[tsss]

Doesn't reentrancy defeat the serial processing property that makes locks unnecessary? If a new message is accepted before the previous one has finished processing, then it can change the mutable state inside the actor. Essentially, you can never know what the state will be because at any blocking point some other message can make arbitrary changes. At that point the actor is just a crappy class with message passing instead of method calls and all the annoyances that entails.