How does the select statement work in Go and what are its key properties?

// Basic select — whichever channel has data first
ch1 := make(chan string, 1)
ch2 := make(chan string, 1)
ch1 <- "one"
ch2 <- "two"
select {
case msg := <-ch1:
    fmt.Println("ch1:", msg)
case msg := <-ch2:
    fmt.Println("ch2:", msg)
}
// If MULTIPLE cases are ready: Go picks ONE AT RANDOM

// Non-blocking operation with default
ch := make(chan int, 1)
select {
case v := <-ch:
    fmt.Println("received:", v)
default:
    fmt.Println("no value ready — returns immediately")
}

// Timeout pattern
func fetchWithTimeout(url string, d time.Duration) ([]byte, error) {
    result := make(chan []byte, 1) // buffered — prevents goroutine leak!
    go func() {
        resp, _ := http.Get(url)
        body, _ := io.ReadAll(resp.Body)
        result <- body
    }()
    select {
    case data := <-result:
        return data, nil
    case <-time.After(d):
        return nil, fmt.Errorf("timeout after %v", d)
    }
}

// Cancellation with context (production preferred)
func processJobs(ctx context.Context, jobs <-chan Job) {
    for {
        select {
        case <-ctx.Done():
            return
        case job, ok := <-jobs:
            if !ok { return }
            process(job)
        }
    }
}