Add another check for stopped scraper.

retrieval/target.go

@@ -277,6 +277,13 @@ func (t *target) RunScraper(ingester extraction.Ingester, interval time.Duration
 				// actual scrape interval increase as long as a scrape takes
 				// longer than the interval we are aiming for.
 				time.Sleep(took - interval)
+				// After the sleep, we should check again if we have been stopped.
+				select {
+				case <-t.scraperStopping:
+					return
+				default:
+					// Do nothing.
+				}
 				t.scrape(ingester)
 			}
 		}