scrape/scrape.go
func (sp *scrapePool) Sync(tgs []*targetgroup.Group) {
	start := time.Now()

	var all []*Target
	sp.mtx.Lock()
	sp.droppedTargets = []*Target{}
	for _, tg := range tgs {
		targets, err := targetsFromGroup(tg, sp.config)
		if err != nil {
			level.Error(sp.logger).Log("msg", "creating targets failed", "err", err)
			continue
		}
		for _, t := range targets {
			if t.Labels().Len() > 0 {
				all = append(all, t)
			} else if t.DiscoveredLabels().Len() > 0 {
				sp.droppedTargets = append(sp.droppedTargets, t)
			}
		}
	}
	sp.mtx.Unlock()
	sp.sync(all)

	targetSyncIntervalLength.WithLabelValues(sp.config.JobName).Observe(
		time.Since(start).Seconds(),
	)
	targetScrapePoolSyncsCounter.WithLabelValues(sp.config.JobName).Inc()
}
func (sp *scrapePool) Sync(tgs []*targetgroup.Group) {
	start := time.Now()

	var all []*Target
	sp.mtx.Lock()
	sp.droppedTargets = []*Target{}
	for _, tg := range tgs {
		targets, err := targetsFromGroup(tg, sp.config)
		if err != nil {
			level.Error(sp.logger).Log("msg", "creating targets failed", "err", err)
			continue
		}
		for _, t := range targets {
			if t.Labels().Len() > 0 {
				all = append(all, t)
			} else if t.DiscoveredLabels().Len() > 0 {
				sp.droppedTargets = append(sp.droppedTargets, t)
			}
		}
	}
	sp.mtx.Unlock()
	sp.sync(all)

	targetSyncIntervalLength.WithLabelValues(sp.config.JobName).Observe(
		time.Since(start).Seconds(),
	)
	targetScrapePoolSyncsCounter.WithLabelValues(sp.config.JobName).Inc()
}
// Sync converts target groups into actual scrape targets and synchronizes
// the currently running scraper with the resulting set and returns all scraped and dropped targets.