[OMPI users] Problems with GATHERV on one process

[Moreland, Kenneth]

I recently ran into a problem with GATHERV while running some randomized
tests on my MPI code.  The problem seems to occur when running
MPI_Gatherv with a displacement on a communicator with a single process.
The code listed below exercises this errant behavior.  I have tried it
on OpenMPI 1.1.2 and 1.2.4.

Granted, this is not a situation that one would normally run into in a
real application, but I just wanted to check to make sure I was not
doing anything wrong.

-Ken



#include <mpi.h>

#include <stdlib.h>
#include <stdio.h>

int main(int argc, char **argv)
{
  int rank;
  MPI_Comm smallComm;
  int senddata[4], recvdata[4], length, offset;

  MPI_Init(&argc, &argv);

  MPI_Comm_rank(MPI_COMM_WORLD, &rank);

  // Split up into communicators of size 1.
  MPI_Comm_split(MPI_COMM_WORLD, rank, 0, &smallComm);

  // Now try to do a gatherv.
  senddata[0] = 5; senddata[1] = 6; senddata[2] = 7; senddata[3] = 8;
  recvdata[0] = 0; recvdata[1] = 0; recvdata[2] = 0; recvdata[3] = 0;
  length = 3;
  offset = 1;
  MPI_Gatherv(senddata, length, MPI_INT,
              recvdata, &length, &offset, MPI_INT, 0, smallComm);
  if (senddata[0] != recvdata[offset])
    {
    printf("%d: %d != %d?\n", rank, senddata[0], recvdata[offset]);
    }
  else
    {
    printf("%d: Everything OK.\n", rank);
    }

  return 0;
}

   ****      Kenneth Moreland
    ***      Sandia National Laboratories
***********  
*** *** ***  email: kmo...@sandia.gov
**  ***  **  phone: (505) 844-8919
    ***      fax:   (505) 845-0833