[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.17 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.23 by root, Mon May 26 06:04:38 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 {
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
…		…
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, 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
66	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
…		…
75	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
76	module.	76	module.
77		77
78	During the first call of any watcher-creation method, the module tries	78	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	79	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,	80	following modules is already loaded: EV, Event, Glib,
81	Glib, Tk. The first one found is used. If none are found, the module	81	AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82	tries to load these modules in the stated order. The first one that can	82	used. If none are found, the module tries to load these modules
		83	(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
		84	always succeed) in the order given. The first one that can be
83	be successfully loaded will be used. If, after this, still none could be	85	successfully loaded will be used. If, after this, still none could be
84	found, AnyEvent will fall back to a pure-perl event loop, which is not	86	found, AnyEvent will fall back to a pure-perl event loop, which is not
85	very efficient, but should work everywhere.	87	very efficient, but should work everywhere.
86		88
87	Because AnyEvent first checks for modules that are already loaded,	89	Because AnyEvent first checks for modules that are already loaded,
88	loading an event model explicitly before first using AnyEvent will	90	loading an event model explicitly before first using AnyEvent will
…		…
102	explicitly.	104	explicitly.
103		105
104	WATCHERS	106	WATCHERS
105	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
106	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
107	the callback to call, the filehandle to watch, etc.	109	the callback to call, the file handle to watch, etc.
108		110
109	These watchers are normal Perl objects with normal Perl lifetime. After	111	These watchers are normal Perl objects with normal Perl lifetime. After
110	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
111	callback when the event occurs (of course, only when the event model is	113	callback when the event occurs (of course, only when the event model is
112	in control).	114	in control).
…		…
129		131
130	Note that "my $w; $w =" combination. This is necessary because in Perl,	132	Note that "my $w; $w =" combination. This is necessary because in Perl,
131	my variables are only visible after the statement in which they are	133	my variables are only visible after the statement in which they are
132	declared.	134	declared.
133		135
134	IO WATCHERS	136	I/O WATCHERS
135	You can create an I/O watcher by calling the "AnyEvent->io" method with	137	You can create an I/O watcher by calling the "AnyEvent->io" method with
136	the following mandatory key-value pairs as arguments:	138	the following mandatory key-value pairs as arguments:
137		139
138	"fh" the Perl file handle (not file descriptor) to watch for events.	140	"fh" the Perl file handle (not file descriptor) to watch for events.
139	"poll" must be a string that is either "r" or "w", which creates a	141	"poll" must be a string that is either "r" or "w", which creates a
140	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	142	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
141	is the callback to invoke each time the file handle becomes ready.	143	is the callback to invoke each time the file handle becomes ready.
142		144
143	File handles will be kept alive, so as long as the watcher exists, the	145	Although the callback might get passed parameters, their value and
144	file handle 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.
145		148
		149	The I/O watcher might use the underlying file descriptor or a copy of
146	It is not allowed to close a file handle as long as any watcher is	150	it. You must not close a file handle as long as any watcher is active on
147	active on the underlying file descriptor.	151	the underlying file descriptor.
148		152
149	Some event loops issue spurious readyness notifications, so you should	153	Some event loops issue spurious readyness notifications, so you should
150	always use non-blocking calls when reading/writing from/to your file	154	always use non-blocking calls when reading/writing from/to your file
151	handles.	155	handles.
152		156
…		…
162	TIME WATCHERS	166	TIME WATCHERS
163	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
164	with the following mandatory arguments:	168	with the following mandatory arguments:
165		169
166	"after" specifies after how many seconds (fractional values are	170	"after" specifies after how many seconds (fractional values are
167	supported) should the timer activate. "cb" the callback to invoke in	171	supported) the callback should be invoked. "cb" is the callback to
168	that case.	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.
169		177
170	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
171	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
172	and Glib).	180	and Glib).
173		181
…		…
200	o'clock").	208	o'clock").
201		209
202	While most event loops expect timers to specified in a relative way,	210	While most event loops expect timers to specified in a relative way,
203	they use absolute time internally. This makes a difference when your	211	they use absolute time internally. This makes a difference when your
204	clock "jumps", for example, when ntp decides to set your clock backwards	212	clock "jumps", for example, when ntp decides to set your clock backwards
205	from the wrong 2014-01-01 to 2008-01-01, a watcher that you created to	213	from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
206	fire "after" a second might actually take six years to finally fire.	214	supposed to fire "after" a second might actually take six years to
		215	finally fire.
207		216
208	AnyEvent cannot compensate for this. The only event loop that is	217	AnyEvent cannot compensate for this. The only event loop that is
209	conscious about these issues is EV, which offers both relative	218	conscious about these issues is EV, which offers both relative
210	(ev_timer) and absolute (ev_periodic) timers.	219	(ev_timer, based on true relative time) and absolute (ev_periodic, based
		220	on wallclock time) timers.
211		221
212	AnyEvent always prefers relative timers, if available, matching the	222	AnyEvent always prefers relative timers, if available, matching the
213	AnyEvent API.	223	AnyEvent API.
214		224
215	SIGNAL WATCHERS	225	SIGNAL WATCHERS
216	You can watch for signals using a signal watcher, "signal" is the signal	226	You can watch for signals using a signal watcher, "signal" is the signal
217	name without any "SIG" prefix, "cb" is the Perl callback to be invoked	227	name without any "SIG" prefix, "cb" is the Perl callback to be invoked
218	whenever a signal occurs.	228	whenever a signal occurs.
219		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
220	Multiple signals occurances can be clumped together into one callback	234	Multiple signal occurrences can be clumped together into one callback
221	invocation, and callback invocation will be synchronous. synchronous	235	invocation, and callback invocation will be synchronous. Synchronous
222	means that it might take a while until the signal gets handled by the	236	means that it might take a while until the signal gets handled by the
223	process, but it is guarenteed not to interrupt any other callbacks.	237	process, but it is guaranteed not to interrupt any other callbacks.
