Effective Akka

Chapter 2. Patterns of Actor Usage

Now that we understand the varying types of actor systems that can be created, what are some patterns of usage that we can define so that we can avoid making common mistakes when writing actor-based applications? Let’s look at a few of them.

The Extra Pattern

One of the most difficult tasks in asynchronous programming is trying to capture context so that the state of the world at the time the task was started can be accurately represented at the time the task finishes. However, creating anonymous instances of Akka actors is a very simple and lightweight solution for capturing the context at the time the message was handled to be utilized when the tasks are successfully completed. They are like extras in the cast of a movie—helping provide realistic context to the primary actors who are working around them.

The Problem

A great example is an actor that is sequentially handling messages in its mailbox but performing the tasks based on those messages off-thread with futures. This is a great way to design your actors in that they will not block waiting for responses, allowing them to handle more messages concurrently and increase your application’s performance. However, the state of the actor will likely change with every message.

Let’s define the boilerplate of this example. These are classes that will be reused for each of the iterations of our development process going forward. Note that all of this code is available in my GitHub repository, should you ...