Akka远程处理-询问路线不会返回答案

Question

I am trying to ask something to an actor that has been created remotely in a SmallestMailboxPool but I never seem to get a response. My feeling is that this is because I send the message to the Router , but the Routee is the actor that is responding - not knowing the exact internals of Akka's ask, I can imagine that the replied must be the same as where the message was sent to. On the other hand, this seems so rudimentary that I cannot imagine it wouldn't work.

I am using Play framework 2.3.x and Akka remote 2.3.4

Actor Setup I have 2 machines with 2 actors on these machines. I will try to keep the example as brief as possible.

Machine A/Actor A

The actual ask is being initiated on Machine A, I added some println statements to show actor addresses. The code is as follows.

class ActorA(remoteActor: ActorRef) extends Actor with ActorLogging {
    ...
    def receive() = {
        case a: String => {
            println("Remote actor: " + remoteActor)
            println("Self: " + self)
            // This is where I get a timeout because I never get a reply
            Await.result((remoteActor ? a), timeout.duration)
        }
    }
}

The output I am getting on Machine A is the following:

Remote actor: Actor[akka.tcp://application@192.168.0.101:2552/user/actorB_6f9bac20-2302-4408-9a1b-feece8c20bc3#-1920529606]
Self: Actor[akka://application/user/9df0190a-11fb-438c-9124-4869d015fc4d#-867250738]

Note that the ActorRef I am passing on to ActorA (called remoteActor ), is the val actorRef that I create on Machine B (see below), having the MailboxPool.

Machine B/Actor B

On Machine B, I have an Actor B that is created in a SmallestMailboxPool and recieves the message from Actor A (via the Router) after which it replies.

The creation is as follows:

// Creation of the mailbox/Router
val actorRef = Akka.system.actorOf(
    SmallestMailboxPool(1).props(
        // sourceActor is the actorRef of Actor A, living on machine A
        Props(ActorB, sourceActor)
    ),
    name = java.util.UUID.randomUUID.toString
)
println("Mailbox is: " + actorRef)

The actual Actor B does the following:

class ActorB(sourceActor: ActorRef) extends Actor with ActorLogging {
    println("I am: " + self)
    def receive() = {
        case a: String => {
            println("I got data from " + sender)
            println("Sending it back to: " + sourceActor)
            sourceActor ! d
        }
    }
}

What I am getting from Actor B is the following printlines:

Mailbox is Actor[akka://application/user/actorB_6f9bac20-2302-4408-9a1b-feece8c20bc3#-1920529606]
I am Actor[akka://application/user/actorB_6f9bac20-2302-4408-9a1b-feece8c20bc3/$a#46262703]
I got data from Actor[akka.tcp://application@192.168.0.132:2552/temp/$e]
I am sending it back to: Actor[akka.tcp://application@192.168.0.132:2552/user/9df0190a-11fb-438c-9124-4869d015fc4d#-867250738]

So what I don't get is why the actor address from ActorA appears as temp/$e on ActorB's side. As can also be seen, ActorB gets the message from ActorA, which actually sends it to the Router. ActorB then rightfully tries to reply back to ActorA, but it always gets a timeout - is this because ActorB has a different ActorRef/address than the Router/Mailbox? I also tried sending back to sender instead of the parameter-given sourceActor , but to no avail.

I know I can ask the Mailbox for all its Routees and send an ask directly to them (haven't tried this yet), but that defies the whole purpose of a MailboxPool. EDIT : Tried this, didn't work either

EDIT:

The weirdest of this entire story, is that if I create ActorB on machine A (eg. not remotely), everything works just fine - I can ask the Router's ActorRef and I get a proper reply. As soon as ActorB is created on machine B, I never get a reply anymore. I also tried to see what happens if I just tell ActorB and continue in ActorA without caring for the result. What happens then is that I do get the message from ActorB that should be my response to the original ask... ActorB is hence perfectly capable of sending back to ActorA but for some reason, Akka won't use it as the reply to my original ask...

Answer 1

I managed to get it work. Turns out I was passing around an ActorRef to ActorB to which it was supposed to send, but at ask-time from ActorA, it seems like Akka makes some sort of temp actor that actually needs to be sent to from ActorB (ie. I can't just send to the ActorRef of ActorA that I passed on to ActorB and stored earlier). Using sender was a fix for me. (Although I am still puzzled why sender was actually not my ActorA).

My actual use case is far too complex to share on SO, but I made a small example (where this problem doesn't occur - everything works) for people interested: https://github.com/ErikTromp/AkkaRemoteAskTest . It uses Play's Iteratee library too, since that is part of my use case too.