code: def get_core_source_partial():
      
      global _core_source_partial
  
      if _core_source_partial is None:
          _core_source_lock.acquire()
          try:
              if _core_source_partial is None:
                  _core_source_partial = PartialZlib(
                      _get_core_source().encode('utf-8')
                  )
          finally:
              _core_source_lock.release()
  
      return _core_source_partial
docs: _get_core_source() is expensive, even with @lru_cache in minify.py, threads
      can enter it simultaneously causing severe slowdowns.