Locking HttpRuntime.Cache for lazy loading

lock (locker)
{
    if (HttpRuntime.Cache[cacheKey] == null)
    {
        HttpRuntime.Cache.Insert(cacheKey, GetSomeDataToCache(), null, DateTime.Today.AddDays(1), Cache.NoSlidingExpiration);
    }
    return ((SomeData)HttpRuntime.Cache[cacheKey]).Copy();
}