Locking line_items on API update

app/controllers/spree/api/line_items_controller_decorator.rb

@@ -1,9 +1,17 @@
 Spree::Api::LineItemsController.class_eval do
   after_filter :apply_enterprise_fees, only: :update
-
+  around_filter :lock, only: :update
 
   private
 
+  def lock
+    authorize! :read, order
+    @line_item = order.line_items.find(params[:id])
+    @line_item.with_lock do
+      yield
+    end
+  end
+
   def apply_enterprise_fees
     authorize! :read, order
     order.update_distribution_charge!