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Comparing AnyEvent/README (file contents):
Revision 1.39 by root, Sun Jun 7 16:48:38 2009 UTC vs.
Revision 1.61 by root, Wed Apr 28 14:15:55 2010 UTC

…		…
1	NAME	1	NAME
2	AnyEvent - provide framework for multiple event loops	2	AnyEvent - the DBI of event loop programming
3		3
4	EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	event loops.	5	Qt and POE are various supported event loops/environments.
6		6
7	SYNOPSIS	7	SYNOPSIS
8	use AnyEvent;	8	use AnyEvent;
9		9
		10	# if you prefer function calls, look at the L<AE> manpage for
		11	# an alternative API.
		12
10	# file descriptor readable	13	# file handle or descriptor readable
11	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });	14	my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12		15
13	# one-shot or repeating timers	16	# one-shot or repeating timers
14	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });	17	my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
15	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...	18	my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
37		40
38	INTRODUCTION/TUTORIAL	41	INTRODUCTION/TUTORIAL
39	This manpage is mainly a reference manual. If you are interested in a	42	This manpage is mainly a reference manual. If you are interested in a
40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro	43	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
41	manpage.	44	manpage.
		45
		46	SUPPORT
		47	There is a mailinglist for discussing all things AnyEvent, and an IRC
		48	channel, too.
		49
		50	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		51	Repository, at <http://anyevent.schmorp.de>, for more info.
42		52
43	WHY YOU SHOULD USE THIS MODULE (OR NOT)	53	WHY YOU SHOULD USE THIS MODULE (OR NOT)
44	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	54	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
45	nowadays. So what is different about AnyEvent?	55	nowadays. So what is different about AnyEvent?
46		56
…		…
166	Note that "my $w; $w =" combination. This is necessary because in Perl,	176	Note that "my $w; $w =" combination. This is necessary because in Perl,
167	my variables are only visible after the statement in which they are	177	my variables are only visible after the statement in which they are
168	declared.	178	declared.
169		179
170	I/O WATCHERS	180	I/O WATCHERS
		181	$w = AnyEvent->io (
		182	fh => <filehandle_or_fileno>,
		183	poll => <"r" or "w">,
		184	cb => <callback>,
		185	);
		186
171	You can create an I/O watcher by calling the "AnyEvent->io" method with	187	You can create an I/O watcher by calling the "AnyEvent->io" method with
172	the following mandatory key-value pairs as arguments:	188	the following mandatory key-value pairs as arguments:
173		189
174	"fh" is the Perl file handle (not file descriptor) to watch for	190	"fh" is the Perl file handle (or a naked file descriptor) to watch for
175	events (AnyEvent might or might not keep a reference to this file	191	events (AnyEvent might or might not keep a reference to this file
176	handle). Note that only file handles pointing to things for which	192	handle). Note that only file handles pointing to things for which
177	non-blocking operation makes sense are allowed. This includes sockets,	193	non-blocking operation makes sense are allowed. This includes sockets,
178	most character devices, pipes, fifos and so on, but not for example	194	most character devices, pipes, fifos and so on, but not for example
179	files or block devices.	195	files or block devices.
…		…
203	warn "read: $input\n";	219	warn "read: $input\n";
204	undef $w;	220	undef $w;
205	});	221	});
206		222
207	TIME WATCHERS	223	TIME WATCHERS
		224	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		225
		226	$w = AnyEvent->timer (
		227	after => <fractional_seconds>,
		228	interval => <fractional_seconds>,
		229	cb => <callback>,
		230	);
		231
208	You can create a time watcher by calling the "AnyEvent->timer" method	232	You can create a time watcher by calling the "AnyEvent->timer" method
209	with the following mandatory arguments:	233	with the following mandatory arguments:
210		234
211	"after" specifies after how many seconds (fractional values are	235	"after" specifies after how many seconds (fractional values are
212	supported) the callback should be invoked. "cb" is the callback to	236	supported) the callback should be invoked. "cb" is the callback to
…		…
333	time, which might affect timers and time-outs.	357	time, which might affect timers and time-outs.
334		358
335	When this is the case, you can call this method, which will update	359	When this is the case, you can call this method, which will update
336	the event loop's idea of "current time".	360	the event loop's idea of "current time".
337		361
		362	A typical example would be a script in a web server (e.g.
		363	"mod_perl") - when mod_perl executes the script, then the event loop
		364	will have the wrong idea about the "current time" (being potentially
		365	far in the past, when the script ran the last time). In that case
		366	you should arrange a call to "AnyEvent->now_update" each time the
		367	web server process wakes up again (e.g. at the start of your script,
		368	or in a handler).
		369
338	Note that updating the time might cause some events to be handled.	370	Note that updating the time might cause some events to be handled.
339		371
340	SIGNAL WATCHERS	372	SIGNAL WATCHERS
		373	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		374
341	You can watch for signals using a signal watcher, "signal" is the signal	375	You can watch for signals using a signal watcher, "signal" is the signal
342	name in uppercase and without any "SIG" prefix, "cb" is the Perl	376	name in uppercase and without any "SIG" prefix, "cb" is the Perl
343	callback to be invoked whenever a signal occurs.	377	callback to be invoked whenever a signal occurs.
344		378
345	Although the callback might get passed parameters, their value and	379	Although the callback might get passed parameters, their value and
…		…
350	invocation, and callback invocation will be synchronous. Synchronous	384	invocation, and callback invocation will be synchronous. Synchronous
351	means that it might take a while until the signal gets handled by the	385	means that it might take a while until the signal gets handled by the
352	process, but it is guaranteed not to interrupt any other callbacks.	386	process, but it is guaranteed not to interrupt any other callbacks.
353		387
354	The main advantage of using these watchers is that you can share a	388	The main advantage of using these watchers is that you can share a
355	signal between multiple watchers.	389	signal between multiple watchers, and AnyEvent will ensure that signals
		390	will not interrupt your program at bad times.
356		391
357	This watcher might use %SIG, so programs overwriting those signals	392	This watcher might use %SIG (depending on the event loop used), so
358	directly will likely not work correctly.	393	programs overwriting those signals directly will likely not work
		394	correctly.
359		395
360	Example: exit on SIGINT	396	Example: exit on SIGINT
361		397
362	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	398	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
363		399
		400	Restart Behaviour
		401	While restart behaviour is up to the event loop implementation, most
		402	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		403	pure perl implementation).
		404
		405	Safe/Unsafe Signals
		406	Perl signals can be either "safe" (synchronous to opcode handling) or
		407	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		408	latter might corrupt your memory.
		409
		410	AnyEvent signal handlers are, in addition, synchronous to the event
		411	loop, i.e. they will not interrupt your running perl program but will
		412	only be called as part of the normal event handling (just like timer,
		413	I/O etc. callbacks, too).
		414
		415	Signal Races, Delays and Workarounds
		416	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		417	callbacks to signals in a generic way, which is a pity, as you cannot do
		418	race-free signal handling in perl, requiring C libraries for this.
		419	AnyEvent will try to do it's best, which means in some cases, signals
		420	will be delayed. The maximum time a signal might be delayed is specified
		421	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		422	can be changed only before the first signal watcher is created, and
		423	should be left alone otherwise. This variable determines how often
		424	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		425	will cause fewer spurious wake-ups, which is better for power and CPU
		426	saving.
		427
		428	All these problems can be avoided by installing the optional
		429	Async::Interrupt module, which works with most event loops. It will not
		430	work with inherently broken event loops such as Event or Event::Lib (and
		431	not with POE currently, as POE does it's own workaround with one-second
		432	latency). For those, you just have to suffer the delays.
		433
364	CHILD PROCESS WATCHERS	434	CHILD PROCESS WATCHERS
		435	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		436
365	You can also watch on a child process exit and catch its exit status.	437	You can also watch on a child process exit and catch its exit status.
