package com.gc.test;

/**
 * Created by jiji on 2018/12/30.
 */



import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveTask;

import org.junit.Test;

//
/**
 * 
 *  計算0L-------100000000000L 進行累加求和
 *
 *
 *
 */
public class CalultTestSum {
    public static  void  main(String arg[]){
        Instant start = Instant.now();
        ForkJoinPool pool = new ForkJoinPool();
        ForkJoinSumCalculate forkJoinSumCalculate = new ForkJoinSumCalculate(0L, 100000000000L);
        Long invoke = pool.invoke(forkJoinSumCalculate);
        System.out.print(invoke);
        Instant end = Instant.now();
        System.out.print("花費時間:"+ Duration.between(start,end).toMillis());
        /**
         *  
         * 
         * 使用 fork  join  
         * 
         * 
         * 計算範圍                               結果                                                                          時間
         * 1000000000L    500000000500000000       花費時間:436
         * 10000000000L   -5340232216128654848     花費時間:4379
         * 100000000000L  932356074711512064       花費時間:43193 
         */
    }

    
    
    
    /**  普通for迴圈等待2分鐘未計算出結果
     * 
     * 計算範圍                               結果                                                             時間
     * 1000000000L  500000000500000000    花費時間:406
     * 10000000000L -5340232216128654848  花費時間:5860
     * 100000000000L 932356074711512064   花費時間:39409
     *
     */
         @Test
        public void testFor(){
        Instant start = Instant.now();
        long sum= 0L;
            for (long i=0L;i<=100000000000L;i++){ 
                sum+=i;
            }
            Instant end = Instant.now();
            System.err.println(sum);
            System.out.print("花費時間:"+ Duration.between(start,end).toMillis());
        }



}


class ForkJoinSumCalculate extends RecursiveTask<Long>{

	private static final long serialVersionUID = 1L;
	private long start;
	private long end ;
private  static final long THURSHOLD = 10000000L;
    @Override
    protected Long compute() {
        long length = end -start;
        if(length<=THURSHOLD){//小於臨界值
            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();
            ForkJoinSumCalculate right = new ForkJoinSumCalculate(middle+1,end);
            right.fork();
            return  left.join()+right.join();
        }

    }
    public ForkJoinSumCalculate(long start,long end){
        this.start =start;
        this.end=end;
    }
}