{"id":865,"date":"2018-07-20T09:03:14","date_gmt":"2018-07-20T01:03:14","guid":{"rendered":"https:\/\/blog.jsjs.org\/?p=865"},"modified":"2018-07-20T09:03:14","modified_gmt":"2018-07-20T01:03:14","slug":"%e3%80%90jvm%e3%80%91jvm%e7%b3%bb%e5%88%97%e4%b9%8b%e5%86%85%e5%ad%98%e6%a8%a1%e5%9e%8b%ef%bc%88%e5%85%ad%ef%bc%89","status":"publish","type":"post","link":"https:\/\/blog.jsjs.org\/?p=865","title":{"rendered":"\u3010JVM\u3011JVM\u7cfb\u5217\u4e4b\u5185\u5b58\u6a21\u578b\uff08\u516d\uff09"},"content":{"rendered":"

\u4e00\u3001\u524d\u8a00<\/strong><\/p>\n

\u7ecf\u8fc7\u524d\u9762\u7684\u5b66\u4e60\uff0c\u6211\u4eec\u7ec8\u4e8e\u8fdb\u5165\u4e86\u865a\u62df\u673a\u6700\u540e\u4e00\u90e8\u5206\u7684\u5b66\u4e60\uff0c\u5185\u5b58\u6a21\u578b\u3002\u7406\u89e3\u5185\u5b58\u6a21\u578b\u5bf9\u6211\u4eec\u7406\u89e3\u865a\u62df\u673a\u3001\u6b63\u786e\u4f7f\u7528\u591a\u7ebf\u7a0b\u7f16\u7a0b\u63d0\u4f9b\u5f88\u5927\u5e2e\u52a9\u3002\u4e0b\u9762\u5f00\u59cb\u6b63\u5f0f\u5b66\u4e60\u3002<\/p>\n

\u4e8c\u3001Java\u5e76\u53d1\u57fa\u7840<\/strong><\/p>\n

\u5728\u5e76\u53d1\u7f16\u7a0b\u4e2d\u5b58\u5728\u4e24\u4e2a\u5173\u952e\u95ee\u9898\u2460\u7ebf\u7a0b\u4e4b\u95f4\u5982\u4f55\u901a\u4fe1 \u2461\u7ebf\u7a0b\u4e4b\u95f4\u5982\u4f55\u540c\u6b65\u3002<\/p>\n

2.1 \u901a\u4fe1<\/p>\n

\u901a\u4fe1\u662f\u6307\u7ebf\u7a0b\u4e4b\u95f4\u4ee5\u4f55\u79cd\u673a\u5236\u6765\u4ea4\u6362\u4fe1\u606f\u3002\u5728\u547d\u4ee4\u5f0f\u7f16\u7a0b\u4e2d\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u7684\u901a\u4fe1\u673a\u5236\u6709\u4e24\u79cd\uff1a\u5171\u4eab\u5185\u5b58\u548c\u6d88\u606f\u4f20\u9012\u3002<\/p>\n

\u5728\u5171\u4eab\u5185\u5b58\u7684\u5e76\u53d1\u6a21\u578b\u91cc\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u5171\u4eab\u7a0b\u5e8f\u7684\u516c\u5171\u72b6\u6001\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u901a\u8fc7\u5199-\u8bfb\u5185\u5b58\u4e2d\u7684\u516c\u5171\u72b6\u6001\u6765\u9690\u5f0f\u8fdb\u884c\u901a\u4fe1\u3002<\/p>\n

\u5728\u6d88\u606f\u4f20\u9012\u7684\u5e76\u53d1\u6a21\u578b\u91cc\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u6ca1\u6709\u516c\u5171\u72b6\u6001\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u5fc5\u987b\u901a\u8fc7\u660e\u786e\u7684\u53d1\u9001\u6d88\u606f\u6765\u663e\u5f0f\u8fdb\u884c\u901a\u4fe1\u3002<\/p>\n

2.2 \u540c\u6b65<\/p>\n

\u540c\u6b65\u662f\u6307\u7a0b\u5e8f\u7528\u4e8e\u63a7\u5236\u4e0d\u540c\u7ebf\u7a0b\u4e4b\u95f4\u64cd\u4f5c\u53d1\u751f\u76f8\u5bf9\u987a\u5e8f\u7684\u673a\u5236\u3002<\/p>\n

\u5728\u5171\u4eab\u5185\u5b58\u5e76\u53d1\u6a21\u578b\u91cc\uff0c\u540c\u6b65\u662f\u663e\u5f0f\u8fdb\u884c\u7684\u3002\u7a0b\u5e8f\u5458\u5fc5\u987b\u663e\u5f0f\u6307\u5b9a\u67d0\u4e2a\u65b9\u6cd5\u6216\u67d0\u6bb5\u4ee3\u7801\u9700\u8981\u5728\u7ebf\u7a0b\u4e4b\u95f4\u4e92\u65a5\u8bbf\u95ee\u3002<\/p>\n

\u5728\u6d88\u606f\u4f20\u9012\u7684\u5e76\u53d1\u6a21\u578b\u91cc\uff0c\u7531\u4e8e\u6d88\u606f\u7684\u53d1\u9001\u5fc5\u987b\u5728\u6d88\u606f\u7684\u63a5\u6536\u4e4b\u524d\uff0c \u56e0\u6b64\u540c\u6b65\u662f\u9690\u5f0f\u8fdb\u884c\u7684\u3002<\/p>\n

Java\u5e76\u53d1\u91c7\u7528\u7684\u662f\u5171\u4eab\u5185\u5b58\u6a21\u578b\uff0c\u901a\u4fe1\u9690\u5f0f\u8fdb\u884c\uff1b\u540c\u6b65\u663e\u793a\u6307\u5b9a\u3002<\/p>\n

\u4e09\u3001Java\u5185\u5b58\u6a21\u578b<\/strong><\/p>\n

Java\u5185\u5b58\u6a21\u578bJMM\uff08Java Memory Model\uff09\u4e3b\u8981\u76ee\u6807\u662f\u5b9a\u4e49\u7a0b\u5e8f\u4e2d\u5404\u4e2a\u53d8\u91cf(\u975e\u7ebf\u7a0b\u79c1\u6709)\u7684\u8bbf\u95ee\u89c4\u5219\uff0c\u5373\u5728\u865a\u62df\u673a\u4e2d\u5c06\u53d8\u91cf\u5b58\u50a8\u5230\u5185\u5b58\u548c\u4ece\u5185\u5b58\u53d6\u51fa\u53d8\u91cf\u8fd9\u6837\u7684\u5e95\u5c42\u7ec6\u8282\u3002Java\u4e2d\u6bcf\u4e2a\u7ebf\u7a0b\u90fd\u6709\u81ea\u5df1\u79c1\u6709\u7684\u5de5\u4f5c\u5185\u5b58\u3002\u5de5\u4f5c\u5185\u5b58\u4fdd\u5b58\u4e86\u88ab\u8be5\u7ebf\u7a0b\u4f7f\u7528\u7684\u53d8\u91cf\u7684\u4e3b\u5185\u5b58\u526f\u672c\u62f7\u8d1d\uff0c\u7ebf\u7a0b\u5bf9\u53d8\u91cf\u7684\u8bfb\u5199\u64cd\u4f5c\u90fd\u5fc5\u987b\u5728\u5de5\u4f5c\u5185\u5b58\u8fdb\u884c\uff0c\u65e0\u6cd5\u76f4\u63a5\u8bfb\u5199\u4e3b\u5185\u5b58\u4e2d\u7684\u53d8\u91cf\u3002\u4e24\u4e2a\u7ebf\u7a0b\u65e0\u6cd5\u76f4\u63a5\u8bbf\u95ee\u5bf9\u65b9\u7684\u5de5\u4f5c\u5185\u5b58\u3002<\/p>\n

3.1 \u7ebf\u7a0b\u3001\u5de5\u4f5c\u5185\u5b58\u3001\u5185\u5b58\u5173\u7cfb<\/p>\n

\u7406\u89e3\u7ebf\u7a0b\u3001\u4e3b\u5185\u5b58\u3001\u5de5\u4f5c\u5185\u5b58\u4e4b\u95f4\u7684\u5173\u7cfb\u65f6\uff0c\u6211\u4eec\u53ef\u4ee5\u7c7b\u6bd4\u7269\u7406\u673a\u4e2dCPU\u3001\u9ad8\u901f\u7f13\u5b58\u3001\u5185\u5b58\u4e4b\u95f4\u5173\u7cfb\uff0c\u5b66\u8fc7\u8ba1\u7b97\u673a\u7ec4\u6210\u539f\u7406\uff0c\u6211\u4eec\u77e5\u9053CPU\u3001\u9ad8\u901f\u7f13\u5b58\u3001\u5185\u5b58\u4e4b\u95f4\u7684\u5173\u7cfb\u5982\u4e0b<\/p>\n

\"\"<\/p>\n

\u7ebf\u7a0b\u3001\u4e3b\u5185\u5b58\u3001\u5de5\u4f5c\u5185\u5b58\u7684\u5173\u7cfb\u56fe\u5982\u4e0b<\/p>\n

\"\"<\/p>\n

\u8bf4\u660e\uff1a\u7ebf\u7a0b\u7684\u5de5\u4f5c\u5185\u5b58\u53ef\u4ee5\u7c7b\u6bd4\u9ad8\u901f\u7f13\u5b58\uff0cJMM\u63a7\u53ef\u4ee5\u7c7b\u6bd4\u7f13\u5b58\u4e00\u81f4\u6027\u534f\u8bae\uff0c\u662f\u5de5\u4f5c\u5185\u5b58\u4e0e\u4e3b\u5185\u5b58\u8fdb\u884c\u4fe1\u606f\u4ea4\u6362\u7684\u5177\u4f53\u534f\u8bae\u3002\u82e5\u7ebf\u7a0bA\u8981\u4e0e\u7ebf\u7a0bB\u901a\u4fe1(\u8bbf\u95ee\u53d8\u91cf)\u3002\u9996\u5148\uff0c\u7ebf\u7a0bA\u628a\u5de5\u4f5c\u7ebf\u7a0b\u4e2d\u7684\u5171\u4eab\u53d8\u91cf\u5237\u65b0\u5230\u4e3b\u5185\u5b58\u4e2d\u3002\u7136\u540e\uff0c\u7ebf\u7a0bB\u4ece\u4e3b\u5185\u5b58\u8bfb\u53d6\u66f4\u65b0\u8fc7\u7684\u53d8\u91cf\u3002<\/p>\n

3.2 \u5185\u5b58\u95f4\u901a\u4fe1\u7684\u6307\u4ee4<\/p>\n

\u5185\u5b58\u89c1\u901a\u4fe1\uff0c\u4e3b\u8981\u6307\u7ebf\u7a0b\u79c1\u6709\u7684\u5de5\u4f5c\u5185\u5b58\u4e0e\u4e3b\u5185\u5b58\u4e4b\u95f4\u7684\u901a\u4fe1\uff0c\u5982\u7ebf\u7a0b\u95f4\u5171\u4eab\u53d8\u91cf\u7684\u4f20\u9012\u3002\u4e3b\u8981\u6709\u5982\u4e0b\u64cd\u4f5c\u3002<\/p>\n

\"\"<\/p>\n

\u8bf4\u660e\uff1a\u2460\u53d8\u91cf\u4ece\u4e3b\u5185\u5b58\u653e\u5165\u5de5\u4f5c\u5185\u5b58\u53d8\u91cf\u526f\u672c\u4e2d\u5b9e\u9645\u662f\u5206\u4e3a\u4e24\u6b65\u7684\uff0c\u7b2c\u4e00\u6b65\u662f\u5148\u628a\u4e3b\u5185\u5b58\u7684\u503c\u653e\u5728\u5de5\u4f5c\u5185\u5b58\u4e2d\uff0c\u6b64\u65f6\u8fd8\u6ca1\u6709\u653e\u5165\u53d8\u91cf\u526f\u672c\u4e2d\uff1b\u7b2c\u4e8c\u90e8\u628a\u5df2\u7ecf\u653e\u5728\u5de5\u4f5c\u5185\u5b58\u7684\u503c\u653e\u5165\u53d8\u91cf\u526f\u672c\u4e2d\u3002\u76f8\u53cd\uff0c\u53d8\u91cf\u526f\u672c\u4ece\u5de5\u4f5c\u5185\u5b58\u5230\u4e3b\u5185\u5b58\u4e5f\u662f\u5206\u4e3a\u4e24\u6b65\uff0c\u4e0e\u524d\u9762\u7c7b\u4f3c\uff0c\u4e0d\u518d\u7d2f\u8d58\u3002\u603b\u4e4b\uff0c\u4e24\u4e2a\u5185\u5b58\u7a7a\u95f4\u7684\u53d8\u91cf\u503c\u7684\u4f20\u9012\u9700\u8981\u4e24\u4e2a\u64cd\u4f5c\u624d\u80fd\u5b8c\u6210\uff0c\u8fd9\u6837\u505a\u662f\u4e3a\u4e86\u63d0\u9ad8cpu\u7684\u6548\u7387\uff0c\u4e0d\u7b49\u5f85\u4e3b\u5185\u5b58\u5199\u5165\u5b8c\u6210\u3002\u2461read\u3001load\u64cd\u4f5c\uff1bstore\u3001write\u64cd\u4f5c\u5fc5\u987b\u6309\u987a\u5e8f\u6267\u884c\uff08\u5e76\u975e\u8fde\u7eed\u6267\u884c\uff09\u3002<\/p>\n

\u4e0a\u8ff0\u76848\u4e2a\u64cd\u4f5c\u9700\u8981\u6ee1\u8db3\u5982\u4e0b\u89c4\u5219<\/p>\n

\"\"\u3000\u30003.3 \u91cd\u6392\u5e8f<\/p>\n

\u5728\u6267\u884c\u7a0b\u5e8f\u65f6\u4e3a\u4e86\u63d0\u9ad8\u6027\u80fd\uff0c\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u5e38\u5e38\u4f1a\u5bf9\u6307\u4ee4\u505a\u91cd\u6392\u5e8f\u3002\u91cd\u6392\u5e8f\u4f1a\u9075\u5b88\u6570\u636e\u7684\u4f9d\u8d56\u6027\uff0c\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u4e0d\u4f1a\u6539\u53d8\u5b58\u5728\u6570\u636e\u4f9d\u8d56\u5173\u7cfb\u7684\u4e24\u4e2a\u64cd\u4f5c\u7684\u6267\u884c\u987a\u5e8f\u3002\u91cd\u6392\u5e8f\u5206\u4e3a\u5982\u4e0b\u4e09\u79cd\u7c7b\u578b\u3002<\/p>\n

1. \u7f16\u8bd1\u5668\u4f18\u5316\u7684\u91cd\u6392\u5e8f\u3002\u7f16\u8bd1\u5668\u5728\u4e0d\u6539\u53d8\u5355\u7ebf\u7a0b\u7a0b\u5e8f\u8bed\u4e49\u7684\u524d\u63d0\u4e0b\uff0c\u53ef\u4ee5\u91cd\u65b0\u5b89\u6392\u8bed\u53e5\u7684\u6267\u884c\u987a\u5e8f\u3002<\/p>\n

2. \u6307\u4ee4\u7ea7\u5e76\u884c\u7684\u91cd\u6392\u5e8f\u3002\u73b0\u4ee3\u5904\u7406\u5668\u91c7\u7528\u4e86\u6307\u4ee4\u7ea7\u5e76\u884c\u6280\u672f\uff08Instruction-Level Parallelism\uff0c ILP\uff09\u6765\u5c06\u591a\u6761\u6307\u4ee4\u91cd\u53e0\u6267\u884c\u3002\u5982\u679c\u4e0d\u5b58\u5728\u6570\u636e\u4f9d\u8d56\u6027\uff0c\u5904\u7406\u5668\u53ef\u4ee5\u6539\u53d8\u8bed\u53e5\u5bf9\u5e94\u673a\u5668\u6307\u4ee4\u7684\u6267\u884c\u987a\u5e8f\u3002<\/p>\n

