BTrace实现浅析
2015-07-19 22:38
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在之前的文章中我们简单介绍了BTrace的用法，今天我们通过源代码来看看BTrace是如何实现的。
从BTrace的启动脚本中可以找到相关入口，
所以
BTrace脚本的编译细节（包括脚本解析等）我们暂不深究。看第3步之前先来看第4步提交的请求，
现在我们再来看第3步，也就是
可以看到这个地方使用了Attach API。最后调用了
来看下
处理客户端请求，
其实主要就是Attach API的使用，通过
上面使用的很多类的包名都是
最后简单总结一下，
BTrace脚本编译；
BTrace客户端使用Attach API attach到目标VM，并加载agent包；
agent打开socket来与客户端进行通信；
客户端给agent发送
agent通过Attach API和ASM来完成满足BTrace脚本的字节码修改工作；
从BTrace的启动脚本中可以找到相关入口，
[code]${J***A_HOME}/bin/java -Dcom.sun.btrace.probeDescPath=. -Dcom.sun.btrace.dumpClasses=false -Dcom.sun.btrace.debug=false -Dcom.sun.btrace.unsafe=false -cp ${BTRACE_HOME}/build/btrace-client.jar:${TOOLS_JAR}:/usr/share/lib/java/dtrace.jar com.sun.btrace.client.Main $*所以
Main-Class就是
com.sun.btrace.client.Main了，来看看它的
main方法，
[code] public static void main(String[] args) {
////////////////////////////////////////
// 1. 参数解析
////////////////////////////////////////
if (args.length < 2) {
usage();
}
int port = BTRACE_DEFAULT_PORT;
String classPath = ".";
String includePath = null;
int count = 0;
boolean portDefined = false;
boolean classpathDefined = false;
boolean includePathDefined = false;
for (;;) {
if (args[count].charAt(0) == '-') {
if (args.length <= count+1) {
usage();
}
if (args[count].equals("-p") && !portDefined) {
try {
port = Integer.parseInt(args[++count]);
if (isDebug()) debugPrint("accepting port " + port);
} catch (NumberFormatException nfe) {
usage();
}
portDefined = true;
} else if ((args[count].equals("-cp") ||
args[count].equals("-classpath"))
&& !classpathDefined) {
classPath = args[++count];
if (isDebug()) debugPrint("accepting classpath " + classPath);
classpathDefined = true;
} else if (args[count].equals("-I") && !includePathDefined) {
includePath = args[++count];
if (isDebug()) debugPrint("accepting include path " + includePath);
includePathDefined = true;
} else {
usage();
}
count++;
if (count >= args.length) {
break;
}
} else {
break;
}
}
if (! portDefined) {
if (isDebug()) debugPrint("assuming default port " + port);
}
if (! classpathDefined) {
if (isDebug()) debugPrint("assuming default classpath '" + classPath + "'");
}
if (args.length < (count + 1)) {
usage();
}
String pid = args[count];
String fileName = args[count + 1];
String[] btraceArgs = new String[args.length - count];
if (btraceArgs.length > 0) {
System.arraycopy(args, count, btraceArgs, 0, btraceArgs.length);
}
try {
Client client = new Client(port, PROBE_DESC_PATH,
DEBUG, TRACK_RETRANSFORM, UNSAFE, DUMP_CLASSES, DUMP_DIR);
if (! new File(fileName).exists()) {
errorExit("File not found: " + fileName, 1);
}
////////////////////////////////////////
// 2. 编译btrace脚本
////////////////////////////////////////
byte[] code = client.compile(fileName, classPath, includePath);
if (code == null) {
errorExit("BTrace compilation failed", 1);
}
////////////////////////////////////////
// 3. attach到目标VM
////////////////////////////////////////
client.attach(pid);
registerExitHook(client);
if (con != null) {
registerSignalHandler(client);
}
if (isDebug()) debugPrint("submitting the BTrace program");
////////////////////////////////////////
// 4. 提交btrace请求
////////////////////////////////////////
client.submit(fileName, code, btraceArgs,
createCommandListener(client));
} catch (IOException exp) {
errorExit(exp.getMessage(), 1);
}
}BTrace脚本的编译细节（包括脚本解析等）我们暂不深究。看第3步之前先来看第4步提交的请求，
com.sun.btrace.client.Client#submit，
[code] /**
* Submits the compiled BTrace .class to the VM
* attached and passes given command line arguments.
* Receives commands from the traced JVM and sends those
* to the command listener provided.
