public void in_event() {
        //  TODO: Do we want to limit number of commands I/O thread can
        //  process in a single go?

        while (true) {

            //  Get the next command. If there is none, exit.
            Command cmd = mailbox.recv (0);
            if (cmd == null)
                break;

            //  Process the command.
            
            cmd.destination().process_command (cmd);
        }

    }