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

Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.6 by root, Wed Apr 17 19:43:48 2013 UTC vs.
Revision 1.35 by root, Wed Nov 20 16:17:22 2013 UTC

…		…
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;
…		…
24	$cv->recv;	26	$cv->recv;
25		27
26	=head1 DESCRIPTION	28	=head1 DESCRIPTION
27		29
28	This module implements a simple RPC protocol and backend for processes	30	This module implements a simple RPC protocol and backend for processes
29	created via L<AnyEvent::Fork>, allowing you to call a function in the	31	created via L<AnyEvent::Fork> or L<AnyEvent::Fork::Remote>, allowing you
30	child process and receive its return values (up to 4GB serialised).	32	to call a function in the child process and receive its return values (up
		33	to 4GB serialised).
31		34
32	It implements two different backends: a synchronous one that works like a	35	It implements two different backends: a synchronous one that works like a
33	normal function call, and an asynchronous one that can run multiple jobs	36	normal function call, and an asynchronous one that can run multiple jobs
34	concurrently in the child, using AnyEvent.	37	concurrently in the child, using AnyEvent.
35		38
36	It also implements an asynchronous event mechanism from the child to the	39	It also implements an asynchronous event mechanism from the child to the
37	parent, that could be used for progress indications or other information.	40	parent, that could be used for progress indications or other information.
38		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.
…		…
55		58
56	my $rpc = AnyEvent::Fork	59	my $rpc = AnyEvent::Fork
57	->new	60	->new
58	->require ("MyWorker")	61	->require ("MyWorker")
59	->AnyEvent::Fork::RPC::run ("MyWorker::run",	62	->AnyEvent::Fork::RPC::run ("MyWorker::run",
60	on_error => sub { warn "FATAL: $_[0]"; exit 1 },	63	on_error => sub { warn "ERROR: $_[0]"; exit 1 },
61	on_event => sub { warn "$_[0] requests handled\n" },	64	on_event => sub { warn "$_[0] requests handled\n" },
62	on_destroy => $done,	65	on_destroy => $done,
63	);	66	);
64		67
65	for my $id (1..6) {	68	for my $id (1..6) {
…		…
134		137
135	And as a final remark, there is a fine module on CPAN that can	138	And as a final remark, there is a fine module on CPAN that can
136	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently	139	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
137	than this example, namely L<IO::AIO>.	140	than this example, namely L<IO::AIO>.
138		141
		142	=head3 Example 1a: the same with the asynchronous backend
		143
		144	This example only shows what needs to be changed to use the async backend
		145	instead. Doing this is not very useful, the purpose of this example is
		146	to show the minimum amount of change that is required to go from the
		147	synchronous to the asynchronous backend.
		148
		149	To use the async backend in the previous example, you need to add the
		150	C<async> parameter to the C<AnyEvent::Fork::RPC::run> call:
		151
		152	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		153	async => 1,
		154	...
		155
		156	And since the function call protocol is now changed, you need to adopt
		157	C<MyWorker::run> to the async API.
		158
		159	First, you need to accept the extra initial C<$done> callback:
		160
		161	sub run {
		162	my ($done, $cmd, $path) = @_;
		163
		164	And since a response is now generated when C<$done> is called, as opposed
		165	to when the function returns, we need to call the C<$done> function with
		166	the status:
		167
		168	$done->($status or (0, "$!"));
		169
		170	A few remarks are in order. First, it's quite pointless to use the async
		171	backend for this example - but it I<is> possible. Second, you can call
		172	C<$done> before or after returning from the function. Third, having both
		173	returned from the function and having called the C<$done> callback, the
		174	child process may exit at any time, so you should call C<$done> only when
		175	you really I<are> done.
		176
		177	=head2 Example 2: Asynchronous Backend
		178
		179	This example implements multiple count-downs in the child, using
		180	L<AnyEvent> timers. While this is a bit silly (one could use timers in the
		181	parent just as well), it illustrates the ability to use AnyEvent in the
		182	child and the fact that responses can arrive in a different order then the
		183	requests.
		184
		185	It also shows how to embed the actual child code into a C<__DATA__>
		186	section, so it doesn't need any external files at all.
		187
		188	And when your parent process is often busy, and you have stricter timing
		189	requirements, then running timers in a child process suddenly doesn't look
		190	so silly anymore.
