# Copyright 2017 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Decorators for applying timeout arguments to functions.
These decorators are used to wrap API methods to apply either a constant
or exponential timeout argument.
For example, imagine an API method that can take a while to return results,
such as one that might block until a resource is ready:
.. code-block:: python
def is_thing_ready(timeout=None):
response = requests.get('https://example.com/is_thing_ready')
response.raise_for_status()
return response.json()
This module allows a function like this to be wrapped so that timeouts are
automatically determined, for example:
.. code-block:: python
timeout_ = timeout.ExponentialTimeout()
is_thing_ready_with_timeout = timeout_(is_thing_ready)
for n in range(10):
try:
is_thing_ready_with_timeout({'example': 'data'})
except:
pass
In this example the first call to ``is_thing_ready`` will have a relatively
small timeout (like 1 second). If the resource is available and the request
completes quickly, the loop exits. But, if the resource isn't yet available
and the request times out, it'll be retried - this time with a larger timeout.
In the broader context these decorators are typically combined with
:mod:`google.api_core.retry` to implement API methods with a signature that
matches ``api_method(request, timeout=None, retry=None)``.
"""
from __future__ import unicode_literals
import datetime
import six
from google.api_core import datetime_helpers
from google.api_core import general_helpers
_DEFAULT_INITIAL_TIMEOUT = 5.0 # seconds
_DEFAULT_MAXIMUM_TIMEOUT = 30.0 # seconds
_DEFAULT_TIMEOUT_MULTIPLIER = 2.0
# If specified, must be in seconds. If none, deadline is not used in the
# timeout calculation.
_DEFAULT_DEADLINE = None
[docs]@six.python_2_unicode_compatible
class ConstantTimeout(object):
"""A decorator that adds a constant timeout argument.
This is effectively equivalent to
``functools.partial(func, timeout=timeout)``.
Args:
timeout (Optional[float]): the timeout (in seconds) to applied to the
wrapped function. If `None`, the target function is expected to
never timeout.
"""
def __init__(self, timeout=None):
self._timeout = timeout
[docs] def __call__(self, func):
"""Apply the timeout decorator.
Args:
func (Callable): The function to apply the timeout argument to.
This function must accept a timeout keyword argument.
Returns:
Callable: The wrapped function.
"""
@general_helpers.wraps(func)
def func_with_timeout(*args, **kwargs):
"""Wrapped function that adds timeout."""
kwargs["timeout"] = self._timeout
return func(*args, **kwargs)
return func_with_timeout
def __str__(self):
return "<ConstantTimeout timeout={:.1f}>".format(self._timeout)
def _exponential_timeout_generator(initial, maximum, multiplier, deadline):
"""A generator that yields exponential timeout values.
Args:
initial (float): The initial timeout.
maximum (float): The maximum timeout.
multiplier (float): The multiplier applied to the timeout.
deadline (float): The overall deadline across all invocations.
Yields:
float: A timeout value.
"""
if deadline is not None:
deadline_datetime = datetime_helpers.utcnow() + datetime.timedelta(
seconds=deadline
)
else:
deadline_datetime = datetime.datetime.max
timeout = initial
while True:
now = datetime_helpers.utcnow()
yield min(
# The calculated timeout based on invocations.
timeout,
# The set maximum timeout.
maximum,
# The remaining time before the deadline is reached.
float((deadline_datetime - now).seconds),
)
timeout = timeout * multiplier
[docs]@six.python_2_unicode_compatible
class ExponentialTimeout(object):
"""A decorator that adds an exponentially increasing timeout argument.
This is useful if a function is called multiple times. Each time the
function is called this decorator will calculate a new timeout parameter
based on the the number of times the function has been called.
For example
.. code-block:: python
Args:
initial (float): The initial timeout to pass.
maximum (float): The maximum timeout for any one call.
multiplier (float): The multiplier applied to the timeout for each
invocation.
deadline (Optional[float]): The overall deadline across all
invocations. This is used to prevent a very large calculated
timeout from pushing the overall execution time over the deadline.
This is especially useful in conjuction with
:mod:`google.api_core.retry`. If ``None``, the timeouts will not
be adjusted to accomodate an overall deadline.
"""
def __init__(
self,
initial=_DEFAULT_INITIAL_TIMEOUT,
maximum=_DEFAULT_MAXIMUM_TIMEOUT,
multiplier=_DEFAULT_TIMEOUT_MULTIPLIER,
deadline=_DEFAULT_DEADLINE,
):
self._initial = initial
self._maximum = maximum
self._multiplier = multiplier
self._deadline = deadline
[docs] def with_deadline(self, deadline):
"""Return a copy of this teimout with the given deadline.
Args:
deadline (float): The overall deadline across all invocations.
Returns:
ExponentialTimeout: A new instance with the given deadline.
"""
return ExponentialTimeout(
initial=self._initial,
maximum=self._maximum,
multiplier=self._multiplier,
deadline=deadline,
)
[docs] def __call__(self, func):
"""Apply the timeout decorator.
Args:
func (Callable): The function to apply the timeout argument to.
This function must accept a timeout keyword argument.
Returns:
Callable: The wrapped function.
"""
timeouts = _exponential_timeout_generator(
self._initial, self._maximum, self._multiplier, self._deadline
)
@general_helpers.wraps(func)
def func_with_timeout(*args, **kwargs):
"""Wrapped function that adds timeout."""
kwargs["timeout"] = next(timeouts)
return func(*args, **kwargs)
return func_with_timeout
def __str__(self):
return (
"<ExponentialTimeout initial={:.1f}, maximum={:.1f}, "
"multiplier={:.1f}, deadline={:.1f}>".format(
self._initial, self._maximum, self._multiplier, self._deadline
)
)
