Broaden asyncio fast path for loop subclasses

Author: KRRT7

Modules/_asynciomodule.c

@@ -366,6 +366,66 @@ get_event_loop(asyncio_state *state)
 }
 
 
+static int
+is_asyncio_base_event_loop_subclass(PyTypeObject *loop_type)
+{
+    for (PyTypeObject *base = loop_type; base != NULL; base = base->tp_base) {
+        if (strcmp(base->tp_name, "BaseEventLoop") != 0) {
+            continue;
+        }
+
+        PyObject *module_name =
+            PyDict_GetItemWithError(base->tp_dict, &_Py_ID(__module__));
+        if (module_name == NULL) {
+            if (PyErr_Occurred()) {
+                return -1;
+            }
+            continue;
+        }
+
+        if (PyUnicode_Check(module_name) &&
+            PyUnicode_CompareWithASCIIString(module_name, "asyncio.base_events") == 0) {
+            return 1;
+        }
+    }
+
+    return 0;
+}
+
+static int
+loop_has_instance_call_soon_shadow(PyObject *loop)
+{
+    PyTypeObject *loop_type = Py_TYPE(loop);
+    PyObject *attr = NULL;
+
+    if ((loop_type->tp_flags & Py_TPFLAGS_INLINE_VALUES) &&
+        _PyObject_TryGetInstanceAttribute(loop, &_Py_ID(call_soon), &attr)) {
+        int has_shadow = attr != NULL;
+        Py_XDECREF(attr);
+        return has_shadow;
+    }
+
+    PyObject *dict;
+    if (loop_type->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
+        dict = (PyObject *)_PyObject_GetManagedDict(loop);
+    }
+    else {
+        PyObject **dictptr = _PyObject_ComputedDictPointer(loop);
+        dict = dictptr != NULL ? FT_ATOMIC_LOAD_PTR_ACQUIRE(*dictptr) : NULL;
+    }
+
+    if (dict == NULL) {
+        return 0;
+    }
+
+    int rc = PyDict_GetItemRef(dict, &_Py_ID(call_soon), &attr);
+    if (rc < 0) {
+        return -1;
+    }
+    Py_XDECREF(attr);
+    return rc > 0;
+}
+
 static int
 call_soon(asyncio_state *state, PyObject *loop, PyObject *func, PyObject *arg,
           PyObject *ctx)
@@ -374,28 +434,31 @@ call_soon(asyncio_state *state, PyObject *loop, PyObject *func, PyObject *arg,
     PyObject *handle = NULL;
 
     PyTypeObject *loop_type = Py_TYPE(loop);
+    int is_base_event_loop_subclass =
+        is_asyncio_base_event_loop_subclass(loop_type);
+    int is_stdlib_base_event_loop =
+        strcmp(loop_type->tp_name, "BaseEventLoop") == 0;
+    PyObject *call_soon_attr =
+        PyDict_GetItemWithError(loop_type->tp_dict, &_Py_ID(call_soon));
+    if (call_soon_attr == NULL && PyErr_Occurred()) {
+        return -1;
+    }
+    int has_instance_call_soon_shadow = loop_has_instance_call_soon_shadow(loop);
+    if (has_instance_call_soon_shadow < 0) {
+        return -1;
+    }
+
     PyObject *module_name = PyDict_GetItemWithError(loop_type->tp_dict, &_Py_ID(__module__));
     if (module_name == NULL && PyErr_Occurred()) {
         return -1;
     }
 
     int use_fastpath = (
+        is_base_event_loop_subclass &&
         module_name != NULL &&
         PyUnicode_Check(module_name) &&
-        (
-            (strcmp(loop_type->tp_name, "BaseEventLoop") == 0 &&
-             PyUnicode_CompareWithASCIIString(module_name, "asyncio.base_events") == 0) ||
-            (strcmp(loop_type->tp_name, "BaseSelectorEventLoop") == 0 &&
-             PyUnicode_CompareWithASCIIString(module_name, "asyncio.selector_events") == 0) ||
-            (strcmp(loop_type->tp_name, "_UnixSelectorEventLoop") == 0 &&
-             PyUnicode_CompareWithASCIIString(module_name, "asyncio.unix_events") == 0) ||
-            (strcmp(loop_type->tp_name, "_WindowsSelectorEventLoop") == 0 &&
-             PyUnicode_CompareWithASCIIString(module_name, "asyncio.windows_events") == 0) ||
-            (strcmp(loop_type->tp_name, "BaseProactorEventLoop") == 0 &&
-             PyUnicode_CompareWithASCIIString(module_name, "asyncio.proactor_events") == 0) ||
-            (strcmp(loop_type->tp_name, "ProactorEventLoop") == 0 &&
-             PyUnicode_CompareWithASCIIString(module_name, "asyncio.windows_events") == 0)
-        )
+        !has_instance_call_soon_shadow &&
+        (is_stdlib_base_event_loop || call_soon_attr == NULL)
     );
 
     if (use_fastpath) {