"send".
		389
		390	$cv->croak ($error)
		391	Similar to send, but causes all call's to "->recv" to invoke
		392	"Carp::croak" with the given error message/object/scalar.
		393
		394	This can be used to signal any errors to the condition variable
		395	user/consumer.
		396
		397	$cv->begin ([group callback])
		398	$cv->end
		399	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		400
		401	These two methods can be used to combine many transactions/events
		402	into one. For example, a function that pings many hosts in parallel
		403	might want to use a condition variable for the whole process.
		404
		405	Every call to "->begin" will increment a counter, and every call to
		406	"->end" will decrement it. If the counter reaches 0 in "->end", the
		407	(last) callback passed to "begin" will be executed. That callback is
		408	supposed to call "->send", but that is not required. If no
		409	callback was set, "send" will be called without any arguments.
		410
		411	Let's clarify this with the ping example:
		412
		413	my $cv = AnyEvent->condvar;
		414
		415	my %result;
		416	$cv->begin (sub { $cv->send (\%result) });
		417
		418	for my $host (@list_of_hosts) {
		419	$cv->begin;
		420	ping_host_then_call_callback $host, sub {
		421	$result{$host} = ...;
		422	$cv->end;
		423	};
		424	}
		425
		426	$cv->end;
		427
		428	This code fragment supposedly pings a number of hosts and calls
		429	"send" after results for all then have have been gathered - in any
		430	order. To achieve this, the code issues a call to "begin" when it
		431	starts each ping request and calls "end" when it has received some
		432	result for it. Since "begin" and "end" only maintain a counter, the
		433	order in which results arrive is not relevant.
		434
		435	There is an additional bracketing call to "begin" and "end" outside
		436	the loop, which serves two important purposes: first, it sets the
		437	callback to be called once the counter reaches 0, and second, it
		438	ensures that "send" is called even when "no" hosts are being pinged
		439	(the loop doesn't execute once).
		440
		441	This is the general pattern when you "fan out" into multiple
		442	subrequests: use an outer "begin"/"end" pair to set the callback and
		443	ensure "end" is called at least once, and then, for each subrequest
		444	you start, call "begin" and for each subrequest you finish, call
		445	"end".
		446
		447	METHODS FOR CONSUMERS
		448	These methods should only be used by the consuming side, i.e. the code
		449	awaits the condition.
		450
		451	$cv->recv
165	Wait (blocking if necessary) until the "->broadcast" method has been	452	Wait (blocking if necessary) until the "->send" or "->croak" methods
166	called on c<$cv>, while servicing other watchers normally.	453	have been called on c<$cv>, while servicing other watchers normally.
167		454
168	You can only wait once on a condition - additional calls will return	455	You can only wait once on a condition - additional calls are valid
169	immediately.	456	but will return immediately.
		457
		458	If an error condition has been set by calling "->croak", then this
		459	function will call "croak".
		460
		461	In list context, all parameters passed to "send" will be returned,
		462	in scalar context only the first one will be returned.
170		463
171	Not all event models support a blocking wait - some die in that case	464	Not all event models support a blocking wait - some die in that case
172	(programs might want to do that so they stay interactive), so *if	465	(programs might want to do that to stay interactive), so *if you are
173	you are using this from a module, never require a blocking wait*,	466	using this from a module, never require a blocking wait*, but let
174	but let the caller decide wether the call will block or not (for	467	the caller decide whether the call will block or not (for example,
175	example, by coupling condition variables with some kind of request	468	by coupling condition variables with some kind of request results
176	results and supporting callbacks so the caller knows that getting	469	and supporting callbacks so the caller knows that getting the result
177	the result will not block, while still suppporting blocking waits if	470	will not block, while still supporting blocking waits if the caller
178	the caller so desires).	471	so desires).
179		472
180	Another reason never to "->wait" in a module is that you cannot	473	Another reason never to "->recv" in a module is that you cannot
181	sensibly have two "->wait"'s in parallel, as that would require	474	sensibly have two "->recv"'s in parallel, as that would require
182	multiple interpreters or coroutines/threads, none of which	475	multiple interpreters or coroutines/threads, none of which
183	"AnyEvent" can supply (the coroutine-aware backends "Coro::EV" and	476	"AnyEvent" can supply.
184	"Coro::Event" explicitly support concurrent "->wait"'s from
185	different coroutines, however).
