gh-132719: Skip multiprocessing test if missing ctypes

[vstinner]

Skip test_lock_locked_2processes() if multiprocessing.sharedctypes is missing (need ctypes).

• Issue: AMD64 FreeBSD14/15 3.x multiprocessing test failures #132719

[vstinner]

Example of error: https://buildbot.python.org/#/builders/1232/builds/5434

ERROR: test_rlock_locked_2processes (test.test_multiprocessing_forkserver.test_processes.WithProcessesTestLock.test_rlock_locked_2processes)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.opsec-fbsd14/build/Lib/test/_test_multiprocessing.py", line 1609, in test_rlock_locked_2processes
    res = self.Value('b', 0)
  File "/home/buildbot/buildarea/3.x.opsec-fbsd14/build/Lib/multiprocessing/context.py", line 134, in Value
    from .sharedctypes import Value
  File "/home/buildbot/buildarea/3.x.opsec-fbsd14/build/Lib/multiprocessing/sharedctypes.py", line 10, in <module>
    import ctypes
  File "/home/buildbot/buildarea/3.x.opsec-fbsd14/build/Lib/ctypes/__init__.py", line 8, in <module>
    from _ctypes import Union, Structure, Array
ModuleNotFoundError: No module named '_ctypes'

[sobolevn]

Thank you!

[vstinner]

I also contacted the FreeBSD buildbot owner to ask him if he can install libffi (ctypes dependency).

[vstinner]

Oh no, I missed the rlock test: I wrote #132846 to skip also the rlock test.

[YvesDup]

@unittest.skipUnless(HAS_SHAREDCTYPES, 'needs sharedctypes') should also apply to test_rlock_locked_2processes

I can rewrite these tests without self.value variable ?

[vstinner]

I can rewrite these tests without self.value variable ?

It seems safer to always use self.Value, no?

[YvesDup]

It seems safer to always use self.Value, no?

I can use a multiprocessing.Manager().list() to avoid ctypes.

[vstinner]

Ah, I understood that you asked to choice between Value and self.Value.

[YvesDup]

I understand that there are 2 problems when HAS_SHAREDCTYPES is False.

1. You can't use Value but only self.Value.
2. you can't use ctypes as the first argument of [self.]Value.

That's why I suggest using a list from multiprocessing.Manager.

[vstinner]

It's ok to skip tests when ctypes is missing. Ctypes should be available most of the time.

[vstinner]

I merged my PR to skip rlock test to repair FreeBSD buildbots, but feel free to propose a PR if you want to avoid ctypes in the tests.

[YvesDup]

I merged my PR to skip rlock test to repair FreeBSD buildbots, but feel free to propose a PR if you want to avoid ctypes in the tests.

It is okay for to skip these test. Thank for the fix