		191
		192	Without further ado, here is the code:
		193
		194	use AnyEvent;
		195	use AnyEvent::Fork;
		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 "ERROR: $_[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
		292	=head2 Example 3: Asynchronous backend with Coro
		293
		294	With L<Coro> you can create a nice asynchronous backend implementation by
		295	defining an rpc server function that creates a new Coro thread for every
		296	request that calls a function "normally", i.e. the parameters from the
		297	parent process are passed to it, and any return values are returned to the
		298	parent process, e.g.:
		299
		300	package My::Arith;
		301
		302	sub add {
		303	return $_[0] + $_[1];
		304	}
		305
		306	sub mul {
		307	return $_[0] * $_[1];
		308	}
		309
		310	sub run {
		311	my ($done, $func, @arg) = @_;
		312
		313	Coro::async_pool {
		314	$done->($func->(@arg));
		315	};
		316	}
		317
		318	The C<run> function creates a new thread for every invocation, using the
		319	first argument as function name, and calls the C<$done> callback on it's
		320	return values. This makes it quite natural to define the C<add> and C<mul>
		321	functions to add or multiply two numbers and return the result.
		322
		323	Since this is the asynchronous backend, it's quite possible to define RPC
		324	function that do I/O or wait for external events - their execution will
		325	overlap as needed.
		326
		327	The above could be used like this:
		328
		329	my $rpc = AnyEvent::Fork
		330	->new
		331	->require ("MyWorker")
		332	->AnyEvent::Fork::RPC::run ("My::Arith::run",
		333	on_error => ..., on_event => ..., on_destroy => ...,
		334	);
		335
		336	$rpc->(add => 1, 3, Coro::rouse_cb); say Coro::rouse_wait;
		337	$rpc->(mul => 3, 2, Coro::rouse_cb); say Coro::rouse_wait;
		338
		339	The C<say>'s will print C<4> and C<6>.
		340
		341	=head2 Example 4: Forward AnyEvent::Log messages using C<on_event>
		342
		343	This partial example shows how to use the C<event> function to forward
		344	L<AnyEvent::Log> messages to the parent.
		345
		346	For this, the parent needs to provide a suitable C<on_event>:
		347
		348	->AnyEvent::Fork::RPC::run (
		349	on_event => sub {
		350	if ($_[0] eq "ae_log") {
		351	my (undef, $level, $message) = @_;
		352	AE::log $level, $message;
		353	} else {
		354	# other event types
		355	}
		356	},
		357	)
		358
		359	In the child, as early as possible, the following code should reconfigure
		360	L<AnyEvent::Log> to log via C<AnyEvent::Fork::RPC::event>:
		361
		362	$AnyEvent::Log::LOG->log_cb (sub {
		363	my ($timestamp, $orig_ctx, $level, $message) = @{+shift};
		364
		365	if (defined &AnyEvent::Fork::RPC::event) {
		366	AnyEvent::Fork::RPC::event (ae_log => $level, $message);
		367	} else {
		368	warn "[$$ before init] $message\n";
		369	}
		370	});
		371
		372	There is an important twist - the C<AnyEvent::Fork::RPC::event> function
		373	is only defined when the child is fully initialised. If you redirect the
		374	log messages in your C<init> function for example, then the C<event>
		375	function might not yet be available. This is why the log callback checks
		376	whether the fucntion is there using C<defined>, and only then uses it to
		377	log the message.
		378
139	=head1 PARENT PROCESS USAGE	379	=head1 PARENT PROCESS USAGE
140		380
141	This module exports nothing, and only implements a single function:	381	This module exports nothing, and only implements a single function:
142		382
143	=over 4	383	=over 4
…		…
150		390
151	use Errno ();	391	use Errno ();
152	use Guard ();	392	use Guard ();
153		393
154	use AnyEvent;	394	use AnyEvent;
155	#use AnyEvent::Fork;
156		395
157	our $VERSION = 0.1;	396	our $VERSION = 1.21;
158		397
159	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	398	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
160		399
161	The traditional way to call it. But it is way cooler to call it in the	400	The traditional way to call it. But it is way cooler to call it in the
162	following way:	401	following way:
…		…
182	Called on (fatal) errors, with a descriptive (hopefully) message. If	421	Called on (fatal) errors, with a descriptive (hopefully) message. If
183	this callback is not provided, but C<on_event> is, then the C<on_event>	422	this callback is not provided, but C<on_event> is, then the C<on_event>
184	callback is called with the first argument being the string C<error>,	423	callback is called with the first argument being the string C<error>,
185	followed by the error message.	424	followed by the error message.
