---

name: concurrency description: Goroutine ownership, errgroup patterns, worker pools, and graceful shutdown. Use when writing concurrent code or parallel request handling. userInvokable: true

Concurrency

References: Examples

Core Rule

No fire-and-forget goroutines. Every goroutine must have managed lifecycle.

Pattern Selection

Do / Don't

errgroup for Parallel Requests

Example

Copyg, ctx := errgroup.WithContext(ctx)

g.Go(func() error { return fetchA(ctx) })
g.Go(func() error { return fetchB(ctx) })
g.Go(func() error { return fetchC(ctx) })

if err := g.Wait(); err != nil {
    return fmt.Errorf("parallel fetch: %w", err)
}

Bounded Concurrency

Example

Copyg, ctx := errgroup.WithContext(ctx)
g.SetLimit(10)  // Max 10 concurrent goroutines

for _, item := range items {
    item := item
    g.Go(func() error { return process(ctx, item) })
}

return g.Wait()

Worker Pool

Example

For high-volume processing with backpressure control.

Graceful Shutdown

Example

Always handle context cancellation in long-running goroutines.