GarbageCollection.cpp File Reference

#include "UObject/GarbageCollection.h"
#include "Algo/Find.h"
#include "Async/UniqueLock.h"
#include "AutoRTFM.h"
#include "Containers/ConsumeAllMpmcQueue.h"
#include "Containers/Deque.h"
#include "Containers/StaticBitArray.h"
#include "HAL/MallocLeakDetection.h"
#include "HAL/ThreadSafeBool.h"
#include "Misc/TimeGuard.h"
#include "HAL/IConsoleManager.h"
#include "Misc/App.h"
#include "Misc/CoreDelegates.h"
#include "Tasks/Task.h"
#include "UObject/ScriptInterface.h"
#include "UObject/UObjectAllocator.h"
#include "UObject/UObjectBase.h"
#include "UObject/Object.h"
#include "UObject/ObjectHandle.h"
#include "UObject/ObjectPtr.h"
#include "UObject/Class.h"
#include "UObject/UObjectIterator.h"
#include "UObject/UnrealType.h"
#include "UObject/LinkerLoad.h"
#include "UObject/GCObject.h"
#include "UObject/GCScopeLock.h"
#include "HAL/ExceptionHandling.h"
#include "UObject/UObjectClusters.h"
#include "HAL/LowLevelMemTracker.h"
#include "UObject/GarbageCollectionVerification.h"
#include "UObject/Package.h"
#include "Async/ParallelFor.h"
#include "ProfilingDebugging/CsvProfiler.h"
#include "HAL/Runnable.h"
#include "HAL/RunnableThread.h"
#include "HAL/ThreadHeartBeat.h"
#include "UObject/FieldPathProperty.h"
#include "UObject/GarbageCollectionHistory.h"
#include "UObject/GarbageCollectionInternalFlags.h"
#include "UObject/GarbageCollectionTesting.h"
#include "UObject/InstanceDataObjectUtils.h"
#include "UObject/PropertyBagRepository.h"
#include "UObject/PropertyOptional.h"
#include "UObject/ExpandingChunkedList.h"
#include "UObject/ReachabilityAnalysisState.h"
#include "UObject/ReachabilityAnalysis.h"
#include "UObject/RemoteObjectPrivate.h"
#include <atomic>
#include "UObject/FastReferenceCollector.h"

Classes
struct	FGCTimingInfo
class	FGCHashTableScopeLock
struct	UE::GC::FDetailedClassStats
class	FObjectPurge
class	UE::GC::FContextPool
class	UE::GC::FContextPoolScope
struct	UE::GC::TAddAdapter< Options >
struct	UE::GC::FMutableReference
struct	UE::GC::FImmutableReference
struct	UE::GC::FReferenceArray
struct	UE::GC::FResolvedMutableReference
struct	UE::GC::FReferenceMetadata
class	UE::GC::FPageAllocator
class	UE::GC::FBatcherBase
struct	UE::GC::FBatcherBase::TBatchQueue< EntryType, Capacity, PrefetchCapacity >
struct	UE::GC::FBatcherBase::FValidatedBitmask
class	UE::GC::TReferenceBatcher< UnvalidatedReferenceType, ValidatedReferenceType, ProcessorType >
struct	UE::GC::FStructArrayBlock
class	UE::GC::FStructBlockifier
struct	UE::GC::FSparseStructArray
struct	UE::GC::FStructArrayWithoutStride
class	UE::GC::FStructBatcher
class	UE::GC::FWorkerIndexAllocator
class	UE::GC::FBoundedWorkstealingQueue
class	UE::GC::FWorkstealingQueue
struct	UE::GC::FWorkstealingManager
struct	UE::GC::FAROBlock
class	UE::GC::FAROQueue
struct	UE::GC::FAROQueue::FFew
struct	UE::GC::FAROQueue::FMany
class	UE::GC::FAROQueueStore
class	UE::GC::FSlowAROManager
class	UE::GC::TSingleton< T >
class	UE::GC::TReachabilityProcessor< InOptions >
struct	UE::GC::TBatchDispatcher< ProcessorType >
class	UE::GC::TReachabilityCollectorBase< Options >
class	UE::GC::TReachabilityCollector< Options >
class	UE::GC::TDebugReachabilityProcessor< InOptions >
class	UE::GC::TDebugReachabilityCollector< Options >
class	UE::GC::FRealtimeGC
struct	UE::GC::FRealtimeGC::FMarkClustersArrays
class	UE::GC::FWeakReferenceEliminator
class	UE::GC::FWorkCoordinator
	UE_BUILD_SHIPPING. More...