186		425
187	If neither handler is provided it prints the error to STDERR and will	426	If neither handler is provided, then the error is reported with loglevel
188	start failing badly.	427	C<error> via C<AE::log>.
189		428
190	=item on_event => $cb->(...)	429	=item on_event => $cb->(...)
191		430
192	Called for every call to the C<AnyEvent::Fork::RPC::event> function in the	431	Called for every call to the C<AnyEvent::Fork::RPC::event> function in the
193	child, with the arguments of that function passed to the callback.	432	child, with the arguments of that function passed to the callback.
…		…
215	It is called very early - before the serialisers are created or the	454	It is called very early - before the serialisers are created or the
216	C<$function> name is resolved into a function reference, so it could be	455	C<$function> name is resolved into a function reference, so it could be
217	used to load any modules that provide the serialiser or function. It can	456	used to load any modules that provide the serialiser or function. It can
218	not, however, create events.	457	not, however, create events.
219		458
		459	=item done => $function (default C<CORE::exit>)
		460
		461	The function to call when the asynchronous backend detects an end of file
		462	condition when reading from the communications socket I<and> there are no
		463	outstanding requests. It's ignored by the synchronous backend.
		464
		465	By overriding this you can prolong the life of a RPC process after e.g.
		466	the parent has exited by running the event loop in the provided function
		467	(or simply calling it, for example, when your child process uses L<EV> you
		468	could provide L<EV::loop> as C<done> function).
		469
		470	Of course, in that case you are responsible for exiting at the appropriate
		471	time and not returning from
		472
220	=item async => $boolean (default: 0)	473	=item async => $boolean (default: 0)
221		474
222	The default server used in the child does all I/O blockingly, and only	475	The default server used in the child does all I/O blockingly, and only
223	allows a single RPC call to execute concurrently.	476	allows a single RPC call to execute concurrently.
224		477
225	Setting C<async> to a true value switches to another implementation that	478	Setting C<async> to a true value switches to another implementation that
226	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.	479	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it
		480	does not support recursion in the event loop however, blocking condvar
		481	calls will fail).
227		482
228	The actual API in the child is documented in the section that describes	483	The actual API in the child is documented in the section that describes
229	the calling semantics of the returned C<$rpc> function.	484	the calling semantics of the returned C<$rpc> function.
230		485
231	If you want to pre-load the actual back-end modules to enable memory	486	If you want to pre-load the actual back-end modules to enable memory
…		…
233	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	488	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
234		489
235	If you use a template process and want to fork both sync and async	490	If you use a template process and want to fork both sync and async
236	children, then it is permissible to load both modules.	491	children, then it is permissible to load both modules.
237		492
238	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	493	=item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER)
239		494
240	All arguments, result data and event data have to be serialised to be	495	All arguments, result data and event data have to be serialised to be
241	transferred between the processes. For this, they have to be frozen and	496	transferred between the processes. For this, they have to be frozen and
242	thawed in both parent and child processes.	497	thawed in both parent and child processes.
243		498
244	By default, only octet strings can be passed between the processes, which	499	By default, only octet strings can be passed between the processes, which
245	is reasonably fast and efficient.	500	is reasonably fast and efficient and requires no extra modules.
246		501
247	For more complicated use cases, you can provide your own freeze and thaw	502	For more complicated use cases, you can provide your own freeze and thaw
248	functions, by specifying a string with perl source code. It's supposed to	503	functions, by specifying a string with perl source code. It's supposed to
249	return two code references when evaluated: the first receives a list of	504	return two code references when evaluated: the first receives a list of
250	perl values and must return an octet string. The second receives the octet	505	perl values and must return an octet string. The second receives the octet
…		…
252		507
253	If you need an external module for serialisation, then you can either	508	If you need an external module for serialisation, then you can either
254	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>	509	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
255	or C<require> statement into the serialiser string. Or both.	510	or C<require> statement into the serialiser string. Or both.
256		511
		512	Here are some examples - some of them are also available as global
		513	variables that make them easier to use.
