Marek LinkaandMarc Schier
4018bfec91
# Description As already discussed in #3173, there is a significant memory leak in the way complex types are handled in the original, reflection-based `ComplexTypeSystem`. Even though there is now a newer version of this code that does not use reflection, the reflection code is still available for consumers, meaning the leak can still impact people out there. With a minimal repro (attached), I managed to isolate the issue a bit further than the original report. The leak was not just kernel handles for events or semaphores but the whole dynamic assembly - with the `AssemblyBuilderAccess.Run` flag set, the GC could never free that assembly. Changing the flag to `RunAndCollect` resolves that problem, allowing the dynamic assembly to be collected once all references to it are lost. My repro code proves that the assembly gets collected and memory no longer accumulates with each `complexTypeSystem.LoadAsync`. ### Repro Simple single-file C# project, should be pointed to a checkout of this repo via a project reference to allow compilation. It runs a loop of opening and closing a session, each session then uses `ComplexTypeBuilderFactory` to build the dynamic assembly of complex types. Each session is then disconnected and disposed. Every 100 iterations, the repro forces full GC and reports several statistics: current GC-managed memory, current proces private memory, number of the generated dynamic assemblies (counted via name), and total number of open handles. [repro.zip](https://github.com/user-attachments/files/32555109/repro.zip) ### Repro output `AssemblyBuilderAccess.Run`: ``` [Start] Memory consumption: [GC] 3641352, [Private] 36499456, [DynamicAssemblies] 0, [Handles] 381 [Step 0] Memory consumption: [GC] 10459408, [Private] 50515968, [DynamicAssemblies] 1, [Handles] 401 [Step 100] Memory consumption: [GC] 10568320, [Private] 75034624, [DynamicAssemblies] 101, [Handles] 614 [Step 200] Memory consumption: [GC] 10539488, [Private] 93138944, [DynamicAssemblies] 201, [Handles] 814 [Step 300] Memory consumption: [GC] 10933536, [Private] 113786880, [DynamicAssemblies] 301, [Handles] 1015 [Step 400] Memory consumption: [GC] 11031496, [Private] 140181504, [DynamicAssemblies] 401, [Handles] 1215 [Step 500] Memory consumption: [GC] 11064296, [Private] 161914880, [DynamicAssemblies] 501, [Handles] 1415 [Step 600] Memory consumption: [GC] 11094168, [Private] 180477952, [DynamicAssemblies] 601, [Handles] 1608 [Step 700] Memory consumption: [GC] 11127368, [Private] 207298560, [DynamicAssemblies] 701, [Handles] 1811 [Step 800] Memory consumption: [GC] 11160168, [Private] 228204544, [DynamicAssemblies] 801, [Handles] 2008 ... ``` As you can see, each iteration leads to a new dynamic assembly being created and they are all being retained, even though the sessions they belong to have been disposed. This also means increase in kernel handles and the process' private memory (about 200 kB per session, not a trivial amount). `AssemblyBuilderAccess.RunAndCollect`: ``` [Start] Memory consumption: [GC] 3641400, [Private] 36446208, [DynamicAssemblies] 0, [Handles] 379 [Step 0] Memory consumption: [GC] 10630800, [Private] 50372608, [DynamicAssemblies] 1, [Handles] 401 [Step 100] Memory consumption: [GC] 10982808, [Private] 53596160, [DynamicAssemblies] 1, [Handles] 410 [Step 200] Memory consumption: [GC] 11048288, [Private] 46280704, [DynamicAssemblies] 1, [Handles] 413 [Step 300] Memory consumption: [GC] 10956664, [Private] 45817856, [DynamicAssemblies] 1, [Handles] 417 [Step 400] Memory consumption: [GC] 10915352, [Private] 47124480, [DynamicAssemblies] 1, [Handles] 410 [Step 500] Memory consumption: [GC] 10914776, [Private] 44843008, [DynamicAssemblies] 1, [Handles] 410 [Step 600] Memory consumption: [GC] 10890776, [Private] 44810240, [DynamicAssemblies] 1, [Handles] 408 [Step 700] Memory consumption: [GC] 10916144, [Private] 46235648, [DynamicAssemblies] 1, [Handles] 408 [Step 800] Memory consumption: [GC] 10901248, [Private] 45531136, [DynamicAssemblies] 1, [Handles] 411 ... ``` This time, we only ever retain a single dynamic assembly, the one being used for the currently open session, which is expected. The memory footprint stays flat, as does the number of open handles. ## Related Issues Fixes #3173 ## Checklist _Put an `x` in the boxes that apply. You can complete these step by step after opening the PR._ - [x] I have signed the [CLA](https://opcfoundation.org/license/cla/ContributorLicenseAgreementv1.0.pdf) and read the [CONTRIBUTING](https://github.com/OPCFoundation/UA-.NETStandard/blob/master/CONTRIBUTING.md) doc. - [x] I have added tests that prove my fix is effective or that my feature works and increased code coverage. - [ ] I have added all necessary documentation. - [ ] I have verified that my changes do not introduce (new) build or analyzer warnings. - [ ] I ran **all** tests locally using the **UA.slnx** solution against at least .net **framework** and .net **10**, and all passed. - [ ] I fixed **all** failing and flaky tests in the CI pipelines and **all** CodeQL warnings. - [ ] I have addressed **all** PR feedback received. --------- Co-authored-by: Marc Schier <marcschier@users.noreply.github.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 certified, 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, and .NET Standard 2.1; ships Native-AOT-friendly assemblies.
- Certified for compliance — the reference server has been certified through an OPC Foundation Certification Test Lab and is continuously verified against the latest Compliance Test Tool (CTT).
- Companion-spec coverage — Part 9 (Alarms & Conditions), 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), 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), OPC 40001-1 (Industrial Automation), OPC 40010-1 (Robotics).
- Modern developer surface — first-class
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
You need the .NET 10 SDK to build the repo. 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
pulls in everything, or reference 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, Vision, Robotics,
Redundancy, Positioning, OpenUSD, ISA95, AI, and DI package families remain
preview packages when the root version is promoted to a stable version, and
keep their own -preview.N versions on nuget.org. See
docs/ReleaseProcess.md for how and when stable
versions are released.
Samples
The stack also includes a large collection of platform-independent sample applications that turn its core services and companion models into runnable client/server workflows. More applications, including platform-specific examples, are available in the companion OPC UA .NET Samples repository.
Developer tools
- OPC UA MCP Server — installable .NET tool and container that exposes OPC UA client operations as MCP tools for LLMs and Copilot. The tools also ship as libraries (
…Opc.Ua.Mcp.Core,.PubSub,.Diagnostics,.PubSub.Diagnostics) so an application can embed them next to its own MCP tools.
🔧 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 small residual manual patterns. The skill knows which sub-doc to load for each symptom so it stays context-efficient.
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.