{"id":10008328,"date":"2023-09-25T19:55:07","date_gmt":"2023-09-25T11:55:07","guid":{"rendered":"https:\/\/blog.itmax.cn\/?p=10008328"},"modified":"2023-09-25T19:55:07","modified_gmt":"2023-09-25T11:55:07","slug":"%e4%b8%80%e4%b8%aa-println-%e7%ab%9f%e7%84%b6%e6%af%94-volatile-%e8%bf%98%e5%a5%bd%e4%bd%bf%ef%bc%9f-%e4%ba%ac%e4%b8%9c%e4%ba%91%e6%8a%80%e6%9c%af%e5%9b%a2%e9%98%9f","status":"publish","type":"post","link":"https:\/\/itmax.cn\/?p=10008328","title":{"rendered":"\u4e00\u4e2a println \u7adf\u7136\u6bd4 volatile \u8fd8\u597d\u4f7f\uff1f | \u4eac\u4e1c\u4e91\u6280\u672f\u56e2\u961f"},"content":{"rendered":"

\u524d\u4e24\u5929\u4e00\u4e2a\u5c0f\u4f19\u4f34\u7a81\u7136\u627e\u6211\u6c42\u52a9\uff0c\u8bf4\u51c6\u5907\u6362\u4e2a\u5751\uff0c\u6700\u8fd1\u5728\u7cfb\u7edf\u590d\u4e60\u591a\u7ebf\u7a0b\u77e5\u8bc6\uff0c\u4f46\u9047\u5230\u4e86\u4e00\u4e2a\u5237\u65b0\u8ba4\u77e5\u7684\u95ee\u9898\u2026\u2026<\/p>\n

\u5c0f\u4f19\u4f34\uff1aEffective JAVA \u91cc\u7684\u5e76\u53d1\u7ae0\u8282\u91cc\uff0c\u6709\u4e00\u6bb5\u5173\u4e8e\u53ef\u89c1\u6027\u7684\u63cf\u8ff0\u3002\u4e0b\u9762\u8fd9\u6bb5\u4ee3\u7801\u4f1a\u51fa\u73b0\u6b7b\u5faa\u73af\uff0c\u8fd9\u4e2a\u6211\u80fd\u7406\u89e3\uff0cJMM \u5185\u5b58\u6a21\u578b\u561b\uff0cJMM \u4e0d\u4fdd\u8bc1 stopRequested \u7684\u4fee\u6539\u80fd\u88ab\u53ca\u65f6\u7684\u89c2\u6d4b\u5230\u3002<\/p><\/blockquote>\n

static boolean stopRequested = false;\n\npublic static void main(String[] args) throws InterruptedException {\n\n    Thread backgroundThread = new Thread(() -> {\n        int i = 0;\n        while (!stopRequested) {\n            i++;\n        }\n    }) ;\n    backgroundThread.start();\n    TimeUnit.MICROSECONDS.sleep(10);\n    stopRequested = true ;\n}\n\n\n\n<\/code><\/pre>\n
\u4f46\u5947\u602a\u7684\u662f\u5728\u6211\u52a0\u4e86\u4e00\u884c\u6253\u5370\u4e4b\u540e\uff0c\u5c31\u4e0d\u4f1a\u51fa\u73b0\u6b7b\u5faa\u73af\u4e86\uff01\u96be\u9053\u6211\u4e00\u884c println \u80fd\u6bd4 volatile \u8fd8\u597d\u4f7f\u554a\uff1f\u8fd9\u4fe9\u4e5f\u6ca1\u5173\u7cfb\u554a<\/p><\/blockquote>\n
static boolean stopRequested = false;\n\npublic static void main(String[] args) throws InterruptedException {\n\n    Thread backgroundThread = new Thread(() -> {\n        int i = 0;\n        while (!stopRequested) {\n            \n            \/\/ \u52a0\u4e0a\u4e00\u884c\u6253\u5370\uff0c\u5faa\u73af\u5c31\u80fd\u9000\u51fa\u4e86\uff01\n            System.out.println(i++);\n        }\n    }) ;\n    backgroundThread.start();\n    TimeUnit.MICROSECONDS.sleep(10);\n    stopRequested = true ;\n}\n\n\n\n<\/code><\/pre>\n
\n
\u6211\uff1a\u5c0f\u4f19\u5b50\u516b\u80a1\u6587\u80cc\u7684\u633a\u719f\u554a\uff0cJMM \u5f20\u53e3\u5c31\u6765\u3002  
