[Python-Dev] RE: CVS Python is unstable

[Tim Peters]

More info on the debug-mode

    test_weakref test_xmllib

blowup in gc_list_append, and with the .pyc files already there.

While running test_weakref, we call collect() once.

Ditto while running test_xmllib:  that's when it blows up.

collect_generations() is here (***):

	else {
		generation = 0;
		collections0++;
		if (generation0.gc_next != &generation0) {
***			n = collect(&generation0, &generation1);
		}
	}

collect() is here:

	gc_list_init(&reachable);
	move_roots(young, &reachable);
***	move_root_reachable(&reachable);

move_root_reachable is here:

***		(void) traverse(op,
			       (visitproc)visit_reachable,
			       (void *)reachable);

And that's really calling dict_traverse, which is iterating over the dict.

At blowup time, the dict key is of PyString_Type, with value "ref3", and so
presumably left over from test_weakref.  The dict value is of
PyWeakProxy_Type, has a refcount of 2, and has

    wr_object   pointing to Py_NoneStruct
    wr_callback NULL
    hash        0xffffffff
    wr_prev     NULL
    wr_next     NULL

It's dying while calling visit() (really visit_reachable) on the latter.

Inside visit_reachable, we have:

		if (gc && gc->gc_refs != GC_MOVED) {

and that's interesting too, because gc->gc_refs is 0xcdcdcdcd, which is the
MS debug-mode "clean landfill" value:  freshly malloc'ed memory is filled
with 0xcd bytes (so gc->gc_refs is uninitialized trash).

My conclusion:  it's really hosed.  Take it away, Neil <wink>!