[gentoo-portage-dev] [PATCH 2/4] Add ExponentialBackoff and RandomExponentialBackoff

[Zac Medico]

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