{"id":4070,"date":"2019-04-01T13:29:28","date_gmt":"2019-04-01T05:29:28","guid":{"rendered":"http:\/\/www.xttblog.com\/?p=4070"},"modified":"2019-04-01T13:29:28","modified_gmt":"2019-04-01T05:29:28","slug":"unsafe-%e7%9a%84-cas-%e5%92%8c%e5%86%85%e5%ad%98%e6%93%8d%e4%bd%9c%e7%9a%84%e5%8e%9f%e7%90%86%e3%80%81%e6%ba%90%e7%a0%81%e8%a7%a3%e6%af%92","status":"publish","type":"post","link":"https:\/\/www.xttblog.com\/?p=4070","title":{"rendered":"Unsafe \u7684 CAS \u548c\u5185\u5b58\u64cd\u4f5c\u7684\u539f\u7406\u3001\u6e90\u7801\u89e3\u6bd2"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Java \u8bed\u8a00\u7684\u4e00\u5927\u7279\u70b9\u5c31\u662f\u8de8\u5e73\u53f0\uff0c\u5e76\u4e14\u63d0\u4f9b\u7684\u6709\u4e00\u5957\u5b8c\u7f8e\u7684\u5185\u5b58\u7ba1\u7406\u673a\u5236\u3002\u4f46\u8fd9\u90fd\u662f JVM \u63d0\u4f9b\u7684\uff0c\u5982\u679c\u6211\u4eec\u60f3\u8981\u76f4\u63a5\u8bbf\u95ee\u7cfb\u7edf\u5185\u5b58\u8d44\u6e90\u3001\u81ea\u4e3b\u7ba1\u7406\u5185\u5b58\u8d44\u6e90\u7b49\u5c31\u65e0\u6cd5\u5b9e\u73b0\u3002\u4e8e\u662f Java \u53c8\u63d0\u4f9b\u4e86\u4e00\u4e2a\u9b54\u6cd5\u7c7b\uff1aUnsafe\u3002 <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Unsafe \u7c7b\u4f4d\u4e8e sun.misc \u5305\u4e2d\u3002\u4ece\u540d\u5b57\u770b\uff0c\u8fd9\u4e2a\u7c7b\u5c31\u662f\u4e00\u4e2a\u4e0d\u5b89\u5168\u7684\u7c7b\uff0c\u5b9e\u9645\u4e0a\u5b83\u786e\u5b9e\u662f\u5c01\u88c5\u4e86\u4e00\u4e9b\u4e0d\u5b89\u5168\u7684\u64cd\u4f5c\uff01 <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Unsafe \u7c7b\u548c String \u7c7b\u4e00\u6837\u7684\u88ab\u5b9a\u4e49\u4e3a final\uff0c\u4e5f\u5c31\u662f\u8bf4\u5b83\u4e0d\u53ef\u4ee5\u88ab\u7ee7\u627f\u3002\u5e76\u4e14\u00a0Unsafe \u88ab\u8bbe\u8ba1\u6210\u4e86\u5355\u4f8b\uff0c\u6784\u9020\u51fd\u6570\u662f\u79c1\u6709\u7684\uff0c\u53ea\u80fd\u901a\u8fc7 getUnsafe \u65b9\u6cd5\u83b7\u5f97\u5b83\u3002\u9664\u6b64\u4e4b\u5916\uff0cgetUnsafe \u65b9\u6cd5\u8fd8\u8bbe\u7f6e\u4e86\u9650\u5236\u6761\u4ef6\uff0c\u53ea\u6709\u6388\u4fe1\u7684\u4ee3\u7801\u624d\u80fd\u83b7\u5f97\u8be5\u7c7b\u7684\u5b9e\u4f8b\u3002\u54ea\u4e9b\u662f\u6388\u4fe1\u7684\u4ee3\u7801\u5462\uff1f\u5f53\u7136\u662f JDK \u5e93\u91cc\u9762\u7684\u7c7b\u662f\u53ef\u4ee5\u968f\u610f\u4f7f\u7528\u7684\u3002 <\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>public final class Unsafe {\n  \/\/ \u5355\u4f8b\u5bf9\u8c61\n  private static final Unsafe theUnsafe;\n  private Unsafe() {}\n  @CallerSensitive\n  public static Unsafe getUnsafe() {\n    Class