[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.29 by root, Tue Jul 29 10:20:33 2008 UTC vs.
Revision 1.46 by root, Sat Jul 18 05:19:09 2009 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, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
5	loops	5	event loops.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# file descriptor readable
10	my $w = AnyEvent->io (fh => $fh, poll => "r\|w", cb => sub { ... });	11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
11		12
		13	# one-shot or repeating timers
12	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
13	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
14		16
15	print AnyEvent->now; # prints current event loop time	17	print AnyEvent->now; # prints current event loop time
16	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.	18	print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
17		19
		20	# POSIX signal
18	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });	21	my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
19		22
		23	# child process exit
20	my $w = AnyEvent->child (pid => $pid, cb => sub {	24	my $w = AnyEvent->child (pid => $pid, cb => sub {
21	my ($pid, $status) = @_;	25	my ($pid, $status) = @_;
22	...	26	...
23	});	27	});
		28
		29	# called when event loop idle (if applicable)
		30	my $w = AnyEvent->idle (cb => sub { ... });
24		31
25	my $w = AnyEvent->condvar; # stores whether a condition was flagged	32	my $w = AnyEvent->condvar; # stores whether a condition was flagged
26	$w->send; # wake up current and all future recv's	33	$w->send; # wake up current and all future recv's
27	$w->recv; # enters "main loop" till $condvar gets ->send	34	$w->recv; # enters "main loop" till $condvar gets ->send
28	# use a condvar in callback mode:	35	# use a condvar in callback mode:
132	These watchers are normal Perl objects with normal Perl lifetime. After	139	These watchers are normal Perl objects with normal Perl lifetime. After
133	creating a watcher it will immediately "watch" for events and invoke the	140	creating a watcher it will immediately "watch" for events and invoke the
134	callback when the event occurs (of course, only when the event model is	141	callback when the event occurs (of course, only when the event model is
135	in control).	142	in control).
136		143
		144	Note that callbacks must not permanently change global variables
		145	potentially in use by the event loop (such as $_ or $[) and that
		146	callbacks must not "die". The former is good programming practise in
		147	Perl and the latter stems from the fact that exception handling differs
		148	widely between event loops.
		149
137	To disable the watcher you have to destroy it (e.g. by setting the	150	To disable the watcher you have to destroy it (e.g. by setting the
138	variable you store it in to "undef" or otherwise deleting all references	151	variable you store it in to "undef" or otherwise deleting all references
139	to it).	152	to it).
140		153
141	All watchers are created by calling a method on the "AnyEvent" class.	154	All watchers are created by calling a method on the "AnyEvent" class.
…		…
156		169
157	I/O WATCHERS	170	I/O WATCHERS
158	You can create an I/O watcher by calling the "AnyEvent->io" method with	171	You can create an I/O watcher by calling the "AnyEvent->io" method with
159	the following mandatory key-value pairs as arguments:	172	the following mandatory key-value pairs as arguments:
160		173
161	"fh" the Perl file handle (not file descriptor) to watch for events	174	"fh" is the Perl file handle (or a naked file descriptor) to watch for
162	(AnyEvent might or might not keep a reference to this file handle).	175	events (AnyEvent might or might not keep a reference to this file
		176	handle). Note that only file handles pointing to things for which
		177	non-blocking operation makes sense are allowed. This includes sockets,
		178	most character devices, pipes, fifos and so on, but not for example
		179	files or block devices.
		180
163	"poll" must be a string that is either "r" or "w", which creates a	181	"poll" must be a string that is either "r" or "w", which creates a
164	watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"	182	watcher waiting for "r"eadable or "w"ritable events, respectively.
		183
165	is the callback to invoke each time the file handle becomes ready.	184	"cb" is the callback to invoke each time the file handle becomes ready.
166		185
167	Although the callback might get passed parameters, their value and	186	Although the callback might get passed parameters, their value and
168	presence is undefined and you cannot rely on them. Portable AnyEvent	187	presence is undefined and you cannot rely on them. Portable AnyEvent
169	callbacks cannot use arguments passed to I/O watcher callbacks.	188	callbacks cannot use arguments passed to I/O watcher callbacks.
170		189
…		…
302	In either case, if you care (and in most cases, you don't), then you	321	In either case, if you care (and in most cases, you don't), then you
303	can get whatever behaviour you want with any event loop, by taking	322	can get whatever behaviour you want with any event loop, by taking
304	the difference between "AnyEvent->time" and "AnyEvent->now" into	323	the difference between "AnyEvent->time" and "AnyEvent->now" into
305	account.	324	account.
306		325
		326	AnyEvent->now_update
		327	Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
		328	current time for each loop iteration (see the discussion of
		329	AnyEvent->now, above).
		330
		331	When a callback runs for a long time (or when the process sleeps),
		332	then this "current" time will differ substantially from the real
		333	time, which might affect timers and time-outs.
		334
		335	When this is the case, you can call this method, which will update
		336	the event loop's idea of "current time".
		337
		338	Note that updating the time might cause some events to be handled.
		339
307	SIGNAL WATCHERS	340	SIGNAL WATCHERS
308	You can watch for signals using a signal watcher, "signal" is the signal	341	You can watch for signals using a signal watcher, "signal" is the signal
309	name in uppercase and without any "SIG" prefix, "cb" is the Perl	342	name in uppercase and without any "SIG" prefix, "cb" is the Perl
310	callback to be invoked whenever a signal occurs.	343	callback to be invoked whenever a signal occurs.
311		344
…		…
317	invocation, and callback invocation will be synchronous. Synchronous	350	invocation, and callback invocation will be synchronous. Synchronous
318	means that it might take a while until the signal gets handled by the	351	means that it might take a while until the signal gets handled by the
319	process, but it is guaranteed not to interrupt any other callbacks.	352	process, but it is guaranteed not to interrupt any other callbacks.
320		353
321	The main advantage of using these watchers is that you can share a	354	The main advantage of using these watchers is that you can share a
322	signal between multiple watchers.	355	signal between multiple watchers, and AnyEvent will ensure that signals
		356	will not interrupt your program at bad times.
323		357
324	This watcher might use %SIG, so programs overwriting those signals	358	This watcher might use %SIG (depending on the event loop used), so
325	directly will likely not work correctly.	359	programs overwriting those signals directly will likely not work
		360	correctly.
		361
		362	Also note that many event loops (e.g. Glib, Tk, Qt, IO::Async) do not
		363	support attaching callbacks to signals, which is a pity, as you cannot
		364	do race-free signal handling in perl. AnyEvent will try to do it's best,
		365	but in some cases, signals will be delayed. The maximum time a signal
		366	might be delayed is specified in $AnyEvent::MAX_SIGNAL_LATENCY (default:
		367	10 seconds). This variable can be changed only before the first signal
		368	watcher is created, and should be left alone otherwise. Higher values
		369	will cause fewer spurious wake-ups, which is better for power and CPU
		370	saving. All these problems can be avoided by installing the optional
		371	Async::Interrupt module.
326		372
327	Example: exit on SIGINT	373	Example: exit on SIGINT
328		374
329	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	375	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
330		376
331	CHILD PROCESS WATCHERS	377	CHILD PROCESS WATCHERS
332	You can also watch on a child process exit and catch its exit status.	378	You can also watch on a child process exit and catch its exit status.
