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Comparing AnyEvent/README (file contents):
Revision 1.38 by root, Sun Apr 26 18:12:53 2009 UTC vs.
Revision 1.58 by root, Sun Dec 20 22:49:52 2009 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, POE - various supported event	4	EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5	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	# file descriptor readable	10	# file descriptor readable
37		37
38	INTRODUCTION/TUTORIAL	38	INTRODUCTION/TUTORIAL
39	This manpage is mainly a reference manual. If you are interested in a	39	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	40	tutorial or some gentle introduction, have a look at the AnyEvent::Intro
41	manpage.	41	manpage.
		42
		43	SUPPORT
		44	There is a mailinglist for discussing all things AnyEvent, and an IRC
		45	channel, too.
		46
		47	See the AnyEvent project page at the Schmorpforge Ta-Sa Software
		48	Repository, at <http://anyevent.schmorp.de>, for more info.
42		49
43	WHY YOU SHOULD USE THIS MODULE (OR NOT)	50	WHY YOU SHOULD USE THIS MODULE (OR NOT)
44	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen	51	Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
45	nowadays. So what is different about AnyEvent?	52	nowadays. So what is different about AnyEvent?
46		53
…		…
166	Note that "my $w; $w =" combination. This is necessary because in Perl,	173	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	174	my variables are only visible after the statement in which they are
168	declared.	175	declared.
169		176
170	I/O WATCHERS	177	I/O WATCHERS
		178	$w = AnyEvent->io (
		179	fh => <filehandle_or_fileno>,
		180	poll => <"r" or "w">,
		181	cb => <callback>,
		182	);
		183
171	You can create an I/O watcher by calling the "AnyEvent->io" method with	184	You can create an I/O watcher by calling the "AnyEvent->io" method with
172	the following mandatory key-value pairs as arguments:	185	the following mandatory key-value pairs as arguments:
173		186
174	"fh" is the Perl file handle (not file descriptor) to watch for	187	"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	188	events (AnyEvent might or might not keep a reference to this file
176	handle). Note that only file handles pointing to things for which	189	handle). Note that only file handles pointing to things for which
177	non-blocking operation makes sense are allowed. This includes sockets,	190	non-blocking operation makes sense are allowed. This includes sockets,
178	most character devices, pipes, fifos and so on, but not for example	191	most character devices, pipes, fifos and so on, but not for example
179	files or block devices.	192	files or block devices.
…		…
203	warn "read: $input\n";	216	warn "read: $input\n";
204	undef $w;	217	undef $w;
205	});	218	});
206		219
207	TIME WATCHERS	220	TIME WATCHERS
		221	$w = AnyEvent->timer (after => <seconds>, cb => <callback>);
		222
		223	$w = AnyEvent->timer (
		224	after => <fractional_seconds>,
		225	interval => <fractional_seconds>,
		226	cb => <callback>,
		227	);
		228
208	You can create a time watcher by calling the "AnyEvent->timer" method	229	You can create a time watcher by calling the "AnyEvent->timer" method
209	with the following mandatory arguments:	230	with the following mandatory arguments:
210		231
211	"after" specifies after how many seconds (fractional values are	232	"after" specifies after how many seconds (fractional values are
212	supported) the callback should be invoked. "cb" is the callback to	233	supported) the callback should be invoked. "cb" is the callback to
…		…
333	time, which might affect timers and time-outs.	354	time, which might affect timers and time-outs.
334		355
335	When this is the case, you can call this method, which will update	356	When this is the case, you can call this method, which will update
336	the event loop's idea of "current time".	357	the event loop's idea of "current time".
337		358
		359	A typical example would be a script in a web server (e.g.
		360	"mod_perl") - when mod_perl executes the script, then the event loop
		361	will have the wrong idea about the "current time" (being potentially
		362	far in the past, when the script ran the last time). In that case
		363	you should arrange a call to "AnyEvent->now_update" each time the
		364	web server process wakes up again (e.g. at the start of your script,
		365	or in a handler).
		366
338	Note that updating the time might cause some events to be handled.	367	Note that updating the time might cause some events to be handled.
339		368
340	SIGNAL WATCHERS	369	SIGNAL WATCHERS
		370	$w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
		371
341	You can watch for signals using a signal watcher, "signal" is the signal	372	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	373	name in uppercase and without any "SIG" prefix, "cb" is the Perl
343	callback to be invoked whenever a signal occurs.	374	callback to be invoked whenever a signal occurs.
344		375
345	Although the callback might get passed parameters, their value and	376	Although the callback might get passed parameters, their value and
…		…
350	invocation, and callback invocation will be synchronous. Synchronous	381	invocation, and callback invocation will be synchronous. Synchronous
351	means that it might take a while until the signal gets handled by the	382	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.	383	process, but it is guaranteed not to interrupt any other callbacks.
353		384
354	The main advantage of using these watchers is that you can share a	385	The main advantage of using these watchers is that you can share a
355	signal between multiple watchers.	386	signal between multiple watchers, and AnyEvent will ensure that signals
		387	will not interrupt your program at bad times.
356		388
357	This watcher might use %SIG, so programs overwriting those signals	389	This watcher might use %SIG (depending on the event loop used), so
358	directly will likely not work correctly.	390	programs overwriting those signals directly will likely not work
		391	correctly.
359		392
360	Example: exit on SIGINT	393	Example: exit on SIGINT
361		394
362	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });	395	my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
363		396
		397	Restart Behaviour
		398	While restart behaviour is up to the event loop implementation, most
		399	will not restart syscalls (that includes Async::Interrupt and AnyEvent's
		400	pure perl implementation).
		401
		402	Safe/Unsafe Signals
		403	Perl signals can be either "safe" (synchronous to opcode handling) or
		404	"unsafe" (asynchronous) - the former might get delayed indefinitely, the
		405	latter might corrupt your memory.
		406
		407	AnyEvent signal handlers are, in addition, synchronous to the event
		408	loop, i.e. they will not interrupt your running perl program but will
		409	only be called as part of the normal event handling (just like timer,
		410	I/O etc. callbacks, too).
		411
		412	Signal Races, Delays and Workarounds
		413	Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
		414	callbacks to signals in a generic way, which is a pity, as you cannot do
		415	race-free signal handling in perl, requiring C libraries for this.
		416	AnyEvent will try to do it's best, which means in some cases, signals
		417	will be delayed. The maximum time a signal might be delayed is specified
		418	in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
		419	can be changed only before the first signal watcher is created, and
		420	should be left alone otherwise. This variable determines how often
		421	AnyEvent polls for signals (in case a wake-up was missed). Higher values
		422	will cause fewer spurious wake-ups, which is better for power and CPU
		423	saving.
		424
		425	All these problems can be avoided by installing the optional
		426	Async::Interrupt module, which works with most event loops. It will not
		427	work with inherently broken event loops such as Event or Event::Lib (and
		428	not with POE currently, as POE does it's own workaround with one-second
		429	latency). For those, you just have to suffer the delays.
