Re: MMM and MCL 2.0.1

[reti@cambridge.apple.com (Kalman Reti)]

At 15:45 3/6/95 -0500, Bill St. Clair wrote:
>At 10:40 AM 2/28/95, David Neves wrote:
>>In article <dgaxiola-2802950129390001@silent-mobius.mit.edu>,
>>dgaxiola@mit.edu (David Gabriel Gaxiola) wrote:
>>
>>:  I've been using MCL 2.0.1 on my PowerMac 6100 for the past few weeks with
>>:  the modern memory manager on.  I've been told/read that for MCL to work
>>:  right, MMM should be turned off.  I've not seen any problems so far.  Am I
>>:  just setting myself up for disaster?
>>We can reliably crash MCL (with MMM on) with Quicktime.  I bet anything
>>that deals with the Mac Heap may cause problems.  If you are just doing
>>standard Lisp stuff without using the graphics interface you might be
>>successful.
>>-David
>
>Kalman has investigated this more than I, but I believe the problem
>occurs if MCL's growzone procedure is called. The growzone procedure
>is called when there is not enough room in the (Mac) heap to satisfy
>a NewPtr or NewHandle request. MCL's growzone uses undocumented
>information about how the heap is represented in order to move the
>boundary between the Mac heap and the Lisp heap. The MMM changes
>this undocumented representation in a way that is incompatible with
>MCL.

There are more problems than this.  Any GC can potentially trash your
heap.  Don't use MMM with 2.0.1.