ARTS

ARTS-02.md

Algorithm

Print in Order（1114）

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Suppose we have a class:

public class Foo {
  public void one() { print("one"); }
  public void two() { print("two"); }
  public void three() { print("three"); }
}
The same instance of Foo will be passed to three different threads. Thread A will call one(), thread B will call two(), and thread C will call three(). Design a mechanism and modify the program to ensure that two() is executed after one(), and three() is executed after two().

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/print-in-order
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

解题思路：
leetcode关于多线程的新题，考察多线程中的按序执行。
可以用以下方法解：

  1. 利用CountDownLatch 来控制执行的顺序。
  2. 利用volatile 创建全局可见的变量，通过对该变量的原子性更新来保证执行顺序。
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import java.util.concurrent.CountDownLatch;

class Foo {
    private CountDownLatch c2;
    private CountDownLatch c3;

    public Foo() {
        c2 = new CountDownLatch(1);
        c3 = new CountDownLatch(1);
    }

    public void first(Runnable printFirst) throws InterruptedException {
        
        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run();
        c2.countDown();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        c2.await();
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        c3.countDown();
    }

    public void third(Runnable printThird) throws InterruptedException {
        c3.await();
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
    }
}
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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.
        printFirst.run();
        flag = 2;
    }

    public void second(Runnable printSecond) throws InterruptedException {
        while(flag != 2);
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        flag = 3;
    }

    public void third(Runnable printThird) throws InterruptedException {
        while(flag != 3);
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
    }
}

Reading

Faircode, an alternative to Open Source that aims to get developers paid
https://hackernoon.com/faircode-an-alternative-to-open-source-89cdc65df3fa

在2017年作者提出了Faircode这个概念，旨在给开发者一个新的盈利方式。不同于“闭源软件”，Faircode 打算以向大公司收费而对小公司免费的形势获利。然而不幸的是，作者发起的Faircode 及相关的license 已经被删除了。作者想法在当时比较前卫，可能在推行的过程中成效不大吧。

Tip

https://javarevisited.blogspot.com/2018/05/10-tips-to-become-better-java-developer.html

Share

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