Permit empty unique_on kwarg to lock on name only

Author: dmartin

README.md

@@ -138,6 +138,8 @@ task2 = do_something.delay(username='bob', otherarg=100)  # this is a duplicate
 assert task1 == task2
 ```
 
+Specify an empty list to consider the task name only.
+
 ### raise\_on\_duplicate
 
 When this option is enabled the task's `delay` and `apply_async` method will raise a `DuplicateTaskError` exception when attempting to spawn a duplicate task instead of returning the existing task's `AsyncResult`

celery_singleton/singleton.py

@@ -57,14 +57,16 @@ def generate_lock(self, task_name, task_args=None, task_kwargs=None):
         unique_on = self.unique_on
         task_args = task_args or []
         task_kwargs = task_kwargs or {}
-        if unique_on:
+        if unique_on is not None:
             if isinstance(unique_on, str):
                 unique_on = [unique_on]
-            sig = inspect.signature(self.run)
-            bound = sig.bind(*task_args, **task_kwargs).arguments
-
+            if not any(unique_on):
+                unique_kwargs = {}
+            else:
+                sig = inspect.signature(self.run)
+                bound = sig.bind(*task_args, **task_kwargs).arguments
+                unique_kwargs = {key: bound[key] for key in unique_on}
             unique_args = []
-            unique_kwargs = {key: bound[key] for key in unique_on}
         else:
             unique_args = task_args
             unique_kwargs = task_kwargs

tests/test_singleton.py

@@ -232,6 +232,34 @@ def unique_on_kwargs_task(a, b=2, c=3, d=4):
             assert mock_gen.call_count == 2
             assert [list(a) for a in mock_gen.call_args_list] == expected_args
 
+    @mock.patch.object(
+        util, "generate_lock", autospec=True, side_effect=util.generate_lock
+    )
+    def test__unique_on_empty__lock_on_task_name_only(
+        self, mock_gen, scoped_app, celery_session_worker
+    ):
+        with scoped_app as app:
+
+            @celery_session_worker.app.task(base=Singleton, unique_on=[])
+            def unique_on_empty_task(a, b=2, c=3, d=4):
+                return a * b * c * d
+
+            celery_session_worker.reload()  # So task is registered
+
+            result = unique_on_empty_task.delay(2, b=3, c=4, d=5)
+
+            result.get()
+            time.sleep(0.05)  # Small delay for on_success
+
+            expected_args = [
+                [
+                    (unique_on_empty_task.name, [], {}),
+                    {"key_prefix": unique_on_empty_task.singleton_config.key_prefix},
+                ]
+            ] * 2
+            assert mock_gen.call_count == 2
+            assert [list(a) for a in mock_gen.call_args_list] == expected_args
+
     @mock.patch.object(
         util, "generate_lock", autospec=True, side_effect=util.generate_lock
     )