[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 1.15 by root, Thu Apr 18 13:15:23 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 (
…		…
34	concurrently in the child, using AnyEvent.	34	concurrently in the child, using AnyEvent.
35		35
36	It also implements an asynchronous event mechanism from the child to the	36	It also implements an asynchronous event mechanism from the child to the
37	parent, that could be used for progress indications or other information.	37	parent, that could be used for progress indications or other information.
38		38
		39	Loading this module also always loads L<AnyEvent::Fork>, so you can make a
		40	separate C<use AnyEvent::Fork> if you wish, but you don't have to.
		41
39	=head1 EXAMPLES	42	=head1 EXAMPLES
40		43
41	=head2 Synchronous Backend	44	=head2 Example 1: Synchronous Backend
42		45
43	Here is a simple example that implements a backend that executes C<unlink>	46	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	47	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	48	number of requests it has processed every three requests, which is clearly
46	silly, but illustrates the use of events.	49	silly, but illustrates the use of events.
47		50
48	First the parent process:	51	First the parent process:
49		52
50	use AnyEvent;	53	use AnyEvent;
51	use AnyEvent::Fork;
52	use AnyEvent::Fork::RPC;	54	use AnyEvent::Fork::RPC;
53		55
54	my $done = AE::cv;	56	my $done = AE::cv;
55		57
56	my $rpc = AnyEvent::Fork	58	my $rpc = AnyEvent::Fork
…		…
103	dies with a fatal error - obviously, you must never let this happen :).	105	dies with a fatal error - obviously, you must never let this happen :).
104		106
105	Eventually it returns the status value true if the command was successful,	107	Eventually it returns the status value true if the command was successful,
106	or the status value 0 and the stringified error message.	108	or the status value 0 and the stringified error message.
107		109
108	On my system, running the first cdoe fragment with the given	110	On my system, running the first code fragment with the given
109	F<MyWorker.pm> in the current directory yields:	111	F<MyWorker.pm> in the current directory yields:
110		112
111	/tmp/somepath/1: No such file or directory	113	/tmp/somepath/1: No such file or directory
112	/tmp/somepath/2: No such file or directory	114	/tmp/somepath/2: No such file or directory
113	3 requests handled	115	3 requests handled
…		…
134		136
135	And as a final remark, there is a fine module on CPAN that can	137	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	138	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
137	than this example, namely L<IO::AIO>.	139	than this example, namely L<IO::AIO>.
138		140
		141	=head3 Example 1a: the same with the asynchronous backend
		142
		143	This example only shows what needs to be changed to use the async backend
		144	instead. Doing this is not very useful, the purpose of this example is
		145	to show the minimum amount of change that is required to go from the
		146	synchronous to the asynchronous backend.
		147
		148	To use the async backend in the previous example, you need to add the
		149	C<async> parameter to the C<AnyEvent::Fork::RPC::run> call:
		150
		151	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		152	async => 1,
		153	...
		154
		155	And since the function call protocol is now changed, you need to adopt
		156	C<MyWorker::run> to the async API.
		157
		158	First, you need to accept the extra initial C<$done> callback:
		159
		160	sub run {
		161	my ($done, $cmd, $path) = @_;
		162
		163	And since a response is now generated when C<$done> is called, as opposed
		164	to when the function returns, we need to call the C<$done> function with
		165	the status:
		166
		167	$done->($status or (0, "$!"));
		168
		169	A few remarks are in order. First, it's quite pointless to use the async
		170	backend for this example - but it I<is> possible. Second, you can call
		171	C<$done> before or after returning from the function. Third, having both
		172	returned from the function and having called the C<$done> callback, the
		173	child process may exit at any time, so you should call C<$done> only when
		174	you really I<are> done.
		175
		176	=head2 Example 2: Asynchronous Backend
		177
		178	This example implements multiple count-downs in the child, using
		179	L<AnyEvent> timers. While this is a bit silly (one could use timers in te
		180	parent just as well), it illustrates the ability to use AnyEvent in the
		181	child and the fact that responses can arrive in a different order then the
		182	requests.
		183
		184	It also shows how to embed the actual child code into a C<__DATA__>
		185	section, so it doesn't need any external files at all.
		186
		187	And when your parent process is often busy, and you have stricter timing
		188	requirements, then running timers in a child process suddenly doesn't look
		189	so silly anymore.
