| <!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/balance/p2c/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 </span><span class="kw">super</span>::<span class="kw">super</span>::error; |
| <span class="kw">use </span><span class="kw">crate</span>::discover::{Change, Discover}; |
| <span class="kw">use </span><span class="kw">crate</span>::load::Load; |
| <span class="kw">use </span><span class="kw">crate</span>::ready_cache::{error::Failed, ReadyCache}; |
| <span class="kw">use </span>futures_core::ready; |
| <span class="kw">use </span>futures_util::future::{<span class="self">self</span>, TryFutureExt}; |
| <span class="kw">use </span>pin_project_lite::pin_project; |
| <span class="kw">use </span>rand::{rngs::SmallRng, Rng, SeedableRng}; |
| <span class="kw">use </span>std::hash::Hash; |
| <span class="kw">use </span>std::marker::PhantomData; |
| <span class="kw">use </span>std::{ |
| fmt, |
| future::Future, |
| pin::Pin, |
| task::{Context, Poll}, |
| }; |
| <span class="kw">use </span>tokio::sync::oneshot; |
| <span class="kw">use </span>tower_service::Service; |
| <span class="kw">use </span>tracing::{debug, trace}; |
| |
| <span class="doccomment">/// Efficiently distributes requests across an arbitrary number of services. |
| /// |
| /// See the [module-level documentation](..) for details. |
| /// |
| /// Note that [`Balance`] requires that the [`Discover`] you use is [`Unpin`] in order to implement |
| /// [`Service`]. This is because it needs to be accessed from [`Service::poll_ready`], which takes |
| /// `&mut self`. You can achieve this easily by wrapping your [`Discover`] in [`Box::pin`] before you |
| /// construct the [`Balance`] instance. For more details, see [#319]. |
| /// |
| /// [`Box::pin`]: std::boxed::Box::pin() |
| /// [#319]: https://github.com/tower-rs/tower/issues/319 |
| </span><span class="kw">pub struct </span>Balance<D, Req> |
| <span class="kw">where |
| </span>D: Discover, |
| D::Key: Hash, |
| { |
| discover: D, |
| |
| services: ReadyCache<D::Key, D::Service, Req>, |
| ready_index: <span class="prelude-ty">Option</span><usize>, |
| |
| rng: SmallRng, |
| |
| _req: PhantomData<Req>, |
| } |
| |
| <span class="kw">impl</span><D: Discover, Req> fmt::Debug <span class="kw">for </span>Balance<D, Req> |
| <span class="kw">where |
| </span>D: fmt::Debug, |
| D::Key: Hash + fmt::Debug, |
| D::Service: fmt::Debug, |
| { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| f.debug_struct(<span class="string">"Balance"</span>) |
| .field(<span class="string">"discover"</span>, <span class="kw-2">&</span><span class="self">self</span>.discover) |
| .field(<span class="string">"services"</span>, <span class="kw-2">&</span><span class="self">self</span>.services) |
| .finish() |
| } |
| } |
| |
| <span class="macro">pin_project! </span>{ |
| <span class="doccomment">/// A Future that becomes satisfied when an `S`-typed service is ready. |
| /// |
| /// May fail due to cancelation, i.e., if [`Discover`] removes the service from the service set. |
| </span><span class="kw">struct </span>UnreadyService<K, S, Req> { |
| key: <span class="prelude-ty">Option</span><K>, |
| <span class="attribute">#[pin] |
| </span>cancel: oneshot::Receiver<()>, |
| service: <span class="prelude-ty">Option</span><S>, |
| |
| _req: PhantomData<Req>, |
| } |
| } |
| |
| <span class="kw">enum </span>Error<E> { |
| Inner(E), |
| Canceled, |
| } |
| |
| <span class="kw">impl</span><D, Req> Balance<D, Req> |
| <span class="kw">where |
| </span>D: Discover, |
| D::Key: Hash, |
| D::Service: Service<Req>, |
| <D::Service <span class="kw">as </span>Service<Req>>::Error: Into<<span class="kw">crate</span>::BoxError>, |
| { |
| <span class="doccomment">/// Constructs a load balancer that uses operating system entropy. |
| </span><span class="kw">pub fn </span>new(discover: D) -> <span class="self">Self </span>{ |
| <span class="self">Self</span>::from_rng(discover, <span class="kw-2">&mut </span>rand::thread_rng()).expect(<span class="string">"ThreadRNG must be valid"</span>) |
| } |
| |
| <span class="doccomment">/// Constructs a load balancer seeded with the provided random number generator. |
| </span><span class="kw">pub fn </span>from_rng<R: Rng>(discover: D, rng: R) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>, rand::Error> { |
