Java ForkJoinPool线程池的使用之并行计算数组求和实例

package com.zhangxueliang.juc;

import java.io.IOException;
import java.util.Arrays;
import java.util.Random;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
import java.util.concurrent.RecursiveTask;

public class ForkJoinPoolDemo {
	static int[] nums = new int[1000000];
	static final int MAX_NUM = 50000;
	static Random r = new Random();
	
	static {
		for(int i=0; i<nums.length; i++) {
			nums[i] = r.nextInt(100);
		}
		
		System.out.println("---" + Arrays.stream(nums).sum()); //stream api
	}
	

	static class AddTask extends RecursiveAction {

		int start, end;

		AddTask(int s, int e) {
			start = s;
			end = e;
		}

		@Override
		protected void compute() {

			if(end-start <= MAX_NUM) {
				long sum = 0L;
				for(int i=start; i<end; i++) sum += nums[i];
				System.out.println("from:" + start + " to:" + end + " = " + sum);
			} else {

				int middle = start + (end-start)/2;

				AddTask subTask1 = new AddTask(start, middle);
				AddTask subTask2 = new AddTask(middle, end);
				subTask1.fork();
				subTask2.fork();
			}


		}

	}

	
	static class AddTaskRet extends RecursiveTask<Long> {
		
		private static final long serialVersionUID = 1L;
		int start, end;
		
		AddTaskRet(int s, int e) {
			start = s;
			end = e;
		}

		@Override
		protected Long compute() {
			
			if(end-start <= MAX_NUM) {
				long sum = 0L;
				for(int i=start; i<end; i++) sum += nums[i];
				return sum;
			} 
			
			int middle = start + (end-start)/2;
			
			AddTaskRet subTask1 = new AddTaskRet(start, middle);
			AddTaskRet subTask2 = new AddTaskRet(middle, end);
			subTask1.fork();
			subTask2.fork();
			
			return subTask1.join() + subTask2.join();
		}
		
	}
	
	public static void main(String[] args) throws IOException {
		/*ForkJoinPool fjp = new ForkJoinPool();
		AddTask task = new AddTask(0, nums.length);
		fjp.execute(task);*/

		ForkJoinPoolDemo temp = new ForkJoinPoolDemo();

		ForkJoinPool fjp = new ForkJoinPool();
		AddTaskRet task = new AddTaskRet(0, nums.length);
		fjp.execute(task);
		long result = task.join();
		System.out.println(result);
		
		//System.in.read();
		
	}
}

static int[] nums = new int[1000000];  // 创建包含100万个元素的数组
static final int MAX_NUM = 50000;     // 任务分割的阈值
static Random r = new Random();        // 随机数生成器

// 静态初始化块：填充数组并计算总和
static {
    for(int i=0; i<nums.length; i++) {
        nums[i] = r.nextInt(100);  // 每个元素赋值为0-99的随机数
    }
    System.out.println("---" + Arrays.stream(nums).sum()); // 使用stream API计算总和作为验证基准
}

static class AddTask extends RecursiveAction {
    int start, end;
    
    AddTask(int s, int e) {
        start = s;
        end = e;
    }

    @Override
    protected void compute() {
        if(end-start <= MAX_NUM) {  // 如果任务足够小，直接计算
            long sum = 0L;
            for(int i=start; i<end; i++) sum += nums[i];
            System.out.println("from:" + start + " to:" + end + " = " + sum);
        } else {  // 否则分割任务
            int middle = start + (end-start)/2;
            AddTask subTask1 = new AddTask(start, middle);
            AddTask subTask2 = new AddTask(middle, end);
            subTask1.fork();  // 异步执行子任务
            subTask2.fork();
        }
    }
}

static class AddTaskRet extends RecursiveTask<Long> {
    int start, end;
    
    AddTaskRet(int s, int e) {
        start = s;
        end = e;
    }

    @Override
    protected Long compute() {
        if(end-start <= MAX_NUM) {  // 如果任务足够小，直接计算并返回结果
            long sum = 0L;
            for(int i=start; i<end; i++) sum += nums[i];
            return sum;
        } 
        
        // 分割任务
        int middle = start + (end-start)/2;
        AddTaskRet subTask1 = new AddTaskRet(start, middle);
        AddTaskRet subTask2 = new AddTaskRet(middle, end);
        subTask1.fork();  // 异步执行子任务
        subTask2.fork();
        
        return subTask1.join() + subTask2.join();  // 合并子任务结果
    }
}

public static void main(String[] args) throws IOException {
    // 创建ForkJoinPool实例
    ForkJoinPool fjp = new ForkJoinPool();
    
    // 创建有返回值的任务
    AddTaskRet task = new AddTaskRet(0, nums.length);
    
    // 执行任务
    fjp.execute(task);
    
    // 获取并打印结果
    long result = task.join();
    System.out.println(result);
}