fauna.client.retryable

 1import abc
 2from dataclasses import dataclass
 3from random import random
 4from time import sleep
 5from typing import Callable, Optional, TypeVar, Generic
 6
 7from fauna.errors import RetryableFaunaException
 8
 9
10class RetryStrategy:
11
12  @abc.abstractmethod
13  def wait(self) -> float:
14    pass
15
16
17class ExponentialBackoffStrategy(RetryStrategy):
18
19  def __init__(self, max_backoff: int):
20    self._max_backoff = float(max_backoff)
21    self._i = 0.0
22
23  def wait(self) -> float:
24    """Returns the number of seconds to wait for the next call."""
25    backoff = random() * (2.0**self._i)
26    self._i += 1.0
27    return min(backoff, self._max_backoff)
28
29
30T = TypeVar('T')
31
32
33@dataclass
34class RetryableResponse(Generic[T]):
35  attempts: int
36  response: T
37
38
39class Retryable(Generic[T]):
40  """
41    Retryable is a wrapper class that acts on a Callable that returns a T type.
42    """
43  _strategy: RetryStrategy
44  _error: Optional[Exception]
45
46  def __init__(
47      self,
48      max_attempts: int,
49      max_backoff: int,
50      func: Callable[..., T],
51      *args,
52      **kwargs,
53  ):
54    self._max_attempts = max_attempts
55    self._strategy = ExponentialBackoffStrategy(max_backoff)
56    self._func = func
57    self._args = args
58    self._kwargs = kwargs
59    self._error = None
60
61  def run(self) -> RetryableResponse[T]:
62    """Runs the wrapped function. Retries up to max_attempts if the function throws a RetryableFaunaException. It propagates
63        the thrown exception if max_attempts is reached or if a non-retryable is thrown.
64
65        Returns the number of attempts and the response
66        """
67    attempt = 0
68    while True:
69      sleep_time = 0.0 if attempt == 0 else self._strategy.wait()
70      sleep(sleep_time)
71
72      try:
73        attempt += 1
74        qs = self._func(*self._args, **self._kwargs)
75        return RetryableResponse[T](attempt, qs)
76      except RetryableFaunaException as e:
77        if attempt >= self._max_attempts:
78          raise e