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

Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.3 by root, Wed Apr 17 17:16:48 2013 UTC vs.
Revision 1.29 by root, Sun Aug 25 21:52:15 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
		42	=head1 EXAMPLES
		43
		44	=head2 Example 1: Synchronous Backend
		45
		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
		48	number of requests it has processed every three requests, which is clearly
		49	silly, but illustrates the use of events.
		50
		51	First the parent process:
		52
		53	use AnyEvent;
		54	use AnyEvent::Fork;
		55	use AnyEvent::Fork::RPC;
		56
		57	my $done = AE::cv;
		58
		59	my $rpc = AnyEvent::Fork
		60	->new
		61	->require ("MyWorker")
		62	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		63	on_error => sub { warn "ERROR: $_[0]"; exit 1 },
		64	on_event => sub { warn "$_[0] requests handled\n" },
		65	on_destroy => $done,
		66	);
		67
		68	for my $id (1..6) {
		69	$rpc->(rmdir => "/tmp/somepath/$id", sub {
		70	$_[0]
		71	or warn "/tmp/somepath/$id: $_[1]\n";
		72	});
		73	}
		74
		75	undef $rpc;
		76
		77	$done->recv;
		78
		79	The parent creates the process, queues a few rmdir's. It then forgets
		80	about the C<$rpc> object, so that the child exits after it has handled the
		81	requests, and then it waits till the requests have been handled.
		82
		83	The child is implemented using a separate module, C<MyWorker>, shown here:
		84
		85	package MyWorker;
		86
		87	my $count;
		88
		89	sub run {
		90	my ($cmd, $path) = @_;
		91
		92	AnyEvent::Fork::RPC::event ($count)
		93	unless ++$count % 3;
		94
		95	my $status = $cmd eq "rmdir" ? rmdir $path
		96	: $cmd eq "unlink" ? unlink $path
		97	: die "fatal error, illegal command '$cmd'";
		98
		99	$status or (0, "$!")
		100	}
		101
		102	1
		103
		104	The C<run> function first sends a "progress" event every three calls, and
		105	then executes C<rmdir> or C<unlink>, depending on the first parameter (or
		106	dies with a fatal error - obviously, you must never let this happen :).
		107
		108	Eventually it returns the status value true if the command was successful,
		109	or the status value 0 and the stringified error message.
		110
		111	On my system, running the first code fragment with the given
		112	F<MyWorker.pm> in the current directory yields:
		113
		114	/tmp/somepath/1: No such file or directory
		115	/tmp/somepath/2: No such file or directory
		116	3 requests handled
		117	/tmp/somepath/3: No such file or directory
		118	/tmp/somepath/4: No such file or directory
		119	/tmp/somepath/5: No such file or directory
		120	6 requests handled
		121	/tmp/somepath/6: No such file or directory
		122
		123	Obviously, none of the directories I am trying to delete even exist. Also,
		124	the events and responses are processed in exactly the same order as
		125	they were created in the child, which is true for both synchronous and
		126	asynchronous backends.
		127
		128	Note that the parentheses in the call to C<AnyEvent::Fork::RPC::event> are
		129	not optional. That is because the function isn't defined when the code is
		130	compiled. You can make sure it is visible by pre-loading the correct
		131	backend module in the call to C<require>:
		132
		133	->require ("AnyEvent::Fork::RPC::Sync", "MyWorker")
		134
		135	Since the backend module declares the C<event> function, loading it first
		136	ensures that perl will correctly interpret calls to it.
		137
		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
		140	than this example, namely L<IO::AIO>.
