Atomicity of Cells

[David Hopwood]

Raphael Collet wrote:
> Dear Christopher,
> 
>>Exchange is atomic on cells, what about '@' and Cell.access?  I am
> 
> If C is a cell, then X=@C is the same as X={Access C}, which is the same
> as {Exchange C X X}.  There is only *one* stateful operation, so it is
> atomic by definition.

I don't mean to be pedantic, but the fact that there is only one visible
operation doesn't necessarily mean that it is implemented in only one
step. Your argument would also depend on the fact that steps are strictly
interleaved, which is true of Oz but not some other concurrency models.

Exchange operations are atomic, but that's a specified property of Exchange
rather than being true by definition.

-- 
David Hopwood <david.nospam.hopwood at blueyonder.co.uk>