concurrent.interpreters - buggy code leads to a crash during finalization

[bluetech]

Crash report

What happened?

I experimented a bit with concurrent.interpreters using Python 3.14.0b4 (uv installed version). The code is both wrong in the usage, and contains a typo - the line mv[0] = 1 refers to an unbound variable. But it crashes with a "Fatal Python error" which I think is something that should not be possible even for buggy programs (correct me if I'm wrong).

import time
from concurrent import interpreters

def sub(mv: memoryview):
    time.sleep(1)
    print(mv[0])

def main():
    buf = bytearray(1)
    interp = interpreters.create()
    t = interp.call_in_thread(sub, memoryview(buf))
    mv[0] = 1
    t.join()

main()

Output:

Traceback (most recent call last):
  File "/home/ran/test.py", line 15, in <module>
    main()
    ~~~~^^
  File "/home/ran/test.py", line 12, in main
    mv[0] = 1
    ^^
NameError: name 'mv' is not defined
Exception in thread Thread-1 (_call):
Exception: AttributeError: module '__main__' has no attribute 'sub'

The above exception was the direct cause of the following exception:

concurrent.interpreters.NotShareableError: object could not be unpickled

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/threading.py", line 1081, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/threading.py", line 1023, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/concurrent/interpreters/__init__.py", line 215, in _call
    res, excinfo = _interpreters.call(self._id, callable, args, kwargs, restrict=True)
                   ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
concurrent.interpreters.NotShareableError: func not shareable
Exception ignored while joining a thread in _thread._shutdown():
Traceback (most recent call last):
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/threading.py", line 1582, in _shutdown
    _thread_shutdown()
PythonFinalizationError: cannot join thread at interpreter shutdown
Fatal Python error: Py_EndInterpreter: not the last thread
Python runtime state: finalizing (tstate=0x0000000001b40a48)

Current thread 0x00007f27ee43d780 [python3.14] (most recent call first):
  <no Python frame>

Thread 0x00007f27ecd8b6c0 [Thread-1 (_call] (most recent call first):
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/concurrent/interpreters/__init__.py", line 215 in _call
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/threading.py", line 1023 in run
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/threading.py", line 1081 in _bootstrap_inner
  File "/home/ran/.local/share/uv/python/cpython-3.14.0b4-linux-x86_64-gnu/lib/python3.14/threading.py", line 1043 in _bootstrap
Aborted (core dumped)

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.14.0b4 (main, Jul 8 2025, 21:00:06) [Clang 20.1.4 ]

[ZeroIntensity]

Thanks for the report, this is a duplicate of #128639. Dangling threads in subinterpreters break finalization at the moment.