224		238
225	The main advantage of using these watchers is that you can share a	239	The main advantage of using these watchers is that you can share a
226	signal between multiple watchers.	240	signal between multiple watchers.
227		241
228	This watcher might use %SIG, so programs overwriting those signals	242	This watcher might use %SIG, so programs overwriting those signals
…		…
237		251
238	The child process is specified by the "pid" argument (if set to 0, it	252	The child process is specified by the "pid" argument (if set to 0, it
239	watches for any child process exit). The watcher will trigger as often	253	watches for any child process exit). The watcher will trigger as often
240	as status change for the child are received. This works by installing a	254	as status change for the child are received. This works by installing a
241	signal handler for "SIGCHLD". The callback will be called with the pid	255	signal handler for "SIGCHLD". The callback will be called with the pid
242	and exit status (as returned by waitpid).	256	and exit status (as returned by waitpid), so unlike other watcher types,
		257	you can rely on child watcher callback arguments.
243		258
244	Example: wait for pid 1333	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;
245		277
246	my $w = AnyEvent->child (	278	my $w = AnyEvent->child (
247	pid => 1333,	279	pid => $pid,
248	cb => sub {	280	cb => sub {
249	my ($pid, $status) = @_;	281	my ($pid, $status) = @_;
250	warn "pid $pid exited with status $status";	282	warn "pid $pid exited with status $status";
		283	$done->send;
251	},	284	},
252	);	285	);
253		286
		287	# do something else, then wait for process exit
		288	$done->recv;
		289
254	CONDITION VARIABLES	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
255	Condition variables can be created by calling the "AnyEvent->condvar"	301	Condition variables can be created by calling the "AnyEvent->condvar"
256	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.
257		305
258	A condition variable waits for a condition - precisely that the	306	After creation, the condition variable is "false" until it becomes
259	"->broadcast" method has been called.	307	"true" by calling the "send" method (or calling the condition variable
		308	as if it were a callback, read about the caveats in the description for
		309	the "->send" method).
260		310
261	They are very useful to signal that a condition has been fulfilled, for	311	Condition variables are similar to callbacks, except that you can
		312	optionally wait for them. They can also be called merge points - points
		313	in time where multiple outstanding events have been processed. And yet
		314	another way to call them is transactions - each condition variable can
		315	be used to represent a transaction, which finishes at some point and
		316	delivers a result.
		317
		318	Condition variables are very useful to signal that something has
262	example, if you write a module that does asynchronous http requests,	319	finished, for example, if you write a module that does asynchronous http
263	then a condition variable would be the ideal candidate to signal the	320	requests, then a condition variable would be the ideal candidate to
264	availability of results.	321	signal the availability of results. The user can either act when the
		322	callback is called or can synchronously "->recv" for the results.
265		323
266	You can also use condition variables to block your main program until an	324	You can also use them to simulate traditional event loops - for example,
267	event occurs - for example, you could "->wait" in your main program	325	you can block your main program until an event occurs - for example, you
268	until the user clicks the Quit button in your app, which would	326	could "->recv" in your main program until the user clicks the Quit
269	"->broadcast" the "quit" event.	327	button of your app, which would "->send" the "quit" event.
270		328
271	Note that condition variables recurse into the event loop - if you have	329	Note that condition variables recurse into the event loop - if you have
272	two pirces of code that call "->wait" in a round-robbin fashion, you	330	two pieces of code that call "->recv" in a round-robin fashion, you
273	lose. Therefore, condition variables are good to export to your caller,	331	lose. Therefore, condition variables are good to export to your caller,
274	but you should avoid making a blocking wait yourself, at least in	332	but you should avoid making a blocking wait yourself, at least in
275	callbacks, as this asks for trouble.	333	callbacks, as this asks for trouble.
276		334
277	This object has two methods:	335	Condition variables are represented by hash refs in perl, and the keys
		336	used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
		337	(it is often useful to build your own transaction class on top of
		338	AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
		339	it's "new" method in your own "new" method.
278		340
279	$cv->wait	341	There are two "sides" to a condition variable - the "producer side"
		342	which eventually calls "-> send", and the "consumer side", which waits
		343	for the send to occur.
		344
		345	Example: wait for a timer.
		346
		347	# wait till the result is ready
		348	my $result_ready = AnyEvent->condvar;
		349
		350	# do something such as adding a timer
		351	# or socket watcher the calls $result_ready->send
		352	# when the "result" is ready.
		353	# in this case, we simply use a timer:
		354	my $w = AnyEvent->timer (
		355	after => 1,
		356	cb => sub { $result_ready->send },
		357	);
		358
		359	# this "blocks" (while handling events) till the callback
		360	# calls send
		361	$result_ready->recv;
		362
		363	Example: wait for a timer, but take advantage of the fact that condition
		364	variables are also code references.
		365
		366	my $done = AnyEvent->condvar;
		367	my $delay = AnyEvent->timer (after => 5, cb => $done);
		368	$done->recv;
		369
		370	METHODS FOR PRODUCERS
		371	These methods should only be used by the producing side, i.e. the
		372	code/module that eventually sends the signal. Note that it is also the
		373	producer side which creates the condvar in most cases, but it isn't
		374	uncommon for the consumer to create it as well.
		375
		376	$cv->send (...)
		377	Flag the condition as ready - a running "->recv" and all further
		378	calls to "recv" will (eventually) return after this method has been
		379	called. If nobody is waiting the send will be remembered.
		380
		381	If a callback has been set on the condition variable, it is called
		382	immediately from within send.
		383
		384	Any arguments passed to the "send" call will be returned by all
		385	future "->recv" calls.
