Re: The evil Perl reads freed things

On Tue, Jun 22, 2004 at 02:09:01PM +0100, Nicholas Clark wrote:
> On Fri, Jun 18, 2004 at 08:36:59PM +0100, Nicholas Clark wrote:
> 
> > Other tests fail in strange ways, and valgrind reports errors which are
> > reads in the heads of now-free scalars.
> > 
> > So, I'm not sure what to do, as this assumption that you can read any
> > head even after it's undead seems to be quite deeply ingrained. And it
> > needs to be solved before we can usefully replace heads with PMCs.

[I wrote the next two paragraphs on Friday but didn't send it]

Perl5 doesn't refcount what it puts on the stack. Assuming that's
the cause of many/most of these cases, perhaps ponie will need to.

But then again, won't that problem go away if/when ponie starts
using GC instead of ref counting?

> It seems that I can work round this problem by deferring free()ing the SV
> heads until the next time temporaries are freed. So they're now put into
> a linked list, and freed by free_tmps().

Seems reasonable. (I wonder if that timing is reliable or if there
are cases where they'd need to be held for longer. Can't think of any.
Though free_tmps may trigger DESTROYs so freeing the list at the
end of free_tmps would be wise, but you're probably doing that anyway.)

> Ponie in CVS now has SV* being a pointer to a PMC. (and all tests pass)

Yeah. Good work.

How's the performance situation?

Tim.