var0 = Reflection.getCallerClass();\n    \/\/ \u4ec5\u5728\u5f15\u5bfc\u7c7b\u52a0\u8f7d\u5668`BootstrapClassLoader`\u52a0\u8f7d\u65f6\u624d\u5408\u6cd5\n    if(!VM.isSystemDomainLoader(var0.getClassLoader())) {    \n      throw new SecurityException(\"Unsafe\");\n    } else {\n      return theUnsafe;\n    }\n  }\n  ...... \u7701\u7565\u5176\u4ed6\u4ee3\u7801\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u8bf4\u4e86\u534a\u5929\uff0c\u8fd9\u4e2a\u7c7b\uff0c\u6211\u4eec\u65e0\u6cd5\u4f7f\u7528\uff0c\u4f60\u8bb2\u5b83\u53c8\u4f55\u610f\u4e49\uff1f<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u522b\u6025\uff0cJava \u867d\u7136\u4e0d\u5efa\u8bae\u6211\u4eec\u4f7f\u7528\u5b83\uff0c\u4f46\u662f\u6211\u4eec\u8fd8\u662f\u53ef\u4ee5\u901a\u8fc7\u4e24\u79cd\u65b9\u5f0f\u6765\u4f7f\u7528\u5b83\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u7b2c\u4e00\u79cd\u65b9\u5f0f\u662f\uff1a\u8ba9\u6211\u4eec\u7684\u4ee3\u7801\u5728\u542f\u52a8\u65f6\u201c\u6388\u4fe1\u201d\u3002\u5728\u8fd0\u884c\u7a0b\u5e8f\u65f6\uff0c\u6307\u5b9a bootclasspath \u9009\u9879\uff0c\u8ba9\u4f60\u4f7f\u7528 Unsafe \u5b9e\u4f8b\u7684\u7c7b\u88ab\u5f15\u5bfc\u7c7b\u52a0\u8f7d\u5668\u52a0\u8f7d\uff0c\u4ece\u800c\u901a\u8fc7 Unsafe.getUnsafe \u65b9\u6cd5\u5b89\u5168\u7684\u83b7\u53d6 Unsafe \u5b9e\u4f8b\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>java -Xbootclasspath:\/usr\/jdk1.7.0\/jre\/lib\/rt.jar:. com.xttblog.UnsafeTest<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u8fd9\u4e2a\u505a\u6cd5\u6bd4\u8f83\u5c11\u7528\uff0c\u6240\u4ee5\u63a8\u8350\u5927\u5bb6\u91c7\u7528\u7b2c\u4e8c\u79cd\u65b9\u6cd5\uff1a\u901a\u8fc7\u53cd\u5c04\u6765\u4f7f\u7528\u5b83\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Field f = Unsafe.class.getDeclaredField(\"theUnsafe\");\nf.setAccessible(true);\nUnsafe unsafe = (Unsafe) f.get(null);<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u6ce8\u610f\u6709\u7684 IDE \u53ef\u80fd\u652f\u6301\u7684\u4e0d\u662f\u5f88\u53cb\u597d\u3002\u6bd4\u5982\uff1aeclipse \u663e\u793a\u201dAccess restriction\u2026\u201d\u9519\u8bef\uff0c\u4f46\u5982\u679c\u4f60\u8fd0\u884c\u4ee3\u7801\uff0c\u5b83\u5c06\u6b63\u5e38\u8fd0\u884c\u3002\u5982\u679c\u8fd9\u4e2a\u9519\u8bef\u63d0\u793a\u4ee4\u4eba\u70e6\u607c\uff0c\u53ef\u4ee5\u901a\u8fc7\u4ee5\u4e0b\u8bbe\u7f6e\u6765\u907f\u514d\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Preferences -&gt; Java -&gt; Compiler -&gt; Errors\/Warnings -&gt;\nDeprecated and restricted API -&gt; Forbidden