Function with_timeout

tornado/gen.py:592–670

Wraps a `.Future` (or other yieldable object) in a timeout. Raises `tornado.util.TimeoutError` if the input future does not complete before ``timeout``, which may be specified in any form allowed by `.IOLoop.add_timeout` (i.e. a `datetime.timedelta` or an absolute time relative to `

(
    timeout: Union[float, datetime.timedelta],
    future: _Yieldable,
    quiet_exceptions: "Union[Type[Exception], Tuple[Type[Exception], ...]]" = (),
)

def with_timeout(
    timeout: Union[float, datetime.timedelta],
    future: _Yieldable,
    quiet_exceptions: "Union[Type[Exception], Tuple[Type[Exception], ...]]" = (),
) -> Future:
    """Wraps a `.Future` (or other yieldable object) in a timeout.

    Raises `tornado.util.TimeoutError` if the input future does not
    complete before ``timeout``, which may be specified in any form
    allowed by `.IOLoop.add_timeout` (i.e. a `datetime.timedelta` or
    an absolute time relative to `.IOLoop.time`)

    If the wrapped `.Future` fails after it has timed out, the exception
    will be logged unless it is either of a type contained in
    ``quiet_exceptions`` (which may be an exception type or a sequence of
    types), or an ``asyncio.CancelledError``.

    The wrapped `.Future` is not canceled when the timeout expires,
    permitting it to be reused. `asyncio.wait_for` is similar to this
    function but it does cancel the wrapped `.Future` on timeout.

    .. versionadded:: 4.0

    .. versionchanged:: 4.1
       Added the ``quiet_exceptions`` argument and the logging of unhandled
       exceptions.

    .. versionchanged:: 4.4
       Added support for yieldable objects other than `.Future`.

    .. versionchanged:: 6.0.3
       ``asyncio.CancelledError`` is now always considered "quiet".

    .. versionchanged:: 6.2
       ``tornado.util.TimeoutError`` is now an alias to ``asyncio.TimeoutError``.

    """
    # It's tempting to optimize this by cancelling the input future on timeout
    # instead of creating a new one, but A) we can't know if we are the only
    # one waiting on the input future, so cancelling it might disrupt other
    # callers and B) concurrent futures can only be cancelled while they are
    # in the queue, so cancellation cannot reliably bound our waiting time.
    future_converted = convert_yielded(future)
    result = _create_future()
    chain_future(future_converted, result)
    io_loop = IOLoop.current()

    def error_callback(future: Future) -> None:
        try:
            future.result()
        except asyncio.CancelledError:
            pass
        except Exception as e:
            if not isinstance(e, quiet_exceptions):
                app_log.error(
                    "Exception in Future %r after timeout", future, exc_info=True
                )