LRU cache design

Question

Least Recently Used (LRU) Cache is to discard the least recently used items first How do you design and implement such a cache class? The design requirements are as follows:

Answer 1

Is cache a data structure that supports retrieval value by key like hash table? LRU means the cache has certain size limitation that we need drop least used entries periodically.

If you implement with linked-list + hashtable of pointers how can you do O(1) retrieval of value by key?

I would implement LRU cache with a hash table that the value of each entry is value + pointers to prev/next entry.

Regarding the multi-threading access, I would prefer reader-writer lock (ideally implemented by spin lock since contention is usually fast) to monitor.