Actors as people

In the previous section, you learned that an actor encapsulates state, interacting with the outside world through messages. Actors make concurrent programming more intuitive because they behave a little bit like an ideal workforce.

Let's think of an actor system representing a start-up with five people. There's Chris, the CEO, and Mark, who's in charge of marketing. Then there's Sally, who heads the engineering team. Sally has two minions, Bob and Kevin. As every good organization needs an organizational chart, refer to the following diagram:

Let's say that Chris receives an order. He will look at the order, decide whether it is something that he can process himself, and if not, he will forward it to Mark or Sally. Let's assume that the order asks for a small program so Bob forwards the order to Sally. Sally is very busy working on a backlog of orders so she cannot process the order message straightaway, and it will just sit in her mailbox for a short while. When she finally...