From 46bf360471c05bf246d9e34692bb1b7b5f8f8c2b Mon Sep 17 00:00:00 2001
From: Preston Van Loon <preston@prysmaticlabs.com>
Date: Thu, 6 Feb 2020 08:06:27 -0800
Subject: [PATCH] Use balancesLength and randaoMixesLength to save copy on read
 (#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   |  5 ++--
 .../core/epoch/precompute/reward_penalty.go   |  3 +--
 beacon-chain/state/getters.go                 | 24 +++++++++++++++++++
 3 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/beacon-chain/core/epoch/epoch_processing.go b/beacon-chain/core/epoch/epoch_processing.go
index 1be30be576ba..34369a7b916a 100644
--- a/beacon-chain/core/epoch/epoch_processing.go
+++ b/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,
 		)
 	}
diff --git a/beacon-chain/core/epoch/precompute/reward_penalty.go b/beacon-chain/core/epoch/precompute/reward_penalty.go
index afafa97d86db..aadd2e3c4e66 100644
--- a/beacon-chain/core/epoch/precompute/reward_penalty.go
+++ b/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")
 	}
 
diff --git a/beacon-chain/state/getters.go b/beacon-chain/state/getters.go
index 132da19a471e..2df3f42e8a9f 100644
--- a/beacon-chain/state/getters.go
+++ b/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 {