Java线程--ForkJoinPool使用

原创:转载需注明原创地址 https://www.cnblogs.com/fanerwei222/p/11871099.html

Java线程--ForkJoinPool使用

简单解释下:

  Fork是执行的意思, Join是等待的意思, 结合使用就是先用Fork来执行子任务, 然后再用Join等待子任务全部执行完毕之后再统一处理或者返回 .

public static void main(String[] args) throws InterruptedException, ExecutionException {
        /**
         * 多线程框架
         */
        Executor executor = null;
        /**
         * Executor 的子接口
         */
        ExecutorService service = null;
        /**
         * ExecutorService 的抽象子类
         */
        AbstractExecutorService service1 = null;
        /**
         * AbstractExecutorService 的子类
         * 执行由一个大任务拆分成的多个小任务
         * 完成一个任务的分段执行, 最后再统一处理
         * 配合 ForkJoinTask 使用
         */
        ForkJoinPool xxxx = new ForkJoinPool();

        /**
         * 异步计算返回的结果
         */
        Future future = null;
        /**
         * Future的抽象子类
         */
        ForkJoinTask forkJoinTask = null;
        /**
         * 没有返回值, ForkJoinTask的抽象子类
         */
        RecursiveAction recursiveAction = null;
        /**
         * 有返回值, ForkJoinTask的抽象子类
         */
        RecursiveTask recursiveTask = null;

        /**
         * 来 300 个打印的任务
         */
        PrintTasks printTasks = new PrintTasks(0, 200);
        /**
         * 来一个任务存储器
         */
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        /**
         * 提交任务
         */
        forkJoinPool.submit(printTasks);
        /**
         * 等待所有任务完成
         */
        forkJoinPool.awaitTermination(20, TimeUnit.SECONDS);
        forkJoinPool.shutdown();

        int[] intArr = new int[100];
        Random random = new Random();
        int total = 0;
        int len = intArr.length;
        for (int i = 0; i < len ; i++) {
            int tmp = random.nextInt(5);
            total += (intArr[i] = tmp);
        }
        System.out.println("初始化时的数组总和 : " + total);
        SumTask sumTask = new SumTask(intArr, 0, len);
        /**
         * 通用池
         */
        ForkJoinPool pool = ForkJoinPool.commonPool();
        Future<Integer> future1 = pool.submit(sumTask);
        System.out.println("任务执行结果: " + future1.get());
        pool.shutdown();
    }
/**
 * 继承 RecursiveAction 来实现任务可分解
 */
class PrintTasks extends RecursiveAction {

    private static final int THRESHOLD = 20; // 设置一个最多打印的数
    private int start;
    private int end;

    public PrintTasks(int start, int end) {
        super();
        this.start = start;
        this.end = end;
    }

    @Override
    protected void compute() {
        /**
         * 进行小任务划分
         */
        if (end - start < THRESHOLD) {
            for(int i=start; i<end ; i++){
                System.out.println(Thread.currentThread().getName()+"的i : "+i);
            }
        } else {
            /**
             * 二分法, 直到任务的规模小于规定的规模为止
             */
            int middle =(start+end)/2;
            PrintTasks left = new PrintTasks(start, middle);
            PrintTasks right = new PrintTasks(middle, end);
            /**
             * fork() 就是执行的意思
             * 这里并行执行以下
             */
            left.fork();
            right.fork();
        }
    }
}
/**
 * 统计总数的任务
 */
class SumTask extends RecursiveTask<Integer> {

    /**
     * 每个小任务 最多只累加5个数
     */
    private static final int THRESHOLD = 5;
    /**
     * 数据的数组
     */
    private int arry[];
    private int start;
    private int end;

    public SumTask(int[] arry, int start, int end) {
        super();
        this.arry = arry;
        this.start = start;
        this.end = end;
    }

    /**
     * 类种是什么类型的值就返回什么类型的值
     * @return
     */
    @Override
    protected Integer compute() {
        int sum =0;
        /**
         * 当end与start之间的差小于设定任务数量时,才开始进行实际的累加
         */
        if(end - start <THRESHOLD){
            for(int i= start;i<end;i++){
                sum += arry[i];
            }
            return sum;
        }else {
            /**
             * 任务数量超过规定执行数量时 , 进行二分法拆分
             */
            int middle = (start+ end)/2;
            SumTask small = new SumTask(arry, start, middle);
            SumTask big = new SumTask(arry, middle, end);
            /**
             * 执行任务
             */
            small.fork();
            big.fork();
            /**
             * 把各个小任务累加的结果合并起来并且返回
             * join() 会等待子任务执行完并得到其结果
             */
            return small.join()+big.join();
        }
    }
}

打印结果如下:

