19 lines
18 KiB
HTML
19 lines
18 KiB
HTML
<!doctype html>
|
||
<html lang="en" dir="ltr">
|
||
<head>
|
||
<meta charset="UTF-8">
|
||
<meta name="viewport" content="width=device-width,initial-scale=1">
|
||
<meta name="generator" content="Docusaurus v2.0.0-beta.5">
|
||
<link rel="search" type="application/opensearchdescription+xml" title="HZFE - 剑指前端 Offer" href="/awesome-interview/opensearch.xml">
|
||
<link rel="preconnect" href="https://hm.baidu.com">
|
||
<script>var _hmt=_hmt||[];!function(){var e=document.createElement("script");e.src="https://hm.baidu.com/hm.js?c7cd0fd77ac518cc6ef46461cdc9524b";var c=document.getElementsByTagName("script")[0];c.parentNode.insertBefore(e,c)}()</script><title data-react-helmet="true">垃圾回收机制 | HZFE - 剑指前端 Offer</title><meta data-react-helmet="true" name="twitter:card" content="summary_large_image"><meta data-react-helmet="true" property="og:url" content="https://hzfe.github.io/awesome-interview/book2/browser-garbage"><meta data-react-helmet="true" name="docsearch:language" content="en"><meta data-react-helmet="true" name="docsearch:version" content="current"><meta data-react-helmet="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-react-helmet="true" property="og:title" content="垃圾回收机制 | HZFE - 剑指前端 Offer"><meta data-react-helmet="true" name="description" content="相关问题"><meta data-react-helmet="true" property="og:description" content="相关问题"><link data-react-helmet="true" rel="shortcut icon" href="/awesome-interview/img/favicon.ico"><link data-react-helmet="true" rel="canonical" href="https://hzfe.github.io/awesome-interview/book2/browser-garbage"><link data-react-helmet="true" rel="alternate" href="https://hzfe.github.io/awesome-interview/book2/browser-garbage" hreflang="en"><link data-react-helmet="true" rel="alternate" href="https://hzfe.github.io/awesome-interview/book2/browser-garbage" hreflang="x-default"><link data-react-helmet="true" rel="preconnect" href="https://61YWQXP6JY-dsn.algolia.net" crossorigin="anonymous"><link rel="stylesheet" href="/awesome-interview/assets/css/styles.304d13b7.css">
|
||
<link rel="preload" href="/awesome-interview/assets/js/runtime~main.50b7dd91.js" as="script">
|
||
<link rel="preload" href="/awesome-interview/assets/js/main.178fbfc5.js" as="script">
|
||
</head>
|
||
<body>
|
||
<script>!function(){function t(t){document.documentElement.setAttribute("data-theme",t)}var e=function(){var t=null;try{t=localStorage.getItem("theme")}catch(t){}return t}();t(null!==e?e:"light")}()</script><div id="__docusaurus">
|
||
<div><a href="#" class="skipToContent_1oUP">Skip to main content</a></div><nav class="navbar navbar--fixed-top navbarHideable_2qcr"><div class="navbar__inner"><div class="navbar__items"><button aria-label="Navigation bar toggle" class="navbar__toggle clean-btn" type="button" tabindex="0"><svg width="30" height="30" viewBox="0 0 30 30" aria-hidden="true"><path stroke="currentColor" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2" d="M4 7h22M4 15h22M4 23h22"></path></svg></button><a class="navbar__brand" href="/awesome-interview/"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--light_3UqQ navbar__logo"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--dark_hz6m navbar__logo"><b class="navbar__title">剑指前端 Offer</b></a></div><div class="navbar__items navbar__items--right"><a