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之前的文章详细介绍了关于非JDK类库的静态方法、构造方法、实例方法的增强拦截流程#xff0c;本文会详细分析JDK类库中的类是如何被增强拦截的
回到最开始的SkyWalkingAgent#premain
try {/** 里面有个重点逻辑 把一些类注入到Boostrap类加载器中 为了解决Bootstrap类…前言
之前的文章详细介绍了关于非JDK类库的静态方法、构造方法、实例方法的增强拦截流程本文会详细分析JDK类库中的类是如何被增强拦截的
回到最开始的SkyWalkingAgent#premain
try {/** 里面有个重点逻辑 把一些类注入到Boostrap类加载器中 为了解决Bootstrap类加载器不能访问App类加载器中的内容的问题* */agentBuilder BootstrapInstrumentBoost.inject(pluginFinder, instrumentation, agentBuilder, edgeClasses);
} catch (Exception e) {LOGGER.error(e, SkyWalking agent inject bootstrap instrumentation failure. Shutting down.);return;
}BootstrapInstrumentBoost.inject
这里是将必要的类注入到Bootstrap ClassLoader
public static AgentBuilder inject(PluginFinder pluginFinder, Instrumentation instrumentation,AgentBuilder agentBuilder, JDK9ModuleExporter.EdgeClasses edgeClasses) throws PluginException {//所有要注入到 Bootstrap ClassLoader 里的类MapString, byte[] classesTypeMap new LinkedHashMap();//针对于目标类是JDK核心类库的插件这里根据插件的拦截点的不同(实例方法、静态方法、构造方法)//使用不同的模板(XxxTemplate)来定义新的拦截器的核心处理逻辑并且将插件本身定义的拦截器的全类名赋值给模板的//TARGET_INTERCEPTOR字段。 最后这些新的拦截器的核心处理逻辑都会被放入 Bootstrap ClassLoader 中if (!prepareJREInstrumentation(pluginFinder, classesTypeMap)) {return agentBuilder;}if (!prepareJREInstrumentationV2(pluginFinder, classesTypeMap)) {return agentBuilder;}for (String highPriorityClass : HIGH_PRIORITY_CLASSES) {loadHighPriorityClass(classesTypeMap, highPriorityClass);}for (String highPriorityClass : ByteBuddyCoreClasses.CLASSES) {loadHighPriorityClass(classesTypeMap, highPriorityClass);}/*** Prepare to open edge of necessary classes.*/for (String generatedClass : classesTypeMap.keySet()) {edgeClasses.add(generatedClass);}/*** Inject the classes into bootstrap class loader by using Unsafe Strategy.* ByteBuddy adapts the sun.misc.Unsafe and jdk.internal.misc.Unsafe automatically.*//*** 把一些类注入到Boostrap类加载器中 为了解决Bootstrap类加载器不能访问App类加载器中的内容的问题* */ClassInjector.UsingUnsafe.Factory factory ClassInjector.UsingUnsafe.Factory.resolve(instrumentation);factory.make(null, null).injectRaw(classesTypeMap);agentBuilder agentBuilder.with(new AgentBuilder.InjectionStrategy.UsingUnsafe.OfFactory(factory));return agentBuilder;
}BootstrapInstrumentBoost#prepareJREInstrumentation
private static boolean prepareJREInstrumentation(PluginFinder pluginFinder,MapString, byte[] classesTypeMap) throws PluginException {TypePool typePool TypePool.Default.of(BootstrapInstrumentBoost.class.getClassLoader());// 所有要对JDK核心类库生效的插件ListAbstractClassEnhancePluginDefine bootstrapClassMatchDefines pluginFinder.getBootstrapClassMatchDefine();for (AbstractClassEnhancePluginDefine define : bootstrapClassMatchDefines) {// 是否定义实例方法拦截点if (Objects.nonNull(define.getInstanceMethodsInterceptPoints())) {for (InstanceMethodsInterceptPoint point : define.getInstanceMethodsInterceptPoints()) {if (point.isOverrideArgs()) {generateDelegator(classesTypeMap, typePool, INSTANCE_METHOD_WITH_OVERRIDE_ARGS_DELEGATE_TEMPLATE, point.getMethodsInterceptor());} else {generateDelegator(classesTypeMap, typePool, INSTANCE_METHOD_DELEGATE_TEMPLATE, point.getMethodsInterceptor());}}}// 是否定义构造器拦截点if (Objects.nonNull(define.getConstructorsInterceptPoints())) {for (ConstructorInterceptPoint point : define.getConstructorsInterceptPoints()) {generateDelegator(classesTypeMap, typePool, CONSTRUCTOR_DELEGATE_TEMPLATE, point.getConstructorInterceptor());}}// 