[ViewVC] Diff of: cvs/AnyEvent-Fork-RPC/RPC.pm

Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.4 by root, Wed Apr 17 19:38:25 2013 UTC vs.
Revision 1.16 by root, Thu Apr 18 14:07:15 2013 UTC

…		…
2		2
3	AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork	3	AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;
8	use AnyEvent::Fork::RPC;	7	use AnyEvent::Fork::RPC;
		8	# use AnyEvent::Fork is not needed
9		9
10	my $rpc = AnyEvent::Fork	10	my $rpc = AnyEvent::Fork
11	->new	11	->new
12	->require ("MyModule")	12	->require ("MyModule")
13	->AnyEvent::Fork::RPC::run (	13	->AnyEvent::Fork::RPC::run (
14	"MyModule::server",	14	"MyModule::server",
15	);	15	);
16		16
		17	use AnyEvent;
		18
17	my $cv = AE::cv;	19	my $cv = AE::cv;
18		20
19	$rpc->(1, 2, 3, sub {	21	$rpc->(1, 2, 3, sub {
20	print "MyModule::server returned @_\n";	22	print "MyModule::server returned @_\n";
21	$cv->send;	23	$cv->send;
…		…
34	concurrently in the child, using AnyEvent.	36	concurrently in the child, using AnyEvent.
35		37
36	It also implements an asynchronous event mechanism from the child to the	38	It also implements an asynchronous event mechanism from the child to the
37	parent, that could be used for progress indications or other information.	39	parent, that could be used for progress indications or other information.
38		40
		41	Loading this module also always loads L<AnyEvent::Fork>, so you can make a
		42	separate C<use AnyEvent::Fork> if you wish, but you don't have to.
		43
39	=head1 EXAMPLES	44	=head1 EXAMPLES
40		45
41	=head2 Synchronous Backend	46	=head2 Example 1: Synchronous Backend
42		47
43	Here is a simple example that implements a backend that executes C<unlink>	48	Here is a simple example that implements a backend that executes C<unlink>
44	and C<rmdir> calls, and reports their status back. It also reports the	49	and C<rmdir> calls, and reports their status back. It also reports the
45	number of requests it has processed every three requests, which is clearly	50	number of requests it has processed every three requests, which is clearly
46	silly, but illustrates the use of events.	51	silly, but illustrates the use of events.
47		52
48	First the parent process:	53	First the parent process:
49		54
50	use AnyEvent;	55	use AnyEvent;
51	use AnyEvent::Fork;
52	use AnyEvent::Fork::RPC;	56	use AnyEvent::Fork::RPC;
53		57
54	my $done = AE::cv;	58	my $done = AE::cv;
55		59
56	my $rpc = AnyEvent::Fork	60	my $rpc = AnyEvent::Fork
57	->new	61	->new
58	->require ("MyWorker")	62	->require ("MyWorker")
59	->AnyEvent::Fork::RPC::run ("MyWorker::run",	63	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		64	on_error => sub { warn "FATAL: $_[0]"; exit 1 },
60	on_event => sub { warn "$_[0] requests handled\n" },	65	on_event => sub { warn "$_[0] requests handled\n" },
61	on_destroy => $done,	66	on_destroy => $done,
62	);	67	);
63		68
64	for my $id (1..6) {	69	for my $id (1..6) {
…		…
102	dies with a fatal error - obviously, you must never let this happen :).	107	dies with a fatal error - obviously, you must never let this happen :).
103		108
104	Eventually it returns the status value true if the command was successful,	109	Eventually it returns the status value true if the command was successful,
105	or the status value 0 and the stringified error message.	110	or the status value 0 and the stringified error message.
106		111
107	On my system, running the first cdoe fragment with the given	112	On my system, running the first code fragment with the given
108	F<MyWorker.pm> in the current directory yields:	113	F<MyWorker.pm> in the current directory yields:
109		114
110	/tmp/somepath/1: No such file or directory	115	/tmp/somepath/1: No such file or directory
111	/tmp/somepath/2: No such file or directory	116	/tmp/somepath/2: No such file or directory
112	3 requests handled	117	3 requests handled
…		…
133		138
134	And as a final remark, there is a fine module on CPAN that can	139	And as a final remark, there is a fine module on CPAN that can
135	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently	140	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
136	than this example, namely L<IO::AIO>.	141	than this example, namely L<IO::AIO>.