		386
		387	Condition variables are overloaded so one can call them directly (as
		388	a code reference). Calling them directly is the same as calling
		389	"send". Note, however, that many C-based event loops do not handle
		390	overloading, so as tempting as it may be, passing a condition
		391	variable instead of a callback does not work. Both the pure perl and
		392	EV loops support overloading, however, as well as all functions that
		393	use perl to invoke a callback (as in AnyEvent::Socket and
		394	AnyEvent::DNS for example).
		395
		396	$cv->croak ($error)
		397	Similar to send, but causes all call's to "->recv" to invoke
		398	"Carp::croak" with the given error message/object/scalar.
		399
		400	This can be used to signal any errors to the condition variable
		401	user/consumer.
		402
		403	$cv->begin ([group callback])
		404	$cv->end
		405	These two methods are EXPERIMENTAL and MIGHT CHANGE.
		406
		407	These two methods can be used to combine many transactions/events
		408	into one. For example, a function that pings many hosts in parallel
		409	might want to use a condition variable for the whole process.
		410
		411	Every call to "->begin" will increment a counter, and every call to
		412	"->end" will decrement it. If the counter reaches 0 in "->end", the
		413	(last) callback passed to "begin" will be executed. That callback is
		414	supposed to call "->send", but that is not required. If no
		415	callback was set, "send" will be called without any arguments.
		416
		417	Let's clarify this with the ping example:
		418
		419	my $cv = AnyEvent->condvar;
		420
		421	my %result;
		422	$cv->begin (sub { $cv->send (\%result) });
		423
		424	for my $host (@list_of_hosts) {
		425	$cv->begin;
		426	ping_host_then_call_callback $host, sub {
		427	$result{$host} = ...;
		428	$cv->end;
		429	};
		430	}
		431
		432	$cv->end;
		433
		434	This code fragment supposedly pings a number of hosts and calls
		435	"send" after results for all then have have been gathered - in any
		436	order. To achieve this, the code issues a call to "begin" when it
		437	starts each ping request and calls "end" when it has received some
		438	result for it. Since "begin" and "end" only maintain a counter, the
		439	order in which results arrive is not relevant.
		440
		441	There is an additional bracketing call to "begin" and "end" outside
		442	the loop, which serves two important purposes: first, it sets the
		443	callback to be called once the counter reaches 0, and second, it
		444	ensures that "send" is called even when "no" hosts are being pinged
		445	(the loop doesn't execute once).
		446
		447	This is the general pattern when you "fan out" into multiple
		448	subrequests: use an outer "begin"/"end" pair to set the callback and
		449	ensure "end" is called at least once, and then, for each subrequest
		450	you start, call "begin" and for each subrequest you finish, call
		451	"end".
		452
		453	METHODS FOR CONSUMERS
		454	These methods should only be used by the consuming side, i.e. the code
		455	awaits the condition.
		456
		457	$cv->recv
280	Wait (blocking if necessary) until the "->broadcast" method has been	458	Wait (blocking if necessary) until the "->send" or "->croak" methods
281	called on c<$cv>, while servicing other watchers normally.	459	have been called on c<$cv>, while servicing other watchers normally.
282		460
283	You can only wait once on a condition - additional calls will return	461	You can only wait once on a condition - additional calls are valid
284	immediately.	462	but will return immediately.
		463
		464	If an error condition has been set by calling "->croak", then this
		465	function will call "croak".
		466
		467	In list context, all parameters passed to "send" will be returned,
		468	in scalar context only the first one will be returned.
285		469
286	Not all event models support a blocking wait - some die in that case	470	Not all event models support a blocking wait - some die in that case
287	(programs might want to do that to stay interactive), so *if you are	471	(programs might want to do that to stay interactive), so *if you are
288	using this from a module, never require a blocking wait*, but let	472	using this from a module, never require a blocking wait*, but let
289	the caller decide whether the call will block or not (for example,	473	the caller decide whether the call will block or not (for example,
290	by coupling condition variables with some kind of request results	474	by coupling condition variables with some kind of request results
291	and supporting callbacks so the caller knows that getting the result	475	and supporting callbacks so the caller knows that getting the result
292	will not block, while still suppporting blocking waits if the caller	476	will not block, while still supporting blocking waits if the caller
293	so desires).	477	so desires).
294		478
295	Another reason never to "->wait" in a module is that you cannot	479	Another reason never to "->recv" in a module is that you cannot
296	sensibly have two "->wait"'s in parallel, as that would require	480	sensibly have two "->recv"'s in parallel, as that would require
297	multiple interpreters or coroutines/threads, none of which	481	multiple interpreters or coroutines/threads, none of which
298	"AnyEvent" can supply (the coroutine-aware backends	482	"AnyEvent" can supply.
299	AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
300	support concurrent "->wait"'s from different coroutines, however).
301		483
302	$cv->broadcast	484	The Coro module, however, can and does supply coroutines and, in
303	Flag the condition as ready - a running "->wait" and all further	485	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
304	calls to "wait" will (eventually) return after this method has been	486	versions and also integrates coroutines into AnyEvent, making
305	called. If nobody is waiting the broadcast will be remembered..	487	blocking "->recv" calls perfectly safe as long as they are done from
		488	another coroutine (one that doesn't run the event loop).
306		489
307	Example:	490	You can ensure that "-recv" never blocks by setting a callback and
		491	only calling "->recv" from within that callback (or at a later
		492	time). This will work even when the event loop does not support
		493	blocking waits otherwise.
308		494
309	# wait till the result is ready	495	$bool = $cv->ready
310	my $result_ready = AnyEvent->condvar;	496	Returns true when the condition is "true", i.e. whether "send" or
		497	"croak" have been called.
311		498
312	# do something such as adding a timer	499	$cb = $cv->cb ([new callback])
313	# or socket watcher the calls $result_ready->broadcast	500	This is a mutator function that returns the callback set and
314	# when the "result" is ready.	501	optionally replaces it before doing so.
