[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 1.46 by root, Sun Sep 15 20:18:14 2019 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 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 function is there using C<defined>, and only then uses it to
		377	log the message.
		378
39	=head1 PARENT PROCESS USAGE	379	=head1 PARENT PROCESS USAGE
40		380
41	This module exports nothing, and only implements a single function:	381	This module exports nothing, and only implements a single function:
42		382
43	=over 4	383	=over 4
…		…
50		390
51	use Errno ();	391	use Errno ();
52	use Guard ();	392	use Guard ();
53		393
54	use AnyEvent;	394	use AnyEvent;
55	#use AnyEvent::Fork;
56		395
57	our $VERSION = 0.1;	396	our $VERSION = '2.0';
58		397
59	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	398	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
60		399
61	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
62	following way:	401	following way:
…		…
82	Called on (fatal) errors, with a descriptive (hopefully) message. If	421	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>	422	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>,	423	callback is called with the first argument being the string C<error>,
85	followed by the error message.	424	followed by the error message.
86		425
87	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
88	start failing badly.	427	C<error> via C<AE::log>.
89		428
90	=item on_event => $cb->(...)	429	=item on_event => $cb->(...)
91		430
92	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
93	child, with the arguments of that function passed to the callback.	432	child, with the arguments of that function passed to the callback.
94		433
95	Also called on errors when no C<on_error> handler is provided.	434	Also called on errors when no C<on_error> handler is provided.
96		435
		436	=item on_destroy => $cb->()
		437
		438	Called when the C<$rpc> object has been destroyed and all requests have
		439	been successfully handled. This is useful when you queue some requests and
		440	want the child to go away after it has handled them. The problem is that
		441	the parent must not exit either until all requests have been handled, and
		442	this can be accomplished by waiting for this callback.
		443
97	=item init => $function (default none)	444	=item init => $function (default: none)
98		445
99	When specified (by name), this function is called in the child as the very	446	When specified (by name), this function is called in the child as the very
100	first thing when taking over the process, with all the arguments normally	447	first thing when taking over the process, with all the arguments normally
101	passed to the C<AnyEvent::Fork::run> function, except the communications	448	passed to the C<AnyEvent::Fork::run> function, except the communications
102	socket.	449	socket.
103		450
104	It can be used to do one-time things in the child such as storing passed	451	It can be used to do one-time things in the child such as storing passed
105	parameters or opening database connections.	452	parameters or opening database connections.
106		453
		454	It is called very early - before the serialisers are created or the
		455	C<$function> name is resolved into a function reference, so it could be
		456	used to load any modules that provide the serialiser or function. It can
		457	not, however, create events.
		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 is 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::run> 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
107	=item async => $boolean (default: 0)	473	=item async => $boolean (default: C<0>)
108		474
109	The default server used in the child does all I/O blockingly, and only	475	The default server used in the child does all I/O blockingly, and only
110	allows a single RPC call to execute concurrently.	476	allows a single RPC call to execute concurrently.
111		477
112	Setting C<async> to a true value switches to another implementation that	478	Setting C<async> to a true value switches to another implementation that
113	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls.	479	uses L<AnyEvent> in the child and allows multiple concurrent RPC calls (it
		480	does not support recursion in the event loop however, blocking condvar
		481	calls will fail).
114		482
115	The actual API in the child is documented in the section that describes	483	The actual API in the child is documented in the section that describes
116	the calling semantics of the returned C<$rpc> function.	484	the calling semantics of the returned C<$rpc> function.
117		485
118	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
119	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for	487	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
120	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	488	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
121		489
122	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	490	If you use a template process and want to fork both sync and async
		491	children, then it is permissible to load both modules.
		492
		493	=item serialiser => $string (default: C<$AnyEvent::Fork::RPC::STRING_SERIALISER>)
123		494
124	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
125	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
126	thawed in both parent and child processes.	497	thawed in both parent and child processes.
