(j3.2006) [ukfortran] (SC22WG5.5059) WG5 vote on draft TS on further coarray features

[Bill Long]

On 8/6/13 8:20 AM, Bill Long wrote:
>
>
> On 8/5/13 7:26 PM, Van Snyder wrote:
>
>> It seems that if an image on an SMP node has several cores, between
>> which work is shared using OpenMP, one needs an intrinsic, perhaps
>> having nothing to do with coarrays, that shows how many cores are
>> available for that image.  Is this already part of OpenMP?

I should have added that, yes, OpenMP provides inquiry functions that 
return the number of threads and various other execution time information.


>
> Why is anything like that needed?  OpenMP directives are typically
> independent of the  number of threads.    The number is relevant when
> you launch the program.  OpenMP provides an environment variable to
> specify the number of threads.  Similarly, program launchers may specify
> this value.  The program can, and should be, written independent of how
> many threads/image and how many images are used for execution.
>
>>
>> Are coarrays really intended to be a replacement for both OpenMP and
>> MPI, as originally sold at Tokyo (and earlier), or just for MPI?  It was
>
> Coarrays are part of the Fortran 2008 parallel programming feature.  The
> feature is designed so that it can be implemented in a shared memory
> environment, a distributed memory environment, or a combination of both.
>    That's it.  What you decide to "replace" is up to you.
>
> The names "MPI" and "OpenMP" are not part of the normative text in the
> standard.  There is an implicit assumption, for practical reasons, that
> implementations will "play nice" with these two models so that
> incremental code change is possible.   Formal specification of those
> interactions are the responsibilities of the MPI and OpenMP groups
> respectively.
>
>> my understanding that the distinction between communication using an
>> interconnect between nodes (whether or not using a global address
>> space), and using shared memory on a single node, would be handled
>> "under the covers" by a competent coarray implementation.  Is that no
>> longer the expectation?
>
> That has always been the expectation.  I have no idea why you imagine
> otherwise.
>
> Cheers,
> Bill
>

-- 
Bill Long                                           longb at cray.com
Fortran Technical Support    &                 voice: 651-605-9024
Bioinformatics Software Development            fax:   651-605-9142
Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101