1 Commits

Author	SHA1	Message	Date
Marc Schier	e05a820c91	Removal of the exposed diagnostics and node locks (#4188) ... ## What this is Design analysis for `Opc.Ua.Server`, the two rounds of design exploration behind it, and the first two implementation chunks it recommends. Draft: the analyses are ready to read, but the *conclusions* deserve discussion before the larger phases proceed. Later chunks stack onto this PR as they land. | File | Kind | Lines | |---|---|---:| | `plans/NodeManagerAnalysis.md` | Evidence — the node-manager plugin surface | 488 | | `plans/ServerRuntimeAnalysis.md` | Evidence — the server runtime cluster | 576 | | `plans/ServerDesignExploration.md` | Design round 2 — delivery strategy | 1,394 | | `plans/ServerDesignExplorationAlt.md` | Design round 1 — four interface designs | 2,119 | | `src/Opc.Ua.Types/State/NodeState.cs` | **Code** — node self-guards attributes | | | `src/Opc.Ua.Types/State/BaseVariableState.cs` | **Code** — value accessors take the lock | | | `src/Opc.Ua.Server/NodeManager/AsyncCustomNodeManager.cs` | **Code** — 6 external locks removed | | | `tests/…/NodeStateAttributeConcurrencyTests.cs` | **Code** — concurrency safety net | 449 | `docs/` is untouched — it holds shipped feature documentation, and none of this is shipped API. ## The analyses Counted mechanically over `src`, `samples` and `tests`; **every figure is reproducible** from commands printed in each document. **Node manager surface.** `AsyncCustomNodeManager` declares **93 `virtual`/`abstract` members** (80 distinct names). Across the repository: **112 override sites, 25 distinct names ever overridden, 55 of 80 never**. Six carry nearly all real use. For scale, `ReferenceNodeManager` is 6,373 lines and overrides **8**. **Server runtime.** Seven findings, **two of which recommend no change**. Findings 1–5 are filed as #4183–#4187. The headline is an `object`-typed sync root published on three public interfaces and taken in **88 `lock` statements across 7 files**, including a shipped sample. **What is deliberately not flagged.** `IStandardServer` — 9 members over 5,575 lines, 16 of 37 virtuals used — is identified as the reference shape to preserve. `IApplicationInstance` and the already-`[Obsolete]` `Stop()` are examined and left alone. ## The design exploration **Round 1** explored four alternative interfaces in parallel under the current back-compat constraint. Its value is the convergence: four designers who never saw each other's work independently arrived at a 6–9 member `IServerContext` replacing the 57-member locator, removal of the `object` node-manager handle, elimination of the `Processed` protocol, and `IHistorianProvider` as the pattern to copy. **Round 2** re-runs it with back-compat lifted and asks how to deliver: full rewrite versus side-by-side fork. **Both option designers independently declined to recommend their own assignment.** Three structural facts were verified: 1. **The fork line already sits at `IAsyncNodeManager`** — old and new node managers can coexist with zero runtime changes, so a fork duplicates ~10% of the assembly, not all of it. 2. **`[OpcUaShim]` cannot shim an inheritance surface** — honest auto-fix ceiling for the authoring surface is **~10%**, against ~70% for the shipped analyzers. 3. **A second lock leak exists** — `NodeState` takes `lock (this)` under a `CA2002` suppression whose own comment documents the contract. Recommendation: **neither pure option**, but a staged path reaching the rewrite end state incrementally, gated on migrating the five framework-internal node managers that today make it impossible for the old base to ever freeze. ## Implementation: NodeState now guards its own attributes This removes the prose-only contract in which `NodeState` took `lock(this)` and every external caller was required to take `lock(source)` on the node instance. The code already carried a TODO describing exactly this fix and noting it required updating every external site. - The node self-guards rather than relying on callers. `BaseVariableState` gains a **fully private** `System.Threading.Lock` covering its value fields; `NodeState`'s other collections keep their existing private locks. - All **6** `lock(this)` sites and both `CA2002`/`RCS1059` suppressions are gone. - `Value`, `Timestamp` and `StatusCode` on `BaseVariableState` take the lock too — without that, a direct property write raced an attribute read once the external lock was gone. - **6 of 9** external sites removed. Five were already redundant (`GetReferences`, `GetChildren`, `ReferenceExists` and `SetAreEventsMonitored` guard themselves; `FindMethod` reaches its state via `GetChildren`); the sixth was an attribute read now covered by the node's own lock. - Attribute read/write deliberately take **no** node-wide lock: both dispatch to caller-supplied handlers (`OnReadValue` and siblings) that may take locks of their own, and holding a lock on the node across one gives the node no fixed place in the lock order. - **3 deliberately retained and annotated in code**: two `CreateBrowser` calls, which are not internally synchronized (tracked in #4216), and one in `CustomNodeManager`, whose class is slated for deletion so refactoring its lock would be wasted work. ### No lock is exposed anywhere, to anyone An earlier revision put the attribute lock on `NodeState` as `private protected`, which still published a lock-sharing contract on the inheritance surface. Review pushed back and it is gone: `BaseVariableState` was the only user, so the lock moved there as a plain `private readonly Lock`. There is no member for a derived type to call, in this assembly or any other. `BaseVariableValue` was the last public leak — it handed out the lock guarding its value through a `public Lock` property, so any caller could hold it across a call back into the stack. That property is removed: - Derived value classes (what the source generator