366		438
367	The child process is specified by the "pid" argument (if set to 0, it	439	The child process is specified by the "pid" argument (one some backends,
368	watches for any child process exit). The watcher will triggered only	440	using 0 watches for any child process exit, on others this will croak).
369	when the child process has finished and an exit status is available, not	441	The watcher will be triggered only when the child process has finished
370	on any trace events (stopped/continued).	442	and an exit status is available, not on any trace events
		443	(stopped/continued).
371		444
372	The callback will be called with the pid and exit status (as returned by	445	The callback will be called with the pid and exit status (as returned by
373	waitpid), so unlike other watcher types, you can rely on child watcher	446	waitpid), so unlike other watcher types, you can rely on child watcher
374	callback arguments.	447	callback arguments.
375		448
…		…
380		453
381	There is a slight catch to child watchers, however: you usually start	454	There is a slight catch to child watchers, however: you usually start
382	them after the child process was created, and this means the process	455	them after the child process was created, and this means the process
383	could have exited already (and no SIGCHLD will be sent anymore).	456	could have exited already (and no SIGCHLD will be sent anymore).
384		457
385	Not all event models handle this correctly (POE doesn't), but even for	458	Not all event models handle this correctly (neither POE nor IO::Async
		459	do, see their AnyEvent::Impl manpages for details), but even for event
386	event models that do handle this correctly, they usually need to be	460	models that do handle this correctly, they usually need to be loaded
387	loaded before the process exits (i.e. before you fork in the first	461	before the process exits (i.e. before you fork in the first place).
388	place).	462	AnyEvent's pure perl event loop handles all cases correctly regardless
		463	of when you start the watcher.
389		464
390	This means you cannot create a child watcher as the very first thing in	465	This means you cannot create a child watcher as the very first thing in
391	an AnyEvent program, you have to create at least one watcher before	466	an AnyEvent program, you have to create at least one watcher before
392	you "fork" the child (alternatively, you can call "AnyEvent::detect").	467	you "fork" the child (alternatively, you can call "AnyEvent::detect").
		468
		469	As most event loops do not support waiting for child events, they will
		470	be emulated by AnyEvent in most cases, in which the latency and race
		471	problems mentioned in the description of signal watchers apply.
393		472
394	Example: fork a process and wait for it	473	Example: fork a process and wait for it
395		474
396	my $done = AnyEvent->condvar;	475	my $done = AnyEvent->condvar;
397		476
…		…
408		487
409	# do something else, then wait for process exit	488	# do something else, then wait for process exit
410	$done->recv;	489	$done->recv;
411		490
412	IDLE WATCHERS	491	IDLE WATCHERS
413	Sometimes there is a need to do something, but it is not so important to	492	$w = AnyEvent->idle (cb => <callback>);
414	do it instantly, but only when there is nothing better to do. This
415	"nothing better to do" is usually defined to be "no other events need
416	attention by the event loop".
417		493
418	Idle watchers ideally get invoked when the event loop has nothing better	494	Repeatedly invoke the callback after the process becomes idle, until
419	to do, just before it would block the process to wait for new events.	495	either the watcher is destroyed or new events have been detected.
420	Instead of blocking, the idle watcher is invoked.
421		496
422	Most event loops unfortunately do not really support idle watchers (only	497	Idle watchers are useful when there is a need to do something, but it is
		498	not so important (or wise) to do it instantly. The callback will be
		499	invoked only when there is "nothing better to do", which is usually
		500	defined as "all outstanding events have been handled and no new events
		501	have been detected". That means that idle watchers ideally get invoked
		502	when the event loop has just polled for new events but none have been
		503	detected. Instead of blocking to wait for more events, the idle watchers
		504	will be invoked.
		505
		506	Unfortunately, most event loops do not really support idle watchers
423	EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent	507	(only EV, Event and Glib do it in a usable fashion) - for the rest,
424	will simply call the callback "from time to time".	508	AnyEvent will simply call the callback "from time to time".
425		509
426	Example: read lines from STDIN, but only process them when the program	510	Example: read lines from STDIN, but only process them when the program
427	is otherwise idle:	511	is otherwise idle:
428		512
429	my @lines; # read data	513	my @lines; # read data
…		…
442	}	526	}
443	});	527	});
444	});	528	});
445		529
446	CONDITION VARIABLES	530	CONDITION VARIABLES
		531	$cv = AnyEvent->condvar;
		532
		533	$cv->send (<list>);
		534	my @res = $cv->recv;
		535
447	If you are familiar with some event loops you will know that all of them	536	If you are familiar with some event loops you will know that all of them
448	require you to run some blocking "loop", "run" or similar function that	537	require you to run some blocking "loop", "run" or similar function that
449	will actively watch for new events and call your callbacks.	538	will actively watch for new events and call your callbacks.
450		539
451	AnyEvent is different, it expects somebody else to run the event loop	540	AnyEvent is slightly different: it expects somebody else to run the
452	and will only block when necessary (usually when told by the user).	541	event loop and will only block when necessary (usually when told by the
		542	user).
453		543
454	The instrument to do that is called a "condition variable", so called	544	The instrument to do that is called a "condition variable", so called
455	because they represent a condition that must become true.	545	because they represent a condition that must become true.
456		546
		547	Now is probably a good time to look at the examples further below.
		548
457	Condition variables can be created by calling the "AnyEvent->condvar"	549	Condition variables can be created by calling the "AnyEvent->condvar"
458	method, usually without arguments. The only argument pair allowed is	550	method, usually without arguments. The only argument pair allowed is
459
460	"cb", which specifies a callback to be called when the condition	551	"cb", which specifies a callback to be called when the condition
461	variable becomes true, with the condition variable as the first argument	552	variable becomes true, with the condition variable as the first argument
462	(but not the results).	553	(but not the results).
463		554
464	After creation, the condition variable is "false" until it becomes	555	After creation, the condition variable is "false" until it becomes
…		…
469	Condition variables are similar to callbacks, except that you can	560	Condition variables are similar to callbacks, except that you can
470	optionally wait for them. They can also be called merge points - points	561	optionally wait for them. They can also be called merge points - points
471	in time where multiple outstanding events have been processed. And yet	562	in time where multiple outstanding events have been processed. And yet
472	another way to call them is transactions - each condition variable can	563	another way to call them is transactions - each condition variable can
473	be used to represent a transaction, which finishes at some point and	564	be used to represent a transaction, which finishes at some point and
474	delivers a result.	565	delivers a result. And yet some people know them as "futures" - a
		566	promise to compute/deliver something that you can wait for.
475		567
476	Condition variables are very useful to signal that something has	568	Condition variables are very useful to signal that something has
477	finished, for example, if you write a module that does asynchronous http	569	finished, for example, if you write a module that does asynchronous http
478	requests, then a condition variable would be the ideal candidate to	570	requests, then a condition variable would be the ideal candidate to
479	signal the availability of results. The user can either act when the	571	signal the availability of results. The user can either act when the
…		…
500	which eventually calls "-> send", and the "consumer side", which waits	592	which eventually calls "-> send", and the "consumer side", which waits
501	for the send to occur.	593	for the send to occur.
