code: def rate_limited_iter(l):
      "a thread pre-processes the next element"
      pool = ThreadPool(1)
      res = None
  
      def next_or_None():
          try:
              return next(l)
          except StopIteration:
              return None
  
      while True:
          res_next = pool.apply_async(next_or_None)
          if res is not None:
              res = res.get()
              if res is None:
                  return
              yield res
          res = res_next
  
file_path: faiss/benchs/distributed_ondisk/make_index_vslice.py
imports: import os
  import time
  import numpy
  import faiss
  import argparse
  from multiprocessing.pool import ThreadPool
label_desc: Use image node_id 4 for calling a global function with example usage: rate_limited_iter(l) and returns: next, None