Fix: Daylight saving time issue with scheduler (#47)

django_q/cluster.py

@@ -6,6 +6,7 @@ import socket
 import traceback
 import uuid
 from datetime import datetime, timedelta
+from pytz import timezone as pytz_timezone
 from multiprocessing import Event, Process, Value, current_process
 from time import sleep
 
@@ -43,7 +44,7 @@ from django_q.signals import post_execute, pre_execute
 from django_q.signing import BadSignature, SignedPackage
 from django_q.status import Stat, Status
 
-from .utils import add_months, add_years, get_func_repr
+from .utils import get_func_repr, localtime
 
 
 class Cluster:
@@ -700,33 +701,7 @@ def scheduler(broker: Broker = None):
                 if s.schedule_type != s.ONCE:
                     next_run = s.next_run
                     while True:
-                        if s.schedule_type == s.MINUTES:
-                            next_run = next_run + timedelta(minutes=(s.minutes or 1))
-                        elif s.schedule_type == s.HOURLY:
-                            next_run = next_run + timedelta(hours=1)
-                        elif s.schedule_type == s.DAILY:
-                            next_run = next_run + timedelta(days=1)
-                        elif s.schedule_type == s.WEEKLY:
-                            next_run = next_run + timedelta(weeks=1)
-                        elif s.schedule_type == s.BIWEEKLY:
-                            next_run = next_run + timedelta(weeks=2)
-                        elif s.schedule_type == s.MONTHLY:
-                            next_run = add_months(next_run, 1)
-                        elif s.schedule_type == s.BIMONTHLY:
-                            next_run = add_months(next_run, 2)
-                        elif s.schedule_type == s.QUARTERLY:
-                            next_run = add_months(next_run, 3)
-                        elif s.schedule_type == s.YEARLY:
-                            next_run = add_years(next_run, 1)
-                        elif s.schedule_type == s.CRON:
-                            if not croniter:
-                                raise ImportError(
-                                    _(
-                                        "Please install croniter to enable cron "
-                                        "expressions"
-                                    )
-                                )
-                            next_run = croniter(s.cron, localtime()).get_next(datetime)
+                        next_run = s.calculate_next_run(next_run)
                         if Conf.CATCH_UP or next_run > localtime():
                             break
 
@@ -842,10 +817,3 @@ def rss_check():
         elif psutil:
             return psutil.Process().memory_info().rss >= Conf.MAX_RSS * 1024
     return False
-
-
-def localtime() -> datetime:
-    """Override for timezone.localtime to deal with naive times and local times"""
-    if settings.USE_TZ:
-        return timezone.localtime()
-    return datetime.now()

django_q/conf.py

@@ -211,6 +211,11 @@ class Conf:
     # to manage workarounds during testing
     TESTING = conf.get("testing", False)
 
+    # Timezone for next_run, overrules Django timezone
+    TIME_ZONE = None
+    if settings.USE_TZ:
+        TIME_ZONE = conf.get("time_zone", settings.TIME_ZONE)
+
 
 # logger
 logger = logging.getLogger("django-q")

django_q/models.py

@@ -1,3 +1,5 @@
+from datetime import datetime, timedelta
+
 # Django
 from django import get_version
 from django.core.exceptions import ValidationError
@@ -5,6 +7,7 @@ from django.db import models
 from django.template.defaultfilters import truncatechars
 from django.urls import reverse
 from django.utils import timezone
+from django.utils.timezone import is_aware
 from django.utils.html import format_html
 from django.utils.translation import gettext_lazy as _
 
@@ -13,8 +16,9 @@ from picklefield import PickledObjectField
 from picklefield.fields import dbsafe_decode
 
 # Local
-from django_q.conf import croniter
+from django_q.conf import croniter, Conf
 from django_q.signing import SignedPackage
+from django_q.utils import localtime, add_months, add_years
 
 from .utils import get_func_repr
 
@@ -208,6 +212,59 @@ class Schedule(models.Model):
     task = models.CharField(max_length=100, null=True, editable=False)
     cluster = models.CharField(max_length=100, default=None, null=True, blank=True)
 
