threading.Thread fails to pickle in python > 3.13.0a5 #654
Description
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
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>>> 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)
>>>