code: func NewManager(logger log.Logger, app Appendable) *Manager {
  	if logger == nil {
  		logger = log.NewNopLogger()
  	}
  	return &Manager{
  		append:        app,
  		logger:        logger,
  		scrapeConfigs: make(map[string]*config.ScrapeConfig),
  		scrapePools:   make(map[string]*scrapePool),
  		graceShut:     make(chan struct{}),
  		triggerReload: make(chan struct{}, 1),
  	}
  }
docs: // NewManager is the Manager constructor