127		498
128	By default, only octet strings can be passed between the processes, which	499	By default, only octet strings can be passed between the processes,
129	is reasonably fast and efficient.	500	which is reasonably fast and efficient and requires no extra modules
		501	(the C<AnyEvent::Fork::RPC> distribution does not provide these extra
		502	serialiser modules).
130		503
131	For more complicated use cases, you can provide your own freeze and thaw	504	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	505	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	506	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	507	perl values and must return an octet string. The second receives the octet
…		…
136		509
137	If you need an external module for serialisation, then you can either	510	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>	511	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.	512	or C<require> statement into the serialiser string. Or both.
140		513
		514	Here are some examples - all of them are also available as global
		515	variables that make them easier to use.
		516
		517	=over 4
		518
		519	=item C<$AnyEvent::Fork::RPC::STRING_SERIALISER> - octet strings only
		520
		521	This serialiser (currently the default) concatenates length-prefixes octet
		522	strings, and is the default. That means you can only pass (and return)
		523	strings containing character codes 0-255.
		524
		525	The main advantages of this serialiser are the high speed and that it
		526	doesn't need another module. The main disadvantage is that you are very
		527	limited in what you can pass - only octet strings.
		528
		529	Implementation:
		530
		531	(
		532	sub { pack "(w/a)", @_ },
		533	sub { unpack "(w/a)", shift }
		534	)
		535
		536	=item C<$AnyEvent::Fork::RPC::CBOR_XS_SERIALISER> - uses L<CBOR::XS>
		537
		538	This serialiser creates CBOR::XS arrays - you have to make sure the
		539	L<CBOR::XS> module is installed for this serialiser to work. It can be
		540	beneficial for sharing when you preload the L<CBOR::XS> module in a template
		541	process.
		542
		543	L<CBOR::XS> is about as fast as the octet string serialiser, but supports
		544	complex data structures (similar to JSON) and is faster than any of the
		545	other serialisers. If you have the L<CBOR::XS> module available, it's the
		546	best choice.
		547
		548	The encoder enables C<allow_sharing> (so this serialisation method can
		549	encode cyclic and self-referencing data structures).
		550
		551	Implementation:
		552
		553	use CBOR::XS ();
		554	(
		555	sub { CBOR::XS::encode_cbor_sharing \@_ },
		556	sub { @{ CBOR::XS::decode_cbor shift } }
		557	)
		558
		559	=item C<$AnyEvent::Fork::RPC::JSON_SERIALISER> - uses L<JSON::XS> or L<JSON>
		560
		561	This serialiser creates JSON arrays - you have to make sure the L<JSON>
		562	module is installed for this serialiser to work. It can be beneficial for
		563	sharing when you preload the L<JSON> module in a template process.
		564
		565	L<JSON> (with L<JSON::XS> installed) is slower than the octet string
		566	serialiser, but usually much faster than L<Storable>, unless big chunks of
		567	binary data need to be transferred.
		568
		569	Implementation:
		570
		571	use JSON ();
		572	(
		573	sub { JSON::encode_json \@_ },
		574	sub { @{ JSON::decode_json shift } }
		575	)
		576
		577	=item C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER> - L<Storable>
		578
		579	This serialiser uses L<Storable>, which means it has high chance of
		580	serialising just about anything you throw at it, at the cost of having
		581	very high overhead per operation. It also comes with perl. It should be
		582	used when you need to serialise complex data structures.
