[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.18 by root, Thu Apr 24 09:13:26 2008 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	EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt -	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
5	various supported 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 {
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 whether 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
…		…
46	that isn't itself. What's worse, all the potential users of your module	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.	47	are also forced to use the same event loop you use.
48		48
49	AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works	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	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	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.	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	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	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	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).	56	event loops to AnyEvent, too, so it is future-proof).
57		57
58	In addition to 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
59	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
60	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
61	to follow. AnyEvent, on the other hand, is lean and up to the point, by	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	62	only offering the functionality that is necessary, in as thin as a
63	wrapper as technically possible.	63	wrapper as technically possible.
64		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
65	Of course, if you want lots of policy (this can arguably be somewhat	71	Now, if you do want lots of policy (this can arguably be somewhat
66	useful) and you want to force your users to use the one and only event	72	useful) and you want to force your users to use the one and only event
67	model, you should not use this module.	73	model, you should not use this module.
68		74
69	DESCRIPTION	75	DESCRIPTION
70	AnyEvent provides an identical interface to multiple event loops. This	76	AnyEvent provides an identical interface to multiple event loops. This
…		…
75	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
76	module.	82	module.
77		83
78	During the first call of any watcher-creation method, the module tries	84	During the first call of any watcher-creation method, the module tries
79	to detect the currently loaded event loop by probing whether one of the	85	to detect the currently loaded event loop by probing whether one of the
80	following modules is already loaded: Coro::EV, Coro::Event, EV, Event,	86	following modules is already loaded: EV, Event, Glib,
81	Glib, Tk, Event::Lib, Qt. The first one found is used. If none are	87	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	found, the module tries to load these modules (excluding Event::Lib and	88	used. If none are found, the module tries to load these modules
83	Qt) in the order given. The first one that can be successfully loaded	89	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
84	will be used. If, after this, still none could be found, AnyEvent will	90	always succeed) in the order given. The first one that can be
85	fall back to a pure-perl event loop, which is not very efficient, but	91	successfully loaded will be used. If, after this, still none could be
86	should work everywhere.	92	found, AnyEvent will fall back to a pure-perl event loop, which is not
		93	very efficient, but should work everywhere.
87		94
88	Because AnyEvent first checks for modules that are already loaded,	95	Because AnyEvent first checks for modules that are already loaded,
89	loading an event model explicitly before first using AnyEvent will	96	loading an event model explicitly before first using AnyEvent will
90	likely make that model the default. For example:	97	likely make that model the default. For example:
91		98
…		…
98	starts using it, all bets are off. Maybe you should tell their authors	105	starts using it, all bets are off. Maybe you should tell their authors
99	to use AnyEvent so their modules work together with others seamlessly...	106	to use AnyEvent so their modules work together with others seamlessly...
100		107
101	The pure-perl implementation of AnyEvent is called	108	The pure-perl implementation of AnyEvent is called
102	"AnyEvent::Impl::Perl". Like other event modules you can load it	109	"AnyEvent::Impl::Perl". Like other event modules you can load it
103	explicitly.	110	explicitly and enjoy the high availability of that event loop :)
104		111
105	WATCHERS	112	WATCHERS
106	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
107	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
108	the callback to call, the filehandle to watch, etc.	115	the callback to call, the file handle to watch, etc.
109		116
110	These watchers are normal Perl objects with normal Perl lifetime. After	117	These watchers are normal Perl objects with normal Perl lifetime. After
111	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
112	callback when the event occurs (of course, only when the event model is	119	callback when the event occurs (of course, only when the event model is
113	in control).	120	in control).
…		…
130		137
131	Note that "my $w; $w =" combination. This is necessary because in Perl,	138	Note that "my $w; $w =" combination. This is necessary because in Perl,
132	my variables are only visible after the statement in which they are	139	my variables are only visible after the statement in which they are
133	declared.	140	declared.
134		141
135	IO WATCHERS	142	I/O WATCHERS
136	You can create an I/O watcher by calling the "AnyEvent->io" method with	143	You can create an I/O watcher by calling the "AnyEvent->io" method with
137	the following mandatory key-value pairs as arguments:	144	the following mandatory key-value pairs as arguments:
138		145
139	"fh" the Perl file handle (not file descriptor) to watch for events.	146	"fh" the Perl file handle (not file descriptor) to watch for events.
