Stores a strong handle controlling the lifetime of the data in the LRU
cache, and a doubly-linked list node specifying where in the current LRU
order this element exists. These items are themselves backed by a freelist
to minimize heap allocations and improve cache access patterns.
Index of an LRU tracking element
The main public interface to the LRU cache
Stores the data supplied by the user to be cached, and an index
into the LRU tracking freelist for this element.
Internal implementation of the LRU tracking list