Observer Change manger

In the book, Design Patterns: Elements of Reusable Object-Oriented Software (1994) (The "Gang of Four": Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides), the chapter on the observer to the pattern tells about the change manager. But his description is very short. Especially its type based on an acyclic dependency graph (DAGChangeManager) between subjects and their observers. Can anyone give a small example DAGChangeManager in C++ (or Java) ?