void send(void *buf, int count, int dest, int tag) {
  $atomic{
    $message out = $message_pack(rank, dest, tag, buf, count*sizeof(double));
    $comm_enqueue(&MPI_COMM_WORLD, out);}
  }

  void recv(void *buf, int count, int source, int tag) {
  $atomic{
    $message in = $comm_dequeue(&MPI_COMM_WORLD, source, rank, tag);
    $message_unpack(in, buf, count*sizeof(double));}
  }

  $when (__start);