I've got a strange problem with Fortran90 and MPI_BCAST call on a large application. I've isolated the problem in this short program samples.
With fortran we can use subarrays in functions calls. Example, with passing a subarray to the "change" procedure:

MODULE mymod
IMPLICIT NONE
CONTAINS
  SUBROUTINE change(tab,i)
    IMPLICIT NONE
    INTEGER, INTENT(INOUT),DIMENSION(:)::tab
    INTEGER, INTENT(IN) :: i
    tab(:)=i
  END SUBROUTINE change
END MODULE mymod

PROGRAM toto
  USE mymod
  IMPLICIT NONE
  INTEGER, PARAMETER::nx=6, ny=4
  INTEGER, DIMENSION(nx,ny):: tab
  INTEGER::i

  tab=-1
  DO i=1,nx
    CALL change(tab(i,:),i)
  ENDDO
  PRINT*,tab
END PROGRAM toto


But If I use subarrays with MPI_BCAST() like in this example:

PROGRAM bide
USE mpi
   IMPLICIT NONE
   INTEGER :: nbcpus
   INTEGER :: my_rank
   INTEGER :: ierr,i,buf
   INTEGER, ALLOCATABLE:: tab(:,:)

    CALL MPI_INIT(ierr)
    CALL MPI_COMM_RANK(MPI_COMM_WORLD,my_rank,ierr)
    CALL MPI_COMM_SIZE(MPI_COMM_WORLD,nbcpus,ierr)

    ALLOCATE (tab(0:nbcpus-1,4))

    tab(:,:)=-1
    tab(my_rank,:)=my_rank
    DO i=0,nbcpus-1
       CALL MPI_BCAST(tab(i,:),4,MPI_INTEGER,i,MPI_COMM_WORLD,ierr)
    ENDDO
    IF (my_rank .EQ. 0) print*,tab
    CALL MPI_FINALIZE(ierr)

END PROGRAM bide


It doesn't work! With openMPI 1.2.8 (OpenSuse 11.4 X86_64) I have random segfault: it works sometime, with few cpus (2, 4, 8...) and does'nt work sometime with a larger number of cpus (32, 48, 64...). With OpenMPI 1.4.4 (build from sources) it hangs (most of the array tab remains at the -1 initialization value).
Such procedure calls are allowed with fortran90 so I do not understand why they fail here. I have to use a buffer array (called tabl in the following program) to solve the problem.

PROGRAM bide
USE mpi
   IMPLICIT NONE
   INTEGER :: nbcpus
   INTEGER :: my_rank
   INTEGER :: ierr,i,buf
   INTEGER, ALLOCATABLE:: tab(:,:)
   INTEGER::tab1(4)

    CALL MPI_INIT(ierr)
    CALL MPI_COMM_RANK(MPI_COMM_WORLD,my_rank,ierr)
    CALL MPI_COMM_SIZE(MPI_COMM_WORLD,nbcpus,ierr)

    ALLOCATE (tab(0:nbcpus-1,4))

    tab=-1
    tab1=-1
    DO i=0,nbcpus-1
       IF(my_rank.EQ.i) tab1=my_rank
       CALL MPI_BCAST(tab1,4,MPI_INTEGER,i,MPI_COMM_WORLD,ierr)
       tab(i,:)=tab1
    ENDDO
    IF (my_rank .EQ. 0) print*,tab
    CALL MPI_FINALIZE(ierr)

END PROGRAM bide


Any idea about this behavior ?

Patrick
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