On Feb 19, 2009, at 9:00 AM, Bill Long wrote:

Aleksandar Donev wrote:

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Hi Craig,

Since I wasn't in Vegas I will read the papers and try to reconstruct what you guys talked about, and in particular, to understand why "TYPE(*), DIMENSION(*)" was not a possibility (excluding scalar actuals if necessary---handle that by a separate procedure if need be).

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interface subroutine MPI_Send(buf, ...) BIND(C) TYPE(*), DIMENSION(..), INTENT(in) :: buf ... end subroutine end interface I think using TYPE(*) and DIMENSION(..) is an excellent solution for MPI 3.0. The advantages are: I am in agreement that this is a good solution. BUT: 1. Current user code won't have to change beyond using the MPI3 module. That makes no sense. If the array is passed by descriptor, there is absolutely no need to also pass its size as an argument. Even the type, at least for the set of predefined intrinsic interoperable types, does not need to be passed.

Either we keep the interfaces as close to what they are (pass-by- address), or, we refine them. Otherwise you get something that neither satisfies existing codes/implementations nor does it satisfy demanding users (read: me :-)

I would note (for the MPI folks) that discussions at J3 meetings suggest that Aleks is not the only one who would like a "modern" MPI interface for Fortran. J3 has no official position on this one way or the other. We are working to make such an interface possible (as part of a larger scope C interoperability TR), but it is up to the MPI group to decide what to support. The hard reality is that there is a enormous amount of legacy MPI code out there and the "don't make me change my code" crowd is a significant fraction (most likely the majority) of MPI/Fortran users. So, I think that continuing to support the current style of interface is not really optional. The question is whether to support an additional interface that is more in tune with modern Fortran, and offers definite advantages to authors of new codes. I don't think it is either/or, but rather one or two.

This topic has come up frequently at MPI Forum meetings and in discussions between Jeff Squyres and myself. The answer to the question is that there will be a low level interface that follows the current C standard as closely as possible, but provides type checking where feasible and solves/provide guidance on the asynchronous problem. There is also interest in providing a high level (real Fortran) interface that takes advantage of the full features in Fortran. This would be a separate effort and not part of the MPI standardization effort. I'll still awaiting news whether there will be funding for this or not. Regards, Craig