/* Class Msg_port implements a simple communication
   port of the server that processes transactions              */

public class Msg_port {           // type of monitor

  private Message port_memory;    // buffer for the message
  private boolean empty;          // flag

  public Msg_port () {empty = true;}

  public boolean empty_port() {return empty;}

  synchronized public void write (Message request) {
    while (!empty) try {
      wait();                     // calling thread waits
    } catch (InterruptedException e) {}
    port_memory = request;
    empty = false;
    notify();                     // awaking of a waiting thread
  }

  synchronized public Message read () {
    while (empty) try {
      wait();
    } catch (InterruptedException e) {}
    empty = true;
    notify();
    return port_memory;
  }
}