GR cancel_fn return value
Linda Stanberry (linda@k2.llnl.gov)
Wed, 16 Apr 1997 16:34:13 -0700 (PDT)
Yesterday I thought the return values from the GR callbacks would
not be needed, but today as I am working on implementing this, I see
that it would be terribly convenient if the cancel_fn would return
MPI_SUCCESS if the cancellation of the unknown blocking op was
successful, and ! MPI_SUCCESS otherwise. In fact, without this, I
don't know how MPI_CANCEL will know how to update the request object
to reflect that it is not only marked for cancellation but also to
indicate whether the cancellation succeeded or failed. That is, MPI
itself has no way of knowing whether or not the cancel succeeded, but
has to rely on the cancel_fn specific to this request to determine
that. If so, I am also wondering if there can be an MPI_NULL_QUERY
(MPI_QUERY_NULL ?) without specifying a default return value such as
assuming a cancel can never succeed for this request.
Was this discussed previously? I think in earlier GR proposals, the
cancel_fn was used to return this information to MPI_Cancel, so it
may have been assumed to still be doing this. However, the spec says
nothing about the return value of the cancel_fn.
Linda