https://github.com/python/cpython/commit/57a0e570d36f41b953a91bbaf4262a5d05d0391b
commit: 57a0e570d36f41b953a91bbaf4262a5d05d0391b
branch: main
author: Saul Cooperman <[email protected]>
committer: JelleZijlstra <[email protected]>
date: 2026-05-18T16:26:08-07:00
summary:
gh-146452: Improve locking granularity in pickle's batch_dict_exact and fix
race condition (#150025)
Remove assertion that could fail in rare race condition.
Replace the coarse critical section wrapping the entire function with
fine-grained sections covering only PyDict_Next + Py_INCREF.
Also handle PyDict_Next returning 0 in the single-item fast path.
files:
A Misc/NEWS.d/next/Library/2026-05-18-15-30-34.gh-issue-146452.RM0EVJ.rst
M Modules/_pickle.c
diff --git
a/Misc/NEWS.d/next/Library/2026-05-18-15-30-34.gh-issue-146452.RM0EVJ.rst
b/Misc/NEWS.d/next/Library/2026-05-18-15-30-34.gh-issue-146452.RM0EVJ.rst
new file mode 100644
index 00000000000000..66f9acf6c710a7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-05-18-15-30-34.gh-issue-146452.RM0EVJ.rst
@@ -0,0 +1,2 @@
+Fix race condition when pickling dictionaries in free threaded builds. Also
+reduce critical section cover.
diff --git a/Modules/_pickle.c b/Modules/_pickle.c
index 7b87be23269d40..15d95c658d6f90 100644
--- a/Modules/_pickle.c
+++ b/Modules/_pickle.c
@@ -3450,9 +3450,12 @@ batch_dict(PickleState *state, PicklerObject *self,
PyObject *iter, PyObject *or
* Returns 0 on success, -1 on error.
*
* Note that this currently doesn't work for protocol 0.
+
+ * gh-146452: Wrap the dict iteration in a critical sections to prevent
+ * concurrent mutation from invalidating PyDict_Next() iteration state.
*/
static int
-batch_dict_exact_impl(PickleState *state, PicklerObject *self, PyObject *obj)
+batch_dict_exact(PickleState *state, PicklerObject *self, PyObject *obj)
{
PyObject *key = NULL, *value = NULL;
int i;
@@ -3466,15 +3469,24 @@ batch_dict_exact_impl(PickleState *state, PicklerObject
*self, PyObject *obj)
assert(self->proto > 0);
dict_size = PyDict_GET_SIZE(obj);
- assert(dict_size);
/* Write in batches of BATCHSIZE. */
Py_ssize_t total = 0;
do {
if (dict_size - total == 1) {
- PyDict_Next(obj, &ppos, &key, &value);
- Py_INCREF(key);
- Py_INCREF(value);
+ int next;
+ Py_BEGIN_CRITICAL_SECTION(obj);
+ next = PyDict_Next(obj, &ppos, &key, &value);
+ if (next) {
+ Py_INCREF(key);
+ Py_INCREF(value);
+ }
+ Py_END_CRITICAL_SECTION();
+ if (!next) {
+ PyErr_SetString(PyExc_RuntimeError,
+ "dictionary changed size during iteration");
+ goto error;
+ }
if (save(state, self, key, 0) < 0) {
goto error;
}
@@ -3492,9 +3504,18 @@ batch_dict_exact_impl(PickleState *state, PicklerObject
*self, PyObject *obj)
i = 0;
if (_Pickler_Write(self, &mark_op, 1) < 0)
return -1;
- while (PyDict_Next(obj, &ppos, &key, &value)) {
- Py_INCREF(key);
- Py_INCREF(value);
+ int next;
+ while (1) {
+ Py_BEGIN_CRITICAL_SECTION(obj);
+ next = PyDict_Next(obj, &ppos, &key, &value);
+ if (next) {
+ Py_INCREF(key);
+ Py_INCREF(value);
+ }
+ Py_END_CRITICAL_SECTION();
+ if (!next) {
+ break;
+ }
if (save(state, self, key, 0) < 0) {
goto error;
}
@@ -3525,18 +3546,6 @@ batch_dict_exact_impl(PickleState *state, PicklerObject
*self, PyObject *obj)
return -1;
}
-/* gh-146452: Wrap the dict iteration in a critical section to prevent
- concurrent mutation from invalidating PyDict_Next() iteration state. */
-static int
-batch_dict_exact(PickleState *state, PicklerObject *self, PyObject *obj)
-{
- int ret;
- Py_BEGIN_CRITICAL_SECTION(obj);
- ret = batch_dict_exact_impl(state, self, obj);
- Py_END_CRITICAL_SECTION();
- return ret;
-}
-
static int
save_dict(PickleState *state, PicklerObject *self, PyObject *obj)
{
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