+    def calculate_next_run(self, next_run=None):
+        # next run is always in UTC
+        next_run = next_run or self.next_run
+
+        if self.schedule_type == self.CRON:
+            if not croniter:
+                raise ImportError(
+                    _("Please install croniter to enable cron expressions")
+                )
+            return croniter(self.cron, localtime()).get_next(datetime)
+
+        if self.schedule_type == self.MINUTES:
+            add = timedelta(minutes=(self.minutes or 1))
+        elif self.schedule_type == self.HOURLY:
+            add = timedelta(hours=1)
+        elif self.schedule_type == self.DAILY:
+            add = timedelta(days=1)
+        elif self.schedule_type == self.WEEKLY:
+            add = timedelta(weeks=1)
+        elif self.schedule_type == self.BIWEEKLY:
+            add = timedelta(weeks=2)
+        elif self.schedule_type == self.MONTHLY:
+            add = timedelta(days=(add_months(next_run, 1) - next_run).days)
+        elif self.schedule_type == self.BIMONTHLY:
+            add = timedelta(days=(add_months(next_run, 2) - next_run).days)
+        elif self.schedule_type == self.QUARTERLY:
+            add = timedelta(days=(add_months(next_run, 3) - next_run).days)
+        elif self.schedule_type == self.YEARLY:
+            add = timedelta(days=(add_years(next_run, 1) - next_run).days)
+
+        # add normal timedelta, we will correct this later based on timezone
+        next_run += add
+
+        # DST differencers don't matter with minutes, hourly or yearly, so skip those
+        if self.schedule_type not in [self.MINUTES, self.HOURLY, self.YEARLY]:
+            # Get localtimes and then remove the tzinfo, so we can get the actual difference
+            current_next_run = localtime(next_run - add).replace(tzinfo=None)
+            new_next_run = localtime(next_run).replace(tzinfo=None)
+
+            # get the difference between them, this should be (-)1 or (-)0.5 hour
+            # based on DST active or not
+            extra_diff = (new_next_run - current_next_run) - add
+
+            # if we have one positive hour difference, then subtract it, so we are even
+            # and vice versa. In most cases, this will be 0, as there won't be a
+            # timezone diff
+            if extra_diff > timedelta(hours=0):
+                next_run -= extra_diff
+            else:
+                next_run += extra_diff
+
+        return next_run
+
     def success(self):
         if self.task and Task.objects.filter(id=self.task):
             return Task.objects.get(id=self.task).success

django_q/tests/settings.py

@@ -75,7 +75,7 @@ DATABASES = {
 
 LANGUAGE_CODE = "en-us"
 
-TIME_ZONE = "UTC"
+TIME_ZONE = "Europe/Amsterdam"
 
 USE_I18N = True
 

django_q/tests/test_scheduler.py

@@ -1,5 +1,6 @@
 import os
-from datetime import timedelta
+import pytz
+from datetime import datetime, timedelta
 from multiprocessing import Event, Value
 from unittest import mock
 
@@ -83,6 +84,63 @@ MULTIPLE_APPS_DATABASES = {
 }
 
 
+@pytest.mark.django_db
+def test_scheduler_daylight_saving_time_daily(broker, monkeypatch):
+    # Set up a startdate in the Amsterdam timezone (without dst 1 hour ahead). The
+    # 28th of March 2021 is the day when sunlight saving starts (at 2 am)
+
+    monkeypatch.setattr(Conf, "TIME_ZONE", "Europe/Amsterdam")
+    tz = pytz.timezone('Europe/Amsterdam')
+    broker.list_key = "scheduler_test:q"
+    # Let's start a schedule at 1 am on the 27th of March. This is in AMS timezone.
+    # So, 2021-03-27 00:00:00 when saved (due to TZ being Amsterdam and saved in UTC)
+    start_date = datetime(2021, 3, 27, 1, 0, 0)
+
+    # Create schedule with the next run date on the start date. It will move one day
+    # forward when we run the scheduler
+    schedule = create_schedule(
+        "math.copysign",
+        1,
+        -1,
+        name="test math",
+        schedule_type=Schedule.DAILY,
+        next_run=start_date,
+    )
+
+    # Run scheduler so we get the next run date
+    scheduler(broker=broker)
+    schedule.refresh_from_db()
+
+    # It's now the day after exactly at midnight UTC
+    next_run = schedule.next_run
+    assert str(next_run) == "2021-03-28 00:00:00+00:00"
+
+    # In the Amsterdam timezone, it's 1 hour over midnight (+01)
+    next_run = next_run.astimezone(tz)
+    assert str(next_run) == "2021-03-28 01:00:00+01:00"
+
+    # Run scheduler so we get the next run date
+    scheduler(broker=broker)
+    schedule.refresh_from_db()
+
+    next_run = schedule.next_run
+
+    assert str(next_run) == "2021-03-28 23:00:00+00:00"
+    next_run = next_run.astimezone(tz)
+    # In the Amsterdam timezone, it's 1 hour over midnight (+02)
+    assert str(next_run) == "2021-03-29 01:00:00+02:00"
+
+    # Run scheduler so we get the next run date
+    scheduler(broker=broker)
+    schedule.refresh_from_db()
+
+    next_run = schedule.next_run
+
+    assert str(next_run) == "2021-03-29 23:00:00+00:00"
+    next_run = next_run.astimezone(tz)
+    assert str(next_run) == "2021-03-30 01:00:00+02:00"
+
+
 @pytest.mark.django_db
 def test_scheduler(broker, monkeypatch):
     broker.list_key = "scheduler_test:q"

django_q/utils.py

@@ -1,7 +1,13 @@
+from datetime import datetime
+import pytz
 import calendar
 import inspect
 from datetime import date
 
+from django.utils import timezone
+from django.conf import settings
+
+from django_q.conf import Conf
 
 # credits: https://stackoverflow.com/a/4131114
 # Made them aware of timezone
@@ -39,3 +45,13 @@ def get_func_repr(func):
         )
     else:
         return str(func)
+
+
+def localtime(value=None) -> datetime:
+    """Override for timezone.localtime to deal with naive times and local times"""
+    if settings.USE_TZ:
+        return timezone.localtime(value=value, timezone=pytz.timezone(Conf.TIME_ZONE))
+    if value is None:
+        return datetime.now()
+    else:
+        return value