186		477
187	$cv->broadcast	478	The Coro module, however, can and does supply coroutines and, in
188	Flag the condition as ready - a running "->wait" and all further	479	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
189	calls to "wait" will return after this method has been called. If	480	versions and also integrates coroutines into AnyEvent, making
190	nobody is waiting the broadcast will be remembered..	481	blocking "->recv" calls perfectly safe as long as they are done from
		482	another coroutine (one that doesn't run the event loop).
191		483
192	Example:	484	You can ensure that "-recv" never blocks by setting a callback and
		485	only calling "->recv" from within that callback (or at a later
		486	time). This will work even when the event loop does not support
		487	blocking waits otherwise.
193		488
194	# wait till the result is ready	489	$bool = $cv->ready
195	my $result_ready = AnyEvent->condvar;	490	Returns true when the condition is "true", i.e. whether "send" or
		491	"croak" have been called.
196		492
197	# do something such as adding a timer	493	$cb = $cv->cb ([new callback])
198	# or socket watcher the calls $result_ready->broadcast	494	This is a mutator function that returns the callback set and
199	# when the "result" is ready.	495	optionally replaces it before doing so.
200		496
201	$result_ready->wait;	497	The callback will be called when the condition becomes "true", i.e.
		498	when "send" or "croak" are called. Calling "recv" inside the
		499	callback or at any later time is guaranteed not to block.
202		500
203	SIGNAL WATCHERS	501	GLOBAL VARIABLES AND FUNCTIONS
204	You can listen for signals using a signal watcher, "signal" is the
205	signal name without any "SIG" prefix. Multiple signals events can be
206	clumped together into one callback invocation, and callback invocation
207	might or might not be asynchronous.
208
209	These watchers might use %SIG, so programs overwriting those signals
210	directly will likely not work correctly.
211
212	Example: exit on SIGINT
213
214	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
215
216	CHILD PROCESS WATCHERS
217	You can also listen for the status of a child process specified by the
218	"pid" argument (or any child if the pid argument is 0). The watcher will
219	trigger as often as status change for the child are received. This works
220	by installing a signal handler for "SIGCHLD". The callback will be
221	called with the pid and exit status (as returned by waitpid).
222
223	Example: wait for pid 1333
224
225	my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
226
227	GLOBALS
228	$AnyEvent::MODEL	502	$AnyEvent::MODEL
229	Contains "undef" until the first watcher is being created. Then it	503	Contains "undef" until the first watcher is being created. Then it
230	contains the event model that is being used, which is the name of	504	contains the event model that is being used, which is the name of
231	the Perl class implementing the model. This class is usually one of	505	the Perl class implementing the model. This class is usually one of
232	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	506	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
233	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	507	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
234		508
235	The known classes so far are:	509	The known classes so far are:
236		510
237	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
238	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
239	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	511	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
240	AnyEvent::Impl::Event based on Event, also second best choice :)	512	AnyEvent::Impl::Event based on Event, second best choice.
		513	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
241	AnyEvent::Impl::Glib based on Glib, third-best choice.	514	AnyEvent::Impl::Glib based on Glib, third-best choice.
242	AnyEvent::Impl::Tk based on Tk, very bad choice.	515	AnyEvent::Impl::Tk based on Tk, very bad choice.
243	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	516	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		517	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		518	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		519
		520	There is no support for WxWidgets, as WxWidgets has no support for
		521	watching file handles. However, you can use WxWidgets through the
		522	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		523	second, which was considered to be too horrible to even consider for
		524	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		525	using it's adaptor.
		526
		527	AnyEvent knows about Prima and Wx and will try to use POE when
		528	autodetecting them.
244		529
245	AnyEvent::detect	530	AnyEvent::detect
246	Returns $AnyEvent::MODEL, forcing autodetection of the event model	531	Returns $AnyEvent::MODEL, forcing autodetection of the event model
247	if necessary. You should only call this function right before you	532	if necessary. You should only call this function right before you
248	would have created an AnyEvent watcher anyway, that is, very late at	533	would have created an AnyEvent watcher anyway, that is, as late as
249	runtime.	534	possible at runtime.
		535
		536	$guard = AnyEvent::post_detect { BLOCK }
		537	Arranges for the code block to be executed as soon as the event
		538	model is autodetected (or immediately if this has already happened).
		539
		540	If called in scalar or list context, then it creates and returns an
		541	object that automatically removes the callback again when it is
		542	destroyed. See Coro::BDB for a case where this is useful.
