Example of race condition fs2 branch 0.10.0: Signal completes before we can get any values out.

race.scala

import fs2._
import cats.effect._
import fs2.async.mutable.Signal
import scala.concurrent.ExecutionContext.Implicits.global

implicit val ioInstance = Effect[IO]

val input = Stream.range(1,20).covary[IO] // <-- try changing this to range(1,2), result is empty!
val output : Stream[IO,Signal[IO,Option[Int]]] =
  Stream eval async.signalOf[IO,Option[Int]](Some(0)) flatMap { sig =>
    Stream(sig) concurrently input.noneTerminate.evalMap(sig.set).drain
  }

val apis = output flatMap { o =>
  val api1 = o.discrete.unNoneTerminate.fold(Nil : List[Int])((l,i) => i :: l)
  val api2 = o.discrete.unNoneTerminate.fold(Nil : List[Int])((l,i) => i :: l)
  api1 merge api2
}

apis.runLog.unsafeRunSync()