		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
39	=head1 PARENT PROCESS USAGE	341	=head1 PARENT PROCESS USAGE
40		342
41	This module exports nothing, and only implements a single function:	343	This module exports nothing, and only implements a single function:
42		344
43	=over 4	345	=over 4
…		…
50		352
51	use Errno ();	353	use Errno ();
52	use Guard ();	354	use Guard ();
53		355
54	use AnyEvent;	356	use AnyEvent;
55	#use AnyEvent::Fork;
56		357
57	our $VERSION = 0.1;	358	our $VERSION = 1.1;
58		359
59	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	360	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
60		361
61	The traditional way to call it. But it is way cooler to call it in the	362	The traditional way to call it. But it is way cooler to call it in the
62	following way:	363	following way:
…		…
82	Called on (fatal) errors, with a descriptive (hopefully) message. If	383	Called on (fatal) errors, with a descriptive (hopefully) message. If
83	this callback is not provided, but C<on_event> is, then the C<on_event>	384	this callback is not provided, but C<on_event> is, then the C<on_event>
84	callback is called with the first argument being the string C<error>,	385	callback is called with the first argument being the string C<error>,
85	followed by the error message.	386	followed by the error message.
86		387
87	If neither handler is provided it prints the error to STDERR and will	388	If neither handler is provided, then the error is reported with loglevel
88	start failing badly.	389	C<error> via C<AE::log>.
89		390
90	=item on_event => $cb->(...)	391	=item on_event => $cb->(...)
91		392
92	Called for every call to the C<AnyEvent::Fork::RPC::event> function in the	393	Called for every call to the C<AnyEvent::Fork::RPC::event> function in the
93	child, with the arguments of that function passed to the callback.	394	child, with the arguments of that function passed to the callback.
94		395
95	Also called on errors when no C<on_error> handler is provided.	396	Also called on errors when no C<on_error> handler is provided.
		397
		398	=item on_destroy => $cb->()
		399
		400	Called when the C<$rpc> object has been destroyed and all requests have
		401	been successfully handled. This is useful when you queue some requests and
		402	want the child to go away after it has handled them. The problem is that
		403	the parent must not exit either until all requests have been handled, and
		404	this can be accomplished by waiting for this callback.
96		405
97	=item init => $function (default none)	406	=item init => $function (default none)
98		407
99	When specified (by name), this function is called in the child as the very	408	When specified (by name), this function is called in the child as the very
100	first thing when taking over the process, with all the arguments normally	409	first thing when taking over the process, with all the arguments normally
…		…
102	socket.	411	socket.
103		412
104	It can be used to do one-time things in the child such as storing passed	413	It can be used to do one-time things in the child such as storing passed
105	parameters or opening database connections.	414	parameters or opening database connections.
106		415
		416	It is called very early - before the serialisers are created or the
		417	C<$function> name is resolved into a function reference, so it could be
		418	used to load any modules that provide the serialiser or function. It can
		419	not, however, create events.
		420
107	=item async => $boolean (default: 0)	421	=item async => $boolean (default: 0)
108		422
109	The default server used in the child does all I/O blockingly, and only	423	The default server used in the child does all I/O blockingly, and only
110	allows a single RPC call to execute concurrently.	424	allows a single RPC call to execute concurrently.
111		425
112	Setting C<async> to a true value switches to another implementation that	426	Setting C<async> to a true value switches to another implementation that
113	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.	427	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it
		428	does not support recursion in the event loop however, blocking condvar
		429	calls will fail).
114		430
115	The actual API in the child is documented in the section that describes	431	The actual API in the child is documented in the section that describes
116	the calling semantics of the returned C<$rpc> function.	432	the calling semantics of the returned C<$rpc> function.
117		433
118	If you want to pre-load the actual back-end modules to enable memory	434	If you want to pre-load the actual back-end modules to enable memory
119	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for	435	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
120	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	436	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
121		437
122	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	438	If you use a template process and want to fork both sync and async
		439	children, then it is permissible to load both modules.
		440
		441	=item serialiser => $string (default: $AnyEvent::Fork::RPC::STRING_SERIALISER)
123		442
124	All arguments, result data and event data have to be serialised to be	443	All arguments, result data and event data have to be serialised to be
125	transferred between the processes. For this, they have to be frozen and	444	transferred between the processes. For this, they have to be frozen and
126	thawed in both parent and child processes.	445	thawed in both parent and child processes.
127		446
128	By default, only octet strings can be passed between the processes, which	447	By default, only octet strings can be passed between the processes, which
129	is reasonably fast and efficient.	448	is reasonably fast and efficient and requires no extra modules.