href="https://github.com/hzfe/awesome-interview" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link"><span>GitHub<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_3J9K"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></span></a><div class="searchBox_1Doo"><button type="button" class="DocSearch DocSearch-Button" aria-label="Search"><span class="DocSearch-Button-Container"><svg width="20" height="20" class="DocSearch-Search-Icon" viewBox="0 0 20 20"><path d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z" stroke="currentColor" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"></path></svg><span class="DocSearch-Button-Placeholder">Search</span></span><span class="DocSearch-Button-Keys"></span></button></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div class="main-wrapper docs-wrapper docs-doc-page"><div class="docPage_31aa"><button class="clean-btn backToTopButton_35hR" type="button"><svg viewBox="0 0 24 24" width="28"><path d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z" fill="currentColor"></path></svg></button><aside class="docSidebarContainer_3Kbt"><div class="sidebar_15mo sidebarWithHideableNavbar_267A"><a tabindex="-1" class="sidebarLogo_3h0W" href="/awesome-interview/"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--light_3UqQ"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--dark_hz6m"><b>剑指前端 Offer</b></a><nav class="menu thin-scrollbar menu_Bmed menuWithAnnouncementBar_2WvA"><ul class="menu__list"><li class="menu__list-item"><a class="menu__link" href="/awesome-interview/about">关于我们</a></li><li class="menu__list-item"><a class="menu__link" href="/awesome-interview/">前言</a></li><li class="menu__list-item menu__list-item--collapsed"><a class="menu__link menu__link--sublist" href="#">模拟题一</a></li><li class="menu__list-item"><a class="menu__link menu__link--sublist menu__link--active" href="#">模拟题二</a><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/browser-render-mechanism">浏览器:浏览器渲染机制</a></li><li class="menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="/awesome-interview/book2/browser-garbage">浏览器:垃圾回收机制</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/engineer-babel">工程化:Babel 的原理</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/frame-react-fiber">框架:React Fiber 的作用和原理</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/frame-react-hoc-hooks">框架:HOC vs Render Props vs Hooks</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/js-inherite">基础:ES5、ES6 如何实现继承</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/js-new">基础:New 操作符的原理</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/css-preprocessor">样式:谈谈 CSS 预处理器</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/network-http-cache">网络:HTTP 缓存机制</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/coding-throttle-debounce">编码:实现节流去抖函数</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/algorithm-reverse-linked-list">算法:反转链表</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/topic-multi-pics-site-optimize">综合:多图站点性能优化</a></li></ul></li><li class="menu__list-item menu__list-item--collapsed"><a class="menu__link menu__link--sublist" href="#">模拟题三</a></li></ul></nav><button type="button" title="Collapse sidebar" aria-label="Collapse sidebar" class="button button--secondary button--outline collapseSidebarButton_1CGd"><svg width="20" height="20" aria-hidden="true" class="collapseSidebarButtonIcon_3E-R"><g fill="#7a7a7a"><path d="M9.992 10.023c0 .2-.062.399-.172.547l-4.996 7.492a.982.982 0 01-.828.454H1c-.55 0-1-.453-1-1 