From 658914ba276958c992f704f224357dc57b7316b7 Mon Sep 17 00:00:00 2001
From: conorbroderick <cjayjayb@gmail.com>
Date: Thu, 4 Jan 2018 14:13:31 +0000
Subject: [PATCH] Fix dropped target list growing forever

---
 retrieval/scrape.go      |  3 +++
 retrieval/scrape_test.go | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/retrieval/scrape.go b/retrieval/scrape.go
index 8d1173cd5..0d4a55338 100644
--- a/retrieval/scrape.go
+++ b/retrieval/scrape.go
@@ -250,6 +250,8 @@ 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 {
@@ -264,6 +266,7 @@ func (sp *scrapePool) Sync(tgs []*targetgroup.Group) {
 			}
 		}
 	}
+	sp.mtx.Unlock()
 	sp.sync(all)
 
 	targetSyncIntervalLength.WithLabelValues(sp.config.JobName).Observe(
diff --git a/retrieval/scrape_test.go b/retrieval/scrape_test.go
index b3a0466ab..ed82afc37 100644
--- a/retrieval/scrape_test.go
+++ b/retrieval/scrape_test.go
@@ -33,6 +33,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/prometheus/prometheus/config"
+	"github.com/prometheus/prometheus/discovery/targetgroup"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/timestamp"
 	"github.com/prometheus/prometheus/pkg/value"
@@ -58,6 +59,41 @@ func TestNewScrapePool(t *testing.T) {
 	}
 }
 
+func TestDroppedTargetsList(t *testing.T) {
+	var (
+		app = &nopAppendable{}
+		cfg = &config.ScrapeConfig{
+			JobName:        "dropMe",
+			ScrapeInterval: model.Duration(1),
+			RelabelConfigs: []*config.RelabelConfig{
+				{
+					Action:       config.RelabelDrop,
+					Regex:        mustNewRegexp("dropMe"),
+					SourceLabels: model.LabelNames{"job"},
+				},
+			},
+		}
+		tgs = []*targetgroup.Group{
+			{
+				Targets: []model.LabelSet{
+					model.LabelSet{model.AddressLabel: "127.0.0.1:9090"},
+				},
+			},
+		}
+		sp                     = newScrapePool(cfg, app, nil)
+		expectedLabelSetString = "{__address__=\"127.0.0.1:9090\", __metrics_path__=\"\", __scheme__=\"\", job=\"dropMe\"}"
+		expectedLength         = 1
+	)
+	sp.Sync(tgs)
+	sp.Sync(tgs)
+	if len(sp.droppedTargets) != expectedLength {
+		t.Fatalf("Length of dropped targets exceeded expected length, expected %v, got %v", expectedLength, len(sp.droppedTargets))
+	}
+	if sp.droppedTargets[0].DiscoveredLabels().String() != expectedLabelSetString {
+		t.Fatalf("Got %v, expected %v", sp.droppedTargets[0].DiscoveredLabels().String(), expectedLabelSetString)
+	}
+}
+
 type testLoop struct {
 	startFunc func(interval, timeout time.Duration, errc chan<- error)
 	stopFunc  func()