| <span class="kw">let </span>rng = SmallRng::from_rng(rng)<span class="question-mark">?</span>; |
| <span class="prelude-val">Ok</span>(<span class="self">Self </span>{ |
| rng, |
| discover, |
| services: ReadyCache::default(), |
| ready_index: <span class="prelude-val">None</span>, |
| |
| _req: PhantomData, |
| }) |
| } |
| |
| <span class="doccomment">/// Returns the number of endpoints currently tracked by the balancer. |
| </span><span class="kw">pub fn </span>len(<span class="kw-2">&</span><span class="self">self</span>) -> usize { |
| <span class="self">self</span>.services.len() |
| } |
| |
| <span class="doccomment">/// Returns whether or not the balancer is empty. |
| </span><span class="kw">pub fn </span>is_empty(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.services.is_empty() |
| } |
| } |
| |
| <span class="kw">impl</span><D, Req> Balance<D, Req> |
| <span class="kw">where |
| </span>D: Discover + Unpin, |
| D::Key: Hash + Clone, |
| D::Error: Into<<span class="kw">crate</span>::BoxError>, |
| D::Service: Service<Req> + Load, |
| <D::Service <span class="kw">as </span>Load>::Metric: std::fmt::Debug, |
| <D::Service <span class="kw">as </span>Service<Req>>::Error: Into<<span class="kw">crate</span>::BoxError>, |
| { |
| <span class="doccomment">/// Polls `discover` for updates, adding new items to `not_ready`. |
| /// |
| /// Removals may alter the order of either `ready` or `not_ready`. |
| </span><span class="kw">fn </span>update_pending_from_discover( |
| <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">Option</span><<span class="prelude-ty">Result</span><(), error::Discover>>> { |
| <span class="macro">debug!</span>(<span class="string">"updating from discover"</span>); |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span><span class="macro">ready!</span>(Pin::new(<span class="kw-2">&mut </span><span class="self">self</span>.discover).poll_discover(cx)) |
| .transpose() |
| .map_err(|e| error::Discover(e.into()))<span class="question-mark">? |
| </span>{ |
| <span class="prelude-val">None </span>=> <span class="kw">return </span>Poll::Ready(<span class="prelude-val">None</span>), |
| <span class="prelude-val">Some</span>(Change::Remove(key)) => { |
| <span class="macro">trace!</span>(<span class="string">"remove"</span>); |
| <span class="self">self</span>.services.evict(<span class="kw-2">&</span>key); |
| } |
| <span class="prelude-val">Some</span>(Change::Insert(key, svc)) => { |
| <span class="macro">trace!</span>(<span class="string">"insert"</span>); |
| <span class="comment">// If this service already existed in the set, it will be |
| // replaced as the new one becomes ready. |
| </span><span class="self">self</span>.services.push(key, svc); |
| } |
| } |
| } |
| } |
| |
| <span class="kw">fn </span>promote_pending_to_ready(<span class="kw-2">&mut </span><span class="self">self</span>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) { |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span><span class="self">self</span>.services.poll_pending(cx) { |
| Poll::Ready(<span class="prelude-val">Ok</span>(())) => { |
| <span class="comment">// There are no remaining pending services. |
| </span><span class="macro">debug_assert_eq!</span>(<span class="self">self</span>.services.pending_len(), <span class="number">0</span>); |
| <span class="kw">break</span>; |
| } |
| Poll::Pending => { |
| <span class="comment">// None of the pending services are ready. |
| </span><span class="macro">debug_assert!</span>(<span class="self">self</span>.services.pending_len() > <span class="number">0</span>); |
| <span class="kw">break</span>; |
| } |
| Poll::Ready(<span class="prelude-val">Err</span>(error)) => { |
| <span class="comment">// An individual service was lost; continue processing |
| // pending services. |
| </span><span class="macro">debug!</span>(%error, <span class="string">"dropping failed endpoint"</span>); |
| } |
| } |
| } |
| <span class="macro">trace!</span>( |
| ready = %<span class="self">self</span>.services.ready_len(), |
| pending = %<span class="self">self</span>.services.pending_len(), |
| <span class="string">"poll_unready" |
| </span>); |
| } |
| |
| <span class="doccomment">/// Performs P2C on inner services to find a suitable endpoint. |
| </span><span class="kw">fn </span>p2c_ready_index(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><usize> { |
