romanettandClaude Opus 5.5
8b1cc6b7e3
Q7 of the request-queue comparison with ASP.NET Core/Kestrel. Stacked on #4917 (Q4 + Q5): review only the last two commits. ## Q7: requests run on concurrency permits instead of queue workers Without an isolation provider (the SharedOnly profile), the request queue used to grow workers one at a time under `m_workerGate`. Workers were never retired before stop. Requests went through a bounded `Channel`, and the "thread" settings were really limits on concurrent requests. Now: - `ScheduleIncomingRequest` takes one of `MaxRequestThreadCount` permits (a counter under the existing gate) and queues the handler on the ThreadPool directly (`IThreadPoolWorkItem` on .NET, `WaitCallback` on net48). A `Queue<QueuedRequest>` holds only the requests that are waiting for a permit. Waiting requests go first, so ordering stays FIFO. - A request that finishes, or parks with `DecoupleHeldPublishRequests`, hands its permit to the oldest waiting request and runs it on the same thread, as a worker loop did. Otherwise it returns the permit. - External behaviour is unchanged: same configuration, `BadServerTooBusy` once `MaxQueuedRequestCount` requests wait, parking releases the permit. `StopCoreAsync` rejects waiting requests with `BadServerHalted` and waits for executing and parked handlers. It also waits for permits whose request has not started yet, so `m_cts` is disposed only after every permit is back. - `FairRequestQueue` and its worker loop are unchanged; `WorkerLoopAsync` now serves only the fair queue. - `InitializeRequestQueue` no longer raises `MaxRequestThreadCount` values below 100 to 100. The value is still raised to `MinRequestThreadCount`, which is at least 1. - The doc comments of `MinRequestThreadCount` and `MaxRequestThreadCount` and `docs/ServerScalability.md` now describe the settings as concurrency limits. I considered `System.Threading.RateLimiting.ConcurrencyLimiter` and did not use it: every `AttemptAcquire` and queued `AcquireAsync` allocates a lease. A plain counter under the gate the queue already takes per request costs nothing extra. ### Release note (behaviour change) > `MaxRequestThreadCount` values below 100 are no longer raised to 100: the configured value is the limit on requests executing at once. With the SharedOnly isolation profile, requests no longer run on retained queue workers; `MinRequestThreadCount` only starts workers for the other isolation profiles. ## Measurements Paired A/B with `perf/ab.sh`: baseline = #4917 head, candidate = this branch. 20 sessions, SharedOnly. The second commit adds `--isolation sharedonly` to the load harness, because `StandardServer`'s default Balanced profile uses the fair queue and never reaches this path. Quiet run (7 paired rounds, medians, server side): | Scenario | req/s | p99 | server B/req | server CPU µs/req | lock contention | |---|---|---|---|---|---| | read 1 value, 10 in flight | 358k → 407k (+14 %, 7/7 rounds) | 6.2 → 2.8 ms | 2253 → 2241 | 23.2 → 24.1 | −94 % | | read 100 values | 47.0k → 47.4k (+1 %, 7/7 rounds) | 1.98 → 1.96 ms | 52550 → 52480 | 229 → 228 | −99 % | | sub 5×100, pub 100 ms | flat | 9.4 → 9.2 ms | 1821 → 1818 | 24.4 → 25.3 | +12 % | A first run (5 rounds, 6 scenarios) overlapped other sessions' builds, so its throughput varied 4x within each side. Its deterministic numbers agree. Server bytes per request: read 1 value 2336 → 2272, write 100 values 71.7k → 71.8k, browse 32.9k → 32.8k, sub 1825 → 1827. Lock contention was −96 % on every read scenario. ## Tests - New `RequestQueueTests`: - the shared queue starts no workers - permits limit concurrency, and waiters are served in FIFO order (with the executing/queued gauges) - a configured limit below 100 is honoured - stop rejects waiting requests and drains executing and parked handlers - a concurrent stop either halts or runs every request - `Opc.Ua.Core.Tests` `Stack.Server`: 1951 passed (net10.0). net48 build compiles. - `Opc.Ua.Stress.Tests` `Category=Contract|Integration` (not in PR CI): 45/45 passed. - To run the permit path under real servers, I temporarily forced the default isolation mode to SharedOnly (local patch, not committed): - Stress Contract/Integration: 45/45 passed. - `Opc.Ua.Sessions.Tests`: 865 passed, 0 failed, 379 skipped. This includes the load tests. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
OPC UA .NET Standard Stack
🆕 This is version 2.0 of the OPC UA .NET Standard Stack (current
master).Looking for the supported 1.x release? It lives on the
master378branch (last release:1.5.378). All new feature work happens here onmaster;master378continues to receive security and critical-bug fixes for the 1.x line.
