Return_Values

   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.