		583
		584	Implementation:
		585
		586	use Storable ();
		587	(
		588	sub { Storable::freeze \@_ },
		589	sub { @{ Storable::thaw shift } }
		590	)
		591
		592	=item C<$AnyEvent::Fork::RPC::NSTORABLE_SERIALISER> - portable Storable
		593
		594	This serialiser also uses L<Storable>, but uses it's "network" format
		595	to serialise data, which makes it possible to talk to different
		596	perl binaries (for example, when talking to a process created with
		597	L<AnyEvent::Fork::Remote>).
		598
		599	Implementation:
		600
		601	use Storable ();
		602	(
		603	sub { Storable::nfreeze \@_ },
		604	sub { @{ Storable::thaw shift } }
		605	)
		606
141	=back	607	=back
142		608
		609	=item buflen => $bytes (default: C<512 - 16>)
		610
		611	The starting size of the read buffer for request and response data.
		612
		613	C<AnyEvent::Fork::RPC> ensures that the buffer for reeading request and
		614	response data is large enough for at leats aingle request or response, and
		615	will dynamically enlarge the buffer if needed.
		616
		617	While this ensures that memory is not overly wasted, it typically leads
		618	to having to do one syscall per request, which can be inefficient in some
		619	cases. In such cases, it can be beneficient to increase the buffer size to
		620	hold more than one request.
		621
		622	=item buflen_req => $bytes (default: same as C<buflen>)
		623
		624	Overrides C<buflen> for request data (as read by the forked process).
		625
		626	=item buflen_res => $bytes (default: same as C<buflen>)
		627
		628	Overrides C<buflen> for response data (replies read by the parent process).
		629
		630	=back
		631
		632	See the examples section earlier in this document for some actual
		633	examples.
		634
143	=cut	635	=cut
144		636
145	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	637	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
146		638	our $CBOR_XS_SERIALISER = 'use CBOR::XS (); (sub { CBOR::XS::encode_cbor_sharing \@_ }, sub { @{ CBOR::XS::decode_cbor shift } })';
147	# ideally, we want (SvLEN - SvCUR) \|\| 1024 or somesuch...	639	our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
148	sub rlen($) { ($_[0] < 384 ? 512 + 16 : 2 << int +(log $_[0] + 512) / log 2) - $_[0] - 16 }	640	our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
		641	our $NSTORABLE_SERIALISER = 'use Storable (); (sub { Storable::nfreeze \@_ }, sub { @{ Storable::thaw shift } })';
149		642
150	sub run {	643	sub run {
151	my ($self, $function, %arg) = @_;	644	my ($self, $function, %arg) = @_;
152		645
153	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;	646	my $serialiser = delete $arg{serialiser} \|\| $STRING_SERIALISER;
154	my $on_event = delete $arg{on_event};	647	my $on_event = delete $arg{on_event};
155	my $on_error = delete $arg{on_error};	648	my $on_error = delete $arg{on_error};
		649	my $on_destroy = delete $arg{on_destroy};
156		650
157	# default for on_error is to on_event, if specified	651	# default for on_error is to on_event, if specified
158	$on_error \|\|= $on_event	652	$on_error \|\|= $on_event
159	? sub { $on_event->(error => shift) }	653	? sub { $on_event->(error => shift) }
160	: sub { die "AnyEvent::Fork::RPC: uncaught error: $_[0].\n" };	654	: sub { AE::log die => "AnyEvent::Fork::RPC: uncaught error: $_[0]." };
161		655
162	# default for on_event is to raise an error	656	# default for on_event is to raise an error
163	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	657	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
164		658
165	my ($f, $t) = eval $serialiser; die $@ if $@;	659	my ($f, $t) = eval $serialiser; die $@ if $@;
166		660
167	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rbuf, $rw);	661	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
		662	my ($rlen, $rbuf, $rw) = $arg{buflen_res} \|\| $arg{buflen} \|\| 512 - 16;
168		663