3. \u5185\u5b58\u7cfb\u7edf\u7684\u91cd\u6392\u5e8f\u3002\u7531\u4e8e\u5904\u7406\u5668\u4f7f\u7528\u7f13\u5b58\u548c\u8bfb\/\u5199\u7f13\u51b2\u533a\uff0c\u8fd9\u4f7f\u5f97\u52a0\u8f7d\u548c\u5b58\u50a8\u64cd \u4f5c\u770b\u4e0a\u53bb\u53ef\u80fd\u662f\u5728\u4e71\u5e8f\u6267\u884c\u3002<\/p>\n

\u800c\u6211\u4eec\u7f16\u5199\u7684Java\u6e90\u7a0b\u5e8f\u4e2d\u7684\u8bed\u53e5\u987a\u5e8f\u5e76\u4e0d\u5bf9\u5e94\u6307\u4ee4\u4e2d\u7684\u76f8\u5e94\u987a\u5e8f\uff0c\u5982\uff08int a = 0; int b = 0\uff1b\u7ffb\u8bd1\u6210\u673a\u5668\u6307\u4ee4\u540e\u5e76\u4e0d\u80fd\u4fdd\u8bc1a = 0\u64cd\u4f5c\u5728b = 0\u64cd\u4f5c\u4e4b\u524d\uff09\u3002\u56e0\u4e3a\u7f16\u8bd1\u5668\u3001\u5904\u7406\u5668\u4f1a\u5bf9\u6307\u4ee4\u8fdb\u884c\u91cd\u6392\u5e8f\uff0c\u901a\u5e38\u800c\u8a00\uff0cJava\u6e90\u7a0b\u5e8f\u53d8\u6210\u6700\u540e\u7684\u673a\u5668\u6267\u884c\u6307\u4ee4\u4f1a\u7ecf\u8fc7\u5982\u4e0b\u7684\u91cd\u6392\u5e8f\u3002<\/p>\n

\"\"<\/p>\n

\u8bf4\u660e\uff1a\u2460\u7f16\u8bd1\u5668\u4f18\u5316\u91cd\u6392\u5e8f\u5c5e\u4e8e\u7f16\u8bd1\u5668\u91cd\u6392\u5e8f\uff0c\u6307\u4ee4\u7ea7\u5e76\u884c\u91cd\u6392\u5e8f\u3001\u5185\u5b58\u7cfb\u7edf\u91cd\u6392\u5e8f\u5c5e\u4e8e\u5904\u7406\u5668\u91cd\u6392\u5e8f\u3002\u2461\u8fd9\u4e9b\u91cd\u6392\u5e8f\u53ef\u80fd\u4f1a\u5bfc\u81f4\u591a\u7ebf\u7a0b\u7a0b\u5e8f\u51fa\u73b0\u5185\u5b58\u53ef\u89c1\u6027\u95ee\u9898\u3002\u2462JMM\u7f16\u8bd1\u5668\u91cd\u6392\u5e8f\u89c4\u5219\u4f1a\u7981\u6b62\u7279\u5b9a\u7c7b\u578b\u7684\u7f16\u8bd1\u5668\u91cd\u6392\u5e8f\u3002\u2463JMM\u7684\u5904\u7406\u5668\u91cd\u6392\u5e8f\u4f1a\u8981\u6c42Java\u7f16\u8bd1\u5668\u5728\u751f\u6210\u6307\u4ee4\u5e8f\u5217\u65f6\uff0c\u63d2\u5165\u7279\u5b9a\u7c7b\u578b\u7684\u5185\u5b58\u5c4f\u969c\u6307\u4ee4\uff0c\u901a\u8fc7\u5185\u5b58\u5c4f\u969c\u6307\u4ee4\u6765\u7981\u6b62\u7279\u5b9a\u7c7b\u578b\u7684\u5904\u7406\u5668\u91cd\u6392\u5e8f\u3002<\/p>\n

\u4e0b\u9762\u4e00\u4e2a\u4f8b\u5b50\u8bf4\u660e\u4e86\u91cd\u6392\u5e8f<\/p>\n

\"\"<\/p>\n

\u4e0b\u9762\u662fProcess A\u4e0eProcess B\u4e0e\u5185\u5b58\u4e4b\u95f4\u7684\u4ea4\u4e92\u56fe<\/p>\n

\"\"<\/p>\n

\u5bf9\u4e8e\u6700\u540e\u7684\u7ed3\u679cx = y = 0\u800c\u8a00\uff0c\u4ece\u5185\u5b58\u7684\u89d2\u5ea6\u770b\uff0c\u6574\u4e2a\u6307\u4ee4\u5e8f\u5217\u53ef\u80fd\u5982\u4e0b\uff0cA2 -> B2 -> A1 -> B2 -> A3 -> B3\u3002\u6309\u7167\u8fd9\u6837\u7684\u6307\u4ee4\u6392\u5e8f\uff0c\u6700\u540e\u5f97\u5230\u7684\u7ed3\u679c\u5c31\u65f6x = y = 0\u3002<\/p>\n

\u8bf4\u660e\uff1a\u2460\u4ece\u5185\u5b58\u89d2\u5ea6\u770b\uff0cA1\u4e0eA3\u64cd\u4f5c\u4e00\u8d77\u624d\u7b97\u662f\u5b8c\u6210\u4e86a\u53d8\u91cf\u7684\u5199\uff0cA1\u64cd\u4f5c\u662f\u5728\u5904\u7406\u5668A\u7684\u7f13\u51b2\u533a\u4e2d\u5b8c\u6210\u5199\uff0c\u4e4b\u540eA3\u64cd\u4f5c\u5c06\u7f13\u51b2\u533a\u7684\u53d8\u91cf\u503c\u540c\u6b65\u5230\u5185\u5b58\u4e2d\u3002\u2461\u5728\u7a0b\u5e8f\u4e2d\uff0cA1\u53d1\u751f\u5728A2\u4e4b\u524d\uff0c\u7136\u800c\u5b9e\u9645\u7684\u6307\u4ee4\u5e8f\u5217\u4e2d\uff0cA2\u53d1\u751f\u5728A1\u4e4b\u524d\uff0c\u8fd9\u5c31\u662f\u53d1\u751f\u4e86\u91cd\u6392\u5e8f\uff0c\u5904\u7406\u5668\u64cd\u4f5c\u5185\u5b58\u7684\u987a\u5e8f\u53d1\u751f\u4e86\u53d8\u5316\u3002\u540c\u7406\uff0cB1\u4e0eB2\u6307\u4ee4\u4e5f\u53d1\u751f\u4e86\u91cd\u6392\u5e8f\u3002<\/p>\n

3.4 \u5185\u5b58\u5c4f\u969c\u6307\u4ee4<\/p>\n

\u4e3a\u4e86\u4fdd\u8bc1\u5185\u5b58\u53ef\u89c1\u6027\uff0cJava\u7f16\u8bd1\u5668\u5728\u751f\u6210\u6307\u4ee4\u5e8f\u5217\u7684\u9002\u5f53\u4f4d\u7f6e\u4f1a\u63d2\u5165\u5185\u5b58\u5c4f\u969c\u6307\u4ee4\u6765\u7981\u6b62\u7279\u5b9a\u7c7b\u578b\u7684\u5904\u7406\u5668\u91cd\u6392\u5e8f\u3002\u5185\u5b58\u5c4f\u969c\u6307\u4ee4\u5206\u4e3a\u5982\u4e0b\u56db\u79cd<\/p>\n

\"\"<\/p>\n

3.5 \u5148\u884c\u53d1\u751f\u539f\u5219\uff08happens before\uff09<\/p>\n

\u5148\u884c\u53d1\u751f\u539f\u5219\u662f\u5224\u65ad\u6570\u636e\u662f\u5426\u5b58\u5728\u7ade\u4e89\u3001\u7ebf\u7a0b\u662f\u5426\u5b89\u5168\u7684\u4e3b\u8981\u4f9d\u636e\u3002\u5982\u679c\u4e00\u4e2a\u64cd\u4f5c\u6267\u884c\u7684\u7ed3\u679c\u9700\u8981\u5bf9\u53e6\u4e00\u4e2a\u64cd\u4f5c\u53ef\u89c1\uff0c\u90a3\u4e48\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u4e4b\u95f4\u5fc5\u987b\u8981\u5b58\u5728 happens-before \u5173\u7cfb\uff0c\u5982\u5982\u679c\u64cd\u4f5cA\u5148\u884c\u53d1\u751f\u4e0e\u64cd\u4f5cB\uff0c\u5373A\u64cd\u4f5c\u4ea7\u751f\u7684\u7ed3\u679c\u80fd\u591f\u88ab\u64cd\u4f5cB\u89c2\u5bdf\u5230\u3002<\/p>\n

\u5982\u4e0b\u56fe\u793a\u4f8b<\/p>\n

\u7ebf\u7a0bA\u3000\u3000\u7ebf\u7a0bB<\/p>\n

i = 3;\u3000\u3000j = i;<\/p>\n

\u7ed3\u679c\uff1aj = 3;<\/p>\n

\u8bf4\u660e\uff1a\u7ebf\u7a0bA\u4e2d\u7684i = 3\u5148\u884c\u53d1\u751f\u4e8ej = i;\u5219\u7ed3\u679c\u4e00\u5b9a\u662fj = 3\u3002<\/p>\n

\u5177\u4f53\u7684happens-before\u539f\u5219\u5982\u4e0b<\/p>\n

1. \u7a0b\u5e8f\u987a\u5e8f\u89c4\u5219\uff1a\u4e00\u4e2a\u7ebf\u7a0b\u4e2d\u7684\u6bcf\u4e2a\u64cd\u4f5c\uff0chappens- before \u4e8e\u8be5\u7ebf\u7a0b\u4e2d\u7684\u4efb\u610f\u540e\u7eed\u64cd\u4f5c\uff08\u63a7\u5236\u6d41\u64cd\u4f5c\u800c\u4e0d\u662f\u7a0b\u5e8f\u4ee3\u7801\u987a\u5e8f\uff09\u3002<\/p>\n

2. \u76d1\u89c6\u5668\u9501\u89c4\u5219\uff1a\u5bf9\u4e00\u4e2a\u76d1\u89c6\u5668\u7684\u89e3\u9501\uff0chappens- before \u4e8e\u968f\u540e\u5bf9\u8fd9\u4e2a\u76d1\u89c6\u5668\u7684\u52a0\u9501\u3002<\/p>\n

3. volatile\u53d8\u91cf\u89c4\u5219\uff1a\u5bf9\u4e00\u4e2a volatile\u57df\u7684\u5199\uff0chappens- before\u4e8e\u4efb\u610f\u540e\u7eed\u5bf9\u8fd9\u4e2avolatile\u57df\u7684\u8bfb\u3002<\/p>\n

4. \u7ebf\u7a0b\u542f\u52a8\u89c4\u5219\uff1aThread\u5bf9\u8c61\u7684start()\u65b9\u6cd5happens – before \u4e8e\u6b64\u7ebf\u7a0b\u7684\u6bcf\u4e00\u4e2a\u52a8\u4f5c\u3002<\/p>\n

5. \u7ebf\u7a0b\u7ec8\u6b62\u89c4\u5219\uff1a\u7ebf\u7a0b\u4e2d\u6240\u6709\u64cd\u4f5c\u90fdhappens – before \u4e8e\u5bf9\u6b64\u7ebf\u7a0b\u7684\u7ec8\u6b62\u68c0\u6d4b\u3002<\/p>\n

6. \u7ebf\u7a0b\u4e2d\u65ad\u89c4\u5219\uff1a\u5bf9\u7ebf\u7a0binterrupt()\u65b9\u6cd5\u7684\u8c03\u7528happens – before \u4e8e\u88ab\u4e2d\u65ad\u7ebf\u7a0b\u7684\u4ee3\u7801\u68c0\u6d4b\u5230\u4e2d\u65ad\u4e8b\u4ef6\u7684\u53d1\u751f\u3002<\/p>\n

7. \u5bf9\u8c61\u7ec8\u7ed3\u89c4\u5219\uff1a\u4e00\u4e2a\u5bf9\u8c61\u7684\u521d\u59cb\u5316\u5b8c\u6210\uff08\u6784\u9020\u51fd\u6570\u6267\u884c\u7ed3\u675f\uff09happens – before \u4e8e\u5b83\u7684finalize()\u65b9\u6cd5\u7684\u5f00\u59cb\u3002<\/p>\n

8. \u4f20\u9012\u6027\uff1a\u5982\u679c A happens- before B\uff0c\u4e14 B happens- before C\uff0c\u90a3\u4e48 A happens- before C\u3002<\/p>\n

\u8bf4\u660e\uff1ahappens-before \u4ec5\u4ec5\u8981\u6c42\u524d\u4e00\u4e2a\u64cd\u4f5c\uff08\u6267\u884c\u7684\u7ed3\u679c\uff09\u5bf9\u540e\u4e00\u4e2a\u64cd\u4f5c\u53ef\u89c1\uff0c\u4e14\u524d\u4e00\u4e2a\u64cd\u4f5c\u6309\u987a\u5e8f\u6392\u5728\u7b2c\u4e8c\u4e2a\u64cd\u4f5c\u4e4b\u524d\uff08\u53ef\u80fd\u4f1a\u53d1\u751f\u6307\u4ee4\u91cd\u6392\uff09\u3002\u65f6\u95f4\u5148\u540e\u987a\u5e8f\u4e0ehappens – before\u539f\u5219\u4e4b\u95f4\u6ca1\u6709\u592a\u5927\u7684\u5173\u7cfb\u3002<\/p>\n

3.6 as-if-serial\u8bed\u4e49<\/p>\n

as-if-serial\u7684\u8bed\u4e49\u662f\uff1a\u4e0d\u7ba1\u600e\u4e48\u91cd\u6392\u5e8f\uff08\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u4e3a\u4e86\u63d0\u9ad8\u5e76\u884c\u5ea6\uff09\uff0c\uff08\u5355\u7ebf\u7a0b\uff09\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u4e0d\u80fd\u88ab\u6539\u53d8\u3002\u7f16\u8bd1\u5668\uff0cruntime \u548c\u5904\u7406\u5668\u90fd\u5fc5\u987b\u9075\u5b88 as-if-serial \u8bed\u4e49\u3002\u4e3a\u4e86\u9075\u5b88 as-if-serial \u8bed\u4e49\uff0c\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u4e0d\u4f1a\u5bf9\u5b58\u5728\u6570\u636e\u4f9d\u8d56\u5173\u7cfb\u7684\u64cd\u4f5c\u505a\u91cd\u6392\u5e8f\uff0c\u56e0\u4e3a\u8fd9\u79cd\u91cd\u6392\u5e8f\u4f1a\u6539\u53d8\u6267\u884c\u7ed3\u679c\u3002\u4f46\u662f\uff0c\u5982\u679c\u64cd\u4f5c\u4e4b\u95f4\u4e0d\u5b58\u5728\u6570\u636e\u4f9d\u8d56\u5173\u7cfb\uff0c\u8fd9\u4e9b\u64cd\u4f5c\u5c31\u53ef\u80fd\u88ab\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u91cd\u6392\u5e8f\u3002\u5982\u5982\u4e0b\u4ee3\u7801\u7247\u6bb5<\/p>\n

