Enable tilde trigger with Akka and sbt

Question

With sbt it is possible to do ~run to recompile and run the program when the source changes. However once an ActorSystem is created it does not work anymore.

When the system is shutdown it works, but I don't want to shutdown the system.

import akka.actor.ActorSystem

object Test {
  def main(args: Array[String]) : Unit = {
    val system = ActorSystem()

    // if this line is removed, source code detection is disabled
    system.shutdown()
  }
}

Is there any workaround ?

Answer 1

You have to remember that SBTs ~run by itself is not hot-reloading, it is simply "once the process finishes, run it again please". Akka's thread-pools are non-daemonic, which means that until the ActorSystem is "alive" the program will not terminate, thus SBT's ~run won't trigger again.

Instead you might want to look into the sbt-revolver SBT plugin, which can do what you're looking for (including for Akka based apps).