333		379
334	The child process is specified by the "pid" argument (if set to 0, it	380	The child process is specified by the "pid" argument (if set to 0, it
335	watches for any child process exit). The watcher will trigger as often	381	watches for any child process exit). The watcher will triggered only
336	as status change for the child are received. This works by installing a	382	when the child process has finished and an exit status is available, not
337	signal handler for "SIGCHLD". The callback will be called with the pid	383	on any trace events (stopped/continued).
338	and exit status (as returned by waitpid), so unlike other watcher types,	384
339	you can rely on child watcher callback arguments.	385	The callback will be called with the pid and exit status (as returned by
		386	waitpid), so unlike other watcher types, you can rely on child watcher
		387	callback arguments.
		388
		389	This watcher type works by installing a signal handler for "SIGCHLD",
		390	and since it cannot be shared, nothing else should use SIGCHLD or reap
		391	random child processes (waiting for specific child processes, e.g.
		392	inside "system", is just fine).
340		393
341	There is a slight catch to child watchers, however: you usually start	394	There is a slight catch to child watchers, however: you usually start
342	them after the child process was created, and this means the process	395	them after the child process was created, and this means the process
343	could have exited already (and no SIGCHLD will be sent anymore).	396	could have exited already (and no SIGCHLD will be sent anymore).
344		397
345	Not all event models handle this correctly (POE doesn't), but even for	398	Not all event models handle this correctly (neither POE nor IO::Async
		399	do, see their AnyEvent::Impl manpages for details), but even for event
346	event models that do handle this correctly, they usually need to be	400	models that do handle this correctly, they usually need to be loaded
347	loaded before the process exits (i.e. before you fork in the first	401	before the process exits (i.e. before you fork in the first place).
348	place).	402	AnyEvent's pure perl event loop handles all cases correctly regardless
		403	of when you start the watcher.
349		404
350	This means you cannot create a child watcher as the very first thing in	405	This means you cannot create a child watcher as the very first thing in
351	an AnyEvent program, you have to create at least one watcher before	406	an AnyEvent program, you have to create at least one watcher before
352	you "fork" the child (alternatively, you can call "AnyEvent::detect").	407	you "fork" the child (alternatively, you can call "AnyEvent::detect").
353		408
		409	As most event loops do not support waiting for child events, they will
		410	be emulated by AnyEvent in most cases, in which the latency and race
		411	problems mentioned in the description of signal watchers apply.
		412
354	Example: fork a process and wait for it	413	Example: fork a process and wait for it
355		414
356	my $done = AnyEvent->condvar;	415	my $done = AnyEvent->condvar;
357		416
358	my $pid = fork or exit 5;	417	my $pid = fork or exit 5;
359		418
360	my $w = AnyEvent->child (	419	my $w = AnyEvent->child (
361	pid => $pid,	420	pid => $pid,
362	cb => sub {	421	cb => sub {
363	my ($pid, $status) = @_;	422	my ($pid, $status) = @_;
364	warn "pid $pid exited with status $status";	423	warn "pid $pid exited with status $status";
365	$done->send;	424	$done->send;
366	},	425	},
367	);	426	);
368		427
369	# do something else, then wait for process exit	428	# do something else, then wait for process exit
370	$done->recv;	429	$done->recv;
		430
		431	IDLE WATCHERS
		432	Sometimes there is a need to do something, but it is not so important to
		433	do it instantly, but only when there is nothing better to do. This
		434	"nothing better to do" is usually defined to be "no other events need
		435	attention by the event loop".
		436
		437	Idle watchers ideally get invoked when the event loop has nothing better
		438	to do, just before it would block the process to wait for new events.
		439	Instead of blocking, the idle watcher is invoked.
		440
		441	Most event loops unfortunately do not really support idle watchers (only
		442	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
		443	will simply call the callback "from time to time".
		444
		445	Example: read lines from STDIN, but only process them when the program
		446	is otherwise idle:
		447
		448	my @lines; # read data
		449	my $idle_w;
		450	my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
		451	push @lines, scalar <STDIN>;
		452
		453	# start an idle watcher, if not already done
		454	$idle_w \|\|= AnyEvent->idle (cb => sub {
		455	# handle only one line, when there are lines left
		456	if (my $line = shift @lines) {
		457	print "handled when idle: $line";
		458	} else {
		459	# otherwise disable the idle watcher again
		460	undef $idle_w;
		461	}
		462	});
		463	});
371		464
372	CONDITION VARIABLES	465	CONDITION VARIABLES
373	If you are familiar with some event loops you will know that all of them	466	If you are familiar with some event loops you will know that all of them
374	require you to run some blocking "loop", "run" or similar function that	467	require you to run some blocking "loop", "run" or similar function that
375	will actively watch for new events and call your callbacks.	468	will actively watch for new events and call your callbacks.
376		469
377	AnyEvent is different, it expects somebody else to run the event loop	470	AnyEvent is slightly different: it expects somebody else to run the
378	and will only block when necessary (usually when told by the user).	471	event loop and will only block when necessary (usually when told by the
		472	user).
379		473
380	The instrument to do that is called a "condition variable", so called	474	The instrument to do that is called a "condition variable", so called
381	because they represent a condition that must become true.	475	because they represent a condition that must become true.
382		476
		477	Now is probably a good time to look at the examples further below.
		478
383	Condition variables can be created by calling the "AnyEvent->condvar"	479	Condition variables can be created by calling the "AnyEvent->condvar"
384	method, usually without arguments. The only argument pair allowed is	480	method, usually without arguments. The only argument pair allowed is
385
386	"cb", which specifies a callback to be called when the condition	481	"cb", which specifies a callback to be called when the condition
387	variable becomes true, with the condition variable as the first argument	482	variable becomes true, with the condition variable as the first argument
388	(but not the results).	483	(but not the results).
389		484
390	After creation, the condition variable is "false" until it becomes	485	After creation, the condition variable is "false" until it becomes
…		…
439	after => 1,	534	after => 1,
440	cb => sub { $result_ready->send },	535	cb => sub { $result_ready->send },
441	);	536	);
442		537
443	# this "blocks" (while handling events) till the callback	538	# this "blocks" (while handling events) till the callback
444	# calls send	539	# calls -<send
445	$result_ready->recv;	540	$result_ready->recv;
446		541
447	Example: wait for a timer, but take advantage of the fact that condition	542	Example: wait for a timer, but take advantage of the fact that condition
448	variables are also code references.	543	variables are also callable directly.
449		544
450	my $done = AnyEvent->condvar;	545	my $done = AnyEvent->condvar;
451	my $delay = AnyEvent->timer (after => 5, cb => $done);	546	my $delay = AnyEvent->timer (after => 5, cb => $done);
452	$done->recv;	547	$done->recv;
453		548
…		…
459		554
460	...	555	...