\n
double pi = 3.14; \/\/A\ndouble r  = 1.0;   \/\/B\ndouble area = pi * r * r; \/\/C<\/pre>\n<\/div>\n
\u5176\u4e2d\uff0c\u64cd\u4f5cA\u3001B\u3001C\u4e4b\u95f4\u7684\u4f9d\u8d56\u6027\u5982\u4e0b<\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1aA\u548cC\u4e4b\u95f4\u5b58\u5728\u6570\u636e\u4f9d\u8d56\u5173\u7cfb\uff0c\u540c\u65f6B\u548cC\u4e4b\u95f4\u4e5f\u5b58\u5728\u6570\u636e\u4f9d\u8d56\u5173\u7cfb\u3002\u56e0\u6b64\u5728\u6700\u7ec8\u6267\u884c\u7684\u6307\u4ee4\u5e8f\u5217\u4e2d\uff0cC\u4e0d\u80fd\u88ab\u91cd\u6392\u5e8f\u5230A\u548cB\u7684\u524d\u9762\uff08C\u6392\u5230A\u548cB\u7684\u524d\u9762\uff0c\u7a0b\u5e8f\u7684\u7ed3\u679c\u5c06\u4f1a\u88ab\u6539\u53d8\uff09\u3002\u4f46A\u548cB\u4e4b\u95f4\u6ca1\u6709\u6570\u636e\u4f9d\u8d56\u5173\u7cfb\uff0c\u7f16\u8bd1\u5668\u548c \u5904\u7406\u5668\u53ef\u4ee5\u91cd\u6392\u5e8fA\u548cB\u4e4b\u95f4\u7684\u6267\u884c\u987a\u5e8f\u3002\u56e0\u6b64\uff0c\u6700\u540e\u7684\u6307\u4ee4\u5e8f\u5217\u53ef\u80fd\u662f:<\/p>\n
A -> B -> C\uff1b<\/p>\n
B -> A -> C\uff1b\u3000\u3000\/\/ \u91cd\u6392\u5e8f\u4e86<\/p>\n
\u5957\u7528happens – before\u89c4\u5219\u6211\u4eec\u53ef\u4ee5\u77e5\u9053\uff1a<\/p>\n
A happens – before B\uff1b\u3000\u3000\/\/ \u7a0b\u5e8f\u987a\u5e8f\u89c4\u5219<\/p>\n
B happens – before C\uff1b\u3000\u3000\/\/ \u7a0b\u5e8f\u987a\u5e8f\u89c4\u5219<\/p>\n
A happens – before C\uff1b\u3000\u3000\/\/ \u4f20\u9012\u6027<\/p>\n
\u8bf4\u660e\uff1aA happens- before B\uff0c\u4f46\u5b9e\u9645\u6267\u884c\u65f6 B \u5374\u53ef\u4ee5\u6392\u5728 A \u4e4b\u524d\u6267\u884c\uff08\u7b2c\u4e8c\u79cd\u6307\u4ee4\u6267\u884c\u987a\u5e8f\uff09\u3002\u5728\u524d\u9762\u6211\u4eec\u8bb2\u5230\uff0c\u5982\u679c\u00a0A happens- before B\uff0cJMM \u5e76\u4e0d\u8981\u6c42 A \u4e00\u5b9a\u8981\u5728 B \u4e4b\u524d\u6267\u884c\u3002JMM \u4ec5\u4ec5\u8981\u6c42\u524d\u4e00\u4e2a\u64cd\u4f5c\uff08\u6267\u884c\u7684\u7ed3\u679c\uff09\u5bf9\u540e\u4e00\u4e2a\u64cd\u4f5c\u53ef\u89c1\uff0c\u4e14\u524d\u4e00\u4e2a\u64cd\u4f5c\u6309\u987a\u5e8f\u6392\u5728\u7b2c\u4e8c\u4e2a\u64cd\u4f5c\u4e4b\u524d\u3002\u8fd9\u91cc\u64cd\u4f5c A \u7684\u6267\u884c\u7ed3\u679c\u4e0d\u9700\u8981\u5bf9\u64cd\u4f5c B \u53ef\u89c1\uff1b\u800c\u4e14\u91cd\u6392\u5e8f\u64cd\u4f5c A \u548c\u64cd\u4f5c B \u540e\u7684\u6267\u884c\u7ed3\u679c\uff0c\u4e0e\u64cd\u4f5c A \u548c\u64cd\u4f5c B \u6309 happens- before \u987a\u5e8f\u6267\u884c\u7684\u7ed3\u679c\u4e00\u81f4\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0cJMM \u4f1a\u8ba4\u4e3a\u8fd9\u79cd\u91cd\u6392\u5e8f\u5e76\u4e0d\u975e\u6cd5\uff0cJMM \u5141\u8bb8\u8fd9\u79cd\u91cd\u6392\u5e8f\u3002<\/p>\n
\u5bf9\u4e8e\u5355\u7ebf\u7a0b\uff0cJMM\u53ef\u4ee5\u8fdb\u884c\u6307\u4ee4\u91cd\u6392\u5e8f\uff0c\u4f46\u662f\u4e00\u5b9a\u8981\u9075\u5b88as-if-serial\u8bed\u4e49\uff0c\u8fd9\u6837\u624d\u80fd\u4fdd\u8bc1\u5355\u7ebf\u7a0b\u7684\u6b63\u786e\u6027\u3002<\/p>\n
\u5bf9\u4e8e\u591a\u7ebf\u7a0b\u800c\u8a00\uff0cJMM\u7684\u6307\u4ee4\u91cd\u6392\u5e8f\u53ef\u80fd\u4f1a\u5f71\u54cd\u591a\u7ebf\u7a0b\u7a0b\u5e8f\u7684\u6b63\u786e\u6027\u3002\u4e0b\u9762\u4e3a\u591a\u7ebf\u7a0b\u793a\u4f8b\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
class ReorderExample {\n    int a = 0;\n    boolean flag = false;\n\n    public void writer() {\n        a = 1;    \/\/\u64cd\u4f5cA\n        flag = true;    \/\/\u64cd\u4f5cB\n    }\n\n\n    public void reader() {\n        if (flag) {    \/\/\u64cd\u4f5cC\n            int i =    a * a;    \/\/\u64cd\u4f5cD\n        }\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a\u53d8\u91cfflag\u7528\u4e8e\u6807\u8bc6\u53d8\u91cfa\u662f\u5426\u5df2\u7ecf\u5199\u5165\u3002\u82e5\u7ebf\u7a0bA\u5148\u6267\u884cwriter\u51fd\u6570\uff0c\u7136\u540e\u7ebf\u7a0bB\u6267\u884creader\u51fd\u6570\u3002\u7531happens – before \u89c4\u5219\uff08\u7a0b\u5e8f\u987a\u5e8f\u89c4\u5219\uff09\u6211\u4eec\u77e5\u9053\uff0c\u64cd\u4f5cA happens – before B\uff0c\u4f46\u662f\u7531\u4e8e\u64cd\u4f5cA\u4e0e\u64cd\u4f5cB\u4e4b\u95f4\u6ca1\u6709\u6570\u636e\u4f9d\u8d56\uff0c\u6240\u4ee5\u53ef\u4ee5\u8fdb\u884c\u91cd\u6392\u5e8f\u3002\u540c\u7406\uff0c\u64cd\u4f5cC\u4e0e\u64cd\u4f5cD\u4e4b\u95f4\u4e5f\u65e0\u6570\u636e\u4f9d\u8d56\u5173\u7cfb\uff08\u4f46\u5b58\u5728\u63a7\u5236\u4f9d\u8d56\u5173\u7cfb\uff0cJMM\u5141\u8bb8\u5bf9\u5b58\u5728\u6570\u636e\u4f9d\u8d56\u7684\u6307\u4ee4\u8fdb\u884c\u91cd\u6392\u5e8f\uff09\uff0c\u4e5f\u53ef\u8fdb\u884c\u91cd\u6392\u5e8f\u3002<\/p>\n
\u4e0b\u56fe\u5c55\u793a\u4e86\u91cd\u6392\u5e8f\u64cd\u4f5cA\u3001\u64cd\u4f5cB\u6240\u53ef\u80fd\u4ea7\u751f\u7684\u7ed3\u679c\u3002<\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u5047\u8bbe\u91cd\u6392\u5e8f\u64cd\u4f5cA\u3001\u64cd\u4f5cB\uff0c\u4e14\u64cd\u4f5cC\u3001\u64cd\u4f5cD\u5728\u64cd\u4f5cA\u3001\u64cd\u4f5cB\u7684\u4e2d\u95f4\uff0c\u90a3\u4e48\u6700\u540e\u7ebf\u7a0bB\u7684\u53d8\u91cfi\u7684\u7ed3\u679c\u4e3a0\uff1bflag\u4e3atrue\uff0c\u5219\u5bf9i\u8fdb\u884c\u5199\u5165\u3002\u7136\u800c\uff0c\u6b64\u65f6\u7684a\u8fd8\u672a\u5199\u5165\uff0c\u6b64\u65f6\uff0c\u91cd\u6392\u5e8f\u7834\u574f\u4e86\u591a\u7ebf\u7a0b\u7684\u8bed\u4e49\uff0c\u6700\u540e\u5199\u5165\u7684i\u503c\u662f\u4e0d\u6b63\u786e\u7684\u3002<\/p>\n
\u4e0b\u56fe\u5c55\u793a\u4e86\u91cd\u6392\u5e8f\u64cd\u4f5cC\u3001\u64cd\u4f5cD\u53ef\u80fd\u4ea7\u751f\u7684\u6267\u884c\u7ed3\u679c\u3002<\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u5b58\u5728\u63a7\u5236\u4f9d\u8d56\u7684\u6307\u4ee4\u4e5f\u4f1a\u88ab\u91cd\u6392\u5e8f\uff0c\u63a7\u5236\u4f9d\u8d56\u4f1a\u5f71\u54cd\u5e76\u884c\u5ea6\u3002temp\u53d8\u91cf\u7684\u51fa\u73b0\u662f\u56e0\u4e3a\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u4f1a\u91c7\u7528\u731c\u6d4b\u6267\u884c\u6765\u514b\u670d\u63a7\u5236\u76f8\u5173\u6027\u5bf9\u5e76\u884c\u5ea6\u7684\u5f71\u54cd\uff0c\u4ece\u56fe\u4e2d\u6211\u4eec\u53ef\u4ee5\u77e5\u9053\u91cd\u6392\u5e8f\u7834\u574f\u4e86\u591a\u7ebf\u7a0b\u7684\u8bed\u4e49\uff0c\u6700\u540e\u5199\u5165i\u7684\u503c\u662f\u4e0d\u6b63\u786e\u7684\u3002<\/p>\n
\u5728\u5355\u7ebf\u7a0b\u7a0b\u5e8f\u4e2d\uff0c\u5bf9\u5b58\u5728\u63a7\u5236\u4f9d\u8d56\u7684\u64cd\u4f5c\u91cd\u6392\u5e8f\uff0c\u4e0d\u4f1a\u6539\u53d8\u6267\u884c\u7ed3\u679c\uff08\u8fd9\u4e5f\u662f as- if-serial \u8bed\u4e49\u5141\u8bb8\u5bf9\u5b58\u5728\u63a7\u5236\u4f9d\u8d56\u7684\u64cd\u4f5c\u505a\u91cd\u6392\u5e8f\u7684\u539f\u56e0\uff09\uff1b\u4f46\u5728\u591a\u7ebf\u7a0b\u7a0b\u5e8f\u4e2d\uff0c\u5bf9\u5b58\u5728\u63a7\u5236\u4f9d\u8d56\u7684\u64cd\u4f5c\u91cd\u6392\u5e8f\uff0c\u53ef\u80fd\u4f1a\u6539\u53d8\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u3002<\/p>\n
\u5728\u591a\u7ebf\u7a0b\u4e2d\u4e3a\u4e86\u4fdd\u8bc1\u7a0b\u5e8f\u7684\u6b63\u786e\u6027\uff0c\u6211\u4eec\u9700\u8981\u8fdb\u884c\u9002\u5f53\u7684\u540c\u6b65\uff0c\u4ee5\u4fdd\u8bc1\u6b63\u786e\u7684\u7ed3\u679c\u3002<\/p>\n
\u56db\u3001\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b<\/strong><\/p>\n
\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u65f6JMM\u7684\u53c2\u8003\u6a21\u578b\uff0c\u5b83\u63d0\u4f9b\u4e86\u5f88\u5f3a\u7684\u5185\u5b58\u4e00\u81f4\u6027\u4e0e\u53ef\u89c1\u6027\uff0c\u662f\u4e00\u4e2a\u88ab\u8ba1\u7b97\u673a\u79d1\u5b66\u5bb6\u7406\u60f3\u5316\u4e86\u7684\u7406\u8bba\u53c2\u8003\u6a21\u578b\uff0c\u5b83\u4e3a\u7a0b\u5e8f\u5458\u63d0\u4f9b\u4e86\u6781\u5f3a\u7684\u5185\u5b58\u53ef\u89c1\u6027\u4fdd\u8bc1\u3002JMM\u5bf9\u6b63\u786e\u540c\u6b65\u7684\u591a\u7ebf\u7a0b\u7a0b\u5e8f\u7684\u5185\u5b58\u4e00\u81f4\u6027\u505a\u4e86\u5982\u4e0b\u4fdd\u8bc1<\/p>\n
\u5982\u679c\u7a0b\u5e8f\u662f\u6b63\u786e\u540c\u6b65\u7684\uff0c\u7a0b\u5e8f\u7684\u6267\u884c\u5c06\u5177\u6709\u987a\u5e8f\u4e00\u81f4\u6027\uff08sequentially consistent\uff09– \u5373\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u4e0e\u8be5\u7a0b\u5e8f\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4e2d\u7684\u6267\u884c\u7ed3\u679c\u76f8\u540c\u3002\u9a6c\u4e0a\u6211\u4eec\u5c06\u4f1a\u770b\u5230\uff0c\u8fd9\u5bf9\u4e8e\u7a0b\u5e8f\u5458\u6765\u8bf4\u662f\u4e00\u4e2a\u6781\u5f3a\u7684\u4fdd\u8bc1\u3002\u8fd9\u91cc\u7684\u540c\u6b65\u662f\u6307\u5e7f\u4e49\u4e0a\u7684\u540c\u6b65\uff0c\u5305\u62ec\u5bf9\u5e38\u7528\u540c\u6b65\u539f\u8bed\uff08synchronized\uff0cvolatile \u548c final\uff09\u7684\u6b63\u786e\u4f7f\u7528\u3002<\/p>\n
\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u5305\u62ec\u5982\u4e0b\u4e24\u4e2a\u7279\u6027\uff1a<\/p>\n
1. \u4e00\u4e2a\u7ebf\u7a0b\u4e2d\u7684\u6240\u6709\u64cd\u4f5c\u5fc5\u987b\u6309\u7167\u7a0b\u5e8f\u7684\u987a\u5e8f\u6765\u6267\u884c\u3002<\/p>\n
2. \uff08\u4e0d\u7ba1\u7a0b\u5e8f\u662f\u5426\u540c\u6b65\uff09\u6240\u6709\u7ebf\u7a0b\u90fd\u53ea\u80fd\u770b\u5230\u4e00\u4e2a\u5355\u4e00\u7684\u64cd\u4f5c\u6267\u884c\u987a\u5e8f\u3002\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4e2d\uff0c\u6bcf\u4e2a\u64cd\u4f5c\u90fd\u5fc5\u987b\u539f\u5b50\u6267\u884c\u4e14\u7acb\u523b\u5bf9\u6240\u6709\u7ebf\u7a0b\u53ef\u89c1\uff08JMM\u4e2d\u5e76\u4e0d\u4fdd\u8bc1\uff09\u3002<\/p>\n
 <\/p>\n
\n
\u3000\u3000\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4e3a\u7a0b\u5e8f\u5458\u63d0\u4f9b\u7684\u89c6\u56fe\u5982\u4e0b\uff1a<\/p>\n<\/div>\n
 <\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u6bcf\u4e00\u65f6\u523b\u53ea\u6709\u4e00\u4e2a\u7ebf\u7a0b\u53ef\u4ee5\u8bbf\u95ee\u5185\u5b58\uff0c\u5f53\u591a\u4e2a\u7ebf\u7a0b\u5e76\u53d1\u6267\u884c\u65f6\uff0c\u56fe\u4e2d\u7684\u5f00\u5173\u88c5\u7f6e\u80fd\u628a\u6240\u6709\u7ebf\u7a0b\u7684\u6240\u6709\u5185\u5b58\u8bfb\/\u5199\u64cd\u4f5c\u4e32\u884c\u5316\uff08\u5373\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u4e2d\uff0c\u6240\u6709\u64cd\u4f5c\u4e4b\u95f4\u5177\u6709\u5168\u5e8f\u5173\u7cfb\uff09\u3002\u4e0b\u9762\u8fd9\u4e2a\u4f8b\u5b50\u66f4\u8fdb\u4e00\u6b65\u9610\u660e\u4e86\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4e2d\u5404\u7ebf\u7a0b\u64cd\u4f5c\u4e4b\u95f4\u7684\u5173\u7cfb\u3002<\/p>\n
