(j3.2006) co-array variable

[Van Snyder]

On Thu, 2007-05-31 at 12:42 -0500, Bill Long wrote:
> 
> 
> Craig Rasmussen wrote:
> > 
> > 
> > Could you please tell me what you mean by atomic in terms of the  
> > standard.  I searched for atomic and it didn't come up.  I worry  
> > about trying to equate scalar with atomic operations, but perhaps  
> > that wasn't your point.
> >   
> 
> It is probably better to avoid the use of "atomic" here since there is
> a widely used concept of "atomic memory operations" which is
> different. AMO's have been discussed as an addition to Fortran, but
> not accepted, so far.
> 
> If you have a volatile variable, it is understood that it might be
> changed by some agent not visible to the local execution context.
> Thus, any reference needs to effectively involve a reload from memory,
> as opposed to using a copy held in a register.  The underlying
> assumption for volatile is that the memory system operations are
> sufficiently serialized that the load from memory will always get
> either the old value or the new value, and not some bits from one and
> the remaining bits from the other, at least on the granularity of a
> numeric storage unit.     The only thing new with co-arrays is that
> the "agent not visible to the local execution context" could be a
> definition of the variable by a different image. 

Should this require the co-array variable to have the VOLATILE
attribute, or perhaps explicitly imply it?

> Cheers,
> Bill
> 
> 
> 
> -- 
> Bill Long                                   longb at cray.com
> Fortran Technical Support    &              voice: 651-605-9024
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