gh-150505: Revert "fix data race in Unpickler_set_memo under free-threading"

Author: Ahmed Magdy Ali

Lib/test/test_pickle.py

@@ -17,7 +17,6 @@
 from test import support
 from test.support import cpython_only, import_helper, os_helper
 from test.support.import_helper import ensure_lazy_imports
-from test.support import threading_helper
 
 from test.pickletester import AbstractHookTests
 from test.pickletester import AbstractUnpickleTests
@@ -809,20 +808,6 @@ def test_unknown_flag(self):
         self.assertStartsWith(stderr.getvalue(), 'usage: ')
 
 
-class UnpicklerMemoThreadSafetyTest(unittest.TestCase):
-    @unittest.skipUnless(support.Py_GIL_DISABLED, 'this test can only possibly fail with GIL disabled')
-    @threading_helper.reap_threads
-    @threading_helper.requires_working_threading()
-    def test_memo_assignment_race(self):
-        from threading import Thread
-        shared = pickle.Unpickler(io.BytesIO(b''))
-        def assign():
-            for _ in range(10000):
-                shared.memo = {j: j for j in range(100)}
-        threads = [Thread(target=assign) for _ in range(8)]
-        for t in threads: t.start()
-        for t in threads: t.join()
-
 def load_tests(loader, tests, pattern):
     tests.addTest(doctest.DocTestSuite(pickle))
     return tests

Misc/NEWS.d/next/Library/2026-05-28-11-46-23.gh-issue-150505.avtcRy.rst

@@ -7786,38 +7786,24 @@ Unpickler_set_memo(PyObject *op, PyObject *obj, void *Py_UNUSED(closure))
         if (new_memo == NULL)
             return -1;
 
-        bool goto_error = false;
-        Py_BEGIN_CRITICAL_SECTION(self);
         while (PyDict_Next(obj, &i, &key, &value)) {
             Py_ssize_t idx;
             if (!PyLong_Check(key)) {
                 PyErr_SetString(PyExc_TypeError,
                                 "memo key must be integers");
-                goto_error = true;
-                break;
+                goto error;
             }
             idx = PyLong_AsSsize_t(key);
-            if (idx == -1 && PyErr_Occurred()) {
-                goto_error = true;
-                break;
-            }
+            if (idx == -1 && PyErr_Occurred())
+                goto error;
             if (idx < 0) {
                 PyErr_SetString(PyExc_ValueError,
                                 "memo key must be positive integers.");
-                goto_error = true;
-                break;
+                goto error;
             }
-
             if (_Unpickler_MemoPut(self, idx, value) < 0)
-            {
-                goto_error = true;
-                break;
-            }
+                goto error;
         }
-        Py_END_CRITICAL_SECTION();
-        if (goto_error)
-            goto error;
-
     }
     else {
         PyErr_Format(PyExc_TypeError,
@@ -7826,24 +7812,9 @@ Unpickler_set_memo(PyObject *op, PyObject *obj, void *Py_UNUSED(closure))
         return -1;
     }
 
-    Py_ssize_t old_memo_size, i;
-    PyObject **old_memo;
-
-    Py_BEGIN_CRITICAL_SECTION(self);
-    old_memo_size = self->memo_size;
-    old_memo = self->memo;
+    _Unpickler_MemoCleanup(self);
     self->memo_size = new_memo_size;
     self->memo = new_memo;
-    Py_END_CRITICAL_SECTION();
-
-    if (old_memo == NULL) {
-        return 0;
-    }
-    i = old_memo_size;
-    while (--i >= 0) {
-        Py_XDECREF(old_memo[i]);
-    }
-    PyMem_Free(old_memo);
 
     return 0;