Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!tektronix!zeus!bobr
From: bobr@zeus.TEK.COM (Robert Reed)
Newsgroups: comp.lang.smalltalk
Subject: Re: Smalltalk for (embedded) real-time
Message-ID: <2381@zeus.TEK.COM>
Date: Tue, 8-Sep-87 18:53:05 EDT
Article-I.D.: zeus.2381
Posted: Tue Sep  8 18:53:05 1987
Date-Received: Thu, 10-Sep-87 05:30:20 EDT
References: <1881@tekig4.TEK.COM> <80500016@uiucdcsp>
Reply-To: bobr@zeus.UUCP (Robert Reed)
Organization: CAE Systems Division, Tektronix Inc., Beaverton OR
Lines: 25

In article <80500016@uiucdcsp> johnson@uiucdcsp.cs.uiuc.edu writes:

    There is another problem with Smalltalk that is more severe.  Smalltalk
    uses garbage collection a lot.  Garbage collection can easily interfere
    with real-time requirements.  The solution is to go back to using the
    reference counting techniques that implementors are now ignoring, use
    parallel garbage collection, or program very carefully and ensure that
    no garbasge is produced.  Of course, any program that produces a lot of
    garbage won't convert to Objective C very well, since I think that it
    has no garbage collector.  Please correct me if I am wrong.

This comment shows a basic lack of understanding about "garbage collection"
and "reference counting."  In fact, most Smalltalk implementations employ
BOTH reference counting AND garbage collection.  Reference counting is used
to detect "dead" objects (i.e. objects which are no longer referenced by any
other object).  The space occupied by these objects may or may not then be
moved to a free list.  

Eventually, fragmentation resulting from allocation and reallocation of a
given segment of memory may require garbage collection (i.e. the relocation
of "live" objects to coalesce the free memory of the segment into one block)
in order to keep the system from going belly up.  Garbage collection has
nothing particular to do with reference counting.
-- 
Robert Reed, Tektronix CAE Systems Division, bobr@zeus.TEK