[New-bugs-announce] [issue39778] collections.OrderedDict and weakref.ref raises "refcount is too small" assertion

[Leonard Lausen]

New submission from Leonard Lausen <leonard at lausen.nl>:

Below sample program, will raise "Modules/gcmodule.c:110: gc_decref: Assertion "gc_get_refs(g) > 0" failed: refcount is too small" on Python 3.8.2 debug build.
On 3.7.6 debug build, "Modules/gcmodule.c:277: visit_decref: Assertion `_PyGCHead_REFS(gc) != 0' failed." is raised.

```
import collections
import gc
import weakref

hooks_dict = collections.OrderedDict()
hooks_dict_ref = weakref.ref(hooks_dict)
gc.collect()

print('Hello world')
```


The complete error message on 3.8.2 debug build is

```
Modules/gcmodule.c:110: gc_decref: Assertion "gc_get_refs(g) > 0" failed: refcount is too small
Memory block allocated at (most recent call first):
  File "/home/$USER/test.py", line 6

object  : <weakref at 0x7ff788208a70; to 'collections.OrderedDict' at 0x7ff7881fab90>
type    : weakref
refcount: 1
address : 0x7ff788208a70
Fatal Python error: _PyObject_AssertFailed
Python runtime state: initialized

Current thread 0x00007ff789f9c080 (most recent call first):
  File "/home/$USER/test.py", line 7 in <module>
zsh: abort      PYTHONTRACEMALLOC=1 python ~/test.py
```

----------
components: C API
messages: 362846
nosy: leezu
priority: normal
severity: normal
status: open
title: collections.OrderedDict and weakref.ref raises "refcount is too small" assertion
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39778>
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