(j3.2006) (SC22WG5.3655) [ukfortran] FW: Notes on WG5 coarray papers

[Malcolm Cohen]

Hi folks,

Reinhold Bader wrote:
>
> [discussion on restriction I want but cannot get]
>
> Do you think this is then only a matter of telling users
> "don't use volatile (array, derived type) coarrays thusly" or
> something which needs fixing in the standard in a more
> appropriate manner than suggested by me?
>   
Probably more the latter than the former.  I usually prefer to have less 
ambiguity in my standards.
>>> Example 2.4 ("Protected Context") is non-conforming since the cited
>>> restriction is violated by the object in question being VOLATILE within
>>> the scope of the DO loop. This would apply even if the CASE(1) statements
>>> were not present.
>>>
>>>       
>> There is no restriction that says a DO index variable cannot have the
>> VOLATILE attribute, and the "cited restriction" does not even mention
>> VOLATILE.  So I cannot agree with your reasoning.  (In fact I think the
>> example is conforming when used as described in the paper.)
>>     
>
> I don't agree with that one. Referring to 08-007r2, we have
>
> 5.3.19 para1: The VOLATILE attribute specifies that an object may be referenced,
>                        defined, or become undefined, by means not specified by the program,
>                        or by another image without synchronization.
>
> so if the DO index variable is volatile, it will by virtue of its volatility violate the cited
> restriction, won't it?
No.

It only violates the restriction if it actually *IS*  defined etc.

This is not a static restriction but a dynamic one.
>  Or do you consider the program conforming (statistically
> conforming?) as long as simply by chance the index isn't stomped on by anyone
> else while DO executes?
>   
That is *EXACTLY* what those words mean.

Like in the Fortran 90 program snippet

   INTEGER x(100)
   EQUIVALENCE(x(50),i)
   x = 0
   DO i=1,10
     READ *,j
     x(j) = i
   END DO

That is not conforming if the user types in a number <1 or >100 
(subscript error) or ==50 (updating a DO index error); it is conforming 
otherwise.

Cheers,
-- 
.........................Malcolm Cohen, Nihon NAG, Tokyo.