Chapter 2. Simplifying Concurrent Programming with Actors

Before we get started on our refactoring journey (which I promise will start in earnest in Chapter 3, Curing Anemic Models with Domain-Driven Design), it makes sense to refresh ourselves on the actor model and Akka's implementation of it. We will tear down the walls and reframe our house with new programming techniques, but Akka's actors will always be the foundation to that house. Even though some of the newer aspects of Akka (such as Streams and HTTP) abstract up one level from directly using actors, the actor is still a core building block of those frameworks. As such, we should have a solid understanding of what an actor is and how they fit into the world of concurrent programming. We'll even do a little bit of refactoring work in this chapter as we have some bad actor debt (the SalesOrderManager) to clean up first. Here are the things you can expect to learn in this chapter:

• The origins of the actor model and how Akka originated from it
• What concurrency and parallelism are, and how you can use Akka actors to achieve them
• The different types of Dispatchers and Mailboxes in Akka and what use cases each one is good for
• How to employ Akka's FSM feature to simplify the coding of complex workflows
• The different types of automated testing within the testing pyramid
• How to test your Akka actors