Avoid copying Activity tags and links when sampling

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/Activity.cs

@@ -1197,7 +1197,10 @@ internal static Activity Create(ActivitySource source, string name, ActivityKind
             activity.IdFormat = idFormat;
             activity._traceState = traceState;
 
-            if (links != null)
+            // Links and creation tags are unnecessary for activities sampled as PropagationData, so skip copying them.
+            bool copyData = request is ActivitySamplingResult.AllData or ActivitySamplingResult.AllDataAndRecorded;
+
+            if (copyData && links != null)
             {
                 using (IEnumerator<ActivityLink> enumerator = links.GetEnumerator())
                 {
@@ -1208,7 +1211,7 @@ internal static Activity Create(ActivitySource source, string name, ActivityKind
                 }
             }
 
-            if (tags != null)
+            if (copyData && tags != null)
             {
                 using (IEnumerator<KeyValuePair<string, object?>> enumerator = tags.GetEnumerator())
                 {

src/libraries/System.Diagnostics.DiagnosticSource/src/System/Diagnostics/ActivitySource.cs

@@ -153,8 +153,16 @@ public bool HasListeners()
         /// <param name="name">The operation name of the Activity.</param>
         /// <param name="kind">The <see cref="ActivityKind"/></param>
         /// <param name="parentContext">The parent <see cref="ActivityContext"/> object to initialize the created Activity object with.</param>
-        /// <param name="tags">The optional tags list to initialize the created Activity object with.</param>
-        /// <param name="links">The optional <see cref="ActivityLink"/> list to initialize the created Activity object with.</param>
+        /// <param name="tags">
+        /// The optional tags list to initialize the created Activity object with. The tags are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
+        /// <param name="links">
+        /// The optional <see cref="ActivityLink"/> list to initialize the created Activity object with. The links are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
         /// <param name="idFormat">The default Id format to use.</param>
         /// <returns>The created <see cref="Activity"/> object or null if there is no any listener.</returns>
         /// <remarks>
@@ -169,8 +177,16 @@ public bool HasListeners()
         /// <param name="name">The operation name of the Activity.</param>
         /// <param name="kind">The <see cref="ActivityKind"/></param>
         /// <param name="parentId">The parent Id to initialize the created Activity object with.</param>
-        /// <param name="tags">The optional tags list to initialize the created Activity object with.</param>
-        /// <param name="links">The optional <see cref="ActivityLink"/> list to initialize the created Activity object with.</param>
+        /// <param name="tags">
+        /// The optional tags list to initialize the created Activity object with. The tags are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
+        /// <param name="links">
+        /// The optional <see cref="ActivityLink"/> list to initialize the created Activity object with. The links are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
         /// <param name="idFormat">The default Id format to use.</param>
         /// <returns>The created <see cref="Activity"/> object or null if there is no any listener.</returns>
         /// <remarks>
@@ -194,8 +210,16 @@ public bool HasListeners()
         /// <param name="name">The operation name of the Activity.</param>
         /// <param name="kind">The <see cref="ActivityKind"/></param>
         /// <param name="parentContext">The parent <see cref="ActivityContext"/> object to initialize the created Activity object with.</param>
-        /// <param name="tags">The optional tags list to initialize the created Activity object with.</param>
-        /// <param name="links">The optional <see cref="ActivityLink"/> list to initialize the created Activity object with.</param>
+        /// <param name="tags">
+        /// The optional tags list to initialize the created Activity object with. The tags are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
+        /// <param name="links">
+        /// The optional <see cref="ActivityLink"/> list to initialize the created Activity object with. The links are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
         /// <param name="startTime">The optional start timestamp to set on the created Activity object.</param>
         /// <returns>The created <see cref="Activity"/> object or null if there is no any listener.</returns>
         public Activity? StartActivity(string name, ActivityKind kind, ActivityContext parentContext, IEnumerable<KeyValuePair<string, object?>>? tags = null, IEnumerable<ActivityLink>? links = null, DateTimeOffset startTime = default)
@@ -207,8 +231,16 @@ public bool HasListeners()
         /// <param name="name">The operation name of the Activity.</param>
         /// <param name="kind">The <see cref="ActivityKind"/></param>
         /// <param name="parentId">The parent Id to initialize the created Activity object with.</param>
-        /// <param name="tags">The optional tags list to initialize the created Activity object with.</param>
-        /// <param name="links">The optional <see cref="ActivityLink"/> list to initialize the created Activity object with.</param>
+        /// <param name="tags">
+        /// The optional tags list to initialize the created Activity object with. The tags are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
+        /// <param name="links">
+        /// The optional <see cref="ActivityLink"/> list to initialize the created Activity object with. The links are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
         /// <param name="startTime">The optional start timestamp to set on the created Activity object.</param>
         /// <returns>The created <see cref="Activity"/> object or null if there is no any listener.</returns>
         public Activity? StartActivity(string name, ActivityKind kind, string? parentId, IEnumerable<KeyValuePair<string, object?>>? tags = null, IEnumerable<ActivityLink>? links = null, DateTimeOffset startTime = default)
@@ -219,8 +251,16 @@ public bool HasListeners()
         /// </summary>
         /// <param name="kind">The <see cref="ActivityKind"/></param>
         /// <param name="parentContext">The parent <see cref="ActivityContext"/> object to initialize the created Activity object with.</param>
-        /// <param name="tags">The optional tags list to initialize the created Activity object with.</param>
-        /// <param name="links">The optional <see cref="ActivityLink"/> list to initialize the created Activity object with.</param>
+        /// <param name="tags">
+        /// The optional tags list to initialize the created Activity object with. The tags are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
+        /// <param name="links">
+        /// The optional <see cref="ActivityLink"/> list to initialize the created Activity object with. The links are made available to sampling callbacks,
+        /// but are only copied to the created Activity if the combined sampling result is <see cref="ActivitySamplingResult.AllData"/>
+        /// or <see cref="ActivitySamplingResult.AllDataAndRecorded"/>.
+        /// </param>
         /// <param name="startTime">The optional start timestamp to set on the created Activity object.</param>
         /// <param name="name">The operation name of the Activity.</param>
         /// <returns>The created <see cref="Activity"/> object or null if there is no any listener.</returns>

