This routine initializes the thread attributes object specified
    by the attr argument with a set of default attribute values. A
    thread attributes object is used to specify the attributes of
    one or more threads when they are created. The attributes object
    created by this routine is used only in calls to the pthread_
    create() routine.

    The following routines change individual attributes of an
    initialized thread attributes object:

       pthread_attr_setdetachstate()
       pthread_attr_setguardsize()
       pthread_attr_setinheritsched()
       pthread_attr_setschedparam()
       pthread_attr_setschedpolicy()
       pthread_attr_setscope()
       pthread_attr_setstackaddr()
       pthread_attr_setstacksize()

    The attributes of the thread attributes object are initialized to
    default values. The default value of each attribute is discussed
    in the reference description for each routine previously listed.

    When a thread attributes object is used to create a thread,
    the object's attribute values determine the characteristics
    of the new thread. Thus, attributes objects act as additional
    arguments to thread creation. Changing the attributes of a
    thread attributes object does not affect any threads that were
    previously created using that attributes object.

    You can use the same thread attributes object in successive calls
    to pthread_create(), from any thread. (However, you cannot use
    the same value of the stack address attribute to create multiple
    threads that might run concurrently; threads cannot share a
    stack.) If more than one thread might change the attributes in
    a shared attributes object, your program must use a mutex to
    protect the integrity of the attributes object's contents.

    When you set the scheduling policy or scheduling parameters,
    or both, in a thread attributes object, you must disable
    scheduling inheritance if you want the scheduling attributes
    you set to be used at thread creation. To disable scheduling
    inheritance, before creating the new thread use the pthread_attr_
    setinheritsched() routine to specify the value PTHREAD_EXPLICIT_
    SCHED for the inherit argument.