Java
Java 容器化的历史坑（史坑） - 资源限制篇
· ☕ 5 分钟

由来

时间回到 2017 年，老东家要上 Kubernetes 了，有幸参与和学习（主要是学习）。当时遇到的一了所有 Java 容器化者都遇到的坑：JDK8 不为容器化设计综合症。最简单的例子是Runtime.getRuntime().availableProcessors()返回了主机的 CPU 数，而非期望的容器自身的cpu share/quota，或说 k8s 的 cpu request/limit。

Java 内置 Class Loader
· ☕ 3 分钟

内置 Classloader

The class loader delegation model

Class loaders load classes and resources present on their respective classpath:

  • System or application class loaders load classes from the application classpath
  • Extension class loaders search on the Extension classpath (JRE/lib/ext)
  • Bootstrap class loader looks on the Bootstrap classpath (JRE/lib/rt.jar)

We can customize the default class loading behavior as well. We can explicitly specify the class loader while loading a class dynamically.

However, we should note that if we load the same class from different types of class loaders, these will be seen as different resources by the JVM.

Opentelemetry Java Agent 浅度解构
· ☕ 2 分钟

Agent initialization sequence

Agent classloader state

Conf

Creating spans around methods with otel.instrumentation.methods.include

Ref: https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/docs/manual-instrumentation.md

Format is "java -Dotel.instrumentation.methods.include=my.package.MyClass1[method1,method2];my.package.MyClass2[method3]"

Classloader

[arthas@16908]$ classloader -t
+-BootstrapClassLoader                                                                                                 
+-io.opentelemetry.javaagent.bootstrap.AgentClassLoader@379619aa                                                       
+-sun.misc.Launcher$ExtClassLoader@41fa769c                                                                            
  +-com.taobao.arthas.agent.ArthasClassloader@3697b340                                                                 
  +-sun.misc.Launcher$AppClassLoader@18b4aac2                                                                          
    +-java.net.URLClassLoader@71b2d611                                                                                 
    +-java.net.URLClassLoader@69cd1085                                                                                 
    | +-WebAppClassLoader=266661735@fe4ef67                                                                            
    | | +-com.mycom.sig.foundation.servicediscovery.ExtendedClassLoader@573f7aae                                    
    | +-WebAppClassLoader=Server Initiated@1ccb04b3                                                                    
    | | +-com.mycom.sig.foundation.servicediscovery.ExtendedClassLoader@4b3b9a06                                    
    | | +-jnr.ffi.provider.jffi.AsmClassLoader@73cb9ccb                                                                
    | | +-jnr.ffi.provider.jffi.AsmClassLoader@7c380e94                                                                
    | | +-jnr.ffi.provider.jffi.AsmClassLoader@69ec5d1f                                                                
    | +-WebAppClassLoader=OAuth Server@10d98940                                                                        
    | | +-com.mycom.ece.common.svcfinder.ExtendedClassLoader@3528968e                                               
    | | +-com.mycom.sig.foundation.servicediscovery.ExtendedClassLoader@2919aff3                                    
    | | +-jnr.ffi.provider.jffi.AsmClassLoader@1b0e6bac                                                                
    | | +-jnr.ffi.provider.jffi.AsmClassLoader@2f12d8d1                                                                
    | | +-jnr.ffi.provider.jffi.AsmClassLoader@73123f21                                                                
    | +-WebAppClassLoader=1133988396@43974a2c                                                                          
    |   +-com.mycom.sig.foundation.servicediscovery.ExtendedClassLoader@39d87c5f                                    
    +-java.net.URLClassLoader@1b4c457c                                                                                 
    +-java.net.URLClassLoader@3a477cf5                                                                                 
Affect(row-cnt:24) cost in 31 ms.

