正确运用synchronized和二次判断 实现多线程安全，做出高效二符合预期的程序，特别是多个线程跑一个对象的时候，如下图所示： 

测试代码如下： 
特别注意if(shutdownRequested){ *部分不同的写法。

不然就会输出与逻辑不符的现象： 
如：

runner—-false—-我没有关闭。。。

runner—-true—-我没有关闭。。。

runner—-true—-我关闭了=====»>

---

package com.xue.gang.volatiler;

import java.util.concurrent.CountDownLatch;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

public class VolatileRunner{

public static void main(String args[]) throws InterruptedException {

    int size=1000;

    CountDownLatch countDownLatch = new CountDownLatch(size);

    TomRunner tomRunner = new TomRunner(false,countDownLatch,"runner");

    ExecutorService executorService = Executors.newCachedThreadPool();

    for(int i=1;i<=size;i++){

        executorService.execute(new Thread2RunTomRunner(countDownLatch,tomRunner,i+"_号"));

    }

    countDownLatch.await();

    executorService.shutdown();

    //new Thread(volatileRunner).start();

}

static class Thread2RunTomRunner implements Runnable{

    private CountDownLatch  countDownLatch;

    private TomRunner tomRunner;

    private String name;

    public Thread2RunTomRunner(CountDownLatch countDownLatch,

            TomRunner tomRunner, String name) {

        super();

        this.countDownLatch = countDownLatch;

        this.tomRunner = tomRunner;

        this.name = name;

    }

    public void run() {

        System.out.println(this.name+":running...");

        this.tomRunner.doWork();

        System.out.println(this.name+":结束...");

        this.countDownLatch.countDown();

    }

}

static class TomRunner{

    volatile boolean shutdownRequested = false;

    //boolean shutdownRequested = false;

    String name;

    public TomRunner(boolean shutdownRequested,

            CountDownLatch countDownLatch, String name) {

        super();

        this.shutdownRequested = shutdownRequested;

        this.name = name;

    }

    public void shutdown() {

        this.shutdownRequested = true;

    }

    public void doWork() {

        while (true) {

            /**

             *多个线程的代码去执行：  System.out.println(this.name + "----" + this.shutdownRequested +"----" +"我没有关闭。。。");

             * */

               /*if(shutdownRequested){

                    System.out.println(this.name + "----" + this.shutdownRequested +"----" +"我关闭了=====>>>");

                    break;

                }else{

                    System.out.println(this.name + "----" + this.shutdownRequested +"----" +"我没有关闭。。。");

                    shutdown();

                }*/

            /**

             * 如果没有二次判断，也会出现比较脏数据.

             * */

            /*

                if(shutdownRequested){

                    System.out.println(this.name + "----" + this.shutdownRequested +"----" +"我关闭了=====>>>");

                    break;

                }

                synchronized (this) {

                    System.out.println(this.name + "----" + this.shutdownRequested +"----" +"我没有关闭。。。");

                    shutdown();

                }*/

            /**

             * 加上二次判断,能够正确

             * */

            if(shutdownRequested){

                System.out.println(this.name + "----" + this.shutdownRequested +"----" +"我关闭了=====>>>");

                break;

            }

                synchronized (this) {

                if(!shutdownRequested){

                    System.out.println(this.name + "----" + this.shutdownRequested +"----" +"我没有关闭。。。");

                    shutdown();

                }

            }

        }

    }

}

}

原：http://my.oschina.net/u/177808/blog/165442