|
|
<!doctypehtml><html lang=zh-CN><meta charset=UTF-8><meta content=width=device-width name=viewport><meta media="(prefers-color-scheme: light)" content=#222 name=theme-color><meta media="(prefers-color-scheme: dark)" content=#222 name=theme-color><meta content="Hexo 7.3.0" name=generator><link href=https://cdnjs.cloudflare.com rel=preconnect><link href=/images/apple-touch-icon-next.png rel=apple-touch-icon sizes=180x180><link href=/images/favicon-32x32-next.png rel=icon sizes=32x32 type=image/png><link href=/images/favicon-16x16-next.png rel=icon sizes=16x16 type=image/png><link color=#222 href=/images/logo.svg rel=mask-icon><meta content=2X6S9P7CAjXjVvw8YyQR8pCu-B0oEu7O9quLgxXuWyA name=google-site-verification><meta content=dV8JGNzi0c name=baidu-site-verification><script>!function(){var t=!1;function e(){var e;t||(t=!0,(e=document.createElement("script")).setAttribute("data-ad-client","ca-pub-7480618470784058"),e.async=!0,e.src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js",document.head.appendChild(e))}function a(){"requestIdleCallback"in window?window.requestIdleCallback(e,{timeout:5e3}):window.setTimeout(e,5e3)}"complete"===document.readyState?a():window.addEventListener("load",a,{once:!0})}()</script><link href=/css/main.css rel=stylesheet><link crossorigin=anonymous href=https://cdnjs.cloudflare.com/ajax/libs/font-awesome/7.0.0/css/all.min.css integrity=sha256-VHqXKFhhMxcpubYf9xiWdCiojEbY9NexQ4jh8AxbvcM= rel=stylesheet><link crossorigin=anonymous href=https://cdnjs.cloudflare.com/ajax/libs/fancyapps-ui/6.1.14/fancybox/fancybox.css integrity=sha256-mdaMxrItEW6hMIVJJNPKuX0B7KCSJQVEv3mVY4N2we4= rel=stylesheet><script class=next-config data-name=main type=application/json>{"hostname":"nicksxs.me","root":"/","images":"/images","scheme":"Pisces","darkmode":true,"version":"8.29.0","exturl":false,"sidebar":{"position":"left","width_expanded":320,"width_dual_column":240,"display":"post","padding":18,"offset":12},"hljswrap":true,"codeblock":{"theme":{"light":"default","dark":"stackoverflow-dark"},"prism":{"light":"prism","dark":"prism-dark"},"copy_button":{"enable":true,"style":"default"},"fold":{"enable":false,"height":500},"language":false},"bookmark":{"enable":false,"color":"#222","save":"auto"},"mediumzoom":false,"pangu":false,"comments":{"style":"tabs","active":null,"storage":true,"lazyload":true,"nav":null},"stickytabs":false,"motion":{"enable":false,"async":false,"duration":200,"transition":{"menu_item":"fadeInDown","post_block":"fadeIn","post_header":"fadeInDown","post_body":"fadeInDown","coll_header":"fadeInLeft","sidebar":"fadeInUp"}},"prism":false,"i18n":{"placeholder":"搜索...","empty":"没有找到任何搜索结果:${query}","hits_time":"找到 ${hits} 个搜索结果(用时 ${time} 毫秒)","hits":"找到 ${hits} 个搜索结果"},"algolia":{"appID":"663Q99OQQD","apiKey":"e461a1371d12cec1491c1153b288a9ed","indexName":"nicksxs","hits":{"per_page":10}}}</script><script defer src=/js/config.js></script><meta content="对 Java 的 gc 实现比较感兴趣,原先一般都是看周志明的书,但其实并没有讲具体的 gc 源码,而是把整个思路和流程讲解了一下 特别是 G1 的具体实现 一般对 G1 的理解其实就是把原先整块的新生代老年代分成了以 region 为单位的小块内存,简而言之,就是原先对新生代…" name=description><meta content=article property=og:type><meta content=JVM源码分析之G1垃圾收集器分析一 property=og:title><meta content=https://nicksxs.me/2019/12/07/JVM-G1-Part-1/index.html property=og:url><meta content="Nicksxs's Blog" property=og:site_name><meta content="对 Java 的 gc 实现比较感兴趣,原先一般都是看周志明的书,但其实并没有讲具体的 gc 源码,而是把整个思路和流程讲解了一下 特别是 G1 的具体实现 一般对 G1 的理解其实就是把原先整块的新生代老年代分成了以 region 为单位的小块内存,简而言之,就是原先对新生代…" property=og:description><meta content=zh_CN property=og:locale><meta content=2019-12-06T16:54:19.000Z property=article:published_time><meta content=2019-12-19T16:01:42.000Z property=article:modified_time><meta content=Nicksxs property=article:author><meta content=C++ property=article:tag><meta content=Java property=article:tag><meta content=JVM property=article:tag><meta content=summary name=twitter:card><link href=https://nicksxs.me/2019/12/07/JVM-G1-Part-1/ rel=canonical><script class=next-config data-name=page type=application/json>{"sidebar":"","isHome":false,"isPost":true,"lang":"zh-CN","comments":true,"permalink":"https://nicksxs.me/2019/12/07/JVM-G1-Part-1/","path":"2019/12/07/JVM-G1-Part-1/","title":"JVM源码分析之G1垃圾收集器分析一"}</script><script class=next-config data-name=calendar type=application/json>""</script><title>JVM源码分析之G1垃圾收集器分析一 | Nicksxs's Blog</title><script async src=https://www.googletagmanager.com/gtag/js?id=UA-61358619-1></script><script class=next-config data-name=google_analytics type=application/json>{"tracking_id":"UA-61358619-1","only_pageview":false,"measure_protocol_api_secret":null}</script><script defer src=/js/third-party/analytics/google-analytics.js></script><script defer src=/js/third-party/analytics/baidu-analytics.js></script><script async src=https://hm.baidu.com/hm.js?20f33b3c0c0eff9b1522999c0015646d></script><script crossorigin=anonymous defer integrity=sha256-QnJV4HT5r8i89ovZGRD86iynZqHerEbT2xt69vDM36I= src=https://cdnjs.cloudflare.com/ajax/libs/fancyapps-ui/6.1.14/fancybox/fancybox.umd.js></script><script defer src=/js/utils.js></script><script defer src=/js/sidebar.js></script><script defer src=/js/next-boot.js></script><script data-algolia-integrity=sha256-o49zoHLDPBm9WLg6AiliAVi3axCRTqe3ltTxLvhzAVg= data-algolia-src=https://cdnjs.cloudflare.com/ajax/libs/algoliasearch/5.36.0/lite/builds/browser.umd.js data-search-src=/js/third-party/search/algolia-search.js src=/js/third-party/search/algolia-search-loader.js></script><script defer src=/js/third-party/fancybox.js></script><noscript><link href=/css/noscript.css rel=stylesheet></noscript><link title="Nicksxs's Blog" href=/atom.xml rel=alternate type=application/atom+xml><body itemscope itemtype=http://schema.org/WebPage><div class=headband></div><main class=main><div class=column><header class=header itemscope itemtype=http://schema.org/WPHeader><div class=site-brand-container><div class=site-nav-toggle><div aria-label=切换导航栏 class=toggle role=button><span class=toggle-line></span><span class=toggle-line></span><span class=toggle-line></span></div></div><div class=site-meta><a class=brand href=/ rel=start><i class=logo-line></i><p class=site-title>Nicksxs's Blog</p><i class=logo-line></i></a><p class=site-subtitle itemprop=description>Java 运行时、生产诊断与 AI 工程实践</div><div class=site-nav-right><div class="toggle popup-trigger" aria-label=搜索 role=button><i class="fa fa-search fa-fw fa-lg"></i></div></div></div><nav class=site-nav><ul class="main-menu menu"><li class="menu-item menu-item-home"><a href=/ rel=section><i class="fa fa-home fa-fw"></i>首页</a><li class="menu-item menu-item-专题"><a href=/topics/ rel=section><i class="fa fa-layer-group fa-fw"></i>专题</a><li class="menu-item menu-item-工具"><a href=/tools/ rel=section><i class="fa fa-toolbox fa-fw"></i>工具</a><li class="menu-item menu-item-about"><a href=/about/ rel=section><i class="fa fa-user fa-fw"></i>关于我</a><li class="menu-item menu-item-tags"><a href=/tags/ rel=section><i class="fa fa-tags fa-fw"></i>标签</a><li class="menu-item menu-item-categories"><a href=/categories/ rel=section><i class="fa fa-th fa-fw"></i>分类</a><li class="menu-item menu-item-archives"><a href=/archives/ rel=section><i class="fa fa-archive fa-fw"></i>归档</a><li class="menu-item menu-item-search"><a class=popup-trigger role=button><i class="fa fa-search fa-fw"></i>搜索</a></ul></nav><div class=search-pop-overlay><div class="popup search-popup"><div class=search-header><span class=search-icon><i class="fa fa-search"></i></span><div class=search-input-container><input autocapitalize=off autocomplete=off class=search-input maxlength=80 placeholder=搜索... spellcheck=false type=search></div><span class=popup-btn-close role=button><i class="fa fa-times-circle"></i></span></div><div class=search-result-container><div class=search-result-icon><i class="fab fa-algolia fa-5x"></i></div></div></div></div></header><aside class=sidebar><div class="sidebar-inner sidebar-overview-active"><ul class=sidebar-nav><li class=sidebar-nav-toc>文章目录<li class=sidebar-nav-overview>站点概览</ul><div class=sidebar-panel-container><div class="post-toc-wrap sidebar-panel"></div><div class="site-overview-wrap sidebar-panel"><div class="site-author animated" itemprop=author itemscope itemtype=http://schema.org/Person><img alt=Nicksxs class=site-author-image itemprop=image src=/uploads/avatar.jpg><p class=site-author-name itemprop=name>Nicksxs<div class=site-description itemprop=description>Nicksxs 的技术博客,深入 Java 运行时与生产诊断、低成本大模型推理和 Agent 工程实践。</div></div><div class="site-state-wrap animated"><nav class=site-state><div class="site-state-item site-state-posts"><a href=/archives/><span class=site-state-item-count>389</span> <span class=site-state-item-name>日志</span></a></div><div class="site-state-item site-state-categories"><a href=/categories/><span class=site-state-item-count>179</span> <span class=site-state-item-name>分类</span></a></div><div class="site-state-item site-state-tags"><a href=/tags/><span class=site-state-item-count>332</span> <span class=site-state-item-name>标签</span></a></div></nav></div><div class="links-of-author animated"><span class=links-of-author-item><a rel="noopener me" title="GitHub → https://github.com/nicksxs" href=https://github.com/nicksxs target=_blank><i class="fab fa-github fa-fw"></i>GitHub</a> </span><span class=links-of-author-item><a rel="noopener me" title="E-Mail → mailto:nicksxs1202@gmail.com" href=mailto:nicksxs1202@gmail.com target=_blank><i class="fa fa-envelope fa-fw"></i>E-Mail</a></span></div><div class="cc-license animated" itemprop=license><a class=cc-opacity href=https://creativecommons.org/licenses/by-nc-sa/4.0/ rel=noopener target=_blank><img alt="Creative Commons" src=https://cdnjs.cloudflare.com/ajax/libs/creativecommons-vocabulary/2020.11.3/assets/license_badges/small/by_nc_sa.svg></a></div><div class="widget-wrap sidebar-tag-cloud"><div class=tag-cloud-tags><a class=tag-cloud-10 href=/tags/Java/ style=font-size:16px>Java</a><a class=tag-cloud-9 href=/tags/leetcode/ style=font-size:15.64px>leetcode</a><a class=tag-cloud-9 href=/tags/%E7%94%9F%E6%B4%BB/ style=font-size:15.29px>生活</a><a class=tag-cloud-8 href=/tags/LLM/ style=font-size:14.93px>LLM</a><a class=tag-cloud-7 href=/tags/%E9%A2%98%E8%A7%A3/ style=font-size:14.57px>题解</a><a class=tag-cloud-6 href=/tags/SpringBoot/ style=font-size:14.21px>SpringBoot</a><a class=tag-cloud-6 href=/tags/MySQL/ style=font-size:14.21px>MySQL</a><a class=tag-cloud-6 href=/tags/C/ style=font-size:13.86px>C++</a><a class=tag-cloud-5 href=/tags/Redis/ style=font-size:13.5px>Redis</a><a class=tag-cloud-4 href=/tags/Tomcat/ style=font-size:13.14px>Tomcat</a><a class=tag-cloud-4 href=/tags/Mybatis/ style=font-size:13.14px>Mybatis</a><a class=tag-cloud-4 href=/tags/%E5%B0%8F%E6%8A%80%E5%B7%A7/ style=font-size:12.79px>小技巧</a><a class=tag-cloud-3 href=/tags/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84/ style=font-size:12.43px>数据结构</a><a class=tag-cloud-3 href=/tags/%E6%BA%90%E7%A0%81/ style=font-size:12.43px>源码</a><a class=tag-cloud-2 href=/tags/MQ/ style=font-size:12.07px>MQ</a><a class=tag-cloud-2 href=/tags/%E6%B6%88%E6%81%AF%E9%98%9F%E5%88%97/ style=font-size:12.07px>消息队列</a><a class=tag-cloud-2 href=/tags/RocketMQ/ style=font-size:12.07px>RocketMQ</a><a class=tag-cloud-2 href=/tags/%E8%BF%90%E5%8A%A8/ style=font-size:12.07px>运动</a><a class=tag-cloud-1 href=/tags/php/ style=font-size:11.71px>php</a><a class=tag-cloud-1 href=/tags/Spring/ style=font-size:11.36px>Spring</a><a class=tag-cloud-1 href=/tags/linux/ style=font-size:11.36px>linux</a><a class=tag-cloud-1 href=/tags/%E5%87%8F%E8%82%A5/ style=font-size:11.36px>减肥</a><a class=tag-cloud-1 href=/tags/%E8%B7%91%E6%AD%A5/ style=font-size:11.36px>跑步</a><a class=tag-cloud-0 href=/tags/Dubbo/ style=font-size:11px>Dubbo</a></div></div><div class="affiliate-creative affiliate-creative--sidebar" data-affiliate-id=tencent-cloud-general><a rel="sponsored noopener" aria-label=腾讯云产品优惠 href=https://cloud.tencent.com/act/cps/redirect?redirect=2446&cps_key=2e33a1eedb380997d03618b4a5ba6ca7&from=console target=_blank><img alt=腾讯云服务器、数据库和云产品优惠 decoding=async height=419 loading=lazy src=/uploads/affiliate/tencent-cloud-general.webp width=690> </a><span class=affiliate-disclosure>推广</span></div></div></div></div><div class="sidebar-inner sidebar-blogroll"><div class="links-of-blogroll animated"><div class=links-of-blogroll-title><i class="fa fa-globe fa-fw"></i> 链接</div><ul class=links-of-blogroll-list><li class=links-of-blogroll-item><a href=https://covermusic.cn/ rel=noopener target=_blank title=https://covermusic.cn>69伙伴</a></ul></div></div></aside></div><div class="main-inner post posts-expand"><div class=post-block><article class=post-content itemscope itemtype=http://schema.org/Article lang=zh-CN><link href=https://nicksxs.me/2019/12/07/JVM-G1-Part-1/ itemprop=mainEntityOfPage><span hidden itemprop=author itemscope itemtype=http://schema.org/Person><meta content=/uploads/avatar.jpg itemprop=image><meta content=Nicksxs itemprop=name></span><span hidden itemprop=publisher itemscope itemtype=http://schema.org/Organization><meta content="Nicksxs's Blog" itemprop=name><meta content="Nicksxs 的技术博客,深入 Java 运行时与生产诊断、低成本大模型推理和 Agent 工程实践。" itemprop=description></span><span hidden itemprop=post itemscope itemtype=http://schema.org/CreativeWork><meta content="JVM源码分析之G1垃圾收集器分析一 | Nicksxs's Blog" itemprop=name><meta content="对 Java 的 gc 实现比较感兴趣,原先一般都是看周志明的书,但其实并没有讲具体的 gc 源码,而是把整个思路和流程讲解了一下 特别是 G1 的具体实现 一般对 G1 的理解其实就是把原先整块的新生代老年代分成了以 region 为单位的小块内存,简而言之,就是原先对新生代…" itemprop=description></span><header class=post-header><h1 itemprop="name headline" class=post-title>JVM源码分析之G1垃圾收集器分析一</h1><div class=post-meta-container><div class=post-meta><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar"></i> </span><span class=post-meta-item-text>发表于</span> <time itemprop="dateCreated datePublished" title="创建时间:2019-12-07 00:54:19" datetime=2019-12-07T00:54:19+08:00>2019-12-07</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-calendar-check"></i> </span><span class=post-meta-item-text>更新于</span> <time title="修改时间:2019-12-20 00:01:42" datetime=2019-12-20T00:01:42+08:00 itemprop=dateModified>2019-12-20</time> </span><span class=post-meta-item><span class=post-meta-item-icon><i class="far fa-folder"></i> </span><span class=post-meta-item-text>分类于</span> <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/ itemprop=url rel=index><span itemprop=name>Java</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/JVM/ itemprop=url rel=index><span itemprop=name>JVM</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/C/ itemprop=url rel=index><span itemprop=name>C++</span></a> </span>, <span itemprop=about itemscope itemtype=http://schema.org/Thing><a href=/categories/Java/GC/ itemprop=url rel=index><span itemprop=name>GC</span></a> </span></span><span class="post-meta-item cloudflare-page-counter" data-increment=true data-path=/2019/12/07/JVM-G1-Part-1/ data-title=JVM源码分析之G1垃圾收集器分析一 title=阅读次数><span class=post-meta-item-icon><i class="far fa-eye"></i> </span><span class=post-meta-item-text>阅读次数:</span> <span class=cloudflare-page-counter-count></span></span></div><div class=post-description>对 Java 的 gc 实现比较感兴趣,原先一般都是看周志明的书,但其实并没有讲具体的 gc 源码,而是把整个思路和流程讲解了一下 特别是 G1 的具体实现 一般对 G1 的理解其实就是把原先整块的新生代老年代分成了以 region 为单位的小块内存,简而言之,就是原先对新生代…</div></div></header><div class=post-body itemprop=articleBody><p>对 Java 的 gc 实现比较感兴趣,原先一般都是看周志明的书,但其实并没有讲具体的 gc 源码,而是把整个思路和流程讲解了一下<br>特别是 G1 的具体实现<br>一般对 G1 的理解其实就是把原先整块的新生代老年代分成了以 region 为单位的小块内存,简而言之,就是原先对新生代老年代的收集会涉及到整个代的堆内存空间,而G1 把它变成了更细致的小块内存<br>这带来了一个很明显的好处和一个很明显的坏处,好处是内存收集可以更灵活,耗时会变短,但整个收集的处理复杂度就变高了<br>目前看了一点点关于 G1 收集的预期时间相关的代码<figure class="highlight c++"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br></pre><td class=code><pre><span class=line><span class=function>HeapWord* <span class=title>G1CollectedHeap::do_collection_pause</span><span class=params>(<span class=type>size_t</span> word_size,</span></span></span><br><span class=line><span class=params><span class=function> uint gc_count_before,</span></span></span><br><span class=line><span class=params><span class=function> <span class=type>bool</span>* succeeded,</span></span></span><br><span class=line><span class=params><span class=function> GCCause::Cause gc_cause)</span> </span>{</span><br><span class=line> <span class=built_in>assert_heap_not_locked_and_not_at_safepoint</span>();</span><br><span class=line> <span class=function>VM_G1CollectForAllocation <span class=title>op</span><span class=params>(word_size,</span></span></span><br><span class=line><span class=params><span class=function> gc_count_before,</span></span></span><br><span class=line><span class=params><span class=function> gc_cause,</span></span></span><br><span class=line><span class=params><span class=function> <span class=literal>false</span>, <span class=comment>/* should_initiate_conc_mark */</span></span></span></span><br><span class=line><span class=params><span class=function> g1_policy()->max_pause_time_ms())</span></span>;</span><br><span class=line> VMThread::<span class=built_in>execute</span>(&op);</span><br><span class=line></span><br><span class=line> HeapWord* result = op.<span class=built_in>result</span>();</span><br><span class=line> <span class=type>bool</span> ret_succeeded = op.<span class=built_in>prologue_succeeded</span>() && op.<span class=built_in>pause_succeeded</span>();</span><br><span class=line> <span class=built_in>assert</span>(result == <span class=literal>NULL</span> || ret_succeeded,</span><br><span class=line> <span class=string>"the result should be NULL if the VM did not succeed"</span>);</span><br><span class=line> *succeeded = ret_succeeded;</span><br><span class=line></span><br><span class=line> <span class=built_in>assert_heap_not_locked</span>();</span><br><span class=line> <span class=keyword>return</span> result;</span><br><span class=line>}</span><br></pre></table></figure><p>这里就是收集时需要停顿的,其中<code>VMThread::execute(&op);</code>是具体执行的,真正执行的是<code>VM_G1CollectForAllocation::doit</code>方法<figure class="highlight c++"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br><span class=line>65</span><br><span class=line>66</span><br><span class=line>67</span><br><span class=line>68</span><br><span class=line>69</span><br><span class=line>70</span><br><span class=line>71</span><br><span class=line>72</span><br><span class=line>73</span><br><span class=line>74</span><br><span class=line>75</span><br><span class=line>76</span><br><span class=line>77</span><br><span class=line>78</span><br><span class=line>79</span><br><span class=line>80</span><br><span class=line>81</span><br><span class=line>82</span><br><span class=line>83</span><br><span class=line>84</span><br><span class=line>85</span><br></pre><td class=code><pre><span class=line><span class=function><span class=type>void</span> <span class=title>VM_G1CollectForAllocation::doit</span><span class=params>()</span> </span>{</span><br><span class=line> G1CollectedHeap* g1h = G1CollectedHeap::<span class=built_in>heap</span>();</span><br><span class=line> <span class=built_in>assert</span>(!_should_initiate_conc_mark || g1h-><span class=built_in>should_do_concurrent_full_gc</span>(_gc_cause),</span><br><span class=line> <span class=string>"only a GC locker, a System.gc(), stats update, whitebox, or a hum allocation induced GC should start a cycle"</span>);</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (_word_size > <span class=number>0</span>) {</span><br><span class=line> <span class=comment>// An allocation has been requested. So, try to do that first.</span></span><br><span class=line> _result = g1h-><span class=built_in>attempt_allocation_at_safepoint</span>(_word_size,</span><br><span class=line> <span class=literal>false</span> <span class=comment>/* expect_null_cur_alloc_region */</span>);</span><br><span class=line> <span class=keyword>if</span> (_result != <span class=literal>NULL</span>) {</span><br><span class=line> <span class=comment>// If we can successfully allocate before we actually do the</span></span><br><span class=line> <span class=comment>// pause then we will consider this pause successful.</span></span><br><span class=line> _pause_succeeded = <span class=literal>true</span>;</span><br><span class=line> <span class=keyword>return</span>;</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=function>GCCauseSetter <span class=title>x</span><span class=params>(g1h, _gc_cause)</span></span>;</span><br><span class=line> <span class=keyword>if</span> (_should_initiate_conc_mark) {</span><br><span class=line> <span class=comment>// It's safer to read old_marking_cycles_completed() here, given</span></span><br><span class=line> <span class=comment>// that noone else will be updating it concurrently. Since we'll</span></span><br><span class=line> <span class=comment>// only need it if we're initiating a marking cycle, no point in</span></span><br><span class=line> <span class=comment>// setting it earlier.</span></span><br><span class=line> _old_marking_cycles_completed_before = g1h-><span class=built_in>old_marking_cycles_completed</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// At this point we are supposed to start a concurrent cycle. We</span></span><br><span class=line> <span class=comment>// will do so if one is not already in progress.