Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!BARILVM.BITNET!P85025
From: P85025@BARILVM.BITNET (Doron Shikmoni)
Newsgroups: comp.lang.asm370
Subject: Re: More pet ALC tricks...
Message-ID: <8911131336.AA27002@brazos.rice.edu>
Date: 13 Nov 89 07:36:28 GMT
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Reply-To: IBM 370 Assembly Programming Discussion List <ASM370%UCF1VM.BITNET@ricevm1.rice.edu>
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>Thanks, Valdis and Doron, for your info on CS and CDS.  Somehow, I had a
>mental block for those guys, and a few others as well.  Also, I agree
>that there must be something similar for AP and MP environments.  Any
>clues yet???

What do you mean? CS and CDS *are* for AP and MP, exactly. The whole
idea of "Compare-and-Swap" is that the action can be seen as "atomic",
in the aspect of storage references; the system control ensures that
all storage accesses are serialized before and after CS, CDS, TS etc.
- that is, no other processor can interfere with this action, or fetch
an operand between the "Compare" and the "Swap". (Mind you, this is far
from being a simple task, if you take into account central storage caching
and pre-fetch pipelining). This *is* the way to serialize in an AP/MP
environment, virtual or real.

Note, that CS/CDS/TS should be used only if you really need to serialize;
if you just want to compare-and-then-swap, and think of using these since
"It's one instruction", in a simple "application" program, don't; these
instructions are expensive.

Doron