Merge pull request #17046 from LinHu2016/v0.37.0-release

(0.37) Handle continuation scanning in pending to be mounted case

runtime/gc_base/GCExtensions.cpp

@@ -311,29 +311,44 @@ MM_GCExtensions::releaseNativesForContinuationObject(MM_EnvironmentBase* env, j9
 }
 
 bool
-MM_GCExtensions::needScanStacksForContinuationObject(J9VMThread *vmThread, j9object_t objectPtr, bool isGlobalGC)
+MM_GCExtensions::needScanStacksForContinuationObject(J9VMThread *vmThread, j9object_t objectPtr, bool isConcurrentGC, bool isGlobalGC, bool beingMounted)
 {
 	bool needScan = false;
 #if JAVA_SPEC_VERSION >= 19
-	jboolean started = J9VMJDKINTERNALVMCONTINUATION_STARTED(vmThread, objectPtr);
-	jboolean finished = J9VMJDKINTERNALVMCONTINUATION_FINISHED(vmThread, objectPtr);
 	J9VMContinuation *continuation = J9VMJDKINTERNALVMCONTINUATION_VMREF(vmThread, objectPtr);
-	/**
-	 * We don't scan mounted continuations:
-	 *
-	 * for concurrent GCs, since stack is actively changing. Instead, we scan them during preMount or during root scanning if already mounted at cycle start or during postUnmount (might be indirectly via card cleaning) or during final STW (via root re-scan) if still mounted at cycle end
-	 * for sliding compacts to avoid double slot fixups
-	 *
-	 * For fully STW GCs, there is no harm to scan them, but it's a waste of time since they are scanned during root scanning already.
-	 *
-	 * We don't scan currently scanned for the same collector either - one scan is enough for the same collector, but there could be concurrent scavenger(local collector) and concurrent marking(global collector) overlapping,
-	 * they are irrelevant and both are concurrent, we handle them independently and separately, they are not blocked or ignored each other.
-	 *
-	 * we don't scan the continuation object before started and after finished - java stack does not exist.
-	 */
-	if (started && !finished) {
-		Assert_MM_true(NULL != continuation);
-		needScan = !VM_VMHelpers::isContinuationMountedOrConcurrentlyScanned(continuation, isGlobalGC);
+	if (NULL != continuation) {
+		/**
+		 * We don't scan mounted continuations:
+		 *
+		 * for concurrent GCs, since stack is actively changing. Instead, we scan them during preMount
+		 * or during root scanning if already mounted at cycle start or during postUnmount (might
+		 * be indirectly via card cleaning) or during final STW (via root re-scan) if still mounted
+		 * at cycle end.
+		 * for sliding compacts to avoid double slot fixups
+		 * If continuation is currently being mounted by this thread, we must be in preMount/postUnmount
+		 * callback and must scan.
+		 *
+		 * For fully STW GCs, there is no harm to scan them, but it's a waste of time since they are
+		 * scanned during root scanning already.
+		 *
+		 * We don't scan currently scanned for the same collector either - one scan is enough for
+		 * the same collector, but there could be concurrent scavenger(local collector) and
+		 * concurrent marking(global collector) overlapping, they are irrelevant and both are
+		 * concurrent, we handle them independently and separately, they are not blocked or ignored
+		 * each other.
+		 *
+		 * we don't scan the continuation object before started and after finished - java stack
+		 * does not exist.
+		 */
+		if (isConcurrentGC) {
+			needScan = VM_VMHelpers::tryWinningConcurrentGCScan(continuation, isGlobalGC, beingMounted);
+		} else {
+			/* for STW GCs */
+			uintptr_t continuationState = continuation->state;
+			Assert_MM_false(beingMounted);
+			Assert_MM_false(VM_VMHelpers::isConcurrentlyScanned(continuationState));
+			needScan = VM_VMHelpers::isActive(continuationState) && !VM_VMHelpers::isContinuationFullyMounted(continuationState);
+		}
 	}
 #endif /* JAVA_SPEC_VERSION >= 19 */
 	return needScan;

runtime/gc_base/GCExtensions.hpp

@@ -307,7 +307,7 @@ class MM_GCExtensions : public MM_GCExtensionsBase {
 	 * @param[in] isGlobalGC
 	 * @return true if we need to scan the java stack
 	 */
-	static bool needScanStacksForContinuationObject(J9VMThread *vmThread, j9object_t objectPtr, bool isGlobalGC);
+	static bool needScanStacksForContinuationObject(J9VMThread *vmThread, j9object_t objectPtr, bool isConcurrentGC, bool isGlobalGC, bool beingMounted);
 
