Proper usage of Monix 3.2.2 Observable with Doobie 0.9.0 - scala

Question

I would like to use Monix Observable with Doobie (fs2) stream, but can't seem to get it working properly. Without streaming, my test app exits just fine but after using streaming, my TaskApp seems to hang on shutdown and can't figure out why.
Here is a minimal example to re-produce the problem:
package example
import java.util.concurrent.Executors
import doobie.implicits._
import cats.effect.{Blocker, ContextShift, ExitCode, Resource}
import doobie.hikari.HikariTransactor
import monix.eval.{Task, TaskApp}
import com.typesafe.scalalogging.StrictLogging
import fs2.interop.reactivestreams._
import monix.reactive.Observable
import scala.concurrent.ExecutionContext
object Hello extends TaskApp with StrictLogging {
private def resources()(implicit contextShift: ContextShift[Task]): Resource[Task, Resources] = {
for {
transactor <- Database.transactor("org.postgresql.Driver", "jdbc:postgresql://localhost/fubar", "fubar", "fubar")
} yield Resources(transactor)
}
def run(args: List[String]): Task[ExitCode] = resources().use(task)
.flatMap(_ => Task { println("All Done!") })
.flatMap(_ => Task(ExitCode.Success))
def task(resources: Resources): Task[Unit] = {
val publisher =
sql"""select id from message;"""
.query[(Long)]
.stream
.transact(resources.transactor)
.toUnicastPublisher()
Observable.fromReactivePublisher(publisher)
.foreachL(id => logger.info(id.toString))
}
}
case class Resources(transactor: HikariTransactor[Task])
object Database {
val ecBlocking = ExecutionContext.fromExecutor(Executors.newFixedThreadPool(8))
def transactor(dbDriver: String, dbUrl: String, dbUser: String, dbPassword: String)(implicit contextShift: ContextShift[Task]): Resource[Task, HikariTransactor[Task]] = {
HikariTransactor.newHikariTransactor[Task](dbDriver, dbUrl, dbUser, dbPassword, ecBlocking, Blocker.liftExecutionContext(ecBlocking))
}
}
I have converted fs2 stream to Monix observable according to Monix documentation: https://monix.io/docs/current/reactive/observable.html#fs2
Do I need to somehow close the fs2 stream or the Observable to get the application exit cleanly?
Appreciate any tips to get this working or tips how to properly debug this.

Answer 1

The problem was that ExecutionContext needs to be shutdown. See the authors' answer here.
Correct usage can been seen in the documentation.