Why does that exception management code stinks?

Question

Why it is not advised (in a best pratice meaning) to manage all the exceptions of a system from the entry point.

class Program
    {
        static void Main(string[] args)
        {
              try
              {
                 [...]//all the program stuff
              }catch(Exception ex)
              {
                    [...]
              }
        }
    }

edit : in a second point does it change something for the performance?

Answer 1

It's not advised in the meaning that you should catch exceptions in places where you can actually handle them in a useful way.

If there is nothing you can do about the exception but crash, your solution works, but consider for example a missing file giving you an exception. Would you rather handle it with a dialog in the "OpenFile" method (or in this case maybe the part of the method where you open the file) and possibly give the user a chance to browse to where the file is before proceeding, or would you rather have it throw back to main and have no real option except "log and crash"?

Answer 2

This approach:

• Doesn't emphasise catching expected exceptions in the right place, i.e. where they can be dealt with in the same context that they happened.
• Won't catch an exception on another thread, so it won't work in a mutli-thread environment.
• Won't catch many Windows Forms exceptions, as they're intercepted by the .NET Framework.
• Swallows every exception, except when the process is corrupted. This isn't a good approach because you shouldn't swallow an exception when you don't understand it.

A better approach is to catch expected exceptions in the context-specific method, where the most knowledge is available for them to be handled properly. To catch unexpected exceptions, your Main method might look something like this:

// Event handler for handling all UI thread exceptions.
Application.ThreadException += 
    new ThreadExceptionEventHandler(App_UiThreadException);

// Force all Windows Forms errors to go through our handler.
// NB In .NET 4, this doesn't apply when the process state is corrupted.
Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException);

// Event handler for handling all non-UI thread exceptions. 
AppDomain.CurrentDomain.UnhandledException += new 
    UnhandledExceptionEventHandler(App_NonUiThreadException);

// Run the application.