Re: MPS: weak hash tables

[Pip Cet <pipcet@protonmail.com>]

On Monday, July 1st, 2024 at 21:16, Pip Cet <pipcet@protonmail.com> wrote:
> On Monday, July 1st, 2024 at 20:47, Gerd Möllmann gerd.moellmann@gmail.com wrote:
> > I think that the index is given 2 * table_size room ATM, but I'm not
> > sure if I read that right, and it's late. Is it sure that that suffices?
> 
> I believe it is, but it needs fixing anyway. Will do that next.

Actually, I've run into another bug which needs to be fixed first: when the hash table's strong part is allocated from MPS but t->table_size is still Qnil, we sometimes end up scanning it (when trying to allocate the weak part), and then XFIXNUM (Qnil) dies, as it rightfully should, except it's in the middle of a scan so it dies quite horribly.

Is it correct that all IGC objects need to be scannable when they're still zeroed-out from allocation?

(I'm currently trying to simply delay setting the weak->strong and strong->weak pointers until the parts are initialized, and to turn the scan into a nop if they aren't. I'm not convinced that's sufficient to prevent the compiler from reordering the initialization so an invalid state becomes visible to the scan function, though...)

Also, any opinions on :weakness 'key-or-value? Can we just not support it and use strong hash tables instead?

Pip