StateGuard

[Adeynack]

Idea

Ensures that state mutation is thread safe by holding the state value itself internally and making it available only when a task is dispatched to it.

This works better if the state is an immutable class using immutable collections, for total encapsulation.

To be done AFTER

• SequencedExecutor #1 SequencedExecutor

Main features

Those are main ideas and not final interfaces.

mutate

User submits a lambda receiving the actual state and returning the new value of the state. The method itself returns a CompletionStage<Void> to allow to caller to react upon the completion of the submitted task.

public CompletionStage<Void> addUser(User user) {
    return stateGuard.mutate(actual -> {
        log.info("Adding user " + user.getName());
        List<User> updatedUserList = new ArrayList<User>(actual.getUserList());
        updatedUserList.add(user);
        UserServiceState newState = new UserServiceState(updatedUserList);
        return newState;
    });    
}

provide

User submits a lambda receiving the actual state and returning a value to pass down to the caller of the method.

public CompletionStage<List<String>> getUserNames() {
    return stateGuard.provide((actual) -> {
       new ArrayList(actual.getUserList().stream().map(u -> u.getName())
    });    
}

mutateAndProvide

User submits a lambda receiving the actual state and returning both the value to return as a result of the operation and the new value of the state.

return stateGuard.mutateAndProvide(actual -> {
  log.info("Adding user " + user.getName());
  
  List<User> updatedUserList = new ArrayList<User>(actual.getUserList());
  updatedUserList.add(user);
  UserServiceState newState = new UserServiceState(updatedUserList);

  List<String> userNames = new ArrayList(actual.getUserList().stream().map(u -> u.getName());

  return new MutateAndProvideDecision(newState, userNames);
});