137		142
		143	=head3 Example 1a: the same with the asynchronous backend
		144
		145	This example only shows what needs to be changed to use the async backend
		146	instead. Doing this is not very useful, the purpose of this example is
		147	to show the minimum amount of change that is required to go from the
		148	synchronous to the asynchronous backend.
		149
		150	To use the async backend in the previous example, you need to add the
		151	C<async> parameter to the C<AnyEvent::Fork::RPC::run> call:
		152
		153	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		154	async => 1,
		155	...
		156
		157	And since the function call protocol is now changed, you need to adopt
		158	C<MyWorker::run> to the async API.
		159
		160	First, you need to accept the extra initial C<$done> callback:
		161
		162	sub run {
		163	my ($done, $cmd, $path) = @_;
		164
		165	And since a response is now generated when C<$done> is called, as opposed
		166	to when the function returns, we need to call the C<$done> function with
		167	the status:
		168
		169	$done->($status or (0, "$!"));
		170
		171	A few remarks are in order. First, it's quite pointless to use the async
		172	backend for this example - but it I<is> possible. Second, you can call
		173	C<$done> before or after returning from the function. Third, having both
		174	returned from the function and having called the C<$done> callback, the
		175	child process may exit at any time, so you should call C<$done> only when
		176	you really I<are> done.
		177
		178	=head2 Example 2: Asynchronous Backend
		179
		180	This example implements multiple count-downs in the child, using
		181	L<AnyEvent> timers. While this is a bit silly (one could use timers in te
		182	parent just as well), it illustrates the ability to use AnyEvent in the
		183	child and the fact that responses can arrive in a different order then the
		184	requests.
		185
		186	It also shows how to embed the actual child code into a C<__DATA__>
		187	section, so it doesn't need any external files at all.
		188
		189	And when your parent process is often busy, and you have stricter timing
		190	requirements, then running timers in a child process suddenly doesn't look
		191	so silly anymore.
		192
		193	Without further ado, here is the code:
		194
		195	use AnyEvent;
		196	use AnyEvent::Fork::RPC;
		197
		198	my $done = AE::cv;
		199
		200	my $rpc = AnyEvent::Fork
		201	->new
		202	->require ("AnyEvent::Fork::RPC::Async")
		203	->eval (do { local $/; <DATA> })
		204	->AnyEvent::Fork::RPC::run ("run",
		205	async => 1,
		206	on_error => sub { warn "FATAL: $_[0]"; exit 1 },
		207	on_event => sub { print $_[0] },
		208	on_destroy => $done,
		209	);
		210
		211	for my $count (3, 2, 1) {
		212	$rpc->($count, sub {
		213	warn "job $count finished\n";
		214	});
		215	}
		216
		217	undef $rpc;
		218
		219	$done->recv;
		220
		221	__DATA__
		222
		223	# this ends up in main, as we don't use a package declaration
		224
		225	use AnyEvent;
		226
		227	sub run {
		228	my ($done, $count) = @_;
		229
		230	my $n;
		231
		232	AnyEvent::Fork::RPC::event "starting to count up to $count\n";
		233
		234	my $w; $w = AE::timer 1, 1, sub {
		235	++$n;
		236
		237	AnyEvent::Fork::RPC::event "count $n of $count\n";
		238
		239	if ($n == $count) {
		240	undef $w;
		241	$done->();
		242	}
		243	};
		244	}
		245
		246	The parent part (the one before the C<__DATA__> section) isn't very
		247	different from the earlier examples. It sets async mode, preloads
		248	the backend module (so the C<AnyEvent::Fork::RPC::event> function is
		249	declared), uses a slightly different C<on_event> handler (which we use
		250	simply for logging purposes) and then, instead of loading a module with
		251	the actual worker code, it C<eval>'s the code from the data section in the
		252	child process.
		253
		254	It then starts three countdowns, from 3 to 1 seconds downwards, destroys
		255	the rpc object so the example finishes eventually, and then just waits for
		256	the stuff to trickle in.
		257
		258	The worker code uses the event function to log some progress messages, but
		259	mostly just creates a recurring one-second timer.
