metrics: fix goroutine leak in meterTicker loop

metrics/meter.go

@@ -124,35 +124,95 @@ func (m *Meter) tick() {
 	m.a15.tick()
 }
 
-var arbiter = meterTicker{meters: make(map[*Meter]struct{})}
+var arbiter = newMeterTicker()
 
 // meterTicker ticks meters every 5s from a single goroutine.
 // meters are references in a set for future stopping.
 type meterTicker struct {
 	mu       sync.RWMutex
-
-	once   sync.Once
+	quit     chan struct{}
+	started  bool
 	meters   map[*Meter]struct{}
+	running  bool
+	initOnce sync.Once
 }
 
-// add a *Meter to the arbiter
+// newMeterTicker creates a new meterTicker.
+func newMeterTicker() *meterTicker {
+	return &meterTicker{
+		meters: make(map[*Meter]struct{}),
+		quit:   make(chan struct{}),
+	}
+}
+
+// add adds another *Meter to the arbiter, and lazily starts the arbiter ticker
+// only when metrics are enabled and at least one meter is added.
 func (ma *meterTicker) add(m *Meter) {
 	ma.mu.Lock()
 	defer ma.mu.Unlock()
+
 	ma.meters[m] = struct{}{}
+
+	// Only start the ticker if metrics are enabled and we haven't started yet
+	if metricsEnabled && !ma.started {
+		ma.initOnce.Do(func() {
+			ma.started = true
+			ma.running = true
+			go ma.loop()
+		})
+	}
 }
 
 // remove removes a meter from the set of ticked meters.
 func (ma *meterTicker) remove(m *Meter) {
 	ma.mu.Lock()
+	defer ma.mu.Unlock()
+
 	delete(ma.meters, m)
-	ma.mu.Unlock()
+
+	// If we have no more meters and the ticker is running, consider stopping
+	if len(ma.meters) == 0 && ma.running {
+		ma.stop()
+	}
 }
 
-// loop ticks meters on a 5-second interval.
+// stop stops the ticker goroutine.
+func (ma *meterTicker) stop() {
+	if ma.running {
+		close(ma.quit)
+		ma.running = false
+		ma.started = false
+		// Create a new quit channel for future use
+		ma.quit = make(chan struct{})
+		// Reset the init once so we can start again if needed
+		ma.initOnce = sync.Once{}
+	}
+}
+
+// ensureStarted ensures the ticker is started if metrics are enabled
+// and there are meters to process.
+func (ma *meterTicker) ensureStarted() {
+	ma.mu.Lock()
+	defer ma.mu.Unlock()
+
+	if metricsEnabled && len(ma.meters) > 0 && !ma.started {
+		ma.initOnce.Do(func() {
+			ma.started = true
+			ma.running = true
+			go ma.loop()
+		})
+	}
+}
+
+// loop ticks meters on a 5 second interval.
 func (ma *meterTicker) loop() {
 	ticker := time.NewTicker(5 * time.Second)
-	for range ticker.C {
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			// Skip processing if metrics are disabled
 			if !metricsEnabled {
 				continue
 			}
@@ -161,10 +221,24 @@ func (ma *meterTicker) loop() {
 				meter.tick()
 			}
 			ma.mu.RUnlock()
+		case <-ma.quit:
+			return
+		}
 	}
 }
 
-// startMeterTickerLoop will start the arbiter ticker.
-func startMeterTickerLoop() {
-	arbiter.once.Do(func() { go arbiter.loop() })
+// EnableMetricsTicking ensures that the metrics ticker is running
+// if metrics are enabled and meters exist.
+func EnableMetricsTicking() {
+	arbiter.ensureStarted()
+}
+
+// DisableMetricsTicking stops the metrics ticker.
+func DisableMetricsTicking() {
+	arbiter.mu.Lock()
+	defer arbiter.mu.Unlock()
+
+	if arbiter.running {
+		arbiter.stop()
+	}
 }

metrics/meter_test.go

@@ -81,3 +81,59 @@ func TestMeterRepeat(t *testing.T) {
 		t.Errorf("m.Count(): 10100 != %v\n", count)
 	}
 }
+
+func TestMeterTickerLifecycle(t *testing.T) {
+	// Make sure metrics are disabled initially
+	oldEnabled := metricsEnabled
+	metricsEnabled = false
+	defer func() {
+		metricsEnabled = oldEnabled
+	}()
+
+	// Reset the arbiter
+	oldArbiter := arbiter
+	arbiter = newMeterTicker()
+	defer func() {
+		arbiter = oldArbiter
+	}()
+
+	// Create a new meter but metrics are disabled
+	// This should not start the ticker
+	m := NewMeter()
+	if arbiter.started || arbiter.running {
+		t.Error("Ticker started when metrics are disabled")
+	}
+
+	// Enable metrics, which should start the ticker
+	metricsEnabled = true
+	EnableMetricsTicking()
+
+	// Check if the ticker is started
+	arbiter.mu.RLock()
+	started := arbiter.started
+	running := arbiter.running
+	arbiter.mu.RUnlock()
+
+	if !started || !running {
+		t.Error("Ticker not started when metrics are enabled")
+	}
+
+	// Stop the meter
+	m.Stop()
+
+	// Ticker should be stopped as there are no more meters
+	arbiter.mu.RLock()
+	running = arbiter.running
+	arbiter.mu.RUnlock()
+
+	if running {
+		t.Error("Ticker still running after all meters are stopped")
+	}
+
+	// Disable metrics, which should stop the ticker
+	metricsEnabled = false
+	Disable()
+
+	// Checking for any goroutine leaks would require a more complex test
+	// with runtime.NumGoroutine() checks
+}

metrics/metrics.go

@@ -30,7 +30,15 @@ func Enabled() bool {
 // the program, before any metrics collection will happen.
 func Enable() {
 	metricsEnabled = true
-	startMeterTickerLoop()
+	// Ensure metrics ticker is started if there are any meters
+	EnableMetricsTicking()
+}
+
+// Disable disables the metrics system and stops any running metric tickers.
+func Disable() {
+	metricsEnabled = false
+	// Stop the metrics ticker
+	DisableMetricsTicking()
 }
 
 var threadCreateProfile = pprof.Lookup("threadcreate")