{"id":3859,"date":"2025-07-12T13:21:28","date_gmt":"2025-07-12T05:21:28","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=3859"},"modified":"2025-07-12T13:21:28","modified_gmt":"2025-07-12T05:21:28","slug":"cas%ef%bc%88compare-and-swap%ef%bc%8c%e6%af%94%e8%be%83%e5%b9%b6%e4%ba%a4%e6%8d%a2%ef%bc%89","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/07\/12\/cas%ef%bc%88compare-and-swap%ef%bc%8c%e6%af%94%e8%be%83%e5%b9%b6%e4%ba%a4%e6%8d%a2%ef%bc%89\/","title":{"rendered":"CAS\uff08Compare-And-Swap\uff0c\u6bd4\u8f83\u5e76\u4ea4\u6362\uff09"},"content":{"rendered":"\n<p><strong>CAS\uff08Compare-And-Swap\uff0c\u6bd4\u8f83\u5e76\u4ea4\u6362\uff09<\/strong> \u662f Java \u5e76\u53d1\u7f16\u7a0b\u4e2d\u5b9e\u73b0\u65e0\u9501\uff08lock-free\uff09\u7ebf\u7a0b\u5b89\u5168\u7684\u91cd\u8981\u673a\u5236\uff0c\u662f <code>java.util.concurrent<\/code> \u5305\u5982 <code>AtomicInteger<\/code>\u3001<code>ConcurrentHashMap<\/code>\u3001<code>ThreadPoolExecutor<\/code> \u7b49\u5e95\u5c42\u5e76\u53d1\u7c7b\u7684\u6838\u5fc3\u57fa\u7840\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\u3001CAS \u662f\u4ec0\u4e48\uff1f<\/h2>\n\n\n\n<p><strong>CAS \u662f\u4e00\u79cd\u539f\u5b50\u64cd\u4f5c\u6307\u4ee4<\/strong>\uff0c\u5b83\u7684\u4f5c\u7528\u662f\uff1a<strong>\u5982\u679c\u5185\u5b58\u4e2d\u7684\u503c\u548c\u9884\u671f\u503c\u76f8\u540c\uff0c\u5219\u5c06\u5176\u66f4\u65b0\u4e3a\u65b0\u503c\uff1b\u5426\u5219\u4e0d\u505a\u4efb\u4f55\u64cd\u4f5c\u3002<\/strong><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">\u57fa\u672c\u64cd\u4f5c\u539f\u7406\uff1a<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>CAS(V, E, N)\n\nV\uff1a\u5185\u5b58\u4e2d\u7684\u53d8\u91cf\uff08volatile\uff09\nE\uff1a\u671f\u671b\u503c\uff08Expected\uff09\nN\uff1a\u65b0\u503c\uff08New\uff09\n\n\u542b\u4e49\uff1a\u5982\u679c V == E\uff0c\u5219 V \u2190 N\uff0c\u5426\u5219\u4ec0\u4e48\u90fd\u4e0d\u505a<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\"> \u4e8c\u3001CAS \u5728 Java \u4e2d\u7684\u5b9e\u73b0\uff08Unsafe\uff09<\/h2>\n\n\n\n<p>Java \u4e2d\u7684 CAS \u662f\u901a\u8fc7 <code>sun.misc.Unsafe<\/code> \u7c7b\u5c01\u88c5\u7684 <code>compareAndSwapInt()<\/code> \/ <code>compareAndSwapLong()<\/code> \u7b49\u65b9\u6cd5\u5b9e\u73b0\u7684\uff0c\u6700\u7ec8\u8c03\u7528\u7684\u662f CPU \u63d0\u4f9b\u7684<strong>\u539f\u5b50\u6307\u4ee4\uff08\u5982 x86 \u7684 CMPXCHG\uff09<\/strong>\u3002<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u4e09\u3001CAS \u793a\u4f8b\uff08\u4ee5 AtomicInteger \u4e3a\u4f8b\uff09<\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>AtomicInteger count = new AtomicInteger(0);\n\npublic void increment() {\n    while (true) {\n        int oldValue = count.get();\n        int newValue = oldValue + 1;\n        \/\/ \u5982\u679c\u65e7\u503c\u6ca1\u6709\u88ab\u5176\u4ed6\u7ebf\u7a0b\u66f4\u6539\uff0c\u5219\u66f4\u65b0\u6210\u529f\n        if (count.compareAndSet(oldValue, newValue)) {\n            break;\n        }\n        \/\/ \u5426\u5219\u81ea\u65cb\uff0c\u7ee7\u7eed\u91cd\u8bd5\n    }\n}<\/code><\/pre>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p>\u2705 <code>compareAndSet()<\/code> \u65b9\u6cd5\u5e95\u5c42\u5c31\u662f\u4e00\u4e2a CAS \u539f\u5b50\u64cd\u4f5c\u3002<\/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\">\u56db\u3001CAS \u7684\u4f18\u70b9<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u4f18\u70b9<\/th><th>\u8bf4\u660e<\/th><\/tr><\/thead><tbody><tr><td>\u2705 \u65e0\u9700\u52a0\u9501<\/td><td>\u63d0\u9ad8\u5e76\u53d1\u6027\u80fd\uff0c\u907f\u514d\u4e0a\u4e0b\u6587\u5207\u6362<\/td><\/tr><tr><td>\u2705 \u539f\u5b50\u6027\u5f3a<\/td><td>\u7531 CPU \u4fdd\u8bc1\u7684\u786c\u4ef6\u7ea7\u539f\u5b50\u64cd\u4f5c<\/td><\/tr><tr><td>\u2705 \u9ad8\u6548<\/td><td>\u5728\u7ade\u4e89\u4e0d\u4e25\u91cd\u7684\u573a\u666f\u4e0b\u6027\u80fd\u4f18\u4e8e\u9501<\/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\">\u4e94\u3001CAS \u7684\u4e09\u5927\u95ee\u9898\u53ca\u89e3\u51b3\u65b9\u6848<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">1\u3001ABA \u95ee\u9898<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u95ee\u9898\uff1a<\/strong> CAS \u5224\u65ad\u7684\u662f\u503c\u662f\u5426\u76f8\u7b49\uff0c\u5982\u679c\u503c\u4ece A \u2192 B \u2192 A\uff0c\u4f1a\u8bef\u5224\u4e3a\u6ca1\u53d8\u3002<\/li>\n\n\n\n<li><strong>\u89e3\u51b3\uff1a<\/strong> \u5f15\u5165\u7248\u672c\u53f7\u673a\u5236\uff0c\u5982 <code>AtomicStampedReference<\/code>\u3002<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>AtomicStampedReference&lt;String&gt; ref = new AtomicStampedReference&lt;&gt;(\"A\", 1);<\/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\u81ea\u65cb\u5f00\u9500\u5927<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u95ee\u9898\uff1a<\/strong> \u5982\u679c CAS \u4e00\u76f4\u5931\u8d25\uff0c\u4f1a\u4e0d\u65ad\u91cd\u8bd5\uff08\u81ea\u65cb\uff09\uff0c\u6d6a\u8d39 CPU\u3002<\/li>\n\n\n\n<li><strong>\u89e3\u51b3\uff1a<\/strong><\/li>\n\n\n\n<li>\u63a7\u5236\u91cd\u8bd5\u6b21\u6570<\/li>\n\n\n\n<li>\u4f7f\u7528 <code>LongAdder<\/code> \u7b49\u5206\u6bb5\u65b9\u5f0f\u964d\u4f4e\u51b2\u7a81<\/li>\n\n\n\n<li>\u5728\u7ade\u4e89\u4e25\u91cd\u573a\u666f\u7528\u9501\u66ff\u4ee3<\/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\">3\u3001\u53ea\u80fd\u4fdd\u8bc1\u5355\u53d8\u91cf\u539f\u5b50\u6027<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u95ee\u9898\uff1a<\/strong> CAS \u53ea\u80fd\u4fdd\u8bc1\u4e00\u4e2a\u53d8\u91cf\u7684\u539f\u5b50\u64cd\u4f5c<\/li>\n\n\n\n<li><strong>\u89e3\u51b3\uff1a<\/strong><\/li>\n\n\n\n<li>\u4f7f\u7528\u9501\u4fdd\u8bc1\u591a\u4e2a\u53d8\u91cf\u7684\u4e00\u81f4\u6027<\/li>\n\n\n\n<li>\u6216\u4f7f\u7528\u539f\u5b50\u5f15\u7528\uff08<code>AtomicReference<\/code>\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\">\u516d\u3001CAS vs \u9501\uff08synchronized \/ ReentrantLock\uff09<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u5bf9\u6bd4\u70b9<\/th><th>CAS<\/th><th>\u9501\uff08synchronized\uff09<\/th><\/tr><\/thead><tbody><tr><td>\u539f\u5b50\u6027\u4fdd\u969c<\/td><td>CPU \u6307\u4ee4\u5c42\u9762<\/td><td>JVM \u4fdd\u8bc1<\/td><\/tr><tr><td>\u662f\u5426\u963b\u585e<\/td><td>\u274c \u975e\u963b\u585e\uff0c\u81ea\u65cb<\/td><td>\u2705 \u963b\u585e<\/td><\/tr><tr><td>\u6027\u80fd\uff08\u4f4e\u7ade\u4e89\uff09<\/td><td>\u2705 \u9ad8\u6027\u80fd<\/td><td>\u8f83\u6162\uff08\u6709\u4e0a\u4e0b\u6587\u5207\u6362\uff09<\/td><\/tr><tr><td>\u6027\u80fd\uff08\u9ad8\u7ade\u4e89\uff09<\/td><td>\u274c \u81ea\u65cb\u6d6a\u8d39\u8d44\u6e90<\/td><td>\u2705 \u7ebf\u7a0b\u6302\u8d77\u7b49\u5f85\uff0c\u7cfb\u7edf\u8d44\u6e90\u5c11\u5360\u7528<\/td><\/tr><tr><td>\u591a\u53d8\u91cf\u539f\u5b50\u6027<\/td><td>\u274c \u4e0d\u652f\u6301<\/td><td>\u2705 \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\">\u4e03\u3001CAS \u4f7f\u7528\u7684\u7c7b\uff08JDK \u5e76\u53d1\u5305\uff09<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>\u7c7b\u540d<\/th><th>\u4f7f\u7528 CAS \u7684\u5b57\u6bb5<\/th><\/tr><\/thead><tbody><tr><td><code>AtomicInteger<\/code><\/td><td><code>value<\/code><\/td><\/tr><tr><td><code>AtomicReference<\/code><\/td><td>\u5f15\u7528\u5bf9\u8c61<\/td><\/tr><tr><td><code>ConcurrentHashMap<\/code><\/td><td><code>Node.val<\/code>\u3001\u8868\u521d\u59cb\u5316<\/td><\/tr><tr><td><code>ThreadPoolExecutor<\/code><\/td><td><code>ctl<\/code><\/td><\/tr><tr><td><code>LongAdder<\/code><\/td><td>\u5206\u6bb5\u7d2f\u52a0\u5668\u63a7\u5236\u903b\u8f91<\/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\">\u516b\u3001CPU \u5c42\u7ea7\u5b9e\u73b0<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>CAS \u7684 CPU \u6307\u4ee4\uff1a<code>CMPXCHG<\/code>\uff08x86 \u67b6\u6784\uff09<\/li>\n\n\n\n<li>\u539f\u5b50\u6027\u4fdd\u969c\uff1a\u901a\u8fc7\u603b\u7ebf\u9501\u6216\u7f13\u5b58\u4e00\u81f4\u6027\u534f\u8bae\uff08MESI\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\">\u4e5d\u3001\u53c2\u8003\u94fe\u63a5<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\ud83d\udd17 <a href=\"https:\/\/docs.oracle.com\/javase\/8\/docs\/api\/java\/util\/concurrent\/atomic\/AtomicInteger.html\">Java \u5b98\u65b9\u6587\u6863\uff1a<code>AtomicInteger<\/code><\/a><\/li>\n\n\n\n<li>\ud83d\udd17 <a href=\"https:\/\/developer.aliyun.com\/article\/753243\">\u963f\u91cc\u5df4\u5df4\u5e76\u53d1\u7f16\u7a0b\u89c4\u8303\uff08CAS \u90e8\u5206\uff09<\/a><\/li>\n\n\n\n<li>\ud83d\udd17 <a href=\"https:\/\/www.cnblogs.com\/crazymakercircle\/p\/11471107.html\">\u6df1\u5165\u7406\u89e3 CAS \u4e0e Java \u539f\u5b50\u7c7b\u5b9e\u73b0\u539f\u7406<\/a><\/li>\n\n\n\n<li>\ud83d\udd17 <a href=\"https:\/\/github.com\/openjdk\/jdk\/blob\/master\/src\/java.base\/share\/classes\/jdk\/internal\/misc\/Unsafe.java\">Unsafe \u6e90\u7801<\/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\">\u5341\u3001\u603b\u7ed3\u8bb0\u5fc6\uff08\u53e3\u8bc0\uff09<\/h2>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p><strong>CAS \u4e09\u5143\u7ec4\uff0c\u6bd4\u8f83\u6362\u66f4\u65b0\uff1b\u8f7b\u91cf\u4e0d\u52a0\u9501\uff0c\u4e09\u5927\u95ee\u9898\u8b66\u60d5\uff1b\u7ed3\u5408\u539f\u5b50\u7c7b\uff0c\u9ad8\u6548\u4fdd\u7ebf\u7a0b\u3002<\/strong><\/p>\n<\/blockquote>\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>CAS\uff08Compare-And-Swap\uff0c\u6bd4\u8f83\u5e76\u4ea4\u6362\uff09 \u662f Java \u5e76\u53d1\u7f16\u7a0b\u4e2d\u5b9e\u73b0\u65e0\u9501\uff08lock-free\uff09 [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":3860,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[86],"tags":[],"class_list":["post-3859","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\/3859","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=3859"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3859\/revisions"}],"predecessor-version":[{"id":3861,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/3859\/revisions\/3861"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media\/3860"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=3859"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=3859"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=3859"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}