id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
8001,stl_input_iterator generators garbage collection problems,Wichert Akkerman <wichert@…>,Ralf W. Grosse-Kunstleve,"I am running into some unexpected errors when using stl_input_iterator. I have a fairly simple converter registered to convert an iterable list of values (custom enum) to a unordered_set. The code looks like this:

{{{#!c++
struct advicetype_set_from_python {
	advicetype_set_from_python() {
		converter::registry::push_back(&convertible, &construct, type_id<std::unordered_set<AdviceType>>());
	}

	static void* convertible(PyObject *obj) {
		if (obj==Py_None)
			return obj;

		PyObject* iter = PyObject_GetIter(obj);
		if (iter==NULL) {
			throw_error_already_set();
			return 0;
		}
		Py_DECREF(iter);
		return obj;
	}

	static void construct(PyObject* obj, converter::rvalue_from_python_stage1_data *data) {
		std::unordered_set<AdviceType> result;
		if (obj!=Py_None) {
			object o = object(handle<>(obj));
			stl_input_iterator<AdviceType> begin(o), end;
			result.insert(begin, end);
		}
		void *storage = ((converter::rvalue_from_python_storage<std::unordered_set<AdviceType>>*)data)->storage.bytes;
		new (storage) std::unordered_set<AdviceType>(result);
		data->convertible = storage;
	}
};
}}}

When using this code we were seeing segfaults due to what appears to be invalid reference counters. Since I suspected a problem in this convertor I wrote a simple test which triggers the converter a number of times:

{{{#!python
for i in range(5000):
    my_func({AdviceType.one, AdviceType.two})
}}}

Which had an interesting result: the tests immediately aborted with a ""Fatal Python error: GC object already tracked"" error. Commenting out the contents of the if-statement in construct() made the problem go away, which makes we think the bug is in the stl_input_iterator used there. To test this I rewrote my code to use a standard !PyObject_GetIter / !PyIter_Next loop and that indeed made all problems go away.",Bugs,closed,To Be Determined,python USE GITHUB,Boost 1.52.0,Problem,invalid,,