461		556
462	my @info = $couchdb->info->recv;	557	my @info = $couchdb->info->recv;
463		558
464	And this is how you would just ste a callback to be called whenever the	559	And this is how you would just set a callback to be called whenever the
465	results are available:	560	results are available:
466		561
467	$couchdb->info->cb (sub {	562	$couchdb->info->cb (sub {
468	my @info = $_[0]->recv;	563	my @info = $_[0]->recv;
469	});	564	});
…		…
484		579
485	Any arguments passed to the "send" call will be returned by all	580	Any arguments passed to the "send" call will be returned by all
486	future "->recv" calls.	581	future "->recv" calls.
487		582
488	Condition variables are overloaded so one can call them directly (as	583	Condition variables are overloaded so one can call them directly (as
489	a code reference). Calling them directly is the same as calling	584	if they were a code reference). Calling them directly is the same as
490	"send". Note, however, that many C-based event loops do not handle	585	calling "send".
491	overloading, so as tempting as it may be, passing a condition
492	variable instead of a callback does not work. Both the pure perl and
493	EV loops support overloading, however, as well as all functions that
494	use perl to invoke a callback (as in AnyEvent::Socket and
495	AnyEvent::DNS for example).
496		586
497	$cv->croak ($error)	587	$cv->croak ($error)
498	Similar to send, but causes all call's to "->recv" to invoke	588	Similar to send, but causes all call's to "->recv" to invoke
499	"Carp::croak" with the given error message/object/scalar.	589	"Carp::croak" with the given error message/object/scalar.
500		590
501	This can be used to signal any errors to the condition variable	591	This can be used to signal any errors to the condition variable
502	user/consumer.	592	user/consumer. Doing it this way instead of calling "croak" directly
		593	delays the error detetcion, but has the overwhelmign advantage that
		594	it diagnoses the error at the place where the result is expected,
		595	and not deep in some event clalback without connection to the actual
		596	code causing the problem.
503		597
504	$cv->begin ([group callback])	598	$cv->begin ([group callback])
505	$cv->end	599	$cv->end
506	These two methods are EXPERIMENTAL and MIGHT CHANGE.
507
508	These two methods can be used to combine many transactions/events	600	These two methods can be used to combine many transactions/events
509	into one. For example, a function that pings many hosts in parallel	601	into one. For example, a function that pings many hosts in parallel
510	might want to use a condition variable for the whole process.	602	might want to use a condition variable for the whole process.
511		603
512	Every call to "->begin" will increment a counter, and every call to	604	Every call to "->begin" will increment a counter, and every call to
513	"->end" will decrement it. If the counter reaches 0 in "->end", the	605	"->end" will decrement it. If the counter reaches 0 in "->end", the
514	(last) callback passed to "begin" will be executed. That callback is	606	(last) callback passed to "begin" will be executed. That callback is
515	supposed to call "->send", but that is not required. If no	607	supposed to call "->send", but that is not required. If no
516	callback was set, "send" will be called without any arguments.	608	callback was set, "send" will be called without any arguments.
517		609
518	Let's clarify this with the ping example:	610	You can think of "$cv->send" giving you an OR condition (one call
		611	sends), while "$cv->begin" and "$cv->end" giving you an AND
		612	condition (all "begin" calls must be "end"'ed before the condvar
		613	sends).
		614
		615	Let's start with a simple example: you have two I/O watchers (for
		616	example, STDOUT and STDERR for a program), and you want to wait for
		617	both streams to close before activating a condvar:
		618
		619	my $cv = AnyEvent->condvar;
		620
		621	$cv->begin; # first watcher
		622	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		623	defined sysread $fh1, my $buf, 4096
		624	or $cv->end;
		625	});
		626
		627	$cv->begin; # second watcher
		628	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		629	defined sysread $fh2, my $buf, 4096
		630	or $cv->end;
		631	});
		632
		633	$cv->recv;
		634
		635	This works because for every event source (EOF on file handle),
		636	there is one call to "begin", so the condvar waits for all calls to
		637	"end" before sending.
		638
		639	The ping example mentioned above is slightly more complicated, as
		640	the there are results to be passwd back, and the number of tasks
		641	that are begung can potentially be zero:
519		642
520	my $cv = AnyEvent->condvar;	643	my $cv = AnyEvent->condvar;
521		644
522	my %result;	645	my %result;
523	$cv->begin (sub { $cv->send (\%result) });	646	$cv->begin (sub { $cv->send (\%result) });
…		…
543	the loop, which serves two important purposes: first, it sets the	666	the loop, which serves two important purposes: first, it sets the
544	callback to be called once the counter reaches 0, and second, it	667	callback to be called once the counter reaches 0, and second, it
545	ensures that "send" is called even when "no" hosts are being pinged	668	ensures that "send" is called even when "no" hosts are being pinged
546	(the loop doesn't execute once).	669	(the loop doesn't execute once).
547		670
548	This is the general pattern when you "fan out" into multiple	671	This is the general pattern when you "fan out" into multiple (but
549	subrequests: use an outer "begin"/"end" pair to set the callback and	672	potentially none) subrequests: use an outer "begin"/"end" pair to
550	ensure "end" is called at least once, and then, for each subrequest	673	set the callback and ensure "end" is called at least once, and then,
551	you start, call "begin" and for each subrequest you finish, call	674	for each subrequest you start, call "begin" and for each subrequest
552	"end".	675	you finish, call "end".
553		676
554	METHODS FOR CONSUMERS	677	METHODS FOR CONSUMERS
555	These methods should only be used by the consuming side, i.e. the code	678	These methods should only be used by the consuming side, i.e. the code
556	awaits the condition.	679	awaits the condition.
557		680
…		…
566	function will call "croak".	689	function will call "croak".
567		690
568	In list context, all parameters passed to "send" will be returned,	691	In list context, all parameters passed to "send" will be returned,
569	in scalar context only the first one will be returned.	692	in scalar context only the first one will be returned.
570		693
		694	Note that doing a blocking wait in a callback is not supported by
		695	any event loop, that is, recursive invocation of a blocking "->recv"
		696	is not allowed, and the "recv" call will "croak" if such a condition
		697	is detected. This condition can be slightly loosened by using
		698	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		699	thread that doesn't run the event loop itself.
		700
571	Not all event models support a blocking wait - some die in that case	701	Not all event models support a blocking wait - some die in that case
572	(programs might want to do that to stay interactive), so *if you are	702	(programs might want to do that to stay interactive), so *if you are
573	using this from a module, never require a blocking wait*, but let	703	using this from a module, never require a blocking wait*. Instead,
574	the caller decide whether the call will block or not (for example,	704	let the caller decide whether the call will block or not (for
575	by coupling condition variables with some kind of request results	705	example, by coupling condition variables with some kind of request
576	and supporting callbacks so the caller knows that getting the result	706	results and supporting callbacks so the caller knows that getting
577	will not block, while still supporting blocking waits if the caller	707	the result will not block, while still supporting blocking waits if
578	so desires).	708	the caller so desires).
