Forward fix MPRS request index cycle

Summary:
Per title. The bug is introduced in D46408394, we should only advance request index when limit has not been reached

And fix an OSS lint Error

Reviewed By: NivekT

Differential Revision: D46520106

fbshipit-source-id: c17277626fb749c60ffd0c260a3a2e7420d47a49

torchdata/dataloader2/communication/iter.py

@@ -431,16 +431,17 @@ def __iter__(self):
  disabled_pipe[res_idx] = True
  cnt_disabled_pipes += 1
  disabled = True
+ req_idx = next(req_idx_cycle)
  else:
  # Only request if buffer is empty and has not reached the limit
  if len(self.res_buffers[res_idx]) == 0 and (
  self._limit is None or self._request_cnt < self._limit
  ):
  self.datapipes[req_idx].protocol.request_next()
+ req_idx = next(req_idx_cycle)
  self._request_cnt += 1
  total_req_cnt += 1
  total_res_cnt += 1
- req_idx = next(req_idx_cycle)
  res_idx = next(res_idx_cycle)
  if not disabled:
  yield response.value

torchdata/dataloader2/reading_service.py

@@ -632,9 +632,7 @@ def restore(self, datapipe, serialized_state: bytes) -> DataPipe:
  if hasattr(rs, "restore") and callable(rs.restore):
  datapipe = rs.restore(datapipe, state)
  else:
- warnings.warn(
- f"{rs} doesn't support `restore` from state, initialize from scratch"
- )
+ warnings.warn(f"{rs} doesn't support `restore` from state, initialize from scratch")
  datapipe = rs.initialize(datapipe)
  return datapipe