{"id":117,"date":"2023-02-18T10:19:58","date_gmt":"2023-02-18T02:19:58","guid":{"rendered":"https:\/\/www.appblog.cn\/?p=117"},"modified":"2023-02-18T10:21:08","modified_gmt":"2023-02-18T02:21:08","slug":"jvm-persistent-rise-of-perm-region","status":"publish","type":"post","link":"https:\/\/www.appblog.cn\/index.php\/2023\/02\/18\/jvm-persistent-rise-of-perm-region\/","title":{"rendered":"JVM\u4e2dPerm\u533a\u6301\u7eed\u4e0a\u6da8\u95ee\u9898"},"content":{"rendered":"

Java\u5e94\u7528Perm\u533a\u4e00\u76f4\u5448\u4e0a\u6da8\u8d8b\u52bf\u7684\u539f\u56e0\u53ef\u4ee5\u7528\u4e00\u4e2a\u7b80\u5355\u7684\u529e\u6cd5\u6392\u67e5\uff0c\u5c31\u662f\u7528btrace<\/code>\u53bb\u8ddf\u8e2a\u4e0b\u662f\u4ec0\u4e48\u5730\u65b9\u5728\u8c03\u7528ClassLoader.defineClass<\/code>\uff0c\u5728\u5927\u591a\u6570\u60c5\u51b5\u4e0b\u8fd9\u62db\u90fd\u662f\u7ba1\u7528\u7684\u3002<\/p>\n

Perm\u533a\u5b58\u653e\u7684\u5565\u4fe1\u606f\uff1f<\/h2>\n

Perm\u53eb\u505a\u6301\u4e45\u4ee3\uff0c\u5b58\u653e\u4e86\u7c7b\u7684\u4fe1\u606f\u3001\u7c7b\u7684\u9759\u6001\u53d8\u91cf\u3001\u7c7b\u4e2dfinal\u7c7b\u578b\u7684\u53d8\u91cf\u3001\u7c7b\u7684\u65b9\u6cd5\u4fe1\u606f\uff0cPerm\u662f\u5168\u5c40\u5171\u4eab\u7684\uff0c\u5728\u4e00\u5b9a\u6761\u4ef6\u4e0b\u4f1a\u88abGC\u6389\uff0c\u65b9\u6240\u8981\u627f\u8f7d\u7684\u6570\u636e\u8d85\u8fc7\u5185\u5b58\u533a\u57df\u540e\uff0c\u5c31\u4f1a\u51fa\u73b0OOM\u5f02\u5e38\u3002\u53ef\u4ee5\u901a\u8fc7-XX\uff1aPermSize<\/code>\u548c-XX\uff1aMaxPermSize<\/code>\u6765\u6307\u5b9a\u8fd9\u4e2a\u533a\u57df\u7684\u6700\u5c0f\u503c\u548c\u6700\u5927\u503c\u3002\u6301\u4e45\u4ee3\u7684\u56de\u6536\u4e3b\u8981\u5305\u62ec\u4e24\u90e8\u5206\uff0c\u5e9f\u5f03\u5e38\u91cf\u548c\u65e0\u7528\u7684\u7c7b\uff0c\u5e9f\u5f03\u7684\u5e38\u91cf\u6bd4\u8f83\u5bb9\u6613\u5224\u522b\uff0c\u6ca1\u6709\u4efb\u4f55String\u7c7b\u578b\u7684\u5bf9\u8c61\u5f15\u7528\u8fd9\u4e2a\u5c31\u7b97\u53ef\u4ee5\u5e9f\u5f03\u7684\u4e86\uff0c\u4f46\u662f\u65e0\u7528\u7684\u7c7b\u5224\u522b\u6bd4\u8f83\u590d\u6742\uff0c\uff08\u8be5\u7c7b\u6240\u6709\u7684\u5b9e\u4f8b\u5df2\u7ecf\u88ab\u56de\u6536\uff0cJVM\u4e2d\u6ca1\u6709\u4efb\u4f55\u7c7b\u7684\u5b9e\u4f8b\uff1b\u52a0\u8f7d\u8be5\u7c7b\u7684ClassLoader\u88ab\u56de\u6536\uff1b\u8be5\u7c7b\u5bf9\u5e94\u7684java.lang.Class<\/code>\u6ca1\u6709\u5730\u65b9\u5f15\u7528\uff09\u3002\u53ef\u4ee5\u4f7f\u7528-verbose:class<\/code>\u4ee5\u53ca-XX:TraceClassLoading<\/code>\u548c-XX:TraceClassUnLoading<\/code>\u6765\u67e5\u770b\u7c7b\u7684\u52a0\u8f7d\u548c\u5378\u8f7d\u60c5\u51b5\u3002<\/p>\n

