Question

public class Queue {
    int value = 0;
    boolean isEmpty = true;
    public synchronized void put(int n){
        if (!isEmpty){
            try {
                System.out.println("producer is waiting");
                wait();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
        value += n;
        isEmpty = false;
        System.out.println("The number of products："+value);
        notifyAll();
    }
    public synchronized void get(){
        if (isEmpty){
            try{
                System.out.println("customer is waiting");
                wait();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
        value --;
        if(value<1){
            isEmpty = true;
        }
        System.out.println("there are "+value+" left");
        notifyAll();
    }
}


public class Producer extends Thread{
    private Queue queue;
    public Producer(String name,Queue queue){
        super(name);
        this.queue = queue;
    }

    @Override
    public void run() {
        for (int i = 0; i < 5; i++) {
            queue.put(i+1);
        }
    }

}

public class Producer extends Thread{
    private Queue queue;
    public Producer(String name,Queue queue){
        super(name);
        this.queue = queue;
    }

    @Override
    public void run() {
        for (int i = 0; i < 5; i++) {
            queue.put(i+1);
        }
    }
}


public class Main {

    public static void main(String[] args) {
        Queue queue = new Queue();
        Thread customer1 = new Customer("customer1",queue);
        Thread producer1 = new Producer("producer1",queue);
        customer1.setPriority(4);
        producer1.setPriority(7);
        producer1.start();
        customer1.start();

    }

}

输出：

 
The number of products：1    
producer is waiting    
there are 0left    
customer is waiting    
The number of products：2    
producer is waiting    
there are 1left    
there are 0left    
customer is waiting    
The number of products：3    
producer is waiting    
there are 2left    
there are 1left    
there are 0left     
customer is waiting   
The number of products：4    
producer is waiting    
there are 3left    
there are 2left    
there are 1left    
there are 0left    
customer is waiting    
The number of products：5    
there are 4left    
there are 3left    
there are 2left    
there are 1left    
there are 0left    
customer is waiting

我不知道为什么输出顺序是这样的。

为什么不输出像

这样的结果

The number of products：3  
producer is waiting      
there are 2left    
The number of products: 6       
there are 5left            
The number of products: 10     
there are 9left    
The number of products: 15        
there are 14left

Answer 1

我认为问题在于您在收到通知后没有检查您的情况。

你做了

if (condition){
  wait();
}
increment();

虽然您的线程可以从另一个上下文通知，但它不会检查，如果条件仍然存在或已被另一个线程解决并且仍然执行增量。正确的是在醒来时重新检查你的情况，例如：

while (condition){
  wait();
}
increment();

Java消费者/制作人

1 个答案: