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Fix for #217

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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.
This commit is contained in:
Fabio Manganiello 2022-04-28 00:57:49 +02:00
parent 820a1c8184
commit 41d0725ebf
Signed by: blacklight
GPG key ID: D90FBA7F76362774
3 changed files with 148 additions and 63 deletions
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100
platypush/cron/scheduler.py
View file

@ -7,11 +7,20 @@ import croniter
from dateutil.tz import gettz
from platypush.procedure import Procedure
from platypush.utils import is_functional_cron
from platypush.utils import is_functional_cron, set_thread_name
logger = logging.getLogger('platypush:cron')
def get_now() -> datetime.datetime:
"""
:return: A timezone-aware representation of `now`
"""
return datetime.datetime.now().replace(
tzinfo=gettz()
) # lgtm [py/call-to-non-callable]
class CronjobState(enum.IntEnum):
IDLE = 0
WAIT = 1
@ -20,21 +29,36 @@ class CronjobState(enum.IntEnum):
ERROR = 4
class CronjobEvent(enum.IntEnum):
NONE = 0
STOP = 1
TIME_SYNC = 2
class Cronjob(threading.Thread):
def __init__(self, name, cron_expression, actions):
super().__init__()
self.cron_expression = cron_expression
self.name = name
self.state = CronjobState.IDLE
self._should_stop = threading.Event()
self._event = threading.Event()
self._event_type = CronjobEvent.NONE
self._event_lock = threading.RLock()
if isinstance(actions, dict) or isinstance(actions, list):
self.actions = Procedure.build(name=name + '__Cron', _async=False, requests=actions)
if isinstance(actions, (list, dict)):
self.actions = Procedure.build(
name=name + '__Cron', _async=False, requests=actions
)
else:
self.actions = actions
def notify(self, event: CronjobEvent):
with self._event_lock:
self._event_type = event
self._event.set()
def run(self):
self.state = CronjobState.WAIT
set_thread_name(f'cron:{self.name}')
self.wait()
if self.should_stop():
return
@ -57,26 +81,38 @@ class Cronjob(threading.Thread):
self.state = CronjobState.ERROR
def wait(self):
now = datetime.datetime.now().replace(tzinfo=gettz()) # lgtm [py/call-to-non-callable]
cron = croniter.croniter(self.cron_expression, now)
next_run = cron.get_next()
self._should_stop.wait(next_run - now.timestamp())
with self._event_lock:
self.state = CronjobState.WAIT
self._event.clear()
self._event_type = CronjobEvent.TIME_SYNC
while self._event_type == CronjobEvent.TIME_SYNC:
now = get_now()
self._event_type = CronjobEvent.NONE
cron = croniter.croniter(self.cron_expression, now)
next_run = cron.get_next()
self._event.wait(max(0, next_run - now.timestamp()))
def stop(self):
self._should_stop.set()
self._event_type = CronjobEvent.STOP
self._event.set()
def should_stop(self):
return self._should_stop.is_set()
return self._event_type == CronjobEvent.STOP
class CronScheduler(threading.Thread):
def __init__(self, jobs):
def __init__(self, jobs, poll_seconds: float = 0.5):
super().__init__()
self.jobs_config = jobs
self._jobs = {}
self._poll_seconds = max(1e-3, poll_seconds)
self._should_stop = threading.Event()
logger.info('Cron scheduler initialized with {} jobs'.
format(len(self.jobs_config.keys())))
logger.info(
'Cron scheduler initialized with {} jobs'.format(
len(self.jobs_config.keys())
)
)
def _get_job(self, name, config):
job = self._jobs.get(name)
@ -84,14 +120,21 @@ class CronScheduler(threading.Thread):
return job
if isinstance(config, dict):
self._jobs[name] = Cronjob(name=name, cron_expression=config['cron_expression'],
actions=config['actions'])
self._jobs[name] = Cronjob(
name=name,
cron_expression=config['cron_expression'],
actions=config['actions'],
)
elif is_functional_cron(config):
self._jobs[name] = Cronjob(name=name, cron_expression=config.cron_expression,
actions=config)
self._jobs[name] = Cronjob(
name=name, cron_expression=config.cron_expression, actions=config
)
else:
raise AssertionError('Expected type dict or function for cron {}, got {}'.format(
name, type(config)))
raise AssertionError(
'Expected type dict or function for cron {}, got {}'.format(
name, type(config)
)
)
return self._jobs[name]
@ -112,7 +155,22 @@ class CronScheduler(threading.Thread):
if job.state == CronjobState.IDLE:
job.start()
self._should_stop.wait(timeout=0.5)
t_before_wait = get_now().timestamp()
self._should_stop.wait(timeout=self._poll_seconds)
t_after_wait = get_now().timestamp()
time_drift = abs(t_after_wait - t_before_wait) - self._poll_seconds
if not self.should_stop() and time_drift > 1:
# If the system clock has been adjusted by more than one second
# (e.g. because of DST change or NTP sync) then ensure that the
# registered cronjobs are synchronized with the new datetime
logger.info(
'System clock drift detected: %f secs. Synchronizing the cronjobs',
time_drift,
)
for job in self._jobs.values():
job.notify(CronjobEvent.TIME_SYNC)
logger.info('Terminating cron scheduler')

41
tests/etc/scripts/test_cron.py
View file

@ -2,25 +2,34 @@ import datetime
from platypush.cron import cron
from tests.test_cron import tmp_files, tmp_files_ready, \
test_timeout, expected_cron_file_content
from tests.test_cron import test_timeout, cron_queue
def make_cron_expr(cron_time: datetime.datetime):
return '{min} {hour} {day} {month} * {sec}'.format(
min=cron_time.minute,
hour=cron_time.hour,
day=cron_time.day,
month=cron_time.month,
sec=cron_time.second,
)
# Prepare a cronjob that should start test_timeout/2 seconds from the application start
cron_time = datetime.datetime.now() + datetime.timedelta(seconds=test_timeout/2)
cron_expr = '{min} {hour} {day} {month} * {sec}'.format(
min=cron_time.minute, hour=cron_time.hour, day=cron_time.day,
month=cron_time.month, sec=cron_time.second)
cron_time = datetime.datetime.now() + datetime.timedelta(seconds=test_timeout / 2)
@cron(cron_expr)
@cron(make_cron_expr(cron_time))
def cron_test(**_):
"""
Simple cronjob that awaits for ``../test_cron.py`` to be ready and writes the expected
content to the monitored temporary file.
"""
files_ready = tmp_files_ready.wait(timeout=test_timeout)
assert files_ready, \
'The test did not prepare the temporary files within {} seconds'.format(test_timeout)
cron_queue.put('cron_test')
with open(tmp_files[0], 'w') as f:
f.write(expected_cron_file_content)
# Prepare another cronjob that should start 1hr + test_timeout/2 seconds from the application start
cron_time = datetime.datetime.now() + datetime.timedelta(
hours=1, seconds=test_timeout / 2
)
@cron(make_cron_expr(cron_time))
def cron_1hr_test(**_):
cron_queue.put('cron_1hr_test')

70
tests/test_cron.py
View file

@ -1,43 +1,61 @@
import os
import datetime
import queue
import pytest
import tempfile
import threading
import time
tmp_files = []
tmp_files_ready = threading.Event()
from dateutil.tz import gettz
from mock import patch
test_timeout = 10
expected_cron_file_content = 'The cronjob ran successfully!'
cron_queue = queue.Queue()
@pytest.fixture(scope='module', autouse=True)
def tmp_file(*_):
tmp_file = tempfile.NamedTemporaryFile(prefix='platypush-test-cron-',
suffix='.txt', delete=False)
tmp_files.append(tmp_file.name)
tmp_files_ready.set()
yield tmp_file.name
class MockDatetime(datetime.datetime):
timedelta = datetime.timedelta()
for f in tmp_files:
if os.path.isfile(f):
os.unlink(f)
@classmethod
def now(cls):
return super().now(tz=gettz()) + cls.timedelta
def test_cron_execution(tmp_file):
def _test_cron_queue(expected_msg: str):
msg = None
test_start = time.time()
while time.time() - test_start <= test_timeout and msg != expected_msg:
try:
msg = cron_queue.get(block=True, timeout=test_timeout)
except queue.Empty:
break
assert msg == expected_msg, 'The expected cronjob has not been executed'
def test_cron_execution():
"""
Test that the cronjob in ``../etc/scripts/test_cron.py`` runs successfully.
"""
actual_cron_file_content = None
test_start = time.time()
_test_cron_queue('cron_test')
while actual_cron_file_content != expected_cron_file_content and \
time.time() - test_start < test_timeout:
with open(tmp_file, 'r') as f:
actual_cron_file_content = f.read()
time.sleep(0.5)
assert actual_cron_file_content == expected_cron_file_content, \
'cron_test failed to run within {} seconds'.format(test_timeout)
def test_cron_execution_upon_system_clock_change():
"""
Test that the cronjob runs at the right time even upon DST or other
system clock changes.
"""
# Mock datetime.datetime with a class that has overridable timedelta
patcher = patch('datetime.datetime', MockDatetime)
try:
patcher.start()
time.sleep(1)
# Simulate a +1hr shift on the system clock
MockDatetime.timedelta = datetime.timedelta(hours=1)
time.sleep(1)
finally:
patcher.stop()
# Ensure that the cronjob that was supposed to run in an hour is now running
_test_cron_queue('cron_1hr_test')
if __name__ == '__main__':