forked from platypush/platypush
Fix for #217
The cron scheduler has been made more robust against changes in the system clock (caused by e.g. DST changes, NTP syncs or manual setting). A more granular management for cronjob events has been introduced, now supporting a `TIME_SYNC` event besides the usual `STOP`. When the cron scheduler detects a system clock drift (i.e. the timestamp offset before and after a blocking wait is >1 sec) then all the cronjobs are notified and forced to refresh their state.
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3 changed files with 148 additions and 63 deletions
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@ -7,11 +7,20 @@ import croniter
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from dateutil.tz import gettz
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from platypush.procedure import Procedure
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from platypush.utils import is_functional_cron
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from platypush.utils import is_functional_cron, set_thread_name
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logger = logging.getLogger('platypush:cron')
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def get_now() -> datetime.datetime:
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"""
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:return: A timezone-aware representation of `now`
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"""
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return datetime.datetime.now().replace(
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tzinfo=gettz()
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) # lgtm [py/call-to-non-callable]
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class CronjobState(enum.IntEnum):
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IDLE = 0
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WAIT = 1
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@ -20,21 +29,36 @@ class CronjobState(enum.IntEnum):
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ERROR = 4
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class CronjobEvent(enum.IntEnum):
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NONE = 0
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STOP = 1
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TIME_SYNC = 2
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class Cronjob(threading.Thread):
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def __init__(self, name, cron_expression, actions):
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super().__init__()
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self.cron_expression = cron_expression
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self.name = name
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self.state = CronjobState.IDLE
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self._should_stop = threading.Event()
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self._event = threading.Event()
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self._event_type = CronjobEvent.NONE
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self._event_lock = threading.RLock()
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if isinstance(actions, dict) or isinstance(actions, list):
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self.actions = Procedure.build(name=name + '__Cron', _async=False, requests=actions)
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if isinstance(actions, (list, dict)):
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self.actions = Procedure.build(
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name=name + '__Cron', _async=False, requests=actions
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)
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else:
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self.actions = actions
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def notify(self, event: CronjobEvent):
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with self._event_lock:
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self._event_type = event
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self._event.set()
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def run(self):
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self.state = CronjobState.WAIT
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set_thread_name(f'cron:{self.name}')
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self.wait()
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if self.should_stop():
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return
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@ -57,26 +81,38 @@ class Cronjob(threading.Thread):
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self.state = CronjobState.ERROR
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def wait(self):
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now = datetime.datetime.now().replace(tzinfo=gettz()) # lgtm [py/call-to-non-callable]
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with self._event_lock:
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self.state = CronjobState.WAIT
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self._event.clear()
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self._event_type = CronjobEvent.TIME_SYNC
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while self._event_type == CronjobEvent.TIME_SYNC:
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now = get_now()
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self._event_type = CronjobEvent.NONE
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cron = croniter.croniter(self.cron_expression, now)
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next_run = cron.get_next()
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self._should_stop.wait(next_run - now.timestamp())
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self._event.wait(max(0, next_run - now.timestamp()))
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def stop(self):
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self._should_stop.set()
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self._event_type = CronjobEvent.STOP
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self._event.set()
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def should_stop(self):
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return self._should_stop.is_set()
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return self._event_type == CronjobEvent.STOP
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class CronScheduler(threading.Thread):
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def __init__(self, jobs):
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def __init__(self, jobs, poll_seconds: float = 0.5):
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super().__init__()
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self.jobs_config = jobs
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self._jobs = {}
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self._poll_seconds = max(1e-3, poll_seconds)
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self._should_stop = threading.Event()
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logger.info('Cron scheduler initialized with {} jobs'.
