[BUG] Memory leak when constructing empty frozendicts

[squahtx]

Similar to #55, frozendict() and frozendict({}) leak memory.

OS version: Ubuntu 20.04.4 LTS
Python3 version (python3 -V -V): Python 3.8.10

Steps to reproduce

Borrowing code from #55:

import resource
import frozendict

print("frozendict version:", frozendict.__version__)
print()

c = 0
while True:
    fz = frozendict.frozendict({})
    
    if (c % 10000) == 0:
        max_rss = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
        print(f"iteration: {c}, max rss: {max_rss} kb")
    
    c += 1

Actual result

frozendict version: 2.3.2

iteration: 0, max rss: 11292 kb
iteration: 10000, max rss: 12188 kb
iteration: 20000, max rss: 12980 kb
iteration: 30000, max rss: 13772 kb
...
iteration: 3150000, max rss: 263252 kb
iteration: 3160000, max rss: 264044 kb
iteration: 3170000, max rss: 265100 kb

[squahtx]

I think we might be missing a Py_DECREF(self) when we decide to return an empty frozendict in _frozendict_new?

python-frozendict/frozendict/src/3_8/frozendictobject.c

Lines 1562 to 1575 in 8def42c

	PyObject* self = frozendict_new_barebone(type);
	PyFrozenDictObject* mp = (PyFrozenDictObject*) self;
	if (frozendict_update_common(self, arg, kwds)) {
	Py_DECREF(self);
	return NULL;
	}
	PyObject* empty = frozendict_create_empty(mp, type, use_empty_frozendict);
	if (empty != NULL) {
	return empty;
	}

[Marco-Sulla]

Thank you for the report. Fixed in 81e163a can you confirm?

[squahtx]

That seems to have fixed it. Thank for your the fast response!
Can we have a PyPI release with the fix?

[Marco-Sulla]

Done.

[squahtx]

Thanks again for getting the bugs fixed!