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* Copyright (C) 2009-2018 Lightbend Inc. <>
import scala.collection.mutable.ListBuffer
* Requirements are as follows:
* The first thing the actor needs to do, is to subscribe to a channel of events,
* Then it must replay (process) all "old" events
* Then it has to wait for a GoAhead signal to begin processing the new events
* It mustn't "miss" events that happen between catching up with the old events and getting the GoAhead signal
class UnnestedReceives extends Actor {
import context.become
//If you need to store sender/senderFuture you can change it to ListBuffer[(Any, Channel)]
val queue = new ListBuffer[Any]()
//This message processes a message/event
def process(msg: Any): Unit = println("processing: " + msg)
//This method subscribes the actor to the event bus
def subscribe(): Unit = {} //Your external stuff
//This method retrieves all prior messages/events
def allOldMessages() = List()
override def preStart: Unit = {
//We override preStart to be sure that the first message the actor gets is
//'Replay, that message will start to be processed _after_ the actor is started
self ! 'Replay
//Then we subscribe to the stream of messages/events
def receive = {
case 'Replay //Our first message should be a 'Replay message, all others are invalid
allOldMessages() foreach process //Process all old messages/events
become { //Switch behavior to look for the GoAhead signal
case 'GoAhead //When we get the GoAhead signal we process all our buffered messages/events
queue foreach process
become { //Then we change behavior to process incoming messages/events as they arrive
case msg process(msg)
case msg //While we haven't gotten the GoAhead signal, buffer all incoming messages
queue += msg //Here you have full control, you can handle overflow etc