circuitbreaker.CircuitBreaker.fallback_function() - Code Metrics - Inspection of "Release 1.3.0" - fabfuel/circuitbreaker - Measure and Improve Code Quality continuously with Scrutinizer

Passed

Pull Request — master (#12)

by Fabian

created 2020-04-02 13:21 UTC

circuitbreaker.CircuitBreaker.fallback_function() A

↳ Parent: circuitbreaker

Complexity

Conditions

Size

Total Lines	3
Code Lines	3

Duplication

Lines	0
Ratio	0 %

Code Coverage

Tests	2
CRAP Score	1

Importance

Changes

Metric	Value
cc	1
eloc	3
nop	1
dl	0
loc	3
ccs	2
cts	2
cp	1
crap	1
rs	10
c	0
b	0
f	0

# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from __future__ import division
from __future__ import print_function
from __future__ import absolute_import

from functools import wraps
from datetime import datetime, timedelta
from typing import AnyStr, Iterable

STATE_CLOSED = 'closed'
STATE_OPEN = 'open'
STATE_HALF_OPEN = 'half_open'


class CircuitBreaker(object):
    FAILURE_THRESHOLD = 5
    RECOVERY_TIMEOUT = 30
    EXPECTED_EXCEPTION = Exception
    FALLBACK_FUNCTION = None

    def __init__(self,
                 failure_threshold=None,
                 recovery_timeout=None,
                 expected_exception=None,
                 name=None,
                 fallback_function=None):
        self._last_failure = None
        self._failure_count = 0
        self._failure_threshold = failure_threshold or self.FAILURE_THRESHOLD
        self._recovery_timeout = recovery_timeout or self.RECOVERY_TIMEOUT
        self._expected_exception = expected_exception or self.EXPECTED_EXCEPTION
        self._fallback_function = fallback_function or self.FALLBACK_FUNCTION
        self._name = name
        self._state = STATE_CLOSED
        self._opened = datetime.utcnow()

    def __call__(self, wrapped):
        return self.decorate(wrapped)

    def decorate(self, function):
        """
        Applies the circuit breaker to a function
        """
        if self._name is None:
            self._name = function.__name__

        CircuitBreakerMonitor.register(self)

        @wraps(function)
        def wrapper(*args, **kwargs):
            return self.call(function, *args, **kwargs)

        return wrapper

    def call(self, func, *args, **kwargs):
        """
        Calls the decorated function and applies the circuit breaker
        rules on success or failure
        :param func: Decorated function
        """
        if self.opened:
            if self.fallback_function:
                self.fallback_function(*args, **kwargs)
            else:
                raise CircuitBreakerError(self)
        try:
            result = func(*args, **kwargs)
        except self._expected_exception as e:
            self._last_failure = e
            self.__call_failed()
            raise

        self.__call_succeeded()
        return result

    def __call_succeeded(self):
        """
        Close circuit after successful execution and reset failure count
        """
        self._state = STATE_CLOSED
        self._last_failure = None
        self._failure_count = 0

    def __call_failed(self):
        """
        Count failure and open circuit, if threshold has been reached
        """
        self._failure_count += 1
        if self._failure_count >= self._failure_threshold:
            self._state = STATE_OPEN
            self._opened = datetime.utcnow()

    @property
    def state(self):
        if self._state == STATE_OPEN and self.open_remaining <= 0:
            return STATE_HALF_OPEN
        return self._state

    @property
    def open_until(self):
        """
        The datetime, when the circuit breaker will try to recover
        :return: datetime
        """
        return self._opened + timedelta(seconds=self._recovery_timeout)

    @property
    def open_remaining(self):
        """
        Number of seconds remaining, the circuit breaker stays in OPEN state
        :return: int
        """
        return (self.open_until - datetime.utcnow()).total_seconds()

    @property
    def failure_count(self):
        return self._failure_count

    @property
    def closed(self):
        return self.state == STATE_CLOSED

    @property
    def opened(self):
        return self.state == STATE_OPEN

    @property
    def name(self):
        return self._name

    @property
    def last_failure(self):
        return self._last_failure

    @property
    def fallback_function(self):
        return self._fallback_function

    def __str__(self, *args, **kwargs):
        return self._name


class CircuitBreakerError(Exception):
    def __init__(self, circuit_breaker, *args, **kwargs):
        """
        :param circuit_breaker:
        :param args:
        :param kwargs:
        :return:
        """
        super(CircuitBreakerError, self).__init__(*args, **kwargs)
        self._circuit_breaker = circuit_breaker

    def __str__(self, *args, **kwargs):
        return 'Circuit "%s" OPEN until %s (%d failures, %d sec remaining) (last_failure: %r)' % (
            self._circuit_breaker.name,
            self._circuit_breaker.open_until,
            self._circuit_breaker.failure_count,
            round(self._circuit_breaker.open_remaining),
            self._circuit_breaker.last_failure,
        )


class CircuitBreakerMonitor(object):
    circuit_breakers = {}

    @classmethod
    def register(cls, circuit_breaker):
        cls.circuit_breakers[circuit_breaker.name] = circuit_breaker