		543
		544	@AnyEvent::post_detect
		545	If there are any code references in this array (you can "push" to it
		546	before or after loading AnyEvent), then they will called directly
		547	after the event loop has been chosen.
		548
		549	You should check $AnyEvent::MODEL before adding to this array,
		550	though: if it contains a true value then the event loop has already
		551	been detected, and the array will be ignored.
		552
		553	Best use "AnyEvent::post_detect { BLOCK }" instead.
250		554
251	WHAT TO DO IN A MODULE	555	WHAT TO DO IN A MODULE
252	As a module author, you should "use AnyEvent" and call AnyEvent methods	556	As a module author, you should "use AnyEvent" and call AnyEvent methods
253	freely, but you should not load a specific event module or rely on it.	557	freely, but you should not load a specific event module or rely on it.
254		558
255	Be careful when you create watchers in the module body - Anyevent will	559	Be careful when you create watchers in the module body - AnyEvent will
256	decide which event module to use as soon as the first method is called,	560	decide which event module to use as soon as the first method is called,
257	so by calling AnyEvent in your module body you force the user of your	561	so by calling AnyEvent in your module body you force the user of your
258	module to load the event module first.	562	module to load the event module first.
259		563
		564	Never call "->recv" on a condition variable unless you know that the
		565	"->send" method has been called on it already. This is because it will
		566	stall the whole program, and the whole point of using events is to stay
		567	interactive.
		568
		569	It is fine, however, to call "->recv" when the user of your module
		570	requests it (i.e. if you create a http request object ad have a method
		571	called "results" that returns the results, it should call "->recv"
		572	freely, as the user of your module knows what she is doing. always).
		573
260	WHAT TO DO IN THE MAIN PROGRAM	574	WHAT TO DO IN THE MAIN PROGRAM
261	There will always be a single main program - the only place that should	575	There will always be a single main program - the only place that should
262	dictate which event model to use.	576	dictate which event model to use.
263		577
264	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	578	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
265	do anything special and let AnyEvent decide which implementation to	579	do anything special (it does not need to be event-based) and let
266	chose.	580	AnyEvent decide which implementation to chose if some module relies on
		581	it.
267		582
268	If the main program relies on a specific event model (for example, in	583	If the main program relies on a specific event model. For example, in
269	Gtk2 programs you have to rely on either Glib or Glib::Event), you	584	Gtk2 programs you have to rely on the Glib module. You should load the
270	should load it before loading AnyEvent or any module that uses it,	585	event module before loading AnyEvent or any module that uses it:
271	generally, as early as possible. The reason is that modules might create	586	generally speaking, you should load it as early as possible. The reason
272	watchers when they are loaded, and AnyEvent will decide on the event	587	is that modules might create watchers when they are loaded, and AnyEvent
273	model to use as soon as it creates watchers, and it might chose the	588	will decide on the event model to use as soon as it creates watchers,
274	wrong one unless you load the correct one yourself.	589	and it might chose the wrong one unless you load the correct one
		590	yourself.
275		591
276	You can chose to use a rather inefficient pure-perl implementation by	592	You can chose to use a rather inefficient pure-perl implementation by
277	loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is	593	loading the "AnyEvent::Impl::Perl" module, which gives you similar
278	generally better.	594	behaviour everywhere, but letting AnyEvent chose is generally better.
		595
		596	OTHER MODULES
		597	The following is a non-exhaustive list of additional modules that use
		598	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		599	in the same program. Some of the modules come with AnyEvent, some are
		600	available via CPAN.
		601
		602	AnyEvent::Util
		603	Contains various utility functions that replace often-used but
		604	blocking functions such as "inet_aton" by event-/callback-based
		605	versions.
		606
		607	AnyEvent::Handle
		608	Provide read and write buffers and manages watchers for reads and
		609	writes.
		610
		611	AnyEvent::Socket
		612	Provides various utility functions for (internet protocol) sockets,
		613	addresses and name resolution. Also functions to create non-blocking
		614	tcp connections or tcp servers, with IPv6 and SRV record support and
		615	more.
		616
		617	AnyEvent::HTTPD
		618	Provides a simple web application server framework.
		619
		620	AnyEvent::DNS
		621	Provides rich asynchronous DNS resolver capabilities.
		622
		623	AnyEvent::FastPing
		624	The fastest ping in the west.
		625
		626	Net::IRC3
		627	AnyEvent based IRC client module family.
		628
		629	Net::XMPP2
		630	AnyEvent based XMPP (Jabber protocol) module family.
		631
		632	Net::FCP
		633	AnyEvent-based implementation of the Freenet Client Protocol,
		634	birthplace of AnyEvent.
