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

Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.5 by root, Wed Apr 17 19:39:54 2013 UTC vs.
Revision 1.23 by root, Mon Apr 22 20:05:03 2013 UTC

…		…
1	=head1 NAME	1	=head1 NAME
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	THE API IS NOT FINISHED, CONSIDER THIS A BETA RELEASE
		6
5	=head1 SYNOPSIS	7	=head1 SYNOPSIS
6		8
7	use AnyEvent::Fork;
8	use AnyEvent::Fork::RPC;	9	use AnyEvent::Fork::RPC;
		10	# use AnyEvent::Fork is not needed
9		11
10	my $rpc = AnyEvent::Fork	12	my $rpc = AnyEvent::Fork
11	->new	13	->new
12	->require ("MyModule")	14	->require ("MyModule")
13	->AnyEvent::Fork::RPC::run (	15	->AnyEvent::Fork::RPC::run (
14	"MyModule::server",	16	"MyModule::server",
15	);	17	);
16		18
		19	use AnyEvent;
		20
17	my $cv = AE::cv;	21	my $cv = AE::cv;
18		22
19	$rpc->(1, 2, 3, sub {	23	$rpc->(1, 2, 3, sub {
20	print "MyModule::server returned @_\n";	24	print "MyModule::server returned @_\n";
21	$cv->send;	25	$cv->send;
34	concurrently in the child, using AnyEvent.	38	concurrently in the child, using AnyEvent.
35		39
36	It also implements an asynchronous event mechanism from the child to the	40	It also implements an asynchronous event mechanism from the child to the
37	parent, that could be used for progress indications or other information.	41	parent, that could be used for progress indications or other information.
38		42
		43	Loading this module also always loads L<AnyEvent::Fork>, so you can make a
		44	separate C<use AnyEvent::Fork> if you wish, but you don't have to.
		45
39	=head1 EXAMPLES	46	=head1 EXAMPLES
40		47
41	=head2 Synchronous Backend	48	=head2 Example 1: Synchronous Backend
42		49
43	Here is a simple example that implements a backend that executes C<unlink>	50	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	51	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	52	number of requests it has processed every three requests, which is clearly
46	silly, but illustrates the use of events.	53	silly, but illustrates the use of events.
47		54
48	First the parent process:	55	First the parent process:
49		56
50	use AnyEvent;	57	use AnyEvent;
51	use AnyEvent::Fork;
52	use AnyEvent::Fork::RPC;	58	use AnyEvent::Fork::RPC;
53		59
54	my $done = AE::cv;	60	my $done = AE::cv;
55		61
56	my $rpc = AnyEvent::Fork	62	my $rpc = AnyEvent::Fork
…		…
103	dies with a fatal error - obviously, you must never let this happen :).	109	dies with a fatal error - obviously, you must never let this happen :).
104		110
105	Eventually it returns the status value true if the command was successful,	111	Eventually it returns the status value true if the command was successful,
106	or the status value 0 and the stringified error message.	112	or the status value 0 and the stringified error message.
107		113
108	On my system, running the first cdoe fragment with the given	114	On my system, running the first code fragment with the given
109	F<MyWorker.pm> in the current directory yields:	115	F<MyWorker.pm> in the current directory yields:
110		116
111	/tmp/somepath/1: No such file or directory	117	/tmp/somepath/1: No such file or directory
112	/tmp/somepath/2: No such file or directory	118	/tmp/somepath/2: No such file or directory
113	3 requests handled	119	3 requests handled
…		…
134		140
135	And as a final remark, there is a fine module on CPAN that can	141	And as a final remark, there is a fine module on CPAN that can
136	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently	142	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
137	than this example, namely L<IO::AIO>.	143	than this example, namely L<IO::AIO>.
138		144
		145	=head3 Example 1a: the same with the asynchronous backend
		146
		147	This example only shows what needs to be changed to use the async backend
		148	instead. Doing this is not very useful, the purpose of this example is
		149	to show the minimum amount of change that is required to go from the
		150	synchronous to the asynchronous backend.
		151
		152	To use the async backend in the previous example, you need to add the
		153	C<async> parameter to the C<AnyEvent::Fork::RPC::run> call:
		154
		155	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		156	async => 1,
		157	...
		158
		159	And since the function call protocol is now changed, you need to adopt
		160	C<MyWorker::run> to the async API.
		161
		162	First, you need to accept the extra initial C<$done> callback:
		163
		164	sub run {
		165	my ($done, $cmd, $path) = @_;
		166
		167	And since a response is now generated when C<$done> is called, as opposed
		168	to when the function returns, we need to call the C<$done> function with
		169	the status:
		170
		171	$done->($status or (0, "$!"));
		172
		173	A few remarks are in order. First, it's quite pointless to use the async
		174	backend for this example - but it I<is> possible. Second, you can call
		175	C<$done> before or after returning from the function. Third, having both
		176	returned from the function and having called the C<$done> callback, the
		177	child process may exit at any time, so you should call C<$done> only when
		178	you really I<are> done.
		179
		180	=head2 Example 2: Asynchronous Backend
		181
		182	This example implements multiple count-downs in the child, using
		183	L<AnyEvent> timers. While this is a bit silly (one could use timers in te
		184	parent just as well), it illustrates the ability to use AnyEvent in the
		185	child and the fact that responses can arrive in a different order then the
		186	requests.
		187
		188	It also shows how to embed the actual child code into a C<__DATA__>
		189	section, so it doesn't need any external files at all.
		190
		191	And when your parent process is often busy, and you have stricter timing
		192	requirements, then running timers in a child process suddenly doesn't look
		193	so silly anymore.
		194
		195	Without further ado, here is the code:
		196
		197	use AnyEvent;
		198	use AnyEvent::Fork::RPC;
		199
		200	my $done = AE::cv;
		201
		202	my $rpc = AnyEvent::Fork
		203	->new
		204	->require ("AnyEvent::Fork::RPC::Async")
		205	->eval (do { local $/; <DATA> })
		206	->AnyEvent::Fork::RPC::run ("run",
		207	async => 1,
		208	on_error => sub { warn "FATAL: $_[0]"; exit 1 },
		209	on_event => sub { print $_[0] },
		210	on_destroy => $done,
		211	);
		212
		213	for my $count (3, 2, 1) {
		214	$rpc->($count, sub {
		215	warn "job $count finished\n";
		216	});
		217	}
		218
		219	undef $rpc;
		220
		221	$done->recv;
		222
		223	__DATA__
		224
		225	# this ends up in main, as we don't use a package declaration
		226
		227	use AnyEvent;
		228
		229	sub run {
		230	my ($done, $count) = @_;
		231
		232	my $n;
		233
		234	AnyEvent::Fork::RPC::event "starting to count up to $count\n";
		235
		236	my $w; $w = AE::timer 1, 1, sub {
		237	++$n;
		238
		239	AnyEvent::Fork::RPC::event "count $n of $count\n";
		240
		241	if ($n == $count) {
		242	undef $w;
		243	$done->();
		244	}
		245	};
		246	}
		247
		248	The parent part (the one before the C<__DATA__> section) isn't very
		249	different from the earlier examples. It sets async mode, preloads
		250	the backend module (so the C<AnyEvent::Fork::RPC::event> function is
		251	declared), uses a slightly different C<on_event> handler (which we use
		252	simply for logging purposes) and then, instead of loading a module with
		253	the actual worker code, it C<eval>'s the code from the data section in the
		254	child process.
		255
		256	It then starts three countdowns, from 3 to 1 seconds downwards, destroys
		257	the rpc object so the example finishes eventually, and then just waits for
		258	the stuff to trickle in.
		259
		260	The worker code uses the event function to log some progress messages, but
		261	mostly just creates a recurring one-second timer.
		262
		263	The timer callback increments a counter, logs a message, and eventually,
		264	when the count has been reached, calls the finish callback.
		265
		266	On my system, this results in the following output. Since all timers fire
		267	at roughly the same time, the actual order isn't guaranteed, but the order
		268	shown is very likely what you would get, too.
		269
		270	starting to count up to 3
		271	starting to count up to 2
		272	starting to count up to 1
		273	count 1 of 3
		274	count 1 of 2
		275	count 1 of 1
		276	job 1 finished
		277	count 2 of 2
		278	job 2 finished
		279	count 2 of 3
		280	count 3 of 3
		281	job 3 finished
		282
		283	While the overall ordering isn't guaranteed, the async backend still
		284	guarantees that events and responses are delivered to the parent process
		285	in the exact same ordering as they were generated in the child process.
