<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def call_nowait(self, cb_name):
 """ pick a callback command and call it without waiting for it to finish """

        if self.bootstrapping:
            return
        if cb_name in (ACTION_ON_START, ACTION_ON_STOP, ACTION_ON_RESTART, ACTION_ON_ROLE_CHANGE):
            self.__cb_called = True

        if self.callback and cb_name in self.callback:
            cmd = self.callback[cb_name]
            try:
                cmd = shlex.split(self.callback[cb_name]) + [cb_name, self.role, self.scope]
                self._callback_executor.call(cmd)
            except Exception:
                logger.exception('callback %s %s %s %s failed', cmd, cb_name, self.role, self.scope)