| <!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="This module defines a load-balanced pool of services that adds new services when load is high."><meta name="keywords" content="rust, rustlang, rust-lang, pool"><title>tower::balance::pool - Rust</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="../../../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 mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../../tower/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><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><h2 class="location"><a href="#">Module pool</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#structs">Structs</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><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="main-heading"><h1 class="fqn">Module <a href="../../index.html">tower</a>::<wbr><a href="../index.html">balance</a>::<wbr><a class="mod" href="#">pool</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../../src/tower/balance/pool/mod.rs.html#1-459">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>This module defines a load-balanced pool of services that adds new services when load is high.</p> |
| <p>The pool uses <code>poll_ready</code> as a signal indicating whether additional services should be spawned |
| to handle the current level of load. Specifically, every time <code>poll_ready</code> on the inner service |
| returns <code>Ready</code>, <a href="struct.Pool.html" title="Pool"><code>Pool</code></a> consider that a 0, and every time it returns <code>Pending</code>, <a href="struct.Pool.html" title="Pool"><code>Pool</code></a> |
| considers it a 1. <a href="struct.Pool.html" title="Pool"><code>Pool</code></a> then maintains an <a href="https://en.wikipedia.org/wiki/Moving_average#Exponential_moving_average">exponential moving |
| average</a> over those |
| samples, which gives an estimate of how often the underlying service has been ready when it was |
| needed “recently” (see <a href="struct.Builder.html#method.urgency" title="Builder::urgency"><code>Builder::urgency</code></a>). If the service is loaded (see |
| <a href="struct.Builder.html#method.loaded_above" title="Builder::loaded_above"><code>Builder::loaded_above</code></a>), a new service is created and added to the underlying <a href="../p2c/struct.Balance.html" title="Balance"><code>Balance</code></a>. |
| If the service is underutilized (see <a href="struct.Builder.html#method.underutilized_below" title="Builder::underutilized_below"><code>Builder::underutilized_below</code></a>) and there are two or |
| more services, then the latest added service is removed. In either case, the load estimate is |
| reset to its initial value (see <a href="struct.Builder.html#method.initial" title="Builder::initial"><code>Builder::initial</code></a> to prevent services from being rapidly |
| added or removed.</p> |
| </div></details><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Builder.html" title="tower::balance::pool::Builder struct">Builder</a></div><div class="item-right docblock-short">A <a href="https://rust-lang-nursery.github.io/api-guidelines/type-safety.html#builders-enable-construction-of-complex-values-c-builder">builder</a> that lets you configure how a <a href="struct.Pool.html" title="Pool"><code>Pool</code></a> determines whether the underlying service is |
| loaded or not. See the <a href="index.html">module-level documentation</a> and the builder’s methods for |
| details.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Pool.html" title="tower::balance::pool::Pool struct">Pool</a></div><div class="item-right docblock-short">A dynamically sized, load-balanced pool of <code>Service</code> instances.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.PoolDiscoverer.html" title="tower::balance::pool::PoolDiscoverer struct">PoolDiscoverer</a></div><div class="item-right docblock-short">A wrapper around <code>MakeService</code> that discovers a new service when load is high, and removes a |
| service when load is low. See <a href="struct.Pool.html" title="Pool"><code>Pool</code></a>.</div></div></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> |
