code: def get_oembed_providers():
      
      global _provider_list, _provider_lock
      if _provider_list is not None:
          return _provider_list
  
      # Allow only one thread to build the list, or make request to embed.ly.
      _provider_lock.acquire()
      try:
          # And check whether that already succeeded when the lock is granted.
          if _provider_list is None:
              _provider_list = _build_provider_list()
      finally:
          # Always release if there are errors
          _provider_lock.release()
  
      return _provider_list
docs: Get the list of OEmbed providers.