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

Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.5 by root, Wed Apr 17 19:39:54 2013 UTC vs.
Revision 1.12 by root, Thu Apr 18 10:40:34 2013 UTC

…		…
2		2
3	AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork	3	AnyEvent::Fork::RPC - simple RPC extension for AnyEvent::Fork
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::Fork;
8	use AnyEvent::Fork::RPC;	7	use AnyEvent::Fork::RPC;
		8	# use AnyEvent::Fork is not needed
9		9
10	my $rpc = AnyEvent::Fork	10	my $rpc = AnyEvent::Fork
11	->new	11	->new
12	->require ("MyModule")	12	->require ("MyModule")
13	->AnyEvent::Fork::RPC::run (	13	->AnyEvent::Fork::RPC::run (
…		…
34	concurrently in the child, using AnyEvent.	34	concurrently in the child, using AnyEvent.
35		35
36	It also implements an asynchronous event mechanism from the child to the	36	It also implements an asynchronous event mechanism from the child to the
37	parent, that could be used for progress indications or other information.	37	parent, that could be used for progress indications or other information.
38		38
		39	Loading this module also always loads L<AnyEvent::Fork>, so you can make a
		40	separate C<use AnyEvent::Fork> if you wish, but you don't have to.
		41
39	=head1 EXAMPLES	42	=head1 EXAMPLES
40		43
41	=head2 Synchronous Backend	44	=head2 Example 1: Synchronous Backend
42		45
43	Here is a simple example that implements a backend that executes C<unlink>	46	Here is a simple example that implements a backend that executes C<unlink>
44	and C<rmdir> calls, and reports their status back. It also reports the	47	and C<rmdir> calls, and reports their status back. It also reports the
45	number of requests it has processed every three requests, which is clearly	48	number of requests it has processed every three requests, which is clearly
46	silly, but illustrates the use of events.	49	silly, but illustrates the use of events.
47		50
48	First the parent process:	51	First the parent process:
49		52
50	use AnyEvent;	53	use AnyEvent;
51	use AnyEvent::Fork;
52	use AnyEvent::Fork::RPC;	54	use AnyEvent::Fork::RPC;
53		55
54	my $done = AE::cv;	56	my $done = AE::cv;
55		57
56	my $rpc = AnyEvent::Fork	58	my $rpc = AnyEvent::Fork
…		…
103	dies with a fatal error - obviously, you must never let this happen :).	105	dies with a fatal error - obviously, you must never let this happen :).
104		106
105	Eventually it returns the status value true if the command was successful,	107	Eventually it returns the status value true if the command was successful,
106	or the status value 0 and the stringified error message.	108	or the status value 0 and the stringified error message.
107		109
108	On my system, running the first cdoe fragment with the given	110	On my system, running the first code fragment with the given
109	F<MyWorker.pm> in the current directory yields:	111	F<MyWorker.pm> in the current directory yields:
110		112
111	/tmp/somepath/1: No such file or directory	113	/tmp/somepath/1: No such file or directory
112	/tmp/somepath/2: No such file or directory	114	/tmp/somepath/2: No such file or directory
113	3 requests handled	115	3 requests handled
…		…
134		136
135	And as a final remark, there is a fine module on CPAN that can	137	And as a final remark, there is a fine module on CPAN that can
136	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently	138	asynchronously C<rmdir> and C<unlink> and a lot more, and more efficiently
137	than this example, namely L<IO::AIO>.	139	than this example, namely L<IO::AIO>.
138		140
		141	=head3 Example 1a: the same with the asynchronous backend
		142
		143	This example only shows what needs to be changed to use the async backend
		144	instead. Doing this is not very useful, the purpose of this example is
		145	to show the minimum amount of change that is required to go from the
		146	synchronous to the asynchronous backend.
		147
		148	To use the async backend in the previous example, you need to add the
		149	C<async> parameter to the C<AnyEvent::Fork::RPC::run> call:
		150
		151	->AnyEvent::Fork::RPC::run ("MyWorker::run",
		152	async => 1,
		153	...
