Disable flag for TracerProvider / MeterProvider

src/OpenTelemetry.Api/Metrics/MeterProvider.cs

@@ -27,5 +27,10 @@ public class MeterProvider : BaseProvider
         protected MeterProvider()
         {
         }
+
+        /// <summary>
+        /// Gets the default <see cref="MeterProvider"/>.
+        /// </summary>
+        internal static MeterProvider Default { get; } = new MeterProvider();
     }
 }

src/OpenTelemetry/Metrics/MeterProviderBuilderBase.cs

@@ -32,6 +32,10 @@ public abstract class MeterProviderBuilderBase : MeterProviderBuilder
     {
         internal const int MaxMetricsDefault = 1000;
         internal const int MaxMetricPointsPerMetricDefault = 2000;
+
+        // Builds noop MeterProvider when this flag is set.
+        // This flag is controlled through reflection.
+        private static bool disableMeterProviderBuilder = false;
         private readonly List<InstrumentationFactory> instrumentationFactories = new();
         private readonly List<string> meterSources = new();
         private readonly List<Func<Instrument, MetricStreamConfiguration>> viewConfigs = new();
@@ -142,14 +146,21 @@ internal MeterProviderBuilder SetMaxMetricPointsPerMetricStream(int maxMetricPoi
         /// <returns><see cref="MeterProvider"/>.</returns>
         protected MeterProvider Build()
         {
-            return new MeterProviderSdk(
+            if (!disableMeterProviderBuilder)
+            {
+                return new MeterProviderSdk(
                 this.resourceBuilder.Build(),
                 this.meterSources,
                 this.instrumentationFactories,
                 this.viewConfigs,
                 this.maxMetricStreams,
                 this.maxMetricPointsPerMetricStream,
                 this.MetricReaders.ToArray());
+            }
+            else
+            {
+                return MeterProvider.Default;
+            }
         }
 
         internal readonly struct InstrumentationFactory

src/OpenTelemetry/Trace/Builder/TracerProviderBuilderBase.cs

@@ -33,6 +33,10 @@ public abstract class TracerProviderBuilderBase : TracerProviderBuilder, IDeferr
     {
         internal readonly TracerProviderBuilderState? State;
 
+        // Builds noop TracerProvider when this flag is set.
+        // This flag is controlled through reflection.
+        private static bool disableTracerProviderBuilder = false;
+
         private readonly bool ownsServices;
         private IServiceCollection? services;
 
@@ -264,7 +268,14 @@ protected TracerProvider Build()
 
             var serviceProvider = services.BuildServiceProvider();
 
-            return new TracerProviderSdk(serviceProvider, ownsServiceProvider: true);
+            if (!disableTracerProviderBuilder)
+            {
+                return new TracerProviderSdk(serviceProvider, ownsServiceProvider: true);
+            }
+            else
+            {
+                return TracerProvider.Default;
+            }
         }
 
         private static BaseProcessor<Activity> BuildExportProcessor(

test/OpenTelemetry.Tests/Metrics/MeterProviderTests.cs

@@ -15,6 +15,7 @@
 // </copyright>
 
 using System.Collections.Generic;
+using System.Reflection;
 using OpenTelemetry.Exporter;
 using Xunit;
 
@@ -34,6 +35,21 @@ public void MeterProviderFindExporterTest()
             Assert.False(meterProvider.TryFindExporter(out MyExporter myExporter));
         }
 
+        [Fact]
+        public void NoopMeterProviderWithDisabledMeterProviderBuilderFlag()
+        {
+            var buildMeterProviderBuilderField = typeof(MeterProviderBuilderBase).GetField("disableMeterProviderBuilder", BindingFlags.Static | BindingFlags.NonPublic);
+            buildMeterProviderBuilderField.SetValue(null, true);
+
+            var exportedItems = new List<Metric>();
+            using var meterProvider = Sdk.CreateMeterProviderBuilder()
+                .AddInMemoryExporter(exportedItems)
+                .Build();
+
+            Assert.Same(meterProvider, MeterProvider.Default);
+            buildMeterProviderBuilderField.SetValue(null, false);
+        }
+
         private class MyExporter : BaseExporter<Metric>
         {
             public override ExportResult Export(in Batch<Metric> batch)

test/OpenTelemetry.Tests/Trace/TracerProviderSdkTest.cs

@@ -18,6 +18,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Reflection;
 using OpenTelemetry.Instrumentation;
 using OpenTelemetry.Resources;
 using OpenTelemetry.Tests;
@@ -1209,6 +1210,21 @@ public void SdkSamplesAndProcessesLegacySourceWhenAddLegacySourceIsCalledWithWil
             Assert.Contains(nonLegacyActivity.OperationName, onStopProcessedActivities);  // Processor.OnEnd is called since we added a legacy OperationName
         }
 
+        [Fact]
+        public void NoopTracerProviderWithDisabledTracerProviderBuilderFlag()
+        {
+            var buildTracerProviderBuilderField = typeof(TracerProviderBuilderBase).GetField("disableTracerProviderBuilder", BindingFlags.Static | BindingFlags.NonPublic);
+            buildTracerProviderBuilderField.SetValue(null, true);
+
+            using var source1 = new ActivitySource($"{Utils.GetCurrentMethodName()}.1");
+            var builder = Sdk.CreateTracerProviderBuilder();
+            builder.AddSource(source1.Name);
+            using var provider = builder.Build();
+
+            Assert.Same(provider, TracerProvider.Default);
+            buildTracerProviderBuilderField.SetValue(null, false);
+        }
+
         public void Dispose()
         {
             GC.SuppressFinalize(this);