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From: sakkinen@tukki.jyu.fi (Markku Sakkinen)
Newsgroups: comp.object
Subject: Re: What is Objective C?
Message-ID: <1990Sep12.074154.657@tukki.jyu.fi>
Date: 12 Sep 90 07:41:54 GMT
References: <3864@bingvaxu.cc.binghamton.edu> <77500056@m.cs.uiuc.edu> <PCG.90Sep11165843@athene.cs.aber.ac.uk>
Reply-To: sakkinen@jytko.jyu.fi (Markku Sakkinen)
Organization: University of Jyvaskyla, Finland
Lines: 29

In article <PCG.90Sep11165843@athene.cs.aber.ac.uk> pcg@cs.aber.ac.uk (Piercarlo Grandi) writes:
>On 4 Sep 90 22:36:00 GMT, johnson@m.cs.uiuc.edu said: 
> ...
>johnson> Although I agreed with most of what Paul Chisholm said, I
>johnson> disagree with this statement.  My experience with C++ is that
>johnson> memory management takes a lot of CPU time.  We use reference
>johnson> counting, and have to lock objects before changing their
>johnson> reference count (we are using a multiprocessor).
>
>For example, this is *not* necessary in many cases. Since you *must*
>eventually invoke a garbage collector to reclaim cycles, you can just
>accept imprecise reference counting, that is counting that misses some
>count decrements. Or you can use reference count logs, etc...

Perhaps you didn't notice that Prof. Johnson wrote specifically
about C++. Because of pointer arithmetic, it is not *possible*
to use garbage collection safely with C++ (or any C-based language).
(I have read Boehm's article in Software - Practice and Experience,
but the reason for his success seemed to be that those large pieces
of existing C software that he experienced with were amazingly
constrained and well-behaving in their use of pointers.)

Markku Sakkinen
Department of Computer Science and Information Systems
University of Jyvaskyla (a's with umlauts)
Seminaarinkatu 15
SF-40100 Jyvaskyla (umlauts again)
Finland
          SAKKINEN@FINJYU.bitnet (alternative network address)