Why is Scheduler#scheduler not interruptible?

[alexandru]

Looking at the behaviour exemplified by this test:

  test("schedule cancellation doesn't abort inner code") {
    Async.blocking:
      var bodyRan = false
      val fut = Promise[Unit]()
      val cancellable = Async.current.scheduler.schedule(
        50.milliseconds,
        () =>
          fut.complete(Success(()))
          Async.blocking:
            sleep(500)
            bodyRan = true
      )

      // cancel after body started running
      fut.await
      cancellable.cancel()

      sleep(1000)

      assert(bodyRan)
  }

What's the reason for this contract? Cancelling a scheduled task, while running, is a fair use-case. Java exposes a mayInterruptIfRunning boolean flag, for such cases, however, in its absence, the better default would be to interrupt if running. Because you can make any scheduled code to be non-interruptible.

[natsukagami]

In gears we are currently settling with not requiring Scheduler tasks to be fully interruptible. This cannot be done e.g. in Scala Native without tracking the underlying running thread and try to send an interrupt signal to it.

I think for now, while we're looking at preemption patterns, that this is not something I'd be eager to expose.