21 lines
21 KiB
HTML
21 lines
21 KiB
HTML
<!doctype html>
|
||
<html lang="en" dir="ltr" class="docs-wrapper docs-doc-page docs-version-current plugin-docs plugin-id-default docs-doc-id-book2/browser-garbage">
|
||
<head>
|
||
<meta charset="UTF-8">
|
||
<meta name="viewport" content="width=device-width,initial-scale=1">
|
||
<meta name="generator" content="Docusaurus v2.0.0-beta.18">
|
||
<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>
|
||
<script src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js" async data-ad-client="ca-pub-9889934432771967"></script>
|
||
<script src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js?client=ca-pub-9889934432771967" async crossorigin="anonymous"></script><title data-rh="true">垃圾回收机制 | HZFE - 剑指前端 Offer</title><meta data-rh="true" name="twitter:card" content="summary_large_image"><meta data-rh="true" property="og:url" content="https://febook.hzfe.org/awesome-interview/book2/browser-garbage"><meta data-rh="true" name="docusaurus_locale" content="en"><meta data-rh="true" name="docsearch:language" content="en"><meta data-rh="true" name="docusaurus_version" content="current"><meta data-rh="true" name="docusaurus_tag" content="docs-default-current"><meta data-rh="true" name="docsearch:version" content="current"><meta data-rh="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-rh="true" property="og:title" content="垃圾回收机制 | HZFE - 剑指前端 Offer"><meta data-rh="true" name="description" content="相关问题"><meta data-rh="true" property="og:description" content="相关问题"><link data-rh="true" rel="icon" href="/awesome-interview/img/favicon.ico"><link data-rh="true" rel="canonical" href="https://febook.hzfe.org/awesome-interview/book2/browser-garbage"><link data-rh="true" rel="alternate" href="https://febook.hzfe.org/awesome-interview/book2/browser-garbage" hreflang="en"><link data-rh="true" rel="alternate" href="https://febook.hzfe.org/awesome-interview/book2/browser-garbage" hreflang="x-default"><link data-rh="true" rel="preconnect" href="https://PED5MQGL7T-dsn.algolia.net" crossorigin="anonymous"><link rel="stylesheet" href="/awesome-interview/assets/css/styles.62902d4b.css">
|
||
<link rel="preload" href="/awesome-interview/assets/js/runtime~main.16895322.js" as="script">
|
||
<link rel="preload" href="/awesome-interview/assets/js/main.a6349f88.js" as="script">
|
||
</head>
|
||
<body class="navigation-with-keyboard">
|
||
<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 role="region"><a href="#" class="skipToContent_ZgBM">Skip to main content</a></div><nav class="navbar navbar--fixed-top navbarHideable_ObN2"><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/"><div class="navbar__logo"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_W2Cr themedImage--light_TfLj"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_W2Cr themedImage--dark_oUvU"></div><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">GitHub<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_I5OW"><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></a><div class="searchBox_qEbK"><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"><div class="docPage_P2Lg"><button aria-label="Scroll back to top" class="clean-btn theme-back-to-top-button backToTopButton_RiI4" type="button"></button><aside class="theme-doc-sidebar-container docSidebarContainer_rKC_"><div class="sidebar_RiAD sidebarWithHideableNavbar_d0QC"><a tabindex="-1" class="sidebarLogo_YUvz" href="/awesome-interview/"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_W2Cr themedImage--light_TfLj"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_W2Cr themedImage--dark_oUvU"><b>剑指前端 Offer</b></a><nav class="menu thin-scrollbar menu_izAj"><ul class="theme-doc-sidebar-menu menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="/awesome-interview/about">关于我们</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-1 menu__list-item"><a class="menu__link" href="/awesome-interview/">前言</a></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/awesome-interview/book1/browser-cross-origin">模拟题一</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret menu__link--active" aria-expanded="true" href="/awesome-interview/book2/browser-render-mechanism">模拟题二</a></div><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/coding-throttle-debounce">编码：实现节流防抖函数</a></li><li class="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-link theme-doc-sidebar-item-link-level-2 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="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/awesome-interview/book3/browser-event-loop">模拟题三</a></div></li><li class="theme-doc-sidebar-item-category theme-doc-sidebar-item-category-level-1 