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Revision 1.30 by root, Sun Aug 25 22:21:15 2013 UTC vs.
Revision 1.37 by root, Thu May 12 16:43:08 2016 UTC

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175you really I<are> done. 175you really I<are> done.
176 176
177=head2 Example 2: Asynchronous Backend 177=head2 Example 2: Asynchronous Backend
178 178
179This example implements multiple count-downs in the child, using 179This example implements multiple count-downs in the child, using
180L<AnyEvent> timers. While this is a bit silly (one could use timers in te 180L<AnyEvent> timers. While this is a bit silly (one could use timers in the
181parent just as well), it illustrates the ability to use AnyEvent in the 181parent just as well), it illustrates the ability to use AnyEvent in the
182child and the fact that responses can arrive in a different order then the 182child and the fact that responses can arrive in a different order then the
183requests. 183requests.
184 184
185It also shows how to embed the actual child code into a C<__DATA__> 185It also shows how to embed the actual child code into a C<__DATA__>
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391use Errno (); 391use Errno ();
392use Guard (); 392use Guard ();
393 393
394use AnyEvent; 394use AnyEvent;
395 395
396our $VERSION = 1.1; 396our $VERSION = 1.21;
397 397
398=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...] 398=item my $rpc = AnyEvent::Fork::RPC::run $fork, $function, [key => value...]
399 399
400The traditional way to call it. But it is way cooler to call it in the 400The traditional way to call it. But it is way cooler to call it in the
401following way: 401following way:
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454It is called very early - before the serialisers are created or the 454It is called very early - before the serialisers are created or the
455C<$function> name is resolved into a function reference, so it could be 455C<$function> name is resolved into a function reference, so it could be
456used to load any modules that provide the serialiser or function. It can 456used to load any modules that provide the serialiser or function. It can
457not, however, create events. 457not, however, create events.
458 458
459=item done => $function (default C<CORE::exit>)
460
461The function to call when the asynchronous backend detects an end of file
462condition when reading from the communications socket I<and> there are no
463outstanding requests. It's ignored by the synchronous backend.
464
465By overriding this you can prolong the life of a RPC process after e.g.
466the 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
468could provide L<EV::run> as C<done> function).
469
470Of course, in that case you are responsible for exiting at the appropriate
471time and not returning from
472
459=item async => $boolean (default: 0) 473=item async => $boolean (default: 0)
460 474
461The default server used in the child does all I/O blockingly, and only 475The default server used in the child does all I/O blockingly, and only
462allows a single RPC call to execute concurrently. 476allows a single RPC call to execute concurrently.
463 477
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480 494
481All arguments, result data and event data have to be serialised to be 495All arguments, result data and event data have to be serialised to be
482transferred between the processes. For this, they have to be frozen and 496transferred between the processes. For this, they have to be frozen and
483thawed in both parent and child processes. 497thawed in both parent and child processes.
484 498
485By default, only octet strings can be passed between the processes, which 499By default, only octet strings can be passed between the processes,
486is reasonably fast and efficient and requires no extra modules. 500which is reasonably fast and efficient and requires no extra modules
501(the C<AnyEvent::Fork::RPC> distribution does not provide these extra
502serialiser modules).
487 503
488For more complicated use cases, you can provide your own freeze and thaw 504For more complicated use cases, you can provide your own freeze and thaw
489functions, by specifying a string with perl source code. It's supposed to 505functions, by specifying a string with perl source code. It's supposed to
490return two code references when evaluated: the first receives a list of 506return two code references when evaluated: the first receives a list of
491perl values and must return an octet string. The second receives the octet 507perl values and must return an octet string. The second receives the octet
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498Here are some examples - some of them are also available as global 514Here are some examples - some of them are also available as global
499variables that make them easier to use. 515variables that make them easier to use.
500 516
501=over 4 517=over 4
502 518
503=item octet strings - C<$AnyEvent::Fork::RPC::STRING_SERIALISER> 519=item C<$AnyEvent::Fork::RPC::STRING_SERIALISER> - octet strings only
504 520
505This serialiser concatenates length-prefixes octet strings, and is the 521This serialiser (currently the default) concatenates length-prefixes octet
506default. That means you can only pass (and return) strings containing 522strings, and is the default. That means you can only pass (and return)
507character codes 0-255. 523strings containing character codes 0-255.
524
525The main advantages of this serialiser are the high speed and that it
526doesn't need another module. The main disadvantage is that you are very
527limited in what you can pass - only octet strings.
