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2 changes: 1 addition & 1 deletion 2023/04/11/JUC-CAS是什么？/index.html
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Expand Up @@ -64,7 +64,7 @@ <h2 id="CAS的优点与缺点"><a href="#CAS的优点与缺点" class="headerlin
<p>缺点：</p>
<ol>
<li>如果长时间循环对CPU的开销很大</li>
<li>只能保证一个共享变量的原子操作</li>
<li>CAS只能保证对一个变量的操作是原子性的，无法实现对多行代码实现原子性。</li>
<li>ABA问题</li>
<li>不能保证变量的内存可见性。CAS获取共享变量的值时，需要和volatile配合使用，来保证共享变量的可见性</li>
</ol>
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11 changes: 10 additions & 1 deletion 2023/04/21/JUC-JMM/index.html
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error: '复制错误',
noSupport: '浏览器不支持'
}
} </script></head><body><canvas class="fireworks"></canvas><i class="fa fa-arrow-right" id="toggle-sidebar" aria-hidden="true"></i><div id="sidebar"><div class="toggle-sidebar-info text-center"><span data-toggle="切换文章详情">切换站点概览</span><hr></div><div class="sidebar-toc"><div class="sidebar-toc__title">目录</div><div class="sidebar-toc__progress"><span class="progress-notice">你已经读了</span><span class="progress-num">0</span><span class="progress-percentage">%</span><div class="sidebar-toc__progress-bar"></div></div><div class="sidebar-toc__content"><ol class="toc"><li class="toc-item toc-level-3"><a class="toc-link" href="#JMM"><span class="toc-number">1.</span> <span class="toc-text">JMM</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#内存模型"><span class="toc-number">1.1.</span> <span class="toc-text">内存模型</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#内存交互"><span class="toc-number">1.2.</span> <span class="toc-text">内存交互</span></a></li></ol></li></ol></div></div><div class="author-info hide"><div class="author-info__avatar text-center"><img src="https://images5.alphacoders.com/423/423529.jpg"></div><div class="author-info__name text-center">GeYu</div><div class="author-info__description text-center">Do what you want to do !</div><div class="follow-button"><a href="https://github.com/NUISTGY">Follow Me</a></div><hr><div class="author-info-articles"><a class="author-info-articles__archives article-meta" href="/archives"><span class="pull-left">文章</span><span class="pull-right">223</span></a><a class="author-info-articles__tags article-meta" href="/tags"><span class="pull-left">标签</span><span class="pull-right">79</span></a><a class="author-info-articles__categories article-meta" href="/categories"><span class="pull-left">分类</span><span class="pull-right">43</span></a></div></div></div><div id="content-outer"><div id="top-container" style="background-image: url(https://i.328888.xyz/2022/12/21/ARudF.png)"><div id="page-header"><span class="pull-left"> <a id="site-name" href="/">Yu's Blog</a></span><i class="fa fa-bars toggle-menu pull-right" aria-hidden="true"></i><span class="pull-right menus"><a class="site-page" href="/">Home</a><a class="site-page" href="/archives">Archives</a><a class="site-page" href="/tags">Tags</a><a class="site-page" href="/categories">Categories</a><a class="site-page" href="/about">About</a></span></div><div id="post-info"><div id="post-title">JUC-JMM</div><div id="post-meta"><time class="post-meta__date"><i class="fa fa-calendar" aria-hidden="true"></i> 2023-04-21</time><span class="post-meta__separator">|</span><i class="fa fa-inbox post-meta__icon" aria-hidden="true"></i><a class="post-meta__categories" href="/categories/JUC/">JUC</a><div class="post-meta-wordcount"><span>字数总计: </span><span class="word-count">830</span><span class="post-meta__separator">|</span><span>阅读时长: 2 分钟</span></div></div></div></div><div class="layout" id="content-inner"><article id="post"><div class="article-container" id="post-content"><script src="/assets/js/APlayer.min.js"> </script><h3 id="JMM"><a href="#JMM" class="headerlink" title="JMM"></a>JMM</h3><h4 id="内存模型"><a href="#内存模型" class="headerlink" title="内存模型"></a>内存模型</h4><p>Java 内存模型是 Java Memory Model（JMM），本身是一种<strong>抽象的概念</strong>，实际上并不存在，描述的是一组规则或规范，通过这组规范定义了程序中各个变量（包括实例字段，静态字段和构成数组对象的元素）的访问方式</p>
