Akka Actor not terminating if an exception is thrown

The proper way to handle problems inside akka actors is not to throw an exception but rather to set supervisor hierarchies

“Throwing an exception in concurrent code (let’s assume we are using
non-linked actors), will just simply blow up the thread that currently
executes the actor.

There is no way to find out that things went wrong (apart from
inspecting the stack trace).
There is nothing you can do about it.”

see Fault Tolerance Through Supervisor Hierarchies (1.2)

* note * the above is true for old versions of Akka (1.2)
In newer versions (e.g. 2.2) you’d still set a supervisor hierarchy but it will trap Exceptions thrown by child processes. e.g.

class Child extends Actor {
    var state = 0
    def receive = {
      case ex: Exception ⇒ throw ex
      case x: Int        ⇒ state = x
      case "get"         ⇒ sender ! state
    }
  }

and in the supervisor:

class Supervisor extends Actor {
    import akka.actor.OneForOneStrategy
    import akka.actor.SupervisorStrategy._
    import scala.concurrent.duration._

    override val supervisorStrategy =
      OneForOneStrategy(maxNrOfRetries = 10, withinTimeRange = 1 minute) {
        case _: ArithmeticException      ⇒ Resume
        case _: NullPointerException     ⇒ Restart
        case _: IllegalArgumentException ⇒ Stop
        case _: Exception                ⇒ Escalate
      }

    def receive = {
      case p: Props ⇒ sender ! context.actorOf(p)
    }
  }

see Fault Tolerance Through Supervisor Hierarchies (2.2)