chore: Made DynamicSampleContext mutable

jamescrosswell · jamescrosswell · commit e9b3962e8820 · 2025-08-20T15:42:31.000+12:00
Resolves #4381 - #4381 #skip-changelog
diff --git a/src/Sentry/DynamicSamplingContext.cs b/src/Sentry/DynamicSamplingContext.cs
@@ -9,16 +9,16 @@ namespace Sentry;
 /// <seealso href="https://develop.sentry.dev/sdk/performance/dynamic-sampling-context"/>
 internal class DynamicSamplingContext
 {
-    public IReadOnlyDictionary<string, string> Items { get; }
+    public Dictionary<string, string> Items { get; }
 
     public bool IsEmpty => Items.Count == 0;
 
-    private DynamicSamplingContext(IReadOnlyDictionary<string, string> items) => Items = items;
+    private DynamicSamplingContext(Dictionary<string, string> items) => Items = items;
 
     /// <summary>
     /// Gets an empty <see cref="DynamicSamplingContext"/> that can be used to "freeze" the DSC on a transaction.
     /// </summary>
-    public static readonly DynamicSamplingContext Empty = new(new Dictionary<string, string>().AsReadOnly());
+    public static DynamicSamplingContext Empty => new(new Dictionary<string, string>());
 
     private DynamicSamplingContext(SentryId traceId,
         string publicKey,
@@ -98,34 +98,19 @@ private DynamicSamplingContext(SentryId traceId,
 
     public BaggageHeader ToBaggageHeader() => BaggageHeader.Create(Items, useSentryPrefix: true);
 
-    public DynamicSamplingContext WithSampleRate(double sampleRate)
+    public void SetSampleRate(double sampleRate)
     {
-        if (Items.TryGetValue("sample_rate", out var dscSampleRate))
-        {
-            if (double.TryParse(dscSampleRate, NumberStyles.Float, CultureInfo.InvariantCulture, out var rate))
-            {
-                if (Math.Abs(rate - sampleRate) > double.Epsilon)
-                {
-                    var items = Items.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
-                    items["sample_rate"] = sampleRate.ToString(CultureInfo.InvariantCulture);
-                    return new DynamicSamplingContext(items);
-                }
-            }
-        }
-
-        return this;
+        Items["sample_rate"] = sampleRate.ToString(CultureInfo.InvariantCulture);
     }
 
-    public DynamicSamplingContext WithReplayId(IReplaySession? replaySession)
+    internal DynamicSamplingContext Clone() => new(new Dictionary<string, string>(Items));
+
+    public void SetReplayId(IReplaySession? replaySession)
     {
-        if (replaySession?.ActiveReplayId is not { } replayId || replayId == SentryId.Empty)
+        if (replaySession?.ActiveReplayId is { } replayId && replayId != SentryId.Empty)
         {
-            return this;
+            Items["replay_id"] = replayId.ToString();
         }
-
-        var items = Items.ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
-        items["replay_id"] = replayId.ToString();
-        return new DynamicSamplingContext(items);
     }
 
     public static DynamicSamplingContext? CreateFromBaggageHeader(BaggageHeader baggage, IReplaySession? replaySession)
diff --git a/src/Sentry/Internal/Hub.cs b/src/Sentry/Internal/Hub.cs
@@ -193,7 +193,7 @@ internal ITransactionTracer StartTransaction(
                 isSampled = SampleRandHelper.IsSampled(sampleRand, samplerSampleRate);
 
                 // Ensure the actual sampleRate is set on the provided DSC (if any) when the TracesSampler reached a sampling decision
-                dynamicSamplingContext = dynamicSamplingContext?.WithSampleRate(samplerSampleRate);
+                dynamicSamplingContext?.SetSampleRate(samplerSampleRate);
             }
         }
 
@@ -207,12 +207,12 @@ internal ITransactionTracer StartTransaction(
             if (context.IsSampled is null && _options.TracesSampleRate is not null)
             {
                 // Ensure the actual sampleRate is set on the provided DSC (if any) when not IsSampled upstream but the TracesSampleRate reached a sampling decision
-                dynamicSamplingContext = dynamicSamplingContext?.WithSampleRate(_options.TracesSampleRate.Value);
+                dynamicSamplingContext?.SetSampleRate(_options.TracesSampleRate.Value);
             }
         }
 