是否定义静态方法拦截点if (Objects.nonNull(define.getStaticMethodsInterceptPoints())) {for (StaticMethodsInterceptPoint point : define.getStaticMethodsInterceptPoints()) {if (point.isOverrideArgs()) {generateDelegator(classesTypeMap, typePool, STATIC_METHOD_WITH_OVERRIDE_ARGS_DELEGATE_TEMPLATE, point.getMethodsInterceptor());} else {generateDelegator(classesTypeMap, typePool, STATIC_METHOD_DELEGATE_TEMPLATE, point.getMethodsInterceptor());}}}}return bootstrapClassMatchDefines.size() 0;
}总结
在之前PluginFinder对象初始化时就会将加载的所有插件做分类要对JDK核心类库生效的插件都放入到bootstrapClassMatchDefine集合中然后调用getBootstrapClassMatchDefine()就是拿到所有要对JDK核心类库生效的插件循环所有要对JDK核心类库生效的插件分别判断是否定义实例方法拦截点、是否定义构造器拦截点、是否定义静态方法拦截点
下面我们来进入实例方法的增强并不重写原方法为例来分析详细的流程
private static String INSTANCE_METHOD_DELEGATE_TEMPLATE org.apache.skywalking.apm.agent.core.plugin.bootstrap.template.InstanceMethodInterTemplate;generateDelegator(classesTypeMap, typePool, INSTANCE_METHOD_DELEGATE_TEMPLATE, point.getMethodsInterceptor());这里会调用generateDelegator方法生成一个代理器其中的参数INSTANCE_METHOD_DELEGATE_TEMPLATE是一个模版类名来传入模版名为org.apache.skywalking.apm.agent.core.plugin.bootstrap.template.InstanceMethodInterTemplate,这个是模板不是作为实际的类和对象来调用的
InstanceMethodInterTemplate模板
/*** --------CLASS TEMPLATE---------* pAuthor, Wu Sheng /p* pComment, dont change this unless you are 100% sure the agent core mechanism for bootstrap class* instrumentation./p* pDate, 24th July 2019/p* -------------------------------* p* This class wouldnt be loaded in real env. This is a class template for dynamic class generation.* * 这个类是不会被加载的,这是一个类模板用于动态类生成*/
public class InstanceMethodInterTemplate {/*** This field is never set in the template, but has value in the runtime.*/private static String TARGET_INTERCEPTOR;private static InstanceMethodsAroundInterceptor INTERCEPTOR;private static IBootstrapLog LOGGER;/*** Intercept the target instance method.** param obj target class instance.* param allArguments all method arguments* param method method description.* param zuper the origin call ref.* return the return value of target instance method.* throws Exception only throw exception because of zuper.call() or unexpected exception in sky-walking ( This is a* bug, if anything triggers this condition ).*/RuntimeTypepublic static Object intercept(This Object obj, AllArguments Object[] allArguments, SuperCall Callable? zuper,Origin Method method) throws Throwable {EnhancedInstance targetObject (EnhancedInstance) obj;prepare();MethodInterceptResult result new MethodInterceptResult();try {if (INTERCEPTOR ! null) {INTERCEPTOR.beforeMethod(targetObject, method, allArguments, method.getParameterTypes(), result);}} catch (Throwable t) {if (LOGGER ! null) {LOGGER.error(t, class[{}] before method[{}] intercept failure, obj.getClass(), method.getName());}}Object ret null;try {if (!result.isContinue()) {ret result._ret();} else {ret zuper.call();}} catch (Throwable t) {try {if (INTERCEPTOR ! null) {INTERCEPTOR.handleMethodException(targetObject, method, allArguments, method.getParameterTypes(), t);}} catch (Throwable t2) {if (LOGGER ! null) {LOGGER.error(t2, class[{}] handle method[{}] exception failure, obj.getClass(), method.getName());}}throw t;} finally {try {if (INTERCEPTOR ! null) {ret INTERCEPTOR.afterMethod(targetObject, method, allArguments, method.getParameterTypes(), ret);}} catch (Throwable t) {if (LOGGER ! null) {LOGGER.error(t, class[{}] after method[{}] intercept failure, obj.getClass(), method.getName());}}}return ret;}/*** Prepare the context. Link to the agent core in AppClassLoader.