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format(len(self.jobs_config.keys())))
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logger.info(
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'Cron scheduler initialized with {} jobs'.format(
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len(self.jobs_config.keys())
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)
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)
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def _get_job(self, name, config):
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job = self._jobs.get(name)
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@ -84,14 +120,21 @@ class CronScheduler(threading.Thread):
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return job
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if isinstance(config, dict):
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self._jobs[name] = Cronjob(name=name, cron_expression=config['cron_expression'],
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actions=config['actions'])
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self._jobs[name] = Cronjob(
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name=name,
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cron_expression=config['cron_expression'],
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actions=config['actions'],
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)
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elif is_functional_cron(config):
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self._jobs[name] = Cronjob(name=name, cron_expression=config.cron_expression,
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actions=config)
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self._jobs[name] = Cronjob(
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name=name, cron_expression=config.cron_expression, actions=config
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)
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else:
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raise AssertionError('Expected type dict or function for cron {}, got {}'.format(
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name, type(config)))
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raise AssertionError(
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'Expected type dict or function for cron {}, got {}'.format(
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name, type(config)
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)
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)
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return self._jobs[name]
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@ -112,7 +155,22 @@ class CronScheduler(threading.Thread):
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if job.state == CronjobState.IDLE:
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job.start()
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self._should_stop.wait(timeout=0.5)
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t_before_wait = get_now().timestamp()
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self._should_stop.wait(timeout=self._poll_seconds)
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t_after_wait = get_now().timestamp()
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time_drift = abs(t_after_wait - t_before_wait) - self._poll_seconds
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if not self.should_stop() and time_drift > 1:
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# If the system clock has been adjusted by more than one second
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# (e.g. because of DST change or NTP sync) then ensure that the
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# registered cronjobs are synchronized with the new datetime
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logger.info(
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'System clock drift detected: %f secs. Synchronizing the cronjobs',
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time_drift,
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)
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for job in self._jobs.values():
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job.notify(CronjobEvent.TIME_SYNC)
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logger.info('Terminating cron scheduler')
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@ -2,25 +2,34 @@ import datetime
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from platypush.cron import cron
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from tests.test_cron import tmp_files, tmp_files_ready, \
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test_timeout, expected_cron_file_content
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from tests.test_cron import test_timeout, cron_queue
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def make_cron_expr(cron_time: datetime.datetime):
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return '{min} {hour} {day} {month} * {sec}'.format(
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min=cron_time.minute,
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hour=cron_time.hour,
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day=cron_time.day,
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month=cron_time.month,
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sec=cron_time.second,
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)
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# Prepare a cronjob that should start test_timeout/2 seconds from the application start
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cron_time = datetime.datetime.now() + datetime.timedelta(seconds=test_timeout/2)
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cron_expr = '{min} {hour} {day} {month} * {sec}'.format(
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min=cron_time.minute, hour=cron_time.hour, day=cron_time.day,
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month=cron_time.month, sec=cron_time.second)
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cron_time = datetime.datetime.now() + datetime.timedelta(seconds=test_timeout / 2)
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@cron(cron_expr)
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@cron(make_cron_expr(cron_time))
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def cron_test(**_):
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"""
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Simple cronjob that awaits for ``../test_cron.py`` to be ready and writes the expected
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content to the monitored temporary file.
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"""
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files_ready = tmp_files_ready.wait(timeout=test_timeout)
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assert files_ready, \
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'The test did not prepare the temporary files within {} seconds'.format(test_timeout)
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cron_queue.put('cron_test')
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with open(tmp_files[0], 'w') as f:
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f.write(expected_cron_file_content)
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# Prepare another cronjob that should start 1hr + test_timeout/2 seconds from the application start
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cron_time = datetime.datetime.now() + datetime.timedelta(
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hours=1, seconds=test_timeout / 2
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)
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@cron(make_cron_expr(cron_time))
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def cron_1hr_test(**_):
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cron_queue.put('cron_1hr_test')
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@ -1,43 +1,61 @@
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import os
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import datetime
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import queue
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import pytest
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import tempfile
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import threading
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import time
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tmp_files = []
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tmp_files_ready = threading.Event()
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from dateutil.tz import gettz
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from mock import patch
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test_timeout = 10
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expected_cron_file_content = 'The cronjob ran successfully!'
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cron_queue = queue.Queue()
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@pytest.fixture(scope='module', autouse=True)
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def tmp_file(*_):
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tmp_file = tempfile.NamedTemporaryFile(prefix='platypush-test-cron-',
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suffix='.txt', delete=False)
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tmp_files.append(tmp_file.name)
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tmp_files_ready.set()
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yield tmp_file.name
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class MockDatetime(datetime.datetime):
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timedelta = datetime.timedelta()
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for f in tmp_files:
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if os.path.isfile(f):
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os.unlink(f)
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@classmethod
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def now(cls):
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return super().now(tz=gettz()) + cls.timedelta
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def test_cron_execution(tmp_file):
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def _test_cron_queue(expected_msg: str):
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msg = None
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test_start = time.time()
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while time.time() - test_start <= test_timeout and msg != expected_msg:
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try:
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msg = cron_queue.get(block=True, timeout=test_timeout)
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except queue.Empty:
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break
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assert msg == expected_msg, 'The expected cronjob has not been executed'
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def test_cron_execution():
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"""
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Test that the cronjob in ``../etc/scripts/test_cron.py`` runs successfully.
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"""
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actual_cron_file_content = None
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test_start = time.time()
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_test_cron_queue('cron_test')
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while actual_cron_file_content != expected_cron_file_content and \
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time.time() - test_start < test_timeout:
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with open(tmp_file, 'r') as f:
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actual_cron_file_content = f.read()
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time.sleep(0.5)
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assert actual_cron_file_content == expected_cron_file_content, \
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'cron_test failed to run within {} seconds'.format(test_timeout)
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def test_cron_execution_upon_system_clock_change():
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"""
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Test that the cronjob runs at the right time even upon DST or other
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system clock changes.
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"""
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# Mock datetime.datetime with a class that has overridable timedelta
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patcher = patch('datetime.datetime', MockDatetime)
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try:
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patcher.start()
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time.sleep(1)
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# Simulate a +1hr shift on the system clock
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MockDatetime.timedelta = datetime.timedelta(hours=1)
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time.sleep(1)
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finally:
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patcher.stop()
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# Ensure that the cronjob that was supposed to run in an hour is now running
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_test_cron_queue('cron_1hr_test')
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if __name__ == '__main__':
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