| <span class="kw">match </span><span class="self">self</span>.services.ready_len() { |
| <span class="number">0 </span>=> <span class="prelude-val">None</span>, |
| <span class="number">1 </span>=> <span class="prelude-val">Some</span>(<span class="number">0</span>), |
| len => { |
| <span class="comment">// Get two distinct random indexes (in a random order) and |
| // compare the loads of the service at each index. |
| </span><span class="kw">let </span>idxs = rand::seq::index::sample(<span class="kw-2">&mut </span><span class="self">self</span>.rng, len, <span class="number">2</span>); |
| |
| <span class="kw">let </span>aidx = idxs.index(<span class="number">0</span>); |
| <span class="kw">let </span>bidx = idxs.index(<span class="number">1</span>); |
| <span class="macro">debug_assert_ne!</span>(aidx, bidx, <span class="string">"random indices must be distinct"</span>); |
| |
| <span class="kw">let </span>aload = <span class="self">self</span>.ready_index_load(aidx); |
| <span class="kw">let </span>bload = <span class="self">self</span>.ready_index_load(bidx); |
| <span class="kw">let </span>chosen = <span class="kw">if </span>aload <= bload { aidx } <span class="kw">else </span>{ bidx }; |
| |
| <span class="macro">trace!</span>( |
| a.index = aidx, |
| a.load = <span class="question-mark">?</span>aload, |
| b.index = bidx, |
| b.load = <span class="question-mark">?</span>bload, |
| chosen = <span class="kw">if </span>chosen == aidx { <span class="string">"a" </span>} <span class="kw">else </span>{ <span class="string">"b" </span>}, |
| <span class="string">"p2c"</span>, |
| ); |
| <span class="prelude-val">Some</span>(chosen) |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Accesses a ready endpoint by index and returns its current load. |
| </span><span class="kw">fn </span>ready_index_load(<span class="kw-2">&</span><span class="self">self</span>, index: usize) -> <D::Service <span class="kw">as </span>Load>::Metric { |
| <span class="kw">let </span>(<span class="kw">_</span>, svc) = <span class="self">self</span>.services.get_ready_index(index).expect(<span class="string">"invalid index"</span>); |
| svc.load() |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>discover_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>D { |
| <span class="kw-2">&mut </span><span class="self">self</span>.discover |
| } |
| } |
| |
| <span class="kw">impl</span><D, Req> Service<Req> <span class="kw">for </span>Balance<D, Req> |
| <span class="kw">where |
| </span>D: Discover + Unpin, |
| D::Key: Hash + Clone, |
| D::Error: Into<<span class="kw">crate</span>::BoxError>, |
| D::Service: Service<Req> + Load, |
| <D::Service <span class="kw">as </span>Load>::Metric: std::fmt::Debug, |
| <D::Service <span class="kw">as </span>Service<Req>>::Error: Into<<span class="kw">crate</span>::BoxError>, |
| { |
| <span class="kw">type </span>Response = <D::Service <span class="kw">as </span>Service<Req>>::Response; |
| <span class="kw">type </span>Error = <span class="kw">crate</span>::BoxError; |
| <span class="kw">type </span>Future = future::MapErr< |
| <D::Service <span class="kw">as </span>Service<Req>>::Future, |
| <span class="kw">fn</span>(<D::Service <span class="kw">as </span>Service<Req>>::Error) -> <span class="kw">crate</span>::BoxError, |
| >; |
| |
| <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">// `ready_index` may have already been set by a prior invocation. These |
| // updates cannot disturb the order of existing ready services. |
| </span><span class="kw">let _ </span>= <span class="self">self</span>.update_pending_from_discover(cx)<span class="question-mark">?</span>; |
| <span class="self">self</span>.promote_pending_to_ready(cx); |
| |
| <span class="kw">loop </span>{ |
| <span class="comment">// If a service has already been selected, ensure that it is ready. |
| // This ensures that the underlying service is ready immediately |
| // before a request is dispatched to it (i.e. in the same task |
| // invocation). If, e.g., a failure detector has changed the state |
| // of the service, it may be evicted from the ready set so that |
| // another service can be selected. |
| </span><span class="kw">if let </span><span class="prelude-val">Some</span>(index) = <span class="self">self</span>.ready_index.take() { |
