Use read lock

beacon-chain/blockchain/process_attestation_helpers.go

@@ -42,9 +42,11 @@ func (s *Service) getAttPreState(ctx context.Context, c *ethpb.Checkpoint) (stat
 	if err != nil {
 		return nil, err
 	}
-	baseState, err = transition.ProcessSlotsIfPossible(ctx, baseState, epochStartSlot)
-	if err != nil {
-		return nil, errors.Wrapf(err, "could not process slots up to epoch %d", c.Epoch)
+	if epochStartSlot > baseState.Slot() {
+		baseState, err = transition.ProcessSlotsUsingNextSlotCache(ctx, baseState, c.Root, epochStartSlot)
+		if err != nil {
+			return nil, errors.Wrapf(err, "could not process slots up to epoch %d", c.Epoch)
+		}
 	}
 
 	// Sharing the same state across caches is perfectly fine here, the fetching

beacon-chain/core/transition/trailing_slot_state_cache.go

@@ -13,7 +13,7 @@ import (
 )
 
 type nextSlotCache struct {
-	sync.Mutex
+	sync.RWMutex
 	prevRoot  []byte
 	lastRoot  []byte
 	prevState state.BeaconState
@@ -37,8 +37,8 @@ var (
 // It returns the last updated state if it matches. Otherwise it returns the previously
 // updated state if it matches its root. If no root matches it returns nil
 func NextSlotState(root []byte) state.BeaconState {
-	nsc.Lock()
-	defer nsc.Unlock()
+	nsc.RLock()
+	defer nsc.RUnlock()
 	if bytes.Equal(root, nsc.lastRoot) {
 		nextSlotCacheHit.Inc()
 		return nsc.lastState.Copy()
@@ -74,8 +74,8 @@ func UpdateNextSlotCache(ctx context.Context, root []byte, state state.BeaconSta
 
 // LastCachedState returns the last cached state and root in the cache
 func LastCachedState() ([]byte, state.BeaconState) {
-	nsc.Lock()
-	defer nsc.Unlock()
+	nsc.RLock()
+	defer nsc.RUnlock()
 	if nsc.lastState == nil {
 		return nil, nil
 	}

beacon-chain/core/transition/transition.go

@@ -160,6 +160,7 @@ func ProcessSlotsUsingNextSlotCache(
 	if err != nil {
 		return nil, errors.Wrap(err, "could not process slots")
 	}
+
 	return parentState, nil
 }