 	/**
 	 * Create a GCExtensions object

runtime/gc_glue_java/CompactSchemeFixupObject.cpp

@@ -75,15 +75,16 @@ MM_CompactSchemeFixupObject::fixupContinuationNativeSlots(MM_EnvironmentStandard
 	 * mounted Virtual threads later during root fixup, we will skip it during this heap fixup pass
 	 * (hence passing true for scanOnlyUnmounted parameter).
 	 */
+	const bool isConcurrentGC = false;
 	const bool isGlobalGC = true;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	const bool beingMounted = false;
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4CompactSchemeFixupObject localData;
 		localData.compactSchemeFixupObject = this;
 		localData.env = env;
 		localData.fromObject = objectPtr;
-		const bool isConcurrentGC = false;
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForCompactScheme, false, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForCompactScheme, false, false);
 	}
 }
 

runtime/gc_glue_java/HeapWalkerDelegate.cpp

@@ -60,17 +60,17 @@ MM_HeapWalkerDelegate::doContinuationNativeSlots(MM_EnvironmentBase *env, omrobj
 {
 	J9VMThread *currentThread = (J9VMThread *)env->getLanguageVMThread();
 
+	const bool isConcurrentGC = false;
 	const bool isGlobalGC = true;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	const bool beingMounted = false;
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4HeapWalker localData;
 		localData.heapWalker = _heapWalker;
 		localData.env = env;
 		localData.fromObject = objectPtr;
 		localData.function = function;
 		localData.userData = userData;
-		/* so far there is no case we need ClassWalk for heapwalker, so we set stackFrameClassWalkNeeded = false */
-		const bool isConcurrentGC = false;
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForHeapWalker, false, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForHeapWalker, false, false);
 	}
 }

runtime/gc_glue_java/MarkingDelegate.cpp

@@ -261,8 +261,11 @@ void
 MM_MarkingDelegate::scanContinuationNativeSlots(MM_EnvironmentBase *env, omrobjectptr_t objectPtr)
 {
 	J9VMThread *currentThread = (J9VMThread *)env->getLanguageVMThread();
+	/* In STW GC there are no racing carrier threads doing mount and no need for the synchronization. */
+	bool isConcurrentGC = J9_ARE_ANY_BITS_SET(currentThread->privateFlags, J9_PRIVATE_FLAGS_CONCURRENT_MARK_ACTIVE);
 	const bool isGlobalGC = true;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	const bool beingMounted = false;
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4MarkingDelegate localData;
 		localData.markingDelegate = this;
 		localData.env = env;
@@ -272,10 +275,11 @@ MM_MarkingDelegate::scanContinuationNativeSlots(MM_EnvironmentBase *env, omrobje
 #if defined(J9VM_GC_DYNAMIC_CLASS_UNLOADING)
 		stackFrameClassWalkNeeded = isDynamicClassUnloadingEnabled();
 #endif /* J9VM_GC_DYNAMIC_CLASS_UNLOADING */
-		/* In STW GC there are no racing carrier threads doing mount and no need for the synchronization. */
-		bool isConcurrentGC = J9_ARE_ANY_BITS_SET(currentThread->privateFlags, J9_PRIVATE_FLAGS_CONCURRENT_MARK_ACTIVE);
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForMarkingDelegate, stackFrameClassWalkNeeded, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForMarkingDelegate, stackFrameClassWalkNeeded, false);
+		if (isConcurrentGC) {
+			VM_VMHelpers::exitConcurrentGCScan(currentThread, objectPtr, isGlobalGC);
+		}
 	}
 }
 

runtime/gc_glue_java/MetronomeDelegate.cpp

@@ -1644,11 +1644,12 @@ stackSlotIteratorForRealtimeGC(J9JavaVM *javaVM, J9Object **slotPtr, void *local
 }
 
