The sigwaitinfo function behaves the same as the sigwait function
    if the info argument is NULL.

    If the info argument is non-NULL, the sigwaitinfo function
    behaves the same as sigwait, except that the selected signal
    number is stored in the si_signo member of the siginfo structure,
    and the cause of the signal is stored in the si_code member.
    If any value is queued to the selected signal, the first such
    queued value is dequeued and the value is stored in the si_value
    member of info. The system resource used to queue the signal is
    released and made available to queue other signals. If no value
    is queued, the content of the si_value member is undefined. If no
    further signals are queued for the selected signal, the pending
    indication for that signal is reset.

    See also sigtimedwait and sigwait.

    See the "Error and Signal Handling" chapter of the HP C RTL
    Reference Manual for more information on signal handling.