The official OPC Foundation reference implementation of OPC UA for .NET — a cross-platform stack with client, server, PubSub, GDS, complex types, and source-generated tooling. Used in production across industrial control, manufacturing, energy, and IoT systems.
📦 What it is
- A full-stack OPC UA implementation — Core / Client / Server / PubSub / GDS / LDS / Complex Types / Device Integration / Positioning libraries built on .NET, with UA-TCP and HTTPS transports.
- Cross-platform — runs on .NET 10, .NET 9, .NET 8 (LTS), .NET Framework 4.8; ships Native-AOT-friendly assemblies.
- Conformance regression testing — the reference server is tested with the Compliance Test Tool (CTT) through the CTT regression workflow. These results identify regressions; they do not constitute product certification.
- Companion-spec coverage — Part 9 (Alarms & Conditions), Part 10 (Programs), Part 11 (Historical Access), Part 13 (Aggregates), Part 16 (State Machines), Part 17 (Alias Names), Part 18 (Role Management), Part 20 (File Transfer), Part 100 (Device Integration), Part 110 (Asset Management Basics), Parts 210/211 (Relative Spatial Location and Global Positioning), OPC-10030 (ISA-95 Common Model) with OPC-10031-4 Job Control V1/V2, OPC 30270 / OPC UA for Asset Administration Shell V2 and V3, OPC 10100-1 (WoT Connectivity), Part 200 (Industrial Automation), OPC 40001-1/-2/-3/-4/-101 (Machinery with Process Values, Job Management, Energy and Result Transfer), OPC 34100 (Energy Consumption Management), OPC 30081 (PA-DIM), OPC 40010-1 (Robotics), OPC 40100-1/-2 (Machine Vision control and asset management), OPC 40501-1 and OPC 40505 (Machine Tools and independent wireless peripherals), OPC 40210 (Geometric Measurement Systems, with its documented upstream Production-facet exception), OPC 40020-1 (Cranes and Hoists), OPC 40223 (Pumps and Vacuum Pumps), OPC 30010 (AutoID Devices), OPC 40200 (Weighing Technology) with OPC 30050 (PackML).
- Hosting and code generation —
Microsoft.Extensions.DependencyInjectionhosting (services.AddOpcUa()), fluent server + client builders, source-generated NodeManagers and DataTypes, and an MCP server so LLMs / Copilot can drive an OPC UA client.
For the full feature breakdown see OPC UA Profiles and Facets and the What's New in 2.0 tour.
🚀 Getting started
To run a first OPC UA client and server, from NuGet packages or from the samples in this repository, follow Getting started. The documentation index then leads from the core concepts to advanced and experimental features.
The recycling operator console demonstrates live browser monitoring, native companion-specification inspection, material genealogy, and authorized controls over the synthetic recycling line.
You need a stable .NET SDK
version 10.0.400 or later to build the repo. global.json selects the
highest installed stable SDK, including newer major versions. From the repository root:
dotnet restore UA.slnx
dotnet build UA.slnx
For the supported target frameworks and platform notes see
the Developer Guide. The official NuGet packages
are published to nuget.org under the OPCFoundation.NetStandard
prefix — the meta package
OPCFoundation.NetStandard.Opc.Ua
bundles a default set of stack packages; see its
package inventory.
Reference PubSub and other optional feature packages separately, or select
individual packages directly, e.g.