ForkJoinPool-2-worker-1的i : 187
ForkJoinPool-2-worker-2的i : 87
ForkJoinPool-2-worker-2的i : 88
ForkJoinPool-2-worker-2的i : 89
ForkJoinPool-2-worker-2的i : 90
ForkJoinPool-2-worker-2的i : 91
ForkJoinPool-2-worker-2的i : 92
ForkJoinPool-2-worker-2的i : 93
ForkJoinPool-2-worker-2的i : 94
ForkJoinPool-2-worker-2的i : 95
ForkJoinPool-2-worker-2的i : 96
ForkJoinPool-2-worker-2的i : 97
ForkJoinPool-2-worker-2的i : 98
ForkJoinPool-2-worker-2的i : 99
ForkJoinPool-2-worker-2的i : 75
ForkJoinPool-2-worker-2的i : 76
ForkJoinPool-2-worker-2的i : 77
ForkJoinPool-2-worker-2的i : 78
ForkJoinPool-2-worker-2的i : 79
ForkJoinPool-2-worker-2的i : 80
ForkJoinPool-2-worker-2的i : 81
ForkJoinPool-2-worker-2的i : 82
ForkJoinPool-2-worker-2的i : 83
ForkJoinPool-2-worker-2的i : 84
ForkJoinPool-2-worker-2的i : 85
ForkJoinPool-2-worker-2的i : 86
ForkJoinPool-2-worker-2的i : 62
ForkJoinPool-2-worker-2的i : 63
ForkJoinPool-2-worker-2的i : 64
ForkJoinPool-2-worker-2的i : 65
ForkJoinPool-2-worker-2的i : 66
ForkJoinPool-2-worker-2的i : 67
ForkJoinPool-2-worker-2的i : 68
ForkJoinPool-2-worker-2的i : 69
ForkJoinPool-2-worker-2的i : 70
ForkJoinPool-2-worker-2的i : 71
ForkJoinPool-2-worker-2的i : 72
ForkJoinPool-2-worker-2的i : 73
ForkJoinPool-2-worker-2的i : 74
ForkJoinPool-2-worker-2的i : 50
ForkJoinPool-2-worker-2的i : 51
ForkJoinPool-2-worker-2的i : 52
ForkJoinPool-2-worker-2的i : 53
ForkJoinPool-2-worker-2的i : 54
ForkJoinPool-2-worker-2的i : 55
ForkJoinPool-2-worker-1的i : 188
ForkJoinPool-2-worker-1的i : 189
ForkJoinPool-2-worker-1的i : 190
ForkJoinPool-2-worker-1的i : 191
ForkJoinPool-2-worker-1的i : 192
ForkJoinPool-2-worker-1的i : 193
ForkJoinPool-2-worker-1的i : 194
ForkJoinPool-2-worker-1的i : 195
ForkJoinPool-2-worker-1的i : 196
ForkJoinPool-2-worker-1的i : 197
ForkJoinPool-2-worker-1的i : 198
ForkJoinPool-2-worker-1的i : 199
ForkJoinPool-2-worker-1的i : 175
ForkJoinPool-2-worker-1的i : 176
ForkJoinPool-2-worker-1的i : 177
ForkJoinPool-2-worker-1的i : 178
ForkJoinPool-2-worker-1的i : 179
ForkJoinPool-2-worker-1的i : 180
ForkJoinPool-2-worker-1的i : 181
ForkJoinPool-2-worker-1的i : 182
ForkJoinPool-2-worker-1的i : 183
ForkJoinPool-2-worker-1的i : 184
ForkJoinPool-2-worker-1的i : 185
ForkJoinPool-2-worker-1的i : 186
ForkJoinPool-2-worker-1的i : 162
ForkJoinPool-2-worker-1的i : 163
ForkJoinPool-2-worker-1的i : 164
ForkJoinPool-2-worker-1的i : 165
ForkJoinPool-2-worker-1的i : 166
ForkJoinPool-2-worker-1的i : 167
ForkJoinPool-2-worker-1的i : 168
ForkJoinPool-2-worker-1的i : 169
ForkJoinPool-2-worker-1的i : 170
ForkJoinPool-2-worker-1的i : 171
ForkJoinPool-2-worker-1的i : 172
ForkJoinPool-2-worker-1的i : 173
ForkJoinPool-2-worker-1的i : 174
ForkJoinPool-2-worker-1的i : 150
ForkJoinPool-2-worker-1的i : 151
ForkJoinPool-2-worker-1的i : 152
ForkJoinPool-2-worker-1的i : 153
ForkJoinPool-2-worker-1的i : 154
ForkJoinPool-2-worker-2的i : 56
ForkJoinPool-2-worker-2的i : 57
ForkJoinPool-2-worker-2的i : 58
ForkJoinPool-2-worker-2的i : 59
ForkJoinPool-2-worker-2的i : 60
ForkJoinPool-2-worker-2的i : 61
ForkJoinPool-2-worker-2的i : 37
ForkJoinPool-2-worker-2的i : 38
ForkJoinPool-2-worker-2的i : 39
ForkJoinPool-2-worker-2的i : 40
ForkJoinPool-2-worker-2的i : 41
ForkJoinPool-2-worker-2的i : 42
ForkJoinPool-2-worker-2的i : 43
ForkJoinPool-2-worker-2的i : 44
ForkJoinPool-2-worker-2的i : 45
ForkJoinPool-2-worker-2的i : 46
