fix callbacks to copy it always

Author: kumaraditya303

Lib/test/test_asyncio/test_futures.py

@@ -697,6 +697,17 @@ def test_future_del_segfault(self):
         with self.assertRaises(AttributeError):
             del fut._log_traceback
 
+    def test_callbacks_copy(self):
+        fut = self._new_future(loop=self.loop)
+        f1 = lambda _: 1
+        f2 = lambda _: 2
+        fut.add_done_callback(f1)
+        fut.add_done_callback(f2)
+        callbacks = fut._callbacks
+        self.assertIsNot(callbacks, fut._callbacks)
+        fut.remove_done_callback(f1)
+        self.assertIsNot(callbacks, fut._callbacks)
+
 
 @unittest.skipUnless(hasattr(futures, '_CFuture'),
                      'requires the C _asyncio module')

Modules/_asynciomodule.c

@@ -1267,10 +1267,6 @@ FutureObj_get_callbacks(FutureObj *fut, void *Py_UNUSED(ignored))
     asyncio_state *state = get_asyncio_state_by_def((PyObject *)fut);
     ENSURE_FUTURE_ALIVE(state, fut)
 
-    if (fut->fut_callback0 == NULL && fut->fut_callbacks == NULL) {
-        Py_RETURN_NONE;
-    }
-
     Py_ssize_t len = 0;
     if (fut->fut_callback0 != NULL) {
         len++;
@@ -1279,6 +1275,10 @@ FutureObj_get_callbacks(FutureObj *fut, void *Py_UNUSED(ignored))
         len += PyList_GET_SIZE(fut->fut_callbacks);
     }
 
+    if (len == 0) {
+        Py_RETURN_NONE;
+    }
+
     PyObject *callbacks = PyList_New(len);
     if (callbacks == NULL) {
         return NULL;