169	my $wcb = sub {	664	my $wcb = sub {
170	my $len = syswrite $fh, $wbuf;	665	my $len = syswrite $fh, $wbuf;
171		666
172	if (!defined $len) {	667	unless (defined $len) {
173	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	668	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
174	undef $rw; undef $ww; # it ends here	669	undef $rw; undef $ww; # it ends here
175	$on_error->("$!");	670	$on_error->("$!");
176	}	671	}
177	}	672	}
…		…
184	}	679	}
185	};	680	};
186		681
187	my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");	682	my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");
188		683
189	$self->require ($module)	684	$self->eval ("use $module 2 ()")
190	->send_arg ($function, $arg{init}, $serialiser)	685	->send_arg (
		686	function => $function,
		687	init => $arg{init},
		688	serialiser => $serialiser,
		689	done => $arg{done} \|\| "$module\::do_exit",
		690	rlen => $arg{buflen_req} \|\| $arg{buflen} \|\| 512 - 16,
		691	-10 # the above are 10 arguments
		692	)
191	->run ("$module\::run", sub {	693	->run ("$module\::run", sub {
192	$fh = shift;	694	$fh = shift
		695	or return $on_error->("connection failed");
		696
		697	my ($id, $len);
193	$rw = AE::io $fh, 0, sub {	698	$rw = AE::io $fh, 0, sub {
		699	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
194	my $len = sysread $fh, $rbuf, rlen length $rbuf, length $rbuf;	700	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
195		701
196	if ($len) {	702	if ($len) {
197	while (5 <= length $rbuf) {	703	while (8 <= length $rbuf) {
198	$len = unpack "L", $rbuf;	704	($id, $len) = unpack "NN", $rbuf;
199	4 + $len <= length $rbuf	705	8 + $len <= length $rbuf
200	or last;	706	or last;
201		707
202	my @r = $t->(substr $rbuf, 4, $len);	708	my @r = $t->(substr $rbuf, 8, $len);
203	substr $rbuf, 0, $len + 4, "";	709	substr $rbuf, 0, 8 + $len, "";
		710
		711	if ($id) {
		712	if (@rcb) {
		713	(shift @rcb)->(@r);
		714	} elsif (my $cb = delete $rcb{$id}) {
		715	$cb->(@r);
		716	} else {
		717	undef $rw; undef $ww;
		718	$on_error->("unexpected data from child");
204		719	}
205	if (pop @r) {	720	} else {
206	$on_event->(@r);	721	$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	}	722	}
213	}	723	}
214	} elsif (defined $len) {	724	} elsif (defined $len) {
215	undef $rw; undef $ww; # it ends here	725	undef $rw; undef $ww; # it ends here
		726
		727	if (@rcb \|\| %rcb) {
216	$on_error->("unexpected eof")	728	$on_error->("unexpected eof");
217	if @rcb;	729	} else {
		730	$on_destroy->()
		731	if $on_destroy;
		732	}
218	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	733	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
219	undef $rw; undef $ww; # it ends here	734	undef $rw; undef $ww; # it ends here
220	$on_error->("read: $!");	735	$on_error->("read: $!");
221	}	736	}
222	};	737	};
…		…
224	$ww \|\|= AE::io $fh, 1, $wcb;	739	$ww \|\|= AE::io $fh, 1, $wcb;
225	});	740	});
226		741
227	my $guard = Guard::guard {	742	my $guard = Guard::guard {
228	$shutdown = 1;	743	$shutdown = 1;
229	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	744
		745	shutdown $fh, 1 if $fh && !$ww;
230	};	746	};
231		747
		748	my $id;
		749
		750	$arg{async}
232	sub {	751	? sub {
233	push @rcb, pop;	752	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		753	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
234		754
		755	$rcb{$id} = pop;
		756
235	$guard; # keep it alive	757	$guard if 0; # keep it alive
236		758
237	$wbuf .= pack "L/a*", &$f;	759	$wbuf .= pack "NN/a*", $id, &$f;
238	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	760	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
239	}	761	}
		762	: sub {
		763	push @rcb, pop;
		764
		765	$guard; # keep it alive
		766
		767	$wbuf .= pack "N/a*", &$f;
		768	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		769	}
240	}	770	}
241		771
		772	=item $rpc->(..., $cb->(...))
