concurrency-patterns-go

Go Concurrency Patterns

Write safe, efficient concurrent Go code using goroutines, channels, sync primitives, and context-based cancellation.

When to Use

• Processing items concurrently (HTTP requests, file I/O, computations)
• Building worker pools for bounded concurrency
• Coordinating multiple goroutines with channels or sync primitives
• Implementing timeouts and cancellation with context.Context
• Designing fan-in/fan-out data pipelines

Core Patterns

Pattern 1: Goroutines with sync.WaitGroup

Spawn goroutines and wait for all to complete.

func processItems(items []Item) error {
    var (
        wg   sync.WaitGroup
        mu   sync.Mutex
        errs []error
    )

    for _, item := range items {
        wg.Add(1)
        go func() {
            defer wg.Done()
            if err := process(item); err != nil {
                mu.Lock()
                errs = append(errs, fmt.Errorf("item %s: %w", item.ID, err))
                mu.Unlock()
            }
        }()
    }

    wg.Wait()
    return errors.Join(errs...)
}

Pattern 2: Worker Pool with Bounded Concurrency

Limit concurrent work to avoid overwhelming resources.

func workerPool(ctx context.Context, jobs <-chan Job, workers int) <-chan Result {
    results := make(chan Result, workers)

    var wg sync.WaitGroup
    for range workers {
        wg.Add(1)
        go func() {
            defer wg.Done()
            for job := range jobs {
                select {
                case <-ctx.Done():
                    return
                default:
                    result, err := processJob(ctx, job)
                    if err != nil {
                        results <- Result{Err: err}
                        continue
                    }
                    results <- Result{Data: result}
                }
            }
        }()
    }

    go func() {
        wg.Wait()
        close(results)
    }()

    return results
}

// Usage
func run(ctx context.Context) error {
    jobs := make(chan Job, 100)

    go func() {
        defer close(jobs)
        for _, j := range allJobs {
            select {
            case jobs <- j:
            case <-ctx.Done():
                return
            }
        }
    }()

    for result := range workerPool(ctx, jobs, 10) {
        if result.Err != nil {
            slog.Error("job failed", "error", result.Err)
            continue
        }
        handleResult(result.Data)
    }
    return nil
}