DataTable多线程写不安全

如下代码:

class test
{
    private DataTable ftable;

    public test()
    {
        ftable = new DataTable();

        DataColumn col = new DataColumn("COL_1", typeof(int));
        ftable.Columns.Add(col);
        col = new DataColumn("COL_2", typeof(int));
        ftable.Columns.Add(col);

        for (int i = 1; i < 100; i++)
        {
            DataRow row = ftable.NewRow();
            row["COL_1"] = i;
            row["COL_2"] = i * 2;
            ftable.Rows.Add(row);
        }
    }

    public void AddColTest()
    {
        DataColumn col = new DataColumn("COL_Test", typeof(int));
        ftable.Columns.Add(col);

        Parallel.For(0, ftable.Rows.Count, (index) =>
            {
                Thread.Sleep(500);

                DataRow row = ftable.Rows[index];
                row["COL_Test"] = Convert.ToInt32(row["COL_1"]) + Convert.ToInt32(row["COL_2"]);
            });
    }

    public void ShowTable()
    {
        for(int index = 0; index < ftable.Rows.Count; ++index)
        {
            DataRow row = ftable.Rows[index];
            Console.WriteLine(String.Format("{0} \t\t {1} \t\t {2}", row["COL_1"], row["COL_2"], row["COL_Test"]));
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        test t = new test();
        t.AddColTest();

        t.ShowTable();
        Console.ReadKey();
    }
}

我本来以为虽然DataTable不是线程安全的… 但是我并没有对任何一个数据做增删…我只是修改了现有单元格的值…理应不会出现任何问题…DataTable应该是已经分配好的内存…

结果现实还是给了我一记响亮的耳光…程序运行失败了… 运行的时候,在这一句row[“COL_Test”] = Convert.ToInt32(row[“COL_1”]) + Convert.ToInt32(row[“COL_2”]);随机抛出一个异常,说索引错误…

具体原因我也不知道为什么会是索引错误… 但是如果把这段关键代码改改,就可以运行很正常了…

Parallel.For(0, ftable.Rows.Count, (index) =>
    {
        Thread.Sleep(500);

		lock(ftable)
		{
		    DataRow row = ftable.Rows[index];
			row["COL_Test"] = Convert.ToInt32(row["COL_1"]) + Convert.ToInt32(row["COL_2"]);
		}
    });