{"id":4779,"date":"2020-02-13T20:29:46","date_gmt":"2020-02-13T12:29:46","guid":{"rendered":"https:\/\/www.xttblog.com\/?p=4779"},"modified":"2020-02-13T20:29:46","modified_gmt":"2020-02-13T12:29:46","slug":"%e8%81%8a%e8%81%8a-java-%e7%9a%84%e5%87%a0%e6%8a%8a-jvm-%e7%ba%a7%e9%94%81","status":"publish","type":"post","link":"https:\/\/www.xttblog.com\/?p=4779","title":{"rendered":"\u804a\u804a Java \u7684\u51e0\u628a JVM \u7ea7\u9501"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">\u7b80\u4ecb<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u8ba1\u7b97\u673a\u884c\u4e1a\u6709\u4e00\u4e2a\u5b9a\u5f8b\u53eb&#8221;\u6469\u5c14\u5b9a\u5f8b&#8221;\uff0c\u5728\u6b64\u5b9a\u5f8b\u4e0b\uff0c\u8ba1\u7b97\u673a\u7684\u6027\u80fd\u7a81\u98de\u731b\u8fdb\uff0c\u800c\u4e14\u4ef7\u683c\u4e5f\u968f\u4e4b\u8d8a\u6765\u8d8a\u4fbf\u5b9c\uff0c CPU \u4ece\u5355\u6838\u5230\u4e86\u591a\u6838\uff0c\u7f13\u5b58\u6027\u80fd\u4e5f\u5f97\u5230\u4e86\u5f88\u5927\u63d0\u5347\uff0c\u5c24\u5176\u662f\u591a\u6838 CPU \u6280\u672f\u7684\u5230\u6765\uff0c\u8ba1\u7b97\u673a\u540c\u4e00\u65f6\u523b\u53ef\u4ee5\u5904\u7406\u591a\u4e2a\u4efb\u52a1\u3002\u5728\u786c\u4ef6\u5c42\u9762\u7684\u53d1\u5c55\u5e26\u6765\u7684\u6548\u7387\u6781\u5927\u63d0\u5347\u4e2d\uff0c\u8f6f\u4ef6\u5c42\u9762\u7684\u591a\u7ebf\u7a0b\u7f16\u7a0b\u5df2\u7ecf\u6210\u4e3a\u5fc5\u7136\u8d8b\u52bf\uff0c\u7136\u800c\u591a\u7ebf\u7a0b\u7f16\u7a0b\u5c31\u4f1a\u5f15\u5165\u6570\u636e\u5b89\u5168\u6027\u95ee\u9898\uff0c\u6709\u77db\u5fc5\u6709\u76fe\uff0c\u4e8e\u662f\u53d1\u660e\u4e86\u201c\u9501\u201d\u6765\u89e3\u51b3\u7ebf\u7a0b\u5b89\u5168\u95ee\u9898\u3002\u5728\u8fd9\u7bc7\u6587\u7ae0\u4e2d\uff0c\u603b\u7ed3\u4e86 Java \u4e2d\u51e0\u628a\u7ecf\u5178\u7684 JVM \u7ea7\u522b\u7684\u9501\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">synchronized<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">synchronized \u5173\u952e\u5b57\u662f\u4e00\u628a\u7ecf\u5178\u7684\u9501\uff0c\u4e5f\u662f\u6211\u4eec\u5e73\u65f6\u7528\u5f97\u6700\u591a\u7684\u3002\u5728 JDK1.6 \u4e4b\u524d\uff0c syncronized \u662f\u4e00\u628a\u91cd\u91cf\u7ea7\u7684\u9501\uff0c\u4e0d\u8fc7\u968f\u7740 JDK \u7684\u5347\u7ea7\uff0c\u4e5f\u5728\u5bf9\u5b83\u8fdb\u884c\u4e0d\u65ad\u7684\u4f18\u5316\uff0c\u5982\u4eca\u5b83\u53d8\u5f97\u4e0d\u90a3\u4e48\u91cd\u4e86\uff0c\u751a\u81f3\u5728\u67d0\u4e9b\u573a\u666f\u4e0b\uff0c\u5b83\u7684\u6027\u80fd\u53cd\u800c\u4f18\u4e8e\u8f7b\u91cf\u7ea7\u9501\u3002\u5728\u52a0\u4e86 syncronized \u5173\u952e\u5b57\u7684\u65b9\u6cd5\u3001\u4ee3\u7801\u5757\u4e2d\uff0c\u4e00\u6b21\u53ea\u5141\u8bb8\u4e00\u4e2a\u7ebf\u7a0b\u8fdb\u5165\u7279\u5b9a\u4ee3\u7801\u6bb5\uff0c\u4ece\u800c\u907f\u514d\u591a\u7ebf\u7a0b\u540c\u65f6\u4fee\u6539\u540c\u4e00\u6570\u636e\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">synchronized \u9501\u6709\u5982\u4e0b\u51e0\u4e2a\u7279\u70b9\uff1a<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u6709\u9501\u5347\u7ea7\u8fc7\u7a0b<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728 JDK1.5 (\u542b)\u4e4b\u524d\uff0c synchronized \u7684\u5e95\u5c42\u5b9e\u73b0\u662f\u91cd\u91cf\u7ea7\u7684\uff0c\u6240\u4ee5\u4e4b\u524d\u4e00\u81f4\u79f0\u547c\u5b83\u4e3a&#8221;\u91cd\u91cf\u7ea7\u9501&#8221;\uff0c\u5728 JDK1.5 \u4e4b\u540e\uff0c\u5bf9 synchronized \u8fdb\u884c\u4e86\u5404\u79cd\u4f18\u5316\uff0c\u5b83\u53d8\u5f97\u4e0d\u90a3\u4e48\u91cd\u4e86\uff0c\u5b9e\u73b0\u539f\u7406\u5c31\u662f\u9501\u5347\u7ea7\u7684\u8fc7\u7a0b\u3002\u6211\u4eec\u5148\u804a\u804a 1.5 \u4e4b\u540e\u7684 synchronized \u5b9e\u73b0\u539f\u7406\u662f\u600e\u6837\u7684\u3002\u8bf4\u5230 synchronized \u52a0\u9501\u539f\u7406\uff0c\u5c31\u4e0d\u5f97\u4e0d\u5148\u8bf4 Java \u5bf9\u8c61\u5728\u5185\u5b58\u4e2d\u7684\u5e03\u5c40\uff0c Java \u5bf9\u8c61\u5185\u5b58\u5e03\u5c40\u5982\u4e0b\uff1a<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img decoding=\"async\" src=\"https:\/\/gitee.com\/xmtblog\/img\/raw\/master\/1581595820221.jpg\" alt=\"\" \/><figcaption>Java \u5bf9\u8c61\u5728\u5185\u5b58\u4e2d\u7684\u5e03\u5c40<\/figcaption><\/figure><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u4e0a\u56fe\u6240\u793a\uff0c\u5728\u521b\u5efa\u4e00\u4e2a\u5bf9\u8c61\u540e\uff0c\u5728 JVM \u865a\u62df\u673a( HotSpot )\u4e2d\uff0c\u5bf9\u8c61\u5728 Java \u5185\u5b58\u4e2d\u7684\u5b58\u50a8\u5e03\u5c40 \u53ef\u5206\u4e3a\u4e09\u5757:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u5bf9\u8c61\u5934\u533a\u57df\u6b64\u5904\u5b58\u50a8\u7684\u4fe1\u606f\u5305\u62ec\u4e24\u90e8\u5206\uff1a<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>\u5bf9\u8c61\u81ea\u8eab\u7684\u8fd0\u884c\u65f6\u6570\u636e( MarkWord )\uff1a\u5b58\u50a8 hashCode\u3001GC \u5206\u4ee3\u5e74\u9f84\u3001\u9501\u7c7b\u578b\u6807\u8bb0\u3001\u504f\u5411\u9501\u7ebf\u7a0b ID \u3001 CAS \u9501\u6307\u5411\u7ebf\u7a0b LockRecord \u7684\u6307\u9488\u7b49\uff0c synconized \u9501\u7684\u673a\u5236\u4e0e\u8fd9\u4e2a\u90e8\u5206( markwork )\u5bc6\u5207\u76f8\u5173\uff0c\u7528 markword \u4e2d\u6700\u4f4e\u7684\u4e09\u4f4d\u4ee3\u8868\u9501\u7684\u72b6\u6001\uff0c\u5176\u4e2d\u4e00\u4f4d\u662f\u504f\u5411\u9501\u4f4d\uff0c\u53e6\u5916\u4e24\u4f4d\u662f\u666e\u901a\u9501\u4f4d\u3002<\/li><li>\u5bf9\u8c61\u7c7b\u578b\u6307\u9488( Class Pointer )\uff1a\u5bf9\u8c61\u6307\u5411\u5b83\u7684\u7c7b\u5143\u6570\u636e\u7684\u6307\u9488\u3001 JVM \u5c31\u662f\u901a\u8fc7\u5b83\u6765\u786e\u5b9a\u662f\u54ea\u4e2a Class \u7684\u5b9e\u4f8b\u3002<\/li><\/ol>\n\n\n\n<h2 class=\"wp-block-heading\">\u5b9e\u4f8b\u6570\u636e\u533a\u57df <\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u6b64\u5904\u5b58\u50a8\u7684\u662f\u5bf9\u8c61\u771f\u6b63\u6709\u6548\u7684\u4fe1\u606f\uff0c\u6bd4\u5982\u5bf9\u8c61\u4e2d\u6240\u6709\u5b57\u6bb5\u7684\u5185\u5bb9<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u5bf9\u9f50\u586b\u5145\u533a\u57df<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">JVM \u7684\u5b9e\u73b0 HostSpot \u89c4\u5b9a\u5bf9\u8c61\u7684\u8d77\u59cb\u5730\u5740\u5fc5\u987b\u662f 8 \u5b57\u8282\u7684\u6574\u6570\u500d\uff0c\u6362\u53e5\u8bdd\u6765\u8bf4\uff0c\u73b0\u5728 64 \u4f4d\u7684 OS \u5f80\u5916\u8bfb\u53d6\u6570\u636e\u7684\u65f6\u5019\u4e00\u6b21\u6027\u8bfb\u53d6 64bit \u6574\u6570\u500d\u7684\u6570\u636e\uff0c\u4e5f\u5c31\u662f 8 \u4e2a\u5b57\u8282\uff0c\u6240\u4ee5 HotSpot \u4e3a\u4e86\u9ad8\u6548\u8bfb\u53d6\u5bf9\u8c61\uff0c\u5c31\u505a\u4e86&#8221;\u5bf9\u9f50&#8221;\uff0c\u5982\u679c\u4e00\u4e2a\u5bf9\u8c61\u5b9e\u9645\u5360\u7684\u5185\u5b58\u5927\u5c0f\u4e0d\u662f 8byte \u7684\u6574\u6570\u500d\u65f6\uff0c\u5c31&#8221;\u8865\u4f4d&#8221;\u5230 8byte \u7684\u6574\u6570\u500d\u3002\u6240\u4ee5\u5bf9\u9f50\u586b\u5145\u533a\u57df\u7684\u5927\u5c0f\u4e0d\u662f\u56fa\u5b9a\u7684\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u5f53\u7ebf\u7a0b\u8fdb\u5165\u5230 synchronized \u5904\u5c1d\u8bd5\u83b7\u53d6\u8be5\u9501\u65f6\uff0c synchronized \u9501\u5347\u7ea7\u6d41\u7a0b\u5982\u4e0b\uff1a<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img