一定要使用-server参数来调试并发程序

在阅读JCIP的时候想手工测试一下，结果发现总是没有出现书中描述的并发问题

后来我琢磨，以前记得书上说过，在debugging的环境下，JVM是低并发的，一定要在server的环境下测试，让JVM在高并发的情况下使用，才容易测试出并发BUG，最简便的方法就是给JVM添加上-server的运行参数

代码如下，JCIP Listing3.15

 class Holder {
     private int n;
     private static Random random = new Random();
     public Holder(int n) {
         this.n = n;
     }
     public void changeValue() {
         n = random.nextInt();
     }
     public void assertSanity() {
         if (n != n) {
             throw new AssertionError("n != n");
         }
     }
 }

 class Checker implements Runnable {
     private boolean stop = false;
     private Holder holder;
     public Checker(Holder holder) {
         this.holder = holder;
     }
     public synchronized void stop() {
         stop = true;
     }
     @Override
     public void run() {
         while (!stop) {
             try {
                 // System.out.println("checking");
                 holder.assertSanity(); //! Possible to throw exception in concurrent circumstances
             } catch (Throwable e) {
                 System.out.println(e);
                 stop();
             }
         }
     }
 }

 class Modifier implements Runnable {
     private boolean stop = false;
     private Holder holder;
     public Modifier(Holder holder) {
         this.holder = holder;
     }
     public synchronized void stop() {
         stop = true;
     }
     @Override
     public void run() {
         while (!stop) {
             // System.out.println("modifying");
             holder.changeValue();
         }
     }
 }

 public class Listing3_15 {
     public static void main(String[] args) {
         ExecutorService exec = null;
         Holder holder = null;
         Modifier m1 = null, m2 = null;
         Checker checker = null;
         Scanner scanner = null;
         try {
             exec = Executors.newCachedThreadPool();
             holder = new Holder(10);
             m1 = new Modifier(holder);
             m2 = new Modifier(holder);
             checker = new Checker(holder);
             exec.execute(checker);
             exec.execute(m1);
             exec.execute(m2);
             scanner = new Scanner(System.in);
             scanner.next(); // pause
         } finally {
             m1.stop();
             m2.stop();
             checker.stop();
             exec.shutdown();
             scanner.close();
         }
     }
 }

果然，在debug的环境下，JVM跑不出这个并发BUG，添加-server参数之后，JVM就跑出这个并发BUG了，在eclipse中设置-server参数的方法如下：Run>Run Configurations>Arguments>VM Arguments，写上-server即可