[3.15] gh-151218: Replace sys.flags in PyConfig_Set() (GH-151402) (#151552)
gh-151218: Replace sys.flags in PyConfig_Set() (GH-151402)
PyConfig_Set() and sys.set_int_max_str_digits() now replace
sys.flags (create a new object), instead of modifying sys.flags in-place.
Modifying sys.flags in-place can lead to data races when multiple
threads are reading or writing sys.flags in parallel.
Use _Py_atomic functions to get and set max_str_digits members.
(cherry picked from commit b16d23fc9fe9cb72fa15c8a3036753e5437b5b8c)
Co-authored-by: Victor Stinner <vstinner@python.org>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
diff --git a/Doc/c-api/init_config.rst b/Doc/c-api/init_config.rst
index 209e487..d6b9837 100644
--- a/Doc/c-api/init_config.rst
+++ b/Doc/c-api/init_config.rst
@@ -623,6 +623,10 @@
.. versionadded:: 3.14
+ .. versionchanged:: next
+ The function now replaces :data:`sys.flags` (create a new object),
+ instead of modifying :data:`sys.flags` in-place.
+
.. _pyconfig_api:
diff --git a/Lib/test/test_capi/test_config.py b/Lib/test/test_capi/test_config.py
index f10ad50..c750a6c 100644
--- a/Lib/test/test_capi/test_config.py
+++ b/Lib/test/test_capi/test_config.py
@@ -356,9 +356,11 @@ def expect_bool_not(value):
for value in new_values:
expected, expect_flag = expect_func(value)
+ old_flags = sys.flags
config_set(name, value)
self.assertEqual(config_get(name), expected)
self.assertEqual(getattr(sys.flags, sys_flag), expect_flag)
+ self.assertIsNot(sys.flags, old_flags)
if name == "write_bytecode":
self.assertEqual(getattr(sys, "dont_write_bytecode"),
expect_flag)
diff --git a/Lib/test/test_free_threading/test_sys.py b/Lib/test/test_free_threading/test_sys.py
new file mode 100644
index 0000000..37b53bd
--- /dev/null
+++ b/Lib/test/test_free_threading/test_sys.py
@@ -0,0 +1,28 @@
+import sys
+import unittest
+from test.support import threading_helper
+
+
+class SysModuleTest(unittest.TestCase):
+ def test_int_max_str_digits_thread(self):
+ # gh-151218: Check that it's safe to call get_int_max_str_digits() and
+ # set_int_max_str_digits() in parallel. Previously, this test triggered
+ # warnings in TSan on a free threaded build.
+
+ old_limit = sys.get_int_max_str_digits()
+ self.addCleanup(sys.set_int_max_str_digits, old_limit)
+
+ def worker(worker_id):
+ if not worker_id:
+ for i in range (20_000):
+ sys.get_int_max_str_digits()
+ else:
+ for i in range (20_000):
+ sys.set_int_max_str_digits(4300 + (i & 7))
+
+ workers = [lambda: worker(i) for i in range(5)]
+ threading_helper.run_concurrently(workers)
+
+
+if __name__ == "__main__":
+ unittest.main()
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 3002fa5..8be7e50 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -1359,6 +1359,26 @@ def test_pystats(self):
def test_disable_gil_abi(self):
self.assertEqual('t' in sys.abiflags, support.Py_GIL_DISABLED)
+ def test_int_max_str_digits(self):
+ old_limit = sys.get_int_max_str_digits()
+ self.assertIsInstance(old_limit, int)
+ self.assertGreaterEqual(old_limit, 0)
+ self.addCleanup(sys.set_int_max_str_digits, old_limit)
+
+ sys.set_int_max_str_digits(0)
+ self.assertEqual(sys.get_int_max_str_digits(), 0)
+
+ sys.set_int_max_str_digits(2_048)
+ self.assertEqual(sys.get_int_max_str_digits(), 2_048)
+
+ with self.assertRaises(ValueError):
+ # the minimum is 640 digits
+ sys.set_int_max_str_digits(5)
+ with self.assertRaises(ValueError):
+ sys.set_int_max_str_digits(-2)
+ with self.assertRaises(TypeError):
+ sys.set_int_max_str_digits(2_048.0)
+
@test.support.cpython_only
@test.support.force_not_colorized_test_class
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-06-12-15-30-25.gh-issue-151218.5M_nv8.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-12-15-30-25.gh-issue-151218.5M_nv8.rst
new file mode 100644
index 0000000..46539ef
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-12-15-30-25.gh-issue-151218.5M_nv8.rst
@@ -0,0 +1,3 @@
+:c:func:`PyConfig_Set` and :func:`sys.set_int_max_str_digits` now replace
+:data:`sys.flags` (create a new object), instead of modifying :data:`sys.flags`
+in-place. Patch by Victor Stinner.