    @classmethod
    def all_closed(cls):
        # type: () -> bool
        return len(list(cls.get_open())) == 0

    @classmethod
    def get_circuits(cls):
        # type: () -> Iterable[CircuitBreaker]
        return cls.circuit_breakers.values()

    @classmethod
    def get(cls, name):
        # type: (AnyStr) -> CircuitBreaker
        return cls.circuit_breakers.get(name)

    @classmethod
    def get_open(cls):
        # type: () -> Iterable[CircuitBreaker]
        for circuit in cls.get_circuits():
            if circuit.opened:
                yield circuit

    @classmethod
    def get_closed(cls):
        # type: () -> Iterable[CircuitBreaker]
        for circuit in cls.get_circuits():
            if circuit.closed:
                yield circuit


def circuit(failure_threshold=None,
            recovery_timeout=None,
            expected_exception=None,
            name=None,
            fallback_function=None,
            cls=CircuitBreaker):

    # if the decorator is used without parameters, the
    # wrapped function is provided as first argument
    if callable(failure_threshold):
        return cls().decorate(failure_threshold)
    else:
        return cls(
            failure_threshold=failure_threshold,
            recovery_timeout=recovery_timeout,
            expected_exception=expected_exception,
            name=name,
            fallback_function=fallback_function)


1		# -- coding: utf-8 --
2	1	from __future__ import unicode_literals
3	1	from __future__ import division
4	1	from __future__ import print_function
5	1	from __future__ import absolute_import
6
7	1	from functools import wraps
8	1	from datetime import datetime, timedelta
9	1	from typing import AnyStr, Iterable
10
11	1	STATE_CLOSED = 'closed'
12	1	STATE_OPEN = 'open'
13	1	STATE_HALF_OPEN = 'half_open'
14
15
16	1	class CircuitBreaker(object):
17	1	FAILURE_THRESHOLD = 5
18	1	RECOVERY_TIMEOUT = 30
19	1	EXPECTED_EXCEPTION = Exception
20	1	FALLBACK_FUNCTION = None
21
22	1	def __init__(self,
23		failure_threshold=None,
24		recovery_timeout=None,
25		expected_exception=None,
26		name=None,
27		fallback_function=None):
28	1	self._last_failure = None
29	1	self._failure_count = 0
30	1	self._failure_threshold = failure_threshold or self.FAILURE_THRESHOLD
31	1	self._recovery_timeout = recovery_timeout or self.RECOVERY_TIMEOUT
32	1	self._expected_exception = expected_exception or self.EXPECTED_EXCEPTION
33	1	self._fallback_function = fallback_function or self.FALLBACK_FUNCTION
34	1	self._name = name
35	1	self._state = STATE_CLOSED
36	1	self._opened = datetime.utcnow()
37
38	1	def __call__(self, wrapped):
39	1	return self.decorate(wrapped)
40
41	1	def decorate(self, function):
42		"""
43		Applies the circuit breaker to a function
44		"""
45	1	if self._name is None:
46	1	self._name = function.__name__
47
48	1	CircuitBreakerMonitor.register(self)
49
50	1	@wraps(function)
51		def wrapper(args, *kwargs):
52	1	return self.call(function, args, *kwargs)
53
54	1	return wrapper
55
56	1	def call(self, func, args, *kwargs):
57		"""
58		Calls the decorated function and applies the circuit breaker
59		rules on success or failure
60		:param func: Decorated function
61		"""
62	1	if self.opened:
63	1	if self.fallback_function:
64	1	self.fallback_function(args, *kwargs)
65		else:
66	1	raise CircuitBreakerError(self)
67	1	try:
68	1	result = func(args, *kwargs)
69	1	except self._expected_exception as e:
70	1	self._last_failure = e
71	1	self.__call_failed()
72	1	raise
73
74	1	self.__call_succeeded()
75	1	return result
76
77	1	def __call_succeeded(self):
78		"""
79		Close circuit after successful execution and reset failure count
80		"""
81	1	self._state = STATE_CLOSED
82	1	self._last_failure = None
83	1	self._failure_count = 0
84
85	1	def __call_failed(self):
