def get_download_cache(self, destination, subfolder='<STR_LIT>'):
<EOL>if destination is None:<EOL><INDENT>destination = self._get_setting('<STR_LIT>', <EOL>SINGULARITY_CACHE)<EOL>destination = get_tmpdir(destination)<EOL><DEDENT>if not destination.endswith(subfolder):<EOL><INDENT>destination = "<STR_LIT>" %(destination, subfolder)<EOL><DEDENT>mkdir_p(destination)<EOL>return destination<EOL>
determine the user preference for atomic download of layers. If
       the user has set a singularity cache directory, honor it. Otherwise,
       use the Singularity default.