How do you correctly propagate errors from concurrent goroutines in a Go service?

When multiple goroutines run in parallel, errors must be collected and propagated without data races or goroutine leaks. The idiomatic tools are errgroup for structured concurrency and buffered channels for ad-hoc patterns.

import "golang.org/x/sync/errgroup"

// Pattern 1: errgroup — run N tasks, fail fast on first error
func fetchUserProfile(ctx context.Context, userID int) (*Profile, error) {
    g, ctx := errgroup.WithContext(ctx)
    // gctx cancelled when any goroutine fails or g.Wait() returns

    var user *User
    g.Go(func() error {
        var err error
        user, err = userRepo.FindByID(ctx, userID)
        return fmt.Errorf("fetching user: %w", err)
    })

    var orders []Order
    g.Go(func() error {
        var err error
        orders, err = orderRepo.ListByUser(ctx, userID)
        return fmt.Errorf("fetching orders: %w", err)
    })

    if err := g.Wait(); err != nil {
        return nil, err // first error from any goroutine
    }
    return buildProfile(user, orders), nil
}

// Pattern 2: collect ALL errors (don't fail fast)
func validateItems(ctx context.Context, items []Item) error {
    errs := make([]error, len(items))
    var wg sync.WaitGroup
    wg.Add(len(items))

    for i, item := range items {
        go func(idx int, it Item) {
            defer wg.Done()
            errs[idx] = validateItem(ctx, it) // each goroutine writes its own slot
        }(i, item)
    }
    wg.Wait()

    // Filter nil errors and join
    var nonNil []error
    for _, e := range errs { if e != nil { nonNil = append(nonNil, e) } }
    return errors.Join(nonNil...)
}

// errgroup with concurrency limit (Go 1.20+)
g.SetLimit(10)  // max 10 goroutines running at once
for _, item := range items {
    item := item
    g.Go(func() error { return process(ctx, item) })
}

Invest now in Acorns!!! 🚀
Join Acorns and get your $5 bonus!

Acorns is a micro-investing app that automatically invests your "spare change" from daily purchases into diversified, expert-built portfolios of ETFs. It is designed for beginners, allowing you to start investing with as little as $5. The service automates saving and investing. Disclosure: I may receive a referral bonus.

Invest now!!! Get Free equity stock (US, UK only)!

Use Robinhood app to invest in stocks. It is safe and secure. Use the Referral link to claim your free stock when you sign up!.

The Robinhood app makes it easy to trade stocks, crypto and more.

Webull! Receive free stock by signing up using the link: Webull signup.