Java之Timer的schedule方法period参数分析

2019-11-06 11:20:09  阅读 214 次 评论 0 条

下面为一段标准的Timer用法

private void runTimer(){
    Log.d("bloguan", "run:" + Thread.currentThread().getId());

    new Timer().schedule(new TimerTask() {
        @Override
        public void run() {
            Log.d("bloguan", "begin:" + Thread.currentThread().getId());
            Log.d("bloguan", "end:" + Thread.currentThread().getId());
        }
    },1000, 5000);
}

执行结果

11-06 11:25:04.105 2385-2385/com.bloguan.demo D/bloguan: run:1
11-06 11:25:05.106 2385-2410/com.bloguan.demo D/bloguan: begin:139
11-06 11:25:05.106 2385-2410/com.bloguan.demo D/bloguan: end:139
11-06 11:25:10.108 2385-2410/com.bloguan.demo D/bloguan: begin:139
11-06 11:25:10.108 2385-2410/com.bloguan.demo D/bloguan: end:139

分析:Timer延时1秒执行,每5秒循环一次,TimerTask的run运行在子线程


那么,有个疑问,如果run里面执行耗时操作,每5秒的循环周期还准吗?

试一下,我们在run中加一个2秒“耗时操作”

private void runTimer(){
    Log.d("bloguan", "run:" + Thread.currentThread().getId());

    new Timer().schedule(new TimerTask() {
        @Override
        public void run() {
            Log.d("bloguan", "begin:" + Thread.currentThread().getId());
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            Log.d("bloguan", "end:" + Thread.currentThread().getId());
        }
    },1000, 5000);
}

执行结果

11-06 11:30:27.947 2496-2496/com.bloguan.demo D/bloguan: run:1
11-06 11:30:28.948 2496-2514/com.bloguan.demo D/bloguan: begin:143
11-06 11:30:30.956 2496-2514/com.bloguan.demo D/bloguan: end:143
11-06 11:30:33.949 2496-2514/com.bloguan.demo D/bloguan: begin:143
11-06 11:30:35.949 2496-2514/com.bloguan.demo D/bloguan: end:143
11-06 11:30:38.951 2496-2514/com.bloguan.demo D/bloguan: begin:143
11-06 11:30:40.952 2496-2514/com.bloguan.demo D/bloguan: end:143

分析:定时器仍然每5秒触发一次,run里面的2秒耗时操作不会叠加到5秒这个周期上


如果耗时操作大于period这个周期呢?

把上面代码中的sleep改为6秒

Thread.sleep(6000);

执行结果

11-06 11:43:22.544 2586-2586/com.bloguan.demo D/bloguan: run:1
11-06 11:43:23.546 2586-2604/com.bloguan.demo D/bloguan: begin:147
11-06 11:43:29.546 2586-2604/com.bloguan.demo D/bloguan: end:147
11-06 11:43:29.546 2586-2604/com.bloguan.demo D/bloguan: begin:147
11-06 11:43:35.593 2586-2604/com.bloguan.demo D/bloguan: end:147
11-06 11:43:35.593 2586-2604/com.bloguan.demo D/bloguan: begin:147

分析:Timer的周期先到,但run没执行完,会等到执行完成后再次循环


结论:

1、TimerTask的run运行在子线程,非UI线程

2、如果TimerTask的run中有耗时操作

    当耗时操作小于period周期时,仍以period时间为准进行周期循环

    当耗时操作大于period周期时,等run执行完后,立即进行下一次

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