Helper class for actors that need to retry some of the messages they send to other actors until a certain acknowledgement message (ACK) is received. Messages can be sent individually or in batches.

This class is instantiated by providing functions that extract an identifier from sent messages and from ACK messages. This can be an arbitrary identifier, as long as it uniquely associates a received ACK with the original sent message. Optional per-message filtering functions can be given, as well as the frequency of the retries and an optional timeout. Finally, the onComplete method, which is executed after a message or group of messages is acknowledged, must be implemented.

A Retrier can be used as follows:

case class ChangeData(reqId: Long, data: String)
case class ChangeDataAck(reqId: Long)
case class Replicate(reqId: Long, data: String)
case class ReplicateAck(reqId: Long)

class Master(val replica: ActorRef) extends Actor {
  import Retrier._

  val retrier = new Retrier[(ActorRef, ChangeData), Replicate, ReplicateAck, Long](_.reqId, _.reqId) {
    def onComplete(req: (ActorRef, ChangeData)) = req._1 ! ChangeDataAck(req._2.reqId)
  }

  def receive: Receive = ({
    case msg @ ChangeData(reqId, data) =>
      // change data internally here
      retrier.dispatch((sender, msg), Replicate(reqId, data), replica)

  }: Receive).orRetryWith(retrier)
}

In the previous example, every time a Master actor receives a ChangeData message, it sends a Replicate message to a replica actor and only responds to the original sender after an acknowledgement from the replica is received. The Replicate message is retried periodically.