0-.2.059-.403.168-.551l4.629-6.942L.168 3.078A.939.939 0 010 2.528c0-.548.45-.997 1-.997h2.996c.352 0 .649.18.828.45L9.82 9.472c.11.148.172.347.172.55zm0 0"></path><path d="M19.98 10.023c0 .2-.058.399-.168.547l-4.996 7.492a.987.987 0 01-.828.454h-3c-.547 0-.996-.453-.996-1 0-.2.059-.403.168-.551l4.625-6.942-4.625-6.945a.939.939 0 01-.168-.55 1 1 0 01.996-.997h3c.348 0 .649.18.828.45l4.996 7.492c.11.148.168.347.168.55zm0 0"></path></g></svg></button></div></aside><main class="docMainContainer_3ufF"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_3FnS"><div class="docItemContainer_33ec"><article><div class="tocCollapsible_1PrD tocMobile_3Hoh"><button type="button" class="clean-btn tocCollapsibleButton_2O1e">On this page</button></div><div class="markdown"><header><h1>垃圾回收机制</h1></header><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="相关问题"></a>相关问题<a class="hash-link" href="#相关问题" title="Direct link to heading">#</a></h2><ul><li>什么是内存泄漏</li><li>常见的垃圾回收算法</li><li>如何排查内存泄漏</li></ul><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="回答关键点"></a>回答关键点<a class="hash-link" href="#回答关键点" title="Direct link to heading">#</a></h2><p><code>引用计数法</code> <code>标记清除法</code> <code>Mark-Compact(标记整理)</code> <code>Scavenger(清道夫)</code></p><p>GC(Garbage Collection,垃圾回收)是一种内存自动管理机制, 垃圾回收器(Garbage Collector)可以自动回收分配给程序的已经不再使用的内存。常见的 GC 算法有引用计数法和标记清除法等。V8(JavaScript 引擎,提供执行 JavaScript 的运行时环境)的垃圾回收器算法主要由 Mark-Compact 和 Scavenger 构成。</p><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="知识点深入"></a>知识点深入<a class="hash-link" href="#知识点深入" title="Direct link to heading">#</a></h2><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="1-内存泄漏"></a>1. 内存泄漏<a class="hash-link" href="#1-内存泄漏" title="Direct link to heading">#</a></h3><p>内存泄漏是指,应当被回收的对象没有被正常回收,变成常驻老生代的对象,导致内存占用越来越高。内存泄漏会导致应用程序速度变慢、高延时、崩溃等问题。</p><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="11-内存生命周期"></a>1.1 内存生命周期<a class="hash-link" href="#11-内存生命周期" title="Direct link to heading">#</a></h4><ol><li>分配:按需分配内存。</li><li>使用:读写已分配的内存。</li><li>释放:释放不再需要的内存。</li></ol><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="12-内存泄漏常见原因"></a>1.2 内存泄漏常见原因<a class="hash-link" href="#12-内存泄漏常见原因" title="Direct link to heading">#</a></h4><ul><li>创建全局变量,且没有手动回收。</li><li>事件监听器 / 定时器 / 闭包等未正常清理。</li><li>使用 JavaScript 对象来做缓存,且不设置过期策略和对象大小控制。</li><li>队列拥塞所带来的消费不及时问题。</li></ul><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="2-reference-counting引用计数"></a>2. Reference Counting(引用计数)<a class="hash-link" href="#2-reference-counting引用计数" title="Direct link to heading">#</a></h3><p>Reference Counting 是常见的垃圾回收算法,其核心思路是:将资源(比如对象)的被引用次数保存起来,当被引用次数为零时释放。该方法的局限性:当出现<strong>循环引用</strong>时,互相引用的对象不会被回收。</p><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="3-v8-垃圾回收机制"></a>3. V8 垃圾回收机制<a class="hash-link" href="#3-v8-垃圾回收机制" title="Direct link to heading">#</a></h3><p>V8 中有两个垃圾收集器。主要的 GC 使用 <strong>Mark-Compact</strong> 垃圾回收算法,从整个堆中收集垃圾。小型 GC 使用 <strong>Scavenger</strong> 垃圾回收算法,收集新生代垃圾。</p><p>两种不同的算法应对不同的场景:</p><ul><li>使用 Scavenger 算法主要处理<strong>存活周期短</strong>的对象中的可访问对象。</li><li>使用 Mark-Compact 算法主要处理<strong>存活周期长</strong>的对象中的不可访问的对象。</li></ul><p>因为新生代中存活的可访问对象占少数,老生代中的不可访问对象占少数,所以这两种回收算法配合使用十分高效。</p><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="31-分代垃圾收集"></a>3.1 分代垃圾收集<a class="hash-link" href="#31-分代垃圾收集" title="Direct link to heading">#</a></h4><p>在 V8 中,所有的 JavaScript 对象都通过<strong>堆</strong>来分配。V8 将其管理的堆分成两代:新生代和老生代。