* - 让BootstrapClassLoader 和 AgentClassloader能够相通* - 获取到ILog生成日志对象* - 获取到插件自定义的拦截器增强类实例* - 替代非JDK核心类库插件运行逻辑里的interceptor InterceptorInstanceLoader.load(instanceMethodsAroundInterceptorClassName, classLoader); */private static void prepare() {if (INTERCEPTOR null) {ClassLoader loader BootstrapInterRuntimeAssist.getAgentClassLoader();if (loader ! null) {IBootstrapLog logger BootstrapInterRuntimeAssist.getLogger(loader, TARGET_INTERCEPTOR);if (logger ! null) {LOGGER logger;INTERCEPTOR BootstrapInterRuntimeAssist.createInterceptor(loader, TARGET_INTERCEPTOR, LOGGER);}} else {LOGGER.error(Runtime ClassLoader not found when create {}. TARGET_INTERCEPTOR);}}}
}能看出这个模板类的intercept()方法和实例方法中非jdk类库增强的intercept()方法里面的逻辑都大致差不多
下面来详细分析generateDelegator方法
generateDelegator
/*** Generate the delegator class based on given template class. This is preparation stage level code generation.* 根据给定的模板类生成代理器类,这是准备阶段级别的代码生成* p* One key step to avoid class confliction between AppClassLoader and BootstrapClassLoader* 避免AppClassLoader和BootstrapClassLoader之间的类冲突的一个关键步骤** param classesTypeMap hosts injected binary of generated class 。要注入到Bootstrap类加载器中的类和字节码的映射* key:全类名 value:字节码* param typePool to generate new class 。加载BootstrapInstrumentBoost的ClassLoader的类型池* param templateClassName represents the class as template in this generation process. The templates are* pre-defined in SkyWalking agent core。 要进行增强的模板里面就是环绕增强逻辑的模板* * param methodsInterceptor 要进行增强逻辑的拦截增强类 */
private static void generateDelegator(MapString, byte[] classesTypeMap, TypePool typePool,String templateClassName, String methodsInterceptor) {//要进行具体增强逻辑的拦截增强类名 _internalString internalInterceptorName internalDelegate(methodsInterceptor);try {//某个类加载器 已经加载了10个类但这个类加载器的classpath下有400个类//typePool.describe可以获取到这个类加载器的classpath下还没有加载类的描述信息TypeDescription templateTypeDescription typePool.describe(templateClassName).resolve();//把模板通过ByteBuddy编译成字节码DynamicType.Unloaded interceptorType new ByteBuddy().redefine(templateTypeDescription, ClassFileLocator.ForClassLoader.of(BootstrapInstrumentBoost.class.getClassLoader())).name(internalInterceptorName).field(named(TARGET_INTERCEPTOR)).value(methodsInterceptor).make();classesTypeMap.put(internalInterceptorName, interceptorType.getBytes());InstrumentDebuggingClass.INSTANCE.log(interceptorType);} catch (Exception e) {throw new PluginException(Generate Dynamic plugin failure, e);}
}此方法是将模板类交给ByteBuddy去编译成字节码改了新的类名并将TARGET_INTERCEPTOR属性赋值为插件拦截器全类名然后就放入到classesTypeMap中此Map是要注入到Bootstrap类加载器中的类和字节码的映射key:全类名 value:字节码
接下来回到BootstrapInstrumentBoost.inject(pluginFinder, instrumentation, agentBuilder, edgeClasses)方法继续分析剩下的部分
ClassInjector.UsingUnsafe.Factory.resolve(instrumentation)
/*** 把一些必要的类注入到Boostrap类加载器中 为了解决Bootstrap类加载器不能访问App类加载器中的内容的问题* */
ClassInjector.UsingUnsafe.Factory factory ClassInjector.UsingUnsafe.Factory.resolve(instrumentation);
factory.make(null, null).injectRaw(classesTypeMap);
agentBuilder agentBuilder.with(new AgentBuilder.InjectionStrategy.UsingUnsafe.OfFactory(factory));将之前生成模版的方法中类和字节码的映射的Mapinstrumentation,注入到Bootstrap ClassLoader,此步骤是使用模版进行字节码增强的前提
