VMS Help System Services, $BRKTHRUW  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Sends a message to one or more terminals. The $BRKTHRUW service
    operates synchronously; that is, it returns to the caller after
    the message has been sent to the specified terminals.

    For asynchronous operations, use the Breakthrough ($BRKTHRU)
    service; $BRKTHRU returns to the caller after queuing the message
    request, without waiting for the message to be delivered.

    Aside from the preceding, $BRKTHRUW is identical to $BRKTHRU. For
    all other information about the $BRKTHRUW service, refer to the
    description of $BRKTHRU.

    The $BRKTHRU and $BRKTHRUW services supersede the Broadcast
    ($BRDCST) service. When writing new programs, you should use
    $BRKTHRU or $BRKTHRUW instead of $BRDCST. When updating old
    programs, you should change all uses of $BRDCST to $BRKTHRU or
    $BRKTHRUW. $BRDCST is now an obsolete system service and is no
    longer being enhanced.

    Format

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

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

                    [,astprm]

    C Prototype

      int sys$brkthruw  (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);