source: CIVL/examples/concurrency/mp_proc.cvh

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

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

  void sendrecv(void *sendbuf, int sendcount, int dest, int sendtag,
              void *recvbuf, int recvcount, int source, int recvtag, $comm comm) {
    $message out = $message_pack(rank, dest, sendtag, sendbuf, sendcount*sizeof(double));
    $message in;
    _Bool probe = $comm_probe(comm, source, recvtag);

    $choose {
      $when (1){ 
        $comm_enqueue(comm, out);
        in = $comm_dequeue(comm, source, recvtag);
      }
      $when (probe){
        in = $comm_dequeue(comm, source, recvtag);
        $comm_enqueue(comm, out);
      }
    }
    $message_unpack(in, recvbuf, recvcount*sizeof(double));
  }

  $when (__start);