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

Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.7 by root, Wed Apr 17 20:19:41 2013 UTC vs.
Revision 1.30 by root, Sun Aug 25 22:21:15 2013 UTC

…		…
2		2
3	AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork	3	AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
		7	use AnyEvent::Fork;
7	use AnyEvent::Fork::RPC;	8	use AnyEvent::Fork::RPC;
8	# use AnyEvent::Fork is not needed
9		9
10	my $rpc = AnyEvent::Fork	10	my $rpc = AnyEvent::Fork
11	->new	11	->new
12	->require ("MyModule")	12	->require ("MyModule")
13	->AnyEvent::Fork::RPC::run (	13	->AnyEvent::Fork::RPC::run (
14	"MyModule::server",	14	"MyModule::server",
15	);	15	);
16		16
		17	use AnyEvent;
		18
17	my $cv = AE::cv;	19	my $cv = AE::cv;
18		20
19	$rpc->(1, 2, 3, sub {	21	$rpc->(1, 2, 3, sub {
20	print "MyModule::server returned @_\n";	22	print "MyModule::server returned @_\n";
21	$cv->send;	23	$cv->send;
…		…
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	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
42	=head1 EXAMPLES	42	=head1 EXAMPLES
43		43
44	=head2 Synchronous Backend	44	=head2 Example 1: Synchronous Backend
45		45
46	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>
47	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
48	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
49	silly, but illustrates the use of events.	49	silly, but illustrates the use of events.
…		…
58		58
59	my $rpc = AnyEvent::Fork	59	my $rpc = AnyEvent::Fork
60	->new	60	->new
61	->require ("MyWorker")	61	->require ("MyWorker")
62	->AnyEvent::Fork::RPC::run ("MyWorker::run",	62	->AnyEvent::Fork::RPC::run ("MyWorker::run",
63	on_error => sub { warn "FATAL: $_[0]"; exit 1 },	63	on_error => sub { warn "ERROR: $_[0]"; exit 1 },
64	on_event => sub { warn "$_[0] requests handled\n" },	64	on_event => sub { warn "$_[0] requests handled\n" },
65	on_destroy => $done,	65	on_destroy => $done,
66	);	66	);
67		67
68	for my $id (1..6) {	68	for my $id (1..6) {
…		…
137		137
138	And as a final remark, there is a fine module on CPAN that can	138	And as a final remark, there is a fine module on CPAN that can
139	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently	139	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
140	than this example, namely L<IO::AIO>.	140	than this example, namely L<IO::AIO>.
141		141
		142	=head3 Example 1a: the same with the asynchronous backend
		143
		144	This example only shows what needs to be changed to use the async backend
		145	instead. Doing this is not very useful, the purpose of this example is
		146	to show the minimum amount of change that is required to go from the
		147	synchronous to the asynchronous backend.
		148
		149	To use the async backend in the previous example, you need to add the
		150	C<async> parameter to the C<AnyEvent::Fork::RPC::run> call:
		151
		152	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		153	async => 1,
		154	...
		155
		156	And since the function call protocol is now changed, you need to adopt
		157	C<MyWorker::run> to the async API.
		158
		159	First, you need to accept the extra initial C<$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 te
		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
142	=head1 PARENT PROCESS USAGE	379	=head1 PARENT PROCESS USAGE
143		380
144	This module exports nothing, and only implements a single function:	381	This module exports nothing, and only implements a single function:
145		382
146	=over 4	383	=over 4
…		…
153		390
154	use Errno ();	391	use Errno ();
155	use Guard ();	392	use Guard ();
156		393
157	use AnyEvent;	394	use AnyEvent;
158	use AnyEvent::Fork; # we don't actually depend on it, this is for convenience
159		395
160	our $VERSION = 0.1;	396	our $VERSION = 1.1;
161		397
162	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	398	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
163		399
164	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
165	following way:	401	following way:
…		…
185	Called on (fatal) errors, with a descriptive (hopefully) message. If	421	Called on (fatal) errors, with a descriptive (hopefully) message. If
186	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>
187	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>,
188	followed by the error message.	424	followed by the error message.
189		425
190	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
191	start failing badly.	427	C<error> via C<AE::log>.
