docstr: preload the calendar for cache
docstr_tok: ["preload","the","calendar","for","cache"]
code: def _prepare_calender_cache(self):
      """preload the calendar for cache"""
  
      # This code used the copy-on-write feature of Linux
      # to avoid calculating the calendar multiple times in the subprocess.
      # This code may accelerate, but may be not useful on Windows and Mac Os
      Cal.calendar(freq=self.freq)
      get_calendar_day(freq=self.freq)
  
imports: import os
  import time
  import datetime
  from typing import Optional
  import qlib
  from qlib import get_module_logger
  from qlib.data import D
  from qlib.config import REG_CN
  from qlib.utils import init_instance_by_config
  from qlib.data.dataset.handler import DataHandlerLP
  from qlib.data.data import Cal
  from qlib.contrib.ops.high_freq import get_calendar_day, DayLast, FFillNan, BFillNan, Date, Select, IsNull, IsInf, Cut
  import pickle
  from joblib import Parallel, delayed
label_desc: Use image node_id 5 for calling the HighFreqProvider obj's underlying member method code with example usage: obj._prepare_calender_cache() without return types