		430
364	CHILD PROCESS WATCHERS	431	CHILD PROCESS WATCHERS
		432	$w = AnyEvent->child (pid => <process id>, cb => <callback>);
		433
365	You can also watch on a child process exit and catch its exit status.	434	You can also watch on a child process exit and catch its exit status.
366		435
367	The child process is specified by the "pid" argument (if set to 0, it	436	The child process is specified by the "pid" argument (one some backends,
368	watches for any child process exit). The watcher will triggered only	437	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	438	The watcher will be triggered only when the child process has finished
370	on any trace events (stopped/continued).	439	and an exit status is available, not on any trace events
		440	(stopped/continued).
371		441
372	The callback will be called with the pid and exit status (as returned by	442	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	443	waitpid), so unlike other watcher types, you can rely on child watcher
374	callback arguments.	444	callback arguments.
375		445
…		…
380		450
381	There is a slight catch to child watchers, however: you usually start	451	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	452	them after the child process was created, and this means the process
383	could have exited already (and no SIGCHLD will be sent anymore).	453	could have exited already (and no SIGCHLD will be sent anymore).
384		454
385	Not all event models handle this correctly (POE doesn't), but even for	455	Not all event models handle this correctly (neither POE nor IO::Async
		456	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	457	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	458	before the process exits (i.e. before you fork in the first place).
388	place).	459	AnyEvent's pure perl event loop handles all cases correctly regardless
		460	of when you start the watcher.
389		461
390	This means you cannot create a child watcher as the very first thing in	462	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	463	an AnyEvent program, you have to create at least one watcher before
392	you "fork" the child (alternatively, you can call "AnyEvent::detect").	464	you "fork" the child (alternatively, you can call "AnyEvent::detect").
393		465
		466	As most event loops do not support waiting for child events, they will
		467	be emulated by AnyEvent in most cases, in which the latency and race
		468	problems mentioned in the description of signal watchers apply.
		469
394	Example: fork a process and wait for it	470	Example: fork a process and wait for it
395		471
396	my $done = AnyEvent->condvar;	472	my $done = AnyEvent->condvar;
397		473
398	my $pid = fork or exit 5;	474	my $pid = fork or exit 5;
399		475
400	my $w = AnyEvent->child (	476	my $w = AnyEvent->child (
401	pid => $pid,	477	pid => $pid,
402	cb => sub {	478	cb => sub {
403	my ($pid, $status) = @_;	479	my ($pid, $status) = @_;
404	warn "pid $pid exited with status $status";	480	warn "pid $pid exited with status $status";
405	$done->send;	481	$done->send;
406	},	482	},
407	);	483	);
408		484
409	# do something else, then wait for process exit	485	# do something else, then wait for process exit
410	$done->recv;	486	$done->recv;
411		487
412	IDLE WATCHERS	488	IDLE WATCHERS
		489	$w = AnyEvent->idle (cb => <callback>);
		490
413	Sometimes there is a need to do something, but it is not so important to	491	Sometimes there is a need to do something, but it is not so important to
414	do it instantly, but only when there is nothing better to do. This	492	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	493	"nothing better to do" is usually defined to be "no other events need
416	attention by the event loop".	494	attention by the event loop".
417		495
…		…
442	}	520	}
443	});	521	});
444	});	522	});
445		523
446	CONDITION VARIABLES	524	CONDITION VARIABLES
		525	$cv = AnyEvent->condvar;
		526
		527	$cv->send (<list>);
		528	my @res = $cv->recv;
		529
447	If you are familiar with some event loops you will know that all of them	530	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	531	require you to run some blocking "loop", "run" or similar function that
449	will actively watch for new events and call your callbacks.	532	will actively watch for new events and call your callbacks.
450		533
451	AnyEvent is different, it expects somebody else to run the event loop	534	AnyEvent is slightly different: it expects somebody else to run the
452	and will only block when necessary (usually when told by the user).	535	event loop and will only block when necessary (usually when told by the
		536	user).
453		537
454	The instrument to do that is called a "condition variable", so called	538	The instrument to do that is called a "condition variable", so called
455	because they represent a condition that must become true.	539	because they represent a condition that must become true.
456		540
		541	Now is probably a good time to look at the examples further below.
		542
457	Condition variables can be created by calling the "AnyEvent->condvar"	543	Condition variables can be created by calling the "AnyEvent->condvar"
458	method, usually without arguments. The only argument pair allowed is	544	method, usually without arguments. The only argument pair allowed is
459
460	"cb", which specifies a callback to be called when the condition	545	"cb", which specifies a callback to be called when the condition
461	variable becomes true, with the condition variable as the first argument	546	variable becomes true, with the condition variable as the first argument
462	(but not the results).	547	(but not the results).
463		548
464	After creation, the condition variable is "false" until it becomes	549	After creation, the condition variable is "false" until it becomes
…		…
469	Condition variables are similar to callbacks, except that you can	554	Condition variables are similar to callbacks, except that you can
470	optionally wait for them. They can also be called merge points - points	555	optionally wait for them. They can also be called merge points - points
471	in time where multiple outstanding events have been processed. And yet	556	in time where multiple outstanding events have been processed. And yet
472	another way to call them is transactions - each condition variable can	557	another way to call them is transactions - each condition variable can
473	be used to represent a transaction, which finishes at some point and	558	be used to represent a transaction, which finishes at some point and
474	delivers a result.	559	delivers a result. And yet some people know them as "futures" - a
		560	promise to compute/deliver something that you can wait for.
475		561
476	Condition variables are very useful to signal that something has	562	Condition variables are very useful to signal that something has
477	finished, for example, if you write a module that does asynchronous http	563	finished, for example, if you write a module that does asynchronous http
478	requests, then a condition variable would be the ideal candidate to	564	requests, then a condition variable would be the ideal candidate to
479	signal the availability of results. The user can either act when the	565	signal the availability of results. The user can either act when the
…		…
513	after => 1,	599	after => 1,
514	cb => sub { $result_ready->send },	600	cb => sub { $result_ready->send },
515	);	601	);
516		602
517	# this "blocks" (while handling events) till the callback	603	# this "blocks" (while handling events) till the callback
518	# calls send	604	# calls ->send
519	$result_ready->recv;	605	$result_ready->recv;
520		606
521	Example: wait for a timer, but take advantage of the fact that condition	607	Example: wait for a timer, but take advantage of the fact that condition
522	variables are also code references.	608	variables are also callable directly.
523		609
524	my $done = AnyEvent->condvar;	610	my $done = AnyEvent->condvar;
525	my $delay = AnyEvent->timer (after => 5, cb => $done);	611	my $delay = AnyEvent->timer (after => 5, cb => $done);
526	$done->recv;	612	$done->recv;
527		613
…		…
533		619
534	...	620	...
