#golang#sync#waitgroup

group.go

	var (
		wg            sync.WaitGroup
		seriesSetChan = make(chan genericSeriesSet)
	)
	// Schedule all Selects for all queriers we know about.
	for _, querier := range q.queriers {
		wg.Add(1)
		go func(qr genericQuerier) {
			defer wg.Done()

			// We need to sort for NewMergeSeriesSet to work.
			seriesSetChan <- qr.Select(true, hints, matchers...)
		}(querier)
	}
	go func() {
		wg.Wait()
		close(seriesSetChan)
	}()

	// 获取series
	for r := range seriesSetChan {
		seriesSets = append(seriesSets, r)
	}