Use MapIter.SetKey/SetValue and sync.Pool to improve memory allocation

Since go 1.18, the reflect package introduces MapIter.SetKey and
MapIter.SetValue that will do fewer memory allocation for map
iteration which is frequently used for CBOR encode operation. Plus,
usage of sync.Pool will further reduce memory allocation by reusing
the shared memory in the pool. Lastly, the Value.SetZero method
(available since go 1.20) is helpful to release memory allocation
to the GC when is no longer needed.

Signed-off-by: Vu Dinh <vudinh@outlook.com>

Author: dinhxuanvu

encode_map.go

@@ -0,0 +1,79 @@
+// Copyright (c) Faye Amacker. All rights reserved.
+// Licensed under the MIT License. See LICENSE in the project root for license information.
+
+//go:build go1.20
+
+package cbor
+
+import (
+	"reflect"
+	"sync"
+)
+
+type mapKeyValueEncodeFunc struct {
+	kf, ef       encodeFunc
+	kpool, vpool sync.Pool
+}
+
+func (me *mapKeyValueEncodeFunc) encodeKeyValues(e *encoderBuffer, em *encMode, v reflect.Value, kvs []keyValue) error {
+	trackKeyValueLength := len(kvs) == v.Len()
+	iterk := me.kpool.Get().(*reflect.Value)
+	defer func() {
+		iterk.SetZero()
+		me.kpool.Put(iterk)
+	}()
+	iterv := me.vpool.Get().(*reflect.Value)
+	defer func() {
+		iterv.SetZero()
+		me.vpool.Put(iterv)
+	}()
+	iter := v.MapRange()
+	for i := 0; iter.Next(); i++ {
+		off := e.Len()
+		iterk.SetIterKey(iter)
+		iterv.SetIterValue(iter)
+
+		if err := me.kf(e, em, *iterk); err != nil {
+			return err
+		}
+		if trackKeyValueLength {
+			kvs[i].keyLen = e.Len() - off
+		}
+
+		if err := me.ef(e, em, *iterv); err != nil {
+			return err
+		}
+		if trackKeyValueLength {
+			kvs[i].keyValueLen = e.Len() - off
+		}
+	}
+
+	return nil
+}
+
+func getEncodeMapFunc(t reflect.Type) encodeFunc {
+	kf, _ := getEncodeFunc(t.Key())
+	ef, _ := getEncodeFunc(t.Elem())
+	if kf == nil || ef == nil {
+		return nil
+	}
+	mkv := &mapKeyValueEncodeFunc{
+		kf: kf,
+		ef: ef,
+		kpool: sync.Pool{
+			New: func() interface{} {
+				rk := reflect.New(t.Key()).Elem()
+				return &rk
+			},
+		},
+		vpool: sync.Pool{
+			New: func() interface{} {
+				rv := reflect.New(t.Elem()).Elem()
+				return &rv
+			},
+		},
+	}
+	return mapEncodeFunc{
+		e: mkv.encodeKeyValues,
+	}.encode
+}

encode_map_go117.go

@@ -1,6 +1,8 @@
 // Copyright (c) Faye Amacker. All rights reserved.
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 
+//go:build !go1.20
+
 package cbor
 
 import (

go.mod

@@ -1,5 +1,5 @@
 module github.com/fxamacker/cbor/v2
 
-go 1.12
+go 1.20
 
 require github.com/x448/float16 v0.8.4