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gh-127582: Make object resurrection thread-safe for free threading. (GH-127612)

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Objects may be temporarily "resurrected" in destructors when calling
finalizers or watcher callbacks. We previously undid the resurrection
by decrementing the reference count using `Py_SET_REFCNT`. This was not
thread-safe because other threads might be accessing the object
(modifying its reference count) if it was exposed by the finalizer,
watcher callback, or temporarily accessed by a racy dictionary or list
access.

This adds internal-only thread-safe functions for temporary object
resurrection during destructors.
This commit is contained in:
Sam Gross 2024-12-05 21:07:31 +00:00 • committed by GitHub
parent 657d0e99aa
commit f4f530804b
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6 changed files with 87 additions and 20 deletions
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7
Objects/dictobject.c
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@ -3162,14 +3162,11 @@ dict_dealloc(PyObject *self)
{
PyDictObject *mp = (PyDictObject *)self;
PyInterpreterState *interp = _PyInterpreterState_GET();
assert(Py_REFCNT(mp) == 0);
Py_SET_REFCNT(mp, 1);
_PyObject_ResurrectStart(self);
_PyDict_NotifyEvent(interp, PyDict_EVENT_DEALLOCATED, mp, NULL, NULL);
if (Py_REFCNT(mp) > 1) {
Py_SET_REFCNT(mp, Py_REFCNT(mp) - 1);
if (_PyObject_ResurrectEnd(self)) {
return;
}
Py_SET_REFCNT(mp, 0);
PyDictValues *values = mp->ma_values;
PyDictKeysObject *keys = mp->ma_keys;
Py_ssize_t i, n;