</span></span><br><span class=line> <span class=type>bool</span> res = g1h-><span class=built_in>g1_policy</span>()->force_initial_mark_if_outside_cycle(_gc_cause);</span><br><span class=line></span><br><span class=line> <span class=comment>// The above routine returns true if we were able to force the</span></span><br><span class=line> <span class=comment>// next GC pause to be an initial mark; it returns false if a</span></span><br><span class=line> <span class=comment>// marking cycle is already in progress.</span></span><br><span class=line> <span class=comment>//</span></span><br><span class=line> <span class=comment>// If a marking cycle is already in progress just return and skip the</span></span><br><span class=line> <span class=comment>// pause below - if the reason for requesting this initial mark pause</span></span><br><span class=line> <span class=comment>// was due to a System.gc() then the requesting thread should block in</span></span><br><span class=line> <span class=comment>// doit_epilogue() until the marking cycle is complete.</span></span><br><span class=line> <span class=comment>//</span></span><br><span class=line> <span class=comment>// If this initial mark pause was requested as part of a humongous</span></span><br><span class=line> <span class=comment>// allocation then we know that the marking cycle must just have</span></span><br><span class=line> <span class=comment>// been started by another thread (possibly also allocating a humongous</span></span><br><span class=line> <span class=comment>// object) as there was no active marking cycle when the requesting</span></span><br><span class=line> <span class=comment>// thread checked before calling collect() in</span></span><br><span class=line> <span class=comment>// attempt_allocation_humongous(). Retrying the GC, in this case,</span></span><br><span class=line> <span class=comment>// will cause the requesting thread to spin inside collect() until the</span></span><br><span class=line> <span class=comment>// just started marking cycle is complete - which may be a while. So</span></span><br><span class=line> <span class=comment>// we do NOT retry the GC.</span></span><br><span class=line> <span class=keyword>if</span> (!res) {</span><br><span class=line> <span class=built_in>assert</span>(_word_size == <span class=number>0</span>, <span class=string>"Concurrent Full GC/Humongous Object IM shouldn't be allocating"</span>);</span><br><span class=line> <span class=keyword>if</span> (_gc_cause != GCCause::_g1_humongous_allocation) {</span><br><span class=line> _should_retry_gc = <span class=literal>true</span>;</span><br><span class=line> }</span><br><span class=line> <span class=keyword>return</span>;</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// Try a partial collection of some kind.</span></span><br><span class=line> _pause_succeeded = g1h-><span class=built_in>do_collection_pause_at_safepoint</span>(_target_pause_time_ms);</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (_pause_succeeded) {</span><br><span class=line> <span class=keyword>if</span> (_word_size > <span class=number>0</span>) {</span><br><span class=line> <span class=comment>// An allocation had been requested. Do it, eventually trying a stronger</span></span><br><span class=line> <span class=comment>// kind of GC.</span></span><br><span class=line> _result = g1h-><span class=built_in>satisfy_failed_allocation</span>(_word_size, &_pause_succeeded);</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=type>bool</span> should_upgrade_to_full = !g1h-><span class=built_in>should_do_concurrent_full_gc</span>(_gc_cause) &&</span><br><span class=line> !g1h-><span class=built_in>has_regions_left_for_allocation</span>();</span><br><span class=line> <span class=keyword>if</span> (should_upgrade_to_full) {</span><br><span class=line> <span class=comment>// There has been a request to perform a GC to free some space. We have no</span></span><br><span class=line> <span class=comment>// information on how much memory has been asked for. In case there are</span></span><br><span class=line> <span class=comment>// absolutely no regions left to allocate into, do a maximally compacting full GC.</span></span><br><span class=line> <span class=built_in>log_info</span>(gc, ergo)(<span class=string>"Attempting maximally compacting collection"</span>);</span><br><span class=line> _pause_succeeded = g1h-><span class=built_in>do_full_collection</span>(<span class=literal>false</span>, <span class=comment>/* explicit gc */</span></span><br><span class=line> <span class=literal>true</span> <span class=comment>/* clear_all_soft_refs */</span>);</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> <span class=built_in>guarantee</span>(_pause_succeeded, <span class=string>"Elevated collections during the safepoint must always succeed."</span>);</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=built_in>assert</span>(_result == <span class=literal>NULL</span>, <span class=string>"invariant"</span>);</span><br><span class=line> <span class=comment>// The only reason for the pause to not be successful is that, the GC locker is</span></span><br><span class=line> <span class=comment>// active (or has become active since the prologue was executed). In this case</span></span><br><span class=line> <span class=comment>// we should retry the pause after waiting for the GC locker to become inactive.</span></span><br><span class=line> _should_retry_gc = <span class=literal>true</span>;</span><br><span class=line> }</span><br><span class=line>}</span><br></pre></table></figure><p>这里可以看到核心的是<code>G1CollectedHeap::do_collection_pause_at_safepoint</code>这个方法,它带上了目标暂停时间的值<figure class="highlight c++"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br><span class=line>65</span><br><span class=line>66</span><br><span class=line>67</span><br><span class=line>68</span><br><span class=line>69</span><br><span class=line>70</span><br><span class=line>71</span><br><span class=line>72</span><br><span class=line>73</span><br><span class=line>74</span><br><span class=line>75</span><br><span class=line>76</span><br><span class=line>77</span><br><span class=line>78</span><br><span class=line>79</span><br><span class=line>80</span><br><span class=line>81</span><br><span class=line>82</span><br><span class=line>83</span><br><span class=line>84</span><br><span class=line>85</span><br><span class=line>86</span><br><span class=line>87</span><br><span class=line>88</span><br><span class=line>89</span><br><span class=line>90</span><br><span class=line>91</span><br><span class=line>92</span><br><span class=line>93</span><br><span class=line>94</span><br><span class=line>95</span><br><span class=line>96</span><br><span class=line>97</span><br><span class=line>98</span><br><span class=line>99</span><br><span class=line>100</span><br><span class=line>101</span><br><span class=line>102</span><br><span class=line>103</span><br><span class=line>104</span><br><span class=line>105</span><br><span class=line>106</span><br><span class=line>107</span><br><span class=line>108</span><br><span class=line>109</span><br><span class=line>110</span><br><span class=line>111</span><br><span class=line>112</span><br><span class=line>113</span><br><span class=line>114</span><br><span class=line>115</span><br><span class=line>116</span><br><span class=line>117</span><br><span class=line>118</span><br><span class=line>119</span><br><span class=line>120</span><br><span class=line>121</span><br><span class=line>122</span><br><span class=line>123</span><br><span class=line>124</span><br><span class=line>125</span><br><span class=line>126</span><br><span class=line>127</span><br><span class=line>128</span><br><span class=line>129</span><br><span class=line>130</span><br><span class=line>131</span><br><span class=line>132</span><br><span class=line>133</span><br><span class=line>134</span><br><span class=line>135</span><br><span class=line>136</span><br><span class=line>137</span><br><span class=line>138</span><br><span class=line>139</span><br><span class=line>140</span><br><span class=line>141</span><br><span class=line>142</span><br><span class=line>143</span><br><span class=line>144</span><br><span class=line>145</span><br><span class=line>146</span><br><span class=line>147</span><br><span class=line>148</span><br><span class=line>149</span><br><span class=line>150</span><br><span class=line>151</span><br><span class=line>152</span><br><span class=line>153</span><br><span class=line>154</span><br><span class=line>155</span><br><span class=line>156</span><br><span class=line>157</span><br><span class=line>158</span><br><span class=line>159</span><br><span class=line>160</span><br><span class=line>161</span><br><span class=line>162</span><br><span class=line>163</span><br><span class=line>164</span><br><span class=line>165</span><br><span class=line>166</span><br><span class=line>167</span><br><span class=line>168</span><br><span class=line>169</span><br><span class=line>170</span><br><span class=line>171</span><br><span class=line>172</span><br><span class=line>173</span><br><span class=line>174</span><br><span class=line>175</span><br><span class=line>176</span><br><span class=line>177</span><br><span class=line>178</span><br><span class=line>179</span><br><span class=line>180</span><br><span class=line>181</span><br><span class=line>182</span><br><span class=line>183</span><br><span class=line>184</span><br><span class=line>185</span><br><span class=line>186</span><br><span class=line>187</span><br><span class=line>188</span><br><span class=line>189</span><br><span class=line>190</span><br><span class=line>191</span><br><span class=line>192</span><br><span class=line>193</span><br><span class=line>194</span><br><span class=line>195</span><br><span class=line>196</span><br><span class=line>197</span><br><span class=line>198</span><br><span class=line>199</span><br><span class=line>200</span><br><span class=line>201</span><br><span class=line>202</span><br><span class=line>203</span><br><span class=line>204</span><br><span class=line>205</span><br><span class=line>206</span><br><span class=line>207</span><br><span class=line>208</span><br><span class=line>209</span><br><span class=line>210</span><br><span class=line>211</span><br><span class=line>212</span><br><span class=line>213</span><br><span class=line>214</span><br><span class=line>215</span><br><span class=line>216</span><br><span class=line>217</span><br><span class=line>218</span><br><span class=line>219</span><br><span class=line>220</span><br><span class=line>221</span><br><span class=line>222</span><br><span class=line>223</span><br><span