Add traces sampling function support for Windows and Linux

CHANGELOG.md

@@ -10,11 +10,14 @@
   - `CaptureUserFeedback` function in `SentrySubsystem` replaced with `CaptureFeedback`
   - `CreateSentryUserFeedback` function in `SentryLibrary` replaced with `CreateSentryFeedback`
 - On Windows and Linux, `ToString` function of `SentryId` class now returns the ID without dashes
+- `StartTransactionWithContextAndOptions` function in `SentrySubsystem` now accepts `FSentryTransactionOptions` struct instead of string map
+- `GetCustomSamplingContext` function in `SentrySamplingContext` now returns `TMap<FString, FSentryVariant>` instead of string map
 
 ### Features
 
 - Add functionality to give/revoke user consent for crash uploads ([#1053](https://github.com/getsentry/sentry-unreal/pull/1053))
 - Add new API for capturing user feedback ([#1051](https://github.com/getsentry/sentry-unreal/pull/1051))
+- Add Traces sampling function support for Windows and Linux ([#1057](https://github.com/getsentry/sentry-unreal/pull/1057))
 - Read `DSN`, `Environment` and `Release` options from environment variables ([#1054](https://github.com/getsentry/sentry-unreal/pull/1054))
 
 ### Dependencies

plugin-dev/Source/Sentry/Private/Android/AndroidSentrySamplingContext.cpp

@@ -24,15 +24,15 @@ TSharedPtr<ISentryTransactionContext> FAndroidSentrySamplingContext::GetTransact
 	return MakeShareable(new FAndroidSentryTransactionContext(*transactionContext));
 }
 
-TMap<FString, FString> FAndroidSentrySamplingContext::GetCustomSamplingContext() const
+TMap<FString, FSentryVariant> FAndroidSentrySamplingContext::GetCustomSamplingContext() const
 {
 	auto customSamplingContext = CallObjectMethod<jobject>(GetCustomSamplingContextMethod);
 	if (!customSamplingContext)
-		return TMap<FString, FString>();
+		return TMap<FString, FSentryVariant>();
 
 	FSentryJavaObjectWrapper NativeCustomSamplingContext(SentryJavaClasses::CustomSamplingContext, *customSamplingContext);
 	FSentryJavaMethod GetDataMethod = NativeCustomSamplingContext.GetMethod("getData", "()Ljava/util/Map;");
 
 	auto data = NativeCustomSamplingContext.CallObjectMethod<jobject>(GetDataMethod);
-	return FAndroidSentryConverters::StringMapToUnreal(*data);
+	return FAndroidSentryConverters::VariantMapToUnreal(*data);
 }

plugin-dev/Source/Sentry/Private/Android/AndroidSentrySamplingContext.h

@@ -14,7 +14,7 @@ class FAndroidSentrySamplingContext : public ISentrySamplingContext, public FSen
 	void SetupClassMethods();
 
 	virtual TSharedPtr<ISentryTransactionContext> GetTransactionContext() const override;
-	virtual TMap<FString, FString> GetCustomSamplingContext() const override;
+	virtual TMap<FString, FSentryVariant> GetCustomSamplingContext() const override;
 
 private:
 	FSentryJavaMethod GetTransactionContextMethod;

plugin-dev/Source/Sentry/Private/Android/AndroidSentrySubsystem.cpp

@@ -297,12 +297,12 @@ TSharedPtr<ISentryTransaction> FAndroidSentrySubsystem::StartTransactionWithCont
 	return StartTransactionWithContext(context);
 }
 
-TSharedPtr<ISentryTransaction> FAndroidSentrySubsystem::StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const TMap<FString, FString>& options)
+TSharedPtr<ISentryTransaction> FAndroidSentrySubsystem::StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const FSentryTransactionOptions& options)
 {
 	TSharedPtr<FAndroidSentryTransactionContext> transactionContextAndroid = StaticCastSharedPtr<FAndroidSentryTransactionContext>(context);
 
