Question

I have an extension method on the HttpApplicationState object for getting my IoC container out of the application. This same code will also create the container if it doesn’t exist.

I have 2 questions:

1. Is my code actually thread safe as I intend it to be
2. Is this considered the best practice for dealing with the application state

Code as follows:

private const string GlobalContainerKey = 'UnityContainerKey';  public static IUnityContainer GetContainer(this HttpApplicationState application) {     var container = application[GlobalContainerKey] as IUnityContainer;      if (container == null)     {         try         {             application.Lock();             container = application[GlobalContainerKey] as IUnityContainer;              if (container == null)             {                 container = new UnityContainer();                 application[GlobalContainerKey] = container;             }         }         finally         {             application.UnLock();         }     }      return container; } 

Answer 1

You need to put

var container = application[GlobalContainerKey] as IUnityContainer; 

in the lock as well, otherwise many threads may create a new container in sequence.

private const string GlobalContainerKey = 'UnityContainerKey'; private const object lockObject = new object();  public static IUnityContainer GetContainer(this HttpApplicationState application) {     var IUnityContainer container = null;      lock (lockObject)     {         container = application[GlobalContainerKey] as IUnityContainer;         if (container == null)         {             container = new UnityContainer();             application[GlobalContainerKey] = container;         }     }      return container; }