class=line>224</span><br><span class=line>225</span><br><span class=line>226</span><br><span class=line>227</span><br><span class=line>228</span><br><span class=line>229</span><br><span class=line>230</span><br><span class=line>231</span><br><span class=line>232</span><br><span class=line>233</span><br><span class=line>234</span><br><span class=line>235</span><br><span class=line>236</span><br><span class=line>237</span><br><span class=line>238</span><br><span class=line>239</span><br><span class=line>240</span><br><span class=line>241</span><br><span class=line>242</span><br><span class=line>243</span><br><span class=line>244</span><br><span class=line>245</span><br><span class=line>246</span><br><span class=line>247</span><br><span class=line>248</span><br><span class=line>249</span><br><span class=line>250</span><br><span class=line>251</span><br><span class=line>252</span><br><span class=line>253</span><br><span class=line>254</span><br><span class=line>255</span><br><span class=line>256</span><br><span class=line>257</span><br><span class=line>258</span><br><span class=line>259</span><br><span class=line>260</span><br><span class=line>261</span><br><span class=line>262</span><br><span class=line>263</span><br><span class=line>264</span><br><span class=line>265</span><br><span class=line>266</span><br><span class=line>267</span><br><span class=line>268</span><br><span class=line>269</span><br><span class=line>270</span><br><span class=line>271</span><br><span class=line>272</span><br><span class=line>273</span><br><span class=line>274</span><br><span class=line>275</span><br><span class=line>276</span><br><span class=line>277</span><br><span class=line>278</span><br><span class=line>279</span><br><span class=line>280</span><br><span class=line>281</span><br><span class=line>282</span><br><span class=line>283</span><br><span class=line>284</span><br><span class=line>285</span><br><span class=line>286</span><br><span class=line>287</span><br><span class=line>288</span><br><span class=line>289</span><br><span class=line>290</span><br><span class=line>291</span><br><span class=line>292</span><br><span class=line>293</span><br><span class=line>294</span><br><span class=line>295</span><br><span class=line>296</span><br><span class=line>297</span><br><span class=line>298</span><br><span class=line>299</span><br><span class=line>300</span><br><span class=line>301</span><br><span class=line>302</span><br><span class=line>303</span><br><span class=line>304</span><br><span class=line>305</span><br><span class=line>306</span><br><span class=line>307</span><br><span class=line>308</span><br><span class=line>309</span><br><span class=line>310</span><br><span class=line>311</span><br><span class=line>312</span><br><span class=line>313</span><br><span class=line>314</span><br><span class=line>315</span><br><span class=line>316</span><br><span class=line>317</span><br><span class=line>318</span><br><span class=line>319</span><br><span class=line>320</span><br><span class=line>321</span><br><span class=line>322</span><br><span class=line>323</span><br><span class=line>324</span><br><span class=line>325</span><br><span class=line>326</span><br><span class=line>327</span><br><span class=line>328</span><br><span class=line>329</span><br><span class=line>330</span><br></pre><td class=code><pre><span class=line>G1CollectedHeap::<span class=built_in>do_collection_pause_at_safepoint</span>(<span class=type>double</span> target_pause_time_ms) {</span><br><span class=line> <span class=built_in>assert_at_safepoint_on_vm_thread</span>();</span><br><span class=line> <span class=built_in>guarantee</span>(!<span class=built_in>is_gc_active</span>(), <span class=string>"collection is not reentrant"</span>);</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (GCLocker::<span class=built_in>check_active_before_gc</span>()) {</span><br><span class=line> <span class=keyword>return</span> <span class=literal>false</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> _gc_timer_stw-><span class=built_in>register_gc_start</span>();</span><br><span class=line></span><br><span class=line> GCIdMark gc_id_mark;</span><br><span class=line> _gc_tracer_stw-><span class=built_in>report_gc_start</span>(<span class=built_in>gc_cause</span>(), _gc_timer_stw-><span class=built_in>gc_start</span>());</span><br><span class=line></span><br><span class=line> <span class=function>SvcGCMarker <span class=title>sgcm</span><span class=params>(SvcGCMarker::MINOR)</span></span>;</span><br><span class=line> ResourceMark rm;</span><br><span class=line></span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>note_gc_start</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>wait_for_root_region_scanning</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>print_heap_before_gc</span>();</span><br><span class=line> <span class=built_in>print_heap_regions</span>();</span><br><span class=line> <span class=built_in>trace_heap_before_gc</span>(_gc_tracer_stw);</span><br><span class=line></span><br><span class=line> _verifier-><span class=built_in>verify_region_sets_optional</span>();</span><br><span class=line> _verifier-><span class=built_in>verify_dirty_young_regions</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// We should not be doing initial mark unless the conc mark thread is running</span></span><br><span class=line> <span class=keyword>if</span> (!_cm_thread-><span class=built_in>should_terminate</span>()) {</span><br><span class=line> <span class=comment>// This call will decide whether this pause is an initial-mark</span></span><br><span class=line> <span class=comment>// pause. If it is, in_initial_mark_gc() will return true</span></span><br><span class=line> <span class=comment>// for the duration of this pause.</span></span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>decide_on_conc_mark_initiation</span>();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// We do not allow initial-mark to be piggy-backed on a mixed GC.</span></span><br><span class=line> <span class=built_in>assert</span>(!<span class=built_in>collector_state</span>()-><span class=built_in>in_initial_mark_gc</span>() ||</span><br><span class=line> <span class=built_in>collector_state</span>()-><span class=built_in>in_young_only_phase</span>(), <span class=string>"sanity"</span>);</span><br><span class=line></span><br><span class=line> <span class=comment>// We also do not allow mixed GCs during marking.</span></span><br><span class=line> <span class=built_in>assert</span>(!<span class=built_in>collector_state</span>()-><span class=built_in>mark_or_rebuild_in_progress</span>() || <span class=built_in>collector_state</span>()-><span class=built_in>in_young_only_phase</span>(), <span class=string>"sanity"</span>);</span><br><span class=line></span><br><span class=line> <span class=comment>// Record whether this pause is an initial mark. When the current</span></span><br><span class=line> <span class=comment>// thread has completed its logging output and it's safe to signal</span></span><br><span class=line> <span class=comment>// the CM thread, the flag's value in the policy has been reset.</span></span><br><span class=line> <span class=type>bool</span> should_start_conc_mark = <span class=built_in>collector_state</span>()-><span class=built_in>in_initial_mark_gc</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// Inner scope for scope based logging, timers, and stats collection</span></span><br><span class=line> {</span><br><span class=line> EvacuationInfo evacuation_info;</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>collector_state</span>()-><span class=built_in>in_initial_mark_gc</span>()) {</span><br><span class=line> <span class=comment>// We are about to start a marking cycle, so we increment the</span></span><br><span class=line> <span class=comment>// full collection counter.</span></span><br><span class=line> <span class=built_in>increment_old_marking_cycles_started</span>();</span><br><span class=line> _cm-><span class=built_in>gc_tracer_cm</span>()-><span class=built_in>set_gc_cause</span>(<span class=built_in>gc_cause</span>());</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> _gc_tracer_stw-><span class=built_in>report_yc_type</span>(<span class=built_in>collector_state</span>()-><span class=built_in>yc_type</span>());</span><br><span class=line></span><br><span class=line> GCTraceCPUTime tcpu;</span><br><span class=line></span><br><span class=line> G1HeapVerifier::G1VerifyType verify_type;</span><br><span class=line> FormatBuffer<> <span class=built_in>gc_string</span>(<span class=string>"Pause Young "</span>);</span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>collector_state</span>()-><span class=built_in>in_initial_mark_gc</span>()) {</span><br><span class=line> gc_string.<span class=built_in>append</span>(<span class=string>"(Concurrent Start)"</span>);</span><br><span class=line> verify_type = G1HeapVerifier::G1VerifyConcurrentStart;</span><br><span class=line> } <span class=keyword>else</span> <span class=keyword>if</span> (<span class=built_in>collector_state</span>()-><span class=built_in>in_young_only_phase</span>()) {</span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>collector_state</span>()-><span class=built_in>in_young_gc_before_mixed</span>()) {</span><br><span class=line> gc_string.<span class=built_in>append</span>(<span class=string>"(Prepare Mixed)"</span>);</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> gc_string.<span class=built_in>append</span>(<span class=string>"(Normal)"</span>);</span><br><span class=line> }</span><br><span class=line> verify_type = G1HeapVerifier::G1VerifyYoungNormal;</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> gc_string.