 	TSharedPtr<FAndroidSentryTransactionOptions> transactionOptionsAndroid = MakeShareable(new FAndroidSentryTransactionOptions());
-	transactionOptionsAndroid->SetCustomSamplingContext(options);
+	transactionOptionsAndroid->SetCustomSamplingContext(options.CustomSamplingContext);
 
 	auto transaction = FSentryJavaObjectWrapper::CallStaticObjectMethod<jobject>(SentryJavaClasses::Sentry, "startTransaction", "(Lio/sentry/TransactionContext;Lio/sentry/TransactionOptions;)Lio/sentry/ITransaction;",
 		transactionContextAndroid->GetJObject(), transactionOptionsAndroid->GetJObject());

plugin-dev/Source/Sentry/Private/Android/AndroidSentrySubsystem.h

@@ -37,7 +37,7 @@ class FAndroidSentrySubsystem : public ISentrySubsystem
 	virtual TSharedPtr<ISentryTransaction> StartTransaction(const FString& name, const FString& operation) override;
 	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContext(TSharedPtr<ISentryTransactionContext> context) override;
 	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContextAndTimestamp(TSharedPtr<ISentryTransactionContext> context, int64 timestamp) override;
-	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const TMap<FString, FString>& options) override;
+	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const FSentryTransactionOptions& options) override;
 	virtual TSharedPtr<ISentryTransactionContext> ContinueTrace(const FString& sentryTrace, const TArray<FString>& baggageHeaders) override;
 
 	virtual void HandleAssert() override;

plugin-dev/Source/Sentry/Private/Android/AndroidSentryTransactionOptions.cpp

@@ -16,14 +16,14 @@ void FAndroidSentryTransactionOptions::SetupClassMethods()
 	SetCustomSamplingContextMethod = GetMethod("setCustomSamplingContext", "(Lio/sentry/CustomSamplingContext;)V");
 }
 
-void FAndroidSentryTransactionOptions::SetCustomSamplingContext(const TMap<FString, FString>& data)
+void FAndroidSentryTransactionOptions::SetCustomSamplingContext(const TMap<FString, FSentryVariant>& data)
 {
 	FSentryJavaObjectWrapper NativeCustomSamplingContext(SentryJavaClasses::CustomSamplingContext, "()V");
 	FSentryJavaMethod SetMethod = NativeCustomSamplingContext.GetMethod("set", "(Ljava/lang/String;Ljava/lang/Object;)V");
 
 	for (const auto& dataItem : data)
 	{
-		NativeCustomSamplingContext.CallMethod<void>(SetMethod, *GetJString(dataItem.Key), *GetJString(dataItem.Value));
+		NativeCustomSamplingContext.CallMethod<void>(SetMethod, *GetJString(dataItem.Key), FAndroidSentryConverters::VariantToNative(dataItem.Value)->GetJObject());
 	}
 
 	CallMethod<void>(SetCustomSamplingContextMethod, NativeCustomSamplingContext.GetJObject());

plugin-dev/Source/Sentry/Private/Android/AndroidSentryTransactionOptions.h

@@ -2,6 +2,8 @@
 
 #pragma once
 
+#include "SentryVariant.h"
+
 #include "Infrastructure/AndroidSentryJavaObjectWrapper.h"
 
 class FAndroidSentryTransactionOptions : public FSentryJavaObjectWrapper
@@ -11,7 +13,7 @@ class FAndroidSentryTransactionOptions : public FSentryJavaObjectWrapper
 
 	void SetupClassMethods();
 
-	void SetCustomSamplingContext(const TMap<FString, FString>& data);
+	void SetCustomSamplingContext(const TMap<FString, FSentryVariant>& data);
 
 private:
 	FSentryJavaMethod SetCustomSamplingContextMethod;

plugin-dev/Source/Sentry/Private/Apple/AppleSentrySamplingContext.cpp

@@ -22,9 +22,9 @@ TSharedPtr<ISentryTransactionContext> FAppleSentrySamplingContext::GetTransactio
 	return MakeShareable(new FAppleSentryTransactionContext(SamplingContext.transactionContext));
 }
 
-TMap<FString, FString> FAppleSentrySamplingContext::GetCustomSamplingContext() const
+TMap<FString, FSentryVariant> FAppleSentrySamplingContext::GetCustomSamplingContext() const
 {
-	return FAppleSentryConverters::StringMapToUnreal(SamplingContext.customSamplingContext);
+	return FAppleSentryConverters::VariantMapToUnreal(SamplingContext.customSamplingContext);
 }
 
