如何实现重试逻辑？

Answer 1

即使这个问题有点过时，我还是想发布一个答案，因为 Retry 状态已添加到 transitions 在发布 0.9 中。 Retry 本身只会计算重新进入状态的频率，这意味着当转换源和目标相等时计数器将增加，否则将重置。它完全是被动的，需要另一种方法来触发事件。除了Retry 之外，通常使用Timeout 状态扩展来实现此目的。在下面的示例中，状态机装饰有Retry 和Timeout 状态扩展，允许使用几个关键字来定义状态：

• timeout - 进入状态后触发超时前的时间（以秒为单位）
• on_timeout- 触发 timeout 时调用的回调
• retries - 重新进入状态时调用失败回调之前的重试次数
• on_failure - 当重入计数器到达 retries 时调用的回调

该示例将重新输入pinging，除非随机生成的介于 0 和 1 之间的数字大于 0.8。这可以解释为一个服务器，它粗略地只回答每五个请求。当您执行该示例时，达到“已初始化”所需的重试可能会有所不同，甚至在达到retries 时会失败。

from transitions import Machine
from transitions.extensions.states import add_state_features, Retry, Timeout

import random
import time

# create a custom machine with state extension features and also 
# add enter callbacks for the states 'pinging', 'initialized' and 'init_failed'
@add_state_features(Retry, Timeout)
class RetryMachine(Machine):
    def on_enter_pinging(self):
        print("pinging server...")
        if random.random() > 0.8:
            self.to_initialized()

    def on_enter_initialized(self):
        print("server answered")

    def on_enter_init_failed(self):
        print("server did not answer!")


states = ["init",
          {"name": "pinging",
           "timeout": 0.5,  # after 0.5s we assume the "server" wont answer
           "on_timeout": "to_pinging",  # when timeout enter 'pinging' again
           "retries": 3,  # three pinging attempts will be conducted
           "on_failure": "to_init_failed"},
          "initialized",
          "init_failed"]

# we don't pass a model to the machine which will result in the machine 
# itself acting as a model; if we add another model, the 'on_enter_<state>'
# methods must be defined on the model and not machine
m = RetryMachine(states=states, initial="init")
assert m.is_init()
m.to_pinging()
while m.is_pinging():
    time.sleep(0.2)