\u5047\u8bbe\u7ebf\u7a0bA\u6709A1\u3001A2\u3001A3\u4e09\u4e2a\u64cd\u4f5c\uff0c\u7ebf\u7a0bB\u6709B1\u3001B2\u3001B3\u4e09\u4e2a\u64cd\u4f5c\u3002<\/p>\n
\u2460 \u82e5\u4f7f\u7528\u76d1\u89c6\u5668\u9501\u6765\u8fdb\u884c\u540c\u6b65\uff0c\u5728A\u7684\u4e09\u4e2a\u64cd\u4f5c\u5b8c\u6210\u540e\uff0c\u91ca\u653e\u76d1\u89c6\u5668\u9501\uff0c\u4e4b\u540eB\u83b7\u5f97\u76d1\u89c6\u5668\u9501\uff0c\u90a3\u4e48\u6574\u4e2a\u64cd\u4f5c\u5e8f\u5217\u4e3a\uff1aA1 -> A2 -> A3 ->\u00a0B1 -> B2 -> B3\u3002<\/p>\n
\u2461 \u82e5\u4e0d\u4f7f\u7528\u76d1\u89c6\u5668\u9501\u6765\u8fdb\u884c\u540c\u6b65\uff0c\u90a3\u4e48\u6574\u4e2a\u5e8f\u5217\u53ef\u80fd\u4e3a\uff1aA1 -> B1 -> A2 ->\u00a0B2 -> B3 -> A3\u3002\u5176\u4e2d\u7ebf\u7a0bA\u3001B\u7684\u4e09\u4e2a\u64cd\u4f5c\u662f\u6709\u5e8f\u7684\uff0c\u5e76\u4e14\u7ebf\u7a0bA\u3001B\u770b\u5230\u7684\u64cd\u4f5c\u5e8f\u5217\u90fd\u662f\u540c\u4e00\u64cd\u4f5c\u5e8f\u5217\uff0c\u6bcf\u4e2a\u64cd\u4f5c\u90fd\u5fc5\u987b\u539f\u5b50\u6267\u884c\u4e14\u7acb\u523b\u5bf9\u6240\u6709\u7ebf\u7a0b\u53ef\u89c1\uff0c\u4f46\u662f\u6574\u4f53\u7684\u64cd\u4f5c\u65e0\u5e8f\u3002<\/p>\n
\u672a\u540c\u6b65\u7a0b\u5e8f\u5728 JMM \u4e2d\u4e0d\u4f46\u6574\u4f53\u7684\u6267\u884c\u987a\u5e8f\u662f\u65e0\u5e8f\u7684\uff0c\u800c\u4e14\u6240\u6709\u7ebf\u7a0b\u770b\u5230\u7684\u64cd\u4f5c\u6267\u884c\u987a\u5e8f\u4e5f\u53ef\u80fd\u4e0d\u4e00\u81f4\u3002\u6bd4\u5982\uff0c\u5728\u5f53\u524d\u7ebf\u7a0b\u628a\u5199\u8fc7\u7684\u6570\u636e\u7f13\u5b58\u5728\u672c\u5730\u5185\u5b58\u4e2d\uff0c\u5728\u8fd8\u6ca1\u6709\u5237\u65b0\u5230\u4e3b\u5185\u5b58\u4e4b\u524d\uff0c\u8fd9\u4e2a\u5199\u64cd\u4f5c\u4ec5\u5bf9\u5f53\u524d\u7ebf\u7a0b\u53ef\u89c1\uff1b\u4ece\u5176\u4ed6\u7ebf\u7a0b\u7684\u89d2\u5ea6\u6765\u89c2\u5bdf\uff0c\u4f1a\u8ba4\u4e3a\u8fd9\u4e2a\u5199\u64cd\u4f5c\u6839\u672c\u8fd8\u6ca1\u6709\u88ab\u5f53\u524d\u7ebf\u7a0b\u6267\u884c\u3002\u53ea\u6709\u5f53\u524d\u7ebf\u7a0b\u628a\u672c\u5730\u5185\u5b58\u4e2d\u5199\u8fc7\u7684\u6570\u636e\u5237\u65b0\u5230\u4e3b\u5185\u5b58\u4e4b\u540e\uff0c\u8fd9\u4e2a\u5199\u64cd\u4f5c\u624d\u80fd\u5bf9\u5176\u4ed6\u7ebf\u7a0b\u53ef\u89c1\u3002\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u5f53\u524d\u7ebf\u7a0b\u548c\u5176\u5b83\u7ebf\u7a0b\u770b\u5230\u7684\u64cd\u4f5c\u6267\u884c\u987a\u5e8f\u5c06\u4e0d\u4e00\u81f4\uff0c\u5f53\u524d\u7ebf\u7a0b\u8ba4\u4e3a\u5199\u6570\u636e\u5230\u7f13\u51b2\u533a\u5c31\u5b8c\u6210\u4e86\u5199\u64cd\u4f5c\uff0c\u5176\u4ed6\u7ebf\u7a0b\u8ba4\u4e3a\u53ea\u6709\u6570\u636e\u5237\u65b0\u5230\u4e3b\u5185\u5b58\u624d\u7b97\u5b8c\u6210\u4e86\u5199\u64cd\u4f5c\uff0c\u6240\u4ee5\u5c31\u5bfc\u81f4\u4e86\u7ebf\u7a0b\u4e4b\u95f4\u770b\u5230\u7684\u64cd\u4f5c\u5e8f\u5217\u4e0d\u76f8\u540c\u3002<\/p>\n
\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u662f\u901a\u8fc7\u5185\u5b58\u89c4\u5219\u4fdd\u8bc1\u987a\u5e8f\u4e00\u81f4\u6027\uff0c\u987a\u5e8f\u4e00\u81f4\u6027\u662fJMM\u8ffd\u6c42\u7684\u76ee\u6807\uff0c\u4f46\u662fJMM\u6a21\u578b\u672c\u8eab\u5e76\u4e0d\u8fdb\u884c\u4fdd\u8bc1\uff0c\u5fc5\u987b\u901a\u8fc7\u9002\u5f53\u7684\u540c\u6b65\u4fdd\u8bc1\u3002<\/p>\n
4.1 \u540c\u6b65\u7a0b\u5e8f\u7684\u6267\u884c\u7279\u6027<\/p>\n
\u4e0b\u9762\u4f8b\u5b50\u5c55\u793a\u4e00\u4e2a\u6b63\u786e\u540c\u6b65\u7684\u7a0b\u5e8f\u5728JMM\u548c\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u7684\u64cd\u4f5c\u5e8f\u5217\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
class SynchronizedExample {\n    int a = 0;\n    boolean flag = false;\n\n    public synchronized void writer() { \/\/ \u83b7\u53d6\u9501\n        a = 1;    \/\/\u64cd\u4f5cA\n        flag = true;    \/\/\u64cd\u4f5cB\n    } \/\/ \u91ca\u653e\u9501\n\n    public synchronized void reader() { \/\/ \u83b7\u53d6\u9501\n        if (flag) {    \/\/\u64cd\u4f5cC\n            int i = a;    \/\/\u64cd\u4f5cD\n        }\n    } \/\/ \u91ca\u653e\u9501\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
 <\/p>\n
\u8bf4\u660e\uff1a\u7ebf\u7a0bA\u5148\u6267\u884cwriter\u65b9\u6cd5\uff0c\u7ebf\u7a0bB\u6267\u884creader\u65b9\u6cd5\u3002\u8fd9\u662f\u4e00\u4e2a\u6b63\u786e\u540c\u6b65\u7684\u7a0b\u5e8f\uff0c\u5728JMM\u7684\u64cd\u4f5c\u5e8f\u5217\u4e0e\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u7684\u64cd\u4f5c\u5e8f\u5217\u662f\u76f8\u540c\u7684\u3002<\/p>\n
 <\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1aJMM\u6a21\u578b\u4e2d\u5141\u8bb8\u4e34\u754c\u533a\u7684\u64cd\u4f5c\u91cd\u6392\u5e8f\uff08\u5373\u4f7f\u6709\u63a7\u5236\u4f9d\u8d56\uff09\uff0c\u800c\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4e2d\u5219\u6309\u7167\u7a0b\u5e8f\u987a\u5e8f\u6267\u884c\u3002\u7ebf\u7a0b A \u5728\u4e34\u754c\u533a\u5185\u505a\u4e86\u91cd\u6392\u5e8f\uff0c\u4f46\u7531\u4e8e\u76d1\u89c6\u5668\u7684\u4e92\u65a5\u6267\u884c\u7684\u7279\u6027\uff0c\u8fd9\u91cc\u7684\u7ebf\u7a0b B \u6839\u672c\u65e0\u6cd5\u201c\u89c2\u5bdf\u201d\u5230\u7ebf\u7a0b A \u5728\u4e34\u754c\u533a\u5185\u7684\u91cd\u6392\u5e8f\u3002\u8fd9\u79cd\u91cd\u6392\u5e8f\u65e2\u63d0\u9ad8\u4e86\u6267\u884c\u6548\u7387\uff0c\u53c8\u6ca1\u6709\u6539\u53d8\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u3002\u540c\u65f6\uff0cJMM \u4f1a\u5728\u9000\u51fa\u4e34\u754c\u533a\u548c\u8fdb\u5165\u4e34\u754c\u533a\u8fd9\u4e24\u4e2a\u5173\u952e\u65f6\u95f4\u70b9\u505a\u4e00\u4e9b\u7279\u522b\u5904\u7406\uff0c\u4f7f\u5f97\u7ebf\u7a0b\u5728\u8fd9\u4e24\u4e2a\u65f6\u95f4\u70b9\u5177\u6709\u4e0e\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u76f8\u540c\u7684\u5185\u5b58\u89c6\u56fe\u3002<\/p>\n
\u4ece\u8fd9\u91cc\u6211\u4eec\u53ef\u4ee5\u770b\u5230 JMM \u5728\u5177\u4f53\u5b9e\u73b0\u4e0a\u7684\u57fa\u672c\u65b9\u9488\uff1a\u5728\u4e0d\u6539\u53d8\uff08\u6b63\u786e\u540c\u6b65\u7684\uff09\u7a0b\u5e8f\u6267\u884c\u7ed3\u679c\u7684\u524d\u63d0\u4e0b\uff0c\u5c3d\u53ef\u80fd\u7684\u4e3a\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u7684\u4f18\u5316\u6253\u5f00\u65b9\u4fbf\u4e4b\u95e8\u3002<\/p>\n
4.2 \u672a\u540c\u6b65\u7a0b\u5e8f\u7684\u6267\u884c\u7279\u6027<\/p>\n
\u5bf9\u4e8e\u672a\u540c\u6b65\u6216\u672a\u6b63\u786e\u540c\u6b65\u7684\u591a\u7ebf\u7a0b\u7a0b\u5e8f\uff0cJMM\u53ea\u63d0\u4f9b\u6700\u5c0f\u5b89\u5168\u6027\uff1a\u7ebf\u7a0b\u6267\u884c\u65f6\u8bfb\u53d6\u5230\u7684\u503c\uff0c\u8981\u4e48\u662f\u4e4b\u524d\u67d0\u4e2a\u7ebf\u7a0b\u5199\u5165\u7684\u503c\uff0c\u8981\u4e48\u662f\u9ed8\u8ba4\u503c\uff080\uff0cnull\uff0cfalse\uff09\uff0cJMM\u4fdd\u8bc1\u7ebf\u7a0b\u8bfb\u64cd\u4f5c\u8bfb\u53d6\u5230\u7684\u503c\u4e0d\u4f1a\u65e0\u4e2d\u751f\u6709\u7684\u5192\u51fa\u6765\u3002\u4e3a\u4e86 \u5b9e\u73b0\u6700\u5c0f\u5b89\u5168\u6027\uff0cJVM\u5728\u5806\u4e0a\u5206\u914d\u5bf9\u8c61\u65f6\uff0c\u9996\u5148\u4f1a\u6e05\u96f6\u5185\u5b58\u7a7a\u95f4\uff0c\u7136\u540e\u624d\u4f1a\u5728\u4e0a\u9762\u5206\u914d\u5bf9\u8c61\uff08JVM\u5185\u90e8\u4f1a\u540c\u6b65\u8fd9\u4e24\u4e2a\u64cd\u4f5c\uff09\u3002\u56e0\u6b64\uff0c\u5728\u5df2\u6e05\u96f6\u7684\u5185\u5b58\u7a7a\u95f4\u5206\u914d\u5bf9\u8c61\u65f6\uff0c\u57df\u7684\u9ed8\u8ba4\u521d\u59cb\u5316\u5df2\u7ecf\u5b8c\u6210\u4e86\u3002<\/p>\n
JMM \u4e0d\u4fdd\u8bc1\u672a\u540c\u6b65\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u4e0e\u8be5\u7a0b\u5e8f\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u4e2d\u7684\u6267\u884c\u7ed3\u679c\u4e00\u81f4\u3002\u56e0\u4e3a\u5982\u679c\u60f3\u8981\u4fdd\u8bc1\u6267\u884c\u7ed3\u679c\u4e00\u81f4\uff0cJMM\u9700\u8981\u7981\u6b62\u5927\u91cf\u7684\u5904\u7406\u5668\u548c\u7f16\u8bd1\u5668\u7684\u4f18\u5316\uff0c\u8fd9\u5bf9\u7a0b\u5e8f\u7684\u6267\u884c\u6027\u80fd\u4f1a\u4ea7\u751f\u5f88\u5927\u7684\u5f71\u54cd\u3002\u800c\u4e14\u672a\u540c\u6b65\u7a0b\u5e8f\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u4e2d\u6267\u884c\u65f6\uff0c\u6574\u4f53\u662f\u65e0\u5e8f\u7684\uff0c\u5176\u6267\u884c\u7ed3\u679c\u5f80\u5f80\u65e0\u6cd5\u9884\u77e5\u3002\u4fdd\u8bc1\u672a\u540c\u6b65\u7a0b\u5e8f\u5728\u8fd9\u4e24\u4e2a\u6a21\u578b\u4e2d\u7684\u6267\u884c\u7ed3\u679c\u4e00\u81f4\u6ca1\u4ec0\u4e48\u610f\u4e49\u3002<\/p>\n
\u672a\u540c\u6b65\u7a0b\u5e8f\u5728 JMM \u4e2d\u7684\u6267\u884c\u65f6\uff0c\u6574\u4f53\u4e0a\u662f\u65e0\u5e8f\u7684\uff0c\u5176\u6267\u884c\u7ed3\u679c\u65e0\u6cd5\u9884\u77e5\u3002\u672a\u540c\u6b65\u7a0b\u5e8f\u5728\u4e24\u4e2a\u6a21\u578b\u4e2d\u7684\u6267\u884c\u7279\u6027\u6709\u4e0b\u9762\u51e0\u4e2a\u5dee\u5f02\uff1a<\/p>\n
\n
\u3000\u3000\u2460 \u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u4fdd\u8bc1\u5355\u7ebf\u7a0b\u5185\u7684\u64cd\u4f5c\u4f1a\u6309\u7a0b\u5e8f\u7684\u987a\u5e8f\u6267\u884c\uff0c\u800c JMM \u4e0d\u4fdd\u8bc1\u5355\u7ebf\u7a0b\u5185\u7684\u64cd\u4f5c\u4f1a\u6309\u7a0b\u5e8f\u7684\u987a\u5e8f\u6267\u884c\uff08\u4f1a\u8fdb\u884c\u91cd\u6392\u5e8f\uff09\u3002<\/p>\n
\u2461 \u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u4fdd\u8bc1\u6240\u6709\u7ebf\u7a0b\u53ea\u80fd\u770b\u5230\u4e00\u81f4\u7684\u64cd\u4f5c\u6267\u884c\u987a\u5e8f\uff0c\u800c JMM \u4e0d\u4fdd\u8bc1\u6240\u6709\u7ebf\u7a0b\u80fd\u770b\u5230\u4e00\u81f4\u7684\u64cd\u4f5c\u6267\u884c\u987a\u5e8f\u3002<\/p>\n
\u2462 JMM\u4e0d\u4fdd\u8bc1\u5bf9 64 \u4f4d\u7684 long \u578b\u548c double \u578b\u53d8\u91cf\u7684\u8bfb\/\u5199\u64cd\u4f5c\u5177\u6709\u539f\u5b50\u6027\uff08JDK5\u4e4b\u540e\u7684\u8bfb\u5177\u6709\u539f\u5b50\u6027\uff0c\u5199\u4e0d\u5177\u6709\uff09\uff0c\u800c\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u4fdd\u8bc1\u5bf9\u6240\u6709\u7684\u5185\u5b58\u8bfb\/\u5199\u64cd\u4f5c\u90fd\u5177\u6709\u539f\u5b50\u6027\u3002<\/p>\n