其中新生代又可细分为两个子代(Nursery、Intermediate)。</p><p>即新生代中的对象为存活时间较短的对象,老生代中的对象为存活时间较长或常驻内存的对象。</p><p><img src="https://user-images.githubusercontent.com/17002181/126338733-69da76cd-33f3-4d0b-9a8e-c0e67ce0a331.png" alt="image"></p><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="32-mark-compact-算法major-gc"></a>3.2 Mark-Compact 算法(Major GC)<a class="hash-link" href="#32-mark-compact-算法major-gc" title="Direct link to heading">#</a></h4><p>Mark-Compact 算法可以看作是 Mark-Sweep(标记清除)算法和 Cheney 复制算法的结合。该算法主要分为三个阶段:标记、清除、整理。</p><p><img src="https://user-images.githubusercontent.com/17002181/126341694-f3a454c4-4d88-4f7c-80b8-f323843eb6a3.png" alt="image"></p><ol><li><p>标记(Mark)</p><p>标记是找所有可访问对象的过程。GC 会从一组已知的对象指针(称为根集,包括执行堆栈和全局对象等)中,进行递归标记可访问对象。</p></li><li><p>清除(Sweep)</p><p>清除是将不可访问的对象留下的内存空间,添加到空闲链表(free list)的过程。未来为新对象分配内存时,可以从空闲链表中进行再分配。</p></li><li><p>整理(Compact)</p><p>整理是将可访问对象,往内存一端移动的过程。主要解决标记清除阶段后,内存空间出现较多内存碎片时,可能导致无法分配大对象,而提前触发垃圾回收的问题。</p></li></ol><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="33-scavenger-算法minor-gc"></a>3.3 Scavenger 算法(Minor GC)<a class="hash-link" href="#33-scavenger-算法minor-gc" title="Direct link to heading">#</a></h4><p>V8 对新生代内存空间采用了 Scavenger 算法,该算法使用了 semi-space(半空间) 的设计:将堆一分为二,始终只使用一半的空间:From-Space 为使用空间,To-Space 为空闲空间。</p><p><img src="https://user-images.githubusercontent.com/17002181/126367817-b5a12c03-18ea-4eb9-8bdb-84d2fd3e8aad.png" alt="image"></p><p>新生代在 From-Space 中分配对象;在垃圾回收阶段,检查并按需复制 From-Space 中的可访问对象到 To-Space 或老生代,并释放 From-Space 中的不可访问对象占用的内存空间;最后 From-Space 和 To-Space 角色互换。</p><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="参考资料"></a>参考资料<a class="hash-link" href="#参考资料" title="Direct link to heading">#</a></h2><ol><li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Memory_Management" target="_blank" rel="noopener noreferrer">Memory Management</a></li><li><a href="https://v8.dev/blog/trash-talk" target="_blank" rel="noopener noreferrer">Trash talk: the Orinoco garbage collector</a></li></ol></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><div class="pagination-nav__item"><a class="pagination-nav__link" href="/awesome-interview/book2/browser-render-mechanism"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">« 浏览器:浏览器渲染机制</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book2/engineer-babel"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">工程化:Babel 的原理 »</div></a></div></nav></div></div><div class="col col--3"><div class="tableOfContents_35-E thin-scrollbar"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#相关问题" class="table-of-contents__link">相关问题</a></li><li><a href="#回答关键点" class="table-of-contents__link">回答关键点</a></li><li><a href="#知识点深入" class="table-of-contents__link">知识点深入</a><ul><li><a href="#1-内存泄漏" class="table-of-contents__link">1. 内存泄漏</a></li><li><a href="#2-reference-counting引用计数" class="table-of-contents__link">2. Reference Counting(引用计数)</a></li><li><a href="#3-v8-垃圾回收机制" class="table-of-contents__link">3. V8 垃圾回收机制</a></li></ul></li><li><a href="#参考资料" class="table-of-contents__link">参考资料</a></li></ul></div></div></div><div class="row"><div class="col"><div class="react-utterences"><div>Loading script...</div></div></div><div class="col col--3"></div></div></div></main></div></div></div>
|
||
<script src="/awesome-interview/assets/js/runtime~main.50b7dd91.js"></script>
|
||
<script src="/awesome-interview/assets/js/main.178fbfc5.js"></script>
|
||
</body>
|
||
</html> |