579
580	Another reason never to "->recv" in a module is that you cannot
581	sensibly have two "->recv"'s in parallel, as that would require
582	multiple interpreters or coroutines/threads, none of which
583	"AnyEvent" can supply.
584
585	The Coro module, however, can and does supply coroutines and, in
586	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
587	versions and also integrates coroutines into AnyEvent, making
588	blocking "->recv" calls perfectly safe as long as they are done from
589	another coroutine (one that doesn't run the event loop).
590		709
591	You can ensure that "-recv" never blocks by setting a callback and	710	You can ensure that "-recv" never blocks by setting a callback and
592	only calling "->recv" from within that callback (or at a later	711	only calling "->recv" from within that callback (or at a later
593	time). This will work even when the event loop does not support	712	time). This will work even when the event loop does not support
594	blocking waits otherwise.	713	blocking waits otherwise.
…		…
604	The callback will be called when the condition becomes "true", i.e.	723	The callback will be called when the condition becomes "true", i.e.
605	when "send" or "croak" are called, with the only argument being the	724	when "send" or "croak" are called, with the only argument being the
606	condition variable itself. Calling "recv" inside the callback or at	725	condition variable itself. Calling "recv" inside the callback or at
607	any later time is guaranteed not to block.	726	any later time is guaranteed not to block.
608		727
		728	SUPPORTED EVENT LOOPS/BACKENDS
		729	The available backend classes are (every class has its own manpage):
		730
		731	Backends that are autoprobed when no other event loop can be found.
		732	EV is the preferred backend when no other event loop seems to be in
		733	use. If EV is not installed, then AnyEvent will try Event, and,
		734	failing that, will fall back to its own pure-perl implementation,
		735	which is available everywhere as it comes with AnyEvent itself.
		736
		737	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		738	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		739	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		740
		741	Backends that are transparently being picked up when they are used.
		742	These will be used when they are currently loaded when the first
		743	watcher is created, in which case it is assumed that the application
		744	is using them. This means that AnyEvent will automatically pick the
		745	right backend when the main program loads an event module before
		746	anything starts to create watchers. Nothing special needs to be done
		747	by the main program.
		748
		749	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		750	AnyEvent::Impl::Tk based on Tk, very broken.
		751	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		752	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		753
		754	Backends with special needs.
		755	Qt requires the Qt::Application to be instantiated first, but will
		756	otherwise be picked up automatically. As long as the main program
		757	instantiates the application before any AnyEvent watchers are
		758	created, everything should just work.
		759
		760	AnyEvent::Impl::Qt based on Qt.
		761
		762	Support for IO::Async can only be partial, as it is too broken and
		763	architecturally limited to even support the AnyEvent API. It also is
		764	the only event loop that needs the loop to be set explicitly, so it
		765	can only be used by a main program knowing about AnyEvent. See
		766	AnyEvent::Impl::Async for the gory details.
		767
		768	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		769
		770	Event loops that are indirectly supported via other backends.
		771	Some event loops can be supported via other modules:
		772
		773	There is no direct support for WxWidgets (Wx) or Prima.
		774
		775	WxWidgets has no support for watching file handles. However, you can
		776	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		777	simply polls 20 times per second, which was considered to be too
		778	horrible to even consider for AnyEvent.
		779
		780	Prima is not supported as nobody seems to be using it, but it has a
		781	POE backend, so it can be supported through POE.
		782
		783	AnyEvent knows about both Prima and Wx, however, and will try to
		784	load POE when detecting them, in the hope that POE will pick them
		785	up, in which case everything will be automatic.
		786
609	GLOBAL VARIABLES AND FUNCTIONS	787	GLOBAL VARIABLES AND FUNCTIONS
		788	These are not normally required to use AnyEvent, but can be useful to
		789	write AnyEvent extension modules.
		790
610	$AnyEvent::MODEL	791	$AnyEvent::MODEL
611	Contains "undef" until the first watcher is being created. Then it	792	Contains "undef" until the first watcher is being created, before
		793	the backend has been autodetected.
		794
612	contains the event model that is being used, which is the name of	795	Afterwards it contains the event model that is being used, which is
613	the Perl class implementing the model. This class is usually one of	796	the name of the Perl class implementing the model. This class is
614	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	797	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
615	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	798	other class in the case AnyEvent has been extended at runtime (e.g.
616		799	in rxvt-unicode it will be "urxvt::anyevent").
617	The known classes so far are:
618
619	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
620	AnyEvent::Impl::Event based on Event, second best choice.
621	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
622	AnyEvent::Impl::Glib based on Glib, third-best choice.
623	AnyEvent::Impl::Tk based on Tk, very bad choice.
624	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
625	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
626	AnyEvent::Impl::POE based on POE, not generic enough for full support.
627
628	There is no support for WxWidgets, as WxWidgets has no support for
629	watching file handles. However, you can use WxWidgets through the
630	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
631	second, which was considered to be too horrible to even consider for
632	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
633	using it's adaptor.
634
635	AnyEvent knows about Prima and Wx and will try to use POE when
636	autodetecting them.
637		800
638	AnyEvent::detect	801	AnyEvent::detect
639	Returns $AnyEvent::MODEL, forcing autodetection of the event model	802	Returns $AnyEvent::MODEL, forcing autodetection of the event model
640	if necessary. You should only call this function right before you	803	if necessary. You should only call this function right before you
641	would have created an AnyEvent watcher anyway, that is, as late as	804	would have created an AnyEvent watcher anyway, that is, as late as
642	possible at runtime.	805	possible at runtime, and not e.g. while initialising of your module.
		806
		807	If you need to do some initialisation before AnyEvent watchers are
		808	created, use "post_detect".
643		809
644	$guard = AnyEvent::post_detect { BLOCK }	810	$guard = AnyEvent::post_detect { BLOCK }
645	Arranges for the code block to be executed as soon as the event	811	Arranges for the code block to be executed as soon as the event
646	model is autodetected (or immediately if this has already happened).	812	model is autodetected (or immediately if this has already happened).
		813
		814	The block will be executed after the actual backend has been
		815	detected ($AnyEvent::MODEL is set), but before any watchers have
		816	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		817	other initialisations - see the sources of AnyEvent::Strict or
		818	AnyEvent::AIO to see how this is used.
		819
		820	The most common usage is to create some global watchers, without
		821	forcing event module detection too early, for example, AnyEvent::AIO
		822	creates and installs the global IO::AIO watcher in a "post_detect"
		823	block to avoid autodetecting the event module at load time.
647		824
648	If called in scalar or list context, then it creates and returns an	825	If called in scalar or list context, then it creates and returns an
649	object that automatically removes the callback again when it is	826	object that automatically removes the callback again when it is
650	destroyed. See Coro::BDB for a case where this is useful.	827	destroyed. See Coro::BDB for a case where this is useful.
651		828
…		…
653	If there are any code references in this array (you can "push" to it	830	If there are any code references in this array (you can "push" to it
654	before or after loading AnyEvent), then they will called directly	831	before or after loading AnyEvent), then they will called directly
655	after the event loop has been chosen.	832	after the event loop has been chosen.