OPCFoundation.NetStandard.Opc.Ua.Client for clients or
OPCFoundation.NetStandard.Opc.Ua.Server for servers. Preview builds from
every successful master build are available from the
GitHub Packages NuGet feed,
which is the only feed they are published to. nuget.org receives a version
only through a manually approved promotion from a release/<major>.<minor>
branch — that is where the 2.0.0-preview.N packages already on nuget.org
came from, via the earlier release/2.0.0 line. To use those, enable
prerelease packages and float with 2.0.0-preview.* until 2.0.0 is
released. The XRegistry, WoT Connectivity, Robotics, CranesHoists,
Redundancy, Positioning, OpenUSD, and AI package families, the Vision.OpenUsd
renderer, and the Robotics MCP extension remain
preview packages when the root version is promoted to a stable version, and
keep their own -preview.N versions on nuget.org. This includes all CranesHoists
model/server/client/MCP packages and their Debug variants.
The Vision, MachineVision, MachineTool (including WMTP), and GMS
model/client/server packages and their MCP packages follow the root version
without a preview-only override;
development builds still inherit the root prerelease version. See
docs/ReleaseProcess.md for how and when stable
versions are released.
Samples
The platform-independent sample applications show how to use the stack's core services and companion models in client/server workflows. More applications, including platform-specific examples, are available in the companion OPC UA .NET Samples repository.
Developer tools
- UaLens — NativeAOT-capable desktop engineering workspace for secure connections, monitoring, alarms, structured values, history, administration, PubSub, continuity diagnostics, and guided companion-model tasks. See build and artifact qualification.
- OPC UA MCP Server — installable .NET tool and container exposing OPC UA client operations to LLMs and Copilot. Embeddable libraries provide Part 4 services, PubSub, diagnostics, Robotics and Vision, plus industrial companion profiles for AMB, Machinery, Scales, Pumps, AutoID, Device Integration, ISA-95 and Positioning. The WoT and xRegistry profiles add asset/registry management and bounded document validation, planning and NodeSet conversion. Stack workflow profiles provide GDS/credential issuance, roles/users, files, alarms, history, schemas, and host-authorized PubSub and live WoT execution.
🔧 Migrating from 1.5.378 to 2.0
The 2.0 release introduces breaking API changes, and comes with a full prescriptive migration guide that links to per-area documentation for the migration sub-topics.
Most of the mechanical migration work is automated:
OPCFoundation.NetStandard.Opc.Ua.MigrationAnalyzerNuGet — install it in your project to get 26 analyzer rules throughUA0030(excludingUA0013,UA0016,UA0017, and the shim-onlyUA0029) plus one-click code fixes for the patterns in the guide. Setup steps are in the package's NugetREADME.md.- Migration agent skill — the
opcua-v20-migrationskill walks Copilot / Claude / any coding agent through installing the NuGet, runningdotnet format analyzersto apply auto-fixes, and handling the remaining manual changes. It selects the migration sub-document for each symptom.
Copilot CLI discovers the skill automatically inside a clone. To install it for use in any repository:
copilot plugin marketplace add OPCFoundation/UA-.NETStandard
copilot plugin install opcua-v20-migration@opcua-dotnet
If you are still on 1.x and not ready to upgrade, stay on the
master378
branch — it continues to receive security and critical-bug fixes.
🤝 Contributing and license
Community contributions are welcome. Fork the repository, make your changes on a branch, and open a pull request; see CONTRIBUTING.md for the contribution workflow.
Contributors must sign the OPC Foundation Contributor License Agreement (CLA). The CLA "I AGREE" gate is presented automatically on your first PR.
The project is licensed under the OPC Foundation MIT License. Report security vulnerabilities via the process documented in SECURITY.md.
📚 Further reading
- Documentation index — every per-feature doc with a one-line description.
- What's New in 2.0 — narrative tour of the 1.5.378 → 2.0 changes grouped by theme and layer.
- OPC UA Profiles and Facets — facets / transports / security policies the stack implements.
- Migration Guide — prescriptive
per-version migration reference (links to
docs/migrate/2.0.x/). - OPC UA Online Reference — the official OPC 10000 series specification index.
- Preview Nuget package feed —
prerelease builds from every successful
masterbuild.