[otlp] Workaround DI containers which create unregistered services

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Builder/OtlpExporterBuilder.cs

@@ -174,9 +174,9 @@ private static void RegisterOtlpExporterServices(IServiceCollection services, st
  services!.AddOtlpExporterTracingServices();
 
  // Note: UseOtlpExporterRegistration is added to the service collection
- // to detect repeated calls to "UseOtlpExporter" and to throw if
- // "AddOtlpExporter" extensions are called
- services!.AddSingleton<UseOtlpExporterRegistration>();
+ // for each invocation to detect repeated calls to "UseOtlpExporter" and
+ // to throw if "AddOtlpExporter" extensions are called
+ services!.AddSingleton(UseOtlpExporterRegistration.Instance);
 
  services!.RegisterOptionsFactory((sp, configuration, name) => new OtlpExporterBuilderOptions(
  configuration,

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Builder/UseOtlpExporterRegistration.cs

@@ -8,4 +8,15 @@ namespace OpenTelemetry.Exporter;
 // calls to signal-specific AddOtlpExporter can throw.
 internal sealed class UseOtlpExporterRegistration
 {
+ public static readonly UseOtlpExporterRegistration Instance = new();
+
+ private UseOtlpExporterRegistration()
+ {
+ // Note: Some dependency injection containers (ex: Unity, Grace) will
+ // automatically create services if they have a public constructor even
+ // if the service was never registered into the IServiceCollection. The
+ // behavior of UseOtlpExporterRegistration requires that it should only
+ // exist if registered. This private constructor is intended to prevent
+ // automatic instantiation.
+ }
 }

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/CHANGELOG.md

@@ -12,6 +12,12 @@ Notes](../../RELEASENOTES.md).
  `CultureInfo.InvariantCulture`.
  ([#5700](https:/open-telemetry/opentelemetry-dotnet/pull/5700))
 
+* Fixed an issue causing `NotSupportedException`s to be thrown on startup when
+ `AddOtlpExporter` registration extensions are called while using custom
+ dependency injection containers which automatically create services (Unity,
+ Grace, etc.).
+ ([#5808](https:/open-telemetry/opentelemetry-dotnet/pull/5808))
+
 ## 1.9.0
 
 Released 2024-Jun-14