         // Make sure there is a replayId (if available) on the provided DSC (if any).
-        dynamicSamplingContext = dynamicSamplingContext?.WithReplayId(_replaySession);
+        dynamicSamplingContext?.SetReplayId(_replaySession);
 
         if (isSampled is false)
         {
diff --git a/test/Sentry.Tests/HubTests.cs b/test/Sentry.Tests/HubTests.cs
@@ -743,6 +743,7 @@ public void StartTransaction_DynamicSamplingContextWithSampleRate_OverwritesSamp
             {"sentry-sample_rate", "0.5"},
             {"sentry-sample_rand", "0.1234"},
         }).CreateDynamicSamplingContext();
+        var originalDsc = dsc?.Clone();
 
         _fixture.Options.TracesSampler = _ => tracesSampler;
         _fixture.Options.TracesSampleRate = tracesSampleRate;
@@ -759,12 +760,12 @@ public void StartTransaction_DynamicSamplingContextWithSampleRate_OverwritesSamp
             transactionTracer.SampleRate.Should().Be(expectedSampleRate);
             if (expectedDscOverwritten)
             {
-                transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
-                transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(expectedSampleRate));
+                transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(originalDsc);
+                transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc.CloneWithSampleRate(expectedSampleRate));
             }
             else
             {
-                transactionTracer.DynamicSamplingContext.Should().BeSameAs(dsc);
+                transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc);
             }
         }
         else
@@ -773,12 +774,12 @@ public void StartTransaction_DynamicSamplingContextWithSampleRate_OverwritesSamp
             unsampledTransaction.SampleRate.Should().Be(expectedSampleRate);
             if (expectedDscOverwritten)
             {
-                unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(dsc);
-                unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(expectedSampleRate));
+                unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(originalDsc);
+                unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc.CloneWithSampleRate(expectedSampleRate));
             }
             else
             {
-                unsampledTransaction.DynamicSamplingContext.Should().BeSameAs(dsc);
+                unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc);
             }
         }
     }
@@ -814,12 +815,12 @@ public void StartTransaction_DynamicSamplingContextWithReplayId_UsesActiveReplay
         transactionTracer.IsSampled.Should().BeTrue();
         transactionTracer.DynamicSamplingContext.Should().NotBeNull();
 
-        var expectedDsc = dsc.ReplaceSampleRate(_fixture.Options.TracesSampleRate.Value);
+        var expectedDsc = dsc.CloneWithSampleRate(_fixture.Options.TracesSampleRate.Value);
         if (replaySessionIsActive)
         {
             // We overwrite the replay_id when we have an active replay session
             // Otherwise we propagate whatever was in the baggage header
-            expectedDsc = expectedDsc.ReplaceReplayId(_fixture.ReplaySession);
+            expectedDsc = expectedDsc.CloneWithReplayId(_fixture.ReplaySession);
         }
         transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(expectedDsc);
     }
@@ -905,6 +906,7 @@ public void StartTransaction_DynamicSamplingContextWithSampleRand_InheritsSample
             {"sentry-sample_rate", "0.5"}, // Required in the baggage header, but ignored by sampling logic
             {"sentry-sample_rand", "0.1234"}
         }).CreateDynamicSamplingContext(dummyReplaySession);
+        var originalDsc = dsc.Clone();
 
         _fixture.Options.TracesSampleRate = 0.4;
         var hub = _fixture.GetSut();
@@ -917,8 +919,8 @@ public void StartTransaction_DynamicSamplingContextWithSampleRand_InheritsSample
         transactionTracer.IsSampled.Should().BeTrue();
         transactionTracer.SampleRate.Should().Be(0.4);
         transactionTracer.SampleRand.Should().Be(0.1234);
-        transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
-        transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(0.4));
+        transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(originalDsc);
+        transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc.CloneWithSampleRate(0.4));
     }
 
     [Theory]
@@ -937,6 +939,7 @@ public void StartTransaction_TraceSampler_UsesSampleRand(double sampleRate, bool
             {"sentry-sample_rate", "0.5"},
             {"sentry-sample_rand", "0.1234"}
         }).CreateDynamicSamplingContext(_fixture.ReplaySession);
+        var originalDsc = dsc.Clone();
 
