Thread stop , XMLexception error

Question

So i start a thread timer and it works but the method in the thread timer reads XML from a yahoo API, sometimes the response to the server is bad, so an XMLexception is thrown. But it seems this stops the thread or something because the thread starts good but when as fast as an exception is thrown all the threads stop. So what´s wrong , could i just start a thread every time another one is stopped? Because all the threads stops and then no threads is started agiend.

try
        {
            System.Threading.Timer timer;
            timer = new System.Threading.Timer(new TimerCallback(TimerHelper), null, 0, 3000);
        }
        catch (Exception)
        {

        }

The TimerHelper(object obj) has try catch for exceptions.

public void TimerHelper(object obj)
    {

        try
        {
            if (dataGridView.Rows.Count > 0 && !(dataGridView.Rows[0].Cells[0].Value == null)) // Updates the rows idividualy as long as first row is not empty
            {
                string[] cells;
                cells = new string[dataGridView.Columns.Count * dataGridView.Rows.Count];
                for (int i = 0; i < dataGridView.RowCount; i++)
                {
                    if (!(dataGridView.Rows[i].Cells[0].Value == null || dataGridView.Rows[i].Cells[0].Value.ToString() == "-")) // Makes sure that the row to update is not an empty row
                    {
                        String symbol;
                        symbol = Convert.ToString(dataGridView.Rows[i].Cells[0].Value);
                        String URLString2 = "http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.quotes%20where%20symbol%20in%20(%22" + symbol + "%22)%0A%09%09&diagnostics=true&env=http%3A%2F%2Fdatatables.org%2Falltables.env";
                        for (int t = 2; t < dataGridView.Columns.Count; t++)
                        {
                            dataGridView.SuspendLayout();
                            XmlTextReader reader2 = new XmlTextReader(URLString2); // Makes the reader read from the string abow ( URL )
                            string NasdaqOpenTime = "09:00:00";

                            // if the market haven't been open for the day then theres no DaysLow value
                            if (dataGridView.Columns[t].HeaderText == "DaysLow" && DateTime.Now.CompareTo(DateTime.Parse(NasdaqOpenTime)) == -1)
                            {
                                cells[t - 2] = "0";
                            }

                            // if the market haven't been open for the day then theres no DaysHigh value
                            if (dataGridView.Columns[t].HeaderText == "DaysHigh" && DateTime.Now.CompareTo(DateTime.Parse(NasdaqOpenTime)) == -1)
                            {
                                cells[t - 2] = "0";
                            }
                            else
                            {
                                reader2.ReadToFollowing(dataGridView.Columns[t].HeaderText);  // Reada until it fins the elemnt Bid , then stops on it
                                reader2.ReadStartElement(dataGridView.Columns[t].HeaderText); // Recognizes Bid as start element (Bid)
                                string temporary;
                                temporary = reader2.ReadString();
                                Trace.WriteLine(dataGridView.Columns[t].HeaderText + ": " + temporary);
                                cells[t - 2] = temporary; // Reads the text in between (Declared as a string) actualy the bid value
                                reader2.ReadEndElement();  // Checks that the current nod is an end element (/Bid) if so then continue
                                reader2.ResetState();
                            }

                        }

                    }
                }
                for (int h = 0; h < dataGridView.Rows.Count; h++)
                {
                    for (int t = 2; t < dataGridView.Columns.Count; t++)
                    {
                        dataGridView.Rows[h].Cells[t].Value = cells[t - 2];
                    }
                }
            }
        }
        catch (XmlException)
        {
        }
        catch (Exception)
        {

        }
    }

Here is a sample output the values are traced in TimerHelper(object obj).

    'FetchBySymbol.vshost.exe' (Managed (v4.0.30319)): Loaded 'C:\Users\Mattias\documents\visual studio 2012\Projects\FetchBySymbol\FetchBySymbol\bin\Debug\FetchBySymbol.exe', Symbols loaded.
    'FetchBySymbol.vshost.exe' (Managed (v4.0.30319)): Loaded 'C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Configuration\v4.0_4.0.0.0__b03f5f7f11d50a3a\System.Configuration.dll'
    Ask: 37.44
    Bid: 37.43
...
...
...
    Ask: 37.44
    Bid: 37.43
    Ask: 37.42
    Bid: 37.41
    The thread '<No Name>' (0x104c) has exited with code 0 (0x0).
    The thread '<No Name>' (0x1920) has exited with code 0 (0x0).
    A first chance exception of type 'System.Net.WebException' occurred in System.dll
    A first chance exception of type 'System.Net.WebException' occurred in System.Xml.dll
    The thread '<No Name>' (0xe3c) has exited with code 0 (0x0).
    The thread '<No Name>' (0x1af0) has exited with code 0 (0x0).
    The thread '<No Name>' (0x1b18) has exited with code 0 (0x0).
    The thread '<No Name>' (0xb90) has exited with code 0 (0x0).
    The thread '<No Name>' (0x20) has exited with code 0 (0x0).

