线程:Wait()和notify()

Question

执行下面的代码并抛出IllegalMonitorStateException异常。我收到错误信息，因为：

java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at com.blt.ThreadExample.main(ThreadExample.java:21)

我是多线程的新手，我想在代码中使用wait()和notify()。

package com.blt;



public class ThreadExample implements Runnable {
    public static void main(String args[])
    {


        System.out.println("A");
        Thread T = new Thread(new ThreadExample());
        Thread T1 = new Thread(new ThreadExample());

        System.out.println("B");
        try
        {
        T.setName("thread 1");
        T.start();
        T1.setName("thread 2");
        System.out.println("C");
        T.notify();

        System.out.println("D");
        T1.start();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
    }


        public  void run()
{


            synchronized(ThreadExample.class)
            {


        for(int i=0; i<5; i++)
    {

        try
        {
            Thread.currentThread().wait(400);
         System.out.println("Inside run=>"+Thread.currentThread().getName());
         Thread.currentThread().sleep(2000);




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

Answer 1

试试这个..。如果你有doudt就告诉我。

package com.blt;

public class ThreadExample implements Runnable {
    public static void main(String args[]) {
        Thread T1 = new Thread(new ThreadExample());
        Thread T2 = new Thread(new ThreadExample());
        try {
            T1.setName("thread 1");
            T1.start();
            T2.setName("thread 2");
            T2.start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void run() {

        synchronized (ThreadExample.class) {
            for (int i = 0; i < 5; i++) {
                try {
                    ThreadExample.class.notify();
                    System.out.println("Thread going to wait state::"+ Thread.currentThread().getName());
                    ThreadExample.class.wait(400);
                    System.out.println("Thread notified is::"+ Thread.currentThread().getName());
                    System.out.println("Thread going to sleep state::"+ Thread.currentThread().getName());
                    Thread.sleep(2000);
                    System.out.println("==========");

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

Answer 2

正如the javadoc中所解释的，您需要在使用对象作为监视器的synchronized块中，才能对该对象调用notify或wait。

Thread.currentThread()将很难跟踪，所以我建议您使用另一个对象。例如：

public class ThreadExample implements Runnable {

    private static final Object lock = new Object();

    public static void main(String args[]) {
        System.out.println("A");
        Thread T = new Thread(new ThreadExample());
        Thread T1 = new Thread(new ThreadExample());

        System.out.println("B");
        try {
            T.setName("thread 1");
            T.start();
            T1.setName("thread 2");
            System.out.println("C");
            synchronized(lock) {
                lock.notify();
            }
            System.out.println("D");
            T1.start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void run() {
        synchronized (lock) {
            for (int i = 0; i < 5; i++) {
                try {
                    lock.wait(400);
                    System.out.println("Inside run=>" + Thread.currentThread().getName());
                    Thread.currentThread().sleep(2000);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

请注意，您的代码中还有其他几个问题，特别是：

details)

• sleep是一种静态方法，不需要使用Thread.currentThread().sleep(2000); - sleep(2000);也会做同样的事情。

Answer 3

这些方法必须包含在synchronized块中。阅读有关java tutorial中的对象锁的内容。

换句话说：

//thread 1
synchronized (commonObj) {
  commonObj.wait();
}

//thread 2:
synchronized (commonObj) {
  commonObj.notify();
}

同样的问题：How to use wait and notify in Java?