Re: What does atomic_read actually do?

From: Paolo Ornati
Date: Sat Dec 18 2004 - 12:14:18 EST

On Sat, 18 Dec 2004 11:23:37 -0500
"Joseph Seigh" <jseigh_02@xxxxxxxxxx> wrote:

> It doesn't do anything that would actually guarantee that the fetch
> from memory would be atomic as far as I can see, at least in the x86
> version. The C standard has nothing to say about atomicity w.r.t.
> multithreading or multiprocessing. Is this a gcc compiler thing? If
> so, does gcc guarantee that it will fetch aligned ints with a single
> instruction on all platforms or just x86? And what's with volatile
> since if the C standard implies nothing about multithreading then it
> follows that volatile has no meaning with respect to multithreading
> either? Also a gcc thing? Are volatile semantics well defined enough
> that you can use it to make the compiler synchronize memory state as
> far as it is concerned?

Paolo Ornati
Gentoo Linux (kernel 2.6.9-gentoo-r6)
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