		635
		636	Event::ExecFlow
		637	High level API for event-based execution flow control.
		638
		639	Coro
		640	Has special support for AnyEvent via Coro::AnyEvent.
		641
		642	AnyEvent::AIO, IO::AIO
		643	Truly asynchronous I/O, should be in the toolbox of every event
		644	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		645	together.
		646
		647	AnyEvent::BDB, BDB
		648	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
		649	fuses IO::AIO and AnyEvent together.
		650
		651	IO::Lambda
		652	The lambda approach to I/O - don't ask, look there. Can use
		653	AnyEvent.
279		654
280	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	655	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		656	This is an advanced topic that you do not normally need to use AnyEvent
		657	in a module. This section is only of use to event loop authors who want
		658	to provide AnyEvent compatibility.
		659
281	If you need to support another event library which isn't directly	660	If you need to support another event library which isn't directly
282	supported by AnyEvent, you can supply your own interface to it by	661	supported by AnyEvent, you can supply your own interface to it by
283	pushing, before the first watcher gets created, the package name of the	662	pushing, before the first watcher gets created, the package name of the
284	event module and the package name of the interface to use onto	663	event module and the package name of the interface to use onto
285	@AnyEvent::REGISTRY. You can do that before and even without loading	664	@AnyEvent::REGISTRY. You can do that before and even without loading
286	AnyEvent.	665	AnyEvent, so it is reasonably cheap.
287		666
288	Example:	667	Example:
289		668
290	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];	669	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
291		670
292	This tells AnyEvent to (literally) use the "urxvt::anyevent::"	671	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
293	package/class when it finds the "urxvt" package/module is loaded. When	672	package/class when it finds the "urxvt" package/module is already
		673	loaded.
		674
294	AnyEvent is loaded and asked to find a suitable event model, it will	675	When AnyEvent is loaded and asked to find a suitable event model, it
295	first check for the presence of urxvt.	676	will first check for the presence of urxvt by trying to "use" the
		677	"urxvt::anyevent" module.
296		678
297	The class should provide implementations for all watcher types (see	679	The class should provide implementations for all watcher types. See
298	AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code)	680	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
299	and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to	681	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
300	see the sources).	682	the sources.
301		683
		684	If you don't provide "signal" and "child" watchers than AnyEvent will
		685	provide suitable (hopefully) replacements.
		686
302	The above isn't fictitious, the rxvt-unicode (a.k.a. urxvt) uses the	687	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
303	above line as-is. An interface isn't included in AnyEvent because it	688	terminal emulator uses the above line as-is. An interface isn't included
304	doesn't make sense outside the embedded interpreter inside	689	in AnyEvent because it doesn't make sense outside the embedded
305	rxvt-unicode, and it is updated and maintained as part of the	690	interpreter inside rxvt-unicode, and it is updated and maintained as
306	rxvt-unicode distribution.	691	part of the rxvt-unicode distribution.
307		692
308	rxvt-unicode also cheats a bit by not providing blocking access to	693	rxvt-unicode also cheats a bit by not providing blocking access to
309	condition variables: code blocking while waiting for a condition will	694	condition variables: code blocking while waiting for a condition will
310	"die". This still works with most modules/usages, and blocking calls	695	"die". This still works with most modules/usages, and blocking calls
311	must not be in an interactive application, so it makes sense.	696	must not be done in an interactive application, so it makes sense.
312		697
313	ENVIRONMENT VARIABLES	698	ENVIRONMENT VARIABLES
314	The following environment variables are used by this module:	699	The following environment variables are used by this module:
315		700
316	"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event	701	"PERL_ANYEVENT_VERBOSE"
317	model gets used.	702	By default, AnyEvent will be completely silent except in fatal
		703	conditions. You can set this environment variable to make AnyEvent
		704	more talkative.
318		705
319	EXAMPLE	706	When set to 1 or higher, causes AnyEvent to warn about unexpected
		707	conditions, such as not being able to load the event model specified
		708	by "PERL_ANYEVENT_MODEL".
		709
		710	When set to 2 or higher, cause AnyEvent to report to STDERR which
		711	event model it chooses.
