Console scala app doesn't stop when using reactive mongo driver

Question

I'm playing with Mongo database through the Reactive Mongo driver

import org.slf4j.LoggerFactory

import reactivemongo.api.MongoDriver
import reactivemongo.api.collections.default.BSONCollection
import reactivemongo.bson.BSONDocument

import scala.concurrent.Future
import scala.concurrent.duration._
import scala.concurrent.ExecutionContext.Implicits.global

object Main {

  val log = LoggerFactory.getLogger("Main")

  def main(args: Array[String]): Unit = {

    log.info("Start")

    val conn = new MongoDriver().connection(List("localhost"))
    val db = conn("test")

    log.info("Done")

  }
}

My build.sbt file:

lazy val root = (project in file(".")).
  settings(
    name := "simpleapp",
    version := "1.0.0",
    scalaVersion := "2.11.4",
    libraryDependencies ++= Seq(
      "org.reactivemongo" %% "reactivemongo" % "0.10.5.0.akka23",
      "ch.qos.logback" % "logback-classic" % "1.1.2"
    )
  )

When I run: sbt compile run

I get this output:

$ sbt compile run
[success] Total time: 0 s, completed Apr 25, 2015 5:36:51 PM
[info] Running Main 
ERROR StatusLogger No log4j2 configuration file found. Using default configuration: logging only errors to the console.
17:36:52.328 [run-main-0] INFO  Main - Start
17:36:52.333 [run-main-0] INFO  Main - Done

And application doesn't stop.... :/

I have to press Ctrl + C to kill it

I've read that MongoDriver() creates ActorSystem so I tried to close connection manually with conn.close() but I get this:

[info] Running Main 
ERROR StatusLogger No log4j2 configuration file found. Using default configuration: logging only errors to the console.
17:42:23.252 [run-main-0] INFO  Main - Start
17:42:23.258 [run-main-0] INFO  Main - Done
17:42:23.403 [reactivemongo-akka.actor.default-dispatcher-2] ERROR reactivemongo.core.actors.MongoDBSystem - (State: Closing) UNHANDLED MESSAGE: ChannelConnected(-973180998)
[INFO] [04/25/2015 17:42:23.413] [reactivemongo-akka.actor.default-dispatcher-3] [akka://reactivemongo/deadLetters] Message [reactivemongo.core.actors.Closed$] from Actor[akka://reactivemongo/user/$b#-1700211063] to Actor[akka://reactivemongo/deadLetters] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
[INFO] [04/25/2015 17:42:23.414] [reactivemongo-akka.actor.default-dispatcher-3] [akka://reactivemongo/user/$a] Message [reactivemongo.core.actors.Close$] from Actor[akka://reactivemongo/user/$b#-1700211063] to Actor[akka://reactivemongo/user/$a#-1418324178] was not delivered. [2] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'. 

And app doesn't exit also

So, what am i doing wrong? I can'f find answer...

And it seems to me that official docs doesn't explain whether i should care about graceful shutdown at all.

I don't have much experience with console apps, i use play framework in my projects but i want to create sub-project that works with mongodb

I see many templates (in activator) such as: Play + Reactive Mongo, Play + Akka + Mongo but there's no Scala + Reactive Mongo that would explain how to work properly :/

Answer 1

I was having the same problem. The solution I found was invoking close on both object, the driver and the connection:

val driver = new MongoDriver
val connection = driver.connection(List("localhost"))
...
connection.close()
driver.close()

If you close only the connection, then the akka system remains alive.

Tested with ReactiveMongo 0.12

Answer 2

This looks like a known issue with Reactive Mongo, see the relevant thread on GitHub

A fix for this was introduced in this pull request #241 by reid-spencer, merged on the 3rd of February 2015

You should be able to fix it by using a newer version. If no release has been made since February, you could try checking out a version that includes this fix and building the code yourself.

As far as I can see, there's no mention of this bugfix in the release notes for version 0.10.5

3. Bugfixes:
   • BSON library: fix BSONDateTimeNumberLike typeclass
   • Cursor: fix exception propagation
   • Commands: fix ok deserialization for some cases
   • Commands: fix CollStatsResult
   • Commands: fix AddToSet in aggregation
   • Core: fix connection leak in some cases
   • GenericCollection: do not ignore WriteConcern in save()
   • GenericCollection: do not ignore WriteConcern in bulk inserts
   • GridFS: fix uploadDate deserialization field
   • Indexes: fix parsing for Ascending and Descending
   • Macros: fix type aliases
   • Macros: allow custom annotations

The name of the committer does not appear as well:

Here is the list of the commits included in this release (since 0.9, the top commit is the most recent one):

$ git shortlog -s -n refs/tags/v0.10.0..0.10.5.x.akka23
39  Stephane Godbillon
 5  Andrey Neverov
 4  lucasrpb
 3  Faissal Boutaounte
 2  杨博 (Yang Bo)
 2  Nikolay Sokolov
 1  David Liman
 1  Maksim Gurtovenko
 1  Age Mooij
 1  Paulo "JCranky" Siqueira
 1  Daniel Armak
 1  Viktor Taranenko
 1  Vincent Debergue
 1  Andrea Lattuada
 1  pavel.glushchenko
 1  Jacek Laskowski

Looking at the commit history for 0.10.5.0.akka23 (the one you reference in build.sbt), it seems the fix was not merged into it.