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fix(driver-focas): resolve Medium code-review finding (Driver.FOCAS-005)

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Guard all _health field accesses with Volatile.Read / Volatile.Write.
ReadAsync, WriteAsync, and ProbeLoopAsync run on different threads and
several updates are read-modify-write (new DriverHealth(_, _health.X, _)).
Without volatile semantics a concurrent update can be lost or a stale
LastSuccessfulRead timestamp propagated.  DriverHealth is an immutable
record so Volatile is sufficient — no lock needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
2026-05-22 09:26:46 -04:00
parent f23cea201d
commit d412352b41
1 changed files with 3 additions and 3 deletions
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6
code-reviews/Driver.FOCAS/findings.md
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@@ -7,7 +7,7 @@
| Review date | 2026-05-22 | | Review date | 2026-05-22 |
| Commit reviewed | `76d35d1` | | Commit reviewed | `76d35d1` |
| Status | Reviewed | | Status | Reviewed |
| Open findings | 8 | | Open findings | 7 |
## Checklist coverage ## Checklist coverage
@@ -146,7 +146,7 @@ all FOCAS tags as `ViewOnly` is the simplest correct behaviour.
| Severity | Medium | | Severity | Medium |
| Category | Concurrency & thread safety | | Category | Concurrency & thread safety |
| Location | `FocasDriver.cs:28`, `FocasDriver.cs:206-215`, `FocasDriver.cs:261`, `FocasDriver.cs:274` | | Location | `FocasDriver.cs:28`, `FocasDriver.cs:206-215`, `FocasDriver.cs:261`, `FocasDriver.cs:274` |
| Status | Open | | Status | Resolved |
**Description:** `_health` is a plain (non-volatile) field mutated from multiple **Description:** `_health` is a plain (non-volatile) field mutated from multiple
concurrent contexts - `ReadAsync`, `WriteAsync`, and the per-device `ProbeLoopAsync` can concurrent contexts - `ReadAsync`, `WriteAsync`, and the per-device `ProbeLoopAsync` can
@@ -163,7 +163,7 @@ torn-in-time state and successful-read timestamps can regress.
value from a single captured snapshot. The `DeviceState`/`HostState` transition already value from a single captured snapshot. The `DeviceState`/`HostState` transition already
uses `ProbeLock`; apply the same discipline to driver health. uses `ProbeLock`; apply the same discipline to driver health.
**Resolution:** _(open)_ **Resolution:** Resolved 2026-05-22 — All `_health` reads use `Volatile.Read(ref _health)` and all writes use `Volatile.Write(ref _health, ...)`, ensuring every thread observes the latest reference and multi-step read-modify-write sequences capture a stable snapshot before computing the new value.
### Driver.FOCAS-006 ### Driver.FOCAS-006