JUC-线程间通信(让线程按照我们要求的顺序进行执行)-概述和案例分析、虚假唤醒问题

￡神魔★判官ぃ 2024-04-06 09:49 65阅读 0赞

![552c7860e3c1413e968dc1fb122cd789.png][]

package com.nanjing.juc;
    
    //第一步 创建资源类，定义属性和操作方法
    class Share{
        //初始值
        private int number = 0;
        //+1的方法
        public synchronized void add() throws InterruptedException {
            //第二步 判断 干活 通知
            if(number != 0){
                //判断number的值是否是0，如果不是0，等待
                this.wait();
            }
            //如果number是0，+1
            number++;
            System.out.println(Thread.currentThread().getName()+" ===== "+number);
            //通知其他的线程
            this.notifyAll();
        }
        //-1的方法
        public synchronized void delete() throws InterruptedException {
            //判断
            if(number != 1){
                this.wait();
            }
            //干活
            number--;
            System.out.println(Thread.currentThread().getName()+" ===== "+number);
            //通知其他的线程
            this.notifyAll();
        }
    
    }
    public class ThreadDemo_04 {
        public static void main(String[] args) {
            //第三步 创建多个线程，调用资源类的操作方法
            Share share = new Share();
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        share.add();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"刘德华").start();
    
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        share.delete();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"张学友").start();
        }
    
    }

![74e908fea0604b4f85367da4afcadd01.png][]

--------------------

虚假唤醒问题

出现匪夷所思的现象

![3b3f1eef55cc4b048c54376a02f75f39.png][]

查看JDK：

![8476a12ccd9840b08be0a32da131a72c.png][]

![a83f088abd8545d9a61d0bf08ebd1f59.png][]

this.wait()方法有个特点，在哪里睡就在哪里醒
    
    if(number != 0)只会判断一次
    
    用while(number != 0) 不管你什么时候睡什么时候醒，都要经过while循环判断

修改代码后：

package com.nanjing.juc;
    
    //第一步 创建资源类，定义属性和操作方法
    class Share{
        //初始值
        private int number = 0;
        //+1的方法
        public synchronized void add() throws InterruptedException {
            //第二步 判断 干活 通知
            while(number != 0){
                //判断number的值是否是0，如果不是0，等待
                this.wait();
            }
            //如果number是0，+1
            number++;
            System.out.println(Thread.currentThread().getName()+" ===== "+number);
            //通知其他的线程
            this.notifyAll();
        }
        //-1的方法
        public synchronized void delete() throws InterruptedException {
            //判断
            while(number != 1){
                this.wait();
            }
            //干活
            number--;
            System.out.println(Thread.currentThread().getName()+" ===== "+number);
            //通知其他的线程
            this.notifyAll();
        }
    
    }
    public class ThreadDemo_04 {
        public static void main(String[] args) {
            //第三步 创建多个线程，调用资源类的操作方法
            Share share = new Share();
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        share.add();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"刘德华").start();
    
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        share.delete();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"张学友").start();
    
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        share.add();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"黎明").start();
    
            new Thread(()->{
                for (int i = 0; i < 30; i++) {
                    try {
                        share.delete();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"郭富城").start();
        }
    
    }

![a5202d7ecec54cd3858a4b230a5b3dcd.png][]

[552c7860e3c1413e968dc1fb122cd789.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/cca95500a04a474cb566eb374d346b1a.png
[74e908fea0604b4f85367da4afcadd01.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/838ae0cc3ca849fb8860acc418f63c51.png
[3b3f1eef55cc4b048c54376a02f75f39.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/c0438278643f48ca9361883afc503e99.png
[8476a12ccd9840b08be0a32da131a72c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/bec7e4f5c99a495e91f98010866e798f.png
[a83f088abd8545d9a61d0bf08ebd1f59.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/e6af4b62e9654d3eb3414e6001a7f328.png
[a5202d7ecec54cd3858a4b230a5b3dcd.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/06/ff06c0ef814f4b8683fe9185ba503d59.png