c# How to Check if an Exception Was Already Thrown

Question

I feel like I'm over thinking this or perhaps going the wrong way about it, but high level all I am trying to do is to catch errors that are thrown in my application, log them in the database, then redirect to a soft error page.

In my Global.asax, I have the following:

protected void Application_Error(object sender, EventArgs e)
    {
        try
        {
            ErrorLog error = new ErrorLog(Server.GetLastError().GetBaseException(), true);
            Response.Redirect("/error.aspx?id=" + error.ID);
        }
        catch(Exception err)
        {
            Response.Redirect("/error.aspx");
        }           
    }

Error log is a class I created that performs the record insertion and stuff like that.

Now the problem I am running into is that if there is something wonky with the database, like it being offline, an error in the stored procedure, etc, I get caught into an infinite loop of errors being inserted.

A solution I was trying to come up with this to resolve this behavior was to perhaps check if an error was already thrown, and if so, do not attempt to try a record insertion, but I haven't been able to find much on this.

Again, maybe I'm not going about this the correct way? Any help would be greatly appreciated. Thank you in advanced.

Answer 1

It is actually possible to do this, but I really don't think it's a good idea.

You can theoretically use Marshal.GetExceptionPointers() to detect it. If it returns IntPtr.Zero, it probably means that there is no exception in flight; otherwise, it probably means that there is.

I say "probably" because the MSDN documentation for Marshal.GetExceptionPointers() says under remarks:

GetExceptionPointers is exposed for compiler support of structured exception handling (SEH) only.

So that sounds like a big fat "don't use this" to me.

With that proviso, this program will actually tell you whether an exception is in flight or not, without using a try/catch to do so:

Warning: Nasty code ahead

using System;
using System.Runtime.InteropServices;

namespace Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                using (new Test())
                {
                    // All is well.
                }

                using (new Test())
                {
                    throw new InvalidOperationException("Eeep");
                }
            }

            catch (Exception ex)
            {
                Console.WriteLine("Exception detected: " + ex.Message);
            }
        }
    }

    sealed class Test: IDisposable
    {
        public void Dispose()
        {
            Console.WriteLine(
                Marshal.GetExceptionPointers() == IntPtr.Zero
                ? "Disposing test normally."
                : "Disposing test because of an exception.");
        }
    }
}

Answer 2

You can make a check if you are already on that page and redirect only if you are not as:

string cTheFile = HttpContext.Current.Request.Path;

if(!cTheFile.EndsWith("error.aspx", StringComparison.InvariantCultureIgnoreCase))
    Response.Redirect("/error.aspx");

Answer 3

Override Exception class with ErrorLogDBInsertException and throw this one if something bad with DB stuff. Catch a specific Error

protected void Application_Error(object sender, EventArgs e)
{
    try
    {
        ErrorLog.Log();
        Response.Redirect("/error.aspx?id=" + error.ID);
    }
    catch(ErrorLogDBInsertException err)
    {

        try 
        {
            // here you can log into event log
        }
        catch {}
        Response.Redirect("/SimpleNoDBCallPage_error.aspx");

    } 
    catch(Exception err)
    {
        Response.Redirect("/PageThatCallsDB_error.aspx");
    }           
}