trie: add sync pool

trie/hasher.go

@@ -110,10 +110,19 @@ func (h *hasher) encodeShortNode(n *shortNode) []byte {
 	return h.encodedBytes()
 }
 
+var fnEncoderPool = sync.Pool{
+	New: func() interface{} {
+		var enc fullnodeEncoder
+		return &enc
+	},
+}
+
 // encodeFullNode returns a copy of the supplied fullNode, with its child
 // being replaced by either the hash or an embedded node if the child is small.
 func (h *hasher) encodeFullNode(n *fullNode) []byte {
-	var fn fullnodeEncoder
+	fn := fnEncoderPool.Get().(*fullnodeEncoder)
+	fn.reset()
+
 	if h.parallel {
 		var wg sync.WaitGroup
 		for i := 0; i < 16; i++ {
@@ -142,6 +151,8 @@ func (h *hasher) encodeFullNode(n *fullNode) []byte {
 		fn.Children[16] = n.Children[16].(valueNode)
 	}
 	fn.encode(h.encbuf)
+	fnEncoderPool.Put(fn)
+
 	return h.encodedBytes()
 }
 

trie/node_enc.go

@@ -43,7 +43,7 @@ func (n *fullNode) encode(w rlp.EncoderBuffer) {
 func (n *fullnodeEncoder) encode(w rlp.EncoderBuffer) {
 	offset := w.List()
 	for i, c := range n.Children {
-		if c == nil {
+		if len(c) == 0 {
 			w.Write(rlp.EmptyString)
 		} else {
 			if i == 16 {
@@ -60,6 +60,14 @@ func (n *fullnodeEncoder) encode(w rlp.EncoderBuffer) {
 	w.ListEnd(offset)
 }
 
+func (n *fullnodeEncoder) reset() {
+	for i, c := range n.Children {
+		if len(c) != 0 {
+			n.Children[i] = n.Children[i][:0]
+		}
+	}
+}
+
 func (n *shortNode) encode(w rlp.EncoderBuffer) {
 	offset := w.List()
 	w.WriteBytes(n.Key)