Blazor Multi-threaded Benchmarking (.NET 10)

This project demonstrates a high-performance, multi-threaded Blazor WebAssembly application using .NET 10. It enables native C# threading and the Task Parallel Library (TPL) within the browser environment.

Architecture & Implementation

1. WebAssembly Threads

The project is configured to use the WasmEnableThreads capability of the .NET WebAssembly runtime. This allows the instantiation of real background Web Workers that map directly to .NET Threads.

• Configuration: Enabled via <WasmEnableThreads>true</WasmEnableThreads> in Client.csproj.
• Worker Pool: Presets a pool of 4 workers using <WasmWorkerPoolSize>4</WasmWorkerPoolSize> to reduce startup latency.

2. COOP/COEP Header Injection (The Service Worker Hack)

Browser security requirements for SharedArrayBuffer (required for multi-threading) necessitate specific cross-origin isolation headers. Since standard local development servers often don't provide these, we utilize a Service Worker interception strategy.

• Mechanism: The Service Worker (service-worker.js) intercepts all fetch requests and appends:
  • Cross-Origin-Embedder-Policy: require-corp
  • Cross-Origin-Opener-Policy: same-origin
• Bootstrapping: index.html includes a script that detects if the page is crossOriginIsolated. If not, and a service worker controller is present, it forces a reload to apply the headers to the current session.

3. Debugger Optimization

Multithreading in Blazor WASM can cause "phantom breakpoints" or startup hitches when the .NET Debug Proxy attempts to synchronize worker threads.

• Fix: The inspectUri has been removed from launchSettings.json to prevent the debug proxy from attaching to workers.
• Filtering: The Service Worker explicitly ignores traffic to _framework/debug and _framework/blazor-hotreload to ensure initialization messages are not modified.

Benchmarks

The application includes several workloads designed to stress background threads while keeping the main UI thread at a consistent 144 FPS:

• CPU Threads: Intensive prime number calculation (Thread and Task.Run).
• Memory Stress: Massive array allocations and concurrent Array.Sort operations.
• Parallel TPL: Demonstrates Parallel.For with configurable degrees of parallelism.

Project Structure

• /Pages: Benchmark implementations and the UI thread FPS visualizer.
• /Components: SmoothnessVisualizer.razor monitors the main thread responsiveness.
• /wwwroot/service-worker.js: The header injection engine.
• Client.csproj: MSBuild properties for threading and stability.

How to Run

1. Navigate to src/Client.
2. Execute dotnet run.
3. Open the browser and ensure the Service Worker is active.
4. Note: If headers are not applying, unregister the Service Worker in DevTools and perform a Hard Refresh (Ctrl+F5).

Requirements

• .NET 10 SDK or higher.
• A modern browser with SharedArrayBuffer support (Chrome, Edge, Firefox).