*/
public void submit(String fileName, byte[] code, String[] args,
CommandListener listener) throws IOException {
if (sock != null) {
throw new IllegalStateException();
}
submitDTrace(fileName, code, args, listener);
try {
if (debug) {
debugPrint("opening socket to " + port);
}
////////////////////////////////////////
// 与目标VM通过Socket进行通信
////////////////////////////////////////
sock = new Socket("localhost", port);
oos = new ObjectOutputStream(sock.getOutputStream());
if (debug) {
debugPrint("sending instrument command");
}
////////////////////////////////////////
// 给目标VM发送InstrumentCommand
////////////////////////////////////////
WireIO.write(oos, new InstrumentCommand(code, args));
ois = new ObjectInputStream(sock.getInputStream());
if (debug) {
debugPrint("entering into command loop");
}
commandLoop(listener);
} catch (UnknownHostException uhe) {
throw new IOException(uhe);
}
}现在我们再来看第3步，也就是
com.sun.btrace.client.Client#attach，
[code] /**
* Attach the BTrace client to the given Java process.
* Loads BTrace agent on the target process if not loaded
* already.
*/
public void attach(String pid) throws IOException {
try {
String agentPath = "/btrace-agent.jar";
String tmp = Client.class.getClassLoader().getResource("com/sun/btrace").toString();
tmp = tmp.substring(0, tmp.indexOf("!"));
tmp = tmp.substring("jar:".length(), tmp.lastIndexOf("/"));
agentPath = tmp + agentPath;
agentPath = new File(new URI(agentPath)).getAbsolutePath();
attach(pid, agentPath, null, null);
} catch (RuntimeException re) {
throw re;
} catch (IOException ioexp) {
throw ioexp;
} catch (Exception exp) {
throw new IOException(exp.getMessage());
}
}[code] /**
* Attach the BTrace client to the given Java process.
* Loads BTrace agent on the target process if not loaded
* already. Accepts the full path of the btrace agent jar.
* Also, accepts system classpath and boot classpath optionally.
*/
public void attach(String pid, String agentPath, String sysCp, String bootCp) throws IOException {
try {
VirtualMachine vm = null;
if (debug) {
debugPrint("attaching to " + pid);
}
vm = VirtualMachine.attach(pid);
if (debug) {
debugPrint("checking port availability: " + port);
}
Properties serverVmProps = vm.getSystemProperties();
int serverPort = Integer.parseInt(serverVmProps.getProperty("btrace.port", "-1"));
if (serverPort != -1) {
if (serverPort != port) {
throw new IOException("Can not attach to PID " + pid + " on port " + port + ". There is already a BTrace server active on port " + serverPort + "!");
}
} else {
if (!isPortAvailable(port)) {
throw new IOException("Port " + port + " unavailable.");
}
}
if (debug) {
debugPrint("attached to " + pid);
}
if (debug) {
debugPrint("loading " + agentPath);
}
String agentArgs = "port=" + port;
if (debug) {
agentArgs += ",debug=true";
}
if (unsafe) {
agentArgs += ",unsafe=true";
}
if (dumpClasses) {
agentArgs += ",dumpClasses=true";
agentArgs += ",dumpDir=" + dumpDir;
}
if (trackRetransforms) {
agentArgs += ",trackRetransforms=true";
}
if (bootCp != null) {
agentArgs += ",bootClassPath=" + bootCp;
}
if (sysCp == null) {
sysCp = getToolsJarPath(
serverVmProps.getProperty("java.class.path"),
serverVmProps.getProperty("java.home")
);
}
String cmdQueueLimit = System.getProperty(BTraceRuntime.CMD_QUEUE_LIMIT_KEY, null);
if (cmdQueueLimit != null) {
agentArgs += ",cmdQueueLimit=" + cmdQueueLimit;
}
agentArgs += ",systemClassPath=" + sysCp;
agentArgs += ",probeDescPath=" + probeDescPath;
if (debug) {
debugPrint("agent args: " + agentArgs);
}
vm.loadAgent(agentPath, agentArgs);
if (debug) {
debugPrint("loaded " + agentPath);
}
} catch (RuntimeException re) {
throw re;
} catch (IOException ioexp) {
throw ioexp;
} catch (Exception exp) {
throw new IOException(exp.getMessage());
}
}可以看到这个地方使用了Attach API。最后调用了
VirtualMachine#loadAgent方法，加载的agent是
$BTRACE_HOME/build/btrace-agent.jar，它的
MANIFEST.MF是这样的，
[code]Manifest-Version: 1.0 Ant-Version: Apache Ant 1.8.0 Created-By: 1.7.0_07-b10 (Oracle Corporation) Premain-Class: com.sun.btrace.agent.Main Agent-Class: com.sun.btrace.agent.Main Boot-Class-Path: btrace-boot.jar Can-Redefine-Classes: true Can-Retransform-Classes: true
VirtualMachine#loadAgent的时候会调用
Agent-Class的
agentmain方法，这里也就是
com.sun.btrace.agent.Main#agentmain，