reference -&gt; Warning<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">Unsafe \u6709 8 \u5927\u529f\u80fd\uff0c\u5f88\u591a\u53f7\u4e3b\u53ea\u8bb2\u4e86\u5b83\u7684 CAS \u529f\u80fd\u3002<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/images.weserv.nl\/?url=https:\/\/wx1.sinaimg.cn\/large\/8fa5dcfcgy1g1n2bdwqs1j20sd0cnabk.jpg\" alt=\"\" \/><figcaption>Unsafe \u7684 8 \u5927\u529f\u80fd<br><\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u4e0a\u56fe\u6240\u793a\uff0cUnsafe \u63d0\u4f9b\u7684 105 \u4e2a API \u5927\u81f4\u53ef\u5206\u4e3a\u5185\u5b58\u64cd\u4f5c\u3001CAS\u3001Class \u76f8\u5173\u3001\u5bf9\u8c61\u64cd\u4f5c\u3001\u7ebf\u7a0b\u8c03\u5ea6\u3001\u7cfb\u7edf\u4fe1\u606f\u83b7\u53d6\u3001\u5185\u5b58\u5c4f\u969c\u3001\u6570\u7ec4\u64cd\u4f5c\u7b49\u3002\u4eca\u5929\u6211\u5148\u6765\u8bf4\u4e24\u4e2a\u5927\u529f\u80fd\uff1aCAS \u548c\u5185\u5b58\u64cd\u4f5c\uff08\u548c\u6211\u524d\u9762\u7684\u300a<a href=\"https:\/\/mp.weixin.qq.com\/s\/bsPxOC7L3qnKN98LYAvySw\">\u624b\u628a\u624b\u6559\u4f60\u901a\u8fc7Java\u4ee3\u7801\u4f53\u9a8c\u5f3a\u5f15\u7528\u3001\u8f6f\u5f15\u7528\u3001\u5f31\u5f15\u7528\u3001\u865a\u5f15\u7528\u7684\u533a\u522b<\/a>\u300b\u3001\u300a<a href=\"https:\/\/mp.weixin.qq.com\/s\/ZxCcVhxMyjvWvFbzbQIY1g\">90%\u7684\u7a0b\u5e8f\u5458\u53ef\u80fd\u90fd\u4e0d\u4e86\u89e3\u7684\u5806\u5916\u5185\u5b58<\/a>\u300b\u90fd\u6709\u4e9b\u5173\u8054\uff0c\u8fd9\u662f\u4e00\u4e2a\u7cfb\u5217\uff09\u3002 <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">CAS \u64cd\u4f5c\u4e3b\u8981\u6d89\u53ca\u5230\u4e0b\u9762 3 \u4e2a API\u3002 <\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/**\n  *  CAS\n  * @param o         \u5305\u542b\u8981\u4fee\u6539field\u7684\u5bf9\u8c61\n  * @param offset    \u5bf9\u8c61\u4e2d\u67d0field\u7684\u504f\u79fb\u91cf\n  * @param expected  \u671f\u671b\u503c\n  * @param update    \u66f4\u65b0\u503c\n  * @return          true | false\n  *\/\npublic final native boolean compareAndSwapObject(Object o, \n  long offset,  Object expected, Object update);\npublic final native boolean compareAndSwapInt(Object o, \n  long offset, int expected,int update);\npublic final native boolean compareAndSwapLong(Object o, \n  long offset, long expected, long update);<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">CAS \u5373\u6bd4\u8f83\u5e76\u66ff\u6362\uff0c\u5b9e\u73b0\u5e76\u53d1\u7b97\u6cd5\u65f6\u5e38\u7528\u5230\u7684\u4e00\u79cd\u6280\u672f\u3002CAS \u64cd\u4f5c\u5305\u542b\u4e09\u4e2a\u64cd\u4f5c\u6570\u2014\u2014\u5185\u5b58\u4f4d\u7f6e\u3001\u9884\u671f\u539f\u503c\u53ca\u65b0\u503c\u3002\u6267\u884c CAS \u64cd\u4f5c\u7684\u65f6\u5019\uff0c\u5c06\u5185\u5b58\u4f4d\u7f6e\u7684\u503c\u4e0e\u9884\u671f\u539f\u503c\u6bd4\u8f83\uff0c\u5982\u679c\u76f8\u5339\u914d\uff0c\u90a3\u4e48\u5904\u7406\u5668\u4f1a\u81ea\u52a8\u5c06\u8be5\u4f4d\u7f6e\u503c\u66f4\u65b0\u4e3a\u65b0\u503c\uff0c\u5426\u5219\uff0c\u5904\u7406\u5668\u4e0d\u505a\u4efb\u4f55\u64cd\u4f5c\u3002\u6211\u4eec\u90fd\u77e5\u9053\uff0cCAS \u662f\u4e00\u6761 CPU \u7684\u539f\u5b50\u6307\u4ee4\uff08cmpxchg \u6307\u4ee4\uff09\uff0c\u4e0d\u4f1a\u9020\u6210\u6240\u8c13\u7684\u6570\u636e\u4e0d\u4e00\u81f4\u95ee\u9898\uff0cUnsafe \u63d0\u4f9b\u7684 CAS \u65b9\u6cd5\uff08\u5982 compareAndSwapXXX\uff09\u5e95\u5c42\u5b9e\u73b0\u5373\u4e3a CPU \u6307\u4ee4 cmpxchg\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">CAS \u5728 java.util.concurrent.atomic \u76f8\u5173\u7c7b\u3001Java AQS\u3001CurrentHashMap \u7b49\u5b9e\u73b0\u4e0a\u6709\u975e\u5e38\u5e7f\u6cdb\u7684\u5e94\u7528\u3002\u6bd4\u5982\uff0c\u5728 AtomicInteger \u7684\u5b9e\u73b0\u4e2d\uff0c\u9759\u6001\u5b57\u6bb5 valueOffset \u5373\u4e3a\u5b57\u6bb5 value \u7684\u5185\u5b58\u504f\u79fb\u5730\u5740\uff0cvalueOffset \u7684\u503c\u5728 AtomicInteger \u521d\u59cb\u5316\u65f6\uff0c\u5728\u9759\u6001\u4ee3\u7801\u5757\u4e2d\u901a\u8fc7 Unsafe \u7684 objectFieldOffset \u65b9\u6cd5\u83b7\u53d6\u3002\u5728 AtomicInteger \u4e2d\u63d0\u4f9b\u7684\u7ebf\u7a0b\u5b89\u5168\u65b9\u6cd5\u4e2d\uff0c\u901a\u8fc7\u5b57\u6bb5 valueOffset \u7684\u503c\u53ef\u4ee5\u5b9a\u4f4d\u5230 AtomicInteger \u5bf9\u8c61\u4e2d value \u7684\u5185\u5b58\u5730\u5740\uff0c\u4ece\u800c\u53ef\u4ee5\u6839\u636e CAS \u5b9e\u73b0\u5bf9 value \u5b57\u6bb5\u7684\u539f\u5b50\u64cd\u4f5c\u3002<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/images.weserv.nl\/?url=https:\/\/wx1.sinaimg.cn\/large\/8fa5dcfcgy1g1n2d85qh3j20jr07p758.jpg\" alt=\"\" \/><figcaption>CAS \u539f\u5b50\u6027\u64cd\u4f5c\u539f\u7406<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">\u6bd4\u5982\uff0c\u4e0b\u56fe\u5c31\u4e3a\u67d0\u4e2a AtomicInteger \u5bf9\u8c61\u81ea\u589e\u64cd\u4f5c\u524d\u540e\u7684\u5185\u5b58\u793a\u610f\u56fe\uff0c\u5bf9\u8c61\u7684\u57fa\u5730\u5740 baseAddress=\u201c0x110000\u201d\uff0c\u901a\u8fc7 baseAddress+valueOffset \u5f97\u5230 value \u7684\u5185\u5b58\u5730\u5740 valueAddress=\u201c0x11000c\u201d\uff1b\u7136\u540e\u901a\u8fc7 CAS \u8fdb\u884c\u539f\u5b50\u6027\u7684\u66f4\u65b0\u64cd\u4f5c\uff0c\u6210\u529f\u5219\u8fd4\u56de\uff0c\u5426\u5219\u7ee7\u7eed\u91cd\u8bd5\uff0c\u76f4\u5230\u66f4\u65b0\u6210\u529f\u4e3a\u6b62\u3002<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/images.weserv.nl\/?url=https:\/\/wx1.sinaimg.cn\/large\/8fa5dcfcgy1g1n2erne9uj20ln0fuwfr.jpg\" alt=\"\" \/><figcaption>\u56fe\u89e3 AtomicInteger CAS \u64cd\u4f5c\u8fc7\u7a0b<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">\u8bf4\u5b8c CAS\uff0c\u6211\u4eec\u518d\u6765\u8bf4\u8bf4 Unsafe \u7684\u5185\u5b58\u64cd\u4f5c\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u5185\u5b58\u64cd\u4f5c\u4e3b\u8981\u6709\u4e0b\u9762 9 \u4e2a API\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/\u5206\u914d\u5185\u5b58, \u76f8\u5f53\u4e8eC++\u7684malloc\u51fd\u6570\npublic native long allocateMemory(long bytes);\n\/\/\u6269\u5145\u5185\u5b58\npublic native long reallocateMemory(long address, long bytes);\n\/\/\u91ca\u653e\u5185\u5b58\npublic native void freeMemory(long address);\n\/\/\u5728\u7ed9\u5b9a\u7684\u5185\u5b58\u5757\u4e2d\u8bbe\u7f6e\u503c\npublic native void setMemory(Object o, long offset, long bytes, byte value);\n\/\/\u5185\u5b58\u62f7\u8d1d\npublic native void copyMemory(Object srcBase, \n  long srcOffset, Object destBase, long destOffset, long bytes);\n\/\/\u83b7\u53d6\u7ed9\u5b9a\u5730\u5740\u503c\uff0c\u5ffd\u7565\u4fee\u9970\u9650\u5b9a\u7b26\u7684\u8bbf\u95ee\u9650\u5236\u3002\u4e0e\u6b64\u7c7b\u4f3c\u64cd\u4f5c\u8fd8\u6709: getInt\uff0cgetDouble\uff0cgetLong\uff0cgetChar\u7b49\npublic native Object getObject(Object o, long offset);\n\/\/\u4e3a\u7ed9\u5b9a\u5730\u5740\u8bbe\u7f6e\u503c\uff0c\u5ffd\u7565\u4fee\u9970\u9650\u5b9a\u7b26\u7684\u8bbf\u95ee\u9650\u5236\uff0c\u4e0e\u6b64\u7c7b\u4f3c\u64cd\u4f5c\u8fd8\u6709: putInt,putDouble\uff0cputLong\uff0cputChar\u7b49\npublic native void putObject(Object o, long offset, Object x);\n\/\/\u83b7\u53d6\u7ed9\u5b9a\u5730\u5740\u7684byte\u7c7b\u578b\u7684\u503c\uff08\u5f53\u4e14\u4ec5\u5f53\u8be5\u5185\u5b58\u5730\u5740\u4e3aallocateMemory\u5206\u914d\u65f6\uff0c\u6b64\u65b9\u6cd5\u7ed3\u679c\u4e3a\u786e\u5b9a\u7684\uff09\npublic native byte getByte(long address);\n\/\/\u4e3a\u7ed9\u5b9a\u5730\u5740\u8bbe\u7f6ebyte\u7c7b\u578b\u7684\u503c\uff08\u5f53\u4e14\u4ec5\u5f53\u8be5\u5185\u5b58\u5730\u5740\u4e3aallocateMemory\u5206\u914d\u65f6\uff0c\u6b64\u65b9\u6cd5\u7ed3\u679c\u624d\u662f\u786e\u5b9a\u7684\uff09\npublic native void putByte(long address, byte