535		621
536	my @info = $couchdb->info->recv;	622	my @info = $couchdb->info->recv;
537		623
538	And this is how you would just ste a callback to be called whenever the	624	And this is how you would just set a callback to be called whenever the
539	results are available:	625	results are available:
540		626
541	$couchdb->info->cb (sub {	627	$couchdb->info->cb (sub {
542	my @info = $_[0]->recv;	628	my @info = $_[0]->recv;
543	});	629	});
…		…
558		644
559	Any arguments passed to the "send" call will be returned by all	645	Any arguments passed to the "send" call will be returned by all
560	future "->recv" calls.	646	future "->recv" calls.
561		647
562	Condition variables are overloaded so one can call them directly (as	648	Condition variables are overloaded so one can call them directly (as
563	a code reference). Calling them directly is the same as calling	649	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	650	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		651
571	$cv->croak ($error)	652	$cv->croak ($error)
572	Similar to send, but causes all call's to "->recv" to invoke	653	Similar to send, but causes all call's to "->recv" to invoke
573	"Carp::croak" with the given error message/object/scalar.	654	"Carp::croak" with the given error message/object/scalar.
574		655
575	This can be used to signal any errors to the condition variable	656	This can be used to signal any errors to the condition variable
576	user/consumer.	657	user/consumer. Doing it this way instead of calling "croak" directly
		658	delays the error detetcion, but has the overwhelmign advantage that
		659	it diagnoses the error at the place where the result is expected,
		660	and not deep in some event clalback without connection to the actual
		661	code causing the problem.
577		662
578	$cv->begin ([group callback])	663	$cv->begin ([group callback])
579	$cv->end	664	$cv->end
580	These two methods are EXPERIMENTAL and MIGHT CHANGE.
581
582	These two methods can be used to combine many transactions/events	665	These two methods can be used to combine many transactions/events
583	into one. For example, a function that pings many hosts in parallel	666	into one. For example, a function that pings many hosts in parallel
584	might want to use a condition variable for the whole process.	667	might want to use a condition variable for the whole process.
585		668
586	Every call to "->begin" will increment a counter, and every call to	669	Every call to "->begin" will increment a counter, and every call to
587	"->end" will decrement it. If the counter reaches 0 in "->end", the	670	"->end" will decrement it. If the counter reaches 0 in "->end", the
588	(last) callback passed to "begin" will be executed. That callback is	671	(last) callback passed to "begin" will be executed, passing the
589	supposed to call "->send", but that is not required. If no	672	condvar as first argument. That callback is supposed to call
		673	"->send", but that is not required. If no group callback was set,
590	callback was set, "send" will be called without any arguments.	674	"send" will be called without any arguments.
591		675
592	Let's clarify this with the ping example:	676	You can think of "$cv->send" giving you an OR condition (one call
		677	sends), while "$cv->begin" and "$cv->end" giving you an AND
		678	condition (all "begin" calls must be "end"'ed before the condvar
		679	sends).
		680
		681	Let's start with a simple example: you have two I/O watchers (for
		682	example, STDOUT and STDERR for a program), and you want to wait for
		683	both streams to close before activating a condvar:
593		684
594	my $cv = AnyEvent->condvar;	685	my $cv = AnyEvent->condvar;
595		686
		687	$cv->begin; # first watcher
		688	my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
		689	defined sysread $fh1, my $buf, 4096
		690	or $cv->end;
		691	});
		692
		693	$cv->begin; # second watcher
		694	my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
		695	defined sysread $fh2, my $buf, 4096
		696	or $cv->end;
		697	});
		698
		699	$cv->recv;
		700
		701	This works because for every event source (EOF on file handle),
		702	there is one call to "begin", so the condvar waits for all calls to
		703	"end" before sending.
		704
		705	The ping example mentioned above is slightly more complicated, as
		706	the there are results to be passwd back, and the number of tasks
		707	that are begung can potentially be zero:
		708
		709	my $cv = AnyEvent->condvar;
		710
596	my %result;	711	my %result;
597	$cv->begin (sub { $cv->send (\%result) });	712	$cv->begin (sub { shift->send (\%result) });
598		713
599	for my $host (@list_of_hosts) {	714	for my $host (@list_of_hosts) {
600	$cv->begin;	715	$cv->begin;
601	ping_host_then_call_callback $host, sub {	716	ping_host_then_call_callback $host, sub {
602	$result{$host} = ...;	717	$result{$host} = ...;
…		…
617	the loop, which serves two important purposes: first, it sets the	732	the loop, which serves two important purposes: first, it sets the
618	callback to be called once the counter reaches 0, and second, it	733	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	734	ensures that "send" is called even when "no" hosts are being pinged
620	(the loop doesn't execute once).	735	(the loop doesn't execute once).
621		736
622	This is the general pattern when you "fan out" into multiple	737	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	738	potentially none) subrequests: use an outer "begin"/"end" pair to
624	ensure "end" is called at least once, and then, for each subrequest	739	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	740	for each subrequest you start, call "begin" and for each subrequest
626	"end".	741	you finish, call "end".
627		742
628	METHODS FOR CONSUMERS	743	METHODS FOR CONSUMERS
629	These methods should only be used by the consuming side, i.e. the code	744	These methods should only be used by the consuming side, i.e. the code
630	awaits the condition.	745	awaits the condition.
631		746
…		…
640	function will call "croak".	755	function will call "croak".
641		756
642	In list context, all parameters passed to "send" will be returned,	757	In list context, all parameters passed to "send" will be returned,
643	in scalar context only the first one will be returned.	758	in scalar context only the first one will be returned.
644		759
		760	Note that doing a blocking wait in a callback is not supported by
		761	any event loop, that is, recursive invocation of a blocking "->recv"
		762	is not allowed, and the "recv" call will "croak" if such a condition
		763	is detected. This condition can be slightly loosened by using
		764	Coro::AnyEvent, which allows you to do a blocking "->recv" from any
		765	thread that doesn't run the event loop itself.
		766
645	Not all event models support a blocking wait - some die in that case	767	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	768	(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	769	using this from a module, never require a blocking wait*. Instead,
648	the caller decide whether the call will block or not (for example,	770	let the caller decide whether the call will block or not (for
649	by coupling condition variables with some kind of request results	771	example, by coupling condition variables with some kind of request
650	and supporting callbacks so the caller knows that getting the result	772	results and supporting callbacks so the caller knows that getting
651	will not block, while still supporting blocking waits if the caller	773	the result will not block, while still supporting blocking waits if
652	so desires).	774	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		775
665	You can ensure that "-recv" never blocks by setting a callback and	776	You can ensure that "-recv" never blocks by setting a callback and
666	only calling "->recv" from within that callback (or at a later	777	only calling "->recv" from within that callback (or at a later
667	time). This will work even when the event loop does not support	778	time). This will work even when the event loop does not support
668	blocking waits otherwise.	779	blocking waits otherwise.
