db: Give the Idle Queue a way to handle high priority tasks

If we have a high priority task, then we want to push it to the front of
the idle queue so it runs as soon as possible.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

emmental/db/idle.py

@@ -65,12 +65,13 @@ class Queue(GObject.GObject):
         self.cancel()
 
     def push(self, func: typing.Callable, *args,
-             now: bool = False) -> bool | None:
+             now: bool = False, first: bool = False) -> bool | None:
         """Add a task to the Idle Queue."""
         if not self.enabled or now:
             return func(*args)
 
-        self._tasks.append((func, *args))
+        pos = 0 if first else len(self._tasks)
+        self._tasks.insert(pos, (func, *args))
         self.total += 1
         self.__start()
 

tests/db/test_idle.py

@@ -139,6 +139,17 @@ class TestIdleQueue(unittest.TestCase):
         mock_idle_add.assert_not_called()
         func.assert_called_with(1)
 
+    def test_push_first(self, mock_idle_add: unittest.mock.Mock,
+                        mock_source_removed: unittest.mock.Mock):
+        """Test pushing an idle task with first=True."""
+        self.queue.push(1)
+        self.queue.push(0, first=True)
+        self.assertListEqual(self.queue._tasks, [(0,), (1,)])
+        self.queue.push(2, first=False)
+        self.assertListEqual(self.queue._tasks, [(0,), (1,), (2,)])
+        self.queue.push(3)
+        self.assertListEqual(self.queue._tasks, [(0,), (1,), (2,), (3,)])
+
     def test_push_many_enabled(self, mock_idle_add: unittest.mock.Mock,
                                mock_source_removed: unittest.mock.Mock):
         """Test adding several calls to one function at one time."""