		286
		287	And unless your system is I<very> busy, it should clearly show that the
		288	job started last will finish first, as it has the lowest count.
		289
		290	This concludes the async example. Since L<AnyEvent::Fork> does not
		291	actually fork, you are free to use about any module in the child, not just
		292	L<AnyEvent>, but also L<IO::AIO>, or L<Tk> for example.
		293
139	=head1 PARENT PROCESS USAGE	294	=head1 PARENT PROCESS USAGE
140		295
141	This module exports nothing, and only implements a single function:	296	This module exports nothing, and only implements a single function:
142		297
143	=over 4	298	=over 4
…		…
150		305
151	use Errno ();	306	use Errno ();
152	use Guard ();	307	use Guard ();
153		308
154	use AnyEvent;	309	use AnyEvent;
155	#use AnyEvent::Fork;	310	# explicit version on next line, as some cpan-testers test with the 0.1 version,
		311	# ignoring dependencies, and this line will at least give a clear indication of that.
		312	use AnyEvent::Fork 0.6; # we don't actually depend on it, this is for convenience
156		313
157	our $VERSION = 0.1;	314	our $VERSION = 0.2;
158		315
159	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	316	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
160		317
161	The traditional way to call it. But it is way cooler to call it in the	318	The traditional way to call it. But it is way cooler to call it in the
162	following way:	319	following way:
…		…
198		355
199	Called when the C<$rpc> object has been destroyed and all requests have	356	Called when the C<$rpc> object has been destroyed and all requests have
200	been successfully handled. This is useful when you queue some requests and	357	been successfully handled. This is useful when you queue some requests and
201	want the child to go away after it has handled them. The problem is that	358	want the child to go away after it has handled them. The problem is that
202	the parent must not exit either until all requests have been handled, and	359	the parent must not exit either until all requests have been handled, and
203	this cna be accomplished by waiting for this callback.	360	this can be accomplished by waiting for this callback.
204		361
205	=item init => $function (default none)	362	=item init => $function (default none)
206		363
207	When specified (by name), this function is called in the child as the very	364	When specified (by name), this function is called in the child as the very
208	first thing when taking over the process, with all the arguments normally	365	first thing when taking over the process, with all the arguments normally
…		…
221		378
222	The default server used in the child does all I/O blockingly, and only	379	The default server used in the child does all I/O blockingly, and only
223	allows a single RPC call to execute concurrently.	380	allows a single RPC call to execute concurrently.
224		381
225	Setting C<async> to a true value switches to another implementation that	382	Setting C<async> to a true value switches to another implementation that
226	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.	383	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it
		384	does not support recursion in the event loop however, blocking condvar
		385	calls will fail).
227		386
228	The actual API in the child is documented in the section that describes	387	The actual API in the child is documented in the section that describes
229	the calling semantics of the returned C<$rpc> function.	388	the calling semantics of the returned C<$rpc> function.
230		389
231	If you want to pre-load the actual back-end modules to enable memory	390	If you want to pre-load the actual back-end modules to enable memory
232	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for	391	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
233	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	392	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
234		393
235	If you use a template process and want to fork both sync and async	394	If you use a template process and want to fork both sync and async
236	children, then it is permissible to laod both modules.	395	children, then it is permissible to load both modules.
237		396
238	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	397	=item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER)
239		398
240	All arguments, result data and event data have to be serialised to be	399	All arguments, result data and event data have to be serialised to be
241	transferred between the processes. For this, they have to be frozen and	400	transferred between the processes. For this, they have to be frozen and
242	thawed in both parent and child processes.	401	thawed in both parent and child processes.
243		402
244	By default, only octet strings can be passed between the processes, which	403	By default, only octet strings can be passed between the processes, which
245	is reasonably fast and efficient.	404	is reasonably fast and efficient and requires no extra modules.
246		405
247	For more complicated use cases, you can provide your own freeze and thaw	406	For more complicated use cases, you can provide your own freeze and thaw
248	functions, by specifying a string with perl source code. It's supposed to	407	functions, by specifying a string with perl source code. It's supposed to
249	return two code references when evaluated: the first receives a list of	408	return two code references when evaluated: the first receives a list of
250	perl values and must return an octet string. The second receives the octet	409	perl values and must return an octet string. The second receives the octet
…		…
252		411
253	If you need an external module for serialisation, then you can either	412	If you need an external module for serialisation, then you can either
254	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>	413	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
255	or C<require> statement into the serialiser string. Or both.	414	or C<require> statement into the serialiser string. Or both.
