diff --git a/core/main.go b/core/main.go
index 8870331..960ea8d 100644
--- a/core/main.go
+++ b/core/main.go
@@ -2,6 +2,7 @@ package core
 
 import (
 	"context"
+	"sync"
 
 	"github.com/alireza0/s-ui/logger"
 
@@ -28,6 +29,7 @@ var (
 )
 
 type Core struct {
+	mu        sync.RWMutex
 	isRunning bool
 	instance  *Box
 }
@@ -46,10 +48,15 @@ func (c *Core) GetCtx() context.Context {
 }
 
 func (c *Core) GetInstance() *Box {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
 	return c.instance
 }
 
 func (c *Core) Start(sbConfig []byte) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
 	var opt option.Options
 	err := opt.UnmarshalJSONContext(globalCtx, sbConfig)
 	if err != nil {
@@ -66,6 +73,7 @@ func (c *Core) Start(sbConfig []byte) error {
 
 	err = c.instance.Start()
 	if err != nil {
+		c.instance = nil
 		return err
 	}
 
@@ -81,13 +89,20 @@ func (c *Core) Start(sbConfig []byte) error {
 }
 
 func (c *Core) Stop() error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
 	c.isRunning = false
 	if c.instance == nil {
 		return nil
 	}
-	return c.instance.Close()
+	err := c.instance.Close()
+	c.instance = nil
+	return err
 }
 
 func (c *Core) IsRunning() bool {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
 	return c.isRunning
 }
diff --git a/service/config.go b/service/config.go
index 85a41b9..8a99510 100644
--- a/service/config.go
+++ b/service/config.go
@@ -117,7 +117,7 @@ func (s *ConfigService) restartCoreWithConfig(config json.RawMessage) error {
 		}
 	}()
 	if corePtr.IsRunning() {
-		err = corePtr.GetInstance().Close()
+		err = corePtr.Stop()
 		if err != nil {
 			return err
 		}