656		833
657	You should check $AnyEvent::MODEL before adding to this array,	834	You should check $AnyEvent::MODEL before adding to this array,
658	though: if it contains a true value then the event loop has already	835	though: if it is defined then the event loop has already been
659	been detected, and the array will be ignored.	836	detected, and the array will be ignored.
660		837
661	Best use "AnyEvent::post_detect { BLOCK }" instead.	838	Best use "AnyEvent::post_detect { BLOCK }" when your application
		839	allows it,as it takes care of these details.
		840
		841	This variable is mainly useful for modules that can do something
		842	useful when AnyEvent is used and thus want to know when it is
		843	initialised, but do not need to even load it by default. This array
		844	provides the means to hook into AnyEvent passively, without loading
		845	it.
662		846
663	WHAT TO DO IN A MODULE	847	WHAT TO DO IN A MODULE
664	As a module author, you should "use AnyEvent" and call AnyEvent methods	848	As a module author, you should "use AnyEvent" and call AnyEvent methods
665	freely, but you should not load a specific event module or rely on it.	849	freely, but you should not load a specific event module or rely on it.
666		850
…		…
717	variable somewhere, waiting for it, and sending it when the program	901	variable somewhere, waiting for it, and sending it when the program
718	should exit cleanly.	902	should exit cleanly.
719		903
720	OTHER MODULES	904	OTHER MODULES
721	The following is a non-exhaustive list of additional modules that use	905	The following is a non-exhaustive list of additional modules that use
722	AnyEvent and can therefore be mixed easily with other AnyEvent modules	906	AnyEvent as a client and can therefore be mixed easily with other
723	in the same program. Some of the modules come with AnyEvent, some are	907	AnyEvent modules and other event loops in the same program. Some of the
724	available via CPAN.	908	modules come with AnyEvent, most are available via CPAN.
725		909
726	AnyEvent::Util	910	AnyEvent::Util
727	Contains various utility functions that replace often-used but	911	Contains various utility functions that replace often-used but
728	blocking functions such as "inet_aton" by event-/callback-based	912	blocking functions such as "inet_aton" by event-/callback-based
729	versions.	913	versions.
…		…
735	more.	919	more.
736		920
737	AnyEvent::Handle	921	AnyEvent::Handle
738	Provide read and write buffers, manages watchers for reads and	922	Provide read and write buffers, manages watchers for reads and
739	writes, supports raw and formatted I/O, I/O queued and fully	923	writes, supports raw and formatted I/O, I/O queued and fully
740	transparent and non-blocking SSL/TLS.	924	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
741		925
742	AnyEvent::DNS	926	AnyEvent::DNS
743	Provides rich asynchronous DNS resolver capabilities.	927	Provides rich asynchronous DNS resolver capabilities.
744		928
745	AnyEvent::HTTP	929	AnyEvent::HTTP
…		…
766		950
767	AnyEvent::GPSD	951	AnyEvent::GPSD
768	A non-blocking interface to gpsd, a daemon delivering GPS	952	A non-blocking interface to gpsd, a daemon delivering GPS
769	information.	953	information.
770		954
		955	AnyEvent::IRC
		956	AnyEvent based IRC client module family (replacing the older
		957	Net::IRC3).
		958
		959	AnyEvent::XMPP
		960	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		961	older Net::XMPP2>.
		962
771	AnyEvent::IGS	963	AnyEvent::IGS
772	A non-blocking interface to the Internet Go Server protocol (used by	964	A non-blocking interface to the Internet Go Server protocol (used by
773	App::IGS).	965	App::IGS).
774		966
775	Net::IRC3
776	AnyEvent based IRC client module family.
777
778	Net::XMPP2
779	AnyEvent based XMPP (Jabber protocol) module family.
780
781	Net::FCP	967	Net::FCP
782	AnyEvent-based implementation of the Freenet Client Protocol,	968	AnyEvent-based implementation of the Freenet Client Protocol,
783	birthplace of AnyEvent.	969	birthplace of AnyEvent.
784		970
785	Event::ExecFlow	971	Event::ExecFlow
786	High level API for event-based execution flow control.	972	High level API for event-based execution flow control.
787		973
788	Coro	974	Coro
789	Has special support for AnyEvent via Coro::AnyEvent.	975	Has special support for AnyEvent via Coro::AnyEvent.
790		976
791	IO::Lambda	977	ERROR AND EXCEPTION HANDLING
792	The lambda approach to I/O - don't ask, look there. Can use	978	In general, AnyEvent does not do any error handling - it relies on the
793	AnyEvent.	979	caller to do that if required. The AnyEvent::Strict module (see also the
		980	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
		981	checking of all AnyEvent methods, however, which is highly useful during
		982	development.
794		983
795	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	984	As for exception handling (i.e. runtime errors and exceptions thrown
796	This is an advanced topic that you do not normally need to use AnyEvent	985	while executing a callback), this is not only highly event-loop
797	in a module. This section is only of use to event loop authors who want	986	specific, but also not in any way wrapped by this module, as this is the
798	to provide AnyEvent compatibility.	987	job of the main program.
799		988
800	If you need to support another event library which isn't directly	989	The pure perl event loop simply re-throws the exception (usually within
801	supported by AnyEvent, you can supply your own interface to it by	990	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
802	pushing, before the first watcher gets created, the package name of the	991	Glib uses "install_exception_handler" and so on.
803	event module and the package name of the interface to use onto
804	@AnyEvent::REGISTRY. You can do that before and even without loading
805	AnyEvent, so it is reasonably cheap.
806
807	Example:
808
809	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
810
811	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
812	package/class when it finds the "urxvt" package/module is already
813	loaded.
814
815	When AnyEvent is loaded and asked to find a suitable event model, it
816	will first check for the presence of urxvt by trying to "use" the
817	"urxvt::anyevent" module.
818
819	The class should provide implementations for all watcher types. See
820	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
821	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
822	the sources.
823
824	If you don't provide "signal" and "child" watchers than AnyEvent will
825	provide suitable (hopefully) replacements.
826
827	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
828	terminal emulator uses the above line as-is. An interface isn't included
829	in AnyEvent because it doesn't make sense outside the embedded
830	interpreter inside rxvt-unicode, and it is updated and maintained as
831	part of the rxvt-unicode distribution.
832
833	rxvt-unicode also cheats a bit by not providing blocking access to
834	condition variables: code blocking while waiting for a condition will
835	"die". This still works with most modules/usages, and blocking calls
836	must not be done in an interactive application, so it makes sense.
837		992
838	ENVIRONMENT VARIABLES	993	ENVIRONMENT VARIABLES
839	The following environment variables are used by this module:	994	The following environment variables are used by this module or its
		995	submodules.
		996
		997	Note that AnyEvent will remove all environment variables starting with
		998	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		999	enabled.