256		415
		416	Here are some examples - some of them are also available as global
		417	variables that make them easier to use.
		418
		419	=over 4
		420
		421	=item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER>
		422
		423	This serialiser concatenates length-prefixes octet strings, and is the
		424	default.
		425
		426	Implementation:
		427
		428	(
		429	sub { pack "(w/a)", @_ },
		430	sub { unpack "(w/a)", shift }
		431	)
		432
		433	=item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER>
		434
		435	This serialiser creates JSON arrays - you have to make sure the L<JSON>
		436	module is installed for this serialiser to work. It can be beneficial for
		437	sharing when you preload the L<JSON> module in a template process.
		438
		439	L<JSON> (with L<JSON::XS> installed) is slower than the octet string
		440	serialiser, but usually much faster than L<Storable>, unless big chunks of
		441	binary data need to be transferred.
		442
		443	Implementation:
		444
		445	use JSON ();
		446	(
		447	sub { JSON::encode_json \@_ },
		448	sub { @{ JSON::decode_json shift } }
		449	)
		450
		451	=item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER>
		452
		453	This serialiser uses L<Storable>, which means it has high chance of
		454	serialising just about anything you throw at it, at the cost of having
		455	very high overhead per operation. It also comes with perl.
		456
		457	Implementation:
		458
		459	use Storable ();
		460	(
		461	sub { Storable::freeze \@_ },
		462	sub { @{ Storable::thaw shift } }
		463	)
		464
257	=back	465	=back
258		466
		467	=back
		468
		469	See the examples section earlier in this document for some actual
		470	examples.
		471
259	=cut	472	=cut
260		473
261	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	474	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
		475	our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
		476	our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
262		477
263	sub run {	478	sub run {
264	my ($self, $function, %arg) = @_;	479	my ($self, $function, %arg) = @_;
265		480
266	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;	481	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
…		…
276	# default for on_event is to raise an error	491	# default for on_event is to raise an error
277	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	492	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
278		493
279	my ($f, $t) = eval $serialiser; die $@ if $@;	494	my ($f, $t) = eval $serialiser; die $@ if $@;
280		495
281	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);	496	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
282	my ($rlen, $rbuf) = 512 - 16;	497	my ($rlen, $rbuf, $rw) = 512 - 16;
283		498
284	my $wcb = sub {	499	my $wcb = sub {
285	my $len = syswrite $fh, $wbuf;	500	my $len = syswrite $fh, $wbuf;
286		501
287	if (!defined $len) {	502	unless (defined $len) {
288	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	503	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
289	undef $rw; undef $ww; # it ends here	504	undef $rw; undef $ww; # it ends here
290	$on_error->("$!");	505	$on_error->("$!");
291	}	506	}
292	}	507	}
…		…
303		518
304	$self->require ($module)	519	$self->require ($module)
305	->send_arg ($function, $arg{init}, $serialiser)	520	->send_arg ($function, $arg{init}, $serialiser)
306	->run ("$module\::run", sub {	521	->run ("$module\::run", sub {
307	$fh = shift;	522	$fh = shift;
		523
		524	my ($id, $len);
308	$rw = AE::io $fh, 0, sub {	525	$rw = AE::io $fh, 0, sub {
309	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;	526	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
310	my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;	527	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
311		528
312	if ($len) {	529	if ($len) {
313	while (5 <= length $rbuf) {	530	while (8 <= length $rbuf) {
314	$len = unpack "L", $rbuf;	531	($id, $len) = unpack "LL", $rbuf;
315	4 + $len <= length $rbuf	532	8 + $len <= length $rbuf
316	or last;	533	or last;
317		534
318	my @r = $t->(substr $rbuf, 4, $len);	535	my @r = $t->(substr $rbuf, 8, $len);
319	substr $rbuf, 0, $len + 4, "";	536	substr $rbuf, 0, 8 + $len, "";
		537
		538	if ($id) {
		539	if (@rcb) {
		540	(shift @rcb)->(@r);
		541	} elsif (my $cb = delete $rcb{$id}) {
		542	$cb->(@r);
		543	} else {
		544	undef $rw; undef $ww;
		545	$on_error->("unexpected data from child");
320		546	}
321	if (pop @r) {	547	} else {
322	$on_event->(@r);	548	$on_event->(@r);
323	} elsif (@rcb) {
324	(shift @rcb)->(@r);