menu__list-item menu__list-item--collapsed"><div class="menu__list-item-collapsible"><a class="menu__link menu__link--sublist menu__link--sublist-caret" aria-expanded="false" href="/awesome-interview/book4/browser-router">模拟题四</a></div></li></ul></nav><button type="button" title="Collapse sidebar" aria-label="Collapse sidebar" class="button button--secondary button--outline collapseSidebarButton_FykI"><svg width="20" height="20" aria-hidden="true" class="collapseSidebarButtonIcon_DTRl"><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_TCnq"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_DM6M"><div class="docItemContainer_vinB"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Xlws" aria-label="breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a class="breadcrumbs__link" href="/awesome-interview/">🏠</a></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><span class="breadcrumbs__link" itemprop="item name">模拟题二</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="item name">浏览器：垃圾回收机制</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_jdIR theme-doc-toc-mobile tocMobile_TmEX"><button type="button" class="clean-btn tocCollapsibleButton_Fzxq">On this page</button></div><div class="theme-doc-markdown markdown"><h1>垃圾回收机制</h1><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="相关问题">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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="回答关键点">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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="知识点深入">知识点深入<a class="hash-link" href="#知识点深入" title="Direct link to heading"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="1-内存泄漏">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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="11-内存生命周期">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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="12-内存泄漏常见原因">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></ul><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="2-reference-counting引用计数">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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="3-v8-垃圾回收机制">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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="31-分代垃圾收集">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 loading="lazy" src="https://user-images.githubusercontent.com/17002181/126338733-69da76cd-33f3-4d0b-9a8e-c0e67ce0a331.png" alt="image" class="img_E7b_"></p><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="32-mark-compact-算法major-gc">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 loading="lazy" src="https://user-images.githubusercontent.com/17002181/126341694-f3a454c4-4d88-4f7c-80b8-f323843eb6a3.png" alt="image" class="img_E7b_"></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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="33-scavenger-算法minor-gc">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 loading="lazy" src="https://user-images.githubusercontent.com/17002181/126367817-b5a12c03-18ea-4eb9-8bdb-84d2fd3e8aad.png" alt="image" class="img_E7b_"></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 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="参考资料">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_cNA8 thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#相关问题" class="table-of-contents__link toc-highlight">相关问题</a></li><li><a href="#回答关键点" class="table-of-contents__link toc-highlight">回答关键点</a></li><li><a href="#知识点深入" class="table-of-contents__link toc-highlight">知识点深入</a><ul><li><a href="#1-内存泄漏" class="table-of-contents__link toc-highlight">1. 内存泄漏</a><ul><li><a href="#11-内存生命周期" class="table-of-contents__link toc-highlight">1.1 内存生命周期</a></li><li><a href="#12-内存泄漏常见原因" class="table-of-contents__link toc-highlight">1.2 内存泄漏常见原因</a></li></ul></li><li><a href="#2-reference-counting引用计数" class="table-of-contents__link toc-highlight">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 toc-highlight">3. V8 垃圾回收机制</a><ul><li><a href="#31-分代垃圾收集" class="table-of-contents__link toc-highlight">3.1 分代垃圾收集</a></li><li><a href="#32-mark-compact-算法major-gc" class="table-of-contents__link toc-highlight">3.2 Mark-Compact 算法（Major GC）</a></li><li><a href="#33-scavenger-算法minor-gc" class="table-of-contents__link toc-highlight">3.3 Scavenger 算法（Minor GC）</a></li></ul></li></ul></li><li><a href="#参考资料" class="table-of-contents__link toc-highlight">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.16895322.js"></script>
|
||
<script src="/awesome-interview/assets/js/main.a6349f88.js"></script>
|
||
</body>
|
||
</html> |