<span class=built_in>append</span>(<span class=string>"(Mixed)"</span>);</span><br><span class=line> verify_type = G1HeapVerifier::G1VerifyMixed;</span><br><span class=line> }</span><br><span class=line> <span class=built_in>GCTraceTime</span>(Info, gc) <span class=built_in>tm</span>(gc_string, <span class=literal>NULL</span>, <span class=built_in>gc_cause</span>(), <span class=literal>true</span>);</span><br><span class=line></span><br><span class=line> uint active_workers = AdaptiveSizePolicy::<span class=built_in>calc_active_workers</span>(<span class=built_in>workers</span>()-><span class=built_in>total_workers</span>(),</span><br><span class=line> <span class=built_in>workers</span>()-><span class=built_in>active_workers</span>(),</span><br><span class=line> Threads::<span class=built_in>number_of_non_daemon_threads</span>());</span><br><span class=line> active_workers = <span class=built_in>workers</span>()-><span class=built_in>update_active_workers</span>(active_workers);</span><br><span class=line> <span class=built_in>log_info</span>(gc,task)(<span class=string>"Using %u workers of %u for evacuation"</span>, active_workers, <span class=built_in>workers</span>()-><span class=built_in>total_workers</span>());</span><br><span class=line></span><br><span class=line> <span class=function>TraceCollectorStats <span class=title>tcs</span><span class=params>(g1mm()->incremental_collection_counters())</span></span>;</span><br><span class=line> <span class=function>TraceMemoryManagerStats <span class=title>tms</span><span class=params>(&_memory_manager, gc_cause(),</span></span></span><br><span class=line><span class=params><span class=function> collector_state()->yc_type() == Mixed <span class=comment>/* allMemoryPoolsAffected */</span>)</span></span>;</span><br><span class=line></span><br><span class=line> <span class=function>G1HeapTransition <span class=title>heap_transition</span><span class=params>(<span class=keyword>this</span>)</span></span>;</span><br><span class=line> <span class=type>size_t</span> heap_used_bytes_before_gc = <span class=built_in>used</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// Don't dynamically change the number of GC threads this early. A value of</span></span><br><span class=line> <span class=comment>// 0 is used to indicate serial work. When parallel work is done,</span></span><br><span class=line> <span class=comment>// it will be set.</span></span><br><span class=line></span><br><span class=line> { <span class=comment>// Call to jvmpi::post_class_unload_events must occur outside of active GC</span></span><br><span class=line> IsGCActiveMark x;</span><br><span class=line></span><br><span class=line> <span class=built_in>gc_prologue</span>(<span class=literal>false</span>);</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (VerifyRememberedSets) {</span><br><span class=line> <span class=built_in>log_info</span>(gc, verify)(<span class=string>"[Verifying RemSets before GC]"</span>);</span><br><span class=line> VerifyRegionRemSetClosure v_cl;</span><br><span class=line> <span class=built_in>heap_region_iterate</span>(&v_cl);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> _verifier-><span class=built_in>verify_before_gc</span>(verify_type);</span><br><span class=line></span><br><span class=line> _verifier-><span class=built_in>check_bitmaps</span>(<span class=string>"GC Start"</span>);</span><br><span class=line></span><br><span class=line><span class=meta>#<span class=keyword>if</span> COMPILER2_OR_JVMCI</span></span><br><span class=line> DerivedPointerTable::<span class=built_in>clear</span>();</span><br><span class=line><span class=meta>#<span class=keyword>endif</span></span></span><br><span class=line></span><br><span class=line> <span class=comment>// Please see comment in g1CollectedHeap.hpp and</span></span><br><span class=line> <span class=comment>// G1CollectedHeap::ref_processing_init() to see how</span></span><br><span class=line> <span class=comment>// reference processing currently works in G1.</span></span><br><span class=line></span><br><span class=line> <span class=comment>// Enable discovery in the STW reference processor</span></span><br><span class=line> _ref_processor_stw-><span class=built_in>enable_discovery</span>();</span><br><span class=line></span><br><span class=line> {</span><br><span class=line> <span class=comment>// We want to temporarily turn off discovery by the</span></span><br><span class=line> <span class=comment>// CM ref processor, if necessary, and turn it back on</span></span><br><span class=line> <span class=comment>// on again later if we do. Using a scoped</span></span><br><span class=line> <span class=comment>// NoRefDiscovery object will do this.</span></span><br><span class=line> <span class=function>NoRefDiscovery <span class=title>no_cm_discovery</span><span class=params>(_ref_processor_cm)</span></span>;</span><br><span class=line></span><br><span class=line> <span class=comment>// Forget the current alloc region (we might even choose it to be part</span></span><br><span class=line> <span class=comment>// of the collection set!).</span></span><br><span class=line> _allocator-><span class=built_in>release_mutator_alloc_region</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// This timing is only used by the ergonomics to handle our pause target.</span></span><br><span class=line> <span class=comment>// It is unclear why this should not include the full pause. We will</span></span><br><span class=line> <span class=comment>// investigate this in CR 7178365.</span></span><br><span class=line> <span class=comment>//</span></span><br><span class=line> <span class=comment>// Preserving the old comment here if that helps the investigation:</span></span><br><span class=line> <span class=comment>//</span></span><br><span class=line> <span class=comment>// The elapsed time induced by the start time below deliberately elides</span></span><br><span class=line> <span class=comment>// the possible verification above.</span></span><br><span class=line> <span class=type>double</span> sample_start_time_sec = os::<span class=built_in>elapsedTime</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>record_collection_pause_start</span>(sample_start_time_sec);</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>collector_state</span>()-><span class=built_in>in_initial_mark_gc</span>()) {</span><br><span class=line> <span class=built_in>concurrent_mark</span>()-><span class=built_in>pre_initial_mark</span>();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>finalize_collection_set</span>(target_pause_time_ms, &_survivor);</span><br><span class=line></span><br><span class=line> evacuation_info.<span class=built_in>set_collectionset_regions</span>(<span class=built_in>collection_set</span>()-><span class=built_in>region_length</span>());</span><br><span class=line></span><br><span class=line> <span class=comment>// Make sure the remembered sets are up to date. This needs to be</span></span><br><span class=line> <span class=comment>// done before register_humongous_regions_with_cset(), because the</span></span><br><span class=line> <span class=comment>// remembered sets are used there to choose eager reclaim candidates.</span></span><br><span class=line> <span class=comment>// If the remembered sets are not up to date we might miss some</span></span><br><span class=line> <span class=comment>// entries that need to be handled.</span></span><br><span class=line> <span class=built_in>g1_rem_set</span>()-><span class=built_in>cleanupHRRS</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>register_humongous_regions_with_cset</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>assert</span>(_verifier-><span class=built_in>check_cset_fast_test</span>(), <span class=string>"Inconsistency in the InCSetState table."</span>);</span><br><span class=line></span><br><span class=line> <span class=comment>// We call this after finalize_cset() to</span></span><br><span class=line> <span class=comment>// ensure that the CSet has been finalized.</span></span><br><span class=line> _cm-><span class=built_in>verify_no_cset_oops</span>();</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (_hr_printer.<span class=built_in>is_active</span>()) {</span><br><span class=line> <span class=function>G1PrintCollectionSetClosure <span class=title>cl</span><span class=params>(&_hr_printer)</span></span>;</span><br><span class=line> _collection_set.<span class=built_in>iterate</span>(&cl);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// Initialize the GC alloc regions.</span></span><br><span class=line> _allocator-><span class=built_in>init_gc_alloc_regions</span>(evacuation_info);</span><br><span class=line></span><br><span class=line> <span class=function>G1ParScanThreadStateSet <span class=title>per_thread_states</span><span class=params>(<span class=keyword>this</span>, workers()->active_workers(), collection_set()->young_region_length())</span></span>;</span><br><span class=line> <span class=built_in>pre_evacuate_collection_set</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// Actually do the work...</span></span><br><span class=line> <span class=built_in>evacuate_collection_set</span>(&per_thread_states);</span><br><span class=line></span><br><span class=line> <span class=built_in>post_evacuate_collection_set</span>(evacuation_info, &per_thread_states);</span><br><span class=line></span><br><span class=line> <span class=type>const</span> <span class=type>size_t</span>* surviving_young_words = per_thread_states.<span class=built_in>surviving_young_words</span>();</span><br><span class=line> <span class=built_in>free_collection_set</span>(&_collection_set, evacuation_info, surviving_young_words);</span><br><span class=line></span><br><span class=line> <span class=built_in>eagerly_reclaim_humongous_regions</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>record_obj_copy_mem_stats</span>();</span><br><span class=line> _survivor_evac_stats.<span class=built_in>adjust_desired_plab_sz</span>();</span><br><span class=line> _old_evac_stats.<span class=built_in>adjust_desired_plab_sz</span>();</span><br><span class=line></span><br><span class=line> <span class=type>double</span> start = os::<span class=built_in>elapsedTime</span>();</span><br><span class=line> <span class=built_in>start_new_collection_set</span>();</span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>phase_times</span>()-><span class=built_in>record_start_new_cset_time_ms</span>((os::<span class=built_in>elapsedTime</span>() - start) * <span class=number>1000.0</span>);</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>evacuation_failed</span>()) {</span><br><span class=line> <span class=built_in>set_used</span>(<span class=built_in>recalculate_used</span>());</span><br><span class=line> <span class=keyword>if</span> (_archive_allocator != <span class=literal>NULL</span>) {</span><br><span class=line> _archive_allocator-><span class=built_in>clear_used</span>();</span><br><span class=line> }</span><br><span class=line> <span class=keyword>for</span> (uint i = <span class=number>0</span>; i < ParallelGCThreads; i++) {</span><br><span class=line> <span class=keyword>if</span> (_evacuation_failed_info_array[i].<span class=built_in>has_failed</span>()) {</span><br><span class=line> _gc_tracer_stw-><span class=built_in>report_evacuation_failed</span>(_evacuation_failed_info_array[i]);</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=comment>// The "used" of the the collection set have already been subtracted</span></span><br><span class=line> <span class=comment>// when they were freed. Add in the bytes evacuated.