[Patches] Trashcan vs. GC vs. TRACE_REFS
Charles G Waldman
Tue, 25 Apr 2000 14:17:26 -0500
Hi Christian et al.
Well, I said there was nothing wrong with Trashcan, but I spoke a
little too soon ;-)
With the current gc-cycle patch and Py_TRACE_REFS set, we get a core
The culprit is this little piece of code in object.c
destructor dealloc = op->ob_type->tp_dealloc;
*** if (_PyTrash_delete_nesting < PyTrash_UNWIND_LEVEL-1)
*** op->ob_type = NULL;
I'd really love to understand what those lines marked "***" are for.
If you set ob_type to NULL before doing a dealloc, you get into
trouble, because the new GC dealloc functions need to check ob_type to
decide if the object being deleted has GC info. By setting type to
NULL you are breaking this.
But what really seems odd to me is that the _Py_Dealloc function above
is only used when Py_TRACE_REFS is set. Normally the following macro
definition is used instead (see object.h)
#define _Py_Dealloc(op) (*(op)->ob_type->tp_dealloc)((PyObject *)(op))
#endif /* !Py_TRACE_REFS */
So, what is the point of worrying about _PyTrash_UNWIND_LEVEL only in
a function which is only used in special builds? If this is really
important, I'd think you'd be doing it in the _Py_Dealloc macro as
well. But, of course, you can't be clobbering ob_type at all, because
the gc dealloc functions *need* that ob_type.
As far as I can tell, building with Py_TRACE_REFS is not too widely
done. But I'm finding it incredibly useful for tracking down those
reference leaks which still remain even with Neil's GC patches in