public void Add(string key, object value, TimeSpan timeout)
        {
            CacheItemRemovedCallback callback = null;

            // only need call back if item is in the locking states
            if (CacheEntries.ContainsKey(key))
            {
                callback = ItemRemovedCallback;
            }

            Insert(key, value, null, timeout, CacheItemPriority.Normal, callback);
        }