Cannot Contact Server, Application Does not open

Question

I'm currently running a sandbox Web Server on my local machine & using my Application, I am grabbing the contents of a text file (currently single line) and displaying it back onto the main form.

When the Web Server is alive, the application will run normally, which is as expected. When the web server is down, the application refuses to open.. Let alone spawn the process.

I thought i was approaching the application correctly. I've used a try catch block in the event that the web server is down. The code is to follow:

public String UpdaterURL = "http://192.168.0.12/DestinyScreening/Updater/Revision.txt";

public int UpdaterVersion(int CurrentVersion)
        {
            try
            {
                var RemoteRevision = (new WebClient()).DownloadString(UpdaterURL);
                return Int32.Parse(RemoteRevision);
            }
            catch
            {
                var Date = DateTime.Now.ToString("yyyy-MM-dd");
                var Time = DateTime.Now.ToString("HH:mm");
                StreamWriter file = new StreamWriter("ErrorReports\\" + Date + ".txt",true);
                file.WriteLine(Time + " - Could Not Contact Update Server");
                file.Close();
                return CurrentVersion;
            }
        }

Now, when I say the application does not run. It essentially does run in Debug mode via Visual Studio.. I have swapped from Debug to Release and built the solution, which running the executable does not run.

I've trawled through the code provided, everything works as expected. It's just a complete baffle to me, as to why the application does not spawn a process when double clicking the exe?

So, the overall question. With everything which looks like is running as normal through debug mode on Visual Studio.. What could be going on behind the scenes which will stop a process from spawning?

---

I'm unable to trace this error as it's to do with the release build (double clicking the executable not running through Visual studio). Event Viewer shows the following (which is of no use):

 <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
 <System>
  <Provider Name="Application Error" /> 
  <EventID Qualifiers="0">1000</EventID> 
  <Level>2</Level> 
  <Task>100</Task> 
  <Keywords>0x80000000000000</Keywords> 
  <TimeCreated SystemTime="2015-10-13T22:54:20.000000000Z" /> 
  <EventRecordID>12976</EventRecordID> 
  <Channel>Application</Channel> 
  <Computer>Daryls8</Computer> 
  <Security /> 
  </System>
  <EventData>
  <Data>DestinyScreening.exe</Data> 
  <Data>1.0.0.0</Data> 
  <Data>561d8b7c</Data> 
  <Data>KERNELBASE.dll</Data> 
  <Data>10.0.10240.16384</Data> 
  <Data>559f3b2a</Data> 
  <Data>e0434352</Data> 
  <Data>000b3e28</Data> 
  <Data>20bc</Data> 
  <Data>01d1060a17c9bb47</Data> 
  <Data>C:\Users\Daryl\Documents\Visual Studio 2015\Projects\DestinyScreening\DestinyScreening\bin\Release\DestinyScreening.exe</Data> 
  <Data>C:\WINDOWS\SYSTEM32\KERNELBASE.dll</Data> 
  <Data>0ba5af44-c01c-4d4f-a318-855d84d4148e</Data> 
  <Data /> 
  <Data /> 
  </EventData>
  </Event>

Answer 1

When you hit this line

var RemoteRevision = (new WebClient()).DownloadString(UpdaterURL); 

and the web server is down, the thread executing that code will block until the timeout value for WebClient is reached, then it should throw an exception.

If you are running this on your UI thread, your UI will freeze up while waiting for the timeout.

When you say

when I say the application does not run. It essentially does run in Debug mode via Visual Studio

I strongly suspect that you are checking for the remote version in your startup code, which runs on the UI thread. With the UI thread blocked, the application becomes unresponsive and appears not to run.

Instead, make use of DownloadFileAsync() and the async/await pattern.

Note that you may need to disable your main form, or certain menu options/buttons, until the async operation completes depending on the requirements of your application, to prevent the user from interacting with functionality before the RemoteRevision has been determined, or you determine that the website is down.

You can also change the timeout for WebClient if the default is too long for your needs.

UPDATE

The async check would allow your app to continue processing windows events while the check is happening. This means the UI remains responsive to user input.

In the normal case (web server is available, and the remote call is fast), you will know quickly whether it is OK to proceed or you want to update, so the user will not notice async.

In the case where the web server is down, the UI remains responsive to the user because the event loop is being processed. You probably want to disable most of your UI until the async call completes. That way, if the web server is not available or if the call just takes longer than expected, the user cannot start using the UI early. You will still be able to show a MessageBox (or selectively enable parts of your UI) to alert the user that a new version is to be downloaded. I think you can probably accomplish this along the lines of

Form1.Enabled = false; // Whatever your main form is called
// Make the async call here
if (isNewVersionAvailable)
{
    MessageBox.Show("Exiting now to update the app version.");
    // Do whatever you do to update the app, and exit this program
}
Form1.Enabled = true;