Java MultiThreading跳过循环并给出错误结果

问题描述

Java MultiThreading跳过循环并给出错误结果

Java MultiThreading skips loop and gives wrong result

package Threading;

class DemoThread extends Thread{   //Thread Class
    static int count=0;   // variable incremented by both the threads

    public DemoThread(String name) {
        // TODO Auto-generated constructor stub
        super(name);
    }

    public void run() {
        for(int i=0;i<100000;i++) {
            count++;
            System.out.println(Thread.currentThread()+"Count"+count);  // print thread operating on count variable
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}


public class MyThreadClass {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        DemoThread t1=new DemoThread("T1");
        DemoThread t2=new DemoThread("T2");
        t1.start();
        t2.start();
        try {
            t1.join();
            t2.join();  //allowing both the threads to complee before main thread
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println("Main Thread ends"+DemoThread.count);  //final value of count
    }
}

count的最终值应为199998，但未提供期望的结果.为什么线程缺少循环????

The final value of count should be 199998 but it is not giving the desired result.Why the threads are missing the loops ???

推荐答案

之所以发生，是因为线程T1和T2会同时(并发)更新 count ，

It happened because Thread T1 and T2 will update count at the same time (concurrency) like that:

Thread[T1,5,main]Count10
Thread[T2,5,main]Count10
Thread[T1,5,main]Count12
Thread[T2,5,main]Count12
Thread[T2,5,main]Count14
Thread[T1,5,main]Count14
Thread[T1,5,main]Count15
Thread[T2,5,main]Count16

您应该使用 AtomicInteger

并更新您的代码:

static int count = 0; 转换为 static AtomicInteger count = new AtomicInteger();

count ++; 到 count.incrementAndGet();

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