110 lines
3.8 KiB
Python
110 lines
3.8 KiB
Python
# Copyright 2013-2017 DataStax, Inc.
|
|
#
|
|
# 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.
|
|
|
|
"""
|
|
This module contains utilities for generating timestamps for client-side
|
|
timestamp specification.
|
|
"""
|
|
|
|
import logging
|
|
import time
|
|
from threading import Lock
|
|
|
|
log = logging.getLogger(__name__)
|
|
|
|
class MonotonicTimestampGenerator(object):
|
|
"""
|
|
An object that, when called, returns ``int(time.time() * 1e6)`` when
|
|
possible, but, if the value returned by ``time.time`` doesn't increase,
|
|
drifts into the future and logs warnings.
|
|
Exposed configuration attributes can be configured with arguments to
|
|
``__init__`` or by changing attributes on an initialized object.
|
|
|
|
.. versionadded:: 3.8.0
|
|
"""
|
|
|
|
warn_on_drift = True
|
|
"""
|
|
If true, log warnings when timestamps drift into the future as allowed by
|
|
:attr:`warning_threshold` and :attr:`warning_interval`.
|
|
"""
|
|
|
|
warning_threshold = 1
|
|
"""
|
|
This object will only issue warnings when the returned timestamp drifts
|
|
more than ``warning_threshold`` seconds into the future.
|
|
Defaults to 1 second.
|
|
"""
|
|
|
|
warning_interval = 1
|
|
"""
|
|
This object will only issue warnings every ``warning_interval`` seconds.
|
|
Defaults to 1 second.
|
|
"""
|
|
|
|
def __init__(self, warn_on_drift=True, warning_threshold=1, warning_interval=1):
|
|
self.lock = Lock()
|
|
with self.lock:
|
|
self.last = 0
|
|
self._last_warn = 0
|
|
self.warn_on_drift = warn_on_drift
|
|
self.warning_threshold = warning_threshold
|
|
self.warning_interval = warning_interval
|
|
|
|
def _next_timestamp(self, now, last):
|
|
"""
|
|
Returns the timestamp that should be used if ``now`` is the current
|
|
time and ``last`` is the last timestamp returned by this object.
|
|
Intended for internal and testing use only; to generate timestamps,
|
|
call an instantiated ``MonotonicTimestampGenerator`` object.
|
|
|
|
:param int now: an integer to be used as the current time, typically
|
|
representing the current time in seconds since the UNIX epoch
|
|
:param int last: an integer representing the last timestamp returned by
|
|
this object
|
|
"""
|
|
if now > last:
|
|
self.last = now
|
|
return now
|
|
else:
|
|
self._maybe_warn(now=now)
|
|
self.last = last + 1
|
|
return self.last
|
|
|
|
def __call__(self):
|
|
"""
|
|
Makes ``MonotonicTimestampGenerator`` objects callable; defers
|
|
internally to _next_timestamp.
|
|
"""
|
|
with self.lock:
|
|
return self._next_timestamp(now=int(time.time() * 1e6),
|
|
last=self.last)
|
|
|
|
def _maybe_warn(self, now):
|
|
# should be called from inside the self.lock.
|
|
diff = self.last - now
|
|
since_last_warn = now - self._last_warn
|
|
|
|
warn = (self.warn_on_drift and
|
|
(diff >= self.warning_threshold * 1e6) and
|
|
(since_last_warn >= self.warning_interval * 1e6))
|
|
if warn:
|
|
log.warn(
|
|
"Clock skew detected: current tick ({now}) was {diff} "
|
|
"microseconds behind the last generated timestamp "
|
|
"({last}), returned timestamps will be artificially "
|
|
"incremented to guarantee monotonicity.".format(
|
|
now=now, diff=diff, last=self.last))
|
|
self._last_warn = now
|