When you are performing thread-synchronous "wait-form" system
    service calls on OpenVMS such as $QIOW, $ENQW, $GETJPIW, and
    so on, you should use this routine and tis_sync() with the
    asynchronous form of the service (in other words, without the
    "W"), and specify the address of tis_io_complete() as the
    completion AST routine (the AST argument if any is ignored).
    That must also specify an IOSB (or equivalent, such as an LKSB)
    and if possible a unique event flag (see lib$get_ef). Once the
    library code is ready to wait for the I/O, it simply calls tis_
    sync() (just as if it were calling $SYNC).