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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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GPG key ID: B5690EEEBB952194
9 changed files with 110 additions and 33 deletions
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29
Python/uniqueid.c
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@ -86,7 +86,7 @@ _PyObject_AssignUniqueId(PyObject *obj)
if (pool->freelist == NULL) {
if (resize_interp_type_id_pool(pool) < 0) {
UNLOCK_POOL(pool);
return -1;
return _Py_INVALID_UNIQUE_ID;
}
}
@ -94,7 +94,9 @@ _PyObject_AssignUniqueId(PyObject *obj)
pool->freelist = entry->next;
entry->obj = obj;
_PyObject_SetDeferredRefcount(obj);
Py_ssize_t unique_id = (entry - pool->table);
// The unique id is one plus the index of the entry in the table.
Py_ssize_t unique_id = (entry - pool->table) + 1;
assert(unique_id > 0);
UNLOCK_POOL(pool);
return unique_id;
}
@ -106,8 +108,9 @@ _PyObject_ReleaseUniqueId(Py_ssize_t unique_id)
struct _Py_unique_id_pool *pool = &interp->unique_ids;
LOCK_POOL(pool);
assert(unique_id >= 0 && unique_id < pool->size);
_Py_unique_id_entry *entry = &pool->table[unique_id];
assert(unique_id > 0 && unique_id <= pool->size);
Py_ssize_t idx = unique_id - 1;
_Py_unique_id_entry *entry = &pool->table[idx];
entry->next = pool->freelist;
pool->freelist = entry;
UNLOCK_POOL(pool);
@ -116,18 +119,18 @@ _PyObject_ReleaseUniqueId(Py_ssize_t unique_id)
static Py_ssize_t
clear_unique_id(PyObject *obj)
{
Py_ssize_t id = -1;
Py_ssize_t id = _Py_INVALID_UNIQUE_ID;
if (PyType_Check(obj)) {
if (PyType_HasFeature((PyTypeObject *)obj, Py_TPFLAGS_HEAPTYPE)) {
PyHeapTypeObject *ht = (PyHeapTypeObject *)obj;
id = ht->unique_id;
ht->unique_id = -1;
ht->unique_id = _Py_INVALID_UNIQUE_ID;
}
}
else if (PyCode_Check(obj)) {
PyCodeObject *co = (PyCodeObject *)obj;
id = co->_co_unique_id;
co->_co_unique_id = -1;
co->_co_unique_id = _Py_INVALID_UNIQUE_ID;
}
else if (PyDict_Check(obj)) {
PyDictObject *mp = (PyDictObject *)obj;
@ -141,23 +144,23 @@ void
_PyObject_DisablePerThreadRefcounting(PyObject *obj)
{
Py_ssize_t id = clear_unique_id(obj);
if (id >= 0) {
if (id != _Py_INVALID_UNIQUE_ID) {
_PyObject_ReleaseUniqueId(id);
}
}
void
_PyObject_ThreadIncrefSlow(PyObject *obj, Py_ssize_t unique_id)
_PyObject_ThreadIncrefSlow(PyObject *obj, size_t idx)
{
_PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
if (unique_id < 0 || resize_local_refcounts(tstate) < 0) {
if (((Py_ssize_t)idx) < 0 || resize_local_refcounts(tstate) < 0) {
// just incref the object directly.
Py_INCREF(obj);
return;
}
assert(unique_id < tstate->refcounts.size);
tstate->refcounts.values[unique_id]++;
assert(idx < (size_t)tstate->refcounts.size);
tstate->refcounts.values[idx]++;
#ifdef Py_REF_DEBUG
_Py_IncRefTotal((PyThreadState *)tstate);
#endif
@ -217,7 +220,7 @@ _PyObject_FinalizeUniqueIdPool(PyInterpreterState *interp)
if (obj != NULL) {
Py_ssize_t id = clear_unique_id(obj);
(void)id;
assert(id == i);
assert(id == i + 1);
}
}
PyMem_Free(pool->table);