java CountDownLatch

wyk1184 發(fā)布于2019-08-16 17:45 / 3309人閱讀

摘要：介紹類位于包下，利用它可以實(shí)現(xiàn)類似計(jì)數(shù)器的功能。是通過一個(gè)計(jì)數(shù)器來實(shí)現(xiàn)的，計(jì)數(shù)器的初始值為線程的數(shù)量。當(dāng)計(jì)數(shù)器值到達(dá)時(shí)，它表示所有的線程已經(jīng)完成了任務(wù)，然后在閉鎖上等待的線程就可以恢復(fù)執(zhí)行任務(wù)。

CountDownLatch 介紹

CountDownLatch 類位于java.util.concurrent包下，利用它可以實(shí)現(xiàn)類似計(jì)數(shù)器的功能。比如有一個(gè)任務(wù)A，它要等待其他幾個(gè)任務(wù)執(zhí)行完畢之后才能執(zhí)行，此時(shí)就可以利用CountDownLatch來實(shí)現(xiàn)這種功能了。CountDownLatch是通過一個(gè)計(jì)數(shù)器來實(shí)現(xiàn)的，計(jì)數(shù)器的初始值為線程的數(shù)量。每當(dāng)一個(gè)線程完成了自己的任務(wù)后，計(jì)數(shù)器的值就會(huì)減1。當(dāng)計(jì)數(shù)器值到達(dá)0時(shí)，它表示所有的線程已經(jīng)完成了任務(wù)，然后在閉鎖上等待的線程就可以恢復(fù)執(zhí)行任務(wù)。

定義兩個(gè)線程

線程1

public class Thread1 extends Thread {
    private CountDownLatch countDownLatch;
    public Thread1(CountDownLatch countDownLatch) {
        this.countDownLatch = countDownLatch;
    }

    @Override
    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("thread-1");
        countDownLatch.countDown();
    }
}

線程2

public class Thread2 extends Thread {
    private CountDownLatch countDownLatch;

    public Thread2(CountDownLatch countDownLatch) {
        this.countDownLatch = countDownLatch;
    }

    @Override
    public void run() {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("thread-2");
        countDownLatch.countDown();
    }
}

請(qǐng)求

@RequestMapping("test-countdownlatch")
    public void testCountDownLatch() {
        CountDownLatch countDownLatch = new CountDownLatch(2);
        Thread1 thread1 = new Thread1(countDownLatch);
        Thread2 thread2 = new Thread2(countDownLatch);
        thread1.start();
        thread2.start();
        try {
            countDownLatch.await();
            System.out.println("main...");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

結(jié)果

"main..."總是等待兩個(gè)線程完成后打印

CountDownLatch代碼