Hi group.
I have a problem with some C extensions I am working with and
hope that some of you can help. Basically, I am wrapping a a tree
structure from C where I have python methods for extracting either the
entire tree or subtrees; since I don't want the full tree to be
deallocated while python has references to the subtrees, I INCREF the
full tree whenever I hand out a subtree reference. I don't want any of
the subtrees to be deallocated while the full tree lives, either, so I
want the fulltree to have a reference to each of the subtrees. Naturally,
this gives me a cyclik reference structure, and I want to be able to
garbage collect it. But this is where my problems begin...
For some reason, when I turn on the cyclic garbage collection for my
types, a deallocation automatically gives me a segfault. That is, if my
type new type contains any data whatsoever, I cannot garbage collect
without dumping core. I have boiled the problem down to the code shown
below. It contains no cyclic structure, it is as simple as it gets, but
it still seqfaults for me. If I comment out the magic void-pointer (which
isn't used for anything) I don't get the segfault.
#include <Python.h>
struct SimpleObject;
static PyObject * Simple_new (PyTypeObject *type,
PyObject *args,
PyObject *kwds);
static int Simple_init (struct SimpleObject *self,
PyObject *args,
PyObject *kwds);
static int Simple_traverse(struct SimpleObject *self,
visitproc visit,
void *arg);
static void Simple_dealloc (struct SimpleObject *self);
typedef struct SimpleObject {
/* object stuff */
PyObject_HEAD
/* dark magic */
void *magic;
} SimpleObject;
static PyTypeObject simple_SimpleType = {
PyObject_HEAD_INIT(NULL)
0, /*ob_size*/
"simple.Simple", /*tp_name*/
sizeof(SimpleObject), /*tp_basicsize*/
0, /*tp_itemsize*/
(destructor)Simple_dealloc, /*tp_dealloc*/
0, /*tp_print*/
0, /*tp_getattr*/
0, /*tp_setattr*/
0, /*tp_compare*/
0, /*tp_repr*/
0, /*tp_as_number*/
0, /*tp_as_sequence*/
0, /*tp_as_mapping*/
0, /*tp_hash */
0, /*tp_call*/
0, /*tp_str*/
0, /*tp_getattro*/
0, /*tp_setattro*/
0, /*tp_as_buffer*/
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC, /*tp_flags*/
"Simple objects", /*tp_doc*/
(traverseproc)Simple_traverse, /*tp_traverse*/
0, /*tp_clear*/
0, /*tp_richcompare*/
0, /*tp_weaklistoffset*/
0, /*tp_iter*/
0, /*tp_iternext*/
0, /*tp_methods*/
0, /*tp_members*/
0, /*tp_getset*/
0, /*tp_base*/
0, /*tp_dict*/
0, /*tp_descr_get*/
0, /*tp_descr_set*/
0, /*tp_dictoffset*/
(initproc)Simple_init, /*tp_init*/
0, /*tp_alloc*/
Simple_new, /*tp_new*/
0 /*...the rest...*/
};
static PyObject *
Simple_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
{
SimpleObject *self = (SimpleObject *)type->tp_alloc(type, 0);
return (PyObject*)self;
}
static int
Simple_init(SimpleObject *self, PyObject *args, PyObject *kwds)
{
return 0;
}
/* cyclic gc */
static int
Simple_traverse (SimpleObject *self, visitproc visit, void *arg)
{
fprintf(stderr,"Simple_traverse...\n");
return 0;
}
static int
Simple_clear(SimpleObject *self)
{
fprintf(stderr,"Simple_clear...\n");
return 0;
}
static void
Simple_dealloc(SimpleObject *self)
{
fprintf(stderr,"Simple_dealloc %p\n", self);
self->ob_type->tp_free((PyObject*)self); /* <= segfault here */
return;
}
static PyMethodDef simple_methods[] = {
{0} /* sentinel */
};
void
initsimple(void)
{
if (PyType_Ready(&simple_SimpleType) < 0) return;
Py_INCREF(&simple_SimpleType);
PyObject* m = Py_InitModule3("simple", simple_methods, "Simple module.");
PyModule_AddObject(m,"Simple",(PyObject*)&simple_S impleType);
}
A script sufficient to provoke the fault is this:
import simple
simple.Simple()
Can anyone explain what I'm doing wrong? Or perhaps suggest a better
solution to my "real" problem, if I'm approaching the problem completely
wrong :-)
Yours,
/mailund
