# Buggy code
def allocate_top_resources(self, fetch_requests=False):
    """
    Allocate resources given the order in AssignerActor
    """
    t = time.time()
    if self._worker_metrics is None or self._worker_metric_time + 1 < time.time():
        # update worker metrics from ResourceActor
        self._worker_metrics = self._resource_ref.get_workers_meta()
        self._worker_metric_time = t
    if not self._worker_metrics:
        return

    if fetch_requests:
        requests = self._assigner_ref.get_allocate_requests()
        if not requests:
            return
        max_allocates = (
            sys.maxsize if any(v is None for v in requests) else sum(requests)
        )
    else:
        max_allocates = sys.maxsize

    unassigned = []
    reject_workers = set()
    assigned = 0
    # the assigning procedure will continue till all workers rejected
    # or max_allocates reached
    while len(reject_workers) < len(self._worker_metrics) and assigned < max_allocates:
        item = self._assigner_ref.pop_head()
        if not item:
            break

        try:
            alloc_ep, rejects = self._allocate_resource(
                item.session_id,
                item.op_key,
                item.op_info,
                item.target_worker,
                reject_workers=reject_workers,
            )
        except:  # noqa: E722
            logger.exception("Unexpected error occurred in %s", self.uid)
            if item.callback:  # pragma: no branch
                self.tell_promise(item.callback, *sys.exc_info(), _accept=False)
            continue

        # collect workers failed to assign operand to
        reject_workers.update(rejects)
        if alloc_ep:
            # assign successfully, we remove the application
            self._assigner_ref.remove_apply(item.op_key, _tell=True)
            self._session_last_assigns[item.session_id] = time.time()
            assigned += 1
        else:
            # put the unassigned item into unassigned list to add back to the queue later
            unassigned.append(item)
    if unassigned:
        # put unassigned back to the queue, if any
        self._assigner_ref.extend(unassigned, _tell=True)

    if not fetch_requests:
        self._assigner_ref.get_allocate_requests(_tell=True, _wait=False)


# Traceback (AttributeError)
AttributeError                            Traceback (most recent call last)
<ipython-input-3-a85925f048d0> in <module>
1 start=time.time()
2 df_mars=df_mars.to_gpu()
----> 3 print(df_mars.sum().to_frame(name="sum").execute())

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/core.py in execute(self, session, **kw)
580
581     def execute(self, session=None, **kw):
--> 582         self._data.execute(session, **kw)
583         return self
584

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/core.py in execute(self, session, **kw)
368
369         # no more fetch, thus just fire run
--> 370         session.run(self, **kw)
371         # return Tileable or ExecutableTuple itself
372         return self

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/session.py in run(self, *tileables, **kw)
460         tileables = tuple(mt.tensor(t) if not isinstance(t, (Entity, Base)) else t
461                           for t in tileables)
--> 462         result = self._sess.run(*tileables, **kw)
463
464         for t in tileables:

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/session.py in run(self, *tileables, **kw)
105             # set number of running cores
106             self.context.set_ncores(kw['n_parallel'])
--> 107             res = self._executor.execute_tileables(tileables, **kw)
108             return res
109

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/utils.py in _wrapped(*args, **kwargs)
406                 _kernel_mode.eager = False
407             _kernel_mode.eager_count = enter_eager_count + 1
--> 408             return func(*args, **kwargs)
409         finally:
410             _kernel_mode.eager_count -= 1

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/utils.py in inner(*args, **kwargs)
500     def inner(*args, **kwargs):
501         with build_mode():
--> 502             return func(*args, **kwargs)
503     return inner
504

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in execute_tileables(self, tileables, fetch, n_parallel, n_thread, print_progress, mock, compose, name)
878                                    n_parallel=n_parallel or n_thread,
879                                    print_progress=print_progress, mock=mock,
--> 880                                    chunk_result=chunk_result)
881
882                 # update shape of tileable and its chunks whatever it's successful or not

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in execute_graph(self, graph, keys, n_parallel, print_progress, mock, no_intermediate, compose, retval, chunk_result)
688             print_progress=print_progress, mock=mock, mock_max_memory=self._mock_max_memory,
689             fetch_keys=fetch_keys, no_intermediate=no_intermediate)
--> 690         res = graph_execution.execute(retval)
691         self._mock_max_memory = max(self._mock_max_memory, graph_execution._mock_max_memory)
692         if mock:

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in execute(self, retval)
569         # wait until all the futures completed
570         for future in executed_futures:
--> 571             future.result()
572
573         if retval:

