func doWork(ctx context.Context) {
  for {
    select {
    case <-ctx.Done():
      return
    default:
    }

    time.Sleep(1 * time.Second)
    fmt.Println("doing work...")
  }
}

func main() {
  bgCtx := context.Background()
  innerCtx, cancel := context.WithCancel(bgCtx)

  go doWork(innerCtx) // call goroutine
  time.Sleep(3 * time.Second) // do work in main

  // well, if `doWork` is still not done, just cancel it
  cancel()
}