decoding=\"async\" src=\"https:\/\/gitee.com\/xmtblog\/img\/raw\/master\/1581595833137.jpg\" alt=\"\" \/><figcaption>synchronized \u9501\u5347\u7ea7\u6d41\u7a0b<\/figcaption><\/figure><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u4e0a\u56fe\u6240\u793a\uff0c synchronized \u9501\u5347\u7ea7\u7684\u987a\u5e8f\u4e3a\uff1a\u504f\u5411\u9501-&gt;\u8f7b\u91cf\u7ea7\u9501-&gt;\u91cd\u91cf\u7ea7\u9501\uff0c\u6bcf\u4e00\u6b65\u89e6\u53d1\u9501\u5347\u7ea7\u7684\u60c5\u51b5\u4e0b\u9762\u5206\u522b\u8bf4\u660e\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u504f\u5411\u9501<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728 JDK1.8 \u4e2d\uff0c\u5176\u5b9e\u9ed8\u8ba4\u662f\u8f7b\u91cf\u7ea7\u9501\uff0c\u4f46\u5982\u679c\u8bbe\u5b9a\u4e86 -XX:BiasedLockingStartupDelay = 0 \uff0c\u90a3\u5728\u5bf9\u4e00\u4e2a Object \u505a syncronized \u7684\u65f6\u5019\uff0c\u4f1a\u7acb\u5373\u4e0a\u4e00\u628a\u504f\u5411\u9501\u3002\u5f53\u5904\u4e8e\u504f\u5411\u9501\u72b6\u6001\u65f6\uff0c markwork \u4f1a\u8bb0\u5f55\u5f53\u524d\u7ebf\u7a0b ID \u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u5347\u7ea7\u5230\u8f7b\u91cf\u7ea7\u9501<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u5f53\u4e0b\u4e00\u4e2a\u7ebf\u7a0b\u53c2\u4e0e\u5230\u504f\u5411\u9501\u7ade\u4e89\u65f6\uff0c\u4f1a\u5148\u5224\u65ad markword \u4e2d\u4fdd\u5b58\u7684\u7ebf\u7a0b ID \u662f\u5426\u4e0e\u8fd9\u4e2a\u7ebf\u7a0b ID \u76f8\u7b49\uff0c\u5982\u679c\u4e0d\u76f8\u7b49\uff0c\u4f1a\u7acb\u5373\u64a4\u9500\u504f\u5411\u9501\uff0c\u5347\u7ea7\u4e3a\u8f7b\u91cf\u7ea7\u9501\u3002\u6bcf\u4e2a\u7ebf\u7a0b\u5728\u81ea\u5df1\u7684\u7ebf\u7a0b\u6808\u4e2d\u751f\u6210\u4e00\u4e2a LockRecord ( LR )\uff0c\u7136\u540e\u6bcf\u4e2a\u7ebf\u7a0b\u901a\u8fc7 CAS (\u81ea\u65cb)\u7684\u64cd\u4f5c\u5c06\u9501\u5bf9\u8c61\u5934\u4e2d\u7684 markwork \u8bbe\u7f6e\u4e3a\u6307\u5411\u81ea\u5df1\u7684 LR \u7684\u6307\u9488\uff0c\u54ea\u4e2a\u7ebf\u7a0b\u8bbe\u7f6e\u6210\u529f\uff0c\u5c31\u610f\u5473\u7740\u83b7\u5f97\u9501\u3002\u5173\u4e8e synchronized \u4e2d\u6b64\u65f6\u6267\u884c\u7684 CAS \u64cd\u4f5c\u662f\u901a\u8fc7 native \u7684\u8c03\u7528 HotSpot \u4e2d bytecodeInterpreter.cpp \u6587\u4ef6 C++ \u4ee3\u7801\u5b9e\u73b0\u7684\uff0c\u6709\u5174\u8da3\u7684\u53ef\u4ee5\u7ee7\u7eed\u6df1\u6316\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u5347\u7ea7\u5230\u91cd\u91cf\u7ea7\u9501<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u679c\u9501\u7ade\u4e89\u52a0\u5267(\u5982\u7ebf\u7a0b\u81ea\u65cb\u6b21\u6570\u6216\u8005\u81ea\u65cb\u7684\u7ebf\u7a0b\u6570\u8d85\u8fc7\u67d0\u9608\u503c\uff0c JDK1.6 \u4e4b\u540e\uff0c\u7531 JVM \u81ea\u5df1\u63a7\u5236\u8be5\u89c4\u5219)\uff0c\u5c31\u4f1a\u5347\u7ea7\u4e3a\u91cd\u91cf\u7ea7\u9501\u3002\u6b64\u65f6\u5c31\u4f1a\u5411\u64cd\u4f5c\u7cfb\u7edf\u7533\u8bf7\u8d44\u6e90\uff0c\u7ebf\u7a0b\u6302\u8d77\uff0c\u8fdb\u5165\u5230\u64cd\u4f5c\u7cfb\u7edf\u5185\u6838\u6001\u7684\u7b49\u5f85\u961f\u5217\u4e2d\uff0c\u7b49\u5f85\u64cd\u4f5c\u7cfb\u7edf\u8c03\u5ea6\uff0c\u7136\u540e\u6620\u5c04\u56de\u7528\u6237\u6001\u3002\u5728\u91cd\u91cf\u7ea7\u9501\u4e2d\uff0c\u7531\u4e8e\u9700\u8981\u505a\u5185\u6838\u6001\u5230\u7528\u6237\u6001\u7684\u8f6c\u6362\uff0c\u800c\u8fd9\u4e2a\u8fc7\u7a0b\u4e2d\u9700\u8981\u6d88\u8017\u8f83\u591a\u65f6\u95f4\uff0c\u4e5f\u5c31\u662f&#8221;\u91cd&#8221;\u7684\u539f\u56e0\u4e4b\u4e00\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u53ef\u91cd\u5165<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">synchronized \u62e5\u6709\u5f3a\u5236\u539f\u5b50\u6027\u7684\u5185\u90e8\u9501\u673a\u5236\uff0c\u662f\u4e00\u628a\u53ef\u91cd\u5165\u9501\u3002\u56e0\u6b64\uff0c\u5728\u4e00\u4e2a\u7ebf\u7a0b\u4f7f\u7528 synchronized \u65b9\u6cd5\u65f6\u8c03\u7528\u8be5\u5bf9\u8c61\u53e6\u4e00\u4e2a synchronized \u65b9\u6cd5\uff0c\u5373\u4e00\u4e2a\u7ebf\u7a0b\u5f97\u5230\u4e00\u4e2a\u5bf9\u8c61\u9501\u540e\u518d\u6b21\u8bf7\u6c42\u8be5\u5bf9\u8c61\u9501\uff0c\u662f\u6c38\u8fdc\u53ef\u4ee5\u62ff\u5230\u9501\u7684\u3002\u5728 Java \u4e2d\u7ebf\u7a0b\u83b7\u5f97\u5bf9\u8c61\u9501\u7684\u64cd\u4f5c\u662f\u4ee5\u7ebf\u7a0b\u4e3a\u5355\u4f4d\u7684\uff0c\u800c\u4e0d\u662f\u4ee5\u8c03\u7528\u4e3a\u5355\u4f4d\u7684\u3002 synchronized \u9501\u7684\u5bf9\u8c61\u5934\u7684 markwork \u4e2d\u4f1a\u8bb0\u5f55\u8be5\u9501\u7684\u7ebf\u7a0b\u6301\u6709\u8005\u548c\u8ba1\u6570\u5668\uff0c\u5f53\u4e00\u4e2a\u7ebf\u7a0b\u8bf7\u6c42\u6210\u529f\u540e\uff0c JVM \u4f1a\u8bb0\u4e0b\u6301\u6709\u9501\u7684\u7ebf\u7a0b\uff0c\u5e76\u5c06\u8ba1\u6570\u5668\u8ba1\u4e3a1\u3002\u6b64\u65f6\u5176\u4ed6\u7ebf\u7a0b\u8bf7\u6c42\u8be5\u9501\uff0c\u5219\u5fc5\u987b\u7b49\u5f85\u3002\u800c\u8be5\u6301\u6709\u9501\u7684\u7ebf\u7a0b\u5982\u679c\u518d\u6b21\u8bf7\u6c42\u8fd9\u4e2a\u9501\uff0c\u5c31\u53ef\u4ee5\u518d\u6b21\u62ff\u5230\u8fd9\u4e2a\u9501\uff0c\u540c\u65f6\u8ba1\u6570\u5668\u4f1a\u9012\u589e\u3002\u5f53\u7ebf\u7a0b\u9000\u51fa\u4e00\u4e2a  synchronized \u65b9\u6cd5\/\u5757\u65f6\uff0c\u8ba1\u6570\u5668\u4f1a\u9012\u51cf\uff0c\u5982\u679c\u8ba1\u6570\u5668\u4e3a 0 \u5219\u91ca\u653e\u8be5\u9501\u9501\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u60b2\u89c2\u9501(\u4e92\u65a5\u9501\u3001\u6392\u4ed6\u9501)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">synchronized \u662f\u4e00\u628a\u60b2\u89c2\u9501(\u72ec\u5360\u9501)\uff0c\u5f53\u524d\u7ebf\u7a0b\u5982\u679c\u83b7\u53d6\u5230\u9501\uff0c\u4f1a\u5bfc\u81f4\u5176\u5b83\u6240\u6709\u9700\u8981\u9501\u8be5\u7684\u7ebf\u7a0b\u7b49\u5f85\uff0c\u4e00\u76f4\u7b49\u5f85\u6301\u6709\u9501\u7684\u7ebf\u7a0b\u91ca\u653e\u9501\u624d\u7ee7\u7eed\u8fdb\u884c\u9501\u7684\u4e89\u62a2\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">ReentrantLock<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">ReentrantLock \u4ece\u5b57\u9762\u53ef\u4ee5\u770b\u51fa\u662f\u4e00\u628a\u53ef\u91cd\u5165\u9501\uff0c\u8fd9\u70b9\u548c synchronized \u4e00\u6837\uff0c\u4f46\u5b9e\u73b0\u539f\u7406\u4e5f\u4e0e syncronized \u6709\u5f88\u5927\u5dee\u522b\uff0c\u5b83\u662f\u57fa\u4e8e\u7ecf\u5178\u7684 AQS(AbstractQueueSyncronized) \u5b9e\u73b0\u7684, AQS \u662f\u57fa\u4e8e volitale \u548c CAS \u5b9e\u73b0\u7684\uff0c\u5176\u4e2d AQS \u4e2d\u7ef4\u62a4\u4e00\u4e2a valitale \u7c7b\u578b\u7684\u53d8\u91cf state \u6765\u505a\u4e00\u4e2a\u53ef\u91cd\u5165\u9501\u7684\u91cd\u5165\u6b21\u6570\uff0c\u52a0\u9501\u548c\u91ca\u653e\u9501\u4e5f\u662f\u56f4\u7ed5\u8fd9\u4e2a\u53d8\u91cf\u6765\u8fdb\u884c\u7684\u3002 ReentrantLock \u4e5f\u63d0\u4f9b\u4e86\u4e00\u4e9b synchronized \u6ca1\u6709\u7684\u7279\u70b9\uff0c\u56e0\u6b64\u6bd4 synchronized \u597d\u7528\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">AQS\u6a21\u578b\u5982\u4e0b\u56fe\uff1a<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img decoding=\"async\" src=\"https:\/\/gitee.com\/xmtblog\/img\/raw\/master\/1581595848001.jpg\" alt=\"\" \/><figcaption>AQS \u6a21\u578b<\/figcaption><\/figure><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">ReentrantLock \u6709\u5982\u4e0b\u7279\u70b9\uff1a<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>\u53ef\u91cd\u5165\u3002ReentrantLock \u548c syncronized \u5173\u952e\u5b57\u4e00\u6837\uff0c\u90fd\u662f\u53ef\u91cd\u5165\u9501\uff0c\u4e0d\u8fc7\u4e24\u8005\u5b9e\u73b0\u539f\u7406\u7a0d\u6709\u5dee\u522b\uff0c RetrantLock \u5229\u7528 AQS \u7684\u7684 state \u72b6\u6001\u6765\u5224\u65ad\u8d44\u6e90\u662f\u5426\u5df2\u9501\uff0c\u540c\u4e00\u7ebf\u7a0b\u91cd\u5165\u52a0\u9501\uff0c state \u7684\u72b6\u6001 +1 ; \u540c\u4e00\u7ebf\u7a0b\u91cd\u5165\u89e3\u9501, state \u72b6\u6001 -1 (\u89e3\u9501\u5fc5\u987b\u4e3a\u5f53\u524d\u72ec\u5360\u7ebf\u7a0b\uff0c\u5426\u5219\u5f02\u5e38); \u5f53 state \u4e3a 0 \u65f6\u89e3\u9501\u6210\u529f\u3002<\/li><li> \u9700\u8981\u624b\u52a8\u52a0\u9501\u3001\u89e3\u9501\u3002synchronized \u5173\u952e\u5b57\u662f\u81ea\u52a8\u8fdb\u884c\u52a0\u9501\u3001\u89e3\u9501\u7684\uff0c\u800c ReentrantLock \u9700\u8981 lock() \u548c unlock() \u65b9\u6cd5\u914d\u5408 try\/finally \u8bed\u53e5\u5757\u6765\u5b8c\u6210\uff0c\u6765\u624b\u52a8\u52a0\u9501\u3001\u89e3\u9501\u3002<\/li><li> \u652f\u6301\u8bbe\u7f6e\u9501\u7684\u8d85\u65f6\u65f6\u95f4\u3002synchronized \u5173\u952e\u5b57\u65e0\u6cd5\u8bbe\u7f6e\u9501\u7684\u8d85\u65f6\u65f6\u95f4\uff0c\u5982\u679c\u4e00\u4e2a\u83b7\u5f97\u9501\u7684\u7ebf\u7a0b\u5185\u90e8\u53d1\u751f\u6b7b\u9501\uff0c\u90a3\u4e48\u5176\u4ed6\u7ebf\u7a0b\u5c31\u4f1a\u4e00\u76f4\u8fdb\u5165\u963b\u585e\u72b6\u6001\uff0c\u800c ReentrantLock \u63d0\u4f9b tryLock \u65b9\u6cd5\uff0c\u5141\u8bb8\u8bbe\u7f6e\u7ebf\u7a0b\u83b7\u53d6\u9501\u7684\u8d85\u65f6\u65f6\u95f4\uff0c\u5982\u679c\u8d85\u65f6\uff0c\u5219\u8df3\u8fc7\uff0c\u4e0d\u8fdb\u884c\u4efb\u4f55\u64cd\u4f5c\uff0c\u907f\u514d\u6b7b\u9501\u7684\u53d1\u751f\u3002<\/li><li> \u652f\u6301\u516c\u5e73\/\u975e\u516c\u5e73\u9501\u3002synchronized \u5173\u952e\u5b57\u662f\u4e00\u79cd\u975e\u516c\u5e73\u9501\uff0c\u5148\u62a2\u5230\u9501\u7684\u7ebf\u7a0b\u5148\u6267\u884c\u3002\u800c ReentrantLock \u7684\u6784\u9020\u65b9\u6cd5\u4e2d\u5141\u8bb8\u8bbe\u7f6e true\/false \u6765\u5b9e\u73b0\u516c\u5e73\u3001\u975e\u516c\u5e73\u9501\uff0c\u5982\u679c\u8bbe\u7f6e\u4e3a true \uff0c\u5219\u7ebf\u7a0b\u83b7\u53d6\u9501\u8981\u9075\u5faa&#8221;\u5148\u6765\u540e\u5230&#8221;\u7684\u89c4\u5219\uff0c\u6bcf\u6b21\u90fd\u4f1a\u6784\u9020\u4e00\u4e2a\u7ebf\u7a0b Node \uff0c\u7136\u540e\u5230\u53cc\u5411\u94fe\u8868\u7684&#8221;\u5c3e\u5df4&#8221;\u540e\u9762\u6392\u961f\uff0c\u7b49\u5f85\u524d\u9762\u7684 Node \u91ca\u653e\u9501\u8d44\u6e90\u3002<\/li><li> \u53ef\u4e2d\u65ad\u9501\u3002ReentrantLock \u4e2d\u7684 lockInterruptibly() \u65b9\u6cd5\u4f7f\u5f97\u7ebf\u7a0b\u53ef\u4ee5\u5728\u88ab\u963b\u585e\u65f6\u54cd\u5e94\u4e2d\u65ad\uff0c\u6bd4\u5982\u4e00\u4e2a\u7ebf\u7a0b t1 \u901a\u8fc7 lockInterruptibly() \u65b9\u6cd5\u83b7\u53d6\u5230\u4e00\u4e2a\u53ef\u91cd\u5165\u9501\uff0c\u5e76\u6267\u884c\u4e00\u4e2a\u957f\u65f6\u95f4\u7684\u4efb\u52a1\uff0c\u53e6\u4e00\u4e2a\u7ebf\u7a0b\u901a\u8fc7 interrupt() \u65b9\u6cd5\u5c31\u53ef\u4ee5\u7acb\u523b\u6253\u65ad t1 \u7ebf\u7a0b\u7684\u6267\u884c\uff0c\u6765\u83b7\u53d6t1\u6301\u6709\u7684\u90a3\u4e2a\u53ef\u91cd\u5165\u9501\u3002\u800c\u901a\u8fc7 ReentrantLock \u7684 lock() \u65b9\u6cd5\u6216\u8005 Synchronized \u6301\u6709\u9501\u7684\u7ebf\u7a0b\u662f\u4e0d\u4f1a\u54cd\u5e94\u5176\u4ed6\u7ebf\u7a0b\u7684 interrupt() \u65b9\u6cd5\u7684\uff0c\u76f4\u5230\u8be5\u65b9\u6cd5\u4e3b\u52a8\u91ca\u653e\u9501\u4e4b\u540e\u624d\u4f1a\u54cd\u5e94 interrupt() \u65b9\u6cd5\u3002<\/li><\/ol>\n\n\n\n<h2 class=\"wp-block-heading\">ReentrantReadWriteLock<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">ReentrantReadWriteLock (\u8bfb\u5199\u9501)\u5176\u5b9e\u662f\u4e24\u628a\u9501\uff0c\u4e00\u628a\u662f WriteLock (\u5199\u9501)\uff0c\u4e00\u628a\u662f\u8bfb\u9501\uff0c ReadLock \u3002\u8bfb\u5199\u9501\u7684\u89c4\u5219\u662f\uff1a\u8bfb\u8bfb\u4e0d\u4e92\u65a5\u3001\u8bfb\u5199\u4e92\u65a5\u3001\u5199\u5199\u4e92\u65a5\u3002\u5728\u4e00\u4e9b\u5b9e\u9645\u7684\u573a\u666f\u4e2d\uff0c\u8bfb\u64cd\u4f5c\u7684\u9891\u7387\u8fdc\u8fdc\u9ad8\u4e8e\u5199\u64cd\u4f5c\uff0c\u5982\u679c\u76f4\u63a5\u7528\u4e00\u822c\u7684\u9501\u8fdb\u884c\u5e76\u53d1\u63a7\u5236\u7684\u8bdd\uff0c\u5c31\u4f1a\u8bfb\u8bfb\u4e92\u65a5\u3001\u8bfb\u5199\u4e92\u65a5\u3001\u5199\u5199\u4e92\u65a5\uff0c\u6548\u7387\u4f4e\u4e0b\uff0c\u8bfb\u5199\u9501\u7684\u4ea7\u751f\u5c31\u662f\u4e3a\u4e86\u4f18\u5316\u8fd9\u79cd\u573a\u666f\u7684\u64cd\u4f5c\u6548\u7387\u3002\u4e00\u822c\u60c5\u51b5\u4e0b\u72ec\u5360\u9501\u7684\u6548\u7387\u4f4e\u6765\u6e90\u4e8e\u9ad8\u5e76\u53d1\u4e0b\u5bf9\u4e34\u754c\u533a\u7684\u6fc0\u70c8\u7ade\u4e89\u5bfc\u81f4\u7ebf\u7a0b\u4e0a\u4e0b\u6587\u5207\u6362\u3002\u56e0\u6b64\u5f53\u5e76\u53d1\u4e0d\u662f\u5f88\u9ad8\u7684\u60c5\u51b5\u4e0b\uff0c\u8bfb\u5199\u9501\u7531\u4e8e\u9700\u8981\u989d\u5916\u7ef4\u62a4\u8bfb\u9501\u7684\u72b6\u6001\uff0c\u53ef\u80fd\u8fd8\u4e0d\u5982\u72ec\u5360\u9501\u7684\u6548\u7387\u9ad8\uff0c\u56e0\u6b64\u9700\u8981\u6839\u636e\u5b9e\u9645\u60c5\u51b5\u9009\u62e9\u4f7f\u7528\u3002 <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">ReentrantReadWriteLock \u7684\u539f\u7406\u4e5f\u662f\u57fa\u4e8e AQS \u8fdb\u884c\u5b9e\u73b0\u7684\uff0c\u4e0e ReentrantLock \u7684\u5dee\u522b\u5728\u4e8e ReentrantReadWriteLock \u9501\u62e5\u6709\u5171\u4eab\u9501\u3001\u6392\u4ed6\u9501\u5c5e\u6027\u3002\u8bfb\u5199\u9501\u4e2d\u7684\u52a0\u9501\u3001\u91ca\u653e\u9501\u4e5f\u662f\u57fa\u4e8e Sync (\u7ee7\u627f\u4e8e AQS )\uff0c\u5e76\u4e14\u4e3b\u8981\u4f7f\u7528 AQS \u4e2d\u7684 state \u548c node \u4e2d\u7684 waitState \u53d8\u91cf\u8fdb\u884c\u5b9e\u73b0\u7684\u3002\u5b9e\u73b0\u8bfb\u5199\u9501\u4e0e\u5b9e\u73b0\u666e\u901a\u4e92\u65a5\u9501\u7684\u4e3b\u8981\u533a\u522b\u5728\u4e8e\u9700\u8981\u5206\u522b\u8bb0\u5f55\u8bfb\u9501\u72b6\u6001\u53ca\u5199\u9501\u72b6\u6001\uff0c\u5e76\u4e14\u7b49\u5f85\u961f\u5217\u4e2d\u9700\u8981\u533a\u522b\u5904\u7406\u4e24\u79cd\u52a0\u9501\u64cd\u4f5c\u3002 ReentrantReadWriteLock \u4e2d\u5c06 AQS \u4e2d\u7684 int \u7c7b\u578b\u7684 state \u5206\u4e3a\u9ad8 16 \u4f4d\u4e0e\u7b2c 16 \u4f4d\u5206\u522b\u8bb0\u5f55\u8bfb\u9501\u548c\u5199\u9501\u7684\u72b6\u6001\uff0c\u5982\u4e0b\u56fe\u6240\u793a\uff1a<br><\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img decoding=\"async\" src=\"https:\/\/gitee.com\/xmtblog\/img\/raw\/master\/1581595861902.jpg\" alt=\"\" \/><figcaption>ReentrantReadWriteLock \u7684\u539f\u7406<\/figcaption><\/figure><\/div>\n\n\n\n<h2 class=\"wp-block-heading\">WriteLock(\u5199\u9501)\u662f\u60b2\u89c2\u9501(\u6392\u4ed6\u9501\u3001\u4e92\u65a5\u9501)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u901a\u8fc7\u8ba1\u7b97 state&amp;((1&lt;&lt;16)-1) \uff0c\u5c06 state \u7684\u9ad8 16 \u4f4d\u5168\u90e8\u62b9\u53bb\uff0c\u56e0\u6b64 state \u7684\u4f4e\u4f4d\u8bb0\u5f55\u7740\u5199\u9501\u7684\u91cd\u5165\u8ba1\u6570\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u83b7\u53d6\u5199\u9501\u6e90\u7801\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\n\/**\n * \u83b7\u53d6\u5199\u9501 Acquires the write lock.