C#轮询模式不懂

[Tony_Xian]

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ParallelForeach1
{
    delegate long MyDel(int first,int second);
    class Program
    {
        static long Sum(int x, int y)
        {
            Console.WriteLine("         Inside Sum");
            Thread.Sleep(100);
            return x + y;
        }
        static void Main()
        {
            MyDel del = new MyDel(Sum);
            IAsyncResult iar = del.BeginInvoke(3, 5, null, null);
            Console.WriteLine("After BeginInvoke");
            while (!iar.IsCompleted)
            {
                Console.WriteLine("Not Done");
                Console.WriteLine("Hello World");
            }
            Console.WriteLine("Done");
            long result = del.EndInvoke(iar);
            Console.WriteLine("Result: {0}", result);
            Console.Read();
        }
    }
}

运行会出现两个版本
第一种

第二中

大神来解答下原因，谢谢！

[ilikeff8]

加个延迟

            while (!iar.IsCompleted)
            {
                Thread.Sleep(10);

                Console.WriteLine("Not Done");
                Console.WriteLine("Hello World");
            }