[shard] singleflight on committees bls public keys (#2546)

shard/shard_state.go

@@ -7,14 +7,17 @@ import (
 	"errors"
 	"math/big"
 	"sort"
+	"time"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/harmony-one/bls/ffi/go/bls"
+	"github.com/harmony-one/harmony/crypto/hash"
 	common2 "github.com/harmony-one/harmony/internal/common"
 	"github.com/harmony-one/harmony/internal/ctxerror"
 	"github.com/harmony-one/harmony/numeric"
 	"golang.org/x/crypto/sha3"
+	"golang.org/x/sync/singleflight"
 )
 
 var (
@@ -382,12 +385,21 @@ func (c *Committee) DeepCopy() Committee {
 	return r
 }
 
-// BLSPublicKeys ..
-func (c *Committee) BLSPublicKeys() ([]*bls.PublicKey, error) {
-	if c == nil {
-		return nil, ErrSubCommitteeNil
-	}
+// Hash ..
+func (c *Committee) Hash() common.Hash {
+	return hash.FromRLPNew256(c)
+}
 
+var (
+	blsKeyCache singleflight.Group
+)
+
+func lookupBLSPublicKeys(
+	c *Committee,
+) ([]*bls.PublicKey, error) {
+	key := c.Hash().Hex()
+	results, err, _ := blsKeyCache.Do(
+		key, func() (interface{}, error) {
 			slice := make([]*bls.PublicKey, len(c.Slots))
 			for j := range c.Slots {
 				committerKey := &bls.PublicKey{}
@@ -398,7 +410,27 @@ func (c *Committee) BLSPublicKeys() ([]*bls.PublicKey, error) {
 				}
 				slice[j] = committerKey
 			}
+			// Only made once
+			go func() {
+				time.Sleep(25 * time.Minute)
+				blsKeyCache.Forget(key)
+			}()
 			return slice, nil
+		},
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	return results.([]*bls.PublicKey), nil
+}
+
+// BLSPublicKeys ..
+func (c *Committee) BLSPublicKeys() ([]*bls.PublicKey, error) {
+	if c == nil {
+		return nil, ErrSubCommitteeNil
+	}
+	return lookupBLSPublicKeys(c)
 }
 
 var (