[OMPI users] MPI_Comm_get_attr fails for sub-communicators created by MPI_Comm_split

[Weiqun Zhang]

Hi,

It appears that MPI_Comm_get_attr fails to get MPI_TAG_UB for
sub-communicators created by MPI_Comm_split.  I have tested the following
programs with openmpi 3.1.1 and openmpi 1.10.2.  MPI_Comm_get_attr works on
MPI_COMM_WORLD, but not on sub-communicators.  Is this expected?

#include <stdio.h>
#include <mpi.h>

int main(int argc, char** argv)
{
    MPI_Init(&argc, &argv);

    int rank;
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    void* p; int flag;
    MPI_Comm_get_attr(MPI_COMM_WORLD, MPI_TAG_UB, &p, &flag);
    if (!flag) {
        printf("MPI_COMM_WORLD: rank %d failed to get MPI_TAG_UB\n", rank);
    } else {
        printf("MPI_COMM_WORLD: rank %d succeeded to get MPI_TAG_UB\n",
rank);
    }

    int color = rank%2;
    MPI_Comm comm;
    MPI_Comm_split(MPI_COMM_WORLD, color, rank, &comm);
    int rank2;
    MPI_Comm_rank(comm, &rank2);
    MPI_Comm_get_attr(comm, MPI_TAG_UB, &p, &flag);
    if (!flag) {
        printf("Subcommunicator %d rank %d failed to get MPI_TAG_UB\n",
color, rank2);
    } else {
        printf("Subcommunicator %d rank %d succeeded to get MPI_TAG_UB\n",
color, rank2);
    }

    MPI_Finalize();
}

program main

  use mpi
  implicit none

  integer :: ierr, rank, color, comm, rank2
  integer(kind=MPI_ADDRESS_KIND) :: attrval
  logical :: flag

  call MPI_Init(ierr)

  call MPI_Comm_rank(MPI_COMM_WORLD, rank, ierr)
  call MPI_Comm_get_attr(MPI_COMM_WORLD, MPI_TAG_UB, attrval, flag, ierr)
  if (.not.flag) then
     print *, "MPI_COMM_WORLD: rank ", rank, " failed to get MPI_TAG_UB."
  else
     print *, "MPI_COMM_WORLD: rank ", rank, " succeeded to get MPI_TAG_UB."
  end if

  color = modulo(rank,2)
  call MPI_Comm_split(MPI_COMM_WORLD, color, rank, comm, ierr)
  call MPI_Comm_rank(comm, rank2, ierr)
  call MPI_Comm_get_attr(comm, MPI_TAG_UB, attrval, flag, ierr)
  if (.not.flag) then
     print *, "Subcommunicator ", color, " rank ", rank2, " failed to get
MPI_TAG_UB."
  else
     print *, "Subcommunicator ", color, " rank ", rank2, " succeeded to
get MPI_TAG_UB."
  end if

  call MPI_Finalize(ierr)

end program main

Thanks,

Weiqun

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