1 import java.io.IOException;
2 import java.util.Arrays;
3 import java.util.Random;
4 import java.util.concurrent.RecursiveAction;
5 import java.util.concurrent.RecursiveTask;
6
7 /**
8 * 分割 合并 线程池
9 * 类似于递归的归并排序，这个是多线程的递归排序
10 * jdk1.7之后加的
11 */
12 public class ForkJoinPool {
13
14 static int[] nums = new int[1000000];
15 static final int MAX_NUM = 50000;
16 static Random random = new Random();
17
18 static {
19 for(int i=0; i<nums.length; i++) {
20 nums[i] = random.nextInt(100);
21 }
22 System.out.println("总和1:" + Arrays.stream(nums).sum());
23 }
24
25 /**
26 * ForkJoinPool里面必须是ForkJoinTask，
27 * 直接继承ForkJoinTask类写起来比较麻烦，
28 * 可以继承RecursiveAction(无返回值)和RecursiveTask(递归任务，有返回值)
29 */
30 // static class AddTask extends RecursiveAction {
31 //
32 // int start, end;
33 //
34 // public AddTask(int start, int end) {
35 // this.start = start;
36 // this.end = end;
37 // }
38 //
39 // @Override
40 // protected void compute() {
41 // if(end-start <= MAX_NUM) {
42 // long sum = 0L;
43 // for(int i=start; i<end; i++) sum += nums[i];
44 // System.out.println("from:" + start + " to:" + end + " =" + sum);
45 // }else{
46 // int middle = start + (end - start) / 2;
47 //
48 // AddTask subTask1 = new AddTask(start, middle);
49 // AddTask subTask2 = new AddTask(middle, end);
50 // subTask1.fork();
51 // subTask2.fork();
52 // }
53 // }
54 // }
55
56 /**
57 * 有返回值
58 */
59 static class AddTask extends RecursiveTask<Long> {
60
61 int start, end;
62
63 public AddTask(int start, int end) {
64 this.start = start;
65 this.end = end;
66 }
67
68 @Override
69 protected Long compute() {
70 if(end-start <= MAX_NUM) {
71 long sum = 0L;
72 for(int i=start; i<end; i++) sum += nums[i];
73 System.out.println("from:" + start + " to:" + end + " =" + sum);
74 return sum;
75 }
76
77 int middle = start + (end - start) / 2;
78 AddTask subTask1 = new AddTask(start, middle);
79 AddTask subTask2 = new AddTask(middle, end);
80 subTask1.fork();
81 subTask2.fork();
82 return subTask1.join() + subTask2.join();
83 }
84 }
85
86 public static void main(String[] args) {
87
88 java.util.concurrent.ForkJoinPool pool = new java.util.concurrent.ForkJoinPool();
89 AddTask task = new AddTask(0, nums.length);
90 pool.execute(task); //精灵线程
91 System.out.println("总和2:" + task.join());
92 try {
93 System.in.read(); //阻塞主线程
94 } catch (IOException e) {
95 e.printStackTrace();
96 }
97 }
98
99 }
