juc之java并发编程

线程间内存可见性问题

• 内存可见性问题

public class TestVolatile {

    public static void main(String[] args){
        ThreadDemo threadDemo=new ThreadDemo();
        new Thread(threadDemo).start();
        while (true){
            if(threadDemo.getFlag()){
                System.out.println(Thread.currentThread().getName()+threadDemo.getFlag()+"========");
            }
        }

    }

}
class ThreadDemo implements Runnable{
    private Boolean flag=false;

    public Boolean getFlag() {
        return flag;
    }

    public void setFlag(Boolean flag) {
        this.flag = flag;
    }

    @Override
    public void run() {
        try {
            Thread.sleep(2000);
            flag=true;
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        if(flag){
            System.out.println(Thread.currentThread().getName()+flag+"======");
        }
    }
}

==运行结果如下==

主线程中始终不会输出此时就出现了线程间的内存可见性问题

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