\u200b<\/p>\n
\u6211\uff1a\u8fd9\u4e2a\u2026\u2026\u5176\u5b9e\u662f JIT \u5e72\u7684\u597d\u4e8b\uff0c\u5bfc\u81f4\u4f60\u7684\u5faa\u73af\u65e0\u6cd5\u9000\u51fa\u3002JMM \u53ea\u662f\u4e00\u4e2a\u903b\u8f91\u4e0a\u7684\u5185\u5b58\u6a21\u578b\u89c4\u8303\uff0cJIT\u53ef\u4ee5\u6839\u636eJMM\u7684\u89c4\u8303\u6765\u8fdb\u884c\u4f18\u5316\u3002<\/p>\n
\u6bd4\u5982\u4f60\u7b2c\u4e00\u4e2a\u4f8b\u5b50\u91cc\uff0c\u4f60\u7528-Xint<\/code>\u7981\u7528 JIT\uff0c\u5c31\u53ef\u4ee5\u9000\u51fa\u6b7b\u5faa\u73af\u4e86\uff0c\u4e0d\u4fe1\u4f60\u8bd5\u8bd5\uff1f<\/p>\n
\u5c0f\u4f19\u4f34\uff1aWK\uff0c\u771f\u7684\u53ef\u4ee5\uff0c\u52a0\u4e0a -Xint \u5faa\u73af\u5c31\u9000\u51fa\u4e86\uff0c\u597d\u795e\u5947\uff01JIT \u662f\u4e2a\u5565\u554a\uff1f\u8fd8\u80fd\u6709\u8fd9\u79cd\u529f\u6548\uff1f<\/p>\n<\/blockquote>\n
\"image.png\"<\/p>\n
JIT\uff08Just-in-Time\uff09 \u7684\u4f18\u5316<\/h2>\n
\u4f17\u6240\u5468\u77e5\uff0cJAVA \u4e3a\u4e86\u5b9e\u73b0\u8de8\u5e73\u53f0\uff0c\u589e\u52a0\u4e86\u4e00\u5c42 JVM\uff0c\u4e0d\u540c\u5e73\u53f0\u7684 JVM \u8d1f\u8d23\u89e3\u91ca\u6267\u884c\u5b57\u8282\u7801\u6587\u4ef6\u3002\u867d\u7136\u6709\u4e00\u5c42\u89e3\u91ca\u4f1a\u5f71\u54cd\u6548\u7387\uff0c\u4f46\u597d\u5904\u662f\u8de8\u5e73\u53f0\uff0c\u5b57\u8282\u7801\u6587\u4ef6\u662f\u5e73\u53f0\u65e0\u5173\u7684\u3002  
\"image.png\"  
\u5728 JAVA 1.2 \u4e4b\u540e\uff0c\u589e\u52a0\u4e86\u5373\u65f6\u7f16\u8bd1\uff08Just-in-Time Compilation\uff0c\u7b80\u79f0 JIT\uff09<\/strong>\u7684\u673a\u5236\uff0c\u5728\u8fd0\u884c\u65f6\u53ef\u4ee5\u5c06\u6267\u884c\u6b21\u6570\u8f83\u591a\u7684\u70ed\u70b9\u4ee3\u7801\u7f16\u8bd1\u4e3a\u673a\u5668\u7801\uff0c\u8fd9\u6837\u5c31\u4e0d\u9700\u8981 JVM \u518d\u89e3\u91ca\u4e00\u904d\u4e86\uff0c\u53ef\u4ee5\u76f4\u63a5\u6267\u884c\uff0c\u589e\u52a0\u8fd0\u884c\u6548\u7387\u3002  
\"image.png\"  
\u200b<\/p>\n
\u4f46 JIT \u7f16\u8bd1\u5668\u5728\u7f16\u8bd1\u5b57\u8282\u7801\u65f6\uff0c\u53ef\u4e0d\u4ec5\u4ec5\u662f\u7b80\u5355\u7684\u76f4\u63a5\u5c06\u5b57\u8282\u7801\u7ffb\u8bd1\u6210\u673a\u5668\u7801<\/strong>\uff0c\u5b83\u5728\u7f16\u8bd1\u7684\u540c\u65f6\u8fd8\u4f1a\u505a\u5f88\u591a\u4f18\u5316\uff0c\u6bd4\u5982\u5faa\u73af\u5c55\u5f00\u3001\u65b9\u6cd5\u5185\u8054\u7b49\u7b49\u2026\u2026  
\u200b<\/p>\n
\u8fd9\u4e2a\u95ee\u9898\u51fa\u73b0\u7684\u539f\u56e0\uff0c\u5c31\u662f\u56e0\u4e3a JIT \u7f16\u8bd1\u5668\u7684\u4f18\u5316\u6280\u672f\u4e4b\u4e00 –\u8868\u8fbe\u5f0f\u63d0\u5347\uff08expression hoisting\uff09<\/strong>\u5bfc\u81f4\u7684\u3002<\/p>\n
\u8868\u8fbe\u5f0f\u63d0\u5347\uff08expression hoisting\uff09<\/h4>\n
