// Use a CAS so we do not inadvertantly stomp on a mark another thread placed on the item.
if (old_next == next || SYNC_CAS(&new_item->next[level], old_next, next) == old_next)
// Use a CAS so we do not inadvertantly stomp on a mark another thread placed on the item.
if (old_next == next || SYNC_CAS(&new_item->next[level], old_next, next) == old_next)