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gh-123471: Make concurrent iteration over itertools.accumulate thread-safe #144486

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gh-123471: Make concurrent iteration over itertools.accumulate thread-safe #144486

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e77b639
Make accumulate thread-safe
eendebakpt Feb 3, 2026
2621b88
add ft test for accumulate
eendebakpt Feb 4, 2026
bd4fa04
reduce test duration
eendebakpt Feb 4, 2026
124450b
📜🤖 Added by blurb_it.
blurb-it[bot] Feb 4, 2026
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9 changes: 8 additions & 1 deletion Lib/test/test_free_threading/test_itertools.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
import unittest
from itertools import batched, chain, combinations_with_replacement, cycle, permutations
from itertools import accumulate, batched, chain, combinations_with_replacement, cycle, permutations
from test.support import threading_helper


Expand All @@ -16,6 +16,13 @@ def work_iterator(it):

class ItertoolsThreading(unittest.TestCase):

@threading_helper.reap_threads
def test_accumulate(self):
number_of_iterations = 10
for _ in range(number_of_iterations):
it = accumulate(tuple(range(40)))
threading_helper.run_concurrently(work_iterator, nthreads=10, args=[it])

@threading_helper.reap_threads
def test_batched(self):
number_of_iterations = 10
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2026-02-04-20-30-59.gh-issue-123471.1dnPvs.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Make concurrent iteration over :class:`itertools.accumulate` safe under free-threading.
12 changes: 11 additions & 1 deletion Modules/itertoolsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3063,7 +3063,7 @@ accumulate_traverse(PyObject *op, visitproc visit, void *arg)
}

static PyObject *
accumulate_next(PyObject *op)
accumulate_next_lock_held(PyObject *op)
{
accumulateobject *lz = accumulateobject_CAST(op);
PyObject *val, *newtotal;
Expand Down Expand Up @@ -3095,6 +3095,16 @@ accumulate_next(PyObject *op)
return newtotal;
}

static PyObject *
accumulate_next(PyObject *op)
{
PyObject *result;
Py_BEGIN_CRITICAL_SECTION(op);
result = accumulate_next_lock_held(op);
Py_END_CRITICAL_SECTION()
return result;
}

static PyType_Slot accumulate_slots[] = {
{Py_tp_dealloc, accumulate_dealloc},
{Py_tp_getattro, PyObject_GenericGetAttr},
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