从头认识多线程-3.2 使用volatile声明的变量的写操作是非原子性的

这一章节我们来讨论一下使用volatile声明的变量的各种操作是非原子性的。

1.上一章节我们已经提到，volatile把工作内存里面变量的改变同步到主内存，使得各个线程能够把该变量当成是整体的状态控制

2.但是，使用volatile声明的变量的写操作是非原子性的

代码清单：

package com.ray.deepintothread.ch03.topic_2;

public class VolatileTest extends Thread {

	private volatile int id = 0;

	@Override
	public void run() {
		for (int i = 0; i < 10; i++) {
			System.out.println("Thread name :" + Thread.currentThread().getName() + " id :" + id++);
			try {
				sleep(50);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}

	public static void main(String[] args) throws InterruptedException {
		VolatileTest volatileTest1 = new VolatileTest();
		VolatileTest volatileTest2 = new VolatileTest();
		volatileTest1.start();
		Thread.sleep(100);
		volatileTest2.start();
	}
}

输出：

Thread name :Thread-0 id :0
Thread name :Thread-0 id :1
Thread name :Thread-1 id :0
Thread name :Thread-0 id :2
Thread name :Thread-1 id :1
Thread name :Thread-0 id :3
Thread name :Thread-1 id :2
Thread name :Thread-0 id :4
Thread name :Thread-1 id :3
Thread name :Thread-0 id :5
Thread name :Thread-1 id :4
Thread name :Thread-0 id :6
Thread name :Thread-1 id :5
Thread name :Thread-0 id :7
Thread name :Thread-1 id :6
Thread name :Thread-0 id :8
Thread name :Thread-1 id :7
Thread name :Thread-0 id :9
Thread name :Thread-1 id :8
Thread name :Thread-1 id :9