InheritedContext.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "HAL/LowLevelMemTracker.h"
#include "ProfilingDebugging/MetadataTrace.h"
#include "ProfilingDebugging/TagTrace.h"
 
namespace UE
{
#if ENABLE_LOW_LEVEL_MEM_TRACKER
    struct FLLMActiveTagsCapture
    {
        const UE::LLMPrivate::FTagData* LLMTags[static_cast<uint32>(ELLMTagSet::Max)];
 
        void CaptureActiveTagData()
        {
            for (int32 TagSetIndex = 0; TagSetIndex < static_cast<int32>(ELLMTagSet::Max); ++TagSetIndex)
            {
                LLMTags[TagSetIndex] = FLowLevelMemTracker::IsEnabled() ?
                    FLowLevelMemTracker::Get().GetActiveTagData(ELLMTracker::Default, static_cast<ELLMTagSet>(TagSetIndex))
                    : nullptr;
            }
        }
    };
 
    struct FLLMActiveTagsScope
    {
        TArray<FLLMScope, TFixedAllocator<static_cast<uint32>(ELLMTagSet::Max)>> LLMScopes;
 
        explicit FLLMActiveTagsScope(const FLLMActiveTagsCapture& InActiveTagsCapture)
        {
            CaptureLLMScopes(InActiveTagsCapture);
        }
 
        void CaptureLLMScopes(const FLLMActiveTagsCapture& InActiveTagsCapture)
        {
            for (int32 TagSetIndex = 0; TagSetIndex < static_cast<int32>(ELLMTagSet::Max); ++TagSetIndex)
            {
                LLMScopes.Emplace(InActiveTagsCapture.LLMTags[TagSetIndex], false /* bIsStatTag */, static_cast<ELLMTagSet>(TagSetIndex), ELLMTracker::Default);
            }
        }
    };
#endif
 
    // Restores an inherited contex for the current scope.
    // An instance must be obtained by calling `FInheritedContextBase::RestoreInheritedContext()`
    class FInheritedContextScope
    {
    private:
        UE_NONCOPYABLE(FInheritedContextScope);
 
        friend class FInheritedContextBase; // allow construction only by `FInheritedContextBase`
        
        FInheritedContextScope(
#if ENABLE_LOW_LEVEL_MEM_TRACKER
            const FLLMActiveTagsCapture& InInheritedLLMTag
    #if UE_TRACE_ENABLED && (UE_MEMORY_TAGS_TRACE_ENABLED || UE_TRACE_METADATA_ENABLED)
            ,
    #endif
#endif
#if (UE_MEMORY_TAGS_TRACE_ENABLED && UE_TRACE_ENABLED)
            int32 InInheritedMemTag
    #if (UE_TRACE_METADATA_ENABLED && UE_TRACE_ENABLED)
            ,
    #endif
#endif
#if (UE_TRACE_METADATA_ENABLED && UE_TRACE_ENABLED)
            uint32 InInheritedMetadataId
#endif
        )
#if ENABLE_LOW_LEVEL_MEM_TRACKER
            : LLMScopes(InInheritedLLMTag)
    #if UE_TRACE_ENABLED && (UE_MEMORY_TAGS_TRACE_ENABLED || UE_TRACE_METADATA_ENABLED)
            ,
    #endif
#endif
#if (UE_MEMORY_TAGS_TRACE_ENABLED && UE_TRACE_ENABLED)
    #if !ENABLE_LOW_LEVEL_MEM_TRACKER
            :
    #endif
            MemScope(InInheritedMemTag)
    #if (UE_TRACE_METADATA_ENABLED && UE_TRACE_ENABLED)
            ,
    #endif
#endif
#if (UE_TRACE_METADATA_ENABLED && UE_TRACE_ENABLED)
    #if !ENABLE_LOW_LEVEL_MEM_TRACKER && !(UE_MEMORY_TAGS_TRACE_ENABLED && UE_TRACE_ENABLED)
            :
    #endif
            MetaScope(InInheritedMetadataId)
#endif
        {
        }
 
    private:
#if ENABLE_LOW_LEVEL_MEM_TRACKER
        FLLMActiveTagsScope LLMScopes;
#endif
 
#if (UE_MEMORY_TAGS_TRACE_ENABLED && UE_TRACE_ENABLED)
        FMemScope MemScope;
#endif
 
#if (UE_TRACE_METADATA_ENABLED && UE_TRACE_ENABLED) 
        FMetadataRestoreScope MetaScope;
#endif
    };
 
    // this class extends the inherited context (see private members for what the inherited context is) to cover async execution. 
    // Is intended to be used as a base class, if the inherited context is compiled out it takes 0 space
    class FInheritedContextBase
    {
    public:
        // must be called in the inherited context, e.g. on launching an async task
        void CaptureInheritedContext()
        {
#if ENABLE_LOW_LEVEL_MEM_TRACKER
            InheritedLLMTags.CaptureActiveTagData();
#endif
 
#if UE_MEMORY_TAGS_TRACE_ENABLED && UE_TRACE_ENABLED
            InheritedMemTag = MemoryTrace_GetActiveTag();
#endif
 
#if UE_TRACE_METADATA_ENABLED && UE_TRACE_ENABLED
            InheritedMetadataId = UE_TRACE_METADATA_SAVE_STACK();
#endif
        }
 
        // must be called where the inherited context should be restored, e.g. at the start of an async task execution
        [[nodiscard]] CORE_API FInheritedContextScope RestoreInheritedContext();
 
    private:
#if ENABLE_LOW_LEVEL_MEM_TRACKER
        FLLMActiveTagsCapture InheritedLLMTags;
#endif
 
#if UE_MEMORY_TAGS_TRACE_ENABLED && UE_TRACE_ENABLED
        int32 InheritedMemTag;
#endif
 
#if UE_TRACE_METADATA_ENABLED && UE_TRACE_ENABLED
        uint32 InheritedMetadataId;
#endif
    };
}