https://Orangex-position0.github.io/tags/concurrency/Recent content in Concurrency on Orangex-position0的技术博客Hugo -- gohugo.iozh-cnMon, 16 Mar 2026 11:05:04 +0800https://Orangex-position0.github.io/posts/java/concurrent-hashmap/Mon, 16 Mar 2026 11:05:04 +0800https://Orangex-position0.github.io/posts/java/concurrent-hashmap/<h2 id="概述"><a href="#%e6%a6%82%e8%bf%b0" class="header-anchor"></a>概述 </h2><p><code>ConcurrentHashMap</code> 是 Java 并发包中最重要的并发容器之一，本文将深入分析其实现原理。</p> <h2 id="核心特点"><a href="#%e6%a0%b8%e5%bf%83%e7%89%b9%e7%82%b9" class="header-anchor"></a>核心特点 </h2><ol> <li><strong>线程安全</strong>：无需额外同步措施即可在多线程环境下使用</li> <li><strong>高性能</strong>：采用分段锁/ CAS 机制，减少锁竞争</li> <li><strong>弱一致性</strong>：迭代器不保证强一致性，但不会抛出 <code>ConcurrentModificationException</code></li> </ol> <h2 id="jdk-17-实现分段锁"><a href="#jdk-17-%e5%ae%9e%e7%8e%b0%e5%88%86%e6%ae%b5%e9%94%81" class="header-anchor"></a>JDK 1.7 实现：分段锁 </h2><h3 id="segment-结构"><a href="#segment-%e7%bb%93%e6%9e%84" class="header-anchor"></a>Segment 结构 </h3><div class="highlight"><pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">static</span><span class="w"> </span><span class="kd">final</span><span class="w"> </span><span class="kd">class</span> <span class="nc">Segment</span><span class="o">&lt;</span><span class="n">K</span><span class="p">,</span><span class="n">V</span><span class="o">&gt;</span><span class="w"> </span><span class="kd">extends</span><span class="w"> </span><span class="n">ReentrantLock</span><span class="w"> </span><span class="p">{</span><span class="w"> </span></span></span><span class="line"><span class="cl"><span class="w"> </span><span class="kd">transient</span><span class="w"> </span><span class="kd">volatile</span><span class="w"> </span><span class="n">HashEntry</span><span class="o">&lt;</span><span class="n">K</span><span class="p">,</span><span class="n">V</span><span class="o">&gt;[]</span><span class="w"> </span><span class="n">table</span><span class="p">;</span><span class="w"> </span></span></span><span class="line"><span class="cl"><span class="w"> </span><span class="c1">// ...</span><span class="w"> </span></span></span><span class="line"><span class="cl"><span class="p">}</span><span class="w"> </span></span></span></code></pre></div><h2 id="jdk-18-实现cas--synchronized"><a href="#jdk-18-%e5%ae%9e%e7%8e%b0cas--synchronized" class="header-anchor"></a>JDK 1.8 实现：CAS + synchronized </h2><h3 id="核心改进"><a href="#%e6%a0%b8%e5%bf%83%e6%94%b9%e8%bf%9b" class="header-anchor"></a>核心改进 </h3><ul> <li>取消 Segment 分段，直接使用 Node 数组</li> <li>使用 CAS + synchronized 实现更细粒度的锁</li> <li>红黑树优化链表过长问题</li> </ul> <h2 id="总结"><a href="#%e6%80%bb%e7%bb%93" class="header-anchor"></a>总结 </h2><p>ConcurrentHashMap 的演进体现了 Java 在并发领域的持续优化。</p>