Singleton Per Call Context (Web Request) in Unity

Question

A few days ago, I had an issue with ASP.Net threading. I wanted to have a singleton object per web request. I actually need this for my unit of work. I wanted to instantiate

Answer 1

While this is fine calling this PerCallContextLifeTimeManager, I'm pretty sure this is not "safe" to be considered an ASP.Net Per-request LifeTimeManager.

If ASP.Net does its thread-swap then the only thing taken across to the new thread through CallContext is the current HttpContext - anything else you store in CallContext will be gone. This means under heavy load the code above could have unintended results - and I imagine it would be a real pain to track down why!

The only "safe" way to do this is with HttpContext.Current.Items, or doing something like:

public class PerCallContextOrRequestLifeTimeManager : LifetimeManager
{
    private string _key = string.Format("PerCallContextOrRequestLifeTimeManager_{0}", Guid.NewGuid());

    public override object GetValue()
    {
      if(HttpContext.Current != null)
        return GetFromHttpContext();
      else
        return GetFromCallContext();
    }

    public override void SetValue(object newValue)
    {
      if(HttpContext.Current != null)
        return SetInHttpContext();
      else
        return SetInCallContext();
    }

    public override void RemoveValue()
    {
    }
}

This obviously means taking dependencies on System.Web :-(

Much more information on this available at:

http://piers7.blogspot.com/2005/11/threadstatic-callcontext-and_02.html