plugin/metrcs: fix datarace on listeners (#2835)

This fixes a data race on the listener(s) that get started in the
metrics plugins.

It also restore pkg/uniq to its former glory and removes and state being
carried in there; this means for metrics that registry.go was to
replicate that behavior *with* locking (as pkg/uniq doesn't do, or need
that).

Also renamed uniqAddr to just u, to make it slightly shorter.

Signed-off-by: Miek Gieben <miek@miek.nl>

1 files changed, 18 insertions, 11 deletions

diff --git a/plugin/metrics/metrics.go b/plugin/metrics/metrics.go
index acf31c0a8..2b165e5b9 100644
--- a/plugin/metrics/metrics.go
+++ b/plugin/metrics/metrics.go
@@ -15,22 +15,24 @@ import (
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-// Metrics holds the prometheus configuration. The metrics' path is fixed to be /metrics
+// Metrics holds the prometheus configuration. The metrics' path is fixed to be /metrics .
 type Metrics struct {
-	Next    plugin.Handler
-	Addr    string
-	Reg     *prometheus.Registry
+	Next plugin.Handler
+	Addr string
+	Reg  *prometheus.Registry
+
 	ln      net.Listener
 	lnSetup bool
-	mux     *http.ServeMux
-	srv     *http.Server
+
+	mux *http.ServeMux
+	srv *http.Server
 
 	zoneNames []string
 	zoneMap   map[string]struct{}
 	zoneMu    sync.RWMutex
 }
 
-// New returns a new instance of Metrics with the given address
+// New returns a new instance of Metrics with the given address.
 func New(addr string) *Metrics {
 	met := &Metrics{
 		Addr:    addr,
@@ -101,14 +103,19 @@ func (m *Metrics) OnStartup() error {
 
 	m.ln = ln
 	m.lnSetup = true
-	ListenAddr = m.ln.Addr().String() // For tests
 
 	m.mux = http.NewServeMux()
 	m.mux.Handle("/metrics", promhttp.HandlerFor(m.Reg, promhttp.HandlerOpts{}))
-	m.srv = &http.Server{Handler: m.mux}
+
+	// creating some helper variables to avoid data races on m.srv and m.ln
+	server := &http.Server{Handler: m.mux}
+	m.srv = server
+
 	go func() {
-		m.srv.Serve(m.ln)
+		server.Serve(ln)
 	}()
+
+	ListenAddr = ln.Addr().String() // For tests.
 	return nil
 }
 
@@ -117,7 +124,7 @@ func (m *Metrics) OnRestart() error {
 	if !m.lnSetup {
 		return nil
 	}
-	uniqAddr.Unset(m.Addr)
+	u.Unset(m.Addr)
 	return m.stopServer()
 }