#include <mpi.h>
#include <stdio.h>

#define CHK(err) if(err) return err

int main (int argc, char **argv)
{
  MPI_Comm    comm;
  MPI_Request req;
  MPI_Message message;
  MPI_Status  status;
  int         send, recv;
  int         rank, size, err;

  err = MPI_Init(&argc, &argv); CHK(err);

  comm = MPI_COMM_WORLD;

  err = MPI_Comm_size(comm, &size); CHK(err);

  err = MPI_Comm_rank(comm, &rank); CHK(err);

  send = rank;

  if ((size % 2 == 0) || rank < size - 1) {
    err = MPI_Isend(&send, 1, MPI_INT, rank ^ 1, 0, comm, &req); CHK(err);
    printf("[%d]: post Isend\n", rank);
    err = MPI_Mprobe(rank ^ 1, 0, comm, &message, MPI_STATUS_IGNORE); CHK(err);
    printf("[%d]: post Mprobe\n", rank);
    err = MPI_Mrecv(&recv, 1, MPI_INT, &message, MPI_STATUS_IGNORE); CHK(err);
    printf("[%d]: post Mrecv\n", rank);
    err = MPI_Wait(&req, MPI_STATUS_IGNORE); CHK(err);
    printf("[%d]: post Wait\n", rank);
    if (recv != rank ^ 1) printf("[%d]: expected %d, got %d\n",rank, rank ^ 1, recv);
  }

  err = MPI_Finalize();

  return err;
}