src/libraries/System.Diagnostics.DiagnosticSource/tests/ActivitySourceTests.cs

@@ -734,6 +734,194 @@ public void PropagationDataSamplingTest()
             }).Dispose();
         }
 
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void PropagationDataSamplingDoesNotCopyTagsAndLinksTest()
+        {
+            RemoteExecutor.Invoke(() => {
+                Activity.ForceDefaultIdFormat = true;
+                Activity.DefaultIdFormat = ActivityIdFormat.W3C;
+
+                using ActivitySource aSource = new ActivitySource("PropagationDataTagsAndLinksTest");
+
+                ActivitySamplingResult result = ActivitySamplingResult.PropagationData;
+                int sampledTags = 0;
+                int sampledLinks = 0;
+
+                using ActivityListener listener = new ActivityListener
+                {
+                    ShouldListenTo = (activitySource) => ReferenceEquals(activitySource, aSource),
+                    Sample = (ref ActivityCreationOptions<ActivityContext> activityOptions) =>
+                    {
+                        sampledTags = activityOptions.Tags.Count();
+                        sampledLinks = activityOptions.Links.Count();
+                        return result;
+                    }
+                };
+
+                ActivitySource.AddActivityListener(listener);
+
+                KeyValuePair<string, object>[] tags = [new("tag1", "value1"), new("tag2", "value2")];
+                ActivityLink[] links = [new ActivityLink(new ActivityContext(ActivityTraceId.CreateRandom(), ActivitySpanId.CreateRandom(), ActivityTraceFlags.None))];
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, default(ActivityContext), tags, links))
+                {
+                    Assert.NotNull(a);
+                    Assert.False(a.IsAllDataRequested);
+                    Assert.Empty(a.TagObjects);
+                    Assert.Empty(a.Links);
+                    Assert.Equal(2, sampledTags);
+                    Assert.Equal(1, sampledLinks);
+                }
+
+                result = ActivitySamplingResult.AllData;
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, default(ActivityContext), tags, links))
+                {
+                    Assert.NotNull(a);
+                    Assert.True(a.IsAllDataRequested);
+                    Assert.Equal(2, a.TagObjects.Count());
+                    Assert.Single(a.Links);
+                }
+            }).Dispose();
+        }
+
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void PropagationDataSamplingWithParentIdDoesNotCopyTagsAndLinksTest()
+        {
+            RemoteExecutor.Invoke(() => {
+                Activity.ForceDefaultIdFormat = true;
+                Activity.DefaultIdFormat = ActivityIdFormat.W3C;
+
+                using ActivitySource aSource = new ActivitySource("PropagationDataParentIdTest");
+
+                ActivitySamplingResult result = ActivitySamplingResult.PropagationData;
+                int sampledTags = 0;
+                int sampledLinks = 0;
+
+                using ActivityListener listener = new ActivityListener
+                {
+                    ShouldListenTo = (activitySource) => ReferenceEquals(activitySource, aSource),
+                    SampleUsingParentId = (ref ActivityCreationOptions<string> activityOptions) =>
+                    {
+                        sampledTags = activityOptions.Tags.Count();
+                        sampledLinks = activityOptions.Links.Count();
+                        return result;
+                    }
+                };
+
+                ActivitySource.AddActivityListener(listener);
+
+                string parentId = "00-0123456789abcdef0123456789abcdef-0123456789abcdef-01";
+                KeyValuePair<string, object>[] tags = [new("tag1", "value1")];
+                ActivityLink[] links = [new ActivityLink(new ActivityContext(ActivityTraceId.CreateRandom(), ActivitySpanId.CreateRandom(), ActivityTraceFlags.None))];
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, parentId, tags, links))
+                {
+                    Assert.NotNull(a);
+                    Assert.False(a.IsAllDataRequested);
+                    Assert.Equal(parentId, a.ParentId);
+                    Assert.Empty(a.TagObjects);
+                    Assert.Empty(a.Links);
+                    Assert.Equal(1, sampledTags);
+                    Assert.Equal(1, sampledLinks);
+                }
+
+                result = ActivitySamplingResult.AllData;
