func worker(ctx context.Context, jobs <-chan Job, results chan<- Result) {
    for {
        select {
        case <-ctx.Done():
            return
        case job, ok := <-jobs:
            if !ok {
                return
            }
            result := process(job)
            select {
            case results <- result:
            case <-ctx.Done():
                return
            }
        }
    }
}