		712
		713	"PERL_ANYEVENT_MODEL"
		714	This can be used to specify the event model to be used by AnyEvent,
		715	before auto detection and -probing kicks in. It must be a string
		716	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		717	gets prepended and the resulting module name is loaded and if the
		718	load was successful, used as event model. If it fails to load
		719	AnyEvent will proceed with auto detection and -probing.
		720
		721	This functionality might change in future versions.
		722
		723	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		724	could start your program like this:
		725
		726	PERL_ANYEVENT_MODEL=Perl perl ...
		727
		728	"PERL_ANYEVENT_PROTOCOLS"
		729	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		730	preferences for IPv4 or IPv6. The default is unspecified (and might
		731	change, or be the result of auto probing).
		732
		733	Must be set to a comma-separated list of protocols or address
		734	families, current supported: "ipv4" and "ipv6". Only protocols
		735	mentioned will be used, and preference will be given to protocols
		736	mentioned earlier in the list.
		737
		738	This variable can effectively be used for denial-of-service attacks
		739	against local programs (e.g. when setuid), although the impact is
		740	likely small, as the program has to handle connection errors
		741	already-
		742
		743	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		744	IPv6, but support both and try to use both.
		745	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		746	resolve or contact IPv6 addresses.
		747	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		748	prefer IPv6 over IPv4.
		749
		750	"PERL_ANYEVENT_EDNS0"
		751	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		752	for DNS. This extension is generally useful to reduce DNS traffic,
		753	but some (broken) firewalls drop such DNS packets, which is why it
		754	is off by default.
		755
		756	Setting this variable to 1 will cause AnyEvent::DNS to announce
		757	EDNS0 in its DNS requests.
		758
		759	EXAMPLE PROGRAM
320	The following program uses an io watcher to read data from stdin, a	760	The following program uses an I/O watcher to read data from STDIN, a
321	timer to display a message once per second, and a condvar to exit the	761	timer to display a message once per second, and a condition variable to
322	program when the user enters quit:	762	quit the program when the user enters quit:
323		763
324	use AnyEvent;	764	use AnyEvent;
325		765
326	my $cv = AnyEvent->condvar;	766	my $cv = AnyEvent->condvar;
327		767
328	my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {	768	my $io_watcher = AnyEvent->io (
		769	fh => \*STDIN,
		770	poll => 'r',
		771	cb => sub {
329	warn "io event <$_[0]>\n"; # will always output <r>	772	warn "io event <$_[0]>\n"; # will always output <r>
330	chomp (my $input = <STDIN>); # read a line	773	chomp (my $input = <STDIN>); # read a line
331	warn "read: $input\n"; # output what has been read	774	warn "read: $input\n"; # output what has been read
332	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	775	$cv->send if $input =~ /^q/i; # quit program if /^q/i
		776	},
333	});	777	);
334		778
335	my $time_watcher; # can only be used once	779	my $time_watcher; # can only be used once
336		780
337	sub new_timer {	781	sub new_timer {
338	$timer = AnyEvent->timer (after => 1, cb => sub {	782	$timer = AnyEvent->timer (after => 1, cb => sub {
…		…
341	});	785	});
342	}	786	}
343		787
344	new_timer; # create first timer	788	new_timer; # create first timer
345		789
346	$cv->wait; # wait until user enters /^q/i	790	$cv->recv; # wait until user enters /^q/i
347		791
348	REAL-WORLD EXAMPLE	792	REAL-WORLD EXAMPLE
349	Consider the Net::FCP module. It features (among others) the following	793	Consider the Net::FCP module. It features (among others) the following
350	API calls, which are to freenet what HTTP GET requests are to http:	794	API calls, which are to freenet what HTTP GET requests are to http:
351		795
…		…
400	syswrite $txn->{fh}, $txn->{request}	844	syswrite $txn->{fh}, $txn->{request}
401	or die "connection or write error";	845	or die "connection or write error";
402	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	846	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
403		847
404	Again, "fh_ready_r" waits till all data has arrived, and then stores the	848	Again, "fh_ready_r" waits till all data has arrived, and then stores the
405	result and signals any possible waiters that the request ahs finished:	849	result and signals any possible waiters that the request has finished:
406		850
407	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	851	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
408		852
409	if (end-of-file or data complete) {	853	if (end-of-file or data complete) {
410	$txn->{result} = $txn->{buf};	854	$txn->{result} = $txn->{buf};
411	$txn->{finished}->broadcast;	855	$txn->{finished}->send;
412	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	856	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
413	}	857	}
414		858
415	The "result" method, finally, just waits for the finished signal (if the	859	The "result" method, finally, just waits for the finished signal (if the
416	request was already finished, it doesn't wait, of course, and returns	860	request was already finished, it doesn't wait, of course, and returns
417	the data:	861	the data:
418		862
419	$txn->{finished}->wait;	863	$txn->{finished}->recv;
420	return $txn->{result};	864	return $txn->{result};
421		865
422	The actual code goes further and collects all errors ("die"s,	866	The actual code goes further and collects all errors ("die"s,
423	exceptions) that occured during request processing. The "result" method	867	exceptions) that occurred during request processing. The "result" method
424	detects wether an exception as thrown (it is stored inside the $txn	868	detects whether an exception as thrown (it is stored inside the $txn
425	object) and just throws the exception, which means connection errors and	869	object) and just throws the exception, which means connection errors and
426	other problems get reported tot he code that tries to use the result,	870	other problems get reported tot he code that tries to use the result,
427	not in a random callback.	871	not in a random callback.