315	# in this case, we simply use a timer:
316	my $w = AnyEvent->timer (
317	after => 1,
318	cb => sub { $result_ready->broadcast },
319	);
320		502
321	# this "blocks" (while handling events) till the watcher	503	The callback will be called when the condition becomes "true", i.e.
322	# calls broadcast	504	when "send" or "croak" are called. Calling "recv" inside the
323	$result_ready->wait;	505	callback or at any later time is guaranteed not to block.
324		506
325	GLOBAL VARIABLES AND FUNCTIONS	507	GLOBAL VARIABLES AND FUNCTIONS
326	$AnyEvent::MODEL	508	$AnyEvent::MODEL
327	Contains "undef" until the first watcher is being created. Then it	509	Contains "undef" until the first watcher is being created. Then it
328	contains the event model that is being used, which is the name of	510	contains the event model that is being used, which is the name of
…		…
330	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	512	the "AnyEvent::Impl:xxx" modules, but can be any other class in the
331	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	513	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).
332		514
333	The known classes so far are:	515	The known classes so far are:
334		516
335	AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
336	AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
337	AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).	517	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
338	AnyEvent::Impl::Event based on Event, also second best choice :)	518	AnyEvent::Impl::Event based on Event, second best choice.
		519	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
339	AnyEvent::Impl::Glib based on Glib, third-best choice.	520	AnyEvent::Impl::Glib based on Glib, third-best choice.
340	AnyEvent::Impl::Tk based on Tk, very bad choice.	521	AnyEvent::Impl::Tk based on Tk, very bad choice.
341	AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.	522	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
		523	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		524	AnyEvent::Impl::POE based on POE, not generic enough for full support.
		525
		526	There is no support for WxWidgets, as WxWidgets has no support for
		527	watching file handles. However, you can use WxWidgets through the
		528	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
		529	second, which was considered to be too horrible to even consider for
		530	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
		531	using it's adaptor.
		532
		533	AnyEvent knows about Prima and Wx and will try to use POE when
		534	autodetecting them.
342		535
343	AnyEvent::detect	536	AnyEvent::detect
344	Returns $AnyEvent::MODEL, forcing autodetection of the event model	537	Returns $AnyEvent::MODEL, forcing autodetection of the event model
345	if necessary. You should only call this function right before you	538	if necessary. You should only call this function right before you
346	would have created an AnyEvent watcher anyway, that is, as late as	539	would have created an AnyEvent watcher anyway, that is, as late as
347	possible at runtime.	540	possible at runtime.
348		541
		542	$guard = AnyEvent::post_detect { BLOCK }
		543	Arranges for the code block to be executed as soon as the event
		544	model is autodetected (or immediately if this has already happened).
		545
		546	If called in scalar or list context, then it creates and returns an
		547	object that automatically removes the callback again when it is
		548	destroyed. See Coro::BDB for a case where this is useful.
		549
		550	@AnyEvent::post_detect
		551	If there are any code references in this array (you can "push" to it
		552	before or after loading AnyEvent), then they will called directly
		553	after the event loop has been chosen.
		554
		555	You should check $AnyEvent::MODEL before adding to this array,
		556	though: if it contains a true value then the event loop has already
		557	been detected, and the array will be ignored.
		558
		559	Best use "AnyEvent::post_detect { BLOCK }" instead.
		560
349	WHAT TO DO IN A MODULE	561	WHAT TO DO IN A MODULE
350	As a module author, you should "use AnyEvent" and call AnyEvent methods	562	As a module author, you should "use AnyEvent" and call AnyEvent methods
351	freely, but you should not load a specific event module or rely on it.	563	freely, but you should not load a specific event module or rely on it.
352		564
353	Be careful when you create watchers in the module body - AnyEvent will	565	Be careful when you create watchers in the module body - AnyEvent will
354	decide which event module to use as soon as the first method is called,	566	decide which event module to use as soon as the first method is called,
355	so by calling AnyEvent in your module body you force the user of your	567	so by calling AnyEvent in your module body you force the user of your
356	module to load the event module first.	568	module to load the event module first.
357		569
358	Never call "->wait" on a condition variable unless you know that the	570	Never call "->recv" on a condition variable unless you know that the
359	"->broadcast" method has been called on it already. This is because it	571	"->send" method has been called on it already. This is because it will
360	will stall the whole program, and the whole point of using events is to	572	stall the whole program, and the whole point of using events is to stay
361	stay interactive.	573	interactive.
362		574
363	It is fine, however, to call "->wait" when the user of your module	575	It is fine, however, to call "->recv" when the user of your module
364	requests it (i.e. if you create a http request object ad have a method	576	requests it (i.e. if you create a http request object ad have a method
365	called "results" that returns the results, it should call "->wait"	577	called "results" that returns the results, it should call "->recv"
366	freely, as the user of your module knows what she is doing. always).	578	freely, as the user of your module knows what she is doing. always).
367		579
368	WHAT TO DO IN THE MAIN PROGRAM	580	WHAT TO DO IN THE MAIN PROGRAM
369	There will always be a single main program - the only place that should	581	There will always be a single main program - the only place that should
370	dictate which event model to use.	582	dictate which event model to use.
…		…
372	If it doesn't care, it can just "use AnyEvent" and use it itself, or not	584	If it doesn't care, it can just "use AnyEvent" and use it itself, or not
373	do anything special (it does not need to be event-based) and let	585	do anything special (it does not need to be event-based) and let
374	AnyEvent decide which implementation to chose if some module relies on	586	AnyEvent decide which implementation to chose if some module relies on
375	it.	587	it.
