生产者消费者问题显示顺序错误

Question

以下生产者消费者代码显示错误顺序（在生产者生产消费者消费之前。有时生产者生产许多物品（cubbyhole 只允许一件物品））。这是为什么？

  public class CubbyHole {
    private int content;
    private boolean available=false;

   public synchronized int get() {
      while (available == false) {
         try {
            wait();
         } catch (InterruptedException e) {}
      }
      available = false;
      notify();
      return content;
   }
   public synchronized void put(int value) {
      while (available == true) {
         try {            
            wait();
         } catch (InterruptedException e) { } 
      }
      content = value;
      available = true;
      notifyAll();
      }
   } 

public class Consumer extends Thread {
    CubbyHole c;

    public Consumer(CubbyHole c){
        this.c=c;
    }

    public void run(){
        int val=0;
        for(int i =0;i<10;i++){
            val=c.get();
            System.out.println("consumer gets "+val);
        }
    }

}

public class Producer extends Thread {
    CubbyHole c;

    public Producer(CubbyHole c){
        this.c=c;
    }
    public void run(){
        for(int i=0;i<10;i++){
            c.put(i);
            System.out.println("Producer puts "+i);
        }

    }

}
public class Dimo {

    public static void main(String[] args) {
        CubbyHole c = new CubbyHole();
        Producer p = new Producer(c);
        Consumer con = new Consumer(c);
        p.start();
        con.start();

    }
}

此代码得到以下输出

Producer puts 0
Producer puts 1
consumer gets 0
consumer gets 1
Producer puts 2
Producer puts 3
consumer gets 2
consumer gets 3
Producer puts 4
consumer gets 4
consumer gets 5
Producer puts 5
Producer puts 6
consumer gets 6
Producer puts 7
Producer puts 8
consumer gets 7
consumer gets 8
Producer puts 9
consumer gets 9

任何人都可以解释这段代码有什么问题吗？如何在此代码中获得正确的顺序？

Answer 1

检查这两行：

val=c.get();
System.out.println("consumer gets "+val);

可能发生的情况是消费者呼叫小房间并在空闲时在那里等待。然后它获取值并释放它。现在在这两行之间——在 c.get() 之后和 printlin 之前，另一个线程可以完成它的整个过程——调用 put(i) 并打印。那时您将获得两个 producer.put() 值。

您应该将打印部件移到小孔代码内，以确保打印出您想要的内容。

生产者消费者问题显示顺序错误

Producer consumer problem display a wrong order

java

oop

producer-consumer