public CoordListener(int port, JobTracker tracker) {
		slaveMonitor = new SlaveMonitor(Configuration.HEART_BEAT_INTERVAL,
				Configuration.RETRY_NUM, tracker);
		// start the monitor as a new slave
		Thread monitor = new Thread(slaveMonitor);
		monitor.setDaemon(false);
		monitor.start();
		try {
			this.serverSocket = new ServerSocket(port);
			this.tracker = tracker;
			System.out.println("listening on port " + port);

		} catch (IOException e) {
			System.out.println("Cannot listen on port " + port);
			e.printStackTrace();
		}
	}