x);<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u300a<a href=\"https:\/\/mp.weixin.qq.com\/s\/bsPxOC7L3qnKN98LYAvySw\">\u624b\u628a\u624b\u6559\u4f60\u901a\u8fc7Java\u4ee3\u7801\u4f53\u9a8c\u5f3a\u5f15\u7528\u3001\u8f6f\u5f15\u7528\u3001\u5f31\u5f15\u7528\u3001\u865a\u5f15\u7528\u7684\u533a\u522b<\/a>\u300b\u548c\u300a<a href=\"https:\/\/mp.weixin.qq.com\/s\/ZxCcVhxMyjvWvFbzbQIY1g\">90%\u7684\u7a0b\u5e8f\u5458\u53ef\u80fd\u90fd\u4e0d\u4e86\u89e3\u7684\u5806\u5916\u5185\u5b58<\/a>\u300b\u4e24\u7bc7\u6587\u7ae0\u4e2d\uff0c\u6211\u5df2\u7ecf\u8bb2\u8fc7\u4e86\u3002\u5728 Java \u4e2d\u521b\u5efa\u7684\u5bf9\u8c61\u90fd\u5904\u4e8e\u5806\u5185\u5185\u5b58\uff08heap\uff09\u4e2d\uff0c\u5806\u5185\u5185\u5b58\u662f\u7531 JVM \u6240\u7ba1\u63a7\u7684 Java \u8fdb\u7a0b\u5185\u5b58\uff0c\u5e76\u4e14\u5b83\u4eec\u9075\u5faa JVM \u7684\u5185\u5b58\u7ba1\u7406\u673a\u5236\uff0cJVM \u4f1a\u91c7\u7528\u5783\u573e\u56de\u6536\u673a\u5236\u7edf\u4e00\u7ba1\u7406\u5806\u5185\u5b58\u3002\u4e0e\u4e4b\u76f8\u5bf9\u7684\u662f\u5806\u5916\u5185\u5b58\uff0c\u5b58\u5728\u4e8e JVM \u7ba1\u63a7\u4e4b\u5916\u7684\u5185\u5b58\u533a\u57df\uff0cJava \u4e2d\u5bf9\u5806\u5916\u5185\u5b58\u7684\u64cd\u4f5c\uff0c\u4f9d\u8d56\u4e8e Unsafe \u63d0\u4f9b\u7684\u64cd\u4f5c\u5806\u5916\u5185\u5b58\u7684 native \u65b9\u6cd5\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u4f7f\u7528\u5806\u5916\u5185\u5b58\u7684\u539f\u56e0\u662f\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>\u5bf9\u5783\u573e\u56de\u6536\u505c\u987f\u7684\u6539\u5584\u3002\u7531\u4e8e\u5806\u5916\u5185\u5b58\u662f\u76f4\u63a5\u53d7\u64cd\u4f5c\u7cfb\u7edf\u7ba1\u7406\u800c\u4e0d\u662f JVM\uff0c\u6240\u4ee5\u5f53\u6211\u4eec\u4f7f\u7528\u5806\u5916\u5185\u5b58\u65f6\uff0c\u5373\u53ef\u4fdd\u6301\u8f83\u5c0f\u7684\u5806\u5185\u5185\u5b58\u89c4\u6a21\u3002\u4ece\u800c\u5728 GC \u65f6\u51cf\u5c11\u56de\u6536\u505c\u987f\u5bf9\u4e8e\u5e94\u7528\u7684\u5f71\u54cd\u3002<\/li><li>\u63d0\u5347\u7a0b\u5e8f I\/O \u64cd\u4f5c\u7684\u6027\u80fd\u3002\u901a\u5e38\u5728 I\/O \u901a\u4fe1\u8fc7\u7a0b\u4e2d\uff0c\u4f1a\u5b58\u5728\u5806\u5185\u5185\u5b58\u5230\u5806\u5916\u5185\u5b58\u7684\u6570\u636e\u62f7\u8d1d\u64cd\u4f5c\uff0c\u5bf9\u4e8e\u9700\u8981\u9891\u7e41\u8fdb\u884c\u5185\u5b58\u95f4\u6570\u636e\u62f7\u8d1d\u4e14\u751f\u547d\u5468\u671f\u8f83\u77ed\u7684\u6682\u5b58\u6570\u636e\uff0c\u90fd\u5efa\u8bae\u5b58\u50a8\u5230\u5806\u5916\u5185\u5b58\u3002<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">\u6211\u524d\u9762\u63d0\u5230\u7684 