记录技术和生活 Zola 2021-06-27T10:00:00+08:00 https://blog.laofu.online/tags/jvm/atom.xml 2021-06-27T10:00:00+08:00 2021-06-27T10:00:00+08:00 bigfish https://blog.laofu.online/blog/cms-three-color-mark/

<h3 id="wei-shen-me-yin-ru-san-se-biao-ji-fa"><a class="zola-anchor" href="#wei-shen-me-yin-ru-san-se-biao-ji-fa" aria-label="Anchor link for: wei-shen-me-yin-ru-san-se-biao-ji-fa">为什么引入三色标记法</a></h3> <p>为了提供 JVM 垃圾回收的性能，从 CMS 垃圾收集器开始，引入了并发标记的概念（此处的并发标记是指与用户线程一起工作）。引入并发标记的过程就会带来一个问题，在业务执行的过程中，会对现有的引用关系链出现改变。具体如下图：</p> <p><img src="/img/three-color-mark/20210626215542908.png" alt="image-20210626215542908" loading="lazy" decoding="async" /></p>

2020-09-12T10:00:00+08:00 2020-09-12T10:00:00+08:00 bigfish https://blog.laofu.online/blog/g1-oom/

<p>最近又碰到的 oom 的问题，一直在尝试定位中，由于现实使用的 G1 的垃圾回收器。所以今天打算线上的排查历程和方案查询出来。</p> <h4 id="jvm-chang-yong-can-shu"><a class="zola-anchor" href="#jvm-chang-yong-can-shu" aria-label="Anchor link for: jvm-chang-yong-can-shu">jvm 常用参数</a></h4> <pre class="giallo z-l-code z-d-code" ><code data-lang="plain"><span class="giallo-l"><span>-Xmx1024m 最大堆内存</span></span> <span class="giallo-l"><span>-Xms1024m 最小堆内存</span></span> <span class="giallo-l"><span>-Xss256k 设置栈的大小。栈都是每个线程独有一个，所有一般都是几百k的大小。</span></span> <span class="giallo-l"><span>-XX:MetaspaceSize=128m 元空间的大小</span></span> <span class="giallo-l"><span>-XX:MaxMetaspaceSize=256m 最大元空间大小</span></span> <span class="giallo-l"><span>-XX:MaxGCPauseMillis=200 设置每次年轻代垃圾回收的最长时间，如果无法满足此时间，JVM会自动调整年轻代大小，以满足此值</span></span> <span class="giallo-l"><span>-XX:+UseG1GC 使用 G1 垃圾回收器</span></span> <span class="giallo-l"><span>-XX:-OmitStackTraceInFastThrow 当一些异常在代码里某个特定位置被抛出很多次的话，HotSpot Server Compiler（C2）会用fast throw来优化这个抛出异常的地方。</span></span> <span class="giallo-l"><span>-XX:MinHeapFreeRatio=30</span></span> <span class="giallo-l"><span>-XX:MaxHeapFreeRatio=50</span></span> <span class="giallo-l"><span>-XX:MaxDirectMemorySize=100M 直接内存大小</span></span> <span class="giallo-l"><span>-XX:+PrintGCDetails 打印 GC 详细信息</span></span> <span class="giallo-l"><span>-XX:+DisableExplicitGC 禁止显示GC</span></span> <span class="giallo-l"></span></code></pre>

2020-06-10T10:00:00+08:00 2020-06-10T10:00:00+08:00 bigfish https://blog.laofu.online/blog/jvm-run/

<h4 id="mo-ni-jvmzhi-ling-de-yun-xing"><a class="zola-anchor" href="#mo-ni-jvmzhi-ling-de-yun-xing" aria-label="Anchor link for: mo-ni-jvmzhi-ling-de-yun-xing">模拟JVM指令的运行</a></h4> <p>模拟JVM的运行，需要有两个个方面的知识准备</p> <ol> <li>JVM的结构</li> <li>字节码的含义</li> </ol>

2020-06-05T10:00:00+08:00 2020-06-05T10:00:00+08:00 bigfish https://blog.laofu.online/blog/jvm-class-file/

<h2 id="javade-yun-xing-guo-cheng"><a class="zola-anchor" href="#javade-yun-xing-guo-cheng" aria-label="Anchor link for: javade-yun-xing-guo-cheng">java的运行过程</a></h2> <p>在运行一段 java 代码的时候需要经过<code>编译</code>,<code>验证</code>,<code>加载</code>和<code>运行</code>,具体如下图：</p> <p><img src="/img/jvm/01.png" alt="运行过程" loading="lazy" decoding="async" /></p> <p>对于 Java 源码变成字节码的编译过程，我们暂且跳过不讨论。</p> <p>想弄清楚 java 代码的运行原理，其实本质就是 java 字节码如何被 jvm 执行。</p>