840		1000
841	"PERL_ANYEVENT_VERBOSE"	1001	"PERL_ANYEVENT_VERBOSE"
842	By default, AnyEvent will be completely silent except in fatal	1002	By default, AnyEvent will be completely silent except in fatal
843	conditions. You can set this environment variable to make AnyEvent	1003	conditions. You can set this environment variable to make AnyEvent
844	more talkative.	1004	more talkative.
…		…
847	conditions, such as not being able to load the event model specified	1007	conditions, such as not being able to load the event model specified
848	by "PERL_ANYEVENT_MODEL".	1008	by "PERL_ANYEVENT_MODEL".
849		1009
850	When set to 2 or higher, cause AnyEvent to report to STDERR which	1010	When set to 2 or higher, cause AnyEvent to report to STDERR which
851	event model it chooses.	1011	event model it chooses.
		1012
		1013	When set to 8 or higher, then AnyEvent will report extra information
		1014	on which optional modules it loads and how it implements certain
		1015	features.
852		1016
853	"PERL_ANYEVENT_STRICT"	1017	"PERL_ANYEVENT_STRICT"
854	AnyEvent does not do much argument checking by default, as thorough	1018	AnyEvent does not do much argument checking by default, as thorough
855	argument checking is very costly. Setting this variable to a true	1019	argument checking is very costly. Setting this variable to a true
856	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1020	value will cause AnyEvent to load "AnyEvent::Strict" and then to
857	thoroughly check the arguments passed to most method calls. If it	1021	thoroughly check the arguments passed to most method calls. If it
858	finds any problems it will croak.	1022	finds any problems, it will croak.
859		1023
860	In other words, enables "strict" mode.	1024	In other words, enables "strict" mode.
861		1025
862	Unlike "use strict" it is definitely recommended ot keep it off in	1026	Unlike "use strict" (or it's modern cousin, "use common::sense", it
863	production.	1027	is definitely recommended to keep it off in production. Keeping
		1028	"PERL_ANYEVENT_STRICT=1" in your environment while developing
		1029	programs can be very useful, however.
864		1030
865	"PERL_ANYEVENT_MODEL"	1031	"PERL_ANYEVENT_MODEL"
866	This can be used to specify the event model to be used by AnyEvent,	1032	This can be used to specify the event model to be used by AnyEvent,
867	before auto detection and -probing kicks in. It must be a string	1033	before auto detection and -probing kicks in. It must be a string
868	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1034	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
887	mentioned will be used, and preference will be given to protocols	1053	mentioned will be used, and preference will be given to protocols
888	mentioned earlier in the list.	1054	mentioned earlier in the list.
889		1055
890	This variable can effectively be used for denial-of-service attacks	1056	This variable can effectively be used for denial-of-service attacks
891	against local programs (e.g. when setuid), although the impact is	1057	against local programs (e.g. when setuid), although the impact is
892	likely small, as the program has to handle connection errors	1058	likely small, as the program has to handle conenction and other
893	already-	1059	failures anyways.
894		1060
895	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over	1061	Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
896	IPv6, but support both and try to use both.	1062	IPv6, but support both and try to use both.
897	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to	1063	"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
898	resolve or contact IPv6 addresses.	1064	resolve or contact IPv6 addresses.
…		…
909	EDNS0 in its DNS requests.	1075	EDNS0 in its DNS requests.
910		1076
911	"PERL_ANYEVENT_MAX_FORKS"	1077	"PERL_ANYEVENT_MAX_FORKS"
912	The maximum number of child processes that	1078	The maximum number of child processes that
913	"AnyEvent::Util::fork_call" will create in parallel.	1079	"AnyEvent::Util::fork_call" will create in parallel.
		1080
		1081	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1082	The default value for the "max_outstanding" parameter for the
		1083	default DNS resolver - this is the maximum number of parallel DNS
		1084	requests that are sent to the DNS server.
		1085
		1086	"PERL_ANYEVENT_RESOLV_CONF"
		1087	The file to use instead of /etc/resolv.conf (or OS-specific
		1088	configuration) in the default resolver. When set to the empty
		1089	string, no default config will be used.
		1090
		1091	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1092	When neither "ca_file" nor "ca_path" was specified during
		1093	AnyEvent::TLS context creation, and either of these environment
		1094	variables exist, they will be used to specify CA certificate
		1095	locations instead of a system-dependent default.
		1096
		1097	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1098	When these are set to 1, then the respective modules are not loaded.
		1099	Mostly good for testing AnyEvent itself.
		1100
		1101	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
		1102	This is an advanced topic that you do not normally need to use AnyEvent
		1103	in a module. This section is only of use to event loop authors who want
		1104	to provide AnyEvent compatibility.
		1105
		1106	If you need to support another event library which isn't directly
		1107	supported by AnyEvent, you can supply your own interface to it by
		1108	pushing, before the first watcher gets created, the package name of the
		1109	event module and the package name of the interface to use onto
		1110	@AnyEvent::REGISTRY. You can do that before and even without loading
		1111	AnyEvent, so it is reasonably cheap.
		1112
		1113	Example:
		1114
		1115	push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
		1116
		1117	This tells AnyEvent to (literally) use the "urxvt::anyevent::"
		1118	package/class when it finds the "urxvt" package/module is already
		1119	loaded.
		1120
		1121	When AnyEvent is loaded and asked to find a suitable event model, it
		1122	will first check for the presence of urxvt by trying to "use" the
		1123	"urxvt::anyevent" module.
		1124
		1125	The class should provide implementations for all watcher types. See
		1126	AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and
		1127	so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see
		1128	the sources.
		1129
		1130	If you don't provide "signal" and "child" watchers than AnyEvent will
		1131	provide suitable (hopefully) replacements.
		1132
		1133	The above example isn't fictitious, the rxvt-unicode (a.k.a. urxvt)
		1134	terminal emulator uses the above line as-is. An interface isn't included
		1135	in AnyEvent because it doesn't make sense outside the embedded
		1136	interpreter inside rxvt-unicode, and it is updated and maintained as
		1137	part of the rxvt-unicode distribution.
		1138
		1139	rxvt-unicode also cheats a bit by not providing blocking access to
		1140	condition variables: code blocking while waiting for a condition will
		1141	"die". This still works with most modules/usages, and blocking calls
		1142	must not be done in an interactive application, so it makes sense.
914		1143
915	EXAMPLE PROGRAM	1144	EXAMPLE PROGRAM
916	The following program uses an I/O watcher to read data from STDIN, a	1145	The following program uses an I/O watcher to read data from STDIN, a
917	timer to display a message once per second, and a condition variable to	1146	timer to display a message once per second, and a condition variable to
918	quit the program when the user enters quit:	1147	quit the program when the user enters quit:
…		…
1105	destroy is the time, in microseconds, that it takes to destroy a	1334	destroy is the time, in microseconds, that it takes to destroy a
1106	single watcher.	1335	single watcher.