\u4e94\u3001volatile\u578b\u53d8\u91cf\u8bf4\u660e<\/strong><\/p>\n
\u5173\u952e\u5b57volatile\u662fJava\u865a\u62df\u673a\u63d0\u4f9b\u7684\u6700\u8f7b\u91cf\u7ea7\u7684\u540c\u6b65\u673a\u5236\uff0c\u5f53\u4e00\u4e2a\u53d8\u91cf\u5b9a\u4e49\u4e3avolatile\u65f6\uff0c\u5b83\u5c06\u5177\u5907\u4e24\u79cd\u7279\u6027\uff0c\u53ef\u89c1\u6027\u4e0e\u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\u4f18\u5316\u3002volatile\u901a\u5e38\u4f1a\u4e0esynchronize\u5173\u952e\u5b57\u505a\u5bf9\u6bd4\u3002<\/p>\n
\u2460 \u53ef\u89c1\u6027\u3002\u5f53\u4e00\u6761\u7ebf\u7a0b\u4fee\u6539\u4e86\u8fd9\u4e2a\u53d8\u91cf\u7684\u503c\uff0c\u65b0\u503c\u5bf9\u4e8e\u5176\u4ed6\u7ebf\u7a0b\u6765\u8bf4\u662f\u53ef\u4ee5\u7acb\u5373\u83b7\u5f97\u7684\uff0c\u4f46\u662f\u57fa\u4e8evolatile\u53d8\u91cf\u7684\u64cd\u4f5c\u5e76\u4e0d\u662f\u5b89\u5168\u7684\uff08\u5982\u81ea\u589e\u64cd\u4f5c\uff09\uff0c\u4e0b\u9762\u4e24\u79cd\u60c5\u51b5\u5c31\u4e0d\u592a\u9002\u5408\u4f7f\u7528volatile\uff0c\u800c\u9700\u8981\u4f7f\u7528\u52a0\u9501\uff08synchronize\u3001\u539f\u5b50\u7c7b\uff09\u6765\u4fdd\u8bc1\u539f\u5b50\u6027\u3002<\/p>\n
1. \u8fd0\u7b97\u7ed3\u679c\u5e76\u4e0d\u4f9d\u8d56\u53d8\u91cf\u7684\u5f53\u524d\u503c\uff0c\u6216\u8005\u80fd\u591f\u786e\u4fdd\u53ea\u6709\u5355\u4e00\u7684\u7ebf\u7a0b\u4fee\u6539\u53d8\u91cf\u7684\u503c\u3002<\/p>\n
2. \u53d8\u91cf\u4e0d\u9700\u8981\u4e0e\u5176\u4ed6\u7684\u72b6\u6001\u53d8\u91cf\u5171\u540c\u53c2\u4e0e\u4e0d\u53d8\u7ea6\u675f\u3002<\/p>\n
\u2461 \u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\u4f18\u5316\u3002\u4e0d\u5141\u8bb8\u5bf9volatile\u64cd\u4f5c\u6307\u4ee4\u8fdb\u884c\u91cd\u6392\u5e8f\u3002<\/p>\n
\u4e0b\u9762\u662f\u662f\u4e00\u4e2avolatile\u7684\u4f8b\u5b50\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
class VolatileFeaturesExample {\n    volatile long vl = 0L; \/\/\u4f7f\u7528 volatile \u58f0\u660e 64 \u4f4d\u7684 long \u578b\u53d8\u91cf\n\n    public void set(long l) {\n        vl = l;    \/\/\u5355\u4e2a volatile \u53d8\u91cf\u7684\u5199\n    }\n\n    public void getAndIncrement () {\n        vl++; \/\/\u590d\u5408\uff08\u591a\u4e2a\uff09volatile \u53d8\u91cf\u7684\u8bfb\/\u5199\n    }\n\n    public long get() {\n        return vl; \/\/\u5355\u4e2a volatile \u53d8\u91cf\u7684\u8bfb\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a\u4e0a\u8ff0\u4f7f\u7528volatile\u5173\u952e\u5b57\u7684\u7a0b\u5e8f\u4e0e\u4e0b\u9762\u4f7f\u7528synchronize\u5173\u952e\u5b57\u7684\u7a0b\u5e8f\u6548\u679c\u7b49\u6548\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
class VolatileFeaturesExample {\n    long vl = 0L; \/\/ 64 \u4f4d\u7684 long \u578b\u666e\u901a\u53d8\u91cf\n\n    public synchronized void set(long l) { \/\/\u5bf9\u5355\u4e2a\u7684\u666e\u901a\u53d8\u91cf\u7684\u5199\u7528\u540c\u4e00\u4e2a\n        vl = l;\n    }\n\n    public void getAndIncrement () { \/\/\u666e\u901a\u65b9\u6cd5\u8c03\u7528\n        long temp = get(); \/\/\u8c03\u7528\u5df2\u540c\u6b65\u7684\u8bfb\u65b9\u6cd5\n        temp += 1L; \/\/\u666e\u901a\u5199\u64cd\u4f5c\n        set(temp); \/\/\u8c03\u7528\u5df2\u540c\u6b65\u7684\u5199\u65b9\u6cd5\n    }\n\n    public synchronized long get() { \/\/ \u5bf9\u5355\u4e2a\u7684\u666e\u901a\u53d8\u91cf\u7684\u8bfb\u7528\u540c\u4e00\u4e2a\u9501\u540c\u6b65\n        return vl;\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
volatile\u53d8\u91cf\u7684\u8bfb\u5199\u4e0e\u9501\u7684\u91ca\u653e\u4e0e\u83b7\u53d6\u76f8\u5bf9\u5e94\u3002\u8bfb\u5bf9\u5e94\u7740\u9501\u7684\u91ca\u653e\uff0c\u5199\u5bf9\u5e94\u9501\u7684\u83b7\u53d6\u3002<\/p>\n
5.1 volatile\u7684happens – before\u5173\u7cfb<\/p>\n
\u524d\u9762\u6211\u4eec\u77e5\u9053happens – before \u5173\u7cfb\u662f\u4fdd\u8bc1\u5185\u5b58\u53ef\u89c1\u6027\u7684\u91cd\u8981\u4f9d\u636e\u3002\u90a3\u4e48\u5728volatile\u53d8\u91cf\u4e0ehappens – before \u4e4b\u95f4\u662f\u4ec0\u4e48\u5173\u7cfb\u5462\uff0c\u6211\u4eec\u901a\u8fc7\u4e00\u4e2a\u793a\u4f8b\u8bf4\u660e<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
class VolatileExample {\n    int    a = 0;\n    volatile boolean flag = false;\n\n    public void writer() {\n        a = 1; \/\/1\n        flag = true; \/\/2\n    }\n\n    public void reader() {\n        if (flag) { \/\/3\n            int i =    a; \/\/4\n        }\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a\u5047\u5b9a\u7ebf\u7a0bA\u5148\u6267\u884cwriter\u65b9\u6cd5\uff0c\u7ebf\u7a0bB\u540e\u6267\u884creader\u65b9\u6cd5\uff0c\u90a3\u4e48\u6839\u636ehappens – before\u5173\u7cfb\uff0c\u6211\u4eec\u53ef\u4ee5\u77e5\u9053\uff1a<\/p>\n
1. \u6839\u636e\u7a0b\u5e8f\u987a\u5e8f\u89c4\u5219\uff0c1\u00a0happens before 2; 3 happens before 4\u3002<\/p>\n
2. \u6839\u636e volatile\u53d8\u91cf\u89c4\u5219\uff0c2 happens before 3\u3002<\/p>\n
3. \u6839\u636e happens before \u7684\u4f20\u9012\u6027\uff0c1 happens before 4\u3002<\/p>\n<\/div>\n
\u3000\u3000\u5177\u4f53\u7684happens – before\u56fe\u5f62\u5316\u5982\u4e0b<\/div>\n
\"\"<\/div>\n
\u3000\u3000\u8bf4\u660e\uff1a\u4e0a\u8ff0\u56fe\u4e2d\u5b58\u5728\u7bad\u5934\u8868\u793a\u4e24\u8005\u4e4b\u95f4\u5b58\u5728happens – before\u5173\u7cfb\u3002<\/div>\n
5.2 volatile\u8bfb\u5199\u5185\u5b58\u8bed\u4e49<\/p>\n
1. \u8bfb\u5185\u5b58\u8bed\u4e49\u3002\u5f53\u8bfb\u4e00\u4e2a volatile \u53d8\u91cf\u65f6\uff0cJMM \u4f1a\u628a\u8be5\u7ebf\u7a0b\u5bf9\u5e94\u7684\u672c\u5730\u5185\u5b58\u7f6e\u4e3a\u65e0\u6548\u3002\u7ebf\u7a0b\u4e4b\u540e\u5c06\u4ece\u4e3b\u5185\u5b58\u4e2d\u8bfb\u53d6\u5171\u4eab\u53d8\u91cf\u3002<\/p>\n
2. \u5199\u5185\u5b58\u8bed\u4e49\u3002\u5f53\u5199\u4e00\u4e2a volatile \u53d8\u91cf\u65f6\uff0cJMM \u4f1a\u628a\u8be5\u7ebf\u7a0b\u5bf9\u5e94\u7684\u672c\u5730\u5185\u5b58\u4e2d\u7684\u5171\u4eab\u53d8\u91cf\u503c\u5237\u65b0\u5230\u4e3b\u5185\u5b58\u3002\u8fd9\u6837\u5c31\u4fdd\u8bc1\u4e86volatile\u7684\u5185\u5b58\u53ef\u89c1\u6027\u3002<\/p>\n
\n
\u3000\u3000volatile\u8bfb\u5199\u5185\u5b58\u8bed\u4e49\u603b\u7ed3\u4e3a\u5982\u4e0b\u4e09\u6761\uff1a<\/p>\n
1. \u7ebf\u7a0b A \u5199\u4e00\u4e2a volatile \u53d8\u91cf\uff0c\u5b9e\u8d28\u4e0a\u662f\u7ebf\u7a0b A \u5411\u63a5\u4e0b\u6765\u5c06\u8981\u8bfb\u8fd9\u4e2a volatile \u53d8\u91cf\u7684\u67d0\u4e2a\u7ebf\u7a0b\u53d1\u51fa\u4e86\uff08\u5176\u5bf9\u5171\u4eab\u53d8\u91cf\u6240\u5728\u4fee\u6539\u7684\uff09\u6d88\u606f\u3002<\/p>\n
\n
\u3000\u30002. \u7ebf\u7a0b B \u8bfb\u4e00\u4e2a volatile \u53d8\u91cf\uff0c\u5b9e\u8d28\u4e0a\u662f\u7ebf\u7a0b B \u63a5\u6536\u4e86\u4e4b\u524d\u67d0\u4e2a\u7ebf\u7a0b\u53d1\u51fa\u7684\uff08\u5728\u5199\u8fd9\u4e2a volatile \u53d8\u91cf\u4e4b\u524d\u5bf9\u5171\u4eab\u53d8\u91cf\u6240\u505a\u4fee\u6539\u7684\uff09\u6d88\u606f\u3002<\/p>\n
3. \u7ebf\u7a0b A \u5199\u4e00\u4e2a volatile \u53d8\u91cf\uff0c\u968f\u540e\u7ebf\u7a0b B \u8bfb\u8fd9\u4e2a volatile \u53d8\u91cf\uff0c\u8fd9\u4e2a\u8fc7\u7a0b\u5b9e\u8d28\u4e0a\u662f\u7ebf\u7a0b A \u901a\u8fc7\u4e3b\u5185\u5b58\u5411\u7ebf\u7a0b B \u53d1\u9001\u6d88\u606f\u3002<\/p>\n
5.3 volatile\u5185\u5b58\u8bed\u4e49\u7684\u5b9e\u73b0<\/p>\n
\u524d\u9762\u8bb2\u5230\uff0cvolatile\u53d8\u91cf\u4f1a\u7981\u6b62\u7f16\u8bd1\u5668\u3001\u5904\u7406\u5668\u91cd\u6392\u5e8f\u3002\u4e0b\u9762\u662fvolatile\u5177\u4f53\u7684\u6392\u5e8f\u89c4\u5219\u8868<\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u4ece\u56fe\u4e2d\u53ef\u4ee5\u77e5\u9053\u5f53\u7b2c\u4e00\u4e2a\u64cd\u4f5c\u4e3avolatile\u8bfb\u65f6\uff0c\u65e0\u8bba\u7b2c\u4e8c\u4e2a\u64cd\u4f5c\u4e3a\u4f55\u79cd\u64cd\u4f5c\uff0c\u90fd\u4e0d\u5141\u8bb8\u91cd\u6392\u5e8f\uff1b\u5f53\u7b2c\u4e8c\u4e2a\u64cd\u4f5c\u4e3avolatile\u5199\u65f6\uff0c\u65e0\u8bba\u7b2c\u4e00\u4e2a\u64cd\u4f5c\u4e3a\u4f55\u79cd\u64cd\u4f5c\uff0c\u90fd\u4e0d\u5141\u8bb8\u91cd\u6392\u5e8f\uff1b\u5f53\u7b2c\u4e00\u4e2a\u64cd\u4f5c\u4e3avolatile\u5199\u65f6\uff0c\u7b2c\u4e8c\u4e2a\u64cd\u4f5c\u4e3avolatile\u8bfb\u65f6\uff0c\u4e0d\u5141\u8bb8\u91cd\u6392\u5e8f\u3002<\/p>\n
\u4e3a\u4e86\u5b9e\u73b0 volatile \u7684\u5185\u5b58\u8bed\u4e49\uff0c\u7f16\u8bd1\u5668\u5728\u751f\u6210\u5b57\u8282\u7801\u65f6\uff0c\u4f1a\u5728\u6307\u4ee4\u5e8f\u5217\u4e2d\u63d2\u5165\u5185\u5b58\u5c4f\u969c\u6765\u7981\u6b62\u7279\u5b9a\u7c7b\u578b\u7684\u5904\u7406\u5668\u91cd\u6392\u5e8f\u3002\u5bf9\u4e8e\u7f16\u8bd1\u5668\u6765\u8bf4\uff0c\u53d1\u73b0\u4e00\u4e2a\u6700\u4f18\u5e03\u7f6e\u6765\u6700\u5c0f\u5316\u63d2\u5165\u5c4f\u969c\u7684\u603b\u6570\u51e0\u4e4e\u4e0d\u53ef\u80fd\uff0c\u4e3a\u6b64\uff0cJMM \u91c7\u53d6\u4fdd\u5b88\u7b56\u7565\u3002\u4e0b\u9762\u662f\u57fa\u4e8e\u4fdd\u5b88\u7b56\u7565\u7684 JMM \u5185\u5b58\u5c4f\u969c\u63d2\u5165\u7b56\u7565\uff1a<\/p>\n
1. \u5728\u6bcf\u4e2a volatile \u5199\u64cd\u4f5c\u7684\u524d\u9762\u63d2\u5165\u4e00\u4e2a StoreStore \u5c4f\u969c\u3002<\/p>\n
\n
\u3000\u30002. \u5728\u6bcf\u4e2a volatile \u5199\u64cd\u4f5c\u7684\u540e\u9762\u63d2\u5165\u4e00\u4e2a StoreLoad \u5c4f\u969c\uff08\u5bf9volatile\u5199\u3001\u666e\u901a\u8bfb\u5199\u5b9e\u73b0\u4e3a\u4e0d\u5141\u8bb8\u91cd\u6392\u5e8f\uff0c\u53ef\u80fd\u4f1a\u5f71\u54cd\u6027\u80fd\uff09\u3002<\/p>\n
3. \u5728\u6bcf\u4e2a volatile \u8bfb\u64cd\u4f5c\u7684\u540e\u9762\u63d2\u5165\u4e00\u4e2a LoadLoad \u5c4f\u969c\u3002<\/p>\n
4. \u5728\u6bcf\u4e2a volatile \u8bfb\u64cd\u4f5c\u7684\u540e\u9762\u63d2\u5165\u4e00\u4e2a LoadStore \u5c4f\u969c\uff08\u666e\u901a\u8bfb\u5199\u3001volatile\u8bfb\u5b9e\u73b0\u4e3a\u4e0d\u5141\u8bb8\u91cd\u6392\u5e8f\uff0c\u53ef\u80fd\u4f1a\u5f71\u54cd\u6027\u80fd\uff09\u3002<\/p>\n<\/div>\n