 void
-MM_MetronomeDelegate::scanContinuationNativeSlots(MM_EnvironmentRealtime *env, J9Object *objectPtr)
+MM_MetronomeDelegate::scanContinuationNativeSlots(MM_EnvironmentRealtime *env, J9Object *objectPtr, bool beingMounted)
 {
 	J9VMThread *currentThread = (J9VMThread *)env->getLanguageVMThread();
+	bool isConcurrentGC = _realtimeGC->isCollectorConcurrentTracing();
 	const bool isGlobalGC = true;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4RealtimeMarkingScheme localData;
 		localData.realtimeMarkingScheme = _markingScheme;
 		localData.env = env;
@@ -1659,9 +1660,11 @@ MM_MetronomeDelegate::scanContinuationNativeSlots(MM_EnvironmentRealtime *env, J
 		stackFrameClassWalkNeeded = isDynamicClassUnloadingEnabled();
 #endif /* J9VM_GC_DYNAMIC_CLASS_UNLOADING */
 		/* In STW GC there are no racing carrier threads doing mount and no need for the synchronization. */
-		bool isConcurrentGC = _realtimeGC->isCollectorConcurrentTracing();
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForRealtimeGC, stackFrameClassWalkNeeded, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForRealtimeGC, stackFrameClassWalkNeeded, false);
+		if (isConcurrentGC) {
+			VM_VMHelpers::exitConcurrentGCScan(currentThread, objectPtr, isGlobalGC);
+		}
 	}
 }
 

runtime/gc_glue_java/MetronomeDelegate.hpp

@@ -176,7 +176,7 @@ class MM_MetronomeDelegate : public MM_BaseNonVirtual
 	void setUnmarkedImpliesCleared();
 	void unsetUnmarkedImpliesCleared();
 
-	void  scanContinuationNativeSlots(MM_EnvironmentRealtime *env, J9Object *objectPtr);
+	void  scanContinuationNativeSlots(MM_EnvironmentRealtime *env, J9Object *objectPtr, bool beingMounted = false);
 	UDATA scanContinuationObject(MM_EnvironmentRealtime *env, J9Object *objectPtr);
 
 #if defined(J9VM_GC_DYNAMIC_CLASS_UNLOADING)

runtime/gc_glue_java/ScavengerDelegate.cpp

@@ -340,22 +340,32 @@ stackSlotIteratorForScavenge(J9JavaVM *javaVM, J9Object **slotPtr, void *localDa
 }
 
 bool
-MM_ScavengerDelegate::scanContinuationNativeSlots(MM_EnvironmentStandard *env, omrobjectptr_t objectPtr, MM_ScavengeScanReason reason)
+MM_ScavengerDelegate::scanContinuationNativeSlots(MM_EnvironmentStandard *env, omrobjectptr_t objectPtr, MM_ScavengeScanReason reason, bool beingMounted)
 {
 	bool shouldRemember = false;
 
 	J9VMThread *currentThread = (J9VMThread *)env->getLanguageVMThread();
+	/* In STW GC there are no racing carrier threads doing mount and no need for the synchronization. */
+	bool isConcurrentGC = false;
+	if (MUTATOR_THREAD == env->getThreadType()) {
+		isConcurrentGC = _extensions->isConcurrentScavengerInProgress();
+	} else {
+#if defined(OMR_GC_CONCURRENT_SCAVENGER)
+		isConcurrentGC = _extensions->scavenger->isCurrentPhaseConcurrent();
+#endif /* defined(OMR_GC_CONCURRENT_SCAVENGER) */
+	}
 	const bool isGlobalGC = false;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4Scavenge localData;
 		localData.scavengerDelegate = this;
 		localData.env = env;
 		localData.reason = reason;
 		localData.shouldRemember = &shouldRemember;
-		/* In STW GC there are no racing carrier threads doing mount and no need for the synchronization. */
-		bool isConcurrentGC = _extensions->isConcurrentScavengerInProgress();
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForScavenge, false, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForScavenge, false, false);
+		if (isConcurrentGC) {
+			VM_VMHelpers::exitConcurrentGCScan(currentThread, objectPtr, isGlobalGC);
+		}
 	}
 	return 	shouldRemember;
 }

runtime/gc_glue_java/ScavengerDelegate.hpp

@@ -156,7 +156,7 @@ class MM_ScavengerDelegate : public MM_BaseNonVirtual {
 
 	void setShouldScavengeUnfinalizedObjects(bool shouldScavenge) { _shouldScavengeUnfinalizedObjects = shouldScavenge; }
 	void setShouldScavengeContinuationObjects(bool shouldScavenge) { _shouldScavengeContinuationObjects = shouldScavenge; }
-	bool scanContinuationNativeSlots(MM_EnvironmentStandard *env, omrobjectptr_t objectPtr, MM_ScavengeScanReason reason);
+	bool scanContinuationNativeSlots(MM_EnvironmentStandard *env, omrobjectptr_t objectPtr, MM_ScavengeScanReason reason, bool beingMounted = false);
 
