How to use Elmah to log the TaskScheduler.UnobservedTaskException exceptions

Question

I'm developing a asp.net mvc application. And I want to log all application exceptions.

After googled, I found the best solution is to use the Elmah to log exceptions. But I can't find anyone tell if it's possible to log the exceptions  in the TaskScheduler.UnobservedTaskException event with Elmah.

Can anybody give a clue?

Thanks.

Answer 1

I've never used Elmah, but doing a quick search on Bing for how to use it programmatically, you could try something like:

TaskScheduler.UnobservedTaskException += (s,e) =>
{
    ErrorSignal.FromCurrentContext().Raise(e.Exception);
    e.SetObserved();
};

I hope that helps.

Answer 2

I've tested to do as below:

protected void Application_Start()
{
	...

	TaskScheduler.UnobservedTaskException += (object sender, UnobservedTaskExceptionEventArgs excArgs) =>
	{
		ErrorSignal.FromCurrentContext().Raise(excArgs.Exception);      
		excArgs.SetObserved();
	};
}

but when the UnobservedTaskException event is fired, the application crashed with exception as below:

System.ArgumentNullException was unhandled
   Message=Value cannot be null.
   Parameter name: context
   Source=Elmah
   ParamName=context
StackTrace:
       at Elmah.ErrorSignal.FromContext(HttpContext context) in c:\builds\ELMAH\src\Elmah\ErrorSignal.cs:line 67
       at MyMvcApplication.<Application_Start>b__0(Object sender, UnobservedTaskExceptionEventArgs excArgs) in ...\Global.asax.cs:line 82
       at System.Threading.Tasks.TaskScheduler.PublishUnobservedTaskException(Object sender, UnobservedTaskExceptionEventArgs ueea)
       at System.Threading.Tasks.TaskExceptionHolder.Finalize()

Answer 3

I see. Elmah is expecting to only be used in the context of an HTTP request, and UnobservedTaskException is occurring later on in the finalizer thread.  You'll need to find out how to log an exception to Elmah more generally.

Answer 4

Maybe it's impossible to do it.

Thanks.