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 6e6011c..7a38ae8 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -2125,7 +2125,7 @@ long_to_decimal_string_internal(PyObject *aa,
if (size_a >= 10 * _PY_LONG_MAX_STR_DIGITS_THRESHOLD
/ (3 * PyLong_SHIFT) + 2) {
PyInterpreterState *interp = _PyInterpreterState_GET();
- int max_str_digits = interp->long_state.max_str_digits;
+ int max_str_digits = _Py_atomic_load_int(&interp->long_state.max_str_digits);
if ((max_str_digits > 0) &&
(max_str_digits / (3 * PyLong_SHIFT) <= (size_a - 11) / 10)) {
PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_STR,
@@ -2206,7 +2206,7 @@ long_to_decimal_string_internal(PyObject *aa,
}
if (strlen > _PY_LONG_MAX_STR_DIGITS_THRESHOLD) {
PyInterpreterState *interp = _PyInterpreterState_GET();
- int max_str_digits = interp->long_state.max_str_digits;
+ int max_str_digits = _Py_atomic_load_int(&interp->long_state.max_str_digits);
Py_ssize_t strlen_nosign = strlen - negative;
if ((max_str_digits > 0) && (strlen_nosign > max_str_digits)) {
Py_DECREF(scratch);
@@ -3021,7 +3021,7 @@ long_from_string_base(const char **str, int base, PyLongObject **res)
* quadratic algorithm. */
if (digits > _PY_LONG_MAX_STR_DIGITS_THRESHOLD) {
PyInterpreterState *interp = _PyInterpreterState_GET();
- int max_str_digits = interp->long_state.max_str_digits;
+ int max_str_digits = _Py_atomic_load_int(&interp->long_state.max_str_digits);
if ((max_str_digits > 0) && (digits > max_str_digits)) {
PyErr_Format(PyExc_ValueError, _MAX_STR_DIGITS_ERROR_FMT_TO_INT,
max_str_digits, digits);
diff --git a/Python/initconfig.c b/Python/initconfig.c
index bebadcc..185b5b1 100644
--- a/Python/initconfig.c
+++ b/Python/initconfig.c
@@ -4596,7 +4596,8 @@ config_get(const PyConfig *config, const PyConfigSpec *spec,
if (strcmp(spec->name, "int_max_str_digits") == 0) {
PyInterpreterState *interp = _PyInterpreterState_GET();
- return PyLong_FromLong(interp->long_state.max_str_digits);
+ int maxdigits = _Py_atomic_load_int(&interp->long_state.max_str_digits);
+ return PyLong_FromLong(maxdigits);
}
}
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 3113324..3933c32 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -428,7 +428,8 @@ interpreter_update_config(PyThreadState *tstate, int only_update_path_config)
}
}
- tstate->interp->long_state.max_str_digits = config->int_max_str_digits;
+ _Py_atomic_store_int(&tstate->interp->long_state.max_str_digits,
+ config->int_max_str_digits);
// Update the sys module for the new configuration
if (_PySys_UpdateConfig(tstate) < 0) {
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index b79ebf5..aa9ff9e 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -1904,7 +1904,8 @@ sys_get_int_max_str_digits_impl(PyObject *module)
/*[clinic end generated code: output=0042f5e8ae0e8631 input=77fb74e987ba7ecb]*/
{
PyInterpreterState *interp = _PyInterpreterState_GET();
- return PyLong_FromLong(interp->long_state.max_str_digits);
+ int maxdigits = _Py_atomic_load_int(&interp->long_state.max_str_digits);