 	volatile bool getShouldScavengeFinalizableObjects() { return _shouldScavengeFinalizableObjects; }
 	volatile bool getShouldScavengeUnfinalizedObjects() { return _shouldScavengeUnfinalizedObjects; }

runtime/gc_modron_standard/StandardAccessBarrier.cpp

@@ -1042,10 +1042,11 @@ MM_StandardAccessBarrier::preMountContinuation(J9VMThread *vmThread, j9object_t
 {
 #if defined(OMR_GC_CONCURRENT_SCAVENGER)
 	if (_extensions->isConcurrentScavengerInProgress()) {
-		/* concurrent scavenger in progress */
+		/* concurrent scavenger in active */
 		MM_EnvironmentStandard *env = MM_EnvironmentStandard::getEnvironment(vmThread->omrVMThread);
 		MM_ScavengeScanReason reason = SCAN_REASON_SCAVENGE;
-		_scavenger->getDelegate()->scanContinuationNativeSlots(env, contObject, reason);
+		const bool beingMounted = true;
+		_scavenger->getDelegate()->scanContinuationNativeSlots(env, contObject, reason, beingMounted);
 	}
 #endif /* OMR_GC_CONCURRENT_SCAVENGER */
 }

runtime/gc_realtime/RealtimeAccessBarrier.cpp

@@ -955,7 +955,8 @@ MM_RealtimeAccessBarrier::preMountContinuation(J9VMThread *vmThread, j9object_t
 {
 	MM_EnvironmentRealtime *env =  MM_EnvironmentRealtime::getEnvironment(vmThread->omrVMThread);
 	if (isBarrierActive(env)) {
-		_realtimeGC->getRealtimeDelegate()->scanContinuationNativeSlots(env, contObject);
+		const bool beingMounted = true;
+		_realtimeGC->getRealtimeDelegate()->scanContinuationNativeSlots(env, contObject, beingMounted);
 	}
 }
 

runtime/gc_structs/VMThreadStackSlotIterator.cpp

@@ -130,21 +130,22 @@ GC_VMThreadStackSlotIterator::scanSlots(
 }
 
 void
-GC_VMThreadStackSlotIterator::scanSlots(
+GC_VMThreadStackSlotIterator::scanContinuationSlots(
 			J9VMThread *vmThread,
 			j9object_t continuationObjectPtr,
 			void *userData,
 			J9MODRON_OSLOTITERATOR *oSlotIterator,
 			bool includeStackFrameClassReferences,
-			bool trackVisibleFrameDepth,
-			bool isConcurrentGC,
-			bool isGlobalGC
+			bool trackVisibleFrameDepth
 		)
 {
 	J9StackWalkState stackWalkState;
-
 	initializeStackWalkState(&stackWalkState, vmThread, userData, oSlotIterator, includeStackFrameClassReferences, trackVisibleFrameDepth);
-	VM_VMHelpers::walkContinuationStackFramesWrapper(vmThread, continuationObjectPtr, &stackWalkState, isConcurrentGC, isGlobalGC);
+
+#if JAVA_SPEC_VERSION >= 19
+	J9VMContinuation *continuation = J9VMJDKINTERNALVMCONTINUATION_VMREF(vmThread, continuationObjectPtr);
+	vmThread->javaVM->internalVMFunctions->walkContinuationStackFrames(vmThread, continuation, &stackWalkState);
+#endif /* JAVA_SPEC_VERSION >= 19 */
 }
 
 #if JAVA_SPEC_VERSION >= 19

runtime/gc_structs/VMThreadStackSlotIterator.hpp

@@ -60,15 +60,13 @@ class GC_VMThreadStackSlotIterator
 			bool includeStackFrameClassReferences,
 			bool trackVisibleFrameDepth);
 
-	static void scanSlots(
+	static void scanContinuationSlots(
 			J9VMThread *vmThread,
 			j9object_t continuationObjectPtr,
 			void *userData,
 			J9MODRON_OSLOTITERATOR *oSlotIterator,
 			bool includeStackFrameClassReferences,
-			bool trackVisibleFrameDepth,
-			bool isConcurrentGC,
-			bool isGlobalGC);
+			bool trackVisibleFrameDepth);
 