130		449
131	For more complicated use cases, you can provide your own freeze and thaw	450	For more complicated use cases, you can provide your own freeze and thaw
132	functions, by specifying a string with perl source code. It's supposed to	451	functions, by specifying a string with perl source code. It's supposed to
133	return two code references when evaluated: the first receives a list of	452	return two code references when evaluated: the first receives a list of
134	perl values and must return an octet string. The second receives the octet	453	perl values and must return an octet string. The second receives the octet
…		…
136		455
137	If you need an external module for serialisation, then you can either	456	If you need an external module for serialisation, then you can either
138	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>	457	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
139	or C<require> statement into the serialiser string. Or both.	458	or C<require> statement into the serialiser string. Or both.
140		459
		460	Here are some examples - some of them are also available as global
		461	variables that make them easier to use.
		462
		463	=over 4
		464
		465	=item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER>
		466
		467	This serialiser concatenates length-prefixes octet strings, and is the
		468	default. That means you can only pass (and return) strings containing
		469	character codes 0-255.
		470
		471	Implementation:
		472
		473	(
		474	sub { pack "(w/a)", @_ },
		475	sub { unpack "(w/a)", shift }
		476	)
		477
		478	=item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER>
		479
		480	This serialiser creates JSON arrays - you have to make sure the L<JSON>
		481	module is installed for this serialiser to work. It can be beneficial for
		482	sharing when you preload the L<JSON> module in a template process.
		483
		484	L<JSON> (with L<JSON::XS> installed) is slower than the octet string
		485	serialiser, but usually much faster than L<Storable>, unless big chunks of
		486	binary data need to be transferred.
		487
		488	Implementation:
		489
		490	use JSON ();
		491	(
		492	sub { JSON::encode_json \@_ },
		493	sub { @{ JSON::decode_json shift } }
		494	)
		495
		496	=item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER>
		497
		498	This serialiser uses L<Storable>, which means it has high chance of
		499	serialising just about anything you throw at it, at the cost of having
		500	very high overhead per operation. It also comes with perl. It should be
		501	used when you need to serialise complex data structures.
		502
		503	Implementation:
		504
		505	use Storable ();
		506	(
		507	sub { Storable::freeze \@_ },
		508	sub { @{ Storable::thaw shift } }
		509	)
		510
		511	=item portable storable - C<$AnyEvent::Fork::RPC::NSTORABLE_SERIALISER>
		512
		513	This serialiser also uses L<Storable>, but uses it's "network" format
		514	to serialise data, which makes it possible to talk to different
		515	perl binaries (for example, when talking to a process created with
		516	L<AnyEvent::Fork::Remote>).
		517
		518	Implementation:
		519
		520	use Storable ();
		521	(
		522	sub { Storable::nfreeze \@_ },
		523	sub { @{ Storable::thaw shift } }
		524	)
		525
141	=back	526	=back
142		527
		528	=back
		529
		530	See the examples section earlier in this document for some actual
		531	examples.
