docs: def get_global_cache_dir(appname='default', ensure=False):
      """ Returns (usually) writable directory for an application cache """
      if appname is None or  appname == 'default':
          appname = get_default_appname()
      global_cache_dir = util_cplat.get_app_resource_dir(appname,
                                                         meta_util_constants.global_cache_dname)
      if ensure:
          util_path.ensuredir(global_cache_dir)
      return global_cache_dir