| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/tower-0.4.13/src/buffer/service.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>service.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../source-script.js"></script><script defer src="../../../source-files.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../tower/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../tower/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use super</span>::{ |
| future::ResponseFuture, |
| message::Message, |
| worker::{Handle, Worker}, |
| }; |
| |
| <span class="kw">use </span>futures_core::ready; |
| <span class="kw">use </span>std::sync::Arc; |
| <span class="kw">use </span>std::task::{Context, Poll}; |
| <span class="kw">use </span>tokio::sync::{mpsc, oneshot, OwnedSemaphorePermit, Semaphore}; |
| <span class="kw">use </span>tokio_util::sync::PollSemaphore; |
| <span class="kw">use </span>tower_service::Service; |
| |
| <span class="doccomment">/// Adds an mpsc buffer in front of an inner service. |
| /// |
| /// See the module documentation for more details. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>Buffer<T, Request> |
| <span class="kw">where |
| </span>T: Service<Request>, |
| { |
| <span class="comment">// Note: this actually _is_ bounded, but rather than using Tokio's bounded |
| // channel, we use Tokio's semaphore separately to implement the bound. |
| </span>tx: mpsc::UnboundedSender<Message<Request, T::Future>>, |
| <span class="comment">// When the buffer's channel is full, we want to exert backpressure in |
| // `poll_ready`, so that callers such as load balancers could choose to call |
| // another service rather than waiting for buffer capacity. |
| // |
| // Unfortunately, this can't be done easily using Tokio's bounded MPSC |
| // channel, because it doesn't expose a polling-based interface, only an |
| // `async fn ready`, which borrows the sender. Therefore, we implement our |
| // own bounded MPSC on top of the unbounded channel, using a semaphore to |
| // limit how many items are in the channel. |
| </span>semaphore: PollSemaphore, |
| <span class="comment">// The current semaphore permit, if one has been acquired. |
| // |
| // This is acquired in `poll_ready` and taken in `call`. |
| </span>permit: <span class="prelude-ty">Option</span><OwnedSemaphorePermit>, |
| handle: Handle, |
| } |
| |
| <span class="kw">impl</span><T, Request> Buffer<T, Request> |
| <span class="kw">where |
| </span>T: Service<Request>, |
| T::Error: Into<<span class="kw">crate</span>::BoxError>, |
| { |
| <span class="doccomment">/// Creates a new [`Buffer`] wrapping `service`. |
| /// |
| /// `bound` gives the maximal number of requests that can be queued for the service before |
| /// backpressure is applied to callers. |
| /// |
| /// The default Tokio executor is used to run the given service, which means that this method |
| /// must be called while on the Tokio runtime. |
| /// |
| /// # A note on choosing a `bound` |
| /// |
| /// When [`Buffer`]'s implementation of [`poll_ready`] returns [`Poll::Ready`], it reserves a |
| /// slot in the channel for the forthcoming [`call`]. However, if this call doesn't arrive, |
| /// this reserved slot may be held up for a long time. As a result, it's advisable to set |
| /// `bound` to be at least the maximum number of concurrent requests the [`Buffer`] will see. |
| /// If you do not, all the slots in the buffer may be held up by futures that have just called |
| /// [`poll_ready`] but will not issue a [`call`], which prevents other senders from issuing new |
| /// requests. |
| /// |
| /// [`Poll::Ready`]: std::task::Poll::Ready |
| /// [`call`]: crate::Service::call |
| /// [`poll_ready`]: crate::Service::poll_ready |
| </span><span class="kw">pub fn </span>new(service: T, bound: usize) -> <span class="self">Self |
| </span><span class="kw">where |
| </span>T: Send + <span class="lifetime">'static</span>, |
| T::Future: Send, |
| T::Error: Send + Sync, |
| Request: Send + <span class="lifetime">'static</span>, |
| { |
| <span class="kw">let </span>(service, worker) = <span class="self">Self</span>::pair(service, bound); |
| tokio::spawn(worker); |
| service |
| } |
| |
| <span class="doccomment">/// Creates a new [`Buffer`] wrapping `service`, but returns the background worker. |
| /// |
| /// This is useful if you do not want to spawn directly onto the tokio runtime |
| /// but instead want to use your own executor. This will return the [`Buffer`] and |
| /// the background `Worker` that you can then spawn. |
| </span><span class="kw">pub fn </span>pair(service: T, bound: usize) -> (Buffer<T, Request>, Worker<T, Request>) |
| <span class="kw">where |
| </span>T: Send + <span class="lifetime">'static</span>, |
| T::Error: Send + Sync, |
| Request: Send + <span class="lifetime">'static</span>, |
| { |
| <span class="kw">let </span>(tx, rx) = mpsc::unbounded_channel(); |