		190
		191	Without further ado, here is the code:
		192
		193	use AnyEvent;
		194	use AnyEvent::Fork::RPC;
		195
		196	my $done = AE::cv;
		197
		198	my $rpc = AnyEvent::Fork
		199	->new
		200	->require ("AnyEvent::Fork::RPC::Async")
		201	->eval (do { local $/; <DATA> })
		202	->AnyEvent::Fork::RPC::run ("run",
		203	async => 1,
		204	on_error => sub { warn "FATAL: $_[0]"; exit 1 },
		205	on_event => sub { print $_[0] },
		206	on_destroy => $done,
		207	);
		208
		209	for my $count (3, 2, 1) {
		210	$rpc->($count, sub {
		211	warn "job $count finished\n";
		212	});
		213	}
		214
		215	undef $rpc;
		216
		217	$done->recv;
		218
		219	__DATA__
		220
		221	# this ends up in main, as we don't use a package declaration
		222
		223	use AnyEvent;
		224
		225	sub run {
		226	my ($done, $count) = @_;
		227
		228	my $n;
		229
		230	AnyEvent::Fork::RPC::event "starting to count up to $count\n";
		231
		232	my $w; $w = AE::timer 1, 1, sub {
		233	++$n;
		234
		235	AnyEvent::Fork::RPC::event "count $n of $count\n";
		236
		237	if ($n == $count) {
		238	undef $w;
		239	$done->();
		240	}
		241	};
		242	}
		243
		244	The parent part (the one before the C<__DATA__> section) isn't very
		245	different from the earlier examples. It sets async mode, preloads
		246	the backend module (so the C<AnyEvent::Fork::RPC::event> function is
		247	declared), uses a slightly different C<on_event> handler (which we use
		248	simply for logging purposes) and then, instead of loading a module with
		249	the actual worker code, it C<eval>'s the code from the data section in the
		250	child process.
		251
		252	It then starts three countdowns, from 3 to 1 seconds downwards, destroys
		253	the rpc object so the example finishes eventually, and then just waits for
		254	the stuff to trickle in.
		255
		256	The worker code uses the event function to log some progress messages, but
		257	mostly just creates a recurring one-second timer.
		258
		259	The timer callback increments a counter, logs a message, and eventually,
		260	when the count has been reached, calls the finish callback.
		261
		262	On my system, this results in the following output. Since all timers fire
		263	at roughly the same time, the actual order isn't guaranteed, but the order
		264	shown is very likely what you would get, too.
		265
		266	starting to count up to 3
		267	starting to count up to 2
		268	starting to count up to 1
		269	count 1 of 3
		270	count 1 of 2
		271	count 1 of 1
		272	job 1 finished
		273	count 2 of 2
		274	job 2 finished
		275	count 2 of 3
		276	count 3 of 3
		277	job 3 finished
		278
		279	While the overall ordering isn't guaranteed, the async backend still
		280	guarantees that events and responses are delivered to the parent process
		281	in the exact same ordering as they were generated in the child process.
		282
		283	And unless your system is I<very> busy, it should clearly show that the
		284	job started last will finish first, as it has the lowest count.
		285
		286	This concludes the async example. Since L<AnyEvent::Fork> does not
		287	actually fork, you are free to use about any module in the child, not just
		288	L<AnyEvent>, but also L<IO::AIO>, or L<Tk> for example.
		289
139	=head1 PARENT PROCESS USAGE	290	=head1 PARENT PROCESS USAGE
140		291
141	This module exports nothing, and only implements a single function:	292	This module exports nothing, and only implements a single function:
142		293
143	=over 4	294	=over 4
…		…
150		301
151	use Errno ();	302	use Errno ();
152	use Guard ();	303	use Guard ();
153		304
154	use AnyEvent;	305	use AnyEvent;
155	#use AnyEvent::Fork;	306	use AnyEvent::Fork; # we don't actually depend on it, this is for convenience
156		307
157	our $VERSION = 0.1;	308	our $VERSION = 0.1;
158		309
159	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	310	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
160		311
…		…
198		349
199	Called when the C<$rpc> object has been destroyed and all requests have	350	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	351	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	352	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	353	the parent must not exit either until all requests have been handled, and
203	this cna be accomplished by waiting for this callback.	354	this can be accomplished by waiting for this callback.