\u5148\u6765\u770b\u4e2a\u4f8b\u5b50\uff0c\u5728\u8fd9\u4e2ahoisting<\/code>\u65b9\u6cd5\u4e2d\uff0cfor \u5faa\u73af\u91cc\u6bcf\u6b21\u90fd\u4f1a\u5b9a\u4e49\u4e00\u4e2a\u53d8\u91cfy<\/code>\uff0c\u7136\u540e\u901a\u8fc7\u5c06 x*y \u7684\u7ed3\u679c\u5b58\u50a8\u5728\u4e00\u4e2a result \u53d8\u91cf\u4e2d\uff0c\u7136\u540e\u4f7f\u7528\u8fd9\u4e2a\u53d8\u91cf\u8fdb\u884c\u5404\u79cd\u64cd\u4f5c<\/p>\n
public void hoisting(int x) {\n    for (int i = 0; i < 1000; i = i + 1) {\n        \/\/ \u5faa\u73af\u4e0d\u53d8\u7684\u8ba1\u7b97 \n        int y = 654;\n        int result = x * y;\n        \n        \/\/ ...... \u57fa\u4e8e\u8fd9\u4e2a result \u53d8\u91cf\u7684\u5404\u79cd\u64cd\u4f5c\n    }\n}\n\n\n\n<\/code><\/pre>\n
\u4f46\u662f\u8fd9\u4e2a\u4f8b\u5b50\u91cc\uff0cresult \u7684\u7ed3\u679c\u662f\u56fa\u5b9a\u7684\uff0c\u5e76\u4e0d\u4f1a\u8ddf\u7740\u5faa\u73af\u800c\u66f4\u65b0\u3002\u6240\u4ee5\u5b8c\u5168\u53ef\u4ee5\u5c06 result \u7684\u8ba1\u7b97\u63d0\u53d6\u5230\u5faa\u73af\u4e4b\u5916\uff0c\u8fd9\u6837\u5c31\u4e0d\u7528\u6bcf\u6b21\u8ba1\u7b97\u4e86\u3002JIT \u5206\u6790\u540e\u4f1a\u5bf9\u8fd9\u6bb5\u4ee3\u7801\u8fdb\u884c\u4f18\u5316\uff0c\u8fdb\u884c\u8868\u8fbe\u5f0f\u63d0\u5347\u7684\u64cd\u4f5c\uff1a<\/p>\n
public void hoisting(int x) {\n    int y = 654;\n    int result = x * y;\n    \n    for (int i = 0; i < 1000; i = i + 1) {    \n        \/\/ ...... \u57fa\u4e8e\u8fd9\u4e2a result \u53d8\u91cf\u7684\u5404\u79cd\u64cd\u4f5c\n    }\n}\n\n\n\n<\/code><\/pre>\n
\u8fd9\u6837\u4e00\u6765\uff0cresult \u4e0d\u7528\u6bcf\u6b21\u8ba1\u7b97\u4e86\uff0c\u800c\u4e14\u4e5f\u5b8c\u5168\u4e0d\u5f71\u54cd\u6267\u884c\u7ed3\u679c\uff0c\u5927\u5927\u63d0\u5347\u4e86\u6267\u884c\u6548\u7387\u3002<\/p>\n
\u6ce8\u610f\uff0c\u7f16\u8bd1\u5668\u66f4\u559c\u6b22\u5c40\u90e8\u53d8\u91cf\uff0c\u800c\u4e0d\u662f\u9759\u6001\u53d8\u91cf\u6216\u8005\u6210\u5458\u53d8\u91cf\uff1b\u56e0\u4e3a\u9759\u6001\u53d8\u91cf\u662f\u201c\u9003\u9038\u5728\u5916\u7684\u201d\uff0c\u591a\u4e2a\u7ebf\u7a0b\u90fd\u53ef\u4ee5\u8bbf\u95ee\u5230\uff0c\u800c\u5c40\u90e8\u53d8\u91cf\u662f\u7ebf\u7a0b\u79c1\u6709\u7684\uff0c\u4e0d\u4f1a\u88ab\u5176\u4ed6\u7ebf\u7a0b\u8bbf\u95ee\u548c\u4fee\u6539\u3002  
\u200b<\/p>\n
\u7f16\u8bd1\u5668\u5728\u5904\u7406\u9759\u6001\u53d8\u91cf\/\u6210\u5458\u53d8\u91cf\u65f6\uff0c\u4f1a\u6bd4\u8f83\u4fdd\u5b88\uff0c\u4e0d\u4f1a\u8f7b\u6613\u4f18\u5316\u3002  
\u200b<\/p>\n
\u50cf\u4f60\u95ee\u9898\u91cc\u7684\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\uff0cstopRequested<\/code>\u5c31\u662f\u4e2a\u9759\u6001\u53d8\u91cf\uff0c\u7f16\u8bd1\u5668\u672c\u4e0d\u5e94\u8be5\u5bf9\u5176\u8fdb\u884c\u4f18\u5316\u5904\u7406\uff1b<\/p>\n
