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fix(driver-abcip): resolve Medium code-review finding (Driver.AbCip-006)

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`PlcTagHandle` and `DeviceState.TagHandles` were dead scaffolding: the
`ReleaseHandle` no-op never called `plc_tag_destroy` and the dict was
never populated. Removed the file, the dead dict, and its
`DisposeHandles` loop. Updated the `AbCipDriver` class doc to document
that native lifetime is owned by libplctag.NET `Tag.Dispose()` (invoked
from `DisposeHandles`) with the library's own finalizer covering any
GC-collected instances. Two test methods that only exercised the dead
`PlcTagHandle` class removed from `AbCipDriverTests`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
2026-05-22 09:22:42 -04:00
parent 1679344ace
commit 37945deb0a
4 changed files with 163 additions and 66 deletions
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4
code-reviews/Driver.AbCip/findings.md
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@@ -108,13 +108,13 @@
| Severity | Medium |
| Category | OtOpcUa conventions |
| Location | `PlcTagHandle.cs:28-59`, `AbCipDriver.cs:806-807,832-833`, `LibplctagTagRuntime.cs:117` |
| Status | Open |
| Status | Resolved |
**Description:** `driver-specs.md` makes the SafeHandle-wrapped native handle a non-negotiable Tier-B protection ("Wrap every libplctag handle in a SafeHandle with finalizer calling plc_tag_destroy"). The repo ships `PlcTagHandle : SafeHandle` for this, but it is dead code: `ReleaseHandle` is a permanent no-op (the comment says the `plc_tag_destroy` P/Invoke "is deferred to PR 3", well past the commit under review), and `DeviceState.TagHandles` is never populated anywhere in the driver. The real native lifetime is delegated to the libplctag.NET `Tag` object own `Dispose()`. The mandated finalizer-backed leak protection therefore does not exist: if a `LibplctagTagRuntime` is GC-collected without `Dispose` (owning thread crashes, exception bypasses the device dispose path), whether the native tag is freed depends entirely on whether libplctag.NET `Tag` has its own finalizer, which is not guaranteed by this driver code as the design requires.
**Recommendation:** Either delete `PlcTagHandle` and `DeviceState.TagHandles` as misleading dead scaffolding and document that native lifetime is owned by libplctag.NET `Tag` finalizer (verifying that `Tag` actually has one), or finish the intended design by making `LibplctagTagRuntime` hold a real `PlcTagHandle` with a working `ReleaseHandle` calling `plc_tag_destroy`.
**Resolution:** _(open)_
**Resolution:** Resolved 2026-05-22 — `PlcTagHandle.cs` deleted; `DeviceState.TagHandles` removed from `DeviceState`; its `DisposeHandles` loop cleaned up. The class-level doc comment on `AbCipDriver` updated to document that native lifetime is owned by libplctag.NET `Tag.Dispose()` (called in `DisposeHandles`) with the library's own finalizer covering GC-collected instances. The two dead-code test methods for `PlcTagHandle` removed from `AbCipDriverTests`.
### Driver.AbCip-007