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[Python-Dev] No longer enable Py_TRACE_REFS by default in debug build

Victor Stinner vstinner at redhat.com
Wed Apr 10 18:29:34 EDT 2019 
Le mer. 10 avr. 2019 à 20:09, Steve Dower <steve.dower at python.org> a écrit :
> > The main question is if anyone ever used Py_TRACE_REFS? Does someone
> > use sys.getobjects() or PYTHONDUMPREFS environment variable?
> >
> > Using PYTHONDUMPREFS=1 on a debug build (with Py_TRACE_REFS) does
> > simply crash Python 3.7 at exit. So I don't think that anyone use it
> > :-)
>
> How do we track reference leaks in the buildbots? Can/should we be using
> this?

Ah, maybe there is a misunderstanding. You don't need Py_TRACE_REFS to
track memory leaks: "python3 -m test -R 3:3" works without that.
test_regrtest contains an unit test for reference leaks (I know it
that I wrote the test :-)), and you can see that the test pass on my
PR. I also checked manually by adding a memory leak into a test: it is
still detected :-)

regrtest uses sys.gettotalrefcount(), sys.getallocatedblocks() and
support.fd_count() to track reference, memory and file descriptor
leaks. None of these functions are related to Py_TRACE_REFS.

Again, the question is who rely on Py_TRACE_REFS. If nobody rely on
it, I don't see the point of keeping this expensive feature (at least,
not by default).

> It doesn't crash on Python 3.8, so I suspect fixing the bug is a better
> option than using it as an excuse to remove the feature.

It's not what I said. I only said that it seems that nobody uses
PYTHONDUMPREFS, since it's broken for a long time. It's just a hint
about the usage of Py_TRACE_REFS.

I don't propose to remove the feature, but to disable it by default.

Victor
-- 
Night gathers, and now my watch begins. It shall not end until my death.
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