140	"poll" must be a string that is either "r" or "w", which creates a	147	"poll" must be a string that is either "r" or "w", which creates a
141	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	148	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
142	is the callback to invoke each time the file handle becomes ready.	149	is the callback to invoke each time the file handle becomes ready.
143		150
144	As long as the I/O watcher exists it will keep the file descriptor or a	151	Although the callback might get passed parameters, their value and
145	copy of it alive/open.	152	presence is undefined and you cannot rely on them. Portable AnyEvent
		153	callbacks cannot use arguments passed to I/O watcher callbacks.
146		154
		155	The I/O watcher might use the underlying file descriptor or a copy of
147	It is not allowed to close a file handle as long as any watcher is	156	it. You must not close a file handle as long as any watcher is active on
148	active on the underlying file descriptor.	157	the underlying file descriptor.
149		158
150	Some event loops issue spurious readyness notifications, so you should	159	Some event loops issue spurious readyness notifications, so you should
151	always use non-blocking calls when reading/writing from/to your file	160	always use non-blocking calls when reading/writing from/to your file
152	handles.	161	handles.
153		162
…		…
163	TIME WATCHERS	172	TIME WATCHERS
164	You can create a time watcher by calling the "AnyEvent->timer" method	173	You can create a time watcher by calling the "AnyEvent->timer" method
165	with the following mandatory arguments:	174	with the following mandatory arguments:
166		175
167	"after" specifies after how many seconds (fractional values are	176	"after" specifies after how many seconds (fractional values are
168	supported) should the timer activate. "cb" the callback to invoke in	177	supported) the callback should be invoked. "cb" is the callback to
169	that case.	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.
170		183
171	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
172	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
173	and Glib).	186	and Glib).
174		187
…		…
213	on wallclock time) timers.	226	on wallclock time) timers.
214		227
215	AnyEvent always prefers relative timers, if available, matching the	228	AnyEvent always prefers relative timers, if available, matching the
216	AnyEvent API.	229	AnyEvent API.
217		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
218	SIGNAL WATCHERS	293	SIGNAL WATCHERS
219	You can watch for signals using a signal watcher, "signal" is the signal	294	You can watch for signals using a signal watcher, "signal" is the signal
220	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	295	name without any "SIG" prefix, "cb" is the Perl callback to be invoked
221	whenever a signal occurs.	296	whenever a signal occurs.
222		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
223	Multiple signal occurances can be clumped together into one callback	302	Multiple signal occurrences can be clumped together into one callback
224	invocation, and callback invocation will be synchronous. synchronous	303	invocation, and callback invocation will be synchronous. Synchronous
225	means that it might take a while until the signal gets handled by the	304	means that it might take a while until the signal gets handled by the
226	process, but it is guarenteed not to interrupt any other callbacks.	305	process, but it is guaranteed not to interrupt any other callbacks.
227		306
228	The main advantage of using these watchers is that you can share a	307	The main advantage of using these watchers is that you can share a
229	signal between multiple watchers.	308	signal between multiple watchers.
230		309
231	This watcher might use %SIG, so programs overwriting those signals	310	This watcher might use %SIG, so programs overwriting those signals
…		…
240		319
241	The child process is specified by the "pid" argument (if set to 0, it	320	The child process is specified by the "pid" argument (if set to 0, it
242	watches for any child process exit). The watcher will trigger as often	321	watches for any child process exit). The watcher will trigger as often
243	as status change for the child are received. This works by installing a	322	as status change for the child are received. This works by installing a
244	signal handler for "SIGCHLD". The callback will be called with the pid	323	signal handler for "SIGCHLD". The callback will be called with the pid
245	and exit status (as returned by waitpid).	324	and exit status (as returned by waitpid), so unlike other watcher types,
		325	you can rely on child watcher callback arguments.
