added set_epoch for distributed sampler, fix for #224 (#225)

Author: ananyahjha93

pytorch_lightning/trainer/trainer.py

@@ -929,6 +929,10 @@ def __run_pretrain_routine(self, model):
  def __train(self):
  # run all epochs
  for epoch_nb in range(self.current_epoch, self.max_nb_epochs):
+ # set seed for distributed sampler (enables shuffling for each epoch)
+ if self.use_ddp:
+ self.tng_dataloader.sampler.set_epoch(epoch_nb)
+
  # get model
  model = self.__get_model()