{"id":41,"date":"2023-02-21T08:34:50","date_gmt":"2023-02-21T08:34:50","guid":{"rendered":"https:\/\/blessingcr.com\/?p=41"},"modified":"2023-02-21T08:34:52","modified_gmt":"2023-02-21T08:34:52","slug":"cas","status":"publish","type":"post","link":"https:\/\/blessingcr.com\/?p=41","title":{"rendered":"CAS\u00a0"},"content":{"rendered":"\n

compare and set\/compare and swap<\/h1>\n\n\n\n

\u542b\u4e49<\/h1>\n\n\n\n

\u65e0\u9501\uff0c\u81ea\u65cb\u9501\uff0c\u4e50\u89c2\u9501\uff0c\u8f7b\u91cf\u7ea7\u9501<\/p>\n\n\n\n

\u4e0d\u4f1a\u963b\u585e, \u4e0d\u6d89\u53ca\u7ebf\u7a0b\u5207\u6362\uff0c\u4e0d\u8bbe\u8ba1\u64cd\u4f5c\u7cfb\u7edf\u8d44\u6e90\u5207\u6362\uff0c\u4e0a\u4e0b\u6587\u5185\u5bb9<\/p>\n\n\n\n

public class A {<\/p>\n\n\n\n

   AtomicInteger a;<\/p>\n\n\n\n

   public void increase() {<\/p>\n\n\n\n

\/\/        a.incrementAndGet();<\/p>\n\n\n\n

       while (true) {<\/p>\n\n\n\n

           int oldVal = a.get();<\/p>\n\n\n\n

           int newVal = oldVal + 1;<\/p>\n\n\n\n

           if (a.compareAndSet(oldVal, newVal)) {<\/p>\n\n\n\n

               break;<\/p>\n\n\n\n

           }<\/p>\n\n\n\n

       }<\/p>\n\n\n\n

   }<\/p>\n\n\n\n

}<\/p>\n\n\n\n

\u539f\u5b50\u6027\u95ee\u9898<\/h1>\n\n\n\n

compareAndSet \u4e2d\uff0c\u9700\u8981\u5148compare \u518d set\uff0c \u8be5\u64cd\u4f5c\u4e3a\u539f\u5b50\u64cd\u4f5c\uff0c compare&set\u5e95\u5c42\u6c47\u7f16\u4e00\u6b65\u5b8c\u6210\uff08\u5177\u4f53\u6c47\u7f16\u4ee3\u7801\u5404\u4e2a\u7cfb\u7edf\u4e0d\u4e00\u6837\uff09<\/p>\n\n\n\n

\u5e95\u5c42\u6c47\u7f16\u4e2d\uff0c\u67e5\u8be2\u662f\u5426\u662f\u591a\u6838\u64cd\u4f5c\u7cfb\u7edf\uff0c\u5982\u679c\u662f\u591a\u6838\uff0clock + comp&set \u5b8c\u6210\uff0c \u5b9e\u9645\u5728\u6c47\u7f16\u4e2d\u6709\u9501<\/p>\n\n\n\n

\u6c47\u7f16\u4e2dlock\u52a0\u7684\u9501\uff0c\u5982\u679c\u9700\u8981\u9501\u7684\u5185\u5b58\u5df2\u7ecf\u5728cache\u5185\uff0c\u4e14\u5728\u4e00\u4e2acache\u884c\u5185\uff0864\u5b57\u8282\uff09\uff0c\u4f1a\u52a0\u7f13\u5b58\u884c\u9501\uff0c\u5426\u5219\u52a0\u603b\u7ebf\u9501\uff08\u5185\u5b58\u7684\u603b\u7ebf\uff0c\u5185\u5b58\u53ea\u6709\u4e00\u4e2a\u603b\u7ebf\uff0c\u8bfb\u5199\u5185\u5b58\u90fd\u8981\u7528\u5230\u603b\u7ebf\uff09<\/p>\n\n\n\n