Namespaces
namespace	UE
namespace	UE::GC
namespace	UE::GC::Private
namespace	UE::GC::Test

Macros
#define	PERF_DETAILED_PER_CLASS_GC_STATS   (LOOKING_FOR_PERF_ISSUES || 0)
#define	UE_LOG_FGCScopeGuard_LockAsync_Time   0

Typedefs
using	UE::GC::Private::FGatherUnreachableObjectsState = TThreadedGather< TArray< UE::GC::FUnreachableObject > >
using	UE::GC::FStridedReferenceArray = Private::FStridedReferenceArray
using	UE::GC::FStridedReferenceView = Private::FStridedReferenceView

Enumerations
enum class	UE::GC::EKillable { UE::GC::No , UE::GC::Yes }

Functions
	DEFINE_LOG_CATEGORY (LogGarbage)
	CSV_DEFINE_CATEGORY_MODULE (COREUOBJECT_API, GC, true)
	TSAN_ATOMIC (bool) GIsGarbageCollecting
void	NotifyUnreachableObjects (const TArrayView< FUObjectItem * > &UnreachableObjects)
bool	IsGarbageCollectionLocked ()
void	UE::GC::MarkAsReachable (const UObject *Obj)
EGCOptions	UE::GC::GetReferenceCollectorOptions (bool bPerformFullPurge)
EGatherOptions	UE::GC::GetObjectGatherOptions ()
void	UE::GC::Private::SetSkipDestroy (bool bSkip)
void	UE::GC::Private::ProcessDirtyRootNoLock (int32 Index)
void	UE::GC::Private::ProcessDirtyRootsNoLock ()
void	UE::GC::Private::MarkRootAsDirty (int32 Index)
COREUOBJECT_API bool	UE::GC::Test::IsReachable (const UObject *Object)
COREUOBJECT_API bool	UE::GC::Test::IsMaybeUnreachable (const UObject *Object)
COREUOBJECT_API void	UE::GC::Test::SetMaybeUnreachable (UObject *Object)
void	OnDisregardForGCSetDisabled (int32 NumObjects)
int32	UE::GC::GetNumSlowAROs ()
FORCEINLINE UObject *	UE::GC::GetObject (FImmutableReference In)
FORCEINLINE UObject *	UE::GC::GetObject (FMutableReference In)
FORCEINLINE void	UE::GC::PrefetchObjectPointer (FImmutableReference)
FORCEINLINE void	UE::GC::PrefetchObjectPointer (FMutableReference In)
FORCEINLINE FImmutableReference	UE::GC::ToImmutableReference (FMutableReference In)
FORCEINLINE FImmutableReference	UE::GC::ToResolvedReference (FImmutableReference In)
FORCEINLINE FResolvedMutableReference	UE::GC::ToResolvedReference (FMutableReference In)
template<class RefType >
RefType	UE::GC::ToReference (FMutableReference In)
template<>
FORCEINLINE FImmutableReference	UE::GC::ToReference (FMutableReference In)
template<>
FORCEINLINE FMutableReference	UE::GC::ToReference (FMutableReference In)
template<class RefType >
RefType	UE::GC::MakeReference (UObject *&Object)
template<>
FORCEINLINE FImmutableReference	UE::GC::MakeReference (UObject *&Object)
template<>
FORCEINLINE FMutableReference	UE::GC::MakeReference (UObject *&Object)
FORCEINLINE_DEBUGGABLE void	UE::GC::CheckValid (FSchemaView Schema)
void	UE::GC::PadObjectArray (TArray< UObject * > &Objects)
FORCEINLINE_DEBUGGABLE void	UE::GC::PadBlock (FWorkBlock &Block)
void	UE::GC::RegisterSlowImplementation (ObjectAROFn ARO, EAROFlags Flags)
int32	UE::GC::FindSlowImplementation (ObjectAROFn ARO)
FORCEINLINE_DEBUGGABLE void	UE::GC::KillReference (UObject *&Object)
template<EGCOptions Options>
constexpr FORCEINLINE EKillable	UE::GC::MayKill (EOrigin Origin, bool bAllowKill)
void	ShutdownGarbageCollection ()