<\/p>\n

ClassLoader\u4e2d\u7684defineClass\u662f\u5e72\u5565\u7684\uff1f<\/h2>\n

\u8be5\u65b9\u6cd5\u7528\u4e8e\u5c06\u4e8c\u8fdb\u5236\u7684\u5b57\u8282\u7801\u8f6c\u6362\u4e3aClass\u5bf9\u8c61\uff0c\u5bf9\u4e8e\u81ea\u5b9a\u4e49\u52a0\u8f7d\u7c7b\u975e\u5e38\u91cd\u8981\uff0c\u5982\u679c\u4e8c\u8fdb\u5236\u7684\u5b57\u8282\u7801\u4e0d\u7b26\u5408JVM\u7684\u89c4\u8303\uff0c\u5c31\u4f1a\u62a5ClassFormatError<\/code>\uff0c\u5982\u679c\u751f\u6210\u7684\u7c7b\u540d\u548c\u4e8c\u8fdb\u5236\u4e2d\u7684\u4e0d\u7b26\uff0c\u62a5NoClassDefFoundError<\/code>\u5f02\u5e38\uff0c\u5982\u679c\u52a0\u8f7d\u7684class\u662f\u53d7\u4fdd\u62a4\u7684\uff0c\u5219\u62a5SecurityException<\/code>\uff0c\u5982\u679c\u6b64\u7c7b\u5df2\u7ecf\u5728ClassLoader\u5df2\u7ecf\u52a0\u8f7d\uff0c\u4f1a\u62a5LinkageError<\/code>\u3002<\/p>\n

\u4f8b\u5b501\uff1a\u8fd0\u884c\u65f6\u5e38\u91cf\u6ea2\u51fa<\/h3>\n

\u5411\u5e38\u91cf\u6c60\u4e2d\u6dfb\u52a0\u6570\u636e\uff0c\u53ef\u4ee5\u8c03\u7528String.intern()<\/code>\uff0c\u8fd9\u4e2a\u662fnative\u65b9\u6cd5\uff0c\u5982\u679c\u5e38\u91cf\u6c60\u4e2d\u5df2\u7ecf\u5b58\u5728\u4e00\u4e2a\uff0c\u5219\u8fd4\u56de\uff0c\u5426\u5219\u6dfb\u52a0\u5230\u5e38\u91cf\u6c60\u4e2d\u3002<\/p>\n

