Use weakref.finalize instead of __del__ for RandomState._generator destruction

[mroeschke]

Sometimes upon interpreter exit and using RandomState, the following exception can occur

Exception ignored in: <function RandomState.__del__ at 0x7f0cc41dadd0>
Traceback (most recent call last):
  File "/home/coder/.conda/envs/rapids/lib/python3.10/site-packages/cupy/random/_generator.py", line 65, in __del__
ModuleNotFoundError: import of cupy_backends.cuda.libs halted; None in sys.modules

In order to more robustly destroy RandomState._generator upon exit, a weakref.finalize should be used https://docs.python.org/3/library/weakref.html#comparing-finalizers-with-del-methods

[bdice]

Thanks for this @mroeschke! We see this a lot in RAPIDS CI. A fix would be really helpful.

[leofang]

@mroeschke have you found a reliable way to reproduce the shundown warning? This treatment has a long history (the earliest I could find is #2806) but it seems wearkref had never been considered for some reason. If we can reproduce the behavior locally and then check with your patch, it'd be great!

[mroeschke]

Sorry for the delay here @leofang. Here's a reproducer

Before:

>>> import cupy
>>> import sys
>>> cupy.__version__
'13.0.0rc1'
>>> rng = cupy.random.RandomState(1)
>>> sys.exit(1)
Exception ignored in: <function RandomState.__del__ at 0x7fc40cd675b0>
Traceback (most recent call last):
  File "/home/nfs/mroeschke/miniforge3/lib/python3.10/site-packages/cupy/random/_generator.py", line 65, in __del__
ImportError: sys.meta_path is None, Python is likely shutting down

After (with the following local modification)

diff --git a/cupy/random/_generator.py b/cupy/random/_generator.py
index 04e6c67b0..f2ddb5145 100644
--- a/cupy/random/_generator.py
+++ b/cupy/random/_generator.py
@@ -59,7 +59,11 @@ class RandomState(object):
         if method is None:
             method = curand.CURAND_RNG_PSEUDO_DEFAULT
         self._generator = curand.createGenerator(method)
-        self._finalizer = weakref.finalize(self, curand.destroyGenerator, self._generator)
+        
+        def destroyer(*args, **kwargs):
+            print("destroying generator")
+            curand.destroyGenerator(*args)
+        self._finalizer = weakref.finalize(self, destroyer, self._generator)
         self.method = method
         self.seed(seed)

>>> import cupy
>>> import sys
>>> rng = cupy.random.RandomState(1)
>>> sys.exit(1)
destroying generator