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 cond is not a valid condition
                variable or the value specified by mutex is not a
                valid mutex, or

                Different mutexes are supplied for concurrent
                tis_cond_wait()  operations on the same condition
                variable, or

                The mutex was not owned by the calling thread at the
                time of the call.