\u521a\u5f00\u59cb\u7684\u4f8b\u5b50\u5982\u4e0b\uff1a<\/p>\n

public class PermTest {\n    public static void main(String[] args) {\n        int i = 0;\n        while (true) {\n            String.valueOf(i++).intern();\n            System.out.println(i);\n        }\n    }\n}<\/code><\/pre>\n
\u53d1\u73b0\u6ca1\u6709\u629b\u51faOOM\u5f02\u5e38\uff0c\u7528JConsole\u67e5\u770b\uff0c\uff08PermSize\u548cMaxPermSize\u90fd\u662f10M\uff09\u572810M\u7684\u65f6\u5019\u66f2\u7ebf\u53c8\u4e0b\u53bb\u4e86\uff0c\u539f\u6765\u662fFullGC\u628a\u5e38\u91cf\u6c60\u4e2d\u6ca1\u6709\u7684\u5f15\u7528GC\u6389\u4e86\uff0c\u6240\u4ee5\u6ca1\u6709OOM\u3002<\/p>\n
\u589e\u52a0\u4e86\u4e00\u4e2aList\uff0c\u6301\u6709\u8fd9\u4e2a\u5f15\u7528\uff0c\u5c31\u4e0d\u4f1a\u88abGC\u6389\u4e86\u3002<\/p>\n
public class PermTest {\n    public static void main(String[] args) {\n        List<String> all = new ArrayList<String>();\n        int i = 0;\n        while (true) {\n            all.add(String.valueOf(i++).intern());\n        }\n    }\n}<\/code><\/pre>\n
Exception in thread  "main"  java.lang.OutOfMemoryError: PermGen space\n    at java.lang.String.intern(Native Method)\n    at PermTest.main(PermTest.java: 10 )<\/code><\/pre>\n
\u4f8b\u5b502\uff1a\u7528cglib\u4ea7\u751f\u4ee3\u7406\u7c7b\uff0c\u4e0d\u65ad\u7684\u521b\u5efa\u7c7b<\/h3>\n
import java.lang.reflect.Method;\nimport net.sf.cglib.proxy.Enhancer;\nimport net.sf.cglib.proxy.MethodInterceptor;\nimport net.sf.cglib.proxy.MethodProxy;\n\npublic class PermTest {\n    public static void main(String[] args) {\n        while (true) {\n            Enhancer enhancer = new Enhancer();\n            enhancer.setSuperclass(PermTestClass. class);\n            enhancer.setUseCache(false);\n            enhancer.setCallback(new MethodInterceptor() {\n                @Override\n                public Object intercept(Object obj, Method method, Object[] args,\n                        MethodProxy proxy) throws Throwable {\n                    return proxy.invoke(obj, args);\n                }\n            });\n            enhancer.create();\n        }\n    }\n\n    static class PermTestClass {\n    }\n}<\/code><\/pre>\n
Caused by: java.lang.OutOfMemoryError: PermGen space\n    at java.lang.ClassLoader.defineClass1(Native Method)\n    at java.lang.ClassLoader.defineClassCond(ClassLoader.java: 631)\n    at java.lang.ClassLoader.defineClass(ClassLoader.java: 615)\n    ...  8  more<\/code><\/pre>\n
Btrace\u7684\u811a\u672c\u6587\u4ef6\u5982\u4e0b\uff08\u67e5\u770b\u54ea\u91cc\u8c03\u7528\u4e86defineClass<\/code>\u4fe1\u606f\uff09\uff1a<\/p>\n
import static com.sun.btrace.BTraceUtils.*;\nimport com.sun.btrace.annotations.*;\n\n@BTrace\npublic class BtraceAll {\n    @TLS\n    private static long beginTime;\n\n    @OnMethod (\n        clazz= "java.lang.ClassLoader",\n        method= "defineClass"\n    )\n    public static void traceMethodBegin() {\n        beginTime = timeMillis();\n    }\n\n    @OnMethod (\n        clazz= "java.lang.ClassLoader",\n        method= "defineClass",\n        location= @Location(Kind.RETURN)\n    )\n    public static void traceMethdReturn(\n            @Return String result,\n            @ProbeClassName String clazzName,\n            @ProbeMethodName String methodName) {\n        println("===========================================================================");\n        println(strcat(strcat(clazzName, "."), methodName));\n        println(strcat("Time taken : ", str(timeMillis() - beginTime)));\n        println("java thread method trace:---------------------------------------------------");\n        jstack();\n        println("----------------------------------------------------------------------------");\n        println(strcat("Reuslt :", str(result)));\n        println("============================================================================");\n    }\n}<\/code><\/pre>\n
\u8fd0\u884c\u540e\uff0c\u53d1\u73b0cglib\u5728\u521b\u5efa\u4ee3\u7406\u7c7b\u7684\u65f6\u5019\uff0c\u786e\u5b9e\u8c03\u7528\u4e86defineClass<\/code>\u65b9\u6cd5<\/p>\n
===========================================================================\njava.lang.ClassLoader.defineClass\nTime taken : 79\njava thread method trace:---------------------------------------------------\njava.lang.ClassLoader.defineClass(ClassLoader.java: 615)\nsun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)\nsun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java: 25)\njava.lang.reflect.Method.invoke(Method.java: 597)\nnet.sf.cglib.core.ReflectUtils.defineClass(ReflectUtils.java: 384 )\nnet.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java: 219)\nnet.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java: 377)\nnet.sf.cglib.proxy.Enhancer.create(Enhancer.java: 285)\nPermTest.main(PermTest.java: 19)\n----------------------------------------------------------------------------\nReuslt : class  PermTest$PermTestClass$$EnhancerByCGLIB$$1ed16944_8\n============================================================================<\/code><\/pre>\n
\u81f3\u6b64\uff0c\u95ee\u9898\u573a\u666f\u4ee5\u53ca\u5982\u4f55\u6392\u67e5\uff0c\u6e05\u6670\u4e86\u3002\u3002\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
Java\u5e94\u7528Perm\u533a\u4e00\u76f4\u5448\u4e0a\u6da8\u8d8b\u52bf\u7684\u539f\u56e0\u53ef\u4ee5\u7528\u4e00\u4e2a\u7b80\u5355\u7684\u529e\u6cd5\u6392\u67e5\uff0c\u5c31\u662f\u7528btrace\u53bb\u8ddf\u8e2a\u4e0b\u662f\u4ec0\u4e48\u5730\u65b9\u5728\u8c03\u7528 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[43],"tags":[59],"class_list":["post-117","post","type-post","status-publish","format-standard","hentry","category-java-basic","tag-jvm"],"_links":{"self":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/posts\/117","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/comments?post=117"}],"version-history":[{"count":0,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/posts\/117\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/media?parent=117"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/categories?post=117"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.appblog.cn\/index.php\/wp-json\/wp\/v2\/tags?post=117"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}