		773
		774	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
		775	reference. There are two things you can do with it: call it, and let it go
		776	out of scope (let it get destroyed).
		777
		778	If C<async> was false when C<$rpc> was created (the default), then, if you
		779	call C<$rpc>, the C<$function> is invoked with all arguments passed to
		780	C<$rpc> except the last one (the callback). When the function returns, the
		781	callback will be invoked with all the return values.
		782
		783	If C<async> was true, then the C<$function> receives an additional
		784	initial argument, the result callback. In this case, returning from
		785	C<$function> does nothing - the function only counts as "done" when the
		786	result callback is called, and any arguments passed to it are considered
		787	the return values. This makes it possible to "return" from event handlers
		788	or e.g. Coro threads.
		789
		790	The other thing that can be done with the RPC object is to destroy it. In
		791	this case, the child process will execute all remaining RPC calls, report
		792	their results, and then exit.
		793
		794	See the examples section earlier in this document for some actual
		795	examples.
		796
242	=back	797	=back
243		798
244	=head1 CHILD PROCESS USAGE	799	=head1 CHILD PROCESS USAGE
245		800
246	These functions are not available in this module. They are only available	801	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	802	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	803	without having to load any extra modules. They are part of the child-side
249	L<AnyEvent::Fork::RPC>.	804	API of L<AnyEvent::Fork::RPC>.
		805
		806	Note that these functions are typically not yet declared when code is
		807	compiled into the child, because the backend module is only loaded when
		808	you call C<run>, which is typically the last method you call on the fork
		809	object.
		810
		811	Therefore, you either have to explicitly pre-load the right backend module
		812	or mark calls to these functions as function calls, e.g.:
		813
		814	AnyEvent::Fork::RPC::event (0 => "five");
		815	AnyEvent::Fork::RPC::event->(0 => "five");
		816	&AnyEvent::Fork::RPC::flush;
250		817
251	=over 4	818	=over 4
252		819
253	=item AnyEvent::Fork::RPC::event ...	820	=item AnyEvent::Fork::RPC::event (...)
254		821
255	Send an event to the parent. Events are a bit like RPC calls made by the	822	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	823	child process to the parent, except that there is no notion of return
257	values.	824	values.
258		825
		826	See the examples section earlier in this document for some actual
		827	examples.
		828
		829	Note: the event data, like any data send to the parent, might not be sent
		830	immediatelly but queued for later sending, so there is no guarantee that
		831	the event has been sent to the parent when the call returns - when you
		832	e.g. exit directly after calling this function, the parent might never
		833	receive the event. See the next function for a remedy.
		834
		835	=item $success = AnyEvent::Fork::RPC::flush ()
		836
		837	Synchronously wait and flush the reply data to the parent. Returns true on
		838	success and false otherwise (i.e. when the reply data cannot be written at
		839	all). Ignoring the success status is a common and healthy behaviour.
		840
		841	Only the "async" backend does something on C<flush> - the "sync" backend
		842	is not buffering reply data and always returns true from this function.
		843
		844	Normally, reply data might or might not be written to the parent
		845	immediatelly but is buffered. This can greatly improve performance and
		846	efficiency, but sometimes can get in your way: for example. when you want
		847	to send an error message just before exiting, or when you want to ensure
		848	replies timely reach the parent before starting a long blocking operation.
		849
		850	In these cases, you can call this function to flush any outstanding reply
		851	data to the parent. This is done blockingly, so no requests will be
		852	handled and no event callbacks will be called.
		853
		854	For example, you could wrap your request function in a C<eval> block and
		855	report the exception string back to the caller just before exiting:
		856
		857	sub req {
		858	...
		859
		860	eval {
		861	...
		862	};
		863
		864	if ($@) {
		865	AnyEvent::RPC::event (throw => "$@");
		866	AnyEvent::RPC::flush ();
		867	exit;
		868	}
		869
		870	...
