LeetCode 1114. 按序打印-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_45817392/article/details/124542639

本文介绍了Java中实现三个线程按特定顺序执行的四种方法：使用同步原语、原子操作类、CountDownLatch和Semaphore。这些方法都是为了解决多线程环境下线程间的协作问题，确保打印顺序的正确性。

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1114. 按序打印 - 力扣（LeetCode） (leetcode-cn.com)

方法一：同步原语


    private volatile int flag = 1;
    private final Object object = new Object();

    public Foo() {

    }

    public void first(Runnable printFirst) throws InterruptedException {
        synchronized (object) {
            while(flag!=1){
                object.wait();
            }
            printFirst.run();
            flag = 2;
            object.notifyAll();
        }
    }

    public void second(Runnable printSecond) throws InterruptedException {
        synchronized (object) {
            while(flag != 2) {
                object.wait();
            }
            printSecond.run();
            flag = 3;
            object.notifyAll();
        }

    }

    public void third(Runnable printThird) throws InterruptedException {
        synchronized (object) {
            while (flag != 3) {
                object.wait();
            }
            printThird.run();
        }

    }

方式二：原子操作类


import java.util.concurrent.atomic.AtomicInteger;

class Foo {

    private final AtomicInteger flag = new AtomicInteger(0);

    public Foo() {

    }

    public void first(Runnable printFirst) throws InterruptedException {
       printFirst.run();
       flag.incrementAndGet();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        while (flag.get() != 1) {

        }
        printSecond.run();
        flag.incrementAndGet();
    }

    public void third(Runnable printThird) throws InterruptedException {
        while (flag.get() != 2) {

        }
        printThird.run();
    }
}

方式三：CountDownLatch


class Foo {

    private final CountDownLatch first;
    private final CountDownLatch second;

    public Foo() {
        first = new CountDownLatch(1);
        second = new CountDownLatch(1);
    }

    public void first(Runnable printFirst) throws InterruptedException {
        printFirst.run();
        first.countDown();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        first.await();
        printSecond.run();
        second.countDown();
    }

    public void third(Runnable printThird) throws InterruptedException {
        second.await();
        printThird.run();
    }
}

方法四：Semaphore

private Semaphore semaphore = new Semaphore(0);
    
    public Foo() {
    }

    public void first(Runnable printFirst) throws InterruptedException {
        printFirst.run();
        semaphore.release();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        while(semaphore.availablePermits() != 1) {
            
        }
        printSecond.run();
        semaphore.release();
    }

    public void third(Runnable printThird) throws InterruptedException {
        while(semaphore.availablePermits()!=2) {
            
        }
        printThird.run();
    }