ABA \u95ee\u9898<\/h1>\n\n\n\n

\u7ecf\u5178\u8f6c\u8d26\u6848\u4f8b<\/p>\n\n\n\n

\u5047\u8bbe\u5c0f\u7433\u94f6\u884c\u5361\u6709 100 \u5757\u94b1\u4f59\u989d\uff0c\u4e14\u5047\u5b9a\u94f6\u884c\u8f6c\u8d26\u64cd\u4f5c\u5c31\u662f\u4e00\u4e2a\u5355\u7eaf\u7684 CAS \u547d\u4ee4\uff0c\u5bf9\u6bd4\u4f59\u989d\u65e7\u503c\u662f\u5426\u4e0e\u5f53\u524d\u503c\u76f8\u540c\uff0c\u5982\u679c\u76f8\u540c\u5219\u53d1\u751f\u6263\u51cf\/\u589e\u52a0\uff0c\u6211\u4eec\u5c06\u8fd9\u4e2a\u6307\u4ee4\u7528 CAS(origin,expect) \u8868\u793a\u3002\u4e8e\u662f\uff0c\u6211\u4eec\u770b\u770b\u63a5\u4e0b\u6765\u53d1\u751f\u4e86\u4ec0\u4e48\uff1a<\/p>\n\n\n\n

1 \u5c0f\u7433\u5728 ATM 1 \u8f6c\u8d26 100 \u5757\u94b1\u7ed9\u5c0f\u674e\uff1b<\/p>\n\n\n\n

2 \u7531\u4e8eATM 1 \u51fa\u73b0\u4e86\u7f51\u7edc\u62e5\u585e\u7684\u539f\u56e0\u5361\u4f4f\u4e86\uff0c\u8fd9\u65f6\u5019\u5c0f\u7433\u8dd1\u5230\u65c1\u8fb9\u7684 ATM 2 \u518d\u6b21\u64cd\u4f5c\u8f6c\u8d26\uff1b<\/p>\n\n\n\n

3 ATM 2 \u6ca1\u8ba9\u5c0f\u7433\u5931\u671b\uff0c\u6267\u884c\u4e86 CAS(100,0)\uff0c\u5f88\u75db\u5feb\u5730\u5b8c\u6210\u4e86\u8f6c\u8d26\uff0c\u6b64\u65f6\u5c0f\u7433\u7684\u8d26\u6237\u4f59\u989d\u4e3a 0\uff1b<\/p>\n\n\n\n

4 \u5c0f\u738b\u8fd9\u65f6\u5019\u53c8\u7ed9\u5c0f\u7433\u8d26\u4e0a\u8f6c\u4e86 100\uff0c\u6b64\u65f6\u5c0f\u7433\u8d26\u4e0a\u4f59\u989d\u4e3a 100\uff1b<\/p>\n\n\n\n

5 \u8fd9\u65f6\u5019 ATM 1 \u7f51\u7edc\u6062\u590d\uff0c\u7ee7\u7eed\u6267\u884c CAS(100,0)\uff0c\u5c45\u7136\u6267\u884c\u6210\u529f\u4e86\uff0c\u5c0f\u7433\u8d26\u6237\u4e0a\u4f59\u989d\u53c8\u53d8\u4e3a\u4e86 0\uff1b<\/p>\n\n\n\n

6 \u8fd9\u65f6\u5019\u5c0f\u738b\u5fae\u4fe1\u8ddf\u5c0f\u7433\u8bf4\u8f6c\u4e86 100 \u8fc7\u53bb\uff0c\u662f\u5426\u6536\u5230\u5462\uff1f\u5c0f\u7433\u53bb\u67e5\u4e86\u4e0b\u8d26\uff0c\u6447\u4e86\u6447\u5934\uff0c\u90a3\u4e48\u95ee\u9898\u6765\u4e86\uff0c\u94b1\u53bb\u4e86\u54ea\u5462\uff1f<\/p>\n\n\n\n

