I have following classes :

    package com.akshu.multithreading;

    public class ThreadResource {

        static int a;
     static boolean Value =false;
        public synchronized int getA() {
            while(Value == false){
                try {
                    wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            Value= false;
            notify();


            return a;
        }

        public synchronized void setA(int a) {
            while(Value == true)
            {
                try {
                    wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

            ThreadResource.a = a;
            Value=true;
            notify();

        }


    }


    ------------------


    /**
     *
     */
    package com.akshu.multithreading;

    /**
     * @author akshu
     *
     */
    public class MyThreadA implements Runnable  {

        int a = 0;
        ThreadResource tR= new ThreadResource();

        @Override
        public void run() {


        for (int i = 0; i < 15; i++) {



            tR.setA(++a);
            System.out.println(" value of a :"+a);





        }

        }
    }

    ------------

    package com.akshu.multithreading;

    public class MyThreadB implements Runnable {

        @Override
    public void run() {
        // TODO Auto-generated method stub
        ThreadResource tR =new ThreadResource();
        for (int i = 0; i < 15; i++) {

        System.out.println("getA()"+tR.getA());

                }
    }
    }
    ----

    package com.akshu.multithreading;

    public class ThreadExecutionPoint {

        public static void main(String args[])  {

            Thread th1 = new Thread(new MyThreadA());
            Thread th2 = new Thread(new MyThreadB());

            th1.start();
            th2.start();
        }
    }


我试图通过上面的代码来理解生产者消费者的问题。当我执行上面的代码时,我得到了

    value of a :1
    getA()1


程序仅卡在这里(不终止)。

有人请解释我在做什么错?

最佳答案

Value声明为volatile
static volatile boolean Value =false;
您已经声明了set/get方法synchronized。这意味着它们已锁定在this(对象的固有锁定)上。
但是在您的代码中,您为每个线程实例化了一个不同的ThreadResource,因此没有使它们成为synchronized,因为每种情况下this是不同的。
更改您的代码,如下所示:

public class MyThreadA implements Runnable {
    ThreadResource tR;

     public MyThreadA(ThreadResource tr) {
        this.tR = tr;
    }
// your run method here NOT declaring a ThreadResource anymore!!!
}


MyThreadB相同

然后在ThreadExecutionPoint

ThreadResource tr = new ThreadResource();
Thread th1 = new Thread(new MyThreadA(tr));
Thread th2 = new Thread(new MyThreadB(tr));

10-05 22:50
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