		154
		155	And since the function call protocol is now changed, you need to adopt
		156	C<MyWorker::run> to the async API.
		157
		158	First, you need to accept the extra initial C<$done> callback:
		159
		160	sub run {
		161	my ($done, $cmd, $path) = @_;
		162
		163	And since a response is now generated when C<$done> is called, as opposed
		164	to when the function returns, we need to call the C<$done> function with
		165	the status:
		166
		167	$done->($status or (0, "$!"));
		168
		169	A few remarks are in order. First, it's quite pointless to use the async
		170	backend for this example - but it I<is> possible. Second, you can call
		171	C<$done> before or after returning from the function. Third, having both
		172	returned from the function and having called the C<$done> callback, the
		173	child process may exit at any time, so you should call C<$done> only when
		174	you really I<are> done.
		175
		176	=head2 Example 2: Asynchronous Backend
		177
		178	This example implements multiple count-downs in the child, using
		179	L<AnyEvent> timers. While this is a bit silly (one could use timers in te
		180	parent just as well), it illustrates the ability to use AnyEvent in the
		181	child and the fact that responses can arrive in a different order then the
		182	requests.
		183
		184	It also shows how to embed the actual child code into a C<__DATA__>
		185	section, so it doesn't need any external files at all.
		186
		187	And when your parent process is often busy, and you have stricter timing
		188	requirements, then running timers in a child process suddenly doesn't look
		189	so silly anymore.
		190
		191	Without further ado, here is the code:
		192
		193	use AnyEvent;
		194	use AnyEvent::Fork::RPC;
		195
		196	my $done = AE::cv;
		197
		198	my $rpc = AnyEvent::Fork
		199	->new
		200	->require ("AnyEvent::Fork::RPC::Async")
		201	->eval (do { local $/; <DATA> })
		202	->AnyEvent::Fork::RPC::run ("run",
		203	async => 1,
		204	on_error => sub { warn "FATAL: $_[0]"; exit 1 },
		205	on_event => sub { print $_[0] },
		206	on_destroy => $done,
		207	);
		208
		209	for my $count (3, 2, 1) {
		210	$rpc->($count, sub {
		211	warn "job $count finished\n";
		212	});
		213	}
		214
		215	undef $rpc;
		216
		217	$done->recv;
		218
		219	__DATA__
		220
		221	# this ends up in main, as we don't use a package declaration
		222
		223	use AnyEvent;
		224
		225	sub run {
		226	my ($done, $count) = @_;
		227
		228	my $n;
		229
		230	AnyEvent::Fork::RPC::event "starting to count up to $count\n";
		231
		232	my $w; $w = AE::timer 1, 1, sub {
		233	++$n;
		234
		235	AnyEvent::Fork::RPC::event "count $n of $count\n";
		236
		237	if ($n == $count) {
		238	undef $w;
		239	$done->();
		240	}
		241	};
		242	}
		243
		244	The parent part (the one before the C<__DATA__> section) isn't very
		245	different from the earlier examples. It sets async mode, preloads
		246	the backend module (so the C<AnyEvent::Fork::RPC::event> function is
		247	declared), uses a slightly different C<on_event> handler (which we use
		248	simply for logging purposes) and then, instead of loading a module with
		249	the actual worker code, it C<eval>'s the code from the data section in the
		250	child process.
		251
		252	It then starts three countdowns, from 3 to 1 seconds downwards, destroys
		253	the rpc object so the example finishes eventually, and then just waits for
		254	the stuff to trickle in.
		255
		256	The worker code uses the event function to log some progress messages, but
		257	mostly just creates a recurring one-second timer.
		258
		259	The timer callback increments a counter, logs a message, and eventually,
		260	when the count has been reached, calls the finish callback.
		261
		262	On my system, this results in the following output. Since all timers fire
		263	at roughly the same time, the actual order isn't guaranteed, but the order
		264	shown is very likely what you would get, too.