         _fixture.Options.TracesSampler = _ => sampleRate;
         var hub = _fixture.GetSut();
@@ -951,17 +954,17 @@ public void StartTransaction_TraceSampler_UsesSampleRand(double sampleRate, bool
             transactionTracer.IsSampled.Should().BeTrue();
             transactionTracer.SampleRate.Should().Be(sampleRate);
             transactionTracer.SampleRand.Should().Be(0.1234);
-            transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
-            transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
+            transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(originalDsc);
+            transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc.CloneWithSampleRate(sampleRate));
         }
         else
         {
             var unsampledTransaction = transaction.Should().BeOfType<UnsampledTransaction>().Subject;
             unsampledTransaction.IsSampled.Should().BeFalse();
             unsampledTransaction.SampleRate.Should().Be(sampleRate);
             unsampledTransaction.SampleRand.Should().Be(0.1234);
-            unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(dsc);
-            unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
+            unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(originalDsc);
+            unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc.CloneWithSampleRate(sampleRate));
         }
     }
 
@@ -981,6 +984,7 @@ public void StartTransaction_StaticSampler_UsesSampleRand(double sampleRate, boo
             {"sentry-sample_rate", "0.5"}, // Static sampling ignores this and uses options.TracesSampleRate instead
             {"sentry-sample_rand", "0.1234"}
         }).CreateDynamicSamplingContext(dummyReplaySession);
+        var originalDsc = dsc.Clone();
 
         _fixture.Options.TracesSampleRate = sampleRate;
         var hub = _fixture.GetSut();
@@ -995,17 +999,17 @@ public void StartTransaction_StaticSampler_UsesSampleRand(double sampleRate, boo
             transactionTracer.IsSampled.Should().BeTrue();
             transactionTracer.SampleRate.Should().Be(sampleRate);
             transactionTracer.SampleRand.Should().Be(0.1234);
-            transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(dsc);
-            transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
+            transactionTracer.DynamicSamplingContext.Should().NotBeSameAs(originalDsc);
+            transactionTracer.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc.CloneWithSampleRate(sampleRate));
         }
         else
         {
             var unsampledTransaction = transaction.Should().BeOfType<UnsampledTransaction>().Subject;
             unsampledTransaction.IsSampled.Should().BeFalse();
             unsampledTransaction.SampleRate.Should().Be(sampleRate);
             unsampledTransaction.SampleRand.Should().Be(0.1234);
-            unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(dsc);
-            unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(dsc.ReplaceSampleRate(sampleRate));
+            unsampledTransaction.DynamicSamplingContext.Should().NotBeSameAs(originalDsc);
+            unsampledTransaction.DynamicSamplingContext.Should().BeEquivalentTo(originalDsc.CloneWithSampleRate(sampleRate));
         }
     }
 
@@ -1255,7 +1259,7 @@ public void GetBaggage_SpanActive_ReturnsBaggageFromSpan(bool isSampled)
         baggage.Members.Should().Equal([
             new KeyValuePair<string, string>("sentry-trace_id", "43365712692146d08ee11a729dfbcaca"),
             new KeyValuePair<string, string>("sentry-public_key", "d4d82fc1c2c4032a83f3a29aa3a3aff"),
-            new KeyValuePair<string, string>("sentry-sample_rate", isSampled ? "1" : "0.0"),
+            new KeyValuePair<string, string>("sentry-sample_rate", isSampled ? "1" : "0"),
             new KeyValuePair<string, string>("sentry-sample_rand", sampleRand!.Value.ToString(CultureInfo.InvariantCulture)),
         ]);
     }
@@ -2409,63 +2413,19 @@ internal partial class HubTestsJsonContext : JsonSerializerContext
 #nullable enable
 file static class DynamicSamplingContextExtensions
 {
-    public static DynamicSamplingContext ReplaceSampleRate(this DynamicSamplingContext? dsc, double sampleRate)
+    public static DynamicSamplingContext CloneWithSampleRate(this DynamicSamplingContext? dsc, double sampleRate)
     {
         Assert.NotNull(dsc);
-
-        var value = sampleRate.ToString(CultureInfo.InvariantCulture);
-        return dsc.Replace("sentry-sample_rate", value);
+        var newDsc = dsc.Clone();
+        newDsc.SetSampleRate(sampleRate);
+        return newDsc;
     }
 