192		428
193	=item on_event => $cb->(...)	429	=item on_event => $cb->(...)
194		430
195	Called for every call to the C<AnyEvent::Fork::RPC::event> function in the	431	Called for every call to the C<AnyEvent::Fork::RPC::event> function in the
196	child, with the arguments of that function passed to the callback.	432	child, with the arguments of that function passed to the callback.
…		…
224		460
225	The default server used in the child does all I/O blockingly, and only	461	The default server used in the child does all I/O blockingly, and only
226	allows a single RPC call to execute concurrently.	462	allows a single RPC call to execute concurrently.
227		463
228	Setting C<async> to a true value switches to another implementation that	464	Setting C<async> to a true value switches to another implementation that
229	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.	465	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it
		466	does not support recursion in the event loop however, blocking condvar
		467	calls will fail).
230		468
231	The actual API in the child is documented in the section that describes	469	The actual API in the child is documented in the section that describes
232	the calling semantics of the returned C<$rpc> function.	470	the calling semantics of the returned C<$rpc> function.
233		471
234	If you want to pre-load the actual back-end modules to enable memory	472	If you want to pre-load the actual back-end modules to enable memory
…		…
236	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	474	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
237		475
238	If you use a template process and want to fork both sync and async	476	If you use a template process and want to fork both sync and async
239	children, then it is permissible to load both modules.	477	children, then it is permissible to load both modules.
240		478
241	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	479	=item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER)
242		480
243	All arguments, result data and event data have to be serialised to be	481	All arguments, result data and event data have to be serialised to be
244	transferred between the processes. For this, they have to be frozen and	482	transferred between the processes. For this, they have to be frozen and
245	thawed in both parent and child processes.	483	thawed in both parent and child processes.
246		484
247	By default, only octet strings can be passed between the processes, which	485	By default, only octet strings can be passed between the processes, which
248	is reasonably fast and efficient.	486	is reasonably fast and efficient and requires no extra modules.
249		487
250	For more complicated use cases, you can provide your own freeze and thaw	488	For more complicated use cases, you can provide your own freeze and thaw
251	functions, by specifying a string with perl source code. It's supposed to	489	functions, by specifying a string with perl source code. It's supposed to
252	return two code references when evaluated: the first receives a list of	490	return two code references when evaluated: the first receives a list of
253	perl values and must return an octet string. The second receives the octet	491	perl values and must return an octet string. The second receives the octet
…		…
255		493
256	If you need an external module for serialisation, then you can either	494	If you need an external module for serialisation, then you can either
257	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>	495	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
258	or C<require> statement into the serialiser string. Or both.	496	or C<require> statement into the serialiser string. Or both.
259		497
		498	Here are some examples - some of them are also available as global
		499	variables that make them easier to use.
		500
		501	=over 4
		502
		503	=item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER>
		504
		505	This serialiser concatenates length-prefixes octet strings, and is the
		506	default. That means you can only pass (and return) strings containing
		507	character codes 0-255.
		508
		509	Implementation:
		510
		511	(
		512	sub { pack "(w/a)", @_ },
		513	sub { unpack "(w/a)", shift }
		514	)
		515
		516	=item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER>
		517
		518	This serialiser creates JSON arrays - you have to make sure the L<JSON>
		519	module is installed for this serialiser to work. It can be beneficial for
		520	sharing when you preload the L<JSON> module in a template process.
		521
		522	L<JSON> (with L<JSON::XS> installed) is slower than the octet string
		523	serialiser, but usually much faster than L<Storable>, unless big chunks of
		524	binary data need to be transferred.
		525
		526	Implementation:
		527
		528	use JSON ();
		529	(
		530	sub { JSON::encode_json \@_ },
		531	sub { @{ JSON::decode_json shift } }
		532	)
		533
		534	=item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER>
		535
		536	This serialiser uses L<Storable>, which means it has high chance of
		537	serialising just about anything you throw at it, at the cost of having
		538	very high overhead per operation. It also comes with perl. It should be
		539	used when you need to serialise complex data structures.
