Question

I’m currently doing maintenance on a Windows service and at certain points in the code there is some exception handling (e.g. in callbacks from timers and other external events):

try {
  ...
}
catch (Exception ex) {
   _logger.Log("Unhandled exception: {0}\r\n{1}", ex.Message, ex.StackTrace);
   Environment.FailFast("Fatal error.");
}

Logging the exception information helps troubleshooting what went wrong. However, sometimes the interesting information is the inner exception which makes it hard to determine the root cause of the problem. For instance a TypeInitializationException can be hard to understand.

Is there a better way to log exception information for troubleshooting purposes?

Answer 1

Is there a better way to log exception information for troubleshooting purposes?

Yes there is. Don’t be “smart” and use ex.Message and ex.StackTrace. Just use ex.ToString(). It will recurse into inner exceptions (multiple levels if required) and show the complete stacktrace.

try {
  ...
}
catch (Exception ex) {
   _logger.Log("Unhandled exception:\r\n{0}", ex);
   Environment.FailFast("Fatal error.");
}

To provide a small example, this is what you get if you create an instance of a class that throws an exception in the static constructor of the class. This exception throw will be wrapped in a TypeInitializationException.

Before:

Unhandled exception: The type initializer for 'SomeClass' threw an exception.
   at SomeNamespace.SomeClass..ctor()
   at SomeNamespace.Callback() in c:\ExceptionHandlingDemo.cs:line 34

Not very helpful. It is hard to determine what went wrong.

After:

Unhandled exception:
System.TypeInitializationException: The type initializer for 'SomeClass' threw an exception. ---> System.ArgumentException: An item with the same key has already been added.
   at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at SomeNamespace.SomeClass..cctor() in c:\ExceptionHandlingDemo.cs:line 43
   --- End of inner exception stack trace ---
   at SomeNamespace.SomeClass..ctor()
   at SomeNamespace.Callback() in c:\ExceptionHandlingDemo.cs:line 34

Now you can quite easily determine the root cause of the problem being a duplicate key in a dictionary and pinpoint it to line 43 in the source file.