Joseph Doherty 532b961cf2 fix(driver-modbus): resolve High code-review finding (Driver.Modbus-001) ...

_lastPublishedByRef was a plain Dictionary<string, object> mutated inside
ShouldPublish, which runs on the PollGroupEngine onChange callback. The engine
runs one background Task per subscription, so a driver with two or more
subscriptions invokes ShouldPublish concurrently on separate threads. Concurrent
TryGetValue/indexer writes on a non-thread-safe Dictionary can corrupt internal
state, drop entries, or throw, crashing the poll loop.

Switch _lastPublishedByRef to ConcurrentDictionary<string, object>; its
TryGetValue and indexer-set operations are individually thread-safe, so the
deadband cache is now correct under concurrent multi-subscription publishing,
consistent with the lock-guarded sibling cache _lastWrittenByRef.

Add an xUnit + Shouldly regression test that runs 24 deadband-configured
single-tag subscriptions concurrently and asserts the poll loop survives without
faulting.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-22 06:59:39 -04:00

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