\n *  \u5982\u679c\u6b64\u65f6\u6ca1\u6709\u4efb\u4f55\u7ebf\u7a0b\u6301\u6709\u5199\u9501\u6216\u8005\u8bfb\u9501\uff0c\u90a3\u4e48\u5f53\u524d\u7ebf\u7a0b\u6267\u884cCAS\u64cd\u4f5c\u66f4\u65b0status\uff0c\n *  \u82e5\u66f4\u65b0\u6210\u529f\uff0c\u5219\u8bbe\u7f6e\u8bfb\u9501\u91cd\u5165\u6b21\u6570\u4e3a1\uff0c\u5e76\u7acb\u5373\u8fd4\u56de\n * &lt;p&gt;Acquires the write lock if neither the read nor write lock\n * are held by another thread\n * and returns immediately, setting the write lock hold count to\n * one.\n *  \u5982\u679c\u5f53\u524d\u7ebf\u7a0b\u5df2\u7ecf\u6301\u6709\u8be5\u5199\u9501\uff0c\u90a3\u4e48\u5c06\u5199\u9501\u6301\u6709\u6b21\u6570\u8bbe\u7f6e\u4e3a1\uff0c\u5e76\u7acb\u5373\u8fd4\u56de\n * &lt;p&gt;If the current thread already holds the write lock then the\n * hold count is incremented by one and the method returns\n * immediately.\n *  \u5982\u679c\u8be5\u9501\u5df2\u7ecf\u88ab\u53e6\u5916\u4e00\u4e2a\u7ebf\u7a0b\u6301\u6709\uff0c\u90a3\u4e48\u505c\u6b62\u8be5\u7ebf\u7a0b\u7684CPU\u8c03\u5ea6\u5e76\u8fdb\u5165\u4f11\u7720\u72b6\u6001\uff0c\n *  \u76f4\u5230\u8be5\u5199\u9501\u88ab\u91ca\u653e\uff0c\u4e14\u6210\u529f\u5c06\u5199\u9501\u6301\u6709\u6b21\u6570\u8bbe\u7f6e\u4e3a1\u624d\u8868\u793a\u83b7\u53d6\u5199\u9501\u6210\u529f\n * &lt;p&gt;If the lock is held by another thread then the current\n * thread becomes disabled for thread scheduling purposes and\n * lies dormant until the write lock has been acquired, at which\n * time the write lock hold count is set to one.\n *\/\npublic void lock() {\n    sync.acquire(1);\n}\n\/**\n * \u8be5\u65b9\u6cd5\u4e3a\u4ee5\u72ec\u5360\u6a21\u5f0f\u83b7\u53d6\u9501\uff0c\u5ffd\u7565\u4e2d\u65ad\n * \u5982\u679c\u8c03\u7528\u4e00\u6b21\u8be5\u201ctryAcquire\u201d\u65b9\u6cd5\u66f4\u65b0status\u6210\u529f\uff0c\u5219\u76f4\u63a5\u8fd4\u56de\uff0c\u4ee3\u8868\u62a2\u9501\u6210\u529f\n * \u5426\u5219\uff0c\u5c06\u4f1a\u8fdb\u5165\u540c\u6b65\u961f\u5217\u7b49\u5f85\uff0c\u4e0d\u65ad\u6267\u884c\u201ctryAcquire\u201d\u65b9\u6cd5\u5c1d\u8bd5CAS\u66f4\u65b0status\u72b6\u6001\uff0c\u76f4\u5230\u6210\u529f\u62a2\u5230\u9501\n * \u5176\u4e2d\u201ctryAcquire\u201d\u65b9\u6cd5\u5728NonfairSync(\u516c\u5e73\u9501)\u4e2d\u548cFairSync(\u975e\u516c\u5e73\u9501)\u4e2d\u90fd\u6709\u5404\u81ea\u7684\u5b9e\u73b0\n *\n * Acquires in exclusive mode, ignoring interrupts.  Implemented\n * by invoking at least once {@link #tryAcquire},\n * returning on success.  Otherwise the thread is queued, possibly\n * repeatedly blocking and unblocking, invoking {@link\n * #tryAcquire} until success.  This method can be used\n * to implement method {@link Lock#lock}.\n *\n * @param arg the acquire argument.  This value is conveyed to\n *        {@link #tryAcquire} but is otherwise uninterpreted and\n *        can represent anything you like.\n *\/\npublic final void acquire(int arg) {\n    if (!tryAcquire(arg) &amp;&amp;\n        acquireQueued(addWaiter(Node.EXCLUSIVE), arg))\n        selfInterrupt();\n}\nprotected final boolean tryAcquire(int acquires) {\n    \/*\n     * Walkthrough:\n     * 1\u3001\u5982\u679c\u8bfb\u5199\u9501\u7684\u8ba1\u6570\u4e0d\u4e3a0\uff0c\u4e14\u6301\u6709\u9501\u7684\u7ebf\u7a0b\u4e0d\u662f\u5f53\u524d\u7ebf\u7a0b\uff0c\u5219\u8fd4\u56defalse\n     * 1. If read count nonzero or write count nonzero\n     *    and owner is a different thread, fail.\n     * 2\u3001\u5982\u679c\u6301\u6709\u9501\u7684\u8ba1\u6570\u4e0d\u4e3a0\u4e14\u8ba1\u6570\u603b\u6570\u8d85\u8fc7\u9650\u5b9a\u7684\u6700\u5927\u503c\uff0c\u4e5f\u8fd4\u56defalse\n     * 2. If count would saturate, fail. (This can only\n     *    happen if count is already nonzero.)\n     * 3\u3001\u5982\u679c\u8be5\u9501\u662f\u53ef\u91cd\u5165\u6216\u8be5\u7ebf\u7a0b\u5728\u961f\u5217\u4e2d\u7684\u7b56\u7565\u662f\u5141\u8bb8\u5b83\u5c1d\u8bd5\u62a2\u9501\uff0c\u90a3\u4e48\u8be5\u7ebf\u7a0b\u5c31\u80fd\u83b7\u53d6\u9501\n     * 3. Otherwise, this thread is eligible for lock if\n     *    it is either a reentrant acquire or\n     *    queue policy allows it. If so, update state\n     *    and set owner.\n     *\/\n    Thread current = Thread.currentThread();\n    \/\/\u83b7\u53d6\u8bfb\u5199\u9501\u7684\u72b6\u6001\n    int c = getState();\n    \/\/\u83b7\u53d6\u8be5\u5199\u9501\u91cd\u5165\u7684\u6b21\u6570\n    int w = exclusiveCount(c);\n    \/\/\u5982\u679c\u8bfb\u5199\u9501\u72b6\u6001\u4e0d\u4e3a0\uff0c\u8bf4\u660e\u5df2\u7ecf\u6709\u5176\u4ed6\u7ebf\u7a0b\u83b7\u53d6\u4e86\u8bfb\u9501\u6216\u5199\u9501\n    if (c != 0) {\n        \/\/\u5982\u679c\u5199\u9501\u91cd\u5165\u6b21\u6570\u4e3a0\uff0c\u8bf4\u660e\u6709\u7ebf\u7a0b\u83b7\u53d6\u5230\u8bfb\u9501\uff0c\u6839\u636e\u201c\u8bfb\u5199\u9501\u4e92\u65a5\u201d\u539f\u5219\uff0c\u8fd4\u56defalse\n        \/\/\u6216\u8005\u5982\u679c\u5199\u9501\u91cd\u5165\u6b21\u6570\u4e0d\u4e3a0\uff0c\u4e14\u83b7\u53d6\u5199\u9501\u7684\u7ebf\u7a0b\u4e0d\u662f\u5f53\u524d\u7ebf\u7a0b\uff0c\u6839\u636e\"\u5199\u9501\u72ec\u5360\"\u539f\u5219\uff0c\u8fd4\u56defalse\n        \/\/ (Note: if c != 0 and w == 0 then shared count != 0)\n        if (w == 0 || current != getExclusiveOwnerThread())\n            return false;\n       \/\/\u5982\u679c\u5199\u9501\u53ef\u91cd\u5165\u6b21\u6570\u8d85\u8fc7\u6700\u5927\u6b21\u6570\uff0865535\uff09\uff0c\u5219\u629b\u5f02\u5e38\n        if (w + exclusiveCount(acquires) &gt; MAX_COUNT)\n            throw new Error(\"Maximum lock count exceeded\");\n        \/\/\u5230\u8fd9\u91cc\u8bf4\u660e\u8be5\u7ebf\u7a0b\u662f\u91cd\u5165\u5199\u9501\uff0c\u66f4\u65b0\u91cd\u5165\u5199\u9501\u7684\u8ba1\u6570(+1)\uff0c\u8fd4\u56detrue\n        \/\/ Reentrant acquire\n        setState(c + acquires);\n        return true;\n    }\n    \/\/\u5982\u679c\u8bfb\u5199\u9501\u72b6\u6001\u4e3a0,\u8bf4\u660e\u8bfb\u9501\u548c\u5199\u9501\u90fd\u6ca1\u6709\u88ab\u83b7\u53d6\uff0c\u4f1a\u8d70\u4e0b\u9762\u4e24\u4e2a\u5206\u652f\uff1a\n    \/\/\u5982\u679c\u8981\u963b\u585e\u6216\u8005\u6267\u884cCAS\u64cd\u4f5c\u66f4\u65b0\u8bfb\u5199\u9501\u7684\u72b6\u6001\u5931\u8d25\uff0c\u5219\u8fd4\u56defalse\n    \/\/\u5982\u679c\u4e0d\u9700\u8981\u963b\u585e\u4e14CAS\u64cd\u4f5c\u6210\u529f\uff0c\u5219\u5f53\u524d\u7ebf\u7a0b\u6210\u529f\u62ff\u5230\u9501\uff0c\u8bbe\u7f6e\u9501\u7684owner\u4e3a\u5f53\u524d\u7ebf\u7a0b\uff0c\u8fd4\u56detrue\n    if (writerShouldBlock() ||\n        !compareAndSetState(c, c + acquires))\n        return false;\n    setExclusiveOwnerThread(current);\n    return true;\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u91ca\u653e\u5199\u9501\u6e90\u7801\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/*\n  * Note that tryRelease and tryAcquire can be called by\n  * Conditions. So it is possible that their arguments contain\n  * both read and write holds that are all released during a\n  * condition wait and re-established in tryAcquire.