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

Reviewed-by: rriggs, mchung

Author: liach

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

@@ -3820,12 +3820,13 @@ public boolean isRecord() {
     // Fetches the factory for reflective objects
     @SuppressWarnings("removal")
     private static ReflectionFactory getReflectionFactory() {
-        if (reflectionFactory == null) {
-            reflectionFactory =
-                java.security.AccessController.doPrivileged
-                    (new ReflectionFactory.GetReflectionFactoryAction());
+        var factory = reflectionFactory;
+        if (factory != null) {
+            return factory;
         }
-        return reflectionFactory;
+        return reflectionFactory =
+                java.security.AccessController.doPrivileged
+                        (new ReflectionFactory.GetReflectionFactoryAction());
     }
     private static ReflectionFactory reflectionFactory;