rust-pathauditor: use interior mutability for use in multi-threaded contexts...
rust-pathauditor: use interior mutability for use in multi-threaded contexts
The usual recommendation for using `RwLock` or `Mutex` is that if there are
about as many write as there are reads, use `Mutex`, and if there are more
reads than writes, use `RwLock`.
If after the main bottleneck (i.e. parallel traversal) is removed this shows
up on profiles, we should investigate using the `parking_lot` since we don't
need a poisoning API, or maybe move to different types of caches entirely.
Differential Revision:
https://phab.mercurial-scm.org/D8213