		265
		266	starting to count up to 3
		267	starting to count up to 2
		268	starting to count up to 1
		269	count 1 of 3
		270	count 1 of 2
		271	count 1 of 1
		272	job 1 finished
		273	count 2 of 2
		274	job 2 finished
		275	count 2 of 3
		276	count 3 of 3
		277	job 3 finished
		278
		279	While the overall ordering isn't guaranteed, the async backend still
		280	guarantees that events and responses are delivered to the parent process
		281	in the exact same ordering as they were generated in the child process.
		282
		283	And unless your system is I<very> busy, it should clearly show that the
		284	job started last will finish first, as it has the lowest count.
		285
		286	This concludes the async example. Since L<AnyEvent::Fork> does not
		287	actually fork, you are free to use about any module in the child, not just
		288	L<AnyEvent>, but also L<IO::AIO>, or L<Tk> for example.
		289
139	=head1 PARENT PROCESS USAGE	290	=head1 PARENT PROCESS USAGE
140		291
141	This module exports nothing, and only implements a single function:	292	This module exports nothing, and only implements a single function:
142		293
143	=over 4	294	=over 4
…		…
150		301
151	use Errno ();	302	use Errno ();
152	use Guard ();	303	use Guard ();
153		304
154	use AnyEvent;	305	use AnyEvent;
155	#use AnyEvent::Fork;	306	use AnyEvent::Fork; # we don't actually depend on it, this is for convenience
156		307
157	our $VERSION = 0.1;	308	our $VERSION = 0.1;
158		309
159	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]	310	=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
160		311
…		…
198		349
199	Called when the C<$rpc> object has been destroyed and all requests have	350	Called when the C<$rpc> object has been destroyed and all requests have
200	been successfully handled. This is useful when you queue some requests and	351	been successfully handled. This is useful when you queue some requests and
201	want the child to go away after it has handled them. The problem is that	352	want the child to go away after it has handled them. The problem is that
202	the parent must not exit either until all requests have been handled, and	353	the parent must not exit either until all requests have been handled, and
203	this cna be accomplished by waiting for this callback.	354	this can be accomplished by waiting for this callback.
204		355
205	=item init => $function (default none)	356	=item init => $function (default none)
206		357
207	When specified (by name), this function is called in the child as the very	358	When specified (by name), this function is called in the child as the very
208	first thing when taking over the process, with all the arguments normally	359	first thing when taking over the process, with all the arguments normally
…		…
231	If you want to pre-load the actual back-end modules to enable memory	382	If you want to pre-load the actual back-end modules to enable memory
232	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for	383	sharing, then you should load C<AnyEvent::Fork::RPC::Sync> for
233	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.	384	synchronous, and C<AnyEvent::Fork::RPC::Async> for asynchronous mode.
234		385
235	If you use a template process and want to fork both sync and async	386	If you use a template process and want to fork both sync and async
236	children, then it is permissible to laod both modules.	387	children, then it is permissible to load both modules.
237		388
238	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')	389	=item serialiser => $string (default: '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })')
239		390
240	All arguments, result data and event data have to be serialised to be	391	All arguments, result data and event data have to be serialised to be
241	transferred between the processes. For this, they have to be frozen and	392	transferred between the processes. For this, they have to be frozen and
…		…
253	If you need an external module for serialisation, then you can either	404	If you need an external module for serialisation, then you can either
254	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>	405	pre-load it into your L<AnyEvent::Fork> process, or you can add a C<use>
255	or C<require> statement into the serialiser string. Or both.	406	or C<require> statement into the serialiser string. Or both.
256		407
257	=back	408	=back
		409
		410	See the examples section earlier in this document for some actual
		411	examples.