 SentrySamplingContext* FAppleSentrySamplingContext::GetNativeObject()

plugin-dev/Source/Sentry/Private/Apple/AppleSentrySamplingContext.h

@@ -13,7 +13,7 @@ class FAppleSentrySamplingContext : public ISentrySamplingContext
 	virtual ~FAppleSentrySamplingContext() override;
 
 	virtual TSharedPtr<ISentryTransactionContext> GetTransactionContext() const override;
-	virtual TMap<FString, FString> GetCustomSamplingContext() const override;
+	virtual TMap<FString, FSentryVariant> GetCustomSamplingContext() const override;
 
 	SentrySamplingContext* GetNativeObject();
 

plugin-dev/Source/Sentry/Private/Apple/AppleSentrySubsystem.cpp

@@ -387,12 +387,12 @@ TSharedPtr<ISentryTransaction> FAppleSentrySubsystem::StartTransactionWithContex
 	return StartTransactionWithContext(context);
 }
 
-TSharedPtr<ISentryTransaction> FAppleSentrySubsystem::StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const TMap<FString, FString>& options)
+TSharedPtr<ISentryTransaction> FAppleSentrySubsystem::StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const FSentryTransactionOptions& options)
 {
 	TSharedPtr<FAppleSentryTransactionContext> transactionContextIOS = StaticCastSharedPtr<FAppleSentryTransactionContext>(context);
 
 	id<SentrySpan> transaction = [SENTRY_APPLE_CLASS(SentrySDK) startTransactionWithContext:transactionContextIOS->GetNativeObject()
-																	  customSamplingContext:FAppleSentryConverters::StringMapToNative(options)];
+																	  customSamplingContext:FAppleSentryConverters::VariantMapToNative(options.CustomSamplingContext)];
 
 	return MakeShareable(new FAppleSentryTransaction(transaction));
 }

plugin-dev/Source/Sentry/Private/Apple/AppleSentrySubsystem.h

@@ -37,7 +37,7 @@ class FAppleSentrySubsystem : public ISentrySubsystem
 	virtual TSharedPtr<ISentryTransaction> StartTransaction(const FString& name, const FString& operation) override;
 	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContext(TSharedPtr<ISentryTransactionContext> context) override;
 	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContextAndTimestamp(TSharedPtr<ISentryTransactionContext> context, int64 timestamp) override;
-	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const TMap<FString, FString>& options) override;
+	virtual TSharedPtr<ISentryTransaction> StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const FSentryTransactionOptions& options) override;
 	virtual TSharedPtr<ISentryTransactionContext> ContinueTrace(const FString& sentryTrace, const TArray<FString>& baggageHeaders) override;
 
 	virtual void HandleAssert() override {}

plugin-dev/Source/Sentry/Private/GenericPlatform/GenericPlatformSentrySamplingContext.cpp

@@ -0,0 +1,33 @@
+// Copyright (c) 2025 Sentry. All Rights Reserved.
+
+#include "GenericPlatformSentrySamplingContext.h"
+#include "GenericPlatformSentryTransactionContext.h"
+
+#include "Infrastructure/GenericPlatformSentryConverters.h"
+
+#include "Convenience/GenericPlatformSentryInclude.h"
+
+#if USE_SENTRY_NATIVE
+
+FGenericPlatformSentrySamplingContext::FGenericPlatformSentrySamplingContext(sentry_transaction_context_t* transactionContext, sentry_value_t customSamplingContext)
+{
+	TransactionContext = transactionContext;
+	CustomSamplingContext = customSamplingContext;
+}
+
+FGenericPlatformSentrySamplingContext::~FGenericPlatformSentrySamplingContext()
+{
+	// Put custom destructor logic here if needed
+}
+
+TSharedPtr<ISentryTransactionContext> FGenericPlatformSentrySamplingContext::GetTransactionContext() const
+{
+	return MakeShareable(new FGenericPlatformSentryTransactionContext(TransactionContext));
+}
+
+TMap<FString, FSentryVariant> FGenericPlatformSentrySamplingContext::GetCustomSamplingContext() const
+{
+	return FGenericPlatformSentryConverters::VariantToUnreal(CustomSamplingContext);
+}
+
+#endif

plugin-dev/Source/Sentry/Private/GenericPlatform/GenericPlatformSentrySamplingContext.h