376		588
377	If the main program relies on a specific event model. For example, in	589	If the main program relies on a specific event model - for example, in
378	Gtk2 programs you have to rely on the Glib module. You should load the	590	Gtk2 programs you have to rely on the Glib module - you should load the
379	event module before loading AnyEvent or any module that uses it:	591	event module before loading AnyEvent or any module that uses it:
380	generally speaking, you should load it as early as possible. The reason	592	generally speaking, you should load it as early as possible. The reason
381	is that modules might create watchers when they are loaded, and AnyEvent	593	is that modules might create watchers when they are loaded, and AnyEvent
382	will decide on the event model to use as soon as it creates watchers,	594	will decide on the event model to use as soon as it creates watchers,
383	and it might chose the wrong one unless you load the correct one	595	and it might chose the wrong one unless you load the correct one
384	yourself.	596	yourself.
385		597
386	You can chose to use a rather inefficient pure-perl implementation by	598	You can chose to use a pure-perl implementation by loading the
387	loading the "AnyEvent::Impl::Perl" module, which gives you similar	599	"AnyEvent::Impl::Perl" module, which gives you similar behaviour
388	behaviour everywhere, but letting AnyEvent chose is generally better.	600	everywhere, but letting AnyEvent chose the model is generally better.
		601
		602	MAINLOOP EMULATION
		603	Sometimes (often for short test scripts, or even standalone programs who
		604	only want to use AnyEvent), you do not want to run a specific event
		605	loop.
		606
		607	In that case, you can use a condition variable like this:
		608
		609	AnyEvent->condvar->recv;
		610
		611	This has the effect of entering the event loop and looping forever.
		612
		613	Note that usually your program has some exit condition, in which case it
		614	is better to use the "traditional" approach of storing a condition
		615	variable somewhere, waiting for it, and sending it when the program
		616	should exit cleanly.
		617
		618	OTHER MODULES
		619	The following is a non-exhaustive list of additional modules that use
		620	AnyEvent and can therefore be mixed easily with other AnyEvent modules
		621	in the same program. Some of the modules come with AnyEvent, some are
		622	available via CPAN.
		623
		624	AnyEvent::Util
		625	Contains various utility functions that replace often-used but
		626	blocking functions such as "inet_aton" by event-/callback-based
		627	versions.
		628
		629	AnyEvent::Handle
		630	Provide read and write buffers and manages watchers for reads and
		631	writes.
		632
		633	AnyEvent::Socket
		634	Provides various utility functions for (internet protocol) sockets,
		635	addresses and name resolution. Also functions to create non-blocking
		636	tcp connections or tcp servers, with IPv6 and SRV record support and
		637	more.
		638
		639	AnyEvent::DNS
		640	Provides rich asynchronous DNS resolver capabilities.
		641
		642	AnyEvent::HTTPD
		643	Provides a simple web application server framework.
		644
		645	AnyEvent::FastPing
		646	The fastest ping in the west.
		647
		648	Net::IRC3
		649	AnyEvent based IRC client module family.
		650
		651	Net::XMPP2
		652	AnyEvent based XMPP (Jabber protocol) module family.
		653
		654	Net::FCP
		655	AnyEvent-based implementation of the Freenet Client Protocol,
		656	birthplace of AnyEvent.
		657
		658	Event::ExecFlow
		659	High level API for event-based execution flow control.
		660
		661	Coro
		662	Has special support for AnyEvent via Coro::AnyEvent.
		663
		664	AnyEvent::AIO, IO::AIO
		665	Truly asynchronous I/O, should be in the toolbox of every event
		666	programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
		667	together.
		668
		669	AnyEvent::BDB, BDB
		670	Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
		671	fuses IO::AIO and AnyEvent together.
		672
		673	IO::Lambda
		674	The lambda approach to I/O - don't ask, look there. Can use
		675	AnyEvent.
389		676
390	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	677	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
391	This is an advanced topic that you do not normally need to use AnyEvent	678	This is an advanced topic that you do not normally need to use AnyEvent
392	in a module. This section is only of use to event loop authors who want	679	in a module. This section is only of use to event loop authors who want
393	to provide AnyEvent compatibility.	680	to provide AnyEvent compatibility.
…		…
431	must not be done in an interactive application, so it makes sense.	718	must not be done in an interactive application, so it makes sense.
432		719
433	ENVIRONMENT VARIABLES	720	ENVIRONMENT VARIABLES
434	The following environment variables are used by this module:	721	The following environment variables are used by this module:
435		722
436	"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, cause AnyEvent to	723	"PERL_ANYEVENT_VERBOSE"
437	report to STDERR which event model it chooses.	724	By default, AnyEvent will be completely silent except in fatal
		725	conditions. You can set this environment variable to make AnyEvent
		726	more talkative.
		727
		728	When set to 1 or higher, causes AnyEvent to warn about unexpected
		729	conditions, such as not being able to load the event model specified
		730	by "PERL_ANYEVENT_MODEL".
		731
		732	When set to 2 or higher, cause AnyEvent to report to STDERR which
		733	event model it chooses.
		734
		735	"PERL_ANYEVENT_MODEL"
		736	This can be used to specify the event model to be used by AnyEvent,
		737	before auto detection and -probing kicks in. It must be a string
		738	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
		739	gets prepended and the resulting module name is loaded and if the
		740	load was successful, used as event model. If it fails to load
		741	AnyEvent will proceed with auto detection and -probing.
		742
		743	This functionality might change in future versions.
		744
		745	For example, to force the pure perl model (AnyEvent::Impl::Perl) you
		746	could start your program like this:
		747
		748	PERL_ANYEVENT_MODEL=Perl perl ...
		749
		750	"PERL_ANYEVENT_PROTOCOLS"
		751	Used by both AnyEvent::DNS and AnyEvent::Socket to determine
		752	preferences for IPv4 or IPv6. The default is unspecified (and might
		753	change, or be the result of auto probing).
		754
		755	Must be set to a comma-separated list of protocols or address
		756	families, current supported: "ipv4" and "ipv6". Only protocols
		757	mentioned will be used, and preference will be given to protocols
		758	mentioned earlier in the list.
