/******************************************************************************
 * FILE: mpi_bug1.c
 * DESCRIPTION: 
 *   This program has a bug that causes it to hang.
 * AUTHOR: Blaise Barney 
 * LAST REVISED: 04/13/05
 ******************************************************************************/
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>

int main (int argc, char *argv[])
{
  int numtasks, rank, dest, tag, source, rc, count;
  char inmsg, outmsg='x';
  MPI_Status Stat;

  MPI_Init(&argc,&argv);
  MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  printf("Task %d starting...\n",rank);

  if (rank == 0) {
    if (numtasks > 2) 
      printf("Numtasks=%d. Only 2 needed. Ignoring extra...\n",numtasks);
    dest = rank + 1;
    source = dest;
    tag = rank;
    rc = MPI_Send(&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
    printf("Sent to task %d...\n",dest);
    rc = MPI_Recv(&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
    printf("Received from task %d...\n",source);
  }

  else if (rank == 1) {
    dest = rank - 1;
    source = dest;
    tag = rank;
    rc = MPI_Recv(&inmsg, 1, MPI_CHAR, source, tag, MPI_COMM_WORLD, &Stat);
    printf("Received from task %d...\n",source);
    rc = MPI_Send(&outmsg, 1, MPI_CHAR, dest, tag, MPI_COMM_WORLD);
    printf("Sent to task %d...\n",dest);
  }

  if (rank < 2) {
    rc = MPI_Get_count(&Stat, MPI_CHAR, &count);
    printf("Task %d: Received %d char(s) from task %d with tag %d \n",
	   rank, count, Stat.MPI_SOURCE, Stat.MPI_TAG);
  }

  MPI_Finalize();
}
