Python 3.9: AttributeError: Can't pickle local object 'TestSuite.__init__.<locals>.<lambda>'

[ligurio]

Traceback (most recent call last):
  File "/Users/tntmac01.tarantool.i/tarantool/build/test/../../test/test-run.py", line 235, in <module>
    status = main_parallel()
  File "/Users/tntmac01.tarantool.i/tarantool/build/test/../../test/test-run.py", line 150, in main_parallel
    res = main_loop_parallel()
  File "/Users/tntmac01.tarantool.i/tarantool/build/test/../../test/test-run.py", line 109, in main_loop_parallel
    dispatcher.start()
  File "/Users/tntmac01.tarantool.i/tarantool/test-run/dispatcher.py", line 165, in start
    self.run_max_workers()
  File "/Users/tntmac01.tarantool.i/tarantool/test-run/dispatcher.py", line 161, in run_max_workers
    ok = self.add_worker()
  File "/Users/tntmac01.tarantool.i/tarantool/test-run/dispatcher.py", line 214, in add_worker
    process = task_queue_disp.add_worker(self.worker_next_id,
  File "/Users/tntmac01.tarantool.i/tarantool/test-run/dispatcher.py", line 409, in add_worker
    process.start()
  File "/usr/local/Cellar/python@3.9/3.9.1_6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/process.py", line 121, in start
    self._popen = self._Popen(self)
  File "/usr/local/Cellar/python@3.9/3.9.1_6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/context.py", line 224, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.1_6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/context.py", line 284, in _Popen
    return Popen(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.1_6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/popen_spawn_posix.py", line 32, in __init__
    super().__init__(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.1_6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)
  File "/usr/local/Cellar/python@3.9/3.9.1_6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/popen_spawn_posix.py", line 47, in _launch
    reduction.dump(process_obj, fp)
  File "/usr/local/Cellar/python@3.9/3.9.1_6/Frameworks/Python.framework/Versions/3.9/lib/python3.9/multiprocessing/reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
AttributeError: Can't pickle local object 'TestSuite.__init__.<locals>.<lambda>'

Python 3.9 is default python3 interpreter on Mac OS.

Preliminary investigation:

spawn mode in multiprocessing module became default on mac https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods. One can force fork mode in multiprocessing module on mac but it may work unstable, see https://bugs.python.org/issue33725

To workaround it can be possible to force fork mode with multiprocessing.set_start_method('fork'), but Tarantool process start sometime failed before running tests.