diff --git a/Lib/test/test_free_threading/test_set.py b/Lib/test/test_free_threading/test_set.py new file mode 100644 index 00000000000000..a66e03bcc4c9d1 --- /dev/null +++ b/Lib/test/test_free_threading/test_set.py @@ -0,0 +1,41 @@ +import unittest + +from threading import Thread, Barrier +from unittest import TestCase + +from test.support import threading_helper + + +@threading_helper.requires_working_threading() +class TestSet(TestCase): + def test_repr_clear(self): + """Test repr() of a set while another thread is calling clear()""" + NUM_ITERS = 10 + NUM_REPR_THREADS = 10 + barrier = Barrier(NUM_REPR_THREADS + 1) + s = {1, 2, 3, 4, 5, 6, 7, 8} + + def clear_set(): + barrier.wait() + s.clear() + + def repr_set(): + barrier.wait() + set_reprs.append(repr(s)) + + for _ in range(NUM_ITERS): + set_reprs = [] + threads = [Thread(target=clear_set)] + for _ in range(NUM_REPR_THREADS): + threads.append(Thread(target=repr_set)) + for t in threads: + t.start() + for t in threads: + t.join() + + for set_repr in set_reprs: + self.assertIn(set_repr, ("set()", "{1, 2, 3, 4, 5, 6, 7, 8}")) + + +if __name__ == "__main__": + unittest.main() diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-02-10-20-01-56.gh-issue-129967.J60tEl.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-10-20-01-56.gh-issue-129967.J60tEl.rst new file mode 100644 index 00000000000000..69ec03d2ae3824 --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-02-10-20-01-56.gh-issue-129967.J60tEl.rst @@ -0,0 +1,2 @@ +Fix a race condition in the :term:`free threading` build when ``repr(set)`` +is called concurrently with ``set.clear()``. diff --git a/Objects/setobject.c b/Objects/setobject.c index 26ab352ca6d989..1978ae2b165d18 100644 --- a/Objects/setobject.c +++ b/Objects/setobject.c @@ -535,9 +535,18 @@ set_repr_lock_held(PySetObject *so) return PyUnicode_FromFormat("%s()", Py_TYPE(so)->tp_name); } - keys = PySequence_List((PyObject *)so); - if (keys == NULL) + // gh-129967: avoid PySequence_List because it might re-lock the object + // lock or the GIL and allow something to clear the set from underneath us. + keys = PyList_New(so->used); + if (keys == NULL) { goto done; + } + + Py_ssize_t pos = 0, idx = 0; + setentry *entry; + while (set_next(so, &pos, &entry)) { + PyList_SET_ITEM(keys, idx++, Py_NewRef(entry->key)); + } /* repr(keys)[1:-1] */ listrepr = PyObject_Repr(keys);