Java开发网 - 请教多线程同步问题

Topic: 请教多线程同步问题

1.请教多线程同步问题

Posted by: ballfly
Posted on: 2006-03-08 00:33

import java.io.*;
public class fourThread implements Runnable
{
  public static void main(String args[])
  {
    fourThread th=new fourThread();
    Thread th1=new Thread(th);
    Thread th2=new Thread(th);
    Thread th3=new Thread(th);
    Thread th4=new Thread(th);
    th1.start();
    th2.start();
    th3.start();
    th4.start();


  }

   int i=100;

  public void run()
  {


      for(;i>=50;i--)
      {
        System.out.println(Thread.currentThread().getName()+":"+i);
      }





  }
}

为何屏幕会打印出4个重复的93数字呢？
我的目的是：从100到50的不重复打印（用四个线程实现）
请问如何解决？

2.Re:请教多线程同步问题 [Re: ballfly]

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Posted by: Skybus
Posted on: 2006-03-08 10:11

这个程序应该可以实现的,关键是对i的操作进行同步保护!


public class ThreadTest {
    public static void main(String args[]) {
        Threadnew th = new Threadnew();
        new Thread(th).start();
        new Thread(th).start();
        new Thread(th).start();
        new Thread(th).start();
    }
}

class Threadnew implements Runnable {
    int i = 100;

    Object obj = new Object();

    public void run() {

        while (true) {
            synchronized (obj) {//同步块
                if (i >= 50) {
                    try {
                        Thread.sleep(10);
                        System.out.println(Thread.currentThread().getName()
                                + ":" + i);
                        i--;

                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }

            }
            if (i < 50)
                break;
        }

    }
}

3.Re:请教多线程同步问题 [Re: ballfly]	Copy to clipboard
Posted by: ballfly Posted on: 2006-03-08 16:24 谢谢