508 528
509Implementation: 529Implementation:
510 530
511 ( 531 (
512 sub { pack "(w/a*)*", @_ }, 532 sub { pack "(w/a*)*", @_ },
513 sub { unpack "(w/a*)*", shift } 533 sub { unpack "(w/a*)*", shift }
514 ) 534 )
515 535
516=item json - C<$AnyEvent::Fork::RPC::JSON_SERIALISER> 536=item C<$AnyEvent::Fork::RPC::CBOR_XS_SERIALISER> - uses L<CBOR::XS>
537
538This serialiser creates CBOR::XS arrays - you have to make sure the
539L<CBOR::XS> module is installed for this serialiser to work. It can be
540beneficial for sharing when you preload the L<CBOR::XS> module in a template
541process.
542
543L<CBOR::XS> is about as fast as the octet string serialiser, but supports
544complex data structures (similar to JSON) and is faster than any of the
545other serialisers. If you have the L<CBOR::XS> module available, it's the
546best choice.
547
548The encoder enables C<allow_sharing> (so this serialisation method can
549encode cyclic and self-referencing data structures).
550
551Implementation:
552
553 use CBOR::XS ();
554 (
555 sub { CBOR::XS::encode_cbor_sharing \@_ },
556 sub { @{ CBOR::XS::decode_cbor shift } }
557 )
558
559=item C<$AnyEvent::Fork::RPC::JSON_SERIALISER> - uses L<JSON::XS> or L<JSON>
517 560
518This serialiser creates JSON arrays - you have to make sure the L<JSON> 561This serialiser creates JSON arrays - you have to make sure the L<JSON>
519module is installed for this serialiser to work. It can be beneficial for 562module is installed for this serialiser to work. It can be beneficial for
520sharing when you preload the L<JSON> module in a template process. 563sharing when you preload the L<JSON> module in a template process.
521 564
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529 ( 572 (
530 sub { JSON::encode_json \@_ }, 573 sub { JSON::encode_json \@_ },
531 sub { @{ JSON::decode_json shift } } 574 sub { @{ JSON::decode_json shift } }
532 ) 575 )
533 576
534=item storable - C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER> 577=item C<$AnyEvent::Fork::RPC::STORABLE_SERIALISER> - L<Storable>
535 578
536This serialiser uses L<Storable>, which means it has high chance of 579This serialiser uses L<Storable>, which means it has high chance of
537serialising just about anything you throw at it, at the cost of having 580serialising just about anything you throw at it, at the cost of having
538very high overhead per operation. It also comes with perl. It should be 581very high overhead per operation. It also comes with perl. It should be
539used when you need to serialise complex data structures. 582used when you need to serialise complex data structures.
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544 ( 587 (
545 sub { Storable::freeze \@_ }, 588 sub { Storable::freeze \@_ },
546 sub { @{ Storable::thaw shift } } 589 sub { @{ Storable::thaw shift } }
547 ) 590 )
548 591
549=item portable storable - C<$AnyEvent::Fork::RPC::NSTORABLE_SERIALISER> 592=item C<$AnyEvent::Fork::RPC::NSTORABLE_SERIALISER> - portable Storable
550 593
551This serialiser also uses L<Storable>, but uses it's "network" format 594This serialiser also uses L<Storable>, but uses it's "network" format
552to serialise data, which makes it possible to talk to different 595to serialise data, which makes it possible to talk to different
553perl binaries (for example, when talking to a process created with 596perl binaries (for example, when talking to a process created with
554L<AnyEvent::Fork::Remote>). 597L<AnyEvent::Fork::Remote>).
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569examples. 612examples.
570 613
571=cut 614=cut
572 615
573our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })'; 616our $STRING_SERIALISER = '(sub { pack "(w/a*)*", @_ }, sub { unpack "(w/a*)*", shift })';
617our $CBOR_XS_SERIALISER = 'use CBOR::XS (); (sub { CBOR::XS::encode_cbor_sharing \@_ }, sub { @{ CBOR::XS::decode_cbor shift } })';
574our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })'; 618our $JSON_SERIALISER = 'use JSON (); (sub { JSON::encode_json \@_ }, sub { @{ JSON::decode_json shift } })';
575our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })'; 619our $STORABLE_SERIALISER = 'use Storable (); (sub { Storable::freeze \@_ }, sub { @{ Storable::thaw shift } })';
576our $NSTORABLE_SERIALISER = 'use Storable (); (sub { Storable::nfreeze \@_ }, sub { @{ Storable::thaw shift } })'; 620our $NSTORABLE_SERIALISER = 'use Storable (); (sub { Storable::nfreeze \@_ }, sub { @{ Storable::thaw shift } })';
577 621
578sub run { 622sub run {
579 my ($self, $function, %arg) = @_; 623 my ($self, $function, %arg) = @_;
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615 }; 659 };
616 660
617 my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync"); 661 my $module = "AnyEvent::Fork::RPC::" . ($arg{async} ? "Async" : "Sync");
618 662
619 $self->require ($module) 663 $self->require ($module)
620 ->send_arg ($function, $arg{init}, $serialiser) 664 ->send_arg ($function, $arg{init}, $serialiser, $arg{done} || "$module\::do_exit")
621 ->run ("$module\::run", sub { 665 ->run ("$module\::run", sub {
622 $fh = shift; 666 $fh = shift;
623 667
624 my ($id, $len); 668 my ($id, $len);
625 $rw = AE::io $fh, 0, sub { 669 $rw = AE::io $fh, 0, sub {
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741See the examples section earlier in this document for some actual 785See the examples section earlier in this document for some actual
742examples. 786examples.
