Add method and benchmarks for pooling metric options

CHANGELOG.md

@@ -14,6 +14,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Added support exporting logs via OTLP over gRPC in `go.opentelemetry.io/contrib/config`. (#6340)
 - The `go.opentelemetry.io/contrib/bridges/otellogr` module.
   This module provides an OpenTelemetry logging bridge for `github.com/go-logr/logr`. (#6386)
+- Use a pool for the semantic convention metrics options in `go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp`. (#6394)
 
 ### Changed
 

instrumentation/net/http/otelhttp/internal/semconv/env.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"os"
 	"strings"
+	"sync"
 
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/codes"
@@ -102,18 +103,27 @@ type MetricData struct {
 	ElapsedTime float64
 }
 
+var metricAddOptionPool = &sync.Pool{
+	New: func() interface{} {
+		return &[]metric.AddOption{}
+	},
+}
+
 func (s HTTPServer) RecordMetrics(ctx context.Context, md ServerMetricData) {
 	if s.requestBytesCounter == nil || s.responseBytesCounter == nil || s.serverLatencyMeasure == nil {
-		// This will happen if an HTTPServer{} is used instead of NewHTTPServer.
+		// This will happen if an HTTPServer{} is used insted of NewHTTPServer.
 		return
 	}
 
 	attributes := oldHTTPServer{}.MetricAttributes(md.ServerName, md.Req, md.StatusCode, md.AdditionalAttributes)
 	o := metric.WithAttributeSet(attribute.NewSet(attributes...))
-	addOpts := []metric.AddOption{o}
-	s.requestBytesCounter.Add(ctx, md.RequestSize, addOpts...)
-	s.responseBytesCounter.Add(ctx, md.ResponseSize, addOpts...)
+	addOpts := metricAddOptionPool.Get().(*[]metric.AddOption)
+	*addOpts = append(*addOpts, o)
+	s.requestBytesCounter.Add(ctx, md.RequestSize, *addOpts...)
+	s.responseBytesCounter.Add(ctx, md.ResponseSize, *addOpts...)
 	s.serverLatencyMeasure.Record(ctx, md.ElapsedTime, o)
+	*addOpts = (*addOpts)[:0]
+	metricAddOptionPool.Put(addOpts)
 
 	// TODO: Duplicate Metrics
 }
@@ -206,7 +216,7 @@ func (c HTTPClient) MetricOptions(ma MetricAttributes) MetricOpts {
 
 func (s HTTPClient) RecordMetrics(ctx context.Context, md MetricData, opts MetricOpts) {
 	if s.requestBytesCounter == nil || s.latencyMeasure == nil {
-		// This will happen if an HTTPClient{} is used instead of NewHTTPClient().
+		// This will happen if an HTTPClient{} is used insted of NewHTTPClient().
 		return
 	}
 
@@ -218,7 +228,7 @@ func (s HTTPClient) RecordMetrics(ctx context.Context, md MetricData, opts Metri
 
 func (s HTTPClient) RecordResponseSize(ctx context.Context, responseData int64, opts metric.AddOption) {
 	if s.responseBytesCounter == nil {
-		// This will happen if an HTTPClient{} is used instead of NewHTTPClient().
+		// This will happen if an HTTPClient{} is used insted of NewHTTPClient().
 		return
 	}
 

instrumentation/net/http/otelhttp/internal/semconv/env_test.go

@@ -132,3 +132,42 @@ func NewTestHTTPClient() HTTPClient {
 		latencyMeasure:       &testInst{},
 	}
 }
+
+func BenchmarkRecordMetrics(b *testing.B) {
+	benchmarks := []struct {
+		name   string
+		server HTTPServer
+	}{
+		{
+			name:   "empty",
+			server: HTTPServer{},
+		},
+		{
+			name:   "nil meter",
+			server: NewHTTPServer(nil),
+		},
+		{
+			name:   "with Meter",
+			server: NewHTTPServer(noop.Meter{}),
+		},
+	}
+
+	for _, bm := range benchmarks {
+		b.Run(bm.name, func(b *testing.B) {
+			req, _ := http.NewRequest("GET", "http://example.com", nil)
+			_ = bm.server.RequestTraceAttrs("stuff", req)
+			_ = bm.server.ResponseTraceAttrs(ResponseTelemetry{StatusCode: 200})
+			ctx := context.Background()
+			b.ReportAllocs()
+			b.ResetTimer()
+			for i := 0; i < b.N; i++ {
+				bm.server.RecordMetrics(ctx, ServerMetricData{
+					ServerName: bm.name,
+					MetricAttributes: MetricAttributes{
+						Req: req,
+					},
+				})
+			}
+		})
+	}
+}