		260
		261	The timer callback increments a counter, logs a message, and eventually,
		262	when the count has been reached, calls the finish callback.
		263
		264	On my system, this results in the following output. Since all timers fire
		265	at roughly the same time, the actual order isn't guaranteed, but the order
		266	shown is very likely what you would get, too.
		267
		268	starting to count up to 3
		269	starting to count up to 2
		270	starting to count up to 1
		271	count 1 of 3
		272	count 1 of 2
		273	count 1 of 1
		274	job 1 finished
		275	count 2 of 2
		276	job 2 finished
		277	count 2 of 3
		278	count 3 of 3
		279	job 3 finished
		280
		281	While the overall ordering isn't guaranteed, the async backend still
		282	guarantees that events and responses are delivered to the parent process
		283	in the exact same ordering as they were generated in the child process.
		284
		285	And unless your system is I<very> busy, it should clearly show that the
		286	job started last will finish first, as it has the lowest count.
		287
		288	This concludes the async example. Since L<AnyEvent::Fork> does not
		289	actually fork, you are free to use about any module in the child, not just
		290	L<AnyEvent>, but also L<IO::AIO>, or L<Tk> for example.
		291
138	=head1 PARENT PROCESS USAGE	292	=head1 PARENT PROCESS USAGE
139		293
140	This module exports nothing, and only implements a single function:	294	This module exports nothing, and only implements a single function:
141		295
142	=over 4	296	=over 4
…		…
149		303
150	use Errno ();	304	use Errno ();
151	use Guard ();	305	use Guard ();
152		306
153	use AnyEvent;	307	use AnyEvent;
154	#use AnyEvent::Fork;	308	use AnyEvent::Fork; # we don't actually depend on it, this is for convenience
155		309
156	our $VERSION = 0.1;	310	our $VERSION = 0.1;
157		311
158	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	312	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
159		313
…		…
197		351
198	Called when the C<$rpc> object has been destroyed and all requests have	352	Called when the C<$rpc> object has been destroyed and all requests have
199	been successfully handled. This is useful when you queue some requests and	353	been successfully handled. This is useful when you queue some requests and
200	want the child to go away after it has handled them. The problem is that	354	want the child to go away after it has handled them. The problem is that
201	the parent must not exit either until all requests have been handled, and	355	the parent must not exit either until all requests have been handled, and
202	this cna be accomplished by waiting for this callback.	356	this can be accomplished by waiting for this callback.
203		357
204	=item init => $function (default none)	358	=item init => $function (default none)
205		359
206	When specified (by name), this function is called in the child as the very	360	When specified (by name), this function is called in the child as the very
207	first thing when taking over the process, with all the arguments normally	361	first thing when taking over the process, with all the arguments normally
…		…
220		374
221	The default server used in the child does all I/O blockingly, and only	375	The default server used in the child does all I/O blockingly, and only
222	allows a single RPC call to execute concurrently.	376	allows a single RPC call to execute concurrently.
223		377
224	Setting C<async> to a true value switches to another implementation that	378	Setting C<async> to a true value switches to another implementation that
225	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.	379	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it
		380	does not support recursion in the event loop however, blocking condvar
		381	calls will fail).
226		382
227	The actual API in the child is documented in the section that describes	383	The actual API in the child is documented in the section that describes
228	the calling semantics of the returned C<$rpc> function.	384	the calling semantics of the returned C<$rpc> function.
229		385
230	If you want to pre-load the actual back-end modules to enable memory	386	If you want to pre-load the actual back-end modules to enable memory
231	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for	387	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
232	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	388	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
233		389
234	If you use a template process and want to fork both sync and async	390	If you use a template process and want to fork both sync and async
235	children, then it is permissible to laod both modules.	391	children, then it is permissible to load both modules.
236		392
237	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	393	=item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER)
238		394
239	All arguments, result data and event data have to be serialised to be	395	All arguments, result data and event data have to be serialised to be
240	transferred between the processes. For this, they have to be frozen and	396	transferred between the processes. For this, they have to be frozen and
241	thawed in both parent and child processes.	397	thawed in both parent and child processes.
242		398
243	By default, only octet strings can be passed between the processes, which	399	By default, only octet strings can be passed between the processes, which
244	is reasonably fast and efficient.	400	is reasonably fast and efficient and requires no extra modules.