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, parentId, tags, links))
+                {
+                    Assert.NotNull(a);
+                    Assert.True(a.IsAllDataRequested);
+                    Assert.Single(a.TagObjects);
+                    Assert.Single(a.Links);
+                }
+            }).Dispose();
+        }
+
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void PropagationDataSamplingCopiesSamplingTagsButNotCreationTagsTest()
+        {
+            RemoteExecutor.Invoke(() => {
+                using ActivitySource aSource = new ActivitySource("PropagationDataSamplingTagsTest");
+
+                ActivitySamplingResult result = ActivitySamplingResult.PropagationData;
+
+                using ActivityListener listener = new ActivityListener
+                {
+                    ShouldListenTo = (activitySource) => ReferenceEquals(activitySource, aSource),
+                    Sample = (ref ActivityCreationOptions<ActivityContext> activityOptions) =>
+                    {
+                        activityOptions.SamplingTags.Add("sampler.tag", "value");
+                        return result;
+                    }
+                };
+
+                ActivitySource.AddActivityListener(listener);
+
+                KeyValuePair<string, object>[] tags = [new("creation.tag", "value")];
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, default(ActivityContext), tags))
+                {
+                    Assert.NotNull(a);
+                    Assert.False(a.IsAllDataRequested);
+                    Assert.Equal([new KeyValuePair<string, object>("sampler.tag", "value")], a.TagObjects);
+                }
+
+                result = ActivitySamplingResult.AllData;
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, default(ActivityContext), tags))
+                {
+                    Assert.NotNull(a);
+                    Assert.True(a.IsAllDataRequested);
+                    Assert.Contains(a.TagObjects, t => t.Key == "creation.tag" && (string)t.Value == "value");
+                    Assert.Contains(a.TagObjects, t => t.Key == "sampler.tag" && (string)t.Value == "value");
+                }
+            }).Dispose();
+        }
+
+        [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        public void PropagationDataSamplingWithMultipleListenersCopiesTagsAndLinksIfAnyRequestsDataTest()
+        {
+            RemoteExecutor.Invoke(() => {
+                using ActivitySource aSource = new ActivitySource("PropagationDataMultipleListenersTest");
+
+                using ActivityListener propagationListener = new ActivityListener
+                {
+                    ShouldListenTo = (activitySource) => ReferenceEquals(activitySource, aSource),
+                    Sample = (ref ActivityCreationOptions<ActivityContext> activityOptions) => ActivitySamplingResult.PropagationData
+                };
+
+                ActivitySource.AddActivityListener(propagationListener);
+
+                KeyValuePair<string, object>[] tags = [new("tag1", "value1")];
+                ActivityLink[] links = [new ActivityLink(new ActivityContext(ActivityTraceId.CreateRandom(), ActivitySpanId.CreateRandom(), ActivityTraceFlags.None))];
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, default(ActivityContext), tags, links))
+                {
+                    Assert.NotNull(a);
+                    Assert.False(a.IsAllDataRequested);
+                    Assert.Empty(a.TagObjects);
+                    Assert.Empty(a.Links);
+                }
+
+                using ActivityListener allDataListener = new ActivityListener
+                {
+                    ShouldListenTo = (activitySource) => ReferenceEquals(activitySource, aSource),
+                    Sample = (ref ActivityCreationOptions<ActivityContext> activityOptions) => ActivitySamplingResult.AllData
+                };
+
+                ActivitySource.AddActivityListener(allDataListener);
+
+                using (Activity a = aSource.StartActivity("a", ActivityKind.Server, default(ActivityContext), tags, links))
+                {
+                    Assert.NotNull(a);
+                    Assert.True(a.IsAllDataRequested);
+                    Assert.Single(a.TagObjects);
+                    Assert.Single(a.Links);
+                }
+            }).Dispose();
+        }
+
         [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
         public void TestExpectedListenersReturnValues()
         {