Exponential backoff 指数避退算法

维基百科的定义

Example exponential backoff algorithm

1. When a collision first occurs, send a "Jamming signal" to prevent further data from being sent.
2. Resend a frame after either 0 seconds or 51.2 μs, chosen at random.
3. If that fails, resend the frame after either 0 s, 51.2 μs, 102.4 μs, or 153.6 μs.
4. If that still doesn't work, resend the frame after k · 51.2 μs, where k is a random integer between 0 and 2³ − 1.
5. In general, after the cth failed attempt, resend the frame after k · 51.2 μs, where k is a random integer between 0 and 2^c − 1.

简单的 Python 实现，

import functools
import random
import time


def retry(tries, back_off=0.5):
    def _retry(func):
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            max_retries = tries
            result = func(*args, **kwargs)
            while max_retries > 0:
                if result:
                    return result
                max_retries -= 1
                d = random.randint(0, (tries - max_retries) ** 2 - 1)
                print(f"第{tries - max_retries}次重试,时间为{d}*0.5")
                time.sleep(d * back_off)
                result = func(*args, **kwargs)
            return result

        return wrapper

    return _retry


@retry(5)
def get_response():
    print("get http response")


if __name__ == '__main__':
    get_response()

输出结果为

get http response
第1次重试,时间为0*0.5
get http response
第2次重试,时间为1*0.5
get http response
第3次重试,时间为7*0.5
get http response
第4次重试,时间为4*0.5
get http response
第5次重试,时间为10*0.5
get http response

设置的基本避退时间为 0.5 ，重试次数为 5