Adds a new map type WeakReferenceMap, which stores weak
references to values, and a WeakReferenceThreadMap subclass
to more closely resemble a thread local type, as it is a
map of threadId to value.
Construct it with a factory method and optional callback
for notification on loss and regeneration.
WeakReferenceThreadMap<WrappingAuditSpan> activeSpan =
new WeakReferenceThreadMap<>(
(k) -> getUnbondedSpan(),
this::noteSpanReferenceLost);
This is used in ActiveAuditManagerS3A for span tracking.
Relates to
* HADOOP-17511. Add an Audit plugin point for S3A
* HADOOP-18094. Disable S3A auditing by default.
Contributed by Steve Loughran.
Change-Id: Ibf7bb082fd47298f7ebf46d92f56e80ca9b2aaf8
088684ec60