245		401
246	For more complicated use cases, you can provide your own freeze and thaw	402	For more complicated use cases, you can provide your own freeze and thaw
247	functions, by specifying a string with perl source code. It's supposed to	403	functions, by specifying a string with perl source code. It's supposed to
248	return two code references when evaluated: the first receives a list of	404	return two code references when evaluated: the first receives a list of
249	perl values and must return an octet string. The second receives the octet	405	perl values and must return an octet string. The second receives the octet
…		…
251		407
252	If you need an external module for serialisation, then you can either	408	If you need an external module for serialisation, then you can either
253	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>	409	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
254	or C<require> statement into the serialiser string. Or both.	410	or C<require> statement into the serialiser string. Or both.
255		411
		412	Here are some examples - some of them are also available as global
		413	variables that make them easier to use.
		414
		415	=over 4
		416
		417	=item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER>
		418
		419	This serialiser concatenates length-prefixes octet strings, and is the
		420	default.
		421
		422	Implementation:
		423
		424	(
		425	sub { pack "(w/a)", @_ },
		426	sub { unpack "(w/a)", shift }
		427	)
		428
		429	=item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER>
		430
		431	This serialiser creates JSON arrays - you have to make sure the L<JSON>
		432	module is installed for this serialiser to work. It can be beneficial for
		433	sharing when you preload the L<JSON> module in a template process.
		434
		435	L<JSON> (with L<JSON::XS> installed) is slower than the octet string
		436	serialiser, but usually much faster than L<Storable>, unless big chunks of
		437	binary data need to be transferred.
		438
		439	Implementation:
		440
		441	use JSON ();
		442	(
		443	sub { JSON::encode_json \@_ },
		444	sub { @{ JSON::decode_json shift } }
		445	)
		446
		447	=item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER>
		448
		449	This serialiser uses L<Storable>, which means it has high chance of
		450	serialising just about anything you throw at it, at the cost of having
		451	very high overhead per operation. It also comes with perl.
		452
		453	Implementation:
		454
		455	use Storable ();
		456	(
		457	sub { Storable::freeze \@_ },
		458	sub { @{ Storable::thaw shift } }
		459	)
		460
256	=back	461	=back
257		462
		463	=back
		464
		465	See the examples section earlier in this document for some actual
		466	examples.
		467
258	=cut	468	=cut
259		469
260	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	470	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
		471	our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
		472	our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
261		473
262	sub run {	474	sub run {
263	my ($self, $function, %arg) = @_;	475	my ($self, $function, %arg) = @_;
264		476
265	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;	477	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
…		…
275	# default for on_event is to raise an error	487	# default for on_event is to raise an error
276	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	488	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
277		489
278	my ($f, $t) = eval $serialiser; die $@ if $@;	490	my ($f, $t) = eval $serialiser; die $@ if $@;
279		491
280	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);	492	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
281	my ($rlen, $rbuf) = 512 - 16;	493	my ($rlen, $rbuf, $rw) = 512 - 16;
282		494
283	my $wcb = sub {	495	my $wcb = sub {
284	my $len = syswrite $fh, $wbuf;	496	my $len = syswrite $fh, $wbuf;
285		497
286	if (!defined $len) {	498	unless (defined $len) {
287	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	499	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
288	undef $rw; undef $ww; # it ends here	500	undef $rw; undef $ww; # it ends here
289	$on_error->("$!");	501	$on_error->("$!");
290	}	502	}
291	}	503	}
…		…
302		514
303	$self->require ($module)	515	$self->require ($module)
304	->send_arg ($function, $arg{init}, $serialiser)	516	->send_arg ($function, $arg{init}, $serialiser)
305	->run ("$module\::run", sub {	517	->run ("$module\::run", sub {
306	$fh = shift;	518	$fh = shift;
		519
		520	my ($id, $len);
307	$rw = AE::io $fh, 0, sub {	521	$rw = AE::io $fh, 0, sub {
308	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;	522	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
