summary: fix Unregister behaviour for summary metric type (#16)

The change covers two things:
1. Cleanup of Set.a metrics list from per-quantile metrics
for summary.
2. Register summary metric and per-quantile metrics in one take.
This prevents registry corruption when Unregister called in the
middle of metric register process.

set.go

@@ -324,13 +324,20 @@ func (s *Set) NewSummary(name string) *Summary {
 //
 // The returned summary is safe to use from concurrent goroutines.
 func (s *Set) NewSummaryExt(name string, window time.Duration, quantiles []float64) *Summary {
+	if err := validateMetric(name); err != nil {
+		panic(fmt.Errorf("BUG: invalid metric name %q: %s", name, err))
+	}
 	sm := newSummary(window, quantiles)
-	s.registerMetric(name, sm)
-	registerSummary(sm)
-	s.registerSummaryQuantiles(name, sm)
+
 	s.mu.Lock()
+	// defer will unlock in case of panic
+	// checks in tests
+	defer s.mu.Unlock()
+
+	s.mustRegisterLocked(name, sm)
+	registerSummaryLocked(sm)
+	s.registerSummaryQuantilesLocked(name, sm)
 	s.summaries = append(s.summaries, sm)
-	s.mu.Unlock()
 	return sm
 }
 
@@ -379,21 +386,17 @@ func (s *Set) GetOrCreateSummaryExt(name string, window time.Duration, quantiles
 			name:   name,
 			metric: sm,
 		}
-		mustRegisterQuantiles := false
 		s.mu.Lock()
 		nm = s.m[name]
 		if nm == nil {
 			nm = nmNew
 			s.m[name] = nm
 			s.a = append(s.a, nm)
-			registerSummary(sm)
-			mustRegisterQuantiles = true
+			registerSummaryLocked(sm)
+			s.registerSummaryQuantilesLocked(name, sm)
 		}
 		s.summaries = append(s.summaries, sm)
 		s.mu.Unlock()
-		if mustRegisterQuantiles {
-			s.registerSummaryQuantiles(name, sm)
-		}
 	}
 	sm, ok := nm.metric.(*Summary)
 	if !ok {
@@ -408,14 +411,14 @@ func (s *Set) GetOrCreateSummaryExt(name string, window time.Duration, quantiles
 	return sm
 }
 
-func (s *Set) registerSummaryQuantiles(name string, sm *Summary) {
+func (s *Set) registerSummaryQuantilesLocked(name string, sm *Summary) {
 	for i, q := range sm.quantiles {
 		quantileValueName := addTag(name, fmt.Sprintf(`quantile="%g"`, q))
 		qv := &quantileValue{
 			sm:  sm,
 			idx: i,
 		}
-		s.registerMetric(quantileValueName, qv)
+		s.mustRegisterLocked(quantileValueName, qv)
 	}
 }
 
@@ -424,6 +427,16 @@ func (s *Set) registerMetric(name string, m metric) {
 		panic(fmt.Errorf("BUG: invalid metric name %q: %s", name, err))
 	}
 	s.mu.Lock()
+	// defer will unlock in case of panic
+	// checks in test
+	defer s.mu.Unlock()
+	s.mustRegisterLocked(name, m)
+}
+
+// mustRegisterLocked registers given metric with
+// the given name. Panics if the given name was
+// already registered before.
+func (s *Set) mustRegisterLocked(name string, m metric) {
 	nm, ok := s.m[name]
 	if !ok {
 		nm = &namedMetric{
@@ -433,7 +446,6 @@ func (s *Set) registerMetric(name string, m metric) {
 		s.m[name] = nm
 		s.a = append(s.a, nm)
 	}
-	s.mu.Unlock()
 	if ok {
 		panic(fmt.Errorf("BUG: metric %q is already registered", name))
 	}
@@ -455,32 +467,34 @@ func (s *Set) UnregisterMetric(name string) bool {
 
 	delete(s.m, name)
 
-	// remove metric from s.a
-	found := false
-	for i, nm := range s.a {
-		if nm.name == name {
-			s.a = append(s.a[:i], s.a[i+1:]...)
-			found = true
-			break
+	deleteFromList := func(metricName string) {
+		for i, nm := range s.a {
+			if nm.name == metricName {
+				s.a = append(s.a[:i], s.a[i+1:]...)
+				return
+			}
 		}
-	}
-	if !found {
 		panic(fmt.Errorf("BUG: cannot find metric %q in the list of registered metrics", name))
 	}
+
+	// remove metric from s.a
+	deleteFromList(name)
+
 	sm, ok := m.(*Summary)
 	if !ok {
-		// There is no need in cleaning up s.summaries.
+		// There is no need in cleaning up summary.
 		return true
 	}
 
-	// Remove summary metric name including quantile labels from set
+	// cleanup registry from per-quantile metrics
 	for _, q := range sm.quantiles {
 		quantileValueName := addTag(name, fmt.Sprintf(`quantile="%g"`, q))
 		delete(s.m, quantileValueName)
+		deleteFromList(quantileValueName)
 	}
 
