Question

我有一个问题。为什么此代码（带有1个“ while”程序）运行死循环，而2个“ while”程序却没有死循环？

public class VolatileTest2 {
    private volatile   static boolean isOver = false;

    public static void main(String[] args) {
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                int a=0;

                while (!isOver){//1
                    a=5;
                } ;

               /* while (true){ //2
                    a=5;
                    if(!isOver)break;
                } ;*/
                System.out.println(a);
            }
        });
        thread.start();
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        isOver = true;
    }
}

Answer 1

这不是不确定的。只是执行得太快。如果您在代码中添加一些输出并在内部添加一些睡眠，您将了解发生了什么。

public class VolitileTest {

private volatile   static boolean isOver = false;

public static void main(String[] args) {
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            int a=0;

            System.out.println("IsOver before while =" + isOver);
            while (!isOver){//1
                System.out.println("IsOver in =" + isOver);
                try {
                    Thread.sleep(50);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                a=5;
            } ;


        /*    while (true){ //2
                a=5;
                System.out.println("IsOver in =" + isOver);
                if(!isOver) {
                    break;
                }
            }*/
            System.out.println("Out of while: " + a);
        }
    });
    thread.start();
    try {
        Thread.sleep(100);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println("IsOver before set true =" + isOver);
    isOver = true;
    System.out.println("IsOver after set true =" + isOver);
}

输出：

IsOver before while =false
IsOver in =false
IsOver in =false
IsOver in =false
IsOver before set true =false
IsOver after set true =true
Out of while: 5

线程代码中带有死循环的奇数问题

1 个答案: