[mpiwg-rma] MPI_Win_create on unmapped memory?

William Gropp wgropp at illinois.edu
Tue Jan 2 14:19:15 CST 2018

It was certainly the intent that the memory be allocated.  Specifically, if a is the pointer and the region is of length L, then (assuming char *a and ) a[0] … a[L-1] must be valid r and l values at the point of the call.


William Gropp
Director and Chief Scientist, NCSA
Thomas M. Siebel Chair in Computer Science
University of Illinois Urbana-Champaign

> On Jan 2, 2018, at 1:52 PM, Jeff Hammond <jeff.science at gmail.com> 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?
> 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)
> 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’"
> Thanks,
> Jeff
> --
> Jeff Hammond
> jeff.science at gmail.com <mailto:jeff.science at gmail.com>
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