From c6acb9e120c00f327fcaa7ea58ebc0f74996b584 Mon Sep 17 00:00:00 2001
From: Utkarsh Umesan Pillai <66651184+utpilla@users.noreply.github.com>
Date: Fri, 1 Dec 2023 16:22:09 -0800
Subject: [PATCH] Use static Histogram

---
 .../AspNetCoreMetrics.cs                        | 10 +---------
 .../Implementation/HttpInMetricsListener.cs     | 17 +++++++++++------
 .../MeterProviderBuilderExtensions.cs           |  2 +-
 3 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/src/OpenTelemetry.Instrumentation.AspNetCore/AspNetCoreMetrics.cs b/src/OpenTelemetry.Instrumentation.AspNetCore/AspNetCoreMetrics.cs
index 14ab42d511b..7d8dce970a2 100644
--- a/src/OpenTelemetry.Instrumentation.AspNetCore/AspNetCoreMetrics.cs
+++ b/src/OpenTelemetry.Instrumentation.AspNetCore/AspNetCoreMetrics.cs
@@ -15,8 +15,6 @@
 // </copyright>
 
 #if !NET8_0_OR_GREATER
-using System.Diagnostics.Metrics;
-using System.Reflection;
 using OpenTelemetry.Instrumentation.AspNetCore.Implementation;
 
 namespace OpenTelemetry.Instrumentation.AspNetCore;
@@ -26,12 +24,6 @@ namespace OpenTelemetry.Instrumentation.AspNetCore;
 /// </summary>
 internal sealed class AspNetCoreMetrics : IDisposable
 {
-    internal static readonly AssemblyName AssemblyName = typeof(HttpInListener).Assembly.GetName();
-    internal static readonly string InstrumentationName = AssemblyName.Name;
-    internal static readonly string InstrumentationVersion = AssemblyName.Version.ToString();
-
-    private static readonly Meter InstrumentationMeter = new(InstrumentationName, InstrumentationVersion);
-
     private static readonly HashSet<string> DiagnosticSourceEvents = new()
     {
         "Microsoft.AspNetCore.Hosting.HttpRequestIn",
@@ -48,7 +40,7 @@ internal sealed class AspNetCoreMetrics : IDisposable
 
     internal AspNetCoreMetrics()
     {
-        var metricsListener = new HttpInMetricsListener("Microsoft.AspNetCore", InstrumentationMeter);
+        var metricsListener = new HttpInMetricsListener("Microsoft.AspNetCore");
         this.diagnosticSourceSubscriber = new DiagnosticSourceSubscriber(metricsListener, this.isEnabled, AspNetCoreInstrumentationEventSource.Log.UnknownErrorProcessingEvent);
         this.diagnosticSourceSubscriber.Subscribe();
     }
diff --git a/src/OpenTelemetry.Instrumentation.AspNetCore/Implementation/HttpInMetricsListener.cs b/src/OpenTelemetry.Instrumentation.AspNetCore/Implementation/HttpInMetricsListener.cs
index a47ee19858e..b3631d0ef21 100644
--- a/src/OpenTelemetry.Instrumentation.AspNetCore/Implementation/HttpInMetricsListener.cs
+++ b/src/OpenTelemetry.Instrumentation.AspNetCore/Implementation/HttpInMetricsListener.cs
@@ -16,6 +16,7 @@
 
 using System.Diagnostics;
 using System.Diagnostics.Metrics;
+using System.Reflection;
 using Microsoft.AspNetCore.Http;
 using OpenTelemetry.Internal;
 
@@ -33,21 +34,25 @@ internal sealed class HttpInMetricsListener : ListenerHandler
 
     internal const string OnUnhandledHostingExceptionEvent = "Microsoft.AspNetCore.Hosting.UnhandledException";
     internal const string OnUnhandledDiagnosticsExceptionEvent = "Microsoft.AspNetCore.Diagnostics.UnhandledException";
+
+    internal static readonly AssemblyName AssemblyName = typeof(HttpInListener).Assembly.GetName();
+    internal static readonly string InstrumentationName = AssemblyName.Name;
+    internal static readonly string InstrumentationVersion = AssemblyName.Version.ToString();
+    internal static readonly Meter Meter = new(InstrumentationName, InstrumentationVersion);
+
     private const string OnStopEvent = "Microsoft.AspNetCore.Hosting.HttpRequestIn.Stop";
+
     private const string EventName = "OnStopActivity";
     private const string NetworkProtocolName = "http";
     private static readonly PropertyFetcher<Exception> ExceptionPropertyFetcher = new("Exception");
     private static readonly PropertyFetcher<HttpContext> HttpContextPropertyFetcher = new("HttpContext");
     private static readonly object ErrorTypeHttpContextItemsKey = new();
 
-    private readonly Meter meter;
-    private readonly Histogram<double> httpServerRequestDuration;
+    private static readonly Histogram<double> HttpServerRequestDuration = Meter.CreateHistogram<double>(HttpServerRequestDurationMetricName, "s", "Duration of HTTP server requests.");
 
-    internal HttpInMetricsListener(string name, Meter meter)
+    internal HttpInMetricsListener(string name)
         : base(name)
     {
-        this.meter = meter;
-        this.httpServerRequestDuration = meter.CreateHistogram<double>(HttpServerRequestDurationMetricName, "s", "Duration of HTTP server requests.");
     }
 
     public override void OnEventWritten(string name, object payload)
@@ -130,6 +135,6 @@ public void OnStopEventWritten(string name, object payload)
         // We are relying here on ASP.NET Core to set duration before writing the stop event.
         // https://github.com/dotnet/aspnetcore/blob/d6fa351048617ae1c8b47493ba1abbe94c3a24cf/src/Hosting/Hosting/src/Internal/HostingApplicationDiagnostics.cs#L449
         // TODO: Follow up with .NET team if we can continue to rely on this behavior.
-        this.httpServerRequestDuration.Record(Activity.Current.Duration.TotalSeconds, tags);
+        HttpServerRequestDuration.Record(Activity.Current.Duration.TotalSeconds, tags);
     }
 }
diff --git a/src/OpenTelemetry.Instrumentation.AspNetCore/MeterProviderBuilderExtensions.cs b/src/OpenTelemetry.Instrumentation.AspNetCore/MeterProviderBuilderExtensions.cs
index c394a3590ee..06e41eedc15 100644
--- a/src/OpenTelemetry.Instrumentation.AspNetCore/MeterProviderBuilderExtensions.cs
+++ b/src/OpenTelemetry.Instrumentation.AspNetCore/MeterProviderBuilderExtensions.cs
@@ -44,7 +44,7 @@ public static MeterProviderBuilder AddAspNetCoreInstrumentation(
         _ = TelemetryHelper.BoxedStatusCodes;
         _ = RequestMethodHelper.KnownMethods;
 
-        builder.AddMeter(AspNetCoreMetrics.InstrumentationName);
+        builder.AddMeter(HttpInMetricsListener.InstrumentationName);
 
         builder.AddInstrumentation(new AspNetCoreMetrics());