325	} else {
326	undef $rw; undef $ww;
327	$on_error->("unexpected data from child");
328	}	549	}
329	}	550	}
330	} elsif (defined $len) {	551	} elsif (defined $len) {
331	undef $rw; undef $ww; # it ends here	552	undef $rw; undef $ww; # it ends here
332		553
333	if (@rcb) {	554	if (@rcb \|\| %rcb) {
334	$on_error->("unexpected eof");	555	$on_error->("unexpected eof");
335	} else {	556	} else {
336	$on_destroy->();	557	$on_destroy->()
		558	if $on_destroy;
337	}	559	}
338	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	560	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
339	undef $rw; undef $ww; # it ends here	561	undef $rw; undef $ww; # it ends here
340	$on_error->("read: $!");	562	$on_error->("read: $!");
341	}	563	}
…		…
344	$ww \|\|= AE::io $fh, 1, $wcb;	566	$ww \|\|= AE::io $fh, 1, $wcb;
345	});	567	});
346		568
347	my $guard = Guard::guard {	569	my $guard = Guard::guard {
348	$shutdown = 1;	570	$shutdown = 1;
349	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	571
		572	shutdown $fh, 1 if $fh && !$ww;
350	};	573	};
351		574
		575	my $id;
		576
		577	$arg{async}
352	sub {	578	? sub {
353	push @rcb, pop;	579	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		580	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
354		581
		582	$rcb{$id} = pop;
		583
355	$guard; # keep it alive	584	$guard if 0; # keep it alive
356		585
357	$wbuf .= pack "L/a*", &$f;	586	$wbuf .= pack "LL/a*", $id, &$f;
358	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	587	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
359	}	588	}
		589	: sub {
		590	push @rcb, pop;
		591
		592	$guard; # keep it alive
		593
		594	$wbuf .= pack "L/a*", &$f;
		595	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		596	}
360	}	597	}
361		598
362	=item $rpc->(..., $cb->(...))	599	=item $rpc->(..., $cb->(...))
363		600
364	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code	601	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
…		…
379		616
380	The other thing that can be done with the RPC object is to destroy it. In	617	The other thing that can be done with the RPC object is to destroy it. In
381	this case, the child process will execute all remaining RPC calls, report	618	this case, the child process will execute all remaining RPC calls, report
382	their results, and then exit.	619	their results, and then exit.
383		620
		621	See the examples section earlier in this document for some actual
		622	examples.
		623
384	=back	624	=back
385		625
386	=head1 CHILD PROCESS USAGE	626	=head1 CHILD PROCESS USAGE
387		627
388	The following function is not available in this module. They are only	628	The following function is not available in this module. They are only
…		…
396		636
397	Send an event to the parent. Events are a bit like RPC calls made by the	637	Send an event to the parent. Events are a bit like RPC calls made by the
398	child process to the parent, except that there is no notion of return	638	child process to the parent, except that there is no notion of return
399	values.	639	values.
400		640
		641	See the examples section earlier in this document for some actual
		642	examples.
		643
401	=back	644	=back
402		645
		646	=head1 ADVANCED TOPICS
		647
		648	=head2 Choosing a backend
		649
		650	So how do you decide which backend to use? Well, that's your problem to
		651	solve, but here are some thoughts on the matter:
		652
		653	=over 4
		654
		655	=item Synchronous
		656
		657	The synchronous backend does not rely on any external modules (well,
		658	except L<common::sense>, which works around a bug in how perl's warning
		659	system works). This keeps the process very small, for example, on my
		660	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		661	after C<use warnings; use strict> (for people who grew up with C64s around
		662	them this is probably shocking every single time they see it). The worker
		663	process in the first example in this document uses 1792kB.
		664
		665	Since the calls are done synchronously, slow jobs will keep newer jobs
		666	from executing.
		667
		668	The synchronous backend also has no overhead due to running an event loop
		669	- reading requests is therefore very efficient, while writing responses is
		670	less so, as every response results in a write syscall.
		671
		672	If the parent process is busy and a bit slow reading responses, the child
		673	waits instead of processing further requests. This also limits the amount
		674	of memory needed for buffering, as never more than one response has to be
		675	buffered.