@@ -0,0 +1,27 @@
+// Copyright (c) 2025 Sentry. All Rights Reserved.
+
+#pragma once
+
+#include "Convenience/GenericPlatformSentryInclude.h"
+
+#include "Interface/SentrySamplingContextInterface.h"
+
+#if USE_SENTRY_NATIVE
+
+class FGenericPlatformSentrySamplingContext : public ISentrySamplingContext
+{
+public:
+	FGenericPlatformSentrySamplingContext(sentry_transaction_context_t* transactionContext, sentry_value_t customSamplingContext);
+	virtual ~FGenericPlatformSentrySamplingContext() override;
+
+	virtual TSharedPtr<ISentryTransactionContext> GetTransactionContext() const override;
+	virtual TMap<FString, FSentryVariant> GetCustomSamplingContext() const override;
+
+private:
+	sentry_transaction_context_t* TransactionContext;
+	sentry_value_t CustomSamplingContext;
+};
+
+typedef FGenericPlatformSentrySamplingContext FPlatformSentrySamplingContext;
+
+#endif

plugin-dev/Source/Sentry/Private/GenericPlatform/GenericPlatformSentrySubsystem.cpp

@@ -6,6 +6,7 @@
 #include "GenericPlatformSentryEvent.h"
 #include "GenericPlatformSentryFeedback.h"
 #include "GenericPlatformSentryId.h"
+#include "GenericPlatformSentrySamplingContext.h"
 #include "GenericPlatformSentryScope.h"
 #include "GenericPlatformSentryTransaction.h"
 #include "GenericPlatformSentryTransactionContext.h"
@@ -17,6 +18,7 @@
 #include "SentryDefines.h"
 #include "SentryEvent.h"
 #include "SentryModule.h"
+#include "SentrySamplingContext.h"
 #include "SentrySettings.h"
 
 #include "SentryTraceSampler.h"
@@ -44,6 +46,8 @@ extern CORE_API bool GIsGPUCrashed;
 
 #if USE_SENTRY_NATIVE
 
+static FGenericPlatformSentrySubsystem* GGenericPlatformSentrySubsystem;
+
 void PrintVerboseLog(sentry_level_t level, const char* message, va_list args, void* userdata)
 {
 	char buffer[512];
@@ -96,6 +100,18 @@ void PrintVerboseLog(sentry_level_t level, const char* message, va_list args, vo
 	}
 }
 
+/* static */ double FGenericPlatformSentrySubsystem::HandleTraceSampling(const sentry_transaction_context_t* transaction_ctx, sentry_value_t custom_sampling_ctx, const int* parent_sampled)
+{
+	if (GGenericPlatformSentrySubsystem)
+	{
+		return StaticCast<FGenericPlatformSentrySubsystem*>(GGenericPlatformSentrySubsystem)->OnTraceSampling(transaction_ctx, custom_sampling_ctx, parent_sampled);
+	}
+	else
+	{
+		return parent_sampled != nullptr ? *parent_sampled : 0.0;
+	}
+}
+
 sentry_value_t FGenericPlatformSentrySubsystem::OnBeforeSend(sentry_value_t event, void* hint, void* closure, bool isCrash)
 {
 	if (!closure || this != closure)
@@ -187,6 +203,42 @@ sentry_value_t FGenericPlatformSentrySubsystem::OnCrash(const sentry_ucontext_t*
 	return OnBeforeSend(event, nullptr, closure, true);
 }
 