309	my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;	523	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
310		524
311	if ($len) {	525	if ($len) {
312	while (5 <= length $rbuf) {	526	while (8 <= length $rbuf) {
313	$len = unpack "L", $rbuf;	527	($id, $len) = unpack "LL", $rbuf;
314	4 + $len <= length $rbuf	528	8 + $len <= length $rbuf
315	or last;	529	or last;
316		530
317	my @r = $t->(substr $rbuf, 4, $len);	531	my @r = $t->(substr $rbuf, 8, $len);
318	substr $rbuf, 0, $len + 4, "";	532	substr $rbuf, 0, 8 + $len, "";
		533
		534	if ($id) {
		535	if (@rcb) {
		536	(shift @rcb)->(@r);
		537	} elsif (my $cb = delete $rcb{$id}) {
		538	$cb->(@r);
		539	} else {
		540	undef $rw; undef $ww;
		541	$on_error->("unexpected data from child");
319		542	}
320	if (pop @r) {	543	} else {
321	$on_event->(@r);	544	$on_event->(@r);
322	} elsif (@rcb) {
323	(shift @rcb)->(@r);
324	} else {
325	undef $rw; undef $ww;
326	$on_error->("unexpected data from child");
327	}	545	}
328	}	546	}
329	} elsif (defined $len) {	547	} elsif (defined $len) {
330	undef $rw; undef $ww; # it ends here	548	undef $rw; undef $ww; # it ends here
331		549
332	if (@rcb) {	550	if (@rcb \|\| %rcb) {
333	$on_error->("unexpected eof");	551	$on_error->("unexpected eof");
334	} else {	552	} else {
335	$on_destroy->();	553	$on_destroy->();
336	}	554	}
337	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	555	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
…		…
346	my $guard = Guard::guard {	564	my $guard = Guard::guard {
347	$shutdown = 1;	565	$shutdown = 1;
348	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	566	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
349	};	567	};
350		568
		569	my $id;
		570
		571	$arg{async}
351	sub {	572	? sub {
352	push @rcb, pop;	573	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		574	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
353		575
		576	$rcb{$id} = pop;
		577
354	$guard; # keep it alive	578	$guard; # keep it alive
355		579
356	$wbuf .= pack "L/a*", &$f;	580	$wbuf .= pack "LL/a*", $id, &$f;
357	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	581	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
358	}	582	}
		583	: sub {
		584	push @rcb, pop;
		585
		586	$guard; # keep it alive
		587
		588	$wbuf .= pack "L/a*", &$f;
		589	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		590	}
359	}	591	}
360		592
361	=item $rpc->(..., $cb->(...))	593	=item $rpc->(..., $cb->(...))
362		594
363	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code	595	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
…		…
378		610
379	The other thing that can be done with the RPC object is to destroy it. In	611	The other thing that can be done with the RPC object is to destroy it. In
380	this case, the child process will execute all remaining RPC calls, report	612	this case, the child process will execute all remaining RPC calls, report
381	their results, and then exit.	613	their results, and then exit.
382		614
		615	See the examples section earlier in this document for some actual
		616	examples.
		617
383	=back	618	=back
384		619
385	=head1 CHILD PROCESS USAGE	620	=head1 CHILD PROCESS USAGE
386		621
387	The following function is not available in this module. They are only	622	The following function is not available in this module. They are only
…		…
395		630
396	Send an event to the parent. Events are a bit like RPC calls made by the	631	Send an event to the parent. Events are a bit like RPC calls made by the
397	child process to the parent, except that there is no notion of return	632	child process to the parent, except that there is no notion of return
398	values.	633	values.
399		634
		635	See the examples section earlier in this document for some actual
		636	examples.
		637
400	=back	638	=back
401		639
		640	=head1 ADVANCED TOPICS
		641
		642	=head2 Choosing a backend
		643
		644	So how do you decide which backend to use? Well, that's your problem to
		645	solve, but here are some thoughts on the matter:
		646
		647	=over 4
		648
		649	=item Synchronous
		650
		651	The synchronous backend does not rely on any external modules (well,
		652	except L<common::sense>, which works around a bug in how perl's warning
		653	system works). This keeps the process very small, for example, on my
		654	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		655	after C<use warnings; use strict> (for people who grew up with C64s around
		656	them this is probably shocking every single time they see it). The worker
		657	process in the first example in this document uses 1792kB.
		658
		659	Since the calls are done synchronously, slow jobs will keep newer jobs
		660	from executing.
