private bool LockSessionItem(string id, SessionItem currentItem)
        {
            if(currentItem == null)
                throw new ArgumentNullException("currentItem");

            if (currentItem.Locked)
                return false;

            using(var c = this.MemcachedClient)
            {
                currentItem.Locked = true;
                currentItem.LockDate = DateTime.UtcNow;
                c.Store(StoreMode.Replace, id, currentItem, _timeout);
                return true;
            }
        }
 private TimeSpan GetLockAge(SessionItem item)
 {
     return DateTime.UtcNow.Subtract(item.LockDate);
 }