batch_dict(PicklerObject *self, PyObject *iter)
{
    PyObject *obj = NULL;
    PyObject *firstitem = NULL;
    int i, n;

    const char mark_op = MARK;
    const char setitem_op = SETITEM;
    const char setitems_op = SETITEMS;

    assert(iter != NULL);

    if (self->proto == 0) {
        /* SETITEMS isn't available; do one at a time. */
        for (;;) {
            obj = PyIter_Next(iter);
            if (obj == NULL) {
                if (PyErr_Occurred())
                    return -1;
                break;
            }
            if (!PyTuple_Check(obj) || PyTuple_Size(obj) != 2) {
                PyErr_SetString(PyExc_TypeError, "dict items "
                                "iterator must return 2-tuples");
                return -1;
            }
            i = save(self, PyTuple_GET_ITEM(obj, 0), 0);
            if (i >= 0)
                i = save(self, PyTuple_GET_ITEM(obj, 1), 0);
            Py_DECREF(obj);
            if (i < 0)
                return -1;
            if (_Pickler_Write(self, &setitem_op, 1) < 0)
                return -1;
        }
        return 0;
    }

    /* proto > 0:  write in batches of BATCHSIZE. */
    do {
        /* Get first item */
        firstitem = PyIter_Next(iter);
        if (firstitem == NULL) {
            if (PyErr_Occurred())
                goto error;

            /* nothing more to add */
            break;
        }
        if (!PyTuple_Check(firstitem) || PyTuple_Size(firstitem) != 2) {
            PyErr_SetString(PyExc_TypeError, "dict items "
                                "iterator must return 2-tuples");
            goto error;
        }

        /* Try to get a second item */
        obj = PyIter_Next(iter);
        if (obj == NULL) {
            if (PyErr_Occurred())
                goto error;

            /* Only one item to write */
            if (save(self, PyTuple_GET_ITEM(firstitem, 0), 0) < 0)
                goto error;
            if (save(self, PyTuple_GET_ITEM(firstitem, 1), 0) < 0)
                goto error;
            if (_Pickler_Write(self, &setitem_op, 1) < 0)
                goto error;
            Py_CLEAR(firstitem);
            break;
        }

        /* More than one item to write */

        /* Pump out MARK, items, SETITEMS. */
        if (_Pickler_Write(self, &mark_op, 1) < 0)
            goto error;

        if (save(self, PyTuple_GET_ITEM(firstitem, 0), 0) < 0)
            goto error;
        if (save(self, PyTuple_GET_ITEM(firstitem, 1), 0) < 0)
            goto error;
        Py_CLEAR(firstitem);
        n = 1;

        /* Fetch and save up to BATCHSIZE items */
        while (obj) {
            if (!PyTuple_Check(obj) || PyTuple_Size(obj) != 2) {
                PyErr_SetString(PyExc_TypeError, "dict items "
                    "iterator must return 2-tuples");
                goto error;
            }
            if (save(self, PyTuple_GET_ITEM(obj, 0), 0) < 0 ||
                save(self, PyTuple_GET_ITEM(obj, 1), 0) < 0)
                goto error;
            Py_CLEAR(obj);
            n += 1;

            if (n == BATCHSIZE)
                break;

            obj = PyIter_Next(iter);
            if (obj == NULL) {
                if (PyErr_Occurred())
                    goto error;
                break;
            }
        }

        if (_Pickler_Write(self, &setitems_op, 1) < 0)
            goto error;

    } while (n == BATCHSIZE);
    return 0;

  error:
    Py_XDECREF(firstitem);
    Py_XDECREF(obj);
    return -1;
}