fix(ddtrace/tracer): TestTracerTwiceStartRuntimeMetrics (#4086)

Co-authored-by: felix.geisendoerfer <[email protected]>

Author: felixge

ddtrace/tracer/tracer.go

@@ -234,6 +234,16 @@ func Start(opts ...StartOption) error {
 		return nil
 	}
 
+	if t.config.runtimeMetricsV2 {
+		l := slog.New(slogHandler{})
+		opts := &runtimemetrics.Options{Logger: l}
+		if t.runtimeMetrics, err = runtimemetrics.NewEmitter(t.statsd, opts); err == nil {
+			l.Debug("Runtime metrics v2 enabled.")
+		} else {
+			l.Error("Failed to enable runtime metrics v2", "err", err.Error())
+		}
+	}
+
 	// Start AppSec with remote configuration
 	cfg := remoteconfig.DefaultClientConfig()
 	cfg.AgentURL = t.config.agentURL.String()
@@ -454,15 +464,6 @@ func newTracer(opts ...StartOption) (*tracer, error) {
 			t.reportRuntimeMetrics(defaultMetricsReportInterval)
 		}()
 	}
-	if c.runtimeMetricsV2 {
-		l := slog.New(slogHandler{})
-		opts := &runtimemetrics.Options{Logger: l}
-		if t.runtimeMetrics, err = runtimemetrics.NewEmitter(t.statsd, opts); err == nil {
-			l.Debug("Runtime metrics v2 enabled.")
-		} else {
-			l.Error("Failed to enable runtime metrics v2", "err", err.Error())
-		}
-	}
 	if c.debugAbandonedSpans {
 		log.Info("Abandoned spans logs enabled.")
 		t.abandonedSpansDebugger = newAbandonedSpansDebugger()

ddtrace/tracer/tracer_test.go

@@ -2924,3 +2924,19 @@ func TestNewUnstartedTracerDDAgentHostNotFound(t *testing.T) {
 	_, err := newUnstartedTracer()
 	assert.NoError(t, err)
 }
+
+func TestTracerTwiceStartRuntimeMetrics(t *testing.T) {
+	// This checks that starting the tracer twice properly shuts down the
+	// previous tracer, specifically the runtime metrics emitter.
+	tp := new(log.RecordLogger)
+	err := Start(WithLogger(tp))
+	require.NoError(t, err)
+	err = Start(WithLogger(tp))
+	require.NoError(t, err)
+	Stop()
+
+	// Check that runtime metrics emitters lifetimes did not overlap.
+	for _, logMsg := range tp.Logs() {
+		assert.NotContains(t, logMsg, "runtimemetrics has already been started")
+	}
+}