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# Copyright 2022 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.
import random
import time
# The default amount of retry attempts
_DEFAULT_RETRY_TOTAL_ATTEMPTS = 3
# The default initial backoff period (1.0 second).
_DEFAULT_INITIAL_INTERVAL_SECONDS = 1.0
# The default randomization factor (0.1 which results in a random period ranging
# between 10% below and 10% above the retry interval).
_DEFAULT_RANDOMIZATION_FACTOR = 0.1
# The default multiplier value (2 which is 100% increase per back off).
_DEFAULT_MULTIPLIER = 2.0
"""Exponential Backoff Utility
This is a private module that implements the exponential back off algorithm.
It can be used as a utility for code that needs to retry on failure, for example
an HTTP request.
"""
class ExponentialBackoff:
"""An exponential backoff iterator. This can be used in a for loop to
perform requests with exponential backoff.
Args:
total_attempts Optional[int]:
The maximum amount of retries that should happen.
The default value is 3 attempts.
initial_wait_seconds Optional[int]:
The amount of time to sleep in the first backoff. This parameter
should be in seconds.
The default value is 1 second.
randomization_factor Optional[float]:
The amount of jitter that should be in each backoff. For example,
a value of 0.1 will introduce a jitter range of 10% to the
current backoff period.
The default value is 0.1.
multiplier Optional[float]:
The backoff multipler. This adjusts how much each backoff will
increase. For example a value of 2.0 leads to a 200% backoff
on each attempt. If the initial_wait is 1.0 it would look like
this sequence [1.0, 2.0, 4.0, 8.0].
The default value is 2.0.
"""
def __init__(
self,
total_attempts=_DEFAULT_RETRY_TOTAL_ATTEMPTS,
initial_wait_seconds=_DEFAULT_INITIAL_INTERVAL_SECONDS,
randomization_factor=_DEFAULT_RANDOMIZATION_FACTOR,
multiplier=_DEFAULT_MULTIPLIER,
):
self._total_attempts = total_attempts
self._initial_wait_seconds = initial_wait_seconds
self._current_wait_in_seconds = self._initial_wait_seconds
self._randomization_factor = randomization_factor
self._multiplier = multiplier
self._backoff_count = 0
def __iter__(self):
self._backoff_count = 0
self._current_wait_in_seconds = self._initial_wait_seconds
return self
def __next__(self):
if self._backoff_count >= self._total_attempts:
raise StopIteration
self._backoff_count += 1
jitter_variance = self._current_wait_in_seconds * self._randomization_factor
jitter = random.uniform(
self._current_wait_in_seconds - jitter_variance,
self._current_wait_in_seconds + jitter_variance,
)
time.sleep(jitter)
self._current_wait_in_seconds *= self._multiplier
return self._backoff_count
@property
def total_attempts(self):
"""The total amount of backoff attempts that will be made."""
return self._total_attempts
@property
def backoff_count(self):
"""The current amount of backoff attempts that have been made."""
return self._backoff_count
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