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java如何把数据同步到主内存?

Consumer.run()里面执行n.conusme()时,count值为5
但是之后的n.getCount()得到的是4

public class ThreadDemo {
    public static void main(String[] args) {
        Apple n = new Apple();
        Thread a1 = new Thread(new Producer(n), "Producer");
        Thread a2 = new Thread(new Consumer(n), "Consumer");

        a1.start();
        try{
            Thread.sleep(1000) ;
        }catch(InterruptedException e){
            e.printStackTrace() ;
        }
        a2.start();
    }

}
class Producer implements Runnable {
    Apple n;

    public Producer(Apple n) {
        this.n = n;
    }
    volatile boolean keepRunning = true;
    @Override
    public void run() {
        while (true) {
            while (keepRunning) {
                if (n.getCount() < 5) {
                    n.produce();
                    System.out.println(Thread.currentThread().getName()
                            + " produced an apple," + n.getCount() + " apple(s) left");
                }
                if (n.getCount() >= 5) {
                    keepRunning = false;
                }
                Thread.yield();
            }
            if (n.getCount() < 5) {
                keepRunning = true;
            }
        }

    }
}
class Consumer implements Runnable {
    Apple n;
    public Consumer(Apple n) {
        this.n = n;
    }
    volatile boolean keepRunning = true;
    @Override
    public void run() {
        while (true) {
            while (keepRunning) {
                if (n.getCount() <= 5 && n.getCount() > 0) {
                    n.consume();
                    System.out.println(Thread.currentThread().getName()
                            + " consumed an apple," + n.getCount() + " apple(s) left");////here is 5
                }
                if (n.getCount() <= 0) {
                    keepRunning = false;
                }
                Thread.yield();
            }
            if (n.getCount() > 0) {
                keepRunning = true;
            }
        }

    }
}
class Apple {
    private int count = 0;

    public int getCount() {
        return count;
    }
    public synchronized void produce() {
        count++;

        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public synchronized void consume() {
        count--;
        System.out.println("count="+count);//here is 4
    }
}

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蛮大人123 2016-02-27 19:09:42 1853 0
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  • 可以使用几个方案保证内存可见: 1、加锁 2、使用volatile 会保证多线程间数据的修改是可见的 3、使用Atomic
    2019-07-17 18:49:16
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  • 我说我不帅他们就打我,还说我虚伪

    因为getcount方法没有使用sychronized,所以当你调用consumer方法时,getcount方法也会同时执行。

    2019-07-17 18:49:16
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