Runs a function in a ``concurrent.futures.Executor``. If
        ``executor`` is ``None``, the IO loop's default executor will be used.

        Use `functools.partial` to pass keyword arguments to ``func``.

        .. versionadded:: 5.0

def run_in_executor(
        self,
        executor: Optional[concurrent.futures.Executor],
        func: Callable[..., _T],
        *args: Any
    ) -> Awaitable[_T]:
        """Runs a function in a ``concurrent.futures.Executor``. If
        ``executor`` is ``None``, the IO loop's default executor will be used.

        Use `functools.partial` to pass keyword arguments to ``func``.

        .. versionadded:: 5.0
        """
        if executor is None:
            if not hasattr(self, "_executor"):
                from tornado.process import cpu_count

                self._executor = concurrent.futures.ThreadPoolExecutor(
                    max_workers=(cpu_count() * 5)
                )  # type: concurrent.futures.Executor
            executor = self._executor
        c_future = executor.submit(func, *args)
        # Concurrent Futures are not usable with await. Wrap this in a
        # Tornado Future instead, using self.add_future for thread-safety.
        t_future = Future()  # type: Future[_T]
        self.add_future(c_future, lambda f: chain_future(f, t_future))
        return t_future