- I1: the poll engine belongs to a teardown generation. ShutdownAsync/Dispose
retire the current engine and install a fresh one in the same swap as the
device/tag tables, then dispose the retired one (possibly in the background
after a cancelled or over-budget shutdown). A subscription made after the
next InitializeAsync can no longer land in an engine whose late dispose tail
would dispose its CTS without cancelling it (a loop no UnsubscribeAsync could
find). Poll handles are generation-qualified (TwinCATPollHandle) because each
engine numbers handles from 1; SubscribeAsync re-homes a subscription that
raced a retirement.
- M1: a write's status feeds per-device health - Good clears that device's
comms fault and advances LastSuccessfulRead, a comms status degrades, a
refusal keeps the state.
- M2: a symbol-version re-arm bumps a per-registration epoch; an in-flight
retry that fails afterwards no longer re-imposes the backoff.
- M3: a re-arm restarts the refusal backoff at 30 s.
- M4: documented that PLC-not-in-RUN detection needs the probe.
- M5: WSTRING and multi-dimensional array encode-plan tests; the cancelled-
shutdown test asserts Unknown health and awaits its background teardown.
- M6: an infinity spelled as a string ('Infinity', '-inf') passes like a
float/double infinity; a finite overflow stays BadOutOfRange.
Refs #739
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
- IMPORTANT: a successful probe records the PLC's ADS state; a PLC not in Run
keeps the driver Degraded with 'PLC in {state}' while LastSuccessfulRead
still advances (the device answered). RecordDeviceAnswered never restores
Healthy while any device is out of Run.
- Health is per device, rolled up worst-of: a comms fault is remembered on the
device it was seen on and only that device answering clears it (device A
answering no longer clears device B's fault).
- Refused (non-comms) dead registrations back off 30 s doubling to 10 min and
are re-armed by a symbol-version change or retried by the reconnect replay;
comms-class failures keep the every-tick retry. A retry whose failure class
changes republishes the tag's status, once.
- Bit-RMW gates are kept across generations and teardowns (never cleared).
- ShutdownAsync honours its CancellationToken: it stops waiting, finishes the
bookkeeping and throws OperationCanceledException.
- Remarks on why a superseded InitializeAsync throws OperationCanceledException.
- REAL / LREAL values (scalar or array element) outside the target range are
OverflowException -> BadOutOfRange instead of being written as Infinity.
- String / array write encoding factored into AdsTwinCATClient.PlanStringWrite
/ PlanArrayWrite; the fake runs them so a driver-level test covers the real
encode path against a fake resolved symbol.
- Timing-fragile tests use condition waits / measured probe-tick windows; the
dispose-during-shutdown test asserts ordering with a 1 s bound.
Refs #739
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty