On Thursday 07 April 2005 16:39, David Schwartz wrote:
A bit off-topic, but...

> If you mean 'volatile', no, that doesn't do anything. Specifically,
> 'volatile' has no special semantics for multi-processors. There may be
> specific compilers where it has such semantics, but the standard doesn't
> provide them.


According to ISO 9899-1990, section 6.5.3:

An object that has volatile-qualified type may be modified in ways unknown to
the implementation or have other unknown side effects. Therefore any
expression referring to such an object shall be evaluated strictly according
to the rules of the abstract machine, as described in 5.1.2.3. Furthermore,
at every sequence point the value last stored in the object shall agree with
that prescribed by the abstract machine, EXCEPT AS MODIFIED BY THE UNKNOWN
FACTORS MENTIONED PREVIOUSLY [emphasis added].

Translation: The compiler can't make assumptions about the state of a
variable marked "volatile", and MUST generate code that writes every result
stored there as well as code that reads the variable EVERY SINGLE TIME it
appears in an expression. It has nothing to do with multi-processor
coherency. Any compiler that generates code that deviates from this (even a
little bit) isn't compliant with the standard.
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