def call_soon(self, callback, *args):
        return self.call_later(0, callback, *args)

    def call_later(self, delay, callback, *args):
        raise NotImplementedError

    def call_at(self, when, callback, *args):
        raise NotImplementedError

    def __schedule_callbacks(self):
        ...
        for callback, ctx in callbacks:
            self._loop.call_soon(callback, self, context=ctx)