volatile保证可见性

volatile的可见性作用，我们必须意思到被volatile修饰的变量对所有线程总是可见的，对volatile变量的所有写操作总是能立刻反应到其他线程的。

public class VolatileVisibilitySample {
    
    
    volatile boolean initFlag = false;

    public void save(){
    
    
        this.initFlag = true;
        String threadName = Thread.currentThread().getName();
        System.out.println("线程："+threadName +":修改共享变量的initFlag");
    }

    public void load(){
    
    
        String  threadName = Thread.currentThread().getName();

        while(!initFlag){
    
    
            //在此处循环，等待initFlag状态改变
        }
        System.out.println("线程:"+ threadName +"当前线程嗅到了initFlag的状态的改变");
    }

    public static void main( String[] args ) {
    
    
        VolatileVisibilitySample sample = new VolatileVisibilitySample();

        Thread threadA = new Thread(()->{
    
    
            sample.save();
        },"threadA");

        Thread threadB = new Thread(()->{
    
    
            sample.load();
        },"threadB");

        threadB.start();

        try {
    
    
            Thread.sleep(1000);
        }catch (Exception e){
    
    

        }
        threadA.start();
    }

}

1、initFlag加上volatile关键字

线程A改变initFlag属性之后，线程B马上感知到

2、initFlag不加volatile关键字

线程B感知不到

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