Fix: Switch to lazy init() in decoder and encoder (#490)

* Switch to lazy init() in decoder and encoder

This will prevent go-json from consuming heap unless it is used.

* limit changes to initEncoder and initDecoder

Author: toddtreece

internal/decoder/compile.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"reflect"
 	"strings"
+	"sync"
 	"sync/atomic"
 	"unicode"
 	"unsafe"
@@ -17,22 +18,27 @@ var (
 	typeAddr         *runtime.TypeAddr
 	cachedDecoderMap unsafe.Pointer // map[uintptr]decoder
 	cachedDecoder    []Decoder
+	initOnce         sync.Once
 )
 
-func init() {
-	typeAddr = runtime.AnalyzeTypeAddr()
-	if typeAddr == nil {
-		typeAddr = &runtime.TypeAddr{}
-	}
-	cachedDecoder = make([]Decoder, typeAddr.AddrRange>>typeAddr.AddrShift+1)
+func initDecoder() {
+	initOnce.Do(func() {
+		typeAddr = runtime.AnalyzeTypeAddr()
+		if typeAddr == nil {
+			typeAddr = &runtime.TypeAddr{}
+		}
+		cachedDecoder = make([]Decoder, typeAddr.AddrRange>>typeAddr.AddrShift+1)
+	})
 }
 
 func loadDecoderMap() map[uintptr]Decoder {
+	initDecoder()
 	p := atomic.LoadPointer(&cachedDecoderMap)
 	return *(*map[uintptr]Decoder)(unsafe.Pointer(&p))
 }
 
 func storeDecoder(typ uintptr, dec Decoder, m map[uintptr]Decoder) {
+	initDecoder()
 	newDecoderMap := make(map[uintptr]Decoder, len(m)+1)
 	newDecoderMap[typ] = dec
 

internal/decoder/compile_norace.go

@@ -10,6 +10,7 @@ import (
 )
 
 func CompileToGetDecoder(typ *runtime.Type) (Decoder, error) {
+	initDecoder()
 	typeptr := uintptr(unsafe.Pointer(typ))
 	if typeptr > typeAddr.MaxTypeAddr {
 		return compileToGetDecoderSlowPath(typeptr, typ)

internal/decoder/compile_race.go

@@ -13,6 +13,7 @@ import (
 var decMu sync.RWMutex
 
 func CompileToGetDecoder(typ *runtime.Type) (Decoder, error) {
+	initDecoder()
 	typeptr := uintptr(unsafe.Pointer(typ))
 	if typeptr > typeAddr.MaxTypeAddr {
 		return compileToGetDecoderSlowPath(typeptr, typ)

internal/encoder/compiler.go

@@ -5,6 +5,7 @@ import (
 	"encoding"
 	"encoding/json"
 	"reflect"
+	"sync"
 	"sync/atomic"
 	"unsafe"
 
@@ -24,14 +25,17 @@ var (
 	cachedOpcodeSets       []*OpcodeSet
 	cachedOpcodeMap        unsafe.Pointer // map[uintptr]*OpcodeSet
 	typeAddr               *runtime.TypeAddr
+	initEncoderOnce        sync.Once
 )
 
-func init() {
-	typeAddr = runtime.AnalyzeTypeAddr()
-	if typeAddr == nil {
-		typeAddr = &runtime.TypeAddr{}
-	}
-	cachedOpcodeSets = make([]*OpcodeSet, typeAddr.AddrRange>>typeAddr.AddrShift+1)
+func initEncoder() {
+	initEncoderOnce.Do(func() {
+		typeAddr = runtime.AnalyzeTypeAddr()
+		if typeAddr == nil {
+			typeAddr = &runtime.TypeAddr{}
+		}
+		cachedOpcodeSets = make([]*OpcodeSet, typeAddr.AddrRange>>typeAddr.AddrShift+1)
+	})
 }
 
 func loadOpcodeMap() map[uintptr]*OpcodeSet {

internal/encoder/compiler_norace.go

@@ -4,6 +4,7 @@
 package encoder
 
 func CompileToGetCodeSet(ctx *RuntimeContext, typeptr uintptr) (*OpcodeSet, error) {
+	initEncoder()
 	if typeptr > typeAddr.MaxTypeAddr || typeptr < typeAddr.BaseTypeAddr {
 		codeSet, err := compileToGetCodeSetSlowPath(typeptr)
 		if err != nil {

internal/encoder/compiler_race.go

@@ -10,6 +10,7 @@ import (
 var setsMu sync.RWMutex
 
 func CompileToGetCodeSet(ctx *RuntimeContext, typeptr uintptr) (*OpcodeSet, error) {
+	initEncoder()
 	if typeptr > typeAddr.MaxTypeAddr || typeptr < typeAddr.BaseTypeAddr {
 		codeSet, err := compileToGetCodeSetSlowPath(typeptr)
 		if err != nil {