246		326
247	Example: wait for pid 1333	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;
248		345
249	my $w = AnyEvent->child (	346	my $w = AnyEvent->child (
250	pid => 1333,	347	pid => $pid,
251	cb => sub {	348	cb => sub {
252	my ($pid, $status) = @_;	349	my ($pid, $status) = @_;
253	warn "pid $pid exited with status $status";	350	warn "pid $pid exited with status $status";
		351	$done->send;
254	},	352	},
255	);	353	);
256		354
		355	# do something else, then wait for process exit
		356	$done->recv;
		357
257	CONDITION VARIABLES	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
258	Condition variables can be created by calling the "AnyEvent->condvar"	369	Condition variables can be created by calling the "AnyEvent->condvar"
259	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.
260		373
261	A condition variable waits for a condition - precisely that the	374	After creation, the condition variable is "false" until it becomes
262	"->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).
263		378
264	They are very useful to signal that a condition has been fulfilled, for	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.
		385
		386	Condition variables are very useful to signal that something has
265	example, if you write a module that does asynchronous http requests,	387	finished, for example, if you write a module that does asynchronous http
266	then a condition variable would be the ideal candidate to signal the	388	requests, then a condition variable would be the ideal candidate to
267	availability of results.	389	signal the availability of results. The user can either act when the
		390	callback is called or can synchronously "->recv" for the results.
268		391
269	You can also use condition variables to block your main program until an	392	You can also use them to simulate traditional event loops - for example,
270	event occurs - for example, you could "->wait" in your main program	393	you can block your main program until an event occurs - for example, you
271	until the user clicks the Quit button in your app, which would	394	could "->recv" in your main program until the user clicks the Quit
272	"->broadcast" the "quit" event.	395	button of your app, which would "->send" the "quit" event.
273		396
274	Note that condition variables recurse into the event loop - if you have	397	Note that condition variables recurse into the event loop - if you have
275	two pirces of code that call "->wait" in a round-robbin fashion, you	398	two pieces of code that call "->recv" in a round-robin fashion, you
276	lose. Therefore, condition variables are good to export to your caller,	399	lose. Therefore, condition variables are good to export to your caller,
277	but you should avoid making a blocking wait yourself, at least in	400	but you should avoid making a blocking wait yourself, at least in
278	callbacks, as this asks for trouble.	401	callbacks, as this asks for trouble.
279		402
280	This object has two methods:	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.
281		408
282	$cv->wait	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	$cv->recv
283	Wait (blocking if necessary) until the "->broadcast" method has been	526	Wait (blocking if necessary) until the "->send" or "->croak" methods
284	called on c<$cv>, while servicing other watchers normally.	527	have been called on c<$cv>, while servicing other watchers normally.
285		528
286	You can only wait once on a condition - additional calls will return	529	You can only wait once on a condition - additional calls are valid
287	immediately.	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.
288		537
289	Not all event models support a blocking wait - some die in that case	538	Not all event models support a blocking wait - some die in that case
290	(programs might want to do that to stay interactive), so *if you are	539	(programs might want to do that to stay interactive), so *if you are
291	using this from a module, never require a blocking wait*, but let	540	using this from a module, never require a blocking wait*, but let
292	the caller decide whether the call will block or not (for example,	541	the caller decide whether the call will block or not (for example,
293	by coupling condition variables with some kind of request results	542	by coupling condition variables with some kind of request results
294	and supporting callbacks so the caller knows that getting the result	543	and supporting callbacks so the caller knows that getting the result
295	will not block, while still suppporting blocking waits if the caller	544	will not block, while still supporting blocking waits if the caller
296	so desires).	545	so desires).
297		546
298	Another reason never to "->wait" in a module is that you cannot	547	Another reason never to "->recv" in a module is that you cannot
299	sensibly have two "->wait"'s in parallel, as that would require	548	sensibly have two "->recv"'s in parallel, as that would require
300	multiple interpreters or coroutines/threads, none of which	549	multiple interpreters or coroutines/threads, none of which
301	"AnyEvent" can supply (the coroutine-aware backends	550	"AnyEvent" can supply.
302	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
303	support concurrent "->wait"'s from different coroutines, however).
