Example code (mnist) does not work under torch.utils.bottleneck

[sakaia]

Example code (mnist) does not work under torch.utils.bottleneck. This is solved by changing the value num_workers from 1 to 0. It needs to check other examples also.

Reference https://github.com/pytorch/pytorch/issues/6313 https://discuss.pytorch.org/t/cannot-measure-cuda-usage-on-mnist-example/21600/2