		514
		515	=over 4
		516
		517	=item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER>
		518
		519	This serialiser concatenates length-prefixes octet strings, and is the
		520	default. That means you can only pass (and return) strings containing
		521	character codes 0-255.
		522
		523	Implementation:
		524
		525	(
		526	sub { pack "(w/a)", @_ },
		527	sub { unpack "(w/a)", shift }
		528	)
		529
		530	=item json - C<$AnyEvent::Fork::RPC::CBOR_XS_SERIALISER>
		531
		532	This serialiser creates CBOR::XS arrays - you have to make sure the
		533	L<CBOR::XS> module is installed for this serialiser to work. It can be
		534	beneficial for sharing when you preload the L<CBOR::XS> module in a template
		535	process.
		536
		537	L<CBOR::XS> is about as fast as the octet string serialiser, but supports
		538	complex data structures (similar to JSON) and is faster than any of the
		539	other serialisers. If you have the L<CBOR::XS> module available, it's the
		540	best choice.
		541
		542	Note that the CBOR::XS module supports some extensions to encode cyclic
		543	and self-referencing data structures, which are not enabled. You need to
		544	write your own serialiser to take advantage of these.
		545
		546	Implementation:
		547
		548	use CBOR::XS ();
		549	(
		550	sub { CBOR::XS::encode_cbor \@_ },
		551	sub { @{ CBOR::XS::decode_cbor shift } }
		552	)
		553
		554	=item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER>
		555
		556	This serialiser creates JSON arrays - you have to make sure the L<JSON>
		557	module is installed for this serialiser to work. It can be beneficial for
		558	sharing when you preload the L<JSON> module in a template process.
		559
		560	L<JSON> (with L<JSON::XS> installed) is slower than the octet string
		561	serialiser, but usually much faster than L<Storable>, unless big chunks of
		562	binary data need to be transferred.
		563
		564	Implementation:
		565
		566	use JSON ();
		567	(
		568	sub { JSON::encode_json \@_ },
		569	sub { @{ JSON::decode_json shift } }
		570	)
		571
		572	=item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER>
		573
		574	This serialiser uses L<Storable>, which means it has high chance of
		575	serialising just about anything you throw at it, at the cost of having
		576	very high overhead per operation. It also comes with perl. It should be
		577	used when you need to serialise complex data structures.
		578
		579	Implementation:
		580
		581	use Storable ();
		582	(
		583	sub { Storable::freeze \@_ },
		584	sub { @{ Storable::thaw shift } }
		585	)
		586
		587	=item portable storable - C<$AnyEvent::Fork::RPC::NSTORABLE_SERIALISER>
		588
		589	This serialiser also uses L<Storable>, but uses it's "network" format
		590	to serialise data, which makes it possible to talk to different
		591	perl binaries (for example, when talking to a process created with
		592	L<AnyEvent::Fork::Remote>).
		593
		594	Implementation:
		595
		596	use Storable ();
		597	(
		598	sub { Storable::nfreeze \@_ },
		599	sub { @{ Storable::thaw shift } }
		600	)
		601
257	=back	602	=back
258		603
		604	=back
		605
		606	See the examples section earlier in this document for some actual
		607	examples.
