Scala/Akka/ReactiveMongo: process does not terminate after system.shutdown() - scala

Question

I just started learning Scala and Akka and now I am trying to develop an application that uses ReactiveMongo framework to connect to a MongoDb server.
The problem is that when I call system.shutdown() in the end of my App object, the process does not terminate and just hangs forever.
I am now testing the case when there is no connection available, so my MongoDB server is not running. I have the following actor class for querying the database:
class MongoDb(val db: String, val nodes: Seq[String], val authentications: Seq[Authenticate] = Seq.empty, val nbChannelsPerNode: Int = 10) extends Actor with ActorLogging {
def this(config: Config) = this(config.getString("db"), config.getStringList("nodes").asScala.toSeq,
config.getList("authenticate").asScala.toSeq.map(c => {
val l = c.unwrapped().asInstanceOf[java.util.HashMap[String, String]]; Authenticate(l.get("db"), l.get("user"), l.get("password"))
}),
config.getInt("nbChannelsPerNode"))
implicit val ec = context.system.dispatcher
val driver = new MongoDriver(context.system)
val connection = driver.connection(nodes, authentications, nbChannelsPerNode)
connection.monitor.ask(WaitForPrimary)(Timeout(30.seconds)).onFailure {
case reason =>
log.error("Waiting for MongoDB primary connection timed out: {}", reason)
log.error("MongoDb actor kills itself as there is no connection available")
self ! PoisonPill
}
val dbConnection = connection(db)
val tasksCollection = dbConnection("tasks")
val taskTargetsCollection = dbConnection("taskTargets")
import Protocol._
override def receive: Receive = {
case GetPendingTask =>
sender ! NoPendingTask
}
}
My app class looks like this:
object HelloAkkaScala extends App with LazyLogging {
import scala.concurrent.duration._
// Create the 'helloakka' actor system
val system = ActorSystem("helloakka")
implicit val ec = system.dispatcher
//val config = ConfigFactory.load(ConfigFactory.load.getString("my.helloakka.app.environment"))
val config = ConfigFactory.load
logger.info("Creating MongoDb actor")
val db = system.actorOf(Props(new MongoDb(config.getConfig("my.helloakka.db.MongoDb"))))
system.scheduler.scheduleOnce(Duration.create(60, TimeUnit.SECONDS), new Runnable() { def run() = {
logger.info("Shutting down the system")
system.shutdown()
logger.info("System has been shut down!")
}})
}
And the log output in my terminal looks like this:
[DEBUG] [08/07/2014 00:32:06.358] [run-main-0] [EventStream(akka://helloakka)] logger log1-Logging$DefaultLogger started
[DEBUG] [08/07/2014 00:32:06.358] [run-main-0] [EventStream(akka://helloakka)] Default Loggers started
00:32:06.443 INFO [run-main-0] [HelloAkkaScala$] - Creating MongoDb actor
00:32:06.518 DEBUG [helloakka-akka.actor.default-dispatcher-3] [reactivemongo.core.actors.MonitorActor] - Actor[akka://helloakka/temp/$a] is waiting for a primary... not available, warning as soon a primary is available.
00:32:06.595 DEBUG [helloakka-akka.actor.default-dispatcher-2] [reactivemongo.core.actors.MongoDBSystem] - Channel #-774976050 unavailable (ChannelClosed(-774976050)).
00:32:06.599 DEBUG [helloakka-akka.actor.default-dispatcher-2] [reactivemongo.core.actors.MongoDBSystem] - The entire node set is still unreachable, is there a network problem?
00:32:06.599 DEBUG [helloakka-akka.actor.default-dispatcher-2] [reactivemongo.core.actors.MongoDBSystem] - -774976050 is disconnected
00:32:08.573 DEBUG [helloakka-akka.actor.default-dispatcher-3] [reactivemongo.core.actors.MongoDBSystem] - ConnectAll Job running... Status: Node[localhost: Unknown (0/10 available connections), latency=0], auth=Set()
00:32:08.574 DEBUG [helloakka-akka.actor.default-dispatcher-3] [reactivemongo.core.actors.MongoDBSystem] - Channel #-73322193 unavailable (ChannelClosed(-73322193)).
00:32:08.575 DEBUG [helloakka-akka.actor.default-dispatcher-3] [reactivemongo.core.actors.MongoDBSystem] - The entire node set is still unreachable, is there a network problem?
00:32:08.575 DEBUG [helloakka-akka.actor.default-dispatcher-3] [reactivemongo.core.actors.MongoDBSystem] - -73322193 is disconnected
... (the last 3 messages repeated many times as per documentation the MongoDriver tries to re-connect with 2 seconds interval)
[ERROR] [08/07/2014 00:32:36.474] [helloakka-akka.actor.default-dispatcher-3] [akka://helloakka/user/$a] Waiting for MongoDB primary connection timed out: akka.pattern.AskTimeoutException: Ask timed out on [Actor[akka://helloakka/user/$c#1684233695]] after [30000 ms]
[ERROR] [08/07/2014 00:32:36.475] [helloakka-akka.actor.default-dispatcher-3] [akka://helloakka/user/$a] MongoDb actor kills itself as there is no connection available
... (the same 3 messages repeated again)
00:32:46.461 INFO [helloakka-akka.actor.default-dispatcher-4] [HelloAkkaScala$] - Shutting down the system
00:32:46.461 INFO [helloakka-akka.actor.default-dispatcher-4] [HelloAkkaScala$] - Awaiting system termination...
00:32:46.465 WARN [helloakka-akka.actor.default-dispatcher-2] [reactivemongo.core.actors.MongoDBSystem] - MongoDBSystem Actor[akka://helloakka/user/$b#537715233] stopped.
00:32:46.465 DEBUG [helloakka-akka.actor.default-dispatcher-5] [reactivemongo.core.actors.MonitorActor] - Monitor Actor[akka://helloakka/user/$c#1684233695] stopped.
[DEBUG] [08/07/2014 00:32:46.468] [helloakka-akka.actor.default-dispatcher-2] [EventStream] shutting down: StandardOutLogger started
00:32:46.483 INFO [helloakka-akka.actor.default-dispatcher-4] [HelloAkkaScala$] - System has been terminated!
And after that the process hands forever and does never terminate. What am I doing wrong?

Answer 1

You aren't doing anything incorrect. This is a known issue.
https://github.com/ReactiveMongo/ReactiveMongo/issues/148