Kernel threads allow a multithreaded application to have a thread
    executing on every CPU in a multiprocessor system. The /THREADS_
    ENABLE qualifier allows you to turn kernel threads on and off on
    a per-image basis.

    When you specify this qualifier, the OpenVMS linker sets the
    appropriate bits in the dynamic segment (I64) or the image header
    (Alpha and VAX) of the image being linked. These bits control the
    following:

    o  Whether the image is allowed to enter a multiple kernel
       threads environment

    o  Whether the image can receive upcalls from the OpenVMS
       scheduler

    Format

      /THREADS_ENABLE[=(MULTIPLE_KERNEL_THREADS,UPCALLS)]

      /NOTHREADS_ENABLE (default)

1 - Qualifier Values

 MULTIPLE_KERNEL_THREADS

    On I64 and Alpha systems, this keyword sets the MULTIPLE_KERNEL_
    THREADS bit in the dynamic segment (I64) or the image header
    (Alpha) of the image being built. This bit indicates to the image
    activator that the image can be run in a multiple kernel threads
    environment.

    If you specify this keyword for OpenVMS VAX links, it is ignored.

 UPCALLS

    This qualifier sets the UPCALLS bit in the OpenVMS dynamic
    segment (I64) or image header (Alpha and VAX) of the image being
    built. This bit indicates to the image activator that the process
    can receive upcalls from the OpenVMS scheduler.

    When the /THREADS_ENABLE qualifier is specified without either
    the MULTIPLE_KERNEL_THREADS or UPCALLS keyword, the linker sets
    both bits by default.