DirectByteBuffer\uff0c\u5728 Netty\u3001MINA \u7b49 NIO \u6846\u67b6\u4e2d\u5e94\u7528\u5e7f\u6cdb\u3002DirectByteBuffer \u5bf9\u4e8e\u5806\u5916\u5185\u5b58\u7684\u521b\u5efa\u3001\u4f7f\u7528\u3001\u9500\u6bc1\u7b49\u903b\u8f91\u5747\u7531 Unsafe \u63d0\u4f9b\u7684\u5806\u5916\u5185\u5b58 API \u6765\u5b9e\u73b0\u3002<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/images.weserv.nl\/?url=https:\/\/wx1.sinaimg.cn\/large\/8fa5dcfcgy1g1n2i53kj6j20o00d3q4q.jpg\" alt=\"\" \/><figcaption>DirectByteBuffer \u6e90\u7801\u89e3\u8bfb<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e0a\u56fe\u4e3a DirectByteBuffer \u6784\u9020\u51fd\u6570\uff0c\u521b\u5efa DirectByteBuffer \u7684\u65f6\u5019\uff0c\u901a\u8fc7 Unsafe.allocateMemory \u5206\u914d\u5185\u5b58\u3001Unsafe.setMemory \u8fdb\u884c\u5185\u5b58\u521d\u59cb\u5316\uff0c\u800c\u540e\u6784\u5efa Cleaner \u5bf9\u8c61\u7528\u4e8e\u8ddf\u8e2a DirectByteBuffer \u5bf9\u8c61\u7684\u5783\u573e\u56de\u6536\uff0c\u4ee5\u5b9e\u73b0\u5f53 DirectByteBuffer \u88ab\u5783\u573e\u56de\u6536\u65f6\uff0c\u5206\u914d\u7684\u5806\u5916\u5185\u5b58\u4e00\u8d77\u88ab\u91ca\u653e\u3002\u5177\u4f53\u7684\u91ca\u653e\u5c31\u662f\u6211\u524d\u9762\u8bb2\u7684 PhantomReference \u865a\u5f15\u7528\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u4ee5\u4e0a\u5c31\u662f Unsafe \u7c7b 8 \u5927\u4e3b\u8981\u529f\u80fd\u7684 2 \u4e2a\u91cd\u8981\u7684\u529f\u80fd\u3002\u5176\u4ed6\u529f\u80fd\uff0c\u6211\u4f1a\u5728\u5bf9\u5e94\u4f7f\u7528\u5230\u7684\u6846\u67b6\u8111\u56fe\u4e2d\u4e32\u8d77\u6765\u8bb2\u3002\u5f53\u7136\uff0c\u5982\u679c\u4f60\u4eec\u73b0\u5728\u5e0c\u671b\u4e86\u89e3\u7684\u8bdd\uff0c\u6211\u4e5f\u53ef\u4ee5\u63d0\u524d\u5199\u4e00\u4e0b\u8fd9\u65b9\u4fbf\u7684\u5185\u5bb9\u3002\u9009\u62e9\u6743\u5728\u4e8e\u4f60\u4eec\u7684\u7559\u8a00\u548c\u8bc4\u8bba\uff01<\/p>\n<!-- <audio autoplay=\"autoplay\" height=\"100\" width=\"100\" hidden=\"true\"><source src=\"https:\/\/c.coka.la\/orAvPR.mp3\" type=\"audio\/mp3\"\/><\/audio><img decoding=\"async\" src=\"https:\/\/images.weserv.nl\/?url=https:\/\/ws3.sinaimg.cn\/large\/8fa5dcfcgy1g4em3rzar5j20ib089ae0.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/> --><p><!-- <img decoding=\"async\" src=\"https:\/\/raw.githubusercontent.com\/xmt1139057136\/xttblog\/master\/8fa5dcfcgy1g4em3rzar5j20ib089ae0.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/>--><img decoding=\"async\" src=\"https:\/\/saas.51autoparts.cn\/api\/admin\/sys-file\/oss\/file?fileName=84db51f8561e448f9a4fda2eff0811f9.