2.3.6原子类也并不完全安全

Posted 2020-10-17 成功的路上总是离不开贵人的帮助，名师的指点和小人的刺激。

原子类在具有逻辑的情况下输出结果也具有随机性

package com.cky.thread;

import java.util.concurrent.atomic.AtomicLong;

/**
 * Created by edison on 2017/12/9.
 */
public class MyService {
    public static AtomicLong ai= new AtomicLong();
    public void addNum() {
        System.out.println(Thread.currentThread().getName() +"  加了100之后的值是"+ ai.getAndAdd(100));
        ai.getAndAdd(1);
    }
}

package com.cky.thread;

/**
 * Created by edison on 2017/12/9.
 */
public class MyThread extends Thread{
   private MyService service;
   public MyThread(MyService service) {
       this.service =service;
   }

    @Override
    public void run() {
        super.run();
        service.addNum();
    }
}

package com.cky.test;

import com.cky.thread.MyService;
import com.cky.thread.MyThread;

/**
 * Created by edison on 2017/12/9.
 */
public class Run {
    public static void main(String[] args) {
        try {
            MyService myService = new MyService();
            MyThread[] myThreads = new MyThread[5];
            for (int i = 0; i < myThreads.length; i++) {
                myThreads[i] = new MyThread(myService);
            }
            for (int i = 0; i < myThreads.length; i++) {
                myThreads[i].start();
            }

            Thread.sleep(1000);
            System.out.println(myService.ai.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Thread-1  加了100之后的值是0
Thread-4  加了100之后的值是400
Thread-2  加了100之后的值是300
Thread-3  加了100之后的值是200
Thread-0  加了100之后的值是100
505

 

结果分析：

打印顺序出错了，应该每次加100在加一次1，出现这样的情况原因是addAndGet()方法是原子的，但方法和方法直接的调用却不是原子的

解决方案同步

package com.cky.thread;

import java.util.concurrent.atomic.AtomicLong;

/**
 * Created by edison on 2017/12/9.
 */
public class MyService {
    public static AtomicLong ai= new AtomicLong();
    synchronized public void addNum() {
        System.out.println(Thread.currentThread().getName() +"  加了100之后的值是"+ ai.getAndAdd(100));
        ai.getAndAdd(1);
    }
}

Thread-1  加了100之后的值是0
Thread-3  加了100之后的值是101
Thread-4  加了100之后的值是202
Thread-0  加了100之后的值是303
Thread-2  加了100之后的值是404
505