8261404: Class.getReflectionFactory() is not thread-safe

Backport-of: 905b7639424a0fa80f81f734f6fdae1b5018a14a

src/java.base/share/classes/java/lang/Class.java

@@ -3788,13 +3788,14 @@ public final class Class<T> implements java.io.Serializable,
     // Fetches the factory for reflective objects
     @SuppressWarnings("removal")
     private static ReflectionFactory getReflectionFactory() {
-        if (reflectionFactory == null) {
-            reflectionFactory =
+        var factory = reflectionFactory;
+        if (factory != null) {
+            return factory;
+        }
+        return reflectionFactory =
                 java.security.AccessController.doPrivileged
                         (new ReflectionFactory.GetReflectionFactoryAction());
     }
-        return reflectionFactory;
-    }
     private static ReflectionFactory reflectionFactory;
 
     /**