Plain Job doesn't wait for children on join()

A Job that isn’t backed by a coroutine doesn’t seem to wait for its children to complete when join() is called after cancelling. Given the following tests, I would expect them both to pass but only one does.

  private fun runTest(cancelAndJoinBlock: suspend (Job) -> Unit) {
    runBlocking {
      val parentJob = Job()

      val finishedLast = AtomicReference<String>()

      launch(parent = parentJob) {
        // Something "long-running" that doesn't suspend
        Thread.sleep(500)
        finishedLast.set("child")
      }

      // Give the child enough time to have started
      delay(200, TimeUnit.MILLISECONDS)

      cancelAndJoinBlock(parentJob)
      finishedLast.set("join")

      // Give the child enough time to have finished
      delay(1, TimeUnit.SECONDS)

      // The child should have finished before the join on the parent returned
      assertEquals("join", finishedLast.get())
    }
  }

  // This one fails
  @Test fun parentJobWithCancelAndJoin() {
    runTest { parentJob ->
      parentJob.cancel()
      parentJob.join()
    }
  }

  // This one passes
  @Test fun parentJobWithCancelAndJoinChildren() {
    runTest { parentJob ->
      parentJob.cancelChildren()
      parentJob.joinChildren()
    }
  }

[elizarov]

After investigation I’ve found that this is a bug and it will be fixed in the next update. When Job is cancelled it should go into cancelling state while it has children and the join should wait until it becomes cancelled (that is, when all its children become cancelled).

[elizarov]

It does make sense.