-    public static DynamicSamplingContext ReplaceReplayId(this DynamicSamplingContext? dsc, IReplaySession replaySession)
+    public static DynamicSamplingContext CloneWithReplayId(this DynamicSamplingContext? dsc, IReplaySession replaySession)
     {
         Assert.NotNull(dsc);
-
-        if (!replaySession.ActiveReplayId.HasValue)
-        {
-            throw new InvalidOperationException($"No {nameof(IReplaySession.ActiveReplayId)}.");
-        }
-
-        var value = replaySession.ActiveReplayId.Value.ToString();
-        return dsc.Replace("sentry-replay_id", value);
-    }
-
-    private static DynamicSamplingContext Replace(this DynamicSamplingContext dsc, string key, string newValue)
-    {
-        var items = dsc.ToBaggageHeader().Members.ToList();
-        var index = items.FindSingleIndex(key);
-
-        var oldValue = items[index].Value;
-        if (oldValue == newValue)
-        {
-            throw new InvalidOperationException($"{key} already is {oldValue}.");
-        }
-
-        items[index] = new KeyValuePair<string, string>(key, newValue);
-
-        var baggage = BaggageHeader.Create(items);
-        var dynamicSamplingContext = DynamicSamplingContext.CreateFromBaggageHeader(baggage, null);
-        if (dynamicSamplingContext is null)
-        {
-            throw new InvalidOperationException($"Invalid {nameof(BaggageHeader)}: {baggage}");
-        }
-
-        return dynamicSamplingContext;
-    }
-
-    private static int FindSingleIndex(this List<KeyValuePair<string, string>> items, string key)
-    {
-        var index = items.FindIndex(item => item.Key == key);
-        if (index == -1)
-        {
-            throw new InvalidOperationException($"{key} not found.");
-        }
-
-        if (items.FindLastIndex(item => item.Key == key) != index)
-        {
-            throw new InvalidOperationException($"Duplicate {key} found.");
-        }
-
-        return index;
+        var newDsc = dsc.Clone();
+        newDsc.SetReplayId(replaySession);
+        return newDsc;
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -193,7 +193,7 @@ internal ITransactionTracer StartTransaction(`
`193`	`193`	`isSampled = SampleRandHelper.IsSampled(sampleRand, samplerSampleRate);`
`194`	`194`
`195`	`195`	`// Ensure the actual sampleRate is set on the provided DSC (if any) when the TracesSampler reached a sampling decision`
`196`		`- dynamicSamplingContext = dynamicSamplingContext?.WithSampleRate(samplerSampleRate);`
	`196`	`+ dynamicSamplingContext?.SetSampleRate(samplerSampleRate);`
`197`	`197`	`}`
`198`	`198`	`}`
`199`	`199`
`@@ -207,12 +207,12 @@ internal ITransactionTracer StartTransaction(`
`207`	`207`	`if (context.IsSampled is null && _options.TracesSampleRate is not null)`
`208`	`208`	`{`
`209`	`209`	`// Ensure the actual sampleRate is set on the provided DSC (if any) when not IsSampled upstream but the TracesSampleRate reached a sampling decision`
`210`		`- dynamicSamplingContext = dynamicSamplingContext?.WithSampleRate(_options.TracesSampleRate.Value);`
	`210`	`+ dynamicSamplingContext?.SetSampleRate(_options.TracesSampleRate.Value);`
`211`	`211`	`}`
`212`	`212`	`}`
`213`	`213`
`214`	`214`	`// Make sure there is a replayId (if available) on the provided DSC (if any).`
`215`		`- dynamicSamplingContext = dynamicSamplingContext?.WithReplayId(_replaySession);`
	`215`	`+ dynamicSamplingContext?.SetReplayId(_replaySession);`
`216`	`216`
`217`	`217`	`if (isSampled is false)`
`218`	`218`	`{`