Java中Fork/Join框架

最新推荐文章于 2025-06-27 16:02:15 发布

原创最新推荐文章于 2025-06-27 16:02:15 发布 · 238 阅读

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本文介绍了一种使用Java并发框架Fork/Join Pool实现的分治法计算大规模数值求和的方法。通过将大任务分解为小任务并行计算，最后合并结果，实现了高效的求和计算。

分割任务，然后把子任务的结果再合并起来。分治的思想。

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

public class CountTask extends RecursiveTask<Integer>{

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	private static final int THRESHOLD = 1000;
	
	private int start;
	
	private int end;
	
	public CountTask(int start, int end) {
		this.start = start;
		this.end = end;
	}


	@Override
	protected Integer compute() {
		int sum = 0;
		boolean canCompute = (end - start) <= THRESHOLD;
		if (canCompute) {
			for (int i = start; i <= end; i++)
				sum += i;
		} else {
			//如果任务大于阀值，就分裂成两个子任务计算
			int mid = (start + end) / 2;
			CountTask leftTask = new CountTask(start, mid);
			CountTask rightTask = new CountTask(mid+1, end);
			
			//执行子任务
			leftTask.fork();
			rightTask.fork();
			
			//等待子任务执行完，并得到结果
			int leftResult = (int)leftTask.join();
			int rightResult = (int)rightTask.join();
			
			sum = leftResult + rightResult;
		}
		
		return sum;
	}
	

	public static void main(String[] args) {
		ForkJoinPool forkJoinPool = new ForkJoinPool();
		
        //生成一个计算资格，负责计算1+2+3+4  
        CountTask task = new CountTask(1, 100000000); 
        Future<Integer> result = forkJoinPool.submit(task);
        try {
        	long start = System.currentTimeMillis();
        	System.out.println(result.get());
        	System.out.println("所用时长： " + (System.currentTimeMillis() - start) + "毫秒");
		} catch (Exception e) {
		}
	}
}