		759
		760	This variable can effectively be used for denial-of-service attacks
		761	against local programs (e.g. when setuid), although the impact is
		762	likely small, as the program has to handle connection errors
		763	already-
		764
		765	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
		766	IPv6, but support both and try to use both.
		767	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
		768	resolve or contact IPv6 addresses.
		769	"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
		770	prefer IPv6 over IPv4.
		771
		772	"PERL_ANYEVENT_EDNS0"
		773	Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
		774	for DNS. This extension is generally useful to reduce DNS traffic,
		775	but some (broken) firewalls drop such DNS packets, which is why it
		776	is off by default.
		777
		778	Setting this variable to 1 will cause AnyEvent::DNS to announce
		779	EDNS0 in its DNS requests.
438		780
439	EXAMPLE PROGRAM	781	EXAMPLE PROGRAM
440	The following program uses an IO watcher to read data from STDIN, a	782	The following program uses an I/O watcher to read data from STDIN, a
441	timer to display a message once per second, and a condition variable to	783	timer to display a message once per second, and a condition variable to
442	quit the program when the user enters quit:	784	quit the program when the user enters quit:
443		785
444	use AnyEvent;	786	use AnyEvent;
445		787
…		…
450	poll => 'r',	792	poll => 'r',
451	cb => sub {	793	cb => sub {
452	warn "io event <$_[0]>\n"; # will always output <r>	794	warn "io event <$_[0]>\n"; # will always output <r>
453	chomp (my $input = <STDIN>); # read a line	795	chomp (my $input = <STDIN>); # read a line
454	warn "read: $input\n"; # output what has been read	796	warn "read: $input\n"; # output what has been read
455	$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i	797	$cv->send if $input =~ /^q/i; # quit program if /^q/i
456	},	798	},
457	);	799	);
458		800
459	my $time_watcher; # can only be used once	801	my $time_watcher; # can only be used once
460		802
…		…
465	});	807	});
466	}	808	}
467		809
468	new_timer; # create first timer	810	new_timer; # create first timer
469		811
470	$cv->wait; # wait until user enters /^q/i	812	$cv->recv; # wait until user enters /^q/i
471		813
472	REAL-WORLD EXAMPLE	814	REAL-WORLD EXAMPLE
473	Consider the Net::FCP module. It features (among others) the following	815	Consider the Net::FCP module. It features (among others) the following
474	API calls, which are to freenet what HTTP GET requests are to http:	816	API calls, which are to freenet what HTTP GET requests are to http:
475		817
…		…
524	syswrite $txn->{fh}, $txn->{request}	866	syswrite $txn->{fh}, $txn->{request}
525	or die "connection or write error";	867	or die "connection or write error";
526	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });	868	$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
527		869
528	Again, "fh_ready_r" waits till all data has arrived, and then stores the	870	Again, "fh_ready_r" waits till all data has arrived, and then stores the
529	result and signals any possible waiters that the request ahs finished:	871	result and signals any possible waiters that the request has finished:
530		872
531	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};	873	sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
532		874
533	if (end-of-file or data complete) {	875	if (end-of-file or data complete) {
534	$txn->{result} = $txn->{buf};	876	$txn->{result} = $txn->{buf};
535	$txn->{finished}->broadcast;	877	$txn->{finished}->send;
536	$txb->{cb}->($txn) of $txn->{cb}; # also call callback	878	$txb->{cb}->($txn) of $txn->{cb}; # also call callback
537	}	879	}
538		880
539	The "result" method, finally, just waits for the finished signal (if the	881	The "result" method, finally, just waits for the finished signal (if the
540	request was already finished, it doesn't wait, of course, and returns	882	request was already finished, it doesn't wait, of course, and returns
541	the data:	883	the data:
542		884
543	$txn->{finished}->wait;	885	$txn->{finished}->recv;
544	return $txn->{result};	886	return $txn->{result};
545		887
546	The actual code goes further and collects all errors ("die"s,	888	The actual code goes further and collects all errors ("die"s,
547	exceptions) that occured during request processing. The "result" method	889	exceptions) that occurred during request processing. The "result" method
548	detects whether an exception as thrown (it is stored inside the $txn	890	detects whether an exception as thrown (it is stored inside the $txn
549	object) and just throws the exception, which means connection errors and	891	object) and just throws the exception, which means connection errors and
550	other problems get reported tot he code that tries to use the result,	892	other problems get reported tot he code that tries to use the result,
551	not in a random callback.	893	not in a random callback.
552		894
…		…
583		925
584	my $quit = AnyEvent->condvar;	926	my $quit = AnyEvent->condvar;
585		927
586	$fcp->txn_client_get ($url)->cb (sub {	928	$fcp->txn_client_get ($url)->cb (sub {
587	...	929	...
588	$quit->broadcast;	930	$quit->send;
589	});	931	});
590		932
591	$quit->wait;	933	$quit->recv;
		934
		935	BENCHMARKS
		936	To give you an idea of the performance and overheads that AnyEvent adds
		937	over the event loops themselves and to give you an impression of the
		938	speed of various event loops I prepared some benchmarks.
		939
		940	BENCHMARKING ANYEVENT OVERHEAD
		941	Here is a benchmark of various supported event models used natively and
		942	through AnyEvent. The benchmark creates a lot of timers (with a zero
		943	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
		944	which it is), lets them fire exactly once and destroys them again.
		945
		946	Source code for this benchmark is found as eg/bench in the AnyEvent
		947	distribution.
		948
		949	Explanation of the columns
		950	watcher is the number of event watchers created/destroyed. Since
		951	different event models feature vastly different performances, each event
		952	loop was given a number of watchers so that overall runtime is
		953	acceptable and similar between tested event loop (and keep them from
		954	crashing): Glib would probably take thousands of years if asked to
		955	process the same number of watchers as EV in this benchmark.