static boolean stopRequested = false;\/\/ \u9759\u6001\u53d8\u91cf\n\npublic static void main(String[] args) throws InterruptedException {\n\n    Thread backgroundThread = new Thread(() -> {\n        int i = 0;\n        while (!stopRequested) {\n            \/\/ leaf method\n            i++;\n        }\n    }) ;\n    backgroundThread.start();\n    TimeUnit.MICROSECONDS.sleep(10);\n    stopRequested = true ;\n}\n\n\n\n<\/code><\/pre>\n
\u4f46\u7531\u4e8e\u4f60\u8fd9\u4e2a\u5faa\u73af\u662f\u4e2aleaf method<\/code>\uff0c\u5373\u6ca1\u6709\u8c03\u7528\u4efb\u4f55\u65b9\u6cd5\uff0c\u6240\u4ee5\u5728\u5faa\u73af\u4e4b\u4e2d\u4e0d\u4f1a\u6709\u5176\u4ed6\u7ebf\u7a0b\u4f1a\u89c2\u6d4b\u5230stopRequested<\/code>\u503c\u7684\u53d8\u5316\u3002\u90a3\u4e48\u7f16\u8bd1\u5668\u5c31\u5192\u8fdb\u7684\u8fdb\u884c\u4e86\u8868\u8fbe\u5f0f\u63d0\u5347<\/strong>\u7684\u64cd\u4f5c\uff0c\u5c06stopRequested<\/code>\u63d0\u5347\u5230\u8868\u8fbe\u5f0f\u4e4b\u5916\uff0c\u4f5c\u4e3a\u5faa\u73af\u4e0d\u53d8\u91cf\uff08loop invariant\uff09\u5904\u7406\uff1a<\/p>\n
int i = 0;\n\nboolean hoistedStopRequested = stopRequested;\/\/ \u5c06stopRequested \u63d0\u5347\u4e3a\u5c40\u90e8\u53d8\u91cf\nwhile (!hoistedStopRequested) {    \n    i++;\n}\n\n\n\n<\/code><\/pre>\n
\u8fd9\u6837\u4e00\u6765\uff0c\u6700\u540e\u5c06stopRequested<\/code>\u8d4b\u503c\u4e3a true \u7684\u64cd\u4f5c\uff0c\u5f71\u54cd\u4e0d\u4e86\u63d0\u5347\u7684hoistedStopRequested<\/code>\u7684\u503c\uff0c\u81ea\u7136\u5c31\u65e0\u6cd5\u5f71\u54cd\u5faa\u73af\u7684\u6267\u884c\u4e86\uff0c\u6700\u7ec8\u5bfc\u81f4\u65e0\u6cd5\u9000\u51fa\u3002  
\u200b<\/p>\n
\u81f3\u4e8e\u4f60\u589e\u52a0\u4e86println<\/code>\u4e4b\u540e\uff0c\u5faa\u73af\u5c31\u53ef\u4ee5\u9000\u51fa\u7684\u95ee\u9898\u3002\u662f\u56e0\u4e3a\u4f60\u8fd9\u884c println \u4ee3\u7801\u5f71\u54cd\u4e86\u7f16\u8bd1\u5668\u7684\u4f18\u5316\u3002println \u65b9\u6cd5\u7531\u4e8e\u6700\u7ec8\u4f1a\u8c03\u7528 FileOutputStream.writeBytes \u8fd9\u4e2a native \u65b9\u6cd5\uff0c\u6240\u4ee5\u65e0\u6cd5\u88ab\u5185\u8054\u4f18\u5316\uff08inling\uff09<\/strong>\u3002\u800c\u672a\u88ab\u5185\u655b\u7684\u65b9\u6cd5\u8c03\u7528\u4ece\u7f16\u8bd1\u5668\u7684\u89d2\u5ea6\u770b\u662f\u4e00\u4e2a\u201cfull memory kill\u201d\uff0c\u4e5f\u5c31\u662f\u8bf4\u526f\u4f5c\u7528\u4e0d\u660e<\/strong>\u3001\u5fc5\u987b\u5bf9\u5185\u5b58\u7684\u8bfb\u5199\u64cd\u4f5c\u505a\u4fdd\u5b88\u5904\u7406<\/strong>\u3002  
\u200b<\/p>\n
\u5728\u8fd9\u4e2a\u4f8b\u5b50\u91cc\uff0c\u4e0b\u4e00\u8f6e\u5faa\u73af\u7684stopRequested<\/code>\u8bfb\u53d6\u64cd\u4f5c\u6309\u987a\u5e8f\u8981\u53d1\u751f\u5728\u4e0a\u4e00\u8f6e\u5faa\u73af\u7684 println \u4e4b\u540e\u3002\u8fd9\u91cc\u201c\u4fdd\u5b88\u5904\u7406\u201d\u4e3a\uff1a\u5c31\u7b97\u4e0a\u4e00\u8f6e\u6211\u5df2\u7ecf\u8bfb\u53d6\u4e86stopRequested<\/code>\u7684\u503c\uff0c\u7531\u4e8e\u7ecf\u8fc7\u4e86\u4e00\u4e2a\u526f\u4f5c\u7528\u4e0d\u660e<\/strong>\u7684\u5730\u65b9\uff0c\u518d\u5230\u4e0b\u4e00\u6b21\u8bbf\u95ee\u5c31\u5fc5\u987b\u91cd\u65b0\u8bfb\u53d6\u4e86\u3002  
