Leetcode_1114_按序打印_多线程_leetcode 1114 多线程按序打印 python-优快云博客

本文介绍了两种实现线程间顺序执行的方法：一种是利用volatile变量监控任务完成状态，适用于简单场景；另一种采用重入锁与Condition组合，能更精细地控制线程通知与等待，适合复杂同步需求。

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用volatile的可见性或者用重入锁+Condition来控制先后顺序
官方题解的原子类我还没学QAQ

第一种方法的优势在于无锁，缺点在于不满足顺序性的时候还是会进行顺序性是否符合的询问。
第二种方法优势在于，不满足顺序性的时候会让线程等待，缺点在于需要上锁和解锁。

方法1：volatile

class Foo {
    
    private volatile boolean isFirstFinished = false;
    private volatile boolean isSecondFinished = false;

    public Foo() {
        
    }

    public void first(Runnable printFirst) throws InterruptedException {
        
        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run();
        isFirstFinished = true;
    }

    public void second(Runnable printSecond) throws InterruptedException {
        while(isFirstFinished == false)
        {Thread.yield();}
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        isSecondFinished = true;
    }

    public void third(Runnable printThird) throws InterruptedException {
        while(isSecondFinished == false)
        {Thread.yield();}
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
    }
}

方法2：重入锁+Condition

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

class Foo {

    int num = 1;
    Lock lock;
    //精确的通知和唤醒线程
    Condition condition2, condition3;

    public Foo() {
        lock = new ReentrantLock();
        condition2 = lock.newCondition();
        condition3 = lock.newCondition();
    }

    public void first(Runnable printFirst) throws InterruptedException {
        lock.lock();
        printFirst.run();
        num = 2;
        condition2.signal();
        lock.unlock();
        
    }

    public void second(Runnable printSecond) throws InterruptedException {
        lock.lock();
        while (num != 2) {
            condition2.await();
        }
        printSecond.run();
        num = 3;
        condition3.signal();
        lock.unlock();
    }

    public void third(Runnable printThird) throws InterruptedException {
        lock.lock();
        while (num != 3) {
            condition3.await();
        }
        printThird.run();
        lock.unlock();
    }
}