+ return PyLong_FromLong(maxdigits);
}
@@ -3528,14 +3529,39 @@ sys_set_flag(PyObject *flags, Py_ssize_t pos, PyObject *value)
int
_PySys_SetFlagObj(Py_ssize_t pos, PyObject *value)
{
- PyObject *flags = PySys_GetAttrString("flags");
- if (flags == NULL) {
- return -1;
+ PyObject *new_flags = NULL;
+ PyObject *flags_str = &_Py_ID(flags); // immortal ref
+
+ PyObject *old_flags = PySys_GetAttr(flags_str);
+ if (old_flags == NULL) {
+ goto error;
}
- sys_set_flag(flags, pos, value);
- Py_DECREF(flags);
- return 0;
+ new_flags = PyStructSequence_New(&FlagsType);
+ if (new_flags == NULL) {
+ goto error;
+ }
+
+ for (Py_ssize_t i = 0; i < (Py_ssize_t)(Py_ARRAY_LENGTH(flags_fields) - 1); i++) {
+ if (i != pos) {
+ PyObject *old_value;
+ old_value = PyStructSequence_GET_ITEM(old_flags, i); // borrowed ref
+ sys_set_flag(new_flags, i, old_value);
+ }
+ else {
+ sys_set_flag(new_flags, pos, value);
+ }
+ }
+
+ int res = _PySys_SetAttr(flags_str, new_flags);
+ Py_DECREF(old_flags);
+ Py_DECREF(new_flags);
+ return res;
+
+error:
+ Py_XDECREF(old_flags);
+ Py_XDECREF(new_flags);
+ return -1;
}
@@ -3559,8 +3585,6 @@ set_flags_from_config(PyInterpreterState *interp, PyObject *flags)
const PyPreConfig *preconfig = &interp->runtime->preconfig;
const PyConfig *config = _PyInterpreterState_GetConfig(interp);
- // _PySys_UpdateConfig() modifies sys.flags in-place:
- // Py_XDECREF() is needed in this case.
Py_ssize_t pos = 0;
#define SetFlagObj(expr) \
do { \
@@ -4071,7 +4095,7 @@ _PySys_InitCore(PyThreadState *tstate, PyObject *sysdict)
/* implementation */
SET_SYS("implementation", make_impl_info(version_info));
- // sys.flags: updated in-place later by _PySys_UpdateConfig()
+ // sys.flags: updated later by _PySys_UpdateConfig()
ENSURE_INFO_TYPE(FlagsType, flags_desc);
SET_SYS("flags", make_flags(tstate->interp));
@@ -4191,16 +4215,21 @@ _PySys_UpdateConfig(PyThreadState *tstate)
#undef COPY_LIST
#undef COPY_WSTR
- // sys.flags
- PyObject *flags = PySys_GetAttrString("flags");
- if (flags == NULL) {
+ // replace sys.flags
+ PyObject *new_flags = PyStructSequence_New(&FlagsType);
+ if (new_flags == NULL) {
return -1;
}
- if (set_flags_from_config(interp, flags) < 0) {
- Py_DECREF(flags);
+ if (set_flags_from_config(interp, new_flags) < 0) {
+ Py_DECREF(new_flags);
return -1;
}
- Py_DECREF(flags);
+
+ res = _PySys_SetAttr(&_Py_ID(flags), new_flags);
+ Py_DECREF(new_flags);
+ if (res < 0) {
+ return -1;
+ }
SET_SYS("dont_write_bytecode", PyBool_FromLong(!config->write_bytecode));
@@ -4713,7 +4742,7 @@ _PySys_SetIntMaxStrDigits(int maxdigits)
// Set PyInterpreterState.long_state.max_str_digits
// and PyInterpreterState.config.int_max_str_digits.
PyInterpreterState *interp = _PyInterpreterState_GET();
- interp->long_state.max_str_digits = maxdigits;
- interp->config.int_max_str_digits = maxdigits;
+ _Py_atomic_store_int(&interp->long_state.max_str_digits, maxdigits);
+ _Py_atomic_store_int(&interp->config.int_max_str_digits, maxdigits);
return 0;
}
