[3.14] gh-123471: Make concurrent iteration over `itertools.permutati…

…ons` and `itertools.combinations_with_replacement` thread-safe (gh-144402) (cherry picked from commit 009c8c0) Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>
nascheme · Jul 17, 2026 · Jun 2, 2025 · Jun 30, 2025 · Jun 30, 2025 · Feb 4, 2026
commit 98af9225dd6d49f0450544e6e09ee56fbc9e9153
@@ -2,7 +2,9 @@
 from threading import Thread, Barrier
 from itertools import (
     chain,
+    combinations_with_replacement,
     cycle,
+    permutations,
     tee,
 )
 from test.support import threading_helper
@@ -11,6 +13,14 @@
 threading_helper.requires_working_threading(module=True)
 
 
+def work_iterator(it):
+    while True:
+        try:
+            next(it)
+        except StopIteration:
+            break
+
+
 class ItertoolsThreading(unittest.TestCase):
 
     @threading_helper.reap_threads
@@ -65,6 +75,20 @@ def work(it):
 
             barrier.reset()
 
+    @threading_helper.reap_threads
+    def test_combinations_with_replacement(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = combinations_with_replacement(tuple(range(2)), 2)
+            threading_helper.run_concurrently(work_iterator, nthreads=6, args=[it])
+
+    @threading_helper.reap_threads
+    def test_permutations(self):
+        number_of_iterations = 6
+        for _ in range(number_of_iterations):
+            it = permutations(tuple(range(2)), 2)
+            threading_helper.run_concurrently(work_iterator, nthreads=6, args=[it])
+
 
 
 class TestTeeConcurrent(unittest.TestCase):

diff --git a/Misc/NEWS.d/next/Library/2026-02-03-08-50-58.gh-issue-123471.yF1Gym.rst b/Misc/NEWS.d/next/Library/2026-02-03-08-50-58.gh-issue-123471.yF1Gym.rst
@@ -0,0 +1 @@
+Make concurrent iteration over :class:`itertools.combinations_with_replacement` and :class:`itertools.permutations` safe under free-threading.
@@ -2684,7 +2684,7 @@ cwr_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-cwr_next(PyObject *op)
+cwr_next_lock_held(PyObject *op)
 {
     cwrobject *co = cwrobject_CAST(op);
     PyObject *elem;
@@ -2763,6 +2763,16 @@ cwr_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+cwr_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = cwr_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef cwr_methods[] = {
     {"__sizeof__", cwr_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */
@@ -2943,7 +2953,7 @@ permutations_traverse(PyObject *op, visitproc visit, void *arg)
 }
 
 static PyObject *
-permutations_next(PyObject *op)
+permutations_next_lock_held(PyObject *op)
 {
     permutationsobject *po = permutationsobject_CAST(op);
     PyObject *elem;
@@ -3033,6 +3043,16 @@ permutations_next(PyObject *op)
     return NULL;
 }
 
+static PyObject *
+permutations_next(PyObject *op)
+{
+    PyObject *result;
+    Py_BEGIN_CRITICAL_SECTION(op);
+    result = permutations_next_lock_held(op);
+    Py_END_CRITICAL_SECTION()
+    return result;
+}
+
 static PyMethodDef permuations_methods[] = {
     {"__sizeof__", permutations_sizeof, METH_NOARGS, sizeof_doc},
     {NULL,              NULL}   /* sentinel */
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Make concurrent iteration over :class:`itertools.combinations_with_replacement` and :class:`itertools.permutations` safe under free-threading.