304		551
305	$cv->broadcast	552	The Coro module, however, can and does supply coroutines and, in
306	Flag the condition as ready - a running "->wait" and all further	553	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
307	calls to "wait" will (eventually) return after this method has been	554	versions and also integrates coroutines into AnyEvent, making
308	called. If 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).
309		557
310	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.
311		562
312	# wait till the result is ready	563	$bool = $cv->ready
313	my $result_ready = AnyEvent->condvar;	564	Returns true when the condition is "true", i.e. whether "send" or
		565	"croak" have been called.
314		566
315	# do something such as adding a timer	567	$cb = $cv->cb ([new callback])
316	# or socket watcher the calls $result_ready->broadcast	568	This is a mutator function that returns the callback set and
317	# when the "result" is ready.	569	optionally replaces it before doing so.
318	# in this case, we simply use a timer:
319	my $w = AnyEvent->timer (
320	after => 1,
321	cb => sub { $result_ready->broadcast },
322	);
323		570
324	# this "blocks" (while handling events) till the watcher	571	The callback will be called when the condition becomes "true", i.e.
325	# calls broadcast	572	when "send" or "croak" are called. Calling "recv" inside the
326	$result_ready->wait;	573	callback or at any later time is guaranteed not to block.
327		574
328	GLOBAL VARIABLES AND FUNCTIONS	575	GLOBAL VARIABLES AND FUNCTIONS
329	$AnyEvent::MODEL	576	$AnyEvent::MODEL
330	Contains "undef" until the first watcher is being created. Then it	577	Contains "undef" until the first watcher is being created. Then it
331	contains the event model that is being used, which is the name of	578	contains the event model that is being used, which is the name of
…		…
333	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	580	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
334	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	581	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
335		582
336	The known classes so far are:	583	The known classes so far are:
337		584
338	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
339	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
340	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).	585	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
341	AnyEvent::Impl::Event based on Event, second best choice.	586	AnyEvent::Impl::Event based on Event, second best choice.
		587	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
342	AnyEvent::Impl::Glib based on Glib, third-best choice.	588	AnyEvent::Impl::Glib based on Glib, third-best choice.
343	AnyEvent::Impl::Tk based on Tk, very bad choice.	589	AnyEvent::Impl::Tk based on Tk, very bad choice.
344	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
345	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).	590	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
346	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.	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.
347		603
348	AnyEvent::detect	604	AnyEvent::detect
349	Returns $AnyEvent::MODEL, forcing autodetection of the event model	605	Returns $AnyEvent::MODEL, forcing autodetection of the event model
350	if necessary. You should only call this function right before you	606	if necessary. You should only call this function right before you
351	would have created an AnyEvent watcher anyway, that is, as late as	607	would have created an AnyEvent watcher anyway, that is, as late as
352	possible at runtime.	608	possible at runtime.
353		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.
		628
354	WHAT TO DO IN A MODULE	629	WHAT TO DO IN A MODULE
355	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
356	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.
357		632
358	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
359	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,
360	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
361	module to load the event module first.	636	module to load the event module first.
362		637
363	Never call "->wait" on a condition variable unless you know that the	638	Never call "->recv" on a condition variable unless you know that the
364	"->broadcast" method has been called on it already. This is because it	639	"->send" method has been called on it already. This is because it will
365	will stall the whole program, and the whole point of using events is to	640	stall the whole program, and the whole point of using events is to stay
366	stay interactive.	641	interactive.
367		642
368	It is fine, however, to call "->wait" when the user of your module	643	It is fine, however, to call "->recv" when the user of your module
369	requests it (i.e. if you create a http request object ad have a method	644	requests it (i.e. if you create a http request object ad have a method
370	called "results" that returns the results, it should call "->wait"	645	called "results" that returns the results, it should call "->recv"
371	freely, as the user of your module knows what she is doing. always).	646	freely, as the user of your module knows what she is doing. always).
372		647
373	WHAT TO DO IN THE MAIN PROGRAM	648	WHAT TO DO IN THE MAIN PROGRAM
374	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
375	dictate which event model to use.	650	dictate which event model to use.
