* until one is ready. If there are no ready queues, or if other threads have everything under
   * control this will return null. If there is more than a single task ready to execute immediately
   * this will launch another thread to handle that work.
   */
  fun awaitTaskToRun(): Task? {
    lock.assertHeld()

    while (true) {
      if (readyQueues.isEmpty()) {
        return null // Nothing to do.
      }