Log to Elmah in async Task - asp.net-mvc-3

Question

I need some Elmah logging in a async task executing on my webserver. But when I try to log the error it fails because of the HttpContext.
var httpContext = HttpContext.Current;
Task.Factory.StartNew(() =>
{
HttpContext.Current = httpContext;
try
{
//Execute some code
}
catch (Exception ex)
{
//Generate some error for the user and log the error in Elmah
try
{
ErrorLog.GetDefault(HttpContext.Current).Log(new Error(ex));
}
catch(Exception ex)
{
}
}
});
To get the progress for the task I implemented some polling mechanism. Currently none of the errors are logged to Elmah which make it difficult to solve them.
Also providing the context as parameter doesn't work.
It doesn't work. I get an ArgumentException telling me the expected value doesn't fall within the expected range. With the following stacktrace:
at System.Runtime.InteropServices.Marshal.ThrowExceptionForHRInternal(Int32 errorCode, IntPtr errorInfo)
at System.Web.Hosting.IIS7WorkerRequest.GetServerVariableInternal(String name)
at System.Web.HttpRequest.AddServerVariableToCollection(String name)
at System.Web.HttpRequest.FillInServerVariablesCollection()
at System.Web.HttpServerVarsCollection.Populate()
at System.Web.HttpServerVarsCollection.Get(String name)
at Elmah.ErrorLog.InferApplicationName(HttpContext context)
at Elmah.ErrorLog.GetDefaultImpl(HttpContext context)
at Elmah.ServiceContainer.GetService(Type serviceType)
at Elmah.ServiceCenter.GetService(Object context, Type serviceType)
at Elmah.ErrorLog.GetDefault(HttpContext context)
at Bis.Utilities.Log.ElmahErrorLog.TryLogError(Exception exeption) in D:\Users\A500535\Documents\Projecten\Biobank\Bis\src\Utilities\Log\ElmahErrorLog.cs:line 13

Answer 1

Below is one ugly hack that might get the job done. Essentially, it creates an Error object on a bogus Exception (the prototype) so that the context can be captured while the request is still in flight. Later, when the task started as a result of the request fails, another Error object is created off the actual exception that occurred and then the interesting and contextual bits are selectively copied off the earlier prototype. Unfortunately, the prototype Error has to be created whether or not an exception will occur.
// Create an error that will capture the context
// and serve as a prototype in case a real exception
// needs logging
var prototype = new Error(new Exception(), context);
Task.Factory.StartNew(() =>
{
try
{
// Execute some code
}
catch (Exception ex)
{
// Generate some error for the user and log the error in ELMAH
try
{
// Create a new error without contextual information
// but then copy over the interesting bits from the
// prototype capture at time of request.
var error = new Error(ex)
{
HostName = prototype.HostName,
User = prototype.User,
};
error.ServerVariables.Add(prototype.ServerVariables);
error.QueryString.Add(prototype.QueryString);
error.Cookies.Add(prototype.Cookies);
error.Form.Add(prototype.Form);
ErrorLog.GetDefault(null).Log(error);
}
catch(Exception)
{
}
}
});

Answer 2

When you start a new thread it doesn't get the HttpContext structure. Since Elmah logging requires the HttpContext data, it will fail.
See the following QA:
Elmah Does not email in a fire and forget scenario
for me this worked in a async task called with Task.Run:
Elmah.ErrorLog.GetDefault(null).Log(new Elmah.Error(new NotSupportedException("elmah logging test")));