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Re: [PATCH] Adding callbacks to the core

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From:
Robin Houston
Date:
August 22, 2001 08:29
Subject:
Re: [PATCH] Adding callbacks to the core
Message ID:
20010822162920.A29760@puffinry.freeserve.co.uk
David M Lloyd wrote:
> for instance no matter how the CPU threads, it wouldn't make logical
> sense to do a comparison with a variable before or during an
> assignment that precedes the comparision.

Presumably it can't _literally_ do that, but are you sure it can
never appear that way to other processors?

I would have thought that, if your processor is caching the
variable, it might well *appear* that the comparison has been
done before the assignment.

Multi-processor Alpha systems apparently exhibit some particularly
counter-intuitive behaviour wrt apparent ordering of instructions.
There's a nice explanation here:
  http://www.cs.umd.edu/~pugh/java/memoryModel/AlphaReordering.html

I'm definitely not an expert on this, but it definitely seems that
if you're _not_ an expert then this stuff is nearly impossible to get
right if you start trying to be clever.

 .robin.

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