redis.backoff 源代码

import random
from abc import ABC, abstractmethod

# Maximum backoff between each retry in seconds
DEFAULT_CAP = 0.512
# Minimum backoff between each retry in seconds
DEFAULT_BASE = 0.008




class AbstractBackoff(ABC):
    """Backoff interface"""



    def reset(self):
        """
        Reset internal state before an operation.
        `reset` is called once at the beginning of
        every call to `Retry.call_with_retry`
        """
        pass




    @abstractmethod
    def compute(self, failures: int) -> float:
        """Compute backoff in seconds upon failure"""
        pass






class ConstantBackoff(AbstractBackoff):
    """Constant backoff upon failure"""

    def __init__(self, backoff: float) -> None:
        """`backoff`: backoff time in seconds"""
        self._backoff = backoff



    def compute(self, failures: int) -> float:
        return self._backoff






class NoBackoff(ConstantBackoff):
    """No backoff upon failure"""

    def __init__(self) -> None:
        super().__init__(0)





class ExponentialBackoff(AbstractBackoff):
    """Exponential backoff upon failure"""

    def __init__(self, cap: float = DEFAULT_CAP, base: float = DEFAULT_BASE):
        """
        `cap`: maximum backoff time in seconds
        `base`: base backoff time in seconds
        """
        self._cap = cap
        self._base = base



    def compute(self, failures: int) -> float:
        return min(self._cap, self._base * 2**failures)






class FullJitterBackoff(AbstractBackoff):
    """Full jitter backoff upon failure"""

    def __init__(self, cap: float = DEFAULT_CAP, base: float = DEFAULT_BASE) -> None:
        """
        `cap`: maximum backoff time in seconds
        `base`: base backoff time in seconds
        """
        self._cap = cap
        self._base = base



    def compute(self, failures: int) -> float:
        return random.uniform(0, min(self._cap, self._base * 2**failures))






class EqualJitterBackoff(AbstractBackoff):
    """Equal jitter backoff upon failure"""

    def __init__(self, cap: float = DEFAULT_CAP, base: float = DEFAULT_BASE) -> None:
        """
        `cap`: maximum backoff time in seconds
        `base`: base backoff time in seconds
        """
        self._cap = cap
        self._base = base



    def compute(self, failures: int) -> float:
        temp = min(self._cap, self._base * 2**failures) / 2
        return temp + random.uniform(0, temp)






class DecorrelatedJitterBackoff(AbstractBackoff):
    """Decorrelated jitter backoff upon failure"""

    def __init__(self, cap: float = DEFAULT_CAP, base: float = DEFAULT_BASE) -> None:
        """
        `cap`: maximum backoff time in seconds
        `base`: base backoff time in seconds
        """
        self._cap = cap
        self._base = base
        self._previous_backoff = 0



    def reset(self) -> None:
        self._previous_backoff = 0




    def compute(self, failures: int) -> float:
        max_backoff = max(self._base, self._previous_backoff * 3)
        temp = random.uniform(self._base, max_backoff)
        self._previous_backoff = min(self._cap, temp)
        return self._previous_backoff




def default_backoff():
    return EqualJitterBackoff()