Description
For Future, poll should not be called again after it returns Poll::Ready (terminating the future).
For Stream, poll_next should not be called again after it returns Poll::Ready(None) (terminating the stream).
I would like clarification on the equivalent contract for Sink, when one of its methods emits an error.
The documentation blurbs for poll_ready, start_send, and poll_flush state:
In most cases, if the sink encounters an error, the sink will permanently be unable to receive items.
Whereas the blurb for poll_close states:
If this function encounters an error, the sink should be considered to have failed permanently, and no more Sink methods should be called.
I'm interpreting this to mean that if any of poll_ready, start_send, and poll_flush emit an error, than none of poll_ready, start_send, or poll_flush can be called again on the same sink; however, poll_close can still be called. Whereas if poll_close emits an error, than none of poll_ready, start_send, poll_flush, or poll_close can be called again on the same sink.
Do I have that right? The phrase "unable to receive items" is not totally clear. For example, I could understand interpreting it to mean that poll_flush may be called again after poll_ready emits an error, as poll_flush is not about "receiving items", only processing ones that have already been submitted. However, that would imply that poll_flush can be called again after poll_flush emits an error, which I find strange.