502		594
503	Example: wait for a timer.	595	Example: wait for a timer.
504		596
505	# wait till the result is ready	597	# condition: "wait till the timer is fired"
506	my $result_ready = AnyEvent->condvar;	598	my $timer_fired = AnyEvent->condvar;
507		599
508	# do something such as adding a timer	600	# create the timer - we could wait for, say
509	# or socket watcher the calls $result_ready->send	601	# a handle becomign ready, or even an
510	# when the "result" is ready.	602	# AnyEvent::HTTP request to finish, but
511	# in this case, we simply use a timer:	603	# in this case, we simply use a timer:
512	my $w = AnyEvent->timer (	604	my $w = AnyEvent->timer (
513	after => 1,	605	after => 1,
514	cb => sub { $result_ready->send },	606	cb => sub { $timer_fired->send },
515	);	607	);
516		608
517	# this "blocks" (while handling events) till the callback	609	# this "blocks" (while handling events) till the callback
518	# calls send	610	# calls ->send
519	$result_ready->recv;	611	$timer_fired->recv;
520		612
521	Example: wait for a timer, but take advantage of the fact that condition	613	Example: wait for a timer, but take advantage of the fact that condition
522	variables are also code references.	614	variables are also callable directly.
523		615
524	my $done = AnyEvent->condvar;	616	my $done = AnyEvent->condvar;
525	my $delay = AnyEvent->timer (after => 5, cb => $done);	617	my $delay = AnyEvent->timer (after => 5, cb => $done);
526	$done->recv;	618	$done->recv;
527		619
…		…
533		625
534	...	626	...
535		627
536	my @info = $couchdb->info->recv;	628	my @info = $couchdb->info->recv;
537		629
538	And this is how you would just ste a callback to be called whenever the	630	And this is how you would just set a callback to be called whenever the
539	results are available:	631	results are available:
540		632
541	$couchdb->info->cb (sub {	633	$couchdb->info->cb (sub {
542	my @info = $_[0]->recv;	634	my @info = $_[0]->recv;
543	});	635	});
…		…
558		650
559	Any arguments passed to the "send" call will be returned by all	651	Any arguments passed to the "send" call will be returned by all
560	future "->recv" calls.	652	future "->recv" calls.
561		653
562	Condition variables are overloaded so one can call them directly (as	654	Condition variables are overloaded so one can call them directly (as
563	a code reference). Calling them directly is the same as calling	655	if they were a code reference). Calling them directly is the same as
564	"send". Note, however, that many C-based event loops do not handle	656	calling "send".
565	overloading, so as tempting as it may be, passing a condition
566	variable instead of a callback does not work. Both the pure perl and
567	EV loops support overloading, however, as well as all functions that
568	use perl to invoke a callback (as in AnyEvent::Socket and
569	AnyEvent::DNS for example).
570		657
571	$cv->croak ($error)	658	$cv->croak ($error)
572	Similar to send, but causes all call's to "->recv" to invoke	659	Similar to send, but causes all call's to "->recv" to invoke
573	"Carp::croak" with the given error message/object/scalar.	660	"Carp::croak" with the given error message/object/scalar.
574		661
575	This can be used to signal any errors to the condition variable	662	This can be used to signal any errors to the condition variable
576	user/consumer.	663	user/consumer. Doing it this way instead of calling "croak" directly
		664	delays the error detetcion, but has the overwhelmign advantage that
		665	it diagnoses the error at the place where the result is expected,
		666	and not deep in some event clalback without connection to the actual
		667	code causing the problem.
577		668
578	$cv->begin ([group callback])	669	$cv->begin ([group callback])
579	$cv->end	670	$cv->end
580	These two methods are EXPERIMENTAL and MIGHT CHANGE.
581
582	These two methods can be used to combine many transactions/events	671	These two methods can be used to combine many transactions/events
583	into one. For example, a function that pings many hosts in parallel	672	into one. For example, a function that pings many hosts in parallel
584	might want to use a condition variable for the whole process.	673	might want to use a condition variable for the whole process.
585		674
586	Every call to "->begin" will increment a counter, and every call to	675	Every call to "->begin" will increment a counter, and every call to
587	"->end" will decrement it. If the counter reaches 0 in "->end", the	676	"->end" will decrement it. If the counter reaches 0 in "->end", the
588	(last) callback passed to "begin" will be executed. That callback is	677	(last) callback passed to "begin" will be executed, passing the
589	supposed to call "->send", but that is not required. If no	678	condvar as first argument. That callback is supposed to call
		679	"->send", but that is not required. If no group callback was set,
590	callback was set, "send" will be called without any arguments.	680	"send" will be called without any arguments.
591		681
592	Let's clarify this with the ping example:	682	You can think of "$cv->send" giving you an OR condition (one call
		683	sends), while "$cv->begin" and "$cv->end" giving you an AND
		684	condition (all "begin" calls must be "end"'ed before the condvar
		685	sends).
		686
		687	Let's start with a simple example: you have two I/O watchers (for
		688	example, STDOUT and STDERR for a program), and you want to wait for
		689	both streams to close before activating a condvar:
593		690
594	my $cv = AnyEvent->condvar;	691	my $cv = AnyEvent->condvar;
595		692
		693	$cv->begin; # first watcher
		694	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		695	defined sysread $fh1, my $buf, 4096
		696	or $cv->end;
		697	});
		698
		699	$cv->begin; # second watcher
		700	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		701	defined sysread $fh2, my $buf, 4096
		702	or $cv->end;
		703	});
		704
		705	$cv->recv;
		706
		707	This works because for every event source (EOF on file handle),
		708	there is one call to "begin", so the condvar waits for all calls to
		709	"end" before sending.
		710
		711	The ping example mentioned above is slightly more complicated, as
		712	the there are results to be passwd back, and the number of tasks
		713	that are begung can potentially be zero:
		714
		715	my $cv = AnyEvent->condvar;
		716
596	my %result;	717	my %result;
597	$cv->begin (sub { $cv->send (\%result) });	718	$cv->begin (sub { shift->send (\%result) });
598		719
599	for my $host (@list_of_hosts) {	720	for my $host (@list_of_hosts) {
600	$cv->begin;	721	$cv->begin;
601	ping_host_then_call_callback $host, sub {	722	ping_host_then_call_callback $host, sub {
602	$result{$host} = ...;	723	$result{$host} = ...;
…		…
617	the loop, which serves two important purposes: first, it sets the	738	the loop, which serves two important purposes: first, it sets the
618	callback to be called once the counter reaches 0, and second, it	739	callback to be called once the counter reaches 0, and second, it
619	ensures that "send" is called even when "no" hosts are being pinged	740	ensures that "send" is called even when "no" hosts are being pinged
620	(the loop doesn't execute once).	741	(the loop doesn't execute once).
621		742
622	This is the general pattern when you "fan out" into multiple	743	This is the general pattern when you "fan out" into multiple (but
623	subrequests: use an outer "begin"/"end" pair to set the callback and	744	potentially none) subrequests: use an outer "begin"/"end" pair to
624	ensure "end" is called at least once, and then, for each subrequest	745	set the callback and ensure "end" is called at least once, and then,
625	you start, call "begin" and for each subrequest you finish, call	746	for each subrequest you start, call "begin" and for each subrequest
626	"end".	747	you finish, call "end".
627		748
628	METHODS FOR CONSUMERS	749	METHODS FOR CONSUMERS
629	These methods should only be used by the consuming side, i.e. the code	750	These methods should only be used by the consuming side, i.e. the code
630	awaits the condition.	751	awaits the condition.
631		752
…		…
640	function will call "croak".	761	function will call "croak".
641		762
642	In list context, all parameters passed to "send" will be returned,	763	In list context, all parameters passed to "send" will be returned,
643	in scalar context only the first one will be returned.	764	in scalar context only the first one will be returned.
644		765
		766	Note that doing a blocking wait in a callback is not supported by
		767	any event loop, that is, recursive invocation of a blocking "->recv"
		768	is not allowed, and the "recv" call will "croak" if such a condition
		769	is detected. This condition can be slightly loosened by using
		770	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		771	thread that doesn't run the event loop itself.
