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
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 th1 = new Thread(myRunnable);
Thread th2 = new Thread(myRunnable);
th1.start();
th2.start();
th1.join();
th2.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。
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