## Copyright 2013-2014 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 six
import sys
import time
import traceback
# sys.maxint / 2, since Python 3.2 doesn't have a sys.maxint...
MAX_WAIT = 1073741823
def retry(*dargs, **dkw):
"""
Decorator function that instantiates the Retrying object
@param *dargs: positional arguments passed to Retrying object
@param **dkw: keyword arguments passed to the Retrying object
"""
# support both @retry and @retry() as valid syntax
if len(dargs) == 1 and callable(dargs[0]):
def wrap_simple(f):
@six.wraps(f)
def wrapped_f(*args, **kw):
return Retrying().call(f, *args, **kw)
return wrapped_f
return wrap_simple(dargs[0])
else:
def wrap(f):
@six.wraps(f)
def wrapped_f(*args, **kw):
return Retrying(*dargs, **dkw).call(f, *args, **kw)
return wrapped_f
return wrap
class Retrying(object):
def __init__(self,
stop=None, wait=None,
stop_max_attempt_number=None,
stop_max_delay=None,
wait_fixed=None,
wait_random_min=None, wait_random_max=None,
wait_incrementing_start=None, wait_incrementing_increment=None,
wait_exponential_multiplier=None, wait_exponential_max=None,
retry_on_exception=None,
retry_on_result=None,
wrap_exception=False,
stop_func=None,
wait_func=None,
wait_jitter_max=None):
self._stop_max_attempt_number = 5 if stop_max_attempt_number is None else stop_max_attempt_number
self._stop_max_delay = 100 if stop_max_delay is None else stop_max_delay
self._wait_fixed = 1000 if wait_fixed is None else wait_fixed
self._wait_random_min = 0 if wait_random_min is None else wait_random_min
self._wait_random_max = 1000 if wait_random_max is None else wait_random_max
self._wait_incrementing_start = 0 if wait_incrementing_start is None else wait_incrementing_start
self._wait_incrementing_increment = 100 if wait_incrementing_increment is None else wait_incrementing_increment
self._wait_exponential_multiplier = 1 if wait_exponential_multiplier is None else wait_exponential_multiplier
self._wait_exponential_max = MAX_WAIT if wait_exponential_max is None else wait_exponential_max
self._wait_jitter_max = 0 if wait_jitter_max is None else wait_jitter_max
# TODO add chaining of stop behaviors
# stop behavior
stop_funcs = []
if stop_max_attempt_number is not None:
stop_funcs.append(self.stop_after_attempt)
if stop_max_delay is not None:
stop_funcs.append(self.stop_after_delay)
if stop_func is not None:
self.stop = stop_func
elif stop is None:
self.stop = lambda attempts, delay: any(f(attempts, delay) for f in stop_funcs)
else:
self.stop = getattr(self, stop)
# TODO add chaining of wait behaviors
# wait behavior
wait_funcs = [lambda *args, **kwargs: 0]
if wait_fixed is not None:
wait_funcs.append(self.fixed_sleep)
if wait_random_min is not None or wait_random_max is not None:
wait_funcs.append(self.random_sleep)
if wait_incrementing_start is not None or wait_incrementing_increment is not None:
wait_funcs.append(self.incrementing_sleep)
if wait_exponential_multiplier is not None or wait_exponential_max is not None:
wait_funcs.append(self.exponential_sleep)
if wait_func is not None:
self.wait = wait_func
elif wait is None:
self.wait = lambda attempts, delay: max(f(attempts, delay) for f in wait_funcs)
else:
self.wait = getattr(self, wait)
# 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 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[1])
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:
tb = sys.exc_info()
attempt = Attempt(tb, 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):
if not self._wrap_exception and attempt.has_exception:
# get() on an attempt with an exception should cause it to be raised, but raise just in case
raise attempt.get()
else:
raise RetryError(attempt)
else:
sleep = self.wait(attempt_number, delay_since_first_attempt_ms)
if self._wait_jitter_max:
jitter = random.random() * self._wait_jitter_max
sleep = sleep + max(0, jitter)
time.sleep(sleep / 1000.0)
attempt_number += 1
class Attempt(object):
"""
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:
six.reraise(self.value[0], self.value[1], self.value[2])
else:
return self.value
def __repr__(self):
if self.has_exception:
return "Attempts: {0}, Error:\n{1}".format(self.attempt_number, "".join(traceback.format_tb(self.value[2])))
else:
return "Attempts: {0}, Value: {1}".format(self.attempt_number, self.value)
[docs]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 "RetryError[{0}]".format(self.last_attempt)
