class_docstr: Modified from https://github.com/ChenRocks/UNITER.
  
  overlap compute and cuda data transfer
  (copied and then modified from nvidia apex)
class_docstr_tok: ["Modified","from","https",":","\/\/github.com\/ChenRocks\/UNITER",".","overlap","compute","and","cuda","data","transfer","(","copied","and","then","modified","from","nvidia","apex",")"]
code: def __len__(self):
      return len(self.loader)
  
imports: import time
  import random
  import torch
  from lavis.datasets.data_utils import move_to_cuda
  from torch.utils.data import DataLoader
label_desc: Use image node_id 3 for calling the PrefetchLoader obj's underlying member method code with example usage: obj.__len__() and returns: len