258		412
259	=cut	413	=cut
260		414
261	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';	415	our $STRING_SERIALISER = '(sub { pack "(w/a)", @_ }, sub { unpack "(w/a)", shift })';
262		416
…		…
276	# default for on_event is to raise an error	430	# default for on_event is to raise an error
277	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };	431	$on_event \|\|= sub { $on_error->("event received, but no on_event handler") };
278		432
279	my ($f, $t) = eval $serialiser; die $@ if $@;	433	my ($f, $t) = eval $serialiser; die $@ if $@;
280		434
281	my (@rcb, $fh, $shutdown, $wbuf, $ww, $rw);	435	my (@rcb, %rcb, $fh, $shutdown, $wbuf, $ww);
282	my ($rlen, $rbuf) = 512 - 16;	436	my ($rlen, $rbuf, $rw) = 512 - 16;
283		437
284	my $wcb = sub {	438	my $wcb = sub {
285	my $len = syswrite $fh, $wbuf;	439	my $len = syswrite $fh, $wbuf;
286		440
287	if (!defined $len) {	441	unless (defined $len) {
288	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	442	if ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
289	undef $rw; undef $ww; # it ends here	443	undef $rw; undef $ww; # it ends here
290	$on_error->("$!");	444	$on_error->("$!");
291	}	445	}
292	}	446	}
…		…
303		457
304	$self->require ($module)	458	$self->require ($module)
305	->send_arg ($function, $arg{init}, $serialiser)	459	->send_arg ($function, $arg{init}, $serialiser)
306	->run ("$module\::run", sub {	460	->run ("$module\::run", sub {
307	$fh = shift;	461	$fh = shift;
		462
		463	my ($id, $len);
308	$rw = AE::io $fh, 0, sub {	464	$rw = AE::io $fh, 0, sub {
309	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;	465	$rlen = $rlen * 2 + 16 if $rlen - 128 < length $rbuf;
310	my $len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;	466	$len = sysread $fh, $rbuf, $rlen - length $rbuf, length $rbuf;
311		467
312	if ($len) {	468	if ($len) {
313	while (5 <= length $rbuf) {	469	while (8 <= length $rbuf) {
314	$len = unpack "L", $rbuf;	470	($id, $len) = unpack "LL", $rbuf;
315	4 + $len <= length $rbuf	471	8 + $len <= length $rbuf
316	or last;	472	or last;
317		473
318	my @r = $t->(substr $rbuf, 4, $len);	474	my @r = $t->(substr $rbuf, 8, $len);
319	substr $rbuf, 0, $len + 4, "";	475	substr $rbuf, 0, 8 + $len, "";
		476
		477	if ($id) {
		478	if (@rcb) {
		479	(shift @rcb)->(@r);
		480	} elsif (my $cb = delete $rcb{$id}) {
		481	$cb->(@r);
		482	} else {
		483	undef $rw; undef $ww;
		484	$on_error->("unexpected data from child");
320		485	}
321	if (pop @r) {	486	} else {
322	$on_event->(@r);	487	$on_event->(@r);
323	} elsif (@rcb) {
324	(shift @rcb)->(@r);
325	} else {
326	undef $rw; undef $ww;
327	$on_error->("unexpected data from child");
328	}	488	}
329	}	489	}
330	} elsif (defined $len) {	490	} elsif (defined $len) {
331	undef $rw; undef $ww; # it ends here	491	undef $rw; undef $ww; # it ends here
332		492
333	if (@rcb) {	493	if (@rcb \|\| %rcb) {
		494	use Data::Dump;ddx[\@rcb,\%rcb];#d#
334	$on_error->("unexpected eof");	495	$on_error->("unexpected eof");
335	} else {	496	} else {
336	$on_destroy->();	497	$on_destroy->();
337	}	498	}
338	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {	499	} elsif ($! != Errno::EAGAIN && $! != Errno::EWOULDBLOCK) {
…		…
347	my $guard = Guard::guard {	508	my $guard = Guard::guard {
348	$shutdown = 1;	509	$shutdown = 1;
349	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	510	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
350	};	511	};
351		512
		513	my $id;
		514
		515	$arg{async}
352	sub {	516	? sub {
353	push @rcb, pop;	517	$id = ($id == 0xffffffff ? 0 : $id) + 1;
		518	$id = ($id == 0xffffffff ? 0 : $id) + 1 while exists $rcb{$id}; # rarely loops
354		519
		520	$rcb{$id} = pop;
		521
355	$guard; # keep it alive	522	$guard; # keep it alive
356		523
357	$wbuf .= pack "L/a*", &$f;	524	$wbuf .= pack "LL/a*", $id, &$f;
358	$ww \|\|= $fh && AE::io $fh, 1, $wcb;	525	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
359	}	526	}
		527	: sub {
		528	push @rcb, pop;
		529
		530	$guard; # keep it alive
		531
		532	$wbuf .= pack "L/a*", &$f;
		533	$ww \|\|= $fh && AE::io $fh, 1, $wcb;
		534	}
360	}	535	}
361		536
362	=item $rpc->(..., $cb->(...))	537	=item $rpc->(..., $cb->(...))
