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# Copyright 2018 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
__all__ = (
'ExponentialBackoff',
'RandomExponentialBackoff',
)
import random
import sys
class ExponentialBackoff(object):
"""
An object that when called with number of previous tries, calculates
an exponential delay for the next try.
"""
def __init__(self, multiplier=1, base=2, limit=sys.maxsize):
"""
@param multiplier: constant multiplier
@type multiplier: int or float
@param base: maximum number of tries
@type base: int or float
@param limit: maximum number of seconds to delay
@type limit: int or float
"""
self._multiplier = multiplier
self._base = base
self._limit = limit
def __call__(self, tries):
"""
Given a number of previous tries, calculate the amount of time
to delay the next try.
@param tries: number of previous tries
@type tries: int
@return: amount of time to delay the next try
@rtype: int
"""
try:
return min(self._limit, self._multiplier * (self._base ** tries))
except OverflowError:
return self._limit
class RandomExponentialBackoff(ExponentialBackoff):
"""
Equivalent to ExponentialBackoff, with an extra multiplier that uses
a random distribution between 0 and 1.
"""
def __call__(self, tries):
return random.random() * super(RandomExponentialBackoff, self).__call__(tries)
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