743 787
744=back 788=back
745 789
790=head2 PROCESS EXIT
791
792If and when the child process exits depends on the backend and
793configuration. Apart from explicit exits (e.g. by calling C<exit>) or
794runtime conditions (uncaught exceptions, signals etc.), the backends exit
795under these conditions:
796
797=over 4
798
799=item Synchronous Backend
800
801The synchronous backend is very simple: when the process waits for another
802request to arrive and the writing side (usually in the parent) is closed,
803it will exit normally, i.e. as if your main program reached the end of the
804file.
805
806That means that if your parent process exits, the RPC process will usually
807exit as well, either because it is idle anyway, or because it executes a
808request. In the latter case, you will likely get an error when the RPc
809process tries to send the results to the parent (because agruably, you
810shouldn't exit your parent while there are still outstanding requests).
811
812The process is usually quiescent when it happens, so it should rarely be a
813problem, and C<END> handlers can be used to clean up.
814
815=item Asynchronous Backend
816
817For the asynchronous backend, things are more complicated: Whenever it
818listens for another request by the parent, it might detect that the socket
819was closed (e.g. because the parent exited). It will sotp listening for
820new requests and instead try to write out any remaining data (if any) or
821simply check whether the socket can be written to. After this, the RPC
822process is effectively done - no new requests are incoming, no outstanding
823request data can be written back.
824
825Since chances are high that there are event watchers that the RPC server
826knows nothing about (why else would one use the async backend if not for
827the ability to register watchers?), the event loop would often happily
828continue.
829
830This is why the asynchronous backend explicitly calls C<CORE::exit> when
831it is done (under other circumstances, such as when there is an I/O error
832and there is outstanding data to write, it will log a fatal message via
833L<AnyEvent::Log>, also causing the program to exit).
834
835You can override this by specifying a function name to call via the C<done>
836parameter instead.
837
838=back
839
746=head1 ADVANCED TOPICS 840=head1 ADVANCED TOPICS
747 841
748=head2 Choosing a backend 842=head2 Choosing a backend
749 843
750So how do you decide which backend to use? Well, that's your problem to 844So how do you decide which backend to use? Well, that's your problem to
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803are queued and the jobs are slow, they will all run concurrently. The 897are queued and the jobs are slow, they will all run concurrently. The
804child must implement some queueing/limiting mechanism if this causes 898child must implement some queueing/limiting mechanism if this causes
805problems. Alternatively, the parent could limit the amount of rpc calls 899problems. Alternatively, the parent could limit the amount of rpc calls
806that are outstanding. 900that are outstanding.
807 901
808Blocking use of condvars is not supported. 902Blocking use of condvars is not supported (in the main thread, outside of
903e.g. L<Coro> threads).
809 904
810Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is 905Using event-based modules such as L<IO::AIO>, L<Gtk2>, L<Tk> and so on is
811easy. 906easy.
812 907
813=back 908=back
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879gory details. 974gory details.
880 975
881=head1 EXCEPTIONS 976=head1 EXCEPTIONS
882 977
883There are no provisions whatsoever for catching exceptions at this time - 978There are no provisions whatsoever for catching exceptions at this time -
884in the child, exeptions might kill the process, causing calls to be lost 979in the child, exceptions might kill the process, causing calls to be lost
885and the parent encountering a fatal error. In the parent, exceptions in 980and the parent encountering a fatal error. In the parent, exceptions in
886the result callback will not be caught and cause undefined behaviour. 981the result callback will not be caught and cause undefined behaviour.
887 982
888=head1 SEE ALSO 983=head1 SEE ALSO
889 984

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