Hi,

> Weak references can leave dangling pointers if the weak
> object is in old space and it points to a new space object.

Your observation troubles me greatly. This should not happen, and as far as
I know it cannot happen. Do you have a reproducable example?

> The problem occurs when the new space object is incrementally
> collected but the old space weak object remains. The weak object
> now has a dangling pointer to where the new space object was.

This must not happen. Never. Not once. When a weak object becomes old it
will be marked as "root" and root objects are always traced as if they are
non-weak (the reason being that treating them weak would have complicated GC
logic more than I liked).

The way this works is subtle however: When GC kicks in we trace the roots
via #markAndTrace: and here, we have basically the same logic as in startObj
*except* that we set lastField regardless of whether the root is weak or not
(and lastField ultimately determines whether the GC logic finds an object
via reference). Therefore, if a weak object is a root, it will be traced as
if non-weak. You can test this by doing something like:

weakRef := WeakValueAssociation new.
Smalltalk garbageCollect. "make it old"
weakRef value: Object new.
Smalltalk garbageCollectMost. "incr. GC"
weakRef value. "and it's still there"

As far as I can tell, your changes should have no effect whatsoever.

Troubled,
  - Andreas