If ModelB needs to wait for ModelA, and it already is aware of ModelA (which your code requires) - why not make ModelA into an eventDispatcher, have ModelB list

If ModelB needs to wait for ModelA, and it already is aware of ModelA (which your code requires) - why not make ModelA into an eventDispatcher, have ModelB listen to ModelA, and have ModelA dispatch an event when it's done (Or write a small onX function in ModelA). It's also clearer, easier to implement, already implemented in tons of frameworks and easier to unit test (since you no longer need to mock the appDispatcher). You should probably try to avoid using a global eventDispatcher (as any other global), whether you can specify order of execution or not.