		772
645	Not all event models support a blocking wait - some die in that case	773	Not all event models support a blocking wait - some die in that case
646	(programs might want to do that to stay interactive), so *if you are	774	(programs might want to do that to stay interactive), so *if you are
647	using this from a module, never require a blocking wait*, but let	775	using this from a module, never require a blocking wait*. Instead,
648	the caller decide whether the call will block or not (for example,	776	let the caller decide whether the call will block or not (for
649	by coupling condition variables with some kind of request results	777	example, by coupling condition variables with some kind of request
650	and supporting callbacks so the caller knows that getting the result	778	results and supporting callbacks so the caller knows that getting
651	will not block, while still supporting blocking waits if the caller	779	the result will not block, while still supporting blocking waits if
652	so desires).	780	the caller so desires).
653
654	Another reason never to "->recv" in a module is that you cannot
655	sensibly have two "->recv"'s in parallel, as that would require
656	multiple interpreters or coroutines/threads, none of which
657	"AnyEvent" can supply.
658
659	The Coro module, however, can and does supply coroutines and, in
660	fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
661	versions and also integrates coroutines into AnyEvent, making
662	blocking "->recv" calls perfectly safe as long as they are done from
663	another coroutine (one that doesn't run the event loop).
664		781
665	You can ensure that "-recv" never blocks by setting a callback and	782	You can ensure that "-recv" never blocks by setting a callback and
666	only calling "->recv" from within that callback (or at a later	783	only calling "->recv" from within that callback (or at a later
667	time). This will work even when the event loop does not support	784	time). This will work even when the event loop does not support
668	blocking waits otherwise.	785	blocking waits otherwise.
…		…
673		790
674	$cb = $cv->cb ($cb->($cv))	791	$cb = $cv->cb ($cb->($cv))
675	This is a mutator function that returns the callback set and	792	This is a mutator function that returns the callback set and
676	optionally replaces it before doing so.	793	optionally replaces it before doing so.
677		794
678	The callback will be called when the condition becomes "true", i.e.	795	The callback will be called when the condition becomes (or already
679	when "send" or "croak" are called, with the only argument being the	796	was) "true", i.e. when "send" or "croak" are called (or were
680	condition variable itself. Calling "recv" inside the callback or at	797	called), with the only argument being the condition variable itself.
		798	Calling "recv" inside the callback or at any later time is
681	any later time is guaranteed not to block.	799	guaranteed not to block.
		800
		801	SUPPORTED EVENT LOOPS/BACKENDS
		802	The available backend classes are (every class has its own manpage):
		803
		804	Backends that are autoprobed when no other event loop can be found.
		805	EV is the preferred backend when no other event loop seems to be in
		806	use. If EV is not installed, then AnyEvent will fall back to its own
		807	pure-perl implementation, which is available everywhere as it comes
		808	with AnyEvent itself.
		809
		810	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		811	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		812
		813	Backends that are transparently being picked up when they are used.
		814	These will be used when they are currently loaded when the first
		815	watcher is created, in which case it is assumed that the application
		816	is using them. This means that AnyEvent will automatically pick the
		817	right backend when the main program loads an event module before
		818	anything starts to create watchers. Nothing special needs to be done
		819	by the main program.
		820
		821	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		822	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		823	AnyEvent::Impl::Tk based on Tk, very broken.
		824	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		825	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		826	AnyEvent::Impl::Irssi used when running within irssi.
		827
		828	Backends with special needs.
		829	Qt requires the Qt::Application to be instantiated first, but will
		830	otherwise be picked up automatically. As long as the main program
		831	instantiates the application before any AnyEvent watchers are
		832	created, everything should just work.
		833
		834	AnyEvent::Impl::Qt based on Qt.
		835
		836	Support for IO::Async can only be partial, as it is too broken and
		837	architecturally limited to even support the AnyEvent API. It also is
		838	the only event loop that needs the loop to be set explicitly, so it
		839	can only be used by a main program knowing about AnyEvent. See
		840	AnyEvent::Impl::Async for the gory details.
		841
		842	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		843
		844	Event loops that are indirectly supported via other backends.
		845	Some event loops can be supported via other modules:
		846
		847	There is no direct support for WxWidgets (Wx) or Prima.
		848
		849	WxWidgets has no support for watching file handles. However, you can
		850	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		851	simply polls 20 times per second, which was considered to be too
		852	horrible to even consider for AnyEvent.
		853
		854	Prima is not supported as nobody seems to be using it, but it has a
		855	POE backend, so it can be supported through POE.
		856
		857	AnyEvent knows about both Prima and Wx, however, and will try to
		858	load POE when detecting them, in the hope that POE will pick them
		859	up, in which case everything will be automatic.
682		860
683	GLOBAL VARIABLES AND FUNCTIONS	861	GLOBAL VARIABLES AND FUNCTIONS
		862	These are not normally required to use AnyEvent, but can be useful to
		863	write AnyEvent extension modules.
		864
684	$AnyEvent::MODEL	865	$AnyEvent::MODEL
685	Contains "undef" until the first watcher is being created. Then it	866	Contains "undef" until the first watcher is being created, before
		867	the backend has been autodetected.
		868
686	contains the event model that is being used, which is the name of	869	Afterwards it contains the event model that is being used, which is
687	the Perl class implementing the model. This class is usually one of	870	the name of the Perl class implementing the model. This class is
688	the "AnyEvent::Impl:xxx" modules, but can be any other class in the	871	usually one of the "AnyEvent::Impl:xxx" modules, but can be any
689	case AnyEvent has been extended at runtime (e.g. in rxvt-unicode).	872	other class in the case AnyEvent has been extended at runtime (e.g.
690		873	in rxvt-unicode it will be "urxvt::anyevent").
691	The known classes so far are:
692
693	AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
694	AnyEvent::Impl::Event based on Event, second best choice.
695	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
696	AnyEvent::Impl::Glib based on Glib, third-best choice.
697	AnyEvent::Impl::Tk based on Tk, very bad choice.
698	AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
699	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
700	AnyEvent::Impl::POE based on POE, not generic enough for full support.
701
702	There is no support for WxWidgets, as WxWidgets has no support for
703	watching file handles. However, you can use WxWidgets through the
704	POE Adaptor, as POE has a Wx backend that simply polls 20 times per
705	second, which was considered to be too horrible to even consider for
706	AnyEvent. Likewise, other POE backends can be used by AnyEvent by
707	using it's adaptor.
708
709	AnyEvent knows about Prima and Wx and will try to use POE when
710	autodetecting them.
711		874
712	AnyEvent::detect	875	AnyEvent::detect
713	Returns $AnyEvent::MODEL, forcing autodetection of the event model	876	Returns $AnyEvent::MODEL, forcing autodetection of the event model
714	if necessary. You should only call this function right before you	877	if necessary. You should only call this function right before you
715	would have created an AnyEvent watcher anyway, that is, as late as	878	would have created an AnyEvent watcher anyway, that is, as late as
716	possible at runtime.	879	possible at runtime, and not e.g. while initialising of your module.
		880
		881	If you need to do some initialisation before AnyEvent watchers are
		882	created, use "post_detect".
717		883
718	$guard = AnyEvent::post_detect { BLOCK }	884	$guard = AnyEvent::post_detect { BLOCK }
719	Arranges for the code block to be executed as soon as the event	885	Arranges for the code block to be executed as soon as the event
720	model is autodetected (or immediately if this has already happened).	886	model is autodetected (or immediately if this has already happened).
721		887
		888	The block will be executed after the actual backend has been
		889	detected ($AnyEvent::MODEL is set), but before any watchers have
		890	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		891	other initialisations - see the sources of AnyEvent::Strict or
		892	AnyEvent::AIO to see how this is used.
		893
		894	The most common usage is to create some global watchers, without
		895	forcing event module detection too early, for example, AnyEvent::AIO
		896	creates and installs the global IO::AIO watcher in a "post_detect"
		897	block to avoid autodetecting the event module at load time.
