Concurrency guide with Akka HTTP and Play JSON in Scala 2.13.5
I keep running into I'm working with a concurrency scenario while processing requests using Akka HTTP in combination with Play JSON library in Scala 2.13.5... My goal is to deserialize a JSON body into a case class and then do some processing asynchronously. However, I'm getting a `java.lang.IllegalStateException: need to change the state of the Future once it is completed` behavior when multiple requests are made simultaneously. Here's a basic example of how I'm currently handling the requests: ```scala import akka.http.scaladsl.server.Directives._ import akka.http.scaladsl.model.HttpResponse import akka.http.scaladsl.marshallers.jackson.JacksonSupport import scala.concurrent.Future import scala.concurrent.ExecutionContext.Implicits.global import play.api.libs.json.{Json, OFormat} case class User(name: String, age: Int) object User { implicit val format: OFormat[User] = Json.format[User] } val route = path("user") { post { entity(as[User]) { user => val responseFuture: Future[HttpResponse] = Future { // Simulate some processing if (user.age < 0) throw new IllegalArgumentException("Age want to be negative") HttpResponse(entity = s"User ${user.name} processed successfully") } complete(responseFuture) } } } ``` I've tried wrapping the processing logic in a `Future`, but it seems that the behavior occurs when multiple requests are processed at the same time. I've also checked if the case class deserialization is thread-safe, and it appears that `Play JSON` should handle this properly. The stack trace indicates that the scenario arises during the completion of the `Future`. How can I ensure that the processing is thread-safe and avoid this `IllegalStateException`? Is there a better way to structure this to handle concurrent requests effectively? Any help would be greatly appreciated!