找不到参数超时的隐式值：akka.util.Timeout

Question

I have this code, where I am making an ask request in Scala:

someActorRef ? SomeMessage()

However, I'm getting this message:

could not find implicit value for parameter timeout: akka.util.Timeout

I also tried this:

Await.ready(someActorRef ? SomeMessage(), Duration("3 seconds")).asInstanceOf[String]

But I get the same message.

Anyway, I don't want to block. I want to get a Future and then later on give it an onComplete callback.

Can I ask for a message from another actor without blocking?

Answer 1

ask needs an implicit Timeout , after which it will just fail the Future with a TimeoutException .

import akka.pattern.ask
import akka.util.Timeout
import scala.concurrent.duration._

implicit val timeout = Timeout(5 seconds)
val f = someActorRef ? SomeMessage()

Note that nothing will block for those 5 seconds, the ask pattern is fully async/non-blocking. It will give you back a Future , on which you can block (NOT RECOMMENDED) or attach a callback (as you wish)

f.onComplete(doSomething(_))

More info here .

Answer 2

You can. But don't use ask . Just pipe result to the sender. Eg let's say this is an actor which performs long running task and returns a future:

class LongRunningTaskPerformer extends Actor {
  import context.dispatcher

  override def receive: Receive = {
    case PerformTask => someLongRunningTask() pipeTo sender()
  }
}

class QueryPerformer extends Actor {

  val longRunningTaskPerformer = context.actorOf(LongRunningTaskPerformer.props())  

  override def receive: Receive = {
    case TriggerLongRunningTask => longRunningTaskPerformer ! PerformTask
    case result @ Result         => // do something with your result
  }
}

In this case, I'm sending a message PerformTask to LongRunningTaskPerformer actor. When the future is being completed, result will be sent to my QueryPerformer . No blocking. Easy.