		532
143	=cut	533	=cut
144		534
145	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	535	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
146		536	our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
147	# ideally, we want (SvLEN - SvCUR) \|\| 1024 or somesuch...	537	our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
148	sub rlen($) { ($_[0] < 384 ? 512 + 16 : 2 << int +(log $_[0] + 512) / log 2) - $_[0] - 16 }	538	our $NSTORABLE_SERIALISER = 'use Storable (); (sub { Storable::nfreeze \@_ }, sub { @{ Storable::thaw shift } })';
149		539
150	sub run {	540	sub run {
151	my ($self, $function, %arg) = @_;	541	my ($self, $function, %arg) = @_;
152		542
153	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;	543	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
154	my $on_event = delete $arg{on_event};	544	my $on_event = delete $arg{on_event};
155	my $on_error = delete $arg{on_error};	545	my $on_error = delete $arg{on_error};
		546	my $on_destroy = delete $arg{on_destroy};
156		547
157	# default for on_error is to on_event, if specified	548	# default for on_error is to on_event, if specified
158	$on_error \|\|= $on_event	549	$on_error \|\|= $on_event
159	? sub { $on_event->(error => shift) }	550	? sub { $on_event->(error => shift) }
160	: sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" };	551	: sub { AE::log die => "AnyEvent::Fork::RPC: uncaught error: $_[0]." };
161		552
162	# default for on_event is to raise an error	553	# default for on_event is to raise an error
163	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	554	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
164		555
165	my ($f, $t) = eval $serialiser; die $@ if $@;	556	my ($f, $t) = eval $serialiser; die $@ if $@;
166		557
167	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rbuf, $rw);	558	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
		559	my ($rlen, $rbuf, $rw) = 512 - 16;
168		560
169	my $wcb = sub {	561	my $wcb = sub {
170	my $len = syswrite $fh, $wbuf;	562	my $len = syswrite $fh, $wbuf;
171		563
172	if (!defined $len) {	564	unless (defined $len) {
173	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	565	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
174	undef $rw; undef $ww; # it ends here	566	undef $rw; undef $ww; # it ends here
175	$on_error->("$!");	567	$on_error->("$!");
176	}	568	}
177	}	569	}
…		…
188		580
189	$self->require ($module)	581	$self->require ($module)
190	->send_arg ($function, $arg{init}, $serialiser)	582	->send_arg ($function, $arg{init}, $serialiser)
191	->run ("$module\::run", sub {	583	->run ("$module\::run", sub {
192	$fh = shift;	584	$fh = shift;
		585
		586	my ($id, $len);
193	$rw = AE::io $fh, 0, sub {	587	$rw = AE::io $fh, 0, sub {
		588	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
194	my $len = sysread $fh, $rbuf, rlen length $rbuf, length $rbuf;	589	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
195		590
196	if ($len) {	591	if ($len) {
197	while (5 <= length $rbuf) {	592	while (8 <= length $rbuf) {
198	$len = unpack "L", $rbuf;	593	($id, $len) = unpack "NN", $rbuf;
199	4 + $len <= length $rbuf	594	8 + $len <= length $rbuf
200	or last;	595	or last;
201		596
202	my @r = $t->(substr $rbuf, 4, $len);	597	my @r = $t->(substr $rbuf, 8, $len);
203	substr $rbuf, 0, $len + 4, "";	598	substr $rbuf, 0, 8 + $len, "";
		599
		600	if ($id) {
		601	if (@rcb) {
		602	(shift @rcb)->(@r);
		603	} elsif (my $cb = delete $rcb{$id}) {
		604	$cb->(@r);
		605	} else {
		606	undef $rw; undef $ww;
		607	$on_error->("unexpected data from child");
204		608	}
205	if (pop @r) {	609	} else {
206	$on_event->(@r);	610	$on_event->(@r);
207	} elsif (@rcb) {
208	(shift @rcb)->(@r);
209	} else {
210	undef $rw; undef $ww;
211	$on_error->("unexpected data from child");
212	}	611	}
213	}	612	}
214	} elsif (defined $len) {	613	} elsif (defined $len) {
215	undef $rw; undef $ww; # it ends here	614	undef $rw; undef $ww; # it ends here
		615
		616	if (@rcb \|\| %rcb) {
216	$on_error->("unexpected eof")	617	$on_error->("unexpected eof");
217	if @rcb;	618	} else {
		619	$on_destroy->()
		620	if $on_destroy;
		621	}
218	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	622	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
219	undef $rw; undef $ww; # it ends here	623	undef $rw; undef $ww; # it ends here
220	$on_error->("read: $!");	624	$on_error->("read: $!");
221	}	625	}
222	};	626	};
…		…
224	$ww \|\|= AE::io $fh, 1, $wcb;	628	$ww \|\|= AE::io $fh, 1, $wcb;
225	});	629	});
226		630
227	my $guard = Guard::guard {	631	my $guard = Guard::guard {
228	$shutdown = 1;	632	$shutdown = 1;
229	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	633
		634	shutdown $fh, 1 if $fh && !$ww;
230	};	635	};
231		636
		637	my $id;
		638
		639	$arg{async}
232	sub {	640	? sub {
233	push @rcb, pop;	641	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		642	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
234		643
		644	$rcb{$id} = pop;
		645
235	$guard; # keep it alive	646	$guard if 0; # keep it alive
236		647
237	$wbuf .= pack "L/a*", &$f;	648	$wbuf .= pack "NN/a*", $id, &$f;
238	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	649	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
239	}	650	}
		651	: sub {
		652	push @rcb, pop;
		653
		654	$guard; # keep it alive
		655
		656	$wbuf .= pack "N/a*", &$f;
		657	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		658	}
240	}	659	}
241		660
		661	=item $rpc->(..., $cb->(...))