		898
722	If called in scalar or list context, then it creates and returns an	899	If called in scalar or list context, then it creates and returns an
723	object that automatically removes the callback again when it is	900	object that automatically removes the callback again when it is
		901	destroyed (or "undef" when the hook was immediately executed). See
724	destroyed. See Coro::BDB for a case where this is useful.	902	AnyEvent::AIO for a case where this is useful.
		903
		904	Example: Create a watcher for the IO::AIO module and store it in
		905	$WATCHER. Only do so after the event loop is initialised, though.
		906
		907	our WATCHER;
		908
		909	my $guard = AnyEvent::post_detect {
		910	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		911	};
		912
		913	# the \|\|= is important in case post_detect immediately runs the block,
		914	# as to not clobber the newly-created watcher. assigning both watcher and
		915	# post_detect guard to the same variable has the advantage of users being
		916	# able to just C<undef $WATCHER> if the watcher causes them grief.
		917
		918	$WATCHER \|\|= $guard;
725		919
726	@AnyEvent::post_detect	920	@AnyEvent::post_detect
727	If there are any code references in this array (you can "push" to it	921	If there are any code references in this array (you can "push" to it
728	before or after loading AnyEvent), then they will called directly	922	before or after loading AnyEvent), then they will called directly
729	after the event loop has been chosen.	923	after the event loop has been chosen.
730		924
731	You should check $AnyEvent::MODEL before adding to this array,	925	You should check $AnyEvent::MODEL before adding to this array,
732	though: if it contains a true value then the event loop has already	926	though: if it is defined then the event loop has already been
733	been detected, and the array will be ignored.	927	detected, and the array will be ignored.
734		928
735	Best use "AnyEvent::post_detect { BLOCK }" instead.	929	Best use "AnyEvent::post_detect { BLOCK }" when your application
		930	allows it, as it takes care of these details.
		931
		932	This variable is mainly useful for modules that can do something
		933	useful when AnyEvent is used and thus want to know when it is
		934	initialised, but do not need to even load it by default. This array
		935	provides the means to hook into AnyEvent passively, without loading
		936	it.
		937
		938	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		939	together, you could put this into Coro (this is the actual code used
		940	by Coro to accomplish this):
		941
		942	if (defined $AnyEvent::MODEL) {
		943	# AnyEvent already initialised, so load Coro::AnyEvent
		944	require Coro::AnyEvent;
		945	} else {
		946	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		947	# as soon as it is
		948	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		949	}
736		950
737	WHAT TO DO IN A MODULE	951	WHAT TO DO IN A MODULE
738	As a module author, you should "use AnyEvent" and call AnyEvent methods	952	As a module author, you should "use AnyEvent" and call AnyEvent methods
739	freely, but you should not load a specific event module or rely on it.	953	freely, but you should not load a specific event module or rely on it.
740		954
…		…
791	variable somewhere, waiting for it, and sending it when the program	1005	variable somewhere, waiting for it, and sending it when the program
792	should exit cleanly.	1006	should exit cleanly.
793		1007
794	OTHER MODULES	1008	OTHER MODULES
795	The following is a non-exhaustive list of additional modules that use	1009	The following is a non-exhaustive list of additional modules that use
796	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1010	AnyEvent as a client and can therefore be mixed easily with other
797	in the same program. Some of the modules come with AnyEvent, some are	1011	AnyEvent modules and other event loops in the same program. Some of the
798	available via CPAN.	1012	modules come with AnyEvent, most are available via CPAN.
799		1013
800	AnyEvent::Util	1014	AnyEvent::Util
801	Contains various utility functions that replace often-used but	1015	Contains various utility functions that replace often-used but
802	blocking functions such as "inet_aton" by event-/callback-based	1016	blocking functions such as "inet_aton" by event-/callback-based
803	versions.	1017	versions.
…		…
809	more.	1023	more.
810		1024
811	AnyEvent::Handle	1025	AnyEvent::Handle
812	Provide read and write buffers, manages watchers for reads and	1026	Provide read and write buffers, manages watchers for reads and
813	writes, supports raw and formatted I/O, I/O queued and fully	1027	writes, supports raw and formatted I/O, I/O queued and fully
814	transparent and non-blocking SSL/TLS.	1028	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
815		1029
816	AnyEvent::DNS	1030	AnyEvent::DNS
817	Provides rich asynchronous DNS resolver capabilities.	1031	Provides rich asynchronous DNS resolver capabilities.
818		1032
819	AnyEvent::HTTP	1033	AnyEvent::HTTP
…		…
840		1054
841	AnyEvent::GPSD	1055	AnyEvent::GPSD
842	A non-blocking interface to gpsd, a daemon delivering GPS	1056	A non-blocking interface to gpsd, a daemon delivering GPS
843	information.	1057	information.
844		1058
		1059	AnyEvent::IRC
		1060	AnyEvent based IRC client module family (replacing the older
		1061	Net::IRC3).
		1062
		1063	AnyEvent::XMPP
		1064	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		1065	older Net::XMPP2>.
		1066
845	AnyEvent::IGS	1067	AnyEvent::IGS
846	A non-blocking interface to the Internet Go Server protocol (used by	1068	A non-blocking interface to the Internet Go Server protocol (used by
847	App::IGS).	1069	App::IGS).
848		1070
849	AnyEvent::IRC
850	AnyEvent based IRC client module family (replacing the older
851	Net::IRC3).
852
853	Net::XMPP2
854	AnyEvent based XMPP (Jabber protocol) module family.
855
856	Net::FCP	1071	Net::FCP
857	AnyEvent-based implementation of the Freenet Client Protocol,	1072	AnyEvent-based implementation of the Freenet Client Protocol,
858	birthplace of AnyEvent.	1073	birthplace of AnyEvent.
859		1074
860	Event::ExecFlow	1075	Event::ExecFlow
861	High level API for event-based execution flow control.	1076	High level API for event-based execution flow control.
862		1077
863	Coro	1078	Coro
864	Has special support for AnyEvent via Coro::AnyEvent.	1079	Has special support for AnyEvent via Coro::AnyEvent.
865		1080
866	IO::Lambda	1081	SIMPLIFIED AE API
867	The lambda approach to I/O - don't ask, look there. Can use	1082	Starting with version 5.0, AnyEvent officially supports a second, much
868	AnyEvent.	1083	simpler, API that is designed to reduce the calling, typing and memory
		1084	overhead by using function call syntax and a fixed number of parameters.
		1085
		1086	See the AE manpage for details.
869		1087
870	ERROR AND EXCEPTION HANDLING	1088	ERROR AND EXCEPTION HANDLING
871	In general, AnyEvent does not do any error handling - it relies on the	1089	In general, AnyEvent does not do any error handling - it relies on the
872	caller to do that if required. The AnyEvent::Strict module (see also the	1090	caller to do that if required. The AnyEvent::Strict module (see also the
873	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1091	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
883	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1101	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
884	Glib uses "install_exception_handler" and so on.	1102	Glib uses "install_exception_handler" and so on.
885		1103
886	ENVIRONMENT VARIABLES	1104	ENVIRONMENT VARIABLES
887	The following environment variables are used by this module or its	1105	The following environment variables are used by this module or its
888	submodules:	1106	submodules.
		1107
		1108	Note that AnyEvent will remove all environment variables starting with
		1109	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1110	enabled.
889		1111
890	"PERL_ANYEVENT_VERBOSE"	1112	"PERL_ANYEVENT_VERBOSE"
891	By default, AnyEvent will be completely silent except in fatal	1113	By default, AnyEvent will be completely silent except in fatal
892	conditions. You can set this environment variable to make AnyEvent	1114	conditions. You can set this environment variable to make AnyEvent
893	more talkative.	1115	more talkative.
