optimized interval_meter

utils/uptime/interval_meter.go

@@ -10,7 +10,7 @@ import (
 )
 
 const (
-	maxSkippedIntervals = 5
+	maxSkippedIntervals = 32
 )
 
 type intervalMeter struct {
@@ -55,26 +55,51 @@ func (a *intervalMeter) Read() float64 {
 	if !currentTime.After(a.lastUpdated) {
 		return a.value
 	}
-	if totalTime := currentTime.Sub(a.lastUpdated); totalTime > maxSkippedIntervals*a.halflife {
+
+	// try to finish the current round
+	if currentTime.After(a.nextHalvening) {
 		if a.running {
-			a.value = 1
-		} else {
-			a.value = 0
+			additionalRunningTime := float64(a.nextHalvening.Sub(a.lastUpdated)) / float64(a.halflife)
+			a.value += additionalRunningTime / 2
 		}
-	} else {
-		for !currentTime.Before(a.nextHalvening) {
+		a.lastUpdated = a.nextHalvening
+		a.nextHalvening = a.nextHalvening.Add(a.halflife)
+		a.value /= 2
+
+		// try to skip future rounds
+		if totalTime := currentTime.Sub(a.lastUpdated); totalTime > a.halflife {
+			numSkippedPeriods := totalTime / a.halflife
+			if numSkippedPeriods > maxSkippedIntervals {
+				// If this meter hasn't been read in a long time, avoid
+				// potential shifting overflow issues and just jump to a
+				// reasonable value.
+				if a.running {
+					a.value = 1
+				} else {
+					a.value = 0
+				}
+				a.lastUpdated = currentTime
+				a.nextHalvening = a.lastUpdated.Add(a.halflife)
+				return a.value
+			}
+
+			invFactor := 1 << uint(numSkippedPeriods)
+			factor := 1 / float64(invFactor)
+			a.value *= factor
 			if a.running {
-				additionalRunningTime := float64(a.nextHalvening.Sub(a.lastUpdated)) / float64(a.halflife)
-				a.value += additionalRunningTime / 2
+				a.value += 1 - factor
 			}
-			a.lastUpdated = a.nextHalvening
-			a.nextHalvening = a.nextHalvening.Add(a.halflife)
 			a.value /= 2
+			skippedDuration := a.halflife * numSkippedPeriods
+			a.lastUpdated = a.lastUpdated.Add(skippedDuration)
+			a.nextHalvening = a.nextHalvening.Add(skippedDuration)
 		}
-		if a.running {
-			additionalRunningTime := float64(currentTime.Sub(a.lastUpdated)) / float64(a.halflife)
-			a.value += additionalRunningTime / 2
-		}
+	}
+
+	// increment the value for the current round
+	if a.running {
+		additionalRunningTime := float64(currentTime.Sub(a.lastUpdated)) / float64(a.halflife)
+		a.value += additionalRunningTime / 2
 	}
 	a.lastUpdated = currentTime
 	return a.value

utils/uptime/interval_meter_benchmark_test.go

@@ -16,7 +16,7 @@ func BenchmarkIntervalMeterSeconds(b *testing.B) {
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		currentTime = currentTime.Add(4 * time.Second)
+		currentTime = currentTime.Add(10*time.Second + 500*time.Millisecond)
 		m.clock.Set(currentTime)
 		time.Now()
 

utils/uptime/interval_meter_test.go

@@ -69,6 +69,22 @@ func TestIntervalMeter(t *testing.T) {
 	if uptime := m.Read(); math.Abs(uptime-.625) > epsilon {
 		t.Fatalf("Wrong uptime value. Expected %f got %f", .625, uptime)
 	}
+
+	currentTime = currentTime.Add((maxSkippedIntervals + 2) * halflife)
+	m.clock.Set(currentTime)
+
+	if uptime := m.Read(); math.Abs(uptime-1) > epsilon {
+		t.Fatalf("Wrong uptime value. Expected %d got %f", 1, uptime)
+	}
+
+	m.Stop()
+
+	currentTime = currentTime.Add((maxSkippedIntervals + 2) * halflife)
+	m.clock.Set(currentTime)
+
+	if uptime := m.Read(); math.Abs(uptime-0) > epsilon {
+		t.Fatalf("Wrong uptime value. Expected %d got %f", 0, uptime)
+	}
 }
 
 func TestIntervalMeterTimeTravel(t *testing.T) {

utils/uptime/meter_benchmark_test.go

@@ -16,7 +16,7 @@ func BenchmarkMeterSeconds(b *testing.B) {
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		currentTime = currentTime.Add(4 * time.Second)
+		currentTime = currentTime.Add(10*time.Second + 500*time.Millisecond)
 		m.clock.Set(currentTime)
 		time.Now()