CODEWITHSUNDEEP
scalashared-memoryactorakka
Matroska
Matroska

Reputation: 6923

Scala actors and shared state

I am trying to implement a dispatcher actor that either process the request or delegates the processing to another actor in case of failure (actually it is the exponential backoff algorithm). The dispatcher actor has a boolean variable that is used to decide how to route the processing.

Is it correct to mantain some state in the actor? What problems could happen? Should I use a transactor (akka) or STM to avoid problems? (I am using akka actors)

class DispatcherActor extends Actor {

   var backoff = false

   def receive = {
    case SendMessage(registrationId, message) => {
      if (backoff) {
        //put on the queue
        backoffManagerActor ! AddMessageToQueue(message)
      } else {
        httpClient.sendNotificationToClient(message, this)
      }
    }
    case BackoffCompleted => //set backoff to false
      backoff = false
    }

   def otherMethod = {
      backoff=true
   } 
}

Upvotes: 2

Views: 2222

Answers (1)

Rex Kerr
Rex Kerr

Reputation: 167901

Actors should maintain state, but it's easiest to reason about them if they only change that state in response to messages or their internally-generated actions; if other entities want them to change state, they should send a message.

In your case, I'd change

def otherMethod { backoff = true }

to, within receive,

case BeginBackoff => backoff = true

and have whoever was going to call otherMethod send BeginBackoff instead. (If you need to preferentially process the backoff messages, you should use the two-level receive others have demonstrated e.g. in response to your previous question about actors.)

Upvotes: 4

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