解决多线程volatile不具备原子性案例

我会带着你远行 2021-11-16 07:52 277阅读 0赞

### 一、volatile不具备原子性案例 ###

volatile可以强制线程从主内存中读取最新的数据，但是不能保证原子性像++操作

package com.zhq;
    
    class VolatileNoAtomic extends Thread {
        private static volatile int count;
        @Override
        public  void run(){
            for(int i=0;i<1000;i++){
                count++;
            }
            System.out.println(getName()+"---->"+count);
        }
    
    
    }
    
    /**
     * @program: ThreadDemo
     * @description: Volatile具有可见性，不具有原子性
     * @author: hq.zheng
     * @create: 2019-07-29 21:28
     */
    public class VolatileNoAtomicDemo {
        public static void main(String[] args) {
            //初始化10个线程
            VolatileNoAtomic[] volatileNoAtomics=new VolatileNoAtomic[10];
            for(int i=0;i<volatileNoAtomics.length;i++){
                //创建每个线程
                volatileNoAtomics[i]=new VolatileNoAtomic();
            }
            for(int i=0;i<volatileNoAtomics.length;i++){
                //启动线程
                volatileNoAtomics[i].start();
            }
    
        }
    }

最后结果不确定可能不为10000

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3htMzkzMzkyNjI1_size_16_color_FFFFFF_t_70][]

### 二、修改解决原子性问题  ###

package com.zhq;
    
    import java.util.concurrent.atomic.AtomicInteger;
    
    class VolatileNoAtomic extends Thread {
        private static AtomicInteger count = new AtomicInteger(0);
        @Override
        public void run() {
            for (int i = 0; i < 1000; i++) {
                count.incrementAndGet();
            }
            System.out.println(getName() + "---->" + count);
        }
    
    
    }
    
    /**
     * @program: ThreadDemo
     * @description: Volatile具有可见性，不具有原子性
     * @author: hq.zheng
     * @create: 2019-07-29 21:28
     */
    public class VolatileNoAtomicDemo {
        public static void main(String[] args) {
            //初始化10个线程
            VolatileNoAtomic[] volatileNoAtomics = new VolatileNoAtomic[10];
            for (int i = 0; i < volatileNoAtomics.length; i++) {
                //创建每个线程
                volatileNoAtomics[i] = new VolatileNoAtomic();
            }
            for (int i = 0; i < volatileNoAtomics.length; i++) {
                //启动线程
                volatileNoAtomics[i].start();
            }
    
        }
    }

最后结果可以确定是10000

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3htMzkzMzkyNjI1_size_16_color_FFFFFF_t_70 1][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3htMzkzMzkyNjI1_size_16_color_FFFFFF_t_70]: /images/20211116/6edc0e69ddec472baa0c4d4da420cca0.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3htMzkzMzkyNjI1_size_16_color_FFFFFF_t_70 1]: /images/20211116/dd99f689cf6e423384717b2ae404b593.png