一千万个数，高效求和,forkjoin

  

   

    

     

    
    

     

      private 
      class SumTask extends RecursiveTask<Long> {
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
    
      private 
      static 
      final 
      int THRESHOLD = 
      1250000;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
    
      private 
      long arr[];
     
    
   

    

     

    
    

     
    
      private 
      int start;
     
    
   

    

     

    
    

     
    
      private 
      int end;
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
    
      public SumTask(long[] arr, int start, int end) {
     
    
   

    

     

    
    

     
        
      this.arr = arr;
     
    
   

    

     

    
    

     
        
      this.start = start;
     
    
   

    

     

    
    

     
        
      this.end = end;
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
    
      /**
     
    
   

    

     

    
    

     

       * 小计
     
    
   

    

     

    
    

     

       */
     
    
   

    

     

    
    

     
    
      private long subtotal() {
     
    
   

    

     

    
    

     
        
      long sum = 
      0;
     
    
   

    

     

    
    

     
        
      for (
      int i = start; i < end; i++) {
     
    
   

    

     

    
    

     

                  sum += arr[i];
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
        
      return sum;
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
    
      @Override
     
    
   

    

     

    
    

     
    
      protected Long compute() {
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
        
      if ((end - start) <= THRESHOLD) {
     
    
   

    

     

    
    

     
            
      return subtotal();
     
    
   

    

     

    
    

     

              }
      else {
     
    
   

    

     

    
    

     
            
      int middle = (start + end) / 
      2;
     
    
   

    

     

    
    

     

                  SumTask left = 
      new SumTask(arr, start, middle);
     
    
   

    

     

    
    

     

                  SumTask right = 
      new SumTask(arr, middle, end);
     
    
   

    

     

    
    

     

                  left.fork();
     
    
   

    

     

    
    

     

                  right.fork();
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
            
      return left.join() + right.join();
     
    
   

    

     

    
    

     

              }
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     

      }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      public static void main(String[] args) throws ExecutionException, InterruptedException{
     
    
   

    

     

    
    

     
    
      int num = Runtime.getRuntime().availableProcessors();
     
    
   

    

     

    
    

     
    
      long time = System.currentTimeMillis();
     
    
   

    

     

    
    

     
    
      long[] arr = 
      new 
      long[
      10000000];
     
    
   

    

     

    
    

     
    
      for (
      int i =
      0 ; i < 
      10000000; i++) {
     
    
   

    

     

    
    

     

              arr[i] =i+
      1;
     
    
   

    

     

    
    

     

          }
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

          ForkJoinPool pool = 
      new ForkJoinPool();
     
    
   

    

     

    
    

     

          ForkJoinTask<Long> result = pool.submit(
      new ForkJoinTest().new SumTask(arr, 
      0, arr.length));
     
    
   

    

     

    
    

     

          System.out.println(
      "最终计算结果: " + result.invoke()+
      "耗时："+(System.currentTimeMillis() - time)+
      "，毫秒");
     
    
   

    

     

    
    

     

          pool.shutdown();
     
    
   

    

     

    
    

     

      }