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max-open-requests 后 akka 客户端 http 被阻止

我从 akka http doc 中拿了这个简单的例子:
http://doc.akka.io/docs/akka-http/current/scala/http/client-side/request-level.html

我稍微修改了一下以请求一百个请求。应用程序在 32 个请求后阻塞(默认 max-open-requests 配置)。
为什么？

import akka.actor.{Actor, ActorLogging, ActorSystem, Props}
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.stream.{ActorMaterializer, ActorMaterializerSettings}
import akka.util.ByteString

import scala.io.StdIn

object AkkaClientExample extends App {
  val system: ActorSystem = ActorSystem("BatchAkka")
  try {
    val unformattedAddresses = (1 to 100).map(i => s"Rue de la Gracieuse $i, Préverenges, Switzerland")

    val googleGeocoder = system.actorOf(GoogleGeocoder.props, "GoogleGeocoder")

    unformattedAddresses.foreach(e => googleGeocoder ! GoogleGeocoder.GeoCode(e))

    println(">>> Press ENTER to exit <<<")
    StdIn.readLine()
  } finally {
    system.terminate()
  }
}

object GoogleGeocoder {
  def props: Props = Props[GoogleGeocoder]

  final case class GeoCode(unformattedAddress: String)
}

class GoogleGeocoder extends Actor with ActorLogging {
  import GoogleGeocoder._
  import akka.pattern.pipe
  import context.dispatcher

  final implicit val materializer: ActorMaterializer = ActorMaterializer(ActorMaterializerSettings(context.system))

  val http = Http(context.system)

  def receive = {
    case GeoCode(unformattedAddress) =>
      log.info(s"GeoCode $unformattedAddress")
      http
        .singleRequest(HttpRequest(uri = url(unformattedAddress)))
        .map(r => (unformattedAddress, r))
        .pipeTo(self)

    case (unformattedAddress: String, resp @ HttpResponse(StatusCodes.OK, headers, entity, _)) =>
      log.info(s"Success response comming for $unformattedAddress")
      entity.dataBytes.runFold(ByteString(""))(_ ++ _).foreach { body =>
        val response = body.utf8String.replaceAll("\\s+", " ").take(50)
        log.info(s"Success response for $unformattedAddress: $response")
      }

    case (unformattedAddress: String, resp @ HttpResponse(code, _, _, _)) =>
      log.info(s"Request failed, response code: $code for $unformattedAddress")
      resp.discardEntityBytes()
  }

  def url(unformattedAddress: String): String =
    //s"https://maps.googleapis.com/maps/api/geocode/json?address=${URLEncoder.encode(unformattedAddress, "UTF-8")}&key=${URLEncoder.encode(googleApiKey, "UTF-8")}"
    s"https://www.epfl.ch/"
}

输出:
[INFO] [07/28/2017 20:08:26.977] [BatchAkka-akka.actor.default-dispatcher-4] [akka://BatchAkka/user/GoogleGeocoder] GeoCode Rue de la Gracieuse 1, Préverenges, Switzerland
[INFO] [07/28/2017 20:08:27.080] [BatchAkka-akka.actor.default-dispatcher-4] [akka://BatchAkka/user/GoogleGeocoder] GeoCode Rue de la Gracieuse 2, Préverenges, Switzerland
...
[INFO] [07/28/2017 20:08:27.098] [BatchAkka-akka.actor.default-dispatcher-13] [akka://BatchAkka/user/GoogleGeocoder] GeoCode Rue de la Gracieuse 99, Préverenges, Switzerland
[INFO] [07/28/2017 20:08:27.098] [BatchAkka-akka.actor.default-dispatcher-13] [akka://BatchAkka/user/GoogleGeocoder] GeoCode Rue de la Gracieuse 100, Préverenges, Switzerland

[INFO] [07/28/2017 20:08:27.615] [BatchAkka-akka.actor.default-dispatcher-11] [akka://BatchAkka/user/GoogleGeocoder] Success response comming for Rue de la Gracieuse 1, Préverenges, Switzerland
[INFO] [07/28/2017 20:08:27.620] [BatchAkka-akka.actor.default-dispatcher-11] [akka://BatchAkka/user/GoogleGeocoder] Success response comming for Rue de la Gracieuse 4, Préverenges, Switzerland
[INFO] [07/28/2017 20:08:27.668] [BatchAkka-akka.actor.default-dispatcher-17] [akka://BatchAkka/user/GoogleGeocoder] Success response for Rue de la Gracieuse 4, Préverenges, Switzerland: <!doctype html><html lang="fr" class="no-js"><head
[INFO] [07/28/2017 20:08:27.668] [BatchAkka-akka.actor.default-dispatcher-21] [akka://BatchAkka/user/GoogleGeocoder] Success response for Rue de la Gracieuse 1, Préverenges, Switzerland: <!doctype html><html lang="fr" class="no-js"><head
...
[INFO] [07/28/2017 20:08:27.787] [BatchAkka-akka.actor.default-dispatcher-5] [akka://BatchAkka/user/GoogleGeocoder] Success response comming for Rue de la Gracieuse 31, Préverenges, Switzerland
[INFO] [07/28/2017 20:08:27.795] [BatchAkka-akka.actor.default-dispatcher-15] [akka://BatchAkka/user/GoogleGeocoder] Success response comming for Rue de la Gracieuse 32, Préverenges, Switzerland
[INFO] [07/28/2017 20:08:27.802] [BatchAkka-akka.actor.default-dispatcher-16] [akka://BatchAkka/user/GoogleGeocoder] Success response for Rue de la Gracieuse 31, Préverenges, Switzerland: <!doctype html><html lang="fr" class="no-js"><head
[INFO] [07/28/2017 20:08:27.806] [BatchAkka-akka.actor.default-dispatcher-17] [akka://BatchAkka/user/GoogleGeocoder] Success response for Rue de la Gracieuse 32, Préverenges, Switzerland: <!doctype html><html lang="fr" class="no-js"><head

