[issue41984] Empty __slots__ can create untracked reference cycles

[Brandt Bucher]

New submission from Brandt Bucher <brandtbucher at gmail.com>:

Currently, we don't track instances of certain heap types based on the assumption that "no members" == "no reference cycles".

Unfortunately, it's still possible to create untracked reference cycles with one's parents. The following program leaks memory:

while True:
    class C:
        __slots__ = ()
    C.i = C()
    del C

The fix is simple: track all instances of user-defined classes, no exceptions. I'm not sure we were actually getting any real wins from the old behavior anyways.

----------
assignee: brandtbucher
components: Interpreter Core
messages: 378337
nosy: brandtbucher, pablogsal
priority: low
severity: normal
status: open
title: Empty __slots__ can create untracked reference cycles
type: resource usage
versions: Python 3.10, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41984>
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