fix a race condition on IsForeignKey that is being detected by -race sometimes.

model_struct.go

@@ -17,6 +17,10 @@ var DefaultTableNameHandler = func(db *DB, defaultTableName string) string {
 	return defaultTableName
 }
 
+// lock for mutating global cached model metadata
+var structsLock sync.Mutex
+
+// global cache of model metadata
 var modelStructsMap sync.Map
 
 // ModelStruct model definition
@@ -419,8 +423,12 @@ func (scope *Scope) GetModelStruct() *ModelStruct {
 									for idx, foreignKey := range foreignKeys {
 										if foreignField := getForeignField(foreignKey, toFields); foreignField != nil {
 											if associationField := getForeignField(associationForeignKeys[idx], modelStruct.StructFields); associationField != nil {
-												// source foreign keys
+												// mark field as foreignkey, use global lock to avoid race
+												structsLock.Lock()
 												foreignField.IsForeignKey = true
+												structsLock.Unlock()
+
+												// association foreign keys
 												relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, associationField.Name)
 												relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, associationField.DBName)
 
@@ -523,8 +531,12 @@ func (scope *Scope) GetModelStruct() *ModelStruct {
 								for idx, foreignKey := range foreignKeys {
 									if foreignField := getForeignField(foreignKey, toFields); foreignField != nil {
 										if scopeField := getForeignField(associationForeignKeys[idx], modelStruct.StructFields); scopeField != nil {
+											// mark field as foreignkey, use global lock to avoid race
+											structsLock.Lock()
 											foreignField.IsForeignKey = true
-											// source foreign keys
+											structsLock.Unlock()
+
+											// association foreign keys
 											relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, scopeField.Name)
 											relationship.AssociationForeignDBNames = append(relationship.AssociationForeignDBNames, scopeField.DBName)
 
@@ -582,7 +594,10 @@ func (scope *Scope) GetModelStruct() *ModelStruct {
 								for idx, foreignKey := range foreignKeys {
 									if foreignField := getForeignField(foreignKey, modelStruct.StructFields); foreignField != nil {
 										if associationField := getForeignField(associationForeignKeys[idx], toFields); associationField != nil {
+											// mark field as foreignkey, use global lock to avoid race
+											structsLock.Lock()
 											foreignField.IsForeignKey = true
+											structsLock.Unlock()
 
 											// association foreign keys
 											relationship.AssociationForeignFieldNames = append(relationship.AssociationForeignFieldNames, associationField.Name)

model_struct_test.go

@@ -0,0 +1,93 @@
+package gorm_test
+
+import (
+	"sync"
+	"testing"
+
+	"github.com/jinzhu/gorm"
+)
+
+type ModelA struct {
+	gorm.Model
+	Name string
+
+	ModelCs []ModelC `gorm:"foreignkey:OtherAID"`
+}
+
+type ModelB struct {
+	gorm.Model
+	Name string
+
+	ModelCs []ModelC `gorm:"foreignkey:OtherBID"`
+}
+
+type ModelC struct {
+	gorm.Model
+	Name string
+
+	OtherAID uint64
+	OtherA   *ModelA `gorm:"foreignkey:OtherAID"`
+	OtherBID uint64
+	OtherB   *ModelB `gorm:"foreignkey:OtherBID"`
+}
+
+// This test will try to cause a race condition on the model's foreignkey metadata
+func TestModelStructRaceSameModel(t *testing.T) {
+	// use a WaitGroup to execute as much in-sync as possible
+	// it's more likely to hit a race condition than without
+	n := 32
+	start := sync.WaitGroup{}
+	start.Add(n)
+
+	// use another WaitGroup to know when the test is done
+	done := sync.WaitGroup{}
+	done.Add(n)
+
+	for i := 0; i < n; i++ {
+		go func() {
+			start.Wait()
+
+			// call GetStructFields, this had a race condition before we fixed it
+			DB.NewScope(&ModelA{}).GetStructFields()
+
+			done.Done()
+		}()
+
+		start.Done()
+	}
+
+	done.Wait()
+}
+
+// This test will try to cause a race condition on the model's foreignkey metadata
+func TestModelStructRaceDifferentModel(t *testing.T) {
+	// use a WaitGroup to execute as much in-sync as possible
+	// it's more likely to hit a race condition than without
+	n := 32
+	start := sync.WaitGroup{}
+	start.Add(n)
+
+	// use another WaitGroup to know when the test is done
+	done := sync.WaitGroup{}
+	done.Add(n)
+
+	for i := 0; i < n; i++ {
+		i := i
+		go func() {
+			start.Wait()
+
+			// call GetStructFields, this had a race condition before we fixed it
+			if i%2 == 0 {
+				DB.NewScope(&ModelA{}).GetStructFields()
+			} else {
+				DB.NewScope(&ModelB{}).GetStructFields()
+			}
+
+			done.Done()
+		}()
+
+		start.Done()
+	}
+
+	done.Wait()
+}