…		…
673		784
674	$cb = $cv->cb ($cb->($cv))	785	$cb = $cv->cb ($cb->($cv))
675	This is a mutator function that returns the callback set and	786	This is a mutator function that returns the callback set and
676	optionally replaces it before doing so.	787	optionally replaces it before doing so.
677		788
678	The callback will be called when the condition becomes "true", i.e.	789	The callback will be called when the condition becomes (or already
679	when "send" or "croak" are called, with the only argument being the	790	was) "true", i.e. when "send" or "croak" are called (or were
680	condition variable itself. Calling "recv" inside the callback or at	791	called), with the only argument being the condition variable itself.
		792	Calling "recv" inside the callback or at any later time is
681	any later time is guaranteed not to block.	793	guaranteed not to block.
		794
		795	SUPPORTED EVENT LOOPS/BACKENDS
		796	The available backend classes are (every class has its own manpage):
		797
		798	Backends that are autoprobed when no other event loop can be found.
		799	EV is the preferred backend when no other event loop seems to be in
		800	use. If EV is not installed, then AnyEvent will fall back to its own
		801	pure-perl implementation, which is available everywhere as it comes
		802	with AnyEvent itself.
		803
		804	AnyEvent::Impl::EV based on EV (interface to libev, best choice).
		805	AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
		806
		807	Backends that are transparently being picked up when they are used.
		808	These will be used when they are currently loaded when the first
		809	watcher is created, in which case it is assumed that the application
		810	is using them. This means that AnyEvent will automatically pick the
		811	right backend when the main program loads an event module before
		812	anything starts to create watchers. Nothing special needs to be done
		813	by the main program.
		814
		815	AnyEvent::Impl::Event based on Event, very stable, few glitches.
		816	AnyEvent::Impl::Glib based on Glib, slow but very stable.
		817	AnyEvent::Impl::Tk based on Tk, very broken.
		818	AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
		819	AnyEvent::Impl::POE based on POE, very slow, some limitations.
		820	AnyEvent::Impl::Irssi used when running within irssi.
		821
		822	Backends with special needs.
		823	Qt requires the Qt::Application to be instantiated first, but will
		824	otherwise be picked up automatically. As long as the main program
		825	instantiates the application before any AnyEvent watchers are
		826	created, everything should just work.
		827
		828	AnyEvent::Impl::Qt based on Qt.
		829
		830	Support for IO::Async can only be partial, as it is too broken and
		831	architecturally limited to even support the AnyEvent API. It also is
		832	the only event loop that needs the loop to be set explicitly, so it
		833	can only be used by a main program knowing about AnyEvent. See
		834	AnyEvent::Impl::Async for the gory details.
		835
		836	AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
		837
		838	Event loops that are indirectly supported via other backends.
		839	Some event loops can be supported via other modules:
		840
		841	There is no direct support for WxWidgets (Wx) or Prima.
		842
		843	WxWidgets has no support for watching file handles. However, you can
		844	use WxWidgets through the POE adaptor, as POE has a Wx backend that
		845	simply polls 20 times per second, which was considered to be too
		846	horrible to even consider for AnyEvent.
		847
		848	Prima is not supported as nobody seems to be using it, but it has a
		849	POE backend, so it can be supported through POE.
		850
		851	AnyEvent knows about both Prima and Wx, however, and will try to
		852	load POE when detecting them, in the hope that POE will pick them
		853	up, in which case everything will be automatic.
682		854
683	GLOBAL VARIABLES AND FUNCTIONS	855	GLOBAL VARIABLES AND FUNCTIONS
		856	These are not normally required to use AnyEvent, but can be useful to
		857	write AnyEvent extension modules.
		858
684	$AnyEvent::MODEL	859	$AnyEvent::MODEL
685	Contains "undef" until the first watcher is being created. Then it	860	Contains "undef" until the first watcher is being created, before
		861	the backend has been autodetected.
		862
686	contains the event model that is being used, which is the name of	863	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	864	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	865	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).	866	other class in the case AnyEvent has been extended at runtime (e.g.
690		867	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		868
712	AnyEvent::detect	869	AnyEvent::detect
713	Returns $AnyEvent::MODEL, forcing autodetection of the event model	870	Returns $AnyEvent::MODEL, forcing autodetection of the event model
714	if necessary. You should only call this function right before you	871	if necessary. You should only call this function right before you
715	would have created an AnyEvent watcher anyway, that is, as late as	872	would have created an AnyEvent watcher anyway, that is, as late as
716	possible at runtime.	873	possible at runtime, and not e.g. while initialising of your module.
		874
		875	If you need to do some initialisation before AnyEvent watchers are
		876	created, use "post_detect".
717		877
718	$guard = AnyEvent::post_detect { BLOCK }	878	$guard = AnyEvent::post_detect { BLOCK }
719	Arranges for the code block to be executed as soon as the event	879	Arranges for the code block to be executed as soon as the event
720	model is autodetected (or immediately if this has already happened).	880	model is autodetected (or immediately if this has already happened).
721		881
		882	The block will be executed after the actual backend has been
		883	detected ($AnyEvent::MODEL is set), but before any watchers have
		884	been created, so it is possible to e.g. patch @AnyEvent::ISA or do
		885	other initialisations - see the sources of AnyEvent::Strict or
		886	AnyEvent::AIO to see how this is used.
		887
		888	The most common usage is to create some global watchers, without
		889	forcing event module detection too early, for example, AnyEvent::AIO
		890	creates and installs the global IO::AIO watcher in a "post_detect"
		891	block to avoid autodetecting the event module at load time.
		892
722	If called in scalar or list context, then it creates and returns an	893	If called in scalar or list context, then it creates and returns an
723	object that automatically removes the callback again when it is	894	object that automatically removes the callback again when it is
		895	destroyed (or "undef" when the hook was immediately executed). See
724	destroyed. See Coro::BDB for a case where this is useful.	896	AnyEvent::AIO for a case where this is useful.
		897
		898	Example: Create a watcher for the IO::AIO module and store it in
		899	$WATCHER. Only do so after the event loop is initialised, though.
		900
		901	our WATCHER;
		902
		903	my $guard = AnyEvent::post_detect {
		904	$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
		905	};
		906
		907	# the \|\|= is important in case post_detect immediately runs the block,
		908	# as to not clobber the newly-created watcher. assigning both watcher and
		909	# post_detect guard to the same variable has the advantage of users being
		910	# able to just C<undef $WATCHER> if the watcher causes them grief.
		911
		912	$WATCHER \|\|= $guard;
725		913
726	@AnyEvent::post_detect	914	@AnyEvent::post_detect
727	If there are any code references in this array (you can "push" to it	915	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	916	before or after loading AnyEvent), then they will called directly
729	after the event loop has been chosen.	917	after the event loop has been chosen.