</span></span><br><span class=line> <span class=built_in>increase_used</span>(<span class=built_in>g1_policy</span>()-><span class=built_in>bytes_copied_during_gc</span>());</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>collector_state</span>()-><span class=built_in>in_initial_mark_gc</span>()) {</span><br><span class=line> <span class=comment>// We have to do this before we notify the CM threads that</span></span><br><span class=line> <span class=comment>// they can start working to make sure that all the</span></span><br><span class=line> <span class=comment>// appropriate initialization is done on the CM object.</span></span><br><span class=line> <span class=built_in>concurrent_mark</span>()-><span class=built_in>post_initial_mark</span>();</span><br><span class=line> <span class=comment>// Note that we don't actually trigger the CM thread at</span></span><br><span class=line> <span class=comment>// this point. We do that later when we're sure that</span></span><br><span class=line> <span class=comment>// the current thread has completed its logging output.</span></span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=built_in>allocate_dummy_regions</span>();</span><br><span class=line></span><br><span class=line> _allocator-><span class=built_in>init_mutator_alloc_region</span>();</span><br><span class=line></span><br><span class=line> {</span><br><span class=line> <span class=type>size_t</span> expand_bytes = _heap_sizing_policy-><span class=built_in>expansion_amount</span>();</span><br><span class=line> <span class=keyword>if</span> (expand_bytes > <span class=number>0</span>) {</span><br><span class=line> <span class=type>size_t</span> bytes_before = <span class=built_in>capacity</span>();</span><br><span class=line> <span class=comment>// No need for an ergo logging here,</span></span><br><span class=line> <span class=comment>// expansion_amount() does this when it returns a value > 0.</span></span><br><span class=line> <span class=type>double</span> expand_ms;</span><br><span class=line> <span class=keyword>if</span> (!<span class=built_in>expand</span>(expand_bytes, _workers, &expand_ms)) {</span><br><span class=line> <span class=comment>// We failed to expand the heap. Cannot do anything about it.</span></span><br><span class=line> }</span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>phase_times</span>()-><span class=built_in>record_expand_heap_time</span>(expand_ms);</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// We redo the verification but now wrt to the new CSet which</span></span><br><span class=line> <span class=comment>// has just got initialized after the previous CSet was freed.</span></span><br><span class=line> _cm-><span class=built_in>verify_no_cset_oops</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// This timing is only used by the ergonomics to handle our pause target.</span></span><br><span class=line> <span class=comment>// It is unclear why this should not include the full pause. We will</span></span><br><span class=line> <span class=comment>// investigate this in CR 7178365.</span></span><br><span class=line> <span class=type>double</span> sample_end_time_sec = os::<span class=built_in>elapsedTime</span>();</span><br><span class=line> <span class=type>double</span> pause_time_ms = (sample_end_time_sec - sample_start_time_sec) * MILLIUNITS;</span><br><span class=line> <span class=type>size_t</span> total_cards_scanned = <span class=built_in>g1_policy</span>()-><span class=built_in>phase_times</span>()-><span class=built_in>sum_thread_work_items</span>(G1GCPhaseTimes::ScanRS, G1GCPhaseTimes::ScanRSScannedCards);</span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>record_collection_pause_end</span>(pause_time_ms, total_cards_scanned, heap_used_bytes_before_gc);</span><br><span class=line></span><br><span class=line> evacuation_info.<span class=built_in>set_collectionset_used_before</span>(<span class=built_in>collection_set</span>()-><span class=built_in>bytes_used_before</span>());</span><br><span class=line> evacuation_info.<span class=built_in>set_bytes_copied</span>(<span class=built_in>g1_policy</span>()-><span class=built_in>bytes_copied_during_gc</span>());</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (VerifyRememberedSets) {</span><br><span class=line> <span class=built_in>log_info</span>(gc, verify)(<span class=string>"[Verifying RemSets after GC]"</span>);</span><br><span class=line> VerifyRegionRemSetClosure v_cl;</span><br><span class=line> <span class=built_in>heap_region_iterate</span>(&v_cl);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> _verifier-><span class=built_in>verify_after_gc</span>(verify_type);</span><br><span class=line> _verifier-><span class=built_in>check_bitmaps</span>(<span class=string>"GC End"</span>);</span><br><span class=line></span><br><span class=line> <span class=built_in>assert</span>(!_ref_processor_stw-><span class=built_in>discovery_enabled</span>(), <span class=string>"Postcondition"</span>);</span><br><span class=line> _ref_processor_stw-><span class=built_in>verify_no_references_recorded</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// CM reference discovery will be re-enabled if necessary.</span></span><br><span class=line> }</span><br><span class=line></span><br><span class=line><span class=meta>#<span class=keyword>ifdef</span> TRACESPINNING</span></span><br><span class=line> ParallelTaskTerminator::<span class=built_in>print_termination_counts</span>();</span><br><span class=line><span class=meta>#<span class=keyword>endif</span></span></span><br><span class=line></span><br><span class=line> <span class=built_in>gc_epilogue</span>(<span class=literal>false</span>);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// Print the remainder of the GC log output.</span></span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>evacuation_failed</span>()) {</span><br><span class=line> <span class=built_in>log_info</span>(gc)(<span class=string>"To-space exhausted"</span>);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=built_in>g1_policy</span>()-><span class=built_in>print_phases</span>();</span><br><span class=line> heap_transition.<span class=built_in>print</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// It is not yet to safe to tell the concurrent mark to</span></span><br><span class=line> <span class=comment>// start as we have some optional output below. We don't want the</span></span><br><span class=line> <span class=comment>// output from the concurrent mark thread interfering with this</span></span><br><span class=line> <span class=comment>// logging output either.</span></span><br><span class=line></span><br><span class=line> _hrm.<span class=built_in>verify_optional</span>();</span><br><span class=line> _verifier-><span class=built_in>verify_region_sets_optional</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>TASKQUEUE_STATS_ONLY</span>(<span class=built_in>print_taskqueue_stats</span>());</span><br><span class=line> <span class=built_in>TASKQUEUE_STATS_ONLY</span>(<span class=built_in>reset_taskqueue_stats</span>());</span><br><span class=line></span><br><span class=line> <span class=built_in>print_heap_after_gc</span>();</span><br><span class=line> <span class=built_in>print_heap_regions</span>();</span><br><span class=line> <span class=built_in>trace_heap_after_gc</span>(_gc_tracer_stw);</span><br><span class=line></span><br><span class=line> <span class=comment>// We must call G1MonitoringSupport::update_sizes() in the same scoping level</span></span><br><span class=line> <span class=comment>// as an active TraceMemoryManagerStats object (i.e. before the destructor for the</span></span><br><span class=line> <span class=comment>// TraceMemoryManagerStats is called) so that the G1 memory pools are updated</span></span><br><span class=line> <span class=comment>// before any GC notifications are raised.</span></span><br><span class=line> <span class=built_in>g1mm</span>()-><span class=built_in>update_sizes</span>();</span><br><span class=line></span><br><span class=line> _gc_tracer_stw-><span class=built_in>report_evacuation_info</span>(&evacuation_info);</span><br><span class=line> _gc_tracer_stw-><span class=built_in>report_tenuring_threshold</span>(_g1_policy-><span class=built_in>tenuring_threshold</span>());</span><br><span class=line> _gc_timer_stw-><span class=built_in>register_gc_end</span>();</span><br><span class=line> _gc_tracer_stw-><span class=built_in>report_gc_end</span>(_gc_timer_stw-><span class=built_in>gc_end</span>(), _gc_timer_stw-><span class=built_in>time_partitions</span>());</span><br><span class=line> }</span><br><span class=line> <span class=comment>// It should now be safe to tell the concurrent mark thread to start</span></span><br><span class=line> <span class=comment>// without its logging output interfering with the logging output</span></span><br><span class=line> <span class=comment>// that came from the pause.</span></span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (should_start_conc_mark) {</span><br><span class=line> <span class=comment>// CAUTION: after the doConcurrentMark() call below,</span></span><br><span class=line> <span class=comment>// the concurrent marking thread(s) could be running</span></span><br><span class=line> <span class=comment>// concurrently with us. Make sure that anything after</span></span><br><span class=line> <span class=comment>// this point does not assume that we are the only GC thread</span></span><br><span class=line> <span class=comment>// running. Note: of course, the actual marking work will</span></span><br><span class=line> <span class=comment>// not start until the safepoint itself is released in</span></span><br><span class=line> <span class=comment>// SuspendibleThreadSet::desynchronize().