We are running a very large web application in asp.net MVC .NET 4.0. Recently we had an audit done
and the performance team says that there were a lot of null reference exceptions.
So I started investigating it from the dumps
and event viewer.
My understanding was as follows:
We are using Asyn Tasks in our controllers. We rely on HttpContext.Current.Items hashtable to store a lot of Application level values.
Task<Articles>.Factory.StartNew(() =>
{
System.Web.HttpContext.Current = ControllerContext.HttpContext.ApplicationInstance.Context;
var service = new ArticlesService(page);
return service.GetArticles();
}).ContinueWith(t => SetResult(t, "articles"));
So we are copying the context object onto the new thread that is spawned from Task factory. This context.Items is used again in the thread wherever necessary.
Say for ex:
public class SomeClass
{
internal static int StreamID
{
get
{
if (HttpContext.Current != null)
{
return (int)HttpContext.Current.Items["StreamID"];
}
else
{
return DEFAULT_STREAM_ID;
}
}
}
This runs fine as long as number of parallel requests are optimal. My
questions are as follows:
1. When the load is more
and there are too many parallel requests, I notice that HttpContext.Current.Items is empty. I am not able to figure out a reason for this
and this causes all the null reference exceptions.
2. How do we make sure it is not null ? Any workaround if present ?
NOTE: I read through in StackOverflow
and people have
questions like HttpContext.Current is null - but in my case it is not null
and its empty. I was reading one more article where the author says that sometimes request object is terminated
and it may cause problems since dispose is already called on objects. I am doing a copy of Context object - its just a shallow copy
and not a deep copy.