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/><\/p><p>\u6700\u540e\uff0c\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u4e2a\u4eba\u5fae\u4fe1\u516c\u4f17\u53f7\uff1a\u4e1a\u4f59\u8349\uff08yyucao\uff09\uff01<b>\u53ef\u52a0\u4f5c\u8005\u5fae\u4fe1\u53f7\uff1a<font color=\"red\">xttblog2<\/font>\u3002\u5907\u6ce8\uff1a\u201c1\u201d\uff0c\u6dfb\u52a0\u535a\u4e3b\u5fae\u4fe1\u62c9\u4f60\u8fdb\u5fae\u4fe1\u7fa4\u3002\u5907\u6ce8\u9519\u8bef\u4e0d\u4f1a\u540c\u610f\u597d\u53cb\u7533\u8bf7\u3002<\/b>\u518d\u6b21\u611f\u8c22\u60a8\u7684\u5173\u6ce8\uff01\u540e\u7eed\u6709\u7cbe\u5f69\u5185\u5bb9\u4f1a\u7b2c\u4e00\u65f6\u95f4\u53d1\u7ed9\u60a8\uff01\u539f\u521b\u6587\u7ae0\u6295\u7a3f\u8bf7\u53d1\u9001\u81f3532009913@qq.com\u90ae\u7bb1\u3002\u5546\u52a1\u5408\u4f5c\u4e5f\u53ef\u6dfb\u52a0\u4f5c\u8005\u5fae\u4fe1\u8fdb\u884c\u8054\u7cfb\uff01<\/p><p>\u672c\u6587\u539f\u6587\u51fa\u5904\uff1a<a href=\"https:\/\/www.xttblog.com\">\u4e1a\u4f59\u8349<\/a>\uff1a &raquo; <a href=\"https:\/\/www.xttblog.com\/?p=4070\">Unsafe \u7684 CAS \u548c\u5185\u5b58\u64cd\u4f5c\u7684\u539f\u7406\u3001\u6e90\u7801\u89e3\u6bd2<\/a><\/p><!-- <div class=\"bd-reward-stl\"><button id=\"bdRewardBtn\"><span><\/span><\/button><\/div> -->","protected":false},"excerpt":{"rendered":"<p>Java \u8bed\u8a00\u7684\u4e00\u5927\u7279\u70b9\u5c31\u662f\u8de8\u5e73\u53f0\uff0c\u5e76\u4e14\u63d0\u4f9b\u7684\u6709\u4e00\u5957\u5b8c\u7f8e\u7684\u5185\u5b58\u7ba1\u7406\u673a\u5236\u3002\u4f46\u8fd9\u90fd\u662f JVM \u63d0\u4f9b\u7684\uff0c\u5982\u679c\u6211\u4eec\u60f3\u8981 [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[1740,1753,1954,731,1751],"class_list":["post-4070","post","type-post","status-publish","format-standard","hentry","category-java","tag-atomicinteger","tag-cas","tag-currenthashmap","tag-jvm","tag-unsafe"],"_links":{"self":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/4070","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4070"}],"version-history":[{"count":1,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/4070\/revisions"}],"predecessor-version":[{"id":4071,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/4070\/revisions\/4071"}],"wp:attachment":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4070"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4070"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4070"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}