https://github.com/python/cpython/commit/1d091a336e60b703a7d7ae4124f652eabe144f4e
commit: 1d091a336e60b703a7d7ae4124f652eabe144f4e
branch: main
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2026-03-06T12:01:06-05:00
summary:
gh-145566: Skip stop-the-world when reassigning `__class__` on newly created
objects (gh-145567)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-03-05-19-10-56.gh-issue-145566.H4RupyYN.rst
M Objects/typeobject.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-03-05-19-10-56.gh-issue-145566.H4RupyYN.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-03-05-19-10-56.gh-issue-145566.H4RupyYN.rst
new file mode 100644
index 00000000000000..723b81ddc5f897
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-03-05-19-10-56.gh-issue-145566.H4RupyYN.rst
@@ -0,0 +1,2 @@
+In the free threading build, skip the stop-the-world pause when reassigning
+``__class__`` on a newly created object.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 1fdd3cbdaaa639..27ec8bb40a929f 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -7568,7 +7568,11 @@ object_set_class_world_stopped(PyObject *self,
PyTypeObject *newto)
assert(_PyObject_GetManagedDict(self) == dict);
- if (_PyDict_DetachFromObject(dict, self) < 0) {
+ int err;
+ Py_BEGIN_CRITICAL_SECTION(dict);
+ err = _PyDict_DetachFromObject(dict, self);
+ Py_END_CRITICAL_SECTION();
+ if (err < 0) {
return -1;
}
@@ -7608,10 +7612,15 @@ object_set_class(PyObject *self, PyObject *value, void
*closure)
return -1;
}
- types_stop_world();
+ int unique = _PyObject_IsUniquelyReferenced(self);
+ if (!unique) {
+ types_stop_world();
+ }
PyTypeObject *oldto = Py_TYPE(self);
int res = object_set_class_world_stopped(self, newto);
- types_start_world();
+ if (!unique) {
+ types_start_world();
+ }
if (res == 0) {
if (oldto->tp_flags & Py_TPFLAGS_HEAPTYPE) {
Py_DECREF(oldto);
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