JDK类库方法的增强过程
想让我们回到ClassEnhancePluginDefine#enhanceInstance再看一下实例方法的在进行增强是的判断逻辑
if (existedConstructorInterceptPoint) {//获取所有构造方法的切点for (ConstructorInterceptPoint constructorInterceptPoint : constructorInterceptPoints) {//要增加的类是Bootstrap类加载器加载的if (isBootstrapInstrumentation()) {newClassBuilder newClassBuilder.constructor(constructorInterceptPoint.getConstructorMatcher()).intercept(SuperMethodCall.INSTANCE.andThen(MethodDelegation.withDefaultConfiguration().to(BootstrapInstrumentBoost.forInternalDelegateClass(constructorInterceptPoint.getConstructorInterceptor()))));} else {newClassBuilder newClassBuilder.constructor(constructorInterceptPoint.getConstructorMatcher()).intercept(SuperMethodCall.INSTANCE.andThen(MethodDelegation.withDefaultConfiguration().to(new ConstructorInter(constructorInterceptPoint.getConstructorInterceptor(), classLoader))));}}
}/*** 3. enhance instance methods*/
if (existedMethodsInterceptPoints) {//获取所有实例方法的切点for (InstanceMethodsInterceptPoint instanceMethodsInterceptPoint : instanceMethodsInterceptPoints) {String interceptor instanceMethodsInterceptPoint.getMethodsInterceptor();if (StringUtil.isEmpty(interceptor)) {throw new EnhanceException(no InstanceMethodsAroundInterceptor define to enhance class enhanceOriginClassName);}ElementMatcher.JunctionMethodDescription junction not(isStatic()).and(instanceMethodsInterceptPoint.getMethodsMatcher());if (instanceMethodsInterceptPoint instanceof DeclaredInstanceMethodsInterceptPoint) {//拦截到的方法必须是当前类上的 注解匹配到的方法有可能不是当前类上的junction junction.and(ElementMatchers.MethodDescriptionisDeclaredBy(typeDescription));}if (instanceMethodsInterceptPoint.isOverrideArgs()) {//要增加的类是Bootstrap类加载器加载的if (isBootstrapInstrumentation()) {newClassBuilder newClassBuilder.method(junction).intercept(MethodDelegation.withDefaultConfiguration().withBinders(Morph.Binder.install(OverrideCallable.class)).to(BootstrapInstrumentBoost.forInternalDelegateClass(interceptor)));} else {newClassBuilder newClassBuilder.method(junction).intercept(MethodDelegation.withDefaultConfiguration().withBinders(Morph.Binder.install(OverrideCallable.class)).to(new InstMethodsInterWithOverrideArgs(interceptor, classLoader)));}} else {//要增加的类是Bootstrap类加载器加载的if (isBootstrapInstrumentation()) {newClassBuilder newClassBuilder.method(junction).intercept(MethodDelegation.withDefaultConfiguration().to(BootstrapInstrumentBoost.forInternalDelegateClass(interceptor)));} else {newClassBuilder newClassBuilder.method(junction).intercept(MethodDelegation.withDefaultConfiguration().to(new InstMethodsInter(interceptor, classLoader)));}}}
}能看到如果是要增强的类是JDK类库中的都是调用到BootstrapInstrumentBoost.forInternalDelegateClass的方法
BootstrapInstrumentBoost.forInternalDelegateClass
public static Class forInternalDelegateClass(String methodsInterceptor) {try {return Class.forName(internalDelegate(methodsInterceptor));} catch (ClassNotFoundException e) {throw new PluginException(e.getMessage(), e);}
}public static String internalDelegate(String methodsInterceptor) {return methodsInterceptor _internal;
}通过Class.forName()加载插件拦截器全类名_internal的类这个类在Agent启动流程根据模板类生成并注入到Bootstrap ClassLoader中所以这里是能加载到再看一下模版InstanceMethodInterTemplate
