这多线程程序问题在哪

Question

写了个测试程序，主要是多线程情况下交换数组的两个成员，我这程序最后的结果出了问题，数组的元素和原来的不一样．请问哪出问题了？
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;namespace ConsoleApplication2
{
    class Program
    {        static int k = 0;
        static int cou = 10000;
        static int[] arr = new int[10] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        static object obj = new object();        static void Main(string[] args)
        {
            Thread thread1 = new Thread(fun1);
            Thread thread2 = new Thread(fun2);
            Thread thread3 = new Thread(fun3);
            Thread thread4 = new Thread(fun4);
            Thread thread5 = new Thread(fun5);            thread1.Start();
            thread2.Start();
            thread3.Start();
            thread4.Start();
            thread5.Start();            for (int i = 0; i < 10; i++)
            {
                Console.WriteLine(arr[i].ToString());
            }            Console.ReadLine();
        }
        static void test()
        {
            
            
                for (int i = 0; i < cou; i++)
                {
                    Random ran = new Random();
                    int m = ran.Next(10);                    int n = ran.Next(10);                    while (m == n)
                    {
                        n = ran.Next(10);                    }
                    lock (obj)
                    {
                        int temp = arr[m];
                        arr[m] = arr[n];
                        arr[n] = temp;
                    }
                }
            
        }        static void fun1()
        {
            test();
        
        }        static void fun2()
        {
            test();
        }
        static void fun3()
        {
            test();
        }
        static void fun4()
        {
            test();
        }
        static void fun5()
        {
            test();
        }    }
}

Answer 1

为了一致性，就算是读数据（ Console.WriteLine(arr[i].ToString()) 你也要 lock。