[Phoenix-pm] More: Re: Coro(utine) support from the perl core

[Scott Walters]

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Date: Thu, 9 Mar 2006 20:06:24 +0100
From: demerphq <demerphq at gmail.com>
To: Marc Lehmann <schmorp at schmorp.de>
Subject: Re: Coro(utine) support from the perl core
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References: <20060309010716.GA13267 at schmorp.de>
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	 <20060309144512.GA22421 at schmorp.de>
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On 3/9/06, Marc Lehmann <schmorp at schmorp.de> wrote:
> On Thu, Mar 09, 2006 at 03:48:09PM +0100, demerphq <demerphq at gmail.com> wrote:
> > > The simple case can already be done using e.g. Storable.
> >
> > You can use Data::Dump::Streamer to serialize closures... Although im
> > not certain its relevent to this conversation.
>
> No, you can't, here is an example:
>
>    ...
>    my $var;
>    my $closure = sub { $var++ };
>    dumpevalandcall $closure;
>    print $var;
>
>    sub dumpevalandcall {
>       my $source = Data::Dumper::Dumper $_[0];
>       (eval $source)->();
>    }
>
> There is no way to serialise the closure so that the deserialised version
> still refers to $var.

Well, I think it depends on what you mean. Terms are slippery in this
part of the world.

Consider the following code:

use Data::Dump::Streamer;
sub make_subs {
    my $var=shift;
    my $inc = sub { $var++ };
    my $dec = sub { $var-- };
    my $get = sub { \$var };
    return ($inc,$dec,$get)
}

my ($i,$d,$g)=make_subs(123);
Dump(${$g->()},$i,$d,$g)->Out();

__END__
$var = 123;
$CODE1 = sub {
           $var++;
         };
$CODE2 = sub {
           $var--;
         };
$CODE3 = sub {
           \$var;
         };


As you can see, the output the subs bound to the same var. So in one
sense your statement is wrong. Using DDS you can serialize a set of
closures and other data elements such that when eval'ed the result has
shared data as is appropriate.

However, you are correct in that DDS wont help you reattach to the
same $var as was used  in the first place, but thats a little
different a problem I think, and with a bit of work I suspect its not
a showstopper.

> Now consider killing the process and restarting it between dumping and
> eval'ing: which $var does it refer to?

Well, actually, I think if done carefully the recreated closures would
reference the correct var. I think the attached example suggests ways
this could be accomplished.

Im still not saying that coroutines are any easier with this stuff,
just trying to make it clear that with Data::Dump::Streamer you _can_
serialize closures properly for at least one IMO reasonable definition
of properly.

yves
ps: Im not sure why you used an example that used Data::Dumper to say
that Data::Dump::Streamer can't do something....



--
perl -Mre=debug -e "/just|another|perl|hacker/"
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