Cancellation

Canonical guidance

• caller owns cancellation intent
• pass cancellation through context.Context
• stop goroutines promptly when ctx.Done() closes
• clean up timers, channels, and spawned work

Use when

• request handlers
• background operations with deadlines
• pipelines and fan-out work

Avoid

• detached goroutines with no stop condition
• custom cancellation channels when context already fits
• ignoring ctx.Err() in long-running loops

Preferred pattern

for {
	select {
	case <-ctx.Done():
		return ctx.Err()
	case item := <-in:
		_ = item
	}
}

Anti-pattern

go func() {
	for item := range in {
		process(item)
	}
}()

• if nothing can stop this loop early, it can leak work

Explanation: This anti-pattern is common in rushed concurrency code because the goroutine appears independent, but without cancellation it can outlive the caller and leak work.

Why

• cancellation is a resource-management concern, not just a timeout feature