x                  Upon successful completion, the signal number
                       selected is returned.
    -1                 Indicates that an error occurred; errno is set
                       to one of the following values:

                       o  EINVAL - The timeout argument specified a
                          tv_nsec value less than 0 or greater than
                          or equal to 1 billion.

                       o  EINTR - The wait was interrupted by an
                          unblocked, intercepted signal.

                       o  EAGAIN - No signal specified by set was
                          generated within the specified timeout
                          period.