麻烦大家解释一下代码Queue谢谢.

Question

实现要求:生产者通过Queue把生产的东西给消费者,消费者通过Queue获取生产者的信息.
代码如下:
package lizi;class Test
{
        public static void main(String[] args)
        {
                Queue q=new Queue();
                Producer p=new Producer(q);
                Consumer c=new Consumer(q);
                p.start();
                c.start();
        }
}class Producer extends Thread
{
        Queue q;
        Producer(Queue q)
        {
                this.q=q;
        }
        public void run()
        {
                for(int i=0;i<10;i++)
                {
                        q.put(i);
                        System.out.println("Producer put "+i);
                }
        }
}
class Consumer extends Thread
{
        Queue q;
        Consumer(Queue q)
        {
                this.q=q;
        }
        public void run()
        {
                while(true)
                {
                        System.out.println("Consumer get "+q.get());
                }
        }
}
class Queue
{
        int value;
        boolean bFull=false;
        public synchronized void put(int i)
        {
                if(!bFull)
                {
                        value=i;
                        bFull=true;
                        notify();
                }
                try
                {
                        wait();
                }
                catch(Exception e)
                {
                        e.printStackTrace();
                }        }
        public synchronized int get()
        {
                if(!bFull)
                {
                        try
                        {
                                wait();
                        }
                        catch(Exception e)
                        {
                                e.printStackTrace();
                        }
                }
                bFull=false;
                notify();
                return value;
        }
}执行结果如下:
Producer put 0
Consumer get 0
Producer put 1
Consumer get 1
Producer put 2
Consumer get 2
Consumer get 3//出现错误现象,先get
Producer put 3
Consumer get 4//error
Producer put 4
Producer put 5
Consumer get 5
Producer put 6
Consumer get 6
Consumer get 7
Producer put 7
Consumer get 8
Producer put 8
Consumer get 9
Producer put 9上面的代码在配置低机器上运行取得正确结果.********************************************************
修改后的代码:package lizi;
class Test
{
        public static void main(String[] args)
        {
                Queue q=new Queue();
                Producer p=new Producer(q);
                Consumer c=new Consumer(q);
                p.start();
                c.start();
        }
}class Producer extends Thread
{
        Queue q;
        Producer(Queue q)
        {
                this.q=q;
        }
        public void run()
        {
                for(int i=0;i<10;i++)
                {
                        q.put(i);
                         System.out.println("Producer put "+i);
                }
        }
}
class Consumer extends Thread
{
        Queue q;
        Consumer(Queue q)
        {
                this.q=q;
        }
        public void run()
        {
                while(true)
                {
                        System.out.println("Consumer get "+q.get());
                }
        }
}
class Queue
{
        int value;
        boolean bFull=false;
        public synchronized void put(int i)
        {
                if(!bFull)
                {
                        value=i;
                        bFull=true;
                        notify();
                }
                try
                {
                        wait();
                }
                catch(Exception e)
                {
                        e.printStackTrace();
                }        }
        public synchronized int get()
        {
                if(!bFull)
                {
                        try
                        {
                                wait();
                        }
                        catch(Exception e)
                        {
                                e.printStackTrace();
                        }
                }
                bFull=false;
                notify();
             try{                            //修改的地方
                        Thread.sleep(1);
                }
                  catch(Exception e)
                  {
                  e.printStackTrace();
                  }
                return value;
        }
}运行结果
Producer put 0
Consumer get 0
Producer put 1
Consumer get 1
Producer put 2
Consumer get 2
Producer put 3
Consumer get 3
Producer put 4
Consumer get 4
Producer put 5
Consumer get 5
Producer put 6
Consumer get 6
Producer put 7
Consumer get 7
Producer put 8
Consumer get 8
Producer put 9
Consumer get 9取得正确结果,想请教为什么上面没有修改的代码put,跟get抢cpu没有全抢?而是有的出现错误,有的没有.而在慢机器上运行正常,机器配置跟结果有多大关系?
请教高手.谢谢

Answer 1

其实这个程序没有问题, cuonsumer get总是在producer put之后才会执行.q.put(i);//--1
System.out.println("Producer put "+i);//--2System.out.println("Consumer get "+q.get());//--3在执行1的时候,如果Queue里的bFull等于true,也就是有产品可取的时候,q.get()才会返回结果,
3语句才得以执行.但时由于1 和 2,3是在两个线程里执行, 所以当1执行后, bFull已经等于true,
而此时2与3都可以执行, 至于谁先执行,那是不可预测的.有可能某个线程被由于系统资源或其它的原因被阻塞,因而导致延迟.Thread.sleep(1);//加这句只是让get()执行的时间延长,那么3的执行时间就会相应延长.所以2就有更多的机会在3之前执行.

Answer 2

改正错误:但时由于1 和 2,3是在两个线程里执行
应该是
1,2 和 3 是在两个线程里执行(Producer 和 Consumer), 它们在操作系统里是并行的,没有次序.
1执行完之后, 3里的q.get()就可以返回结果, 因此3就可以将字串打印出来.