So in theory, the actors should be able to cope with messages coming in in whatever order the mailbox spits them out. When actors have local state that is dependent on the message history though, how can you keep this up?
Looking at the example of the actor chat: how would the chatroom still be functional if it got, say, all the messages in the wrong order? (logout, post, post, login e.g.) ?
Clearly the actor behaviour IS dependant on global time (or the global view of events) and that's part of the design philosophy when it comes to actors with local state.
Why choose such an example as first example when it's exactly contrary to what is being discussed on page 38?
Now you could, of course, point to footnote 3 on p. 38 saying that the order IS indeed defined in the scala actor environment, and this is a book about actors in scala, so the complaint is void.
Well, as far as I understand fn.3 it says that messages sent from ONE actor arrive in the same order on the receiver as they were sent. In the face of concurrency this means though that in presence of MULTIPLE actors communicating with the ChatRoom the relative order of the different senders is again indetermined, which, though, will leave us with the same problem again - the local state can be 'corrupted' by different actors messaging - and the ChatRoom relying on good-willing and cooperative actors so to speak to not f*** up its local state.
Again, how does this example blend in with the information on p.38?
Previous Topic