\u4e0b\u9762\u901a\u8fc7\u4e00\u4e2a\u793a\u4f8b\u5c55\u793avolatile\u7684\u5185\u5b58\u8bed\u4e49\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
class VolatileBarrierExample {\n    int a;\n    volatile int v1 = 1;\n    volatile int v2 = 2;\n\n    void readAndWrite() {\n        int i = v1;    \/\/ \u7b2c\u4e00\u4e2a volatile \u8bfb\n        int j = v2; \/\/ \u7b2c\u4e8c\u4e2a volatile \u8bfb\n        a = i + j; \/\/ \u666e\u901a\u5199\n        v1 = i + 1; \/\/ \u7b2c\u4e00\u4e2a volatile \u5199\n        v2 = j * 2; \/\/ \u7b2c\u4e8c\u4e2a volatile \u5199\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n<\/div>\n<\/div>\n
\u6839\u636e\u7a0b\u5e8f\uff0c\u6700\u540e\u7684\u6307\u4ee4\u5e8f\u5217\u5982\u4e0b\u56fe\u6240\u793a<\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u7f16\u8bd1\u5668\u3001\u5904\u7406\u5668\u4f1a\u6839\u636e\u4e0a\u4e0b\u6587\u8fdb\u884c\u4f18\u5316\uff0c\u5e76\u4e0d\u662f\u5b8c\u5168\u6309\u7167\u4fdd\u5b88\u7b56\u7565\u8fdb\u884c\u63d2\u5165\u76f8\u5e94\u7684\u5c4f\u969c\u6307\u4ee4\u3002<\/p>\n
\u516d\u3001\u9501<\/strong><\/p>\n
\u9501\u662fJava\u5e76\u53d1\u7f16\u7a0b\u4e2d\u6700\u91cd\u8981\u7684\u540c\u6b65\u673a\u5236\u3002\u9501\u9664\u4e86\u8ba9\u4e34\u754c\u533a\u4e92\u65a5\u6267\u884c\u5916\uff0c\u8fd8\u53ef\u4ee5\u8ba9\u91ca\u653e\u9501\u7684\u7ebf\u7a0b\u5411\u83b7\u53d6\u540c\u4e00\u4e2a\u9501\u7684\u7ebf\u7a0b\u53d1\u9001\u6d88\u606f\u3002<\/p>\n
6.1 \u9501\u7684happens – before \u5173\u7cfb<\/p>\n
\u4e0b\u9762\u4e00\u4e2a\u793a\u4f8b\u5c55\u793a\u4e86\u9501\u7684\u4f7f\u7528<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
class MonitorExample {\n    int a = 0;\n\n    public synchronized void writer() {    \/\/ 1\n        a++; \/\/ 2\n    } \/\/ 3\n\n    public synchronized void reader() { \/\/ 4\n        int i = a; \/\/ 5\n    } \/\/ 6\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a\u5047\u8bbe\u7ebf\u7a0b A \u6267\u884c writer()\u65b9\u6cd5\uff0c\u968f\u540e\u7ebf\u7a0b B \u6267\u884c reader()\u65b9\u6cd5\u3002\u8be5\u7a0b\u5e8f\u7684happens – before\u5173\u7cfb\u5982\u4e0b\uff1a<\/p>\n
1. \u6839\u636e\u7a0b\u5e8f\u987a\u5e8f\u89c4\u5219\uff0c1 happens before 2, 2 happens before 3; 4 happens before 5, 5 happens before 6\u3002<\/p>\n
2. \u6839\u636e\u76d1\u89c6\u5668\u9501\u89c4\u5219\uff0c3 happens before 4\u3002<\/p>\n
3. \u6839\u636e\u4f20\u9012\u6027\uff0c2 happens before 5\u3002<\/p>\n
\u56fe\u5f62\u5316\u8868\u793a\u5982\u4e0b\uff1a<\/p>\n
\"\"<\/p>\n
6.2 \u9501\u91ca\u653e\u83b7\u53d6\u7684\u5185\u5b58\u8bed\u4e49<\/p>\n
1. \u5f53\u7ebf\u7a0b\u91ca\u653e\u9501\u65f6\uff0cJMM\u4f1a\u628a\u8be5\u7ebf\u7a0b\u5bf9\u5e94\u7684\u5de5\u4f5c\u5185\u5b58\u4e2d\u7684\u5171\u4eab\u53d8\u91cf\u5237\u65b0\u5230\u4e3b\u5185\u5b58\u4e2d\uff0c\u4ee5\u786e\u4fdd\u4e4b\u540e\u7684\u7ebf\u7a0b\u53ef\u4ee5\u83b7\u53d6\u5230\u6700\u65b0\u7684\u503c\u3002<\/p>\n
2. \u5f53\u7ebf\u7a0b\u83b7\u53d6\u9501\u65f6\uff0cJMM\u4f1a\u628a\u8be5\u7ebf\u7a0b\u5bf9\u5e94\u7684\u672c\u5730\u5185\u5b58\u7f6e\u4e3a\u65e0\u6548\u3002\u4ece\u800c\u4f7f\u5f97\u88ab\u76d1\u89c6\u5668\u4fdd\u62a4\u7684\u4e34\u754c\u533a\u4ee3\u7801\u5fc5\u987b\u8981\u4ece\u4e3b\u5185\u5b58\u4e2d\u53bb\u8bfb\u53d6\u5171\u4eab\u53d8\u91cf\u3002<\/p>\n
\u9501\u91ca\u653e\u4e0e\u83b7\u53d6\u603b\u7ed3\u4e3a\u5982\u4e0b\u4e09\u6761<\/p>\n
1. \u7ebf\u7a0b A \u91ca\u653e\u4e00\u4e2a\u9501\uff0c\u5b9e\u8d28\u4e0a\u662f\u7ebf\u7a0b A \u5411\u63a5\u4e0b\u6765\u5c06\u8981\u83b7\u53d6\u8fd9\u4e2a\u9501\u7684\u67d0\u4e2a\u7ebf\u7a0b\u53d1\u51fa \u4e86\uff08\u7ebf\u7a0b A \u5bf9\u5171\u4eab\u53d8\u91cf\u6240\u505a\u4fee\u6539\u7684\uff09\u6d88\u606f\u3002<\/p>\n
2. \u7ebf\u7a0b B \u83b7\u53d6\u4e00\u4e2a\u9501\uff0c\u5b9e\u8d28\u4e0a\u662f\u7ebf\u7a0b B \u63a5\u6536\u4e86\u4e4b\u524d\u67d0\u4e2a\u7ebf\u7a0b\u53d1\u51fa\u7684\uff08\u5728\u91ca\u653e\u8fd9\u4e2a \u9501\u4e4b\u524d\u5bf9\u5171\u4eab\u53d8\u91cf\u6240\u505a\u4fee\u6539\u7684\uff09\u6d88\u606f\u3002<\/p>\n
3. \u7ebf\u7a0b A \u91ca\u653e\u9501\uff0c\u968f\u540e\u7ebf\u7a0b B \u83b7\u53d6\u8fd9\u4e2a\u9501\uff0c\u8fd9\u4e2a\u8fc7\u7a0b\u5b9e\u8d28\u4e0a\u662f\u7ebf\u7a0b A \u901a\u8fc7\u4e3b\u5185\u5b58 \u5411\u7ebf\u7a0b B \u53d1\u9001\u6d88\u606f\u3002<\/p>\n
6.3 \u9501\u5185\u5b58\u8bed\u4e49\u7684\u5b9e\u73b0<\/p>\n
\u9501\u7684\u5185\u5b58\u8bed\u4e49\u7684\u5177\u4f53\u5b9e\u73b0\u501f\u52a9\u4e86volatile\u53d8\u91cf\u7684\u5185\u5b58\u8bed\u4e49\u7684\u5b9e\u73b0\u3002<\/p>\n
\u4e03\u3001final<\/strong><\/p>\n
\u5bf9\u4e8e final \u57df\uff0c\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u8981\u9075\u5b88\u4e24\u4e2a\u91cd\u6392\u5e8f\u89c4\u5219\uff1a<\/p>\n
1. \u5728\u6784\u9020\u51fd\u6570\u5185\u5bf9\u4e00\u4e2a final \u57df\u7684\u5199\u5165\uff0c\u4e0e\u968f\u540e\u628a\u8fd9\u4e2a\u88ab\u6784\u9020\u5bf9\u8c61\u7684\u5f15\u7528\u8d4b\u503c\u7ed9\u4e00\u4e2a\u5f15\u7528\u53d8\u91cf\uff0c\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u4e4b\u95f4\u4e0d\u80fd\u91cd\u6392\u5e8f\u3002<\/p>\n
2. \u521d\u6b21\u8bfb\u4e00\u4e2a\u5305\u542b final \u57df\u7684\u5bf9\u8c61\u7684\u5f15\u7528\uff0c\u4e0e\u968f\u540e\u521d\u6b21\u8bfb\u8fd9\u4e2a final \u57df\uff0c\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u4e4b\u95f4\u4e0d\u80fd\u91cd\u6392\u5e8f\u3002<\/p>\n
\u5982\u4e0b\u9762\u793a\u4f8b\u5c55\u793a\u4e86final\u4e24\u79cd\u91cd\u6392\u5e8f\u89c4\u5219\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
public final class FinalExample {\n    final int i;\n    public FinalExample() {\n        i = 3; \/\/ 1\n    }\n\n    public static void main(String[] args) {\n        FinalExample fe = new FinalExample(); \/\/ 2\n        int ele = fe.i; \/\/ 3\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a \u64cd\u4f5c1\u4e0e\u64cd\u4f5c2\u7b26\u5408\u91cd\u6392\u5e8f\u89c4\u52191\uff0c\u4e0d\u80fd\u91cd\u6392\uff0c\u64cd\u4f5c2\u4e0e\u64cd\u4f5c3\u7b26\u5408\u91cd\u6392\u5e8f\u89c4\u52192\uff0c\u4e0d\u80fd\u91cd\u6392\u3002<\/p>\n
\u7531\u4e0b\u9762\u7684\u793a\u4f8b\u6211\u4eec\u6765\u5177\u4f53\u7406\u89e3final\u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
public class FinalExample {\n    int i; \/\/ \u666e\u901a\u53d8\u91cf\n    final int j; \/\/ final\u53d8\u91cf\n    static FinalExample obj; \/\/ \u9759\u6001\u53d8\u91cf\n\n    public void FinalExample () { \/\/ \u6784\u9020\u51fd\u6570\n        i = 1; \/\/ \u5199\u666e\u901a\u57df\n        j = 2; \/\/ \u5199final\u57df\n    }\n\n    public static void writer () { \/\/ \u5199\u7ebf\u7a0bA\u6267\u884c\n        obj = new FinalExample();\n    }\n\n    public static void reader () { \/\/ \u8bfb\u7ebf\u7a0bB\u6267\u884c\n        FinalExample object = obj; \/\/ \u8bfb\u5bf9\u8c61\u5f15\u7528\n        int a = object.i; \/\/ \u8bfb\u666e\u901a\u57df\n        int b = object.j; \/\/ \u8bfbfinal\u57df\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a\u5047\u8bbe\u7ebf\u7a0bA\u5148\u6267\u884cwriter()\u65b9\u6cd5\uff0c\u968f\u540e\u53e6\u4e00\u4e2a\u7ebf\u7a0bB\u6267\u884creader()\u65b9\u6cd5\u3002\u4e0b\u9762\u6211\u4eec\u901a\u8fc7\u8fd9\u4e24\u4e2a\u7ebf\u7a0b\u7684\u4ea4\u4e92\u6765\u8bf4\u660e\u8fd9\u4e24\u4e2a\u89c4\u5219\u3002<\/p>\n
7.1 \u5199final\u57df\u91cd\u6392\u5e8f\u89c4\u5219<\/p>\n
\u5199 final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u7981\u6b62\u628a final \u57df\u7684\u5199\u91cd\u6392\u5e8f\u5230\u6784\u9020\u51fd\u6570\u4e4b\u5916\u3002\u8fd9\u4e2a\u89c4\u5219\u7684\u5b9e \u73b0\u5305\u542b\u4e0b\u9762\u4e24\u4e2a\u65b9\u9762\uff1a<\/p>\n
1. JMM \u7981\u6b62\u7f16\u8bd1\u5668\u628a final \u57df\u7684\u5199\u91cd\u6392\u5e8f\u5230\u6784\u9020\u51fd\u6570\u4e4b\u5916\u3002<\/p>\n
2. \u7f16\u8bd1\u5668\u4f1a\u5728 final \u57df\u7684\u5199\u4e4b\u540e\uff0c\u6784\u9020\u51fd\u6570 return \u4e4b\u524d\uff0c\u63d2\u5165\u4e00\u4e2a StoreStore \u5c4f\u969c\u3002\u8fd9\u4e2a\u5c4f\u969c\u7981\u6b62\u5904\u7406\u5668\u628a final \u57df\u7684\u5199\u91cd\u6392\u5e8f\u5230\u6784\u9020\u51fd\u6570\u4e4b\u5916\u3002<\/p>\n
writer\u65b9\u6cd5\u7684obj =\u00a0new\u00a0FinalExample();\u5176\u5b9e\u5305\u62ec\u4e24\u6b65\uff0c\u9996\u5148\u662f\u5728\u5806\u4e0a\u5206\u914d\u4e00\u5757\u5185\u5b58\u7a7a\u95f4\u7b80\u5386FinalExample\u5bf9\u8c61\uff0c\u7136\u540e\u5c06\u8fd9\u4e2a\u5bf9\u8c61\u7684\u5730\u5740\u8d4b\u503c\u7ed9obj\u5f15\u7528\u3002\u5047\u8bbe\u7ebf\u7a0b B \u8bfb\u5bf9\u8c61\u5f15\u7528\u4e0e\u8bfb\u5bf9\u8c61\u7684\u6210\u5458\u57df\u4e4b\u95f4\u6ca1\u6709\u91cd\u6392\u5e8f\uff0c\u5219\u53ef\u80fd\u7684\u65f6\u5e8f\u56fe\u5982\u4e0b<\/p>\n
 <\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u5199\u666e\u901a\u57df\u7684\u64cd\u4f5c\u88ab\u7f16\u8bd1\u5668\u91cd\u6392\u5e8f\u5230\u4e86\u6784\u9020\u51fd\u6570\u4e4b\u5916\uff0c\u8bfb\u7ebf\u7a0b B \u9519\u8bef\u7684\u8bfb\u53d6\u4e86\u666e\u901a\u53d8\u91cf i \u521d\u59cb\u5316\u4e4b\u524d\u7684\u503c\u3002\u800c\u5199 final \u57df\u7684\u64cd\u4f5c\uff0c\u88ab\u5199 final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219 \u201c\u9650\u5b9a\u201d\u5728\u4e86\u6784\u9020\u51fd\u6570\u4e4b\u5185\uff0c\u8bfb\u7ebf\u7a0b B \u6b63\u786e\u7684\u8bfb\u53d6\u4e86 final \u53d8\u91cf\u521d\u59cb\u5316\u4e4b\u540e\u7684\u503c\u3002\u5199 final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u53ef\u4ee5\u786e\u4fdd\uff1a\u5728\u5bf9\u8c61\u5f15\u7528\u4e3a\u4efb\u610f\u7ebf\u7a0b\u53ef\u89c1\u4e4b\u524d\uff0c\u5bf9\u8c61\u7684 final \u57df\u5df2\u7ecf\u88ab\u6b63\u786e\u521d\u59cb\u5316\u8fc7\u4e86\uff0c\u800c\u666e\u901a\u57df\u4e0d\u5177\u6709\u8fd9\u4e2a\u4fdd\u969c\u3002\u4ee5\u4e0a\u56fe\u4e3a\u4f8b\uff0c\u5728\u8bfb\u7ebf\u7a0b B \u201c\u770b\u5230\u201d\u5bf9\u8c61\u5f15\u7528 obj \u65f6\uff0c\u5f88\u53ef\u80fd obj \u5bf9\u8c61\u8fd8\u6ca1\u6709\u6784\u9020\u5b8c\u6210\uff08\u5bf9\u666e\u901a\u57df i \u7684\u5199\u64cd\u4f5c\u88ab\u91cd\u6392\u5e8f\u5230\u6784\u9020\u51fd\u6570\u5916\uff0c\u6b64\u65f6\u521d\u59cb\u503c 2 \u8fd8\u6ca1\u6709\u5199\u5165\u666e\u901a\u57df i\uff09\u3002<\/p>\n