		956
		957	bytes is the number of bytes (as measured by the resident set size,
		958	RSS) consumed by each watcher. This method of measuring captures both C
		959	and Perl-based overheads.
		960
		961	create is the time, in microseconds (millionths of seconds), that it
		962	takes to create a single watcher. The callback is a closure shared
		963	between all watchers, to avoid adding memory overhead. That means
		964	closure creation and memory usage is not included in the figures.
		965
		966	invoke is the time, in microseconds, used to invoke a simple callback.
		967	The callback simply counts down a Perl variable and after it was invoked
		968	"watcher" times, it would "->send" a condvar once to signal the end of
		969	this phase.
		970
		971	destroy is the time, in microseconds, that it takes to destroy a
		972	single watcher.
		973
		974	Results
		975	name watchers bytes create invoke destroy comment
		976	EV/EV 400000 244 0.56 0.46 0.31 EV native interface
		977	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers
		978	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal
		979	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation
		980	Event/Event 16000 516 31.88 31.30 0.85 Event native interface
		981	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers
		982	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour
		983	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers
		984	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event
		985	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select
		986
		987	Discussion
		988	The benchmark does not measure scalability of the event loop very
		989	well. For example, a select-based event loop (such as the pure perl one)
		990	can never compete with an event loop that uses epoll when the number of
		991	file descriptors grows high. In this benchmark, all events become ready
		992	at the same time, so select/poll-based implementations get an unnatural
		993	speed boost.
		994
		995	Also, note that the number of watchers usually has a nonlinear effect on
		996	overall speed, that is, creating twice as many watchers doesn't take
		997	twice the time - usually it takes longer. This puts event loops tested
		998	with a higher number of watchers at a disadvantage.
		999
		1000	To put the range of results into perspective, consider that on the
		1001	benchmark machine, handling an event takes roughly 1600 CPU cycles with
		1002	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
		1003	CPU cycles with POE.
		1004
		1005	"EV" is the sole leader regarding speed and memory use, which are both
		1006	maximal/minimal, respectively. Even when going through AnyEvent, it uses
		1007	far less memory than any other event loop and is still faster than Event
		1008	natively.
		1009
		1010	The pure perl implementation is hit in a few sweet spots (both the
		1011	constant timeout and the use of a single fd hit optimisations in the
		1012	perl interpreter and the backend itself). Nevertheless this shows that
		1013	it adds very little overhead in itself. Like any select-based backend
		1014	its performance becomes really bad with lots of file descriptors (and
		1015	few of them active), of course, but this was not subject of this
		1016	benchmark.
		1017
		1018	The "Event" module has a relatively high setup and callback invocation
		1019	cost, but overall scores in on the third place.
		1020
		1021	"Glib"'s memory usage is quite a bit higher, but it features a faster
		1022	callback invocation and overall ends up in the same class as "Event".
		1023	However, Glib scales extremely badly, doubling the number of watchers
		1024	increases the processing time by more than a factor of four, making it
		1025	completely unusable when using larger numbers of watchers (note that
		1026	only a single file descriptor was used in the benchmark, so
		1027	inefficiencies of "poll" do not account for this).
		1028
		1029	The "Tk" adaptor works relatively well. The fact that it crashes with
		1030	more than 2000 watchers is a big setback, however, as correctness takes
		1031	precedence over speed. Nevertheless, its performance is surprising, as
		1032	the file descriptor is dup()ed for each watcher. This shows that the
		1033	dup() employed by some adaptors is not a big performance issue (it does
		1034	incur a hidden memory cost inside the kernel which is not reflected in
		1035	the figures above).
		1036
		1037	"POE", regardless of underlying event loop (whether using its pure perl
		1038	select-based backend or the Event module, the POE-EV backend couldn't be
		1039	tested because it wasn't working) shows abysmal performance and memory
		1040	usage with AnyEvent: Watchers use almost 30 times as much memory as EV
		1041	watchers, and 10 times as much memory as Event (the high memory
		1042	requirements are caused by requiring a session for each watcher).
		1043	Watcher invocation speed is almost 900 times slower than with AnyEvent's
		1044	pure perl implementation.
		1045
		1046	The design of the POE adaptor class in AnyEvent can not really account
		1047	for the performance issues, though, as session creation overhead is
		1048	small compared to execution of the state machine, which is coded pretty
		1049	optimally within AnyEvent::Impl::POE (and while everybody agrees that
		1050	using multiple sessions is not a good approach, especially regarding
		1051	memory usage, even the author of POE could not come up with a faster
		1052	design).
		1053
		1054	Summary
		1055	* Using EV through AnyEvent is faster than any other event loop (even
		1056	when used without AnyEvent), but most event loops have acceptable
		1057	performance with or without AnyEvent.
		1058
		1059	* The overhead AnyEvent adds is usually much smaller than the overhead
		1060	of the actual event loop, only with extremely fast event loops such
		1061	as EV adds AnyEvent significant overhead.
		1062
		1063	* You should avoid POE like the plague if you want performance or
		1064	reasonable memory usage.
		1065
		1066	BENCHMARKING THE LARGE SERVER CASE
		1067	This benchmark actually benchmarks the event loop itself. It works by
		1068	creating a number of "servers": each server consists of a socket pair, a
		1069	timeout watcher that gets reset on activity (but never fires), and an
		1070	I/O watcher waiting for input on one side of the socket. Each time the
		1071	socket watcher reads a byte it will write that byte to a random other
		1072	"server".
		1073
		1074	The effect is that there will be a lot of I/O watchers, only part of
		1075	which are active at any one point (so there is a constant number of
		1076	active fds for each loop iteration, but which fds these are is random).
		1077	The timeout is reset each time something is read because that reflects
		1078	how most timeouts work (and puts extra pressure on the event loops).
		1079
		1080	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
		1081	100 (1%) are active. This mirrors the activity of large servers with
		1082	many connections, most of which are idle at any one point in time.
