Use balancesLength and randaoMixesLength to save copy on read (prysma…

…ticlabs#4769)

* Use balancesLength and randaoMixesLength to save copy on read

* Update beacon-chain/state/getters.go

Co-Authored-By: shayzluf <thezluf@gmail.com>

Co-authored-by: prylabs-bulldozer[bot] <58059840+prylabs-bulldozer[bot]@users.noreply.github.com>
Co-authored-by: shayzluf <thezluf@gmail.com>

beacon-chain/core/epoch/epoch_processing.go

@@ -274,11 +274,10 @@ func ProcessFinalUpdates(state *stateTrie.BeaconState) (*stateTrie.BeaconState,
 
 	// Set RANDAO mix.
 	randaoMixLength := params.BeaconConfig().EpochsPerHistoricalVector
-	mixes := state.RandaoMixes()
-	if len(mixes) != int(randaoMixLength) {
+	if state.RandaoMixesLength() != int(randaoMixLength) {
 		return nil, fmt.Errorf(
 			"state randao length %d different than EpochsPerHistoricalVector %d",
-			len(mixes),
+			state.RandaoMixesLength(),
 			randaoMixLength,
 		)
 	}

beacon-chain/core/epoch/precompute/reward_penalty.go

@@ -22,9 +22,8 @@ func ProcessRewardsAndPenaltiesPrecompute(
 	}
 
 	numOfVals := state.NumValidators()
-	bals := state.Balances()
 	// Guard against an out-of-bounds using validator balance precompute.
-	if len(vp) != numOfVals || len(vp) != len(bals) {
+	if len(vp) != numOfVals || len(vp) != state.BalancesLength() {
 		return state, errors.New("precomputed registries not the same length as state registries")
 	}
 

beacon-chain/state/getters.go

@@ -431,6 +431,18 @@ func (b *BeaconState) BalanceAtIndex(idx uint64) (uint64, error) {
 	return b.state.Balances[idx], nil
 }
 
+// BalancesLength returns the length of the balances slice.
+func (b *BeaconState) BalancesLength() int {
+	if b.state.Balances == nil {
+		return 0
+	}
+
+	b.lock.RLock()
+	defer b.lock.RUnlock()
+
+	return len(b.state.Balances)
+}
+
 // RandaoMixes of block proposers on the beacon chain.
 func (b *BeaconState) RandaoMixes() [][]byte {
 	if b.state.RandaoMixes == nil {
@@ -467,6 +479,18 @@ func (b *BeaconState) RandaoMixAtIndex(idx uint64) ([]byte, error) {
 	return root, nil
 }
 
+// RandaoMixesLength returns the length of the randao mixes slice.
+func (b *BeaconState) RandaoMixesLength() int {
+	if b.state.RandaoMixes == nil {
+		return 0
+	}
+
+	b.lock.RLock()
+	defer b.lock.RUnlock()
+
+	return len(b.state.RandaoMixes)
+}
+
 // Slashings of validators on the beacon chain.
 func (b *BeaconState) Slashings() []uint64 {
 	if b.state.Slashings == nil {