// RunScraper implements Target.
func (t *Target) RunScraper(sampleAppender storage.SampleAppender) {
defer close(t.scraperStopped)
lastScrapeInterval := t.interval()
log.Debugf("Starting scraper for target %v...", t)
select {
case <-time.After(t.offset(lastScrapeInterval)):
// Continue after scraping offset.
case <-t.scraperStopping:
return
}
ticker := time.NewTicker(lastScrapeInterval)
defer ticker.Stop()
t.scrape(sampleAppender)
// Explanation of the contraption below:
//
// In case t.scraperStopping has something to receive, we want to read
// from that channel rather than starting a new scrape (which might take very
// long). That's why the outer select has no ticker.C. Should t.scraperStopping
// not have anything to receive, we go into the inner select, where ticker.C
// is in the mix.
for {
select {
case <-t.scraperStopping:
return
default:
select {
case <-t.scraperStopping:
return
case <-ticker.C:
took := time.Since(t.status.LastScrape())
intervalStr := lastScrapeInterval.String()
// On changed scrape interval the new interval becomes effective
// after the next scrape.
if iv := t.interval(); iv != lastScrapeInterval {
ticker.Stop()
ticker = time.NewTicker(iv)
lastScrapeInterval = iv
}
targetIntervalLength.WithLabelValues(intervalStr).Observe(
float64(took) / float64(time.Second), // Sub-second precision.
)
if sampleAppender.NeedsThrottling() {
targetSkippedScrapes.WithLabelValues(intervalStr).Inc()
t.status.setLastError(errSkippedScrape)
continue
}
t.scrape(sampleAppender)
}
}
}
}
