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.
    [EAGAIN]    The system lacks the necessary resources to
                initialize another condition variable, or

                The system-imposed limit on the total number of
                condition variables under execution by a single user
                is exceeded.
    [EBUSY]     The implementation has detected an attempt to
                reinitialize the object referenced by cond, a
                previously initialized, but not yet destroyed
                condition variable.
    [EINVAL]    The value specified by attr is not a valid attributes
                object.
    [ENOMEM]    Insufficient memory exists to initialize the
                condition variable.