Do not add Own.Sync. object to the list if scan wasn't successfull

If Ownable Synchronizer object scan has not been successful (caused Copy
Forward abort) it should not be aadded to the list right away. This
object is remembered in the work packet and is going to be rescanned for
the second time.

Relates #20395

Signed-off-by: Dmitri Pivkine <Dmitri_Pivkine@ca.ibm.com>

runtime/gc_vlhgc/CopyForwardScheme.cpp

@@ -2285,14 +2285,21 @@ MM_CopyForwardScheme::updateMarkMapAndCardTableOnCopy(MM_EnvironmentVLHGC *env,
 MMINLINE void
 MM_CopyForwardScheme::scanOwnableSynchronizerObjectSlots(MM_EnvironmentVLHGC *env, MM_AllocationContextTarok *reservingContext, J9Object *objectPtr, ScanReason reason)
 {
-	if (SCAN_REASON_COPYSCANCACHE == reason) {
-		addOwnableSynchronizerObjectInList(env, objectPtr);
-	} else if (SCAN_REASON_PACKET == reason) {
-		if (isObjectInEvacuateMemoryNoCheck(objectPtr)) {
+	if (scanMixedObjectSlots(env, reservingContext, objectPtr, reason)) {
+		/*
+		 * If object has been scanned without triggering abort add it to the list here.
+		 * If object scan triggered abort, it has been added to work packet
+		 * and is going to be rescanned again. It should not be added to the list here
+		 * to prevent duplication during second scan.
+		 */
+		if (SCAN_REASON_COPYSCANCACHE == reason) {
 			addOwnableSynchronizerObjectInList(env, objectPtr);
+		} else if (SCAN_REASON_PACKET == reason) {
+			if (isObjectInEvacuateMemoryNoCheck(objectPtr)) {
+				addOwnableSynchronizerObjectInList(env, objectPtr);
+			}
 		}
 	}
-	scanMixedObjectSlots(env, reservingContext, objectPtr, reason);
 }
 
 void
@@ -2416,7 +2423,7 @@ MM_CopyForwardScheme::iterateAndCopyforwardSlotReference(MM_EnvironmentVLHGC *en
 	return success;
 }
 
-void
+bool
 MM_CopyForwardScheme::scanMixedObjectSlots(MM_EnvironmentVLHGC *env, MM_AllocationContextTarok *reservingContext, J9Object *objectPtr, ScanReason reason)
 {
 	if (_tracingEnabled) {
@@ -2432,6 +2439,7 @@ MM_CopyForwardScheme::scanMixedObjectSlots(MM_EnvironmentVLHGC *env, MM_Allocati
 	}
 
 	updateScanStats(env, objectPtr, reason);
+	return success;
 }
 
 void

runtime/gc_vlhgc/CopyForwardScheme.hpp

@@ -318,8 +318,9 @@ class MM_CopyForwardScheme : public MM_BaseNonVirtual
 	 * @param reservingContext[in] The context to which we would prefer to copy any objects discovered in this method
 	 * @param objectPtr current object being scanned.
 	 * @param reason to scan (dirty card, packet, scan cache, overflow)
+	 * @return true if all slots have been copied successfully
 	 */
-	void scanMixedObjectSlots(MM_EnvironmentVLHGC *env, MM_AllocationContextTarok *reservingContext, J9Object *objectPtr, ScanReason reason);
+	bool scanMixedObjectSlots(MM_EnvironmentVLHGC *env, MM_AllocationContextTarok *reservingContext, J9Object *objectPtr, ScanReason reason);
 	/**
 	 * Scan the slots of a reference mixed object.
 	 * Copy and forward all relevant slots values found in the object.