Hits more than total requests - scala

Question

So I started learning Scala and Akka actors, Akka-Http. I tried to implement a simple hits counter using Akka Http which counts every hit on the localhost page. I used wrk tool to run 10 threads with 100 connections, after which there is a mismatch between the count and the total requests(Seen on wrk).
This is my code :
object WebServer3 {
var number: Int = 0
final case class Inc()
class ActorClass extends Actor with ActorLogging {
def receive = {
case Inc => number = number + 1
}
}
def main(args: Array[String]) {
implicit val system = ActorSystem("my-system")
implicit val materializer = ActorMaterializer()
implicit val executionContext = system.dispatcher
val actor1 = system.actorOf(Props[ActorClass], "SimpleActor")
val route =
path("Counter") {
get {
actor1 ! Inc
complete(HttpEntity(ContentTypes.`text/html(UTF-8)`, s"<h1>You visited $number times</h1>"))
}
}
val bindingFuture = Http().bindAndHandle(route, "localhost", 8080)
println(s"Server online at http://localhost:8080/\nPress RETURN to stop...")
StdIn.readLine() // let it run until user presses return
bindingFuture
.flatMap(_.unbind()) // trigger unbinding from the port
.onComplete(_ => system.terminate()) // and shutdown when done
}
}
Pardon my immature/amateurish coding skills. I am still learning and I know this has to do with concurrency. But I cannot find a solution yet. Please help.
edit#1 : I tried AtomicInteger too. That did not help.
edit#2 : I tried the complete akka-http way with ask and await too. that did not help either.

Answer 1

There are few problems with your code.
You're defining a case class final case class Inc() but you're sending a companion object actor1 ! Inc. Though, you still match companion object case Inc => and your code works. But it's should not be done this way.
Other problem, we're storing and modifying and retrieving var number: Int = 0 outside of actor boundaries. And I think this is why you have miscounts. Actor must change only internal state.
I modified your code by introducing ask pattern so a value can be retrieved from within an actor.
import akka.actor.{Actor, ActorLogging, ActorSystem, Props}
import akka.http.scaladsl.Http
import akka.http.scaladsl.model.{ContentTypes, HttpEntity}
import akka.http.scaladsl.server.Directives._
import akka.pattern.ask
import akka.stream.ActorMaterializer
import akka.util.Timeout
import scala.concurrent.duration._
import scala.io.StdIn
object WebServer3 {
final case object IncAndGet //not a case class anymore
class ActorClass extends Actor with ActorLogging {
private var number: Int = 0 //inner state must be private and not accessible from outside of an actor
def receive = {
case IncAndGet =>
number += 1
context.sender() ! number // send current value back to sender
}
}
def main(args: Array[String]) {
implicit val system = ActorSystem("my-system")
implicit val materializer = ActorMaterializer()
implicit val executionContext = system.dispatcher
implicit val timeout: Timeout = 2.seconds
val actor1 = system.actorOf(Props[ActorClass], "SimpleActor")
val route =
path("counter") {
get {
onComplete((actor1 ? IncAndGet).mapTo[Int]) { number =>
complete(
HttpEntity(ContentTypes.`text/html(UTF-8)`,
s"<h1>You visited $number times</h1>"))
}
}
}
val bindingFuture = Http().bindAndHandle(route, "localhost", 8080)
println(s"Server online at http://localhost:8080/\nPress RETURN to stop...")
StdIn.readLine() // let it run until user presses return
val _ = bindingFuture
.flatMap(_.unbind()) // trigger unbinding from the port
}
}