[gclist] Re: gclist-digest V2 #76

[Michael Spertus]

At 11:51 AM 12/10/97 -0500, P. T. Withington wrote:
>At 20:54 -0600 11/6/97, Michael Spertus wrote:
>>Finally, observe that 64-bit machines turn conservative collectors
>>automatically  into precise collectors!
>
>How so?
>
As long as the collector is well-designed, 64-bit address space is so large
that you'd be better off worrying about meteors hitting your computer than
significant data value/pointer misidentification.

There is a way in which unnecessary retention can occur even in a 64-bit
collector. If the stack shrinks and then grows, there may be stale pointers
in "holes" in the stack. While aggressive stack-zeroing, as practiced by us
and the Boehm collector can substantially reduce this problem, I am not
aware of a way to entirely eliminate it without compiler support.
Fortunately, it is O(1). I think that there is currently insufficient data
to infer whether or not it will ever be a problem in practice.


Michael Spertus                            mps@geodesic.com
Geodesic Systems                           (312) 832-1221
414 N Orleans, Suite 410                   http://www.geodesic.com
Chicago, IL 60610