n                  Upon successful completion, a nonnegative
                       value is returned, indicating the number of
                       file descriptors for which poll has set the
                       revents bitmask.
    0                  poll has timed out and has not set any of the
                       revents bitmasks.
    -1                 An error occurred. errno is set to indicate
                       the error:

                       o  EAGAIN - Allocation of internal data
                          structures failed. A later call to the
                          poll function might complete successfully.

                       o  EINTR - A signal was intercepted during the
                          poll function, and the signal handler was
                          installed with an indication that functions
                          are not to be restarted.

                       o  EINVAL - The nfds parameter is greater than
                          OPEN_MAX, or one of the fd members refers
                          to a stream or multiplexer that is linked
                          (directly or indirectly) downstream from a
                          multiplexer.