		540
		541	Implementation:
		542
		543	use Storable ();
		544	(
		545	sub { Storable::freeze \@_ },
		546	sub { @{ Storable::thaw shift } }
		547	)
		548
		549	=item portable storable - C<$AnyEvent::Fork::RPC::NSTORABLE_SERIALISER>
		550
		551	This serialiser also uses L<Storable>, but uses it's "network" format
		552	to serialise data, which makes it possible to talk to different
		553	perl binaries (for example, when talking to a process created with
		554	L<AnyEvent::Fork::Remote>).
		555
		556	Implementation:
		557
		558	use Storable ();
		559	(
		560	sub { Storable::nfreeze \@_ },
		561	sub { @{ Storable::thaw shift } }
		562	)
		563
260	=back	564	=back
261		565
		566	=back
		567
		568	See the examples section earlier in this document for some actual
		569	examples.
		570
262	=cut	571	=cut
263		572
264	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	573	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
		574	our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
		575	our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
		576	our $NSTORABLE_SERIALISER = 'use Storable (); (sub { Storable::nfreeze \@_ }, sub { @{ Storable::thaw shift } })';
265		577
266	sub run {	578	sub run {
267	my ($self, $function, %arg) = @_;	579	my ($self, $function, %arg) = @_;
268		580
269	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;	581	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
…		…
272	my $on_destroy = delete $arg{on_destroy};	584	my $on_destroy = delete $arg{on_destroy};
273		585
274	# default for on_error is to on_event, if specified	586	# default for on_error is to on_event, if specified
275	$on_error \|\|= $on_event	587	$on_error \|\|= $on_event
276	? sub { $on_event->(error => shift) }	588	? sub { $on_event->(error => shift) }
277	: sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" };	589	: sub { AE::log die => "AnyEvent::Fork::RPC: uncaught error: $_[0]." };
278		590
279	# default for on_event is to raise an error	591	# default for on_event is to raise an error
280	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	592	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
281		593
282	my ($f, $t) = eval $serialiser; die $@ if $@;	594	my ($f, $t) = eval $serialiser; die $@ if $@;
283		595
284	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);	596	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
285	my ($rlen, $rbuf) = 512 - 16;	597	my ($rlen, $rbuf, $rw) = 512 - 16;
286		598
287	my $wcb = sub {	599	my $wcb = sub {
288	my $len = syswrite $fh, $wbuf;	600	my $len = syswrite $fh, $wbuf;
289		601
290	if (!defined $len) {	602	unless (defined $len) {
291	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	603	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
292	undef $rw; undef $ww; # it ends here	604	undef $rw; undef $ww; # it ends here
293	$on_error->("$!");	605	$on_error->("$!");
294	}	606	}
295	}	607	}
…		…
306		618
307	$self->require ($module)	619	$self->require ($module)
308	->send_arg ($function, $arg{init}, $serialiser)	620	->send_arg ($function, $arg{init}, $serialiser)
309	->run ("$module\::run", sub {	621	->run ("$module\::run", sub {
310	$fh = shift;	622	$fh = shift;
		623
		624	my ($id, $len);
311	$rw = AE::io $fh, 0, sub {	625	$rw = AE::io $fh, 0, sub {
312	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;	626	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
313	my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;	627	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
314		628
315	if ($len) {	629	if ($len) {
316	while (4 <= length $rbuf) {	630	while (8 <= length $rbuf) {
317	$len = unpack "L", $rbuf;	631	($id, $len) = unpack "NN", $rbuf;
318	4 + $len <= length $rbuf	632	8 + $len <= length $rbuf
319	or last;	633	or last;
320		634
321	my @r = $t->(substr $rbuf, 4, $len);	635	my @r = $t->(substr $rbuf, 8, $len);
322	substr $rbuf, 0, $len + 4, "";	636	substr $rbuf, 0, 8 + $len, "";
		637
		638	if ($id) {
		639	if (@rcb) {
		640	(shift @rcb)->(@r);
		641	} elsif (my $cb = delete $rcb{$id}) {
		642	$cb->(@r);
		643	} else {
		644	undef $rw; undef $ww;
		645	$on_error->("unexpected data from child");
323		646	}
324	if (pop @r) {	647	} else {
325	$on_event->(@r);	648	$on_event->(@r);
326	} elsif (@rcb) {
327	(shift @rcb)->(@r);
328	} else {
329	undef $rw; undef $ww;
330	$on_error->("unexpected data from child");
331	}	649	}
332	}	650	}
333	} elsif (defined $len) {	651	} elsif (defined $len) {
334	undef $rw; undef $ww; # it ends here	652	undef $rw; undef $ww; # it ends here
335		653