[arthas@16908]$ classloader
 name                                                              numberOfInstances  loadedCountTotal                 
 org.eclipse.jetty.webapp.WebAppClassLoader                        4                  24687                            
 BootstrapClassLoader                                              1                  4341                             
 io.opentelemetry.javaagent.bootstrap.AgentClassLoader             1                  3502                             
 com.taobao.arthas.agent.ArthasClassloader                         1                  1430                             
 java.net.URLClassLoader                                           4                  1252                             
 sun.misc.Launcher$AppClassLoader                                  1                  570                              
 sun.reflect.DelegatingClassLoader                                 378                378                              
 sun.misc.Launcher$ExtClassLoader                                  1                  56                               
 jnr.ffi.provider.jffi.AsmClassLoader                              6                  8                                
 com.mycom.sig.foundation.servicediscovery.ExtendedClassLoader  4                  6                                
 com.mycom.ece.common.svcfinder.ExtendedClassLoader             1                  1  

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[arthas@16908]$ jad -c 1ccb04b3 com.mycom.jee.abc.client.service.payload.ClientResponse setProjectName

ClassLoader:                                                                                                           
+-WebAppClassLoader=Server Initiated@1ccb04b3                                                                          
  +-java.net.URLClassLoader@69cd1085                                                                                   
    +-sun.misc.Launcher$AppClassLoader@18b4aac2                                                                        
      +-sun.misc.Launcher$ExtClassLoader@41fa769c                                                                      

Location:                                                                                                              
/var/lib/modules/DP-OAuth-Traffic/tmp/server-initiated-aa-war.war/webapp/WEB-INF/lib/clients-api-3.19.5.jar            

            public void setProjectName(String string) {                                                                
                StackTraceElement[] stackTraceElementArray;
/*729*/         Context context = null;                                                                                
                Scope scope = null;               
                try {                                                                                                  
                    stackTraceElementArray = Thread.currentThread().getStackTrace();                                                                                                                                                          
                    context = MethodTracer.tracer().startSpan(ClientResponse.class.getMethod("setProjectName", String.class), stackTraceElementArray, new Object[]{string});
                    if (context != null) {
                        scope = context.makeCurrent();
                    }
                }
                catch (Throwable throwable) {
                    try {
                        LoggerFactory.getLogger(ExceptionLogger.class).debug("Failed to handle exception in instrumentation for com.mycom.jee.abc.client.service.payload.ClientResponse on sun.misc.Launcher$AppClassLoader@18b4aac2", thr$
wable);
                    }
                    catch (Throwable throwable2) {
                    }
                }
                stackTraceElementArray = this;
                String projectName = string;
                try {
                    this.projectName = projectName;
                    stackTraceElementArray = null;
                }
                catch (Throwable throwable) {
                    // empty catch block
                }
                try {
                    if (context != null) {
                        scope.close();
                        if (stackTraceElementArray != null) {
                            MethodTracer.tracer().endExceptionally(context, (Throwable)stackTraceElementArray);
                        } else {
                            Span span = Span.fromContext(context);
                            span.setAttribute(MethodTracer.JAVA_METHOD_RETURN.getKey(), null == null ? "null" : ((Object)null).toString());
                            MethodTracer.tracer().end(context);
                        }
                    }
                }
                catch (Throwable throwable) {
                    try {
                        LoggerFactory.getLogger(ExceptionLogger.class).debug("Failed to handle exception in instrumentation for com.mycom.jee.abc.client.service.payload.ClientResponse on sun.misc.Launcher$AppClassLoader@18b4aac2", thro
wable);
                    }
                    catch (Throwable throwable3) {
                    }
                }
                if (stackTraceElementArray != null) {
                    throw stackTraceElementArray;
                }
            }

[arthas@16908]$ sc io.opentelemetry.javaagent.instrumentation.methods.MethodInstrumentationModule
io.opentelemetry.javaagent.instrumentation.methods.MethodInstrumentationModule
Affect(row-cnt:1) cost in 54 ms.
[arthas@16908]$ sc -d io.opentelemetry.javaagent.instrumentation.methods.MethodInstrumentationModule
 class-info        io.opentelemetry.javaagent.instrumentation.methods.MethodInstrumentationModule                      
 code-source       /                                                                                                   
 name              io.opentelemetry.javaagent.instrumentation.methods.MethodInstrumentationModule                      
 isInterface       false                                                                                               
 isAnnotation      false                                                                                               
 isEnum            false                                                                                               
 isAnonymousClass  false                                                                                               
 isArray           false                                                                                               
 isLocalClass      false                                                                                               
 isMemberClass     false                                                                                               
 isPrimitive       false                                                                                               
 isSynthetic       false                                                                                               
 simple-name       MethodInstrumentationModule                                                                         
 modifier          public                                                                                              
 annotation                                                                                                            
 interfaces                                                                                                            
 super-class       +-io.opentelemetry.javaagent.tooling.InstrumentationModule                                          
                     +-java.lang.Object                                                                                
 class-loader      +-io.opentelemetry.javaagent.bootstrap.AgentClassLoader@379619aa                                    
 classLoaderHash   379619aa 

