The Synchronize at a Barrier routine causes the caller to wait at
    the specified barrier. The barrier is in effect from the time the
    first participant calls PPL$WAIT_AT_BARRIER until each member of
    the quorum has issued the call. At that time, the wait concludes
    and all are released for further execution.

    Format

      PPL$WAIT_AT_BARRIER  barrier-id ,flags ,spin