		661
		662	The synchronous backend also has no overhead due to running an event loop
		663	- reading requests is therefore very efficient, while writing responses is
		664	less so, as every response results in a write syscall.
		665
		666	If the parent process is busy and a bit slow reading responses, the child
		667	waits instead of processing further requests. This also limits the amount
		668	of memory needed for buffering, as never more than one response has to be
		669	buffered.
		670
		671	The API in the child is simple - you just have to define a function that
		672	does something and returns something.
		673
		674	It's hard to use modules or code that relies on an event loop, as the
		675	child cannot execute anything while it waits for more input.
		676
		677	=item Asynchronous
		678
		679	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		680	but still comes at a price: On my system, the worker from example 1a uses
		681	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		682	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		683	L<vars>, L<Exporter>...).
		684
		685	It batches requests and responses reasonably efficiently, doing only as
		686	few reads and writes as needed, but needs to poll for events via the event
		687	loop.
		688
		689	Responses are queued when the parent process is busy. This means the child
		690	can continue to execute any queued requests. It also means that a child
		691	might queue a lot of responses in memory when it generates them and the
		692	parent process is slow accepting them.
		693
		694	The API is not a straightforward RPC pattern - you have to call a
		695	"done" callback to pass return values and signal completion. Also, more
		696	importantly, the API starts jobs as fast as possible - when 1000 jobs
		697	are queued and the jobs are slow, they will all run concurrently. The
		698	child must implement some queueing/limiting mechanism if this causes
		699	problems. Alternatively, the parent could limit the amount of rpc calls
		700	that are outstanding.
		701
		702	Blocking use of condvars is not supported.
		703
		704	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		705	easy.
		706
		707	=back
		708
		709	=head2 Passing file descriptors
		710
		711	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		712	descriptor passing abilities.
		713
		714	The reason is that passing file descriptors is extraordinary tricky
		715	business, and conflicts with efficient batching of messages.
		716
		717	There still is a method you can use: Create a
		718	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		719	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		720
		721	Whenever you want to pass a file descriptor, send an rpc request to the
		722	child process (so it expects the descriptor), then send it over the other
		723	half of the socketpair. The child should fetch the descriptor from the
		724	half it has passed earlier.
		725
		726	Here is some (untested) pseudocode to that effect:
		727
		728	use AnyEvent::Util;
		729	use AnyEvent::Fork::RPC;
		730	use IO::FDPass;
		731
		732	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		733
		734	my $rpc = AnyEvent::Fork
		735	->new
		736	->send_fh ($s2)
		737	->require ("MyWorker")
		738	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		739	init => "MyWorker::init",
		740	);
		741
		742	undef $s2; # no need to keep it around
		743
		744	# pass an fd
		745	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		746
		747	IO::FDPass fileno $s1, fileno $handle_to_pass;
		748
		749	$cv->recv;
		750
		751	The MyWorker module could look like this:
		752
		753	package MyWorker;
		754
		755	use IO::FDPass;
		756
		757	my $s2;
		758
		759	sub init {
		760	$s2 = $_[0];
		761	}
		762
		763	sub run {
		764	if ($_[0] eq "i'll send some fd now, please expect it!") {
		765	my $fd = IO::FDPass::recv fileno $s2;
		766	...
		767	}
		768	}
		769
		770	Of course, this might be blocking if you pass a lot of file descriptors,
		771	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		772	gory details.
		773
402	=head1 SEE ALSO	774	=head1 SEE ALSO
403		775
404	L<AnyEvent::Fork> (to create the processes in the first place),	776	L<AnyEvent::Fork>, to create the processes in the first place.
		777
405	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	778	L<AnyEvent::Fork::Pool>, to manage whole pools of processes.
406		779
407	=head1 AUTHOR AND CONTACT INFORMATION	780	=head1 AUTHOR AND CONTACT INFORMATION
408		781
409	Marc Lehmann <schmorp@schmorp.de>	782	Marc Lehmann <schmorp@schmorp.de>
410	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC	783	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents): Revision 1.4 by root, Wed Apr 17 19:38:25 2013 UTC vs. Revision 1.16 by root, Thu Apr 18 14:07:15 2013 UTC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
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Revision 1.16 by root, Thu Apr 18 14:07:15 2013 UTC