\u200b<\/p>\n
\u6240\u4ee5\u5728\u4f60\u589e\u52a0\u4e86 prinltln \u4e4b\u540e\uff0cJIT \u7531\u4e8e\u8981\u4fdd\u5b88\u5904\u7406\uff0c\u91cd\u65b0\u8bfb\u53d6\uff0c\u81ea\u7136\u5c31\u4e0d\u80fd\u505a\u4e0a\u9762\u7684\u8868\u8fbe\u5f0f\u63d0\u5347<\/strong>\u4f18\u5316\u4e86\u3002  
\u200b<\/p>\n
\u4ee5\u4e0a\u5bf9\u8868\u8fbe\u5f0f\u63d0\u5347<\/strong>\u7684\u89e3\u91ca\uff0c\u603b\u7ed3\u6458\u6284\u81eaR\u5927<\/strong>\u7684\u77e5\u4e4e\u56de\u7b54<\/a>\u3002R\u5927\uff0c\u884c\u8d70\u7684 JVM Wiki\uff01  
\u200b<\/p>\n
\n
\u6211\uff1a\u201c\u8fd9\u4e0b\u660e\u767d\u4e86\u5427\uff0c\u8fd9\u90fd\u662f JIT \u5e72\u7684\u597d\u4e8b\uff0c\u4f60\u8981\u662f\u7981\u7528 JIT \u5c31\u6ca1\u8fd9\u95ee\u9898\u4e86\u201d<\/p>\n
\u5c0f\u4f19\u4f34\uff1a\u201cWK\ud83d\udc02\ud83c\udf7a\uff0c\u4e00\u4e2a\u7b80\u5355\u7684 for \u5faa\u73af\u4e5f\u592a\u591a\u673a\u5236\u4e86\uff0c\u6ca1\u60f3\u5230 JIT \u8fd9\u4e48\u667a\u80fd\uff0c\u4e5f\u6ca1\u60f3\u5230 R \u5927\u8fd9\u4e48\ud83d\udc02\ud83c\udf7a\u201d<\/p>\n
\u5c0f\u4f19\u4f34\uff1a\u201c\u90a3 JIT \u4e00\u5b9a\u5f88\u591a\u4f18\u5316\u673a\u5236\u5427\uff0c\u9664\u4e86\u8fd9\u4e2a\u8868\u8fbe\u5f0f\u63d0\u5347\u8fd8\u6709\u5565\uff1f\u201d<\/p>\n
\u6211\uff1a\u6211\u4e5f\u4e0d\u662f\u641e\u7f16\u8bd1\u5668\u7684\u2026\u2026\u54ea\u4e86\u89e3\u8fd9\u4e48\u591a\uff0c\u5c31\u77e5\u9053\u4e00\u4e9b\u5e38\u7528\u7684\uff0c\u7b80\u5355\u7ed9\u4f60\u8bf4\u8bf4\u5427<\/p>\n<\/blockquote>\n
\u8868\u8fbe\u5f0f\u4e0b\u6c89\uff08expression sinking\uff09<\/h4>\n
\u548c\u8868\u8fbe\u5f0f\u63d0\u5347\u7c7b\u4f3c\u7684\uff0c\u8fd8\u6709\u4e2a\u8868\u8fbe\u5f0f\u4e0b\u6c89\u7684\u4f18\u5316\uff0c\u6bd4\u5982\u4e0b\u9762\u8fd9\u6bb5\u4ee3\u7801\uff1a<\/p>\n
public void sinking(int i) {\n    int result = 543 * i;\n\n    if (i % 2 == 0) {\n        \/\/ \u4f7f\u7528 result \u503c\u7684\u4e00\u4e9b\u903b\u8f91\u4ee3\u7801\n    } else {\n        \/\/ \u4e00\u4e9b\u4e0d\u4f7f\u7528 result \u7684\u503c\u7684\u903b\u8f91\u4ee3\u7801\n    }\n}\n\n\n\n<\/code><\/pre>\n
\u7531\u4e8e\u5728 else \u5206\u652f\u91cc\uff0c\u5e76\u6ca1\u6709\u4f7f\u7528 result \u7684\u503c\uff0c\u53ef\u6bcf\u6b21\u4e0d\u7ba1\u4ec0\u4e48\u5206\u652f\u90fd\u4f1a\u5148\u8ba1\u7b97 result\uff0c\u8fd9\u5c31\u6ca1\u5fc5\u8981\u4e86\u3002JIT \u4f1a\u628a result \u7684\u8ba1\u7b97\u8868\u8fbe\u5f0f\u79fb\u52a8\u5230 if \u5206\u652f\u91cc\uff0c\u8fd9\u6837\u5c31\u907f\u514d\u4e86\u6bcf\u6b21\u5bf9 result \u7684\u8ba1\u7b97\uff0c\u8fd9\u4e2a\u64cd\u4f5c\u5c31\u53eb\u8868\u8fbe\u5f0f\u4e0b\u6c89\uff1a<\/p>\n
