Optimization for median raw stake and staking new methods (#2192)

* [chain][network] Factor out block reward from internal chain to proper package

* [network] Fill out record intended for RPC

* [staking][network] NewUtilityMetricSnapshot

* Expose rewards to RPC API

* Change json field

* Fix lint

* Remove marshalling

* Remove import

* Optimize median raw stake, total stake, get stake methods

* Remove unnecessary methods and add thread safety

* Review feedback

* Remove lock/unlock

Co-authored-by: Edgar Aroutiounian <edgar.factorial@gmail.com>

README.md

@@ -190,6 +190,14 @@ Tx Generator:
 ./scripts/go_executable_build.sh txgen
 ```
 
+### Harmony docs and guides
+
+https://docs.harmony.one
+
+### API guides
+
+https://docs.harmony.one/home/developers/api
+
 ## Usage
 
 You may build the src/harmony.go locally and run local test.

hmy/api_backend.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"math/big"
 	"sort"
+	"sync"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/math"
@@ -28,6 +29,11 @@ import (
 // APIBackend An implementation of internal/hmyapi/Backend. Full client.
 type APIBackend struct {
 	hmy              *Harmony
+	MedianStakeCache struct {
+		sync.Mutex
+		BlockHeight    int64
+		MedianRawStake *big.Int
+	}
 }
 
 // ChainDb ...
@@ -323,9 +329,16 @@ var (
 
 // GetMedianRawStakeSnapshot ..
 func (b *APIBackend) GetMedianRawStakeSnapshot() *big.Int {
+	b.MedianStakeCache.Lock()
+	defer b.MedianStakeCache.Unlock()
+	if b.MedianStakeCache.BlockHeight != -1 && b.MedianStakeCache.BlockHeight > int64(rpc.LatestBlockNumber)-20 {
+		return b.MedianStakeCache.MedianRawStake
+	}
 	candidates := b.hmy.BlockChain().ValidatorCandidates()
 	if len(candidates) == 0 {
-		return big.NewInt(0)
+		b.MedianStakeCache.Lock()
+		b.MedianStakeCache.MedianRawStake = big.NewInt(0)
+		return b.MedianStakeCache.MedianRawStake
 	}
 	stakes := []*big.Int{}
 	for i := range candidates {
@@ -347,14 +360,16 @@ func (b *APIBackend) GetMedianRawStakeSnapshot() *big.Int {
 	}
 
 	const isEven = 0
+
 	switch l := len(stakes); l % 2 {
 	case isEven:
 		left := stakes[(l/2)-1]
 		right := stakes[l/2]
-		return new(big.Int).Div(new(big.Int).Add(left, right), two)
+		b.MedianStakeCache.MedianRawStake = new(big.Int).Div(new(big.Int).Add(left, right), two)
 	default:
-		return stakes[l/2]
+		b.MedianStakeCache.MedianRawStake = stakes[l/2]
 	}
+	return b.MedianStakeCache.MedianRawStake
 }
 
 // GetValidatorStats returns the stats of validator

hmy/backend.go

@@ -2,6 +2,7 @@ package hmy
 
 import (
 	"math/big"
+	"sync"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/bloombits"
@@ -74,7 +75,16 @@ func New(
 		networkID:      1, // TODO(ricl): this should be from config
 		shardID:        shardID,
 	}
-	hmy.APIBackend = &APIBackend{hmy}
+	hmy.APIBackend = &APIBackend{hmy: hmy,
+		MedianStakeCache: struct {
+			sync.Mutex
+			BlockHeight    int64
+			MedianRawStake *big.Int
+		}{
+			BlockHeight:    -1,
+			MedianRawStake: big.NewInt(0),
+		},
+	}
 	return hmy, nil
 }