Add PyUnstable_Object_IsUniquelyReferenced

ngoldbaum · ngoldbaum · commit 78ff37e81a79 · 2025-08-26T12:43:25.000-06:00
diff --git a/pythoncapi_compat.h b/pythoncapi_compat.h
@@ -2211,6 +2211,24 @@ PyConfig_GetInt(const char *name, int *value)
 }
 #endif  // PY_VERSION_HEX > 0x03090000 && !defined(PYPY_VERSION)
 
+// gh-133144 added PyUnstable_Object_IsUniquelyReferenced() to Python 3.14.0b1
+// Adapted from  _PyObject_IsUniquelyReferenced implementation
+#if PY_VERSION_HEX < 0x030E00B0
+static inline int PyUnstable_Object_IsUniquelyReferenced(PyObject *obj)
+{
+#if !defined(Py_GIL_DISABLED)
+    return Py_REFCNT(ob) == 1;
+#else
+    // NOTE: the entire ob_ref_shared field must be zero, including flags, to
+    // ensure that other threads cannot concurrently create new references to
+    // this object.
+    return (_Py_IsOwnedByCurrentThread(obj) &&
+            _Py_atomic_load_uint32_relaxed(&obj->ob_ref_local) == 1 &&
+            _Py_atomic_load_ssize_relaxed(&obj->ob_ref_shared) == 0);
+#endif
+}
+#endif
+
 
 #if PY_VERSION_HEX < 0x030F0000
 static inline PyObject*
diff --git a/tests/test_pythoncapi_compat_cext.c b/tests/test_pythoncapi_compat_cext.c
@@ -1953,6 +1953,27 @@ test_unicodewriter_format(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(args))
 }
 #endif
 
+static PyObject *
+test_uniquely_referenced(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(args))
+{
+    const char *str = "Hello World";
+    PyObject *obj = PyUnicode_FromString(str);
+    if (obj == NULL) {
+        return NULL;
+    }
+
+    assert(PyUnstable_Object_IsUniquelyReferenced(obj));
+
+    Py_INCREF(obj);
+
+    assert(!PyUnstable_Object_IsUniquelyReferenced(obj));
+
+    Py_DECREF(obj);
+    Py_DECREF(obj);
+
+    Py_RETURN_NONE;
+}
+
 
 static PyObject *
 test_bytes(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
@@ -2309,6 +2330,7 @@ static struct PyMethodDef methods[] = {
     {"test_config", test_config, METH_NOARGS, _Py_NULL},
 #endif
     {"test_sys", test_sys, METH_NOARGS, _Py_NULL},
+    {"test_uniquely_referenced", test_uniquely_referenced, METH_NOARGS, _Py_NULL},
     {_Py_NULL, _Py_NULL, 0, _Py_NULL}
 };
 
