(j3.2006) (SC22WG5.3643) [ukfortran] A comment on John Wallin's comments on Nick MacLaren's comments

[Bill Long]

N.M. Maclaren wrote:
> John Wallin wrote:
>   
>
>> In short, coarrays would make my head hurt less.
>>     
>
> Most of the users I have dealt with have backed off shared-memory
> paradigms when they found that they couldn't debug or tune them, and
> gone back to MPI.  The problem is that there are, and can be, no tools
> to trap race conditions.
>   

This is, of course, one of the main arguments in favor of coarrays.  The 
programming model, is SPMD,  as with MPI, which experience has shown to 
work, and to be the most popular.   Shared-memory models, like OpenMP, 
do have their place, but have limitations. 

>   
>> I would suggest talking to the UPC forum about this.  They have a lot
>> of experience with this, and can address it directly.
>>     
>
> Not much, actually.  There aren't many versions, and UPC isn't much
> used by real scientists.  

Well, "real" scientists would not be using any variant of C. :)  
However, I think UPC will gain even more traction once it is formally 
standardized.  User's want some assurance of language stability before 
they dive into a large coding project.  Similarly for vendors providing 
compilers.  Same argument applies for why standardization of coarrays is 
needed.

>
>
> I am talking about programs that have no deadlocks in, but where they
> are introduced by the implementation.
>
>
>   

Deadlocks introduced by the implementation should be reported as bugs to 
the vendor. 

Cheers,
Bill


-- 
Bill Long                                   longb at cray.com
Fortran Technical Support    &              voice: 651-605-9024
Bioinformatics Software Development         fax:   651-605-9142
Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120