{"id":3856,"date":"2025-07-12T13:15:16","date_gmt":"2025-07-12T05:15:16","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=3856"},"modified":"2025-07-12T13:15:16","modified_gmt":"2025-07-12T05:15:16","slug":"concurrenthashmap-%e5%ba%95%e5%b1%82%e5%85%b7%e4%bd%93%e5%ae%9e%e7%8e%b0%e7%9f%a5%e9%81%93%e5%90%97%ef%bc%9f%e5%ae%9e%e7%8e%b0%e5%8e%9f%e7%90%86%e6%98%af%e4%bb%80%e4%b9%88%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/07\/12\/concurrenthashmap-%e5%ba%95%e5%b1%82%e5%85%b7%e4%bd%93%e5%ae%9e%e7%8e%b0%e7%9f%a5%e9%81%93%e5%90%97%ef%bc%9f%e5%ae%9e%e7%8e%b0%e5%8e%9f%e7%90%86%e6%98%af%e4%bb%80%e4%b9%88%ef%bc%9f\/","title":{"rendered":"ConcurrentHashMap \u5e95\u5c42\u5177\u4f53\u5b9e\u73b0\u77e5\u9053\u5417\uff1f\u5b9e\u73b0\u539f\u7406\u662f\u4ec0\u4e48\uff1f"},"content":{"rendered":"\n<p><code>ConcurrentHashMap<\/code> \u662f Java \u4e2d\u7528\u4e8e<strong>\u9ad8\u5e76\u53d1\u73af\u5883\u4e0b\u7ebf\u7a0b\u5b89\u5168\u7684\u54c8\u5e0c\u8868<\/strong>\uff0c\u5b83\u7684\u5e95\u5c42\u5b9e\u73b0\u7ecf\u5386\u4e86\u51e0\u4e2a\u9636\u6bb5\u7684\u6f14\u8fdb\uff0c\u5c24\u5176\u4ece JDK 1.7 \u5230 JDK 1.8\uff0c\u6709\u4e86\u8f83\u5927\u7684\u7ed3\u6784\u6027\u53d8\u5316\u3002<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u4e00\u3001\u6838\u5fc3\u7ed3\u8bba\u5148\u884c<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u7279\u6027<\/th><th>Java 7 \u5b9e\u73b0<\/th><th>Java 8 \u5b9e\u73b0<\/th><\/tr><\/thead><tbody><tr><td>\u6570\u636e\u7ed3\u6784<\/td><td>\u5206\u6bb5\u9501\uff08Segment + HashEntry\uff09<\/td><td>\u6570\u7ec4 + \u94fe\u8868 + \u7ea2\u9ed1\u6811\uff08Node[] + TreeNode\uff09<\/td><\/tr><tr><td>\u5e76\u53d1\u63a7\u5236<\/td><td><code>Segment<\/code> \u7ea7\u522b\u7684\u9501<\/td><td>CAS + synchronized + \u81ea\u65cb<\/td><\/tr><tr><td>\u9501\u7c92\u5ea6<\/td><td>\u9ed8\u8ba4 16 \u4e2a Segment\uff0c\u9501\u7c92\u5ea6\u8f83\u7c97<\/td><td>\u8282\u70b9\u7ea7\u9501\uff0c\u7c92\u5ea6\u66f4\u7ec6<\/td><\/tr><tr><td>\u6027\u80fd<\/td><td>\u4e2d\u7b49\uff08\u9501\u51b2\u7a81\u8f83\u591a\uff09<\/td><td>\u66f4\u9ad8\uff08\u6781\u4f4e\u51b2\u7a81\u573a\u666f\u51e0\u4e4e\u65e0\u9501\uff09<\/td><\/tr><tr><td>\u662f\u5426\u652f\u6301 null key\/value<\/td><td>\u274c \u4e0d\u652f\u6301<\/td><td>\u274c \u4e0d\u652f\u6301<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u4e8c\u3001JDK 1.8 \u4e2d\u7684\u5e95\u5c42\u7ed3\u6784\uff08\u91cd\u70b9\uff09<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">\u4e3b\u7ed3\u6784\uff1a<code>Node&lt;K,V>[] table<\/code><\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>transient volatile Node&lt;K,V&gt;&#91;] table;<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u6574\u4f53\u7c7b\u4f3c\u4e8e <code>HashMap<\/code>\uff0c\u4f46\u6570\u7ec4\u5143\u7d20\u662f <code>Node<\/code> \u5bf9\u8c61\uff08\u975e Entry\uff09<\/li>\n\n\n\n<li>\u6bcf\u4e2a\u6876\uff08bucket\uff09\u53ef\u80fd\u662f\uff1a<\/li>\n\n\n\n<li>\u7a7a<\/li>\n\n\n\n<li>\u94fe\u8868\uff08Node -> Node -> \u2026\uff09<\/li>\n\n\n\n<li>\u7ea2\u9ed1\u6811\uff08TreeNode\uff09<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Node \u7ed3\u6784<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>static class Node&lt;K,V&gt; implements Map.Entry&lt;K,V&gt; {\n    final int hash;\n    final K key;\n    volatile V val;\n    volatile Node&lt;K,V&gt; next;\n}<\/code><\/pre>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p>\u6ce8\u610f\uff1a<code>val<\/code> \u548c <code>next<\/code> \u662f volatile \u7684\uff0c\u786e\u4fdd\u53ef\u89c1\u6027\uff1b\u4f46\u7ed3\u6784\u66f4\u65b0\u4f7f\u7528\u7684\u662f CAS\uff08compareAndSwap\uff09<\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u4e09\u3001\u5e76\u53d1\u63a7\u5236\u673a\u5236\u8be6\u89e3\uff08JDK 1.8\uff09<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">1\u3001\u8bfb\u64cd\u4f5c\uff08get\uff09<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u91c7\u7528\u65e0\u9501\u64cd\u4f5c\uff08\u53ea\u8bfb volatile \u5b57\u6bb5\uff09<\/li>\n\n\n\n<li>\u904d\u5386\u94fe\u8868\u6216\u7ea2\u9ed1\u6811\u67e5\u627e\u503c\uff0c<strong>\u5b8c\u5168\u4e0d\u52a0\u9501<\/strong> \u2192 \u9ad8\u6027\u80fd<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>public V get(Object key) {\n    Node&lt;K,V&gt;&#91;] tab; Node&lt;K,V&gt; e; int n; K k;\n    \/\/ ... \u8ba1\u7b97 hash\u3001\u5b9a\u4f4d\u6876\u4f4d ...\n    \/\/ \u904d\u5386\u94fe\u8868 \/ \u7ea2\u9ed1\u6811\u83b7\u53d6 key \u5bf9\u5e94\u7684\u503c\n}<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">2\u3001\u5199\u64cd\u4f5c\uff08put\uff09<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u5148\u901a\u8fc7 <code>CAS<\/code>\uff08compare-and-swap\uff09\u5c1d\u8bd5\u63d2\u5165\u7a7a\u6876 \u2192 \u65e0\u9700\u52a0\u9501<\/li>\n\n\n\n<li>\u5982\u679c CAS \u5931\u8d25\uff08\u51b2\u7a81\uff09\uff0c\u5219\u8fdb\u5165 <code>synchronized<\/code> \u5757\u9501\u4f4f\u8be5\u6876\u5934\u8282\u70b9<\/li>\n\n\n\n<li>\u63d2\u5165\u65f6\uff1a<\/li>\n\n\n\n<li>\u6876\u4e2d\u662f\u94fe\u8868\uff1a\u63d2\u5165\u5c3e\u90e8\uff0c\u5982\u679c\u94fe\u8868\u8fc7\u957f \u2192 \u8f6c\u4e3a\u7ea2\u9ed1\u6811<\/li>\n\n\n\n<li>\u6876\u4e2d\u662f\u7ea2\u9ed1\u6811\uff1a\u6267\u884c\u7ea2\u9ed1\u6811\u63d2\u5165\u7b97\u6cd5\uff08\u5982\u5e73\u8861\u3001\u65cb\u8f6c\uff09<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>synchronized (f) {\n    \/\/ \u6876\u5934 f \u975e null\uff0c\u8fdb\u884c\u94fe\u8868\/\u6811\u66f4\u65b0\n}<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">3\u3001\u6269\u5bb9\u64cd\u4f5c\uff08resize\uff09<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u4e0e <code>HashMap<\/code> \u7c7b\u4f3c\uff0c\u4f46\u4f7f\u7528<strong>\u591a\u7ebf\u7a0b\u534f\u4f5c\u6269\u5bb9<\/strong><\/li>\n\n\n\n<li>\u5229\u7528**<code>ForwardingNode<\/code> \u5360\u4f4d\u7b26**\u6807\u8bb0\u65e7\u6876\u5df2\u8f6c\u79fb<\/li>\n\n\n\n<li>\u4f7f\u7528\u4e00\u4e2a <code>transferIndex<\/code> \u8868\u793a\u4e0b\u4e00\u4e2a\u8fc1\u79fb\u7684\u6876\u6bb5\u4f4d\u7f6e\uff0c\u6bcf\u4e2a\u7ebf\u7a0b\u642c\u8fc1\u4e00\u90e8\u5206\u6876\u4f4d<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/ \u591a\u7ebf\u7a0b\u6269\u5bb9\u65f6\uff0c\u6bcf\u4e2a\u7ebf\u7a0b\u5904\u7406\u4e00\u90e8\u5206\u6876\nif ((f instanceof ForwardingNode)) {\n    \/\/ \u5e2e\u52a9\u6269\u5bb9\n}<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">4\u3001TreeNode \u7ed3\u6784\uff08\u7ea2\u9ed1\u6811\uff09<\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>static final class TreeNode&lt;K,V&gt; extends Node&lt;K,V&gt; {\n    TreeNode&lt;K,V&gt; parent;\n    TreeNode&lt;K,V&gt; left, right;\n    boolean red;\n    \/\/ \u7ea2\u9ed1\u6811\u63d2\u5165\u3001\u67e5\u627e\u3001\u65cb\u8f6c...\n}<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u5982\u679c\u67d0\u6876\u94fe\u8868\u957f\u5ea6 > 8 \u4e14\u6876\u6570\u7ec4\u5bb9\u91cf >= 64\uff0c\u5c31\u8f6c\u6362\u6210\u7ea2\u9ed1\u6811<\/li>\n\n\n\n<li>\u5426\u5219\u4ecd\u7528\u94fe\u8868\uff08\u8282\u7701\u7a7a\u95f4\uff09<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u56db\u3001\u5199\u65f6\u7684\u5e76\u53d1\u5b89\u5168\u5982\u4f55\u5b9e\u73b0\uff1f<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u64cd\u4f5c<\/th><th>\u5b9e\u73b0\u65b9\u5f0f<\/th><\/tr><\/thead><tbody><tr><td>put()<\/td><td>\u5148\u5c1d\u8bd5 CAS\uff0c\u5931\u8d25\u540e\u9501\u4f4f\u6876\u5934\uff08synchronized\uff09<\/td><\/tr><tr><td>remove()<\/td><td>\u7c7b\u4f3c put\uff0c\u5148\u5b9a\u4f4d\uff0c\u518d\u52a0\u9501\u5220\u9664<\/td><\/tr><tr><td>resize()<\/td><td>\u591a\u7ebf\u7a0b\u5e76\u53d1\u8fc1\u79fb\uff0c\u4f7f\u7528 <code>ForwardingNode<\/code> \u534f\u4f5c<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u5b83\u5e76\u4e0d\u4f7f\u7528\u5168\u8868\u9501\uff0c\u4e5f\u4e0d\u4f7f\u7528\u4f20\u7edf\u9501\u8868\u6bb5\uff08Segment\uff09\uff0c<strong>\u9501\u7c92\u5ea6\u975e\u5e38\u5c0f<\/strong><\/li>\n\n\n\n<li>\u501f\u52a9 volatile \u4fdd\u8bc1\u5185\u5b58\u53ef\u89c1\u6027\uff0cCAS \u4fdd\u8bc1\u539f\u5b50\u6027<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u4e94\u3001\u5bf9\u6bd4\uff1a<code>HashMap<\/code> vs <code>ConcurrentHashMap<\/code><\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u7279\u6027<\/th><th><code>HashMap<\/code><\/th><th><code>ConcurrentHashMap<\/code><\/th><\/tr><\/thead><tbody><tr><td>\u7ebf\u7a0b\u5b89\u5168\u6027<\/td><td>\u274c \u975e\u7ebf\u7a0b\u5b89\u5168<\/td><td>\u2705 \u7ebf\u7a0b\u5b89\u5168<\/td><\/tr><tr><td>\u5e76\u53d1\u8bfb\u5199<\/td><td>\u274c \u53ef\u80fd\u629b\u5f02\u5e38<\/td><td>\u2705 \u5b89\u5168<\/td><\/tr><tr><td>null \u952e\/\u503c\u652f\u6301<\/td><td>\u2705 \u652f\u6301<\/td><td>\u274c \u90fd\u4e0d\u652f\u6301<\/td><\/tr><tr><td>\u7528\u4e8e\u5e76\u53d1\u573a\u666f<\/td><td>\u274c \u4e0d\u5efa\u8bae<\/td><td>\u2705 \u63a8\u8350<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u516d\u3001\u6e90\u7801\u5165\u53e3 &amp; \u5b98\u65b9\u6587\u6863<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\ud83d\udd17 <a href=\"https:\/\/github.com\/openjdk\/jdk\/blob\/jdk8-b120\/jdk\/src\/share\/classes\/java\/util\/concurrent\/ConcurrentHashMap.java\">JDK 8 \u6e90\u7801\uff1aConcurrentHashMap<\/a><\/li>\n\n\n\n<li>\ud83d\udd17 <a href=\"https:\/\/docs.oracle.com\/javase\/8\/docs\/api\/java\/util\/concurrent\/ConcurrentHashMap.html\">Java \u5b98\u65b9\u6587\u6863\uff1aConcurrentHashMap<\/a><\/li>\n\n\n\n<li>\ud83d\udd17 <a href=\"http:\/\/gee.cs.oswego.edu\/dl\/papers\/HashTable.pdf\">Doug Lea \u539f\u59cb\u8bbe\u8ba1\u6587\u6863<\/a><\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u4e03\u3001\u9762\u8bd5\u5fc5\u4f1a\u91cd\u70b9\u603b\u7ed3<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u95ee\u9898<\/th><th>\u56de\u7b54\u6982\u8981<\/th><\/tr><\/thead><tbody><tr><td>\u662f\u5426\u652f\u6301\u5e76\u53d1\u8bfb\u5199\uff1f<\/td><td>\u2705 \u662f\uff0c\u5e76\u53d1\u8bfb\u65e0\u9501\uff0c\u5199\u9501\u7c92\u5ea6\u5c0f<\/td><\/tr><tr><td>\u662f\u5426\u652f\u6301 null\uff1f<\/td><td>\u274c \u4e0d\u652f\u6301 key \u6216 value \u4e3a null<\/td><\/tr><tr><td>\u4e3a\u4ec0\u4e48\u5199\u64cd\u4f5c\u52a0\u9501\uff1f<\/td><td>\u4fdd\u8bc1\u5e76\u53d1\u5b89\u5168\uff0c\u907f\u514d\u94fe\u8868\/\u6811\u7ed3\u6784\u7ade\u4e89<\/td><\/tr><tr><td>\u6269\u5bb9\u662f\u5426\u4f1a\u963b\u585e\uff1f<\/td><td>\u274c \u4e0d\u4f1a\uff0c\u91c7\u7528\u591a\u7ebf\u7a0b\u534f\u4f5c\u8fc1\u79fb<\/td><\/tr><tr><td>\u5e95\u5c42\u7ed3\u6784\u662f\u4ec0\u4e48\uff1f<\/td><td>Node \u6570\u7ec4 + \u94fe\u8868 + \u7ea2\u9ed1\u6811<\/td><\/tr><tr><td>\u5982\u4f55\u4fdd\u8bc1\u7ebf\u7a0b\u5b89\u5168\uff1f<\/td><td>CAS + volatile + synchronized<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"<p>ConcurrentHashMap \u662f Java \u4e2d\u7528\u4e8e\u9ad8\u5e76\u53d1\u73af\u5883\u4e0b\u7ebf\u7a0b\u5b89\u5168\u7684\u54c8\u5e0c\u8868\uff0c\u5b83\u7684\u5e95\u5c42\u5b9e\u73b0\u7ecf\u5386\u4e86\u51e0\u4e2a\u9636 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":3857,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[86],"tags":[],"class_list":["post-3856","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-java-"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3856","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=3856"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3856\/revisions"}],"predecessor-version":[{"id":3858,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3856\/revisions\/3858"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media\/3857"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=3856"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=3856"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=3856"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}