public void sinking(int i) {\n    if (i % 2 == 0) {\n        int result = 543 * i;\n        \/\/ \u4f7f\u7528 result \u503c\u7684\u4e00\u4e9b\u903b\u8f91\u4ee3\u7801\n    } else {\n        \/\/ \u4e00\u4e9b\u4e0d\u4f7f\u7528 result \u7684\u503c\u7684\u903b\u8f91\u4ee3\u7801\n    }\n}\n\n\n\n<\/code><\/pre>\n
JIT \u8fd8\u6709\u90a3\u4e9b\u5e38\u89c1\u4f18\u5316\uff1f<\/h2>\n
\u9664\u4e86\u4e0a\u9762\u4ecb\u7ecd\u7684\u8868\u8fbe\u5f0f\u63d0\u5347\/\u8868\u8fbe\u5f0f\u4e0b\u6c89\u4ee5\u5916\uff0c\u8fd8\u6709\u4e00\u4e9b\u5e38\u89c1\u7684\u7f16\u8bd1\u5668\u4f18\u5316\u673a\u5236\u3002<\/p>\n
\u5faa\u73af\u5c55\u5f00\uff08Loop unwinding\/loop unrolling\uff09<\/h4>\n
\u4e0b\u9762\u8fd9\u4e2a for \u5faa\u73af\uff0c\u4e00\u5171\u8981\u5faa\u73af 10w \u6b21\uff0c\u6bcf\u6b21\u90fd\u9700\u8981\u68c0\u67e5\u6761\u4ef6\u3002<\/p>\n
for (int i = 0; i < 100000; i++) {\n    delete(i);\n}\n\n\n\n<\/code><\/pre>\n
\u5728\u7f16\u8bd1\u5668\u7684\u4f18\u5316\u540e\uff0c\u4f1a\u5220\u9664\u4e00\u5b9a\u7684\u5faa\u73af\u6b21\u6570\uff0c\u4ece\u800c\u964d\u4f4e\u7d22\u5f15\u9012\u589e\u548c\u6761\u4ef6\u68c0\u67e5\u64cd\u4f5c\u800c\u5f15\u8d77\u7684\u5f00\u9500\uff1a<\/p>\n
for (int i = 0; i < 20000; i+=5) {\n    delete(i);\n    delete(i + 1);\n    delete(i + 2);\n    delete(i + 3);\n    delete(i + 4);\n}\n\n\n\n<\/code><\/pre>\n
\u9664\u4e86\u5faa\u73af\u5c55\u5f00\uff0c\u5faa\u73af\u8fd8\u6709\u4e00\u4e9b\u4f18\u5316\u673a\u5236\uff0c\u6bd4\u5982\u5faa\u73af\u5265\u79bb\u3001\u5faa\u73af\u4ea4\u6362\u3001\u5faa\u73af\u5206\u88c2\u3001\u5faa\u73af\u5408\u5e76\u2026\u2026<\/p>\n
\u5185\u8054\u4f18\u5316\uff08Inling\uff09<\/h4>\n
JVM \u7684\u65b9\u6cd5\u8c03\u7528\u662f\u4e2a\u6808\u7684\u6a21\u578b\uff0c\u6bcf\u6b21\u65b9\u6cd5\u8c03\u7528\u90fd\u9700\u8981\u4e00\u4e2a\u538b\u6808\uff08push\uff09\u548c\u51fa\u6808\uff08pop\uff09\u7684\u64cd\u4f5c\uff0c\u7f16\u8bd1\u5668\u4e5f\u4f1a\u5bf9\u8c03\u7528\u6a21\u578b\u8fdb\u884c\u4f18\u5316\uff0c\u5c06\u4e00\u4e9b\u65b9\u6cd5\u7684\u8c03\u7528\u8fdb\u884c\u5185\u8054\u3002  
\u200b<\/p>\n
\u5185\u8054\u5c31\u662f\u62bd\u53d6\u8981\u8c03\u7528\u7684\u65b9\u6cd5\u4f53\u4ee3\u7801\uff0c\u5230\u5f53\u524d\u65b9\u6cd5\u4e2d\u76f4\u63a5\u6267\u884c\uff0c\u8fd9\u6837\u5c31\u53ef\u4ee5\u907f\u514d\u4e00\u6b21\u538b\u6808\u51fa\u6808\u7684\u64cd\u4f5c\uff0c\u63d0\u5347\u6267\u884c\u6548\u7387\u3002\u6bd4\u5982\u4e0b\u9762\u8fd9\u4e2a\u65b9\u6cd5\uff1a<\/p>\n
public  void inline(){\n    int a = 5;\n    int b = 10;\n    int c = calculate(a, b);\n    \n    \/\/ \u4f7f\u7528 c \u5904\u7406\u2026\u2026\n}\n\npublic int calculate(int a, int b){\n    return a + b;\n}\n\n\n\n<\/code><\/pre>\n
