On 01/02/18 20:52, Jeff Hammond wrote:

If a user passes a (base,size) pair that corresponds to a range of addresses that are not allocated and/or mapped, is that a correct MPI program?

Such a thing wouldn't be a valid object pointer in C/C++ or a variable in Fortran, i.e. both languages prohibit this.

The only text I can find that implies that buffers passed to MPI_Win_create have to be allocated is the following, assuming that one interprets "existing memory" this way.

"Each process specifies a window of existing memory that it exposes to RMA accesses by the processes in the group of comm." (MPI 3.1 11.2.1)

Since MPI is a library standard I would still expect all the guarantees of the language standards involved to hold and the above to only be an additional clarification?

The Fortran-specific text is similarly suggestive, but it only says that a user can pass a simply contiguous array, not that such a thing is required.

"In Fortran, one can pass the first element of a memory region or a whole array, which must be ‘simply contiguous’"

That's most probably because of the Fortran storage association "feature" which is more about how arrays were passed in pre-Fortran 90 times, i.e. it's legal for a caller C to pass some array element A(i) to a subprogram P accepting an array argument B(*) provided the effective size (that is the indices of B used in P match to valid indices of A). Regards, Thomas -- Thomas Jahns HD(CP)^2 Abteilung Anwendungssoftware Deutsches Klimarechenzentrum GmbH Bundesstraße 45a • D-20146 Hamburg • Germany Phone: +49 40 460094-151 Fax: +49 40 460094-270 Email: Thomas Jahns <[email protected]> URL: www.dkrz.de Geschäftsführer: Prof. Dr. Thomas Ludwig Sitz der Gesellschaft: Hamburg Amtsgericht Hamburg HRB 39784