| <!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/load/mod.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>mod.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="doccomment">//! Service load measurement |
| //! |
| //! This module provides the [`Load`] trait, which allows measuring how loaded a service is. |
| //! It also provides several wrapper types that measure load in different ways: |
| //! |
| //! - [`Constant`] — Always returns the same constant load value for a service. |
| //! - [`PendingRequests`] — Measures load by tracking the number of in-flight requests. |
| //! - [`PeakEwma`] — Measures load using a moving average of the peak latency for the service. |
| //! |
| //! In general, you will want to use one of these when using the types in [`tower::balance`] which |
| //! balance services depending on their load. Which load metric to use depends on your exact |
| //! use-case, but the ones above should get you quite far! |
| //! |
| //! When the `discover` feature is enabled, wrapper types for [`Discover`] that |
| //! wrap the discovered services with the given load estimator are also provided. |
| //! |
| //! # When does a request complete? |
| //! |
| //! For many applications, the request life-cycle is relatively simple: when a service responds to |
| //! a request, that request is done, and the system can forget about it. However, for some |
| //! applications, the service may respond to the initial request while other parts of the system |
| //! are still acting on that request. In such an application, the system load must take these |
| //! requests into account as well, or risk the system underestimating its own load. |
| //! |
| //! To support these use-cases, the load estimators in this module are parameterized by the |
| //! [`TrackCompletion`] trait, with [`CompleteOnResponse`] as the default type. The behavior of |
| //! [`CompleteOnResponse`] is what you would normally expect for a request-response cycle: when the |
| //! response is produced, the request is considered "finished", and load goes down. This can be |
| //! overriden by your own user-defined type to track more complex request completion semantics. See |
| //! the documentation for [`completion`] for more details. |
| //! |
| //! # Examples |
| //! |
| //! ```rust |
| //! # #[cfg(feature = "util")] |
| //! use tower::util::ServiceExt; |
| //! # #[cfg(feature = "util")] |
| //! use tower::{load::Load, Service}; |
| //! # #[cfg(feature = "util")] |
| //! async fn simple_balance<S1, S2, R>( |
| //! svc1: &mut S1, |
| //! svc2: &mut S2, |
| //! request: R |
| //! ) -> Result<S1::Response, S1::Error> |
| //! where |
| //! S1: Load + Service<R>, |
| //! S2: Load<Metric = S1::Metric> + Service<R, Response = S1::Response, Error = S1::Error> |
| //! { |
| //! if svc1.load() < svc2.load() { |
| //! svc1.ready().await?.call(request).await |
| //! } else { |
| //! svc2.ready().await?.call(request).await |
| //! } |
| //! } |
| //! ``` |
| //! |
| //! [`tower::balance`]: crate::balance |
| //! [`Discover`]: crate::discover::Discover |
| //! [`CompleteOnResponse`]: crate::load::completion::CompleteOnResponse |
| </span><span class="comment">// TODO: a custom completion example would be good here |
| |
| </span><span class="kw">pub mod </span>completion; |
| <span class="kw">mod </span>constant; |
| <span class="kw">pub mod </span>peak_ewma; |
| <span class="kw">pub mod </span>pending_requests; |
| |
| <span class="kw">pub use </span><span class="self">self</span>::{ |
| completion::{CompleteOnResponse, TrackCompletion}, |
| constant::Constant, |
| peak_ewma::PeakEwma, |
| pending_requests::PendingRequests, |
| }; |
| |
| <span class="attribute">#[cfg(feature = <span class="string">"discover"</span>)] |
| </span><span class="kw">pub use </span><span class="self">self</span>::{peak_ewma::PeakEwmaDiscover, pending_requests::PendingRequestsDiscover}; |
| |
| <span class="doccomment">/// Types that implement this trait can give an estimate of how loaded they are. |
| /// |
| /// See the module documentation for more details. |
| </span><span class="kw">pub trait </span>Load { |
| <span class="doccomment">/// A comparable load metric. |
| /// |
| /// Lesser values indicate that the service is less loaded, and should be preferred for new |
| /// requests over another service with a higher value. |
| </span><span class="kw">type </span>Metric: PartialOrd; |
| |
| <span class="doccomment">/// Estimate the service's current load. |
| </span><span class="kw">fn </span>load(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="self">Self</span>::Metric; |
| } |
| </code></pre></div> |
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