Type Definition futures::
type Poll<T, E> = Result<Async<T>, E>;
A convenience wrapper for
Poll is the return type of the
poll method on the
Ok(Async::Ready(t))means the future has successfully resolved.
Ok(Async::Pending)means the future is not able to fully resolve yet. The current task will be awoken when the future can make further progress.
Err(e)means that an error was encountered when attempting to complete the future.
Futures which have returned errors are complete, and should not be polled again. However,
Streams that have returned errors may not be complete and should still be polled.