(j3.2006) (SC22WG5.3650) [ukfortran] A comment on John Wallin's comments on Nick MacLaren's comments

[N.M. Maclaren]

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.

Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:  nmm1 at cam.ac.uk
Tel.:  +44 1223 334761    Fax:  +44 1223 334679