fix: prevent tasks dying from temporary loss of db connection

api/task_processor/threads.py

@@ -1,7 +1,9 @@
 import logging
 import time
+import traceback
 from threading import Thread
 
+from django.db import DatabaseError
 from django.utils import timezone
 
 from task_processor.processor import run_recurring_tasks, run_tasks
@@ -27,12 +29,22 @@ def __init__(
     def run(self) -> None:
         while not self._stopped:
             self.last_checked_for_tasks = timezone.now()
-            try:
-                run_tasks(self.queue_pop_size)
-            except Exception as e:
-                logger.exception(e)
-            run_recurring_tasks(self.queue_pop_size)
+            self.run_iteration()
             time.sleep(self.sleep_interval_millis / 1000)
 
+    def run_iteration(self) -> None:
+        try:
+            run_tasks(self.queue_pop_size)
+            run_recurring_tasks(self.queue_pop_size)
+        except DatabaseError as e:
+            # To prevent task threads from dying if they get an error retrieving the tasks from the
+            # database this will allow the thread to continue trying to retrieve tasks if it can
+            # successfully re-establish a connection to the database.
+            # TODO: is this also what is causing tasks to get stuck as locked? Can we unlock
+            #  tasks here?
+
+            logger.error("Received database error retrieving tasks: %s.", e)
+            logger.debug(traceback.format_exc())
+
     def stop(self):
         self._stopped = True

api/tests/unit/task_processor/conftest.py

@@ -1,6 +1,35 @@
+import logging
+import typing
+
 import pytest
 
 
 @pytest.fixture
 def run_by_processor(monkeypatch):
     monkeypatch.setenv("RUN_BY_PROCESSOR", "True")
+
+
+class GetTaskProcessorCaplog(typing.Protocol):
+    def __call__(
+        self, log_level: str | int = logging.INFO
+    ) -> pytest.LogCaptureFixture: ...
+
+
+@pytest.fixture
+def get_task_processor_caplog(
+    caplog: pytest.LogCaptureFixture,
+) -> GetTaskProcessorCaplog:
+    # caplog doesn't allow you to capture logging outputs from loggers that don't
+    # propagate to root. Quick hack here to get the task_processor logger to
+    # propagate.
+    # TODO: look into using loguru.
+
+    def _inner(log_level: str | int = logging.INFO) -> pytest.LogCaptureFixture:
+        task_processor_logger = logging.getLogger("task_processor")
+        task_processor_logger.propagate = True
+        # Assume required level for the logger.
+        task_processor_logger.setLevel(log_level)
+        caplog.set_level(log_level)
+        return caplog
+
+    return _inner

api/tests/unit/task_processor/test_unit_task_processor_decorators.py

@@ -1,5 +1,4 @@
 import json
-import logging
 from datetime import timedelta
 from unittest.mock import MagicMock
 
@@ -16,19 +15,7 @@
 from task_processor.models import RecurringTask, Task, TaskPriority
 from task_processor.task_registry import get_task
 from task_processor.task_run_method import TaskRunMethod
-
-
-@pytest.fixture
-def capture_task_processor_logger(caplog: pytest.LogCaptureFixture) -> None:
-    # caplog doesn't allow you to capture logging outputs from loggers that don't
-    # propagate to root. Quick hack here to get the task_processor logger to
-    # propagate.
-    # TODO: look into using loguru.
-    task_processor_logger = logging.getLogger("task_processor")
-    task_processor_logger.propagate = True
-    # Assume required level for the logger.
-    task_processor_logger.setLevel(logging.INFO)
-    caplog.set_level(logging.INFO)
+from tests.unit.task_processor.conftest import GetTaskProcessorCaplog
 
 
 @pytest.fixture
@@ -44,11 +31,12 @@ def mock_thread_class(
 
 @pytest.mark.django_db
 def test_register_task_handler_run_in_thread__transaction_commit__true__default(
-    capture_task_processor_logger: None,
-    caplog: pytest.LogCaptureFixture,
+    get_task_processor_caplog: GetTaskProcessorCaplog,
     mock_thread_class: MagicMock,
 ) -> None:
     # Given
+    caplog = get_task_processor_caplog()
+
     @register_task_handler()
     def my_function(*args: str, **kwargs: str) -> None:
         pass
@@ -77,11 +65,12 @@ def my_function(*args: str, **kwargs: str) -> None:
 
 
 def test_register_task_handler_run_in_thread__transaction_commit__false(
-    capture_task_processor_logger: None,
-    caplog: pytest.LogCaptureFixture,
+    get_task_processor_caplog: GetTaskProcessorCaplog,
     mock_thread_class: MagicMock,
 ) -> None:
     # Given
+    caplog = get_task_processor_caplog()
+
     @register_task_handler(transaction_on_commit=False)
     def my_function(*args, **kwargs):
         pass

api/tests/unit/task_processor/test_unit_task_processor_threads.py

@@ -0,0 +1,38 @@
+import logging
+
+from django.db import DatabaseError
+from pytest_django.fixtures import SettingsWrapper
+from pytest_mock import MockerFixture
+
+from task_processor.threads import TaskRunner
+from tests.unit.task_processor.conftest import GetTaskProcessorCaplog
+
+
+def test_task_runner_is_resilient_to_database_errors(
+    db: None,
+    mocker: MockerFixture,
+    get_task_processor_caplog: GetTaskProcessorCaplog,
+    settings: SettingsWrapper,
+) -> None:
+    # Given
+    caplog = get_task_processor_caplog(logging.DEBUG)
+
+    task_runner = TaskRunner()
+    mocker.patch(
+        "task_processor.threads.run_tasks", side_effect=DatabaseError("Database error")
+    )
+
+    # When
+    task_runner.run_iteration()
+
+    # Then
+    assert len(caplog.records) == 2
+
+    assert caplog.records[0].levelno == logging.ERROR
+    assert (
+        caplog.records[0].message
+        == "Received database error retrieving tasks: Database error."
+    )
+
+    assert caplog.records[1].levelno == logging.DEBUG
+    assert caplog.records[1].message.startswith("Traceback")