		1083
		1084	Source code for this benchmark is found as eg/bench2 in the AnyEvent
		1085	distribution.
		1086
		1087	Explanation of the columns
		1088	sockets is the number of sockets, and twice the number of "servers"
		1089	(as each server has a read and write socket end).
		1090
		1091	create is the time it takes to create a socket pair (which is
		1092	nontrivial) and two watchers: an I/O watcher and a timeout watcher.
		1093
		1094	request, the most important value, is the time it takes to handle a
		1095	single "request", that is, reading the token from the pipe and
		1096	forwarding it to another server. This includes deleting the old timeout
		1097	and creating a new one that moves the timeout into the future.
		1098
		1099	Results
		1100	name sockets create request
		1101	EV 20000 69.01 11.16
		1102	Perl 20000 73.32 35.87
		1103	Event 20000 212.62 257.32
		1104	Glib 20000 651.16 1896.30
		1105	POE 20000 349.67 12317.24 uses POE::Loop::Event
		1106
		1107	Discussion
		1108	This benchmark does measure scalability and overall performance of the
		1109	particular event loop.
		1110
		1111	EV is again fastest. Since it is using epoll on my system, the setup
		1112	time is relatively high, though.
		1113
		1114	Perl surprisingly comes second. It is much faster than the C-based event
		1115	loops Event and Glib.
		1116
		1117	Event suffers from high setup time as well (look at its code and you
		1118	will understand why). Callback invocation also has a high overhead
		1119	compared to the "$_->() for .."-style loop that the Perl event loop
		1120	uses. Event uses select or poll in basically all documented
		1121	configurations.
		1122
		1123	Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
		1124	clearly fails to perform with many filehandles or in busy servers.
		1125
		1126	POE is still completely out of the picture, taking over 1000 times as
		1127	long as EV, and over 100 times as long as the Perl implementation, even
		1128	though it uses a C-based event loop in this case.
		1129
		1130	Summary
		1131	* The pure perl implementation performs extremely well.
		1132
		1133	* Avoid Glib or POE in large projects where performance matters.
		1134
		1135	BENCHMARKING SMALL SERVERS
		1136	While event loops should scale (and select-based ones do not...) even to
		1137	large servers, most programs we (or I :) actually write have only a few
		1138	I/O watchers.
		1139
		1140	In this benchmark, I use the same benchmark program as in the large
		1141	server case, but it uses only eight "servers", of which three are active
		1142	at any one time. This should reflect performance for a small server
		1143	relatively well.
		1144
		1145	The columns are identical to the previous table.
		1146
		1147	Results
		1148	name sockets create request
		1149	EV 16 20.00 6.54
		1150	Perl 16 25.75 12.62
		1151	Event 16 81.27 35.86
		1152	Glib 16 32.63 15.48
		1153	POE 16 261.87 276.28 uses POE::Loop::Event
		1154
		1155	Discussion
		1156	The benchmark tries to test the performance of a typical small server.
		1157	While knowing how various event loops perform is interesting, keep in
		1158	mind that their overhead in this case is usually not as important, due
		1159	to the small absolute number of watchers (that is, you need efficiency
		1160	and speed most when you have lots of watchers, not when you only have a
		1161	few of them).
		1162
		1163	EV is again fastest.
		1164
		1165	Perl again comes second. It is noticeably faster than the C-based event
		1166	loops Event and Glib, although the difference is too small to really
		1167	matter.
		1168
		1169	POE also performs much better in this case, but is is still far behind
		1170	the others.
		1171
		1172	Summary
		1173	* C-based event loops perform very well with small number of watchers,
		1174	as the management overhead dominates.
		1175
		1176	FORK
		1177	Most event libraries are not fork-safe. The ones who are usually are
		1178	because they rely on inefficient but fork-safe "select" or "poll" calls.
		1179	Only EV is fully fork-aware.
		1180
		1181	If you have to fork, you must either do so before creating your first
		1182	watcher OR you must not use AnyEvent at all in the child.
		1183
		1184	SECURITY CONSIDERATIONS
		1185	AnyEvent can be forced to load any event model via
		1186	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
		1187	to execute arbitrary code or directly gain access, it can easily be used
		1188	to make the program hang or malfunction in subtle ways, as AnyEvent
		1189	watchers will not be active when the program uses a different event
		1190	model than specified in the variable.
		1191
		1192	You can make AnyEvent completely ignore this variable by deleting it
		1193	before the first watcher gets created, e.g. with a "BEGIN" block:
		1194
		1195	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
		1196
		1197	use AnyEvent;
		1198
		1199	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
		1200	be used to probe what backend is used and gain other information (which
		1201	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
592		1202
593	SEE ALSO	1203	SEE ALSO
594	Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event,	1204	Utility functions: AnyEvent::Util.
595	Glib::Event, Glib, Coro, Tk.
596		1205
597	Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV,	1206	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
598	AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib,	1207	Event::Lib, Qt, POE.
		1208
		1209	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
599	AnyEvent::Impl::Tk, AnyEvent::Impl::Perl.	1210	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
		1211	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
600		1212
		1213	Non-blocking file handles, sockets, TCP clients and servers:
		1214	AnyEvent::Handle, AnyEvent::Socket.
		1215
		1216	Asynchronous DNS: AnyEvent::DNS.
		1217
		1218	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
		1219
601	Nontrivial usage examples: Net::FCP, Net::XMPP2.	1220	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
602		1221
603	AUTHOR	1222	AUTHOR
604	Marc Lehmann <schmorp@schmorp.de>	1223	Marc Lehmann <schmorp@schmorp.de>
605	http://home.schmorp.de/	1224	http://home.schmorp.de/
606		1225

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Revision 1.17 by root, Tue Apr 22 05:12:19 2008 UTC vs.
Revision 1.23 by root, Mon May 26 06:04:38 2008 UTC