 	// Remove sm from s.summaries
-	found = false
+	found := false
 	for i, xsm := range s.summaries {
 		if xsm == sm {
 			s.summaries = append(s.summaries[:i], s.summaries[i+1:]...)

set_test.go

@@ -2,7 +2,9 @@ package metrics
 
 import (
 	"fmt"
+	"sync"
 	"testing"
+	"time"
 )
 
 func TestNewSet(t *testing.T) {
@@ -64,31 +66,38 @@ func TestSetListMetricNames(t *testing.T) {
 
 func TestSetUnregisterMetric(t *testing.T) {
 	s := NewSet()
+	const cName, smName = "counter_1", "summary_1"
 	// Initialize a few metrics
-	for i := 0; i < 5; i++ {
-		c := s.NewCounter(fmt.Sprintf("counter_%d", i))
-		c.Inc()
-		sm := s.NewSummary(fmt.Sprintf("summary_%d", i))
-		sm.Update(float64(i))
-	}
+	c := s.NewCounter(cName)
+	c.Inc()
+	sm := s.NewSummary(smName)
+	sm.Update(1)
+
 	// Unregister existing metrics
-	if !s.UnregisterMetric("counter_1") {
-		t.Fatalf("UnregisterMetric(counter_1) must return true")
+	if !s.UnregisterMetric(cName) {
+		t.Fatalf("UnregisterMetric(%s) must return true", cName)
 	}
-	if !s.UnregisterMetric("summary_1") {
-		t.Fatalf("UnregisterMetric(summary_1) must return true")
+	if !s.UnregisterMetric(smName) {
+		t.Fatalf("UnregisterMetric(%s) must return true", smName)
 	}
 
 	// Unregister twice must return false
-	if s.UnregisterMetric("counter_1") {
-		t.Fatalf("UnregisterMetric(counter_1) must return false on unregistered metric")
+	if s.UnregisterMetric(cName) {
+		t.Fatalf("UnregisterMetric(%s) must return false on unregistered metric", cName)
 	}
-	if s.UnregisterMetric("summary_1") {
-		t.Fatalf("UnregisterMetric(summary_1) must return false on unregistered metric")
+	if s.UnregisterMetric(smName) {
+		t.Fatalf("UnregisterMetric(%s) must return false on unregistered metric", smName)
+	}
+
+	// verify that registry is empty
+	if len(s.m) != 0 {
+		t.Fatalf("expected metrics map to be empty; got %d elements", len(s.m))
+	}
+	if len(s.a) != 0 {
+		t.Fatalf("expected metrics list to be empty; got %d elements", len(s.a))
 	}
 
 	// Validate metrics are removed
-	const cName, smName = "counter_1", "summary_1"
 	ok := false
 	for _, n := range s.ListMetricNames() {
 		if n == cName || n == smName {
@@ -104,3 +113,40 @@ func TestSetUnregisterMetric(t *testing.T) {
 	s.NewCounter(cName).Inc()
 	s.NewSummary(smName).Update(float64(1))
 }
+
+// TestRegisterUnregister tests concurrent access to
+// metrics during registering and unregistering.
+// Should be tested specifically with `-race` enabled.
+func TestRegisterUnregister(t *testing.T) {
+	const (
+		workers    = 16
+		iterations = 1e3
+	)
+	wg := sync.WaitGroup{}
+	wg.Add(workers)
+	for n := 0; n < workers; n++ {
+		go func() {
+			defer wg.Done()
+			now := time.Now()
+			for i := 0; i < iterations; i++ {
+				iteration := i % 5
+				counter := fmt.Sprintf(`counter{iteration="%d"}`, iteration)
+				GetOrCreateCounter(counter).Add(i)
+				UnregisterMetric(counter)
+
+				histogram := fmt.Sprintf(`histogram{iteration="%d"}`, iteration)
+				GetOrCreateHistogram(histogram).UpdateDuration(now)
+				UnregisterMetric(histogram)
+
+				gauge := fmt.Sprintf(`gauge{iteration="%d"}`, iteration)
+				GetOrCreateGauge(gauge, func() float64 { return 1 })
+				UnregisterMetric(gauge)
+
+				summary := fmt.Sprintf(`summary{iteration="%d"}`, iteration)
+				GetOrCreateSummary(summary).Update(float64(i))
+				UnregisterMetric(summary)
+			}
+		}()
+	}
+	wg.Wait()
+}

summary.go

@@ -203,7 +203,7 @@ func addTag(name, tag string) string {
 	return fmt.Sprintf("%s,%s}", name[:len(name)-1], tag)
 }
 
-func registerSummary(sm *Summary) {
+func registerSummaryLocked(sm *Summary) {
 	window := sm.window
 	summariesLock.Lock()
 	summaries[window] = append(summaries[window], sm)