| <span class="kw">match </span><span class="self">self</span>.services.check_ready_index(cx, index) { |
| <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>) => { |
| <span class="comment">// The service remains ready. |
| </span><span class="self">self</span>.ready_index = <span class="prelude-val">Some</span>(index); |
| <span class="kw">return </span>Poll::Ready(<span class="prelude-val">Ok</span>(())); |
| } |
| <span class="prelude-val">Ok</span>(<span class="bool-val">false</span>) => { |
| <span class="comment">// The service is no longer ready. Try to find a new one. |
| </span><span class="macro">trace!</span>(<span class="string">"ready service became unavailable"</span>); |
| } |
| <span class="prelude-val">Err</span>(Failed(<span class="kw">_</span>, error)) => { |
| <span class="comment">// The ready endpoint failed, so log the error and try |
| // to find a new one. |
| </span><span class="macro">debug!</span>(%error, <span class="string">"endpoint failed"</span>); |
| } |
| } |
| } |
| |
| <span class="comment">// Select a new service by comparing two at random and using the |
| // lesser-loaded service. |
| </span><span class="self">self</span>.ready_index = <span class="self">self</span>.p2c_ready_index(); |
| <span class="kw">if </span><span class="self">self</span>.ready_index.is_none() { |
| <span class="macro">debug_assert_eq!</span>(<span class="self">self</span>.services.ready_len(), <span class="number">0</span>); |
| <span class="comment">// We have previously registered interest in updates from |
| // discover and pending services. |
| </span><span class="kw">return </span>Poll::Pending; |
| } |
| } |
| } |
| |
| <span class="kw">fn </span>call(<span class="kw-2">&mut </span><span class="self">self</span>, request: Req) -> <span class="self">Self</span>::Future { |
| <span class="kw">let </span>index = <span class="self">self</span>.ready_index.take().expect(<span class="string">"called before ready"</span>); |
| <span class="self">self</span>.services |
| .call_ready_index(index, request) |
| .map_err(Into::into) |
| } |
| } |
| |
| <span class="kw">impl</span><K, S: Service<Req>, Req> Future <span class="kw">for </span>UnreadyService<K, S, Req> { |
| <span class="kw">type </span>Output = <span class="prelude-ty">Result</span><(K, S), (K, Error<S::Error>)>; |
| |
| <span class="kw">fn </span>poll(<span class="self">self</span>: Pin<<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="self">Self</span>::Output> { |
| <span class="kw">let </span>this = <span class="self">self</span>.project(); |
| |
| <span class="kw">if let </span>Poll::Ready(<span class="prelude-val">Ok</span>(())) = this.cancel.poll(cx) { |
| <span class="kw">let </span>key = this.key.take().expect(<span class="string">"polled after ready"</span>); |
| <span class="kw">return </span>Poll::Ready(<span class="prelude-val">Err</span>((key, Error::Canceled))); |
| } |
| |
| <span class="kw">let </span>res = <span class="macro">ready!</span>(this |
| .service |
| .as_mut() |
| .expect(<span class="string">"poll after ready"</span>) |
| .poll_ready(cx)); |
| |
| <span class="kw">let </span>key = this.key.take().expect(<span class="string">"polled after ready"</span>); |
| <span class="kw">let </span>svc = this.service.take().expect(<span class="string">"polled after ready"</span>); |
| |
| <span class="kw">match </span>res { |
| <span class="prelude-val">Ok</span>(()) => Poll::Ready(<span class="prelude-val">Ok</span>((key, svc))), |
| <span class="prelude-val">Err</span>(e) => Poll::Ready(<span class="prelude-val">Err</span>((key, Error::Inner(e)))), |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><K, S, Req> fmt::Debug <span class="kw">for </span>UnreadyService<K, S, Req> |
| <span class="kw">where |
| </span>K: fmt::Debug, |
| S: fmt::Debug, |
| { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter) -> fmt::Result { |
| <span class="kw">let </span><span class="self">Self </span>{ |
| key, |
| cancel, |
| service, |
| _req, |
| } = <span class="self">self</span>; |
| f.debug_struct(<span class="string">"UnreadyService"</span>) |
| .field(<span class="string">"key"</span>, key) |
| .field(<span class="string">"cancel"</span>, cancel) |
| .field(<span class="string">"service"</span>, service) |
| .finish() |
| } |
| } |
| </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> |