730		918
731	You should check $AnyEvent::MODEL before adding to this array,	919	You should check $AnyEvent::MODEL before adding to this array,
732	though: if it contains a true value then the event loop has already	920	though: if it is defined then the event loop has already been
733	been detected, and the array will be ignored.	921	detected, and the array will be ignored.
734		922
735	Best use "AnyEvent::post_detect { BLOCK }" instead.	923	Best use "AnyEvent::post_detect { BLOCK }" when your application
		924	allows it, as it takes care of these details.
		925
		926	This variable is mainly useful for modules that can do something
		927	useful when AnyEvent is used and thus want to know when it is
		928	initialised, but do not need to even load it by default. This array
		929	provides the means to hook into AnyEvent passively, without loading
		930	it.
		931
		932	Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
		933	together, you could put this into Coro (this is the actual code used
		934	by Coro to accomplish this):
		935
		936	if (defined $AnyEvent::MODEL) {
		937	# AnyEvent already initialised, so load Coro::AnyEvent
		938	require Coro::AnyEvent;
		939	} else {
		940	# AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
		941	# as soon as it is
		942	push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
		943	}
736		944
737	WHAT TO DO IN A MODULE	945	WHAT TO DO IN A MODULE
738	As a module author, you should "use AnyEvent" and call AnyEvent methods	946	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.	947	freely, but you should not load a specific event module or rely on it.
740		948
…		…
791	variable somewhere, waiting for it, and sending it when the program	999	variable somewhere, waiting for it, and sending it when the program
792	should exit cleanly.	1000	should exit cleanly.
793		1001
794	OTHER MODULES	1002	OTHER MODULES
795	The following is a non-exhaustive list of additional modules that use	1003	The following is a non-exhaustive list of additional modules that use
796	AnyEvent and can therefore be mixed easily with other AnyEvent modules	1004	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	1005	AnyEvent modules and other event loops in the same program. Some of the
798	available via CPAN.	1006	modules come with AnyEvent, most are available via CPAN.
799		1007
800	AnyEvent::Util	1008	AnyEvent::Util
801	Contains various utility functions that replace often-used but	1009	Contains various utility functions that replace often-used but
802	blocking functions such as "inet_aton" by event-/callback-based	1010	blocking functions such as "inet_aton" by event-/callback-based
803	versions.	1011	versions.
…		…
809	more.	1017	more.
810		1018
811	AnyEvent::Handle	1019	AnyEvent::Handle
812	Provide read and write buffers, manages watchers for reads and	1020	Provide read and write buffers, manages watchers for reads and
813	writes, supports raw and formatted I/O, I/O queued and fully	1021	writes, supports raw and formatted I/O, I/O queued and fully
814	transparent and non-blocking SSL/TLS.	1022	transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
815		1023
816	AnyEvent::DNS	1024	AnyEvent::DNS
817	Provides rich asynchronous DNS resolver capabilities.	1025	Provides rich asynchronous DNS resolver capabilities.
818		1026
819	AnyEvent::HTTP	1027	AnyEvent::HTTP
…		…
840		1048
841	AnyEvent::GPSD	1049	AnyEvent::GPSD
842	A non-blocking interface to gpsd, a daemon delivering GPS	1050	A non-blocking interface to gpsd, a daemon delivering GPS
843	information.	1051	information.
844		1052
		1053	AnyEvent::IRC
		1054	AnyEvent based IRC client module family (replacing the older
		1055	Net::IRC3).
		1056
		1057	AnyEvent::XMPP
		1058	AnyEvent based XMPP (Jabber protocol) module family (replacing the
		1059	older Net::XMPP2>.
		1060
845	AnyEvent::IGS	1061	AnyEvent::IGS
846	A non-blocking interface to the Internet Go Server protocol (used by	1062	A non-blocking interface to the Internet Go Server protocol (used by
847	App::IGS).	1063	App::IGS).
848		1064
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	1065	Net::FCP
857	AnyEvent-based implementation of the Freenet Client Protocol,	1066	AnyEvent-based implementation of the Freenet Client Protocol,
858	birthplace of AnyEvent.	1067	birthplace of AnyEvent.
859		1068
860	Event::ExecFlow	1069	Event::ExecFlow
861	High level API for event-based execution flow control.	1070	High level API for event-based execution flow control.
862		1071
863	Coro	1072	Coro
864	Has special support for AnyEvent via Coro::AnyEvent.	1073	Has special support for AnyEvent via Coro::AnyEvent.
865		1074
866	IO::Lambda	1075	SIMPLIFIED AE API
867	The lambda approach to I/O - don't ask, look there. Can use	1076	Starting with version 5.0, AnyEvent officially supports a second, much
868	AnyEvent.	1077	simpler, API that is designed to reduce the calling, typing and memory
		1078	overhead.
		1079
		1080	See the AE manpage for details.
869		1081
870	ERROR AND EXCEPTION HANDLING	1082	ERROR AND EXCEPTION HANDLING
871	In general, AnyEvent does not do any error handling - it relies on the	1083	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	1084	caller to do that if required. The AnyEvent::Strict module (see also the
873	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict	1085	"PERL_ANYEVENT_STRICT" environment variable, below) provides strict
…		…
883	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",	1095	"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
884	Glib uses "install_exception_handler" and so on.	1096	Glib uses "install_exception_handler" and so on.
885		1097
886	ENVIRONMENT VARIABLES	1098	ENVIRONMENT VARIABLES
887	The following environment variables are used by this module or its	1099	The following environment variables are used by this module or its
888	submodules:	1100	submodules.
		1101
		1102	Note that AnyEvent will remove all environment variables starting with
		1103	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1104	enabled.
889		1105
890	"PERL_ANYEVENT_VERBOSE"	1106	"PERL_ANYEVENT_VERBOSE"
891	By default, AnyEvent will be completely silent except in fatal	1107	By default, AnyEvent will be completely silent except in fatal
892	conditions. You can set this environment variable to make AnyEvent	1108	conditions. You can set this environment variable to make AnyEvent
893	more talkative.	1109	more talkative.
…		…
896	conditions, such as not being able to load the event model specified	1112	conditions, such as not being able to load the event model specified
897	by "PERL_ANYEVENT_MODEL".	1113	by "PERL_ANYEVENT_MODEL".
898		1114
899	When set to 2 or higher, cause AnyEvent to report to STDERR which	1115	When set to 2 or higher, cause AnyEvent to report to STDERR which
900	event model it chooses.	1116	event model it chooses.
		1117
		1118	When set to 8 or higher, then AnyEvent will report extra information
		1119	on which optional modules it loads and how it implements certain
		1120	features.
