JUC forkjoinpool branch merge framework - work theft

package org.meng.juc;

import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;
import java.util.stream.LongStream;
 
import org.junit.Test;
 
public class TestForkJoinPool {
	
	public static void main(String[] args) {
		Instant start = Instant.now();
		
		ForkJoinPool pool = new ForkJoinPool();
		
		ForkJoinTask<Long> task = new ForkJoinSumCalculate(0L, 50000000000L);
		
		Long sum = pool.invoke(task);
		
		System.out.println(sum);
		
		Instant end = Instant.now();
		
		System.out.println(" Time consuming ：" + Duration.between(start, end).toMillis());//166-1996-10590
	}
	
	@Test
	public void test1(){
		Instant start = Instant.now();
		
		long sum = 0L;
		
		for (long i = 0L; i <= 50000000000L; i++) {
			sum += i;
		}
		
		System.out.println(sum);
		
		Instant end = Instant.now();
		
		System.out.println(" Time consuming ：" + Duration.between(start, end).toMillis());//35-3142-15704
	}
	
	//java8  New characteristics 
	@Test
	public void test2(){
		Instant start = Instant.now();
		
		Long sum = LongStream.rangeClosed(0L, 50000000000L)
							 .parallel()
							 .reduce(0L, Long::sum);
		
		System.out.println(sum);
		
		Instant end = Instant.now();
		
		System.out.println(" Time consuming ：" + Duration.between(start, end).toMillis());//1536-8118
	}
 
}
 
class ForkJoinSumCalculate extends RecursiveTask<Long>{
 
	/**
	 * 
	 */
	private static final long serialVersionUID = -259195479995561737L;
	
	private long start;
	private long end;
	
	private static final long THURSHOLD = 10000L;  // critical value 
	
	public ForkJoinSumCalculate(long start, long end) {
		this.start = start;
		this.end = end;
	}
 
	@Override
	protected Long compute() {
		long length = end - start;
		
		if(length <= THURSHOLD){
			long sum = 0L;
			
			for (long i = start; i <= end; i++) {
				sum += i;
			}
			
			return sum;
		}else{
			long middle = (start + end) / 2;
			
			ForkJoinSumCalculate left = new ForkJoinSumCalculate(start, middle); 
			left.fork(); // To break up , At the same time, press into the thread queue 
			
			ForkJoinSumCalculate right = new ForkJoinSumCalculate(middle+1, end);
			right.fork(); //
			
			return left.join() + right.join();
		}
	}
	
}