简单线程同步问题

Question

在下面的代码中，无论是否同步bar方法，输出都不会有所不同-我在做什么错？ 我相信，同步“ bar”将使“ ThreaOne”被打印10次，然后仅开始打印“ ThreadTwo”，但事实并非如此。 我得到的输出如下：

---

I am Test thread:Thread OneOneOneOne
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread OneOneOneOne
I am in main now
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread Two
I am Test thread:Thread Two
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread Two
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread Two
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread Two
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread Two
I am Test thread:Thread OneOneOneOne
I am Test thread:Thread Two
I am Test thread:Thread Two
I am Test thread:Thread Two
I am Test thread:Thread Two
I am in main now

等等。 这是我的代码：

package com.rahul;

class ThreadTest implements Runnable{
    @Override
    public void run() {
        bar();
    }
    public synchronized void bar() {
        for(int i=0;i<10;i++){
            System.out.println("I am Test thread:"+Thread.currentThread().getName());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }
}

public class Test{
    public static void main(String[] args) {
        Thread t1 = new Thread(new ThreadTest(),"Thread OneOneOneOne");
        Thread t2 = new Thread(new ThreadTest(),"Thread Two");
        t1.start();
        try{
            Thread.sleep(4000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        t2.start();
        while(true){
            System.out.println("I am in main now");
            try {
                t2.join();
                Thread.sleep(4000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

Answer 1

您有ThreadTest 两个实例 。 他们彼此无关。 您没有调用相同的bar()

如果您改为这样做：

ThreadTest tt = new ThreadTest();
Thread t1 = new Thread(tt,"Thread OneOneOneOne");
Thread t2 = new Thread(tt,"Thread Two");

然后，两个线程共享一个ThreadTest实例，并且只有一个线程一次可以在单个实例上调用bar() 。

Answer 2

声明要synchronized的方法不会达到您期望的效果。 每个线程都在其自己的ThreadTest实例上同步，因此调用不会交互。 您需要在一个共享对象上同步一个线程才能阻止另一个线程。 例如：

class ThreadTest implements Runnable{
    private static Object LOCK_OBJECT = new Object();
    @Override
    public void run() {
        bar();
    }
    public void bar() {
        synchronized (LOCK_OBJECT) {
            for(int i=0;i<10;i++){
                System.out.println("I am Test thread:"+Thread.currentThread().getName());
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }
}

Answer 3

您正在同步的方法仅由一个线程访问，因为它们是实例方法，因此每个线程都在调用它自己的 bar方法。

也许您想将bar方法声明为static 。