JAVA堆外内存

本文建立在对instrumentation和agent有初步的了解的前提下阅读，关于这2个类的讲解在其它文章中。

这是一个maven项目，pom中需要的配置，lib中有asm的jar包

pom.xml文件：

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.dxz</groupId>
    <artifactId>chama</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>chama</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-test</artifactId>
            <version>6.2</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-analysis</artifactId>
            <version>6.2</version>
        </dependency>
        <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-commons</artifactId>
            <version>6.2</version>
        </dependency>
                <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-tree</artifactId>
            <version>6.2</version>
        </dependency>
                <dependency>
            <groupId>org.ow2.asm</groupId>
            <artifactId>asm-util</artifactId>
            <version>6.2</version>
        </dependency>
        <dependency>
            <groupId>javassist</groupId>
            <artifactId>javassist</artifactId>
            <version>3.12.1.GA</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/cglib/cglib -->
        <dependency>
            <groupId>cglib</groupId>
            <artifactId>cglib</artifactId>
            <version>3.2.5</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/oro/oro -->
        <dependency>
            <groupId>oro</groupId>
            <artifactId>oro</artifactId>
            <version>2.0.8</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <encoding>utf-8</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.0.0</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer
                                    implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <manifestEntries>
                                        <!-- <Premain-Class>com.dxz.chama.javaagent.patter.TimeMonitorPatterAgent</Premain-Class> -->
                                        <!-- <Premain-Class>com.dxz.chama.javaagent.StatAgent</Premain-Class> -->
                                        <Premain-Class>com.dxz.chama.javaagent.asm.UdAgent</Premain-Class>
                                    </manifestEntries>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

打包后的agent的jar包中manifest属性如下：

agent类，只有一个方法，就是把自定义的类修改器添加到instrumentation中。

package com.dxz.chama.javaagent.asm;

import java.lang.instrument.Instrumentation;

public class UdAgent {
    public static void premain(String agentArgs, Instrumentation instrumentation){
        instrumentation.addTransformer(new LogTransformer());
    }
}

类转换器实现：

package com.dxz.chama.javaagent.asm;

import java.io.IOException;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;

public class LogTransformer implements ClassFileTransformer {
    @Override
    public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
            ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
        try {
            ClassReader cr = new ClassReader(className);
            ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
            TimeCountAdpter timeCountAdpter = new TimeCountAdpter(cw);

            cr.accept(timeCountAdpter, ClassReader.EXPAND_FRAMES);

            return cw.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

实际修改字节码的方法，这里给每个类添加了一个字段UDASMCN，用于记录当前类的名字（方便打印信息）。同时记录每个方法的名字，以及执行时间。

package com.dxz.chama.javaagent.asm;

import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
import org.objectweb.asm.commons.AnalyzerAdapter;
import org.objectweb.asm.commons.LocalVariablesSorter;

public class TimeCountAdpter extends ClassVisitor implements Opcodes {
    private String owner;
    private boolean isInterface;
    private String filedName = "UDASMCN";
    private int acc = Opcodes.ACC_PUBLIC + Opcodes.ACC_STATIC + Opcodes.ACC_FINAL;
    private boolean isPresent = false;

    private String methodName;

    public TimeCountAdpter(ClassVisitor classVisitor) {
        super(ASM6, classVisitor);
    }

    @Override
    public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) {
        super.visit(version, access, name, signature, superName, interfaces);
        owner = name;
        isInterface = (access & ACC_INTERFACE) != 0;
    }

    @Override
    public FieldVisitor visitField(int access, String name, String descriptor, String signature, Object value) {
        if (name.equals(filedName)) {
            isPresent = true;
        }
        return super.visitField(access, name, descriptor, signature, value);
    }

    @Override
    public MethodVisitor visitMethod(int access, String name, String descriptor, String signature,
            String[] exceptions) {
        MethodVisitor mv = cv.visitMethod(access, name, descriptor, signature, exceptions);

        if (!isInterface && mv != null && !name.equals("<init>") && !name.equals("<clinit>")) {
            methodName = name;
            AddTimerMethodAdapter at = new AddTimerMethodAdapter(mv);
            at.aa = new AnalyzerAdapter(owner, access, name, descriptor, at);
            at.lvs = new LocalVariablesSorter(access, descriptor, at.aa);

            return at.lvs;
        }

        return mv;
    }

    public void visitEnd() {
        if (!isInterface) {
            FieldVisitor fv = cv.visitField(acc, filedName, "Ljava/lang/String;", null, owner);
            if (fv != null) {
                fv.visitEnd();
            }
        }
        cv.visitEnd();
    }

    class AddTimerMethodAdapter extends MethodVisitor {
        private int time;
        private int maxStack;
        public LocalVariablesSorter lvs;
        public AnalyzerAdapter aa;

        public AddTimerMethodAdapter(MethodVisitor methodVisitor) {
            super(ASM6, methodVisitor);
        }

        @Override
        public void visitCode() {
            mv.visitCode();
            mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);
            time = lvs.newLocal(Type.LONG_TYPE);
            mv.visitVarInsn(LSTORE, time);
            maxStack = 4;
        }

        @Override
        public void visitInsn(int opcode) {
            if (((opcode >= IRETURN && opcode <= RETURN) || opcode == ATHROW) && !isPresent) {
                mv.visitMethodInsn(INVOKESTATIC, "java/lang/System", "nanoTime", "()J", false);
                mv.visitVarInsn(LLOAD, time);
                mv.visitInsn(LSUB);
                mv.visitVarInsn(LSTORE, time);

                mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");

                mv.visitTypeInsn(NEW, "java/lang/StringBuilder");
                mv.visitInsn(DUP);
                mv.visitMethodInsn(INVOKESPECIAL, "java/lang/StringBuilder", "<init>", "()V", false);
                mv.visitFieldInsn(GETSTATIC, owner, filedName, "Ljava/lang/String;");
                mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",
                        "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

                mv.visitLdcInsn("  " + methodName + ":");
                mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append",
                        "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false);

                mv.visitVarInsn(LLOAD, time);
                mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(J)Ljava/lang/StringBuilder;",
                        false);
                mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false);
                mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);

                maxStack = Math.max(aa.stack.size() + 4, maxStack);
            }
            mv.visitInsn(opcode);
        }

        @Override
        public void visitMaxs(int maxStack, int maxLocals) {
            super.visitMaxs(Math.max(maxStack, this.maxStack), maxLocals);
        }
    }

}

打包成jar包后，在另一个程序启动时调用，启动参数如下：

-javaagent:D:\study\chama\target\chama-0.0.1-SNAPSHOT.jar
执行效果：
时间单位是纳秒，可以看到每个方法执行完时，都会打印这个方法 的执行时间，以com/Main main:11457636为例，说明类com/Main的main方法执行力11毫秒。