} </script></head><body><canvas class="fireworks"></canvas><i class="fa fa-arrow-right" id="toggle-sidebar" aria-hidden="true"></i><div id="sidebar"><div class="toggle-sidebar-info text-center"><span data-toggle="切换文章详情">切换站点概览</span><hr></div><div class="sidebar-toc"><div class="sidebar-toc__title">目录</div><div class="sidebar-toc__progress"><span class="progress-notice">你已经读了</span><span class="progress-num">0</span><span class="progress-percentage">%</span><div class="sidebar-toc__progress-bar"></div></div><div class="sidebar-toc__content"><ol class="toc"><li class="toc-item toc-level-3"><a class="toc-link" href="#JMM"><span class="toc-number">1.</span> <span class="toc-text">JMM</span></a><ol class="toc-child"><li class="toc-item toc-level-4"><a class="toc-link" href="#内存模型"><span class="toc-number">1.1.</span> <span class="toc-text">内存模型</span></a></li><li class="toc-item toc-level-4"><a class="toc-link" href="#内存交互"><span class="toc-number">1.2.</span> <span class="toc-text">内存交互</span></a></li></ol></li></ol></div></div><div class="author-info hide"><div class="author-info__avatar text-center"><img src="https://images5.alphacoders.com/423/423529.jpg"></div><div class="author-info__name text-center">GeYu</div><div class="author-info__description text-center">Do what you want to do !</div><div class="follow-button"><a href="https://github.com/NUISTGY">Follow Me</a></div><hr><div class="author-info-articles"><a class="author-info-articles__archives article-meta" href="/archives"><span class="pull-left">文章</span><span class="pull-right">223</span></a><a class="author-info-articles__tags article-meta" href="/tags"><span class="pull-left">标签</span><span class="pull-right">79</span></a><a class="author-info-articles__categories article-meta" href="/categories"><span class="pull-left">分类</span><span class="pull-right">43</span></a></div></div></div><div id="content-outer"><div id="top-container" style="background-image: url(https://i.328888.xyz/2022/12/21/ARudF.png)"><div id="page-header"><span class="pull-left"> <a id="site-name" href="/">Yu's Blog</a></span><i class="fa fa-bars toggle-menu pull-right" aria-hidden="true"></i><span class="pull-right menus"><a class="site-page" href="/">Home</a><a class="site-page" href="/archives">Archives</a><a class="site-page" href="/tags">Tags</a><a class="site-page" href="/categories">Categories</a><a class="site-page" href="/about">About</a></span></div><div id="post-info"><div id="post-title">JUC-JMM</div><div id="post-meta"><time class="post-meta__date"><i class="fa fa-calendar" aria-hidden="true"></i> 2023-04-21</time><span class="post-meta__separator">|</span><i class="fa fa-inbox post-meta__icon" aria-hidden="true"></i><a class="post-meta__categories" href="/categories/JUC/">JUC</a><div class="post-meta-wordcount"><span>字数总计: </span><span class="word-count">1k</span><span class="post-meta__separator">|</span><span>阅读时长: 3 分钟</span></div></div></div></div><div class="layout" id="content-inner"><article id="post"><div class="article-container" id="post-content"><script src="/assets/js/APlayer.min.js"> </script><blockquote>
<p><a href="https://blog.csdn.net/qq_43842093/article/details/127200931" target="_blank" rel="noopener">https://blog.csdn.net/qq_43842093/article/details/127200931</a></p>
</blockquote>
<h3 id="JMM"><a href="#JMM" class="headerlink" title="JMM"></a>JMM</h3><h4 id="内存模型"><a href="#内存模型" class="headerlink" title="内存模型"></a>内存模型</h4><p>Java 内存模型是 Java Memory Model（JMM），本身是一种<strong>抽象的概念</strong>，实际上并不存在，描述的是一组规则或规范，通过这组规范定义了程序中各个变量（包括实例字段，静态字段和构成数组对象的元素）的访问方式</p>
<p>JMM 作用：</p>
<ul>
<li>屏蔽各种硬件和操作系统的内存访问差异，实现让 Java 程序在各种平台下都能达到一致的内存访问效果</li>
Expand All @@ -20,11 +23,17 @@
<li>主内存：计算机的内存，也就是经常提到的 8G 内存，16G 内存，存储所有共享变量的值</li>
<li>工作内存：存储该线程使用到的共享变量在主内存的的值的副本拷贝</li>
</ul>
<p>CPU处理速度非常快，相对CPU来说，去主内存获取数据这个事情太慢了，CPU就提供了L1，L2，L3的三级缓存，每次去主内存拿完数据后，就会存储到CPU的三级缓存，每次去三级缓存拿数据，效率肯定会提升。</p>
<p>这就带来了问题，现在CPU都是多核，每个线程的工作内存（CPU三级缓存）都是独立的，会告知每个线程中做修改时，只改自己的工作内存，没有及时的同步到主内存，导致数据不一致问题。</p>
<p><img src="https://fynotefile.oss-cn-zhangjiakou.aliyuncs.com/fynote/fyfile/2746/1654095150060/b3e82a21b18741a1ab3898e3c3ce95a7.png" alt></p>
<p><strong>JVM 和 JMM 之间的关系</strong>：JMM 中的主内存、工作内存与 JVM 中的 Java 堆、栈、方法区等并不是同一个层次的内存划分，这两者基本上是没有关系的，如果两者一定要勉强对应起来：</p>
<ul>
<li>主内存主要对应于 Java 堆中的对象实例数据部分，而工作内存则对应于虚拟机栈中的部分区域</li>
<li>从更低层次上说，主内存直接对应于物理硬件的内存，工作内存对应寄存器和高速缓存</li>
</ul>
<blockquote>
<p><a href="https://blog.csdn.net/fox_bert/article/details/88661569?utm_medium=distribute.pc_relevant.none-task-blog-2~default~baidujs_baidulandingword~default-4-88661569-blog-122598335.235^v38^pc_relevant_anti_t3_base&amp;spm=1001.2101.3001.4242.3&amp;utm_relevant_index=5" target="_blank" rel="noopener">https://blog.csdn.net/fox_bert/article/details/88661569?utm_medium=distribute.pc_relevant.none-task-blog-2~default~baidujs_baidulandingword~default-4-88661569-blog-122598335.235^v38^pc_relevant_anti_t3_base&amp;spm=1001.2101.3001.4242.3&amp;utm_relevant_index=5</a></p>
</blockquote>
<h4 id="内存交互"><a href="#内存交互" class="headerlink" title="内存交互"></a>内存交互</h4><p>Java 内存模型定义了 8 个操作来完成主内存和工作内存的交互操作，每个操作都是<strong>原子</strong>的</p>
<p>非原子协定：没有被 volatile 修饰的 long、double 外，默认按照两次 32 位的操作</p>
<img src="https://seazean.oss-cn-beijing.aliyuncs.com/img/Java/JMM-内存交互.png" style="zoom: 67%;">
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