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Subject: Re: [OMPI devel] MPI_Grequest_start and MPI_Wait clarification
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-11-02 21:15:15

On Oct 25, 2009, at 9:10 PM, Christopher Yeoh wrote:

> I've been running some threaded test suites against OpenMPI and was
> just wanting to clarify something in the specification and how OpenMPI
> implements it.

Sorry for the delay in replying (my inbox has become a disaster lately
-- please don't be shy about pinging us again if you don't get an
answer! Or get Brad to kick us; whichever works better ;-) ).

> One page 360 of the 2.1 spec there is (in reference to
> mpi_grequest_start query function):
> Advice to users. query_fn must not set the error field of status
> since query_fn may be called by MPI_WAIT or MPI_TEST, in which
> case the error field of status should not change. The MPI library
> knows the “context” in which query_fn is invoked and can decide
> correctly when to put in the error field of status the returned
> error code. (End of advice to users.)
> So presumably this means that you just return an error code in the
> return value of query function. But in ompi/request/req_wait.c there
> is
> /* return status. If it's a generalized request, we *have* to
> invoke the query_fn, even if the user procided STATUS_IGNORE.
> MPI-2:8.2. */
> if (OMPI_REQUEST_GEN == req->req_type) {
> ompi_grequest_invoke_query(req, &req->req_status);
> }
> which ignores the value returned by the quesry function. And it just
> uses the MPI_ERROR value in the status object instead.
> So is this just incorrect on the part of OpenMPI? Am happy to
> provide a
> patch if its not right.

I had to go re-read that whole section on generalized requests; I
agree with your analysis. Could you open a ticket and submit a
patch? You might want to look at the back ends to MPI_TEST[_ANY] and
MPI_WAIT_ANY as well (if you haven't already).


Jeff Squyres