Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ukma!rex!uflorida!beach.cis.ufl.edu!mfi
From: mfi@beach.cis.ufl.edu (Mark Interrante)
Newsgroups: comp.sys.mac.programmer
Subject: Re: System 7.0 Q & A -- memory protection (none)
Message-ID: <20305@uflorida.cis.ufl.EDU>
Date: 17 May 89 11:40:35 GMT
References: <1838@internal.Apple.COM> <7320@hoptoad.uucp>
Sender: news@uflorida.cis.ufl.EDU
Reply-To: mfi@beach.cis.ufl.edu ()
Organization: UF CIS Department
Lines: 27

In article <7320@hoptoad.uucp> tim@hoptoad.UUCP (Tim Maroney) writes:
>..I think the probability of one application trashing
>another actually increases in System 7.0.  To be useful, virtual memory
>requires that process sizes be able to increase.  Given one large
>address space, the only way to do this on the Mac is by discontiguous
>heaps -- that is, when the application heap runs out of memory, a new
>chunk is added at a discontiguous location in the global address
>space.  So after a few applications grow, their heaps are thoroughly
>intertwined.  One of the more common program errors consists of
>assuming that heap block is larger than it actually is and writing past
>the end.  In 7.0, that has a good chance of writing into another
>application's heap instead of simply corrupting one's own heap.
>Very messy, and it seems like a giant step backwards.

I know very little about the insides of the mac memory manager (i use lisp :)
but it seems that if the manager would start applications far enough apart 
from each other then the odds of a collision would be very low.  If the 
applications were started say 20mb apart then you could still have a large
number of active apllications.  



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Mark Interrante   		  Software Engineering Research Center
mfi@beach.cis.ufl.edu		  CIS Department, University of Florida 32611
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"X is just raster-op on wheels" - Bill Joy, January 1987