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author | Zac Medico <zmedico@gentoo.org> | 2018-03-19 00:37:38 -0700 |
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committer | Zac Medico <zmedico@gentoo.org> | 2018-04-02 09:53:23 -0700 |
commit | 6d822cbc2a7a68e39583991b3f69ff76b032d585 (patch) | |
tree | 831a6d44fa79ec67241d0bd353bf7700ae4effbd | |
parent | Add ForkExecutor (bug 649588) (diff) | |
download | portage-6d822cbc2a7a68e39583991b3f69ff76b032d585.tar.gz portage-6d822cbc2a7a68e39583991b3f69ff76b032d585.tar.bz2 portage-6d822cbc2a7a68e39583991b3f69ff76b032d585.zip |
Add ExponentialBackoff and RandomExponentialBackoff
This will be useful as parameters for retry decorators.
-rw-r--r-- | pym/portage/util/backoff.py | 53 |
1 files changed, 53 insertions, 0 deletions
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) |