\u5173\u4e8e\u94b1\u7684\u53bb\u5411\uff0c\u6709\u4e00\u79cd\u53ef\u80fd\u5c31\u662f\u5c0f\u738b\u7ed9\u5c0f\u7433\u7684 100 \u5927\u6d0b\uff0c\u56e0\u4e3a ATM 1 \u7f51\u7edc\u6062\u590d\u518d\u6b21\u88ab\u8f6c\u7ed9\u4e86\u5c0f\u674e\uff0c\u6bd5\u7adf\u5c0f\u7433\u5c1d\u8bd5\u4e86\u4e24\u6b21\u8f6c\u8d26\uff0c\u51fa\u73b0\u8fd9\u79cd\u60c5\u51b5\u867d\u4e0d\u5408\u7406\uff0c\u4f46\u60c5\u6709\u53ef\u539f\u3002\u5047\u8bbe\u6211\u4eec\u4f5c\u4e3a\u94f6\u884c\u7cfb\u7edf\u8bbe\u8ba1\u8005\u548c\u5f00\u53d1\u8005\uff0c\u4e0d\u63a5\u53d7\u8fd9\u79cd\u60c5\u51b5\u5b58\u5728\uff0c\u90a3\u6211\u4eec\u5c31\u9700\u8981\u7740\u624b\u5904\u7406\u8fd9\u79cd ABA \u95ee\u9898\u4e86\u3002<\/p>\n\n\n\n

A\u7ebf\u7a0b\u9700\u8981 \u5c06V1->V2<\/p>\n\n\n\n

B\u7ebf\u7a0b\u9700\u8981 \u5c06V1->V2 -> V1<\/p>\n\n\n\n

ABA\u89e3\u51b3\u65b9\u6cd5\uff1a \u52a0\u7248\u672c\u53f7<\/h1>\n\n\n\n

A\u7ebf\u7a0b\u9700\u8981 \u5c06V1\uff08\u7248\u672c0\uff09<\/p>\n\n\n\n

B\u7ebf\u7a0b\u9700\u8981 \u5c06V1\uff08\u7248\u672c0\uff09->V2\uff08\u7248\u672c1\uff09 -> V1\uff08\u7248\u672c2\uff09<\/p>\n\n\n\n

\u6b64\u65f6A\u7ebf\u7a0b\u5c06V1\uff08\u7248\u672c2\uff09->V2\uff08\u7248\u672c2\uff09 \u62a5\u9519<\/p>\n\n\n\n

\u4ee3\u7801\u53ef\u4ee5\u4f7f\u7528AtomicStampedReference<\/p>\n\n\n\n

\u8f7b\u91cf\u7ea7\u9501\u4e00\u5b9a\u6bd4\u91cd\u91cf\u7ea7\u9501\u597d\u5417\uff1f<\/h1>\n\n\n\n

cas\u8f7b\u91cf\u7ea7\u9501\uff0c \u504f\u5411\u9501 \u4e0d\u4e00\u5b9a\u6bd4 synchronize\u597d<\/p>\n\n\n\n

\u5728\u5927\u91cf\u7ebf\u7a0b\u589e\u5f3a\u7684\u65f6\u5019CAS\u4f1a\u4e00\u76f4\u5faa\u73af\uff0c\u4e00\u76f4\u81ea\u65cb\uff0c\u4e0d\u5982\u91cd\u91cf\u7ea7\u9501<\/p>\n","protected":false},"excerpt":{"rendered":"

compare and set\/compare and swap \u542b\u4e49 \u65e0\u9501\uff0c\u81ea\u65cb\u9501\uff0c\u4e50\u89c2\u9501\uff0c\u8f7b\u91cf\u7ea7\u9501 \u4e0d\u4f1a\u963b […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[],"class_list":["post-41","post","type-post","status-publish","format-standard","hentry","category-6"],"_links":{"self":[{"href":"https:\/\/blessingcr.com\/index.php?rest_route=\/wp\/v2\/posts\/41","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blessingcr.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blessingcr.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blessingcr.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blessingcr.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=41"}],"version-history":[{"count":1,"href":"https:\/\/blessingcr.com\/index.php?rest_route=\/wp\/v2\/posts\/41\/revisions"}],"predecessor-version":[{"id":42,"href":"https:\/\/blessingcr.com\/index.php?rest_route=\/wp\/v2\/posts\/41\/revisions\/42"}],"wp:attachment":[{"href":"https:\/\/blessingcr.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=41"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blessingcr.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=41"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blessingcr.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=41"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}