MPI-3 page 483 says: "two concurrently running threads may make MPI
calls and the outcome will be as if the calls executed in some order,
even if their execution is interleaved."

The outcome of my program where the calls execute in some order is
well-defined: the first call completes the request and the second call
returns immediately since req=MPI_REQUEST_NULL.

Furthermore, MPI-3 page 486 says that MPI_THREAD_MULTIPLE is defined
to mean "Multiple threads may call MPI, with no restrictions."
Without restriction implies that data races are valid.  The prior
statement ensures that the result of a program with MPI-related races
is well-defined.

Do you disagree with my interpretation of MPI-3?

Jeff

On Thu, Jan 15, 2015 at 9:41 PM, Thakur, Rajeev <thakur@mcs.anl.gov> wrote:

I would say the program is erroneous. It is calling MPI_Wait concurrently on the same request, i.e., you are completing one operation twice. You can call MPI_Wait concurrently, but with different requests.

Rajeev

On Jan 15, 2015, at 11:32 PM, Jeff Hammond <jeff.science@gmail.com>
wrote:

I am trying to run the following program.  It's obviously a silly
program but I wrote it to make an argument about the MPI standard.  I
don't believe it violates the MPI standard, but please let me know if
I am mistaken.

smakramu-mobl:MPI jrhammon$ cat wait-race.c
#include <stdio.h>
#include <omp.h>
#include <mpi.h>

int main(int argc, char * argv[])
{
  int provided;
  MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &provided);
  if (provided<MPI_THREAD_MULTIPLE) {
      printf("inadequate thread support\n");
      MPI_Finalize();
  }

  MPI_Request req;
  MPI_Ibarrier(MPI_COMM_WORLD, &req);
  //req = MPI_REQUEST_NULL;
#pragma omp parallel num_threads(2) shared(req)
  {
      MPI_Wait(&req, MPI_STATUS_IGNORE);
  }

  printf("test finished\n");
  MPI_Finalize();
  return 0;
}

I compile the program with MPICH git master and GCC 4.9.2 from about a week ago:

smakramu-mobl:MPI jrhammon$ mpicc -fopenmp -g -Wall wait-race.c

smakramu-mobl:MPI jrhammon$ mpichversion
MPICH Version:        3.2a2
MPICH Release date:   unreleased development copy
MPICH Device:         ch3:nemesis
MPICH configure:      CC=gcc-4.9 CXX=g++-4.9 FC=gfortran-4.9
F77=gfortran-4.9 --disable-cxx --enable-fortran
--enable-threads=runtime --enable-g=dbg --with-pm=hydra
--prefix=/opt/mpich/dev/gcc/default --enable-wrapper-rpath
--enable-static --enable-shared
MPICH CC:     gcc-4.9    -g -O2
MPICH CXX:    no   -g
MPICH F77:    gfortran-4.9   -g -O2
MPICH FC:     gfortran-4.9   -g -O2

Sometimes the program runs fine:

smakramu-mobl:MPI jrhammon$ mpiexec -n 2 ./a.out
test finished
test finished

And sometimes it fails like this:

smakramu-mobl:MPI jrhammon$ mpiexec -n 2 ./a.out
test finished
Fatal error in MPI_Wait: Internal MPI error!, error stack:
MPI_Wait(187).............: MPI_Wait(request=0x7fff5b51ee88, status=0x1) failed
MPIR_Wait_impl(84)........:
MPIR_Request_complete(232): INTERNAL ERROR: unexpected value in case
statement (value=78309520)

So either my program violates the MPI standard or there's a bug in
MPICH.  Please let me know which it is.

Thanks,

Jeff

--
Jeff Hammond
jeff.science@gmail.com
http://jeffhammond.github.io/
_______________________________________________
discuss mailing list     discuss@mpich.org
To manage subscription options or unsubscribe:
https://lists.mpich.org/mailman/listinfo/discuss

_______________________________________________
discuss mailing list     discuss@mpich.org
To manage subscription options or unsubscribe:
https://lists.mpich.org/mailman/listinfo/discuss

--
Jeff Hammond
jeff.science@gmail.com
http://jeffhammond.github.io/
_______________________________________________
discuss mailing list     discuss@mpich.org
To manage subscription options or unsubscribe:
https://lists.mpich.org/mailman/listinfo/discuss