EM_Task/CoreUObject/Private/UObject/UObjectLinker.cpp

// Copyright Epic Games, Inc. All Rights Reserved.

/*=============================================================================
        UObjectLinker.cpp: Unreal object linker relationship management
=============================================================================*/

#include "CoreMinimal.h"
#include "UObject/UObjectBaseUtility.h"
#include "UObject/Object.h"
#include "UObject/LinkerLoad.h"
#include "UObject/Package.h"
#include "UObject/UObjectAnnotation.h"

DEFINE_LOG_CATEGORY_STATIC(LogUObjectLinker, Log, All);

//@todo UE4 Console - Check that the mapping of UObjects to linkers is sparse and that we aren't spending a ton of time with these lookups.

struct FLinkerIndexPair
{
    /**
     * default contructor
     * Default constructor must be the default item
     */
    FLinkerIndexPair(): Linker(NULL),
                        LinkerIndex(INDEX_NONE)
    {
        CheckInvariants();
    }
    /**
     * Determine if this linker pair is the default
     * @return true is this is a default pair. We only check the linker because CheckInvariants rules out bogus combinations
     */
    FORCEINLINE bool IsDefault()
    {
        CheckInvariants();
        return Linker == nullptr;
    }

    /**
     * Constructor
     * @param InLinker linker to assign
     * @param InLinkerIndex linker index to assign
     */
    FLinkerIndexPair(FLinkerLoad* InLinker, int32 InLinkerIndex): Linker(InLinker),
                                                                  LinkerIndex(InLinkerIndex)
    {
        CheckInvariants();
    }

    /**
     * check() that either the linker and the index is valid or neither of them are
     */
    FORCEINLINE void CheckInvariants()
    {
        check(!((Linker == nullptr) ^ (LinkerIndex == INDEX_NONE)));  // you need either a valid linker and index or neither valid
    }

    /**
     * Linker that contains the FObjectExport resource corresponding to
     * this object.  NULL if this object is native only (i.e. never stored
     * in an Unreal package), or if this object has been detached from its
     * linker, for e.g. renaming operations, saving the package, etc.
     */
    FLinkerLoad* Linker;

    /**
     * Index into the linker's ExportMap array for the FObjectExport resource
     * corresponding to this object.
     */
    int32 LinkerIndex;
};

template <>
struct TIsPODType<FLinkerIndexPair>
{
    enum
    {
        Value = false
    };
};

/**
 * Annotation to relate linkers, indices and uobjects
 *
 * Q: Why is this data structure not "garbage collection aware"
 * A: It does not need to be. This is GC-Safe.
 * Objects are detached from their linkers prior to destruction of either the linker or the object
 *
 * NOTE: We're currently using chunked annotations for linkers to emphasize memory
 * usage, but might want to revisit this decision on platforms that are memory limited.
 *
 * LINUX SERVER NOTE: For servers we are using Sparse to emphasize speed over memory usage
 */
#if PLATFORM_LINUX && UE_SERVER
static FUObjectAnnotationSparse<FLinkerIndexPair, false> LinkerAnnotation;
#else
static FUObjectAnnotationChunked<FLinkerIndexPair, false> LinkerAnnotation;
#endif

/** Remove all annotations on exit. This is to prevent issues with the order of static destruction of singletons. */
void CleanupLinkerAnnotations()
{
    // Remove all annotations and remove LinkerAnnotation from UObject delete listeners.
    LinkerAnnotation.RemoveAllAnnotations();
}

void UObject::SetLinker(FLinkerLoad* LinkerLoad, int32 LinkerIndex, bool bShouldDetachExisting)
{
    FLinkerIndexPair Existing = LinkerAnnotation.GetAnnotation(this);
    Existing.CheckInvariants();
    // Detach from existing linker.
    if (Existing.Linker && bShouldDetachExisting)
    {
        checkf(!HasAnyFlags(RF_NeedLoad | RF_NeedPostLoad), TEXT("Detaching from existing linker for %s while object %s needs loaded"), *Existing.Linker->GetArchiveName(), *GetFullName());
        check(Existing.Linker->ExportMap[Existing.LinkerIndex].Object != nullptr);
        check(Existing.Linker->ExportMap[Existing.LinkerIndex].Object == this);
        Existing.Linker->ExportMap[Existing.LinkerIndex].ResetObject();
    }

    if (Existing.Linker == LinkerLoad)
    {
        bShouldDetachExisting = false;  // no change so don't call notify
    }
    // if we have a valid annotation and are setting a new valid linker, remove the annotation first
    else if (!Existing.IsDefault() && LinkerLoad != nullptr)
    {
        LinkerAnnotation.RemoveAnnotation(this);
    }
    if (Existing.Linker != LinkerLoad || Existing.LinkerIndex != LinkerIndex)
    {
        LinkerAnnotation.AddAnnotation(this, FLinkerIndexPair(LinkerLoad, LinkerIndex));
    }
    if (bShouldDetachExisting)
    {
#if WITH_EDITOR
        PostLinkerChange();
#else
        UE_CLOG(Existing.Linker && LinkerLoad, LogUObjectLinker, Fatal,
                TEXT("It is only legal to change linkers in the editor. Trying to change linker on %s from %s (Existing->LinkerRoot=%s) to %s (LinkerLoad->LinkerRoot=%s)"),
                *GetFullName(),
                *Existing.Linker->Filename,
                *GetNameSafe(Existing.Linker->LinkerRoot),
                *LinkerLoad->Filename,
                *GetNameSafe(LinkerLoad->LinkerRoot));
#endif
    }
}

/**
 * Returns the linker for this object.
 *
 * @return	a pointer to the linker for this object, or NULL if this object has no linker
 */
FLinkerLoad* UObjectBaseUtility::GetLinker() const
{
    FLinkerIndexPair Existing = LinkerAnnotation.GetAnnotation(this);
    Existing.CheckInvariants();
    return Existing.Linker;
}
/**
 * Returns this object's LinkerIndex.
 *
 * @return	the index into my linker's ExportMap for the FObjectExport
 *			corresponding to this object.
 */
int32 UObjectBaseUtility::GetLinkerIndex() const
{
    FLinkerIndexPair Existing = LinkerAnnotation.GetAnnotation(this);
    Existing.CheckInvariants();
    return Existing.LinkerIndex;
}