We've implemented parallel cache rebuild protection in 5.2.0-B1 by setting
lock before creating new cache. This ensured that all other requests were
receiving old cache version or just waiting for a lock to be released.

However I've found a bug in that system too, when multiple visitors, who
encountered a missing/outdated cache would set lock in parallel and start
rebuild process. This of course would be slightly smaller number of
parallel rebuild requests then without protection added in 5.2.0-B1, but
still needs to be fixed.

Task:

Ready for testing.

--
Best Regards,

http://www.in-portal.com
http://www.alex-time.com

parallel_cache_rebuild_fix.patch