428		872
429	All of this enables the following usage styles:	873	All of this enables the following usage styles:
…		…
459		903
460	my $quit = AnyEvent->condvar;	904	my $quit = AnyEvent->condvar;
461		905
462	$fcp->txn_client_get ($url)->cb (sub {	906	$fcp->txn_client_get ($url)->cb (sub {
463	...	907	...
464	$quit->broadcast;	908	$quit->send;
465	});	909	});
466		910
467	$quit->wait;	911	$quit->recv;
		912
		913	BENCHMARKS
		914	To give you an idea of the performance and overheads that AnyEvent adds
		915	over the event loops themselves and to give you an impression of the
		916	speed of various event loops I prepared some benchmarks.
		917
		918	BENCHMARKING ANYEVENT OVERHEAD
		919	Here is a benchmark of various supported event models used natively and
		920	through AnyEvent. The benchmark creates a lot of timers (with a zero
		921	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		922	which it is), lets them fire exactly once and destroys them again.
		923
		924	Source code for this benchmark is found as eg/bench in the AnyEvent
		925	distribution.
		926
		927	Explanation of the columns
		928	watcher is the number of event watchers created/destroyed. Since
		929	different event models feature vastly different performances, each event
		930	loop was given a number of watchers so that overall runtime is
		931	acceptable and similar between tested event loop (and keep them from
		932	crashing): Glib would probably take thousands of years if asked to
		933	process the same number of watchers as EV in this benchmark.
		934
		935	bytes is the number of bytes (as measured by the resident set size,
		936	RSS) consumed by each watcher. This method of measuring captures both C
		937	and Perl-based overheads.
		938
		939	create is the time, in microseconds (millionths of seconds), that it
		940	takes to create a single watcher. The callback is a closure shared
		941	between all watchers, to avoid adding memory overhead. That means
		942	closure creation and memory usage is not included in the figures.
		943
		944	invoke is the time, in microseconds, used to invoke a simple callback.
		945	The callback simply counts down a Perl variable and after it was invoked
		946	"watcher" times, it would "->send" a condvar once to signal the end of
		947	this phase.
		948
		949	destroy is the time, in microseconds, that it takes to destroy a
		950	single watcher.
		951
		952	Results
		953	name watchers bytes create invoke destroy comment
		954	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		955	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		956	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		957	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		958	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		959	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		960	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		961	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		962	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		963	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		964
		965	Discussion
		966	The benchmark does not measure scalability of the event loop very
		967	well. For example, a select-based event loop (such as the pure perl one)
		968	can never compete with an event loop that uses epoll when the number of
		969	file descriptors grows high. In this benchmark, all events become ready
		970	at the same time, so select/poll-based implementations get an unnatural
		971	speed boost.
		972
		973	Also, note that the number of watchers usually has a nonlinear effect on
		974	overall speed, that is, creating twice as many watchers doesn't take
		975	twice the time - usually it takes longer. This puts event loops tested
		976	with a higher number of watchers at a disadvantage.
		977
		978	To put the range of results into perspective, consider that on the
		979	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		980	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		981	CPU cycles with POE.
		982
		983	"EV" is the sole leader regarding speed and memory use, which are both
		984	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		985	far less memory than any other event loop and is still faster than Event
		986	natively.
