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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 __hash__(self) -> int:
return hash((self._backoff,))
def __eq__(self, other) -> bool:
if not isinstance(other, ConstantBackoff):
return NotImplemented
return self._backoff == other._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 __hash__(self) -> int:
return hash((self._base, self._cap))
def __eq__(self, other) -> bool:
if not isinstance(other, ExponentialBackoff):
return NotImplemented
return self._base == other._base and self._cap == other._cap
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 __hash__(self) -> int:
return hash((self._base, self._cap))
def __eq__(self, other) -> bool:
if not isinstance(other, FullJitterBackoff):
return NotImplemented
return self._base == other._base and self._cap == other._cap
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 __hash__(self) -> int:
return hash((self._base, self._cap))
def __eq__(self, other) -> bool:
if not isinstance(other, EqualJitterBackoff):
return NotImplemented
return self._base == other._base and self._cap == other._cap
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 __hash__(self) -> int:
return hash((self._base, self._cap))
def __eq__(self, other) -> bool:
if not isinstance(other, DecorrelatedJitterBackoff):
return NotImplemented
return self._base == other._base and self._cap == other._cap
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
class ExponentialWithJitterBackoff(AbstractBackoff):
"""Exponential backoff upon failure, with jitter"""
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 __hash__(self) -> int:
return hash((self._base, self._cap))
def __eq__(self, other) -> bool:
if not isinstance(other, ExponentialWithJitterBackoff):
return NotImplemented
return self._base == other._base and self._cap == other._cap
def compute(self, failures: int) -> float:
return min(self._cap, random.random() * self._base * 2**failures)
def default_backoff():
return EqualJitterBackoff()
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