CUDA: Make arg optional for Stream.add_callback()

numba/cuda/cudadrv/driver.py

@@ -2238,7 +2238,7 @@ def auto_synchronize(self):
         yield self
         self.synchronize()
 
-    def add_callback(self, callback, arg):
+    def add_callback(self, callback, arg=None):
         """
         Add a callback to a compute stream.
         The user provided function is called from a driver thread once all
@@ -2256,7 +2256,7 @@ def add_callback(self, callback, arg):
         eventual deprecation and may be replaced in a future CUDA release.
 
         :param callback: Callback function with arguments (stream, status, arg).
-        :param arg: User data to be passed to the callback function.
+        :param arg: Optional user data to be passed to the callback function.
         """
         data = (self, callback, arg)
         _py_incref(data)

numba/cuda/tests/cudadrv/test_streams.py

@@ -29,6 +29,17 @@ def callback(stream, status, event):
         stream.add_callback(callback, callback_event)
         self.assertTrue(callback_event.wait(1.0))
 
+    def test_add_callback_with_default_arg(self):
+        callback_event = threading.Event()
+
+        def callback(stream, status, arg):
+            self.assertIsNone(arg)
+            callback_event.set()
+
+        stream = cuda.stream()
+        stream.add_callback(callback)
+        self.assertTrue(callback_event.wait(1.0))
+
     @with_asyncio_loop
     async def test_async_done(self):
         stream = cuda.stream()