		662
		663	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
		664	reference. There are two things you can do with it: call it, and let it go
		665	out of scope (let it get destroyed).
		666
		667	If C<async> was false when C<$rpc> was created (the default), then, if you
		668	call C<$rpc>, the C<$function> is invoked with all arguments passed to
		669	C<$rpc> except the last one (the callback). When the function returns, the
		670	callback will be invoked with all the return values.
		671
		672	If C<async> was true, then the C<$function> receives an additional
		673	initial argument, the result callback. In this case, returning from
		674	C<$function> does nothing - the function only counts as "done" when the
		675	result callback is called, and any arguments passed to it are considered
		676	the return values. This makes it possible to "return" from event handlers
		677	or e.g. Coro threads.
		678
		679	The other thing that can be done with the RPC object is to destroy it. In
		680	this case, the child process will execute all remaining RPC calls, report
		681	their results, and then exit.
		682
		683	See the examples section earlier in this document for some actual
		684	examples.
		685
242	=back	686	=back
243		687
244	=head1 CHILD PROCESS USAGE	688	=head1 CHILD PROCESS USAGE
245		689
246	These functions are not available in this module. They are only available	690	The following function is not available in this module. They are only
247	in the namespace of this module when the child is running, without	691	available in the namespace of this module when the child is running,
248	having to load any extra module. They are part of the child-side API of	692	without having to load any extra modules. They are part of the child-side
249	L<AnyEvent::Fork::RPC>.	693	API of L<AnyEvent::Fork::RPC>.
250		694
251	=over 4	695	=over 4
252		696
253	=item AnyEvent::Fork::RPC::event ...	697	=item AnyEvent::Fork::RPC::event ...
254		698
255	Send an event to the parent. Events are a bit like RPC calls made by the	699	Send an event to the parent. Events are a bit like RPC calls made by the
256	child process to the parent, except that there is no notion of return	700	child process to the parent, except that there is no notion of return
257	values.	701	values.
258		702
		703	See the examples section earlier in this document for some actual
		704	examples.
		705
259	=back	706	=back
260		707
		708	=head1 ADVANCED TOPICS
		709
		710	=head2 Choosing a backend
		711
		712	So how do you decide which backend to use? Well, that's your problem to
		713	solve, but here are some thoughts on the matter:
		714
		715	=over 4
		716
		717	=item Synchronous
		718
		719	The synchronous backend does not rely on any external modules (well,
		720	except L<common::sense>, which works around a bug in how perl's warning
		721	system works). This keeps the process very small, for example, on my
		722	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		723	after C<use warnings; use strict> (for people who grew up with C64s around
		724	them this is probably shocking every single time they see it). The worker
		725	process in the first example in this document uses 1792kB.
		726
		727	Since the calls are done synchronously, slow jobs will keep newer jobs
		728	from executing.
		729
		730	The synchronous backend also has no overhead due to running an event loop
		731	- reading requests is therefore very efficient, while writing responses is
		732	less so, as every response results in a write syscall.
		733
		734	If the parent process is busy and a bit slow reading responses, the child
		735	waits instead of processing further requests. This also limits the amount
		736	of memory needed for buffering, as never more than one response has to be
		737	buffered.
		738
		739	The API in the child is simple - you just have to define a function that
		740	does something and returns something.
		741
		742	It's hard to use modules or code that relies on an event loop, as the
		743	child cannot execute anything while it waits for more input.
		744
		745	=item Asynchronous
		746
		747	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		748	but still comes at a price: On my system, the worker from example 1a uses
		749	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		750	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		751	L<vars>, L<Exporter>...).
