fork join example

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

public class SumArrayTask extends RecursiveTask<Long> {
    private static final int THRESHOLD = 1000; // 小任务阈值
    private final long[] array;
    private final int start, end;

    public SumArrayTask(long[] array, int start, int end) {
        this.array = array;
        this.start = start;
        this.end = end;
    }

    @Override
    protected Long compute() {
        if (end - start <= THRESHOLD) {
            long sum = 0;
            for (int i = start; i < end; i++) {
                sum += array[i];
            }
            return sum;
        } else {
            int mid = (start + end) / 2;
            SumArrayTask leftTask = new SumArrayTask(array, start, mid);
            SumArrayTask rightTask = new SumArrayTask(array, mid, end);
            leftTask.fork(); // 异步执行左半部分
            long rightResult = rightTask.compute(); // 当前线程计算右半部分
            long leftResult = leftTask.join(); // 等待左半部分完成
            return leftResult + rightResult;
        }
    }

    public static void main(String[] args) {
        long[] array = new long[10_000];
        for (int i = 0; i < array.length; i++) array[i] = i + 1;

        ForkJoinPool pool = new ForkJoinPool();
        long total = pool.invoke(new SumArrayTask(array, 0, array.length));
        System.out.println("Total sum: " + total);
    }
}