Sends a message to one or more terminals. The $BRKTHRU service
    completes asynchronously; that is, it returns to the caller after
    queuing the message request, without waiting for the message to
    be written to the specified terminals.

    For synchronous completion, use the Breakthrough and Wait
    ($BRKTHRUW) service. The $BRKTHRUW service is identical to the
    $BRKTHRU service in every way except that $BRKTHRUW returns
    to the caller after the message is written to the specified
    terminals.

    The $BRKTHRU service supersedes the Broadcast ($BRDCST) service.
    When writing new programs, you should use $BRKTHRU instead of
    $BRDCST. When updating old programs, you should change all uses
    of $BRDCST to $BRKTHRU.

    Format

      SYS$BRKTHRU  [efn] ,msgbuf [,sendto] [,sndtyp] [,iosb]

                   [,carcon] [,flags] [,reqid] [,timout] [,astadr]

                   [,astprm]

    C Prototype

      int sys$brkthru  (unsigned int efn, void *msgbuf, void *sendto,

                       unsigned int sndtyp, struct _iosb *iosb,

                       unsigned int carcon, unsigned int flags,

                       unsigned int reqid, unsigned int timout, void

                       (*astadr)(__unknown_params), int astprm);