Mutable collections in akka Actor return NullPointerException - scala

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 =>
???
}