		608
259	=cut	609	=cut
260		610
261	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	611	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
		612	our $CBOR_XS_SERIALISER = 'use CBOR::XS (); (sub { CBOR::XS::encode_cbor \@_ }, sub { @{ CBOR::XS::decode_cbor shift } })';
		613	our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
		614	our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
		615	our $NSTORABLE_SERIALISER = 'use Storable (); (sub { Storable::nfreeze \@_ }, sub { @{ Storable::thaw shift } })';
262		616
263	sub run {	617	sub run {
264	my ($self, $function, %arg) = @_;	618	my ($self, $function, %arg) = @_;
265		619
266	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;	620	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
…		…
269	my $on_destroy = delete $arg{on_destroy};	623	my $on_destroy = delete $arg{on_destroy};
270		624
271	# default for on_error is to on_event, if specified	625	# default for on_error is to on_event, if specified
272	$on_error \|\|= $on_event	626	$on_error \|\|= $on_event
273	? sub { $on_event->(error => shift) }	627	? sub { $on_event->(error => shift) }
274	: sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" };	628	: sub { AE::log die => "AnyEvent::Fork::RPC: uncaught error: $_[0]." };
275		629
276	# default for on_event is to raise an error	630	# default for on_event is to raise an error
277	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	631	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
278		632
279	my ($f, $t) = eval $serialiser; die $@ if $@;	633	my ($f, $t) = eval $serialiser; die $@ if $@;
280		634
281	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);	635	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
282	my ($rlen, $rbuf) = 512 - 16;	636	my ($rlen, $rbuf, $rw) = 512 - 16;
283		637
284	my $wcb = sub {	638	my $wcb = sub {
285	my $len = syswrite $fh, $wbuf;	639	my $len = syswrite $fh, $wbuf;
286		640
287	if (!defined $len) {	641	unless (defined $len) {
288	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	642	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
289	undef $rw; undef $ww; # it ends here	643	undef $rw; undef $ww; # it ends here
290	$on_error->("$!");	644	$on_error->("$!");
291	}	645	}
292	}	646	}
…		…
300	};	654	};
301		655
302	my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");	656	my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");
303		657
304	$self->require ($module)	658	$self->require ($module)
305	->send_arg ($function, $arg{init}, $serialiser)	659	->send_arg ($function, $arg{init}, $serialiser, $arg{done} \|\| "$module\::do_exit")
306	->run ("$module\::run", sub {	660	->run ("$module\::run", sub {
307	$fh = shift;	661	$fh = shift;
		662
		663	my ($id, $len);
308	$rw = AE::io $fh, 0, sub {	664	$rw = AE::io $fh, 0, sub {
309	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;	665	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
310	my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;	666	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
311		667
312	if ($len) {	668	if ($len) {
313	while (5 <= length $rbuf) {	669	while (8 <= length $rbuf) {
314	$len = unpack "L", $rbuf;	670	($id, $len) = unpack "NN", $rbuf;
315	4 + $len <= length $rbuf	671	8 + $len <= length $rbuf
316	or last;	672	or last;
317		673
318	my @r = $t->(substr $rbuf, 4, $len);	674	my @r = $t->(substr $rbuf, 8, $len);
319	substr $rbuf, 0, $len + 4, "";	675	substr $rbuf, 0, 8 + $len, "";
		676
		677	if ($id) {
		678	if (@rcb) {
		679	(shift @rcb)->(@r);
		680	} elsif (my $cb = delete $rcb{$id}) {
		681	$cb->(@r);
		682	} else {
		683	undef $rw; undef $ww;
		684	$on_error->("unexpected data from child");
320		685	}
321	if (pop @r) {	686	} else {
322	$on_event->(@r);	687	$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	}	688	}
329	}	689	}
330	} elsif (defined $len) {	690	} elsif (defined $len) {
331	undef $rw; undef $ww; # it ends here	691	undef $rw; undef $ww; # it ends here
332		692
333	if (@rcb) {	693	if (@rcb \|\| %rcb) {
334	$on_error->("unexpected eof");	694	$on_error->("unexpected eof");
335	} else {	695	} else {
336	$on_destroy->();	696	$on_destroy->()
		697	if $on_destroy;
337	}	698	}
338	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	699	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
339	undef $rw; undef $ww; # it ends here	700	undef $rw; undef $ww; # it ends here
340	$on_error->("read: $!");	701	$on_error->("read: $!");
341	}	702	}
…		…
344	$ww \|\|= AE::io $fh, 1, $wcb;	705	$ww \|\|= AE::io $fh, 1, $wcb;
345	});	706	});
346		707
347	my $guard = Guard::guard {	708	my $guard = Guard::guard {
348	$shutdown = 1;	709	$shutdown = 1;
349	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	710
		711	shutdown $fh, 1 if $fh && !$ww;
350	};	712	};
351		713
		714	my $id;
		715
		716	$arg{async}
352	sub {	717	? sub {
353	push @rcb, pop;	718	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		719	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
354		720
		721	$rcb{$id} = pop;
		722
355	$guard; # keep it alive	723	$guard if 0; # keep it alive
356		724
357	$wbuf .= pack "L/a*", &$f;	725	$wbuf .= pack "NN/a*", $id, &$f;
358	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	726	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
359	}	727	}
		728	: sub {
		729	push @rcb, pop;
		730
		731	$guard; # keep it alive
		732
		733	$wbuf .= pack "N/a*", &$f;
		734	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		735	}
360	}	736	}
361		737
362	=item $rpc->(..., $cb->(...))	738	=item $rpc->(..., $cb->(...))
