标签:style blog color io 使用 java ar for 2014
<span style="font-size: 18px; font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);"> 在多线程开发中,经常会遇见在run方法里面调用一个公共的属性的事情,由于每次start都会创建一个线程,因此</span>
<span style="font-size: 18px; font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">所</span><span style="font-size: 18px; font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">有的线程共享一个属性,当其中任何一个线程更改了这个属性的值,这个属性在下面的使用过程中都会被改变,这</span>
<span style="font-size: 18px; font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">回导</span><span style="font-size: 18px; font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);">致很多不期望发生的事情发生,这就叫做线程不安全的。先来一个例子说明这个问题。</span>
<span style="font-size: 18px; font-family: Arial, Helvetica, sans-serif; background-color: rgb(255, 255, 255);"> </span>
package com.bird.concursey; import java.util.Date; import java.util.concurrent.TimeUnit; public class UnsafeTask implements Runnable{ private Date startDate; @Override public void run() { startDate = new Date(); System.out.println("start thread " + Thread.currentThread().getId() + " " + startDate); try { TimeUnit.SECONDS.sleep((int)Math.rint(Math.random() * 10)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Thread finish " + Thread.currentThread().getId() + " " + startDate); } public static void main(String[] args) { UnsafeTask task = new UnsafeTask(); for(int i = 0; i < 10; i++) { Thread thread = new Thread(task); thread.start(); try { TimeUnit.SECONDS.sleep(2); } catch (InterruptedException e) { e.printStackTrace(); } } } }
运行完毕后,他们的结束时间都是一样的,运行结果如下。
start thread 8 Tue Sep 16 20:21:50 CST 2014 start thread 9 Tue Sep 16 20:21:52 CST 2014 start thread 10 Tue Sep 16 20:21:54 CST 2014 start thread 11 Tue Sep 16 20:21:56 CST 2014 start thread 12 Tue Sep 16 20:21:58 CST 2014 Thread finish 10 Tue Sep 16 20:21:58 CST 2014 Thread finish 11 Tue Sep 16 20:21:58 CST 2014 Thread finish 8 Tue Sep 16 20:21:58 CST 2014 start thread 13 Tue Sep 16 20:22:00 CST 2014 Thread finish 9 Tue Sep 16 20:22:00 CST 2014 start thread 14 Tue Sep 16 20:22:02 CST 2014 start thread 15 Tue Sep 16 20:22:04 CST 2014 Thread finish 14 Tue Sep 16 20:22:04 CST 2014 start thread 16 Tue Sep 16 20:22:06 CST 2014 Thread finish 12 Tue Sep 16 20:22:06 CST 2014 start thread 17 Tue Sep 16 20:22:08 CST 2014 Thread finish 16 Tue Sep 16 20:22:08 CST 2014 Thread finish 13 Tue Sep 16 20:22:08 CST 2014 Thread finish 15 Tue Sep 16 20:22:08 CST 2014 Thread finish 17 Tue Sep 16 20:22:08 CST 2014
的期望是每个Thread都有自己的属性的值,大家都是独立的,那该怎么做呢。
package com.bird.concursey; import java.util.Date; import java.util.concurrent.TimeUnit; public class SafeTask implements Runnable { private static ThreadLocal<Date> startDate = new ThreadLocal<Date>() { protected Date initialValue() { return new Date(); }; }; @Override public void run() { System.out.println("start thread " + Thread.currentThread().getId() + " " + startDate.get()); try { TimeUnit.SECONDS.sleep((int) Math.rint(Math.random() * 10)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("Thread finish " + Thread.currentThread().getId() + " " + startDate.get()); } public static void main(String[] args) { SafeTask task = new SafeTask(); for (int i = 0; i < 10; i++) { Thread thread = new Thread(task); thread.start(); try { TimeUnit.SECONDS.sleep(2); } catch (InterruptedException e) { e.printStackTrace(); } } } }
会去调用他的initvalue方法给这个属性付一个初值,然后每个线程都会自己维护这个值,各个线程之间都是独立的,
我们通过get方法就能获得对应的值,当然他也提供了set方法来更改他的值,或者remove等等,反正现在就是线程安
全的了。
标签:style blog color io 使用 java ar for 2014
原文地址:http://blog.csdn.net/a352193394/article/details/39322981