pytest segfault, not with -v

[Marco Sulla]

Indeed I have introduced a command line parameter in my bench.py
script that simply specifies the number of times the benchmarks are
performed. This way I have a sort of segfault checker.

But I don't bench any part of the library. I suppose I have to create
a separate script that does a simple loop for all the cases, and
remove the optional parameter from bench. How boring.
PS: is there a way to monitor the Python consumed memory inside Python
itself? In this way I could also trap memory leaks.

On Sat, 20 Nov 2021 at 01:46, MRAB <python at mrabarnett.plus.com> wrote:
>
> On 2021-11-19 23:44, Marco Sulla wrote:
> > On Fri, 19 Nov 2021 at 20:38, MRAB <python at mrabarnett.plus.com> wrote:
> >>
> >> On 2021-11-19 17:48, Marco Sulla wrote:
> >> > I have a battery of tests done with pytest. My tests break with a
> >> > segfault if I run them normally. If I run them using pytest -v, the
> >> > segfault does not happen.
> >> >
> >> > What could cause this quantical phenomenon?
> >> >
> >> Are you testing an extension that you're compiling? That kind of problem
> >> can occur if there's an uninitialised variable or incorrect reference
> >> counting (Py_INCREF/Py_DECREF).
> >
> > Ok, I know. But why can't it be reproduced if I do pytest -v? This way
> > I don't know which test fails.
> > Furthermore I noticed that if I remove the __pycache__ dir of tests,
> > pytest does not crash, until I re-ran it with the __pycache__ dir
> > present.
> > This way is very hard for me to understand what caused the segfault.
> > I'm starting to think pytest is not good for testing C extensions.
> >
> If there are too few Py_INCREF or too many Py_DECREF, it'll free the
> object too soon, and whether or when that will cause a segfault will
> depend on whatever other code is running. That's the nature of the
> beast: it's unpredictable!
>
> You could try running each of the tests in a loop to see which one
> causes a segfault. (Trying several in a loop will let you narrow it down
> more quickly.)
>
> pytest et al. are good for testing behaviour, but not for narrowing down
> segfaults.
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