/*** --------CLASS TEMPLATE---------* pAuthor, Wu Sheng /p* pComment, dont change this unless you are 100% sure the agent core mechanism for bootstrap class* instrumentation./p* pDate, 24th July 2019/p* -------------------------------* p* This class wouldnt be loaded in real env. This is a class template for dynamic class generation.* * 这个类是不会被加载的,这是一个类模板用于动态类生成*/
public class InstanceMethodInterTemplate {/*** This field is never set in the template, but has value in the runtime.*/private static String TARGET_INTERCEPTOR;private static InstanceMethodsAroundInterceptor INTERCEPTOR;private static IBootstrapLog LOGGER;/*** Intercept the target instance method.** param obj target class instance.* param allArguments all method arguments* param method method description.* param zuper the origin call ref.* return the return value of target instance method.* throws Exception only throw exception because of zuper.call() or unexpected exception in sky-walking ( This is a* bug, if anything triggers this condition ).*/RuntimeTypepublic static Object intercept(This Object obj, AllArguments Object[] allArguments, SuperCall Callable? zuper,Origin Method method) throws Throwable {EnhancedInstance targetObject (EnhancedInstance) obj;prepare();MethodInterceptResult result new MethodInterceptResult();try {if (INTERCEPTOR ! null) {INTERCEPTOR.beforeMethod(targetObject, method, allArguments, method.getParameterTypes(), result);}} catch (Throwable t) {if (LOGGER ! null) {LOGGER.error(t, class[{}] before method[{}] intercept failure, obj.getClass(), method.getName());}}Object ret null;try {if (!result.isContinue()) {ret result._ret();} else {ret zuper.call();}} catch (Throwable t) {try {if (INTERCEPTOR ! null) {INTERCEPTOR.handleMethodException(targetObject, method, allArguments, method.getParameterTypes(), t);}} catch (Throwable t2) {if (LOGGER ! null) {LOGGER.error(t2, class[{}] handle method[{}] exception failure, obj.getClass(), method.getName());}}throw t;} finally {try {if (INTERCEPTOR ! null) {ret INTERCEPTOR.afterMethod(targetObject, method, allArguments, method.getParameterTypes(), ret);}} catch (Throwable t) {if (LOGGER ! null) {LOGGER.error(t, class[{}] after method[{}] intercept failure, obj.getClass(), method.getName());}}}return ret;}/*** Prepare the context. Link to the agent core in AppClassLoader.* - 让BootstrapClassLoader 和 AgentClassloader能够相通* - 获取到ILog生成日志对象* - 获取到插件自定义的拦截器增强类实例* - 替代非JDK核心类库插件运行逻辑里的interceptor InterceptorInstanceLoader.load(instanceMethodsAroundInterceptorClassName, classLoader); */private static void prepare() {if (INTERCEPTOR null) {ClassLoader loader BootstrapInterRuntimeAssist.getAgentClassLoader();if (loader ! null) {IBootstrapLog logger BootstrapInterRuntimeAssist.getLogger(loader, TARGET_INTERCEPTOR);if (logger ! null) {LOGGER logger;INTERCEPTOR BootstrapInterRuntimeAssist.createInterceptor(loader, TARGET_INTERCEPTOR, LOGGER);}} else {LOGGER.error(Runtime ClassLoader not found when create {}. TARGET_INTERCEPTOR);}}}
}JDK类库的类做增强会交给模板InstanceMethodInterTemplate生成的类来处理实际是模板中的TARGET_INTERCEPTOR赋值为插件拦截器全类名和实例方法插桩的InstMethodsInter的intercept()方法相比这里多调用了一个prepare()方法prepare()方法是让BootstrapClassLoader能够和AgentClassLoader相同的关键
prepare()
/*** Prepare the context. Link to the agent core in AppClassLoader.* - 让BootstrapClassLoader 和 AgentClassloader能够相通* - 获取到ILog生成日志对象* - 获取到插件自定义的拦截器增强类实例* - 替代非JDK核心类库插件运行逻辑里的interceptor InterceptorInstanceLoader.load(instanceMethodsAroundInterceptorClassName, classLoader); */
