The six plain-bool lock flags (Plex, Trakt, Emby/Jellyfin/Plex collections,
troubleshooting playback) used a non-atomic check-then-set, so two concurrent
Lock* callers could both win. Convert them to int flags mutated only via
Interlocked.CompareExchange, so the caller that wins the 0->1 transition is the
sole owner and the only one that fires the change event. The three
ConcurrentDictionary-backed kinds (Library/Playout/RemoteMediaSource) were
already atomic; drop their redundant ContainsKey pre-checks.
Define the ownership contract (tokenless single-owner discipline, no interface
change) on IEntityLocker and in docs/decisions.md: a true from Lock* confers
ownership of exactly one release; Unlock* on an unlocked slot returns false,
fires no event, and logs a warning (the double-release / non-owner tripwire).
Adds EntityLockerTests (real locker, parallel-caller races) proving exactly one
winner per kind, one-releaser-per-slot, and event-fires-once-per-transition.
Ref #231. Scan-lifecycle call-site fixes that consume this contract land in the
same PR (#232); the BuildPlayout/subtitle finally-gating is #234.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
timothyandClaude Opus 4.8
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