Race fix. Changes modelStructsMap implementation from map with mutex to sync.Map (#2022)

* fix (https://github.com/jinzhu/gorm/issues/1407)

* changed map with mutex to sync.Map (https://github.com/jinzhu/gorm/issues/1407)

* removed newModelStructsMap func

* commit to rerun pipeline, comment changed

main.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"reflect"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -162,7 +163,7 @@ func (s *DB) HasBlockGlobalUpdate() bool {
 
 // SingularTable use singular table by default
 func (s *DB) SingularTable(enable bool) {
-	modelStructsMap = newModelStructsMap()
+	modelStructsMap = sync.Map{}
 	s.parent.singularTable = enable
 }
 

model_struct.go

@@ -17,28 +17,7 @@ var DefaultTableNameHandler = func(db *DB, defaultTableName string) string {
 	return defaultTableName
 }
 
-type safeModelStructsMap struct {
+var modelStructsMap sync.Map
-	m map[reflect.Type]*ModelStruct
-	l *sync.RWMutex
-}
-
-func (s *safeModelStructsMap) Set(key reflect.Type, value *ModelStruct) {
-	s.l.Lock()
-	defer s.l.Unlock()
-	s.m[key] = value
-}
-
-func (s *safeModelStructsMap) Get(key reflect.Type) *ModelStruct {
-	s.l.RLock()
-	defer s.l.RUnlock()
-	return s.m[key]
-}
-
-func newModelStructsMap() *safeModelStructsMap {
-	return &safeModelStructsMap{l: new(sync.RWMutex), m: make(map[reflect.Type]*ModelStruct)}
-}
-
-var modelStructsMap = newModelStructsMap()
 
 // ModelStruct model definition
 type ModelStruct struct {
@@ -48,7 +27,7 @@ type ModelStruct struct {
 	defaultTableName string
 }
 
-// TableName get model's table name
+// TableName returns model's table name
 func (s *ModelStruct) TableName(db *DB) string {
 	if s.defaultTableName == "" && db != nil && s.ModelType != nil {
 		// Set default table name
@@ -152,8 +131,8 @@ func (scope *Scope) GetModelStruct() *ModelStruct {
 	}
 
 	// Get Cached model struct
-	if value := modelStructsMap.Get(reflectType); value != nil {
+	if value, ok := modelStructsMap.Load(reflectType); ok && value != nil {
-		return value
+		return value.(*ModelStruct)
 	}
 
 	modelStruct.ModelType = reflectType
@@ -601,7 +580,7 @@ func (scope *Scope) GetModelStruct() *ModelStruct {
 		}
 	}
 
-	modelStructsMap.Set(reflectType, &modelStruct)
+	modelStructsMap.Store(reflectType, &modelStruct)
 
 	return &modelStruct
 }