https://github.com/python/cpython/commit/5d6e8dd683b25348bfe45f6321f9734868199a23 commit: 5d6e8dd683b25348bfe45f6321f9734868199a23 branch: main author: Shrey Naithani <[email protected]> committer: encukou <[email protected]> date: 2026-03-11T13:08:48+01:00 summary:
gh-145587: fix busy loop in multiprocessing.connection.wait on Windows (GH-145597) Ensure wait() blocks for the specified timeout when object_list is empty, preventing 100% CPU usage. This aligns the Windows behavior with the Unix implementation. Co-authored-by: AN Long <[email protected]> files: A Misc/NEWS.d/next/Library/2026-03-07-14-34-39.gh-issue-145587.flFQ5-.rst M Lib/multiprocessing/connection.py M Lib/test/_test_multiprocessing.py diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py index 41b36066c62fcb..9ce996c9ccd211 100644 --- a/Lib/multiprocessing/connection.py +++ b/Lib/multiprocessing/connection.py @@ -1085,14 +1085,22 @@ def wait(object_list, timeout=None): Returns list of those objects in object_list which are ready/readable. ''' + object_list = list(object_list) + + if not object_list: + if timeout is None: + while True: + time.sleep(1e6) + elif timeout > 0: + time.sleep(timeout) + return [] + if timeout is None: timeout = INFINITE elif timeout < 0: timeout = 0 else: timeout = int(timeout * 1000 + 0.5) - - object_list = list(object_list) waithandle_to_obj = {} ov_list = [] ready_objects = set() diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py index cc07062eee6f98..d67fd13fa33bed 100644 --- a/Lib/test/_test_multiprocessing.py +++ b/Lib/test/_test_multiprocessing.py @@ -3890,6 +3890,19 @@ def test_context(self): self.assertRaises(OSError, a.recv) self.assertRaises(OSError, b.recv) + @warnings_helper.ignore_fork_in_thread_deprecation_warnings() + def test_wait_empty(self): + if self.TYPE != 'processes': + self.skipTest('test not appropriate for {}'.format(self.TYPE)) + # gh-145587: wait() with empty list should respect timeout + timeout = 0.5 + start = time.monotonic() + res = self.connection.wait([], timeout=timeout) + duration = time.monotonic() - start + + self.assertEqual(res, []) + self.assertGreaterEqual(duration, timeout - 0.1) + class _TestListener(BaseTestCase): ALLOWED_TYPES = ('processes',) diff --git a/Misc/NEWS.d/next/Library/2026-03-07-14-34-39.gh-issue-145587.flFQ5-.rst b/Misc/NEWS.d/next/Library/2026-03-07-14-34-39.gh-issue-145587.flFQ5-.rst new file mode 100644 index 00000000000000..c17d01f36b8c64 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-03-07-14-34-39.gh-issue-145587.flFQ5-.rst @@ -0,0 +1 @@ +Resolved a performance regression in ``multiprocessing.connection.wait`` on Windows that caused infinite busy loops when called with no objects. The function now properly yields control to the OS to conserve CPU resources. Patch By Shrey Naithani _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
