Py_DECREF() in interpreter doesn't call `_PyReftracerTrack(op, PyRefTracer_DESTROY)`

[colesbury]

Bug report

cpython/Python/ceval.c

Lines 72 to 85 in 6c450f4

	#undef Py_DECREF
	#define Py_DECREF(arg) \
	do { \
	PyObject *op = _PyObject_CAST(arg); \
	if (_Py_IsImmortal(op)) { \
	_Py_DECREF_IMMORTAL_STAT_INC(); \
	break; \
	} \
	_Py_DECREF_STAT_INC(); \
	if (--op->ob_refcnt == 0) { \
	destructor dealloc = Py_TYPE(op)->tp_dealloc; \
	(*dealloc)(op); \
	} \
	} while (0)

Tracemalloc only handles PyRefTracer_CREATE events and we don't have any tests for PyRefTracer_DESTROY events.

EDIT: _testcapimodule.c tests PyRefTracer_DESTROY events, but only through the C API and not the Python interpreter.

Linked PRs

• gh-130382: add missing _PyReftracerTrack to ceval DECREF #130689
• gh-130382: Add missing reftracer call to ceval.c #130700
• [3.13] gh-130382: add missing _PyReftracerTrack to ceval Py_DECREF (GH-130689) #131195

[tom-pytel]

There is a super-basic reftracer test in _testcapimodule.c, but no python interface that I can see, so added one to tracemalloc module to keep track of created and destroyed refs. Do you want this?

Example:

import tracemalloc

tracemalloc.start()

refs = tracemalloc.get_traced_refs()
print(refs)

tracemalloc.reset_peak()
i = []
refs = tracemalloc.get_traced_refs()
print(refs)

tracemalloc.reset_peak()
j = [], []
del j
refs = tracemalloc.get_traced_refs()
print(refs)

import ssl
refs = tracemalloc.get_traced_refs()
print(refs)

tracemalloc.stop()

Run:

$ ./python reftrace.py
(0, 0)
(1, 0)
(3, 3)
(16722, 8671)