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

    On Alpha processors, you can set watchpoints on variables or
    arbitrary program locations in global sections. A global section
    is a region of memory that is shared among all processes of a
    multiprocess program. A watchpoint that is set on a location in
    a global section (a global section watchpoint) triggers when any
    process modifies the contents of that location.

    You set a global section watchpoint just as you would set a
    watchpoint on a static variable. However, because of the way the
    debugger monitors global section watchpoints, note the following
    point. When setting watchpoints on arrays or records, performance
    is improved if you specify individual elements rather than the
    entire structure with the SET WATCH command.

    If you set a watchpoint on a location that is not yet mapped to
    a global section, the watchpoint is treated as a conventional
    static watchpoint. When the location is subsequently mapped
    to a global section, the watchpoint is automatically treated
    as a global section watchpoint and an informational message is
    issued. The watchpoint is then visible from each process of the
    multiprocess program.