Build the safeguards
Eight explained steps, tradeoffs, pitfalls and a checkpoint before moving on.
Read the tutorialGo / Concurrency / Cancellation
Who left these workers running?
The customer cancels. The collector stops. The workers keep waiting. See the difference between starting concurrent work and owning its whole lifetime.
The idea in plain language
A goroutine needs an owner and a way to finish. A bounded worker pool limits active work; cancellation must reach both producers and workers; joining them establishes that shutdown has actually completed.
The browser runs the same Go engine compiled to WebAssembly inside a dedicated worker. Goroutines run concurrently, but this browser target is not a multicore throughput benchmark. A harness cleans up the deliberately blocked example after recording it. The native download includes an HTTP adapter and Go tests.
Your independent testing environment
Make the failure visible.
Keep the default 12 messages, 3 workers and early cancellation. Run without safeguards, then with safeguards. Compare peak active work and workers left at cancellation. Reset starts over and stops pending work.
Ready to try
—Peak active work
—Messages completed
—Workers at cancellation
—Workers after cleanup
Follow the decision
Inspect the result
Your result and database records will appear here.
Why the change matters
Show the canceled collector first. Explain who owns the queue, who closes it, how blocked work stops and why the function waits for workers. Separate concurrency safety from the delivery guarantee.
Use the code viewer to inspect the original source that produced this release. Each file is checked against the release manifest before it is displayed. The complete download includes the runnable example, tests, setup instructions and third-party notices.
Keep exploring
Follow the question you have next.
Compare the choices
Choose a pattern and an environment for the problem you actually have.
Compare approachesTry it on your own
A beginner route, a local setup and an extension challenge.
Open the how-to guideQuestions before you start
Do I need to know how to code?
No. Start with the default example, read the trace and compare the two implementations. The tutorial introduces the code after you have seen the result.
Does this use real customer data or send anything?
No. Examples use invented records and simulated downstream work. Each lab keeps its own transient environment; resetting it stops the experiment.
What can this experiment prove?
The browser runs the same Go engine compiled to WebAssembly inside a dedicated worker. Goroutines run concurrently, but this browser target is not a multicore throughput benchmark. A harness cleans up the deliberately blocked example after recording it. The native download includes an HTTP adapter and Go tests.
Can I use or change the source?
The original lesson and application source are MIT-licensed. Third-party runtimes retain their own licenses. Download the package and follow GETTING_STARTED before changing it.