commit: 6d822cbc2a7a68e39583991b3f69ff76b032d585 Author: Zac Medico <zmedico <AT> gentoo <DOT> org> AuthorDate: Mon Mar 19 07:37:38 2018 +0000 Commit: Zac Medico <zmedico <AT> gentoo <DOT> org> CommitDate: Mon Apr 2 16:53:23 2018 +0000 URL: https://gitweb.gentoo.org/proj/portage.git/commit/?id=6d822cbc
Add ExponentialBackoff and RandomExponentialBackoff This will be useful as parameters for retry decorators. pym/portage/util/backoff.py | 53 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) diff --git a/pym/portage/util/backoff.py b/pym/portage/util/backoff.py new file mode 100644 index 000000000..ee39007ef --- /dev/null +++ b/pym/portage/util/backoff.py @@ -0,0 +1,53 @@ +# 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)