winfromFTP大文件上传问题。急！

winfrom使用FTP进行大文件上传时，没有加入线程的时候，上传上去，服务器直接把数据写入到文件，是可以断点续传的，但是用户界面假死；加入线程或者backgroundwork之后，用户界面不会假死，但是上传上去的文件没有及时的写入，关闭程序之后，服务器上面的文件什么都没有写入，还把之前的删掉了。请问有没有方法可以解决这个问题？急！！

不知道你是怎么加入线程的。以及你是怎么上传的。该同步的有没有同步。

我现在用的是backgroundwork.界面上有个上传按钮，点击按钮后开始这个方法。
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
if (!client.Connected)
client.Connect();

        string[] dirs = client.Dir(remotingFolder + "");
        client.ChDir(remotingFolder);  //改变目录
        if (this.textBox1.Text != "")
        {
            bool flag = true;
            foreach (string dir in dirs)
            {
                string[] infos = dir.Split(' ');
                string info = infos[infos.Length - 1].Replace("\r", "");
                FileInfo fileInfo = new FileInfo(this.textBox1.Text);
                string localfile = fileInfo.Name;

                if (info == localfile)//断点续传
                {
                    flag = false;
                    long remotingSize = client.GetFileSize(info);
                    long localSize = fileInfo.Length;

                    int i = (int)(remotingSize * 100 / localSize);
                    this.backgroundWorker1.ReportProgress(i,0);

                    if (remotingSize != localSize)
                    {
                        client.PutBrokenFile(info, remotingFolder, this.textBox1.Text, remotingSize);
                    }
                }
            }
            if (flag)
                client.Put(this.textBox1.Text);
        }
    }

上传代码如下：
///
/// 上传一批文件
///
/// 本地目录(不得以\结束)
/// 文件名匹配字符(可以包含*和?)
public void Put(string strFolder, string strFileNameMask)
{
string[] strFiles = Directory.GetFiles(strFolder, strFileNameMask);
foreach (string strFile in strFiles)
{
//strFile是完整的文件名(包含路径)
Put(strFile);
}
}

    /// <summary>
    /// 上传一个文件
    /// </summary>
    /// <param name="strFileName">本地文件名</param>
    public void Put(string strFileName)
    {
        if (!bConnected)
        {
            Connect();
        }
        Socket socketData = CreateDataSocket();
        SendCommand("STOU " + Path.GetFileName(strFileName));
        long size = new FileInfo(strFileName).Length;
        if (!(iReplyCode == 125 || iReplyCode == 150))
        {
            throw new IOException(strReply.Substring(4));
        }
        FileStream input = new
        FileStream(strFileName, FileMode.Open);

        int iBytes = 0;
        long current = 0;
        while ((iBytes = input.Read(buffer, 0, buffer.Length)) > 0)
        {
            int i = socketData.Send(buffer, iBytes, 0);
            current += i;
            keepProgress(current, size);
        }
        input.Close();
        if (socketData.Connected)
        {
            socketData.Close();
        }
        if (!(iReplyCode == 226 || iReplyCode == 250))
        {
            ReadReply();
            if (!(iReplyCode == 226 || iReplyCode == 250))
            {
                throw new IOException(strReply.Substring(4));
            }
        }
    }

    /// <summary>
    /// 断点上传
    /// </summary>
    /// <param name="strRemoteFileName">要上传的文件名</param>
    /// <param name="strFolder">本地目录(不得以\结束)</param>
    /// <param name="strLocalFileName">保存在本地时的文件名</param>
    public void PutBrokenFile(string strRemoteFileName, string strFolder, string strLocalFileName, long size)
    {
        if (!bConnected)
        {
            Connect();
        }
        SetTransferType(TransferType.Binary);

        Socket socketData = CreateDataSocket();
        SendCommand("APPE " + Path.GetFileName(strLocalFileName));
        long localsize = new FileInfo(strLocalFileName).Length;
        if (!(iReplyCode == 125 || iReplyCode == 150))
        {
            throw new IOException(strReply.Substring(4));
        }
        FileStream input = new
        FileStream(strLocalFileName, FileMode.Open);
        int iBytes = 0;
        input.Seek(size, SeekOrigin.Current);
        long current = size;
        while ((iBytes = input.Read(buffer, 0, buffer.Length)) > 0)
        {
            current += iBytes;
            socketData.Send(buffer, iBytes, 0);
            keepProgress(current, localsize);
        }
        input.Close();
        if (socketData.Connected)
        {
            socketData.Close();
        }
        if (!(iReplyCode == 226 || iReplyCode == 250))
        {
            ReadReply();
            if (!(iReplyCode == 226 || iReplyCode == 250))
            {
                throw new IOException(strReply.Substring(4));
            }
        }
    }

已经解决了，socket非正常关闭。数据就会丢失，正常关闭，数据就能保存。那么问题又来了，如果传输过程中网络中断。socket非正常关闭。那么之前的数据怎么保存？