8000 gh-126595: fix a crash when calling `itertools.count(sys.maxsize)` by picnixz · Pull Request #126617 · python/cpython · GitHub
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gh-126595: fix a crash when calling itertools.count(sys.maxsize) #126617

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Merged
merged 6 commits into from
Nov 12, 2024
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gh-126595: fix a crash when calling itertools.count(sys.maxsize) #126617

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9b7d2ba
Fix `itertools.count` invariants
picnixz Nov 9, 2024
6138762
blurb
picnixz Nov 9, 2024
eb15e71
fix a crash in `__repr__`
picnixz Nov 9, 2024
91558ca
Revert "fix a crash in `__repr__`"
picnixz Nov 9, 2024
66174a1
optimize if-branches
picnixz Nov 10, 2024
28bdd4e
move code with a step in the dedicate test
picnixz Nov 11, 2024
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fix a crash in __repr__
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@picnixz
picnixz committed Nov 9, 2024
commit eb15e7187df323b4409ca6dd2b404d2ca08ee8f1
38 changes: 36 additions & 2 deletions Modules/itertoolsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3386,13 +3386,35 @@ count_nextlong(countobject *lz)
return long_cnt;
}

static inline int
count_switch_to_slow_mode(countobject *lz)
{
assert(lz->cnt == PY_SSIZE_T_MAX);
assert(lz->long_cnt == NULL);
/* Switch to slow_mode */
PyObject *long_cnt = PyLong_FromSsize_t(PY_SSIZE_T_MAX);
if (long_cnt == NULL) {
return -1;
}
lz->long_cnt = long_cnt;
return 0;
}

static PyObject *
count_next(countobject *lz)
{
#ifndef Py_GIL_DISABLED
if (lz->cnt == PY_SSIZE_T_MAX)
return count_nextlong(lz);
return PyLong_FromSsize_t(lz->cnt++);
PyObject *res = PyLong_FromSsize_t(lz->cnt++);
if (lz->cnt == PY_SSIZE_T_MAX && lz->long_cnt == NULL) {
/* populate lz->long_cnt since it could be used by repr() */
if (count_switch_to_slow_mode(lz) < 0) {
Py_DECREF(res);
return NULL;
}
}
return res;
#else
// free-threading version
// fast mode uses compare-exchange loop
Expand All @@ -3409,7 +3431,19 @@ count_next(countobject *lz)
return returned;
}
if (_Py_atomic_compare_exchange_ssize(&lz->cnt, &cnt, cnt + 1)) {
return PyLong_FromSsize_t(cnt);
/* populate lz->long_cnt now since it could be used by repr() */
returned = PyLong_FromSsize_t(cnt);
if (lz->cnt == PY_SSIZE_T_MAX && lz->long_cnt == NULL) {
int rc;
Py_BEGIN_CRITICAL_SECTION(lz);
rc = count_switch_to_slow_mode(lz);
Py_END_CRITICAL_SECTION();
if (rc < 0) {
Py_DECREF(returned);
return NULL;
}
}
return returned;
}
}
#endif
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