336	if (@rcb) {	654	if (@rcb \|\| %rcb) {
337	$on_error->("unexpected eof");	655	$on_error->("unexpected eof");
338	} else {	656	} else {
339	$on_destroy->();	657	$on_destroy->()
		658	if $on_destroy;
340	}	659	}
341	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	660	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
342	undef $rw; undef $ww; # it ends here	661	undef $rw; undef $ww; # it ends here
343	$on_error->("read: $!");	662	$on_error->("read: $!");
344	}	663	}
…		…
347	$ww \|\|= AE::io $fh, 1, $wcb;	666	$ww \|\|= AE::io $fh, 1, $wcb;
348	});	667	});
349		668
350	my $guard = Guard::guard {	669	my $guard = Guard::guard {
351	$shutdown = 1;	670	$shutdown = 1;
352	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	671
		672	shutdown $fh, 1 if $fh && !$ww;
353	};	673	};
354		674
		675	my $id;
		676
		677	$arg{async}
355	sub {	678	? sub {
356	push @rcb, pop;	679	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		680	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
357		681
		682	$rcb{$id} = pop;
		683
358	$guard; # keep it alive	684	$guard if 0; # keep it alive
359		685
360	$wbuf .= pack "L/a*", &$f;	686	$wbuf .= pack "NN/a*", $id, &$f;
361	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	687	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
362	}	688	}
		689	: sub {
		690	push @rcb, pop;
		691
		692	$guard; # keep it alive
		693
		694	$wbuf .= pack "N/a*", &$f;
		695	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		696	}
363	}	697	}
364		698
365	=item $rpc->(..., $cb->(...))	699	=item $rpc->(..., $cb->(...))
366		700
367	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code	701	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
…		…
382		716
383	The other thing that can be done with the RPC object is to destroy it. In	717	The other thing that can be done with the RPC object is to destroy it. In
384	this case, the child process will execute all remaining RPC calls, report	718	this case, the child process will execute all remaining RPC calls, report
385	their results, and then exit.	719	their results, and then exit.
386		720
		721	See the examples section earlier in this document for some actual
		722	examples.
		723
387	=back	724	=back
388		725
389	=head1 CHILD PROCESS USAGE	726	=head1 CHILD PROCESS USAGE
390		727
391	The following function is not available in this module. They are only	728	The following function is not available in this module. They are only
…		…
399		736
400	Send an event to the parent. Events are a bit like RPC calls made by the	737	Send an event to the parent. Events are a bit like RPC calls made by the
401	child process to the parent, except that there is no notion of return	738	child process to the parent, except that there is no notion of return
402	values.	739	values.
403		740
		741	See the examples section earlier in this document for some actual
		742	examples.
		743
404	=back	744	=back
405		745
		746	=head1 ADVANCED TOPICS
		747
		748	=head2 Choosing a backend
		749
		750	So how do you decide which backend to use? Well, that's your problem to
		751	solve, but here are some thoughts on the matter:
		752
		753	=over 4
		754
		755	=item Synchronous
		756
		757	The synchronous backend does not rely on any external modules (well,
		758	except L<common::sense>, which works around a bug in how perl's warning
		759	system works). This keeps the process very small, for example, on my
		760	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		761	after C<use warnings; use strict> (for people who grew up with C64s around
		762	them this is probably shocking every single time they see it). The worker
		763	process in the first example in this document uses 1792kB.
		764
		765	Since the calls are done synchronously, slow jobs will keep newer jobs
		766	from executing.
		767
		768	The synchronous backend also has no overhead due to running an event loop
		769	- reading requests is therefore very efficient, while writing responses is
		770	less so, as every response results in a write syscall.
		771
		772	If the parent process is busy and a bit slow reading responses, the child
		773	waits instead of processing further requests. This also limits the amount
		774	of memory needed for buffering, as never more than one response has to be
		775	buffered.
		776
		777	The API in the child is simple - you just have to define a function that
		778	does something and returns something.
		779
		780	It's hard to use modules or code that relies on an event loop, as the
		781	child cannot execute anything while it waits for more input.
