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from functools import wraps |
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from datetime import datetime, timedelta |
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STATE_CLOSED = 'closed' |
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STATE_OPEN = 'open' |
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STATE_HALF_OPEN = 'half_open' |
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class CircuitBreaker(object): |
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def __init__(self, expected_exception=Exception, failure_threshold=5, recover_timeout=30, name=None): |
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self._expected_exception = expected_exception |
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self._failure_count = 0 |
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self._failure_threshold = failure_threshold |
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self._recover_timeout = recover_timeout |
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self._state = STATE_CLOSED |
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self._opened = datetime.utcnow() |
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self._name = name |
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def __call__(self, wrapped): |
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""" |
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Applies the circuit breaker decorator to a function |
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""" |
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if self._name is None: |
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self._name = wrapped.__name__ |
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CircuitBreakerMonitor.register(self) |
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@wraps(wrapped) |
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def wrapper(*args, **kwargs): |
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return self.call(wrapped, *args, **kwargs) |
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return wrapper |
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def call(self, func, *args, **kwargs): |
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""" |
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Calls the decorated function and applies the circuit breaker rules on success or failure |
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:param func: Decorated function |
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""" |
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if not self.__is_closed(): |
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raise CircuitBreakerError(self) |
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try: |
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result = func(*args, **kwargs) |
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except self._expected_exception: |
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self.__failure() |
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raise |
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self.__success() |
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return result |
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def __is_closed(self): |
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""" |
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Check if state is CLOSED |
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Set state to HALF_OPEN and allow the next execution, if recovery timeout has been reached |
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""" |
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if self._state == STATE_OPEN and self.open_remaining <= 0: |
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self._state = STATE_HALF_OPEN |
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return True |
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return self._state == STATE_CLOSED |
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def __success(self): |
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""" |
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Close circuit after successful execution |
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""" |
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self.close() |
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def __failure(self): |
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""" |
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Count failure and open circuit, if threshold has been reached |
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""" |
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self._failure_count += 1 |
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if self._failure_count >= self._failure_threshold: |
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self.open() |
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def open(self): |
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""" |
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Open the circuit breaker |
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""" |
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self._state = STATE_OPEN |
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self._opened = datetime.utcnow() |
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def close(self): |
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""" |
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Close the circuit breaker |
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""" |
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self._state = STATE_CLOSED |
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self._failure_count = 0 |
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@property |
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def open_until(self): |
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""" |
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The datetime, when the circuit breaker will try to recover |
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:return: datetime |
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""" |
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return self._opened + timedelta(seconds=self._recover_timeout) |
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@property |
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def open_remaining(self): |
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""" |
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Number of seconds (int) remaining, the circuit breaker stays in OPEN state |
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:return: int |
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""" |
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return (self.open_until - datetime.utcnow()).total_seconds() |
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@property |
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def failure_count(self): |
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return self._failure_count |
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@property |
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def closed(self): |
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return self._state is not STATE_OPEN |
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@property |
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def name(self): |
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return self._name |
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@property |
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def state(self): |
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return self._state |
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def __str__(self, *args, **kwargs): |
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return self._name |
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class CircuitBreakerError(Exception): |
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def __init__(self, circuit_breaker, *args, **kwargs): |
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""" |
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:param circuit_breaker: |
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:param args: |
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:param kwargs: |
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:return: |
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""" |
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super().__init__(*args, **kwargs) |
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self._circuit_breaker = circuit_breaker |
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def __str__(self, *args, **kwargs): |
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return 'CIRCUIT "%s" OPEN until %s (%d failures, %d sec remaining)' % ( |
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self._circuit_breaker.name, |
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self._circuit_breaker.open_until, |
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self._circuit_breaker.failure_count, |
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round(self._circuit_breaker.open_remaining) |
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) |
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144
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class CircuitBreakerMonitor(object): |
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circuit_breakers = {} |
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148
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@classmethod |
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def register(cls, circuit_breaker): |
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cls.circuit_breakers[circuit_breaker.name] = circuit_breaker |
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152
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@classmethod |
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def all_closed(cls): |
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if list(cls.get_open()): |
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return False |
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return True |
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@classmethod |
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def get_circuits(cls): |
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return cls.circuit_breakers.values() |
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@classmethod |
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def get(cls, name): |
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return cls.circuit_breakers.get(name) |
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166
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@classmethod |
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def get_open(cls): |
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for circuit in cls.get_circuits(): |
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if circuit.state is STATE_OPEN: |
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yield circuit |
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@classmethod |
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def get_closed(cls): |
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for circuit in cls.get_circuits(): |
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if circuit.state is not STATE_OPEN: |
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yield circuit |
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fabfuel /
circuitbreaker
