(j3.2006) Comment on Fortran WG5 ballot N1846

[Dan Nagle]

Hello,

On Apr 20, 2011, at 13:17 , Van Snyder wrote:
> 
> I don't anticipate that a processor will have a global "pending" flag
> for every variable with the ASYNCHRONOUS attribute.

But the processor must keep a pending/done signal per transfer,
otherwise inquire id= won't work.  So it can be checked.

>> If the asynchronous attribute applies further, to arbitrary
>> communications, the processor must make worst-case assumptions every
>> time.
> 
> I anticipate processors will always make the worst-case assumptions
> concerning asynchronous objects because doing anything else would almost
> certainly be a net loss.

The point being, the compiler knows exactly what "worst-case"
means when it knows that asynchronous applies only to its own
f08 asynchronous i/o.

(In the example I gave, the compiler knows that actual data transfers
may happen only in write statements or in wait statements, and not elsewhere.)

The difficulty is that "worst-case" means something different
when it may also apply to an arbitrary asynchronous communications
library.

(The difficulty of defining what is communications and what is
other processing is icing on the cake merely.)

-- 
Cheers!

Dan Nagle