java - 生产者消费者使用等待和通知: Consumer does not receive messages

Question

我已经使用Java中的等待和通知机制准备了一个生产者消费者。下面是代码:

class Producer implements Runnable {

    private int i = 0;
    private ArrayList<Integer> arrayList;
    private static final int MAX_SIZE = 5; 

    public Producer(ArrayList<Integer> arrayList) {
        this.arrayList = arrayList;
    }

    @Override
    public void run() {

        while(true) {
            try {
                produce(i++);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }           
        }
    }

    private synchronized void produce(int i) throws InterruptedException {

        while(arrayList.size() == MAX_SIZE) {

            System.out.println("The Queue is Full. Producer thread needs to wait.");

            wait();         
        }
        arrayList.add(i);
        System.out.println("Added Element: "+i);
        notifyAll();
        Thread.sleep(3000);         
    }
}

class Consumer implements Runnable {

    private ArrayList<Integer> arrayList;

    public Consumer(ArrayList<Integer> arrayList) {
        this.arrayList = arrayList;
    }   

    @Override
    public void run() {

        while(true) {   
            try {
                consume();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 
        }
    }

    private synchronized void consume() throws InterruptedException {

        while(arrayList.isEmpty()) {

            System.out.println("The Queue is empty. Consumer thread needs to wait.");

            wait();                 
        }
        int data = arrayList.remove(0);
        System.out.println("Removed Element: "+data);
        notifyAll();
        Thread.sleep(3000);
    }   
}

public class ProducerConsumerExample {

    public static void main(String[] args) {
        ArrayList<Integer> arrayList = new ArrayList<Integer>();
        Thread producer = new Thread(new Producer(arrayList), "Producer Thread");
        Thread consumer = new Thread(new Consumer(arrayList), "Consumer Thread");       
        producer.start();
        consumer.start();       
    }
}

下面是示例输出

The Queue is empty. Consumer thread needs to wait.
Added Element: 0
Added Element: 1
Added Element: 2
Added Element: 3
Added Element: 4
The Queue is Full. Producer thread needs to wait.

问题是消费者线程要么没有收到通知，要么通知丢失。我尝试理解代码，但没有得到任何关于我哪里出错的线索。

Answer 1

The issue is that the consumer thread is either not getting the notification or the notification is getting lost

发生这种情况的原因是生产者和消费者没有在同一个实例上同步。它们在自己的实例(即 this)上独立同步。要解决此问题，Producer 和 Consumer 都可以在 ArrayList 或另一个实例上进行同步>共享对象。