		871	}
		872
259	=back	873	=back
260		874
		875	=head2 PROCESS EXIT
		876
		877	If and when the child process exits depends on the backend and
		878	configuration. Apart from explicit exits (e.g. by calling C<exit>) or
		879	runtime conditions (uncaught exceptions, signals etc.), the backends exit
		880	under these conditions:
		881
		882	=over 4
		883
		884	=item Synchronous Backend
		885
		886	The synchronous backend is very simple: when the process waits for another
		887	request to arrive and the writing side (usually in the parent) is closed,
		888	it will exit normally, i.e. as if your main program reached the end of the
		889	file.
		890
		891	That means that if your parent process exits, the RPC process will usually
		892	exit as well, either because it is idle anyway, or because it executes a
		893	request. In the latter case, you will likely get an error when the RPc
		894	process tries to send the results to the parent (because agruably, you
		895	shouldn't exit your parent while there are still outstanding requests).
		896
		897	The process is usually quiescent when it happens, so it should rarely be a
		898	problem, and C<END> handlers can be used to clean up.
		899
		900	=item Asynchronous Backend
		901
		902	For the asynchronous backend, things are more complicated: Whenever it
		903	listens for another request by the parent, it might detect that the socket
		904	was closed (e.g. because the parent exited). It will sotp listening for
		905	new requests and instead try to write out any remaining data (if any) or
		906	simply check whether the socket can be written to. After this, the RPC
		907	process is effectively done - no new requests are incoming, no outstanding
		908	request data can be written back.
		909
		910	Since chances are high that there are event watchers that the RPC server
		911	knows nothing about (why else would one use the async backend if not for
		912	the ability to register watchers?), the event loop would often happily
		913	continue.
		914
		915	This is why the asynchronous backend explicitly calls C<CORE::exit> when
		916	it is done (under other circumstances, such as when there is an I/O error
		917	and there is outstanding data to write, it will log a fatal message via
		918	L<AnyEvent::Log>, also causing the program to exit).
		919
		920	You can override this by specifying a function name to call via the C<done>
		921	parameter instead.
		922
		923	=back
		924
		925	=head1 ADVANCED TOPICS
		926
		927	=head2 Choosing a backend
		928
		929	So how do you decide which backend to use? Well, that's your problem to
		930	solve, but here are some thoughts on the matter:
		931
		932	=over 4
		933
		934	=item Synchronous
		935
		936	The synchronous backend does not rely on any external modules (well,
		937	except L<common::sense>, which works around a bug in how perl's warning
		938	system works). This keeps the process very small, for example, on my
		939	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		940	after C<use warnings; use strict> (for people who grew up with C64s around
		941	them this is probably shocking every single time they see it). The worker
		942	process in the first example in this document uses 1792kB.
		943
		944	Since the calls are done synchronously, slow jobs will keep newer jobs
		945	from executing.
		946
		947	The synchronous backend also has no overhead due to running an event loop
		948	- reading requests is therefore very efficient, while writing responses is
		949	less so, as every response results in a write syscall.
		950
		951	If the parent process is busy and a bit slow reading responses, the child
		952	waits instead of processing further requests. This also limits the amount
		953	of memory needed for buffering, as never more than one response has to be
		954	buffered.
		955
		956	The API in the child is simple - you just have to define a function that
		957	does something and returns something.
		958
		959	It's hard to use modules or code that relies on an event loop, as the
		960	child cannot execute anything while it waits for more input.
		961
		962	=item Asynchronous
		963
		964	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		965	but still comes at a price: On my system, the worker from example 1a uses
		966	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		967	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		968	L<vars>, L<Exporter>...).
		969
		970	It batches requests and responses reasonably efficiently, doing only as
		971	few reads and writes as needed, but needs to poll for events via the event
		972	loop.
		973
		974	Responses are queued when the parent process is busy. This means the child
		975	can continue to execute any queued requests. It also means that a child
		976	might queue a lot of responses in memory when it generates them and the
		977	parent process is slow accepting them.
