HashMap在JDK1.8中并发操作，代码测试以及源码分析

HashMap在JDK1.8中并发操作不会出现死循环，只会出现缺数据。测试如下：

 

 1 package JDKSource;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 import java.util.concurrent.TimeUnit;
 6 
 7 /**
 8  * @Auther: wenbochang
 9  * @Date: 2018/8/5 11
10  */
11 public class TestHashMap {
12     /**
13      * NUMBER = 10，表示十个线程执行put方法执行了十次
14      * 也就是map中总共有10 * 10 = 100 条数据
15      */
16     public static final int NUMBER = 10;
17     public static void main(String[] args) throws InterruptedException {
18 
19         Map<String, String> map = new HashMap<>(2);
20 
21         for (int i = 0; i < NUMBER; i++) {
22             new Thread(new A(map)).start();
23         }
24         TimeUnit.SECONDS.sleep(1);
25         int cnt = 0;
26         for (Map.Entry<String, String> mp : map.entrySet()) {
27             cnt++;
28             System.out.println(mp.getKey() + "  " + mp.getValue());
29         }
30         // 观察cnt的值是否等于插入的数量，就可以判断数据是否丢失了
31         System.out.println("cnt = " + cnt);
32     }
33 }
34 
35 class A implements Runnable {
36 
37     Map<String, String> map;
38 
39     public A(Map<String, String> map) {
40         this.map = map;
41     }
42 
43     @Override
44     public void run() {
45         for (int i = 0; i < TestHashMap.NUMBER; i++) {
46             map.put(i + "  " + Thread.currentThread().getName(), "test");
47         }
48     }
49 }

 

1： 10个线程执行10次put方法：

　　结果如下： 结果太长我给折叠了，主要看 最后的 cnt值为多少

 1 1  Thread-0  test
 2 1  Thread-1  test
 3 9  Thread-1  test
 4 2  Thread-8  test
 5 9  Thread-0  test
 6 2  Thread-7  test
 7 2  Thread-6  test
 8 2  Thread-5  test
 9 2  Thread-4  test
10 2  Thread-3  test
11 2  Thread-2  test
12 2  Thread-1  test
13 9  Thread-9  test
14 9  Thread-8  test
15 9  Thread-7  test
16 9  Thread-6  test
17 9  Thread-5  test
18 9  Thread-4  test
19 9  Thread-3  test
20 9  Thread-2  test
21 2  Thread-9  test
22 0  Thread-2  test
23 3  Thread-9  test
24 3  Thread-8  test
25 3  Thread-3  test
26 3  Thread-2  test
27 3  Thread-1  test
28 3  Thread-0  test
29 3  Thread-7  test
30 3  Thread-6  test
31 3  Thread-5  test
32 3  Thread-4  test
33 7  Thread-8  test
34 7  Thread-9  test
35 7  Thread-6  test
36 7  Thread-7  test
37 7  Thread-4  test
38 7  Thread-5  test
39 7  Thread-2  test
40 7  Thread-3  test
41 7  Thread-0  test
42 7  Thread-1  test
43 4  Thread-0  test
44 4  Thread-1  test
45 4  Thread-2  test
46 4  Thread-3  test
47 4  Thread-4  test
48 4  Thread-5  test
49 4  Thread-6  test
50 4  Thread-7  test
51 4  Thread-8  test
52 4  Thread-9  test
53 1  Thread-4  test
54 1  Thread-5  test
55 1  Thread-2  test
56 1  Thread-3  test
57 1  Thread-8  test
58 1  Thread-9  test
59 1  Thread-6  test
60 1  Thread-7  test
61 5  Thread-3  test
62 5  Thread-2  test
63 5  Thread-5  test
64 5  Thread-4  test
65 5  Thread-1  test
66 5  Thread-0  test
67 5  Thread-7  test
68 5  Thread-6  test
69 5  Thread-9  test
70 5  Thread-8  test
71 6  Thread-6  test
72 6  Thread-5  test
73 6  Thread-8  test
74 6  Thread-7  test
75 6  Thread-9  test
76 6  Thread-0  test
77 6  Thread-2  test
78 6  Thread-1  test
79 6  Thread-4  test
80 6  Thread-3  test
81 0  Thread-8  test
82 0  Thread-7  test
83 0  Thread-9  test
84 0  Thread-4  test
85 0  Thread-3  test
86 0  Thread-6  test
87 0  Thread-5  test
88 8  Thread-2  test
89 8  Thread-1  test
90 8  Thread-0  test
91 8  Thread-6  test
92 8  Thread-5  test
93 8  Thread-4  test
94 8  Thread-3  test
95 8  Thread-9  test
96 8  Thread-8  test
97 8  Thread-7  test
98 cnt = 97

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