How to make parallel Http request using Akka-Http?

Question

I am new to Scala and trying to implement a library where I will get thousands of URLs. My job is to download the content from those URLs. I would have opted for simple scalaj-http library but it does not serve my purpose. The code I came with is this:

    class ProxyHttpClient {
      def get(url: String, proxy: ProxySettings,urlDownloaderConfig: 
    UrlDownloaderConfig)(implicit ec: ExecutionContext): Either[HttpError, 
    HttpSuccessResponse] = {
        implicit val system: ActorSystem = ActorSystem()
        implicit val materializer: ActorMaterializer = ActorMaterializer()


        val auth = headers.BasicHttpCredentials(proxy.userName, 
    proxy.secret)
    val httpsProxyTransport = 
      ClientTransport.httpsProxy(InetSocketAddress.createUnresolved(
    proxy.host, proxy.port), auth)
    val settings = 
ConnectionPoolSettings(system).withTransport(httpsProxyTransport)
    val response: Future[HttpResponse] = 

Http().singleRequest(HttpRequest().
withMethod(HttpMethods.GET).withUri(url), settings = settings)

    val data: Future[Either[HttpError, HttpSuccessResponse]] = `response.map {`
      case response@HttpResponse(StatusCodes.OK, _, _, _) => {
        val content: Future[String] = Unmarshal(response.entity).to[String]
        val finalContent = Await.ready(content, timeToWaitForContent).value.get.get.getBytes
        Right(HttpSuccessResponse(url, response.status.intValue(), finalContent))
      }
      case errorResponse@HttpResponse(StatusCodes.GatewayTimeout, _, _, _) => Left(HttpError(url, errorResponse.status.intValue(), errorResponse.entity.toString))
    }
    val result: Try[Either[HttpError, HttpSuccessResponse]] = Await.ready(data, timeToWaitForResponse).value.get
    val pop: Either[HttpError, HttpSuccessResponse] = try {
      result.get
    } catch {
      case e: Exception => Left(HttpError(url, HttpStatus.SC_INTERNAL_SERVER_ERROR, e.getMessage))
    }
    pop
  }
}

For calling get method I am using

val forkJoinPool = new scala.concurrent.forkjoin.ForkJoinPool(8)
picList.par.tasksupport = new ForkJoinTaskSupport(forkJoinPool)
picList.par.map(testUrl => {
      val resp = get(url, Option(proxy))

    })

It ran smoothly few times but when I tried to invoke method for 1000 urls to fetch images in batch size of 100 it threw below error. After that even for single URL I am getting same error.

**java.lang.OutOfMemoryError: unable to create new native thread**

Should I use actors here instead of actorsystem and dedicate a separate dispatcher to it?
Since I am holding the content of image which is binary do I have to take care of removing it from memory after their purpose is served?

Code snippet will be more helpful. Thanks in advance

I tried to follow online suggestions where people have suggested to use

val blockingExecutionContext = system.dispatchers.lookup("blocking-dispatcher")

But when I tried, system.dispatchers.lookup is returning of type MessageDispacther.

implicit val system: ActorSystem = ActorSystem()
    val ex: MessageDispatcher =system.dispatchers.lookup("io-blocking-dispatcher")

Is there any library or import missing for me?

Ivan Stanislavciuc Ivan Stanislavciuc · Accepted Answer · 2019-03-07T08:36:31

Your problem is most probably related to creation of actor system for each http call. Actor system is usually one per whole application.

Do a small refactoring and try with it.

class ProxyHttpClient() {
  private implicit val system: ActorSystem = ActorSystem()
  private implicit val materializer: ActorMaterializer = ActorMaterializer()

  def get(url: String, proxy: ProxySettings,urlDownloaderConfig: 
    UrlDownloaderConfig)(implicit ec: ExecutionContext): Either[HttpError, 
    HttpSuccessResponse] = {???}
}

Or extract actor system and pass it as implicit argument

class ProxyHttpClient() {

  def get(url: String, proxy: ProxySettings,urlDownloaderConfig: 
    UrlDownloaderConfig)(implicit ec: ExecutionContext, system: ActorSystem, materializer: ActorMaterializer): Either[HttpError, 
    HttpSuccessResponse] = {???}
}

How to make parallel Http request using Akka-Http?

1 Answers