(j3.2006) (SC22WG5.3650) [ukfortran] A comment on John Wallin's comments on Nick MacLaren's comments
Fri Nov 7 17:09:31 EST 2008
On Nov 7 2008, Bill Long wrote:
>> The (simplified) issue is whether SYNC MEMORY is allowed to wait until
>> the image that owns the data it is accessing reaches the next image
>> control statement. No more than that.
>I would have to say no to the idea of allowing SYNC MEMORY to wait for
>other images to arrive at an image control statement. It lacks an
>exclusion for volatile coarrays. For the important case of the
>spin-loop synchronization you could end up with a hung program. Even in
>the non-volatile case, I don't see it as necessary.
I don't have a major problem with that, but the standard needs to say so,
and to say exactly what it does permit. Currently, it doesn't.
>Finally, it is
>inconsistent with the semantics that SYNC MEMORY is a local operation
>(irrespective of how it might be actually implemented).
It is always a bad idea to specify something that is logically and
physically unrealistic. Those semantics are not deliverable, in general.
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