\n  *\/\n protected final boolean tryRelease(int releases) {\n     \/\/\u82e5\u9501\u7684\u6301\u6709\u8005\u4e0d\u662f\u5f53\u524d\u7ebf\u7a0b\uff0c\u629b\u51fa\u5f02\u5e38\n     if (!isHeldExclusively())\n         throw new IllegalMonitorStateException();\n     \/\/\u5199\u9501\u7684\u53ef\u91cd\u5165\u8ba1\u6570\u51cf\u6389releases\u4e2a\n     int nextc = getState() - releases;\n     \/\/\u5982\u679c\u5199\u9501\u91cd\u5165\u8ba1\u6570\u4e3a0\u4e86\uff0c\u5219\u8bf4\u660e\u5199\u9501\u88ab\u91ca\u653e\u4e86\n     boolean free = exclusiveCount(nextc) == 0;\n     if (free)\n        \/\/\u82e5\u5199\u9501\u88ab\u91ca\u653e\uff0c\u5219\u5c06\u9501\u7684\u6301\u6709\u8005\u8bbe\u7f6e\u4e3anull\uff0c\u8fdb\u884cGC\n        setExclusiveOwnerThread(null);\n     \/\/\u66f4\u65b0\u5199\u9501\u7684\u91cd\u5165\u8ba1\u6570\n     setState(nextc);\n     return free;\n }<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">ReadLock(\u8bfb\u9501)\u662f\u5171\u4eab\u9501(\u4e50\u89c2\u9501)<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u901a\u8fc7\u8ba1\u7b97 state&gt;&gt;&gt;16 \u8fdb\u884c\u65e0\u7b26\u53f7\u8865 0 \uff0c\u53f3\u79fb 16 \u4f4d\uff0c\u56e0\u6b64 state \u7684\u9ad8\u4f4d\u8bb0\u5f55\u7740\u5199\u9501\u7684\u91cd\u5165\u8ba1\u6570.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u8bfb\u9501\u83b7\u53d6\u9501\u7684\u8fc7\u7a0b\u6bd4\u5199\u9501\u7a0d\u5fae\u590d\u6742\u4e9b\uff0c\u9996\u5148\u5224\u65ad\u5199\u9501\u662f\u5426\u4e3a 0 \u5e76\u4e14\u5f53\u524d\u7ebf\u7a0b\u4e0d\u5360\u6709\u72ec\u5360\u9501\uff0c\u76f4\u63a5\u8fd4\u56de\uff1b\u5426\u5219\uff0c\u5224\u65ad\u8bfb\u7ebf\u7a0b\u662f\u5426\u9700\u8981\u88ab\u963b\u585e\u5e76\u4e14\u8bfb\u9501\u6570\u91cf\u662f\u5426\u5c0f\u4e8e\u6700\u5927\u503c\u5e76\u4e14\u6bd4\u8f83\u8bbe\u7f6e\u72b6\u6001\u6210\u529f\uff0c\u82e5\u5f53\u524d\u6ca1\u6709\u8bfb\u9501\uff0c\u5219\u8bbe\u7f6e\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0b firstReader \u548c firstReaderHoldCount \uff1b\u82e5\u5f53\u524d\u7ebf\u7a0b\u7ebf\u7a0b\u4e3a\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0b\uff0c\u5219\u589e\u52a0 firstReaderHoldCount \uff1b\u5426\u5219\uff0c\u5c06\u8bbe\u7f6e\u5f53\u524d\u7ebf\u7a0b\u5bf9\u5e94\u7684 HoldCounter \u5bf9\u8c61\u7684\u503c\uff0c\u66f4\u65b0\u6210\u529f\u540e\u4f1a\u5728 firstReaderHoldCount \u4e2d readHolds ( ThreadLocal \u7c7b\u578b\u7684)\u7684\u672c\u7ebf\u7a0b\u526f\u672c\u4e2d\u8bb0\u5f55\u5f53\u524d\u7ebf\u7a0b\u91cd\u5165\u6570\uff0c\u8fd9\u662f\u4e3a\u4e86\u5b9e\u73b0 JDK1.6 \u4e2d\u52a0\u5165\u7684 getReadHoldCount ()\u65b9\u6cd5\u7684\uff0c\u8fd9\u4e2a\u65b9\u6cd5\u80fd\u83b7\u53d6\u5f53\u524d\u7ebf\u7a0b\u91cd\u5165\u5171\u4eab\u9501\u7684\u6b21\u6570( state \u4e2d\u8bb0\u5f55\u7684\u662f\u591a\u4e2a\u7ebf\u7a0b\u7684\u603b\u91cd\u5165\u6b21\u6570)\uff0c\u52a0\u5165\u4e86\u8fd9\u4e2a\u65b9\u6cd5\u8ba9\u4ee3\u7801\u590d\u6742\u4e86\u4e0d\u5c11\uff0c\u4f46\u662f\u5176\u539f\u7406\u8fd8\u662f\u5f88\u7b80\u5355\u7684\uff1a\u5982\u679c\u5f53\u524d\u53ea\u6709\u4e00\u4e2a\u7ebf\u7a0b\u7684\u8bdd\uff0c\u8fd8\u4e0d\u9700\u8981\u52a8\u7528 ThreadLocal \uff0c\u76f4\u63a5\u5f80 firstReaderHoldCount \u8fd9\u4e2a\u6210\u5458\u53d8\u91cf\u91cc\u5b58\u91cd\u5165\u6570\uff0c\u5f53\u6709\u7b2c\u4e8c\u4e2a\u7ebf\u7a0b\u6765\u7684\u65f6\u5019\uff0c\u5c31\u8981\u52a8\u7528 ThreadLocal \u53d8\u91cf readHolds \u4e86\uff0c\u6bcf\u4e2a\u7ebf\u7a0b\u62e5\u6709\u81ea\u5df1\u7684\u526f\u672c\uff0c\u7528\u6765\u4fdd\u5b58\u81ea\u5df1\u7684\u91cd\u5165\u6570\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u83b7\u53d6\u8bfb\u9501\u6e90\u7801\uff1a <\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/**\n * \u83b7\u53d6\u8bfb\u9501\n * Acquires the read lock.\n * \u5982\u679c\u5199\u9501\u672a\u88ab\u5176\u4ed6\u7ebf\u7a0b\u6301\u6709\uff0c\u6267\u884cCAS\u64cd\u4f5c\u66f4\u65b0status\u503c\uff0c\u83b7\u53d6\u8bfb\u9501\u540e\u7acb\u5373\u8fd4\u56de\n * &lt;p&gt;Acquires the read lock if the write lock is not held by\n * another thread and returns immediately.\n *\n * \u5982\u679c\u5199\u9501\u88ab\u5176\u4ed6\u7ebf\u7a0b\u6301\u6709\uff0c\u90a3\u4e48\u505c\u6b62\u8be5\u7ebf\u7a0b\u7684CPU\u8c03\u5ea6\u5e76\u8fdb\u5165\u4f11\u7720\u72b6\u6001\uff0c\u76f4\u5230\u8be5\u8bfb\u9501\u88ab\u91ca\u653e\n * &lt;p&gt;If the write lock is held by another thread then\n * the current thread becomes disabled for thread scheduling\n * purposes and lies dormant until the read lock has been acquired.\n *\/\npublic void lock() {\n    sync.acquireShared(1);\n}\n\/**\n * \u8be5\u65b9\u6cd5\u4e3a\u4ee5\u5171\u4eab\u6a21\u5f0f\u83b7\u53d6\u8bfb\u9501\uff0c\u5ffd\u7565\u4e2d\u65ad\n * \u5982\u679c\u8c03\u7528\u4e00\u6b21\u8be5\u201ctryAcquireShared\u201d\u65b9\u6cd5\u66f4\u65b0status\u6210\u529f\uff0c\u5219\u76f4\u63a5\u8fd4\u56de\uff0c\u4ee3\u8868\u62a2\u9501\u6210\u529f\n * \u5426\u5219\uff0c\u5c06\u4f1a\u8fdb\u5165\u540c\u6b65\u961f\u5217\u7b49\u5f85\uff0c\u4e0d\u65ad\u6267\u884c\u201ctryAcquireShared\u201d\u65b9\u6cd5\u5c1d\u8bd5CAS\u66f4\u65b0status\u72b6\u6001\uff0c\u76f4\u5230\u6210\u529f\u62a2\u5230\u9501\n * \u5176\u4e2d\u201ctryAcquireShared\u201d\u65b9\u6cd5\u5728NonfairSync(\u516c\u5e73\u9501)\u4e2d\u548cFairSync(\u975e\u516c\u5e73\u9501)\u4e2d\u90fd\u6709\u5404\u81ea\u7684\u5b9e\u73b0\n * (\u770b\u8fd9\u6ce8\u91ca\u662f\u4e0d\u662f\u548c\u5199\u9501\u5f88\u5bf9\u79f0)\n * Acquires in shared mode, ignoring interrupts.  Implemented by\n * first invoking at least once {@link #tryAcquireShared},\n * returning on success.  Otherwise the thread is queued, possibly\n * repeatedly blocking and unblocking, invoking {@link\n * #tryAcquireShared} until success.\n *\n * @param arg the acquire argument.  This value is conveyed to\n *        {@link #tryAcquireShared} but is otherwise uninterpreted\n *        and can represent anything you like.\n *\/\npublic final void acquireShared(int arg) {\n    if (tryAcquireShared(arg) &lt; 0)\n        doAcquireShared(arg);\n}\nprotected final int tryAcquireShared(int unused) {\n    \/*\n     * Walkthrough:\n     * 1\u3001\u5982\u679c\u5df2\u7ecf\u6709\u5176\u4ed6\u7ebf\u7a0b\u83b7\u53d6\u5230\u4e86\u5199\u9501\uff0c\u6839\u636e\u201c\u8bfb\u5199\u4e92\u65a5\u201d\u539f\u5219\uff0c\u62a2\u9501\u5931\u8d25\uff0c\u8fd4\u56de-1\n     * 1.If write lock held by another thread, fail.\n     * 2\u3001\u5982\u679c\u8be5\u7ebf\u7a0b\u672c\u8eab\u6301\u6709\u5199\u9501\uff0c\u90a3\u4e48\u770b\u4e00\u4e0b\u662f\u5426\u8981readerShouldBlock\uff0c\u5982\u679c\u4e0d\u9700\u8981\u963b\u585e\uff0c\n     *    \u5219\u6267\u884cCAS\u64cd\u4f5c\u66f4\u65b0state\u548c\u91cd\u5165\u8ba1\u6570\u3002\n     *    \u8fd9\u91cc\u8981\u6ce8\u610f\u7684\u662f\uff0c\u4e0a\u9762\u7684\u6b65\u9aa4\u4e0d\u68c0\u67e5\u662f\u5426\u53ef\u91cd\u5165(\u56e0\u4e3a\u8bfb\u9501\u5c5e\u4e8e\u5171\u4eab\u9501\uff0c\u5929\u751f\u652f\u6301\u53ef\u91cd\u5165)\n     * 2. Otherwise, this thread is eligible for\n     *    lock wrt state, so ask if it should block\n     *    because of queue policy. If not, try\n     *    to grant by CASing state and updating count.