VMS Help POSIX Threads, PTHREAD routines, pthread_attr_setschedpolicy, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This routine sets the scheduling policy of a thread that is
    created using the attributes object specified by the attr
    argument. The default value of the scheduling attribute is SCHED_
    OTHER.

    By default, a created thread inherits the policy of the thread
    calling pthread_create(). To specify a policy using this routine,
    scheduling inheritance must be disabled at the time the thread
    is created. Before calling pthread_create(), call pthread_attr_
    setinheritsched() and specify the value PTHREAD_EXPLICIT_SCHED
    for the inherit argument.

    Preemption is caused by both scheduling and policy. Never attempt
    to use scheduling as a mechanism for synchronization.