Code review comment for lp:~mkanat/loggerhead/synchronize-lru_cache

Check out: lp:///~jameinel/bzr/lru_locking

It still needs tests, and possibly 'live-fire' testing, hammering the cache structure with lots of threads. However, I'm fairly sure that I've gotten a minimal locked section (we lock as little as possible), while still maintaining correctness.

LRUCache.add() is not specifically thread-safe if you have cleanups and are adding different values for the same key. We might want to consider putting a big lock around all of add() for that case, but callers could also do that...

The main reason I poked at it was because you can't get 'fine-grained' locking around the LRU double-linked-list unless it is implemented in the cache itself.