363		739
364	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code	740	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
…		…
379		755
380	The other thing that can be done with the RPC object is to destroy it. In	756	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	757	this case, the child process will execute all remaining RPC calls, report
382	their results, and then exit.	758	their results, and then exit.
383		759
		760	See the examples section earlier in this document for some actual
		761	examples.
		762
384	=back	763	=back
385		764
386	=head1 CHILD PROCESS USAGE	765	=head1 CHILD PROCESS USAGE
387		766
388	The following function is not available in this module. They are only	767	The following function is not available in this module. They are only
…		…
396		775
397	Send an event to the parent. Events are a bit like RPC calls made by the	776	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	777	child process to the parent, except that there is no notion of return
399	values.	778	values.
400		779
		780	See the examples section earlier in this document for some actual
		781	examples.
		782
401	=back	783	=back
402		784
		785	=head2 PROCESS EXIT
		786
		787	If and when the child process exits depends on the backend and
		788	configuration. Apart from explicit exits (e.g. by calling C<exit>) or
		789	runtime conditions (uncaught exceptions, signals etc.), the backends exit
		790	under these conditions:
		791
		792	=over 4
		793
		794	=item Synchronous Backend
		795
		796	The synchronous backend is very simple: when the process waits for another
		797	request to arrive and the writing side (usually in the parent) is closed,
		798	it will exit normally, i.e. as if your main program reached the end of the
		799	file.
		800
		801	That means that if your parent process exits, the RPC process will usually
		802	exit as well, either because it is idle anyway, or because it executes a
		803	request. In the latter case, you will likely get an error when the RPc
		804	process tries to send the results to the parent (because agruably, you
		805	shouldn't exit your parent while there are still outstanding requests).
		806
		807	The process is usually quiescent when it happens, so it should rarely be a
		808	problem, and C<END> handlers can be used to clean up.
		809
		810	=item Asynchronous Backend
		811
		812	For the asynchronous backend, things are more complicated: Whenever it
		813	listens for another request by the parent, it might detect that the socket
		814	was closed (e.g. because the parent exited). It will sotp listening for
		815	new requests and instead try to write out any remaining data (if any) or
		816	simply check whether the socket can be written to. After this, the RPC
		817	process is effectively done - no new requests are incoming, no outstanding
		818	request data can be written back.
		819
		820	Since chances are high that there are event watchers that the RPC server
		821	knows nothing about (why else would one use the async backend if not for
		822	the ability to register watchers?), the event loop would often happily
		823	continue.
		824
		825	This is why the asynchronous backend explicitly calls C<CORE::exit> when
		826	it is done (under other circumstances, such as when there is an I/O error
		827	and there is outstanding data to write, it will log a fatal message via
		828	L<AnyEvent::Log>, also causing the program to exit).
		829
		830	You can override this by specifying a function name to call via the C<done>
		831	parameter instead.
		832
		833	=back
		834
		835	=head1 ADVANCED TOPICS
		836
		837	=head2 Choosing a backend
		838
		839	So how do you decide which backend to use? Well, that's your problem to
		840	solve, but here are some thoughts on the matter:
		841
		842	=over 4
		843
		844	=item Synchronous
		845
		846	The synchronous backend does not rely on any external modules (well,
		847	except L<common::sense>, which works around a bug in how perl's warning
		848	system works). This keeps the process very small, for example, on my
		849	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		850	after C<use warnings; use strict> (for people who grew up with C64s around
		851	them this is probably shocking every single time they see it). The worker
		852	process in the first example in this document uses 1792kB.
		853
		854	Since the calls are done synchronously, slow jobs will keep newer jobs
		855	from executing.
		856
		857	The synchronous backend also has no overhead due to running an event loop
		858	- reading requests is therefore very efficient, while writing responses is
		859	less so, as every response results in a write syscall.
		860
		861	If the parent process is busy and a bit slow reading responses, the child
		862	waits instead of processing further requests. This also limits the amount
		863	of memory needed for buffering, as never more than one response has to be
		864	buffered.
		865
		866	The API in the child is simple - you just have to define a function that
		867	does something and returns something.