7.2 \u8bfbfinal\u57df\u91cd\u6392\u5e8f\u89c4\u5219<\/p>\n
\u8bfb final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u5982\u4e0b\uff1a<\/p>\n
\u5728\u4e00\u4e2a\u7ebf\u7a0b\u4e2d\uff0c\u521d\u6b21\u8bfb\u5bf9\u8c61\u5f15\u7528\u4e0e\u521d\u6b21\u8bfb\u8be5\u5bf9\u8c61\u5305\u542b\u7684 final \u57df\uff0cJMM \u7981\u6b62\u5904\u7406\u5668\u91cd\u6392\u5e8f\u8fd9\u4e24\u4e2a\u64cd\u4f5c\uff08\u6ce8\u610f\uff0c\u8fd9\u4e2a\u89c4\u5219\u4ec5\u4ec5\u9488\u5bf9\u5904\u7406\u5668\uff09\u3002\u7f16\u8bd1\u5668\u4f1a\u5728\u8bfb final \u57df\u64cd\u4f5c\u7684\u524d\u9762\u63d2\u5165\u4e00\u4e2a LoadLoad \u5c4f\u969c\u3002\u521d\u6b21\u8bfb\u5bf9\u8c61\u5f15\u7528\u4e0e\u521d\u6b21\u8bfb\u8be5\u5bf9\u8c61\u5305\u542b\u7684 final \u57df\uff0c\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u4e4b\u95f4\u5b58\u5728\u95f4\u63a5\u4f9d\u8d56\u5173\u7cfb\u3002\u7531\u4e8e\u7f16\u8bd1\u5668\u9075\u5b88\u95f4\u63a5\u4f9d\u8d56\u5173\u7cfb\uff0c\u56e0\u6b64\u7f16\u8bd1\u5668\u4e0d\u4f1a\u91cd\u6392\u5e8f\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u3002\u5927\u591a\u6570\u5904\u7406\u5668\u4e5f\u4f1a\u9075\u5b88\u95f4\u63a5\u4f9d\u8d56\uff0c\u5927\u591a\u6570\u5904\u7406\u5668\u4e5f\u4e0d\u4f1a\u91cd\u6392\u5e8f\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u3002\u4f46\u6709\u5c11\u6570\u5904\u7406\u5668\u5141\u8bb8\u5bf9\u5b58\u5728\u95f4\u63a5\u4f9d\u8d56\u5173\u7cfb\u7684\u64cd\u4f5c\u505a\u91cd\u6392\u5e8f\uff08\u6bd4\u5982 alpha \u5904\u7406\u5668\uff09\uff0c\u8fd9\u4e2a\u89c4\u5219\u5c31\u662f\u4e13\u95e8\u7528\u6765\u9488\u5bf9\u8fd9\u79cd\u5904\u7406\u5668\u3002<\/p>\n
reader\u65b9\u6cd5\u5305\u542b\u4e09\u4e2a\u64cd\u4f5c\uff1a\u2460 \u521d\u6b21\u8bfb\u5f15\u7528\u53d8\u91cf obj\u3002\u2461 \u521d\u6b21\u8bfb\u5f15\u7528\u53d8\u91cf obj \u6307\u5411\u5bf9\u8c61\u7684\u666e\u901a\u57df i\u3002\u2462 \u521d\u6b21\u8bfb\u5f15\u7528\u53d8\u91cf obj \u6307\u5411\u5bf9\u8c61\u7684 final \u57df j\u3002\u5047\u8bbe\u5199\u7ebf\u7a0b A \u6ca1\u6709\u53d1\u751f\u4efb\u4f55\u91cd\u6392\u5e8f\uff0c\u540c\u65f6\u7a0b\u5e8f\u5728\u4e0d\u9075\u5b88\u95f4\u63a5\u4f9d\u8d56\u7684\u5904\u7406\u5668\u4e0a\u6267\u884c\uff0c\u4e0b\u9762\u662f\u4e00\u79cd\u53ef\u80fd\u7684\u6267\u884c\u65f6\u5e8f\uff1a<\/p>\n
\"\"<\/div>\n
\u3000\u3000\u8bf4\u660e\uff1areader\u64cd\u4f5c\u4e2d1\u30012\u64cd\u4f5c\u91cd\u6392\u4e86\uff0c\u5373\u8bfb\u5bf9\u8c61\u7684\u666e\u901a\u57df\u7684\u64cd\u4f5c\u88ab\u5904\u7406\u5668\u91cd\u6392\u5e8f\u5230\u8bfb\u5bf9\u8c61\u5f15\u7528\u4e4b\u524d\u3002\u8bfb\u666e\u901a\u57df\u65f6\uff0c\u8be5\u57df\u8fd8\u6ca1\u6709\u88ab\u5199\u7ebf\u7a0b A \u5199\u5165\uff0c\u8fd9\u662f\u4e00\u4e2a\u9519\u8bef\u7684\u8bfb\u53d6\u64cd\u4f5c\u3002\u800c\u8bfb final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u4f1a\u628a\u8bfb\u5bf9\u8c61 final \u57df\u7684\u64cd\u4f5c\u201c\u9650\u5b9a\u201d\u5728\u8bfb\u5bf9\u8c61\u5f15\u7528\u4e4b\u540e\uff0c\u6b64\u65f6\u8be5 final \u57df\u5df2\u7ecf\u88ab A \u7ebf\u7a0b\u521d\u59cb\u5316\u8fc7\u4e86\uff0c\u8fd9\u662f\u4e00\u4e2a\u6b63\u786e\u7684\u8bfb\u53d6\u64cd\u4f5c\u3002\u8bfb final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u53ef\u4ee5\u786e\u4fdd\uff1a\u5728\u8bfb\u4e00\u4e2a\u5bf9\u8c61\u7684 final \u57df\u4e4b\u524d\uff0c\u4e00\u5b9a\u4f1a\u5148\u8bfb\u5305\u542b\u8fd9\u4e2a final \u57df\u7684\u5bf9\u8c61\u7684\u5f15\u7528\u3002\u5728\u8fd9\u4e2a\u793a\u4f8b\u7a0b\u5e8f\u4e2d\uff0c\u5982\u679c\u8be5\u5f15\u7528\u4e0d\u4e3a null\uff0c\u90a3\u4e48\u5f15\u7528\u5bf9\u8c61\u7684 final \u57df\u4e00\u5b9a\u5df2\u7ecf\u88ab A \u7ebf\u7a0b\u521d\u59cb\u5316\u8fc7\u4e86\u3002<\/div>\n
7.3 final\u57df\u662f\u5f15\u7528\u7c7b\u578b<\/p>\n
\u3000\u3000\u4e0a\u9762\u6211\u4eec\u7684\u4f8b\u5b50\u4e2d\uff0cfinal\u57df\u662f\u57fa\u672c\u6570\u636e\u7c7b\u578b\uff0c\u5982\u679cfinal\u4e0e\u4e3a\u5f15\u7528\u7c7b\u578b\u7684\u8bdd\u60c5\u51b5\u4f1a\u7a0d\u5fae\u4e0d\u540c\u3002\u5bf9\u4e8e\u5f15\u7528\u7c7b\u578b\uff0c\u5199 final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u5bf9\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u589e\u52a0\u4e86\u5982\u4e0b\u7ea6\u675f<\/div>\n
\u3000\u30001. \u5728\u6784\u9020\u51fd\u6570\u5185\u5bf9\u4e00\u4e2a final \u5f15\u7528\u7684\u5bf9\u8c61\u7684\u6210\u5458\u57df\u7684\u5199\u5165\uff0c\u4e0e\u968f\u540e\u5728\u6784\u9020\u51fd\u6570\u5916\u628a\u8fd9\u4e2a\u88ab\u6784\u9020\u5bf9\u8c61\u7684\u5f15\u7528\u8d4b\u503c\u7ed9\u4e00\u4e2a\u5f15\u7528\u53d8\u91cf\uff0c\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u4e4b\u95f4\u4e0d\u80fd\u91cd\u6392\u5e8f\u3002<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
public class FinalReferenceExample {\n    final int[] intArray; \/\/ final \u662f\u5f15\u7528\u7c7b\u578b\n    static FinalReferenceExample obj;\n\n    public FinalReferenceExample () { \/\/ \u6784\u9020\u51fd\u6570\n        int Array = new int[1]; \/\/ 1\n        int    Array[0] = 1; \/\/ 2\n    }\n\n    public static void writerOne () { \/\/ \u5199\u7ebf\u7a0b A \u6267\u884c\n        obj = new FinalReferenceExample (); \/\/ 3\n    }\n\n    public static void writerTwo () { \/\/ \u5199\u7ebf\u7a0b B \u6267\u884c\n        obj.intArray[0] = 2; \/\/ 4\n    }\n\n    public static void reader () { \/\/ \u8bfb\u7ebf\u7a0b C \u6267\u884c\n        if (obj != null) {    \/\/5\n            int temp1 = obj.intArray[0]; \/\/ 6\n        }\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a\u5047\u8bbe\u9996\u5148\u7ebf\u7a0b A \u6267\u884c writerOne()\u65b9\u6cd5\uff0c\u6267\u884c\u5b8c\u540e\u7ebf\u7a0b B \u6267\u884c writerTwo()\u65b9\u6cd5\uff0c\u6267\u884c\u5b8c\u540e\u7ebf\u7a0b C \u6267\u884c reader ()\u65b9\u6cd5\u3002\u4e0b\u9762\u662f\u4e00\u79cd\u53ef\u80fd\u7684\u7ebf\u7a0b\u6267\u884c\u65f6\u5e8f\uff1a<\/p>\n
\"\"
\n\u8bf4\u660e\uff1a1 \u662f\u5bf9 final \u57df\u7684\u5199\u5165\uff0c2 \u662f\u5bf9\u8fd9\u4e2a final \u57df\u5f15\u7528\u7684\u5bf9\u8c61\u7684\u6210\u5458\u57df\u7684\u5199\u5165\uff0c3 \u662f\u628a\u88ab\u6784\u9020\u7684\u5bf9\u8c61\u7684\u5f15\u7528\u8d4b\u503c\u7ed9\u67d0\u4e2a\u5f15\u7528\u53d8\u91cf\u3002\u8fd9\u91cc\u9664\u4e86\u524d\u9762\u63d0\u5230\u7684 1 \u4e0d\u80fd \u548c 3 \u91cd\u6392\u5e8f\u5916\uff0c2 \u548c 3 \u4e5f\u4e0d\u80fd\u91cd\u6392\u5e8f\u3002JMM \u53ef\u4ee5\u786e\u4fdd\u8bfb\u7ebf\u7a0b C \u81f3\u5c11\u80fd\u770b\u5230\u5199\u7ebf\u7a0b A \u5728\u6784\u9020\u51fd\u6570\u4e2d\u5bf9 final \u5f15\u7528\u5bf9\u8c61\u7684\u6210\u5458\u57df\u7684\u5199\u5165\u3002\u5373 C \u81f3\u5c11\u80fd\u770b\u5230\u6570\u7ec4\u4e0b\u6807 0 \u7684\u503c\u4e3a 1\u3002\u800c\u5199\u7ebf\u7a0b B \u5bf9\u6570\u7ec4\u5143\u7d20\u7684\u5199\u5165\uff0c\u8bfb\u7ebf\u7a0b C \u53ef\u80fd\u770b\u7684\u5230\uff0c\u4e5f\u53ef\u80fd\u770b\u4e0d\u5230\u3002JMM \u4e0d\u4fdd\u8bc1\u7ebf\u7a0b B \u7684\u5199\u5165\u5bf9\u8bfb\u7ebf\u7a0b C \u53ef\u89c1\uff0c\u56e0\u4e3a\u5199\u7ebf\u7a0b B \u548c\u8bfb\u7ebf\u7a0b C \u4e4b\u95f4\u5b58\u5728\u6570\u636e\u7ade\u4e89\uff0c\u6b64\u65f6\u7684\u6267\u884c\u7ed3\u679c\u4e0d\u53ef\u9884\u77e5\u3002<\/p>\n
\n
\u3000\u3000\u5982\u679c\u60f3\u8981\u786e\u4fdd\u8bfb\u7ebf\u7a0b C \u770b\u5230\u5199\u7ebf\u7a0b B \u5bf9\u6570\u7ec4\u5143\u7d20\u7684\u5199\u5165\uff0c\u5199\u7ebf\u7a0b B \u548c\u8bfb\u7ebf\u7a0b C \u4e4b\u95f4\u9700\u8981\u4f7f\u7528\u540c\u6b65\u539f\u8bed\uff08lock \u6216 volatile\uff09\u6765\u786e\u4fdd\u5185\u5b58\u53ef\u89c1\u6027\u3002<\/p>\n
7.4 final\u9038\u51fa<\/p>\n
\u5199 final \u57df\u7684\u91cd\u6392\u5e8f\u89c4\u5219\u53ef\u4ee5\u786e\u4fdd\uff1a\u5728\u5f15\u7528\u53d8\u91cf\u4e3a\u4efb\u610f\u7ebf\u7a0b\u53ef\u89c1 \u4e4b\u524d\uff0c\u8be5\u5f15\u7528\u53d8\u91cf\u6307\u5411\u7684\u5bf9\u8c61\u7684 final \u57df\u5df2\u7ecf\u5728\u6784\u9020\u51fd\u6570\u4e2d\u88ab\u6b63\u786e\u521d\u59cb\u5316\u8fc7\u4e86\u3002\u5176 \u5b9e\u8981\u5f97\u5230\u8fd9\u4e2a\u6548\u679c\uff0c\u8fd8\u9700\u8981\u4e00\u4e2a\u4fdd\u8bc1\uff1a\u5728\u6784\u9020\u51fd\u6570\u5185\u90e8\uff0c\u4e0d\u80fd\u8ba9\u8fd9\u4e2a\u88ab\u6784\u9020\u5bf9\u8c61\u7684 \u5f15\u7528\u4e3a\u5176\u4ed6\u7ebf\u7a0b\u53ef\u89c1\uff0c\u4e5f\u5c31\u662f\u5bf9\u8c61\u5f15\u7528\u4e0d\u80fd\u5728\u6784\u9020\u51fd\u6570\u4e2d\u201c\u9038\u51fa\u201d\u3002\u6211\u4eec\u6765\u770b\u4e0b\u9762\u793a\u4f8b\u4ee3\u7801\uff1a<\/p>\n
\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n
public class FinalReferenceEscapeExample {\n    final int i;\n    static FinalReferenceEscapeExample obj;\n\n    public FinalReferenceEscapeExample () {\n        i = 1;    \/\/1 \u5199 final \u57df\n        obj = this;    \/\/2 this \u5f15\u7528\u5728\u6b64\u201c\u9038\u51fa\u201d\n    }\n\n    public static void writer() {\n        new FinalReferenceEscapeExample ();\n    }\n\n    public static void reader {\n        if (obj != null) {    \/\/3\n        int temp = obj.i;    \/\/4\n        }\n    }\n}<\/pre>\n
\"\u590d\u5236\u4ee3\u7801\"<\/a><\/span><\/div>\n<\/div>\n
