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From: ge@kunivv1.sci.kun.nl (Ge' Weijers)
Newsgroups: comp.sys.mac.programmer
Subject: Re: How to do garbage collection in C
Message-ID: <555@kunivv1.sci.kun.nl>
Date: 4 Dec 89 10:15:30 GMT
References: <153@fornax.UUCP>
Organization: University of Nijmegen, The Netherlands.
Lines: 32

About your GC problem. There is still a way to do it if you want, although
Your C source code needs to be adapted for this method.
What you do is to allocate a root stack, that is used by the garbage collector
to find references on. If you call the garbage collector (or a routine that
might call the garbage collector) you have to save and restore root pointers
to this stack. An example:

any_routine(HeapPointer p1)
{
	HeapPointer p2 = .....; /* a C pointer into the GC heap */

	SavePointer(p1);
	SavePointer(p2);

	RoutineCallingGC();

	/* p1 and p2 might point to garbage. restore them */

	p2 = GetPointer();
	p1 = GetPointer();
}

This is not the ultimate in efficiency, but if you implement SavePointer and
GetPointer using macros it might have a reasonable performance. Also check
for stack overruns. It's the only way I know of to implement a compacting GC
for C. Sigh.

Ge' Weijers
Ge' Weijers                                    Internet/UUCP: ge@cs.kun.nl
Faculty of Mathematics and Computer Science,   (uunet.uu.net!cs.kun.nl!ge)
University of Nijmegen, Toernooiveld 1         
6525 ED Nijmegen, the Netherlands              tel. +3180612483 (UTC-2)