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gh-157875: Fix a reference leak when rewinding JIT traces by Wulian233 · Pull Request #157888 · python/cpython · GitHub

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gh-157875: Fix a reference leak when rewinding JIT traces #157888

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gh-157875: Fix a reference leak when rewinding JIT traces #157888

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gh-157875: Fix a reference leak when rewinding JIT traces
Wulian233 Sep 21, 2026
5349219
Update test_opt.py
Wulian233 Sep 21, 2026
2698b49
Update test_opt.py
Wulian233 Sep 22, 2026
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22 changes: 22 additions & 0 deletions Lib/test/test_capi/test_opt.py
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Expand Up @@ -6016,6 +6016,28 @@ def f1():
"""), PYTHON_JIT="1")
self.assertEqual(result[0].rc, 0, result)

def test_157875_rewound_trace_reference_leak(self):

johng Oct 2, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Should this test assert that the rewinding happened? Or would that make the test too brittle?
# https://github.com/python/cpython/issues/157875
import weakref

def run():
class C:
def __iter__(self):
return self

def __next__(self):
raise StopIteration

obj = C()
for _ in range(TIER2_THRESHOLD):
for _ in obj:
pass
return weakref.ref(C)

ref = run()
gc.collect()
self.assertIsNone(ref())

def test_144068_daemon_thread_jit_cleanup(self):
result = script_helper.run_python_until_end('-c', textwrap.dedent("""
import threading
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-09-21-16-00-00.gh-issue-157875.7Qn4Jp.rst
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@@ -0,0 +1,2 @@
Fix a reference leak in the JIT when a trace is rewound after encountering
unsupported bytecode.

johng Oct 2, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

maybe just say when tracing is rewound? I think this get's triggered for standard supported JIT traces hit natural endings such as jumps

Wulian233 Oct 2, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

It seems too detailed. We can ask others?👀
3 changes: 3 additions & 0 deletions Python/optimizer.c
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Expand Up @@ -789,6 +789,9 @@ _PyJit_translate_single_bytecode_to_trace(
{
_PyUOpInstruction *curr = uop_buffer_last(trace);
while (curr->opcode != _SET_IP && uop_buffer_length(trace) > 2) {
if (_PyUop_Flags[curr->opcode] & HAS_RECORDS_VALUE_FLAG) {
Py_XDECREF((PyObject *)(uintptr_t)curr->operand0);

johng Oct 2, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

we now have a very similar pattern three times in this file, maybe worth seeing if it's worth to make it a common operation

Wulian233 Oct 2, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I think it would be better to focus on the bug fix scope of this PR. However, currently the JIT has been suspended and only bug fixes are accepted
}
trace->next--;
curr = uop_buffer_last(trace);
}
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