my current code

HashTable cacheName
{
get{gettingHashTableFromApplication();}
set{settingHashTableToApplication();}
}

if (HttpContext.Current.Cache[cacheName] == null)
        {
            //Checks if the hashtable contains the key so if not it will add it
            if (!cacheNames.Contains(cacheName))
               lock (cacheNames) // Lock the HashTable to add the key
                {
                    if (!cacheNames.Contains(cacheName)) // check again the hashtable if contains the key
                    {
                        //cacheNames.Add(cacheName, new LockType()); // add the key with a LockType.
                        cacheNames.Add(cacheName, cacheName); // add the key with a LockType.
                    }
                }

string locker = (string)cacheNames[cacheName]; // Get the corect LockType Object from the hashtable
            lock (locker) //lock the object so if another thread will try to load the ac to cache  it will block it.
            {
                if (HttpContext.Current.Cache[cacheName] == null )
                {
                    GetFromDB();
                }
            }
        }