\u5728\u7f16\u8bd1\u5668\u5185\u8054\u4f18\u5316\u540e\uff0c\u4f1a\u5c06calculate<\/code>\u7684\u65b9\u6cd5\u4f53\u62bd\u53d6\u5230inline<\/code>\u65b9\u6cd5\u4e2d\uff0c\u76f4\u63a5\u6267\u884c\uff0c\u800c\u4e0d\u7528\u8fdb\u884c\u65b9\u6cd5\u8c03\u7528\uff1a<\/p>\n
public  void inline(){\n    int a = 5;\n    int b = 10;\n    int c = a + b;\n    \n    \/\/ \u4f7f\u7528 c \u5904\u7406\u2026\u2026\n}\n\n\n\n<\/code><\/pre>\n
\u4e0d\u8fc7\u8fd9\u4e2a\u5185\u8054\u4f18\u5316\u662f\u6709\u4e00\u4e9b\u9650\u5236\u7684\uff0c\u6bd4\u5982 native \u7684\u65b9\u6cd5\u5c31\u4e0d\u80fd\u5185\u8054\u4f18\u5316<\/strong><\/p>\n
\u63d0\u524d\u7f6e\u7a7a<\/h4>\n
\u6765\u5148\u770b\u4e00\u4e2a\u4f8b\u5b50\uff0c\u5728\u8fd9\u4e2a\u4f8b\u5b50\u4e2dwas finalized!<\/code>\u4f1a\u5728done.<\/code>\u4e4b\u524d\u8f93\u51fa\uff0c\u8fd9\u4e2a\u4e5f\u662f\u56e0\u4e3a JIT \u7684\u4f18\u5316\u5bfc\u81f4\u7684\u3002<\/p>\n
class A {\n    \/\/ \u5bf9\u8c61\u88ab\u56de\u6536\u524d\uff0c\u4f1a\u89e6\u53d1 finalize\n    @Override protected void finalize() {\n        System.out.println(this + " was finalized!");\n    }\n\n    public static void main(String[] args) throws InterruptedException {\n        A a = new A();\n        System.out.println("Created " + a);\n        for (int i = 0; i < 1_000_000_000; i++) {\n            if (i % 1_000_00 == 0)\n                System.gc();\n        }\n        System.out.println("done.");\n    }\n}\n\n\/\/\u6253\u5370\u7ed3\u679c\nCreated A@1be6f5c3\nA@1be6f5c3 was finalized!\/\/finalize\u65b9\u6cd5\u8f93\u51fa\ndone.\n\n\n\n<\/code><\/pre>\n
\u4ece\u4f8b\u5b50\u4e2d\u53ef\u4ee5\u770b\u5230\uff0c\u5982\u679ca<\/code>\u5728\u5faa\u73af\u5b8c\u6210\u540e\u5df2\u7ecf\u4e0d\u518d\u4f7f\u7528\u4e86\uff0c\u5219\u4f1a\u51fa\u73b0\u5148\u6267\u884cfinalize\u7684\u60c5\u51b5\uff1b\u867d\u7136\u4ece\u5bf9\u8c61\u4f5c\u7528\u57df\u6765\u8bf4\uff0c\u65b9\u6cd5\u6ca1\u6709\u6267\u884c\u5b8c\uff0c\u6808\u5e27\u5e76\u6ca1\u6709\u51fa\u6808\uff0c\u4f46\u662f\u8fd8\u662f\u4f1a\u88ab\u63d0\u524d\u6267\u884c\u3002  
\u200b<\/p>\n
\u8fd9\u5c31\u662f\u56e0\u4e3a JIT \u8ba4\u4e3aa<\/code>\u5bf9\u8c61\u5728\u5faa\u73af\u5185\u548c\u5faa\u73af\u540e\u90fd\u4e0d\u4f1a\u5728\u4f7f\u7528\uff0c\u6240\u4ee5\u63d0\u524d\u7ed9\u5b83\u7f6e\u7a7a\u4e86\uff0c\u5e2e\u52a9 GC \u56de\u6536\uff1b\u5982\u679c\u7981\u7528 JIT\uff0c\u90a3\u5c31\u4e0d\u4f1a\u51fa\u73b0\u8fd9\u4e2a\u95ee\u9898\u3002  
\u200b<\/p>\n
\u8fd9\u4e2a\u63d0\u524d\u56de\u6536\u7684\u673a\u5236\uff0c\u8fd8\u662f\u6709\u70b9\u98ce\u9669\u7684\uff0c\u5728\u67d0\u4e9b\u573a\u666f\u4e0b\u53ef\u80fd\u4f1a\u5f15\u8d77 BUG\u2026\u2026<\/p>\n
HotSpot VM JIT \u7684\u5404\u79cd\u4f18\u5316\u9879<\/h2>\n
