EM_Task/CoreUObject/Private/Serialization/FindReferencersArchive.cpp

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

#include "Serialization/FindReferencersArchive.h"
#include "UObject/UObjectGlobals.h"
#include "UObject/Class.h"

/*----------------------------------------------------------------------------
        FFindReferencersArchive.
----------------------------------------------------------------------------*/
/**
 * Constructor
 *
 * @param	PotentialReferencer		the object to serialize which may contain references to our target objects
 * @param	InTargetObjects			array of objects to search for references to
 * @param	bFindAlsoWeakReferences should we also look into weak references?
 */
FFindReferencersArchive::FFindReferencersArchive(UObject* InPotentialReferencer, const TArray<UObject*>& InTargetObjects, bool bFindAlsoWeakReferences)
{
    // use the optimized RefLink to skip over properties which don't contain object references
    ArIsObjectReferenceCollector = true;

    // look also for weak references if user asked for it (we won't modify them, but there is no archive option for that)
    ArIsModifyingWeakAndStrongReferences = bFindAlsoWeakReferences;

    // ALL objects reference their outers...it's just log spam here
    ArIgnoreOuterRef = true;

    // initialize the map
    TargetObjects.Reserve(InTargetObjects.Num());
    for (int32 ObjIndex = 0; ObjIndex < InTargetObjects.Num(); ObjIndex++)
    {
        UObject* TargetObject = InTargetObjects[ObjIndex];
        if (TargetObject != nullptr)
        {
            TargetObjects.AddObject(TargetObject);
        }
    }
    TargetObjects.Freeze();

    PotentialReferencer = nullptr;
    ResetPotentialReferencer(InPotentialReferencer);
}

void FFindReferencersArchive::ResetPotentialReferencer(UObject* InPotentialReferencer)
{
    if (PotentialReferencer)
    {
        // Reset all reference counts
        TargetObjects.ResetRefCounts();
    }

    PotentialReferencer = InPotentialReferencer;

    if (PotentialReferencer)
    {
        // now start the search
        PotentialReferencer->Serialize(*this);

        // search for references coming from AddReferencedObjects
        class FArchiveProxyCollector: public FReferenceCollector
        {
            /** Archive we are a proxy for */
            FArchive& Archive;

        public:
            FArchiveProxyCollector(FArchive& InArchive)
                : Archive(InArchive)
            {
            }
            virtual void HandleObjectReference(UObject*& Object, const UObject* ReferencingObject, const FProperty* ReferencingProperty) override
            {
                Archive << Object;
            }
            virtual void HandleObjectReferences(UObject** InObjects, const int32 ObjectNum, const UObject* InReferencingObject, const FProperty* InReferencingProperty) override
            {
                for (int32 ObjectIndex = 0; ObjectIndex < ObjectNum; ++ObjectIndex)
                {
                    UObject*& Object = InObjects[ObjectIndex];
                    Archive << Object;
                }
            }
            virtual bool IsIgnoringArchetypeRef() const override
            {
                return false;
            }
            virtual bool IsIgnoringTransient() const override
            {
                return false;
            }
        } ArchiveProxyCollector(*this);
        PotentialReferencer->GetClass()->CallAddReferencedObjects(PotentialReferencer, ArchiveProxyCollector);
    }
}

/**
 * Retrieves the number of references from PotentialReferencer to the object specified.
 *
 * @param	TargetObject	the object to might be referenced
 * @param	out_ReferencingProperties
 *							receives the list of properties which were holding references to TargetObject
 *
 * @return	the number of references to TargetObject which were encountered when PotentialReferencer
 *			was serialized.
 */
int32 FFindReferencersArchive::GetReferenceCount(UObject* TargetObject, TArray<FProperty*>* out_ReferencingProperties /*=nullptr*/) const
{
    int32 Result = 0;
    if (TargetObject != nullptr && PotentialReferencer != TargetObject)
    {
        const int32* pCount = TargetObjects.TryGetRefCountPtr(TargetObject);
        if (pCount != nullptr && (*pCount) > 0)
        {
            Result = *pCount;
            if (out_ReferencingProperties != nullptr)
            {
                TArray<FProperty*> PropertiesReferencingObj;
                ReferenceMap.MultiFind(TargetObject, PropertiesReferencingObj);

                out_ReferencingProperties->Empty(PropertiesReferencingObj.Num());
                for (int32 PropIndex = PropertiesReferencingObj.Num() - 1; PropIndex >= 0; PropIndex--)
                {
                    out_ReferencingProperties->Add(PropertiesReferencingObj[PropIndex]);
                }
            }
        }
    }

    return Result;
}

/**
 * Retrieves the number of references from PotentialReferencer list of TargetObjects
 *
 * @param	out_ReferenceCounts		receives the number of references to each of the TargetObjects
 *
 * @return	the number of objects which were referenced by PotentialReferencer.
 */
int32 FFindReferencersArchive::GetReferenceCounts(TMap<class UObject*, int32>& out_ReferenceCounts) const
{
    out_ReferenceCounts.Empty();
    for (int32 Index = 0; Index < TargetObjects.RefCountNum(); ++Index)
    {
        if (TargetObjects.GetRefCount(Index) > 0 && TargetObjects.GetObject(Index) != PotentialReferencer)
        {
            out_ReferenceCounts.Add(TargetObjects.GetObject(Index), TargetObjects.GetRefCount(Index));
        }
    }

    return out_ReferenceCounts.Num();
}

/**
 * Retrieves the number of references from PotentialReferencer list of TargetObjects
 *
 * @param	out_ReferenceCounts			receives the number of references to each of the TargetObjects
 * @param	out_ReferencingProperties	receives the map of properties holding references to each referenced object.
 *
 * @return	the number of objects which were referenced by PotentialReferencer.
 */
int32 FFindReferencersArchive::GetReferenceCounts(TMap<class UObject*, int32>& out_ReferenceCounts, TMultiMap<class UObject*, class FProperty*>& out_ReferencingProperties) const
{
    GetReferenceCounts(out_ReferenceCounts);
    if (out_ReferenceCounts.Num() > 0)
    {
        out_ReferencingProperties.Empty();
        for (TMap<UObject*, int32>::TIterator It(out_ReferenceCounts); It; ++It)
        {
            UObject* Object = It.Key();

            TArray<FProperty*> PropertiesReferencingObj;
            ReferenceMap.MultiFind(Object, PropertiesReferencingObj);

            for (int32 PropIndex = PropertiesReferencingObj.Num() - 1; PropIndex >= 0; PropIndex--)
            {
                out_ReferencingProperties.Add(Object, PropertiesReferencingObj[PropIndex]);
            }
        }
    }

    return out_ReferenceCounts.Num();
}

/**
 * Serializer - if Obj is one of the objects we're looking for, increments the reference count for that object
 */
FArchive& FFindReferencersArchive::operator<<(UObject*& Obj)
{
    if (Obj != nullptr && Obj != PotentialReferencer)
    {
        int32* pReferenceCount = TargetObjects.GetRefCountPtr(Obj);
        if (pReferenceCount != nullptr)
        {
            // if this object was serialized via a FProperty, add it to the list
            if (GetSerializedProperty() != nullptr)
            {
                ReferenceMap.AddUnique(Obj, GetSerializedProperty());
            }

            // now increment the reference count for this target object
            (*pReferenceCount)++;
        }
    }

    return *this;
}