Akka中的async io延迟回复

Question

我使用akka已经有一段时间了。我开始在我的代码中看到一些模式来解决异步回复的延迟问题。这个实现可以吗？还有另一种不阻塞的延迟回复的方法吗？

class ApplicationApi(asyncIo : ActorRef) extends Actor {
    // store senders to late reply
    val waiting = Map[request, ActorRef]()

    def receive = {
        // an actore request for a user, store it to late reply and ask for asyncIo actor to do the real job
        case request : GetUser => 
            waiting += (sender -> request)
            asyncIo ! AsyncGet("http://app/user/" + request.userId)
        // asyncio response, parse and reply
        case response : AsyncResponse =>
            val user = parseUser(response.body)
            waiting.remove(response.request) match {
                case Some(actor) => actor ! GetUserResponse(user)
            }
    }
}

Answer 1

在等待回复时避免阻塞的一种方法是使用ask方法发送。?运算符-返回Future (与返回()的!不同)。

使用onSuccess或foreach方法，您可以指定在将来完成回复时要执行的操作。要使用此特性，您需要混合使用AskSupport特征：

class ApplicationApi(asyncIo : ActorRef) extends Actor with AskSupport {

  def receive = {
    case request: GetUser =>
      val replyTo = sender
      asyncIo ? AsyncGet("http://app/user/" + request.userId) onSuccess {
        case response: AsyncResponse =>
          val user = parseUser(response.body)
          replyTo ! GetUserResponse(user)
      }

}

避免使用此技术执行任何修改ApplicationApi执行元状态的副作用，因为该效果将与接收循环不同步地发生。不过，向其他参与者转发消息应该是安全的。

顺便说一句，这里有一个技巧可以捕获当前的sender作为模式匹配的一部分，避免以后将其赋值给变量。

trait FromSupport { this: Actor =>
  case object from {
    def unapply(msg: Any) = Some(msg, sender)
  }
}

class MyActor extends Actor with FromSupport {
  def receive = {
    case (request: GetUser) from sender =>
      // sender is now a variable (shadowing the method) that is safe to use in a closure
  }
}