| <!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/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">//! Middleware that allows balancing load among multiple services. |
| //! |
| //! In larger systems, multiple endpoints are often available for a given service. As load |
| //! increases, you want to ensure that that load is spread evenly across the available services. |
| //! Otherwise, clients could see spikes in latency if their request goes to a particularly loaded |
| //! service, even when spare capacity is available to handle that request elsewhere. |
| //! |
| //! This module provides two pieces of middleware that helps with this type of load balancing: |
| //! |
| //! First, [`p2c`] implements the "[Power of Two Random Choices]" algorithm, a simple but robust |
| //! technique for spreading load across services with only inexact load measurements. Use this if |
| //! the set of available services is not within your control, and you simply want to spread load |
| //! among that set of services. |
| //! |
| //! [Power of Two Random Choices]: http://www.eecs.harvard.edu/~michaelm/postscripts/handbook2001.pdf |
| //! |
| //! Second, [`pool`] implements a dynamically sized pool of services. It estimates the overall |
| //! current load by tracking successful and unsuccessful calls to [`poll_ready`], and uses an |
| //! exponentially weighted moving average to add (using [`MakeService`]) or remove (by dropping) |
| //! services in response to increases or decreases in load. Use this if you are able to |
| //! dynamically add more service endpoints to the system to handle added load. |
| //! |
| //! # Examples |
| //! |
| //! ```rust |
| //! # #[cfg(feature = "util")] |
| //! # #[cfg(feature = "load")] |
| //! # fn warnings_are_errors() { |
| //! use tower::balance::p2c::Balance; |
| //! use tower::load::Load; |
| //! use tower::{Service, ServiceExt}; |
| //! use futures_util::pin_mut; |
| //! # use futures_core::Stream; |
| //! # use futures_util::StreamExt; |
| //! |
| //! async fn spread<Req, S: Service<Req> + Load>(svc1: S, svc2: S, reqs: impl Stream<Item = Req>) |
| //! where |
| //! S::Error: Into<tower::BoxError>, |
| //! # // this bound is pretty unfortunate, and the compiler does _not_ help |
| //! S::Metric: std::fmt::Debug, |
| //! { |
| //! // Spread load evenly across the two services |
| //! let p2c = Balance::new(tower::discover::ServiceList::new(vec![svc1, svc2])); |
| //! |
| //! // Issue all the requests that come in. |
| //! // Some will go to svc1, some will go to svc2. |
| //! pin_mut!(reqs); |
| //! let mut responses = p2c.call_all(reqs); |
| //! while let Some(rsp) = responses.next().await { |
| //! // ... |
| //! } |
| //! } |
| //! # } |
| //! ``` |
| //! |
| //! [`MakeService`]: crate::MakeService |
| //! [`poll_ready`]: crate::Service::poll_ready |
| |
| </span><span class="kw">pub mod </span>error; |
| <span class="kw">pub mod </span>p2c; |
| <span class="kw">pub mod </span>pool; |
| </code></pre></div> |
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