source: CIVL/examples/mpi/mpiFeature/simple_nb_bad.c

/******************************************************************************
* FILE: mpi_ringtopo.c
* DESCRIPTION:
*   MPI tutorial example code: Non-Blocking Send/Receive
* AUTHOR: Blaise Barney
* LAST REVISED: 04/02/05
******************************************************************************/
#include "mpi.h"
#include <stdio.h>
#include <stdlib.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, tag1, 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();
}