使用Runnable实现数据共享,供大家参考,具体内容如下
先上代码:
public class TestThread { private static final Logger logger = LoggerFactory.getLogger(TestThread.class); private final class MyRunnable implements Runnable { private int i; public MyRunnable() { this.i = 10; } public void run() { while(i > 0) { synchronized (this) { if (i > 0) { i--; logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i); } } } } } @Test public void testRunable() throws InterruptedException{ MyRunnable myRunnable = new MyRunnable(); Thread th2 = new Thread(myRunnable); Thread th3 = new Thread(myRunnable); th2.start(); th3.start(); th2.join(); th3.join(); } }
楼上的代码很简单,模拟一个售票系统。通过两个Thread对象开启两条线程同时运行一个MyRunnable实例。
几个注意点:
1. 没有加上synchronised关键词的话,即
public void run() { while(i > 0) { if (i > 0) { i--; logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i); } } }
系统的运行结果:
Thread-1 buy one ticket, 8 left. Thread-2 buy one ticket, 8 left. Thread-2 buy one ticket, 6 left. Thread-1 buy one ticket, 6 left. Thread-2 buy one ticket, 5 left. Thread-1 buy one ticket, 4 left. Thread-2 buy one ticket, 3 left. Thread-1 buy one ticket, 2 left. Thread-2 buy one ticket, 1 left. Thread-1 buy one ticket, 0 left.
可以看到,缺少同步的程序输出明显有问题。
2. 在进入同步代码块之后,还需要对i的值再进行一次判断,即,如果不加if判断:
public void run() { while(i > 0) { synchronized (this) { i--; logger.debug("{} buy one ticket, {} left. ", Thread.currentThread().getName(), i); } } }
程序的运行结果为:
Thread-2 buy one ticket, 9 left. Thread-2 buy one ticket, 8 left. Thread-2 buy one ticket, 7 left. Thread-2 buy one ticket, 6 left. Thread-2 buy one ticket, 5 left. Thread-2 buy one ticket, 4 left. Thread-2 buy one ticket, 3 left. Thread-2 buy one ticket, 2 left. Thread-2 buy one ticket, 1 left. Thread-2 buy one ticket, 0 left. Thread-1 buy one ticket, -1 left.
可以看出,出现了“多卖”的现象, 所以需要在进入同步代码块中再进行一次if判断。
总结
synchronised用于互斥访问共享变量, 并在同步代码块中使用if判断更新共享变量。
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持亿速云。
免责声明:本站发布的内容(图片、视频和文字)以原创、转载和分享为主,文章观点不代表本网站立场,如果涉及侵权请联系站长邮箱:is@yisu.com进行举报,并提供相关证据,一经查实,将立刻删除涉嫌侵权内容。