363		538
364	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code	539	The RPC object returned by C<AnyEvent::Fork::RPC::run> is actually a code
…		…
379		554
380	The other thing that can be done with the RPC object is to destroy it. In	555	The other thing that can be done with the RPC object is to destroy it. In
381	this case, the child process will execute all remaining RPC calls, report	556	this case, the child process will execute all remaining RPC calls, report
382	their results, and then exit.	557	their results, and then exit.
383		558
		559	See the examples section earlier in this document for some actual
		560	examples.
		561
384	=back	562	=back
385		563
386	=head1 CHILD PROCESS USAGE	564	=head1 CHILD PROCESS USAGE
387		565
388	The following function is not available in this module. They are only	566	The following function is not available in this module. They are only
…		…
396		574
397	Send an event to the parent. Events are a bit like RPC calls made by the	575	Send an event to the parent. Events are a bit like RPC calls made by the
398	child process to the parent, except that there is no notion of return	576	child process to the parent, except that there is no notion of return
399	values.	577	values.
400		578
		579	See the examples section earlier in this document for some actual
		580	examples.
		581
401	=back	582	=back
		583
		584	=head1 ADVANCED TOPICS
		585
		586	=head2 Choosing a backend
		587
		588	So how do you decide which backend to use? Well, that's your problem to
		589	solve, but here are some thoughts on the matter:
		590
		591	=over 4
		592
		593	=item Synchronous
		594
		595	The synchronous backend does not rely on any external modules (well,
		596	except L<common::sense>, which works around a bug in how perl's warning
		597	system works). This keeps the process very small, for example, on my
		598	system, an empty perl interpreter uses 1492kB RSS, which becomes 2020kB
		599	after C<use warnings; use strict> (for people who grew up with C64s around
		600	them this is probably shocking every single time they see it). The worker
		601	process in the first example in this document uses 1792kB.
		602
		603	Since the calls are done synchronously, slow jobs will keep newer jobs
		604	from executing.
		605
		606	The synchronous backend also has no overhead due to running an event loop
		607	- reading requests is therefore very efficient, while writing responses is
		608	less so, as every response results in a write syscall.
		609
		610	If the parent process is busy and a bit slow reading responses, the child
		611	waits instead of processing further requests. This also limits the amount
		612	of memory needed for buffering, as never more than one response has to be
		613	buffered.
		614
		615	The API in the child is simple - you just have to define a function that
		616	does something and returns something.
		617
		618	It's hard to use modules or code that relies on an event loop, as the
		619	child cannot execute anything while it waits for more input.
		620
		621	=item Asynchronous
		622
		623	The asynchronous backend relies on L<AnyEvent>, which tries to be small,
		624	but still comes at a price: On my system, the worker from example 1a uses
		625	3420kB RSS (for L<AnyEvent>, which loads L<EV>, which needs L<XSLoader>
		626	which in turn loads a lot of other modules such as L<warnings>, L<strict>,
		627	L<vars>, L<Exporter>...).
		628
		629	It batches requests and responses reasonably efficiently, doing only as
		630	few reads and writes as needed, but needs to poll for events via the event
		631	loop.
