多线程练习

leetcode 1114. 按序打印

题目：https://leetcode.cn/problems/print-in-order/description/

方法一：使用 while 循环

class Foo {

  private AtomicInteger firstJobDone = new AtomicInteger(0);
  private AtomicInteger secondJobDone = new AtomicInteger(0);

  public Foo() {}

  public void first(Runnable printFirst) throws InterruptedException {
    // printFirst.run() outputs "first".
    printFirst.run();
    // mark the first job as done, by increasing its count.
    firstJobDone.incrementAndGet();
  }

  public void second(Runnable printSecond) throws InterruptedException {
    while (firstJobDone.get() != 1) {
      // waiting for the first job to be done.
    }
    // printSecond.run() outputs "second".
    printSecond.run();
    // mark the second as done, by increasing its count.
    secondJobDone.incrementAndGet();
  }

  public void third(Runnable printThird) throws InterruptedException {
    while (secondJobDone.get() != 1) {
      // waiting for the second job to be done.
    }
    // printThird.run() outputs "third".
    printThird.run();
  }
}

方法二：使用锁 + wait

class Foo {

    private volatile int flag = 1;

    public Foo() {

    }

    public void first(Runnable printFirst) throws InterruptedException {

        // printFirst.run() outputs "first". Do not change or remove this line.
        synchronized (this){
            while (flag != 1) this.wait();
            printFirst.run();
            flag = 2;
            this.notifyAll();
        }
    }

    public void second(Runnable printSecond) throws InterruptedException {

        // printSecond.run() outputs "second". Do not change or remove this line.
        synchronized (this){
            while (flag != 2) this.wait();
            flag = 3;
            printSecond.run();
            this.notifyAll();
        }


    }

    public void third(Runnable printThird) throws InterruptedException {

        // printThird.run() outputs "third". Do not change or remove this line.
        synchronized (this){
            while (flag != 3) this.wait();
            printThird.run();
        }

    }
}

方法三：使用信号量

import java.util.concurrent.Semaphore;
class Foo {
    public Semaphore seam_first_two = new Semaphore(0);
    
    public Semaphore seam_two_second = new Semaphore(0);
    
    public Foo() {
        
    }

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

    public void second(Runnable printSecond) throws InterruptedException {
        seam_first_two.acquire();
        printSecond.run();
        seam_two_second.release();
    }

    public void third(Runnable printThird) throws InterruptedException {
        seam_two_second.acquire();
        printThird.run();
    }
}