106 lines
3.7 KiB
Python
106 lines
3.7 KiB
Python
"""
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The MIT License (MIT)
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Copyright (c) 2015-present Rapptz
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Permission is hereby granted, free of charge, to any person obtaining a
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copy of this software and associated documentation files (the "Software"),
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to deal in the Software without restriction, including without limitation
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the rights to use, copy, modify, merge, publish, distribute, sublicense,
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and/or sell copies of the Software, and to permit persons to whom the
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Software is furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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DEALINGS IN THE SOFTWARE.
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"""
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from __future__ import annotations
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import time
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import random
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from typing import Callable, Generic, Literal, TypeVar, overload, Union
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T = TypeVar('T', bool, Literal[True], Literal[False])
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__all__ = (
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'ExponentialBackoff',
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)
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class ExponentialBackoff(Generic[T]):
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"""An implementation of the exponential backoff algorithm
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Provides a convenient interface to implement an exponential backoff
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for reconnecting or retrying transmissions in a distributed network.
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Once instantiated, the delay method will return the next interval to
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wait for when retrying a connection or transmission. The maximum
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delay increases exponentially with each retry up to a maximum of
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2^10 * base, and is reset if no more attempts are needed in a period
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of 2^11 * base seconds.
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Parameters
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----------
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base: :class:`int`
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The base delay in seconds. The first retry-delay will be up to
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this many seconds.
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integral: :class:`bool`
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Set to ``True`` if whole periods of base is desirable, otherwise any
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number in between may be returned.
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"""
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def __init__(self, base: int = 1, *, integral: T = False):
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self._base: int = base
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self._exp: int = 0
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self._max: int = 10
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self._reset_time: int = base * 2 ** 11
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self._last_invocation: float = time.monotonic()
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# Use our own random instance to avoid messing with global one
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rand = random.Random()
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rand.seed()
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self._randfunc: Callable[..., Union[int, float]] = rand.randrange if integral else rand.uniform # type: ignore
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@overload
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def delay(self: ExponentialBackoff[Literal[False]]) -> float:
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...
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@overload
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def delay(self: ExponentialBackoff[Literal[True]]) -> int:
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...
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@overload
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def delay(self: ExponentialBackoff[bool]) -> Union[int, float]:
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...
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def delay(self) -> Union[int, float]:
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"""Compute the next delay
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Returns the next delay to wait according to the exponential
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backoff algorithm. This is a value between 0 and base * 2^exp
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where exponent starts off at 1 and is incremented at every
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invocation of this method up to a maximum of 10.
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If a period of more than base * 2^11 has passed since the last
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retry, the exponent is reset to 1.
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"""
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invocation = time.monotonic()
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interval = invocation - self._last_invocation
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self._last_invocation = invocation
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if interval > self._reset_time:
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self._exp = 0
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self._exp = min(self._exp + 1, self._max)
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return self._randfunc(0, self._base * 2 ** self._exp)
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