Go context propagation and cancellation patterns

Need to properly propagate cancellation signals through goroutine hierarchies and clean up resources.

Use context.WithCancel/WithTimeout/WithDeadline for hierarchical cancellation.

func processRequest(ctx context.Context) error {
    // Create child context with timeout
    ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
    defer cancel() // Always defer cancel

    // Pass context to all downstream calls
    result, err := fetchData(ctx)
    if err != nil {
        return err
    }

    // Check cancellation in long loops
    for _, item := range result.Items {
        select {
        case <-ctx.Done():
            return ctx.Err()
        default:
            process(item)
        }
    }
    return nil
}

Rules:

1. Always pass context as first parameter
2. Always defer cancel()
3. Check ctx.Done() in loops
4. Never store context in structs

Context cancellation prevents goroutine leaks and ensures resources are freed when parent operations complete or time out.

Any Go application with concurrent operations or HTTP handlers