Peter,
>Von: "Peter Smet" <peter.smet at flinders.edu.au>
 If
> the arguments of any message refer back to a publisher or a subscriber, you
> get a circular reference that effectively prevents the gc from ever
> collecting these objects. This turns out to be a very common situation.

This reminds me of a tutorial I attended at OOPSLA '97 about Ephemerons.
They are used in VisualWorks to implement finalization. They require support
by the garbage collector, and do solve the problem you described.

All this I only remember vaguely, so please check the conference
proceedings...

Wolfgang