What does atomic_read actually do?

[Joseph Seigh]

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?

Joe Seigh

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