Path: utzoo!attcan!uunet!wuarchive!decwrl!shelby!portia!dhinds
From: dhinds@portia.Stanford.EDU (David Hinds)
Newsgroups: comp.lang.pascal
Subject: Re: TP Dynamic variable disposal
Summary: Memory allocation in TP v3.0 vs 4.0, etc
Message-ID: <6979@portia.Stanford.EDU>
Date: 24 Nov 89 20:02:46 GMT
References: <21510@adm.BRL.MIL> <4620@ncsuvx.ncsu.edu> <6957@portia.Stanford.EDU> <4645@ncsuvx.ncsu.edu>
Sender: David Hinds <dhinds@Portia.stanford.edu>
Organization: Stanford University
Lines: 19

In article <4645@ncsuvx.ncsu.edu>, unkydave@shumv1.uucp (David Bank) writes:
> 
> It was my understanding, and it may be in error, that dynamic memory
> allocation handling underwent significant alteration between versions
> 3.0 and 4.0 (along with just about everything else).
> 
    My description applies to all versions of TP, as far as I know.  I don't
remember for sure, but I think the early TP dispose() routine wasn't capable
of reclaiming the disposed space for later calls to new().  The newer versions
maintain a list of free blocks of memory within the heap.  Heap variables are
created starting at the base of the heap, and the free list grows downward
from the top.  The early versions (3.0 or earlier?) didn't maintain a free
list.  The DOS-level memory allocation is basically the same in all versions.
In fact, for early versions of DOS, the "dispose block" routine never worked
right, and it would have been disasterous for TP to use it for heap memory
management.

David Hinds
dhinds@portia.stanford.edu