119 lines
3.9 KiB
Rust
119 lines
3.9 KiB
Rust
use super::{
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future::ResponseFuture,
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message::Message,
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worker::{Handle, Worker},
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BatchControl,
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};
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use futures_core::ready;
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use std::task::{Context, Poll};
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use tokio::sync::{mpsc, oneshot};
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use tower::Service;
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/// Allows batch processing of requests.
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///
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/// See the module documentation for more details.
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#[derive(Debug)]
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pub struct Batch<T, Request>
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where
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T: Service<BatchControl<Request>>,
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{
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tx: mpsc::Sender<Message<Request, T::Future>>,
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handle: Handle,
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}
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impl<T, Request> Batch<T, Request>
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where
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T: Service<BatchControl<Request>>,
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T::Error: Into<crate::BoxError>,
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{
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/// Creates a new `Batch` wrapping `service`.
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///
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/// The wrapper is responsible for telling the inner service when to flush a
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/// batch of requests. Two parameters control this policy:
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///
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/// * `max_items` gives the maximum number of items per batch.
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/// * `max_latency` gives the maximum latency for a batch item.
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///
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/// The default Tokio executor is used to run the given service, which means
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/// that this method must be called while on the Tokio runtime.
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pub fn new(service: T, max_items: usize, max_latency: std::time::Duration) -> Self
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where
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T: Send + 'static,
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T::Future: Send,
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T::Error: Send + Sync,
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Request: Send + 'static,
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{
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// XXX(hdevalence): is this bound good
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let (tx, rx) = mpsc::channel(1);
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let (handle, worker) = Worker::new(service, rx, max_items, max_latency);
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tokio::spawn(worker.run());
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Batch { tx, handle }
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}
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fn get_worker_error(&self) -> crate::BoxError {
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self.handle.get_error_on_closed()
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}
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}
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impl<T, Request> Service<Request> for Batch<T, Request>
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where
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T: Service<BatchControl<Request>>,
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T::Error: Into<crate::BoxError>,
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{
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type Response = T::Response;
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type Error = crate::BoxError;
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type Future = ResponseFuture<T::Future>;
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fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
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// If the inner service has errored, then we error here.
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if ready!(self.tx.poll_ready(cx)).is_err() {
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Poll::Ready(Err(self.get_worker_error()))
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} else {
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Poll::Ready(Ok(()))
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}
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}
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fn call(&mut self, request: Request) -> Self::Future {
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// TODO:
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// ideally we'd poll_ready again here so we don't allocate the oneshot
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// if the try_send is about to fail, but sadly we can't call poll_ready
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// outside of task context.
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let (tx, rx) = oneshot::channel();
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// get the current Span so that we can explicitly propagate it to the worker
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// if we didn't do this, events on the worker related to this span wouldn't be counted
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// towards that span since the worker would have no way of entering it.
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let span = tracing::Span::current();
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tracing::trace!(parent: &span, "sending request to batch worker");
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match self.tx.try_send(Message { request, span, tx }) {
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Err(mpsc::error::TrySendError::Closed(_)) => {
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ResponseFuture::failed(self.get_worker_error())
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}
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Err(mpsc::error::TrySendError::Full(_)) => {
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// When `mpsc::Sender::poll_ready` returns `Ready`, a slot
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// in the channel is reserved for the handle. Other `Sender`
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// handles may not send a message using that slot. This
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// guarantees capacity for `request`.
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//
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// Given this, the only way to hit this code path is if
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// `poll_ready` has not been called & `Ready` returned.
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panic!("buffer full; poll_ready must be called first");
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}
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Ok(_) => ResponseFuture::new(rx),
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}
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}
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}
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impl<T, Request> Clone for Batch<T, Request>
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where
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T: Service<BatchControl<Request>>,
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{
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fn clone(&self) -> Self {
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Self {
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tx: self.tx.clone(),
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handle: self.handle.clone(),
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}
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}
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}
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