Source code for cassandra.timestamps

# Copyright DataStax, Inc.
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"""
This module contains utilities for generating timestamps for client-side
timestamp specification.
"""

import logging
import time
from threading import Lock

log = logging.getLogger(__name__)

[docs]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
[docs] 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 microseconds 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.warning( "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