</span></span><br><span class=line> <span class=built_in>do_concurrent_mark</span>();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>return</span> <span class=literal>true</span>;</span><br><span class=line>}</span><br></pre></table></figure><p>往下走就是这一步<code>G1Policy::finalize_collection_set</code>,去处理新生代和老年代<figure class="highlight c++"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br></pre><td class=code><pre><span class=line><span class=function><span class=type>void</span> <span class=title>G1Policy::finalize_collection_set</span><span class=params>(<span class=type>double</span> target_pause_time_ms, G1SurvivorRegions* survivor)</span> </span>{</span><br><span class=line> <span class=type>double</span> time_remaining_ms = _collection_set-><span class=built_in>finalize_young_part</span>(target_pause_time_ms, survivor);</span><br><span class=line> _collection_set-><span class=built_in>finalize_old_part</span>(time_remaining_ms);</span><br><span class=line>}</span><br></pre></table></figure><p>这里分别调用了两个方法,可以看到剩余时间是往下传的,来看一下具体的方法<figure class="highlight c++"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br></pre><td class=code><pre><span class=line><span class=function><span class=type>double</span> <span class=title>G1CollectionSet::finalize_young_part</span><span class=params>(<span class=type>double</span> target_pause_time_ms, G1SurvivorRegions* survivors)</span> </span>{</span><br><span class=line> <span class=type>double</span> young_start_time_sec = os::<span class=built_in>elapsedTime</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>finalize_incremental_building</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>guarantee</span>(target_pause_time_ms > <span class=number>0.0</span>,</span><br><span class=line> <span class=string>"target_pause_time_ms = %1.6lf should be positive"</span>, target_pause_time_ms);</span><br><span class=line></span><br><span class=line> <span class=type>size_t</span> pending_cards = _policy-><span class=built_in>pending_cards</span>();</span><br><span class=line> <span class=type>double</span> base_time_ms = _policy-><span class=built_in>predict_base_elapsed_time_ms</span>(pending_cards);</span><br><span class=line> <span class=type>double</span> time_remaining_ms = <span class=built_in>MAX2</span>(target_pause_time_ms - base_time_ms, <span class=number>0.0</span>);</span><br><span class=line></span><br><span class=line> <span class=built_in>log_trace</span>(gc, ergo, cset)(<span class=string>"Start choosing CSet. pending cards: "</span> SIZE_FORMAT <span class=string>" predicted base time: %1.2fms remaining time: %1.2fms target pause time: %1.2fms"</span>,</span><br><span class=line> pending_cards, base_time_ms, time_remaining_ms, target_pause_time_ms);</span><br><span class=line></span><br><span class=line> <span class=comment>// The young list is laid with the survivor regions from the previous</span></span><br><span class=line> <span class=comment>// pause are appended to the RHS of the young list, i.e.</span></span><br><span class=line> <span class=comment>// [Newly Young Regions ++ Survivors from last pause].</span></span><br><span class=line></span><br><span class=line> uint survivor_region_length = survivors-><span class=built_in>length</span>();</span><br><span class=line> uint eden_region_length = _g1h-><span class=built_in>eden_regions_count</span>();</span><br><span class=line> <span class=built_in>init_region_lengths</span>(eden_region_length, survivor_region_length);</span><br><span class=line></span><br><span class=line> <span class=built_in>verify_young_cset_indices</span>();</span><br><span class=line></span><br><span class=line> <span class=comment>// Clear the fields that point to the survivor list - they are all young now.</span></span><br><span class=line> survivors-><span class=built_in>convert_to_eden</span>();</span><br><span class=line></span><br><span class=line> _bytes_used_before = _inc_bytes_used_before;</span><br><span class=line> time_remaining_ms = <span class=built_in>MAX2</span>(time_remaining_ms - _inc_predicted_elapsed_time_ms, <span class=number>0.0</span>);</span><br><span class=line></span><br><span class=line> <span class=built_in>log_trace</span>(gc, ergo, cset)(<span class=string>"Add young regions to CSet. eden: %u regions, survivors: %u regions, predicted young region time: %1.2fms, target pause time: %1.2fms"</span>,</span><br><span class=line> eden_region_length, survivor_region_length, _inc_predicted_elapsed_time_ms, target_pause_time_ms);</span><br><span class=line></span><br><span class=line> <span class=comment>// The number of recorded young regions is the incremental</span></span><br><span class=line> <span class=comment>// collection set's current size</span></span><br><span class=line> <span class=built_in>set_recorded_rs_lengths</span>(_inc_recorded_rs_lengths);</span><br><span class=line></span><br><span class=line> <span class=type>double</span> young_end_time_sec = os::<span class=built_in>elapsedTime</span>();</span><br><span class=line> <span class=built_in>phase_times</span>()-><span class=built_in>record_young_cset_choice_time_ms</span>((young_end_time_sec - young_start_time_sec) * <span class=number>1000.0</span>);</span><br><span class=line></span><br><span class=line> <span class=keyword>return</span> time_remaining_ms;</span><br><span class=line>}</span><br></pre></table></figure><p>下面是老年代的部分<figure class="highlight c++"><table><tr><td class=gutter><pre><span class=line>1</span><br><span class=line>2</span><br><span class=line>3</span><br><span class=line>4</span><br><span class=line>5</span><br><span class=line>6</span><br><span class=line>7</span><br><span class=line>8</span><br><span class=line>9</span><br><span class=line>10</span><br><span class=line>11</span><br><span class=line>12</span><br><span class=line>13</span><br><span class=line>14</span><br><span class=line>15</span><br><span class=line>16</span><br><span class=line>17</span><br><span class=line>18</span><br><span class=line>19</span><br><span class=line>20</span><br><span class=line>21</span><br><span class=line>22</span><br><span class=line>23</span><br><span class=line>24</span><br><span class=line>25</span><br><span class=line>26</span><br><span class=line>27</span><br><span class=line>28</span><br><span class=line>29</span><br><span class=line>30</span><br><span class=line>31</span><br><span class=line>32</span><br><span class=line>33</span><br><span class=line>34</span><br><span class=line>35</span><br><span class=line>36</span><br><span class=line>37</span><br><span class=line>38</span><br><span class=line>39</span><br><span class=line>40</span><br><span class=line>41</span><br><span class=line>42</span><br><span class=line>43</span><br><span class=line>44</span><br><span class=line>45</span><br><span class=line>46</span><br><span class=line>47</span><br><span class=line>48</span><br><span class=line>49</span><br><span class=line>50</span><br><span class=line>51</span><br><span class=line>52</span><br><span class=line>53</span><br><span class=line>54</span><br><span class=line>55</span><br><span class=line>56</span><br><span class=line>57</span><br><span class=line>58</span><br><span class=line>59</span><br><span class=line>60</span><br><span class=line>61</span><br><span class=line>62</span><br><span class=line>63</span><br><span class=line>64</span><br><span class=line>65</span><br><span class=line>66</span><br><span class=line>67</span><br><span class=line>68</span><br><span class=line>69</span><br><span class=line>70</span><br><span class=line>71</span><br><span class=line>72</span><br><span class=line>73</span><br><span class=line>74</span><br><span class=line>75</span><br><span class=line>76</span><br><span class=line>77</span><br><span class=line>78</span><br><span class=line>79</span><br><span class=line>80</span><br><span class=line>81</span><br><span class=line>82</span><br><span class=line>83</span><br><span class=line>84</span><br><span class=line>85</span><br><span class=line>86</span><br><span class=line>87</span><br><span class=line>88</span><br><span class=line>89</span><br><span class=line>90</span><br><span class=line>91</span><br><span class=line>92</span><br><span class=line>93</span><br><span class=line>94</span><br><span class=line>95</span><br><span class=line>96</span><br><span class=line>97</span><br><span class=line>98</span><br><span class=line>99</span><br><span class=line>100</span><br></pre><td class=code><pre><span class=line><span class=function><span class=type>void</span> <span class=title>G1CollectionSet::finalize_old_part</span><span class=params>(<span class=type>double</span> time_remaining_ms)</span> </span>{</span><br><span class=line> <span class=type>double</span> non_young_start_time_sec = os::<span class=built_in>elapsedTime</span>();</span><br><span class=line> <span class=type>double</span> predicted_old_time_ms = <span class=number>0.0</span>;</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>collector_state</span>()-><span class=built_in>in_mixed_phase</span>()) {</span><br><span class=line> <span class=built_in>cset_chooser</span>()-><span class=built_in>verify</span>();</span><br><span class=line> <span class=type>const</span> uint min_old_cset_length = _policy-><span class=built_in>calc_min_old_cset_length</span>();</span><br><span class=line> <span class=type>const</span> uint max_old_cset_length = _policy-><span class=built_in>calc_max_old_cset_length</span>();</span><br><span class=line></span><br><span class=line> uint expensive_region_num = <span class=number>0</span>;</span><br><span class=line> <span class=type>bool</span> check_time_remaining = _policy-><span class=built_in>adaptive_young_list_length</span>();</span><br><span class=line></span><br><span class=line> HeapRegion* hr = <span class=built_in>cset_chooser</span>()-><span class=built_in>peek</span>();</span><br><span class=line> <span class=keyword>while</span> (hr != <span class=literal>NULL</span>) {</span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>old_region_length</span>() >= max_old_cset_length) {</span><br><span class=line> <span class=comment>// Added maximum number of old regions to the CSet.</span></span><br><span class=line> <span class=built_in>log_debug</span>(gc, ergo, cset)(<span class=string>"Finish adding old regions to CSet (old CSet region num reached max). old %u regions, max %u regions"</span>,</span><br><span class=line> <span class=built_in>old_region_length</span>(), max_old_cset_length);</span><br><span class=line> <span class=keyword>break</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// Stop adding regions if the remaining reclaimable space is</span></span><br><span class=line> <span class=comment>// not above G1HeapWastePercent.</span></span><br><span class=line> <span class=type>size_t</span> reclaimable_bytes = <span class=built_in>cset_chooser</span>()-><span class=built_in>remaining_reclaimable_bytes</span>();</span><br><span class=line> <span class=type>double</span> reclaimable_percent = _policy-><span class=built_in>reclaimable_bytes_percent</span>(reclaimable_bytes);</span><br><span class=line> <span class=type>double</span> threshold = (<span class=type>double</span>) G1HeapWastePercent;</span><br><span class=line> <span class=keyword>if</span> (reclaimable_percent <= threshold) {</span><br><span class=line> <span class=comment>// We've added enough old regions that the amount of uncollected</span></span><br><span class=line> <span class=comment>// reclaimable space is at or below the waste threshold. Stop</span></span><br><span class=line> <span class=comment>// adding old regions to the CSet.