Hey. I ran into the same problem, loading attribute labels from large(1 GB+) numpy array saved as .npy on the server. It seems that I cannot load them using multiple workers(num_worker>0 does not work and the code just hang there, waiting).When I set num_worker=0,  each 100 iteration costs 100 seconds on loading& pre processing data and 50 seconds for training(forward backward step), which is really slow compared to not loading those numpy labels. I got stuck on this problem and eagerly looking for solutions. Would you give me some advice?
Sincerely.