\u8bf4\u660e\uff1a\u5047\u8bbe\u4e00\u4e2a\u7ebf\u7a0b A \u6267\u884c writer()\u65b9\u6cd5\uff0c\u53e6\u4e00\u4e2a\u7ebf\u7a0b B \u6267\u884c reader()\u65b9\u6cd5\u3002\u8fd9\u91cc\u7684\u64cd\u4f5c 2 \u4f7f\u5f97\u5bf9\u8c61\u8fd8\u672a\u5b8c\u6210\u6784\u9020\u524d\u5c31\u4e3a\u7ebf\u7a0b B \u53ef\u89c1\u3002\u5373\u4f7f\u8fd9\u91cc\u7684\u64cd\u4f5c 2 \u662f\u6784\u9020\u51fd\u6570\u7684\u6700\u540e\u4e00\u6b65\uff0c\u4e14\u5373\u4f7f\u5728\u7a0b\u5e8f\u4e2d\u64cd\u4f5c 2 \u6392\u5728\u64cd\u4f5c 1 \u540e\u9762\uff0c\u6267\u884c read()\u65b9\u6cd5\u7684\u7ebf\u7a0b\u4ecd\u7136\u53ef\u80fd\u65e0 \u6cd5\u770b\u5230 final \u57df\u88ab\u521d\u59cb\u5316\u540e\u7684\u503c\uff0c\u56e0\u4e3a\u8fd9\u91cc\u7684\u64cd\u4f5c 1 \u548c\u64cd\u4f5c 2 \u4e4b\u95f4\u53ef\u80fd\u88ab\u91cd\u6392\u5e8f\u3002\u5b9e\u9645\u7684\u6267\u884c\u65f6\u5e8f\u53ef\u80fd\u5982\u4e0b\u56fe\u6240\u793a\uff1a<\/p>\n<\/div>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u5728\u6784\u9020\u51fd\u6570\u8fd4\u56de\u524d\uff0c\u88ab\u6784\u9020\u5bf9\u8c61\u7684\u5f15\u7528\u4e0d\u80fd\u4e3a\u5176\u4ed6\u7ebf\u7a0b\u53ef\u89c1\uff0c\u56e0\u4e3a\u6b64\u65f6\u7684 final \u57df\u53ef\u80fd\u8fd8\u6ca1\u6709\u88ab\u521d\u59cb\u5316\u3002\u5728\u6784\u9020\u51fd\u6570\u8fd4\u56de\u540e\uff0c\u4efb\u610f\u7ebf\u7a0b\u90fd\u5c06\u4fdd\u8bc1\u80fd\u770b\u5230 final \u57df\u6b63\u786e\u521d\u59cb\u5316\u4e4b\u540e\u7684\u503c\u3002<\/p>\n
\u516b\u3001JMM\u603b\u7ed3<\/strong><\/p>\n
\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u662f\u4e00\u4e2a\u7406\u8bba\u53c2\u8003\u6a21\u578b\uff0cJMM \u548c\u5904\u7406\u5668\u5185\u5b58\u6a21\u578b\u5728\u8bbe\u8ba1\u65f6\u901a\u5e38 \u4f1a\u628a\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4f5c\u4e3a\u53c2\u7167\u3002JMM\u548c\u5904\u7406\u5668\u5185\u5b58\u6a21\u578b\u5728\u8bbe\u8ba1\u65f6\u4f1a\u5bf9\u987a\u5e8f\u4e00 \u81f4\u6027\u6a21\u578b\u505a\u4e00\u4e9b\u653e\u677e\uff0c\u56e0\u4e3a\u5982\u679c\u5b8c\u5168\u6309\u7167\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u6765\u5b9e\u73b0\u5904\u7406\u5668\u548c JMM\uff0c \u90a3\u4e48\u5f88\u591a\u7684\u5904\u7406\u5668\u548c\u7f16\u8bd1\u5668\u4f18\u5316\u90fd\u8981\u88ab\u7981\u6b62\uff0c\u8fd9\u5bf9\u6267\u884c\u6027\u80fd\u5c06\u4f1a\u6709\u5f88\u5927\u7684\u5f71\u54cd\u3002<\/p>\n
8.1 JMM\u7684happens- before\u89c4\u5219<\/p>\n
JMM \u7684happens – before\u89c4\u5219\u8981\u6c42\u7981\u6b62\u7684\u91cd\u6392\u5e8f\u5206\u4e3a\u4e86\u4e0b\u9762\u4e24\u7c7b\uff1a<\/p>\n
1. \u4f1a\u6539\u53d8\u7a0b\u5e8f\u6267\u884c\u7ed3\u679c\u7684\u91cd\u6392\u5e8f\u3002<\/p>\n
2. \u4e0d\u4f1a\u6539\u53d8\u7a0b\u5e8f\u6267\u884c\u7ed3\u679c\u7684\u91cd\u6392\u5e8f\u3002<\/p>\n
JMM \u5bf9\u8fd9\u4e24\u79cd\u4e0d\u540c\u6027\u8d28\u7684\u91cd\u6392\u5e8f\uff0c\u91c7\u53d6\u4e86\u4e0d\u540c\u7684\u7b56\u7565\uff1a<\/p>\n
1. \u5bf9\u4e8e\u4f1a\u6539\u53d8\u7a0b\u5e8f\u6267\u884c\u7ed3\u679c\u7684\u91cd\u6392\u5e8f\uff0cJMM \u8981\u6c42\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u5fc5\u987b\u7981\u6b62\u8fd9\u79cd\u91cd\u6392\u5e8f\u3002<\/p>\n
2. \u5bf9\u4e8e\u4e0d\u4f1a\u6539\u53d8\u7a0b\u5e8f\u6267\u884c\u7ed3\u679c\u7684\u91cd\u6392\u5e8f\uff0cJMM \u5bf9\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u4e0d\u4f5c\u8981\u6c42\uff08JMM \u5141\u8bb8\u8fd9\u79cd\u91cd\u6392\u5e8f\uff09<\/p>\n
JMM\u7684happens – before\u8bbe\u8ba1\u793a\u610f\u56fe\u5982\u4e0b<\/p>\n
\"\"<\/p>\n
\u8bf4\u660e\uff1a\u4ece\u4e0a\u56fe\u53ef\u77e5<\/p>\n
1. JMM \u5411\u7a0b\u5e8f\u5458\u63d0\u4f9b\u7684 happens- before \u89c4\u5219\u80fd\u6ee1\u8db3\u7a0b\u5e8f\u5458\u7684\u9700\u6c42\u3002JMM \u7684 happens- before \u89c4\u5219\u4e0d\u4f46\u7b80\u5355\u6613\u61c2\uff0c\u800c\u4e14\u4e5f\u5411\u7a0b\u5e8f\u5458\u63d0\u4f9b\u4e86\u8db3\u591f\u5f3a\u7684\u5185\u5b58\u53ef \u89c1\u6027\u4fdd\u8bc1\uff08\u6709\u4e9b\u5185\u5b58\u53ef\u89c1\u6027\u4fdd\u8bc1\u5176\u5b9e\u5e76\u4e0d\u4e00\u5b9a\u771f\u5b9e\u5b58\u5728\uff0c\u6bd4\u5982\u4e0a\u9762\u7684 A happens- before B\uff09\u3002<\/p>\n
\n
\u3000\u30002. JMM \u5bf9\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u7684\u675f\u7f1a\u5df2\u7ecf\u5c3d\u53ef\u80fd\u7684\u5c11\u3002\u4ece\u4e0a\u9762\u7684\u5206\u6790\u6211\u4eec\u53ef\u4ee5\u770b\u51fa\uff0c JMM \u5176\u5b9e\u662f\u5728\u9075\u5faa\u4e00\u4e2a\u57fa\u672c\u539f\u5219\uff1a\u53ea\u8981\u4e0d\u6539\u53d8\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\uff08\u6307\u7684\u662f\u5355\u7ebf\u7a0b \u7a0b\u5e8f\u548c\u6b63\u786e\u540c\u6b65\u7684\u591a\u7ebf\u7a0b\u7a0b\u5e8f\uff09\uff0c\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u600e\u4e48\u4f18\u5316\u90fd\u884c\u3002\u6bd4\u5982\uff0c\u5982\u679c\u7f16\u8bd1\u5668\u7ecf\u8fc7\u7ec6\u81f4\u7684\u5206\u6790\u540e\uff0c\u8ba4\u5b9a\u4e00\u4e2a\u9501\u53ea\u4f1a\u88ab\u5355\u4e2a\u7ebf\u7a0b\u8bbf\u95ee\uff0c\u90a3\u4e48\u8fd9\u4e2a\u9501\u53ef\u4ee5\u88ab\u6d88\u9664\u3002\u518d\u6bd4\u5982\uff0c\u5982\u679c\u7f16\u8bd1\u5668\u7ecf\u8fc7\u7ec6\u81f4\u7684\u5206\u6790\u540e\uff0c\u8ba4\u5b9a\u4e00\u4e2a volatile \u53d8\u91cf\u4ec5\u4ec5\u53ea\u4f1a\u88ab\u5355\u4e2a\u7ebf\u7a0b\u8bbf\u95ee\uff0c\u90a3\u4e48\u7f16\u8bd1\u5668\u53ef\u4ee5\u628a\u8fd9\u4e2a volatile \u53d8\u91cf\u5f53\u4f5c\u4e00\u4e2a\u666e\u901a\u53d8\u91cf\u6765\u5bf9\u5f85\u3002\u8fd9\u4e9b\u4f18\u5316\u65e2\u4e0d\u4f1a\u6539\u53d8\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\uff0c\u53c8\u80fd\u63d0\u9ad8\u7a0b\u5e8f\u7684\u6267\u884c\u6548\u7387\u3002<\/p>\n<\/div>\n<\/div>\n
8.2 JMM\u7684\u5185\u5b58\u53ef\u89c1\u6027<\/p>\n
Java \u7a0b\u5e8f\u7684\u5185\u5b58\u53ef\u89c1\u6027\u4fdd\u8bc1\u6309\u7a0b\u5e8f\u7c7b\u578b\u53ef\u4ee5\u5206\u4e3a\u4e0b\u5217\u4e09\u7c7b\uff1a<\/p>\n
1. \u5355\u7ebf\u7a0b\u7a0b\u5e8f\u3002\u5355\u7ebf\u7a0b\u7a0b\u5e8f\u4e0d\u4f1a\u51fa\u73b0\u5185\u5b58\u53ef\u89c1\u6027\u95ee\u9898\u3002\u7f16\u8bd1\u5668\uff0cruntime \u548c\u5904\u7406\u5668\u4f1a\u5171\u540c\u786e\u4fdd\u5355\u7ebf\u7a0b\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u4e0e\u8be5\u7a0b\u5e8f\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u6a21\u578b\u4e2d\u7684\u6267\u884c\u7ed3\u679c\u76f8\u540c\u3002<\/p>\n
2. \u6b63\u786e\u540c\u6b65\u7684\u591a\u7ebf\u7a0b\u7a0b\u5e8f\u3002\u6b63\u786e\u540c\u6b65\u7684\u591a\u7ebf\u7a0b\u7a0b\u5e8f\u7684\u6267\u884c\u5c06\u5177\u6709\u987a\u5e8f\u4e00\u81f4\u6027\uff08\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u4e0e\u8be5\u7a0b\u5e8f\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4e2d\u7684\u6267\u884c\u7ed3\u679c\u76f8\u540c\uff09\u3002\u8fd9\u662f JMM \u5173\u6ce8\u7684\u91cd\u70b9\uff0cJMM \u901a\u8fc7\u9650\u5236\u7f16\u8bd1\u5668\u548c\u5904\u7406\u5668\u7684\u91cd\u6392\u5e8f\u6765\u4e3a\u7a0b\u5e8f\u5458\u63d0\u4f9b\u5185\u5b58\u53ef\u89c1\u6027\u4fdd\u8bc1\u3002<\/p>\n
3. \u672a\u540c\u6b65\/\u672a\u6b63\u786e\u540c\u6b65\u7684\u591a\u7ebf\u7a0b\u7a0b\u5e8f\u3002JMM \u4e3a\u5b83\u4eec\u63d0\u4f9b\u4e86\u6700\u5c0f\u5b89\u5168\u6027\u4fdd\u969c\uff1a\u7ebf\u7a0b\u6267\u884c\u65f6\u8bfb\u53d6\u5230\u7684\u503c\uff0c\u8981\u4e48\u662f\u4e4b\u524d\u67d0\u4e2a\u7ebf\u7a0b\u5199\u5165\u7684\u503c\uff0c\u8981\u4e48\u662f\u9ed8\u8ba4\u503c\uff080\uff0cnull\uff0c false\uff09\u3002<\/p>\n
\u8fd9\u4e09\u7c7b\u7a0b\u5e8f\u5728 JMM \u4e2d\u4e0e\u5728\u987a\u5e8f\u4e00\u81f4\u6027\u5185\u5b58\u6a21\u578b\u4e2d\u7684\u6267\u884c\u7ed3\u679c\u7684\u5f02\u540c\u5982\u4e0b<\/p>\n
\"\"<\/p>\n
\u4e5d\u3001\u603b\u7ed3<\/strong><\/p>\n
\u8fd9\u4e00\u7bc7\u7684\u5b8c\u7ed3\u4e5f\u610f\u5473\u7740\u770b\u5b8c\u4e86\u6574\u4e2aJVM\uff0c\u660e\u767d\u4e86\u5f88\u591aJVM\u5e95\u5c42\u7684\u77e5\u8bc6\uff0c\u8bfb\u5b8c\u540e\u611f\u89c9\u53d7\u76ca\u532a\u6d45\uff0c\u6574\u4e2a\u5b66\u4e60\u7b14\u8bb0\u6709\u70b9\u539a\uff0c\u65b9\u4fbf\u81ea\u5df1\u4ee5\u540e\u518d\u7cbe\u8bfb\u3002\u8fd8\u6709\u4e00\u4e2a\u5f88\u6df1\u7684\u611f\u89e6\u5c31\u662f\uff0c\u53ea\u6709\u8bb0\u4e0b\u6765\u7684\u77e5\u8bc6\u624d\u662f\u81ea\u5df1\u7684\uff0c\u517b\u6210\u8bb0\u5f55\u7684\u597d\u4e60\u60ef\uff0c\u4e00\u6b65\u6b65\u53d8\u6210\u9ad8\u624b\u3002\u8c22\u8c22\u5404\u4f4d\u56ed\u53cb\u7684\u89c2\u770b~<\/p>\n","protected":false},"excerpt":{"rendered":"
\u4e00\u3001\u524d\u8a00 \u7ecf\u8fc7\u524d\u9762\u7684\u5b66\u4e60\uff0c\u6211\u4eec\u7ec8\u4e8e\u8fdb\u5165\u4e86\u865a\u62df\u673a\u6700\u540e\u4e00\u90e8\u5206\u7684\u5b66\u4e60\uff0c\u5185\u5b58\u6a21\u578b\u3002\u7406\u89e3\u5185\u5b58\u6a21\u578b\u5bf9\u6211\u4eec\u7406\u89e3\u865a\u62df\u673a\u3001\u6b63\u786e\u4f7f\u7528\u591a\u7ebf\u7a0b\u7f16\u7a0b\u63d0\u4f9b\u5f88\u5927\u5e2e\u52a9\u3002\u4e0b\u9762\u5f00\u59cb\u6b63\u5f0f\u5b66\u4e60\u3002 \u4e8c\u3001Java\u5e76\u53d1\u57fa\u7840 \u5728\u5e76\u53d1\u7f16\u7a0b\u4e2d\u5b58\u5728\u4e24\u4e2a\u5173\u952e\u95ee\u9898\u2460\u7ebf\u7a0b\u4e4b\u95f4\u5982\u4f55\u901a\u4fe1 \u2461\u7ebf\u7a0b\u4e4b\u95f4\u5982\u4f55\u540c\u6b65\u3002 2.1 \u901a\u4fe1 \u901a\u4fe1\u662f\u6307\u7ebf\u7a0b\u4e4b\u95f4\u4ee5\u4f55\u79cd\u673a\u5236\u6765\u4ea4\u6362\u4fe1\u606f\u3002\u5728\u547d\u4ee4\u5f0f\u7f16\u7a0b\u4e2d\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u7684\u901a\u4fe1\u673a\u5236\u6709\u4e24\u79cd\uff1a\u5171\u4eab\u5185\u5b58\u548c\u6d88\u606f\u4f20\u9012\u3002 \u5728\u5171\u4eab\u5185\u5b58\u7684\u5e76\u53d1\u6a21\u578b\u91cc\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u5171\u4eab\u7a0b\u5e8f\u7684\u516c\u5171\u72b6\u6001\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u901a\u8fc7\u5199-\u8bfb\u5185\u5b58\u4e2d\u7684\u516c\u5171\u72b6\u6001\u6765\u9690\u5f0f\u8fdb\u884c\u901a\u4fe1\u3002 \u5728\u6d88\u606f\u4f20\u9012\u7684\u5e76\u53d1\u6a21\u578b\u91cc\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u6ca1\u6709\u516c\u5171\u72b6\u6001\uff0c\u7ebf\u7a0b\u4e4b\u95f4\u5fc5\u987b\u901a\u8fc7\u660e\u786e\u7684\u53d1\u9001\u6d88\u606f\u6765\u663e\u5f0f\u8fdb\u884c\u901a\u4fe1\u3002 2.2 \u540c\u6b65 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