如何统计所有线程执行耗时

Posted on In

想法一：在 main 线程中打印当前时间，设置一个守护线程，在所有线程结束后获取当前时间减去初始时间。

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public class Test {
    public static void main(String[] args) throws InterruptedException {
        // 初始时间
        final long start = System.currentTimeMillis();
        Thread daemon = new Thread(() ->
                System.out.println("所有线程执行耗时(ms)：" + (System.currentTimeMillis() - start)));

        daemon.setDaemon(true);
        daemon.start();

        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                //do something
                long count = 0;
                for (int j = 0; j < 90000000; j++){
                    count+=j;
                }
                System.out.println("count="+count);
            }).start();
        }

    }
}

想法二：使用线程的 join() 方法，统计 main 线程从开始到结束的时间。

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public class Test {
    public static void main(String[] args) throws InterruptedException {

        long start = System.currentTimeMillis();
        List<Thread> threads = new ArrayList<>();

        for (int i = 0; i < 10; i++) {
            Thread t = new Thread(() -> {
                long count = 0;
                for (int j = 0; j < 90000000; j++) {
                    count += j;
                }
                System.out.println("count=" + count);
            }, "thread" + i);
            threads.add(t);
            t.start();
        }

        for (Thread t : threads) {
            t.join();
        }

        long end = System.currentTimeMillis();
        System.out.println("所有线程执行耗时(ms)：" + (end - start));

    }
}

想法三：使用 java.util.concurrent 包下的同步辅助类 CountDownLatch。

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public class Test {
    public static void main(String[] args) throws InterruptedException {

        final CountDownLatch latch = new CountDownLatch(10);

        long start = System.currentTimeMillis();

        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                long count = 0;
                for (int j = 0; j < 90000000; j++) {
                    count += j;
                }
                System.out.println("count=" + count);
                latch.countDown();
            }).start();
        }

        latch.await();// 当前线程阻塞

        System.out.println("所有线程执行耗时(ms)：" + (System.currentTimeMillis() - start));

    }
}