Hi,

Um. While that is true, to a first approximation, it isn't really. The reason is that all three of those have subtly different constraints on when a compiler must not use copy-in/copy-out and other optimisations. While this is true, I am really not sure what your message was meant to illustrate or clarify...it was confusing even to me (and I am at least familiar with the subtleties).

The only one of those that ABSOLUTELY blocks copy-in/copy-out and the more-or-less equivalent optimisations is VOLATILE. ASYNCHRONOUS does the least blocking, and is therefore the most efficient. As far as copy in/out is concerned, VOLATILE and ASYNCHRONOUS are identical as far as the standard is concerned. Specifically, a situation where copy in/out may be required to be performed is prohibited by compile-time constraints. This is not quite identical to saying "though shall not perform copy in/out", but the reason the compile-time constraints are there is so as to ensure that the argument passing can be done by pass-by-reference.

I never objected to using ASYNCHRONOUS to handle non-blocking data transfers, as you know well. However, I want to (partially) agree with Bill that to truly properly integrate non-blocking operations with the Fortran standard *both* the TARGET and the ASYNCHRONOUS attribute are required for the buffer, both the dummy *and* the actual. The ASYNCHRONOUS attribute does not have guarantees about pointer association persisting across argument passing (this is equivalent to guarantees against copy in/out)...only TARGET does and it is the intended way to allow routines to save pointers to the actual inside a routine (which MPI does). At the same time, TARGET does not allow you to asynchronously change the value of the target. So both are needed. That said, the ASYNCHRONOUS attribute, or a new attribute with similar semantics, can be extended to include the effects of pointer association argument passing semantics of TARGET. Best, Aleks