C# hang and stuck after Application.Run() at for loop

Question

Im building a program that surf to several websites and do something.

After surfing to like 5 urls successfully, the program hangs after the Application.Run() line. The program doesn't even enter the Handler function and just stuck. the CPU usage is 0 at this point.

I tried closing the threads in any possible way. What i'm doing wrong?

I'm doing it like that:

[STAThread]
private static void Main(string[] args) 
{
    for (int i = 0; i < urls.Count; i++) 
    {
        var th = new Thread(() = > 
        {
            var weBrowser = new WebBrowser();
            weBrowser.AllowNavigation = true;
            weBrowser.DocumentCompleted += Handler;
            weBrowser.Navigate(urls[i]);
            Application.Run();
        });
        th.SetApartmentState(ApartmentState.STA);
        th.Start();
        th.Join();
    }
}

And my Handle function is:

private static void Handler(object sender, WebBrowserDocumentCompletedEventArgs e) 
{
    WebBrowser weBrowser = sender as WebBrowser;
    var htmlDocument = weBrowser.Document;

    /*do something*/

    Application.Exit();
    Application.ExitThread();

    weBrowser.Dispose();
    weBrowser.Stop();

    Thread.CurrentThread.Abort();
}

My problem is very similar to this one: Application.Run() leads to application hanging

There is no answer in this question either.

Thanks!

Answer 1

I think you are doing several mistakes:

• you are joining inside the for look
• you are calling Application.Exit() in each handler call

You should move the joining outside the for loop and do not call Application.Exit.

The following sample seems to work well:

static class Program
{
  [STAThread]
  static void Main()
  {
     var urls = new List<string>() { 
        "http://stackoverflow.com",
        "http://stackoverflow.com",
        "http://stackoverflow.com",
        "http://stackoverflow.com",
        "http://stackoverflow.com",
        "http://stackoverflow.com",
        "http://stackoverflow.com",
        "http://stackoverflow.com"};

     var threads = new Thread[urls.Count];

     for (int i = 0; i < urls.Count; i++)
     {
        threads[i] = new Thread((url) =>
        {
           var weBrowser = new WebBrowser();
           weBrowser.AllowNavigation = true;
           weBrowser.DocumentCompleted += Handler;
           weBrowser.Navigate(url as string);
           Application.Run();
        });
        threads[i].SetApartmentState(ApartmentState.STA);
        threads[i].Start(urls[i]);
     }

     foreach (var t in threads)
        t.Join();

     Application.EnableVisualStyles();
     Application.SetCompatibleTextRenderingDefault(false);
     Application.Run(new Form1());
  }

  private static void Handler(object sender, WebBrowserDocumentCompletedEventArgs e)
  {
     WebBrowser weBrowser = sender as WebBrowser;

     var htmlDocument = weBrowser.Document;

     /*do something*/

     Application.ExitThread();

     weBrowser.Dispose();
     weBrowser.Stop();
  }
}

Answer 2

Usage of urls[i] in your original snippets is wrong. Search C# documentation for closures. You will need to make a local copy before using it.

Furthermore, you should swap weBrowser.Dispose() and weBrowser.Stop(). You can't stop the disposed browser anymore (if Stop is necessary at all).

Finally, don't abort the thread - it will finish itself.

Answer 3

You may be running into the maximum number of concurrent connections for the WebBrowser. By explicitly setting this to a higher number, you can have additional streams reading through the browser at once.

// Example Usage:
ServicePointManager.DefaultConnectionLimit = 10;

Keep in mind that there is a performance hit by increasing this number above the default (I think it is 4) as you will have much more network traffic that needs processed.

See the MSDN article for ConnectionLimit for more information.

Answer 4

I don't understand what would you like to achieve with Application.Run inside for loop.

Why are you using WebBrowser component? If you are just parsing web page it is better to use

string urlAddress = "http://stackoverflow.com"; 
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(urlAddress);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
if (response.StatusCode == HttpStatusCode.OK)
{
    StreamReader reader= null;
    if (response.CharacterSet == null)
        reader = new StreamReader(response.GetResponseStream());
    else
        reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding(response.CharacterSet));
    string data = reader.ReadToEnd();
    response.Close();
    reader.Close();
}

or

using (WebClient client = new WebClient())
{
    string html = client.DownloadString("http://stackoverflow.com");
}

For parsing html look at Html Agility Pack or something similar.

If this is console application you don't need to call Application.Run(), otherwise you should consider showing splash screen with progress to give user some feedback.