My main problem with the ask pattern is that it can "break code at a
distance". Consider this:
case object Subscribe; case class Publish(msg: Any); case class
Image(state: Any)
class Manager extends Actor {
private var subscribers = Set.empty[ActorRef]
def receive = {
case Subscribe => subscribers += sender(); sender() ! Image(stuff)
case p: Publish => subscribers foreach (_ ! p)
}
}
And then
class Client(manager: ActorRef) extends Actor {
manager ! Subscribe
def receive = {
case Image(state) => //do sth
case Publish(data) => //do sth else
}
}
Let's say I decide to change the Client class slightly. I make this
modification:
manager ? Subscribe
Oh dear: I just broke my code! And the bit of code which is now "behaving
differently" is not even in the same *class* as the line I changed. D'oh!
Chris
On Wednesday, 28 May 2014 09:15:09 UTC+1, Ketil Johannessen wrote:
>
> I sometimes run into cases where I instantiate a child actor ,then
> subsequently ask that child with a message, only to discover that the ask
> became dead letter due to the child not been initialized yet. I guess my
> mistake is to apply a synchronous mindset instead of realizing that the
> child actor creation happens asynchronously, and I could avoid this by
> passing in a constructor parameter to the child instance instead.
>
> Or should the usage of ask be minimized whenever possible, since an
> important implicit part of the ask contract is the expectation that you
> will receive a response within a given time interval (something which
> really an async architecture cannot guarantee anyway)?
>
> Is ask something that should only be used at the boundary between the
> synchronous world and the asynchronous actor world, eg in handling http
> requests?
>
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