Library /sys$common/syshlp/dbg$help.hlb DEBUG, SET, THREAD, Qualifiers, /PRIORITY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /PRIORITY=n

    When the event facility is THREADS, use the PTHREAD
    tset -s thread-number command.

    Sets the priority of a specified task to n, where n is a decimal
    integer from 0 to 15. This does not prevent the priority from
    later changing in the course of execution, for example, while
    executing an Ada rendezvous or POSIX Threads synchronization
    event. This qualifier does not affect a task's scheduling policy.

    You can get help on POSIX Threads debugger commands by typing
    PTHREAD HELP.

    See the Guide to POSIX Threads Library for more information about
    using the POSIX Threads debugger.