ForkJoinPool-2-worker-2的i : 47
ForkJoinPool-2-worker-2的i : 48
ForkJoinPool-2-worker-2的i : 49
ForkJoinPool-2-worker-2的i : 25
ForkJoinPool-2-worker-2的i : 26
ForkJoinPool-2-worker-2的i : 27
ForkJoinPool-2-worker-2的i : 28
ForkJoinPool-2-worker-2的i : 29
ForkJoinPool-2-worker-2的i : 30
ForkJoinPool-2-worker-2的i : 31
ForkJoinPool-2-worker-2的i : 32
ForkJoinPool-2-worker-2的i : 33
ForkJoinPool-2-worker-2的i : 34
ForkJoinPool-2-worker-2的i : 35
ForkJoinPool-2-worker-2的i : 36
ForkJoinPool-2-worker-2的i : 12
ForkJoinPool-2-worker-2的i : 13
ForkJoinPool-2-worker-2的i : 14
ForkJoinPool-2-worker-2的i : 15
ForkJoinPool-2-worker-2的i : 16
ForkJoinPool-2-worker-2的i : 17
ForkJoinPool-2-worker-2的i : 18
ForkJoinPool-2-worker-2的i : 19
ForkJoinPool-2-worker-2的i : 20
ForkJoinPool-2-worker-2的i : 21
ForkJoinPool-2-worker-2的i : 22
ForkJoinPool-2-worker-2的i : 23
ForkJoinPool-2-worker-2的i : 24
ForkJoinPool-2-worker-2的i : 0
ForkJoinPool-2-worker-2的i : 1
ForkJoinPool-2-worker-2的i : 2
ForkJoinPool-2-worker-2的i : 3
ForkJoinPool-2-worker-2的i : 4
ForkJoinPool-2-worker-2的i : 5
ForkJoinPool-2-worker-2的i : 6
ForkJoinPool-2-worker-2的i : 7
ForkJoinPool-2-worker-2的i : 8
ForkJoinPool-2-worker-2的i : 9
ForkJoinPool-2-worker-2的i : 10
ForkJoinPool-2-worker-2的i : 11
ForkJoinPool-2-worker-2的i : 137
ForkJoinPool-2-worker-2的i : 138
ForkJoinPool-2-worker-2的i : 139
ForkJoinPool-2-worker-2的i : 140
ForkJoinPool-2-worker-2的i : 141
ForkJoinPool-2-worker-2的i : 142
ForkJoinPool-2-worker-2的i : 143
ForkJoinPool-2-worker-2的i : 144
ForkJoinPool-2-worker-2的i : 145
ForkJoinPool-2-worker-2的i : 146
ForkJoinPool-2-worker-2的i : 147
ForkJoinPool-2-worker-2的i : 148
ForkJoinPool-2-worker-2的i : 149
ForkJoinPool-2-worker-2的i : 125
ForkJoinPool-2-worker-2的i : 126
ForkJoinPool-2-worker-2的i : 127
ForkJoinPool-2-worker-2的i : 128
ForkJoinPool-2-worker-2的i : 129
ForkJoinPool-2-worker-2的i : 130
ForkJoinPool-2-worker-2的i : 131
ForkJoinPool-2-worker-2的i : 132
ForkJoinPool-2-worker-2的i : 133
ForkJoinPool-2-worker-2的i : 134
ForkJoinPool-2-worker-2的i : 135
ForkJoinPool-2-worker-2的i : 136
ForkJoinPool-2-worker-2的i : 112
ForkJoinPool-2-worker-2的i : 113
ForkJoinPool-2-worker-2的i : 114
ForkJoinPool-2-worker-2的i : 115
ForkJoinPool-2-worker-2的i : 116
ForkJoinPool-2-worker-2的i : 117
ForkJoinPool-2-worker-2的i : 118
ForkJoinPool-2-worker-2的i : 119
ForkJoinPool-2-worker-2的i : 120
ForkJoinPool-2-worker-2的i : 121
ForkJoinPool-2-worker-2的i : 122
ForkJoinPool-2-worker-2的i : 123
ForkJoinPool-2-worker-2的i : 124
ForkJoinPool-2-worker-2的i : 100
ForkJoinPool-2-worker-2的i : 101
ForkJoinPool-2-worker-2的i : 102
ForkJoinPool-2-worker-2的i : 103
ForkJoinPool-2-worker-2的i : 104
ForkJoinPool-2-worker-2的i : 105
ForkJoinPool-2-worker-2的i : 106
ForkJoinPool-2-worker-2的i : 107
ForkJoinPool-2-worker-2的i : 108
ForkJoinPool-2-worker-2的i : 109
ForkJoinPool-2-worker-2的i : 110
ForkJoinPool-2-worker-2的i : 111
ForkJoinPool-2-worker-1的i : 155
ForkJoinPool-2-worker-1的i : 156
ForkJoinPool-2-worker-1的i : 157
ForkJoinPool-2-worker-1的i : 158
ForkJoinPool-2-worker-1的i : 159
ForkJoinPool-2-worker-1的i : 160
ForkJoinPool-2-worker-1的i : 161
初始化时的数组总和 : 204
任务执行结果: 204
执行结果

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转载自www.cnblogs.com/fanerwei222/p/11871099.html
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