If an error condition occurs, this routine returns an integer
    value indicating the type of error. Possible return values are as
    follows:

    Return      Description

    0           Successful completion.
    [EINVAL]    The value specified by the attr argument is not a
                valid thread attributes object, or the inheritsched
                argument contains an invalid value.
    [ENOTSUP]   An attempt was made to set the attribute to an
                unsupported value.