How does the select statement work with multiple channels, including a default case?

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Accepted Answer

// Basic select with timeout and cancellation
func fetchWithTimeout(ctx context.Context, id string) (*User, error) {
    resultCh := make(chan *User, 1)
    errCh := make(chan error, 1)

go func() {
        user, err := db.FindUser(id)
        if err != nil { errCh <- err; return }
        resultCh <- user
    }()

select {
    case user := <-resultCh:
        return user, nil
    case err := <-errCh:
        return nil, err
    case <-ctx.Done():
        return nil, ctx.Err() // timeout or cancellation
    }
}

// Non-blocking send with default
func tryNotify(ch chan<- Event, event Event) bool {
    select {
    case ch <- event:
        return true
    default:
        // channel full or no receiver — drop or handle
        return false
    }
}

// Ticker + done channel pattern
func heartbeat(ctx context.Context) {
    ticker := time.NewTicker(5 * time.Second)
    defer ticker.Stop()
    for {
        select {
        case <-ticker.C:
            sendPing()
        case <-ctx.Done():
            return
        }
    }
} When multiple cases are ready, select picks one uniformly at random — no priority ordering Nil channels are never ready — use this to dynamically disable a case time.After creates a new timer and channel on every call — use time.NewTimer in loops to avoid leaks default makes select non-blocking — runs immediately if no channel is ready select with only a default case and no channels is a spin loop — avoid

How does the select statement work with multiple channels, including a default case?

select blocks until one of its cases can proceed, choosing randomly when multiple are ready. A default case makes it non-blocking, executing immediately if no channel is ready.

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