将数据加载到 SQL Server 时出现 C# 多线程问题

我有一个大约 7030 个项目的列表。我将列表中的项目保存到 SQL 服务器中的表中。我想，我可以使用多线程来加快该过程，它确实出现了一个问题。

上传到数据库的项目数没有变化，但是当我在运行代码后查询表中的记录数时，它总是不同的，比如一次它将上传 6925，下一次上传 6831 等。我不明白为什么会发生这种情况。

在我获取数据的课堂上

 void DatabaseUploadMultiThreading()
    {
        DateTime dtUpload = Program.UploadDate();
        int numThread = 8;          
        int splitNum = _holdingList.Count / numThread;
        int leftOver = _holdingList.Count - (splitNum * (numThread - 1));
        DatabaseWriter[] dbArray = new DatabaseWriter[numThread];
        List<Holding>[] holdingArray = new List<Holding>[numThread];
        Task[] taskDB = new Task[numThread];
        for (int i = 0; i < holdingArray.Length; i++)
        {
            dbArray[i] = new DatabaseWriter(i + 1, dtUpload);
            if (i == (numThread - 1))
                holdingArray[i] = _holdingList.GetRange(i * splitNum, leftOver);
            else
                holdingArray[i] = _holdingList.GetRange(i * splitNum, splitNum);
        }
        for (int i = 0; i < taskDB.Length; i++)
            taskDB[i] = Task.Factory.StartNew(dbArray[i].UploadHoldings, holdingArray[i]);
        try
        {
            Task.WaitAll(taskDB);                   // wait for all the threads to complete
        }
        catch (AggregateException ex)
        {
            ExceptionDispatchInfo.Capture(ex.InnerException).Throw();
        }
    }

数据库编写器类狙击手

 class DatabaseWriter : IDisposable
{
    #region variable declaration
    private SqlConnection _connection;
    private SqlCommand _command;
    private static readonly string _connectionString = "myConnectionString";
    public void UploadHoldings(object objHoldingList)
    {
        List<Holding> holdingList = (List<Holding>)objHoldingList;
        using (_connection = new SqlConnection(_connectionString))
        {
            _connection.Open();
            DataReImported(_dtUpload);
            for (int i = 0; i < holdingList.Count; i++)
            {
                string cmdText = "INSERT INTO HOLDINGS([FUND_CD], [SEDOLCHK], [NOMINAL], [CURR], [PRICE], [DATEU]) " +
                                    "VALUES(@fundcode, @sedol, @nominal, @curr, @price, @dtUpload)";
                _command = new SqlCommand(cmdText, _connection);
                _command.Parameters.Add("@fundCode", SqlDbType.VarChar).Value = holdingList[i].FundCode;
                _command.Parameters.Add("@sedol", SqlDbType.VarChar).Value = holdingList[i].IdSedol;
                _command.Parameters.Add("@nominal", SqlDbType.Decimal).Value = holdingList[i].Nominal;
                _command.Parameters.Add("@curr", SqlDbType.VarChar).Value = holdingList[i].Currency;
                _command.Parameters.Add("@price", SqlDbType.Decimal).Value = holdingList[i].Price;
                _command.Parameters.Add("@dtUpload", SqlDbType.Date).Value = _dtUpload;
                _command.ExecuteNonQuery();
                Console.WriteLine("Thread Number:" + _threadNum + " Security Number uploaded: " + i + " of " + holdingList.Count);
            }
            _connection.Close();
        }
    }

}