source: CIVL/examples/concurrency/ring2.cvl

#include <civlc.cvh>
/* Create nprocs processes.  Have them exchange data in a cycle.
 * Commandline example:
 *     civl verify -input_mpi_nprocs=3 ring2.cvl -simplify=false
 */
#include<comm.cvh>
#include<stdio.h>
#include "mp_root2.cvh"

void MPI_Process (int __rank) {
#include "mp_proc2.cvh"

// ******************* BEGIN PROGRAM SOURCE *************************

  int rank, nprocs, count;
  double x, y;
  MPI_Status stat;
  MPI_Comm MPI_COMM_WORLD = $comm_create($here, __MPI_Comm_World, __rank);
  
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
  x = rank;
  MPI_Sendrecv(&x, 1, MPI_DOUBLE, (rank+1)%nprocs, 0, &y, 1, MPI_DOUBLE, 
           (rank+nprocs-1)%nprocs, 0, MPI_COMM_WORLD, &stat);
  $assert(y == (rank+nprocs-1)%nprocs);
  MPI_Get_count(&stat, MPI_DOUBLE, &count);
  $assert(count == 1);
  $assert(stat.MPI_SOURCE == (rank+nprocs-1)%nprocs);
  $assert(stat.MPI_TAG == 0);
  $comm_destroy(MPI_COMM_WORLD);

// ******************** END PROGRAM SOURCE ***************************

}