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bpo-30156: Remove property_descr_get() optimization #9541

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Merged
vstinner merged 1 commit into from
Oct 1, 2018
Merged

bpo-30156: Remove property_descr_get() optimization #9541

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4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2018-09-24-17-51-15.bpo-30156.pH0j5j.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
The C function ``property_descr_get()`` uses a "cached" tuple to optimize
function calls. But this tuple can be discovered in debug mode with
:func:`sys.getobjects()`. Remove the optimization, it's not really worth it
and it causes 3 different crashes last years.
33 changes: 5 additions & 28 deletions Objects/descrobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1331,42 +1331,19 @@ property_dealloc(PyObject *self)
static PyObject *
property_descr_get(PyObject *self, PyObject *obj, PyObject *type)
{
static PyObject * volatile cached_args = NULL;
PyObject *args;
PyObject *ret;
propertyobject *gs = (propertyobject *)self;

if (obj == NULL || obj == Py_None) {
Py_INCREF(self);
return self;
}

propertyobject *gs = (propertyobject *)self;
if (gs->prop_get == NULL) {
PyErr_SetString(PyExc_AttributeError, "unreadable attribute");
return NULL;
}
args = cached_args;
cached_args = NULL;
if (!args) {
args = PyTuple_New(1);
if (!args)
return NULL;
_PyObject_GC_UNTRACK(args);
}
Py_INCREF(obj);
PyTuple_SET_ITEM(args, 0, obj);
ret = PyObject_Call(gs->prop_get, args, NULL);
if (cached_args == NULL && Py_REFCNT(args) == 1) {
assert(PyTuple_GET_SIZE(args) == 1);
assert(PyTuple_GET_ITEM(args, 0) == obj);
cached_args = args;
Py_DECREF(obj);
}
else {
assert(Py_REFCNT(args) >= 1);
_PyObject_GC_TRACK(args);
Py_DECREF(args);
}
return ret;

PyObject *args[1] = {obj};
return _PyObject_FastCall(gs->prop_get, args, 1);
}

static int
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