Re: [OMPI users] MPI_DATATYPE_NULL and MPI_AlltoallW

[Jim Edwards]

Maybe the example is too simple.  Here is another one which
when run on two tasks sends two integers from each task to
task 0.   Task 1 receives nothing.  This works with mpich and impi
but fails with openmpi.

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

 my_mpi_test(int rank, int ntasks)
{
  MPI_Datatype stype, rtype;
  int sbuf[2];
  int rbuf[4];

  int slen[ntasks], sdisp[ntasks], stypes[ntasks], rlen[ntasks],
rdisp[ntasks], rtypes[ntasks];
  sbuf[0]=rank;
  sbuf[1]=ntasks+rank;
  slen[0]=2;
  slen[1]=0;
  stypes[0]=MPI_INT;
  stypes[1]=MPI_DATATYPE_NULL;
  sdisp[0]=0;
  sdisp[1]=4;
  if(rank==0){
    rlen[0]=2;
    rlen[1]=2;
    rtypes[0]=MPI_INT;
    rtypes[1]=MPI_INT;
    rdisp[0]=0;
    rdisp[1]=8;

  }else{
    rlen[0]=0;
    rlen[1]=0;
    rtypes[0]=MPI_DATATYPE_NULL;
    rtypes[1]=MPI_DATATYPE_NULL;
    rdisp[0]=0;
    rdisp[1]=0;
  }

  MPI_Alltoallw(sbuf, slen, sdisp, stypes, rbuf, rlen, rdisp, rtypes,
MPI_COMM_WORLD);
  if(rank==0){
    printf("%d %d %d %d\n",rbuf[0],rbuf[1],rbuf[2],rbuf[3]);
  }

int main(int argc, char **argv)
{
  int rank, ntasks;

  MPI_Init(&argc, &argv);

  MPI_Comm_rank(MPI_COMM_WORLD,&rank);
  MPI_Comm_size(MPI_COMM_WORLD, &ntasks);

  printf("rank %d ntasks %d\n",rank, ntasks);

  my_mpi_test(rank,ntasks);


  MPI_Finalize();
}