[arthas@16908]$ sc -d io.opentelemetry.javaagent.instrumentation.methods.MethodTracer
 class-info        io.opentelemetry.javaagent.instrumentation.methods.MethodTracer                                     
 code-source                                                                                                           
 name              io.opentelemetry.javaagent.instrumentation.methods.MethodTracer                                     
 isInterface       false                                                                                               
 isAnnotation      false                                                                                               
 isEnum            false                                                                                               
 isAnonymousClass  false                                                                                               
 isArray           false                                                                                               
 isLocalClass      false                                                                                               
 isMemberClass     false                                                                                               
 isPrimitive       false                                                                                               
 isSynthetic       false                                                                                               
 simple-name       MethodTracer                                                                                        
 modifier          public                                                                                              
 annotation                                                                                                            
 interfaces                                                                                                            
 super-class       +-io.opentelemetry.javaagent.shaded.instrumentation.api.tracer.BaseTracer                           
                     +-java.lang.Object                                                                                
 class-loader      +-WebAppClassLoader=Server Initiated@1ccb04b3                                                       
                     +-java.net.URLClassLoader@69cd1085                                                                
                       +-sun.misc.Launcher$AppClassLoader@18b4aac2                                                     
                         +-sun.misc.Launcher$ExtClassLoader@41fa769c                                                   
 classLoaderHash   1ccb04b3                                                                                            

 class-info        io.opentelemetry.javaagent.instrumentation.methods.MethodTracer                                     
 code-source                                                                                                           
 name              io.opentelemetry.javaagent.instrumentation.methods.MethodTracer                                     
 isInterface       false                                                                                               
 isAnnotation      false                                                                                               
 isEnum            false                                                                                               
 isAnonymousClass  false                                                                                               
 isArray           false                                                                                               
 isLocalClass      false                                                                                               
 isMemberClass     false                                                                                               
 isPrimitive       false                                                                                               
 isSynthetic       false                                                                                               
 simple-name       MethodTracer                                                                                        
 modifier          public                                                                                              
 annotation                                                                                                            
 interfaces                                                                                                            
 super-class       +-io.opentelemetry.javaagent.shaded.instrumentation.api.tracer.BaseTracer                           
                     +-java.lang.Object                                                                                
 class-loader      +-WebAppClassLoader=OAuth Server@10d98940                                                           
                     +-java.net.URLClassLoader@69cd1085                                                                
                       +-sun.misc.Launcher$AppClassLoader@18b4aac2                                                     
                         +-sun.misc.Launcher$ExtClassLoader@41fa769c                                                   
 classLoaderHash   10d98940

shaded

io.opentelemetry.instrumentation.api.config.Config
->
sc -d io.opentelemetry.javaagent.shaded.instrumentation.api.config.Config

[arthas@16908]$ sc -d io.opentelemetry.javaagent.shaded.instrumentation.api.config.Config                                                                                            

 class-info        io.opentelemetry.javaagent.shaded.instrumentation.api.config.Config                                 
 code-source                                                                                                           
 name              io.opentelemetry.javaagent.shaded.instrumentation.api.config.Config                                 
 isInterface       false                                                                                               
 isAnnotation      false                                                                                               
 isEnum            false                                                                                               
 isAnonymousClass  false                                                                                               
 isArray           false                                                                                               
 isLocalClass      false                                                                                               
 isMemberClass     false                                                                                               
 isPrimitive       false                                                                                               
 isSynthetic       false                                                                                               
 simple-name       Config                                                                                              
 modifier          abstract,public                                                                                     
 annotation                                                                                                            
 interfaces                                                                                                            
 super-class       +-java.lang.Object                                                                                  
 class-loader                                                                                                          
 classLoaderHash   null