901		1121
902	"PERL_ANYEVENT_STRICT"	1122	"PERL_ANYEVENT_STRICT"
903	AnyEvent does not do much argument checking by default, as thorough	1123	AnyEvent does not do much argument checking by default, as thorough
904	argument checking is very costly. Setting this variable to a true	1124	argument checking is very costly. Setting this variable to a true
905	value will cause AnyEvent to load "AnyEvent::Strict" and then to	1125	value will cause AnyEvent to load "AnyEvent::Strict" and then to
906	thoroughly check the arguments passed to most method calls. If it	1126	thoroughly check the arguments passed to most method calls. If it
907	finds any problems it will croak.	1127	finds any problems, it will croak.
908		1128
909	In other words, enables "strict" mode.	1129	In other words, enables "strict" mode.
910		1130
911	Unlike "use strict", it is definitely recommended ot keep it off in	1131	Unlike "use strict" (or it's modern cousin, "use common::sense", it
912	production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment	1132	is definitely recommended to keep it off in production. Keeping
		1133	"PERL_ANYEVENT_STRICT=1" in your environment while developing
913	while developing programs can be very useful, however.	1134	programs can be very useful, however.
914		1135
915	"PERL_ANYEVENT_MODEL"	1136	"PERL_ANYEVENT_MODEL"
916	This can be used to specify the event model to be used by AnyEvent,	1137	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	1138	before auto detection and -probing kicks in. It must be a string
918	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"	1139	consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
…		…
959	EDNS0 in its DNS requests.	1180	EDNS0 in its DNS requests.
960		1181
961	"PERL_ANYEVENT_MAX_FORKS"	1182	"PERL_ANYEVENT_MAX_FORKS"
962	The maximum number of child processes that	1183	The maximum number of child processes that
963	"AnyEvent::Util::fork_call" will create in parallel.	1184	"AnyEvent::Util::fork_call" will create in parallel.
		1185
		1186	"PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
		1187	The default value for the "max_outstanding" parameter for the
		1188	default DNS resolver - this is the maximum number of parallel DNS
		1189	requests that are sent to the DNS server.
		1190
		1191	"PERL_ANYEVENT_RESOLV_CONF"
		1192	The file to use instead of /etc/resolv.conf (or OS-specific
		1193	configuration) in the default resolver. When set to the empty
		1194	string, no default config will be used.
		1195
		1196	"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
		1197	When neither "ca_file" nor "ca_path" was specified during
		1198	AnyEvent::TLS context creation, and either of these environment
		1199	variables exist, they will be used to specify CA certificate
		1200	locations instead of a system-dependent default.
		1201
		1202	"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
		1203	When these are set to 1, then the respective modules are not loaded.
		1204	Mostly good for testing AnyEvent itself.
964		1205
965	SUPPLYING YOUR OWN EVENT MODEL INTERFACE	1206	SUPPLYING YOUR OWN EVENT MODEL INTERFACE
966	This is an advanced topic that you do not normally need to use AnyEvent	1207	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	1208	in a module. This section is only of use to event loop authors who want
968	to provide AnyEvent compatibility.	1209	to provide AnyEvent compatibility.
…		…
1023	warn "read: $input\n"; # output what has been read	1264	warn "read: $input\n"; # output what has been read
1024	$cv->send if $input =~ /^q/i; # quit program if /^q/i	1265	$cv->send if $input =~ /^q/i; # quit program if /^q/i
1025	},	1266	},
1026	);	1267	);
1027		1268
1028	my $time_watcher; # can only be used once
1029
1030	sub new_timer {
1031	$timer = AnyEvent->timer (after => 1, cb => sub {	1269	my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
1032	warn "timeout\n"; # print 'timeout' about every second	1270	warn "timeout\n"; # print 'timeout' at most every second
1033	&new_timer; # and restart the time
1034	});
1035	}	1271	});
1036
1037	new_timer; # create first timer
1038		1272
1039	$cv->recv; # wait until user enters /^q/i	1273	$cv->recv; # wait until user enters /^q/i
1040		1274
1041	REAL-WORLD EXAMPLE	1275	REAL-WORLD EXAMPLE
1042	Consider the Net::FCP module. It features (among others) the following	1276	Consider the Net::FCP module. It features (among others) the following
…		…
1169	through AnyEvent. The benchmark creates a lot of timers (with a zero	1403	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,	1404	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.	1405	which it is), lets them fire exactly once and destroys them again.
1172		1406
1173	Source code for this benchmark is found as eg/bench in the AnyEvent	1407	Source code for this benchmark is found as eg/bench in the AnyEvent
1174	distribution.	1408	distribution. It uses the AE interface, which makes a real difference
		1409	for the EV and Perl backends only.
1175		1410
1176	Explanation of the columns	1411	Explanation of the columns
1177	watcher is the number of event watchers created/destroyed. Since	1412	watcher is the number of event watchers created/destroyed. Since
1178	different event models feature vastly different performances, each event	1413	different event models feature vastly different performances, each event
1179	loop was given a number of watchers so that overall runtime is	1414	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	1433	destroy is the time, in microseconds, that it takes to destroy a
1199	single watcher.	1434	single watcher.
1200		1435
1201	Results	1436	Results
1202	name watchers bytes create invoke destroy comment	1437	name watchers bytes create invoke destroy comment
1203	EV/EV 400000 224 0.47 0.35 0.27 EV native interface	1438	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	1439	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	1440	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	1441	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	1442	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	1443	Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
		1444	IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
		1445	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	1446	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	1447	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	1448	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	1449	POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1213		1450
1214	Discussion	1451	Discussion
1215	The benchmark does not measure scalability of the event loop very	1452	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)	1453	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	1454	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	1465	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	1466	EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1230	CPU cycles with POE.	1467	CPU cycles with POE.
1231		1468
1232	"EV" is the sole leader regarding speed and memory use, which are both	1469	"EV" is the sole leader regarding speed and memory use, which are both
1233	maximal/minimal, respectively. Even when going through AnyEvent, it uses	1470	maximal/minimal, respectively. When using the AE API there is zero
		1471	overhead (when going through the AnyEvent API create is about 5-6 times
		1472	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	1473	any other event loop and is still faster than Event natively).
1235	natively.
1236		1474
1237	The pure perl implementation is hit in a few sweet spots (both the	1475	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	1476	constant timeout and the use of a single fd hit optimisations in the
1239	perl interpreter and the backend itself). Nevertheless this shows that	1477	perl interpreter and the backend itself). Nevertheless this shows that
1240	it adds very little overhead in itself. Like any select-based backend	1478	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	1480	few of them active), of course, but this was not subject of this
1243	benchmark.	1481	benchmark.
1244		1482
1245	The "Event" module has a relatively high setup and callback invocation	1483	The "Event" module has a relatively high setup and callback invocation
1246	cost, but overall scores in on the third place.	1484	cost, but overall scores in on the third place.
		1485
		1486	"IO::Async" performs admirably well, about on par with "Event", even
		1487	when using its pure perl backend.
