public Object call() throws Exception {
		Object result = null;
		try{
			result = this.execute();//ִ
		}catch(Exception e){
			e.printStackTrace();
		}
		synchronized (lock) {
			//ҵݼ߳ͬʱ߳
			lock.thread_count--;
			lock.notifyAll();
		}
		return result;
	}