+double FGenericPlatformSentrySubsystem::OnTraceSampling(const sentry_transaction_context_t* transaction_ctx, sentry_value_t custom_sampling_ctx, const int* parent_sampled)
+{
+	USentryTraceSampler* Sampler = GetTraceSampler();
+	if (!Sampler)
+	{
+		// If custom sampler isn't set skip further processing
+		return parent_sampled != nullptr ? *parent_sampled : 0.0;
+	}
+
+	if (FUObjectThreadContext::Get().IsRoutingPostLoad)
+	{
+		UE_LOG(LogSentrySdk, Log, TEXT("Executing traces sampler is not allowed during object post-loading."));
+		return parent_sampled != nullptr ? *parent_sampled : 0.0;
+	}
+
+	if (IsGarbageCollecting())
+	{
+		// If traces sampling happens during garbage collection we can't instantiate UObjects safely or obtain a GC lock
+		// since it will cause a deadlock (see https://github.com/getsentry/sentry-unreal/issues/850).
+		// In this case event will be reported without calling a `beforeSend` handler.
+		UE_LOG(LogSentrySdk, Log, TEXT("Executing traces sampler is not allowed during garbage collection."));
+		return parent_sampled != nullptr ? *parent_sampled : 0.0;
+	}
+
+	USentrySamplingContext* Context = USentrySamplingContext::Create(
+		MakeShareable(new FGenericPlatformSentrySamplingContext(const_cast<sentry_transaction_context_t*>(transaction_ctx), custom_sampling_ctx)));
+
+	float samplingValue;
+	if (Sampler->Sample(Context, samplingValue))
+	{
+		return samplingValue;
+	}
+
+	return parent_sampled != nullptr ? *parent_sampled : 0.0;
+}
+
 void FGenericPlatformSentrySubsystem::InitCrashReporter(const FString& release, const FString& environment)
 {
 	crashReporter = MakeShareable(new FGenericPlatformSentryCrashReporter);
@@ -233,6 +285,7 @@ void FGenericPlatformSentrySubsystem::AddByteAttachment(TSharedPtr<ISentryAttach
 FGenericPlatformSentrySubsystem::FGenericPlatformSentrySubsystem()
 	: beforeSend(nullptr)
 	, beforeBreadcrumb(nullptr)
+	, sampler(nullptr)
 	, crashReporter(nullptr)
 	, isEnabled(false)
 	, isStackTraceEnabled(true)
@@ -244,8 +297,11 @@ FGenericPlatformSentrySubsystem::FGenericPlatformSentrySubsystem()
 
 void FGenericPlatformSentrySubsystem::InitWithSettings(const USentrySettings* settings, USentryBeforeSendHandler* beforeSendHandler, USentryBeforeBreadcrumbHandler* beforeBreadcrumbHandler, USentryTraceSampler* traceSampler)
 {
+	GGenericPlatformSentrySubsystem = this;
+
 	beforeSend = beforeSendHandler;
 	beforeBreadcrumb = beforeBreadcrumbHandler;
+	sampler = traceSampler;
 
 	sentry_options_t* options = sentry_options_new();
 
@@ -290,7 +346,7 @@ void FGenericPlatformSentrySubsystem::InitWithSettings(const USentrySettings* se
 	}
 	if (settings->EnableTracing && settings->SamplingType == ESentryTracesSamplingType::TracesSampler)
 	{
-		UE_LOG(LogSentrySdk, Warning, TEXT("The Native SDK doesn't currently support sampling functions"));
+		sentry_options_set_traces_sampler(options, HandleTraceSampling);
 	}
 
 	ConfigureHandlerPath(options);
@@ -672,10 +728,17 @@ TSharedPtr<ISentryTransaction> FGenericPlatformSentrySubsystem::StartTransaction
 	return nullptr;
 }
 
-TSharedPtr<ISentryTransaction> FGenericPlatformSentrySubsystem::StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const TMap<FString, FString>& options)
+TSharedPtr<ISentryTransaction> FGenericPlatformSentrySubsystem::StartTransactionWithContextAndOptions(TSharedPtr<ISentryTransactionContext> context, const FSentryTransactionOptions& options)
 {
-	UE_LOG(LogSentrySdk, Log, TEXT("Transaction options currently not supported (and therefore ignored) on generic platform."));
-	return StartTransactionWithContext(context);
+	if (TSharedPtr<FGenericPlatformSentryTransactionContext> platformTransactionContext = StaticCastSharedPtr<FGenericPlatformSentryTransactionContext>(context))
+	{
+		if (sentry_transaction_t* nativeTransaction = sentry_transaction_start(platformTransactionContext->GetNativeObject(), FGenericPlatformSentryConverters::VariantMapToNative(options.CustomSamplingContext)))
+		{
+			return MakeShareable(new FGenericPlatformSentryTransaction(nativeTransaction));
+		}
+	}
+
+	return nullptr;
 }
 
 TSharedPtr<ISentryTransactionContext> FGenericPlatformSentrySubsystem::ContinueTrace(const FString& sentryTrace, const TArray<FString>& baggageHeaders)
@@ -699,6 +762,11 @@ USentryBeforeBreadcrumbHandler* FGenericPlatformSentrySubsystem::GetBeforeBreadc
 	return beforeBreadcrumb;
 }
 
+USentryTraceSampler* FGenericPlatformSentrySubsystem::GetTraceSampler()
+{
+	return sampler;
+}
+
 void FGenericPlatformSentrySubsystem::TryCaptureScreenshot()
 {
 	const FString& ScreenshotPath = GetScreenshotPath();