1247		1488
1248	"Glib"'s memory usage is quite a bit higher, but it features a faster	1489	"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".	1490	callback invocation and overall ends up in the same class as "Event".
1250	However, Glib scales extremely badly, doubling the number of watchers	1491	However, Glib scales extremely badly, doubling the number of watchers
1251	increases the processing time by more than a factor of four, making it	1492	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	1548	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	1549	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.	1550	many connections, most of which are idle at any one point in time.
1310		1551
1311	Source code for this benchmark is found as eg/bench2 in the AnyEvent	1552	Source code for this benchmark is found as eg/bench2 in the AnyEvent
1312	distribution.	1553	distribution. It uses the AE interface, which makes a real difference
		1554	for the EV and Perl backends only.
1313		1555
1314	Explanation of the columns	1556	Explanation of the columns
1315	sockets is the number of sockets, and twice the number of "servers"	1557	sockets is the number of sockets, and twice the number of "servers"
1316	(as each server has a read and write socket end).	1558	(as each server has a read and write socket end).
1317		1559
…		…
1322	single "request", that is, reading the token from the pipe and	1564	single "request", that is, reading the token from the pipe and
1323	forwarding it to another server. This includes deleting the old timeout	1565	forwarding it to another server. This includes deleting the old timeout
1324	and creating a new one that moves the timeout into the future.	1566	and creating a new one that moves the timeout into the future.
1325		1567
1326	Results	1568	Results
1327	name sockets create request	1569	name sockets create request
1328	EV 20000 69.01 11.16	1570	EV 20000 62.66 7.99
1329	Perl 20000 73.32 35.87	1571	Perl 20000 68.32 32.64
1330	Event 20000 212.62 257.32	1572	IOAsync 20000 174.06 101.15 epoll
1331	Glib 20000 651.16 1896.30	1573	IOAsync 20000 174.67 610.84 poll
		1574	Event 20000 202.69 242.91
		1575	Glib 20000 557.01 1689.52
1332	POE 20000 349.67 12317.24 uses POE::Loop::Event	1576	POE 20000 341.54 12086.32 uses POE::Loop::Event
1333		1577
1334	Discussion	1578	Discussion
1335	This benchmark does measure scalability and overall performance of the	1579	This benchmark does measure scalability and overall performance of the
1336	particular event loop.	1580	particular event loop.
1337		1581
1338	EV is again fastest. Since it is using epoll on my system, the setup	1582	EV is again fastest. Since it is using epoll on my system, the setup
1339	time is relatively high, though.	1583	time is relatively high, though.
1340		1584
1341	Perl surprisingly comes second. It is much faster than the C-based event	1585	Perl surprisingly comes second. It is much faster than the C-based event
1342	loops Event and Glib.	1586	loops Event and Glib.
		1587
		1588	IO::Async performs very well when using its epoll backend, and still
		1589	quite good compared to Glib when using its pure perl backend.
1343		1590
1344	Event suffers from high setup time as well (look at its code and you	1591	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	1592	will understand why). Callback invocation also has a high overhead
1346	compared to the "$_->() for .."-style loop that the Perl event loop	1593	compared to the "$_->() for .."-style loop that the Perl event loop
1347	uses. Event uses select or poll in basically all documented	1594	uses. Event uses select or poll in basically all documented
…		…
1398		1645
1399	Summary	1646	Summary
1400	* C-based event loops perform very well with small number of watchers,	1647	* C-based event loops perform very well with small number of watchers,
1401	as the management overhead dominates.	1648	as the management overhead dominates.
1402		1649
		1650	THE IO::Lambda BENCHMARK
		1651	Recently I was told about the benchmark in the IO::Lambda manpage, which
		1652	could be misinterpreted to make AnyEvent look bad. In fact, the
		1653	benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
		1654	better (which shouldn't come as a surprise to anybody). As such, the
		1655	benchmark is fine, and mostly shows that the AnyEvent backend from
		1656	IO::Lambda isn't very optimal. But how would AnyEvent compare when used
		1657	without the extra baggage? To explore this, I wrote the equivalent
		1658	benchmark for AnyEvent.
		1659
		1660	The benchmark itself creates an echo-server, and then, for 500 times,
		1661	connects to the echo server, sends a line, waits for the reply, and then
		1662	creates the next connection. This is a rather bad benchmark, as it
		1663	doesn't test the efficiency of the framework or much non-blocking I/O,
		1664	but it is a benchmark nevertheless.
		1665
		1666	name runtime
		1667	Lambda/select 0.330 sec
		1668	+ optimized 0.122 sec
		1669	Lambda/AnyEvent 0.327 sec
		1670	+ optimized 0.138 sec
		1671	Raw sockets/select 0.077 sec
		1672	POE/select, components 0.662 sec
		1673	POE/select, raw sockets 0.226 sec
		1674	POE/select, optimized 0.404 sec
		1675
		1676	AnyEvent/select/nb 0.085 sec
		1677	AnyEvent/EV/nb 0.068 sec
		1678	+state machine 0.134 sec
		1679
		1680	The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
		1681	benchmarks actually make blocking connects and use 100% blocking I/O,
		1682	defeating the purpose of an event-based solution. All of the newly
		1683	written AnyEvent benchmarks use 100% non-blocking connects (using
		1684	AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
		1685	resolver), so AnyEvent is at a disadvantage here, as non-blocking
		1686	connects generally require a lot more bookkeeping and event handling
		1687	than blocking connects (which involve a single syscall only).
		1688
		1689	The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
		1690	offers similar expressive power as POE and IO::Lambda, using
		1691	conventional Perl syntax. This means that both the echo server and the
		1692	client are 100% non-blocking, further placing it at a disadvantage.
		1693
		1694	As you can see, the AnyEvent + EV combination even beats the
		1695	hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
		1696	backend easily beats IO::Lambda and POE.
		1697
		1698	And even the 100% non-blocking version written using the high-level (and
		1699	slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
		1700	higher level ("unoptimised") abstractions by a large margin, even though
		1701	it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
		1702
		1703	The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
		1704	eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
		1705	part of the IO::Lambda distribution and were used without any changes.
		1706
1403	SIGNALS	1707	SIGNALS
1404	AnyEvent currently installs handlers for these signals:	1708	AnyEvent currently installs handlers for these signals:
1405		1709
1406	SIGCHLD	1710	SIGCHLD
1407	A handler for "SIGCHLD" is installed by AnyEvent's child watcher	1711	A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1408	emulation for event loops that do not support them natively. Also,	1712	emulation for event loops that do not support them natively. Also,
1409	some event loops install a similar handler.	1713	some event loops install a similar handler.
		1714
		1715	Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
		1716	then AnyEvent will reset it to default, to avoid losing child exit
		1717	statuses.
1410		1718
1411	SIGPIPE	1719	SIGPIPE
1412	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is	1720	A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1413	"undef" when AnyEvent gets loaded.	1721	"undef" when AnyEvent gets loaded.