 #if JAVA_SPEC_VERSION >= 19
 	static void scanSlots(

runtime/gc_vlhgc/CopyForwardScheme.cpp

@@ -2322,8 +2322,10 @@ MMINLINE void
 MM_CopyForwardScheme::scanContinuationNativeSlots(MM_EnvironmentVLHGC *env, MM_AllocationContextTarok *reservingContext, J9Object *objectPtr, ScanReason reason)
 {
 	J9VMThread *currentThread = (J9VMThread *)env->getLanguageVMThread();
+	const bool isConcurrentGC = false;
 	const bool isGlobalGC = false;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	const bool beingMounted = false;
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4CopyForward localData;
 		localData.copyForwardScheme = this;
 		localData.env = env;
@@ -2333,9 +2335,8 @@ MM_CopyForwardScheme::scanContinuationNativeSlots(MM_EnvironmentVLHGC *env, MM_A
 #if defined(J9VM_GC_DYNAMIC_CLASS_UNLOADING)
 		stackFrameClassWalkNeeded = isDynamicClassUnloadingEnabled();
 #endif /* J9VM_GC_DYNAMIC_CLASS_UNLOADING */
-		const bool isConcurrentGC = false;
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForCopyForwardScheme, stackFrameClassWalkNeeded, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForCopyForwardScheme, stackFrameClassWalkNeeded, false);
 	}
 }
 

runtime/gc_vlhgc/GlobalMarkCardScrubber.cpp

@@ -192,16 +192,17 @@ bool MM_GlobalMarkCardScrubber::scrubContinuationNativeSlots(MM_EnvironmentVLHGC
 {
 	bool doScrub = true;
 	J9VMThread *currentThread = (J9VMThread *)env->getLanguageVMThread();
+	const bool isConcurrentGC = false;
 	const bool isGlobalGC = true;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	const bool beingMounted = false;
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4GlobalMarkCardScrubber localData;
 		localData.globalMarkCardScrubber = this;
 		localData.env = env;
 		localData.doScrub = &doScrub;
 		localData.fromObject = objectPtr;
-		const bool isConcurrentGC = false;
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForGlobalMarkCardScrubber, false, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForGlobalMarkCardScrubber, false, false);
 	}
 	return doScrub;
 }

runtime/gc_vlhgc/GlobalMarkingScheme.cpp

@@ -792,8 +792,11 @@ void
 MM_GlobalMarkingScheme::scanContinuationNativeSlots(MM_EnvironmentVLHGC *env, J9Object *objectPtr, ScanReason reason)
 {
 	J9VMThread *currentThread = (J9VMThread *)env->getLanguageVMThread();
+	/* In STW GC there are no racing carrier threads doing mount and no need for the synchronization. */
+	bool isConcurrentGC = (MM_VLHGCIncrementStats::mark_concurrent == static_cast<MM_CycleStateVLHGC*>(env->_cycleState)->_vlhgcIncrementStats._globalMarkIncrementType);
 	const bool isGlobalGC = true;
-	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isGlobalGC)) {
+	const bool beingMounted = false;
+	if (MM_GCExtensions::needScanStacksForContinuationObject(currentThread, objectPtr, isConcurrentGC, isGlobalGC, beingMounted)) {
 		StackIteratorData4GlobalMarkingScheme localData;
 		localData.globalMarkingScheme = this;
 		localData.env = env;
@@ -802,10 +805,11 @@ MM_GlobalMarkingScheme::scanContinuationNativeSlots(MM_EnvironmentVLHGC *env, J9
 #if defined(J9VM_GC_DYNAMIC_CLASS_UNLOADING)
 		stackFrameClassWalkNeeded = isDynamicClassUnloadingEnabled();
 #endif /* J9VM_GC_DYNAMIC_CLASS_UNLOADING */
-		/* In STW GC there are no racing carrier threads doing mount and no need for the synchronization. */
-		bool isConcurrentGC = (MM_VLHGCIncrementStats::mark_concurrent == static_cast<MM_CycleStateVLHGC*>(env->_cycleState)->_vlhgcIncrementStats._globalMarkIncrementType);
 
-		GC_VMThreadStackSlotIterator::scanSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForGlobalMarkingScheme, stackFrameClassWalkNeeded, false, isConcurrentGC, isGlobalGC);
+		GC_VMThreadStackSlotIterator::scanContinuationSlots(currentThread, objectPtr, (void *)&localData, stackSlotIteratorForGlobalMarkingScheme, stackFrameClassWalkNeeded, false);
+		if (isConcurrentGC) {
+			VM_VMHelpers::exitConcurrentGCScan(currentThread, objectPtr, isGlobalGC);
+		}
 	}
 }