.NET Global exception handler in console application

Question

Question: I want to define a global exception handler for unhandled exceptions in my console application. In asp.net, one can define one in global.asax, and in windows appli

Answer 1

I just inherited an old VB.NET console application and needed to set up a Global Exception Handler. Since this question mentions VB.NET a few times and is tagged with VB.NET, but all the other answers here are in C#, I thought I would add the exact syntax for a VB.NET application as well.

Public Sub Main()
    REM Set up Global Unhandled Exception Handler.
    AddHandler System.AppDomain.CurrentDomain.UnhandledException, AddressOf MyUnhandledExceptionEvent

    REM Do other stuff
End Sub

Public Sub MyUnhandledExceptionEvent(ByVal sender As Object, ByVal e As UnhandledExceptionEventArgs)
    REM Log Exception here and do whatever else is needed
End Sub

I used the REM comment marker instead of the single quote here because Stack Overflow seemed to handle the syntax highlighting a bit better with REM.

Answer 2

No, that's the correct way to do it. This worked exactly as it should, something you can work from perhaps:

using System;

class Program {
    static void Main(string[] args) {
        System.AppDomain.CurrentDomain.UnhandledException += UnhandledExceptionTrapper;
        throw new Exception("Kaboom");
    }

    static void UnhandledExceptionTrapper(object sender, UnhandledExceptionEventArgs e) {
        Console.WriteLine(e.ExceptionObject.ToString());
        Console.WriteLine("Press Enter to continue");
        Console.ReadLine();
        Environment.Exit(1);
    }
}

Do keep in mind that you cannot catch type and file load exceptions generated by the jitter this way. They happen before your Main() method starts running. Catching those requires delaying the jitter, move the risky code into another method and apply the [MethodImpl(MethodImplOptions.NoInlining)] attribute to it.

Answer 3

What you are trying should work according to the MSDN doc's for .Net 2.0. You could also try a try/catch right in main around your entry point for the console app.

static void Main(string[] args)
{
    try
    {
        // Start Working
    }
    catch (Exception ex)
    {
        // Output/Log Exception
    }
    finally
    {
        // Clean Up If Needed
    }
}

And now your catch will handle anything not caught (in the main thread). It can be graceful and even restart where it was if you want, or you can just let the app die and log the exception. You woul add a finally if you wanted to do any clean up. Each thread will require its own high level exception handling similar to the main.

Edited to clarify the point about threads as pointed out by BlueMonkMN and shown in detail in his answer.

Answer 4

If you have a single-threaded application, you can use a simple try/catch in the Main function, however, this does not cover exceptions that may be thrown outside of the Main function, on other threads, for example (as noted in other comments). This code demonstrates how an exception can cause the application to terminate even though you tried to handle it in Main (notice how the program exits gracefully if you press enter and allow the application to exit gracefully before the exception occurs, but if you let it run, it terminates quite unhappily):

static bool exiting = false;

static void Main(string[] args)
{
   try
   {
      System.Threading.Thread demo = new System.Threading.Thread(DemoThread);
      demo.Start();
      Console.ReadLine();
      exiting = true;
   }
   catch (Exception ex)
   {
      Console.WriteLine("Caught an exception");
   }
}

static void DemoThread()
{
   for(int i = 5; i >= 0; i--)
   {
      Console.Write("24/{0} =", i);
      Console.Out.Flush();
      Console.WriteLine("{0}", 24 / i);
      System.Threading.Thread.Sleep(1000);
      if (exiting) return;
   }
}

You can receive notification of when another thread throws an exception to perform some clean up before the application exits, but as far as I can tell, you cannot, from a console application, force the application to continue running if you do not handle the exception on the thread from which it is thrown without using some obscure compatibility options to make the application behave like it would have with .NET 1.x. This code demonstrates how the main thread can be notified of exceptions coming from other threads, but will still terminate unhappily:

static bool exiting = false;

static void Main(string[] args)
{
   try
   {
      System.Threading.Thread demo = new System.Threading.Thread(DemoThread);
      AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
      demo.Start();
      Console.ReadLine();
      exiting = true;
   }
   catch (Exception ex)
   {
      Console.WriteLine("Caught an exception");
   }
}

static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
   Console.WriteLine("Notified of a thread exception... application is terminating.");
}

static void DemoThread()
{
   for(int i = 5; i >= 0; i--)
   {
      Console.Write("24/{0} =", i);
      Console.Out.Flush();
      Console.WriteLine("{0}", 24 / i);
      System.Threading.Thread.Sleep(1000);
      if (exiting) return;
   }
}

So in my opinion, the cleanest way to handle it in a console application is to ensure that every thread has an exception handler at the root level:

static bool exiting = false;

static void Main(string[] args)
{
   try
   {
      System.Threading.Thread demo = new System.Threading.Thread(DemoThread);
      demo.Start();
      Console.ReadLine();
      exiting = true;
   }
   catch (Exception ex)
   {
      Console.WriteLine("Caught an exception");
   }
}

static void DemoThread()
{
   try
   {
      for (int i = 5; i >= 0; i--)
      {
         Console.Write("24/{0} =", i);
         Console.Out.Flush();
         Console.WriteLine("{0}", 24 / i);
         System.Threading.Thread.Sleep(1000);
         if (exiting) return;
      }
   }
   catch (Exception ex)
   {
      Console.WriteLine("Caught an exception on the other thread");
   }
}

Answer 5

You also need to handle exceptions from threads:

static void Main(string[] args) {
Application.ThreadException += MYThreadHandler;
}

private void MYThreadHandler(object sender, Threading.ThreadExceptionEventArgs e)
{
    Console.WriteLine(e.Exception.StackTrace);
}

Whoop, sorry that was for winforms, for any threads you're using in a console application you will have to enclose in a try/catch block. Background threads that encounter unhandled exceptions do not cause the application to end.