		782
		783	=item Asynchronous
		784
		785	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		786	but still comes at a price: On my system, the worker from example 1a uses
		787	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		788	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		789	L<vars>, L<Exporter>...).
		790
		791	It batches requests and responses reasonably efficiently, doing only as
		792	few reads and writes as needed, but needs to poll for events via the event
		793	loop.
		794
		795	Responses are queued when the parent process is busy. This means the child
		796	can continue to execute any queued requests. It also means that a child
		797	might queue a lot of responses in memory when it generates them and the
		798	parent process is slow accepting them.
		799
		800	The API is not a straightforward RPC pattern - you have to call a
		801	"done" callback to pass return values and signal completion. Also, more
		802	importantly, the API starts jobs as fast as possible - when 1000 jobs
		803	are queued and the jobs are slow, they will all run concurrently. The
		804	child must implement some queueing/limiting mechanism if this causes
		805	problems. Alternatively, the parent could limit the amount of rpc calls
		806	that are outstanding.
		807
		808	Blocking use of condvars is not supported.
		809
		810	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		811	easy.
		812
		813	=back
		814
		815	=head2 Passing file descriptors
		816
		817	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		818	descriptor passing abilities.
		819
		820	The reason is that passing file descriptors is extraordinary tricky
		821	business, and conflicts with efficient batching of messages.
		822
		823	There still is a method you can use: Create a
		824	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		825	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		826
		827	Whenever you want to pass a file descriptor, send an rpc request to the
		828	child process (so it expects the descriptor), then send it over the other
		829	half of the socketpair. The child should fetch the descriptor from the
		830	half it has passed earlier.
		831
		832	Here is some (untested) pseudocode to that effect:
		833
		834	use AnyEvent::Util;
		835	use AnyEvent::Fork;
		836	use AnyEvent::Fork::RPC;
		837	use IO::FDPass;
		838
		839	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		840
		841	my $rpc = AnyEvent::Fork
		842	->new
		843	->send_fh ($s2)
		844	->require ("MyWorker")
		845	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		846	init => "MyWorker::init",
		847	);
		848
		849	undef $s2; # no need to keep it around
		850
		851	# pass an fd
		852	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		853
		854	IO::FDPass fileno $s1, fileno $handle_to_pass;
		855
		856	$cv->recv;
		857
		858	The MyWorker module could look like this:
		859
		860	package MyWorker;
		861
		862	use IO::FDPass;
		863
		864	my $s2;
		865
		866	sub init {
		867	$s2 = $_[0];
		868	}
		869
		870	sub run {
		871	if ($_[0] eq "i'll send some fd now, please expect it!") {
		872	my $fd = IO::FDPass::recv fileno $s2;
		873	...
		874	}
		875	}
		876
		877	Of course, this might be blocking if you pass a lot of file descriptors,
		878	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		879	gory details.
		880
		881	=head1 EXCEPTIONS
		882
		883	There are no provisions whatsoever for catching exceptions at this time -
		884	in the child, exeptions might kill the process, causing calls to be lost
		885	and the parent encountering a fatal error. In the parent, exceptions in
		886	the result callback will not be caught and cause undefined behaviour.
		887
406	=head1 SEE ALSO	888	=head1 SEE ALSO
407		889
408	L<AnyEvent::Fork> (to create the processes in the first place),	890	L<AnyEvent::Fork>, to create the processes in the first place.
		891
		892	L<AnyEvent::Fork::Remote>, likewise, but helpful for remote processes.
		893
409	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	894	L<AnyEvent::Fork::Pool>, to manage whole pools of processes.
410		895
411	=head1 AUTHOR AND CONTACT INFORMATION	896	=head1 AUTHOR AND CONTACT INFORMATION
412		897
413	Marc Lehmann <schmorp@schmorp.de>	898	Marc Lehmann <schmorp@schmorp.de>
414	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC	899	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents): Revision 1.7 by root, Wed Apr 17 20:19:41 2013 UTC vs. Revision 1.30 by root, Sun Aug 25 22:21:15 2013 UTC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.7 by root, Wed Apr 17 20:19:41 2013 UTC vs.
Revision 1.30 by root, Sun Aug 25 22:21:15 2013 UTC