https://github.com/python/cpython/commit/5236b0281b91a874b14cf15f3fdef9b7beffb22f
commit: 5236b0281b91a874b14cf15f3fdef9b7beffb22f
branch: main
author: Neil Schemenauer <nas-git...@arctrix.com>
committer: nascheme <nas-git...@arctrix.com>
date: 2025-07-30T02:44:10Z
summary:
GH-116738: document thread-safety of bisect (GH-136555)
files:
A Lib/test/test_free_threading/test_bisect.py
M Doc/library/bisect.rst
diff --git a/Doc/library/bisect.rst b/Doc/library/bisect.rst
index 78da563397b625..d02ffe469adb1a 100644
--- a/Doc/library/bisect.rst
+++ b/Doc/library/bisect.rst
@@ -24,6 +24,16 @@ method to determine whether a value has been found.
Instead, the
functions only call the :meth:`~object.__lt__` method and will return an
insertion
point between values in an array.
+.. note::
+
+ The functions in this module are not thread-safe. If multiple threads
+ concurrently use :mod:`bisect` functions on the same sequence, this
+ may result in undefined behaviour. Likewise, if the provided sequence
+ is mutated by a different thread while a :mod:`bisect` function
+ is operating on it, the result is undefined. For example, using
+ :py:func:`~bisect.insort_left` on the same list from multiple threads
+ may result in the list becoming unsorted.
+
.. _bisect functions:
The following functions are provided:
diff --git a/Lib/test/test_free_threading/test_bisect.py
b/Lib/test/test_free_threading/test_bisect.py
new file mode 100644
index 00000000000000..bd7732da035257
--- /dev/null
+++ b/Lib/test/test_free_threading/test_bisect.py
@@ -0,0 +1,56 @@
+import unittest
+from test.support import import_helper, threading_helper
+import random
+
+py_bisect = import_helper.import_fresh_module('bisect', blocked=['_bisect'])
+c_bisect = import_helper.import_fresh_module('bisect', fresh=['_bisect'])
+
+
+NTHREADS = 4
+OBJECT_COUNT = 500
+
+
+class TestBase:
+ def do_racing_insort(self, insert_method):
+ def insert(data):
+ for _ in range(OBJECT_COUNT):
+ x = random.randint(-OBJECT_COUNT, OBJECT_COUNT)
+ insert_method(data, x)
+
+ data = list(range(OBJECT_COUNT))
+ threading_helper.run_concurrently(
+ worker_func=insert, args=(data,), nthreads=NTHREADS
+ )
+ if False:
+ # These functions are not thread-safe and so the list can become
+ # unsorted. However, we don't want Python to crash if these
+ # functions are used concurrently on the same sequence. This
+ # should also not produce any TSAN warnings.
+ self.assertTrue(self.is_sorted_ascending(data))
+
+ def test_racing_insert_right(self):
+ self.do_racing_insort(self.mod.insort_right)
+
+ def test_racing_insert_left(self):
+ self.do_racing_insort(self.mod.insort_left)
+
+ @staticmethod
+ def is_sorted_ascending(lst):
+ """
+ Check if the list is sorted in ascending order (non-decreasing).
+ """
+ return all(lst[i - 1] <= lst[i] for i in range(1, len(lst)))
+
+
+@threading_helper.requires_working_threading()
+class TestPyBisect(unittest.TestCase, TestBase):
+ mod = py_bisect
+
+
+@threading_helper.requires_working_threading()
+class TestCBisect(unittest.TestCase, TestBase):
+ mod = c_bisect
+
+
+if __name__ == "__main__":
+ unittest.main()
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