…		…
377	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
378	do anything special (it does not need to be event-based) and let	653	do anything special (it does not need to be event-based) and let
379	AnyEvent decide which implementation to chose if some module relies on	654	AnyEvent decide which implementation to chose if some module relies on
380	it.	655	it.
381		656
382	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
383	Gtk2 programs you have to rely on the Glib module. You should load the	658	Gtk2 programs you have to rely on the Glib module - you should load the
384	event module before loading AnyEvent or any module that uses it:	659	event module before loading AnyEvent or any module that uses it:
385	generally speaking, you should load it as early as possible. The reason	660	generally speaking, you should load it as early as possible. The reason
386	is that modules might create watchers when they are loaded, and AnyEvent	661	is that modules might create watchers when they are loaded, and AnyEvent
387	will decide on the event model to use as soon as it creates watchers,	662	will decide on the event model to use as soon as it creates watchers,
388	and it might chose the wrong one unless you load the correct one	663	and it might chose the wrong one unless you load the correct one
389	yourself.	664	yourself.
390		665
391	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
392	loading the "AnyEvent::Impl::Perl" module, which gives you similar	667	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
393	behaviour everywhere, but letting AnyEvent chose is 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.
394		744
395	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	745	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
396	This is an advanced topic that you do not normally need to use AnyEvent	746	This is an advanced topic that you do not normally need to use AnyEvent
397	in a module. This section is only of use to event loop authors who want	747	in a module. This section is only of use to event loop authors who want
398	to provide AnyEvent compatibility.	748	to provide AnyEvent compatibility.
…		…
437		787
438	ENVIRONMENT VARIABLES	788	ENVIRONMENT VARIABLES
439	The following environment variables are used by this module:	789	The following environment variables are used by this module:
440		790
441	"PERL_ANYEVENT_VERBOSE"	791	"PERL_ANYEVENT_VERBOSE"
		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.
		795
		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
442	When set to 2 or higher, cause AnyEvent to report to STDERR which	800	When set to 2 or higher, cause AnyEvent to report to STDERR which
443	event model it chooses.	801	event model it chooses.
444		802
445	"PERL_ANYEVENT_MODEL"	803	"PERL_ANYEVENT_MODEL"
446	This can be used to specify the event model to be used by AnyEvent,	804	This can be used to specify the event model to be used by AnyEvent,
447	before autodetection and -probing kicks in. It must be a string	805	before auto detection and -probing kicks in. It must be a string
448	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	806	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
449	gets prepended and the resulting module name is loaded and if the	807	gets prepended and the resulting module name is loaded and if the
450	load was successful, used as event model. If it fails to load	808	load was successful, used as event model. If it fails to load
451	AnyEvent will proceed with autodetection and -probing.	809	AnyEvent will proceed with auto detection and -probing.
452		810
453	This functionality might change in future versions.	811	This functionality might change in future versions.
454		812
455	For example, to force the pure perl model (AnyEvent::Impl::Perl) you	813	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
456	could start your program like this:	814	could start your program like this:
