The mpubsub from flaviovs

"cannot pickle 'weakref.ReferenceType' object" on linux with start_method "spawn"

Hi, thank you for the tutorial and what looks to be a good library. However I can't get it to run on linux as long as mp.set_start_method('spawn') is used. I'm currently on python 3.12, but the same thing happens with a python 3.7 venv. It must be a plattform issue then? I can't figure out which object is being passed that is not pickleable. I tried refactoring the demo to remove all global variables, moving the subscriber and publisher functions into separate modules and removing all accesses to the logging library.
Do you have an Idea what might cause this? I'd like to stick with spawn instead of fork to not copy a large amount of global imports from the main into each process.

3.7:

2024-05-24 16:31:12,247 I MainProcess: Starting demo with 3 publishers and 3 subscribers
Traceback (most recent call last):
  File "demo.py", line 165, in <module>
    main()
  File "demo.py", line 137, in main
    broker_process.start()
  File "/usr/lib/python3.7/multiprocessing/process.py", line 112, in start
    self._popen = self._Popen(self)
  File "/usr/lib/python3.7/multiprocessing/context.py", line 223, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "/usr/lib/python3.7/multiprocessing/context.py", line 284, in _Popen
    return Popen(process_obj)
  File "/usr/lib/python3.7/multiprocessing/popen_spawn_posix.py", line 32, in __init__
    super().__init__(process_obj)
  File "/usr/lib/python3.7/multiprocessing/popen_fork.py", line 20, in __init__
    self._launch(process_obj)
  File "/usr/lib/python3.7/multiprocessing/popen_spawn_posix.py", line 47, in _launch
    reduction.dump(process_obj, fp)
  File "/usr/lib/python3.7/multiprocessing/reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
TypeError: can't pickle weakref objects

3.12:

2024-05-24 16:36:40,439 I MainProcess: Starting demo with 3 publishers and 3 subscribers
Traceback (most recent call last):
  File "/home/h3po/git/github/mpubsub/src/demo.py", line 165, in <module>
    main()
  File "/home/h3po/git/github/mpubsub/src/demo.py", line 137, in main
    broker_process.start()
  File "/usr/lib/python3.12/multiprocessing/process.py", line 121, in start
    self._popen = self._Popen(self)
                  ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/multiprocessing/context.py", line 224, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/multiprocessing/context.py", line 289, in _Popen
    return Popen(process_obj)
           ^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/multiprocessing/popen_spawn_posix.py", line 32, in __init__
    super().__init__(process_obj)
  File "/usr/lib/python3.12/multiprocessing/popen_fork.py", line 19, in __init__
    self._launch(process_obj)
  File "/usr/lib/python3.12/multiprocessing/popen_spawn_posix.py", line 47, in _launch
    reduction.dump(process_obj, fp)
  File "/usr/lib/python3.12/multiprocessing/reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
TypeError: cannot pickle 'weakref.ReferenceType' object

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"cannot pickle 'weakref.ReferenceType' object" on linux with start_method "spawn"

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