C# Runtime

This page documents how the .polybench/runtime-env/csharp/ project is set up, how codegen works, and how execution is performed.

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Overview

The C# runtime uses a .NET project. The generated benchmark code overwrites Program.cs. poly-bench writes global.json to pin the SDK version (e.g. 8.0.0 for net8.0). The target framework defaults to net8.0. The runtime crate is runtimes-csharp; templates come from poly-bench-project.

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What Init Does

When you run poly-bench init --languages csharp, poly-bench:

1. Creates .polybench/runtime-env/csharp/
2. Writes polybench.csproj with target framework from [csharp] target_framework (default net8.0)
3. Writes Program.cs with a minimal public static void Main() {} placeholder
4. Writes NuGet.config with the vs-impl feed (for roslyn-language-server and other .NET tools)

No dotnet restore at init. Dependencies are restored when you run poly-bench build or when the executor runs dotnet build.

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What Build/Install Does

When you run poly-bench build or poly-bench install:

1. Regenerates polybench.csproj if --force is used
2. Adds user dependencies from [csharp] dependencies to the csproj
3. Runs dotnet restore (skipped with --skip-install)

The executor writes global.json at run time to pin the SDK version (e.g. 8.0.0 for net8.0). This ensures dotnet build uses the correct SDK even when multiple SDKs are installed.

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Design Rationale

• Overwrite Program.cs — Same pattern as Rust: codegen produces a complete program. The placeholder exists for a valid project structure before the first run.
• global.json at run time — The executor writes it when executing benchmarks. Pinning the SDK avoids "which SDK?" ambiguity when the user has .NET 6, 7, and 8 installed.
• Default net8.0 — .NET 8 is the current LTS. Override in polybench.toml if you have only .NET 6 or 7.
• NuGet.config vs-impl feed — Some .NET tools (e.g. roslyn-language-server) are published to the vs-impl feed. Adding it ensures dotnet tool install and restore can resolve them.
• UseAppHost: false — Reduces build output; the benchmark runs via dotnet run or by invoking the DLL directly.

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Scaffolded Files (Init/Build)

When you run poly-bench init --languages csharp or poly-bench build, the following is created in .polybench/runtime-env/csharp/:

The global.json ensures dotnet build uses the correct SDK. Override the target framework in polybench.toml: [csharp] target_framework = "net9.0".

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Codegen

When poly-bench run executes a benchmark, the C# runtime:

1. Calls generate_csharp_source(spec, suite, for_check) in runtimes-csharp/src/codegen.rs
2. Produces a complete Program.cs with: fixture decoding, setup/init code, helper functions, and the benchmark loop
3. Writes the source to Program.cs (overwriting the placeholder)

Generated files:

• Program.cs — overwritten with full benchmark harness

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Build Pipeline

The executor uses dotnet run which builds and runs. The global.json pin ensures the correct SDK is used.

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Execution Model

1. Precompile: Write Program.cs, run dotnet build
2. Run: Spawn dotnet run (or equivalent) with the benchmark name and iterations
3. Collect: Parse stdout for timing output

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Technical Gotchas

• Default net8.0 — Target framework defaults to net8.0. Override in polybench.toml if you have .NET 6 or 7 only.
• global.json pins SDK — poly-bench writes global.json to pin the SDK version. Ensures dotnet build uses the correct SDK.
• LSP: csharp-ls — poly-bench uses csharp-ls 0.16.0 for .NET 8; newer versions may require .NET 10.

See Requirements — C# for user-facing setup and gotchas.