https://github.com/python/cpython/commit/0533c1faf27d1e50b062bb623dfad93288757f57
commit: 0533c1faf27d1e50b062bb623dfad93288757f57
branch: main
author: Pieter Eendebak <[email protected]>
committer: kumaraditya303 <[email protected]>
date: 2025-06-30T16:36:58+05:30
summary:
gh-123471: Make itertools.chain thread-safe (#135689)
files:
A Misc/NEWS.d/next/Library/2025-06-18-19-25-32.gh-issue-123471.lx1Xbt.rst
M Lib/test/test_free_threading/test_itertools.py
M Modules/itertoolsmodule.c
diff --git a/Lib/test/test_free_threading/test_itertools.py
b/Lib/test/test_free_threading/test_itertools.py
index b8663ade1d4aca..9d366041917bb3 100644
--- a/Lib/test/test_free_threading/test_itertools.py
+++ b/Lib/test/test_free_threading/test_itertools.py
@@ -1,6 +1,6 @@
import unittest
from threading import Thread, Barrier
-from itertools import batched, cycle
+from itertools import batched, chain, cycle
from test.support import threading_helper
@@ -17,7 +17,7 @@ def work(it):
barrier.wait()
while True:
try:
- _ = next(it)
+ next(it)
except StopIteration:
break
@@ -62,6 +62,34 @@ def work(it):
barrier.reset()
+ @threading_helper.reap_threads
+ def test_chain(self):
+ number_of_threads = 6
+ number_of_iterations = 20
+
+ barrier = Barrier(number_of_threads)
+ def work(it):
+ barrier.wait()
+ while True:
+ try:
+ next(it)
+ except StopIteration:
+ break
+
+ data = [(1, )] * 200
+ for it in range(number_of_iterations):
+ chain_iterator = chain(*data)
+ worker_threads = []
+ for ii in range(number_of_threads):
+ worker_threads.append(
+ Thread(target=work, args=[chain_iterator]))
+
+ with threading_helper.start_threads(worker_threads):
+ pass
+
+ barrier.reset()
+
+
if __name__ == "__main__":
unittest.main()
diff --git
a/Misc/NEWS.d/next/Library/2025-06-18-19-25-32.gh-issue-123471.lx1Xbt.rst
b/Misc/NEWS.d/next/Library/2025-06-18-19-25-32.gh-issue-123471.lx1Xbt.rst
new file mode 100644
index 00000000000000..6f395024a9e179
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-06-18-19-25-32.gh-issue-123471.lx1Xbt.rst
@@ -0,0 +1 @@
+Make concurrent iterations over :class:`itertools.chain` safe under
:term:`free threading`.
diff --git a/Modules/itertoolsmodule.c b/Modules/itertoolsmodule.c
index 2003546ce84cef..e6536c250109b1 100644
--- a/Modules/itertoolsmodule.c
+++ b/Modules/itertoolsmodule.c
@@ -1880,8 +1880,8 @@ chain_traverse(PyObject *op, visitproc visit, void *arg)
return 0;
}
-static PyObject *
-chain_next(PyObject *op)
+static inline PyObject *
+chain_next_lock_held(PyObject *op)
{
chainobject *lz = chainobject_CAST(op);
PyObject *item;
@@ -1919,6 +1919,16 @@ chain_next(PyObject *op)
return NULL;
}
+static PyObject *
+chain_next(PyObject *op)
+{
+ PyObject *result;
+ Py_BEGIN_CRITICAL_SECTION(op);
+ result = chain_next_lock_held(op);
+ Py_END_CRITICAL_SECTION()
+ return result;
+}
+
PyDoc_STRVAR(chain_doc,
"chain(*iterables)\n\
--\n\
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