1107		1336
1108	Results	1337	Results
1109	name watchers bytes create invoke destroy comment	1338	name watchers bytes create invoke destroy comment
1110	EV/EV 400000 244 0.56 0.46 0.31 EV native interface	1339	EV/EV 400000 224 0.47 0.35 0.27 EV native interface
1111	EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers	1340	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers
1112	CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal	1341	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal
1113	Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation	1342	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation
1114	Event/Event 16000 516 31.88 31.30 0.85 Event native interface	1343	Event/Event 16000 517 32.20 31.80 0.81 Event native interface
1115	Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers	1344	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers
		1345	IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll
		1346	IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll
1116	Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour	1347	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour
1117	Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers	1348	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers
1118	POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event	1349	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event
1119	POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select	1350	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select
1120		1351
1121	Discussion	1352	Discussion
1122	The benchmark does not measure scalability of the event loop very	1353	The benchmark does not measure scalability of the event loop very
1123	well. For example, a select-based event loop (such as the pure perl one)	1354	well. For example, a select-based event loop (such as the pure perl one)
1124	can never compete with an event loop that uses epoll when the number of	1355	can never compete with an event loop that uses epoll when the number of
…		…
1149	few of them active), of course, but this was not subject of this	1380	few of them active), of course, but this was not subject of this
1150	benchmark.	1381	benchmark.
1151		1382
1152	The "Event" module has a relatively high setup and callback invocation	1383	The "Event" module has a relatively high setup and callback invocation
1153	cost, but overall scores in on the third place.	1384	cost, but overall scores in on the third place.
		1385
		1386	"IO::Async" performs admirably well, about on par with "Event", even
		1387	when using its pure perl backend.
1154		1388
1155	"Glib"'s memory usage is quite a bit higher, but it features a faster	1389	"Glib"'s memory usage is quite a bit higher, but it features a faster
1156	callback invocation and overall ends up in the same class as "Event".	1390	callback invocation and overall ends up in the same class as "Event".
1157	However, Glib scales extremely badly, doubling the number of watchers	1391	However, Glib scales extremely badly, doubling the number of watchers
1158	increases the processing time by more than a factor of four, making it	1392	increases the processing time by more than a factor of four, making it
…		…
1229	single "request", that is, reading the token from the pipe and	1463	single "request", that is, reading the token from the pipe and
1230	forwarding it to another server. This includes deleting the old timeout	1464	forwarding it to another server. This includes deleting the old timeout
1231	and creating a new one that moves the timeout into the future.	1465	and creating a new one that moves the timeout into the future.
1232		1466
1233	Results	1467	Results
1234	name sockets create request	1468	name sockets create request
1235	EV 20000 69.01 11.16	1469	EV 20000 69.01 11.16
1236	Perl 20000 73.32 35.87	1470	Perl 20000 73.32 35.87
		1471	IOAsync 20000 157.00 98.14 epoll
		1472	IOAsync 20000 159.31 616.06 poll
1237	Event 20000 212.62 257.32	1473	Event 20000 212.62 257.32
1238	Glib 20000 651.16 1896.30	1474	Glib 20000 651.16 1896.30
1239	POE 20000 349.67 12317.24 uses POE::Loop::Event	1475	POE 20000 349.67 12317.24 uses POE::Loop::Event
1240		1476
1241	Discussion	1477	Discussion
1242	This benchmark does measure scalability and overall performance of the	1478	This benchmark does measure scalability and overall performance of the
1243	particular event loop.	1479	particular event loop.
1244		1480
1245	EV is again fastest. Since it is using epoll on my system, the setup	1481	EV is again fastest. Since it is using epoll on my system, the setup
1246	time is relatively high, though.	1482	time is relatively high, though.
1247		1483
1248	Perl surprisingly comes second. It is much faster than the C-based event	1484	Perl surprisingly comes second. It is much faster than the C-based event
1249	loops Event and Glib.	1485	loops Event and Glib.
		1486
		1487	IO::Async performs very well when using its epoll backend, and still
		1488	quite good compared to Glib when using its pure perl backend.
1250		1489
1251	Event suffers from high setup time as well (look at its code and you	1490	Event suffers from high setup time as well (look at its code and you
1252	will understand why). Callback invocation also has a high overhead	1491	will understand why). Callback invocation also has a high overhead
1253	compared to the "$_->() for .."-style loop that the Perl event loop	1492	compared to the "$_->() for .."-style loop that the Perl event loop
1254	uses. Event uses select or poll in basically all documented	1493	uses. Event uses select or poll in basically all documented
…		…
1305		1544
1306	Summary	1545	Summary
1307	* C-based event loops perform very well with small number of watchers,	1546	* C-based event loops perform very well with small number of watchers,
1308	as the management overhead dominates.	1547	as the management overhead dominates.
1309		1548
		1549	THE IO::Lambda BENCHMARK
		1550	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1551	could be misinterpreted to make AnyEvent look bad. In fact, the
		1552	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1553	better (which shouldn't come as a surprise to anybody). As such, the
		1554	benchmark is fine, and mostly shows that the AnyEvent backend from
		1555	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1556	without the extra baggage? To explore this, I wrote the equivalent
		1557	benchmark for AnyEvent.
		1558
		1559	The benchmark itself creates an echo-server, and then, for 500 times,
		1560	connects to the echo server, sends a line, waits for the reply, and then
		1561	creates the next connection. This is a rather bad benchmark, as it
		1562	doesn't test the efficiency of the framework or much non-blocking I/O,
		1563	but it is a benchmark nevertheless.
		1564
		1565	name runtime
		1566	Lambda/select 0.330 sec
		1567	+ optimized 0.122 sec
		1568	Lambda/AnyEvent 0.327 sec
		1569	+ optimized 0.138 sec
		1570	Raw sockets/select 0.077 sec
		1571	POE/select, components 0.662 sec
		1572	POE/select, raw sockets 0.226 sec
		1573	POE/select, optimized 0.404 sec
		1574
		1575	AnyEvent/select/nb 0.085 sec
		1576	AnyEvent/EV/nb 0.068 sec
		1577	+state machine 0.134 sec
		1578
		1579	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1580	benchmarks actually make blocking connects and use 100% blocking I/O,
		1581	defeating the purpose of an event-based solution. All of the newly
		1582	written AnyEvent benchmarks use 100% non-blocking connects (using
		1583	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1584	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1585	connects generally require a lot more bookkeeping and event handling
		1586	than blocking connects (which involve a single syscall only).
		1587
		1588	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1589	offers similar expressive power as POE and IO::Lambda, using
		1590	conventional Perl syntax. This means that both the echo server and the
		1591	client are 100% non-blocking, further placing it at a disadvantage.
		1592
		1593	As you can see, the AnyEvent + EV combination even beats the
		1594	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1595	backend easily beats IO::Lambda and POE.
		1596
		1597	And even the 100% non-blocking version written using the high-level (and
		1598	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
		1599	large margin, even though it does all of DNS, tcp-connect and socket I/O
		1600	in a non-blocking way.
		1601
		1602	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1603	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1604	part of the IO::lambda distribution and were used without any changes.
		1605
		1606	SIGNALS
		1607	AnyEvent currently installs handlers for these signals:
		1608
		1609	SIGCHLD
		1610	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
		1611	emulation for event loops that do not support them natively. Also,
		1612	some event loops install a similar handler.
