def signal_wait(num=None):
    """Waits for the given of any signal.

    Block the process/thread/async core until a signal is received. Use signal_received to get the number of
    the signal received. If a registered handler handles a signal, signal_wait will be interrupted and the actual
    handler will handle the signal.

    * http://uwsgi-docs.readthedocs.io/en/latest/Signals.html#signal-wait-and-signal-received

    :param int num:

    :rtype: str|unicode

    :raises SystemError: If something went wrong.
    """