private static void prepare() {if (INTERCEPTOR null) {ClassLoader loader BootstrapInterRuntimeAssist.getAgentClassLoader();if (loader ! null) {IBootstrapLog logger BootstrapInterRuntimeAssist.getLogger(loader, TARGET_INTERCEPTOR);if (logger ! null) {LOGGER logger;INTERCEPTOR BootstrapInterRuntimeAssist.createInterceptor(loader, TARGET_INTERCEPTOR, LOGGER);}} else {LOGGER.error(Runtime ClassLoader not found when create {}. TARGET_INTERCEPTOR);}}
}BootstrapInterRuntimeAssist
public class BootstrapInterRuntimeAssist {private static final String AGENT_CLASSLOADER_DEFAULT org.apache.skywalking.apm.agent.core.plugin.loader.AgentClassLoader;private static final String DEFAULT_AGENT_CLASSLOADER_INSTANCE DEFAULT_LOADER;private static final String LOG_MANAGER_CLASS org.apache.skywalking.apm.agent.core.plugin.bootstrap.BootstrapPluginLogBridge;private static final String LOG_MANAGER_GET_LOGGER_METHOD getLogger;private static final PrintStream OUT System.out;public static ClassLoader getAgentClassLoader() {try {ClassLoader loader Thread.currentThread().getContextClassLoader();if (loader null) {return null;}Class? agentClassLoaderClass Class.forName(AGENT_CLASSLOADER_DEFAULT, true, loader);Field defaultLoaderField agentClassLoaderClass.getDeclaredField(DEFAULT_AGENT_CLASSLOADER_INSTANCE);defaultLoaderField.setAccessible(true);ClassLoader defaultAgentClassLoader (ClassLoader) defaultLoaderField.get(null);return defaultAgentClassLoader;} catch (Exception e) {e.printStackTrace(OUT);return null;}}public static IBootstrapLog getLogger(ClassLoader defaultAgentClassLoader, String interceptor) {try {Class? logManagerClass Class.forName(LOG_MANAGER_CLASS, true, defaultAgentClassLoader);Method getLogger logManagerClass.getMethod(LOG_MANAGER_GET_LOGGER_METHOD, String.class);return (IBootstrapLog) getLogger.invoke(null, interceptor _internal);} catch (Exception e) {e.printStackTrace(OUT);return null;}}public static T T createInterceptor(ClassLoader defaultAgentClassLoader, String className, IBootstrapLog log) {try {Class? interceptor Class.forName(className, true, defaultAgentClassLoader);return (T) interceptor.newInstance();} catch (Exception e) {log.error(e, Interceptor[{}] not found, className);}return null;}
}prepare()总结
获取到AgentClassLoader用AgentClassLoader加载桥接器BootstrapPluginLogBridge类然后调用getLogger方法传入TARGET_INTERCEPTOR_internal得到这个传入的实际类名的BootstrapPluginLogBridge的对象将得到的BootstrapPluginLogBridge赋给模板类的成员属性LOGGER用AgentClassLoader加载插件自定义的拦截器实例
为什么要用prepare()来特意的利用桥接来绕一下呢
因为InstanceMethodInterTemplate生成的类是由BootstrapClassLoader去加载的而日志对象和插件自定义的拦截器都是通过AgentClassLoader去加载的prepare()方法的作用就是将BootstrapClassLoader和AgentClassLoader能够相同
举例说明:
如果BootstrapClassLoader加载的由InstanceMethodInterTemplate生成的类是org.apache.skywalking.xxx.HttpClientInterceptor_internalAgentClassLoader加载了日志用到的ILog和插件拦截器HttpClientIntercepotrAgentClassLoader的顶层父类加载器为BootstrapClassLoader根据双亲委派模型从下往上加载是可以拿到的但是从上往下加载是拿不到的,BootstrapClassLoader中不能拿到ILog和HttpClientIntercepotr所以需要通过prepare()方法打通BootstrapClassLoader和AgentClassLoader
总结
准备工作使用对应的Template模板来生成实际的拦截增强实际类名为xxx_internalprepare()方法 将BootstrapClassLoader和AgentClassLoader能够相通获取到日志对象ILog实例化插件定义的拦截器用来代替非JDK类库增强中的InterceptorInstanceLoader.load(instanceMethodsAroundInterceptorClassName, classLoader) 后续的增强逻辑和非JDK类库的流程相同
