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From: Cory Nelson (phrosty_at_[hidden])
Date: 2007-10-10 14:36:53

On 10/10/07, Markus Schöpflin <markus.schoepflin_at_[hidden]> wrote:
> Ion Gaztañaga schrieb:
> > Markus Schöpflin escribió:
> >> Hello,
> >>
> >> this may be a silly question, but I have been wondering what the atomic
> >> read and write primitives are actually supposed to do?
> >>
> >> I mean, from the readers or writers POV a read or write is always atomic,
> >> isn't it? Am I missing something very obvious here?
> >
> > In some architectures, a 32 read might not be atomic (even if the read
> > is aligned). I think that Intel system is always atomic. They are there
> > for completeness, to support systems where read or write might not be
> > atomic.
> Sorry for being dense, but what exactly do you mean when you say a read
> might not be atomic? Are you thinking of memory barriers here? Or is it
> something else? Is there somewhere a definition of what atomic exactly
> means here?

I believe he is referring to cache coherency - on x86 and x64, read
and write are always atomic in the sense that a read will never see
half of the old value and half of a write.

Cory Nelson

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