		632
		633	Responses are queued when the parent process is busy. This means the child
		634	can continue to execute any queued requests. It also means that a child
		635	might queue a lot of responses in memory when it generates them and the
		636	parent process is slow accepting them.
		637
		638	The API is not a straightforward RPC pattern - you have to call a
		639	"done" callback to pass return values and signal completion. Also, more
		640	importantly, the API starts jobs as fast as possible - when 1000 jobs
		641	are queued and the jobs are slow, they will all run concurrently. The
		642	child must implement some queueing/limiting mechanism if this causes
		643	problems. Alternatively, the parent could limit the amount of rpc calls
		644	that are outstanding.
		645
		646	Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
		647	easy.
		648
		649	=back
		650
		651	=head2 Passing file descriptors
		652
		653	Unlike L<AnyEvent::Fork>, this module has no in-built file handle or file
		654	descriptor passing abilities.
		655
		656	The reason is that passing file descriptors is extraordinary tricky
		657	business, and conflicts with efficient batching of messages.
		658
		659	There still is a method you can use: Create a
		660	C<AnyEvent::Util::portable_socketpair> and C<send_fh> one half of it to
		661	the process before you pass control to C<AnyEvent::Fork::RPC::run>.
		662
		663	Whenever you want to pass a file descriptor, send an rpc request to the
		664	child process (so it expects the descriptor), then send it over the other
		665	half of the socketpair. The child should fetch the descriptor from the
		666	half it has passed earlier.
		667
		668	Here is some (untested) pseudocode to that effect:
		669
		670	use AnyEvent::Util;
		671	use AnyEvent::Fork::RPC;
		672	use IO::FDPass;
		673
		674	my ($s1, $s2) = AnyEvent::Util::portable_socketpair;
		675
		676	my $rpc = AnyEvent::Fork
		677	->new
		678	->send_fh ($s2)
		679	->require ("MyWorker")
		680	->AnyEvent::Fork::RPC::run ("MyWorker::run"
		681	init => "MyWorker::init",
		682	);
		683
		684	undef $s2; # no need to keep it around
		685
		686	# pass an fd
		687	$rpc->("i'll send some fd now, please expect it!", my $cv = AE::cv);
		688
		689	IO::FDPass fileno $s1, fileno $handle_to_pass;
		690
		691	$cv->recv;
		692
		693	The MyWorker module could look like this:
		694
		695	package MyWorker;
		696
		697	use IO::FDPass;
		698
		699	my $s2;
		700
		701	sub init {
		702	$s2 = $_[0];
		703	}
		704
		705	sub run {
		706	if ($_[0] eq "i'll send some fd now, please expect it!") {
		707	my $fd = IO::FDPass::recv fileno $s2;
		708	...
		709	}
		710	}
		711
		712	Of course, this might be blocking if you pass a lot of file descriptors,
		713	so you might want to look into L<AnyEvent::FDpasser> which can handle the
		714	gory details.
402		715
403	=head1 SEE ALSO	716	=head1 SEE ALSO
404		717
405	L<AnyEvent::Fork> (to create the processes in the first place),	718	L<AnyEvent::Fork> (to create the processes in the first place),
406	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).	719	L<AnyEvent::Fork::Pool> (to manage whole pools of processes).

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents): Revision 1.5 by root, Wed Apr 17 19:39:54 2013 UTC vs. Revision 1.12 by root, Thu Apr 18 10:40:34 2013 UTC

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Comparing AnyEvent-Fork-RPC/RPC.pm (file contents):
Revision 1.5 by root, Wed Apr 17 19:39:54 2013 UTC vs.
Revision 1.12 by root, Thu Apr 18 10:40:34 2013 UTC