J.U.C 的同步工具类

 1 import java.util.ArrayList;
 2 import java.util.Collections;
 3 import java.util.List;
 4 import java.util.Random;
 5 import java.util.concurrent.BrokenBarrierException;
 6 import java.util.concurrent.CyclicBarrier;
 7 
   // 这个demo，是多个线程随机产生数字，放在list中，等到所有线程都产生完数字后（共同栅栏），再对所有数字进行求和
   // 测试结果，自己运行一下就好！
 8 public class CyclicBarrierDemo {
 9     
10     private CyclicBarrier cyclicBarrier;
11     private List<List<Integer>> partialResults
12      = Collections.synchronizedList(new ArrayList<>());
13     private Random random = new Random();
14     private int NUM_PARTIAL_RESULTS;
15     private int NUM_WORKERS;
16     
17     class NumberCruncherThread implements Runnable {
18          
19         @Override
20         public void run() {
21             String thisThreadName = Thread.currentThread().getName();
22             List<Integer> partialResult = new ArrayList<>();
23  
24             // Crunch some numbers and store the partial result
25             for (int i = 0; i < NUM_PARTIAL_RESULTS; i++) {    
26                 Integer num = random.nextInt(10);
27                 System.out.println(thisThreadName
28                   + ": Crunching some numbers! Final result - " + num);
29                 partialResult.add(num);
30             }
31  
32             partialResults.add(partialResult);
33             try {
34                 System.out.println(thisThreadName 
35                   + " waiting for others to reach barrier.");
36                 cyclicBarrier.await();
37                 
                   // 红色部分添加的目的就是，纯粹是为了展示cyclicbarrier可以多次重复设置共同栅栏
38                 System.out.println("No.2 thread name " + thisThreadName);
39                 cyclicBarrier.await();
40                 
41                 System.out.println("No.3 thread name " + thisThreadName);
42                 cyclicBarrier.await();
43             } catch (InterruptedException e) {
44                 // ...
45             } catch (BrokenBarrierException e) {
46                 // 当await超时，所示await阻塞的线程被中断时，那么所有阻塞的线程将被终止，并报出BrokenBarrierException 
47             }
48         }
49     }
50     
51     class AggregatorThread implements Runnable {
52          
53         @Override
54         public void run() {
55  
56             String thisThreadName = Thread.currentThread().getName();
57  
58             System.out.println(
59               thisThreadName + ": Computing sum of " + NUM_WORKERS 
60               + " workers, having " + NUM_PARTIAL_RESULTS + " results each.");
61             int sum = 0;
62  
63             for (List<Integer> threadResult : partialResults) {
64                 System.out.print("Adding ");
65                 for (Integer partialResult : threadResult) {
66                     System.out.print(partialResult+" ");
67                     sum += partialResult;
68                 }
69                 System.out.println();
70             }
71             System.out.println(thisThreadName + ": Final result = " + sum);
72         }
73     }
74     
75     public void runSimulation(int numWorkers, int numberOfPartialResults) {
76         NUM_PARTIAL_RESULTS = numberOfPartialResults;
77         NUM_WORKERS = numWorkers;
78  
79         cyclicBarrier = new CyclicBarrier(NUM_WORKERS, new AggregatorThread());
80  
81         System.out.println("Spawning " + NUM_WORKERS
82           + " worker threads to compute "
83           + NUM_PARTIAL_RESULTS + " partial results each");
84   
85         for (int i = 0; i < NUM_WORKERS; i++) {
86             Thread worker = new Thread(new NumberCruncherThread());
87             worker.setName("Thread " + i);
88             worker.start();
89         }
90     }
91  
92     public static void main(String[] args) {
93         CyclicBarrierDemo demo = new CyclicBarrierDemo();
94         demo.runSimulation(5, 3);
95     }
96 }