On successful completion, this routine returns the previous
    cancelability type in oldtype.

    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 specified type is not PTHREAD_CANCEL_DEFERRED or
                PTHREAD_CANCEL_AYNCHRONOUS.