多線程交替順序打印100

遇到一個(gè)面試題涯呻，三個(gè)線程交替打印至100，線程1打印1,4,7;線程二打印2,5,8;線程三打印3,6,9腻要；當(dāng)時(shí)沒(méi)有想到复罐，補(bǔ)上自己的實(shí)現(xiàn)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 {
    /**
     * 線程交替執(zhí)行控制器
     */
    private static int thread_index = 0;
    /**
     * 執(zhí)行打印計(jì)數(shù)器，用于判斷循環(huán)退出條件雄家，需要加volatile效诅，保證可見(jiàn)性
     */
    private static volatile int count = 0;
    /**
     * 線程爭(zhēng)搶的鎖對(duì)象，持有該對(duì)象的鎖方可執(zhí)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();
    }

    /**
     * 順序打印100
     *
     * @param i 線程序號(hào)
     */
    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);
                }
            }
        }
    }
}

執(zhí)行結(jié)果

在這里插入圖片描述

使用Semaphore實(shí)現(xiàn)

import java.util.concurrent.Semaphore;

/**
 * 功能描述 基于Semaphore實(shí)現(xiàn)順序打印
 *
 * @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();
                }
            }
        }
    }

}

執(zhí)行結(jié)果

在這里插入圖片描述

路漫漫其修遠(yuǎn)兮趟济，吾將上下而求索