\n     *    Note that step does not check for reentrant\n     *    acquires, which is postponed to full version\n     *    to avoid having to check hold count in\n     *    the more typical non-reentrant case.\n     * 3\u3001\u5982\u679c\u56e0\u4e3aCAS\u66f4\u65b0status\u5931\u8d25\u6216\u8005\u91cd\u5165\u8ba1\u6570\u8d85\u8fc7\u6700\u5927\u503c\u5bfc\u81f4\u6b65\u9aa42\u6267\u884c\u5931\u8d25\n     *    \u90a3\u5c31\u8fdb\u5165\u5230fullTryAcquireShared\u65b9\u6cd5\u8fdb\u884c\u6b7b\u5faa\u73af\uff0c\u76f4\u5230\u62a2\u9501\u6210\u529f\n     * 3. If step 2 fails either because thread\n     *    apparently not eligible or CAS fails or count\n     *    saturated, chain to version with full retry loop.\n     *\/\n\n    \/\/\u5f53\u524d\u5c1d\u8bd5\u83b7\u53d6\u8bfb\u9501\u7684\u7ebf\u7a0b\n    Thread current = Thread.currentThread();\n    \/\/\u83b7\u53d6\u8be5\u8bfb\u5199\u9501\u72b6\u6001\n    int c = getState();\n    \/\/\u5982\u679c\u6709\u7ebf\u7a0b\u83b7\u53d6\u5230\u4e86\u5199\u9501 \uff0c\u4e14\u83b7\u53d6\u5199\u9501\u7684\u4e0d\u662f\u5f53\u524d\u7ebf\u7a0b\u5219\u8fd4\u56de\u5931\u8d25\n    if (exclusiveCount(c) != 0 &amp;&amp;\n        getExclusiveOwnerThread() != current)\n        return -1;\n    \/\/\u83b7\u53d6\u8bfb\u9501\u7684\u91cd\u5165\u8ba1\u6570\n    int r = sharedCount(c);\n    \/\/\u5982\u679c\u8bfb\u7ebf\u7a0b\u4e0d\u5e94\u8be5\u88ab\u963b\u585e\uff0c\u4e14\u91cd\u5165\u8ba1\u6570\u5c0f\u4e8e\u6700\u5927\u503c\uff0c\u4e14CAS\u6267\u884c\u8bfb\u9501\u91cd\u5165\u8ba1\u6570+1\u6210\u529f\uff0c\u5219\u6267\u884c\u7ebf\u7a0b\u91cd\u5165\u7684\u8ba1\u6570\u52a01\u64cd\u4f5c\uff0c\u8fd4\u56de\u6210\u529f\n    if (!readerShouldBlock() &amp;&amp;\n        r &lt; MAX_COUNT &amp;&amp;\n        compareAndSetState(c, c + SHARED_UNIT)) {\n        \/\/\u5982\u679c\u8fd8\u672a\u6709\u7ebf\u7a0b\u83b7\u53d6\u5230\u8bfb\u9501\uff0c\u5219\u5c06firstReader\u8bbe\u7f6e\u4e3a\u5f53\u524d\u7ebf\u7a0b\uff0cfirstReaderHoldCount\u8bbe\u7f6e\u4e3a1\n        if (r == 0) {\n            firstReader = current;\n            firstReaderHoldCount = 1;\n        } else if (firstReader == current) {\n            \/\/\u5982\u679cfirstReader\u662f\u5f53\u524d\u7ebf\u7a0b\uff0c\u5219\u5c06firstReader\u7684\u91cd\u5165\u8ba1\u6570\u53d8\u91cffirstReaderHoldCount\u52a01\n            firstReaderHoldCount++;\n        } else {\n            \/\/\u5426\u5219\u8bf4\u660e\u6709\u81f3\u5c11\u4e24\u4e2a\u7ebf\u7a0b\u5171\u4eab\u8bfb\u9501\uff0c\u83b7\u53d6\u5171\u4eab\u9501\u91cd\u5165\u8ba1\u6570\u5668HoldCounter\n            \/\/\u4eceHoldCounter\u4e2d\u62ff\u5230\u5f53\u524d\u7ebf\u7a0b\u7684\u7ebf\u7a0b\u53d8\u91cfcachedHoldCounter\uff0c\u5c06\u6b64\u7ebf\u7a0b\u7684\u91cd\u5165\u8ba1\u6570count\u52a01\n            HoldCounter rh = cachedHoldCounter;\n            if (rh == null || rh.tid != getThreadId(current))\n                cachedHoldCounter = rh = readHolds.get();\n            else if (rh.count == 0)\n                readHolds.set(rh);\n            rh.count++;\n        }\n        return 1;\n    }\n    \/\/\u5982\u679c\u4e0a\u9762\u7684if\u6761\u4ef6\u6709\u4e00\u4e2a\u90fd\u4e0d\u6ee1\u8db3\uff0c\u5219\u8fdb\u5165\u5230\u8fd9\u4e2a\u65b9\u6cd5\u91cc\u8fdb\u884c\u6b7b\u5faa\u73af\u91cd\u65b0\u83b7\u53d6\n    return fullTryAcquireShared(current);\n}\n\/**\n * \u7528\u4e8e\u5904\u7406CAS\u64cd\u4f5cstate\u5931\u8d25\u548ctryAcquireShared\u4e2d\u672a\u6267\u884c\u83b7\u53d6\u53ef\u91cd\u5165\u9501\u52a8\u4f5c\u7684full\u65b9\u6cd5(\u8865\u507f\u65b9\u6cd5\uff1f)\n * Full version of acquire for reads, that handles CAS misses\n * and reentrant reads not dealt with in tryAcquireShared.\n *\/\nfinal int fullTryAcquireShared(Thread current) {\n    \/*\n     * \u6b64\u4ee3\u7801\u4e0etryAcquireShared\u4e2d\u7684\u4ee3\u7801\u6709\u90e8\u5206\u76f8\u4f3c\u7684\u5730\u65b9\uff0c\n     * \u4f46\u603b\u4f53\u4e0a\u66f4\u7b80\u5355\uff0c\u56e0\u4e3a\u4e0d\u4f1a\u4f7ftryAcquireShared\u4e0e\u91cd\u8bd5\u548c\u5ef6\u8fdf\u8bfb\u53d6\u4fdd\u6301\u8ba1\u6570\u4e4b\u95f4\u7684\u590d\u6742\u5224\u65ad\n     * This code is in part redundant with that in\n     * tryAcquireShared but is simpler overall by not\n     * complicating tryAcquireShared with interactions between\n     * retries and lazily reading hold counts.\n     *\/\n    HoldCounter rh = null;\n    \/\/\u6b7b\u5faa\u73af\n    for (;;) {\n        \/\/\u83b7\u53d6\u8bfb\u5199\u9501\u72b6\u6001\n        int c = getState();\n        \/\/\u5982\u679c\u6709\u7ebf\u7a0b\u83b7\u53d6\u5230\u4e86\u5199\u9501\n        if (exclusiveCount(c) != 0) {\n            \/\/\u5982\u679c\u83b7\u53d6\u5199\u9501\u7684\u7ebf\u7a0b\u4e0d\u662f\u5f53\u524d\u7ebf\u7a0b\uff0c\u8fd4\u56de\u5931\u8d25\n            if (getExclusiveOwnerThread() != current)\n                return -1;\n            \/\/ else we hold the exclusive lock; blocking here\n            \/\/ would cause deadlock.\n        } else if (readerShouldBlock()) {\/\/\u5982\u679c\u6ca1\u6709\u7ebf\u7a0b\u83b7\u53d6\u5230\u5199\u9501\uff0c\u4e14\u8bfb\u7ebf\u7a0b\u8981\u963b\u585e\n            \/\/ Make sure we're not acquiring read lock reentrantly\n            \/\/\u5982\u679c\u5f53\u524d\u7ebf\u7a0b\u4e3a\u7b2c\u4e00\u4e2a\u83b7\u53d6\u5230\u8bfb\u9501\u7684\u7ebf\u7a0b\n            if (firstReader == current) {\n                \/\/ assert firstReaderHoldCount &gt; 0;\n            } else { \/\/\u5982\u679c\u5f53\u524d\u7ebf\u7a0b\u4e0d\u662f\u7b2c\u4e00\u4e2a\u83b7\u53d6\u5230\u8bfb\u9501\u7684\u7ebf\u7a0b(\u4e5f\u5c31\u662f\u8bf4\u81f3\u5c11\u6709\u6709\u4e00\u4e2a\u7ebf\u7a0b\u83b7\u53d6\u5230\u4e86\u8bfb\u9501)\n                \/\/\n                if (rh == null) {\n                    rh = cachedHoldCounter;\n                    if (rh == null || rh.tid != getThreadId(current)) {\n                        rh = readHolds.get();\n                        if (rh.count == 0)\n                            readHolds.remove();\n                    }\n                }\n                if (rh.count == 0)\n                    return -1;\n            }\n        }\n        \/**\n         *\u4e0b\u9762\u662f\u65e2\u6ca1\u6709\u7ebf\u7a0b\u83b7\u53d6\u5199\u9501\uff0c\u5f53\u524d\u7ebf\u7a0b\u53c8\u4e0d\u9700\u8981\u963b\u585e\u7684\u60c5\u51b5\n         *\/\n        \/\/\u91cd\u5165\u6b21\u6570\u7b49\u4e8e\u6700\u5927\u91cd\u5165\u6b21\u6570\uff0c\u629b\u5f02\u5e38\n        if (sharedCount(c) == MAX_COUNT)\n            throw new Error(\"Maximum lock count exceeded\");\n        \/\/\u5982\u679c\u6267\u884cCAS\u64cd\u4f5c\u6210\u529f\u5c06\u8bfb\u5199\u9501\u7684\u91cd\u5165\u8ba1\u6570\u52a01\uff0c\u5219\u5bf9\u5f53\u524d\u6301\u6709\u8fd9\u4e2a\u5171\u4eab\u8bfb\u9501\u7684\u7ebf\u7a0b\u7684\u91cd\u5165\u8ba1\u6570\u52a01\uff0c\u7136\u540e\u8fd4\u56de\u6210\u529f\n        if (compareAndSetState(c, c + SHARED_UNIT)) {\n            if (sharedCount(c) == 0) {\n                firstReader = current;\n                firstReaderHoldCount = 1;\n            } else if (firstReader == current) {\n                firstReaderHoldCount++;\n            } else {\n                if (rh == null)\n                    rh = cachedHoldCounter;\n                if (rh == null || rh.tid != getThreadId(current))\n                    rh = readHolds.get();\n                else if (rh.count == 0)\n                    readHolds.set(rh);\n                rh.count++;\n                cachedHoldCounter = rh; \/\/ cache for release\n            }\n            return 1;\n        }\n    }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u91ca\u653e\u8bfb\u9501\u6e90\u7801\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/**\n  * Releases in shared mode.  