		978
		979	The API is not a straightforward RPC pattern - you have to call a
		980	"done" callback to pass return values and signal completion. Also, more
		981	importantly, the API starts jobs as fast as possible - when 1000 jobs
		982	are queued and the jobs are slow, they will all run concurrently. The
		983	child must implement some queueing/limiting mechanism if this causes
		984	problems. Alternatively, the parent could limit the amount of rpc calls
		985	that are outstanding.
		986
		987	Blocking use of condvars is not supported (in the main thread, outside of
		988	e.g. L<Coro> threads).
		989
		990	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		991	easy.
		992
		993	=back
		994
		995	=head2 Passing file descriptors
		996
		997	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		998	descriptor passing abilities.
		999
		1000	The reason is that passing file descriptors is extraordinary tricky
		1001	business, and conflicts with efficient batching of messages.
		1002
		1003	There still is a method you can use: Create a
		1004	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		1005	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		1006
		1007	Whenever you want to pass a file descriptor, send an rpc request to the
		1008	child process (so it expects the descriptor), then send it over the other
		1009	half of the socketpair. The child should fetch the descriptor from the
		1010	half it has passed earlier.
		1011
		1012	Here is some (untested) pseudocode to that effect:
		1013
		1014	use AnyEvent::Util;
		1015	use AnyEvent::Fork;
		1016	use AnyEvent::Fork::RPC;
		1017	use IO::FDPass;
		1018
		1019	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		1020
		1021	my $rpc = AnyEvent::Fork
		1022	->new
		1023	->send_fh ($s2)
		1024	->require ("MyWorker")
		1025	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		1026	init => "MyWorker::init",
		1027	);
		1028
		1029	undef $s2; # no need to keep it around
		1030
		1031	# pass an fd
		1032	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		1033
		1034	IO::FDPass fileno $s1, fileno $handle_to_pass;
		1035
		1036	$cv->recv;
		1037
		1038	The MyWorker module could look like this:
		1039
		1040	package MyWorker;
		1041
		1042	use IO::FDPass;
		1043
		1044	my $s2;
		1045
		1046	sub init {
		1047	$s2 = $_[0];
		1048	}
		1049
		1050	sub run {
		1051	if ($_[0] eq "i'll send some fd now, please expect it!") {
		1052	my $fd = IO::FDPass::recv fileno $s2;
		1053	...
		1054	}
		1055	}
		1056
		1057	Of course, this might be blocking if you pass a lot of file descriptors,
		1058	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		1059	gory details.
		1060
		1061	=head1 EXCEPTIONS
		1062
		1063	There are no provisions whatsoever for catching exceptions at this time -
		1064	in the child, exceptions might kill the process, causing calls to be lost
		1065	and the parent encountering a fatal error. In the parent, exceptions in
		1066	the result callback will not be caught and cause undefined behaviour.
		1067
261	=head1 SEE ALSO	1068	=head1 SEE ALSO
262		1069
263	L<AnyEvent::Fork> (to create the processes in the first place),	1070	L<AnyEvent::Fork>, to create the processes in the first place.
		1071
		1072	L<AnyEvent::Fork::Remote>, likewise, but helpful for remote processes.
		1073
264	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	1074	L<AnyEvent::Fork::Pool>, to manage whole pools of processes.
265		1075
266	=head1 AUTHOR AND CONTACT INFORMATION	1076	=head1 AUTHOR AND CONTACT INFORMATION
267		1077
268	Marc Lehmann <schmorp@schmorp.de>	1078	Marc Lehmann <schmorp@schmorp.de>
269	http://software.schmorp.de/pkg/AnyEvent-Fork-RPC	1079	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 1.46 by root, Sun Sep 15 20:18:14 2019 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 1.46 by root, Sun Sep 15 20:18:14 2019 UTC