		987
		988	The pure perl implementation is hit in a few sweet spots (both the
		989	constant timeout and the use of a single fd hit optimisations in the
		990	perl interpreter and the backend itself). Nevertheless this shows that
		991	it adds very little overhead in itself. Like any select-based backend
		992	its performance becomes really bad with lots of file descriptors (and
		993	few of them active), of course, but this was not subject of this
		994	benchmark.
		995
		996	The "Event" module has a relatively high setup and callback invocation
		997	cost, but overall scores in on the third place.
		998
		999	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1000	callback invocation and overall ends up in the same class as "Event".
		1001	However, Glib scales extremely badly, doubling the number of watchers
		1002	increases the processing time by more than a factor of four, making it
		1003	completely unusable when using larger numbers of watchers (note that
		1004	only a single file descriptor was used in the benchmark, so
		1005	inefficiencies of "poll" do not account for this).
		1006
		1007	The "Tk" adaptor works relatively well. The fact that it crashes with
		1008	more than 2000 watchers is a big setback, however, as correctness takes
		1009	precedence over speed. Nevertheless, its performance is surprising, as
		1010	the file descriptor is dup()ed for each watcher. This shows that the
		1011	dup() employed by some adaptors is not a big performance issue (it does
		1012	incur a hidden memory cost inside the kernel which is not reflected in
		1013	the figures above).
		1014
		1015	"POE", regardless of underlying event loop (whether using its pure perl
		1016	select-based backend or the Event module, the POE-EV backend couldn't be
		1017	tested because it wasn't working) shows abysmal performance and memory
		1018	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1019	watchers, and 10 times as much memory as Event (the high memory
		1020	requirements are caused by requiring a session for each watcher).
		1021	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1022	pure perl implementation.
		1023
		1024	The design of the POE adaptor class in AnyEvent can not really account
		1025	for the performance issues, though, as session creation overhead is
		1026	small compared to execution of the state machine, which is coded pretty
		1027	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1028	using multiple sessions is not a good approach, especially regarding
		1029	memory usage, even the author of POE could not come up with a faster
		1030	design).
		1031
		1032	Summary
		1033	* Using EV through AnyEvent is faster than any other event loop (even
		1034	when used without AnyEvent), but most event loops have acceptable
		1035	performance with or without AnyEvent.
		1036
		1037	* The overhead AnyEvent adds is usually much smaller than the overhead
		1038	of the actual event loop, only with extremely fast event loops such
		1039	as EV adds AnyEvent significant overhead.
		1040
		1041	* You should avoid POE like the plague if you want performance or
		1042	reasonable memory usage.
		1043
		1044	BENCHMARKING THE LARGE SERVER CASE
		1045	This benchmark actually benchmarks the event loop itself. It works by
		1046	creating a number of "servers": each server consists of a socket pair, a
		1047	timeout watcher that gets reset on activity (but never fires), and an
		1048	I/O watcher waiting for input on one side of the socket. Each time the
		1049	socket watcher reads a byte it will write that byte to a random other
		1050	"server".
		1051
		1052	The effect is that there will be a lot of I/O watchers, only part of
		1053	which are active at any one point (so there is a constant number of
		1054	active fds for each loop iteration, but which fds these are is random).
		1055	The timeout is reset each time something is read because that reflects
		1056	how most timeouts work (and puts extra pressure on the event loops).
		1057
		1058	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1059	100 (1%) are active. This mirrors the activity of large servers with
		1060	many connections, most of which are idle at any one point in time.
		1061
		1062	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1063	distribution.
		1064
		1065	Explanation of the columns
		1066	sockets is the number of sockets, and twice the number of "servers"
		1067	(as each server has a read and write socket end).
		1068
		1069	create is the time it takes to create a socket pair (which is
		1070	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1071
		1072	request, the most important value, is the time it takes to handle a
		1073	single "request", that is, reading the token from the pipe and
		1074	forwarding it to another server. This includes deleting the old timeout
		1075	and creating a new one that moves the timeout into the future.
		1076
		1077	Results
		1078	name sockets create request
		1079	EV 20000 69.01 11.16
		1080	Perl 20000 73.32 35.87
		1081	Event 20000 212.62 257.32
		1082	Glib 20000 651.16 1896.30
		1083	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1084
		1085	Discussion
		1086	This benchmark does measure scalability and overall performance of the
		1087	particular event loop.
		1088
		1089	EV is again fastest. Since it is using epoll on my system, the setup
		1090	time is relatively high, though.