204		355
205	=item init => $function (default none)	356	=item init => $function (default none)
206		357
207	When specified (by name), this function is called in the child as the very	358	When specified (by name), this function is called in the child as the very
208	first thing when taking over the process, with all the arguments normally	359	first thing when taking over the process, with all the arguments normally
…		…
221		372
222	The default server used in the child does all I/O blockingly, and only	373	The default server used in the child does all I/O blockingly, and only
223	allows a single RPC call to execute concurrently.	374	allows a single RPC call to execute concurrently.
224		375
225	Setting C<async> to a true value switches to another implementation that	376	Setting C<async> to a true value switches to another implementation that
226	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.	377	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it
		378	does not support recursion in the event loop however, blocking condvar
		379	calls will fail).
227		380
228	The actual API in the child is documented in the section that describes	381	The actual API in the child is documented in the section that describes
229	the calling semantics of the returned C<$rpc> function.	382	the calling semantics of the returned C<$rpc> function.
230		383
231	If you want to pre-load the actual back-end modules to enable memory	384	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	385	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
233	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	386	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
234		387
235	If you use a template process and want to fork both sync and async	388	If you use a template process and want to fork both sync and async
236	children, then it is permissible to laod both modules.	389	children, then it is permissible to load both modules.
237		390
238	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	391	=item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER)
239		392
240	All arguments, result data and event data have to be serialised to be	393	All arguments, result data and event data have to be serialised to be
241	transferred between the processes. For this, they have to be frozen and	394	transferred between the processes. For this, they have to be frozen and
242	thawed in both parent and child processes.	395	thawed in both parent and child processes.
243		396
244	By default, only octet strings can be passed between the processes, which	397	By default, only octet strings can be passed between the processes, which
245	is reasonably fast and efficient.	398	is reasonably fast and efficient and requires no extra modules.
246		399
247	For more complicated use cases, you can provide your own freeze and thaw	400	For more complicated use cases, you can provide your own freeze and thaw
248	functions, by specifying a string with perl source code. It's supposed to	401	functions, by specifying a string with perl source code. It's supposed to
249	return two code references when evaluated: the first receives a list of	402	return two code references when evaluated: the first receives a list of
250	perl values and must return an octet string. The second receives the octet	403	perl values and must return an octet string. The second receives the octet
…		…
252		405
253	If you need an external module for serialisation, then you can either	406	If you need an external module for serialisation, then you can either
254	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>	407	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
255	or C<require> statement into the serialiser string. Or both.	408	or C<require> statement into the serialiser string. Or both.
256		409
		410	Here are some examples - some of them are also available as global
		411	variables that make them easier to use.
		412
		413	=over 4
		414
		415	=item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER>
		416
		417	This serialiser concatenates length-prefixes octet strings, and is the
		418	default.
		419
		420	Implementation:
		421
		422	(
		423	sub { pack "(w/a)", @_ },
		424	sub { unpack "(w/a)", shift }
		425	)
		426
		427	=item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER>
		428
		429	This serialiser creates JSON arrays - you have to make sure the L<JSON>
		430	module is installed for this serialiser to work. It can be beneficial for
		431	sharing when you preload the L<JSON> module in a template process.
		432
		433	L<JSON> (with L<JSON::XS> installed) is slower than the octet string
		434	serialiser, but usually much faster than L<Storable>, unless big chunks of
		435	binary data need to be transferred.
		436
		437	Implementation:
		438
		439	use JSON ();
		440	(
		441	sub { JSON::encode_json \@_ },
		442	sub { @{ JSON::decode_json shift } }
		443	)
		444
		445	=item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER>
		446
		447	This serialiser uses L<Storable>, which means it has high chance of
		448	serialising just about anything you throw at it, at the cost of having
		449	very high overhead per operation. It also comes with perl.
		450
		451	Implementation:
		452
		453	use Storable ();
		454	(
		455	sub { Storable::freeze \@_ },
		456	sub { @{ Storable::thaw shift } }
		457	)
		458
257	=back	459	=back
258		460
		461	=back
		462
		463	See the examples section earlier in this document for some actual
		464	examples.