…		…
896	conditions, such as not being able to load the event model specified	1118	conditions, such as not being able to load the event model specified
897	by "PERL_ANYEVENT_MODEL".	1119	by "PERL_ANYEVENT_MODEL".
898		1120
899	When set to 2 or higher, cause AnyEvent to report to STDERR which	1121	When set to 2 or higher, cause AnyEvent to report to STDERR which
900	event model it chooses.	1122	event model it chooses.
		1123
		1124	When set to 8 or higher, then AnyEvent will report extra information
		1125	on which optional modules it loads and how it implements certain
		1126	features.
901		1127
902	"PERL_ANYEVENT_STRICT"	1128	"PERL_ANYEVENT_STRICT"
903	AnyEvent does not do much argument checking by default, as thorough	1129	AnyEvent does not do much argument checking by default, as thorough
904	argument checking is very costly. Setting this variable to a true	1130	argument checking is very costly. Setting this variable to a true
905	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1131	value will cause AnyEvent to load "AnyEvent::Strict" and then to
906	thoroughly check the arguments passed to most method calls. If it	1132	thoroughly check the arguments passed to most method calls. If it
907	finds any problems it will croak.	1133	finds any problems, it will croak.
908		1134
909	In other words, enables "strict" mode.	1135	In other words, enables "strict" mode.
910		1136
911	Unlike "use strict", it is definitely recommended ot keep it off in	1137	Unlike "use strict" (or it's modern cousin, "use common::sense", it
912	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1138	is definitely recommended to keep it off in production. Keeping
		1139	"PERL_ANYEVENT_STRICT=1" in your environment while developing
913	while developing programs can be very useful, however.	1140	programs can be very useful, however.
914		1141
915	"PERL_ANYEVENT_MODEL"	1142	"PERL_ANYEVENT_MODEL"
916	This can be used to specify the event model to be used by AnyEvent,	1143	This can be used to specify the event model to be used by AnyEvent,
917	before auto detection and -probing kicks in. It must be a string	1144	before auto detection and -probing kicks in. It must be a string
918	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1145	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
959	EDNS0 in its DNS requests.	1186	EDNS0 in its DNS requests.
960		1187
961	"PERL_ANYEVENT_MAX_FORKS"	1188	"PERL_ANYEVENT_MAX_FORKS"
962	The maximum number of child processes that	1189	The maximum number of child processes that
963	"AnyEvent::Util::fork_call" will create in parallel.	1190	"AnyEvent::Util::fork_call" will create in parallel.
		1191
		1192	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1193	The default value for the "max_outstanding" parameter for the
		1194	default DNS resolver - this is the maximum number of parallel DNS
		1195	requests that are sent to the DNS server.
		1196
		1197	"PERL_ANYEVENT_RESOLV_CONF"
		1198	The file to use instead of /etc/resolv.conf (or OS-specific
		1199	configuration) in the default resolver. When set to the empty
		1200	string, no default config will be used.
		1201
		1202	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1203	When neither "ca_file" nor "ca_path" was specified during
		1204	AnyEvent::TLS context creation, and either of these environment
		1205	variables exist, they will be used to specify CA certificate
		1206	locations instead of a system-dependent default.
		1207
		1208	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1209	When these are set to 1, then the respective modules are not loaded.
		1210	Mostly good for testing AnyEvent itself.
964		1211
965	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1212	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
966	This is an advanced topic that you do not normally need to use AnyEvent	1213	This is an advanced topic that you do not normally need to use AnyEvent
967	in a module. This section is only of use to event loop authors who want	1214	in a module. This section is only of use to event loop authors who want
968	to provide AnyEvent compatibility.	1215	to provide AnyEvent compatibility.
…		…
1023	warn "read: $input\n"; # output what has been read	1270	warn "read: $input\n"; # output what has been read
1024	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1271	$cv->send if $input =~ /^q/i; # quit program if /^q/i
1025	},	1272	},
1026	);	1273	);
1027		1274
1028	my $time_watcher; # can only be used once
1029
1030	sub new_timer {
1031	$timer = AnyEvent->timer (after => 1, cb => sub {	1275	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1032	warn "timeout\n"; # print 'timeout' about every second	1276	warn "timeout\n"; # print 'timeout' at most every second
1033	&new_timer; # and restart the time
1034	});
1035	}	1277	});
1036
1037	new_timer; # create first timer
1038		1278
1039	$cv->recv; # wait until user enters /^q/i	1279	$cv->recv; # wait until user enters /^q/i
1040		1280
1041	REAL-WORLD EXAMPLE	1281	REAL-WORLD EXAMPLE
1042	Consider the Net::FCP module. It features (among others) the following	1282	Consider the Net::FCP module. It features (among others) the following
…		…
1114		1354
1115	The actual code goes further and collects all errors ("die"s,	1355	The actual code goes further and collects all errors ("die"s,
1116	exceptions) that occurred during request processing. The "result" method	1356	exceptions) that occurred during request processing. The "result" method
1117	detects whether an exception as thrown (it is stored inside the $txn	1357	detects whether an exception as thrown (it is stored inside the $txn
1118	object) and just throws the exception, which means connection errors and	1358	object) and just throws the exception, which means connection errors and
1119	other problems get reported tot he code that tries to use the result,	1359	other problems get reported to the code that tries to use the result,
1120	not in a random callback.	1360	not in a random callback.
1121		1361
1122	All of this enables the following usage styles:	1362	All of this enables the following usage styles:
1123		1363
1124	1. Blocking:	1364	1. Blocking:
…		…
1169	through AnyEvent. The benchmark creates a lot of timers (with a zero	1409	through AnyEvent. The benchmark creates a lot of timers (with a zero
1170	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,	1410	timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1171	which it is), lets them fire exactly once and destroys them again.	1411	which it is), lets them fire exactly once and destroys them again.
1172		1412
1173	Source code for this benchmark is found as eg/bench in the AnyEvent	1413	Source code for this benchmark is found as eg/bench in the AnyEvent
1174	distribution.	1414	distribution. It uses the AE interface, which makes a real difference
		1415	for the EV and Perl backends only.
1175		1416
1176	Explanation of the columns	1417	Explanation of the columns
1177	watcher is the number of event watchers created/destroyed. Since	1418	watcher is the number of event watchers created/destroyed. Since
1178	different event models feature vastly different performances, each event	1419	different event models feature vastly different performances, each event
1179	loop was given a number of watchers so that overall runtime is	1420	loop was given a number of watchers so that overall runtime is
…		…
1198	destroy is the time, in microseconds, that it takes to destroy a	1439	destroy is the time, in microseconds, that it takes to destroy a
1199	single watcher.	1440	single watcher.
1200		1441
1201	Results	1442	Results
1202	name watchers bytes create invoke destroy comment	1443	name watchers bytes create invoke destroy comment
1203	EV/EV 400000 224 0.47 0.35 0.27 EV native interface	1444	EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1204	EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers	1445	EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1205	CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal	1446	Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1206	Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation	1447	Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1207	Event/Event 16000 517 32.20 31.80 0.81 Event native interface	1448	Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1208	Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers	1449	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1450	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1451	IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1209	Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour	1452	Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1210	Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers	1453	Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1211	POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event	1454	POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1212	POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select	1455	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1213		1456
1214	Discussion	1457	Discussion
1215	The benchmark does not measure scalability of the event loop very	1458	The benchmark does not measure scalability of the event loop very
1216	well. For example, a select-based event loop (such as the pure perl one)	1459	well. For example, a select-based event loop (such as the pure perl one)
1217	can never compete with an event loop that uses epoll when the number of	1460	can never compete with an event loop that uses epoll when the number of
…		…
1228	benchmark machine, handling an event takes roughly 1600 CPU cycles with	1471	benchmark machine, handling an event takes roughly 1600 CPU cycles with
1229	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000	1472	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1230	CPU cycles with POE.	1473	CPU cycles with POE.
