This routine obtains the value of the contention scope attribute
    of the thread attributes object specified in the attr argument
    and stores it in the location specified by the scope argument.
    The specified attributes object must already be initialized at
    the time this routine is called.

    The contention scope attribute specifies the set of threads
    with which a thread must compete for processing resources. The
    contention scope attribute specifies whether the new thread
    competes for processing resources only with other threads in its
    own process, called process contention scope, or with all threads
    on the system, called system contention scope.

    The Threads Library selects at most one thread to execute on
    each processor at any point in time. The Threads Library resolves
    the contention based on each thread's scheduling attributes (for
    example, priority) and scheduling policy (for example, round-
    robin).

    A thread created using a thread attributes object whose
    contention scope attribute is set to PTHREAD_SCOPE_PROCESS
    contends for processing resources with other threads within its
    own process that also were created with PTHREAD_SCOPE_PROCESS.
    It is unspecified how such threads are scheduled relative to
    threads in other processes or threads in the same process that
    were created with PTHREAD_SCOPE_SYSTEM contention scope.

    A thread created using a thread attributes object whose
    contention scope attribute is set to PTHREAD_SCOPE_SYSTEM
    contends for processing resources with other threads in any
    process that also were created with PTHREAD_SCOPE_SYSTEM.

    Note that the value of the contention scope attribute of a
    particular thread attributes object does not necessarily
    correspond to the actual scheduling contention scope of any
    existing thread in your multithreaded program.