java - 线程 :Wait() and notify()

Question

执行下面的代码并抛出IllegalMonitorStateException之后 异常(exception)。我收到错误信息:

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

我是多线程新手，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

如 the javadoc 中所述，您需要在使用该对象作为监视器的同步块(synchronized block)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:

• 你应该总是在循环中调用 wait(阅读 javadoc 了解更多细节)
• sleep是一个静态方法，不需要使用Thread.currentThread().sleep(2000); - sleep(2000); 也会这样做。