def start(self, segment):
if self.closed:<EOL><INDENT>raise UserCritical(msg='<STR_LIT>',<EOL>hint='<STR_LIT>')<EOL><DEDENT>g = gevent.Greenlet(self.transferer, segment)<EOL>g.link(self._complete_execution)<EOL>self.greenlets.add(g)<EOL>self.expect += <NUM_LIT:1><EOL>g.start()<EOL>
Begin transfer for an indicated wal segment.