[mpiwg-rma] MPI_Win_create on unmapped memory?

[Jeff Hammond]

I agree with all of these comments, but a user is arguing that these
requirements are not clear from the text, e.g. because the meaning of
existence in "existing memory" is not defined.  It seems that what is
obvious to us is not obvious to users.

Jeff


On Tue, Jan 2, 2018 at 12:54 PM, William Gropp <wgropp at illinois.edu> wrote:

> Yes.  The r and l values must remain valid until the free.
>
> Bill
>
> William Gropp
> Director and Chief Scientist, NCSA
> Thomas M. Siebel Chair in Computer Science
> University of Illinois Urbana-Champaign
>
>
>
>
>
>
> On Jan 2, 2018, at 2:52 PM, Nathan Hjelm <hjelmn at mac.com> wrote:
>
> I would expect that the intent is also that the memory should not be
> freed/unmapped before the matching call to MPI_Win_free() correct?
>
> -Nathan
>
> On Jan 02, 2018, at 01:19 PM, William Gropp <wgropp at illinois.edu> wrote:
>
> 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.
>
> Bill
>
> 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
> http://jeffhammond.github.io/
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-- 
Jeff Hammond
jeff.science at gmail.com
http://jeffhammond.github.io/
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