public synchronized int addSlave(String host) {
		// report the dfs node
		dfs.addSlave(getSlaveID(), host);
		// initialize the lists
		ArrayDeque<MapTask> hs = new ArrayDeque<MapTask>();
		slaveMapTaskList.put(slaveID, hs);
		HashSet<MapTask> t = new HashSet<MapTask>();
		slaveRunningTask.put(slaveID, t);
		return slaveID;
	}