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.
ad_page_contract_filters 38042679
api_proc_doc 37717019
ad_page_contract_filter_rules 26036060
::xotcl::THREAD 18628540
OACS_FULLQUERIES 17771146
ds_properties 7855339
rp_extension_handlers 6837414
apm_subsite_packages_list 3524672
apm_reload_watch 3514474
apm_properties 3514472