[code] public static void agentmain(String args, Instrumentation inst) {
main(args, inst);
}[code] private static synchronized void main(final String args, final Instrumentation inst) {
if (Main.inst != null) {
return;
} else {
Main.inst = inst;
}
////////////////////////////////////////
// 1. 参数解析
////////////////////////////////////////
if (isDebug()) debugPrint("parsing command line arguments");
parseArgs(args);
if (isDebug()) debugPrint("parsed command line arguments");
/////// Boot-Class-Path: btrace-boot.jar
String bootClassPath = argMap.get("bootClassPath");
if (bootClassPath != null) {
if (isDebug()) {
debugPrint("Bootstrap ClassPath: " + bootClassPath);
}
StringTokenizer tokenizer = new StringTokenizer(bootClassPath, File.pathSeparator);
try {
while (tokenizer.hasMoreTokens()) {
String path = tokenizer.nextToken();
inst.appendToBootstrapClassLoaderSearch(new JarFile(new File(path)));
}
} catch (IOException ex) {
debugPrint("adding to boot classpath failed!");
debugPrint(ex);
return;
}
}
String systemClassPath = argMap.get("systemClassPath");
if (systemClassPath != null) {
if (isDebug()) {
debugPrint("System ClassPath: " + systemClassPath);
}
StringTokenizer tokenizer = new StringTokenizer(systemClassPath, File.pathSeparator);
try {
while (tokenizer.hasMoreTokens()) {
String path = tokenizer.nextToken();
inst.appendToSystemClassLoaderSearch(new JarFile(new File(path)));
}
} catch (IOException ex) {
debugPrint("adding to boot classpath failed!");
debugPrint(ex);
return;
}
}
String tmp = argMap.get("noServer");
boolean noServer = tmp != null && !"false".equals(tmp);
if (noServer) {
if (isDebug()) debugPrint("noServer is true, server not started");
return;
}
////////////////////////////////////////
// 2. 启动agent线程
////////////////////////////////////////
Thread agentThread = new Thread(new Runnable() {
public void run() {
BTraceRuntime.enter();
try {
startServer();
} finally {
BTraceRuntime.leave();
}
}
});
BTraceRuntime.enter();
try {
agentThread.setDaemon(true);
if (isDebug()) debugPrint("starting agent thread");
agentThread.start();
} finally {
BTraceRuntime.leave();
}
}startServer方法，
[code] private static void startServer() {
int port = BTRACE_DEFAULT_PORT;
String p = argMap.get("port");
if (p != null) {
try {
port = Integer.parseInt(p);
} catch (NumberFormatException exp) {
error("invalid port assuming default..");
}
}
ServerSocket ss;
try {
if (isDebug()) debugPrint("starting server at " + port);
System.setProperty("btrace.port", String.valueOf(port));
if (scriptOutputFile != null && scriptOutputFile.length() > 0) {
System.setProperty("btrace.output", scriptOutputFile);
}
ss = new ServerSocket(port);
} catch (IOException ioexp) {
ioexp.printStackTrace();
return;
}
while (true) {
try {
if (isDebug()) debugPrint("waiting for clients");
////////////////////////////////////////
// 等待客户端连接上来
////////////////////////////////////////
Socket sock = ss.accept();
if (isDebug()) debugPrint("client accepted " + sock);
////////////////////////////////////////
// 生成RemoteClient
////////////////////////////////////////
Client client = new RemoteClient(inst, sock);
registerExitHook(client);
////////////////////////////////////////
// 处理客户端请求
////////////////////////////////////////
handleNewClient(client);
} catch (RuntimeException re) {
if (isDebug()) debugPrint(re);
} catch (IOException ioexp) {
if (isDebug()) debugPrint(ioexp);
}
}
}来看下
RemoteClient的构造函数，
[code] RemoteClient(Instrumentation inst, Socket sock) throws IOException {
super(inst);
this.sock = sock;
this.ois = new ObjectInputStream(sock.getInputStream());
this.oos = new ObjectOutputStream(sock.getOutputStream());
////////////////////////////////////////
// 读取客户端提交过来的InstrumentCommand
////////////////////////////////////////
Command cmd = WireIO.read(ois);
if (cmd.getType() == Command.INSTRUMENT) {
if (debug) Main.debugPrint("got instrument command");
////////////////////////////////////////
// 保存编译后的btrace脚本代码到Client#btraceCode
////////////////////////////////////////
Class btraceClazz = loadClass((InstrumentCommand)cmd);
if (btraceClazz == null) {
throw new RuntimeException("can not load BTrace class");
}
} else {
errorExit(new IllegalArgumentException("expecting instrument command!"));
throw new IOException("expecting instrument command!");
}
...