void	AcquireGCLock ()
void	ReleaseGCLock ()
void	IncrementalPurgeGarbage (bool bUseTimeLimit, double TimeLimit)
bool	IsIncrementalPurgePending ()
bool	IsGarbageCollectingAndLockingUObjectHashTables ()
void	DissolveUnreachableClusters (UE::GC::EGatherOptions Options)
void	GatherUnreachableObjects (bool bForceSingleThreaded)
template<bool bPerformFullPurge>
FORCENOINLINE void	UE::GC::CollectGarbageImpl (EObjectFlags KeepFlags)
FORCEINLINE void	UE::GC::CollectGarbageInternal (EObjectFlags KeepFlags, bool bPerformFullPurge)
template<bool bPerformFullPurge>
void	UE::GC::PreCollectGarbageImpl (EObjectFlags KeepFlags)
template<bool bPerformFullPurge>
void	UE::GC::CollectGarbageImpl (EObjectFlags KeepFlags)
template<bool bPerformFullPurge>
void	UE::GC::PostCollectGarbageImpl (EObjectFlags KeepFlags)
void	SetIncrementalReachabilityAnalysisEnabled (bool bEnabled)
bool	GetIncrementalReachabilityAnalysisEnabled ()
void	SetReachabilityAnalysisTimeLimit (float TimeLimitSeconds)
float	GetReachabilityAnalysisTimeLimit ()
bool	IsIncrementalReachabilityAnalysisPending ()
void	PerformIncrementalReachabilityAnalysis (double TimeLimit)
void	FinalizeIncrementalReachabilityAnalysis ()
UE::GC::Private::FStats	UE::GC::Private::GetGarbageCollectionStats ()
double	GetLastGCTime ()
double	GetLastGCDuration ()
bool	IsIncrementalUnhashPending ()
bool	UnhashUnreachableObjects (bool bUseTimeLimit, double TimeLimit)
void	CollectGarbage (EObjectFlags KeepFlags, bool bPerformFullPurge)
bool	TryCollectGarbage (EObjectFlags KeepFlags, bool bPerformFullPurge)
void	PurgeAllUObjectsOnExit ()
void	UE::GC::SuspendWork (FWorkerContext &Context)
ELoot	UE::GC::StealWork (FWorkerContext &Context, FReferenceCollector &Collector, FWorkBlock *&OutBlock, EGCOptions Options)
TArrayView< FWorkerContext * >	UE::GC::InitializeAsyncProcessingContexts (FWorkerContext &InContext)
void	UE::GC::ReleaseAsyncProcessingContexts (FWorkerContext &InContext, TArrayView< FWorkerContext * > Contexts)
void	UE::GC::ProcessAsync (void(*ProcessSync)(void *, FWorkerContext &), void *Processor, FWorkerContext &InContext)
int32	GetNumCollectReferenceWorkers ()

Variables
COREUOBJECT_API bool	GShouldVerifyGCAssumptionsOnFullPurge
COREUOBJECT_API float	GVerifyGCAssumptionsChance
FThreadSafeCounter	GObjectCountDuringLastMarkPhase
std::atomic< bool >	GIsGarbageCollectingAndLockingUObjectHashTables = false
std::atomic< bool >	GObjIncrementalPurgeIsInProgress = false
std::atomic< bool >	GObjUnhashUnreachableIsInProgress = false
double	GCStartTime = 0.
FGCCSyncObject *	GGCSingleton
int32	GGarbageReferenceTrackingEnabled = 0
int32	GDelayReachabilityIterations = 0
EInternalObjectFlags	UE::GC::GReachableObjectFlag = EInternalObjectFlags::ReachabilityFlag0
EInternalObjectFlags	UE::GC::GUnreachableObjectFlag = EInternalObjectFlags::Unreachable
EInternalObjectFlags	UE::GC::GMaybeUnreachableObjectFlag = EInternalObjectFlags::ReachabilityFlag2
bool	UE::GC::GIsIncrementalReachabilityPending = false
class FObjectPurge	GUObjectPurge
FReachabilityAnalysisState	UE::GC::GReachabilityState

