使用XmlReader时BackgroundWorker DoWork委托失败

Question

I'm trying to read an XML stream using BackgroundWorker :

    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
            NetworkStream serverStream = clientSocket.GetStream();
            XmlReader r = XmlReader.Create(serverStream);

            while (r.Read())
            {
  output something using backgroundWorker1.ReportProgress object
            }
    }

I call this using backgroundWorker1.RunWorkerAsync(null) in a button click event.

The program compiles and runs fine but the process stalls at XmlReader.Create . No errors, but it says that it can not evaluate expression because a native frame is on top of the call stack. So, it's probably waiting for the process to finish.

The problem is that if I do this directly from the mouse click without using the backgroundWorker object, the program runs just fine.

Any ideas? Thanks.

Answer 1

The documentation states that XmlReader.Create reads the first few bytes to determine the encoding.
I think the problem is, that your stream doesn't return any data. This might be the case because another thread already read all the data.

Answer 2

It sounds like the XML reader creation is getting blocked on reading the stream.

• There might be a deadlock situation whereby the server stream will not send bytes until the background worker thread has performed some task (seems unlikely however)

• As @Daniel Hilgarth suggests, perhaps another thread has fully read the stream previously?

There could also be some synchronisation issues here. Try adding a lock statement around the code, eg:-

private readonly object streamLocker = new object();

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    lock(streamLocker)
    {
        NetworkStream serverStream = clientSocket.GetStream();
        XmlReader r = XmlReader.Create(serverStream);

        while (r.Read())
        {
          //  output something using backgroundWorker1.ReportProgress object
        }
    }
}