		752
		753	It batches requests and responses reasonably efficiently, doing only as
		754	few reads and writes as needed, but needs to poll for events via the event
		755	loop.
		756
		757	Responses are queued when the parent process is busy. This means the child
		758	can continue to execute any queued requests. It also means that a child
		759	might queue a lot of responses in memory when it generates them and the
		760	parent process is slow accepting them.
		761
		762	The API is not a straightforward RPC pattern - you have to call a
		763	"done" callback to pass return values and signal completion. Also, more
		764	importantly, the API starts jobs as fast as possible - when 1000 jobs
		765	are queued and the jobs are slow, they will all run concurrently. The
		766	child must implement some queueing/limiting mechanism if this causes
		767	problems. Alternatively, the parent could limit the amount of rpc calls
		768	that are outstanding.
		769
		770	Blocking use of condvars is not supported.
		771
		772	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		773	easy.
		774
		775	=back
		776
		777	=head2 Passing file descriptors
		778
		779	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		780	descriptor passing abilities.
		781
		782	The reason is that passing file descriptors is extraordinary tricky
		783	business, and conflicts with efficient batching of messages.
		784
		785	There still is a method you can use: Create a
		786	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		787	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		788
		789	Whenever you want to pass a file descriptor, send an rpc request to the
		790	child process (so it expects the descriptor), then send it over the other
		791	half of the socketpair. The child should fetch the descriptor from the
		792	half it has passed earlier.
		793
		794	Here is some (untested) pseudocode to that effect:
		795
		796	use AnyEvent::Util;
		797	use AnyEvent::Fork;
		798	use AnyEvent::Fork::RPC;
		799	use IO::FDPass;
		800
		801	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		802
		803	my $rpc = AnyEvent::Fork
		804	->new
		805	->send_fh ($s2)
		806	->require ("MyWorker")
		807	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		808	init => "MyWorker::init",
		809	);
		810
		811	undef $s2; # no need to keep it around
		812
		813	# pass an fd
		814	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		815
		816	IO::FDPass fileno $s1, fileno $handle_to_pass;
		817
		818	$cv->recv;
		819
		820	The MyWorker module could look like this:
		821
		822	package MyWorker;
		823
		824	use IO::FDPass;
		825
		826	my $s2;
		827
		828	sub init {
		829	$s2 = $_[0];
		830	}
		831
		832	sub run {
		833	if ($_[0] eq "i'll send some fd now, please expect it!") {
		834	my $fd = IO::FDPass::recv fileno $s2;
		835	...
		836	}
		837	}
		838
		839	Of course, this might be blocking if you pass a lot of file descriptors,
		840	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		841	gory details.
		842
		843	=head1 EXCEPTIONS
		844
		845	There are no provisions whatsoever for catching exceptions at this time -
		846	in the child, exeptions might kill the process, causing calls to be lost
		847	and the parent encountering a fatal error. In the parent, exceptions in
		848	the result callback will not be caught and cause undefined behaviour.
		849
261	=head1 SEE ALSO	850	=head1 SEE ALSO
262		851
263	L<AnyEvent::Fork> (to create the processes in the first place),	852	L<AnyEvent::Fork>, to create the processes in the first place.
		853
		854	L<AnyEvent::Fork::Remote>, likewise, but helpful for remote processes.
		855
264	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	856	L<AnyEvent::Fork::Pool>, to manage whole pools of processes.
265		857
266	=head1 AUTHOR AND CONTACT INFORMATION	858	=head1 AUTHOR AND CONTACT INFORMATION
267		859
268	Marc Lehmann <schmorp@schmorp.de>	860	Marc Lehmann <schmorp@schmorp.de>
269	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC	861	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents): Revision 1.3 by root, Wed Apr 17 17:16:48 2013 UTC vs. Revision 1.29 by root, Sun Aug 25 21:52:15 2013 UTC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.3 by root, Wed Apr 17 17:16:48 2013 UTC vs.
Revision 1.29 by root, Sun Aug 25 21:52:15 2013 UTC