86		"""
87		Count failure and open circuit, if threshold has been reached
88		"""
89	1	self._failure_count += 1
90	1	if self._failure_count >= self._failure_threshold:
91	1	self._state = STATE_OPEN
92	1	self._opened = datetime.utcnow()
93
94	1	@property
95		def state(self):
96	1	if self._state == STATE_OPEN and self.open_remaining <= 0:
97	1	return STATE_HALF_OPEN
98	1	return self._state
99
100	1	@property
101		def open_until(self):
102		"""
103		The datetime, when the circuit breaker will try to recover
104		:return: datetime
105		"""
106	1	return self._opened + timedelta(seconds=self._recovery_timeout)
107
108	1	@property
109		def open_remaining(self):
110		"""
111		Number of seconds remaining, the circuit breaker stays in OPEN state
112		:return: int
113		"""
114	1	return (self.open_until - datetime.utcnow()).total_seconds()
115
116	1	@property
117		def failure_count(self):
118	1	return self._failure_count
119
120	1	@property
121		def closed(self):
122	1	return self.state == STATE_CLOSED
123
124	1	@property
125		def opened(self):
126	1	return self.state == STATE_OPEN
127
128	1	@property
129		def name(self):
130	1	return self._name
131
132	1	@property
133		def last_failure(self):
134	1	return self._last_failure
135
136	1	@property
137		def fallback_function(self):
138	1	return self._fallback_function
139
140	1	def __str__(self, args, *kwargs):
141	1	return self._name
142
143
144	1	class CircuitBreakerError(Exception):
145	1	def __init__(self, circuit_breaker, args, *kwargs):
146		"""
147		:param circuit_breaker:
148		:param args:
149		:param kwargs:
150		:return:
151		"""
152	1	super(CircuitBreakerError, self).__init__(args, *kwargs)
153	1	self._circuit_breaker = circuit_breaker
154
155	1	def __str__(self, args, *kwargs):
156	1	return 'Circuit "%s" OPEN until %s (%d failures, %d sec remaining) (last_failure: %r)' % (
157		self._circuit_breaker.name,
158		self._circuit_breaker.open_until,
159		self._circuit_breaker.failure_count,
160		round(self._circuit_breaker.open_remaining),
161		self._circuit_breaker.last_failure,
162		)
163
164
165	1	class CircuitBreakerMonitor(object):
166	1	circuit_breakers = {}
167
168	1	@classmethod
169		def register(cls, circuit_breaker):
170	1	cls.circuit_breakers[circuit_breaker.name] = circuit_breaker
171
172	1	@classmethod
173		def all_closed(cls):
174		# type: () -> bool
175	1	return len(list(cls.get_open())) == 0
176
177	1	@classmethod
178		def get_circuits(cls):
179		# type: () -> Iterable[CircuitBreaker]
180	1	return cls.circuit_breakers.values()
181
182	1	@classmethod
183		def get(cls, name):
184		# type: (AnyStr) -> CircuitBreaker
185	1	return cls.circuit_breakers.get(name)
186
187	1	@classmethod
188		def get_open(cls):
189		# type: () -> Iterable[CircuitBreaker]
190	1	for circuit in cls.get_circuits():
191	1	if circuit.opened:
192	1	yield circuit
193
194	1	@classmethod
195		def get_closed(cls):
196		# type: () -> Iterable[CircuitBreaker]
197	1	for circuit in cls.get_circuits():
198	1	if circuit.closed:
199	1	yield circuit
200
201
202	1	def circuit(failure_threshold=None,
203		recovery_timeout=None,
204		expected_exception=None,
205		name=None,
206		fallback_function=None,
207		cls=CircuitBreaker):
208
209		# if the decorator is used without parameters, the
210		# wrapped function is provided as first argument
211	1	if callable(failure_threshold):
212	1	return cls().decorate(failure_threshold)
213		else:
214	1	return cls(
215		failure_threshold=failure_threshold,
216		recovery_timeout=recovery_timeout,
217		expected_exception=expected_exception,
218		name=name,
219		fallback_function=fallback_function)
220

fabfuel / circuitbreaker

Pull Request — master (#12)

circuitbreaker.CircuitBreaker.fallback_function() A

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