74 lines
2.1 KiB
Rust
74 lines
2.1 KiB
Rust
//! Future types for the `Batch` middleware.
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use super::{error::Closed, message};
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use futures_core::ready;
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use pin_project::pin_project;
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use std::{
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future::Future,
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pin::Pin,
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task::{Context, Poll},
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};
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/// Future that completes when the batch processing is complete.
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#[pin_project]
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#[derive(Debug)]
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pub struct ResponseFuture<T> {
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#[pin]
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state: ResponseState<T>,
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}
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#[pin_project(project = ResponseStateProj)]
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#[derive(Debug)]
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enum ResponseState<T> {
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Failed(Option<crate::BoxError>),
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Rx(#[pin] message::Rx<T>),
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Poll(#[pin] T),
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}
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impl<T> ResponseFuture<T> {
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pub(crate) fn new(rx: message::Rx<T>) -> Self {
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ResponseFuture {
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state: ResponseState::Rx(rx),
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}
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}
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pub(crate) fn failed(err: crate::BoxError) -> Self {
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ResponseFuture {
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state: ResponseState::Failed(Some(err)),
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}
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}
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}
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impl<F, T, E> Future for ResponseFuture<F>
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where
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F: Future<Output = Result<T, E>>,
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E: Into<crate::BoxError>,
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{
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type Output = Result<T, crate::BoxError>;
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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let mut this = self.project();
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// CORRECTNESS
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//
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// The current task must be scheduled for wakeup every time we return
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// `Poll::Pending`.
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//
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// This loop ensures that the task is scheduled as required, because it
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// only returns Pending when another future returns Pending.
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loop {
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match this.state.as_mut().project() {
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ResponseStateProj::Failed(e) => {
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return Poll::Ready(Err(e.take().expect("polled after error")));
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}
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ResponseStateProj::Rx(rx) => match ready!(rx.poll(cx)) {
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Ok(Ok(f)) => this.state.set(ResponseState::Poll(f)),
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Ok(Err(e)) => return Poll::Ready(Err(e.into())),
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Err(_) => return Poll::Ready(Err(Closed::new().into())),
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},
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ResponseStateProj::Poll(fut) => return fut.poll(cx).map_err(Into::into),
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}
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}
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}
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}
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