can be called simultaneously by different threads on the same hint_table
. For optimization, it can be enforced that every client of the
location hint manager should have a structure/pointer dedicated for the
use of hint manager. This pointer can be used as a back-reference to
the container so that operations like forget_hint can happen without any
kind of searching.
. the hints may already be being referred by another client. The slot
should still be reserved but should not be freshly refereable (by