Add ServerWithCustomDispatcher

Author: pbernet

src/main/scala/akkahttp/ServerWithCustomDispatcher.scala

@@ -0,0 +1,56 @@
+package akkahttp
+
+import org.apache.pekko.actor.ActorSystem
+import org.apache.pekko.http.scaladsl.Http
+import org.apache.pekko.http.scaladsl.model.{HttpResponse, StatusCodes}
+import org.apache.pekko.http.scaladsl.server.Directives.{complete, extractRequest, path, withExecutionContext}
+import org.apache.pekko.http.scaladsl.server.Route
+import org.slf4j.{Logger, LoggerFactory}
+
+import scala.concurrent.{ExecutionContextExecutor, Future}
+import scala.util.{Failure, Success}
+
+/**
+  * By default, route directives run on the default dispatcher.
+  * The `withExecutionContext` directive alone doesn't force execution on the custom dispatcher
+  * it only makes the custom execution context available.
+  * Wrapping a task in a Future explicitly runs the task on the custom execution context.
+  *
+  * Full example for this answer:
+  * https://stackoverflow.com/questions/79141989/executioncontext-issue-in-akka-http-server/79145603#79145603
+  */
+object ServerWithCustomDispatcher extends App {
+  val logger: Logger = LoggerFactory.getLogger(this.getClass)
+  implicit val system: ActorSystem = ActorSystem()
+
+  implicit val myExCon: ExecutionContextExecutor = system.dispatchers.lookup(
+    "custom-dispatcher-fork-join"
+  )
+
+  val route: Route = {
+    path("hello") {
+      withExecutionContext(myExCon) {
+        extractRequest { request =>
+          // Move the operation inside a Future to ensure it runs on the custom dispatcher
+          val result = Future {
+            logger.info(s"Got request from client: ${request.getHeader("User-Agent")}")
+            val msg = s"Execution context: $myExCon with thread: ${Thread.currentThread.getName}"
+            logger.info(msg)
+            HttpResponse(StatusCodes.OK, entity = s"$msg")
+          }(myExCon)
+          complete(result)
+        }
+      }
+    }
+  }
+
+  val bindingFuture = Http().newServerAt("localhost", 9000).bindFlow(route)
+
+  bindingFuture.onComplete {
+    case Success(b) =>
+      println("Server started, listening on: http://" + b.localAddress)
+    case Failure(e) =>
+      println(s"Server could not bind to... Exception message: ${e.getMessage}")
+      system.terminate()
+  }
+}