1231		1474
1232	"EV" is the sole leader regarding speed and memory use, which are both	1475	"EV" is the sole leader regarding speed and memory use, which are both
1233	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1476	maximal/minimal, respectively. When using the AE API there is zero
		1477	overhead (when going through the AnyEvent API create is about 5-6 times
		1478	slower, with other times being equal, so still uses far less memory than
1234	far less memory than any other event loop and is still faster than Event	1479	any other event loop and is still faster than Event natively).
1235	natively.
1236		1480
1237	The pure perl implementation is hit in a few sweet spots (both the	1481	The pure perl implementation is hit in a few sweet spots (both the
1238	constant timeout and the use of a single fd hit optimisations in the	1482	constant timeout and the use of a single fd hit optimisations in the
1239	perl interpreter and the backend itself). Nevertheless this shows that	1483	perl interpreter and the backend itself). Nevertheless this shows that
1240	it adds very little overhead in itself. Like any select-based backend	1484	it adds very little overhead in itself. Like any select-based backend
…		…
1242	few of them active), of course, but this was not subject of this	1486	few of them active), of course, but this was not subject of this
1243	benchmark.	1487	benchmark.
1244		1488
1245	The "Event" module has a relatively high setup and callback invocation	1489	The "Event" module has a relatively high setup and callback invocation
1246	cost, but overall scores in on the third place.	1490	cost, but overall scores in on the third place.
		1491
		1492	"IO::Async" performs admirably well, about on par with "Event", even
		1493	when using its pure perl backend.
1247		1494
1248	"Glib"'s memory usage is quite a bit higher, but it features a faster	1495	"Glib"'s memory usage is quite a bit higher, but it features a faster
1249	callback invocation and overall ends up in the same class as "Event".	1496	callback invocation and overall ends up in the same class as "Event".
1250	However, Glib scales extremely badly, doubling the number of watchers	1497	However, Glib scales extremely badly, doubling the number of watchers
1251	increases the processing time by more than a factor of four, making it	1498	increases the processing time by more than a factor of four, making it
…		…
1307	In this benchmark, we use 10000 socket pairs (20000 sockets), of which	1554	In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1308	100 (1%) are active. This mirrors the activity of large servers with	1555	100 (1%) are active. This mirrors the activity of large servers with
1309	many connections, most of which are idle at any one point in time.	1556	many connections, most of which are idle at any one point in time.
1310		1557
1311	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1558	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1312	distribution.	1559	distribution. It uses the AE interface, which makes a real difference
		1560	for the EV and Perl backends only.
1313		1561
1314	Explanation of the columns	1562	Explanation of the columns
1315	sockets is the number of sockets, and twice the number of "servers"	1563	sockets is the number of sockets, and twice the number of "servers"
1316	(as each server has a read and write socket end).	1564	(as each server has a read and write socket end).
1317		1565
…		…
1322	single "request", that is, reading the token from the pipe and	1570	single "request", that is, reading the token from the pipe and
1323	forwarding it to another server. This includes deleting the old timeout	1571	forwarding it to another server. This includes deleting the old timeout
1324	and creating a new one that moves the timeout into the future.	1572	and creating a new one that moves the timeout into the future.
1325		1573
1326	Results	1574	Results
1327	name sockets create request	1575	name sockets create request
1328	EV 20000 69.01 11.16	1576	EV 20000 62.66 7.99
1329	Perl 20000 73.32 35.87	1577	Perl 20000 68.32 32.64
1330	Event 20000 212.62 257.32	1578	IOAsync 20000 174.06 101.15 epoll
1331	Glib 20000 651.16 1896.30	1579	IOAsync 20000 174.67 610.84 poll
		1580	Event 20000 202.69 242.91
		1581	Glib 20000 557.01 1689.52
1332	POE 20000 349.67 12317.24 uses POE::Loop::Event	1582	POE 20000 341.54 12086.32 uses POE::Loop::Event
1333		1583
1334	Discussion	1584	Discussion
1335	This benchmark does measure scalability and overall performance of the	1585	This benchmark does measure scalability and overall performance of the
1336	particular event loop.	1586	particular event loop.
1337		1587
1338	EV is again fastest. Since it is using epoll on my system, the setup	1588	EV is again fastest. Since it is using epoll on my system, the setup
1339	time is relatively high, though.	1589	time is relatively high, though.
1340		1590
1341	Perl surprisingly comes second. It is much faster than the C-based event	1591	Perl surprisingly comes second. It is much faster than the C-based event
1342	loops Event and Glib.	1592	loops Event and Glib.
		1593
		1594	IO::Async performs very well when using its epoll backend, and still
		1595	quite good compared to Glib when using its pure perl backend.
1343		1596
1344	Event suffers from high setup time as well (look at its code and you	1597	Event suffers from high setup time as well (look at its code and you
1345	will understand why). Callback invocation also has a high overhead	1598	will understand why). Callback invocation also has a high overhead
1346	compared to the "$_->() for .."-style loop that the Perl event loop	1599	compared to the "$_->() for .."-style loop that the Perl event loop
1347	uses. Event uses select or poll in basically all documented	1600	uses. Event uses select or poll in basically all documented
…		…
1398		1651
1399	Summary	1652	Summary
1400	* C-based event loops perform very well with small number of watchers,	1653	* C-based event loops perform very well with small number of watchers,
1401	as the management overhead dominates.	1654	as the management overhead dominates.
1402		1655
		1656	THE IO::Lambda BENCHMARK
		1657	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1658	could be misinterpreted to make AnyEvent look bad. In fact, the
		1659	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1660	better (which shouldn't come as a surprise to anybody). As such, the
		1661	benchmark is fine, and mostly shows that the AnyEvent backend from
		1662	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1663	without the extra baggage? To explore this, I wrote the equivalent
		1664	benchmark for AnyEvent.
		1665
		1666	The benchmark itself creates an echo-server, and then, for 500 times,
		1667	connects to the echo server, sends a line, waits for the reply, and then
		1668	creates the next connection. This is a rather bad benchmark, as it
		1669	doesn't test the efficiency of the framework or much non-blocking I/O,
		1670	but it is a benchmark nevertheless.
		1671
		1672	name runtime
		1673	Lambda/select 0.330 sec
		1674	+ optimized 0.122 sec
		1675	Lambda/AnyEvent 0.327 sec
		1676	+ optimized 0.138 sec
		1677	Raw sockets/select 0.077 sec
		1678	POE/select, components 0.662 sec
		1679	POE/select, raw sockets 0.226 sec
		1680	POE/select, optimized 0.404 sec
		1681
		1682	AnyEvent/select/nb 0.085 sec
		1683	AnyEvent/EV/nb 0.068 sec
		1684	+state machine 0.134 sec
		1685
		1686	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1687	benchmarks actually make blocking connects and use 100% blocking I/O,
		1688	defeating the purpose of an event-based solution. All of the newly
		1689	written AnyEvent benchmarks use 100% non-blocking connects (using
		1690	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1691	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1692	connects generally require a lot more bookkeeping and event handling
		1693	than blocking connects (which involve a single syscall only).
		1694
		1695	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1696	offers similar expressive power as POE and IO::Lambda, using
		1697	conventional Perl syntax. This means that both the echo server and the
		1698	client are 100% non-blocking, further placing it at a disadvantage.
		1699
		1700	As you can see, the AnyEvent + EV combination even beats the
		1701	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1702	backend easily beats IO::Lambda and POE.
		1703
		1704	And even the 100% non-blocking version written using the high-level (and
		1705	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1706	higher level ("unoptimised") abstractions by a large margin, even though
		1707	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1708
		1709	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1710	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1711	part of the IO::Lambda distribution and were used without any changes.