		465
259	=cut	466	=cut
260		467
261	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	468	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
		469	our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
		470	our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
262		471
263	sub run {	472	sub run {
264	my ($self, $function, %arg) = @_;	473	my ($self, $function, %arg) = @_;
265		474
266	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;	475	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
…		…
276	# default for on_event is to raise an error	485	# default for on_event is to raise an error
277	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	486	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
278		487
279	my ($f, $t) = eval $serialiser; die $@ if $@;	488	my ($f, $t) = eval $serialiser; die $@ if $@;
280		489
281	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);	490	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
282	my ($rlen, $rbuf) = 512 - 16;	491	my ($rlen, $rbuf, $rw) = 512 - 16;
283		492
284	my $wcb = sub {	493	my $wcb = sub {
285	my $len = syswrite $fh, $wbuf;	494	my $len = syswrite $fh, $wbuf;
286		495
287	if (!defined $len) {	496	unless (defined $len) {
288	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	497	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
289	undef $rw; undef $ww; # it ends here	498	undef $rw; undef $ww; # it ends here
290	$on_error->("$!");	499	$on_error->("$!");
291	}	500	}
292	}	501	}
…		…
303		512
304	$self->require ($module)	513	$self->require ($module)
305	->send_arg ($function, $arg{init}, $serialiser)	514	->send_arg ($function, $arg{init}, $serialiser)
306	->run ("$module\::run", sub {	515	->run ("$module\::run", sub {
307	$fh = shift;	516	$fh = shift;
		517
		518	my ($id, $len);
308	$rw = AE::io $fh, 0, sub {	519	$rw = AE::io $fh, 0, sub {
309	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;	520	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
310	my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;	521	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
311		522
312	if ($len) {	523	if ($len) {
313	while (5 <= length $rbuf) {	524	while (8 <= length $rbuf) {
314	$len = unpack "L", $rbuf;	525	($id, $len) = unpack "LL", $rbuf;
315	4 + $len <= length $rbuf	526	8 + $len <= length $rbuf
316	or last;	527	or last;
317		528
318	my @r = $t->(substr $rbuf, 4, $len);	529	my @r = $t->(substr $rbuf, 8, $len);
319	substr $rbuf, 0, $len + 4, "";	530	substr $rbuf, 0, 8 + $len, "";
		531
		532	if ($id) {
		533	if (@rcb) {
		534	(shift @rcb)->(@r);
		535	} elsif (my $cb = delete $rcb{$id}) {
		536	$cb->(@r);
		537	} else {
		538	undef $rw; undef $ww;
		539	$on_error->("unexpected data from child");
320		540	}
321	if (pop @r) {	541	} else {
322	$on_event->(@r);	542	$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	}	543	}
329	}	544	}
330	} elsif (defined $len) {	545	} elsif (defined $len) {
331	undef $rw; undef $ww; # it ends here	546	undef $rw; undef $ww; # it ends here
332		547
333	if (@rcb) {	548	if (@rcb \|\| %rcb) {
334	$on_error->("unexpected eof");	549	$on_error->("unexpected eof");
335	} else {	550	} else {
336	$on_destroy->();	551	$on_destroy->();
337	}	552	}
338	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	553	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
…		…
347	my $guard = Guard::guard {	562	my $guard = Guard::guard {
348	$shutdown = 1;	563	$shutdown = 1;
349	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	564	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
350	};	565	};
351		566
		567	my $id;
		568
		569	$arg{async}
352	sub {	570	? sub {
353	push @rcb, pop;	571	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		572	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
354		573
		574	$rcb{$id} = pop;
		575
355	$guard; # keep it alive	576	$guard; # keep it alive
356		577
357	$wbuf .= pack "L/a*", &$f;	578	$wbuf .= pack "LL/a*", $id, &$f;
358	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	579	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
359	}	580	}
		581	: sub {
		582	push @rcb, pop;
		583
		584	$guard; # keep it alive
		585
		586	$wbuf .= pack "L/a*", &$f;
		587	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		588	}
360	}	589	}
361		590
362	=item $rpc->(..., $cb->(...))	591	=item $rpc->(..., $cb->(...))
363		592
364	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code	593	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
…		…
379		608
380	The other thing that can be done with the RPC object is to destroy it. In	609	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	610	this case, the child process will execute all remaining RPC calls, report
382	their results, and then exit.	611	their results, and then exit.
383		612
		613	See the examples section earlier in this document for some actual
		614	examples.
		615
384	=back	616	=back
385		617
386	=head1 CHILD PROCESS USAGE	618	=head1 CHILD PROCESS USAGE
387		619
388	The following function is not available in this module. They are only	620	The following function is not available in this module. They are only
…		…
396		628
397	Send an event to the parent. Events are a bit like RPC calls made by the	629	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	630	child process to the parent, except that there is no notion of return
399	values.	631	values.
400		632
		633	See the examples section earlier in this document for some actual
		634	examples.