457		815
458	PERL_ANYEVENT_MODEL=Perl perl ...	816	PERL_ANYEVENT_MODEL=Perl perl ...
459		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
460	EXAMPLE PROGRAM	853	EXAMPLE PROGRAM
461	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
462	timer to display a message once per second, and a condition variable to	855	timer to display a message once per second, and a condition variable to
463	quit the program when the user enters quit:	856	quit the program when the user enters quit:
464		857
465	use AnyEvent;	858	use AnyEvent;
466		859
…		…
471	poll => 'r',	864	poll => 'r',
472	cb => sub {	865	cb => sub {
473	warn "io event <$_[0]>\n"; # will always output <r>	866	warn "io event <$_[0]>\n"; # will always output <r>
474	chomp (my $input = <STDIN>); # read a line	867	chomp (my $input = <STDIN>); # read a line
475	warn "read: $input\n"; # output what has been read	868	warn "read: $input\n"; # output what has been read
476	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	869	$cv->send if $input =~ /^q/i; # quit program if /^q/i
477	},	870	},
478	);	871	);
479		872
480	my $time_watcher; # can only be used once	873	my $time_watcher; # can only be used once
481		874
…		…
486	});	879	});
487	}	880	}
488		881
489	new_timer; # create first timer	882	new_timer; # create first timer
490		883
491	$cv->wait; # wait until user enters /^q/i	884	$cv->recv; # wait until user enters /^q/i
492		885
493	REAL-WORLD EXAMPLE	886	REAL-WORLD EXAMPLE
494	Consider the Net::FCP module. It features (among others) the following	887	Consider the Net::FCP module. It features (among others) the following
495	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:
496		889
…		…
545	syswrite $txn->{fh}, $txn->{request}	938	syswrite $txn->{fh}, $txn->{request}
546	or die "connection or write error";	939	or die "connection or write error";
547	$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 });
548		941
549	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
550	result and signals any possible waiters that the request ahs finished:	943	result and signals any possible waiters that the request has finished:
551		944
552	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	945	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
553		946
554	if (end-of-file or data complete) {	947	if (end-of-file or data complete) {
555	$txn->{result} = $txn->{buf};	948	$txn->{result} = $txn->{buf};
556	$txn->{finished}->broadcast;	949	$txn->{finished}->send;
557	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	950	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
558	}	951	}
559		952
560	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
561	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
562	the data:	955	the data:
563		956
564	$txn->{finished}->wait;	957	$txn->{finished}->recv;
565	return $txn->{result};	958	return $txn->{result};
566		959
567	The actual code goes further and collects all errors ("die"s,	960	The actual code goes further and collects all errors ("die"s,
568	exceptions) that occured during request processing. The "result" method	961	exceptions) that occurred during request processing. The "result" method
569	detects whether an exception as thrown (it is stored inside the $txn	962	detects whether an exception as thrown (it is stored inside the $txn
570	object) and just throws the exception, which means connection errors and	963	object) and just throws the exception, which means connection errors and
571	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,
572	not in a random callback.	965	not in a random callback.
573		966
…		…
604		997
605	my $quit = AnyEvent->condvar;	998	my $quit = AnyEvent->condvar;
606		999
607	$fcp->txn_client_get ($url)->cb (sub {	1000	$fcp->txn_client_get ($url)->cb (sub {
608	...	1001	...
609	$quit->broadcast;	1002	$quit->send;
610	});	1003	});
611		1004
612	$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.
613		1247
614	FORK	1248	FORK
615	Most event libraries are not fork-safe. The ones who are usually are	1249	Most event libraries are not fork-safe. The ones who are usually are
616	because they are so inefficient. Only EV is fully fork-aware.	1250	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1251	Only EV is fully fork-aware.
617		1252
618	If you have to fork, you must either do so before creating your first	1253	If you have to fork, you must either do so before creating your first
619	watcher OR you must not use AnyEvent at all in the child.	1254	watcher OR you must not use AnyEvent at all in the child.
620		1255
621	SECURITY CONSIDERATIONS	1256	SECURITY CONSIDERATIONS
…		…
631		1266
632	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1267	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
633		1268
634	use AnyEvent;	1269	use AnyEvent;
635		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).
		1274
636	SEE ALSO	1275	SEE ALSO
637	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1276	Utility functions: AnyEvent::Util.
638	Glib::Event, Glib, Coro, Tk, Event::Lib, Qt.
639		1277
640	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1278	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
641	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1279	Event::Lib, Qt, POE.
642	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib,
643	AnyEvent::Impl::Qt.
644		1280
		1281	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
		1282	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1283	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
		1284
		1285	Non-blocking file handles, sockets, TCP clients and servers:
		1286	AnyEvent::Handle, AnyEvent::Socket.
		1287
		1288	Asynchronous DNS: AnyEvent::DNS.
		1289
		1290	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1291
645	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1292	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
646		1293
647	AUTHOR	1294	AUTHOR
648	Marc Lehmann <schmorp@schmorp.de>	1295	Marc Lehmann <schmorp@schmorp.de>
649	http://home.schmorp.de/	1296	http://home.schmorp.de/
650		1297

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Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC