Mutable collections in akka Actor return NullPointerException

Question

I have an actor which is calling a websocket and updating a map everytime it receives an update form the web socket. the same map is being used by the actor at another point in the command.

class MyActor(broker: InMemoryBroker) extends Actor {
val myMap: TrieMap[String, String] = new TrieMap[String, String]()

//Gets a response every 1 second 
webSocket.get(onReponse= r=> myMap(r.key) = r.value)


def receive()={
 case MyCommand(key)=>
   if(myMap.get(key).isDefined){     //Null pointer exception is thrown here
       //Do stuff
   }
}

I was expecting TrieMap to be thread safe and not have such issues. Any suggestions?

Answer 1

You should do as much processing as possible in the receive method. So rather than updating the map directly in onResponse, send yourself a message and update the map when you receive it:

class MyActor(broker: InMemoryBroker) extends Actor {
  val myMap: TrieMap[String, String] = new TrieMap[String, String]()

  private case class UpdateMap(r: ???)

  //Gets a response every 1 second 
  webSocket.get(onReponse = r => self ! UpdateMap(r))

  def receive() = {
    case UpdateMap(r) =>
      myMap(r.key) = r.value

    case MyCommand(key) =>
      if (myMap.get(key).isDefined) { //Null pointer exception is thrown here
        //Do stuff
      }
  }
}

With the method the TrieMap is only accessed from a single thread at a time.

Also, that test is better done as:

myMap.get(key).foreach{ value =>
  ???
}