(j3.2006) Comment on Fortran WG5 ballot N1846

[Dan Nagle]

Hello,

On Apr 20, 2011, at 02:29 , Van Snyder wrote:

> This is all true, but is irrelevant to the fact that in the program
> 
> asynchronous X
> external A, B
> call A ( X )
> call B
> print *, X
> end
> 
> the processor can't know if or how X is asynchronous.

The processor doesn't know where the asynchronous i/o happens,
nor where the wait happens.  So what.  The processor does know
the limits of what asynchronous means, provided asynchronous
is restricted to f08 asynchronous i/o.

>  If it provides asynchronous I/O, it has to respect the ASYNCHRONOUS attribute, no matter whether or how the "asynchronous" happens in A.

Note the hypothesis:  "If it provides asynchronous I/O".

Knowing how asynchronous happens, including if it happens at all,
is the point.  The processor can do the minimum is knows it needs to do
if the asynchronous attribute applies only to f08 asynchronous i/o.

For example, a processor could generate two code paths for each basic
optimization block, and use a run-time test of the pending/done indicator
to select which block to execute, if asynchronous is restricted to its own
f08 standard asynchronous i/o.  The processor can't do that if asynchronous
is enlarged to include anything anyone considers
to be asynchronous "communications".

If the asynchronous attribute applies further, to arbitrary communications,
the processor must make worst-case assumptions every time.

>> The red herring is how many levels of call are involved.

-- 
Cheers!

Dan Nagle