		676
		677	The API in the child is simple - you just have to define a function that
		678	does something and returns something.
		679
		680	It's hard to use modules or code that relies on an event loop, as the
		681	child cannot execute anything while it waits for more input.
		682
		683	=item Asynchronous
		684
		685	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		686	but still comes at a price: On my system, the worker from example 1a uses
		687	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		688	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		689	L<vars>, L<Exporter>...).
		690
		691	It batches requests and responses reasonably efficiently, doing only as
		692	few reads and writes as needed, but needs to poll for events via the event
		693	loop.
		694
		695	Responses are queued when the parent process is busy. This means the child
		696	can continue to execute any queued requests. It also means that a child
		697	might queue a lot of responses in memory when it generates them and the
		698	parent process is slow accepting them.
		699
		700	The API is not a straightforward RPC pattern - you have to call a
		701	"done" callback to pass return values and signal completion. Also, more
		702	importantly, the API starts jobs as fast as possible - when 1000 jobs
		703	are queued and the jobs are slow, they will all run concurrently. The
		704	child must implement some queueing/limiting mechanism if this causes
		705	problems. Alternatively, the parent could limit the amount of rpc calls
		706	that are outstanding.
		707
		708	Blocking use of condvars is not supported.
		709
		710	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		711	easy.
		712
		713	=back
		714
		715	=head2 Passing file descriptors
		716
		717	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		718	descriptor passing abilities.
		719
		720	The reason is that passing file descriptors is extraordinary tricky
		721	business, and conflicts with efficient batching of messages.
		722
		723	There still is a method you can use: Create a
		724	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		725	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		726
		727	Whenever you want to pass a file descriptor, send an rpc request to the
		728	child process (so it expects the descriptor), then send it over the other
		729	half of the socketpair. The child should fetch the descriptor from the
		730	half it has passed earlier.
		731
		732	Here is some (untested) pseudocode to that effect:
		733
		734	use AnyEvent::Util;
		735	use AnyEvent::Fork::RPC;
		736	use IO::FDPass;
		737
		738	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		739
		740	my $rpc = AnyEvent::Fork
		741	->new
		742	->send_fh ($s2)
		743	->require ("MyWorker")
		744	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		745	init => "MyWorker::init",
		746	);
		747
		748	undef $s2; # no need to keep it around
		749
		750	# pass an fd
		751	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		752
		753	IO::FDPass fileno $s1, fileno $handle_to_pass;
		754
		755	$cv->recv;
		756
		757	The MyWorker module could look like this:
		758
		759	package MyWorker;
		760
		761	use IO::FDPass;
		762
		763	my $s2;
		764
		765	sub init {
		766	$s2 = $_[0];
		767	}
		768
		769	sub run {
		770	if ($_[0] eq "i'll send some fd now, please expect it!") {
		771	my $fd = IO::FDPass::recv fileno $s2;
		772	...
		773	}
		774	}
		775
		776	Of course, this might be blocking if you pass a lot of file descriptors,
		777	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		778	gory details.
		779
		780	=head1 EXCEPTIONS
		781
		782	There are no provisions whatsoever for catching exceptions at this time -
		783	in the child, exeptions might kill the process, causing calls to be lost
		784	and the parent encountering a fatal error. In the parent, exceptions in
		785	the result callback will not be caught and cause undefined behaviour.
		786
403	=head1 SEE ALSO	787	=head1 SEE ALSO
404		788
405	L<AnyEvent::Fork> (to create the processes in the first place),	789	L<AnyEvent::Fork>, to create the processes in the first place.
		790
406	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	791	L<AnyEvent::Fork::Pool>, to manage whole pools of processes.
407		792
408	=head1 AUTHOR AND CONTACT INFORMATION	793	=head1 AUTHOR AND CONTACT INFORMATION
409		794
410	Marc Lehmann <schmorp@schmorp.de>	795	Marc Lehmann <schmorp@schmorp.de>
411	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC	796	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents): Revision 1.5 by root, Wed Apr 17 19:39:54 2013 UTC vs. Revision 1.23 by root, Mon Apr 22 20:05:03 2013 UTC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.5 by root, Wed Apr 17 19:39:54 2013 UTC vs.
Revision 1.23 by root, Mon Apr 22 20:05:03 2013 UTC