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## Copyright 2013 Ray Holder
##
## Licensed under the Apache License, Version 2.0 (the "License");
## you may not use this file except in compliance with the License.
## You may obtain a copy of the License at
##
## http://www.apache.org/licenses/LICENSE-2.0
##
## Unless required by applicable law or agreed to in writing, software
## distributed under the License is distributed on an "AS IS" BASIS,
## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
## See the License for the specific language governing permissions and
## limitations under the License.
import random
import time
# sys.maxint / 2, since Python 3.2 doesn't have a sys.maxint...
MAX_WAIT = 1073741823
def retry(*dargs, **dkw):
"""
TODO comment
"""
def wrap(f):
def wrapped_f(*args, **kw):
return Retrying(*dargs, **dkw).call(f, *args, **kw)
return wrapped_f
def wrap_simple(f):
def wrapped_f(*args, **kw):
return Retrying().call(f, *args, **kw)
return wrapped_f
# support both @retry and @retry() as valid syntax
if len(dargs) == 1 and callable(dargs[0]):
return wrap_simple(dargs[0])
else:
return wrap
class Retrying:
def __init__(self,
stop='never_stop',
stop_max_attempt_number=5,
stop_max_delay=100,
wait='no_sleep',
wait_fixed=1000,
wait_random_min=0, wait_random_max=1000,
wait_incrementing_start=0, wait_incrementing_increment=100,
wait_exponential_multiplier=1, wait_exponential_max=MAX_WAIT,
retry_on_exception=None,
retry_on_result=None,
wrap_exception=False):
# TODO add chaining of stop behaviors
# stop behavior
self.stop = getattr(self, stop)
self._stop_max_attempt_number = stop_max_attempt_number
self._stop_max_delay = stop_max_delay
# TODO add chaining of wait behaviors
# wait behavior
self.wait = getattr(self, wait)
self._wait_fixed = wait_fixed
self._wait_random_min = wait_random_min
self._wait_random_max = wait_random_max
self._wait_incrementing_start = wait_incrementing_start
self._wait_incrementing_increment = wait_incrementing_increment
self._wait_exponential_multiplier = wait_exponential_multiplier
self._wait_exponential_max = wait_exponential_max
# retry on exception filter
if retry_on_exception is None:
self._retry_on_exception = self.always_reject
else:
self._retry_on_exception = retry_on_exception
# TODO simplify retrying by Exception types
# retry on result filter
if retry_on_result is None:
self._retry_on_result = self.never_reject
else:
self._retry_on_result = retry_on_result
self._wrap_exception = wrap_exception
def never_stop(self, previous_attempt_number, delay_since_first_attempt_ms):
"""Never stop retrying."""
return False
def stop_after_attempt(self, previous_attempt_number, delay_since_first_attempt_ms):
"""Stop after the previous attempt >= stop_max_attempt_number."""
return previous_attempt_number >= self._stop_max_attempt_number
def stop_after_delay(self, previous_attempt_number, delay_since_first_attempt_ms):
"""Stop after the time from the first attempt >= stop_max_delay."""
return delay_since_first_attempt_ms >= self._stop_max_delay
def no_sleep(self, previous_attempt_number, delay_since_first_attempt_ms):
"""Don't sleep at all before retrying."""
return 0
def fixed_sleep(self, previous_attempt_number, delay_since_first_attempt_ms):
"""Sleep a fixed amount of time between each retry."""
return self._wait_fixed
def random_sleep(self, previous_attempt_number, delay_since_first_attempt_ms):
"""Sleep a random amount of time between wait_random_min and wait_random_max"""
return random.randint(self._wait_random_min, self._wait_random_max)
def incrementing_sleep(self, previous_attempt_number, delay_since_first_attempt_ms):
"""
Sleep an incremental amount of time after each attempt, starting at
wait_incrementing_start and incrementing by wait_incrementing_increment
"""
result = self._wait_incrementing_start + (self._wait_incrementing_increment * (previous_attempt_number - 1))
if result < 0:
result = 0
return result
def exponential_sleep(self, previous_attempt_number, delay_since_first_attempt_ms):
exp = 2 ** previous_attempt_number
result = self._wait_exponential_multiplier * exp
if result > self._wait_exponential_max:
result = self._wait_exponential_max
if result < 0:
result = 0
return result
def never_reject(self, result):
return False
def always_reject(self, result):
return True
def should_reject(self, attempt):
reject = False
if attempt.has_exception:
reject |= self._retry_on_exception(attempt.value)
else:
reject |= self._retry_on_result(attempt.value)
return reject
def call(self, fn, *args, **kwargs):
start_time = int(round(time.time() * 1000))
attempt_number = 1
while True:
try:
attempt = Attempt(fn(*args, **kwargs), attempt_number, False)
except BaseException as e:
attempt = Attempt(e, attempt_number, True)
if not self.should_reject(attempt):
return attempt.get(self._wrap_exception)
delay_since_first_attempt_ms = int(round(time.time() * 1000)) - start_time
if self.stop(attempt_number, delay_since_first_attempt_ms):
raise RetryError(attempt)
else:
sleep = self.wait(attempt_number, delay_since_first_attempt_ms)
time.sleep(sleep / 1000.0)
attempt_number += 1
class Attempt:
"""
An Attempt encapsulates a call to a target function that may end as a
normal return value from the function or an Exception depending on what
occurred during the execution.
"""
def __init__(self, value, attempt_number, has_exception):
self.value = value
self.attempt_number = attempt_number
self.has_exception = has_exception
def get(self, wrap_exception=False):
"""
Return the return value of this Attempt instance or raise an Exception.
If wrap_exception is true, this Attempt is wrapped inside of a
RetryError before being raised.
"""
if self.has_exception:
if wrap_exception:
raise RetryError(self)
else:
raise self.value
else:
return self.value
class RetryError(Exception):
"""
A RetryError encapsulates the last Attempt instance right before giving up.
"""
def __init__(self, last_attempt):
self.last_attempt = last_attempt
def __str__(self):
return "Last attempt: %s" % str(self.last_attempt)
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