This will be useful as parameters for retry decorators. --- pym/portage/util/backoff.py | 48 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) create mode 100644 pym/portage/util/backoff.py
diff --git a/pym/portage/util/backoff.py b/pym/portage/util/backoff.py new file mode 100644 index 000000000..d8854337c --- /dev/null +++ b/pym/portage/util/backoff.py @@ -0,0 +1,48 @@ +# Copyright 2018 Gentoo Foundation +# Distributed under the terms of the GNU General Public License v2 + +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) -- 2.13.6