		1712
1403	SIGNALS	1713	SIGNALS
1404	AnyEvent currently installs handlers for these signals:	1714	AnyEvent currently installs handlers for these signals:
1405		1715
1406	SIGCHLD	1716	SIGCHLD
1407	A handler for "SIGCHLD" is installed by AnyEvent's child watcher	1717	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1408	emulation for event loops that do not support them natively. Also,	1718	emulation for event loops that do not support them natively. Also,
1409	some event loops install a similar handler.	1719	some event loops install a similar handler.
		1720
		1721	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1722	then AnyEvent will reset it to default, to avoid losing child exit
		1723	statuses.
1410		1724
1411	SIGPIPE	1725	SIGPIPE
1412	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is	1726	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1413	"undef" when AnyEvent gets loaded.	1727	"undef" when AnyEvent gets loaded.
1414		1728
…		…
1422	it is that this way, the handler will be restored to defaults on	1736	it is that this way, the handler will be restored to defaults on
1423	exec.	1737	exec.
1424		1738
1425	Feel free to install your own handler, or reset it to defaults.	1739	Feel free to install your own handler, or reset it to defaults.
1426		1740
		1741	RECOMMENDED/OPTIONAL MODULES
		1742	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1743	it's built-in modules) are required to use it.
		1744
		1745	That does not mean that AnyEvent won't take advantage of some additional
		1746	modules if they are installed.
		1747
		1748	This section explains which additional modules will be used, and how
		1749	they affect AnyEvent's operation.
		1750
		1751	Async::Interrupt
		1752	This slightly arcane module is used to implement fast signal
		1753	handling: To my knowledge, there is no way to do completely
		1754	race-free and quick signal handling in pure perl. To ensure that
		1755	signals still get delivered, AnyEvent will start an interval timer
		1756	to wake up perl (and catch the signals) with some delay (default is
		1757	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1758
		1759	If this module is available, then it will be used to implement
		1760	signal catching, which means that signals will not be delayed, and
		1761	the event loop will not be interrupted regularly, which is more
		1762	efficient (and good for battery life on laptops).
		1763
		1764	This affects not just the pure-perl event loop, but also other event
		1765	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1766
		1767	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1768	natively, and either employ their own workarounds (POE) or use
		1769	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1770	Installing Async::Interrupt does nothing for those backends.
		1771
		1772	EV This module isn't really "optional", as it is simply one of the
		1773	backend event loops that AnyEvent can use. However, it is simply the
		1774	best event loop available in terms of features, speed and stability:
		1775	It supports the AnyEvent API optimally, implements all the watcher
		1776	types in XS, does automatic timer adjustments even when no monotonic
		1777	clock is available, can take avdantage of advanced kernel interfaces
		1778	such as "epoll" and "kqueue", and is the fastest backend by far.
		1779	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1780	Glib::EV).
		1781
		1782	If you only use backends that rely on another event loop (e.g.
		1783	"Tk"), then this module will do nothing for you.
		1784
		1785	Guard
		1786	The guard module, when used, will be used to implement
		1787	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1788	uses a lot less memory), but otherwise doesn't affect guard
		1789	operation much. It is purely used for performance.
		1790
		1791	JSON and JSON::XS
		1792	One of these modules is required when you want to read or write JSON
		1793	data via AnyEvent::Handle. JSON is also written in pure-perl, but
		1794	can take advantage of the ultra-high-speed JSON::XS module when it
		1795	is installed.
		1796
		1797	Net::SSLeay
		1798	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1799	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1800	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1801
		1802	Time::HiRes
		1803	This module is part of perl since release 5.008. It will be used
		1804	when the chosen event library does not come with a timing source on
		1805	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1806	additionally use it to try to use a monotonic clock for timing
		1807	stability.
		1808
1427	FORK	1809	FORK
1428	Most event libraries are not fork-safe. The ones who are usually are	1810	Most event libraries are not fork-safe. The ones who are usually are
1429	because they rely on inefficient but fork-safe "select" or "poll" calls.	1811	because they rely on inefficient but fork-safe "select" or "poll" calls
1430	Only EV is fully fork-aware.	1812	- higher performance APIs such as BSD's kqueue or the dreaded Linux
		1813	epoll are usually badly thought-out hacks that are incompatible with
		1814	fork in one way or another. Only EV is fully fork-aware and ensures that
		1815	you continue event-processing in both parent and child (or both, if you
		1816	know what you are doing).
		1817
		1818	This means that, in general, you cannot fork and do event processing in
		1819	the child if the event library was initialised before the fork (which
		1820	usually happens when the first AnyEvent watcher is created, or the
		1821	library is loaded).
1431		1822
1432	If you have to fork, you must either do so before creating your first	1823	If you have to fork, you must either do so before creating your first
1433	watcher OR you must not use AnyEvent at all in the child.	1824	watcher OR you must not use AnyEvent at all in the child OR you must do
		1825	something completely out of the scope of AnyEvent.
		1826
		1827	The problem of doing event processing in the parent and the child is
		1828	much more complicated: even for backends that are fork-aware or
		1829	fork-safe, their behaviour is not usually what you want: fork clones all
		1830	watchers, that means all timers, I/O watchers etc. are active in both
		1831	parent and child, which is almost never what you want. USing "exec" to
		1832	start worker children from some kind of manage rprocess is usually
		1833	preferred, because it is much easier and cleaner, at the expense of
		1834	having to have another binary.
1434		1835
1435	SECURITY CONSIDERATIONS	1836	SECURITY CONSIDERATIONS
1436	AnyEvent can be forced to load any event model via	1837	AnyEvent can be forced to load any event model via
1437	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1838	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1438	to execute arbitrary code or directly gain access, it can easily be used	1839	to execute arbitrary code or directly gain access, it can easily be used
…		…
1448	use AnyEvent;	1849	use AnyEvent;
1449		1850
1450	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1851	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1451	be used to probe what backend is used and gain other information (which	1852	be used to probe what backend is used and gain other information (which
1452	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),	1853	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1453	and $ENV{PERL_ANYEGENT_STRICT}.	1854	and $ENV{PERL_ANYEVENT_STRICT}.
		1855
		1856	Note that AnyEvent will remove all environment variables starting with
		1857	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1858	enabled.
1454		1859
1455	BUGS	1860	BUGS
1456	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1861	Perl 5.8 has numerous memleaks that sometimes hit this module and are
1457	hard to work around. If you suffer from memleaks, first upgrade to Perl	1862	hard to work around. If you suffer from memleaks, first upgrade to Perl
1458	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other	1863	5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
…		…
1465	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,	1870	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1466	Event::Lib, Qt, POE.	1871	Event::Lib, Qt, POE.
1467		1872
1468	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1873	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1469	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1874	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1470	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1875	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1876	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1471		1877
1472	Non-blocking file handles, sockets, TCP clients and servers:	1878	Non-blocking file handles, sockets, TCP clients and servers:
1473	AnyEvent::Handle, AnyEvent::Socket.	1879	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1474		1880
1475	Asynchronous DNS: AnyEvent::DNS.	1881	Asynchronous DNS: AnyEvent::DNS.
1476		1882
1477	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1883	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1478		1884
1479	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1885	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1886	AnyEvent::HTTP.
1480		1887
1481	AUTHOR	1888	AUTHOR
1482	Marc Lehmann <schmorp@schmorp.de>	1889	Marc Lehmann <schmorp@schmorp.de>
1483	http://home.schmorp.de/	1890	http://home.schmorp.de/
1484		1891

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Comparing AnyEvent/README (file contents): Revision 1.39 by root, Sun Jun 7 16:48:38 2009 UTC vs. Revision 1.61 by root, Wed Apr 28 14:15:55 2010 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.39 by root, Sun Jun 7 16:48:38 2009 UTC vs.
Revision 1.61 by root, Wed Apr 28 14:15:55 2010 UTC