Start time heap block fix (#636)

* Update schedulers.py

* Update test_schedulers.py

* Update schedulers.py

* Update test_schedulers.py

* Update schedulers.py

* Update schedulers.py

* Update test_schedulers.py

* Update schedulers.py

Author: sidhavratha

django_celery_beat/schedulers.py

@@ -85,6 +85,13 @@ def __init__(self, model, app=None):
 
         if not model.last_run_at:
             model.last_run_at = self._default_now()
+            # if last_run_at is not set and
+            # model.start_time last_run_at should be in way past.
+            # This will trigger the job to run at start_time
+            # and avoid the heap block.
+            if self.model.start_time:
+                model.last_run_at = model.last_run_at \
+                    - datetime.timedelta(days=365 * 30)
 
         self.last_run_at = model.last_run_at
 

t/unit/test_schedulers.py

@@ -599,6 +599,29 @@ def test_heap_always_return_the_first_item(self):
                     s.sync()
         assert len(tried) == 1 and tried == {e1.name}
 
+    def test_starttime_trigger(self, monkeypatch):
+        # Ensure there is no heap block in case of new task with start_time
+        PeriodicTask.objects.all().delete()
+        s = self.Scheduler(app=self.app)
+        assert not s._heap
+        m1 = self.create_model_interval(schedule(timedelta(seconds=3)))
+        m1.save()
+        s.tick()
+        assert len(s._heap) == 2
+        m2 = self.create_model_interval(
+            schedule(timedelta(days=1)),
+            start_time=make_aware(
+                datetime.now() + timedelta(seconds=2)))
+        m2.save()
+        s.tick()
+        assert s._heap[0][2].name == m2.name
+        assert len(s._heap) == 3
+        assert s._heap[0]
+        time.sleep(2)
+        s.tick()
+        assert s._heap[0]
+        assert s._heap[0][2].name == m1.name
+
 
 @pytest.mark.django_db()
 class test_models(SchedulerCase):