fix(tasks): newly assigned `None` in registry (#2381)

sanic/app.py

@@ -1268,10 +1268,9 @@ class Sanic(BaseSanic, RunnerMixin, metaclass=TouchUpMeta):
                 ...
 
     def purge_tasks(self):
-        for task in self.tasks:
+        for key, task in self._task_registry.items():
             if task.done() or task.cancelled():
-                name = task.get_name()
-                self._task_registry[name] = None
+                self._task_registry[key] = None
 
         self._task_registry = {
             k: v for k, v in self._task_registry.items() if v is not None

tests/test_tasks.py

@@ -80,6 +80,18 @@ async def test_purge_tasks(app: Sanic):
     assert len(app._task_registry) == 0
 
 
+async def test_purge_tasks_with_create_task(app: Sanic):
+    app.add_task(asyncio.create_task(dummy(3)), name="dummy")
+
+    await app.cancel_task("dummy")
+
+    assert len(app._task_registry) == 1
+
+    app.purge_tasks()
+
+    assert len(app._task_registry) == 0
+
+
 def test_shutdown_tasks_on_app_stop():
     class TestSanic(Sanic):
         shutdown_tasks = Mock()