Implemented by unblocking one or more\n  * threads if {@link #tryReleaseShared} returns true.\n  *\n  * @param arg the release argument.  This value is conveyed to\n  *        {@link #tryReleaseShared} but is otherwise uninterpreted\n  *        and can represent anything you like.\n  * @return the value returned from {@link #tryReleaseShared}\n  *\/\npublic final boolean releaseShared(int arg) {\n    if (tryReleaseShared(arg)) {\/\/\u5c1d\u8bd5\u91ca\u653e\u4e00\u6b21\u5171\u4eab\u9501\u8ba1\u6570\n        doReleaseShared();\/\/\u771f\u6b63\u91ca\u653e\u9501\n        return true;\n    }\n        return false;\n}\n\/**\n *\u6b64\u65b9\u6cd5\u8868\u793a\u8bfb\u9501\u7ebf\u7a0b\u91ca\u653e\u9501\u3002\n *\u9996\u5148\u5224\u65ad\u5f53\u524d\u7ebf\u7a0b\u662f\u5426\u4e3a\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0bfirstReader\uff0c\n *\u82e5\u662f\uff0c\u5219\u5224\u65ad\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0b\u5360\u6709\u7684\u8d44\u6e90\u6570firstReaderHoldCount\u662f\u5426\u4e3a1\uff0c\n  \u82e5\u662f\uff0c\u5219\u8bbe\u7f6e\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0bfirstReader\u4e3a\u7a7a\uff0c\u5426\u5219\uff0c\u5c06\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0b\u5360\u6709\u7684\u8d44\u6e90\u6570firstReaderHoldCount\u51cf1\uff1b\n  \u82e5\u5f53\u524d\u7ebf\u7a0b\u4e0d\u662f\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0b\uff0c\n  \u90a3\u4e48\u9996\u5148\u4f1a\u83b7\u53d6\u7f13\u5b58\u8ba1\u6570\u5668\uff08\u4e0a\u4e00\u4e2a\u8bfb\u9501\u7ebf\u7a0b\u5bf9\u5e94\u7684\u8ba1\u6570\u5668 \uff09\uff0c\n  \u82e5\u8ba1\u6570\u5668\u4e3a\u7a7a\u6216\u8005tid\u4e0d\u7b49\u4e8e\u5f53\u524d\u7ebf\u7a0b\u7684tid\u503c\uff0c\u5219\u83b7\u53d6\u5f53\u524d\u7ebf\u7a0b\u7684\u8ba1\u6570\u5668\uff0c\n  \u5982\u679c\u8ba1\u6570\u5668\u7684\u8ba1\u6570count\u5c0f\u4e8e\u7b49\u4e8e1\uff0c\u5219\u79fb\u9664\u5f53\u524d\u7ebf\u7a0b\u5bf9\u5e94\u7684\u8ba1\u6570\u5668\uff0c\n  \u5982\u679c\u8ba1\u6570\u5668\u7684\u8ba1\u6570count\u5c0f\u4e8e\u7b49\u4e8e0\uff0c\u5219\u629b\u51fa\u5f02\u5e38\uff0c\u4e4b\u540e\u518d\u51cf\u5c11\u8ba1\u6570\u5373\u53ef\u3002\n  \u65e0\u8bba\u4f55\u79cd\u60c5\u51b5\uff0c\u90fd\u4f1a\u8fdb\u5165\u6b7b\u5faa\u73af\uff0c\u8be5\u5faa\u73af\u53ef\u4ee5\u786e\u4fdd\u6210\u529f\u8bbe\u7f6e\u72b6\u6001state\n *\/\nprotected final boolean tryReleaseShared(int unused) {\n    \/\/ \u83b7\u53d6\u5f53\u524d\u7ebf\u7a0b\n    Thread current = Thread.currentThread();\n    if (firstReader == current) { \/\/ \u5f53\u524d\u7ebf\u7a0b\u4e3a\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0b\n        \/\/ assert firstReaderHoldCount &gt; 0;\n       if (firstReaderHoldCount == 1) \/\/ \u8bfb\u7ebf\u7a0b\u5360\u7528\u7684\u8d44\u6e90\u6570\u4e3a1\n            firstReader = null;\n        else \/\/ \u51cf\u5c11\u5360\u7528\u7684\u8d44\u6e90\n            firstReaderHoldCount--;\n   } else { \/\/ \u5f53\u524d\u7ebf\u7a0b\u4e0d\u4e3a\u7b2c\u4e00\u4e2a\u8bfb\u7ebf\u7a0b\n       \/\/ \u83b7\u53d6\u7f13\u5b58\u7684\u8ba1\u6570\u5668\n       HoldCounter rh = cachedHoldCounter;\n       if (rh == null || rh.tid != getThreadId(current)) \/\/ \u8ba1\u6570\u5668\u4e3a\u7a7a\u6216\u8005\u8ba1\u6570\u5668\u7684tid\u4e0d\u4e3a\u5f53\u524d\u6b63\u5728\u8fd0\u884c\u7684\u7ebf\u7a0b\u7684tid\n           \/\/ \u83b7\u53d6\u5f53\u524d\u7ebf\u7a0b\u5bf9\u5e94\u7684\u8ba1\u6570\u5668\n           rh = readHolds.get();\n       \/\/ \u83b7\u53d6\u8ba1\u6570\n       int count = rh.count;\n       if (count &lt;= 1) { \/\/ \u8ba1\u6570\u5c0f\u4e8e\u7b49\u4e8e1\n           \/\/ \u79fb\u9664\n           readHolds.remove();\n           if (count &lt;= 0) \/\/ \u8ba1\u6570\u5c0f\u4e8e\u7b49\u4e8e0\uff0c\u629b\u51fa\u5f02\u5e38\n               throw unmatchedUnlockException();\n       }\n       \/\/ \u51cf\u5c11\u8ba1\u6570\n       --rh.count;\n   }\n   for (;;) { \/\/ \u6b7b\u5faa\u73af\n       \/\/ \u83b7\u53d6\u72b6\u6001\n       int c = getState();\n       \/\/ \u83b7\u53d6\u72b6\u6001\n       int nextc = c - SHARED_UNIT;\n       if (compareAndSetState(c, nextc)) \/\/ \u6bd4\u8f83\u5e76\u8fdb\u884c\u8bbe\u7f6e\n           \/\/ Releasing the read lock has no effect on readers,\n           \/\/ but it may allow waiting writers to proceed if\n           \/\/ both read and write locks are now free.\n           return nextc == 0;\n   }\n}\n\/**\u771f\u6b63\u91ca\u653e\u9501\n* Release action for shared mode -- signals successor and ensures\n* propagation. (Note: For exclusive mode, release just amounts\n* to calling unparkSuccessor of head if it needs signal.)\n*\/\nprivate void doReleaseShared() {\n    \/*\n     * Ensure that a release propagates, even if there are other\n     * in-progress acquires\/releases.  This proceeds in the usual\n     * way of trying to unparkSuccessor of head if it needs\n     * signal. But if it does not, status is set to PROPAGATE to\n     * ensure that upon release, propagation continues.\n     * Additionally, we must loop in case a new node is added\n     * while we are doing this. Also, unlike other uses of\n     * unparkSuccessor, we need to know if CAS to reset status\n     * fails, if so rechecking.\n     *\/\n    for (;;) {\n        Node h = head;\n        if (h != null &amp;&amp; h != tail) {\n            int ws = h.waitStatus;\n            if (ws == Node.SIGNAL) {\n                if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0))\n                    continue;            \/\/ loop to recheck cases\n                unparkSuccessor(h);\n            }\n            else if (ws == 0 &amp;&amp;\n                     !compareAndSetWaitStatus(h, 0, Node.PROPAGATE))\n                continue;                \/\/ loop on failed CAS\n        }\n        if (h == head)                   \/\/ loop if head changed\n            break;\n    }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u901a\u8fc7\u5206\u6790\u53ef\u4ee5\u770b\u51fa\uff1a<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u7ebf\u7a0b\u6301\u6709\u8bfb\u9501\u7684\u60c5\u51b5\u4e0b\uff0c\u8be5\u7ebf\u7a0b\u4e0d\u80fd\u53d6\u5f97\u5199\u9501(\u56e0\u4e3a\u83b7\u53d6\u5199\u9501\u7684\u65f6\u5019\uff0c\u5982\u679c\u53d1\u73b0\u5f53\u524d\u7684\u8bfb\u9501\u88ab\u5360\u7528\uff0c\u5c31\u9a6c\u4e0a\u83b7\u53d6\u5931\u8d25\uff0c\u4e0d\u7ba1\u8bfb\u9501\u662f\u4e0d\u662f\u88ab\u5f53\u524d\u7ebf\u7a0b\u6301\u6709)\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u7ebf\u7a0b\u6301\u6709\u5199\u9501\u7684\u60c5\u51b5\u4e0b\uff0c\u8be5\u7ebf\u7a0b\u53ef\u4ee5\u7ee7\u7eed\u83b7\u53d6\u8bfb\u9501\uff08\u83b7\u53d6\u8bfb\u9501\u65f6\u5982\u679c\u53d1\u73b0\u5199\u9501\u88ab\u5360\u7528\uff0c\u53ea\u6709\u5199\u9501\u6ca1\u6709\u88ab\u5f53\u524d\u7ebf\u7a0b\u5360\u7528\u7684\u60c5\u51b5\u624d\u4f1a\u83b7\u53d6\u5931\u8d25\uff09\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">LongAdder<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u9ad8\u5e76\u53d1\u7684\u60c5\u51b5\u4e0b\uff0c\u6211\u4eec\u5bf9\u4e00\u4e2a Integer \u7c7b\u578b\u7684\u6574\u6570\u76f4\u63a5\u8fdb\u884c i++ \u7684\u65f6\u5019\uff0c\u65e0\u6cd5\u4fdd\u8bc1\u64cd\u4f5c\u7684\u539f\u5b50\u6027\uff0c\u4f1a\u51fa\u73b0\u7ebf\u7a0b\u5b89\u5168\u7684\u95ee\u9898\u3002\u4e3a\u6b64\u6211\u4eec\u4f1a\u7528 juc \u4e0b\u7684 AtomicInteger \uff0c\u5b83\u662f\u4e00\u4e2a\u63d0\u4f9b\u539f\u5b50\u64cd\u4f5c\u7684 Interger \u7c7b\uff0c\u5185\u90e8\u4e5f\u662f\u901a\u8fc7 CAS \u5b9e\u73b0\u7ebf\u7a0b\u5b89\u5168\u7684\u3002\u4f46\u5f53\u5927\u91cf\u7ebf\u7a0b\u540c\u65f6\u53bb\u8bbf\u95ee\u65f6\uff0c\u5c31\u4f1a\u56e0\u4e3a\u5927\u91cf\u7ebf\u7a0b\u6267\u884c CAS \u64cd\u4f5c\u5931\u8d25\u800c\u8fdb\u884c\u7a7a\u65cb\u8f6c\uff0c\u5bfc\u81f4 CPU \u8d44\u6e90\u6d88\u8017\u8fc7\u591a\uff0c\u800c\u4e14\u6267\u884c\u6548\u7387\u4e5f\u4e0d\u9ad8\u3002 Doug Lea \u5927\u795e\u5e94\u8be5\u4e5f\u4e0d\u6ee1\u610f\uff0c\u4e8e\u662f\u5728 JDK1.8 \u4e2d\u5bf9 CAS \u8fdb\u884c\u4e86\u4f18\u5316\uff0c\u63d0\u4f9b\u4e86 LongAdder \uff0c\u5b83\u662f\u57fa\u4e8e\u4e86 CAS \u5206\u6bb5\u9501\u7684\u601d\u60f3\u5b9e\u73b0\u7684\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u7ebf\u7a0b\u53bb\u8bfb\u5199\u4e00\u4e2a LongAdder \u7c7b\u578b\u7684\u53d8\u91cf\u65f6\uff0c\u6d41\u7a0b\u5982\u4e0b\uff1a<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img decoding=\"async\" src=\"https:\/\/gitee.com\/xmtblog\/img\/raw\/master\/1581595881391.jpg\" alt=\"\" \/><figcaption>LongAdder \u539f\u7406<\/figcaption><\/figure><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">LongAdder \u4e5f\u662f\u57fa\u4e8e Unsafe \u63d0\u4f9b\u7684 CAS \u64cd\u4f5c +valitale \u53bb\u5b9e\u73b0\u7684\u3002\u5728 LongAdder \u7684\u7236\u7c7b Striped64 \u4e2d\u7ef4\u62a4\u7740\u4e00\u4e2a base \u53d8\u91cf\u548c\u4e00\u4e2a cell \u6570\u7ec4\uff0c\u5f53\u591a\u4e2a\u7ebf\u7a0b\u64cd\u4f5c\u4e00\u4e2a\u53d8\u91cf\u7684\u65f6\u5019\uff0c\u5148\u4f1a\u5728\u8fd9\u4e2a base \u53d8\u91cf\u4e0a\u8fdb\u884c cas \u64cd\u4f5c\uff0c\u5f53\u5b83\u53d1\u73b0\u7ebf\u7a0b\u589e\u591a\u7684\u65f6\u5019\uff0c\u5c31\u4f1a\u4f7f\u7528 cell \u6570\u7ec4\u3002\u6bd4\u5982\u5f53 base \u5c06\u8981\u66f4\u65b0\u7684\u65f6\u5019\u53d1\u73b0\u7ebf\u7a0b\u589e\u591a\uff08\u4e5f\u5c31\u662f\u8c03\u7528 casBase \u65b9\u6cd5\u66f4\u65b0 base \u503c\u5931\u8d25\uff09\uff0c\u90a3\u4e48\u5b83\u4f1a\u81ea\u52a8\u4f7f\u7528 cell \u6570\u7ec4\uff0c\u6bcf\u4e00\u4e2a\u7ebf\u7a0b\u5bf9\u5e94\u4e8e\u4e00\u4e2a cell \uff0c\u5728\u6bcf\u4e00\u4e2a\u7ebf\u7a0b\u4e2d\u5bf9\u8be5 cell \u8fdb\u884c cas \u64cd\u4f5c\uff0c\u8fd9\u6837\u5c31\u53ef\u4ee5\u5c06\u5355\u4e00 value \u7684\u66f4\u65b0\u538b\u529b\u5206\u62c5\u5230\u591a\u4e2a value \u4e2d\u53bb\uff0c\u964d\u4f4e\u5355\u4e2a value \u7684 \u201c\u70ed\u5ea6\u201d\uff0c\u540c\u65f6\u4e5f\u51cf\u5c11\u4e86\u5927\u91cf\u7ebf\u7a0b\u7684\u7a7a\u8f6c\uff0c\u63d0\u9ad8\u5e76\u53d1\u6548\u7387\uff0c\u5206\u6563\u5e76\u53d1\u538b\u529b\u3002\u8fd9\u79cd\u5206\u6bb5\u9501\u9700\u8981\u989d\u5916\u7ef4\u62a4\u4e00\u4e2a\u5185\u5b58\u7a7a\u95f4 cells \uff0c\u4e0d\u8fc7\u5728\u9ad8\u5e76\u53d1\u573a\u666f\u4e0b\uff0c\u8fd9\u70b9\u6210\u672c\u51e0\u4e4e\u53ef\u4ee5\u5ffd\u7565\u3002\u5206\u6bb5\u9501\u662f\u4e00\u79cd\u4f18\u79c0\u7684\u4f18\u5316\u601d\u60f3\uff0c juc \u4e2d\u63d0\u4f9b\u7684\u7684 ConcurrentHashMap \u4e5f\u662f\u57fa\u4e8e\u5206\u6bb5\u9501\u4fdd\u8bc1\u8bfb\u5199\u64cd\u4f5c\u7684\u7ebf\u7a0b\u5b89\u5168\u3002<\/p>\n<!-- <audio autoplay=\"autoplay\" height=\"100\" width=\"100\" hidden=\"true\"><source src=\"https:\/\/c.coka.la\/orAvPR.mp3\" type=\"audio\/mp3\"\/><\/audio><img decoding=\"async\" src=\"https:\/\/images.weserv.nl\/?url=https:\/\/ws3.sinaimg.cn\/large\/8fa5dcfcgy1g4em3rzar5j20ib089ae0.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/> --><p><!-- <img decoding=\"async\" src=\"https:\/\/raw.githubusercontent.com\/xmt1139057136\/xttblog\/master\/8fa5dcfcgy1g4em3rzar5j20ib089ae0.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/>--><img decoding=\"async\" src=\"https:\/\/saas.51autoparts.cn\/api\/admin\/sys-file\/oss\/file?fileName=84db51f8561e448f9a4fda2eff0811f9.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/><\/p><p>\u6700\u540e\uff0c\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u4e2a\u4eba\u5fae\u4fe1\u516c\u4f17\u53f7\uff1a\u4e1a\u4f59\u8349\uff08yyucao\uff09\uff01<b>\u53ef\u52a0\u4f5c\u8005\u5fae\u4fe1\u53f7\uff1a<font color=\"red\">xttblog2<\/font>\u3002\u5907\u6ce8\uff1a\u201c1\u201d\uff0c\u6dfb\u52a0\u535a\u4e3b\u5fae\u4fe1\u62c9\u4f60\u8fdb\u5fae\u4fe1\u7fa4\u3002\u5907\u6ce8\u9519\u8bef\u4e0d\u4f1a\u540c\u610f\u597d\u53cb\u7533\u8bf7\u3002<\/b>\u518d\u6b21\u611f\u8c22\u60a8\u7684\u5173\u6ce8\uff01\u540e\u7eed\u6709\u7cbe\u5f69\u5185\u5bb9\u4f1a\u7b2c\u4e00\u65f6\u95f4\u53d1\u7ed9\u60a8\uff01\u539f\u521b\u6587\u7ae0\u6295\u7a3f\u8bf7\u53d1\u9001\u81f3532009913@qq.com\u90ae\u7bb1\u3002\u5546\u52a1\u5408\u4f5c\u4e5f\u53ef\u6dfb\u52a0\u4f5c\u8005\u5fae\u4fe1\u8fdb\u884c\u8054\u7cfb\uff01<\/p><p>\u672c\u6587\u539f\u6587\u51fa\u5904\uff1a<a href=\"https:\/\/www.xttblog.com\">\u4e1a\u4f59\u8349<\/a>\uff1a &raquo; <a href=\"https:\/\/www.xttblog.com\/?p=4779\">\u804a\u804a Java \u7684\u51e0\u628a JVM \u7ea7\u9501<\/a><\/p><!-- <div class=\"bd-reward-stl\"><button id=\"bdRewardBtn\"><span><\/span><\/button><\/div> -->","protected":false},"excerpt":{"rendered":"<p>\u7b80\u4ecb 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[&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[2079,2080,1761,1751,2081],"class_list":["post-4779","post","type-post","status-publish","format-standard","hentry","category-java","tag-longadder","tag-readlock","tag-reentrantreadwritelock","tag-unsafe","tag-writelock"],"_links":{"self":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/4779","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4779"}],"version-history":[{"count":1,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/4779\/revisions"}],"predecessor-version":[{"id":4780,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/4779\/revisions\/4780"}],"wp:attachment":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4779"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4779"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4779"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}