用不同风格的相同代码ForkJoinPool不同的延迟

基础概念

ForkJoinPool 是 Java 7 引入的一个线程池，特别适用于分治算法（Divide and Conquer）。它通过工作窃取（Work Stealing）算法来提高并发执行的效率。ForkJoinPool 中的任务分为两类：RecursiveAction（无返回值）和 RecursiveTask（有返回值）。

不同风格的代码示例

风格一：递归任务

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;

public class ForkJoinExample {
    public static void main(String[] args) {
        ForkJoinPool pool = new ForkJoinPool();
        int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        SumTask task = new SumTask(array, 0, array.length);
        int result = pool.invoke(task);
        System.out.println("Sum: " + result);
    }

    static class SumTask extends RecursiveTask<Integer> {
        private final int[] array;
        private final int start;
        private final int end;

        SumTask(int[] array, int start, int end) {
            this.array = array;
            this.start = start;
            this.end = end;
        }

        @Override
        protected Integer compute() {
            if (end - start <= 2) {
                int sum = 0;
                for (int i = start; i < end; i++) {
                    sum += array[i];
                }
                return sum;
            } else {
                int mid = (start + end) / 2;
                SumTask leftTask = new SumTask(array, start, mid);
                SumTask rightTask = new SumTask(array, mid, end);
                leftTask.fork();
                int rightResult = rightTask.compute();
                int leftResult = leftTask.join();
                return leftResult + rightResult;
            }
        }
    }
}

风格二：使用 lambda 表达式

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;

public class ForkJoinLambdaExample {
    public static void main(String[] args) {
        ForkJoinPool pool = new ForkJoinPool();
        int[] array = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        SumTask task = new SumTask(array, 0, array.length);
        int result = pool.invoke(task);
        System.out.println("Sum: " + result);
    }

    static class SumTask extends RecursiveTask<Integer> {
        private final int[] array;
        private final int start;
        private final int end;

        SumTask(int[] array, int start, int end) {
            this.array = array;
            this.start = start;
            this.end = end;
        }

        @Override
        protected Integer compute() {
            if (end - start <= 2) {
                return java.util.Arrays.stream(array, start, end).sum();
            } else {
                int mid = (start + end) / 2;
                SumTask leftTask = new SumTask(array, start, mid);
                SumTask rightTask = new SumTask(array, mid, end);
                leftTask.fork();
                int rightResult = rightTask.compute();
                int leftResult = leftTask.join();
                return leftResult + rightResult;
            }
        }
    }
}