java fork任務爲多個小任務以提升任務性能

在執行一個大任務時，可以將其fork爲多個小任務，最後join得到結果。

fork任務主要是要設置一個閥值 THRESHOLD，不宜過小，也不宜過大，否則起不到提升性能的作用。

package com.learn.corejava.threading;

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

public class ForkJoinMain {
    public static void main(String[] args) {
        final int SIZE = 10000000;
        double[] numbers = new double[SIZE];
        for (int i = 0; i < SIZE; i++) {
            numbers[i] = Math.random();
        }

        Countr countr = new Countr(numbers, 0, numbers.length, x -> x > 0.5);
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        forkJoinPool.invoke(countr);
        System.out.println(countr.join());
    }
}

class Countr extends RecursiveTask<Integer> {
    public static final int THRESHOLD = 1000;
    private double[] values;
    private int from;
    private int to;
    private DoublePredicate filter;

    public Countr(double[] values, int from, int to, DoublePredicate filter) {
        this.values = values;
        this.from = from;
        this.to = to;
        this.filter = filter;
    }

    @Override
    protected Integer compute() {
        if (to - from < THRESHOLD) {
            int count = 0;
            for (int i = from; i < to; i++) {
                if (filter.test(values[i])) {
                    count++;
                }
            }
            return count;
        } else {
            int mid = (from + to) / 2;
            Countr first = new Countr(values, from, mid, filter);
            Countr second = new Countr(values, mid, to, filter);
            invokeAll(first, second);   // 其它小的任務也提交到池
            return first.join() + second.join();
        }
    }
}

 

原文地址： https://www.zhblog.net/go/java/tutorial/java8-fork-join?t=592