public void start(String taskName) throws IllegalStateException {
        if (this.currentTaskName != null) {
            throw new IllegalStateException("Can't start StopWatch: it's already running");
        }
        this.currentTaskName = taskName;
        this.startTimeMillis = System.currentTimeMillis();
    }

    public void stop() throws IllegalStateException {
        if (this.currentTaskName == null) {
            throw new IllegalStateException("Can't stop StopWatch: it's not running");
        }
        // 消费的时间
        long lastTime = System.currentTimeMillis() - this.startTimeMillis;
        this.totalTimeMillis += lastTime;
        // 任务信息初始化
        this.lastTaskInfo = new TaskInfo(this.currentTaskName, lastTime);
        if (this.keepTaskList) {
            this.taskList.add(this.lastTaskInfo);
        }
        ++this.taskCount;
        this.currentTaskName = null;
    }