(j3.2006) (SC22WG5.3669) [ukfortran] N1755: Request for new features from MPI Forum

[Aleksandar Donev]

Hi,

I am confused as to whether this should go to WG5 or J3. I thought we 
were not to have long technical arguments on WG5?

> Eh? What about NOTE 12.22?
Do you get WG5 e-mails? Did you get my response to your message and take 
a look at paper 08-165 and also 08-165r1.txt from meeting 184? That 
paper of mine changed that Note! I don't have the exact new text (the 
paper gives diff edits), but the intention is:
"That is, the aversion to copy-in/out is only necessary, and therefore
should only apply, if there is any chance that the volatility and/or
asynchronicity is active either before or after the procedure call; 
there is no problem if it is limited to only being within the called 
procedure itself."

The relevant parts of 08-165 are appended below, for your consideration 
(please read that before continuing).

>> 2. "C559 An entity with the VOLATILE attribute shall be a variable that 
>> is not an INTENT (IN) dummy argument." Please explain this one to me. 
> Bill has explained this one.
Except that, in my response, and Van's, we specifically disagreed with 
the "explanation" and essentially called it an obfuscation. Did you read 
those?

Further comments in response to second e-mail follow.
Best,
Aleks

====
What the Note should really say, according to 08-185:

"Just because the dummy argument has the ASYNCHRONOUS attribute does
not imply that the corresponding actual argument necessarily has the
attribute, and vice versa. In particular, if during the execution of
the procedure the actual argument is not a pending I/O storage sequence
affector (9.6.2.5) the dummy argument is not required to have the
ASYNCHRONOUS attribute. Similarly, if all asynchronous I/O involving
the dummy argument completes before the procedure completes execution,
the actual argument is not required to have the ASYNCHRONOUS attribute.

If, however, the values of an actual argument can change due to
an asynchronous I/O operation while the procedure is in execution,
the dummy argument should also have the corresponding (ASYNCHRONOUS
or VOLATILE) attribute. Similarly, if an asynchronous I/O operation
involving the dummy argument begins during the execution of the
procedure but does not complete before the procedure completes
execution, the actual is required to have the ASYNCHRONOUS
attribute. The constraints on actual arguments with the ASYNCHRONOUS
attribute that correspond to a dummy argument with the ASYNCHRONOUS
attribute are designed to avoid forcing a processor to use the
so-called copy in/copy-out argument passing mechanism. If copy
in/copy-out occurs then any changes to the values of the actual due
to asynchronous I/O will be lost when the called procedure returns
and the copy-out overwrites the actual argument, and any changes
of the values of the actual argument will not be visible during the
execution of the procedure. Similarly, if copy in/out occurs and an
asynchronous I/O operation begins but does not complete during the
execution of the procedure, the operation will fail when the copy is
deallocated upon return from the procedure.

Identical considerations apply to the VOLATILE attribute, with the
only difference that the values of the dummy or actual argument change
by means outside of the program, rather than asynchronous I/O."