在前 32 个请求后被阻止。

更新 考虑到@shutty 的回答:

我已经修改了程序如下，它的工作原理:
class GoogleGeocoder extends Actor with ActorLogging {
  import GoogleGeocoder._
  import akka.pattern.pipe
  import context.dispatcher

  final implicit val materializer: ActorMaterializer = ActorMaterializer(ActorMaterializerSettings(context.system))

  val http = Http(context.system)

  val queue = new scala.collection.mutable.Queue[String]
  var currentRequests = 0
  val MaxCurrentRequest = 10

  def receive = {
    case GeoCode(unformattedAddress) =>
      if (currentRequests < MaxCurrentRequest)
        query(unformattedAddress)
      else
        queue += unformattedAddress

    case (unformattedAddress: String, resp @ HttpResponse(StatusCodes.OK, headers, entity, _)) =>
      log.info(s"Success response comming for $unformattedAddress")
      entity.dataBytes.runFold(ByteString(""))(_ ++ _).foreach { body =>
        currentRequests = currentRequests - 1
        queryNext()
        val response = body.utf8String.replaceAll("\\s+", " ").take(50)
        log.info(s"Success response for $unformattedAddress: $response")
      }

    case (unformattedAddress: String, resp @ HttpResponse(code, _, _, _)) =>
      log.info(s"Request failed, response code: $code for $unformattedAddress")
      resp.discardEntityBytes()
      currentRequests = currentRequests - 1
      queryNext()

    case f: Status.Failure =>
      log.info("failure" + textSample(f))

    case m =>
      log.info("unexpected message: " + textSample(m))
  }

  def query(unformattedAddress: String) {
    log.info(s"GeoCode $unformattedAddress")
    http
      .singleRequest(HttpRequest(uri = url(unformattedAddress)))
      .map(r => (unformattedAddress, r))
      .pipeTo(self)
  }

  def queryNext() {
    if (queue.nonEmpty) {
      query(queue.dequeue)
    }
  }

  def url(unformattedAddress: String): String =
    //s"https://maps.googleapis.com/maps/api/geocode/json?address=${URLEncoder.encode(unformattedAddress, "UTF-8")}&key=${URLEncoder.encode(googleApiKey, "UTF-8")}"
    s"https://www.epfl.ch/"
}

所以，基本上是添加一个队列。

但是，有没有更好的方法来实现这一目标？

我想象这个实现可能失败的情况:例如，如果 http.singleRequest 产生一个失败的 future ，currentRequests 不会减少。我可以在 case f: Status.Failure 上处理这个问题，但是，这个解决方案看起来很容易出错。

也许 akka 已经提供了一些处理队列的机制？

有没有办法向客户端添加背压(以便 AkkaClientExample : unformattedAddresses.foreach(e => googleGeocoder ! GoogleGeocoder.GeoCode(e)) 在到达 MaxCurrentRequest 时被阻止)？

最佳答案

如果您使用 akka.logging = DEBUG 运行您的示例，您会注意到以下输出:
InputBuffer (max-open-requests = 32) now filled with 31 request after enqueuing GET / EmptyInputBuffer (max-open-requests = 32) now filled with 32 request after enqueuing GET / EmptyInputBuffer (max-open-requests = 32) exhausted when trying to enqueue GET / EmptyInputBuffer (max-open-requests = 32) exhausted when trying to enqueue GET / EmptyInputBuffer (max-open-requests = 32) exhausted when trying to enqueue GET / Empty
有很多 a comprehensive description akka-http 如何处理客户端请求的池，但简而言之，如果您用超过 max-open-requests 的池重载，它将开始丢弃请求:

http
 .singleRequest(HttpRequest(uri = url(unformattedAddress)))
 .map(r => (unformattedAddress, r)) // <- HERE
 .pipeTo(self)

当您在 Scala 中对 Future 进行映射时，它只会在成功完成 Future 时执行您的回调，而在您的代码中并非如此。如果您以不同的方式重写代码，例如:
http
  .singleRequest(HttpRequest(uri = url(unformattedAddress)))
  .onComplete {
    case Success(r) =>
      self ! (unformattedAddress, r)
    case Failure(ex) =>
      log.error(ex, "pool overflow")
  }

你会看到一堆异常提示 Future 失败。

更新:

至于我自己的观点，当您需要背压时，actor 和流不太适合。作为一种选择，您可以完全在没有参与者的情况下重写代码:
def url(addr: String) = "http://httpbin.org/headers"
implicit val system: ActorSystem = ActorSystem("BatchAkka")
implicit val mat: ActorMaterializer = ActorMaterializer()
import system.dispatcher
val http = Http()
val addresses = (1 to 100).map(i => s"Rue de la Gracieuse $i, Préverenges, Switzerland")
Source(addresses)
  .mapAsync(4)(addr => http.singleRequest(HttpRequest(uri = url(addr))))
  .map(response => println(response.status))
  .runWith(Sink.seq)
  .map(_ => println("done"))

在此解决方案中，您将只有 4 个带有背压、花里胡哨的服务器的并行请求。

关于max-open-requests 后 akka 客户端 http 被阻止，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/45379930/

10-13 05:02
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