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gh-128923: Use zero to indicate unassigned unique id (#128925)

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In the free threading build, the per thread reference counting uses a
unique id for some objects to index into the local reference count
table. Use 0 instead of -1 to indicate that the id is not assigned. This
avoids bugs where zero-initialized heap type objects look like they have
a unique id assigned.
This commit is contained in:
Sam Gross 2025-01-17 10:42:27 -05:00 • committed by GitHub
parent 767c89ba7c
commit d66c08aa75
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9 changed files with 110 additions and 33 deletions
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6
Objects/dictobject.c
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@ -1659,6 +1659,9 @@ _PyDict_EnablePerThreadRefcounting(PyObject *op)
assert(PyDict_Check(op));
#ifdef Py_GIL_DISABLED
Py_ssize_t id = _PyObject_AssignUniqueId(op);
if (id == _Py_INVALID_UNIQUE_ID) {
return;
}
if ((uint64_t)id >= (uint64_t)DICT_UNIQUE_ID_MAX) {
_PyObject_ReleaseUniqueId(id);
return;
@ -1666,8 +1669,7 @@ _PyDict_EnablePerThreadRefcounting(PyObject *op)
PyDictObject *mp = (PyDictObject *)op;
assert((mp->_ma_watcher_tag >> DICT_UNIQUE_ID_SHIFT) == 0);
// Plus 1 so that _ma_watcher_tag=0 represents an unassigned id
mp->_ma_watcher_tag += ((uint64_t)id + 1) << DICT_UNIQUE_ID_SHIFT;
mp->_ma_watcher_tag += (uint64_t)id << DICT_UNIQUE_ID_SHIFT;
#endif
}