[Cython] test crash in Py3.2 (NumPy/memoryview/refcounting related?)

[Stefan Behnel]

Hi,

I keep seeing test crashes in Py3.2 debug builds on Jenkins with the latest
master, referring to ref-counting problems. Here, for example:

https://sage.math.washington.edu:8091/hudson/job/cython-devel-tests/BACKEND=c,PYVERSION=py32-ext/328/console

and likewise in the series of builds starting at #312.

I'm not sure what changed in that corner, it looks like one of those
problems that was there for a while and suddenly starts showing when you
touch that innocent looking brick at the other end of the house that was
holding the balance, until now. In this case, that brick was this commit:

https://github.com/cython/cython/commit/c8f61a668d0ce8af1020f520253e1b5f623cf349

I reverted it here and that fixed the problem at least temporarily:

https://github.com/cython/cython/commit/5aac8caf1ba21933cc85a51af3319c78fc08d675

but it seems to be back now (after my refnanny optimisations). Before
reverting my changes, I was able to reproduce it somewhat reliably on
sage.math by running these three tests together (non-forking):

	memslice numpy_bufacc numpy_memoryview

None of the tests shows the problem when run by itself. I can't tell if
it's also in the latest py3k because I don't have a NumPy lying around that
works there. So 3.2 is basically the latest Python version this can be
tested with, and it doesn't occur in the 3.1 tests. The tests use NumPy
1.6.1, i.e. the latest official release.

Mark, Dag, could any of you take a look to see if it appears in any way
more obvious to you than to me?

Stefan