Java 生产者消费者的实施抛出 java.lang.IllegalMonitorStateException

Question

import java.util.LinkedList;
import java.util.Queue;

class Producer extends PubSub implements Runnable{

    @Override
    public void run() {
        synchronized(queue){
            if (queue.size() == 99){
                try { 
                    wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            queue.add(2);
            try{
                Thread.sleep(1000);
            }
            catch (InterruptedException e){
                e.printStackTrace();
            }
            notify();
            }
        }       
}


class Consumer extends PubSub implements Runnable{

    @Override
    public void run() {
        synchronized(queue){
            if(queue.isEmpty()){
                try {
                    wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }   
            }
            System.out.println(queue.poll());
        }

    }

}
public class PubSub {
    static Integer QUEUE_SIZE = 100;
    Queue<Integer> queue = new LinkedList<Integer>();
    public static void main(String[] args) {
        Producer producer = new Producer();
        Consumer consumer = new Consumer();
        Thread producerThread = new Thread(producer);
        Thread consumerThread = new Thread(consumer);
        producerThread.start();
        consumerThread.start();
        System.out.println("Started both the threads");
    }

}

我在 wait() 部分得到一个 java.lang.IllegalMonitorStateException。我想知道我在这里做错了什么。有什么想法吗？？

我得到的完整异常如下。

Exception in thread "Thread-1" Started both the threads
java.lang.IllegalMonitorStateException
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Object.java:502)
    at Consumer.run(PubSub.java:36)
    at java.lang.Thread.run(Thread.java:745)
Exception in thread "Thread-0" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at Producer.run(PubSub.java:23)
    at java.lang.Thread.run(Thread.java:745)

Answer 1

你呼叫的是wait()，相当于this.wait()，但你并没有持有this的监听。您在 queue 上拿着显示器。所以应该是queue.wait()。（与 notify() 相同）。

Answer 2

查看 Javadoc 以了解 IllegalMonitorStateException

https://docs.oracle.com/javase/7/docs/api/java/lang/IllegalMonitorStateException.html

当您尝试 wait()（或 notify()）您未持有监视器的对象时抛出异常；您已在队列上同步，但试图在 this 上 wait()，这不是队列，而是可运行的。将 wait() 更改为 queue.wait() 并将 notify() 更改为 queue.notify() 应该有效。

Answer 3

我想我让你的代码工作了...

正如 JB Nizet 所述，您必须在 queue 对象上调用等待和通知。我认为必须声明这样的对象 static 才能由生产者和消费者共享。

我为代码添加了 while 循环以继续运行直到时间结束。

此外，在生产者和消费者之前还需要一个额外的notify wait

这是包含更改的代码：

import java.util.LinkedList;
import java.util.Queue;

class Producer extends PubSub implements Runnable{

    @Override
    public void run() {
         int index = 0;

         while (true) {
            synchronized(queue){
                while (queue.size() == QUEUE_SIZE){
                    try {
                        System.out.println("Producer waits");
                        queue.notify();
                        queue.wait();
                    } catch (InterruptedException e) {
                       e.printStackTrace();
                    }
                }

                System.out.println("Produce element " + (++index));
                queue.add(2);
                queue.notify();

                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e){
                    e.printStackTrace();
                }


            }
        }
    }
}


class Consumer extends PubSub implements Runnable{

     @Override
     public void run() {
         while (true) {
             synchronized(queue) {

                while (queue.isEmpty()){
                    try {
                         System.out.println("Consumer waits");
                         queue.notify();
                         queue.wait();
                    } catch (InterruptedException e) {
                         e.printStackTrace();
                    }
                }

                System.out.println("Consume element " + queue.poll());
                queue.notify();

            }
         }

     }

  }

public class PubSub {
     static Integer QUEUE_SIZE = 100;

     static Queue<Integer> queue = new LinkedList<Integer>();

     public static void main(String[] args) {
          Producer producer = new Producer();
          Consumer consumer = new Consumer();

          Thread producerThread = new Thread(producer);
          Thread consumerThread = new Thread(consumer);

          producerThread.start();
          consumerThread.start();

          System.out.println("Started both the threads");
     }

 }

Answer 4

线程只能在它已经获得锁的对象上调用 notify() 或 wait() 。在您的程序中，线程锁定了队列对象，然后您的线程正在调用等待。

Java 生产者消费者的实施抛出 java.lang.IllegalMonitorStateException

Java implementation of Producer Consumer throws java.lang.IllegalMonitorStateException

java

multithreading

exception-handling

producer-consumer