\u4e0a\u9762\u53ea\u662f\u4ecb\u7ecd\u4e86\u51e0\u4e2a\u7b80\u5355\u5e38\u7528\u7684\u7f16\u8bd1\u4f18\u5316\u673a\u5236\uff0cJVM JIT \u66f4\u591a\u7684\u4f18\u5316\u673a\u5236\u53ef\u4ee5\u53c2\u8003\u4e0b\u9762\u8fd9\u4e2a\u56fe\u3002\u8fd9\u662f OpenJDK \u6587\u6863\u4e2d\u63d0\u4f9b\u7684\u4e00\u4e2a pdf \u6750\u6599\uff0c\u91cc\u9762\u5217\u51fa\u4e86 HotSpot JVM \u7684\u5404\u79cd\u4f18\u5316\u673a\u5236\uff0c\u76f8\u5f53\u591a\u2026\u2026  
\"image.png\"<\/p>\n
\u5982\u4f55\u907f\u514d\u56e0 JIT \u5bfc\u81f4\u7684\u95ee\u9898\uff1f<\/h2>\n
\u5c0f\u4f19\u4f34\uff1a\u201cJIT \u8fd9\u4e48\u591a\u4f18\u5316\u673a\u5236\uff0c\u5f88\u5bb9\u6613\u51fa\u95ee\u9898\u554a\uff0c\u6211\u5e73\u65f6\u5199\u4ee3\u7801\u8981\u600e\u4e48\u907f\u5f00\u8fd9\u4e9b\u5462\u201d<\/p><\/blockquote>\n
\u200b<\/p>\n
\u5e73\u65f6\u5728\u7f16\u7801\u7684\u65f6\u5019\uff0c\u4e0d\u7528\u523b\u610f\u7684\u53bb\u5173\u5fc3 JIT \u7684\u4f18\u5316\uff0c\u5c31\u6bd4\u5982\u4e0a\u9762\u90a3\u4e2a println \u95ee\u9898\uff0cJMM \u672c\u6765\u5c31\u4e0d\u4fdd\u8bc1\u4fee\u6539\u5bf9\u5176\u4ed6\u7ebf\u7a0b\u53ef\u89c1\uff0c\u5982\u679c\u6309\u7167\u89c4\u8303\u53bb\u52a0\u9501\u6216\u8005\u7528 volatile \u4fee\u9970\uff0c\u6839\u672c\u5c31\u4e0d\u4f1a\u6709\u8fd9\u79cd\u95ee\u9898\u3002  
\u200b<\/p>\n
\u800c\u90a3\u4e2a\u63d0\u524d\u7f6e\u7a7a\u5bfc\u81f4\u7684\u95ee\u9898\uff0c\u51fa\u73b0\u7684\u51e0\u7387\u4e5f\u5f88\u4f4e\uff0c\u53ea\u8981\u4f60\u89c4\u8303\u5199\u4ee3\u7801\u57fa\u672c\u4e0d\u4f1a\u9047\u5230\u7684\u3002<\/p>\n
\n
\u6211\uff1a\u6240\u4ee5\uff0c\u8fd9\u4e0d\u662f JIT \u7684\u9505\uff0c\u662f\u4f60\u7684\u2026\u2026<\/p>\n
\u5c0f\u4f19\u4f34\uff1a\u201c\u61c2\u4e86\uff0c\u4f60\u8fd9\u662f\u8bf4\u6211\u83dc\uff0c\u8bf4\u6211\u4ee3\u7801\u5199\u7684\u5c4e\u554a\u2026\u2026\u201d<\/p>\n<\/blockquote>\n
\u603b\u7ed3<\/h2>\n
\u5728\u65e5\u5e38\u7f16\u7801\u8fc7\u7a0b\u4e2d\uff0c\u4e0d\u7528\u523b\u610f\u7684\u731c\u6d4b JIT \u7684\u4f18\u5316\u673a\u5236\uff0cJVM \u4e5f\u4e0d\u4f1a\u5b8c\u6574\u7684\u544a\u8bc9\u4f60\u6240\u6709\u7684\u4f18\u5316\u3002\u800c\u4e14\u8fd9\u79cd\u4e1c\u897f\u4e0d\u540c\u7248\u672c\u6548\u679c\u4e0d\u4e00\u6837\uff0c\u5c31\u7b97\u641e\u660e\u767d\u4e86\u4e00\u4e2a\u673a\u5236\uff0c\u53ef\u80fd\u5230\u4e0b\u4e2a\u7248\u672c\u5c31\u4f1a\u5b8c\u5168\u4e0d\u4e00\u6837\u3002  
\u200b<\/p>\n
\u6240\u4ee5\uff0c\u5982\u679c\u4e0d\u662f\u641e\u7f16\u8bd1\u5668\u5f00\u53d1\u7684\u8bdd\uff0cJIT \u76f8\u5173\u7684\u7f16\u8bd1\u77e5\u8bc6\uff0c\u4f5c\u4e3a\u4e00\u4e2a\u77e5\u8bc6\u50a8\u5907\u5c31\u597d\u3002<\/p>\n
\u4e5f\u4e0d\u7528\u53bb\u731c\u6d4b JIT \u5230\u5e95\u4f1a\u600e\u4e48\u4f18\u5316\u4f60\u7684\u4ee3\u7801\uff0c\u4f60\uff08\u53ef\u80fd\uff09\u731c\u4e0d\u51c6\u2026\u2026<\/strong><\/p>\n
\u672c\u6545\u4e8b\u7eaf\u5c5e\u778e\u7f16\uff0c\u8bf7\u52ff\u968f\u610f\u5bf9\u53f7\u5165\u5ea7<\/p>\n
\u53c2\u8003<\/h3>\n