/* nonb.c */
#include <stdio.h>
#include "mpi.h"

int main (int argc, char *argv[])
{
  int numtasks, rank, next, prev, buf[2],
    tag1=1, tag2=2;
  MPI_Request reqs[4];
  MPI_Status stats[4];
  
  MPI_Init(&argc,&argv);
  MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  
  prev = rank-1;   next = rank+1;

  if (rank == 0)               prev = numtasks - 1;
  if (rank == (numtasks - 1))  next = 0;
  
  MPI_Irecv(&buf[0], 1, MPI_INT, prev, tag1, MPI_COMM_WORLD, &reqs[0]);
  MPI_Irecv(&buf[1], 1, MPI_INT, next, tag2, MPI_COMM_WORLD, &reqs[1]);
  

  MPI_Isend(&rank, 1, MPI_INT, prev, tag2, MPI_COMM_WORLD, &reqs[2]);
  MPI_Isend(&rank, 1, MPI_INT, next, tag1, MPI_COMM_WORLD, &reqs[3]);
  
  MPI_Waitall(4, reqs, stats);
  printf("Task %d communicated with tasks %d & %d\n",rank,prev,next);
  
  MPI_Finalize();
}