| <span class="kw">let </span>semaphore = Arc::new(Semaphore::new(bound)); |
| <span class="kw">let </span>(handle, worker) = Worker::new(service, rx, <span class="kw-2">&</span>semaphore); |
| <span class="kw">let </span>buffer = Buffer { |
| tx, |
| handle, |
| semaphore: PollSemaphore::new(semaphore), |
| permit: <span class="prelude-val">None</span>, |
| }; |
| (buffer, worker) |
| } |
| |
| <span class="kw">fn </span>get_worker_error(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw">crate</span>::BoxError { |
| <span class="self">self</span>.handle.get_error_on_closed() |
| } |
| } |
| |
| <span class="kw">impl</span><T, Request> Service<Request> <span class="kw">for </span>Buffer<T, Request> |
| <span class="kw">where |
| </span>T: Service<Request>, |
| T::Error: Into<<span class="kw">crate</span>::BoxError>, |
| { |
| <span class="kw">type </span>Response = T::Response; |
| <span class="kw">type </span>Error = <span class="kw">crate</span>::BoxError; |
| <span class="kw">type </span>Future = ResponseFuture<T::Future>; |
| |
| <span class="kw">fn </span>poll_ready(<span class="kw-2">&mut </span><span class="self">self</span>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="prelude-ty">Result</span><(), <span class="self">Self</span>::Error>> { |
| <span class="comment">// First, check if the worker is still alive. |
| </span><span class="kw">if </span><span class="self">self</span>.tx.is_closed() { |
| <span class="comment">// If the inner service has errored, then we error here. |
| </span><span class="kw">return </span>Poll::Ready(<span class="prelude-val">Err</span>(<span class="self">self</span>.get_worker_error())); |
| } |
| |
| <span class="comment">// Then, check if we've already acquired a permit. |
| </span><span class="kw">if </span><span class="self">self</span>.permit.is_some() { |
| <span class="comment">// We've already reserved capacity to send a request. We're ready! |
| </span><span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(())); |
| } |
| |
| <span class="comment">// Finally, if we haven't already acquired a permit, poll the semaphore |
| // to acquire one. If we acquire a permit, then there's enough buffer |
| // capacity to send a new request. Otherwise, we need to wait for |
| // capacity. |
| </span><span class="kw">let </span>permit = |
| <span class="macro">ready!</span>(<span class="self">self</span>.semaphore.poll_acquire(cx)).ok_or_else(|| <span class="self">self</span>.get_worker_error())<span class="question-mark">?</span>; |
| <span class="self">self</span>.permit = <span class="prelude-val">Some</span>(permit); |
| |
| Poll::Ready(<span class="prelude-val">Ok</span>(())) |
| } |
| |
| <span class="kw">fn </span>call(<span class="kw-2">&mut </span><span class="self">self</span>, request: Request) -> <span class="self">Self</span>::Future { |
| <span class="macro">tracing::trace!</span>(<span class="string">"sending request to buffer worker"</span>); |
| <span class="kw">let </span>_permit = <span class="self">self |
| </span>.permit |
| .take() |
| .expect(<span class="string">"buffer full; poll_ready must be called first"</span>); |
| |
| <span class="comment">// get the current Span so that we can explicitly propagate it to the worker |
| // if we didn't do this, events on the worker related to this span wouldn't be counted |
| // towards that span since the worker would have no way of entering it. |
| </span><span class="kw">let </span>span = tracing::Span::current(); |
| |
| <span class="comment">// If we've made it here, then a semaphore permit has already been |
| // acquired, so we can freely allocate a oneshot. |
| </span><span class="kw">let </span>(tx, rx) = oneshot::channel(); |
| |
| <span class="kw">match </span><span class="self">self</span>.tx.send(Message { |
| request, |
| span, |
| tx, |
| _permit, |
| }) { |
| <span class="prelude-val">Err</span>(<span class="kw">_</span>) => ResponseFuture::failed(<span class="self">self</span>.get_worker_error()), |
| <span class="prelude-val">Ok</span>(<span class="kw">_</span>) => ResponseFuture::new(rx), |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T, Request> Clone <span class="kw">for </span>Buffer<T, Request> |
| <span class="kw">where |
| </span>T: Service<Request>, |
| { |
| <span class="kw">fn </span>clone(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="self">Self </span>{ |
| <span class="self">Self </span>{ |
| tx: <span class="self">self</span>.tx.clone(), |
| handle: <span class="self">self</span>.handle.clone(), |
| semaphore: <span class="self">self</span>.semaphore.clone(), |
| <span class="comment">// The new clone hasn't acquired a permit yet. It will when it's |
| // next polled ready. |
| </span>permit: <span class="prelude-val">None</span>, |
| } |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tower" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
