threading.Thread fails to pickle in python > 3.13.0a5

[mmckerns]

Starting in python 3.13.0a5, a threading.Thread instance is not serializable. This is due to the thread attribute pointing to an unserializable _thread._ThreadHandle instance, where in earlier versions the _thread instance pointed to None. Deleting the _ThreadHandle enables the Thread to be serializable again. Presumably, there's a good way to obtain an appropriate thread handle from the thread or using the threading module.

Python 3.13.0a5 (main, Mar 16 2024, 18:36:37) [Clang 14.0.0 (clang-1400.0.29.202)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import threading
>>> t = threading.Thread()
>>> t.start()
>>> import dill
>>> dill.dumps(t)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    dill.dumps(t)
    ~~~~~~~~~~^^^
  File "/Users/mmckerns/lib/python3.13/site-packages/dill/_dill.py", line 280, in dumps
    dump(obj, file, protocol, byref, fmode, recurse, **kwds)#, strictio)
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/mmckerns/lib/python3.13/site-packages/dill/_dill.py", line 252, in dump
    Pickler(file, protocol, **_kwds).dump(obj)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "/Users/mmckerns/lib/python3.13/site-packages/dill/_dill.py", line 420, in dump
    StockPickler.dump(self, obj)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 483, in dump
    self.save(obj)
    ~~~~~~~~~^^^^^
  File "/Users/mmckerns/lib/python3.13/site-packages/dill/_dill.py", line 414, in save
    StockPickler.save(self, obj, save_persistent_id)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 599, in save
    self.save_reduce(obj=obj, *rv)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 713, in save_reduce
    save(state)
    ~~~~^^^^^^^
  File "/Users/mmckerns/lib/python3.13/site-packages/dill/_dill.py", line 414, in save
    StockPickler.save(self, obj, save_persistent_id)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 556, in save
    f(self, obj)  # Call unbound method with explicit self
    ~^^^^^^^^^^^
  File "/Users/mmckerns/lib/python3.13/site-packages/dill/_dill.py", line 1217, in save_module_dict
    StockPickler.save_dict(pickler, obj)
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 968, in save_dict
    self._batch_setitems(obj.items())
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 992, in _batch_setitems
    save(v)
    ~~~~^^^
  File "/Users/mmckerns/lib/python3.13/site-packages/dill/_dill.py", line 414, in save
    StockPickler.save(self, obj, save_persistent_id)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/pickle.py", line 574, in save
    rv = reduce(self.proto)
         ~~~~~~^^^^^^^^^^^^
TypeError: cannot pickle '_thread._ThreadHandle' object
>>> t.__dict__
{'_name': 'Thread-1', '_daemonic': False, '_ident': 123145514024960, '_native_id': 9483263, '_tstate_lock': <unlocked _thread.lock object at 0x1107a61c0>, '_handle': <_thread._ThreadHandle object: ident=123145514024960>, '_started': <threading.Event at 0x10fdfdf10: set>, '_is_stopped': False, '_initialized': True, '_stderr': <_io.TextIOWrapper name='<stderr>' mode='w' encoding='utf-8'>, '_invoke_excepthook': <function _make_invoke_excepthook.<locals>.invoke_excepthook at 0x110772ca0>}
>>> t._handle = None
>>> pt = dill.dumps(t)
>>> _t = dill.loads(pt)
>>>

[mmckerns]

while it's not directly related, might be an opportunity to deal with objects in #334