a.rb

scala> object Test {
     |   def main(args: Array[String]): Unit = {
     |     import scala.concurrent._
     |     import ExecutionContext.Implicits.global
     |     val source1 = Promise[Int]()
     |     val source2 = Promise[Int]()
     |
     |     val done = Promise[Boolean]()
     |     val future2 = source2.completeWith(source1.future).future
     |     future2.onComplete {
     |       case _ => done.success(true)
     |     }
     |     source2.tryFailure(new TimeoutException)
     |     source1.success(123)
     |     import duration._
     |     assert(Await.result(done.future, 10.minutes))
     |   }
     | }
defined object Test

scala>

scala> (1 to 1000) foreach {i => print("."); Test.main(null)}
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scala> (1 to 1000) foreach {i => print("."); Test.main(null)}
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