</span></span><br><span class=line> <span class=built_in>log_debug</span>(gc, ergo, cset)(<span class=string>"Finish adding old regions to CSet (reclaimable percentage not over threshold). "</span></span><br><span class=line> <span class=string>"old %u regions, max %u regions, reclaimable: "</span> SIZE_FORMAT <span class=string>"B (%1.2f%%) threshold: "</span> UINTX_FORMAT <span class=string>"%%"</span>,</span><br><span class=line> <span class=built_in>old_region_length</span>(), max_old_cset_length, reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);</span><br><span class=line> <span class=keyword>break</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=type>double</span> predicted_time_ms = <span class=built_in>predict_region_elapsed_time_ms</span>(hr);</span><br><span class=line> <span class=keyword>if</span> (check_time_remaining) {</span><br><span class=line> <span class=keyword>if</span> (predicted_time_ms > time_remaining_ms) {</span><br><span class=line> <span class=comment>// Too expensive for the current CSet.</span></span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>old_region_length</span>() >= min_old_cset_length) {</span><br><span class=line> <span class=comment>// We have added the minimum number of old regions to the CSet,</span></span><br><span class=line> <span class=comment>// we are done with this CSet.</span></span><br><span class=line> <span class=built_in>log_debug</span>(gc, ergo, cset)(<span class=string>"Finish adding old regions to CSet (predicted time is too high). "</span></span><br><span class=line> <span class=string>"predicted time: %1.2fms, remaining time: %1.2fms old %u regions, min %u regions"</span>,</span><br><span class=line> predicted_time_ms, time_remaining_ms, <span class=built_in>old_region_length</span>(), min_old_cset_length);</span><br><span class=line> <span class=keyword>break</span>;</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// We'll add it anyway given that we haven't reached the</span></span><br><span class=line> <span class=comment>// minimum number of old regions.</span></span><br><span class=line> expensive_region_num += <span class=number>1</span>;</span><br><span class=line> }</span><br><span class=line> } <span class=keyword>else</span> {</span><br><span class=line> <span class=keyword>if</span> (<span class=built_in>old_region_length</span>() >= min_old_cset_length) {</span><br><span class=line> <span class=comment>// In the non-auto-tuning case, we'll finish adding regions</span></span><br><span class=line> <span class=comment>// to the CSet if we reach the minimum.</span></span><br><span class=line></span><br><span class=line> <span class=built_in>log_debug</span>(gc, ergo, cset)(<span class=string>"Finish adding old regions to CSet (old CSet region num reached min). old %u regions, min %u regions"</span>,</span><br><span class=line> <span class=built_in>old_region_length</span>(), min_old_cset_length);</span><br><span class=line> <span class=keyword>break</span>;</span><br><span class=line> }</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=comment>// We will add this region to the CSet.</span></span><br><span class=line> time_remaining_ms = <span class=built_in>MAX2</span>(time_remaining_ms - predicted_time_ms, <span class=number>0.0</span>);</span><br><span class=line> predicted_old_time_ms += predicted_time_ms;</span><br><span class=line> <span class=built_in>cset_chooser</span>()-><span class=built_in>pop</span>(); <span class=comment>// already have region via peek()</span></span><br><span class=line> _g1h-><span class=built_in>old_set_remove</span>(hr);</span><br><span class=line> <span class=built_in>add_old_region</span>(hr);</span><br><span class=line></span><br><span class=line> hr = <span class=built_in>cset_chooser</span>()-><span class=built_in>peek</span>();</span><br><span class=line> }</span><br><span class=line> <span class=keyword>if</span> (hr == <span class=literal>NULL</span>) {</span><br><span class=line> <span class=built_in>log_debug</span>(gc, ergo, cset)(<span class=string>"Finish adding old regions to CSet (candidate old regions not available)"</span>);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=keyword>if</span> (expensive_region_num > <span class=number>0</span>) {</span><br><span class=line> <span class=comment>// We print the information once here at the end, predicated on</span></span><br><span class=line> <span class=comment>// whether we added any apparently expensive regions or not, to</span></span><br><span class=line> <span class=comment>// avoid generating output per region.</span></span><br><span class=line> <span class=built_in>log_debug</span>(gc, ergo, cset)(<span class=string>"Added expensive regions to CSet (old CSet region num not reached min)."</span></span><br><span class=line> <span class=string>"old: %u regions, expensive: %u regions, min: %u regions, remaining time: %1.2fms"</span>,</span><br><span class=line> <span class=built_in>old_region_length</span>(), expensive_region_num, min_old_cset_length, time_remaining_ms);</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=built_in>cset_chooser</span>()-><span class=built_in>verify</span>();</span><br><span class=line> }</span><br><span class=line></span><br><span class=line> <span class=built_in>stop_incremental_building</span>();</span><br><span class=line></span><br><span class=line> <span class=built_in>log_debug</span>(gc, ergo, cset)(<span class=string>"Finish choosing CSet. old: %u regions, predicted old region time: %1.2fms, time remaining: %1.2f"</span>,</span><br><span class=line> <span class=built_in>old_region_length</span>(), predicted_old_time_ms, time_remaining_ms);</span><br><span class=line></span><br><span class=line> <span class=type>double</span> non_young_end_time_sec = os::<span class=built_in>elapsedTime</span>();</span><br><span class=line> <span class=built_in>phase_times</span>()-><span class=built_in>record_non_young_cset_choice_time_ms</span>((non_young_end_time_sec - non_young_start_time_sec) * <span class=number>1000.0</span>);</span><br><span class=line></span><br><span class=line> QuickSort::<span class=built_in>sort</span>(_collection_set_regions, _collection_set_cur_length, compare_region_idx, <span class=literal>true</span>);</span><br><span class=line>}</span><br></pre></table></figure><p>上面第三行是个判断,当前是否是 mixed 回收阶段,如果不是的话其实是没有老年代什么事的,所以可以看到代码基本是从这个 if 判断<br><code>if (collector_state()->in_mixed_phase()) {</code>开始往下走的<br>先写到这,偏向于做笔记用,有错轻拍</div><footer class=post-footer><div class="affiliate-creative affiliate-creative--post-end" data-affiliate-id=tencent-cloud-general><a rel="sponsored noopener" aria-label=腾讯云产品优惠 href=https://cloud.tencent.com/act/cps/redirect?redirect=2446&cps_key=2e33a1eedb380997d03618b4a5ba6ca7&from=console target=_blank><img alt=腾讯云服务器、数据库和云产品优惠 decoding=async height=419 loading=lazy src=/uploads/affiliate/tencent-cloud-general.webp width=690> </a><span class=affiliate-disclosure>推广</span></div><div class=reward-container><div>请我一杯咖啡吧!</div><button>赞赏</button><div class=post-reward><div><img alt="Nicksxs 微信" src=https://i.loli.net/2020/01/12/NUlWanT31E8LQGx.png><span>微信</span></div><div><img alt="Nicksxs 支付宝" src=https://ooo.0o0.ooo/2016/08/17/57b421e773057.jpg><span>支付宝</span></div></div></div><div class=post-copyright><ul><li class=post-copyright-author><strong>本文作者: </strong>Nicksxs<li class=post-copyright-link><strong>本文链接:</strong> <a href=https://nicksxs.me/2019/12/07/JVM-G1-Part-1/ title=JVM源码分析之G1垃圾收集器分析一>https://nicksxs.me/2019/12/07/JVM-G1-Part-1/</a><li class=post-copyright-license><strong>版权声明: </strong>本博客所有文章除特别声明外,均采用 <a href=https://creativecommons.org/licenses/by-nc-sa/4.0/ rel=noopener target=_blank><i class="fab fa-fw fa-creative-commons"></i>BY-NC-SA</a> 许可协议。转载请注明出处!</ul></div><div class=post-tags><a href=/tags/C/ rel=tag># C++</a><a href=/tags/Java/ rel=tag># Java</a><a href=/tags/JVM/ rel=tag># JVM</a></div><div class=post-nav><div class=post-nav-item><a href=/2019/09/23/AbstractQueuedSynchronizer/ rel=prev title=AbstractQueuedSynchronizer><i class="fa fa-angle-left"></i> AbstractQueuedSynchronizer</a></div><div class=post-nav-item><a href=/2019/12/10/Redis-Part-1/ rel=next title=Redis_分布式锁>Redis_分布式锁 <i class="fa fa-angle-right"></i></a></div></div></footer></article></div><div class=comments id=disqus_thread><noscript>Please enable JavaScript to view the comments powered by Disqus.</noscript></div></div></main><footer class=footer><div class=footer-inner><div class=beian><a href=https://beian.miit.gov.cn/ rel=noopener target=_blank>浙ICP备16002580号-2 </a><img alt src=/uploads/beian.png><a href=https://beian.mps.gov.cn/#/query/webSearch?code=33010602011094 rel=noopener target=_blank>浙公网安备 33010602011094号</a></div><div class=copyright>© <span itemprop=copyrightYear>2026</span><span class=with-love><i class="fa fa-heart"></i> </span><span class=author itemprop=copyrightHolder>Nicksxs</span></div></div></footer><div class="toggle sidebar-toggle" role=button><span class=toggle-line></span><span class=toggle-line></span><span class=toggle-line></span></div><div class=sidebar-dimmer></div><div aria-label=返回顶部 class=back-to-top role=button><i class="fa fa-arrow-up fa-lg"></i><span>0%</span></div><a aria-label="在 GitHub 上关注我" title="在 GitHub 上关注我" class=github-corner href=https://github.com/nicksxs rel=noopener target=_blank><svg viewbox="0 0 250 250" aria-hidden=true height=80 width=80><path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path><path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2" style="transform-origin:130px 106px" class=octo-arm fill=currentColor></path><path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z" class=octo-body fill=currentColor></path></svg></a><noscript><div class=noscript-warning>Theme NexT works best with JavaScript enabled</div></noscript><script data-cloudflare-page-counter-config type=application/json>{"enable":true,"endpoint":"https://counter.nicksxs.me","site":"nicksxs","local_cache":true,"timeout":5000,"icon":"far fa-eye","item_text":true}</script><script src=/js/cloudflare-page-counter.js></script><script class=next-config data-name=disqus type=application/json>{"enable":true,"shortname":"nicksxs","count":false,"i18n":{"disqus":"disqus"}}</script><script defer src=/js/third-party/comments/disqus.js></script>
|