private SlaveWorker pickSlave(String addr) {
		if (slaveList.size() <= 0) {
			System.out.println("No connected slaves!");
			System.exit(-1);
		}
		if (addr != null) {
			SlaveWorker w = slaveList.get(Integer.parseInt(addr));
			return w;
		}

		SlaveWorker w = slaveList.get(0);
		return w;
	}