		1091
		1092	Perl surprisingly comes second. It is much faster than the C-based event
		1093	loops Event and Glib.
		1094
		1095	Event suffers from high setup time as well (look at its code and you
		1096	will understand why). Callback invocation also has a high overhead
		1097	compared to the "$_->() for .."-style loop that the Perl event loop
		1098	uses. Event uses select or poll in basically all documented
		1099	configurations.
		1100
		1101	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1102	clearly fails to perform with many filehandles or in busy servers.
		1103
		1104	POE is still completely out of the picture, taking over 1000 times as
		1105	long as EV, and over 100 times as long as the Perl implementation, even
		1106	though it uses a C-based event loop in this case.
		1107
		1108	Summary
		1109	* The pure perl implementation performs extremely well.
		1110
		1111	* Avoid Glib or POE in large projects where performance matters.
		1112
		1113	BENCHMARKING SMALL SERVERS
		1114	While event loops should scale (and select-based ones do not...) even to
		1115	large servers, most programs we (or I :) actually write have only a few
		1116	I/O watchers.
		1117
		1118	In this benchmark, I use the same benchmark program as in the large
		1119	server case, but it uses only eight "servers", of which three are active
		1120	at any one time. This should reflect performance for a small server
		1121	relatively well.
		1122
		1123	The columns are identical to the previous table.
		1124
		1125	Results
		1126	name sockets create request
		1127	EV 16 20.00 6.54
		1128	Perl 16 25.75 12.62
		1129	Event 16 81.27 35.86
		1130	Glib 16 32.63 15.48
		1131	POE 16 261.87 276.28 uses POE::Loop::Event
		1132
		1133	Discussion
		1134	The benchmark tries to test the performance of a typical small server.
		1135	While knowing how various event loops perform is interesting, keep in
		1136	mind that their overhead in this case is usually not as important, due
		1137	to the small absolute number of watchers (that is, you need efficiency
		1138	and speed most when you have lots of watchers, not when you only have a
		1139	few of them).
		1140
		1141	EV is again fastest.
		1142
		1143	Perl again comes second. It is noticeably faster than the C-based event
		1144	loops Event and Glib, although the difference is too small to really
		1145	matter.
		1146
		1147	POE also performs much better in this case, but is is still far behind
		1148	the others.
		1149
		1150	Summary
		1151	* C-based event loops perform very well with small number of watchers,
		1152	as the management overhead dominates.
		1153
		1154	FORK
		1155	Most event libraries are not fork-safe. The ones who are usually are
		1156	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1157	Only EV is fully fork-aware.
		1158
		1159	If you have to fork, you must either do so before creating your first
		1160	watcher OR you must not use AnyEvent at all in the child.
		1161
		1162	SECURITY CONSIDERATIONS
		1163	AnyEvent can be forced to load any event model via
		1164	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
		1165	to execute arbitrary code or directly gain access, it can easily be used
		1166	to make the program hang or malfunction in subtle ways, as AnyEvent
		1167	watchers will not be active when the program uses a different event
		1168	model than specified in the variable.
		1169
		1170	You can make AnyEvent completely ignore this variable by deleting it
		1171	before the first watcher gets created, e.g. with a "BEGIN" block:
		1172
		1173	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1174
		1175	use AnyEvent;
		1176
		1177	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1178	be used to probe what backend is used and gain other information (which
		1179	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
468		1180
469	SEE ALSO	1181	SEE ALSO
470	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1182	Utility functions: AnyEvent::Util.
471	Glib::Event, Glib, Coro, Tk.
472		1183
473	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1184	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
474	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1185	Event::Lib, Qt, POE.
		1186
		1187	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
475	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl.	1188	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1189	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
476		1190
		1191	Non-blocking file handles, sockets, TCP clients and servers:
		1192	AnyEvent::Handle, AnyEvent::Socket.
		1193
		1194	Asynchronous DNS: AnyEvent::DNS.
		1195
		1196	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1197
477	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1198	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
478		1199
		1200	AUTHOR
		1201	Marc Lehmann <schmorp@schmorp.de>
		1202	http://home.schmorp.de/
479		1203

Diff Legend

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

Comparing AnyEvent/README (file contents): Revision 1.15 by root, Wed Apr 16 15:10:10 2008 UTC vs. Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.15 by root, Wed Apr 16 15:10:10 2008 UTC vs.
Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC