如何从内存流中读取文本文件而不丢失字节

我正在编写一些代码来学习新的c#异步设计模式。所以我想写一个小的windows窗体程序，它可以计算文本文件的行和字，并显示阅读进度。

为了避免磁盘交换，我将文件读取到MemoryStream中，然后构建一个StreamReader来逐行读取文本并计数。

问题是我无法正确更新进度条。我读了一个文件，但总是缺少字节，所以进度条没有完全填满。

需要一只手或一个想法来实现这一点。感谢

public async Task Processfile(string fname)
{
  MemoryStream m;
  fname.File2MemoryStream(out m); // custom extension which read file into
                                  // MemoryStream
  int flen = (int)m.Length;       // store File length
  string line = string.Empty;     // used later to read lines from streamreader

  int linelen = 0;                // store current line bytes
  int readed = 0;                 // total bytes read

    progressBar1.Minimum = 0;     // progressbar bound to winforms ui
    progressBar1.Maximum = flen;
    using (StreamReader sr = new StreamReader(m)) // build streamreader from ms
    {
       while ( ! sr.EndOfStream ) // tried ( line = await sr.ReadLineAsync() ) != null
       {
          line = await sr.ReadLineAsync();
            await Task.Run(() =>
            {
              linelen = Encoding.UTF8.GetBytes(line).Length;  // get & update
              readed += linelen;                              // bytes read
                                                         // custom function
              Report(new Tuple<int, int>(flen, readed)); // implements Iprogress
                                                         // to feed progress bar
             });                     
         }
     }
        m.Close();    //  releases MemoryStream
        m = null;            
 }