Part 3 of scalability improvement: provide lock-free implementation of ad_page_contract_filter_rules. If nothing bad shows up, the underlaying nsv-arrays can be removed completely.
If one looks at the top 10 nsv mutex locks of a rather busy site (nsd running for 3 days), one can see the ad_page_contract_filters and ad_page_contract_filter_rules belong to the most frequent mutex locks, which can be avoided at completely. These two arrays make up of nearly 40% of the top 10 nsv locks.