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Re: Garbage collection (was Re: JWZ on s/Java/Perl/)

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Damien Neil
February 15, 2001 10:31
Re: Garbage collection (was Re: JWZ on s/Java/Perl/)
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On Thu, Feb 15, 2001 at 08:07:39AM -0300, Branden wrote:
> I think you just said all about why we shouldn't bother giving objects
> deterministic finalization, and I agree with you. If we explicitly want to
> free resources (files, database connections), then we explicitly call close.
> Otherwise, it will be called when DESTROY is eventually called.

No, the question of whether Perl 6 wants deterministic finalization
or not is a separate one.  If it doesn't have it, we will be losing
a very common Perl idiom:

    my $fh = IO::File->new("file");
    print $fh $data;

It's nice to know that when the above block exits, $fh will be closed.
Remember that "closed" doesn't just refer to freeing the resources
associated with it -- it also includes flushing buffers and the like.

Without deterministic finalization, you will almost always want to
write the above to include an explicit $fh->close().  The problem is
that you can not only count on $fh's DESTROY being called at the end of
the block, you often can't count on it ever happening.  Consider the
case where the interpreter dies on a signal, for example -- DESTROY
methods will quite possibly not be called.

I'm not certain that Perl should lose deterministic finalization.  On
the other hand, I really wish that Perl had a more modern GC scheme,
if only so that circular structures could be properly collected.  In
the end, however, I don't think that any of our opinions will decide
this -- either Dan's forthcoming PDD will show how Perl 6 can have
its cake and eat it too, or Larry will decide.

                        - Damien

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