Mastering Functional Programming

Fault tolerance

To keep the example simple, in the parallel example we have used the fetch function from the sequential example to fetch the contents of a certain URL:

val links = fetch(url).getOrElse(Set()).filter(!visited(_))

The motivation for having this function return an Option was fault tolerance in the sequential example—if the result cannot be computed, we return a None. However, in an actor setting, Akka provides you with a framework to specify what to do if an actor has failed. So in principle, we could further refine our example with a dedicated fetch function that is perfectly capable of throwing exceptions. However, you might want to specify the actor-level logic on how to restart itself and how to keep its state through this ...