Macro Definition Documentation

PERF_DETAILED_PER_CLASS_GC_STATS

#define PERF_DETAILED_PER_CLASS_GC_STATS   (LOOKING_FOR_PERF_ISSUES || 0)

UE_LOG_FGCScopeGuard_LockAsync_Time

#define UE_LOG_FGCScopeGuard_LockAsync_Time   0

Function Documentation

AcquireGCLock()

void AcquireGCLock

(

)

CollectGarbage()

void CollectGarbage	(	EObjectFlags	KeepFlags,
		bool	bPerformFullPurge = true
	)

Deletes all unreferenced objects, keeping objects that have any of the passed in KeepFlags set. Will wait for other threads to unlock GC.

Parameters

KeepFlags	objects with those flags will be kept regardless of being referenced or not
bPerformFullPurge	if true, perform a full purge after the mark pass

CSV_DEFINE_CATEGORY_MODULE()

CSV_DEFINE_CATEGORY_MODULE	(	COREUOBJECT_API	,
		GC	,
		true
	)

DEFINE_LOG_CATEGORY()

DEFINE_LOG_CATEGORY

(

LogGarbage

)

DissolveUnreachableClusters()

void DissolveUnreachableClusters

(

UE::GC::EGatherOptions

Options

)

FinalizeIncrementalReachabilityAnalysis()

void FinalizeIncrementalReachabilityAnalysis

(

)

Finalizes incremental reachability analysis (if currently running) without any time limit

GatherUnreachableObjects()

void GatherUnreachableObjects

(

bool

bForceSingleThreaded

)

Gathers unreachable objects for IncrementalPurgeGarbage.

Parameters

bForceSingleThreaded

true to force the process to just one thread

GetIncrementalReachabilityAnalysisEnabled()

bool GetIncrementalReachabilityAnalysisEnabled

(

)

Returns true if incremental reachability analysis is enabled

GetLastGCDuration()

double GetLastGCDuration

(

)

Gets the duration of the last GC run.

Returns

Returns the last GC duration, -1 if GC has never run.

GetLastGCTime()

double GetLastGCTime

(

)

Gets the last time that the GC was run.

Returns

Returns the FPlatformTime::Seconds() for the last garbage collection, 0 if GC has never run.

GetNumCollectReferenceWorkers()

int32 GetNumCollectReferenceWorkers

(

)

GetReachabilityAnalysisTimeLimit()

float GetReachabilityAnalysisTimeLimit

(

)

Returns the time limit for incremental rachability analysis.

Returns

time limit (in seconds) for incremental rachability analysis.

IncrementalPurgeGarbage()

void IncrementalPurgeGarbage	(	bool	bUseTimeLimit,
		double	TimeLimit
	)

Incrementally purge garbage by deleting all unreferenced objects after routing Destroy.

Calling code needs to be EXTREMELY careful when and how to call this function as RF_Unreachable cannot change on any objects unless any pending purge has completed!

Parameters

bUseTimeLimit	whether the time limit parameter should be used
TimeLimit	soft time limit for this function call

IsGarbageCollectingAndLockingUObjectHashTables()

bool IsGarbageCollectingAndLockingUObjectHashTables

(

)

Whether garbage collection is locking the global uobject hash tables

IsGarbageCollectionLocked()

bool IsGarbageCollectionLocked

(

)

Returns true if we're inside a FGCScopeGuard

IsIncrementalPurgePending()

bool IsIncrementalPurgePending

(

)

Returns whether an incremental purge is still pending/ in progress.

Returns

true if incremental purge needs to be kicked off or is currently in progress, false othwerise.

IsIncrementalReachabilityAnalysisPending()

bool IsIncrementalReachabilityAnalysisPending

(

)

Returns whether an incremental reachability analysis is still pending/ in progress.

Returns

true if incremental reachability analysis needs to be kicked off or is currently in progress, false othwerise.

