gh-123471: Make concurrent iteration over itertools.repeat safe under free-threading...

diff --git a/Misc/NEWS.d/next/Library/2025-03-14-14-18-49.gh-issue-123471.sduBKk.rst b/Misc/NEWS.d/next/Library/2025-03-14-14-18-49.gh-issue-123471.sduBKk.rst
new file mode 100644 (file)
index 0000000..b3829c7
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-03-14-14-18-49.gh-issue-123471.sduBKk.rst
@@ -0,0 +1 @@
+Make concurrent iterations over :class:`itertools.repeat` safe under free-threading.

diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index c0448efed19a443e3bedd36838a48904117e81d8..943c1e8607b38ffff505b4a8b5675b30db5972f5 100644 (file)
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -3628,10 +3628,14 @@ static PyObject *
 repeat_next(PyObject *op)
 {
     repeatobject *ro = repeatobject_CAST(op);
-    if (ro->cnt == 0)
+    Py_ssize_t cnt = FT_ATOMIC_LOAD_SSIZE_RELAXED(ro->cnt);
+    if (cnt == 0) {
         return NULL;
-    if (ro->cnt > 0)
-        ro->cnt--;
+    }
+    if (cnt > 0) {
+        cnt--;
+        FT_ATOMIC_STORE_SSIZE_RELAXED(ro->cnt, cnt);
+    }
     return Py_NewRef(ro->element);
 }