🧵 Goroutine Lab — see and step through 27 Go concurrency patterns

[burrows99]

Goroutine Lab is a hands-on visualizer for Go concurrency — 27 real patterns you can watch run in slow motion, and step through like a debugger.

Every demo is genuine Go (real goroutines, channels, select, context, sync), instrumented so the browser animates what the runtime is actually doing: goroutines starting and blocking, values flowing through channels, mutexes being held, contexts cancelling.

The highlight — open the Go source tab and debug it:

• 🔴 set breakpoints on real statements
• ⏭️ single-step, line by line
• ✨ the executing line highlights in lock-step with the animation

Under the hood it uses Go's own go/ast to strip the instrumentation and map every animation step back to the exact source line, so you read (and step through) clean, idiomatic Go.

Patterns include worker pools, fan-out/fan-in, pipelines, semaphores, rate limiting, pub/sub, mutex vs. the data race, sync.Once, errgroup, graceful shutdown, and the classic goroutine leak (+ the fix).

Stack: Go standard library only, Server-Sent Events, and React + Vite with dependency-free SVG. MIT licensed.

👉 Get started: https://github.com/burrows99/goroutine-lab#install
🎥 There's a 35-second demo right at the top of the README.

Feedback, questions, and PRs are very welcome — adding a new pattern is a great first contribution. What concurrency pattern would you want to see visualized next?