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See https://dev.azure.com/Python/cpython/_build/results?buildId=53812&view=ms.vss-test-web.build-test-results-tab
Traceback (most recent call last):
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/unittest/case.py", line 60, in testPartExecutor
 yield
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/unittest/case.py", line 659, in run
 self._callTestMethod(testMethod)
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/unittest/case.py", line 616, in _callTestMethod
 method()
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/test/test_fcntl.py", line 149, in test_lockf_exclusive
 p.start()
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/multiprocessing/process.py", line 121, in start
 self._popen = self._Popen(self)
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/multiprocessing/context.py", line 224, in _Popen
 return _default_context.get_context().Process._Popen(process_obj)
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/multiprocessing/context.py", line 283, in _Popen
 return Popen(process_obj)
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/multiprocessing/popen_spawn_posix.py", line 32, in __init__
 super().__init__(process_obj)
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/multiprocessing/popen_fork.py", line 19, in __init__
 self._launch(process_obj)
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/multiprocessing/popen_spawn_posix.py", line 47, in _launch
 reduction.dump(process_obj, fp)
 File "/Users/runner/runners/2.160.0/work/1/s/Lib/multiprocessing/reduction.py", line 60, in dump
 ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'TestFcntl.test_lockf_exclusive.<locals>.try_lockf_on_other_process'

This issue was reported from victor
See https://bugs.python.org/msg356607
And I attached the patch for this on GH 17154.
Please take a look at the patch also.
I apologize for the trouble as the original test code author.

This cause of failure PR 17010 was due to change of start methods as follows:
https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods
Changed in version 3.8: On macOS, the spawn start method is now the default. The fork start method should be considered unsafe as it can lead to crashes of the subprocess. See bpo-33725.
So I updated the test through PR 17154 and I check that my local mac machine works well. (I did not check it on my local mac machine when I submitted PR 17010 since open description lock was Linux feature, this was my mistake)
And thanks to the tip from Michael Felt, I update the test to skip on the AIX machine. So I expect that when PR 17154 is landed, everything will go well.