多线程交替顺序打印100

遇到一个面试题，三个线程交替打印至100，线程1打印1,4,7;线程二打印2,5,8;线程三打印3,6,9；当时没有想到，补上自己的实现方法mark一下

package com.study.hc.net.designPattern;

/**
 * 功能描述
 *
 * @author Gandalf-z
 * @date 2021/3/6 16:44
 */
public class MultiThreadPrint {
    /**
     * 线程交替执行控制器
     */
    private static int thread_index = 0;
    /**
     * 执行打印计数器，用于判断循环退出条件，需要加volatile，保证可见性
     */
    private static volatile int count = 0;
    /**
     * 线程争抢的锁对象，持有该对象的锁方可执行操作
     */
    private static Object obj = new Object();

    public static void main(String[] args) {

        new Thread(() -> {
            printByOrder(0);
        }, "Thread-1").start();
        new Thread(() -> {
            printByOrder(1);
        }, "Thread-2").start();
        new Thread(() -> {
            printByOrder(2);
        }, "Thread-3").start();
    }

    /**
     * 顺序打印100
     *
     * @param i 线程序号
     */
    public static void printByOrder(int i) {
        while (count < 100) {
            if (thread_index % 3 == i) {
                synchronized (obj) {
                    count++;
                    thread_index++;
                    System.out.println(Thread.currentThread().getName() + "：" + count);
                }
            }
        }
    }
}

执行结果

在这里插入图片描述

使用Semaphore实现

import java.util.concurrent.Semaphore;

/**
 * 功能描述 基于Semaphore实现顺序打印
 *
 * @author Gandalf-z
 * @date 2021/3/6 20:02
 */
public class MultiPrintSemaphore {
    public static Semaphore semaphore = new Semaphore(1);
    public static volatile int count = 0;
    public static int index = 0;

    public static void main(String[] args) {
        new Thread(() -> {
            printOrderBySemaphore(0);
        }, "Thread-1").start();
        new Thread(() -> {
            printOrderBySemaphore(1);
        }, "Thread-2").start();
        new Thread(() -> {
            printOrderBySemaphore(2);
        }, "Thread-3").start();
    }

    private static void printOrderBySemaphore(int i) {
        while (count < 100) {
            if (index % 3 == i) {
                try {
                    semaphore.acquire();
                    count++;
                    index++;
                    System.out.println(Thread.currentThread().getName() + "：" + count);
                    semaphore.release();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

执行结果

在这里插入图片描述

路漫漫其修远兮，吾将上下而求索