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

 1 class Holder {
 2     private int n;
 3     private static Random random = new Random();
 4     public Holder(int n) {
 5         this.n = n;
 6     }
 7     public void changeValue() {
 8         n = random.nextInt();
 9     }
10     public void assertSanity() {
11         if (n != n) {
12             throw new AssertionError("n != n");
13         }
14     }
15 }
16 
17 class Checker implements Runnable {
18     private boolean stop = false;
19     private Holder holder;
20     public Checker(Holder holder) {
21         this.holder = holder;
22     }
23     public synchronized void stop() {
24         stop = true;
25     }
26     @Override
27     public void run() {
28         while (!stop) {
29             try {
30                 // System.out.println("checking");
31                 holder.assertSanity(); //! Possible to throw exception in concurrent circumstances
32             } catch (Throwable e) {
33                 System.out.println(e);
34                 stop();
35             }
36         }
37     }
38 }
39 
40 class Modifier implements Runnable {
41     private boolean stop = false;
42     private Holder holder;
43     public Modifier(Holder holder) {
44         this.holder = holder;
45     }
46     public synchronized void stop() {
47         stop = true;
48     }
49     @Override
50     public void run() {
51         while (!stop) {
52             // System.out.println("modifying");
53             holder.changeValue();
54         }
55     }
56 }
57 
58 public class Listing3_15 {
59     public static void main(String[] args) {
60         ExecutorService exec = null;
61         Holder holder = null;
62         Modifier m1 = null, m2 = null;
63         Checker checker = null;
64         Scanner scanner = null;
65         try {
66             exec = Executors.newCachedThreadPool();
67             holder = new Holder(10);
68             m1 = new Modifier(holder);
69             m2 = new Modifier(holder);
70             checker = new Checker(holder);
71             exec.execute(checker);
72             exec.execute(m1);
73             exec.execute(m2);
74             scanner = new Scanner(System.in);
75             scanner.next(); // pause
76         } finally {
77             m1.stop();
78             m2.stop();
79             checker.stop();
80             exec.shutdown();
81             scanner.close();
82         }
83     }
84 }

 

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