		635
401	=back	636	=back
		637
		638	=head1 ADVANCED TOPICS
		639
		640	=head2 Choosing a backend
		641
		642	So how do you decide which backend to use? Well, that's your problem to
		643	solve, but here are some thoughts on the matter:
		644
		645	=over 4
		646
		647	=item Synchronous
		648
		649	The synchronous backend does not rely on any external modules (well,
		650	except L<common::sense>, which works around a bug in how perl's warning
		651	system works). This keeps the process very small, for example, on my
		652	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		653	after C<use warnings; use strict> (for people who grew up with C64s around
		654	them this is probably shocking every single time they see it). The worker
		655	process in the first example in this document uses 1792kB.
		656
		657	Since the calls are done synchronously, slow jobs will keep newer jobs
		658	from executing.
		659
		660	The synchronous backend also has no overhead due to running an event loop
		661	- reading requests is therefore very efficient, while writing responses is
		662	less so, as every response results in a write syscall.
		663
		664	If the parent process is busy and a bit slow reading responses, the child
		665	waits instead of processing further requests. This also limits the amount
		666	of memory needed for buffering, as never more than one response has to be
		667	buffered.
		668
		669	The API in the child is simple - you just have to define a function that
		670	does something and returns something.
		671
		672	It's hard to use modules or code that relies on an event loop, as the
		673	child cannot execute anything while it waits for more input.
		674
		675	=item Asynchronous
		676
		677	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		678	but still comes at a price: On my system, the worker from example 1a uses
		679	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		680	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		681	L<vars>, L<Exporter>...).
		682
		683	It batches requests and responses reasonably efficiently, doing only as
		684	few reads and writes as needed, but needs to poll for events via the event
		685	loop.
		686
		687	Responses are queued when the parent process is busy. This means the child
		688	can continue to execute any queued requests. It also means that a child
		689	might queue a lot of responses in memory when it generates them and the
		690	parent process is slow accepting them.
		691
		692	The API is not a straightforward RPC pattern - you have to call a
		693	"done" callback to pass return values and signal completion. Also, more
		694	importantly, the API starts jobs as fast as possible - when 1000 jobs
		695	are queued and the jobs are slow, they will all run concurrently. The
		696	child must implement some queueing/limiting mechanism if this causes
		697	problems. Alternatively, the parent could limit the amount of rpc calls
		698	that are outstanding.
		699
		700	Blocking use of condvars is not supported.
		701
		702	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		703	easy.
		704
		705	=back
		706
		707	=head2 Passing file descriptors
		708
		709	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		710	descriptor passing abilities.
		711
		712	The reason is that passing file descriptors is extraordinary tricky
		713	business, and conflicts with efficient batching of messages.
		714
		715	There still is a method you can use: Create a
		716	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		717	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		718
		719	Whenever you want to pass a file descriptor, send an rpc request to the
		720	child process (so it expects the descriptor), then send it over the other
		721	half of the socketpair. The child should fetch the descriptor from the
		722	half it has passed earlier.
		723
		724	Here is some (untested) pseudocode to that effect:
		725
		726	use AnyEvent::Util;
		727	use AnyEvent::Fork::RPC;
		728	use IO::FDPass;
		729
		730	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		731
		732	my $rpc = AnyEvent::Fork
		733	->new
		734	->send_fh ($s2)
		735	->require ("MyWorker")
		736	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		737	init => "MyWorker::init",
		738	);
		739
		740	undef $s2; # no need to keep it around
		741
		742	# pass an fd
		743	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		744
		745	IO::FDPass fileno $s1, fileno $handle_to_pass;
		746
		747	$cv->recv;
		748
		749	The MyWorker module could look like this:
		750
		751	package MyWorker;
		752
		753	use IO::FDPass;
		754
		755	my $s2;
		756
		757	sub init {
		758	$s2 = $_[0];
		759	}
		760
		761	sub run {
		762	if ($_[0] eq "i'll send some fd now, please expect it!") {
		763	my $fd = IO::FDPass::recv fileno $s2;
		764	...
		765	}
		766	}
		767
		768	Of course, this might be blocking if you pass a lot of file descriptors,
		769	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		770	gory details.
402		771
403	=head1 SEE ALSO	772	=head1 SEE ALSO
404		773
405	L<AnyEvent::Fork> (to create the processes in the first place),	774	L<AnyEvent::Fork> (to create the processes in the first place),
406	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	775	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).

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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 1.15 by root, Thu Apr 18 13:15:23 2013 UTC