Re: Hash Tables and GC

[DDYER@RIVERSIDE.SCRC.Symbolics.COM]

Just to throw a little light into this discussion:   On Symbolics systems there
is a list of forms to be evaluated before any gc flip (ephemeral or dynamic).
It's possible to implement whatever kind of weak pointers strategy you want by 
explicitly clearing whatever pointers are "weak" before the flip occurs.  The
list is called SI:GC-EVERY-FLIP-LIST