		1613
		1614	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1615	then AnyEvent will reset it to default, to avoid losing child exit
		1616	statuses.
		1617
		1618	SIGPIPE
		1619	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
		1620	"undef" when AnyEvent gets loaded.
		1621
		1622	The rationale for this is that AnyEvent users usually do not really
		1623	depend on SIGPIPE delivery (which is purely an optimisation for
		1624	shell use, or badly-written programs), but "SIGPIPE" can cause
		1625	spurious and rare program exits as a lot of people do not expect
		1626	"SIGPIPE" when writing to some random socket.
		1627
		1628	The rationale for installing a no-op handler as opposed to ignoring
		1629	it is that this way, the handler will be restored to defaults on
		1630	exec.
		1631
		1632	Feel free to install your own handler, or reset it to defaults.
		1633
		1634	RECOMMENDED/OPTIONAL MODULES
		1635	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1636	it's built-in modules) are required to use it.
		1637
		1638	That does not mean that AnyEvent won't take advantage of some additional
		1639	modules if they are installed.
		1640
		1641	This section epxlains which additional modules will be used, and how
		1642	they affect AnyEvent's operetion.
		1643
		1644	Async::Interrupt
		1645	This slightly arcane module is used to implement fast signal
		1646	handling: To my knowledge, there is no way to do completely
		1647	race-free and quick signal handling in pure perl. To ensure that
		1648	signals still get delivered, AnyEvent will start an interval timer
		1649	to wake up perl (and catch the signals) with soemd elay (default is
		1650	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1651
		1652	If this module is available, then it will be used to implement
		1653	signal catching, which means that signals will not be delayed, and
		1654	the event loop will not be interrupted regularly, which is more
		1655	efficient (And good for battery life on laptops).
		1656
		1657	This affects not just the pure-perl event loop, but also other event
		1658	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1659
		1660	EV This module isn't really "optional", as it is simply one of the
		1661	backend event loops that AnyEvent can use. However, it is simply the
		1662	best event loop available in terms of features, speed and stability:
		1663	It supports the AnyEvent API optimally, implements all the watcher
		1664	types in XS, does automatic timer adjustments even when no monotonic
		1665	clock is available, can take avdantage of advanced kernel interfaces
		1666	such as "epoll" and "kqueue", and is the fastest backend by far.
		1667	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1668	Glib::EV).
		1669
		1670	Guard
		1671	The guard module, when used, will be used to implement
		1672	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1673	uses a lot less memory), but otherwise doesn't affect guard
		1674	operation much. It is purely used for performance.
		1675
		1676	JSON and JSON::XS
		1677	This module is required when you want to read or write JSON data via
		1678	AnyEvent::Handle. It is also written in pure-perl, but can take
		1679	advantage of the ulta-high-speed JSON::XS module when it is
		1680	installed.
		1681
		1682	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1683	installed.
		1684
		1685	Net::SSLeay
		1686	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1687	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1688	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1689
		1690	Time::HiRes
		1691	This module is part of perl since release 5.008. It will be used
		1692	when the chosen event library does not come with a timing source on
		1693	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1694	additionally use it to try to use a monotonic clock for timing
		1695	stability.
		1696
1310	FORK	1697	FORK
1311	Most event libraries are not fork-safe. The ones who are usually are	1698	Most event libraries are not fork-safe. The ones who are usually are
1312	because they rely on inefficient but fork-safe "select" or "poll" calls.	1699	because they rely on inefficient but fork-safe "select" or "poll" calls.
1313	Only EV is fully fork-aware.	1700	Only EV is fully fork-aware.
1314		1701
1315	If you have to fork, you must either do so before creating your first	1702	If you have to fork, you must either do so before creating your first
1316	watcher OR you must not use AnyEvent at all in the child.	1703	watcher OR you must not use AnyEvent at all in the child OR you must do
		1704	something completely out of the scope of AnyEvent.
1317		1705
1318	SECURITY CONSIDERATIONS	1706	SECURITY CONSIDERATIONS
1319	AnyEvent can be forced to load any event model via	1707	AnyEvent can be forced to load any event model via
1320	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1708	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1321	to execute arbitrary code or directly gain access, it can easily be used	1709	to execute arbitrary code or directly gain access, it can easily be used
…		…
1325		1713
1326	You can make AnyEvent completely ignore this variable by deleting it	1714	You can make AnyEvent completely ignore this variable by deleting it
1327	before the first watcher gets created, e.g. with a "BEGIN" block:	1715	before the first watcher gets created, e.g. with a "BEGIN" block:
1328		1716
1329	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1717	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1330		1718
1331	use AnyEvent;	1719	use AnyEvent;
1332		1720
1333	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1721	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1334	be used to probe what backend is used and gain other information (which	1722	be used to probe what backend is used and gain other information (which
1335	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	1723	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1336	and $ENV{PERL_ANYEGENT_STRICT}.	1724	and $ENV{PERL_ANYEVENT_STRICT}.
		1725
		1726	Note that AnyEvent will remove all environment variables starting with
		1727	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1728	enabled.
1337		1729
1338	BUGS	1730	BUGS
1339	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1731	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1340	hard to work around. If you suffer from memleaks, first upgrade to Perl	1732	hard to work around. If you suffer from memleaks, first upgrade to Perl
1341	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	1733	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1342	annoying mamleaks, such as leaking on "map" and "grep" but it is usually	1734	annoying memleaks, such as leaking on "map" and "grep" but it is usually
1343	not as pronounced).	1735	not as pronounced).
1344		1736
1345	SEE ALSO	1737	SEE ALSO
1346	Utility functions: AnyEvent::Util.	1738	Utility functions: AnyEvent::Util.
1347		1739
1348	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1740	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1349	Event::Lib, Qt, POE.	1741	Event::Lib, Qt, POE.
1350		1742
1351	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1743	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1352	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1744	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1353	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1745	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1746	AnyEvent::Impl::IOAsync.
1354		1747
1355	Non-blocking file handles, sockets, TCP clients and servers:	1748	Non-blocking file handles, sockets, TCP clients and servers:
1356	AnyEvent::Handle, AnyEvent::Socket.	1749	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1357		1750
1358	Asynchronous DNS: AnyEvent::DNS.	1751	Asynchronous DNS: AnyEvent::DNS.
1359		1752
1360	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1753	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1361		1754
1362	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1755	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1756	AnyEvent::HTTP.
1363		1757
1364	AUTHOR	1758	AUTHOR
1365	Marc Lehmann <schmorp@schmorp.de>	1759	Marc Lehmann <schmorp@schmorp.de>
1366	http://home.schmorp.de/	1760	http://home.schmorp.de/
1367		1761

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Comparing AnyEvent/README (file contents): Revision 1.29 by root, Tue Jul 29 10:20:33 2008 UTC vs. Revision 1.46 by root, Sat Jul 18 05:19:09 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.29 by root, Tue Jul 29 10:20:33 2008 UTC vs.
Revision 1.46 by root, Sat Jul 18 05:19:09 2009 UTC