aggmetric: clean up ChildrenStorage interface

The interface has a `Do` function which passes an arbitrary
`interface{}` object to the function. The only thing the function can
do with that object is to pass it to `GetChildMetric`.

This dance is strange and unnecessary; we rename `Do` to `ForEach` and
change it to pass `ChildMetric` objects directly.

Informs: #144504
Epic: none
Release note: None

Author: RaduBerinde

pkg/util/metric/aggmetric/agg_metric.go

@@ -108,8 +108,7 @@ func (cs *childSet) Each(
 ) {
 	cs.mu.Lock()
 	defer cs.mu.Unlock()
-	cs.mu.children.Do(func(e interface{}) {
-		cm := cs.mu.children.GetChildMetric(e)
+	cs.mu.children.ForEach(func(cm ChildMetric) {
 		pm := cm.ToPrometheusMetric()
 
 		childLabels := make([]*io_prometheus_client.LabelPair, 0, len(labels)+len(cs.labels))
@@ -130,8 +129,8 @@ func (cs *childSet) Each(
 func (cs *childSet) apply(applyFn func(item MetricItem)) {
 	cs.mu.Lock()
 	defer cs.mu.Unlock()
-	cs.mu.children.Do(func(e interface{}) {
-		applyFn(cs.mu.children.GetChildMetric(e).(MetricItem))
+	cs.mu.children.ForEach(func(cm ChildMetric) {
+		applyFn(cm)
 	})
 }
 
@@ -192,8 +191,7 @@ func (sm *SQLMetric) Each(
 	sm.mu.Lock()
 	defer sm.mu.Unlock()
 
-	sm.mu.children.Do(func(e interface{}) {
-		cm := sm.mu.children.GetChildMetric(e)
+	sm.mu.children.ForEach(func(cm ChildMetric) {
 		pm := cm.ToPrometheusMetric()
 
 		childLabels := make([]*io_prometheus_client.LabelPair, 0, len(labels)+2)
@@ -317,8 +315,9 @@ type ChildrenStorage interface {
 	Get(labelVals ...string) (ChildMetric, bool)
 	Add(metric ChildMetric)
 	Del(key ChildMetric)
-	Do(f func(e interface{}))
-	GetChildMetric(e interface{}) ChildMetric
+
+	// ForEach calls f for each child metric, in arbitrary order.
+	ForEach(f func(metric ChildMetric))
 	Clear()
 }
 
@@ -329,10 +328,6 @@ type UnorderedCacheWrapper struct {
 	cache *cache.UnorderedCache
 }
 
-func (ucw *UnorderedCacheWrapper) GetChildMetric(e interface{}) ChildMetric {
-	return e.(*cache.Entry).Value.(ChildMetric)
-}
-
 func (ucw *UnorderedCacheWrapper) Get(labelVals ...string) (ChildMetric, bool) {
 	hashKey := metricKey(labelVals...)
 	value, ok := ucw.cache.Get(hashKey)
@@ -358,9 +353,9 @@ func (ucw *UnorderedCacheWrapper) Del(metric ChildMetric) {
 	}
 }
 
-func (ucw *UnorderedCacheWrapper) Do(f func(e interface{})) {
+func (ucw *UnorderedCacheWrapper) ForEach(f func(metric ChildMetric)) {
 	ucw.cache.Do(func(e *cache.Entry) {
-		f(e)
+		f(e.Value.(ChildMetric))
 	})
 }
 
@@ -395,17 +390,13 @@ func (b BtreeWrapper) Del(metric ChildMetric) {
 	}
 }
 
-func (b BtreeWrapper) Do(f func(e interface{})) {
+func (b BtreeWrapper) ForEach(f func(metric ChildMetric)) {
 	b.tree.Ascend(func(i btree.Item) bool {
-		f(i)
+		f(i.(ChildMetric))
 		return true
 	})
 }
 
-func (b BtreeWrapper) GetChildMetric(e interface{}) ChildMetric {
-	return e.(ChildMetric)
-}
-
 func (b BtreeWrapper) Clear() {
 	b.tree.Clear(false)
 }

pkg/util/metric/aggmetric/gauge.go

@@ -46,8 +46,8 @@ func NewFunctionalGauge(
 		values := make([]int64, 0)
 		g.childSet.mu.Lock()
 		defer g.childSet.mu.Unlock()
-		g.childSet.mu.children.Do(func(e interface{}) {
-			cg := g.childSet.mu.children.GetChildMetric(e).(*Gauge)
+		g.childSet.mu.children.ForEach(func(metric ChildMetric) {
+			cg := metric.(*Gauge)
 			values = append(values, cg.Value())
 		})
 		return f(values)

pkg/util/metric/aggmetric/histogram.go

@@ -247,8 +247,8 @@ func NewSQLHistogram(opts metric.HistogramOptions) *SQLHistogram {
 func (sh *SQLHistogram) apply(applyFn func(childMetric ChildMetric)) {
 	sh.mu.Lock()
 	defer sh.mu.Unlock()
-	sh.mu.children.Do(func(e interface{}) {
-		applyFn(sh.mu.children.GetChildMetric(e).(*SQLChildHistogram))
+	sh.mu.children.ForEach(func(metric ChildMetric) {
+		applyFn(metric.(*SQLChildHistogram))
 	})
 }