		868
		869	It's hard to use modules or code that relies on an event loop, as the
		870	child cannot execute anything while it waits for more input.
		871
		872	=item Asynchronous
		873
		874	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		875	but still comes at a price: On my system, the worker from example 1a uses
		876	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		877	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		878	L<vars>, L<Exporter>...).
		879
		880	It batches requests and responses reasonably efficiently, doing only as
		881	few reads and writes as needed, but needs to poll for events via the event
		882	loop.
		883
		884	Responses are queued when the parent process is busy. This means the child
		885	can continue to execute any queued requests. It also means that a child
		886	might queue a lot of responses in memory when it generates them and the
		887	parent process is slow accepting them.
		888
		889	The API is not a straightforward RPC pattern - you have to call a
		890	"done" callback to pass return values and signal completion. Also, more
		891	importantly, the API starts jobs as fast as possible - when 1000 jobs
		892	are queued and the jobs are slow, they will all run concurrently. The
		893	child must implement some queueing/limiting mechanism if this causes
		894	problems. Alternatively, the parent could limit the amount of rpc calls
		895	that are outstanding.
		896
		897	Blocking use of condvars is not supported.
		898
		899	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		900	easy.
		901
		902	=back
		903
		904	=head2 Passing file descriptors
		905
		906	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		907	descriptor passing abilities.
		908
		909	The reason is that passing file descriptors is extraordinary tricky
		910	business, and conflicts with efficient batching of messages.
		911
		912	There still is a method you can use: Create a
		913	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		914	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		915
		916	Whenever you want to pass a file descriptor, send an rpc request to the
		917	child process (so it expects the descriptor), then send it over the other
		918	half of the socketpair. The child should fetch the descriptor from the
		919	half it has passed earlier.
		920
		921	Here is some (untested) pseudocode to that effect:
		922
		923	use AnyEvent::Util;
		924	use AnyEvent::Fork;
		925	use AnyEvent::Fork::RPC;
		926	use IO::FDPass;
		927
		928	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		929
		930	my $rpc = AnyEvent::Fork
		931	->new
		932	->send_fh ($s2)
		933	->require ("MyWorker")
		934	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		935	init => "MyWorker::init",
		936	);
		937
		938	undef $s2; # no need to keep it around
		939
		940	# pass an fd
		941	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		942
		943	IO::FDPass fileno $s1, fileno $handle_to_pass;
		944
		945	$cv->recv;
		946
		947	The MyWorker module could look like this:
		948
		949	package MyWorker;
		950
		951	use IO::FDPass;
		952
		953	my $s2;
		954
		955	sub init {
		956	$s2 = $_[0];
		957	}
		958
		959	sub run {
		960	if ($_[0] eq "i'll send some fd now, please expect it!") {
		961	my $fd = IO::FDPass::recv fileno $s2;
		962	...
		963	}
		964	}
		965
		966	Of course, this might be blocking if you pass a lot of file descriptors,
		967	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		968	gory details.
		969
		970	=head1 EXCEPTIONS
		971
		972	There are no provisions whatsoever for catching exceptions at this time -
		973	in the child, exeptions might kill the process, causing calls to be lost
		974	and the parent encountering a fatal error. In the parent, exceptions in
		975	the result callback will not be caught and cause undefined behaviour.
		976
403	=head1 SEE ALSO	977	=head1 SEE ALSO
404		978
405	L<AnyEvent::Fork> (to create the processes in the first place),	979	L<AnyEvent::Fork>, to create the processes in the first place.
		980
		981	L<AnyEvent::Fork::Remote>, likewise, but helpful for remote processes.
		982
406	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	983	L<AnyEvent::Fork::Pool>, to manage whole pools of processes.
407		984
408	=head1 AUTHOR AND CONTACT INFORMATION	985	=head1 AUTHOR AND CONTACT INFORMATION
409		986
410	Marc Lehmann <schmorp@schmorp.de>	987	Marc Lehmann <schmorp@schmorp.de>
411	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC	988	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents): Revision 1.6 by root, Wed Apr 17 19:43:48 2013 UTC vs. Revision 1.35 by root, Wed Nov 20 16:17:22 2013 UTC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.6 by root, Wed Apr 17 19:43:48 2013 UTC vs.
Revision 1.35 by root, Wed Nov 20 16:17:22 2013 UTC