使用Runnable实现数据共享

使用Runnable实现数据共享,供大家参考,具体内容如下

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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创新互联。


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