void Scheduler::RunLoop() {
  while (!run_queue_.IsEmpty() || !sleep_queue_.IsEmpty()) {
    Fiber* next = nullptr;
    while (!sleep_queue_.IsEmpty() && (next = sleep_queue_.TryPop())) {
      next->SetState(FiberState::Runnable);
      run_queue_.PushBack(next);
    }

    if (!run_queue_.IsEmpty()) {
      next = run_queue_.PopFront();
      SwitchTo(next);
      Reschedule(next);
    } else if (!sleep_queue_.IsEmpty()){
      sleep_queue_.Sleep();
    }
  }
}