}处理客户端请求，
[code] private static void handleNewClient(final Client client) {
serializedExecutor.submit(new Runnable() {
public void run() {
try {
if (isDebug()) debugPrint("new Client created " + client);
if (client.shouldAddTransformer()) {
/////////////////////////////////
// 1. 添加ClassFileTransformer
/////////////////////////////////
client.registerTransformer();
/////////////////////////////////
// 2. 获取满足脚本中条件的全部类
/////////////////////////////////
Class[] classes = inst.getAllLoadedClasses();
ArrayList<Class> list = new ArrayList<Class>();
if (isDebug()) debugPrint("filtering loaded classes");
for (Class c : classes) {
if (inst.isModifiableClass(c) && client.isCandidate(c)) {
if (isDebug()) debugPrint("candidate " + c + " added");
list.add(c);
}
}
list.trimToSize();
int size = list.size();
if (isDebug()) debugPrint("added as ClassFileTransformer");
if (size > 0) {
classes = new Class[size];
list.toArray(classes);
client.startRetransformClasses(size);
/////////////////////////////////
// 3. 开始进行retransform
/////////////////////////////////
if (isDebug()) {
for(Class c : classes) {
try {
inst.retransformClasses(c);
} catch (VerifyError e) {
debugPrint("verification error: " + c.getName());
}
}
} else {
inst.retransformClasses(classes);
}
client.skipRetransforms();
}
}
client.getRuntime().send(new OkayCommand());
} catch (UnmodifiableClassException uce) {
if (isDebug()) {
debugPrint(uce);
}
client.getRuntime().send(new ErrorCommand(uce));
}
}
});
}com.sun.btrace.agent.Client#registerTransformer方法中会调用
java.lang.instrument.Instrumentation#addTransformer，
[code] void registerTransformer() {
inst.addTransformer(clInitTransformer, false);
inst.addTransformer(this, true);
}其实主要就是Attach API的使用，通过
java.lang.instrument.Instrumentation#addTransformer添加了
ClassFileTransformer，当调用
java.lang.instrument.Instrumentation#retransformClasses时，上面所添加的
ClassFileTransformer的
transform方法就会被调用，这里也就是
com.sun.btrace.agent.Client#transformer了，该方法最后是调用了
com.sun.btrace.agent.Client#instrument来完成真正的字节码修改工作，
[code] private byte[] instrument(Class clazz, String cname, byte[] target) {
byte[] instrumentedCode;
try {
ClassWriter writer = InstrumentUtils.newClassWriter(target);
ClassReader reader = new ClassReader(target);
Instrumentor i = new Instrumentor(clazz, className, btraceCode, onMethods, writer);
InstrumentUtils.accept(reader, i);
if (Main.isDebug() && !i.hasMatch()) {
Main.debugPrint("*WARNING* No method was matched for class " + cname); // NOI18N
}
instrumentedCode = writer.toByteArray();
} catch (Throwable th) {
Main.debugPrint(th);
return null;
}
Main.dumpClass(className, cname, instrumentedCode);
return instrumentedCode;
}上面使用的很多类的包名都是
com.sun.btrace.org.objectweb.asm，BTrace使用了ASM来完成字节码的修改工作，具体细节暂时也不深究了。
最后简单总结一下，
BTrace脚本编译；
BTrace客户端使用Attach API attach到目标VM，并加载agent包；
agent打开socket来与客户端进行通信；
客户端给agent发送
InstrumentCommand，其中包含BTrace脚本编译后的字节码；
agent通过Attach API和ASM来完成满足BTrace脚本的字节码修改工作；
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