lock forkchoice on calls to Ancestor

beacon-chain/blockchain/chain_info.go

@@ -28,6 +28,15 @@ type ChainInfoFetcher interface {
 	CanonicalFetcher
 	ForkFetcher
 	HeadDomainFetcher
+	ForkchoiceFetcher
+}
+
+// ForkchoiceFetcher defines a common interface for methods that access directly
+// forkchoice information. These typically require a lock and external callers
+// are requested to call methods within this blockchain package that takes care
+// of locking forkchoice
+type ForkchoiceFetcher interface {
+	Ancestor(context.Context, []byte, primitives.Slot) ([]byte, error)
 }
 
 // HeadUpdater defines a common interface for methods in blockchain service
@@ -436,6 +445,41 @@ func (s *Service) IsOptimisticForRoot(ctx context.Context, root [32]byte) (bool,
 	return !isCanonical, nil
 }
 
+// Ancestor returns the block root of an ancestry block from the input block root.
+//
+// Spec pseudocode definition:
+//
+//	def get_ancestor(store: Store, root: Root, slot: Slot) -> Root:
+//	 block = store.blocks[root]
+//	 if block.slot > slot:
+//	     return get_ancestor(store, block.parent_root, slot)
+//	 elif block.slot == slot:
+//	     return root
+//	 else:
+//	     # root is older than queried slot, thus a skip slot. Return most recent root prior to slot
+//	     return root
+func (s *Service) Ancestor(ctx context.Context, root []byte, slot primitives.Slot) ([]byte, error) {
+	ctx, span := trace.StartSpan(ctx, "blockChain.ancestor")
+	defer span.End()
+
+	r := bytesutil.ToBytes32(root)
+	// Get ancestor root from fork choice store instead of recursively looking up blocks in DB.
+	// This is most optimal outcome.
+	s.ForkChoicer().RLock()
+	ar, err := s.cfg.ForkChoiceStore.AncestorRoot(ctx, r, slot)
+	s.ForkChoicer().RUnlock()
+	if err != nil {
+		// Try getting ancestor root from DB when failed to retrieve from fork choice store.
+		// This is the second line of defense for retrieving ancestor root.
+		ar, err = s.ancestorByDB(ctx, r, slot)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return ar[:], nil
+}
+
 // SetGenesisTime sets the genesis time of beacon chain.
 func (s *Service) SetGenesisTime(t time.Time) {
 	s.genesisTime = t

beacon-chain/blockchain/process_block_helpers.go

@@ -146,39 +146,6 @@ func (s *Service) updateFinalized(ctx context.Context, cp *ethpb.Checkpoint) err
 	return nil
 }
 
-// ancestor returns the block root of an ancestry block from the input block root.
-//
-// Spec pseudocode definition:
-//
-//	def get_ancestor(store: Store, root: Root, slot: Slot) -> Root:
-//	 block = store.blocks[root]
-//	 if block.slot > slot:
-//	     return get_ancestor(store, block.parent_root, slot)
-//	 elif block.slot == slot:
-//	     return root
-//	 else:
-//	     # root is older than queried slot, thus a skip slot. Return most recent root prior to slot
-//	     return root
-func (s *Service) ancestor(ctx context.Context, root []byte, slot primitives.Slot) ([]byte, error) {
-	ctx, span := trace.StartSpan(ctx, "blockChain.ancestor")
-	defer span.End()
-
-	r := bytesutil.ToBytes32(root)
-	// Get ancestor root from fork choice store instead of recursively looking up blocks in DB.
-	// This is most optimal outcome.
-	ar, err := s.cfg.ForkChoiceStore.AncestorRoot(ctx, r, slot)
-	if err != nil {
-		// Try getting ancestor root from DB when failed to retrieve from fork choice store.
-		// This is the second line of defense for retrieving ancestor root.
-		ar, err = s.ancestorByDB(ctx, r, slot)
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	return ar[:], nil
-}
-
 // This retrieves an ancestor root using DB. The look up is recursively looking up DB. Slower than `ancestorByForkChoiceStore`.
 func (s *Service) ancestorByDB(ctx context.Context, r [32]byte, slot primitives.Slot) (root [32]byte, err error) {
 	ctx, span := trace.StartSpan(ctx, "blockChain.ancestorByDB")

beacon-chain/blockchain/process_block_test.go

@@ -600,14 +600,14 @@ func TestAncestor_HandleSkipSlot(t *testing.T) {
 	}
 
 	// Slots 100 to 200 are skip slots. Requesting root at 150 will yield root at 100. The last physical block.
-	r, err := service.ancestor(context.Background(), r200[:], 150)
+	r, err := service.Ancestor(context.Background(), r200[:], 150)
 	require.NoError(t, err)
 	if bytesutil.ToBytes32(r) != r100 {
 		t.Error("Did not get correct root")
 	}
 
 	// Slots 1 to 100 are skip slots. Requesting root at 50 will yield root at 1. The last physical block.
-	r, err = service.ancestor(context.Background(), r200[:], 50)
+	r, err = service.Ancestor(context.Background(), r200[:], 50)
 	require.NoError(t, err)
 	if bytesutil.ToBytes32(r) != r1 {
 		t.Error("Did not get correct root")
@@ -648,7 +648,7 @@ func TestAncestor_CanUseForkchoice(t *testing.T) {
 		require.NoError(t, service.cfg.ForkChoiceStore.InsertNode(ctx, st, blkRoot))
 	}
 
-	r, err := service.ancestor(context.Background(), r200[:], 150)
+	r, err := service.Ancestor(context.Background(), r200[:], 150)
 	require.NoError(t, err)
 	if bytesutil.ToBytes32(r) != r100 {
 		t.Error("Did not get correct root")
@@ -696,7 +696,7 @@ func TestAncestor_CanUseDB(t *testing.T) {
 	require.NoError(t, err)
 	require.NoError(t, service.cfg.ForkChoiceStore.InsertNode(ctx, st, blkRoot))
 
-	r, err := service.ancestor(context.Background(), r200[:], 150)
+	r, err := service.Ancestor(context.Background(), r200[:], 150)
 	require.NoError(t, err)
 	if bytesutil.ToBytes32(r) != r100 {
 		t.Error("Did not get correct root")

beacon-chain/blockchain/receive_attestation.go

@@ -56,7 +56,7 @@ func (s *Service) VerifyLmdFfgConsistency(ctx context.Context, a *ethpb.Attestat
 	if err != nil {
 		return err
 	}
-	r, err := s.ancestor(ctx, a.Data.BeaconBlockRoot, targetSlot)
+	r, err := s.Ancestor(ctx, a.Data.BeaconBlockRoot, targetSlot)
 	if err != nil {
 		return err
 	}

beacon-chain/blockchain/testing/mock.go

@@ -74,6 +74,10 @@ func (s *ChainService) ForkChoicer() forkchoice.ForkChoicer {
 	return s.ForkChoiceStore
 }
 
+func (s *ChainService) Ancestor(_ context.Context, _ []byte, _ primitives.Slot) ([]byte, error) {
+	return nil, nil
+}
+
 // StateNotifier mocks the same method in the chain service.
 func (s *ChainService) StateNotifier() statefeed.Notifier {
 	if s.stateNotifier == nil {

beacon-chain/sync/service.go

@@ -100,6 +100,7 @@ type blockchainService interface {
 	blockchain.CanonicalFetcher
 	blockchain.OptimisticModeFetcher
 	blockchain.SlashingReceiver
+	blockchain.ForkchoiceFetcher
 }
 
 // Service is responsible for handling all run time p2p related operations as the