IsIncrementalUnhashPending()

bool IsIncrementalUnhashPending

(

)

Checks if there's objects pending to be unhashed when running incremental purge

Returns

true if the time limit passed and there's still objects pending to be unhashed

NotifyUnreachableObjects()

void NotifyUnreachableObjects

(

const TArrayView< FUObjectItem * > &

UnreachableObjects

)

Call back into the async loading code to inform of the destruction of serialized objects

OnDisregardForGCSetDisabled()

void OnDisregardForGCSetDisabled

(

int32

NumObjects

)

PerformIncrementalReachabilityAnalysis()

void PerformIncrementalReachabilityAnalysis

(

double

TimeLimit

)

Incrementally perform reachability analysis

Parameters

TimeLimit

Time limit (in seconds) for this function call. 0.0 results in no time limit being used.

PurgeAllUObjectsOnExit()

void PurgeAllUObjectsOnExit

(

)

Destroys all existing UObjects when the engine shuts down. Does NOT perform reachability analysis to do so.

ReleaseGCLock()

void ReleaseGCLock

(

)

SetIncrementalReachabilityAnalysisEnabled()

void SetIncrementalReachabilityAnalysisEnabled

(

bool

bEnabled

)

Enables or disables incremental reachability analysis.

Parameters

bEnabled

True if incremental reachability analysis is to be enabled

SetReachabilityAnalysisTimeLimit()

void SetReachabilityAnalysisTimeLimit

(

float

TimeLimitSeconds

)

Sets time limit for incremental rachability analysis (if enabled).

Parameters

TimeLimitSeconds

Time limit (in seconds) for incremental raachability analysis

ShutdownGarbageCollection()

void ShutdownGarbageCollection

(

)

TryCollectGarbage()

bool TryCollectGarbage	(	EObjectFlags	KeepFlags,
		bool	bPerformFullPurge = true
	)

Performs garbage collection only if no other thread holds a lock on GC

Parameters

KeepFlags	objects with those flags will be kept regardless of being referenced or not
bPerformFullPurge	if true, perform a full purge after the mark pass

Returns

true if an actual attempt at garbage collection occurred

TSAN_ATOMIC()

TSAN_ATOMIC

(

bool

)

UnhashUnreachableObjects()

bool UnhashUnreachableObjects	(	bool	bUseTimeLimit,
		double	TimeLimit = 0.0
	)

Calls ConditionalBeginDestroy on unreachable objects

Parameters

bUseTimeLimit	whether the time limit parameter should be used
TimeLimit	soft time limit for this function call

Returns

true if the time limit passed and there's still objects pending to be unhashed

Variable Documentation

GCStartTime

double GCStartTime = 0.

Time the GC started, needs to be reset on return from being in the background on some OSs

GDelayReachabilityIterations

int32 GDelayReachabilityIterations = 0

GGarbageReferenceTrackingEnabled

int32 GGarbageReferenceTrackingEnabled = 0

GGCSingleton

FGCCSyncObject* GGCSingleton

GIsGarbageCollectingAndLockingUObjectHashTables

std::atomic<bool> GIsGarbageCollectingAndLockingUObjectHashTables = false

Whether UObject hash tables are locked by GC

GObjectCountDuringLastMarkPhase

FThreadSafeCounter GObjectCountDuringLastMarkPhase

Object count during last mark phase

GObjIncrementalPurgeIsInProgress

std::atomic<bool> GObjIncrementalPurgeIsInProgress = false

Whether incremental object purge is in progress

GObjUnhashUnreachableIsInProgress

std::atomic<bool> GObjUnhashUnreachableIsInProgress = false

Whether GC is currently routing BeginDestroy to objects

GShouldVerifyGCAssumptionsOnFullPurge

COREUOBJECT_API bool GShouldVerifyGCAssumptionsOnFullPurge

extern

Allows release builds to override not verifying GC assumptions. Useful for profiling as it's hitchy.

If set and VERIFY_DISREGARD_GC_ASSUMPTIONS is set, we verify GC assumptions when performing a full (blocking) purge

GUObjectPurge

class FObjectPurge GUObjectPurge

GVerifyGCAssumptionsChance

COREUOBJECT_API float GVerifyGCAssumptionsChance

extern

If > 0 and VERIFY_DISREGARD_GC_ASSUMPTIONS is set, we verify GC assumptions on that fraction of GCs.