python-s3transfer fails to build with Python 3.14.0a1.

=================================== FAILURES ===================================
____ TestBaseManager.test_can_provide_signal_handler_initializers_to_start _____

self = <tests.unit.test_compat.TestBaseManager testMethod=test_can_provide_signal_handler_initializers_to_start>

    @skip_if_windows('os.kill() with SIGINT not supported on Windows')
    def test_can_provide_signal_handler_initializers_to_start(self):
        manager = self.create_pid_manager()
>       manager.start(signal.signal, (signal.SIGINT, signal.SIG_IGN))

tests/unit/test_compat.py:97: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/usr/lib64/python3.14/multiprocessing/managers.py:565: in start
    self._process.start()
/usr/lib64/python3.14/multiprocessing/process.py:121: in start
    self._popen = self._Popen(self)
/usr/lib64/python3.14/multiprocessing/context.py:300: in _Popen
    return Popen(process_obj)
/usr/lib64/python3.14/multiprocessing/popen_forkserver.py:35: in __init__
    super().__init__(process_obj)
/usr/lib64/python3.14/multiprocessing/popen_fork.py:20: in __init__
    self._launch(process_obj)
/usr/lib64/python3.14/multiprocessing/popen_forkserver.py:47: in _launch
    reduction.dump(process_obj, buf)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

obj = <ForkServerProcess name='PIDManager-1' parent=367 initial>
file = <_io.BytesIO object at 0x7f2b60580630>, protocol = None

    def dump(obj, file, protocol=None):
        '''Replacement for pickle.dump() using ForkingPickler.'''
>       ForkingPickler(file, protocol).dump(obj)
E       _pickle.PicklingError: Can't pickle local object <class 'tests.unit.test_compat.TestBaseManager.create_pid_manager.<locals>.PIDManager'>
E       when serializing tuple item 0
E       when serializing method reconstructor arguments
E       when serializing method object
E       when serializing dict item '_target'
E       when serializing multiprocessing.context.ForkServerProcess state
E       when serializing multiprocessing.context.ForkServerProcess object

/usr/lib64/python3.14/multiprocessing/reduction.py:60: PicklingError


According to https://docs.python.org/dev/whatsnew/3.14.html#multiprocessing

The default start method (see Contexts and start methods) changed from fork to forkserver on platforms other than macOS & Windows where it was already spawn. If you require the threading incompatible fork start method you must explicitly request it using a context from multiprocessing.get_context() (preferred) or change the default via multiprocessing.set_start_method(). (Contributed by Gregory P. Smith in gh-84559.)


https://docs.python.org/3.14/whatsnew/3.14.html

For the build logs, see:
https://copr-be.cloud.fedoraproject.org/results/@python/python3.14/fedora-rawhide-x86_64/08258985-python-s3transfer/

For all our attempts to build python-s3transfer with Python 3.14, see:
https://copr.fedorainfracloud.org/coprs/g/python/python3.14/package/python-s3transfer/

Testing and mass rebuild of packages is happening in copr.
You can follow these instructions to test locally in mock if your package builds with Python 3.14:
https://copr.fedorainfracloud.org/coprs/g/python/python3.14/

Let us know here if you have any questions.

Python 3.14 is planned to be included in Fedora 43.
To make that update smoother, we're building Fedora packages with all pre-releases of Python 3.14.
A build failure prevents us from testing all dependent packages (transitive [Build]Requires),
so if this package is required a lot, it's important for us to get it fixed soon.

We'd appreciate help from the people who know this package best,
but if you don't want to work on this now, let us know so we can try to work around it on our side.