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Observable Non Determinism in the declarative concurrent model? (CTM)


From: Ben Moseley (ben_moseley@mac.com)
Date: Wed Nov 19 2003 - 21:08:05 CET


Hi,

A question has occurred to me whilst reading the Concepts Techniques
and Models book...

On p22 it gives the following as an example of observable
nondeterminism in Oz:

declare
C={NewCell 0}
thread
        C:=1
end
thread
        C:=2
end

There is observable nondeterminism because we can't tell in advance
what the content of C will be.

But isn't there observable nondeterminism in the declarative concurrent
subset of Oz by exactly the same argument:

declare C
thread
        C=1
end
thread
        C=2
end

... with this example you cannot tell in advance which value C will be
bound to. Certainly the other binding attempt will fail, but isn't this
observable nondeterminism nonetheless?

I expect there's a flaw in my argument somewhere - but I can't see it...

--Ben
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