[api] Fix memory leaks in TracerProvider.GetTracer API

src/OpenTelemetry.Api/.publicApi/Stable/net462/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+override OpenTelemetry.Trace.TracerProvider.Dispose(bool disposing) -> void

src/OpenTelemetry.Api/.publicApi/Stable/net6.0/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+override OpenTelemetry.Trace.TracerProvider.Dispose(bool disposing) -> void

src/OpenTelemetry.Api/.publicApi/Stable/netstandard2.0/PublicAPI.Unshipped.txt

@@ -0,0 +1 @@
+override OpenTelemetry.Trace.TracerProvider.Dispose(bool disposing) -> void

src/OpenTelemetry.Api/CHANGELOG.md

@@ -6,6 +6,10 @@
  trace was running (`Activity.Current != null`).
  ([#4890](https:/open-telemetry/opentelemetry-dotnet/pull/4890))
 
+* Added a `Tracer` cache inside of `TracerProvider` to prevent repeated calls to
+ `GetTracer` from leaking memory.
+ ([#4906](https:/open-telemetry/opentelemetry-dotnet/pull/4906))
+
 ## 1.6.0
 
 Released 2023-Sep-05

src/OpenTelemetry.Api/Trace/Tracer.cs

@@ -28,9 +28,9 @@ namespace OpenTelemetry.Trace;
 /// <remarks>Tracer is a wrapper around <see cref="System.Diagnostics.ActivitySource"/> class.</remarks>
 public class Tracer
 {
- internal readonly ActivitySource ActivitySource;
+ internal ActivitySource? ActivitySource;
 
- internal Tracer(ActivitySource activitySource)
+ internal Tracer(ActivitySource? activitySource)
  {
  this.ActivitySource = activitySource;
  }
@@ -213,7 +213,9 @@ private TelemetrySpan StartSpanHelper(
  IEnumerable<Link>? links = null,
  DateTimeOffset startTime = default)
  {
- if (!this.ActivitySource.HasListeners())
+ var activitySource = this.ActivitySource;
+
+ if (!(activitySource?.HasListeners() ?? false))
  {
  return TelemetrySpan.NoopInstance;
  }
@@ -230,7 +232,7 @@ private TelemetrySpan StartSpanHelper(
 
  try
  {
- var activity = this.ActivitySource.StartActivity(name, activityKind, parentContext.ActivityContext, initialAttributes?.Attributes ?? null, activityLinks, startTime);
+ var activity = activitySource.StartActivity(name, activityKind, parentContext.ActivityContext, initialAttributes?.Attributes ?? null, activityLinks, startTime);
  return activity == null
  ? TelemetrySpan.NoopInstance
  : new TelemetrySpan(activity);

src/OpenTelemetry.Api/Trace/TracerProvider.cs

@@ -16,7 +16,10 @@
 
 #nullable enable
 
-using System.Diagnostics;
+using System.Collections;
+#if NET6_0_OR_GREATER
+using System.Diagnostics.CodeAnalysis;
+#endif
 
 namespace OpenTelemetry.Trace;
 
@@ -25,6 +28,10 @@ namespace OpenTelemetry.Trace;
 /// </summary>
 public class TracerProvider : BaseProvider
 {
+ [ThreadStatic]
+ private static TracerKey? threadTracerKey;
+ private Hashtable? tracers = new();
+
  /// <summary>
  /// Initializes a new instance of the <see cref="TracerProvider"/> class.
  /// </summary>
@@ -44,5 +51,92 @@ protected TracerProvider()
  /// <param name="version">Version of the instrumentation library.</param>
  /// <returns>Tracer instance.</returns>
  public Tracer GetTracer(string name, string? version = null)
- => new(new ActivitySource(name ?? string.Empty, version));
+ {
+ var tracers = this.tracers;
+ if (tracers == null)
+ {
+ // Note: Returns a no-op Tracer once dispose has been called.
+ return new(activitySource: null);
+ }
+
+ var key = threadTracerKey == null
+ ? (threadTracerKey = new TracerKey(name, version))
+ : threadTracerKey.Update(name, version);
+
+ if (tracers[key] is not Tracer tracer)
+ {
+ lock (tracers)
+ {
+ tracer = (tracers[key] as Tracer)!;
+ if (tracer == null)
+ {
+ if (this.tracers != null)
+ {
+ tracer = new(new(key.Name, key.Version));
+
+ // Note: key is copied if we write into the hashtable
+ // because it must hold onto something immutable.
+ tracers[key.Copy()] = tracer;
+ }
+ }
+ }
+ }
+
+ return tracer ?? new(activitySource: null);
+ }
+
+ /// <inheritdoc/>
+ protected override void Dispose(bool disposing)
+ {
+ if (disposing)
+ {
+ var tracers = Interlocked.CompareExchange(ref this.tracers, null, this.tracers);
+ if (tracers != null)
+ {
+ lock (tracers)
+ {
+ foreach (DictionaryEntry entry in tracers)
+ {
+ var tracer = (Tracer)entry.Value!;
+ var activitySource = tracer.ActivitySource;
+ tracer.ActivitySource = null;
+ activitySource?.Dispose();
+ }
+
+ tracers.Clear();
+ }
+ }
+ }
+
+ base.Dispose(disposing);
+ }
+
+ private sealed record class TracerKey
+ {
+ public TracerKey(string? name, string? version)
+ {
+ this.Update(name, version);
+ }
+
+ public string Name { get; private set; }
+#if !NET6_0_OR_GREATER
+ = string.Empty;
+#endif
+
+ public string? Version { get; private set; }
+
+#if NET6_0_OR_GREATER
+ [MemberNotNull(nameof(Name))]
+#endif
+ public TracerKey Update(string? name, string? version)
+ {
+ this.Name = name ?? string.Empty;
+ this.Version = version;
+
+ return this;
+ }
+
+ public TracerKey Copy()
+ => new(this.Name, this.Version);
+ }
 }

test/OpenTelemetry.Api.Tests/Trace/TracerTest.cs

@@ -283,6 +283,32 @@ public void CreateSpan_NotSampled()
  Assert.False(span.IsRecording);
  }
 
+ [Fact]
+ public void TracerBecomesNoopWhenParentProviderIsDisposedTest()
+ {
+ TracerProvider provider = null;
+ Tracer tracer = null;
+
+ using (var tracerProvider = Sdk.CreateTracerProviderBuilder()
+ .AddSource("mytracer")
+ .Build())
+ {
+ provider = tracerProvider;
+ tracer = tracerProvider.GetTracer("mytracer");
+
+ var span1 = tracer.StartSpan("foo");
+ Assert.True(span1.IsRecording);
+ }
+
+ var span2 = tracer.StartSpan("foo");
+ Assert.False(span2.IsRecording);
+
+ var tracer2 = provider.GetTracer("mytracer");
+
+ var span3 = tracer2.StartSpan("foo");
+ Assert.False(span3.IsRecording);
+ }
+
  public void Dispose()
  {
  Activity.Current = null;