TST: Cause of test_linsolve.py test failure

[alugowski]

Recent CI runs fail with the following error in the "Prerelease deps and 64-bit BLAS" workflow. I believe I've tracked it down.

FAILED scipy/sparse/linalg/_dsolve/tests/test_linsolve.py::TestSplu::test_threads_parallel - AssertionError: 
Items are not equal:
 ACTUAL: 14
 DESIRED: 20

That test runs the same basic SuperLU tests concurrently in 20 threads and expects them all to pass.

Cause

Removing the exception catchall yields this:

E   Traceback (most recent call last):
E     File "/usr/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
E       self.run()
E     File "/usr/lib/python3.10/threading.py", line 953, in run
E       self._target(*self._args, **self._kwargs)
E     File "/scipy/build-install/lib/python3/dist-packages/scipy/sparse/linalg/_dsolve/tests/test_linsolve.py", line 709, in worker
E       self._internal_test_splu_smoketest()
E     File "/scipy/build-install/lib/python3/dist-packages/scipy/sparse/linalg/_dsolve/tests/test_linsolve.py", line 496, in _internal_test_splu_smoketest
E       self._smoketest(splu, check, np.float64)
E     File "/scipy/build-install/lib/python3/dist-packages/scipy/sparse/linalg/_dsolve/tests/test_linsolve.py", line 460, in _smoketest
E       rng = random.RandomState(1234)
E     File "numpy/random/mtrand.pyx", line 184, in numpy.random.mtrand.RandomState.__init__
E     File "_mt19937.pyx", line 130, in numpy.random._mt19937.MT19937.__init__
E     File "/usr/lib/python3.10/contextlib.py", line 78, in inner
E       with self._recreate_cm():
E     File "/usr/local/lib/python3.10/dist-packages/numpy/core/_ufunc_config.py", line 406, in __enter__
E       raise TypeError("Cannot enter `np.errstate` twice.")
E   TypeError: Cannot enter `np.errstate` twice.

(and the same error on another line)

The image builds using numpy nightly, which is 2.0.0.dev0.

I believe the error is this one: numpy/numpy#24013

Solutions

Wait for the fix in numpy nightly.

If a green CI is desired sooner, I can confirm that protecting both random.RandomState calls with a lock resolves the issue. Happy to make a PR to this effect.

class TestSplu:
    rng_mutex = threading.Lock()

    ...

        with self.rng_mutex:
            rng = random.RandomState(1234)

[steppi]

Thanks for tracking this down @alugowski! I'm +1 for just waiting for the fix in the numpy nightly.

[rgommers]

New nightlies were uploaded ~12 hours ago. This test passed on the most recent PR, gh-18790. So I'll close this. Thanks @alugowski!