Reduce code duplication for resetting expdecaysample

Use single function for creating bounded histogram sample

eth/protocols/eth/handler.go

@@ -218,9 +218,7 @@ func handleMessage(backend Backend, peer *Peer) error {
 		h := fmt.Sprintf("%s/%s/%d/%#02x", p2p.HandleHistName, ProtocolName, peer.Version(), msg.Code)
 		defer func(start time.Time) {
 			sampler := func() metrics.Sample {
-				return metrics.ResettingSample(
+				return metrics.NewBoundedHistogramSample()
-					metrics.NewExpDecaySample(1028, 0.015),
-				)
 			}
 			metrics.GetOrRegisterHistogramLazy(h, nil, sampler).Update(time.Since(start).Microseconds())
 		}(time.Now())

eth/protocols/snap/handler.go

@@ -145,9 +145,7 @@ func HandleMessage(backend Backend, peer *Peer) error {
 		h := fmt.Sprintf("%s/%s/%d/%#02x", p2p.HandleHistName, ProtocolName, peer.Version(), msg.Code)
 		defer func(start time.Time) {
 			sampler := func() metrics.Sample {
-				return metrics.ResettingSample(
+				return metrics.NewBoundedHistogramSample()
-					metrics.NewExpDecaySample(1028, 0.015),
-				)
 			}
 			metrics.GetOrRegisterHistogramLazy(h, nil, sampler).Update(time.Since(start).Microseconds())
 		}(start)

metrics/sample.go

@@ -32,6 +32,12 @@ type Sample interface {
 	Update(int64)
 }
 
+func NewBoundedHistogramSample() Sample {
+	return ResettingSample(
+		NewExpDecaySample(1028, 0.015),
+	)
+}
+
 // ExpDecaySample is an exponentially-decaying sample using a forward-decaying
 // priority reservoir.  See Cormode et al's "Forward Decay: A Practical Time
 // Decay Model for Streaming Systems".

p2p/tracker/tracker.go

@@ -197,9 +197,7 @@ func (t *Tracker) Fulfil(peer string, version uint, code uint64, id uint64) {
 
 	h := fmt.Sprintf("%s/%s/%d/%#02x", waitHistName, t.protocol, req.version, req.reqCode)
 	sampler := func() metrics.Sample {
-		return metrics.ResettingSample(
+		return metrics.NewBoundedHistogramSample()
-			metrics.NewExpDecaySample(1028, 0.015),
-		)
 	}
 	metrics.GetOrRegisterHistogramLazy(h, nil, sampler).Update(time.Since(req.time).Microseconds())
 }

rpc/metrics.go

@@ -42,9 +42,7 @@ func updateServeTimeHistogram(method string, success bool, elapsed time.Duration
 	}
 	h := fmt.Sprintf("%s/%s/%s", serveTimeHistName, method, note)
 	sampler := func() metrics.Sample {
-		return metrics.ResettingSample(
+		return metrics.NewBoundedHistogramSample()
-			metrics.NewExpDecaySample(1028, 0.015),
-		)
 	}
 	metrics.GetOrRegisterHistogramLazy(h, nil, sampler).Update(elapsed.Nanoseconds())
 }