emits for every structure variable) synchronize through a `protected EnterLock()` / `ExitLock()` pair. Callback helpers were the first choice, but the generated bodies pass `ref Variant` / `ref StatusCode` / `ref DateTimeUtc`, and `ref` arguments cannot be captured by a lambda. The lock *object* stays private either way. - `NodeStateTemplates` emits the new form. - `ServerInternalData`, the one cross-assembly caller, was reading the lock back off a value it had itself constructed with that lock. It now takes `m_diagnosticsLock` directly. `NodeBrowser.DataLock` remains `protected` and is tracked in #4215: a subclass extending `Next()` legitimately needs its enumeration state atomic with the base browser's, so the fix needs a base-owned acquisition rather than a deletion. ### Migration coverage for the removed lock members None of the removed lock members get an `[Obsolete]` shim, and the migration guide now says why: a shim would have to be `object`-typed to keep old call sites compiling, and on .NET 9+ `lock (o)` on a statically-`object` reference is `Monitor.Enter`, which does **not** interlock with `Lock.Enter()`. It would compile, run, and silently synchronize nothing — strictly worse than a compile error. Re-adding a member to a downstream-implemented interface is also a break in its own right on `net48` / `netstandard2.0`, where there are no default interface methods. Instead, every removed member has a named replacement on the migration path: | Rule | Covers | Replacement it names | |---|---|---| | `UA0024` | `IServerInternal` / `ISession` / `ISubscription` `DiagnosticsLock`, `DiagnosticsWriteLock` | `UpdateServerDiagnostics(...)` / `UpdateDiagnostics(...)`, `ReadServerDiagnostics` / `ReadDiagnostics` | | `UA0025` | `ILocalNode.DataLock`, `Node.DataLock` | a lock the caller owns; the node guards its own state | | `UA0026` | `BaseVariableValue.Lock` | a lock passed to the `BaseVariableValue` constructor | Each rule fires on sources still written against 1.5.378, where the compiler only says a member is missing. `docs/MigrationGuide.md` gains a section per removal with before/after. ### The tests earned their keep The four concurrency tests were landed **first**, against the unmodified code, because removing a synchronization contract cannot be verified by the compiler and the existing `NodeStateHandlerConcurrencyTests` covers a different concern (racing a handler assignment against a write, not reader/writer exclusion). They now run with **no external locking**, which is what demonstrates the node guards itself. They caught two real problems, and one of them was mine: - The `Value`/`StatusCode`/`Timestamp` setters bypassed the new lock — a genuine race. - One test asserted an invariant the design does not offer. Two property setters are two lock acquisitions, so that pair was **never** atomic; it only passed originally because the test held a lock across both. It now uses a single attribute write carrying a whole `DataValue`, which genuinely is atomic and is the path the server uses. A third issue was found and fixed before it shipped: the reader loops gated on `!writer.IsCompleted`, so a reader scheduled after the writer finished performed zero reads — failing two runs in three on `net48`. Converted to `do…while`; now five consecutive green runs. **Verified:** `Stack.State` 116 passed on `net10.0` *and* `net48`; the concurrency category green 5/5 consecutive on `net48`; `Opc.Ua.Types.Tests` 8,456 passed; the server node-manager suite 1,205 passed, including `NodeManagerLifecycleTests` and `AsyncCustomNodeManagerTests` which exercise the changed paths. ## Two corrections to my own published figures Both were found while starting implementation, and both are recorded on #4183. **`ForceDiagnosticsScan()` was overstated.** The analysis claimed the `DiagnosticsWriteLock` getter *"triggers a full address-space diagnostics rescan"*. It is in fact a single flag assignment (`DiagnosticsNodeManager.cs:700-703`) consumed by the read paths and the periodic timer. The defect stands — a side-effecting property getter with a racy write on a synchronisation path — but its cost was misstated. **The contract was 15 sites, not 19.** A naive search matched ten comment and `#pragma` lines that *mention* `lock(source)` while explaining it. The documents now carry a counting command that excludes comment matches. A third finding expanded scope the other way: the `object`-typed lock leak is **repo-wide**, with ten such members across `Opc.Ua.Core`, `Opc.Ua.Types` and `Opc.Ua.Server` — including `Node.DataLock => this` and `ApplicationConfiguration.PropertiesLock => m_properties`, the same defect class as `Subscription.DiagnosticsLock`. ## Caveats stated in the documents - **Nothing in the designs is implemented or benchmarked.** Every performance claim across all seven designs is a design intention, not a measurement. - The larger phases are a **major undertaking against a live plugin API**; the documents say so rather than letting the neatness of the proposals imply otherwise. - The recommended sequencing puts low-risk, self-contained steps first and notes they are **worth doing regardless** of which strategy is eventually chosen. - Round 2 notes the two option designers' cost estimates are **not independent of their assignments**. ## Review guidance The two analyses make factual claims checkable by running the included commands. The design explorations are exploratory and need not be agreed with to merge. The code change is small, test-backed, and independent of which delivery strategy is eventually chosen. Reasonable outcomes include merging as-is, merging only the analyses and the lock fix, or disagreeing with the recommendation while keeping the evidence. --- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: e9c13dd0-a6e3-4ad2-8ad6-1c3fe6323041 Copilot-Session: d18f87e9-2484-44ce-98ce-463ba6cf5f63	2026-08-10 06:47:50 +02:00