/opt/conda/envs/rapids/lib/python3.6/concurrent/futures/_base.py in result(self, timeout)
423                 raise CancelledError()
424             elif self._state == FINISHED:
--> 425                 return self.__get_result()
426
427             self._condition.wait(timeout)

/opt/conda/envs/rapids/lib/python3.6/concurrent/futures/_base.py in __get_result(self)
382     def __get_result(self):
383         if self._exception:
--> 384             raise self._exception
385         else:
386             return self._result

/opt/conda/envs/rapids/lib/python3.6/concurrent/futures/thread.py in run(self)
54
55         try:
---> 56             result = self.fn(*self.args, **self.kwargs)
57         except BaseException as exc:
58             self.future.set_exception(exc)

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in _execute_operand(self, op)
441             # so we pass the first operand's first output to Executor.handle
442             first_op = ops[0]
--> 443             Executor.handle(first_op, results, self._mock)
444
445             # update maximal memory usage during execution

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/executor.py in handle(cls, op, results, mock)
639                 # The `UFuncTypeError` was introduced by numpy#12593 since v1.17.0.
640                 try:
--> 641                     return runner(results, op)
642                 except UFuncTypeError as e:
643                     raise TypeError(str(e)).with_traceback(sys.exc_info()[2]) from None

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/dataframe/reduction/core.py in execute(cls, ctx, op)
405                 cls._execute_agg(ctx, op)
406             elif op.stage == OperandStage.map:
--> 407                 cls._execute_map(ctx, op)
408             else:
409                 in_data = ctx[op.inputs[0].key]

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/dataframe/reduction/core.py in _execute_map(cls, ctx, op)
380             cls._execute_map_with_count(ctx, op)
381         else:
--> 382             cls._execute_without_count(ctx, op)
383
384     @classmethod

/opt/conda/envs/rapids/lib/python3.6/site-packages/mars/dataframe/reduction/core.py in _execute_without_count(cls, ctx, op, reduction_func)
370                 # cannot just do xdf.DataFrame(r).T
371                 # cuz the dtype will be object since pandas 1.0
--> 372                 df = xdf.DataFrame(OrderedDict((d, [v]) for d, v in r.iteritems()))
373             else:
374                 df = xdf.DataFrame(r)

AttributeError: 'Series' object has no attribute 'iteritems'

# Fixed code
def allocate_top_resources(self, fetch_requests=False):
    """
    Allocate resources given the order in AssignerActor
    """
    t = time.time()
    if self._worker_metrics is None or self._worker_metric_time + 1 < time.time():
        # update worker metrics from ResourceActor
        self._worker_metrics = self._resource_ref.get_workers_meta()
        self._worker_metric_time = t
    if not self._worker_metrics:
        return

    if fetch_requests:
        requests = self._assigner_ref.get_allocate_requests()
        if not requests:
            return
        max_allocates = (
            sys.maxsize if any(v is None for v in requests) else sum(requests)
        )
    else:
        max_allocates = sys.maxsize

    unassigned = []
    reject_workers = set()
    assigned = 0
    # the assigning procedure will continue till all workers rejected
    # or max_allocates reached
    while len(reject_workers) < len(self._worker_metrics) and assigned < max_allocates:
        item = self._assigner_ref.pop_head()
        if not item:
            break

        try:
            alloc_ep, rejects = self._allocate_resource(
                item.session_id,
                item.op_key,
                item.op_info,
                item.target_worker,
                reject_workers=reject_workers,
            )
        except:  # noqa: E722
            logger.exception("Unexpected error occurred in %s", self.uid)
            if item.callback:  # pragma: no branch
                self.tell_promise(item.callback, *sys.exc_info(), _accept=False)
            else:
                self.get_actor_ref(
                    BaseOperandActor.gen_uid(item.session_id, item.op_key)
                ).handle_unexpected_failure(*sys.exc_info(), _tell=True, _wait=False)
            continue

        # collect workers failed to assign operand to
        reject_workers.update(rejects)
        if alloc_ep:
            # assign successfully, we remove the application
            self._assigner_ref.remove_apply(item.op_key, _tell=True)
            self._session_last_assigns[item.session_id] = time.time()
            assigned += 1
        else:
            # put the unassigned item into unassigned list to add back to the queue later
            unassigned.append(item)
    if unassigned:
        # put unassigned back to the queue, if any
        self._assigner_ref.extend(unassigned, _tell=True)

    if not fetch_requests:
        self._assigner_ref.get_allocate_requests(_tell=True, _wait=False)