AkkaHttp: Process incoming requests in parallel with multiple processes - scala

Question

Using AkkaHttp with Scala, the following code provides an endpoint for /api/endpoint/{DoubleNumber}. Querying this endpoint triggers a heavy computation and then returns the result as application/json.
import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer
object Run {
def main(args: Array[String]) = {
implicit val system = ActorSystem("myApi")
implicit val materializer = ActorMaterializer()
implicit val executionContext = system.dispatcher
val e = get {
path("api/endpoint" / DoubleNumber) {
case (myNumberArgument) {
val result = someHeavyComputation(myNumberArgument)
complete(HttpEntity(ContentTypes.`application/json`, result.toString))
}
}
}
}
}
If one sends several concurrent requests from, say, a browser's console, the above code will wait for each request to be completed (and the response returned) before starting to handle the next one.
How to fix the above code to make it work in parallel, in other words launch an additional process for each incoming request, if previous requests are still being processed?

Answer 1

Looks like I came to an answer.
If you have the same problem, simply call someHeavyComputation from inside the complete() block, not before:
val e = get {
path("api/endpoint" / DoubleNumber) {
case (myNumberArgument) {
complete {
val result = someHeavyComputation(myNumberArgument)
HttpEntity(ContentTypes.`application/json`, result.toString)
}
}
}
}
New processes will be launched as necessary.