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From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.sys.apple2
Subject: Re: Multitasking on a II
Message-ID: <14808@smoke.brl.mil>
Date: 10 Jan 91 16:57:13 GMT
References: <11297.apple.net@pro-angmar> <60167@microsoft.UUCP>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 13

In article <60167@microsoft.UUCP> brianw@microsoft.UUCP (Brian WILLOUGHBY) writes:
>I'm not saying that this 80x86 instruction is not useful, but I am
>saying that the design of the Apple ][ system would not be benefitted
>in any way by the existence of such an instruction.

That's not true; in a multiprocessing environment there would certainly
be the need for processes to coordinate access to shared resources.  Some
form of mutual exclusion would definitely be required.  An instruction
that can be exploited to implement some form of "mutex" locking is the
simplest and most efficient way to accomplish this; often there is some
instruction that can be exploited for the purpose even though it wasn't
designed specifically for "test and set" usage.  For example, on the
PDP-11 one could exploit INC and ASRB in this manner.