Why does it exit?

Answer 1

Do not catch generic Exception because using (code from you post)

catch (Exception) { }

can lead to situation where every possible Exception slips thru your fingers.

Try to figure out where System.Net.WebException might occur and name your threads so you have more insight in what's going on, e.g.:

(new Thread(() => {}) { Name = "Some thread" }).Start();

outputs

The thread 'Some thread' (0x260c) has exited with code 0 (0x0).

And in case you wonder what those first chance exceptions are, peek here http://blogs.msdn.com/b/davidklinems/archive/2005/07/12/438061.aspx

As @BlackICE stated, please post the missing piece of code so your problem can be solved.

Edit:

Are you sure you are looking for right place to solve this. As stated, thread exits are not sign of problem (you do want the threads to exit when their work is done) nor first chance exceptions (exception was thrown but handled).

Could it be CGd timer issue, as in this post?

System.Threading.Timer not firing after some time

Edit:

Try something like this, m'kay? It will run forever in a non-blocking fashion. Just add some more detailed exception handling ;).

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
        Task.Factory.StartNew(() => DoTheMagic());
    }

    // Here the magic occurs
    public async Task DoTheMagic()
    {
        while (true)
        {
            string url = "http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.quotes%20where%20symbol%20in%20(%22YHOO%22)&diagnostics=true&env=http://datatables.org/alltables.env";
            string raw = await GetResponse(url);
            var parsed = await ParseXml(raw);

            // Pass results to UI
            Dispatcher.BeginInvoke(new Action(() =>
                {
                    if (parsed == null || !parsed.Any())
                        return;

                    var now = DateTime.Now;
                    foreach (var tuple in parsed)
                        textBox.Text += string.Format("{0} {1} = {2}{3}", now, tuple.Item1, tuple.Item2, Environment.NewLine);
                }));
            Thread.Sleep(3000);
        }
    }

    // Get response from service
    public async Task<string> GetResponse(string url)
    {
        string content = null;
        try
        {
            var request = WebRequest.Create(url);
            var response = await request.GetResponseAsync();
            var stream = response.GetResponseStream();

            if (stream == null)
                return null;

            using (var reader = new StreamReader(stream, Encoding.GetEncoding("utf-8")))
                content = await reader.ReadToEndAsync();
        }
        catch
        {
            System.Diagnostics.Debug.WriteLine("ZOMG!");
        }

        return content;
    }

    // Parse response with your logic
    public Task<List<Tuple<string, string>>> ParseXml(string xml)
    {
        return Task.Factory.StartNew(() =>
            {
                try
                {
                    var nodes = new string[] { "Symbol", "Ask", "Bid" };
                    var result = new List<Tuple<string, string>>();

                    using (var reader = new XmlTextReader(new StringReader(xml)))
                    {
                        reader.MoveToContent();
                        while (reader.Read())
                        {
                            if (reader.NodeType.Equals(XmlNodeType.Element))
                            {
                                if (nodes.Contains(reader.LocalName))
                                    result.Add(new Tuple<string, string>(reader.LocalName, reader.ReadElementContentAsString()));
                            }
                        }
                    }
                    return result;
                }
                catch
                {
                    System.Diagnostics.Debug.WriteLine("I haz exception!!1");
                    return null;
                }
            });
    }
}

Output

Answer 2

The thread exits are normal, look at the exit codes :

The thread '<No Name>' (0xe3c) has exited with code 0 (0x0).

This is going to happen every time the timer fires, and it looks like from your output that the timer is firing periodically (you're getting multiple threads exiting, apparently periodically). You might want to put something in your exception handlers instead of just eating them, then you can set a breakpoint and see why subsequent calls to the timer handler are failing to run your code.