[Mpi-forum] MPI_Request_free restrictions

George Bosilca bosilca at icl.utk.edu
Sat Aug 8 11:53:31 CDT 2020

Similar discussion can be found in the "advice to users" in 3.7.3 (page 63
line 18).


On Sat, Aug 8, 2020 at 12:45 PM Bangalore, Purushotham via mpi-forum <
mpi-forum at lists.mpi-forum.org> wrote:

> I see discussion of this issue here:
> https://github.com/mpi-forum/mpi-forum-historic/issues/83
> Puri
> ------------------------------
> *From:* mpi-forum <mpi-forum-bounces at lists.mpi-forum.org> on behalf of
> Balaji, Pavan via mpi-forum <mpi-forum at lists.mpi-forum.org>
> *Sent:* Saturday, August 8, 2020 8:51 AM
> *To:* mpi-forum at lists.mpi-forum.org <mpi-forum at lists.mpi-forum.org>
> *Cc:* Balaji, Pavan <balaji at anl.gov>
> *Subject:* [Mpi-forum] MPI_Request_free restrictions
> Folks,
> Does someone remember why we disallowed users from calling
> MPI_Request_free on nonblocking collective requests?  I remember the
> reasoning for not allowing cancel (i.e., the operation might have completed
> on some processes, but not all), but not for Request_free.  AFAICT,
> allowing the users to free the request doesn’t make any difference to the
> MPI library.  The MPI library would simply maintain its own refcount to the
> request and continue forward till the operation completes.  One of our
> users would like to free NBC requests so they don’t have to wait for the
> operation to complete in some situations.
> Unfortunately, when I added the Rput/Rget operations in the RMA chapter, I
> copy-pasted that text into RMA as well without thinking too hard about it.
> My bad!  Either the RMA committee missed it too, or they thought of a
> reason that I can’t think of now.
> Can someone clarify or remind me what the reason was?
> Regards,
>   — Pavan
> MPI-3.1 standard, page 197, lines 26-27:
> “It is erroneous to call MPI_REQUEST_FREE or MPI_CANCEL for a request
> associated with a nonblocking collective operation.”
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