KeyedMutex

A map of independent mutexes keyed by K, with mutual exclusion per key.

Two callers using different keys never block each other; two callers using equal keys serialize. Keys need stable equals and hashCode. Entries are created on demand and removed as soon as the last interested caller leaves, so unused keys hold no memory.

Thread safety: this class is safe for concurrent use from multiple coroutines and threads; all internal state is guarded by a Mutex.