Guido van Rossum wrote:
I wouldn't be surprised if this is a genuine bug; the complex type
doesn't get a lot of love from core developers.
Could you come up with a proposed fix, and a unit test showing that it
works (and that the old version doesn't)? (Maybe a good unit test
would require writing a custome C extension; in that case just show
some sample code.)
Attached is a sample module that exposes the problem. The problem goes
away by replacing
op = PyType_GenericAlloc(type, 0);
with
op = type->tp_alloc(type, 0);
in the function
complex_subtype_from_c_complex
in the file complexobject.c (about line #191).
The problem with a unit test is that it might not fail. On my Linux
system, it doesn't complain about the problem unless I first use strict
pointer checking with
export MALLOC_CHECK_=2
Then the code
import bugtest
a = bugtest.newcomplex(3.0)
del a
Aborts
Valgrind also shows the error when running the simple code. It seems
pretty clear to me that the subtype code should be calling the sub-types
tp_alloc code instead of the generic one.
Best regards,
-Travis
#include "Python.h"
typedef struct {
PyObject_HEAD
double real;
double imag;
} PyNewComplexObject;
static PyTypeObject PyComplex_SubType = {
PyObject_HEAD_INIT(NULL)
0, /*ob_size*/
"newcomplex", /*tp_name*/
sizeof(PyNewComplexObject), /*tp_basicsize*/
};
static PyObject *
_complex_alloc(PyTypeObject *type, int nitems)
{
PyObject *obj;
obj = (PyObject *)malloc(_PyObject_SIZE(type));
memset(obj, 0, _PyObject_SIZE(type));
PyObject_INIT(obj, type);
return obj;
}
PyMODINIT_FUNC initbugtest(void) {
PyObject *m, *d;
m = Py_InitModule("bugtest", NULL);
d = PyModule_GetDict(m);
PyComplex_SubType.tp_free = free;
PyComplex_SubType.tp_alloc = _complex_alloc;
PyComplex_SubType.tp_base = &PyComplex_Type;
PyComplex_SubType.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_CHECKTYPES;
PyType_Ready(&PyComplex_SubType);
Py_INCREF(&PyComplex_SubType);
PyDict_SetItemString(d, "newcomplex",
(PyObject *)&PyComplex_SubType);
return;
}
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