1414		1722
…		…
1422	it is that this way, the handler will be restored to defaults on	1730	it is that this way, the handler will be restored to defaults on
1423	exec.	1731	exec.
1424		1732
1425	Feel free to install your own handler, or reset it to defaults.	1733	Feel free to install your own handler, or reset it to defaults.
1426		1734
		1735	RECOMMENDED/OPTIONAL MODULES
		1736	One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
		1737	it's built-in modules) are required to use it.
		1738
		1739	That does not mean that AnyEvent won't take advantage of some additional
		1740	modules if they are installed.
		1741
		1742	This section explains which additional modules will be used, and how
		1743	they affect AnyEvent's operation.
		1744
		1745	Async::Interrupt
		1746	This slightly arcane module is used to implement fast signal
		1747	handling: To my knowledge, there is no way to do completely
		1748	race-free and quick signal handling in pure perl. To ensure that
		1749	signals still get delivered, AnyEvent will start an interval timer
		1750	to wake up perl (and catch the signals) with some delay (default is
		1751	10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
		1752
		1753	If this module is available, then it will be used to implement
		1754	signal catching, which means that signals will not be delayed, and
		1755	the event loop will not be interrupted regularly, which is more
		1756	efficient (and good for battery life on laptops).
		1757
		1758	This affects not just the pure-perl event loop, but also other event
		1759	loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
		1760
		1761	Some event loops (POE, Event, Event::Lib) offer signal watchers
		1762	natively, and either employ their own workarounds (POE) or use
		1763	AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
		1764	Installing Async::Interrupt does nothing for those backends.
		1765
		1766	EV This module isn't really "optional", as it is simply one of the
		1767	backend event loops that AnyEvent can use. However, it is simply the
		1768	best event loop available in terms of features, speed and stability:
		1769	It supports the AnyEvent API optimally, implements all the watcher
		1770	types in XS, does automatic timer adjustments even when no monotonic
		1771	clock is available, can take avdantage of advanced kernel interfaces
		1772	such as "epoll" and "kqueue", and is the fastest backend by far.
		1773	You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
		1774	Glib::EV).
		1775
		1776	Guard
		1777	The guard module, when used, will be used to implement
		1778	"AnyEvent::Util::guard". This speeds up guards considerably (and
		1779	uses a lot less memory), but otherwise doesn't affect guard
		1780	operation much. It is purely used for performance.
		1781
		1782	JSON and JSON::XS
		1783	One of these modules is required when you want to read or write JSON
		1784	data via AnyEvent::Handle. It is also written in pure-perl, but can
		1785	take advantage of the ultra-high-speed JSON::XS module when it is
		1786	installed.
		1787
		1788	In fact, AnyEvent::Handle will use JSON::XS by default if it is
		1789	installed.
		1790
		1791	Net::SSLeay
		1792	Implementing TLS/SSL in Perl is certainly interesting, but not very
		1793	worthwhile: If this module is installed, then AnyEvent::Handle (with
		1794	the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
		1795
		1796	Time::HiRes
		1797	This module is part of perl since release 5.008. It will be used
		1798	when the chosen event library does not come with a timing source on
		1799	it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
		1800	additionally use it to try to use a monotonic clock for timing
		1801	stability.
		1802
1427	FORK	1803	FORK
1428	Most event libraries are not fork-safe. The ones who are usually are	1804	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.	1805	because they rely on inefficient but fork-safe "select" or "poll" calls.
1430	Only EV is fully fork-aware.	1806	Only EV is fully fork-aware.
1431		1807
		1808	This means that, in general, you cannot fork and do event processing in
		1809	the child if a watcher was created before the fork (which in turn
		1810	initialises the event library).
		1811
1432	If you have to fork, you must either do so before creating your first	1812	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.	1813	watcher OR you must not use AnyEvent at all in the child OR you must do
		1814	something completely out of the scope of AnyEvent.
		1815
		1816	The problem of doing event processing in the parent and the child is
		1817	much more complicated: even for backends that are fork-aware or
		1818	fork-safe, their behaviour is not usually what you want: fork clones all
		1819	watchers, that means all timers, I/O watchers etc. are active in both
		1820	parent and child, which is almost never what you want.
1434		1821
1435	SECURITY CONSIDERATIONS	1822	SECURITY CONSIDERATIONS
1436	AnyEvent can be forced to load any event model via	1823	AnyEvent can be forced to load any event model via
1437	$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used	1824	$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	1825	to execute arbitrary code or directly gain access, it can easily be used
…		…
1442		1829
1443	You can make AnyEvent completely ignore this variable by deleting it	1830	You can make AnyEvent completely ignore this variable by deleting it
1444	before the first watcher gets created, e.g. with a "BEGIN" block:	1831	before the first watcher gets created, e.g. with a "BEGIN" block:
1445		1832
1446	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }	1833	BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1447		1834
1448	use AnyEvent;	1835	use AnyEvent;
1449		1836
1450	Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can	1837	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	1838	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),	1839	is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1453	and $ENV{PERL_ANYEGENT_STRICT}.	1840	and $ENV{PERL_ANYEVENT_STRICT}.
		1841
		1842	Note that AnyEvent will remove all environment variables starting with
		1843	"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
		1844	enabled.
1454		1845
1455	BUGS	1846	BUGS
1456	Perl 5.8 has numerous memleaks that sometimes hit this module and are	1847	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	1848	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	1849	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,	1856	Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
1466	Event::Lib, Qt, POE.	1857	Event::Lib, Qt, POE.
1467		1858
1468	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,	1859	Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1469	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,	1860	AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1470	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.	1861	AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
		1862	AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
1471		1863
1472	Non-blocking file handles, sockets, TCP clients and servers:	1864	Non-blocking file handles, sockets, TCP clients and servers:
1473	AnyEvent::Handle, AnyEvent::Socket.	1865	AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1474		1866
1475	Asynchronous DNS: AnyEvent::DNS.	1867	Asynchronous DNS: AnyEvent::DNS.
1476		1868
1477	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,	1869	Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1478		1870
1479	Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.	1871	Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
		1872	AnyEvent::HTTP.
1480		1873
1481	AUTHOR	1874	AUTHOR
1482	Marc Lehmann <schmorp@schmorp.de>	1875	Marc Lehmann <schmorp@schmorp.de>
1483	http://home.schmorp.de/	1876	http://home.schmorp.de/
1484		1877

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Comparing AnyEvent/README (file contents): Revision 1.38 by root, Sun Apr 26 18:12:53 2009 UTC vs. Revision 1.58 by root, Sun Dec 20 22:49:52 2009 UTC

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Comparing AnyEvent/README (file contents):
Revision 1.38 by root, Sun Apr 26 18:12:53 2009 UTC vs.
Revision 1.58 by root, Sun Dec 20 22:49:52 2009 UTC